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High-efficient sodium compensation enabled by dual-carbon coupling catalyst strategy for sodium-ion batteries
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Compensating for the irreversible loss of limited active sodium (Na) is crucial for enhancing the energy density of practical sodium‐ion batteries (SIBs) full‐cell, especially when employing hard carbon anode with initially lower coulombic efficiency. Introducing sacrificial cathode presodiation agents, particularly those that own potential anionic oxidation activity with a high theoretical capacity, can provide additional sodium sources for compensating Na loss. Herein, Ni atoms are precisely implanted at the Na sites within Na2O framework, obtaining a (Na0.89Ni0.05□0.06)2O (Ni–Na2O) presodiation agent. The synergistic interaction between Na vacancies and Ni catalyst effectively tunes the band structure, forming moderate Ni–O covalent bonds, activating the oxidation activity of oxygen anion, reducing the decomposition overpotential to 2.8 V (vs Na/Na⁺), and achieving a high presodiation capacity of 710 mAh/g≈Na2O (Na2O decomposition rate >80%). Incorporating currently‐modified presodiation agent with Na3V2(PO4)3 and Na2/3Ni2/3Mn1/3O2 cathodes, the energy density of corresponding Na‐ion full‐cells presents an essential improvement of 23.9% and 19.3%, respectively. Further, not limited to Ni–Na2O, the structure–function relationship between the anionic oxidation mechanism and electrode–electrolyte interface fabrication is revealed as a paradigm for the development of sacrificial cathode presodiation agent.
Sodium‐based dual ion batteries (SDIBs) have garnered significant attention as novel energy storage devices offering the advantages of high‐voltage and low‐cost. Nonetheless, conventional electrolytes exhibit low resistance to oxidation and poor compatibility with electrode materials, resulting in rapid battery failure. In this study, for the first time, a chlorination design of electrolytes for SDIB, is proposed. Using ethyl methyl carbonate (EMC) as a representative, chlorine (Cl)‐substituted EMC not only demonstrates increased oxidative stability ascribed to the electron‐withdrawing characteristics of chlorine atom, electrolyte compatibility with both the cathode and anode is also greatly improved by forming Cl‐containing interface layers. Consequently, a discharge capacity of 104.6 mAh g⁻¹ within a voltage range of 3.0–5.0 V is achieved for Na||graphite SDIB that employs a high graphite cathode mass loading of 5.0 mg cm⁻², along with almost no capacity decay after 900 cycles. Notably, the Na||graphite SDIB can be revived for an additional 900 cycles through the replacement of a fresh Na anode. As the mass loading of graphite cathode increased to 10 mg cm⁻², Na||graphite SDIB is still capable of sustaining over 700 times with ≈100% capacity retention. These results mark the best outcome among reported SDIBs. This study corroborates the effectiveness of chlorination design in developing high‐voltage electrolytes and attaining enduring cycle stability of Na‐based energy storage devices.
Chemical presodiation (CP) is an effective strategy to enhance energy density of sodium ion batteries. However, the sodiation reagents reported so far are basically polycyclic aromatic hydrocarbons (PAHs) wth low reductive potential (~0.1 V vs. Na⁺/Na), which could easily cause over‐sodiation and structural deterioration of the presodiated cathodes. In this work, Aromatic ketones (AKs) are rationally designed as mild presodiating reagents by introducing a carbonyl group (C=O) into PAHs to balance the conjugated and inductive effect. As the representatives, two compounds 9‐Fluorenoneb (9‐FN) and Benzophenone (BP) manifest favorable equilibrium potential of 1.55 V and 1.07 V (vs. Na⁺/Na), respectively. Note that 9‐FN demonstrates versatile presodiating capability toward multiple Na uptake hosts (tunneled Na0.44MnO2, layered Na0.67Ni0.33Mn0.67O2, polyanionic Na4Fe2.91(PO4)2P2O7, Na3V2(PO4)3 and Na3V2(PO4)2F3), enabling greatly improved initial charging capacity of the cathode to balance the irrevisible capacity of the anode. Our results indicate that the Aromatic ketones are competitive presodiating cathodic reagents for high‐performance sodium‐ion batteries, and will inspire more studies and application attempts in the future.
Sodium‐ion batteries (SIBs) are expected to replace partial reliance on lithium‐ion batteries (LIBs) in the field of large‐scale energy storage as well as low‐speed electric vehicles due to the abundance, wide distribution, and easy availability of sodium metal. Unfortunately, a certain amount of sodium ions are irreversibly trapped in the solid electrolyte interface (SEI) layer during the initial charging process, causing the initial capacity loss (ICL) of the SIBs. A separator capacity‐compensation strategy is proposed, where the capacity compensator on the separator oxidizes below the high cut‐off voltage of the cathode to provide additional sodium ions. This strategy shows attractive advantages, including adaptability to current production processes, no impairment of cell long‐cycle life, controlled pre‐sodiation degree, and strategy universality. The separator capacity‐compensation strategy is applied in the NaNi1/3Fe1/3Mn1/3O2 (NMFO)||HC full cell and achieve a compensated capacity ratio of 18.2%. In the Na3V2(PO4)3 (NVP)||HC full cell, the initial reversible specific capacity is increased from 61.0 mAh g⁻¹ to 83.1 mAh g⁻¹. The separator capacity‐compensation strategy is proven to be universal and provides a new perspective to enhance the energy density of SIBs.
