EP3942624A1

EP3942624A1 - Method for producing a battery

Info

Publication number: EP3942624A1
Application number: EP20705902.3A
Authority: EP
Inventors: Henning Dreger
Original assignee: Volkswagen AG
Current assignee: Volkswagen AG
Priority date: 2019-04-24
Filing date: 2020-02-12
Publication date: 2022-01-26
Also published as: DE102019205825A1; CN114008815A; WO2020216491A1; US20220143894A1

Abstract

The invention relates to a method for producing batteries in which a suspension (12) with a variable product parameter (14) is extruded in an extrusion process by means of an extruder (6) as an electrode paste (4), in which method a number of extrusion parameters (SK, GE, cm, n, V, t, p, T, γ, f) of the extrusion process is determined, an extruder-specific stress model (16) is calculated on the basis of the extrusion parameters (SK, gE, cm, n, V, t, p, τ, γ, f), and the extrusion process is controlled and/or regulated on the basis of the stress model (16).

Description

description

Method of manufacturing a battery

The invention relates to a method for producing a battery, in which a suspension is extruded denpaste in an extrusion process by means of an extruder as an electrode. The invention further relates to an apparatus for performing the method and a battery produced by the method.

Electrically drivable or powered motor vehicles, such as electric or hybrid vehicles, typically have an electric motor as the drive machine, which is coupled to a vehicle-internal electrical (high-voltage) energy store for supplying electrical energy. Such energy storage devices are designed, for example, in the form of (vehicle) batteries.

An electrochemical battery here is to be understood in particular as a so-called secondary battery (secondary battery) of the motor vehicle, in which a used chemical energy can be restored by means of an electrical (charging) process. Such batteries are carried out in particular as electrochemical accumulators, for example as lithium-ion accumulators. To generate or provide a sufficiently high operating voltage, such batteries typically have several individual battery cells, which are connected in a modular manner.

Batteries of the type mentioned have a cathode and an anode as well as a separator and an electrolyte on a battery cell level. The electrodes, i.e. the anode and the cathode, are made from a respective electrode -active material. The electrode active material is a prerequisite for this a powerful battery. To improve the electrical properties, the electrode active materials are often mixed with conductive particles as a conductive additive. Due to their high conductivity, carbon-based conductive particles, for example conductive soot or conductive graphite, are an important component of lithium-ion batteries, which reduce the electrode resistance, and thus the internal resistance of the battery.

Disadvantageously, the production of electrically powered or drivable motor vehicles, in particular for the batteries used for this, requires a high level of energy. It is therefore desirable to reduce the energy consumption and the cost of producing the batteries as much as possible.

For the production of batteries, extrusion processes are possible in which the electrodes of the battery cells are produced from a plastic mass which is pressed from a nozzle element. By integrating a continuous extrusion process into the lithium-ion battery cell production, the high efficiency of the mixing process makes it possible to significantly reduce the process time and the energy required in the production of batteries. The electrodes of the battery or the battery cells are produced here by means of extruded electrode pastes, the paste quality being determined by specific criteria or product parameters, for example by a particle size of the conductive particles. The electrode pastes are then applied, for example, to a respective current conductor, in particular to a copper or aluminum foil.

The regulation and / or control of a continuously operated extruder, that is, the regulation and / or control of its extrusion or operating parameters, for the production of electrode pastes for lithium-ion batteries has so far been carried out manually and after sampling and analysis of the electrode paste.

In other words, machine parameters such as the speed or the mass or volume flow of the extruder are only regulated and / or set manually. This results in a low degree of automation, as a result, there is worsened response times and increased scrap, which has a negative impact on the process capability in the manufacture of batteries. The invention is based on the object of specifying a particularly suitable method for producing a battery. In particular, the most effective and automated extrusion process possible should be made possible. The invention is also based on the object of specifying a particularly suitable device for implementing the method, as well as a battery produced according to such a method.

