Unveiling the origin of cascading degradation in LiFePO4 – lithium metal batteries

Abstract

Lithium iron phosphate (LFP) is widely used in electric vehicles and energy storage systems because of its low cost and excellent cyclability. To address the limited energy density of LFP-based cells, Li || LFP batteries with lithium-metal anodes have attracted significant interest. However, unlike conventional graphite || LFP cells, Li || LFP systems frequently exhibit sudden death during long-term cycling. In this work, we systematically investigate the mechanism responsible for this failure. We reveal that unexpected closed-loop structures, initiated by the high reactivity of lithium metal and accelerated by particle cracking from LFP degradation, drive rapid performance decay. These coupled effects decrease Coulombic efficiency and increase cell impedance. Our findings highlight the critical interplay between lithium metal reactivity and LFP structural degradation, and we demonstrate that optimized electrolytes, electrode microstructural control, and interfacial engineering can effectively mitigate sudden death and improve the performance of Li || LFP batteries.