Monitoring electrolyte concentrations in redox flow battery systems

Abstract

Methods, systems and structures for monitoring, managing electrolyte concentrations in redox flow batteries are provided by introducing a first quantity of a liquid electrolyte into a first chamber of a test cell and introducing a second quantity of the liquid electrolyte into a second chamber of the test cell. The method further provides for measuring a voltage of the test cell, measuring an elapsed time from the test cell reaching a first voltage until the test cell reaches a second voltage; and determining a degree of imbalance of the liquid electrolyte based on the elapsed time.

1 - 26 . (canceled) 
     
     
         27 . A reduction-oxidation (redox) flow battery system, comprising:
 a redox flow battery;   a first test cell fluidically coupled to the redox flow battery, the first test cell having a first chamber separated from a second chamber by a first separator membrane;   an electronic module; and   a processor coupled to the electronic module;   wherein the processor is configured with processor-executable instructions to perform operations comprising:
 causing the electronic module to operate a first electromechanical component to introduce a first sample of a first liquid electrolyte having a first unknown concentration of a first reactant into the first chamber of the first test cell; 
 causing the electronic module to operate the first electromechanical component or a second electromechanical component to introduce a second sample of the first liquid electrolyte having the first unknown concentration into the second chamber of the first test cell; 
 causing the electronic module to charge the first test cell with a first known charging current from a first charging start time to a first predetermined stop point; 
 causing the electronic module to measure a first voltage of the first test cell while charging the first test cell; 
 causing the electronic module to measure a first total charging time from the first charging start time until the first predetermined stop point is reached; 
 determining a first actual concentration of the first reactant in the first liquid electrolyte based on the first total charging time measured by the electronic module. 
   
     
     
         28 . The reduction-oxidation (redox) flow battery system of  claim 27 , further comprising:
 a second test cell fluidically coupled to the redox flow battery, the second test cell having a first chamber separated from a second chamber by a second separator membrane;   wherein the processor is further configured with processor-executable instructions to perform operations comprising:
 causing the electronic module to operate a third electromechanical component to introduce a first sample of a second liquid electrolyte having a second unknown concentration of a second reactant into the first chamber of the second test cell; 
 causing the electronic module to operate the third electromechanical component or a fourth electromechanical component to introduce a second sample of the second liquid electrolyte solution having the second unknown concentration into the second chamber of the second test cell; 
 causing the electronic module to charge the second test cell with a second known charging current from a second charging start time to a second predetermined stop point; 
 causing the electronic module to measure a second voltage of the second test cell while charging the second test cell; 
 causing the electronic module to measure a second total charging time from the second charging start time until the second predetermined stop point is reached; and 
 determining a second actual concentration of the second reactant in the second liquid electrolyte based on the second total charging time measured by the electronic module. 
   
     
     
         29 . The reduction-oxidation (redox) flow battery system of  claim 28 , wherein the processor is further configured with processor-executable instructions to perform operations comprising:
 determining a degree of imbalance between the first reactant and the second reactant based on calculating a difference between the first actual concentration and the second actual concentration.   
     
     
         30 . The reduction-oxidation (redox) flow battery system of  claim 29 , wherein the processor is further configured with processor-executable instructions to perform operations comprising: communicating the determined degree of imbalance to a main controller of the redox flow battery system to improve the operation of the redox flow battery system. 
     
     
         31 . The reduction-oxidation (redox) flow battery system of  claim 30 , wherein the main controller of the redox flow battery system is further configured with processor-executable instructions to perform operations comprising: initiating a rebalancing process in response to the determined degree of imbalance. 
     
     
         32 . The reduction-oxidation (redox) flow battery system of  claim 27 , wherein the processor is further configured with processor-executable instructions to perform operations comprising:
 causing the electronic module to operate one or more of the first electromechanical component and the second electromechanical component to flush one of the first chamber and the second chamber with a quantity of the first liquid electrolyte greater than the first sample.   
     
     
         33 . The reduction-oxidation (redox) flow battery system of  claim 27 , wherein at least one of the first chamber and the second chamber comprises an internal volume of less than about 1 mL. 
     
     
         34 . The reduction-oxidation (redox) flow battery system of  claim 27 , wherein at least one of the first chamber and the second chamber comprises a pointed-oval shape. 
     
     
         35 . The reduction-oxidation (redox) flow battery system of  claim 27 , wherein the first unknown reactant comprises an ionic species produced when charging the first liquid electrolyte in a redox flow battery cell stack. 
     
     
         36 . The reduction-oxidation (redox) flow battery system of  claim 35 , wherein the first unknown reactant comprises Fe 3+ . 
     
     
         37 . The reduction-oxidation (redox) flow battery system of  claim 27 , wherein the second unknown reactant comprises an ionic species produced when charging the second liquid electrolyte in a redox flow battery cell stack. 
     
     
         38 . The reduction-oxidation (redox) flow battery system of  claim 37 , wherein the second unknown reactant comprises Cr 2+ . 
     
     
         39 . The reduction-oxidation (redox) flow battery system of  claim 27 , wherein measuring, using the electronic module, the voltage of the test cell while charging the test cell to a predetermined stop point comprises measuring, using the electronic module, an open-circuit voltage across the first chamber and the second chamber of the test cell. 
     
     
         40 . The reduction-oxidation (redox) flow battery system of  claim 27 , wherein the processor is further configured with processor-executable instructions to perform operations comprising: using the electronic module to charge the test cell with a pulsed charging sequence in which the known charging current is applied during a first time interval followed by a second time interval during which the known charging current is switched off, wherein the application of the known charging current during the first time interval followed by the switching off of the known charging current during the second time interval is repeated until the predetermined stop point is reached. 
     
