Preparation And Pre-lithiation Technology Of Silicon-carbon Anode Materials For Lithium-ion Batteries

Among the anode materials for lithium-ion batteries,silicon oxide anode materials are favored for their high theoretical specific capacity(over 1965 m Ah·g^-1),relatively stable cycling performance and low production cost,and are currently recognized as one of the most likely new materials to replace the traditional graphite anode.However,the silicon oxide cathode material will form SEI film during the first charge and discharge,and at the same time form Li₂O,Li₄SiO₄and other inert materials,which consume active lithium ions,resulting in a low first coulombic efficiency,and the poor electrical conductivity of silicon oxide and electrolyte dissolution of electrode materials also affect the capacity of electrode materials,making it difficult to obtain a higher energy density lithium-ion battery.The above problems can be effectively solved by compounding silicon oxide,carbon material and alumina.Carbon material can effectively inhibit the volume expansion of silicon oxide negative electrode during charging and discharging,and inhibit the rupture and reorganization of SEI film,while the compounding of carbon material can improve the electrical conductivity of electrode material,and alumina can consume the hydrofluoric acid produced by electrolyte during charging and discharging,and slow down the dissolution and pulverization of electrode materials.In this paper,a SiO/graphite/pyrolytic carbon/alumina composite with good cycling stability was prepared and subsequently treated using different pre-lithiation means to improve the first coulometric efficiency of the composite.Firstly,SiO/G@C composites were prepared by adding graphite and carbon cladding using SiO as the basic raw material,followed by the addition of Al₂O₃to prepare SiO/G@C@A anode materials with different graphite and Al₂O₃doping.Among them,the SiO/G@C@A-2 negative electrode materials with 40%graphite addition and 3%Al₂O₃addition exhibited the most excellent electrochemical performance.The first de-lithiuming capacity of the material is 977.1 m Ah·g^-1at a current density of 0.1 A·g^-1,with a coulombic efficiency of 71.15%;after 100 cycles at a current density of 0.5 A·g^-1,the de-lithiuming capacity of 640.7 m Ah·g^-1remains,with a capacity retention rate of 73.56%;when the current density is increased to 2 A·g^-1,it still retains a capacity of 565.6 m Ah·g^-1.When the current density was increased to 2 A·g^-1,the de-lithium capacity of 565.6m Ah·g^-1was retained,with a capacity retention rate of 58.85%compared to the capacity at 0.1 A·g^-1,which showed good cycling and multiplication performance.Secondly,the prepared samples were pre-lithiated to enhance the coulombic efficiency of the material during charging and discharging.A pre-dispersion method of lithium powder and carbon nanotubes（CNTs）in the electrolyte was designed to produce a lithium powder suspension pre-lithiation agent,and then the SiO/G@C@A-2 anode material was pre-lithiated to improve its first coulombic efficiency.The SiO@C@A-1cathode obtained by pre-lithiation with Li/CNTs-1 pre-lithiation agent has better electrochemical performance,with a first de-lithiation specific capacity of 981.3 m Ah·g^-1at a current density of 0.1 A·g^-1and a first coulombic efficiency of 95.65%,which is higher than that of the untreated sample.The first coulometric efficiency was 95.65%,which was about 25%higher than that of the untreated sample.After 100 cycles at a current density of 0.5 A·g^-1,the de-lithium capacity of 648 m Ah·g^-1was maintained with a capacity retention rate of 83.27%,which is about 10%higher than that of the untreated sample,reflecting the good cycling performance.However,there are problems of complicated operation and difficulty in dispersing the lithium powder uniformly during the preparation of the lithium powder suspension pre-lithiation agent,which makes the pre-lithiation process difficult to control.Finally,based on the above pre-lithiation experiments,an external circuit pre-lithiation method was designed to achieve a controlled pre-lithiation process through adjustable resistance and control of pre-lithiation time.An external circuit was used to connect the lithium wafer to the SiO/G@C@A-2 anode material for pre-lithiation,and an adjustable resistor with a maximum resistance of 100Ωwas connected to the external circuit to control the pre-lithiation process.After 20 min of pre-lithiation with an external resistor,the first coulombic efficiency of the SiO@C@A-20 anode material could reach90.84%,which is about 20%higher than the first coulombic efficiency of the untreated sample.After 100 cycles at a current density of 0.5 A·g^-1,the de-lithiation capacity of655.4 m Ah·g^-1was maintained with a capacity retention rate of 82.02%,which is about10%higher than that of the untreated sample,and the cycling performance was significantly improved.