EP4385081A2 - Method for producing partially reacted silicon for the control of the lithium intercalation capacity, for use in lithium batteries - Google Patents

Abstract

The invention relates to a method for producing partially reacted silicon for the control of the lithium intercalation capacity, for use in lithium batteries, wherein a first silicon layer is deposited on a substrate, the first silicon layer subsequently being subjected to rapid thermal processing. The invention also relates to an anode thereby produced. The problem addressed by the present invention of specifying a method that allows control of the capacity of ion intercalation into functional layers for battery production is solved in that a layer of silicon, metal and/or another material is applied as a diffusion barrier, which is subjected to subsequent rapid thermal processing, and partially reacted silicon is formed. (The structure of the diffusion barrier makes the diffusion barrier permeable to lithium.)

Description

Process for preparing partially reacted silicon for controlling lithium storage ability for use in lithium batteries

The invention relates to a method for producing partially reacted silicon to control the lithium storage capability for use in lithium batteries, in which a first silicon layer is deposited on a substrate and is then subjected to short-term tempering.

The invention also relates to an anode that is suitable for use in a lithium battery and is produced using the method according to the invention.

The invention also relates to the use of the method for functional layers in aluminum ion batteries and the use of the method for the production of partially reacted silicon to control the ion intercalation ability in the production of sodium and magnesium batteries.

Electrochemical energy storage is an essential cornerstone of an energy turnaround aimed at worldwide, in order to temporarily store the fluctuating regeneratively generated electricity and to make it available for stationary and mobile applications. In order to counteract a shortage of raw materials and thus an increase in costs, especially for secondary batteries, new materials are required in addition to the diversification of energy storage concepts. On the one hand, these should improve the technical performance of corresponding energy storage concepts (e.g. capacity, energy density, service life), on the other hand they should also minimize the production costs. The latter can be guaranteed in particular through the use of readily available chemical elements, such as silicon, for which there is already a broad technological basis.

Batteries are electrochemical energy stores and are divided into primary and secondary batteries.

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 known as accumulators, on the other hand, are rechargeable electrochemical energy stores in which the chemical reaction taking place is reversible, so that multiple use is possible. Electrical energy is converted into chemical energy when charging, and from chemical energy to electrical energy when discharging.

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

Each Li-ion cell 1 consists of two different electrodes 7, 9, an electrode 7 which is negatively charged when charged and an electrode 9 which is positively charged when charged. Since ions migrate from the negatively charged electrode to the positively charged electrode during energy delivery, i.e. during discharge, the positively charged electrode is called cathode 7 and the negatively charged electrode is called anode 9 . The electrodes settle each composed of a current conductor 2, 8 (also called collector) and an active material applied thereto. Located between the electrodes are 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. Transition metal oxides with cobalt (Co), manganese (Mn) and nickel (Ni) or aluminum oxide (AI2O3) are the most common compounds. The applied metal oxide layer serves to store the lithium ions when the cell is discharged.

The anode of the Li-ion cell can consist of a copper foil as the collector and a layer of carbon as the active material. Natural or artificial graphite is usually used as the carbon compound because it has a low electrode potential and low volume expansion during charging and discharging. During the charging process, lithium ions are reduced and embedded in the graphite layers.

In lithium-ion battery designs, the cathode typically supplies the lithium atoms for charging and discharging in the anode, so the battery capacity is limited by the cathode capacity. As already mentioned, typical cathode materials previously used are e.g. B.

Li(Ni,Co,Mn)O2 and LiFePO.}. Due to the construction of the cathode with lithium metal oxides, an increase in capacity is only possible to an insignificant extent.

It is also known to use silicon instead of carbon in Li battery anodes. silicon as Anode material has a high storage capacity of theoretically about 3579 mAh / g for the Li ₁₅ Si4 phase at room temperature compared to conventional carbon-like materials such. B. graphite with a storage capacity of 372 mAh / g. However, challenges in the use of silicon as anode material arise with regard to the sometimes considerable change in volume (volume contraction and expansion) of the host matrix during storage and removal of the mobile ion species during charging and discharging of corresponding energy stores. The volume change is about 10% for graphite, but about 400% for silicon. The change in volume of the anode material when using silicon leads to internal stresses, cracking, pulverization of the active material of the host matrix (silicon) and finally to the complete destruction of the anode.

Silicon can only be applied directly to metal substrates such as copper foils if there is no temperature step in the further process, as this leads to a reaction of the silicon with the metal substrate. The layers in classic annealing steps react completely by forming silicides, so that they are no longer actively suitable for lithium or generally for clay storage.

The diffusion of metals in silicon and the reaction of silicon with metals is strongly dependent on time and temperature. At temperatures as low as 200°C, a metal silicide is formed with many metals that has one, no or only a very low reversible lithium intercalation capacity. The diffusion of metals takes place very quickly even at room temperature and at elevated temperatures and can only be achieved in classic furnace processes difficult to control. Using the example of copper, a complete layer of silicon has fully reacted after 1s at the latest at 600° C. (see FIG. 2a). Diffusion and reaction can be delayed by installing diffusion barriers. However, since typical furnace processes are very sluggish compared to the diffusion rate, the requirements for the diffusion barriers are very high. A high layer thickness, non-conductive layers or multilayers with many interfaces are examples of how to achieve a good barrier effect even at high temperatures. In the semiconductor industry z. B. uses a special layer of NiSi _x as a diffusion barrier, but its production involves several process steps and is therefore expensive. Other suitable conductive copper diffusion barriers are, in particular, tungsten (W), tantalum (Ta) and titanium (Ti) and their conductive nitrides and silicides.

