MXPA01006760A - Reduced leakage metal-air electrochemical cell - Google Patents

Abstract

The invention relates to a metal-air electrochemical cell which exhibits good discharge performance under relatively high temperature, high humidity conditions. The cell has improved discharge performance at a temperature between about 25°C and about 38°C and a relative humidity external of the cell of between about 45 and about 95 percent. Leakage from the cell also can be reduced.

Description

METAL-AIR ELECTROCHEMICAL CELL WITH REDUCED LEAKS DESCRIPTION OF THE INVENTION The invention is generally concerned with metal-air electrochemical cells. Batteries are commonly used sources of electrical energy. A battery contains a negative electrode, usually called an anode and a positive electrode, usually called the cathode. The anode contains an active material that can be oxidized; The cathode contains or consumes an active material that can be reduced. The active material of the anode is capable of reducing the active material of the cathode. In order to prevent the direct reaction of the anode material and the cathode material, the anode and the cathode are electrically isolated from each other by a sheet-like layer, commonly called the separator. When a battery is used as a source of electrical energy in a device, such as in an auditory aid, electrical contact is made with the anode and the cathode, allowing electrons to flow through the device and allowing oxidation reactions to occur and respective reduction to provide electrical power. An electrolyte in contact with the anode and the cathode contains ions that flow through the separator between the electrodes to maintain charge electrolyte throughout the battery during discharge.

Ref: 131188 A battery configuration is a button cell that has the approximate size and cylindrical shape of a button. In a button cell, the container for the anode and the cathode includes a lower cup-like structure, called the cathode can and an upper cup-like structure retained within the cathode can, called the anode can. The anode and cathode can be separated by an insulator, such as a seal or insulating seal. The anode can and the cathode can are crimped together to form the container. In a metal-air electrochemical cell, oxygen is reduced at the cathode and a metal is oxidized at the anode. Oxygen is supplied to the cathode from the outside atmospheric air to the cell through an air access hole in the container. When the electrolyte in the cell is aqueous, hydrogen gas can be produced at the anode of the cell. The generation of gas can lead to an accumulation of pressure in the cell, ultimately resulting in leakage or structural failure of the cell. The metal of a metal-air electrochemical cell can be zinc. Normally, when zinc is used in a metal-air battery, the zinc is bound or combined with mercury (eg, about 3%) to reduce the evolution of hydrogen gas.

