Study On The Correlation Between Electrochemical Performance Of Lithium-ion Battery Electrode Materials And Electrode Binder

Electrode active materials play a decisive role in the energy density and power density of lithium-ion batteries,but the powdery and granular electrode active materials need to be firmly aggregated with a binder and adhere to the current collector to form a complete electrode sheet.Positive electrode materials usually include electrode active material for positive electrode and conductive agent,while negative electrode materials usually include only electrode active material for negative electrode,without conductive agent.Binder is one of the important auxiliary functional materials in lithium-ion batteries.The amount usually accounts for 1.5%to3%of the total material mass.It is used to bond the electrode material and keep the electrode material on the current collector to achieve electrode activity.The contact and conductive transmission between the material and the conductive agent and between the electrode active material and the current collector are the guarantee for the formation of a stable electrode pole structure,and it has an important impact on the production process of the electrode and the electrochemical performance of the lithium-ion battery.There are three main types of currently used lithium-ion battery binders:polyvinylidene fluoride(PVDF)N-methylpyrrolidone(NMP)solution used in the positive electrode,a composition of styrene-butadiene rubber(SBR)aqueous emulsion and methyl cellulose(CMC)used in the negative electrode,and a polyacrylic acid(ester)aqueous emulsion applied to part of the positive and negative electrodes.Binders for lithium-ion electrodes seek strong adhesion,excellent flexibility,and special functions(such as good electrical conductivity,interface film formation,self-healing,etc.)to keep the electrode structural stability and corresponding excellent electrochemical performance.For different electrode active materials,develop water-based electrode binders with optimized performance,explore the interaction between the binder and the electrode active particle material and between the binder and the electrode current collector,and make full use of the performance of the electrode active material.High-performance lithium-ion batteries and exploring the environmentally friendly use of lithium-ion batteries are of great significance.In this paper,two water-based binders are designed and prepared for the positive and negative electrode active materials of lithium-ion batteries.They have the characteristics of enhancing the interfacial force between the electrode materials and forming a film on the surface of the electrode active material particles.Enhancing the stability of the electrode and improving the porperties of the battery has a certain beneficial effect.The research contents are summarized as follows:(1)A new water-based binder,poly(2-propenoic acid,2-methyl-,3-[(2-aminoethyl)amino]-2-hydroxypropyl ester)(P-HAEAPMA),is synthesized and applied to the silicon/graphite(Si/graphite)anode in lithium-ion batteries to enhance the bonding strength between the electrode active material and the metal current collector,and replace the traditional oily PVDF binder.The P-HAEAPMA binder is rich in polar amino and hydroxyl groups,which not only helps to form strong adhesion between the electrode active material and copper foil but also promotes the transport of Li-ion.The electrochemical properties of the electrode with the P-HAEAPMA binder have been significantly enhanced.After 305 cycles,a specific capacity of485.0m A h g^-1 and a capacity retention rate of 74.8%are achieved,which is higher than 49.9%of LA133 binder and 52.3%of PVDF binder.At the same time,the P-HAEAPMA binder is also suitable for the cathode material Li Fe PO₄,which has good electrochemical properties.(2)The copolymer of water-based binder glycidyl methacrylate(GMA),acrylonitrile(AN)and butyl acrylate(BA)monomers is prepared,and its influence on the electrochemical performance of graphite anode materials was explored.A multifunctional binder,which can be used as an electrolyte additive while owning the basic conditions of the binder,is synthesized.A new binder,GMA-AN-BA radical copolymer(GAB),is applied to the graphite anode in lithium-ion batteries.Cyclic voltammetry curve test is performed and shows that the epoxy group contained in the GAB binder undergoes a ring-opening reaction at a potential of?1.5V,combines with the Li⁺,and promotes the formation of the solid electrolyte interface(SEI).The electrochemical properties of the electrode with GAB binder have been significantly improved.After 208 cycles,the specific capacity of 339.7m A h g^-1 and a capacity retention rate of 96.5%are achieved,which is higher than 93.0%of AB(copolymer of AN-BA)binder and 67.1%of LA133 binder.At the same time,the GAB binder is also suitable for the cathode material Li Fe PO₄,which has good electrochemical properties.(3)Explore the application of water-based binder P-HAEAPMA in electrode material reuse.There is a 3%unqualified rate of the discarded electrode in industrial production,and the discarded electrode is continuously produced with the growth of battery production.Therefore,an exploration process for the reuse of water-based binder electrode waste is designed.The materials on the discarded Si/graphite/P-HAEAPMA electrode can be recycled for use based on water because the P-HAEAPMA binder is easily soluble in water.The discharge capacity and capacity retention rate of the electrode with reused materials,without any other materials supplemented,are lower than those of the original Si/graphite/P-HAEAPMA electrode.After100 cycles,the capacity retention rate of the Si/graphite/P-HAEAPMA electrode prepared by reusing electrode waste reaches 71.0%(396.5m A h g^-1),which is lower than that of the original electrode(89.0%,396.5m A h g^-1).The content of this research has certain reference for how to improve the properties of lithium-ion batteries from the aspect of binder and develop environmentally friendly manufacturing and reusing of lithium-ion batteries.This research is not sufficient for the controllable preparation and the film-forming mechanism of binders,and further work is still needed.