Electrical Energy Store and Method for Operating an Electrical Energy Store

Abstract

An electrical energy store includes an electrode stack which has a plurality of plies disposed one above the other in a stacking direction of electrodes and separators disposed between the electrodes. The electrode stack is disposed between a first pressure plate and a second pressure plate and a pressure is exertable on the electrode stack by the first pressure plate and the second pressure plate. At least one of the first pressure plate and the second pressure plate is movable by an actuator and the actuator is controllable by a control device. The first pressure plate and the second pressure plate are coupled to each other by the actuator and a spacing of the first pressure plate and the second pressure plate from each other is changeable by the control device controlling the actuator.

Claims

1.-10. (canceled)

11. An electrical energy store, comprising: an electrode stack which comprises a plurality of plies disposed one above the other in a stacking direction of electrodes and separators disposed between the electrodes; a first pressure plate and a second pressure plate, wherein the electrode stack is disposed between the first pressure plate and the second pressure plate and wherein a pressure is exertable on the electrode stack by the first pressure plate and the second pressure plate; an actuator, wherein at least one of the first pressure plate and the second pressure plate is movable by the actuator; and a control device, wherein the actuator is controllable by the control device; wherein the first pressure plate and the second pressure plate are coupled to each other by the actuator and wherein a spacing of the first pressure plate and the second pressure plate from each other is changeable by the control device controlling the actuator.

12. The electrical energy store according to claim 11, wherein a supply of the electrode stack with a constant force by the actuator via the first pressure plate and the second pressure plate is initiatable by the control device depending on a thickness of the electrode stack.

13. The electrical energy store according to claim 11, wherein the actuator is disposed between the first pressure plate and the second pressure plate and wherein the actuator has a movement device or is formed as movement device which is connected to the first pressure plate on a first side and to the second pressure plate on a second side.

14. The electrical energy store according to claim 11, wherein the actuator is formed as a fluid regulator having a chamber which receives and emits a fluid.

15. The electrical energy store according to claim 11, wherein the actuator is formed as a mechanical or an electromechanical drive device via which the spacing is changeable.

16. The electrical energy store according to claim 15, wherein the drive device has a threaded spindle or a toothed rod that is mechanically lockable or has a braking device and wherein the threaded spindle or the toothed rod changes the spacing by actuating a lever device.

17. The electrical energy store according to claim 11, further comprising an elastic element disposed between the electrode stack and at least one of the first pressure plate and the second pressure plate.

18. The electrical energy store according to claim 11, wherein a pressure exerted via the first pressure plate and the second pressure plate on the electrode stack is reducible by the control device depending on an operating state of the electrode stack.

19. The electrical energy store according to claim 11, wherein the electrical energy store is formed as a battery cell having a cell housing and wherein the first pressure plate, the second pressure plate, and the electrode stack are disposed inside the cell housing.

20. The electrical energy store according to claim 11, wherein the electrical energy store has a plurality of battery cells disposed between the first pressure plate and the second pressure plate and wherein a respective battery cell has a respective cell housing having the electrode stack disposed in the respective cell housing.

21. A method for operating the electrical energy store according to claim 11, comprising the step of: changing a spacing of the first pressure plate and the second pressure plate from each other by the control device controlling the actuator.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0041] FIG. 1 is a graph in which force-path characteristic curves are depicted by means of curves in a constant force system of an electrical energy store and with electrical energy stores having an elastic element;

[0042] FIG. 2, in a schematic perspective, shows a battery with a plurality of battery cells which are tensioned between two pressure plates, wherein a spacing of the pressure plates from each other can be changed by controlling pneumatic muscles which are connected to the pressure plates;

[0043] FIG. 3 is a side view of a broad side of the battery which has the pressure plates shown in FIG. 2 and the packet of battery cells arranged between the pressure plates;

[0044] FIG. 4 is a side view of a front side of the battery according to FIG. 2;

[0045] FIG. 5 shows a variant of the battery with a constant force system in which the spacing between the pressure plates can be changed by controlling threaded spindles; and

[0046] FIG. 6 shows a further variant of the battery in which the spacing of the pressure plates from each other can be changed by means of a lever system.

DETAILED DESCRIPTION OF THE DRAWINGS

[0047] In the figures, the same or functionally identical elements are provided with the same reference numerals.

[0048] In a graph 10 shown in FIG. 1, an axial pressing force is plotted on a y-axis 12, the axial force being able to be applied in an individual battery cell 14 to an electrode stack of the battery cell 14 or in a battery 16 (c.f. FIG. 2) having a plurality of battery cells 14 to the electrode stack of the battery cells 14 stacked one on the other. Pressing together the plies of electrodes in the form of cathodes and anodes and respective plies arranged between the plies of the cathodes and the anodes of a separator of the electrode stack serves to ensure the function of the electrode stack when then battery cell 14 or the battery 16 is in operation.

