JP2002199601A - Power supply system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a power supply system which has a shelf life and improves the yield of the secondary battery. SOLUTION: A cell control circuit, which controls the secondary battery by each cell, is connected to each lithium ion secondary battery. The secondary battery whose voltage drop rate is large is connected to the cell control circuit whose dark current is small, and the secondary battery whose voltage drop rate is small is connected to the cell control circuit whose dark current is large. Dispersion can be made small by absorbing the voltage drop rate of each secondary battery using the voltage drop rate of the dark current of the control circuit.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a power supply system, and more particularly, to a power supply system including a plurality of secondary batteries and a cell control circuit for controlling the secondary batteries one by one.

[0002]

2. Description of the Related Art In recent years, research and development of an electric vehicle using only a secondary battery as a power source, a hybrid vehicle combining a secondary battery and an internal combustion engine, a load leveling system, and the like have been actively conducted. For such automobiles and systems, for example, a power supply system is used in which a number of secondary batteries having a double oxide containing lithium such as lithium manganate and abundant and inexpensive manganese as a positive electrode active material are connected. I have.

[0003] In order to drive an automobile or the like, a high voltage is usually required as a power supply system. Therefore, tens to hundreds of secondary batteries are connected in series to form one module. However, if the secondary battery in the power supply system differs from the battery characteristics of other secondary batteries, the rate of the secondary battery having a different battery characteristic becomes rate-determining, and the characteristics of the power supply system deteriorate. For this reason, in the power supply system, secondary batteries with similar battery characteristics are selected and used, and a battery control for monitoring battery voltage and / or adjusting the capacity is attached to each secondary battery to control the battery.
Protecting. In particular, in the case of lithium secondary batteries, since the rate of voltage drop affects the life of the battery when left unattended, etc., batteries with the same voltage drop rate are selected, and the battery voltage of each secondary battery is monitored by cell control or the like. The capacity of the next battery is adjusted so that the battery voltage becomes the same voltage.

[0004]

However, when a plurality of rechargeable batteries are connected in series and the voltage drop rates of the rechargeable batteries are greatly different, the voltage variation becomes large and the power supply system becomes inefficient when left for a long time. It does not work well, and in some cases, there is a problem that only a specific secondary battery is severely used and generates heat, or the battery life of the secondary battery and the life of the entire power supply system are shortened. In order to solve this problem, the power supply system generally selects and uses secondary batteries having substantially the same voltage drop rate, that is, a voltage drop rate caused by a variation in internal resistance. However, simply selecting and using the secondary batteries causes a problem that the yield in the production of the secondary batteries is reduced.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a power supply system having a long standing life and capable of improving the yield of constituent secondary batteries.

[0006]

According to the present invention, there is provided a power supply system comprising: a plurality of secondary batteries;
A cell control circuit for controlling the secondary battery one cell at a time, the secondary battery having a large voltage drop rate,
The secondary battery with a small voltage drop rate is connected to a cell control circuit with a large dark current.

According to the present invention, a secondary battery having a large voltage drop rate is connected to a cell control circuit having a small dark current,
By connecting the secondary battery with a small voltage drop to the cell control circuit with a large dark current, the total voltage obtained by adding the voltage drop of the secondary battery and the voltage drop of the secondary battery due to the dark current of the cell controller circuit Since the variation in the drop rate can be reduced between the secondary batteries, that is, the voltage drop rate is absorbed by the voltage drop rate due to the dark current of the cell controller circuit, and the variation in the voltage drop rate between the secondary batteries is reduced. Since the size of the power supply system can be reduced, the life of the power supply system can be maintained for a long time, and the yield of the secondary battery can be improved. Such a power supply system is suitable for a lithium secondary battery that requires protection control for each secondary battery.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of a battery module to which the present invention is applied will be described with reference to the drawings. In the present embodiment, a battery module in which 48 sealed cylindrical lithium ion secondary batteries as secondary batteries are connected in series will be described.

