Zhang Liao, Yang Zhenzhong, Hu Fangxu, Feng Xiang, Li De, Chen Yong
State Key Laboratory on Marine Resource Utilization in South China Sea, Hainan Provincial Key Laboratory of Research on Utilization of Si-Zr-Ti Resources, School of Materials Science and Engineering, Hainan University, Haikou 570228, China.
Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China.
ACS Appl Mater Interfaces. 2020 Apr 15;12(15):17415-17423. doi: 10.1021/acsami.9b22536. Epub 2020 Apr 1.
Among many electrode materials, only a small amount of two-phase electrode materials were found to possess the memory effect, for instance, olivine LiFePO, anatase TiO, and Al-doped LiTiO, in which the underlying mechanism is still not clear beyond the electrochemical kinetics. Here, we further studied the memory effect of Al-doped LiTiO to reveal the microstructure and the microprocess. By controlling the potentiostatic step after discharging, we found that the memory effect of Al-doped LiTiO was closely related to the discharged lattice parameters and the subsequent charge capacity. According to the ex situ magic-angle spinning (MAS) NMR results, we first revealed that the Al ions would move from 8a to 16c sites, when the electrode was discharged and potentiostatic at a low potential, and then move back through charging in the spinel structure of Al-doped LiTiO, which would contribute to the capacity as the Li ions. Therefore, the reversible Al-ion switching between 8a and 16c sites should be the origin of memory effect in Al-doped LiTiO, which would inspire us to explore the memory effect of other electrode materials in Li-ion batteries (LIBs), as well as optimize the performance of electrode materials by controlling the ionic switching.
在众多电极材料中，仅发现少量的两相电极材料具有记忆效应，例如橄榄石型LiFePO₄、锐钛矿型TiO₂以及Al掺杂的LiTiO₂，其潜在机理在电化学动力学之外仍不明确。在此，我们进一步研究了Al掺杂LiTiO₂的记忆效应，以揭示其微观结构和微观过程。通过控制放电后的恒电位步骤，我们发现Al掺杂LiTiO₂的记忆效应与放电后的晶格参数以及随后的充电容量密切相关。根据非原位魔角旋转（MAS）核磁共振结果，我们首次揭示，当电极在低电位下放电并恒电位时，Al离子会从8a位移动到16c位，然后在Al掺杂LiTiO₂的尖晶石结构中通过充电再移回，这将作为Li离子对容量有贡献。因此，8a和16c位之间可逆的Al离子切换应该是Al掺杂LiTiO₂中记忆效应的起源，这将启发我们探索锂离子电池（LIBs）中其他电极材料的记忆效应，以及通过控制离子切换来优化电极材料的性能。
