A review of the use of metal oxide/carbon composite materials to inhibit the shuttle effect in lithium-sulfur batteries

Lithium-sulfur (Li-S) batteries are among the most promising next-generation electrochemical energy-storage systems due to their exceptional theoretical specific capacity, inexpensive production cost and environmental friendliness. However, the poor conductivity of S and Li₂S, severe lithium polysulfide (LiPS) shuttling and the sluggish redox kinetics of the phase transformation greatly hinder their commercialization. Carbonaceous materials could be potentially useful in Li-S batteries to tackle these problems with their high specific surface area to host LiPSs and sulfur and excellent electrical conductivity to increase electron transfer rate. However, non-polar carbon materials are unable to interact closely with the highly polar polysulfides, resulting in a low sulfur utilization and a serious shuttle effect. Because of their advantages of strong polarity and a large number of adsorption sites, integrating transition metal oxides (TMOs) with carbon-based materials (CMs) increases the chemical adsorption of LiPSs and electrochemical reaction activity for LiPSs. The working principles and main challenges of Li-S batteries are discussed followed by a review of recent research on the ex-situ and in-situ synthesis of TMO/CM composites. The formation of TMO/CMs with the dimensionalities of CMs from 1D to 3D are then reviewed together with ways of changing their structure, including heterostructure design, vacancy engineering and facet manipulation. Finally, the outlook for using TMO/CMs in Li-S batteries is considered.