Accumulator cell and lead-acid battery

Abstract

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 the positive and negative electrode plates are each electrically connected to at least one common pole by means of respective pole bridges, characterized in that the positive pole, which is connected to the positive electrode plates via the associated pole bridge, is made of a lead alloy in the form of hard lead.

Description

The invention relates to a battery cell for a lead-acid battery 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 types of lead-acid batteries are distinguished depending on the design 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 consists of a pure lead plate with a lamellar surface structure. The positive active material PbO2 is then formed on the plates through the so-called formation process. The negative electrode plates are cast grids made of lead or a lead alloy. Other cell types include, for example, OPzS cells (stationary armor plate special separation) and OCSM cells (stationary copper (Cu) expanded metal), in which the positive plates are tubular plates whose core grids are cast from a lead-antimony alloy. Lead-coated stationary copper expanded metal grids (OCSM) are also used for industrial negative plate grids. The GroE and OPzS battery types, with standard drop-cast or die-cast grids, are generally designed as sealed batteries. In sealed batteries, the electrolyte is in liquid form and freely mobile, meaning it is not confined. As mentioned previously, oxygen and hydrogen gas are produced at the electrodes through the decomposition of water. This gas must be vented from the battery casing via plugs. Since water is also lost through decomposition, water must be added occasionally. Unlike sealed batteries, there are also sealed batteries in which the electrolyte is contained as a gel or in a fleece. The oxygen produced does not escape but diffuses to the negative plate, where it reacts to form water and lead sulfate. This suppresses the formation of hydrogen. An example of a sealed design is the OPzV cell (Loaded Fixed Armor Plate). The advantages of GroE batteries are their high corrosion resistance and long service 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 safeguard, for example, the control systems of a power plant and supply cooling systems via emergency power circuits. Although lead-acid batteries, especially GroE batteries, have proven their worth in practice, there is still room for improvement. Lead-acid batteries tend to short circuit after a certain operating period, which can occur when conductive corrosion particles detach from the battery terminal of the positive plate and contact adjacent positive and negative electrode plates located inside the battery housing, thus short-circuiting them. The fundamental problem is that lead-based positive electrode plates are subject to an aging process. Even under normal use, corrosion occurs, resulting in the formation of lead dioxide. Lead dioxide is more voluminous than the lead substrate, so over time, corrosion causes it to expand. This expansion creates shear forces that cause the lead-based terminal bridge to flake or peel away. This means that lead particles can literally break off from the terminal or terminal bridge and then fall downwards into the battery casing due to gravity. This effect is particularly detrimental to large-capacity batteries (GroE batteries), as these are designed for a long service life of 20 years or more. Therefore, the negative effects of corrosion have a significant impact on the longevity required of GroE batteries. For reasons of reduced internal resistance, it is preferred in the prior art to use pure lead in order to achieve high electrical conductivity and corrosion resistance. Preferably, both the positive electrode plate and the bridges electrically contacting the electrode plates are made of pure lead. The invention is therefore based on the objective of providing an accumulator cell for a lead-acid battery and a lead-acid battery with such accumulator cells in which the known corrosion effects and / or their effects on the galvanic system of the accumulator cell are prevented. To solve the problem, the invention initially proposes an 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 the positive and negative electrode plates are each electrically connected to at least one common pole by means of respective pole bridges, wherein the positive pole which is connected to the positive electrode plates via the associated pole bridge is formed from a lead alloy in the form of hard lead. The design according to the invention advantageously provides a pole that is significantly more resistant to aging than the previously used pole made of pure lead. According to the invention, the pole of a positive plate is not made of pure lead, but of a lead alloy, in order to minimize flaking or peeling due to corrosion. Preferably, a material separation between pure lead and the lead alloy occurs at the transition between the bridge and the pole. The bridge is still made of pure lead, while the pole is not, but instead of a lead alloy. It has been found that hard lead possesses sufficient conductivity, so that any difference in the characteristics of the accumulator cell during practical operation, if any, is negligible. Thus, for the first time, an accumulator cell and a lead-acid battery can be provided whose poles remain corrosion-resistant even over a comparatively long period. The disadvantage known from the prior art, in which short circuits between positive and negative electrode plates become virtually unavoidable after a certain time due to chafing of the pole material, is therefore avoided or at least delayed. Particularly with regard to large-capacity batteries (GroE batteries), this results in a significant increase in service life due to a substantial reduction in the tendency to short-circuit. While GroE batteries known from the prior art regularly fail to achieve their planned long service life of 20 years or more due to the aforementioned disadvantages, this is no longer the case for GroE batteries according to the invention with battery cells according to the invention. Instead, batteries designed according to the invention can be used for much longer periods. According to a preferred feature of the invention, a pole bridge is provided which is significantly more resistant to aging than the pole bridge used previously. Prior art pole bridges were manufactured, among other materials, from a lead-antimony alloy. It has now been found that the use of pure lead for the pole bridge on the one hand and hard lead for the pole on the other produces an unexpected synergistic effect with regard to the overall improvement of corrosion resistance. According to a preferred feature of the invention, the at least one pole bridge, which connects the positive electrode plates to the pole, is therefore made of pure lead. This ensures high electrical conductivity in the connection path between the electrode plates and the pole.Furthermore, it has been shown that the negative corrosion effects with regard to pure lead are almost exclusively limited to the pole, while the pole bridge is not affected. According to the invention, the positive pole is formed from hard lead. Hard lead is a lead-antimony alloy with a comparatively low antimony content. Preferably, hard lead consists of the following components: -1 wt.