AU2016343239B2

AU2016343239B2 - A metal hydride battery with added hydrogen gas, oxygen gas or hydrogen peroxide

Info

Publication number: AU2016343239B2
Application number: AU2016343239A
Authority: AU
Inventors: Dag NORÉUS
Original assignee: Nilar International AB
Current assignee: Nilar International AB
Priority date: 2015-10-21
Filing date: 2016-10-19
Publication date: 2022-07-28
Anticipated expiration: 2036-10-19
Also published as: JP6903649B2; CN108370021A; KR102406764B1; KR102270417B1; JP2021153068A; EP3365932A1; KR20210077802A; AU2022256203A1; EP3365932B1; WO2017069691A1; US20190058225A1; CN108370021B; US11196093B2; AU2016343239A1; BR112018007971B1; US10637104B2; SE1551360A1; JP7315624B2; EP4120426A1; SE540479C2

Abstract

The invention relates to a starved metal hydride battery. The battery is

Description

A METAL HYDRIDE BATTERY WITH ADDED HYDROGEN OR OXYGEN GAS

Technical field of the Invention

The present invention relates generally to the field of

starved 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 of the Invention

Nickel metal hydride (NiMH) batteries have long cycle life and

have rapid charge and discharge capabilities. During charge and

discharge the electrodes interact with each other through the

alkaline electrolyte as hydrogen is transported in the form of

water molecules between the electrodes. During discharge hydrogen

is released from the negative electrode and is allowed to migrate

to the positive electrode (nickel electrode) where it

intercalates. This binding results in energy being released.

During charging the hydrogen migration is reversed, see Figure 1.

Especially NiMH batteries are designed to be nickel electrode

limited with a starved electrolyte. This is done in order to be

able to avoid overcharge and overdischarge states of the battery

cells by controlling the cell chemistry and state-of-charge via

the gas phase.

When the cell is charged, hydrogen is transported from

the nickel hydroxide to the metal hydride by water molecules in

the aqueous alkaline electrolyte. During discharge hydrogen is

transported back to the nickel hydroxide electrode, again in the

form of water molecules. If the cell is charged beyond the capacity of the nickel

electrode, hydrogen will still be transported and intercalated

into the metal hydride electrode by water molecules, but in this

case hydrogen will be taken from the aqueous electrolyte resulting

in a production of oxygen gas. The overcharging reaction is thus (EG denoted: 40H- = 2H 2 0 + 02 + 4e- = +0.401V). A cell with a

starved electrolyte means in contrast to a flooded cell, that the

amount of electrolyte is so limited that open spaces and channels

188186071 (GHMattes) P44066AU00 exists between the electrodes through the separator. These open channels can now transport the oxygen to the metal hydride electrodes, where it can be recombined to form water. This recombination reaction is denoted: 2MH + 02 = 2H 20 + 2M. The metal hydride electrode has thus a certain overcharge capacity reserve in relation to the nickel electrode. If the cell on the other hand is overdischarged, hydrogen will be transported to the nickel electrode. But as the capacity of the nickel electrode is below that of the metal hydride electrode, hydrogen will be released as hydrogen gas molecules instead of being intercalated into the nickel hydroxide. These hydrogen gas molecules can also migrate through the open channels to the metal hydride electrode and be recombined into water. A certain overdischarge capacity of the metal hydride electrode is usually created by adding cobalt to the nickel electrode, which results in a controlled pre-charging of the metal hydride electrode during the formation of the battery cells. A proper balance of the nickel electrode capacity with respect to the metal hydride electrode capacity with suitable amounts of both overcharge- and overdischarge reserves are essential for a well-functioning battery, enabling it to reach a stable long time charge/discharge performance, Figure 2. This essential balancing of the two electrodes' capacity with respect to each other is unfortunately impaired by several mechanisms as the battery cells age.

