Separator, accumulator cell and lead-acid battery

Abstract

Separator for a lead-acid battery cell, comprising a substrate made of a textile fabric, wherein the substrate carries a microporous mass, characterized in that the substrate and mass are PVC-free.

Description

The invention relates to a separator for a lead-acid battery cell. Furthermore, the invention relates to a lead-acid battery cell and a lead-acid battery. Lead-acid battery cells generally consist of positive and negative electrode plates and an electrolyte. The active material, i.e., the material involved in the chemical reaction, is lead dioxide (PbO2) in the case of the positive electrode and lead (Pb) in the case of the negative electrode. The electrolyte is dilute sulfuric acid (H2SO4). A lead-acid battery consists of several electrically connected lead-acid cells. During discharge of a lead-acid battery, lead, lead dioxide, and sulfuric acid react to form lead sulfate (PbSO4) and water (H2O). During charging, the processes are reversed, meaning lead sulfate and water react again to form lead, lead dioxide, and sulfuric acid. Unlike other battery types, the electrolyte participates in this reaction. An undesired side reaction occurs when water (H2O) decomposes into oxygen (O2) and hydrogen (H2). Lead-acid batteries typically consist of multiple positive and negative electrode plates. Electrode plates of the same polarity are connected to each other via terminal blocks or bridges. Separators are generally provided between the electrode plates to prevent contact between the differently polarized plates and thus a short circuit. At the same time, however, the separators must allow the migration of ions involved in the reaction. They must therefore be electrically insulating on the one hand and ion-permeable on the other. In addition, they should be acid- and oxidation-resistant. Suitable materials for lead-acid batteries include, for example, polyethylene (PE), polyvinyl chloride (PVC), or phenolic resins. The components of lead-acid batteries are typically housed in plastic casings consisting of a base and a lid. The terminals must extend through the lid. This is also known as a terminal bushing. The terminal bushing must be as electrolyte-tight as possible. Different lead-acid battery designs are distinguished depending on the structure of the positive and negative electrode plates. In the GroE design (acronym for large surface plates, close installation) according to DIN 40 738, the positive electrode plate initially consists of a pure lead plate with a lamellar surface structure. Through formation processes, the positively active mass PbO2 is then formed on the lamellae. The negative electrode plates are cast grids made of lead or a lead alloy. Other types include, for example, the OPzS (Local Fixed Armor Plate Special Separation) and the OCSM (Local Fixed Copper (Cu) Expanded Metal), in which the positive plates are tubular plates with a lead-antimony alloy as the lead core. The GroE, OPzS, and OCSM battery types are generally designed as sealed batteries. In these sealed batteries, the electrolyte is liquid or non-impregnated, and, as mentioned previously, oxygen or hydrogen gas is produced at the electrodes through a decomposition reaction. This gas must be vented from the battery casing via plugs. Since decomposition also results in water loss, water must be added occasionally. Unlike sealed batteries, there are also sealed batteries in which the electrolyte is immobilized as a gel or in a fleece. This prevents the oxygen produced from escaping, allowing it to migrate to the negative plate where it reacts to form lead oxide. The formation of hydrogen is thus suppressed. An example of a sealed design is the OPzV (Local Fixed Armored Plate Sealed). The advantages of GroE batteries include high corrosion resistance and a long design life. They are particularly suitable for short, high-current discharges and therefore for emergency power supply in power plants, for example. In the event of a malfunction, GroE batteries thus safeguard, for example, the control systems of a power plant and supply cooling and lubrication pumps. Although lead-acid batteries, especially GroE batteries, have proven their worth in practice, there is still room for improvement. It has been shown that, in particular, large-capacity batteries (GroE batteries) cannot provide the expected performance over their comparatively long service life. This results in an undesirable loss of performance that cannot be explained by the known aging processes and their expected effects within the battery or battery cell. The invention is therefore based on the objective of preventing the power loss that occurs within the accumulator cells of a lead-acid battery, in particular a GroE accumulator. To solve the problem, the invention first proposes a separator for a battery cell of a lead-acid battery, comprising a substrate made of a textile fabric, wherein the substrate carries a microporous mass, characterized in that the substrate and microporous mass are PVC-free. It has been found that PVC-containing separators used in the prior art for lead-acid batteries, particularly GroE batteries, are the cause of the performance loss. Although the exact mechanism is still unclear, the applicant, without being bound by this theory, assumes that a chemical reaction takes place between the PVC-containing separator and sulfuric acid, which is used as an electrolyte in lead-acid batteries, and that this leads to the undesirable, continuous release of chloride species. This instability of the PVC structure appears to be the cause of the performance loss. This is because these performance losses and corrosion phenomena were successfully