Method for operating redox flow battery

Abstract

The present disclosure relate to a method for operating a redox flow battery, which includes the steps of discharging the redox flow battery having an anode electrolyte and a cathode electrolyte when a volume difference between the anode electrolyte and the cathode electrolyte is within 20% of a total volume of the anode electrolyte and the cathode electrolyte, while maintaining an open circuit voltage of lower than 1.3 V/cell, and moving the anode electrolyte and/or the cathode electrolyte so that the volume difference is 2% or less between the anode electrolyte and the cathode electrolyte in the redox flow battery after the discharging.

Claims

1. A method for operating a redox flow battery, the method comprising the steps of: discharging the redox flow battery having an anode electrolyte and a cathode electrolyte when a volume difference between the anode electrolyte and the cathode electrolyte is 10 to 20% of a total volume of the anode electrolyte and the cathode electrolyte, while maintaining an open circuit voltage of lower than 1.3 V/cell; and moving the anode electrolyte and/or the cathode electrolyte so that the volume difference is 2% or less between the anode electrolyte and the cathode electrolyte in the redox flow battery after the discharging.

2. The method for operating a redox flow battery according to claim 1, further comprising charging the redox flow battery after the moving of the anode electrolyte and/or the cathode electrolyte.

3. The method for operating a redox flow battery according to claim 1, wherein the discharging comprises overdischarging the redox flow battery under conditions of a constant current or a constant voltage.

4. The method for operating a redox flow battery according to claim 1, wherein the discharging comprises discharging the redox flow battery until the open circuit voltage becomes 0.6 to 0.8 V/cell.

5. The method for operating a redox flow battery according to claim 1, wherein the discharging of the redox flow battery until the open circuit voltage becomes 0.6 to 0.8 V/cell precedes the moving of the anode electrolyte and/or the cathode electrolyte so that the volume difference is 2% or less.

6. The method for operating a redox flow battery according to claim 1, wherein the redox flow battery is a vanadium redox battery, a polysulfide bromide redox flow battery, or a zinc-bromine redox flow battery.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a graph showing charge retention rates of a redox flow battery of Comparative Example 1 with respect to a charging and discharging cycle.

(2) FIG. 2 is a graph showing charge retention rates of redox flow batteries of Example 1 and Comparative Example 1, when respectively operated in a charging and discharging cycle.

DETAILED DESCRIPTION OF THE EMBODIMENTS

(3) Below, the present invention will be described in more detail by way of examples. However, these examples are provided only for illustration of the present invention, and should not be construed as limiting the scope of the present invention to these examples.

Examples and Comparative Examples: Operation of a Redox Flow Battery

(4) The examples and comparative examples below utilize redox flow batteries for comparison by different operating methods, which are made to have a cathode and an anode positioned on the left and right about a separation membrane with a current collector and an electrolyte inlet and outlet on the top and bottom, respectively.

(5) For a vanadium electrolytic solution, the redox flow battery uses a 2 M vanadium solution dissolved in aqueous sulfuric acid. In addition, a charging completion voltage was 1.60 V/cell, and a discharge completion voltage was set to 1.0 V/cell. Further, the charge retention rate was measured based on the discharge capacity retention rate compared to the initial value at each cycle.

(6) Table 1 below details the respective constituents of the manufactured redox flow battery.

(7) TABLE-US-00001 TABLE 1 Item Electrode Maker (Product Name) SGL (GFD 3) Thickness (mm) 3 Separation Membrane Maker (Product Name) GEFC (104) Thickness (m) 100 Bipolar Plate Maker (Product Name) Morgan Thickness (mm) 3

Example 1

(8) The amount of electrolyte movement is equal to or less than 10% of the total volume of the electrolytes with an open circuit voltage after the discharging is maintained at lower than 1.3 V/cell, and the experimental results are shown in Table 2. A, B and C, D respectively represent data of two cycles immediately before and after moving the electrolytic solution, where C is the duration of moving the electrolytic solution by the volume difference between the electrolytes due to crossover.

(9) TABLE-US-00002 TABLE 2 Post-charge Post-discharge Charge Discharge Charge Open Circuit Open Circuit Classifi- Capacity Capacity EE CE VE Retention Voltage Voltage cation (Ah/cell) (Ah/cell) (%) (%) (%) Rate (%) (V/cell) (V/cell) 3.23 3.10 84 96 87 82 1.51 1.24 B 3.22 3.08 84 96 87 81 1.51 1.23 C D 3.96 3.78 84 95 88 100 1.52 1.23 E 3.88 3.72 84 96 88 98 1.51 1.24

Example 2

(10) The amount of electrolyte movement is greater than 10% and less than 15% of the total volume of the electrolytes with an open circuit voltage after the discharging is maintained at lower than 1.3 V/cell, and the experimental results are shown in Table 3 below.

