Preparation And Electrochemical Performance Of Li₂MoO₃ And SiO@F-doped C As Anodes For Lithium-ion Batteries

With the development of new energy vehicles and smart grids,lithium-ion batteries with high power and high energy density are urgently needed.The electrode material,which is one of main components in lithium-ion batteries,plays the most important role in this way.Currently,graphite is widely used as anodes in commercial lithium-ion batteries.However,due to low theoretical specific capacity and poor charge/discharge performance at high current densities,the application of graphite in high-capacity lithium-ion batteries has been limited.In order to exploit high-performance anode materials for the next-generation lithium-ion batteries,in this paper,Li₂MoO₃,SiO@F-doped C and SiO@F-doped C/Li₂MoO₃ are synthesized and their lithium storage properties are studied as anodes for lithium-ion batteries.Firstly,submicron Li₂MoO₃ is synthesized via simple liquid chemical reaction,followed by thermal reduction.The as-prepared Li₂MoO₃ is polycrystalline with layered structure,and the electrochemical performance of sample is investigated as anodes for lithium-ion batteries.At a current density of 100 m A g-1 over a voltage window of 0.0-3.0 V,the compound presents a first discharge capacity of about 836 mAh g-1 with an initial coulombic efficiency of 94.5%.After 200 cycles at a current density of 300 mA g-1,a discharge capacity of 654 mAh g-1 is preserved.At a high current density of 1600 mA g-1,the composite still keeps a discharge capacity for 489 mAh g-1.Moreover,Li₂MoO₃ is also produced through the combination of ball milling and thermal reduction.The electrochemical performance and reaction mechanism of the material are investigated.It is revealed that the synthesized Li₂MoO₃ follows mixed insertion/conversion reaction mechanism.Secondly,a novel SiO@F-doped carbon composite（SiO@F-doped C）is fabricated by the heat treatment of the SiO with the assistance of polytetrafluoroethylene（PTFE）,in which both core-shell forming and F-doped carbon coating of SiO are synchronously performed.The synthesized SiO@F-doped C composite exhibits high reversible capacity with excellent cycling performance and rate capability.At a current density of 100 mA g-1 over a voltage window of 0.02-1.2 V,this composite shows a stable discharge capacity of about 990 mAh g-1.After the current density increases to 1600 mAh g-1,a stable discharge capacity of about 553 mAh g-1 can be achieved.At a current density of 400 mA g-1,this compound shows a discharge capacity of 830 mAh g-1,after 400 cycles,the capacity retention of which is 75.2% versus the discharge capacity in the second cycle.During cycling,the pores in the composite provide an extra room for the volume expansion of silicon monoxide,while F-doped carbon improves the conductivity of the electrodes,which should be responsible for the excellent electrochemical performance.Finally,to exploit the synergistic effect of SiO@F-doped C and Li₂MoO₃ during the electrode reaction,SiO@F-doped C/Li₂MoO₃ composite is prepared and its electrochemical performance is investigated under different charge-discharge cut-off voltage range.In a range is 0.0-3.0 V,SiO@F-doped C/Li₂MoO₃ with a mass ratio of 7:3 has better cycling performance than others and its reversible specific capacity of 960 mAh g-1 is delivered after 100 cycles at a current rate of 100 mA g-1.The electrochemical performance of SiO@F-doped C/Li₂MoO₃ composite with mass ratio 7:3 is also investigated in the different voltage range from 0.02 V to different charge cut-off voltage.The highest revesible capacity is presented when the cut-off voltage is 3.0 V,but the cyclic stability is the lowest.Meanwhile,when the cut-off voltage is 1.2 V,the capacity decreases but the cycling stability increases.The capacity rentention rate is close to 90% after 500 cycles at a current density of 400 m A g-1.The good performance is attributed to the fact that SiO@F-doped C and Li₂MoO₃ have different lithium insertion/extraction potentials,which have a good buffer to the volume effects each other.When the charge cut-off voltage is reduced,the volume change of Li₂MoO₃ decreases while the structural stability is enhanced.