Research On Lithium-ion Battery Parameters With Direct Current Impedance Spectroscopy

Since the 21st century,with the increasingly prominent environmental problems,electric vehicles have received more and more attention and support.Power lithium battery is the core of the power system of electric vehicle.When the lithium battery is in an environment or condition outside the standard,rapid self-heating or thermal runaway may occur and then fail,and other materials may be ignited,causing fire and endangering the personal and property safety of the user.Therefore,it is important to have technology that can diagnose on-board lithium-ion batteries,quickly obtain information about battery health,and give early warning when batteries are at risk of losing control.The capacity of a battery is usually used to determine the health of a battery,but the capacity of a lithium-ion battery is mainly represented by its internal resistance.Therefore,in order to diagnose and evaluate the health of a lithium-ion battery,the detection method of the internal resistance of a battery is essential.At present,many technologies can detect the internal resistance of power lithium batteries,such as using DC or AC pulse signals to detect lithium batteries.Among them,electrochemical impedance spectroscopy(EIS),which uses AC pulse signal,is the most recognized and the most potential method at present.However,it also has the problems of complex test system,long test time and high cost of test device.For electric vehicles,it is difficult to carry out real-time measurement and diagnosis of their power lithium batteries.In order to solve the above problems,this project is based on the equivalent circuit model of lithium ion battery,and uses a new method--DC impedance spectroscopy(DCIS)to study lithium ion battery.This method has the advantages of high accuracy of EIS,but also has the advantages of low cost,and can be tested quickly.Different from EIS,DCIS obtains internal parameters of lithium battery through time domain rather than frequency domain.This method can detect and collect electrolyte resistance(RΩ),solid electrolyte interface resistance(RSEI)and charge transfer resistance(Rct)respectively by controlling the pulse current width of battery discharge.According to these parameters,the health state of lithium battery is studied.This paper firstly compared the new method DCIS with the widely used EIS,verified the accuracy and effectiveness of DCIS,and then tested and analyzed the relationship between the aging degree of lithium batteries and the internal resistance.Then,we added the temperature variable to study the change rule of internal resistance affected by temperature,which made the detection method more accurate.Combined with the aging mechanism of lithium batteries and the causes of runaway,this paper proposed a detection method based on the electrochemical principle to detect the activation energy of lithium batteries by using DCIS to characterize the transport capacity of lithium ions at the internal interface of batteries,so as to give early warning to the internal thermal runaway of lithium batteries.In order to verify the feasibility of this method,Arrhenius formula and internal battery parameters detected by DCIS were used to obtain the activation energy of sample batteries under different aging degrees,and the performance of DCIS detection of activation energy was evaluated,laying a foundation for the subsequent practical application in electric vehicles.