WO2023055273A1

WO2023055273A1 - A metal hydride battery with means for introducing a gas into the battery

Info

Publication number: WO2023055273A1
Application number: PCT/SE2022/050858
Authority: WO
Inventors: Joacim ALTBERG; Christer FYHR; Simon ÅBERG; Thomas Stenvall
Original assignee: Nilar International Ab
Priority date: 2021-09-28
Filing date: 2022-09-27
Publication date: 2023-04-06

Abstract

A starved electrolyte battery (1) having a housing (2) containing at least one cell wherein the cell comprises a first and a second electrode, and a porous separator (7) and an aqueous alkaline electrolyte arranged between the first and the second electrode, wherein the separator and the first and the second electrodes are configured to allow exchange of hydrogen and oxygen by allowing gas to migrate to a gas space between the two electrodes. The housing (2) comprises an outer casing (11) which has a first opening (12) which communicates with said gas space and which first opening (12) houses a pressure sensor (13) for detecting the gas pressure in said gas space, and a second opening (14), which houses a valve device (15) for connection to an external gas source, and there is provided a first channel (16) via which the second opening (14) communicates with the first opening (12) and with the gas space, and said first channel (16) is integrated in the outer casing (11).

Description

A METAL HYDRIDE BATTERY WITH MEANS FOR INTRODUCING A GAS INTO THE BATTERY

Technical field of the Invention

The present invention relates generally to the field of starved electrolyte metal hydride batteries. The device comprises a metal hydride battery where hydrogen or oxygen gas or hydrogen peroxide is added to improve performance. Further, the present invention relates specifically to the field of increasing the life time of the battery.

Background

NiMH batteries are known which comprise a battery having a housing containing plurality of battery cells wherein each battery cell comprises a first and a second electrode, and a porous separator and an aqueous alkaline electrolyte arranged between the first and the second electrode, wherein the separator and the first and the second electrodes are configured to allow exchange of hydrogen and oxygen by allowing gas to migrate to a gas space between the two electrodes, whereby the gas spaces of the individual battery cells are in communication with each other and thereby form a common gas space in the battery.

The present applicant has discovered that adding oxygen gas, hydrogen gas or hydrogen peroxide provides a suitable overcharge and discharge reserve and replenishes the electrolyte, which prolongs the life time of the battery and increases the number of possible cycles. Without being bound by any theory this may be due to that the addition of gas restores the electrode balance resulting in that the internal gas pressure decreases since the gas recombination is improved. Thus the battery becomes less sensitive to unintentional overcharging and over discharging. The pressure in the common gas space reflects the condition of the battery, and may therefore be used as an indicator of when addition of oxygen gas, hydrogen gas or hydrogen peroxide is to be performed.

In order to enable such adding of gas to the battery, batteries may be provided with means for adding a gas or a liquid to the housing. Such means may comprise a valve device to which an exterior gas source may be connected. There may also be provided a sensor by means of which the pressure in the common gas space in the battery is measured. On basis of such measurement it may be decided at what point of time that gas should be added to the battery via the valve device.

Object of the Invention

SUBSTITUTE SHEET (Rule 26) It is an object of the present invention to present a battery design which enables efficient and reliable control of the timing and performing of filling of the battery with gas with regard taken to the existing pressure in the common gas space in the battery.

Summary

The object of the invention is achieved by means of a starved electrolyte battery having a housing containing at least one cell wherein the cell comprises a first and a second electrode, and a porous separator and an aqueous alkaline electrolyte arranged between the first and the second electrode, wherein the separator and the first and the second electrodes are configured to allow exchange of hydrogen and oxygen by allowing gas to migrate to a gas space between the two electrodes, wherein

-the housing comprises an outer casing which has a first opening which communicates with said gas space and which first opening houses a pressure sensor for detecting the gas pressure in said gas space,

-and a second opening, which houses a valve device for connection to an external gas source, and wherein there is provided a first channel via which the second opening communicates with the first opening and with the gas space, and wherein said first channel is integrated in the outer casing.

The valve device preferably comprises a nipple screwed into the second opening and provided with means for quick coupling to a corresponding coupling which in its turn is connected to a gas source. The valve device may comprise a safety valve or a regulator for the purpose of allowing gas to exit the battery via the valve device, typically as a response to an excessive pressure being built up in the gas space. The outer casing is preferably made of a polymer. Thanks to the first channel being integrated in the outer casing, and thus being confined by the material of the outer casing, the number of components defining the channel is kept at a minimum, which contributes to safety and reliability.

