Cell module

A cell module includes a plurality of battery cells each having a safety valve at a first end in a height direction, a first current collector plate including a main body having a through hole that at least partly overlaps the safety valve when viewed along the height direction and a lead extending into the through hole from the main body and being electrically connected to a first terminal of each of the battery cells, an exhaust duct disposed over a surface of the first current collector plate remote from the battery cells, and an insulating film being made of an insulating material and covering an area of the first current collector plate facing the exhaust duct. The safety valve opens when an internal pressure of any of the battery cells reaches or exceeds a predetermined level.

This application is a U.S. national stage application of the PCT International Application No. PCT/JP2017/040172 filed on Nov. 8, 2017, which claims the benefit of foreign priority of Japanese patent application No. 2016-231959 filed on Nov. 30, 2016, the contents all of which are incorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates to a cell module.

BACKGROUND ART

A conventional cell module, as described in PTL 1, 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 cell module has the plurality of the parallel-connected battery cells and is designed to separate any battery cell through which a large 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 large current through the battery cell.

As described in PTL 2, a cell module has a safety valve on one end face of each battery cell in a height direction. The cell module is configured to let the safety valve break and discharge an emission including a high-temperature gas from any of the battery cells if the battery cell reaches an abnormally high temperature and the pressure inside the battery cell rises. The discharged emission passes through a through hole formed in a place of a current collector plate overlapping the battery cell in the height direction and is guided into an exhaust duct disposed over a surface of the current collector plate remote from the battery cells. This configuration allows the emission to flow through the exhaust duct and be discharged outside from an outlet of the exhaust duct and thereby hinders the emission including the high-temperature gas discharged from the abnormally high-temperature battery cell from having an impact on the other battery cells.

CITATION LIST

Patent Literature

SUMMARY OF THE INVENTION

Technical Problem

The emission discharged from the battery cell due to a brake in the safety valve described above contains many conductive materials such as copper foil. If these conductive materials extend between a positive electrode of the battery cell and the current collector plate, a path of the conductive materials is formed between the positive electrode of the battery cell and the current collector plate and an electric current flows into the path of the conductive materials. Thus, an electric circuit originally designed in the module is changed into a very different one. In addition, the path of the conductive materials hinders a large current from flowing into a fuse for the abnormally high-temperature battery cell. As a result, the fuse may not be blown. This prevents the separation of the abnormally high-temperature battery cell from the circuit of the parallel-connected battery cells, so that the abnormally high-temperature battery cell may further generate heat because of an electric current flowing inside.

It is an object of the present disclosure to provide a cell module that hinders a conductive material contained in an emission from a battery cell from forming a path between an electrode of the battery cell and a current collector plate and thus enables reliable separation of the battery cell having reached an abnormally high temperature from an electric circuit.

Advantageous Effect of Invention

A cell module according to the present disclosure includes a plurality of battery cells that each includes a battery element and a cell case containing the battery element and having a safety valve at a first end in a height direction, the safety valve being configured to open when an internal pressure inside the cell case reaches or exceeds a predetermined level, and a first current collector plate configured to electrically connect first terminals of the plurality of the battery cells. The first current collector plate includes a main body having a through hole that at least partly overlaps the safety valve when viewed along the height direction, and a lead extending into the through hole from the main body and being electrically connected to the first terminal of each of the battery cells. The cell module further includes an exhaust duct disposed over a surface of the first current collector plate remote from the battery cells, the exhaust duct being configured to guide an emission being discharged from at least one of the plurality of the battery cells and passing through the through hole to an outside of the cell module when the safety valve of the at least one battery cell is opened, and an insulating film being made of an insulating material and covering an area of the first current collector plate facing the exhaust duct.

Advantageous Effect of Invention

In the cell module according to the present disclosure, the area of the first current collector plate facing the exhaust duct is covered with the insulating film. Hence, even if an emission containing a conductive material flows into the exhaust duct such that a path of the conductive material is formed to join an inner surface of the exhaust duct and an electrode of any of the battery cells together, the insulating film prevents the path from reaching the first current collector plate. Accordingly, the emission discharged into the exhaust duct does not establish any electrical connection between the electrode of the battery cell and the first current collector plate. This configuration hinders a conductive material contained in an emission from a battery cell having reached an abnormally high temperature from forming a path to a current collector plate and thus enables reliable separation of the abnormally high-temperature battery cell from an electric circuit.

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 description given hereinafter, cylindrical cells11are incorporated in cell module10and a side of each cylindrical cell11adjacent to a positive electrode (adjacent to exhaust duct70) in a height direction (in an axis direction) is defined as an upper side.

