SE416008B - MAINTENANCE-FREE NORMALLY CLOSED ELECTROCHEMICAL CELL FOR A BLYACKUMULATOR - Google Patents

Description

7109853-7. utilized casing, to which the electrolyte is usually added in the form of a free liquid. The container usually contains a pressure relief valve, which opens at a very low pressure difference to allow the release of released gases despite attempts to reduce the electrolyte evaporation. Water losses in connection with the gas discharge result in a loss of the cell's capacity in ampere hours.

Typically, the plates of this type are rather thick, and the plates are sometimes reinforced by frames and have a small geometric area per ampere-hour capacity. The utilization of the active material therefore decreases, especially at high discharge rates. Thick separators must therefore be arranged together with the thick plates, which means a high internal resistance.

All known lead-acid cells, including the maintenance-free cells, are made in such a way that the plates have structural integrity to be self-supporting. Consequently, the grids in the maintenance-free cells usually contain at least 0.1% calcium or some other contaminant, calculated on the lead weight. The use of such contaminants in amounts greater than 0.11 will provide structural integrity, so that the plates become self-supporting. These amounts of contaminants are used despite the fact that the presence of this amount of calcium or other contaminants leads to a decrease in the conductivity of lead with a concomitant increase in the internal resistance of the cell. This in turn leads to a passivation of the lead grid due to the generation of an insulating layer between the surface and the active material during prolonged charging.

Separators have usually been made stiff and strong to separate the plates. This is necessary because the plates sometimes fold and distort and because the separators must have the ability to keep the plates separate. On the other hand, the separators have been designed to contain a sufficient amount of electrolyte to provide hydrogen and bisulfate ions and water for maintaining the electrochemical reaction. Sometimes a gelled electrolyte is used in combination with rigid corrugated separators. The separation of the plates is maintained, but this construction increases the internal resistance of the cell due to the fact that the gel reduces the diffusion rate carried by the electrolyte. The gelled electrolyte also provides poorer contact between the surface of the plates and the active electrolyte, when gas is released at the plates.

The life cycle of maintenance-free cells is limited by water and electrolyte losses due to gas release, since the maintenance-free cells generally do not have replacement water supply devices. Although attempts have been made to reduce losses by using materials with high hydrogen and high oxygen overvoltages and by limiting the charge to prevent overcharging, it is known that a certain degree of overcharging is required at the positive plate in order to maintain use. -of the active material. During this supercharging, some gas will be released, and typically the maintenance-free cell is therefore provided with a ventilation drain above the separator and plate structure. Such a ventilation drain means that the cell cannot be used in all conceivable situations. In addition, electrolyte loss from the cell can occur if the cell is used in all conceivable positions and especially during the gas release.

To overcome the disadvantages of the conventional maintenance-free lead-acid batteries, it is an object of the invention to provide such a maintenance-free lead-acid cell which has unique structural features which enable the use of a relatively low degree of contamination in lead lattices which have high purity and is non-self-supporting. Another object of the invention is to provide a design which provides an improved high energy per unit volume and per unit weight within a wider range of discharge conditions and high power per unit volume and per unit weight at low impedance. Yet another object of the invention is to provide a maintenance-free lead-acid cell which has devices for reconnecting oxygen enriched at the positive plate and for reducing the hydrogen release in order thereby enabling a significant overcharging. Yet another object of the invention is to provide a maintenance-free lead-acid cell which is useful in any orientation position without the risk of electrolyte leakage or alteration of the electrical operating characteristics.

A further object of the invention is to provide a maintenance-free cell which does not require additional addition of electrolyte or regulation of the amount of electrolyte during the useful life of the cell.

The cells of the present invention utilize very thin, flexible, structurally free, non-self-supporting grids, which may have been formed into various shapes. The lead used in the grids has a better purity than 99.9! and contains no material to increase the stiffness, so that no concomitant reduction in hydrogen or oxygen overvoltage is obtained. The grids are pasteurized with materials similar to the materials of conventional pasteurized cells, but unique variations are available to simplify cell construction.

Highly retaining and porous, flexible separators are placed between plates of opposite polarity, and these separators together with the plates are possible to stack or shape or wrap; spiral and enclose in a container, which can have a variety of designs and shapes. The separators are highly absorbent and have the ability to retain the electrolyte in intimate contact with the plates regardless of the alignment position of the cell. The cell can therefore be used in any position.