prevented when using the PVC-free separator according to the invention. Furthermore, a certain relationship between the acid density and the separator material seems to exist.This allows for particularly good results in maintaining performance and preventing or weakening battery characteristics within a specific density range of the sulfuric acid used as the electrolyte. Due to this interaction, further synergistic advantages can be achieved by monitoring and, if necessary, readjusting the electrolyte density. Therefore, the invention also includes electrolyte properties precisely tailored to the separator according to the invention and design measures for the battery cell according to the invention that are precisely tailored to the electrolyte, as will be explained in detail below. However, the following section will first describe features of the claimed separator that are inventive and preferred. According to the invention, the substrate is formed as a textile sheet. The term "textile sheet" essentially encompasses all two-dimensional textile products. To manufacture these, several yarns are structured in a defined arrangement relative to one another, or many individual fibers are laid flat on top of each other. Yarn-based textile sheets are subdivided into interlaced yarn systems (knitted fabrics), interlaced yarn systems (woven fabrics), or stretched yarn systems (non-woven fabrics). Fiber-based textile sheets are nonwovens. This provides, on the one hand, a mechanically load-bearing support for the microporous mass. On the other hand, textile sheets themselves possess a certain porosity that is advantageous for the separator's function. The nonwoven design has proven to be a particularly preferred sheet.Given the challenge of eliminating PVC as a material, a sheet structure made of polyester fibers, especially a polyester fleece, has proven particularly advantageous. Unlike PVC-containing substrates known from the prior art, this does not undergo a chemical reaction (especially aging through oxidation) with sulfuric acid. According to a preferred feature of the invention, the substrate layer thickness is between 0.2 mm and 1 mm, particularly between 0.35 mm and 0.9 mm. Such a thickness provides sufficient mechanical stability to support and / or accommodate the microporous mass. Furthermore, at the selected layer thickness, it offers sufficient inherent porosity. This also results in a particularly low electrical resistance at the interface and reduces displacement reactions by the sulfuric acid. Preferably, the electrical resistance is between 0.05 and 0.15 Ωcm². It is important to note that the electrical resistance decreases with decreasing layer thickness. While an electrical resistance of 0.08 Ωcm² exists at a layer thickness of 0.2 mm, it is approximately 0.14 Ωcm² at a layer thickness of 1 mm. The values ​​for acid displacement behave similarly.Preferably, the acid displacement value is between 150 ml / m² and 380 ml / m². This value decreases with decreasing layer thickness. While a layer thickness of 0.2 mm results in a value of 180 ml / m², it is approximately 370 ml / m² at a layer thickness of 1 mm. According to the invention, the substrate carries the microporous mass. During the manufacture of the separator, the substrate is treated with a chemical precursor of the microporous mass, in particular impregnated, preferably saturated, with it. The chemical precursor is then cured to form, in particular three-dimensional cross-linking. Curing preferably takes place under the influence of heat and / or UV light. The microporous mass primarily provides the porosity required for ion exchange through the separator for the battery to function. In addition, it must exhibit the necessary resistance to the sulfuric acid used as the electrolyte. It is particularly preferred that the microporous mass be a thermosetting plastic. It is especially preferred that the thermosetting plastic be a phenol-formaldehyde resin. This material has proven to be particularly advantageous.In particular, the material is completely free of PVC according to the invention. According to the invention, the separator has a specific porosity. This results in a particularly low electrical resistance at the interface and reduces displacement reactions by the sulfuric acid. The porosity is preferably 60% to 80%, more particularly 65% ​​to 75%, and more preferably 70%. The average pore size is preferably 0.3 µm to 0.8 µm, more preferably 0.4 µm to 0.6 µm, and more particularly 0.5 µm. Preferably, the pore size distribution is comparatively small. In particular, at least 90% of all pores lie within the preferred pore size range. This advantageously reduces the risk of short circuits that can occur due to breakthrough of lead and lead oxide particles through the separator. Preferably, the electrical resistance is between 0.05 and 0.15 Ωcm². According to a preferred feature of the invention, the surface of the microporous mass is provided with ribs. This advantageously improves the filling of the battery cell with electrolyte. The ribs serve as flow guides, which is particularly beneficial when filling the cell with liquid electrolyte. Furthermore, surface adhesion is reduced, which is particularly advantageous when filling the cell with a gel-based electrolyte. It is preferred that a plurality of ribs are formed in the microporous mass, uniformly distributed over the entire surface, with the individual ribs running parallel to each other. It is also preferred that the substrate is rectangular, with each rib forming an angle α of equal magnitude between itself and one side of the rectangular substrate.The angle α is preferably between 115° and 75°, in particular 100°, 90° or 