Block copolymer electrolyte with adjustable functional units for solid polymer lithium metal battery

Solid polymer electrolytes have been considered as the promising candidates to improve the safety and stability of high-energy lithium metal batteries. However, the practical applications of solid polymer electrolytes are still limited by the low ionic conductivity, poor interfacial contact with electrodes, narrow electrochemical window and weak mechanical strength. Here, a series of novel block copolymer electrolytes with three-dimensional networks are designed by cross-linked copolymerization of the polyethylene glycol soft segments and hexamethylene diisocyanate trimer hard segments. Their ionic migration performances and interface compatibilities with Li metal anode have been optimized delicately by tailoring the ratio of these functional units. The optimized block copolymer electrolyte has shown an amorphous crystalline structure, a high ionic conductivity of ~5.7 × 10−4 S cm−1, high lithium ion transference number (~0.49), wide electrochemical window up to ~4.65 V (vs. Li+/Li) and favorable mechanical strength at 55 °C. Furthermore, the enhanced interface compatibility can well support the normal operations of lithium metal batteries using both LiFePO4 and LiNi0.8Co0.15Al0.05O2 cathodes. This study not only paves a new way to develop solid polymer electrolyte with optimizing functional units, but also provides a polymer electrolyte design strategy for the application demand of lithium metal battery.