JP2019040733A - Battery pack - Google Patents

Abstract

To provide a battery pack having a long cycle life while maintaining a large electrical capacity.SOLUTION: A battery pack 2 is formed by combining a plurality of single cells 4. When a plurality of single cells 4 (6) located in a central portion is assumed to be a first single cell group 10 and a plurality of single cells 4 (8) located on both sides of the central portion is assumed to be a second single cell group 12, an electrolyte used in the cells 4 (6) contained in the first single cell group 10 is a first alkaline electrolyte containing NaOH as a main component of the solute and an electrolyte used in the cells 4 (8) contained in the second single cell group 12 is a second alkaline electrolyte containing KOH as a main component of the solute.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an assembled battery formed by combining a plurality of unit cells, and more particularly to an assembled battery using an alkaline storage battery as the unit cell.

  In recent years, needs for power storage and backup systems are expanding for the purpose of effective use of renewable energy such as photovoltaic power generation, or power outage countermeasures in an emergency. In order to meet such needs, the demand for large-capacity storage batteries is increasing, and development of large-capacity products is being promoted for alkaline storage batteries. Here, in order to increase the capacity of the storage battery, for example, a plurality of unit cells are combined to form an assembled battery.

  By the way, in a storage battery, with charge / discharge, reaction heat and Joule heat are generated by battery reaction, and the temperature rises. When the number of single cells is increased in order to increase the capacity of the assembled battery, the amount of heat generated increases. Therefore, the assembled battery is more likely to rise in temperature than the case of a single cell, and is exposed to a high temperature. When a storage battery is exposed to a high temperature and affected by heat, it deteriorates and its discharge capacity decreases. For this reason, an assembled battery whose temperature is likely to rise as compared with the case where a single battery is used alone has a problem in that the discharge capacity is likely to decrease due to thermal effects.

  In addition, when a plurality of rectangular unit cells are prepared as a unit cell and the assembled battery is formed by combining such a plurality of unit cell units, the unit cell is compared with the unit cell formed by combining a plurality of cylindrical cells. Since the contact area between them increases, it is difficult for heat to dissipate, and in particular, the central portion tends to be in a high temperature state because heat is likely to accumulate. On the other hand, heat tends to dissipate as it goes from the central portion to both end portions. For this reason, the part away from the central part is less likely to reach a higher temperature than the central part. Thus, in an assembled battery, a temperature difference arises according to a place. For this reason, the unit cell located in the part which becomes higher temperature has a high degree of exposure to high temperature, and is easily affected by heat, compared to the unit cell located in the other part. As described above, in the assembled battery, there are a single cell that is affected by heat and a single cell that is not significantly affected by heat.

  Generally, a battery deteriorates when it is affected by heat. Specifically, the charging efficiency is lowered, and the discharge capacity is lowered accordingly. Accordingly, the discharge capacity of the single battery in the assembled battery varies depending on the position in the assembled battery. For this reason, in the assembled battery, a single cell having a large degree of decrease in discharge capacity and a single cell having a small degree of decrease in discharge capacity tend to coexist, and the discharge capacity tends to be unbalanced. Such a tendency is more prominent when the assembled battery is used in a high-temperature environment where the temperature is higher than room temperature (about 25 ° C.), or when high-rate charge / discharge that increases the calorific value of the unit cell itself is performed. Appears in

  In general, in a battery, when charging and discharging are repeated, the battery deteriorates as the charging and discharging cycle progresses, and the discharge capacity decreases. The cycle life is exhausted when the discharge capacity of the battery falls below a predetermined value (lower limit value).

  Here, the cycle life of the assembled battery depends on the unit cell having a large degree of reduction in discharge capacity. That is, a single battery with a large degree of decrease in discharge capacity falls below the lower limit value of the discharge capacity earlier, so that an assembled battery having a single battery with a large degree of decrease in discharge capacity has a shorter life.

  In an assembled battery, when the above-described discharge capacity imbalance occurs, there is a problem that the cycle life of the entire assembled battery is shortened.

  In order to solve the above-described problems, a battery pack is provided with a cooling mechanism for suppressing an increase in temperature. As such a cooling mechanism, for example, a heat dissipation partition plate that partitions adjacent unit cells as shown in Patent Document 1 is known. The heat radiating partition plate has ventilation holes, and cools the cells by circulating cooling air through the ventilation holes.

