Role of Mo and N doping ratios in regulating the zinc storage performance of δ-MnO2: a systematic study from single to co-doping

Abstract

Manganese-based cathode materials are highly promising for large-scale aqueous zinc-ion batteries (AZIBs) due to their high specific capacity, low cost, and environmental benignity. However, structural instability and severe Mn dissolution at the cathode/electrolyte interface during cycling lead to rapid capacity degradation, which greatly limits their practical application. To address these critical issues, this work proposes an innovative Mo/N cation–anion co-doping strategy for δ-MnO₂, which differs from single Mo or N doping and achieves synergistic optimization of structural and electrochemical properties. Specifically, Mo doping effectively modulates the lattice parameters of δ-MnO₂ to expand ion diffusion channels, while N doping strengthens the layered framework and suppresses Mn dissolution. Their synergistic effect significantly enhances electronic conductivity and structural robustness compared with single-doped or pristine δ-MnO₂ samples. The optimized Mo_0.1/N₁-δ-MnO₂ cathode delivers a high discharge specific capacity of 370.8 mAh g⁻¹ at 0.2 A g⁻¹, retaining 270.0 mAh g⁻¹ after 200 cycles; it also delivers 140.0 mAh g⁻¹ at a high current density of 1 A g⁻¹ and still retains a capacity of 80.6 mAh g⁻¹ after 800 cycles. Combined with in situ EIS, ex situ XRD, and DFT calculations, the underlying mechanism is quantitatively revealed through Mo/N co-doping induced reduction of the Zn²⁺ diffusion barrier, optimization of ion migration pathways, and regulation of the reversible Zn²⁺/H⁺ co-intercalation mechanism. This work provides clear mechanistic insights and establishes a reliable cation–anion co-doping design principle for high-performance Mn-based AZIB cathodes.