Preparation And Electrochemical Li-Storage Properties Of SiO-Based Multiphase Composite Anode Materials

With the continuous development of the social economy,people's demand for energy is increasing.It is necessary to develop the safe,convenient and efficient energy storage for solving energy proplems.Owing to their high energy density,high capacity,and long cycling life,lithium ion batteries?LIBs?have been widely used in our daily life.However,with the rapid development of portable electronic devices and electric vehicles,conventional lithium ion batteries using graphite as a negative electrode have been difficult to meet market demands due to their low energy density.Therefore,the development of new lithium-ion batteries with high energy density and long cycle stability is imperative.Silicon monoxide?SiO?shows a small volume change upon lithiation and delithiation because its unique composition and structure,consequently offering better cycling stability than that of Si.However,the disadvantages of SiO anode materials generally include poor conductivity,low first coulomb efficiency and cycle stability,which severely limit their practical applications.Herein,to improve the electrochemical properties of SiO,the influence and mechanism of B and N-doping and particle size on its structure,morphology and electrochemical properties were sustematically studied.The structure and electrochemical performance of the combination of micro-sized SiO and lithium borohydride were first studied.The B-containing SiOx composites SiO/xLiBH₄?x =0.1,0.2,0.3,0.4?were prepared by first ball milling the mixtures of SiO-xLiBH₄ and subsequently heating.Composition and structure characterization showed that SiO/xLiBH₄ mainly composed of amorphous/nanocrystalline Si,SiOx,B,B₂O₃,and Li₂SiO₃,with increasing LiBH content,the Li 1s and B 1s intensities were increased slightly.The newly formed Li_Si0_,B,and B₂O₃ are mostly located at the surface,creating a core-shell-like structure.The as-prepared SiO/xLiBH₄ samples exhibited superior electrochemical lithium storage performance when used as anode material,in particular for the sample prepared from SiO/0.3LiBH_.At 100 mAg¹,the specifc capacity of SiO/0.3LiBH4 sample was 1190 mAhg^-1 after 100 cycles.The calculated capacity retention was 81.0%,which is more than two times higher than that of pristine SiO?33.9%?.Even at 1.6 Ag^-1,the specifc capacity of SiO/0.3LiBH4 sample was still 530 mAhg^-1,which was much higher than the specific capacity of the pristine SiO?167 mAhg^-1?at the same current density.When the current density was reduced to 100 mAg^-1 again,the specific capacity of the SiO/xLiBH₄?x=0.3?sample rapidly rise to 1411 mAh^-1.Further EIS and XPS revealed that the surface of SiO/xLiBH₄ composites have the presence of a stable SEI flm.The presence of amorphous B,B₂O₃,and nanocrystalline Li₂SiO₃ could observably enhance the mechanical properties of Si/SiOx active materials.This outcome enabled good accommodation of the volume change of the Si/SiOx active materials during lithiation/delithiation,consequently depressing the particle pulverization and fracture,and stabilizing the SEI flm that formed during the initial cycling.Followed by the above results,the effect of LiNH on the structure and electrochemical Li storage properties of SiO was also evaluated.The results showed that the SiO/xLiNH_{x = 0.1,0.2,0.3,0.4}composites were mainly composed of amorphous/nanocrystalline Si,SiOx,Li₂SiO₃ and SiNx?the bonding Si-N?.Electrochemical measurements reveal that the SiO/0.3LiNH₂mple showed a significantly improved electrochemical performance as anode active material of Li-ion batteries.At 100 mAg^-1,the specifc capacity of SiO/0.3LiNH sample was 1209 mAhg^-1 after 100 cycles.The calculated capacity retention was 75.1%,which is more than two times higher than that of pristine SiO?33.9%?.Even at 1.6 Ag^-1 the specifc capacity of SiO/0.3LiNH₂sample was still 660 mAhg^-1,which was much higher than the specific capacity of the pristine SiO?167 mAhg^-1?at the same current density.When the current density was reduced to 100 mAg^-1 again,the specific capacity of the SiO/xLiNH₂x = 0.3)sample rapidly rise to 1517 mAhg^-1.The presence of N-doped materials and new formed Li₂SiO₃ were the main reasons for the improvement of electrochemical performance.Finally,the influence and mechanism of particle size on the electrochemical performance of SiO-based anode were further studied.SiO-based composite materials with different particle sizes were prepared by high-energy ball milling using SiO/0.3LiBH₄as raw material.It was found that the ball milling can significantly reduce the particle size of the composite.After 3 h of ball milling,the average particle size of the sample is about 2 ?m,and the particle size of the 9 h sample is reduced to less than 0.5 ?m.XRD characterization shows that the ball milling process can reduce the particle size of the sample and promote the disproportionation of the SiO-based composite material to some extent.The electrochemical performance characterization showed that the BM9h sample showed a more excellent comprehensive electrochemical performance,its charge specific capacity remained at 1170 mAhg^-1 after 50 charge and discharge at a current density of 100 mAg^-1.The capacity retention rate was 86.9%.According to the mechanism study,ball milling can reduce the particle size of the sample and increase the contact area between the particles and the electrolyte,thereby improving the electrochemical performance of the sample.