Eco‐Friendly Soy Protein‐Based Solid‐State Electrolyte Exhibiting Stable High‐Rate Cyclic Performances by Molecular Regulation Design

Abstract Solid‐state electrolytes play critical roles in solid‐state lithium‐ion batteries. In this study, soy protein (SP), a green and renewable biomass polymer, is explored as a backbone for solid‐state electrolytes. SP‐based solid‐state electrolytes (SPPV@VEC‐SSEs) are prepared with the soft‐hard interpenetrating network by modulating the molecular structure of SP. In this process, the active groups on SP are utilized to form hydrogen bonds with polyvinylidene difluoride (PVDF), constructing a hard phase cross‐linked network, which causes the folded quaternary structure of the SP to unfold and create more lithium ion transport channels; Then vinylethylene carbonate (VEC) monomers are infused into this network and are cross‐linked through free radical polymerization to form a soft‐hard interpenetrating cross‐linked network, enhancing both the availability of lithium‐ion transport sites and the improvement of interfacial performance. The SP‐based solid‐state electrolytes exhibit high ionic conductivity (7.95 × 10 −4 S cm −1 ) and Li + transference number (0.78) at 60 °C. The corresponding LFP||SPPV3@VEC‐SSEs||Li battery delivers good cyclic stability up to >800 cycles under high temperature of 120 °C and high cycling rate of 2 C. Results of experimental and theoretical analysis reveal that the construction of the soft‐hard interpenetrating network facilitates the unfolding of the quaternary structure of SP, exposing more oxygen‐containing groups and cationic groups which effectively bind with Li + ions and anions of lithium salts. The zwitterionic structure of SP not only gives rise to high ionic conductivity but promotes the formation of a stable interface layer between the solid‐state electrolyte and electrodes. Compared to organic polymer electrolytes (polyethylene oxide (PEO) and poly(trimethyl carbonate) (PTMC)), the SPPV@VEC‐SSEs exhibit an order of magnitude lower release of organic volatiles, significantly reducing their environmental impact across the entire lifecycle. This work provides a pathway for preparing bio‐based sustainable solid‐state electrolytes with long lifespans under extreme conditions.