JP7700770B2 - Battery Module - Google Patents

Description

This disclosure relates to the structure of a battery module.

In recent years, storage batteries that have become widespread for use in automobiles are generally large-capacity battery packs made by connecting multiple single cells. In particular, storage batteries for electric vehicles require high output, so lithium-ion secondary batteries with high energy density are used.

Patent Document 1 discloses a battery pack that is both overcharge resistant and high rate resistant. The battery pack is formed by arranging single cells and elastic bodies alternately and integrating them. The single cells include an electrode body having a positive electrode and a negative electrode, and a battery case that houses the electrode body and has a pair of long sides that face the elastic body. The elastic body includes a pressing portion on the surface that faces the long sides of the single cells, which presses a part of the reaction portion in the arrangement direction. The pressing portion is configured to press only a specific area and avoid excessive pressing.

JP 2018-181765 A

Lithium-ion secondary batteries used as batteries for electric vehicles need to have a certain level of cooling performance from the viewpoint of safety. To this end, lithium-ion secondary batteries are designed to maintain cooling performance by providing an elastic body with cooling passages between the cells that make up the battery to allow cooling air to flow. However, in order to increase the density of capacity, lithium-ion secondary batteries for electric vehicles are structured so that the cells are subjected to a large external restraining force, and depending on the structure of the elastic body, high pressure is applied to the cells. As a result, the distance between the positive and negative electrodes that make up the cells becomes locally small, which can cause current concentration. Current concentration leads to the precipitation of lithium inside the cells, and the precipitated lithium can cause internal short circuits.

The purpose of this disclosure is to provide a battery module that suppresses lithium precipitation inside the battery due to external constraints.

A first aspect of the present disclosure relates to a battery module.
A battery module including a plurality of battery cells and a plurality of elastic bodies arranged alternately in one direction,
The battery cell includes an electrode body, a current collecting foil pulled out from an edge of the electrode body, and a battery case that houses the electrode body and the current collecting foil. The electrode body includes a first region that includes the edge from which the current collecting foil is pulled out and in which current concentrates during charging, and a second region that is located on the opposite side of the first region from the current collecting foil and in which current concentrates less during charging than in the first region. The elastic body includes a first rib that faces the first region across the battery case, and a plurality of second ribs that face the second region across the battery case. The contact area between the first rib and the battery case is larger than the contact area between the largest of the plurality of second ribs and the battery case.

This disclosure makes it possible to provide a battery module that suppresses lithium precipitation inside the battery due to external constraints.

FIG. 1 is an overall view of a battery module. FIG. 2 is a schematic diagram showing a part of the internal structure of the battery cell. FIG. 3 is a diagram showing the structure of the elastic body. FIG. 4 is a schematic diagram showing the current flow inside a battery cell. FIG. 5 is a diagram showing the contact state between the battery cell and the elastic body.

Figure 1 is an overall view of the battery module in this embodiment.

The battery module 1 comprises a plurality of battery cells 2 and a plurality of elastic bodies 3 arranged alternately in one direction. The battery module 1 further comprises an end plate 4, a terminal connection portion 5, a restraint plate 6, and a cover 7.

The battery cells 2 are sandwiched from both sides by elastic bodies 3. Specifically, each battery cell 2 has a pair of long sides in the arrangement direction, and is sandwiched from both sides of the long sides by two elastic bodies 3.

The elastic body 3 holds the battery cell 2 from both sides in the arrangement direction. Specifically, one elastic body 3 contacts two different battery cells 2 on both sides.

The end plates 4 are arranged at both ends in the arrangement direction so as to sandwich the multiple battery cells 2 and multiple elastic bodies 3 from both sides in the arrangement direction. The end plates 4 contact the battery cells 2 at both ends in the arrangement direction. The end plates 4 contact the restraint plates 6 and receive a force from the restraint plates 6 in the direction in which the battery cells 2 and elastic bodies 3 are arranged.

The terminal connection part 5 connects a positive terminal drawn out to the outside of the battery cell 2 with a negative terminal drawn out to the outside of another battery cell 2. In this embodiment, multiple terminal connection parts 5 are provided, and multiple battery cells 2 are electrically connected in series.

