METHOD AND DEVICE FOR FORMING BUNDLES OF NANOFILAMENTS

Abstract

A device can be used as an electrode for a lithium-ion battery. The device comprises an electrically conductive substrate to the surface of which nanofilaments having an ion-absorbing coating are applied. The nanofilaments are combined by the application of light into a plurality of bundles, each having multiple nanofilaments. A spacer gap is formed between neighboring bundles.

Claims

1. A method, comprising: uniformly arranging nanofilaments (2) over a surface of an electrically conductive substrate (1), wherein each of the nanofilaments (2) has a fixed end connected to the electrically conductive substrate (1) and a free end; and exposing the nanofilaments (2) to light from a first light source (18) of such an intensity that the light causes the respective free ends of a plurality of adjacent nanofilaments (2) to abut each other so as to form bundles (3) of nanofilaments (2), wherein the bundles (3) are separated from one another by spaces.

2. The method of claim 1, wherein the nanofilaments (2) are carbon nanotubes (CNT).

3. The method of claim 1, wherein a cross-sectional distance through one of the bundles (3) is between 0.5 and 5 μm.

4. The method of claim 1, further comprising applying an ion-absorbing coating (5) to the bundles (3), the ion-absorbing coating (5) comprising nanoparticles (4) that are connected to one another and to the bundles (3).

5. The method of claim 4, wherein the nanoparticles (4) comprise at least one of silicon, sulfur, titanium oxide, a phosphite, a nitrite, carbon, SiO.sub.2, TiO.sub.2, CrO.sub.2, LiCoO, LiTiO, LiNiO, LiMnO, LiFePO, LiCoPO, LiMnPO, V.sub.2O.sub.5, Ge, Sn, Pb or ZnO.

6. The method of claim 1, wherein the first light source (18) comprises a xenon lamp or a laser.

7. The method of claim 1, wherein the light from the first light source (18) comprises a laser beam that is generated continuously or in a pulsed manner and expanded into a strip, the method further comprising moving the laser beam over the nanofilaments (2) at a constant speed.

8. The method of claim 4, further comprising: applying silicon nanoparticles (4) onto the bundles (3) during the application of the ion-absorbing coating (5); and applying energy to the silicon nanoparticles (4) so as to connect the silicon nanoparticles (4) to one another and to the bundles (3).

9. The method of claim 8, wherein light from a second light source (21) is used for connecting the silicon nanoparticles (4) to one another and to the bundles (3), the method further comprising moving the light from the second light source (21) over the surface of the electrically conductive substrate (1) so as to melt a surface of the silicon nanoparticles (4).

10. A device, comprising: a processing device (10) comprising: a first coating station (11) configured to form nanofilaments (2) on a substrate (1), wherein the substrate (1) is electrically conductive; and a forming station (12) arranged directly behind the first coating station (11) in a transport direction, wherein the forming station (12) comprises a first light source (18) for exposing the nanofilaments (2) on the substrate (1) to light in such a way that the nanofilaments (2) combine into bundles (3) of nanofilaments (2); an entry arrangement (22) for supplying the substrate (1) into the processing device (10); an exit arrangement (23) for removing the substrate (1) from the processing device (10); and transport means for transporting the substrate (1) through the processing device (10) in the transport direction from the entry arrangement (22) to the exit arrangement (23).

11. The device of claim 10, wherein the processing device (10) further comprises a second coating station (13) for applying a coating (5) on the bundles (3) formed in the forming station (12).

12. The device of claim 10, further comprising: a first roll (7) on which a first portion of the substrate (1) is wound; and a second roll (8) on which a second portion of the substrate (1) is wound, wherein the first roll (7) is disposed upstream from the entry arrangement (22) with respect to the transport direction, and the second roll (8) is disposed downstream of the exit arrangement (23) with respect to the transport direction.

13. The device of claim 10, wherein the first light source (18) comprises a laser.

14. The device of claim 11, wherein the second coating station (13) comprises a spraying device (20) for spraying nanoparticles (4) on the bundles (3) produced in the forming station (12).

