Preparation And Electrochemical Property Study Of Silicon And Carbon Composite Anode

Being considered as one of the promising candidates of anode material for the next-generation lithium-ion batteries,silicon,nontoxic and abundant resource in nature,has the high theoretical capacity of 3579 m Ah g^-1 and relatively low average de-lithiation potential（～0.4 V vs Li/Li⁺）.However,the low electroconductibility and serious volume expansion（～300%）during lithiation/delithiation contribute to the cracks and separation of the electrode and finally break the interparticle electronic contact,which means the capacity will rapidly fade and the capacity retention is low at the same time.During the expansion,the lithium is constantly consumed for the preparation of SEI because of its poor stability,resulting from the poor initial coulombic efficiency（ICE）.And these problems restrict the application of the silicon on the industrial production.For meeting the challenges,we combine the plasma technology for the preparation of silicon and carbon composite and study its electrochemical properties:（1）The nickel foam surface is tailored to form the temperature-dependent nanostructures by the Ar/H₂ plasma.And a 3D Si/C nano-composite structure is constructed in combination of silicon via magnetron sputtering and carbon through the inductively coupled plasma vapor deposition（ICP-CVD）.The plasma modified nickel foam generates more nanostructure for the deposition of active material Si/C composite,increasing the loading rate of which.Besides,the plasma-activated nickel foam surface,the Ni O being reduced by H₂ plasma,leads to the crystallization of the sputtered silicon,directly improving the conductivity of it.The temperature rising during the growth of the carbon film from room temperature to 300 degrees contributes to the defects and then ameliorates the lithium-ion conductivity of integral electrode.The prepared silicon and carbon composite shows the delithiation capacity of 972.7 m Ah g^-1 at the current of 1.6 A g^-1 after 500 cycles.（2）To further improve the electrochemical performance of the Si/C composites based on the work（1）,the N₂/H₂ plasma of plasma technology is applied ulteriorly for the modification,N-doping,of the carbon film deposited by ICP-CVD method.During the process of plasma modification,the nitrogen content（up to 9.55%according XPS results）and its chemical configurations（pyridinic-,pyrrolic-and quaternary-N）can be precisely controlled just through adjusting the N₂/H₂processing time.The N₂/H₂ plasma modified carbon film contributes to the kinetics of Li⁺during lithiation/delithiation,stability of SEI formation and then to higher initial CE,as well as the integrity of the electrode during the cycling.Through optimizing of the processing time,the electrochemical performance of Si/C composite anode was improved dramatically.When comparing with the non-processed sample of0-C/Si/PMN,the specific capacity is improved efficaciously by 40%.Especially the initial CE is promoted actually from 51.80%to 80.80%and the specific capacity is improved from 802.5 to 1120.7 m Ah g^-1 at current of 2 A g^-1 after 1500 cycles.On the basic of our previous work,the N₂/H₂ plasma processing on carbon film further consummates the plasma strategy for high-quality Si/C composite anode by combing the modification of the current collector,Si/C interface,and the top carbon layer with the active materials preparation.（3）Apart from the plasma technology being applied for the preparation and modification on the film electrode of silicon and carbon composite,such as work（1）and（2）,powder of which the surface modification through plasma technology can be also achieved for the exploration of the industrial application.The oxygen vacancy is introduced by Ar/H₂ plasma into the Ti O₂ under the mild condition（400^oC,30min）with an excellent efficiency and repeatability.It is discussed that the vacancy makes a difference on the lithium-ion conductivity.The plasma modified one shows ICE of76.4%at 0.1A g^-1 and 308.2 m Ah g^-1 at 2 A g^-1 after 1000 cycles.Compared with the unmodified one,it is improved 37%of the delithiation capacity and 28.1%of ICE while compared with the pure Si O_x,it is increased 98.8%of the delithiation capacity and 41.7%of ICE under the same condition.