Method for producing silicon electrodes as anodes for lithium ion batteries and a silicon electrode produced using same

Abstract

The invention relates to a method for producing a silicon electrode as an anode for a lithium ion battery, in which an active layer is deposited on a substrate, preferably copper, and then undergoes a rapid tempering, as well as an anode produced using same. The object of the invention of providing a method, which dispenses with the need for a vacuum section for depositing the active material, in particular silicon, for the production of anodes for lithium ion batteries, and thereby allows for an extremely cost-optimised production of almost pure silicon anodes for lithium ion batteries, is achieved in that the active layer is formed from a silicon and metal particle mixture, which is applied to the substrate in a dry process and stabilised in a controlled manner via the rapid tempering to form a semi-porous active layer and fixed to the substrate.

Description

[0001] Process for producing silicon electrodes as anodes for lithium-ion batteries and a silicon electrode produced thereby

[0002] The invention relates to a method for producing a silicon electrode as an anode for a lithium-ion battery, in which an active layer is deposited on a substrate, preferably copper, which is then subjected to a short-time annealing.

[0003] The invention also relates to an anode which is suitable for use in a lithium-ion battery and is produced by the process according to claims 1 to 10.

[0004] Electrochemical energy storage is a key pillar of the globally desired energy transition, with the aim of temporarily storing fluctuating electricity generated from renewable sources and making it available for stationary and mobile applications. In order to counteract raw material shortages and the resulting increase in costs, particularly for secondary batteries, new materials are needed in addition to the diversification of energy storage concepts. These materials should, on the one hand, improve the technical performance of corresponding energy storage concepts (e.g. capacity, energy density, service life), and, on the other hand, minimize production costs. The latter can be ensured in particular by using readily available chemical elements such as silicon, for which a broad technology base already exists.

[0005] Batteries are electrochemical energy storage devices and are divided into primary and secondary batteries.

[0006] Primary batteries are electrochemical power sources in which chemical energy is irreversibly converted into electrical energy. A primary battery is therefore not rechargeable. Secondary batteries, also called accumulators, on the other hand, are rechargeable electrochemical energy storage devices in which the chemical reaction is reversible, allowing multiple uses. Electrical energy is converted into chemical energy during charging, and from chemical energy into electrical energy during discharging.

[0007] Battery is the generic term for interconnected cells. Cells are galvanic units consisting of two electrodes, an electrolyte, a separator, and a cell casing. Figure 1 shows an example of the structure and function of a lithium-ion cell during the discharge process. The components of a cell are briefly explained below.

[0008] Each Li-ion cell consists of two different electrodes 7, 9, one which is negatively charged when charged and one which is positively charged when charged. Since ions migrate from the negatively charged electrode to the positively charged electrode during energy release, i.e. during discharge, the positively charged electrode is called the cathode 7 and the negatively charged electrode the anode 9. The electrodes each consist of a current collector 2, 8 (also called a collector) and an active material applied to it. Between the electrodes there is the ion-conducting electrolyte 4, which enables the necessary charge exchange, and the separator 5, which ensures the electrical separation of the electrodes. The cathode consists, for example, of mixed oxides applied to an aluminum collector.

[0009] Transition metal oxides with cobalt ( Co ), manganese (Mn) and nickel (Ni ) or aluminum oxide (AI2O3 ) are the most common

[0010] Compounds. The applied metal oxide layer serves to store the lithium ions during cell discharge.

[0011] The anode of a lithium-ion cell can consist of a copper foil as a collector and a layer of carbon as the active material. Natural or synthetic graphite is typically used as the carbon compound because it has a low electrode potential and exhibits low volume expansion during charging and discharging. During the charging process, lithium ions are reduced and incorporated into the graphite layers.

[0012] In lithium-ion battery designs, the cathode typically supplies the lithium atoms for charging and discharging in the anode; the battery capacity is therefore limited by the cathode capacity. As already mentioned, typical cathode materials used to date include, for example,

[0013] Li (Ni, Co, Mn) O2 and LiFePO-j. Due to the cathode's lithium metal oxide structure, an increase in capacity is only possible to a limited extent.

