Synergistic effect of oxygen vacancies and Bi doping enables the β-MnO₂ as a high-capacity cathode for quasi-solid-state wide temperature adaptability Zn-ion batteries

Optimizing the cathode structure and designing the hydrogel electrolyte system were key strategies for enhancing the performance of zinc-ion batteries (ZIB), and preventing the freezing of liquid electrolytes. Herein, a quasi-solid-state ZIB was constructed by a synergistic optimization strategy, with rich oxygen vacancies and Bi³⁺ doping β-MnO₂ cathode, an antifreeze polymer hydrogel electrolyte, and zinc anode. The synergistic effect of oxygen vacancies and Bi³⁺ doping β-MnO₂ cathode reduced Zn²⁺ steric hindrance, and accelerated transport kinetics. The assembled button battery demonstrated an initial capacity of up to 483 mAh g⁻¹ at 0.1 A g⁻¹. After 5000 cycles, the good capacity retention rate was 95 % at 2 A g⁻¹, indicating its remarkable cycle stability. In addition, a three-dimensional network polymer hydrogel electrolyte was engineered, which contained a large number of hydrogen bonds. Simultaneously, glycerol and PAM broke the hydrogen bonds between water molecules and firmly entrapped H₂O within the hydrogel, which bestowing upon the gel electrolyte with low-temperature adaptability. The DFT calculation further demonstrated that the incorporation of glycerol altered the affinity of H₂O and Zn²⁺ for the oxygen-containing functional groups within the hydrogel, thereby regulating the bond interactions within the system. Subsequently, the quasi-solid batteries exhibited outstanding electrochemical performance (275 mAh g⁻¹ at 20 °C and 130 mAh g⁻¹ at −20 °C, under a current density of 0.2 A g⁻¹) and wide temperature adaptability (at −20 °C and 40 °C).