JP 2010-199089 A

  However, the cooling effect in the case of using the heat dissipation partition plate as described above is still not sufficient. Further, a heat dissipation partition plate must be interposed between the single cells, and the entire assembled battery becomes large. Such an assembled battery cannot sufficiently meet the needs for downsizing in order to save space in recent years.

  When not using a cooling mechanism like patent document 1, the aspect using the heat-resistant type electrolyte solution which is electrolyte solution which can suppress the fall of charging efficiency even if exposed to high temperature is also considered. In this case, the discharge capacity imbalance can be suppressed to some extent without providing a cooling mechanism.

  However, the heat-resistant electrolyte as described above has a low original discharge capacity and it is difficult to increase the capacity of the assembled battery.

  The present invention has been made based on the above circumstances, and an object of the present invention is to provide an assembled battery having a long cycle life while maintaining a large electric capacity.

  According to the present invention, in the assembled battery formed by combining a plurality of unit cells, each of the unit cells has a flat box shape, and the surface having the largest area among the surfaces in the box shape. A plurality of single cells that are combined and connected in a straight line so as to be in contact with each other and located in a central portion in the longitudinal direction in the straight line form a first single battery group, and the length in the straight line When a plurality of the unit cells located on both sides sandwiching the central portion in the direction is a second unit cell group, the electrolytic solution used for the unit cells included in the first unit cell group Is a first alkaline electrolyte containing NaOH as a main component of the solute, and the electrolyte used in the unit cells included in the second unit cell group is a second electrolyte containing KOH as the main component of the solute. An alkaline electrolyte, The battery is provided.

  The sum of the concentrations of the alkali components in the first alkaline electrolyte and the sum of the concentrations of the alkali components in the second alkaline electrolyte are both 5.30 mol / l or more and 8.50 mol / l or less, The concentration of NaOH in the first alkaline electrolyte is 4.75 mol / l to 8.00 mol / l, and the concentration of KOH in the second alkaline electrolyte is 5.20 mol / l to 8.00 mol / l. It is preferable that the configuration is 1 or less.

  It is preferable that the number of the unit cells constituting the first unit cell group is 33% or more and 50% or less of the total number of the unit cells included in the assembled battery.

  The total number of the unit cells is preferably 10 or more.

  In the assembled battery of the present invention, the first alkaline electrolyte containing NaOH as a main component of solute is used as the electrolyte used in the first unit cell group located in the central portion. The first alkaline electrolyte containing NaOH as a main component of solute is not easily affected by heat and can suppress deterioration of the unit cell due to heat. By using the first alkaline electrolyte having excellent heat resistance in the central portion where heat is likely to accumulate, the degree of imbalance of the discharge capacity can be reduced, and the cycle life of the assembled battery can be extended accordingly. . On the other hand, since the 2nd alkaline electrolyte which uses KOH which is excellent in discharge characteristics as a main ingredient of a solute is used except for a central part, a large capacity can be maintained as a whole assembled battery. Therefore, according to the present invention, it is possible to provide an assembled battery having a long cycle life while maintaining a large electric capacity.

It is the perspective view which showed schematically the assembled battery which concerns on one Embodiment of this invention. 6 is a perspective view schematically showing an assembled battery of Comparative Example 1. FIG. 10 is a perspective view schematically showing an assembled battery of Comparative Example 2. FIG. It is the graph which showed the relationship between a capacity | capacitance maintenance factor and the cycle number about the assembled battery of Example 1, the comparative example 1, and the comparative example 2. FIG. It is the perspective view which showed schematically the assembled battery for temperature distribution measurement. It is the graph which showed the relationship between the temperature measured by each thermocouple, and time passage.

  Hereinafter, an assembled battery 2 to which the present invention is applied will be described with reference to the drawings.

  For example, as shown in FIG. 1, the assembled battery 2 is formed by combining ten cuboid unit cells 4.

  Here, in FIG. 1, when three directions are indicated by arrows X, Y, and Z, the base end side of arrow X is left, the tip end side of arrow X is right, and the base end side of arrow Y is The bottom side of the arrow Y is the top, the base side of the arrow Z is the front, and the tip side of the arrow Z is the back. It should be noted that the relationship between the upper, lower, left, and right directions is the same in other drawings depicting the assembled battery described later.