80°. According to a further preferred feature of the invention, a glass fiber mat is provided on which the substrate is applied with one of its flat sides. The glass fiber mat serves as an additional mechanical stabilizing element for the substrate supporting the porous mass. The glass fiber mat is also preferably designed to be PVC-free as part of the separator according to the invention. The total layer thickness of the separator is preferably between 2 mm and 5.5 mm. Preferably, the total layer thickness is between 2 mm and 3 mm if the separator consists only of substrate and microporous material. The separator according to the invention is preferably formed with a rectangular contour. It has a height of 85 mm to 1250 mm and a width of 65 mm to 800 mm. By selecting the appropriate size, the separator is suitable for use in GroE battery cells. The invention further relates to a battery cell for a lead-acid battery, comprising a cell housing and a cell cover that seals the cell housing in a fluid-tight manner, wherein positive and negative electrode plates and an electrolyte surrounding the electrode plates are arranged alternately within the cell housing. A separator according to the invention is arranged between each positive and negative electrode plate. It has been shown that, in addition to the specific design of the separator, a specific design of the electrolyte can also influence the previously undesirable power loss. As already indicated, a relationship between the acid density and the separator material also plays a role here. Particularly good results in terms of power retention and the prevention or mitigation of battery characteristics can be achieved within a specific density range of the sulfuric acid used as the electrolyte. Due to this interaction, further synergistic advantages can be achieved by monitoring and, if necessary, readjusting the density of the electrolyte. Therefore, the invention also includes electrolyte properties precisely tailored to the separator according to the invention and design measures for the battery cell according to the invention that are precisely tailored to the electrolyte. In this context, it is preferred if the electrolyte is formed by sulfuric acid with a density between 75 lb / ft3 and 78 lb / ft3, in particular between 76 lb / ft3 and 77 lb / ft3, especially of 76.16 lb / ft3. According to a preferred feature of the invention, it is further provided that the density of the electrolyte can be monitored and / or adjusted during operation of the battery cell. This ensures maximum performance throughout the entire service life of the battery cell in synergistic combination with the separator according to the invention. For this purpose, it is preferably provided that the cell cover has a closable opening, in particular a bore, which provides access to the electrolyte inside the cell housing. Preferably, two openings are provided. The first opening serves to sample the electrolyte to determine the electrolyte density, while the second opening serves to adjust the electrolyte density by adding electrolyte. The first opening has a smaller diameter than the second opening. According to a preferred feature of the invention, the first opening is designed to accommodate a sampling device for taking an electrolyte sample in the unsealed state. For this purpose, the accumulator cell has a measuring device for continuously measuring the electrolyte density, which is in contact with the electrolyte via the opening. The opening can be closed by means of a separate cover. Alternatively, the measuring device itself acts as a fluid-tight seal when inserted. For further evaluation and, if necessary, automated control of the electrolyte density, the measuring device is designed to be in communication communication with an evaluation unit. To simplify the adjustment of the electrolyte density, the cell housing is preferably made of a translucent, particularly transparent, plastic. This allows the electrolyte level to be visually detected. It is further preferred that the cell housing has a scale, particularly a measuring scale, attached to it for quantitatively accurate reading of the electrolyte level. In combination with the electrolyte level visible through the cell housing wall, the scale provides visual information about the current electrolyte level. This also facilitates and improves the accuracy of refilling the electrolyte. The invention also relates to a lead-acid battery formed from a plurality of battery cells according to the invention. For further evaluation and, if necessary, automated control of the electrolyte density and / or the electrolyte level in the individual battery cells, the lead-acid battery has an evaluation unit that is in communication technology connection with the respective measuring devices of the battery cells. Preferably, a control unit is provided with which the electrolyte density and / or electrolyte level can be continuously adjusted to a predefinable target value by comparing an actual value measured by the respective measuring device. The evaluation unit is preferably part of the control unit. Preferably, the control unit is connected to an automatic water supply device, which can be inserted into the second opening of a cell housing for the purpose of adjusting the electrolyte level. According to a preferred feature of the invention, a recombination unit is provided. The recombination unit has a housing that provides an interior space for a precious metal catalyst. The housing also has an opening that provides a flow path to this interior space. During operation of the GroE battery cell, the recombination unit is inserted into the second opening of the housing cover of the cell