Performance Study Of Fast-filled Lithium-ion Batteries

A kind of fast-charging lithium ion battery was intended to develop in this paper.The soft package of battery with 400 mAh was designed with LiCoO2 as cathode and graphite as anode,and the electrochemical performance,structure and morphology of electrode materials and the thermal effect of the battery were analyzed under the condition of large current charging.Effect of battery manufacturing process parameters on the performance of fast-charging battery was tested.In addition,the L333-graphite fast charge system was studied preliminarily and the influence of L333 crystal morphology on the fast-charge properties was mainly discussed.The change rule of electrochemical properties under the condition of large current charging was studied through the charging and discharging,ac impedance(EIS)and electrochemical cycle test.Results showed that there was larger polarization in the lithium ion battery in the charging process which affecting the fast charge performance of the battery seriously,so reducing polarization could improve the large current charging performance,while the smaller internal resistance could effectively reduce electrode polarization phenomenon.Therefore,different conductive agent with different proportion was adopted,and the production processes were studied to improving fast charge performance of battery.Results showed that the uniformity of the conductive agent with electrode active substance and the proportion had influence on the electrode resistance in the pulping process.The comprehensive performance was best with the content of conductive agent of 4%.The SEI film was more stable and corresponding resistance was smaller when in 0.2 C current and reduced the degree of polarization in a certain extent.And stable SEI film had a great influence on later cycle performance.The polarization was smaller and the better cycle stability of the battery charging in large current when the electrode material of surface density was smaller.So the capacity retention rate is still 80% after 1700 cycle times in 6C charging when the cathode surface density was 153 g/m2.The battery had the minimum polarization and resistance and the best cycle performance when the cathode material of compaction ratio was 3.6 g/cm3.The changes of the heat and specific heat capacity of the large rechargeable battery was tested through accelerating rate calorimeter(ARC).The results showed that the specific heat capacity was 2.02 J/(K*g)and surface temperature of battery rose 5?±0.1?.This part of internal heating could improve the efficiency of electrochemical reaction without security risk.The structure and morphology of electrode materials before and after the cycling were characterized by the X ray diffraction(XRD),field emission transmission electron microscopic analysis(TEM)and scanning electron microscopic(SEM).Results showed that the structure of cathode material had changed after 1000 cycle times under large charging current.There were defects and lack of lithium ion in the structure,(001)crystal plane spacing and cell size became larger and crystallization degree reduced.For the cathode materials,interplanar spacing became smaller and the lattice fringe became vague after cycling,and there was part of the amorphous phenomenon.The distribution of particle size of electrode materials has influence on fast charging performance of the battery.The charging performance of the cathode materials with different particle sizes was compared and analyzed and the results showed that reducing the material grain size was conducive to improve charging rate capability.The structure characteristic of anode materials also affected the performance of the battery.So the performance of lamellar graphite,spherical graphite and mesocarbon microbeads(MCMB)was studied.After the lamellar graphite anode was modification by KOH solution,the energy density of the battery increased to 128Wh/kg and circulation capacity remain at a rate of 80.3% after 1000 times.In addition,the fast-charging performance of lithium ion battery with L333 cathode material was researched in this paper.The results showed that the smaller size single crystal material had better rate performance.And capacity remained to 80 m Ah/g when energy density increased to 130wh/kg after 1000 times by using modified graphite.