Heterocyclic polymer supported cathode/Li interface layers to lower the operational temperature of PEO-based Li-batteries

High-performance poly (ethylene oxide) (PEO)-based solid-state polymer Li-batteries (SSLBs) at low temperature (≤ 25 ℃) is hindered by high interfacial resistance and low ionic conductivity. Herein, we simultaneously construct cathode and anode interface layers via in-situ heat-induced heterocyclic polymerization reaction, where the cathode-electrolyte interface layer (PPL) consists of bromine-doped poly (3,4-ethylene-dioxy-thiophene) (PEDOT), PEO and bis-trifluoromethanesulfonimide (LiTFSI), featuring with mixed ionic/electronic conduction, and the anode-electrolyte interface layer (PVCL) was formed by poly (vinyl carbonate) (PVC), PEO and LiTFSI, having a robust fast ionic conduction. Benefiting from the PEDOT conductivity, high mechanical strength of PVC and good interface affinity aroused by heat-induced reaction, the solid-state PEO-based LiFePO4||Li cell shows low interfacial resistance of 11.02 Ω that decreased by 92% compared to the cell without interface modification, and delivering a discharge capacity of 164.4 mAh g−1 at 0.1 C (25 ℃), as high as 115.9 mAh g−1 at 10 ℃. X-ray photoelectron spectroscopy revealed the enrichment of LiF, Li3N and LiBr on the lithium metal surface after cycling, further enhancing stable cycling Li-batteries. The dual interface-constructed strategy provides a reliable way to resolve the bottle-neck interfacial issues of SSLBs.