Electrodes, their use, batteries, and processes for manufacturing electrodes

Abstract

The present invention relates to an electrode 21, more particularly to an electrode 21 for a lithium-ion battery 28a; 28b. According to the invention, the electrode 21 comprises at least one porous silicon layer 12a, 12b, 12c, 12d and a copper layer 15. The invention further relates to batteries 28a; 28b comprising such an electrode 21, a method for producing such an electrode 21, and the use of such an electrode 21 in batteries 28a; 28b.

Description

[Technical Field]

[0001] This invention relates particularly to electrodes for lithium-ion batteries and their use. Furthermore, the invention relates to batteries and processes for manufacturing electrodes. [Background technology]

[0002] Lithium-ion batteries are a widely used type of battery, found in numerous devices, particularly mobile devices and electric vehicles.

[0003] In lithium-ion batteries, electrodes containing graphite are often used as anodes. Due to the relatively low lithium uptake capacity of graphite, such electrodes have a limited specific charge capacity of only up to 500 mAh / g.

[0004] Silicon is an electrode material that can replace graphite. Theoretically, a specific charge capacity of 4200 mAh / g can be achieved using silicon-based electrodes. However, silicon has a disadvantage compared to graphite in that lithium intercalation causes a significant expansion of silicon volume. When silicon-based electrodes are used in lithium-ion batteries, this significant expansion of silicon volume can lead to battery failure after a few charge cycles. [Overview of the Initiative]

[0005] The object of the present invention is to provide an electrode capable of achieving high specific charge capacity and long lifespan, and to define a process for manufacturing such an electrode.

[0006] With respect to electrodes, the present invention achieves this problem with the electrode described in claim 1. With respect to processes, the present invention achieves this problem with the process described in claim 6.

[0007] A further objective of the present invention is to provide a battery capable of achieving high specific charge capacity and a long lifespan.

[0008] The present invention achieves this objective through the use described in claim 16 and the battery described in claim 17, respectively.

[0009] Further preferred developments of the present invention are the subject of further patent claims.

[0010] The electrode of the present invention has at least one porous silicon layer and one copper layer.

[0011] The use of silicon as an electrode material makes it possible to achieve a high specific charge capacity, which is a result of silicon's high lithium uptake capacity, particularly compared to that of graphite.

[0012] For example, in the case of volume expansion resulting from lithium intercalation, pores in at least one silicon layer allow the silicon to expand into the cavity formed by the pores. This allows the silicon to withstand volume expansion without damage, thus enabling the electrode to achieve a long lifespan.

[0013] Furthermore, at least one porous silicon layer can be manufactured at low cost. For example, masking and / or multi-stage etching processes can be omitted during manufacturing. The ability to manufacture at least one porous silicon layer at low cost is advantageous in that the entire electrode can be manufactured at low cost.

[0014] The at least one porous silicon layer preferably takes the form of a sponge-like structure. The pores of the at least one porous silicon layer are advantageously at least 10 nm in size. This allows for a cavity large enough to withstand volume expansion without damage to the silicon. In particular, larger pores can potentially have an adverse effect on the stability of the at least one porous silicon layer, so it is even more advantageous if the pores have a size of 10,000 nm or less.

[0015] Furthermore, at least one porous silicon layer may be embedded at least partially in the copper layer. That is, the copper layer may be formed so as to expand into at least a portion of the pores of at least one porous silicon layer.

[0016] In a preferred embodiment, the copper layer is disposed directly on at least one porous silicon layer, particularly on at least one porous silicon layer.

[0017] It is advantageous for the copper layer to have a thickness of at least 1 μm, preferably at least 2 μm. In particular, such a minimum thickness of the copper layer is advantageous for the manufacturing process because it facilitates the removal of the copper layer from the silicon substrate along with at least one porous silicon layer. Furthermore, it is advantageous for the copper layer to have a thickness of 20 μm or less, preferably 12 μm or less, as a copper layer thickness exceeding 20 μm can potentially be detrimental to the mechanical flexibility of the electrode.

[0018] In an advantageous further development of the present invention, the electrode comprises a multilayer system consisting of a plurality of porous silicon layers, preferably arranged vertically to one another, wherein at least one porous silicon layer is one of these layers. The layers may differ from one another, for example, in that each of the porous silicon layers has a different porosity, a different pore size, and / or a different pore shape.

[0019] If the electrode comprises such a multilayer system, the copper layer of the electrode is preferably placed on one of the porous silicon layers of the multilayer system, and in particular, directly on one of the porous silicon layers of the multilayer system.

[0020] It is advantageous for the electrodes to be designed as a film, particularly as a rollable film. Designing the electrodes in the form of a rollable film makes it possible to use the electrodes in a rolled state, for example, in a battery having a cylindrical structure. Alternatively or in addition, the film may be foldable. This makes it possible to realize electrodes with a rectangular base, for example.

[0021] In a preferred embodiment of the present invention, lithium is intercalated into at least one layer of porous silicon layer of the electrode. When the electrode has a multi-layer system composed of a plurality of porous silicon layers, lithium can be intercalated into two or more, particularly all, of the porous silicon layers of the multi-layer system.

[0022] The process of the present invention for manufacturing the electrode of the present invention includes the following process steps: - forming at least one layer of porous silicon layer by etching a silicon substrate; - depositing a copper layer on at least one layer of porous silicon layer; and comprises.

[0023] For the purpose of forming at least one layer of porous silicon layer, the silicon substrate can be etched, for example, by wet chemical etching. That is, the etching of the silicon substrate can be, in particular, wet chemical etching.

