HK1071472B - A bipolar battery and a biplate assembly - Google Patents

Description

Bipolar battery and bipolar plate assembly

Technical Field

The present invention relates to a bipolar battery comprising a pressure relief device as defined in the preamble of claim 1. The invention also relates to a biplate assembly as defined in the preamble of claim 8.

Background

In theory, bipolar batteries can be used to increase battery energy storage capacity on a weight and volume basis, reduce packaging weight and volume, provide stable battery performance, and low internal resistance.

Bipolar battery structures comprise an electrically conductive bipolar layer, a so-called bipolar plate, which serves as an electrical interconnection between adjacent cells in the battery and as a partition between the cells. To successfully utilize a bipolar structure, the bipolar plate must be sufficiently conductive to transmit current from one cell to another, chemically stable in the cell environment, capable of making and maintaining good contact to the electrodes, capable of being electrically insulated and sealed around the boundaries of the cells to contain electrolyte in the cells.

These needs are more difficult to achieve in rechargeable batteries because the charging potential can accelerate bipolar plate corrosion; these needs are more difficult to achieve in alkaline cells due to the peristaltic nature of the electrolyte. Achieving the right combination of these characteristics has proven to be very difficult. For maintenance-free operation, it is desirable to have the rechargeable battery operate in a sealed configuration. However, sealed bipolar designs typically utilize flat electrodes and a stacked cell structure that is less effective at retaining gases present and generated during cell operation. In the sealed structure, it is necessary to chemically recombine gas generated during charging in the unit cell for stable operation. The requirement of a retention pressure presents more challenges to the design of a stable bipolar structure.

Battery manufacturers have not commercially developed bipolar batteries because it has always been a problem to implement a sealed design. Most of the development work to date has been directed entirely to lead/acid technology. Sealing is difficult to achieve due to galvanic creep of the electrolyte, corrosion conditions, and heat and pressure generated by the cell. Other manufacturers strive to achieve leak-proof seals and use rigorous methods, but eventually fail due to thermal expansion and pressure changes. In the disclosure, if the pressure exceeds a predetermined value, the pressure developed in each battery cell may be discharged through the pressure vessel.

A new need in the fields of transmission, communication, medical and power tools is a power generation requirement that cannot be met by existing batteries. These include higher cycle life and the need for rapid, efficient recharging.

It is believed that NiMH systems can be selected to meet cycle life, but the cost of conventional manufacturing is currently too high.

In recharging an ideal battery, energy is stored at 100% efficiency, and recharging is terminated when 100% conditions are reached. In most batteries, this can be determined by knowing the relationship between the battery temperature and the desired final voltage. Because the battery is not 100% efficient, 104% (for a new lead-acid battery) may be required to achieve 100% recharge. Lead acid batteries exhibit a rather rapid increase in cell voltage as they reach full charge. The power supply may be set to read the voltage and terminate the charge at that point. Alternatively, the power supply may be designed to provide a limited additional amount of charging when the set voltage is reached. Nickel-cadmium and nickel-metal hydride cells have different characteristics: when full charge is reached, the voltage begins to decrease.

The charging voltage is typically higher than the battery open circuit voltage because it must overcome the resistive losses that add to the required voltage to recharge the cells. The higher voltage amount is proportional to the recharge rate. Nickel batteries receive current at low voltage, high temperature. Problems can occur when attempting to fully recharge, or when the recharging electrode is not uniformly discharged.

The electrode portion having the lower resistance or fully charged begins to overcharge before the remainder of the cell is charged. These regions convert the charging energy into oxygen by means of electrolysis. Then, oxygen is recombined to the negative electrode generating the same amount of heat, and the temperature of the single cell increases. The temperature increase is greater in the overcharged and recombined regions, so that an increased amount of the recharge flows through the hotter regions. This also prevents the possibility of determining that the battery is fully charged based on the battery voltage when it is time to damage the cells. In US5344723 to Bronoel et al, a bipolar battery is disclosed having a common gas chamber formed by providing openings through the bipolar plate (conductive support/separator). The opening is also provided with a hydrophobic barrier to prevent electrolyte from flowing through the hole. Although the problem of the pressure difference between the single cells is solved, the disadvantages of the battery remain. The external seal around the edges of each bipolar plate still has to be fluid tight, which is very difficult to achieve. If the external seal is not fluid tight, the electrolyte contained in the separator between the electrodes may migrate from one cell to another.

