Suppression of structural degradation in molybdenum-modified layered oxides for high-performance potassium-ion...

Layered manganese-based transition metal (TM) oxides exhibit great potential as cathodes for potassium-ion batteries (PIBs) due to their cost-effectiveness, high efficiency, and facile synthesis. However, structural transformations and transition metal migration severely limit their broader energy storage applications. This study introduces a strategy to mitigate these issues by incorporating molybdenum as a dopant into the cathode material K_0.5MnO₂. The incorporation of Mo⁶⁺ into TM sites of K_0.5MnO₂ stabilizes the crystal structure by mitigating Mn dissolution through Mn-O-Mo bond formation and alleviating Jahn-Teller effects. These effects effectively suppress interlayer slip of metal oxide layers and alleviate frequent occurrence of phase transformations, stabilizing the octahedral structure and enhancing the K⁺ diffusion rate. As a result, K_0.5Mn_0.95Mo_0.05O₂ (KMMO), synthesized via solid-state sintering using MoO₃ as the Mo⁶⁺ source, exhibits superior discharge capacity of 71.93 mAh g^-1 at 1C after 500 cycles. The energy density is significantly improved from 175.48 Wh/kg (for KMO) to 224.87 Wh/kg (for KMMO). Additionally, a full-cell configuration employing KMMO as the cathode and nano-graphite as the anode demonstrates a discharge specific capacity of 67.8 mAh g^-1 at 0.5 C. The present study highlights the potential of effective structural regulation of layered oxides through the incorporation of appropriate metallic elements.