US-20260128332-A1 - METHOD AND SYSTEM FOR CONTROLLING WATER BALANCE IN METAL-AIR ELECTROCHEMICAL CELLS

US20260128332A1US 20260128332 A1US20260128332 A1US 20260128332A1US-20260128332-A1

Abstract

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

Inventors

Liam Andrew TONER

Assignees

E-ZINC INC.

Dates

Publication Date: 20260507
Application Date: 20251029

Claims (17)

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 partial pressure of water vapor in an inlet supply of air to equilibrium water vapor pressure of an electrolyte of the metal-air electrochemical cell, wherein controlling the ratio is done by controlling one or both of the partial pressure of water vapor in the inlet supply of air and the equilibrium water vapor pressure of the electrolyte.
2 . The method of claim 1 , wherein the partial pressure of water vapor in the inlet supply of air is controlled, and the partial pressure of water vapor in the inlet supply of air is controlled by changing one or both of temperature and relative humidity of the air in the inlet supply of air.
3 . The method of claim 1 , wherein the equilibrium water vapor pressure of the electrolyte is controlled, and the equilibrium water vapor pressure of the electrolyte is controlled by changing one or both of temperature and concentration of the electrolyte.
4 . The method of claim 1 , wherein 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 temperature and relative humidity of the air in the inlet supply of air are changed to add or remove water from the electrolyte or to maintain water in the electrolyte at a same level.
5 . The method of claim 1 , wherein mass flow rate of water in the inlet supply of air is controlled by changing the partial pressure of water vapor in the inlet supply of air based on a difference between the partial pressure of water vapor in the inlet air supply and the saturation vapor pressure of the electrolyte that will yield a target amount of cell water addition/loss to/from the cell.
6 . The method of claim 1 , wherein controlling the ratio is done by: determining temperature and concentration of the electrolyte; determining the equilibrium water vapor pressure of the electrolyte based on the temperature and concentration of the electrolyte; determining temperature and relative humidity of the inlet supply of air; determining the partial pressure of water vapor in the inlet supply of air based on the temperature and relative humidity of the air; performing one of the following: for net water gain, increasing the partial pressure of water vapor in the inlet supply of air above the equilibrium vapor pressure of the electrolyte by increasing the temperature and/or relative humidity of the inlet supply of air; for net water loss, decreasing the partial pressure of water vapor in the inlet supply of air below the equilibrium vapor pressure of the electrolyte by decreasing the temperature and/or relative humidity of the inlet supply of air; for net water balance, altering the partial pressure of water vapor in the inlet supply of air, by altering the temperature and/or relative humidity of the inlet supply of air, to equal the equilibrium vapor pressure of the electrolyte; and, continuing to supply the air until a target amount of water has been added, removed or maintained in balance.
7 . The method of claim 5 , wherein the concentration of the electrolyte is determined by manual titration measurement or state of charge estimation.
8 . The method of claim 5 , further comprising determining mass flow rate of the inlet supply of air 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 . The method of claim 1 , wherein the electrochemical cell is one cell of a plurality of electrochemical cells, the temperature and concentration of the electrolyte comprises determining an average temperature and concentration of the electrolytes across all the cells in the plurality of electrochemical cells receiving the air from the inlet supply of air, and determining the equilibrium water vapor pressure of the electrolyte is based on the average temperature and concentration.
10 . The method of claim 1 , wherein: a target cell water balance is identified; a target water vapor pressure difference between the partial pressure of water vapor in the inlet supply of air and the equilibrium water vapor pressure of the electrolyte, which would result in achieving the target cell water balance, is determined empirically from a time series dataset correlating the vapor pressure difference to the cell water balance; and, temperature and relative humidity of the inlet supply of air are adjusted based on temperature and relative humidity setpoints determined from the target water vapor pressure difference.
11 . The method of claim 10 , wherein the time series dataset correlating the vapor pressure difference to the cell water balance is obtained from: a continuous calibration curve using data from a plurality of tests; and/or, a series of discrete points of the vapor pressure difference vs. the cell water balance recorded in a lookup table and interpolated to find the cell water balance given the vapor pressure difference or vice-versa.
12 . The method of claim 1 , wherein the electrolyte comprises potassium hydroxide.
13 . The method of claim 1 , wherein the electrochemical cell is a zinc-air electrochemical cell.
14 . The method of claim 1 , wherein the electrochemical cell is a battery.