Object of the Invention The primary object of the present invention aims at obviating the afore-mentioned disadvantages and failings of previously known prior art, and at providing an improved battery. But it can also be used to control the balancing of the electrodes without the use of cobalt addition, thus reducing material cost. A first aspect of the present invention is to provide an improved battery of the initially defined type claim 1. A second aspect of the present invention is to provide a battery which comprises cobalt hydroxide. In such a battery the precharge created by the cobalt hydroxide in the nickel electrode can be adjusted. In third aspect the present invention relates to a

18818607_1 (GHMatters) P44066AU00 method of preparing the battery according to the present invention. In a fourth aspect the present invention relates to a method of counteracting the negative effects of corrosion in a metal hydride battery. In a fifth aspect the present invention relates to a method of replenishing an alkaline electrolyte in a metal hydride battery. In a sixth aspect the present invention relates to a method of rebalancing the electrodes in a metal hydride battery.

Summary of the Invention

According to the invention at least the primary aspect is

attained by means of the initially defined battery and method of

preparing the battery having the features defined in the

independent claims. Preferred embodiments of the present invention are further defined in the dependent claims.

According to a first aspect of the present invention, there is

provided a starved battery of the initially defined type, which is

characterized in that the housing of the battery contains added

oxygen gas, hydrogen gas or hydrogen peroxide.

The battery has a housing containing at least one cell wherein

said at least one cell comprises a first electrode, a second

electrode, a porous separator arranged between the first electrode

and the second electrode, and an aqueous alkaline electrolyte

arranged between the first electrode and the second electrode.

When it is stated that the aqueous alkaline electrolyte is arranged between the first electrode and the second electrode, it

is meant that the electrolyte is in contact with the first and

second electrodes. The separator, the first electrode and the

second electrode are configured to allow exchange of hydrogen and

oxygen by allowing gas to migrate between the two electrodes. The

housing further comprises means for adding a gas or a liquid to

the housing. The battery further comprises added oxygen gas or

hydrogen gas or hydrogen peroxide or a combination thereof in

order to rebalance the electrodes and replenish the electrolyte by

reactions with the electrode materials. According to a second aspect of the present invention, there

is provided a starved battery according to claim 17.

18818607_1 (GHMatters) P44066AU00

Such a starved battery has a housing containing at least one

cell wherein the said at least one cell comprises a first

electrode, a second electrode, and an aqueous alkaline electrolyte

arranged between the first electrode and the second electrode. The

first electrode is a metal hydride electrode (MH) and the second

electrode is a nickel hydroxide electrode (Ni(OH) 2 /NiOOH) further

comprising cobalt hydroxide (Co(OH) 2 /CoOOH). The housing further

comprises means for adding a gas or a liquid to the housing, and

the battery further comprises added hydrogen peroxide.

Thus, the present invention is based on the insight of 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 or the

addition of oxygen in the peroxide 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.

Further features applicable to the battery according to the first and/or second aspects are outlined below.

In a preferred embodiment of the present invention, the

battery comprises nickel hydroxide electrode (Ni(OH) 2 /NiOOH).

For example, the first electrode may be a metal hydride

electrode (MH) and the second electrode may be a nickel hydroxide electrode (Ni(OH) 2 /NiOOH). The first electrode may be a cadmium

electrode (Cd) and the second electrode may be a nickel hydroxide

electrode (Ni(OH) 2 /NiOOH). The first electrode may be a zinc

electrode (Zn) and the second electrode may be a nickel hydroxide

electrode (Ni(OH) 2 /NiOOH).

The battery may comprise one or more cells, such as two or

more cells, and may further comprise a common gas space for all of

the two or more cells.

The amount of added oxygen or hydrogen may be up to 2 moles

per mole of active metal hydroxide, such as Ni(OH) 2 /Ni(OOH),

content in the battery.

The hydrogen peroxide addition may be up to 2 moles per mole

of active metal hydride content in the battery.

18818607_1 (GHMatters) P44066AU00

The first electrode may be a metal hydride electrode (MH) and the second electrode may be a nickel hydroxide electrode

(Ni(OH) 2 /NiOOH) further comprising cobalt hydroxide

(Co(OH)2 /CoOOH). The second electrode may optionally further

comprise zinc hydroxide (Zn(OH)2 ). The first electrode may be a metal hydride electrode (MH) and

the second electrode may be a nickel hydroxide electrode

(Ni(OH) 2 /NiOOH) further comprising zinc hydroxide (Zn (OH) 2 ). The

second electrode may optionally further comprise cobalt hydroxide

(Co(OH) 2 /CoOOH).

