JPH10154504A - Battery pack - Google Patents

Abstract

PROBLEM TO BE SOLVED: To clarify the permissive range of the dispersion of a unit battery of a battery group constituting a battery pack which is provided with an over- discharge prevention circuit and/or an over-charge circuit, and two or more series connections, and enhance productivity. SOLUTION: When the rated capacity of a unit battery constituting a battery pack is expressed by X, the average actual capacity of the unit battery constituting the battery pack, by Y, the parallel connection number of battery groups in the battery pack, by (n), the maximum value of a battery group actual capacity connected in parallel in the battery pack, by (a), and the minimum value of the battery group actual capacity connected in parallel in the battery pack, by (b), X<=Y and a-b<=0.15×n×Y are satisfied.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a battery pack composed of secondary batteries.

[0002]

2. Description of the Related Art A secondary battery is mainly used in the form of an assembled battery, except for a lead storage battery installed in an automobile having an engine. With the spread of portable devices in recent years, secondary batteries having a high energy density have become widespread. At present, a lithium secondary battery using a non-aqueous electrolyte has the highest energy density among secondary batteries on the market. Since the performance of such a nonaqueous electrolyte secondary battery is significantly deteriorated due to overcharge and overdischarge, each battery usually has a protection circuit (an overcharge prevention circuit and / or an overdischarge prevention circuit). .

[0003]

However, as described above, if each of the batteries is provided with a protection circuit, the battery capacity of the assembled battery is small even if the capacity of the manufactured batteries varies. The protection circuit is activated first and controls the capacity of the whole battery pack, and a sufficient capacity cannot be obtained. Therefore, each unit cell is charged and discharged one or more times before forming the assembled battery, and the battery capacity is checked. An object of the present invention is to provide a battery pack having two or more series-connected batteries each having an overdischarge prevention circuit and / or an overcharge prevention circuit, and to allow for variations in the capacity of cells or battery groups. The purpose is to clarify the range and reduce the yield of assembled battery production.

[0004]

In order to solve the above-mentioned problems, a battery group formed by connecting two or more cells having an overdischarge prevention circuit and / or an overcharge prevention circuit of the present invention in parallel is provided. , A battery pack configured by connecting in series, the rated capacity of the battery cell is X, the average of the actual capacities of the battery cells that constitute the battery pack is Y, the number of parallel connected battery groups that constitute the battery pack is n, Where a is the maximum value of the actual capacity of the battery group constituting the battery group and b is the minimum value of the actual capacity of the battery group constituting the assembled battery, X ≦ Y
And ab ≦ 0.15 × n × Y. Further, in order to solve the above-mentioned problem, an assembled battery in which cells having the overdischarge prevention circuit and / or the overcharge prevention circuit of the present invention are connected in series, has a rated capacity of X, X The average of the actual capacities of the cells constituting the battery is Y,
When the maximum value of the actual capacity of the unit cells constituting the assembled battery is a and the minimum value of the actual capacity of the unit cells constituting the assembled battery is b,
It is characterized in that X ≦ Y and ab ≦ 0.15 × Y are satisfied. The rated capacity refers to the amount of ampere-hour electricity announced by the manufacturer that the battery can be taken out of full charge under specified temperature, discharge current, and cut-off voltage conditions according to the standard of SBA 6004. For this reason, the rated capacity value is a reference for the charging rate and the charging amount when the battery is charged by the charger. The actual capacity is an actual discharge capacity value when the battery is used in a predetermined use state (charge and discharge conditions). The actual capacity value differs in each cycle by repeating the charge / discharge cycle. Therefore, the actual capacity in the present invention is one to charge and discharge under a predetermined use condition.
It is defined as one of the discharge capacity values after 50 repetitions.

