Layered Oxide Cathode Research Articles

A universal multifunctional dual cation doping strategy towards stabilized ultra-high nickel cobalt-free lithium layered oxide cathode

Ultra-high nickel cobalt-free lithium layered oxides are promising cathode material for lithium-ion batteries (LIBs) because of their relatively high capacity and low cost. Nevertheless, the high nickel content would induce bulk structure degradation and interfacial environment deterioration, and the absence of Co element reduces the lithium diffusion kinetics, severely limiting the performance liberation of this kind of cathodes. Herein, a multifunctional Ti/Zr dual cation co-doping strategy has been employed to improve the lithium storage performance of LiNi0.9Mn0.1O2 (NM91) cathode. On the one hand, the Ti/Zr co-doping weakens the Li+/Ni2+ mixing through magnetic interactions due to the inexistence of unpaired electrons for Ti4+ and Zr4+, increasing the lithium diffusion rate and suppressing the harmful coexistence of H1 and H2 phases. On the other hand, they enhance the lattice oxygen stability because of the strong Ti–O and Zr–O bonds, inhibiting the undesired H3 phase transition and lattice oxygen loss, improving the bulk structure and cathode-electrolyte interface stability. As a result, the Ti/Zr co-doped NM91 (NMTZ) exhibits a 91.2% capacity retention rate after 100 cycles, while that of NM91 is only 82.9%. Also, the NMTZ displays better rate performance than NM91 with output capacities of 115 and 93 mA h g−1 at a high current density of 5 C, respectively. Moreover, the designed NMTZ could enable the full battery to deliver an energy density up to 263 W h kg−1, making the ultra-high nickel cobalt-free lithium layered oxide cathode closer to practical applications.

Advancements in Addressing Microcrack Formation in Ni–Rich Layered Oxide Cathodes for Lithium–Ion Batteries

AbstractNickel–rich layered oxides of LiNi1–x–yCoxMn(Al)yO2 (where 1–x–y>0.6) are considered promising cathode active materials for lithium‐ion batteries (LIBs) due to their high reversible capacity and energy density. However, the widespread application of NCM(A) is limited by microstructural degradation caused by the anisotropic shrinkage and expansion of primary particles during the H2→H3 phase transition. In this mini–review, we comprehensively discuss the formation of microcracks, subsequent material degradation, and related alleviation strategies in nickel–rich layered NCM(A). Firstly, theories on microcracks′ formation and evolution mechanisms are presented and critically analyzed. Secondly, recent advancements in mitigation strategies to prevent degradation in Ni–rich NCM/NCA are highlighted. These strategies include doping, surface coating, structural optimization, and morphology engineering. Finally, we provide an outlook and perspective to identify promising strategies that may enable the practical application of Ni–rich NCM/NCA in commercial settings.

Effective incorporation of cobalt near surface region for cobalt-free cathodes in lithium-ion batteries

Cobalt-free cathode materials, particularly Ni-rich layered oxide cathode materials, are ideal for electric vehicle Li-ion batteries, offering high energy density and cost-effectiveness. However, high Ni content in high-temperature synthesis leads to issues like increased Li/Ni cation mixing and reduced rate capability, mainly due to the absence of Co. Therefore, this study investigated the utilization of a small amount of Co instead of completely removing it to enhance electrochemical performance. A simple pre-calcination process was used to induce Co substitution beneath the Ni-rich layered oxide cathode materials surface. A coating process was also performed for comparison. The Li/Ni cation mixing in the Co-substituted sample during high-temperature calcination was 2.43%, demonstrating a superior value compared to the Co-coating process. Rate capability tests showed superior performance for Co-substituted sample (164.2 mAh g−1) at 2 C compared to coated sample (151.0 mAh g−1). Moreover, Co substitution improved not only the cycle stability but also the high-temperature stability at an elevated state of charge.This study focuses on the surface modification of cobalt-free cathode, providing direct insight into the effects of Co substitution and typical Co coating and suggests an optimal process that uses small amounts of Co.