WO 2017/140581 A1 describes a method for producing silicon-based anodes for secondary batteries, in which a silicon (Si) layer is deposited on a metal substrate, which serves as an integrated current conductor, and is then subjected to flash lamp annealing. Typically, a flashlamp process is used to rapidly and locally melt and crystallize silicon, e.g. B. for solar cells. However, that is not the aim of the method described in WO 2017/140581 A1. Instead, flash lamp tempering is used to the following extent: In general, crystallization of the silicon can only be brought about at approx. 700°C. After flash lamp annealing, these Si atoms are free atoms and can already at lower temperatures, from approx. 200°C, diffuse along the grain boundaries of the metal substrate, since the covalent bonding of the Si atoms is weakened at the interface to a metal. This has already been demonstrated for several metal/semiconductor systems (e.g. Au/a-Si and Ag/a-Si) and found to be energetically favored, as in the paper ZM Wang, JY Wang, LPH Jeurgens, EJ Mittemeijer: Thermodynamics and mechanism of metal-induced crystallization in immiscible alloy systems: Experiments and calculations on Al/a-Ge and Al/a-Si bilayers, Physical Review B 77, 045424 (2008). In addition, the silicon can be crystallized by introducing metal at a comparatively low temperature. This is referred to as metal-induced crystallization. To put it very simply, crystalline growth can begin after falling below the melting temperature, which can be used as a criterion for the phase transformation. With the method described in WO 2017/140581 A1, multi-phase silicon-metal structures can be produced which cushion the volume change brought about by delithiation and lithiation and ensure stabilization of the entire material composite. Under the lithiation the incorporation of the lithium ions in the host material, z. B. understood the silicon or graphite.

The Si anodes that can be produced using the method known from WO 2017/140581 A1 are a mixture of silicon, pure metals and silicides if only a copper (Cu) foil is used as the substrate and on which a silicon layer is deposited, ie it a structure of copper, copper silicide and silicon is formed. The advantages of Si anodes produced in this way compared to Si anodes Nanoparticles or nanowires have a high electrical conductivity compared to pure silicon and also conventional graphite, since silicides have an approx. have two orders of magnitude better electrical conductivity than graphite. Furthermore, a very good adhesion between the Si layer as active material and the copper substrate is achieved, with the copper from a copper foil being grounded in the deposited Si layer by the flash lamp annealing. Due to the active areas for the lithium intercalation, which are formed by the pure silicon and the inactive areas, which are formed by the silicides/metals in the matrix, the well-known disadvantageous volume expansion during charging is compensated. It is also advantageous that due to the layer structure, only a small area forms a boundary layer to the electrolyte, with the small surface area resulting in less electrolyte decomposition than with nanostructured active material.

A disadvantage of the method described in WO 2017/140581 A1, however, is that as a result of the flash lamp annealing, the Si layer reacts in an uncontrolled manner to form copper silicide, with the conversion reaction always beginning at the Cu-Si layer interface. As a result of the reaction, either no silicon remains as an active material for the storage of the lithium, or if the energy input is so low, an insufficient reaction takes place and the layer is not sufficiently stable during battery operation, thus leading to a loss of battery capacity. Sufficiently thick Si layers (up to 10 pm) are necessary for a sufficient target capacity in the production of the lithium battery. Becomes the conversion reaction from Cu + Si to copper silicide is set in motion in an uncontrolled manner by an annealing process, including flash lamp annealing, which would damage the entire copper substrate, e.g. B. a copper foil, react with the silicon completely to form copper silicide and result in the loss of the lithium battery's current collector. It is therefore not possible to produce stable structures and anodes with a high surface storage density using the method described in WO 2017/140581 A1.

It is therefore the object of the present invention to specify a method that allows control of the ion storage capacity in functional layers for battery production. For lithium-ion batteries in particular, it should be possible to adjust the proportions of silicon to silicide and metal in a controlled manner, i .e . H . a method for producing partially reacted silicon would be advantageous. A compromise should be found between the maximum proportion of pure silicon, in the best case amorphous or nano-crystalline, that must be available as the active material for lithium intercalation, while at the same time having a sufficient number of inactive areas to ensure stability and good electrical conductivity achieve, and with a sufficient anode layer thickness with a high proportion of silicon to ensure a high capacity.

The object is solved by a method according to independent claim 1 .

In the method for producing partially reacted silicon for controlling lithium storage ability for use in lithium batteries, in which on a substrate a first silicon layer is deposited, which is then subjected to short-term annealing, according to the invention a layer of silicon, metal and/or another material is applied as a diffusion barrier, which is subjected to subsequent short-term annealing and as a result a layer of partially reacted silicon is formed. The deposition and the short-term annealing are repeated once more, so that a multi-layer structure made of partially reacted silicon is formed.

Short-term tempering is understood to mean, in particular, flash lamp tempering and/or laser tempering. The flash lamp annealing takes place with a pulse duration or annealing time in the range from 0.3 to 20 ms and a pulse energy in the range from 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 site to produce an energy density of 0.1 to 100 J/cm ² . The heating ramps achieved in the short-term tempering are in the range of 10 ^A 4-10 ^A 7 K/s required for the process. Flashlamp annealing uses a spectrum in the visible wavelength range for this, whereas laser annealing uses discrete wavelengths in the infrared (TR) to ultraviolet (UV) spectrum.