According to one embodiment, each of said first and second electrodes of each cell defines a plate and the casing comprises a plate which is generally parallel with the first and second electrodes of each cell. According to one embodiment, the battery has an orthogonal shape, having a rear side, an opposite front side and four lateral sides connecting the front side with the rear side, and the outer casing forms a plate on a front side of the battery, wherein the first and second openings are both arranged in said front side and accessible from outside the battery. Thereby, accessibility to the pressure sensor and to the valve device is provided for without any need of opening the battery or dismounting the outer casing.

SUBSTITUTE SHEET (Rule 26) According to one embodiment, the battery comprises a plurality of cells and wherein said gas space of each cell is in communication with the gas spaces of the other cells, thereby defining a common gas space.

According to one embodiment, the common gas space is defined by a second channel extending from said first opening and through each cell.

According to one embodiment, the first opening is in alignment with the second channel.

According to one embodiment, the first opening is a through hole through the outer casing.

According to one embodiment, the outer casing forms a rectangular end plate of the housing, and the first opening is located adjacent a corner of said rectangular end plate.

According to one embodiment, the second opening is located closer to a center of the rectangular end plate than is the first opening. Thereby accessibility to the valve device is improved.

According to one embodiment of the present invention, the battery comprises nickel hydroxide electrode (Ni(OH)2/NiOOH).

According to one embodiment, the first electrode is a metal hydride electrode (MH) and the second electrode is a nickel hydroxide electrode (Ni(OH)2/NiOOH), or wherein the first electrode is a cadmium electrode (Cd) and the second electrode is a nickel hydroxide electrode (Ni(OH)2/NiOOH), or wherein the first electrode is a zinc electrode (Zn) and the second electrode is a nickel hydroxide electrode (Ni(OH)₂/NiOOH).

The object of the invention is also achieved by means of a method of conditioning a battery according to the invention, wherein the battery has a housing containing at least one cell and wherein the cell comprises the first and the second electrode and an aqueous alkaline electrolyte arranged between the first and the second electrode, wherein the first electrode is a metal hydride electrode (MH) and the second electrode is a nickel hydroxide electrode (Ni(OH)2/NiOOH), wherein the method comprises the steps of:

-detecting a pressure the gas space of the at least one battery cell by means of the pressure sensor, and, as a response to a predetermined pressure being detected,

-adding oxygen gas or hydrogen gas or hydrogen peroxide or a combination thereof to the battery through the valve device.

Brief description of the drawing

Fig. 1 is a schematic figure of a metal hydride battery, in a perspective view,

SUBSTITUTE SHEET (Rule 26) Fig. 2 is an end view of the battery shown in fig. 1,

Fig. 3 is a cross-section according to A-A in fig. 2,

Fig. 4 is a cross section of a battery module of the battery in figs. 1-3,

Fig. 5 is an exploded view of an outer casing of the battery shown in figs. 1-4,

Fig. 6 is an end view of the outer casing shown in fig. 5, and

Fig. 7 is cross-section according to A-A in fig. 6.

Detailed description of preferred embodiments of the invention

Figs. 1-4 show a starved electrolyte battery 1 having a housing 2 containing a plurality of modules 7, each of which comprises a plurality of battery cells 3 (see fig. 4). Each battery cell 3 comprises a first and a second electrode 4, 5, and a porous separator 6 and an aqueous alkaline electrolyte arranged between the first and the second electrode 4, 5. The separator 6 and the first and the second electrodes 4, 5 are configured to allow exchange of hydrogen and oxygen by allowing gas to migrate to a gas space 8 between the two electrodes 4, 5. The individual gas spaces 8 of the respective electrodes 4, 5, or cells, and of the modules communicate with each other, such that they together define a common gas space 10.

The battery comprises nickel hydroxide electrodes (Ni(OH)2/NiOOH). According to alternative embodiments, the first electrode 4 is a metal hydride electrode (MH) and the second electrode 5 is a nickel hydroxide electrode (Ni(OH)2/NiOOH), or the first electrode 4 is a cadmium electrode (Cd) and the second electrode 5 is a nickel hydroxide electrode (Ni(OH)2/NiOOH), or the first electrode 4 is a zinc electrode (Zn) and the second electrode 5 is a nickel hydroxide electrode (Ni(OH)2/NiOOH).

