LEAD STORAGE BATTERY

Abstract

Lead-acid storage battery, including: positive electrode plates, each containing a positive electrode grid and an active material of the positive electrode, and negative electrode plates, each containing a negative electrode grid and an active material of the negative electrode, wherein the positive electrode plates and the negative electrode plates are stacked alternately with a separating element between the positive electrode plate and the negative electrode plate to form an electrode plate group; a battery container comprising a plurality of cell chambers, each containing the electrode plate group and an electrolyte; and a cover that seals an opening in the battery container, wherein the active material of the positive electrode has a pore diameter distribution with a peak in region A of 0.03 µm to 0.1 µm and a peak in region B of 0.2 µm to 1.0 µm, and a ratio AM / BM of a peak AM in region A to a peak BM in region B is 0.34 or more and 0.70 or less, and The negative electrode grid contains bismuth in amounts of 1 ppm or more and 300 ppm or less.

Description

[TECHNICAL FIELD]

[0001] The present invention relates to a lead-acid storage battery for a vehicle starter. [BACKGROUND OF THE INVENTION]

[0002] Lead-acid storage batteries for a vehicle starter are assumed to be those intended for installation in vehicles equipped with an idle stop system, which will be deeply discharged to a range of relatively low SOC (state of charge), and therefore require resistance to repeated deep discharge.

[0003] Patents 1 and 2 disclose techniques for optimizing the pore structure of an active material of a positive electrode based on the results of a cyclic lifetime test that includes a relatively deep discharge and other factors. These techniques appear potentially applicable to the aforementioned lead-acid storage batteries used in vehicles equipped with an idle stop system. [Bibliography][Patent Literature] [PDL 1] JP H1069900 A [PDL 2] JP H1173950 A [SUMMARY OF THE INVENTION][TECHNICAL PROBLEM]

[0004] Since the use of vehicles equipped with an idle stop system has increased in recent years, some cases arise where the lead-acid storage battery is operated not only under deep discharge conditions but also under various other severe conditions. Under such circumstances, even when using the techniques described in patents 1 and 2, the battery often fails to exhibit sufficient cyclic life characteristics in practical use within the vehicle when subjected to repeated charging and discharging.

[0005] The present disclosure was carried out with regard to the above problem and aims to provide a highly reliable lead-acid storage battery that can adequately exercise its cyclic lifetime characteristics, even when operated under comparatively severe idling and stopping conditions. [SOLUTION TO THE PROBLEM]

[0006] A lead-acid storage battery according to the present disclosure comprises: positive electrode plates, each comprising a positive electrode grid and a positive active electrode material, and negative electrode plates, each comprising a negative electrode grid and a negative active electrode material. The positive electrode plates and the negative electrode plates are stacked alternately with a separating element between the positive and negative electrode plates to form an electrode plate group. The lead-acid storage battery further comprises: a battery container with a plurality of cell chambers, each comprising the electrode plate group and an electrolyte, and a cover that seals an opening of the battery container.The positive active electrode material has a pore diameter distribution with a peak in region A of 0.03 µm to 0.1 µm and a peak in region B of 0.2 µm to 1.0 µm, and an AM / BM ratio of one peak of AM in region A to one peak of BM in region B of 0.34 or more or 0.70 or less. The negative electrode grid contains bismuth in amounts of 1 ppm or more and 300 ppm or less.

[0007] In a preferred embodiment, at least the positive electrode plate is provided on one surface thereof with a retaining mat formed from a non-woven material comprising glass, polyester or the like. [BENEFICIAL EFFECTS OF THE INVENTION]

[0008] According to the present disclosure, it is possible to provide a highly reliable lead-acid storage battery that can adequately demonstrate its cyclic lifetime characteristics, even when operated under comparatively severe idle stop conditions. [Brief description of the drawings]

[0009] The drawings show: Fig. 1 a schematic overview of a lead-acid storage battery according to an embodiment of the present invention; Fig. 2 an exemplary view of an essential part of the lead-acid storage battery according to an embodiment of the present invention; and Fig. 3 an exemplary pore distribution of a positive active electrode material according to an embodiment of the present invention. [Description of embodiments]

[0010] Embodiments of the present invention are described in detail below with reference to the drawings. Fig. Figure 1 is a schematic overview of a lead-acid storage battery according to an embodiment of the present invention. Fig. Figure 2 is an exemplary view of a negative electrode plate, an essential part of the lead-acid storage battery according to an embodiment of the present invention.

[0011] A plurality of electrode plate groups 4, each comprising positive electrode plates 1 and negative electrode plates 2 stacked alternately on top of each other with a separating element 3 between them, are arranged in a battery container 5, which has a plurality of cell chambers 5a, together with an electrolyte (not shown). The opening of the battery container 5 is sealed with a cover 6. The positive electrode plate 1 comprises a positive electrode grid 1a and a positive active electrode material 1b, and the negative electrode plate 2 comprises a negative electrode grid 2a and a negative active electrode material 2b.

