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 was proposed to boost the capacity and structural stability of δ-MnO2 (Ce-MnO2). Ce4+ can preferentially occupy the Mn sites with the same and stable valence state to Mn4+, effectively suppress structural collapse during charge and discharge processes. Ce3+ could contribute to improved electronic conductivity through aliovalent substitution leading to charge compensation and altered 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 in powering a PNIPAM hydrogel actuator, Zn//MnO2 ion batteries exhibited potential for actuator-driven technologies.