Electrochemical properties of yolk-shell structured cobalt hydroxy chloride-carbon composite as an anode for lithium-ion batteries

Heterojunction structures from transition metal compound (TMC) with multiple anions are considered promising to improve the electrochemical performance of anode materials for lithium-ion batteries. In this study, yolk-shell structures consisting of cobalt hydroxy chloride yolk and carbon shell (CoOHCl@C) were synthesized through simple infiltration and in-situ hydroxylation. The capillary force caused the dissolved cobalt chloride to permeate into the hollow carbon, and then, during the hydroxylation process, water molecules facilitated Ostwald ripening to centralize cobalt hydroxy chloride. This novel synthesis process is eco-friendly and economical because this method generates no by-product and effluent. Especially, the hydroxylation step could be easily applied in classic heating furnace. The synthesized cobalt hydroxy chloride formed a heterojunction structure of cobalt hydroxide and cobalt chloride crystals after the first discharge and charge step, and the nanocrystals induced a built-in electric field at the heterointerfaces to decrease charge transfer resistance and improve the rate performance. In addition, the applied carbon shell synergized with the heterojunction structure to improve the stability during repeated cycling. The CoOHCl@C anode exhibited stable cycle performance over 100 cycles at 2.0 A g⁻¹, wherein a discharge capacity of 665 mA h g⁻¹ was delivered at the 100th cycle, and its capacity retention was 91.5%.