Interface Engineering via Constructing Enhanced Ligand Enables Highly Stable Li‐Rich Layered Oxide Cathode

AbstractHigh‐energy‐density and cost‐effective lithium‐rich oxides (LRO) are considered as the promising cathode materials for the next‐generation lithium‐ion batteries . Nevertheless, the elevated cut‐off voltage and the complex interface interactions have presented significant challenges that can lead to material degradation. Specifically, the inevitable release of lattice oxygen and the highly reactive interface‐driven irreversible migration of transition metal (TM) ions in LRO make the construction of a robust interface extremely important. Herein, an effective and efficient coating approach is applied to stabilize the interface structure of LRO by introducing a coordination bond between the strong ligand of polyurethane (PU) and the surface of LRO particles. This functional coating stabilizes the crystal field stabilization energies of LRO by acting as a strong ligand in spectrochemistry to form a coordination bond with Mn4+ in Li2MnO3 at high voltage. Consequently, irreversible oxygen release and TM ions migration are greatly inhibited. Overall, the LRO‐PU cathode exhibits superior electrochemical cyclability with a retention of 80.0% at 1C after 300 cycles and enhanced rate capability with a retention of 80.9% at 0.1C after rate cycles, marking a significant step toward commercial implementation.

Interfacial Engineering of P2-Type Ni/Mn-Based Layered Oxides by a Facile Water-Washing Method for Superior Sodium-Ion Batteries.

Owing to the strong basicity and reactivity, residual sodium compounds (RSCs) on the surface of Na-based layered oxides for sodium-ion batteries (SIBs) cause the deterioration of the electrochemical performance and processability of the oxide cathode materials. Herein, considering P2-type Na0.66Ni0.26Zn0.07Mn0.67O2 as the model material, the water-washing treatment is proven to be a facile, economic, and highly efficient method to improve the electrochemical performance of P2-type Ni/Mn-based layered oxides. Experimental results show that RSCs on material surfaces can be effectively removed by water washing without causing severe damage to the bulk structure. Notably, water washing triggers the formation of an ultrathin (2-3 nm thick) Na-poor disordered interfacial layer on the surface of Na0.66Ni0.26Zn0.07Mn0.67O2. This layer plays a passivating role in further enhancing the material's resistance to water and reduces the reactivity of the material surface with the electrolyte. These compositional and structural optimizations for P2-type Na0.66Ni0.26Zn0.07Mn0.67O2 effectively suppress the release of gaseous CO2, formation of thick cathode-electrolyte interphase films, and consumption of active Na+, enabling good Na+ transport kinetics during cycling. The water-washed Na0.66Ni0.26Zn0.07Mn0.67O2 exhibits significantly improved cycling stability with a capacity retention of 89.1% at 100 mA g-1 after 100 cycles and rate capability with a discharge capacity of 76.3 mA g-1 at 2000 mA g-1; these values are higher than those of the unwashed Na0.66Ni0.26Zn0.07Mn0.67O2 (83.3%, 71.4 mA h g-1). This work provides fundamental insights into the detrimental effect of RSCs on the electrochemical performance of layered oxides and highlights the importance of regulating interfacial compositions for developing high-performance layered-oxide cathode materials for SIBs.

Designing ultrastable P2/O3-type layered oxides for sodium ion batteries by regulating Na distribution and oxygen redox chemistry

P2/O3-type Ni/Mn-based layered oxides are promising cathode materials for sodium-ion batteries (SIBs) owing to their high energy density. However, exploring effective ways to enhance the synergy between the P2 and O3 phases remains a necessity. Herein, we design a P2/O3-type Na0.76Ni0.31Zn0.07Mn0.50Ti0.12O2 (NNZMT) with high chemical/electrochemical stability by enhancing the coupling between the two phases. For the first time, a unique Na+ extraction is observed from a Na-rich O3 phase by a Na-poor P2 phase and systematically investigated. This process is facilitated by Zn2+/Ti4+ dual doping and calcination condition regulation, allowing a higher Na+ content in the P2 phase with larger Na+ transport channels and enhancing Na+ transport kinetics. Because of reduced Na+ in the O3 phase, which increases the difficulty of H+/Na+ exchange, the hydrostability of the O3 phase in NNZMT is considerably improved. Furthermore, Zn2+/Ti4+ presence in NNZMT synergistically regulates oxygen redox chemistry, which effectively suppresses O2/CO2 gas release and electrolyte decomposition, and completely inhibits phase transitions above 4.0 V. As a result, NNZMT achieves a high discharge capacity of 144.8 mA h g−1 with a median voltage of 3.42 V at 20 mA g−1 and exhibits excellent cycling performance with a capacity retention of 77.3% for 1000 cycles at 2000 mA g−1. This study provides an effective strategy and new insights into the design of high-performance layered-oxide cathode materials with enhanced structure/interface stability for SIBs.