% to 13 wt.% antimony; Residual lead. It has been found that the required mechanical strength and corrosion resistance are achieved when the hard lead consists of the following components: -4 wt.% to 5 wt.% antimony; Residual lead. For the purposes of the invention, the term “residual lead” includes not only lead as the main alloying component, but can also include alloying components such as As, Se, Sn and Cu and impurities which, in the case of impurities, can either not be removed from the alloy and / or the individual components at all, or not in an economically viable way, particularly due to the respective method of production of antimony and / or lead. These traces, which may be present individually or cumulatively in the hard lead alloy, include: -Max 0.04 wt% bismuth, -Max 0.01 wt% silver, -Max 0.001 wt.% Cadmium, -Max 0.001 wt% iron, -Max 0.001 wt.% zinc, -Max 0.001 wt% tellurium and / or -Max 0.001 wt% nickel It is preferred that the combined weight fraction of the traces of other metals does not exceed 0.4 wt.%. According to a preferred feature of the invention, the pole bridge, which connects the positive plates to the positive pole, and the positive pole are metallurgically bonded. This bond is achieved by a metallic connection. Preferably, the material of the pole bridge and the material of the pole form an intermetallic phase at the interface. Preferably, the connection is formed by welding. The disadvantages known from the prior art, due to their long service life, particularly affect accumulator cells for GroE accumulators and thus GroE accumulators themselves. Specifically, a GroE accumulator cell is therefore subject to this claim. This cell is characterized in particular by a specific size and area of ​​its electrode plates. This is because this type of accumulator must be able to deliver a consistently high power output over a long period of time in order to meet the technical requirements of its intended use. In this context, it is preferred that the positive and negative electrode plates each have a height of 200 mm to 500 mm, in particular 220 mm to 420 mm, preferably 229 mm to 400 mm, and more preferably 229 mm or 400 mm.Furthermore, it is preferred that the positive and negative electrode plates each have a width of 120 mm to 300 mm, in particular 130 mm to 270 mm, preferably 139 mm to 268 mm, and more preferably 136 mm or 268 mm. Two types of construction with different electrical performance characteristics are particularly distinguished. Firstly, a GroE accumulator cell with electrode plates having a height of 229 mm and a width of 136 mm, and secondly, a GroE accumulator cell with electrode plates having a height of 400 mm and a width of 268 mm. All the above dimensions include possible tolerances in the range of ±0.5 mm to ±2 mm. In addition to or as an alternative to selecting the pole material according to the invention, the effects of the aging process of the pole bridge or pole material can be further reduced or prevented, either solely or additionally, by providing a retention device that mechanically captures and thus retains the flaking particles. In the simplest case, nets or grids are used whose mesh size is selected such that particles large enough to cause short circuits are retained. Smaller particles, which are not large enough to short-circuit two adjacent electrodes, fall through and can thus pass between two plates to the bottom of the container. Regarding the mesh or grid designs for containment, two embodiments are conceivable, which can also be combined. The first embodiment uses mesh tubes that are slipped over the respective pole. The second embodiment uses plate-shaped meshes or grids that completely cover the housing cross-section below the respective pole bridges and thus above the electrode plates. In this context, it is preferable in the second embodiment to choose a self-supporting grid structure rather than a mesh device. The reason for the preferred or alternative retention device is that it has been shown that the use of optimized hard lead cannot completely rule out skimming or flaking of the pole as a result of corrosion. Therefore, according to the invention, alternatively or preferably at least a retention device is provided which serves to catch particles flaked off from the positive pole and thus prevent short-circuit-causing contact with the electrode plates. According to a preferred feature of the invention, the retention device is formed by a mesh and / or a grid. Preferably, the mesh and / or grid are made of an electrically insulating material. More preferably, the mesh and / or grid are made of a material resistant to sulfuric acid. It is preferred that the mesh size of the net and / or grid is designed such that short-circuit-causing particles above a certain size are retained, while non-short-circuit-causing particles can pass through the retention device unhindered. This results in particle retention according to the size exclusion principle. This measure is based on the understanding that particles cleaved from the pole or pole bridge are only capable of generating a short circuit above a certain size. This occurs when, due to their size, they are able to bridge at least the distance between two adjacent positive and negative electrode plates. Smaller particles, on the other hand, cannot cause short circuits in the first place. According to a first preferred embodiment, the retaining device is formed in the form of a mesh tube surrounding the positive pole. According to a further preferred embodiment, the retaining device is formed in the form of a planar mesh and / or grid, which is arranged, and in particular stretched, in the vertical direction between the positive pole, in particular the associated pole bridge, on the one hand, and the electrode plates on the other. Preferably, it is attached to fastening devices provided by the cell housing for this purpose. The fastening devices can, in particular, be formed by hooks that interact with, and in particular engage in, corresponding hook receptacles formed on the mesh or grid. It is preferably provided that the mesh and / or grid extends with its respective flat side substantially over the entire cross-sectional area of ​​the cell housing. This ensures that particles flaking off from the terminal do not fall past the retention device into the plate space. This can occur, for example, when the accumulator cell is moved during transport or maintenance. The disadvantages known from the prior art, due to their long service life, particularly affect accumulator cells for GroE accumulators and thus GroE accumulators themselves. Specifically, a GroE accumulator cell is therefore subject to certain demands. As already described, this cell is characterized by a specific size and surface area of ​​its electrode plates. Furthermore, it is characterized by comparatively long service lives of more than 20 years. For this reason, it