A need exists for a battery: it is easy to manufacture at an affordable price, and it is safe to cope with charging and discharging processes.

Disclosure of Invention

It is an object of the present invention to provide a bipolar battery, preferably a bipolar NiMH battery, having improved sealing properties compared to prior art bipolar batteries.

This object is achieved by the bipolar battery and the bipolar plate assembly of the present invention.

According to an aspect of the present invention, there is provided a bipolar battery having at least two unit cells, comprising: sealing the container; a negative terminal plate having a negative electrode; a positive terminal plate having a positive electrode; at least one bipolar plate assembly disposed in a sandwich configuration between the negative and positive end plates, each bipolar plate assembly having a negative electrode mounted on a negative side of the bipolar plate and a positive electrode mounted on a positive side of the bipolar plate opposite the negative side, and at least one hole being provided through each bipolar plate interconnecting each cell with an adjacent cell, thereby establishing a common gas space in the cell for all cells; a separator provided between each negative electrode and each positive electrode forming each single cell, the separator including an electrolytic solution; the negative electrode and the positive electrode are arranged in such a manner that each electrode covers only the central portion of each side of the bipolar plate; and providing an outer seal around the edges of each bipolar plate assembly and each end plate to provide the sealed container; the method is characterized in that: disposing an inner barrier layer of hydrophobic material around at least one electrode adjacent a first side edge of each bipolar plate; and the at least one hole through each bipolar plate is disposed between the barrier layer and the outer seal, whereby the inner barrier layer prevents electrolyte from flowing from one cell to the other.

According to another aspect of the present invention, there is provided a bipolar plate assembly comprising a bipolar plate, a positive electrode disposed on a first side of the bipolar plate and a negative electrode disposed on a second side of the bipolar plate opposite the first side, and at least one aperture is disposed through each bipolar plate to provide gas passages through the bipolar plate, the negative and positive electrodes being disposed such that each electrode covers only a central portion of each side of the bipolar plate; the method is characterized in that: disposing an inner barrier layer of hydrophobic material around at least one electrode adjacent a first side edge of each bipolar plate; and the at least one hole through each bipolar plate is disposed between the barrier layer and the edge, whereby the inner barrier layer prevents electrolyte from flowing from one side of the bipolar plate assembly to the other.

An advantage of the present invention is that the bipolar battery is easy to manufacture compared to prior art bipolar batteries.

Another advantage is that the cost of manufacturing the bipolar battery and the bipolar plate assembly is substantially reduced while maintaining, or even improving, the operating performance of the bipolar battery.

Other objects and advantages of the present invention will become more apparent from the bipolar electrochemical cell and bipolar plate assembly described in detail below.

Drawings

The various embodiments shown in the drawings are not to scale or to scale, but are exaggerated for clarity to indicate different important features.

Figure 1 shows a plan view of a first embodiment of a bipolar assembly according to the present invention.

Fig. 2 shows a cross-sectional view along a-a of fig. 1.

Figure 3 shows a partial cross-sectional view of a bipolar plate assembly having a molded frame.

Figure 4 shows a plan view of a second embodiment of a bipolar plate assembly according to the present invention.

Fig. 5 shows a cross-sectional view along a-a of fig. 4.

Figure 6 shows a partial cross-sectional view of a second embodiment of a bipolar plate assembly having a molded frame.

Fig. 7 shows a bipolar battery according to the present invention.

Fig. 8 shows an alternative structure of the bipolar battery according to the present invention.

Detailed Description

The main advantages of bipolar cell design are simplicity and low resistive losses. The cell has a relatively small number of components and consists only of end plates and bipolar plates with appropriate components and sealing elements. By stacking a desired number of bipolar plates, a stack having a desired voltage is constructed. Since each bipolar plate is electrically conductive and impermeable to the electrolyte, electrical connection between the cells is made when the cells are stacked.