(Production of lithium ion secondary battery) Lithium manganate (LiMn ₂ O ₄ ) powder 80% by weight (hereinafter referred to as wt%) as a positive electrode active material, carbon powder 15% by weight as a conductive agent, Polyvinylidene fluoride (hereinafter referred to as PVDF) as a binder (binder)
5 wt% and N-methyl-2-pyrrolidone (hereinafter referred to as N
Notated as MP. ) And kneaded to prepare a slurry (mixture solution).

[0010] As shown in FIGS. 1A and 2, the obtained mixture solution was applied to an aluminum foil 3 using a comma roll.
(Positive electrode current collector) and dried to form a positive electrode active material layer. The required length of the electrode was continuously applied, and 30 mm of the uncoated portion not applied to the aluminum foil 3 was left so as to be in front and back. Next, the required width of the positive electrode active material layer 1 was secured by cutting the opposite side positive electrode active material layer. And
The aluminum foil 3 side remaining 30 mm was cut out by punching to form a positive electrode tab terminal 8. 80 ° C ~
1. Using a roll press having a roll heated to 120 ° C. at a press pressure (linear pressure) of 0.2 to 0.5 kg / cm.
It was compressed to 7 g / cm ³ to produce a belt-shaped positive electrode hoop.

Next, an amorphous carbon powder capable of inserting and removing lithium ions into and from the negative electrode active material is used.
NMP was added to a mixture of wt% and PVDF 10 wt% and kneaded to obtain a slurry. This slurry was applied to a copper foil 4 serving as a negative electrode current collector and dried to form a negative electrode active material layer. As shown in FIG. 1B and FIG. 2, similar to the positive electrode,
The required length for the battery electrode was continuously applied and cut to secure the required width of the negative electrode active material layer 2, and the negative electrode tab terminal 9 was formed by punching. 80 ° C ~ 120 °
1.0 g / c at a press pressure (linear pressure) of 0.2 to 0.5 kg / cm by a roll press having a roll heated to C
to produce a negative electrode hoop strip is compressed until m ^3.

As shown in FIG. 2, the prepared band-shaped positive electrode hoop and negative electrode hoop are arranged such that the positive electrode tab terminal 8 and the negative electrode tab terminal 9 are on opposite sides in the vertical direction. The positive and negative electrode hoops were cut to the required electrode plate length. As the separator 5, a microporous polyethylene sheet was used.

The positive electrode tab terminal 8 of the wound electrode body was resistance-welded to the periphery of the positive electrode current collecting ring 11 and the negative electrode tab terminal 9 was resistance-welded to the periphery of the negative electrode current collecting ring 12. The positive electrode lead plate was welded and connected to the positive electrode current collecting ring 11 and the battery cover 7, respectively, and the tip of the hat of a conductor ring having an inverted hat shape in cross section supporting the negative electrode current collecting ring 12 was joined to the bottom surface of the battery can 6. A solution obtained by mixing ethylene carbonate (EC) and dimethyl carbonate (DMC) at a volume ratio of 1: 2 is added to a solution.
After injecting an electrolytic solution in which lithium fluorophosphate (LiPF ₆ ) is dissolved at 1 mol / liter, the opening of the battery can 6 is closed with a battery lid 7 via a gasket 10 to close the sealed cylindrical lithium ion secondary battery 20. Was assembled. Then, by performing initial charging at a predetermined voltage and current, the lithium ion secondary battery 20 was given a function as a battery.

(Preparation of Cell Control) As shown in FIG. 3, in the cell control of this embodiment, the voltage of each of the eight series lithium ion secondary batteries 20 is divided (partial voltage 1 to partial voltage 8) and each voltage is controlled. Amplifies the voltage division ratio by differential amplification (differential amplification 1 to differential amplification 8) to obtain a detection voltage of each battery. The voltage division is performed in such a manner that the voltage of the lithium ion secondary battery is increased up to about 35 V in the case of eight series connections, which exceeds the withstand voltage of a generally used inexpensive differential amplifier. This is because the differential amplifier is used within the withstand voltage range.

