Article

Effect of Substitution (Ta, Al, Ga) on the Conductivity of Li7La3Zr2O12

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Abstract

Cubic garnets of composition Li6.75La3Zr1.75Ta0.25O12, Li6.15La3Zr1.75Ta0.25Al0.2O12, and Li6.15La3Zr1.75Ta0.25Ga0.2O12 were prepared from a co-precipitated precursor and consolidated by hot-pressing to a relative density of ∼96–98%. The total Li-ion conductivities at 298 K and activation energies (in parentheses) of Li6.75La3Zr1.75Ta0.25O12, Li6.15La3Zr1.75Ta0.25Al0.2O12 and Li6.15La3Zr1.75Ta0.25Ga0.2O12 were 0.87 mS cm−1 (0.22 eV), 0.37 mS cm−1 (0.30 eV) and 0.41 mS cm−1 (0.27 eV), respectively. The above results suggest that cubic stabilizing substitutions outside of the Li-ion sub-lattice are preferable to obtain faster Li-ion conductivity.

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... To date, LLZO electrolytes can be processed either as bulk pellets or tapes with thicknesses generally > 25 mm (tapes < 100 mm can be brittle and difficult to handle) [22,23] or as thin films with thicknesses between 0.2 and 10 mm (Fig-ure 1a). [1,8,24] Depending on the form and desired thickness of LLZO, either sintering (> 1050°C for pellets or tapes) [21,[25][26][27][28][29][30][31][32][33] or annealing (> 650°C for films) [8,24,[34][35][36][37][38] are required to synthesize LLZO in its highly conductive cubic phase (Figure 1b), see Ref. [39] for high-statistics data mining on sintering. An additional summary of the bulk and thin-film LLZO synthesis is presented in Table S1. Figure 1. ...
... These temperatures are particularly attractive for reducing interfacial degradation during LLZO-cathode co-processing. Figure 7. Comparison of the maximum processing temperature and processing time of bulk [21,[25][26][27][28][29][30][31][32] (pellets and tapes) and thin-film [8,24,[34][35][36][37] LLZO via different synthesis routes. ...
... The bulk pellet and tapes processed via conventional synthesis + sintering generally require a high-temperature sintering process at 1050-1230°C for 1-36 h (generally > 5 h) to eliminate pores and achieve complete densification. [21,[25][26][27] There are a few variations of the conventional synthesis + sintering routes for which the LLZO powder (starting material for LLZO pellet sintering) may be synthesized via different routes, including sol-gel synthesis + sintering [30,31] and co-precipitation + sintering; [32] hot pressing may also be used to facilitate densification during these processes. [31,32] However, this method is not cost-effective for LLZO-cathode co-processing because of the high sintering temperature and long sintering time. ...
Article
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Efficient and affordable synthesis of Li⁺ functional ceramics is crucial for the scalable production of solid electrolytes for batteries. Li‐garnet Li7La3Zr2O12−d (LLZO), especially its cubic phase (cLLZO), attracts attention due to its high Li⁺ conductivity and wide electrochemical stability window. However, high sintering temperatures raise concerns about the cathode interface stability, production costs, and energy consumption for scalable manufacture. We show an alternative “sinter‐free” route to stabilize cLLZO as films at half of its sinter temperature. Specifically, we establish a time‐temperature‐transformation (TTT) diagram which captures the amorphous‐to‐crystalline LLZO transformation based on crystallization enthalpy analysis and confirm stabilization of thin‐film cLLZO at record low temperatures of 500 °C. Our findings pave the way for low‐temperature processing via TTT diagrams, which can be used for battery cell design targeting reduced carbon footprints in manufacturing.
... S3 (see also Refs. [40,41,50,[57][58][59][60][61][62][63][64][65][66][67][68][69][70][71][72][73] therein). The surface composition (C surf ) was calculated as ...
... The structures were illustrated with VESTA [85] and OVITO [86] computer programs. [59][60][61][62][63]. The same O 2 chemical potential is obtained under lower temperature and pressure [T = 950 K, P(O 2 ) = 10 −4 atm], which is more typical for pulsed laser deposition of LLZO [64][65][66][67][68][69]. ...
Article
Interfacial charge transfer kinetics between solid electrolyte (SE) and Li metal in all-solid-state Li-ion batteries is one of the limiting factors for their practical use. The mechanism of interfacial charge transfer is still poorly understood. In this work, we study the Li-ion charge transfer at interfaces between perspective SE of garnet-type Li7La3Zr2O12 (LLZO) and Li metal, utilizing the density functional theory and nudged elastic band method (DFT-NEB). We demonstrate that it is crucial to consider the relatively long percolating conduction pathway through the interface. Due to the formation of energy minima for Li vacancies, the activation energies for Li+ charge transfer additionally increase by 0.1–0.3 eV compared with Li+ migration barriers in bulk LLZO. We show that the formation of interfacial energy minima is because of the electronic density redistribution from the metallic Li to the LLZO region. These results improve our understanding of interfacial charge transfer in solid-state batteries with metallic lithium.
... The sol-gel method involves solubilizing raw materials to form a molecular dispersion, followed by calcination at temperatures between 1000-1200 °C for about 6 hours [22][23][24]. The co-precipitation technique involves dissolving and precipitating reagents (usually with NH 4 OH), followed by mixing the precipitates and drying at ~800°C to remove organic compounds [25][26][27]. While these methods can synthesize particles of nanometric sizes, the reduction in diameter size increases surface energy, resulting in the formation of agglomerated particles to reduce the total energy of the system. ...
... 14,15 However, achieving sufficient Li-ion conductivities in oxides require dense pellets obtained through energy-intensive sintering processes, which are difficult to scale. 3,17 Additionally, the ionic conductivity of oxide SEs is typically lower than that of sulfide SEs. [11][12][13] Finally, ternary halide SEs, with formula Li i MX j (X= F, Cl, Br; i and j determined by the oxidation state of metal M) display high electrochemical oxidative stabilities (>4 V vs. Li/Li + ), [18][19][20][21][22] but are unstable against Li metal. ...
Preprint
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Considering the lack of solid electrolytes that are electrochemically stable in contact with a high-voltage cathode and a low-voltage metallic anode, bilayer separators in all-solid-state batteries are gaining increasing attention. However, previous studies have shown that the chemical reactivity between the materials comprising the electrolyte bilayer is one of the contributing factors to the deterioration of battery performance during cycling. Here, we computationally screen the chemical compatibility of an extensive range of materials forming a bilayer separator using first-principles calculations. Notably, several bilayer separators are found to be thermodynamically stable, amongst them, the stability of the Li3PO4/Li3InCl6 pairing is further verified experimentally using a combination of X-ray diffraction, solid-state nuclear magnetic resonance, and X-ray photoelectron spectroscopy. This study underscores the importance of understanding the chemical compatibility of bilayer separators when engineering high-energy density all-solid-state batteries.