The porous separator 6 may be made of any suitable material. For example, the separator 6 may be made of a plastic material such as a polyolefin (polyethylene, polypropylene for example) or a polyamide or a natural polymer such as cotton, nylon or polyesters such as poly(ethylene terephthalate) or polytetrafluorethylene or polyvinyl chloride, or a combination thereof. The polymeric separator 6 may be a non-woven material. The pores may have a size of lO-lOOOnm such as 20-500nm, such as 30 to lOOnm.

The electrolyte is an aqueous alkaline electrolyte which may comprise, besides water, alkali or alkali earth metal hydroxides. In one embodiment the electrolyte comprises potassium hydroxide. In another embodiment the electrolyte comprises lithium hydroxide. In yet another embodiment the electrolyte

SUBSTITUTE SHEET (Rule 26) comprises sodium hydroxide. In one embodiment the electrolyte comprises lithium, sodium and/or potassium hydroxide (LiOH, NaOH, KOH).

The housing 2 comprises an outer casing 11 which has a first opening 12 which communicates with said common gas space 10 and which first opening 12 houses a pressure sensor 13 for detecting the gas pressure in said gas common space 10. The outer casing 12 is shown in isolation in figs. 4-6.

The outer casing 11 further comprises a second opening 14, which houses a valve device 15 for connection to an external gas source (not shown). There is provided a first channel 16 via which the second opening 14 communicates with the first opening 12 and with the common gas space 10. The first channel 16 is integrated in the outer casing 11. The battery has an orthogonal shape, having a rear side, an opposite front side and four lateral sides connecting the front side with the rear side, and the outer casing 11 forms a plate on a front side of the battery, wherein the first and second openings 12, 14 are both arranged in said front side and accessible from outside the battery.

The common gas space 10 is defined by a second channel extending from said first opening 12 and through each cell 3. On the rear side of the housing 2 there is provided a third opening 17, which communicates with the common gas space 10 and which houses a relief valve 22, in this case defined by a ratchet disc.

The exploded view in fig. 4 also shows some further components belonging to the battery and arranged at the outer casing 11, namely a connecting device 18 aimed for connecting the pressure sensor 13 to a control unit (not shown) or the like, a pressure sensor screw 19 for the attachment of sensor 13 in the first opening 12, pressure sensor sealing 20, and a plug 21 for plugging an end opening of the first channel 16.

In the embodiment shown, the first opening is in alignment with the second channel. The first opening 12 is a through hole through the outer casing 11.

The outer casing 11 forms a rectangular end plate of the housing 2, and the first opening 12 is located adjacent a corner of said rectangular end plate defined by the outer casing 11.

The second opening 14 is located closer to a center of the rectangular end plate than is the first opening 12.

A method of conditioning a battery according to the invention comprises the steps of detecting a pressure in the common gas space 10 by means of the pressure sensor 13, and, as a response to a predetermined pressure being detected, adding oxygen gas or hydrogen gas or hydrogen peroxide or a combination thereof to the common space 10 of the battery 1 through the valve device 15. Apart from

SUBSTITUTE SHEET (Rule 26) functioning as a valve through which gas is added to the common gas space 10, the valve device 15 is also a relief valve which will allow gas to be evacuated from the common gas space 10 at a predetermined pressure in the gas common gas space 10.

The present invention aims at providing a battery that rebalances, replenishes and counteracts the detrimental effect of corrosion and this be accomplished by adding oxygen, hydrogen or hydrogen peroxide to the cell. The oxygen, hydrogen or hydrogen peroxide may be added separately or consecutively. The starved electrolyte design means that only a minimal amount of electrolyte is available in the battery. Any loss of electrolyte will impair performance mainly manifested in an increased internal resistance. Electrolyte dry-out is the main cause for limiting the cycle life. The electrolyte dry-out is mainly caused by either excessive internal cell pressure, which may open the valve device 15 or the relief valve 22, thereby releasing either oxygen or hydrogen gas dependent upon abusive overcharge or overdischarge. Electrolyte dry-out is also a result of absorption of electrolyte into the nickel hydroxide structure or by corrosion of the metal hydride alloy. The latter is especially detrimental as the corrosion produces hydrogen, which offsets the capacity balance between the nickel- and the metal hydride electrodes. This results in an increased overdischarge reserve, but also a reduced overcharge capacity leading to an excessive internal gas pressure buildup. This increases the risk of venting the battery cells and accelerating the dry-out. The effect is aggravated by the shift of the metal hydride working point to higher equilibrium hydrogen pressures. This increases the hydrogen partial pressure, which in turn reduces the efficiency of the oxygen recombination reaction. Adding oxygen gas to the cell will prohibit this development in two ways