Sodium‐ion batteries (SIBs) are considered as a low‐cost complementary or alternative system to prestigious lithium‐ion batteries (LIBs) because of their similar working principle to LIBs, cost‐effectiveness, and sustainable availability of sodium resources, especially in large‐scale energy storage systems (EESs). Among various cathode candidates for SIBs, Na‐based layered transition metal oxides have received extensive attention for their relatively large specific capacity, high operating potential, facile synthesis, and environmental benignity. However, there are a series of fatal issues in terms of poor air stability, unstable cathode/electrolyte interphase, and irreversible phase transition that lead to unsatisfactory battery performance from the perspective of preparation to application, outside to inside of layered oxide cathodes, which severely limit their practical application. This work is meant to review these critical problems associated with layered oxide cathodes to understand their fundamental roots and degradation mechanisms, and to provide a comprehensive summary of mainstream modification strategies including chemical substitution, surface modification, structure modulation, and so forth, concentrating on how to improve air stability, reduce interfacial side reaction, and suppress phase transition for realizing high structural reversibility, fast Na⁺ kinetics, and superior comprehensive electrochemical performance. The advantages and disadvantages of different strategies are discussed, and insights into future challenges and opportunities for layered oxide cathodes are also presented.
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Carbon materials, including graphite, hard carbon, soft carbon, graphene, and carbon nanotubes, are widely used as high‐performance negative electrodes for sodium‐ion and potassium‐ion batteries (SIBs and PIBs). Compared with other materials, carbon materials are abundant, low‐cost, and environmentally friendly, and have excellent electrochemical properties, which make them especially suitable for negative electrode materials of SIBs and PIBs. Compared with traditional carbon materials, modifications of the morphology and size of nanomaterials represent effective strategies to improve the quality of electrode materials. Different nanostructures make different contributions toward improving the electrochemical performance of electrode materials, so the synthesis of nanomaterials is promising for controlling the morphology and size of electrode materials. This paper reviews the progress made and challenges in the use of carbon materials as negative electrode materials for SIBs and PIBs in recent years. The differences in Na+ and K+ storage mechanisms among different types of carbon materials are emphasized. Carbon materials represent one of the most promising candidates for negative electrode materials of sodium‐ion and potassium‐ion batteries (SIBs and PIBs). This review focuses on the research progress of carbon materials such as graphite, hard carbon, soft carbon, graphene and carbon nanotubes, and other carbon nanomaterials as negative electrode materials for SIBs and PIBs.
Phase change materials (PCMs) are a unique and exciting class of materials with bright prospects in wide‐ranging sustainable technologies such as thermal and electrochemical energy storage. While impressive, the effect of gaseous species on PCMs remains largely unexplored hitherto. Here, the gaseous co‐solvent is reported that can facilitate melting and modulate physical properties such as viscosity and ion conduction of PCMs. Especially for the appealing application of PCMs as electrolytes, gaseous species also have a critical influence on both Li+‐electrolyte structure and resultant solid electrolyte interphase (SEI). Specifically, theoretical simulations and experimental analysis evidence that CO2 can promote melting while reconfiguring the solvation structure of succinonitrile‐derived Li+‐phase change electrolyte (Li+‐PCE) model system. Due to the enhanced interaction between Li+ cations and bis(trifluoromethanesulphonyl)imide (TFSI–) anions in the reconfigured solvation structure, more TFSI– derived F‐rich component and extra CO2‐derived Li2CO3 form in the upgraded SEI layer, thereby endowing proof‐of‐concept Li‐metal batteries with prolonged cyclability. Our findings may stimulate widespread interest in gas leverage to innovate electrolyte chemistry. This article is protected by copyright. All rights reserved
Rechargeable lithium‐based batteries generally exhibit gradual capacity losses resulting in decreasing energy and power densities. For negative electrode materials the capacity losses are largely attributed to the formation of a solid electrolyte interphase (SEI) layer and volume expansion effects. For positive electrode materials, the capacity losses are, instead, mainly ascribed to structural changes and metal ion dissolution. This Review focuses on another, so far largely unrecognized, type of capacity loss stemming from diffusion of lithium atoms or ions as a result of concentration gradients present in the electrode. An incomplete delithiation step is then seen for a negative electrode material while an incomplete lithiation step is obtained for a positive electrode material. Evidence for diffusion‐controlled capacity losses is presented based on published experimental data and results obtained in recent studies focusing on this trapping effect. The implications of the diffusion‐controlled Li‐trapping induced capacity losses, which are discussed using a straightforward diffusion‐based model, are compared with those of other phenomena expected to give capacity losses. Approaches that can be used to identify and circumvent the diffusion‐controlled Li‐trapping problem (e.g., regeneration of cycled batteries) are discussed, in addition to remaining challenges and proposed future research directions within this important research area. This article is protected by copyright. All rights reserved
Significance
Hard carbon (HC) is one of the most promising anode materials for alkali metal-ion batteries, which is generally prepared by annealing in a tubular furnace with a low heating rate and long duration at a target temperature. Herein, we report an innovating sintering method to quickly fabricate HC even within one minute and ultrafast heating rate by multifield-regulated spark plasma sintering (SPS) technology. This is a universal way to the rapid preparation of various HCs from different carbon precursors. Notably, HCs prepared from SPS possess significantly lower oxygen contents and higher electronic conductivity than the traditional sintering way due to the remarkably accelerated pyrolysis reaction, leading to excellent electrochemical Na-ion storage performance.
