ZnNi_xMn_xCo_{2–2 x}O₄ Spinel as a High-Voltage and High-Capacity Cathode Material for Nonaqueous Zn-Ion Batteries

Nonaqueous Zn-ion batteries are regarded as one alternative for Li-ion batteries. Such batteries not only afford attractive attributes of cost, but also embody the advantages of the high-specific capacities of Zn anodes, as well as the wide potential window of nonaqueous electrolytes. To fully exploit these advantages, improved cathode materials are highly desired. In this manuscript, a new series of spinels, ZnNi_xMn_xCo_{2–2 x}O₄, are reported as cathode materials for nonaqueous Zn-ion batteries. Full cells constructed using this new spinel (x = 1/2) as a cathode paired with a metal anode showed capacities over 200 cycles of 174 mAh g⁻¹ and an open circuit potential of 2.05 V. The battery exhibits an energy density of 305 Wh kg⁻¹, which is the highest energy density yet reported for a Zn-intercalation cathode. The data show that the Zn²⁺ ions reversibly intercalate into the spinel structure during the charge/discharge processes, a compositional transformation directly correlated with a multiply reversible conversion between Co⁴⁺/Co³⁺, Ni⁴⁺/Ni³⁺/Ni²⁺, and Mn⁴⁺/Mn³⁺ oxidation states within the lattice. The data suggest that Mn, Ni cosubstitution for Co in ZnCo₂O₄ is an efficient method to facilitate Zn-deintercalation and enhance discharge capacity, which may provide some guidelines for designing more attractive multivalent cathodes materials.