Method for operating a rechargeable lithium-containing and / or sodium-containing battery

Abstract

Method (24) for operating a rechargeable, lithium-containing and / or sodium-containing battery (14), in which in a discharge state (32) and when a condition (28) is present, the battery (14) is actively discharged further, wherein the discharge state (32) corresponds to the charge state of the battery (14) from which the final discharge voltage is applied to it, wherein a specific electrical voltage (36) is applied to the battery (14) for discharging.

Description

[0001] The invention relates to a method for operating a rechargeable lithium-containing and / or sodium-containing battery. Furthermore, the invention relates to a battery system comprising a rechargeable lithium-containing and / or sodium-containing battery and a method for operating a motor vehicle.

[0002] Increasingly, motor vehicles are being powered, at least partially, by an electric motor, resulting in electric or hybrid vehicles. A high-voltage battery, typically comprising several individual battery modules, is used to power the electric motor. These battery modules are usually identical in construction and electrically connected in series and / or parallel, so that the voltage applied to the high-voltage battery is a multiple of the voltage provided by each individual battery module. Each battery module, in turn, contains several batteries, usually housed in a common module casing, which are also electrically connected in series and / or parallel.

[0003] Each battery typically comprises several battery cells, also known as a galvanic cell. These cells each have two electrodes, namely an anode and a cathode, as well as a separator between them and an electrolyte containing freely moving charge carriers. A liquid is one example of a suitable electrolyte. Alternatively, the battery can be a solid-state battery, in which the electrolyte is a solid. The anode and cathode, which form the battery's electrodes, are usually enclosed in a substrate that acts as a current collector. An active material is typically attached to this substrate; this active material is part of a layer applied to the substrate. The electrolyte may already be present in this layer, or it may be added subsequently.At the very least, the active material is suitable for absorbing the working ions, e.g., lithium ions. Depending on its use as an anode or cathode, a different material is used for the support and a different type of layer material.

[0004] During relatively rapid battery charging, lithium can accumulate at the edges of the anode surface. This kinetically delays and / or prevents further lithium penetration into the layer and thus reaction with the active material in this area. Consequently, the battery's capacity is reduced. To address this problem, known as lithium plating or simply plating, the anode is made larger than the cathode, creating a supernatant. When the battery is stored at a high state of charge, some of the lithium diffuses into this supernatant. Within this supernatant, the movement of lithium ions towards the cathode is kinetically inhibited. Therefore, a reduced amount of lithium is available for charge transport, which also reduces the battery's capacity, albeit to a lesser extent.

[0005] Consequently, it is necessary to choose a relatively precise ratio between the size of the anode and the cathode so that the two negative effects are comparatively small and an optimum is achieved while maintaining capacity. This necessitates relatively tight manufacturing tolerances, which increases production costs. Alternatively, a relatively thin layer can be chosen, but this leads to a reduced energy density. Another option is to reactivate the deactivated lithium, which typically involves heating the battery. However, this leads to increased energy consumption and thus reduced efficiency. It is also possible that additional thermally induced chemical reactions may occur within the layer, leading to further undesirable effects.

[0006] The invention is based on the objective of providing a particularly suitable method for operating a rechargeable lithium-containing and / or sodium-containing battery, a particularly suitable battery system with a rechargeable lithium-containing and / or sodium-containing battery, and a particularly suitable method for operating a motor vehicle, wherein an energy density is advantageously increased and / or safe operation is enabled and / or aging effects are reduced.

[0007] German patent application DE 10 2013 204 527 A1 discloses a method for monitoring a battery cell. If a limit value for a permissible charging current is exceeded, lithium deposits can occur. When this is detected, the cell is to be discharged or quickly discharged and / or a bypass activated so that no further charging current flows into the electrochemical battery cell.

[0008] From DE 24 46 958 A1, a device for monitoring the state of discharge of a battery is known. The reading of a display device is influenced by a discharge current and a battery voltage.

[0009] DE 101 58 029 A1 discloses a method for determining the dynamic state of charge of a battery subjected to periodic charging and discharging in a system. Correction factors are determined for various operating conditions of current, temperature, and state of charge, which are related to a relative discharge and charge efficiency, using a reference set of conditions.

[0010] DE 100 06 420 A1 shows an operating control system for rechargeable batteries.