  When specified as described above, the unit cell 4 is positioned on the left side surface located on the left side, the right side surface located on the right side, the lower surface located on the lower side, the upper surface located on the upper side, the front surface located on the front side, and the rear side. It has each surface of the rear surface. Here, the width in the front-rear direction of the left side, upper surface, right side, and lower surface is smaller than the vertical and horizontal widths of the front and rear surfaces, and the unit cell 4 has a flat box shape as a whole.

  More specifically, in the unit cell 4, when the length in the arrow Z direction is the unit length U, the length W in the arrow X direction is 5 to 6 times the unit length U. The length L in the Y direction preferably has a box shape that is 7 to 8 times the unit length U.

  The unit cell 4 is a so-called rectangular alkaline storage battery, and includes therein an electrode group in which a positive electrode and a negative electrode are overlapped via a separator, and an alkaline electrolyte.

  What is generally used as a positive electrode of an alkaline storage battery is used for the positive electrode. For example, a positive electrode containing nickel hydroxide is used as the positive electrode active material.

  What is generally used as a negative electrode of an alkaline storage battery is used for a negative electrode. For example, a negative electrode including a hydrogen storage alloy capable of storing and releasing hydrogen as a negative electrode active material is used.

  As a separator, what is generally used as a separator of an alkaline storage battery is used. For example, those obtained by imparting a hydrophilic functional group to a nonwoven fabric made of polyamide fiber, those obtained by imparting a hydrophilic functional group to a nonwoven fabric made of polyolefin fiber such as polyethylene or polypropylene, and the like are used.

  As the alkaline electrolyte, an aqueous solution containing at least one of NaOH and KOH is used as the solute of the alkaline component.

  In the present invention, a first alkaline electrolyte containing NaOH as a main component of a solute among alkali components and a second alkaline electrolyte containing KOH as a main component of a solute among alkali components are prepared. Here, a main component refers to the component contained most in a solute.

  The first alkaline electrolyte is an electrolyte having excellent heat resistance that can suppress a decrease in charging efficiency even in a high temperature environment.

  The second alkaline electrolyte is an electrolyte having excellent discharge characteristics although it is somewhat affected by heat.

  In addition, in the above-mentioned alkaline electrolyte, it is preferable to add LiOH as needed. In the case where LiOH is added, in the obtained single cell, the oxygen generation potential can be pushed up, so that charging characteristics at a high rate are improved.

  In any of the above alkaline electrolytes, the total concentration of the alkali components is preferably 5.30 mol / l or more and 8.50 mol / l or less. Further, in the first alkaline electrolyte, the concentration of NaOH is preferably 4.75 mol / l or more and 8.00 mol / l or less, and the concentration of KOH in the second alkaline electrolyte is 5.20 mol. / L or more and 8.00 mol / l or less is preferable. Furthermore, the LiOH concentration is preferably 1.25 mol / l or less.

  Regarding the total concentration of the alkali components described above, if the concentration is out of the above-described concentration range, the conductivity of the electrolytic solution is lowered, and it is difficult to ensure sufficient charge / discharge characteristics.

  Further, in the first alkaline electrolyte, when the concentration of NaOH is out of the above-described concentration range, the conductivity of the electrolyte decreases, and it becomes difficult to ensure sufficient charge / discharge characteristics.

  Further, in the second alkaline electrolyte, when the KOH is out of the above-described concentration range, the conductivity of the electrolyte is lowered, and it is difficult to ensure sufficient charge / discharge characteristics.

  About LiOH, since it will precipitate when it exceeds 1.25 mol / l, it is preferable to make this density | concentration into an upper limit. Since LiOH is an auxiliary component and does not necessarily need to be contained, the lower limit is 0 mol / l.

  In the single battery 4, a first single battery 6 including the first alkaline electrolyte described above and a second single battery 8 including the second alkaline electrolyte described above are prepared. That is, the first unit cell 6 is excellent in heat resistance, and the second unit cell 8 is excellent in discharge characteristics.