The overall performance of electrochemical energy storage devices (EESDs) is intrinsically correlated with surfaces and interfaces. As a promising electrode architecture, 3D nanoarrays (3D‐NAs) possess relatively ordered, continuous, and fully exposed active surfaces of individual nanostructures, facilitating mass and electron transport within the electrode and charge transfer across interfaces and providing an ideal platform for engineering. Herein, a critical overview of the surface and interface engineering of 3D‐NAs, from electrode and interface designs to device integration, is presented. The general merits of 3D‐NAs and surface/interface engineering principles of 3D‐NA hybrid electrodes are highlighted. The focus is on the use of 3D‐NAs as a superior platform to regulate the interface nature and unveiling new mechanism/materials without the interference of binders. The engineering and utilization of the surface of 3D‐NAs to develop flexible/solid‐state EESDs with 3D integrated electrode/electrolyte interfaces, or 3D triphase interfaces involving other active species, which are characteristic of (quasi‐)solid‐state electrolyte infiltration into the entire device, are also considered. Finally, the challenges and future directions of surface/interface engineering of 3D‐NAs are outlined. In particular, potential strategies to obtain electrode charge balance, optimize the multiphase solid‐state interface, and attain 3D solid electrolyte infiltration are proposed.
Sodium‐ion batteries have gained much attention for their potential application in large‐scale stationary energy storage due to the low cost and abundant sodium sources in the earth. However, the electrochemical performance of sodium‐ion full cells (SIFCs) suffers severely from the irreversible consumption of sodium ions of cathode during the solid electrolyte interphase (SEI) formation of hard carbon anode. Here, a high‐efficiency cathode sodiation compensation reagent, sodium oxalate (Na2C2O4), which possesses both a high theoretical capacity of 400 mA h g⁻¹ and a capacity utilization as high as 99%, is proposed. The implementation of Na2C2O4 as sacrificial sodium species is successfully realized by decreasing its oxidation potential from 4.41 to 3.97 V through tuning conductive additives with different physicochemical features, and the corresponding mechanism of oxidation potential manipulation is analyzed. Electrochemical results show that in the full cell based on a hard carbon anode and a P2‐Na2/3Ni1/3Mn1/3Ti1/3O2 cathode with Na2C2O4 as a sodium reservoir to compensate for sodium loss during SEI formation, the capacity retention is increased from 63% to 85% after 200 cycles and the energy density is improved from 129.2 to 172.6 W h kg⁻¹. This work can provide a new avenue for accelerating the development of SIFCs.
With ever‐increasing efforts focused on basic research of sodium‐ion batteries (SIBs) and growing energy demand, sodium‐ion full cells (SIFCs), as unique bridging technology between sodium‐ion half‐cells (SIHCs) and commercial batteries, have attracted more and more interest and attention. To promote the development of SIFCs in a better way, it is essential to gain a systematic and profound insight into their key issues and research status. This Review mainly focuses on the interface issues, major challenges, and recent progresses in SIFCs based on diversified electrolytes (i.e., nonaqueous liquid electrolytes, quasi‐solid‐state electrolytes, and all‐solid‐state electrolytes) and summarizes the modification strategies to improve their electrochemical performance, including interface modification, cathode/anode matching, capacity ratio, electrolyte optimization, and sodium compensation. Outlooks and perspectives on the future research directions to build better SIFCs are also provided.
