WO2012010347A1

WO2012010347A1 - Battery module comprising a resilient pressure plate

Info

Publication number: WO2012010347A1
Application number: PCT/EP2011/058343
Authority: WO
Inventors: Andreas Ruehle
Original assignee: Sb Limotive Company Ltd.; Sb Limotive Germany Gmbh
Priority date: 2010-07-22
Filing date: 2011-05-23
Publication date: 2012-01-26
Also published as: DE102010031641A1

Abstract

The invention relates to a battery module (1), comprising a plurality of battery cells (10), preferably lithium ion battery cells, which are arranged along a first axis (x) to form a stack. The battery module (1) further comprises at least one pressure plate (20), which is arranged on an outer face (11) of an outermost battery cell (10) of the stack. A clamping unit (30) surrounds the plurality of battery cells (10) together with the at least one pressure plate (20) and clamps same together. The at least one pressure plate (20) is resilient and, when in the clamped state by means of the clamping unit (30), exerts a restoring force on the clamping unit (30). The invention further relates to a motor vehicle comprising a corresponding battery module (1).

Description

Description title

Battery module with a spring-loaded pressure plate

The present invention relates to a battery module having a plurality of battery cells, preferably lithium-ion battery cells, in which by means of at least one pressure plate, a pressure on the battery cells is exercised. The invention further relates to a motor vehicle with a battery module according to the invention.

State of the art

Batteries for storing electrical energy, in particular

Lithium-ion batteries, expand during charging and contract when unloading. These volume or length changes are due to the storage and removal processes of lithium ions in the

Active materials of the electrodes conditionally. By incorporating lithium into the carbon material, the material expands. This increase in volume is transmitted via the battery cell shell with appropriate deformability of the cell further out and thus leads to a change in at least one geometric dimension of the battery. This is especially true for

Versions in which the battery comprises several cells. As a result, due to the expansion and contraction of the electrode materials, the individual layers arranged in the cell (metal layer,

Cathode material, separator, anode material, if necessary film) may be exposed to mechanical stress. The consequence of this is an increase in electrical resistance in the battery and thus reduced performance.

Further mechanical loads on a battery or a battery cell can be caused, for example, by an increase in temperature within the cell and from it resulting evaporation of contained electrolytes, wherein the vapor leads to a further increase in pressure within the cell. In particular, at elevated temperatures chemical reactions in the battery or in a cell can also come about, from which gases are produced, which generate an additional pressure increase within the battery cell.

These loads are higher, the greater the state of charge fluctuations in the operation of the battery.

Furthermore, for applications of batteries, in particular

Lithium-ion batteries, to drive motor vehicles, many individual electrochemical battery cells are assembled and supported. This can be done by placing the individual cells in a housing, a frame and / or wrapping the individual cells with a Verspannband. Between the Verspannband and the outer single cells can to

Pressurization of a pressure to be arranged a pressure plate. Such an example is known from EP 1 760 806 A2. The contact pressure should counteract the described expansion of the battery cells and prevent the unwanted detachment of individual layers of the electrode materials. Such contact pressure is used in particular for battery cells for hybrid vehicles application.

However, it is difficult to transfer a contact pressure homogeneously to the battery cells, as different areas of the battery cells

expand to different extents and the Verspannband different areas applied to different degrees with pressure.

Disclosure of the invention

According to the invention, a battery module is proposed, which comprises a plurality of battery cells, preferably lithium-ion battery cells, which are arranged along a first axis to form a stack. Furthermore, the

Battery module at least one pressure plate, which is arranged on an outer side of an outermost battery cell of the stack. A clamping unit surrounds the plurality of battery cells together with the at least one pressure plate and clamps them together. The at least one pressure plate is resilient and exerts in the braced by the clamping unit a restoring force on the clamping unit.

The battery module according to the invention has the advantage that a contact pressure on the outermost battery cell can be made more homogeneous. As a result, a better efficiency over the life of the battery module or the battery cells is achieved.

