Method and device for discharging energy storage devices

Abstract

The invention relates to a device (10) for discharging energy storage devices (12), the device comprising first electrical terminals (11) for the energy storage device (12), a control unit (17), and second electrical terminals (14) for an electrical load (15). When the energy storage device (12) and the electrical load (15) are connected, the control unit (17) is connected thereto to form a discharge circuit (18) for a discharge current (19). The control unit (17) is designed to modulate the discharge current (19).

Description

Method and device for discharging energy storage devices

[0001] The present invention relates to a method for discharging energy storage devices, in which the energy storage device is connected to an electrical consumer and a control unit to form a discharge circuit for a discharge current, and to a corresponding device comprising a control unit, first electrical connections for the energy storage device and an electrical consumer or second electrical connections for the electrical consumer.

[0002] Such devices and methods are known from the prior art.

[0003] The term "energy storage" in this application refers to a chemical energy storage device for the reversible storage of electrical energy. A well-known example of such energy storage devices are rechargeable secondary batteries, which are increasingly used in all areas of life, such as in electric vehicles, mobile phones, cordless screwdrivers, etc.

[0004] The smallest functional units of such energy storage devices are battery cells, which comprise two electrodes, namely an anode and a cathode, a separator for electrical separation of the electrodes, and an electrolyte for ion transport, which are enclosed in an airtight housing on which current collectors are provided on the outside for contacting the electrodes.

[0005] Several such battery cells are typically combined to form a battery module, which may be combined with further battery modules to create a secondary battery. The terms secondary battery and battery cell are used synonymously in this application. The secondary battery is then provided with the usual terminals for discharging and recharging.

[0006] Examples of such battery cells are lithium-ion battery cells, sodium-ion battery cells, nickel-metal hydride battery cells, and nickel-cadmium battery cells.

[0007] Battery cells, and therefore also the secondary batteries equipped with them, age over time and lose more and more of their original storage capacity for electrical energy until they are no longer usable and have thus reached the end of their functional lifespan, and ideally are recycled.

[0008] A particular disadvantage of such energy storage devices is their tendency to spontaneously combust, often resulting from overheating of the battery cells due to excessive discharge current and / or internal short circuits. This problem occurs not only during their intended use as secondary batteries, but also spontaneously during transport, storage, and disposal, for example through recycling, if the chemical energy storage device still carries an electrical charge.

[0009] For these reasons, secondary batteries are deep-discharged before disposal. "Deep discharge" in this context means discharging the energy storage device below its irreversible limit.

[0010] For lithium-ion batteries with a voltage range between 2.5 volts and the respective nominal voltage, this means a discharge to below 2.5 volts, ideally to approximately 0 volts.

[0011] Even during deep discharge, self-ignition due to overheating must be avoided, which is why in the methods used so far the current strength of the discharge current is limited so that the temperature of the secondary battery to be discharged remains below its critical temperature for self-ignition.

[0012] This critical temperature is determined by the structure of the battery cells and is known for many types of battery cells.

[0013] Problems with spontaneous combustion occur particularly with lithium-ion batteries whose charge / discharge cycles lie between a maximum and a minimum voltage and which consequently are not discharged to 0 V. Thus, even a "depleted" lithium-ion battery that has reached the end of its functional life still contains enough energy to become an ignition source or to spontaneously ignite during transport or storage. Therefore, it seems advisable to subject secondary batteries to a deep discharge at the end of their functional life before they are stored, transported, or recycled.

[0014] This deep discharge must not be induced by an electrical short circuit of the battery cells, because the high discharge current would heat the battery cells above the temperature critical for spontaneous combustion. Instead, a secondary battery to be discharged is currently short-circuited via an electrical resistor, which dissipates the electrical energy extracted from the battery cells as ohmic heat and is dimensioned to maintain a sufficient safety margin from the critical temperature. Therefore, the discharge process often takes up to 10 hours.

[0015] In the context of the present invention, "end of functional life" means not only insufficient residual storage capacity, but also mechanical damage, technical problems, technical obsolescence, etc., so that no further uses are available for the secondary batteries and battery cells that are technically and / or economically sensible or justifiable.

[0016] The long discharge times required for safety reasons during deep discharge represent a problem that has not yet been solved, and which the inventors of the present invention have addressed.

[0017] EP 4164024 Bl discloses a method for discharging a battery cell, in which the battery cell is surrounded by a cooling medium in a conditioning unit to keep it below a certain temperature. The battery cell is connected to a discharge current source, through which a discharge current is introduced into the battery cell to discharge it. The discharge current is to be maintained until the electrical voltage of the battery cell has been negative for a defined holding period.