With regard to the method, the object is achieved according to the invention with the features of claim 1 and with regard to the device with the features of claim 9 and with regard to the battery with the features of claim 10. Advantageous refinements and developments are the subject of the sub-claims. The advantages and features mentioned with regard to the process can also be applied to the extruder and the battery, and vice versa. The method according to the invention is suitable and designed for the production of batteries, in particular for the production of lithium-ion battery cells. According to the method, a suspension with a variable product parameter is extruded as an electrode paste in an extrusion process by means of an extruder, that is to say is produced essentially continuously. An electrode paste is to be understood here as the extrudate, that is to say the extruded composite of the suspension. The suspension is essentially a solid composition consisting of an electrode active material and a binder (binding agent), it being possible for additional conductive additives to be added. In a first process step, a number of extrusion parameters are determined as operating or machine parameters of the extrusion process or of the extruder. These extrusion parameters are used in a In the following process step, an extruder-specific load model is calculated.

The extrusion process is then controlled and / or regulated on the basis of the stored stress model. The conjunction “and / or” is to be understood here and below in such a way that the features linked by means of this conjunction can be formed both together and as alternatives to one another. This means that the extruder or its extrusion parameters are automatically and preferably continuously or continuously controlled and / or regulated during operation by means of the calculated stress model, in particular with regard to the product parameter. This realizes a particularly suitable method for producing a battery.

The method according to the invention essentially realizes a real-time adaptation of the extrusion parameters, that is to say of the production parameters, whereby production rejects are reduced. In particular, through automatic regulation and / or control based on the stress model, constant product quality is possible, even with changed product parameters, without manual intervention by a user being necessary. The extrusion parameters are recorded, for example, as analysis data, for example in the form of viscosity data or dwell time data, and processed by the stored stress model in such a way that independent and automatic regulation and / or control of the extruder is possible. The extrusion parameters can, for example, initially be provided by external sensors that are not part of the extruder (offline analysis) and, in the course of operation, additionally or alternatively by extruder-integrated sensors (inline analysis), or predicted using appropriate models or be forecast. In a preferred development, a dispersion of conductive particles in the suspension is used as the product parameter. This means that conductive particles are added to the suspension as a conductive additive, with the extruder-specific load model for continuous and homogeneous dispersion, i.e. the most uniform possible distribution, the conductive particles in the suspension will be calculated.

In an advantageous embodiment, in order to calculate the stress model, a product parameter or a quality parameter of the conductive particles, for example a particle size distribution of the conductive particles, is correlated with a specific energy required for a deagglomeration of the conductive particles of this product parameter. In other words, the stress model is based on a calculation of a specific energy contribution which is required for the deagglomeration (digestion) of the conductive particles. This enables particularly reliable and efficient control and / or regulation of the extruder operation, which is advantageously transferred to the manufacture of the battery.

To calculate or determine the stress model, for example, the product parameter is characterized by means of a measurement and plotted against the specific energy occurring with the respective extrusion or process parameters. A model curve is then adapted or (adapted) fitted to this data. This correlation enables the production of an electrode paste with a specific product parameter, since the specific energy required for this can be determined from the stored model curve, and the extrusion parameters can thus be controlled and / or regulated using the stress model.

The specific energy is to be understood in particular as a specific mechanical energy input. As an extrusion parameter, the specific energy is a measure of the stress on the product (the electrode paste) from the extrusion process. The specific energy characterizes the extruded electrode paste regardless of the size or dimensions of the extruder. Thus, the correlation or the link between the specific energy and the product parameter is an essentially material-specific constant of the electrode paste. This makes it possible to easily scale (scale-up) a manufacturing plant or device operated with the method, as a result of which the production of the battery is simplified. In a suitable embodiment, in particular a particle size of the conducting particles is used as the product parameter. The conductive particles as conductive additive should be distributed as homogeneously or evenly as possible in the suspension in order to ensure improved electrical performance of the battery. Due to the optical properties and the process-related changes in the

Particle size is a particularly suitable product parameter for calculating the stress model. During dispersing, the conductive particles, which are largely present as agglomerates, are stressed and disagglomerated. This stress, which is primarily caused by shear, results in changes in the agglomerate or aggregate size of the lead particles, i.e. structural changes in the suspension, which can be easily detected with a suitable analysis or measurement method and thus used as a product parameter or assessment criterion .

The specific energy is dependent on a speed and a (volume or mass) throughput of the extruder, and can be determined, for example, by measuring the torque on an extruder shaft of the extruder. With increasing speed and / or decreasing throughput, the specific energy increases. In the manufacture of electrode pastes, the problem arises that the torques that occur are close to an no-load output of the extruder, where comparatively large inaccuracies in the determination of the specific energy occur. According to the method, it is therefore provided in a preferred embodiment that the specific energy is determined as a function of a shear stress and a degree of filling and a suspension density. This enables a reliable and precise determination of the specific energy.