With the terminals at each end, the current flows perpendicular to the plates, which ensures a uniform current and voltage distribution. Since the current path is very short, the voltage drop is significantly reduced.

The bipolar plate also has significantly reduced weight, volume and manufacturing costs due to the elimination of components and manufacturing processes.

A major problem that has not been solved commercially before with bipolar batteries is how to obtain a reliable seal between the single cells in a bipolar battery. Another problem is how to avoid overcharging the cell and thereby generating high voltages in the cell that can lead to cell rupture. Solutions to these problems are listed below.

The sealing of the single cells is of paramount importance for all types of batteries, and bipolar batteries are no exception. Each cell contains an active material (for NiMH, the active materials are a nickel hydroxide positive electrode and a metal hydride hydrogen storage alloy negative electrode, respectively), a separator, and an electrolyte. The electrolyte is required to perform ion transport between the electrodes. The best design to optimize life, weight and volume requires recombination of gases.

When batteries are charged, they typically produce gas. As the battery approaches full charge, the rate of gas generation increases, reaching a maximum when the battery is fully charged. The gases produced are oxygen and hydrogen.

Batteries used as power supplies have thin electrodes. Long life, light weight and small volume are desirable characteristics, which require a sealing structure.

Oxygen is recombined quite rapidly, and therefore the cell is designed to: if the cell is overcharged or overdischarged, oxygen is allowed to become the first gas generated. This requires two conditions:

1) the anode active material is made to be in excess, typically 30% excess, to ensure that the oxygen producing anode produces gas first.

2) Providing a gas path from the anode to the cathode where oxygen will recombine. The gas passage is obtained by controlling the content of the electrolyte in the pores of the electrode and through the separator. All electrode surfaces must be covered by a thin layer of electrolyte for ion transport, but the layer must be thin enough to allow diffusion of the gas through the layer, and the gas must pass through the entire active layer and separator.

If overcharged, the negative electrode generates hydrogen. Since hydrogen cannot recombine rapidly, the pressure within the cell increases. The recombination of oxygen effectively causes the negative electrode to discharge at the same rate as it is charged, thereby preventing overcharge of the negative electrode.

The active material surface area combined with the uniform voltage distribution of the bipolar design enhances rapid recombination.

The bipolar approach ensures that the voltage drop across the active material is uniform over the entire area so that the entire electrode reaches a fully charged state at the same time. This will solve the main problem in the conventional structure: some electrodes overcharge and produce gas, while other (remote) regions of the electrode are not yet fully charged.

Sealing of the cells in a regular battery pack to contain the electrolyte is performed both for the unique performance of the cells and to prevent electrolyte paths from forming between adjacent cells. The presence of electrolyte paths between the cells causes the electrolyte of the connected cells to be released at a rate determined by the resistance of the paths (length and cross-section of the paths). Sealing of bipolar batteries becomes more important because the electrolyte path tends to be shorter. It should be noted that the main feature of the present description is the use of a horizontal electrolyte barrier, thereby significantly increasing the potential path length. Another concern is the heat generated by the operation of the cells. Depending on the amount of heat generated, the design must be able to release the heat and maintain a safe operating temperature.

If electrolyte paths are formed between the cells, a small amount of inter-cell leakage can be overcome by periodic full charging of the battery. The battery can be overcharged by a set amount and at a low rate. The low rate allows the fully charged cell to recombine with the gas without generating pressure and release heat from the recombination/overcharge. Cells with a small number of inter-cell electrical leakage paths will become balanced.

The heat flow that occurs in the bipolar cells in the radial direction, in practice, preferably slightly insulates the end plates to ensure that they operate at the same temperature as the rest of the battery.