[0011] With regard to the method for operating a battery, this problem is solved according to the invention by the features of claim 1, with regard to the battery system by the features of claim 8, and with regard to the method for operating a motor vehicle by the features of claim 9. Advantageous further developments and embodiments are the subject of the respective dependent claims.

[0012] The method serves to operate a rechargeable, lithium-containing battery. The battery is therefore, in particular, a secondary battery. Preferably, the battery, in its intended state, is a component of a motor vehicle. The battery is suitable for this purpose, and in particular designed and configured for it. In its intended state, the battery is, for example, a component of a motor vehicle battery system that comprises several such batteries. Preferably, the batteries are divided into several battery modules, which are identical in construction. The batteries are, in particular, arranged in a housing of the battery system or the respective battery module and are electrically connected in parallel and / or in series with one another. Thus, the electrical voltage applied to the battery system / battery module is a multiple of the electrical voltage provided by each of the individual batteries.Conveniently, all batteries are identical in construction, which simplifies manufacturing.

[0013] The housing of the battery system or the respective battery module is preferably made of a metal, for example, steel such as stainless steel, or an aluminum alloy. Manufacturing processes include, for example, die casting, deep drawing, casting presses, or extrusion. In particular, the housing of the battery system or the respective battery module is designed to be sealed. Advantageously, an interface is incorporated into the housing of the battery system or the respective battery module, forming a connection for the battery system / battery module. This interface is electrically connected to the batteries, allowing electrical energy to be supplied to and / or withdrawn from the batteries from outside the battery system, provided a suitable connector is plugged into the connection.

[0014] The motor vehicle can be used for maritime applications or be an aircraft, but is preferably land-based and preferably has a number of wheels, at least one, preferably several or all, of which are driven by a drive system. In particular, one, preferably several, of the wheels is designed to be steerable. Thus, it is possible to move the motor vehicle independently of a specific roadway, such as rails or the like. It is advantageously possible to position the motor vehicle essentially arbitrarily on a roadway, which is made, in particular, of asphalt, tar, or concrete. The motor vehicle is, for example, a commercial vehicle such as a truck or a bus. However, it is particularly preferred that the motor vehicle be a passenger car.

[0015] The drive system expediently propels the motor vehicle. For example, the drive system, particularly the main drive, is at least partially electric, and the motor vehicle is, for instance, an electric vehicle. The electric motor is powered, for example, by the battery system, which is suitably designed as a high-voltage battery. The high-voltage battery expediently provides a direct current voltage, the voltage being, for example, between 200 V and 800 V, and, for example, substantially 400 V. Preferably, an electrical converter is arranged between the battery system and the electric motor, by means of which the current supplied to the electric motor is regulated. Alternatively, the drive system also includes an internal combustion engine, so that the motor vehicle is designed as a hybrid vehicle.Alternatively, the battery system supplies a low-voltage electrical system of the motor vehicle, and in particular, the battery system provides a direct current voltage of 12 V, 24 V or 48 V.

[0016] In another alternative scenario, the battery is a component of a forklift, an industrial plant, or a handheld device, such as a power tool, particularly a cordless screwdriver. In yet another alternative scenario, the battery is part of a power supply system and is used, for example, as a buffer battery. In yet another alternative scenario, the battery is a component of a portable device, such as a mobile phone or other wearable. It is also possible to use such a battery in camping, model making, or for other outdoor activities.

[0017] The battery preferably comprises an anode and a cathode, which in particular form the electrodes of the battery. Advantageously, a separator is arranged between the anode and the cathode. The electrodes preferably comprise a metallic current collector, also referred to as a support. This is made of a metal and provided with an active material. The active material serves to absorb working ions and is suitable, designed, and configured for this purpose. For example, an alkali metal oxide, such as sodium metal oxide or a lithium metal oxide, such as lithium cobalt(III) oxide (LiCoO2), NMC, for example NMC622 or NMC811, NCA, LFP, or Prussian blue derivatives, is used as the active material for the cathode, and GIC, LTO, graphite, silicon-based, hard carbon, or silicon-based materials are used for the anode. In particular, the active material is a component of a respective layer that is applied to the respective current collector.The layer advantageously comprises a conductive additive, such as conductive carbon black, and, for example, a binder. Aluminum is used, for example, as the metal of the cathode conductor, and copper as the metal of the anode conductor. In particular, the conductors are designed in a foil-like form and advantageously have a thickness of less than 0.1 mm. Preferably, the battery comprises several such anodes and cathodes, which are preferably stacked on top of each other, with a separator preferably arranged between each. Alternatively, the anodes / cathodes are arranged as wound electrode strips, in particular as so-called "jelly rolls".

