This invention relates to a method of manufacture of a bipolar battery and sealing the bipolar plates thereof
A thin, bipolar, lead-acid battery includes one or more cells, each of which is provided with a one-way vent valve for allowing the gases to vent before the pressure inside the system goes beyond the designed value.
This battery consists of a single container with a complimentary block to accommodate all the bipolar and end plates and also to seal the entire system of battery. This container is provided with all the required routings to fill the electrolyte and to vent the gases out through a number of valves as demanded by the design.
This invention is described herein with reference to two embodiments. The first embodiment is provided with a valve and its routing channel parallel to the cell. The second embodiment is provided with a vertical channel which leads the primary routing channel of every cell to the top surface of the battery where a valve is provided at the end of the vertical channel. The specification herein also describes an arrangement of the terminal plate to achieve better current distribution.
The bipolar batteries are gaining increasing importance due to their potential advantages of weight reduction, effective material utilization, low internal resistance and increased life. In particular, they are suitable for automotive applications (starting, lighting, and Ignition) due to their high rate discharge capabilities.
A bipolar battery is one that consists of a number of bipolar plates, two end plates and required number of separators stacked in a particular order. Each bipolar plate has a positive active material pasted on one side and a negative active material pasted on the other side with a common conducting base. The end plate consists of either positive active material or negative active materia]1 with a conducting base and a current collector.
The active material is supported with the help of either a plastic mesh or a acid resistant metallic mesh. The arrangement of all the above-mentioned components to construct a good functioning battery is a challenging task

because of smaller dimensions involved. Many variations have been ; proposed to seal and stack all the necessary components.
This invention is about constructing a bipolar battery by stacking bipolar plates and end plates with separators in between them and arranging the slack in injection molded container. This container consists of all routings to fill electrolyte and to vent gases through embedded valves. The objective of providing an individual valve in every cell is to utilize the concept of oxygen recombination technology to generate water within the system, which forms a maintenance free battery. This can be summarized as follows.
1. In the present invention, a single container is developed to seal the entire stack of bipolar plates, end plates and separators. The container has proper slots to accommodate and support the stack of bipolar plates, and end plates. It has two channels to pressurize electrolyte into the system and create vacuum in the system. It has all the routings necessary for vent gases to access valve. In this case unlike frame design work, acid does not leak from the battery. But it may leak from one cell to other cell.
2. A vent valve is provided in the container itself to utilize oxygen recombination phenomena to regenerate water in the system. The valve routing is provided in a way to avoid valve failure and acid leakage. To overcome the disadvantage of port blockage a lengthy primary channel is provided along the length of the container with access to the separator through another secondary channel throughout it's length so that the gases can access the primary channel at every point along the length of the channel (the path of vent gases is shown in section. The valve is provided at the end of the primary channel. In such an arrangement valve does not fail even when the channel is blocked at a few locations.
3. Based on the specifications of the battery design and dimensional constraints, one vent valve may not provide sufficient venting at higher charging currents. This point can be elaborated as follows. Thin electrodes and separators limit the diameter of the valve. The amount of gases generated is a function of charging current that in turn depends on ampere-hour capacity. In a case, where the smaller diameter vent valve may not provide sufficient venting for higher ampere-hour batteries at high charging currents two valves of the same diameter can be provided at both the ends of a primary channel. One more added advantage is if one valve fails accidentally, the other one can work and prevent the cell from

failure. The first embodiment describes these concepts.
4. Another disadvantage of the above configuration is acid may leak, through the valve as nothing prevents the acid from reaching the primary channel. Though the leakage is expected to be very little as the acid is immobilized in a separator, over a period of time it can become significant. In addition to that the presence of acid in between the rubber valve and valve stem may alter the operating parameters of the valve that lead to improper functioning of valve. As a remedy to this situation, valves can be provided in vertical direction with respect to cell electrode plane. (Electrode plane is horizontal as demanded by the layout of the battery in our specific application). This concept not only solves the acid leakage and valve damage problems but also solves the problem of accommodation of valves in the battery. Here the valves can be provided along the length of the battery without any difficulty unlike the other case where all the valves are to be accommodated along the height, which is a very difficult task and may not be possible. This concept is described in the second embodiment.
5. In a bipolar battery uniform current distribution on the electrode gives more life to the battery. If current distribution is uniform, base conductor corrosion will be very uniform and the corrosion inhibition by the active material will be more effective. However, current distribution at the terminal end plates is not uniform like ordinary battery. To improve the situation an alternative way of distributing current is found. In this strategy, the current does get distributed in a number of predetermined branches and then reaches the end plate at different predetermined locations.
This invention will now be described with reference to the accompanying drawings which illustrate, by way of example and not by way of limitation, embodiments of this invention, wherein
FIG. I is an isometric view of a container with its complimentary block 2. It also shows the top sectional view (section C-C), sectional view along the length (section A-A), and a sectional view along the width (section B-B). All the routings can be clearly seen in the top sectional view of the container.