1) Oxygen will restore the balance between the electrodes by oxidizing the hydrogen produced in the corrosion described above into water. This will result in a reduced pressure build up during overcharge, (figure 3)

2) The water produced in (1) will replenish the amount of electrolyte and reduce internal resistance, (figure 4)

Adding water only to the battery cells will reduce the internal resistance but not the pressure build-up as the electrode imbalance remains. Adding peroxide H2O2 would on the other hand replenish the electrolyte as well as reestablishing the electrode balance. Adding consecutively hydrogen gas and oxygen gas can add a controlled volume of water to the electrolyte as well as it is a method to control the balance between electrodes. The latter can thus be another way to adjust the electrode balance without using a cobalt addition to the nickel electrode as described above.

SUBSTITUTE SHEET (Rule 26)

Claims

7 Claims

1. A starved electrolyte battery (1) having a housing (2) containing at least one cell (3) wherein the cell (3) comprises a first and a second electrode (4, 5), and a porous separator (6) and an aqueous alkaline electrolyte arranged between the first and the second electrode 4, 5), wherein the separator and the first and the second electrodes (4, 5) are configured to allow exchange of hydrogen and oxygen by allowing gas to migrate to a gas space (8) between the two electrodes (4, 5), wherein:

-the housing (2) comprises an outer casing (11) which has a first opening (12) which communicates with said gas space (8) and which first opening (12) houses a pressure sensor (13) for detecting the gas pressure in said gas space (8),

-and a second opening (14), which houses a valve device (15) for connection to an external gas source, and wherein there is provided a first channel (16) via which the second opening (14) communicates with the first opening (12) and with the gas space (8), and wherein said first channel (16) is integrated in the outer casing (11).

2. The battery according to claim 1, wherein the outer casing (11) defines a plate and wherein the first channel (16) has a longitudinal axis which is parallel with an extension plane of said plate.

3. The battery according to claim 1 or 2, wherein each of said first and second electrodes (4, 5) of each cell (3) defines a plate and wherein the casing (11) comprises a plate which is generally parallel with the first and second electrodes (4, 5) of each cell (3).

4. The battery according to any one of claims 1-3, wherein the battery comprises a plurality of cells (3) and wherein said gas space of each cell (3) is in communication with the gas spaces of the other cells, thereby defining a common gas space (10).

5. The battery according to claim 4, wherein the common gas space (10) is defined by a second channel extending from said first opening (12) and through each cell (3).

6. The battery according to claim 5, wherein the first opening (12) is in alignment with the second channel.

7. The battery according to any one of claims 1-6, wherein the first opening (12) is a through hole through the outer casing (11).

8. The battery according to any one of claims 1-7, wherein the outer casing (11) forms a rectangular end plate of the housing (2), and wherein the first opening (12) is located adjacent a corner of said rectangular end plate.

SUBSTITUTE SHEET (Rule 26) 8

9. The battery according to claim 8, wherein the second opening (14) is located closer to a center of the rectangular end plate than is the first opening (12).

10. The battery according to any one of claims 1-8 wherein the first electrode (4) is a metal hydride electrode (MH) and the second electrode (5) is a nickel hydroxide electrode (Ni(OH)2/NiOOH), or wherein the first electrode (4) is a cadmium electrode (Cd) and the second electrode (5) is a nickel hydroxide electrode (Ni(OH)2/NiOOH), or wherein the first electrode (4)is a zinc electrode (Zn) and the second electrode (5) is a nickel hydroxide electrode (Ni(OH)2/NiOOH).

11. A method of conditioning a battery according to any one of claims 1-10, wherein the battery has a housing (2) containing at least one cell (3) wherein the cell (3) comprises the first and the second electrode (4, 5) and an aqueous alkaline electrolyte arranged between the first and the second electrode (4, 5), wherein the first electrode (4) is a metal hydride electrode (MH) and the second electrode (5) is a nickel hydroxide electrode (Ni(OH)2/NiOOH), and wherein the method comprises the steps of:

-detecting a pressure in the gas space (8) of the at least one battery cell (3) by means of the pressure sensor (13), and, as a response to a predetermined pressure being detected,

-adding oxygen gas or hydrogen gas or hydrogen peroxide or a combination thereof to the battery through the valve device (15).

SUBSTITUTE SHEET (Rule 26)