Interlayer and O-vacancy engineering co-boosting fast kinetics and stable structure of hydrated sodium ammonium vanadate for aqueous zinc-ion battery

Abstract

The electrochemical properties of layered vanadate cathode materials for aqueous zinc ion batteries (AZIBs) are still restricted by sluggish reaction kinetics, low conductivity, and poor structural stability. Herein, the Na-doped hydrated NH₄V₄O₁₀ (NaNVOH) with different contents of interlayered H₂O/NH₄⁺ and O-vacancies are obtained with optimized electrostatic interaction between [VO_n] framework and H₂O/NH₄⁺/Na⁺ as well as Zn²⁺ diffusion kinetics. Experimental evidence and theoretical calculations show that the optimal interlayered H₂O/NH₄⁺ and more O-vacancies in NaNVOH (NaNVOH2) reinforce the bond strength, narrow the band gap, and promote Zn²⁺ diffusion coefficients. The reduced H⁺ insertion hinders cathode/electrolyte interfacial side reaction, ensures sufficient Zn²⁺ diffusion coefficients at voltage range of 0.6–0.2 V. Meantime, the high electrochemical reversibility of Zn₃(OH)₂V₂O₇·2H₂O by-product is also validated by in-situ and ex-situ characterizations. As a result, the NaNVOH2 cathode shows a high specific capacity (519 mAh g^-1 at 0.5 C, 1 C = 500 mA g⁻¹), good rate capability (236 mAh g^-1 at 10 C), and a stable cycling life (without obvious capacity decay over 3000 cycles at 15 C). This study is of great significance for developing high-performance layered vanadate toward the practical application of AZIBs.