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.