Further elevating the energy density of aqueous zinc-ion hybrid capacitors toward batteries through voltage-window-expansion engineering

Although increasing the voltage window should be more effective by square rewarding than the specific capacitance for enhancing the energy density of zinc-ion hybrid capacitors (ZIC), the lack of an ideal cathode has hindered its realization. Herein, Ti₃C₂T_x-PPy/Bi₂S₃ composite was fabricated through voltage-window-expansion engineering, where Ti₃C₂T_x layers were covered by a tremella-like network of PPy through hydrogen bonds (-N—H···O- and -N—H···F-), and then compounded with pseudocapacitive Bi₂S₃. Due to the redox reactions of Bi₂S₃ and PPy at low and high potentials, the working voltage window of AZIC-TPB//ZnSO₄//Zn was elevated up to 2.1 V with low-cost electrolyte ZnSO₄, exhibiting a high energy density comparable to that of batteries (269.09 Wh Kg⁻¹ with a power density of 1564.73 W Kg⁻¹). Even at a power density of 12947.15 W Kg⁻¹, the energy density of AZIC kept as high as 107 Wh Kg⁻¹, far exceeding the common level. Density functional theory (DFT) calculation demonstrated the obvious electron transfer between Ti₃C₂T_x and PPy (or Bi₂S₃) and advanced conductivity, which promoted the redox reaction and facilitate the charge transfer in the electrochemical process. The strategy of voltage-window-expansion engineering here can be further extended to aqueous energy storage devices, offering a viable path to enhancing energy density. © 2023 Elsevier B.V.