Protection device for propulsion battery against

Abstract

The present application relates to a protection device against discharge by the human body, comprising an electrically conductive element (40) electrically connected between a cathode (14) of a battery cell (12) of a vehicle propulsion battery module (10) and a metal casing (20) surrounding said battery cell (12), the electrically conductive element (40) showing a resistance characteristic, the invention relates to a battery unit (12) for limiting stray capacitance energy through a human body when the human body is in contact with a conductor of the battery unit (12).

Description

Technical Field

[0001] The present application relates to the accumulation of stray capacitance in large propulsion battery systems for electric drive vehicles. Background Art

[0002] When developing heavy electric vehicles (such as trucks, vans and buses), large battery systems are required to provide the necessary capacity and driving range between charges. These battery systems include a battery pack with multiple battery modules, each of which includes multiple battery cells. Each battery cell is composed of an anode and a cathode, which are separated by a separator and immersed in an electrolyte solution, which can be placed in a metal casing. The battery cells can be prismatic or cylindrical. The battery cells are assembled or stacked in compartments (commonly referred to as modules) to form a battery pack. These battery packs are then typically placed together in a structure to form a battery pack. Large vehicles that require a lot of energy usually place several battery packs in different locations of the vehicle in order to distribute the weight and also be able to handle the battery packs during maintenance or replacement.

[0003] Since many of the battery prismatic cells have a metal casing, usually made of aluminum, there is a risk of corrosion in the battery cells. To deal with this, the casing is usually galvanically connected to the cathode of the battery cell. This is usually achieved by welding the cathode to the aluminum casing, thus providing a very low-ohmic galvanic contact.

[0004] Stray capacitance is also a problem in electric vehicles, especially heavy vehicles. Stray capacitance can accumulate between the vehicle propulsion electrical system and the vehicle's ground, to which the metal housing of the battery module or battery pack is connected. In addition, when low-ohmic connections are used as described above to deal with corrosion issues, the low-ohmic connections can result in high peak currents during the potential discharge of the stray capacitance. Therefore, if a person comes into contact with the conductors of the electric vehicle propulsion system, there is a risk of high peak current discharge of the stray capacitance.

[0005] The danger of stray capacitance discharge increases with the size of the battery system. This is because stray capacitance is generated between the surfaces of the chassis ground (i.e., the housing of the module and the housing of the battery cell), thereby forming multiple board capacitors, and since large battery systems include a very large number of battery cells, the stray capacitance can be quite significant. This can be understood by the capacitance equation of the board capacitor:

[0006]

[0007] Where d is the distance between the plates, and in the case of a battery, the distance between the battery and the surrounding metal housing of the module. A is the area where the two plates intersect, and ε is the dielectric constant of the isolating material. In order to produce a battery system that is as compact as possible, it is desirable to minimize the size of the battery pack, where the distance between the battery cells and the outer body of the module is reduced, and from the above equation it can be seen that a reduction in the distance d, will result in an increase in the value of the stray capacitance.

[0008] For large battery systems, there is a risk that the discharge of stray capacitance may reach a level that is lethal to the human body if the discharge passes through the human body in contact with the conductor. It is further desirable to increase the operating voltage of the battery system, especially for large capacity systems. However, the increase in voltage leads to an increase in the discharge energy, because the discharge energy is U 2 function of the stray capacitance, thus increasing the risk of a fatal situation even further. This may be the case especially during maintenance of the vehicle, removal or replacement of battery modules. Thus, there is a challenge of balancing the desire for compact battery systems with large capacity and higher voltage with the safety aspects regarding stray capacitance in these systems. Summary of the invention

[0009] The present application aims at reducing the risk of personal injury as described above. This object is solved by a protective device according to the independent patent claims. Preferred embodiments form the subject matter of the dependent patent claims.

[0010] According to a main aspect, a protection device for preventing discharge through a human body is provided, which protection device may include a conductive element electrically connected between a cathode of a battery cell of a vehicle propulsion battery module and a metal casing surrounding the battery cell, and the conductive element may exhibit a resistive characteristic for limiting stray capacitive energy passing through the human body in the event that a person comes into contact with a conductor of the battery cell.

