Designing cobalt-based coordination polymers for high-performance sodium and lithium storage: from controllable synthesis to mechanism detection

The coordination polymers (CPs) possessing beneficial molecular structure and functionality are essential to improve the applications in sodium-ion batteries (SIBs) and lithium-ion batteries (LIBs). This work reports cobalt-based coordination polymers with varied morphologies controlled by microwave irradiation. The metal ion and organic ligands are both active for reversible storage of Na or Li ions. When evaluated as negative electrode for both SIBs and LIBs for the first time, the unique porous flower-like Co-CP product delivers large reversible capacities of 554/1,064 mAh/g for SIBs/LIBs at 100 mA/g and long cycle life at small and large currents in 300–500 cycles. Based on the ex situ XPS spectra, in situ FTIR spectra and electrochemical probing, the energy storage mechanism of Co-CP during sodiation and desodiation is determined to be promising 10 electrons involved redox chemistry associated with both Co ions and C=O bonds of the organic ligands.