Device for cell voltage-sensitive overcurrent interruption, lithium-ion battery

Abstract

Disconnecting device (30, 30') for a battery comprising several interconnected battery cells (21, 22, 23, 24) and a first and a second power supply connection (18, 19), wherein the disconnecting device (30, 30') comprises a disconnecting element (31), in particular a pyrotechnic disconnecting element (31), with which the battery cells (21, 22, 23, 24) or a part thereof can be disconnected from at least one power supply connection (18, 19) in the event of a short circuit, and wherein the disconnecting device (30, 30') further comprises a passive current- or voltage-controlled release circuit (32) which is connected in parallel to one or more battery cells (21, 22, 23, 24), wherein the release circuit (32) is a current-controlled release circuit and the release element (321) is an RC circuit (C1, R11, R12) with a capacitor (C1) serving as a current source, which is connected in series with at least one series resistor (R11, R12),wherein the triggering circuit (32) further comprises an ignition circuit (33) connected in parallel to a triggering element, which is adapted to trigger upon a predefined voltage drop in one or more of the battery cells (21, 22, 23, 24) and to close the current path to the pyrotechnic isolating element (31), and the ignition circuit (33) comprises at least a fuse resistor (R2) and a thyristor (T1), characterized in that the triggering circuit (32) is a current-controlled triggering circuit and the fuse resistor (R2) is smaller than a series resistor (R11, R12).

Description

[0001] The present invention relates to a battery separator according to the features mentioned in the preamble of claim 1, and to a lithium-ion battery according to the features mentioned in the preamble of claim 4. State of the art

[0002] In electrically powered vehicles, such as plug-in hybrid electric vehicles (PHEVs), an accumulator or battery comprising multiple battery cells serves as the energy source. Lithium-based battery cells are often used because, compared to nickel- or lead-acid-based batteries, they offer the highest energy density available at the lowest weight. To achieve the required performance and energy specifications, several battery cells are typically connected in series and sometimes also in parallel, resulting in a resting voltage of several hundred volts for the overall system. The voltage considered safe for humans is 60 volts or less. A short circuit at the vehicle's battery terminals, or even a short circuit within the battery in certain cell configurations, leads to very high currents of up to several thousand amperes.These short-circuit currents must be interrupted by appropriate measures.

[0003] Currently, such short-circuit currents are interrupted by fuses. The operating principle of these fuses is based on the heat input from the high current flowing, which causes the conductors inside the fuse to melt. Typically, a fuse is used that ideally halves the total voltage of the battery pack upon tripping, although partial voltages above 100 volts usually remain. A fuse circuit using such fuses is disclosed, for example, in German patent applications DE 10 2011 082 650 A1, DE 10 2012 212 563 A1, and DE 697 38 310 T2.

[0004] The publication DE 10 2011 082 650 A1 discloses a disconnecting device for a battery with a fuse and an electrical switching element which opens the fuse when closed.

[0005] The publication DE 10 2012 212 563 A1 discloses a battery system with a fuse which is arranged within the short-circuit path of the battery cells and which can be a fusible link, and a switching device which can short-circuit the series connection of the battery.

[0006] German patent application DE 697 38 310 T2 discloses a protection circuit for a battery unit, which has several switching elements, each configured to disconnect an electrical connection in response to an active signal. Furthermore, this protection circuit has a voltage monitoring circuit by which the active signal is output to the switching elements when the voltage of at least one battery cell in any cell section falls outside a certain range.