[0018] Because of the required conditioning unit, the barely comprehensible discharge procedure, and the defined holding time with negative battery voltage, this method does not seem suitable for everyday use.

[0019] German patent DE 102022204121 describes a method for discharging battery cells as completely as possible at the end of their service life in order to utilize the stored residual energy before recycling. For this purpose, the direct current (DC) voltage drawn from the battery cells is converted into a multi-phase alternating current (AC) voltage, which is fed into an AC power grid. To achieve this, battery cells are connected to a switching arrangement and selectively connected in series via a multitude of switches. The switching arrangement is connected to a power converter circuit that converts the applied DC voltage into the AC voltage. How overheating of the battery cells is addressed is not described.

[0020] Connecting many battery cells in series is intended to allow the discharge of battery cells whose residual energy is too low for isolated discharge. The device described for carrying out this method is complex and unsuitable for the rapid and, above all, safe discharge of battery cells.

[0021] German patent DE 1020222 110424 Al deals with the management of battery storage systems, in particular with how such energy storage systems can be heated to a higher temperature for fast charging or to prevent damage in winter. The method is also intended to be carried out during power consumption, for example, during the operation of an electric car on a ferry.

[0022] Instead of the heating resistors known in the prior art, individual battery cells of a secondary battery are temporarily short-circuited by transistors, so that their own heating also heats the other battery cells in the secondary battery.

[0023] The switches are opened and closed at a specific switching frequency, with the switching being pulse-width modulated. Very short short-circuit times of a maximum of 1 ms are intended to prevent damage to the battery cells. As the duration of the short circuit increases, so does the current drawn and thus the self-heating.

[0024] The proposed method is neither intended nor suitable for deep discharging battery cells, as it is designed to ensure that battery cells are used gently and effectively throughout their functional lifespan through the described battery management system.

[0025] Against this background, the present invention aims to further develop the method and apparatus of the type mentioned above in such a way as to avoid the disadvantages and problems known from the prior art. In particular, it should enable fast and safe discharge, preferably deep discharge, of secondary batteries and battery cells.

[0026] In the aforementioned method, these and other problems are solved by the control unit modulating the discharge current, wherein the control unit preferably switches the discharge current on and off with a clock rate TR and a clock ratio TV, wherein the clock rate TR is preferably between 1 and 100 Hz, preferably at approximately 10 Hz, and / or the clock ratio TV is between 1:10 and 10:1, preferably at 1:1. The electrical load can comprise at least one ohmic resistor.

[0027] In the aforementioned device, these and other tasks are solved by the control unit being configured to modulate the discharge current, preferably according to the new method, wherein the electrical load preferably comprises at least one ohmic resistor. The control unit preferably includes a function generator that switches the discharge current on and off with a clock rate TR and a duty cycle TV. By connecting the energy storage device and, if applicable, the electrical load (if provided externally), the control unit is connected to these components to form the discharge circuit.

[0028] The problem underlying the invention is thus completely solved.

[0029] Various energy storage devices can be connected to the first electrical terminals to quickly discharge them deeply or to discharge them to a specific state of charge. Deep discharge means that the discharged energy storage devices can no longer be recharged and generally cannot (partially) regenerate themselves through internal chemical processes.

[0030] In addition to the secondary batteries discussed at the beginning, the new method and the new device can also be used to discharge primary batteries whose voltage range goes down to 0 volts.

[0031] For the purposes of this application, an electrical load is generally understood to be a component or device that converts electrical energy drawn from the energy storage device into another form of energy, such as heat or motion, or stores it, such as in another secondary battery, or by electrolysis of water into hydrogen, which can be stored for later use. An ohmic resistor is the simplest form of an electrical load; it converts electrical energy into thermal energy in the form of heat.

[0032] The electrical load can either be provided in the device or permanently connected to it, whereby it should be possible to replace the electrical load so that the new device can be used to discharge different energy storage devices.

[0033] On the other hand, the new device may have second electrical connections to which different electrical consumers can be connected if necessary.

[0034] The dissipation of heat generated in a discharge resistor can be passively supported by cooling fins or actively by cooling via airflow or coolant.

[0035] In one embodiment, the electrical device is connected to the new device, thus becoming part of it. Preferably, the device includes a cooling port for the electrical device to dissipate the heat it generates. This cooling port can be designed, for example, for airflow or a coolant.

[0036] In the context of this application, "modulating" means influencing the current profile of the discharge current over time. According to one embodiment, this can be achieved by the control unit successively switching ohmic resistors with different resistance values ​​into the discharge circuit during the discharge process. For example, a 40 mΩ discharge resistor is switched into the discharge circuit first, followed after a certain period by a 60 mΩ discharge resistor, then a 70 mΩ resistor, and so on, until finally a 110 mΩ discharge resistor is present in the discharge circuit.