It is rare that the battery be fully charged to achieve its useful function. Conventionally, the battery pack is overdimensioned and formed in excess. If 50AH (amp hour) is required for operation, this requirement is usually specified to be at least above 10%. Since batteries lose capacity over their lifetime, the anticipated loss increases the capacity of the new battery, resulting in a need for a new battery that may be 70AH in this embodiment. The producer may have a median design target of 75AH to allow for changes in the manufacturing process. This excessive constitution compensates for the deterioration of the life capacity caused by the overcharge.

Fig. 1 is a plan view and fig. 2 is a cross-sectional view (along a-a of fig. 1) of an embodiment of a bipolar plate assembly. Typically, the bipolar plate assembly requires a frame to construct each cell within the cell, but the frame is omitted from fig. 1 and 2 for clarity. However, a bipolar battery may be constructed from a bipolar plate assembly without a frame, as described in connection with fig. 8.

The bipolar plate assembly includes a bipolar plate 11, preferably made of nickel or nickel-plated steel. A positive electrode 12 and a negative electrode 13 are connected to each side of the bipolar plate 11, respectively. The electrodes are arranged to cover only the central part of each side of the bipolar plate 11, leaving room for mounting sealing and heat conducting means. Electrolyte barriers 14 preventing electrolyte leakage are provided on both sides of the bipolar plate between the electrodes and the elastic body 15. The elastomer 15 serves to form a seal between the inside and the outside of the battery. The elastomer is disposed between the barrier layer 14 and the edge 16 on both sides of the bipolar plate 11.

Between the elastomer ring 15 and the electrolyte barrier 14, a hole 21 is provided through the bipolar plate. The function of this aperture 21 is more apparent in connection with the description of fig. 3. A second electrolyte barrier layer 22 is provided around the holes 21 on both sides of the bipolar plate 11 to eliminate electrolyte leakage paths between adjacent cells.

A series of holes 17 are also provided around the perimeter between the elastomer 15 and the edge 16, extending through the bipolar plate 11. The holes 17 in the bipolar plate 11 are described in more detail in connection with figure 3.

The electrodes 12, 13 may be connected to the bipolar plate 11 in various ways, but it is preferred to manufacture the electrodes directly on the bipolar plate using a pressurized powder, as disclosed in PCT application PCT/SE02/01359 of the same applicant under the name "a method for manufacturing a bipolar assembly, a bipolar assembly and a bipolar battery". By using a method of pressing the powder directly onto the bipolar plate, a thin electrode having less active material can be manufactured.

The bipolar plates are preferably rectangular in shape to maximize the useful area of the bipolar plates, better utilizing the bipolar plates for heat transfer purposes. The maximum heat path will be defined as half the length of the shortest side of the rectangle. In this embodiment, a corner is cut away to provide space for the aperture 21.

Electrolyte barrier layers 14 and 22 are made of a suitable hydrophobic material, such as a fluoropolymer (fluropolymer) or similar material. The hydrophobic material may be provided to the bipolar plate as a liquid or solid material and then cured in situ, which will bond the barrier layer to the bipolar plate in an efficient manner to prevent electrolyte leakage between the cells.

Figure 3 shows a partial cross-sectional view of the complete biplate assembly including the frame 18. In this embodiment, the frame 18 surrounds the elastomeric rings 15 on the negative and positive sides of the bipolar plate 11. The frame 18 may be resilient and, when several bipolar plate assemblies 10 are stacked on top of one another, the frame 18 may be compressed, thereby providing good sealing of the cells within the cell. Tie rods (not shown) may be provided around the periphery of the cell to provide the appropriate pressure required to obtain cell sealing.

On the other hand, if the frame 18 is not made of an elastomeric material, a final sealing material, such as an epoxy, must be employed to provide a seal between the end plate and the bipolar plate assembly.

The frame 18 is provided with guides to more easily align the stacked bipolar assemblies. These guiding means comprise a tongue 10 arranged on a first side of the frame, for example the side corresponding to the positive side, and a corresponding recess 20 arranged on a second side, for example the side corresponding to the negative side. The tongue 19 and the recess 20 are each disposed directly above the elastomeric ring 15 on each side of the bipolar plate. The elastomer is preferably more resilient than the material of the frame 18.

