| With the vigorous development of a new round of global technological revolution and industrial transformation,new energy vehicles represented by electric vehicles have become the development trend of the automobile industry.Power battery is one of the key technologies of new energy vehicles,but the working performance of lithium-ion battery is greatly affected by ambient temperature,especially at low temperature,the practicability and safety of battery will be seriously degraded.In practical applications,the use of lithium-ion batteries at low temperature will have two major hidden dangers.First,the reduction of battery available capacity and the reduction of peak charging and discharging power will seriously affect the starting,acceleration and other power characteristics and cruising range of electric vehicles.Second,lithium deposition is prone to occur on the surface of the graphite negative electrode during the charging process of the battery in low temperature environment,which leads to irreversible capacity decay of the battery and accelerates the aging of the battery.If lithium metal is continuously deposited,lithium dendrites will be formed,and the continuous growth of lithium dendrites will pierce through the separator and cause a short circuit inside the battery,causing permanent damage to the battery,and even causing extreme safety accidents such as fire and explosion.Therefore,it is necessary to heat the lithium-ion battery in a low temperature environment.Compared with other heating methods,alternating current(AC)heating has the advantages of good temperature uniformity,fast heating speed and low cost,so it has great research and application significance.In this paper,the NCR18650 B lithium-ion battery is used to study the AC heating in low temperature environment,and develop a heating strategy to inhibit battery aging.The specific research contents are as follows:First,based on four commonly used equivalent circuit models,including first-order RC,second-order RC,first-order RQ,and second-order RQ models,the expression of the real part of the impedance is derived,and the heat generation model in the frequency domain is established.Then,a battery experimental platform is built to study the low-temperature characteristics of NCR18650 B lithium-ion batteries,including low-temperature discharge characteristics,open circuit voltage,electrochemical impedance spectra at different SOC and temperature,AC heating with different amplitudes and frequencies,and equivalent convective heat transfer coefficient,and so on.Based on the experimental data of electrochemical impedance spectroscopy,the parameters of the first-order RC,secondorder RC,first-order RQ and second-order RQ models are identified,and the polynomial models of the respective model parameters related to temperature and SOC are established.Combined with other physical parameters and boundary conditions of the battery,four electrothermal coupling models are established to simulate the AC heating process and compared with the experimental data.Based on the root mean square error of the simulated temperature and voltage with the experimental results,the model with the best accuracy is selected to study the heating strategy.Finally,based on the second-order RQ electrothermal coupling model,the lithium deposition model and the cut-off voltage are used as constraints to inhibit battery aging,and the relationship between the maximum current amplitude,the maximum heat generation power and AC parameters(amplitude and frequency)is studied.Combining the constraints,with the goal of shortening the heating time,a temperature-adaptive AC heating strategy is developed and verified.To verify the effectiveness of this heating strategy in inhibiting battery aging,80 cycles of heating experiments are performed.In addition,the heating strategy is applied to the battery module to study the temperature rise and temperature distribution of the batteries in the battery module to verify the applicability of the model and heating strategy. |
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