Abstract:
A lead acid battery has a positive plate containing antimony, a negative plate; and a separator containing an organic compound capable of capturing metal ions. The organic compound is preferably lignin.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to improvement of a lead acid battery. 
     2. Description of the Related Art 
     In a conventional liquid lead acid battery, a lead-antimony alloy grid is used as a positive electrode grid. If antimony is contained in a positive plate, however, antimony is eluted from a positive electrode grid body during charge/discharge operation. The eluted antimony moves in electrolyte, and precipitates on a negative plate to thereby reduce hydrogen overvoltage. Accordingly, the yield of hydrogen due to water decomposition increases, so that the water loss characteristic is lowered. Therefore, in some lead acid batteries, a lead-calcium alloy is used for a grid body. However, when charge and discharge cycles including deep discharge are performed with a lead-calcium alloy, a lead sulfate which is a dense insulator is generated in the interface between the grid and active materials during discharge, so that the capacity is reduced in early stages, or the connection among lead dioxide particles which are active materials is reduced, so that the active materials become easy to come off. In addition, in comparison with a lead-antimony alloy, a lead-calcium alloy is so soft that shortcircuit may be caused easily by extension of the grid. 
     If antimony is added to the positive plate, the connection strength among lead dioxide particles is increased. Therefore, there is no fear of reduction of the capacity in early stages or coming-off of the active materials. Further, if a lead-antimony alloy is used for the positive grid body, a corrosion layer generated in the interface between the grid and the active materials is made porous, and shortcircuit due to extension of the grid is hardly generated. 
     In addition, a retainer type battery which is one of valve-regulated lead acid batteries of such a type that oxygen gas generated during charge is absorbed in a negative electrode is configured such that a mat-like separator made from fine fibers (for example, a glass separator) is inserted between a positive plate and a negative plate for retaining sulfuric acid electrolyte required for discharge, and for separating both electrodes from each other. 
     If antimony is added to a positive plate, the hydrogen overvoltage of a negative plate is reduced by the same reason as mentioned above, so that the yield of hydrogen by water decomposition increases. As a result, fatal dry-up occurs to make the battery dead. Therefore, in the conventional retainer valve-regulated lead acid battery, a lead-calcium alloy is used for the positive electrode grid, and antimony is not contained in the positive plate. 
     Therefore, a lead-calcium alloy is used for a grid body in retainer batteries. However, for the same reason as mentioned above, in such retainer batteries, there are problems that the cycle endurance is short, and shortcircuit is caused easily. 
     If antimony is added to a positive plate, for example, by using a lead-antimony alloy for the positive electrode grid, and if antimony can be prevented from moving from the positive electrode to the negative electrode, it is possible to manufacture lead acid batteries superior in the cycle life performance. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a lead acid battery which is superior in the charge and discharge cycle endurance. 
     According to a first aspect of the present invention, antimony is contained in a positive plate, and an organic matter capable of capturing metal ions is contained in a separator between the positive plate and a negative plate. 
     According to a second aspect of the present invention, in the lead acid battery according to the first aspect, the organic compound is lignin. 
     According to a third aspect of the present invention, in the lead acid battery according to the second aspect, the lignin contained in the separator is thiolignin. 
     According to a fourth aspect of the present invention, in the lead acid battery according to the second aspect, the average particle size of the lignin contained in the separator is not larger than 10 μm according to SEM observation. Further, the particle size of the lignin contained in the separator is not less than 0.05 μm. Such a small particle lignin having a particle size less than 0.05 μm is difficult to manufacture and is hard to be held by a separator. Accordingly, such a small particle lignin is not applied for a practical use. 
