Method for applying an insulation layer to a motor vehicle battery cell

Abstract

Due to the dynamic mechanical loads to which motor vehicle traction batteries are subjected, housings of battery cells of the traction batteries are covered at least in part by an electrically insulating layer made from a coating material. For this purpose, a method and a coating station for carrying out the method are proposed. The method is performed with a liquid electrically insulating coating material, by applying separately produced individual drops of the coating material using a coating applicator. The drops form coating points on an outer surface of the housing, which coating points are applied sequentially with the coating applicator, adjacently to one another or overlapping, so that together they form coating lines.

Claims

1. A method for applying an external insulation layer to the housing of a battery cell, the method comprising: coating an outer surface of the housing with a liquid electrically insulating coating material; the step of coating includes using a coating applicator, and applying discretely produced single drops of the coating material, which single drops of the coating material form coating points on the outer surface of the housing; and applying the coating points in a sequentially adjoining or overlapping manner with one another with the coating applicator, so that together the coating points form coating lines.

2. The method as claimed in claim 1, wherein the step of coating includes applying a multiplicity of coating lines sequentially next to one another to form a contiguous coating surface over a surface area of the housing.

3. The method as claimed in claim 1, including coating two outer surfaces of the housing oriented opposite one another at the same time using two coating applicators.

4. The method as claimed in claim 1, including holding the housing during the step of coating with a workpiece holder having two holding elements, the holding elements fixing the battery cell in a region of pole elements of the battery cell.

5. The method as claimed in claim 1, including least one of the following steps: coating at least a planar outer surface of the housing while the planar outer surface is vertically oriented; and/or coating at least a planar outer surface of the housing while the outer surface is vertically oriented, and applying coating lines in a vertically aligned manner; and/or coating at least a planar outer surface of the housing while the planar outer surface is horizontally oriented and while the planar outer surface is oriented in an upwardly facing orientation.

6. The method as claimed in claim 1, including at least one of the following: the coating material comprises at least one component that cures under radiation; and/or the coating material comprises a component that cures by polyaddition or polycondensation; and/or the coating material comprises a component which both cures by polyaddition or polycondensation and requires radiation for curing.

7. The method as claimed in claim 1, further including discharging the liquid electrically insulating coating material with the coating applicator, the coating applicator having a nozzle chamber and a nozzle opening, the nozzle opening adjoining the nozzle chamber and being located downstream of the nozzle chamber, and a displaceable plunger, the displaceable plunger periodically entering the nozzle chamber along a longitudinal axis thereof and thereby forcing contents of the nozzle chamber through the nozzle opening as discrete single drops.

8. The method as claimed in claim 7, including moving the plunger with a frequency of between 100 Hz and 1000 Hz.

9. The method as claimed in claim 1 including at least one of the following: the step of coating takes place with single drops having a drop volume of between 0.2 mm.sup.3 and 1.0 mm.sup.3; and/or the coating points have a maximum thickness of between 50 ?m and 100 ?m and are arranged in an overlapping manner such that an average layer thickness of between 60 ?m and 120 ?m is obtained; and/or the coating points have a diameter of between 1 mm and 2 mm; and/or the coating takes place through a nozzle opening with a nozzle diameter of between 0.2 mm and 0.8 mm; and/or the coating takes place with a distance between the nozzle opening and the outer surface to be coated of between 3 mm and 8 mm; and/or feeding the coating material into the nozzle chamber with a pressure of between 3 bar and 5 bar; and/or a relative speed between the coating applicator and an outer surface of the housing during delivery of the coating material is between 300 mm/sec and 700 mm/sec; and/or before being discharged, the coating material is heated to a temperature of between 35? C. and 45? C.

10. The method as claimed in claim 1, including coating at least a planar outer surface of the housing while the planar outer surface is vertically oriented, and applying horizontal coating lines one after the other from a top of the housing downward.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Further advantages and aspects of the invention emerge from the claims and from the following description of preferred exemplary embodiments of the invention, which are explained below on the basis of the figures.

(2) FIGS. 1 to 3 show a motor vehicle battery and a single cell of this motor vehicle battery and its housing.

(3) FIGS. 4 to 5 illustrate the coating method according to the invention for coating the housing by means of a coating applicator, which is designed for discharging discrete single drops.

