Electrochemical Performance And Safety Evaluation Of High Power Lithium Ion Battery

The lithium ion batteries possess the advantages of good cycling performance, large energy density, high voltage plateau and so on, which have become the current domestic and international research hotspot in power battery field. In this paper, the electrochemical and safety performance of the high power lithium ion batteries was investigated systemically, which has important theoretical significance and practical value.The electrochemical and safety performance of the LiCoO2, Li(Ni1/3Co1/3Mn1/3)O2, spinel LiMn2O4 and olivine LiFePO4 batteries was investigated systemically in the paper using cyclic voltammogram(CV), electrochemical impedance spectroscopy (EIS), X-ray diffraction (XRD), thermogravimetric and differential thermal analysis (DTA-TG) and other experimental methods. The effects of the formation charge current and temperature on the electrochemical performance of lithium ion batteries were studied for the first time. The thermal stability of fully charged and discharged LiCoO2 cathode and graphite anode in nitrogen and air atmospheres was analyzed. The electrochemical and safety characteristics of layered Li(Ni1/3Co1/3Mn1/3)O2, spinel LiMn2O4 and olivine LiFePO4 high power batteries were extensively investigated and evaluated for the first time.Results show that the electrochemical performance of lithium ion batteries is influenced greatly by the formation charge current and temperature. The cycling performance of the batteries at high temperature becomes worse with increase of formation charge current and temperature. The coulombic efficiency of the first charge and discharge for the batteries reduced greatly with increase of the formation temperature. The thermal stability of electrodes are influenced by the environment atmospheres and state of charge(SOC) of electrodes. The thermal stability of materials reduced obviously with the rise of SOC. The prepared 18650 Li(Ni1/3Co1/3Mn1/3)O2/graphite high power batteries show excellent electrochemical and safety performance. The microstructure of Li(Ni1/3Co1/3Mn1/3)O2 materials and EIS of high power batteries changes with the increase in SOC of batteries. The discharge rate and temperature influences the discharge plateau obviously. The high rate discharge and cycling performance is affected by the batteries working temperature. The electrochemical, storage and safety performance of the 18650 spinel LiMn2O4/graphite high power batteries changes greatly with the increase of temperature and SOC of batteries, whereas the EIS of batteries varies little along of the SOC. The high power batteries show good rate discharge and safety performance, while which shows relatively bad cycling performance. The prepared liquid state soft pack carbon-coated LiFePO4/graphite high power batteries show well rate discharge and high power cycling performance. The lithium-ion diffusion coefficient in LiFePO4 electrode changes obviously with the increase of SOC. The solid electrolyte interphase(SEI) formation on the anode at the beginning of charge and the larger polarization of LiFePO4 electrode at the end of charge are the main reasons for the lower coulombic efficiency at the first charge and discharge of the batteries.In conclusion,the electrochemical performance of high power batteries using Li(Ni1/3Co1/3Mn1/3)O2 and LiFePO4 as cathode materials is better that that of the LiMn2O4 high power batteries. The structure stability of LiMn2O4 cathode material is worse than that of Li(Ni1/3Co1/3Mn1/3)O2 and LiFePO4 materials during the high power batteries cycling. The electrolyte oxidative decomposition reactivity on the Li(Ni1/3Co1/3Mn1/3)O2 cathode surface during overcharge is larger than that on the LiMn2O4 and LiFePO4 cathode surface.