Composite scaffold of electrospun nano-porous cellulose acetate membrane casted with chitosan for flexible solid-state sodium-ion batteries

Emerging as a safe and economically viable alternative to lithium-ion batteries, the solid-state sodium ion battery (ss-SIB) has captured increasing attention as a transformative technology for realizing a decarbonized economy and ensuring a sustainable energy supply. Here we report a nanoarchitecture strategy of biodegradable, biocompatible, and naturally abundant cellulose derivative (cellulose acetate, CA) and chitosan (CH) biopolymer-based nano-porous electrospun composite electrolyte (ECE) for flexible and wearable ss-SIBs. A simple combination of electrospinning and solution casting was utilized to fabricate mechanically robust (13.76 MPa), thin-film (0.067 mm), and highly flexible ECE. The ionic conductivity of ECE was enhanced through optimization, taking into account the amount of sodium salt (NaPF₆). The resulting ECE exhibited a sodium-ion conductivity of 1.04 ×10⁻⁴ S·cm⁻¹ and a sodium ion transference number of 0.48 at room temperature (RT=23 °C). The obtained Na⁺ transference number of 0.48 and a low activation energy (Ea = 0.13 eV) indicate the easy charge carrier diffusion ability of as-prepared ECE. The electrochemical stability window (ESW = 4.04 V) of ECE is studied by the linear sweep voltammetry (LSV) with the assembly of stainless steel and sodium metal electrodes. Without any interfacial modification, a uniform, stable, and long-time room temperature (RT) galvanostatic Na plating-stripping was observed for 1000 hrs at 0.5 mA·cm⁻² current density in a symmetric (Na|ECE|Na) cell, this underscores impressive electrochemical stability and compatibility of ECE with sodium metal. Utilizing Na₃V₂(PO₄)₃ (NVP) as cathode, fabricated ECE, and Na metal as anode in a hybrid full cell, a notable RT specific discharge capacity of 98.1 mA·h·g⁻¹ was attained at a rate of 0.1 C with a capacity retention of 93.4 % over 120 charge-discharge cycles. This highlights the practical applicability of the nanostructured electrospun composite electrolyte for flexible and wearable ss-SIBs.