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HighlightsThe flower-like δ-MnO2 nanostructures with controlled oxygen vacancies as an extraordinary ZIBs cathode are innovatively developed.The cathode can present large capacity and high-rate zinc-ion storage.DFT analysis substantially unveils the effects of various vacancy concentrations on their electrochemical performances.In recent years, manganese-based oxides as an advanced class of cathode materials for zinc-ion batteries (ZIBs) have attracted a great deal of attentions from numerous researchers. However, their slow reaction kinetics, limited active sites and poor electrical conductivity inevitably give rise to the severe performance degradation. To solve these problems, herein, we introduce abundant oxygen vacancies into the flower-like δ-MnO2 nanostructure and effectively modulate the vacancy defects to reach the optimal level (δ-MnO2−x−2.0). The smart design intrinsically tunes the electronic structure, guarantees ion chemisorption–desorption equilibrium and increases the electroactive sites, which not only effectively accelerates charge transfer rate during reaction processes, but also endows more redox reactions, as verified by first-principle calculations. These merits can help the fabricated δ-MnO2−x−2.0 cathode to present a large specific capacity of 551.8 mAh g−1 at 0.5 A g−1, high-rate capability of 262.2 mAh g−1 at 10 A g−1 and an excellent cycle lifespan (83% of capacity retention after 1500 cycles), which is far superior to those of the other metal compound cathodes. In addition, the charge/discharge mechanism of the δ-MnO2−x−2.0 cathode has also been elaborated through ex situ techniques. This work opens up a new pathway for constructing the next-generation high-performance ZIBs cathode materials.

The ever‐growing demand for high‐energy lithium‐ion batteries in portable electronics and electric vehicles has triggered intensive research efforts over the past decade. An efficient strategy to boost the energy and power density of lithium‐ion batteries is to increase the Ni content in the cathode materials. However, a higher Ni content in the cathode materials gives rise to safety issues. Herein, thermal expansion and oxygen vacancies are proposed as new critical factors that affect the thermal stability of charged Ni‐rich cathode materials based on a systematic synchrotron‐based X‐ray study of Li0.33Ni0.5+xCo0.2Mn0.3‐xO2 (x = 0, 0.1, 0.2) cathode materials during a heating process. Charged cathode materials with higher Ni contents show larger thermal expansion, which accelerates transition metal migration to the Li layers. Oxygen vacancies are formed and accumulate mainly around Ni ions until the layered‐to‐spinel phase transition begins. The oxygen vacancies also facilitate transition metal migration to the Li layers. Thermal expansion and the presence of oxygen vacancies decrease the energy barrier for cation migration and facilitate the phase transitions in charged cathode materials during the heating process. These results provide valuable guidance for developing new cathode materials with improved safety characteristics. Close relationship between Ni content and inherent thermal instability of Ni‐rich cathode material has been widely investigated. However, the underlying cause of thermal instability of Ni‐rich cathode material involving Ni has not been fully studied. The thermal expansion and oxygen vacancy are newly proposed as critical factors to affect the inherent thermal instability of Ni‐rich cathode materials.

The FeF 3 ·0.33H 2 O cathode material can exhibit a high capacity and high energy density through transfer of multiple electrons in the conversion reaction and has attracted great attention from researchers. However, the low conductivity of FeF 3 ·0.33H 2 O greatly restricts its application. Generally, carbon nanotubes (CNTs) and graphene can be used as conductive networks to improve the conductivities of active materials. In this work, the FeF 3 ·0.33H 2 O cathode material was synthesized via a liquid-phase method, and the FeF 3 ·0.33H 2 O/CNT + graphene nanocomposite was successfully fabricated by introduction of CNTs and graphene conductive networks. The electrochemical results illustrate that FeF 3 ·0.33H 2 O/CNT + graphene nanocomposite delivers a high discharge capacity of 234.2 mAh g −1 in the voltage range of 1.8–4.5 V (vs. Li + /Li) at 0.1 C rate, exhibits a prominent cycling performance (193.1 mAh g −1 after 50 cycles at 0.2 C rate), and rate capability (140.4 mAh g −1 at 5 C rate). Therefore, the electronic conductivity and electrochemical performance of the FeF 3 ·0.33H 2 O cathode material modified with CNTs and graphene composite conductive network can be effectively improved.