The aqueous alkaline electrolyte may comprise a mixture of

lithium-, sodium- and potassium hydroxide (LiOH, NaOH, KOH).

The first or the second electrode may further comprise one or

more of Cerium (Ce), Lanthanum (La), Praseodymium (Pr), Manganese (Mn), Niobium (Nb), Cobalt (Co), Nickel (Ni), Magnesium (Mg),

Neodymium (Nd), Titanium (Ti), Zirconium (Zr) Vanadium (V),

Chromium (Cr), Tin (Sn), Yttrium (Y) or Aluminium (Al), such as

one or more of Cerium (Ce), Lanthanum (La), Praseodymium (Pr),

Manganese (Mn), Niobium (Nb),Nickel (Ni), Magnesium (Mg),

Neodymium (Nd), Titanium (Ti), Zirconium (Zr) Vanadium (V),

Chromium (Cr), Tin (Sn), or Aluminium (Al). Preferably the first

electrode may comprise one of more of these elements.

The added hydrogen gas, oxygen gas or hydrogen peroxide may be

added separately, or consecutively, or in a mixture of hydrogen

gas and oxygen gas, or oxygen gas and hydrogen peroxide, or

hydrogen gas and hydrogen peroxide.

The porous separator may be made of a polyamide or a

polyolefin such as polypropylene.

The second electrode may be a nickel hydroxide electrode

(Ni(OH) 2 /NiOOH). This nickel hydroxide electrode (Ni(OH) 2 /NiOOH)

may optionally further comprise cobalt hydroxide (Co(OH) 2 /CoOOH)

and/or zinc hydroxide (Zn(OH)2 .

The housing may comprise a means for reducing the pressure in

the housing. The means for adding a gas or a liquid to the housing

and the means for reducing the pressure in the housing may be the

same. The housing may comprise a safety vent arranged to limit the

maximum internal pressure prevailing in the housing.

18818607_1 (GHMatters) P44066AU00

The housing may comprise a single housing, or the housing may comprises two or more sub-housings, wherein each sub-housing is in

gaseous communication with at least one other sub-housing by means

of a gas conduit.

According to another aspect of the present invention, there

is provided a method of preparing the battery described above, as

disclosed in the appended claims. The method of preparing the

battery comprising the steps:

a. providing a housing, a first electrode, a second electrode, and

an aqueous alkaline electrolyte, wherein the housing comprises a means for reducing the pressure in the housing and means for

adding a gas or a liquid to the housing;

b. arranging the first electrode and the second electrode and the

alkaline electrolyte in the housing in order to prepare a starved battery;

c. evacuating the housing using said means for reducing the

pressure in the housing in order to create a reduced pressure; and

d. adding oxygen gas, hydrogen gas or hydrogen peroxide to the

housing using said means for adding a gas or a liquid to the

housing. The steps c and d may be repeated at least once,

preferably twice.

According to a further aspect, there is provided a method of

counteracting the negative effects of corrosion of a metal hydride

electrode in a starved-electrolyte battery. The battery may have a

housing containing at least one cell wherein the said at least one cell comprises a first electrode, a 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), and wherein the housing further comprises means for adding a gas or a liquid to the housing. The

method comprises adding oxygen gas or hydrogen peroxide or a

combination thereof to the battery when the battery has reached a

state of charge of at least 50%.