     According to a fifth aspect of the present invention, in the lead acid battery according to the second aspect, the BET specific surface of the lignin contained in the separator is not smaller than 2.5 m 2 /g. In this case, the BET specific surface of the lignin contained in the separator is not larger than 500 m 2 /g. 
     According to a sixth aspect of the present invention, in the lead acid battery according to the second aspect, the lignin contained in the separator is contained in a condition that the lignin is carried by granular silica. 
     According to a seventh aspect of the present invention, in the lead acid battery according to the first aspect, the lead acid battery is a retainer-type valve-regulated lead acid battery in which electrolyte is held in a mat-like separator, and oxygen gas generated in a positive electrode during charging is absorbed in a negative electrode; and antimony in a range of 50 ppm to 8,000 ppm is contained in the positive plate. 
     According to an eighth aspect of the present invention, in the lead acid battery according to the seventh aspect, antimony in a range of from 0.5% to 1.7% is contained in a positive electrode grid alloy. 
     According to a ninth aspect of the present invention, in the lead acid battery according to the seventh aspect, the separator has a multi-layer structure of not less than two layers, lignin is contained in at least one of the separator layers which are not in contact with the positive plate, the lignin content in the at least one separator layer being largest among the lignin contents in all the separator layers. 
     According to a tenth aspect of the present invention, in the lead acid battery according to the ninth aspect, the lignin content in the separator layer which is not in contact with the positive plate or a negative plate is largest among the lignin contents in all the separator layers. 
     Since antimony is contained in the positive plate, it is possible to prevent early-stage capacity reduction of the positive plate, coming-off of the active materials, and extension of the grid. If the material for capturing antimony ions is contained in a separator layer between the positive and negative plates, antimony can be captured in the separator layer. Therefore the increase of water decomposition can be prevented as mentioned above. Accordingly, features of maintenance free and water supply free can be given to the battery in the same manner as a lead acid battery containing no antimony in a positive plate. It was found that there was a large effect to prevent antimony from moving from the positive electrode to the negative electrode when lignin was contained, as the antimony ion capturing materials, between the positive and negative electrodes. In addition, it was found that a larger effect to capture antimony ions could be obtained when the contained lignin was, for example, made fine in its particle size, or carried by granular silica, so that the specific surface was made larger. Further, if the separator between the positive and negative electrodes is designed to have a multi-layer structure of two or more layers and if one of the separator layers which is in contact with the positive plate contains lignin the content of which is smaller than that in other separator layers, it is possible to restrain a bad influence due to decomposition of lignin in the positive plate during charging the battery. In addition, if the content of lignin in the separator layer which is in contact with the negative plate is made smaller than that in other separator layers, it is possible to restrain a bad influence such as deterioration of charge acceptance of the negative plate due to an excessive amount of lignin around the negative plate. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the accompanying drawings: 
     FIG. 1A is a diagram showing a sectional view between electrodes of a conventional retainer battery; 
     FIG. 1B is a diagram showing a sectional view between electrodes of an embodiment according to the present invention; 
     FIG. 2 is a diagram showing a sectional view between electrodes of another embodiment according to the present invention, in which a separator is constituted by two layers; 
     FIG. 3 is a diagram showing a sectional view between electrodes of still another embodiment according to the present invention, in which a separator is constituted by three layers; 
     FIG. 4 is a characteristic graph showing the change in capacity during the cycle endurance test; 
     FIG. 5 is a characteristic graph showing the amount of liquid reduction during the cycle endurance test; 
     FIG. 6 is a characteristic graph showing the change in capacity during the cycle endurance test; 
     FIG. 7 is a characteristic graph showing the number of cycles till the capacity is reduced to 80% of its original during the cycle endurance test; and 