Cobalt‐free LiNi0.5Mn1.5O4 (LNMO) has recently emerged as a highly promising cathode material owing to its benefits of a high operating voltage platform (≈4.7 V vs Li), high theoretical energy density (≈650 Wh kg−1), eco‐friendliness, and resource abundance. However, it has also demonstrated low cycle and poor rate performances. Researchers have hitherto identified multiple LNMO failure and degradation mechanisms, including the Jahn‐Teller effect, Transition Metal (TM) dissolution, electrolyte decomposition, and Oxygen Vacancies (OVs). The Jahn‐Teller effect causes structural material degradation, while TM dissolution could lead to the loss of reactive species and interfacial side reactions. On the other hand, OVs and electrolyte decomposition accelerate capacity decay. Notably, deeply understanding LNMO structural failure mechanisms and the targeting of corresponding modifications presents a vital avenue for modulating its surface‐interface structure and improving its electrochemical performance. Although researchers have extensively investigated the failure mechanisms of LNMO to elucidate its modification strategies, a comprehensive and detailed summary of the latest research advancements has yet to be provided. In this work, the research background, encompassing the advantages and disadvantages of LNMO cathode materials, is first introduced. The crystal structure and discharge mechanisms, among other fundamental principles of LNMO, are subsequently analyzed. Finally, recent research findings on the aforementioned failure mechanisms in high‐voltage spinel LNMO are synthesized. Subsequently, a critical assessment of recent advancements in modification strategies targeting the failure mechanisms of LNMO is performed, encompassing the tools employed (e.g., doping modification, surface coating, morphology and size management, and surface orientation management) as well as their synergistic effects. Finally, potential future research directions to guide the rational design of high‐performance LNMO, particularly manganese‐based spinel cathode material, are proposed. This review provides an overview of the development history, working mechanisms, and scientific challenges of LiNi0.5Mn1.5O4 cathode materials for Lithium‐ion battery and discusses the strategies to improve the electrochemical performance of LiNi0.5Mn1.5O4.

High‐nickel ternary cathode (HNCM) materials are regarded as the primary choice for lithium‐ion batteries (LIBs) due to their high energy density. However, their development is limited by lithium–nickel mixing, microcrack generation, and surface side reactions. Herein, a combined roll‐to‐roll and vacuum vapor deposition process is used to prepare LiNi0.9Co0.05Mn0.05O2 (NCM9055) cathode material with a dense, ultrathin, and robust lithium fluoride (LiF) protective layer. Compared with traditional methods, this approach allows precise control over the thickness and rate of the deposited LiF layer, producing a uniform and robust protective layer that enhances surface stability. This approach not only effectively reduces direct contact between the electrolyte and the electrode surface, mitigating corrosion and side reactions, but also strengthens the structural integrity of the cathode, thereby significantly improving cycling stability. The NCM9055 with a 10 nm LiF layer exhibits enhanced electrochemical performance, especially at cut‐off voltages of 4.3 and 4.5 V, and also excellent cycling performance at 1 C. Additionally, the introduction of the LiF layer improves the thermal stability of NCM9055, further enhancing the safety of high‐nickel batteries. This study not only demonstrates the combination of roll‐to‐roll processing and vacuum vapor deposition as a fast and effective modification technique but also highlights the advantages of vacuum vapor deposition in forming a homogeneous and robust LiF layer, which is essential for rapid production and for improving the safety and energy density of HNCM materials in advanced LIBs. Employs roll‐to‐roll compatible vacuum vapor deposition to uniformly coat NCM9055 cathodes with LiF, enhancing electrochemical performance and safety in high‐nickel ternary lithium‐ion batteries. This method shields the cathode from electrolyte erosion, reduces interface erosion, and improves cycling stability, leading to enhanced performance at high cutoff voltage and under high current densities.

Copper (Cu) doping is recognized as an effective strategy to enhance the electrochemical properties of LiNi1−x−yCoxMnyO2 (NCM) cathode materials. However, the influence of Cu2+ doping on particle size and grain boundary fusion remains insufficiently explored. A simple microwave-assisted solution combustion synthesis method was used to introduce Cu2+ into LiNi0.5Co0.2Mn0.3O2 (NCM523), aiming to regulate particle size and grain boundary fusion. The results demonstrate that increasing the Cu2+ doping content promotes particle growth, while an appropriate doping level reduces the degree of grain boundary fusion and cation mixing. Benefiting from these structural improvements, the optimized LiNi0.5Co0.2Mn0.29Cu0.01O2 (Cu–1) cathode exhibits significantly enhanced electrochemical performance, delivering a discharge capacity of 128.6 mAh g−1 after 100 cycles at 0.2 C, which is 32 mAh g−1 higher than value of the undoped sample (96.6 mAh g−1). These findings underscore that tailored Cu2+ doping can effectively optimize the microstructure of NCM523, leading to superior cycling stability, and provide new insights into the design of high-performance NCM cathodes.

Transition metal fluorides (TMFs) cathode materials have shown extraordinary promises for electrochemical energy storage, but the understanding of their electrochemical reaction mechanisms is still a matter of debate due to the complicated and continuous changing in the battery internal environment. Here, we design a novel iron fluoride (FeF2) aggregate assembled with cylindrical nanoparticles as cathode material to build FeF2 lithium‐ion batteries (LIBs) and employ advanced in situ magnetometry to detect their intrinsic electronic structure during cycling in real time. The results show that FeF2 cannot be involved in complete conversion reactions when the FeF2 LIBs operate between the conventional voltage range of 1.0–4.0 V, and that the corresponding conversion ratio of FeF2 can be further estimated. Importantly, we first demonstrate that the spin‐polarized surface capacitance exists in the FeF2 cathode by monitoring the magnetic responses over various voltage ranges. The research presents an original and insightful method to examine the conversion mechanism of TMFs and significantly provides an important reference for the future artificial design of energy systems based on spin‐polarized surface capacitance. In situ magnetometry was first employed to investigate the charge storage mechanism of FeF2 cathode, which clearly reveals that spin‐polarized surface capacitance and incomplete conversion occur when the battery operates between 1.0 and 4.0 V and the corresponding conversion ratio of FeF2 can be further estimated.