MnMoO4 nanoparticles were synthesized by employing solvothermal method at optimized experimental condition to explore their electrochemical properties. The fundamental characterization studies such as X-ray diffraction, Raman spectroscopy, and Fourier transform infrared spectra confirmed the formation of pure phase of monoclinic crystal structure with C2/m space group. X-ray photoelectron spectroscopy studies revealed that the core-level Mn-2p spectrum peaks observed at 641.2 eV can be attributed to Mn-2p3/2 and that at 654.1 eV can be indexed to the binding energy of Mn-2p5/2. Major infrared peaks observed at 725, 800, 867, and 946 cm⁻¹ could be designated to the characteristics bands of tetrahedral MoO4 groups in MnMoO4 nanoparticles. Raman peaks observed at 351, 823, 886, and 932 cm⁻¹ corresponded to characteristics bands for MnMoO4 nanoparticles. The cyclic voltammetry studies at different scan rates (i.e., 10, 20, 30, 50, 80, and 100 mV s⁻¹) were performed for all three MnMoO4 nanoparticles and displayed similar redox peaks in the positive and negative current regions, reflecting the pseudocapacitive nature. From galvanostatic charge–discharge profiles, it was found that MnMoO4 nanorods (R2) show high- capacitance of 697.4 F g⁻¹ at 0.5 A g⁻¹ current density and 40% increment in specific capacitance than other nanoparticles and can be considered as suitable nanomaterials as electrode for energy storage applications.
Heteroatom‐doping is a promising strategy to tuning the microstructure of carbon material toward improved electrochemical storage performance. However, it is a big challenge to control the doping sites for heteroatom‐doping and the rational design of doping is urgently needed. Herein, S doping sites and the influence of interlayer spacing for two kinds of hard carbon, perfect structure and vacancy defect structure, are explored by the first‐principles method. S prefers doping in the interlayer for the former with interlayer distance of 3.997 Å, while S is doped on the carbon layer for the latter with interlayer distance of 3.695 Å. More importantly, one step molten salts method is developed as a universal synthetic strategy to fabricate hard carbon with tunable microstructure. It is demonstrated by the experimental results that S‐doping hard carbon with fewer pores exhibits a larger interlayer spacing than that of porous carbon, agreeing well with the theoretical prediction. Furthermore, the S‐doping carbon with larger interlayer distance and fewer pores exhibits remarkably large reversible capacity, excellent rate performance, and long‐term cycling stability for Na‐ion storage. A stable and reversible capacity of ≈200 mAh g−1 is steadily kept even after 4000 cycles at 1 A g−1. Two kinds of S‐doped hard carbon with different microsctructures are synthesized by a universal synthetic strategy. It is demonstrated that S‐doping hard carbon with fewer pores exhibits a larger interlayer spacing than that of porous carbon, and an excellent Na‐ion storage performance with a stable capacity of ≈200 mAh g−1 after 4000 cycles at 1 A g−1 is displayed.
As one of the most fascinating cathode candidates for Na-ion batteries (NIBs), P2-type Na layered oxides usually exhibit various single-phase domains accompanied by different Na+/vacancy-ordered superstructures, depending on the Na concentration when explored in a limited electrochemical window. Therefore, their Na+ kinetics and cycling stability at high rates are subjected to these superstructures, incurring obvious voltage plateaus in the electrochemical profiles and insufficient battery performance as cathode materials for NIBs. We show that this problem can be effectively diminished by reasonable structure modulation to construct a completely disordered arrangement of Na-vacancy within Na layers. The combined analysis of scanning transmission electron microscopy, ex situ x-ray absorption spectroscopy, and operando x-ray diffraction experiments, coupled with density functional theory calculations, reveals that Na+/vacancy disordering between the transition metal oxide slabs ensures both fast Na mobility (10−10 to 10−9 cm2 s−1) and a low Na diffusion barrier (170 meV) in P2-type compounds. As a consequence, the designed P2-Na2/3Ni1/3Mn1/3Ti1/3O2 displays extra-long cycle life (83.9% capacity retention after 500 cycles at 1 C) and unprecedented rate capability (77.5% of the initial capacity at a high rate of 20 C). These findings open up a new route to precisely design high-rate cathode materials for rechargeable NIBs.
Sucrose derived carbon coated silicon nanowires (SDCC-SiNWs) were prepared by drop casting of sucrose derived carbon (SDC) slurries and used as active electrode material for supercapacitors. It was observed that the SDC particles were coated over SiNWs. The results obtained by cyclic voltammetry, galvanostatic charge/discharge measurements of SDCC-SiNWs showed superior capacitive performance compared to just SDC based supercapacitors. SDCC-SiNWs has a significantly higher areal capacitance of 3.3 mF/cm² as compared to that of bare SiNWs (96 µF/cm²) or SDC based electrode (817 µF/cm²).
Energy production and storage technologies have attracted a great deal of attention for day-to-day applications. In recent decades, advances in lithium-ion battery (LIB) technology have improved living conditions around the globe. LIBs are used in most mobile electronic devices as well as in zero-emission electronic vehicles. However, there are increasing concerns regarding load leveling of renewable energy sources and the smart grid as well as the sustainability of lithium sources due to their limited availability and consequent expected price increase. Therefore, whether LIBs alone can satisfy the rising demand for small- and/or mid-to-large-format energy storage applications remains unclear. To mitigate these issues, recent research has focused on alternative energy storage systems. Sodium-ion batteries (SIBs) are considered as the best candidate power sources because sodium is widely available and exhibits similar chemistry to that of LIBs; therefore, SIBs are promising next-generation alternatives. Recently, sodiated layer transition metal oxides, phosphates and organic compounds have been introduced as cathode materials for SIBs. Simultaneously, recent developments have been facilitated by the use of select carbonaceous materials, transition metal oxides (or sulfides), and intermetallic and organic compounds as anodes for SIBs. Apart from electrode materials, suitable electrolytes, additives, and binders are equally important for the development of practical SIBs. Despite developments in electrode materials and other components, there remain several challenges, including cell design and electrode balancing, in the application of sodium ion cells. In this article, we summarize and discuss current research on materials and propose future directions for SIBs. This will provide important insights into scientific and practical issues in the development of SIBs.
