From Solid Electrolyte to Zinc Cathode: Vanadium Substitution in ZnPS₃

Abstract

Development of next generation batteries is predicated on the design and discovery of new, functional materials. Divalent cations are promising options that go beyond the canonical Li-based systems, but the development of new materials for divalent ion batteries is hindered due to difficulties in promoting divalent ion conduction. We have developed a family of cathode materials based on the divalent cation conductor ZnPS₃. Substitution of V for Zn in the lattice concomitant with vacancy introduction yields isostructural but redox-active materials that can reversibly store Zn²⁺ in the vacancies. A range of voltammetry and galvanostatic cycling experiments along with x-ray photoelectron spectroscopy support that redox is indeed centered on V and that capacity is dependent on the V content. The voltage of the materials is limited by the irreversible decomposition of the [P₂S₆]⁴⁻ polyanion above 1.4 V vs. Zn/Zn²⁺. The reversible capacity before anion decomposition is limited to half the vacancies and is due to the relative ratios of oxidized and reduced V centers. Such observations provide useful design rules for cathode materials for divalent cation based battery technologies, and highlight the necessity for a holistic interpretation of physical and electronic structural changes upon cycling.

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