Study On Properties Of Porous Silicon/Metal/Carbon-Coated Anode Materials For Lithium Ion Batteries

High performance electrode materials are an important prerequisite for the development of high energy density lithium-ion batteries.At present,the theoretical specific capacity of traditional graphite anode materials for lithium-ion batteries is only 372 m Ah g^-1,which is difficult to meet the high energy density needs of the rapidly developing electric vehicle industry.Among many anode materials,the theoretical specific capacity of silicon-based anode materials is 4200 m Ah g^-1.In addition,silicon-based anode materials also have the advantages of stable charge and discharge voltage platform,high abundance in nature and no pollution to the environment.Therefore,they are considered by researchers to be the most potential anode materials for the next generation of lithium-ion batteries.However,with the in-depth research of researchers,it is found that the silicon anode material is accompanied by huge volume change in the process of lithiation/delithiation.In the long cycle process,the huge volume change effect will usually lead to the pulverization and rupture of silicon particles,and finally fall off from the collector and lose electrical contact.At the same time,the intrinsic conductivity of silicon material is low,which limits the transmission of ions and electrons.These two main problems seriously affect the long cycle performance and limit the industrial application of silicon anode materials.In order to alleviate the volume expansion of silicon anode material and improve the conductivity of silicon,two modification schemes are proposed in this paper.Firstly,the porous silicon structure was etched on the silicon surface by copper assisted chemical etching,and then the porous silicon/copper/carbon-coated（p Si/Cu@C）composite anode material was obtained by carbon coating with asphalt as carbon source.Secondly,considering that the carbon-coated may be broken by stress under the huge volume expansion effect of silicon,a non-filled carbon-coated structure is designed.Silver is deposited on the surface of silicon particles by electroless metal deposition process,and then the carbon layer is coated by high-temperature heat treatment.Finally,the porous structure is etched in the carbon-coated to obtain the non-filled carbon-coated porous silicon/silver/carbon（p Si/Ag@C）composite anode material with excellent electrochemical performance.The main research contents of this paper are summarized as follows:Using submicron silicon particles as raw materials,the porous structure is constructed by two-step copper assisted chemical etching,and then the carbon layer is coated with asphalt as carbon source.Finally,the p Si/Cu@C composite anode material is obtained.The modified p Si/Cu@C anode material showed excellent electrochemical properties.The discharge specific capacity remained 820 m Ah g^-1after 200 cycles at a current density of 0.5 C(1 C=4.2 A g^-1),while the silicon raw material（Si raw）had only 229 m Ah g^-1after the same cycle test.In addition,the specific discharge capacity of p Si/Cu@C material is maintained at 774 m Ah g^-1at a high rate of 2 C,showing good rate performance.In order to better maintain the stability of charge/discharge of carbon coating under long cycle and high current density,p Si/Ag@C composites with non-filled carbon-coated structure were designed.The modified p Si/Ag@C material still maintains a high specific discharge capacity of 904 m Ah g^-1after 200 cycles at a current density of 0.5 C.In the rate performance test,the specific discharge capacity of p Si/Ag@C material at high rate of 2 C is 1015.3 m Ah g^-1.At the same time,when the p Si/Ag@C returns from the large rate of 2 C to the initial rate of 0.1 C,its discharge specific capacity can still be restored to 1920.5 m Ah g^-1,showing an excellent capacity recovery rate.