Boosting Aqueous Zn/MnO₂ Batteries via a Synergy of Edge/Defect-Rich Cathode and Dendrite-Free Anode

Aqueous Zn/MnO₂ batteries exhibit huge potential for grid-scale energy storage but suffer from poor cycling stability derived from both structural instability of cathode and Zn dendrite growth of anode. Here, we report a high-performance aqueous Zn/MnO₂ battery with ZnSO₄-based electrolyte, comprising a nanoparticle-like cathode with abundant surface oxygen defects (MO-V_o) and a dendrite-free Zn anode. The transformation from nanowire (α-MnO₂) to nanoparticle (MO-V_o) was found by tuning the annealing conditions in an argon flow. Moreover, the small size of MO-V_o nanoparticles can effectively promote the spatially uniform distribution of volume stress during carrier intercalation, boosting the structural stability of the MO-V_o cathode. Moreover, it was found that the intercalation pseudocapacitive behavior of Zn²⁺ in the MO-V_o cathode can be strongly boosted by tailoring the surface oxygen defect of MnO₂ based on the calculations and experiments, thereby achieving enhanced cycling stability and redox kinetics. Additionally, the addition of K₂SO₄ additive into the electrolyte can tailor the deposition behavior of Zn²⁺, enabling stable Zn stripping/plating without dendrites. Therefore, the assembled Zn/MO-V_o batteries exhibit a high energy density and excellent long-term cyclability over 1400 cycles. Besides, the reaction mechanism of pseudocapacitive Zn²⁺ intercalation and H⁺ intercalation for the MO-V_o cathode was revealed via ex situ characterizations.