housing. This creates a flow path between the cell housing and the housing of the recombination unit. When the recombination unit is in use, the gases produced during water decomposition in the GroE battery cell—hydrogen and oxygen—are directed into the interior space of the recombination unit provided by the housing. The gases flow over the precious metal catalyst and are thereby recombined.This process generates water vapor. The water vapor condenses on the inner walls of the housing. The resulting water droplets flow downwards and are returned to the GroE battery cell. The recombination of the gases occurs with an efficiency of up to 98%. The significantly reduced water consumption leads to lower maintenance costs throughout the GroE battery's service life. Furthermore, the reduced gas formation lowers ventilation requirements and operating costs. The recombination unit is preferably interchangeably connected to the second opening. For connecting the automated water supply system, it is designed that it can be removed at least temporarily and then reinserted, or vice versa. The invention is explained below using an exemplary embodiment. Fig. 1 shows a schematic perspective view of an accumulator cell according to the invention; Fig. 1 shows a schematic perspective view of a GroE accumulator cell 1 according to the invention. The accumulator cell 1 has a cell housing 2 and a cell cover 3, which seals the cell housing 2 fluid-tight in the fully assembled state. Within the cell housing 2, positive and negative electrode plates 4 and 5 are arranged alternately. An electrolyte (not shown) is also located within the cell housing 2, which surrounds the electrode plates 4 and 5 in the fully assembled state of the battery cell 1. In this case, the electrolyte is sulfuric acid with a density of 76.16 lb / ft³. Furthermore, a separator 19 according to the invention is arranged between each positive and negative electrode plate 4, 5. Each separator 19 consists of a substrate made of a textile fabric which carries a microporous mass. Both the substrate and the microporous mass are PVC-free. The substrate is a polyester fleece. The substrate layer thickness is 0.4 mm. The total separator layer thickness is 2 mm. The electrical resistance is therefore 0.09 Ωcm². The acid displacement value is 190 ml / m². The substrate supports the microporous mass. In this case, the microporous mass is a thermosetting plastic in the form of phenol-formaldehyde resin. The porosity of separator 19 is 70%. The average pore size is 0.5 µm. The pore size distribution is comparatively small. In particular, at least 90% of all pores lie within the preferred pore size range. The surface of the microporous mass is provided with a plurality of ribs. These are evenly distributed across the entire surface. The individual ribs run parallel to each other. In this case, the substrate (and the separator 19) is rectangular, with each rib forming an angle α of equal magnitude between itself and one side of the rectangular substrate (or the separator). The angle α is optionally 100°, 90°, or 80°. The separator 19 according to the invention is preferably formed with a rectangular contour. Like the electrode plates 4, 5, it has a height of 400 mm and a width of 268 mm. All the above dimensions include possible tolerances in the range between ±0.5 mm and ±2 mm. As can also be seen in Fig. 1, the negative electrode plates 4 on the one hand and the positive electrode plates 5 on the other hand are each electrically contacted with each other, for which purpose pole bridges are provided, namely the pole bridge 6 with respect to the negative electrode plates 4 and the pole bridge 7 with respect to the positive electrode plates 5. By means of the respective pole bridges 6 and 7, the negative electrode plates 4 on the one hand and the positive electrode plates 5 on the other are electrically connected to poles 8, 9, 10 and 11, which pass through openings in the cell cover 3. Thus, a total of four poles are provided, with the negative and positive electrode plates 4 and 5 each being connected to two poles: the negative electrode plates 4 to poles 8 and 9, and the positive electrode plates to poles 10 and 11. The pole bridges 6, 7 are in turn electrically connected to the respective positive and negative electrode plates via current collectors 12, 13, namely with respect to the negative electrode plates 4 the current collector 12 and with respect to the positive electrode plates 5 the current collector 13. The invention also includes such a configuration in which a total of eight poles are provided, wherein the negative and positive electrode plates 4 and 5 are each connected via the associated pole bridges 6, 7 to four positive poles on the one hand and four negative poles on the other. Figure 1 also shows a first closable opening 14 formed in the cell cover 3. The first opening 14 is a bore and serves to provide access to the electrolyte located inside the cell housing 2. The first opening 14 is designed to accommodate a sampling device (not shown) for the purpose of taking an electrolyte sample in the unsealed state. The device features two openings, 14 and 15. The first opening, 14, is used for sampling the electrolyte to determine its density, while the second opening, 15, is used to adjust the electrolyte density by adding more electrolyte. The first opening, 14, has a smaller diameter than the second opening, 15. For this purpose, the cell cover 3 has a second opening 15, which is closed with an insert 16, but not in a fluid- and / or gas-tight manner, so that undesirable overpressure formations in the cell housing 2 are avoided, especially during a recharging process. In this case, poles 8, 9, 10 and 11 