Lithium-ion battery anode material based on spherical natural graphite containing silicates
Materials and novel methods for producing carbon anodes for Li-ion batteries are described. These materials use natural flake graphite that has been processed to improve physical properties but retains residual impurities including silicates and other silicon containing minerals that are difficult to eliminate economically. For the purposes of battery anode material production, further purification is required and traditionally uses hydrofluoric acid, adding significant cost and environmental management requirements. Alternate novel processes result in less costly and more environmentally friendly methods when compared against the standard acid purification with hydrofluoric acid. Methods for direct graphitization of unpurified spheroidized graphite material that includes a carbonaceous coating in production of a lithium ion battery anode are provided. Materials generated using these methods may be blended with artificial graphite and particulate Silicon or SiO x materials for enhanced properties.
1 . A method for heat treatment of a coated graphite material, comprising
a. combining a natural graphite material including silicon-based impurities with a carbonaceous material, and
b. subjecting the natural graphite material and carbonaceous material combination to a first temperature treatment step in a range between 900° C. and 1900° C. to effect carbonization of the carbonaceous material, and a second temperature treatment step in a range between 2200° C. and 3000° C. to increase graphite purity and effect graphitization of the carbonaceous material, wherein the silicon-based impurities are retained at a level of at least 0.5 weight % of silicon relative to the weight of the treated natural graphite material,
thereby producing a temperature-treated coated graphite that is effective for use as a lithium ion battery anode material.
2 . The method according to claim 1 , wherein the carbonaceous material comprises at least one of petroleum tar pitch, coal tar pitch, a polymeric material, a hydrocarbon liquid and a hydrocarbon gas.
3 . The method according to claim 2 , wherein the carbonaceous material is a polymer material selected from the group consisting of an epoxy resin, a phenolic resin, polyacrylonitrile, polyvinyl alcohol and polystyrene.
4 . The method according to claim 1 , wherein the second temperature treatment step results in direct graphitization of the carbonaceous material.
5 . The method according to claim 1 , further comprising blending the temperature-treated coated graphite after the second temperature treatment step with at least one of artificial graphite, SiO, SiO 2 , or a silicon precursor.
6 . The method according to claim 1 , wherein the natural graphite material is not subjected to an acid treatment step.
7 . The method according to claim 1 , wherein the natural graphite material is subjected to an acid treatment step, but wherein such acid treatment step does not include treatment with HF.
8 . A coated graphite material produced according to the method of claim 1 .
9 . A lithium ion battery anode fabricated, at least in part, from the coated graphite material produced according to the method of claim 8 .