The sequence of the layers results in a total layer thickness of the multi-layer structure of typically 4-15 μm made of partially reacted silicon, which is sufficient for battery operation. Under partially reacted silicon for the purposes of the invention, a layer is understood, the areas of pure silicon, in amorphous or nano-crystalline at best, and regions of corresponding silicides formed by partial to complete reaction with the metal.

A layer within the meaning of this invention is understood to be a layer sequence made of silicon, a metal and/or another material that serves as a diffusion barrier, which together result in a defined, partially reacted silicon layer, which is formed by short-term annealing. A layer is therefore a layer sequence that results in a defined, partially reacted silicon/silicide layer. The diffusion barrier limits the amount of metal supplied externally, the amount of metal supplied in the layer is available for a defined reaction with the silicon supplied in this layer. A silicide layer that is formed can already serve as a sufficient diffusion barrier to prevent further reaction with silicon, which means that an additional diffusion barrier made of another material that is different from the metal is not absolutely necessary. The diffusion rate of metals in silicides is then lower than in silicon.

Diffusion and silicide formation in a layer can be controlled with short-time annealing, so that silicide formation proceeds gradually perpendicular to the surface. This is advantageous for adhesion of the Si layer to copper foil, since silicide is partially formed and active silicon is still available. Process control during short-term tempering can be improved by using suitable diffusion barriers. A time delay in diffusion Passing through a barrier allows a higher process control in the time interval of the energy input of the short-time annealing. In contrast to classic diffusion barriers, the diffusion of metal atoms should only be weakened to the extent that a significantly reduced diffusion occurs in the time window of the energy input of the short-term annealing, in contrast to the diffusion of the metal atoms in silicon. Accordingly, the design and thickness of the diffusion barrier is greatly simplified in the method according to the invention, as a result of which material and process time can be saved.

At the same time, the diffusion of lithium is not reduced, or only to a small extent, and is therefore suitable for use in a lithium-ion battery. A suitable diffusion barrier is thus understood to be a barrier which locally weakens the diffusion, in particular of copper, during short-term annealing and inhibits silicide formation, but at the same time allows lithium to diffuse.

In one embodiment of the method, a diffusion and reaction of metal with the silicon in a flash lamp annealing by a pulse duration in the range of 0.3 to 20 ms, a pulse energy in the range of 0.3 to 100 J / cm ² and a preheating or Cooling is controlled in the range of 4°C to 200°C of the flash lamp annealing and thus produces partially reacted silicon in every layer.

If laser annealing is used as short-term annealing, diffusion and reaction of metal with the silicon is achieved by an annealing 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 up to 100 J/cm ² as well as preheating or cooling in the range of 4 °C to 200 °C of the laser annealing is controlled and thus partially reacted silicon is produced in every layer. External cooling has the effect that the cooling of the substrate is better controlled. Otherwise, undesirable reactions outside the annealing area can occur.

The metal can be the copper from a copper substrate on which the multilayer structure for producing the active layer of an anode for lithium batteries is deposited. The diffusion of copper in a silicon layer can be controlled by the adjustable pulse duration, pulse energy and preheating or cooling of the flash lamp tempering. A gradual course without a complete reaction of the layer is possible. A high concentration of copper can be measured in the area of the Cu foil, which gradually disappears up to the surface of the deposited layer. Correspondingly, in the area of the Cu foil, a large part has reacted to form copper silicide. A chemical reaction takes place in the border area, which greatly improves the adhesion of the layer. Due to the high proportion of silicide, less/no lithium is stored, which means that the volume expansion is lower and the stress at the interface is significantly reduced. With the gradual build-up of the layer, the stress of volume expansion during lithium intercalation is evenly distributed in the layer. A single-layer Si layer treated with short-term annealing shows a greatly improved cycle stability with almost the same utilization of the Li storage capacity compared to untreated layers. A cycle is a complete charging and discharging of a battery understood. The lifespan of a battery is linked to the number of cycles. The disadvantage, however, is that subsequent annealing steps allow the layer to continue to react and the structure is therefore limited to one annealing step or only a few layers. This disadvantage can be circumvented or adapted to the target thickness of the overall layer by using suitable diffusion barriers as intermediate layers. Suitable copper diffusion barriers are listed below.

In another embodiment of the method according to the invention, a diffusion and reaction of metal from the substrate with the silicon is controlled by a previously applied diffusion barrier.

So that the multilayer structure applied to the substrate does not react in an uncontrolled manner with the metal, for example copper, to form silicide, a diffusion barrier can be applied as the first layer on the substrate. This has a sufficient barrier effect, so that z. B. in a flash lamp annealing by the flash energy, the flash duration or minimal thickness adjustments of the diffusion barrier layer, the diffusion and reaction of the metal atoms from the substrate with the silicon can be controlled.

In another embodiment of the method according to the invention, the layers are deposited by means of physical vapor deposition, e.g. B. sputtering or evaporation or by means of chemical vapor deposition.