A central ventilation pipe can be placed in the cell near the center of the mass of plates and separator. The ventilation device is provided with a pressure relief valve, which is normally actuated to a closed position and which is activated only at excessive gas pressure, for example during overcharging or at extremely high temperatures. In normal cases, however, the pressure relief valve is closed under the normal relatively high operating pressures of the cell.

Neutralization devices are provided to neutralize any outgoing acid droplets that may be trapped in the outgoing gas.

The cell operates in a "starvation" state with virtually no unabsorbed electrolyte. The plates have active edges, which are exposed to the gas volume. The capacity of the negative plate (Ah) is greater than the capacity of the positive plate, so that the positive plate can be supercharged before the negative plate. Oxygen, which can be released during the supercharging, will thus be able to diffuse and reconnect at the exposed portions of the negative plate.

The invention will be described in more detail below with reference to the accompanying drawings. Fig. 1 shows in perspective and section all the components of a composite cell according to the present invention. 2 shows a partially wound spiral construction, which consists of the positive and negative grids and an intermediate separator. Fig. 3 shows a cell of the type with stacked components, the parts being taken apart. Figures U-6 show three diagrams in which known cells and the lead-acid cells according to the invention are compared with each other in certain respects.

To begin with, the lead grid 10 according to the invention has the form of a flexible, non-self-supporting and non-reinforced structure.

It is preferred according to the invention to use substantially pure expanded metal type lead, which further reduces the self-carrying capacity of the grid and which reduces its weight. With regard to the structure, obviously other types of non-self-supporting grids can be used, such as thin flexible sheet sheets or thin cast grids or lead foils. However, a stretch lead grid is preferred.

The base grid of the present invention differs from the normal grid in maintenance-free type lead-acid cells. According to the present invention, the grid consists of lead of very high purity. As pointed out above, the lead in the usual maintenance-free lead-acid cells contains a sufficient amount of impurities to give the grid structural integrity so that it is self-supporting.

The presence of contaminants is neither necessary nor desirable in the grid of the present invention. According to the invention, lead is used which contains only very small amounts of impurities, such as calcium, these impurities generally being present in an amount of less than 0.02% by weight, calculated on the weight of lead. The small amount of contaminants reduces the gas release at the plate but allows the formation of nucleation points for a grain structure, so that minimal grain size can be achieved. This refinement of the grain structure is also advantageous in that a reduction in the corrosion at the positive grid is thereby obtained. Since the grids of the present invention are not self-supporting, lead of the commercially available purity grades 99,991 or better can be used. For this reason, it is possible to procure and use lead of a purity of 99.992 or even 99.9999%, although the cost is thereby slightly increased. However, the increased cost may be justified in order to reduce other harmful effects of the pollutants.

A preferred alloying element is calcium, with as little as 0.001% by weight of calcium being used in the lead. It is possible to use this small amount, as other measures are used to give the grid structural integrity. Although amounts as low as 0.001% by weight can be used, efforts are made to reduce the content to less than 0.03% by weight and down to as little as 0.006% by weight, while an amount of 0.01% is perfectly acceptable. Other materials, such as silver, copper, arsenic and tellurium, are effective as nucleating agents for refining grain size. Silver can be used in amounts of 0.005-0.1% by weight. If copper was used as the nucleating agent, the copper was used in an amount of 0.001-0.1% by weight. Arsenic is used in an amount of 0.002-0.1% by weight, and tellurium is used in an amount of 0.002-0.1% by weight.

A relatively small amount, compared to that found in the standard maintenance-free lead-acid battery, is used and provides a reduction in the likelihood of passivation and also the likelihood of corrosion.

The grids 10 for use in connection with the present invention can be made by casting, embossing, forging or perforating lead foil sheets. A preferred method is to "expand" or stretch die cast lead sheet and then cut out this expanded metal into the desired shape. The strand thickness of the stretch grid is of some importance especially in the positive plate, since the plate must be as thin as is reasonable but must have at least the thickness of the grid strings. However, the grid strands in the positive plate are slowly converted from lead to lead dioxide, and if the strand thickness is too small, the strands will eventually be converted to oxide and the grid will no longer function properly as a current collector. Normally it is suitable to have a strand thickness of 0.0508-1.14 cm when the plates 11 have a thickness of 0.0508-1.52 cm.

