Study On Impedance Model Of Lithium Ion Battery

Lithium ion battery is one of rechargeable batteries that have already been applied widely.Impedance model of lithium ion battery is established and analyzed by a method of electrochemistry in this research that aims at providing theory basis and method for detection of ohmic resistance and polarization resistance of battery.Impedance model contains a lot of information that can indicate performance of battery.Therefore,establishment of accurate impedance model is very important.Lithium ion battery of LiCoO2 as positive electrode material is chosen as the research object in this paper.Through the analysis of internal structure and work principle of battery and combinatio,with electrode dynamics theory,the equivalent circuit of electrode based on electron movement theory is adopted and the impedance model of battery is established,with other apartment considered.Electrochemical impedance spectroscopy as an experiment method is adopted in this research . Measuring the electrochemical impedance spectroscopy of battery through electrochemical instrument and amending the impedance model according to the character of impedance spectroscopy curve and frequency response of equivalent element,which makes the curve character of the amended model as similar as the character of measurement curve . Impedance spectroscopy data is analyzed and fitted by special electrochemical software.Therefore,the conclusion is drawn through the above research,which the impedance model of battery is series connection of two parallel connections of double-layer capacitance and polarization resistance , ohmic resistance and a parallel connection of inductance and resistance.Based on the impedance model , with the analysis of impedance spectroscopy data of battery at different state of charge,the conclusion is drawn,which the value of ohmic resistance is reduced with increase of battery's state of charge,and the value of polarization resistance is increased with increase of battery's state of charge . With the analysis of impedance spectroscopy data of different circulation period of battery,the conclusion is drawn,which the value of internal resistance is increased with increase of used count and with reduction of capacitance.Impedance model of frequency domain is equivalent to impedance model under direct current impulse through the method of equivalent circuit,by which the element that is difficult to detect under direct current is transformed to capacitance,the detection of polarization resistance and ohmic resistance by measuring the zero-response of battery is realized.