Study On Preparation And Electrochemical Performance Of Silicon-based Anode Materials For Lithium-ion Batteries

With the shortage of non-renewable energy and the deterioration of environmental issue,the development of new energy sources has become particularly important.Lithium-ion batteries（LIBs）,as efficient energy storage devices,have advantages such as high specific capacity,long cycle life,and environmental friendliness,making them widely used in mobile smart devices and electric vehicles.Nowadays,the rapid development of economy and industrial technology has put forward much higher requirements for the performance of LIBs.Therefore,designing and developing high-capacity anode materials has become one of the most imprtant factors.Due to high specific capacity,low lithium insertion potential,green environmental protection and abundant reserves,silicon-based materials are considered to be the potential anode materials.However,the low intrinsic conductivity and huge volume changes during the lithiation/delithiation process limit their real-world applications.In this work,in order to suppress volume expansion and improve electrical conductivity,nitrogen-doped carbon coating,inert matrix and carrier were applied into raw material of silicon monoxide to prepare composite materials.Moreover,the electrochemical performance of silicon-based anode materials was optimized.The following research results were obtained:1.Gelatin and polyvinylpyrrolidone（PVP）are used as carbon and nitrogen sources,respectively,to prepare a binder-free integrated silicon-carbon composite electrode Si O@GC/Cu through a one-step carbonization method.In the integrated composite anode,the strong interfacial bonding between nitrogen-doped carbon coating and current collector can improve the adhesion of Si O@GC on Cu foil and thus enhance the transfer of electrons.When the carbonization temperature is set as 450°C,the integrated Si O@GC/Cu-450 composite anode has a discharge specific capacity of 1270 m Ah·g^-1after 50 cycles at a current density of 200 m A·g^-1.At 500 m A·g^-1,the specific discharge capacity after 150 cycles is 540 m Ah·g^-1.2.In order to improve the electrochemical performance of integrated Si O@GC/Cu composite anode,high-energy ball milling was used to introduce red phosphorus to prepare a binder-free integrated Si O/P@GC composite anode.Red phosphorus can form a covalent bond with carbon coating,which further inhibits the nitrogen-doped carbon layer from falling off.When the carbonization temperature is at 550°C,the integrated Si O/P@GC-550 composite anode has a discharge specific capacity of 779 m Ah·g^-1 after cycling 50 times at a current density of 200 m A·g^-1.At 500 m A·g^-1,the specific discharge capacity was 617.6 m Ah·g^-1 after 150 cycles,and the reversible discharge specific capacity of 458 m Ah·g^-1 was maintained after 200 cycles.3.Using polyacrylonitrile（PAN）as both carbon and nitrogen source,red phosphorus as chemical binder,graphite as core-shell carrier,3D core-shell Si O/P@C composite material was prepared by high-energy ball milling and carbonization method.The carbonized Si O/P particles are firmly anchored on graphite matrix.The as-prepared Si O/P@C-2 sample has the superior electrochemical performance.Specific capacities at200,500,1000 and 1500 m A·g^-1 are 1109.8,1027.2,821.0 and 718.7 m Ah·g^-1,respectively.When the current density is returned to 100 m A·g^-1,the discharge specific capacity is recovered back to 1192.2 m Ah·g^-1.