[0014] It is also known to use silicon instead of carbon for lithium battery anodes. Silicon as an anode material has a high storage capacity of 3579 mAh / g at room temperature compared to conventional carbonaceous materials, such as graphite with a storage capacity of 372 mAh / g. However, challenges in using silicon as an anode material arise from the sometimes considerable volume change (volume contraction and expansion) during the incorporation and release of mobile ion species during charging and discharging of corresponding energy storage devices. The volume change upon lithium incorporation is approximately 10% for graphite, but up to 400% for silicon. The volume change of the anode material when using silicon leads to internal stresses, cracking, pulverization of the active material (silicon), loss of electrical contact and ultimately to the complete destruction of the anode.

[0015] Common processes for the large-scale industrial production of silicon-containing anodes for lithium-ion batteries use silicon powder or silicon particles, which are applied to copper current collectors in slurries with carbon-containing binders using wet or dry roll-to-roll processes. Slurries are mixtures of solids in which the solids are dispersed in a liquid. In slurry-based processes, a layer of silicon particles with a carbon-containing binder is applied or calendered onto a current collector. The binder ensures adhesion and electrical contact between the particles and to the current collector. In most cases, this requires a drying section to drive off solvents that are detrimental to further processing.The advantages of these slurry-based processes are the high scalability of the processes, the ability to adjust the capacity of the anodes produced by varying the applied layer thickness, and the simple and inexpensive addition of active material through external processes. The disadvantage of these slurry-based processes is the usually expensive starting materials, such as ultrapure silicon, powder with a defined grain size, carbon binders, and other non-active components.

[0016] Homogeneity and porosity, etc., as well as the energy costs of the necessary drying section. Typically, nanoscale silicon particles are used in the slurries to compensate for the stress applied when the active layers expand during lithiation in the lithium-ion battery. The main causes of failure of such structures for lithium-ion batteries, particularly the loss of capacity in lithium-ion batteries, are the loss of electrical contact between the Si structures and the loss of electrolyte from the large surface area of ​​the active layer.

[0017] It is also known that there are new processes that use almost 100% pure silicon as the anode material in order to enable maximum storage capacity. Loose or powdered nanoscale starting materials are not suitable for establishing electrical contact with the current collector because they are not fixed to the current collector. Active layers made of 100% silicon can currently only be produced using vacuum processes. In this process, silicon is applied to pre-structured surfaces to enable nanostructuring of the Si structures, so-called columnar structures, and to ensure sufficient adhesion. A PECVD process or sputtering process is typically used for this (see also: 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) oder 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.

[0018] The disadvantages of a slurry-based silicon anode structure were circumvented in optimized processes by applying the active material or the anode structure for a lithium-ion battery as a planar layer in a vacuum system using PVD processes such as sputtering or evaporation. A novel process involving short-term annealing allows the active material to be stabilized and fixed to the current collector. This avoids the removal of unnecessary components in the process chain, such as solvents in the slurries or residues of binder components. However, the use of PVD deposition processes entails other disadvantages, such as the high energy requirement for operating a vacuum line in order to apply a layer thickness to the current collector that is unusual for PVD processes.

[0019] It is therefore the object of the present invention to provide a method that eliminates the need for a vacuum line to deposit the active material, in particular silicon, for the production of anodes for lithium-ion batteries, thus enabling extremely cost-optimized production of virtually pure silicon anodes for lithium-ion batteries. Furthermore, the manufacturing method should be easily integrated into existing roll-to-roll processes with slurry-based layer production, i.e., replace the slurry-based binders while still ensuring sufficient current contact both between the layers and with the current collector.

[0020] The object of the invention is achieved by a method according to the independent method claim 1.

[0021] In the method for producing a silicon electrode as an anode for a lithium-ion battery, in which an active layer is deposited on a substrate, preferably copper, which is then subjected to a short-time annealing, the active layer is formed from a silicon and metal particle mixture, which is applied to the substrate in a dry process and is stabilized in a controlled manner by the short-time annealing to form a partially porous active layer and fixed to the substrate.