Full‐manganese (Mn) Li‐rich materials have gained attention owing to the limited availability of cobalt‐ or nickel‐based cathodes commonly used in batteries, which greatly restricts their potential for large‐scale application. However, their practical implementation is hindered by the rapid voltage/capacity decay during cycling and the long‐standing problem of redox kinetics due to their poor ionic conductivity based on the ordered honeycomb structure. In this study, the kinetic and thermodynamic properties of intralayer disordered and ordered Li‐rich full‐Mn‐based cathode materials were compared, demonstrating that the disordered R 3 ¯ m Li0.6[Li0.2Mn0.8]O2 (D‐LMO) delivers a significant advantage of rate capability over the ordered C 2 / m Li0.6[Li0.2Mn0.8]O2 (O‐LMO). Meanwhile, the D‐LMO keeps superior capacity retention of up to 99% after 50 cycles under 25 mA g−1. In comparsion, the capacity retention of the O‐LMO drops to just 70%, and its average discharge voltage is 0.2 V lower than that of the D‐LMO. Herein, we conducted systematic density functional theory (DFT) simulations, focusing on the electronic structure modulation governing the voltage platform between the ordered and disordered phases. The ab initio molecular dynamics (AIMD) results indicated that the energy of the intralayer disordered structure fluctuates around the equilibrium position without any abrupt drops, demonstrating excellent stability. This study enhances the understanding of intralayer disordered full‐Mn Li‐rich material and provides insights into the design of low‐cost, high‐performance cathode materials for Li‐ion batteries. The researchers successfully synthesized ordered/disordered Li0.6[Li0.2Mn0.8]O2 material. Based on the results of ab initio molecular dynamics (AIMD) simulations, the structure exhibits stability as evidenced by energy fluctuations around the equilibrium position without any abrupt drops. The disorder Li0.6[Li0.2Mn0.8]O2 delivers the lithiated structure containing disordered Li and Mn, which has a higher predicted voltage and superior rate capability.

Lithium manganese oxide (LiMn2O4) is an effective cathode material for high-capacity lithium-ion (Li-ion) batteries. Therefore, to optimize battery efficiency, it is essential to understand how sputtering deposition conditions affect the quality and performance of LiMn2O4. This research examines how argon deposition pressure affects the stoichiometric characteristics and electrochemical performance of LiMn2O4. The study finds that changing argon deposition pressures, from a low of 5 mTorr to a high of 30 mTorr, results in the formation of different coating stoichiometries. At low argon deposition pressures, stoichiometric LiMn2O4 cathode coatings formed, exhibiting the highest discharge capacity of 115 mAh/g. Conversely, at high argon deposition pressures, non-stoichiometric LiMn2O4 with lithium deficiency was produced. These coatings exhibited diminished electrochemical behavior, achieving a discharge capacity of only 70 mAh/g at 5 mTorr. The lack of lithium resulted in a significant reduction in electrochemical performance, indicated by a high surface charge transfer resistance (R2 = 48,529 Ω), which led to a low discharge capacity of 40 mAh/g.

Research on the regeneration of cathode materials of spent lithium-ion batteries for resource reclamation and environmental protection is attracting more and more attention today. However, the majority of studies on recycling lithium-ion batteries (LIBs) placed the emphasis only on recovering target metals, such as Co, Ni, and Li, from the cathode materials, or how to recycle spent LIBs by conventional means. Effective reclamation strategies (e.g., pyrometallurgical technologies, hydrometallurgy techniques, and biological strategies) have been used in research on recycling used LIBs. Nevertheless, none of the existing reviews of regenerating cathode materials from waste LIBs elucidated the strategies to regenerate lithium nickel manganese cobalt oxide (NCM or LiNixCoyMnzO2) cathode materials directly from spent LIBs containing other than NCM cathodes but, at the same time, frequently used commercial cathode materials such as LiCoO2 (LCO), LiFePO4 (LFP), LiMn2O4 (LMO), etc. or from spent mixed cathode materials. This review showcases the strategies and techniques for regenerating LiNixCoyMnzO2 cathode active materials directly from some commonly used and different types of mixed-cathode materials. The article summarizes the various technologies and processes of regenerating LiNixCoyMnzO2 cathode active materials directly from some individual cathode materials and the mixed-cathode scraps of spent LIBs without their preliminary separation. In the meantime, the economic benefits and diverse synthetic routes of regenerating LiNixCoyMnzO2 cathode materials reported in the literature are analyzed systematically. This minireview can lay guidance and a theoretical basis for restoring LiNixCoyMnzO2 cathode materials.