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Recent Advancements in Li-Ion Conductors for All-Solid-State Li-Ion Batteries
Abstract
Inorganic solid lithium ion conductors are potential candidates as replacement for conventional organic electrolytes for safety concerns. However, achieving a Li-ion conductivity comparable to that in existing liquid electrolytes (>1m S cm−1) remains a challenge in solid-state electrolytes. One of the approaches to achieve a desirable conductivity is doping of various elements into the lattice framework. Our discussion on the structure and conductivity of crystalline Li-ion conductors includes description on NASICON (NAtrium Super Ionic CONductor)-type conductors, garnet-type conductors; perovskite-type conductors, and Lithium Super Ionic CONductor (LISICON)-type conductors. Moreover, we discuss the different strategies currently used to enhance ionic conductivity including theoretical approaches; ultimately optimizing electrolyte/electrode interface and improving cell performance.
... Seen as a safer alternative to the flammable and toxic components in traditional liquid electrolytes, solid electrolytes are now a major focus in the research and development of various types of solid-state battery systems (SSBs). 3,4 Solid electrolyte systems offer several advantages over liquid systems. These include thermal, chemical, and electrochemical stability against lithium metal and cathode active materials, high ionic conductivity in the mS cm À1 range (which is close to that of liquid systems at 0.1 mS cm À1 ), and low electronic conductivity (10 À9 -10 À10 mS cm À1 ). ...
... Therefore, for the practical deployment of solid-state batteries, solid electrolytes must exhibit high ionic conductivity, low electronic conductivity, and electrochemical and chemical stability with respect to both the active materials and lithium metal. 4,8,68 Notably, the increase in electronic conductivity of solid electrolyte can be attributed to the different valences of components and the formation of side reaction components or impurity phases. Therefore, the presence of electronic conductivity in solid electrolytes impacts their performance due to their complex structures. ...
Conventional lithium-ion batteries (LIBs) have become widely used in small and large applications, but the use of toxic and flammable liquid electrolytes can lead to safety issues and reduced cell performance. New generation solid-state lithium batteries (SSBs) have the potential to replace LIBs due to their safety and potentially high energy density (>450 W h kg⁻¹). The solid electrolyte (SE) is a crucial component in solid-state batteries. Among the available options, sulfide- and halide-based solid electrolytes stand out as promising candidates due to their high ionic conductivity and ease of processing. They are among the most prominent topics in solid electrolyte research for solid-state batteries. Despite their advantages like good compatibility with high-voltage cathodes and easy manufacturing, solid electrolytes still face issues of degradation of the Li metal/solid electrolyte interface. This is due to the formation of side reaction products at the interface, which inhibits lithium transport across it. The primary issue stems from the poor chemical and electrochemical stability of sulfide- and halide-based solid electrolytes when in contact with lithium metal. In this study, we have demonstrated that the composite electrolytes (Li3YCl4Br2:Li6PS5Cl) comprising halide and argyrodite can prevent the formation of unfavorable interactions between the solid electrolyte and the Li metal anode. The Li/Li-symmetric cells employing the Li3YCl4Br2:Li6PS5Cl electrolytes exhibited enhanced cycle life and high critical current density (CCD) from C/20 to C/2, compared to the symmetric cells utilizing only Li3YCl4Br2 or Li6PS5Cl electrolyte. Furthermore, the Li/Li3YCl4Br2/NCM half-cells demonstrated high initial coulombic efficiency and extended cycle life compared to half-cells utilizing traditional halide and argyrodite electrolytes. The approach described here offers a pathway to enhance halide-based solid-state batteries, providing a relatively simple and effective strategy.
... A comparison between the benefits and disadvantages of these SSEs is given in the references. 6,[9][10][11][12][13] Lithium lanthanum titanate perovskites (Li x La 1-x TiO 3 , LLTO) are an excellent option for SSE applications since they present wide versatility in their physical properties. They have a perovskite-like structure characterized by the general chemical formula ABO 3 , where in this case, B species are Ti cations (Ti 3+ or Ti 4+ ) surrounded by six oxygen anions (O 2− ), achieving an octahedral geometry. ...
... Therefore, using the LDA CA-PZ functional can be obtained excellent results for the elastic properties, being computationally cheaper than LDA+U; LTO bulk modulus (B) has an error of only 6% concerning the experimental value data (190 GPa). 70 In materials with an orthorhombic unit cell, nine C ij values are independent: C , 11 C , 12 C , 13 C , 22 C , 23 C , 33 C , 44 C , 55 and C . 66 71 In this work, to characterize the elastic properties of the LTO and LLTO electrolytes, these C ij values were computed through the finite strain method. ...
Lithium lanthanum titanate perovskites (LLTO) are excellent solid electrolytes because of their good ionic conductivity and elasticity. Here, the effects of high hydrostatic pressure and the impact of the position of Li impurities on the structural, electronic, elastic, and Li-ion diffusion properties of LaTiO 3 perovskite (LTO) and its LLTO substitutional solid solutions, were studied. Density-functional theory (DFT) and Hubbard-corrected local density approximation (LDA+U) were used. Due to hydrostatic pressure, the octahedral distortion of LTO, LLTO-layered (L), and -rock-salt (RS) electrolytes decreases, while it increases for the LLTO-columnar (C). On the other hand, the energy band gap (E g ) of LTO and LLTO-C decrease as hydrostatic pressure increases. For the LLTO-L, E g increases with pressure. For the LLTO-RS, E g decreases from zero to 20 GPa and increases from 20 to 30 GPa. Pugh’s criterion indicates that all systems are ductile regardless of applied pressure. Poisson’s ratio shows that bonds in the LTO are metallic, and LLTO-C is ionic-covalent. Likewise, LLTO-L and -RS electrolytes have a transition from ionic-covalent to metallic behavior, as pressure increases. Li-ion diffusion barriers of LLTO electrolytes increase with increasing hydrostatic pressure, indicating a decrease in Li ionic conductivity.
... In parallel, the G-LZTPx glasses showed ionic conductivities ranging from 9.96 × 10 -11 to 1.74 × 10 -10 Ω -1 . cm -1 at room temperature, which is lower than those of crystalline materials [60] and other glass systems [61]. However, glasses still offer advantages such as stability and reduced grain boundary resistance, making them suitable for specific applications despite their lower conductivity values. ...
This study investigates novel ZnO-doped lithium-titanium-phosphate glasses, synthesized via the melt-quenching method, and characterizes their physical, structural, thermal, optical, chemical, mechanical, and electrical properties, with a focus on the impact of varying ZnO content on these properties. An increase in ZnO content from 20 mol% to 27.27 mol% induces significant local structural changes, promoting enhanced network polymerization, density, and chemical durability, while concurrently reducing thermal stability and mechanical strength. EPR analysis confirmed that titanium remained in the Ti4+ state, while optical measurements revealed an increased band gap, attributed to the role of ZnO in preventing Ti4+ reduction and minimizing localized states. The electrical conductivity decreases with increasing ZnO content, with the highest value measured at 1.73 × 10− 10 Ω− 1 cm−1. High-ZnO glasses exhibit mainly electronic conductivity of 4.02 × 10− 9 Ω− 1 cm− 1 at room temperature. The frequency-dependent conductivity follows Jonscher’s power law, with the charge transport governed by a correlated barrier hopping mechanism, remaining stable across temperatures and compositions.
... A comprehensive treatise on the design, synthesis, and computational protocols for using ionic liquids has been provided here [104]. Now we will discuss the solid electrolytes that are the prime drivers for realizing the all-solid-state batteries [105][106][107][108][109]. In the study by Honrao et al [110], an ML model for identifying solid-state electrolytes for LIBs was developed. ...
The world is rapidly transitioning towards clean energy solutions, and batteries are the key drivers of this transition. With increasing demand for large-scale energy storage systems, the need for cost-effective and sustainable battery storage systems is also increasing. Until now, lithium-ion batteries have completely dominated the commercial rechargeable battery storage space. Due to sodium’s greater affordability and abundance compared to lithium, sodium-ion batteries have drawn interest as a complementary technology to lithium-ion batteries in various applications, like grid storage devices. First-principles studies are often used today to effectively study the key properties of alkali-ion batteries that are difficult to access otherwise, such as the electronic structure effects, ion diffusivity, and quantitative comparison with experiments, to name a few. Understanding the electronic structure of battery materials can help researchers design more efficient and longer-lasting batteries. Recently, machine learning (ML) approaches have emerged as a very attractive tool both for prediction (forward) problems as well as design (or inverse) problems. Dramatic reductions in computational costs, coupled with the rapid development of ML tools in general and deep learning methods in particular, have kindled keen interest. This is so because they can supplement the traditional experimental, theoretical, and computational tools to significantly augment the quest for rapid development and deployment of new products. Furthermore, the integration of electronic structure calculations and ML benefits society by accelerating the development at considerably lower costs for more efficient and sustainable batteries, which can lead to longer-lasting portable devices, cleaner energy storage solutions, and lower environmental impact. This topical review article will focus on how density functional theory (DFT) and ML can facilitate Li-ion and Na-ion battery research via material discovery, rapid screening, and tuning of the electrode properties.
... c The electrochemical stability window of some inorganic solid state lithium-ion conductors grouped by the anion type, along with the typically more stable but non-conducting binary compounds [233]. Copyright 2019, Springer Nature LISICON, NASICON, garnet, perovskite and argyrodite [227][228][229]. While the room temperature ionic conductivity was initially an issue, conductivities on the order of 10 −3 -10 -2 S cm −1 , comparable to liquid organic electrolytes, has been achieved in many of these systems (Fig. 16a). ...