... While some success was witnessed especially for sulfide-based electrolytes that are mechanically malleable with the external pressure adjustment 5,7 , it is questionable whether the additional pressure devices can be practically viable for commercial ASSBs. Moreover, these approaches are not eligible for oxide-based electrolytes (e.g., perovskite, NASICON, and garnet-type electrolytes) 2,[9][10][11][12] , which are typically rigid and fragile. The brittle mechanical properties of oxide electrolytes inherently result in inferior interfacial contact between particles in composite cathodes when fabricated at ambient temperature [13][14][15][16] , thus requiring co-sintering process at high temperatures (e.g., above 1000°C with the garnet-type [14][15][16][17] , NASICON solid electrolyte [18][19][20] , and perovskite 21,22 ). ...
Article
Full-text available
A critical bottleneck toward all-solid-state batteries lies in how the solid(electrode)-solid(electrolyte) interface is fabricated and maintained over repeated cycles. Conventional composite cathodes, with crystallographically distinct electrode/electrolyte interfaces of random particles, create complexities with varying (electro)chemical compatibilities. To address this, we employ an epitaxial model system where the crystal orientations of cathode and solid electrolyte are precisely controlled, and probe the interfaces in real-time during co-sintering by in situ electron microscopy. The interfacial reaction is highly dependent on crystal orientation/alignment, especially the availability of open ion channels. Interfaces bearing open ion paths of NCM are more susceptible to interdiffusion, but stabilize with the early formed passivation layer. Conversely, interfaces with closed ion pathway exhibit stability at intermediate temperatures, but deteriorate rapidly at high temperature due to oxygen evolution, increasing interfacial resistance. The elucidation of these distinct interfacial behaviors emphasizes the need for decoupling collective interfacial properties to enable rational design in solid-state batteries.
... [58,59] The obtained ionic and electronic conductivities as well as E a values are close to those previously reported values for LLZTO synthesized using conventional methods (e.g., solid-state and sol-gel). [60][61][62][63][64] These results imply that using Li 2 ZrO 3 precursor instead of ZrO 2 in synthesizing LLZTO solid electrolytes enhances Li + conductivity by reducing the E a value, while concurrently lowering the electronic conductivity. The electron and Li + transport mechanisms within LLZTO LZO and LLZTO ZO solid electrolytes are schematically illustrated in Figure 2e. ...
Article
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Garnet‐type Li6.5La3Zr1.5Ta0.5O12 (LLZTO) solid electrolytes provide the necessary electrochemical stability and ionic conductivity for solid‐state lithium‐metal batteries (SSLMBs). However, their wider application is hindered by their high interfacial resistance with electrodes and a lengthy synthesis process. This study presents the synthesis of densified LLZTO electrolytes using unconventional Li2O and Li2ZrO3 precursors through an ultrafast (≈60 s) Joule heat‐assisted synthesis approach in a single‐step process. The lower sintering temperature of Li2ZrO3 compared to traditional ZrO2 precursor yields LLZTO with larger grains, resulting in enhanced Li⁺ conductivity (7.0 × 10⁻⁴ S cm⁻¹ at 25 °C), reduced electronic conductivity (1.7 × 10⁻¹⁰ S cm⁻¹), and higher density (94.2%). Applying a 52–80 nm Sn:SnF2 coating on the LLZTO surface using a melt‐quenching approach produces a uniform interlayer that chemically converts to Li‐Sn alloy and LiF upon contact with lithium, resulting in a near‐zero interfacial resistance and a critical current density of 4.2 mA cm⁻² at 25 °C. The SSLMBs, incorporating Sn:SnF2‐coated LLZTO electrolyte with NMC811 cathode, demonstrate remarkable initial capacity (181.1 mAh g⁻¹) and cycle performance (88.63% capacity retention at 3000th cycle). The results indicate that this approach has the potential to advance the commercial fabrication technology for high‐performance solid electrolytes for SSLMBs.
... 16,17 In contrast, oxide solid electrolytes have an ionic conductivity of approximately 10 −3 -10 −4 S cm −1 at room temperature and have properties comparable to those of sulfides. [18][19][20][21] In particular, garnetbased Li 7 La 3 Zr 2 O 12 (LLZO) has the widest potential window among oxide materials and no reactivity with Li metal, making it possible to implement high-voltage ASLBs. 22 However, the oxide material makes the fabrication of the electrode and electrolyte layer difficult because of the nonuniform shape and rigid characteristics in the sintering process. ...
Article
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Sulfide-based solid electrolyte such as Li6PS5Cl (LPSCl) is unstable in contact with Li metal electrode due to decomposing to by-product resulting in poor performance. Therefore, the introduction of an interlayer to suppress reactivity is essential. In this study, instead of an interlayer, an oxide/polymer composite electrolyte was applied to suppress side reactions, while a sulfide-based electrolyte was used at the cathode to improve interfacial control between the cathode and the electrolyte. All-solid-state lithium batteries (ASLBs) were prepared by applying sulfide-based solid electrolyte (argyrodite, Li6PS5Cl) including NCM424, polyvinylidene fluoride (PVDF), and Super-P in a composite cathode layer, and a composite solid electrolyte (CSE) layer by mixing an oxide-based solid electrolyte (garnet, Al-doped Li7La3Zr2O12 (LLZO)), polymer (PEO, polyethylene oxide) and lithium metal as the anode. In this study, NCM424 powder was coated with LiNbO3 to prevent chemical reaction with the sulfide electrolyte. As the PVDF binder was applied to the cathode of the ASLB, the discharge capacity of the cell was approximately 163 mAh g⁻¹ at 70 °C, 0.1 C, and 4.2 V cut-off and its capacity retention was 83% after 50 cycles. The effects of the PVDF were evaluated using both pouch-type cells. The capacity and cycle retention are greatly dependent on the PVDF content of the cathode materials and the drying temperature during the fabrication of the cathode. When the cathode with PVDF binder was dried at 130 °C, initial cycling was required for activation of the pouch cell, and it was possible to overcome this by adding a plasticizer.
... To achieve high density garnet pellets, ceramic sintering techniques with additional driving force for sintering, such as hotpressing and spark plasma sintering 73,74 or sintering aids (e.g. Al 2 O 3 , Ga 2 O 3 , Li 3 BO 4 , Li 4 SiO 4 ) as a densification strategy, 75,76 have previously been applied in the literature. ...