First Exemplary Embodiment

FIG. 1is a schematic cross-sectional view of cell module10according to a first exemplary embodiment of the present disclosure, viewed along central axes of two or more cylindrical cells11out of a plurality of cylindrical cells11included in cell module10.

As shown inFIG. 1, cell module10includes a plurality of cylindrical cells11and cell holder20having a plurality of containers18to contain cylindrical cells11. In the example shown inFIG. 1, the plurality of containers18is arranged in a matrix when viewed from above, with a left-right direction of the figure representing one direction and a direction perpendicular to the figure representing the other direction. However, the plurality of the containers may be arranged in a staggered manner when viewed from above.

Cylindrical cell11is an example of a battery cell and is, for example, formed of a secondary cell such as a lithium ion secondary cell. Cylindrical cell11includes 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 plate14sealing an opening of cell case body13. Sealing plate14has safety valve16. Safety valve16includes annular breaking portion15that breaks first when an internal pressure of the cell exceeds a predetermined level and a portion surrounded by breaking portion15. The sealing plate is electrically connected to a positive electrode of the battery element. Sealing plate14constitutes the positive electrode terminal to act as a first terminal of cylindrical cell11. In the present exemplary embodiment, an outer peripheral side surface of cell case body13is covered with an insulating resin film and a bottom surface of cell case body13constitutes the negative electrode terminal. The outer peripheral side surface of cell case body may not be covered with an insulating resin film, and the cell case body may constitute a negative electrode of the cylindrical cell.

Cell holder20is formed from a curable resin, for example. Cell holder20has first holder21to hold an upper end part of each cylindrical cell11and second holder22to hold a lower end part of each cylindrical cell11, with these holders coupled together. Containers18are each formed of recess21aof first holder21and recess22aof second holder22. The upper end part of cylindrical cell11is inserted into recess21a,and the lower end part of cylindrical cell11is inserted into recess22a.First and second holders21,22have respective cylindrical holes21b,22bwith circular openings at locations overlapping cylindrical cells11when viewed along the height direction. Cell module10may have one or more battery blocks that each includes one cell holder20. Resin-made cell holder20may be replaced by a cell holder that is made of metal. In this case, to insulate each cylindrical cell, insulation boards are preferably disposed between the plurality of the cylindrical cells and respective current collector plates described next.

Positive-electrode current collector plate30is joined to and disposed on first holder21to act as a first current collector plate. Positive-electrode current collector plate30includes lead plate31made of a metallic material and base plate32made of a metallic material. Base plate32is joined to a top surface of lead plate31by welding or other technique. Positive-electrode current collector plate30has cylindrical holes (through holes)30abeing put over cylindrical holes21band smoothly connecting with cylindrical holes21bwhen viewed along the height direction. Cylindrical hole30ahas a circular opening that is substantially identical to the circular opening of cylindrical hole21b.Lead plate31includes main plate34having a plurality of through holes34aand leads35. Lead35extends from an inner surface of through hole34aof main plate34toward a center of through hole34aand curves toward cylindrical cell11. An end of the lead is joined to the positive electrode terminal of cylindrical cell11. Base plate32and main plate34of lead35constitute main body73of positive-electrode current collector plate30. Positive-electrode current collector plate30includes main body73having cylindrical holes30aeach put over entire safety valve16when viewed along the height direction and leads35extending into respective cylindrical holes30afrom main body73and being electrically connected to the positive electrode terminals of cylindrical cells11.

Meanwhile, negative-electrode current collector plate40is joined to and disposed beneath cell holder20. Negative-electrode current collector plate40includes lead plate41made of a metallic material and base plate42made of a metallic material. Base plate42is joined to an undersurface of lead plate41by welding or other technique. Negative-electrode current collector plate40has cylindrical holes40abeing put over cylindrical holes22band smoothly connecting with cylindrical holes22bwhen viewed along the height direction. Lead plate41includes main plate45having a plurality of through holes45aand leads46. Lead46extends from an inner surface of through hole45aof main plate45toward a center of through hole45aand curves toward cylindrical cell11. An end of the lead is joined to the negative electrode terminal of cylindrical cell11. Consequently, the plurality of cylindrical cells11is connected in parallel by positive- and negative-electrode current collector plates30,40. Cell module10is, for example, connected in series with other cell module10adjacently disposed via a bus bar through positive- and negative-electrode current collector plates30and40.

Positive-electrode current collector plate30has an area to which cell holder20is not joined, and insulating film60that is formed from an insulating material having an insulating property, such as a resin material, is disposed on the area. Insulating film60includes surface covering portion61to cover a surface of positive-electrode current collector plate30remote from cylindrical cells11in the height direction and cylindrical hole covering portion62to cover an internal circumference of each cylindrical hole30a.