[0024] The etching of the silicon substrate for the purpose of forming at least one layer of porous silicon layer can, in principle, be carried out as a batch process, for example, by etching the silicon substrate in an immersion tank. In an advantageous embodiment of the present invention, the etching for the purpose of forming at least one layer of porous silicon layer is carried out, for example, in a continuous process that enables a large number of electrodes of the present invention to be manufactured at short time intervals and at low cost.

[0025] In a preferred embodiment, the silicon substrate is for the purpose of forming at least one layer of porous silicon layer with one side etched. For example, it can be the case where only the lower surface of the silicon substrate is etched.

[0026] An advantageous embodiment of the present invention is the case where the silicon substrate is electrochemically etched for the purpose of forming at least one layer of porous silicon layer.

[0027] The silicon substrate can be transported along the transport direction, for example, through a plurality of processing tanks arranged front to back in the transport direction. Each processing tank is filled with an etching medium, and electrodes are placed in each of them. During transport through the processing tanks, the silicon substrate preferably comes into contact with the etching medium present in each processing tank at its underside. It is even more advantageous to alternate the polarity of the electrodes placed in the processing tanks in the transport direction.

[0028] The polarity characteristics of electrodes arranged in alternating processing tanks in the transport direction can be understood as meaning that a positively charged electrode is followed by a negatively charged electrode in the transport direction, and a negatively charged electrode is followed by a positively charged electrode in the transport direction, and that such polarity switching is repeated accordingly when there are four or more consecutive processing tanks in the transport direction. A similar situation also applies when the first electrode is a negatively charged electrode.

[0029] Gas nozzles may be positioned between the two processing tanks, and gas or a gas mixture, such as air, may be blown onto the underside of the substrate by the gas nozzles to remove the etching medium present on the underside of the substrate. The gas nozzles may take the form of what is known as an air knife. It is preferable that an inert gas or protective gas, particularly nitrogen, is blown onto the underside of the substrate by the gas nozzles. This helps to avoid an increased risk of increased oxidation of the substrate and the resulting damage.

[0030] For electrochemical etching, a current of at least 0.5 mA / cm² is preferred. 2 , in particular, at least 1 mA / cm² 2 The current density applied to the silicon substrate is 200 mA / cm². 2 The following, in particular, 120mA / cm 2 The following is even more preferable:

[0031] The etching medium filled into the processing tank preferably contains hydrogen fluoride. The etching medium may be an aqueous solution of hydrogen fluoride in particular. Optionally, the etching medium may contain surfactants and / or additives.

[0032] Furthermore, etching can be carried out, in particular, in the form of a metal-catalyzed chemical etching process (also known among experts as "metal-assisted etching") for the purpose of forming at least one layer of porous silicon.

[0033] The deposition of a copper layer on at least one porous silicon layer can be carried out in various ways. For example, the copper layer can be deposited on at least one porous silicon layer by sputtering a copper target with ions (also known as "ion sputtering"). Alternatively, the copper layer can be deposited by, for example, applying a copper paste onto at least one porous silicon layer by a screen printing and / or rolling process. It is also possible to deposit the copper layer on at least one porous silicon layer by a chemical deposition process.

[0034] The copper layer may be deposited in a two-step process. For example, a first portion of the copper layer may be deposited on at least one porous silicon layer by galvanic substitution in a first deposition step. Then, in a second deposition step, a second portion of the copper layer may be deposited on the first portion of the copper layer by electrochemical deposition. This type of two-step process makes it possible to form a homogeneous and robust copper layer. In particular, the first deposition step can avoid the formation of copper islands during electrochemical deposition. This formation of copper islands proceeds as a result of the high electrical resistance of at least one porous silicon layer or multilayer system, resulting in a heterogeneous copper layer. Both deposition steps can be implemented as batch or continuous processes.

[0035] In a modified alternative process, a nickel layer is deposited on at least one porous silicon layer in a first deposition step. This is followed by a second deposition step of depositing a copper layer onto the nickel layer. The nickel layer improves the adhesion of the copper layer to the silicon layer that follows the nickel layer. The deposition of the nickel layer onto at least one porous silicon layer in the first deposition step can be carried out according to the process already described above in relation to the deposition of the copper layer onto at least one porous silicon layer. Preferably, the nickel layer is deposited on at least one porous silicon layer by electrochemical deposition. In the electrochemical deposition of the nickel layer on the silicon substrate, preferably at least 0.5 mA / cm² 2 The current density, in particular, is at least 10 mA / cm². 2 The current density is applied to the silicon substrate. For the purpose of forming a nickel layer, here it is 150 mA / cm². 2 Preferably, 100 mA / cm² 2 It is advantageous to apply the following current densities. Furthermore, it has been found to be advantageous for the nickel layer to have a thickness of at least 0.1 μm, preferably at least 0.5 μm. It is even more advantageous for the nickel layer to have a thickness of 3 μm or less, preferably 1.5 μm or less. In the second deposition step, the copper layer can be deposited on the nickel layer by electrochemical deposition. Both deposition steps can be implemented as batch or continuous processes.

[0036] Galvanic substitution is a self-limiting process. This is advantageous because it results in the first portion of the copper or nickel layer having a thin thickness of only a few hundred nanometers. The first portion of the copper or nickel layer can, in particular, act as a conductive seed layer, i.e., as a conductive base for the formation of the second portion of the copper layer deposited by electrochemical deposition in the second deposition process.

