METHOD FOR PRODUCING A BATTERY

Abstract

In a method for producing batteries in which a suspension with a variable product parameter is extruded in an extrusion process by means of an extruder as an electrode paste, a number of extrusion parameters of the extrusion process are determined, an extruder-specific stress model is calculated on the basis of the extrusion parameters, and the extrusion process is controlled in an open loop and/or regulated, i.e., controlled in a closed loop, on the basis of the stress model.

Claims

1. A method for producing batteries, comprising: extruding a suspension with a variable product parameter as an electrode paste in an extrusion process by means of an extruder, determining a number of extrusion parameters of the extrusion process, calculating an extruder-specific stress model on the basis of the extrusion parameters, and controlling the extrusion process in an open loop and/or a closed loop on the basis of the stress model.

2. The method as recited in claim 1, wherein the product parameter used is a dispersion of conductive particles in the suspension, and wherein the stress model is calculated for a continuous dispersion of the conductive particles in the suspension.

3. The method as recited in claim 2, wherein, in order to calculate the stress mode, a product characteristic (d.sub.M) of the conductive particles is correlated with a specific energy required to deagglomerate the conductive particles with the product characteristic.

4. The method as recited in claim 3, wherein the product characteristic used is a particle size of the conductive particles.

5. The method as recited in claim 3, wherein the specific energy is determined as a function of a shear stress and a degree of filling and of a density of suspension as extrusion parameters.

6. The method as recited in claim 5, wherein the shear stress is determined by a shear rate test, on the basis of a measured flow curve, and on the basis of geometrical properties of the extruder as extrusion parameters.

7. The method as recited in claim 5, wherein the degree of filling is determined via a mean residence time and a volumetric flow rate as extrusion parameters.

8. The method as recited in claim 1, wherein the extruder used is a twin-shaft extruder.

9. A device for producing batteries, comprising an extruder and a controller for carrying out the method according to claim 1.

10. A battery for a motor vehicle, produced using a method according to claim 1.

Description

[0038] An exemplary embodiment of the invention is described below in more detail with reference to the drawings, in which:

[0039] FIG. 1 is a schematic and simplified view of a device for producing batteries including an extruder and a controller;

[0040] FIG. 2 is a flow chart of a method for producing batteries;

[0041] FIG. 3 is a shear stress-shear rate diagram with five flow curves for different solids contents;

[0042] FIG. 4 is a volumetric flow rate-residence time diagram for different extruder rotational speeds; and

[0043] FIG. 5 is a specific energy-particle size diagram for different electrode pastes and volumetric flow rates.

[0044] Corresponding parts and quantities are given the same reference numerals throughout the figures.

[0045] FIG. 1 shows a device 2 for producing a battery, more particularly, for producing an electrode paste 4 for a battery cell of the battery. Device 2 includes an extruder 6 in the form of a twin-shaft or twin-screw extruder. Extruder 6 has extruder elements 8 (only partially shown) in the form of conveying and/or kneading elements which are driven in co-rotating fashion and configured to closely intermesh with each other. Extruder 6 is coupled to a controller 10.

[0046] In order to produce the battery, electrode paste 4 is extruded as an extrudate using extruder 6. In this process, electrode paste 4 is formed from a suspension 12 (electrode active material and binder) and added conductive particles 14 by means of the extrusion process.

[0047] Controller 10 is suitable and adapted to monitor the extrusion process and extruder 6, in particular to determine extrusion parameters, and to control the extrusion process in open loop and/or closed loop on the basis of a stored stress model 16. In particular, controller 10 is suitable and adapted to control extruder 6 in open loop and/or closed loop with respect to a product characteristic of conductive particles 14 in electrode paste 4. Thus, extruder 6 is controlled in open loop and/or closed loop in such a way that the desired product characteristic of conductive particles 14 is achieved in the extruded electrode paste 4. In this process, the desired product characteristic is achieved in particular by setting a specific energy of the extruder that is required in each case.

[0048] To this end, the product characteristic is correlated in stress model 16 with the specific energy required to deagglomerate the conductive particles of this product characteristic.

[0049] An inventive method for producing a battery is described hereinafter with reference to FIGS. 2 through 5. The method is described here by way of example for conductive particles 14 in the form of carbon black, the desired product characteristic being in particular a particle size d.sub.M of the conductive particles.

[0050] In a first method step 18, a screw configuration SK as well as the geometrical properties g.sub.E of extruder 6; i.e., the geometrical sizes and dimensions of extruder elements 8, in particular the clearance between extruder elements 8 and the inner wall of extruder 8 as well as the intermeshing clearance between intermeshing extruder elements 8, are determined and stored in a memory of controller 10.

[0051] In a method step 20, a minimum average value of the particle size d.sub.M of the conductive particles is determined at a maximum coatable solids content c.sub.m, a maximum (extruder) rotational speed n, and a minimum volumetric flow rate V as extrusion parameters. Subsequently, product characteristic d.sub.M is determined for reduced solids contents c.sub.m, a reduced rotational speed n, and an increased volumetric flow rate V. Also determined in each case are the mean residence time t and the density of suspension ρ in extruder 6.

[0052] In a method step 22, a shear stress τ and a degree of filling f are determined based on these extrusion parameters or analysis data.