The planar deposition by z. B. sputtering or evaporation or by means of chemical vapor deposition allows the layered introduction of diffusion barriers without Extra effort. In contrast to diffusion barriers for classic annealing processes, there are only lower requirements for the diffusion barriers in short-term annealing, the diffusion only has to be sufficiently impeded instead of being completely prevented, as described above. Correspondingly, the thinnest barriers of suitable elements and compounds, such as carbon, nitrides, oxides, metals, are sufficient to enable stable process control in the method according to the invention (stable process window). As a result, several annealing steps are possible with only a small change in the layer structure. A layer in the method according to the invention is understood synonymously for a layer stack made of Si, metal and/or a diffusion barrier made of another material; a layer in the sense of the invention thus consists of sub-layers of a layer stack. Several layers form a multi-layer structure.

In a further embodiment of the method according to the invention, the diffusion barriers are made of one of the materials titanium (Ti), nickel (Ni), aluminum (Al), tin (Sn), gold (Au), silver (Ag), molybdenum (Mo), tungsten (W), carbon (C) and / or mixtures of these materials applied.

In another further embodiment of the method according to the invention, a volume expansion of the silicon in each layer of the multilayer structure is controlled by the partially reacted silicon, with a gradual progression from a high silicide concentration on the side of the multilayer structure facing the substrate to a low silicide concentration on the the side of the multilayer structure facing away from the substrate is set. The gradual progression is gradually approximated by the multi-layer structure. For the silicon in each layer of the multi-layer structure or the multi-layer construction and the subsequent short-term tempering, a reaction Si with the existing metal/copper that is as final as possible is aimed at. As a result, the concentration of metal/copper is reduced with each layer, and almost (<5%) metal-free/copper-free silicon is built up as the last layer of the multilayer structure.

In one embodiment of the method according to the invention, a reaction of metal and silicon to form silicide is controlled across layers by introducing diffusion barriers into a layer to be deposited, and the frequency of short-term annealing can be reduced as the number of layers increases.

A diffusion barrier is inserted after each layer of silicon. This corresponds to the AND link in independent claim 1. It is thus possible to reduce the energy input by reducing the number of short-term temperings. In this way, a gradual structure can also be generated and produced by a maximum possible sequence of layers with only a short-term tempering at the end of the multi-layer structure.

In one embodiment of the method according to the invention, an adjustable amount of metal, in particular copper, nickel, aluminum, titanium, magnesium and/or tin, is inserted into each layer of silicon, metal and diffusion barrier to be deposited in order to produce partially reacted silicon in the entire multilayer structure. The goal and benefit of an adjustable amount of metal in each layer of the Adding to multilayer construction is the creation of a conductive matrix in which silicon is embedded. Furthermore, it serves to increase the conductivity of silicon as a dopant. As a side effect of the partial reaction with silicon to form a non-lithium-reactive silicide/composite, there is a reduction in the lithium storage capacity, but this reduces the critical volumetric expansion of silicon during lithium incorporation. If the first deposited layer of silicon, metal and/or diffusion barrier on the substrate is treated with short-term annealing, there may be no copper from the substrate available for a subsequently deposited layer to form silicide. The adjustable amount of a metal, especially Cu, Ni, Al, Ti, Mg and/or Sn, is added to ensure partially reacted silicon in each layer in a variety of layers. The amount of metal can be varied based on the amount of Si to also produce a gradual build up. The short-term annealing takes place after one or more layers have been deposited in order to ensure a reaction in these layers.

Nickel, for example, can be deposited as the metal. Nickel reacts with silicon to form nickel silicide and at the same time represents a diffusion barrier for copper. This means that the manufacturing process can be simplified with fewer individual steps. A gradual build-up of a partially reacted silicon layer can also be realized with nickel.

The multiple short-term annealing allows the build-up of thick layers of an active layer with silicon for a high ability to store lithium. The control of Diffusion with the help of the layer structure enables completely new variants of the layer structure. Any functional layers can be built up and specifically adjusted to the properties required for stable battery operation through short-term tempering. For example, the diffusion of Cu in silicon can be inhibited by means of sputtered carbon, whereas deposited CuaSi can also increase the diffusion of Cu in silicon. Optimizations for other purposes such as other types of batteries (aluminum ion batteries (Al), sodium (Na) or magnesium (Mg) batteries, etc.) as well as thermoelectrics are also possible due to the high flexibility.

The method according to the invention can therefore advantageously be used to produce functional layers in an aluminum ion battery, for thermoelectrics and/or for sodium or magnesium batteries.

The multiple short-term tempering enables a targeted addition of metal, e.g. B. copper into the silicon, so that layers with defined concentrations can be produced by targeted silicide formation and the storage capacity of lithium in silicon can be adjusted. Other metals such as Ti, Ni, Sn, Al, W, Mo, C or mixtures of these are possible depending on the requirements. A gradual build-up layer by layer is therefore possible.

The object of the invention is also achieved by an anode according to independent claim 12.

The anode is suitable for use in a lithium battery and is manufactured using the method according to the method claims. The anode according to the invention has a current collector, preferably made of copper and a multilayer structure deposited on the current collector, which forms an active layer of the anode, the multilayer structure comprising at least a first partially reacted silicon layer consisting of silicon, a metal and/or another material, which is subjected to short-term annealing, and a second partially reacted silicon layer , which consists of silicon, a metal and/or another material, which is also subjected to short-term annealing.