[0018] The battery contains lithium or sodium. In other words, the battery comprises lithium (atoms) and / or sodium (atoms), and in particular, the lithium / sodium is used for the operation of the battery. Specifically, working ions are formed by means of lithium ions (lithium ions) / sodium ions, and any electrolyte comprises corresponding lithium ions / sodium ions or at least a chemical compound with lithium ions / sodium ions. The active material is suitablely designed to hold the lithium ions / sodium ions. Alternatively or in combination with this, the active material comprises lithium / sodium, which undergoes a chemical reaction, particularly during operation of the battery, i.e., during charging and / or discharging. In other words, the charge state or valence of the lithium / sodium, or at least of lithium / sodium ions or lithium / sodium atoms, changes during operation of the battery.In summary, one of the electrodes and / or the electrolyte in particular comprises lithium / sodium.

[0019] The procedure stipulates that, in a discharge state and under certain conditions, the battery is actively discharged further. In this discharge state, the battery is already discharged, and it is specifically not possible to operate another device, for whose operation the battery is intended and used, or any other component. In this discharge state, the battery has reached the lower end of the defined operating conditions and cannot be discharged by the user without further effort. Specifically, in this discharge state, energy extraction from the battery is not possible without changing the operating conditions and / or without additional effort. However, the state of charge (SOC) is greater than 0%, so electrical energy is still stored in the battery.However, extracting this energy from the battery is essentially impossible for the user, or only possible with additional effort. In other words, extracting the energy still stored in the battery requires an (external) (energy) input.

[0020] The condition is particularly flexible and adaptable, and is determined primarily based on current requirements. For example, the condition is met when the discharge state is reached. For instance, the condition is met when the battery capacity falls below a certain value due to multiple charging and discharging cycles, and / or when a specific number of charging and / or discharging cycles have occurred. With a corresponding number of charging cycles, lithium / sodium is deposited on the anode, particularly in the area of ​​any anode overhang. Consequently, this lithium / sodium is not available for subsequent charging and discharging cycles, thus reducing the battery's capacity. Preferably, the condition is also met when the battery is electrically connected to an external voltage source.

[0021] During active battery discharge, the electrical energy still stored in the battery is extracted, requiring additional processes. Specifically, the battery is forcibly discharged. In other words, energy is applied from outside the battery to remove the electrical energy stored within it. Consequently, the battery's state of charge is further reduced. As a result of active discharge, any lithium / sodium deposited on the anode(s) that is not used during normal charging cycles—especially inactivated lithium or sodium located in the area of ​​any anode overhang—is released due to the additional energy input or other processes. This lithium / sodium is then transferred into the electrolyte. In summary, active discharge actively delithizes the lithium / sodium.Denatrical treatment of the anode(s) was carried out, particularly in the area of ​​any anode overhang / protrusion.

[0022] Due to the delithization of the anode(s), a larger number of lithium / sodium ions are available during subsequent charging, thus increasing the battery's capacity, for example, to its original value or at least to a value greater than before the process. This eliminates or reduces aging effects, and it makes it possible to design the electrode layers to be comparatively thick, thereby increasing the battery's energy density. Furthermore, this method of capacity regeneration essentially avoids uncontrolled chemical reactions, ensuring safe operation.

[0023] In particular, as a final step or after completion of the process, the battery is recharged so that it can then be used to power other components. For example, in this process, the battery is first passively discharged—that is, without any energy input, effort, or the like—in particular by powering the intended component / device until the discharge state is reached. In a further development, active discharge occurs even before the discharge state is reached, so that the discharge state is also achieved through active discharge. This occurs, for example, when a certain condition or another condition is met.

[0024] For example, the battery manufacturer specifies the state of discharge for the user. Preferably, the state of discharge is defined as the point at which the battery can be discharged with a constant current. When the battery's state of charge is higher, it discharges with a constant current, and from a lower state of charge, the current decreases continuously during discharge. The state of charge at which this transition occurs is specifically considered the state of discharge. In particular, for the user of the battery and / or due to the intended use of the battery, discharging with a constant current at a state of charge lower than the state of discharge is not possible.