Sodium-ion batteries have been considered as potential candidates for stationary energy storage because of the low cost and wide availability of Na sources. However, their future commercialization depends critically on control over the solid electrolyte interface formation, as well as the degree of sodiation at the positive electrode. Here we report an easily scalable ball milling approach, which relies on the use of metallic sodium, to prepare a variety of sodium-based alloys, insertion layered oxides and polyanionic compounds having sodium in excess such as the Na4V2(PO4)2F3 phase. The practical benefits of preparing sodium-enriched positive electrodes as reservoirs to compensate for sodium loss during solid electrolyte interphase formation are demonstrated by assembling full C/P'2-Na1[Fe0.5Mn0.5]O2 and C/'Na3+xV2(PO4)2F3' sodium-ion cells that show substantial increases (>10%) in energy storage density. Our findings may offer electrode design principles for accelerating the development of the sodium-ion technology.
Energy production and storage have become key issues concerning our welfare in daily life. Present challenges for batteries are twofold. In the first place, the increasing demand for powering systems of portable electronic devices and zero-emission vehicles stimulates research towards high energy and high voltage systems. In the second place, low cost batteries are required in order to advance towards smart electric grids that integrate discontinuous energy flow from renewable sources, optimizing the performance of clean energy sources. Na-ion batteries can be the key for the second point, because of the huge availability of sodium, its low price and the similarity of both Li and Nainsertion chemistries. In spite of the lower energy density and voltage of Na-ion based technologies, they can be focused on applications where the weight and footprint requirement is less drastic, such as electrical grid storage. Much work has to be done in the field of Na-ion in order to catch up with Li-ion technology. Cathodic and anodic materials must be optimized, and new electrolytes will be the key point for Na-ion success. This review will gather the up-to-date knowledge about Na-ion battery materials, with the aim of providing a wide view of the systems that have already been explored and a starting point for the new research on this battery technology.
Doped porous carbon is a prominent sodium anode material with high specific surface area (SSA) and abundant pore structure. Compared with the traditional “hard template” technique for the synthesis of porous carbon, the “soft template” method offers a more efficient synthesis process and simplified template removal. In response to the urgent need for eco-friendly synthesis methods for functional doping, our research introduces an innovative method using biomass-derived tannic acid as a precursor. We have successfully synthesized N/S double-doped porous spherical carbon materials (DF-N/S) through a self-assembly process driven by hydrogen bonding and solvent evaporation. As an anode material for sodium-ion batteries (SIBs), DF-N/S demonstrates superior electrochemical performance, achieving a specific capacity of 327.04 mAh g−1 at a current density of 0.05 Ag-1 in ether-based electrolytes. The remarkable sodium storage efficiency of DF-N/S has been thoroughly examined through kinetic analyses and ex-situ characterization methods. This study aims to provide a sustainable and widely adaptable method for the soft template production of doped carbon, while also shedding light on the intricacies of energy storage mechanisms in both ether/ester-based electrolytes.
In this work, a strategy is introduced wherein without keeping any excess cathode, a practical full-cell sodium-ion battery has been demonstrated by utilizing a hard carbon (HC) anode and sodium vanadium fluorophosphate and carbon nanotube composite (NVPF@C@CNT) cathode. A thin, robust, and durable solid electrolyte interface (SEI) is created on the surface of HC through its incubation wetted with a fluoroethylene carbonate (FEC)-rich warm electrolyte in direct contact with Na metal. During the incubation, the HC anode is partially sodiated and passivated with a thin SEI layer. The sodium-ion full cell fabricated while maintaining N/P ∼1.1 showed the first cycle Coulombic efficiency of ∼97% and delivered a stable areal capacity of 1.4 mAh cm-2 at a current rate of 0.1 mA cm-2 realized for the first time to the best of our knowledge. The full cell also showed a good rate capability, retaining 1.18 mAh cm-2 of its initial capacity even at a high current rate of 0.5 mA cm-2, and excellent cycling stability, giving a capacity of ∼1.0 mAh cm-2 after 500 cycles. The current strategy presents a practical way to make a sodium-ion full cell, utilizing no excess cathode material, significantly saving cost and time.
