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CN-122000390-A - Method and system for controlling water balance in metal-air electrochemical cells

CN122000390ACN 122000390 ACN122000390 ACN 122000390ACN-122000390-A

Abstract

A method of controlling water balance in a metal-air electrochemical cell during operation of the electrochemical cell, comprising controlling a ratio of a partial pressure of water vapor in an inlet gas supply to an equilibrium water vapor pressure of an electrolyte of the metal-air electrochemical cell. Controlling the ratio is accomplished by controlling one or both of the partial pressure of water vapor in the inlet gas supply and the equilibrium water vapor pressure of the electrolyte. The method may be performed by a system having a programmable controller programmed to perform the method and configured to receive signals from the sensor and to control the relative humidity control device and the temperature control device based on the signals received from the sensor.

Inventors

  • Liam Andrew Tona

Assignees

  • 锌能公司

Dates

Publication Date
20260508
Application Date
20251103
Priority Date
20241101

Claims (17)

  1. 1. A method of controlling water balance in a metal-air electrochemical cell during operation of the electrochemical cell, the method comprising: During operation of the metal-air electrochemical cell, controlling a ratio of a partial pressure of water vapor in an inlet supply to an equilibrium water vapor pressure of an electrolyte of the metal-air electrochemical cell, wherein controlling the ratio is accomplished by controlling one or both of the partial pressure of water vapor in the inlet supply and the equilibrium water vapor pressure of the electrolyte.
  2. 2. The method of claim 1, wherein the water vapor partial pressure in the intake air supply is controlled and is controlled by varying one or both of the temperature and the relative humidity of the air in the intake air supply.
  3. 3. The method of claim 1 or claim 2, wherein the equilibrium water vapor pressure of the electrolyte is controlled and the equilibrium water vapor pressure of the electrolyte is controlled by varying one or both of the temperature and concentration of the electrolyte.
  4. 4. The method of claim 1, wherein the temperature and concentration of the electrolyte are determined, the equilibrium water vapor pressure of the electrolyte is determined based on the temperature and concentration of the electrolyte, and one or both of the temperature and relative humidity of the air in the intake air supply is changed to add or remove water from the electrolyte or to maintain water in the electrolyte at the same level.
  5. 5. The method of claim 1, wherein the water mass flow rate in the inlet supply is controlled by varying the water vapor partial pressure in the inlet supply based on a difference between the water vapor partial pressure in the inlet supply and the saturated vapor pressure of the electrolyte, the difference will produce a target amount of cell water added/lost to/from the cells.
  6. 6. The method of claim 1, wherein controlling the ratio is accomplished by: determining the temperature and concentration of the electrolyte; Determining an equilibrium water vapor pressure of the electrolyte based on the temperature and concentration of the electrolyte; Determining a temperature and a relative humidity of the intake air supply source; Determining a partial pressure of water vapor in the intake air supply based on the temperature and relative humidity of the air; one of the following operations is performed: For clean water absorption, increasing the partial pressure of water vapor in the inlet gas supply to above the equilibrium vapor pressure of the electrolyte by increasing the temperature and/or relative humidity of the inlet gas supply; for clean water loss, reducing the partial pressure of water vapor in the inlet supply to below the equilibrium vapor pressure of the electrolyte by reducing the temperature and/or relative humidity of the inlet supply; For water purification balance, changing the partial pressure of water vapor in the intake air supply source to be equal to the equilibrium vapor pressure of the electrolyte by changing the temperature and/or relative humidity of the intake air supply source, and The supply of air is continued until the target amount of water is added, removed, or equilibrium is maintained.
  7. 7. The method of claim 5 or claim 6, wherein the concentration of the electrolyte is determined by manual titration measurement or state of charge estimation.
  8. 8. The method of any of claims 5-7, further comprising determining a mass flow rate of the intake air supply source, and determining an amount of water to be added or removed from the electrolyte over a given time based on the mass flow rate.
  9. 9. The method of any one of claims 5 to 8, wherein the electrochemical cell is one of a plurality of electrochemical cells, the temperature and concentration of the electrolyte comprising determining an average temperature and an average concentration of the electrolyte across all of the cells of the plurality of electrochemical cells that receive air in the intake air supply, and determining an equilibrium water vapor pressure of the electrolyte based on the average temperature and average concentration.
  10. 10. The method of claim 1, wherein: Identifying the water balance of the target cell; empirically determining a target water vapor pressure differential between a water vapor partial pressure in the inlet supply and an equilibrium water vapor pressure of the electrolyte from a time series data set relating the vapor pressure differential to the cell water balance, the target water vapor pressure differential being such that the target cell water balance is achieved, and The temperature and relative humidity of the intake air supply source are adjusted based on a temperature set point and a relative humidity set point determined from the target water vapor pressure difference.
  11. 11. The method of claim 10, wherein the time series data set relating the vapor pressure differential to the cell water balance is obtained from among: Continuous calibration curve using data from multiple tests, and/or The vapor pressure differential is relative to a series of discrete points of the cell water balance recorded in a lookup table and interpolated to derive the cell water balance from the vapor pressure differential, and vice versa.
  12. 12. The method of any one of claims 1 to 11, wherein the electrolyte comprises potassium hydroxide.
  13. 13. The method of any one of claims 1 to 12, wherein the electrochemical cell is a zinc air electrochemical cell.
  14. 14. The method of any one of claims 1 to 13, wherein the electrochemical cell is a battery.
  15. 15. A system for controlling water balance in a metal-air electrochemical cell during operation of the electrochemical cell, the system comprising: An air supply source; A metal-air electrochemical cell pneumatically connected to the air supply to receive intake air from the air supply; a humidity sensor configured to determine a relative humidity of the intake air; a first temperature sensor configured to determine a temperature of the intake air; a humidity control device and a temperature control device located between the air supply source and the metal-air electrochemical cell for controlling the relative humidity and temperature of the intake air; A second temperature sensor configured to determine a temperature of the electrolyte in the electrochemical cell, and A programmable controller programmed to perform the method of any one of claims 1 to 14 and configured to receive signals from the sensor and to control the relative humidity control device and the temperature control device based on the signals received from the sensor.
  16. 16. The system of claim 15, further comprising at least one pressure sensor for determining a pressure of the intake air.
  17. 17. The system of claim 15 or claim 16, further comprising a water recirculation subsystem that supplements water into the electrolyte when the electrolyte level in the electrochemical cell is below an acceptable electrolyte level.