[0022] A dry process is understood to be a water- or solvent-free process, for example cathode sputtering. The material of the active layer is introduced into the process as a particle layer in the order of magnitude of the layer thickness used. This means that the size of the particles in the silicon and metal particle mixture is in the order of magnitude of the layer thickness to be built up for the active layer. To increase the conductivity, the active material silicon, which is preferably in powder form, is previously mixed with metal powder in particle sizes of a similar size order in the desired

[0023] The silicon particles are mixed in the correct proportions and then fixed to the substrate or to each other by short-term annealing. In contrast to previous processes, the reaction between the silicon and the copper substrate, as well as between the silicon particles and the metal particles, is controlled by the ultrashort energy input of the short-term annealing, so that a complete reaction and thus a loss of active material can be prevented. The parameters of the short-term annealing must be set in such a way that a reaction between the active material, i.e. the silicon particles, and the metal particles is enabled.

[0024] In one embodiment of the process according to the invention, the silicon and metal particle mixture is carbon-free.

[0025] A carbon-free mixture is understood to mean that the weight fraction of carbon in the silicon and metal particle mixture is less than 0.1 wt.%.

[0026] In particular, oxidized surfaces and carbon in and on the active layer to be deposited hinder a successful reaction between the silicon and metal particles and must be sufficiently removed before short-term annealing. This is achieved, for example, by wet-chemical etching or as a dry vacuum process in a reducing plasma, such as Ar / JU.

[0027] In a further embodiment of the method according to the invention, the particles of the silicon and metal particle mixture are in the order of magnitude of the layer thickness to be applied to the active layer of the anode, wherein the active layer of the anode is deposited with a layer thickness of 1 to 30 pm. A preferred average size of the silicon particles and the metal particles measured along a direction of the largest

[0028] Extent is in the range between 10 Onm and 10pm .

[0029] The aim of the method according to the invention is to produce a partially porous layer with an active layer thickness of between 1 and 30 μm, which has a high electrical conductivity and a very good fixation on the current collector. The conductivity is adjusted by the proportion of metal particles in the active layer. With a porosity of the active layer of 50%, i.e. a density ratio of void volume to total volume of the active layer material of 1:1 and a specific capacity of 50% of the ideal capacity, i.e. 25% of the active layer is reacted with Cu, 25% of the active layer is only insufficiently contacted, a total capacity of 4.5 mAh / cm is achieved with an active layer thickness of 30 μm. 2With an active layer porosity of 25% and a Cu-reacted portion of 10% of the active layer, total capacitances of the same order of magnitude can be achieved with an active layer thickness of just 15 pm. This can be easily achieved using the method according to the invention.

[0030] In another further embodiment of the process according to the invention, the silicon particles are amorphous, the silicon particles having a size distribution of d10<100 nm, d50<5 pm, d90<10 pm. The specification d [number] corresponds to a percentile value of a particle distribution function, i.e., for example, with d10, 10% of all particles have a particle size of less than or equal to 10 μm. The average particle size is measured along a direction of the greatest extent of the silicon particles. The value d50 is also called median. According to the invention, the median value should be less than or equal to 5 pm. d90 means 90% of all Si particles have a size of less than or equal to 10 pm.

[0031] The use of amorphous silicon particles is preferable because the initial energy input in the first charging cycle of a lithium-ion battery with an anode produced by the method according to the invention is lower and no energy is required to break up the silicon crystal structure.

[0032] In one embodiment of the method according to the 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 of these materials.

[0033] The insertion of an additional material or metal into the active layer has the advantage that, on the one hand, the copper of the copper substrate reacts only to a very small extent with the applied layers, which ensures particularly good adhesion, and, on the other hand, that the copper of the current collector is not degraded by preventing a reaction with the other deposited layers.

[0034] Furthermore, this creates a semi-porous active layer with high conductivity. The active layer is able to withstand volume expansion during lithium deposition.

[0035] In a further embodiment of the method according to the invention, the short-time tempering is a flash lamp tempering and is carried out by means of a flash lamp with a flash duration in the range of 0.2 to 20 ms and an energy density in the range of 0.6 to 160 J / cm 2and / or preheating or cooling in the range of 4°C to 200°C.

