ELECTRODE, USE THEREOF, BATTERY, AND PROCESS FOR PRODUCING AN ELECTRODE

Abstract

An electrode for a lithium-ion battery. The electrode has at least one porous silicon layer and a copper layer. There is also described a battery with such an electrode, a method for producing an electrode of this kind, and the use of an electrode of this kind in a battery.

Claims

1-17. (canceled)

18. An electrode, comprising: at least one porous silicon layer and a copper layer on said at least one porous silicon layer.

19. The electrode according to claim 18, wherein said copper layer is disposed directly on said at least one porous silicon layer.

20. The electrode according to claim 18, which comprises a multilayer system made up of a plurality of porous silicon layers arranged on top of one another and differing from one another in a quality selected from the group consisting of porosities, pore sizes, and pore shapes, and wherein said at least one porous silicon layer is one of said plurality of porous silicon layers of said multilayer system.

21. The electrode according to claim 18, wherein the electrode is configured as a foil.

22. The electrode according to claim 18, wherein the electrode is configured as a rollable film.

23. The electrode according to claim 18, which comprises lithium intercalated in said at least one porous silicon layer.

24. The electrode according to claim 18 configured for a lithium-ion battery.

25. A process for producing the electrode according to claim 18, the method comprising: etching a silicon substrate for forming at least one porous silicon layer; and depositing a copper layer on the at least one porous silicon layer.

26. The process according to claim 25, wherein the step of forming the at least one porous silicon layer comprises etching the silicon substrate wet-chemically.

27. The process according to claim 26, which comprises etching the silicon substrate in a continuous process.

28. The process according to claim 25, wherein the step of forming the at least one porous silicon layer comprises etching the silicon substrate on one side.

29. The process according to claim 25, wherein the step of forming the at least one porous silicon layer comprises etching the silicon substrate electrochemically, by: transporting the silicon substrate along a direction of transport through a plurality of treatment tanks arranged one after the other in the direction of transport, each of the treatment tanks being filled with an etching medium and each having an electrode arranged therein; during transport through the treatment tanks, contacting the silicon substrate on a substrate underside with the etching medium present in the respective treatment tank; and wherein a polarity of the electrodes arranged in the treatment tanks alternates in the direction of transport.

30. The process according to claim 25, which comprises depositing the copper layer in a two-stage process including: a first deposition step wherein a first portion of the copper layer is deposited on the at least one porous silicon layer by galvanic displacement; and a second deposition step wherein a second portion of the copper layer is deposited on the first portion of the copper layer by electrochemical deposition.

31. The process according to claim 25, which comprises: a first deposition step in which a nickel layer is deposited on the at least one porous silicon layer by electrochemical deposition; and a second deposition step in which the copper layer is deposited on the nickel layer by electrochemical deposition.

32. The process according to claim 25, which comprises: etching the silicon substrate to form a multilayer system made up of a plurality of porous silicon layers that differ from one another in a quality of the porous silicon layers selected from the group consisting of porosities, pore sizes, and pore shapes, and wherein the at least one porous silicon layer is one of the plurality of porous silicon layers of the multilayer system; and forming the multilayer system with the porous silicon layer of the multilayer system having a greatest porosity immediately adjoining an unporosified portion of the silicon substrate.

33. The process according to claim 25, which comprises removing the at least one porous silicon layer together with the copper layer from an unporosified portion of the silicon substrate.

34. The process according to claim 33, wherein the step of removing the at least one porous silicon layer together with the copper layer comprises subjecting the silicon substrate to a thermal treatment.

35. The process according to claim 34, which comprises treating the silicon substrate in a continuous oven.

36. The process according to claim 33, which comprises intercalating lithium in the at least one porous silicon layer after the at least one porous silicon layer has been removed together with the copper layer from the unporosified portion of the silicon substrate.

