Three-dimensional embroidered ball-like α-Fe2O3 synthesised by a microwave hydrothermal method as a sulfur immobilizer for high-performance Li–S batteries

Abstract

The practical application of lithium–sulfur (Li–S) batteries is restrained by the sluggish conversion kinetics of lithium polysulfides (LiPSs) and the consequent shuttle effect. Using polar metal oxides as affinity substances for LiPS adsorption is an effective method, but how to explore the adsorption ability on various faces of metal oxides has not been well investigated. In this work, 3D embroidered ball-like α-Fe₂O₃ was successfully prepared by a microwave hydrothermal method combined with calcination treatment as a sulfur host material to mitigate LiPS dissolution. Rich functional groups, graphene oxides (GOs), guide the (110) crystal plane growth. First-principles density functional theory (DFT) calculations were performed to study the different adsorption energies of LiPSs on the (110) and (104) crystal planes of α-Fe₂O₃, demonstrating that the (110) crystal plane facilitates the conversion of LiPSs and, thus suppresses the shuttle effect. The density of states (DOS) results indicated that the strong negative adsorption energy is mainly derived from the interaction between Fe–d, Fe–s and O–p orbitals. Furthermore, the Fe–S, C–S and S–O bonds as observed from the XPS results further verify the strong internal reaction between the α-Fe₂O₃ substance and LiPSs. Attributed to these benefits, the prepared α-Fe₂O₃/GO-S-25 electrode showed a high initial discharge capacity of 1417 mA h g⁻¹ at 0.1C. Even at a high current density of 2C, the cells delivered a high discharge capacity of 981 mA h g⁻¹. A high area specific capacity of 2.84 mA h cm⁻² was obtained with a sulfur loading mass of 3.36 mg cm⁻² after 100 cycles, indicating a good cyclic stability. This work provides a new idea for exploring the adsorption capacity of metal oxides with different crystal faces toward polysulfides and opens up the possibility for the commercialization of Li–S batteries.