According to yet another aspect, there is provided a method of replenishing an aqueous alkaline electrolyte in a battery. The

battery has a housing containing at least one cell wherein the

said at least one cell comprises a first electrode, a second

18818607_1 (GHMatters) P44066AU00 electrode, and the aqueous alkaline electrolyte arranged between the first electrode 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), and wherein the housing further comprises means for adding a gas or a liquid to the housing. The method comprises adding oxygen gas or hydrogen peroxide or a combination thereof to the battery when the battery has reached a state of charge of at least 50% in order to create water by the recombination reactions of the respective gases with the active electrode materials in the battery. The oxygen gas or hydrogen gas or hydrogen peroxide or a combination thereof may be added to the battery before the battery has reached not less than 50% of state of charge (SOC) or not less than 20% of state of charge (SOC). According to yet a further aspect, there is provided a method of re-establishing the balance between a first electrode and a second electrode in a battery. The battery has a housing containing at least one cell wherein the said at least one cell comprises the first electrode, the second electrode, and an aqueous alkaline electrolyte arranged between the first electrode 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), and wherein the housing further comprises means for adding a gas or a liquid to the housing. The method comprises adding oxygen gas or hydrogen peroxide or a combination thereof to the battery when the battery has reached a state of charge of at least 50%. Further advantages with and features of the invention will be apparent from the other dependent claims as well as from the following detailed description of preferred embodiments. In some embodiments, there is provided a method of preparing a starved electrolyte metal hydride battery having a housing containing at least one cell wherein said at least one cell comprises a first electrode, a second electrode, a porous separator arranged between the first electrode and the second electrode, and an aqueous alkaline electrolyte arranged between the first electrode and the second electrode, wherein the separator, the first electrode and the second electrode are

18818607_1 (GHMatters) P44066AU00 configured to allow exchange of hydrogen and oxygen by allowing gas to migrate between the two electrodes, and wherein the housing further comprises means for adding a gas or a liquid to the housing; wherein the battery further comprises added oxygen gas or hydrogen peroxide or a combination thereof in order to rebalance the electrodes and replenish the electrolyte by reactions with the electrode materials. The method of preparing the battery may comprise the steps: a. providing a housing, a first electrode, a second electrode, and an aqueous alkaline electrolyte, wherein the housing comprises a means for reducing the pressure in the housing and means for adding a gas or a liquid to the housing; b. arranging the first electrode and the second electrode and the alkaline electrolyte in the housing in order to prepare a starved battery; c. evacuating the housing using said means for reducing the pressure in the housing in order to create a reduced pressure; and d. adding oxygen gas, or hydrogen peroxide or a combination thereof to the housing using said means for adding a gas or a liquid to the housing, wherein the oxygen gas or hydrogen peroxide is added to the battery when the battery has reached a state of charge of at least 50 %.

All the embodiments of the present application are applicable

to all of the aspects of the present invention.

Brief description of the drawings

A more complete understanding of the abovementioned and other

features and advantages of the present invention will be apparent

from the following detailed description of preferred embodiments in conjunction with the appended drawings, wherein:

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

Fig. 2 is a graph disclosing how the electrode capacities are

related to the hydrogen equilibrium pressure of the metal hydride used in the negative electrode,

Fig. 3 is a graph disclosing maximum pressure at every cycle,

Fig. 4 is a graph disclosing the resistance at every 50 cycles.

18818607_1 (GHMatters) P44066AU00

Detailed description of preferred embodiments of the invention

The invention is not limited only to the embodiments

described above and shown in the drawings, which primarily have an

illustrative and exemplifying purpose. This patent application is

intended to cover all adjustments and variants of the preferred

embodiments described herein, thus the present invention is

defined by the wording of the appended claims and the equivalents

thereof. Thus, the equipment may be modified in all kinds of ways

within the scope of the appended claims.

It shall also be pointed out that all information

about/concerning terms such as above, under, upper, lower, etc., shall be interpreted/read having the equipment oriented according

to the figures, having the drawings oriented such that the

references can be properly read. Thus, such terms only indicates mutual relations in the shown embodiments, which relations may be

changed if the inventive equipment is provided with another

structure/design.

It shall also be pointed out that even thus it is not

explicitly stated that features from a specific embodiment may be

combined with features from another embodiment, the combination

shall be considered obvious, if the combination is possible.