In general, the invention is concerned with a metal-air electrochemical cell that exhibits good discharge performance under a relatively high temperature, high humidity conditions. Cell leaks can be reduced. The conditions of relatively high temperature, high humidity are a temperature between about 25 ° C and about 38 ° C (for example, 30 ° C) and an external relative humidity of the cell of between about 45 ° and about 95 percent (per example between 70 and 90 percent). The conditions of high temperature, high humidity are similar to the environmental conditions that the cell is exposed during use (for example, approximately 30 ° C and 90 percent relative humidity). For example, a zinc-air cell can be used in a geographical location of high temperature and high humidity, such as the Far East or in a hearing aid that is not hermetically sealed. The hearing aid is placed in an ear canal, which has a relatively high humidity and a high temperature. It is important that the cell has good discharge performance and resist leaks under these operating conditions. In one aspect, the invention is concerned with a metal-air electrochemical cell that includes an anode, a cathode and a separator that electronically separates the anode and the cathode. The anode includes an anode can that has an anode gel. The anode gel includes an electrolyte. The cathode includes a cathode can that has at least one air access hole and that contains a cathode structure. An insulator can be located between the anode can and the cathode can. The cathode structure can include a catalytic mixture and a current collector in electrical contact with the cathode can. The cell may further include an air disperser positioned between the air access port and the cathode structure. The anode can and the cathode can are assembled or spliced (for example crimped together) to form a cell. At the anode, the volume of the anode is the volume within the cell contained between the inner surface of the anode can and the separator. The anode gel occupies most of the volume of the anode. The volume portion of the anode that is not filled with the anode gel is the void volume or void volume. The empty volume of the cell after discharge is between about 7.5 percent and about 15 percent of the volume of the anode. Preferably, the void or void volume is between about 8 percent and about 12 percent (eg, about 10 percent) of the volume of the anode. The overall cell height and diameter dimensions are specified by the International Electrotechnical Commission (IEC). A cell can have one of five sizes: a cell 675 (designation of IEC "PR44") has a diameter between about 11.25 and 11.60 millimeters and a height between about 5.0 and 5.4 millimeters; a cell 13 (designation IEC "PR48") has a diameter between about 7.55 and 7.9 millimeters and a height between about 5.0 and 5.4 millimeters; a cell 312 (designation IEC "PR41") has a diameter between about 7.55 and 7.9 millimeters and a height between about 3.3 and 3.6 millimeters and a cell 10 (IEC designation "PR70") has a diameter between approximately 5.55 and 5.80 millimeters and a height between approximately 3.30 and 3.60 millimeters. A cell 5 has a diameter between approximately 5.55 and 5.80 millimeters and a height between approximately 2.03 and 2.16 millimeters. The cell can have an anode can thickness of approximately 0.1016 mm. The cell can have a cathode can thickness of approximately 0.1016 mm. The metal-air electrochemical cell can be a cell 675. Cell 675 can have a discharge performance of between about 700 mAh and about 480 mAh at a temperature between about 25 ° C and about 38 ° C (for example, 30 ° C) and an external relative humidity of the cell between about 45 and about 95 percent. Preferably, the discharge performance of cell 675 is between about 680 mAh and about 510 mAh, more preferably between about 660 mAh and about 550 mAh (e.g., about 600 mAh). The metal-air electrochemical cell can be a cell 13. Cell 13 can have a discharge performance of between about 295 mAh and about 200 mAh at a temperature between about 25 ° C and about 38 ° C (for example 30 ° C) ) and an external relative humidity of the cell between about 45 and about 95 percent. Preferably, the discharge performance of the cell is between about 290 mAh and about 220 mAh, more preferably between about 280 mAh and about 230 mAh (e.g., about 260 mAh). The metal-air electrochemical cell can be a cell 312. Cell 312 can have a discharge performance of between about 155 mAh and about 110 mAh for a cell 312 at a temperature between about 25 ° C and about 38 ° C (for example, 30 ° C) and an external relative humidity of the cell of between about 45 and about 95 percent. Preferably, the discharge performance of cell 312 is between about 152 mAh and about 115 mAh, more preferably between about 150 mAh and about 120 mAh (e.g., about 135 mAh). The metal-air electrochemical cell can be a cell 10. Cell 10 can have a discharge performance of between about 85 mAh and about 50 mAh at a temperature between about 25 ° C and about 38 ° C (for example 30 ° C) C) and an external relative humidity of the cell between about 45 and about 95 percent. Preferably, the discharge performance of cell 10 is between about 84 mAh and about 55 mAh, more preferably between about 82 mAh and about 60 mAh (e.g., about 70 mAh). The metal-air electrochemical cell can be a cell 5. Cell 5 can have a discharge performance of between about 45 mAh and about 40 mAh (e.g., about 43 mAh) at a temperature between about 25 ° C and about 38 ° C (for example, 30 ° C) and an external relative humidity of the cell of between about 45 and about 95 percent. In another aspect, the invention comprises a method for manufacturing a metal-air electrochemical cell. The method includes assembling or assembling an anode and a cathode to form a cell having a hollow volume or void volume after discharge between 7.5 percent and about 15 percent of the volume of the anode.

In another aspect, the invention further comprises a method for reducing electrolyte leakage from a metal-air electrochemical cell. The method includes assembling or assembling an anode and a cathode to form a cell. The anode is mounted to have a hollow volume or void after discharge that is between about 7.5 percent and about 15 percent of the volume of the anode. The metal-air electrochemical cells of the invention can have improved discharge performance under conditions of high temperature and high relative humidity at 20 ° C and 50 percent relative humidity. The cells have a reduced tendency to leak in relation to the cells of low empty volume. Under conditions of high humidity and high temperature, moisture can enter the cell, accumulating the hydrostatic pressure in the cell. The hydrostatic pressure can lead to flooding of the cathode with electrolyte and finally render the cell useless. The empty volume or higher void volume of the cell increases the tolerance of the cell to take atmospheric moisture. As the empty volume increases, the capacity of the cell decreases. The empty volume can be selected to reduce leakage and improve discharge performance in so much that it maintains the capacity of the appropriate cell. Figure 1 illustrates a cross-sectional view of a metal-air cell.