[0037] In the galvanic replacement method, that is, in the first deposition step, the silicon substrate preferably contacts a deposition solution, particularly an aqueous deposition solution. The deposition solution may contain, for example, copper sulfate in the case of depositing the first part of the copper layer, and may contain, for example, nickel sulfate or nickel sulfamate in the case of depositing the nickel layer. The deposition solution may further contain hydrogen fluoride. Optionally, the deposition solution may contain additives, particularly organic additives, for better wetting of the surface of the silicon substrate, for adjusting the pH, and / or for homogenizing the deposition solution.

[0038] In electrochemical deposition, that is, in the second deposition step, the silicon substrate is preferably wetted with the deposition solution. This preferably contains copper sulfate. Further, it is advantageous to apply a current between the silicon substrate and the above deposition solution.

[0039] Preferably, at least 0.5 mA / cm 2 and particularly at least 1 mA / cm 2 of current density is applied to the first part of the copper sulfate deposited on the silicon substrate for the purpose of depositing the second part of the copper layer in electrochemical deposition. For the purpose of forming the second part of the copper layer, it is more preferable that a current density of 150 mA / cm 2 or less, particularly 100 mA / cm 2 or less is applied to the first part of the copper sulfate deposited on the silicon substrate. In the above-described design modification where the copper layer is deposited on the nickel layer, the described current density can be applied to the nickel layer for the purpose of depositing the copper layer.

[0040] The current density applied to the second part of the copper layer or to the first part of the copper layer or the nickel layer for the purpose of depositing the copper layer can be adjusted so that the current density is constant with respect to time. Alternatively, the current density may be adjusted so that the current density increases according to a specified slope or alternates with respect to time. This enables the deposition of the second part of the copper layer or the copper layer on the nickel layer at an increasing or alternating deposition rate, for example, to achieve better homogeneity of the copper layer.

[0041] In a preferred further development of the present invention, etching of a silicon substrate results in the formation of a multilayer system consisting of multiple porous silicon layers, where at least one porous silicon layer is one of the multiple porous silicon layers in the multilayer system.

[0042] Porous silicon layers may differ from one another, for example, in that each porous silicon layer has a different porosity, different pore size, and / or different pore shape.

[0043] Each porous silicon layer in a multilayer system can have a different function. One of the silicon layers in a multilayer system may be intended, for example, to act as a delamination layer. One or more silicon layers in a multilayer system may act, for example, for lithium intercalation. On the other hand, other silicon layers in a multilayer system may be intended to act as a barrier layer for the deposited copper layer.

[0044] It is particularly advantageous when the multilayer system is formed such that the porous silicon layer having the highest porosity in the multilayer system is directly adjacent to the non-porous portion of the silicon substrate. Preferably, the porous silicon layer having the highest porosity in the multilayer system acts as a release layer, that is, as a layer that acts to release at least a portion of the multilayer system from the non-porous portion of the silicon substrate.

[0045] At least one porous silicon layer is advantageously removed along with the copper layer from the non-porous portion of the silicon substrate.

[0046] When a multilayer system is formed by multiple porous silicon layers, it is advantageous if multiple layers of the multilayer system, particularly all layers, are removed from the non-porous portion of the silicon substrate along with the copper layer.

[0047] To remove at least one porous silicon layer and a copper layer, the silicon substrate is preferably subjected to heat treatment. The heat treatment may be performed, for example, by oven, particularly by continuous oven.

[0048] The heat treatment can, for example, cause the collapse of at least a portion of the pore walls of at least one porous silicon layer and / or possibly at least a portion of the pore walls of one of the other porous silicon layers in a multilayer system, particularly the pore walls of the porous silicon layer having the highest porosity, and as a result, at least one porous silicon layer can be inexpensively removed from the non-porous portion of the silicon substrate together with the copper layer.

[0049] In heat treatment, a temperature gradient is advantageously generated between the silicon substrate and its surroundings. The temperature gradient can be generated in various ways, for example, by a hot plate, by an infrared lamp, by recirculation heating, and / or induction heating.

[0050] In a preferred embodiment, the temperature gradient is at least 20°C, and more particularly at least 30°C. Furthermore, in order to avoid destruction of the porous structure of at least one porous silicon layer, it is preferable that the temperature of the silicon substrate during heat treatment be kept below the melting point of silicon.

[0051] In principle, to remove at least one porous silicon layer and a copper layer, a different method, particularly a mechanical removal method, can be used instead of heat treatment.

[0052] In a preferred further development of the present invention, lithium is intercalated into at least one porous silicon layer. When the multilayer system is formed by multiple porous silicon layers, lithium may be intercalated into two or more or all of the porous silicon layers of the multilayer system.

[0053] Lithium can be intercalated in elemental form, for example, in the form of lithium clusters, and / or as part of a chemical compound, for example, in the form of lithium-silicon mixed crystals.

[0054] Lithium intercalation is preferably performed after at least one porous silicon layer and any other porous silicon layer present has been removed from the non-porous portion of the silicon substrate along with the copper layer.

[0055] After removing at least one porous silicon layer and a copper layer from the non-porous portion of the silicon substrate, any metallic residues such as copper residue or nickel residue and / or any remnants of the porous structure, such as protruding edges, can be removed from the remaining silicon substrate. This makes the remaining silicon substrate reusable. For example, the remaining silicon substrate can be used to manufacture further electrodes, particularly through iterations of the above process, after the removal of any metallic residues such as copper residue or nickel residue and / or any remnants of the porous structure.

