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Cycling and Failing of Lithium Metal Anodes in Carbonate Electrolyte

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journal contribution
posted on 27.08.2018, 00:00 by Yifang Zhang, Yiren Zhong, Qiuwei Shi, Shuquan Liang, Hailiang Wang
Lithium metal electrodes promise high energy density, but their poor cycling stability has been limiting applications in real batteries. In this study, we examine the cycling and failing behaviors of Li metal electrodes in a commercial carbonate electrolyte and their dependence on the electrode thickness and cycling conditions. We find that thick and thin Li metal electrodes fail for different reasons. The cycle life of a Li||Cu cell with a thick (∼80 mAh cm–2) Li foil electrode can be divided into three stages, and the cell stops functioning when ionic transport is blocked by the accumulated solid electrolyte interphase layer on the Cu electrode. In contrast, thin (2 mAh cm–2) Li metal electrodes fail because of Li metal depletion caused by side reactions with the electrolyte, and their cycle life is determined by Coulombic efficiency. The results suggest that application-relevant performance of Li metal anodes should be assessed using thin and deeply cycled electrodes rather than the currently prevalent thick and shallowly cycled ones. We show that a 2 mAh cm–2 Li metal anode, when paired with an excess reagent Li4Ti5O12 cathode, loses all the capacity within 30 cycles. Adding lithium nitrate and fluoroethylene carbonate to the electrolyte can extend the life to 275 cycles.