[0037] This causes the discharge current to decrease over time, so that initially a higher current flows than at the end, as long as the voltage of the secondary battery does not change.

[0038] It is also possible to start with the highest resistance value and then connect resistors with decreasing resistance values ​​into the discharge circuit. As the voltage decreases during discharge, the current remains approximately constant due to the decreasing resistance values.

[0039] If the current increases or decreases during discharge, this can be counteracted by modulating higher resistance values ​​in the discharge circuit in the first case and lower resistance values ​​in the second case.

[0040] The modulation of the discharge current is achieved here by switching resistors with different resistance values ​​into the discharge circuit, so that the current strength of the discharge current always assumes its maximum permissible value.

[0041] This maximum permissible value depends primarily on the temperature of the secondary battery. If the relationship between the temperature of a secondary battery and the discharge curve or the discharge current curve is known, the modulation can be controlled accordingly.

[0042] Resistors with ascending or descending resistance values ​​can be provided as an array of resistors connected in series or parallel. If all resistors are connected in series, a switch is connected in parallel to each resistor, allowing it to be short-circuited. When a resistor is short-circuited, it is not part of the discharge circuit.

[0043] If all resistors are connected in parallel, a switch is arranged in series with each resistor, which can be used to switch the circuit into the discharge circuit.

[0044] Consequently, it is preferred if the electrical load has multiple resistors, and the control unit modulates the discharge current by alternately switching resistors with different resistance values ​​into the discharge circuit.

[0045] Instead of using different discharge resistors that are connected sequentially and individually to the discharge circuit, one embodiment provides that an adjustable discharge resistor in the form of a potentiometer is connected to the discharge circuit, the resistance value of which is adjusted mechanically or electronically by the control unit between, for example, 40 mOhm and 110 mOhm.

[0046] In another version, more or fewer resistors are connected in series or fewer or more resistors are connected in parallel in the discharge circuit.

[0047] All embodiments result in the discharge current being greatest at the beginning of the discharge process, and then decreasing continuously until it reaches a value at which it remains during the remainder of the discharge process or to which it is regulated.

[0048] For the purposes of this application, a control unit is understood to be an electrical or electronic unit in which mechanical and / or electronic switches are provided or which can be controlled by them.

[0049] Furthermore, the control unit can contain a function generator for modulating the discharge current.

[0050] In a simple embodiment, this modulation consists of periodically switching a discharge resistor into the discharge circuit. For an initial period T1, the resistor is in the discharge circuit, through which a discharge current flows. For a subsequent second period T2, the resistor is not in the discharge circuit, so no discharge current flows. Then, the first period T1 with the discharge resistor in the discharge circuit follows again, then for T2 it is not, and so on. The function generator specifies the clock frequencies TK, T1, and T2 and varies them as needed.

[0051] The clock frequency TK, with which the discharge current is switched on and off, is calculated according to TK = 1 / (T1 + T2).

[0052] The inventors of the present application have recognized that by modulating the discharge current, it is possible to quickly bring the battery cells to a temperature that is below the critical temperature for self-ignition, but high enough to reduce the internal resistance of the energy storage device to such an extent that a high discharge current flows, leading to rapid discharge.

[0053] In the case of a lithium-ion battery cell, the internal resistance can thus decrease from, for example, 35 mΩ to 3 mΩ. To achieve this, a high discharge current must be applied at the beginning of the discharge process, which, due to the internal resistance, leads to a rapid increase in the battery cell's temperature. When the temperature rises into the critical range, the discharge current is reduced to prevent the battery cell's temperature from increasing too much.

[0054] In one embodiment, the electrical load is an ohmic resistor (discharge resistor), and the control unit comprises at least one electrical or electronic switch, which is opened and closed, for example, by the function generator at a periodic clock frequency, so that the discharge current is pulsed. The current I of the discharge current flowing when the switch is closed is determined, to a first approximation, according to Ohm's law: I = U / R, where U is the voltage of the battery cell and R is the sum of the value of the internal resistance Ri of the battery cell and the value of the ohmic resistance Rv acting as the electrical load, thus: I = U / (Ri + Rv).

[0055] The time course of the discharge current results in an approximately rectangular curve shape; parasitic capacitances and inductances prevent a pure rectangular shape.

[0056] The current I can now be influenced by changing the clock ratio TV at a given clock frequency TF. Within the scope of this application, clock ratio TV is understood to be the ratio of the time duration TI for the switch being on to the time duration T2 for the switch being off.