Throughout this specification and the claims which follows,

unless the context requires otherwise, the word "comprise", and

variations such as "comprises" or "comprising", will be understood

to imply the inclusion of a stated integer or steps or group of integers or steps but not the exclusion of any other integer or

step or group of integers or steps.

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

and/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 safety valve

18818607_1 (GHMatters) P44066AU00 releasing either oxygen or hydrogen gas dependent upon abusive overcharge or overdischarge, Figures 1 to 4. 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 H 2 0 2 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.

A battery according to the present invention is starved

having a housing containing at least one cell. Each cell comprises at least two electrodes, a first and a second electrode, and a

porous separator. An aqueous alkaline electrolyte and a porous

separator are arranged between the first and the second electrode.

18818607_1 (GHMatters) P44066AU00

The starved configuration allows exchange of hydrogen and oxygen

via the electrolyte and the separator allowing gas to migrate

between the two electrodes. The housing further comprises means

for adding a gas or a liquid to the housing and the battery

further comprises added oxygen gas or hydrogen gas or hydrogen

peroxide or a combination thereof. These are added in order to

rebalance the electrodes and replenish the electrolyte by

reactions with the electrode materials. The addition of oxygen,

hydrogen or hydrogen peroxide may also avoid or minimize the

negative effects of corrosion. The oxygen or hydrogen or hydrogen

peroxide addition in the battery can be made at any state of

charge (SOC). But preferably hydrogen is added at a low SOC and

oxygen and hydrogen peroxide at a high SOC to facilitate their

uptake and consecutively their transformation into water, which is replenishing the electrolyte.

A battery according to the present invention is starved

having a housing containing at least one cell. The housing may

consist of a single discrete structure housing all of the cells of

the battery, or may comprise several sub-housings, each subhousing

housing a fraction of the total number of the cells of the battery. The battery may be of any construction, including those

known in the art, such as cylindrical, prismatic or bi-polar.

Each cell comprises at least two electrodes, a first and a

second electrode, and a porous separator. An aqueous alkaline

electrolyte and a porous separator are arranged between the first and the second electrode. The first electrode is a metal hydride

electrode (MH) and the second electrode is a nickel hydroxide

electrode (Ni(OH) 2 /NiOOH) further comprising cobalt hydroxide

(Co(OH)2 /CoOOH). The housing further comprises means for adding a

gas or a liquid to the housing. The battery may comprise only one cell but the number of

cells may be two or more, or three or more, or four or more. When

the number of cells is two or more the battery may comprise a

common gas space for all or for some of the cells. If the housing

comprises several sub-housings, the common gas space may be

achieved by providing a gas conduit connecting each sub-housiing

to at least one other sub-housing. In this manner, a modular

battery assembly may be achieved.

18818607_1 (GHMatters) P44066AU00

For example, bi-polar batteries having a common gas space are

disclosed in document WO 03/026042 "A bipolar battery and biplate assembly".

Each cell comprises at least two electrodes but it may

comprise four or more, or six or more electrodes. The electrodes

are metal hydrides (MH) or metal hydroxide (MOH). The first

electrode is a metal or metal alloy and may be a metal hydride

electrode (MH). The second electrode may be a nickel hydroxide

electrode (Ni(OH) 2 /Ni(OOH). In one embodiment the first electrode

is a cadmium electrode (Cd) and the second electrode is a nickel

hydroxide electrode (Ni(OH) 2 /NiOOH). In another embodiment the

first electrode is a zinc electrode (Zn) and the second electrode

is a nickel hydroxide electrode (Ni(OH 2 /NiOOH). In one embodiment

the first or the second electrodes comprises one or more of Cerium (Ce), Lanthanum (La), Praseodymium (Pr), Neodynium (Nd), Titanium

(Ti), Zirconium (Zr), Vanadium (V), Chromium (Cr), Tin (Sn),

Manganese (Mn), Niobium (Nb), Cobalt (Co), Nickel (Ni), Magnesium

(Mg), Yttrium (Y) or Aluminium (Al). Preferably the first

electrode contains one or more of these elements. For example, the

first electrode may be of a hydrogen storage alloy known for use in NiMH batteries, such as ABs alloys or A2 alloys. In one

embodiment the second electrode further comprises cobolt or cobolt

hydroxide (Co(OH)2 /CoOOH). The amount of cobolt or cobolt

hydroxide may be 0 to 15 mol% such as 1 to 10 mol% or 2 to 5 mol%

of the content of the electrode. In one embodiment the second electrode further comprises zinc or zinc hydroxide