[0036] In another further embodiment of the method according to the invention, the short-time tempering is a laser tempering and is carried out by means of a laser with a tempering time in the range of 0.01 to 100 ms by setting a scanning speed of a local heating point and an energy density in the range of 0.1 to 100 J / cm 2 and / or with preheating or cooling in the range of 4°C to 200°C.

[0037] The temperature range from 4°C to 200°C refers to the surface temperature of the substrate or the layer to be tempered.

[0038] Short-term 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 of 0.3 to 20 ms and a pulse energy in the range of 0.3 to 100 J / cm 2 . In laser annealing, the annealing time is adjusted from 0.01 to 100 ms by the scanning speed of the local heating point to achieve an energy density of 0.1 to 100 J / cm 2 The heating ramps achieved in the short-time tempering are in the range of 10 A 4-10 A7 K / s . Flash lamp annealing uses a spectrum in the visible wavelength range, whereas laser annealing uses discrete wavelengths in the infrared (TR) to ultraviolet (UV) spectrum. It has been shown that the effect of short-term annealing differs when depositing different materials in the active layer. The cause is thought to be the various chemical processes in connection with silicon, in particular the temperature of alloy formation, which can be seen in the corresponding phase diagrams. This can lead to the formation of different structures in the produced anode layer, e.g. columnar structures in nickel. Furthermore, other silicides can form which, unlike Cu silicides, which can store no or negligible amount of lithium, also store lithium.Exploiting these differences has the advantage of controlling the volume expansion of silicon during lithium deposition. This significantly increases the stability of battery operation.

[0039] In the case of titanium, for example, a Ti silicide is formed, which can be capable of storing Li in the right 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 Li-active / Li-inactive interface, ensuring good electrical contact even during cycling. Other metals, such as aluminum, do not form compounds with silicon, and therefore do not form silicides. This means that these metals mix with silicon, increasing electrical conductivity. In the short-term annealing step, the morphology and hardness of the silicon-metal layer can also be improved compared to hard pure silicon.

[0040] The reactions between the silicon particles and the metal particles forced by the short-term annealing are non-equilibrium processes which can only be realized in the ms range and thus require the use of a flash lamp or a laser.

[0041] The aforementioned reaction is enabled by the defined energy input through short-term annealing of one or more layers of particles. This results in a sufficient reaction between metal and silicon without the silicon reacting completely or leaving insufficient active material. More metal means more reaction possibilities but less active material. More energy means more adhesion but less active material. The optimal result depends on the materials used and the particle size.

[0042] In one embodiment of the method according to the invention, a protective layer, preferably a carbon layer and / or one or more layers of an artificial solid electrolyte interphase (SEI), is deposited on the active layer. The thickness of the protective layer is 10-20 nm for the carbon layer.

[0043] The surface of the deposited active layer can then be post-functionalized, for example by applying a carbon layer or a so-called artificial SEI using standard methods, e.g. in a vacuum or inert gas process, such as an ALD (atomic layer deposition) process. A vacuum system is only required for cleaning the surface of the particles and, if necessary, for surface modification. This minimizes the effort because, on the one hand, all the starting materials are dry and, on the other hand, the actual deposition of the layers in a vacuum is omitted. It is advantageous if the artificial SEI is formed from Al2O3, TiCu, SiCu and / or LiOH because these prevent further oxidation and are still sufficiently permeable for Li+ ions during battery operation. The thickness of the artificial SEI is between 2-20 nm.

[0044] In contrast to similar structures such as silicon nanowires or columnar structures, the process according to the invention avoids vacuum processes as much as possible, as well as cost-intensive drying sections for slurry-based processes. This enables production with minimal material and process costs and can be integrated into existing roll-to-roll systems.

[0045] In another embodiment of the method according to the invention, the parameters of the short-term annealing are adjusted as a function of the size of the particles of the silicon and metal particle mixture, of a mixing ratio of the silicon and metal particle mixture and of the deposited layer thickness.