Thinner plates ll can also be used more efficiently, especially at higher discharge rates. Thinner plates also reduce the internal resistance of a cell with a given capacity (Ah), since a corresponding increase in the geometric surface of the plates is obtained. It is quite obvious that the plates in the cell according to the invention differ drastically from the plates in other cells in that the plates 11 are non-self-supporting but still give far better properties.

Although conventional pasteurization methods can be used, some differences are valuable and lead to an improved result. A material, which mainly consists of 75 weight! b1y (II) oxide and 25% by weight lead red (Pb30u), can be used for the positive plate. As is well known, additional components can be used, eg some type of bulking agent, eg 0.05-0.2% by weight. The density of the paste or pulp in the cell according to the invention should be slightly higher than for other types of maintenance-free lead-acid plates, in order to thereby obtain the best performance properties. A ratio between the weight of the active mass and the grid of 1: 0.6 to 1: 1.5 is acceptable. As explained below, it is important that the active mass of the plate should cover the edges of the plates 12. Especially with the negative plate it is important that the paste or mass and not the solid grid is exposed at the edges. To the above mixture is added a sufficient amount of water for the finished paste to contain 3.6-0.8 g of paste per cubic centimeter of mixture.

The paste mixture is spread on the lead grid to form a completely covered plate 11, and in the case of expanded metal grids not only the holes in the grid are to be filled but also a coating is to be formed on each side. A laminated grating is still non-self-supporting, and this applies regardless of whether the paste or mass is wet or has dried.

The negative and positive plates 11 are designed in essentially the same way using a flexible flexible lead for the grid. In the cell, the negative lead lattice can be coated with a similar type of paste, which consists essentially of 80% lead (II) oxide and mainly 17% by weight of small free lead particles. To this can be added about 1-3% by weight of expander-type material, usually barium sulphate, carbon black. And expansion-type material, eg lignosulfonate. To this mixture is added concentrated sulfuric acid and water to form a pasty material having a density of 3.6 -μ.8 g / cm3. The negative plate should have a slightly larger capacity than the positive plate, but since the two plates normally have approximately the same degree of utilization, the negative plate should have 10-30% more active material than the positive plate.

A separator material 14 is used, and this must not only separate the adjacent plates from each other but must also have a sufficient porosity and sufficient retention capacity to be able to contain in itself practically all the electrolyte necessary to support the electrochemical reactions. Accordingly, an important part of the invention is the use of a separator material with very high wetting heat, SOW facilitates retention of some of the electrolyte in the spacer of the separator except for a small amount of electrolyte present in the pores of the plates 11. It is important that in this cell there is essentially no free electrolyte other than the electrolyte retained inside the separator material itself.

As explained below, various designs have been described; which allows a certain amount of free electrolyte to be formed in the cell either due to excessive gas generation or due to the electrolyte being expelled from the separator at orientation positions other than the upright position of the cell. One of the preferred embodiments of the cell therefore has a separator material 14, which extends both upwards and downwards under the plates to come into contact with at least the lower or the upper inner surface of the container or liner. An alternative design would therefore be a separator material, which surrounds the outermost layer of the plates and which is in contact with at least one inner surface of the container or liner. In such a design, the free electrolyte would be reabsorbed by the separators. Most well-known separator materials, such as microporous rubber, polyvinyl chloride, polyolefins and phenolic resin impregnated paper, can be used in the cell of the invention.

The preferred separator material is a nonwoven, short fiber fiber glass material having a very small fiber diameter. Fiberglass sheets of such material have an extremely large surface area and a correspondingly small fiber diameter, so that the sheets have the ability to retain the electrolyte in the separator itself. To achieve maximum wetting heat, a microfine fiber filament with a high surface area per unit weight or an unoriented fiberglass mat is used. This material has a high electrolyte retention capacity per unit volume of material and is also very flexible. The fiber diameter of these materials is in the range 0.2-10 μm and the materials have a surface area of about 0.1-20 m2 per gram of silica. Such a material has a porosity as high as 85-95%.

