Polyoxometalate-integrated host-guest recognition solid polymer electrolytes for wide-temperature range solid-state lithium metal batteries

Abstract

All-solid-state lithium-metal batteries (ASSLMBs) using poly(ethylene oxide)-based solid polymer electrolytes (PEO-SPEs) hold potential for achieving high energy densities. However, PEO-based ASSLMBs are constrained by the need for elevated operating temperatures, diminished Li⁺ conductivity, and limited electrochemical windows, restricting their practical applications. Herein, a host-guest recognition system was constructed to address these challenges, with polyoxometalates (POMs) and Cyclodextrins (CDs) employed as host and PEO-SPEs as gust to form PW₁₂@CD PEO electrolyte and to further realize wide-temperature range ASSLMBs. Impressively, PW₁₂, characterized by its unique 3D ion transport channels and oxygen-rich surfaces, acted as an effective "host" for PEO electrolytes. This material improved Li⁺ transport kinetics and promoted lithium bis(trifluoromethane)sulfonimide (LiTFSI) decomposition. The PW₁₂@CD PEO system, leveraging the properties of PW₁₂ in the PEO-SPEs, provided dual SEI/CEI protection capability through the formation of a LiF-rich SEI layer and an inorganic compound-rich CEI layer. Therefore, this system enabled stable operation of LiFePO₄ (LFP) across a wide temperature range (-20–60 °C) and high-voltage LiNi_0.5Co_0.2Mn_0.3O₂ (NCM523) cathodes. The assembled Li||PW₁₂@CD PEO||LFP cycled stably for over 100 cycles at high temperature (60 °C), maintaining a favorable specific capacity of 151 mAh g^-1. The Li||gel-PW₁₂@CD PEO||LFP also cycled stably for over 200 cycles under low temperature (-20 °C), with a favorable specific capacity of 110 mAh g^-1. Meanwhile, Li||PW₁₂@CD PEO||LFP pouch cell demonstrated a discharge capacity of approximately 120 mAh g^-1, with an impressive capacity retention of 84.4 % and an average Coulombic efficiency (CE) of 97.7 % after 400 cycles at room temperature.