Battery pack

Abstract

To provide a battery pack 1 including a plurality of battery cells that are stored while being stacked with a spacer interposed therebetween, in which false detection rate can be reduced in a configuration where smoke generation of a battery cell 4 is detected by detecting a pressure rise in a housing 2.SOLUTION: There is provided a battery pack in which a plurality of battery cells are divided into a plurality of groups along the stacking direction thereof, a spacer 5 sandwiched between the battery cells in each group g is formed to allow the transfer of heat between the battery cells such that, when one of the battery cells sandwiching the spacer emits smoke, the other of the battery cells also emits smoke in a chained manner, a spacer 6 sandwiched between the battery cells present at the border between adjacent two groups is formed to block the transfer of heat between the battery cells such that, even when one of the battery cells sandwiching the spacer emits smoke, the other of the battery cells does not emit smoke, and it is detected that smoke generation of battery cells occurs when pressure detection means 7 detects a pressure rise corresponding to a pressure rise in smoke generation of the plurality of battery cells.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a battery pack that houses a plurality of battery cells, and more particularly to a structure for detecting smoke emission (cell smoke) of the battery cells in the battery pack.

Background Art

[0002] In a battery pack mounted as a drive or operation power source for various mechanical devices such as electric vehicles, a plurality of battery cells are housed in a state where they are stacked with spacers interposed therebetween (Patent Document 1). By the way, when the battery cells in such a battery pack emit smoke due to some factor, for example, generation of excessive current due to a short circuit, overcharging, etc., it is necessary to execute measures such as stopping the use of the battery pack and cooling. Therefore, a configuration has been proposed in which, by utilizing the fact that the pressure inside the battery pack increases when the battery cells emit smoke, the pressure inside the battery pack is monitored by a pressure sensor, and when a significant increase in pressure is detected, it is determined that cell smoke has occurred (Patent Document 2).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] When a plurality of battery cells are stacked with a spacer in between in the battery pack as described above, usually, when one battery cell generates heat and emits smoke, the spacer between the battery cells is formed to have a heat insulation effect such that the heat of the smoking battery cell is not easily transmitted to the adjacent battery cell so that the heat generation and smoke emission do not occur in a chain in the adjacent battery cell. Therefore, when one battery cell emits smoke in the battery pack, in order to detect this by pressure, when there is an increase in pressure corresponding to the increase in pressure due to the smoke emission of one battery cell, it is determined that cell smoking has occurred. However, since the pressure in the battery pack fluctuates to some extent even in a normal operating state due to thermal expansion, external force input, vibration, etc., when the pressure increase range that can be caused by the smoke emission of one battery cell is close to the pressure fluctuation range in the normal operating state, it may be difficult to accurately detect the pressure increase due to cell smoking (the ratio of misdetecting the normal range of pressure fluctuations as cell smoking can be high).

[0005] In view of the above circumstances, the main problem of the present invention is to reduce the ratio of misdetection as much as possible in a configuration for detecting cell smoking by detecting an increase in the pressure of a battery pack in which a plurality of battery cells are stored in a state of being stacked with a spacer in between.

Means for Solving the Problem

[0006] According to the present invention, the above problems are solved by a battery pack in which a plurality of battery cells are housed in a case in a state of being stacked with a spacer interposed therebetween, the battery pack having pressure detection means for detecting an increase in pressure inside the case, and when any one of the battery cells emits smoke, the battery pack is configured to detect this by detecting an increase in pressure by the pressure detection means, wherein the plurality of battery cells are divided into a plurality of groups along the stacking direction thereof, and the spacer interposed between the battery cells within each of the groups is formed to allow heat transfer between the battery cells sandwiching the spacer such that when one of the battery cells sandwiching the spacer emits smoke, the other battery cell sandwiching the spacer also emits smoke in a chain reaction, and the spacer interposed between the battery cells at the boundary between two adjacent groups among the groups is formed to block heat transfer between the battery cells sandwiching the spacer such that when one of the battery cells sandwiching the spacer emits smoke, the other battery cell sandwiching the spacer does not emit smoke, and the battery pack is configured such that when the pressure detection means detects an increase in pressure corresponding to an increase in pressure when a plurality of the battery cells emit smoke, it is detected that smoke emission of the battery cells has occurred.

