Study On Modification Of Silicon Anode For High Energy Density Lithium Ion Battery

Lithium-ion batteries are also known as lithium secondary batteries because lithium ions（Li⁺）can travel freely between the cathode and anode electrodes.The anode and cathode materials are the most important part to determine the performance of lithium-ion batteries,while the anode materials are related to the service life,charging time and energy density of LIB.At present,graphite is widely used as anode material in the market,but the theoretical energy density of graphite anode material is low(～370 m Ah g^-1),which severely restricts the improvement of energy density of LIB.While silicon is widely considered as one of the most promising anode materials,because the lithium-silicon bonding mechanism is an alloying reaction,where each silicon atom can be coordinated with four Li⁺(Li₂₂Si₅),and its theoretical capacity is ten times higher than that of graphite anode(for 4200 m A h g^-1).However,the disadvantages of low conductivity and poor cycling performance of silicon-based anode electrodes have seriously limited their development.When silicon material alone is used as the anode material for LIB,it will alloy with lithium during the charging and discharging process,resulting in a volume expansion effect of about 300%at the electrode,making the electrode chalky and the lithium storage capacity poor,and also causing continuous destruction and growth of solid electrolyte interface phase,producing large irreversible capacity loss and making cycle performance poor.Graphene has excellent mechanical properties,good electrical conductivity and large specific surface area,etc.In this paper,we combine nano-Si with amorphous carbon and graphene to carry out rational structural design and modification research.（1）The Si nanoparticles（Si NP）were compounded with graphene oxide（GO）by electrostatic self-assembly,and then a layer of styrene-butadiene rubber（SBR）was wrapped on the surface of Si-GO.And SBR at high temperature carbonization of soft carbon coating layer can effectively restrain the volume expansion effect of Si,inhibition of SEI repeat formation.Then it was self-assembled with porous graphene oxide（HGO）by hydrothermal method to form a three-dimensional porous framework（HGF）,which effective construction of three dimensional conductive network and suppression of volume expansion effect of silicon anode.The HGF/Si/C composite obtained by this method has a high surface loading capacity of 5.5 mg cm^-2,and the capacity was maintained at 3 m A h cm^-2 after 50 cycles.（2）The Si NP was coated with phytic acid doped polyaniline（PANI）by simple solution mixing,Polyaniline coated Si PANI composite and go are compounded.PANI and GO are chemically crosslinked to form a strong hydrogen bond.After carbonization at high temperature,nano silicon is coated with amorphous carbon and anchored on reduced graphene（r GO）.Si@C-r GO composite has a stable structure,good electrical conductivity,excellent mechanical strength,and still has a specific capacity of 768.1 m A h g^-1 after 100 cycles in a charge/discharge test at a current density of 400 m A g^-1.