Process for graphene foam-protected anode active materials for lithium batteries
A lithium-ion battery anode layer, comprising an anode active material embedded in pores of a solid graphene foam composed of multiple pores and pore walls, wherein (a) the pore walls contain a pristine graphene material having essentially no (less than 0.01%) non-carbon elements or a non-pristine graphene material having 0.01% to 5% by weight of non-carbon elements; (b) the anode active material is in an amount from 0.5% to 95% by weight based on the total weight of the graphene foam and the anode active material combined, and (c) some of the multiple pores are lodged with particles of the anode active material and other pores are particle-free, and the graphene foam is sufficiently elastic to accommodate volume expansion and shrinkage of the particles of the anode active material during a battery charge-discharge cycle to avoid expansion of the anode layer. Preferably, the solid graphene foam has a density from 0.01 to 1.7 g/cm 3 , a specific surface area from 50 to 2,000 m 2 /g, a thermal conductivity of at least 100 W/mK per unit of specific gravity, and/or an electrical conductivity no less than 1,000 S/cm per unit of specific gravity.
1. A process for producing an anode layer for a lithium ion battery, said process comprising:
(a) preparing a graphene dispersion having multiple particles of anode active material and multiple sheets of a starting graphene material dispersed in a liquid medium, wherein said starting graphene material comprises pristine graphene material or non-pristine graphene material, where non-pristine is defined as having a content of non-carbon elements greater than 2% by weight, and where said starting graphene material is selected from the group consisting of graphene oxide, reduced graphene oxide, graphene fluoride, graphene chloride, graphene bromide, graphene iodide, hydrogenated graphene, nitrogenated graphene, chemically functionalized graphene, and combinations thereof, and wherein said dispersion contains a blowing agent;
(b) dispensing said graphene dispersion onto a surface of a supporting substrate to form a wet layer of graphene and anode active material mixture, wherein said dispensing procedure includes subjecting said graphene dispersion to an orientation-inducing stress;
(c) partially or completely removing said liquid medium from the wet layer of graphene and anode active material to form a dried layer of mixture material; and
(d) heat treating the dried layer of mixture material at a first heat treatment temperature selected from 80° C. to 3,200° C. at a desired heating rate sufficient to induce volatile gas molecules from said non-carbon elements or to activate said blowing agent for producing a pore-containing graphene foam anode layer.
2. The process of claim 1 , further including a step of heat-treating the graphene foam anode layer at a second heat treatment temperature higher than said first heat treatment temperature for a length of time sufficient for obtaining said anode layer wherein said pores of the pore-containing graphene foam anode layer have walls that contain stacked graphene planes having an inter-plane spacing d 002 from 0.3354 nm to 0.36 nm and a content of non-carbon elements less than 2% by weight.
3. The process of claim 1 , wherein said blowing agent having a blowing agent-to-graphene weight ratio from 0.01/1.0 to 1.0/1.0.
4. The process of claim 1 , wherein said blowing agent is at least one of a physical blowing agent, a chemical blowing agent, a mixture thereof, a dissolution-and-leaching agent, or a mechanically introduced blowing agent.
5. The process of claim 1 , which is a roll-to-roll process wherein said steps (b) and (c) include feeding said supporting substrate from a feeder roller to a deposition zone, continuously or intermittently dispensing or depositing said graphene dispersion onto a surface of said supporting substrate to form said wet layer of graphene material thereon, drying said wet layer of graphene material to form the dried layer of graphene material, and collecting said dried layer of graphene material deposited on said supporting substrate on a collector roller.
6. The process of claim 1 , wherein said first heat treatment temperature is in a range from 100° C. to 1,500° C.
7. The process of claim 2 , wherein said second heat treatment temperature includes a temperature selected from at least one of: (A) 300-1,500° C., (B) 1,500-2,100° C., or (C) 2,100-3,200° C.
8. The process of claim 1 , wherein said step (d) of heat treating the dried layer of mixture material is conducted under a compressive stress.
9. The process of claim 1 , wherein said liquid medium is an oxidizing liquid medium, wherein said graphene dispersion contains graphene oxide and the dispersion is prepared by immersing said starting graphene material in a powder or fibrous form in the liquid medium in a reaction vessel at a reaction temperature for a length of time sufficient to obtain said graphene dispersion and wherein said graphene oxide has an oxygen content no less than 5% by weight.
10. The process of claim 1 , wherein said anode active material is selected from the group consisting of: (a) silicon (Si), germanium (Ge), tin (Sn), lead (Pb), antimony (Sb), bismuth (Bi), zinc (Zn), aluminum (Al), titanium (Ti), nickel (Ni), cobalt (Co), or cadmium (Cd); (b) alloys or intermetallic compounds of Si, Ge, Sn, Pb, Sb, Bi, Zn, Al, Ti, Ni, Co, or Cd with other elements; (c) oxides, carbides, nitrides, sulfides, phosphides, selenides, and tellurides of Si, Ge, Sn, Pb, Sb, Bi, Zn, Al, Ti, Fe, Ni, Co, V, or Cd, and their mixtures, composites, or lithium-containing composites; (d) salts or hydroxides of Sn; (e) lithium titanate, lithium manganate, lithium aluminate, lithium-containing titanium oxide, or lithium transition metal oxide; (f) prelithiated versions thereof; (g) particles of Li, Li alloy, or surface-stabilized Li; and (h) combinations thereof.