each have an insert 17 made of copper and / or a copper alloy. This advantageously results in a reduced internal resistance compared to a pole design without an insert. The electrical connection between the electrode plate pairs and their respective poles 8, 9, 10 and 11 is preferably made of a highly conductive material or at least has areas with inserts of a highly conductive material. This also minimizes the internal resistance. To simplify the adjustment of the electrolyte density, the cell housing 2 is preferably made of a translucent, in particular transparent, plastic. This allows the electrolyte level to be visually detected. Furthermore, the cell housing is equipped with a measuring scale 18 for precise quantitative reading of the electrolyte level. The measuring scale 18, in combination with the electrolyte level visible through the cell housing wall, provides visual information about the current electrolyte level. This allows for the identification of when refilling is necessary and also facilitates and improves the accuracy of electrolyte refilling. A large number of large-capacity accumulator cells 1 according to Fig. 1 can be combined in rows and columns and electrically connected to form a large-capacity accumulator. The accumulator cells 1 combined in this way are arranged within a larger accumulator housing. The accumulator cells 1 are arranged such that they are spaced apart from each other in rows and / or columns, leaving a gap between them. This allows a cooling current to flow between the accumulator cells 1, which, under normal operating conditions, leads to the cooling of the accumulator cells 1. Reference sign 1 Large accumulator cell 2 Cell housing 3 Cell cover 4 Negative electrode plate 5 Positive electrode plate 6 Terminal bridge 7 Terminal bridge 8 Pole 9 Pole 10 Pole 11 Pole 12 Current collector 13 Current collector 14 First opening 15 Second opening 16 Insert 17 Pole insert 18 Measuring scale 19 Separators

Claims

Separator for a lead-acid battery cell, comprising a substrate made of a textile fabric, wherein the substrate carries a microporous mass, characterized in that the substrate and mass are PVC-free. Separator according to claim 1, characterized in that the textile surface structure is formed as a nonwoven fabric. Separator according to one of the preceding claims, characterized in that the textile surface structure is formed from polyester fibers. Separator, characterized in that the layer thickness of the substrate is between 0.2 mm and 1 mm, in particular between 0.35 mm and 0.9 mm. Separator according to one of the preceding claims, characterized in that the microporous mass is a thermosetting plastic. Separator according to claim 5, characterized in that the thermosetting plastic is a phenol-formaldehyde resin. Separator according to one of the preceding claims, characterized in that the surface of the microporous mass is provided with ribs. Separator according to claim 7, characterized in that a plurality of ribs are formed in the microporous mass, which is arranged uniformly over the entire surface, wherein the individual ribs run parallel to each other. Separator according to one of the preceding claims 7 or 8, characterized in that the substrate is rectangular, wherein the ribs each form an angle α of equal magnitude between themselves and a side of the rectangular substrate. Separator according to claim 9, characterized in that the angle α is between 115° and 75°, in particular 100°, 90° or 80°. Separator according to one of the preceding claims, characterized by a porosity of 60% to 80%, in particular 65% to 75%, preferably 70%. Separator according to one of the preceding claims, characterized by an average pore size of 0.3 µm to 0.8 µm, preferably 0.4 µm to 0.6 µm, in particular 0.5 µm. Separator according to one of the preceding claims, characterized by a glass fiber mat on which the substrate is applied with one of its planar sides. Accumulator cell for a lead-acid battery, comprising a cell housing and a cell cover that seals the cell housing in a fluid-tight manner, wherein positive and negative electrode plates and an electrolyte surrounding the electrode plates are arranged alternately within the cell housing, wherein a separator according to one of claims 1 to 13 is arranged between each positive and negative electrode plate, Accumulator cell according to claim 14, characterized in that the electrolyte is formed by sulfuric acid with a density of 76.16 Ib / ft3. Accumulator cell according to one of the preceding claims 14 or 15, characterized in that the cell cover has a closable opening, in particular a bore, which provides access to the electrolyte located inside the cell housing. Accumulator cell according to claim 16, characterized in that the opening is designed to accommodate a sampling device for the purpose of taking an electrolyte sample in the unsealed state. Accumulator cell according to one of the preceding claims 16 or 17, characterized by a measuring device for continuous measurement of the electrolyte density, which is in contact with the electrolyte via the opening and closes the opening in a fluid-tight manner, wherein the measuring device is in communication-technical connection with an evaluation unit. Accumulator cell according to one of the preceding claims 14 to 18, characterized in that the cell housing is made of a translucent, in particular transparent, plastic. Accumulator cell according to claim 19, characterized in that a scale is attached to the cell housing which provides information about the current electrolyte level. Lead-acid battery formed from a plurality of battery cells according to one of claims 14 to 20.

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