Initial development of multiple anionic transition metal hydroxy selenide—A novel negative electrode material for potassium-ion batteries

Multiple anionic anode materials for alkali metal-ion storage systems have received attention because of their remarkable electrochemical behavior in fabricating heterostructures after the initial cycle, which can provide an affirmative effect on ionic/electronic conductivity during cycling. Herein, for the first time, cobalt hydroxy selenide (Co(OH)Se) containing OH⁻ and Se²⁻ ions is prepared via a simple and facile liquid-phase selenization process using NaHSe solution, and its structural and chemical properties are studied by scanning transmission electron microscopy and X-ray photoelectron spectroscopy analyses. The electrochemical mechanisms of Co(OH)Se with potassium ions are investigated systematically through various ex situ and in situ techniques. The conversion reaction between Co(OH)Se and potassium ions can be proposed as the following equation; Co(OH)Se + 3 K⁺ + 3 e⁻ → Co + KOH + K₂Se ↔ ½ Co(OH)₂ + ½ CoSe₂ + 3 K⁺ + 3 e⁻. As an anode material for potassium-ion batteries, Co(OH)Se exhibited excellent cycling stability (414.7 mA h g⁻¹ at 0.1 A g⁻¹ after 60 cycles) and rate capability (194.7 mA h g⁻¹ at 5.0 A g⁻¹). Moreover, carbon-material composited Co(OH)Se@C delivered specific discharge capacity of 353.9 mA h g⁻¹ at 0.1 A g⁻¹ after 150 cycles. This study is a novel approach to the anion regulation strategy, which can be utilized for the synthesis of energy storage materials, electrocatalysts, etc.