[0007] Fig. Figure 1 shows a protection circuit for a battery according to German patent DE 697 38 310 Part 2, which is used, for example, in a portable electronic device. The illustration shows a battery unit 1 with several cell units connected in parallel, which in turn comprise several cells connected in series, as well as a first power terminal 9 and a second power terminal 10. Furthermore, this protection circuit has several switching elements 5-8 which, in response to a fault signal, for example, a short circuit, disconnect the electrical connection of the affected cell unit. The protection circuit also includes a voltage monitoring circuit 2, which generates an active signal. An internal logic circuit compares this signal to determine whether electrical disconnection should be performed, i.e., whether the field-effect transistors 6, 8 (when the battery is charging) or 5, 7 (when the battery is discharging) intended for disconnection should be blocked or not.Additionally, a fuse 3, 4 is proposed as a further safeguard to ensure safe electrical isolation in the event of a fault in the field-effect transistors, such as a short circuit. The double protection circuit disclosed in German patent application DE 697 38 310 T2 makes it possible to guarantee safe charging and discharging of the battery and thus prevent battery deterioration due to excessive currents.

[0008] Another example from the state of the art is in Fig. Figure 2 shows a battery disconnect device according to German patent DE 10 2011 082 650 A1, which is used, for example, in electric or hybrid vehicles. A disconnect device comprises a fuse 40, which is designed, for example, as a thermal fuse or as an electrically controlled, thermally actuated fuse with an associated resistor 41, and an electrical switching element 42, for example, in the form of a power transistor. As soon as this switching element 42 is closed, the fuse 40 opens because an increased current flows through it, causing it to heat up and melt. With this disconnect device, the disconnection only occurs after a certain time, as the fuse only trips once the temperature has risen sufficiently to melt it.

[0009] Another battery disconnect device is disclosed, for example, in DE 10 2011 115 550 A1. This document discloses a battery with an overcurrent protection device comprising switches that close at a defined current and are arranged in transverse branches running perpendicular to the parallel strands. Due to the arrangement of the switches in the transverse branches, lower currents flow compared to the currents in the parallel strands.

[0010] The state of the art in this regard is further detailed in the publications DE 10 2012 214 879 A1, DE 10 2012 214 835 A1 and DE 195 03 809 A1. Disclosure of the invention

[0011] According to the invention, a disconnecting device for a battery is provided, which has several interconnected battery cells as well as a first and a second power supply connection, wherein the disconnecting device includes a safety device with which the battery cells or a part thereof can be disconnected from at least one power supply connection in the event of a short circuit. The disconnecting device has the special feature that it further comprises a disconnecting element with which the battery cells or a part thereof can be disconnected from at least one power supply connection in the event of a short circuit, and that the safety device further comprises a passive current- or voltage-controlled release circuit which is arranged in the release path of the disconnecting element. The disconnecting element can, in particular, be a pyrotechnic disconnecting element.

[0012] The disconnecting device according to the invention offers the advantage over devices known from the prior art that it uses a current- or voltage-based, passive overcurrent detection and disconnection of the short-circuit path, rather than a temperature-based one. Known disconnecting devices often have a tripping delay, as, for example, fuses only melt at a certain temperature. This can lead to excessive current flow, damaging the battery or parts thereof. Furthermore, a slow response time from a battery management system that sends an active signal, or even the fact that the system is switched off, can result in a delayed or even a failed tripping, which in turn can damage the battery or parts thereof.

[0013] According to the invention, the fact that cells have a finite resistance is exploited, and in the event of a short circuit, most of the voltage drops across this internal resistance, causing the terminal voltage of the cell or the monitored unit to collapse. This voltage drop serves as the trigger for the shutdown and has the advantage of a very fast shutdown. Therefore, according to the invention, the disconnection occurs passively, i.e., independently of any active signaling or the state of any electronic monitoring system, such as a battery management system.

[0014] By avoiding the use of fuses, several advantages can be achieved, such as overcoming the problem of fuse aging, thus ensuring increased reliability. Fuse aging results from the fact that fuses are usually connected in series in the current path, meaning that during normal operation, the entire current flows through this fuse, leading to observed fuse aging. Furthermore, the disconnecting device according to the invention allows for the separation of the battery pack into sections with a voltage of less than 60V, which is considered non-critical for humans. Another advantage of the invention is that battery packs can be used for higher operating currents above the 400A currently permitted for fuses, and that safe disconnection is possible for these higher currents.

