Preparation And Electrochemical Properties Of Silicon Matrix Composites For Lithium Ion Battery

Lithium-ion batteries stand out among many energy storage devices due to their high energy density,low REDOX potential and environmental friendliness,and have been used in a variety of portable consumer electronic products and electric vehicles.However,graphite anode materials with specific capacity of only 372 m Ah/g are still used commercially,so the reversible storage capacity of lithium-ion batteries is limited by anode materials.In order to improve the energy density of lithium-ion batteries,advanced electrode materials must be developed to replace the current commercial graphite material.Silicon material has attracted great attention because of its high theoretical specific capacity.In this paper,silicon is directly deposited on the conductive substrate by a simple electrodeposition method,which not only simplifies the preparation process of electrode materials,but also provides a possibility for the preparation of flexible anode materials.(1)Using nickel foil as the substrate,the deposition potential of amorphous Si in the deposition solution(0.5 M Si Cl₄ and 0.1 M Tetrabutylammonium Chloride dissolved in propylene carbonate)was preliminarily determined by LSV test,and the Si/Ni composite material was deposited under this condition.XRD and Raman tests were to analyze the composition of the composite materials,and SEM was used to analyze the thickness and surface morphology of the sedimentary layers during different depositions.The Si/Ni composite was used as anode material for electrochemical tests.The results show that the specific discharge capacity of 350 m Ah/g is maintained for 50 cycles at a current density of 100 m A/g.However,when the current density increases ten times,it only shows a low discharge specific capacity of 187 m Ah/g,which needs to be improved.(2)Using three-dimensional metal material copper foam as the working electrode,under the LSV test results,three electrode deposition devices were used to deposit amorphous silicon through different deposition methods.SEM and cyclic voltammetry tests were used to analyze the morphology and cyclic reversibility of the silicon layer under constant current and constant voltage deposition.The results show that the surface morphology of the silicon layer deposited by constant voltage deposition is flatter and denser,and its reversibility is better.The electrochemical properties of the composites obtained by constant voltage deposition were compared and the best deposition time was determined.The electrochemical performance of the composite showed that the specific discharge capacity of the composite was 871 m Ah/g after 100 charge-discharge times at the current density of 100 m A/g.Compared with the nickel foil substrate,the material properties are improved when the copper foam substrate is deposited,which may be attributed to the three-dimensional structure of the substrate alleviating the volume expansion of the material in the process of charging and discharging to some extent.(3)In order to realize the flexible and self-supporting properties of the electrode material,a three-dimensional porous flexible Ni/PVDF conductive fiber film was prepared by electrospinning and electroless nickel plating.The optimal time of electroless nickel plating was determined to be 10 min by the SEM test.The conductive fiber film was composed of PVDF fiber inner core and outer nickel layer.Each fiber was independent of each other and intersected with each other,forming a porous structure similar to fishing net,which could not only meet the demand of electrical conductivity,but also had a high surface area.Si/Ni/PVDF flexible self-supporting composites were prepared by electrodeposition method on the conductive film substrate.It is found that the composite has high flexibility by bending and folding tests.The results show that the specific discharge capacity of Si/Ni/PVDF flexible self-supporting composites remains530 m Ah/g after 100 cycles.The Coulomb efficiency gradually increases to about 97%and remains in a stable state,showing good cycle inversibility.