Description

Method and system for controlling water balance in metal-air electrochemical cells Cross Reference to Related Applications The present application claims priority from USSN 63/715,244 filed on month 11 of 2024, which is incorporated herein by reference in its entirety. Technical Field The present application relates to electrochemical cells, and in particular to metal-air electrochemical cells and systems and methods for controlling water balance in metal-air electrochemical cells. Background In metal-air electrochemical cells (e.g., zinc-air cells), air flowing through the cell may cause water to be carried away from or added to the electrolyte in the cell. This is especially true for open and semi-open metal-air electrochemical cells. If the cell electrolyte absorbs or loses too much water over time, the electrolyte concentration will deviate from the optimal operating conditions, resulting in performance degradation. If the cell loses too much water over time, the electrolyte level may drop too low, causing partial electrode exposure. If part of the electrode is not immersed in the electrolyte, ions cannot be transferred therebetween, so that the section of the electrode not immersed in the electrolyte cannot participate in the chemical reaction required for the cell operation. If the cell absorbs too much water over time, the volume of electrolyte may increase beyond the cell's capacity, resulting in flooding and electrolyte leakage. Thus, it is desirable to maintain an appropriate water balance in the electrolyte throughout the operation of the cell. There is a need for efficient systems and methods for controlling water balance in metal-air electrochemical cells, particularly zinc-air cells. Disclosure of Invention A method of controlling water balance in a metal-air electrochemical cell during operation of the electrochemical cell includes controlling a ratio of a partial pressure of water vapor in an inlet supply to an equilibrium water vapor pressure of an electrolyte of the metal-air electrochemical cell, wherein controlling the ratio is accomplished by controlling one or both of the partial pressure of water vapor in the inlet supply and the equilibrium water vapor pressure of the electrolyte. A system for controlling water balance in an electrochemical cell during operation of a metal-air electrochemical cell includes an air supply, a metal-air electrochemical cell pneumatically connected to the air supply to receive an intake air from the air supply, a humidity sensor configured to determine a relative humidity of the intake air, a first temperature sensor configured to determine a temperature of the intake air, a humidity control device and a temperature control device located between the air supply and the metal-air electrochemical cell for controlling the relative humidity and temperature of the intake air, a second temperature sensor configured to determine a temperature of an electrolyte in the electrochemical cell, and a programmable controller programmed to perform the method and configured to receive signals from the sensor and control the relative humidity control device and the temperature control device based on the signals received from the sensor. For metal air electrochemical cells, proper vapor pressure balance between the electrolyte and the inlet gas supply is necessary to ensure that the bulk electrolyte does not absorb or lose excessive water over time. The partial pressure of water vapor in the air depends on both the temperature and the relative humidity, and thus it is insufficient to rely on the determination of the relative humidity and the control of the intake air supply source alone. In addition, it is not sufficient to rely on the determination of the relative humidity in the air space in the vicinity of the electrolyte alone. The equilibrium vapor pressure (also referred to as the saturated vapor pressure, or simply vapor pressure) of an electrolyte describes the water evaporation tendency of the electrolyte, and varies with the temperature and concentration of the electrolyte (both of which may vary throughout the battery charge and discharge cycles). The higher the equilibrium vapor pressure of the electrolyte, the more evaporation, the lower the equilibrium vapor pressure of the electrolyte is, and the less evaporation. It has now been found that water balance is achieved if the partial pressure of water vapor of the inlet air supplied to the electrochemical cell is equal to the equilibrium vapor pressure of the electrolyte. In order to maintain proper balance of water in the electrolyte of the electrochemical cell, the water vapor pressure of the inlet supply (i.e., the partial pressure of water vapor in the inlet supply) must be controlled, which varies with temperature and relative humidity. To determine how to control the vapor pressure of the inlet supply, the vapor pressure of the inlet supply is compared to the equilibrium vapor pressure of the electrolyte