[0046] Depending on the particle size of the silicon and the added metal or metals, the mixing ratio of silicon and metal(s), and the layer thickness of the active layer, an optimal energy input can be set by selecting the parameters for the short-term annealing. The short-term annealing takes place after a deposited layer of the active layer. A layer is therefore understood to be a deposited layer of active material which is subsequently subjected to a short-term annealing. Depending on the layer thickness, the active layer of the electrode can be made up of one or more layers. In one embodiment of the method according to the invention, the substrate and / or the contact surfaces between the silicon and metal particles are cleaned before the deposition of the silicon and metal particle mixture.

[0047] For the metals to react with the silicon particles, a clean contact surface must be ensured between the silicon particles / metal particles or between the silicon particles / substrate. This can be achieved by suitable, easily removable protective layers or reducing pre-processes for surface cleaning, e.g., H2-containing plasmas. Another possibility is to create clean surfaces when applying the active layer, for example, spray phase deposition, in which particles are applied to the substrate at high speed and break there. The fracture edges are then suitable for the reaction.

[0048] In a further embodiment of the method according to the invention, the particles of the silicon and metal particle mixture are heated by the short-time tempering in such a way that a reaction of a maximum of 25% of the active material with the substrate takes place and thus a high adhesive strength between the active material and the copper substrate is ensured.

[0049] This embodiment of the method advantageously makes it possible to further increase the stability of the structures without having to use separately produced framework structures made of copper silicides to which (amorphous) silicon is subsequently applied, 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). In the event that clean contact between the particles or .Nanostructures are present among themselves and to the current collector, which are typically produced in a vacuum process using PVD or CVD, and are heated by short-term annealing to such an extent that a partial reaction of a maximum of 25% of the active material with the copper substrate takes place, thus ensuring a significantly increased adhesive strength.

[0050] In another further embodiment of the method according to the invention, further layers of active material are deposited on the active material to increase the capacity of the anode with high stability and electrical conductivity.

[0051] In particular, additional particles of the silicon and metal particle mixture can be deposited onto the surface of the particle and nanostructures produced in a vacuum process using PVD or CVD to create an anode with increased capacity, high stability, and electrical conductivity. If necessary, further cleaning of the surface, e.g., using a reducing plasma, may be necessary.

[0052] The object of the invention is also achieved by an anode according to the independent arrangement claim 13.

[0053] An anode designed for use in a lithium-ion

[0054] Battery is suitable and is produced by the method according to claims 1 to 12, has a current collector, preferably made of copper and an active layer deposited on the current collector, wherein the active layer is formed from a silicon and metal particle mixture which is applied to the substrate in a dry process and stabilized in a controlled manner by short-term annealing to form a partially porous active layer and fixed to the substrate.

[0055] A dry process is a water- or solvent-free process, for example cathode sputtering.

[0056] In one embodiment of the anode according to the invention, the metal particles are made of 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 of these materials.

[0057] In another embodiment of the anode according to the invention, the active layer of the anode has a layer thickness of 1 to 30 pm.

[0058] In another embodiment of the anode according to the invention, the substrate is formed as a copper grid, wherein the active layer is applied to the copper grid.

[0059] The copper grid has open areas compared to a flat copper substrate. The silicon-metal particle mixture, i.e., the powder mixture, is incorporated into this copper grid and then subjected to a short-term annealing process. This allows the weight of the current collector to be significantly reduced. However, the conductivity of the active layer must be high enough for this arrangement to be used as an anode.

[0060] In a further embodiment of the anode according to the invention, the substrate is designed as a sacrificial substrate, wherein the active layer is applied to the sacrificial substrate and is subjected to a short-time annealing, wherein the sacrificial substrate is removed and the active layer has a specific electrical conductivity of greater than l * 10 4 S / cm and the active layer can be contacted from one side.

[0061] If the specific electrical conductivity of the active layer is greater than l * 10 4 S / cm, an anode can also be realized without a current collector. The active layer made of the silicon-metal particle mixture is first applied to a sacrificial substrate and subjected to a short-term annealing. The sacrificial substrate is then removed, and the active layer is directly contacted, for example, on the side of the active layer.