Enhanced all-solid-state battery performance through in-situ construction of interface modification layer

The development of high-performance all-solid-state lithium batteries (ASSLBs) relies on improving the interface stability between layered oxide cathodes and sulfide electrolytes, as well as the structural stability of cathode active materials. While coating technology is considered an effective solution, the fabrication of these coating materials using economically viable and scalable manufacturing processes remains a comprehensive and challenging task. In this study, a combination of first-principles calculations and experiments is employed to propose, for the first time, a simple and scalable aqueous process to in-situ construct an Li3VO4 (LVO) buffer coating on the surface of LiCoO2(LCO) cathode, which exhibits high ionic conductivity, relatively low electronic conductivity, and high oxidation limit. The LVO buffering coating not only facilitates the migration of lithium ions at the interface, effectively suppresses interface side reactions, and reduces interface impedance, but also enhances the mechanical and structural stability of the cathode material. As a result, the LCO/LPSC/Li-In ASSLBs with 2% LVO coating exhibit an initial discharge capacity of up to 145.6 mAh g−1 at room temperature (0.1C), with a capacity retention of 94.89% after 100 cycles. Furthermore, the ASSLBs demonstrate good capacity and cycle stability under extreme testing conditions, including high voltage, high temperature, and low temperature, especially exhibiting an initial discharge capacity of up to 114.9 mAh g−1 at −20 °C.

Synchronous organic-inorganic co-intercalated ammonium vanadate cathode for advanced aqueous zinc-ion batteries

Vanadium-based cathode materials are attractive for aqueous zinc-ion batteries (AZIBs) owing to the high capacity from their open frameworks and multiple valences. However, the cycle stability and rate capability are still restricted by the low electrical conductivity and trapped diffusion kinetics. Here, we propose an organic–inorganic co-intercalation strategy to regulate the structure of ammonium vanadate (NH4V4O10, NVO). The introduction of Al3+ and polyaniline (PANI) induces the optimized layered structure and generation of urchin-like hierarchical construction (AP-NVO), based on heterogeneous nucleation and dissolution–recrystallization growth mechanism. Owing to these favorable features, the AP-NVO electrode delivers a desirable discharge capacity of 386 mA h g−1 at 1.0 A g−1, high-rate capability of 263 mA h g−1 at 5.0 A g−1 and excellent cycling stability with 80.4% capacity retention over 2000 cycles at 5.0 A g−1. Such satisfactory electrochemical performance is believed to result from the enhanced reaction kinetics provided by the stable layered structure and a high intercalation pseudo-capacitance reaction. These results could provide enlightening insights into the design of layered vanadium oxide cathode materials.

Sb-Doped Biphasic P2/O3-Type Mn-Rich Layered Oxide Cathode Material for High-Performance Sodium-Ion Batteries.

Mn-rich P2-type layered oxide cathode materials suffer from severe capacity loss caused by detrimental phase transition and transition metal dissolution, making their implementation difficult in large-scale sodium-ion battery applications. Herein, we introduced a high-valent Sb5+ substitution, leading to a biphasic P2/O3 cathode that suppresses the P2-O2 phase transformation in the high-voltage condition attributed to the stronger Sb-O covalency that introduces extra electrons to the O atom, reducing oxygen loss from the lattices and improving structural stability, as confirmed by first-principle calculations. Besides, the enhanced Na+ diffusion kinetics and thermodynamics in the modified sample are associated with the enlarged lattice parameters. As a result, the proposed cathode delivers a discharge capacity of 142.6 mAh g-1 at 0.1C between 1.5 and 4.3 V and excellent performance at a high mass loading of 8 mg cm3 with a specific capacity of 131 mAh g-1 at 0.2C. Furthermore, it also possesses remarkable rate capability (90.3 mAh g-1 at 5C), specifying its practicality in high-energy-density sodium-ion batteries. Hence, this work provides insights into incorporating high-valent dopants for high-performance Mn-rich cathodes.