[0057] A duty cycle of 1:1 means, for example, that the switch is on and off for the same duration as one period (1 / TF) of the clock frequency (TF). Instead of the duty cycle (TV), the duty cycle (TG) can also be used, which indicates what proportion of the duration of one period (TI) is represented by TG, i.e.: TG = T1 / (T1 + T2).

[0058] A clock ratio TV of 1:1 therefore corresponds to a duty cycle TG of 50%, TV of 10:1 corresponds to TG of 90% and TV of 1:10 corresponds to TG of 10%.

[0059] On average over time, the current Im of the discharge current is calculated from the duty cycle TG as follows: lm = TG x U / (Ri + Rv). Simply by changing TG, l can be determined. m that is, change between zero and the maximum value U / (Ri+Rv).

[0060] However, changing the clock frequency TF has no effect on Im.

[0061] The discharge current can also be modulated between a maximum value and a minimum value, for example by alternately switching a large ohmic resistance Rg (during TI) and a small ohmic resistance Rk (during T2) into the discharge circuit as an electrical load at the clock frequency.

[0062] This results, in addition to the formula above, in an average discharge current Im = TG x U / (Ri + Rk) + (1-TG) x U / (Ri + Rg) = TG x lmax + (1-TG) xl min .

[0063] Switching between two discharge resistors can be advantageous for certain battery cells where abrupt load changes cause problems. Furthermore, this switching can ensure more stable control.

[0064] The control unit therefore clocks or pulses the discharge current between lmax and I min, where I min can be - 0.

[0065] In another embodiment, switching is performed between a discharge resistor and a short circuit, so that the current of the discharge current is greatest in the case of a short circuit and is determined only by the internal resistance of the energy storage device and its tappable voltage.

[0066] By timing or pulsing the discharge current, the strength of the discharge current can be adjusted much more precisely and quickly than by selectively switching on discharge resistors with different resistance values, where only certain current strengths can be set depending on the number and arrangement of the resistors.

[0067] Both methods can also be combined. For example, at the beginning of a discharge, pulsing can ensure rapid heating of the battery, while afterwards a resistor array is used to set an almost constant current so that the temperature is maintained but not exceeded.

[0068] When the voltage and temperature decrease, this is counteracted using resistors with low resistance values.

[0069] For the sake of completeness, it should be mentioned again that the available voltage at the battery terminals can change, and in particular decrease, during discharge. This leads to a decrease in the discharge current, so the resistance value can be reduced to counteract this decrease in discharge current.

[0070] According to the invention, the discharge of the energy storage device begins, for example, with a high duty cycle of 90%. The resulting discharge current leads to rapid heating of the battery cell and thus to a decrease in the value of the internal resistance Ri of the battery cell. Due to the decreasing value of the internal resistance Ri, the discharge current increases at a constant duty cycle, which leads to accelerated heating of the battery cell.

[0071] To prevent excessive heating, the duty cycle is then gradually reduced so that the battery cell does not exceed a target temperature below the critical temperature.

[0072] The duty cycle allows for very precise and rapid control of the discharge current.

[0073] The time course of the duty cycle, i.e. its gradual decrease during discharge, can follow fixed values ​​that have proven useful for the respective type of battery cell based on experience or previous measurements.

[0074] The advantage of this type of modulation is that it is very easy to implement and easy to control.

[0075] Pulsed discharge leads to faster heating of the energy storage device than if it were discharged with a lower continuous current from the start. Because the heating is proportional to I 2Doubling the current leads to a quadrupling of the energy available for heating.

[0076] In a simple embodiment, the duty cycle can be 50% continuously or only at the beginning of the discharge, and further modulation can be achieved via a resistor array. This results in twice the average current l flowing during TI. m , so that the energy storage device heats up quickly, because doubling the current leads to a fourfold increase in heating.

[0077] According to the inventors, the cooling during the power-free period T2 does not compensate for the faster heating during the period TI.

[0078] Once the energy storage device reaches its target temperature, the discharge current is modulated by switching resistors on or off to keep the device below its critical temperature. This modulation can be further enhanced by pulsing the discharge current. However, it is also possible to operate with a continuous discharge current after reaching the target temperature, thus discontinuing the pulsing.

[0079] As already mentioned, pulsing allows for a precise and rapid change in the average current l m , so that the energy storage device can be kept safely below, but as close as possible to, its critical temperature, resulting in very rapid discharge, if desired even to irreversible deep discharge.

[0080] A particular advantage of the new methods and devices is that the energy storage devices can be safely discharged, regardless of whether their state of charge is known, what type of battery it is, or whether the batteries have strong parameter variations due to production.