[0007] In the above configuration, the "battery pack" is, as already described, one in which battery cells are housed inside a case that is mounted on an electric vehicle or other mechanical device for driving or operating the same. The case may be of a type commonly used in this field. Also, the battery cells may be of any type of battery cell commonly used in this field and may be stacked with a spacer interposed therebetween in a normal manner. The "pressure detection means" may be any means capable of detecting an increase in pressure inside the case and may typically be a pressure sensor of any type.

[0008] And the characteristic of the configuration of the present invention is that, as described above, a plurality of stacked battery cells are divided into a plurality of groups along the stacking direction, and within each group, the spacer sandwiched between the battery cells has low heat insulation performance, that is, when one of the battery cells sandwiching the spacer emits smoke, heat transfer is allowed so that the other of the battery cells sandwiching the spacer also emits smoke in a chain reaction. On the other hand, the spacer sandwiched between the battery cells at the boundary of each adjacent group has high heat insulation performance, that is, even if one of the battery cells sandwiching the spacer emits smoke, heat transfer between the battery cells sandwiching the spacer is blocked so that the other of the battery cells sandwiching the spacer does not emit smoke. In short, in the battery pack of the present invention, the spacer interposed between each of the stacked battery cells has high heat insulation performance at the boundary of the groups of battery cells and low heat insulation performance within the groups of battery cells. That is, the heat insulation performance of the spacer is increased at appropriate intervals along the stacking direction of the battery cells so that even if one side of the battery cells emits smoke, the heat is not transferred to the battery cells on the other side. The heat insulation performance of the other spacers is such that when one side of the battery cells emits smoke, the heat is transferred to the battery cells on the other side, causing the battery cells on the other side to emit smoke in a chain reaction.

[0009] When the heat insulation performance of the spacer is set as described above, if a certain battery cell generates heat and emits smoke for some reason, the battery cells belonging to the same group will also generate heat and emit smoke in a chain reaction. Therefore, the pressure increase due to such smoke emission becomes more significant than when only one battery cell emits smoke, and the difference from the pressure fluctuation in the normal operating state becomes clear. Therefore, as described above, by configuring the pressure detection means to detect that smoke emission of the battery cells has occurred when detecting a pressure increase corresponding to the pressure increase when a plurality of battery cells emit smoke, it becomes possible to detect cell smoke emission more accurately.

[0010] In the configuration of the present invention described above, the number of battery cells that smoke in chain reaction to the smoking of one battery cell only needs to be such that the pressure increase caused by the smoking of that number of battery cells significantly exceeds the pressure fluctuation range in the normal operating state. Therefore, the number of battery cells in each group may be set to a number such that the pressure increase expected when all the battery cells in that group smoke significantly exceeds the pressure fluctuation range in the normal operating state. However, the number of battery cells in each group is set so that the calorific value does not become excessive even if all the cells in that group smoke, for example, sufficiently less than the level where fire breaks out outside the battery pack. Typically, if about two or three battery cells smoke simultaneously, the resulting pressure increase exceeds the pressure fluctuation range in the normal operating state, so the number of battery cells in each group may be about two to four.

[0011] In the battery pack with the above configuration, the adjustment of the heat insulation performance of the spacer may be achieved by adjusting the thickness of the heat insulation material used for the spacer. As the heat insulation material, silica aerogel heat insulation material or the like may be used.

[0012] In addition, in the above configuration, when the smoking of the battery cell is detected, the use of the battery is stopped, the operation amount of the cooler is increased, and measures are taken to prevent further chain reaction of the smoking of the battery cell. (The battery pack with cell smoking is to be replaced.)