As shown in FIG. 4, a specific cell control circuit for voltage division and differential amplification for each lithium ion secondary battery 20 includes four voltage dividing resistors R1 to R4 and two differential amplifiers IC1. , IC2 and differential amplifiers IC1, IC2
And four resistors R5 to R8 for amplifying the voltage division ratio. In this circuit, the relationship between the resistance values of the respective resistors is R1 =
R3, R2 = R4, R6 = R7, R5 = R8. Here, assuming that the plus terminal voltage of the battery to be detected with respect to ground (GND) is Vp, the minus terminal voltage is Vm, the detection voltage (voltage output of each battery) is Vout, and the offset voltage of the operational amplifier is Voff, the detection voltage Vout Can be expressed by the following equation (1). The offset voltage of the used operational amplifiers IC1 and IC2 is ± 1.8V.

[0016]

(Equation 1)

As shown in FIG. 5, the resistor R1 shown in FIG.
R8 and the dark current flowing through the DC resistor Rt is i, the dark current ib1 flowing through the battery 1 is represented by Rt and the DC resistance of the cell control circuit including the differential amplifiers IC1 and IC2.
Is i1, and the dark current ib2 flowing through the battery 2 is (i1 + i
2) Similarly, the dark current ib7 flowing through the battery 7 is (i1 +
+ i7) and the dark current ib8 flowing through the battery 8 is (i1 + i2 +... + i8). Therefore, the magnitude of the dark current flowing in each battery is different, and since the battery 1 has one dark current circuit, the current value is the smallest, and the number of circuits through which the dark current flows increases as the battery number increases. In addition, the dark current of the battery 8 is the largest. In the cell control of this example, a dark current of 60 μA flows through the battery 1, the dark current increases proportionately as the battery number increases, and a dark current of 270 μA flows through the battery 8.

(Assembly of Battery Module) The above-described lithium ion secondary battery 20 (hereinafter abbreviated as a cell) has four
Eight cells are connected in series, and the cell control circuits 31 to 38 (hereinafter, these cell control circuits 3
1 to 38 are collectively called cell control. ) Was attached. At this time, the cells were rearranged in descending order of the voltage drop rate in each of the eight cells, and attached to the cell control in the descending order of the voltage drop rate. That is, of the eight cells, the cell with the largest voltage drop rate is assigned to the cell control circuit 31, and the cell with the next largest voltage drop rate is assigned to the cell control circuit 32.
The cell with the smallest voltage drop rate was connected to the cell control circuit 38 in this order.

As shown in FIG. 6, the battery module 100
Has one end of a switch SW connected to the plus side of each cell, and one end of a capacitance adjusting resistor R for adjusting the capacitance of each cell is connected to the other end of the switch SW. The other end of the capacitance adjusting resistor R is connected to the minus side of each cell. Therefore, the capacitance adjusting resistor R is connected in parallel to each cell via the switch SW. The switch SW connected in parallel to each cell and the cell control circuit 31
38 have the same circuit configuration, and the battery module 100 has a total of six sets of cell controls shown in FIGS.

The battery module 100 includes a microcomputer (hereinafter referred to as a microcomputer) 40 for controlling the entire battery module 100. Microcomputer 4
0 denotes a CPU for performing arithmetic processing, a ROM in which programs executed by the CPU and various setting values are stored, a RAM serving as a work area of the CPU, and A / D values detected from six sets of cell control circuits 31 to 38. A to convert
It is configured to include a D converter and an input / output interface serving as a port for input / output signals with the outside.

The above-described cell control circuits 31 to 38
Is connected to the AD conversion input port of the microcomputer 40. Therefore, the cell control circuits 31 to 38 output the voltage between both ends of each cell connected in parallel to the microcomputer 40,
The microcomputer 40 can carry out AD conversion of the input voltage between both ends of each cell and take in the voltage of each cell. Also,
Each switch SW is connected to an output port of the microcomputer 40. The switch SW to which the binary high level signal of the weak current is output from the microcomputer 40 is turned on, and the switch SW to which the binary low level signal is output is turned off. Therefore, when a voltage difference of a certain level or more occurs between the cells, the switch SW is turned on so as to reduce the voltage difference between the cells, thereby reducing the variation in the voltage between the cells. Such capacity adjustment can be performed during charging / discharging or during charging / discharging suspension.

