WO2024170314A1 - Storage unit for electrical energy with at least one battery cell and a sensor for measuring the cell swelling, and method for producing the storage unit for electrical energy - Google Patents

Abstract

The invention further relates to a method for producing a storage unit for electrical energy. The electrical energy storage unit may be a battery module for providing electrical traction energy for a vehicle. The method comprises the step of determining (S10) a spatially resolved distribution (3) of a swelling behaviour of a first battery cell (4) during and/or at the end of cyclization of the first battery cell (4). The method furthermore comprises selecting (S20) a target sensor position (5) depending on the determined spatially resolved distribution (3) of the swelling behaviour and producing (S30) a storage unit for electrical energy comprising one or more second battery cells (6), which are preferably of the same design as the first battery cell (4). A sensor (7) for measuring the swelling behaviour of the second battery cell (6) at the selected target sensor position (5) is arranged on at least one of the one or more second battery cells (6). The present invention furthermore relates to a storage unit for electrical energy produced in this manner. This method (1), the battery module (2) and this vehicle can be used to monitor a state of health of the battery module (2).

Description

Storage device for electrical energy with at least one battery cell and a sensor for detecting cell swelling, as well as a method for producing the storage device for electrical energy

Description

The invention relates to a storage device for electrical energy, comprising at least one battery cell and a sensor for detecting a threshold behavior of a battery cell. The invention further relates to a method for producing such a storage device for electrical energy. The electrical energy storage device can be a battery module for providing electrical traction energy for a vehicle.

With the increasing demand for alternative drives, electric drives are becoming increasingly important. The battery modules used in vehicles are usually made up of several battery cells. In practice, lithium-ion cells have become particularly established because they have a high energy density and can simultaneously provide a comparatively high level of power. Depending on the application, however, other battery types such as nickel-cadmium or nickel-metal hybrid (NiMH) batteries are also used.

As the battery cell ages, various properties of the battery cell change, such as the internal resistance, the maximum available charging capacity, or the currents flowing inside the battery cell. On the one hand, this reduces the performance of the battery cell available for use. On the other hand, the state of age is of crucial importance for the safety assessment of the battery cell, since some state variables that are subject to age-related changes may only be operated within certain limits, otherwise safety risks, such as the risk of fire, increase significantly.

Such battery cells expand during the charging process due to, among other things, changes in the lattice structure of the active layers (electrodes) and due to thermal effects, which leads to an increase in the volume of the cell. During the discharging process, this increase in volume decreases again, except for a small irreversible portion. The irreversible portion of the increase in volume is referred to as swelling, the reversible portion as breathing. The extent of the swelling is an indicator of the aging state of health (SoH) of the cells. It is therefore known from practice that during the manufacture of battery modules, the battery cells are equipped with sensors in order to monitor the swelling and thus the aging state of the battery cells. However, these previous solutions known from practice are not sufficiently suitable, especially for the series production of vehicles, as they are inaccurate, expensive, or difficult to implement.

The invention is therefore based on the object of providing an improved technology for providing such battery modules. The battery modules are intended in particular to enable more cost-effective and simplified monitoring of the swelling behavior and the aging state of one or more battery cells of the battery module.

The problem is solved by the features of the independent claims. Advantageous further developments are specified in the dependent claims and the description.

Within the scope of the invention, it was found that the swelling behavior of a battery cell exhibits a high degree of inhomogeneity across the cell surface of the battery cell. Certain sections of a cell surface exhibit significantly greater swelling than other sections. Local maxima, so-called hotspots, of swelling often form on certain cells, which are characterized, for example, by a local maximum surface pressure compared to other sections of the cell surface. Accordingly, not all locations on the battery cells are suitable and/or equally suitable for monitoring an aging state based on the swelling behavior. The invention takes advantage of this by determining the swelling behavior for a specific cell type during and/or after cycling in a spatially resolved manner, e.g. as part of a test measurement during development. Based on the determined spatially resolved distribution of the swelling behavior, the location (position) on the battery cell, preferably on its outer cell wall, is determined which has a swelling behavior based on which the aging state, in particular an EoL state (“EoL”: English for End of Life) of the battery cell, can be determined and monitored particularly reliably. This location (position) determined in this way is selected as the sensor target position in order to arrange a sensor there to monitor the swelling behavior when subsequently storage devices for electrical energy, e.g. battery modules, with battery cells of the same type or with battery cells for which the previously spatially resolved distribution of the swelling behavior is also valid, are manufactured. If the storage device for electrical energy comprises several battery cells, it is possible for all battery cells of the storage device to be equipped with such a sensor or only some of the battery cells. Only one of the battery cells can also be equipped with such a sensor in order to monitor the entire storage device or all battery cells. provided that the battery cell used is representative of the aging behavior of all battery cells in the storage system. Accordingly, only a (small) part of the battery cell, preferably a part of the cell wall, needs to be monitored with regard to the threshold behavior using a sensor. The sensor can be designed to be compact and inexpensive. In the simplest case, it may be sufficient to simply exceed the threshold at one point on the battery cell.

According to a first general aspect of the present disclosure, a method of manufacturing a battery module for providing electrical traction energy for a vehicle is provided.

The method comprises the step of determining a spatially resolved distribution of a swelling behavior, i.e. the swelling behavior, of a battery cell during and/or at the end of a cycling of the battery cell. The battery cell, based on which the spatially resolved distribution of the swelling behavior is determined, is referred to below as the first battery cell to better distinguish it from other battery cells described below, which are referred to as second battery cells. Cycling refers to the repeated charging and discharging of battery cells and is, for example, an important component in the development and testing of battery cells.

Preferably, the cyclization is carried out in such a way that it causes aging in the first battery cell that is as similar as possible to that expected in the real operation of an energy storage device that comprises at least one battery cell of the same or similar design. This can be achieved, for example, by selecting values for operating parameters that influence cell aging during cyclization that are similar to those that occur in a future target application. Such operating parameters include, for example, a depth of discharge, i.e. the distance between a minimum and a maximum state of charge, a flowing current strength, C rates, cell temperatures and a stress situation of the battery cell during cyclization.

