Method for manufacturing a silicon electrode as an anode for a lithium-ion battery, and a silicon electrode manufactured using the method

Abstract

The present invention relates to a method for manufacturing a silicon electrode as an anode for a lithium-ion battery, the method comprising depositing an active layer, preferably on a copper substrate, and then subjecting it to rapid annealing, and to an anode manufactured using this method. The object of the present invention is to provide a method that eliminates the need for a vacuum chamber for depositing an active material, particularly silicon, for the manufacture of an anode for a lithium-ion battery, thereby enabling a highly cost-optimized manufacture of a nearly pure silicon anode for a lithium-ion battery. This is achieved in that the active layer is formed from a mixture of silicon particles and metal particles, the mixture of silicon particles and metal particles is deposited on the substrate by a dry process, and is stabilized in a controlled manner by rapid annealing to form a semi-porous active layer and is fixed to the substrate.

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a silicon electrode as an anode for a lithium-ion battery, the method comprising depositing an active layer on a substrate, preferably a copper substrate, and then subjecting it to rapid thermal annealing.

[0002] The present invention also relates to an anode suitable for use in a lithium-ion battery and manufactured by the method according to claims 1 to 10.

Background Art

[0003] Electrochemical energy storage is an important foundation in the global effort towards energy conversion, providing temporary storage of the variable power generated by renewable means and making that energy available for stationary and portable applications. To mitigate the shortages and thus cost increases associated with the raw materials for secondary batteries, there is a need not only for diversification of the concept of energy storage but also for new materials. These materials are required to combine the improvement of the technical performance (including capacity, energy density, and lifetime) of such energy storage concepts and the minimization of manufacturing costs. The latter can be ensured, in particular, through the use of readily available chemical elements such as silicon, for which an extensive technological base already exists.

[0004] A battery is an electrochemical energy storage device and is classified into primary and secondary batteries.

[0005] A primary battery is an electrochemical power source in which chemical energy is irreversibly converted into electrical energy. A primary battery is therefore not rechargeable. A secondary battery, also called a storage battery, on the other hand, is a rechargeable electrochemical energy storage device in which the chemical reactions that occur are reversible and multiple uses are possible. During charging, electrical energy is converted into chemical energy, and during discharging, it is converted back from chemical energy into electrical energy.

[0006] A battery is a general term for cells connected to each other. A cell is a galvanic unit composed of two electrodes, an electrolyte, a separator, and a cell housing. Figure 1 shows an exemplary construction and function of a lithium-ion cell during discharge. The components of the cell will be clarified briefly below.

[0007] Each Li-ion cell consists of two different electrodes 7 and 9, an electrode 7 that is negatively charged in the charged state and an electrode 9 that is positively charged in the charged state. Since the release of energy, in other words, discharge, involves the movement of ions from the negatively charged electrode to the positively charged electrode, the positively charged electrode is called the cathode 7 and the negatively charged electrode is called the anode 9. The electrodes are each composed of a current collector 2, 8 (also called a current collector body), and an active material deposited (attached) thereon. First, an ion-conductive electrolyte 4 that enables the necessary exchange of charges and a separator 5 that ensures electrical separation of the electrodes are arranged between the electrodes.

[0008] The cathode consists of, for example, a mixed oxide deposited on an aluminum current collector. Transition metal oxides having cobalt (Co), manganese (Mn), nickel (Ni) or aluminum oxide (Al2O3) are the most common compounds here. The deposited metal oxide layer serves the role of intercalation of lithium ions during discharge of the cell.

[0009] The anode of a Li-ion cell can consist of a copper foil as a current collector and a layer of carbon as an active material. The carbon compound used is usually natural or synthetic graphite, because it has a low electrode potential and exhibits little volume expansion during charging and discharging. During charging, lithium ions are reduced and intercalated into the graphite layer.

[0010] In the construction of a lithium-ion battery, the cathode typically supplies lithium atoms for charging and discharging at the anode, and thus the battery capacity is limited by the cathode capacity. As already mentioned, typical cathode materials used so far are, for example, Li(Ni, Co, Mn)O2 and LiFePO4. For the construction of cathodes with lithium metal oxides, the possibility of increasing the capacity is extremely small.

[0011] It is also known that silicon, rather than carbon, is used with the anode of a Li battery. Silicon as an anode material has a high storage capacity of 3579 mAh / g at room temperature compared to conventional carbon-based materials such as graphite, which has a storage capacity of, for example, 372 mAh / g. However, there is a problem in that, with the use of silicon as an anode material, significant volume changes (volume shrinkage and expansion) may occur during the intercalation and deintercalation of mobile ionic species during charging and discharging of the corresponding energy storage device. In the case of graphite, the volume change during lithium intercalation is about 10%, whereas in the case of silicon, it is up to 400%. The volume change of the anode material when silicon is used leads to internal stress, cracking, pulverization of the active material (silicon), loss of electrical contact, and ultimately complete destruction of the anode.