This very large surface area and the high wetting heat for the electrolytic va surface sulfuric acid wetting tube results in a separator which has a very high electrolyte retention capacity, calculated on the volume of the separator. Although this separator material 14 is not physically strong enough to serve as separators in known and conventional maintenance-free lead cells, the strength is sufficient for the cell of the present invention, since the separator in the cell of the invention need not have the same physical strength as in conventional cells. , because the plates have no tendency to settle during the cycle life. Ibke also has the associated problems in connection with conventional rigid grilles and pole bolt constructions.

The cell can be manufactured in a conventional manner, whereby plates and separators are stacked alternately with the desired shape. Such plates and separators can be stacked and pressed to the desired pressure and placed in a container 15, resulting in a conventional construction with parallel plates. Preferred according to the invention, however, is the use of a continuous long single strip of each plate 11 and separator 1a and to helically wind these two materials on themselves in order to achieve an electrical continuity within the plate. The rolling or winding is performed under tension to maintain a compression of the cell contents; A tensile stress as low as 3U, 5 kPa can be used. A winding voltage of about 275 kPa is preferred to enable a slight compression of the separator 11 and to cause the damp plate 10 to connect to the separator. The assembly 16 is wound before the plates have had sufficient time for drying. The helically wound components 16 can be formed into a cylindrical, oval or rectangular shape in order to be able to select the desired final shape. Regardless of the shape of the subassembly 16 prior to drying, the continuous plate structure will be maintained. Separate wire connection ears 17 are then attached to the negative and positive plates.

A superior current distribution is available through the fabrication of the continuous belt. As explained below, it is preferred that separator material 14 extend up and down from the active edges of the positive and negative plates to facilitate the bonding mechanism.

After winding, the next step of the process is a hardening of the plates 11 or a water hardening process, as this step is called in professional circuits. The hardening can conveniently be carried out at a rather low temperature of 35 ° C. It is important, however, that the hardening takes place in a regulated humidity of substantially 100%. During the hardening, PbO is converted to lead hydroxide, which is generally considered to be Pb (OH) 2. In reality, however, a hydrated lead oxide is obtained, whereby the molar volume of the active components in both plates is considerably increased.

After hardening, the dry subassembly 16 is packed by plates 11 and separators under pressure in a container 15, whereby the fabricated components are converted from a non-self-supporting state to a self-supporting compact and uniform state. By enclosing the components under pressure in the container, a construction is obtained in which the plates 11 are at a clear distance from each other, even though they are still very close to each other.

Due to the pressure, the plates ll can not move relative to each other, and the pressure gives a very compact body 16. The compactness reduces the unobstructed position between the plates and tends to give a consistent current distribution between the plates. In the helically wound embodiments, the winding is usually performed by means of a removable mandrel, which results in an open area 35 being provided along the center axis, which is useful for gas delivery, as described below.

The container may consist of an electrically inert material, but it has been found suitable to use electrically conductive containers and lids, in which case the container is lined with an electrically insulating lining material 18, for example polyolefin, polyvinyl chloride or other similar inactive material, which can provide an encapsulation and electrical insulation of the components from the enclosing container 15, if this is electrically active and consists of, for example, steel sheet, which may have been formed into the desired shape. As previously pointed out, it is convenient to shape the cell into any suitable geometric shape, eg cylindrical, rectangular or oval shape. However, it is important that the composite components 16 be enclosed in the container under pressure, and if the container 15 itself consists of an electrically active material, this must be insulated by means of a lining material 18, which is placed immediately on the inside of the lid 19 and the container 15.

Current conductor connections 17 have been placed between suitable plates 11 and connected to metal tabs by a container lid, which is hermetically mounted on the container. If the container consists of an electrically inert material, a similar plastic lid can be used. If an electrically active container is used, the lid 19 can be lined with a material similar to the container lining 18, so that the lining material can be welded together into a coherent structure. The cylinder head has been designed so that it can be pushed down against the assembly 16 consisting of plates and separator, so that this assembly or this package is strongly locked along the axis of the winding and so that some displacement of the assembly or its individual components is prevented. In addition, this cover minimizes the free gas space in the cell.