Preferably, the battery cell is a prismatic battery cell or a pouch cell. The battery cell is a battery cell that expands due to at least one charging and/or discharging process, and can therefore change its state from a non-expanded state to an expanded state and vice versa. It has already been established above that the swelling behavior describes the irreversible part of the volume increase. The swelling behavior of the battery cell varies for different locations on the battery cell. The Determining the spatially resolved distribution therefore determines the swelling behavior for a number of different locations on the battery cell. Preferably at different locations on the outer cell wall of the battery cell. In this case, local maxima or minima of the swelling behavior can be determined, for example. The spatially resolved distribution of the swelling behavior can be recorded, for example, using a sensor arrangement for measuring the swelling behavior, which is designed to determine a value for the swelling behavior for the number of different locations on the battery cell. The sensor arrangement can, for example, have several sensors assigned to the (measuring) locations, e.g. force, pressure and/or surface pressure sensors.

The method further comprises the step of selecting a sensor target position depending on the determined spatially resolved distribution of the swelling behavior. Based on the determined spatially resolved distribution of the swelling behavior, a location on the battery cell can thus be selected which, for example based on predetermined criteria (parameters), is particularly advantageous or suitable for detecting and/or monitoring the swelling behavior and/or the aging state of the battery cell. A sensor target position can, for example, be a location on the battery cell at which a sensor can be arranged to detect the swelling behavior and at which the local swelling behavior correlates with the overall swelling behavior and/or the overall aging behavior of the battery cell. The sensor target position can be the location on the battery cell which has a maximum of the previously determined swelling behavior.

The steps described above of determining the spatially resolved distribution of the swelling behavior and selecting the sensor target position are preferably carried out as part of a development, testing and/or inspection process for the first battery cells, e.g. in which the first battery cell is cycled on a battery test bench until the end of its life and the swelling behavior is measured during and/or at the end of the cycling. The first battery cell can be measured individually without being installed in a battery module.

The method further comprises the step of producing a storage device for electrical energy (hereinafter also referred to as electrical energy storage device), which comprises one or more battery cells, which are referred to below as second battery cells. The electrical energy storage device can be a battery module, for example a battery cell stack module in which several battery cells are arranged as a battery cell stack, ie the Battery cells are arranged in stacks. However, it is also possible for the battery module to contain only a single battery cell.

The electrical energy storage device can be an electrical energy storage device for providing electrical traction energy for a vehicle, preferably for a commercial vehicle. Alternatively, the electrical energy storage device can also be an electrical energy storage device for mobile applications, e.g. for aircraft, work machines, boats, etc.). Furthermore, the electrical energy storage device can be an energy storage device for stationary applications (e.g. stationary battery storage devices on PV or charging systems).

The second battery cells are preferably identical in construction to the first battery cell, of the same type as the first battery cell and/or battery cells that have the same spatially resolved swelling behavior as the first battery cell. During the manufacture of the electrical energy storage device, a sensor for detecting the swelling behavior of the second battery cell is arranged at the selected sensor target position on at least one of the one or more second battery cells. In other words, the method presented first examines the swelling behavior of the battery cell, e.g. as part of the development work on a battery test bench. In doing so, it is determined spatially resolved at which points the swelling behavior of the battery cell is, for example, strongly pronounced, and at which points the swelling behavior is less pronounced. Based on these test results, a sensor target position is determined at which the swelling behavior and/or the exceeding of a threshold value of the swelling behavior of the battery cell can be monitored using a single sensor. The spatially resolved swelling behavior is typically specific to identically constructed battery cells. When producing the electrical energy storage device, which can be used as a traction battery in an electric vehicle, for example, several battery cells are typically connected to form a module in order to achieve a larger charging capacity and a higher voltage, for example. A sensor for monitoring the swelling behavior of the battery cell is arranged on at least one of these cells at the previously selected sensor target position. The selection of the sensor target position advantageously only needs to be carried out once. Any number of electrical energy storage devices can then be produced. The process is therefore particularly suitable for the economical series production of battery modules.

Furthermore, the method presented can be used to implement a so-called end-of-life (EoL) early warning system, which can be used to monitor the aging state of battery modules in a cost-effective manner, since preferably only one sensor is used to monitor the The monitoring is nevertheless reliable because the sensor is arranged at a previously determined and selected target sensor position that provides sufficient information about the aging state of the entire battery cell. In particular, the aging state of the battery cell is permanently monitored over the entire service life of the battery cell, so that an increased level of safety can be achieved for the vehicle.

According to a preferred embodiment, the sensor target position is a location on the first battery cell and preferably the second battery cell that is a suitable and/or representative location for aging and/or safety assessment of the battery cell and/or that has a threshold behavior from which cell aging and/or reaching an end of life (EoL) state of the battery cell can be deduced. The “end of life” (EoL) is a term for the point in time at which previously defined values of a battery cell are exceeded or undercut due to aging. These previously defined values are usually specified by the manufacturer of the battery cell or can be determined through appropriate tests. These include, for example, a resistance, a current strength, a residual capacity, an energy storage capacity or a pressure inside the battery cell. The service life of a rechargeable battery cell is the period of time between the time of delivery (BoL) and the time of the end of life. When the EoL point is reached, the battery cell is generally still functional (possibly to a limited extent), but should no longer be operated and/or replaced promptly because the performance characteristics of the battery cell have deteriorated (e.g. relevant for the range or efficiency of the vehicle) and/or the probability of safety-relevant events (e.g. outgassing or spontaneous combustion of the battery cell) has increased significantly.