Developing efficient, low-cost, and environment-friendly electrocatalysts for hydrogen generation is critical for lowering energy usage in electrochemical water splitting. Moreover, for commercialization, fabricating cost-efficient, earth-abundant electrocatalysts with superior characteristics is of urgent need. Towards this endeavor, we report the synthesis of PANI-MnMoO4 nanocomposites using a hydrothermal approach and an in situ polymerization method with various concentrations of MnMoO4. The fabricated nanocomposite electrocatalyst exhibits bifunctional electrocatalytic activity towards the oxygen evolution reaction (OER) and the hydrogen evolution reaction (HER) at a lower overpotential of 410 mV at 30 mA cm-2 and 155 mV at 10 mA cm-2, respectively in an alkaline electrolyte. Furthermore, while showing overall water splitting (OWS) performance, the optimized PM-10 (PANI-MnMoO4) electrode reveals the most outstanding OWS performance with a lower cell voltage of 1.65 V (vs. RHE) at a current density of 50 mA cm-2 with an excellent long-term cell resilience of 24 h.
Attempts to utilize lithium-ion batteries (LIBs) in large-scale electrochemical energy storage systems have achieved initial success, and solid-state LIBs using metallic lithium as the anode have also been well developed. However, the sharply increased demands/costs and the limited reserves of the two most important metal elements (Li & Co) for LIBs have raised concerns about future development. Sodium-ion batteries (SIBs) equipped with advanced cobalt-free cathodes show great potential in solving both "lithium panic" and "cobalt panic", and have made remarkable progress in recent years. In this review, we comprehensively summarize the recent advances of high-performance cobalt-free cathode materials for advanced SIBs, systematically analyze the conflicts of structural/electrochemical stability with intrinsic insufficiencies of cobalt-free cathode materials, and extensively discuss the strategies of constructing stable cobalt-free cathode materials by making full use of non-cobalt transition-metal elements and suitable crystal structures, all of which aim to provide insights into the key factors (e.g., phase transformation, particle cracks, crystal defects, lattice distortion, lattice oxygen oxidation, morphology, transition-metal migration/dissolution, and the synergistic effects of composite structures) that can determine the stability of cobalt-free cathode materials, provide guidelines for future research, and stimulate more interest on constructing high-performance cobalt-free cathode materials.
Well-percolated Na2C4O4-based electrodes have been realized to determine the nature of the oxidation products of the squarate anion (C4O4²⁻), and then Na2C4O4 has been applied as a sacrificial material to presodiate the anodic host of a sodium-ion system. During the electrochemical oxidation of C4O4²⁻, a potential plateau with an irreversible capacity close to the theoretical one (339 mAh g⁻¹) was observed ca. 3.6 V vs. Na/Na⁺. The mass variation of the carbon-Na2C4O4 electrodes, together with the electrochemical mass spectrometry analysis of the gas phase, suggested that the oxidation product of the C4O4²⁻ anion is CO, which is further partly disproportionated into CO2 and carbon (confirmed by Raman spectroscopy and nitrogen adsorption), leading to a seven-fold enhancement of the conductivity. Thus, Na2C4O4 has been selected as sacrificial material to overcome the metal deficiency issue in the anodic material of sodium-ion capacitors (NICs). An AC-Na2C4O4//Sn4P3 (AC=activated carbon) cell was realized, and sodium was transferred to Sn4P3 by electrochemical oxidation, giving an AC/NaxSn4P3 NIC. In the voltage range from 2.0 V to 3.8 V, the NIC displayed a high specific energy of 44 Wh kg⁻¹ at 1 kW kg⁻¹. Additionally, it demonstrated an excellent capacitance retention of 94% after ca. 11,000 cycles, owing to the CO2 oxidation product of of C4O4²⁻ which leads to the formation of Na2CO3 passivating very efficiently the NaxSn4P3 anode surface. Hence, Na2C4O4 is a beneficial and easily available sacrificial material enabling to simplify the construction of Na-ion systems and improve significantly their performance.
The development of Na-ion full cells (NIFCs) suffers from the issue that the solid electrolyte interphase formation on the carbon anode consumes the limited sodium from cathode and thus incurs the decreased energy density and poor cyclic stability. To address these issues, we herein report that Na2O2 could be used as a sacrificial Na source through spraying its slurry on the surface of cathode, and investigate its stability as well as electrochemical behavior toward NIFCs. The results show that Na2O2 has good chemical and storage stability under a dry atmosphere and has no negative effect on the electrochemical performance of the cathode. Compared with the pristine cathode, the Na2O2-decorated cathode exhibits higher discharge capacity, superior capacity retention, and rate capability in a full cell with a carbon anode. Our cathode Na compensation strategy provides an effective avenue to make up for the irreversible Na+ loss cause by the formation of solid electrolyte interphase on the anode, thereby promoting the electrochemical performance and energy density of NIFCs toward the large-scale application.
