Silicon-based Anodes Prepared By Ball Milling For High Performance Lithium Ion Batteries

Exploring electrode materials with high energy density is of great significance for the development of lithium ion battery,to match the rapid growth of 3C industry and the field of electric vehicles.Silicon-based materials,including Si O_x,have been regarded as ideal anodes for next-generation high-performance lithium ion batteries due to their high capacity,moderate working potential,abundant reserves and environmentally friendly.However,its huge volume expansion（14.8（?）³/Li）during lithiation and delithiation causes the destruction of electrode structure,which would result in rapid decay of battery capacity and severely limit its practicality.Studies have shown that amorphous/nanosized silicon or Si-based composites can effectively buffer the volume expansion during cycling and improve cyclability.Aiming at the current practical problems of the amorphization/nanocrystallization and compounding of silicon-based materials,amorphous/nano-crystalline Si（a/n-Si）,Si@Si O_x-Cu₃Si and Si O_xhave been synthesized by using mechanical ball milling with microsized polycrystalline silicon powder as the starting materials.The electrochemical properties of as-prepared materials are evaluated when used as lithium ion anodes.The specific research contents are as follows:1)Amorphous/nano-crystalline Si（a/n-Si）with a secondary micro-sized particle has been prepared by mechanical ball milling.Si grain was refined to amorphous/nanocrystalline,with an average size of 1.8 nm.When used as negative electrode for lithium ion battery,it shows the first discharge capacity of 3010 m Ah/g,and there was no phenomenon of uneven volume change caused by Li₁₅Si₄ instantaneous crystallization during charge and discharge.Additionally,the binders for Si-based materials currently in use are screened using a/n-Si as the standard sample.The results show that a/n-Si with 9.83wt%Li PAA aqueous solution prepared by our laboratory showed the highest first coulombic efficiency,and performed similar capacity retention with commercial 10.2wt%Li PAA aqueous solution,close to 50%after cycling 50 times at 0.2C rate.The deep-section XPS was used to analyze the solid-liquid interface（SEI）film formed on the surface of the a/n-Si electrode.It was found that the composition of the SEI film was similar for the electrodes prepared by different binders,but the content ratio was different.The SEI film is thin and stable,which is formed on the surface of the prepared electrode with 9.83wt%Li PAA.Meanwhile,the proportion of the inorganic phase component of the lithium salt is much higher than that of other binders,and the content of the organic phase component is relatively low.Plus,the effect of FEC electrolyte additive on SEI film of a/n-Si electrode has been also discussed.In addition,compared with the 9.83wt%Li PAA aqueous solution with or without FEC additives,the composition of the electrode SEI film is changed.The results show that after FEC is added,the total Li content on the electrode surface will increase significantly,and the proportion of lithium salt in the SEI film increases.2)Si@Si O_x-Cu₃Si composite has been one-step synthesized by plasma ball milling.The composite has a micro-nano structure consisting of nano/amorphous Si,amorphous Si O_x,and Cu₃Si nanoparticles,wherein the average grain size of the nano/amorphous Si is 15.6 nm and is surrounded by in-situ generated Si O_x and Cu₃Si.The micro-nano structure of Si@Si O_x-Cu₃Si can effectively relieve the volume expansion of the electrode during charging and discharging,and the volume expansion rate can be controlled at about 150%.The volumetric capacity of Si@Si Ox-Cu₃Si is 2.5 times higher than that of the current commercial graphite（720 m Ah/cc）,which can reach 1900 m Ah/cc.Si@Si O_x-Cu₃Si composite has been further refined to improve electrochemical performance.Refined Si@Si Ox-Cu₃Si showed a high initial coulombic effiency of 81%,a good capacity retention rate of 75%after 50 cycles at a current density of 160 m A/g.Finally,Si O_x has been extracted from the Si O_x/Cu composite by substitution method and exhibits excellent cycle stability,when used as a negative electrode material for lithium ion battery.3)Si O_x material was synthesized by mechanical ball milling under air atmosphere using a/n-Si prepared in 1)as the starting material.As-prepared Si O_x is a micron-level secondary particle and contains a large amount of amorphous/nanocrystalline Si and amorphous silicon oxide.Used as a negative electrode material for lithium ion batteries,Si O_x shows high volumetric capacity of 1487 m Ah/cc,which is more than twice that of graphite.Its first coulombic efficiency is up to 66.8%,higher than untreated Si O.Si O_xalso shows excellent cycle stability with 1300 m Ah/g after 50 cycles at a current density of 200 m A/g.The results show that Si O_x prepared by this method has practical possibility.