Preparation And Electrochemical Performance Of Co₃O₄/CArbon Composite As Anode Materials For Lithium Ion Battery

Co₃O₄ has a higher theoretical specific capacity(890 mAh g^-1)as a negative electrode material for lithium ion batteries.However,during cycling,there is a large volume effect and poor conductivity.Controlling morphology,nanocrystallization,and carbon composites can reduce volume effect and increase conductivity of Co₃O₄material.In this paper,Co₃O₄ with special morphology was synthesized by solution combustion method and hydrothermal method to suppress the volume effect and improve the contact between active material and electrolyte.Using the ionic liquid as a carbon source,the prepared special morphology Co₃O₄ was coated by carbon to further improve the conductivity.The effect of carbon recombination and morphology control on the electrochemical performance was studied.The details are as follows:?1?The mesoporous Co₃O₄/C composite material was synthesized by the mixed fuel solution combustion method?SCS?.During the combustion reaction,with the release of gas and the growth of Co₃O₄ particles,the residual carbon and Co₃O₄ form a porous network structure,which can significantly improve the rate performance of Co3O4/C composites.After 200 cycles,the reversible discharge/charge specific capacities of Co₃O₄/C composite materials at 1 C,2 C,3 C,and 5 C current densities are 1120/1025,965/930,889/837,and 772/706 mAh g^-1,respectively.?2?Using ionic liquid?[BMIm][N?CN?₂]?as the carbon and nitrogen sources,the nitrogen-doped carbon-coated Co₃O₄ composite material?NDC/Co₃O₄?was synthesized by solution combustion.NDC/Co3O4 is nano-scale particles,and nitrogen-doped carbon is evenly coated on the surface of Co3O4 particles.This structure suppresses the volume effect of Co₃O₄ as well as increases its conductivity during charging and discharging,and significantly improves the cycle stability and rate performance.NDC/Co₃O₄ has an initial specific capacity of 1365.1 mAh g^-1 when used as an anode material for lithium ion batteries.When the charge and discharge rate is 5C,it still has a capacity of 400 mAh g^-1,and can be stably maintained at 700mAh g^-1 when returning to 2C for long cycling,which is much higher than the performance of the sample without nitrogen-doped carbon modification.?3?Nitrogen-doped carbon-coated graded Co₃O₄ nanosheets?NDC/Co₃O₄ NS?was synthesized by ionic liquid hydrothermal method.The prepared NDC/Co₃O₄ NS consists of hexagonal nanoplates with different orientations and thicknesses of 50-100nm.As the anode of the lithium ion batteries,NDC/Co₃O₄ NS has an initial discharge capacity of 1281.4 mAh g^-1 at 445 mA g^-1,and maintains a high reversible capacity of929.4 mAh g^-1 after 50 cycles,more higher than unmodified Co₃O₄ nanosheets(230mAh g^-1).The excellent electrochemical performance can be attributed to the hierarchical structure and the nitrogen-doped carbon coating,which can shorten the ion transmission distance and good conductivity.