A battery pack that satisfies the above conditions has reduced variation in the capacity of the cells constituting the battery pack and satisfies the rated capacity. Therefore, the number of defective battery packs is reduced, and the yield can be improved.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below by taking a battery pack using a lithium secondary battery as an example. The positive electrode plate was prepared by applying a paste active material mainly composed of a lithium-cobalt composite oxide on both surfaces of an aluminum foil having a thickness of 20 μm, drying and rolling, and then cutting the material to a width of 55 mm. The negative electrode plate was prepared by applying a paste-like active material mainly composed of graphite to both surfaces of a copper foil having a thickness of 10 μm, drying and rolling, and then cutting into a width of 56 mm. These positive electrode plate and negative electrode plate are wound through a separator made of a microporous polyethylene film having a thickness of 25 μm and a width of 58 mm to produce a wound body. This wound body is inserted into a negative electrode can, and a tab terminal previously welded to the negative electrode current collector is welded to the bottom of the can. Next, after injecting 5 ml of an electrolytic solution obtained by dissolving LiPF ₆ at a concentration of 1 mol / l into a solvent obtained by mixing propylene carbonate and dimethyl carbonate at a volume ratio of 40:60, the positive electrode current was previously collected through an insulating gasket. The positive electrode tab terminal welded to the body was welded to the positive electrode cap, placed over the negative electrode can, and the upper part of the negative electrode can was caulked to seal the battery. Thus, the rated capacity is 1000
A single cell of a mAh lithium ion secondary battery is obtained. still,
A protection circuit that operates when a voltage of 4.3 V is detected during charging and a voltage of 2.3 V is detected during discharging per unit cell is mounted.

[0007] The cell produced by the above-described method is charged at a constant current of 1000 mA, and when the battery voltage reaches 4.2 V, the battery is switched to constant voltage charging so as to maintain the battery voltage. When the total charging time reaches 2.5 hours, charging is stopped. Then 1000 until the battery voltage becomes 2.5V
The battery is discharged at a constant current of mA, and the actual capacity of each cell is measured. Table 1 shows the actual capacities of the cells A to δ.

[0008]

[Table 1]

A battery group is prepared by connecting in series a battery group in which battery E, battery F, and battery G in Table 1 are connected in parallel, and a battery group in which battery H, battery I, and battery J are connected in parallel. I do. In this battery pack, X = 1000 mAh Y = 1013 mAha a = 1205 mAh b = 915 mAh n = 3 ab = 290 mAh 0.15 × n × Y = 456 mAh. Therefore, X ≦ Y and a−b ≦ 0.15 × n × Y are satisfied. This battery pack is not a target for failure.

[0010] The above-mentioned assembled battery is obtained by connecting two battery groups each having three unit cells connected in parallel, and the number of unit cells in parallel and the number of unit cells or battery groups connected in series are appropriately selected according to the application. It is possible to

[0011]

EXAMPLE Battery groups 1 to 9 in which two to four cells shown in Table 2 were connected in parallel, and a rated capacity (1000
A test in which charging and discharging were repeated 300 times was performed on a single cell satisfying mAh). The unit cells used are those shown in Table 1. The charging conditions are as follows: 1000 mA x number of parallel (n)
When the battery voltage reaches 4.2 V, the battery voltage is switched to constant voltage charging so as to maintain the battery voltage.
When the total charging time reaches 2.5 hours, charging is stopped. The discharge condition is to discharge at a constant current of 1000 mA × the number of parallel (n) until the battery group voltage or the voltage of the unit cell becomes 2.5 V. Table 2 shows the initial discharge capacity (mAh) of each battery group or unit cell,
And the capacity retention rate after 300 cycles (discharge capacity at 300 cycles / discharge capacity at 1st cycle × 100 (%))
Are also shown.

[0012]

[Table 2]

Based on the actual capacities of the cells shown in Table 2 and the capacity retention rates shown in Table 2, the battery groups connected in parallel have a large charge / discharge cycle even if the actual capacities of the cells constituting the cells vary greatly. It can be seen that the deterioration due to the repetition of is not so large as compared with the single cell.

Next, a large number of cells having different actual capacities were manufactured by the manufacturing method described in the embodiment of the invention, and assembled cells 1 to 9 in which the cells were connected in two series and three series were manufactured. The charge and discharge of these assembled batteries and the unit cells as reference examples are 300
Repeated tests were performed. The assembled battery used was constituted by a unit cell having the actual capacity shown in Table 3. The charging condition is 1000m
Charge at constant current of A, switch to constant voltage charging to maintain the battery voltage when the battery voltage becomes 4.2V x number of series, and stop charging when total charging time reaches 2.5 hours Is what you do. The discharge condition is to discharge at a constant current of 1000 mA until the battery group voltage or the voltage of the unit cell becomes 2.5 V × the number of series. Table 3
Shows the initial discharge capacity of each battery pack or cell, and 3
Capacity retention after 00 cycles (discharge capacity at 300th cycle / discharge capacity at 1st cycle × 100 (%)), a−
b (mAh), Y (mAh) and 0.15 × Y (mAh) are also shown. Since the assembled batteries 1 to 9 are unit cells connected in series, the parallel number n = 1.