[0025] The discharge state corresponds to the state of charge of the battery at which the discharge cut-off voltage is applied. This cut-off voltage is determined primarily by the battery's chemical composition, such as the electrodes, and corresponds to a minimum electrical voltage present after the battery has discharged, especially before deep discharge occurs. If the battery continues to discharge, the discharge cut-off voltage will not be undershot; however, at a higher state of charge, the applied electrical voltage will be greater than the discharge cut-off voltage. For example, the discharge cut-off voltage is specified by the battery manufacturer.In particular, the state of discharge thus corresponds to the state of charge of the battery, from which a change occurs between a discharge with a constant (electric) current to a decreasing electric current and a change from a discharge with a decreasing electric voltage to an electric DC voltage, whereby in particular the state of charge is greater than 0%.

[0026] To discharge the battery, a specific electrical voltage is applied. Consequently, no additional structural modifications to the battery are required, meaning the process can be carried out on existing batteries. This also makes the process relatively simple and inexpensive. The applied voltage generates an electric current, which reduces the battery's state of charge.

[0027] For example, the electrical voltage varies over time, allowing a comparatively low state of charge to be achieved through active discharge. However, a direct current (DC) voltage is particularly preferred, which simplifies the process. During discharge, the electrical current varies, becoming dynamic and resulting from the applied DC voltage. Furthermore, this method ensures that the applied DC voltage does not cause deep discharge of the battery, which could lead to irreversible damage.

[0028] The discharge cut-off voltage is particularly preferred as the DC voltage used, and this voltage is determined based on the chemical properties or composition of the battery, especially the active materials used. Using the discharge cut-off voltage ensures that the battery is not deeply discharged and therefore not damaged. For example, a cut-off voltage between 2.5 V and 3.5 V, preferably 3.0 V, is used when the electrode active materials are NMC and silicon and graphite or silicon-containing materials. Preferably, a cut-off voltage between 1.5 V and 2.8 V, preferably 2.0 V, is used when the active materials are LFP and graphite.If the battery is a solid-state battery, a discharge cut-off voltage between 2.5 V and 3.5 V, preferably 3.0 V, is expediently used. Due to the use of these values, a transition to deep discharge is essentially prevented; however, the applied voltage forces the remaining electrical energy contained in the battery to be dissipated, thus resulting in active discharge.

[0029] For example, active discharge is carried out for a specific duration, such as between 1 minute and 5 hours, between 10 minutes and 2 hours, or between 30 minutes and 1 hour. Preferably, however, the discharge is terminated if the current drops below a certain threshold. In other words, the current flowing during discharge is measured and compared to the specified threshold. This ensures that the battery's state of charge corresponds to a specific value after discharge, thus making the battery's state reproducible. Furthermore, this ensures that a minimum amount of lithium / sodium corresponding to the specified threshold is available after the process, thereby achieving a minimum battery capacity.

[0030] For example, the specified limit value is statically predetermined and is, for instance, between 0.01 A and 1 A, or between 0.02 A and 0.5 A. However, it is particularly preferred that the specified limit value depends on the battery's C-rate, i.e., the charging or discharging current relative to its capacity. For example, a battery with a capacity of 225 Ah has a C-rate of 255 A, and a battery with a capacity of 100 Ah has a C-rate of 100 A. In particular, a value between 10% and 2% of the C-rate, and preferably 5% of the C-rate, is used as the specified limit value. Consequently, only a comparatively small discharge current flows when active discharging ends, and the battery's state of charge is comparatively low. Furthermore, such a low state of charge is reached after a relatively short time, so that the battery is available for recharging relatively quickly.

[0031] For example, the discharge process is also terminated if it has already lasted a certain period of time. In other words, even if the current is still higher than the specified limit after the specified period, the discharge is stopped so that the battery can subsequently be used, especially charged. If, for example, only a relatively low discharge current flows at any given time, but it does not fall below the specified limit, particularly due to a certain amount of lithium / sodium deposited on the anode, this ensures that the battery can still be used relatively quickly. Specifically, when the process is repeated, the lithium / sodium that was not removed during the previous active discharge is removed, so that the specified limit is reached during the next attempt.A specific time period is used, for example, between 10 minutes and 5 hours, preferably between 30 minutes and 3 hours, and ideally 2 hours. This ensures that a comparatively large amount of energy is extracted from the battery, so that a relatively large amount of lithium / sodium is available again for further charging cycles. However, this does not excessively increase the duration of the process.