The restoring force is preferably along the first axis or her

directed in the opposite direction. It may also be oriented only in one component along the first axis or in opposite directions. The restoring force of the pressure plate preferably counteracts the force exerted by the tensioning unit.

The battery cells are preferably arranged one behind the other in a stack. Under the outermost sides of the plurality of battery cells, the free ends of the stack are designated. In other words, the pressing plates press on the outer side of the first battery cell, which is opposite to the side of the first battery cell, which is adjacent to the second battery cell of the stack, and the outer side of the last battery cell, which is opposite to the side of the last battery cell which is adjacent to the penultimate battery cell of the stack.

The spring force of the prestressed pressure plate preferably depends on the distance to a center axis of the pressure plate, wherein the center axis extends along a second axis perpendicular to the first axis and / or different from the first axis. The relevant central axis is preferably the vertical center axis of the pressure plate.

This design of the pressure plate, the center region of the outer side of a battery cell is subjected to a higher pressure. In a straight pressure plate, however, the center region is subjected to a lower pressure and the edge region with a relatively higher pressure. The first axis is preferably the x-axis and the second axis is the z-axis. However, other axes can be used, which are preferably formed perpendicular to each other.

The restoring force can also be formed differently in segments. Thus, the vertical center region of the pressure plate may be flat and have no restoring force and only the subsequent thereto

Be formed curved edge region.

The at least one pressure plate is without tension by the bracing convex on the corresponding outermost side of the plurality of battery cells.

The pressure plate may preferably have the form of a leaf spring.

The thickness of the pressure plate is preferably in the range of 1 mm to 6 mm. More preferably, it is between 1.5 to 4 mm, more preferably about 2 mm.

The bracing unit preferably comprises a bracing band and a

Coupling unit for connecting and clamping two ends of the

Verspannbandes. As a result of this design of the clamping unit, the battery cells and the pressure plate can be connected to one another in a simple and efficient manner and pressurized. For this purpose, only the coupling unit must be designed such that the bracing after coupling can be further braced.

The radius of curvature of the pressure plate is preferably in the plane or a parallel plane of the course of the Verspannbandes.

The pressure distribution on the outer side of a battery cell which bears against the at least one pressure plate is preferably substantially homogeneous, more preferably homogeneous in the context of measurement inaccuracy.

It is also proposed a motor vehicle with a battery module according to the invention, wherein the battery module with a drive system of the

Motor vehicle is connected. Advantageous developments of the invention are specified in the subclaims and described in the description.

The term battery in this application also includes battery systems, accumulator batteries, accumulators, accumulator systems, in particular Li-ion systems or Li-polymer ion systems.

drawings

Embodiments of the invention will be explained in more detail with reference to the drawings and the description below. Show it:

1 shows a battery module with a plurality of battery cells and a pressure plate of the prior art,

FIG. 2 shows a pressure distribution on the outer side of the battery module of the prior art,

FIG. 3 shows a pressure plate according to the invention,

Figure 4 shows a pressure plate according to the invention with battery cell, and

5 shows an improved pressure distribution on the outer side of a battery module according to the invention with a pressure plate of Figure 3.

Embodiments of the invention

In the figure 1 a battery module of the prior art is shown. The battery module 1 comprises a plurality of battery cells 10, wherein the battery cells 10 are arranged in a package or in a stack. In Figure 1, the battery cells 10 are arranged one behind the other in a first direction, here the x-direction. To be with a battery, especially one

Lithium-ion battery, better life over life force must be applied to the battery cells. This is usually realized by a tension of the battery cells 10 to form a battery module 1. For this purpose, the battery module 1 of Figure 1 in addition to a clamping unit 30 pressure plates 20, which are arranged at the free ends of the stack of battery cells 10. By the pressure plates 20, the pressure is distributed by the tensioning unit 30 on the side surfaces of the outer battery cells 10.