15. The device of claim 14, wherein the second coating station (13) comprises a second light source (21) for shining light onto the nanoparticles (4) sprayed on the bundles (3) so as to connect the nanoparticles (4) to one another and to the bundles (3).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The invention is described in greater detail below with reference to exemplary embodiments. In the drawings:

[0019] FIG. 1 schematically shows a process sequence for producing the inventive electrode,

[0020] FIG. 2 shows a schematic representation of a first exemplary embodiment of a device for carrying out the method,

[0021] FIG. 3 shows a second exemplary embodiment of a device,

[0022] FIG. 4 shows a third exemplary embodiment of a device,

[0023] FIG. 5 shows a representation according to FIG. 1 concerning a second exemplary embodiment of a method and a device for producing an electrode,

[0024] FIG. 6 shows another exemplary embodiment of a device for carrying out the method schematically illustrated in FIG. 5, and

[0025] FIG. 7 schematically shows a cell of a lithium-ion battery.

DETAILED DESCRIPTION

[0026] FIG. 1 schematically shows the process sequence for producing an electrode for a lithium-ion battery. A thin metallic substrate, e.g. in the form of an aluminum foil or preferably a copper foil, is unwound from a first roll 7 and coated with a microstructure in four successive process steps A, B, C, D. The coated substrate 1 is then wound up again on a second roll 8.

[0027] The substrate 1 is coated with carbon nanotubes 2 in a first process step A. The nanotubes 2 have a fixed end that is rigidly connected to the substrate 1 and a free end that essentially points away from the substrate 1. The coating process takes place in a first coating station 11.

[0028] The second process step B is carried out in a forming station 12 that is arranged downstream of the coating station 11 referred to a transport direction of the substrate 1. Light energy is applied to the layer of nanofilaments, which was deposited on the substrate in the first process step A, by means of the laser beam of a xenon laser. This exposure to light surprisingly causes the nanofilaments 2 to combine in a bundle-like manner. The free ends of the nanofilaments 2, which essentially are uniformly arranged on the surface of the substrate 1, orient themselves into closely adjacent bundles 3 such that clearances 6 are formed between adjacent bundles 3. The length of the bundles 3 measured in the direction, in which the nanofilaments 2 extend, is greater than a cross-sectional distance through the bundle 3 in the region of the fixed ends of the nanofilaments 2. In the region of the free ends of the nanofilaments 2, in which the bundles 3 are in contact with adjacent nanofilaments 2, a characteristic cross-sectional length has a value of less than half of the cross-sectional length of the bundle in the region of the fixed ends of the nanofilaments 2.

[0029] In a third process step C, silicon nanoparticles 4 are sprayed on the bundles with a dry or wet spraying method in a nanoparticle application station 14. The silicon nanoparticles 4 partially penetrate into the bundles 4 and into the intermediate spaces between the bundles.

[0030] The nanoparticle application station 14 forms part of a second coating station 13 that also serves for carrying out a fourth process step D, in which the nanoparticles 4 applied to the bundles 3 are sintered to one another. To this end, energy is applied to the bundles 3 sprayed with nanoparticles 4 in a melting station 15. The energy preferably is applied to the bundles 3 in the form of light, wherein the light may be infrared light, visible light or UV light. However, it is also possible to apply energy in the form of heat. In the fourth process step D, the nanoparticles 4 are fused with one another by means of the applied radiant energy.

[0031] FIG. 2 shows a first exemplary embodiment for carrying out the method, wherein a substrate 1 is coated with nanofilaments 2 on both sides in this case. To this end, the device comprises an entry arrangement that may be realized in the form of a gas-tight gate, through which the substrate 1 is transported into the device 10. The device comprises a first coating station 11 that is arranged in a housing 24. The housing contains two heaters 16, by means of which a process chamber of the coating station 11 is heated to a process temperature. A gas inlet element 17 is located in the process chamber on each side of the flat, electrically conductive substrate 1, wherein process gases are fed into the process chamber through said gas inlet elements. Nanofilaments 2 grow on the substrate 1, which is continuously transported through the coating station 11, due to a pyrolytic reaction. A heater 16 and a gas inlet element 17 are respectively located on both opposite sides of the substrate 1 such that the substrate 1 is coated on both sides.

[0032] The substrate 1 provided with the nanofilaments 2 is transported into another housing 25, which is assigned to a forming station 12, through a gas-flushed gate 9. The housing 25 contains two laser arrangements that apply light energy to both opposite broad sides of the electrically conductive substrate 1, which are respectively coated with nanofilaments 2. The light originates from a xenon lamp or a laser and has such an intensity that the nanofilaments 2 self-orient into bundles 3 due to the application of energy in the form of the laser light. In the process, bundles 3 of the type described in initially cited articles “Behavior of fluids in nanoscopic space” or “Capillarity-driven assembly of two-dimensional cellular carbon nanotube foams” are formed.

