DE102020133958A1 - Discharging an accumulator unit - Google Patents

Abstract

According to a method for discharging an accumulator unit (2) during a large number of successive discharge intervals, at least one pulse parameter is determined by means of a computing unit (4) as a function of at least one state variable of the accumulator unit (2) and/or as a function of at least one material parameter of the accumulator unit (2). During the discharge intervals, at least one current pulse (9, 9a, 9b) of a time-dependent electrical current is generated by the accumulator unit (2) as a function of the at least one pulse parameter.

Description

The present invention relates to a method for discharging an accumulator unit and a corresponding system.

Separators are used in accumulators, in particular in lithium-ion accumulators, but also in nickel accumulators or lead-acid accumulators, in order to spatially and electrically separate the respective electrodes from one another. The separator is permeable to the respective charge carriers, for example lithium ions. Materials that are used for separators include polymers, for example polyethylene, materials based on glass fibers or other membrane-like or porous materials, in particular plastics or ceramic materials.

When the accumulator is discharged, the charge carriers, for example the lithium ions, pass through the openings or pores of the separator, which can lead to these pores becoming clogged or blocked. This leads to a delay in the discharge process due to an increase in the internal resistance of the battery and the resulting thermal load on the system. The internal resistance of the accumulator depends on various influencing factors, such as the current state of charge, the state of aging or the cell chemistry used in the accumulator.

In addition, other effects can influence the internal resistance, such as the stripping off of solvation shells or the passage of boundary layers by the charge carriers. Such boundary layers can arise, for example, as a result of partial decomposition of the electrolyte at an interface between the electrode and the electrolyte, and are then also referred to as the solid-electrolyte interface, SEI. Furthermore, a physical interface between the electrolyte and the electrode can be provided, for example due to the design, such as a cathode interface, which is particularly relevant when discharging the accumulator.

Against this background, it is an object of the present invention to specify an improved concept for discharging an accumulator unit, through which the thermal load can be reduced.

This object is solved by the respective subject matter of the independent patent claims. Advantageous developments and preferred embodiments are the subject matter of the dependent claims.

The improved concept is based on the idea of dividing the discharge time into several successive discharge intervals, with a current pulse of an electrical current being generated by the accumulator unit during each discharge interval as a function of a state variable and/or as a function of a material parameter of the accumulator unit.

According to the improved concept, a method for discharging an accumulator unit during a large number of successive discharge intervals is specified. At least one pulse parameter is determined by means of a computing unit as a function of at least one state variable of the accumulator unit and/or as a function of at least one material parameter of the accumulator unit. During the discharge intervals, at least one current pulse of a time-dependent electrical current is generated by the accumulator unit depending on the at least one pulse parameter.

The battery unit is in particular a component of a battery, for example a battery pack for an electrical device, a power tool, a household appliance, an at least partially electrically drivable small vehicle such as a bicycle or a scooter. The accumulator can also be designed as an accumulator for an at least partially electrically driven motor vehicle, for example a car, a truck, a commercial vehicle and so on. In this context, the accumulator is also referred to as a high-voltage battery.

The accumulator unit contains, in particular, one or more accumulator cells connected in series and/or in parallel. However, the accumulator unit does not necessarily have to contain all the accumulator cells of the accumulator. In particular, the accumulator cells of the accumulator can be combined in several groups, with the accumulator unit corresponding to such a group. However, it is possible for the accumulator unit to correspond exactly to one accumulator cell of the accumulator or to contain several of the groups mentioned or all of the accumulator cells of the accumulator.

Various of the groups of accumulator cells can optionally be discharged independently of one another or separately from one another. Accordingly, the method according to the improved concept can be carried out separately, for example, for different groups of accumulator cells. The individual groups can be used as energy stores for the battery pack. In particular, for example, a first group of accumulator cells can be discharged according to the method described and a second group of accumulator cells can provide energy for generating the at least one current pulse for the first group.

A battery cell of the battery unit contains in particular two electrodes, a cathode and an anode, with a separator being arranged between the electrodes. Such a battery cell is preferably a lithium-ion battery cell.

