The Influence Of Element Doping On Kinetic Properties Of Spinel LiMn₂O₄

The influence of element doping on kinetic properties of spinel LiMn₂O₄ was investigated with powder microelectrode technique.Electrochemical and nonelectrochemical methods,including electrochemical impedance spectrometry(EIS),constant current charging/discharge , linear and cyclic voltammetry,X-ray diffraction(XRD) and scaning electron micrographs(SEM) were used.Kinetic processes of insertion and deinsertion of Li ions in spinel lithium manganese oxide with different crystallinity and with different Cr-doping and Cu-doping were studied.1 Equivalent circuits of the insertion and deinsertion of Li ions in LiMn₂O₄ with different crystallinity was used to fit electrochemical impedance spectra at the potentials between 4.20 and 3.92.The influence of the crystallinity on kinetic properties of spinel LiMn₂O₄ were investigated.The fitting results are in agreement with the experimental results.Results show that the sample with lower crystallinity has smaller charge transfer resistance and larger Li-ion diffusion coefficient.The chemical stabilizations of the samples in electrolyte was studied, by employing microelectrode.Result indicate that the dissolution of manganese in the sample with higher crystallinity is easier.2 The influence of Cr-doping and Cu-doping on kinetic properties of spinel UMn2O4 were investigated by fitting EISs with equivalent circuit.The fitting results are in agreement with the experimental results.The double capacitance C_dl,the charge transfer resistance of Li ion insertion/deinsertion Rct,and Li ion diffusion coefficient D_Li under different potentials are obtained by fitting the model.The charge transfer resistance Ret increases with increasing of the doping compositions,however the Li ion diffusion coefficient D_Li decreases.The double capacitance C_dl increases with increasing of the Cr-doping compositions but the amplitude of the increase is relatively low.The charge transfer resistance R_ct values near CV peak are small.Li ion diffusion coefficient D_Li has two maximum near CV peak.The chemical stabilities of the samples with different Cr-doping and Cu-doping in electrolyte werestudied.Results show that the dissolution of manganese in the sample with Cr-doping or Cu-doping is reduced and the chemical stability of the sample with Cr-doping or Cu-doping in electrolyte is enhanced.The increase of the charge transfer resistance Ret and the decrease of Li ion diffusion coefficient Dy are two important reasons for the capacity decrease.