The first applied silicon layer with subsequent short-term annealing can advantageously function as an adhesive layer by completely reacting the first silicon layer with the copper of the current collector to form copper silicide, thereby reducing the roughness of the current collector, e.g. B. a Cu foil, is increased, a high adhesion is produced and the silicon layer reacted with the copper serves as an adhesive layer for the further layer structure. The copper silicide layer has reacted completely, so that the applied diffusion barrier consists of another material, e.g. B. made of carbon also guarantees a sufficiently stable diffusion barrier during the subsequent process steps. This diffusion barrier is necessary in order to prevent the reaction of silicon in copper to form copper silicide during a further short-term annealing, in particular flash lamp annealing and/or laser annealing. The subsequently sequentially applied further Si, metal and/or diffusion barrier layers made of a further material are stabilized by a further short-time annealing. The anode according to the invention for a lithium battery has a high Storage capacity of up to 4mAh/cm ² or up to 6mAh/cm ² .

In one embodiment of the anode according to the invention, volume expansion of the silicon of the multilayer structure can be controlled by the partially reacted silicon layer when lithium is embedded, with a gradual progression from a high silicide concentration on the side of the active layer facing the current collector to a low silicide concentration on the side of the active layer facing away from the current collector Side of the active layer of the anode is formed and due to the proportion of metal in the multilayer structure, a high electrical conductivity is formed in the active layer of the anode. Good electrical conductivity is understood to mean a specific resistance in the graphite range of 3*10 ^-3 ohm cm, high conductivity is understood to be a specific resistance lower than that of graphite up to pure copper silicides of (10 to 50)*10 ^-6 ohm cm understood .

The gradual progression of a layer is gradually approximated by the multi-layer structure. In this case, for each layer of Si and subsequent short-term annealing, a possible final reaction of Si with the metal present, e.g. B. copper is sought. As a result, the concentration of copper is reduced with each layer, and the last layer is almost (<5%) copper-free silicon.

The amount of metal, which in particular can be copper, nickel, aluminum, titanium, magnesium and/or tin, can be adjusted in each deposited layer of silicon, metal and diffusion barrier in order to produce partially reacted silicon in the entire multilayer structure. The The aim and the advantage of being able to adjust the amount of metal added to each layer of the multilayer structure is the creation of a conductive matrix in which silicon is embedded. The set amount of metal serves to increase the conductivity of silicon as a dopant. Although the partial reaction with silicon to form a non-lithium-reactive silicide/composite leads to a reduction in the lithium storage capacity, this reduces the critical volumetric expansion of silicon during lithium intercalation.

In a further embodiment of the anode according to the invention, the further material forms a diffusion barrier, the diffusion barrier being made from one of the following materials: titanium (Ti), nickel (Ni), aluminum (Al), tin (Sn), gold (Au), silver (Ag) , Molybdenum (Mo), tungsten (W), carbon (C) and their nitrides and silicides and / or mixtures of these materials is formed.

The anode according to the invention can have a diffusion barrier after each layer of silicon. This makes it possible to reduce the energy input by reducing the number of short-term temperings during the production of the anode. A gradual build-up of the active layer of the anode can also be produced by a maximum possible sequence of layers with only one short-time tempering. For example, nickel can be used as a diffusion barrier. Nickel reacts with silicon to form nickel silicide and at the same time represents a diffusion barrier for copper. An anode constructed in this way can be manufactured in fewer individual steps.

In another embodiment of the anode according to the invention the anode has a gradual profile of a metal concentration from a high concentration on the side of the active layer facing the current collector to a low concentration on the side of the active layer of the anode facing away from the current collector. The non-active area in the heterogeneous structure of the overall layer includes at least the concentration of a copper-3-silicide (CuaSi) through CuSi to pure copper. Below the concentration of CuaSi one speaks of a silicon with a high to very high copper concentration. The typical value of metallurgical silicon with ~3% metal is understood as the lower limit for silicon with a high metal concentration. A value of less than 0.1% metal in silicon is referred to as silicon with a low metal concentration.

In another further embodiment of the anode according to the invention, the anode has a gradual progression of a metal concentration in one layer of the multilayer structure, areas with a high silicide concentration forming adhesion and stability of the active layer and areas with a low silicide concentration and high Proportion of silicon have a high lithium storage capacity. A high silicide concentration means a proportion of more than 50% silicide-capable, whereas a low silicide concentration means a proportion of less than 10% silicide-capable.

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

The drawings show 1 exemplary structure and function of a lithium ion cell during the discharging process;

2 Influence of a temperature input on the silicide formation in a silicon anode a) in a classic oven process (prior art) b) with short-time annealing, in particular flash lamp annealing;

3 a) process flow diagram of the method according to the invention; b) Schematic representation of the method according to the invention for checking the ability of lithium to be stored by targeted short-term annealing, in particular flash lamp annealing of functional layers for battery production; c) formation of a gradual progression of the silicide formation according to the method according to the invention;

4 Schematic representation of a multi-layer structure according to the method according to the invention for the production of partially reacted silicon for controlling the lithium storage capability: a) single layer and multi-layer structure composed of several layers of silicon, metal and diffusion barriers; b) Influence of the short-time annealing process parameters and the thickness of the diffusion barrier on the gradient of the silicon/silicide concentration in a layer;

5 a) Schematic representation of the multilayer structure as the active layer of the anode according to the invention; b) Gradual course of the silicide concentration adjusted by a controlled addition of metal, e.g. B. copper in each layer of the multilayer structure separated by diffusion barriers; c) Gradual progression of the metal concentration in each layer of the multilayer structure without diffusion barriers;

6 shows a schematic representation of the gradual progression of the silicon concentration or metal concentration or silicide concentration on a copper substrate: a) within a single layer; b) without and c) with diffusion barriers between the individual layers;

Fig.7 SEM image of a multilayer structure without diffusion barriers.

