Online Detection Method And Application Of Internal Resistance In Lithium-Ion Batteries

As a kind of energy storage carrier,lithium-ion battery has been widely used in electric vehicles,energy storage power stations and other places because of its advantages,such as high power density,high energy density,high energy efficiency,low pollution and strong cycle stability.However,there will be inconsistent capacity,inconsistent capacity attenuation,battery aging and other problems in the use of lithium-ion battery packs,which can lead to over-charge and over-discharge phenomena,and then cause the safety risk of thermal runaway.During the whole process of thermal runaway,the internal resistance of lithium-ion battery will change.Through online detection of internal resistance,the characteristics of early thermal runaway can be identified to give early warning and effectively prevent the occurrence of thermal runaway.In order to achieve high-precision detection of lithium-ion battery internal resistance and apply it to thermal runaway prediction,this paper studies the online detection and application technology of lithium-ion battery internal resistance.Firstly,the principle of AC injection method to measure the internal resistance of lithiumion battery is studied.By studying the chemical principle of lithium-ion battery,the structure,cathode material characteristics,working principle and internal resistance characteristics of lithium-ion battery are analyzed.The equivalent circuit model of the lithium-ion battery is studied in this paper,which is equivalent to the series of a voltage source and an impedance network.And the principle of AC injection method for measuring the equivalent internal resistance of impedance network is studied.Then,aiming at the problems of the traditional AC injection method,such as being susceptible to interference,requiring high accuracy of constant current source and low accuracy of internal resistance measurement,a new AC injection method based on the Second-Order Generalized Integrator(SOGI)is proposed to detect the internal resistance.In the process of injection current measurement and weak voltage signal extraction,SOGI is used to extract AC signals of specific frequency and generate orthogonal components,which is convenient for amplitude calculation.Both theoretical analysis and simulation study show that the SOGI-based AC injection method proposed in this paper can achieve accurate,rapid,and multi-frequency point equivalent series internal resistance detection of lithium-ion batteries.Finally,in order to verify the feasibility of the proposed scheme,the experimental platform of the online internal resistance detection system is built,and the application research of the internal resistance characteristics under the condition of simulated thermal runaway is carried out.The influence of detection frequency on the internal resistance is studied by experiments,and the optimal detection frequency is selected.On this basis,through the comparison experiment of high-precision resistance calibration,it is concluded that the absolute error of internal resistance detection error in the online monitoring system is about 0.1mΩ,and the relative error is less than 5%.By heating lithium-ion battery to simulate the early stage of thermal runaway,the internal resistance online detection system is used to record and analyze the internal resistance changes of lithium-ion battery during the whole heating process.It is found that the internal resistance increases dramatically when the internal temperature of lithium-ion battery reaches 85℃,so that the internal resistance changes of lithium-ion battery can be used as the basis for early warning of thermal runaway.The experimental results show that the proposed internal resistance detection scheme can be used to accurately predict the early thermal runaway of lithium-ion battery.