Dual Strategies of Na+ Electrolyte Additives and Dendrites Protective Ti3C2TX‐MXene/Zn Anode with 2D MXene Nanosheet Encased Niobium Pyrophosphate (NbP2O7) Composite Binder‐Free Cathode for Stable Zinc‐Ion Storage

Utilizing a straightforward drop casting technique, a novel NbP₂O₇/Ti₃C₂T_X-MXene cathode is developed. The dendritic growth on Zn is regulated by the dual strategies of the MXene coating and the Na⁺ electrolyte additive. The solid-state zinc-ion capacitor displays excellent electrochemical cycling performance over 38 000 charge–discharge cycles.

Abstract

Zinc-ion capacitors (ZICs) are promising next-generation energy storage systems (ESS) owing to high safety, material abundance, environmental friendliness, and low cost; however, the energy density of ZICs must be improved to compete with lithium-ion batteries (LIBs). Here, the study implements three strategies to enhance the electrochemical performance and manage dendritic growth on Zn anodes, including crafting a highly efficient redox electroactive niobium pyrophosphate (NbP₂O₇)/Ti₃C₂T_X-MXene binder-free cathode, incorporating a NaClO₄ additive electrolyte, and applying a protective Ti₃C₂T_X-MXene layer on Zn anode. The cathode facilitates rapid Zn²⁺ ion diffusion and a stable host structure. An electrostatic protection layer formed in additive electrolyte and MXene layers regulates the uniform distribution of the electric fields and supports the equalization of nucleation sites. These results are supported by density functional theory (DFT) calculations. The ZICs display an excellent specific capacitance (113.3 F g⁻¹ at 1.5 A g⁻¹) in aqueous additive electrolytes. The flexible solid-state ZICs exhibits a volumetric capacitance of 865.05 mF cm⁻³, and an energy density of 0.347 mWh cm⁻³ at 2.29 mW cm⁻³ along with capacitance retention of >100% over 38 000 charge-discharge cycles.