Preparation And Properties Of Siloxane Binder For Silicon Anode In Lithium Batteries

Lithium-ion batteries(LIBs)have a combination of portability and longevity,promising potential applications as power source as in vehicles,advanced mobile IT devices,sensors,electrical grid storage.To meet the ever-growing needs of consumption,Si-based anode materials is the most promising for LIBs because of their natural abundance,high theoretical specific capacity and low operating potential.However,the silicon particles suffer a serious pulverization due to the immense volume changes during the lithiation and de-lithiation,which leads to a poor electrochemical performance.This is a considerable challenge for the development of Si-based anodes with high specific capacity.In recent years,massive works have been devoted to solving the above problems,including exploring novel binders,adding additive,and modifying Si nano-particles,such as silicon nanostructures,Si thin films and Si/carbon composite.Among the methods mention above,the development of binders has been considered as an effectively method to buffer the adverse volume changes and secure electrode integrity.Poly(vinylidene fluoride)(PVDF)is the most common binder for LIBs,which shows stable chemical and electrochemical performance.Unfortunately,the PVDF is fail to cope with the enormous volume changes due to the weak van der Waals force and strong rigidity caused by its high crystallinity.Therefore,many alternative binders have been explored for Si-based electrode,including natural,bio-inspired,synthetic adhesives.Recent studies show that the hardness and softness of the binder have great influence on the electrode performance.The elastic binders make active materials coalesced together to maintain the integrity of Si electrodes.However,too much elasticity of the binder will lack of rigidness,the problem of silicon anode expansion cannot be solved.High rigidity binders,such as poly(acrylic acid)(PAA),sodium carboxymethyl cellulose,and polyaniline can work normally under the mechanical stress caused by the lithiation/de-lithiation process and thus alleviate the volume changes.Yet,the Si-based electrode with high rigidness binders is more prone to fracture under critical stress.Hence,it is beneficial to integrate the merits of rigid and soft binders for stabilizing the electrochemical performance.Inspired by this strategy,the rigid and flexible polymer,silane terminated ammonia ester polyether(STPE)and poly(tert-butyl acrylate-co-vinyl ethyl trilactate silane)(TBA-VTLES)were designed from silane with silane containing functional groups,respectively.On the one hand,silane terminated polyether polyurethane(STPE)was synthesized via the two-step method.FT-IR spectra measurement were used to identify the structure.Thermal behavior,adhesion behavior and electrochemical behavior were utilized for systematic characterization analysis,the results showed that: the STPE2 had a good chemical stability,mechanical adhesion and electrochemical properties.On the other hand,poly(tert-butyl acrylate-co-vinyl ethyl trilactate silane)(TBA-VTLES)was synthesized via the copolymerization of tert-butyl acrylate(t-BA)and vinyl ethyl tri-lactate silane(VTLES).FT-IR spectra and H-NMR measurement were used to identify the structure.Thermal behavior,adhesion behavior and electrochemical behavior were utilized for systematic characterization analysis,the results showed that: the TBA-VTLES20 had a good chemical stability,mechanical adhesion and electrochemical properties.In summary,the rigidity and flexibility of the binder have a crucial effect on the performance of the silicon anode cell.The silicon anodes with too high elastic binders can’t adapt to the huge volume changes due to the lack of mechanical strength.The silicon-based electrodes with high rigid adhesives are more prone to fracture under critical stress.Therefore,it is very important to harmonize the rigidity and flexibility of polymer binders,which further promotes the development of the silicon anodes in lithium batteries.