The exploration of next-generation sodium-ion batteries (SIBs) is a worldwide concern to replace the current commercial lithium-ion batteries, mitigating the increasing exhaustion of Li resources. Sodium transition metal oxides are considered to be one of the most promising cathode materials for SIBs. The anionic redox reaction in Li-rich transition metal oxides is capable of providing extra capacity in addition to the cationic redox activities in lithium-ion batteries. A similar phenomenon exists in SIBs, which even applies to Na-deficient transition metal oxides. Moreover, transition metal oxides with mixed phase also demonstrate great potential. In this review, studies on anionic redox are first systematically introduced. The up-to-date advances on high-capacity transition metal oxide cathode materials for SIBs are then classified and summarized in different groups associated with or without anionic redox. The existing challenges as well as available solutions and strategies are discussed, and proposals with new insights are made at the end. It is expected that this work can provide new perspectives on controlling the anionic redox activity and finding novel high-capacity oxide cathode materials for SIBs.
During the first charge process of full cells, a solid electrolyte interphase (SEI) film is formed when the active ion from the cathode is consumed, resulting in irreversible capacity loss. This phenomenon has shown to be more serious in sodium-ion full cells than in lithium-ion full cells. Although many strategies have been employed to alleviate the loss of sodium ions, such as presodiation and construction of an artificial solid electrolyte interface, they are both cumbersome and time-consuming. For the first time, NaCrO2 was used as an effective self-sacrificing sodium compensation additive in sodium-ion full cells due to the irreversible phase transition of NaCrO2 in a high voltage region can deliver an irreversible capacity of up to 230 mAh g⁻¹. Based on this design, sodium-ion full cells coupled with hard carbon as the anode exhibited higher capacity, less polarization, greater energy density, and superior cycle stability than those of a pristine electrode. This is mainly attributed to the removal of sodium ions from NaCrO2, which compensates for the loss of sodium ions consumed during the formation of the SEI film on the anode surface during the first charge process. Overall, this work opens up a new avenue for exploring sodium compensation strategy and contributing to practical application of sodium-ion full cells.
Sodium sulfide (Na2S) has been used as sacrificial material for the presodiation of a Sn4P3 negative electrode in order to realize a high-performance sodium-ion capacitor (NIC). In two-electrode cells with Na counter/reference electrode and 1 mol L−1 NaClO4 electrolyte, sodium could be irreversibly extracted from Na2S at potential lower than 3.8 V vs. Na/Na+, with a capacity close to the theoretical value of 687 mAh g−1. In the realization of the composite positive electrode for a NIC, the relatively high capacity of Na2S allows to reduce its amount to 40 wt%, whereas the other materials are activated carbon (AC, 40 wt%), carbon soot (15 wt%) and binder (5 wt%). Once the pre-sodiation of Sn4P3 is completed, activated carbon being a part of the positive electrode stores charges in the electrical double-layer (EDL), while reversible sodium insertion occurs in the Sn4P3 negative electrode. The full NIC demonstrates stable performance in the voltage range 2.0 V–3.8 V with high specific energy ca. 48 Wh kg−1 at specific power of 1 kW kg−1 (per total mass of electrodes). Hence, Na2S is an excellent sacrificial material, which allows the NICs construction to be simplified and consequently the manufacturing costs to be reduced.
Owning to sodium reserve with excellent abundance and high availability, sodium ion batteries (NIBs) hold great promise to meet materials supply and cost demand for large-scale energy storage system (ESS) in the application of renewable energy source and smart grids. However, such a sole cost advantage of stationary NIBs barely makes their commercial success. In this review, we for the first time summarize emerging attractive characteristics of stationary NIBs, such as high-rate capability, all-climate operation and full-battery recyclability. Together with inherent cost advantage, these merits have manifested an excellent compatibility between stationary NIBs and large-scale ESS that dictates their validity in practical applications. Representative electrode materials are highlighted to illustrate the advancements of corresponding features. The insights presented in this review can arouse research interests in NIBs design and serve as a guide for the application of NIBs in large scale stationary energy storage.
MnOx-CeO2 is a potential substitute for commercial Pt-based diesel oxidation catalysts. To better investigate its active sites for NO oxidation reactions, a series of MnOx-CeO2 samples with low Mn doping amounts (≤5%) were synthesized using the incipient-wetness impregnation method. The catalysts were characterized by various techniques (XRD, BET, XPS and H2-TPR). According to XRD and XPS, a trace amount of manganese enriched on the surface of CeO2 exists in higher oxidation states. With the increase of Mn doping, more Mn²⁺ is introduced into the CeO2 lattice. The interaction between the manganese oxides and ceria improves the redox properties of MnOx and the surface oxygen of CeO2. Combining turn over frequency with the initial reducibility from H2-TPR quantitation, it is found that H2 consumption from Mn⁴⁺/Mn³⁺ to Mn3O4 is equivalent to the active site for NO oxidation reactions. In conclusion, Mn⁴⁺/Mn³⁺ is the active species for NO oxidation reactions. © The Royal Society of Chemistry and the Centre National de la Recherche Scientifique.