11. The process of claim 1 , wherein said anode active material contains at least one of: prelithiated Si, prelithiated Ge, prelithiated Sn, prelithiated SnO x , prelithiated SiO x , prelithiated iron oxide, prelithiated VO 2 , prelithiated Co 3 O 4 , prelithiated Ni 3 O 4 , or a combination thereof, wherein 1<x<2.
12. The process of claim 1 , wherein said anode active material is in at least one of the forms of: nanoparticle, nanowire, nanofiber, nanotube, nanosheet, nanobelt, nanoribbon, or nano-coating having a thickness or diameter less than 100 nm.
13. The process of claim 1 , further comprising a lithium-conducting coating deposited onto said anode active material.
14. The process of claim 1 , wherein said anode active material has a dimension less than 20 nm.
15. The process of claim 1 , further comprising a carbon or graphite material in said dispersion, wherein said carbon or graphite material is in electronic contact with or deposited onto said anode active material.
16. The process of claim 15 , wherein said carbon or graphite material is selected from the group consisting of: polymeric carbon, amorphous carbon, chemical vapor deposition carbon, coal tar pitch, petroleum pitch, mesophase pitch, carbon black, coke, acetylene black, activated carbon, fine expanded graphite particle with a dimension smaller than 100 nm, artificial graphite particle, natural graphite particle, and combinations thereof.
17. The process of claim 15 , further comprising a conductive protective coating, selected from the group consisting of a carbon material, electronically conductive polymer, conductive metal oxide, conductive metal coating, and a lithium-conducting material, which then said conductive protective coating is deposited onto or wrapped around said active anode material.
18. The process of claim 1 , wherein said graphene foam anode layer contains pristine graphene and said anode layer has a density from 0.5 to 1.7 g/cm 3 or a pore size from 2 nm to 100 nm.
19. A roll-to-roll process for producing a continuous-length sheet of said anode layer of claim 1 , said process comprising:
(a) preparing said graphene dispersion having said starting graphene material and said anode active material dispersed in said liquid medium, wherein said dispersion contains said blowing agent;
(b) continuously or intermittently dispensing and depositing said graphene dispersion onto a surface of said supporting substrate to form said wet layer of graphene-anode material mixture, wherein said supporting substrate is a continuous thin film supplied from a feeder roller and collected on a collector roller;
(c) partially or completely removing said liquid medium from said wet layer of graphene and anode active material mixture to form said dried layer of mixture material; and
(d) heat treating said dried layer of mixture material at said first heat treatment temperature in the range from 100° C. to 3,000° C. at said desired heating rate sufficient to activate said blowing agent for producing said graphene foam anode layer.
20. The process of claim 1 , which is in a continuous-length roll sheet form having a thickness no greater than 300 μm and a length of at least 2 meters and is produced by a roll-to-roll process.
21. The process of claim 1 , wherein said anode layer has at least one of: a density from 0.01 to 1.7 g/cm 3 , a specific surface area from 50 to 2,000 m 2 /g, a thermal conductivity of at least 100 W/mK per unit of specific gravity, or an electrical conductivity no less than 1,000 S/cm per unit of specific gravity.
22. The process of claim 1 , wherein said anode layer has an oxygen content or non-carbon content less than 1% by weight, and said pores of the pore-containing graphene foam anode layer have walls that have at least one of: an inter-graphene spacing less than 0.35 nm, a thermal conductivity of at least 250 W/mK per unit of specific gravity, or an electrical conductivity no less than 2,500 S/cm per unit of specific gravity.
23. The process of claim 1 , wherein said anode layer has an oxygen content or non-carbon content less than 0.01% by weight and said pores of the pore-containing graphene foam anode layer have walls that have at least one of: stacked graphene planes having an inter-graphene spacing less than 0.34 nm, a thermal conductivity of at least 300 W/mK per unit of specific gravity, or an electrical conductivity no less than 3,000 S/cm per unit of specific gravity.
24. The process of claim 1 , wherein said anode layer has an oxygen content or non-carbon content no greater than 0.01% by weight and said pores of the pore-containing graphene foam anode layer have walls that have at least one of: stacked graphene planes having an inter-graphene spacing less than 0.336 nm, a mosaic spread value no greater than 0.7, a thermal conductivity of at least 350 W/mK per unit of specific gravity, or an electrical conductivity no less than 3,500 S/cm per unit of specific gravity.
25. The process of claim 1 , wherein said anode layer has pores of the pore-containing graphene foam anode layer that have walls that have at least one of: stacked graphene planes having an inter-graphene spacing less than 0.336 nm, a mosaic spread value no greater than 0.4, a thermal conductivity greater than 400 W/mK per unit of specific gravity, or an electrical conductivity greater than 4,000 S/cm per unit of specific gravity.
26. The process of claim 1 , wherein said pores of the pore-containing graphene foam anode layer have walls that include at least one of: stacked graphene planes having an inter-graphene spacing less than 0.337 nm or a mosaic spread value less than 1.0.
27. The process of claim 1 , wherein said anode layer has at least one of: a degree of graphitization no less than 80% or a mosaic spread value less than 0.4.
28. The process of claim 1 , wherein said pores of the pore-containing graphene foam anode layer have walls that contain a 3D network of interconnected graphene planes.
29. The process of claim 1 , wherein said anode layer contains pores having a pore size in the range from 20 nm to 500 nm.