Charge Compensation Mechanism of Lithium-Excess Metal Oxides with Different Covalent and Ionic Characters Revealed by Operando Soft and Hard X-ray Absorption Spectroscopy
Charge Compensation Mechanism of Lithium-Excess Metal Oxides with Different Covalent and Ionic Characters Revealed by Operando Soft and Hard X-ray Absorption Spectroscopy
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DOI：
10.1021/acs.chemmater.9b02838
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发表时间：
2020-01-14
影响因子：
8.6
通讯作者：
Uchimoto, Yoshiharu
中科院分区：
文献类型：
--
作者：
Yamamoto, Kentaro;Zhou, Yingying;Uchimoto, Yoshiharu
当前锂离子电池正极材料的充放电容量受到充放电过程中过渡金属氧化还原的电荷补偿的限制。最近，已经提出使用氧化物离子氧化还原进行电荷补偿以实现比过渡金属氧化还原所观察到的更高的充电/放电容量。已经提出了可逆氧化物离子氧化还原的不同稳定机制。为了阐明机制，需要分析氧周围的电子和局部结构。由于发生氧化物离子氧化还原的高电压区域，通常包括几个反应，例如氧气析出和/或电解质氧化。因此，需要操作性测量来直接证明这一概念并概括对氧化物离子氧化还原的理解。本研究采用操作软/硬X射线吸收光谱结合X射线衍射光谱的四个锂过量电极材料具有不同的化学键性质。实验数据与在线分析所产生的充电气体揭示了两个极端的情况下：显着增强的共价或离子字符的金属氧化学键，这是必要的条件，以稳定氧化物离子的氧化。这一发现为设计基于阴离子氧化还原的高能量密度阴极材料提供了令人兴奋的可能性。
The charge/discharge capacity of current lithium-ion battery cathode materials is limited by the charge compensation of transition-metal redox during the charge/discharge processes. Recently, the use of oxide ion redox for charge compensation has been proposed to realize a higher charge/discharge capacity than that observed for transition metal redox. Different stabilization mechanisms of the reversible oxide ion redox have been proposed. To clarify the mechanism, analysis of the electronic and local structures around oxygen is required. Because of the high-voltage region in which the oxide ion redox occurs, several reactions such as oxygen gas evolution and/or electrolyte oxidation are often included. Thus, operando measurements are required to directly prove this concept and generalize the understanding of the oxide ion redox. This study employs operando soft/hard X-ray absorption spectroscopy combined with X-ray diffraction spectroscopy for four lithium-excess electrode materials with different chemical bond natures. The experimental data together with online analysis of the generated on-charge gas reveal two extreme cases: significantly enhanced covalent or ionic characters in the metal oxygen chemical bonds, which are necessary conditions to stabilize the oxidation of the oxide ions. This finding provides new insights with exciting possibilities for designing high energy density cathode materials based on anion redox.