Functionalized carbon nanotube doped gel electrolytes with enhanced mechanical and electrical properties for battery applications

We report the functionalized carbon nanotubes (fCNTs) and graphene oxide (GO) doped polyvinyl alcohol (PVA) based gel electrolytes (GEs). The multiwalled carbon nanotubes (CNTs) were treated via microwave irradiation to alter the degree of carboxylation. The fCNT doped gel electrolyte (fCNTGE) showed significantly improved ionic conductivity, mechanical strength as well as electrochemical stability when compared to the pure GE and graphene oxide doped gel electrolyte (GOGE). The homogeneous distribution of ionic channels provided by fCNTs served as redox shuttle and facilitated the ion migration in the gel. The fCNTGE exhibited the best performance when the oxygen content was 12.8% by weight. The ionic conductivity was significantly improved by introducing fCNTs into the PVA gel and reached 6.9 × 10⁻² S cm⁻¹, revealing that the diffusion and transport of ions into electrolyte were much better than the GE and GOGE. A significant enhancement in the gel mechanical properties was observed as the Young's module (E = 2.3) and tensile strength (22.3 kPa) of fCNTGE was higher than that of GE and GOGE. Furthermore, the composite Zn–Ag₂O batteries were made and tested using the fCNTGE, GE, and GOGE in the 3D-printed battery casings. The fCNTGE based batteries demonstrated good electrochemical stability with specific capacity reaching 204.3 mAh g⁻¹ (C/20).