To build up pressure, the tension and / or the assembly of the stack of battery cells 10 and pressure plates 20 surrounds a clamping unit 30, the battery cells 10 and the pressure plates 20 and braces them. The tension unit 30 has the function of applying and transmitting power. In the embodiment of Figure 1, the bracing unit 30 is non-limiting realized by a bracing 31 and a coupling unit 32. The coupling unit 32 connects by way of example two ends of the tensioning band 31 with one another and urges the tensioning band 31 with a force. The coupling unit 32 may, for example, have male and female components that intermesh for coupling. The coupling unit 32 can also comprise a thread, for example a worm thread in the manner of a worm thread clamp, with which the bracing strip 31 is braced. But the tension can also be done in other ways.

The pressure plate 20 has the function to distribute the force evenly on the outer side surface of the corresponding battery cell 10. FIG. 1 shows the use of a straight pressure plate 20. If, as shown in Figure 1, the battery cells 10 are arranged in the x-direction one behind the other, is a first pressure plate 20 on the outer side 1 1 of the first battery cell 10 of the stack, which is not adjacent to another battery cell 10. Likewise, a second pressure plate 20 on the outer side 1 1 of the last

Battery cell 10 of the stack abut. The pressure plate 20 extends in Figure 1 in the yz plane. The bracing 31 runs around the battery cells 10 and the pressure plates 20 around, in Figure 1 in an xy plane, preferably halfway up the battery cells 10. The bracing 31 can also be performed differently around the battery cells 10, z. B. in the xz plane, so on the lid and the bottom of each battery cell 10th FIG. 1 shows further connecting elements, which are purely optional. Thus, the battery cell stack can be placed in a frame 40 having front and back 41 and connecting pieces 43 between front and back. In addition, between each two battery cells 10 more

Plates 42 may be arranged.

In the embodiment of Figure 1, the tension by the Verspannband 31 together with the shape of the pressure plate 20, the result that the

Pressure distribution on the outer sides 1 1 of the first and last battery cell 10 of the stack is inhomogeneous. This is shown in FIG. The dark areas of Figure 2 show the areas of higher pressure. On the sides of the pressure plate 20 more pressure is transmitted than in the middle. This is particularly disadvantageous because the center region of the battery cells 10 is the most susceptible to deformation. During operation, in the middle region of a battery cell 10, a stomach can form which is insufficiently counteracted by the pressure plate 20 of the prior art.

The rib structure of the pressure distribution shown in FIG. 2 is based on the use of a frame 40 with corresponding end surfaces 41

attributed as shown in Figure 1. Preferably, the pressure plate 20 is located directly on the outer side 1 1 of the first and last battery cell 10 of the stack. FIG. 3 shows a pressure plate 20 according to the invention, FIG. 4 together with a battery cell 10 before the tensioning. The pressure plate 20 is biased and resilient. In other words, the pressure plate 20 has a radius. It is arched. It is convex on the outside 1 1 of the outermost battery cell 10 of the stack. The curvature runs along the y-axis of FIG. 1. The curvature may also be formed in segments, that is, partial segments of the pressure plate 20 may have a different radius of curvature. In FIG. 4, the central axis 50 of the pressure plate 20 is represented by the lowest point of the pressure plate 20, which has a slope of zero, parallel to the plane of the surface of the outer battery cell 10. In other words, a center of curvature of the pressure plate 20 is preferably located exactly on the vertical center axis 50 of the pressure plate 20, but can also slightly different. To further increase the spring force, the

Pressure plate 20 are executed with beads. These can be designed in any direction.

That is, without tensioning unit 30, a center area is around

Central axis 50 of the clamping unit 30 along the z-axis at the

Battery cell 10 and the outer region of the pressure plate 20 is spaced from the surface of the battery cell 10. This is exactly the area in which the battery cell 10 expands the most. The pressure plate 20 is elastic and has a restoring force, which depends on the distance to the central axis 50. The restoring force acts along the axis of the stacking

Battery cells 10, ie along the first axis or her opposite, depending on which side of the stack, the pressure plate 20 is arranged. If the bracing unit 30 is now arranged in the x-y plane around the battery cells 10 and the pressure plate 20, the sides of the

Pressing plate 20 deformed by the force of the tensioning unit 30 in the direction of the battery cells 10 and are finally there. At the same time, by the curvature of the pressure plate 20, the center region of the pressure plate 20 along the z-axis is also on the outer side 1 1 of the battery cell 10 and exerts a pressure.

