Low‐Enthalpy and High‐Entropy Polymer Electrolytes for Li‐Metal Battery

Ionic‐conductive solid‐state polymer electrolytes are promising for the development of advanced lithium batteries yet a deeper understanding of their underlying ion‐transfer mechanism is needed to improve performance. Here we demonstrate the low‐enthalpy and high‐entropy (LEHE) electrolytes can intrinsically generate remarkably free ions and high mobility, enabling them to efficiently drive lithium‐ion storage. The LEHE electrolytes are constructed on the basis of introducing CsPbI 3 perovskite quantum dots (PQDs) to strengthen PEO@LiTFSI complexes. An extremely stable cycling >1000 h at 0.3 mA cm −2 can be delivered by LEHE electrolytes. Also, the as‐developed Li ¦ LEHE ¦ LiFePO 4 cell retains 92.3% of the initial capacity (160.7 mAh g −1 ) after 200 cycles. This cycling stability is ascribed to the suppressed charge concentration gradient leading to free lithium dendrites. It is realized by a dramatic increment in lithium‐ion transference number (0.57 vs 0.19) and a significant decline in ion‐transfer activation energy (0.14 eV vs 0.22 eV) for LEHE electrolytes comparing with PEO@LiTFSI counterpart. The CsPbI 3 PQDs promote highly structural disorder by inhibiting crystallization and hence endow polymer electrolytes with low melting enthalpy and high structural entropy, which in turn facilitate long‐term cycling stability and excellent rate‐capability of lithium‐metal batteries.