In the absence of the resilience of the frame 18, the tongue 19 and recess 20 also interact to provide a temporary seal, preventing the ingress of the final assembled sealing material, such as epoxy, into the cell.

The holes 17 through the bipolar plate 11 are filled with the same material that constitutes the frame 18, preferably by injection molding the frame 18, but other techniques may be used. The advantage of providing the holes 17 and filling them with injection moulding material is that the outer seal, i.e. the frame 18 and the surrounding ring 15 of elastomer, easily conforms to any variations in the dimensions of the bipolar plate. The size of the bipolar plate 11 is changed according to the heat generated during the charge or discharge of the electrodes. The elasticity of the external seal member can conform to such changes without breaking the seal between adjacent unit cells.

Preferably, the frame 18 does not extend over the holes 21 in the bipolar plate 11. Hydrophobic material 22 is provided around the holes on both sides of the hole 21 in the bipolar plate. The hydrophobic material serves to prevent an electrolyte leakage path from being formed through the holes 21 between the adjacent unit cells in the battery. When several bipolar plate assemblies are stacked on top of each other, as described in connection with fig. 7, a common gas space is formed, which eliminates pressure differences between the cells of the bipolar battery.

The elastomeric ring 15 need not be provided on the bipolar plate assembly. The interconnection of the through-holes 21 equalizes the pressure of the adjacent single cells in the battery, thereby equalizing the pressure inside the battery.

Fig. 4 is a plan view and fig. 5 is a cross-sectional view (along a-a of fig. 4) of a second embodiment of the bipolar plate assembly, where the frame has been omitted for clarity.

The bipolar plate assembly includes a bipolar plate 24, preferably made of nickel or nickel plated steel. The positive electrode 12 and the negative electrode 13 are connected to respective sides of the bipolar plate 24. The electrodes are arranged to cover only a central portion of each side of the bipolar plate 24, as described in connection with fig. 1 and 2. Electrolyte barriers 14 are provided on both sides of the bipolar plate between the electrodes and the edges 16 of the bipolar plate 24 to prevent electrolyte leakage paths.

Between the edge 16 and the electrolyte barrier 14, a through-bipolar plate hole 21 is provided. The function of this aperture 21 is described in connection with fig. 3. A second electrolyte barrier layer 22 is provided around the holes 21 on both sides of the bipolar plate 24 to eliminate electrolyte leakage paths between adjacent cells. A further third electrolyte barrier layer 23 is provided on the inner wall surface of the hole 21.

In this embodiment, no holes are provided around the perimeter of the bipolar plate 24. And the elastomeric ring present in the first embodiment (see fig. 1-3) is omitted.

The bipolar plate 24 is reduced in size compared to the bipolar plate 11 of the first embodiment, but the size of the cut-out corner of the electrode is the same to provide space for the aperture 21.

Electrolyte barrier layers 14, 22 and 23 are made of a suitable hydrophobic material, such as the fluoropolymer (fluropolymer) described above or similar materials. The addition of the third barrier layer 23 further reduces the likelihood of electrolyte paths being formed between adjacent cells of the battery.

Figure 6 shows a partial cross-sectional view of the complete bipolar plate assembly including the frame 18. In this embodiment, the frame 18 surrounds only the edges of the bipolar plate 24 and a portion of each side of the bipolar plate. The frame 18 may have the same properties as described in connection with fig. 3.

The frame 18 is provided with guides to more easily align the stacked bipolar assemblies. These guiding means comprise a tongue 19 arranged on a first side of the frame, for example the side corresponding to the positive side, and a corresponding recess 20 arranged on a second side, for example the side corresponding to the negative side.

Preferably, the frame 18 does not extend over the apertures 21 in the bipolar plate 24. A hydrophobic material is provided around the hole 21, for example, on both sides of the second barrier layer 22, and a hydrophobic material is provided on the inner wall surface of the hole 21, for example, of the third barrier layer 23. The hydrophobic material serves to prevent an electrolyte leakage path from being formed through the holes 21 between the adjacent unit cells in the battery. As described above, the addition of the third barrier layer further reduces the possibility of forming an electrolyte leakage path.