Exhaust duct70is disposed over the surface of positive-electrode current collector plate30remote from cylindrical cells11in the height direction. The plurality of cylindrical cells11is accommodated in module case80, and exhaust duct70is defined by an upper wall part of an inner wall surface of the module case above insulating film60and top surface66of insulating film60remote from cylindrical cells11in the height direction. When safety valve16opens, an interior of cylindrical cell11communicates with exhaust duct70via opened safety valve16, cylindrical hole21bof first holder21, and cylindrical hole30aof positive-electrode current collector plate30. The upper wall part for exhaust duct70has outlet opening67to communicate with an outside. In this case, an emission including a high-temperature gas from the interior of cylindrical cell11moves through exhaust duct70in a direction indicated with arrow A and flows to the outside from outlet opening67.

FIG. 2is a top plan view of a part of the cell module overlapping one cylindrical cell11, omitting illustration of the case.FIG. 3is a plan view of the part of the cell module inFIG. 2, omitting illustration of insulating film60.

As shown inFIGS. 2 and 3, safety valve16is disposed on an upper end face (one end face in the axis direction) of cylindrical cell11and includes annular breaking portion15and a portion surrounded by breaking portion15. Annular breaking portion15is, for example, a groove made in a metallic plate that forms sealing plate14. The breaking portion breaks first ahead of the other part of cell case12in response to a rise in internal pressure following the occurrence of an abnormality in cylindrical cell11. Groove17in breaking portion15is generally called a marking that is formed by stamping cell case12from outside. A section where breaking portion15is formed in sealing plate14is a thin-walled part that is thinner in thickness than the other part.

Safety valve16has the shape of a perfect circle in plan view. However, the safety valve may have the shape of an ellipse, a polygon, or any other shape in plan view. In the present exemplary embodiment, breaking portion15is an annular part having a substantially constant diameter with its center placed at a middle of the upper end face of cylindrical cell11, such that safety valve16is disposed in a central region of the upper end face of cylindrical cell11. If the internal pressure of cylindrical cell11exceeds a predetermined level and breaking portion15breaks, safety valve16opens outward from cylindrical cell11such that an opening is formed in sealing plate14. This allows an emission including a high-temperature gas to be discharged from the opening.

Insulating film60has straight edge60asubstantially perpendicular to plane P that vertically divides the plan view ofFIG. 2into two equal parts. The straight edge60ais positioned at a distance from a tip of the lead. In the plan view shown inFIG. 2, insulating film60is annular, and an inner peripheral edge of the insulating film is made up of straight edge60aand circular edge60bthat is a part of a circle joined to both ends of straight edge60a.Insulating film60includes flange39overlapping a part of safety valve16when viewed along the height direction. In insulating film60, flange39includes projection47that overlaps a protruding region in the height direction. The protruding region extends inward from the circle containing circular edge60b.

In safety valve16, lead opposite region16aon an opposite side of straight edge60afrom the lead overlaps flange39in the height direction. Part15aof breaking portion15overlapping flange39when viewed along the height direction is on an opposite side of a center of cylindrical hole30a(seeFIG. 1) of positive-electrode current collector plate30from a lead connecting part (a part of lead35connected to main plate34) in a direction (indicated with arrow B) along which lead35extends. The part of the breaking portion is positioned at a distance from lead35. When viewed along the height direction, flange39overlapping part15aof breaking portion15does not overlap lead35.

As shown inFIG. 3, the circular opening of cylindrical hole30aof positive-electrode current collector plate30is disposed concentrically with circular groove17forming breaking portion15of safety valve16and is larger in diameter than circular groove17. Thus, when viewed along the height direction, entire safety valve16is put over cylindrical hole30aof positive-electrode current collector plate30.

With reference toFIGS. 4 and 5, operation performed by cell module10according to the first exemplary embodiment and effects produced thereby in response to abnormal heat generation in one cylindrical cell11will now be described.FIG. 4is a schematic cross-sectional view illustrating a problem with a structure of cell module210in a reference example, viewed along a central axis of cylindrical cell211with safety valve216opened due to abnormal heat generation.FIG. 5is a schematic cross-sectional view of a structure corresponding to the structure ofFIG. 4in cell module10according to the first exemplary embodiment.

