Phase Transition Induced Unusual Electrochemical Performance of V₂CT_X MXene for Aqueous Zinc Hybrid-Ion Battery

Nonbattery behavior related phase transition of electrodes is usually not favorable for any batteries because it results in performance degradation at all times. Here, we demonstrate a zinc hybrid-ion battery (ZHIB) with an unusual capacity enhancement even within 18 000 cycles by employing V₂CT_X MXene as the cathode, enormously differing from all reported counterparts with capacity degradation initiated within hundreds of cycles. The dominated mechanisms are determined to be MXene delamination and an unexpected phase transition during cycling. Both the original cathode and secondary derivative contribute to capacity simultaneously, resulting in the unusual capacity enhancement. Consequently, the specific capacity of 508 mAh g^-1 (highest for all reported aqueous zinc-ion batteries) and high energy density of 386.2 Wh kg^-1 are realized. Also, the quasi-solid-state batteries fabricated can output stably at -20 °C and in bending, twisting, stabbing, and cutting conditions. Our work brings an effective approach, that is, utilizing "unstable" electrode materials, which should usually be avoided, to achieve continuously enhanced performance of a battery. The idea to use both original and secondary materials for energy storage may be developed to be a general method to achieve extraordinary cycling stability of batteries.