Investigation On The Interfacial Modification And Improvement Of Pouch Cell Performance Of Commercial NCM And LiCoO₂

Lithium ion batteries（LIBs）possessed the advantages of high energy density and power density has become the focus of research and development in the industry.At present,the cathode material is the main bottleneck restricting the further improvement of the energy density of LIBs.Layered cathode materials with high tap density and high specific capacity are the key to developing high-energy density LIBs.In particular,it is widely expected that a simple and efficient method can be developed to achieve the large-scale modification and development of cathode materials,and prepare practical lithium ion full batteries with high performance,high safety and high energy density,and realize the effective connection from“basic research to lithium ion full batteries application”.Therefore,this work focuses on the problems faced in the application of commercial Li Co O₂（LCO）and Li Ni_0.5Co_0.2Mn_0.3O₂（NCM523）cathode materials,further carries out the research of interface modification,large-scale preparation and the improvement of pouch full cell performance.The main contents are as follows:Firstly,in view of the problems whether the commercial normal voltage LCO can achieve high-voltage performance,ameliorate interface compatibility and unstable high temperature cycling performance of material through modification.A simple,efficient method combining liquid stirring and solid-phase anneal was proposed with coating thermal sensitive Pr₆O₁₁nanoparticles with negative temperature coefficient on the surface of normal voltage LCO material for the first time,which achieve the large-scale preparation of cathode materials with high performance and high-voltage.The electrochemical performance tests showed that the capacity retention rates of the modified sample are 90.8%and 80.5%after 100 cycles between 3.0-4.5 V at 25℃and60℃,respectively,which are much higher than 63.2%and 22.8%of the pure LCO.Combined with KPFM,EIS,XPS etch analysis,material characterization and mechanism analysis methods,it can be found that the coating of Pr₆O₁₁nanoparticles can not only improve the material interface compatibility,but also elevate the Li⁺diffusion kinetics,improve the structural stability,especially promote the cyclic stability of LCO materials under the conditions of high temperature and high-voltage.More importantly,the lithium ion full batteries assembled with modified LCO as cathode electrodes and the graphite as anode electrodes demonstrated excellent cycle life.Obviously,the enhanced energy density of lithium ion full batteries even increased by～42%at the current density of 5 C.This kind of extremely convenient technology has important academic implications for the industrial production of materials.Secondly,the commercial NCM523 cathode material was taken as the research object.Herein,0.5 wt.%graphene and 1.0 wt.%Al₂O₃nanoparticles were added in the pulping process of lithium ion full batteries,and the capacity with 560 m Ah was prepared by matching the graphite anode material.The tests of electrochemical performance,transfer dynamics,XPS analysis and thermal safety were used to study the mechanism of the additive on improving cycle life,and analyse the effect on thermal safety performance.It can be found that,on the one hand,the addition of graphene can improve the conductivity of the materials,promote the transport dynamics of Li⁺,accelerate the heat dissipation capacity of the electrodes,and enhance the safety of the batteries.On the other hand,the oxide property of Al₂O₃can effectively slow down the erosion of NCM material by HF in the electrolyte,and ultimately improve the cycling stability of the batteries.This research provides a unique solution for the development of high performance and high safety LIBs.