FIG. 2b) shows the influence of the short-term annealing, in particular flash lamp annealing, on the silicide formation in a layer system made of copper and silicon. Due to the very short lightning pulse in the range of 0.1 to 10 ms, the silicon does not react completely with the copper to form copper silicide. Flashlamp annealing leaves pure amorphous or nano-crystalline silicon available as the active material for lithium intercalation, with sufficient inactive areas to ensure stability and good electrical conductivity.

FIG. 3a) shows the method steps according to the invention in a flow chart and FIG. 3b) shows the sequence of the method steps based on the anode structure produced in comparison to a classic furnace process in the left-hand part of FIG. 3c). A substrate 14, which also serves as a current collector in a LIB (lithium-ion battery), undergoes a pre-cleaning 13 under vacuum conditions in a plasma atmosphere. This cleaning is necessary because an oxidation layer 15 forms on the substrate 14 in air, which causes a reaction between a subsequently applied silicon layer 16 and the copper substrate 14 during flash lamp annealing (FLA - flash lamp annealing ) would prevent and the silicon layer 16 would thus not adhere to the Cu substrate. A first silicon layer 16, e.g. B. by sputtering. This first silicon layer 16 reacts with the Cu substrate 14 in a transition region to copper silicide 17, thereby reducing the roughness of the substrate 14, e.g. B. a Cu foil, is increased and the reacted with the copper silicon layer serves as a kind of adhesive layer for the further layer structure. The copper silicide layer 17 is completely inactive in a battery, so that in a subsequent step a diffusion barrier 18, e.g. B. is applied from carbon. This diffusion barrier 18 is necessary in order to prevent the reaction of silicon in copper to form copper silicide during further flash lamp annealing. Further Si layers 19 can then be applied sequentially, the layers, which are each formed from silicon and a diffusion barrier layer, being stabilized by flash lamp annealing 11 . The advantage of the repeated Si deposition and subsequent flash lamp annealing 11 is that with each sequence a stable ("reacted") layer forms with a closed interface, which acts as an intermediate layer (interface) for the subsequent layers. This is advantageous for the adhesion of the Si layer on copper foil, since copper silicide is partially formed and active silicon is still available. The The method according to the invention described thus additionally causes a roughening of the surface, so that good adhesion is produced for further layers. The growth of columnar structures is also promoted, so that better ion conductivity is achieved and the copper content for subsequent processes can be well controlled.

After a repeated deposition of silicon, metal and/or diffusion barriers made of another material and subsequent short-term annealing, in particular flash lamp annealing, the diffusion and silicide formation in a layer can be controlled so that a gradual course of silicide formation occurs perpendicular to the surface leaves. This is shown in FIG. 3c) in comparison to a classic furnace process. The Cu substrate 14 with the deposited Si layers 16, 19 and the diffusion barrier 18 is heated in a furnace process. The diffusion barrier 18 made of carbon or nickel, for example, does not have a sufficient barrier effect, so that all of the silicon reacts with the copper to form copper silicide 17.

The situation is different with short-term tempering of the layer using a flash lamp or laser. By introducing suitable diffusion barriers 18, process control during flash lamp or laser annealing can be greatly improved. The copper silicide formation can be gradually adjusted by adjusting the flashlamp energy, the flashlamp duration or the annealing time, by adjusting a scanning speed of a local heating spot and an energy density using a laser and/or by minimally adjusting the thickness of the deposited silicon layer or diffusion barrier, this is in Fig. 3c) shown on the right side. The use of diffusion barriers 18 in connection with the short-term annealing, in particular flash lamp annealing and/or laser annealing 11 is suitable for controlling the ion incorporation in the manufacture of batteries.

A further exemplary embodiment is shown in FIG. 4. FIG. 4a) shows a single layer 21 made of a copper or generally metal layer 20, a silicon layer 16 and a diffusion barrier 18. Each layer 21 can be treated with a short-term tempering 11, so that the silicon 16 and converting the metal 20 to a silicide 17, with the adjustment of the parameters of the short-time annealing process 11 forming a gradual course of the silicide/silicon concentration in a layer. Several layers 21 form a multi-layer structure 22.

The gradual progression of the silicide/silicon concentration in a layer 21 can be set on the one hand by the selected process parameters of the short-time annealing process 11 and on the other hand by the thickness of the deposited diffusion barrier 18. This is shown schematically in FIG. 4b). The higher the energy input z. B. is selected by the flash lamp or the laser 11, the more metal atoms can diffuse into the silicon layer 19 during the short-term annealing process, ie the lower the gradient of the silicide / silicon concentration in the position (compare Fig. 4b) left and middle Illustration) . A low gradient means that the concentration of silicide in a layer or in the active layer of the anode gradually increases from the side of the layer/active layer facing the current collector to the side of the layer/active layer facing away from the current collector decreases. A high gradient means the silicide concentration decreases rapidly. If the thickness of the diffusion barrier 18 is increased with the short-term annealing process parameters remaining the same, the gradient within the deposited layer increases, since fewer metal atoms can diffuse through the diffusion barrier 18 into the deposited layer during the short-term anneal, i.e. the concentration decreases over a shorter distance perpendicular to the Layer surface/active layer . A high silicide concentration forms on the underside of the layer, which rapidly decreases, with only silicon still being present on the upper side, ie the side of the layer/active layer facing away from the current collector. The pure silicon is available for lithium intercalation, while silicide formation increases electrical conductivity.

