Applications Of Silicon 3D Structures In Lithium-ion Battery

Lithium-ion battery has been a new star of battery family due to its merits such as high energy-density,no pollution,and long-life.Silicon material is the best choice of anode material for lithium-ion batteries,which has many advantages like low voltage of lithiation,high theoretical specific capacity,and no pollution.However,the siliconbased material will be accompanied by huge volume expansion(> 300 %)in the lithiation process,which will make the silicon-based material pulverize and make the rapid decline of battery capacity as a result of the side reaction between active silicon material and electrolyte.In addition,the conductivity of silicon-based materials is lower than that of commercial graphite anode materials,which make lithium-ion battery suffer from a lower rate performance.These shortcomings make silicon-based anode materials encounter significant resistance in the process of commercialization.Therefore,the performance improvement of silicon-based anode materials is of critical significance.In this research,we are aim to improving the application of micro-structured silicon anode materials and micro-sized three-dimensional structure in lithium-ion batteries.The improvement of lithium-ion battery’s performance by vertical graphene coating structure was investigated.The effect of aluminum film on silicon anode materials with micron size was studied.The specific research contents and results are as follows:In this study,<100> crystal-oriented silicon micro-pillar array platforms were prepared.The silicon micro-pillar array platform was used for the study of fluorinated vinyl carbonate(FEC),vinyl ethylene carbonate(VEC),vinyl sulfite(ES)and vinyl carbonate(VC)electrolyte additives in LiPF6+EC/DMC electrolyte system using charge/discharge cycles,electrochemical impedance spectroscopy,cyclic voltammetry,scanning electron microscopy and X-ray photoelectron spectroscopy.The results show that the silicon pillar morphology shows cross-shaped expansion after lithiation/delithiation,the inorganic lithium salt makes the silicon pillar morphology intact,and the organic lithium salt content promotes a rougher silicon pillar surface.The presence of poly(VC)components on the surface of FEC and VC electrodes allows the silicon pillar to accommodate greater volume expansion while remaining intact.This work provides a standard,fast and effective test method for the performance analysis of electrolyte additives and provides guidance for the development of new electrolyte additives.A three-dimensional structure of silicon micron square column graphene composite with clear structure and pure composition was prepared.Then the electrochemical performance and structural stability of the silicon micro-pillar 3D electrodes were investigated.The experimental results show that the coulombic efficiency in the first cycle is increased to >90 % by coating of a vertical graphene layer.After 50 cycles,the surface structure of the silicon micropillar-graphene composite three-dimensional electrode remains intact,with the surface covered by a thin layer of SEI film.On the other hand,the silicon micro-pillar electrode without vertical graphene coating is peeled off from the collector surface after 50 cycles.At the same time,the coulombic efficiency and capacity retention rate of the silicon micropillar-graphene composite threedimensional electrode are superior to those of the electrode without graphene coating in the long-term cycle test.Amorphous silicon-aluminum thin film composite structures were prepared on nickel substrates and the performances of was studied.Silicon thin film electrode materials with a total thickness of 1 μm were deposited on nickel collector.The differences among a single layer 50 nm aluminum thin film structure,a pair of 50 nm aluminum thin film and a pair of 25 nm aluminum thin film structures were studied.The results show that the composite electrode of single-layer aluminum film metal improves the coulombic efficiency in the first cycle,the cycle stability increases from380 cycles to 600 cycles,and the cycle life is greatly improved.At the same time,in the exploration of bilayer structure,the composite with pair of 25 nm aluminum structure has the highest coulombic efficiency of 87 %,which is 4.6 % higher than that of composite electrode with single layer aluminum structure.In summary,the results of thesis provide a new method and idea for reducing the cost of research and push forward the development of electrolyte additives for lithiumion batteries and the development of micro-sized silicon anode battery materials.