[0081] The process is inherently safe because every battery discharged using this method is protected from exceeding its own temperature limit.

[0082] Tests have shown that a secondary battery discharges significantly faster if the average discharge current is not drawn as a constant current in a continuous waveform, but is modulated according to the new method.

[0083] In an initial verification test using a provisional setup, a secondary battery was discharged at a target temperature chosen to be a safe distance below the critical temperature. The secondary battery was connected to an 80 mΩ discharge resistor, and the discharge current was modulated with a 1:1 duty cycle. After approximately 12 minutes, the energy storage device was discharged to below 0.5 V.

[0084] In a comparative test, the secondary battery was then discharged without pulsing through a 160 mΩ discharge resistor. After approximately 15 minutes, the energy storage device was discharged to below 0.5 V.

[0085] The output voltage was 3.7 volts in both cases, so the initial mean discharge current l mIn both tests, the current was comparatively low, at approximately 23 A. This result shows that the discharge time can be significantly reduced without compromising safety simply by modulating the discharge current.

[0086] The discharge time can be further reduced by increasing the discharge current, which is why it is preferred if the device includes a temperature sensor connected to the control unit and the discharge current is regulated depending on the temperature of the energy storage device.

[0087] The advantage here is that the current temperature of the battery cell is recorded during discharge and used as the actual value of the controlled variable in a control loop, where the duty cycle is the manipulated variable and a target temperature below the critical temperature is the setpoint of the controlled variable. The duty cycle is then adjusted so that the target temperature is reached but not exceeded.

[0088] While predefined values ​​for the duty cycle already result in a noticeable reduction in the time required for deep discharge of a battery cell, the previously described control method can further reduce this time considerably because the safety margin between the target temperature and the critical temperature is greater with a fixed predefined time curve than with a control method that prevents exceeding the critical temperature.

[0089] In the case of measuring the battery cell temperature, the target temperature can therefore be very close to the critical temperature, which leads to a very rapid discharge of the battery cell.

[0090] The transfer function of the control system should exhibit PL behavior, because this leads, on the one hand, to a rapid approach of the battery cell temperature to the target temperature and, on the other hand, keeps the temperature relatively constant.

[0091] If overshoots in the actual temperature of the battery cell need to be avoided, a control system with PID behavior should be used.

[0092] In the new method, it is even preferred if the energy storage device is discharged to such a maintenance charge that it can be safely stored and transported without losing its storage function.

[0093] In addition to the rapid deep discharge of energy storage devices, the new method and the new device can also be used to quickly discharge energy storage devices to such an extent that they can be stored and transported for later (further) use.

[0094] In other words, lithium-ion batteries discharge quickly but not below their irreversible limit. The voltage range would therefore not be exceeded.

[0095] On the other hand, it is preferred if the new device includes a short-circuit plug for the energy storage device, so that a deeply discharged energy storage device can be safely stored, transported and disassembled for recycling after the short circuit, without the risk of partial recovery of the battery charge through internal chemical processes.

[0096] The new device can be used as follows:

[0097] One purpose is the deep discharge of energy storage devices, especially secondary batteries based on lithium-ion storage technology, towards the end of their functional lifespan, so that they can be safely stored, transported and dismantled without the risk of (spontaneous) self-ignition.

[0098] The new device can be used as a mobile unit on service and emergency vehicles and / or as a stationary unit at recycling centers, gas stations and workshops and / or as a small handheld unit for emergencies.

[0099] Another application is discharging energy storage devices to a safe state of charge. A safe state of charge refers to a maintenance charge from which the energy storage device can be recharged and used again without problems, because its storage function is not impaired despite the rapid discharge.

[0100] This use enables safe storage and / or safe transport of used or new secondary batteries as well as safe repair of a vehicle equipped with the energy storage device, without having to dismantle the energy storage device, because according to the invention it can be quickly brought to a safe state of charge.

[0101] If the new device is used as an on-board unit (OBU) for an electric vehicle or a vehicle with an electric battery, it can quickly deep discharge a vehicle battery if it is in danger of reaching the critical temperature.

[0102] This measure offers advantages in the event of an accident, during transport, repairs, and extended periods of inactivity. When installed, the OBU quickly and immediately discharges the battery after an accident, even before emergency services arrive. This protects occupants and rescue personnel from electric shocks and spontaneous combustion. The OBU can be retrofitted or installed as an original equipment addition to the vehicle's electrical system.

[0103] The electrical device may not be included in the OBU; instead, the second connections are provided for connecting an electrical device that the rescue workers bring or that is available in the workshop.

