Complexation-assisted polymerization for the synthesis of functional silicon oxycarbonitride with well-dispersed ultrafine CoS as high-performance anode for lithium-ion batteries

The silicon oxycarbonitride with ultrafine CoS (CoS@SiOCN) spherical composite as anode material for lithium-ion batteries is synthesized through the pyrolysis of the polymerized product of Co(II) with Schiff-base ligand of aminoethyl-aminopropyl-trimethoxy silane and salicylaldehyde and the simultaneous in-situ formation of CoS. Owing to the molecular level complexation of Co(II) and the subsequent in-situ sulfidation, the generated ultrafine CoS is well-dispersed in SiOCN sphere. Compared with the Co@SiOCN and SiOCN anodes, the CoS@SiOCN anode displays the highest initial reversible capacity of 834 mAh g −1 with an initial Coulombic efficiency of 68.5% at 200 mA g −1 . At 1000 mA g −1 , the CoS@SiOCN anode still exhibits outstanding cycling performance, delivering a reversible capacity of 536 mAh g −1 after 800 cycles with a retention of 80.4%. The full cell with pre-lithiated CoS@SiOCN anode and LiFePO 4 cathode delivers an initial discharge capacity of 146 mAh g −1 at 0.2 C and maintains 115 mAh g −1 at 0.5 C after 50 cycles. The outstanding electrochemical performances can be attributed to the structure of SiOCN with the active SiO x C 4- x (0 ≤  x  ≤ 4) nanodomain and free carbon conductive network, and well-dispersed CoS. The electrochemical analysis indicates both CoS and in-situ formed Co nanoparticles at the high redox voltage can contribute to the electrochemical properties .