High-capacity K⁺-pillared layered manganese dioxide as cathode material for high-rate aqueous zinc-ion battery

Sluggish kinetics and severe structural instability of manganese-based cathode materials for rechargeable aqueous zinc-ion batteries (ZIBs) lead to low-rate capacity and poor cyclability, which hinder their practical applications. Pillaring manganese dioxide (MnO₂) by pre-intercalation is an effective strategy to solve the above problems. However, increasing the pre-intercalation content to realize stable cycling of high capacity at large current densities is still challenging. Here, high-rate aqueous Zn²⁺ storage is realized by a high-capacity K⁺-pillared multi-nanochannel MnO₂ cathode with 1 K per 4 Mn (δ-K_0.25MnO₂). The high content of the K⁺ pillar, in conjunction with the three-dimensional confinement effect and size effect, promotes the stability and electron transport of multi-nanochannel layered MnO₂ in the ion insertion/removal process during cycling, accelerating and accommodating more Zn²⁺ diffusion. Multi-perspective in/ex-situ characterizations conclude that the energy storage mechanism is the Zn²⁺/H⁺ ions co-intercalating and phase transformation process. More specifically, the δ-K_0.25MnO₂ nanospheres cathode delivers an ultrahigh reversible capacity of 297 mAh g^-1 at 1 A g^-1 for 500 cycles, showing over 96 % utilization of the theoretical capacity of δ-MnO₂. Even at 3 A g^-1, it also delivered a 63 % utilization and 64 % capacity retention after 1000 cycles. This study introduces a highly efficient cathode material based on manganese oxide and a comprehensive analysis of its structural dynamics. These findings have the potential to improve energy storage capabilities in ZIBs significantly.