WO2012014289A1 - Lithium ion secondary battery system - Google Patents

Abstract

Provided is a lithium ion secondary battery system which is safer and has higher reliability. This lithium ion secondary battery system is obtained by connecting a plurality of batteries in series, in each of said batteries a plurality of lithium ion secondary cells being connected in parallel. A lithium ion secondary cell comprises a protection circuit, and the protection circuit has: a charge/discharge-side connection terminal; a first fuse and a second fuse, which are connected in series so as to connect the connection terminal and the positive-side electrode of the lithium ion secondary cell; a switching element that is arranged so as to connect a wiring line between the first fuse and the second fuse and the negative electrode of the lithium ion secondary cell; and a detection circuit that is connected to the charge/discharge-side connection terminal, the switching element and the negative electrode of the lithium ion secondary cell and controls on/off of the switching element.

Description

Lithium ion secondary battery system

The present invention relates to a lithium ion secondary battery system formed by combining a plurality of lithium ion secondary batteries.

Lithium ion secondary batteries have the advantage of having a higher energy density than conventional batteries by weight, and have been widely used in portable devices such as notebook computers and mobile phones. In general, a lithium ion battery includes a lithium transition metal oxide in a positive electrode and carbon in a negative electrode, and an electrolyte including a lithium salt therebetween.

By the way, while the lithium ion secondary battery has an advantage such as high energy density, it generates heat due to overcharging and the electrode is eluted, and metallic lithium in the electrode material is deposited, and in the worst case, it may burst or ignite. There is a problem. Therefore, it is common to provide a protection circuit that monitors the state of charge and cuts off the connection between the charger and the battery when an overcharged state occurs. As a technique relating to this known protection circuit, for example, the following Patent Document 1 discloses a technique relating to a secondary battery pack having a protection circuit provided with a fuse.

JP 2006-73457 A

By the way, in order to further utilize the high energy density of the lithium ion secondary battery, a battery system in which a plurality of lithium ion secondary batteries are connected in series or in parallel (hereinafter referred to as a “lithium ion secondary battery system”). ) Has been studied. Thereby, a high-power lithium ion secondary battery system can be obtained for a long time.

However, the above conventional technique has not been studied for application to a system in which a plurality of batteries such as a lithium ion secondary battery system are combined, and even if it is applied temporarily, the output is extremely high. The above problem in the lithium ion secondary battery system cannot be dealt with.

Also, when charging / discharging, if charging is performed while the battery is being discharged, the charging / discharging may stop or operate each time the battery potential changes. In such a case, if this operation is performed at high speed, unnecessary heat loss occurs in the transistor that controls ON / OFF of the operation.

場合 This is not a problem when the power is small, but this effect cannot be ignored in the case of the large power assumed this time. Therefore, there is a method of preventing the input / output transistor from being immediately turned ON / OFF by using potential-like hysteresis because it does not easily cope with potential fluctuations. However, when a lithium ion battery is used, a subtle potential is also actively used. Therefore, a method using such a hysteresis may not be able to sufficiently handle input / output ON / OFF control.

In such a state, the transistors used (mainly MOS-FETs) run out of heat and the battery cannot be turned ON / OFF.

Therefore, the failure caused by the above-mentioned transistor SW can be avoided by performing the response with a negligible heat generated in the transistor by slowly turning it on and off over time.

Therefore, in view of the above problems, the present invention provides a safer and more reliable lithium ion secondary battery system.

That is, a lithium ion secondary battery system according to an aspect of the present invention is a lithium ion secondary battery system in which a plurality of assembled batteries formed by connecting a plurality of lithium ion secondary batteries in parallel are further connected in series. The battery is provided with a protection circuit, and the protection circuit is connected in series so as to connect the charge / discharge side connection terminal, the charge / discharge side connection terminal, and the positive electrode of the lithium ion secondary battery. A switching element arranged to connect between the fuse and the second news, the wiring between the first fuse and the second fuse, and the negative electrode of the lithium ion secondary battery, and a charge / discharge side connection terminal, And a detection circuit that is connected to each of the switching element and the negative electrode of the lithium ion secondary battery and controls on / off of the switching element.