Electrochemical metal-air cells may be zinc-air cells having a relatively high void volume. Zinc-air batteries exhibit good discharge performance under relatively high temperature, high humidity conditions, such as at 30 ° C and 90% relative humidity. By including an empty volume greater than 7.5 percent and less than 15 percent of the cell, significant gains in cell performance can be obtained at relevant temperatures and humidities. In addition, the probability of leakage can be reduced. A zinc-air cell can be a button cell. With reference to Figure 1, a button cell includes an anode 2 and a cathode 4. The anode 2 includes the can 10 of the anode and the gel 60 of the anode. Cathode 4 includes can 20 and cathode. the structure 40 of the cathode. The insulator 30 is placed between the can 10 of the anode and the can 20 of the cathode. The separator 70 is placed between the structure 40 of the cathode and the gel 60 of the anode, preventing electrical contact between these two components. The air access hole 80, located in the anode can 20, allows the air to be exchanged in and out of the cell. The air disperser 50 is located between the air access hole 80 and the cathode structure 40.

The can 10 of the anode and the can 20 of the cathode are crimped together to form the container or container of the cell, which has an internal volume or cell volume. Together, the internal surface 82 of the can 10 of the anode and the separator 70 form the volume 84 of the anode. The volume of the anode 84 contains the gel 60 of the anode. The remainder of the anode volume 84 is void volume 90. A zinc-air cell utilizes zinc as the electrochemically active anode material. The anode gel contains a mixture of zinc and electrolyte. The mixture of zinc and electrolyte can include a gelling agent that can help prevent leakage of the electrolyte from the cell and help suspend the zinc particles within the anode. The cathode structure contains a material (eg, a manganese compound) that can catalyze the reduction of oxygen entering the cell as a component of the atmospheric air that passes through the access holes in the bottom of the can cathode. The overall electrochemical reaction within the cell results in the zinc metal being oxidized to zinc ions and the oxygen in the air reduced to hydroxyl ions. Finally, zinc oxide or zincate is formed at the anode. As long as these chemical reactions are carried out, the electrons are transferred from the anode to the cathode, providing power to the device. The empty volume is determined after the discharge of the cell. The volume of the anode of the cell is established by the geometry of the cell and the dimensions of the components. The amount of the anode volume occupied by the anode gel is determined by the volume of the anode gel added to the cell. As a zinc-air cell is discharged, the zinc in the anode gel is oxidized to zinc oxide. Oxidation of zinc increases the volume occupied by the anode gel, since the density of zinc is greater than the density of zinc oxide. The volume of the anode gel expands during discharge due to the larger volume occupied by oxidized zinc. The amount of expansion of the anode gel after discharge can be calculated from the zinc content of the gel and the change in density of the zinc component. The volume of the anode gel after discharge can then be calculated by adding the volume of expansion with the volume of the anode gel before discharge. Thus, the empty volume after discharge can be calculated by taking the difference between the volume of the anode and the volume of the anode gel after discharge. The empty volume 90 after the discharge can be between approximately 7.5 percent and 15 percent. Increased empty volume can help reduce electrolyte leaks from the cell. The cathode structure has one side fa the anode gel and one side fa the air access holes. The side of the cathode structure fa the anode gel is covered by a separator. The separator can be an electrically insulating, porous polymer, such as polypropylene, which allows the electrolyte to contact the cathode in the air. The side of the cathode structure fa the air access holes is commonly covered by a polytetrafluoroethylene (PTFE) membrane that can help prevent drying of the anode gel and leakage of electrolyte from the cell. The cells may also include an air disperser or dye material, between the PTFE membrane and the air access holes. The air disperser is a porous or fibrous material that helps maintain an air diffusion space between the PTFE membrane and the cathode can. The air disperser can be hydrophilic and absorbent, allowing it to absorb any moisture on the cathode side of the cell. The disperser can also limit the damage done by the electrolytic solution if it penetrates the cathode, which can occur under higher temperature and humidity conditions, particularly when the empty volume of the cell is not large enough to compensate for the generation of gas in the cell. the anode The cathode structure includes a current collector, such as a wire mesh, onto which a cathode mixture is deposited. The wire mesh makes electrical contact with the cathode can. The