Method and battery for heating a battery

Abstract

The invention relates to a method for heating a battery (1) composed of battery individual cells (2.1 to 2.n), between whose poles (5, 6) the battery individual cells (2.1 to 2.n) are arranged semiconductor switching elements ((r), (p), (m), (bp), (bm)). The invention is characterized in that the battery individual cells (2.1 to 2.n) are short-circuited via the semiconductor switching elements ((r), (p), (m), (bp), (bm)) for heating, and time phases in which the battery individual cells (2.1 to 2.n) are short-circuited alternate with time phases in which the battery individual cells (2.1 to 2.n) are not short-circuited. Furthermore, a battery (1) for carrying out the method is also shown.

Description

Technical Field

[0001] The present invention relates to a method for heating a battery composed of individual battery cells, as defined in detail in the superordinate concept of claim 1. Furthermore, the present invention relates to a battery configured as a traction battery designed to implement the above method.

Background Art

[0002] Today, batteries are increasingly being used in at least partially electrically driven vehicles. In most cases, the battery is composed of a number of individual battery cells. For example, the battery is realized as an individual battery cell using lithium-ion technology. For such a battery, a certain operating temperature is required to function properly. Therefore, at very low temperatures significantly below its operating temperature, for example, significantly below the freezing point, it is necessary to heat these individual battery cells in order to guarantee the full performance of the individual battery cells. In the current structure, an electric heater is used, and such a heater is described, for example, in Patent Document 1. There, a heating mat is inserted between the individual battery cells, and the battery is electrically heated. In that case, since the heat has to reach the interior of the battery through the battery housing, overall, this requires a great deal of effort, time, and energy to heat the battery.

[0003] Another prior art related to this type of battery is also known, for example, so-called cell balancing, that is, connecting individual battery cells to each other via corresponding switches, particularly semiconductor switches, in order to perform charge equalization between individual battery cells that are charged or discharged at different strengths as required. In this context, for example, Patent Document 2 can be referred to, or Patent Document 3 having a similar subject matter can also be referred to.

[0004] From Patent Document 4, a method as described at the beginning, in which individual battery cells are heated through a timed short circuit, is known. Patent Document 5 describes a structure in which a system of that kind is considered to be realized in principle. Regarding another prior art, reference can also be made to Patent Document 6. It describes a flexible conductive element on a film.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

Patent Document 6

Summary of the Invention

Problems to be Solved by the Invention

[0006] The problem of the present invention is to provide a method for heating a battery composed of individual battery cells, which is improved compared to the use of known heating mats. Furthermore, a battery suitable for this method should be provided.

Means for Solving the Problems

[0007] The above problems are solved, for the method, by the method according to the invention having the features in claim 1. Advantageous configurations and developments become apparent from the claims dependent on claim 1. A battery suitable for the implementation of this method is described in claim 5. Here too, the advantageous configurations and developments of this battery become apparent from the claims dependent on claim 5.

[0008] The method according to the present invention for heating a battery composed of individual battery cells utilizes semiconductor switching elements arranged between the poles of the individual battery cells, similar to the structure for cell balancing according to the prior art described above. In the method according to the present invention, the individual battery cells are short-circuited via the semiconductor switching elements for heating, and in so doing, a time phase in which the individual battery cells are short-circuited and a time phase in which the individual battery cells are not short-circuited are repeatedly alternated. Due to the short-circuiting of the individual battery cells, electrical energy originating from the individual battery cells themselves generates heat in the individual battery cells, especially in their internal resistance. This has the extremely important advantage that heat can be generated with a minimum amount of energy at the location where heat is required for heating the individual battery cells, i.e., inside the individual battery cells themselves. Irrespective of heat conduction through the housing of the individual battery cells and, in some cases, heat transfer from a refrigerant to the individual battery cells, etc., the heating of the individual battery cells acts precisely on the location where the heating is ultimately required. Therefore, the method according to the present invention for heating individual battery cells is extremely efficient and can be easily implemented at a minimum additional cost, especially for cell balancing, provided that semiconductor switching elements are present in any case.