37. The process according to claim 25, which comprises integrating the electrode as an anode in a battery.

38. A battery, comprising an electrode according to claim 18.

39. The battery according to claim 38, configured as a lithium-ion battery.

Description

[0070] The figures are schematic drawings and are not to scale.

[0071] In the figures:

[0072] FIG. 1 shows a treatment device for the treatment of a substrate;

[0073] FIG. 2 shows a sectional view of a silicon substrate treated using the treatment device from FIG. 1, said substrate having a multilayer system made up of a plurality of porous silicon layers;

[0074] FIG. 3 shows the silicon substrate from FIG. 2 in a view from below;

[0075] FIG. 4 shows, in a sectional view, the silicon substrate and a first portion of a copper layer deposited on the silicon substrate in a first deposition step;

[0076] FIG. 5 shows a sectional view of the silicon substrate and of the copper layer deposited on the silicon substrate in two deposition steps;

[0077] FIG. 6 shows, in a sectional view, the silicon substrate and the copper layer deposited on the silicon substrate after the removal together of the copper layer and of a plurality of porous silicon layers from an unporosified portion of the silicon substrate;

[0078] FIG. 7 shows a sectional view of an electrode for a battery, which is formed by the detached copper layer, the detached porous silicon layers, and the lithium intercalated in the porous silicon layers;

[0079] FIG. 8 shows a sectional view of one of the porous silicon layers of the electrode from FIG. 7 after activation of the electrode;

[0080] FIG. 9 shows, in a side view, the unporosified portion of the silicon substrate and the metal residues and remnants of porous structures present on the unporosified portion of the silicon substrate;

[0081] FIG. 10 shows the unporosified portion of the silicon substrate during removal of the metal residues in a treatment tank;

[0082] FIG. 11 shows the unporosified portion of the silicon substrate after removal of the metal residues, in which the unporosified portion of the silicon substrate is present in a further treatment tank for removal of remnants of porous structures;

[0083] FIG. 12 shows, in a partial sectional view, a lithium-ion battery equipped with the electrode from FIG. 7;

[0084] FIG. 13 shows an alternative construction of a battery with the electrode from FIG. 7;

[0085] FIG. 14 shows an alternative possible arrangement of the electrode from FIG. 7;

[0086] FIG. 1 shows a treatment device 1 for the treatment of a substrate, especially for the electrochemical etching of a substrate on one side. In addition, FIG. 1 shows a silicon substrate 2 to be treated by means of the treatment device 1.

[0087] The treatment device 1 comprises a transport device 3 that is set up to transport the silicon substrate 2 to be treated along a direction of transport 4. In the present working example, the transport device 3 takes the form of a roller conveyor having a plurality of transport rollers 5.

[0088] The treatment device 1 further comprises a plurality of treatment tanks 6 arranged one after the other in the direction of transport 4, which are each filled with an etching medium 7 and in each of which is arranged an electrode 8. In FIG. 1, three treatment tanks 6 are depicted by way of example. The treatment device 1 may in principle have a larger or a smaller number of treatment tanks 6.

[0089] The etching medium 7 is preferably an aqueous hydrogen fluoride solution. Optionally, the etching medium 7 may comprise an additive and/or a surfactant. Each of the electrodes 8 has applied to it an electrical potential, with the polarity of the electrodes 8 alternating in the direction of transport 4.

[0090] The transport device 3 transports the silicon substrate 2 along the direction of transport 4 through the treatment tanks 6, wherein the silicon substrate 2 is contacted with the etching medium 7 present in the treatment tanks 6 only on the substrate underside 9.

[0091] During transport of the silicon substrate 2 through the treatment tanks 6, an electrochemical reaction occurs in which local inhomogeneities in the electric current density cause etching peaks and troughs to arise, which on the substrate underside 9 results in the formation of pores, with the result that a porous structure forms on the substrate underside 9.

[0092] The electrochemical reaction may be regulated via the electric potential of the electrodes 8, which influences the electric current density in the treatment tanks 6. The reaction may be additionally regulated by admixing an additive and/or a surfactant.