The restraint plates 6 clamp the multiple battery cells 2, multiple elastic bodies 3, and end plates 4 that are arranged in one direction. Two restraint plates 6 are arranged facing each other in a direction perpendicular to the arrangement direction.

The cover 7 covers the multiple battery cells 2, multiple elastic bodies 3, and end plate 4 from above the terminal connection portion 5.

Figure 2 is a schematic diagram showing part of the internal structure of the battery cell 2.

The battery cell 2 is composed of a battery case 21, a positive electrode body 25, a negative electrode body 26, a positive electrode collector foil 22, a negative electrode collector foil 23, and a separator 24 arranged between the positive electrode body 25 and the negative electrode body 26.

The battery case 21 is a case having a pair of long sides facing each other in the direction in which the battery cells 2 are arranged, and multiple positive electrode bodies 25, separators 24, and negative electrode bodies 26 are arranged inside.

The positive electrode body 25 is connected to a positive electrode collector foil 22, and the negative electrode body 26 is connected to a negative electrode collector foil 23. The positive electrode collector foil 22 and the negative electrode collector foil 23 are connected to the positive electrode body 25 and the negative electrode body 26, respectively, for the purpose of extracting current outside the electrode body.

The negative electrode body 26 can be divided into a first region E1 including the edge where the negative current collector foil 23 is pulled out, and a second region E2 located on the opposite side of the first region E1 to the negative current collector foil 23. In the negative electrode body 26, current tends to concentrate near the edge where the negative current collector foil 23 is pulled out during charging. In other words, the first region E1 is a region where current concentrates more during charging than the second region E2.

Current concentration in the negative electrode body 26 causes lithium precipitation, resulting in a decrease in charge/discharge efficiency. The elastic body 3 described below is designed to alleviate current concentration in the negative electrode body 26, particularly power concentration in the first region E1.

Figure 3 shows the structure of the elastic body 3.

The elastic body 3 has a first rib 31 and a number of second ribs 32. The first rib 31 and the second rib 32 are provided on both sides of the elastic body center 34 so as to face each other. The first rib 31 and the second rib 32 each contact a different battery cell 2.

The elastic body 3 further has a sealing portion 35. A coolant for cooling the battery cells 2 flows between the ribs provided on the elastic body 3. In this embodiment, the coolant is air, and the air flows between the ribs. The sealing portion 35 is a member provided to prevent the coolant from leaking to the outside. The sealing portion 35 is provided so as to face both sides of the elastic body center 34, similar to the first rib 31 and the second rib 32.

The first rib 31 faces the first region E1 of the negative electrode body 26 in the arrangement direction, sandwiching the battery case 21 between them. The largest second rib 33 faces the second region E2 of the negative electrode body 26 in the arrangement direction, sandwiching the battery case 21 between them.

The size of the first rib 31 is a measure to reduce power concentration in the first region E1. The first rib 31 is the largest of all the ribs. More specifically, the contact area between the first rib 31 and the battery case 21 is larger than the contact area between the second rib 33, which is the largest of the second ribs 32, and the battery case 21.

The second rib 33 is larger than the other second ribs 32 to ensure the strength of the elastic body 3. In addition, the largest second rib 33 is located in the center, which contributes to further improving the strength.

Figure 4 is a schematic diagram showing the current flow inside a battery cell.

The battery cell 2 has a positive electrode body 25 and a negative electrode body 26 facing each other with a separator 24 in between. The positive electrode body 25 is connected to the positive electrode collector foil 22, and the negative electrode body is connected to the negative electrode collector foil 23.

When the battery cell 2 is being charged, a current flows from the positive electrode body 25 to the negative electrode body 26. Specifically, a current flows from an external power source to the positive electrode collector foil 22, and a current flows between the electrodes through the positive electrode body 25. Between the electrodes, the current flows through the separator 24 to the negative electrode body 26. The current that flows to the negative electrode body 26 passes through the negative electrode collector foil 23 and flows to the external circuit.

As shown in FIG. 4, inside the negative electrode body 26, the current flows toward the negative current collector foil 23, so that current concentration occurs in the area (first area E1) directly below the negative current collector foil 23, including the edge where the negative current collector foil 23 is pulled out.

Figure 5 shows the contact state between the battery cell and the elastic body.

The elastic body 3 is arranged so that the first rib 31 and the second rib 32 provided on the elastic body 3 are in contact with the battery case 21.