[0012] One embodiment of the present invention comprises two features. The first is that the active material 1b of the positive electrode has a pore distribution with a peak in region A of 0.03 µm to 0.1 µm and a peak in region B of 0.2 µm to 1.0 µm, and a ratio AM / BM of a peak AM in region A to a peak BM in region B is 0.34 or more and 0.70 or less.

[0013] Fig. Figure 3 is an example of the pore distribution of the active material of the positive electrode according to the first feature of an embodiment of the present invention. The second feature consists in the fact that the negative electrode grid 2a contains bismuth in an amount of 1 ppm or more and 300 ppm or less.

[0014] Among the problems associated with an idle stop control system, deep discharge is considered the most serious problem in the early stages of development because during an idle stop, energy is supplied to the load (a temperature controller, lights, etc.) exclusively from the lead-acid storage battery.

[0015] If such deep discharge is the only problem relevant to idle stop control, the techniques disclosed in patents 1 and 2 might be sufficient to solve the problem. However, in recent years, a significant number of vehicles equipped with an idle stop system have increasingly employed a control method for generating regenerative power during braking and similar events, and for charging the lead-acid battery with this regenerative power. To achieve more efficient charging with the regenerated power, it is desirable to keep the state of charge (SOC) of the lead-acid battery relatively low (to avoid being fully charged).Additionally, it is expected that the lead-acid storage batteries used for idle stop control will be subjected to discharges much more frequently, during which a large current equivalent to several tens of capacitances is drawn directly from the battery, compared to conventional lead-acid storage batteries used for vehicle starters. Under such circumstances, the configuration of the lead-acid storage battery as disclosed in patents 1 or 2, which are optimized by focusing on cycle life based on changes in discharge capacity at a constant current, is insufficient for the battery to exhibit satisfactory operating behavior.

[0016] Since charging and discharging cycles, during which the battery is frequently discharged with a large current, are repeated under conditions where the state of charge (SOC) is below 100%, a phenomenon known as acid stratification occurs. This means that the sulfate ion concentration in the electrolyte becomes lower in the upper layer than in the lower layer. When this occurs, it is unlikely that lead sulfate will be produced as a discharge product in the upper layer where the sulfate ion concentration is relatively low (discharge progression is difficult).

[0017] On the other hand, in the lower layer section where the sulfate ion concentration is relatively high, sulfate ions are unlikely to be separated from the lead sulfate (charge progression is difficult). As a consequence of this imbalance, the excess lead sulfate in the lower layer section is deposited, slowing down the overall discharge reaction. This leads to a deterioration of the cyclic lifetime characteristics. The stratification is eliminated when the electrolyte is moved by the gas generated through electrolyte hydrolysis (gas generation), which occurs in the final stage of a charge. However, under conditions where the state of charge (SOC) is intentionally controlled below 100%, a charge cannot progress to the final stage, and the above effect cannot be expected.

[0018] To solve this problem, one embodiment of the present invention uses the two features described above. The first feature is that the active material 1b of the positive electrode is configured to have a pore distribution with a peak in region A from 0.03 µm to 0.1 µm and a peak in region B from 0.2 µm to 1.0 µm, such that the peak AM in region A and the peak BM in region B have an AM / BM ratio of 0.34 or more and 0.70 or less, respectively.

[0019] In patent specification 1, as disclosed in examples, metal lead and lead monoxide are classified, thereby shifting the tip from region B to a range of 1.0 µm to 5.0 µm. The ordinary active material 1b of the positive electrode, which is not classified, has the tip BM in region B. By adding red lead to a precursor paste thereof, the active material 1b of the positive electrode can have a different tip AM in region A.

[0020] Although the exact causes are not yet clear, the AM tip increases the capacitance of the positive electrode plate 1. However, it should be noted that if the AM / BM ratio is as small as that of a comparative example 1 without red lead from patent specification 1 (AM / BM ratio = 0.31), the capacitance cannot be increased. The present inventors have found, as a result of intensive studies, that if the AM / BM ratio falls below 0.34, the capacitance drops drastically.

[0021] On the other hand, if the battery is repeatedly charged while the SOC is controlled to be relatively low (so as not to be fully charged), lead sulfate builds up and this causes the cyclic life characteristics to deteriorate even further as a result of the high capacity of the positive electrode plate 1.

[0022] The present inventors have found, as a result of intensive studies, that when the AM / BM ratio exceeds 0.70, the deterioration of the cyclic lifetime characteristics, caused by the aforementioned reasons, becomes severe.

[0023] Therefore, the AM / BM ratio should be 0.34 or higher and 0.70 or lower. Specifically, decreasing the amount of red lead added to the paste will decrease the AM, and conversely, increasing the amount of red lead will increase the AM. The AM / BM ratio can thus be optimized by adjusting the amount of red lead added during the paste manufacturing process.