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; a metal-air electrochemical cell pneumatically connected to the air supply to receive inlet air from the air supply; a humidity sensor configured to determine the relative humidity of the inlet air; a first temperature sensor configured to determine the temperature of the inlet air; a humidity control device and a temperature control device between the air supply and the metal-air electrochemical cell for controlling relative humidity and temperature of the inlet air; a second temperature sensor configured to determine the temperature of an electrolyte in the electrochemical cell; and, a programmable controller programmed to perform the method as defined in claim 1 and configured to receive signals from the sensors and control the relative humidity and temperature control devices based on the signals received from the sensors.
16 . The system of claim 15 , further comprising at least one pressure sensor to determine pressure of the inlet air.
17 . The system of claim 15 further comprising a water recycling subsystem that replenishes water in the electrolyte when the electrolyte level in the electrochemical cell is below an acceptable electrolyte level.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS This application claims the benefit of U.S. Ser. No. 63/715,244 filed Nov. 1, 2024, the entire contents of which is herein incorporated by reference. FIELD This application relates to electrochemical cells, in particular to metal-air electrochemical cells, and systems and methods for controlling water balance therein. BACKGROUND In a metal-air electrochemical cell (e.g., a zinc-air cell), air flowing through the cell can either cause water to be stripped from or added to an electrolyte in the cell. This is especially true for open and semi-open metal-air electrochemical cells. If the cell electrolyte gains or loses excessive amounts of water over time, the electrolyte concentration will drift from optimal operating conditions causing performance degradation. If the cell loses excessive water over time, the electrolyte level may drop low enough to expose parts of the electrodes. If parts of the electrodes are not submerged in electrolyte, ions cannot transfer between them so the sections of the electrode that are not submerged in electrolyte cannot participate in the chemical reactions necessary for cell operation. If the cell gains excessive water over time, the volume of the electrolyte may increase beyond the capacity of the cell tank causing flooding and electrolyte leaks. It is therefore desirable to maintain proper water balance in the electrolyte throughout operation of the cell. There is a need for efficient systems and methods for controlling water balance in metal-air electrochemical cells, especially zinc-air cells. SUMMARY A method of controlling water balance in a metal-air electrochemical cell during operation of the electrochemical cell comprises: controlling a ratio of partial pressure of water vapor in an inlet supply of air to equilibrium water vapor pressure of an electrolyte of the metal-air electrochemical cell, wherein controlling the ratio is done by controlling one or both of the partial pressure of water vapor in the inlet supply of air and the equilibrium water vapor pressure of the electrolyte. A system for controlling water balance in a metal-air electrochemical cell during operation of the electrochemical cell comprises: an air supply; a metal-air electrochemical cell pneumatically connected to the air supply to receive inlet air from the air supply; a humidity sensor configured to determine the relative humidity of the inlet air; a first temperature sensor configured to determine the temperature of the inlet air; a humidity control device and a temperature control device between the air supply and the metal-air electrochemical cell for controlling relative humidity and temperature of the inlet air; a second temperature sensor configured to determine the temperature of an electrolyte in the electrochemical cell; and, a programmable controller programmed to perform the method and configured to receive signals from the sensors and control the humidity and temperature control devices based on the signals received from the sensors. For metal-air electrochemical cells, the correct vapor pressure balance between the electrolyte and inlet supply of air is necessary to ensure that the bulk electrolyte does not gain or lose too much water over time. The partial pressure of water vapor in air depends on both temperature and relative humidity, therefore relying solely on relative humidity determination and control of the inlet supply of air is inadequate. Additionally, relying only the determination of the relative humidity in the air space next to the electrolyte is inadequate. The equilibrium vapor pressure (also called saturation vapor pressure, or simply vapor pressure) of the electrolyte describes the propensity of the electrolyte to evaporate water, and it varies with both temperature and the concentration of electrolyte (both of which may change throughout a cell charge and discharge cycle). Higher electrolyte equilibrium vapor pressure yields greater evaporation, lower yields less evaporation. It has now been found that 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, water balance is achieved. To maintain proper balance of water in the electrolyte of the electrochemical cell, the water vapor pressure of the inlet supply of air (i.e., the partial pressure of water vapor in the inlet supply of air) as a function of temperature and relative humidity must be controlled. To determine how to control the water vapor pressure of the inlet supply of air, the water vapor pressure of the inlet supply of air is compared to the equilibrium water vapor pressure of the electrolyte. The equilibrium water vapor pressure of the electrolyte is determined from the temperature and concentration of the electrolyte. If the amount of water in the electrolyte is to be maintained at a current level, the water vapor pressure of the inlet supply of air is controlle