Dual-Ion Pre-Intercalated Vanadium Oxides Derived from V4AlC3 MAX via HF-Free Synthesis for Aqueous Zinc-Ion Batteries

Abstract

Vanadium-based oxides have been considered potential cathodes for aqueous zinc-ion batteries due to their high capacity, multivalent nature, and low cost. However, their widespread application is hampered by intrinsic limitations, including low electrical conductivity and structural collapse during cycling. Conventional syntheses for MAX phase-derived electrodes often require highly corrosive hydrofluoric acid, posing significant safety and environmental concerns. Herein, this work proposes an innovative “HF-free etching and dual-cation pillar” strategy exploiting the amphoteric nature of Al. Controlling the NH3·H2O/HCl ratio, most of the Al layer in V4AlC3 MAX phase is selectively removed, while the residual Al3+ and the introduced Ca2+ co-stabilize the layers, forming a Ca2+/Al3+ dual-pillar structure within a hydrated vanadium oxide framework. This cathode delivers a high capacity of 428.9 mAh g−1 at 0.2 A g−1, a retained capacity of 169.5 mAh g−1 at an ultra-high current density of 10 A g−1, excellent long-term cycle stability with a retention of 90.2% after 7,000 cycles at 5 A g−1, unexpected low-temperature capacity of 70.8 mAh g−1 after 2,000 cycles at 5 A g−1 under −20 °C. This acid-base regulated cation pre-intercalation strategy offers a novel paradigm for designing MAX phase derived materials and high-performance cathodes for multivalent-ion batteries