[0093] When an etching medium comprising hydrogen fluoride is used as etching medium 7, the following reactions in particular occur on the substrate underside 9: Si+6F.sup.−+4h.sup.+.fwdarw.SiF.sub.6.sup.2−. The electric current supplies the surface of the silicon substrate 2 with electron holes (h.sup.+) and the hydrogen fluoride gives rise to hydrogen fluoride ions (F.sup.−) in the solution.

[0094] The electric current density on the treatment tanks 6 may be adjusted so that the porous structure of the silicon substrate 2 is graduated over the depth of the silicon substrate 2, with the result that a plurality of porous silicon layers that differ from one another in their porosity and/or in their pore size and/or in their pore shape is formed on the substrate underside 9.

[0095] Additionally present in the treatment device 1 between each treatment tank 6 is an air knife (not shown in the figures) with which is generated a gas stream 10 of nitrogen for blowing away any etching medium 7 present on the substrate underside 9.

[0096] FIG. 2 shows, in a sectional view, the silicon substrate 2 treated with the aid of the treatment device 1 from FIG. 1.

[0097] The treated silicon substrate 2 has on the substrate underside 9 a multilayer system 11 made up of a plurality of porous silicon layers 12a, 12b, 12c, 12d arranged on top of one another. In FIG. 2, four porous silicon layers 12a, 12b, 12c, 12d are shown by way of example, it being possible in principle for a larger or smaller number of porous silicon layers to form on the substrate underside 9 of the silicon substrate 2 during treatment with the aid of the treatment device 1.

[0098] The porous silicon layers 12a, 12b, 12c, 12d differ in the size of their pores 13 and/or in the shape of their pores 13 and/or in their porosity, wherein the porous silicon layer 12d of the multilayer system 11 having the greatest porosity immediately adjoins an unporosified portion 14 of the silicon substrate 2. This porous silicon layer 12d serves as a detachment layer for the later removal of the multilayer system 11 from the unporosified portion 14 of the silicon substrate 2 (cf. FIG. 6).

[0099] FIG. 3 shows the silicon substrate 2 from FIG. 2 in a view from below.

[0100] In FIG. 3, a plurality of pores 13 of varying shape and size are visible on the substrate underside 9 of the silicon substrate 2.

[0101] After formation of the multilayer system 11, a copper layer 15 is deposited on the multilayer system 11 in a two-stage deposition process (cf. FIGS. 4 and 5).

[0102] In a first deposition step, a first portion 16 of the copper layer 15 is deposited on the multilayer system 11 by means of galvanic displacement. In this deposition step, the silicon substrate 2 is contacted on the substrate underside 9 with an aqueous deposition solution comprising hydrogen fluoride and copper sulfate. The hydrogen fluoride dissolves silicon dioxide from the substrate underside 9 of the silicon substrate 2, leaving behind unoxidized silicon on the substrate underside 9, which, on account of the chemical potential between silicon and copper, is very attractive for the copper ions present in the deposition solution.

[0103] Galvanic displacement is a self-limiting process that stops by itself when the extremely porous silicon layer 12a is completely covered with copper. At the end of the first deposition step, said first portion 16 of the copper layer 15 has formed such that the extremely porous silicon layer 12a is embedded in the first portion 16 of the copper layer 15.

[0104] In a second deposition step, a second portion 17 of the copper layer 15 is then deposited on the first portion 16 of the copper layer 15 by means of electrochemical deposition. The first portion 16 of the copper layer 15 serves as an electrically conductive seed layer for the formation of the second portion 17 of the copper layer 15.

[0105] In the second deposition step, the silicon substrate 2 is wetted on the substrate underside 9 with a deposition solution comprising copper sulfate and an electric current is applied. The silicon substrate 2 serves in the electrochemical deposition as a negatively charged electrode, while the deposition solution serves as a positively charged counter electrode.

