Preparation And Electrochemical Performance Of Nano-silicon Based Anode For Lithium Ion Battery

Electrochemical energy storage devices are deemed as suitable green power sources for portable electronics and electric vehicles.In this regards,the development of advanced lithium-ion batteries?LIBs?with high energy density,superior cyclability and low cost is of crucial importance to satisfy the increasing demands for next-generation energy storage devices.Silicon,featured with the ultrahigh theoretical specific capacity(4200 mAh/g corresponding to Li_4.4Si)and the abundance in nature,has been generally regarded as one of the most promising anode materials.Nevertheless,the application of Si-based anode has been hampered by its low ionic diffusion,poor electrical conductivity and especially the huge volume expansion?about 400%?that occurs in the lithiation/delithiation processes,resulting in drastic capacity degradation eventually.Meanwhile,the volume expansion will inevitably cause the cracking and growth of unstable solid electrolyte interphase layers?SEI?,and harmful pulverization,giving rise to rapid capacity fading and poor rate capability.In order to address these issues,two types of Si-based nanocomposites were developed in this paper.A covalent linkage between polyaniline?PANI?and Si nanoparticles in PANI-encapsulated Si nanocomposites?Si-NH₂@PANI?was proposed and achieved by a facile and economical synthetic strategy,in which NH₂-grafted Si was firstly obtained via a chemical modification of APTES and the polymerization of aniline initiated at NH₂ groups surface was readily accomplished to get PANI shell.Electrochemical tests showed that our proposed Si nanocomposites delivered a high initial specific capacity of2135 mAh/g and retained 848 mAh/g after 100 charge/discharge cycles at a current density of 0.1 A/g.The enhanced electrochemical performance was ascribed to the surface chemical modification and the introduction of chemical bond in the interface.NH₂ group function of Si could improve the homogeneity of encapsulated PANI shell.Additionally,PANI was tightly anchored to Si nanoparticles via a covalent bond between silicon and PANI,which would greatly inhibit the separation of PANI from Si surface during the expansion/contraction of Si particles.Besides,EIS verified that the PANI layer with a unique structure promoted the transport of both electrons and lithium ions.A yolk-shell structured Si@void@C with adjustable nitrogen doping content was developed by a flexible and tunable route,in which Si was firstly encapsulated a SiO₂templet via St?ber method as void space,followed by coated N-doped carbon via copolymerization of aniline?An?and o-phenylenediamine?OPD?to to obtain hollow core–shell structured nanocomposites.Electrochemical tests showed that such yolk-shell structured exhibited a improved electrochemical performance by controlling the synthetic conditions of void space and carbon shell.Furthermore,the content of nitrogen doping can be adjusted by controlling the relative concentration of monomer An and OPD,and the electrochemical performance was further improved.The Si@void@C greatly improve the electrical conductivity and buffer the large volume change of silicon nanoparticles.The tunable void space allows the Si particles to expand freely without breaking the outer carbon shell.Besides,the carbon shells prevents the active particles exposure to the electrolyte.Most importantly,the N-doped carbon shells fabricated by aniline and o-phenylenediamine can provid vacancies and dangling bonds around the nitrogen sites,and serve as efficient Li intercalation sites.