Research On Low-temperature Bidirectional Pulse Charging Of Power Li-ion Battery

At low temperatures,the battery's electrolyte conductivity decreases,the charge transfer power is getting slow,and the solid electrolyte interface's resistance increases as well.As a result,the low-temperature charging polarization is obviously severe,and the cathode is prone to lithium deposition to form lithium dendrites,which severely affects the use of lithium-ion batteries at low temperatures.In order to alleviate the severe internal polarization and lithium ion deposition during charging,this thesis explores from the direction of improving the traditional charging mode of batteries.The commercial ternary lithium-ion battery is taken as the research object,and the difference between its electrochemical performance at low temperature and normal temperature performance is analyzed.The charging method,which is different from the conventional constant-current and constant-voltage charging method,is used to charge the battery.Compared with the constant-current charging in common use,the thesis investigates its effect on lithiumion battery charging at low temperature.The low-temperature performance of the-10 ? ternary lithium ion battery was tested using different pulse current parameters.The low-temperature charge capacity loss of the lithium ion battery and the internal state of the battery were evaluated.The influence of pulse current parameters on the low-temperature performance of the battery was obtained,and the best bidirectional-pulse charging strategy for ternary lithium-ion batteries at low temperature is determined.Using this charging strategy,the cycle capacity decay rate at low temperature 15 cycles is 0.507%.This is more than ten times lower than the battery capacity decay rate after a constant current charging cycle,and the available capacity can be maintained during a longer cycle.This charging strategy can also maintain battery stability.This thesis also conducts relevant experiments to verify the effects of bidirectional pulse charging on the polarization voltage and battery cycle stability during battery charging.We compare the differences in the structure and morphology of the electrode after the bidirectional pulse charging and the conventional constant current charging to explored the effect mechanism of pulse charge experiments.The bidirectional pulse charging method can reduce the polarization accumulation effect during the charging process,slow down the accumulation of lithium ion batteries at the cathode electrode interface,avoid negative phenomena such as reduction of active lithium due to lithium ion accumulation and formation of side reaction products,and improve the capacity of batteries at low temperature.Retention rate,enhance the cycle stability of the battery and extend the life of the battery.