Sodium-ion full cell with hard carbon as anode and a layered oxide cathode based on earth abundant elements i.e., Na0.67[Fe0.5Mn0.5]O2 is reported. The irreversible capacity of the negative electrode in the full cell configuration is compensated by the addition of a sacrificial salt such as NaN3 to the P2-Na0.67[Fe0.5Mn0.5]O2 cathode material. 60% increase in the reversible capacity is achieved with the addition of 10% of sodium azide in the composite cathode without compromise on the cycle life. Though, there is a limit in its use because of the capacity fade which can be observed with the further increase in NaN3 content. The quantification of sodium ions at the end of discharge (at 1 V) after 40 cycles by ex-situ X-ray diffraction and solid state nuclear magnetic resonance supports the electrochemical data. Scanning electron microscopy shows the effect of NaN3 on the electrode microstructure in terms of the porosity created by NaN3 decomposition.
A laboratory project for the upper-division physical chemistry laboratory is described, and it combines IR and Raman spectroscopies with Gaussian electronic structure calculations to determine the structure of the oxalate anion in solid alkali oxalates and in aqueous solution. The oxalate anion has two limiting structures whose vibrational spectra have distinct differences: planar with D2h symmetry and nonplanar with D2d symmetry. In the former case, the IR and Raman spectra are complementary. Students measure the IR and Raman spectra of solid Na2C2O4, K2C2O4, and Cs2C2O4, and a nearly saturated aqueous solution of K2C2O4. They also carry out Gaussian calculations on the oxalate anion to predict the vibrational wavenumbers of both the planar and nonplanar structures and use the results to assign the spectra. By considering their results for the four samples, they decide on the oxalate structure in each and defend their choice in a report. The complexity of the project immerses the students in vibrational spectroscopy so that they learn the subject at a deeper level. © 2016 The American Chemical Society and Division of Chemical Education, Inc.
Room temperature Na-ion secondary battery has been under focus lately due to its feasibility to compete against already well-established Li-ion secondary battery. Although there are many obstacles to overcome before Na-ion battery becomes commercially available, recent research discoveries corroborate that some of the cathode materials for Na-ion battery have indeed indisputable advantages over its Li-ion counterparts. In this publication, a comprehensive review of layered oxides (NaTMO2, TM = Ti, V, Cr, Mn, Fe, Co, Ni, and mixture of 2 or 3 elements) as a viable Na-ion battery cathode is presented. Unary systems are well characterized not only for their electrochemical performance but also for their structural transitions during the cycle. Binary systems are investigated in order to address issues regarding low reversible capacity, capacity retention, operating voltage, and structural stability. In consequence, some materials already have reached energy density of 520 mW h g-1, which is comparable to that of LiFePO4. Furthermore, some ternary system retained more than 72% of its capacity along with over 99.7% Coulombic efficiency for 275 cycles. The goal of this review is to present the development of Na layered oxide materials in the past as well as state of the art today in order to emphasize compatibility and durability of layered oxide as a powerful candidate for Na-ion battery cathode material.
The material's abundance is a simple and clear reason as to why sodium ions are attractive as charge carriers for rechargeable batteries. It is also expected that potassium ions have a further smaller desolvation energy compared with the Li and Na systems in aprotic solvents. However, further energy sacrifice is also unavoidable for the potassium system due to heavy atomic weight. In addition to the oxides, a wide variety of crystal structures is known for polyanionic compounds and the structural chemistry of the Na system is much more complicated in comparison to the Li system. Na ions are apparently coordinated by four fluoride ions at bottleneck sites when the Na ions migrate across the perovskite-type framework structure.
A simple approach is proposed to prepare C-SiO2 composites as anode materials for lithium ion batteries. In this novel approach, nano-sized silica is soaked in sucrose solution and then heat treated at 900°C under nitrogen atmosphere. Transmission electron microscopy (TEM) and X-ray diffraction (XRD) analysis shows that SiO2 is embedded in amorphous carbon matrix. The electrochemical test results indicate that the electrochemical performance of the C-SiO2 composites relates to the SiO2 content of the composite. The C-SiO2 composite with 50.1% SiO2 shows the best reversible lithium storage performance. It delivers an initial discharge capacity of 536mAhg−1 and good cyclability with the capacity of above 500mAhg−1 at 50th cycle. Electrochemical impedance spectra (EIS) indicates that the carbon layer coated on SiO2 particles can diminish interfacial impedance, which leads to its good electrochemical performance.
MnO powder materials are investigated as anode active materials for Li-ion batteries. Lithium is stored reversibly in MnO through conversion reaction and interfacial charging mechanism, according to the results of ex situ XRD, TEM and galvanostatic intermittent titration technique. A layer of the solid electrolyte interphase with a thickness of 20–60nm is covered on MnO particles after full insertion. MnO powder materials show reversible capacity of 650mAhg−1 with average charging voltage of 1.2V. It can deliver 400mAhg−1 at a rate of 400mAg−1. The cyclic performance of MnO is improved significantly after decreasing particle size and coating with a layer of carbon. Among observed transition metal oxides, MnO shows relatively lower voltage hysteresis (