Dissertation
Dissertation > Industrial Technology > Electrotechnical > Independent power supply technology (direct power) > Battery

Electrochemical and Safety Performance of High Rate LiFePO4Battery

Author ZhongHaiJiang
Tutor TangYouGen; LuZhouGuang
School Central South University
Course Applied Chemistry
Keywords LiFePO4 Li-ion battery high rate electrochemicalperformance safety performance
CLC TM912
Type Master's thesis
Year 2012
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As the lithium ion battery cathode materials, Olivine lithium iron phosphate(LiFePO4) has been investigated extensively due to several excellent properties, such as outstanding cycling performances, low cost, safety, environment-friendly and so on. This paper firstly studied properties of three types of LiFePO4cathode materials, and chose the cathode material owning the best properties to manufactured LiFePO4battery. With this sample as LiFePO4cathode materials, the effects of cathode materials, cathode surface density, conductive agent amount and electrode structure on the electrochemical performance were studied in this paper. The safety of high power LiFePO4batteries were also investigated and analyzed.(1)The effects of LiFePO4cathode material on battery properties were investigated by comparing three kinds of commercial LiFePO4cathode materials. The results showed that sample B had better processing and electrochemical performances and rate property, which delivered a discharge capacity of135mAh/g at a rate of0.2C, and sustained97.2%capacity after400cycles. Consequently, sample B was chose as the cathode material of LiFePO4battery in this study.(2)The effects of process design on rate performance were studied in terms of cathode surface density and the content of conductive agent and structure design. It was found that the battery had the best rate capability, as the cathode surface density and the amount of conductive agent are2.5g/dm2or2.8g/dm2and4.0%, respectively. Compared to the structure of unipolar, the internal resistance of the battery with bipolar structure was decreased by50%to about14mΩ, and the surface temperature of the battery kept constant relatively under the charge at5C and discharge at15C, which could meet the requirements of charge and discharge. The optimized battery showed an advanced high rate discharge capacity, which has96.6%and86.1%of discharge capacity of1C at20C and30C, respectively. And the capacity retention rate of the optimized one was86.3%at the300th cycle of1C charge and10C discharge.(3)The safety of LiFePO4battery made in this study was also tested. It could be seen that the battery without optimizations had exploded and burn at3C/10V overcharge, and the surface temperature of the battery reached to137℃. However, the optimized battery was worked safely under the same condition. Thus, the safety performance of optimized battery was improved owe to the advancement of high rate performance. The optimized battery also didn’t explode under heat eoncussion, crush, puneture and short circuit experiments, which proved that the optimized battery could satisfy the safety requirement of lithium ion power batteries.

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