In addition or alternatively, the sensor target position is a point on the first and preferably second battery cell that exhibits the greatest swelling behavior, preferably after the end of cycling. The point with the greatest swelling behavior is the point on the battery cell that, in relation to the determined spatially resolved determination of the distribution of the swelling behavior, has the greatest local maximum of a measured variable that is a measure of the cell swelling (e.g. the surface pressure). The point with the greatest swelling behavior can also be the point on the battery cell that exhibits the greatest change in the swelling of the battery cell before and after the end of cycling. In addition or alternatively, the sensor target position can be a location on the first and preferably second battery cell that has a greatest surface pressure and/or a greatest change in the surface pressure generated by the interior of the battery cell on the battery cell wall, preferably after the end of cycling. The surface pressure refers to a pressure, i.e. a force per area, that the battery cell exerts on a wall of the battery cell due to the swelling behavior.

These locations are particularly suitable as target sensor positions because they provide particularly good information about the aging state of the battery cell. It is also easier to determine a measured value at a target sensor position where the threshold behavior shows the greatest possible difference between the BoL and EoL measured values.

The sensor target position can preferably correspond to a partial area of an outer wall of the battery cell. The sensor target position can preferably correspond to an area of an outer wall of the battery cell that is smaller than 20%, more preferably smaller than 10%, more preferably smaller than 5% of a total outer surface of the battery cell. Advantageously, only a small partial area of the cell wall needs to be monitored with regard to the swelling behavior. The sensors for this can be designed to be compact.

In a further advantageous embodiment, the sensor for detecting the swelling behavior can be a force, pressure and/or surface pressure sensor and/or a sensor for measuring force between two surfaces. With such sensors, in particular, a local geometric expansion behavior of the battery cell can be measured particularly easily. Monitoring non-geometric state variables, e.g. the internal resistance, can also be carried out by such sensors by storing corresponding assignment tables, e.g. which surface pressure at a certain point corresponds to a certain internal resistance. Such assignment tables can be created, for example, as part of determining the spatially resolved distribution of the swelling behavior.

According to a further embodiment, the sensor for detecting the swelling behavior can be designed as a film sensor and/or as a sensor that preferably has a thickness of less than 1 mm, more preferably a thickness of less than 0.5 mm. Such sensors can be particularly easily integrated into the design of the battery module, in particular when the battery cells form a battery cell stack and the sensor is arranged between two adjacent battery cells. In addition, the installation space required by such a sensor is small, so that the charge density, ie the charge capacity per volume of the electrical energy storage device, e.g. the battery module, is not or not significantly reduced.

Additionally or alternatively, the sensor for detecting the swelling behavior can be a sensor switch. The sensor switch has two conductors that only touch when swelling of the battery cell exceeds a predetermined threshold. This threshold can be exceeded, for example, if the battery cell reaches a maximum permissible expansion of the battery cell or a limit value that is a predetermined safety buffer below the maximum permissible expansion. One of the two conductors can be arranged on the battery cell and the other conductor, for example, on a wall of a module housing or neighboring battery cell opposite the battery cell. Corresponding conductors can be, for example, wires or metal foils. As soon as the two conductors touch, a signal is emitted. This makes it particularly easy to monitor whether a limit value for the expansion of the battery cell is exceeded.

In addition or as an alternative, the sensor for detecting the threshold behavior can be designed to generate an output signal that can be measured and/or evaluated directly or only with simple operational amplifier circuits with a microcontroller. In other words, the measurement signal that is output by the sensor is sufficiently large so that a complex amplifier circuit is not necessary. Preferably, the difference between the measurement signal output by the sensor when the EoL is reached is at least 5%, particularly preferably at least 8%, of the measurement signal of the BoL. In this way, a cost-effective implementation of the method can be achieved.

In addition or as an alternative, the sensor for detecting the swelling behavior cannot be designed as a strain gauge. Strain gauges and their implementation are well known in practice and enable very precise measurement of geometric changes, but they require expensive additional components, e.g. complex amplifier circuits, for reliable operation. In addition, the installation of such strain gauges in a battery module is comparatively complex, since they have to be glued to the battery cell over their entire surface, for example. The omission of strain gauges therefore enables a particularly economical implementation of the method presented. The cycling of the first battery cell preferably takes place under conditions that are modeled on those during operation of an electrical energy storage device, e.g. a battery module that includes such battery cells. For this purpose, a certain pressure can be exerted on the battery cell during cycling, for example, which corresponds to a pressure that would be exerted by a housing of the energy storage device or battery module. The first battery cell can advantageously be measured individually without being installed in a battery module.

The aforementioned conditions, in particular the pressure on the first battery cell, can be created, for example, by clamping using a clamping device, e.g. comprising a frame and a force generating unit that generates a desired clamping force on the frame and thus on the first battery cell. According to a further embodiment, determining the spatially resolved distribution of the swelling behavior of the first battery cell during and/or at the end of the cycling of the first battery cell therefore comprises clamping the first battery cell in a clamping device, preferably comprising a frame, for example a rubber frame. By clamping in a clamping device, the test condition can be controlled particularly well during the determination of the spatially resolved swelling behavior. The frame can, for example, run along edges of a prismatic battery cell. Such a frame can be used particularly well to position the battery cell in such a way that the battery cell has enough space for volume expansion, so that the spatially resolved distribution of the swelling behavior can be determined as accurately as possible. The advantage of using elastic material allows the battery cell to be fixed particularly securely without damaging the battery cell casing. In addition, the force transferred to the battery cell by the tension can be precisely controlled.

In addition or alternatively, determining the spatially resolved distribution of the swelling behavior of the first battery cell during and/or at the end of the cycling of the first battery cell can include cycling the first battery cell until the end of its life and after reaching the end of its life, measuring a swelling force per unit area on a housing of the first battery cell and/or measuring a volume expansion of the first battery cell at several measuring points. A value or a temporal progression of the swelling behavior is measured at each measuring point.

