Stretchable Coaxial Gel Polymer Electrolyte Based on a Styrene-Ethylene-Butylene-Styrene Block Copolymer Nanofiber for Stretchable Lithium-Ion Batteries

This paper describes the fabrication of stretchable coaxial gel polymer electrolytes (SC-GPEs) using electrospinning, which is a simple and inexpensive method. By combining a styrene-ethylene-butylene-styrene (SEBS) core and a poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) shell, the SC-GPEs offer a unique combination of mechanical flexibility and electrochemical performance that is ideal for stretchable lithium-ion batteries. Control over the mechanical stretchability and electrochemical properties of the SC-GPEs is achieved by modulating the composition ratio between the core and shell. Morphological investigations via transmission electron microscopy and scanning electron microscopy confirmed the successful integration of the stretchable SEBS core and PVDF-HFP shell within the SC-GPEs, which exhibit a diameter of approximately 1 μm. More importantly, the addition of SEBS significantly improved both the elongation and Young’s modulus of the SC-GPEs, with elongation values ranging from 71.5 to 207.4% depending on the PVDF-HFP/SEBS ratio. Cyclic loading tests show the ability of the SC-GPEs to undergo reversible deformation under mechanical stress, with the SC-GPEs containing SEBS demonstrating superior resilience. Moreover, electrochemical analysis shows that the SC-GPEs exhibit the typical ionic conductivity values ranging from 10^-1 mS cm^-1 and good electrolyte affinity, thus rendering them appropriate for lithium-ion batteries. The Li-ion transference value of the SC-GPEs (0.6-0.7) surpasses that of conventional liquid electrolytes, thus suggesting excellent Li-ion selectivity. The SC-GPEs have a high specific capacity of 140 mA h g^-1 at 0.5 C rates and good cycling performance with 71.0% capacity retention after 100 cycles, which surpasses that of liquid electrolytes (66%). This work presents high-stretchability gel polymer electrolytes and supports investigations into manufacturing processes for flexible functional membranes utilized in stretchable electronics.