Evaluation of the Electrochemical Characterizations of Lithium-Ion Battery (LIB) Slurry with 10-Parameter Electrical Equivalent Circuit (EEC)

A 10-parameter Electrical Equivalent Circuit (10-parameter EEC) has been proposed to evaluate the electrochemical characterizations which are resistance, reactance and relaxation frequency of Lithium-ion battery (LIB) slurry under different components weight ratio of three samples composed of PVDF-NMP solution, Carbon Black (CB) absent slurry and CB present slurry. The 10-parameter EEC is constructed by combining the internal structure of LIB slurry and the electrochemical responses of three samples. Four conclusions are clarified by fitting Electrochemical Impedance Spectroscopy (EIS) Nyquist and Bode plots with the 10-parameter EEC. Firstly, the standard deviation S of the 10-parameter EEC = 14.3% is lower than that of a conventional 8-parameter EEC = 30.6% by ΔS = 16.3%. Secondly, the resistance of electric double layer (EDL) Rdl is firstly increased and then decreased as LiCoO2 particles weight ratio wtLiCoO2 is increased, which is well explained by LiCoO2-PVDF ratio effect. Thirdly, the resistances of PVDF-NMP solution RSO and conductive path Rp are the resistances of LiCoO2-NMP interface dispersion and PVDF-NMP solution dispersion in LIB slurry. Lastly, relaxation frequencies of LiCoO2-NMP interface dispersion frelax,high and PVDF-NMP solution dispersion frelax,low obtained from EIS experiment can be represented by those of frelax1 and frelax2 calculated from the 10-parameter EEC.