DE102009029019A1 - Preload concept for lithium-ion battery systems - Google Patents

Abstract

A belt for tensioning an accumulator cell stack (2) made of prismatic accumulator cells (4-14) in an accumulator is disclosed. The accumulator cell stack (2) has a top surface with the electrical connections (16) of the individual accumulator cells (4-14) of the accumulator cell stack, a base surface opposite the top surface and a jacket surface bounded by the circumference of the top and base surface. According to the invention, the belt (20, 22) is intended to be folded tightly around the outer surface of the accumulator cell stack (2).

Description

State of the art

The invention relates to a belt for clamping a battery cell stack of prismatic battery cells in an accumulator and an accumulator with a battery cell stack of prismatic battery cells.

Lithium-ion battery cells expand during operation and the so-called formation. According to DP Wilkinson, Effects of physical constraints on Li cyclability, Journal of power sources 36, 1991, pages 517 to 527 , the morphology of the lithium in a lithium-ion battery cell becomes porous after a few charge-discharge cycles, if too little pressure (p <0.1 MPa) is applied to the lithium-ion battery cell, so that after a few Charge-discharge cycles fail. Lithium-ion battery cells optimally need a pressure between 0.6 MPa and 2 MPa in order to function well.

Initial research has shown that high pressure must be exerted on today's lithium-ion battery cells for the lithium-ion battery cells to have a lifespan of 15 years. This pressure is approximately between 0.2 MPa and 0.8 MPa. These investigations are still ongoing.

Regardless of the outcome of the investigations, however, a bias concept for lithium-ion battery cells is required to achieve the above-described target performance.

In 6 is a stack 28 from six lithium-ion battery cells 30 shown, which are braced with a conventional pretensioning concept. Every single cell 30 has two holders 32 on, through which the individual cells 30 over a screw 34 or similar components can be clamped. The resulting pressure on the individual lithium-ion battery cells 30 also leads to satisfactory results. However, not only the space required by the necessary connection means is very high, the final accumulator is also very inflexible, since certain geometric boundary conditions are given by the connecting means, so that the number of accumulator cells to be connected 30 can not be easily increased or decreased. Also, the connecting means in a conventional accumulator are like the above-mentioned screws 34 comparatively expensive.

Disclosure of the invention

Object of the present invention is therefore to provide a bracing concept for bracing a battery cell stack of prismatic battery cells in an accumulator, with which the battery cells can be clamped with high pressure, flexible and inexpensive.

The invention therefore provides a belt for clamping a battery cell stack of prismatic battery cells in an accumulator. The accumulator cell stack has a cover surface with the electrical connections of the individual accumulator cells of the accumulator cell stack, a base surface lying opposite the cover surface, and a lateral surface bounded by the peripheries of the cover and base surface. According to the invention, the belt is provided for tightening around the lateral surface of the accumulator cell stack. Since a belt needs much less space than a screw or similar components, the tensioning of the battery cells can take place in a minimal space by bracing a battery cell stack with the belt according to the invention. As a result, the energy density of the accumulator can be increased since more space is now available for the individual accumulator cells. Also, a belt is cheaper than by the meter compared to pieces such as screws or similar components. Furthermore, the construction of a single accumulator can be made very flexible, since the individual accumulator cells of the stack can be clamped independently of the housing. This also allows individual accumulator cells to be easily exchanged from the stack. Finally, the construction of a rechargeable battery is completely independent of the connecting means, since the belt can theoretically be displaced endlessly and can only be cut to the required length on site in order to connect any number of rechargeable battery cells with one another. The accumulator cells themselves can be subjected to arbitrarily large tolerances, so that even larger and thicker battery cells, such as for drive batteries of an electric vehicle, can be clamped.

The basic idea of the invention is therefore to tie the individual accumulator cells of a rechargeable battery with a belt, as is the case in packaging technology for the dispatch of various materials, such as pipes, building materials or cables. Therefore, according to the present invention, tightening the strap around the battery cells means tying it together with the strap, so that the strap can exert a compressive force on the tied battery cells that hold the entire stack of battery cells at the desired pressure, e.g. B. between 0.2 MPa and 2 MPa, in particular 0.6 MPa and 0.8 MPa, compressed. For this technique, plastic bands or steel bands are preferably used according to the invention, since these bands can absorb very high forces. These forces, for example for clamping cells of a lithium-ion battery needed to ensure a sufficiently long life of the battery.