(4) FIG. 6 shows possible paths of the coating applicator for coating the housing.

(5) FIG. 7 shows a processing station for carrying out the coating method.

(6) FIG. 8 shows the coating applicator used in a schematic representation.

(7) FIGS. 9 and 10 show a processing station and the coating procedure with the simultaneous use of two applicators.

(8) FIG. 11 shows a coating installation with a plurality of coating stations and further stations.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

(9) FIG. 1 shows a motor vehicle battery 200. This battery comprises a multiplicity of battery cells 202, which have in each case a prismatic housing. The battery cells 202 lie flush against one another with outer surfaces 210A of their respective housings 204.

(10) In order in the event of damage to one battery cell 202 to prevent the damage from affecting other battery cells, it is provided that the outer surfaces 210A, 210B, 210C of the housings 204 are in each case provided with an insulation layer of a cured coating material. This coating may take place after completed assembly of the battery cell, and consequently in the state of FIG. 2. Alternatively, however, the coating may also take place before assembly, so that at this time the housing 204 is still empty in the way represented in FIG. 3. The housing 204 to be coated is usually produced from aluminum or an aluminum alloy.

(11) In particular if the battery cell 202 is already completely assembled, there is a great risk when coating by classical coating methods with sprayed coating material that, in addition to the outer surfaces 210A, 210B, 210C that are intended to be coated the pole elements 206 of the battery are also partially coated, which is not desired and leads to laborious subsequent work.

(12) As provided by the method according to the invention, it is therefore envisaged that the coating takes place with a coating applicator that is designed for the specifically directed discharge of single drops.

(13) FIGS. 4 and 5 illustrate this method. The method provides that the battery cell 202 or at least its housing 204 is fixed by means of a workpiece holder 70 and holding elements 72 intended for grasping the pole elements 206. Subsequently, a coating applicator 20, which is explained in still more detail below, is positioned in the direct vicinity of the surface to be coated, in the case of the arrangement of FIG. 4 therefore directly in front of the outer surface 210A. The distance between a nozzle opening 24, not represented in FIG. 4, of the coating applicator 20 and the surface to be coated is preferably a few millimeters, in the present case approximately 5 mm.

(14) Beginning from a starting position, the discharge then takes place, in that the coating applicator produces discrete single drops of less than 1 mm.sup.3 in volume with high frequency, which are issued in a defined direction in the direction of the outer surface 210A and, when they hit the surface, form a coating point 104 of approximately 1 to 2 mm in diameter there. In this case, the entire volume of the coating material remains on the surface. If the operating parameters of the coating applicator are suitably chosen, a spray mist does not occur.

(15) During or after the discharge of a single drop 102, and the consequent formation of a coating point on the outer surface 210A, the coating applicator 20 is displaced with respect to the outer surface 210A, as indicated by the arrow 2 and explained in still more detail below. During this movement, further discrete single drops 102 continue to be issued in the direction of the surface, the frequency, the size of the drops and the speed of the coating applicator 20 being made compatible with one another in such a way that the coating points 104 overlap, and thereby form a continuous coating line 106.

(16) As can be seen from FIG. 5, a contiguous coating surface 108 is formed by further coating lines 106, which are applied overlapping with previous coating lines 106.

(17) This procedure is repeated for all of the outer surfaces 210A, 210B, 210C to be coated, so that in the end the surfaces mentioned are in each case completely or partially covered by coating surfaces 108. FIG. 6 shows the housing 204 after completion of the coating.

(18) Even if the quality of the coating as regards the uniformity of the layer thickness is greatest when the discharge takes place onto a horizontal surface, as is the case here with the outer surface 210C, it has been found that high quality can also be achieved on vertically aligned surfaces, as in the present case the outer surfaces 210A, 210B. This also depends however on the arrangement of the paths 3, 5 along which the coating applicator 20 is moved with respect to the housing 204. It applies in principle that it is of advantage if the individual coating lines are aligned parallel to the longest extent of the surface to be coated in each case. In the case of the outer surface 210A, the coating lies are therefore aligned horizontally, while in the case of the outer surface 210B they are aligned vertically. In particular when applying horizontal coating lines 106 to vertically aligned surfaces, that is to say in the present case the outer surfaces 210A, it has been found to be advantageous if the coating lines are placed one below the other from the top downward, as illustrated by the path 3.

