Silicon composite, making method, and non-aqueous electrolyte secondary cell negative electrode material

Abstract

A silicon composite comprises silicon particles whose surface is at least partially coated with a silicon carbide layer. It is prepared by subjecting a silicon powder to thermal CVD with an organic hydrocarbon gas and/or vapor at 900-1,400° C., and heating the powder for removing an excess free carbon layer from the surface through oxidative decomposition.

1 . A silicon composite comprising silicon particles whose surface is at least partially coated with a silicon carbide layer.  
   
   
       2 . The silicon composite of  claim 1  wherein the silicon particles have an average particle size of 50 nm to 50 μm and the silicon particle surface is at least partially fused to silicon carbide.  
   
   
       3 . The silicon composite of  claim 1  wherein a diffraction line attributable to silicon is observed when analyzed by x-ray diffractometry, and which contains free carbon in an amount of up to 5% by weight.  
   
   
       4 . The silicon composite of  claim 1  which contains 5 to 90% by weight of zero-valent silicon capable of generating hydrogen gas when reacted with an alkali hydroxide solution.  
   
   
       5 . The silicon composite of  claim 1  wherein after the silicon composite is treated with a mixture of hydrofluoric acid and an oxidizing agent and heat dried, silicon carbide is left as the evaporation residue.  
   
   
       6 . A method for preparing the silicon composite of  claim 1 , comprising the steps of subjecting a silicon powder to thermochemical vapor deposition treatment with an organic hydrocarbon gas and/or vapor at 900° C. to 1,400° C., and heating the powder for removing a surface excess free carbon layer through oxidation.  
   
   
       7 . A negative electrode material for a non-aqueous electrolyte secondary cell, comprising the silicon composite of  claim 1.