has proven advantageous for GroE accumulator cells if the retention device is designed as a self-stabilizing grid. This ensures that the retention device can fulfill its function throughout its entire service life. In addition to the accumulator cell according to the invention, the invention also relates to a lead-acid accumulator which is formed from a plurality of accumulator cells according to the invention. While individual battery cells may be sufficient for some applications in terms of their performance and electrical characteristics, this is generally not the case. Instead, the performance and characteristics required for a given application can be easily scaled by combining multiple battery cells into a larger lead-acid battery. This connection is made via the respective terminals of the individual battery cells. Preferably, terminal connectors are used for this purpose, ideally in the form of cables with corresponding terminals. To reduce the tendency for short circuits, two synergistic measures are proposed, which are implemented in combination. Firstly, the pole material is changed from pure lead to the significantly more corrosion-resistant hard lead alloy, and secondly, a retention device is installed that separates and retains flaking pole particles according to the size exclusion principle. The invention is explained below with reference to an exemplary embodiment. Fig. 1 shows a schematic perspective view of an accumulator cell according to the invention; Fig. 2 shows a schematic perspective view of the interior of the accumulator cell. 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, negative and positive electrode plates 4 and 5 are arranged alternately, with a separator 17 interposed between each plate, as can be seen particularly in the illustration in Fig. 2. Furthermore, an electrolyte, not shown in detail in the figures, is arranged within the cell housing 2 and surrounds the electrode plates 4 and 5 in the fully assembled state of the accumulator cell 1. Electrode plates 4 and 5 have a height of 400 mm and a width of 268 mm. All dimensions given above include possible tolerances in the range of ±0.5 mm to ±2 mm. As can also be seen in Fig. 2, 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 pole bridge 6 with respect to the negative electrode plates 4 and 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. This relationship is also particularly evident from the illustration in Fig. 2. The pole bridges 6, 7 are in turn electrically connected to the respective positive and negative electrode plates via current collectors 12, 13, also called plate vanes, namely with respect to the negative electrode plates 4 the current collectors 12 and with respect to the positive electrode plates 5 the current collectors 13. The invention also includes such a configuration in which a maximum 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. Since the water content in the electrolyte decreases during normal operation of the battery cell 1, it is necessary to refill the water from time to time. For this purpose, the cell cover 3 has a refill opening 14, which is sealed with an insert, but not in a fluid- and / or gas-tight manner, so that undesirable overpressure build-up in the cell housing 2 is prevented, especially during a recharging process. In this case, poles 8, 9, 10 and 11 each have an insert 15 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. In this case, the pole bridges are made of pure lead. The positive poles 10 and 11, on the other hand, are made of hard lead with a composition of 4.0 wt.% to 4.5 wt.% antimony and a residual lead. The term "residual lead" may also include traces of other metals, the combined weight of which, however, does not exceed 0.4 wt.%. The terminal bridges 6, 7 provided according to the invention are thus significantly more resistant to aging than the previously used hard lead. Consequently, flaking or peeling due to corrosion can be minimized. This results in a material separation between pure lead and lead alloy at the transition between terminal bridge 7 and the respective terminal 10, 11 made of hard lead (Pb-Sb). The disadvantage known from the prior art, in which short circuits between positive and negative electrode plates 4, 5 almost inevitably occur after a certain time due to peeling terminal and terminal bridge material, is therefore avoided or at least delayed. For the present GroE accumulator cell 1, this results in a significant increase in service life by substantially reducing the tendency for short circuits. In addition to the selection of the pole material according to the invention, the accumulator cell 1 has a retention device in the form of a self-stabilizing grid 16. In Fig. 2, the grid 16 is shown only in its front section to allow a clear view of the electrode plates 4, 5. In fact, however, the grid 16 extends over the entire length of the cell housing 2. Furthermore, it can be seen that the grid 16 is arranged above the electrode plates 4, 5 and below the poles 10, 11, as well as below the terminal bridges 6, 7. In the lateral direction, the grid 16 extends on both sides to below the respective terminal bridge 6, 7. In the vertical direction, the grid 16 is therefore arranged between the terminal bridges 6, 7 on the one hand and the electrode plates 4, 5 on the other. The grid 16 according to the invention serves the purpose of mechanically capturing and thus retaining the particles flaking off from the poles 10, 11 – although this is greatly reduced by the material selection according to the invention, but possibly still presently. The grid spacing of the grid 16 is selected such that flaking particles large enough to cause a short circuit are retained. Smaller particles, which are not large enough to short-circuit two adjacent electrode plates 4, 5, fall through the mesh of the grid 16 and can thus pass between two electrode plates 4, 5 to the bottom of the cell housing 2. Furthermore, the grid 16 must be made of an electrically insulating material, in particular a plastic. The material of the grid 16 is also resistant to the electrolyte formed from dilute sulfuric acid. The disadvantages known from the prior art, due to their long service life, particularly affect the present GroE accumulator cell and the GroE accumulators derived from it. While nets can, in principle, also be used as a containment device, the present design of the containment device as a self-stabilizing grid 16 ensures that the containment device can fulfill its function over the entire service life. The present containment device is therefore maintenance-free. However, if appropriate maintenance intervals are provided, containment devices in the form of nets can also be used for GroE accumulator cells 1. A large number of large-capacity (GroE) accumulator cells 1, as shown in Fig. 1, can be combined in series 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 in rows, spaced apart from each other. This allows a cooling current to flow between the accumulator cells 1, which, under normal operating conditions, leads to 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 Refill opening 15 Insertion layers 16 Grid 17 Separator

