High carbon nanotube content fluids
View Patent ↗New homogeneous fluids with a viscosity less than about three Poise comprising discrete carbon nanotubes with volume fractions above the percolation threshold concentration calculated for randomly oriented rods in a liquid are disclosed. A method is also disclosed for production of the new fluids. The fluids are particularly useful for making battery pastes.
1. A homogeneous aqueous fluid comprising:
discrete carbon nanotubes comprising oxygen moieties in a weight range of 0.5 to 8% by weight of the carbon nanotube; and
at least one surfactant,
wherein 0.6≦V*(L/D)≦3, wherein V is the volume fraction, L is the average length of the carbon nanotube in nanometers, D is the average diameter of the carbon nanotube in nanometers, and wherein the fluid has a viscosity less than 3 Poise at 25° C.
2. The fluid of claim 1 wherein at least one of the surfactants is at least partially bound to the discrete carbon nanotube.
3. The fluid of claim 1 wherein a majority of discrete carbon nanotubes are open ended.
4. The fluid of claim 1 wherein residual catalyst from making the carbon nanotubes is less than 2% by weight of the carbon nanotubes.
5. The fluid of claim 1 further comprising at least one other species selected from the group of carbonaceous materials.
6. The fluid of claim 1 wherein the surfactant is present in an amount suitable to obtain a carbon nanotube:surfactant weight ratio from 1:0.2 to 1:3.
7. The fluid of claim 1 wherein the surfactant comprises a polymer soluble in the fluid to at least 0.5% by weight relative to the weight of fluid.
8. The fluid of claim 1 wherein the surfactant comprises a polymer further comprising an oxygen and/or sulfur moiety; preferably having a molecular weight of less than 200 kDa.
9. The fluid of claim 1 wherein the surfactant comprises polyvinyl alcohol or polyvinyl alcohol copolymer, wherein at least 50% by mole of the vinyl units comprise hydroxyl groups.
10. The fluid of claim 1 wherein the surfactant comprises polystyrene sulfonate.
11. The fluid of claim 1 , being temperature stable, wherein the fluid maintains a pourable viscosity from 0° C. to 60° C.
12. The fluid of claim 1 , wherein the surfactant is biocompatible.
13. The fluid of claim 1 , wherein 10% or less of the discrete carbon nanotubes comprise an L/D of 100 to 200, and about 30% or more of the discrete carbon nanotubes comprise an L/D of 40 to 80.
14. The fluid of claim 1 , wherein the L/D distribution is asymmetrical meaning that a relatively small percent of discrete carbon nanotubes has a specific L/D while a greater amount comprises another aspect ratio distribution.
15. A lead acid electroactive paste comprising the fluid of claim 1 .
16. A lithium ion electroactive paste comprising the fluid of claim 1 .
17. A photovoltaic photoactive paste comprising the fluid of claim 1 .
18. An electrolyte comprising the fluid of claim 1 .
19. An ink comprising the fluid of claim 1 .
20. A method to obtain an aqueous homogeneous fluid comprising discrete carbon nanotubes and surfactant, wherein a volume fraction, V, of the carbon nanotubes in the fluid is in the range determined from the equation 0.6<V*(L/D)<3, wherein L is the average length of the carbon nanotube in nanometers, D is the average diameter of the carbon nanotube in nanometers, and wherein the aqueous fluid has a viscosity less than 3 Poise at 25° C., comprising:
a) forming a mixture comprising 2-50% by weight of discrete carbon nanotubes, the discrete carbon nanotubes having surfaces comprising oxygen moieties in the weight range of 0.5 to 8% by weight of the discrete carbon nanotubes, in at least one aqueous fluid,
b) adding at least one surfactant to the carbon nanotube mixture in an amount suitable to obtain a carbon nanotube:surfactant weight ratio from 1:0.2 to 1:3,
c) optionally, adding the surfactant as a solution to the fluid,
d) adjusting pH of the aqueous fluid to between 4 and 9,
e) optionally, adjusting the carbon nanotube volume concentration with additional aqueous fluid, and
f) agitating the mixture while maintaining the temperature below 35° C.