Rechargeable batteries of high energy density and overall performance are becoming a critically important technology in the rapidly changing society of the twenty-first century. While lithium-ion batteries have so far been the dominant choice, numerous emerging applications call for higher capacity, better safety and lower costs while maintaining sufficient cyclability. The design space for potentially better alternatives is extremely large, with numerous new chemistries and
architectures being simultaneously explored. These include other insertion ions (e.g. sodium and numerous multivalent ions), conversion electrode materials (e.g. silicon, metallic anodes, halides and chalcogens) and aqueous and solid electrolytes. However, each of these potential “beyond lithium-ion” alternatives faces numerous challenges that often lead to very poor cyclability, especially at the commercial cell level, while lithium-ion batteries continue to improve in performance and
decrease in cost. This review examines fundamental principles to rationalise these numerous developments, and in each case, a brief overview is given on the advantages, advances, remaining challenges preventing cell-level implementation and the state-of-the-art of the solutions to these challenges. Finally, research and development results obtained in academia are compared to emerging commercial examples, as a commentary on the current and near-future viability of these “beyond lithium-ion” alternatives.
... LiGe 2 (PO 4 ) 3 is a NASICON-type phase which crystallizes in 3 space group from the glass of Li 2 O-GeO 2 -P 2 O 5 -based composition (further called ''glassy LiGe 2 (PO 4 ) 3 ''). It is well-known that structural features greatly affects ion conductivity in solids [3,[13][14][15], thus it is of high importance to study and compare structural aspects of glassy and crystalline LiGe 2 (PO 4 ) 3 , for better understanding of the Li-conducting phenomenon in it and the processes which take place during crystallization of the glass. There are several experimental works devoted to this issue [9,[16][17][18], and accompanying them with theoretical (computational) methods allows getting additional information. ...
... As illustrated in Fig. 2, systems employing Li or Li metal ions exhibit a significantly greater capacity for storing electrical energy compared to conventional rechargeable batteries such as lead-acid, nickel-cadmium (Ni-Cd), and nickel-metal hydride (NiMH) [14]. Furthermore, the small mass of Li ions and its lowest reduction potential (− 3.045 V vs. SHE) enable LIBs to achieve reduced size and weight while delivering high power density [15]. ...
This review presents the development stages of Ni-based cathode materials for second-generation lithium-ion batteries (LIBs). Due to their high volumetric and gravimetric capacity and high nominal voltage, nickel-based cathodes have many applications, from portable devices to electric vehicles. A discussion of the most commonly used methods for cathode synthesis and the standard and advanced characterizations of synthesized materials is presented. The methods for preparing LIBs for electrochemical characterizations for obtaining electricity are also analyzed. The progress of synthesis methods is highlighted, connecting them to the mitigation strategies to overcome the failure mechanisms in Ni-rich cathodes. This review summarizes the state-of-the-art of Ni-based cathode for LIBs through high-impact scientific references.
... All-solidstate batteries (ASSBs) using solid electrolytes solve a number of problems specific to traditional lithium-ion batteries with liquid electrolyte, such as resistive SEI at the electrode interface resulting in capacity loss, electrolytic decomposition at high anode potential values, limiting the use of high-V cathodes, hazardous thermal runaway and leakage, leading to battery failure [1][2][3]. Solid electrolytes (SEs) must have high values of unipolar lithium-ion conductivity of 10 − 3 -10 − 4 S/cm at RT, compatibility with electrode materials, and have stable solid-solid interfaces between the SE and the electrode [2,[4][5][6]. ...
The properties of the Li 1.5 Al 0.5 Ge 1.5 (PO 4) 3 glass-ceramics were modified by the partial substitution of P 5+ by Si 4+ , and the synthesis process is optimized. The thermal behavior of the original Li 1.5+х Al 0.5 Ge 1.5 Si x P 3-x O 12 (0 ≤ x ≤ 0.5) glasses was investigated using differential scanning calorimetry (DSC), optical dilatometry and heating microscopy. The glass transition temperature (T g) decreases from 525 to 457 • C with increasing additive content from x = 0 to x = 0.5. Single-phase glass-ceramics with the NASICON-type structure were synthesized up to x = 1, which was confirmed by X-ray diffraction (XRD), Raman and energy-dispersive X-ray (EDX) mapping data. It has been shown that the SiO 2 addition has a beneficial effect on the electrical properties of glass-ceramics, crystallized at 700 and 750 • C. However, heat treatment at 820 • C leads to a smaller increase in conductivity. Therefore, Si-containing glass-ceramics should be produced at lower temperatures than pure LAGP, which is 750 • C and correlated with the thermal analysis results. The influence of the SiO 2 addition on the bulk and grain boundary conductivity of the Li 1.5 Al 0.5 Ge 1.5 (PO 4) 3 has been studied in detail. The Li 1.52 Al 0.5 Ge 1.5 Si 0.02 P 2.98 O 12 glass-ceramics has the highest total ionic conductivity of 4.55⋅10 − 4 S/cm at RT and negligible electronic conductivity of 7.5⋅10 − 10 S/cm, therefore can be considered as promising solid electrolytes for all-solid-state batteries.
... The Li 2 O-Al 2 O 3 -GeO 2 -P 2 O 5 (LAGP) glass-forming system is a promising NASICON-structured glass-ceramic electrolyte used as a basis for producing electrolytes of the Li 1+x Al x Ge 2− x (PO 4 ) 3 series [17]. These systems possess high thermal stability and good compatibility with 4 V-class electrode materials [18,19], and the Li 1.5 Al 0.5 Ge 1.5 (PO 4 ) 3 composition is reported to have the highest ionic conductivity [20]. Over the past decades, the addition of different dopants in different concentrations in this family of electrolytes was investigated, mainly in terms of resulting ionic mobility [18,[21][22][23][24][25][26]. ...
The development of Li-ion conducting solid-state electrolytes (SSEs) is crucial to achieve increased energy density, operative reliability, and unprecedented safety to replace the state-of-the-art Li-ion battery (LIB). In this regard, we here present the successful melt-casting synthesis of a MgO-added NASICON-type LAGP glass-ceramic electrolyte with composition Li1.5Al0.3Mg0.1Ge1.6(PO4)3, namely LAMGP. The effects of three different additional oxides are investigated, with the aim to improve grain cohesion and consequently enhance Li-ion conductivity. Specifically, yttrium oxide (Y2O3, 5 mol%), boron oxide (B2O3, 0.7 mol%) and silicon oxide (SiO2, 2.4 %mol) are added, yielding LAMGP-Y, LAMGP-B and LAMGP-Si, respectively. Their effects are exhaustively compared in terms of thermal, crystalline, structural/morphological and ion conducting features. Among the three oxides, B2O3 is able to positively act on grain boundaries without bringing along grains deformation and insulating secondary phases formation, achieving enhanced ionic conductivity of 0.21 mS cm⁻¹ at 20 °C as compared to 0.08 mS cm⁻¹ for a commercial LAGP subjected to the same thermal treatment. A remarkable anodic oxidation stability up to 4.8 V vs Li⁺/Li is assessed by LAMGP-B system, which accounts for promising prospects for its use in combination with high-energy (high-V) cathodes.
The growing global energy demand coupled with environmental protection measures is driving the need for advanced energy storage technologies capable of storing power generated from renewable sources such as wind, solar and hydropower. This enables broader integration of sustainable energy systems. Among various energy storage systems, batteries have proven to be the most efficient. In particular, Li-ion batteries (LIBs) have emerged as the most reliable and suitable energy storage devices because of their novel characteristics, including high energy density (Ed), high theoretical capacity, compact design and long-lasting performance compared to other storage systems. However, to enhance their energy and power densities and to address safety concerns caused by dendrite growth in the anodes, further optimization is required. Of the three key parts of a battery namely cathode, anode and electrolyte; electrolyte has a vital role, significantly influencing the electrochemical performance and overall operation. In high performance LIBs, solid polymer electrolytes have garnered significant interest because of their enhanced safety, lack of leakage, broad electrochemical stability window, mechanical flexibility and thermal-stability. This paper discusses various types of polymers including PMMA, PEO, PAN, PVDF, PVC, PS and PC, focusing on their synthesis methods and electrochemical performance. The aim is to provide insights into their potential for the advancement in LIB- technology.
NASICON-type Li1.5Al0.5Ge1.5(PO4)3 (LAGP) solid electrolyte is a promising candidate for next-generation lithium-ion batteries due to its high air stability and excellent Li-ion conductivity. Here, we systematically examine the effect of calcination temperature (500, 600, and 700 °C) on physical properties of LAGP to enhance its suitability for solid state lithium metal batteries. Rietveld refinement confirmed a single phase (R[3 with combining macron]c) for all sintered pellets, with unit cell parameters decreasing at higher calcination temperatures. Li-ion conductivity, with negligible electronic conduction, increased with calcination temperature due to improved relative density and cell contraction. The sample calcined at 700 °C exhibits the highest Li-ion conductivity of 1.63 × 10−4 S cm−1 and a low activation energy of ∼0.33 eV, alongside superior mechanical hardness of ∼9.2 GPa. The fabricated symmetric cell demonstrated low interfacial area specific resistance (∼40 Ω cm2) and high critical current density (1 mA cm−2). Consequently, it exhibited excellent cycling stability for over 500 h with low overpotential at 0.2 mA cm−2 and 25 °C. The full cell with LFP as cathode shows initial discharge capacity ∼142.1 mA h g−1 at 0.1C, with excellent capacity retention. Thus, our study offers valuable insights into optimizing the calcination temperature to enhance the performance of LAGP-based all-solid-state batteries.