Advantages of the Invention

[0013] Thus, according to the configuration of the present invention, when one battery cell emits smoke in the battery pack, other battery cells will also chain - react and emit smoke in a limited number. As a result, the pressure increase in the housing due to the smoke emission becomes significant compared to the pressure fluctuations in the normal operating state. By detecting such a pressure increase, it is expected that the detection of the smoke emission from the battery cell can be achieved with higher accuracy. Also, as described above, the battery cells that chain - react and emit smoke due to the smoke emission of one battery cell are not all the battery cells in the housing, but only the battery cells between the spacers with enhanced heat insulation performance. Therefore, while reducing the false detection rate of cell smoke emission, the safety of the battery pack is also ensured. The battery pack of the present invention may be used in various electric vehicles and other mechanical appliances that operate using the power of batteries.

[0014] Other objects and advantages of the present invention will become apparent from the following description of the preferred embodiments of the present invention.

Brief Description of the Drawings

[0015]

Figure 1

Figure 2

Explanation of Reference Numerals

[0016] 1... Battery pack, 2... Housing, 3... End plate, 4... Battery cell, 5... Spacer, 6... Heat - insulating spacer, 7... Pressure sensor, 8... Control device

Best Mode for Carrying Out the Invention

[0017] The present invention will be described in detail below with reference to the accompanying drawings in several preferred embodiments. In the drawings, the same reference numerals indicate the same parts.

[0018] Configuration of the battery pack Referring to FIG. 1, in the battery pack 1 mounted as a driving or operating power source for a machine such as an electric vehicle according to the present embodiment, in a normal mode, a plurality of battery cells 4 are stored in a housing 2 in a state where they are laminated with a spacer 5 or a heat insulating spacer 6 sandwiched therebetween in their thickness direction between end plates 3. The battery cell 4 may be a battery cell of any type, such as a lithium ion secondary battery, a lead battery, or a nickel metal hydride battery. Although not shown, the components normally provided in the battery pack 1 may be equipped in a normal mode. When any one of the battery cells 4 emits smoke, a pressure sensor 7 for detecting this by a pressure increase is provided at an appropriate part in the housing 2, and the output of the pressure sensor 7 may be transmitted to a control device 8 that controls the operation of the battery pack.

[0019] In the above configuration, particularly in the case of the present embodiment, a plurality of laminated battery cells 4 are divided into a plurality of groups g in the lamination direction, and a spacer 5 having low heat insulation performance is used as the spacer sandwiched between the battery cells 4 within each group g, and a heat insulating spacer 6 having high heat insulation performance is used as the spacer sandwiched between the battery cells 4 at the boundary between the groups g. The number of battery cells 4 in each group may be two or more, for example, 2 to 4. Regarding the spacer 5, its heat insulation performance is set to allow heat transfer between the battery cells 4 so that when one of the battery cells 4 sandwiching it generates heat and emits smoke, the adjacent other battery cell 4 is also heated and emits smoke in a chain reaction. On the other hand, regarding the heat insulating spacer 6, its heat insulation performance is set so that even if one of the battery cells 4 sandwiching it generates heat and emits smoke, the adjacent other battery cell 4 does not emit smoke, and heat transfer from the smoking battery cell 4 to the other can be sufficiently blocked. The spacer 5 and the heat insulating spacer 6 may be formed using any material used as a cell spacer in this field so as to exhibit the above-described respective heat insulation performances. As the heat insulating material, for example, a silicon aerogel heat insulating material may be used.

[0020] In the above configuration, the pressure sensor 7 detects the pressure inside the housing 2. As will be described later, when the pressure inside the housing 2 exceeds the pressure corresponding to the pressure fluctuation range in normal operation and exceeds the pressure when smoking occurs in a plurality of battery cells, the detection threshold value of the pressure sensor 7 is set so as to detect that cell smoking has occurred. When the output value of the pressure sensor 7 exceeds the detection threshold value, the control device 8 determines that cell smoking has occurred (detection of cell smoking) and executes measures for stopping the use and cooling of the battery pack.