The gradual course z. B. the copper concentration in a silicon layer with a copper layer is set by adjusting the pulse duration, the preheating or cooling of the layer structure and a layer thickness of the deposited layers, d. H. by adjusting the energy input (over time and temperature) and the thickness ratio of the silicon layer to the copper layer, whereby the average reaction depth e (diffusion length) should be smaller than the layer thickness of the silicon layer in order to provide enough unreacted silicon for lithium intercalation.

FIG. 5 shows the schematic representation of the multilayer structure as the active layer of the anode according to the invention in different exemplary embodiments. In Fig. 5a) there is a layer 21 of silicon 16, 19, metal 20, 23 and a diffusion barrier 18. This is subjected to short-term tempering 11. Several layers 21 and several Kurzzeittemperungen 11 form a multi-layer structure 22, the layers by a diffusion barrier 18, z. B. of carbon are separated, and wherein additional metal 20 is introduced into the further layers. Each layer is then subjected to short-term tempering 11 . The gradual course of the silicide concentration within each layer is clearly recognizable starting from layer metal 20.

FIG. 5b) shows, in addition to FIG. B. made of carbon. In addition, another layer of metal 23, e.g. B. Aluminum introduced. This allows the gradual course and the metal/silicon reaction to be further refined in each layer.

FIG. 5c) shows the same structure of a multilayer structure 22 as in FIG. 5b), with the difference that no diffusion barriers 18 separate the individual layers 21 in the multilayer structure 22 from one another. The gradation is controlled by the thickness of the metal layers 20 and 23 inserted. An SEM image showing an exemplary structure made of Si/Cu/Si/Al/Si/Cu/Si/Al/Si is shown in FIG. 5d). The intermediate layers are no longer clearly visible; after a flash lamp anneal, the copper reacts with the silicon to form CuSi _x , which can be seen as broad bright areas. The aluminum "dissolves" in silicon. The result is a highly conductive, multi-part, stable multi-layer structure with a high proportion of silicon, i.e. high battery capacity Copper substrate 14 has formed an adhesion layer 24 of CuSi _x with carbon which provides continuity of electrical contact.

Figure 6 shows the schematic representation of the generation of a gradual profile of the silicon concentration or metal concentration or silicide concentration on a copper substrate: Fig. 6a) shows a single layer of silicon with a Si thickness in which the reaction of silicon and metal to form a Silicide is still controllable through the choice of flashlamp process parameters. The layer thickness here is limited to the maximum thickness of silicon that is process-technically stable before flash lamp annealing, typically Ipm. Fig. 6b) shows the generation of the gradual curve starting from a copper substrate with a single layer of silicon, which after flash lamp annealing 11 has completely reacted to form a copper silicide (Fig. 6b-1), then an additional silicon layer 19 is deposited (Fig. 6a-2), which then reacts to a less pronounced silicide layer after flash lamp annealing 11 (FIGS. 6a-3), a concentration gradient can already be seen here. After further depositions of silicon layers and flash lamp annealing 11, an almost gradual progression is created in the multilayer structure (FIGS. 6a-4).

6c) shows the generation of a gradual progression of the silicon concentration or metal concentration or silicide concentration on a copper substrate with diffusion barriers 18, several silicon layers 19 and flash lamp annealing 11 between the individual layers. Here, the reaction and the degree as well as the amount of silicidation can be adjusted in any position compared to FIG. 6b). control much more specifically in order to create a gradual build-up. With increasing distance within the active layer perpendicular to the surface of the copper substrate 14, the concentration of silicon increases and the concentration of silicide decreases. By setting and adjusting the flash lamp annealing process parameters, the gradients can be specifically adjusted starting from one or more layers of silicon. In contrast to FIG. 6a), the multi-layer structure from FIGS. 6b)-4 and FIG. 6c)-3 has the advantage of better control of the transition from silicide

17 to silicon 19 and enables the construction of larger layer thicknesses.

FIG. 7 shows an SEM image of a multilayer structure 22 made of Si/Cu/Si/Cu etc. without diffusion barriers 18 between the individual layers. Only a thin diffusion barrier was applied to the substrate as an adhesive layer.

List of reference symbols Lithium-ion battery Collector on the anode side SEI-Sol id-Electrolyte- Interphase Electrolyte Separator Conductive intermediate phase Cathode, positive electrode Collector on the cathode side Anode, negative electrode Sputtering of the Si layer Flash lamp annealing Repetition of the process steps Plasma pre-cleaning Substrate Oxidation layer First silicon layer copper ersilicide; Metal silicide Diff fusion barrier Additional silicon layer Metal layer Single layer Multilayer structure Additional metal layer Adhesive layer