In this study, the hydrothermal synthesis technique was employed to successfully fabricate Li1.2Al0.2Ti1.7(PO4)2 (LATP), a solid electrolyte renowned for its outstanding electrochemical properties. The research aimed to identify optimal synthesis conditions for LATP, achieving material with exceptional ionic conductivity and high purity. The optimal conditions included sintering the material with an additional 15% lithium hydroxide at 850 °C, which significantly enhanced the ionic conductivity to 3.01 × 10-4 S cm-1. This approach also resulted in a notable purity enhancement, exceeding 92%, and increased sample density by 36% compared to samples sintered without protective powder. The use of lithium hydroxide as a protective powder during sintering was crucial in curbing impurity formation, minimizing lithium loss, and enhancing overall densification. These findings underscore the potential of LATP solid electrolytes synthesized under these conditions for advanced energy storage technologies.
The global adoption of all-solid-state lithium-ion batteries (ASSLBs) technology calls for high-performance solid-state electrolyte (SSE) components and the design of suitable processing strategies required for their integration into practical solid-state cells. Although they face their own unique set of challenges, oxide-based SSEs chemistry holds much promise for the practical demonstration of the next-generation ASSLBs. In this review, we systematically discuss the influence of oxide SSE additives on the electrochemical performance of ASSLBs using high-voltage cathodes and lithium metal anodes. We provide a broad spectrum of research activities on the use of additives to tackle some limited performance aspects surrounding oxide-based SSE single components. We showcase that, using additives, the microstructural and grain boundary engineering tools can provide considerable headroom for improvement of oxide-based SSEs performance in terms of ionic conductivity, mechanical properties and critical current density (CCD). Finally, we demonstrate the impact of additives on the interfacial behavior of oxide SSEs, including their use to design lithiophilic interfaces for Li anodes as well as their efficient role on the optimization of co-sintered all-oxide composite cathodes. To the best of our knowledge, this is the first review paper that covers the influence of oxide SSE additives on ASSLBs performance despite the immense body of literature work published in this area.
A non-crystalline strategy to improve Li ⁺ conductivity in Li 2 ZrCl 6 -family halide solid-state electrolytes for all-solid-state Li batteries.
The crystalline phases of solid-state polymer electrolytes (SPEs) are commonly believed as ionic insulators. Here we show that contrary to this prevailing view, lithium-ion (Li ⁺ ) can transport in crystalline phases...
The successful design of solid-state photo- and electrochemical devices depends on the careful engineering of point defects in solid-state ion conductors. Characterization of point defects is critical to these efforts, but the best-developed techniques are difficult and time-consuming. Raman spectroscopy—with its exceptional speed, flexibility, and accessibility—is a promising alternative. Raman signatures arise from point defects due to local symmetry breaking and structural distortions. Unfortunately, the assignment of these signatures is often hampered by a shortage of reference compounds and corresponding reference spectra. This issue can be circumvented by calculation of defect-induced Raman signatures from first principles, but this is computationally demanding. Here, we introduce an efficient computational procedure for the prediction of point defect Raman signatures in solid-state ion conductors. Our method leverages machine-learning force fields and “atomic Raman tensors”, i.e., polarizability fluctuations due to motions of individual atoms. We find that our procedure reduces computational cost by up to 80% compared to existing first-principles frozen-phonon approaches. These efficiency gains enable synergistic computational–experimental investigations, in our case allowing us to precisely interpret the Raman spectra of Sr(Ti0.94Ni0.06)O3-δ, a model oxygen ion conductor. By predicting Raman signatures of specific point defects, we determine the nature of dominant defects and unravel impacts of temperature and quenching on in situ and ex situ Raman spectra. Specifically, our findings reveal the temperature-dependent distribution and association behavior of oxygen vacancies and nickel substitutional defects. Overall, our approach enables rapid Raman-based characterization of point defects to support defect engineering in novel solid-state ion conductors.
Exploiting the synergy between organic polymer electrolytes and inorganic electrolytes via the development of composite electrolytes can suggest solutions to the current challenges of next‐generation solid‐state lithium‐metal batteries (SSLMBs). Depending upon a mass fraction of inorganic fillers and organic polymers, composite electrolytes are broadly classified into “ceramic‐in‐polymer” (CIP) and “polymer‐in‐ceramic” (PIC) categories, inheriting distinct structure and electrochemical properties. Since the stability and electrochemical characteristics of the inorganic phase are superior to those of the organic phase for lithium‐ion conduction, applying lithium‐enrich active filler in PIC seems more promising. The inorganic phase preserves the primary migratory channels in the PIC electrolyte, while the viscoelastic properties attempt to be introduced from the organic binder or host. The present work overviews the studies on state‐of‐the‐art PIC electrolytes, the fundamental mechanism of ionic conduction, preparation methods, and current progress in materials development for SSLMBs. In addition, the modification strategies for improving the electrode–electrolyte interface are also emphasized. Moreover, it further prospects the current challenges and effective strategies for the future development of PICs‐based CPEs to accelerate the practical application of SSLMBs. This review examines the progress and outlook of PIC‐based electrolytes for next‐generation lithium batteries.
The demand for high-energy-density batteries has prompted exploration into advanced materials for enhancing the safety and performance of lithium metal batteries (LMBs). This study introduces a novel approach, incorporating two-dimensional (2D) pyrazine and imine-linked covalent organic frameworks (COFs) into a polyethylene oxide (PEO)-based solid electrolyte matrix. The synthesized COFs act as multifunctional additives, improving mechanical strength, ionic conductivity (reaching 1.86 x 10-3 S/cm at room temperature), electrochemical window (oxidation resistance up to 5 V vs. Li/Li+), and thermal stability (up to 400oC). The unique electron-rich and polar functionalities of pyrazine and imine linkages facilitate strong interactions with lithium ions (Li+), resulting in a flexible composite solid electrolyte that mitigates dendrite formation and interface instability. Electrochemical performance of LMBs with LiNi0.8Mn0.1Co0.1O2 (NMC811) cathode further confirm the enhanced Li+ conductivity, prolonged cycling stability, and a
stable solid electrolyte interface, showcasing the potential of COFs in improving LMB performance. Overall, this study highlights the promising role of pyrazine and imine-linked COFs as effective additives for polymer-based solid electrolytes and
their potential for developing safer and more efficient LMBs in the future.
Garnet-type Li7La3Zr2O12 (LLZO) has garnered significant attention for solid-state Li-ion batteries due to its commendable Li-ion conductivity, wide electrochemical window, and exceptional chemical and thermal stability. Nonetheless, challenges related to structural instability and air stability persist, impeding its market expansion. Herein, we explore the effects of co-doping (Ga with Sc/Y/In/Er) on the crystal structure and Li-ion conductivity of LLZO through x-ray diffraction (XRD), scanning electron microscope (SEM), and AC impedance measurements. XRD refinement confirms the formation of pure-phase samples with a cubic crystal structure. SEM analysis reveals a dense microstructure with grain sizes exceeding 200 μm and a relative density approaching∼94%. While Ga/Sc and Ga/Y doped LLZO exhibit relatively lower Li-ion conductivity, Ga/Er and Ga/In doped samples demonstrate high conductivity more than 1 mS/cm at room temperature (25°C). Thus, the judicious selection of dopants emerges as an effective strategy for enhancing conductivity in all-solid-state batteries.
Lithium metal batteries (LMBs) enable much higher energy density than lithium‐ion batteries (LIBs) and thus hold great promise for future transportation electrification. However, the adoption of lithium metal (Li) as an anode poses serious concerns about cell safety and performance, which has been hindering LMBs from commercialization. To this end, extensive effort has been invested in understanding the underlying mechanisms theoretically and experimentally and developing technical solutions. In this review, we devote to providing a comprehensive review of the challenges, characterizations, and interfacial engineering of Li anodes in both liquid and solid LMBs. We expect that this work will stimulate new efforts and help peer researchers find new solutions for the commercialization of LMBs.
Sulfide solid-state electrolytes (SSSEs) are considered an auspicious alternative for all-solid-state batteries, because of their ductility and high ionic conductivity. One obstacle that thwarts SSSEs in large-scale applications is their lack of stability upon exposure to humid air. We used Lewis acid additives to treat the argyrodite Li6PS5Cl SSSE particles at the nanoscale level by dispersing them in solution mixtures, a method that had minimal impact on ionic conductivity. A series of investigations were conducted, involving the utilization of X-ray diffraction, in-situ Raman spectroscopy, solid-state nuclear magnetic resonance, and X-ray absorption near-edge structure for characterizations. The SSSE demonstrated notable atmospheric stability by establishing a Lewis acid−base interaction with the additives. This interaction effectively shields the SSSE from moisture in humid air, ensuring that the bulk region remains structurally intact and undeteriorated. Therefore, treating SSSEs using Lewis acid additives is an auspicious approach to improving their moisture stability.
Solid-state composite electrolytes (SCEs) bridge the gap between solid-state polymer electrolytes (SPEs) and solid-state inorganic electrolytes (SIEs), which play an important in developing the expected solid state Li ion batteries...
