Lithium Battery Operating Temperature Optimization Based On Static Energy Storage System

With the rapid development of renewable energy and the rapid growth of the electric vehicle market,energy storage systems are becoming increasingly important.One of the most common forms of energy storage is electrochemical energy storage,in which lithium-ion batteries play an important role.However,lithium-ion batteries are subject to aging during use,which can reduce their performance stability and life span and significantly impact the long-term operation and reliability of energy storage systems.Among them,temperature is an important factor affecting the aging of lithium-ion batteries.Under the charging and discharging behavior of the electrochemical energy storage system,the internal electrochemical reaction will generate a large amount of heat,which will lead to the increase of the internal temperature of the battery and induce various aging mechanisms inside the battery,and may also cause safety accidents due to thermal runaway as a result of the rapid increase of temperature.Therefore,a reasonable and efficient thermal management approach is essential to maintain the performance of lithium-ion batteries.In this paper,based on the electrochemical-thermal coupling characteristics of lithium-ion batteries,we focus on battery aging and battery thermal management,and the main research contents and conclusions are as follows.1.A one-dimensional electrochemical-thermal coupling model was established based on Doyle and Newman’s pseudo-two-dimensional(P2D)and heat transfer models,and chargedischarge experiments were conducted.The obtained experimental results were compared with the model,and the simulation results were in good agreement with a maximum error of6.2%,which was related to the difference between the interpolation function of the opencircuit voltage of each electrode and the actual one,which ensured the accuracy of the model.2.Based on the existing model,an electrochemical-force-thermal coupling model was established,and the model validation was completed.The validation results found that the maximum local error did not exceed 5%,ensuring the accuracy of the model.Based on the aging model,the study of single cell batteries was carried out,mainly considering the influence of charge/discharge rate,ambient temperature and resting time on the relative capacity of the battery.It was found that the battery capacity decay was minimal at ambient temperature without resting time and low rate charge/discharge,and the influence of temperature on battery aging was also minimal;however,with the increase of rate,the internal temperature of the battery increased sharply,and the dominant factor of aging gradually changed from the loss of active material to the growth of SEI film,and the capacity decay was minimal at the ambient temperature of-10 °C.In addition,the effect of resting time on battery capacity decay under cycling condition was studied,and the appropriate increase of resting time can reduce the internal working temperature of the battery and decrease the battery aging.Through the above study,a way to apply pre-cooling to the battery to the internal temperature of the battery is proposed,and the study shows that the effect of pre-cooling temperature on increasing the relative capacity of the battery will be more obvious when the ambient temperature and the charge/discharge rate are high.Finally,based on the above numerical simulation results combined with the RSM model,the effects of single and multiple parameters on the relative capacity were analyzed,and the optimal precooling temperature correlation equation was fitted for calculating the optimal pre-cooling temperature.3.Based on the aging model,the battery aging and temperature rise during the charging and discharging of the battery at high and low rates under variable operating conditions were investigated.It was found that after the battery completed 2000 cycles,the maximum internal temperature of the battery increased by 26 °C and the capacity decay of the battery increased by 9% compared to the low rate.In addition,the operating temperature of the battery is optimized for the high-magnification charge/discharge capacity degradation,and two options of air cooling and liquid cooling are proposed to optimize the initial operating temperature of the battery and thus achieve a reduction in the operating temperature of the battery.Firstly,the air-cooled pre-cooling scheme is investigated.Under the corresponding maximum convection heat transfer coefficient,the air-cooling scheme can achieve the optimal precooling temperature for the initial operating temperature of each charge/discharge condition inside the battery,and the relative capacity of the battery is increased by 6.2%.Secondly,the use of liquid cooling can increase the cooling fluid temperature by 2.5 °C than the use of air cooling.Finally,comparing the economics of different cooling methods and increasing the rate,it is found that the energy consumption of liquid cooling is lower than that of air cooling;After the optimization of operating temperature,the discharge at high rate can both output more power and reduce the capacity decay,which is only 0.7% larger than the discharge at low rate and outputs 13.5 MWh more power.