Study On Preparation And Modification Of Lithium Cobalt Carbonate Anode Materials

Graphite as a anode material of lithium ion battery has been widely applid.However,its lower capacity and density is difficult to meet the new generation of lithium ion batteries.Therefore,there is an urgent need to develop an anode material for higher mass and volumetric energy density.As a typical conversion anode material,cobalt carbonate is rich in natural resources and low in production cost.Compared with graphite anode,the electrochemical performance of cobalt carbonate is more excellent,and its safety is better.However,there are some problems in the cobalt carbonate anode,for example,the conductivity is poor,and the volume change is serious in the process of charging and discharging.Research shows that the cobalt carbonate with nanoporous structure can significantly improve the electrochemical properties of carbonate anode materials.But the complex preparation method and high cost is not conducive to the commercialization of carbonate and the actual promotion.In this paper,CoCO₃ was synthesized by the hydrothermal method.Different structure and morphology of CoCO₃synthesized under various reaction conditions and reaction time.The CoCO₃ with best performance was selected to further modify by Zn doping and composite with conductive material to further improve its electrochemical performance.At last,high density Zn_0.12Co_0.88CO₃/CNT composite anode material was obtained.?1?Through regulation of cobalt source and reaction time,three different microstructures were prepared?water drop,short rod and mixed type?.The charge/discharge and cycle performance of CoCO₃ materials are tested.It is found that CoCO₃ anode material with drop type structure show best electrochemical performance.The CoCO₃/graphene composite at 0.1 C current density after 50 cycles still have the capacity of 642.1 mAh g^-1,and the capacity of CoCO₃ without graphene is only368.4 mAh g^-1.The graphitic structure can relieve the stress of the volume change of particles during to a certain extent,which also can increase the electron and ion transmission rate to improve the electrochemical performance of CoCO₃.?2?Zn doped CoCO₃ were prepared by adjusting Zn and Co molar ratio to control the Zn/Co.The results show that when molar ratio of Zn and Co is 0.3:0.7,the doped product exhibits excellent cycle and rate performance.The zinc ions doping can improve the lithium ion conductivity and conductive electrode.?3?In order to further improve the rate performance of Zn doped CoCO₃,Zn_0.12Co_0.88CO₃/CNT composite was prepared and its capacity at 2 C capacity can reaches 610.7 mAh g^-1,while the capacity of CoCO₃ without doping and CNT coating is only 232.2 mAh g^-1.The excellent electrochemical performance of Zn_0.12Co_0.88CO₃/CNT is mainly due to the zinc doping and carbon nanotube coating,which improves the electrical conductivity and lithium ion diffusion.The carbon nanotube in Zn_0.12Co_0.88CO₃/CNT as excellent electronic conductor not only can effectively reduce the charge transfer resistance,but also can play an effective buffer to suppress the collapse of Zn_0.12Co_0.88CO₃ particles du ring the charge/discharge process.