  A plurality of the unit cells 4 as described above are prepared, and each unit cell 4 is combined and connected in a straight line so that the surfaces having the largest areas of the surfaces in the box shape are in contact with each other. The Specifically, they are combined in such a manner that the rear surface of one unit cell 4 and the front surface of the other unit cell 4 are in contact with each other. In this way, the assembled battery 2 is formed. At this time, four first unit cells 6 are arranged in the central part of the assembled battery, and three second unit cells 8 are arranged on both sides sandwiching the central unit. Here, the four first unit cells 6 positioned in the central portion are defined as a first unit cell group 10, and a total of six second unit cells 8 positioned on both sides of the first unit cell group 10. Is a second cell group 12 (see FIG. 1).

  As described above, the first unit cell group 10 including the first unit cell 6 excellent in heat resistance exists in the central portion where heat is likely to be accumulated, and the end portion where heat is easily radiated is somewhat susceptible to heat. Since the second unit cell group 12 including the second unit cell 8 having excellent discharge characteristics is present, the second unit cell 12 is located in the central portion where heat is easily accumulated even if the unit cell 4 generates heat. Since the single cell 6 is not easily affected by heat, the degree of unbalance of the discharge capacity can be suppressed to be small, which contributes to extending the life of the assembled battery 2. And the 2nd single cell 8 located in the both ends which are easy to radiate | emit heat and do not become high temperature compared with a center part can fully exhibit a discharge characteristic, without receiving thermal influence so much. For this reason, the assembled battery 2 having a long cycle life can be obtained while maintaining a large electric capacity.

  Here, the temperature distribution during charging / discharging of the assembled battery was determined as follows.

  First, as an assembled battery for temperature measurement, an assembled battery 42 in which 12 box-type unit cells 4 were combined as shown in FIG. 5 was prepared. The assembled battery 42 is a general assembled battery that has been used conventionally. In the assembled battery 42, an intermediate position between both ends is set as a center position C. Then, the cells located on the front side of the center position C are arranged in order from the center position C in the order of the front first battery a1, the front second battery a2, the front third battery a3, the front fourth battery a4, and the front fifth battery a5. The front sixth battery a6. Further, the cells located on the rear side of the center position C are arranged in order from the center position C in the order of the rear first battery b1, the rear second battery b2, the rear third battery b3, the rear fourth battery b4, The rear side fifth battery b5 and the rear side sixth battery b6 are designated.

  Next, the first thermocouple t1 is disposed between the front first battery a1 and the rear first battery b1, that is, at the center position C, and the second thermocouple is between the front first battery a1 and the front second battery a2. A thermocouple t2 is disposed, a third thermocouple t3 is disposed between the front second battery a2 and the front third battery a3, and a fourth is disposed between the front third battery a3 and the front fourth battery a4. A thermocouple t4 is disposed, a fifth thermocouple t5 is disposed between the front fourth battery a4 and the front fifth battery a5, and a sixth thermocouple t5 is disposed between the front fifth battery a5 and the front sixth battery a6. A thermocouple t6 was provided. In this way, the temperature between the unit cells described above can be measured. In addition, in each single cell located before and after the center position C, the batteries having the same distance from the center position C (for example, the front third battery a3 and the rear third battery b3) have substantially the same temperature. Assuming that this is the case, only the temperature between the center position C and the front unit cells is measured, and the temperature between the rear unit cells is omitted.

  The assembled battery 42 on which the thermocouple was set was charged for 10 hours at a charging current of 25 A, and then rested for 1 hour. Next, the battery pack 42 after resting was discharged at a discharge current of 50A. This discharge was terminated when the voltage of the assembled battery 42 reached 1.0V. Thereafter, the assembled battery 42 was suspended for 1 hour. The charge / discharge operation was performed under the above conditions, and the temperature between the single cells at that time was measured. A graph showing the relationship between the temperature and the elapsed time between the individual cells is shown in FIG. In FIG. 6, reference numeral t1 is the temperature of the first thermocouple t1, reference numeral t2 is the temperature of the second thermocouple t2, reference numeral t3 is the temperature of the third thermocouple t3, and reference numeral t4 is the fourth thermocouple. The temperature of the pair t4, the reference symbol t5 indicates the temperature of the fifth thermocouple t5, and the reference symbol t6 indicates the temperature of the sixth thermocouple t6.

  On the other hand, the maximum temperature measured by each thermocouple is shown in Table 1.

