Huang Jiangnan, Xue Zhichen, Lee Sang-Jun, Chen Hongyi, Ji Xiaobo, Du Ke
College of Chemistry and Chemical Engineering, Central South University, Changsha, 410083, P. R. China.
School of Metallurgy and Environment, Central South University, Changsha, 410083, P. R. China.
J Am Chem Soc. 2025 Jul 2;147(26):22444-22452. doi: 10.1021/jacs.5c00969. Epub 2025 Jun 17.
The use of anionic redox has become a new paradigm for improving the energy density of rechargeable batteries, which is essential for improving the market competitiveness of sodium-ion batteries. However, issues such as voltage attenuation and cycling stability degradation persist in layered oxide anion redox cathode materials. In this study, we systematically investigate the classic Na-ion cathode material NaLiMnO, and the primary causes of voltage decay are identified as the activation of cations and the reduction in anion redox activity. In addition, the activation of cations is closely associated with anion reactions. Through the application of sophisticated multiscale synchrotron absorption spectroscopy and imaging techniques, we have identified a pronounced pattern of spatially dependent degradation in the evolution of redox couples, which is more evident from the material's surface to its core. With this understanding, we introduced a surface fluorination approach that modulates the local chemical coordination environment. This strategy increases the formation energy of surface oxygen vacancies and locks transition metals oxide state. Consequently, it enables more reversible anionic redox reactions, which block the spatial progression of degradation and mitigates voltage decay.
使用阴离子氧化还原已成为提高可充电电池能量密度的新范例，这对于提高钠离子电池的市场竞争力至关重要。然而，层状氧化物阴离子氧化还原正极材料中仍存在电压衰减和循环稳定性下降等问题。在本研究中，我们系统地研究了经典的钠离子正极材料NaLiMnO，并确定电压衰减的主要原因是阳离子的活化和阴离子氧化还原活性的降低。此外，阳离子的活化与阴离子反应密切相关。通过应用先进的多尺度同步辐射吸收光谱和成像技术，我们在氧化还原对的演变中确定了一种明显的空间依赖性降解模式，从材料表面到核心更为明显。基于此认识，我们引入了一种表面氟化方法来调节局部化学配位环境。该策略提高了表面氧空位的形成能并锁定了过渡金属的氧化态。因此，它能够实现更可逆的阴离子氧化还原反应，阻止降解的空间进展并减轻电压衰减。