Depending on which cell-chemical system, also referred to as cell chemistry, is used for the accumulator cell, the electrodes and the separator can comprise different materials. The electrodes can contain, for example, metallic or other electrically conductive carrier foils that are coated with active materials that contain, for example, transition metal compounds or graphite. In typical lithium-cobalt dioxide accumulators, copper foils and graphite structures with embedded lithium ions and aluminum foils with lithium-cobalt dioxide as the active material are used as electrodes, for example. However, the present invention is not limited to specific cell-chemical systems. In particular, by taking the at least one material parameter into account, the improved concept can be used in a correspondingly flexible manner.

The at least one current pulse can be generated in particular by a battery management system, BMS, of the accumulator. The computing unit can in particular be part of the accumulator, in particular the BMS. However, the processing unit can also be implemented in the form of a server computer or server processing unit or a cloud computer, so that the processing unit is in a wireless communication connection with the accumulator in order to provide the at least one pulse parameter accordingly.

The time-dependent current flows over or through the accumulator unit during the discharging of the accumulator unit. In this case, this current does not necessarily and generally does not correspond to a load current which flows via a load connected during discharging.

For example, the computing unit, the BMS or the accumulator can contain an electronic circuit that is set up to supply the consumer with the required electrical power during the at least one current pulse. In particular, the electronic circuit for this can contain one or more electronic power components, resonant circuits, capacitive energy stores and/or inductive energy stores.

A current pulse can be understood in particular as a unipolar pulse, according to which the value of the time-dependent current rises once from a start value to a target value that differs from the start value, then falls again or, conversely, falls from the start value to the target value and then rises again. After the end of the current pulse, the value of the time-dependent current is not necessarily equal to the starting value. The design of the pulse shape, in particular the flanks of the current pulse, can vary depending on the specific requirements of the application.

The at least one state variable is in particular a variable describing the state of the accumulator unit, which can generally change over the course of the operation of the accumulator, ie during charging or discharging of the accumulator, and/or depending on environmental influences. The at least one state variable can be, for example, a state of charge, SoC, an aging state, which can be referred to as "State of Health", SoH, for example, a core temperature of one or more battery cells of the battery unit, an envelope temperature of one or more battery cells of the battery unit, an outside temperature or ambient temperature of the accumulator unit and so on.

In contrast, the at least one material parameter of the accumulator unit is independent of time and depends on the materials used for the construction of the accumulator cells, in particular on the materials which are used for the electrodes, the separator or as the electrolyte. In other words, the at least one material parameter depends on the cell chemistry used in the accumulator cells.

The at least one pulse parameter can include, for example, a number of current pulses during the corresponding discharge interval, a duty cycle, a pulse duration, a pulse shape, a pulse height, a maximum value or minimum value for the pulse, an edge shape, an edge steepness and so on. The at least one pulse parameter can contain different values for different current pulses of the same discharge interval. The number of current pulses per discharge interval can be one or more.

The application of at least one current pulse can prevent Publ Openings or pores of the separator are clogged or blocked by charge carriers, in particular ions such as lithium ions, or such blockages can be at least partially removed. Depending on the embodiment of the method, the at least one current pulse can contain a negative and/or positive current pulse. With a negative current pulse, the time-dependent current is reduced from the start value to a minimum value and then increased again, while with a positive current pulse the time-dependent current is increased from the start value to a maximum value and then reduced again.

The force with which the charge carriers are pressed onto the separator is temporarily reduced by the negative current pulse, so that the blockage can be released by the brief reversal of direction. In the case of the negative current pulse, however, a current reversal does not necessarily have to take place. However, the negative current pulse can also cause such a current reversal.

The positive current pulse can lead to the charge carriers potentially causing a blockage of the pores or openings of the separator being pressed against and thus possibly through the separator with increased force.

In different configurations of the method, different combinations of positive and/or negative current pulses are possible within different discharge intervals and/or within the same discharge interval.

By taking into account the at least one state parameter and/or the at least one material parameter, the complex relationship between different influencing variables on the effective internal resistance of the accumulator unit can be taken into account. By appropriately selecting the at least one pulse parameter, which also affects the effective internal resistance, the improved concept can be used to specifically address the cell chemistry used or the current state of the accumulator unit, for example to keep the effective internal resistance as low as possible, with the effective internal resistance can be viewed over a period of one discharge interval, for example. This reduces the thermal load on the accumulator unit, which in particular can increase the service life of the accumulator unit.