The "free gas space" is the space present in the cell inside the cell lining, which is occupied by gas. The lid 21 also optionally has a central ventilation pipe 22 and a part of a pressure relief valve 23. In this cell a centrally located ventilation pipe 22 is preferred, since in this way the ventilation outlet can be placed approximately at the center 2ü of the plate 16 and separator package 16 and since it is thereby possible to arrange support devices for the package at the center 17 of the winding. In the event that gas escape would occur through the relief valve 23, the gas must pass out through the central outlet 25 regardless of the position of the cell. Such an outlet path will prevent the effluent gas from bringing with it any remaining free electrolyte, since the free electrolyte cannot accumulate at the center but only at the "bottom" of the cell for gravity.

In such a design as is described in connection with the present invention, the addition of the electrolyte must of course take place in a different manner. Normal types of electrolytes are used, but the electrolyte content is significantly less, so that the cell is more or less "starved" on electrolyte. In other words, it is important to regulate the amount of electrolyte introduced into the cell. The cell must contain enough hydrogen and sulphate ions together with water to support the electrochemical reaction, but no excess electrolyte should be present. In fact, all added electrolyte must be completely absorbed in the separator and in the pores of the plates. Only a small amount or no free electrolyte is located outside the pores 11 of the plates or the inner space of the separator.

As explained below, it is important to maintain a "starvation" electrolyte state to maximize or increase the recombination of oxygen at a negative plate. In addition, free electrolyte would tend to move in the cell depending on the position and orientation of the cell.

To promote the addition of the electrolyte, the addition takes place substantially under vacuum, whereby the cell is mainly evacuated and the electrolyte is added through the central vent hole in the lid. Normally a sulfuric acid electrolyte with a density is 1.3 g per cm; satisfactory and can be added, since the electrolyte is added under the influence of vacuum (negative pressure). The electrolyte essentially fills the cavities in the components but, more importantly, it is substantially completely absorbed by the separator material and the pores of the plates. The cell is now electrolytically completed by applying a rising or constant current charge. In reality, the cell was subjected to heavy overcharging. During this electrolytic completion step, BbS0u and Pb0 in the positive plate will be oxidized to form lead dioxide (PbO2) during the release of oxygen at the positive plate during supercharging. At the negative plate, PbS0u and Pb0 will be reduced to the well-known sponge lead during the release of hydrogen at the negative plate during supercharging.

Negative pressure or vacuum can be re-established to remove free oxygen and hydrogen gases. At this stage, the cell is actually degassed.

While maintaining the degassed condition, the lid is welded to the liner before the central vent hole is closed by a pressure relief valve 23, which may be of the Bunsen type and capable of maintaining at least 69-103 kPa internal pressure. The Bunsen valve consists of an elastomeric or resilient capsule over the central hole, and this capsule is pressed outwards during the pressure relief but is normally kept in the closed state to maintain a higher internal pressure than the ambient atmospheric pressure. A neutralizing material 26, such as sodium bicarbonate, is placed around the pressure relief valve to absorb and neutralize any trapped electrolyte droplets that may escape during any gas pressure relief at excessive pressures.

As can be seen from the preferred embodiment of the invention shown in Fig. 1, a side flange of a plastic liner lid has a niche 27 adjacent the negative connection clamp. Separate from this negative terminal is the positive terminal, which leads out from the connection of the positive plate. At this point, however, there is no unbroken portion on the flange 28 of the plastic liner lid adjacent to the positive clamp. If a metal container 15 is used, the cell cover 19 of metal, preferably steel, is placed above and inside the flange of the central deaeration mechanism; however, the inner surface of the lid is electrically insulated by means of a lining material 21, which may be the same as the lining 18 in the container, if a metal container is used. There is an interruption in the lid lining material 21, at which point the positive connection terminal 31 can be connected with electrical continuity to the lid next to the negative terminal. The liner material extends with an outward flap 28 to electrically insulate the negative clamp from the lid. At this point, however, the negative terminal is electrically connected to the container. If lining material is necessary, for example when a metal container is used, the liner of the lid and the liner of the container are welded together and the upper edge 29 of the container is bent over and around the lid to form a pressure-tight, sealed container. It is convenient and necessary to provide a vent hole 32 in the lid, so that in the event of a serious malfunction of the cell there should be a possibility for an excessive amount of generated gas to be able to escape from the valve devices. The vent hole 32 allows the outlet and prevents the container from breaking due to an excessive increase in pressure. However, due to the use of the valve device 23, the cell will normally operate at a higher pressure than the atmospheric pressure. The gases are retained in the cell but will quickly reconnect to the plate material.