Article
Full-text available
While garnet Li ion conductors are attracting considerable interest as potential solid state electrolytes for Li ion batteries, a key challenge is to improve the conductivity, which is associated with the Li content in the structure, and the density of the sintered electrolyte membranes. In this work we show that Zn can be doped on the 16a octahedral Nb site increasing the Li content, while also leading to substantially improved sintering in Li5+xLa3Nb2−xZrxO12. As a result of the enhanced sintering, and the increase in Li content, the conductivities were significantly enhanced on Zn doping, up to 2.1 × 10⁻⁴ S cm⁻¹ at 25 °C for Li6.6La3ZrNb0.8Zn0.2O12. Computational modelling supports favourable doping of Zn on the Nb site with 3 Li interstitials as per experimental findings. Furthermore, it suggests Li ion diffusion via a knock-on mechanism, but crucially the saturation of sites closest to the Zn means that migration barriers are similar for doped and pure systems, with the increased Li ion conductivity attributed to larger pre-factors due to increased number of Li ions in the doped material. A challenge with these Zn doped garnet is the reduction of Zn in contact with Li metal. Nevertheless, surface fluorination or employing the Zn doped garnet as a buffer layer with an alternative garnet electrolyte is shown to be effective to inhibit dendrite growth, and stable cycling exceeding 250 hours is demonstrated.
... Furthermore, the substitution of Ta for Zr is found to be stable against the Li metal anode. Unlike Al substitution on Li tetrahedral sites, Ta substitution on the Zr sites does not impede the motion of lithium ions [13]. ...
Conference Paper
As the trend toward transportation electrification grows, the demand for batteries is increasing significantly. Thus, the development of the next generation of batteries is significant, considering safety, reliability, energy density, and design improvements. Consequently, solid-state batteries have become a promising candidate. Much research has focused on finding the optimal manufacturing process for a specific type of solid electrolyte to improve its performance. However, there is no comprehensive comparison among different solid electrolytes. In this research, the life cycle assessment was applied to evaluate the environmental concerns, which can provide a fair comparison between solid electrolytes. Also, this research adopted the widely used industrial manufacturing method (tape casting) for solid electrolytes. The environmental impacts of the tape casting for six types of solid electrolytes were assessed based on the ReCiPe method using the standardized process and unified equipment. As a result, the manufacturing processes for solid electrolytes without lanthanum have lower environmental impacts than those containing lanthanum. It was found that Li6PS 5 Cl (LPSCl) and Li 1.4 Al 0.4 Ti 1.6 (PO 4 ) 3 (LATP) solid electrolytes are excellent choices to lower the environmental impact thanks to their environmentally friendly chemistry and manufacturing process.
... It has been suggested that the ideal Li content to form a conductive garnet with cubic structure is 5 < Li < 6.6 per formula unit (Bernstein et al., 2012). This can be seen, for example, in Li 7-3x-y M x La 3 Zr 2−y B y O 12 (M = Al, Ga, B = Ta) (Allen et al., 2012;Thompson et al., 2014;Baklanova et al., 2018). At Li contents larger than 6.6, the cubic structure undergoes a reduction of symmetry to a tetragonal polymorph and the ionic conductivity decreases. ...
Article
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This study explores multi-component garnet-based materials as solid electrolytes for all-solid-state lithium batteries. Through a combination of computational and experimental approaches, we investigate the thermodynamic and structural properties of lithium lanthanum zirconium oxide garnets doped with various elements. Applying density functional theory, the influence of dopants on the thermodynamic stability of these garnets was studied. Probable atomic configurations and their impact on materials’ properties were investigated with the focus on understanding the influence of these configurations on structural stability, phase preference, and ionic conductivity. In addition to the computational study, series of cubic-phase garnet compounds were synthesized and their electrochemical performance was evaluated experimentally. Our findings reveal that the stability of cubic phase in doped Li-garnets is primarily governed by enthalpy, with configurational entropy playing a secondary role. Moreover, we establish that the increased number of doping elements significantly enhances the cubic phase’s stability. This in-depth understanding of materials’ properties at atomic level establishes the basis for optimizing high-entropy ceramics, contributing significantly to the advancement of solid-state lithium batteries and other applications requiring innovative material solutions.
... Nevertheless, stoichiometry LLZO is the tetragonal phase at room temperature with two to three orders of magnitude lower Li + conductivity than the cubic phase [17,18] . Element doping, such as Ta 5+ and Nb 5+ at the Zr-site [19,20] , Al 3+ and Ga 3+ at the Li-site [21,22] , is used to successfully stabilize the cubic phase structure. However, the lab-scale production craft of LLZO is less reported [23] , requiring a reliable method for research. ...
Article
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Solid-state batteries have garnered attention due to their potentiality for increasing energy density and enhanced safety. One of the most promising solid electrolytes is garnet-type Li7La3Zr2O12 (LLZO) ceramic electrolyte because of its high conductivity and ease of manufacture in ambient air. The complex gas-liquid-solid sintering mechanism makes it difficult to prepare LLZO with excellent performance and high consistency. In this study, an in-situ Li2O-atmosphere assisted solvent-free route is developed for producing the LLZO ceramics. First, the lithium-rich additive Li6Zr2O7 (LiZO) is applied to in-situ supply Li2O atmosphere at grain boundaries, where its decomposition products (Li2ZrO3) build the bridge between the grain boundaries. Second, comparisons were studied between the effects of dry and wet routes on the crystallinity, surface contamination, and particle size of calcined powders and sintered ceramics. Third, by analyzing the grain boundary composition and the evolution of ceramic microstructure, the impacts of dry and wet routes and lithium-rich additive LiZO on the ceramic sintering process were studied in detail to elucidate the sintering behavior and mechanism. Lastly, exemplary Nb-doped LLZO pellets with 2 wt% LiZO additives sintered at 1,300 °C × 1 min deliver Li⁺ conductivities of 8.39 × 10⁻⁴ S cm⁻¹ at 25 °C, relative densities of 96.8%, and ultra-high consistency. It is believed that our route sheds light on preparing high-performance LLZO ceramics for solid-state batteries.
... As stated above, covered sintering with mother powder is often adopted to compensate Li-loss. And ionic conductivity [13][14][15][16][17][18]. These previous investigations have certificated that the high-quality LLZObased ceramics electrolytes demand cubic phase with high ionic conductivity of about 10 -4 S cm, high density and fine grains with tight grain boundaries [3,5,10,18]. ...
