Cr-LiF as a high energy density conversion-type cathode for Li-ion solid-state batteries

Transition-metal fluorides (TMFs) are attracting attention as alternative lithium-ion battery cathodes, primarily focusing on Fe-based systems. Here, we report chromium as a previously unexplored transition metal (TM) for TMF cathodes in rechargeable lithium batteries. Utilizing a thin-film solid-state platform, we mitigate the common shortcomings of TMF cathodes, such as sluggish kinetics and electrolyte incompatibility. Coevaporation of Cr and LiF produces a heterogeneous thin film of Cr-LiF with a 1.1:2 stoichiometric ratio, delivering an initial capacity of 435 mAh/g and an energy density of 0.71 Wh/g at a C/10 cycling rate. Experimental measurements and first-principles calculations identify CrF2 as the dominant delithiated phase. The cathode maintains a capacity of 208 mAh/g at both 1C and 5C discharge rates after 1500 cycles. Compared to Fe-LiF (FeF2) analogs, Cr-LiF demonstrates a higher rate capability with 0.255 Wh/g at 3.80 W/g. This work introduces chromium fluorides as a new high-energy conversion cathode, expanding the options of viable positive electrode materials for next-generation batteries. Transition-metal fluorides are being explored as alternative lithium-ion battery cathodes, with a focus on overcoming limitations like inefficient kinetics and electrolyte incompatibility. Here, the authors introduce chromium fluorides as cathode material, demonstrating enhanced rate capability and stability, which could significantly expand the options for high-energy conversion in next-generation batteries.