[0106] FIG. 4 shows a sectional view of the silicon substrate 2 after deposition of the first portion 16 of the copper layer 15 on the multilayer system 11.

[0107] FIG. 5 shows a sectional view of the silicon substrate 2 after deposition of the second portion 17 of the copper layer 15 on the first portion 16 of the copper layer 15.

[0108] After deposition of the copper layer 15, the silicon substrate 2 is subjected to a thermal treatment (cf. FIG. 6). This may for example take place in a continuous oven (not shown in the figure).

[0109] In the thermal treatment, thermal radiation 18 is employed to bring about collapse of the pore walls of the porous silicon layer 12d serving as a detachment layer (cf. FIGS. 2, 4, and 5), this being attributable to differences in the thermal coefficient of expansion between porous silicon layers 12a, 12b, 12c on the one hand and porous silicon layer 12d on the other. This allows the copper layer 15 together with the porous silicon layers 12a, 12b, 12c of the multilayer system 11 to be detached from the unporosified portion 14 of the silicon substrate 2.

[0110] After the thermal treatment, all that remains of the porous silicon layer 12d serving as a detachment layer are slender stumps 19. These respectively adjoin the unporosified portion 14 of the silicon substrate 2 or the porous silicon layer 12c of the multilayer system 11 formerly adjoining the detachment layer.

[0111] FIG. 6 shows, in a sectional view, the silicon substrate 2 and the copper layer 15 deposited on the silicon substrate 2 after the removal together of the copper layer 15 and of the porous silicon layers 12a, 12b, 12c from the unporosified portion 14 of the silicon substrate 2.

[0112] After the removal together of the copper layer 15 and of the porous silicon layers 12a, 12b, 12c from the unporosified portion 14 of the silicon substrate 2, lithium 20 is intercalated in the detached porous silicon layers 12a, 12b, 12c (cf. FIG. 7).

[0113] FIG. 7 shows a sectional view of a working example of an inventive electrode 21 for a battery designed as a rollable film.

[0114] This electrode 21 is formed by the porous silicon layers 12a, 12b, 12c, the copper layer 15, and by the lithium 20 intercalated in the porous silicon layers 12a, 12b, 12c.

[0115] The installation of the electrode 21 in a battery is followed by activation of the electrode 21 by performing a plurality of charge-discharge cycles on the battery.

[0116] The activation of the electrode 21 results in the formation of an island structure in the porous silicon layers 12a, 12b, 12c that does not develop further after a few cycles and remains largely stable over further cycles (cf. FIG. 8). If the silicon of the electrode 21 were non-porous, the electrode 21 would be destroyed during performance of the charge-discharge cycles as a consequence of disordered recrystallization of the silicon. However, in the present case, the porous structure of the silicon results in a self-organized recrystallization of the silicon wherein the portions of the silicon that are embedded in the copper layer 15 serve as seed crystals.

[0117] FIG. 8 shows a sectional view of one of the porous silicon layers 12a, 12b, 12c of the electrode 21 from FIG. 7 after activation of the electrode 21.

[0118] The island structure of the depicted porous silicon layer, which is formed from a plurality of rectangular regions 22, can be seen in FIG. 8.

[0119] Unlike the pores 13 in the porous silicon layer depicted in FIG. 8, the lithium 20 intercalated in the depicted porous silicon layer is in FIG. 8 omitted for better clarity.

[0120] In an alternative working example, in contrast to the first working example described above in connection with FIGS. 1 to 8, a copper layer is by means of an alternative process variant deposited on a multilayer system that corresponds to the multilayer system 11 described in connection with FIG. 2. In this alternative process variant, instead of the first portion 16 of the copper layer 15, a nickel layer is in a first deposition step deposited on the multilayer system. The deposition of the nickel layer on the multilayer system is effected by means of electrochemical deposition. In order to deposit the nickel layer on a silicon substrate having the multilayer system on the substrate underside, the silicon substrate is wetted on the substrate underside with a deposition solution comprising nickel sulfate or nickel sulfamate and an electric current is applied.

