Ultra-stable all-solid-state lithium metal batteries facilitated by in-situ LiF-rich single-ion conductor composite polymer electrolytes

The composite polymer electrolyte (CPE) displays the predictable potential to achieve high-performance of all-solid-state lithium metal batteries (ASSLMBs). However, due to the slow kinetics of Li⁺ transfer and the simultaneous transfer of Li⁺ and anions, the ionic conductivity of CPE is insufficient, and the interface stability between electrolyte and lithium anode is poor, which hinders its practical application on ASSLMBs. In this work, Zr-MOF as a single-ion conductor, composted with polyethylene oxide (PEO) and Li[N(SO₂CF₃)₂] (LiTFSI) to prepare an in-situ LiF-rich single-ion conductor (PLZM-7) composite polymer electrolytes. The results suggest that the decomposition energy barrier of TFSI⁻ is effectively lowered though Zr-O strong charge transfer between Zr-MOF and TFSI⁻, resulting in the in-situ formation of LiF in PLZM-7. This significantly enhances the lithium-ion transference number (0.89) and the ionic conductivity (6.4 × 10⁻⁴ S·cm⁻¹ at 60°C), while also expanding the electrochemical window (5.42 V). The critical current density of the Li|PLZM-7|Li symmetrical battery is as high as 0.43 mA·cm⁻², and the overpotential of Li plating/stripping is only 0.056 V after 750 h, indicating that the in-suit LiF-rich single-ion conductor solid-sate electrolyte PLZM-7 has excellent stability to lithium, The LiFePO₄|PLZM-7|Li exhibits a low-capacity decay rate as 1.04 % after 100 cycles at 0.1C, revealing a good application prospect in ASSLMBs.