The multiple measuring points are preferably arranged in a grid-like manner, for example in a matrix-like manner, and/or cover at least 80% of an area of a housing side of the first Battery cell. The multiple measuring points are arranged on the housing side(s) that have the greatest swelling, i.e. on which the swelling is predominantly evident. The swelling occurs predominantly normal to the electrode stack or electrode winding surface. On this side, the volume expansion or swelling force per unit area is typically particularly easy to measure. The coverage of the area indicates which portion of this housing side the spatially resolved swelling behavior is determined from. The spatial resolution is better the more measuring points are used with the same coverage.

Cycling until the end of life enables a particularly meaningful sensor target position to be selected, since in this case it is known which point on the battery cell indicates the end of life particularly well. In principle, cycling can also be stopped before the end of life is reached and the spatially resolved threshold behavior determined. The spatially resolved threshold behavior, as well as the values required at the end of life, can be determined by extrapolating the determined distribution towards the end of life. Cycling until the end of life of the battery cell, however, makes it possible to forego extrapolation and therefore enables particularly reliable measurement results.

In a preferred embodiment, the sensor target position is selected as the measuring point that has the largest threshold force per unit area and/or the largest volume expansion of all measuring points. These points are particularly informative with regard to the aging state of the battery cell. In addition, a large change in the threshold force per unit area or the volume expansion enables a large change in the measurement signal for the sensor to record the threshold behavior, so that a less sensitive sensor can be used or the sensor signal can be used without complex processing.

According to a further advantageous embodiment, the method further comprises the step of determining a limit value for the sensor for detecting the threshold behavior, which indicates that the first and/or second battery cells have reached the end of their life, depending on the threshold behavior of the first battery cell determined at the sensor target position at the end of the cycling. This means that it is determined which measured value the sensor arranged at the sensor target position for detecting the threshold behavior outputs when the end of the battery cell's life is reached. Preferably, the limit value can be set somewhat lower than it would be at the actual end of life in order to provide additional to have a sufficient safety margin until the actual end of life. This enables particularly simple monitoring and thus particularly safe operation of the battery module produced.

In many cases, it is sufficient for a previously defined limit to be reached at a single point on the battery cell for the battery cell to reach the end of its life. In this case, it is advantageous to select a sensor target position at which such a local limit violation first occurs, for example the maximum permissible pressure of the battery cell on a wall.

In a further embodiment, the manufacture of the battery module includes the provision of a control unit that is in signal connection with the sensor and that is set up to monitor the limit value for the sensor depending on the sensor signals. The control unit can, for example, issue a warning signal when the limit value is reached or when the sensor signal approaches the limit value so that the user knows in good time that the battery module should be replaced. The control unit can correspond to the so-called battery management system (BMS) or the battery management unit (BMU) or a battery module controller, or form a partial functionality of each of these.

In a further embodiment, the control unit can be designed to switch off the battery module when the limit value of the sensor signal is exceeded, thereby indicating that safe operation of the battery module is no longer possible. The control unit can also preferably be designed to reduce the depth of discharge (DoD), i.e. the distance between a minimum and a maximum state of charge, of the battery module when the sensor signal approaches the limit value. In this way, the service life of the battery module can be extended in many cases.

According to a second general aspect of the present disclosure, an electrical energy storage device, e.g. a battery module for providing electrical traction energy for a vehicle, is provided, wherein the electrical energy storage device is manufactured using the method described above. A further aspect of the present disclosure relates to a storage device for electrical energy, e.g. a battery module for providing electrical traction energy for a vehicle. The storage device for electrical energy comprises one or more battery cells, wherein a sensor for detecting a swelling behavior of the battery cell is arranged on at least one of the one or more battery cells at a predetermined sensor target position. The sensor target position is preferably a location on the battery cells that is a location representative of aging and/or safety assessment, and/or that has a swelling behavior from which cell aging and/or the reaching of an end of life, EoL state of the battery cell can be derived. Additionally or alternatively, the sensor target position can be a location on the battery cells that has the greatest swelling behavior and/or the greatest surface pressure generated from the interior of the battery cell on the battery cell wall, preferably after the end of cycling. Whether e.g. For example, whether the greatest swelling behavior or the greatest surface pressure is more advantageous for the selection of the sensor target position depends on the rigidity of the clamping of the battery cell. With a stiffer clamping, the battery cell is prevented from expanding, so that a high surface pressure is formed. With a softer clamping, the battery cell can expand geometrically with less resistance, so that the change in the surface pressure is smaller.

In a further advantageous embodiment, at most one sensor for detecting the swelling behavior can be attached to the one or more battery cells.

According to a further general aspect of the present disclosure, a vehicle, preferably a motor vehicle, comprising a battery module as described above is provided.

In a preferred embodiment, the vehicle is designed as a commercial vehicle. In the latter case, the vehicle can be a motor vehicle which, due to its design and equipment, is designed to transport people, transport goods or tow trailers. For example, the vehicle can be a truck, a bus and/or a semitrailer which is at least partially electrically powered.

To avoid repetition, features disclosed purely in accordance with the method should also be considered as disclosed in accordance with the device and be claimable and vice versa. The advantages, aspects and features according to the invention described in connection with the method, in particular with regard to the sensor target position and the design of the sensor for detecting the swelling behavior, therefore also apply to the device.

The preferred embodiments and features of the invention described above can be combined with one another as desired. Further details and advantages of the invention are described below with reference to the accompanying drawings. They show:

Figure 1 is a flow chart illustrating the method for producing a battery module according to an embodiment of the invention;

Figure 2a is a schematic representation of a first battery cell according to a further embodiment of the invention;

Figure 2b schematically illustrates a determined spatially resolved distribution of a swelling behavior of a first battery cell according to a further embodiment of the invention;

Figure 3 is a schematic representation of a battery module according to a further embodiment of the invention; and

Figure 4 is a schematic representation of a second battery cell and a control unit of a battery module according to a further embodiment of the invention.

The embodiments shown in the figures correspond at least partially, so that similar or identical parts are provided with the same reference numerals and for their explanation reference is also made to the description of the other embodiments or figures in order to avoid repetition.