[0015] Advantageous further training opportunities arise from the characteristics of the dependent requirements.

[0016] According to the invention, the tripping circuit is a current-controlled tripping circuit and comprises, as the tripping element, an RC circuit with a capacitor serving as a current source, which is connected in series with a series resistor. The series resistor can be a single resistor, but can also, for example, consist of two or more resistors connected in series. Furthermore, the effect of such an RC circuit can be replaced by known equivalent circuits. This has the advantage that, during normal operation, the capacitor is charged via the series resistor, and in the event of a short circuit, where a rapid voltage drop occurs across a cell or cell group, the capacitor is discharged, thus triggering a discharge current that trips the pyrotechnic disconnecting element.

[0017] According to the invention, the current- or voltage-controlled triggering circuit further comprises an ignition circuit connected in parallel to the triggering element. This ignition circuit is designed to trigger upon a predefined voltage drop in one or more of the battery cells and to close the current path to the pyrotechnic isolating element. The elements of the isolating circuit are selected according to the desired triggering characteristic, sensitivity, or timing response. This depends on the specific application of the isolating circuit and is known to those skilled in the art; they define the triggering behavior and then select the elements accordingly. The ignition circuit is limited to a single pyrotechnic element.

[0018] According to the invention, the ignition circuit of the current-controlled triggering circuit comprises at least one fuse resistor and one thyristor, wherein the fuse resistor is dimensioned such that it is (significantly) smaller than the sum of the first and second resistances of the triggering element. This activates it in the event of a short circuit, and the resulting current is large enough to activate the pyrotechnic disconnecting element.

[0019] In a further advantageous embodiment, a trigger delay circuit is connected in parallel to the ignition circuit. This preferably comprises an RC network. A trigger delay is suitable, for example, to allow the disconnection of multiple battery sections, so that after disconnection, the battery sections have a voltage preferably less than 60 volts. The dimensioning of the trigger delay circuit or the RC network depends on the required delay or the specific requirements that must be met.

[0020] The invention further relates to a lithium-ion battery, in particular for a vehicle, which comprises at least one separating device according to the invention.

[0021] In a preferred embodiment of the lithium-ion battery, one or more separating devices are arranged such that, when separated by the separating device, the separated battery cells have a voltage of less than or equal to 60 volts. Brief description of the drawings

[0022] The invention and advantageous embodiments according to the features of the further claims are explained in more detail below with reference to the exemplary embodiments shown in the drawings, without thereby limiting the invention.

[0023] They show: Fig. 1. A protection circuit for a battery with a fuse according to a prior art; and Fig. 2 a battery disconnect device according to a further prior art; and Fig. 3 a battery according to the invention with a disconnecting device in a schematic representation; and Fig. 4 a disconnecting device as a current-controlled disconnecting device with a specific design of the release element according to an embodiment of the invention; and Fig. 5 a disconnecting device as a current-controlled disconnecting device with a specific design of the safety device according to an embodiment of the invention; and Fig. 6 a disconnecting device as a current-controlled disconnecting device with an additional trip delay circuit according to a further embodiment of the invention; and Fig. 7 a lithium-ion battery with several separating devices according to the invention arranged between the battery cells. Embodiments of the invention

[0024] In Fig. Figure 3 shows a battery with a disconnect device 30, wherein the battery comprises several interconnected battery cells 21, 22, 23, 24, as well as a first power supply connection 18 and a second power supply connection 19. The battery is preferably used in electric or hybrid vehicles. Preferably, the battery is a lithium-ion battery, since these have the highest energy density available to date at the lowest weight compared to nickel- or lead-based batteries and are therefore best suited for powering a vehicle. However, the invention is not limited to an application with lithium-ion batteries.

