| Silicon is the second most abundant element on earth and silicon monomer has been widely used in the photovoltaic,semiconductor and microelectronics industries.Under the international context of the energy and environmental crisis,renewable energies such as solar energy are being given more attention than ever before.As a result,the silicon materials industry is experiencing unprecedented growth.However,due to the cutting of silicon wafers a large amount(around 40%)of silica sludge waste is generated.The high value recycling of this waste has been a pain point issue for the industry.On the other hand,the rapid development of renewable energy and electric vehicles urgently requires lithium-ion batteries that can be rapidly charged and discharged under high specific capacity conditions.The practical application capacity of graphite anode for existing commercial lithium-ion batteries has reached 350 mA h g-1,close to the theoretical value of 372 mA h g-1 for LiC6.Therefore,graphite will not be able to meet the future demand of lithium-ion batteries for high specific capacity applications in the electric vehicle industry and energy storage.Silicon has a high theoretical specific capacity of 4200 mA h g-1,which is much higher than that of graphite,so the replacement of mainly used graphite by silicon with a high specific capacity is of great interest.In conclusion,the research and exploration of photovoltaic cut silica sludge waste as a silicon anode material for lithium-ion batteries with high performance has significant social value and promising market prospects.In this paper,we have used silicon sludge waste from photovoltaic wafer cutting process as raw material to construct carbon-coated-silicon core-shell structure and successfully prepared carbon/silicon composite anode materials for lithium-ion batteries with excellent electrochemical properties by using low-cost hydrothermal catalysis.Further mechanistic studies and analyses have been carried out.This thesis takes the concept of energy conservation and environmental protection as the starting point,turning waste into treasure and providing ideas for the design of low-cost and high-performance silicon anode for lithium-ion batteries.The work in this paper focuses on the following three aspects(for the sake of technical confidentiality,the nickel catalysts used in this paper are referred to as inorganic nickel and organic nickel):(1)Study on the preparation and electrochemical performance of carbon/silicon core-shell structures catalyzed by inorganic nickel.A core-shell structure Si@C material was hydrothermally fabricated by adding inorganic nickel as a catalyst,selectingphotovoltaic cutting waste silicon as the silicon source and using glucose as the carbon source.The prepared micron Si@C anode material was applied to the anode of lithium-ion batteries and subjected to electrochemical performance test.After 200 cycles of charge/discharge test at a current density of 0.1 C,it still had a specific capacity of 1788.9 mA h g-1.In addition,a specific capacity of 1446.8 mA h g’1 can be maintained under the rate test of 0.1 C to 1.0 C;when the current density is returned to 0.1 C,the specific capacity can be stabilized at about 3000 mA h g-1.(2)Study on the preparation and electrochemical performance of carbon/silicon core-shell cross-linked composite materials catalyzed by organic nickel.Using photovoltaic cutting waste silicon as raw material,glucose was added as a carbon source and organic nickel was used as a catalyst in order to improve the graphitization of the carbon material.The prepared material exhibited excellent electrochemical properties.The charge/discharge cycle at 0.1 C showed a specific capacity of 3317.6 mA h g-1 in the first cycle and an initial Coulomb efficiency of 76.76%;after 360 cycles a specific capacity of 2514.8 mA h g-1 remained,having a capacity retention rate of 75.8%;after 1000 cycles under 0.2 C,a specific capacity of 1548.9 mA h g-1 remained.In addition,under the rate test of 0.1 C to 2.0 C,a specific capacity of 1596.9(1.0 C)and 925.3 mA h g-1(2.0 C)can be maintained,respectively;when the current density is returned to 0.1 C,the specific capacity can be stabilized at about 3000 mA h g-1.(3)Theoretical simulation calculations.Through the establishment of a model,the simulation of the diffusion of lithium ions in the lamellar micron silicon and ordinary granular micron silicon,the molecular dynamics simulation analysis of the lithium insertion behavior of silicon in two models,theoretically explain the reasons for the excellent electrochemical performance of lamellar submicron silicon.This study cleverly combines the photovoltaic industry and lithium-ion batteries in two different fields,having obvious interdisciplinary characteristics.Using the waste silicon from photovoltaic cutting for lithium-ion batteries is,to a certain extent,turning waste into treasure,not only dealing with the waste of the photovoltaic industry,but also preparing high-performance lithium-ion battery anode materials.In addition,the method used in this study is simple,environmentally friendly,efficient and has high potential for commercialization. |
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