[0032] The battery system comprises a rechargeable lithium and / or sodium battery and a control unit. The lithium or sodium battery includes, in particular, one or more anodes and one or more cathodes, with a separator preferably arranged between adjacent anodes and cathodes. The battery also includes an electrolyte, by means of which working ions are suitably provided. The working ions are preferably lithium ions and / or sodium ions. The battery is operated by means of the control unit, which is, for example, a component of or forms part of a battery management system, according to a method in which, when the battery is discharged and a certain condition is met, the battery is actively discharged further. The control unit is thus suitable for this purpose, and in particular is designed and configured for this purpose.Preferably, the battery system comprises several such batteries, with, for example, all batteries being operated by the same control unit. Alternatively, each battery has its own corresponding control unit. In particular, the battery system has a housing within which the control unit(s) and the battery(ies) are arranged. This simplifies the assembly of the battery system. Preferably, the battery system forms a battery module or, more preferably, an energy storage device, such as a high-voltage battery, for a motor vehicle, preferably a passenger car. The battery system expediently serves to power the main drive system of the motor vehicle.

[0033] The method serves to operate a motor vehicle comprising a rechargeable lithium and / or sodium battery, which is operated according to a method in which, when the battery is discharged and a certain condition is met, it is actively discharged further. Preferably, the motor vehicle includes a control unit, which is, for example, a component of a battery system that also includes the battery. For example, the motor vehicle is a commercial vehicle, such as a truck or bus. Preferably, the motor vehicle is a passenger car. The motor vehicle has, in particular, a drive system with an electric motor, which is powered, in particular, by the battery. In other words, the battery serves to operate the electric motor, especially when it is charged.For example, the drive is a component of an auxiliary unit or, more preferably, a main drive by means of which the motor vehicle is propelled.

[0034] The condition is, in particular, a specific mileage of the vehicle or the elapsed time period, i.e., a specific operating time of the vehicle. For example, a mileage between 30,000 km and 80,000 km, between 40,000 km and 60,000 km, and especially 50,000 km are used as specific conditions. The time period is, for example, a value at which the vehicle is due for maintenance, such as 1 year or 2 years. In particular, the condition is fulfilled cyclically, so that the procedure is executed cyclically. Thus, over a comparatively long period, the battery maintains a certain minimum capacity and consequently the vehicle achieves a certain minimum range, especially if the battery powers the vehicle's drive system.

[0035] For example, whether user input has occurred is used as an additional or alternative condition. Thus, active discharge is only carried out if initiated by a vehicle user. In particular, the user is notified, for example, after a certain mileage or the expiration of a specific time period, so that active discharge should be performed to maintain capacity. If the user confirms this, the battery is actively discharged when it reaches the discharge state. Preferably, an additional condition is that the vehicle, or at least the battery, is electrically connected to an external power source, such as a wallbox or charging station. Alternatively, the process can be carried out in a workshop.

[0036] Furthermore, the invention relates to a corresponding motor vehicle in which the method is carried out. The invention also relates to a charging station or wallbox by means of which the method can be carried out, particularly if the battery is electrically connected to the charging station / wallbox, for example by means of a plug, preferably detachable. Suitablely, after completion of the method or at least after the active discharging has ceased, the battery is recharged by means of the charging station / wallbox so that the battery can subsequently be used, in particular for powering the motor vehicle's drive system.

[0037] The advantages and further training described in connection with the two processes can also be applied analogously to the battery system / the motor vehicle / the charging station / wallbox as well as to each other and vice versa.

[0038] An embodiment of the invention is explained in more detail below with reference to a drawing. The drawing shows: Fig. 1 schematically simplified, a motor vehicle that has a battery system with several identical rechargeable lithium and / or sodium batteries, and Fig. 2 a method for operating a motor vehicle, comprising a method for operating a rechargeable lithium and / or sodium battery.

[0039] Corresponding parts are marked with the same reference symbols in all figures.

[0040] In Fig. Figure 1 schematically simplifies the representation of a motor vehicle 2 in the form of a passenger car. The motor vehicle 2 has a number of wheels 4, at least some of which are driven by a drive 6 comprising an electric motor. Thus, the motor vehicle 2 is an electric vehicle or a hybrid vehicle. The drive 6 includes an inverter that supplies power to the electric motor. The inverter of the drive 6, in turn, is powered by a battery system 8 in the form of a high-voltage battery. For this purpose, the drive 6 is connected to a control unit 10 of the battery system 8, which is integrated into a wall of a stainless steel housing 12 of the battery system 8.