The shear stress and the degree of filling as well as the suspension density are extrusion parameters of the extruder or the extrusion process. The shear stress is in particular a measure of the (shear) stress of the extrusion process. The degree of filling is in particular a measure of the filling of the extruder, i.e. a measure of the volume of the suspension in the extruder sion and the conductive particle. The suspension density is in particular the density of the suspension with the conductive particles dispersed therein.

The shear stress is determined indirectly using rheological methods, for example. In a suitable embodiment, the shear stress is preferably determined using a shear rate test in order to determine the shear stress on the suspension in the extruder. This enables a reliable determination or detection of the shear stress. In an advantageous embodiment, the shear stress is preferably determined on the basis of a rheological model in the case of a sufficiently large amount of data. This enables the shear stress to be determined without the availability of physical measurement data. In other words, the shear stress is recorded at the beginning of the method, in particular using shear rate tests, and a model curve is determined in the course of the method on the basis of the recorded data, by means of which the shear stress is then preferably determined without measurement.

For the deagglomeration of the conductive particles in the suspension, the stress caused by shear and its height in the extruder are relevant. The volumes which experience high shear stress are suitably dimensioned to be relatively large in the extruder.

The shear rate is determined, for example, by means of the geometric properties of the extruder, that is to say by means of the geometric dimensions and dimensions of the extruder elements (conveying elements, kneading elements). In the case of a twin-screw or twin-screw extruder, the geometrical properties relevant for determining the shear rate are, for example, a diameter of the housing bores, a distance between the shaft centers, an outer diameter of the conveyor elements, an inner diameter of the conveyor elements, an outer diameter of the kneading elements, and an inner diameter of the kneading elements ments. The play between conveying element and wall and the play between kneading element and are determined from these geometric properties Wall, that is the areas between the housing wall and the screw crest, and the gusset clearance, ie the gusset area between the two extruder screws. In these areas, due to the geometric dimensions, particularly high shear rates occur. The shear rates that occur can be calculated using the clearance dimensions for a given extruder speed, for example using a two-plate model.

In order to be able to estimate the shear stresses that act within the extruder at certain speeds or shear rates on the respective suspension, a shear rate test is carried out in which so-called flow curves are determined by means of rotation tests with the respective electrode paste. Here at a sample of the electrode paste after dispersion in a rotary viscometer between two surfaces is sheared at a precisely defined distance. With this measurement setup, different shear rates can be generated in a targeted manner and the resulting shear stresses can be determined at a certain shear rate, with the shear rates being examined in particular in the area of the gusset clearance and in the areas between the housing wall and the screw crest. The or each shear rate test provides a flow curve for each extruded electrode paste, which can be plotted in a shear rate-shear stress diagram. A corresponding curve profile is then adapted or (fitted) fitted to the measured (electrode paste-specific) flow curves. The course of the curve can be adapted or adapted in particular by means of a so-called Herschel-Bulkley curve. The adapted or fitted curve shape then enables a simple calculation or determination of the shear stress at different shear rates. The course of the curve or the functional parameters of the fit function are expediently stored for later calculations or inter- / extrapolation of the shear stress and / or the specific energy, also for suspensions with unknown rheological properties. Thus it is possible that for suspensions with unknown rheological properties, such as a different solids content with constant proportions of solids, flow curves in Depending on the solids content can be determined, since the fit or function parameters of the adapted Herschel-Bulkley curve have a linear dependency in a wide solids content range. In a possible development, the degree of filling is determined by means of an average dwell time and a volume flow as extrusion parameters. The residence time is a measure of the frequency of stress, i.e. the number of stresses that act on the suspension and the conductive particles or agglomerates in the course of the extrusion process. This enables reliable determination of the degree of filling.