Li‐metal and silicon are potential anode materials in all‐solid‐state Li‐ion batteries (ASSBs) due to high specific capacity. However, both materials form gaps at the interface with solid electrolytes (SEs) during charging/discharging, resulting in increased impedance and uneven current density distribution. In this perspective, the different mechanisms of formation of these gaps are elaborated in detail. For Li‐metal anodes, Li‐ions are repeatedly stripped and unevenly deposited on the surface, leading to gaps and Li dendrite formation, which is an unavoidable electrochemical behavior. For Si‐based anodes, Li‐ions inserting/extracting within the Si‐based electrode causes volume changes and a local separation from the SE, which is a mechanical behavior and avoidable by mitigating the strain mismatch of thin‐film bonding between anode and SE. Si electro–chemical–mechanical behaviors are also described and strategies recommended to synergistically decrease Si‐based electrode strain, including Si materials, Si‐based composites, and electrodes. Last, it is suggested to choose a composite polymer–inorganic SE with favorable elastic properties and high ionic conductivity and form it directly on the Si‐based electrode, beneficial for increasing SE strain to accommodate stack pressure and the stability of the interface. Thus, this perspective sheds light on the development and application of Si‐based ASSBs.
In the present work, a solid‐state reaction (SSR) method is used to prepare a cubic phase Li 7 La 3 Zr 2 O 12 (C‐LLZO) via a two‐step process from tetragonal phase Li 7 La 3 Zr 2 O 12 (T‐LLZO). To identify the tetragonal to cubic phase change region a thermogravimetric analysis (TGA) of the precursor material is carried out. Subsequently, another TGA analysis is carried out for tetragonal sample to identify tetragonal to cubic phase transition regions. TGA of tetragonal sample shows multiple phase transition regions at ≈250°, 400°, and 610 °C. A series of T‐LLZO samples are reheated to obtain C‐LLZO. The T‐LLZO samples reheated at 150 °C, and 650 °C show cubic symmetry, whereas the sample heated at 450 °C and 950 °C show mixed phase. The obtained C‐LLZO samples have lattice constant a = b = c = 12.9389 Å for 150 °C heated sample and a = b = c = 12.9375 Å for 650 °C heated samples with space group I a‐3d. Considering the TGA of the T‐LLZO sample and XRD analysis of the T‐LLZO samples reheated at different temperatures, the transition at ≈150 °C is attributed to the hydration process of T‐LLZO and 650 °C is due to structural deformation of LLZO.
This article provides an overview of solid hybrid electrolytes based on Li ⁺ -conductive oxide and polymer electrolyte for all-solid-state lithium batteries and discusses their composition, conduction mechanism, progress, and perspectives.
Portable electronic devices and electric vehicles have become indispensable in daily life and caused an increasing demand for high‐performance lithium‐ion batteries (LIBs) with high‐energy‐density. This work compares the intrinsic characteristics and Li⁺ conduction mechanisms of various electrolytes, aiming at emphasizing their suitability for high‐energy‐density LIBs. Among all electrolytes, polymer‐based solid‐state electrolytes (SSEs) are the most promising candidates, as they demonstrate the most comprehensive properties. The advantages and disadvantages of commonly used polymer matrix materials of SSEs are discussed, along with typical approaches to address their limitations. As significant issues for high‐energy‐density and cycle stability, the development related to the cathode/electrolyte interfacial contact and wetting, interfacial electrochemical compatibility, and interfacial Li⁺ conduction in LIBs employing polymer‐based SSEs, as well as the anode/electrolyte interfacial chemical stability and lithium dendrite suppression are comprehensively reviewed and analyzed. Finally, perspectives on future research directions for developing high‐energy‐density LIBs are highlighted building upon the existing literature.
Rechargeable battery devices with high energy density are highly demanded by our modern society. The use of metal anodes is extremely attractive for future rechargeable battery devices. However, the notorious metal dendritic and instability of solid electrolyte interface issues pose a series of challenges for metal anodes. Recently, considering the indigestible dynamical behavior of metal anodes, photoelectrochemical engineering of light‐assisted metal anodes have been rapidly developed since they efficiently utilize the integration and synergy of oriented crystal engineering and photocatalysis engineering, which provided a potential way to unlock the interface electrochemical mechanism and deposition reaction kinetics of metal anodes. This review starts with the fundamentals of photoelectrochemical engineering and follows with the state‐of‐art advance of photoelectrochemical engineering for light‐assisted rechargeable metal batteries where photoelectrode materials, working principles, types, and practical applications are explained. The last section summarizes the major challenges and some invigorating perspectives for future research on light‐assisted rechargeable metal batteries.
Solid state electrolytes could address the current safety concerns of lithium-ion batteries as well as provide higher electrochemical stability and energy density. Amongst solid electrolytes contenders, garnet-structured Li7La3Zr2O12 appears as a particularly promising material owing to its wide electrochemical stability window; however its ionic conductivity remains an order of magnitude below that of ubiquitous liquid electrolytes. Here, we present an innovative dual substitution strategy developed to enhance Li-ion mobility in garnet-structured solid electrolytes. A first dopant cation, Ga³⁺, is introduced on the Li sites to stabilize the fast-conducting cubic phase. Simultaneously, a second cation, Sc³⁺, is used to partially populate the Zr sites, which consequently increases the concentration of Li ions by charge compensation. This aliovalent dual substitution strategy allows to fine-tune the number of charge carriers in the cubic Li7La3Zr2O12 according to the resulting stoichiometry, Li7-3x+yGaxLa3Zr2-yScyO12. The co-existence of Ga and Sc cations in the garnet structure is confirmed by a set of simulation and experimental techniques: DFT calculations, XRD, ICP, SEM, STEM, EDS, solid state NMR, and EIS. This thorough characterization highlights a particular cationic distribution in Li6.65Ga0.15La3Zr1.90Sc0.10O12, with preferential Ga³⁺ occupation of tetrahedral Li24d sites over the distorted octahedral Li96h sites. ⁷Li NMR reveals a heterogeneous distribution of Li charge carriers with distinct mobilities. This unique Li local structure has a beneficial effect on the transport properties of the garnet, enhancing the ionic conductivity and lowering the activation energy, with values of 1.8 mS cm⁻¹ at 300 K and 0.29 eV in the temperature range of 180 to 340 K, respectively.
The application of Li7La3Zr2O12 as a Li⁺ solid electrolyte is hampered by the lack of a reliable procedure to obtain and densify the fast-ion conducting cubic garnet polymorph. Dense cubic Li7La3Zr2O12-type phases are typically formed as a result of Al-incorporation in an unreliable reaction with the alumina crucible at elevated temperatures of up to 1230 °C. High Al³⁺-incorporation levels are also believed to hinder the three-dimensional movement of Li⁺ in these materials. Here, a new, facile hybrid sol-gel solid-state approach has been developed in order to accomplish reliable and controllable synthesis of these phases with low Al-incorporation levels. In this procedure, sol-gel processed solid precursors of Li7La3Zr2O12 and Al2O3 nanosheets are simply mixed using a pestle and mortar and allowed to react at 1100 °C for 3 h to produce dense cubic phases. Fast-ion conducting Al-doped Li7La3Zr2O12 phases with the lowest reported Al³⁺-content (∼0.12 mol per formula unit), total conductivities of ∼3 × 10⁴ S cm¹, bulk conductivities up to 0.6 mS and ion conduction activation energies as low as 0.27 eV, have been successfully achieved. The ease of lithium diffusion in these materials is attributed to the formation of dense cubic phases with low Al³⁺ dopant ratios. This approach is applicable to Li7xLa3Zr2xTaxO12 phases and opens up a new synthetic avenue to Li7La3Zr2O12-type materials with greater control over resulting characteristics for energy storage applications.
Li7La3Zr2O12 (LLZO) is a promising electrolyte material for all-solid-state battery due to its high ionic conductivity and good stability with metallic lithium. In this article, we studied the effect of crucibles on the ionic conductivity and air stability by synthesizing 0.25Al doped LLZO pellets in Pt crucibles and alumina crucibles, respectively. The results show that the composition and microstructure of the pellets play important roles influencing the ionic conductivity, relative density, and air stability. Specifically, the 0.25Al-LLZO pellets sintered in Pt crucibles exhibit a high relative density (~96%) and high ionic conductivity (4.48 × 10-4 S cm-1). The ionic conductivity maintains at 3.6 × 10-4 S cm-1 after 3-month air exposure. In contrast, the ionic conductivity of the pellets from alumina crucibles is about 1.81 × 10-4 S cm-1 and drops to 2.39 × 10-5 S cm-1 three months later. The large grains and the reduced grain boundaries in the pellets sintered in Pt crucibles are favorable to obtain high ionic conductivity and good air stability. X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy results suggest that the formation of Li2CO3 on the pellet surface is probably another main reason, which is also closely related to the relative density and the amount of grain boundary within the pellets. This work stresses the importance of synthesis parameters, crucibles included, to obtain the LLZO electrolyte with high ionic conductivity and good air stability.
Here, we investigate the doping effects on the lithium ion transport behavior in garnet Li7La3Zr2O12 (LLZO) from the combined experimental and theoretical approach. The concentration of Li ion vacancy generated by the inclusion of aliovalent dopants such as Al(3+) plays a key role in stabilizing the cubic LLZO. However, it is found that the site preference of Al in 24d position hinders the three dimensionally connected Li ion movement when heavily doped according to the structural refinement and the DFT calculations. In this report, we demonstrate that the multi-doping using additional Ta dopants into the Al-doped LLZO shifts the most energetically favorable sites of Al in the crystal structure from 24d to 96 h Li site, thereby providing more open space for Li ion transport. As a result of these synergistic effects, the multi-doped LLZO shows about three times higher ionic conductivity of 6.14 × 10(-4) S cm(-1) than that of the singly-doped LLZO with a much less efforts in stabilizing cubic phases in the synthetic condition.