Article
Full-text available
Due to the increasingly urgent safety and energy density concerns of lithium-ion batteries, more and more attention has been attracted by the Li7La3Zr2O12 (LLZO)-based solid electrolytes with high ion conductivity and chemical stability against Li-metal. However, to prepare the high-quality LLZO ceramic electrolyte with high-ion conductivity and density, there is still a big challenge of the serious “Li-loss” and the abnormal grain growth during the long-time high-temperature sintering process. A novel covered sintering method is put forward to prepare the high-quality Mo-doped LLZO (LLZMO) ceramic electrolyte. The sintering strategy effectively suppresses the Li-loss to obtain the LLZMO dense ceramics with cubic garnet phase and tight grain boundaries. The LLZMO ceramics sintered at lower temperature of 1050 °C for 2 h via the novel covered sintering exhibit high density (ρr = 92.3%) and high-ionic conductivity of 6.08 × 10–4 S cm⁻¹ at 25 °C, which are close to those of LLZO-based ceramics prepared by hot pressing sintering, ultrafast high-temperature sintering (UHS). The novel covered sintering provides an energy-saving, low-cost and high-efficient strategy to prepare the high-quality LLZO-based ceramics electrolyte.
... While some success was witnessed especially for sul de-based electrolytes that are mechanically malleable with the external pressure adjustment 5,7 , it is questionable whether the additional pressure devices can be practically viable for commercial ASSBs. Moreover, these approaches are not eligible for oxide-based electrolytes (e.g., perovskite, NASICON, and garnet-type electrolytes) 2,[9][10][11][12] , which are typically rigid and fragile. The brittle mechanical properties of oxide electrolytes inherently result in inferior interfacial contact between particles in composite cathodes when fabricated at ambient temperature [13][14][15][16] , thus requiring co-sintering process at high temperatures (e.g., above 1000 ℃ with the garnet-type [14][15][16][17] , NASICON solid electrolyte 18-20 , and perovskite 21,22 ). ...
Preprint
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One of the most critical bottlenecks toward all-solid-state batteries lies in how the solid(electrode)-solid(electrolyte) interface can be seamlessly fabricated and maintained over repeated electrochemical cycles. Conventional composite cathodes, with their randomly distributed cathode and electrolyte particles, present a range of crystallographically distinct electrode/electrolyte interfaces, each with varying chemical and electrochemical compatibilities, thereby adding more considerable complexities. Herein, as a first step to unravel the complexity of the interface, we employ an epitaxial model system in which the crystal orientations of cathode (e.g., Li(Ni1/3Co1/3Mn1/3)O2, NCM) and solid electrolyte (e.g., Li3xLa(2/3)−x⎕(1/3)−2xTiO3, LLTO) are precisely controlled, and probe the corresponding interfaces in real-time during co-sintering process by in situ heating transmission electron microscopy. The in situ observation reveals that the interfacial reaction mechanism and kinetics are highly dependent on the crystal orientation/alignment of cathode and electrolyte particles especially contingent on the availability of open ion channels at the interface. It is shown that the interfaces bearing the open ion paths of NCM such as (104) plane are more susceptible to the interdiffusion even at low temperature, however the early formation of stable passivation layer effectively suppresses the increase in the overall interfacial resistance. On the other hand, the interfaces with the closed ion pathway of NCM such as (003) plane exhibit a relatively high stability up to intermediate temperatures of co-sintering, but deteriorate more rapidly at high temperature as a result of oxygen evolution and decomposition, thereby displaying a higher interfacial resistance. The elucidation of these distinct behaviors of representative interfaces not only deepens our understanding of composite cathodes but also emphasizes the need for decoupling collective interfacial properties to enable rational interfacial design in solid-state batteries.
... All solid-state batteries (ASSBs) employ an inorganic solidstate electrolyte (SSE) and typically pair a lithium metal improvements in the ionic conductivity (up to 1 mS cm −1 ) have been obtained through multivalent cation doping [29] Ta 5+ , Al 3+ , Ga 3+ , Y, 3+ [30][31][32] and by increasing relative density of the sintered compact [33][34][35][36] by hot pressing, [37] spark plasma sintering, [38] fieldassisted sintering [39] and ultrafast high-temperature sintering. [40] The promising ionic conductivity, combined with electrochemical stability and ambient atmosphere self-passivation makes doped LLZO appealing for commercial ASSB applications. ...
Article
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This study illustrates how the microstructure of garnet solid‐state electrolytes (SSE) affects the stress‐state and dendrite growth. Tantalum‐doped lithium lanthanum zirconium oxide (LLZTO, Li6.4La3Zr1.4Ta0.6O12) is synthesized by powder processing and sintering (AS), or with the incorporation of intermediate‐stage high‐energy milling (M). The M compact displays higher density (91.5% vs 82.5% of theoretical), and per quantitative stereology, lower average grain size (5.4 ± 2.6 vs 21.3 ± 11.1 µm) and lower AFM‐derived RMS surface roughness contacting the Li metal (45 vs 161 nm). These differences enable symmetric M cells to electrochemically cycle at constant capacity (0.1 mAh cm⁻²) with enhanced critical current density (CCD) of 1.4 versus 0.3 mA cm⁻². It is demonstrated that LLZTO grain size distribution and internal porosity critically affect electrical short‐circuit failure, indicating the importance of electronic properties. Lithium dendrites propagate intergranularly through regions where LLZTO grains are smaller than the bulk average (7.4 ± 3.8 µm for AS in a symmetric cell, 3.1 ± 1.4 µm for M in a half‐cell). Metal also accumulates in the otherwise empty pores of the sintered compact present along the dendrite path. Mechanistic modeling indicates that reaction and stress heterogeneities are interrelated, leading to current focusing and preferential plating at grain boundaries.
... But the signals from Zr and P elements are detected in both LLZTO and LGP40, which is caused by the overlap of the L 1 characteristic X-rays of Zr with the K 1 characteristic X-rays of P. As for the detection of Ga on both sides of the interface, it may be attributed to the replacement of a part of Li by Ga in LLZTO. [57][58][59] In addition, in order to more fully characterize the interfacial contacts, area specific resistance (ASR) of the Li/LLZTO and LGP40/LLZTO interfaces was measured through solid-state symmetric cells. Figure To investigate the effect of GaP on the Li + diffusion rate, the Li + diffusion coefficients of pure lithium and LGP40 CLA are obtained by linear fitting of the Nyquist plots at low frequency (Figure 3a,b). ...