[0012] A common method for the large-scale industrial production of silicon-containing anodes for lithium-ion batteries utilizes silicon powder or silicon particles that are applied in slurry form to a copper current collector using a carbon-containing binder in a wet or dry roll-to-roll process. A slurry means a mixture of solid substances where the solids are dispersed in a liquid. In slurry-based processes, a layer of silicon particles with a carbon-containing binder is calendared or deposited onto the current collector. The binder ensures adhesion and electrical contact between the particles and with the current collector. In most cases, the process requires a drying section where solvents that are harmful for further processing are expelled. The advantages of these slurry-based methods are the high scalability of the process, the adjustment of the capacity of the anodes thus produced through the thickness of the applied layer, and the easy and convenient supply of the active material by external processing. The disadvantages of these slurry-based methods are the usually expensive starting materials such as ultra-high purity silicon, powders with a defined particle size, carbon binders and other inert components, the homogeneity and porosity, etc., as well as the energy costs of the required drying section. Slurries typically use nanoscale silicon particles to cope with the applied stress when the active layer expands during lithiation in a lithium-ion battery. The main causes of failure of structures thus produced for lithium-ion batteries, more particularly the decrease in the capacity of lithium-ion batteries, are the loss of electrical contact of the Si structure and the depletion of the electrolyte at the large surface area of the active layer.

[0013] Furthermore, a novel method is known that uses substantially 100% pure silicon as the anode material to enable maximum storage capacity. Free or powdered nanoscale starting materials are not suitable for creating electrical contact to the current collector because they do not adhere to the current collector. An active layer composed of 100% silicon can only be manufactured by current state-of-the-art techniques using vacuum processing. Here, the silicon is deposited onto a pre-constructed surface to enable nanostructuring of the Si structure, called a columnar structure, and to provide sufficient adhesion.This is typically done using PECVD processing or sputter processing (see also in this regard: 1. Markevich, E. et al., Amorphous Columnar Silicon Anodes for Advanced High Voltage Lithium Ion Full Cells: Dominant Factors Governing Cycling Performance. J. Electrochem. Soc. 160, A1824 (2013); 2. Piwko, M. et al., Hierarchical columnar silicon anode structures for high energy density lithium sulfur batteries. Journal of Power Sources 351, 183 - 191 (2017). 3. Ravi Chandran, K. S. & Palmer, J., A critical review and assessment of 3D columnar silicon electrode architectures and their performance as negative electrodes in Li-ion cells. Materials Science and Engineering: B 271, 115278 (2021); 4. Haro, M. et al., Nano-vault architecture mitigates stress in silicon-based anodes for lithium-ion batteries. Commun Mater 2, 1 - 10 (2021), or 5. Schlaier, J. et al., Electrochemical Patterning of Cu Current Collectors: An Enabler for Pure Silicon Anodes in High-Energy Lithium-Ion Batteries. Advanced Materials Interfaces n / a, 2200507).

[0014] In an optimized process, the drawbacks of slurry-based construction of silicon anodes are avoided by depositing, as a layer in a vacuum mechanism, the active material or structure of an anode for a lithium-ion battery in a planar manner by a PVD method such as sputtering or vaporization. An innovative process including accelerated annealing enables the active material to be stabilized and adhered to the current collector. This makes it possible to avoid the removal of unnecessary components in the process chain, such as residues of solvent or binder components in the slurry. However, the use of the PVD deposition method has other drawbacks, such as high energy requirements for operating the vacuum compartment, in order to enable deposition of a rare high layer thickness on the current collector.

Prior Art Documents

Non-Patent Documents

[0015]

Non-Patent Document 1

Non-Patent Document 2

Non-Patent Document 3

[0016] Therefore, an object of the present invention is to eliminate the need to utilize a vacuum compartment for depositing an active material, particularly silicon, for manufacturing an anode for a lithium-ion battery, and thus to identify a method that enables the extremely cost-optimized manufacture of a substantially pure silicon anode for a lithium-ion battery. Further, this manufacturing method should be capable of simple integration into existing roll-to-roll methods using slurry-based manufacturing, i.e., it should ensure sufficient current contact both between them and with respect to the current collector while substituting for slurry-based binders. [Means for Solving the Problems]

[0017] The object of the present invention is achieved by the method according to independent claim 1.