It will be apparent to those skilled in the art that in guiding the Verspannbandes 31 over the upper and lower surfaces of the battery cells 10, such that the

Outside 1 1 of the first battery cell 10 is traversed in the z-direction, the curvature of the pressure plate 20 should be rotated accordingly by 90 degrees, so the curvature along the z-axis would have to.

In other words, the radius of curvature of the pressure plate 20 is perpendicular to the outside of the outer battery cell 10 and on the Verspannband 31 and extends in the plane or parallel to the plane of the course of the

Verspannbandes 31 to the battery cell 10. In Figure 1, the runs

Bracing band 31 in x-y plane. The radius of curvature also runs in an x-y plane.

Figure 5 shows the result of a measurement of the improved pressure distribution with the curved pressure plate of Figures 3 and 4. The dark area, the corresponds to a region of high pressure, in the middle of the pressure plate is due to the curvature of the pressure plate 20. The optimal shape of the pressure plate 20 may be, for example, using the

Finite element method can be calculated in order to achieve a uniform distribution of forces. The force needed to compress the

Battery cells 10 and the spring characteristic of the pressure plate 20 are parameters of optimization. The force can be between 5000-10000 N, preferably it is 7000 N.

Due to the pre-curved shape of the pressure plate 20, the

Pressing plate 20 substantially thinner at the same power transmission as a straight pressure plate 20 may be formed. A pressure plate 20 of the prior art from z. As steel or aluminum usually has a thickness of 10 mm. A pressure plate 20 of the same material according to the invention requires for pressurization only a thickness of 1 -6 mm, preferably 1, 5-4 mm, more preferably about 2 mm. Thus, the pressure plate 20 can be made thinner, lighter and cheaper.

Claims

claims

1 . A battery module (1) comprising:

a plurality of battery cells (10) assembled in a stack arranged along a first axis (X);

at least one pressure plate (20) arranged on an outer side (1 1) of an outermost battery cell of the stack (10);

a bracing unit (30) surrounding and clamped together the plurality of battery cells (10) together with the pressure plate (20); characterized in that the at least one pressure plate (20) is resilient and exerts a restoring force on the tensioning unit (30) in the tensioned by the tensioning unit (30) state.

2. The battery module (1) according to claim 1, wherein the restoring force along the first axis (x) or along the negative first axis (x) extends.

3. The battery module (1) according to claim 1 or 2, wherein the restoring force of the pressure plate (20) counteracts the force exerted by the tensioning unit (30) force.

4. The battery module (1) according to one of the preceding claims, wherein the restoring force of the prestressed pressure plate (20) from the distance of a measuring point to a central axis (50) of the pressure plate (20) depends, wherein the central axis (50) along one of the first Axis (x) different and / or perpendicular to the second axis (z) extends.

5. The battery module (1) according to any one of the preceding claims, wherein two pressure plates (20) are provided, which abut against the outside (1 1) of the first and last battery cell (10) of the stack.

6. The battery module (1) according to any one of the preceding claims, wherein the at least one pressure plate (20) bears without distortion by the tensioning unit (30) convexly on the corresponding outermost side of the plurality of battery cells (10).

7. The battery module (1) according to any one of the preceding claims, wherein the thickness of the at least one pressure plate (20) in the range of 1 mm to 6 mm, preferably 2-4 mm.

8. The battery module (1) according to one of the preceding claims, wherein the clamping unit (30) comprises:

a tension band (31) and

a coupling unit (32) for connecting and tensioning two ends of the tensioning band (31).

9. The battery module (1) according to claim 8, wherein the radius of curvature of the pressure plate (20) in the plane or a parallel plane of the course of the Verspannbandes (31).

10. Motor vehicle with a battery module (1) according to one of claims 1 to 9, wherein the battery module (1) with a drive system of

Motor vehicle is connected.