cathode mixture includes a catalyst for redu oxygen, such as a manganese compound. The catalytic mixture is composed of a mixture of a binder (for example, PTFE particles), carbon particles and manganese compounds. The catalyst mixture can be prepared, for example, by heating manganese nitrate or by redu potassium permanganate to produce manganese oxides, such as Mn203, Mn304 and Mn02. The catalyst mixture may include between about 15 and 45 weight percent of polytetrafluoroethylene. For example, the cathode structure can include approximately 40 percent PTFE that can make the structure more resistant to moisture, redu the likelihood of cell electrolyte leaks due to the absorption of moisture from the atmosphere. The electrochemical cell includes an anode formed from an anode gel. The anode gel includes an electrolyte, a zinc material and a gelling agent. In certain embodiments, the zinc content of the anode may be less than 3 weight percent zinc. In other embodiments, the mercury content of the anode zinc may contain less than 2 weight percent mercury. The zinc material can be a zinc alloy powder that includes less than 2 percent mercury. The zinc alloy may include, for example, lead, indium or aluminum. Suitable zinc materials include zinc available from Union Miniere (Overpelt, Belgium), Duracell (USA), Noranda (USA), Grillo (Germany) or Toho Zinc (Japan) or zinc materials described in the application US Patent Serial No. 08 / 905,254 filed August 1, 1997 and US Patent Application Serial No. 09 / 115,867, filed July 15, 1998, each of which is hereby incorporated by reference. reference. The zinc-air anode materials are charged to a cell in the following manner. A gelling agent (approximately 0.33 weight percent) and zinc powder are mixed to form a dry anode mixture. Then the mixture is poured into the anode can and the electrolyte is distributed over the dry anode mixture to form the anode gel. The gelling agent can be a polyacrylate, such as sodium polyacrylate. The gelling agent can be an absorbent polyacrylate. The anode gel includes less than 1 weight percent of the gelling agent in the weight of the anode mixture. Preferably, the content of the gelling agent of the anode mixture is between about 0.2 and 0.8 percent by weight, more preferably between about 0.3 and 0.6 percent by weight and more preferably between about 0.33 percent by weight. The anode gel may include a surfactant or surfactant or other additives. The electrolyte can be an aqueous solution of potassium hydroxide. The electrolyte can include between about 30 and 40 percent potassium hydroxide. The concentration of the electrolyte can affect the proportion at which a cell absorbs water. The higher the concentration of the electrolyte, the more water it tends to absorb from the atmosphere. The electrolyte can also include between about 1 and 2 percent zinc oxide. The anode may be composed of stainless steel having a copper layer on the inner surface of the can and a layer of nickel on the outer surface of the can. The cathode may be composed of cold rolled steel having internal and external nickel layers. The insulator, such as an insulating seal, press fit between the anode can and the cathode can. The insulator can be an insulating polymeric material, such as nylon, polypropylene or polyethylene. The configuration of the can can be a straight-walled design, in which the anode can is straight or a folded design in which the trimmed edge of the anode can, generated during the stamping of the can, is placed on the top, outside the can, away from the inside of the cell. A straight-walled design can be used in conjunction with an L-shaped or J-shaped insulator, preferably L-shaped, that can bury the trimmed edge to the insulation leg. During storage, the air access holes are normally covered by a separable sheet, commonly known as the sealing tab, which is provided at the bottom of the cathode can to cover the air access holes to restrict the flow of air. air between the inside and the outside of the button cell. The user releases the sealing tab of the cathode can before use to allow oxygen from the air to enter the inside of the button cell from the external environment.EXAMPLES The download capacities of five cell sizes were calculated for three different empty volumes in examples 1-5. Each of the cells had a thickness of the anode can of approximately 0.152 mm and a thickness of the cathode can of approximately 0.203 mm. The discharge capacities are listed in Table I. The cell sizes correspond to the cell sizes designated by IEC. The discharge capacities are based on the discharge of zinc-air cells at 20 ° C and 50 percent relative humidity. The discharge capacities of the cells of 5% of empty volume and cells of 20% of empty volume are based on measurements of discharge of manufactured cells. The discharge capacities reported at 10% of empty volume are nominal capacities based on the weight of the anode required to obtain an empty volume of 10%, less an estimated value of the anode efficiency losses. The anode efficiency losses were estimated from those observed for cells of 5% empty volume and 20% empty volume.

