Dielectric Spectrum Measurement System And Application Research For Cathode Materials Of Lithium-ion Batteries As Function Of Temperature In A Wide Range Of Frequency

Lithium batteries play a key role in emerging energy promotion,but there are still many probl ems in practical applications.Battery status,performance and battery aging,moisture,life and ohterissues needs to focused.The internal structure of the battery can not be directly observed,it is ne cessary to measure the characteristics of various physical quantities by macroscopic measurement,and to analyze the internal microstructure characteristics.The measurement data of the variable te mperature broadband dielectric spectrum has a great reference significance for understanding the i nternal ion transport mechanism of lithium batteries.It is important role in optimizing the lithium b attery about making process.In this project,a set of variable temperature broadband dielectric spectroscopy measurement s ystem is built and applied in the dielectric spectrum measurement of the lithium manganate ion bat tery cathode material made by the research group.The frequency range is 20Hz-1MHz and the tem perature range is 30°C-75° C.In the measurement system,we use the impedance analyzer,PID con troller and the insulation furnace cavity,respectively,PC side linking the GPIB interface and serial port connection,and make their own corresponding control procedures to achieve the PC side aut omatically complete the entire frequency and temperature range Measurement process.This paper includes the following sections:Firstly,the dielectric loss frequency characteristics are discussed by using the related theory of dielectric physics,and we get the relationship between complex dielectric constant and the frequency,including the response of the time domain and frequency domain for the dielectric polarization,and the dielectric polarization relaxation,the complex permittivity and its influencing factors,the relaxation-Debye relation in the permittivity and the Cole-Cole diagram.We analyze the influence of the diversion,interfacial polarization and loss on the dielectric properties of the insulating material under the external electric field.Secondly,we introduce the characteristics of each component about the cathode material of lithium battery and establish the dynamic model of cathode material of lithium battery.We analyze the polarization and inverse polarization in the model.Thirdly,we design and realize the variable temperature broadband dielectric spectroscopy measurement system,including Matlab program control measurement impedance design,WK6505 P impedance meter work principle and calibration,in the measurement process,two-wire,three-wire,four-wire impedance measurement principle and analysis;then design and implement the PID temperature control system,including the simulation of the fuzzy PID controller,the program design and parameter setting of the PID control system,and finally is the design of the self-made fixture.We build the relationship between lithium battery cathode material dielectric properties and temperature and frequency,including the electrical conductivity,dielectric constant,dielectric loss and loss angle vary with the temperature and frequency changes.We explain its internal changes in the characteristics of dielectric properties from the microscopic aspects of the material.We compare the theoretical method with practical methods of this measurement and obtain the appropriate temperature of the battery.