[0025] An essential component of batteries is a disconnect device 30, which makes it possible to safely disconnect the battery or parts thereof from the short circuit in the event of an internal or external short circuit. This serves, firstly, to ensure the safety of persons in the vehicle in the event of an accident, and secondly, the safety of rescue personnel. Furthermore, such a disconnect device serves to isolate parts of the battery affected by a short circuit from the rest of the battery in order to prevent damage to the remaining battery. Fig. Figure 3 shows an exemplary disconnecting device 30 according to the present invention, which has a pyrotechnic disconnecting element 31 that, when triggered, disconnects a portion of the battery from the rest of the battery. To achieve this, the disconnecting device additionally comprises a passive current- or voltage-controlled triggering circuit 32, which is located in the current path of the pyrotechnic disconnecting element 31 and which is designed such that, in the event of a short circuit, the pyrotechnic disconnecting element 31 disconnects a portion of the battery from the rest.

[0026] In Fig. 4 is like in Fig. Figure 3 shows the disconnecting device 30 configured as a current-controlled disconnecting device. Furthermore, the release element 321 of the release circuit 32 according to an embodiment of the invention is shown. The release element comprises a capacitor C1 serving as a current source, which is connected in series with a series resistor, here a first resistor R11 and a second resistor R12. The capacitor C1 connected in series with the resistors R11 and R12 thus forms an RC circuit. The capacitor C1 is charged via the resistors R11 and R12 and later supplies the energy required to initiate the disconnecting mechanism for disconnecting parts of the battery by means of the pyrotechnic disconnecting element 31. As soon as the capacitor C1 is charged, no current flows through the resistors R11 and R12.If a short circuit occurs in the battery or parts thereof, a short-circuit current flows, causing a voltage drop across the affected cell 24 or cell assembly. This voltage drop discharges capacitor C1, and a discharge current flows through the circuit via capacitor C1, the first resistor R11, and the second resistor R12. This discharge current flows through fuse 33, which is arranged in parallel with the trip element 321 of the trip circuit 32, thus activating the pyrotechnic disconnect element 31. The fuse must be dimensioned so that it trips only in the event of a sufficiently high and rapid voltage drop, which is predefined according to the type of battery used and the intended application.

[0027] In an alternative embodiment not shown, the disconnecting device 30, which uses the voltage drop across a cell or cell group to activate a disconnecting mechanism by means of a resulting current, can also be implemented as a voltage-controlled disconnecting device in a similar manner to that described above, using contactors, semiconductor-based switches such as bipolar transistors with insulated gate electrodes or other suitable elements, without losing the advantages of current-controlled disconnection.

[0028] Fig. Figure 5 shows a separation device 30 according to the invention with the elements of the release element 321 and the safety device 33 of the release circuit 32 in detail. The release element 321 is the same as in Fig. Figure 4 shows the same reference symbols. In this embodiment, fuse 33 comprises a thyristor T1 and another resistor, the fuse resistor R2. For current to flow through fuse 33, thyristor T1 must be triggered. For this purpose, capacitor C1, the first resistor R11, and the second resistor R12 are selected such that thyristor T1 only triggers upon a sufficiently high and rapid voltage drop, as mentioned above. The fuse resistor R2 must be selected to be much smaller than the sum of resistances R11 and R12, i.e., the following applies: R2< <R11+R12.

[0029] This allows the majority of the current to flow through this path in the event of a short circuit. Thus, the parallel path via the thyristor T1 and the fuse resistor R2 becomes active, and the current flow is large enough to activate the pyrotechnic disconnect element 31 and break the short circuit.

[0030] In Fig. Figure 6 shows a further embodiment of the present invention, wherein the same elements as in Fig. have 5 identical reference symbols. In addition to those in Fig. The separating device 30' according to the invention has elements 5 shown. Fig. 6 a trigger delay circuit 34. The trigger delay circuit is in Fig. 6 is configured as an RC circuit with a capacitor C2 and a resistor R3 and is arranged in parallel to the current path of the pyrotechnic isolating element 31. This element ensures that the current required to trigger the pyrotechnic isolating element does not flow until the capacitor C2 of the RC circuit is charged to a certain degree. Care must be taken during the design phase to ensure that the triggering is not prevented, but only delayed, which in turn depends on the characteristics of the battery and its intended use. This delay allows other identical isolating devices 30' in the battery circuit to also trigger. This measure overcomes the disadvantage that would occur, for example, when using multiple fuses at different points in the battery.When using multiple fuses, the current would drop when one fuse in the circuit trips, preventing another fuse from tripping. This would result in the disadvantage that no battery components with less than 60V could be disconnected using fuses. This disadvantage is overcome by the use of the delay circuit of the present invention.