Figure 1 shows a flow chart to illustrate a method 1 for producing a battery module with one or more battery cells, preferably for providing electrical traction energy for a vehicle.

It has already been established above that battery cells, such as lithium-ion batteries, expand during the charging process, which leads to an increase in the volume of the cell. During the discharge process, this volume increase decreases again, except for a small irreversible portion. The irreversible portion of the volume increase is called swelling, the reversible portion is called breathing. The extent of the swelling is an indicator of the aging state of health (SoH) of the cells.

It is advantageous to equip battery cells with an ageing monitoring system in order to detect when the battery cell has reached its end of life (EoL), i.e. when the ageing state of the battery cell has increased to such an extent that safe and economically viable use of the battery cell is no longer possible.

For this purpose, in step S10 of the method 1 presented, a spatially resolved distribution of a threshold behavior of a first battery cell is determined during and/or at the end of a cyclization. A cyclization refers to the repeated charging and discharging of battery cells, e.g. in a test bench as part of the development work on new or improved battery modules.

Based on the determined spatially resolved distribution of the swelling behavior, in step S20 the location (position) on the battery cell, preferably on its outer cell wall, is determined which has a swelling behavior based on which the aging state, in particular an EoL state of the battery cell, can be determined and monitored particularly reliably. This location (position) determined in this way is selected as the sensor target position in order to arrange a sensor there for monitoring the swelling behavior if battery modules with battery cells of the same type as the first battery cell or with battery cells for which the previously spatially resolved distribution of the swelling behavior is also valid are subsequently manufactured (step S30). The battery cells of the battery module are also referred to as second battery cells. The terms “first battery cell” and “second battery cell” serve only to distinguish the two components and do not refer to a sequence or a number. In particular, the battery module manufactured in step S30 may comprise several second battery cells.

Using the method 1 presented, the aging state of battery modules can be monitored cost-effectively, since only a single sensor is needed to monitor a battery cell. The monitoring is nevertheless reliable, since the sensor is arranged at a previously selected target sensor position, which has sufficient significance for the aging state of the entire battery cell. The two steps S10 and S20 are explained in more detail below using Figures 2a and 2b.

Figure 2a shows a first battery cell 4 during or at the end of a cycling process. The first battery cell 4 is preferably a prismatic battery cell (as shown) or a pouch cell. The first battery cell 4 is a battery cell that expands as a result of at least one charging and/or discharging process, and can therefore change its state from a non-expanded state to an expanded state and vice versa. The swelling behavior of the first battery cell 4 is not necessarily the same everywhere for different locations on the first battery cell 4, but can differ for different locations on the first battery cell 4.

The first battery cell 4 can, for example, be arranged in a battery test stand (not shown), preferably clamped using a frame 11. The frame can be part of a clamping device (so-called “cell jig”) (see below).

Particularly advantageous and precise measurement results can be achieved if the cycling of the first battery cell 4 preferably takes place under conditions that are modeled on those during operation of an electrical energy storage device, e.g. battery module, in which one or more such battery cells are installed. For this purpose, a certain pressure can be exerted on the first battery cell 4 during cycling, for example, which corresponds to a pressure that would be exerted by a housing of the battery module. The method makes it possible for the first battery cell 4 to be measured individually without it being installed in a battery module.

To carry out step S10, the battery test bench and, for example, the clamping device for the first battery cell 4 should therefore preferably be designed in such a way that they are as similar or as accurate as possible to the installation situation of a (further) battery cell in an energy storage device or battery module. This is advantageous because the resulting surface pressure depends on the properties of the battery cell (swelling behavior, stiffness) and the properties of the clamping/installation situation. Appropriate clamping devices (so-called "cell jigs") are already known from practice, with which the stiffness properties of the battery module or module housing can be generated and/or simulated. Such a clamping device can advantageously be used during cycling. Such a clamping device can comprise, for example, rigid plates, e.g. made of steel and/or aluminum, as well as clamping screws for clamping the first battery cell and e.g. of the frame 11 between the plates and for generating the clamping force. The clamping device ensures that the necessary clamping force can be applied or that the clamping force correlates with the state of charge in the same way as in the battery module. In addition, the battery cell can be clamped in a rubber frame that is part of the clamping device or is provided in addition to it. If there are cell intermediate layers in the battery module between the battery cells or between battery cells and other parts of the energy storage device that have a certain elasticity/plasticity and possibly windows (e.g. “gappads”, “rubber frames”), this can also be taken into account by designing the clamping device accordingly in order to observe the same swelling behavior of the first battery cell 4 during cycling as occurs in battery modules in which comparable battery cells are installed.

In Figure 2a, the force F exerted on the first battery cell 4 during cycling is indicated by arrows on both sides of the first battery cell 4. The force F preferably acts evenly on the entire frame 11. In the space between the material of the frame 11, the first battery cell 4 can have space for volume expansion, which corresponds, for example, to the use of rubber frames as cell interlayers in the battery module. The frame 11 is preferably made of elastic material, e.g. rubber. The use of elastic material means that the first battery cell 4 can be securely fixed without damaging the first battery cell 4.

A planar measuring device 17 is preferably arranged on at least one housing side 14 of the housing 12 of the first battery cell 4, with which the spatially resolved distribution 3 of the swelling behavior can be determined in accordance with step S10 of Figure 1. The housing side 14 preferably corresponds to the housing side 14 on which the swelling behavior is particularly pronounced. Typically, this corresponds to the housing side 14 that runs parallel to the electrode stacks or parallel to the electrode winding surfaces of the battery cell, since the swelling usually takes place in the normal direction to the cell winding/cell stack. The planar measuring arrangement 17 preferably covers at least 80% of the area of the housing side 14. Particularly preferably, the entire area occupied by the electrode stacks or the electrode windings inside the first battery cell 4 is covered in order to record a maximum of the swelling behavior of the first battery cell 4 as reliably as possible. The swelling behavior can, for example, be a volume expansion of the battery cell and/or a surface pressure exerted by the battery cell interior 8 on the battery cell wall 9. The planar measuring device 17 is designed, for example, to measure a surface pressure and comprises, for example, several measuring points 13, which are preferably arranged in a grid. The measuring device 17 can comprise several sensors for measuring a surface pressure, each of which is arranged at one of the measuring points 13. A value or a temporal progression of the swelling behavior is measured at each measuring point 13. Figure 2b shows the result of determining the spatially resolved distribution 3 of the swelling behavior using a planar measuring device 17.