[0104] The OBU may also contain an electrical component requiring external cooling. A cooling port is provided for this purpose. In one embodiment, the cooling port is a simple water connection to which a water hose is attached to cool the electrical component integrated into the OBU, which in one configuration is an ohmic discharge resistor.

[0105] Another potential application arises in connection with battery storage systems and suitable charging devices in large energy parks, public or private parking lots, and company parking lots, where the new device enables the rapid withdrawal of electrical energy. The electrical consumer in this case is the power grid, and the new device contributes to grid stability. Electric cars would then essentially be mobile, decentralized energy storage units.

[0106] The new device, together with a suitable charging device, can also be used to investigate and / or induce battery aging. Due to its rapid discharge, numerous charging cycles can be performed in a very short time, resulting in a time advantage compared to previous discharge technologies.

[0107] Further advantages are outlined in the description and the accompanying drawing.

[0108] It is understood that the features mentioned above and those to be explained below can be used not only in the combination specified, but also in other combinations or on their own, without leaving the scope of the present invention.

[0109] An embodiment of the invention is shown in the accompanying drawing and is explained in more detail in the following description. The drawing shows: Fig. 1 shows a first embodiment of the new device for discharging an energy storage device; Fig. 2 shows a second embodiment of the new device for discharging an energy storage device; Fig. 3 shows a current-time diagram to illustrate the basic modulation of the discharge current in the device from Fig. 1; Fig. 4 shows a first embodiment of an array of discharge resistors connected to the device from Fig. 1; and Fig. 5 shows a second embodiment of an array of discharge resistors connected to the device from Fig. 1.

[0110] Fig. 1 schematically shows a first embodiment of a device 10 for discharging an energy storage device 12 connected to first electrical terminals 11 of the device 10, which in the embodiment shown is a secondary battery 13 based on lithium-ion technology.

[0111] The device 10 has second electrical connections 14, to which an electrical consumer 15 is connected, which here is designed as an ohmic resistor and is also referred to as a discharge resistor 16.

[0112] The device 10 contains an electrical control unit 17, which is connected via the first and second electrical terminals 11, 14 to the secondary battery 13 and the discharge resistor 16 to form a discharge circuit 18 in which a discharge current 19 flows.

[0113] Different secondary batteries 13 can be connected to the device 10 via the first terminals 11 and discharged with it, and, if desired, irreversibly deep-discharged. For this purpose, suitable electrical loads 15 are connected to the second terminals 14.

[0114] Instead of discharge resistors 16, which convert and radiate the electrical energy extracted from the secondary battery into ohmic heat, chargers for battery storage, electrolysis devices for water or pumps, etc., can also be connected in order to not release the extracted electrical energy to the environment as heat, but to store it again as electrical energy, in the form of Hz or otherwise, for later use.

[0115] The timing of the discharge current 19 is modulated by the control unit 17, which for this purpose comprises a function generator 20 and a module 21 that, in the simplest case, contains mechanical or electronic switches. The function generator 20 causes the switches in the module 21 to open and close, if necessary, periodically.

[0116] Figure 2 shows a second embodiment of a device 22 for discharging, and if desired, deep discharging, an energy storage device 12, which is then reconnected to the first terminals 11. Unlike the device 10 in Figure 1, in the device 22 of Figure 2, the electrical load 15 is integrated into the device 22 and connected to a cooling inlet 23, through which the load 15 is supplied with coolant and cooled, for example. The coolant absorbs and dissipates the heat generated in the load 15 as a result of discharging the energy storage device 12. The dissipated heat can be used, for example, in heat engines.

[0117] The device 22 can be associated with a temperature measuring device 24, with which the temperature of the energy storage unit 12 is measured and transmitted to the control unit 17.

[0118] As already mentioned, the time course of the discharge current 19 is modulated by the function generator 20 opening and / or closing switches in the assembly 21 as required.

[0119] Figure 3 shows a current diagram 25 as an example of the time course of the discharge current 19. In the current diagram 25, the current I is shown on the vertical axis 26 and the time t is shown on the horizontal axis 27.

[0120] During a first time interval TI, the current I is switched on; during a second time interval T2, it is switched off. TI and T2 can remain constant or be changed during the discharge of the energy storage device 12, thereby modulating the discharge current 19.

[0121] The average current l m is calculated from the current strength of the ion during TI according to l m = Ion x T1 / (T1 + T2). By changing the clock ratio TI : T2, denoted here by TV, it is possible to... mThey can be controlled. A TV ratio of 1:1 means that TI and T2 are the same length.

[0122] If Im is to be increased, TV is increased, e.g. to 2:1, and if Im is to be decreased, TV is reduced, e.g. to 1:5.