Although only one aperture 21 is depicted through the bipolar plates 11 and 24, it will be apparent that a plurality of apertures may be provided through the bipolar plates.

Fig. 7 shows a cross section of a bipolar battery 60 having seven single cells. The battery includes a positive terminal plate 61 and a negative terminal plate 62, the positive and negative terminal plates 61, 62 having a positive electrode 12 and a negative electrode 13, respectively. Six bipolar plate assemblies are stacked on top of each other in a sandwich structure between two end plates 61, 62. A separator 50 is provided between each adjacent positive electrode 12 and negative electrode 13 constituting a single cell, the separator including an electrolyte and a predetermined percentage of gas paths, with about 5% being a typical value for the gas paths.

As is evident from the figure, all the cells share a common gas space through the holes 21 provided between adjacent cells, only some of which are numbered. If the electrode in one cell starts to generate gas before the other cells, this pressure will be distributed completely throughout the common space.

If the pressure in the common space exceeds a predetermined value, the pressure relief valve 70 opens to connect the common gas space to the outside environment. The pressure relief valve 70 is disposed through one of the end plates (in this embodiment, the negative end plate 62) and includes a delivery through hole 71, the through hole 71 having a hydrophobic barrier layer 72, the barrier layer 72 being inside the common gas space and surrounding the opening.

Furthermore, a pressure sensor 73 is also installed through one end plate (in this embodiment, the positive end plate 61) to measure the actual pressure inside the cell. An outer cylinder 66 is provided around the end plates 61, 62 and the stacked bipolar plate assembly to structurally maintain the proper pressure to achieve a sealed container.

The pressure relief valve and the pressure sensor are readily available to those of ordinary skill in the art and will not be described in detail.

Fig. 8 shows an alternative structure of a bipolar battery 80 according to the present invention, comprising a positive terminal plate 61, a negative terminal plate 62 and six stacked bipolar plate assemblies. The structure of this battery differs from the structure of the battery described in conjunction with fig. 7 in the following respects. There is no hydrophobic barrier around the pores 21. Around the negative electrode 13 on the negative side of each bipolar plate 81 there is only one electrolyte barrier layer 14, which barrier layer 14 prevents electrolyte from passing from one cell to the other through the hole 21. Obviously, the electrolyte barrier layer 14 may be provided around only the positive electrode 12, not the negative electrode 13. The electrolyte barrier layer 14 may be provided so as to surround both the positive electrode 12 and the negative electrode 13, but one electrolyte barrier layer is sufficient to prevent the electrolyte from flowing from the positive electrode of one cell to the negative electrode of the adjacent cell. The electrolyte barrier layer 14 may also prevent electrolyte from flowing past the edges 16 of each bipolar plate 81 if an electrolyte barrier layer (not shown) is present around both electrodes 12, 13. Due to the fact that the electrolyte barrier 14 is provided around at least one electrode, a bipolar plate assembly without a frame may be employed to construct the bipolar battery 80. The thickness of the bipolar plate 81 can be reduced if no frame is required. Furthermore, since it is not necessary to form a gas seal between the unit cells, an outer seal member as a continuous, adhesive envelope (preferably including only glass fibers and epoxy resin 83) is necessary in order to constitute a functional battery. The holes 21 provided in the bipolar plate make the pressure difference between the adjacent unit cells zero.

The holes 21 provided in the bipolar plate 81 create a common gas chamber, as described in connection with fig. 7, the electrolyte barrier 14 preventing the flow of electrolyte from one cell to the other. Preferably, a pressure reducing valve 70 having a delivery through hole 71 in the negative terminal plate 62 is provided together with a pressure sensor 73 for monitoring the internal pressure of the battery.