[0024] The second feature is the presence of bismuth in the negative electrode grid 2b at concentrations of 1 ppm or more and 300 ppm or less. The presence of a suitable amount of bismuth in the negative electrode grid 2a reduces the hydrogen overpotential, and hydrogen gas is likely to be generated even when the state of charge (SOC) is below 100%, which facilitates electrolyte diffusion. This diffusion can ultimately eliminate stratification.

[0025] To achieve this effect, it is desirable to incorporate bismuth into the negative electrode grid 2a in an amount of 1 ppm or more. However, if the amount exceeds 300 ppm, the hydrogen overpotential will drop too low, and electrolyte hydrolysis will occur excessively, significantly reducing the electrolyte volume. This accelerates the corrosion of the current collection sections (taps) that protrude from the electrolyte of the positive and negative electrode plates 1 and 2, which in turn leads to a deterioration of the cyclic lifetime characteristics.

[0026] According to an embodiment of the present invention configured to include the two features described above, it is possible to provide a lead-acid storage battery that can sufficiently exercise its lifetime characteristics while maintaining its high capacity, even when it is repeatedly charged and discharged under the condition that the SOC is below 100%.

[0027] The effect of one embodiment of the present invention is further enhanced by providing a retention mat on a surface of the positive electrode plate 1. Since the AM / BM ratio is set to be a relatively large value, the active material 1b of the positive electrode tends to soften and separate from the positive electrode plate 1, leading to a decrease in capacitance (or a deterioration of the cyclic lifetime characteristics). By providing the retention mat, the active material 1b of the positive electrode can be physically held in place, preventing it from separating from the positive electrode plate.

[0028] The advantageous effects of one embodiment of the present invention are now described below with reference to examples. (1) Production of a lead-acid storage battery

[0029] A D26L lead-acid storage battery, as specified in JISD5201, was fabricated in the present example. The cell chambers 5a each accommodate eight positive electrode plates 1 and nine negative electrode plates 2. The positive electrode plates 1 are each provided with a retaining mat on their surface, except for those of battery C-1, so that the retaining mat and the positive electrode plate 1 are in contact with each other.

[0030] The positive electrode plate 1 was obtained by kneading a lead oxide powder with sulfuric acid and purified water to produce a precursor paste of an active material 1b of the positive electrode, and by filling the paste into a positive electrode grid 1a (extended grid) formed from a lead alloy layer (thickness: 1.1 mm) containing calcium.

[0031] The negative electrode plate 2 was obtained by kneading a lead oxide powder, to which carbon and an organic additive had been previously added, with sulfuric acid and purified water to produce a precursor paste of an active material 2b of the negative electrode, and by filling the paste into a negative electrode grid 2a (extended grid) which is formed from a lead alloy layer (thickness: 1.1 mm) containing calcium and, depending on the condition, bismuth.

[0032] The mass ratio of the bismuth contained in the negative electrode grid 2a was changed as shown in Table 1.

[0033] The resulting positive and negative electrode plates 1 and 2 were aged and dried. The negative electrode plates 2 were then each placed within a pocket-shaped separator 3 made of polyethylene and stacked alternately on top of the positive electrode plates 2 to form an electrode plate group 4 comprising eight positive electrode plates 1 and nine negative electrode plates 2, with the separator 3 positioned between the positive and negative electrodes. The electrode plate group 4 was placed in each of six cell compartments 5a, separated by a divider, and six cells were directly connected together. An electrolyte, comprising dilute sulfuric acid, was then injected to initiate chemical formation. A lead-acid storage battery was thus produced. (2) Cyclic lifetime characteristics

[0034] The manufactured lead-acid storage batteries were evaluated by the following steps after the SOC was set to 90%. A. Subject the battery to a discharge at 45 A for 59 seconds B. Subject the battery to a discharge at 300 A for 1 second C. Subject the battery to a 14.0 V constant voltage charge for 60 seconds with a maximum current limited to 100 A. D. After repeating a charge-discharge cycle consisting of A, B and C 3600 times in that order, subject the battery to a refresh charge, i.e. a 14.0 V constant voltage charge for 20 minutes.