FIG. 2 is a top view of the battery with two sectional views; one sectional view along the width (Section B-B) and the other one along the length (Section A-A) with detailed sectional views A, K, J (embodiment 1).
FIG. 3 shows an isometric view of the exploded terminal cover plate.
FIG. 4 is a top view of the battery with three sectional views; one sectional view along the width and the second one along the length (Section A-A), and the last one is the sectional view of the wall along the length (Section B-B) with detailed sectional views I, E, H (embodiment 2).
FIG. 5 is a concept drawing that illustrates the arrangement of valves to avoid valve accommodation problem.
FIG.6(B) is a concept drawing that describes the advantage of a lengthy opening along the width of primary electrolyte channel for the electrolyte to access the separator. FIG. 6(A)shows the disadvantage of having access to the separator at a single point .
FIG. 1 depicts an isometric view of a container and its complimentary block 2 to complete the container. Three sectional views of the battery are shown. The sectional view B-B is along the width, which shows primary valve channel 5a, terminal cover plate 9, separator 7, bipolar plate 11, grooves 10 in the container. Grooves 10 accommodate and support bipolar plates and positive II negative 8 end plates. The block 2 has a groove 12 to accommodate copper terminal bar and electrolyte pressurizing ports 3a as shown. Vacuum creating ports 4a are shown in block 1. Section C-C is the top sectional view of the container. Ports 3a and 4a are provided to fill the electrolyte. These ports are provided at the ends of primary channels 3 b and 4b respectively. These channels3b and 4b are open to separator through secondary channels 3c and 4c respectively so that electrolyte travels through primary channel (4b) and secondary channel (4c) to reach separator. The same kind of arrangement (3a, 3b & 3c) on the other side is provided to create vacuum in the separator to induce electrolyte flow. The construction of primary and secondary channels is done such that die acid can access the separator from primary channel through secondary channel at every point along the length of the channel to avoid zones of separator that are inadequately filled with electrolyte. This is well illustrated in the figure 6. In the figure 6(B), one set of port 22a, primary channel 23a and secondary channel 24a at one end and the other set of port 22b, primary channel 23b

and secondary channel Z4D at other end, are shown. If the electrolyte is pressurized at 22a by applying vacuum at 22b, the electrolyte flows in the separator domain 25 as shown in figure 6(B) only when the acid can access the separator through secondary channel at every point along width.
Figure 6(A)is a simple concept drawing to illustrate the same concept. From the figure 6(A), it can be concluded that if the opening 28a is provided to the primary channel 27a at a single position (in the figure it is at the center), the flow of electrolyte through separator domain 29 takes place as shown in the figure 6(A) leaving some domains 30 of the separator that are inadequately filled with the electrolyte. The Section C-C of figure 1 also shows the routing for venting of gases. The valve routing includes a primary channel 5a, secondary channel 5 b and valve stem 5c arranged in such a way that gases generated inside the separator can reach the valve through 5 b, 5a and 5c. The primary channel 5a is open to separator to provide access for the gases generated inside the separator through secondary channel 5b at every point along its length so that gases generated inside can reach the valve through secondary and primary channel for venting as shown in Section C-C of figure 1.
This arrangement is to reduce the probability of channel blockage and subsequent valve failure. When compared to frame design of bipolar batteries, the single container concept eliminates the leakage of electrolyte from the battery. In the former concept, electrolyte can leak through the improperly sealed gaps between frames and lead to loss of electrolyte. It is not there in single container concept. But the disadvantage of the single container concept is, electrolyte can leak from one cell to the other cell through the small gaps between container groove and bipolar plate. This can be minimized by selecting hydrophobic plastic for container and also covering/ coating the edges of the electrode with hydrophobic plastic/ rubber/ resin. This arrangement not only provides an airtight seal but also minimizes the penetration of acid in to the narrow gaps, as they are non-wetting surfaces.
FIG. 2 depicts the top view of complete battery 13 (embodiment 1) and two sectional views (A-A and B-B) with detailed views (A, J, K) and sealing caps 15. In detail A, primary valve channel 5a, secondary valve channel 5b and valve stem 5c are shown.
Detail J and K shows the ports (3a and 4a) and channels (3b, 4b, 3c, and 4c) and terminal 14. The components of a bipolar plate; positive active material