Anion-Induced Uniform and Robust Cathode-Electrolyte Interphase for Layered Metal Oxide Cathodes of Sodium Ion Batteries.

Layer metal oxides demonstrate great commercial application potential in sodium-ion batteries, while their commercialization is extremely hampered by the unsatisfactory cycling performance caused by the irreversible phase transition and interfacial side reaction. Herein, trimethoxymethylsilane (TMSI) is introduced into electrolytes to construct an advanced cathode/electrolyte interphase by tuning the solvation structure of anions. It is found that due to the stronger interaction between ClO4- and TMSI than that of ClO4- and PC/FEC, the ClO4--TMSI complexes tend to accumulate on the surface of the cathode during the charging process, leading to the formation of a stable cathode/electrolyte interface (CEI). In addition, the Si species with excellent electronic insulation ability are distributed in the TMSI-derived CEI film, which is conducive to inhibiting the continuous side reaction of solvents and the growth of the CEI film. As a result, under a current density of 250 mA g-1, the capacity retention of the NaNi1/3Fe1/3Mn1/3O2 (NFM) cathode after 200 cycles in the TMSI-modified electrolyte is 74.4% in comparison to 51.5% of the bare electrolyte (1 M NaClO4/PC/5% FEC). Moreover, the NFM cathode shows better kinetics, with the specific discharge capacity increasing from 22 to 67 mAh g-1 at 300 mA g-1. It also demonstrates greatly improved rate capability, cycling stability, and Coulombic efficiency under various operating conditions, including high temperature (55 °C) and high cutoff voltage (2.0-4.3 V vs Na+/Na).

Advances in layered transition metal oxide cathodes for sodium-ion batteries

The rapid rise of renewable energy technology has greatly promoted the development of energy storage systems. Breaking decades of stagnation, sodium-ion batteries (SIBs) have now regained momentum in the field of energy storage and they are considered as a low-cost alternative to lithium-ion batteries. The search for suitable materials to reversibly host sodium ions has become a focal point in SIB field. Layered transition metal oxide (NaxTMO2) as the cathode material has attracted increasing attention due to its simple structure, facile synthesis, and high operating potential. Nevertheless, NaxTMO2 still faces severe challenges, including irreversible phase transitions, storage instability, insufficient performance, etc. This work provides a comprehensive review of NaxTMO2 as the cathode material for SIBs, analyzes the challenges encountered by NaxTMO2, and summarizes effective improvement strategies. Strategies including doping, composite cathode materials, high-entropy materials and microstructural modulation can effectively guide the design of NaxTMO2 with excellent performance. SIBs are bound to play a positive role in the new round of energy revolution.

Regulating interfacial chemistry and kinetic behaviors of F/Mo co-doping Ni-rich layered oxide cathode for long-cycling lithium-ion batteries over −20 °C–60 °C

Ni-rich layered oxide cathodes have shown promise for high-energy lithium-ion batteries (LIBs) but are usually limited to mild environments because of their rapid performance degradation under extreme temperature conditions (below 0 °C and above 50 °C). Here, we report the design of F/Mo co-doped LiNi0.8Co0.1Mn0.1O2 (FMNCM) cathode for high-performance LIBs from −20 to 60 °C. F– doping with high electronegativity into the cathode surface is found to enhance the stability of surface lattice structure and protect the interface from side reactions with the electrolyte by generating a LiF-rich surface layer. Concurrently, the Mo6+ doping suppresses phase transition, which blocks Li+/Ni2+ mixing, and stabilizes lithium-ion diffusion pathway. Remarkably, the FMNCM cathode demonstrates excellent cycling stability at a high cutoff voltage of 4.4 V, even at 60 °C, maintaining 90.6% capacity retention at 3 C after 150 cycles. Additionally, at temperatures as low as −20 °C, it retains 77.1% of its room temperature capacity, achieving an impressive 97.5% capacity retention after 500 cycles. Such stable operation under wide temperatures has been further validated in practical Ah-level pouch-cells. This study sheds light on both fundamental mechanisms and practical implications for the design of advanced cathode materials for wide-temperature LIBs, presenting a promising path towards high-energy and long-cycling LIBs with temperature adaptability.

