Silicon carbon composite materials and method for making same

Abstract

The invention relates generally to a method for making a silicon-carbon composite comprising nanoscale silicon and carbon, the method comprising the steps of preparing a dispersion of silicon nanoparticles and the selected form/s of carbon; spray drying the dispersion to form essentially spherical silicon nanoparticles; heat treating the silicon nanoparticles to pyrolyse and/or burn off any polymers, and to strengthen the silicon nanoparticles; coating the silicon nanoparticles with carbon to form the Si:C composite; and optionally, adding additional elements such as lithium, magnesium, nitrogen and halogen gases to the composite, either during the heating step (c) or coating step (d) or during a subsequent heat treatment step. The invention relates further to composites made by such method, an anode made of such composite and a batter comprising such anode.

1 . A silicon-carbon composite comprising nanoscale silicon and carbon in a weight ratio of between about 30:70 and about 70:30, and having a volume fraction of porosity between about 20 and about 70%. 
     
     
         2 - 4 . (canceled) 
     
     
         5 . A composite according to  claim 1 , wherein the porosity of the composite accommodates swelling up to about 300% during the lithiation-delithiation process. 
     
     
         6 . A composite according to  claim 1 , wherein the carbon is a fibrous form of carbon, such as carbon nanotubes (CNTs) and/or thin nanoplates, such as graphene or graphene oxide or reduced graphene oxide, or combinations thereof. 
     
     
         7 . (canceled) 
     
     
         8 . A composite according to  claim 1 , which is sealed with a carbon coating of appropriate thickness. 
     
     
         9 . A composite according to  claim 8 , wherein the coating reduces the available (effective) surface area of the Si:C particles by between about 50 and about 80%. 
     
     
         10 . (canceled) 
     
     
         11 . A composite according to  claim 1 , for use as an anode in a lithium ion battery. 
     
     
         12 . An anode for a lithium ion battery comprising a silicon-carbon composite according to  claim 1 . 
     
     
         13 . A half cell for a lithium ion battery comprising an anode according to  claim 12 , binder and a conducting additive in a weight ratio of composite to binder to conducting additive of about 8:1:1. 
     
     
         14 . A half cell according to  claim 13 , wherein the binder is carboxylmethyl cellulose (CMC)/styrene-butadiene rubber (SBR) and the conducting additive is Imerys C45 carbon black. 
     
     
         15 . A half cell according to  claim 13 , wherein the counter electrode is lithium metal. 
     
     
         16 . A lithium ion battery comprising an anode according to  claim 12 , a cathode, an electrolyte and a separator. 
     
     
         17 . A method for making a silicon-carbon composite comprising nanoscale silicon and carbon, the method comprising the steps of:
 (a) preparing a dispersion of silicon nanoparticles and the selected form/s of carbon;   (b) spray drying the dispersion to form essentially spherical, micrometre-sized composite particles;   (c) heat treating the composite particles to pyrolyse and/or burn off any polymers, and to strengthen the composite particles;   (d) coating the composite particles with carbon to form the Si:C composite; and   (e) optionally, adding additional elements such as lithium, magnesium, nitrogen and halogen gases to the composite, either during the heating step (c) or coating step (d) or during a subsequent heat treatment step.   
     
     
         18 . A method for making a silicon-carbon composite comprising nanoscale silicon and carbon, the method comprising the steps of:
 (a) preparing a dispersion of silicon nanoparticles by milling in water and retaining the mixture of silicon and water;   (b) optionally, preparing a separate dispersion of selected form/s of carbon in water, optionally comprising one or more surfactants;   (c) adding the carbon dispersion and optional surfactant mixture (or carbon in non-dispersed form) to the silicon-water dispersion;   (d) dispersing the resultant mixture;   (e) spray drying the resultant dispersed Si:C mixture to form essentially spherical particles;   heat treating the essentially spherical particles to pyrolyse and/or burn off any polymers, and to strengthen the spherical Si:C particles;   (g) coating the heat treated spherical Si:C particles with carbon using a chemical vapor deposition process to form a carbon-coated Si:C composite; and   (h) optionally, adding additional elements adding additional elements such as lithium, magnesium, nitrogen and halogen gases to the composite to the carbon-coated Si:C composite, either during mixing step (c) or dispersion step (d) or during subsequent heat treatment.   
     
     
         19 . A method according to  claim 17  or  claim 18 , wherein the selected form/s of carbon comprise carbon nanotubes (CNTs) and/or thin nanoplates, such as graphene or graphene oxide or reduced graphene oxide and combinations thereof. 
     
     
         20 . (canceled) 
     
     
         21 . A method according to  claim 17  or  claim 18 , wherein the surfactant/s are acidic. 
     
     
         22 - 34 . (canceled)