Slow-Released Cationic Redox Activity Promoted Stable Anionic Redox and Suppressed Jahn–Teller Distortion in Layered Sodium Manganese Oxides
Ao Zeng, Jianyue Jiao, Hong Zhang, Enyue Zhao, Tao He, Zhenbang Xu, Xiaoling Xiao
Abstract
Manganese-based layered oxides are considered promising cathodes for sodium ion batteries due to their high capacity and low-cost manganese and sodium resources. Triggering the anionic redox reaction (ARR) can exceed the capacity limitation determined by conventional cationic redox. However, the unstable ARR charge compensation and Jahn–Teller distortion of Mn 3+ ions readily result in structural degradation and rapid capacity fade. Here, we report a P2-type Na 0.8 Li 0.2 Mn 0.7 Cu 0.1 O 2 cathode that shows a capacity retention of 84.5% at 200 mA/g after 200 cycles. Combining in situ X-ray diffraction and multi other ex situ characterizations, we reveal that the enhanced cycling stability is ascribed to a slow release of cationic redox activity which can well suppress the Jahn–Teller distortion and favor the ARR reversibility. Furthermore, density-functional theory calculations demonstrate that the inhibited interlayer migration and reduced band gap facilitate the stability and kinetic behavior of ARR. These findings provide a perspective for designing high-energy-density cathode materials with ARR activity.