Synergistic effect of an electrolyte containing a propylene glycol co-solvent and VO₂@V-MXene cathode on enhancing the performance of aqueous zinc-ion batteries

Aqueous Zn-ion batteries (AZIBs) are safer, cost-effective alternatives to Li-ion batteries. However, water-induced side reactions in AZIB electrolytes limit their stability and performance. This study incorporated a co-solvent, propylene glycol (PG), into the AZIB electrolyte with a highly conductive VO₂@V-MXene nanocomposite cathode to minimize the adverse effects of water molecules. A Zn||Zn symmetric cell with PG 30 electrolyte, containing 2 M zinc trifluoromethanesulfonate (Zn(OTf)₂)/PG:H₂O (30:70, w/w), was stably cycled for ~3200 h at 0.5 mA cm⁻² and 0.5 mAh cm⁻². Notably, a Zn||VO₂@V-MXene full cell containing PG 30 delivered 400 mAh g⁻¹ at 0.1 A g⁻¹. Furthermore, it maintained 80 % capacity retention over 2000 cycles at a low current density of 1 A g⁻¹, reaching 359 mAh g⁻¹ and outperforming previously reported AZIBs. These results highlight the importance of long-term stability at low current densities for practical AZIB deployment. Although its high-rate performance is often reported as impressive, it may not accurately reflect actual operating conditions due to suppressed degradation from limited voltage exposure or overestimated capacity caused by dominant proton intercalation. This improvement is attributed to the synergistic effect of PG and VO₂@V-MXene. PG reduced both free water molecules and those within the Zn²⁺ solvation structure. VO₂@V-MXene facilitated rapid Zn²⁺ transport by increasing capacitive contributions while reducing interfacial resistance, enhancing the Zn²⁺ diffusion kinetics. This synergistic strategy offers insights into electrolyte and cathode material design, where Zn²⁺ solvation structure modification mitigates water-induced side reactions, and conductive-composite cathode incorporation enhances Zn²⁺ transport and diffusion kinetics, enabling high-performance AZIBs.