[0015]

[Table 3]

From the results shown in Table 3, the battery packs 7 and 9 that do not satisfy X ≦ Y first satisfy the rated capacity (1000 mAh) even if they satisfy ab ≦ 0.15 × Y. No, it is a target of failure. Also, the assembled battery 6 that does not satisfy ab ≦ 0.15 × Y even though X ≦ Y is satisfied,
8 shows that the value of the capacity retention ratio is lower than that of other assembled batteries satisfying ab ≦ 0.15 × Y. On the other hand, the assembled battery satisfying ab ≦ 0.15 × Y shows a value comparable to the capacity retention rate of the unit cell.

Further, by the manufacturing method described in the embodiment of the present invention, a large number of unit cells having different actual capacities are manufactured, and an assembled battery 10 in which three battery groups in which three unit cells are connected in parallel is connected in series.
13. Assembled batteries 14 to 17 in which two battery groups in which two single cells were connected in parallel were connected in series. A test in which charging and discharging were repeated 300 times was performed on the assembled battery and the unit cell as the reference example. Table 4 shows the actual capacity of each battery group constituting the battery pack. The charging conditions were as follows: first, charging was performed with a constant current of 1000 mA × parallel number, and when the battery voltage became 4.2 V × series number, switching to constant voltage charging was performed so as to maintain the battery voltage. When the time has come, charging is stopped. The discharge condition is 1 until the battery group voltage or the cell voltage becomes 2.5 V × the number of series.
It discharges at a constant current of 000 mA × the number of parallel circuits. Table 4 shows the initial discharge capacity of each battery pack or unit cell, and the capacity retention rate after 300 cycles (discharge capacity at 300 cycles 放電 discharge capacity at 1st cycle x 100 (%)).
Ab (mAh), Y (mAh), and 0.15 × nxY (mAh) are also shown. Note that Y is calculated from the actual capacities of all the cells measured in advance.

[0018]

[Table 4]

From the results shown in Table 4, first, in the case of the assembled batteries 13 and 17 which do not satisfy X ≦ Y, the actual capacity of the actual unit cell is the rated capacity even if ab ≦ 0.15 × n × Y is satisfied. (1000
mAh) is not satisfied, and thus becomes a target of failure. Also,
The assembled batteries 12 and 16 that do not satisfy ab ≦ 0.15 × n × Y even if X ≦ Y are satisfied have ab ≦ 0.15 × nx.
It is understood that the value of the capacity retention ratio is lower than that of other assembled batteries that satisfy Y. On the other hand, ab ≦ 0.15 × n
A battery pack that satisfies XY shows a value comparable to the capacity retention rate of the unit cell.

[0020]

According to the present invention, an allowable range of the variation in the capacity of a single cell or a group of batteries constituting an assembled battery having two or more series connections provided with an overdischarge prevention circuit and / or an overcharge prevention circuit is provided. And the yield of assembled battery production was reduced.

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Koji Higashimoto 2-8-7 Nihonbashi Honcho, Chuo-ku, Tokyo Inside Shin-Kobe Electric Co., Ltd.

Claims (3)

[Claims] 1. An assembled battery comprising two or more cells connected in parallel and provided with an over-discharge prevention circuit and / or an over-charge prevention circuit, and connected in series. The capacity is X, the average of the actual capacities of the cells constituting the assembled battery is Y, the number of parallel connections of the battery group constituting the assembled battery is n,
When the maximum value of the actual capacity of the battery group constituting the assembled battery is a and the minimum value of the actual capacity of the battery group constituting the assembled battery is b,
An assembled battery, wherein X ≦ Y and ab ≦ 0.15 × n × Y are satisfied. 2. An assembled battery comprising a series of cells each having an overdischarge prevention circuit and / or an overcharge prevention circuit, wherein the rated capacity of the cells is X, and the actual size of the cells constituting the assembled battery is X. Assuming that the average capacity is Y, the maximum value of the actual capacity of the cells constituting the assembled battery is a, and the minimum value of the actual capacity of the cells constituting the assembled battery is b, X ≦ Y and a− b ≦ 0.15 ×
A battery pack characterized by satisfying Y. 3. The battery according to claim 1, wherein the battery is a non-aqueous electrolyte secondary battery.
Or the battery pack according to 2.