Study On Synthesis And Electrochemical Properties Of Li₂S/SiO₂ As Cathode/Anode Materials For Lithium-ion Batteries

As a new type of green secondary battery,lithium?ion battery has been occupied the largest share of the small secondary battery market.However,the energy density of the traditional commercial lithium?ion battery is generally not more than 200 Wh kg?1 because of the low specific capacity of the anode and cathode materials.In this work,the high?capacity silicon?based anode materials SiO₂ and Li2 S cathode materials were used as the research object for their low cost and high theoretical capacity.The relationship between synthesis,microstructures and electrochemical properties of the electrode materials was elucidated to reveal the lithium storage mechanism and cycling deteriorateion mechanism of the electrode materials.?1?The sand from the Kubuqi Desert was treated by simple ball milling,and asmilled sand was directly used as the anode material for lithium?ion battery.The composition of the sand and the effect of the ball milling treatment on the crystal structure,microstructure,electrochemical properties and the lithium storage mechanism of the sand were investigated systematically.The results of the constituent analysis show that the main component of the sand is SiO₂ and the rest is metal oxide.The mass ratio of SiO₂ was up to 85% after dilute hydrochloric acid treated.The results of the microstructure studies show that SiO₂ in the pristine sand showed good crystallinity.But the crystallinity gradually degraded and the particle size gradually decreased with the increasing milling time.When the milling time was up to 108 h,the crystalline SiO₂ was completely converted into amorphous one.The electrochemical results show that the first lithium intercalation reaction in the sand produced irreversible products Li4SiO4,Li2 O and the reversible product LixSiy.With the increase of milling time,the initial reversible capacity of the sand gradually increases whereas the cycle stability gradually decreases.The first discharge and charge capacity of the sample milled for 108 h was 906 mAh g?1 and 413 mAh g?1,respectively,which shows the best electrochemical lithium storage activity.After 200 cycles,the capacity retention rates of the sample milled for 60 h and 108 h were 97.9% and 59.6%,respectively,compared with the second discharge capacity.?2?The 108 h postmilled sample and polystyrene?PS?were selected as the raw materials to prepare the sand/C composites.The effect of carbon content on the electrochemical properties of the composites was systematically studied.The results of the microstructure studies show that the using of PS has little effect on the microstructure of the composites.The electrochemical results show that the sample with a sand/PS mass ratio of 1/2 showed the best electrochemical performance,in which the composite has a carbon content of 5.5 wt%.The initial coulomb efficiency of the composites reached 54.2%,and the discharge capacity was 553 mAh g?1 after 170 cycles,correspding to the reversible capacity retention rate of 78.5%.?3?The XRD and FTIR results indicated that Li2 S and Li₂S2 cathode materials were successfully synthesized through facile ball milling by using the different molar ratio of LiH to sublimed sulfur.The specific capacity of the as-synthesized Li2 S was 280 mAh g?1 after 100 cycles,which was slightly higher than the commercial Li2 S.Compared with the Li2 S,Li₂S2 showed a more stable cycle performance in the initial 50 cycles and delivered a specific capacity of 305 mAh g?1 after 100 cycles.In addition,the first activation voltage of Li₂S2 was 3.69 V,which is lower than that of Li2 S.