In Figure 2b, each of the squares shown represents a measuring point 13. For better clarity, only four of the squares have been provided with corresponding reference symbols. The individual measuring points 13 are arranged, for example, in a grid pattern along the x-axis and the y-axis of the coordinate system shown. The coordinate systems of Figures 2a and 2b match. The individual measuring points 13 can be square, i.e. have the same edge lengths in the x-direction and y-direction, but they can also be rectangular, oval or have a completely different shape. The individual measuring points 13 can be directly adjacent to one another or can be arranged with spaces between the individual measuring points 13. An arrangement in which the individual measuring points 13 are arranged in a non-grid pattern is also possible. Such a planar measuring device 17 can be implemented, for example, based on the I-Scan System® from Tekscan® Inc., 333 Providence Highway, Norwood, MA 02062, USA.

Depending on the spatially resolved distribution 3 of the swelling behavior determined by means of the planar measuring device 17, a sensor target position 5 is selected. The sensor target position preferably corresponds to the measuring point 13 that has a swelling behavior that is most meaningful in comparison to the other measuring points 13 in order to determine an aging state, preferably an EoL state, of the battery cell. In other words, the sensor target position 5 can be a point on the first battery cell 4 that is a point representative of aging and/or safety assessment of the first battery cell 4 and/or that has a swelling behavior from which cell aging and/or reaching an end-of-life state of the first battery cell 4 can be derived. The end of life is a term for the point in time at which previously defined values of the first battery cell 4 are undercut due to aging. These previously defined values are specified by the manufacturer of the first battery cell 4 or can be determined by appropriate tests. This includes, for example, a resistance, a current, a Remaining capacity, a remaining energy storage capacity, a pressure inside the first battery cell 4 or a force, e.g. 20 kN, which the first battery cell 4 exerts on a battery cell wall 9.

For example, a location can be selected as the sensor target position 5 which, at the end of the cycling, has the greatest swelling behavior and/or the greatest surface pressure generated by the battery cell interior 8 on the battery cell wall 9. The surface pressure refers to a pressure, i.e. a force per area, which the first battery cell 4 exerts on a wall of the first battery cell 4 due to the swelling behavior. These locations are particularly suitable as sensor target positions because they are particularly informative about the aging state of the rest of the battery cell.

In the example shown in Figure 2b, the color of the respective measuring points 13 represents a measure of the surface pressure or the pressure at the end of the cycling that is exerted by the battery cell interior 8 on the battery cell wall 9. A darker color means a greater surface pressure or a greater pressure. It can be seen that a maximum has formed at the point (x _m , y _m ). In the example shown in Figure 2, this point is selected as the sensor target position 5 in accordance with step S20 of Figure 1. In addition, the limit value that a sensor arranged at the sensor target position 5 indicates when the end of the life of the battery cell 4 is reached is preferably determined.

In addition to a direct measurement of the swelling behavior, e.g. by means of a spatially resolved measurement of the surface pressure of the first battery cell 4, this can alternatively be done, for example, by means of a geometric measurement of the first battery cell 4. Another possibility is to disassemble the first battery cell 4 after cycling and to analyze it in the disassembled state with regard to the swelling behavior. Using the information obtained in the disassembled state, conclusions can be drawn about the distribution 3 of the spatially resolved swelling behavior of the non-disassembled battery cell.

Figure 3 shows a schematic representation of a battery module 2 according to an embodiment of the present disclosure, which was manufactured according to step S30 of Figure 1. The second battery cells 6 of Figure 3 are preferably identical in construction to a first battery cell according to steps S10 and S20 of Figure 1, based on which a sensor target position 5 was selected depending on the determined spatially resolved distribution of a threshold behavior. The battery cells 6 are preferably designed as battery cell stacks The respective battery cells 6 can be connected in series or in parallel, for example by means of so-called cell connectors.

In Figure 3, a sensor 7 for detecting the swelling behavior of the second battery cell is arranged at the sensor target position 5. The sensor 7 for detecting the swelling behavior can be, for example, a force, pressure and/or surface pressure sensor. For example, the sensor 7 for detecting the swelling behavior can be designed as a sensor for measuring force, which outputs the force between two surfaces, for example the battery cell interior and the battery cell wall 9 of the housing 12 of the second battery cell 6, or the battery cell wall 9 and another surface adjacent to it, for example the module casing 20 of the battery module 2. The sensor 7 for detecting the swelling behavior preferably has the following properties:

Sensitivity to the measured quantity to be measured, e.g. a force, a pressure, a surface pressure and/or a geometric expansion, whereby it may be sufficient that an exceedance of a predetermined limit value is detected;

Occupying little or negligible installation space compared to the volume of the battery cell 6 or the battery module 2 in order to avoid a reduction in the energy density of the battery module 2;

Availability in large quantities; easy integration of the sensor 7 into the battery module 2; easy evaluation of the sensor signal, preferably evaluation with existing control units, e.g. a battery control unit, a powertrain control unit and/or a vehicle control unit; and cost-effectiveness.

The sensor 7 for detecting the swelling behavior can particularly preferably be designed as a film sensor and/or as a sensor that preferably has a thickness of less than 1 mm, more preferably a thickness of less than 0.5 mm. The sensor 7 for detecting the swelling behavior can thus be arranged particularly well at a flexibly selectable location on the second battery cell 6.