     FIG. 8 is a characteristic graph showing the number of cycles till the capacity is reduced to 80% of its original during the cycle endurance test. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Detailed description of the present invention will be described as follows accompanying with drawings. 
     Although commercial thiolignin and its products were used as lignin to be contained in a separator in the following embodiment, similar effects were observed when other kinds of lignin were used as the lignin to be contained in the separator. In addition, similar effects could be obtained even in the case where, other than lignin, ion-exchange resins, commercial heavy metal treatments, etc. were used. On the other hand, as for the liquid retaining type of the battery, similar effects were observed in case of any one of the types, such as a liquid type, a retainer type, a gel type, a granular silica type, etc. In addition, according to the present invention, so long as it was a retainer lead acid battery in which antimony was contained in a positive plate, and a glass mat was used for an electrolyte retainer, similar effects could be obtained even in the case of using any method of antimony addition, such as antimony addition by using a lead-antimony alloy grid, by surface treatment of a lead-calcium alloy grid, by application of lead-antimony foil, by addition of antimony to active materials, etc. In addition, as for the material of the separator, similar effects could be recognized even in the case of using any materials, such as glass fibers, resin fibers, other mixed products of plural kinds of materials, etc. In addition, similar effects, that is, the performance that the amount of liquid reduction could be reduced and the endurance could be prolonged, could be recognized regardless of the shape of the separator, or the thickness or shape of fibers themselves, or further in the case of using any method of adding lignin, such as mixing, spraying of suspension and dipping. 
     FIG. 1A is a sectional view of a conventional retainer lead acid battery, and FIGS. 1B,  2  and  3  are sectional views between positive and negative electrodes of embodiments of the products according to the present invention. In FIG. 1, reference numeral  1  represents a single-layer separator;  2 , a negative plate and  3 , positive plate. 
     In FIG. 1B, the negative plate  2  and the positive plate  3  are similar to FIG.  1 A. However, a separator is a single layer separator containing lignin. In FIG. 2, the negative plate  2  and the positive plate  3  are similar to FIG.  1 A. However, a separator is a two-layer separator  11 . The two-layer separator  11  consists of a first layer  11 a containing lignin which is in contact with the negative layer  11   a  and a second layer  11   b  containing no lignin which is in contact with the positive plate. Incidentally, in FIG. 2, the first layer containing lignin is provided to contact with the negative plate  2 . However, it is possible to change the position of the first layer  11   a  and the second layer  11   b  so that a layer containing lignin is in contact with the positive plate  3 . In FIG. 3, the negative plate  2  and the positive plate  3  are similar to FIG.  1 A. However, a separator is a three-layer separator  21 . The three-layer separator  21  consists off a first layer  21   a  containing no lignin which is in contact with the negative layer  2 , a third layer  21   c  containing lignin which is in contact with the positive layer  3 , and a second layer  21   b  containing lignin which is provided between the first layer  21   a  and third layer  21   c.    
     Similar effects could be recognized regardless of the number of separator layers between the positive and negative electrodes, even in the case of a single layer. In addition, even if the lignin content in any one of the separator layers was increased, a similar effect to capture antimony could be obtained so long as the kind of lignin was identical and so long as the total amount of lignin contained between the electrodes was identical. However, when a larger amount of lignin was contained in a separator layer contacting with the positive electrode or the negative electrode, corrosion of a positive electrode grid or deterioration of charge acceptability was recognized. 
     The present invention will be described in detail. 
     EXAMPLE 
     Example 1 
     To make a comparison, a retainer battery having a rated capacity of 60 Ah (3 hR) was prepared as shown in Table 1 by using 10 positive plates of 2.3 mm thickness with a lead—1.7% antimony alloy as a positive electrode grid alloy; 11 negative plates of 1.7 mm thickness; and fine glass fiber separators as electrolyte retainers. The total amount of antimony in the positive plates was 8,000 ppm. 
     