FIG. 4shows an instance in which no insulating film is put on an outer surface of positive-electrode current collector plate230. If safety valve216is opened following abnormal heat generation in cylindrical cell211due to, for example, a minute short circuit between a positive electrode and a negative electrode inside a cell case or other reason, many conductive materials contained in an emission discharged from an interior of the cylindrical cell into exhaust duct270may extend from the interior of the cell through a part of the outer surface of positive-electrode current collector plate230facing exhaust duct270such that path290of the conductive materials is formed to join the cell interior and the outer surface part together. Then, an electric circuit originally designed in the module may be changed into a very different one if electric current flows into path290of the conductive materials. In addition, a large current may be hindered from flowing into a fuse for abnormally high-temperature cylindrical cell211, so that the fuse is not be blown and the module cannot separate abnormally high-temperature cylindrical cell211from the circuit of the parallel-connected cells. As a result, abnormally high-temperature cylindrical cell211may further generate heat because of an electric current flowing inside.

On the other hand, in cell module10according to the first exemplary embodiment, an area of positive-electrode current collector plate30facing exhaust duct70is covered with insulating film60. Thus, even if safety valve16is opened following abnormal heat generation in cylindrical cell11and an emission containing conductive materials flows into exhaust duct70along a direction indicated with arrow C such that a path of the conductive materials is formed to join an inner surface of exhaust duct70and the positive electrode of cylindrical cell11together, insulating film60prevents the path of the conductive materials from reaching positive-electrode current collector plate30. Accordingly, even if the emission is discharged into exhaust duct70, the positive electrode of cylindrical cell11is not electrically connected with positive-electrode current collector plate30by the conductive materials. Consequently, the emission from abnormally high-temperature cylindrical cell11is hindered from forming a high resistance path and the electric circuit originally designed in the module is not changed into a very different one.

Insulating film60also covers a portion of an inner circumferential surface of cylindrical hole30aof positive-electrode current collector plate30other than the lead connecting part. Thus, the conductive materials contained in the emission do not form a path between the interior of cylindrical cell11and the inner circumferential surface of cylindrical hole30aof positive-electrode current collector plate30. This configuration reliably prevents the electric circuit originally designed in the module from being changed into a very different one.

Moreover, when viewed along the height direction, flange39does not overlap lead35, while overlapping part15aof breaking portion15(seeFIG. 2). As a result, part15aof breaking portion15overlapping flange39is supported by and pressed by flange39and is hence difficult to be opened, so that, as shown inFIG. 5, a side of safety valve16adjacent to the lead connecting part in the lead extending direction is solely opened. Thus, the cell module opens the side of safety valve16adjacent to the lead connecting part and thereby cuts lead35and separates cylindrical cell11that has abnormally generated heat from the electric circuit. This configuration reliably ensures safety of cell module10.

In the first exemplary embodiment described above, it is preferable that leads46on the negative electrode side each include a fuse to enable the separation of a cylindrical cell that has abnormally generated heat from the electric circuit even if the lead on the positive electrode side is not cut off by the opened safety valve. However, each lead46on the negative electrode side may not include any fuse. Leads35on the positive electrode side may each include a fuse or may not include any fuse.

In the description given above, the insulating film covers a portion of the inner circumferential surface of cylindrical hole30aformed in positive-electrode current collector plate30other than the lead connecting part. However, the insulating film may not cover the portion of the inner circumferential surface of the through hole formed in the positive-electrode current collector plate other than the lead connecting part.

In the description given above, insulating film60does not cover back side37of positive-electrode current collector plate30adjacent to cylindrical cells11(an undersurface of the current collector plate remote from a side facing exhaust duct70in the height direction) (seeFIG. 1). However, the insulating film may cover the back side of the positive-electrode current collector plate adjacent to the cylindrical cells (the undersurface of the current collector plate remote from a side facing the exhaust duct in the height direction). In particular, if a cell module includes a metallic cell holder instead of resin-made cell holder20, the cell module preferably includes an insulating board between cylindrical cells11and a positive-electrode current collector plate to insulate the cylindrical cells. However, it is preferable that the insulating film also covers the back side of the positive-electrode current collector plate. This configuration prevents the formation of a path connecting the back side of the positive-electrode current collector plate to the interior of any of the cylindrical cells and enables an insulating layer covering the back side to insulate the cylindrical cells. This in turn allows omission of the insulating board.

In the description given above, positive-electrode current collector plate30includes cylindrical holes30athat are each put over entire safety valve16when viewed along the height direction. However, a positive-electrode current collector plate may include through holes that each overlap at least a part of a safety valve when viewed along the height direction. In the description given above, insulating film60overlaps part15aof annular breaking portion15of safety valve16when viewed along the height direction. However, an insulating film may not overlap any part of an annular breaking portion of a safety valve when viewed along the height direction.