Claims (14)

1. A bipolar battery (60, 80) having at least two cells, comprising:

sealing the container;

a negative electrode terminal plate (62) having a negative electrode (13);

a positive electrode terminal plate (61) having a positive electrode (12);

at least one bipolar plate assembly arranged in a sandwich structure between the negative end plate (62) and the positive end plate (61), each bipolar plate assembly having a negative electrode (13) mounted on a negative side of a bipolar plate (11, 24, 81) and a positive electrode (12) mounted on a positive side of the bipolar plate (11, 24, 81) opposite to the negative side, and at least one hole (21) being provided through each bipolar plate (11, 24, 81) interconnecting each cell with an adjacent cell, thereby establishing a common gas space in the battery for all cells;

a separator (50) provided between each negative electrode (13) and each positive electrode (12) forming each single cell, the separator (50) including an electrolytic solution;

the negative electrode (13) and the positive electrode (12) are arranged in such a manner that each electrode covers only the central portion of each side of the bipolar plate (11, 24, 81); and

providing an outer seal (18, 83) around the edge (16) of each bipolar plate assembly and each end plate to provide the sealed container;

the method is characterized in that:

-arranging an inner barrier layer (14) of hydrophobic material around at least one electrode (12, 13) near a first side edge (16) of each bipolar plate (11, 24, 81); and is

The at least one hole (21) through each bipolar plate is arranged between the barrier layer (14) and the outer seal (18, 83),

whereby the internal barrier layer (14) prevents electrolyte from flowing from one cell to the other.

2. The bipolar battery according to claim 1, wherein said hydrophobic material of said inner barrier layer (14) is a fluoropolymer material.

3. The bipolar battery according to claim 1, wherein the first side is a negative side and the inner barrier layer (14) is arranged at least around each negative electrode (13) on the negative side of the bipolar plate (11, 24, 81).

4. The bipolar battery according to claim 3, wherein an inner barrier layer (14) is further provided around each positive electrode (12) on the positive side of the bipolar plates (11, 24, 81).

5. The bipolar battery according to any of claims 1-4, wherein one end plate (62) is provided with a pressure relief valve (70), the pressure relief valve (70) connecting the common gas space to the external environment if the pressure in the common gas space exceeds a predetermined value.

6. The bipolar battery according to any of claims 1-4, wherein a pressure sensor (73) is connected to one end plate (61) to monitor the pressure in the common gas space.

7. The bipolar battery according to any of claims 1-4, wherein the outer seal comprises a frame (18) arranged around the edge (16) of each bipolar plate assembly and each end plate to provide said sealed container.

8. The bipolar battery according to any of claims 1-4, wherein the outer seal comprises a continuous, bonded envelope (83).

9. The bipolar battery according to claim 8, wherein the external seal is made of epoxy and glass fiber

10. A bipolar plate assembly comprising a bipolar plate (11, 24, 81), a positive electrode (21) disposed on a first side of the bipolar plate (11, 24) and a negative electrode (13) disposed on a second side of the bipolar plate (11, 24, 81) opposite the first side, and at least one aperture (21) is disposed through each bipolar plate (11, 24, 81) to provide a gas passage through the bipolar plate, the negative (13) and positive (12) electrodes being disposed in such a way that each electrode covers only a central portion of each side of the bipolar plate (11, 24, 81);

the method is characterized in that:

-arranging an inner barrier layer (14) of hydrophobic material around at least one electrode (12, 13) near a first side edge (16) of each bipolar plate (11, 24, 81); and

the at least one hole (21) through the bipolar plates (11, 24, 81) is arranged between the barrier layer (14) and the edge (16),

whereby the inner barrier layer (14) prevents electrolyte from flowing from one side of the bipolar plate assembly to the other.

11. Bipolar plate assembly according to claim 10, wherein said hydrophobic material of said inner barrier layer (14) is a fluoropolymer material.

12. Bipolar plate assembly according to claim 10, wherein the first side is a negative side and the inner barrier layer (14) is arranged at least around each negative electrode (13) on the negative side of the bipolar plate (11, 24, 81).

13. The bipolar plate assembly according to claim 12, wherein an inner barrier layer (14) is further disposed around each positive electrode (12) on the positive side of the bipolar plates (11, 24, 81).

14. A bipolar plate assembly according to any one of claims 10-13, wherein a frame (18) is provided around the edges of the bipolar plate assembly.