[0041] Within the housing 12 of the battery system 8, several batteries 14 are arranged, which in one embodiment are divided into different battery modules. At least some of the batteries 14 are connected electrically in series with each other, and these modules are in turn connected electrically in parallel with each other. The batteries 14 are identical in construction and each has several anodes and cathodes, which are arranged in a respective battery housing and stacked on top of each other, with a separator between each stack. Each battery housing is also filled with a specific electrolyte. The electrolyte provides working ions, namely lithium ions and / or sodium ions, which are attached to an active material of the anode or cathode during charging or discharging. Consequently, the batteries 14 contain lithium or sodium, and lithium and / or sodium serve as charge carriers during the operation of the batteries 14.

[0042] The batteries 14 are electrically connected to the control unit 10. Due to the electrical circuitry, the voltage supplied to the control unit 10, which is 400 V, is a multiple of the voltage supplied to each of the batteries 14. The control unit 10 controls the withdrawal of electrical energy from the battery system 8. It also allows the supply of electrical energy to the batteries 14 via the control unit 10. Selective charging or discharging of the individual batteries 14 is possible via the control unit 10, and the control unit 10 forms a battery management system for the battery system 8.

[0043] Here, it is possible to supply electrical energy to the drive 6 and from there back to the batteries 14 using the control unit 10, for example during braking. It is also possible to exchange electrical energy between the batteries and a connector 16, which is installed in an outer wall of the vehicle 2. The connector 16 corresponds to a mating connector 18 of a charging station 20, so that the mating connector 18 can be plugged into the connector 16. As a result, an energy exchange between the charging station 20 and the vehicle 2, namely the battery system 8, is enabled.

[0044] The motor vehicle 2 is operated in accordance with a procedure 22 for the operation of a motor vehicle 2, which is in Fig.Figure 2 is shown. Here, the procedure 22 for operating the motor vehicle 2 is carried out at least partially by means of the control unit 10. To carry out the procedure 22 for operating the motor vehicle 2, a procedure 24 for operating a rechargeable, lithium-containing and / or sodium-containing battery 24 is carried out.

[0045] In a first step 26, it is checked whether condition 28 is met. Condition 28 is defined as either the motor vehicle 2 having covered a certain mileage, namely 50,000 km, or a certain period of time, namely two years, having elapsed since the last procedure 24 for operating the battery 14 was carried out. As soon as either of these conditions is met, condition 28 is fulfilled. In a further development, for condition 28 to be met, it is also required that a user of the motor vehicle 2 confirms that the procedure 24 for operating the batteries 14 is to be carried out. For this purpose, the user is first notified by means of a display (not shown in detail) that the additional mileage has been covered or the certain period of time has elapsed since the last execution of the procedure 24 for operating the batteries 14.

[0046] If condition 28 is met and the user inserts the mating plug 18 into the plug 16, thus establishing an electrical connection between the charging station 20 and the battery system 8, a second step 30 is performed. In this step, those batteries 14 are determined that will be used to carry out the procedure 24 for operating the batteries 14. In one embodiment, this may be all batteries 14 of the battery system 8, or only those batteries 14 with a comparatively low remaining capacity may be selected.

[0047] Furthermore, the selected batteries 14, provided they have a state of charge above a state of discharge 32, are discharged via connector 16 and mating connector 18 to the charging station 20, so that electrical energy is transferred to the charging station 20. The discharge current is constant, and no energy is supplied by the charging station 20 to discharge the batteries 14 of the battery system 8. In other words, the batteries 14 are passively discharged to a state of discharge 32. The electrical current flowing between each battery 14 and the charging station 20 is constant.

[0048] After completion of the second work step 30, the batteries 14, for which the procedure 24 for operating the battery 14 is carried out, thus exhibit the discharge state 32. In this state, only the discharge cut-off voltage is applied to the selected batteries 14, and further discharge of the battery would not occur with a constant current. Consequently, the discharge state 32 is defined as the state of charge of the batteries 14 up to which a discharge of the respective battery 14 occurs with a constant (electrical) current.