[0018] A method for manufacturing a silicon electrode as an anode for a lithium-ion battery, in which an active layer is deposited on a substrate, preferably a copper substrate, and then accelerated annealing is performed. In this method, the active layer is formed from a mixture (20) of silicon particles and metal particles. The mixture (20) of silicon particles and metal particles is deposited on the substrate by a dry process and stabilized under the control of accelerated annealing to form a semi-porous active layer, which is fixed to the substrate.

[0019] The dry process means a process that does not require water and solvents, such as cathodic atomization (sputtering). The material of the active layer is introduced into the process in the form of a particle layer of the size order up to the layer thickness to be used. In other words, the size of the particles in the mixture of silicon particles and metal particles is within the size order of the layer thickness constructed for the active layer. To increase the conductivity, the silicon active material, preferably present in powder form, is pre-combined with a metal powder of a similar size-order particle diameter in a desired ratio and then fixed to the substrate and to each other by an accelerated annealing technique. In contrast to existing methods, the reaction between silicon and the copper substrate and between silicon particles and metal particles is controlled by the ultra-short-time energy input of accelerated annealing, thus making it possible to prevent complete reaction and hence depletion of the active material. The parameters of accelerated annealing should be established to enable the reaction of the active material with the metal particles, i.e., the silicon particles.

[0020] In one configuration of the method of the present invention, the mixture of silicon particles and metal particles does not contain carbon.

[0021] The carbon-free mixture means that the weight fraction of carbon in the mixture of silicon particles and metal particles is less than 0.1% by weight.

[0022] The oxidized surfaces and carbon within or on the deposited active layer are particularly obstructive to the successful reaction of silicon particles with metal particles and must be sufficiently removed prior to rapid annealing. This is achieved, for example, by wet chemical etching or in the form of a dry vacuum treatment in a reducing plasma, such as Ar / H2.

[0023] In a further configuration of the method of the present invention, the particles of the mixture of silicon particles and metal particles are within the size order of the layer thickness deposited on the active layer of the anode, and the active layer of the anode is deposited with a layer thickness of 1 to 30 μm. The preferred average size of the silicon particles and metal particles is in the range of 100 nm to 10 μm, measured along the direction of the maximum dimension.

[0024] The goal of the method of the present invention is the production of a semi-porous layer having an active layer thickness between 1 and 30 μm, which also has high electrical conductivity and very good adhesion to the current collector. The conductivity is adjusted by the fraction of metal particles in the active layer. When the porosity of the active layer is 50%, i.e., the density ratio of the cavity volume to the total volume of the active layer material is 1:1, and the specific capacity is 50% of the ideal capacity, i.e., 25% of the active layer reacts with Cu, only 25% of the active layer is insufficiently contacted. When the thickness of the active layer is 30 μm, a total capacity of 4.5 mAh / cm 2 is achievable. When the porosity of the active layer is 25% and the fraction of the active layer reacted with Cu is 10%, the same order of total capacity can be achieved with an active layer thickness of only 15 μm. This can be achieved without difficulty by the method of the present invention.

[0025] In a further different configuration of the method according to the invention, the silicon particles are amorphous, and the silicon particles have a particle size distribution of d10 ≤ 100 nm, d50 ≤ 5 μm, d90 ≤ 10 μm. The numerical value of d[digit] corresponds to the percentile of the particle distribution function, and thus, for example, in the case of d10, it means that 10% of all particles have a particle size of 100 nm or less. The average particle size is measured along the direction of the maximum dimension of the silicon particles. The numerical value of d50 is also called the median. According to the invention, the median needs to be 5 μm or less. d90 means that 90% of all Si particles have a size of 10 μm or less.

[0026] The use of amorphous silicon particles is preferred because it reduces the initial energy input in the first charging cycle into a lithium-ion battery having an anode produced by the method according to the invention, and because energy does not need to be consumed for the destruction of the crystal structure of silicon.

[0027] In one configuration of the method according to the invention, the metal particles are formed from one of the materials of copper (Cu), nickel (Ni), manganese (Mn), cobalt (Co), iron (Fe), aluminum (Al), titanium (Ti), magnesium (Mg), silver (Ag), gold (Au) and / or tin (Sn), and / or a mixture of these materials.

[0028] The insertion of additional materials or metals into the active layer has the advantage that, on the one hand, the copper of the copper substrate reacts only in a very small proportion with the deposited layer, and thus particularly good adhesion is ensured, and on the other hand, the copper of the current collector is not deteriorated by suppressing the reaction with other layers to be deposited.