The battery module 100 further includes a charge / discharge determining unit 50 that detects the charge, discharge, and rest states of the 48 series assembled batteries and outputs the detected state to the microcomputer 40. The charge / discharge determination unit 50 is connected to the microcomputer 40 and detects the direction of current flowing through the battery pack by, for example, a shunt (shunt) resistor to determine whether the battery pack is in a charge, discharge, or rest state. Output to the microcomputer 40. The uppermost cell side of the assembled battery is connected to the battery module 10 via the charge / discharge determination unit 50.
0, and the lowest cell side of the battery pack is connected to the minus terminal of the battery module 100. These terminals are connected to a charger or load.

Next, the battery module 100 of the present embodiment
The operation of will be described. If the lithium ion secondary battery 20 of the present embodiment is left open for about 20 days after the initial charge, the voltage drop rate varies mainly in the range of 2 to 5 mV / day. When a dark current flows from the battery to the cell control circuit, the circuit of the battery 1 causes a voltage drop of 0.5 mV / day at a dark current of 60 μA, and the dark current increases as the battery number increases, and the circuit of the battery 8 also increases. In this case, a voltage drop of 2.5 mV / day occurs at a dark current of 270 μA. Therefore, the voltage drop rate of the circuit of the battery 1 is 4 mV
/ Day is connected, and the circuit of the battery 8 is 2 mV
Connect the battery near / day. As a result, the voltage drop rate of the voltage drop due to the internal resistance of the battery itself and the voltage drop due to the dark current of the cell control is 4 to 5 mV /
In this case, the variation width of the battery voltage of each lithium ion secondary battery can be set to 2 mV / day or less.

On the other hand, instead of the combination of the voltage drop rate of each lithium ion secondary battery and the dark current for cell control as in the battery module of the present embodiment,
When a battery is simply attached to the cell control, the variation in the voltage drop in the battery module is 4 mV / max.
day.

The voltage variation width in the module is 200 m
When the battery module has a battery life of not less than V, a reference is provided that the battery module has a non-lifetime, and a non-lifetime of 100 days is used as a conventional battery module. It is necessary to select a battery having a very small variation in the voltage drop rate. When such a selection is performed, the yield of the secondary battery becomes 30%.

On the other hand, when the voltage drop rate of the secondary battery and the dark current of the cell controller are combined as in the battery module of the present embodiment, variations in the voltage drop rate can be absorbed. The battery yield is 98%. Therefore, in the battery module according to the present embodiment, it is possible to secure the standing life and improve the yield of the secondary battery. In particular, when the secondary battery used is a lithium secondary battery as in the present embodiment, if a voltage variation occurs between the secondary batteries, the secondary battery having a specific rate-determining temperature becomes high. Therefore, a situation that should be considered in terms of safety can be considered. Therefore, a battery module that can absorb variations between the secondary batteries can improve reliability not only in terms of life and yield but also in terms of safety.

In this embodiment, one microcomputer 40
Although an example in which only the microcontroller is used has been described, for example, a microcomputer may control every eight cell controls, and each microcomputer may be entirely controlled by an upper microcomputer. In this case, if information is exchanged between the microcomputer and the higher-level microcomputer by communication (dialogue), the length of the entire wiring can be shortened, and noise is less likely to be picked up.
The number of wirings can be reduced. Further, in this embodiment, an example in which the cell control circuit is connected to all 48 cells has been described. However, the voltage may be sequentially detected (monitored) in units of 8 cells by switching with a switch or the like. Good. Further, in the present embodiment, an example is shown in which the cell control is performed in units of eight cells, but the present invention is not limited to this.

Further, in the present embodiment, the monitoring and the capacity adjustment in which the voltage of each lithium ion secondary battery is detected and the capacity is adjusted when a voltage difference between the batteries exceeds a predetermined value are exemplified. The present invention is not limited to this, and can be applied to a general control circuit in which each secondary battery is individually controlled and a dark current flows.

