Modification Of Nano-silicon Surface And Its Application In Anode Materials Of Lithium-ion Batteries

At present,due to the depletion of non-renewable resources and the increasing importance of environmental protection issues,the scientific researchers have focused on energy storage in the field of new energy.The development of new materials for lithium-ion batteries,as one of the research hotspots in the field of Materials Science in the world,has led a profound revolution in modern electrochemistry in the past two decades.Silicon,with high theoretical specific capacity of 4200 mA h g-1,relatively low working potential and abundant resource,has been widely studied as the anode materials for the next generation lithium ion batteries.However,there are still many difficulties to overcome in order to realize the commercial application of silicon anode materials.For example,in the process of Li+ insertion/removal,silicon will expand enormously,which will cause the surface of silicon to break and pulverize,resulting in low coulomb efficiency and irreversible loss of capacity.Surface coating of silicon material is a proven effective strategy to alleviate the volume expansion of silicon.Firstly,the effect of in-situ silicon oxide thickness on the electrochemical performance of silicon-based anode materials was investigated.It was found that the coating obtained by 30 min oxidation in 600 ? air environment had the most significant effect on the electrochemical performance of silicon-based anode.Then,in order to solve the problem that the initial coulomb efficiency of silicon-based anode material with silica coating is not high,we use lithium borohydride to achieve selective pre-lithization of Si@SiOx material,which not only improves the initial coulomb efficiency,but also achieves excellent Li+ diffusion efficiency.The main research contents of this paper can be summarized as follows:1.Firstly,Si nanoparticles coated with silica were prepared by simple air oxidation method.The thickness of oxide layer on the surface was measured by various characterization methods.It was found that the thickness of oxide layer increased with the increase of oxidation time.The results of electrochemical tests show that the silicon-based anode material prepared by oxidation for 30 minutes at 600 ? has excellent electrochemical performance.At the current density of 1C(1C=3A g-1),the specific capacity of the half-cell is still 969 mA h g-1 after 200 cycles,which shows good constant cycle performance,and its rate performance is also tested.2.Then,we present a simple strategy to fabricate an in-situ formed artificial SEI membrane(Li2SiO3)to protect Si anode by selectively lithiating Si@SiOx coating layer.This in-situ formed artificial SEI coating layer can not only buffer the stress caused by volume expansion to keep the integrity of electrode,but also efficiently improve the ICE of Si anodes.As anode for LIBs,Si@Li2SiO3 exhibit a high ICE of 89.1%,excellent rate capability of 959 mA h g-1 even at 30 A g-1,and long cycling lifespan of 1091 mA h g-1 at 3 A g-1 even after 1000 cycles.In addition,a full cell assembled with Si@Li2SiO3 anode and commercial LiFePO4 cathode,displays a super ICE of 91.1%with a high initial charge/discharge capacity of 150/136.6 mA h g-1.