(19) FIG. 7 shows the construction of a coating station, a robot 38 with a robot arm 40 being used in the present case in order to guide the coating applicator 20 provided at the distal end of the robot arm 40. The supplying of the coating applicator 20 with liquid coating material takes place from a storage reservoir 50, in which the coating material 100 is stored before being discharged. Since the coating materials that come into consideration in particular for the method according to the invention usually have quite a high viscosity at 20? C., the storage reservoir 50 is provided with a heating device 54, in order to keep the coating material at a higher temperature, in particular at a temperature of between 35? C. and 45? C. As an alternative or in addition, heating devices may also be provided in the channels leading to the coating applicator or in the coating applicator 20 itself. Since the coating materials that are suitable in particular for the invention also have a tendency to undergo sedimentation, that is to say the deposition of constituents, when the liquid coating material is at rest, the storage reservoir 50 additionally has a stirring mechanism, by means of which the coating material 100 is permanently homogenized.

(20) Various channels are provided for supplying the coating applicator 20 from the storage reservoir 50. The storage reservoir 50 is provided with an annular channel 56, which has a feed-channel portion 56A and a return-channel portion 56B. The coating material 100 from the storage reservoir is sucked into the feed-channel portion 56A by means of a pump 62 during the coating procedure, but also during brief breaks in the coating procedure, for example when changing a workpiece. The pump 62 brings about a feed pressure of approximately 4 bar downstream.

(21) Provided at the end of the feed-channel portion 56A is a three-way valve 60, by means of which it is controlled whether the coating material is fed through the return-channel portion 56B back into the storage reservoir 50 or through a supply channel 58 in the direction of the coating applicator 20.

(22) The feeding of coating material 100 from the storage reservoir 50, which as far as possible is uninterrupted, serves in particular the purpose of ensuring a consistent quality of the coating material, even if the discharge from the coating applicator 20 pauses. The coating material 100 circulating in the circuit made up of the storage reservoir 50 and the annular channel 56 is subjected to shearing in the annular channel 56, as a result of which its viscosity falls. By contrast, in that part of the channels to the coating applicator 20 that is not part of the annular channel 56, the coating material 100 remains motionless when the coating applicator is deactivated. Depending on the type of coating material, this is usually uncritical for several minutes. If, however, the coating material 100 stays in the supply channel 58 for too long, there is an increase in viscosity and/or sedimentation, so that the coating material should no longer be used for the coating.

(23) The system therefore has a flushing device, which comprises a flushing pump 66, which can feed cleaning fluid out of a flushing-agent tank 64 into the supply channel 58 in order to remove the coating material remaining therein out of the supply channel 58 through the coating applicator 20 or a separate outflow opening, so that subsequently fresh material can be fed out of the annular channel 56 to the supply channel 58.

(24) Against this background, it is preferable to make the supply channel 58 as short as possible and to bring the annular channel 56 as close as possible to the coating applicator.

(25) In the case of a preferred design of the coating method that is further explained below, a plurality of coating applicators are used. In such a case, it is regarded as preferred if they are connected to a common annular channel 56.

(26) FIG. 8 shows a coating applicator 20 in a schematic and sectional representation. It can be seen that the end 59 of the supply channel 58 runs within the coating applicator 20, a further heating device 30 being provided here in order to ensure a particularly uniform temperature, in particular of between 35? C. and 45? C., during the subsequent discharge of the coating material. The supply channel 58 opens out into a nozzle chamber 22, which is adjoined by a nozzle opening 24. The discharge of the coating material in the form of discrete single drops 102 is brought about by a plunger 26, which can be moved by piezo stacks 28 back and forth in the direction of the arrow 6. The plunger is usually operated with a frequency of between 100 Hz and 1000 Hz. If the plunger is withdrawn from the nozzle chamber 22, coating material 100 flows in from the supply channel 58 and, after the subsequent movement of the plunger 26 in the direction of the nozzle chamber 22, is forced through the nozzle opening to the outside and thereby forms a discrete single drop.

