Silicon-based Anode Materials For Lithium Ion Battery

Silicon is considered to be the next generation anode material of lithium-ion battery due to the ultra-high specific capacity and lower voltage versus lithium potential.Nowadays,silicon-based anode materials have been used.However,the application of silicon-based anode materials has been limited severely,because of the low initial efficiency,huge volume change during cycling and the fractures of SEI film.In this paper,the degradation mechanism of silicon-based anode batteries was studied.A series of pouch cells with graphite and three kinds of silicon-based materials as anode were assembled.The cycling performance of pouch cells showed a sharp decrease with high silicon content in anode materials.It was found that the capacity of the positive and negative electrode didn't decay obviously after 50 cycling,which was also been proved by SEM and XRD data.The first discharge capacity of positive and the first charge capacity of the negative were studied after the disassembly of the cells.The main reason for the degradation was the loss of the lithium and the polarization of the cell.ICP and EDS results supported this conclusion.Finally,it is found the contribution capacities of the graphite and SiOx to the battery were both decreased as the battery capacity decays by using of the dQ/dV-V and dV/dQ-Q curves.Considering with the surface cracks and instability of SEI layer,micro-silicon pyramid structure was chosen as the anode material to research with the influence of surface nanostructures,electrolyte additives and high charge-discharge rate.The surface nanopores inhibited the cracking on the surface of the silicon wafer during charge and discharge processes.The electrolyte additives also reduced the degree of cracking on the surface of the silicon wafer.Comparing with low charge-discharge rate,the high rate could inhibite the increase of SEI layer,effectively.The electrolyte additives could also reduces the thickness of SEI layer.And VC worked best and FEC second.The lithium-biphenyl-dimethoxyethane solution was used as a kind of prelithiation reagent to enhance the low initial efficiency of silicon-based anode materials.The results show that the solution can effectively improve the first efficiency of nano-silicon,hard carbon,soft carbon and other anode materials,without bad impact of the cycle performance.The electrical conductivity and ionic conductivity of the solution were also been measured.The total conductivity of the solution was found to allow Arrhenius' s law.The semi-flow battery assembled with this solution and lithium iron phosphate cathode showed high initial efficiency.