A major advantage of the present invention is the improvement in the rate of oxygen reconnection with the lead sponge in the negative plate. Such reconnection allows the cell to be supercharged without harmful effects. Overcharging is actually desirable in the function of the battery in order for the positive plate to be charged to full capacity after each discharge. Strong overcharging of the positive plate allows a balance in the state of charge of series-connected cells, which also enables higher charging speeds and greater flexibility in charging technology.

In the cell according to the invention, the so-called "oxygen cycle" is used, in which only oxygen is released during overcharging and then re-binds to the negative plate at the same rate, so that no net change in the composition of the cell is obtained. The oxygen cycle requires that no oxygen is released during overcharging and that the oxygen has free access to the negative plate or metallic lead. It is known that oxygen reacts very quickly with lead in the presence of sulfuric acid.

However, the cell of the present invention allows the use of very pure materials in the cell, and therefore the negative plate of the cell will have a much higher capacity (Ah) than the positive plate, since the positive plate of the cell of the invention will be supercharged before the negative plate is fully charged.

This is the reason for the need for clean materials, especially in terms of grid composition. This cell is specially designed for the use of clean grids, since the plates do not have to be self-supporting.

The amount of oxygen released during the life of the cell is small enough to be disregarded for all practical purposes.

Finally, the cell itself is well adapted for oxygen to have free access to the lead. As previously explained, the active lead sponge is exposed at the edges 12 of the negative plate, and these edges 12 are not covered by any excess free electrolyte.

Since the entire electrolyte in this cell is in the separator, only a thin layer of electrolyte will be present on the lead sponge, through which the oxygen must diffuse.

After the lead has reacted with oxygen and bisulphate ions, the lead oxide is reduced back to lead during the normal charging reaction.

For this reason, it is important that the lead fungus within the exposed edges 12 have good ionic contact with the rest of the cell. The cell of the present invention has a distinct advantage over conventional maintenance-free lead-acid cells in that the lead sponge is directly exposed to the oxygen. Other known cells require the use of heavy load-bearing grids with structural elements around the edges, thereby preventing the use of the active edge, which, however, is not the case with the cell of the present invention. the cell according to the invention also increases the binding by operating under elevated pressure. For this reason, the pressure relief valve 23 must be set so that it relieves the pressure at as high a pressure level as possible. The cell of the present invention has the ability to self-adjust the component balance in the cell to some extent. If too much electrolyte is introduced into the cell, the fungus of the negative plate will be covered with an excessively thick electrolyte layer, thereby lowering the reconnection rate. If this happens, the oxygen generated by the reaction will leave the system, thus reducing the electrolyte volume. However, if an excessive reduction in the electrolyte volume occurs, the thinner electrolyte layer on the lead sponge will increase the oxygen diffusion to the sponge.

In this way, a self-balance is maintained, as the electrolyte volume is reduced until the reconnection speed is in balance with the supercharging. If the state of charge in the negative plate is simultaneously excessive, hydrogen will be released and leave the system. A loss of hydrogen will in turn lower the state of charge in the negative plate and thereby return the charge to a state of balance.

The cell is specially adapted for other constructions for increasing the bonding rate by reducing the electrolyte film thickness around the lead particles, thereby reducing the diffusion rate of oxygen through the electrolyte. The helical design of the cell is particularly suitable. The film thickness can be reduced by increasing the effective wetting heat of the separator by adding a small amount of colloidal silica or colloidal polytetrafluoroethylene (commercially available as TEFLONC). Polyfluoroethylene powder from a 1% aqueous solution can be applied to the surface of the edges of the negative plate to increase the wetting heat of the fungus. 0.5% by weight of a hydrophobic paste of polyfluoroethylene can be added directly to the paste of the negative plate.

Such hydrophobic powder is usually added in colloidal size from an aqueous solution. A similar effect of edge area increase can be achieved by arranging capillary gas paths to provide paths for the gas and to wet the sponge surface. Hydrophobic rods of porous non-wettable material can be inserted and placed between the negative plate and the separator. An efficient path will thereby be provided for the oxygen, so that the gas can again react with the surface of the plate. It has been discovered that polytetrafluoroethylene rods as small as 0.030 inches are sufficient to increase gas reconnection.