[0035] The above steps A to D were repeated, and at the point where the voltage dropped to 7.2 V or less during discharge at 300 A for 1 second, it was determined that the battery had reached the end of its service life, and the evaluation was terminated. The number of cycles performed until the evaluation was terminated was measured and converted into a percentage (%), with the number of cycles for battery C-1 being set to 100. The percentage thus determined is shown in Table 1 as the cycle life characteristics of each battery, along with the manufacturing conditions. (3) Battery capacity

[0036] The batteries, in a fully charged state, were discharged at a 5-hour rate current until the terminal voltage reached 10.5 V. The amount of electricity discharged at this point was measured and converted into a percentage (%), with the amount of electricity discharged from battery C-1 being set to 100. The percentage thus determined is shown in Table 1 as the discharge capacity of each battery, along with the manufacturing conditions. [Table 1] battery AM / BM ratio Bismuth in the negative electrode grid (ppm) Retaining mat on positive electrode plate Battery capacity Cyclic lifetime characteristics A-1 0.32 150 with 88% 108% A-2 0.34 150 with 95% 109% A-3 0.42 150 with 99% 111% A-4 0.50 150 with 100% 110% A-5 0.60 150 with 105% 105% A-6 0.70 150 with 109% 99% A-7 0.73 150 with 110% 87% B-1 0.50 0.5 with 100% 80% B-2 0 .50 1 with 101% 92% B-3 0.50 10 with 100% 103% B-4 0.50 50 with 100% 105% B-5 0.50 200 with 99% 108% B- 6 0.50 250 with 99% 101% B-7 0.50 300 with 99% 95% B-8 0.50 330 with 99% 86% C-1 0.50 150 without 100% 100%

[0037] A comparison is performed for batteries A-1 to A-7. In battery A-1, where the AM / BM ratio was below 0.34, the battery capacity decreased drastically. This is because the peak AM in region A, which increases the capacity of the positive electrode plate 1, was relatively small. However, it is not yet clear why the ratio exhibits a tipping point at 0.34.

[0038] On the other hand, in battery A-7, where the ratio was above 0.70, the cyclic lifetime characteristics were deteriorated. Battery A-7 was disassembled, and softening of the active material 1b of the positive electrode was observed. This indicates that the AM / BM ratio should preferably be 0.34 or greater and 0.70 or less.

[0039] A comparison was made with batteries B-1 to B-8. In battery B-1, where the amount of bismuth in the negative electrode grid 2a was below 1 ppm, and in battery B-8, where it was above 300 ppm, the cycle life characteristics were deteriorated. Each battery was disassembled, and severe electrolyte stratification was observed in battery B-1, while electrolyte depletion was observed in battery B-8. This indicates that bismuth is preferentially present in the negative electrode grid 2a in amounts of 1 ppm or more and 300 ppm or less.

[0040] The evaluation results of batteries A-1 to A-7 together with those of batteries B-1 to B-8 indicate that it is preferred that both the AM / BM ratio and the amount of bismuth in the negative electrode grid 2a are in the above ranges.

[0041] A comparison was made with batteries C-1 and A-4. These two batteries were similarly configured, except that the retaining mat, as provided on the surface of the positive electrode plate 1 in battery A-4, was not provided in battery C-1. Despite this minor difference, the cycle life characteristics of battery C-1 were deteriorated. The retaining mat plays a role in physically holding the active material 1 of the positive electrode, thus preventing its separation from the positive electrode plate. This effect was likely not achieved in battery C-1 without the retaining mat. Battery C-1 was disassembled, and slight softening and separation of the active material 1b of the positive electrode was observed. It is therefore preferable to provide the retaining mat on the surface of the positive electrode plate 1.

[0042] Although the present invention has been described above with reference to preferred embodiments, such a description should not be considered a limitation of the invention, and various modifications are possible. For example, the positive electrode grid 1a, like the negative electrode grid 2a, can be configured to contain bismuth in amounts of 1 ppm or more and 300 ppm or less. [Commercial Applicability]

[0043] The present invention can advantageously be applied to the lead-acid storage battery used in a vehicle equipped with an idle stop system. [List of reference symbols] 1 positive electrode plate 1a positive electrode grid 1b active material of the positive electrode 2 negative electrode plates 2a negative electrode grid 2b active material of the negative electrode 3 separating element 4 electrode plate groups 5 battery containers 5a cell chamber 6 Cover

Claims

[1] Lead-acid storage battery, comprising: positive electrode plates, each containing a positive electrode grid and a positive electrode active material, and negative electrode plates, each containing a negative electrode grid and a negative electrode active material, wherein the positive electrode plates and the negative electrode plates are alternately stacked with a separator between the positive electrode plate and the negative electrode plate to form an electrode plate group; a battery container having a plurality of cell chambers, each containing the electrode plate group and an electrolyte; and a cover that seals an opening in the battery container, wherein the positive electrode active material has a pore diameter distribution with a peak in a region A of 0.03 µm to 0.1 µm and a peak in a region B of 0.2 µm to 1.0 µm, and a ratio AM / BM of a peak AM in the region A to a peak BM in the region B is 0.34 or more and 0.70 or less, and the negative electrode grid contains bismuth in an amount of 1 ppm or more and 300 ppm or less. [2] A lead-acid storage battery according to claim 1, wherein at least the positive electrode plate is provided with a holding mat on one surface thereof.

Images