In the description given above, the positive electrode terminal acts as the first terminal of the cylindrical cell, and positive-electrode current collector plate30acts as the first current collector plate. However, the negative electrode terminal may act as the first terminal of the cylindrical cell and the negative-electrode current collector plate may act as the first current collector plate such that the safety valve is disposed on a bottom surface of the cylindrical cell adjacent to the negative electrode (an undersurface of the cell in the height direction) and the exhaust duct is disposed over a surface of the negative-electrode current collector plate remote from the cylindrical cells. Then, an area of the negative-electrode current collector plate facing the exhaust duct may be covered with an insulating film that is formed from an insulating material such as a resin material. In addition to the area of the negative-electrode current collector plate facing the exhaust duct, the insulating film may cover a portion of an inner circumferential surface of each through hole formed in the negative-electrode current collector plate other than the lead connecting part. The insulating film may also cover a back side of the negative-electrode current collector plate adjacent to the cylindrical cells.

The safety valves may be disposed on the bottom surface of the cylindrical cell adjacent to the negative electrode as well as a top surface of the cylindrical cell adjacent to the positive electrode, respectively, such that the exhaust ducts are disposed over the surface of the negative-electrode current collector plate remote from the cylindrical cells as well as over the surface of the positive-electrode current collector plate remote from the cylindrical cells, respectively. Then, the area of the negative-electrode current collector plate facing the exhaust duct as well as the area of the positive-electrode current collector plate facing the exhaust duct may be each covered with an insulating film that is formed from an insulating material such as a resin material. In this case as well, in addition to the area of the negative-electrode current collector plate facing the exhaust duct, the insulating film may cover a portion of the inner circumferential surface of each through hole formed in the negative-electrode current collector plate other than the lead connecting part. The insulating film may also cover the back side of the negative-electrode current collector plate adjacent to the cylindrical cells.

In the description given above, all the plurality of cylindrical cells11contained in cell module10is connected in parallel. However, the plurality of the cylindrical cells contained in the cell module may include two or more cylindrical cells that are connected in series. The battery cells described above are cylindrical cells11. However, the battery cells may be rectangular batteries.

Second Exemplary Embodiment

FIG. 6is a schematic cross-sectional view of cell module110according to a second exemplary embodiment of the present disclosure, viewed in the same way asFIG. 1.FIG. 7is a schematic cross-sectional view of a structure corresponding to the structure ofFIG. 5in cell module110according to the second exemplary embodiment. In the second exemplary embodiment, 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. 6, in the second exemplary embodiment, like the first exemplary embodiment, insulating film160that covers a top surface of positive-electrode current collector plate30adjacent to exhaust duct170and an inner circumferential surface of each cylindrical hole30aof positive-electrode current collector plate30includes flange139overlapping part115aof breaking portion15when viewed along the height direction. However, unlike the first exemplary embodiment, flange139overlaps not only part115aof breaking portion15but also part35aof lead35when viewed along the height direction. When viewed along the height direction, part115aof breaking portion15overlapping insulating film160is positioned adjacent to lead connecting part179and away from a center of cylindrical hole30aof positive-electrode current collector plate30in a direction in which lead35extends.

In the second exemplary embodiment, unlike the first exemplary embodiment, leads146on the negative electrode side each include fuse190. Bottom94of cylindrical cell11that constitutes a second terminal of the cylindrical cell is electrically connected to lead146on the negative electrode side. In the second exemplary embodiment, unlike the first exemplary embodiment, outlet opening167of exhaust duct170is not disposed on a right side of the figure but is disposed on a left side of the figure. Other structural elements in the second exemplary embodiment are identical to those in the first exemplary embodiment.

As shown inFIG. 7, in the second exemplary embodiment, flange139of insulating film160overlaps part115aof breaking portion15as well as part35aof lead35when viewed along the height direction. Thus, part115aof breaking portion15overlapping flange139is supported by and pressed by flange139and is hence difficult to be opened, so that, as shown inFIG. 7, a side of safety valve16remote from the lead connecting part in the lead extending direction is solely opened. As a result, even if safety valve16opens and an emission flows along a direction indicated with arrow D, the cell module can maintain and protect electrical connection of lead35to a positive electrode terminal of cylindrical cell11. Since insulating film160prevents conductive materials contained in the emission from forming a path to the current collector plate, this configuration reliably allows a large current to flow into fuse190at the negative electrode side of cylindrical cell11that has abnormally generated heat. This enables the cell module to blow fuse190and hence reliably separate cylindrical cell11that has abnormally generated heat from an electric circuit.

REFERENCE MARKS IN THE DRAWINGS

12: cell case

15: breaking portion

15a,115a: part of breaking portion

16: safety valve

35a: part of lead

73: main body