Battery module

A battery module has a plurality of battery cells each including a cell case and a battery element contained in the cell case. The battery module includes a lead to electrically connect a terminal of each of the battery cells to a current collector and a heat shutoff mechanism to break electrical connection between the terminal and the current collector by heat from the cell case when the cell case reaches a predetermined temperature or higher.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a U.S. national stage application of the PCT International Application No. PCT/JP2017/040171 filed on Nov. 8, 2017, which claims the benefit of foreign priority of Japanese patent application 2016-226592 filed on Nov. 22, 2016, the contents all of which are incorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates to a battery module.

BACKGROUND ART

A conventional battery module is disclosed in PTL 1. This battery module includes a plurality of battery cells arranged in a matrix. Positive electrode terminals of the battery cells are electrically connected to a positive-electrode current collector plate made of a conductive flat board, whereas negative electrode terminals of the battery cells are electrically connected via fuses to a negative-electrode current collector plate made of a conductive flat board. Thus, the battery module has the plurality of the parallel-connected battery cells and is designed to separate any battery cell through which a heavy current greater than or equal to a rated current has flowed from an electric circuit by blowing the fuse of the battery cell with Joule heat. This configuration prevents the battery cell from abnormally generating heat due to the flow of heavy current through the battery cell.

CITATION LIST

Patent Literature

SUMMARY OF THE INVENTION

Technical Problem

Electric current flowing through the fuse varies with factors such as a type of the battery cell (a difference in internal resistance), a number of the parallel-connected battery cells, and a structure of the module (an exhaust system). Thus, the design of fuses involves taking at least these three factors into consideration and the fuses need to be redesigned every time a change is made in the three factors. As a result, the electric circuit is not simple in configuration, unfortunately.

Hence, it is an object of the present disclosure to provide a battery module that facilitates the formation of an electric circuit designed to separate a battery cell that has abnormally generated heat as compared to a conventional battery module including a fuse.

Solution to Problem

A battery module according to an aspect of the present disclosure has a plurality of battery cells each including a cell case and a battery element contained in the cell case. The battery module includes a lead to electrically connect a terminal of each of the battery cells to a current collector plate and a heat shutoff mechanism to break electrical connection between the terminal and the current collector plate by heat from the cell case when the cell case reaches a predetermined temperature or higher.

Advantageous Effect of Invention

In the battery module according to the present disclosure, the heat shutoff mechanism separates a battery cell that has abnormally generated heat from an electric circuit depending on temperature of the cell case of the battery cell, which is less influenced by the type of the battery cell (a difference in internal resistance), a number of the parallel-connected battery cells, and a difference in a structure of the module (an exhaust system) than electric current flowing through the terminal of the battery cell is. As a result, an identical heat shutoff mechanism can be applied to battery modules in an expanded range as compared to an identical fuse that can be applied to battery modules in a certain range. Thus, a battery module according to the present disclosure facilitates the formation of a target electric circuit as compared to a conventional battery module including a fuse.

DESCRIPTION OF EMBODIMENTS

Exemplary embodiments of the present disclosure will now be described in detail with reference to the attached drawings. It is initially envisaged that a new exemplary embodiment can be made by suitably combining some distinctive elements in any of the exemplary embodiments and modifications described hereafter. In the following description and the drawings, a Z direction represents a height direction of cylindrical battery11.

First Exemplary Embodiment

FIG. 1is an exploded perspective view of battery module10according to a first exemplary embodiment of the present disclosure. First, with reference toFIG. 1, an overview of battery module10will be described. As shown inFIG. 1, battery module10includes a plurality of cylindrical batteries11and battery holder20having a plurality of cylindrical containers to hold cylindrical batteries11.

Cylindrical battery11, an example of a battery cell, includes cell case12made of metal, a battery element (not shown) contained in cell case12, a positive electrode terminal, and a negative electrode terminal. The battery element includes a pair of electrodes and a non-aqueous electrolyte to permit the transfer of electric charge. Cell case12is made up of cell case body13that is formed in a bottomed cylindrical shape to contain the battery element and sealing body14sealing an opening of cell case body13. A gasket (not shown) is disposed between cell case body13and sealing body14. For example, sealing body14has a layered structure including a valve and a cap and is electrically connected to a positive electrode of the battery element to function as the positive electrode terminal of cylindrical battery11. Cell case body13functions as a negative electrode of cylindrical battery11. In general, however, an outer peripheral side surface of cell case body13is covered with an insulating resin film and a bottom surface of cell case body13functions as the negative electrode terminal. Cylindrical battery11is contained in hole21of each of the cylindrical containers in battery holder20.