In accordance with at least one embodiment, the accumulator contains the accumulator unit and a first additional accumulator unit. At least one additional pulse parameter is determined by the arithmetic unit as a function of at least one additional state variable of the first additional accumulator unit and/or as a function of at least one additional material parameter of the first additional accumulator unit. During a large number of further discharge intervals, at least one further current pulse of a further time-dependent electric current is generated by the first further accumulator unit depending on the at least one further pulse parameter and independently of the at least one pulse parameter.

The accumulator unit and the first additional accumulator unit correspond in particular to different groups of accumulator cells, as explained above. The further discharge intervals are in particular independent of the discharge intervals for discharging the accumulator unit.

The improved concept can therefore advantageously be used separately for a number of accumulator units.

In accordance with at least one embodiment, the accumulator contains the accumulator unit and a second additional accumulator unit. Electrical energy for generating the at least one current pulse is provided by the second additional accumulator unit.

The second additional accumulator unit can therefore be viewed as an energy store for the accumulator unit or for the accumulator. Sufficient energy can thus be made available by the energy store in order both to supply the required load current for the consumer and to drive the at least one current pulse.

According to at least one embodiment of the method based on the improved concept, at least one pulse parameter of the at least one pulse parameter that is constant over time is determined by means of the computing unit before the start of the plurality of discharge intervals, in particular as a function of the at least one material parameter and/or the at least one state variable, and during each of the Discharge intervals, the time-dependent current is generated as a function of the at least one constant pulse parameter.

The time-dependent current is generated in particular in such a way that one or more current pulses are generated for each of the discharge intervals as a function of the constant pulse parameter will. The at least one pulse parameter that is constant over time is constant in particular over all discharge intervals of the multiplicity of successive discharge intervals. Nevertheless, the at least one pulse parameter that is constant over time can relate to different current pulses within a discharge interval.

By taking the at least one constant pulse parameter into account when generating the time-dependent current, the computational effort and adjustment effort for generating the time-dependent current over the discharge intervals can be reduced. This is particularly useful when considering influencing variables that are independent of time, such as the at least one material parameter, or when considering fundamentally time-dependent influencing variables, which, however, usually do not change significantly during a single discharge and can therefore be regarded as constant, such as for example the aging condition or the ambient temperature. As a result, a compromise can be achieved between the highest possible current and the complexity of the underlying algorithm for determining the at least one pulse parameter.

In particular, the at least one constant pulse parameter can be determined again for each discharge process before the start of the respective plurality of discharge intervals of the corresponding discharge process.

According to at least one embodiment, all pulse parameters of the at least one pulse parameter are constant during the plurality of consecutive discharge intervals, in particular for a given discharge process. However, the pulse parameters can differ from one another for different discharge processes, ie for different numbers of successive discharge intervals.

According to at least one embodiment, at least one time-variable pulse parameter of the at least one pulse parameter for each of the time intervals is individually determined as a function of the at least one state variable by means of the arithmetic unit.

During each of the discharge intervals, the current is generated depending on the at least one variable pulse parameter determined for the respective discharge interval.

In other words, the at least one pulse parameter is defined only for a single one of the discharge intervals and, if necessary, changed for later discharge intervals. This allows the change in the at least one state variable over time to be taken into account, so that the at least one pulse parameter can be optimally adjusted for each discharge interval, in particular to reduce or minimize the effective internal resistance or an average value for the effective internal resistance. In other words, a dynamically controlled current is implemented through the accumulator unit, which is subdivided into the individual discharge intervals, with the at least one pulse parameter being adjusted or controlled over the entire discharge time, in particular in order to minimize the resulting internal resistances per discharge interval or in to minimize their sum. This reduces the thermal load on the accumulator cells of the accumulator unit.

According to at least one embodiment, the at least one variable pulse parameter is determined by the computing unit for each of the discharge intervals using a lookup table, the lookup table assigning the at least one state variable and/or the at least one material parameter to the at least one pulse parameter.

