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Study of Gas Generation Behavior of Lithium Ion Battery

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Tutor: YinGePing
School: Harbin Institute of Technology
Course: Chemical Engineering and Technology
Keywords: lithium ion battery,SEI film,electrolyte,over charging
CLC: TM912
Type: Master's thesis
Year:  2012
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Abstract:
With the development of electric vehicles, the safety performance of lithium ionbattery becomes even more serious. In the process of charging and discharging, the gasproduced by the battery constituted one of the most harmful factors for battery security.On the basis of reviewed the safety performance of the battery, we carry out both MSand IR to characterize and discuss the generation of the gas in the lithium ion battery.In the bottle battery, we analyzed the production of gas in the various stages. Thestudy found that: in the formation stage, the gas produced from2.5V. EC in the voltagebegins to decompose solid material such as lithium carbonate generated, along with thegases of C2H2. At the same time, the electrolyte in the presence of H2O will result in theformation of H2and CO2gas. In the voltages of2.53V, CH4and C2H6was generated,it indicated the decompose of DEC and EMC to form the SEI film. However, the massspectrometry test of C2H4is the largest, indicating that the EC at this stage is still themain component of the film. Into voltage for33.5V, C2H4, CH4and C2H6production isroughly equal, indicating that three kinds of electrolyte components are beginning toplay a role in this voltage range for main range of the film. In the voltage range of3.54.2V, the amount of gas goes to the trend of slow growth, indicating that the SEIfilm has been basically completed in this voltage range.CaF2battery was designed for the infrared test of the gas in the battery. Fornegative, we have different electrolytic material to test gas generated by the SEI filmformed in the different electrolyte system. Found that the gases were mainly determinedby the electrolyte not by the electrode materials. We also investigated the film-formingin different temperature and current. We found that the lower temperatures, smallercurrents are beneficial to the film formation of the SEI film, leading to the generation ofmore gas.For the cathode, the IR test was carried out with different cathode materials indifferent electrolytes as well as different voltage. The study found that Li2CoO3,£¨Ni: Co:Mn=5:3:2£© ternary materials, high-voltage Li2CoO3under overcharge generated C2H5Fgases. The gas caused mainly by trace water in the electrolyte by the reaction betweenLiPF6with electrolyte. As the voltage increasing the amount of gas generated willincrease. With the electrolyte replacement for LiBOB, the gas production decreasedsignificantly. Li2CoO3coated with Al2O3, can improve the cycling performance of theelectrodes. When charging to high voltage, less phase transition would occur reducingthe generation of oxygen, thereby reducing the formation of other gases. The threematerials were significantly different from the amount of CO2, Li2CoO3>£¨Ni: Co: Mn= 5:3:2£© ternary materials, high-voltage Li2CoO3, reflected by the formation of gases,which reflects the oxidative ability of the electrode material for lithium ion battery.
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