(Zn(OH) 2 /CoOOH). The amount of zinc or zinc hydroxide may be 0 to

10 mol%, such as 2 to 5 mol% of the content of the electrode. The

second electrode may further comprise both cobalt hydroxide and

zinc hydoxide in the proportions given above. However, the second

electrode may also be essentially cobalt-free or cobalt-free.

The porous separator may be made of any suitable material for

example the separator 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

18818607_1 (GHMatters) P44066AU00 separator may be a non-woven material. The pores may have a size of 10-1000nm such as 20-500nm, such as 30 to 100nm.

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 comprises sodium

hydroxide. In one embodiment the electrolyte comprises lithium,

sodium and/or potassium hydroxide (LiOH, NaOH, KOH).

The means for adding gas (or removing gas, evacuating the

housing) or liquid may be any suitable means such as a regulator,

valve or check valve.

In order to overcome the drawbacks of the prior art the

battery according to the present invention comprises adding of oxygen gas, hydrogen gas or hydrogen peroxide. In one embodiment

the added hydrogen gas, oxygen gas or hydrogen peroxide is in a

mixture of hydrogen gas and oxygen gas, or oxygen gas and hydrogen

peroxide, or hydrogen gas and hydrogen peroxide. The addition may

repeated one or more times. The amounts mentioned below refer to

amounts added each time or the total added amount during the whole

life cycle of the battery. The amount of added oxygen or hydrogen

is up to 2 moles per mole of active metal hydroxide, such as

Ni(OH) 2 /NiOOH, content in the battery, preferably not less than

0.001 moles per mole active metal hydroxide. The amount of added

oxygen or hydrogen may be up to 1.5 moles per mole active metal hydride, or up to 3 moles. When the electrode comprises cobalt

hydroxide the amount of added oxygen may be 0.1 to 2 moles per

active cobalt hydroxide, such as 0.5 to 1.5 moles per active

cobalt hydroxide. In one embodiment the amount of added oxygen or

hydrogen gas is 0.05 to 2 moles per mole active metal hydroxide, such as 1 to 1.5 moles. The amount of added hydrogen peroxide may

be 1 moles per mole active metal hydride. Hydrogen peroxide is

believed to re-establish the balance of both electrodes similar to

the addition of oxygen gas.

The battery according to the present invention may be prepared by providing a housing, at least two electrodes, a porous

separator and an aqueous alkaline electrolyte and arranging the

two electrodes in the housing together with the electrolyte and

18818607_1 (GHMatters) P44066AU00 the separator. The housing comprises means for adding or removing gas or liquid and the housing is evacuated using said means in order to create a reduced pressure. To the housing oxygen gas, hydrogen gas or hydrogen peroxide is then added using said means.

The step of evacuating the housing and adding oxygen gas, hydrogen

gas or hydrogen peroxide may be repeated in order to obtain a more

controlled environment inside the housing.

By adding oxygen gas, hydrogen gas or hydrogen peroxide to

the housing the negative effects of corrosion of the electrodes

will be reduced.

Addition of oxygen gas or hydrogen gas or hydrogen peroxide

or a combination thereof to the battery results in creation of

water by the recombination reactions of the respective gases or

liquids with the active electrode materials in the battery. The addition may be done at any state of charge (SOC). This will

replenish the electrolyte in the starved battery.

Preferably hydrogen is added at a low SOC and oxygen and

hydrogen peroxide at a high SOC to facilitate their uptake and

consecutively their transformation into water to be added to the

electrolyte. In one embodiment the addition of hydrogen gas may be done to the battery before the battery has reached not less

than 50% of state of charge (SOC) or not less than 20% of state of

charge (SOC). In one embodiment the addition of oxygen gas or

hydrogen peroxide is done to the battery when the battery has

reached a state of charge of at least 50%, or at least 75%.The

addition of oxygen gas, hydrogen gas or hydrogen peroxide may also

re-establish the balance between a first and a second electrode in

the battery. Hydrogen peroxide is believed to re-establish the

balance between the electrodes.