Titanium, tantalum-substituted Li7La3Zr2-xAxO12 (LLZO, A = Ta, Ti) garnets, and chromium-substituted La(2/3)-xLi3xTi1-yCryO3 (LLTO) perovskites were prepared by a conventional solid-state reaction and the Pechini processes. The desired crystal phases were obtained by varying the calcination temperature and time, as well as the substitution concentration. All samples indicated decomposition of the precursors when heated above 750 °C and formation of the desired phase after heat treatment at higher temperatures. Neutron diffraction data shows the formation of a predominant cubic phase in the case of Ta-LLZO, and monoclinic phase with minor impurity phases for Cr-LLTO. Ionic conductivity for Ti-LLZO (Li7La3Zr1.4Ti0.6O12), Ta-LLZO (Li6.03La3Zr1.533Ta0.46O12), and Cr-LLTO (La(2/3)-xLi3xTi0.9Cr0.1O3) at room temperature were found to be 5.21 × 10−6, 1.01 × 10−6, and 1.2 × 10−4 S cm−1, respectively. The activation energies of the compounds were determined from the Arrhenius plot and were 0.44 eV (Ti0.6-LLZO), 0.54 eV (Ta0.5-LLZO), and 0.20 eV (Cr0.1-LLTO).
Lithium (Li) metal is an ideal anode material for rechargeable batteries due to its extremely high theoretical specific capacity (3860 mA h g À1), low density (0.59 g cm À3) and the lowest negative electrochemical potential (À3.040 V vs. the standard hydrogen electrode). Unfortunately, uncontrollable dendritic Li growth and limited Coulombic efficiency during Li deposition/stripping inherent in these batteries have prevented their practical applications over the past 40 years. With the emergence of post-Li-ion batteries, safe and efficient operation of Li metal anodes has become an enabling technology which may determine the fate of several promising candidates for the next generation energy storage systems, including rechargeable Li–air batteries, Li–S batteries, and Li metal batteries which utilize intercalation compounds as cathodes. In this paper, various factors that affect the morphology and Coulombic efficiency of Li metal anodes have been analyzed. Technologies utilized to characterize the morphology of Li deposition and the results obtained by modelling of Li dendrite growth have also been reviewed. Finally, recent development and urgent need in this field are discussed.
The solvent-free hybrid solid electrolytes composed of lithium aluminum germanium phosphate (LAGP) and poly(ethylene oxide) (PEO) were prepared in the form of flexible film, and their electrochemical characteristics were investigated. The addition of ion-conductive LAGP powder into PEO-based solid polymer electrolyte improved the electrical and mechanical properties of solid electrolytes. For the hybrid solid electrolytes examined in this study, the optimum composition of LAGP was found to be about 60∼80 wt% in consideration of ionic conductivity, mechanical stability and formability for flexible thin film. The all solid-state Li/LiFePO4 cell assembled with hybrid solid electrolyte delivered an initial discharge capacity of 137.6 mAh g-1 and exhibited good cycling stability at 55.C.
Lithium solid electrolytes have shown their potential for high-energy density batteries. Use of solid electrolytes will also be able to overcome safety issues associated with conventional carbonated-based electrolytes. However, to achieve the combination of high ionic conductivity and excellent electrochemical stability in lithium solid electrolytes still remains a major challenge. Herein we report a facile strategy to achieve high conduction and excellent electrochemical stability by the substitution of Cl for O based on the concept of bottleneck size and binding energy. The ionic conductivities of Li10.42Si1.5P1.5Cl0.08O11.92 and Li10.42Ge1.5P1.5Cl0.08O11.92 are 1.03×10-5 S cm-1 and 3.7×10-5 S cm-1 at 27 oC, respectively, which is 13 orders of magnitude higher than that of the pure Li3PO4, and 1 order of magnitude higher than that of the pristine Li10.5Si1.5P1.5O12. The electrochemical stability with metallic lithium is up to 9 V vs. Li+/Li, one of the solid electrolytes with most wide electrochemical window. This research also addresses the crystal structure, lithium ions migration mechanism, and battery performance.
The inherent high resistance of electrolyte/electrode interface in all-solid-state-lithium-secondary batteries (SSLB) poses a significant hurdle for the SSLB development. The interfacial resistivity between Li7La3Zr2O12 (LLZ) and LiCoO2 is decreased by introducing a thin Nb layer (∼10 nm) at this interface. The interface modification approach using a Nb interlayer dramatically improves the discharge capacity and rate capability of a SSLB.
Recently, the demand of a high energy density battery for electric vehicles (EVs) has been significantly increased, because the driving range of EVs with conventional lithium-ion batteries is too short compared with vehicles with internal conversion engines. Lithium-air batteries are attractive candidate for the high specific energy density batteries, because of their high theoretical energy density as 3560 Wh kg ⁻¹ for the non-aqueous and 1910 Wh kg ⁻¹ for the aqueous system. Non-aqueous systems have some severe problems that still need to be addressed such as decomposition of the electrolyte by the reaction product, lithium corrosion by water, and high polarization for reduction of the reaction product of Li 2 O 2 . While, some of these problems are not appreciable to the aqueous system. The aqueous system cannot operate without a water stable lithium metal electrode, because lithium reacts violently with water. The idea of the water stable lithium electrode was proposed by Visco et al. in 2004 [1]. The lithium metal was separated with an aqueous electrolyte by the water stable NASICON-type lithium conducting solid electrolyte of Li 1+X Al x Ti 2-x (PO 4 ) 3. In the last half century, many types of high lithium-ion conducting solid electrolytes have been reported, the conductivities of which are in a range of 10 ⁻⁴ -10 ⁻² S/cm at room temperature. Of them, Li 1+x A x Ti 2-x (PO 4 ) 4 and Li 7 La 3 Zr 2 O 12 were reported to be stable in the LiCl saturated aqueous solution. The stability in the aqueous solutions is essential for the lithium protect solid electrolyte in aqueous lithium-air batteries. The Ta doped Li 7 La 3 Zr 2 O 12 exhibited a high lithium ion conductivity of 1x10 ⁻³ S cm ⁻¹ at 25 °C and is stable in contact with lithium metal, but it is difficult to prepare a thin film, because of lithium evaporation during the high temperature sintering. The thin film of Li 1+x A x Ti 2-x (PO 4 ) 4 was prepared by a tape casting method and the ion conductivity of the Li 1.4 Al 0.4 Ti 1.6 (PO 4 ) 3 -3wt% TiO 2 film was 7.7 x10 ⁻⁴ S cm ⁻¹ at 25 °C [2]. .
Since the report by Aono et al. in 1989 [3], the NASICON-type lithium-ion conducting solid electrolytes have been extensively examined. Zhang et al. reported that the electrical conductivity of Li 1+x Al x Ti 2-x (PO 4 ) 3 was enhanced by a partial substitution of Ge, Co, and Fe for Ti. The highest ion conductivity of 1.3×10 ⁻³ S cm ⁻¹ at 25 °C was observed in Li 1.4 Al 0.4 Ge 0.2 Ti 1.4 (PO 4 ) 3 . In this study, we have examined dependence of the substitution of Nb ⁵⁺ for Ti ⁴⁺ in Li 1+x Al x Ti 2-x (PO 4 ) 3 on the electrical conductivity and mechanical properties. Ionic radius of Nb ⁵⁺ (0.064 nm) is slightly higher than that of Ti ⁴⁺ (0.061 nm) and higher than that of Ge ⁴⁺ (0.053 nm). Nb 2 O 5 is considerably cheaper than GeO 2 . Li 1+x-y Al x Nb y Ti 2-x-y (PO 4 ) 3 was synthesized in a range of x=0-0.60 and y=0-0.4 using a conventional solid-state reaction method. The lithium-ion conductivity of 7.5×10 ⁻⁴ S cm ⁻¹ and three-point bending strength of 67 N mm ⁻² for Li 1.3 Al 0.5 Nb 0.2 Ti 1.3 (PO 4 ) 3 and the lithium-ion conductivity of 3x10 ⁻⁴ S cm ⁻¹ and the three-point bending strength of 120 N mm ⁻² for Li 1.35 Al 0.55 Nb 0.2 Ti 1.25 (PO 4 ) 3 at room temperature were observed. The water-stable high lithium-ion conducting solid electrolytes with excellent mechanical properties have potential applications for lithium-air batteries.
References
[1] S.J. Visco et al. in 12 th International Meeting on Lithium Batteries, Abst. # 53, Nara, Japan, 2004
[2] K. Takahashi et al.. J. Electrochem. Soc., 159, A1065 (2012)
[3] H. Aono et al. J. Electrochem. Soc., 136, 590 (1989)
Low ionic conductivity limits the development of NASICON-type LiZr2(PO4)3 (LZP) for solid-state batteries. Here, we present the possible factors that may affect the conductivity, and further establish the relationships among conductivity, crystal structure, relative density, grain size, chemical composition, and elemental distribution. The conditions for the existence of the four phases of LZP (α, α’, β, and β’) and the phase transition processes among them are systematically clarified. With secondary ion mass spectrometry, the spatial distribution of elements within the grains and grain boundaries is clearly pre-sented. Based on our results, proper elemental doping, high sintering temperature, and especially fast cool-down rate are all indispensable to stabilize the high-conductivity (α) phase at room temperature. Finally, we demonstrate the feasibility of lithium-based batteries with this LZP solid electrolyte and commercial cathodes. This work provides insights for preparing LZP with high conductivity and paves the way for the development of solid-state batteries.
