Enhanced corrosion stability and cycling performance of dual-salts polymer electrolytes for Li-metal polymer batteries

Abstract

Mitigating lithium (Li) corrosion during both storage and cycling is crucial for the performance of lithium-metal polymer batteries (LMPBs), as these systems undergo repeated storage and operation. Despite this, research has predominantly focused on enhancing cycling, often neglecting storage stability. Here, we demonstrate that a polymer electrolyte containing LiTFSI/LiBF₄ and FEC (D-LiBF₄ FEC) significantly improves both corrosion resistance and cycling stability. The D-LiBF₄ FEC electrolyte forms a dense, LiF-rich solid-electrolyte interphase (SEI) during storage, effectively reducing polymer decomposition and enhancing long-term performance in repeated cycling-storage conditions. In contrast, conventional LiTFSI/LiBOB and LiTFSI/LiDFOB systems fail to maintain prolonged cycling life after storage, as their organic-rich SEIs exacerbate Li corrosion. Our multi-faceted analysis—including depth-profiling X-ray photoelectron spectroscopy, electron micrography, and electrochemical studies—highlights the critical role of a high LiF-to-organic ratio in the SEI. We further propose a representative cycling-storage protocol, under which our LMPBs demonstrated over 1,500 hours of operation at 0.3 mA cm⁻² and achieved an extended lifespan of 10,000 hours for continuous cycling at 0.1 mA cm⁻² at room temperature. These findings underscore the importance of addressing Li corrosion during storage periods and provide key strategies for designing polymer electrolytes to improve Li-metal electrode performance.