[0062] The invention likewise comprises a metal particle mixture for producing an anode according to claims 15 to 17 using a method according to claims 1 to 12, wherein the metal particle mixture has a size distribution of d10=100nm, d50=3pm, d90=5pm. The specification d [number] corresponds to a percentile value of a particle distribution function, i.e. that, for example, with d10, 10% of all metal particles have a particle size of less than or equal to 10 μm. The average particle size is measured along a direction of the greatest extent of the silicon particles. The value d50 is also called median. According to the invention, the median value of the metal particle mixture should be less than or equal to 3pm. d90 means 90% of all metal particles have a size of less than or equal to 5pm.

[0063] The invention will be explained in more detail below using exemplary embodiments.

[0064] The drawings show

[0065] Fig. 1 Example structure and function of a lithium ion cell during the discharge process;

[0066] Fig. 2 Influence of a temperature input on the silicide formation in a silicon anode a) in a classical furnace process (state of the art) b) with short-time annealing, in particular flash lamp annealing;

[0067] Fig. 3 Schematic representation of different variants of silicon on a copper substrate and the influence of a short-time annealing on the forming copper silicides;

[0068] Fig. 4 Schematic representation of a silicon and metal particle mixture on a copper substrate and the influence of short-time annealing;

[0069] Fig. 5 Schematic representation of a pre-processed substrate surface onto which a silicon and metal particle mixture is deposited and subjected to a short-time annealing;

[0070] Fig. 6 Schematic representation of a partially reacted active layer of the anode according to the invention made of Si and Cu particles.

[0071] The diffusion of metals into silicon, as well as the reaction of silicon with metals, is highly dependent on time and temperature. Even at low temperatures starting at 200°C, many metals 16 form a metal silicide 12 at the interface between metal 16 and silicon 11. This metal silicide has little, no, or only a very low reversible lithium intercalation capacity. The diffusion of metals 16 occurs very rapidly, even at room temperature and at elevated temperatures, and is difficult to control in conventional furnace processes. Using copper as an example, a complete layer of silicon is completely reacted after at most 1 s at 600°C (see Fig. 2a).

[0072] Figure 2b) shows the influence of short-term annealing 15, in particular flash lamp annealing, on the silicide formation 12 at the contact point in a layer system of copper 10 and silicon 11. Due to the very short flash pulse in the range of 0.1 to 10 ms, the silicon 11 does not completely react with the copper 10 to form copper silicide 12. The flash lamp annealing 15 leaves pure amorphous or nanocrystalline silicon 11, which is available as active material for lithium storage, while at the same time there are a sufficient number of inactive regions to ensure stability and good electrical conductivity.

[0073] Figure 3 shows various variants of silicon structures applied to a copper substrate 10 – as a homogeneous layer, as silicon particles 13, or as silicon nanowires 14. A short-term annealing 15, for example, a flash lamp annealing, leads to a controlled local reaction of the silicon 11 with the copper 10, forming copper silicide 12 at their interface. This solidly bonds the silicon to the substrate. The schematic representation shows a linear progression from pure copper 10 via copper silicide 12 to silicon 11, whereby a realistic transition is much more inhomogeneous; the boundary is significantly rougher, up to the formation of Cu / CuSi. x Dentrids in the silicon. Dentrids are tree- or shrub-like crystal structures.

[0074] Figure 4 shows the schematic representation of a silicon and metal particle mixture 20 on a copper substrate 10 and the influence of a short-time annealing 15. Silicon particles 13 are calendered together with metal particles 16, preferably copper as a powder on a copper foil 10. This is followed by a short-time annealing 15, e.g. flash lamp annealing, whereby the silicon particles 13 adhere to the substrate 10 and to one another by means of the metal particles 16, in the example Cu particles. Clean contact between the surfaces is necessary for the reaction, since oxides or organic residues prevent the desired reaction. Pretreatment with, for example, a reducing atmosphere can be helpful for this. The result is a binder-free, dry process for powder processing of 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 partially reacted particles 22 of Cu / CuSi. x / Si .