[0029] Furthermore, a highly conductive semi-porous active layer is thereby produced. The active layer can withstand the volume expansion associated with the intercalation of lithium.

[0030] In a further configuration of the method of the present invention, the rapid annealing is flash lamp annealing, with a flash lamp duration in the range from 0.2 ms to 20 ms and 0.6 J / cm 2 to 160 J / cm 2 and is carried out by a flash lamp having an energy density in this range, and / or using preheating or cooling in the range from 4 °C to 200 °C.

[0031] In a different further configuration of the method of the present invention, the rapid annealing is laser annealing, with an annealing time in the range from 0.01 ms to 100 ms established by the scanning speed of the locally heated spot and 0.1 J / cm 2 to 100 J / cm 2 and is carried out by a laser having an energy density in this range, and / or using preheating or cooling in the range from 4 °C to 200 °C.

[0032] The description of the temperature range from 4 °C to 200 °C refers to the surface temperature of the substrate or layer to be annealed.

[0033] Rapid annealing refers in particular to flash lamp annealing and / or laser annealing. Flash lamp annealing is carried out with a pulse duration or annealing time in the range from 0.3 ms to 20 ms, and a pulse energy in the range from 0.3 J / cm 2 to 100 J / cm 2 In the case of laser annealing, an annealing time of 0.01 - 100 ms is established through the scanning speed of the locally heated spot, generating an energy density of 0.1 - 100 J / cm 2 The heating gradient achieved in rapid annealing is within the range of 10 4 to 10 7 K / s required for the method. For this purpose, flash lamp annealing utilizes the spectrum in the visible light wavelength range, while in the case of laser annealing, discrete wavelengths in the range of the spectrum from infrared (IR) to ultraviolet (UV) are used.

[0034] It has been revealed that the effect of rapid annealing varies depending on the deposition of different materials in the active layer. This is thought to be due to a variety of different chemical events associated with silicon, particularly the temperature of alloy formation, which is evident in the corresponding phase diagram. As a result, different structures, such as the columnar structure in the case of nickel, can be formed in the anode layer that is produced. Furthermore, in contrast to Cu silicides that have a negligible or zero ability to intercalate lithium, different silicides that also intercalate lithium can be formed. The advantage of utilizing the described differences is that it can be used to control the volume expansion of silicon during lithium intercalation. As a result, the stability of the battery operation is significantly improved.

[0035] In the case of titanium, for example, Ti silicide is formed, which may have the ability to intercalate Li in the appropriate phase (see Xu, J et al., Preparation of TiSi2 Powders with Enhanced Lithium-Ion Storage via Chemical Oven Self-Propagating High-Temperature Synthesis. Nanomaterials 11, 2279 (2021)). This has the advantage that there is no clear boundary between Li-active and Li-inactive, resulting in good electrical contact even during cycling. Furthermore, metals such as aluminum, for example, do not form any compounds with silicon, i.e., do not form any silicides. As a result, these metals mix in silicon, increasing the electrical conductivity. In the rapid annealing process, the morphology and hardness of the silicon-metal layer can be further improved compared to hard pure silicon.

[0036] The reaction forced by rapid annealing between silicon particles and metal particles is a non-equilibrium process, which is only achievable in the ms range and thus requires the use of a flash lamp or laser.

[0037] The foregoing reaction is enabled through a defined input of energy by means of an accelerated annealing of one or more layers of particles. In this case, a sufficient reaction occurs between the metal and the silicon without the silicon reacting completely and without an insufficient amount of active material remaining. The more metal there is, the more opportunities for reaction, but the less active material. The greater the energy, the higher the adhesion, but the less active material. The optimal outcome depends on the particle size and material used.

[0038] In one configuration of the method of the present invention, one or more layers of a protective layer, preferably a carbon layer, and / or a solid electrolyte interphase (SEI) are deposited on the active layer. The thickness of the protective layer is 10 - 20 nm in the case of a carbon layer.

[0039] The surface of the deposited active layer can then be subsequently functionalized by standard methods in a vacuum or inert gas treatment, such as an atomic layer deposition (ALD) process, for example, through the deposition of a carbon layer or a so-called artificial SEI. The vacuum mechanism is still required only for cleaning the surface of the particles and, if necessary, perhaps for surface modification. As a result, on the one hand, all of the starting materials are in a dry state, and on the other hand, the actual deposition of the layer under vacuum is unnecessary, minimizing cost and complexity. It is advantageous that the artificial SEI is formed from Al2O3, TiO2, SiO2, and / or LiOH, as these prevent further oxidation and, nevertheless, allow sufficient permeation of Li+ ions during the operation of the battery. The thickness of the artificial SEI is 2 - 20 nm.

