The present invention relates to a manufacturing process for gel batteries and especially to a filling process for gel batteries by an acid-to-gel process, and to an apparatus for carrying out the process.

An electric battery consists of one or more electrochemical cells that convert chemical energy contained in the respective cell into electrical energy. Each cell contains a positive electrode called cathode and a negative electrode called anode and is filled with a chemical mixture called electrolyte.

The cells of the battery may be independent from one another or may be connected with one another in a way allowing a flow of electrolyte from one cell to another cell. Furthermore, several cells electronically may be connected in series with one another forming a block.

The electrodes may be plate-shaped or lattice-shaped, for example. In gel batteries the electrodes contain lead and may even be referred to as pole plates.

The electrolyte may be liquid or paste-like. In gel batteries the electrolyte is usually gelled sulfuric acid H ₂ S0 ₄ . Gelling is usually achieved with an amount of silica, Si0 ₂ , added to the sulfuric acid, H ₂ S0 ₄ . Gel batteries are so-called valve regulated batteries, which do not need any water refilling during the whole service life, see e.g. DE 36 03 196 Al. This type of lead-acid battery is used in a variation of applications, in particular in cycling operations.. As is known e.g. from DE 37 36 069 C2, batteries of this type initially need to be "formed, i.e. the originally equivalent electrodes have to be polarized by a current flowing through them so as to acquire their natures as positive and negative electrodes, respectively. The forming e.g. transforms lead oxide into lead on the one kind of electrodes, and transforms lead oxide into lead dioxide on the other kind of electrodes.

There are several known methods for an initial filling and forming process of gel batteries:

1. The cells of the battery are assembled using pre-formed positive and negative electrodes, then the cells are filled with a gel, and electrochemically charged. The pre-formation of the electrodes takes place in separate tanks filled with acid

This method is the oldest process and gives good quality products. A disadvantage is the high cost of tank formation, and the entire process is not particularly environmentally friendly.

2. Another method is the so-called "jar or block formation" with liquid acid acting as electrolyte. This method starts out from cells containing unformed electrodes, and liquid acid is circulated through the cells of the battery during formation. After the formation the battery is electrochemically discharged to a certain level, followed by drainage of the acid (usually by toppling the battery) and then re-filling with gel.

The disadvantage of this method is the more complicated and costly process, and sometimes variations in cell performance occur.

3. A third method is the so-called "direct gel formation", so far the most economic and easiest process. In this process, the cells are assembled with unformed electrodes, gel is added, and then formation is started.

However, direct gel formation takes a very long time and does not result in good quality product, as the acid concentration in the gel tends to vary widely during the formation.

It is an object of the invention to provide a filling process of the "jar or block formation" broadly related to the above described method no. 2, however without the complicated acid drainage and re-filling process; and an apparatus for efficiently carrying out the process.

According to the invention this problem is resolved by a method as set forth in claim 1, and the apparatus as set forth in claim 7. Further advantageous aspects become evident from the dependent claims.

Figure 1 shows an equipment that may be used for the new filling process which is hereafter described. Figure 2 shows an apparatus according to present invention.

Figure 3 shows a filling plug of an apparatus according to present invention. Figure 4 shows a valve arrangement for an apparatus according to present invention.

At first the cells 10 of a lead-acid battery 12 are assembled using unformed lead electrodes and filled with a sulfuric acid of a specified density, followed by a formation process, such as the one described in DE 37 36 069 C2, and · including acid circulation. After the formation, the cells 10 are discharged electrochemically to a certain level, or else remain fully charged. In either case, the cells are at that time filled essentially with the acid only.

The following gel filling method can be applied to fully charged or to partially discharged ones: Referring to Fig. 1, the top of the cells 10 of batteries 12 are fitted with a plug 14, which has an intake and an outlet duct. The corresponding hoses or tubes 18, 20 are connected with a mixing and filling gel container 16. Alternatively, in some applications the plugs previously employed for the acid circulation may remain in the cells, and instead the hoses are disconnected and other hoses for communicating to the container are connected to the plugs.

The container 16 is filled with a prepared gel mixture, i.e. the required acid (typically H ₂ S0 ₄ ) with an excess amount of the gelling agent, typically Si0 ₂ . A pump system 22 pumps gel from the container 16 into the cells 10 of the battery 12 through the intake tube 18, while the outlet tube 20 transports the acid from top of the cell 10 back to the container 16. The additional acid received in the container from the cells in combination with the reduction of the amount of gel mixture in the container, the gel mixture containing an amount of Si0 ₂ , results in a reduction of the total Si0 ₂ concentration in the container 16.