Tuning the Interface Stability of Nickel-Rich NCM Cathode Against Aggressive Structural Collapse via the Synergistic Effect of Additives.

Nickel-rich layered oxides are envisaged as one of the most promising alternative cathode materials for lithium-ion batteries, considering their capabilities to achieve ultrahigh energy density at an affordable cost. Nonetheless, with increasing Ni content in the cathodes comes a severe extent of Ni4+ redox side reactions on the interface, leading to fast capacity decay and structural stability fading over extended cycles. Herein, dual additives of bis(vinylsulfonyl)methane (BVM) and lithium difluorophosphate (LiDFP) are adopted to synergistically generate the F-, P-, and S-rich passivation layer on the cathode, and the Ni4+ activity and dissolution at high voltage are restricted. The sulfur-rich layer formed by the polymerization of BVM, combined with the Li3PO4 and LiF phases derived from LiDFP, alleviates the problems of increased impedance, cracks, and an irreversible H2-H3 phase transition. Consequently, the Ni-rich LiNixM1-xO2 (x > 0.95) button half-cell cycled in LiDFP + BVM electrolyte exhibits a significant discharging capacity of 181.4 mAh g-1 at 1 C (1 C = 200 mA g-1) with retention of 83.7% after 100 cycles, surpassing the performance of the commercial electrolyte (160.7 mAh g-1) with retention of 53.3%. Remarkably, the NCM95||graphite pouch cell exhibits a remarkable capacity retention of 95.5% after 200 cycles. This work inspires the rational design of electrolyte additives for ultrahigh-energy batteries with nickel-rich layered oxide cathodes.

Regulating local chemical environment in O3-type layered sodium oxides by dual-site Mg2+/B3+ substitution achieves durable and high-rate cathode

The O3-Na0.85Ni0.2Fe0.4Mn0.4O2 layered oxide cathode material possesses the advantages of high specific capacity, low cost, and simple synthesis. However, sluggish kinetics and complicated phase transition caused by the large size difference between Na+ and tetrahedral gaps lead to poor rate and cycling performance. Therefore, a scalable and feasible strategy was proposed to modulate local chemical environment by introducing Mg2+ and B3+ into O3-Na0.85Ni0.2Fe0.4Mn0.4O2, which can distinctly improve kinetic transport rate as well as electrochemical performance. The capacity retention of O3-(Na0.82Mg0.04)(Ni0.2Fe0.4Mn0.4)B0.02O2 (NFMB) increases from 43.3% and 12.4% to 89.5% and 89.0% at 1 C and 3 C after 200 cycles, respectively. Moreover, the electrode still delivers high rate capacity of 93.9 mAh/g when current density increases to 10 C. Mg2+ ions riveted on Na layer act as a “pillar” to stabilize crystal structure and inhibit structural change during the desodiumization process. B3+ ions entering tetrahedral interstice of the TM layer strengthen the TM-O bond, lower Na+ diffusion energy barrier and inhibits the slip of TM layer. Furthermore, the assembled full batteries with the modified cathode material deliver a high energy density of 278.2 Wh/kg with commercial hard carbon as anode. This work provides a strategy for the modification of high-performance SIB layered oxide materials to develop the next-generation cost-effective energy storage grid systems.