Al-doped Li7-xLa3Zr2O12 is found to be more ionically conductive following voltammetric treatment in an all-solid-state Li | Li7-xLa3Zr2O12 | Li cell configuration. This result is consistent with electrical impedance spectroscopy measurements, which reveal that the activation energy for lithium diffusion is reduced from 0.32 eV to 0.26 eV following voltammetric treatment. The Li deposition–dissolution signal has been observed in the voltammograms, and neutron powder diffraction shows an increase in the lithium content of the Li7-xLa3Zr2O12. Furthermore, X-ray photoelectron spectroscopy indicates a local rearrangement of O, resulting in a reduction of defects following voltammetric treatment, with the enhanced conductivity attributable to both the reduction of defect oxygen and increased lithium content. This work, therefore reveals such voltammetric treatment as a simple and inexpensive alternative to existing doping approaches to boost the electrochemical performance of Li7-xLa3Zr2O12. The findings can improve the future development of all-solid-state Li-ion batteries. On the other hand, our approach to understanding the conductivity enhancement via voltammetric treatment may provide a better understanding of the alteration in the ionic conduction of solid electrolytes during solid-state battery operation.
Solid electrolytes with high ionic conductivity are important for all solid state lithium batteries. NASICON typed LiTi2(PO4)3 solid electrolytes are synthesized by a simply LiF assisted solid state reaction. The electrolytes prepared with LiF assist exhibit much larger particle size, less voids and higher crystallinity than that of the sample without LiF assist. The LiTi2(PO4)3 sample synthesized with LiF additive (the molar ratio of LiTi2(PO4)3:LiF = 1:0.5) delivers lithium ion conductivity of 2.318 × 10− 4 S cm− 1 at room temperature with an activation energy as low as 0.28 eV; while the electrolyte prepared without LiF assist exhibits conductivity of 7.181 × 10− 6 S cm− 1 and activation energy of 0.48 eV. The significantly enlarged conductivity and reduced activation energy suggest LiF assist is an effective and simple method to improve the performance of LiTi2(PO4)3 solid electrolytes for all solid state lithium batteries.
Solid electrolytes are key to the evolution of all-solid-state lithium batteries as next-generation energy storage systems. High ionic conductivity and stability of solid electrolytes are critical requirements for designing reliable all-solid-state lithium batteries. Perovskite-type lithium lanthanum titanates Li3xLa(2/3)-x□(1/3)-2xTiO3 (LLTOs) have received much attention as a potential inorganic solid electrolyte to replace current organic liquid electrolytes; however, the practical use of LLTOs is limited by their low total conductivity. With the aim of improving the ionic conductivity, we investigated a correlation between the microstructures and Li⁺ conducting properties of LLTO perovskites. We show that the total conductivity of LLTOs is dominated by the domain boundary resistance, and the synthesis condition of the electrolyte (sintering temperature and Li concentration) has a crucial role in modifying the microstructure and composition of the domain boundaries to significantly reduce the boundary resistance. By controlling the sintering temperature and Li content, in particular, a total Li⁺ conductivity as high as 4.8 × 10⁻⁴ S cm⁻¹ can be achieved at room temperature. The findings of this study would be essential in understanding Li⁺ conducting behaviors and in developing highly conductive perovskite-type LLTO solid electrolytes.
LISICON-related compositions Li4±xSi1-xXx O4 (X = P, Al, Ge) are important materials that have been identified as potential solid electrolytes for all solid state batteries. Here we show that the room temperature lithium ion conductivity can be improved by several orders of magnitude through substitution on Si sites. We apply a combined computer simulation and experimental approach to a wide range of compositions: Li4SiO4, Li3.75Si0.75P0.25O4, Li4.25Si0.75Al0.25O4, Li4Al0.33Si0.33P0.33O4 and Li4Al1/3Si1/6Ge1/6P1/3O4 which include new doped materials. Depending on the temperature, three different Li+ ion diffusion mechanisms are observed. The polyanion mixing introduced by substitution lowers the temperature at which the transition to a superionic state with high Li+ ion conductivity occurs. These insights help to rationalize the mechanism of the lithium ion conductivity enhancement and provide strategies for designing materials with promising transport properties.
In this manuscript, we introduced the nano concept in the oxide solid electrolyte Li7La3Zr2O12 (LLZO). All-solid-state Li/LiFePO4 (LFPO) cell using this solid electrolyte with thickness of several micrometers was assembled with appropriate solvent, dispersant, adhesives and surfactant without cold- or hot-pressing. At room temperature, the Li/LLZO/LFPO cell showed the first discharge capacity of 160.4 mAh g-1, which was the 94.4% of the theoretical capacity of LFPO. And the cell provided a discharge capacity of 136.8 mAh g-1 after 100 cycles. At 60 ℃, the battery presented more stable electrochemical performance. The capacity loss during the cycles form the 2nd to 100th was only 0.06% (0.7 mAh g-1). The excellent performance could be attributed to the ultrathin solid electrolyte film.
In this study, Li2O-TiO2-P2O5-x(Fe2O3) (x = 0, 2.5, 5 and 7.5 weight part) glass and glass-ceramics were synthesized through conventional melt-quenching method and subsequently heat treatment. Glass samples were studied by UV–visible spectroscopy and crystallized samples were characterized by differential thermal analysis, X-ray diffractometry and field emission scanning electron microscopy. Besides, electrical properties were examined according to the electrochemical impedance spectroscopy techniques.
Solid electrolyte materials composed of lithium titanium phosphate (LTP) or lithium aluminum titanium phosphate (LATP) and ionic liquid (IL) were formed and studied by means of X–ray diffractometry, thermogravimetry, scanning electron microscopy, impedance spectroscopy and density methods. Study revealed substantial enhancement of total ionic conductivity of the studied materials compared to the parent LTP or LATP matrixes. Two components of total resistance were identified. One, independent on the IL contents in the material, was attributed to grains. The second one strongly decreased with the IL contents. It was suggested that interaction of the IL with grain boundary was responsible for that.
Li7La3Zr2O12-based Li-rich garnets react with water and carbon dioxide in air to form a Li-ion insulating Li2CO3 layer on the surface of the garnet particles, which results in a large interfacial resistance for Li-ion transfer. Here, we introduce LiF to garnet Li6.5La3Zr1.5Ta0.5O12 (LLZT) to increase the stability of the garnet electrolyte against moist air; the garnet LLZT-2 wt % LiF (LLZT-2LiF) has less Li2CO3 on the surface and shows a small interfacial resistance with Li metal, a solid polymer electrolyte, and organic-liquid electrolytes. An all-solid-state Li/polymer/LLZT-2LiF/LiFePO4 battery has a high Coulombic efficiency and long cycle life; a Li-S cell with the LLZT-2LiF electrolyte as a separator, which blocks the polysulfide transport towards the Li-metal, also has high Coulombic efficiency and kept 93 % of its capacity after 100 cycles.
Due to their extremely high specific energy, rechargeable Li-air batteries could meet the demand for large-scale storage systems to integrate renewable sources into the power grid. Li-air batteries with aqueous catholytes with high solubility of discharge products have a higher potential to reach their slightly lower theoretical limits in practical devices. In this work, we demonstrate aqueous and hybrid Li-air batteries with NASICON-type Li1+xAxGe2−x(PO4)3 ceramic as anode-protecting membrane. The LAGP ceramic pellets with room temperature conductivity >10⁻⁴ S cm⁻¹ are synthesized by melt quenching and subsequently annealed based on our optimized heat treatment cycle. Hybrid Li-air batteries are assembled by sandwiching LAGP membranes between Li-anode chamber and catholyte solutions (of various pH values) with CNT/Pt as air-cathode. When the two electron reduction mechanism prevails, overpotentials below 0.2 V are achieved for currents up to 0.07 mA cm⁻² leading to energy efficiencies exceeding 98%.
A water-stable lithium-ion conducting solid electrolyte with high conductivity and excellent mechanical properties has potential application for aqueous lithium-air batteries. In this study, a water-stable NASICON-type lithium-ion conducting solid electrolyte with a nominal composition of Li1+x − yAlxNbyTi2 − x − y(PO4)3 was synthesized with variation of the Al and Nb contents using a conventional solid-state reaction method, and the electrical conductivity and mechanical properties were examined. The highest lithium-ion conductivity of 7.5 × 10− 4 S cm− 1 at 25 °C and the highest three-point bending strength of 110 N mm− 2 at room temperature were observed for Li1.30Al0.5Nb0.2Ti1.30(PO4)3 and Li1.35Al0.55Nb0.2Ti1.25(PO4)3, respectively. Li1.30Al0.5Nb0.2Ti1.30(PO4)3 was stable in a saturated LiOH aqueous solution with saturated LiCl.