[0123] This modulation ensures that the discharge current 19 is high at the beginning of a discharge process, so that the energy storage device 12 heats up quickly. Afterwards, the discharge current 19 is reduced to prevent the energy storage device 12 from rising to its critical temperature, at which there is a risk of spontaneous combustion.

[0124] Pulsed current control is easy to implement in terms of circuitry and enables fast control. Due to the pulsing, a discharge current 19 flows during TI with a higher current than l. m , which despite an average current intensity acceptable for the energy storage system 12 l mThis causes the energy storage device 12 to heat up faster than if a discharge current of current l were constantly applied. m would flow.

[0125] This heating leads to a reduction in the internal resistance of the energy storage device. If the temperature is below the critical temperature for auto-ignition, but high enough to reduce the internal resistance of the energy storage device to such an extent that a high discharge current flows, this results in rapid discharge.

[0126] The modulation of the discharge current 19 by changing TV can be carried out using preset parameters based on empirical values.

[0127] The discharge process becomes even safer and faster if TV is selected based on the actual temperature of the energy storage device. Then, by appropriately adjusting TV, it can be ensured that the energy storage device 12 is quickly brought down to a temperature just below its critical temperature.

[0128] Once this target temperature is reached, the discharge current 19 is reduced to prevent further heating. If the temperature of the energy storage device 12 drops, TV, and thus the discharge current 19, is increased again.

[0129] If the temperature measuring device 24 is provided, TV is changed depending on the measured temperature of the energy storage device 12, so that its temperature can be kept very close to the critical temperature.

[0130] Regardless of whether their state of charge is known, what type of battery they are, or whether the batteries have strong parameter variations due to production, energy storage devices of any design can be safely and quickly discharged because every battery discharged using the new method is protected from exceeding its own critical temperature.

[0131] Once the deep discharge is complete, the energy storage device 12 is short-circuited to prevent recovery. For this purpose, a short-circuit plug 28 is provided, which is shown schematically in Fig. 2 and has terminals 29 for the terminals of the energy storage device 12 (not shown).

[0132] The electrical load 15 can also be configured as an array of resistors with different resistance values. The control unit 17 then modulates the discharge current 19 by alternately switching resistors with different resistance values ​​into the discharge circuit 18, as will now be discussed with reference to Figures 4 and 5.

[0133] In Fig. 4, an array 31 of resistors 32 and switches 33 is connected to the second terminals 4 of the device 10 from Fig. 1. These switches are actuated by the control unit 17. Each resistor 32 is connected in series with a switch 33, and these series circuits are connected in parallel. A switch 34 with a short-circuit section 35 is connected in parallel with these series circuits. When all switches 32 and 34 are open, no discharge current 19 flows.

[0134] A secondary battery 13 is connected to the first terminals 11 of the device 11, the internal resistance of which is indicated at 36.

[0135] By opening or closing switches 33 and 34, individual resistors 32 or multiple resistors 32 can be connected in parallel to the second terminals 14 and used as an electrical load to discharge the secondary battery 13. When switch 34 is closed, the array 31 is short-circuited and the discharge current 19 is determined solely by the internal resistance 36.

[0136] In Fig. 5, an array 41 of resistors 42 and switches 43 is connected to the second terminals 14 of the device 10 from Fig. 1. These resistors and switches are also controlled by the control unit 17. Each resistor 42 is connected in parallel to a switch 33, and these parallel circuits are connected in series. A switch 44 is arranged in series with this series circuit. When switch 44 is open, no discharge current 19 flows.

[0137] The secondary battery 13 with internal resistance 36 is connected to the first terminals 11 of the device 11.

[0138] By opening or closing the switches 43, individual resistors 42 or multiple resistors 42 can be connected in series to the second terminals 14 and used as an electrical load to discharge the secondary battery 13. If all switches 43 are closed, the array 31 is short-circuited and the discharge current 19 is determined solely by the internal resistance 36.

[0139] The current profile of the discharge current is modulated by the control unit 17 successively switching resistors 32 and 42 with different resistance values ​​into the discharge circuit during the discharge process. If the current increases or decreases during the discharge, this can be counteracted by switching higher resistance values ​​into the discharge circuit in the first case and lower resistance values ​​in the second case.

[0140] The modulation of the discharge current is achieved here by switching resistors with different resistance values ​​into the discharge circuit, so that the current strength of the discharge current always assumes its maximum permissible value.

[0141] This modulation can be carried out using preset parameters that were determined in advance for different energy storage devices and represent average empirical values.

[0142] For safety reasons, these parameters must be chosen so that the temperature of the energy storage device 12 is sufficiently far below its critical temperature. This comes at the expense of the discharge rate.