[0121] The deposition of the nickel layer can be illustrated by FIG. 4. In the representation thereof, the reference numeral 16 would in this alternative working example refer to the nickel layer. In all other respects, the elements of the alternative working example would correspond to the elements shown in FIG. 4.

[0122] In a second deposition step following the deposition of the nickel layer, a copper layer is in the alternative working example deposited on the nickel layer by means of electrochemical deposition. The nickel layer serves here as an electrically conductive seed layer for the formation of the copper layer and provides improved adhesion on the porous silicon layer of the copper layer applied onto the nickel layer. For illustration of the deposition of the copper layer on the nickel layer, reference can be made to FIG. 5. In the representation thereof, the reference numeral 16 would in this alternative working example refer to the nickel layer and the reference numeral 17 to the copper layer deposited on the nickel layer.

[0123] The facts and features described below in connection with FIGS. 9 to 14 refer to the working example shown in FIGS. 1 to 8. Unless otherwise stated, they may also be combined without restriction with the alternative working example described above.

[0124] FIG. 9 shows, in a side view, the unporosified portion 14 of the silicon substrate 2.

[0125] Also shown in FIG. 9 are the remnants of porous structures adjoining the unporosified portion 14 of the silicon substrate 2, which are formed by slender stumps 19, and also the metal residues 23 present on the unporosified portion 14 of the silicon substrate 2, with which the unporosified portion 14 of the silicon substrate 2 will, on deposition of the copper layer 15 according to the first working example described in connection with FIGS. 1 to 8 or on deposition of the nickel layer and of the copper layer according to the alternative working example, be contaminated.

[0126] In order to be able to recycle the unporosified portion 14 of the silicon substrate 2, the stumps 19 and the metal residues 23 are removed in a two-stage wet-chemical etching process (cf. FIGS. 9 and 10). This allows the unporosified portion 14 of the silicon substrate 2 to be used for example for production of a further electrode of the type described above, especially through repetition of the process steps described above.

[0127] FIG. 10 shows the unporosified portion 14 of the silicon substrate 2, the adjoining stumps 19, said metal residues 23, and a treatment tank 24.

[0128] The treatment tank 24 is filled with an acidic etching medium 25 that serves for the removal of the metal residues 23 in the form of copper in the case of the first working example or in the form of copper and nickel in the case of the alternative working example. The etching medium 25 may for example comprise hydrogen fluoride and/or hydrogen chloride and/or nitric acid and/or sulfuric acid and/or hydrogen peroxide and/or ozone.

[0129] Depicted in FIG. 10 is a state in which the unporosified portion 14 of the silicon substrate 2 is immersed in the etching medium 25 and said metal residues 23 have dissolved in the etching medium 25.

[0130] FIG. 11 shows the unporosified portion 14 of the silicon substrate 2 and a further treatment tank 26.

[0131] The treatment tank 26 from FIG. 11 is filled with an etching medium 27 that serves for the removal of the stumps 19 mentioned above. This etching medium 27 may be an alkaline etching medium or an acidic etching medium. In the former case, the etching medium 27 may for example comprise deionized water and also sodium hydroxide and/or potassium hydroxide. In the latter case, the etching medium 27 may for example comprise hydrogen fluoride and/or nitric acid and/or sulfuric acid and/or hydrogen peroxide and/or ozone.

[0132] Depicted in FIG. 11 is a state in which the unporosified portion 14 of the silicon substrate 2 is immersed in the etching medium 27 present in the treatment tank 26. The etching medium 27 brings about a surface polishing of the silicon substrate 2, resulting in this state in removal of the stumps 19 described above from the unporosified portion 14 of the silicon substrate 2 and allowing the unporosified portion 14 of the silicon substrate 2 to be used for further production of an electrode of the type described above.

[0133] FIG. 12 shows, in a partial sectional view, a working example of an inventive battery 28a.

[0134] The battery 28a is in the present working example a lithium-ion battery in a cylindrical construction.

