PVP-bridged γ-LiAlO2 nanolayer on Li1.2Ni0.182Co0.08Mn0.538O2 cathode materials for improving the rate capability and cycling stability

High-Energy-Density Cathode Material Achieved by Upgrading Low-Voltage Li3V2O5 via Ni Doping

High-energy-density lithium-ion batteries have great need for cathode materials with exceptional specific discharge capacity. Li3V2O5 shows great potential because of its high capacity (e.g., 266 mA h g-1 at 0.1 A g-1). However, its low-lying voltage plateau (∼0.6 V vs Li+/Li) restricts its use exclusively to anode applications. This work presents for the first time the development of Li3V2O5 as a high-energy-density cathode material through Ni doping. Structural analysis reveals that Ni-doped Li3V2O5 forms a cation-disordered rock-salt phase with a uniform distribution of Ni. Introducing 1 mol % Ni (denoted as LVON2) prolongs the V-based plateau (∼2.5 V) and results in an additional discharge capacity of 35 mA h g-1. In particular, a plateau ascribed to Ni2+/Ni3+ redox reaction emerges at ∼3.5 V, contributing an extra discharge capacity of 42 mA h g-1. Consequently, LVON2 achieves high specific discharge capacities of 270.8 mA h g-1 at 50 mA g-1 and 339.4 mA h g-1 at 20 mA g-1 (corresponding to an energy density of 837 W h kg-1), surpassing the pristine Li3V2O5 and many latest cathode materials. Density functional theory calculation shows that Ni preferentially occupies the empty tetragonal sites in Li3V2O5, leading to a larger off-center displacement of the neighboring LiO6 octahedra and the expansion of unit cell volume. This structural manipulation improves the electrochemical dynamics of Li3V2O5 with a better rate capability (143.3 mA h g-1 for LVON2 vs 94.1 mA h g-1 for the pristine sample at 1000 mA g-1) and a decreased charge-transfer resistance (159.2 Ω for LVON2 vs 278.6 Ω for the pristine sample). Differential scanning calorimetry and finite element analysis also reveal the enhanced thermal stability of Ni-doped Li3V2O5 at both material and full battery levels. This advancement lays a solid foundation for the development of Li3V2O5-based cathode materials for high-energy-density lithium-ion batteries.

Lattice Reconstruction Engineering Boosts the Extreme Fast Charging/Discharging Performance of Nickel-Rich Layered Cathodes

The low specific capacity and the poor capacity retention at extreme fast charging/discharging limit the nickel-rich layered cathode commercialization in electric vehicles, and the root causes are interface instability and capacity loss induced by birth defects and irreversible phase transition. In this work, we propose a lattice reconstruction strategy combining polyvinylpyrrolidone-assisted wet chemistry and calcination to prepare the aluminum-modified LiNi0.83Co0.11Mn0.06O2 (ANCM). Our method offers distinct advantages in tailoring birth defects (residual alkali and rocksalt phase), reducing Li vacancies and oxygen vacancies, exhibiting gradient Ni concentration distribution, suppressing the Li/Ni intermixing defects, lowering the lattice strain before and after recycling, and inhibiting the microcracks. The ANCM constructs robust crystal lattices and delivers an initial discharge capacity of 155.3 mAh/g with 89.2% capacity retention after 200 cycles at 5 C. This work highlights the importance of synthesis design and structural modification for cathode materials.

Superior conductive 1D and 2D network structured carbon-coated Ni-rich Li1.05Ni0.88Co0.08Mn0.04O2 as high-ion-diffusion cathodes for lithium-ion batteries