[0040] In contrast to similar structures such as silicon nanowires or columnar structures, the method of the present invention avoids, to the extent possible, vacuum treatment and, furthermore, the costly drying section for slurry-based processing. As a result, fabrication with a minimal amount of material and minimal processing costs becomes possible and can be incorporated into existing roll-to-roll mechanisms.

[0041] In different configurations of the method of the present invention, the parameters of the rapid thermal annealing are adjusted as a function of the particle size of the mixture of silicon particles and metal particles, as a function of the mixing ratio of the mixture of silicon and metal particles, and as a function of the thickness of the deposited layer.

[0042] Depending on the particle size of the silicon and of the additional metal or metals added, the mixing ratio of silicon and metal, and the layer thickness of the active layer, an optimal energy input can be established through the selection of the parameters of the rapid thermal annealing. The rapid thermal annealing is carried out after the deposition layer of the active layer. The layer thus refers to the deposition layer of the active material on which the rapid thermal annealing is then carried out, and depending on the thickness of the layer, the active layer of the electrode can be composed of one or more layers.

[0043] In one configuration of the method of the present invention, the substrate before deposition of the mixture of silicon particles and metal particles and / or the contact surface between the silicon particles and the metal particles is cleaned.

[0044] For the reaction of the metal with the silicon particles, a clean contact surface between the silicon particles / metal particles and between the silicon particles / substrate needs to be ensured. This can be achieved by means of a suitable and easily removable protective layer or by an upstream treatment by reduction for surface cleaning, for example by means of an H2-containing plasma. There is a further possibility through the production of a clean surface during the deposition of the active layer when the particles are deposited on the substrate at high speed where they break, for example during spray-phase deposition. The fracture edges are then suitable for the reaction.

[0045] In a further configuration of the method of the present invention, the particles of the mixture of silicon particles and metal particles are heated by rapid thermal annealing such that a reaction of less than 25% of the active material with the substrate occurs, thus ensuring a high strength of adhesion between the active material and the copper substrate.

[0046] The configuration of this method advantageously enables further improvement of the structural stability without the need to use a separately manufactured framework structure composed of copper silicide onto which (amorphous) silicon is deposited retrogradely, as described, for example, in Collins, G.A., Kilian, S., Geaney, H. & Ryan, K.M., A Nanowire Nest Structure Comprising Copper Silicide and Silicon Nanowires for Lithium-Ion Battery Anodes with High Areal Loading. Small 2021, 7, 2102333, or Song, H. et al., Highly Connected Silicon-Copper Alloy Mixture Nanotubes as High-Rate and Durable Anode Materials for Lithium-Ion Batteries. Advanced Functional Materials 26, 524-531 (2016). Clean contacts exist between the particles and / or nanostructures with each other and with respect to the current collector, and when they are typically manufactured by vacuum methods such as PVD or CVD, they are heated by rapid annealing to such an extent that a partial reaction of less than 25% of the active material with the copper substrate occurs, thus ensuring a significantly increased strength of adhesion.

[0047] In a further different configuration of the method of the invention, another layer of active material is deposited on the active material in order to increase the capacity of the anode with high stability and electrical conductivity.

[0048] In particular, further particles of a mixture of silicon particles and metal particles can be deposited on the surface of particle structures and nanostructures manufactured by vacuum methods such as PVD or CVD so as to achieve an anode with increased capacity with high stability and electrical conductivity. For example, it may be necessary to clean the surface again by means of a reducing plasma.

[0049] The object of the invention is likewise achieved by an anode according to independent claim 13 of the device.

[0050] Suitable for use in a lithium-ion battery, the anode manufactured by the method according to any one of claims 1 to 12 preferably comprises a current collector made of copper and an active layer deposited on the current collector, the active layer being formed from a mixture of silicon particles and metal particles, the mixture of silicon particles and metal particles being deposited onto a substrate in a dry process and stabilized under controlled rapid annealing to form a semi-porous active layer that adheres to the substrate.

[0051] The dry process means a process that does not require water and solvents, such as cathodic atomization (sputtering).

[0052] In one configuration of the anode of the present invention, the metal particles are formed from one of the materials copper (Cu), nickel (Ni), manganese (Mn), cobalt (Co), iron (Fe), aluminum (Al), titanium (Ti), magnesium (Mg), silver (Ag), gold (Au) and / or tin (Sn), and / or a mixture thereof.

[0053] In a different configuration of the anode of the present invention, the active layer of the anode has a layer thickness of 1 to 30 μm.