Article
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The urgent demand for high energy and safety batteries has generated the rapid development of Li6.4La3Zr1.4Ta0.6O12 (LLZTO) type solid‐state lithium metal batteries. However, severe dendritic lithium growth, which is caused by poor interfacial contact of the Li/LLZTO interface and loss of electrical contact during cycles due to low intrinsic Li⁺ diffusion coefficient of lithium, greatly hampers its practical application. Here, from the point of view of reducing surface tension and improving ion diffusion of lithium, a composite lithium anode (CLA) with high wettability and ion diffusion coefficient is prepared by adding GaP into molten lithium, thus strengthening the CLA/LLZTO interface even in cycling. As envisioned, compared to pure lithium, CLA presents lower surface tension, larger adhesion work, and higher ion diffusion coefficient, ensuring close contact of the CLA/LLZTO interface. Therefore, the assembled symmetric cells exhibit a low area specific resistance of 4.5 Ω cm², a large critical current density of 2.5 mA cm⁻², and ultra‐long lifespan of 5700 h at 0.3 mA cm⁻² at 25 °C. Meanwhile, full cells coupled with LiFePO4 cathode show a high‐capacity retention of 97.32% after 490 cycles at 1C. This work provides a new solution to the interfacial challenges of solid‐state lithium‐metal batteries.
... These observations suggested that Li content reduction in the LLZO framework through multivalent dopants could lead to the stabilisation of the highly conductive cubic lattice and thus, different combinations of dopants (Al, Ga, Fe, Ta, W, Nb etc.) have been explored to stabilise the cubic polymorph of LLZO and to obtain high Li-ion conductivities [13][14][15][16][17][18] . Among various doped LLZO compounds reported in the literature, Al doped LLZO (Al-LLZO) and ...
Preprint
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The high Li-ion conductivity and wide electrochemical stability of Li-rich garnets (Li7La3Zr2O12) make them one of the leading solid electrolyte candidates for solid-state batteries. Dopants such as Al and Ga are typically used to enable stabilisation of the high Li+ ion-conductive cubic phase at room temperature. Although numerous studies exist that have characterized the electrochemical properties, structure, and lithium diffusion in Al- and Ga-LLZO, the local structure and site occupancy of dopants in these compounds are not well understood. Two broad 27Al or 69,71Ga resonances are often observed with chemical shifts consistent with tetrahedrally coordinated Al/Ga in the magic angle spinning nuclear magnetic resonance (MAS-NMR) spectra of both Al- and Ga-LLZO, which have been assigned to either Al and/or Ga occupying 24d and 96h/48g sites in the LLZO lattice or to the different Al/Ga configurations that arise from different arrangements of Li around these dopants. In this work, we unambiguously show that the side products γ-LiAlO2 and LiGaO2 lead to the high frequency resonance observed by NMR spectroscopy and that both Al and Ga only occupy the 24d site in the LLZO lattice. Furthermore, it was observed that the excess Li often used during synthesis leads to the formation of these side-products by consuming the Al/Ga dopants. In addition, the consumption of Al/Ga dopants lead to the tetragonal phase formation commonly observed in the literature even after careful mixing of precursors. The side-products can exist even after sintering, thus controlling the Al/Ga content in the LLZO lattice, substantially influencing the lithium-ion conductivity in LLZO as measured here by electrochemical impedance spectroscopy.
... And compared to Fe x -LLZO, Fe x -LLZO|LLZTO|Fe x -LLZO have higher ionic conductivity. In the "sandwich" symmetric cell, Fe x -LLZO can effectively increase the interfacial wettability with metal Li and the layers of Fe x -LLZO and LLZTO connect seamlessly that Li + can be transferred between them without barriers due to their same crystal structure [41]. ...
Article
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Due to its high energy density and better safety performance, all-solid-state lithium batteries are regarded as important energy storage devices to replace the traditional liquid electrolyte Li-ion batteries. However, the problems of poor wettability of Li metal anode | solid-state electrolyte interface and easy growth of lithium dendrite have not been well solved. Here, we have constructed Fe-doped Li7-3xFexLa3Zr2O12 (Fe-LLZO) and Li6.5La3Zr1.5Ta0.5O12 (LLZTO) garnet-type double-layer solid electrolyte. The high density of Li7-3xFexLa3Zr2O12 electrolyte and its interfacial wettability to Li metal not only effectively reduced the interface impedance between Li and solid electrolyte but also could stably cycle for more than 200 h without the growth of lithium dendrites at the rate of 0.1 mA cm⁻². In addition, the all-solid-state lithium battery (Li|Fe0.1-LLZO|LLZTO|LFP) with LiFePO4 as a cathode also showed excellent cycle stability and C-rate performance.
Article
Growing market demands on portable electronics, electric vehicles, and energy storage system calls for the development of high‐energy density lithium (Li) batteries. Li metal is considered as a promising anode material owing to their high capacity and low electrochemical potential. However, high reactivity of Li metal with conventional flammable liquid electrolytes easily forms Li dendrites, which may cause short‐circuit and even catching fire, obstructing the wide application of Li metal batteries. Although non−/less‐flammable solid electrolytes have replaced the conventional liquid electrolytes, solid‐state Li metal batteries (SSLMBs) suffer from lower Li ⁺ conductivities, chemical/electrochemical incompatibilities toward Li metal, and inhomogeneous Li ⁺ flux at the interfaces. Therefore, many researchers have devoted themselves to solve these problems. For a better understanding on the current issues and recent advances, this article provides (1) a review on various solid electrolytes with high Li ⁺ conductivity and their interfacial issues in SSLMBs, and (2) recent progress in stabilization of the interface between the Li node and solid electrolytes, including an electrolyte modification (e.g., composition, additives) and introduction of an interlayer.
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Solid-state electrolytes, like Li 7 La 3 Zr 2 O 12 (LLZO), can enable safer, more energy dense and longer lasting batteries. However, there are still challenges concerning dendrite formation and poor Li- ion conductivity. Here we...
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The effective ionic radii of Shannon & Prewitt [Acta Cryst. (1969), B25, 925-945] are revised to include more unusual oxidation states and coordinations. Revisions are based on new structural data, empirical bond strength-bond length relationships, and plots of (1) radii vs volume, (2) radii vs coordination number, and (3) radii vs oxidation state. Factors which affect radii additivity are polyhedral distortion, partial occupancy of cation sites, covalence, and metallic character. Mean Nb5+-O and Mo6+-O octahedral distances are linearly dependent on distortion. A decrease in cation occupancy increases mean Li+-O, Na+-O, and Ag+-O distances in a predictable manner. Covalence strongly shortens Fe2+-X, Co2+-X, Ni2+-X, Mn2+-X, Cu+-X, Ag+-X, and M-H- bonds as the electronegativity of X or M decreases. Smaller effects are seen for Zn2+-X, Cd2+-X, In2+-X, pb2+-X, and TI+-X. Bonds with delocalized electrons and therefore metallic character, e.g. Sm-S, V-S, and Re-O, are significantly shorter than similar bonds with localized electrons.