(27) It has been found to be advantageous if the speed of the plunger during withdrawing movements is comparatively low, since otherwise there is the risk that ambient air is sucked into the nozzle chamber 22 through the nozzle opening 24 and disturbs the formation of drops during the subsequent discharge and/or leads to air inclusions in the single drop 102 and subsequently in the coating point 104. This can in principle be counteracted by an increased pressure in the supply channel 58. However, if a pressure that is well above 4 bar is used here, there is the risk that the single drop 102 is broken up when it is discharged. It is therefore preferred that the speed is lower during the drawing movement than during the rapid forward movement of the plunger 26, preferably by a factor of at least 2.

(28) FIGS. 9 and 10 show a supplemented variant of the method. This is distinguished by the fact that a plurality of coating applicators 20, preferably precisely two coating applications, are guided together, in the present case by a common robot arm 40. The two coating applicators 20 are attached to a common carrier 42 and are aligned with their nozzle openings 24 facing one another, so that they can simultaneously coat two opposite sides of the housing 204. As a result, shorter cycle times can be achieved.

(29) In the case of a very simple variant of such a carrier 42 with two coating applicators 20, they are not automatically movable, but can be changed with regard to their distance only when setting up the station, in order to be adapted to different dimensions of housings 204. It is of advantage however if the distance is also variable while operation is in progress, in order in this way to ensure in each case a uniform distance between the nozzle openings 24 and the respective surfaces for example even when there are slight variations with respect to the dimensions of the housing or when the coating station is used for different types of housings 204. This uniform distance leads to a reproducible discharging behavior and in particular to precise maintenance of a desired overlapping of the coating points 104 and the coating lines 106.

(30) In FIG. 10, the two coating applicators 20 can be seen in operation during simultaneous coating. By being attached to the common carrier 42, they are moved together during the coating, so that they apply the respective coating points 104 and coating lines 106 at the same time to the outer surfaces 210A of the housing 204.

(31) FIG. 11 shows a coating installation 90, which can be used in the industrial large-scale production of electric motor vehicles and by means of which housings 204 of battery cells 202 are coated in a multistage process.

(32) The coating installation 90 has a central round table 98, which is rotatable about the vertical axis and has altogether five workpiece holders 70. Arranged around this round table 98 are two coating stations 10, which correspond essentially to those of FIG. 7 or 9. Furthermore, a drying station 300 and a measuring station 310 for measuring the layer thickness achieved are provided here. The rotary round table 98 is part of a feeding system 92, which also has a transporting robot 96, which removes battery cells 202 or housings 204 from a feed line 94 and positions them on one of the workpiece holders 70 of the round table 98. The transporting robot 96 may in this case be additionally designed for ascertaining after the positioning of the battery cell 202 or the housing 204 on the workpiece holder 70 its exact position, so that in particular the coating stations 10 can adapt their path parameters on the basis of the exact position of the battery cell 202 or the housing 204. Instead of a position detection integrated in the transporting robot 96, a separate device may also be provided for this between the transporting robot and the first coating station 10. Depending on the required accuracy and type of workpiece holders 70, it may also be possible to dispense with ascertaining the precise position.

(33) The housing 204 positioned by the transporting robot 96 on the workpiece holder 70 and fixed there by means of the holding elements 72 is moved to the first coating station, and after coating there, on to the second coating station, by turning the round table 98 in a clockwise direction. The two coating stations apply coatings one after the other in the way described to various outer surfaces 210A, 210B, 210C. The number of coating stations can in this case be adapted according to the type of housings. Once the housing 204 has been provided with the coating on the outer surfaces 210A, 210B, 210C at the coating stations 10, a drying takes place at the drying station 300 by means of UV light. For this, the drying station 300 has a variable-height protective shroud, on the inner side of which corresponding UV light sources, particularly UV LEDs, are provided. After the infeeding of the housing 204 by means of the round table 98, the shroud is lowered, so that it surrounds the housing 204. After completion of the drying, the protective shroud is raised again.

(34) This is followed by an examination at the measuring station 310 of the layer thickness achieved. The station also has a shroud for this purpose, on the inner side of which at least one measuring device for layer thickness measurement is provided, while preferably a plurality of measuring devices may be provided for recording the layer thickness at different measuring points. The measurement preferably takes place inductively.

(35) Finally, the housing is moved by means of the round table 98 into the region of the transporting robot 96 again. There, the holding elements 72 of the workpiece holder 70 are released and the housing 204 or the battery cell 202 is transported back to the feed line 94, while at the same time a further housing 204 or a further battery cell is removed from the feed line 94 and is fed to the round table 98 for coating.