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

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 PEOSPEs, 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 degrees C) and high-voltage LiNi0.5Co0.2Mn0.3O2 (NCM523) cathodes. The assembled Li|| PW12@CD PEO||LFP cycled stably for over 100 cycles at high temperature (60 degrees 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 degrees 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.