The battery cell 2 is pressed by the elastic body 3, and stress concentration areas are generated in the battery case 21 due to the pressure from each rib. Two representative stress concentration areas 28 and 29 are shown in Figure 5. Stress concentration area 28 is an area generated by the pressure from the first rib 31. Stress concentration area 29 is an area generated by the pressure from the largest second rib 33.

Stress concentration area 28 has an area that overlaps with first area E1. Furthermore, stress concentration area 29 has an area that overlaps with second area E2. The stress concentration areas caused by the other second ribs 32 also have areas that overlap with second area E2. However, none of the stress concentration areas caused by any of the second ribs 32 has an area that overlaps with first area E1.

The contact area between the first rib 31 and the battery case 21 is larger than the contact area between the largest second rib 33 and the battery case 21. This means that the pressure that the battery cell 2 receives from the first rib 31 is smaller than the pressure that the battery cell 2 receives from the largest second rib 33. Therefore, the stress applied to the stress concentration area 28 is smaller than the stress applied to any stress concentration area caused by the second rib 32, including the stress concentration area 29.

The stress applied to the first region E1 is affected by the stress applied to the stress concentration region 28. The stress applied to the stress concentration region 28 is smaller than the stress applied to any other stress concentration region, and therefore the stress applied to the first region E1 is smaller than the stress applied to any part of the second region E2. According to this embodiment, the stress applied to the first region E1 is mitigated compared to the stress applied to other regions, so the distance between the positive electrode body 25 and the negative electrode body 26 is secured. Therefore, lithium deposition is suppressed in the first region E1 where current concentration occurs.

However, if the first rib 31 is made too large, it narrows the passage through which the refrigerant flows, adversely affecting cooling performance. Therefore, an upper limit is set for the size of the first rib 31. More specifically, the contact area between the first rib 31 and the battery case 21 is set to be smaller than the total contact area between the second rib 32 and the battery case 21.

Specifically, the contact area between the first rib 31 and the battery case 21 may be 5 to 15% when the total area of contact between the elastic body 3 and one battery case 21 is taken as 100%. The total contact area between the elastic body 3 and the battery case 21 includes the contact area between the sealing portion 35 and the battery case 21. By setting the contact area between the first rib 31 and the battery case 21 within the above range, it is possible to suppress lithium deposition due to current concentration while satisfying the requirements for cooling performance.

In this embodiment, in order to reduce the stress applied to the first region E1, the contact area between the first rib 31 facing the first region E1 and the battery case 21 is increased, but instead of or in addition to this, the first rib 31 may be formed of a material that is softer than the other ribs. A soft material means a material with a low Vickers hardness.

1 Battery module, 2 Battery cell, 3 Elastic body, 4 End plate, 5 Terminal connection part, 6 Constraint plate, 7 Cover, 21 Battery case, 22 Positive electrode current collector foil, 23 Negative electrode current collector foil, 24 Separator, 25 Positive electrode body, 26 Negative electrode body, 28 Stress concentration area, 29 Stress concentration area, 31 First rib, 32 Second rib, 33 Largest second rib, 34 Elastic body center, 35 Sealing part, E1 First area, E2 Second area

Claims (2)

A battery module including a plurality of battery cells and a plurality of elastic bodies arranged alternately in one direction,
The battery cell includes:
An electrode body;
A current collecting foil drawn out from an edge portion of the electrode body;
a battery case that accommodates the electrode body and the current collecting foil;
Equipped with
The electrode body is
a first region including the edge portion from which the current collecting foil is pulled out and in which current is concentrated during charging;
a second region located on the opposite side of the current collecting foil across the first region, the second region having a smaller current concentration during charging than the first region;
Equipped with
The elastic body is
a first rib that faces the first region with the battery case therebetween;
a plurality of second ribs facing the second region with the battery case interposed therebetween;
Equipped with
a contact area between the first rib and the battery case is larger than a maximum contact area among contact areas between each of the second ribs and the battery case ; and
a total contact area between the plurality of second ribs and the battery case is greater than a contact area between the first rib and the battery case . The battery module according to claim 1, characterized in that a contact area between the first rib and the battery case accounts for 5 to 15% of a total contact area between all ribs, including the first rib and the plurality of second ribs, and the battery case.

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