  Here, the temperature indicated by the first thermocouple t1 represents the temperature of the front first battery a1. Note that the temperature of the rear first battery b1 that is symmetrical to the front first battery a1 is also considered to be substantially the same as the temperature indicated by the first thermocouple t1. The temperature indicated by the thermocouple t2 described above represents the temperature of the front second battery a2. Note that the temperature of the rear second battery b2 that is symmetrical to the front second battery a2 is also considered to be substantially the same as the temperature indicated by the second thermocouple t2. The temperature indicated by the thermocouple t3 described above represents the temperature of the front third battery a3. Note that the temperature of the rear third battery b3 that is symmetrical to the front third battery a3 is also considered to be substantially the same as the temperature indicated by the third thermocouple t3. The temperature indicated by the fourth thermocouple t4 described above represents the temperature of the front fourth battery a4. In addition, it is thought that the temperature of the back side 4th battery b4 symmetrical with the front side 4th battery a4 is also substantially the same as the temperature shown by this 4th thermocouple t4. Further, the temperature indicated by the thermocouple t5 described above represents the temperature of the front side fifth battery a5. In addition, it is thought that the temperature of the back side 5th battery b5 symmetrical with the front side 5th battery a5 is also substantially the same as the temperature shown by this 5th thermocouple t5. The temperature indicated by the thermocouple t6 described above represents the temperature of the front side sixth battery a6. In addition, it is thought that the temperature of the back side 6th battery b6 symmetrical with the front side 6th battery a6 is also substantially the same as the temperature shown by this 6th thermocouple t6.

  The maximum temperature indicated by the first thermocouple t1 in Table 1 indicates the temperature at which the first region reaches at least when the region including the front first battery a1 and the rear first battery b1 is defined as the first region. ing. In addition, the maximum temperature indicated by the second thermocouple t2 in Table 1 is a second region including a region from the center position C to the front second battery a2 and a region including the region from the center position C to the rear second battery b2. In this case, the temperature reaches at least the second region. Further, the maximum temperature indicated by the third thermocouple t3 in Table 1 is a third region including a region from the center position C to the front third battery a3 and a region including the region from the center position C to the rear third battery b3. In this case, the temperature reaches at least the third region. In addition, the maximum temperature indicated by the fourth thermocouple t4 in Table 1 is a fourth region that includes a region from the center position C to the front fourth battery a4 and a region from the center position C to the rear fourth battery b4. In this case, the temperature at which the fourth region reaches at least is indicated. In addition, the maximum temperature indicated by the fifth thermocouple t5 in Table 1 is the fifth region including the region from the center position C to the front fifth battery a5 and the region from the center position C to the rear fifth battery b5. In this case, the temperature reaches at least the fifth region. In addition, the maximum temperature indicated by the sixth thermocouple t6 in Table 1 is a sixth region that includes a region from the center position C to the front sixth battery a6 and a region from the center position C to the rear sixth battery b6. In this case, the temperature reaches at least the sixth region.

  Next, Table 1 also shows the number of single cells included in each of the above-described regions and the ratio of each region to the entire assembled battery 42. Specifically, the number of single cells included in the first region is two, which accounts for 17% of the total 12 single cells of the assembled battery 42. In addition, the number of single cells included in the second region is four, accounting for 33% of the total 12 single cells of the assembled battery 42. In addition, the number of single cells included in the above-described third region is six, accounting for 50% of the total 12 single cells of the assembled battery 42. Further, the number of unit cells included in the fourth region is eight, accounting for 67% of the total twelve unit cells of the assembled battery 42. Further, the number of single cells included in the fifth region is 10 and occupies 83% of the total 12 single cells of the assembled battery 42. Further, the number of unit cells included in the sixth region is 12, which occupies 100% of the total 12 unit cells of the assembled battery 42.

  From the graph of FIG. 6, it can be seen that the temperature of each part of the assembled battery 42 at the time of charging is the highest at the center position C and decreases as the distance from the center position C increases. Here, it can be seen that the temperature change behavior of the first thermocouple t1 disposed at the center position C is substantially the same as the temperature change behavior of the second thermocouple t2, and the temperature is also substantially the same.

  From Table 1, the first thermocouple t1 shows 33.1 ° C., the second thermocouple t2 shows 32.9 ° C., and in the assembled battery, the range of 33% of the central portion is almost the same temperature. It can be said that it generates the most heat.

