Abstract:

Carbon-coated silica （SiO₂） and molybdenum carbide （Mo₂C） particles are prepared by sol-gel method using tetraethyl silicate， ammonium molybdate and sucrose as silicon， molybdenum and carbon sources， respectively. The phase composition， morphology and structure of the composite are characterized by means of X-ray diffractometer， transmission electron microscope and other instruments， and the electrochemical performance of the composite as a negative electrode material for lithium ion batteries is also studied. The results show that when the mass ratio of tetraethyl silicate， ammonium molybdate and sucrose is 3∶1∶2 （denoted as SiO₂/Mo₂C/C 2）， it has good electrochemical performance when it is used as the negative electrode material of lithium ion battery. At the current density of 100 mA/g， the first charge and discharge specific capacities are 662 mA·h/g and 896 mA·h/g， respectively， and the reversible capacity can still reach 625 mA·h/g after 200 cycles. Even at a larger current density of 2 A/g， the reversible capacity can still reach 272 mA·h/g. The composite exhibits good rate performance and cycling stability， which is mainly attributed to the good stability and high electrical conductivity of Mo₂C which can effectively improve the poor conductivity of SiO₂ itself. The core material directly reacts with the electrolyte to generate by-products， and in addition， it can be used as a buffer layer to slow down the volume expansion of SiO₂， so the electrochemical performance of the material is significantly improved during the charging and discharging process. The new idea of ??using transition metal carbides to modify the poor conductivity and cycle performance of SiO₂ proposed here can provide new research ideas and broaden the research direction for the modification of other anode materials.

Key words: Silica, Molybdenum carbide, Carbon coating, Lithium-ion battery