Battery module10includes a pair of posts30attached to battery holder20. Posts30are plate-shaped components that cover both lateral faces of battery holder20. Each post30has protrusion31on one surface. Posts30are disposed so as to face each other through battery holder20, with protrusions31facing battery holder20. Protrusions31are fitted into recesses25in battery holder20.

Positive-electrode lead plate41electrically connected to the positive electrode terminals of the plurality of cylindrical batteries11is disposed above battery holder20, with positive-electrode insulation board42interposed between the lead plate and the battery holder. Positive-electrode current collector plate40electrically connected to positive-electrode lead plate41is disposed above the positive-electrode lead plate.

Meanwhile, negative-electrode lead plate46electrically connected to the negative electrode terminals of the plurality of cylindrical batteries11is disposed below battery holder20, with negative-electrode insulation board53interposed between the lead plate and the battery holder. Negative-electrode current collector plate45electrically connected to negative-electrode lead plate46is disposed below the negative-electrode lead plate. The plurality of cylindrical batteries11is connected in parallel with positive- and negative-electrode lead plates41,46. Positive-electrode lead plate41includes positive-electrode plate body43and positive-electrode leads47. Positive-electrode plate body43is electrically connected with the positive electrode of each cylindrical battery11via positive-electrode lead47. Negative-electrode lead plate46includes negative-electrode plate body48and negative-electrode leads50. Negative-electrode plate body48is electrically connected with the negative electrode of each cylindrical battery11via negative-electrode lead50.

Positive- and negative-electrode insulation boards42,53are disposed between battery holder20and respective positive- and negative-electrode lead plates41,46. The insulation boards have holes to partly expose the terminals of the plurality of cylindrical batteries11. Positive-electrode current collector plate40, negative-electrode current collector plate45, and other components are fixed to the pair of posts30using screws (not shown), for example. Battery module10is, for example, connected in series with other adjacently disposed battery module10by positive-electrode current collector plate40and negative-electrode current collector plate45.

FIG. 2Ais a schematic perspective view of a structure of negative-electrode lead50for cylindrical battery11, illustrating an action performed by negative-electrode lead50in response to abnormal heat generation in cylindrical battery11. As shown inFIG. 2A, negative-electrode lead50includes melting member51that is an example of a heat shutoff mechanism and high-melting-point member52with a melting point higher than that of the melting member. Melting member51is made from tin (with a melting point of 232 degrees Celsius), a tin alloy (with a melting point of around 300 degrees Celsius), or a solder alloy (with a melting point of around 180 degrees Celsius), for example. Preferably, melting member51is made of a metallic material with a melting point of 500 degrees Celsius or lower, and is more preferably made of a metallic material with a melting point of 400 degrees Celsius or lower. High-melting-point member52is made from aluminum (with a melting point of 660 degrees Celsius) or copper (with a melting point of 1,085 degrees Celsius), for example, and is preferably made of a metallic material with a melting point of 550 degrees Celsius or higher.

High-melting-point member52constitutes a part of negative-electrode lead50adjacent to negative-electrode plate body48and connects with negative-electrode plate body48. Melting member51constitutes a part of negative-electrode lead50extending in a direction. Melting member51is disposed at a boundary between high-melting-point member52and negative-electrode bottom surface18. Specifically, melting member51is disposed between an end of high-melting-point member52adjacent to cylindrical battery11and negative-electrode bottom surface18of cylindrical battery11. Melting member51is joined to both the end of high-melting-point member52adjacent to cylindrical battery11and negative-electrode bottom surface18by ultrasonic metal welding or laser spot welding. High-melting-point member52is electrically connected with negative-electrode bottom surface18via melting member51.

The action performed by negative-electrode lead50in response to abnormal heat generation in cylindrical battery11will now be described. If cylindrical battery11abnormally generates heat due to a minute short circuit between the positive electrode and the negative electrode inside cell case12or other reason, temperature of the cell case of cylindrical battery11, for example, rises to about 500 degrees Celsius, an example predetermined temperature. Then, melting member51melts with heat from cell case12(negative-electrode bottom surface18) and separates from high-melting-point member52. As a result, electrical connection gets broken between negative-electrode bottom surface18and high-melting-point member52. This separates cylindrical battery11that has abnormally generated heat from an electric circuit (the batteries connected in parallel).