The dependent claims show preferred developments of the invention.

In a particular embodiment, the strap may be a strap. This is particularly advantageous because a band is flat and with its broad side so the power over a large area can be transmitted evenly to the battery cells.

In a further or alternative embodiment, the material of the belt may be at least partially made of metal, in particular of steel, since steel can absorb very high forces.

The invention also provides accumulator with a battery cell stack of prismatic battery cells. The accumulator cell stack has a cover surface with the electrical connections of the individual accumulator cells of the accumulator cell stack, a base surface lying opposite the cover surface, and a lateral surface bounded by the peripheries of the cover and base surface. To the lateral surface of the accumulator cell stack, an inventive belt is tightened. Such a rechargeable battery is very durable due to its taut battery cells.

The lateral surface may have four side surfaces in a particular embodiment, of which each two side surfaces are plane-parallel opposite. At least two plane-parallel opposite side surfaces can then be arranged a plate around which the belt is tightened. Through the plates, the forces generated by the belt are transferred evenly to the outer surface.

In a further embodiment, the belt may be connected at its ends, so that a separation of the battery cell stack is possible by a simple separation of the connection.

The connection can be a welded connection, a screw connection or a clamping connection, since these are easy to implement in terms of manufacturing technology.

In a further development of the invention, the plates can lift the belt at least at the junction of the lateral surface of the accumulator stack.

In an alternative embodiment of the invention, the belt may be connected to the plate at least at its ends.

In another development of the invention, at least one second belt according to the invention may be tightened around the lateral surface of the accumulator cell stack.

The accumulator cells of the accumulator cell stack may be lithium-ion accumulator cells.

The accumulator cell stack can have six accumulator cells.

drawings

Hereinbelow, non-limiting embodiments of the invention will be described in detail with reference to the accompanying drawings. In the drawings show:

1 a stack of juxtaposed lithium-ion battery cells;

2 a perspective view of an accumulator according to the invention according to a first embodiment of the invention;

3 a schematic view of an accumulator according to the invention according to a second embodiment of the invention;

4 a plan view of an accumulator according to the invention according to a third embodiment of the invention;

5 a plan view of an accumulator according to the invention according to a fourth embodiment of the invention;

6 a perspective view of a battery, according to the prior art.

Preferred embodiments of the invention

Hereinafter, with reference to the figures, preferred embodiments of the invention will be described in detail.

In 1 is a stack 2 from six juxtaposed prismatic lithium-ion battery cells 4 to 14 shown. The stack 2 is part of a 12V lithium-ion battery for a vehicle. Each of the accumulator cells 4 to 14 has connections 16 on, for the electrical interconnection of the individual battery cells 4 to 14 between each other and with the electrical load are present.

Experience has shown that the individual accumulator cells expand 4 to 14 in operation and become porous if the expansion does not occur with a pressure 18 counteracted. This pressure 18 should be between 0.2 MPa and 0.8 MPa. To this pressure 18 on the pile shown 2 exercise, high forces are necessary. Conventional tempering concepts that this pressure 18 However, building up is inflexible, expensive and clunky.

In the 2 to 5 is the stack 2 out 1 indicated schematically in the form of a cube. The top of the pile 2 with the electrical connections 16 is indicated in the cube by an "X", which is also in the 1 is drawn.

As in the 2 and 3 can the pressure according to the invention by bracing the stack 2 be reached with one or more straps such as a rope or a strap. In the 2 is the stack 2 with a band 20 braced. In the 3 is the stack 2 with two bands 20 . 22 braced. This technique is the same one used for shipping various materials such as pipes, building materials or cables. Plastic bands or steel bands are used for this technique. Steel bands can absorb very high forces, which is needed for the bracing of lithium-ion cells. For example, a Magnus steel strip 12 mm wide and 0.58 mm thick can withstand forces up to 7.78 kN.

Since the battery is very heavy and requires a lot of space, the energy density must be increased as much as possible. By bracing the stack 2 with one or two bands 20 . 22 Can the tension of lithium-ion battery cells 4 to 14 take place in a minimal space. This can increase the energy density of the cells. The flat and tense bands 20 . 22 , such as the aforementioned Magnus steel strip, require much less space than a screw or similar components.

