Optimized electrode design for graphene based anodes
A negative electrode of a lithium ion electrochemical cell, the negative electrode including an active electrode material that includes a first component and a second component. The first component may include graphene, silicon, or a combination thereof. The second component may include silicon. The active electrode material may include particles in which the second component is encapsulated by the first component. The negative electrode may have an internal porosity of between 40 to 60 percent.
1. An electrode, comprising an electrochemically active material comprising particles disposed in a matrix, wherein the particles each comprise:
a first component comprising graphene, graphene oxide, or a combination thereof; and
a second component encapsulated by the first component,
wherein the electrode is calendered, such that the first component forms an electrically conductive matrix and the electrode comprises channels and has an internal porosity that ranges from about 40 to about 60 percent,
wherein the channels are configured to increase a diffusion rate and volume of lithium ions within the electrode.
2. The electrode of claim 1 , wherein the second component is selected from the group consisting of silicon, silicon oxide, tin, tin oxide, antimony, aluminum, silver, germanium, gallium, magnesium, zinc, lead, bismuth, carbon, titanium oxide, lithium titanium oxide, alloys thereof, intermetallics thereof, and mixtures thereof.
3. The electrode of claim 1 , wherein the particles of the electrochemically active material have a particle size distribution that ranges from about 0.5 μm to about 10 μm.
4. The electrode of claim 1 , wherein the second component has a particle size distribution that ranges from about 30 nm to about 50 nm.
5. The electrode of claim 1 , wherein the electrode has a thickness that ranges from about 5 μm to about 50 μm.
6. The electrode of claim 1 , wherein the internal porosity is measured by the equation:
Internal
Porosity
(
%
)
=
1
-
(
measured
density
theoretical
density
)
,
wherein the measured density is measured by dividing the mass of the dried electrode by its volume and the theoretical density is the density of the electrode that is 100 percent dense.
7. A method of fabricating an electrode of claim 1 , the method comprising:
mixing the electrochemically active material with a binder to create a mixture;
adding a solvent to the mixture to create an electrode slurry;
coating the electrode slurry on a substrate;
drying the electrode slurry to substantially remove the solvent; and
calendering the dried electrode slurry to form an electrode having an internal porosity measured by the equation:
Internal
Porosity
(
%
)
=
1
-
(
measured
density
theoretical
density
)
;
wherein the measured density is measured by dividing the mass of the dried electrode by its volume and the theoretical density is the density of the electrode that is 100 percent dense.
8. The method of claim 7 , wherein the electrochemically active material comprises a second component selected from the group consisting of silicon, silicon oxide, tin, tin oxide, antimony, aluminum, silver, germanium, gallium, magnesium, zinc, lead, bismuth, carbon, titanium oxide, lithium titanium oxide, alloys thereof, intermetallics thereof, and mixtures thereof.
9. The method of claim 8 , wherein the electrode comprises particles comprising the second component encapsulated by the first component.
10. The method of claim 9 , wherein the particles have a particle size distribution that ranges from about 1 μm to about 10 μm.
11. The method of claim 8 , wherein the second component has a particle size distribution that ranges from about 30 nm to about 50 nm.
12. The method of claim 7 , wherein the binder is selected from the group consisting of a fluoro-resin powder, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), poly(acrylic) acid, polyethylenetetrafluoroethylene (ETFE), polyamides, polyimides, ultra-high molecular weight polyethylene (UHMWPE), styrene-butadiene rubber, cellulose, polyacrylate rubber, and copolymers of acrylic acid or acrylate esters with polyhydrocarbons including copolymers of acrylic acid and polyethylene and copolymers of acrylate esters and polypropylene, and mixtures thereof.
13. The method of claim 7 , wherein the solvent is selected from the group consisting of water, ethanol, isopropyl alcohol, ethylene glycol, ethyl acetate, polar protiac solvents, polar aprotic solvents, N-methyl-2-pyrrolidone, and combinations thereof.
14. The method of claim 7 , wherein the adding a solvent to the mixture further comprises adding a dispersant selected from the group consisting of glycol ethers, poly(ethylene oxide), block copolymers, acetylenic diols, 2,5,8,11-tetramethyl-6-dodecyn-5,8-diol ethoxylate, salts of carboxylic acids, alkali metal salt, ammonium salt, polysiloxanes, sodium dodecanoate, alkanolamide, lanolin, polyvinylpyrrolidone, sodium alkyl sulfate, sodium alkyl sulfonate, lecithin, polyacrylate, sodium silicate, including dispersants comprising polyethoxy groups or having the chemical formula (C 2 H 4 O) n C 14 H 22 O, and combinations thereof.
15. An electrochemical cell, comprising:
a negative electrode comprising an active electrode material comprising particles disposed in a matrix, wherein the particles each comprise;
a first component comprising graphene, graphene oxide, or a combination thereof; and
a second component encapsulated in the first component,
wherein the negative electrode is calendered, such that the first component forms an electrically conductive matrix and the negative electrode comprises channels and has an internal porosity that ranges from about 40 to about 60 percent;
a positive electrode comprising a lithium component; and
an ionically conductive electrolyte solution in which the negative and positive electrodes are immersed;
wherein the channels are configured to increase a diffusion rate and volume of lithium ions within the negative electrode.
16. The electrochemical cell of claim 15 , wherein the second component is selected from the group consisting of silicon, silicon oxide, tin, tin oxide, antimony, aluminum, silver, germanium, gallium, magnesium, zinc, lead, bismuth, carbon, titanium oxide, lithium titanium oxide, alloys thereof, intermetallics thereof, and mixtures thereof.
17. The electrochemical cell of claim 15 , wherein the active electrode material has a particle size distribution that ranges from about 0.5 μm to about 10 μm.
18. The electrochemical cell of claim 17 , wherein the second component has a particle size distribution that ranges from about 30 nm to about 100 nm.
19. The electrochemical cell of claim 15 , wherein the negative electrode comprises from about 28 weight percent to about 70 weight percent of the first component, based on the total weight of the negative electrode.
20. The electrochemical cell of claim 19 , wherein the negative electrode comprises from about 30 weight percent to about 70 weight percent of the second component, based on the total weight of the negative electrode.
21. The electrochemical cell of claim 20 , wherein the negative electrode comprises from about 0.01 weight percent to about 5 weight percent of a non-active carbon material, based on the total weight of the negative electrode.
22. The electrode of claim 1 further comprising a binder, wherein the binder is selected from the group consisting of a fluoro-resin powder, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), poly(acrylic) acid, polyethylenetetrafluoroethylene (ETFE), polyamides, polyimides, polyethylene, styrene-butadiene rubber, cellulose, polyacrylate rubber, and copolymers of acrylic acid or acrylate esters with polyhydrocarbons including copolymers of acrylic acid and polyethylene and copolymers of acrylate esters and polypropylene, and mixtures thereof.