Joining of high-melting-point member52to negative-electrode bottom surface18via melting member51may cause the high-melting-point member to be pressed toward negative-electrode bottom surface18because of elasticity high-melting-point member52has. In this case, when melting member51melts with heat from cell case12, force for pressing high-melting-point member52toward negative-electrode bottom surface18disappears, so that high-melting-point member52can freely move. Then, high-melting-point member52moves toward negative-electrode plate body48to correct distortion owing to its internal elasticity, so that the high-melting-point member is separated from melt melting member51. This configuration reliably breaks electrical connection between negative-electrode bottom surface18and high-melting-point member52and reliably separates cylindrical battery11that has abnormally generated heat from the electric circuit.

In the exemplary embodiment described above, the heat shutoff mechanism separates cylindrical battery11that has abnormally generated heat from the electric circuit depending on temperature of cell case12of cylindrical battery11, which is less influenced by the type of cylindrical battery11(a difference in internal resistance), the number of parallel-connected cylindrical batteries11, and a difference in the module structure (the exhaust system) than electric current flowing through the negative-electrode terminal of cylindrical battery11is. As a result, an identical heat shutoff mechanism can be applied to battery modules10with specifications in an expanded range as compared to an identical fuse that can be applied to battery modules10with specifications in a certain range. Thus, a battery module according to the exemplary embodiment facilitates the formation of a target electric circuit as compared to a conventional battery module including a fuse.

In the first exemplary embodiment described above, melting member51is disposed at a boundary between high-melting-point member52and negative-electrode bottom surface18. However, as shown inFIG. 2B, melting member151may constitute a part of negative-electrode lead150other than both ends of the negative-electrode lead extending in a direction. When melting member151melts, the battery module may separate cylindrical battery11that has abnormally generated heat from the electric circuit by dividing high-melting-point member152into portion152aadjacent to the battery and portion152badjacent to the negative-electrode plate body and thereby breaking electrical connection between negative-electrode bottom surface18and negative-electrode plate body48(refer toFIG. 1). In this case, as shown inFIG. 3, i.e. a cross-sectional view of negative-electrode lead350that is viewed when the lead is vertically sectioned into two equal parts by a plane including a direction in which the lead extends and the Z direction, melting member351may be formed of a metallic plate piece having a substantially flat shape. Then, one side surface of the melting member may be joined to portion352aof high-melting-point member352adjacent to the battery, whereas the other side surface of the melting member may be joined to portion352bof high-melting-point member352adjacent to the negative-electrode plate body. This structure is preferable because negative-electrode lead350can be readily assembled.

Alternatively, as shown inFIG. 2C, negative-electrode lead250may be entirely formed of melting member251. This configuration enables the battery module to reliably separate cylindrical battery11that has abnormally generated heat from the electric circuit and is thus preferable.

At least a part of negative-electrode lead50extending in a direction is formed of melting member51. However, at least a part of the positive-electrode lead extending in a direction may be formed of a melting member, or the negative- and the positive-electrode leads extending in directions may be at least partly formed of melting members, respectively. In the battery module described above, all the plurality of cylindrical batteries11is connected in parallel. However, the plurality of the cylindrical batteries may include two or more cylindrical batteries that are connected in series. The battery cells described above are cylindrical batteries11. However, the battery cells may be rectangular batteries.

In the exemplary embodiment described above, the temperature of the cell case of cylindrical battery11that has abnormally generated heat reaches about 500 degrees Celsius. Naturally, the temperature of a cell case of a cylindrical battery that has abnormally generated heat varies from specification to specification. Thus, the melting member may be made from any material depending on the specification of the cylindrical battery with proviso that the material melts with heat from the cell case of the cylindrical battery that has abnormally generated heat. The cell case of the cylindrical battery that has abnormally generated heat may reach any temperature within a range of 100 degrees Celsius to 650 degrees Celsius.

Second Exemplary Embodiment

FIGS. 4A and 4Bare schematic cross-sectional views each illustrating a structure around an end of cylindrical battery11adjacent to a negative electrode terminal in the Z direction in battery module410according to a second exemplary embodiment, viewed when negative-electrode lead450is vertically sectioned into two equal parts by a plane including a direction in which the negative-electrode lead extends and the Z direction.FIG. 4Ais a schematic cross-sectional view taken when cylindrical battery11is in a normal state, andFIG. 4Bis a schematic cross-sectional view taken when cylindrical battery11has abnormally generated heat.FIG. 5is a schematic plan view of the structure ofFIG. 4Awhen viewed from outside negative-electrode bottom surface18along the Z direction.