       
         
               
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                   
                 positive electrode grid 
                   
                   
               
               
                 Battery 
                 alloy 
                 separator 
                 remarks 
               
               
                   
               
             
             
               
                 A 
                 lead-antimony alloy 
                 lignin mixed 
                 FIG. 1B 
               
               
                   
                 (1.7% Sb) 
               
               
                 B 
                 as above 
                 conventional 
               
               
                 C 
                 lead-calcium alloy 
                 conventional 
               
               
                   
               
             
          
         
       
     
     A lead-calcium alloy was used for the negative electrode grid. The battery A was manufactured by mixing commercial lignin into each fine glass fiber separator as electrolyte retainer, so that 0.05 g of lignin was contained per 1 cm 3  between the positive and negative electrodes of the battery. For the sake of comparison, also a conventional battery (B) containing no lignin between the positive and negative electrodes was prepared. In addition, a battery (C) using a lead-calcium alloy in a positive electrode grid was also prepared for comparison. With these batteries, an endurance test of JISD-5301 was performed, and the change of discharge capacity and the amount of liquid reduction were examined. The results are shown in FIG.  4  and FIG.  5 . The discharge capacity is compared with the capacity before the test which is regarded as 100%. The amount of liquid reduction is shown in percents by weight, where the amount before the test is regarded as 0%. 
     The battery B had the shortest endurance, and the amount of liquid reduction was also much. This was because antimony eluted from the positive electrode grid precipitated on the negative plate, so that water decomposition was increased, and the amount of electrolyte was reduced. In the battery C, the endurance was shorter than that of the battery A though the amount of liquid reduction was less. The short endurance was caused by the fact that the active materials in the positive electrode were easy to deteriorate because antimony was not contained, and that the lead-calcium alloy was softer than the lead-antimony alloy so that the grid extended to cause a shortcircuit. On the contrary, in the battery A as a product according to the present invention in which a lead-antimony alloy was used for the positive electrode grid, and a separator containing lignin was used, the obtained result was that the endurance cycle number was longest, and the amount of the liquid reduction was very small. This is because the deterioration of the active materials in the positive electrode as well as the extension of the grid were less, and the lignin contained in the separator delayed the movement of the antimony from the positive electrode to the negative electrode to thereby reduce the amount of liquid reduction. However, even in the battery A, the antimony precipitated on the negative plate in the last stage of its endurance, so that water decomposition was increased to reduce the amount of electrolyte to thereby cause a factor of the mortality. 
     Therefore, the following experiment was made to improve the performance of the lignin for capturing antimony. 
     Example 2 
     After commercial lignin (average particle size according to SEM observation was about 50 μm, and BET specific surface was 0.5 m 2 /g) was dissolved in sodium hydrate water-solution of pH about 10, the lignin was precipitated again by neutralization with a dilute sulfuric acid. By drying this, obtained was lignin powder in which the average particle size according to SEM observation was about 10 μm, and the BET specific surface was 2.5 m 2 /g. This powder was mixed into a fine glass fiber separator of an electrolyte retainer, so that 0.05 g of lignin was contained per 1 cm 3  between the positive and negative electrodes of a battery. The battery D was prepared thus. In addition, commercial lignin (average particle size according to SEM observation was about 50 μm, and BET specific surface was 0.5 m 2 /g) was dissolved in a sodium hydrate water-solution of pH about 10, and granular silica power was added thereto. After that, the solution was neutralized with a dilute sulfuric acid, and the lignin was carried by silica to thereby obtain lignin carrying silica power of BET specific surface of 100 cm 2 /g. This powder was mixed into a fine glass fiber separator of an electrolyte retainer, so that 0.05 g of lignin was contained per 1 cm 3  between the positive and negative electrodes of a battery. The battery E was prepared thus. 
     
       
         
               
               
               
               
             
           
               
                 TABLE 2 
               
               
                   
               
               
                 Battery 
                 grid alloy 
                 form of contained lignin 
                 remarks 
               
               
                   
               
             
             
               
                 D 
                 1.7% Sb alloy 
                 average particle size 
                 FIG. 1B 
               
               
                   
                   
                 10 μm 
               
               
                 E 
                 1.7% Sb alloy 
                 carried by silica 
                 ″ 
               
               
                   
               
             
          
         
       
     
     Tests similar to those in Example 1 were made upon there batteries to examine the change in discharge capacity. The results are shown in FIG.  6 . 
     It was found that it took longer time for antimony to move to the negative electrode in the batteries D and E than in the battery A. The reason is considered that the effective specific surface capable of capturing antimony was increased by reducing the average particle size or having lignin carried by a carrier having a wide surface area to increase the amount of captured antimony. 
     However, even in the batteries D and E, corrosion of a positive electrode grid and accumulation of lead sulfate in negative electrode active materials were observed in the batteries after the endurance test. It is considered that this was caused because a lignin-mixed separator was in contact with the positive and negative plates directly. Therefore, the following experiment was made to prevent such deterioration and make the endurance longer. 
     Example 3 
     Similar tests to those in Example 1 were performed in batteries having one, two and three separator layers as shown in FIGS. 1 to  3 , while changing the position of a separator layer to which lignin was added, or changing the content of the lignin, as shown in Table 3. 
     