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Recent research has shown that certain Li-oxide garnets with high mechanical, thermal, chemical, and electrochemical stability are excellent fast Li-ion conductors. However, the detailed crystal chemistry of Li-oxide garnets is not well understood, nor is the relationship between crystal chemistry and conduction behavior. An investigation was undertaken to understand the crystal chemical and structural properties, as well as the stability relations, of Li(7)La(3)Zr(2)O(12) garnet, which is the best conducting Li-oxide garnet discovered to date. Two different sintering methods produced Li-oxide garnet but with slightly different compositions and different grain sizes. The first sintering method, involving ceramic crucibles in initial synthesis steps and later sealed Pt capsules, produced single crystals up to roughly 100 μm in size. Electron microprobe and laser ablation inductively coupled plasma mass spectrometry (ICP-MS) measurements show small amounts of Al in the garnet, probably originating from the crucibles. The crystal structure of this phase was determined using X-ray single-crystal diffraction every 100 K from 100 K up to 500 K. The crystals are cubic with space group Ia3̅d at all temperatures. The atomic displacement parameters and Li-site occupancies were measured. Li atoms could be located on at least two structural sites that are partially occupied, while other Li atoms in the structure appear to be delocalized. (27)Al NMR spectra show two main resonances that are interpreted as indicating that minor Al occurs on the two different Li sites. Li NMR spectra show a single narrow resonance at 1.2-1.3 ppm indicating fast Li-ion diffusion at room temperature. The chemical shift value indicates that the Li atoms spend most of their time at the tetrahedrally coordinated C (24d) site. The second synthesis method, using solely Pt crucibles during sintering, produced fine-grained Li(7)La(3)Zr(2)O(12) crystals. This material was studied by X-ray powder diffraction at different temperatures between 25 and 200 °C. This phase is tetragonal at room temperature and undergoes a phase transition to a cubic phase between 100 and 150 °C. Cubic "Li(7)La(3)Zr(2)O(12)" may be stabilized at ambient conditions relative to its slightly less conducting tetragonal modification via small amounts of Al(3+). Several crystal chemical properties appear to promote the high Li-ion conductivity in cubic Al-containing Li(7)La(3)Zr(2)O(12). They are (i) isotropic three-dimensional Li-diffusion pathways, (ii) closely spaced Li sites and Li delocalization that allow for easy and fast Li diffusion, and (iii) low occupancies at the Li sites, which may also be enhanced by the heterovalent substitution Al(3+) ⇔ 3Li.
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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).
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Monoclinic Nb12O29 with Wadsley shear structure shows interstitial sites for Li intercalation/extraction reversibly in the voltage windows of 2.5-1.0 V. In spite of its metallic characteristic, samples with carbon coating show an improved rate capability.
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The garnet-related oxide with general formula Li6La3ZrTaO12 was prepared by conventional solid-state reaction. X-ray diffraction (XRD) and AC impedance were used to determine phase formation and the lithium-ion conductivity. The structures were refined by the Rietveld method from powder X-ray diffraction data. Li6La3ZrTaO12 is cubic and crystallizes in the space group Ia-3d with room-temperature lattice parameter a = 12.8873 Å. The bulk and total lithium ion conductivities of Li6La3ZrTaO12 at 25 °C were 2.5 × 10−4 S cm−1 and 1.8 × 10−4 S cm−1, respectively; the activation energy was about 0.42 eV in the temperature range 298–450 K.
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High lithium-ion (Li+) conductive garnet-structured lanthanum lithium zirconate (LLZ) solid electrolyte is prepared by incorporation of appropriate amounts of silicon (Si) and aluminum (Al). The resultant pelletized LLZ obtains total Li+ conductivity of 6.8 × 10− 4 S cm− 1 at 298 K. This improved conductivity is nearly identical with the bulk Li+ conductivity of the LLZ reported earlier, suggesting that the grain boundary resistance is effectively reduced by the incorporation of Si and Al. Microanalyses by transmission electron microscopy coupled with energy-dispersive X-ray microanalysis and electron energy-loss spectroscopy revealed the presence of amorphous Li–Al–Si–O with nano crystalline LiAlSiO4 at grain boundaries. Fast lithium-ion transport around the amorphous Li–Al–Si–O/LiAlSiO4 interface will facilitate Li+ transport between the LLZ particles, resulting in the improvement of the total Li+ conductivity of LLZ.
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Li7La3Zr2O12 electrolytes doped with different amounts of Al (0, 0.2, 0.7, 1.2, and 2.5 wt.%) were prepared by a polymerized complex (Pechini) method. The influence of aluminum on the structure and conductivity of Li7La3Zr2O12 were investigated by X-ray diffraction (XRD), impedance spectroscopy, scanning electron microscopy (SEM), and thermal dilatometry. It was found that even a small amount of Al (e.g. 0.2 wt.%) added to Li7La3Zr2O12 can greatly accelerate densification during the sintering process. SEM micrographs showed the existence of a liquid phase introduced by Al additions which led to the enhanced sintering rate. The addition of Al also stabilized the higher conductivity cubic form of Li7La3Zr2O12 rather than the less conductive tetragonal form. The combination of these two beneficial effects of Al enabled greatly reduced sintering times for preparation of highly conductive Li7La3Zr2O12 electrolyte. With optimal additions of Al (e.g. 1.2 wt.%), Li7La3Zr2O12 electrolyte sintered at 1200 °C for only 6 h showed an ionic conductivity of 2.0 × 10−4 S cm−1 at room temperature.
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Structural properties of Li7 − xLa3TaxZr2 − xO12 garnets with x = 0–2 were clarified by means of Rietveld analysis using results of X-ray diffraction and neutron diffraction at room temperature and at low temperature. In this work the controversy between Awaka [1] and Murugan [2] concerning the crystal structure of Li7La3Zr2O12 was solved. It was shown that the tetragonally derived garnet structure of space group I41/acd described by Awaka [1] is the thermodynamically stable structure for Li7La3Zr2O12. In the three-dimensional sub-network of this structure, lithium is ordered and occupies all octahedral sites as well as one third of the tetrahedral sites. Li7 − xLa3TaxZr2 − xO12 garnets with x = 0.125–2 crystallize in the garnet structure, space group Ia3¯d. As the tantalum content increases, the lattice parameter at room temperature decreases from a = 12.9833(1) Å for Li6.875La3Ta0.125Zr1.875O12 down to a = 12.81224(7) Å for Li5La3Ta2O12. In Li6.5La3Ta0.5Zr1.5O12 garnet, lithium atoms are statistically partitioned among octahedral sites (occ.: 0.80(2)) and tetrahedral sites (occ.: 0.56(4)). In the cases of ordered Li7La3Zr2O12 tetragonally derived garnet and statistically disordered Li6.5La3Ta0.5Zr1.5O12 garnet, lithium partitioning remains unchanged as temperature decreases.
