High performance flow battery
High performance flow batteries, based on alkaline zinc/ferro-ferricyanide rechargeable (“ZnFe”) and similar flow batteries, may include one or more of the following improvements. First, the battery design has a cell stack comprising a low resistance positive electrode in at least one positive half cell and a low resistance negative electrode in at least one negative half cell, where the positive electrode and negative electrode resistances are selected for uniform high current density across a region of the cell stack. Second, a flow of electrolyte, such as zinc species in the ZnFe battery, with a high level of mixing through at least one negative half cell in a Zn deposition region proximate a deposition surface where the electrolyte close to the deposition surface has sufficiently high zinc concentration for deposition rates on the deposition surface that sustain the uniform high current density.
1. A method of charging a flow battery, comprising:
circulating a super-saturated electrolyte over a negative electrode plating zone on a surface of a negative electrode of a negative half cell in the flow battery;
wherein the super-saturated electrolyte is prepared by combining zinc oxide with sodium hydroxide (NaOH) pellets in a silicate-free and phosphate-free solution;
wherein the super-saturated electrolyte has a zinc ion concentration greater than the equilibrium saturation concentration of the zinc ion in the super-saturated electrolyte and a hydroxide concentration of between 2 normal (N) and 5 normal (N); and
wherein a mass transfer coefficient of the super-saturated electrolyte is sufficient to maintain a super-saturated electrolyte concentration of zinc ions in the negative electrode plating zone for a substantially uniform deposition of zinc on the surface at a uniform high current density.
2. The method of claim 1 , wherein the super-saturated electrolyte has a zinc solubility of greater than about 0.7M in 4N NaOH.
3. The method of claim 1 , wherein the super-saturated electrolyte has a zinc solubility of about 0.73M in 4N NaOH.
4. The method of claim 1 , wherein the super-saturated electrolyte is prepared by combining the zinc oxide and the sodium hydroxide pellets in water to form a first solution that comprises a zinc ion concentration greater than 0.7 normal (N) and a hydroxide concentration of greater than 4 normal (N) and mixing the first solution with a second solution to form the super-saturated electrolyte that has a zinc ion concentration of about 0.7 normal (N).
5. The method of claim 1 , wherein the super-saturated electrolyte is prepared by combining the zinc oxide and the sodium hydroxide pellets in water to form a first solution that comprises a zinc ion concentration greater than 0.7 normal (N) and a hydroxide concentration of greater than 4 normal (N) and mixing the first solution with a second solution to form the super-saturated electrolyte that has a zinc ion concentration of between 0.4 N about 0.7 N and a hydroxide concentration of between about 2N and about 4N.
6. The method of claim 1 , wherein circulating the super-saturated electrolyte over the negative plating zone further comprises delivering the super-saturated electrolyte through a porous structure that has a porosity of between 60% and 98% and has a surface that comprises nickel.
7. The method of claim 1 , wherein the uniform high current density is greater than 70 mA/cm 2 .
8. The method of claim 1 , wherein a mass transfer coefficient of the super-saturated electrolyte has a value in the approximate range of 5.3×10 −4 m/s to 12.4×10 −3 m/s.
9. The method of claim 1 , wherein the flow battery is a flow battery selected from the group consisting of: a ZnFe flow battery, a ZnHBr flow battery, a ZnBr flow battery, a CeZn flow battery; and a ZnCl flow battery.
10. The method of claim 1 , further comprising delivering the super-saturated electrolyte through a flow channel that is configured to provide a high rate of mixing within the negative electrode plating zone.
11. A method of charging a flow battery, comprising:
providing a uniform high current density across a positive electrode and a negative electrode, the uniform high current density passing through a negative electrode plating zone on a surface of the negative electrode of the flow battery;
circulating a super-saturated electrolyte through a flow channel of the negative electrode, wherein the flow channel is configured to provide mixing of the super-saturated electrolyte in the negative electrode plating zone on the surface of the negative electrode;
wherein the super-saturated electrolyte is prepared by combining zinc oxide with sodium hydroxide (NaOH) pellets in a silicate-free and phosphate-free solution;
wherein the super-saturated electrolyte has a zinc ion concentration greater than the equilibrium saturation concentration of the zinc ion in the super-saturated electrolyte and a hydroxide concentration of between 2 normal (N) and 5 normal (N); and
wherein a mass transfer coefficient of the super-saturated electrolyte is sufficient to maintain a super-saturated electrolyte concentration of zinc ions in the negative electrode plating zone for a substantially uniform deposition of zinc on the surface at the uniform high current density.
12. The method of claim 11 , wherein the super-saturated electrolyte has a zinc solubility of greater than about 0.7M in 4N NaOH.
13. The method of claim 11 , wherein the super-saturated electrolyte has a zinc solubility of about 0.73M in 4N NaOH.
14. The method of claim 11 , wherein the super-saturated electrolyte is prepared by combining the zinc oxide and the sodium hydroxide pellets in water to form a first solution that comprises a zinc ion concentration greater than 0.7 normal (N) and a hydroxide concentration of greater than 4 normal (N) and mixing the first solution with a second solution to form the super-saturated electrolyte that has a zinc ion concentration of about 0.7 normal (N).
15. The method of claim 11 , wherein the super-saturated electrolyte is prepared by combining the zinc oxide and the sodium hydroxide pellets in water to form a first solution that comprises a zinc ion concentration greater than 0.7 normal (N) and a hydroxide concentration of greater than 4 normal (N) and mixing the first solution with a second solution to form the super-saturated electrolyte that has a zinc ion concentration of between 0.4 N about 0.7 N and a hydroxide concentration of between about 2N and about 4N.
16. The method of claim 11 , wherein circulating the super-saturated electrolyte over the negative plating zone further comprises delivering the super-saturated electrolyte through a porous structure that has a porosity of between 60% and 98% and has a surface that comprises nickel.
17. The method of claim 11 , wherein the uniform high current density is greater than 70 mA/cm 2 .
18. The method of claim 11 , wherein a mass transfer coefficient of the super-saturated electrolyte has a value in the approximate range of 5.3×10 −4 m/s to 12.4×10 −3 m/s.
19. The method of claim 11 , wherein the flow battery is a flow battery selected from the group consisting of: a ZnFe flow battery, a ZnHBr flow battery, a ZnBr flow battery, a CeZn flow battery; and a ZnCl flow battery.
20. The method of claim 11 , wherein the flow channel is configured to provide a high rate of mixing of the super-saturated electrolyte in the negative electrode plating zone proximate the surface of the negative electrode.