The look-up table, which can also be referred to as a conversion table or look-up table, for example, may be multidimensional, so that one or more pulse parameters can be assigned to a number of state variables and/or material parameters. In this case, the look-up table is stored in particular on a storage unit, for example the arithmetic unit or the accumulator. The lookup table can also be stored on some other external storage device, for example a cloud storage device. By using the look-up table, a rapid determination of the at least one pulse parameter can be achieved without relevant computational effort.

According to at least one embodiment, the at least one variable pulse parameter is determined by the computing unit for each of the discharge intervals using a predefined model, with the model relating the at least one state variable and/or the at least one material parameter to an internal resistance or an effective internal resistance of the accumulator unit.

The model can be viewed as a functional relationship between the at least one state variable and/or the at least one material parameter on the one hand and the effective internal resistance on the other hand. The effective one Internal resistance is also functionally dependent on the at least one pulse parameter, so that in such embodiments the effective internal resistance can be minimized by appropriately determining or defining the at least one pulse parameter given at least one state variable and/or at least one material parameter.

By using the previously determined model, the influence of the at least one material parameter and/or the at least one state parameter and the at least one pulse parameter on the effective internal resistance can be taken into account even more precisely, so that the thermal load can be reduced even further.

Both the look-up table and the model can be empirically determined in advance in experimental test series, in which case analytical relationships between the influencing variables and the effective internal resistance can also be used and taken into account at least in part.

According to at least one embodiment, during a given discharge interval of the plurality of discharge intervals, a negative current pulse of the at least one current pulse is generated as a function of the at least one pulse parameter.

The negative current pulse can be designed in such a way that no current reversal takes place. In other embodiments, the time-dependent current can become less than zero during the negative current pulse, resulting in a reversal of the current direction.

A negative current pulse can be viewed as a relaxation pulse, which reduces the force with which the charge carriers are pressed against the separator or even reverses its direction, so that blockages in the pores of the separator can be reduced or prevented.

According to at least one embodiment, the time-dependent current is changed during the negative current pulse in such a way that the current strength of the time-dependent current is temporarily at least approximately equal to zero and/or the current direction of the time-dependent current is temporarily reversed. This increases the effect of the relaxation impulse.

According to at least one embodiment, a positive current pulse of the at least one current pulse is generated depending on the at least one pulse parameter during the given discharge interval, ie during the discharge interval that contains the negative current pulse, after the negative current pulse.

In other words, the time-dependent current is reduced from the starting value to the minimum value during the negative current pulse and then increased again, the time-dependent current temporarily exceeding the original starting value during the positive current pulse.

In this case, in particular, a pulse duration of the negative current pulse can be shorter than a pulse duration of the positive current pulse, for example by a multiple. This ensures that the maximum level of the positive current pulse can be kept low in order to avoid overloading the battery cell.

For example, the positive current pulse can immediately follow the negative current pulse. In particular, in various embodiments the discharge interval can contain exactly two current pulses, namely the negative current pulse and the positive current pulse. In other embodiments, the discharge interval contains only the negative current pulse or only the positive current pulse.

According to at least one embodiment, the at least one pulse parameter is determined by the computing unit as a function of a current state of charge of the accumulator unit and/or as a function of a current aging state of the accumulator unit and/or as a function of a current temperature of the accumulator unit and/or as a function of a current ambient temperature of the accumulator unit .

The temperature of the accumulator unit can in particular correspond to a cell core temperature or envelope temperature of one or more accumulator cells of the accumulator unit.

According to at least one embodiment, the at least one pulse parameter is determined by the computing unit as a function of a cell-chemical system of the accumulator unit.

In particular, the at least one material parameter includes parameters that define the cell-chemical system of the accumulator unit. The cell-chemical system, also referred to as the cell chemistry of the accumulator unit, is given in particular by the materials used and their properties.

According to at least one embodiment, the internal resistance, in particular the effective internal resistance, of the accumulator unit is minimized over the course of a first part of the successive discharge intervals, in that the respective values of the at least one pulse parameter are varied, in particular by means of the computing unit, in particular from one discharge interval to the next. The current is generated during a second portion of the successive discharge intervals according to the at least one optimal pulse parameter.

The first part of the discharge intervals is in particular a subset of the plurality of discharge intervals, the discharge intervals of the first part also following one another. The second part of the discharge intervals is in particular a further subset of the plurality of discharge intervals, the discharge intervals of the second part also following one another and following, in particular directly following, the discharge intervals of the first part.

