Harmonizing Wide Voltage Window and High Energy Density toward Asymmetric All‐Solid‐State Supercapacitor

All-solid-state supercapacitors are known for their safety, stability, and excellent cycling performance. However, their limited voltage window results in lower energy density, restricting their widespread application in practical scenarios. Therefore, in this work, CC/MoO₃@Ti₃C₂T_x negative electrode and Mo₁Al₁-MnO₂/CC positive electrode materials are synthesized and prepared by electrochemical deposition co-coating and one-step hydrothermal methods, respectively, and assembled into an asymmetric supercapacitor (ASC) device based on the two electrode materials. The study reveals that the surface capacitances of the positive and negative electrodes are 1685.5 mF cm^-2 and 1134.98 mF cm^-2 correspondingly, with potential windows of both as high as 1.1 V. Surprisingly, the potential window of the all-solid-state supercapacitor assembled based on the two electrodes reaches 2.2 V, and the energy density reaches 0.44 m W h cm^-2, which is much higher than the performance indicators based on similar electrodes. The resulting excellent performance parameters are mainly attributed to the efficient synergy between the pseudo-capacitance effect of the MoO₃ film and the high electrical conductivity of the Ti₃C₂T_x sheets, as well as the great improvement of the intrinsic electron mobility and ion diffusion channel stability of MnO₂ by Mo and Al bimetallic doping.