[0056] The removal of any residues from the porous structure and / or any metallic residues, such as copper or nickel residues, may be carried out, for example, by a wet chemical etching process, which can be carried out in particular as a batch process or a continuous process.

[0057] If it is necessary to remove residual materials from the porous structure or metallic residues such as copper or nickel residues, these should preferably be removed by a two-stage etching process in which the residual silicon substrate is processed in a first processing tank filled with an etching medium and then in a second processing tank filled with a different etching medium. In a preferred embodiment, metallic residues such as copper or nickel residues are removed in the first step, and residual materials from the porous structure are removed in the second step.

[0058] For the removal of metallic residues such as copper or nickel residues, an acidic etching medium is preferably used. This may include, for example, hydrogen fluoride, hydrogen chloride, nitric acid, sulfuric acid, and / or oxidizing agents, such as hydrogen peroxide and / or ozone.

[0059] To remove residues from porous structures, alkaline or acidic etching media may be used. The former may include, for example, sodium hydroxide and / or potassium hydroxide. The latter may include, for example, hydrogen fluoride, nitric acid and / or sulfuric acid.

[0060] Alternatively or in addition, the removal of any residues of the porous structure and / or any metallic residues, such as copper or nickel residues, may be carried out in different ways, for example, by mechanical grinding and / or polishing, plasma etching and / or laser ablation.

[0061] As described in the introduction, the present invention relates, in particular, to the use of electrodes and batteries.

[0062] In the use of the electrode according to the present invention, the electrode is preferably intended to be used as an anode in a battery. Particularly advantageous, the electrode can be used as an anode in a lithium-ion battery.

[0063] Preferably, the electrodes are activated, for example, by performing multiple charge-discharge cycles of the battery, following the placement of the electrodes within the battery. The charge-discharge cycles may be performed according to one or more specified current-voltage curves. The activation of the electrodes allows the island structure to form in at least one porous silicon layer, particularly as a result of self-aligned recrystallization of silicon, which remains generally stable over subsequent cycles without progressing further after a few cycles. If at least one silicon layer of the electrodes were non-porous, the electrodes would be destroyed during the execution of the charge-discharge cycles.

[0064] As an alternative to, or in addition to, the formation of island structures through electrode activation, a process for structuring the electrodes may be performed before the electrodes are placed in the battery. Electrode structuring can be performed, for example, in the form of mechanical structuring using a negative model, particularly a mask, rollers and / or cylinders, and / or in the form of laser structuring.

[0065] The battery of the present invention is equipped with the electrodes of the present invention. Preferably, the battery is a lithium-ion battery.

[0066] In advantageous design modifications, the electrodes are formed as a windable film. The windable film may be formed by a number of parts welded or joined together. The electrodes may be wound or wound around an axis together with further components of the battery, such as further electrodes and / or separators. These further components of the battery may also be formed as windable films. This makes it possible to realize a battery with a cylindrical structure.

[0067] Alternatively, the battery may be equipped with folded electrodes. Folding techniques may be employed to fold further components of the battery between the electrodes to form a laminate. These further components of the battery may be formed here as individual parts and / or as foldable films. If the further components of the battery are designed as foldable films, they may be folded by Z-folding techniques into a laminate alternating with the film-shaped electrodes. In Z-folding techniques, folding can be performed any number of times, but at least twice, each time in the opposite direction to the previous folding direction. Thus, there are many options for the structure of the battery, such as a cubic structure. The battery may also have a laminated arrangement, in particular a cubic laminated arrangement in which each of the battery electrodes and parts of the further components, especially the rectangular parts, are laminated separately from each other.

[0068] The present invention will be described in more detail below with reference to drawings relating to preferred embodiments of the invention. Where appropriate, identical elements or elements having the same function will be denoted by the same reference numerals. The present invention is not limited to the designs shown in the drawings, such as with respect to functional features. The description herein and the subsequent description of the drawings include a number of features which may be combined in two or more dependent claims. On the other hand, those skilled in the art will also consider these features individually and combine them to form further useful combinations. More specifically, each of these features may be combined individually or in any appropriate combination with the electrodes of the present invention, the processes of the present invention, the uses of the present invention and / or the batteries of the present invention.

[0069] The drawings are schematic and not to scale. [Brief explanation of the drawing]

[0070] [Figure 1] Figure 1 shows the processing apparatus for processing the substrate. [Figure 2] Figure 2 shows a cross-sectional view of a silicon substrate processed using the apparatus shown in Figure 1, and the substrate has a multilayer system consisting of multiple porous silicon layers. [Figure 3] Figure 3 shows the silicon substrate as shown in Figure 2, viewed from below. [Figure 4] Figure 4 shows a cross-sectional view of the silicon substrate and the first portion of the copper layer deposited on the silicon substrate during the first deposition process. [Figure 5] Figure 5 shows cross-sectional views of the silicon substrate and the copper layer deposited on the silicon substrate during the two deposition processes. [Figure 6] Figure 6 shows a cross-sectional view of the silicon substrate and the copper layer deposited on it after both the copper layer and multiple porous silicon layers have been removed from the non-porous portion of the silicon substrate. [Figure 7] Figure 7 shows a cross-sectional view of an electrode for a battery formed from a peeled copper layer, a peeled porous silicon layer, and lithium intercalated into the porous silicon layer. [Figure 8]Figure 8 shows a cross-sectional view of one of the porous silicon layers of the electrode after activation, as shown in Figure 7. [Figure 9] Figure 9 shows a side view of the non-porous portion of the silicon substrate and the metal residue and porous structure remnants present in that non-porous portion of the silicon substrate. [Figure 10] Figure 10 shows the non-porous portion of the silicon substrate during the removal of metal residue in the processing tank. [Figure 11] Figure 11 shows the non-porous portion of the silicon substrate after the removal of metal residues. This non-porous portion of the silicon substrate is located in a further processing tank for the removal of residual materials from the porous structure. [Figure 12] Figure 12 shows a partial cross-sectional view of a lithium-ion battery equipped with the electrodes shown in Figure 7. [Figure 13] Figure 13 shows an alternative structure for the battery with electrodes according to Figure 7. [Figure 14] Figure 14 shows possible alternative arrangements for the electrodes according to Figure 7. [Modes for carrying out the invention]