[0075] In a further embodiment according to Figure 5, the copper substrate 10 can be preprocessed, for example, with silicon nanowires 14. Silicon particles 13 are calendered together with metal particles 16, preferably copper as a powder, on a copper foil 10, wherein both the copper substrate surface 10 and the powder mixture 20 are cleaned 18, e.g., by means of a reducing atmosphere. The silicon and metal particle mixture 20 and the substrate are subjected to a short-term annealing 15, e.g., a flash lamp annealing, wherein adhesion is achieved by the reaction of the silicon particles 13 with the metal particles 16, in the embodiment in particular copper, to form partially reacted particles 22.

[0076] In a further embodiment, an anode for a lithium-ion battery is produced using the method according to the invention (see Fig. 6). First, a suitable silicon-metal particle mixture 20 is prepared, which is applied to a copper substrate 10, which later represents the current collector of the electrode. The deposited powder mixture 20 is subjected to a short-term annealing 15. The short-term annealing 15 can be a flash lamp annealing or a laser annealing. The short-term annealing 15 creates a partially reacted active layer 19 made of silicon-metal particles 20, which is fixed to the current collector 10.

[0077] Through short-term annealing 15, the energy input into the deposited layer can be specifically controlled. Depending on the particle size, mixing ratio, and layer thickness, an optimal energy input can be set. Through the defined energy input, for example, by means of flash lamp annealing 15 after a layer 21 of particles 20, a sufficient reaction occurs between / in the metal-silicon mixture 20 without the silicon 11 completely reacting, i.e., pure Si particles remain, or only insufficient active material remains. More metal 16 means more reaction possibilities but less active material. More energy means more adhesion on the current collector 10 or between the particles 13, 16, but less active material. Partially reacted particles of Cu / CuSi are formed. x / Si 22. The optimal result depends on the materials used and the particle sizes. Insufficiently reacted or enclosed Si particles 13 can be easily removed because they do not adhere. The application of the particle mixture 20 and the short-term annealing 15 can then be repeated.

[0078] After the deposition and tempering of the active layer 19, deposited e.g. by sputtering, the application of a protective layer or an artificial SEI is possible, even in vacuum processes, since no drying is required.

[0079] An advantage of the process according to the invention is that silicon 11 in powder form with a high degree of particle size variation 13 and high impurity can be used as the base material, making it correspondingly cost-effective. Smaller silicon particles 13 enable a multilayer 21 structure and thus easier adjustment of the capacity of the entire anode layer. Amorphous silicon particles 13 are preferred because the initial energy input in the first charging cycle is lower, and no energy is required to break up the Si crystal structure.

[0080] In contrast to previous slurry processes, carbon as a binder is a technical hindrance, since the process according to the invention has shown that even the thinnest carbon layers of up to 5 nm can prevent a satisfactory reaction between Si particles. A process for producing silicon electrodes as anodes for lithium-ion batteries and a silicon electrode produced thereby

[0081] List of reference symbols Lithium-ion battery Collector on anode side SEI -Sol id-Electrolyte- Interphase electrolyte separator

[0082] 6 Conductive intermediate phase Cathode, positive electrode Collector on cathode side Anode, negative electrode 0 Copper substrate 1 Silicon 2 Copper silicide; metal silicide; or boundary contact of the silicide reaction 3 Silicon particles 4 Silicon nanowires 5 Short-term annealing, e.g. flash lamp annealing 6 Copper particles; metal particles 7 Copper oxide / organic residues; impurities 8 Cleaning step 9 Active layer 0 Silicon and metal particle mixture 1 Deposited layer in the active layer 2 Partially reacted particles (e.g. Cu / CuSi x / Si)

Claims

Method for producing silicon electrodes as anodes for lithium-ion batteries and a silicon electrode produced therewith Patent claims 1. A method for producing a silicon electrode as an anode for a lithium-ion battery, in which an active layer (19) is deposited on a substrate, preferably copper, which is subsequently subjected to short-term annealing (15), characterized in that the active layer (19) is formed from a silicon and metal particle mixture (20) which is applied to the substrate (10) in a dry process and is stabilized to a partially porous active layer (19) and fixed on the substrate (10) by short-term annealing (15).

