Preparation And Optimization Of High Capacity Si/C Anode And Solid Composite Electrolytes For Lithium Ion Batteries

With the rapid development of electric vehicles and various energy storage systems,traditional lithium secondary batteries have been unable to meet the people’s needs for higher performance batteries.Therefore,solid-state lithium-ion batteries that possess high energy density and safety become a focus on the research of the next generation lithium secondary batteries.Solid composite electrolytes have not only excellent electrochemical performances,but also superior mechanical capacity and thermal stability and so on,become the main research direction of solid electrolytes at present.By using the solid composite electrolytes,the poor interface compatibility can not only be effectively improved,but also the problem of uneven deposition of lithium ions caused by uneven electric field distribution can be improved.Finally,the cycle performance and life of lithium-ion batteries are reinforced.High energy density and high safety are the thesis’s focus,and the related mechanisms are discussed in detail.The details are as follows:（1）In the chapter,the silicon/carbon nanofiber/carbon（Si/CNF/C）composite materials obtained by thermal decomposition are used as the anode material,and the volume expansion and electrochemical properties of Si materials are systematically studied.Si/CNF/C materials obtained a high specific capacity of 1050 m Ah g^-1 at 100 m A g^-1.Results illustrate that Si/CNF/C materials can effectively suppress the volume expansion of Si materials,and also provide channels for the lithium-ionic migration.（2）In the chapter,the cubic Li_6.4La₃Zr_1.4Ta_0.6O₁₂（LLZTO）material that possess high ionic conductivity was prepared by the solid state reaction.The LLZTO is added in PVDF-HFP polymer,then the SN also is added in the above mixtures.The paper was systematically studied the influences of LLZTO and SN for the PVDF-HFP polymer.As a result,the LLZTO/PVDF-HFP/SN solid composite electrolytes acquire high ionic conductivity,excellent electrochemical performances and thermal stability.The electrolytes are used at solid Li/Li Fe PO₄ cells,the cells show a specific capacity of 150.2 m Ah g^-1 at 0.5C after 269 cycles,and the capacity retention rate is close to 100%.（3）In the chapter,nano materials Ui O-66-NH₂ obtained by a solvothermal process possess an octahedral-like crystal agglomeration morphologies and uniform size（～100 nm）.Ui O-66-NH₂ has a large specific surface area of 512 m² g^-1 and some micropores（～0.54 nm and 1.27 nm）.Ui O-66-NH₂ and S-Zr O₂ are added in PVDF-HFP polymer matrix,the solid composite electrolytes based-PVDF-HFP polymer are successfully prepared by a simple coating method.Results show that the solid composite electrolytes have a high lithium ion transference number of 0.72,a wide electrochemical stability window of 5 V（vs.Li/Li⁺）and a stable interface compatibility against lithium metal.Meanwhile,the solid composite electrolytes can effectively suppress the growth of lithium dendrites.The electrolyte is used in a solid Li/Li Fe PO₄to study the cycle performance,and the reason of capacity declining is systematically studied.The interface compatibility at cathode side is improved by the composite battery.The cell delivered a specific capacity of 158 m Ah g^-1 at 0.2 C,and the coulombic efficiency is nearly 100%.