[0033] The electrically conductive substrate 1 is transported into a second coating station 13 through another gas-flushed gate 9. In the exemplary embodiment illustrated in FIG. 2, the second coating station 13 consists of a nanoparticle application station 14 and a melting station 15 arranged downstream thereof. The coating station 13 comprises a housing 26.

[0034] The nanoparticle application station 14 comprises heaters 19 that are arranged on both sides of the substrate just like the heaters 16. A process chamber of the nanoparticle application station 14 is heated to a temperature between room temperature and 250° C. by means of these heaters.

[0035] The process chamber furthermore comprises spray nozzles 20 or a gas inlet element 20, by means of which nanoparticles 4 can be transported into the process chamber in the direction of a broad face of the substrate 1, particularly with the aid of a carrier gas. The nanoparticles 4 respectively deposit on the bundles 3 of nanofilaments 2 and reach the interior of the bundles 3. A loose bond containing cavities is formed between the nanoparticles 4 and the nanofilaments 2. The heaters 19 and the spray nozzles 20 are arranged in the same housing 26.

[0036] The thusly prepared substrate 1 is transported into the melting station 15 through another gas-flushed gate 9, wherein both broad sides of the substrate 1 are in said melting station exposed to the laser light of a laser 21 or the light of a xenon lamp in such a way that adjacent nanoparticles 4 fuse with one another and/or that nanoparticles 4 connect to the nanofilaments 2. A porous body with a plurality of cavities, which is capable of absorbing lithium ions in solution, is formed in the process. The melting station 15 comprises a separate housing 27.

[0037] The exemplary embodiment illustrated in FIG. 2 comprises three housings 24, 25, 26, 27, which are arranged behind one another in the transport direction of the electrically conductive substrate 1, wherein one of the four processing steps A, B, C, D is carried out in each of the housings 24, 25, 26, 27. The housings 24, 25, 26, 27 are connected to one another by means of gas-flushed gates 9.

[0038] FIG. 3 shows a second exemplary embodiment of the invention, in which all processing stations are arranged in one housing. The heaters 16, the gas inlet elements 17, the xenon laser 18, the heating elements 19 and the spraying device 20 are accommodated in a common housing together with the laser 21. Only the entry arrangement 22 and the exit arrangement 23 form gas-flushed gates, through which the substrate 1 is transported into the device 10 and once again transported out of the device 10.

[0039] In the exemplary embodiment illustrated in FIG. 4, the device 10 consists of two housing parts that are connected to one another by means of a gas-flushed gate 9. The first processing step A is carried out in a housing 16 and the second, third and fourth processing steps B, C, D are carried out in a second housing 29.

[0040] FIGS. 5 and 6 show a variation of a system for producing an electrode of a lithium-ion cell including a method, in which an electrically conductive substrate 1 is unwound from a first roll 7. Nanofilaments 2 are deposited on the substrate 1 in a process step A. Nanoparticles 4 are applied to the nanofilaments 2 in a process step C. The nanoparticles 4 are fused into a coating 5 in a process step D. The nanoparticles also connect to the nanofilaments 2 in the process. The substrate 1 may be pre-treated. For example, its surface may be provided with a seed structure, by virtue of which nanofilaments 2 only grow on predefined zones of the substrate 1. The zones may consist of island-like microzones that are uniformly distributed over the broad face and separated from one another by a clearance.

[0041] The nanofilaments 2 deposited in process step A particularly may also be individually standing nanofilaments. They may be spaced apart from one another so far that adjacent nanofilaments 2 do not contact one another. They may also be realized in the form of ramified nanofilaments 2.

[0042] The device required for carrying out this method may also comprise all processing stations of the devices illustrated in FIGS. 2-4 except for the forming station 12. The invention particularly pertains to a device of the type illustrated in FIG. 6. An entry arrangement 22 is provided, through which the electrically conductive substrate enters the device 10. The electrically conductive substrate 1 once again exits the device through an exit arrangement 23. The entry arrangement 22 and the exit arrangement 23 may be gas-flushed gates. A coating station is arranged adjacently downstream of the entry arrangement 22 referred to a transport direction, in which the substrate 1 is transported. The coating station 11 comprises a housing 24 that contains two heaters 16 and two gas inlet elements 17 arranged between the heaters. The electrically conductive substrate 1 is transported through the intermediate space between the two gas inlet elements 17.