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The garnet-type cubic and tetragonal phases with respective high and low lithium ion conductivity were synthesized using precursors prepared by a sol–gel method. The electrical conductivities of the bulk and grain boundary of the cubic phase were estimated from impedance spectra to be 5.69 × 10−4 and 1.39 × 10− 4 S cm−1 at 25 °C, respectively. The garnet-type cubic phase was stable in a saturated solution of LiCl, and no changes in the XRD pattern or electrical conductivity were observed for a sample immersed in saturated LiCl solution at 50 °C for one week. Elemental analysis confirmed that the chemical compositions of the cubic and tetragonal phases were Li6La3Zr2O11.5 and Li7La3Zr2O12, respectively.
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Due to their favourable combination of high ionic conductivity and stability versus elemental lithium, garnet-related lithium ion conductors Li7La3Zr2O12 have raised strong interest for both all-solid-state batteries and as protective layers for anode materials. Here we study the correlation between structure and ion mobility in Li7−xLa3(Zr2−xMx)O12 (x = 0, 0.25; M = Ta5+, Nb5+) combining Molecular Dynamics (MD) simulations, bond valence (BV) studies and experimental characterisation. In situ XRD demonstrates a tetragonal-to-cubic phase transition above 450 K for LixLa3Zr2O12. MD simulations using our new BV-based Morse-type force field reproduce static (lattice constants, thermal expansion, phase transition) and dynamic characteristics of this material. Simulations and structure refinements for the tetragonal phase accordingly yield an ordered Li distribution. The majority of Li fully occupies the 16f and 32g octahedral sites. Out of the two tetrahedral sites only the 8a site is fully occupied leaving the 16e tetrahedral sites with slightly higher site energy due to the tetragonal distortion vacant. For the cubic phase recent structural studies either suggest a major Li+ redistribution to nearly fully occupied tetrahedral sites and distorted octahedral sites with a low occupancy (which leads to unphysically short Li–Li distances) or suggest the existence of additional Li sites. MD simulations however show that the lithium distribution just above the phase transition closely resembles that in the tetragonal phase with only slightly more than 1/3 of the now equivalent tetrahedral 24d sites and almost half of the distorted octahedral 96h sites occupied, so that overly short Li–Li distances are avoided. Pentavalent doping enhances ionic conductivity by increasing the vacancy concentration and by reducing local Li ordering. At higher temperatures Li is gradually redistributed to the tetrahedral sites that can be occupied up to a site occupancy factor of 0.56. BV pathway analysis and closely harmonizing Li trajectories demonstrate that the two partially occupied Li sites of similar site energy form a 3D network suitable for fast ion conduction. The simulated diffusion coefficient and its activation energy closely match the experimental conductivities. The degree of correlation of the vacancy-type Li+ ion migration is analyzed in terms of the van Hove correlation function.
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Fe-substituted LiCoPO4 exhibits greatly improved cycle life relative to LiCoPO4. Whereas, pure LiCoPO4 loses more than half of its discharge capacity at the 10th cycle, the Fe-substituted LiCoPO4 retains about 100% of its discharge capacity at the 10th cycle and about 80% of its capacity at the 500th cycle. It is suggested that improved cycle life results from Fe3+ substitution on the Li and Co sites. The partial substitution of Li+ by Fe3+ and Co2+ by Fe2+ and Fe3+ was evidenced from Rietveld analysis of X-ray powder diffraction data, infrared spectroscopy, X-ray photoelectron spectroscopy and Mössbauer spectroscopy. The majority of the Fe3+ substitutes at the Co2+ site. The composition of Fe-substituted LiCoPO4 is Li0.92Co0.8Fe2+0.12Fe3+0.08PO4 for a sample of starting composition LiCo0.8Fe0.2PO4.
Article
Li7−xLa3Zr2O12−0.5x (LLZ) ceramics with garnet-type structure were prepared via the conventional solid-state reaction method. The results showed that the sintering temperature has a significant effect on the crystal structure and phase composition, and thus ionic conductivity, of the LLZ ceramics. The ionic conductivity at room temperature of the ceramic samples increased with the crystal structural transition from tetragonal to cubic structure, as the sintering temperature increased; and reached a value of about 3.6×10−4S/cm for the cubic LLZ sample sintered at 1230°C, but LLZ would be decomposed at 1250°C.
Article
The structures of new phases Li6CaLa2Sb2O12 and Li6.4Ca1.4La2Sb2O12 have been characterised using neutron powder diffraction. Rietveld analyses show that both compounds crystallise in the space group la3̄d and contain the lithium cations in a complex arrangement with occupational disorder across oxide tetrahedra and distorted oxide octahedra, with considerable positional disorder in the latter. Variable temperature neutron diffraction experiments on Li6.4Ca1.4La2Sb2O12 show the structure is largely invariant with only a small variation in the lithium distribution as a function of temperature. Impedance spectroscopy measurements show that the total conductivity of Li6CaLa2Sb2O12 is several orders of magnitude smaller than related lithium-stuffed garnets with σ=10−7Scm−1 at 95°C and an activation energy of 0.82(3)eV. The transport properties of the conventional garnets Li3Gd3Te2O12, Li3Tb3Te2O12, Li3Er3Te2O12 and Li3Lu3Te2O12 have been evaluated and consistently show much lower values of conductivity, σ≤4.4×10−6Scm−1 at 285°C and activation energies in the range 0.77(4)≤Ea/eV≤1.21(3).
Article
Our studies on the preparation, via the sol–gel techniques, of MVO5(M = Nb, Ta) oxides have been rewarded here with an increased understanding of the synthesis process. The sol–gel method is at the moment the only procedure for producing NbVO5 as a pure phase. We present results concerning the influences of different parameters on the nature of the final products in the V–Nb–O system. Compounds NbVO5 and TaVO5 are isostructural with orthorhombic unit cells. The structural parameters have been refined using the Rietveld method with space group Pnma. Thermal analyses of the precursor xerogels show that the thermal effects depend on the nature of the M cations. The crystallization and decomposition temperatures are lower for NbVO5 than for TaVO5. The electrochemical insertion of lithium ions into the new MVO5(M = Nb, Ta) mixed oxides has also been investigated. For both materials, this process is complex and consists of three main steps. The maximum insertion degrees (x in LixMVO5) achieved after the reduction process are x= 1.95 for NbVO5 and x= 1.57 for TaVO5. The galvanostatic cycling studies show the good rechargeability of the Li+/e– insertion/deinsertion process in the MVO5 oxides.