Claims

32 Process for the production of partially reacted silicon Lithium storage capability control for use in lithium batteries Expectations . Method for the production of partially reacted silicon for controlling the lithium storage capability for use in lithium batteries, in which a first silicon layer (16) is deposited on a substrate (14), which is then subjected to short-term annealing (11), characterized in that a Layer (21) made of silicon, metal and/or another material is applied as a diffusion barrier (18), which is subjected to a subsequent short-term tempering (11) and partially reacted silicon is formed. . Process for the production of partially reacted silicon for controlling the lithium intercalability according to claim 1, characterized in that the deposition and the short-time annealing (11) are then repeated a further time, so that a multi-layer structure (22) of partially reacted silicon is formed. . Method for the production of partially reacted silicon for controlling the lithium intercalation ability according to claim 1, characterized in that a diffusion and reaction of metal (20, 23) in a flash lamp annealing (11) with the silicon (16, 19) by a pulse duration in the range of 0.3 to 20 ms, a pulse energy in the range from 0.3 to 100J/cm ² and preheating or cooling in the range from 4 °C to 200 ° C flash lamp tempering (11) is controlled and thus partially reacted silicon is generated in each layer (21). Process for the production of partially reacted silicon for controlling the lithium intercalability according to claim 1, characterized in that a diffusion and reaction of metal (20, 23) during laser annealing (11) with the silicon (16, 19) by an annealing time in the range of 0.01 to 100 ms by setting a scanning speed of a local hot spot and an energy density in the range of 0.1 to 100 J/cm ² and a preheating or cooling in the range of 4°C to 200°C of the laser anneal (11). is and thus partially reacted silicon is generated in each layer (21). Method for the production of partially reacted silicon for controlling the lithium intercalation ability according to claim 1, characterized in that a diffusion and reaction of metal (20, 23) from the substrate (14) with the silicon (16, 19) through a previously applied diffusion barrier ( 18) is controlled. Process for the production of partially reacted silicon for controlling the lithium storage capacity according to Claim 1, characterized in that the layers (21) are deposited by means of physical and/or chemical vapor deposition. Process for the production of partially reacted silicon for controlling the lithium storage capacity according to claim 1, characterized in that the diffusion barriers (18) made of one of the materials titanium (Ti), nickel (Ni), aluminum (Al), tin (Sn), gold (Au), silver (Ag ) , molybdenum (Mo), tungsten (W), carbon (C) and their nitrides and silicides and / or mixtures of these materials are formed. Process for the production of partially reacted silicon for controlling the lithium storage capacity according to Claim 1, characterized in that the diffusion barriers (18) allow lithium diffusion. Method for the production of partially reacted silicon for controlling the lithium intercalability according to one of the preceding claims, characterized in that a volume expansion of the silicon in a layer (21) of the multilayer structure (22) is controlled by the partially reacted silicon to form silicide, with a gradual progression of a high silicide concentration on the side of the multilayer structure (22) facing away from the substrate (14) to a low silicide concentration on the side of the multilayer structure (22) facing away from the substrate (14). Method for the production of partially reacted silicon for controlling the lithium storage capacity according to one of the preceding claims, characterized in that by introducing diffusion barriers (18) a reaction of metal (20, 23) and silicon (16, 19) to form silicide across layers is controlled and the frequency of Short-term tempering (11) is reduced with increasing number of layers. Method for the production of partially reacted silicon for controlling the lithium storage capacity according to one of the preceding claims, characterized in that an adjustable quantity of metal (23 ), In particular copper (Cu), nickel (Ni), aluminum (Al), titanium (Ti), magnesium (Mg) and / or tin (Sn) is inserted to produce partially reacted silicon in the entire multi-layer structure (22). Anode suitable for use in a lithium battery and produced by the method according to claims 1 to 11, characterized in that the anode (9) has a current collector (2), preferably made of copper, and a multilayer structure ( 22), which forms an active layer of the anode, wherein the multilayer structure (22) consists of at least a first partially reacted silicon layer consisting of silicon, a metal and/or another material, which is subjected to short-term annealing (11), and one second partially reacted silicon layer, which consists of silicon, a metal and/or another material, which is also subjected to short-term annealing (11). Anode according to claim 12, according to the method according to 36 according to Claims 1 to 11, characterized in that a volume expansion of the silicon of the multilayer structure (22) can be controlled by the partially reacted silicon layer when lithium is embedded, with a gradual progression from a high silicide concentration on the side of the current collector (2) facing Active layer is formed to a low silicide concentration on the current collector (2) facing away from the active layer of the anode and through the proportion of metal in the multilayer structure (22) high electrical conductivity is formed in the active layer of the anode. Anode according to Claim 12, characterized in that the further material forms a diffusion barrier (18), the diffusion barrier (18) being made from one of the materials titanium (Ti), nickel (Ni), aluminum (Al), tin (Sn), gold ( Au), silver (Ag), molybdenum (Mo), tungsten (W), carbon (C) and their nitrides and silicides and / or mixtures of these materials is formed. Anode according to Claim 12, characterized in that the active layer of the anode has a layer thickness of 4 to 15 pm. Anode according to claim 12, characterized in that the anode has a gradual course of a metal concentration in the active layer from a high metal concentration on the current collector (2) side facing the 37 Active layer has a low metal concentration on the current collector (2) facing away from the active layer of the anode. Anode according to Claim 16, d a d a r c h g e n n n d i c h n e t that the anode has a gradual profile of a metal concentration in one layer (21) of the multilayer structure (22), areas with a high silicide concentration forming adhesion and stability of the active layer and areas with a low silicide Concentration and high proportion of silicon have a high lithium storage capacity. Use of the method for the production of partially reacted silicon to control the lithium storage capacity according to claims 1 to 11 for functional layers in an aluminum ion battery. Use of the method for the production of partially reacted silicon for controlling the lithium storage capacity according to claims 1 to 11 for thermoelectrics. Use of the method for the production of partially reacted silicon for controlling the lithium storage capacity according to claims 1 to 11 for sodium or magnesium batteries.