The Failure Research Of LiNi_0.5Mn_0.3Co_0.2O₂ Power Battery Based On The Internal Resistance Changing

As new energy power source,the performance of automobile power battery directly related to the endurance mileage car,degree of life and promote of the car.Even if the initial electrochemical parameters of the battery was the same,but in the process of actual operation,due to the electrochemical parameters of each battery was not the same change trend so that charging and discharging current would appeared deviation,and the different regions of battery also had different temperature.So these differences would cause the inconsistency of the battery.Based on the battery internal resistance,the factors of NCM power cell internal resistance,the effect of charging terminal voltage on battery and the effect of single cell consistency on the battery pack are studied.(1)The change trend of internal resistance by different discharge rate,depth of discharge,overcharge and owe rechargeable of battery was studied in this paper.The results showed that,reducing the discharge current was beneficial to reduce the internal resistance change and attenuation in the range of discharge calibrated current for the battery.There was no surge of internal resistance when the depth of discharge was 50% and 80%.The change of internal resistance was not obvious in the previous cycle when the depth of discharge was 100%,but there was mutation at the late stage of cycle.So the life of the cycle could extend if discharge depth of the battery remained below 80%.(2)Charging and discharging of at 0.5C rate was tested by setting different maximum voltage(4.2 V to 4.6 V and voltage interval was 0.02 V)to simulate the overcharge phenomenon of monomer battery as battery module using.The cycle life of battery were all under 500 times in the range of 4.3 ~ 4.6 V.The capacity had great attenuation at the later cycle.Even many cells appeared 0mAh.The anode had crack and the cathode material showed irreversible phase change.In the range of 4.2V to 4.3 V,the cycle life reached more than 500 times.And in 4.22 V to 4.24 V range,there are still more than 90% retention capacity after 600 cycles.So increasing the upper limit of charging voltage moderately could increase the discharge capacity and the cycle life of battery.(3)A kind of monomer battery group was designed with a convenient method that the sin gle battery can be taken off for a separate test.Unequal capacity batteries with the same intern al resistance and voltage,unplaced power management system,were selected to get a cycle test at 1C.The monomer battery did not reach 100% of its discharge depth during the cyclingprocess,when the battery group cycled to 573 rd still with 80% capacity retention ratio,while the capacity retention ratio for the monomer battery as the compared dropped to 80% only after 346 cycle times.That is to say,the monomer battery had made it a priority to reach 80% capacity retention ratio.The batteries were paired up into diversity groups by different voltage and resistance,but the difference change between internal resistance was big,affecting the bat teries performance.Therefore,the idea of through internal resistance,voltage and capacity co mbined with charge and discharge curve to sort groups of battery were put forward,which eff ectively improved the lifetime for the battery groups.