MXene-Derived Na⁺ -Pillared Vanadate Cathodes for Dendrite-Free Potassium Metal Batteries

Cation-intercalated vanadates, which have considerable promise as the cathode for high-performance potassium metal batteries (PMBs), suffer from structural collapse upon K⁺ insertion and desertion. Exotic cations in the vanadate cathode may ease the collapse, yet their effect on the intrinsic cation remains speculative. Herein, a stable and dendrite-free PMB, composed of a Na⁺ and K⁺ co-intercalated vanadate (NKVO) cathode and a liquid NaK alloy anode, is presented. A series of NKVO with tuneable Na/K ratios are facilely prepared using MXene precursors, in which Na⁺ is testified to be immobilized upon cycling, functioning as a structural pillar. Due to stronger ionic bonding and lower Fermi level of Na⁺ compared to K⁺ , moderate Na⁺ intercalation could reduce K⁺ binding to the solvation sheath and favor K⁺ diffusion kinetics. As a result, the MXene-derived Na⁺ -pillared NKVO exhibits markedly improved specific capacities, rate performance, and cycle stability than the Na⁺ -free counterpart. Moreover, thermally-treated carbon paper, which imitates the microscopic structure of Chinese Xuan paper, allows high surface tension liquid NaK alloy to adhere readily, enabling dendrite-free metal anodes. By clarifying the role of foreign intercalating cations, this study may lead to a more rational design of stable and high-performance electrode materials.