Revealing the Potential and Challenges of High‐Entropy Layered Cathodes for Sodium‐Based Energy Storage

AbstractSodium‐ion batteries (SIBs) reflect a strategic move for scalable and sustainable energy storage. The focus on high‐entropy (HE) cathode materials, particularly layered oxides, has ignited scientific interest due to the unique characteristics and effects to tackle their shortcomings, such as inferior structural stability, sluggish reaction kinetics, severe Jahn‐Teller effects induced lattice distortion, and poor oxygen reversibility at high voltage. This review focuses on high‐entropy oxide materials, highlighting their fundamentals, design principles, and application in layered oxide cathodes for SIBs. It delves into the growth mechanism, composition‐properties correlations, and the functional roles of high‐entropy design in enhancing the performance of layered oxide cathodes. Furthermore, it furnishes a comprehensive survey of recent advancements and persisting challenges within the domain of layered high‐entropy cathode materials, as well as offers insights into potential future research directions in line with the current state of knowledge.

Co/Al Co-Substituted Layered Manganese-Based Oxide Cathode for Stable and High-Rate Potassium-Ion Batteries.

Manganese-based layered oxides are promising cathode materials for potassium-ion batteries (PIBs) due to their low cost and high theoretical energy density. However, the Jahn-Teller effect of Mn3+ and sluggish diffusion kinetics lead to rapid electrode deterioration and a poor rate performance, greatly limiting their practical application. Here, we report a Co/Al co-substitution strategy to construct a P3-type K0.45Mn0.7Co0.2Al0.1O2 cathode material, where Co3+ and Al3+ ions occupy Mn3+ sites. This effectively suppresses the Jahn-Teller distortion and alleviates the severe phase transition during K+ intercalation/de-intercalation processes. In addition, the Co element contributes to K+ diffusion, while Al stabilizes the layer structure through strong Al-O bonds. As a result, the K0.45Mn0.7Co0.2Al0.1O2 cathode exhibits high capacities of 111 mAh g-1 and 81 mAh g-1 at 0.05 A g-1 and 1 A g-1, respectively. It also demonstrates a capacity retention of 71.6% after 500 cycles at 1 A g-1. Compared to the pristine K0.45MnO2, the K0.45Mn0.7Co0.2Al0.1O2 significantly alleviates severe phase transition, providing a more stable and effective pathway for K+ transport, as investigated by in situ X-ray diffraction. The synergistic effect of Co/Al co-substitution significantly enhances the structural stability and electrochemical performance, contributing to the development of new Mn-based cathode materials for PIBs.

Synergistic Effect of Co-Mo Pinning in Lay-Structured Oxide Cathode for Enhancing Stability toward Potassium-Ion Batteries.

Owing to the high economic efficiency and energy density potential, manganese-based layer-structured oxides have attracted great interests as cathode materials for potassium ion batteries. In order to alleviate the continuous phase transition and K+ re-embedding from Jahn-Teller distortion, the [Mn-Co-Mo]O6 octahedra are introduced into P3-K0.45MnO2 herein to optimize the local electron structure. Based on the experimental and computational results, the octahedral center metal molybdenum in [MoO6] octahedra proposes a smaller ionic radius and higher oxidation state to induce second-order JTE (pseudo-JTE) distortion in the adjacent [MnO6] octahedra. This distortion compresses the [MnO6] octahedra along the c-axis, leading to an increased interlayer spacing in the K+ layer. Meanwhile, the Mn3+/Mn4+ is balanced by [CoO6] octahedra and the K+ diffusion pathway is optimized as well. The proposed P3-K0.45Mn0.9Co0.05Mo0.05O2 cathode material shows an enhanced cycling stability and rate performance. It demonstrates a high capacity of 80.2mAhg-1 at 100mAhg-1 and 77.3mAhg-1 at 500mAhg-1. Furthermore, it showcases a 2000 cycles stability with a 59.6% capacity retention. This work presents a promising solution to the challenges faced by manganese-based layered oxide cathodes and offers a deep mechanism understanding and improved electrochemical performance.

