Boosting potassium and sodium-ion storage performance by in-situ self-assembly of a Co-based π-d conjugated coordination polymer on graphene nanosheets

To obtain anode materials with good electrochemical performances in both potassium ion batteries (PIBs) and sodium-ion batteries (SIBs), a Co-based π-d conjugated coordination polymer (Co-HHTP) is in-situ assembled on graphene (G) nanosheets using a facile one-step solvothermal method. The resulting Co-HHTP/G composite shows improved electrochemical performances over pure Co-HHTP. After 300 cycles of using as an anode of PIBs/SIBs for the first time, the reversible specific capacity of the Co-HHTP/G composite is found to be 381/277 mAh g−1 at 100 mA g−1. After undergoing 500 cycles at 1000 mA g−1, the material's reversible specific capacities remain at 234/164 mAh g−1 for PIBs/SIBs. The improved performances of the Co-HHTP/G composite electrode are due to the incorporation of graphene. This incorporation not only reduces structural stacking and promotes active site utilization, but also increases electrical conductivity and structural stability. According to the ex-situ X-ray photoelectron spectrometer (XPS) spectra, the Co-HHTP/G's energy storage mechanism throughout the process of potassisation/depotassisation is found to be linked to the aromatic rings presented in the organic ligands.