Numerous studies have addressed the low electrical conductivity of Li1.05Ni0.88Co0.08Mn0.04O2 (Ni-rich NCM). Among these approaches, surface treatment using multiwalled carbon nanotubes (MWCNTs) has emerged as a promising strategy for enhancing the depolarization of Ni-rich NCM and improving its electrochemical performance. However, MWCNT coatings applied by various methods often result in agglomeration and increase the ion-transfer resistance of the coating layer, leading to degraded electrochemical performance. In this study, 1D and 2D network structures are assembled on Ni-rich NCM surfaces using a MWCNT solution dispersed in ethanol solvent by an incipient method. The resulting highly conductive network structure facilitates electron movement without interfering with Li-ion transport, enhancing the depolarization of Ni-rich NCM and enabling high electrochemical performance. The 1D and 2D network structure coated Ni-rich NCM exhibits an excellent rate capability of 87.64% at 3C/0.2C and a cycle retention of 94.53% after 50 cycles at 1C/1C. Moreover, the incipient method used herein effectively maximizes the electrochemical performance with less coating weight than other methods. These findings highlight the potential of the 1D and 2D network structure coated Ni-rich NCM for advanced energy storage applications.

A green aqueous binder to enhance the electrochemical performance of Li-rich disordered rock salt cathode material

Li-rich disordered rock-salt oxides (DRX) are considered an attractive cathode material in the future battery field due to their excellent energy density and specific capacity. Nevertheless, anionic redox provides high capacity while causing O2 over-oxidation to O2, resulting in voltage hysteresis and capacity decay. Herein, the crystal structure of Li1.3Mn0.4Ti0.3O1.7F0.3 (LMTOF) cathode is stabilized by using sodium carboxymethylcellulose (CMC) binders replacing traditional polyvinylidene difluoride (PVDF) binders. The electrochemical impedance spectroscopy (EIS) and galvanostatic intermittent titration technique (GITT) reveal that the CMC-based LMTOF electrode has higher electronic conductivity and lithium-ion diffusion kinetics. Moreover, CMC has been demonstrated to improve the O2- reversibility, reduce the amounts of byproducts from electrolyte decomposition and suppress transition metal dissolution by Na+/Li+ exchange reaction. Furthermore, the CMC-based LMTOF electrode also exhibits less volume change upon lithiation/delithiation processes compared to the PVDF-based electrode, resulting in enhanced structural stability during cycling. Benefiting from these features, the CMC binders can effectively improve the cycling life and rate performance of the LMTOF cathode, and the CMC-based LMTOF electrode shows good capacity retention of 94.5 % after 30 cycles at 20 mA/g and 66.7 % after 100 cycles at 200 mA/g. This finding indicates that CMC as a binder can efficiently stabilize the structure and improve the electrochemical performance of Li-rich disordered rock-salt oxides cathode, making it possible for practical Li-ion battery applications.

Enhanced Proton Transport of β″-Al2O3 Modified by LiAlO2 as a High-Performance Electrolyte for a Low-Temperature Solid Oxide Fuel Cell and an Electrolyzer

β″-Al2O3 has been proven as a fast ionic conductor in solid batteries due to its unique structure. In this work, β″-Al2O3 was further modified by LiAlO2 and employed as the electrolyte material for low-temperature solid oxide fuel cells and electrolyzers, i.e., proton-conducting ceramic fuel cells and electrolysis cells, named as PCFC and PCEC, respectively. At 550 °C, thanks to this superior electrolyte with a remarkable conductivity of 0.161 S·cm-1, the PCFC reached a high power density up to 1029 mW·cm-2, and the PCEC demonstrated a significant current density of 1.49 A·cm-2 at a low operation voltage of 2.0 V. It has been found that the introduction of the LiAlO2 phase into β″-Al2O3 reduces the total impedance, while it increases the oxygen vacancy concentration and thus promotes the proton transport process with the reduced activation energy. This work provides a new approach for exploring two-dimensional materials with high-ionic conductivity that can be applied for solid oxide fuel cells and water electrolyzers and more wider power-to-X devices such as electrosynthesis for green ammonia production.