Antimony Doping Enabled Radially Aligned Microstructure in LiNi0.91Co0.06Al0.03O2 Cathode for High‐Voltage and Low‐Temperature Lithium Battery

AbstractNi‐rich layered oxide cathode material with Ni contents greater than 90% is considered as a highly promising candidate for lithium‐ion batteries (LIBs) owing to its remarkable specific capacity and cost‐efficiency. However, severe capacity degradation caused by the structural collapse and interfacial instability with electrolyte under high voltage greatly hinders the practical application. Here, an antimony (Sb)‐doped LiNi0.91Co0.06Al0.03O2 (Sb‐NCA91) cathode is proposed, where the Sb doping modifies the morphology of primary particles and enables the radially aligned microstructure. This unique microstructure can disperse the anisotropic mechanical stress caused by the H2‐H3 phase transformation, and mitigate the shrinkage and expansion of the primary particles during high‐voltage and low‐temperature cycling, thus inhibiting the formation of microcracks and structural deterioration. Meanwhile, the closely arranged radial spokes allow fast ion transport in the secondary particles and effectively improve the rate performance and low‐temperature performance of the cathodes. As a result, the Sb modified cathode demonstrates superior capacity retention of ≈84% at 1 C after 200 cycles in 2.7–4.5 V at 25 °C, while the pristine NCA91 cathode only retains ≈79%. Additionally, the capacity retention at −20 °C is significantly increased from ≈61% (NCA91) to ≈88% (Sb‐NCA91) after 100 cycles.

Multiscale Interfacial Regulation of Zn‐V2O5 Pouch Cell via Ultrathin Molecular‐Engineered Separator

AbstractRechargeable aqueous zinc batteries (RAZBs) suffer from the structural degradation of the layered oxide cathode, parasitic side reaction on the Zn foil as well as often‐overlooked self‐discharge phenomenon at the elevated temperatures. Herein, this study presents a thin‐layer (9 µm) molecular‐engineered separator strategy to achieve the concurrent shelf life, cycling endurance, as well as the practical energy density for the RAZBs prototype. On the face‐to‐cathode side, the biphthalic anhydride is anchored onto the polyethylene separator substrate (PE) via a robotic arm‐controlled spray‐coating method, inhibiting the spontaneous vanadium dissolution and shuttle at both the dynamic cycling or static high‐temperature storage; meanwhile the 3,3′‐diamino‐4,4′‐dihydroxydiphenyl sulfone molecular tailoring on the face‐to‐anode side provides ion‐sieving capability to repel detrimental SO42−, yet guiding uniform Zn2+ influx and preferential deposits accumulation along the (002) crystallographic orientation even at the extreme deposition scenario (20 mA cm−2, 20 mAh cm−2). Upon the layer‐stacked assembly of the V2O5 cathode (2.0 mAh cm−2), molecular‐engineered separator as well as the Zn foil (20 µm), the 0.78 Ah pouch‐format prototype exhibits the superior volumetric/gravimetric energy densities of 133.3 Wh L−1/71.4 Wh kg−1 and extreme power output (444.3 W L−1/238.0 W kg−1).

Research on Sodium Storage Performance of Cu and Mg Doped P2 Type Layered Oxide Cathode Materials

The P2-type Ni–Mn-based oxide cathode materials have drawbacks such as the Jahn-Teller effect and crystal phase transition under high pressure. In this study, Cu and Mg modifications were introduced to inhibit the P2–O2 phase transition and increase the lattice spacing, thereby reducing the resistance of sodium ion de-embedding and intercalation to improve the overall electrochemical performance of the battery. A series of P2-type Na0.67Ni0.33−xMn0.67CuxO2 and Na0.67Ni0.33−xMn0.67MgxO2 cathode materials were synthesized through solid-state reaction. Cu substitution significantly alters the structural stability and electrochemical properties. In the voltage range from 1.5 V to 4.2 V and at 0.1 C, the initial discharge specific capacity of Na0.67Ni0.18Mn0.67Cu0.15O2 was 167 mAh·g−1, with 86 mAh·g−1 remaining after 100 cycles at 1 C. Additionally, a high discharge specific capacity of 207 mAh·g−1 was achieved with 0.075 Mg doping, suggesting that part of O2− participated in the internal electrochemical reaction. Furthermore, the rate performance of Na0.67Ni0.28Mn0.67Mg0.05O2 was found to be the best. This phenomenon was attributed to the inactive Mg2+ retaining more Na+ in the interlayer, inhibiting crystal structure transformation and Jahn-Teller distortion. The larger radius of Mg2+ increased the layer spacing, widened the Na+ de-embedding channels, and increased the diffusion coefficient.