[0054] In yet another different configuration of the anode of the present invention, the substrate is embodied as a copper grid and the active layer is deposited onto the copper grid.

[0055] Compared to a sheet-like copper substrate, the copper grid has open areas. The silicon / metal particle mixture, i.e., the powder mixture, is incorporated into this copper grid and then subjected to rapid annealing. This makes it possible to significantly reduce the weight of the current collector. However, the conductivity of the active layer must be high enough to enable the use of this device as an anode.

[0056] In a further configuration of the anode of the present invention, the substrate is embodied as a sacrificial substrate, the active layer is deposited onto the sacrificial substrate, subjected to rapid annealing, the sacrificial substrate is removed, and the active layer is 1×104 It has a specific electrical conductivity exceeding S / cm, and the active layer can be contacted from one side.

[0057] When the specific electrical conductivity of the active layer exceeds 1×10 4 S / cm, the anode can be realized even without a current collector. The active layer composed of a silicon / metal particle mixture is first deposited on a sacrificial substrate and subjected to rapid thermal annealing. The sacrificial substrate is then removed, and the active layer is contacted directly, for example, on the side of the active layer.

[0058] The present invention also includes a mixture of metal particles for manufacturing the anode according to claims 15 to 17 using the method according to claims 1 to 12. The mixture of metal particles has a particle size distribution with d10 = 100 nm, d50 = 3 μm, and d90 = 5 μm. The numerical value of d[digit] corresponds to the percentile of the particle distribution function. Thus, for example, in the case of d10, it means that 10% of all particles have a particle size of 100 nm or less. The average particle size is measured along the direction of the maximum dimension of the silicon particles. The numerical value of d50 is also called the median. According to the present invention, the median of the mixture of metal particles needs to be 3 μm or less. d90 means that 90% of all metal particles have a size of 5 μm or less.

[0059] The present invention will be described in more detail below with reference to exemplary embodiments.

[0060] The content of the drawings is as follows.

Brief Description of the Drawings

[0061]

Figure 1

Figure 2a

Figure 2b

Figure 3

Figure 4

Figure 5

Figure 6

Embodiments for Carrying Out the Invention

[0062] The diffusion of metal into silicon and the reaction of silicon with the metal strongly depend on time and temperature. At very low temperatures from 200 °C and above, many metals 16 form metal silicides 12 at the boundary of the contact between the metal 16 and the silicon 11, and this silicide has a certain capacity, no capacity, or only a very small capacity for reversible lithium intercalation. Metals 16 diffuse even at room temperature and very rapidly at high temperatures, and the diffusion is difficult to control in conventional oven treatments. Taking copper as an example, a complete layer of silicon reacted after within 1 second at 600 °C (see Fig. 2a).

[0063] Figure 2b shows the influence of rapid thermal annealing 15, more particularly flash lamp annealing, on the formation of silicide 12 at the contact positions in a layer system composed of copper 10 and silicon 11. With very short flash pulses in the range from 0.1 to 10 ms, the reaction of silicon 11 with copper 10 to form copper silicide 12 is incomplete. As a result of the flash lamp annealing 15, pure amorphous or nanocrystalline silicon 11 remains and is available as an active material for the intercalation of lithium, while at the same time there is a sufficient amount of an inert region to ensure stability and good electrical conductivity.

[0064] Figure 3 shows different variants of a silicon structure deposited on a copper substrate 10 as a homogeneous layer, as silicon particles 13, or as silicon nanowires 14. Rapid thermal annealing 15, such as flash lamp annealing for example, leads to a controlled local reaction of silicon 11 with copper 10 to form copper silicide 12 at those points of the boundary contact. As a result, the silicon is joined together with the substrate. In a schematic representation, a linear profile from pure copper 10 via copper silicide 12 to silicon 11 is shown, but the actual transition is such that the profile is substantially non-uniform and the boundary is even rougher to the extent that dendrites of Cu / CuSi x are formed in the silicon. A dendrite is a bushy or treelike crystal structure.

[0065] Figure 4 schematically shows a mixture 20 of silicon particles and metal particles on a copper substrate 10, and the influence of accelerated annealing 15. The silicon particles 13 are calendared together with metal particles 16, preferably copper as a powder, on the copper foil 10. This is followed by accelerated annealing 15, for example flash lamp annealing. As a result of the metal particles 16, which are Cu particles in this example, the silicon particles 13 adhere to the substrate 10 and to each other. The reaction requires clean contact of the surfaces since oxides or organic residues would prevent the desired reaction. For example, a pretreatment in a reducing atmosphere may be useful for this purpose. As a result, a dry process is provided that does not require a binder for the powder treatment of the Si particles 13, with high conductivity, increased porosity, and excellent adhesion between the active layer 19 and the substrate 10. The Si particles 13 and the metal particles 16 form partial reaction particles 22 composed of Cu / CuSi x / Si.