Article
The garnet structure, originally solved by Menzer, has become increasingly important in the last ten years. During this period a number of garnet-structure refinements have been carried out; these are reviewed and some of the consequences of the results are discussed. A survey has been made of all the cations which enter the garnet structure and their site preferences are given. Numerous examples of garnets and garnet systems that have been investigated arc listed. Some arc reported here for the first time. The ionic site preference in the garnets is discussed; it appears that relative ionic size is of primary importance, but for certain ions like Cr3+ and Mn3∼. the electronic configuration also plays an important role. Considerable discussion is given to the Co2+ ion for which the evidence maintains that the Co2+ ion prefers, by far, the octahedral sites to the tetrahedral. Garnets have been prepared with Co3+ ion in the tetrahedral and in the octahedral sites. The determination of the distribution of ions in the system Y3Fc5-x.GaxO12 by different techniques is reviewed.
Article
We have successfully synthesized a high-purity polycrystalline sample of tetragonal Li7La3Zr2O12. Single crystals have been also grown by a flux method. The single-crystal X-ray diffraction analysis verifies that tetragonal Li7La3Zr2O12 has the garnet-related type structure with a space group of I41/acd (no. 142). The lattice constants are a=13.134(4)Å and c=12.663(8)Å. The garnet-type framework structure is composed of two types of dodecahedral LaO8 and octahedral ZrO6. Li atoms occupy three crystallographic sites in the interstices of this framework structure, where Li(1), Li(2), and Li(3) atoms are located at the tetrahedral 8a site and the distorted octahedral 16f and 32g sites, respectively. The structure is also investigated by the Rietveld method with X-ray and neutron powder diffraction data. These diffraction patterns are identified as the tetragonal Li7La3Zr2O12 structure determined from the single-crystal data. The present tetragonal Li7La3Zr2O12 sample exhibits a bulk Li-ion conductivity of σb=1.63×10−6Scm−1 and grain-boundary Li-ion conductivity of σgb=5.59×10−7Scm−1 at 300K. The activation energy is estimated to be Ea=0.54eV in the temperature range of 300–560K.
Article
The electrochemical behavior and structural changes of several Nb2-xVxO5 (x=0.2-1.0) were investigated in 1 M LiClO4-propylene carbonate solution as positive electrodes for rechargeable lithium batteries. Using the electrochemical measurements, X-ray diffractometry and X-ray photoelectron spectroscopy (ESCA), the possible electrode reaction with discharge and recharge is shown as follows: Nb2-xVxO5 (x=0.2-1.0)+nLi++ne-αLinNb2-xVxO5. The discharge reaction consists of two main steps. In the first step, a ternary phase LinNb2-xVxO5 (x=0.5-1.0) with a varying n value is formed, and in the second ternary phase LinNb2-xVxO5 (x=0.5-1.0) with a varying n value is formed, and in the second ternary phases LinNb2-xVxO5 with different constant n values may be formed. Good charge-discharge cycling behavior was obtained with the oxides having a higher x value (0.7-0.8), which showed a small crystal lattice change along the a and c axes, while keeping the original lattice arrangement during cycling. © 1988 Elsevier Science Publishers B.V. (North-Holland Physics Publishing Division).
Article
Li7La3Zr2O12 (LLZ) solid electrolyte is one of the promising electrolytes for all-solid-state battery due to its high Li ion conductivity and stability against Li metal anode. However, high calcination temperature for LLZ preparation promotes formation of La2Zr2O7 impurity phase. In this paper, an effect of Al2O3 addition as sintering additive on LLZ solid electrolyte preparation and electrochemical properties of Al2O3-added LLZ were examined. By the Al2O3 addition, sintered LLZ pellet could be obtained after 1000°C calcination, which is 230°C lower than that without Al2O3 addition. Chemical and electrochemical properties of the Al2O3-added LLZ, such as stability against Li metal and ion conductivity, were comparable with the LLZ without Al2O3 addition, i.e. σbulk and σtotal were 2.4×10−4 and 1.4×10−4Scm−1 at 30°C, respectively. All-solid-state battery with Li/Al2O3-added LLZ/LiCoO2 configuration was fabricated and its electrochemical properties were tested. In cyclic voltammogram, clear redox peaks were observed, indicating that the all-solid-state battery with Li metal anode was successfully operated. The redox peaks were still observed even after one year storage of the all-solid-state battery in the Ar-filled globe-box. It can be inferred that the Al2O3-added LLZ electrolyte would be a promising candidate for all-solid-state battery because of facile preparation by the Al2O3 addition, relatively high Li ion conductivity, and good stability against Li metal and LiCoO2 cathode.
Article
The effect of Al and Li concentration on the formation of cubic garnet of nominal composition Li7La3Zr2O12 was investigated. It was determined that at least 0.204 moles of Al is required to stabilize the cubic phase. It was observed for the cubic phase (stabilized by the addition of Al) that as Li content was increased from 6 to 7 moles it transformed to a tetragonal phase. Additionally, powders of cubic Li6.24La3Zr2Al0.24O11.98 were hot-pressed at 1000 deg C and 40 MPa. The hot-pressed material had a relative density of 98%. The room temperature total ionic conductivity of the hot-pressed material was 4.0 x 10(exp -4) S/cm and the electronic conductivity was 2 x 10(exp -8) S/cm.
Article
Reducing our dependence on fossil fuels increases the demand for energy storage. Lithium-ion batteries have transformed portable electronics and will continue to be important but cannot deliver the step change in energy density required in the longer term in markets such as electric vehicles and the storage of electricity from renewables. There are a few alternatives. Here we describe two: Li-air and Li-sulfur batteries. We compare the energy densities of Li-ion, Li-air, and Li-S and discuss their differences and the challenges facing Li-air and Li-S, many of which are materials related.
Article
Lithium garnet-type oxides Li7−XLa3(Zr2−X, NbX)O12 (X=0–2) were synthesized by a solid-state reaction, and their lithium ion conductivity was measured using an AC impedance method at temperatures ranging from 25 to 150°C in air. The lithium ion conductivity increased with increasing Nb content, and reached a maximum of ∼0.8mScm−1 at 25°C. By contrast, the activation energy reached a minimum of ∼30kJmol−1 at the same point with X=0.25. The potential window was examined by cyclic voltammetry (CV), which showed lithium deposition and dissolution peaks around 0V vs. Li+/Li, but showed no evidence of other reactions up to 9V vs. Li+/Li.
Article
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