     
         41 . The reduction-oxidation (redox) flow battery system of  claim 40 , wherein the processor is further configured with processor-executable instructions to perform operations comprising: measuring an open circuit voltage of the test cell during the second time intervals when the known charging current is switched off. 
     
     
         42 . The reduction-oxidation (redox) flow battery system of  claim 27 , wherein the processor is further configured with processor-executable instructions to perform operations comprising: identifying at least one of the first predetermined stop point and the second predetermined stop point by identifying a point in time where a maximum rate of change of the first measured voltage is reached. 
     
     
         43 . The reduction-oxidation (redox) flow battery system of  claim 27 , wherein the processor is further configured with processor-executable instructions to perform operations comprising: identifying the first predetermined stop point when the first voltage is a predetermined open-circuit voltage. 
     
     
         44 . The reduction-oxidation (redox) flow battery system of  claim 27 , wherein the processor is further configured with processor-executable instructions to perform operations comprising: identifying the first predetermined stop point when the first voltage is a predetermined closed-circuit voltage. 
     
     
         45 . The reduction-oxidation (redox) flow battery system of  claim 27 , wherein the first sample of the first liquid electrolyte introduced into the first chamber of the first test cell and the second sample of the first liquid electrolyte introduced into the second chamber of the first test cell, comprise equal volumes. 
     
     
         46 . A reduction-oxidation (redox) flow battery system, comprising:
 a redox flow battery;   a test cell fluidically coupled to the redox flow battery, the test cell comprising a first half-cell chamber with an internal volume of less than about 1 mL, and a second half-cell chamber with an internal volume of less than about 1 mL; and   an electronic controller, comprising:
 a processor; and 
 a non-transitory computer-readable medium coupled to the processor and containing processor-executable instructions to perform operations comprising:
 introducing a first liquid electrolyte into the first half-cell chamber of the test cell, the first liquid electrolyte having a first unknown concentration of a first reactant, 
 introducing a second liquid electrolyte into the second half-cell chamber of the test cell, the second liquid electrolyte having a second unknown concentration of a second reactant, 
 charging the test cell with a known charging current; 
 measuring a voltage of the test cell while charging the test cell with the known charging current, 
 measuring a total charging time from a first point in time when the test cell reaches a first voltage until a second point in time when a voltage test end-point is reached, and 
 determining a degree of imbalance between the first reactant and the second reactant based on the total charging time, wherein the degree of imbalance is a difference between an actual concentration of the first reactant in the first liquid electrolyte and an actual concentration of the second reactant in the second liquid electrolyte; and 
 communicating the determined degree of imbalance to a main controller of the redox flow battery system to improve the operation of the redox flow battery system. 
 
   
     
     
         47 . The reduction-oxidation (redox) flow battery system of  claim 46 , wherein the first half-cell chamber and the second half-cell chamber each have a pointed-oval shape. 
     
     
         48 . A method of operating a reduction-oxidation (redox) flow battery system, the method comprising:
 mixing, using an electrolyte mixing device, a first liquid electrolyte having a first unknown concentration of a first reactant and a second liquid electrolyte having a second unknown concentration of a second reactant to form a mixed liquid electrolyte solution;   operating, using an electronic module, a first electromechanical component to introduce a first volume of the mixed liquid electrolyte solution into a first chamber of a test cell;   operating, using the electronic module, the first electromechanical component or a second electromechanical component to introduce a second volume of the mixed liquid electrolyte solution into a second chamber of the test cell;   charging, using the electronic module, the test cell to a predetermined stop point with a known charging current while measuring a voltage of the test cell;   measuring, using the electronic module, a total charging time from a start time of the charging the test cell to a predetermined stop point until the stop point is reached;   determining, using the electronic module, a degree of imbalance based on the measured total charging time, wherein the degree of imbalance comprises a difference between the first unknown concentration and the second unknown concentration; and   communicating the determined degree of imbalance, from the electronic module to a main controller of the redox flow battery system, to improve the operation of the redox flow battery system.   
     
     
         49 . The method of  claim 48 , wherein measuring, using the electronic module, the voltage of the test cell while charging the test cell to a predetermined stop point comprises measuring, using the electronic module, an open-circuit voltage across the first chamber and the second chamber of the test cell. 
     
     
         50 . The method of  claim 49 , further comprising measuring, using the electronic module, the open circuit voltage during a time interval when the known charging current is not applied. 
     
     
         51 . The method of  claim 48 , wherein charging, using the electronic module, the test cell with a known charging current comprises charging, using the electronic module, the test cell using pulsed charging in which the known charging current is applied during a first time interval followed by a second time interval during which the known charging current is switched off, wherein the application of the known charging current during the first time interval followed by the switching off of the known charging current during the second time interval is repeated until the predetermined stop point is reached. 
     
     
         52 . The method of  claim 51 , wherein measuring, using the electronic module, the voltage of the test cell while charging the test cell to a predetermined stop point comprises measuring an open circuit voltage of the test cell during the second time intervals when the known charging current is switched off. 
     
     
         53 . The method of  claim 48 , wherein the first reactant and the second reactant comprise one of an oxidized ionic species and a reduced ionic species produced during a charging process in the redox flow battery. 
     
     
         54 . The method of  claim 48 , further comprising discharging, using the electronic module, the test cell after operating, using the electronic module, the first electromechanical component to introduce the first volume of the mixed liquid electrolyte solution into the first chamber of the test cell and after operating, using the electronic module, the first electromechanical component or the second electromechanical component to introduce the second volume of the mixed liquid electrolyte solution into the second chamber of the test cell. 
     
     
         55 . The method of  claim 54 , further comprising discharging, using the electronic module, the test cell by short circuiting a pair of electrodes of the test cell.