[0066] In a further exemplary embodiment according to Figure 5, the copper substrate 10 may be pretreated, for example, using silicon nanowires 14. The silicon particles 13 are calendared together with metal particles 16, preferably copper as a powder, on the copper foil 10, and both the copper substrate surface 10 and the powder mixture 20 are cleaned 18, for example, by a reducing atmosphere. The mixture 20 of silicon particles and metal particles and the substrate are subjected to accelerated annealing 15, for example flash lamp annealing, and adhesion is achieved through the reaction of the silicon particles 13 with the metal particles 16, particularly copper in an exemplary embodiment, to form partial reaction particles 22.

[0067] In a further exemplary embodiment, an anode for a lithium-ion battery is manufactured by the method of the present invention (see Figure 6). First, a suitable mixture 20 of silicon / metal particles is made and deposited onto a copper substrate 10 that constitutes the current collector of the electrode. The deposited powder mixture 20 is subjected to accelerated annealing 15. The accelerated annealing 15 can be flash lamp annealing or laser annealing. The accelerated annealing 15 creates a partially reacted active layer 19 of silicon-metal particles 20 that is fixed to the current collector 10.

[0068] Rapid thermal annealing 15 enables targeted control of energy input into the deposited layer. Optimal energy input can be established according to the particle size, mixing ratio, and layer thickness. As a result of the defined energy input by flash lamp annealing 15, for example, after layer 21 of particles 20, sufficient reaction occurs between the metal-silicon mixtures 20 without complete reaction of silicon 11, in other words, pure Si particles remain or only insufficient active material remains. The more metal 16 there is, the more opportunities for reaction, but the less active material. The greater the energy, the higher the adhesion to the current collector 10 and / or between particles 13, 16, but the less active material. Cu / CuSi x Partial reaction particles composed of / Si22 are formed. Optimal results depend on the particle size and material used. The insufficiently reacted and trapped Si particles 13 do not adhere and can therefore be easily removed. Thereafter, deposition of the particle mixture 20 and rapid thermal annealing 15 can be performed again.

[0069] For example, by sputtering, following deposition and annealing of the deposited active layer 19, deposition of a protective layer or artificial SEI is possible, including vacuum treatment, since drying is not required.

[0070] An advantage of the method of the present invention is that silicon 11 in powder form having a large variation in particle size 13 and a high impurity level can be used as a substrate, and thus it is cost-effective accordingly. Relatively small silicon particles 13 enable construction of the multilayer 21 and thus easier adjustment of the capacity of the entire anode layer. Amorphous silicon particles 13 are preferred in that case because the initial energy input in the first charge cycle is smaller and there is no need to consume energy when breaking the Si crystal structure.

[0071] In contrast to existing slurry methods, carbon as a binder has been found to be an obstacle in terms of technical processing, as even an extremely thin carbon layer of up to 5 nm can prevent satisfactory reaction between Si particles in the method of the present invention.

Description of Symbols

[0072] 1 Lithium-ion battery 2 Anode current collector 3 SEI, Solid Electrolyte Interphase 4 Electrolyte 5 Separator 6 Conductive intermediate layer 7 Cathode, Positive electrode 8 Cathode current collector 9 Anode, Negative electrode 10 Copper substrate 11 Silicon 12 Copper silicide, Metal silicide, or Boundary contact of silicide reaction 13 Silicon particles 14 Silicon nanowires 15 Accelerated annealing, e.g., Flash lamp annealing 16 Copper particles, Metal particles 17 Copper oxide / Organic residues, Impurities 18 Cleaning process 19 Active layer 20 Mixture of silicon particles and metal particles 21 Deposition layer in the active layer 22 Half-reaction particles (e.g., Cu / CuSi x / Si)

Claims

1. A method for producing a silicon electrode as an anode for a lithium-ion battery, comprising depositing an active layer (19) on a copper substrate followed by an accelerated anneal (15), the active layer (19) is formed from a mixture (20) of silicon particles and metal particles, which are applied to the substrate (10) by dry processing and stabilized under control by the accelerated annealing (15) to form a semi-porous active layer (19) that is bonded to the substrate (10); the accelerated annealing (15) is a flash lamp annealing, carried out by a flash lamp with a flash light duration in the range of 0.2 to 20 ms and an energy density in the range of 0.6 to 160 J / cm 2 and / or with preheating or cooling in the range of 4°C to 200°C; or The method is characterized in that the accelerated annealing (15) is laser annealing, performed by a laser having an annealing time in the range of 0.01 to 100 ms and an energy density in the range of 0.1 to 100 J / cm 2 by establishing a scanning speed of the localized heating point, and / or using preheating or cooling in the range of 4°C to 200°C.