The second exemplary embodiment and third and fourth exemplary embodiments described later differ from the first exemplary embodiment only in the structure around the negative-electrode lead and are similar to the first exemplary embodiment in the other configuration. In the second to fourth exemplary embodiments, descriptions of effects and modified examples identical to those in the first exemplary embodiment are omitted, and structural elements identical to those in the first exemplary embodiment are assigned with the same reference numerals and redundant descriptions thereof are omitted.

As shown inFIG. 4A, battery module410includes cylindrical batteries11, negative-electrode leads450, and resin foam components465. One end450aof negative-electrode lead450extending in a direction is joined to negative-electrode bottom surface18of cylindrical battery11. Negative-electrode lead450extends so as to be apart from negative-electrode bottom surface18and is connected to negative-electrode plate body48(refer toFIG. 1).

Resin foam component465is made from a resin foam material that forms and expands when heated. Resin foam component465may be, for example, made from a material containing a film forming resin and a thermal expansion capsule and generating gas and expanding when heated or a material containing a urethane resin or a polyethylene resin. Resin foam component465may be made from any resin foam material with proviso that the material forms and expands when heated. Resin foam component465is fixed to negative-electrode bottom surface18. As shown inFIG. 5, resin foam component465overlaps an entire region of a part of negative-electrode lead450(a part indicated with a) extending in a direction. Resin foam component465has a rectangular parallelepiped shape. Side edge488made up of one side of resin foam component465(a side located at the lower left side in the figure) is in contact with an entire region of a widthwise span portion (indicated by arrow A) of negative-electrode lead450extending in the direction.

In the configuration described above, if cylindrical battery11has abnormally generated heat and cell case12(negative-electrode bottom surface18) of cylindrical battery11reaches an abnormally high temperature, resin foam component465foams and expands, as shown inFIG. 4B, and increases in height (a measurement in the Z direction). Then, a part of negative-electrode lead450near side edge488is cut by the side edge and a region around the edge of resin foam component465expanding downward in the figure. As a result, negative-electrode bottom surface18and negative-electrode plate body48are divided from each other and cylindrical battery11that has abnormally generated heat is separated from an electric circuit.

The battery module according to the second exemplary embodiment can readily separate cylindrical battery11that has abnormally generated heat from the electric circuit only with resin foam component465disposed on cell case12. Preferably, a part of the negative-electrode lead is joined to the resin foam component by laser spot welding or any other technique so that the negative-electrode lead can be more reliably cut off. As shown inFIG. 6, i.e. a schematic cross-sectional view of a structure corresponding to the structure ofFIG. 4Ain battery module510according to a modification of the second exemplary embodiment, a part of negative-electrode lead550that is in contact with resin foam component565preferably has cutout570or a slit so that negative-electrode lead550is readily cut off in response to abnormal heat generation in cylindrical battery11.

Third Exemplary Embodiment

FIG. 7Ais a schematic cross-sectional view of a structure corresponding to the structure ofFIG. 4Ain battery module610according to a third exemplary embodiment, andFIG. 7Bis a schematic cross-sectional view of a structure corresponding to the structure ofFIG. 4Bin battery module610according to the third exemplary embodiment.

As shown inFIG. 7A, battery module610includes cylindrical batteries11, negative-electrode leads650, and thermoplastic resin components665that act as an example lead pressing member. Resin component665includes negative-electrode lead pressing part667and battery connecting part668. Resin component665has a substantially L-shaped cross section. In the cross section shown inFIG. 7A, rectangular negative-electrode lead pressing part667and rectangular battery connecting part668are orthogonal to each other. Negative-electrode lead pressing part667has lead contact plane667a. An end of negative-electrode lead650adjacent to negative-electrode bottom surface18has a surface remote from negative-electrode bottom surface18, and lead contact plane667ais fastened to the surface or is in contact with the surface without being fastened. Lead contact plane667aextends in substantially parallel with negative-electrode bottom surface18. Battery connecting part668extends to negative-electrode bottom surface18from a part of negative-electrode lead pressing part667other than lead contact plane667a, and a front end of the battery connecting part is joined to negative-electrode bottom surface18.

Front end650aof negative-electrode lead650adjacent to cylindrical battery11is clamped between lead contact plane667aand negative-electrode bottom surface18. Front end650aof negative-electrode lead650is pressed by pressure from lead contact plane667atoward negative-electrode bottom surface18and is elastically deformed so as to be put into contact with negative-electrode bottom surface18of cylindrical battery11.

