Alkali-Metal-Ion-Pillared MnO2 Cathode for Enhanced Zinc-Ion Storage

Layered MnO2 is regarded as one of the most prospective cathode materials for aqueous zinc-ion batteries (AZIBs), yet it is impeded by its inferior conductivity and the poor cycling stability caused by the manganese dissolution. Herein, a facile alkali-metal-ion intercalation strategy is proposed, where sodium ion and potassium ion are adopted to verify the universality of the alkali-metal-ion intercalators in promoting the zinc-ion storage capability of MnO2. The intercalated alkali-metal ions could not only effectively promote the structural stability by serving as pillars but also improve the conductivity by modulating its electronic structure. Moreover, the extra oxygen defects are introduced during the intercalation of alkali-metal-ion “pillars”, which is conducive to the mitigation of manganese dissolution by regulating the Mn–O bond and acceleration of Zn2+ kinetics. As a result, the proposed Na+-intercalated MnO2 (NMO) and K+-intercalated MnO2 (KMO) present enhanced electrochemical performances and Zn2+ transfer kinetics. Specifically, NMO 600 and KMO 650 deliver the capacities of 236.3 and 158.2 mAh g–1 after 100 cycles at 0.1 A g–1, respectively, which are larger than that of pristine δ-MnO2. This work substantiates the potential of alkali-metal-ion “pillars” in improving the zinc-ion storage capability of layered MnO2 cathode and provides a promising way to develop high-performance manganese-based cathode materials via a facile solid-phase method.