(11) TABLE-US-00003 TABLE 3 Post-charge Post-discharge Charge Discharge Charge Open Circuit Open Circuit Classifi- Capacity Capacity EE CE VE Retention Voltage Voltage cation (Ah/cell) (Ah/cell) (%) (%) (%) Rate (%) (V/cell) (V/cell) 3.83 3.62 84 94 89 85 1.51 1.20 B 3.84 3.63 84 95 89 98 1.51 1.19 C D 4.10 3.87 85 95 90 100 1.53 1.24 E 4.10 3.88 85 95 90 100 1.53 1.24

(12) With the open circuit voltage after the discharging is maintained at lower than 1.3 V/cell and the amount of electrolyte movement is 10% or less or is greater than 10% and less than 15% of the total volume of the electrolytes, the efficiency is maintained, and the charge retention rate rises as identified above.

Example 3

(13) The amount of electrolyte movement is greater than 15% and less than 20% of the total volume of the electrolytes with an open circuit voltage after the discharging is maintained at lower than 1.3 V/cell, and the experimental results are shown in Table 4 below.

(14) TABLE-US-00004 TABLE 4 Post-charge Post-discharge Charge Discharge Charge Open Circuit Open Circuit Classifi- Capacity Capacity EE CE VE Retention Voltage Voltage cation (Ah/cell) (Ah/cell) (%) (%) (%) Rate (%) (V/cell) (V/cell) 3.94 3.64 81 92 88 82 1.51 1.22 B 3.89 3.60 81 92 88 81 1.51 1.23 C D 4.03 3.78 82 94 88 96 1.51 1.24 E 4.05 3.80 82 94 88 96 1.51 1.24

Comparative Example 1

(15) The redox flow battery is operated in the same manner as in Example 1, with the exception that the charge and discharge cycle was performed without a movement of electrolyte. FIG. 1 graphically shows charge retention rates of the redox flow battery of Comparative Example 1 with respect to a charging and discharging cycle.

Comparative Example 2

(16) The redox flow battery was operated in the same manner as in Example 1, with the exception that the amount of electrolyte movement was equal to or less than 10% of the total volume of the electrolytes with an open circuit voltage after the discharging was maintained at higher than 1.3 V/cell, and the experimental results are shown in Table 5 below.

(17) TABLE-US-00005 TABLE 5 Post-charge Post-discharge Charge Discharge Charge Open Circuit Open Circuit Classifi- Capacity Capacity EE CE VE Retention Voltage Voltage cation (Ah/cell) (Ah/cell) (%) (%) (%) Rate (%) (V/cell) (V/cell) 2.13 1.80 74 85 87 50 1.50 1.32 B 1.99 1.68 74 85 87 47 1.50 1.33 C D 0.90 0.85 81 94 86 24 1.49 1.35 E 0.92 0.86 81 94 86 24 1.49 1.35

Comparative Example 3

(18) The redox flow battery was operated in the same manner as in Example 1, with the exception that the amount of electrolyte movement was greater than 10% and less than 15% of the total volume of the electrolytes with an open circuit voltage after the discharging was maintained at higher than 1.3 V/cell, and the experimental results are shown in Table 6 below.

(19) TABLE-US-00006 TABLE 6 Post-charge Post-discharge Charge Discharge Charge Open Circuit Open Circuit Classifi- Capacity Capacity EE CE VE Retention Voltage Voltage cation (Ah/cell) (Ah/cell) (%) (%) (%) Rate (%) (V/cell) (V/cell) 3.10 2.61 76 82 93 79 1.51 1.30 B 2.75 2.33 77 82 94 79 1.51 1.30 C D 2.45 1.91 80 93 86 77 1.52 1.31 E 2.40 1.87 81 93 87 77 1.52 1.31

Comparative Example 4

(20) The redox flow battery was operated in the same manner as in Example 1, with the exception that the amount of electrolyte movement was greater than 15% and less than 20% of the total volume of the electrolytes with an open circuit voltage after the discharging was maintained at higher than 1.3 V/cell, and the experimental results are shown in Table 7 below.

(21) TABLE-US-00007 TABLE 7 Post-charge Post-discharge Charge Discharge Charge Open Circuit Open Circuit Classifi- Capacity Capacity EE CE VE Retention Voltage Voltage cation (Ah/cell) (Ah/cell) (%) (%) (%) Rate (%) (V/cell) (V/cell) 2.61 2.49 79 94 84 69 1.48 1.30 B 2.55 2.40 79 94 84 69 1.48 1.30 C D 1.78 1.70 79 95 83 47 1.48 1.32 E 1.75 1.68 79 95 83 47 1.48 1.32

(22) When an open circuit voltage after the discharging is maintained at higher than 1.3 V/cell, irrespective of the percentage of electrolyte movement of the total volume of the electrolytes, there was no effect of increasing the charge capacity by the movement of the electrolytic solution. The efficiency saw a temporary rise when the charge retention rate declined, resulting in an increased open circuit voltage after the discharging.

Test Example 1

(23) Using the conditions obtained in Example 2, a long-term battery test was conducted. The results thus obtained are shown in FIG. 2.

(24) As shown in FIG. 2, the redox flow battery of Example 2, even after a long-term test, exhibited a charge retention rate that was maintained at more than 80% compared to the initial value, and can prevent the performance of the battery from being degraded.