[0049] A first characteristic curve 18 depicted in the graph 10 in FIG. 1 illustrates the behavior of an elastic element such as a spring, which can be arranged in a cell housing of the battery cell 14 or a battery housing (not shown) of the battery 16 (c.f. FIG. 2), in order to supply the electrode stack(s) with a pressure. In the graph 10 in FIG. 1, the path is plotted on an x-axis 20 around which the spring can be compressed. A first section 22 of the characteristic curve 18 correspondingly constitutes a region of the path around which the spring has to be pressed together to apply a required pre-tensioning force. This pre-tensioning force is set when assembling the battery cell 14 or the battery 16 or such a cell block. In this region of the path, the force that can be applied by the spring cannot be used. In contrast, a further section 24 of the characteristic curve 18 depicts a useable region of the path. In this section 24, the elastic element in the form of the spring applies and increasingly greater axial pressing force on the at least one electrode stack. The force (linearly) increases in this section 24 the further the spring is compressed.

[0050] If the spring is compressed completely, then the characteristic curve 18 increases perpendicularly. A corresponding section 26 of the path available in the battery cell 14 in the battery 16 constitutes a block length of the spring. If the spring is completely compressed, then the electrodes of the electrode stack cannot expand further perpendicularly to their stacking direction, which is illustrated in FIG. 2 by an arrow.

[0051] When using a spring or such an elastic element, the behavior of which is described by the characteristic curve 18 in the graph 10, the increase, caused in principle by the spring characteristic curve, of the pressing force is thus disadvantageous with expanding electrodes of the at least one electrode stack. Correspondingly, the battery cell 14 or the battery 16 or the cell block are set to very high axial forces.

[0052] This is presently avoided by the electrical energy store described in detail below in the form of an individual battery cell 14 or the battery 16 (c.f. FIG. 2) having a constant force system which, according to FIG. 2, comprises actuators formed, for example, as pneumatic muscles 30, a first pressure plate 32, a second pressure plate 34 and a control device 36 for controlling the actuators.

[0053] The actuators in the form of the pneumatic muscles 30, for example, can move the pressure plates 32, 34 onto each other or away from each other. The motion of the pressure plates 32, 34 onto each other is illustrated in FIG. 3 to FIG. 6 by respective arrows 50 and causes a pressure to be exerted on the respective electrode stack of the battery cells 14. In other words, the motion of the pressure plates 32, 34 onto each other causes a compression of a packet 42 of the battery cells 14 and thus the electrode stacks of the battery cells 14 in this packet 42. The packet 42 is presently arranged between the pressure plates 32, 34. Here, it is ensured by the control device 36 that a constant force is exerted in the packet 42 by means of the actuators via the pressure plates 32, 34. Thus, a constant pressures acts on the electrode stacks of the battery cells 14 of the packet 42.

[0054] A characteristic curve 44 illustrating this constant force system is also depicted in the graph 10 in FIG. 1, presently horizontal section 46 of the characteristic curve 44 constitutes the usable region of the path, along which the pressure plates 32, 34 can be moved onto each other or away from each other. It is apparent from the horizontal course of the characteristic curve 44 in the section 46 that the pressure plates 32, 34 supply the packet 42 with the constant force regardless of the path in the constant force system. This applies when supplying the battery cells 14 which have the respective electrode stack and are arranged in the packet 42 of the battery 16 (c.f. FIG. 2) with the force and, analogously, also when supplying the electrode stack arranged in a cell housing of an individual battery cell 14, when this is arranged between the pressure plates 32, 34.

[0055] The pressure plates 32, 34 cannot be moved further onto each other only in a very short end section 48 of the path, which corresponds to the movement clearance available in the battery cell 14 or the battery 16 for at least one of the pressure plates 32, 34. This can be the case, for example, because the pressure plates 32, 34 have compressed the packet 42 as much as possible or because the pneumatic muscles 30 formed as movement devices do not allow any further movement of the pressure plates 32, 34 onto each other.

[0056] Correspondingly, the characteristic curve 44 increases when the constant force system goes to the block. However, the block length or the non-useable path is clearly shorter than with the system illustrated by the characteristic curve 18 in which the spring is used. This can be seen graphically in the graph 10 from the shorter length of the end section 48 in comparison to the section 26. Furthermore, it is obvious from FIG. 1 that the region of the path which cannot be used when using the spring and which corresponds to the length of the section 22 can be used when using the constant force system.

[0057] The use of the constant force system thus ensures that at least one of the pressure plates 32, 34 resting flatly on the electrode stack or the packet 42 is actively moved forwards, i.e., for example in opposition to the stacking direction 28, or backwards, i.e., in the stacking direction 28, corresponding to the thickness change when changing the thickness of the electrode stack in the battery cells 14 or when changing the thickness of the electrode stack of an individual battery cell 14. Correspondingly, a constant axial crimping of the at least one electrode stack of the battery 16 emerges.

