Modification And Electrochemical Performance Of Silicon Monoxide Anode Materials For Lithium Ion Batteries

The anode materials with high specific capacity play a prominent role in increasing the energy density of lithium-ion batteries.Silicon-based anode materials are constituted as the most promising next-generation lithium-ion battery anode materials owing to their abundant natural reserves,low discharge potential,and high theoretical specific capacity.However,elemental silicon will bring about stupendous volume change more than 300%during cycling,leading to the pulverization of active particles,short of contact and the trapping of active lithium due to the repeated growth of solid electrolyte interface(SEI),which severely limit the cycling stability of silicon anode.The most commercially practical candidate in the silicon-based family-silicon monoxide anode material,displays the reduced overall volume change due to the formation of lithium silicate and lithium oxide during the initial lithiation,which act as a buffer to reduce the impact of volume change on the structure.Although irreversible phases such as lithium silicate suppress the volume change,they accordingly cause the loss of active lithium,and the initial coulombic efficiency of the silicon monoxide anode is low.Herein,starting from the improvement of initial coulombic efficiency,micron-sized silicon monoxide anode with excellent comprehensive electrochemical performance is obtained via fixing the oxygen component as a crystalline quartz phase that is inert to lithium,and chemical pre-lithiation on the electrode.The main research contents are depicted as follows:(1)Due to the effect of the alkali metal element and fluorion on promoting atomic rearrangement in the disproportionation process of silicon oxide,a two-phase silicon monoxide material,in which quartz SiO2 crystal phase and Si crystal phase with high crystallinity coexist,can be produced in a short-time disproportionation at 900℃ by using LiF as a dopant.This process not only release more active silicon,improving the reversible capacity,but also fix part of the oxygen,increasing the initial coulombic efficiency.The initial coulombic efficiency is up to 80%and the initial reversible capacity is 1521 mAh g-1 with the higher average coulombic efficiency.In addition,it is found that extending the holding time or increasing the disproportionation temperature can fix more oxygen components into quartz crystals and improve the initial coulombic efficiency,but a large amount of reversible capacity is sacrificed.The conversion of quartz crystal phase and silicon crystal phase in the process of lithium cyclingare investigated by in-situ XRD.(2)1-methylnaphthalene-lithium is selected as the organolithium source for chemical prelithiation of SiO@C anode electrode.It is found that 1-methylnaphthalene-lithium can partially reduce SiO2 on the surface of silicon monoxide,which improves the reversible specific capacity of SiO@C.The reversible specific capacity of the first cycle reaches 2341.4 mAh g-1,which helps to improve the energy density of the battery.The pre-generated SEI in the prelithiation process improves the diffusion rate of lithium ions,which is conducive to the development of high capacity.The initial coulombic efficiency of the full cell deploying the pre-treated electrode matched with LiFePO4 increases from 65%to 80%,achieving a considerable lithium replenishment efficacy.