A single-element heterovalent doping strategy stabilizing the cathode structure for reversible zinc-ion storage to power soft robotics

Abstract

Zinc-ion batteries (ZIBs), recognized for their safe aqueous electrolyte and low-cost, abundant zinc resources, offer significant promise for applications in energy storage. MnO₂ is a promising cathode material due to its environmental friendliness and low cost, but it faces challenges related to low conductivity and structural instability. Herein, a single-element (Ce) heterovalent doping strategy is proposed to boost the capacity and structural stability of δ-MnO₂ (Ce-MnO₂). Ce⁴⁺ can preferentially occupy the Mn sites due to its same and stable valence state as Mn⁴⁺, effectively suppressing structural collapse during charge and discharge processes. Ce³⁺ could contribute to improved electronic conductivity through aliovalent substitution, leading to charge compensation and altering the local chemical environment by creating oxygen vacancies and optimizing Mn–O interactions. Moreover, it can improve the specific surface area and provide active sites, thereby promoting electrochemical activity and facilitating superior ion transport. Consequently, the Ce-MnO₂ cathode achieved a high specific capacity of 374.5 mAh g⁻¹, with 90% capacity retention after 1000 cycles. When further applied to power a PNIPAM hydrogel actuator, Zn//MnO₂ ion batteries exhibited potential for actuator-driven technologies.