Solid solution reinforced V₃CrC₃T_x MXene cathodes for Zn-ion micro-supercapacitors with high areal energy density and superior flexibility

In-plane micro-supercapacitors (MSCs) possess the capabilities of easy integration with planar circuits and feasible flexibility when they are used in flexible and wearable electronics. However, their unsatisfactory energy density limits their wide application. The Zn-ion hybrid supercapacitor is an ideal candidate as it assimilates the high energy-density of the zinc metal anode and high power-density of the pseudocapacitive material cathode. In view of the fact that multiple-metal MXenes could exhibit great potential compared to the single-metal MXenes in energy storage capability, here, Zn//V₃CrC₃T_x supercapacitors are fabricated. It is found that the partial replacement of Cr atoms for V atoms in V₄C₃T_x triggers an expansion of layer spacing of the MXene, the adsorption of Zn ions increases, and ion diffusion is promoted, which dramatically improve the capacitance, discharging potential, and cycle stability. Furthermore, in-plane Zn//V₃CrC₃T_x MSCs on paper demonstrate outstanding electrochemical properties and mechanical flexibility with an ultra-high area energy-density of 51.12 μW h cm⁻², long cycle life of 20 000 cycles (84.5% capacitance retention), and outstanding bendability of 10 000 cycles (80.2% capacitance retention). The areal energy density and flexibility outperform most of the reported in-plane flexible MSCs. Owing to the emerging materials design and consummate flexible nature of the scheme, it can inject fresh strength into the development of flexible electronics.