Composite material with conformal graphene coating, fabricating methods and applications of same
A composite material and a method for fabricating the same. The composite material includes graphene and active material particles. Each surface of the active material particles is conformally coated with said graphene. The method includes forming a mixture containing an active material, graphene, ethyl cellulose (EC) polymer and multiwalled carbon nanotubes, and thermally annealing the mixture at an annealing temperature in an oxidizing environment to decompose the majority of EC, thereby resulting in the composite material having each active material particle coated with a conformal graphene coating.
1. A method for fabricating a composite material, comprising:
forming a mixture containing an active material, graphene, ethyl cellulose (EC) polymer and multiwalled carbon nanotubes (MWCNTs); and
thermally annealing the mixture at an annealing temperature in an oxidizing environment to decompose the majority of EC, thereby resulting in the composite material having each active material particle coated with a conformal graphene coating.
2. The method of claim 1 , wherein said forming the mixture comprises:
dispersing the graphene, the EC polymer and the MWCNTs in a solvent to form a dispersion;
mixing the active material with the dispersion to form a slurry; and
drying the slurry.
3. The method of claim 2 , wherein said forming the mixture further comprises exchanging said solvent with another solvent in the dispersion to promote better homogeneity and slurry stability during electrode casting.
4. The method of claim 3 , wherein said solvent comprises ethanol, and said another solvent comprises N-Methyl 2-pyrrolidone (NMP).
5. The method of claim 4 , wherein said exchanging the solvent exchange comprises adding said another solvent to the dispersion to form a solution, and subsequently removing said solvent by stirring and/heating the solution.
6. The method of claim 2 , wherein said forming the mixture further comprises, prior to said mixing the active material, annealing the active material at a temperature in a range of about 150-350° C., in flowing oxygen.
7. The method of claim 2 , wherein said drying the slurry comprises drying the slurry at a first temperature in a range of about 80-200° C. in a convection oven, followed by a second drying step at a second temperature in a range of about 50-120° C. under dynamic vacuum.
8. The method of claim 1 , wherein the annealing temperature is in a range of about 150-350° C.
9. The method of claim 1 , wherein said graphene comprises solution-exfoliated graphene.
10. The method of claim 1 , wherein the active material comprises lithium cobalt oxide, lithium nickel oxide, lithium iron phosphate, lithium manganese oxide, lithium nickel manganese cobalt oxide, lithium nickel cobalt aluminum oxide, lithium-rich oxides, or a combination thereof.
11. The method of claim 10 , wherein the active material comprises nickel-rich lithium oxides.
12. The method of claim 11 , wherein the active material comprises LiNi 0.8 Co 0.15 Al 0.05 O 2 (NCA), LiNiO 2 (LNO), LiMn 1.5 Ni 0.5 O 4 (LMNO), LiNi x Mn y CO z O 2 (NMC, where x+y+z=1), LiNi 0.8 Co 0.2 O 2 (LNCO), or Li w Ni x Mn y Co z O 2 (lithium-rich NMC, where w >1,x+y+z=1).
13. The method of claim 12 , wherein the active material is doped with elements including Al, B, Zr, Nb, Fe, Cr, Cu, Mo, W, and/or V.
14. A composite material fabricated according to the method of claim 1 .
15. A composite material, comprising: graphene; and an active material, wherein each active material particle is conformally coated with said graphene, wherein each active material particle is conformally coated with a combination of said graphene and an annealation product of ethyl cellulose that comprises amorphous carbon with sp 2 -carbon content, such that Raman spectroscopy of said composite material has a peak at 2D-band, wherein the active material comprises lithium nickel oxide, lithium-rich oxides, or a combination thereof.
16. The composite material of claim 15 , further comprising multiwalled carbon nanotubes (MWCNTs).
17. The composite material of claim 15 , wherein said graphene comprises solution-exfoliated graphene.
18. The composite material of claim 15 , wherein the active material further comprises lithium cobalt oxide, lithium iron phosphate, lithium manganese oxide, lithium nickel cobalt aluminum oxide, lithium nickel manganese cobalt oxide, or a combination thereof.
19. The composite material of claim 18 , wherein the active material comprises nickel-rich lithium oxides.
20. The composite material of claim 19 , wherein the active material comprises LiNi 0.8 Co 0.15 Al 0.05 O 2 (NCA), LiNiO 2 (LNO), LiMn 1.5 Ni 0.5 O 4 (LMNO), LiNi x Mn y Co z O 2 (NMC, where x+y+z=1), LiNi 0.8 Co 0.2 O 2 (LNCO), or Li w Ni x Mn y CO z O 2 (lithium-rich NMC, where w >1, x+y+z=1).
21. The composite material of claim 20 , wherein the active material is doped with elements including Al, B, Zr, Nb, Fe, Cr, Cu, Mo, W, and/or V.
22. An electrode for an electrochemical device, comprising: a composite material comprising graphene, and an active material, wherein each active material particle is conformally coated with said graphene, wherein each active material particle is conformally coated with a combination of said graphene and an annealation product of ethyl cellulose that comprises amorphous carbon with sp 2 -carbon content, such that Raman spectroscopy of said composite material has a peak at 2D-band, wherein the active material comprises lithium nickel oxide, lithium-rich oxides, or a combination thereof.
23. The electrode of claim 22 , wherein the composite material further comprises multiwalled carbon nanotubes (MWCNTs).
24. The electrode of claim 22 , wherein said graphene comprises solution-exfoliated graphene.
25. The composite material of claim 22 , wherein the active material further comprises lithium cobalt oxide, lithium iron phosphate, lithium manganese oxide, lithium nickel cobalt aluminum oxide, lithium nickel manganese cobalt oxide, or a combination thereof.
26. The electrode of claim 25 , wherein the active material comprises nickel-rich lithium oxides.
27. The electrode of claim 26 , wherein the active material comprises LiNi 0.8 Co 0.15 Al 0.05 O 2 (NCA), LiNiO 2 (LNO), LiMn 1.5 Ni 0.5 O 4 (LMNO), LiNi x Mn y Co z O 2 (NMC, where x+y+z=1), LiNi 0.8 Co 0.2 O 2 (LNCO), or Li w Ni x Mn y CO 2 O z (lithium-rich NMC, where w >1,x+y+z=1).
28. The electrode of claim 27 , wherein the active material is doped with elements including Al, B, Zr, Nb, Fe, Cr, Cu, Mo, W, and/or V.
29. The electrode of claim 22 , wherein the conformal graphene coating reduces an accumulation of electrolyte decomposition products on the active material surface and reduces the severity of particle-level chemomechanical degradation.
30. The electrode of claim 22 , wherein the conformal graphene coating promotes spatially uniform charge transfer reactions across the electrode surface during cycling and mitigating mechanical degradation, which delocalizes delithiation-induced strain and reduces the propensity for particle fracture.
31. The electrode of claim 22 , wherein the conformal graphene coating is mechanically compliant towards unit cell volume changes at high states of charge and maintains electrical contact throughout cycling, whereby the electrode achieves substantially improved cycle life and coulombic efficiencies when cycled to high operating voltages.
32. The electrode of claim 22 , wherein the electrode has a discharge capacity of about 203.1 mAh g −1 , during an activation cycle.
33. The electrode of claim 22 , wherein the electrode retains about 70.9% of its initial volumetric capacity over 50 charge-discharge cycles at 0.5 C.
34. An electrochemical device, comprising the electrode of claim 22 .
35. The electrochemical device of claim 34 , being a battery.