[0009] Here, according to the present invention, the time phase in which the individual battery cells are short-circuited is up to 100 milliseconds, and the time phase in which the individual battery cells are not short-circuited is in the range of 10 to 20 seconds. According to an advantageous development, the time phase in which the individual battery cells are not short-circuited is particularly preferably in the range of 5 to 15 seconds.

[0010] Within this relatively short period of up to 100 milliseconds, a considerable amount of heat can already be generated by short-circuiting the individual battery cells. Subsequently, the short-circuit is interrupted, whereupon the individual battery cells are short-circuited again.

[0011] According to a highly preferred development of the method according to the invention, furthermore, the time phase in which the individual battery cells are not short-circuited consists of a first relaxation time section and a subsequent second charging time section, in which case the charging time section lasts longer than the relaxation time section. That is, in the phase using the non-shorted individual battery cells, the individual battery cells are allowed a relaxation time section in which the charge can be evenly redistributed to the individual battery cells again. In the subsequent section in which the individual battery cells are not short-circuited, since the battery is charged, overall, the state of charge of the battery does not at least deteriorate, and on the contrary, in some cases, the state of charge can be further increased by charging the individual battery cells.

[0012] According to a very preferred development of the method according to the invention, the semiconductor switching elements are selected to have an internal resistance lower than the internal resistance of the individual battery cells respectively associated with them, so that most of the heat generated in the electrical resistance occurs inside the individual battery cells rather than in the region of the semiconductor switching elements.

[0013] The semiconductor switching elements themselves can be realized by approximately any type, such as thyristors, IGBTs, etc. Here, the use of MOSFETs is particularly desirable.

[0014] The battery according to the invention is formed as a traction battery for at least partially electrically driven vehicles, such as hybrid vehicles or battery electric vehicles. This battery has the interconnection of its individual battery cells and a control unit designed to carry out the above-described method.

[0015] That is, that type of battery can have a suitable interconnection of the individual battery cells via semiconductor switches, such as MOSFETs, in order to carry out the method appropriately.

[0016] In the battery according to the present invention, three semiconductor switching elements are associated with each individual battery cell, and these semiconductor switching elements can selectively or commonly connect the poles of each individual battery cell to the positive bus line, the negative bus line, or the other pole of an adjacent individual battery cell. That is, an individual battery cell can have three semiconductor switching elements. Since one of the semiconductor switching elements can correspondingly connect the adjacent poles with opposite polarities of adjacent individual battery cells, in general, in a battery or a battery module, a series connection of individual battery cells can be realized. Through another element, each positive electrode can be connected to the positive bus line, and each negative electrode can be connected to the negative bus line. In general, for example, in order to charge and discharge individual battery cells, the individual battery cells can be connected in series. When those semiconductor switching elements are opened for the series connection of individual battery cells and all the positive electrodes are connected to the positive bus line and all the negative electrodes are connected to the negative bus line, in order to perform the heating according to the present invention as described above, the individual battery cells can be short-circuited respectively.

[0017] According to the present invention, the semiconductor switching elements are formed on a flexible conductor film. The kind of flexible conductor film on which the semiconductor switching elements are arranged is a space-saving structure that can be relatively easily integrated into the overall structure of the battery.

[0018] According to a further highly advantageous configuration of the battery according to the invention, one further semiconductor switching element can be arranged on the positive and negative bus lines, respectively, between the connection points to the semiconductor switching elements of the respective individual battery cells. This makes it possible, for example, to disconnect individual battery cells from the overall assembly, and thereby, for example, to bridge defective cells. Furthermore, cell balancing, i.e., charge equalization between the individual battery cells of the battery, which is also disclosed in the prior art described at the beginning, can also be carried out accordingly via that type of interconnection with the five semiconductor switching elements associated with each individual battery cell.