[0011] This solution will limit the discharge current caused by the stray capacitance between the battery housing and the surface of the module, wherein the energy released by the stray capacitance of a person in electrical contact with the battery system is reduced due to the voltage division between the internal resistance of the person (also referred to as internal resistance) and the resistance of the conductive element, because the internal resistance of the person is now connected in series with the resistance of the conductive element. The internal resistance of the human body depends on many factors and can vary from 500 ohms and above. Taking a cautious approach, the internal resistance can be considered to be about 500 ohms. In order to reduce the current through the human body, the conductive element can show a resistance that is at least equivalent to the internal resistance of the human body. Preferably, the conductive element is provided with a resistance that is, for example, 5 to 10 times the internal resistance of the human body. Therefore, the conductive element can show a resistance of at least 100 ohms, preferably at least 500 ohms. More preferably, the resistance of the conductive element is in the range of 1000-5000 ohms, for example, 2500-5000 ohms. Therefore, the released energy is greatly reduced. Furthermore, by providing a resistance in the range of 2500-5000 ohms, there is less risk of the component burning out during an isolation fault than a conductive component having a lower resistance.

[0012] By providing a conductive element connected between the cathode of a battery cell of a vehicle propulsion battery module and the metal housing surrounding the battery cell, wherein the conductive element exhibits a resistance as described herein, it is ensured that the energy of stray capacitance released by a person in electrical contact with the battery system is reduced to a safe level, i.e., a level that can be handled by the person. This result is achieved by providing the resistance of the above magnitude in the above manner.

[0013] The conductive element of the protection device may include a resistor.

[0014] According to a further aspect, a battery cell for a vehicle propulsion battery is provided, which battery cell may be provided with a metal housing and include the protection device as described above. In this regard, a cathode of the battery cell may be electrically connected to the metal housing.

[0015] According to yet another aspect, a battery module comprising several battery cells is provided, wherein at least most of the battery cells may be provided with a protective device as described above. Most refers in this document to "more than half". Thus, more than half of the battery cells in the battery cells may be provided with a protective device as described above. Furthermore, the battery module may include a metal housing which may be connected to the ground of the electric vehicle. Preferably, several such battery modules may be included in a propulsion battery system. In this regard, the capacity of the propulsion battery system may be greater than 300 kWh, because larger propulsion batteries typically require a larger number of battery cells, and because if the number of battery cells increases, this results in an increase in the area of ​​stray capacitance, thereby increasing the discharge energy level, and this requires a protective device as described above.

[0016] These and other aspects and advantages of the present invention will become apparent from the following detailed description of the invention and the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In the following detailed description of the present invention, reference will be made to the accompanying drawings, in which

[0018] Figure 1 is a schematic cross-sectional side view of a propulsion battery module;

[0019] Figures 2 to 3 yes Figure 1 A top view of the propulsion battery module.

[0020] Figure 4 is Figure 1 Schematic diagram of adding stray capacitance to the propulsion battery module.

[0021] Figure 5 is a view of a module provided with a protection device according to the present application,

[0022] Figure 6 is a device having a protective device according to the present application and Figure 4 The corresponding view, and

[0023] Figure 7 is a schematic side view of an electric vehicle that may be provided with a protection device according to the present application. DETAILED DESCRIPTION

[0024] Figure 1 A battery module 10 included in a battery system for propulsion of a vehicle is schematically shown, the battery module comprising a plurality of lithium-ion battery cells 12. Each battery cell 12 comprises a cathode plate 14 and an anode plate 16, with a separator sheet 18 between the cathode and the anode. The plates and sheets are placed in a metal housing 20, typically made of aluminum, and the housing 20 is filled with an electrolyte solution. A separator 22 is also arranged between the plates 14, 16 and the housing 20. The housing 20 may be cylindrical or rectangular. The cathode plate 14 and the anode plate 16 are each provided with a lug or connection point for electrical connection to other battery cells to form the battery module 10. The module 10 typically comprises a generally rectangular metal housing having a bottom 24 and sides 26. These surfaces are typically separated by an insulating material 28. The module is then closed by an upper cover (not shown). The metal housing of the module 10 is further electrically connected to the ground of the vehicle.

[0025] Multiple battery modules are then electrically interconnected in parallel and in series to form a propulsion battery pack for an electric drive vehicle. For large and heavy vehicles, the total capacity of the battery pack of the battery system for the vehicle is typically higher than 300 kWh, which means that several battery packs are installed in the vehicle.

[0026] To prevent galvanic corrosion in the lithium-ion battery cells 12, the cathode 14 of each battery cell is provided with a galvanic connection 30 ( Figure 1 ) in order to obtain a current contact with a very low ohmic value. Figure 1 In the example shown, only one such current connection 30 is shown to simplify understanding. Such a low ohmic contact may result in high peak currents during the discharge of stray capacitance between the propulsion battery system and the ground of the vehicle. The stray capacitance is formed between the battery housing 20 of the battery arranged in the module 10 and the surfaces 24, 26 (bottom and sides) of the module, which act as plate capacitors, see Figure 2 and Figure 3 , showing cylindrical and prismatic battery cells. According to Thevenin's theorem, the capacitive contributions from all surfaces are added, regardless of whether they are at a different potential than the battery cell. Therefore, each and all of the surfaces of the battery housing will interact with the surfaces of the module, resulting in an added stray capacitance, as Figure 4 What I see.