[0071] Figure 1 shows a processing apparatus 1 for processing substrates, particularly for electrochemical etching on one side of the substrate. Furthermore, Figure 1 shows a silicon substrate 2 being processed by the processing apparatus 1.

[0072] The processing apparatus 1 includes a conveying device 3 configured to convey a silicon substrate 2 to be processed along the conveying direction 4. In this embodiment, the conveying device 3 takes the form of a roller conveyor having a plurality of conveying rollers 5.

[0073] The processing apparatus 1 further comprises a plurality of processing tanks 6 arranged front to back in the transport direction 4, each of which is filled with etching medium 7 and each has an electrode 8 placed in it. In Figure 1, three processing tanks 6 are illustrated as an example. In principle, the processing apparatus 1 may have more or fewer processing tanks 6.

[0074] The etching medium 7 is preferably an aqueous solution of hydrogen fluoride. Optionally, the etching medium 7 may contain additives and / or surfactants. A potential is applied to each of the electrodes 8 such that the polarity of the electrode 8 alternates in the transport direction 4.

[0075] The transport device 3 transports the silicon substrate 2 along the transport direction 4 through the processing tank 6, and the silicon substrate 2 comes into contact with the etching medium 7 present in the processing tank 6 only at the bottom surface 9 of the substrate.

[0076] During the transport of the silicon substrate 2 through the processing tank 6, an electrochemical reaction occurs. In this electrochemical reaction, local inhomogeneity of the current density causes etching peaks and troughs, which leads to the formation of pores on the lower surface 9 of the substrate, resulting in the formation of a porous structure on the lower surface 9 of the substrate.

[0077] The electrochemical reaction can be controlled by the potential of electrode 8, which affects the current density in the processing tank 6. The reaction may be further controlled by mixing in additives and / or surfactants.

[0078] When an etching medium containing hydrogen fluoride is used as the etching medium 7, the following reaction occurs in particular on the underside of the substrate 9: Si + 6F - +4h + →SiF6 2- The current is generated at the surface of the silicon substrate 2, through holes (h + ) supplies hydrogen fluoride, and hydrogen fluoride ions (F) are added to the solution. - This causes )

[0079] The current density in the processing tank 6 can be adjusted so that the porous structure of the silicon substrate 2 becomes progressively more porous over the depth of the silicon substrate 2. As a result, multiple porous silicon layers with different porosity, pore size, and / or pore shape are formed on the lower surface 9 of the substrate.

[0080] Furthermore, in the processing apparatus 1, an air knife (not shown) is present between each processing tank 6, thereby generating a nitrogen gas flow 10 to blow away any etching medium 7 present on the lower surface 9 of the substrate.

[0081] Figure 2 shows a cross-sectional view of the silicon substrate 2 processed using the processing apparatus 1 as shown in Figure 1.

[0082] The processed silicon substrate 2 has a multilayer system 11 on its lower surface 9 consisting of multiple porous silicon layers 12a, 12b, 12c, and 12d arranged vertically relative to each other. In Figure 2, the four porous silicon layers 12a, 12b, 12c, and 12d are shown as an example, and in principle, more or fewer porous silicon layers can be formed on the lower surface 9 of the silicon substrate 2 during processing using the processing apparatus 1.

[0083] The porous silicon layers 12a, 12b, 12c, and 12d differ in the size of their pores 13, the shape of their pores 13, and / or their porosity, with the porous silicon layer 12d having the highest porosity in the multilayer system 11 being directly adjacent to the non-porous portion 14 of the silicon substrate 2. This porous silicon layer 12d acts as a release layer for the subsequent removal of the multilayer system 11 from the non-porous portion 14 of the silicon substrate 2 (see Figure 6).

[0084] Figure 3 shows the silicon substrate 2 as shown in Figure 2, viewed from below.

[0085] In Figure 3, multiple pores 13 of various shapes and sizes are visible on the lower surface 9 of the silicon substrate 2.

[0086] After the formation of the multilayer system 11, the copper layer 15 is deposited on the multilayer system 11 in a two-step deposition process (see Figures 4 and 5).

[0087] In the first deposition step, a first portion 16 of the copper layer 15 is deposited on the multilayer system 11 by galvanic substitution. In this deposition step, the silicon substrate 2 comes into contact with a deposition aqueous solution containing hydrogen fluoride and copper sulfate at its bottom surface 9. The hydrogen fluoride dissolves silicon dioxide from the bottom surface 9 of the silicon substrate 2, leaving unoxidized silicon on the bottom surface 9. This is highly attractive to copper ions present in the deposition solution, considering the chemical potential between silicon and copper.

[0088] The galvanic substitution method is a self-limiting process that stops on its own when the porous excess silicon layer 12a is completely covered with copper. Upon completion of the first deposition step, the first portion 16 of the copper layer 15 is formed such that the porous excess silicon layer 12a is integrated into the first portion 16 of the copper layer 15.