Structural Stabilization of Cation-Disordered Rock-Salt Cathode Materials: Coupling between a High-Ratio Inactive Ti4+ Cation and a Mn2+/Mn4+ Two-Electron Redox Pair

Cation-disordered rock-salt cathode materials are featured by their extraordinarily high specific capacities in lithium-ion batteries primarily contributed by anion redox reactions. Unfortunately, anion redox reactions can trigger oxygen release in this class of materials, leading to fast capacity fading and major safety concern. Despite the capability of absorbing structural distortions, high-ratio d⁰ transition-metal cations are considered to be unfavorable in design of a new cation-disordered rock-salt structure because of their electrochemically inactive nature. Herein, we report a new cation-disordered rock-salt compound of Li_1.2Ti_0.6Mn_0.2O₂ with the stoichiometry of Ti⁴⁺ as high as 0.6. The capacity reducing effect by the low-ratio active transition-metal center can be balanced by using a Mn²⁺/Mn⁴⁺ two-electron redox couple. The strengthened networks of strong Ti-O bonds greatly retard the oxygen release and improve the structural stability of cation-disordered rock-salt cathode materials. As expected, Li_1.2Ti_0.6Mn_0.2O₂ delivers significantly improved electrochemical performances and thermal stability compared to the low-ratio Ti⁴⁺ counterpart of Li_1.2Ti_0.4Mn_0.4O₂. Theoretical simulations further reveal that the improved electrochemical performances of Li_1.2Ti_0.6Mn_0.2O₂ are attributed to its lower Li⁺ diffusion energy barrier and enhanced unhybridized O 2p states compared to Li_1.2Ti_0.4Mn_0.4O₂. This concept might be helpful for the improvement of structural stability and electrochemical performances of other cation-disordered rock-salt metal oxide cathode materials.

Tuning the Electronic, Ion Transport, and Stability Properties of Li-rich Manganese-based Oxide Materials with Oxide Perovskite Coatings: A First-Principles Computational Study

Lithium-rich manganese-based oxides (LRMO) are regarded as promising cathode materials for powering electric applications due to their high capacity (250 mAh g^-1) and energy density (∼900 Wh kg^-1). However, poor cycle stability and capacity fading have impeded the commercialization of this family of materials as battery components. Surface modification based on coating has proven successful in mitigating some of these problems, but a microscopic understanding of how such improvements are attained is still lacking, thus impeding systematic and rational design of LRMO-based cathodes. In this work, first-principles density functional theory (DFT) calculations are carried out to fill out such a knowledge gap and to propose a promising LRMO-coating material. It is found that SrTiO₃ (STO), an archetypal and highly stable oxide perovskite, represents an excellent coating material for Li_1.2Ni_0.2Mn_0.6O₂ (LNMO), a prototypical member of the LRMO family. An accomplished atomistic model is constructed to theoretically estimate the structural, electronic, oxygen vacancy formation energy, and lithium-transport properties of the LNMO/STO interface system, thus providing insightful comparisons with the two integrating bulk materials. It is found that (i) electronic transport in the LNMO cathode is enhanced due to partial closure of the LNMO band gap (∼0.4 eV) and (ii) the lithium ions can easily diffuse near the LNMO/STO interface and within STO due to the small size of the involved ion-hopping energy barriers. Furthermore, the formation energy of oxygen vacancies notably increases close to the LNMO/STO interface, thus indicating a reduction in oxygen loss at the cathode surface and a potential inhibition of undesirable structural phase transitions. This theoretical work therefore opens up new routes for the practical improvement of cost-affordable lithium-rich cathode materials based on highly stable oxide perovskite coatings.

Preparation of single-crystal ternary cathode materials via recycling spent cathodes for high performance lithium-ion batteries

With the rapid consumption of lithium-ion batteries (LIBs), the recycling of spent LIBs is becoming imperative. However, the development of effective and environmentally friendly methods towards the recycling of spent LIBs, especially waste electrode materials, still remains a great challenge. Herein, on the basis of a Li-based molten salt, we have developed a facile and effective strategy to recycle spent polycrystalline ternary cathode materials into single-crystal cathodes. The regenerated plate-like single-crystal LiNi_0.6Co_0.2Mn_0.2O₂ material with exposed {010} planes achieves an excellent rate performance and outstanding cycling stability. In particular, a high capacity of 155.1 mA h g^-1 and a superior capacity retention of 94.3% can be achieved by the recycled cathode material even after 240 cycles at 1 C. Meanwhile the single-crystal structure can be well reserved without any cracks or pulverization being observed. Moreover, this recycling method can be expanded to recycle other waste Ni-Co-Mn ternary cathode materials (NCM) or their mixtures for producing high-performance single-crystal cathode materials, demonstrating its versatility and flexibility in practical applications. Therefore, the strategy of converting spent NCM cathodes into single-crystal ones with satisfactory electrochemical performance may open up a cost-effective pathway for resolving the issues caused by the large amounts of spent LIBs, thus facilitating the sustainable development of LIBs.