The at least one pulse parameter can be varied for each discharge interval of the first part, and the effective internal resistance that then occurs during the corresponding discharge interval can be measured or estimated. If a minimum value for the effective internal resistance is reached, the resulting at least one optimal pulse parameter can be stored and set and maintained for the subsequent discharge intervals of the second part, for example until the end of the discharge process. As a result, the mean effective internal resistance can be reduced particularly effectively over the entire discharging process.

According to the improved concept, a system for discharging an accumulator unit during a large number of successive discharge intervals is also specified. The system has a computing unit that is set up to determine at least one pulse parameter as a function of at least one state variable of the accumulator unit and/or as a function of at least one material parameter of the accumulator unit. The system has a control unit that is set up to generate at least one current pulse of a time-dependent electrical current through the accumulator unit during the discharge intervals as a function of the at least one pulse parameter.

The at least one state variable can be measured, for example, by means of one or more sensors, which can be part of the system, for example, and/or calculated or estimated based on corresponding measured variables. The at least one material parameter can be stored, for example, on a memory unit of the system, in particular the computing unit.

The arithmetic unit is connected wirelessly or by wire to the control unit in order to transmit the at least one pulse parameter to the control unit. The processing unit and the control unit can be part of the same component of the system or belong to different components. In particular, the computing unit and the control unit can both be part of the accumulator. In further embodiments, the processing unit can be designed as a server processing unit, and the control unit can be part of the accumulator.

According to at least one embodiment of the system, the system includes the battery unit and the battery unit has one or more battery cells, in particular one or more lithium-ion battery cells.

The cell-chemical system of the lithium-ion battery cell can, for example, a lithium-ion cobalt dioxide system, a lithium-nickel-manganese-cobalt system, a lithium-nickel-cobalt-aluminum system, a lithium-manganese system, a Correspond lithium iron phosphate system or a lithium titanate system. The electrolyte of the accumulator cells can be liquid or the accumulator cells can be lithium polymer accumulator cells.

According to at least one embodiment, the system has the accumulator, which contains the accumulator unit, and the accumulator, in particular a BMS of the accumulator, contains the computing unit.

The control unit can also be part of the accumulator and can be in wireless or wired communication connection with the computing unit.

According to at least one embodiment, the system includes the server processing unit, and the server processing unit includes the processing unit.

The server processing unit can also be understood as part of a cloud or an Internet of Things. In such embodiments, for example, the accumulator contains the control unit and the control unit is in wireless communication with the computing unit.

Embodiments in which the server processing unit includes the processing unit are in particular Particularly advantageous in the model-based determination of the at least one pulse parameter or the determination of the at least one pulse parameter based on the lookup table, since modifications and improvements to the model or the lookup table can be entered without having to access the accumulator itself.

According to at least one embodiment, the system, in particular the computing unit, contains the memory unit and the memory unit stores the look-up table which assigns the at least one pulse parameter to the at least one state variable and/or the at least one material parameter. The computing unit is set up to determine the at least one pulse parameter using the look-up table.

Further embodiments of the system according to the improved concept follow directly from the different embodiments of the method according to the improved concept and vice versa. In particular, a system based on the improved concept can be set up to carry out a method based on the improved concept, or the system carries out such a method.

According to the improved concept, a computer program is also specified with instructions which, when the computer program is executed by a system according to the improved concept, cause the system to carry out a method according to the improved concept.

According to the improved concept, a computer-readable storage medium is also specified, which stores a computer program according to the improved concept.

The features and combinations of features mentioned above in the description and the features and combinations of features mentioned below in the description of the figures and/or shown alone in the figures can be used not only in the combination specified in each case, but also in other combinations without departing from the scope of the invention . Versions and combinations of features are also to be regarded as disclosed which do not have all the features of an originally formulated independent claim and/or which go beyond or deviate from the combinations of features set out in the back references of the claims.