[0027] For large battery systems with large areas of housing from multiple modules as mentioned above, the stray capacitance values ​​may be considerable and may pose a serious risk of injury if a person comes into contact with a conductor of the propulsion battery system and the discharge of the stray capacitance passes through the person's body.

[0028] In order to reduce the risk of stray capacitance discharging through the human body in the above situation, a protection device is provided. The protection device includes a conductive element 40 connected between the cathode of the battery cell and its metal casing, such as Figure 5 The conductive element 40 is provided with a resistance which limits the discharge current caused by the stray capacitance between the battery housing and the surface of the module, wherein the energy released by the stray capacitance of a person in electrical contact with the battery system is reduced due to the voltage division between the internal resistance of the person (e.g., from about 500 ohms) and the resistance of the conductive element.

[0029] Preferably, the conductive element 40 is therefore provided with a resistance at least comparable to the internal resistance of the human body, in order to ensure that the energy released will be low enough for a person to handle. Preferably, the conductive element is provided with a resistance of, for example, 5 to 10 times the internal resistance of the human body. Thus, the energy released will be reduced even further. The resistance of the conductive element may therefore be 100 ohms or more, for example, 500 ohms or more. Preferably, the resistance of the conductive element is in the range of 1000-5000 ohms, for example, 2500-5000 ohms. The conductive element may be a resistor.

[0030] As a high safety measure, all battery cells of a module can be provided with such conductive elements. Figure 6A circuit is shown for the case where each battery cell is provided with a conductive element. However, depending on the size of the module and the number of modules, the generated stray capacitance may not be so high that all battery cells in the module need to be provided with such conductive elements. This will have to be evaluated for each type and size of battery system and vehicle.

[0031] Figure 7 An example of an electrically driven vehicle 60 is shown, here an articulated commuter bus. As can be seen, the bus is arranged with a propulsion battery system 62, which comprises a plurality of battery packs 64, which in turn comprise a plurality of battery modules 10, which are placed in different locations, both on the roof and adjacent to the motor 66 used to propel the vehicle. This type of vehicle requires a large number of battery cells to provide the required energy capacity. In this context, it is important to minimize the impact of stray capacitance using the solution according to the present application, so as to greatly reduce the risk of serious adverse effects in the event of contact between a person and the conductors of the battery system. However, it should be understood that the insulation of the conductors of the battery system for the vehicle is the main protection against electric shock, and the present application is an additional safety measure.

[0032] It is to be understood that the embodiments described above and shown in the drawings are to be regarded only as non-limiting examples and that the application can be modified in many ways within the scope of the patent claims.

Claims

1. A protection device for preventing discharge through a human body, the protection device comprising a conductive element (40) electrically connected between a cathode (14) of a battery cell (12) of a vehicle propulsion battery module (10) and a metal housing (20) surrounding the battery cell (12), the conductive element (40) exhibiting a resistive characteristic for limiting stray capacitance energy passing through a human body in the event that a human body comes into contact with a conductor of the battery cell (12).

2. The protection device according to claim 1, wherein the conductive element (40) exhibits a resistance at least comparable to the internal resistance of the human body.

3. A protection device according to claim 1 or 2, wherein the conductive element (40) exhibits a resistance that is 5 to 10 times the internal resistance of the human body.

4. Protection device according to claim 1 or 2, wherein the conductive element (40) exhibits a resistance of at least 100 Ohm, preferably at least 500 Ohm.

5. Protection device according to any one of claims 1 to 4, wherein the conductive element (40) exhibits a resistance in the range of 1000-5000 Ohm, preferably 2500-5000 Ohm.

6. Protection device according to any of the preceding claims, wherein the conductive element (40) comprises a resistor.

7. A battery cell for a vehicle propulsion battery, the battery cell being provided with a metal housing (20) and comprising a protection device according to any one of the preceding claims.

8. The battery cell according to claim 7, wherein the cathode (14) of the battery cell (12) has a current connection (30) to the metal housing (20).

9. A battery module (10), comprising a plurality of battery cells (12), wherein at least most of the battery cells (12) are provided with the protection device according to claims 1 to 6.

10. The battery module (10) of claim 9, comprising a metal housing (24, 26) connectable to a ground of the electric vehicle.

11. A propulsion battery system (62), comprising a plurality of battery modules (10) according to claims 8 to 10.

12. The propulsion battery system (62) of claim 11, wherein the capacity of the propulsion battery system (62) is greater than 300 kWh.

13. A vehicle (60) comprising a propulsion battery system (62) according to claim 11 or 12.

Images