Study On Fast Charge Method Of Lithium Iron Phosphate Battery Based On Optimized Polarization Voltage

In this paper,in the National Natural Science Foundation of China(No.51675258,51261024,51075372),the Science and Technology Program of Jiangxi Province(No.20141BBE50021)and battery manufacturing enterprises(Original Energy Technology(TianJin)Inc.)funded,for the commonly used charging method charging time is relatively long,the charging efficiency and the energy utilization rate are low,and the polarization phenomenon exists,which affects the charging speed and the battery life,and other issues to study.The subject research mainly includes the following contents:1.The OCV-SOC curves,charge-discharge characteristics,temperature characteristics and charge-discharge cycle life characteristics of lithium iron phosphate batteries in charge and discharge were studied.From the results of the study,it can be seen that there is a difference between the open circuit voltage of the battery during charging and discharging.The OCV-SOC curves are not exactly the same.When modeling,it is necessary to consider the influence of both on t he battery model parameters.From the results of the study,it can be seen that there is a difference between the open circuit voltage of the battery during charging and discharging.The OCV-SOC curves are not exactly the same.When modeling,it is necessary to consider the influence of both on the battery model parameters;charge and discharge early and late,the battery open circuit voltage changes faster,medium-term relatively slow;the greater the charging rate,the faster the battery voltage rises,the greater the discharge rate,the faster the battery voltage drops,and the greater the charge and discharge magnification,the greater the change rate of the terminal voltage,charge and discharge process the battery charge and discharge capacity less;the higher the charge rate,the faster the battery temperature rises and the cumulative phenomenon of heat as the charge;Lithium iron phosphate battery life is longer.2.It is found that the polarization voltage is similar to that of the charge and discharge process,and the ohmic internal resistance is different,and it is a dynamic value.Based on t his,the shortcomings of the traditional second-order RC battery model are improved,The improved model fully considers the effect of charge / discharge ratio,charge and discharge method,temperature and SOC state on the model.The polarization voltage relation is established by the second-order RC improved model,and the method of optimizing the polarization voltage is discussed.At the same time,the characteristics of the polarization voltage SOC interval,the charge and discharge polarization rate characteristics,the polarization time constant,the charging mode on the polarization voltage characteristics,the polarization voltage temperature characteristics and the polarization voltage capacity loss characteristics,the results It can be seen that the polarization voltage is relatively large at the SOC low end and the high value terminal,and the middle end is more balanced.When the charge and discharge current increases in multiples,the polarization voltage does not increase the corresponding multiple,but increases Multiple times gradually smaller,the time constant of the concentration of polarization at different SOC points is much longer than that of the electrochemical polarization voltage,and the former takes longer to eliminate.The polarization voltage has the effect of hysteresis and overshoot.The larger the polarization voltage,the higher the battery temperature The higher the charge capacity,the capacity loss increases with the increase of the polarization voltage.3.The SOC interval characteristics and the rate characteristics of the pendulum optimization polarization voltage are studied.It is found by experiment that when the stop time is within a certain value,the polarization drop voltage is not related to the SOC interval.The stopping time is within a certain range,And the polarization reduction voltage is approximately linear with the charge current.Based on this,the relationship between the stopping time,the charging current and the polarization lowering voltage is established.In addition,the results can be seen from the study,the choice of time to adapt to stop,to not affect the charging time efficiency,but also a good way to reduce the polarization voltage.4.The SOC characteristics and the rate characteristics of the polarization pulse are are studied.It is found that when the discharge pulse width is less than a certain value,the polarization drop voltage of the discharge pulse is independent of the SOC interval.The discharge pulse width is within a certain range,and the polarization drop voltage and the charge current are not Showing a linear relationship,but the phenomenon of irregular,based on t his,to establish the discharge pulse amplitude,pulse width and polarization drop the relationship between the three.In addition,the results obtained from the study,the discharge pulse amplitude and pulse width to choose the right,to not only affect the charging time efficiency,but also a good way to reduce the polarization voltage.5.The charging mode based on t he method of optimizing the polarization charging of lithium iron phosphate battery is proposed,that is,the stage of the current charging,optimizing the polarization current charging and the new stage of the three-stage charging mode.The experimental results show that the stage of the current charge can be a good optimization of the polarization voltage,charging more than the 0.5C standard charge capacity,while allowing the battery to enter the stage can accept high current charge;optimize the polarization voltage high current charging stage,By optimizing the polarization voltage energy efficiency to reduce the polarization voltage,thereby reducing the battery temperature and power loss,while filling more capacity;new stage to reduce the current charge,optimize the effect of polarization voltage significantly lower than the conventional phase Charging is better,while reducing the damage to the battery charge to extend the battery life.Finally,the method of optimizing the charging method of polarized voltage lithium iron phosphate battery is compared with the standard charging and variable current intermittent charging method.The experimental comparison shows that the proposed charging method is superior to the standard charging and variable current intermittent charging method,which improves the charging efficiency and the energy utilization rate,the charging time is greatly reduced,even higher than the efficiency,while reducing the charge to the battery damage.