A cross-linked AB-type alternating perfluoroalkyl-ethylene oxide polymer electrolyte for high-performance all-solid-state lithium-metal batteries

Abstract

Poly(ethylene oxide) (PEO) derivatives are attractive Li⁺-conducting solid polymer electrolytes (SPEs) due to their high lithium salt solubility but face challenges with low ionic conductivity and interfacial stability. In contrast, fluorinated polymers offer superior chemical and mechanical stability but limited salt solubility and conductivity. To address these challenges, we developed a cross-linked AB-type alternating copolymer electrolyte, poly(TEGDVE-OFDIB)-LiTFSI, via iodo-ene photopolymerization of triethylene glycol divinyl ether (TEGDVE) and octafluoro-1,4-diiodobutane (OFDIB) in the presence of LiTFSI. TEGDVE enhances film flexibility and cross-linking while enabling Li⁺ transport through sequential Li⁺ coordination and decoordination, whereas OFDIB serves as both a structural spacer and electrostatic mediator, with its negative electrostatic potential stabilizing the electrochemical interface while facilitating Li⁺ conduction between TEGDVE units. The resulting SPE achieves a Li⁺ conductivity of 1.3 × 10⁻⁴ S cm⁻¹, a transference number of 0.55, and a stability window of 4.98 V at 40 ℃. All solid-state lithium-metal batteries (ASSLMBs) with a LiFePO₄ cathode and the SPE retain 100 % capacity over 500 cycles at 0.5C. With an NMC811 cathode, the cell delivers an initial capacity of 157.7 mAh g⁻¹ with 80 % capacity retention after 100 cycles. This work establishes iodo-ene polymerization as a versatile strategy for designing high-performance AB-type alternating copolymer electrolytes for ASSLMBs.