As described above, the present invention can provide a safer and more reliable lithium ion secondary battery system.

It is a figure which shows the outline of a lithium ion battery system. It is a figure which shows the outline of the equivalent circuit of a lithium ion battery system. It is a figure which shows the outline of the equivalent circuit of the control circuit part of a lithium ion battery. It is a figure which shows an example of the equivalent circuit of a detection circuit.

Hereinafter, the best mode for carrying out the present invention will be specifically described with reference to the drawings. However, it goes without saying that the present invention can be implemented in many different forms.

FIG. 1 is a diagram showing an outline of a lithium ion secondary battery system (hereinafter referred to as “the present secondary battery system”) according to this embodiment, and FIG. 2 shows an assembled battery constituting the present secondary battery system. FIG. 3 is a diagram showing an outline of an equivalent circuit of the lithium ion secondary battery and the control circuit unit. As shown in FIGS. 1 to 3, the secondary battery system 1 is formed by further connecting a plurality of battery packs 4 formed by connecting a plurality of lithium ion secondary batteries 2 in parallel. Each secondary battery is provided with a protection circuit 3, and each protection circuit 3 includes a charge / discharge side connection terminal 31, a charge / discharge side connection terminal 31, and a positive electrode 21 of the lithium ion secondary battery 2. The first fuse 32 and the second fuse 33 connected in series so as to be connected, the wiring 321 between the first fuse 32 and the second fuse 33, and the negative electrode 22 of the lithium ion secondary battery 2 Connected to the switching element 34 disposed between, the charge / discharge side connection terminal 31, the wiring 321 between the first fuse 32 and the second fuse 33, and the negative electrode 22 of the lithium ion secondary battery 2. Is has a detection circuit 35 for controlling on and off of the switching element 33. In addition, FIG. 1 shows a case where five lithium ion secondary batteries are connected in parallel to form one assembled battery, and four assembled batteries are combined in series for specific explanation of the secondary battery system. The description will be made with reference to an example, but it can be adjusted as appropriate and is not limited thereto. The lithium ion battery system is provided with a dedicated circuit 5, and each wiring connected to each assembled battery 4 is connected to the dedicated circuit 5 to turn on and off the power supplied from the external charger (charging). (Discharge) can be controlled and the state of current and voltage in each assembled battery 4 can be monitored. The dedicated circuit 5 is provided with a transistor for controlling charging / discharging of the lithium ion secondary battery, and further, a delay circuit for providing a delay in the switching time is provided. Since this secondary battery system is very high power, a temporary change in voltage that occurs between charging and discharging or between discharging and charging may invert the ON / OFF state of the transistor many times. This unnecessary switching operation may cause overheating of the transistor, leading to destruction of the transistor. Therefore, by arranging this circuit, it is possible to make it difficult to be affected by additional fluctuations and fluctuations in internal power supply, etc., and it is possible to safely turn on / off the transistors while avoiding excessive switching operations.

In the present embodiment, the lithium ion secondary battery 2 is configured to include a positive electrode and a negative electrode, and an electrolyte layer disposed between the positive electrode and the negative electrode. Although a positive electrode contains a lithium oxide and is not necessarily limited, For example, lithium cobaltate, lithium iron oxide, and lithium titanate can be used conveniently. Moreover, although a negative electrode is not limited, For example, porous carbon can be used conveniently. The electrolyte layer may be any electrolyte layer as long as it contains a lithium ion electrolyte, and may be an electrolyte solution in which an electrolyte is dissolved in an organic solvent. Also good. The electrolyte is not limited, but lithium hexafluorophosphate can be suitably used. In addition, although it does not necessarily limit as an organic solvent, It is a preferable example to use carbonate esters, such as ethylene carbonate, propylene carbonate, dimethyl carbonate, ethyl methyl carbonate, and ethyl carbonate, as appropriate. In addition, when this lithium ion secondary battery becomes a structural requirement as a battery in a circuit, a positive electrode is called a positive electrode and a negative electrode is called a negative electrode.

