Method for controlling a discharge process of a battery module with multiple battery cells

Abstract

In various embodiments, a method for controlling a discharging process of a battery module (1) with n battery cells (2) which are arranged next to one another is provided, the method comprising: discharging the battery cells (2) according to a sequence (3), the sequence (3) starting at an outer battery cell (2) and continuing via further battery cells (2) which do not belong to a direct vicinity of the sequence (3).

Description

[0001] The present invention relates to methods for controlling a discharge process of a battery module with a plurality of battery cells, in particular with regard to crash optimization.

[0002] Battery-powered vehicles contain high-capacity batteries. In the event of a collision (crash), individual battery cells within the battery may be damaged. This can trigger a chain reaction and result in a so-called thermal runaway, in which a series of exothermic reactions is triggered, causing further temperature increases. This leads to a self-reinforcing cycle in which the temperature and pressure within the affected battery cell rise uncontrollably in a short period of time, potentially leading to an explosion and / or fire.

[0003] In this context, document US 2015 / 0051771 A1 discloses a system for discharging the electrical charge stored in a traction battery of an electric vehicle or an electric hybrid vehicle. The system comprises a traction battery having a plurality of cells and an associated battery management system. A sensor is provided on the vehicle for detecting a vehicle event, including an accident, flooding of the vehicle, or vehicle maintenance. When the battery management system receives a signal indicating that a vehicle event has occurred, it initiates a discharge cycle of the electrical energy stored in one or more cells of the battery via an energy dissipation device such as a battery regulator or a battery equalizer.

[0004] Document DE 10 2016 224 002 A1 discloses a method for discharging a battery module having at least two battery cells of a battery having at least two battery modules. In each of the battery modules, the respective battery cells are individually activated and deactivated with respect to an energy storage function by means of a cell switching unit. If a fault is detected in one of the battery cells, it is discharged. Subsequently, neighboring battery cells within the battery module are electrically discharged one after the other to prevent a dangerous condition from occurring for the battery module and, consequently, for the battery.

[0005] Document CN 1 14 552 727 A discloses a battery system, an electrical device, a rapid charging method, and a rapid discharging method. By arranging battery modules, each battery module is arranged independently, can be charged and discharged independently, and simultaneous charging of all battery modules is possible. Furthermore, each battery module can be charged independently by simply changing the battery system, thus reducing the voltage platform used during charging and enabling rapid charging of the low-voltage charging platform.

[0006] Based on this, the object of the present invention can be seen in providing a method for operating a battery, in particular a battery of a partially or fully electrically powered vehicle, in which the risk of thermal runaway in the event of an accident is prevented or at least reduced.

[0007] This object is achieved by means of the subject matter of the independent patent claims. Further preferred embodiments can be found in the dependent patent claims.

[0008] According to the invention, a method is provided for controlling a discharging process of a battery module with n battery cells arranged side by side, for example in a row, wherein the method comprises discharging the battery cells according to a predetermined sequence. The predetermined sequence begins with an outer battery cell and continues via further battery cells that are not directly adjacent to the sequence. A direct neighborhood of a battery cell under consideration can, for example, include battery cells that are adjacent to the battery cell under consideration or are at the smallest distance from the battery cell under consideration.

[0009] After a first external battery cell has been discharged, the external battery cell on the other side of the battery module can, for example, be discharged next. The method according to the invention can therefore, in particular, initially comprise discharging the external battery cells in a battery module, i.e. those battery cells which are closest to the lateral housing walls. In any case, the method comprises discharging battery cells which are not directly adjacent to already discharged battery cells. In other words, in this sequence, a battery cell can always be discharged which is spaced unilaterally by at least one and preferably bilaterally by at least one not yet discharged battery cell from battery cells already taken into account in the sequence.

[0010] The method according to the invention can in principle be applied to battery cell arrangements of different stacking sequences, e.g. round cells arranged next to one another, with or without offset between rows arranged one below or one above the other, or longitudinally running pouch cells.

[0011] According to the invention, a discharge scheme for a battery module with multiple battery cells for operating a partially or fully electric vehicle is proposed, which optimizes the arrangement of the battery cells for a crash scenario. According to one embodiment, the battery cells can be discharged starting from the outside, after which every second battery cell in the arrangement is used for energy supply. As soon as the first cell is at least partially, and preferably completely, discharged, the battery cell after the next but one will be responsible for supplying energy to the vehicle, not an immediately adjacent cell.

[0012] If an accident occurs and the vehicle body is deformed, resulting in damage to battery cells, there is a certain probability that battery cells with a low state of charge (e.g. SOC (state of charge) = 40%) or even nominally discharged battery cells (SOC = 0%) will also be deformed. This results in a significantly lower risk of thermal runaway and therefore a lower fire hazard for the battery-powered vehicle, because at least some of the battery cells affected by the damage have been brought to a reduced and, ideally, voltage-free level beforehand, thus reducing the extent of the consequences of a short circuit and avoiding the risk of a short circuit. If a battery cell with a high state of charge is damaged (e.g. SOC = 90%), thermal runaway can be prevented by the neighboring battery cells whose state of charge has been reduced or are discharged.The at least partially discharged battery cells then act as buffers, which are not prone to thermal runaway in the event of mechanical damage.