As in the 4 and 5 shown are the bands 20 . 22 be around the pile 2 from prismatic lithium-ion battery cells 4 to 14 curious; excited.

For the connection of the bands 20 . 22 can be either a clamping mechanism, a screw mechanism or, as in 4 shown a welded joint 23 be used. Further, at the ends of the stack 2 as in the 4 and 5 shown plates 24 . 26 be arranged to ensure a uniform pressure distribution. The bands 20 . 22 can then, as in 5 shown, also on one of the plates 24 . 26 be attached.

By clamping the individual lithium-ion battery cells 4 to 14 The structure of an accumulator can be kept very flexible. Furthermore, the lithium-ion battery cells 4 to 14 be replaced independently of a housing, since the bracing mechanism is not related to the housing.

Adjusting a force can be achieved by this technique when connecting the bands 20 . 22 very flexible. Furthermore, in this construction, a large tolerance of the individual lithium-ion battery cells 4 to 14 completely unproblematic, since the tapes 20 . 22 theoretically can be endlessly long. The method can therefore be adapted very easily to larger and thicker cells, such as for example for the drive accumulators of an electric vehicle. Due to the comparatively wide bands 20 . 22 becomes the pressure force 18 Applied on a comparatively large area.

According to the invention, the individual battery cells are clamped in an accumulator with a belt, such as a belt or a rope in the smallest space in order to apply a sufficiently high compressive force on the battery cells.

In addition to the above disclosure, reference is expressly made to the disclosure of the figures.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited non-patent literature

• According to DP Wilkinson, Effects of physical constraints on Li cyclability, Journal of power sources 36, 1991, pages 517 to 527 [0002]

Claims (12)

Belt for clamping an accumulator cell stack ( 2 ) from prismatic accumulator cells ( 4 - 14 ) in an accumulator, the accumulator cell stack ( 2 ) a top surface with the electrical connections ( 16 ) of the individual battery cells ( 4 - 14 ) of the accumulator cell stack, a base surface opposite the top surface and a limited by the perimeters of the cover and base surface has lateral surface, characterized in that the belt ( 20 . 22 ) for tightening around the lateral surface of the accumulator cell stack ( 2 ) is provided. Belt according to claim 1, wherein the belt ( 20 . 22 ) is a band. Belt according to claim 1 or 2, wherein the material of the belt ( 20 . 22 ) consists at least partially of metal, in particular partially of steel. Accumulator with an accumulator cell stack ( 2 ) from prismatic accumulator cells ( 4 - 14 ), the accumulator cell stack ( 2 ) a top surface with the electrical connections ( 16 ) of the individual battery cells ( 4 - 14 ) of the accumulator cell stack ( 2 ), one of the top surface opposite base surface and a limited by the perimeters of the cover and base surface has a lateral surface, wherein about the lateral surface of the battery cell stack ( 2 ) a belt ( 20 . 22 ) is taut according to one of claims 1 to 3. Accumulator according to claim 4, wherein the lateral surface has four side surfaces, of which in each case two side surfaces are plane-parallel opposite, and wherein at least two two plane-parallel opposite side surfaces a plate ( 24 . 26 ) is arranged around the belt ( 20 . 22 ) is tight. Accumulator according to claim 4 or 5, wherein the belt ( 20 . 22 ) is connected at its ends. Accumulator according to claim 6, wherein the connection is a welded connection ( 23 ), a screw connection or a clamp connection. Accumulator according to claim 6 or 7, wherein the plates ( 24 . 26 ) the belt ( 20 . 22 ) at least at the junction of the lateral surface of the accumulator stack ( 2 ) take off. Accumulator according to one of claims 4 to 7, wherein the belt ( 20 . 22 ) at least at its ends with the plate ( 24 . 26 ) connected is. Accumulator according to one of claims 4 to 9, wherein the outer surface of the accumulator cell stack ( 2 ) at least one second belt ( 20 . 22 ) is taut according to one of claims 1 or 2. Accumulator according to one of Claims 4 to 10, the accumulator cells ( 4 - 14 ) of the accumulator cell stack ( 2 ) Are lithium-ion accumulator cells. Accumulator according to one of claims 4 to 11, wherein the accumulator cell stack ( 2 ) has six battery cells.

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