1h negative active material 11a, conducting base 11c and plastic mesh l1d are shown in detail A. In this embodiment single / dual valves can be provided at one/ both the ends of the primary channel as demanded by the design requirement. Since the valve dimensions are smaller in bipolar batteries, single valve may not meet the design-venting requirement especially at higher charging currents.
FIG.3 describes terminal plate arrangement to achieve more uniform current distribution. It consists of a plastic sheet 9c with openings 9g in it and one more plastic sheet 9b with an opening 9f at the center. It also consists of a copper sheet 9d and terminal 14 and copper sheet 9e as shown in figure 3. Finally it is covered with a plastic plate 9a. The applied current at the terminal does get distributed in to a number of branches (at least two) provided in the terminal plate copper sheet and then enters the electrode for reaction. More uniformity in the current flow can be achieved by providing more number of branches in the copper sheet. This uniform current distribution extends the life of the battery,
FIG.4 describes the second embodiment which has valves provided in vertical direction while the cell has a horizontal configuration (electrode plate is placed horizontally). The top view of the battery is shown in figure along with three sectional views (A-A, B-B, CC) and detail views (E, H, 1). As shown in section C-C, every cell has a vent channel 17a parallel to the cell and one more vertical channel 17b that connects 17a with the valve stem 17c. Acid leakage can be eliminated completely with this routing, as acid cannot reach the valve. The valves for alternate cells are provided on one side while the remaining valves are provided on the other side as shown in detail E and detail H. The valve cover plate 18a and 18b are shown in the top view of the battery. Dual valves can
also be provided in the second embodiment. Then every cell of the battery has a valve on each of its two sides.
FIG. 5 is a simple concept drawing that describes the arrangement of valves to avoid valve accommodation problem on the sides. It discusses about the accommodation of valves on the battery. In vertical valve concept (embodiment 2), since the valves are provided along the length, accommodation problem will not be there. Both single/ dual valves can be easily accommodated along the length of the embodiment. This accommodation problem appears in the case of embodiment 1 only. If it is a

single valve battery the alternative valves 19a & 21a can be provided at one end while the intermediate one 20b is provided at the other end as shown in figure 5 (only three valves for the top three cells are titled as an example).

We Claim
1. A bipolar battery comprising a single container with all the routings to fill
electrolyte and to vent gases; grooves cut inside the container to
accommodate and support plates; a combination of a primary channel and a
secondary channel to vent gases generated inside the cell, the secondary
channel being connected to the primary channel tangentially along the
length; electrolyte inlet channel consisting of a primary and
secondary channel along the width of the battery; a channel to create enough vacuum in the separator to suck electrolyte; sealing of electrolyte filling ports with plastic caps followed by thermal welding or adhesive bonding; single or dual valves; a terminal plateassembly for better current distribution wherein the terminal Js divided into at least two branches, said assembly including two non conducting plastic sheets with perforations; a plastic plate with a cut, a terminal with a conducting metal sheet, and a conducting metal sheet for dividing the current into a number of branches of any predetermined geometry
2. A bipolar battery as claimed in Claim 1 wherein the single or dual valves
are provided at either or both ends of the primary channel.
3 .A bipolar battery as claimed in Claim I wherein the single or dual valves are provided on the top surface of the battery at the end of vertical channels coming from the primary channels of the respective cell; a vertical channel that connects the valve and primary channel of a cell
4. A bipolar battery as claimed in Claim 1 or Claim 2 wherein alternative valves are located at one end and the other end in the single valve arrangement.
5. A bipolar battery as claimed in any one of the preceding Claims wherein projections are provided for the container to hold the stack in a compressive state.
6. A bipolar battery substantially as herein described and illustrated with reference to the accompanying drawings.

A bipolar battery substantially as herein described and illustrated with reference to the accompanying drawings.
A method of manufacture of a bipolar batter}' as claimed in any one of the preceding Claims comprising the selection of a hydrophobic plastic as container material; covering or coating the edges of the plates with hydrophobic thin plastic, rubber, or resin to prevent penetration of acid through the gaps between container grooves and plate edges and to also provide an air-tight seal for the plates in the grooves.
(SJ. A method of manufacture of a bipolar battery substantially as herein described and illustrated.