[0089] Then, in the second deposition process, the second portion 17 of the copper layer 15 is deposited on the first portion 16 of the copper layer 15 by electrochemical deposition. The first portion 16 of the copper layer 15 acts as a conductive seed layer for the formation of the second portion 17 of the copper layer 15.

[0090] In the second deposition process, the silicon substrate 2 is wetted at the bottom surface 9 with a deposition solution containing copper sulfate, and an electric current is applied.

[0091] In electrochemical deposition, the silicon substrate 2 acts as a negatively charged electrode, while the deposition solution acts as a positively charged counter electrode.

[0092] Figure 4 shows a cross-sectional view of the silicon substrate 2 after the deposition of the first portion 16 of the copper layer 15 onto the multilayer system 11.

[0093] Figure 5 shows a cross-sectional view of the silicon substrate 2 after the deposition of the second portion 17 of the copper layer 15 onto the first portion 16 of the copper layer 15.

[0094] After the deposition of the copper layer 15, the silicon substrate 2 undergoes heat treatment (see Figure 6). This can be done, for example, in a continuous oven (not shown).

[0095] During the heat treatment, thermal radiation 18 is employed to cause the pore walls of the porous silicon layer 12d (see Figures 2, 4, and 5), which acts as a delamination layer, to collapse. This is due to the difference in the coefficient of thermal expansion between one porous silicon layer 12a, 12b, 12c and the other porous silicon layer 12d. As a result, the copper layer 15, along with the porous silicon layers 12a, 12b, 12c of the multilayer system 11, can be peeled off from the non-porous portion 14 of the silicon substrate 2.

[0096] After heat treatment, all remaining portions of the porous silicon layer 12d, which acts as a release layer, become elongated cut edges 19. These edges are adjacent to the non-porous portion 14 or the porous silicon layer 12c of the silicon substrate 2 of the multilayer system 11 that were previously adjacent to the release layer.

[0097] Figure 6 shows a cross-sectional view of the silicon substrate 2 and the copper layer 15 deposited on the silicon substrate 2 after both the copper layer 15 and the porous silicon layers 12a, 12b, and 12c have been removed from the non-porous portion 14 of the silicon substrate 2.

[0098] After removing both the copper layer 15 and the porous silicon layers 12a, 12b, and 12c from the non-porous portion 14 of the silicon substrate 2, lithium 20 is intercalated into the peeled porous silicon layers 12a, 12b, and 12c (see Figure 7).

[0099] Figure 7 shows a cross-sectional view of an embodiment of the electrode 21 of the invention for a battery designed as a rollable film.

[0100] This electrode 21 is formed by porous silicon layers 12a, 12b, 12c and copper layer 15, and by lithium intercalated into the porous silicon layers 12a, 12b, 12c.

[0101] Following the installation of the electrodes 21 in the battery, the electrodes 21 are activated by performing multiple charge-discharge cycles in the battery.

[0102] The activation of electrode 21 leads to the formation of island structures in porous silicon layers 12a, 12b, and 12c, which remain largely stable over subsequent cycles without further progression after a few cycles (see Figure 8). If the silicon of electrode 21 were non-porous, electrode 21 would be destroyed during the execution of charge-discharge cycles as a result of irregular recrystallization of silicon. However, in this case, the porous structure of silicon leads to self-aligned recrystallization of silicon, and the silicon portions integrated into the copper layer 15 act as seed crystals.

[0103] Figure 8 shows a cross-sectional view of one of the porous silicon layers 12a, 12b, and 12c of electrode 21 after activation, as shown in Figure 7.

[0104] The island structure of the porous silicon layer shown in the figure, formed from multiple rectangular regions 22, can be seen in Figure 8.

[0105] Unlike the pores 13 in the porous silicon layer shown in Figure 8, the lithium 20 intercalated in the porous silicon layer shown is omitted in Figure 8 for clarity.

[0106] In the alternative embodiment, unlike the first embodiment described in relation to Figures 1-8, the copper layer is deposited on a multilayer system corresponding to the multilayer system 11 described in relation to Figure 2 by an alternative process modification. In this alternative process modification, instead of the first portion 16 of the copper layer 15, a nickel layer is deposited on the multilayer system in a first deposition step. The deposition of the nickel layer on the multilayer system is carried out by electrochemical deposition. To deposit the nickel layer on a silicon substrate having a multilayer system on its underside, the silicon substrate is wetted on its underside with a deposition solution containing nickel sulfate or nickel sulfamate, and an electric current is applied.

[0107] The deposition of the nickel layer can be shown in Figure 4. In that figure, reference numeral 16 indicates the nickel layer in this alternative embodiment. In all other respects, the elements of the alternative embodiment correspond to the elements shown in Figure 4.

[0108] In a second deposition step following the deposition of the nickel layer, the copper layer is deposited on the nickel layer by electrochemical deposition in an alternative embodiment. Here, the nickel layer acts as a conductive seed layer for the formation of the copper layer, providing improved adhesion of the copper layer to the porous silicon layer applied to the nickel layer. Figure 5 illustrates the deposition of the copper layer on the nickel layer. In that figure, reference numeral 16 denotes the nickel layer in this alternative embodiment, and reference numeral 17 denotes the copper layer deposited on the nickel layer.

[0109] The matters and features described below in relation to Figures 9-14 refer to the embodiments shown in Figures 1-8. Unless otherwise specified, they may be combined without limitation with the alternative embodiments described above.

