One-step fabrication of sodium-ion conducting cotton-based solid-state electrolyte for primary battery applications

Lithium-ion batteries and liquid electrolyte-based energy storage systems face intrinsic limitations that necessitate alternative solutions. Sodium-ion batteries with solid-state electrolytes, particularly biopolymer electrolytes, have emerged as promising candidates for sustainable battery technologies. This study developed a biopolymer electrolyte using cotton cellulose and explored its structural, dielectric, and transport properties upon doping with sodium nitrate ($\mathrm{NaN}{O}_3$) salt and bismuth oxide ($B{i}_2{O}_3$) nanoparticles (NPs). Three samples, pristine cotton (PC), $\mathrm{NaN}{O}_3$-doped cotton (PCS), and $\mathrm{NaN}{O}_3$ with $B{i}_2{O}_3$ NPs-doped cotton (PCSN) were prepared using a polymer adsorption palletization technique. XRD, FTIR, and SEM with EDX confirmed successful doping, revealing changes in crystallinity, chemical interactions, and microstructural modifications respectively. The impedance spectroscopy and dielectric studies showed insulating behaviour for pristine cotton, while $\mathrm{NaN}{O}_3$-doped cotton and $\mathrm{NaN}{O}_3$ with $B{i}_2{O}_3$ NPs-doped cotton exhibited ionic conductivities of $1.71\times {10}^{-4}S{\mathrm{cm}}^{-1}$ and $3.81\times {10}^{-5}S{\mathrm{cm}}^{-1}$ respectively. PCS-based cells demonstrated superior performance with open circuit voltage of $2.2V$, current density of $3.55\mathrm{\mu A}{\mathrm{cm}}^{-2}$, power density of $0.29W{\mathrm{Kg}}^{-1}$, energy density of $7.09\mathrm{Wh}{\mathrm{Kg}}^{-1}$, and discharge capacity of $2.32\mathrm{\mu A}{h}^{-1}$.