In the simplest case, it may be sufficient to simply exceed the threshold at one point of the second battery cell 6. In this case, the sensor 7 can be designed as a simple electrical switch, for example. If a battery module 2 consists of several second battery cells 6, it may be sufficient to arrange a sensor 7 only on a second battery cell 6 of the battery module 2 if, for example, the second battery cell 6 on which the sensor 7 is arranged is representative of the aging behavior of all battery cells of the battery module 2.

For simple and cost-effective integration, the change in the sensor output signal when a predetermined trigger threshold is exceeded can preferably be large enough to be measured or evaluated directly or after amplification with simple operational amplifier circuits using standard microcontrollers. For analog inputs of a typical microcontroller, this can mean, for example, that with a voltage range of 0 - 5 V and a resolution of 8 bits, the sensor signal or the sensor signal after the operational amplifier circuit changes by at least 0.1 V when the trigger threshold is exceeded and that the noise is a maximum of 20% of this value. For digital inputs of a typical microcontroller, the difference in the measurement signal can preferably be large enough that when the trigger threshold is reached, a change from "low" (measurement signal below the trigger threshold) to "high" (measurement signal above the trigger threshold), or vice versa from "high" to "low", is reliably triggered at the digital input of the microcontroller. For this, the change in a voltage signal, for example, is preferably at least 2.5 V.

Such a sensor 7 is, for example, a film-like force sensor. Such sensors are particularly advantageous for being attached to the sensor target position. Film-like force sensors are characterized by their low thickness. They can, for example, comprise two film-like layers of carrier material (polyester). A conductive material (e.g. silver) is applied to each layer, followed by a layer of pressure-sensitive, semiconductive ink. Both layers are glued together at the edges. The active sensor surface is defined by the silver above the pressure-sensitive ink. The silver conductor tracks extend from the measuring surface to the connection pins at the other end of the sensor. Such a sensor works as a force-sensitive resistor in an electrical circuit. When the sensor is not loaded, its resistance is very high. If force acts on the sensor, the conductivity of the semiconductive ink increases. The resistance can be read, for example, using a multimeter that is attached to conductive pins on the sensor. Such sensors are known in the art, e.g. B. as Flexi ForceO force sensors from Tekscan®. Of course, other force, pressure and/or surface pressure sensors known from the state of the art can also be used.

The strain gauges frequently used in development work also meet the criteria of sensitivity to the measured variable to be recorded, taking up negligible installation space and being available in large quantities. However, the relative change in resistance output by a strain gauge is typically in the order of magnitude of the relative change in length to be measured. When measuring the swelling behavior, the relative change in length is typically a few 10 to a few 100 pm/m, which corresponds to a relative change in resistance of 10' ⁶ to 10' ^4. Complex and expensive evaluation electronics are required to evaluate such small changes in resistance, so the use of strain gauges is possible, but is associated with higher costs. In addition, a strain gauge must be laboriously connected to the object to be measured for reliable measurement, e.g. glued over the entire surface, which makes it difficult to integrate it into the battery module 2.

In the example in Figure 3, a single sensor 7 can be seen for detecting the threshold behavior. However, several sensors 7 can also be arranged on different second battery cells 6. However, a maximum of one sensor 7 for detecting the threshold behavior is preferably arranged on each of the second battery cells 6 at a single sensor target position 5.

As an example, Figure 3 shows a battery module 2 that includes four second battery cells 6. However, the battery module 2 could also include more or fewer than four second battery cells 6. In addition, the battery module 2 can include additional battery cells (not shown) that are not identical in construction to the second battery cells 6.

Figure 4 shows a schematic representation of a second battery cell 6 according to a further embodiment of the invention. The second battery cell 6 is in turn part of a battery module 2. The battery module and any additional second battery cells 6 of the battery cell stack are not shown here for the sake of clarity. A sensor 7 for detecting the swelling behavior at the selected sensor target position 5 is arranged on the second battery cell 6 in accordance with step S30 of Figure 1. In addition, Figure 4 shows a control unit 15 which is in signal connection 16 with the sensor 7 for detecting the swelling behavior. The control unit 15 receives an output signal 18 from the sensor 7 and is set up to monitor a limit value for the sensor 7 depending on the sensor signals. The limit value is determined depending on the swelling behavior of the first battery cell determined at the sensor target position 5 at the end of the cycling, preferably at the end of the life of the first battery cell. The limit value indicates that the end of the life of the first and/or second battery cell 6 has been reached. This means that it is determined which measured value the sensor 7 arranged at the sensor target position 5 for detecting the swelling behavior outputs when the end of the life of the second battery cell 6 is reached. The limit value can preferably be set somewhat lower than it would be at the actual end of life in order to have an additional safety margin available until the actual end of life. This enables particularly simple monitoring and thus particularly safe operation of the battery module produced.

The control unit 15 can, for example, issue a warning signal to a user when the limit value has been exceeded or the output signal 18 approaches the limit value. The user thus knows that the second battery cell 6 and/or the battery module must be replaced.

Preferably, the control unit 15 is additionally connected to the second battery cell 6 by means of a signal connection 16, so that the control unit 15 can control the second battery cell 6 by means of an input signal 19 received from the battery cell. For example, the control unit 15 can reduce the depth of discharge of the second battery cell 6 when the output signal 18 from the sensor 7 approaches the limit value. In this way, the service life of the second battery cell 6 can be increased. Preferably, the control unit 15 is designed to completely deactivate the second battery cell 6 if a safety limit value is exceeded, above which continued operation of the second battery cell 6 would involve too great a safety risk.

The control unit 15 can, for example, be part of a battery management system of the vehicle or a cell management system of the battery module. The sensor 7 for detecting the threshold behavior is preferably designed to generate an output signal 18, which can be measured and/or processed directly, or with only simple operational amplifier circuits, with a microcontroller 10. Such circuits have the advantage that they can be implemented particularly easily and inexpensively. They are also less susceptible to failure during operation and therefore represent a particularly robust solution.