[0043] A gas-flushed gate 9, through which the substrate 1 is transported, is arranged adjacently downstream of the housing 24.

[0044] Another housing 26 is arranged adjacently downstream of the gas-flushed gate 9. However, the housing 26 may also be directly connected to the housing 24.

[0045] Two heaters 19 are arranged in the housing 26. Two nozzle arrangements 20 are located between the two heaters 19. The substrate 1 is transported through the space between the two nozzle arrangements 20. The housing 26 contains the above-described nanoparticle application station 14.

[0046] A gas-flushed gate 9, through which the substrate is transported, is arranged adjacently downstream of the housing 26. An additional housing 27 is arranged adjacently downstream of the gas-flushed gate 9 and contains a melting station 15 that comprises a laser 21. However, the housing 27 may also be directly connected to the housing 26.

[0047] Energy is applied to both sides of the substrate 1 in the melting station 15 by means of a laser beam 21 such that the nanoparticles 4, which were deposited on the filaments 2 in the nanoparticle application station 14, connect to one another and/or to the nanofilaments 2.

[0048] The exit arrangement 23 is arranged directly downstream of the housing 27.

[0049] In the latter method and in the device for carrying out this method, the nanoparticles 4 are directly applied to the nanofilaments 2. Prior bundling of the nanofilaments 2 is not carried out in this case.

[0050] In variations that are not illustrated in the drawings, only one side of the substrate 1 is provided with the above-described filament layer that is coated with nanoparticles 4. In this case, the correspondingly used device only comprises the elements that are illustrated above or underneath the substrate 1 in the drawings. However, two such devices would also make it possible to provide both sides of the substrate 1 with nanofilaments 2 that are coated with nanoparticles, namely by initially providing a first broad face of the substrate 1 and subsequently providing the second broad face of the substrate 1 with filaments 2 that are coated with nanoparticles.

[0051] The inventive method makes it possible to produce an electrode 34, 35 of the type used in a lithium-ion cell in the inventive device, wherein such a lithium-ion cell is schematically illustrated in FIG. 7. Two electrodes 34, 35 are located on opposite sides of a battery cell 30. A porous wall 33 is located between the electrodes 34, 35. An electrolyte containing lithium ions is accommodated in the volumes 31, 32.

[0052] According to the invention, the nanofilaments 2, which are initially applied to the substrate 1 in a uniformly distributed and essentially structureless manner, are combined into bundles 3. In this case, a group of directly adjacent nanofilaments 2 is directed at a common center. Adjacent bundles respectively comprise nanofilaments 2 that are directed at a common center such that the nanofilaments 2 of adjacent bundles are directed away from a clearance located between multiple bundles 3.

[0053] In the next production step, the bundles 3 are provided with a coating of silicon nanoparticles 4. In this case, each respective bundle 3 may be provided with such a coating, wherein the coatings of silicon nanoparticles are spaced apart from one another.

[0054] The preceding explanations serve for elucidating all inventions that are included in this application and also respectively enhance the prior art independently with at least the following combinations of characteristic features, namely:

[0055] A device, which is characterized in that the nanofilaments are combined into a plurality of bundles, which respectively comprise multiple nanofilaments, wherein a clearance 6 is formed between adjacent bundles 3.

[0056] A method comprising at least the following process steps: [0057] supplying an electrically conductive substrate 1; [0058] applying a layer of nanofilaments 2, which on statistical average are uniformly arranged over the surface of the substrate 1; [0059] respectively combining a plurality of nanofilaments into bundles 3 such that a clearance 6 remains between adjacent bundles 3; [0060] applying an ion-absorbing coating 5 to the bundles 3.

[0061] A method, which is characterized in that the nanofilaments 2 are exposed to light.

[0062] A device or a method, which is characterized in that the nanofilaments 2 are carbon nanotubes CNT.

[0063] A device or a method, which is characterized in that a cross-sectional distance through a bundle 3 respectively lies between 0.5 and 5 μm or between 1.5 and 2.5 μm.

[0064] A device or a method, which is characterized in that the ion-absorbing coating 5 is formed by nanoparticles 4, which are connected to one another and to the bundles of nanofilaments 2.

[0065] A device or a method, which is characterized in that the nanoparticles 4 comprise silicon, sulfur, titanium oxide, a phosphite, a nitrite or carbon and, in particular, SiO.sub.2, TiO.sub.2, CrO.sub.2, S, LiCoO, LiTiO, LiNiO, LiMnO, LiFePO, LiCoPO, LiMnPO, V.sub.2O.sub.5, Ge, Sn, Pb or ZnO.

