Study On Application And Electrochemical Performance Control Of Polyester Based Binder In Lithium-ion Battery

As the demand for flexible wearable electronic devices increases,flexible lithium-ion batteries are receiving attention as energy storage components.However,deformation can cause internal cracks,which can lead to the separation of active particles,conductive particles,and binders,as well as electrode and current collector separation.Unstable stress distribution can also cause active material particles to break,accelerating battery performance degradation and failure,as well as causing safety issues.A new type of self-healing,environmentally friendly,and high-performance lithium battery binder can effectively improve the above phenomena.This project designed and prepared two polyester-based binders,BDO-PDO-IA-SuA-SeA（BPISS）and BDO-LA-IA-SeA（BLIS）,and applied them to high-voltage Li Co O₂（LCO）electrodes to improve the self-healing ability and electrochemical performance of the electrode.The specific research contents are as follows:（1）Polyester-based binder BPISS was synthesized by incorporating monomers derived from biomass,including 2,3-butanediol,2,3-propanediol,itaconic acid,succinic acid,and sebacic acid.BPISS was used as a high-voltage LCO cathode binder to investigate its impact on the self-healing performance and electrochemical properties of the battery.The repaired BPISS-LCO electrode achieved a recovery rate of 75%after undergoing heat treatment to heal the scratches.The results indicate that the LCO electrode exhibited excellent structural stability and electrochemical performance due to the self-healing properties of BPISS.The full BPISS-LCO electrode,cycled 349 times at a current density of 0.2C/0.2C,displayed a discharge capacity of 162.4 mAh g^-1.In contrast,the scratched BPISS-LCO electrode,cycled under the same conditions,exhibited a reduced discharge capacity of 115 mAh g^-1.However,when the damaged BPISS-LCO electrode assembly was subjected to low-temperature heating at 40°C for 1hour,the discharge capacity recovered to 156.6 mAh g^-1 after 349 cycles at a current density of 0.2C/0.2C,with a cell capacity recovery rate reaching 96%.Theoretical data indicate that the adsorption sites are primarily located on the oxygen-containing functional groups,such as-C=O-and-C=O-O-.The relatively high HOMO energy level contributes to the formation of a stable CEI layer on the surface of LCO,as predicted by the theory.（2）Based on the polyester-based binder BPISS,to further enhance the flexibility of the binder,a polyester-based binder named BLIS was synthesized by incorporating monomers such as 2,3-butanediol,lactate,itaconic acid,and sebacic acid.The impact of BLIS as a high-voltage LCO cathode binder on the self-healing performance and electrochemical properties of the battery was investigated,and the repaired BLIS-LCO electrode achieved a recovery rate of 88%after undergoing heat treatment to heal the scratches.BLIS exhibited a tensile strength of 1.45 MPa and an elongation at break of581.21%,demonstrating superior flexibility compared to BPISS.The data indicate that the LCO electrode exhibited excellent structural stability and electrochemical performance due to the self-healing properties of BLIS.The full BLIS-LCO electrode,cycled 200 times at a current density of 0.2C/0.2C,displayed a discharge capacity of172.8 mAh g^-1.The damaged BLIS-LCO electrode,cycled under the same conditions,exhibited a discharge capacity of 167 mAh g^-1.However,after heating the BLIS-LCO electrode at 40°C,the discharge capacity recovered to 173.5 mAh g^-1 after 200 cycles at a current density of 0.2C/0.2C.The primary adsorption sites for the BLIS binder were identified as the-C=O-and-C=O-O-functional groups,while the relatively high HOMO energy level contributed to the formation of a stable CEI layer on the surface of LCO.