The degree of filling is therefore also a measure of the dwell time behavior of the extrusion process, which has a great influence on the product quality of the electrode paste, both during melting and during dispersion. When using a co-rotating twin screw extruder, there is a dwell time distribution. While the minimum residence time is important for dispersive mixing, the residence time distribution is of particular importance for distributive mixing. The dwell time is particularly dependent on the process or extrusion parameters throughput (volume flow) and (extruder) speed as well as a screw configuration. Depending on the configuration, the screw configuration produces a narrow (pure screw conveyor) or a wide (screw with many tooth mixing / kneading elements or return elements) distribution width. The screw configuration is a fixed, known parameter of the extruder, so that an averaged filling level can be determined in a simple manner by measuring or recording the speed and the conveyed volume flow.

In a preferred embodiment, a twin-screw or twin-screw extruder is used as the extruder. As a result, a particularly suitable extruder is used for the manufacture of batteries. The twin-screw extruder here preferably has a co-rotating and closely intermeshing structure with a high mixing and dispersing effect. In a suitable embodiment, a conductive carbon black (CB) is used as the conductive particle. As a result, a particularly suitable conductive additive is used for the battery, in particular for a lithium-ion battery.

In a preferred application, the method is used to operate a device for manufacturing batteries. The device has an extruder, in particular a twin-screw or twin-screw extruder, for extruding electrode pastes, which is coupled to a controller, that is to say a control device. The controller is generally set up here - in terms of program and / or circuitry - to carry out the method according to the invention described above. The controller is thus specifically set up to monitor the extrusion process, in particular to determine the extrusion parameters, and to control and / or regulate the extrusion process on the basis of a stored stress model.

In a preferred embodiment, the controller is at least essentially formed by a microcontroller with a processor and a data memory, in which the functionality for performing the method according to the invention is implemented in the form of operating software (firmware), so that the method - if necessary in interaction with a device user - is carried out automatically when the operating software is executed in the microcontroller. Within the scope of the invention, however, the controller can alternatively also be formed by a non-programmable electronic component, such as an application-specific integrated circuit (ASIC), in which the functionality for performing the method according to the invention is implemented with circuitry.

During the manufacture of a battery, an electrode paste is extruded by means of the extruder. The electrode paste is made from the suspension (electrode active material and binder) and the added conductive particles by means of the

Extrusion process generated. According to the method, for example, the screw configuration of the extruder is first determined and stored in a memory of the con trollers deposited. Then, for example, a minimum average value of the particle size of the conductive particles at a maximum, coatable solids content, a maximum speed and a minimum volume flow is determined as an extrusion parameter. This analysis or extrusion parameter is subsequently determined several times for suspensions with a reduced solids content, at a reduced (extruder) speed and an increased volume flow, the mean residence time in the extruder being determined in each case. Using these extrusion parameters, the shear stress and the degree of filling are determined and fed to the stored stress model. The controller controls and / or regulates the extrusion process based on the stress model with regard to a desired particle size of the conductive particles in the electrode paste by setting a specific energy required for this.

The controller can therefore reliably determine a stress model for safe and effective operation of the device on the basis of a few measurements or tests.

The battery according to the invention is manufactured by means of the method described above. The battery is suitable and set up for a motor vehicle. The battery is designed, for example, as a lithium-ion battery with several interconnected battery cells.

An exemplary embodiment of the invention is explained in more detail below with reference to a drawing. Show in it:

Fig. 1 in a schematic and simplified representation of an apparatus for the manufacture of batteries, with an extruder and a controller,

2 shows a flow diagram of a method for producing batteries,

3 a shear stress-shear rate diagram with five flow curves for different solids contents,

Fig. 4 is a flow rate-residence time diagram for different extruder speeds, and 5 shows a specific energy-particle size diagram for different electrode pastes and volume flows.

Corresponding parts and sizes are always provided with the same reference symbols in all figures.

1 shows a device 2 for positioning a battery, in particular for producing an electrode paste 4 for a battery cell of the battery. The device 2 has an extruder 6 in the form of a twin-screw or twin-screw extruder. The extruder 6 has only parts of Darge presented extruder elements 8 as conveying and / or kneading elements, which are driven in the same direction and are designed to mesh closely with one another. The extruder 6 is coupled to a controller 10. To produce the battery, the electrode paste 4 is extruded as an extrudate by means of the extruder 6. The electrode paste 4 is produced additively by means of the extrusion process from a suspension 12 (electrode active material and binder) as well as added conductive particles 14 as conductive. The controller 10 is suitable and set up to monitor the extrusion process, in particular to determine extrusion parameters, and to control and / or regulate the extrusion process or the extruder 6 on the basis of a stored stress model 16. The controller 10 is particularly suitable and set up to control and / or regulate the extruder 6 with regard to a product parameter of the conductive particles 14 in the electrode paste 4. The extruder 6 is thus controlled and / or regulated in such a way that the desired product parameter of the conductive particles 14 is implemented in the extruded electrode paste 4. The desired product parameter is realized in particular by setting the specific energy required in each case for the extruder.