  From this, it is considered that it is effective to improve the characteristics of the assembled battery to use an electrolytic solution having excellent heat resistance in at least 33% of the central portion with respect to the entire length of the assembled battery. For this reason, in the battery pack 2, the number of battery cells included in the first battery cell group 10 is preferably 33% or more of the total number of battery cells included in the battery pack 2. By setting the number of unit cells included in the first unit cell group 10 to be 33% or more of the total number of unit cells included in the assembled battery 2, the first unit cell 6 that is resistant to heat becomes the assembled battery. This is because, in the central portion of 2, the region that can cover the most heat generating portion is occupied.

  On the other hand, when the number of single cells included in the first single cell group 10 exceeds 50% of the total number of single cells included in the assembled battery 2, the number of second single cells 8 is relatively reduced. Since it becomes difficult to obtain good discharge characteristics, the number of single cells included in the first single cell group 10 is preferably 50% or less of the total number of single cells included in the assembled battery 2.

  The total number of unit cells 4 included in the assembled battery 2 is not particularly limited. However, if the number of unit cells 4 is 10 or more, the needs of the power storage / backup system can be sufficiently met. It is preferable that Further, the larger the total number of unit cells 4 included in the assembled battery 2, the larger the capacity, so it is preferable that the number be as large as possible. However, in consideration of the handling of the assembled battery 2, the number is 30 or less. Is preferred.

  In FIG. 1, the assembled battery 2 is schematically illustrated, and leads and terminals are not illustrated. The same applies to FIG. 2, FIG. 3, and FIG.

[Example]
1. Manufacture of assembled batteries

  (Example 1)

  (1) Manufacture of single cells

  A nickel positive electrode, a hydrogen storage alloy negative electrode, and a separator used for a general nickel metal hydride storage battery were prepared. The prepared nickel positive electrode and the hydrogen storage alloy negative electrode were superposed with a separator interposed therebetween to produce an electrode group. Ten electrode groups were manufactured.

  On the other hand, 10 single cell containers were prepared. This unit cell container has a flat box shape with a length in the arrow X direction in FIG. 1 of 180 mm, a length in the arrow Y direction of 240 mm, and a length in the arrow Z direction of 30 mm.

  Furthermore, two types of alkaline electrolyte were prepared.

  First, one alkaline electrolyte contains NaOH and LiOH as solutes, and the NaOH concentration is adjusted to 7.50 mol / l and the LiOH concentration is adjusted to 0.50 mol / l. This alkaline electrolyte is an alkaline electrolyte containing NaOH as a main component, and is of a type with little deterioration even when exposed to high temperatures. This alkaline electrolyte is used as a first alkaline electrolyte. In addition, the sum total of the density | concentration of the alkaline component of a 1st alkaline electrolyte is 8.00 mol / l.

  The other alkaline electrolyte contains KOH, NaOH and LiOH as solutes, and the KOH concentration is adjusted to 7.50 mol / l, the NaOH concentration is adjusted to 0.25 mol / l, and the LiOH concentration is adjusted to 0.25 mol / l. Has been. This alkaline electrolyte is an alkaline electrolyte containing KOH as a main component and is a type excellent in discharge characteristics. This alkaline electrolyte is used as a second alkaline electrolyte. In addition, the sum total of the density | concentration of the alkaline component of a 2nd alkaline electrolyte is 8.00 mol / l.

  Table 2 below collectively shows the compositions of the first alkaline electrolyte and the second alkaline electrolyte.

  The electrode group prepared as described above was accommodated in a cell container.

  A predetermined amount of the first alkaline electrolyte was injected into 4 out of 10 unit cell containers containing the obtained electrode group. After that, the unit cell container was sealed, and four first unit cells 6 were manufactured.

  On the other hand, a predetermined amount of the second alkaline electrolyte was injected into the remaining 6 out of 10 unit cell containers that housed the obtained electrode group. After that, the unit cell container was sealed to manufacture six second unit cells 8.

  (2) Assembly of assembled battery

  The four first unit cells 6 were connected in a straight line by being combined so that the surfaces having the largest area among the respective surfaces in the box shape were in contact with each other.

