Study On Preparation Of Acrylate Water-based Binder And Its Application In Silicon-carbon Negative Electrode

Lithium-ion battery is one of the most important energy storage devices,which can provide power for various portable mobile devices and vehicles,and promote the development of human society.However,its development is very slow.At present,it has encountered a bottleneck in energy density.Scientists are using various methods to increase the energy density of lithium-ion batteries.By using a material with a high theoretical specific capacity to replace the traditional positive and negative electrode materials,the energy density of the battery can increase effectively.Silicon,as a new type of negative electrode material,has a theoretical specific capacity of up to 4200m Ah g^-1 when fully embedded by lithium,which is extremely promising.However,pure silicon has the disadvantages of large volume change and poor conductivity in practical use.Therefore,a compromise solution is usually adopted to mix silicon and traditional graphite anodes to form silicon-carbon anode materials in practical applications.However,the silicon carbon anode material does not completely eliminate the impact of volume changes on battery performance.So the choice of binder brings a turning point to the application of silicon carbon anode,which plays an important role in the process of silicon carbon anode affecting its performance.As an important component of the lithium ion battery,the binder plays an indispensable role in maintaining the stability of the electrode structure and ensuring the performance of the battery,although its proportion is small.The binder is a polymer with a high molecular weight.It is mixed with the active material to form a slurry,and then coated to prepare an electrode sheet.During this process,the binder and other components in the electrode bind with each other physically or chemically.Generally,the silicon carbon negative electrode requires that the binder has a large number of functional groups,which can attract each other with the active material and form a strong interfacial force.Secondly,the binder should have a chain structure that can penetrate the entire electrode.To maintain the stability of the electrode structure,the binder should minimize the swelling of the electrolyte,so that during the intercalation/deintercalation of lithium ions of silicon-carbon anode,the stress changes caused by volume expansion will not weaken the interface force and the overall mechanical strength of the electrode to maintain a complete conductive network ensuring lithium ion transmission.Based on the above requirements,this paper prepared PS-PEHA-PS by RAFT emulsion polymerization.The introduction of 2-EHA,while ensuring the tensile properties of the polymer,greatly reduced the polymer’s electrolyte swelling degree.The peeling force test showed that the adhesion strength of the two block copolymer in the electrode was greater than SBR;in the silicon carbon anode half-cell,the discharge capacity and capacity retention after 100 cycles were higher than SBR,indicating that the block structure and low swelling characteristics play an important role in maintaining the stability of the electrode structure.In terms of rate performance,because the electrolyte swelling of the two blocks is still slightly larger than SBR,the rate performance is better.EIS tests also show that both R_ct are less than SBR,which means that the lithium ion transmission resistance is small and the high current discharge capacity is better.In this paper,a self-thickening agent ANC was prepared with a reactive emulsifier.The introduction of acrylonitrile monomer reduced the swelling degree（10.8%,70°C/72h）,and at the same time improved the adhesion.The crosslinking process of the thickener reduces the swelling degree,forming a network polymer structure.The rheological properties of the prepared slurry and aqueous solution were tested and compared with the CMC.The initial viscosity of the slurry prepared by the thickener with the same mass fraction was 4460 m Pa·s and 3710 m Pa·s,indicating better thickening effect of ANC than that of CMC;The change in viscosity of ANC aqueous solution with shear rate is more gentle than CMC,showing better slurry stability;the thixotropic recovery rate of ANC is higher than CMC,which are 68.0%and 61.8%,Therefore,ANC is more suitable for slurry coating;G’（storage modulus）>G"（loss modulus）at low strain shows a higher yield stress than CMC and has better suspension stability.The peeling test shows that the adhesion force produced by ANC in the silicon-carbon negative electrode is higher than that of CMC;in terms of cycle performance,the silicon-carbon anode soft-pack battery prepared by ANC as a thickener still has 389m Ah after 100 cycles at 1C,the capacity retention rate is 91.12%,both higher than CMC’s 370.9 m Ah and 88.23%.In terms of high temperature storage performance,the capacity retention rate and capacity recovery rate of ANC batteries after 7×24 h high temperature（60°C）storage are respectively 92.6%and 98.1%,both higher than CMC’s83.7%and 90.8%;In terms of rate performance,the discharge capacity of ANC batteries at 2C and 3C is 368.4 and 248.8 m Ah,respectively,which are slightly lower than CMC’s 396.2 and 262.6 m Ah.The other rate discharge capacity is basically similar,even higher than CMC.In general,ANC has shown some advantages compared to CMC in terms of cycle performance and high-temperature storage stability in silicon carbon anode,but the rate performance is not satisfying compared with CMC.