Table I Volume 5% 10% 20% empty Example lad (mAh) Capacity (mAh) Capacity (mAh) 1 675 610 560 480 2 13 260 240 200 3 312 135 125 110 4 10 70 65 50 5 5 45 43 • 40 The discharge capacities of five cell sizes that have thinner can thickness than in Examples 1-5 were calculated for three different empty volumes in examples 6-10. Each of the cells had an anode can thickness of approximately 0.1016 mm and a cathode can thickness of approximately 0.1016 mm. The external dimensions of the cells fell within the ranges designated by IEC for each cell size. The discharge capacities are listed in Table II.

Table: II Volume 5% 10% 20% empty Example Cell size Capacity (mAh) Capacity (mAh) Capacity (mAh) 6 675 700 645 585 7 13 295 275 225 8 312 155 145 130 9 10 85 80 62 10 5 45 43 40 It is noted that, in relation to this date, the best method known to the applicant to carry out the aforementioned invention, is that which is clear from the present description of the invention.

Claims (29)

1. CLAIMS Having described the invention as above, the content of the following claims is claimed as property: 1. A metal-air electrochemical cell, characterized in that it comprises: an anode including an anode can and an anode gel; a cathode, the cathode includes a cathode can that has at least one air access hole and that contains a cathode structure, the anode can and the cathode can are assembled or assembled to form a cell and a separator that electronically separates the anode and the cathode, positioned between the anode gel and the cathode structure; wherein the anode has an anode volume contained between an internal surface of the anode can and the separator, the anode volume contains an anode gel and a void volume or void volume, the void volume or void volume, after the anode volume. discharge, is approximately 7.5 percent and approximately 15 percent of the anode volume.
2. 2. The metal-air electrochemical cell according to claim 1, characterized in that the empty volume, after discharge, is between about 8 percent and about 12 percent.
3. 3. The metal-air electrochemical cell according to claim 1, characterized in that the empty volume, after discharge, is approximately 10 percent.
4. 4. The metal-air electrochemical cell according to claim 1, characterized in that it has a discharge capacity of between about 700 mAh and about 480 mAh for a cell 675 at a temperature between about 25 ° C and about 38 ° C and an external relative humidity of the cell of between about 45 and about 95 percent.
5. 5. The metal-air electrochemical cell according to claim 1, characterized in that it has a discharge capacity of between about 295 mAh and about 200 mAh for a cell 13 at a temperature between about 25 ° C and about 38 ° C and an external relative humidity of the cell of between about 45 and about 95 percent.
6. The metal-air electrochemical cell according to claim 1, characterized in that it has a discharge capacity of between about 155 mAh and about 110 mAh for a cell 312 at a temperature between about 25 ° C and about 38 ° C and an external relative humidity of the cell of between about 45 and about 95 percent.
7. The metal-air electrochemical cell according to claim 1, characterized in that it has a discharge capacity of between about 85 mAh and about 50 mAh for a cell 10 at a temperature between about 25 ° C and about 38 ° C and an external relative humidity of the cell of between about 45 and about 95 percent.
8. 8. The metal-air electrochemical cell according to claim 1, characterized in that it has a discharge capacity of between about 45 mAh and about 40 mAh for a cell 5 at a temperature between about 25 ° C and about 38 ° C and an external relative humidity of the cell of between about 45 and about 95 percent.
9. 9. The metal-air electrochemical cell according to claim 4, characterized in that the temperature is about 30 ° C.
10. 10. The metal-air electrochemical cell according to claim 9, characterized in that the relative humidity is between about 70 and about 90 percent.
11. 11. The metal-air electrochemical cell according to claim 4, characterized in that the temperature is about 30 ° C and the relative humidity is about 90 percent.
12. 12. The metal-air electrochemical cell according to claim 5, characterized in that the temperature is about 30 ° C and the relative humidity is about 90 percent.
13. 13. The metal-air electrochemical cell according to claim 6, characterized in that the temperature is about 30 ° C and the relative humidity is about 90 percent.
