Electrolytes toward High‐Voltage Na3V2(PO4)2F3 Positive Electrode Durable against Temperature Variation
Electrolytes toward High‐Voltage Na3V2(PO4)2F3 Positive Electrode Durable against Temperature Variation
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DOI：
10.1002/aenm.202001880
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发表时间：
2020-07
影响因子：
27.8
通讯作者：
Jinkwang Hwang;K. Matsumoto;R. Hagiwara
中科院分区：
文献类型：
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作者：
Jinkwang Hwang;K. Matsumoto;R. Hagiwara
构建大型钠二次电池必须考虑高功率和能量密度、长循环性以及宽温度耐受性（季节和日常工作温差）。在这方面，Na3V2(PO4)2F3（NVPF）由于其高能量密度而成为高性能正极材料的研究热点。然而，NVPF的高工作电压导致循环过程中电解液不断分解，导致容量显着衰减和库仑效率低。在这项研究中，研究了 NVPF 电极在有或没有添加剂和离子液体的有机溶剂电解质中在高电压范围和宽温度范围（-20 °C 至 90 °C）下的电化学性能。结果表明，即使有添加剂，有机电解质的性能仍然不足，而离子液体电解质在-20℃至90℃的温度范围内与NVPF电极表现出较高的电化学稳定性和循环性能，实现了超过500次循环的稳定循环。详细的电化学分析结合 X 射线光电子和能量色散 X 射线光谱表明，电极周围坚固的阴极电解质中间相层可保护其在高电压和高温下免受容量衰减，从而实现高库仑效率。
High power and energy density, long cyclability, and tolerance for wide temperature (seasonal and daily operational temperature differences) must be considered to construct large‐scale sodium secondary batteries. In this regard, Na3V2(PO4)2F3 (NVPF) has become a subject of interest as a high‐performance positive electrode material owing to its high energy density. However, the high operating voltage of NVPF causes continuous decomposition of electrolytes during cycles, resulting in significant capacity fading and low Coulombic efficiency. In this study, the electrochemical performance of the NVPF electrode in organic solvent electrolytes with and without additives and an ionic liquid is investigated at high voltage regimes over a wide temperature range (−20 °C to 90 °C). The results reveal that the performance of organic electrolytes is still insufficient even with additives, and the ionic liquid electrolyte demonstrates high electrochemical stability and cyclability with NVPF electrodes over a temperature range from −20 °C to 90 °C, achieving stable cycling over 500 cycles. The detailed electrochemical analysis combined with X‐ray photoelectron and energy dispersive X‐ray spectroscopy indicates that a sturdy cathode electrolyte interphase layer around the electrode protects it from capacity fading at high voltage and elevated temperature, resulting in high Coulombic efficiency.