[0013] According to further embodiments of the method, the sequence can continue between two battery cells that are not in direct proximity to the sequence.

[0014] According to further embodiments of the method, the discharge process may take place according to the sequence until the number of battery cells belonging to the sequence equals n / 2 if n is even and (n+1) / 2 if n is odd.

[0015] According to further embodiments of the method, the sequence can begin with an external battery cell and then include the next but one battery cell from the outside to the inside. In other words, within the deliberately selected discharge sequence, every second battery cell is (initially) skipped in order to create buffer areas within the battery module between still charged battery cells as quickly as possible, each of which has at least one reduced-charge or discharged battery cell.

[0016] As the battery module progresses, depending on the number of battery cells in a battery module, a situation will arise in which a battery cell is provided in the discharge sequence that is located directly next to a battery cell already considered in the sequence. This is unproblematic and even advantageous, as it creates larger buffer zones between battery cells that are still (at least partially) charged and that have more than one reduced-charge or charge-free battery cell.

[0017] The battery cell format can be any suitable format that allows for easy stacking. For example, the battery cells can be prismatic cells or pouch cells.

[0018] According to further embodiments of the method, the sequence can begin with the outermost battery cell located further outward relative to the vehicle center. This method can be applied when the battery cells are arranged perpendicular to the vehicle's longitudinal axis. This has the advantage that the area of ​​the battery module closest to the edge of the vehicle, and thus most exposed in the event of an accident, is provided with deformation buffers in the form of the reduced-charge or discharged battery cells.

[0019] According to further embodiments of the method, the sequence when changing from the outer battery cell to the next battery cell can first comprise a change to the other outer battery cell and then, with each change to the next battery cell, the side of the battery cell module can be changed alternately according to the sequence. The other outer battery cell means the battery cell which, compared to the battery cell initially arranged on one side edge of the battery module, is arranged on the other side edge of the battery module. In other words, in this embodiment, after taking the two outer battery cells within the sequence into account, the side of the battery module can be changed at the same time when selecting the next inner battery cell.

[0020] According to further embodiments of the method, a change from one battery cell to the next can take place according to the sequence when the discharging battery cell has been discharged to a predetermined state of charge. The predetermined state of charge can have a reduced state of charge compared to a fully charged battery cell, for example, SOC=40% or SOC=20%.

[0021] According to further embodiments of the method, the predetermined state of charge may have a lower threshold value, i.e. SOC=0%.

[0022] According to further embodiments of the method, this can be carried out while the vehicle having the battery module is in operation. As the battery discharge level progresses, its degree of optimization can be increased with regard to reducing the risk of thermal runaway.

[0023] According to further embodiments of the method, the discharging battery module can be one of several battery modules of a vehicle, which are discharged according to the sequence defined for the battery cells of a battery module. Thus, at least one external battery module can be discharged first, which is usually a battery module critical in terms of vehicle safety, before the discharging sequence progresses to the battery modules located further inside. The sequence defined according to the invention with respect to the battery cells within a battery module, in which these are discharged, can thus be applied analogously to battery modules within a battery comprising a plurality of battery modules.

[0024] The features mentioned above and those to be explained below can be used not only in the combination specified in each case, but also in other combinations or on their own, without departing from the scope of the present invention.

[0025] Further advantages and embodiments of the invention will become apparent from the following description of embodiments and the accompanying drawings. Fig. 1 shows a first exemplary discharge scheme of a battery module according to the invention. Fig. 2 shows a second exemplary discharge scheme of a battery module according to the invention.

[0026] In the Fig. 1 and Fig. 2 shows two exemplary battery modules 1, each of which has eight battery cells 2. The charge level of each of the battery cells 3 is indicated as a percentage. According to the invention, the battery cells 2 in a battery module 1 are discharged according to a predetermined sequence 3, which will be explained below. The sequence 3 in which the battery cells 2 are discharged completely or to a lower threshold value according to the invention is indicated by the numbers. In the examples shown, it is assumed, without limiting the general case, that one battery cell 2 is completely discharged (SOC=0%) before the sequence advances to the next battery cell 2. However, any number of battery cells 2 in the sequence can be discharged in parallel as required, whereby the discharge processes can start simultaneously or staggered.

