The gamma vanadium oxide as a potential cathode material for rechargeable aqueous multivalent ion batteries

Abstract

The focus of this study is to investigate capabilities of gamma lithium vanadium oxide (γ-LiV<inf>2</inf>O<inf>5</inf>) to accommodate ions beyond Li⁺. The γ-LiV<inf>2</inf>O<inf>5</inf> has been tested electrochemically as a potential candidate for novel aqueous rechargeable batteries based on multivalent ions, namely Mg²⁺, Ca²⁺ and Al³⁺. The γ-LiV<inf>2</inf>O<inf>5</inf> is prepared by a simple solid-state reaction and characterized by XRD, SEM, HRTEM, FTIR, Raman, and Impedance methods, before and after CV cycling. Li⁺ ions can take octahedral cationic sites in the oxide lattice, which leads to γ ↔ γ′ reversible phase transition, but their subsequent occupation of tetrahedral sites incites irreversible γ ↔ ζ transition and capacity fade during extended cycling in LiNO<inf>3</inf>. In contrast, such irreversible behavior is not observed in Ca(NO<inf>3</inf>)<inf>2</inf> and Mg(NO<inf>3</inf>)<inf>2,</inf> where initial repeated cycling, including negative potentials, causes the CV growth. Although Ca²⁺ and Mg²⁺ ions weekly intercalate into the structure, as indicated by BVS analysis, the proton coinsertion, during early cycling stage activates the surface, causing large platelets to crumble and boosting pseudocapacitive-type redox behavior. This results in a high specific capacity in bivalent electrolytes, especially in Ca(NO<inf>3</inf>)<inf>2,</inf> which amounts to 128 mAh g⁻¹ at 1 A g^-1. Although the agglomeration of reduced particles leads to a decline in capacity over extended cycling, the capacity remains high after 150 cycles, reaching 74 mAh g⁻¹. In LiNO<inf>3</inf>, the identification of γ’ phase after long cycling within the stable potential window, together with agglomerated microplatelets (which are not crushed during initial Li⁺, thus limiting capacity to ≈ 27 mA hg⁻¹) is linked to the capacity fade. Furthermore, when cycled in Al³⁺ electrolyte, the material degrades quickly due to the dissolution process at the beginning of cycling. Therefore, the Ca²⁺ electrolyte is identified as the most promising for the development of rechargeable aqueous batteries with gamma phase V<inf>2</inf>O<inf>5</inf> cathode.