High-performance cathode for aqueous zinc-ion batteries: a novel lithium vanadate heterojunction with excellent mixed lithium-ion and electron conduction derived from decavanadate-type polyoxometalate

Abstract

Mixed ion–electron conductors (MIECs), which have the ability to transport both ions and electrons, are widely applied in various electrochemical devices. Nonetheless, the development of MIECs with desirable multi-electron redox properties as electrode materials remains a challenge. In this study, a nanoscale Li_0.3V₂O₅/LiV₃O₈ (LiVO) heterojunction was synthesized using decavanadate-type polyoxometalates as a precursor. Under 98% relative humidity, LiVO exhibits excellent mixed lithium-ion and electron conductivity, with lithium ionic conductivity at 2.50 × 10⁻² S cm⁻¹ and electronic conductivity at 1.27 × 10⁻² S cm⁻¹ at 303 K, reaching maximum values of 1.67 S cm⁻¹ and 5.72 × 10⁻² S cm⁻¹ at 363 K, respectively. Owing to its structural features, mixed ionic–electronic conductivity, and multi-electron redox capability, LiVO shows excellent capacity performance and cycle stability as a cathode for aqueous zinc-ion batteries (AZIBs). The capacity reaches 374.9 mAh g⁻¹ with a capacity retention rate of 94.1% after 140 cycles at 0.2 A g⁻¹. At a high current density of 3 A g⁻¹, the capacity retention rate reaches 92.8% after 2000 cycles. Moreover, the by-product Zn₁₂(CF₃SO₃)₉(OH)₁₅·nH₂O undergoes reversible formation and decomposition during the charging and discharging processes, confirming a co-intercalation/deintercalation energy storage mechanism involving H⁺/Zn²⁺ ions. Significantly, opposite expansions (positive vs. negative expansion) occur on different crystal planes of the Li_0.3V₂O₅ phase within LiVO during the charging and discharging process. This research provides a new direction for high-performing MIECs toward practical applications.