Effect Of The Multistage Carbon On The Electrochemical Properties Of The Silicon-carbon Composite Anode

Lithium-ion batteries dominant the electrochemical energy storage field due to their high energy density,low self-discharge rate and environmental friendliness.The specific capacity of traditional graphite anode materials cannot meet the application needs of high capacity and long life,so that silicon-carbon composites have become the most promising cathode material for lithium-ion batteries,given the high theoretical specific capacity of silicon.Under the guidance of China's policy to promote the continuous cost reduction of relatively mature new energy storage technologies such as lithium ion batteries,preparing low-cost silicon-carbon composite materials through simple processes can improve the cycle performance of LIBs silicon / carbon composite anode materials while improving the specific capacity.Large size silicon particles have large volume changes and poor cyclic stability during charge and discharge.The composite of multistage structure provides a new idea for improving the electrochemical performance of silicon-based anode.In this paper,the silicon-carbon anode with multistage carbon composite is constructed through the regulation and optimization of the type,content,morphology of carbon source,and its electrochemical properties and lithium storage stability are studied.The specific research contents are as follows:(1)Single-stage carbon composited silicon/carbon anode materials are prepared by liquid wrapping and high-temperature pyrolysis process,using micron/submicron silicon powers(200 nm-2 ?m)in silicon waste recycling produced by photovoltaic cell as active material,and liquid carbon source such as phenol-formaldehyde resin and waterborne polyurethane resin as carbon source.The influence of carbon content and pyrolysis carbon elements on the lithium storage performance of single-stage carbon composited silicon-carbon anode is compared and analyzed through the characterization means of electron microscope,energy spectrum and charge-discharge cycle test.The results show that the increase of carbon content in the composite improves the conductivity and cycling stability of the electrode.However,at the same time,the increase of amorphous carbon content will increase lithium ion loss and ion transmission path,resulting in lower initial coulombic efficiency rate performance.When carbon content in composites is around 25 %,the omprehensive performance of the electrode is better.Further,doping N element in the composite can reduce the electrochemical impedance,which is beneficial to improve the capacity and rate characteristics of the negative electrode.(2)The second composite of polyaniline(PANI)is introduced on the basis of single-stage silicon/carbon composite material to prepare secondary carbon composite witth porous mesh bracket.The influence of material structure and composition on the lithium storage properties of silicon-carbon anode is studied.The result show that the secondary composited large-size crystallic silicon-carbon composites(SPF#PANI and SPU#PANI)have the discharge specific capacity of 644.2 and 756.3 m Ah/g afyer 100 cycles,respectively,which is more than twice that of graphite anode,and the specific capacity retention rate reaches 69.2% and 65.1 %,respectively.Secondary carbon composite improves the bonding tightness of silicon and carbon,and its porous bracket provide a buffer for alloying expansion of micron/submicron silicon particles,effectively improved the electrochemical stability of the composite anode.The combination of the porous structure of PANI pyrolysis carbon and silicon reduces the transmission path of lithium ions and electrons.Secondary composite of PANI further deepens the N doping,which effectively enhances the conductivity of lithium ions and electrons,and improves the pseudocapacitance lithium storge effect of the negative electrode.