14. 14. The metal-air electrochemical cell according to claim 7, characterized in that the temperature is about 30 ° C and the relative humidity is about 90 percent.
15. 15. The metal-air electrochemical cell according to claim 8, characterized in that the temperature is about 30 ° C and the relative humidity is about 90 percent.
16. 16. The metal-air electrochemical cell according to claim 1, characterized in that the anode gel includes zinc particles.
17. 17. The metal-air electrochemical cell according to claim 1, characterized in that the zinc particles comprise less than 2 percent by weight of mercury.
18. 18. The metal-air electrochemical cell according to claim 1, characterized in that the anode gel includes a sodium polyacrylate.
19. 19. The metal-air electrochemical cell according to claim 1, characterized in that the cathode structure includes a catalytic mixture and a current collector in electrical contact with the cathode can.
20. 20. The metal-air electrochemical cell according to claim 1, characterized in that the catalytic mixture includes between about 25 and 45 weight percent of polytetrafluoroethylene.
21. 21. The metal-air electrochemical cell according to claim 1, characterized in that it further comprises an air disperser positioned between the air access hole and the cathode structure, the air disperser includes an absorbent material.
22. 22. The metal-air electrochemical cell according to claim 1, characterized in that the anode can has a thickness of approximately 0.1016 mm.
23. 23. The metal-air electrochemical cell according to claim 1, characterized in that the cathode can has a thickness of approximately 0.1016 mm.
24. 24. A method for manufacturing a metal-air electrochemical cell, characterized in that it comprises: assembling or assembling an anode and a cathode to form a cell, the anode includes an anode and an anode gel, the cathode includes a cathode can it has at least one air access hole and contains a cathode structure and the cell includes a separator that electronically separates the anode and the cathode, positioned between the anode gel and the cathode structure; wherein the anode has an anode volume contained between an internal surface of the anode can and the separator, the volume of the anode contains an anode gel and an empty volume, the empty volume, after discharge, is between 7.5 percent and approximately 15 percent of the volume of the anode.
25. 25. The method according to claim 24, characterized in that the empty volume after discharge is between about 8 percent and about 12 percent.
26. 26. The method according to claim 24, characterized in that the anode gel includes zinc particles comprising less than 2 percent by weight of mercury.
27. 27. The method according to claim 24, characterized in that the catalytic mixture includes between about 25 and 45 percent by weight of polytetrafluoroethylene.
28. The method according to claim 24, characterized in that the cell further comprises an air disperser positioned between the air access hole and the cathode structure, the air disperser includes an absorbent material.
29. 29. A method for reducing electrolyte leaks from a metal-air electrochemical cell, characterized in that it comprises: assembling or assembling an anode and a cathode to form a cell, the anode includes an anode and an anode gel, the cathode includes a can of the cathode having at least one air access hole and containing a cathode structure and the cell includes a separator that electronically separates the anode and the cathode, positioned between the anode gel and the cathode structure; wherein the anode is mounted to have an anode volume contained between an inner surface of the anode can and the separator, the anode volume contains an anode gel and an empty volume, the void volume, after discharge, is between about 7.5 percent and about 15 percent of the anode volume. J ff V METAL-AIR ELECTROCHEMICAL CELL WITH REDUCED LEAKS SUMMARY OF THE INVENTION The invention is concerned with a metal-air electrochemical cell that exhibits good discharge performance under conditions of high humidity, relatively high temperature. The cell has improved discharge performance at a temperature between about 25 ° C and about 38 ° C and a relative humidity external to the cell of between about 45 and about 95 percent. Cell leaks can also be reduced. 10