[0066] A method, which is characterized in that the nanofilaments 2 applied to the substrate 1 are formed into bundles 3 by being exposed to light.

[0067] A method, which is characterized in that the layer of nanofilaments 2 is exposed to the light of a xenon lamp or a laser.

[0068] A method, which is characterized in that a laser beam, which is generated continuously or in a pulsed manner and expanded into a strip, is used for exposing the layer of nanofilaments 2 to light, wherein the laser beam preferably moves over the layer with a constant speed.

[0069] A method, which is characterized in that silicon nanoparticles 4 are applied, particularly sprayed, onto the bundles 3 during the application of the coating 5, wherein said silicon nanoparticles are connected to one another and to the nanofilaments 2 lying underneath the nanoparticles by applying energy thereto.

[0070] A method, which is characterized in that light, particularly the light of a laser beam, is used for connecting the nanoparticles 4 to one another and/or to the bundles of nanofilaments 2 lying underneath the nanoparticles, wherein said light moves over the surface of the substrate such that at least the surface of the nanoparticles 4 melts.

[0071] A battery, which is characterized in that the first and/or second electrode 34, 35 is realized in accordance with one of the preceding characteristic features.

[0072] A device, in which at least the following processing stations of the processing device 10 are arranged directly behind one another in the transport direction: [0073] a first coating station 11, in which nanofilaments 2 are applied to the substrate 1; [0074] a second coating station 13, in which the nanofilaments 2 are provided with an ion-absorbing coating 5.

[0075] A device, which is characterized in that a forming station 12, in which the nanofilaments 2 are combined into bundles 3, is provided between the first coating station 11 and the second coating station 13, wherein said bundles 3 are provided with a coating 5 in the second coating station 13.

[0076] A device, which is characterized in that a first roll 7 is provided, on which the substrate 1 is wound up, wherein said substrate passes through the processing device 10 from the entry arrangement 22 to the exit arrangement 23 and is wound up on a second roll 8 downstream of the exit arrangement 23 referred to the transport direction.

[0077] A device, which is characterized in that the forming station 12 comprises a light source 18, particularly a laser, by means of which the layer of nanofilaments 2 applied to the substrate 1 in the first coating station 11 can be exposed to light in such a way that a plurality of nanofilaments 2 combine into bundles 3.

[0078] A device, which is characterized in that the second coating station 13 comprises a spraying device 20, by means of which nanoparticles 4 can be sprayed on the bundles 3 produced in the forming station.

[0079] A device, which is characterized in that the second coating station 13 comprises a light source 21, particularly a laser, by means of which the nanoparticles 4 applied to the bundles 3 or nanofilaments 2 are connected to one another and to the nanofilaments 2.

[0080] All disclosed characteristic features are essential to the invention (individually, but also in combination with one another). The disclosure content of the associated/attached priority documents (copy of the priority application) is hereby fully incorporated into the disclosure of this application, namely also for the purpose of integrating characteristic features of these documents into claims of the present application. The characteristic features of the dependent claims characterize independent inventive enhancements of the prior art, particularly for submitting divisional applications on the basis of these claims.

LIST OF REFERENCE SYMBOLS

[0081] 1 Electrically conductive substrate [0082] 2 Nanofilament [0083] 3 Bundle [0084] 4 Nanoparticle [0085] 5 Coating [0086] 6 Clearance [0087] 7 First roll [0088] 8 Second roll [0089] 9 Gas-flushed gate [0090] 10 Device [0091] 11 Coating station [0092] 12 Forming station [0093] 13 Coating station [0094] 14 Nanoparticle application station [0095] 15 Melting station [0096] 16 Heater [0097] 17 Gas inlet element [0098] 18 Laser [0099] 19 Heater [0100] 20 Spray nozzles [0101] 21 Laser [0102] 22 Entry arrangement [0103] 23 Exit arrangement [0104] 24 Housing [0105] 25 Housing [0106] 26 Housing [0107] 27 Housing [0108] 28 Housing [0109] 29 Housing [0110] 20 Battery cell [0111] 31 Volumes [0112] 32 Volumes [0113] 33 Porous wall [0114] 34 Electrode [0115] 35 Electrode [0116] A Process step/nanofilament growth [0117] B Process step/forming [0118] C Process step/nanoparticle application [0119] D Process step/sintering