Understanding Performance Degradation in Cation-Disordered Rock-Salt Oxide Cathodes
Understanding Performance Degradation in Cation-Disordered Rock-Salt Oxide Cathodes
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DOI：
10.1002/aenm.201901255
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发表时间：
2019-08-01
影响因子：
27.8
通讯作者：
Chen, Guoying
中科院分区：
文献类型：
--
作者：
Chen, Dongchang;Kan, Wang Hay;Chen, Guoying
过渡金属（TM）阳离子和氧阴离子的集体氧化还原活性已被证明增加富锂层状和阳离子无序岩盐阴极中的电荷储存容量。涉及阴离子氧化还原的重复循环已知会引发层状富锂和富锰（LMR）氧化物中的TM迁移和相变，然而，对最近发现的富锂岩盐阴极的详细机理理解在很大程度上缺失。本研究系统地研究了氧氧化还原对Li1.3Nb0.3Mn0.4O2正极的影响，并表明性能恶化与氧氧化还原的程度直接相关。结果表明，电压衰减和滞后开始后，只有在高电压下，开始阴离子氧化还原，这与在更高的电位或延长循环的氧的更深的氧化逐渐增长。与所报道的层状LMR氧化物相反，观察到广泛的TM还原，但在循环氧化物中未检测到相变。因此，提出了致密化/降解机制，阐明了TM的广泛化学还原和阳离子无序岩盐中Li渗滤网络的质量降低的独特组合如何导致这些具有3D Li迁移途径的较新阴极的性能降低。设计策略，以实现平衡的能力和稳定性进行了讨论。
The collective redox activities of transition-metal (TM) cations and oxygen anions have been shown to increase charge storage capacity in both Li-rich layered and cation-disordered rock-salt cathodes. Repeated cycling involving anionic redox is known to trigger TM migration and phase transformation in layered Li- and Mn-rich (LMR) oxides, however, detailed mechanistic understanding on the recently discovered Li-rich rock-salt cathodes is largely missing. The present study systematically investigates the effect of oxygen redox on a Li1.3Nb0.3Mn0.4O2 cathode and demonstrates that performance deterioration is directly correlated to the extent of oxygen redox. It is shown that voltage fade and hysteresis begin only after initiating anionic redox at high voltages, which grows progressively with either deeper oxidation of oxygen at higher potential or extended cycling. In contrast to what is reported on layered LMR oxides, extensive TM reduction is observed but phase transition is not detected in the cycled oxide. A densification/degradation mechanism is proposed accordingly which elucidates how a unique combination of extensive chemical reduction of TM and reduced quality of the Li percolation network in cation-disordered rock-salts can lead to performance degradation in these newer cathodes with 3D Li migration pathways. Design strategies to achieve balanced capacity and stability are also discussed.