A cross-linked polymer containing pendant molecules attached to the polymer framework is shown to form flexible and low-cost membranes, to be a solid Li+ electrolyte up to 2700C, much higher than those based on polyethylene oxide, to be wet by a metallic lithium anode, and to be not decomposed by the metallic anode if the anions of the salt are blocked by a ceramic electrolyte in a polymer/ceramic-membrane/polymer sandwich electrolyte (PCPSE). In this sandwich architecture, the double-layer electric field at the Li/polymer interface is reduced owing to the blocked salt-anion transfer. The polymer layer adheres/wets well the lithium-metal surface and makes the Li-ion flux at the interface more homogeneous. This structure integrates the advantages of the ceramic and polymer. With the PCPSE, all-solid-state Li/LiFePO4 cells showed a notably high coulombic efficiency of 99.8-100% over 640 cycles.
Highly ion conducting glass-ceramics, crystallizing in the Na-superionic conducting (NASICON) structure, have been prepared in the system Li1+xAlxSnyGe2-(x+y)(PO4)3 by crystallization of glassy precursor samples. For modest substitution levels (y = 0.25), these crystalline solid solutions show slightly higher electrical conductivity than corresponding samples without Sn, supporting the rationale that the lattice expansion associated with the substitution of Ge by its larger homologue Sn can enhance ionic conductivity. Higher Sn substitution levels (y = 0.45) do not result in any improvement. The glass-to-crystal transition has been characterized in detail by multinuclear single and double resonance NMR experiments. While substantial changes in the 31P and 27Al MAS NMR spectra indicate that the crystallization of the glasses is accompanied by significant modifications in the local environments of the phosphate and the aluminum species, the dipolar solid state NMR experiments indicate that the structures
This Review is focused on ion-transport mechanisms and fundamental properties of solid-state electrolytes to be used in electrochemical energy-storage systems. Properties of the migrating species significantly affecting diffusion, including the valency and ionic radius, are discussed. The natures of the ligand and metal composing the skeleton of the host framework are analyzed and shown to have large impacts on the performance of solid-state electrolytes. A comprehensive identification of the candidate migrating species and structures is carried out. Not only the bulk properties of the conductors are explored, but the concept of tuning the conductivity through interfacial effects-specifically controlling grain boundaries and strain at the interfaces-is introduced. High-frequency dielectric constants and frequencies of low-energy optical phonons are shown as examples of properties that correlate with activation energy across many classes of ionic conductors. Experimental studies and theoretical results are discussed in parallel to give a pathway for further improvement of solid-state electrolytes. Through this discussion, the present Review aims to provide insight into the physical parameters affecting the diffusion process, to allow for more efficient and target-oriented research on improving solid-state ion conductors.
Lithium metal batteries (LMBs) are among the most promising candidates of high‐energy‐density devices for advanced energy storage. However, the growth of dendrites greatly hinders the practical applications of LMBs in portable electronics and electric vehicles. Constructing stable and efficient solid electrolyte interphase (SEI) is among the most effective strategies to inhibit the dendrite growth and thus to achieve a superior cycling performance. In this review, the mechanisms of SEI formation and models of SEI structure are briefly summarized. The analysis methods to probe the surface chemistry, surface morphology, electrochemical property, dynamic characteristics of SEI layer are emphasized. The critical factors affecting the SEI formation, such as electrolyte component, temperature, current density, are comprehensively debated. The efficient methods to modify SEI layer with the introduction of new electrolyte system and additives, ex‐situ‐formed protective layer, as well as electrode design, are summarized. Although these works afford new insights into SEI research, robust and precise routes for SEI modification with well‐designed structure, as well as understanding of the connection between structure and electrochemical performance, is still inadequate. A multidisciplinary approach is highly required to enable the formation of robust SEI for highly efficient energy storage systems.
A multistep sintering schedule is developed to synthesize Li7La3Zr2O12 (LLZO) doped with 0.2 mol% Al3+. The effect of sintering steps on phase, relative density and ionic conductivity of Al-doped LLZO has been evaluated using powder X-Ray diffraction (XRD), scanning electron microscopy (SEM), 27Al magic spinning nuclear magnetic resonance (NMR) spectroscopy and electrochemical impedance spectroscopy (EIS). The results show that by holding the sample at 900 °C for 6 h, the mixture of tetragonal and cubic garnet phases are obtained; by continuously holding at 1100 °C for 6 h, the tetragonal phase completely transforms into cubic phase; by holding at 1200 °C, the relative density increases without decomposition of the cubic phase. The Al-LLZO pellets after multistep sintering exhibit cubic phase, relative density of 94.25% and ionic conductivity of 4.5 × 10-4 S cm-1 at room temperature. Based on the observation, a sintering model is proposed and discussed.
All solid-state lithium batteries are constructed by using highly conducting Ta-doped Li7La3Zr2O12 (LLZTO) as the solid electrolytes as well as the supports, coated with composite cathodes consisting of poly(vinylidene fluoride) (PVdF):LiTFSI, Ketjen Black, and carbon-coated LiFePO4 on one side and attached with Li anode on the other side. At 60°C, the batteries show the first discharge capacity of 150 mAh g-1 at 0.05 C and 93% capacity retention after 100 cycles. As the current density increases from 0.05 C to 1 C, the specific capacity decreases from 150 mAh g-1 to 100 mAh g-1. Further elevated temperature up to 100°C leads to further improved performance, i.e. 126 mAh g-1 at 1 C and 99% capacity retention after 100 cycles. This good performance can be attributed to the highly conducting ceramic electrolytes, the optimum electronic and ionic conducting networks in the composite cathodes, and closely contacted cathode/LLZTO interface. These results indicate that the present strategy is promising for development of high-performance solid-state Li-ion batteries operated at medium temperature.
LiTi2(PO4)3 (LTP) and related materials based on the structure of NaZr2(PO4)3 (NZP) belong to a family of Li ion conducting compounds for applications in Li ion batteries. Because of their three-dimensional framework of TiO6 octahedra and PO4 tetrahedra, which provide several positions for mobile charge carriers, and the large number of possible compounds crystallizing in this type of structure, they are promising ion conducting materials. In this work, we investigate the migration barriers for an interstitial Li ion and a Li vacancy in the rhombohedral structure of these compounds using density functional theory. Our results show that the substitution of Ti atoms in LTP by a variety of tri-, tetra-, and pentavalent cations X (LXTP) leads to structural changes influencing the Li mobility. The calculated activation energies for migrating vacancies vary between 0.29 and 0.75 eV and are related to the sizes of LiO6 octahedra in the structure. For migrating interstitials in bulk LTP, the calculated activation energy of about 0.19 eV is much lower. However, substitution by trivalent ions like Al introduces interstitial Li ions for charge compensation, but these additional Li ions get trapped near the trivalent ions.
The all-solid-state Li-air battery has been fabricated, which is constructed by a lithium foil anode, a NASICON-type solid state electrolyte Li1+xAlyGe2-y(PO4)3 (LAGP) and single-walled carbon nanotubes (SWCNTs)/LAGP nanoparticles composite as air electrode. Its electrochemical performance and reaction products were investigated in air atmosphere. Particularly, this battery exhibited a larger capacity about 2800 mAh g-1 for the first cycle while comparatively the battery with multi-walled carbon nanotubes (MWCNTs)/LAGP as cathode had a capacity of only about 1700mAhg-1. Also, the battery with SWCNTs/LAGP showed improved cycling performance with a reversible capacity of 1000 mAh g-1 at a current density of 200 mAh g-1. Our result demonstrated that the all-solid-state Li-air battery with SWCNTs/LAGP as cathode catalyst has a considerable potential for practical application.
Understanding of the fundamental mechanisms causing significant enhancement of Li-ionic conductivity by Al3+ doping to a solid LiGe2(PO4)3 (LGP) electrolyte is pursued using first principles density functional theory (DFT) calculations combined with experimental measurements. Our results indicate that partial substitution Al3+ for Ge4+ in LiGe2(PO4)3 (LGP) with aliovalent (Li1+xAlxGe2−x(PO4)3, LAGP) improves the Li-ionic conductivity about four-orders of the magnitude. To unveil the atomic origin we calculate plausible diffusion paths of Li in LGP and LAGP materials using DFT calculations and a nudged elastic band method, and discover that LAGP had additional transport paths for Li with activation barriers as low as only 34% of the LGP. Notably, these new atomic channels manifest subtle electrostatic environments facilitating cooperative motions of at least two Li atoms. Ab-initio molecular dynamics predict Li-ionic conductivity for the LAGP system, which is amazingly agreed experimental measurement on in-house made samples. Consequently, we suggest that the excess amounts of Li caused by the aliovalent Al3+ doping to LGP lead to not only enhancing Li concentration but also opening new conducting paths with substantially decreases activation energies and thus high ionic conductivity of LAGP solid-state electrolyte.
Effect of doping gallium is studied, and thereby, its consequence on the electrical properties of lithium-based Li1.3Al0.3 − x
Ga
x
Ti1.7(PO4)3 (LAGTP) system (where x = 0.01, 0.03, 0.05, and 0.07) is reported. X-ray diffraction (XRD) data is used to interpret the micro-structural properties. Electrical properties of Li+ ion are studied using impedance spectroscopy in the microwave frequency range of 32 MHz to 1 Hz. The effect on Li+ conductivity was studied in a temperature range 303 to 423 K. It was found that the gallium doping enhanced the conductivity of Li+ ions. The maximum Li+ conductivity of ∼4 × 10−3 S/cm was observed for gallium-doped samples at 413 K. The factors affecting the Li+ conductivity are discussed using the results from XRD patterns and impedance spectroscopy.