[0049] In a subsequent third step 34, the selected batteries 14 are actively discharged further by applying a specific electrical voltage 36 to them. This specific electrical voltage 36 is a DC voltage, namely the discharge cut-off voltage of the respective battery 14, which depends on the active material used for the anodes / cathodes of the respective batteries 14. For example, if NMC and silicon are used as the active material, the discharge cut-off voltage is 3 V, and if LFP and graphite are used as the active material, it is 2 V. If the batteries 14 are solid-state batteries, the discharge cut-off voltage is 3.0 volts, which is used as the specific electrical voltage 36.

[0050] Due to the application of a specific electrical voltage 36, an electric current flows from the batteries 14 to the charging station 20, with the decreasing current intensity being monitored. Due to the application of a specific electrical voltage 38, the electrical energy still stored in the batteries 14 is dissipated, leading to delithiation or denatrization of the battery anodes 14. If inactivated lithium or sodium has accumulated on the anodes of the respective batteries 14, for example in the area of ​​an anode overhang, it is released from the anodes and transferred into the electrolyte due to the applied specific electrical voltage 38. The level of the specific electrical voltage 38 ensures that deep discharge of the batteries 14 does not occur.

[0051] The specified electrical voltage 36 is applied until the current falls below a specific limit 38, i.e., until the current drops below the specified limit 38 during discharge. 5% of the C-rate of the respective battery 14 is used as the specified limit 38.

[0052] Following this, a fourth work step 40 is carried out, and the application of the specified electrical voltage 36 is terminated. The fourth work step 40 is also carried out after a specific time interval 42, namely 2 hours after the start of the third work step 34, regardless of whether the current reaches the specified limit value 38. Thus, the fourth work step 40 is carried out no later than 2 hours after the application of the specified electrical voltage 38, and therefore also the application of the electrical voltage 38, i.e., the active discharge of the respective batteries 14.

[0053] Due to the transfer of lithium / sodium into the electrolyte, it is now available for subsequent charging of the batteries 14, which is carried out in a fifth step 44. In this step, electrical energy is transferred from the charging station 20 to the battery system 8, charging the individual batteries 14. The control unit 10 regulates the electrical voltage applied to each battery 14 so that charging follows a specific procedure. After completion of the fifth step 44, the battery system 8 is at least partially charged, and it is possible to operate the drive 6 using the battery system 8 and thus move the vehicle 2.

[0054] The invention is not limited to the embodiment described above. Rather, other variants of the invention can also be derived by a person skilled in the art without departing from the subject matter of the invention. In particular, all individual features described in connection with the embodiment can also be combined with one another in other ways without departing from the subject matter of the invention. Reference symbol list 2 motor vehicles 4-wheeler 6 Drive 8 battery system 10 Control unit 12 cases 14 batteries 16 plugs 18 mating plugs 20 charging stations 22 Procedures for operating a motor vehicle 24 Methods for operating a rechargeable lithium-containing and / or sodium-containing battery 26 first step 28 condition 30 second step 32 Discharge state 34 third step 36 specific electrical voltage 38 certain limit 40 fourth step 42 specific time period 44 fifth step

Claims

[1] Method (24) for operating a rechargeable lithium and / or sodium battery (14) in which, in a discharge state (32) and under a condition (28), the battery (14) is actively discharged further, wherein the discharge state (32) corresponds to the charge state of the battery (14) from which the discharge cut-off voltage is applied to it, wherein a certain electrical voltage (36) is applied to the battery (14) for discharge. [2] Method (24) according to claim 1, characterized by , that the state of charge of the battery (14) is used as the discharge state (32), up to which the battery (14) is discharged with a constant current. [3] Method (24) according to one of claims 1 to 2, characterized by that a direct current voltage is used. [4] Method (24) according to any one of claims 1 to 3, characterized by , that the discharge cut-off voltage is used as the specific electrical voltage (36). [5] Method (24) according to any one of claims 1 to 4, characterized by , that the discharge is aborted if the current during discharge falls below a certain limit (38). [6] Method (24) according to claim 5, characterized by , that 5% of the C-rate is used as a specific limit (38). [7] Method (24) according to claim 5 or 6, characterized by , that the unloading is aborted after a certain period of time (42). [8] Battery system (8) comprising a rechargeable lithium and / or sodium battery (14) and a control unit (10) by means of which the battery (14) is operated according to a method (24) according to any one of claims 1 to 7. [9] Method (22) for operating a motor vehicle (2) which has a rechargeable lithium and / or sodium battery (14) which is operated according to a method (24) according to any one of claims 1 to 7, wherein a certain mileage or the expiry of a certain period of time is used as a condition (28).

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