Silicon material and method of manufacture

Abstract

A silicon material can include a composition with at least about 50% silicon, at most about 45% carbon, and at most about 10% oxygen. The silicon material can have an external expansion that is less than about 40%. The silicon material can include silicon nanoparticles, which can cooperatively form clusters. The silicon nanoparticles can be porous.

We claim: 
     
         1 . A method for manufacturing a silicon material comprising:
 heating a mixture comprising a silica starting material and a metal reducing agent to a first temperature at a first ramp rate;   heating the mixture to a second temperature at a second ramp rate, wherein the mixture is maintained at the second temperature for a first duration of time; and   after the first duration of time has elapsed, heating the mixture to a third temperature at a third ramp rate, wherein the mixture is maintained at the third temperature for a second duration of time;   wherein the silica starting material of the mixture is reduced to the silicon material.   
     
     
         2 . The method of  claim 1 , wherein the first ramp rate is between 10° C./min and 20° C./min. 
     
     
         3 . The method of  claim 2 , wherein the second ramp rate and the third ramp rate are each between VC/min and 10° C./min. 
     
     
         4 . The method of  claim 3 , wherein the first duration of time is between 2-12 hours and wherein the second duration of time is between 1-6 hours. 
     
     
         5 . The method of  claim 1 , wherein the first temperature is approximately 400° C., the second temperature is approximately 600° C., and the third temperature is approximately 800° C. 
     
     
         6 . The method of  claim 1 , wherein the mixture further comprises salt. 
     
     
         7 . The method of  claim 6 , wherein a mass ratio of the silica starting material to salt to the metal reducing agent is approximately 1:5:1. 
     
     
         8 . The method of  claim 1 , further comprising depositing a carbon coating on the silicon material using chemical vapor deposition. 
     
     
         9 . The method of  claim 8 , wherein the carbon coating is between 1-10 nm thick. 
     
     
         10 . The method of  claim 1 , wherein the silica starting material comprises fumed silica. 
     
     
         11 . A method comprising:
 mixing silica particles with a reducing agent to form a mixture; and   reducing the silica particles to silicon particles by heating the mixture to a reducing temperature, wherein the silicon particles comprise 0-5% by mass carbon, 4-10% by mass oxygen, and 85-96% by mass silicon.   
     
     
         12 . The method of  claim 11 , further comprising ball milling the silicon particles at about 500 rpm for between 1-6 hours. 
     
     
         13 . The method of  claim 11 , wherein the silicon particles comprise a specific surface area of 1-10 m 2 /g. 
     
     
         14 . The method of  claim 12 , wherein an external expansion of the silicon particles is at most 40% upon full lithiation of the silicon particles. 
     
     
         15 . The method of  claim 11 , further comprising heating the mixture to an intermediate temperature less than the reducing temperature, wherein the mixture is maintained at the intermediate temperature for a threshold time before heating the mixture to the reducing temperature. 
     
     
         16 . The method of  claim 15 , wherein the mixture is heated to the intermediate temperature using a first ramp rate until the mixture reaches a threshold temperature after which the mixture is heated at a second ramp rate. 
     
     
         17 . The method of  claim 16 , wherein the first ramp rate is at most about 20° C./min and wherein the second ramp rate is at most about 10° C./min. 
     
     
         18 . The method of  claim 11 , wherein mixing the silica particles with the reducing agent to form the mixture further comprises mixing the silica particles with a salt, wherein the mixture comprises the silica particles, the reducing agent, and the salt. 
     
     
         19 . The method of  claim 18 , wherein a mass ratio of the silica particles to the salt to the reducing agent in the mixture is about 1:5:1. 
     
     
         20 . The method of  claim 18 , wherein the salt coats the silica particles 
     
     
         21 . The method of  claim 11 , wherein the silica particles comprise fumed silica.