Construction of a low-defect and highly conductive 3D graphene network to enable a high sulphur content cathode for high performance Li–S/graphene batteries

Abstract

The main hurdle in the practical exploitation of Li–S batteries lies in the difficulty in loading an adequately large percentage of sulphur in the cathode, without a detrimental impact upon the overall structural integrity over the charge–discharge cycles. Here we demonstrate that as much as 88.5 wt% of sulphur could be effectively coupled with high-conductivity graphene (HCG) powder, using a simple one-step ball milling process to obtain sea sponge-like composites wherein sulphur was effectively accommodated within a framework of three-dimensional (3D) networks of interconnected graphene flakes. On the basis of the extremely low defect density, high C/O ratio (24.64) and ultrahigh electrical conductivity (2.05 × 10⁵ S m⁻¹), the HCG networks provided 3D super-highways for ionic and electronic transport, while enabling self-healing to help maintain structural integrity. The mechanical alloying effects resulted in S incorporation into the graphene lattice, thus helping to retain polysulphides within the cathodes. This resulted in a very effective utilization of sulphur in the cathode, so that Li–S/HCG battery cells were realized to deliver a remarkably high full-cathode capacity, a high areal capacity and energy density, an excellent rate-performance and a high cycling stability (4.78 mA h cm⁻² and 1642 W h kg⁻¹ at a sulphur load of 6.0 mg cm⁻²; 555.7 mA h g⁻¹ at 5C; 519 mA h g⁻¹ at 2C after 500 cycles).