2. Method for producing a silicon electrode as an anode for a lithium-ion battery according to claim 1, characterized in that the silicon and metal particle mixture (20) is carbon-free.

3. Method for producing a silicon electrode as an anode for a lithium-ion battery according to claim 1, characterized in that particles (13, 16) of the silicon and metal particle mixture (20) are on the order of the thickness of the active layer (19) of the anode to be applied, wherein the active layer of the anode is deposited with a thickness of 1 to 30 pm. A method for producing a silicon electrode as an anode for a lithium-ion battery according to any one of the preceding claims, characterized in that the silicon particles (13) are amorphous, wherein the Si particles have a size distribution of dl0<100nm, d50<5pm, d90<10pm. A method for producing 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 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.Method for producing a silicon electrode as an anode for a lithium-ion battery according to claim 1, characterized in that the short-term tempering (15) is a flash lamp tempering and is carried out by means of a flash lamp with a flash duration in the range of 0.2 to 20ms and an energy density in the range of 0.6 to 160J / cm. 2 and / or preheating or cooling in the range of 4°C to 200°C. A method for producing a silicon electrode as an anode for a lithium-ion battery according to claim 1, characterized in that the short-term annealing (15) is laser annealing and is carried out by means of a laser with an annealing time in Range from 0.01 to 100ms by setting a scan speed of a local heating point and an energy density in the range of 0.1 to 100 J / cm² 2and / or is carried out with preheating or cooling in the range of 4°C to 200°C. 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, preferably a carbon layer and / or one or more layers of an artificial solid electrolyte interphase (SEI), is deposited onto the active layer (19). A method for producing a silicon electrode as an anode for a lithium-ion battery according to any of the preceding claims, characterized in that the parameters of the short-term tempering (15) are adjusted depending on the size of the particles (13, 16) of the silicon and metal particle mixture (20), on a mixing ratio of the silicon and metal particle mixture (20), and on the deposited layer thickness.Method for producing a silicon electrode as an anode for a lithium-ion battery according to one of the preceding claims, characterized in that the substrate (10) is prepared prior to the deposition of the silicon and metal particle mixture. (20) and / or contact surfaces between the silicon (13) and metal particles (16) are cleaned. Method for producing a silicon electrode as an anode for a lithium-ion battery according to one of the preceding claims, characterized in that the particles (13, 16) of the silicon and metal particle mixture (20) are cleaned by the Short-term tempering (15) such that a Reaction of a maximum of 25% of the active material with the substrate (10) is produced and thus a high Adhesion between the active material and the substrate (10) is ensured. Method for producing a silicon electrode as an anode for a lithium-ion battery according to claim 11, characterized in that further layers (21) of active material are deposited onto the active material to increase the capacity of the anode with high stability and electrical conductivity.An anode designed and intended for use in a lithium-ion battery and manufactured according to the method of claims 1 to 12, characterized in that the anode comprises a substrate as a current collector (10), preferably made of copper, and an active layer (19) deposited on the current collector (10), wherein the active layer (19) is formed from a silicon and metal particle mixture (20) which is applied to the substrate (10) in a dry process and stabilized to a partially porous active layer (19) by a controlled short-term annealing process (15) and fixed to the substrate (10). An anode according to claim 13, characterized in that 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 of these materials. Anode according to claim 13, characterized in that the active layer of the anode has a layer thickness of 1 to 30 pm. Anode according to claim 13, characterized in that the substrate is configured as an open copper grid, wherein the active layer is applied to the open copper grid. Anode according to claim 13, characterized in that the substrate is configured as a sacrificial substrate, wherein the active layer is applied to the sacrificial substrate and subjected to short-term annealing, wherein the sacrificial substrate is removed and the active layer has a specific electrical conductivity of greater than 1*10 4S / cm and the active layer is contactable from one side. Metal particle mixture for producing an anode according to claims 15 to 17 using a method according to claims 1 to 12, wherein the metal particle mixture has a size distribution of dl0=100nm, d50=3pm, d90=5pm.

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