[0031] Fig.Figure 7 shows a battery with several interconnected battery cells 21, 22, 23, 24, and several identical disconnect devices 30 or 30' arranged such that, in the event of a short circuit, portions of the battery remain with a voltage of 60 volts or less. This has the advantage that batteries used and required, for example, in hybrid vehicles with voltages up to 450 volts (achieved by many battery cells connected in series) can be divided into small units with a voltage of less than 60 volts each in the event of a short circuit, thus eliminating the danger to humans. However, it is also possible to arrange the disconnect devices 30, 30' so that a portion with a voltage greater than or less than 60 volts is divided.

[0032] According to the invention, the output terminals are arranged directly on the battery. However, the disconnecting device according to the invention can also be used to safely disconnect output terminals that are not arranged directly on the battery, e.g., those located behind an intermediate circuit or on other modules connected to the battery.

[0033] In summary, this invention provides a disconnect circuit, particularly for lithium-ion batteries used in vehicles, which passively and by current or voltage safely disconnects a short circuit without undesirable tripping delays due to dependence on thermal coupling or on an active signal output by, for example, logic circuits or a battery management system.

Claims

[1] Disconnecting device (30, 30') for a battery which has several interconnected battery cells (21, 22, 23, 24) and a first and a second power supply connection (18, 19), wherein the disconnecting device (30, 30') has a disconnecting element (31), in particular a pyrotechnic disconnecting element (31), with which the battery cells (21, 22, 23, 24) or a part thereof can be disconnected from at least one power supply connection (18, 19) in the event of a short circuit, and wherein the disconnecting device (30, 30') further comprises a passive current- or voltage-controlled release circuit (32) which is connected in parallel to one or more battery cells (21, 22, 23, 24), wherein the release circuit (32) is a current-controlled release circuit and the release element (321) is an RC circuit (C1, R11, R12) with a capacitor (C1) serving as a current source, which is connected in series with at least one series resistor (R11, R12),wherein the triggering circuit (32) further comprises an ignition circuit (33) connected in parallel to a triggering element, which is adapted to trigger upon a predefined voltage drop in one or more of the battery cells (21, 22, 23, 24) and to close the current path to the pyrotechnic isolating element (31), and the ignition circuit (33) comprises at least a fuse resistor (R2) and a thyristor (T1), , characterized by , that the tripping circuit (32) is a current-controlled tripping circuit and the fuse resistor (R2) is smaller than a series resistor (R11, R12). [2] Separating device (30, 30') according to the preceding claim 1, characterized by, that the triggering circuit (32) has a triggering element (321) and an ignition circuit (33) connected in parallel to the triggering element, which is adapted to trigger in the event of a predefined voltage drop in one or more of the battery cells (21, 22, 23, 24) and to close the current path to the pyrotechnic isolating element (31), and a trigger delay circuit (34) is connected in parallel to the ignition circuit (33). [3] Separating device (30, 30') according to the preceding claim 2, characterized by , that the trigger delay circuit (34) includes an RC element (C2, R3). [4] Lithium-ion battery, in particular for a vehicle, comprising at least one disconnecting device (30, 30') according to any one of the preceding claims 1 to 3. [5] Lithium-ion battery according to claim 4, characterized by, that one or more separating devices (30, 30') are arranged such that when separated by the separating device (30, 30') the separated battery cells (21, 22, 23, 24) have a voltage of less than or equal to 60 volts.

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