Liu Xu, Zarrabeitia Maider, Qin Bingsheng, Elia Giuseppe Antonio, Passerini Stefano
Helmholtz Institute Ulm (HIU) Electrochemical Energy Storage, Helmholtzstrasse 11, 89081 Ulm, Germany.
Karlsruhe Institute of Technology (KIT), PO Box 3640, D-76021 Karlsruhe, Germany.
ACS Appl Mater Interfaces. 2020 Dec 9;12(49):54782-54790. doi: 10.1021/acsami.0c16727. Epub 2020 Nov 20.
VO, one of the earliest intercalation-type cathode materials investigated as a Li host, is characterized by an extremely high theoretical capacity (441 mAh g). However, the fast capacity fading upon cycling in conventional carbonate-based electrolytes is an unresolved issue. Herein, we show that using a LiTFSI/tetraglyme (1:1 in mole ratio) electrolyte yields a highly enhanced cycling ability of VO (from 20% capacity retention to 80% after 100 cycles at 50 mA g within 1.5-4.0 V vs Li/Li). The improved performance mostly originates from the VO electrode itself, since refreshing the electrolyte and the lithium electrode of the cycled cells does not help in restoring the VO electrode capacity. Electrochemical impedance spectroscopy (EIS), post-mortem scanning electron microscopy (SEM), energy-dispersive X-ray (EDX) spectroscopy, and X-ray photoelectron spectroscopy (XPS) have been employed to investigate the origin of the improved electrochemical behavior. The results demonstrate that the enhanced cyclability is a consequence of a thinner but more stable cathode-electrolyte interphase (CEI) layer formed in LiTFSI/tetraglyme with respect to the one occurring in 1 M LiPF in EC/DMC (1:1 in weight ratio, LP30). These results show that the cyclability of VO can be effectively improved by simple electrolyte engineering. At the same time, the uncovered mechanism further reveals the vital role of the CEI on the cyclability of VO, which can be helpful for the performance optimization of vanadium-oxide-based batteries.
VO作为最早被研究用作锂宿主的嵌入型阴极材料之一，其理论容量极高（441 mAh g）。然而，在传统碳酸盐基电解质中循环时快速的容量衰减是一个尚未解决的问题。在此，我们表明使用LiTFSI/四甘醇二甲醚（摩尔比为1:1）电解质可使VO的循环能力大幅提高（在1.5 - 4.0 V vs Li/Li下，以50 mA g的电流密度循环100次后，容量保持率从20%提高到80%）。性能的改善主要源于VO电极本身，因为刷新循环电池的电解质和锂电极无助于恢复VO电极的容量。采用电化学阻抗谱（EIS）、循环后的扫描电子显微镜（SEM）、能量色散X射线（EDX）光谱和X射线光电子能谱（XPS）来研究电化学行为改善的起源。结果表明，循环性能的增强是由于在LiTFSI/四甘醇二甲醚中形成的阴极 - 电解质界面（CEI）层比在1 M LiPF₆于碳酸乙烯酯/碳酸二甲酯（重量比1:1，LP30）中形成的更薄但更稳定。这些结果表明，通过简单的电解质工程可以有效提高VO的循环性能。同时，所揭示的机理进一步揭示了CEI对VO循环性能的关键作用，这有助于基于氧化钒的电池的性能优化。