[0021] Detection of smoke from the battery cell In the case where all of the spacers sandwiching the battery cells stacked inside the housing, like the above-described heat insulating spacer 6, block heat transfer so that even if one of the battery cells sandwiching the spacer generates heat and smokes, the other battery cells do not chain-react and do not smoke, as shown in the left diagram of Fig. 2(A), even if one battery cell 4 smokes Cs, the adjacent battery cell 4 does not smoke. Therefore, as shown in the right diagram of Fig. 2(A), the detection threshold value Dth for the pressure increase due to cell smoking needs to be set to the pressure value corresponding to the pressure increase CSs due to the smoking of one battery cell. However, when its magnitude is close to the pressure fluctuation range Nv in normal operation, it is difficult to distinguish between the pressure fluctuation range Nv in normal operation and the pressure increase CSs due to smoking, and there is a high possibility of misdetecting that there has been a pressure increase CSs due to the smoking of the battery cell even though the battery cell has not smoked.

[0022] Therefore, in the battery pack 1 according to the present embodiment, as described above, the heat insulating spacer 6 is not interposed between all of the stacked battery cells 4, but is intermittently interposed, and between the other battery cells 4, a spacer 5 with low heat insulating performance is interposed. According to such a configuration, as shown in the left diagram of Fig. 2(B), when any one of the battery cells 4 stacked between two heat insulating spacers 6 emits smoke (Cs), heat is transmitted to the adjacent battery cell 4 through the spacer 5, and the adjacent battery cell 4 will chain-reaction and emit smoke (Cs’). Then, as shown in the right diagram of Fig. 2(B), the pressure increase width Csp in the housing due to cell smoke is more than twice the pressure increase width CSs due to the smoke of one battery cell. Therefore, the detection threshold Dth for the pressure increase due to cell smoke can be set sufficiently higher than the pressure fluctuation width Nv during normal operation. Thus, a large margin is taken between the detection threshold Dth and the pressure fluctuation width Nv during normal operation, and the possibility of erroneously detecting the pressure fluctuation during normal operation as a pressure increase due to cell smoke is reduced. That is, in the present embodiment, when smoke is detected from one battery cell, the smoke is deliberately induced in a plurality of cells to increase the pressure increase width and clarify the difference from the pressure fluctuation during normal operation, thereby reducing the false detection rate.

[0023] In the above-described present embodiment, the number of battery cells assigned to each group, that is, the number of battery cells stacked between two heat insulating spacers 6, is set to be, for example, sufficiently lower than the case where a fire breaks out outside the battery pack so that even if all of them emit smoke, the heat generation is not excessive. If the pressure increase width due to the chain-reaction smoking battery cells is clearly different from the pressure fluctuation width during normal operation, the number of battery cells assigned to each group can be kept as small as possible. For example, the number of cells can be 2 to 4 or the like.

[0024] The above description has been made in relation to the embodiments of the present invention, but many modifications and changes are easily possible for those skilled in the art. It is obvious that the present invention is not limited only to the embodiments illustrated above, and can be applied to various devices without departing from the concept of the present invention.

Claims

Claim 1 A battery pack in which a plurality of battery cells are stored in a stacked state with a spacer interposed therebetween in a housing, the battery pack having pressure detection means for detecting an increase in pressure in the housing, and configured to detect when any one of the battery cells emits smoke by detecting an increase in pressure by the pressure detection means, wherein the plurality of battery cells are divided into a plurality of groups along their stacking direction, and the spacer interposed between the battery cells within each of the groups is formed to allow heat transfer between the battery cells sandwiching the spacer such that when one of the battery cells sandwiching the spacer emits smoke, the other battery cell sandwiching the spacer also emits smoke in a chain reaction, and the spacer interposed between the battery cells at the boundary between two adjacent groups among the groups is formed to block heat transfer between the battery cells sandwiching the spacer such that when one of the battery cells sandwiching the spacer emits smoke, the other battery cell sandwiching the spacer does not emit smoke, and the pressure detection means is configured to detect that smoke emission has occurred in the battery cells when detecting a pressure increase corresponding to the pressure increase when a plurality of the battery cells emit smoke.

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