In the configuration described above, if cylindrical battery11has abnormally generated heat and cell case12(negative-electrode bottom surface18) of cylindrical battery11reaches an abnormally high temperature, resin component665melts as shown inFIG. 7Band force for pressing negative-electrode lead650toward negative-electrode bottom surface18disappears, so that negative-electrode lead650can freely move. Then, negative-electrode lead650moves toward negative-electrode plate body48to correct distortion owing to its internal elasticity, so that the negative-electrode lead is separated from negative-electrode bottom surface18. This configuration breaks electrical connection between negative-electrode lead650and negative-electrode bottom surface18and separates cylindrical battery11that has abnormally generated heat from an electric circuit.

In the battery module described above, the lead pressing member is resin component665that melts when cell case12of cylindrical battery11reaches an abnormally high temperature. However, the lead pressing member (a component for pressing a negative-electrode lead toward a negative-electrode bottom surface of a cylindrical battery) may be a metallic component (e.g. tin, a tin alloy, or solder) that melts when the cell case of the cylindrical battery reaches an abnormally high temperature.

Fourth Exemplary Embodiment

FIG. 8Ais a schematic cross-sectional view of a structure corresponding to the structure ofFIG. 4Ain battery module710according to a fourth exemplary embodiment, andFIG. 8Bis a schematic cross-sectional view of a structure corresponding to the structure ofFIG. 4Bin battery module710according to the fourth exemplary embodiment.

The fourth exemplary embodiment differs from the third exemplary embodiment in that bimetallic component765that contains bimetal777is used instead of resin component665to act as a lead pressing member (a component for pressing negative-electrode lead650toward negative-electrode bottom surface18of cylindrical battery11). In the fourth exemplary embodiment, structural elements identical to those in the third exemplary embodiment are assigned with the same reference numerals and redundant descriptions thereof are omitted.

As shown inFIG. 8A, bimetallic component765includes negative-electrode lead pressing part767and battery connecting part768. Bimetallic component765has a substantially L-shaped cross section. In the cross section shown inFIG. 8A, rectangular negative-electrode lead pressing part767and rectangular battery connecting part768are orthogonal to each other. Bimetallic component765includes first metal part780having a substantially L-shaped cross section, second metal part781, and insulating film782made from an insulating material such as a resin. Second metal part781is bonded to an outside surface of first metal part780remote from cylindrical battery11by cold rolling. Second metal part781differs from first metal part780in thermal expansion coefficient. Second metal part781and a part of first metal part780to which second metal part781is bonded constitute a bimetal plate. First and second metal parts780,781are each made from an alloy of iron and nickel doped with a substance such as manganese, chromium, or copper, for example. Insulating film782is fastened to an inside surface of first metal part780facing negative-electrode bottom surface18through a gap in the Z direction. A surface of insulating film782adjacent to negative-electrode bottom surface18extends in substantially parallel with negative-electrode bottom surface18.

Front end650aof negative-electrode lead650adjacent to cylindrical battery11is clamped between insulating film782and negative-electrode bottom surface18. Front end650aof negative-electrode lead650is pressed by pressure from insulating film782toward negative-electrode bottom surface18and is elastically deformed so as to be put into contact with negative-electrode bottom surface18of cylindrical battery11.

In the configuration described above, if cylindrical battery11has abnormally generated heat and cell case12(negative-electrode bottom surface18) of cylindrical battery11reaches an abnormally high temperature, the bimetal plate curves so as to be apart from negative-electrode bottom surface18as shown inFIG. 8Band in response to the curvature, negative-electrode lead650moves away from negative-electrode bottom surface18toward negative-electrode plate body48to correct distortion owing to its internal elasticity. This configuration electrically breaks negative-electrode lead650off negative-electrode bottom surface18and separates cylindrical battery11that has abnormally generated heat from an electric circuit.

In the third exemplary embodiment described above, bimetallic component765is used to press negative-electrode lead650toward negative-electrode bottom surface18. However, the bimetallic component may be replaced by an elastic member or a spring that inherently shrinks in response to a rise in temperature to act as a lead pressing member. The elastic member or the spring may be designed to press negative-electrode lead650toward negative-electrode bottom surface18while cylindrical battery11is normal, and shrink and thereby lose pressing force when cylindrical battery11has abnormally generated heat. As described at the beginning of the exemplary embodiments, a new exemplary embodiment may be made by combining two or more structural elements out of structural elements described in the first to third exemplary embodiments and all the modifications. For example, a heat shutoff mechanism may include two or more components out of the melting member of the first exemplary embodiment, the resin foam component of the second exemplary embodiment, and the lead pressing members of the third and fourth exemplary embodiments.