[0053] The shear stress τ acting on the particular suspension 12 within extruder 6 at specific rotational speeds n and shear rates γ are determined by a shear rate test in which so-called “flow curves” are determined by rotational testing of the particular electrode paste 4.

[0054] The or each shear rate test provides for each extruded electrode paste 4 a flow curve, which can be plotted by way of example in a shear rate-shear stress diagram shown in FIG. 3. In FIG. 3, shear rate γ is represented along the abscissa axis (X-axis) and shear stress τ along the ordinate axis (Y-axis) in a double-logarithmic fashion, shear rate γ being plotted in units of s.sup.−1 (second.sup.−1) and shear stress τ in units of Pa (pascal).

[0055] FIG. 3 shows, by way of example, five flow curves 24a, 24b, 24c, 24d and 24e. 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 volumetric flow rate V, and differ only in their respective solids content c.sub.m, flow curve 24a having the highest solids content c.sub.m and flow curve 24e having the lowest solids content c.sub.m. A curve shape is fitted to each of the measured (electrode paste-specific) flow curves 24a, 24b, 24c, 24d and 24e. The curve shape is in particular what is known as a Herschel-Bulkley curve.

[0056] FIG. 4 shows a volumetric flow rate-residence time diagram in which the volumetric flow rate V is plotted along the abscissa axis and the mean residence time t is plotted along the ordinate axis. The volumetric flow rate V is plotted in the unit of l/h (liters per hour) and the mean residence time tin the unit of s (seconds). The diagram of FIG. 4 shows three parabolic curve shapes 26a, 26b and 26c for different rotational speeds n.

[0057] Curves 24a, 24b, 24c, 24d, 26a, 26b and 26c are stored in a memory of controller 10.

[0058] The degree of filling f of extruder 6 is calculated based on the free extruder volume V.sub.free, which can be determined from the geometrical properties g.sub.E, and on a corresponding mean residence time t at a given volumetric flow rate V using the following formula:

[00001]$f=\frac{V}{V_{free}}\times t.$

[0059] Based on the extrusion parameters determined in method step 20 and the stored curves 24a, 24b, 24c, 24d, 26a, 26b and 26c, the shear stress τ and the degree of filling f can thus be easily determined for the particular prevailing extrusion parameters.

[0060] In a method step 28, a specific energy E.sub.m,P is calculated based on the degree of filling f of extruder 6 and based on the shear stress τ within extruder 6 at a prevailing shear rate γ as well as based on the density of the particular electrode paste p. The specific energy E.sub.m,P is derived as follows:

[00002]$E_{m,P}=\frac{1}{f}\times \tau /\rho .$

[0061] In a method step 30, stress model 16 is calculated. To this end, the specific energy E.sub.m,P is correlated with the particle size d.sub.M of conductive particles 14. Such a correlation is illustrated, for example, in FIG. 5 by means of a specific energy-particle size diagram. The calculated specific energy E.sub.m,P is plotted in units of J/kg (joule per kilogram) along the abscissa axis and the particle size d.sub.M in units of μm (micrometer) along the ordinate axis in a double-logarithmic fashion.

[0062] In FIG. 5, the dependence of the resulting particle size d.sub.M in electrode paste 4 is illustrated for two different suspensions 14 and two different respective volumetric flow rates V. The fully filled squares represent a suspension 12 with a cathode active material for a volumetric flow rate V of 1 l/h. The fully filled circles represent a suspension 12 with a cathode active material for a volumetric flow rate V of 2.5 l/h. The half-filled squares represent a suspension 12 with an anode active material for a volumetric flow rate V of 1 l/h. The fully filled circles represent a suspension 12 with an anode active material for a volumetric flow rate V of 2.5 l/h.

[0063] In FIG. 5, the behaviors of the cathode suspensions are each fitted with a respective model curve 32a, 32b, of which model curve 32a describes the behavior for the high volumetric flow rate V.

[0064] In method step 30, model curves 32a, 32b are determined and stored in a memory of controller 10. Controller 10 controls the extrusion process in open loop and/or closed loop on the basis of stress model 16 or model curves 32a, 32b with respect to a desired particle size d.sub.M of conductive particles 14 in electrode paste 4 by setting a specific energy E.sub.m,P required for this.

[0065] The claimed invention is not limited to the exemplary embodiment described above. Rather, other variants of the invention may also be derived therefrom by those skilled in the art within the scope of the disclosed claims without departing from the subject matter of the claimed invention. Furthermore and in particular, all individual features described in connection with the exemplary embodiment may 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 CHARACTERS

[0066] 2 device [0067] 4 electrode paste [0068] 6 extruder [0069] 8 extruder elements [0070] 10 controller [0071] 12 suspension [0072] 14 conductive particles [0073] 16 stress model [0074] 18, 20, 22 method step [0075] 24a, 24b, 24c, 24d, 24e flow curve [0076] 26a, 26b, 26c curve shape [0077] 28, 30 method step [0078] 32a, 32b model curve [0079] d.sub.M product characteristic [0080] SK screw configuration [0081] g.sub.E geometrical property [0082] c.sub.m solids content [0083] n rotational speed [0084] V volumetric flow rate [0085] t residence time [0086] ρ density of suspension [0087] τ shear stress [0088] f degree of filling [0089] γ shear rate [0090] E.sub.m,P specific energy