• 1 eine Blockdarstellung einer beispielhaften Ausführungsform eines Systems zum Entladen einer Akkumulatoreinheit nach dem verbesserten Konzept;
• 2 eine Blockdarstellung einer weiteren beispielhaften Ausführungsform eines Systems nach dem verbesserten Konzept;
• 3 eine Blockdarstellung einer weiteren beispielhaften Ausführungsform eines Systems nach dem verbesserten Konzept;
• 4 eine schematische Darstellung eines Stromverlaufs während einer Vielzahl aufeinanderfolgender Entladeintervalle; und
• 5 eine schematische Darstellung verschiedener Impulsformen.

Show in the figures

• 1 a block diagram of an exemplary embodiment of a system for discharging an accumulator unit according to the improved concept;
• 2 14 is a block diagram of another exemplary embodiment of a system according to the improved concept;
• 3 14 is a block diagram of another exemplary embodiment of a system according to the improved concept;
• 4 a schematic representation of a current curve during a plurality of successive discharge intervals; and
• 5 a schematic representation of different pulse shapes.

In 1 a block diagram of an exemplary embodiment of a system 1 for discharging an accumulator unit 2 is shown. Accumulator unit 2 is in 1 shown schematically as a single accumulator cell with a cathode 2a, an anode 2b and an intermediate separator 2c. However, this is only to be understood as an example, so that the accumulator unit 2 can also contain two or more accumulator cells in various embodiments, which can be connected in series or in parallel to one another.

The system 1 includes a control unit 3 and a computing unit 4. The control unit 3 can be connected to the electrodes 2a, 2b of the accumulator unit 2 and to the computing unit 4.

The computing unit 4 can determine at least one pulse parameter as a function of at least one state variable of the accumulator unit 2 and/or as a function of at least one material parameter of the accumulator unit 2 and transmit this to the control unit 3 . Depending on the at least one pulse parameter, the control unit 3 can then influence an electric current through the accumulator unit 2 as a function of time, as is shown schematically in 4 is shown.

In 4 the current I through the accumulator unit 2 is shown as a function of the time t. According to the improved concept, current pulses 9 are superimposed on a substantially constant current. The current pulses 9 of 4 are shown by way of example as negative current pulses 9, which fall below the value zero, for example, so that the current direction is reversed. The course of the current pulses 9 as shown in 4 shown is to be understood as an example only. In particular, a further positive or negative current pulse can be provided in various embodiments, or the negative current pulse can through be replaced by a positive current pulse and so on. In particular, this can also change from discharge interval to discharge interval.

Also, the pulse shape is not necessarily rectangular and the edge shape of the current pulses 9 can vary depending on the requirements, as in 5 indicated as an example.

It is pointed out that the time-dependent current I corresponds to a current as it flows through the battery unit 2 during the discharging of the battery unit 2 . The current I is not necessarily equal to a load current as it flows through a consumer (not shown) connected during discharging.

For example, the control unit 3 can contain an electronic circuit that is set up to store sufficient energy for the current pulses 9 at a suitably high voltage, to generate the current pulses and to supply the load with current and voltage during this time. In particular, the electronic circuit for this purpose can contain one or more electronic power components, resonant circuits, capacitive energy stores and/or inductive energy stores.

In order to determine the at least one pulse parameter as a function of the state variables and/or the material parameters, the computing unit 4 can, in some embodiments, define fixed pulse parameters as a function of the cell-chemical system of the accumulator cells of the accumulator unit 2, which remain constant for the entire discharging process. The information relating to the cell-chemical system can be stored, for example, on a storage unit 6 , with the computing unit 4 , the control unit 3 or the accumulator being able to contain the storage unit 6 .

In further embodiments, the memory unit 6 can store a look-up table which assigns the pulse parameters to the state variables and/or the material parameters. This allows a certain dynamic to be achieved during the discharging process without the need for complex arithmetic operations.

In further embodiments, the storage unit 6 can store a model or a functional relationship between the pulse parameters, the state variables and/or the material parameters on the one hand and the effective internal resistance on the other hand. In such embodiments, the computing unit 4 can, for example, determine the pulse parameters as a function of the current state variables and/or as a function of the material parameters, possibly while complying with specified boundary conditions, such that the internal resistance is as low as possible. As a result, the effectiveness of the method or of the system 1 can be further increased. For example, once pulse parameters have been determined that lead to a minimum internal resistance, these pulse parameters can be set and maintained for the remainder of the discharge process or part thereof.