Further, in this embodiment, an example was shown in which lithium manganate was used as the lithium manganese double oxide, but in addition to lithium manganate, Li, V, Cr, F
A manganese site or a lithium manganese composite oxide in which a manganese site or a lithium site is substituted by at least one metal selected from e, Co, Ni, Mo, W, Zn, B, and Mg may be used. Further, in the present embodiment, an example in which heating is performed using a roll for the processing method of performing the heat treatment in the pressing step has been described. However, if the binder of the active material can be melted and solidified, heating may be performed by another method. Good.

In this embodiment, EC and D are used in the electrolyte.
An example of a solution obtained by dissolving LiPF ₆ in a solution in which MC and MC are mixed has been exemplified. Other organic solvents for the electrolytic solution include propylene carbonate, 1,2-dimethoxyethane, and 1,2-dimethoxyethane.
Diethoxyethane, dietal carbonate, γ-butyl lactone, tetrahydrofuran, diethyl ether, sulfolane, acetonitrile, or the like alone or a mixed solvent of two or more thereof can be used, and the electrolyte is also LiClO ₄ , LiBF ₄ , LiCl, LiBr,
CH ₃ SO ₃ Li, LiAsF ₆ or the like can be used.

Further, as the carbon material, pitch coke, petroleum coke, graphite, carbon fiber, activated carbon and the like, or a mixture thereof may be used. Further, as a binder, other C4-C12 alkyl esters of acrylic acid and / or methacrylic acid such as isobutyl acrylate, octyl acrylate, nonyl acrylate, butyl methacrylate and 2-ethylhexyl methacrylate, and methacrylic acid, itaconic acid, maleic acid, Copolymers with unsaturated monomers having a functional group such as fumaric acid, polyacrylic acid such as acrylamide and methacrylamide or a functional group of carboxysilyl group or amide group, polyamide, polyamideimide, polyamidebismaleimide, polybutylene terephthalate, and polyethylene terephthalate And the like, and these can be used alone or in combination.

[0032]

As described above, according to the present invention,
A secondary battery with a large voltage drop rate is connected to a cell control circuit with a small dark current, and a secondary battery with a small voltage drop rate is connected to a cell control circuit with a large dark current, so that the voltage drop rate of the cell controller circuit is reduced. The variation in the voltage drop rate between the secondary batteries can be reduced by absorbing the voltage drop rate due to the dark current, so that the power supply system can be maintained for a long time and the secondary battery yield can be improved. Can be obtained.

[Brief description of the drawings]

FIG. 1 is a plan view of an electrode plate hoop of a sealed cylindrical lithium ion secondary battery used in a battery module according to an embodiment to which the present invention can be applied, (A) is a positive electrode hoop, and (B) is a negative electrode hoop. Is shown.

FIG. 2 is a sectional view of a sealed cylindrical lithium ion secondary battery used in the battery module of the embodiment.

FIG. 3 is a block diagram of cell control of the battery module of the embodiment.

FIG. 4 is a circuit diagram of a cell control circuit of the battery module according to the embodiment.

FIG. 5 is an equivalent circuit diagram showing equivalent DC resistance of cell control of the battery module of the embodiment, the equivalent DC resistance, and dark current flowing through each secondary battery.

FIG. 6 is a block diagram of the battery module of the embodiment.

[Explanation of symbols]

 31, 32,..., 38 Cell control 40 Microcomputer 100 Battery module (power supply system)

 ────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kensuke Hironaka 2-7-7 Nihonbashi Honcho, Chuo-ku, Tokyo F-term in Shin-Kobe Electric Co., Ltd. 5G003 BA03 CA14 CC04 5H030 AA01 AS08 BB21 BB23

Claims (2)

[Claims] In a power supply system including a plurality of secondary batteries and a cell control circuit for controlling each of the secondary batteries one by one, a secondary battery having a large voltage drop rate has a small dark current. And the secondary battery having a small voltage drop rate is connected to a cell control circuit having a large dark current. 2. The power supply system according to claim 1, wherein said secondary battery is a lithium secondary battery.