The central channel 22 has been mentioned previously, in particular in connection with the discharge of excess gases to the relief valve 23. The central relief tube allows a more efficient operation of the cell at an overpressure. The lid preferably has a nozzle with an axial inner opening 25. Preferably there are radially outwardly projecting flanges 33. The nozzle serves the dual purpose of providing a gas flow path for the gas which is found only at substantially the center ZB of the cell. The cell can therefore be used in any position without the departure of trapped electrolyte particles. The flanges 33 also serve as a bracket around which the plate and separator assembly 16 can be wound.

This bracket reduces the likelihood of an inward collapse of the plate and separator assembly 16.

The unique design of the cell according to the invention leads to certain remarkable properties compared to the properties of maintenance-free lead-acid cells currently on the market.

The highly rated maintenance-free lead-acid cell, which had a rated capacity of 2.6 Ah, at 6 V, preferably had a weight of 0.59 kg with a volume of 270 cm 3. Such a battery has a nominal energy density of 26.5 Wh / kg and 0.058 Wh / cm 2. However, a cell constructed according to the present invention with a rated capacity of 2.5 Ah at 2 V, has a weight of 0.18 kg and a volume of 56.0 cm 3 and an energy density of 27.6 Wh / kg or 0.088 Wh / cm3.

The relative capacity at different degrees of discharge is equally striking and clearly shows the advantages of the present invention.

Thus, Fig. Ä shows the relative capacity of typical known maintenance-free lead-acid cells in comparison with the relative capacity of a maintenance-free lead-acid cell according to the present invention.

Fig. 5 clearly and dramatically shows the ability of the maintenance-free cell constructed according to the invention to maintain cell current for relatively long periods of time as a function of the charging current. The cell current is maintained at a constant level for a long period of time, whereas the typical known maintenance-free lead-acid cell exhibits a sharp decrease in the cell current, which falls well below the cell current in the cell of the present invention.

As described above, the cell of the invention has such properties that it can handle a relatively large number of charge) discharge cycles and still maintain a consistent capacity (Ah). This is shown in Fig. 6, where the cell according to the invention is compared with a typical example of a maintenance-free known lead-acid cell. When the cell of the invention is charged at 2, BV for 8 hours and a typical known maintenance-free cell is charged at the same voltage for 16 hours, it can be seen that the cell of the present invention at the end of the hundredth cycle has about 50% more capacity (Ah) than the typical known cell.

Claims (7)

7109853-7 16 PATENT REQUIREMENTS 1. A maintenance-free, normally sealed, electrochemical cell for a lead-acid battery operating without any significant evolution of hydrogen, comprising at least one porous, active mass coated negative plate and at least one porous active mass coated positive plate, both plates having lead grids with high purity, an acid electrolyte, an electrolyte absorbing and retaining separator having high wetting heat and large surface area, and a container encapsulating the plates, separator and electrolyte to provide a uniform self-supporting structure, the total amount of electrolyte being absorbed in the pores of the separator and the plates, so that no free electrolyte is present in the cell, characterized in that the material in the separator (lä) has such a large capillary surface that the electrolyte is almost completely absorbed in the separator and is present in the plates (II), which are in intimate contact with the separator, only as a thin layer on the pore surface without filling the pores of the plates, and is n present in an amount insufficient to fill the pores of the plates. 2. A cell according to claim 1, characterized in that the separator is made of nonwoven fiberglass material with microfibers. 3. A cell according to claim 1, characterized in that the separator is made of nonwoven glass fiber material having a fiber diameter of from about 0.2 to about 10 microns. 4. A cell according to claim 3, characterized in that the glass fibers have a surface area in the range from about 0.1 to about 20 m 2 / g of silica. Cell according to one of the preceding claims, characterized in that the glass fiber separator has a porosity of 85-95%. Cell according to one of the preceding claims, characterized in that the grid is non-self-supporting and has a purity of at least 99.9% with a maximum calcium content of 0.03%. Cell according to any one of the preceding claims, characterized in that separator material is placed between the positive and negative plates before insertion into the container, the plates and the separator material between them being strongly and helically wrapped in a spiral body. . in ÅNFÖRDÅ PUBLICATIONS: Sweden 302 319 (H01m 39/00) Great Britain 1,032,852 US 3,085,126 (136-146), 3,170,819 (136-6)