2. 2. The method for producing a silicon electrode as an anode for a lithium-ion battery according to claim 1, wherein the mixture of silicon particles and metal particles (20) is carbon-free.

3. 2. A method for producing a silicon electrode as an anode for a lithium-ion battery according to claim 1, characterized in that the particles (13, 16) of the mixture (20) of silicon particles and metal particles are in the size order of the layer thickness applied to the active layer (19) of the anode, and the active layer of the anode is deposited with a layer thickness of 1 to 30 μm.

4. 4. The method for producing a silicon electrode as an anode for a lithium-ion battery according to claim 3, wherein the silicon particles (13) are amorphous and have a particle size distribution of d10≦100 nm, d50≦5 μm, and d90≦10 μm, where the average particle size is measured along the direction of the largest dimension of the silicon particles.

5. 2. The method for manufacturing a silicon electrode as an anode for a lithium-ion battery according to claim 1, characterized in that the metal particles are formed from one of the following materials: copper (Cu), nickel (Ni), manganese (Mn), cobalt (Co), iron (Fe), aluminum (Al), titanium (Ti), magnesium (Mg), silver (Ag), gold (Au) and / or tin (Sn), and / or a mixture of these materials.

6. 2. A method for producing a silicon electrode as an anode for a lithium-ion battery according to claim 1, characterized in that a protective layer and / or one or more layers of an artificial solid electrolyte interphase (SEI) are deposited on the active layer (19), the protective layer being a carbon layer.

7. The parameters of the accelerated annealing (15) are: a function of the size of the particles (13, 16) of the mixture of silicon particles and metal particles (20); A function of the mixing ratio of the mixture of silicon particles and metal particles (20), and Sediment thickness function 2. The method for manufacturing a silicon electrode as an anode for a lithium ion battery according to claim 1, characterized in that the silicon electrode is prepared as follows:

8. 2. The method for producing a silicon electrode as an anode for a lithium-ion battery according to claim 1, characterized in that the substrate (10) and / or the contact surface between the silicon particles (13) and the metal particles (16) are cleaned before the deposition of the mixture of silicon particles and metal particles (20).

9. 2. The method for manufacturing a silicon electrode as an anode for a lithium-ion battery according to claim 1, wherein the particles (13, 16) of the mixture of silicon particles and metal particles (20) are heated by the accelerated annealing (15) so that no more than 25% of the active material reacts with the substrate (10) and a high degree of bonding is ensured between the active material and the substrate (10).

10. 10. The method for manufacturing a silicon electrode as an anode for a lithium-ion battery according to claim 9, characterized in that another layer (21) of active material is deposited on the active material to increase the capacity of the anode with high stability and electrical conductivity.

11. 1. An anode embodied and intended for use in a lithium-ion battery, said anode comprising a substrate as a current collector (10) made of copper, and an active layer (19) deposited on said current collector (10), said active layer (19) being formed from a mixture of silicon particles and metal particles that are applied to said substrate (10) by dry processing and stabilized under controlled conditions by accelerated annealing (15) to form a semi-porous active layer (19) that is fixed to said substrate (10).

12. 12. The anode according to claim 11, characterized in that the metal particles are formed from one of the following materials: copper (Cu), nickel (Ni), manganese (Mn), cobalt (Co), iron (Fe), aluminum (Al), titanium (Ti), magnesium (Mg), silver (Ag), gold (Au) and / or tin (Sn), and / or a mixture of these materials.

13. 12. The anode according to claim 11, wherein the active layer of the anode has a layer thickness of 1 to 30 μm.

14. 12. The anode according to claim 11, characterized in that the substrate is embodied as an open copper grid and the active layer is deposited on the open copper grid.

15. The substrate is embodied as a sacrificial substrate, the active layer is deposited on the sacrificial substrate, subjected to accelerated annealing, the sacrificial substrate is removed, and the active layer is removed to a thickness of 1×10 ４ 12. The anode of claim 11, characterized in that it has a specific electrical conductivity of more than 100 S / cm and the active layer is accessible from one side.

16. A mixture of metal particles for producing an anode as described in any one of claims 13 to 15, having a particle size distribution of d10 = 100 nm, d50 = 3 μm, d90 = 5 μm, where the average particle size is measured along the direction of the largest dimension of the silicon particles.

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