NASICON-structured Li1.5Al0.5Ge1.5(PO4)3 glass-ceramic is successfully fabricated through melt-quench with post-crystallization. The influence of crystallization temperature on structure and ionic conductivity is studied using X-ray diffraction, nuclear magnetic resonance and impedance analysis, revealing that the Li ion mobility is closely related with crystallization temperature that in turn affects the bulk conductivity. Scanning electron microscopy reveals a progress of transformation from an amorphous phase to a crystalline, and grain growth during the annealing. It is shown that crystallization temperature plays an important role in controlling the ionic conductivity. The highest conductivity of 2.25 × 10−3 S cm−1 with an activation energy of 0.29 eV at room temperature has been obtained for the glass-ceramic specimen crystallized at 825 °C for 8 h.
Due to their high ionic conductivity and stability versus metallic lithium, garnet-related Li7La3Zr2O12 (LLZ) are of interest as Li+ solid electrolytes. The correlation between structure and ion mobility in undoped, Ta5 +, Nb5 +, Ga3 + or Al3 + doped LLZ is studied combining molecular dynamics (MD) simulations and experimental characterisation. Neutron and in situ XRD powder diffraction are employed to analyse the Li and dopant distribution and temperature dependence of the structure. Pentavalent doping enhances ionic conductivity by increasing the vacancy concentration and reducing local Li ordering. Trivalent doping Al3 + or Ga3 + on the Li site is slightly less effective in enhancing conductivity. Ga3 + doping on the La3 + site only helps to retain the cubic phase, but does not affect the mobile charge carrier concentration. The cooling rate after sintering is found to strongly affect both the ionic conductivity and its hysteresis on subsequent thermal cycling in the low temperature range, which can be attributed to local Li ordering as manifested by non-linear variations of the lattice parameters.
High density (∼96%) garnet-type Al-contained Li6.75La3Zr1.75Ta0.25O12 (LLZTO-Al) solid electrolytes are prepared by conventional solid-state reaction and the following flowing oxygen sintering process. An overall ionic conductivity as high as 7.4 × 10−4 S cm−1 at 25 °C is achievable, remarkably higher than that obtained by sintering in other atmospheres. The dependence of density and conductivity of solid electrolytes on sintering under different oxygen partial pressures is discussed. Atmosphere sintering is proved to be an effective method to improve the relative density of lithium oxide ceramics.
Herein, we report a study on the structural and thermodynamic effects that cation size disparity may have in NASICON-type solid solutions. A sol gel procedure was used to synthesize two new NASICON-type lithium-ion conductors with nominal compositions LiGe2-ySny(PO4)(3) and Li1+xAlxGe2-y-(1/2)xSny-(1/2)x(PO4)(3). The effect of tin substitution on structure and lithium-ion conductivity was studied with powder X-ray diffraction, Raman spectroscopy, and dielectric spectroscopy. It is found that, although increased unit-cell dimensions derived from X-ray data suggest that tin incorporation should open the conduction bottleneck regions and improve conductivity, a decrease in conductivity is observed. Analysis of the electrical data shows that the conduction activation energy is comprised of contributions from carrier motion and generation, the latter accounting for up to 20% of the total activation energy. This result, currently unreported for NASICON-type materials, is correlated with local structural distortions observed in Raman spectra. It is deduced that the bottleneck regions suffer distortions due to the large ionic radius disparity among cationic constituents, which results in the "trapping" of charge carriers. Data estimated for the entropy of motion are also presented and discussed, considering the most probable thermodynamic equilibrium states.
High lithium ion conductivity solid electrolytes of Li1 + xCrxTi2 − x(PO4)3 (x = 0–0.5) and Li1.4AlxCr0.4 − xTi1.6(PO4)3 (x = 0–0.4) with the NASICON-type structure were synthesized using a precursor prepared by the sol–gel method. The highest total electrical conductivity of 3.55 × 10− 4 S cm− 1 at 25 °C was obtained for x = 0.4 in Li1 + xCrxTi2 − x(PO4)3 (LACTP) sintered at 1120 °C for 6 h in air. Higher electrical conductivity was observed by the partial substitution of Cr3 + with Al3 +. The highest total electrical conductivity of 1.06 × 10− 3 S cm− 1 and bulk conductivity of 1.77 × 10− 3 S cm− 1 at 25 °C were obtained for x = 0.3 in Li1.4AlxCr0.4 − xTi1.6(PO4)3 sintered at 1070 °C for 6 h in air. The contribution of electronic conductivity to the total conductivity was negligibly small. Li1.4Al0.3Cr0.1Ti1.6(PO4)3 was unstable in water, but stable in saturated LiOH with saturated LiCl aqueous solution.
Fast ion conductors Li1+xAlxTi2−x(PO4)3 (LATP) and Li1+xAlxGe2−x(PO4)3 (LAGP) with 0 ≤ x ≤ 0.5 have been successfully prepared by the solid state reaction method and characterized using X-ray diffraction (XRD), nuclear magnetic resonance (NMR) and impedance spectroscopy (IS) techniques. The structural analysis showed that the main crystalline phase detected in the XRD patterns of prepared samples displays the rhombohedral NASICON-type structure (space group R-3c). From the analysis of the 27Al and 31P MAS-NMR spectra, octahedra occupation and cation distribution have been investigated; from 7Li MAS-NMR spectra, structural sites and local mobility of Li have been analyzed. Information about long-range lithium mobility has been deduced from the analysis of IS data recorded in the frequency 20 Hz to 3 GHz and temperature 100–500 K intervals. The use of the derivative log σ vs. log ω function has enabled the detection of two high frequency responses that have been associated, according to the core-shell model, to the heterogeneous distribution of Al at surface and inside LATP and LAGP particles. IS measurements showed a higher bulk conductivity (3.4 × 10−3 and ∼10−4 S cm−1 at RT) and lower activation energy (0.28 and 0.38 eV) in LATP and LAGP samples, respectively.
The lithium ion conductivities of as-prepared composite membranes consisting of a polyethylene oxide (PEO) matrix with various contents of tetragonal Li7La3Zr2O12 (LLZO) were evaluated, and the optimum composition (52.5% LLZO) was determined by performing AC impedance measurements. The ionic conductivities of the composite membranes pass through a maximum as the LLZO content varies. Therefore, the hybridization of the organic and inorganic components of these membranes results in synergetic effects on their lithium ionic conductivity. In addition, tests of Li/composite membrane/LiNi0.6Co0.2Mn0.2O2 half-cells found that their charge/discharge properties are better than those of a PEO-only membrane and a membrane containing 52.5% Al2O3 instead of LLZO.
Colorless and transparent single crystals of cubic Li7La3Zr2O12 are prepared from mixtures of Li2CO3, La2O3, and ZrO2 in the molar ratio of 3.85:1.5:2.0 (air, 1250 °C).
We report the preparation and characterization of hybrid inorganic-organic membranes based on NASICON-type Li1 + xAlxGe2 (- x)(PO4)(3) (LAGP) as the fast ion conducting ceramic and fast ionic polymeric solid electrolyte PEO: PVDF:LiBF4 for possible application as Li anode protecting membrane in lithium air batteries. The resulting membranes showed enhanced conductivity of 10(-4) S cm(-1) in combination with improved mechanical flexibility when compared to the ceramic along with higher stability in aqueous solutions in comparison with pure polymer.
B2O3-added Li1.5Al0.5Ge1.5(PO4)3 (LAGP) glass ceramics showing a room temperature ionic conductivity of 0.67 mS cm(-1) have been synthesized by using a melt-quenching method. The prepared glass ceramics are observed to be stable in tetraethylene glycol dimethyl ether containing lithium bis(trifluoromethane) sulfonamide. The augmented conductivity of the B2O3-added LAGP glass ceramic has improved the plateau potential during discharge. Furthermore, the B2O3-added LAGP glass ceramics are successfully employed as a solid electrolyte in a Li-O2 battery to obtain a stable cycling lifetime of up to 15 cycles with the limited capacity protocol.
Li1.5Al0.5Ge1.5(PO4)3 (LAGP) is a promising solid electrolyte for all-solid-state Li ion batteries. In this work, it was synthesized using solid-state reaction with an excess amount of Li to improve grain boundary ionic conductivity. The additional Li improved grain boundary conductivity even though the relative density decreased. This improvement may originate from a beneficial characteristic of grain boundary induced by the segregation of some of Li to the grain boundary. This segregation was indirectly observed by the change of morphology of particles in samples with excess Li. The segregation of Li may result in a facile Li transport in grain boundaries, as indicated by low activation energy and a high pre-exponential factor of the grain boundary conductivity. Through improving grain boundary conductivity with excess Li, a high total ionic conductivity of 1.9 × 10− 4 S·cm− 1 is achieved at room temperature even with a low relative density of 78%. This porous and high ionic conducting solid electrolyte can be useful in configuring the electrode composite of all-solid-state cells.
High lithium ion conductivity solid electrolytes of Li1.4FexAl0.4 - xTi1.6(PO4)3 (x = 0−0.4) with the NASICON-type structure were synthesized by using a sol−gel precursor. The highest electrical conductivity was obtained for Li1.4Fe0.25Al0.15Ti1.6(PO4)3 sintered at 1040 °C for 7 h in air. The total, grain boundary, and bulk conductivities of the pellet were 1.01 × 10-3, 2.17 × 10-3 and 1.81 × 10-3 S cm-1 at 25 °C, respectively. The contribution of electron (or hole) conductivity to the total conductivity was negligibly small. Li1.4Fe0.25Al0.15Ti1.6(PO4)3 was unstable in water, but stable in saturated LiOH and LiCl aqueous solutions.