[0058] The change of the thickness of the electrode stack in the respective battery cell 14 or the packet 42 of the battery cells 14 in the battery 16 can be caused by charging the battery cell 14 or the battery cells 14 or discharging them. Furthermore, as a result of the battery cells 14 ageing, the thickness of the electrode stack of the battery cells 14 increases in the stacking direction 28. All these thickness changes can, however, be compensated for by the actively controlled constant force system with the preferably horizontal force-path characteristic curve, i.e., the characteristic curve 44.

[0059] The use of the constant force system is advantageous in particular when the battery cells 14 are formed as solid-body cells, which are formed as lithium ion cells in terms of the cell chemistry. Correspondingly, the positive electrode of the respective battery cell 14 can be provided by lithium compounds.

[0060] According to FIG. 2 and FIG. 3, the battery cells 14 can be formed as so-called pouch cells, in which the respective electrode stack is arranged in a flexible sleeve formed from a film material. This flexible sleeve is encompassed by a respective cell frame 50 of the battery cell 14. Furthermore, the respective battery cell 14 has arrester lugs 52, 54 (c.f. FIG. 3) by means of which electrical ports of the respective battery cell 14 are provided.

[0061] Depending on how these arrester lugs 52, 54 are interconnected to one another in the form of a respective negative pole and a respective positive pole of the battery cells 14, a required nominal voltage and/or a required current strength can be provided by the battery 16, which is preferably greater than the nominal voltage or current strength that can be provided by an individual battery cell 14. In particular, the battery 16 can be formed as a high-voltage battery or as a battery module or cell block of a high-voltage battery for a motor vehicle. Such a high-voltage battery can provide a nominal voltage of more than 60 volts, in particular of more than 100 volts. In FIG. 4, the battery 16 is shown in a view on its narrow side.

[0062] According to FIG. 2 to FIG. 4, the actuators in the form of the pneumatic muscles 30 can be arranged in respective corner regions of the pressure plates 32, 34. Thus, it can be achieved particularly simply that changes to the thickness of at least one electrode stack or packet 42 can be compensated for by actively moving the pressure plate 32, for example, forwards, i.e., in opposition to the stacking direction 28, or backwards, i.e., in the stacking direction 28. In this way, a constant axial crimping of the packet 42 emerges between the pressure plates 32, 34. As already mentioned, the thickness of the electrode stack or the packet 42 or cell stack can change due to the electrode stack or the battery cells 14 charging, discharging or ageing.

[0063] According to FIG. 2 to FIG. 4, the actuators in the form of the pneumatic muscles 30 are connected to the first pressure plate 32 on one side and to the second pressure plate 34 on the other side. Here, the pneumatic muscles 30 are arranged between the pressure plates 32, 34. If the pneumatic muscles 30 expand in the transverse direction, i.e., presently perpendicularly to the stacking direction 28, then the pneumatic muscles 30 contract in their longitudinal direction. This causes the pressure plates 32, 34 to move onto each other. It is advantageous that, in this way, an inherently tensioned system is provided. Thus, no force is transferred to a surrounding battery housing (presently not shown) of the battery 16 or to vehicle structures when arranging the battery 16 in a vehicle.

[0064] The contracting of the pneumatic muscles 30 or such fluid regulators due to a pneumatic control caused by the control device 36 leads to a movement of the pressure plates 32, 34 onto each other corresponding to the arrows 40 depicted in FIG. 3 and FIG. 4. In particular, gas, for example air, can be the fluid with which corresponding chambers formed in the manner of a tube of the pneumatic muscles 30 can be supplied. This has the advantage that air can be suctioned in from the surroundings and let out into the surroundings.

[0065] Alternatively to the pneumatic muscles presently arranged in the four corner regions of the pressure plates 32, 34, respective pneumatic muscles 30 can also be arranged on opposite sides of the packet 42, for example. These two pneumatic muscles 30 then extend along respective narrow sides of the packet 42. Furthermore, it is possible to provide actuators, which can be controlled by the control device 36 and which surround the pressure plates 32, 34 or are looped around a stack comprising the pressure plates 32, 34.

[0066] However, the packet 42, which is arranged between the two pressure plates 32, 34, can also be contracted by actuators other than the pneumatic muscles 30 presently shown by way of example. For example, electromechanical actuators can be used.

