Research On Bio-based Composite Materials Applied To Negative Electrode Of Lithium-Ion Batteries

Since the commercialization of lithium-ion batteries by Sony Corporation of Japan in the 1990s,it has been widely used in various mobile devices,electric vehicles,and energy storage due to its environmentally friendly,high energy density,and wide working range.However,the currently used graphite negative electrode has a specific capacity of only 372 mAh g-1,which has been difficult to meet people’s needs for life in daily production,prompting people to seek higher specific capacity materials.Among many materials,the theoretical specific capacity of silicon(Si)is as high as 4200 mAh g-1.It is considered to be the most likely next-generation high-capacity anode material for commercialization,but the current silicon-based materials have problems such as large volume expansion,low electrical conductivity,and easy formation of unstable SEI films,which leads to unsatisfactory performance and hinders its commercialization.In this paper,we develop two materials that improve the electrochemical performance of silicon-based materials,starting with binder modification and carbon coating.The main research contents of the paper are as follows:1.A novel high-performance 3D polymer binder for silicon anode in lithium-ion batteriesWe use carboxymethyl cellulose(CMC)as a backbone,acrylamide(Acrylamide abbreviated AM),acrylic acid(acrylic acid abbreviated AA)as a branch,and prepare a 3D structure CMC-NaPAA-PAM adhesive through cross-linking branches.An innovative step was developed to remove unreacted monomers by washing with ethanol.Polyacrylamide(PAM)provides a strong adhesion and contributes to the formation of the solid electrolyte intermediate phase(SEI)layers on the surface of electrodes.The results show that CMC and polyacrylic acid(PAA)with carboxyl groups not only strengthened the bonding force between the current collectors and the silicon nanoparticles(SiNPs),also improved the linkage among Si NPs.Therefore,the loading weight of comm ercial Si was about 0.75 mg cm-2,even after 150 deep cycles,and a high capacity of 1210.7 mAh g-1 was resulted in the Si anode.The prepared novel high performance 3D polymer CMC-NaPAA-PAM binder shows a potential application on the silicon anode in lithium-ion batteries.2.Study on the structure and electrochemical properties of bio-based N-doped rGO/C@Si composites.Here,we prepared high-performance N-doped rGO/C@Si anode material with renewable chitosan as both N source and C source and GO as the additive by a simple one-step pyrolysis method without adding reducing agent.Because of containing the biomass amorphous carbon layer and rGO,this bifunctional conductive layer not only alleviates the stress maintaining electrode integrity during lithiation/delithiation,but also compensates for the poor conductivity of Si.N doping can effectively improve the wettability of electrolyte and electrode interface.In addition,the afinity to lithium of amorphous carbon also increases greatly.Therefore,The designed n-doped rGO/c@si negative electrode material shows satisfactory cyclic performance(reserve 1115.8 mAh g-1 after 150 cycles at 420 mA g-1)and rate performance(1077.4 mAh g-1 at 4200mA g-1).By comparing the two technologies,we found that the carbon coating modification can obtain a Si/C composite anode with better rate performance,and the binder modification cost is low.When used in a silicon anode,it has a longer cycle life and volume capacity high..