It is to be understood that, if any prior art publication is

referred to herein, such reference does not constitute an

admission that the publication forms a part of the common general

knowledge in the art, in Australia or any other country.

In the claims which follow and in the preceding description

of the invention, except where the context requires otherwise due

to express language or necessary implication, the word "comprise"

or variations such as "comprises" or "comprising" is used in an

18818607_1 (GHMatters) P44066AU00 inclusive sense, i.e. to specify the presence of the stated features but not to preclude the presence or addition of further features in various embodiments of the invention.

18818607_1(GHMatters) P44066AU00

Claims

Claims 1. A method of preparing a starved electrolyte metal hydride

battery having a housing containing at least one cell wherein said

at least one cell comprises a first electrode, a second electrode,

a porous separator arranged between the first electrode and the

second electrode, and an aqueous alkaline electrolyte arranged

between the first electrode and the second electrode, wherein the

separator, the first electrode and the second electrode are

configured to allow exchange of hydrogen and oxygen by allowing

gas to migrate between the two electrodes, and wherein the housing

further comprises means for adding a gas or a liquid to the

housing;

wherein the battery further comprises added oxygen gas or hydrogen

peroxide or a combination thereof in order to rebalance the electrodes and replenish the electrolyte by reactions with the

electrode materials; and wherein the method of preparing the

battery comprises the steps:

a. providing a housing, a first electrode, a second electrode, and

an aqueous alkaline electrolyte, wherein the housing comprises a means for reducing the pressure in the housing and means for

adding a gas or a liquid to the housing;

b. arranging the first electrode and the second electrode and the

alkaline electrolyte in the housing in order to prepare a starved

battery;

c. evacuating the housing using said means for reducing the

pressure in the housing in order to create a reduced pressure; and

d. adding oxygen gas, or hydrogen peroxide or a combination

thereof to the housing using said means for adding a gas or a

liquid to the housing, wherein the oxygen gas or hydrogen peroxide

is added to the battery when the battery has reached a state of charge of at least 50 %.
2. The method according to claim 1 wherein the steps c and d are

repeated at least once, preferably twice.
3. A method of counteracting the negative effects of corrosion of

a metal hydride electrode in a starved-electrolyte battery wherein

the battery has a housing containing at least one cell wherein the

18818607_1 (GHMatters) P44066AU00 said at least one cell comprises a first electrode, a 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), and wherein the housing further comprises means for adding a gas or a liquid to the housing; wherein the method comprises adding oxygen gas or hydrogen peroxide or a combination thereof to the battery when the battery has reached a state of charge of at least 50%.
4. A method of replenishing an aqueous alkaline electrolyte in a starved-electrolyte battery wherein the battery has a housing containing at least one cell wherein the said at least one cell comprises a first electrode, a second electrode, and the aqueous alkaline electrolyte arranged between the first electrode 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), and wherein the housing further comprises means for adding a gas or a liquid to the housing; wherein the method comprises adding oxygen gas or hydrogen peroxide or a combination thereof to the battery when the battery has reached a state of charge of at least 50% in order to create water by the recombination reactions of the respective gases with the active electrode materials in the battery.
5. A method of re-establishing the balance between a first electrode and a second electrode in a starved-electrolyte battery wherein the battery has a housing containing at least one cell wherein the said at least one cell comprises the first electrode, the second electrode, and an aqueous alkaline electrolyte arranged between the first electrode 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), and wherein the housing further comprises means for adding a gas or a liquid to the housing;

18818607_1 (GHMatters) P44066AU00 wherein the method comprises adding oxygen gas or hydrogen peroxide or a combination thereof to the battery when the battery has reached a state of charge of at least 50%.

18818607_1(GHMatters) P44066AU00