Coupling High Rate Capability and High Capacity in an Intercalation-Type Sodium-Ion Hybrid Capacitor Anode Material of Hydrated Vanadate via Interlayer-Cation Engineering

Layered metal vanadates with intercalation pseudocapacitive behaviors show great promise for applications in sodium-ion hybrid capacitor anode materials due to their large interlayer distances, which benefit the fast Na⁺ solid-state diffusion. However, their charge storage capacity is significantly constrained by the limited available sites that allow the intercalation of Na⁺ ions. In this work, by engineering the interlayer cations, Ni_0.12Zn_0.2V₂O₅·1.07H₂O is designed as a high-performance anode material in sodium-ion hybrid capacitors. The Ni/Zn codoping in the layered vanadate leads to the integration of high rate capability and high specific capacity. Specifically, the spacious interlayer spacing and the pillaring effects of Zn ions together lead to the high rate performance and decent cycling stability, while the redox reactions of the interlayer Ni ions efficiently upgrade the charge storage capacity of this layered material. Accordingly, this work offers a promising avenue to further optimizing the Na⁺ storage performance of layered vanadates via interlayer-cation engineering.

Recent Advances on Materials for Lithium-Ion Batteries

Environmental issues related to energy consumption are mainly associated with the strong dependence on fossil fuels. To solve these issues, renewable energy sources systems have been developed as well as advanced energy storage systems. Batteries are the main storage system related to mobility, and they are applied in devices such as laptops, cell phones, and electric vehicles. Lithium-ion batteries (LIBs) are the most used battery system based on their high specific capacity, long cycle life, and no memory effects. This rapidly evolving field urges for a systematic comparative compilation of the most recent developments on battery technology in order to keep up with the growing number of materials, strategies, and battery performance data, allowing the design of future developments in the field. Thus, this review focuses on the different materials recently developed for the different battery components—anode, cathode, and separator/electrolyte—in order to further improve LIB systems. Moreover, solid polymer electrolytes (SPE) for LIBs are also highlighted. Together with the study of new advanced materials, materials modification by doping or synthesis, the combination of different materials, fillers addition, size manipulation, or the use of high ionic conductor materials are also presented as effective methods to enhance the electrochemical properties of LIBs. Finally, it is also shown that the development of advanced materials is not only focused on improving efficiency but also on the application of more environmentally friendly materials.

Stabilized Lithium, Manganese-Rich Layered Cathode Materials Enabled by Integrating Co-Doping and Nanocoating

While lithium, manganese-rich (LMR) layered oxide cathode materials offer high energy density (>900 Wh kg^-1) and low cost, LMR is susceptible to continuous capacity and voltage decay from the oxygen migration and side reaction with aqueous electrolyte at high voltage. Herein, the integration of Na/F co-doping (CD) and AlF₃ coating on LMR is achieved without the need of complex atomic layer deposition. Akin to pristine and CD samples, CD with 1 wt % AlF₃ (CD-1.0 wt %) shows excellent electrochemical performance with the capacity and voltage retentions of 93 and 91% after 150 cycles at 0.5C, respectively, and increased ionic conductivity. Spectroscopic analysis indicates that the coating mainly influences the Co distribution, where Co is enriched on the surface, and partial diffusion of Al³⁺ ions toward the bulk, leading to a slight change of transition-metal (TM) valence states at the nanometer scale and the formation of a stable Li_x(CoAl)O_y phase. Post-cycling analysis reveals that CD-1.0 wt % can alleviate the formation of rock-salt structure and Mn dissolution. Besides, little to no metal segregation is detected for the cycled CD-1.0 wt % sample. This finding presents the first instance to apply co-doping and AlF₃ coating as a new strategy to enhance the structural homogeneity and takes another step toward their commercial viability.