[0143] As with pulsed discharge, when using different resistors 32, 42 optionally connected in the discharge circuit, the temperature of the energy storage device 12 can be measured and used to control the discharge current as a function of the temperature of the energy storage device 12.

[0144] The pulsed modulation of the discharge current discussed with reference to Fig. 3 enables a fast and precise adjustment of the discharge current strength, so that the target temperature can be close to the critical temperature, which allows for very fast discharge, especially deep discharge.

[0145] In contrast, modulation via different resistors connected in the discharge circuit, as shown in Figures 4 and 5, requires a simpler setup. However, the discharge current cannot be modulated as precisely and quickly as with pulsed modulation.

[0146] Both methods can also be combined by inducing rapid heating and thus a reduction in the internal resistance of the energy storage device 12 at the beginning of a discharge process through pulsed modulation, and then modulating the discharge current with constant TV by switching resistors on and off.

[0147] Initial tests have shown that a constant duty cycle of 1:1 is sufficient to achieve a rapid heating phase, and that during the subsequent discharge process it is also possible to operate without switching, i.e. with a continuous discharge current that is only modulated by switching the resistors.

[0148] With this combination of the two previously described methods for modulating the discharge current, it is not necessary to adjust TV over such a wide range as is desirable for purely pulsed discharge. TV can even be constant and used only during the heating phase.

[0149] This combination allows the TV's adjustment range to be reduced or even set to a constant value, with the duty cycle potentially reaching 100% after the warm-up phase. The control unit 17 can therefore have a simple design.

Claims

Patent claims 1. Method for discharging, preferably deep discharging, energy storage devices (12), in which the energy storage device (12) is connected to an electrical consumer (15) and a control unit (17) to form a discharge circuit (18) for a discharge current (19), characterized in that the control unit (17) modulates the discharge current (19).

2. Method according to claim 1, characterized in that the control unit (17) switches the discharge current (19) on and off with a clock rate TR and a clock ratio TV.

3. Method according to claim 2, characterized in that the clock rate TR is between 0.5 and 1800 Hz, preferably at approximately 10 Hz.

4. Method according to claim 2 or 3, characterized in that the clock ratio TV is between 1:10 and 10:1, preferably 1:

1.

5. Method according to one of claims 1 to 4, characterized in that the electrical consumer (15) comprises at least one ohmic resistor (16, 32, 42).

6. Method according to one of claims 1 to 5, characterized in that the control unit (17) regulates the discharge current (19) depending on the temperature of the energy storage device (12).

7. Method according to one of claims 1 to 6, characterized in that the energy storage device (12) is a secondary battery (13).

8. Method according to one of claims 1 to 7, characterized in that the energy storage device (12) is discharged to a maintenance charge.

9. Method according to any one of claims 1 to 8, characterized in that the electrical load (15) has several resistors (32, 42), and the control unit (17) modulates the discharge current (19) by alternately switching resistors (32, 42) with different resistance values ​​into the discharge circuit (18).

10. Device for discharging, preferably deep discharging, energy storage devices (12), with first electrical connections (11) for the energy storage device (12), a control unit (17), and an electrical load (15), or second electrical connections (14) for an electrical load (15), wherein the control unit (17) is connected to the energy storage device (12) and, optionally, the electrical load (15) to form a discharge circuit (18) for a discharge current (19). characterized in that the control unit (17) is configured to modulate the discharge current (19).

11. Device according to claim 10, characterized in that the electrical consumer (15) comprises at least one ohmic resistor (16, 32, 42).

12. Device according to claim 10 or 11, characterized in that the control unit (17) comprises a function generator (20).

13. Device according to one of claims 10 to 12, characterized in that it comprises a temperature measuring device (24) connected to the control unit (17).

14. Device according to one of claims 10 to 13, characterized in that the control unit (17) is configured to modulate the discharge current according to the method of one of claims 1 to 9.

15. Device according to one of claims 10 to 14, characterized in that the electrical consumer (15) is connected to it, wherein a cooling access (23) for the electrical consumer (15) is provided on the device (10).

16. Device according to any one of claims 10 to 15, comprising a short-circuit plug (28) for the energy storage device. (12).

17. Use of the device (10, 22) according to one of claims 10 to 16 for deep discharging energy storage devices towards the end of their functional lifespan, and / or for discharging energy storage devices to a safe state of charge, and / or as an on-board unit for an electrically powered vehicle, and / or in connection with battery storage systems and suitable charging devices in large storage parks, on public or private parking lots as well as company parking lots for the rapid extraction of energy, and / or for the investigation and / or induction of battery aging, with suitable charging devices.

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