[0019] In a very preferred development of the battery according to the invention, the individual battery cells are formed as prismatic cells with electrical poles arranged on mutually opposing side edges, in which case the electrical poles of adjacent individual battery cells are connected to the semiconductor switching elements via flexible conductor films. That type of structure is very simple and efficient, and the flexible conductor film can, on the one hand, be used to connect the poles of the individual battery cells, and on the other hand, the required switching elements can be integrated directly into the flexible conductor film.

[0020] In particular, according to a very advantageous development of the battery according to the invention, the individual battery cells are stacked with an intervening flexible conductor film and are connected to the battery module or battery and clamped, for example, between a housing or end plates. The flexible conductor film can, in this case, extend substantially in a zigzag between the faces of the battery, so that overall, hardly any additional structural space is required due to its structure. In the region of the semiconductor switching elements, especially when heat losses occur during a short circuit for heating the battery, those heat losses also occur directly in the region between two adjacent individual battery cells, but not inside them, and thus the heat losses generated in that case can ultimately also contribute to heating the battery.

[0021] The method according to the invention, as well as another advantageous configuration of the battery according to the invention for carrying out the method, will also become apparent from the embodiments described in detail below with reference to the drawings.

Brief Description of the Drawings

[0022]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5a

Figure 5b

Figure 5c

Figure 5d

Figure 6

Embodiments for Carrying Out the Invention

[0023] FIG. 1 schematically shows the electrical connection of an exemplary battery 1. The battery 1 consists of a plurality of individual battery cells 2.1 to 2.n, and the adjacent opposite poles of each of the individual battery cells 1 can be switchably connected via one semiconductor switch, for example a MOSFET. Those semiconductor switches are labeled with reference numerals (r). Further, the positive electrodes of each of the individual battery cells 2.1 to 2.n are connected to the positive bus line 3 via a semiconductor switch labeled with reference numeral (p), for example also a MOSFET here, and the negative electrodes of each are connected to the negative bus line 4 via a semiconductor switch (m).

[0024] For the self-heating of the individual battery cells 2.1 to 2.n in the battery 1, the internal resistance of each of the individual battery cells 2.1 to 2.n can be utilized. For this purpose, all three semiconductor switching elements (r), (p), (m) are switched on, thereby achieving a short circuit of the individual battery cells 2.1 to 2.n. When those semiconductor switching elements (r), (p), (m) are selected such that the intrinsic resistance of the series-connected semiconductor switching elements (r), (p), (m) is smaller than the internal resistance of the individual battery cells 2.1 to 2.n, the heat generated by the short circuit is dissipated almost only by the internal resistance of the individual battery cells 2.1 to 2.n, and the cells are directly heated at the locations where heat is required.

[0025] To charge and discharge the battery 1, the semiconductor switches (p) and (m) are switched off accordingly, and as a result, only the series circuit of the individual battery cells 2.1 to 2.n is maintained by the semiconductor switch (r).

[0026] To heat the battery 1 efficiently yet protectively, these two states are switched. That is, in the first time phase, a short circuit always occurs in the individual battery cells 2.1 to 2.n, and then a relaxation period follows. The short circuit period can be, among other things, between 1 millisecond and 100 milliseconds, and the relaxation period can be several seconds, for example, 1 second to 5 seconds, especially about 1.5 seconds. The two graphs in Figure 2 show an exemplary course in which the individual battery cells 2.1 to 2.n are loaded with a very low resistance on the order of 10 Ω for, for example, 50 milliseconds. Subsequently, relaxation takes place for about 1.5 seconds, and then the individual battery cells 2.1 to 2.n are charged for about 7 seconds. This results in the course represented by the graphs in Figure 2. The left graph represents the voltage U of the individual battery cells 2.1 to 2.n over time t, and the right graph represents the current I over time t. Here, within the graph, discharge, that is, ultimately a short circuit, is represented by a solid line, and charging is represented by a dashed line. The voltage drops slightly during the short circuit compared to the voltage during charging, and subsequently, in the relaxation phase, it drops to almost zero. After relaxation, as can be clearly seen especially based on the current-time graph shown on the right, charging is carried out at a constant current intensity, so the voltage rises correspondingly before the entire process can start anew.