For this purpose, in the course of the stress model 16, the product parameter is correlated with the specific energy necessary for a deagglomeration of the conductive particles of this product parameter. A method according to the invention for producing a battery is explained in more detail below with reference to FIGS. 2 to 5. The method is described here by way of example for conductive particles 14 embodied as conductive soot, the desired product parameter being in particular a particle size d of the conductive particles.

In a first process step 18, a screw configuration SK as well as the geometric properties g _{E of} the extruder 6, i.e. the geometric dimensions and dimensions of the extruder elements 8, in particular the play between the extruder elements 8 and the inner wall of the extruder 8 as well as the gusset play between the meshing extruder elements 8, be true, and stored in a memory of the controller 10.

In a method step 20, a minimum average value of

Particle size d _{M of} the conductive particles with a maximum, coatable solids content c _m , a maximum (extruder) speed n and a minimum volume flow V are determined as extrusion parameters. The product parameter d is then determined for reduced solids content c _m , reduced speed n and increased volume flow V, with the mean residence time t and the suspension density p in the extruder 6 being determined.

In a method step 22, a shear stress t and a degree of filling f are determined on the basis of these extrusion parameters or analysis data. The shear stress T, which act on the respective suspension 12 within the extruder 6 at certain speeds n or shear rates g, are determined by means of a shear rate test in which so-called flow curves are determined by means of rotation tests with the respective electrode paste 4. The or each shear rate test provides a flow curve for each extruded electrode paste 4, which can be plotted, for example, in a shear rate / shear stress diagram shown in FIG. In Fig. 3, the shear rate g is along the abscissa axis (X-axis) and the shear stress t is along the ordinate axis (Y-axis) shown in double logarithmic form, the shear rate g is shown in units of s ¹ (second ¹ ) and the shear stress t in units of Pa (Pascal). In FIG. 3, five flow curves 24a, 24b, 24c, 24d and 24e are shown by way of example. The flow curves 24a, 24b, 24c, 24d and 24e were measured for a suspension 12 at the same speed n, the same screw configuration SK, and the same volume flow V, and differ only in their respective solids content c _m , with the flow curve 24a being the largest and the flow curve 24e has the lowest solids content c _m . A corresponding curve profile is adapted or (fitted) fitted to the measured (electrode paste-specific) flow curves 24a, 24b, 24c, 24d and 24e. The course of the curve is in particular a so-called Herschel-Bulkley curve. 4 shows a volume flow-residence time diagram in which the volume flow V is plotted along the abscissa axis and the mean residence time t is plotted along the ordinate axis. The volume flow V is plotted in the unit of l / h (liters per hour) and the mean residence time t in the unit s (seconds). In the diagram of FIG. 4, three parabolic curves 26a, 26b and 26c are shown for different speeds n.

The curves 24a, 24b, 24c, 24d, 26a, 26b and 26c are stored in a memory of the controller 10. The degree of filling f of the extruder 6 is calculated on the basis of the free extruder volume V _free , which can be determined from the geometric properties g _E , and that of a respective mean residence time t at a given volume flow V using the following formula:

Using the extrusion parameters determined in method step 20 and the stored curves 24a, 24b, 24c, 24d, 26a, 26b and 26c, are therefore easier The manner in which the shear stress t and the degree of filling f can be determined for the prevailing extrusion parameters.

