The invention relates to a battery cell, in particular a rechargeable battery cell.
In the majority of areas where battery cells are used, disregarding a low ripple proportion, approximately direct current is drawn off from and/or supplied to said battery cells.
U.S. Pat. No. 5,642,275 A discloses a battery system having an integrated alternating current converting function, in which a row of circuit breakers having separate direct current voltage sources in the form of batteries is provided. Battery systems of this type that are also frequently described as multilevel cascaded inverters render it possible to achieve single-phase or multi-phase systems that comprise a higher degree of efficiency and a higher level of reliability than conventional alternating current converting arrangements.
However, if a battery system of this type is used for example to control an electric machine, a quick conversion of the current flowing through the direct current voltage sources and/or bypassing the direct current voltage sources is required in order to vary the phase voltage. However, as the proportion of the current being converted increases, so does also the influence of the inductance of the direct current voltage sources and as a result when using battery modules the influence of the inductance of the individual battery cells (cell inductance) also increases. In particular, the cell inductances in combination with high currents during switching operations lead to a high level of energy dissipation that is converted into heat in the circuit breakers. As a consequence of the repeated occurrence of switch operations this leads to high thermal dissipation losses in the switches and consequently to a reduced degree of efficiency of the battery system. If the individual battery cells are connected in series in a battery module, then the individual cell inductances are summated and this leads to a correspondingly higher level of thermal dissipation loss. In some applications, an excessively high inductive proportion of the impedance of the battery cells also makes an additional buffer capacity necessary.
Electromagnetic fields associated with distributed cell inductances are also emitted during each switch operation, which without corrective measures could lead to malfunctions in adjacent electronic components, so that complex additional switch measures are frequently necessary in order to comply with EMC regulations (EMC=electromagnetic compatibility).
The present invention provides a battery cell, in particular a rechargeable battery cell, having a first electrode foil and a second electrode foil that together with an interposed separator are rolled up to form a roll, a first terminal connection and a second terminal connection for connecting the battery cell to external circuitry, a first connecting element that electrically connects the first terminal connection to the first electrode foil, and a second connection element that electrically connects the second terminal connection to the second electrode foil. In accordance with the invention, the two connecting elements contact the respective electrode foil on a first end face of the roll.
The total inductance of a battery module is defined on the one hand by the inductances of the individual battery cells (cell inductances) and on the other hand by the inductance of the interconnections of these battery cells. The invention is based on the fundamental idea, of arranging the connecting elements, which electrically connect the electrode foils to the respective terminal connection, on the same end face of the roll and also to contact the electrode foils at that site. In this manner, the gap and consequently the enclosed surface area between the two terminal connections are reduced, which leads to a considerable reduction of the cell inductance. This in turn leads to a reduced level of thermal dissipation loss in the circuit breakers and consequently to a greater level of efficiency of the battery system. The construction in accordance with the invention of the battery cell also reduces the number of electromagnetic malfunctions.
In order to avoid undesired wave effects, resonances or reflections on the second end face of the roll, which second end face lies opposite the first end face, it is provided in accordance with an embodiment of the invention to electrically mutually connect in each case the individual layers of the first electrode foil and the second electrode foil on the second end face of the roll, which second end face lies opposite the first end face.
This can be achieved in a particularly simple manner by virtue of the fact that the roll is folded in such a manner that a first end surface of the previously unfolded roll and a second end surface of the previously unfolded roll come to lie adjacent to one another after being folded into a roll, in particular directly adjacent to one another, such that the first end face of the roll that has been produced in this manner is formed by the two end surfaces. However, if it is decided not to perform a fold of this type, the electrical connection of the electrode foils can also be made in a different manner, for example with the aid of one or more separate contacting elements.
In accordance with an embodiment of the invention, the electrode foils are offset with respect to one another when rolled up, so that the first end surface of the roll is formed by means of the layers of the first electrode foil and the second end surface of the roll is formed by the layers of the second electrode foil. The two connecting elements are embodied in this case in a planar manner and contact at a respective end surface a plurality of layers, in particular all layers, of the respective electrode foil.
In this case, as far as the inductive portion of the layers is concerned, a parallel connection is virtually produced, which leads to a corresponding reduction of the resulting inductance. In the case of a cell roll of a battery cell, in which in a conventional manner a few meters of foil are rolled up, this leads to a high number of “parallel connected” layers and consequently to a parasitical inductance that is negligible in this respect. Both the extremely small amount of remaining inductance and also the fact that all the layers are contacted in a uniform manner prevents wave propagation effects from occurring. Furthermore, the fact that all layers are contacted renders it possible to reduce the contacting resistance and to provide a homogenous current distribution which together lead to reduced ohmic losses.
The effects can be further enhanced, in that the connecting elements contact the respective electrode foil in each case on the entire end surface of the roll.
In order to achieve a low inductive interconnection also in the area of the terminal connections, it is also possible to embody the terminal connections in a planar manner.
It is possible to implement the invention in a particularly simple manner using manufacturing technology if the connecting elements are embodied in each case as one part with the terminal connections.
Further features and advantages of embodiments of the invention are evident from the description hereinunder with reference to the attached drawings.
In which:
Like components and components that function in a like manner are provided with like reference numbers in each case in the figures.
In order to avoid undesired wave effects, resonances or reflections on the second end face 112 of the roll, the individual layers of the first electrode foil 102 and the second electrode foil 103 can be mutually electrically connected in each case on the second end face 112 of the roll, for example with the aid of contact elements that are not illustrated.
A further reduction of the inductive portion of the impedance can be achieved in accordance with a third embodiment of a battery cell 101″ in accordance with the invention by virtue of the fact that terminal connections 105″ and 106″ that are embodied in a planar manner are used (cf.
If a roll 104″′ of this type is folded according to the second and third embodiment of the invention, then the connecting elements 107″′ and 108″′ are embodied in a planar manner similar to that in the third embodiment and a plurality of layers, in particular all the layers, of the respective electrode foil 102 or 103 respectively contact in each case an end surface 109″′ or 111″′ respectively (cf.
Number | Date | Country | Kind |
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102010064301.7 | Dec 2010 | DE | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/EP2011/070009 | 11/14/2011 | WO | 00 | 7/1/2013 |