[0027] As a result, as can be seen from the temperature (T) graph over time t in Figure 3, each individual battery cell 2.1 to 2.n is heated. During the short circuit, relatively strong heating of the individual battery cells 2.1 to 2.n occurs each time, so the temperature rises substantially in steps, and during the subsequent charging process, the temperature also rises, but only minimally compared to the temperature rise during the short circuit. In the illustrated embodiment, starting from an initial temperature of -30 °C, the temperature has risen by about 8 K within about 40 seconds. For example, to further heat to an operating temperature of 40 °C, if the temperature rises linearly on average over time here, it would take about 250 seconds. That is, with this method, the battery 1 can be heated from a very low temperature to a meaningful operating temperature within a few minutes.

[0028] In this case, the behavior of the charge can be understood from the graph of FIG. 4 where time is shown over the state of charge SOC. During the short circuit, mainly the surface charge is consumed, so that the behavior of the charge state on the surface, indicated here by the solid line, occurs. During relaxation and charging, those charges are equalized again, they are further supplied from inside the individual electrodes of the battery 1 and are utilized again in the surface region for subsequent short circuits.

[0029] Here, based on FIG. 5, an exemplary structure for structurally realizing the battery 1, particularly as schematically suggested in FIG. 1, is shown accordingly. FIGS. 5a to 5d respectively show various manufacturing steps during the stacking of the individual battery cells 2.1 to 2.n. In FIG. 5a, the first battery cell 2.1 of the individual battery cells is shown in a three-dimensional view. The individual battery cell 2.1 is arranged within a prismatic housing and has, at its two end faces, two poles 5, 6 as connection lugs, so-called terminal tabs. Subsequently, FIG. 5b shows a flexible conductor film that is correspondingly connected to the terminal tab 6 and includes semiconductor switching elements (p), (m), (r), and optionally another semiconductor switching element, conductor paths, and electronic components. As shown in FIG. 5c, in this structure, the second individual battery cell 2.2 of the battery cells is stacked, and here, its terminal tabs 5, 6 are arranged in reverse, so that the terminal tab 6 protrudes forward and the terminal tab 5 protrudes backward. The two rear terminal tabs 6, 5, which can no longer be seen here, sandwich the flexible conductor film therebetween and are correspondingly in contact with it. In the front region, as can be seen from FIG. 5d, before another individual battery cell 2.3 is stacked, as shown in FIG. 5c, the flexible conductor film 7 is folded again, and through this flexible conductor film, the upper individual battery cell 2.2 is guided backward, whereby the flexible conductor film 7 is sandwiched between the terminal tab 5 and the terminal tab 6 of the individual battery cell 2.2. This sandwiching is done before the above process is repeated again, and the process is repeated until the desired size of the battery is achieved by a sufficient number of individual battery cells 2.1 to 2.n.

[0030] FIG. 6 shows an alternative variant of the battery 1. Here too, various individual battery cells 2.1 to 2.n are correspondingly constructed, and corresponding semiconductor switches similar to those shown in FIG. 1 are used. Here too, reference signs (r), (p), (m) are attached to each of the individual battery cells 2.1 to 2.n of those semiconductor switches. In addition to those three semiconductor switching elements (p), (r), (m) for each of the individual battery cells 2.1 to 2.n, additional semiconductor switching elements (bp) and (bm) are arranged also in the regions of the two bus lines 3, 4. Those semiconductor switching elements (bp), (bm) are arranged between the respective branches of adjacent individual battery cells 2.1 to 2.n, so that a switching element (bp) is arranged between the points where the semiconductor switch (p) is connected to the positive bus line 3. An equivalent structure is also realized in the negative bus line, where a semiconductor switching element (bm) is arranged between each connection of the semiconductor switching elements (m) of adjacent individual battery cells 2.1 to 2.n.

[0031] With this structure, in addition to the method according to the invention for heating the individual battery cells 2.1 to 2.n, it is also possible to further achieve charge equalization between the individual battery cells 2.1 to 2.n. Furthermore, for example, when those individual cells of the individual battery cells 2.1 to 2.n have defects, or have a very low voltage, or the polarity is reversed, etc., it is possible to disconnect those individual cells from the battery 1.

