Investigation of cobalt hydroxysulfide as a new anode material for Li-ion batteries and its conversion reaction mechanism with Li-ions

Multicomponent transition metal compounds (TMCs) with multiple anions have been actively researched due to their superior electrochemical properties. They transform into heterostructured materials with different bandgaps during electrochemical reactions. This study is the first to introduce metal hydroxysulfide as an efficient anode material for use in lithium (Li)-ion batteries (LIBs). A model compound, cobalt hydroxysulfide (CoOHS) was employed to explore certain conversion reaction mechanisms with Li-ions. The reversible conversion reaction mechanism of CoOHS can be described by the reaction: 2Co + 2LiOH + 2Li2S ↔ Co(OH)2 + CoS2 + 6Li+ + 6e−. Bare CoOHS showed a fast Li diffusion rate with high electrochemical kinetic properties, even at high current densities. To enhance its electrochemical properties, CoOHS was then successfully embedded within porous hollow carbon nanospheres using a facile two-step reaction process. In this respect, cobalt hydroxycarbonate was embedded within carbon shells using an in-situ precipitation process and transformed into CoOHS via a room temperature sulfidation process. The synergetic effect of the heterostructured interface originated from the high electrical conductivity of the double-anion transition metal compound and carbon shell, which contributed to the long-term cycle stability and superior rate capability of the newly designed anode material.