Although the invention has been described with reference to particular embodiments, it will be apparent to one skilled in the art that various changes may be made and equivalents may be substituted without departing from the scope of the invention. Accordingly, the invention is not intended to be limited to the disclosed embodiments, but is intended to include all embodiments falling within the scope of the appended claims. In particular, the invention also claims protection for the subject matter and features of the dependent claims independently of the claims referred to.

List of reference symbols

1 procedure

2 Battery module

3 Spatially resolved distribution of a swell behavior

4 First battery cell

5 Sensor target position

6 Second battery cell

7 Sensor for detecting the swelling behaviour

8 Battery cell interior

9 Battery cell wall

10 microcontrollers

11 frames

12 Housing

13 Measuring point

14 Housing side

15 Control unit

16 Signal connection

17 Surface measuring device

18 Output signal

19 Input signal

20 Module cover

Claims

Patent claims 1 . Method (1) for producing a storage device for electrical energy, preferably a battery module (2) for providing electrical traction energy for a vehicle, comprising the steps: Determining (S10) a spatially resolved distribution (3) of a threshold behavior of a first battery cell (4) during and/or at the end of a cycling of the first battery cell (4); Selections (S20), depending on the determined spatially resolved distribution (3) of the threshold behavior, of a sensor target position (5), Production (S30) of a storage device for electrical energy (2) which comprises one or more second battery cells (6) which are preferably structurally identical to the first battery cell (4), wherein a sensor (7) for detecting the swelling behavior of the second battery cell (6) is arranged on at least one of the one or more second battery cells (6) at the selected sensor target position (5). 2. Method (1) according to claim 1, wherein the sensor target position (5) is a location of the first (4) and preferably second (6) battery cell, a) which is a location representative of an aging and/or safety assessment of the battery cell (4, 6); and/or b) which has a threshold behavior from which cell aging and/or reaching an end-of-life, EoL state of the battery cell (4, 6) can be derived. 3. Method (1) according to claim 1 or 2, wherein the sensor target position (5) is a location of the first (4) and preferably second (6) battery cell, a) which has the greatest swelling behavior, and/or b) which has the greatest surface pressure which is generated by the battery cell interior (8) on the battery cell wall (9), preferably after the end of the cycling. 4. Method (1) according to one of the preceding claims, wherein the sensor (5) for detecting the swelling behavior a) is a force, pressure and/or surface pressure sensor, and/or b) is a sensor for measuring force between two surfaces. 5. Method (1) according to one of the preceding claims, wherein the sensor (5) for detecting the swelling behavior a) is designed as a film sensor and/or as a sensor which preferably has a thickness of less than 1 mm, more preferably a thickness of less than 0, 5 mm; and/or b) is a sensor switch having two conductors which only touch each other when a swelling of the battery cell (4, 6) exceeds a predetermined threshold value; and/or c) is designed to generate an output signal (18) which can be measured and/or evaluated directly or only with simple operational amplifier circuits with a microcontroller (10); and/or d) is not designed as a strain gauge. 6. Method (1) according to one of the preceding claims, wherein determining (S10) the spatially resolved distribution of the swelling behavior of the first battery cell (4) during and/or at the end of the cycling of the first battery cell (4) comprises: a) clamping the first battery cell (4) in a clamping device, preferably comprising a frame (11), for example a rubber frame, and/or b) cycling the first battery cell (4) until the end of its life and after reaching the end of its life, measuring a swelling force per unit area on a housing (12) of the first battery cell (4) and/or measuring a volume expansion of the first battery cell (4) at several measuring points (13), wherein the several measuring points (13) are preferably arranged in a grid and/or cover at least 80% of an area of a housing side (14) or a cell coil/or stack of the first battery cell (4). 7. Method (1) according to claim 6, wherein the sensor target position (5) is selected as the measuring point (13) which, of all measuring points (13), has a largest threshold force per unit area and/or a largest volume expansion. 8. Method (1) according to one of the preceding claims, further comprising: depending on the threshold behavior of the first battery cell (4) determined at the sensor target position (5) at the end of the cycling, determining a limit value for the sensor (7) for detecting the threshold behavior, which indicates reaching the end of the life of the first (4) and/or second (6) battery cells. 9. Method (1) according to claim 8, wherein the manufacture (S30) of the memory (2) comprises: Provision of a control unit (15) which is in signal connection (16) with the sensor (7) and which is configured to monitor the limit value for the sensor (7) depending on the sensor signals. 10. Storage device for electrical energy (2), preferably a battery module (2) for providing electrical traction energy for a vehicle, produced by a method (1) according to one of the preceding claims. 11. Storage device for electrical energy (2), preferably battery module (2) for providing electrical traction energy for a vehicle, which has one or more battery cells (6), wherein at least one of the one or more battery cells (6) has a sensor (7) is arranged at a predetermined sensor target position (5) for detecting a swelling behavior of the battery cell (6), wherein the sensor target position (5) is a location on the battery cells (6) a) which is a location representative of aging and/or safety assessment; and/or b) which has a swelling behavior from which cell aging and/or reaching an end-of-life, EoL state of the battery cell (6) can be deduced. 12. Storage device for electrical energy (2) according to claim 11, wherein the sensor target position (5) is a location on the battery cells (6) which a) has the greatest swelling behavior and/or b) has the greatest surface pressure which is generated by the battery cell interior (8) on the battery cell wall (9), preferably after the end of the cycling. 13. Storage device for electrical energy (2) according to one of claims 10 to 12, wherein at most one sensor (7) for detecting the threshold behavior is attached to the one or more battery cells (6). 14. Vehicle, preferably a motor vehicle, comprising a storage device for electrical energy (2) according to one of claims 10 to 12. 15. Vehicle according to claim 14, which is designed as a commercial vehicle, preferably as a truck or bus.