       
         
               
               
               
               
               
               
             
               
               
               
               
               
               
             
           
               
                 TABLE 3 
               
               
                   
               
               
                   
                   
                   
                   
                 layer to 
                   
               
               
                   
                 kind of 
                 amount 
                 number of 
                 which 
               
               
                   
                 grid 
                 of Sb 
                 separator 
                 lignin 
               
               
                 Battery 
                 alloy 
                 (ppm) 
                 layers 
                 was added 
                 remarks 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 F 
                 Ca alloy 
                 0 
                 3 
                 not contact 
                 FIG. 3 
               
               
                 G 
                 Ca alloy 
                 20 
                 3 
                 ″ 
                 FIG. 3 
               
               
                 H 
                 Ca alloy 
                 50 
                 3 
                 ″ 
                 FIG. 3 
               
               
                 I 
                 1.2% Sb 
                 5,400 
                 3 
                 ″ 
                 FIG. 3 
               
               
                   
                 alloy 
               
               
                 J 
                 1.7% Sb 
                 8,000 
                 3 
                 ″ 
                 FIG. 3 
               
               
                   
                 alloy 
               
               
                 K 
                 2.0% Sb 
                 8,900 
                 3 
                 ″ 
                 FIG. 3 
               
               
                   
                 alloy 
               
               
                 L 
                 1.7% Sb 
                 8,000 
                 1 
                 whole 
               
               
                   
                 alloy 
               
               
                 M 
                 1.7% Sb 
                 8,000 
                 2 
                 positive 
               
               
                   
                 alloy 
                   
                   
                 plate 
               
               
                 N 
                 1.7% Sb 
                 8,000 
                 2 
                 negative 
                 FIG. 2 
               
               
                   
                 alloy 
                   
                   
                 plate 
               
               
                 O 
                 1.7% Sb 
                 8,000 
                 3 
                 positive 
               
               
                   
                 alloy 
                   
                   
                 plate 
               
               
                 P 
                 1.7% Sb 
                 8,000 
                 3 
                 not 
                 FIG. 3 
               
               
                   
                 alloy 
                   
                   
                 contact 
               
               
                 Q 
                 1.7% Sb 
                 8,000 
                 3 
                 negative 
               
               
                   
                 alloy 
                   
                   
                 plate 
               
               
                   
               
             
          
         
       
     
     The number of charge/discharge cycles till the capacity was reduced to 80% of its original was examined. In batteries G and H, antimony was added to the positive electrode active materials to be 20 ppm and 50 ppm relative to the electrode plate weight respectively. In the other batteries, antimony was added into the grid alloy to be contained at the ratios shown in Table 3 respectively. Lignin prepared by the method of Example 2 and having average particle size of about 10 μm was used at the lignin to be added to a separator. The results are shown in FIG.  7  and FIG.  8 . Since the endurance of a positive electrode was short when the antimony content in a positive plate was less than 50 ppm (batteries F and G), the batteries deteriorated in early stages regardless of the amount of lignin contained between the positive and negative electrodes. When the antimony content in a positive plate was more than 8,000 ppm (battery K), or when the antimony content in a positive plate was not less than 50 ppm and not more than 8,000 ppm and lignin was not contained between the positive and negative electrodes (battery of the content 0), antimony eluted from a positive electrode grid precipitated on a negative plate to increase water decomposition to thereby reduce the amount of electrolyte, so that the batteries were dead in early stages. 
     In addition, when the content of lignin was made equal, and a separator layer to which lignin was added was changed, the endurance of a battery P in which lignin was added to a separator layer which was not in contact with both the positive and negative electrodes was longest. On the other hand, these batteries were examined before and after their dead cycle. As a result, in batteries L, M and O, corrosion of a positive electrode grid after their endurance was remarkable, and this caused their death. In batteries N and Q, the amount of lead sulfate was comparatively large still before the endurance test, and their death was caused by the lack of capacity of a negative electrode. It was found that there was a serious bad influence of lignin when a separator layer to which a larger amount of lignin was added was in contact with a positive electrode or a negative electrode. 
     From the results of the above experiment, it was found that the endurance performance of a battery in which lignin was added to a separator layer containing antimony of not less than 50 ppm and not more than 8,000 ppm and not contacting with a positive electrode was particularly superior to any other batteries. 
     As is apparent from the above-mentioned examples, in a valve-regulated lead acid battery according to the present invention, the defects in a conventional valve-regulated lead acid battery can be overcome by a method in which antimony is contained in a positive plate, and a separator between positive and negative plates is made to have a multi-layer structure of two or more layers to which lignin is contained. A very great industrial value can be recognized therein.