Ultra-thin and high-voltage-stable Bi-phasic solid polymer electrolytes for high-energy-density Li metal batteries

Solid-state electrolytes (SSEs) are essential materials in all-solid-state lithium-metal batteries. However, a comprehensive SSE possessing high ionic conductivity, broad electrochemical window, and high thermal stability remains elusive. In this work, a novel bi-phase SSE featuring a shape memory effect is developed by in-situ thermal cross-linking of 2-ethyl cyanoacrylate (CA), polyethylene glycol methyl ether acrylate (PEGMEA), succinonitrile (SN), and fluoroethylene carbonate (FEC) additives. Due to the phase separation phenomenon and interfacial Li-ion conduction, the bi-phase SSE exhibits a room-temperature ionic conductivity of 1.9 mS cm−1. Meanwhile, the bi-phase SSE exhibits a high oxidation potential of 4.9 V (vs Li/Li+), and a lithium-ion transference number (tLi+) of 0.56. Coupling with LiNi0.8Co0.1Mn0.1O2 (NCM 811) cathode and 11 µm bi-phase SSE, solid-state lithium metal batteries (SSLMBs) demonstrate long-term cycling stability (capacity retention > 92% after 250 cycles), excellent rate performance (126 mA h g−1 at 2 C, and high-voltage stability (208 mA h g−1 at 4.5 V). This investigation demonstrates the potential of bi-phase SSEs as a promising material for the development of high-performance SSLMBs.