  Further, three second unit cells 8 were similarly connected to both sides so as to sandwich the four first unit cells 6 that were connected. As a result, as shown in FIG. 1, the assembled battery 2 has a configuration in which four first unit cells 6 are arranged in the central portion and three second unit cells 8 are arranged on both sides sandwiching the central portion. Got.

  Each cell 4 has a positive electrode terminal and a negative electrode terminal (both not shown), and these positive electrode terminal and negative electrode terminal are appropriately electrically connected in series by leads (not shown). Yes.

  (3) Initial activation process

  The assembled battery 2 was left for 1 day in an environment of 25 ° C., and then charged for 16 hours with a charging current of 0.1 C. Thereafter, the assembled battery 2 was left in an environment at 25 ° C. for 12 hours. Then, it discharged until the battery voltage became 1.0V with the discharge current of 0.2C. The initial activation process was performed by repeating such charging and discharging operations twice. In this way, the assembled battery 2 was made usable.

  (Comparative Example 1)

  As shown in FIG. 2, in the same manner as in Example 1, except that only the first alkaline electrolyte is used, only the first single cells 6 are manufactured, and only the first single cells 6 are combined. The assembled battery 22 in a usable state was manufactured.

  (Comparative Example 2)

  As shown in FIG. 3, in the same manner as in Example 1, except that only the second alkaline electrolyte is used, only the second single cell 8 is manufactured, and only the second single cell 8 is combined. The assembled battery 32 in a usable state was manufactured.

  Table 3 below collectively shows the configurations of the assembled batteries of Example 1, Comparative Example 1, and Comparative Example 2.

2. Assembled battery evaluation

  (1) Capacity inspection after initial activation process

  The assembled batteries 2, 22, and 32 of Example 1 and Comparative Examples 1 and 2 that have been subjected to the initial activation treatment were charged 100% with a charging current of 0.1 C under an environment of 25 ° C., and then 20 Left for a minute. Then, it discharged until the voltage of the assembled battery became 1.0V with the discharge current of 0.2C in the same environment. The discharge capacity at this time was determined.

  As a result, the capacity value of the assembled battery 32 of Comparative Example 2 is the highest, the capacity value of the assembled battery 2 of Example 1 is next highest, and the capacity value of the assembled battery 22 of Comparative Example 1 is the lowest. It was.

  (2) Cycle life test

  The assembled batteries 2, 22, and 32 of Example 1 and Comparative Examples 1 and 2 that had been subjected to the initial activation treatment were charged at 1.0 It for 1 hour in an environment of 40 ° C., and then left for 20 minutes. . Thereafter, the battery was discharged at 1.0 It until the voltage of the assembled battery became 1.0 V under the same environment, and then left for 10 minutes.

Charging / discharging was repeated with the above-described charging / discharging cycle as one cycle, and the discharge capacity was measured for each cycle. Here, the discharge capacity in charge / discharge at the first cycle was set as the initial capacity, and the capacity maintenance rate for each cycle was calculated from the following formula (I).
Capacity maintenance ratio (%) = (discharge capacity in each cycle / initial capacity) × 100 (I)

  Then, the relationship between the capacity maintenance rate and the number of cycles was determined for each battery, and the results are shown in the graph of FIG.

  (3) Consideration

  (I) About the battery pack of Comparative Example 2

  Since the assembled battery 32 of Comparative Example 2 is composed of only the second single battery 8 using the second alkaline electrolyte having excellent discharge characteristics, the capacity value is the assembled battery 22 of Comparative Example 1. In addition, the value is higher than that of the assembled battery 2 of Example 1.

  However, in a cycle life test under an environment of 40 ° C., it is easily affected by heat, and a decrease in discharge capacity due to a decrease in charging efficiency was observed. Furthermore, since the capacity drop due to the unbalance of the discharge capacity between the single cells occurs with the cycle, the cycle life is the shortest among the three assembled batteries of Example 1, Comparative Example 1 and Comparative Example 2. it is conceivable that.

  (Ii) About the battery pack of Comparative Example 1

  Since the assembled battery 22 of Comparative Example 1 is composed of only the first unit cell 6 using the first alkaline electrolyte that is not easily affected by heat, the battery 22 is exposed to a high temperature due to the accumulation of heat. However, it is difficult to reduce the charging efficiency, and it is considered that the battery life is longer than that of the assembled battery 32 of Comparative Example 2.