Dynamic effects that occur when the charge carriers move through the media involved, in particular when crossing boundary layers, in particular a solid-electrolyte interface, SEI, when passing through or tunneling through pores of the separator 2c or when stripping off solvation shells, etc., can lead to congestion formation or film formations, in particular on the separator 2c, and lead to corresponding non-linear disturbances in the ion migration. This is accompanied by an increase in the effective internal resistance and corresponding thermal losses inside the accumulator cells. As a result, the current is effectively limited to values at which the heat dissipation into the environment is still sufficient to keep the cell heating inside the accumulator unit 2 below a critical limit.

Thanks to the improved concept, the current is modified in a targeted manner for each of the discharge intervals in order to break up these non-linear effects and thus partially compensate for the thermal losses and the increasing internal resistance. This can be done, for example, by negative current pulses 9, ie relief pulses. However, positive current pulses can also be used additionally or alternatively in order to temporarily increase the driving force for the ion migration and, for example, to widen the constrictions or pores of the separator 2c accordingly in order to dissolve blockages and the like.

The frequency, amplitude, pulse width and so on of the current pulses 9, ie the at least one pulse parameter, can be determined depending on the cell chemistry used, the current state of charge, temperatures of the accumulator unit 2 or an aging state. The effective internal resistance can be viewed as a measure of the effectiveness of the specific pulse parameters for the corresponding discharge interval.

In 2 1 is a block diagram of an exemplary further embodiment of the system 1 according to the improved concept, which is also based on the embodiment of FIG 1 based. Here, the system 1 includes the accumulator 7, the contains both the computing unit 4 and the control unit 3 in addition to the accumulator unit 2 .

In 3 1 is a block diagram of another exemplary embodiment of the system 1 of the improved concept, based on the embodiment of FIG 1 based. In the embodiment of 3 a server system 8, in particular a computer cloud, is shown, which contains the computing unit 4 and is in radio communication with the control unit 3.

As described, particularly with regard to the figures, the improved concept makes it possible to discharge an accumulator unit with a lower thermal load. For this purpose, the average effective internal resistance of the accumulator unit is optimized or minimized in that pulse parameters for at least one current pulse of the time-dependent current through the accumulator cell are determined as a function of at least one state variable and/or as a function of at least one material parameter.

The unloading process is divided into individual unloading intervals of variable length. Within a discharge interval, the level of the current through the accumulator cell is systematically changed. The slope profile of the current pulses can be adapted or optimized using the available electrotechnical or electronic equipment, for example voltage control or regulation equipment.

Both the duration of the discharge interval and the duration of the individual current pulses and their level can be modified depending on the electrochemical system, the state of charge, the cell state, the cell aging state, the cell core temperature, the cell envelope temperature, the outside temperature and so on, so that the resulting effective Internal resistance is as low as possible.

The parameterization of the current pulses can be done, for example, using multidimensional lookup tables, also known as multidimensional lookup tables, or using functional relationships that can be known for a specific battery cell from serial tests under laboratory conditions.

The pulse parameters can be persistently stored in the system, e.g. in the accumulator or an external storage device, e.g. a server device, a network data storage device, a computer cloud, an internet-of-things connected cloud and so on. The control unit then sets the defined parameterization.

In preferred embodiments, the battery management system or the computing unit evaluates the effective internal resistance for each or at least for several of the discharge intervals and optimizes the pulse parameters in order to minimize the internal resistance. This can be done, for example, by varying the pulse parameters and evaluating the resulting results from discharge interval to discharge interval, using, for example, conventional optimization methods such as linear or non-linear optimization methods, gradient crawlers, Newton methods, evolutionary methods and so on or on machine learning or artificial Intelligence-based optimization methods can be used. Kalman filters or similar algorithms can be provided, for example, in order to be able to include parameters that cannot be measured directly, for example the cell core temperature, or to minimize effects due to sensor noise.