[0067] It is thus conceivable for the constant force system, in which the pressure plates 32, 34 resting flatly on the outside on the at least one electrode stack or the packet 42 or stack or the battery cells 14 are actively moved onto each other or away from each other, to be designed mechanically, in particular electromechanically. The movement energy for moving at least one of the pressure plates 32, 34 can here be provided by an electric engine 56 (c.f. FIG. 5 and FIG. 6). In FIG. 5 and FIG. 6, the control device 36 formed to control the electric engines 56 of is not shown for the sake of simplicity.

[0068] It is schematically depicted in FIG. 5 how respective movement devices arranged opposite one another perpendicularly to the stacking direction 28 in the form of threaded spindles 58 can be driven by a respective electric engine 56. Respective spindle nuts 60 can here be arranged in the region of one of the pressure plates 32, 34, as is presently shown by way of example in the region of the upper pressure plate 32 in the stacking direction 28. By rotating the threaded spindles 58 in a first direction of rotation, the pressure plates 32, 34 can be moved onto each other and, by rotating the threaded spindles 58 in the opposite direction, can be moved away from each other.

[0069] Thus, if the actuator comprising the respective electric engine 56 and the respective threaded spindle 58 in this variant is controlled by the control device 36, then the packet 42 can be supplied with a constant axial pressing force, i.e., acting in parallel to the stacking direction 28. Analogously, as shown by way of example by means of the threaded spindles 58, the spacing of the pressure plates 32, 34 from each other can also be used to compensate for the thickness changes of the battery cells 14 of the battery 16 by means of actuators, which have toothed rods that can be moved via a cogwheel.

[0070] In FIG. 6, a variant of the battery 16 is shown, in which a lever system, for example in the form of a knee lever 62, is actuated by means of a threaded spindle 58 driven by an electric engine 56. Here, the electric engine 56 and the threaded spindle 58 are arranged between the pressure plates 32, 34. In contrast, in FIG. 5 the electric engines 56 are arranged outside a receiving chamber delimited by the pressure plates 32, 34 in the stacking direction for the packet 42. Furthermore, in the variant of the battery 16 according to FIG. 6, the threaded spindle 58 extends perpendicularly to the stacking direction 28, while in FIG. 5, the threaded spindles 58 run in parallel to the stacking direction 28.

[0071] Also in the variant according to FIG. 6, instead of the threaded spindle 58, a tooth rod or similar can be used. Furthermore, analogously to the variant of the battery shown in FIG. 6, it is possible to arrange the electric engine 56 between the two pressure plates 32, 34 and to drive at least one threaded spindle 58, for example via a worm gear, which ensures that the pressure plates 32, 34 are moved onto each other or away from each other.

[0072] So that no holding energy needs to be applied, in variants in which the threaded spindle 58 is used, the threaded spindle 58 is preferably designed to be self-locking. In variants with the toothed rod (not shown), an active lock without current or brake or braking device is preferably provided.

[0073] In order to prevent a constant reconfiguration of a rigid system, such as the constant force system shown by way of example in FIG. 5 and FIG. 6, it can be useful to arrange an elastic element, such as a thin blocking mat, for example, between the packet 42 and at least one of the pressure plates 32, 34.

[0074] In addition to the variants presently described in detail, combinations of the movement mechanisms explained above are possible. For example, the lever drive shown in FIG. 6 can be activated by a fluid regulator system, such as one of the pneumatic muscles 30 shown in FIG. 2.

[0075] The constant force system can be installed once into an individual battery cell 14 or once into the battery 16. However, it is also possible to install the constant force system several times into an individual battery cell 14 or also into a cell stack such as the packet 42 presently shown by way of example. When a separate constant force system with the two pressure plates is allocated to each individual battery cell 14, for example in a cell block with several battery cells 14, then the battery cells 14 remain in their axial position despite their thickness change, i.e., in a constant position in terms of the stacking direction 28. Thus, a constant and equal grid spacing advantageously emerges.

[0076] All systems described above which comprise the two pressure plates 32, 34 which can be moved onto each other and away from each other have the advantage that they are inherently tensioned system. Correspondingly, module or units, which have the pressure plates 32, 34 and at least one battery cell 15 arranged between the pressure plates 32, 34 or the packet 42 arranged between the pressure plates 32, 34, can be installed particularly easily into a battery housing or into a vehicle. This is because pressure forces do not need to be supported on surrounding elements, such as the battery housing or the vehicle. Thus, in particular exchanging such a module is made simpler.

TABLE-US-00001 List of reference characters: 10 Graph 12 y-axis 14 Battery cell 16 Battery 18 Characteristic curve 20 y-axis 22 Section 24 Section 26 Section 28 Stacking direction 30 Muscle 32 Pressure plate 34 Pressure plate 36 Control device 38 Characteristic curve 40 Arrow 42 Packet 44 Characteristic curve 46 Section 48 End section 50 Cell frame 52 Arrester lug 54 Arrester lug 56 Electric engine 58 Threaded spindle 60 Spindle nut 62 Knee lever