In addition, the shape of the lithium ion secondary battery in the present embodiment is not particularly limited, but may be a sheet shape or a cylinder shape, but the sheet shape is more from the viewpoint of safety and gas tightness. preferable. In a sheet-like lithium secondary battery, a sheet-like positive electrode and a negative electrode are arranged at a predetermined interval, a layer containing an electrolyte is provided between them, and the sheet-like lithium secondary battery is formed into a sheet shape. A battery refers to a battery in which a spiral positive electrode and a negative electrode are arranged at a predetermined interval, a layer containing an electrolyte is provided therebetween, and arranged in a cylinder shape.

In the present embodiment, the assembled battery refers to a battery in which a plurality of lithium ion batteries are connected in parallel. Specifically, the positive electrodes in the lithium ion batteries in the assembled battery are commonly connected, and the negative electrodes are commonly connected. Say something. The number of lithium ion batteries in one assembled battery is not limited and varies depending on the battery capacity, but is 10 or less, more preferably 8 or less in consideration of variation.

In this embodiment, a plurality of assembled batteries are connected in series. That is, in this specification, the “lithium ion battery system” means a plurality of assembled batteries connected in series. The number of battery packs to be connected is not limited, but varies depending on the voltage required by the device using this lithium ion secondary battery system, but is 100 or less, more preferably 2 or more and 50 or less.

Further, as described above, the protection circuit 3 is connected to each lithium secondary battery 2 in the battery system. The protection circuit 3 includes an external connection terminal 31, a first fuse 32 connected to the external connection terminal 31, a second fuse 33 connected in series to the first fuse 32, a first fuse 32, and a second fuse. A switching element 34 connected to the wiring 321 between the fuses 33, the negative electrode 22 of the lithium ion secondary battery, and a detection circuit 35. The detection circuit 35 includes a wiring 321 between the first fuse 32 and the second fuse 33, a switching element 34 connected to the negative electrode 22 (wiring 323) of the lithium ion secondary battery, the external connection terminal 31 and the first Is connected to a wiring 322 (external connection terminal 31) between the fuse 32 and the output of the detection circuit is connected to a gate (wiring 324) of the switching element 34.

The control circuit unit according to the present embodiment is not limited as long as it can be realized. For example, the control circuit unit can be realized by arranging the above-described constituent elements on a printed board formed with wiring on an insulating substrate. be able to.

The first fuse according to the present embodiment can cut off the current when a current of a predetermined set value or more flows in the circuit, and can adopt a known one. . Note that the value of the rated breaking current of the first fuse can be appropriately adjusted depending on the capacity and type of the battery and is not limited, but an example of a preferable range is 1 A or more and 20 A or less.

As the second fuse, the same one as the first fuse can be adopted, and a publicly known one can be adopted. In the present embodiment, the capacity of the second fuse is preferably larger than the capacity of the first fuse. By doing in this way, when a fuse is blown simply due to the effect of overdischarge, the smaller one is blown and the larger fuse remains. For this reason, it is possible to make a major determination of overdischarge or overvoltage depending on the content of the blown fuse. Also, when replacing the fuse, if there are the same capacity, it often breaks two places at the same time. However, if only one of them is kept small, there is a merit that only one place is required in the case of a failure such as a normal overcurrent. . The value of the rated breaking current of the second fuse is preferably 1 to 10 times the value of the rated breaking current of the first fuse, more preferably 5 times or less, and even more preferably about 2 times. It is.

In the present embodiment, the detection circuit 35 is provided to control the second fuse when an overcurrent is detected in each lithium ion secondary battery. An example of an equivalent circuit of the detection circuit is shown in FIG.

As shown in the figure, the detection circuit 35 includes a charge / discharge side connection terminal 31, a wiring 321 between the first fuse 32 and the second fuse 33, and a negative electrode 22 (wiring 323) of the lithium ion secondary battery. , And has a detector for detecting each current. When the detector detects an overcurrent on either the charge / discharge side connection terminal side or the negative electrode side, the detector can turn on the switching element in the control circuit unit. Specifically, a current that is turned on can be supplied to the gate of the switching element 34, and the current can be supplied between the gate and the drain.