This acid/gel-exchange process is typically continued until the S1O2 concentration is equal in the cells 10 and container 16. After this stage is reached, the filling process is discontinued, the filling plug is removed, and the battery sealed.

The container then may be restored to its original S1O2 concentration by replenishing S1O2, potentially appropriately reducing the amount of acid at the same time, for the next batch. The container therefore typically has an inlet opening 24 for adding Si0 ₂ , and an outlet 26 for excess acid; it also typically has a stirrer 28 driven by a motor 30 for agitating the content so as to maintain the prepared gel mixture in a flowable state, i.e. to avoid premature gelling. The container may also have cooling means such as a cooling jacket 32 outside it (shown only in cross section in Fig. 1), and/or cooling pipes inside it, to enable adjusting the temperature of the prepared gel mixture. Naturally, there may also be means provided to measure the temperature of the gel and acid in the container 16. Additionally, there may be means provided for measuring the acidity of the gel and acid, and/or for adjusting the amount of acid. Incidentally, the prepared gel mixture may be cooled (e.g. by 10°-30°C) so as to increase its density. Although the density of the gel is already somewhat larger than that of the acid alone, at the same temperature, cooling the prepared gel mixture is effective in accelerating the gel filling process. A typical initial S1O2 concentration of the gel mixture in the container will be dependent on the desired final S1O2 concentration of the gel in the filled battery; e.g., a reasonable range for the S1O2 concentration in the container will be 50% or higher up to twice or up to three times as high as the desired concentration. The reason is that in each batch, a dilution will occur due to the acid flowing back from the formatted batteries. The extent of this dilution will naturally depend on the volume ratio of the batteries combined and the container, which may typically be on the order of 1-2.

As shown with reference to Fig. 2, a particularly useful apparatus has two essentially parallel tubes 40, 42 for connecting cells of plural individual batteries (usually more than 10 and up to 50, such as a multiple of 12, e.g. 24 or 36 batteries). Each battery may comprise plural, e.g. six to twelve cells. The cells may be communicated with one another, allowing an exchange of gel and acid. One of the tubes 40 is connected to the outlet of the container 16, and the other 42 to its inlet. Both may be equipped with a valve; the same four-way valve may be used for both tubes. Each tube has as many closable outlet/inlets 44 as the maximum number of batteries envisioned to be filled at the same time. One of the tubes may have one extra closable opening per outlet/inlet to accommodate the plug for the respective battery when a smaller number of batteries is to be filled, than the maximum number, or when the apparatus is not in use, to seal the system from the environment. Both tubes may have plugs 46 at their far ends (as seen from the container, or valve if present). These plugs 46 may be replaced by additional tube lengths with outlets/inlets, to provide additional capacity for filling still more batteries simultaneously. Each plug 14 of a battery or cell 10 is connected to the parallel tubes 40, 42 by short interconnecting hoses 48. In a further embodiment shown in Fig. 3, the filling plugs 50 have outlets 52 which are adjustable in height. This enables easy adjustment of the filling height, in the event the type of battery to be filled is changed between batches. Incidentally, the inlet tube 54 of the plugs in some embodiments is angled by an angle a of e.g. between 10° and 80°, or between 20° and 60°.

Fig. 4 shows an arrangement of two tubes 40 and 42 which have been extended to greater length using interconnectors 56. In this arrangement, both tubes 40 and 42 are communicated/discommunicated from the container 16 using a four-way- valve 58. Aside from the pump 22, in this embodiment there is another pump 60 in the outlet tube 20 leading back to the container 16. In the outlet tube branch, there is an additional sensor 62 (e.g. light sensor) operable to sense an increase in the gel concentration in the liquid flowing to the container, so as to enable a control unit 64 to terminate the filling process by closing the valve 58, when the gel starts flowing back to the container 16.

The new method reduces time and cost. The existing filling and formatting equipment can be adapted to the components and procedures of the invention. Only minor modifications to existing installations for gel battery production need to be done to introduce a cleaner production process.

The new production process for gel batteries leads to a reduction in production cost of up to 20%. This is achieved by a reduction in production time (as soon as the liquid is pumped out, gel will be pumped into the block housing) and a reduction in required machinery (no turning function of the block housing is needed). The above exemplary description of embodiments is not to be construed as limiting the invention/the scope of which is defined by the appended claims.