(Invited) Investigating Failure in Anode-Free Lithium-Metal Pouch Cells with Liquid Electrolytes

Anode-free, or zero-excess lithium-metal cells, promise higher energy density than existing lithium-ion batteries. However, the abysmal performance of cells with lithium-metal electrodes prevents them from being used in commercial products that require long-life: electric cars and energy storage products. Many researchers believe all-solid state cells are necessary to achieve the lifetime required for these applications, but solid electrolytes complicate cell manufacturing and incur the huge costs required to rebuild existing production facilities designed to handle cells with liquid electrolytes. If a long-life anode-free cell could be made using a liquid electrolyte, this would be the best path forward for fast and inexpensive introduction into the existing market. In this work, baseline NMC532/Cu anode-free pouch cells with 1M LiPF6 in FEC:DEC (1:2 vol) were tested at 40°C, with C/5 charge and C/2 discharge between 3.6 V – 4.5 V. Cells with this electrolyte lose 80% of their initial capacity before 20 charge-discharge cycles. Liquid electrolytes with different lithium salts are tested and show improved performance. To investigate the capacity loss mechanisms, SEM is used to track lithium morphology, XPS is used to compare SEI composition, and liquid NMR is used to track the electrolyte volume and degradation at various points throughout cycling. The results of these experiments are used to guide further optimization of the electrolyte composition which give incremental improvements in capacity retention. With continued works towards understanding the failure of these cells, a commercializable anode-free lithium-metal cell with liquid electrolyte may be realized.