As described above, the present invention can provide a safer and more reliable lithium ion battery system. The specific operation is apparent from the circuit configuration, but can be described below. First, the lithium ion battery system according to the present embodiment is supplied from the charge / discharge side connection terminal by disposing the first fuse between the charge / discharge side connection terminal and the plus side electrode of the lithium ion secondary battery. When the current is in an overvoltage state, the detection circuit senses that it is overvoltage, turns on the switching element, and electrically connects the plus electrode and the minus electrode of the lithium ion secondary battery. Then, since the current flows more than the rated breaking current value of the second fuse, the second fuse is cut off (cut), and the battery is opened. At this time, since the battery is continuously charged, the first fuse is blown immediately. As a result, supply of current from the external charger is stopped and energy is not supplied, so that a safer and more reliable lithium ion battery system is obtained. If there is only one of the fuses, for example, only the second fuse, the current from the charger will be supplied to SW and the current will continue to flow, which can cause a major accident. On the other hand, when there is only the first fuse, the battery itself cannot be protected because the battery current continues to flow through the switching element. Therefore, the presence of two fuses has an important meaning in this protection circuit. Since the wiring 322 cannot supply power to the circuit in an unstable state where both fuses are blown, power can be supplementarily supplied from the charging side. For this reason, this control circuit can continue to operate stably.

The lithium ion secondary battery system according to the above embodiment was actually created and the effect was confirmed. This will be described below.

On the printed circuit board, a first fuse with a capacity of 5A (manufactured by KOA, model number CCF), a second fuse with a capacity of 10A (manufactured by KOA, model number CCF), and an n-type MOS transistor (manufactured by Toshiba, TPCA 8104) is arranged, and the connection relationship is the same as that described in the above embodiment. Then, 30 lithium ion secondary batteries (manufactured by Hitachi Maxell Co., Ltd.) connected to the lithium ion secondary battery system were prepared, 5 sheets were used as a set of assembled batteries, and 6 stages were combined to form a lithium ion secondary battery system. When a voltage of 12 V was applied to the lithium ion secondary battery system, the lithium ion secondary battery system stopped operation reliably. As a result, it was confirmed that this system is safer and more reliable.

The present invention has industrial applicability as a lithium ion secondary battery system.

DESCRIPTION OF SYMBOLS 1 ... Lithium ion battery system, 2 ... Lithium ion secondary battery, 3 ... Control circuit part, 4 ... Assembly battery, 5 ... Dedicated circuit

Claims (5)

A lithium ion secondary battery system in which a plurality of lithium ion secondary batteries connected in parallel is further connected in series.
The lithium ion secondary battery is provided with a protection circuit,
The protection circuit includes a charge / discharge side connection terminal, a first fuse and a second news connected in series so as to connect the connection terminal and the positive side electrode of the lithium ion secondary battery,
A switching element arranged to connect between the wiring between the first fuse and the second fuse and the negative electrode of the lithium ion secondary battery;
A lithium ion secondary battery system comprising: a detection circuit that is connected to each of the charge / discharge side connection terminal, the switching element, and the negative electrode of the lithium ion secondary battery and controls on / off of the switching element. The lithium ion secondary battery system according to claim 1, wherein the control circuit unit is provided in each of the lithium ion secondary batteries. The switching element is an n-type transistor having a gate, a source, and a drain,
The gate is connected to the detection circuit;
The one of the source and drain is connected to a wiring between the first fuse and the second fuse, and the other is connected to a negative electrode of the lithium ion secondary battery. Lithium ion secondary battery system. The lithium ion secondary battery system according to claim 1, wherein the lithium ion secondary battery is a sheet-like battery. A lithium ion secondary battery system in which a time delay is provided in a transistor that functions as a SW during charging and discharging of a lithium ion battery.

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