In a method step 28, a specific energy E _{m P is} calculated based on the degree of filling f of the extruder 6 and based on the shear stress t within the extruder 6 at a prevailing shear rate g and based on the density of the respective electrode paste p. The specific energy E _{m P} results here at according to

In a method step 30, the stress model 16 is calculated. For this purpose, the specific energy E _{m, p} is correlated with the particle size d _{M of} the conductive particles 14. Such a correlation is shown, for example, in FIG. 5 on the basis of a specific energy-particle size diagram. The calculated specific energy E _{m P} is in units of J / kg (joules per kilogram) along the abscissa axis, and the particle size d _M is plotted logarithmically in units of pm (micrometers) along the ordinate axis. In Fig. 5, the dependency of the resulting particle size d _M in the Electrode paste 4 for two different suspensions 14 and two different volume flows V is shown. The fully filled squares show a suspension 12 with a cathode active material for a volume flow V of 1 l / h. The filled circles show a suspension 12 with the cathode active material for a volume flow V of 2.5 l / h. The half-filled squares show a suspension 12 with an anode active material for a volume flow V of 1 l / h. The filled circles show a suspension 12 with the anode active material for a volume flow V of 2.5 l / h. In FIG. 5, the courses of the cathode suspension are each fitted with a model curve 32a, 32b, the model curve 32a describing the course for the high volume flow V. In method step 30, the model curves 32a, 32b are determined and stored in a memory of the controller 10. The controller 10 controls and / or regulates the extrusion process on the basis of the stress model 16 or the model curves 32a, 32b with regard to a desired particle size d _{M of} the conductive particles 14 in the electrode paste 4 by setting a specific energy E _m required for this _{, p.}

The claimed invention is not limited to the exemplary embodiment described above. Rather, other variants of the invention can also be derived therefrom by the person skilled in the art within the scope of the disclosed claims without departing from the subject matter of the claimed invention. In particular, all individual features described in connection with the exemplary embodiment can also be combined in other ways within the scope of the disclosed claims without departing from the subject matter of the claimed invention.

List of reference symbols

2 device

4 electrode paste

6 extruders

8 extruder elements

10 controllers

12 suspension

14 conductive particles

16 Stress model

18, 20, 22 process step

24a, 24b, 24c, 24d, 24e flow curve

26a, 26b, 26c curve shape

28, 30 method step 32a, 32b model curve d _M product parameter

SK screw configuration

g _E geometric property

c _m solids content

n speed

V volume flow

t dwell time

p suspension density

T shear stress

f filling level

Y shear rate

E _{m, p} specific energy

Claims

Expectations

1. Process for the production of batteries,

- In which a suspension (12) with a variable product parameter (14) in an extrusion process by means of an extruder (6) as

Electrode paste (4) is extruded,

- in which a number of extrusion parameters (SK, g _E , c _m , n, V, t, p, T, Y, f) of the extrusion process are determined,

- in which an extruder-specific stress model (16) is calculated based on the extrusion parameters (SK, g _E , c _m , n, V, t, p, t, g, f), and

- in which the extrusion process is controlled and / or regulated based on the stress model (16).

2. The method according to claim 1,

characterized,

that a dispersion of conductive particles in the suspension (12) is used as the product parameter (14), the stress model (16) being calculated for a continuous dispersion of the conductive particles in the suspension (12).

3. The method according to claim 2,

characterized,

that to calculate the stress model (16) a product parameter (d _M ) of the conductive particles (14) with a specific necessary for a deagglomeration of the conductive particles (14) with this product parameter (d _M )

Energy (E _{m, p} ) is correlated.

4. The method according to claim 3,

characterized,

that a particle size of the conductive particles (14) is used as a product parameter (d _M ).

5. The method according to claim 3 or 4 characterized,

that the specific energy (E _{m, p} ) is determined as an extrusion parameter as a function of a shear stress (T) and a degree of filling (f) as well as a suspension density (p).

6. The method according to claim 5,

characterized,

that the shear stress (T) is determined by means of a shear rate test, in particular on the basis of a measured flow curve (24a, 24b, 24c, 24d, 24e) and on the basis of geometric properties (g _E ) of the extruder (6) as extrusion parameters.

7. The method according to claim 5 or 6,

characterized,

that the degree of filling (f) is determined by means of a mean residence time (t) and a volume flow (V) as extrusion parameters.

8. The method according to any one of claims 1 to 7,

characterized,

that a twin-screw extruder is used as the extruder (6).

9. Device (2) for setting up batteries, with an extruder (6) and with a controller (10) for carrying out the method according to one of claims 1 to 8.

10. Battery for a motor vehicle, produced by a method according to one of claims 1 to 8.