[0110] Figure 9 shows a side view of the non-porous portion 14 of the silicon substrate 2.

[0111] Figure 9 also shows the residue of porous structures adjacent to the non-porous portion 14 of the silicon substrate 2. These are formed by elongated cut edges 19 and by metal residues 23 present on the non-porous portion 14 of the silicon substrate 2, thereby contaminating the non-porous portion 14 of the silicon substrate 2 during the deposition of the copper layer 15 according to the first embodiment described in relation to Figures 1-8, or during the deposition of the nickel and copper layers according to the alternative embodiment.

[0112] To make the non-porous portion 14 of the silicon substrate 2 reusable, the cut edges 19 and metal residues 23 are removed by a two-step wet chemical etching process (see Figures 9 and 10). This makes the non-porous portion 14 of the silicon substrate 2 usable, for example, for the manufacture of further electrodes of the type described above, particularly through iterations of the process steps described above.

[0113] Figure 10 shows the non-porous portion 14 of the silicon substrate 2, the adjacent cut edge 19, the metal residue 23, and the processing tank 24.

[0114] The processing tank 24 is filled with an acidic etching medium 25 that acts to remove the metallic residue 23, which is in the form of copper in the first embodiment or in the form of copper and nickel in the alternative embodiment. The etching medium 25 may include, for example, hydrogen fluoride, hydrogen chloride, nitric acid, sulfuric acid, hydrogen peroxide and / or ozone.

[0115] Figure 10 illustrates the state in which the non-porous portion 14 of the silicon substrate 2 is immersed in the etching medium 25 and the metal residue 23 is dissolved in the etching medium 25.

[0116] Figure 11 shows the non-porous portion 14 of the silicon substrate 2 and a further processing tank 26.

[0117] The processing tank 26 shown in Figure 11 is filled with an etching medium 27 that acts to remove the cut edges 19. This etching medium 27 may be an alkaline etching medium or an acidic etching medium. In the former case, the etching medium 27 may include, for example, deionized water and sodium hydroxide and / or potassium hydroxide. In the latter case, the etching medium 27 may include, for example, hydrogen fluoride, nitric acid, sulfuric acid, hydrogen peroxide and / or ozone.

[0118] Figure 11 shows the state in which the non-porous portion 14 of the silicon substrate 2 is immersed in the etching medium 27 present in the processing tank 26. The etching medium 27 polishes the surface of the silicon substrate 2, and in this state, the cut edges 19 are removed from the non-porous portion 14 of the silicon substrate 2, making the non-porous portion 14 of the silicon substrate 2 usable for further manufacture of electrodes of the above type.

[0119] Figure 12 shows a partial cross-sectional view of an embodiment of the battery 28a of the invention.

[0120] In this embodiment, battery 28a is a lithium-ion battery with a cylindrical structure.

[0121] The battery 28a comprises a cylindrical housing 29a. Furthermore, the battery 28a comprises a cathode 30a, an anode 31a, and a separator 32a positioned between the cathode 30a and the anode 31a. Each of the cathode 30a, anode 31a, and separator 32a is formed as a wound film and placed inside the housing 29a of the battery 28a.

[0122] The anode 31a of battery 28a is the electrode 21 described above (see Figures 7 and 8). In other words, the electrode 21 described above is used as the anode 31a in battery 28a.

[0123] Figure 13 shows a partial cross-sectional view of an embodiment of the battery alternative described in relation to Figure 12. In the embodiment shown in Figure 13, the battery 28b has a structure that replaces the rectangular base.

[0124] In the alternative structure, the battery 28b comprises a cubic housing 29b. Furthermore, the battery 28b comprises a cathode 30b, an anode 31b, and a separator 32b positioned between the cathode 30b and the anode 31b. The cathode 30b, anode 31b, and separator 32b are formed as rectangular portions and are arranged in a predetermined order, stacked vertically on top of each other, inside the housing 29b of the battery 28b.

[0125] The anode 31b of battery 28b is the electrode 21 described above (see Figures 7 and 8). That is, the electrode 21 described above is used as the anode 31b in battery 28b in the form of a rectangular portion.

[0126] Figure 14 shows alternative possible arrangements of the cathode 30b, anode 31b, and separator 32b in the form of a cubic laminate for an alternative embodiment of battery 28b described in relation to Figure 13. Here, the anode 31b is formed as a foldable film. In this alternative possible arrangement, the cathode 30b and separator 32b are folded between the anodes 31b by a Z-folding technique. Here, the cathode 30b and separator 32b may be formed as paired rectangular portions. Preferably, the cathode 30b and separator 32b are formed as foldable films. This makes the superimposed Z-folding technique applicable. This allows the anode 31b, cathode 30b, and separator 32b to be folded into a cubic laminate in the alternative folding process. For example, the cathode 30b and the separator 32b may be folded between the anodes 31b in a first folding step. Then, in a second folding step, the anode 31b may be folded between the cathode 30b and the separator 32b which is positioned opposite each other. After the second folding step, the first folding step becomes possible again. This makes it possible to manufacture a battery 28b having a cubic structure in a low-cost and / or automated manner.