[0135] The battery 28a comprises a cylindrical housing 29a. In addition, the battery 28a comprises a cathode 30a, an anode 31a, and also a separator 32a arranged between the cathode 30a and the anode 31a. The cathode 30a, the anode 31a, and the separator 32a are each formed as a rolled-up film and are arranged in the housing 29a of the battery 28a.

[0136] The anode 31a of the battery 28a is the electrode 21 described above (cf. FIGS. 7 and 8). That is to say, the electrode 21 described above is used as the anode 31a in the battery 28a.

[0137] FIG. 13 shows, in a partial sectional view, an alternative working example of the battery described in connection with FIG. 12. In the working example shown in FIG. 13, the battery 28b has an alternative construction with a rectangular base.

[0138] The battery 28b comprises in the alternative construction a cuboidal housing 29b. In addition, the battery 28b comprises a cathode 30b, an anode 31b, and also a separator 32b arranged between the cathode 30b and the anode 31b. The cathode 30b, the anode 31b, and the separator 32b are formed as rectangular sections and arranged stacked on top of one another in predefine order inside the housing 29b of the battery 28b.

[0139] The anode 31b of the battery 28b is the electrode 21 described above (cf. FIGS. 7 and 8). That is to say, the electrode 21 described above is used as the anode 31b in the battery 28b in the form of rectangular sections.

[0140] FIG. 14 shows an alternative possible arrangement of the cathode 30b, the anode 31b, and the separator 32b in the form of a cuboidal stack for the alternative working example of the battery 28b described in connection with FIG. 13. The anode 31b here is formed as a foldable film. In this alternative possible arrangement, the cathode 30b and the separator 32b are folded between the anode 31b by means of a Z-folding technique. The cathode 30b and the separator 32b may here be formed as rectangular sections in a pairwise manner. Preferably, the cathode 30b and the separator 32b are formed as a foldable film. This allows an overlaid Z-folding technique to be applied. With this it is possible in alternate folding steps for the anode 31b, the cathode 30b, and the separator 32b to be folded into a cuboidal stack. For example, the cathode 30b and the separator 32b can in a first folding step be folded between the anode 31b. In a second folding step, the anode 31b can then be folded between the separator 32b that is arranged in a pairwise manner with the cathode 30b. After the second folding step, the first folding step can be executed afresh. This makes it possible to produce a battery 28b having a cuboidal construction at low cost and/or in an automated manner.

[0141] The invention has been described in detail with reference to the depicted working examples. However, the invention is not limited to or by the disclosed example. Other variants may be derived from this working example by those skilled in the art, without departing from the ideas underlying the invention.

List of Reference Numerals

[0142] 1 Treatment device [0143] 2 Silicon substrate [0144] 3 Transport device [0145] 4 Direction of transport [0146] 5 Transport roller [0147] 6 Treatment tank [0148] 7 Etching medium [0149] 8 Electrode [0150] 9 Substrate underside [0151] 10 Gas stream [0152] 11 Multilayer system [0153] 12a Porous silicon layer [0154] 12b Porous silicon layer [0155] 12c Porous silicon layer [0156] 12d Porous silicon layer [0157] 13 Pore [0158] 14 Unporosified portion of the silicon substrate [0159] 15 Copper layer [0160] 16 First portion of the copper layer [0161] 17 Second portion of the copper layer [0162] 18 Thermal radiation [0163] 19 Stumps [0164] 20 Lithium [0165] 21 Electrode [0166] 22 Rectangular region [0167] 23 Metal residue [0168] 24 Treatment tank [0169] 25 Etching medium [0170] 26 Treatment tank [0171] 27 Etching medium [0172] 28a Battery [0173] 28b Battery [0174] 29a Housing [0175] 29b Housing [0176] 30a Cathode [0177] 30b Cathode [0178] 31a Anode [0179] 31b Anode [0180] 32a Separator [0181] 32b Separator