Voltage decay and capacity fading are the main challenges for the commercialization of Li‐rich Mn‐based layered oxides (LLOs). Now, a three‐in‐one surface treatment is designed via the pyrolysis of urea to improve the voltage and capacity stability of Li1.2Mn0.6Ni0.2O2 (LMNO), by which oxygen vacancies, spinel phase integration, and N‐doped carbon nanolayers are synchronously built on the surface of LMNO microspheres. Oxygen vacancies and spinel phase integration suppress irreversible O2 release and help lithium ion diffusion, while N‐doped carbon nanolayer mitigates the corrosion of electrolyte with excellent conductivity. The electrochemical performance of LMNO after the treatment improves significantly; the capacity retention rate after 500 cycles at 1 C is still as high as 89.9 % with a very small voltage fading rate of 1.09 mV cycle−1. This three‐in‐one surface treatment strategy can suppress the voltage decay and capacity fading of LLOs.

The anionic redox reaction (ARR) has attracted extensive attention due to its potential to enhance the reversible capacity of cathode materials in Li/Na‐ion batteries (LIBs/SIBs). However, the understanding of its activation mechanism is still limited by the insufficient mastering of the underlying thermodynamics and kinetics. Herein, a series of Mg/Li/Zn‐substituted NaxMnO2 and LixMnO2 cathode materials are designed to investigate their ARR behaviors. It is found that the ARR can be activated in only Li‐substituted LixMnO2 and not for Mg‐ and Zn‐substituted ones, while all Mg/Li/Zn‐substituted NaxMnO2 cathode materials exhibit ARR activities. Combining theoretical calculations with experimental results, such a huge difference between Li and Na cathodes is closely related to the migration of substitution ions from the transition metal layer to the alkali metal layer in a kinetic aspect, which generates unique Li(Na)–O–□TM and/or □Li/Na–O–□TM configurations and reducing reaction activation energy to trigger the ARR. Based on these findings, an ion‐migration mechanism is proposed to explain the different ARR behaviors between the NaxMnO2 and LixMnO2, which can not only reveal the origin of ARR in the kinetic aspect, but also provide a new insight for the development of high‐capacity metal oxide cathode materials for LIBs/SIBs.

High-energy-density lithium-rich layered oxides (LLOs) hold the greatest promise to address the range anxiety of electric vehicles. Their application, however, has been prevented by fast voltage decay and capacity fading for years, which mainly originate from irreversible transition-metal migration and undesirable cathode-electrolyte interfacial reactions. Herein, a Ti-based surface integrated layer and bulk doping, which greatly improve the voltage and capacity stability of LLOs is synchronously constructed. More importantly, STEM and Raman results demonstrate that continuous and uniform surface Ti-based integrated layer is a spinel-like rocksalt structure with Fd-3m space group, which is built through by several the replacement of Li ions in surface several atomic layers by Ti ions. After 500 cycles, Ti-150 sample delivers a capacity retention of 85%, and its voltage decay rate from the 30th to the 500th cycle is only ≈0.72 mV/cycle. Spectral results and DFT calculations suggest that bulk Ti-doping mitigates the migration of Mn and Ni ions in the bulk, while Ti-based integrated layer significantly suppresses surface structure evolution and interfacial reactions by impeding the generation of surface Li vacancies during Li extraction as well as preventing direct contact between electrolyte and active materials.

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Li-rich layered oxides (LLOs) suffer from severe voltage decay and capacity fading which have hindered their practical application for years. Herein, Co-free LLO microspheres with Ni/Mn and Al dual concentration-gradients are constructed to mitigate the above obstacles. One concentration-gradient is an electrochemical active gradient (Ni/Mn), and the other is an electrochemical inert gradient (Al). XPS and soft and hard XAS after different cycles prove that the combination of dual concentration-gradients effectively mitigates interfacial reactions, structural evolution, and the generation of lower-valence Mn3+/Mn4+ or Mn2+/Mn3+ redox couples during cycling. As a result, the voltage fading rate of LLO cathode with dual concentration-gradients after 100 cycles is as small as 0.97 mV/cycle at 100 mA g–1. Furthermore, its capacity retention ratio is also as large as 84.1% after 400 cycles at 300 mA g–1. The combination of dual concentration-gradients in this work provides a way to develop advanced LLO cathodes for practical application in the near future.