Reference List

1

system

2

accumulator cell

2a

cathode

2 B

anode

2c

separator

3

control unit

4

unit of account

6

storage unit

7

accumulator

8th

server system

9

current pulses

Claims (15)

A method for discharging an accumulator unit (2) during a plurality of successive discharge intervals, wherein - at least one pulse parameter is determined by means of a computing unit (4) as a function of at least one state variable of the accumulator unit (2) and/or as a function of at least one material parameter of the accumulator unit (2); and - During the discharge intervals, at least one current pulse (9, 9a, 9b) of a time-dependent electric current is generated by the accumulator unit (2) as a function of the at least one pulse parameter. procedure after claim 1 , wherein - at least one constant pulse parameter of the at least one pulse parameter is determined before the start of the discharge intervals; and - during each of the discharge intervals the time-dependent current is generated depending on the at least one constant pulse parameter. Method according to one of the preceding claims, wherein - at least one variable pulse parameter of the at least one pulse parameter is determined for each of the discharge intervals individually as a function of the at least one state variable; and - During each of the discharge intervals, the time-dependent current is generated depending on the at least one variable pulse parameter. procedure after claim 3 , wherein the at least one variable pulse parameter is determined for each of the discharge intervals using a look-up table which associates the at least one state variable and/or the at least one material parameter with the at least one pulse parameter. procedure after claim 3 , wherein the at least one variable pulse parameter is determined for each of the discharge intervals using a predefined model, the model relating the at least one state variable and/or the at least one material parameter to an internal resistance of the accumulator unit (2). Method according to one of the preceding claims, wherein during a discharge interval of the plurality of discharge intervals a negative current pulse (9a) is generated as a function of the at least one pulse parameter. procedure after claim 6 , wherein during the negative current pulse (9a) the time-dependent current is changed in such a way that the current strength of the time-dependent current is at least approximately equal to zero and/or the current direction of the time-dependent current is reversed. Procedure according to one of Claims 6 or 7 , wherein during the discharge interval after the negative current pulse (9a), a positive current pulse (9b) is generated depending on the at least one pulse parameter. Method according to one of the preceding claims, wherein - the at least one pulse parameter depending on a state of charge of the accumulator unit (2) and/or depending on an aging state of the accumulator unit (2) and/or depending on a temperature of the accumulator unit (2) and/or depending on an ambient temperature of the accumulator unit (2) is determined; and or - the at least one pulse parameter is determined as a function of a cell-chemical system of the accumulator unit (2). Method according to one of the preceding claims, wherein - An internal resistance of the accumulator unit (2) is minimized in the course of a first part of the successive discharge intervals by varying the at least one pulse parameter in order to determine at least one optimal pulse parameter; and - the time-dependent current is generated during a second part of the successive discharge intervals according to the at least one optimal pulse parameter. Method according to one of the preceding claims, wherein - An accumulator (7) contains the accumulator unit (2) and a further accumulator unit; - at least one further pulse parameter is determined by means of the computing unit (4) as a function of at least one further state variable of the further accumulator unit and/or as a function of at least one further material parameter of the further accumulator unit; - During a large number of further discharge intervals, at least one further current pulse of a further time-dependent electric current is generated by the further accumulator unit as a function of the at least one further pulse parameter and independently of the at least one pulse parameter. Procedure according to one of Claims 1 until 10 , wherein - an accumulator (7) contains the accumulator unit (2) and a further accumulator unit; - Electrical energy for generating the at least one current pulse (9, 9a, 9b) is provided by means of the additional accumulator unit. System for discharging an accumulator unit (2) during a large number of successive discharging intervals, the system (1) having - a computing unit (4) which is set up as a function of at least one state variable of the accumulator unit (2) and/or as a function of at least one material parameter the accumulator unit (2) to determine at least one pulse parameter; and - a control unit (3) which is set up to send at least one current pulse (9, 9a, 9b) of a time-dependent electric current through the accumulator unit (2) during the discharge intervals. to generate depending on the at least one pulse parameter. system after Claim 13 Having - an accumulator (7), which contains the accumulator unit (2) and the computing unit (4); or - a server processing unit (8) which contains the processing unit (4); or - an accumulator (7) which contains the accumulator unit (2) and the control unit (3). system according to one of the Claims 12 until 14 wherein - the system (1) includes a memory unit (6) storing a look-up table associating the at least one state variable and/or the at least one material parameter with the at least one pulse parameter; and - the computing unit (4) is set up to determine the at least one pulse parameter using the look-up table.

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