[0027] At the Fig. 1, this sequence begins with the outer battery cell 2 on the left and then changes to the outer battery cell 2 on the right. The sequence 3 then continues with alternating sides (i.e., left, right, left, right...) in the direction from outside to inside via the next but one battery cell 2. The direction selected at the beginning, from outside to inside, can be maintained until half of the battery cells 2 in the battery module 1 have been passed through. Upon exceeding the centrally located battery cell(s) 2, the sequence appears to reverse and continue in the direction from inside to outside. Fig. 1, this is the case at the transition from battery cell 2 at discharge position 5 to battery cell 2 at discharge position 7, where the selection direction appears to be from the inside out. However, this direction corresponds to the initial direction from the outside in, which was determined by the beginning of the sequence from the left edge, i.e., by the transition from discharge position 1 to discharge position 3. The same applies to the direction from the outside in with respect to the right edge of the arrangement of battery cells 2, which was determined by the transition from discharge position 2 to discharge position 4.

[0028] The initial direction can therefore correspond to the direction determined by two discharge positions located between a side change within the battery module 1. In the Fig. 1, discharge positions 1 and 3 on the left side of battery module 1 determine the direction from outside to inside. Similarly, discharge positions 2 and 4 on the right side of battery module 1 determine the direction from outside to inside.

[0029] At the Fig. In the exemplary sequence 3 illustrated in Figure 2, this begins with the outermost battery cell 2 on the left and then continues in a direction from outside to inside via the next-but-one battery cell 2. Therefore, no side change is initially performed here. Upon reaching the penultimate battery cell at the other end of the arrangement (with an odd number of battery cells 2, this would be the last battery cell 2 in the arrangement), in this case discharge position 4, the side of the battery module 1 is alternately changed, and the sequence continues in the initial direction from outside to inside.

[0030] Arrow 4 indicates a deformation area that can occur in the event of an accident on the battery module 1. It can be seen that both exemplary discharge sequences result in an advantageous configuration of the sequence of the battery cells 2 in the battery module 1, in which still charged battery cells 2 (SOC=100% and SOC=70%) are each surrounded on both sides by a discharged battery cell 2 (SOC=%).

[0031] The two in the Fig. 1 and Fig. The sequences 3 illustrated in Figure 2 represent only two possible variants of the basic principle. In each case, the sequence 3 in which the battery cells 2 are discharged begins with an external battery cell 2 and continues - with or without a change of sides - via further battery cells 2 between two battery cells 2 not yet belonging to the sequence, until the number of battery cells belonging to the sequence corresponds to n / 2 if n is even, and (n+1) / 2 if n is odd. If this is the case, the primary objective of the method according to the invention is achieved, and an arrangement of battery cells 2 is achieved which has an alternating row of at least partially discharged battery cells 2 and battery cells 2 not yet considered in the sequence and thus not discharged. An at least partially discharged battery cell 2 acts as a buffer between each two still charged battery cells 2.

[0032] When the n / 2-th or [(n+1) / 2]-th battery cell 2 is reached, the Fig. 1, these start at the battery cell 2 located furthest from the center of the arrangement of battery cells 2 and proceed from the outside to the inside, alternating sides. This creates regions at the edges of the battery cell 1 that grow from the outside to the inside, in which all battery cells 2 are at least partially and preferably completely discharged.

[0033] The Fig. 1 and Fig. The sequences 3 shown in Figure 2 can begin at each of the two outer battery cells 2, so that the sequences 3 can begin at the right instead of the left outer battery cell 2 and can be run through inverted compared to the representation shown.

Claims

[1] Method for controlling a discharge process of a battery module (1) with n battery cells (2) arranged next to one another, the method comprising: Discharging the battery cells (2) according to a sequence (3), wherein the sequence (3) begins with an external battery cell (2) and continues via further battery cells (2) not belonging to a direct neighborhood of the sequence (3). [2] Method according to claim 1, wherein the sequence (3) continues between two battery cells (2) not belonging to a direct neighborhood of the sequence (3). [3] Method according to claim 1 or 2, wherein the discharging process takes place according to the sequence (3) until the number of battery cells (2) belonging to the sequence corresponds to n / 2 if n is even, and (n+1) / 2 if n is odd. [4] Method according to one of claims 1 to 3, wherein the sequence (3) begins with an external battery cell (2) and subsequently comprises the next but one battery cell (2) from the outside to the inside. [5] Method according to one of claims 1 to 4, wherein the sequence (2) begins with the outermost battery cell (2) which is arranged further outwards relative to the vehicle centre. [6] Method according to one of claims 1 to 5, wherein the sequence (3) when changing from the external battery cell (2) to a next battery cell (3) first comprises a change to the other external battery cell (2) and then with each change to the next battery cell (2) according to the sequence the side of the battery cell module (1) is changed alternately. [7] Method according to one of claims 1 to 6, wherein a change from one battery cell (2) to the next takes place according to the sequence when the discharging battery cell (2) has been discharged to a predetermined state of charge. [8] A method according to claim 7, wherein the predetermined state of charge has a lower threshold value. [9] Method according to one of claims 1 to 8, wherein the method is carried out during driving operation of the vehicle having the battery module (1). [10] Method according to one of claims 1 to 9, wherein the discharging battery module (1) is one of several battery modules of a vehicle which are discharged according to the sequence defined for the battery cells (2) of a battery module (1).

Images