Claims

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 the positive and negative electrode plates are each electrically connected to at least one common pole by means of respective pole bridges, characterized in that the positive pole, which is connected to the positive electrode plates via the associated pole bridge, is made of a lead alloy in the form of hard lead. Accumulator cell according to claim 1, characterized in that the at least one pole bridge connecting the positive electrode plates to the pole is made of pure lead. Accumulator cell according to one of the preceding claims, characterized in that hard lead is formed from: -1 wt.% to 13 wt.% antimony; Residual lead. Accumulator cell according to one of the preceding claims, characterized in that hard lead is formed from: -4 wt.% to 5 wt.% antimony; Residual lead. Accumulator cell according to one of the preceding claims, characterized in that the pole bridge and the positive pole are connected to each other by a material bond, wherein the material bond is formed by an intermetallic phase. Accumulator cell according to one of the preceding claims, characterized in that the positive and negative electrode plates each have a height of 200 mm to 500 mm, in particular 220 mm to 420 mm, preferably 229 mm to 400 mm, more preferably 229 mm or 400 mm. Accumulator cell according to one of the preceding claims, characterized in that the positive and negative electrode plates each have a width of 120 mm to 300 mm, in particular 130 mm to 270 mm, preferably 139 mm to 268 mm, more preferably 136 mm or 268 mm. Accumulator cell according to one of the preceding claims, characterized by at least one retention device which serves to catch particles flaked off from the positive pole and thus prevent contact with the electrode plates. Accumulator cell according to claim 8, characterized in that the retention device is formed by a net and / or a grid. Accumulator cell according to one of the preceding claims 8 or 9, characterized in that the mesh size of the net and / or grid is designed such that short-circuit-causing particles above a certain size are retained, while non-short-circuit-causing particles can pass through the retention device unhindered. Accumulator cell according to one of the preceding claims 8 to 10, characterized in that the retention device is formed in the form of a mesh tube surrounding the positive pole. Accumulator cell according to one of the preceding claims 8 to 11, characterized in that the retention device is formed in the form of a planar net and / or grid, which is arranged, in particular stretched, in the vertical direction between the positive pole, in particular the associated pole bridge, on the one hand and the electrode plates on the other. Accumulator cell according to one of the preceding claims 8 to 12, characterized in that the mesh and / or grid extends with its respective planar side substantially over the entire cross-sectional area of ​​the cell housing. Accumulator cell according to one of the preceding claims 8 to 13, characterized in that the retention device is formed as a self-stabilizing grid. Lead-acid battery formed from a plurality of battery cells according to one of claims 1 to 14.

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