Study On Interfacial Reaction Mechanism Of Nickey-cobalt Lithium Aluminate Material Electrode

In recent years,lithium-ion batteries can be seen everywhere in our daily life.As lithium-ion batteries are gradually applied to large-scale equipment,they need to have higher energy density and higher power density.Increasing the ratio of active materials and inactive components is an effective way,hence the concept of thick electrodes are emerged.Actually,thick electrodes are porous electrodes,and the interfacial reaction mechanism of their internal structure is still unclear.Therefore,it is important to establish a porous electrode model for theoretical analysis and study the influence of porous electrode parameters on electrochemical performance.This paper firstly analyzed the porous electrode interfacial reaction mechanism based on MATLAB software and secondly studied the analysis and application of the distribution of relaxation times（DRT）based on the radial basis function（RBF）.Finally,this paper studies the influence of different electrode thickness and different pressing pressure on the electrochemical performance of LiNi_0.8Co_0.15Al_0.05O₂（NCA）cathode.The main contents and the conclusions are as follows:（1）The cylindrical pore model of the porous electrode is established.Combining the uniform transmission line theory,the ion transport process in porous electrode pore electrolyte is successfully simulated and analyzed.Then the EIS spectrum of the whole electrochemical process of porous electrode is simulated and analyzed in MATLAB software.Finally,the EIS spectrum of actual porous electrode is analyzed.Combining the numerical simulation with experimental data of EIS confirms the applicability of the model.It plays an important role in studying the interface reaction mechanism of porous electrodes.（2）A set of RBF-based DRT analysis technology has been successfully established.This set of analysis techniques successfully analyzed the Nyquist diagram of typical circuit elements including（RC）circuit elements,（RQ）circuit elements,limited-length Warburg（FLW）circuit elements and the commom electrode materials in lithium-ion batteries including graphite,Li₄Ti₅O₁₂,LiNi_0.5Co_0.2Mn_0.3O₂,LiNi_0.8Co_0.15Al_0.05O₂,LiNi_0.5Mn_1.5O₄,Li Mn_0.8Fe_0.2PO₄.These confirm the feasibility,practicability and accuracy of this analysis technology.（3）LiNi_0.8Co_0.15Al_0.05O₂ material was synthesized by high temperature solid phase method.XRD results show that the prepared NCA material has high purity and perfect crystallinity.SEM results show that the morphology of the prepared NCA material is agglomeration of many small particles into large particles.The charge and discharge test results show that when the thickness is 0.5 mm and the pressure is 10MPa,the reversible capacity and cycle stability are the best.The CV test results show that when the thickness is 0.5 mm and the pressure is 10 MPa,the overlap of the plots is the best,indicating it has good reversibility and high stability.The EIS test results show that as the electrode thickness increases,the middle-high frequency semicircle corresponding to the transport of electrons in the active material and the high frequency semicircle corresponding to the process of lithium ions through SEI film are gradually separated form each other.But as the tableting pressure increases,the middle-high frequency semicircle corresponding to the transport of electrons in the active material and the high frequency semicircle corresponding to the process of lithium ions through the SEI film are gradually merged with each other.The DRT analysis results confirmed the rationality of our division of EIS and the exact number of electrochemical processes.EIS fitting results show that when the thickness is 0.5mm and the pressure is 10 MPa,R_SEI,R_eand R_ctare smallest in the initial charge and discharge process,and the interface stability and cycle stability are the best.