  However, although the first alkaline electrolyte is not easily affected by heat, the discharge characteristic is inferior to that of the second alkaline electrolyte, and thus the original discharge capacity value is low.

  (Iii) About the assembled battery of Example 1

  In the assembled battery 2 of Example 1, the first unit cell 6 using the first alkaline electrolyte that is not easily affected by heat is disposed in the central portion where heat is likely to accumulate. It is difficult for efficiency to decrease. For this reason, it is difficult for the discharge capacity to be unbalanced, and accordingly, the life is extended. And since the 2nd single cell 8 using the 2nd alkaline electrolyte which is excellent in discharge characteristics is arranged in the both sides which are hard to accumulate heat, it is electrically large as a whole assembled battery. Can be maintained. Therefore, it can be said that the assembled battery 2 of Example 1 is an excellent assembled battery having excellent cycle life characteristics while maintaining a large electrical capacity.

  <Aspect of the Present Invention>

  A first aspect of the present invention is an assembled battery formed by combining a plurality of unit cells, each of the unit cells has a flat box shape, and is the most area among each surface in the box shape A plurality of the single cells located in a central portion in the longitudinal direction in the straight line form a first single battery group, and the straight lines are combined. When the plurality of unit cells located on both sides sandwiching the central portion in the longitudinal direction in the shape are used as the second unit cell group, the unit cells included in the first unit cell group are used. The electrolytic solution used is a first alkaline electrolytic solution containing NaOH as a main component of solute, and the electrolytic solution used in the unit cells included in the second single cell group has KOH as a main component of solute. With the second alkaline electrolyte That is a set battery.

  According to a second aspect of the present invention, in the first aspect of the present invention described above, the sum of the concentrations of alkali components in the first alkaline electrolyte and the sum of the concentrations of alkali components in the second alkaline electrolyte are: , Both are 5.30 mol / l or more and 8.50 mol / l or less, and the concentration of NaOH in the first alkaline electrolyte is 4.75 mol / l or more and 8.00 mol / l or less. In the alkaline electrolyte, the assembled battery has a KOH concentration of 5.20 mol / l or more and 8.00 mol / l or less.

  According to a third aspect of the present invention, in the first aspect of the present invention or the second aspect of the present invention described above, the number of the unit cells constituting the first unit cell group is included in the assembled battery. It is an assembled battery that is 33% or more and 50% or less of the total number of the single cells.

  A fourth aspect of the present invention is an assembled battery according to any one of the first to third aspects of the present invention described above, wherein the total number of the unit cells is 10 or more.

2 battery pack (Example 1)
4 unit cell 6 first unit cell 8 second unit cell 10 first unit cell group 12 second unit cell group 22 assembled battery (Comparative Example 1)
32 battery pack (Comparative Example 2)

Claims (4)

In an assembled battery formed by combining a plurality of single cells,
Each of the single cells has a flat box shape, and is combined and linearly connected so that the surfaces with the largest areas of the surfaces in the box shape are in contact with each other.
A plurality of the single cells located at the central portion in the longitudinal direction in the straight line form a first single cell group, and the plurality of single cells located at both sides sandwiching the central portion in the longitudinal direction in the linear shape. In the case of the second unit cell group, the electrolyte used in the unit cell included in the first unit cell group is a first alkaline electrolyte containing NaOH as a main component, An assembled battery, wherein the electrolytic solution used in the unit cells included in the second unit cell group is a second alkaline electrolyte containing KOH as a main component of a solute.   The sum of the concentrations of the alkali components in the first alkaline electrolyte and the sum of the concentrations of the alkali components in the second alkaline electrolyte are both 5.30 mol / l or more and 8.50 mol / l or less, The concentration of NaOH in the first alkaline electrolyte is 4.75 mol / l to 8.00 mol / l, and the concentration of KOH in the second alkaline electrolyte is 5.20 mol / l to 8.00 mol / l. The assembled battery according to claim 1, which is 1 or less.   The assembled battery according to claim 1 or 2, wherein the number of the single cells constituting the first single battery group is 33% or more and 50% or less of the total number of the single cells included in the assembled battery.   The assembled battery according to claim 1, wherein the total number of the single cells is 10 or more.

Images