[0127] The present invention has been described in detail with reference to illustrated embodiments. However, the present invention is not limited to or limited by the disclosed embodiments. Other modifications can be derived from these embodiments by those skilled in the art without departing from the idea inherent in the present invention. [Explanation of symbols]

[0128] 1 Processing Unit 2. Silicon substrate 3. Conveying device 4. Conveying direction 5 Conveyor rollers 6 Processing Tanks 7 Etching medium 8 electrodes 9 Bottom surface of the board 10 Gas flow 11-layer system 12a Porous silicon layer 12b Porous silicon layer 12c porous silicon layer 12d porous silicon layer 13 pores 14 Non-porous portion of silicon substrate 15 copper layer 16. First part of the copper layer 17. Second part of the copper layer 18. Thermal radiation 19 Incisal end 20 Lithium 21 electrodes 22 Rectangular area 23 Metal residue 24 Processing Tanks 25 Etching medium 26 Processing Tanks 27 Etching medium 28a battery 28b battery 29a Housing 29b Housing 30a Cathode 30b Cathode 31a Anode 31b Anode 32a Separator 32b Separator

Claims

1. An electrode (21) for a lithium-ion battery (28a; 28b), comprising at least one porous silicon layer (12a, 12b, 12c, 12d) and a copper layer (15), The electrode (21) is at least partially embedded in the copper layer (15) by the aforementioned porous silicon layer (12a, 12b, 12c, 12d), which is at least one layer of porous silicon.

2. The electrode (21) according to claim 1, wherein the copper layer (15) is disposed on the at least one porous silicon layer (12a, 12b, 12c, 12d).

3. The electrode (21) according to claim 1 or 2, further comprising a multilayer system (11) comprising a plurality of porous silicon layers (12a, 12b, 12c, 12d), wherein each of the plurality of porous silicon layers (12a, 12b, 12c, 12d) is different from the others by having a different porosity, a different pore size and / or a different pore shape, and at least one of the plurality of porous silicon layers (12a, 12b, 12c, 12d) of the multilayer system (11).

4. An electrode (21) according to any one of claims 1 to 3, designed as a film.

5. The electrode (21) according to any one of claims 1 to 4, wherein lithium (20) is intercalated in the at least one porous silicon layer (12a, 12b, 12c, 12d).

6. A process for manufacturing an electrode (21) according to any one of claims 1 to 5, comprising the following process steps: A step of forming at least one porous silicon layer (12a, 12b, 12c, 12d) by etching a silicon substrate (2), A step of depositing a copper layer (15) on the at least one porous silicon layer (12a, 12b, 12c, 12d), It has, A process in which at least one porous silicon layer (12a, 12b, 12c, 12d) is embedded at least partially in the copper layer (15).

7. The process according to claim 6, wherein the silicon substrate (2) is wet chemically etched for the purpose of forming at least one porous silicon layer (12a, 12b, 12c, 12d).

8. The process according to claim 6 or 7, wherein the silicon substrate (2) is etched on one side for the purpose of forming the at least one porous silicon layer (12a, 12b, 12c, 12d).

9. For the purpose of forming the aforementioned at least one porous silicon layer (12a, 12b, 12c, 12d), the silicon substrate (2) is electrochemically etched. The silicon substrate (2) is transported along the transport direction (4) through a plurality of processing tanks (6) arranged front to back in the transport direction (4), each of the plurality of processing tanks (6) is filled with etching medium (7), and electrodes (8) are placed in each of them. During transport through the processing tank (6), the silicon substrate (2) comes into contact with the etching medium (7) present in each processing tank (6) at the bottom surface (9) of the substrate. The process according to any one of claims 6 to 8, wherein the polarity of the electrodes (8) arranged in the processing tank (6) alternates in the transport direction (4).

10. The copper layer (15) is deposited in a two-step process. In the first deposition step, the first portion (16) of the copper layer (15) is deposited on the at least one porous silicon layer (12a, 12b, 12c, 12d) by a galvanic substitution method. The process according to any one of claims 6 to 9, wherein in the second deposition step, the second portion (17) of the copper layer (15) is deposited on the first portion (16) of the copper layer (15) by electrochemical deposition.

11. In the first deposition step, a nickel layer is deposited on the at least one porous silicon layer by electrochemical deposition. The process according to any one of claims 6 to 9, wherein in the second deposition step, the copper layer is deposited on the nickel layer by electrochemical deposition.

12. Etching of the silicon substrate (2) results in the formation of a multilayer system (11) consisting of a plurality of porous silicon layers (12a, 12b, 12c, 12d), each of the plurality of porous silicon layers (12a, 12b, 12c, 12d) being different from each other by having different porosity, different pore size and / or different pore shape, and at least one porous silicon layer (12a, 12b, 12c, 12d) being one of the plurality of porous silicon layers (12a, 12b, 12c, 12d) of the multilayer system (11). The process according to any one of claims 6 to 11, wherein the multilayer system (11) is formed such that the porous silicon layer (12d) having the highest porosity of the multilayer system (11) is directly adjacent to the non-porous portion (14) of the silicon substrate (2).

13. The process according to any one of claims 6 to 12, wherein the at least one porous silicon layer (12a, 12b, 12c, 12d) is removed together with the copper layer (15) from the non-porous portion (14) of the silicon substrate (2).

14. The process according to claim 13, wherein the silicon substrate (2) is subjected to heat treatment for the purpose of removing both the at least one porous silicon layer (12a, 12b, 12c, 12d) and the copper layer (15).

15. The process according to any one of claims 6 to 14, wherein lithium (20) is intercalated into the at least one porous silicon layer (12a, 12b, 12c, 12d).

16. Use of the electrode (21) according to any one of claims 1 to 5 as the anode (31).

17. A battery (28a; 28b) having an electrode (21) according to any one of claims 1 to 5.

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