Study on colloidal synthesis of ZnS nanospheres embedded in reduced graphene oxide materials for sodium-ion batteries and energy storage mechanism

With growing demands for large-scale energy storage, metal sulfides have received great attention due to their high theoretical capacity as anode materials for sodium-ion batteries (SIBs). However, metal sulfides have a problem of poor stability. Thus, it is important to find suitable solutions. In this work, uniform ZnS nanospheres (ZnS NSs) are synthesized through a wet chemical method. And then, by compounding with reduced graphene oxide (rGO), ZnS NSs@rGO are synthesized in which ZnS NSs are evenly distributed on rGO. When we evaluate the cycle performance, ZnS NSs@rGO deliver a high discharge capacity of 634.6 mA h g−1 at a current density of 0.5 Ag−1 after 1000 cycles. Through charge/discharge processes of in-situ XRD analysis, we confirm the sodiation/desodiation mechanism of ZnS NSs@rGO. •ZnS nanospheres (ZnS NSs) were synthesized by a colloidal method and then composite with ZnS NSs and rGO (ZnS NSs@rGO).•Real-time monitoring of phase transition revealed the sodium-ion storage mechanism of ZnS.•An appropriate combination of ZnS NSs and rGO led to outstanding cycle performance and cycle stability (634.6 mA h g−1 at 0.5 Ag−1 after 1000 cycles).