Study On The Application Of Polydopamine-based Cross-linking Binders In Silicon Negative Electrodes Of Lithium Ion Batteries

Fossil energy cannot overcome the challenge of environmental pollution and energy shortage.As an alternative,lithium-ion batteries with high energy density are widely used in electrically cars,information technology and other fields.Silicon,has become one of the most anticipated anode active materials in lithium batteries due to its theoretical specific capacity of 4200 m Ah/g.However,the silicon negative electrode expands by more than 300% during cycling,which causes the silicon particles to fall off,pulverize,and the continuous growth of the solid electrolyte interfaces,resulting in serious battery performance loss.The addition of a binder increases the electrode adhesion,improves electrode integrity,and increases battery cycle stability.This simple and direct method has great potential for improving battery performance.We first crosslinked mussel derivative polydopamine(PDA)and polyacrylic acid(PAA)to synthesize three polymer binders with multifunctional adhesion and good stability,PAA-PDA-1-1,PAA-PDA-1-2,PAA-PDA-2-1,in order to explore the effect of PAA and PDA composition changes on battery performance.In comparison,PAA-PDA-1-1 can obtain the most uniform and cross-linked binder,which has a denser structure and protects the integrity of the entire electrode structure.The electrode prepared with PAA-PDA-1-1 binder obtained an initial discharge specific capacity of 3191 m Ah/g at a rate of 0.2C and a specific capacity decay rate of 32% after two hundred cycles,showing the best cycle performance and capacity characteristic.With the increase of the number of cycles,the attenuation trend of the PAA-PDA-1-1 electrode slowed down,and the capacity retention rate after about 500 cycles was about 56%,showing the long-cycle stability of the PAA-PDA-1-1-based electrodes.In order to further improve the cycling stability of the battery,a lowcost,highly cohesive polyurethane(PU)and biomass polydopamine(PDA)are combined to form a cost-effective,water-soluble polymer binder PUPDA.The surface groups of the PU-PDA binder can form a strong covalent connection with the silicon particles.And the three-dimensional structure formed by cross-linking can prevent the silicon particles from falling off in various directions,and can maintain the integrity of the entire electrode under the change of large volume,leading to an increase in cycle stability.The stability of the PU-PDA-based silicon negative electrode is more excellent with the increase of the number of cycles.The average decay rate per cycle in the first 200 cycles is 0.13%.In the subsequent 300 cycles,the average attenuation ratio per cycle was reduced to 0.04%,which was significantly lower than that Si anodes with PAA-PDA-1-1 binders,showing more excellent cycle stability.This experiment reveals the application potential of PAA-PDA-1-1 and PU-PDA binders in silicon anodes,which provides a good reference value for the commercialization of lithium-silicon batteries.