Semi-Interpenetrating Polymer Network Electrolytes Based on a Spiro-Twisted Benzoxazine for All-Solid-State Lithium-Ion Batteries

A spiro-twisted benzoxazine, namely, 6,6′-(6,6,6′,6′-tetramethyl-6,6′,7,7′-tetrahydro-2H,2′H-8,8′-spirobi[indeno[5,6-e][1,3]oxazin]-3,3′(4H,4′H)-diyl)bis(hexan-1-ol) (TSBZ6D), was successfully developed as a semi-interpenetrating polymer network (s-IPN) matrix for solid polymer electrolytes (SPEs). The designed spiro-twisted molecular structure of TSBZ6D constitutes an SPE matrix with a high fractional free volume that facilitates the transport of lithium ions. In the meantime, its cross-linking network structure enables a remarkable enhancement in the mechanical properties of SPEs. When combined with poly(ethylene oxide) (PEO) electrolytes, the TSBZ6D s-IPN imparts an enhancement of >300 and 1100% in tensile stress and in tensile strain, respectively, to the PEO-TSBZ6D (PT) composite SPEs over the PEO/lithium salt sample. Electrochemical testing of symmetric Li/PT/Li cells indicates the effectiveness of PT SPEs in mitigating the short-circuiting problem caused by Li dendrite formation. We demonstrated that a specific capacity of 166 mAh g–1 (0.1 C) at 80 °C and a promising cycle stability have been achieved by an all-solid-state LiFePO4/PT/Li.