Cobalt Vanadate (Co3V2O8) Hollow Microspheres as a Polysulfide Adsorption and Conversion Catalyst for Li–S Batteries

Abstract

A lithium–sulfur battery (Li–S) is considered as one of the most suitable emerging energy storage technologies for electric vehicles (EVs) due to its higher specific capacity, energy density, and low cost. However, the dissolution of lithium polysulfides (LiPS) in an electrolyte causes a huge shuttle effect, which results in poor cycle life and rate performance. Herein, Co3V2O8 (CVO) hollow microspheres have been prepared by the solvothermal method and used as catalyst additives to the sulfur electrode (cathode host). It was found that CVO acts as a bifunctional additive, the vanadium and oxygen sites immobilize the LiPS through V–S and Li–O interactions, while the cobalt site facilitates the rapid conversion of long-chain LiPS into short ones (Li2S2/Li2S). Furthermore, the hollow microspheres act as a sulfur reservoir and can confine (encapsulate) more LiPS during the electrochemical conversion process, thus inhibiting the shuttle effect. In this work, the chemical adsorption and polysulfide conversion ability of CVO is corroborated by XPS and cyclic voltammetry studies, respectively. Even at a higher sulfur loading of 5.4 mg cm–2, CVO containing the Li–S cell (denoted as S@CVO/CNT Vs Li) demonstrates an initial discharge capacity of 694 mAh g–1 at 0.5 C, and after 200 cycles, the observed capacity is 566 mAh g–1, which amounts to 81% capacity retention. Similarly, the cell delivers an excellent rate capability of up to 5 C rate. At the 1 C rate, the cell shows an initial discharge capacity of 904 mAh g–1 (S-loading of 3 mg cm–2) and 692 mAh g–1 after 300 cycles with 77% capacity retention.