Claims

A method for heating a battery (1) composed of a plurality of individual battery cells (2.1 to 2.n), wherein each of the individual battery cells (2.1 to 2.n) is associated with three semiconductor switching elements ((r), (p), (m)), and the pole of each of the individual battery cells (2.1 to 2.n) and the opposite pole of each adjacent individual battery cell (2.1 to 2.n) are connected via the first semiconductor switching element (r), and the respective positive electrodes of each of the individual battery cells (2.1 to 2.n) are connected to the positive bus line (3) via the second semiconductor switching element (p), and the respective negative electrodes are connected to the negative bus line (4) via the third semiconductor switching element (m), and the plurality of individual battery cells (2.1 to 2.n) are short-circuited via the first, second, and third semiconductor switching elements ((r), (p), (m)) for heating, and a time phase in which the plurality of individual battery cells (2.1 to 2.n) are short-circuited and a time phase in which the plurality of individual battery cells (2.1 to 2.n) are not short-circuited appear alternately, in the method, the time phase in which the plurality of individual battery cells (2.1 to 2.n) are short-circuited is up to 100 milliseconds, and the time phase in which the plurality of individual battery cells (2.1 to 2.n) are not short-circuited is in the range of 1 to 20 seconds, characterized in that, the method.

2. The method according to claim 1, characterized in that the time phase in which the plurality of individual battery cells are not short-circuited is in the range of 5 to 15 seconds.

3. The method according to claim 1 or 2, characterized in that the time phase in which the plurality of individual battery cells (2.1 to 2.n) are not short-circuited consists of a relaxation time section in a state where the first charge and discharge is stopped and a subsequent second charging time section, and the charging time section lasts longer than the relaxation time section.

4. The method according to claim 1 or 2, characterized in that the electrical resistance of each of the semiconductor switching elements ((r), (p), (m)) is selected to be lower than the internal resistance of the individual battery cell (2.1 to 2.n) respectively associated with the semiconductor switching element.

5. A battery (1) as a traction battery for a vehicle that is at least partially electrically driven, comprising an interconnection of a plurality of individual battery cells (2.1 to 2.n) of the battery (1), and a control unit designed to carry out the method according to claim 1 or 2, wherein three semiconductor switching elements ((r), (p), (m)) are associated with each of the plurality of individual battery cells (2.1 to 2.n), and the poles of each of the individual battery cells (2.1 to 2.n) and the opposite poles of each of the adjacent individual battery cells (2.1 to 2.n) are connected via the first semiconductor switching element (r), and the positive pole of each of the individual battery cells (2.1 to 2.n) is connected to the positive bus line (3) via the second semiconductor switching element (p), and the negative pole of each is connected to the negative bus line (4) via the third semiconductor switching element (m), and the plurality of individual battery cells (2.1 to 2.n) can be short-circuited via the first, second and third semiconductor switching elements ((r), (p), (m)) for heating purposes, in the battery (1), The battery (1), characterized in that the first, second and third semiconductor switching elements ((r), (p), (m)) are formed on a flexible conductor film (7).

6. The battery (1) according to claim 5, characterized in that one additional semiconductor switching element ((bp), (bm)) is arranged in each of the positive bus line (3) and the negative bus line (4) between the connection portions to the second and third semiconductor switching elements ((p), (m)) of the respective individual battery cells (2.1 to 2.n).

7. The battery (1) according to claim 5, characterized in that each of the individual battery cells (2.1 to 2.n) is formed as a prismatic cell with electrical poles (5, 6) arranged on opposite side edges, and the electrical poles (5, 6) of the adjacent individual battery cells (2.1 to 2.n) are connected via the flexible conductor film (7).

8. The battery (1) according to claim 7, characterized in that the plurality of individual battery cells (2.1 to 2.n) are laminated with the flexible conductor film (7) interposed therebetween.

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