Study On Critical Process Parameters And Electrochemical Performance Of LiMn₂O₄ Power Battery

Lithium secondary batteries are the new types of cleanliness and recyclable power source.In comparison with conventional battery systems,Li-ion battery possesses intrinsic advantages of high voltage,high energy density,low self-discharge rate and long cyclic life,and is now considered as the competitive power sources for portable electronic equipment,such as communication device,computer and digital electronic products,et al.and then develop toward electric vehicles,hybrid electric vehicles and high-efficient energy storage systems.A big science and technology battle about the innovation of automobile energy resources is brewing.The research, exploitation and industrialization of electric vehicle are becoming the attentive issue in all over the world.The key problem of developing new energy resources vehicle is the batteries.In this paper,the manufacture technology of lithium-ion power battery was introduced,and the difficulties in the technics research were fully studied.The research works focus on the ratio of cathode active material in all cathode materials, balance coefficient of capacity about positive and negative electrodes,compacted density of positive and negative electrode materials,electrolyte content and formation process.At the same time,the electrochemical performance and the safety of 4860110 type lithium ion power battery were studied in detail.The effects of the ratio of cathode active material in all cathode materials on discharge capacity,internal resistance and the capacity retention ratio after cycles were studied,the results showed that the optimal ratio of active material was 92wt.%.According to the process ability of practical production,it has been found that the optimal balance coefficient of capacity is in the range of 1.10 to 1.15 based on the discharge capacity and safety performance of power lithium ion battery.Considering the discharge capacity and rate discharge ability of power lithium ion battery,the optimal process condition is suggested that the compacted density of LiMn₂O₄ is 2.7 g·cm^-3,the compacted density of graphite is 1.55 g·cm^-3 and assembly space is 92%～95%.The relationship of the discharge capacity,internal resistance and the capacity distribution with different electrolyte content was analyzed and discussed,results showed that the optimal electrolyte content was 4.0 g·Ah^-1. The effects of formation procedure on the discharge capacity,internal resistance, charge-discharge efficiency and cycle performance of battery were studied and the optimal formation procedure consists of a dual-current charging,with 0.05C for 2h followed by 0.1C to 3.95 V.Under this formation procedure,the capacity activation of battery was enhanced and the evolution of gases was reduced.The electrochemical tests of 4860110 type power lithium ion battery showed that discharge capacities at the rates of 0.2C,0.5C and 1C were all beyond 20 Ah,and the output power density is 140 W·kg^-1 and the specific energy is 91.5 Wh·kg^-1 at the rate of 1.5C.Besides,0.3C（6A） discharge capacity retains about 91.6%after 180 cycles. Therefore,the storage capability and safety performance of as-prepared power lithium ion battery are better than the standard of QC-T 743-2006 for electric vehicles.