Method for producing partially reacted silicon for controlling lithium intercalation capacity for use in lithium batteries - Patents.com

Abstract

The present invention relates to a method for producing partially reacted silicon for use in lithium batteries to control the lithium intercalation capacity, comprising depositing a first silicon layer on a substrate and subsequently subjecting the first silicon layer to rapid thermal processing. The present invention also relates to an anode produced thereby. The problem addressed by the present invention, which is to identify a method that allows control of the ion intercalation capacity into a functional layer for battery production, is solved by applying a layer of silicon, metal, and / or another material as a diffusion barrier, followed by rapid thermal processing to form partially reacted silicon (the structure of the diffusion barrier makes it permeable to lithium).

Description

[Technical field]

[0001] The present invention relates to a method for producing partially reacted silicon for use in lithium batteries to control the lithium intercalation capacity, comprising depositing a first silicon layer on a substrate followed by an accelerated annealing.

[0002] The present invention also relates to anodes made using the methods of the present invention that are suitable for use in lithium batteries.

[0003] The invention also relates to the use of this method for the functional layer of aluminum-ion batteries, as well as the use of this method for producing partially reacted silicon for controlling the ion intercalation capacity in the production of sodium and magnesium batteries. [Background technology]

[0004] Electrochemical energy storage has become an important pillar in the global effort towards the energy transition, serving to temporarily store fluctuating electricity generated by renewable means and to make this electricity available for stationary and mobile applications. To mitigate the shortage of the raw material base and therefore the rising costs, especially of secondary batteries, a diversification of energy storage concepts is required, but also new materials. These materials should improve the technical performance of such energy storage concepts (including capacity, energy density and lifetime) while minimizing the production costs. The latter can be ensured in particular by the use of readily available chemical elements, such as silicon, for which an extensive technological base already exists.

[0005] Batteries are electrochemical energy storage devices, and a distinction is made between primary and secondary batteries.

[0006] A primary battery is an electrochemical power source that irreversibly converts chemical energy into electrical energy. Therefore, primary batteries are not rechargeable. Secondary batteries, also called storage batteries, on the other hand, are rechargeable electrochemical energy storage devices in which the chemical reactions that occur are reversible and can be used multiple times. During charging, electrical energy is converted into chemical energy, and during discharging, chemical energy is converted back into electrical energy.

[0007] "Battery" is the entry for an interconnected set of cells. A cell is a galvanic unit consisting of two electrodes, an electrolyte, a separator, and a cell casing. Figure 1 shows an exemplary structure and function of a lithium-ion cell during discharge. The components of a cell are briefly described below.

[0008] Each Li-ion cell 1 is composed of two different electrodes 7, 9, namely an electrode 7 that is negatively charged in the charged state and an electrode 9 that is positively charged in the charged state. The release of energy, in other words discharge, involves the transfer of ions from the negatively charged electrode to the positively charged electrode, so the positively charged electrode is called the cathode 7 and the negatively charged electrode the anode 9. Each electrode is composed of a current collector 2, 8 and an active material applied on it. Between the electrodes, firstly, an ionically conductive electrolyte 4 is placed, which allows the necessary exchange of charges, and a separator 5, which ensures the electrical isolation of the electrodes.

[0009] The cathode consists, for example, of a mixed oxide applied onto an aluminum current collector. Transition metal oxides containing cobalt (Co), manganese (Mn) and nickel (Ni) or aluminum oxide (Al2O3) are the most common compounds here. The applied metal oxide layer serves to intercalate lithium ions during the discharge of the cell.

[0010] The anode of a Li-ion cell can consist of a copper foil as a current collector and a carbon layer as an active material. Natural or synthetic graphite is usually used as the carbon compound because it has a low electrode potential and a small volume expansion during charging and discharging. During charging, lithium ions are reduced and intercalated into the graphite layer.

[0011] In the structure of a lithium-ion battery, the cathode typically supplies lithium atoms for charging and discharging the anode, so the battery capacity is limited by the capacity of the cathode. As already mentioned, typical cathode materials used to date are, for example, Li(Ni,Co,Mn)O2 and LiFePO4. Since the cathode structure is based on lithium metal oxide, there is little possibility to increase the capacity.

[0012] It is also known to use silicon, rather than carbon, as the anode for Li batteries. Silicon as an anode material has a storage capacity of 372 mAh / g of Li at room temperature, compared to 372 mAh / g of conventional carbon-based materials such as graphite. 15 The Si4 phase has a high theoretical storage capacity of about 3579 mAh / g. However, a challenge arises when using silicon as an anode material in that the volume of the host matrix can change considerably (volume contraction and expansion) when mobile ionic species intercalate and deintercalate during charging and discharging of the corresponding energy store. For graphite, the volume change is about 10%, whereas for silicon it is about 400%. The volume change of the anode material when using silicon can lead to internal stresses, cracks, crushing of the active material of the host matrix (silicon), and ultimately the complete destruction of the anode.

[0013] Silicon can only be applied directly to a metal substrate such as copper foil if there is no temperature step in the ongoing process, since such a step would cause a reaction between the silicon and the metal substrate. With a conventional annealing step, the layer reacts completely by forming a silicide and is therefore no longer actively suitable for the intercalation of lithium or, in general, ions.

[0014] The diffusion of metals into silicon and the reaction of silicon with metals are highly time and temperature dependent. Already at low temperatures starting from 200 °C, many metals form metal silicides that have little or no reversible lithium intercalation capacity. Metal diffusion occurs even at room temperature and at higher temperatures occurs very rapidly and is difficult to control with conventional oven processes. Taking copper as an example, a complete layer of silicon is reacted at 600 °C after at most 1 second (see figure 2a). The diffusion and reaction can be slowed down by incorporating a diffusion barrier. However, considering that typical oven processes are very slow compared to the diffusion rate, the requirements imposed on the diffusion barrier are very demanding. Examples to achieve a good barrier effect even at high temperatures are high layer thicknesses, non-conductive layers or multilayers with a large number of interfaces. For example, in the semiconductor industry, NiSi is used as a diffusion barrier for metallization with copper. x Special layers of tungsten (W), tantalum (Ta), and titanium (Ti), as well as their conductive nitrides and silicides, are used, the manufacture of which involves several process steps and is therefore complex.

[0015] Patent document 1 describes a method for producing silicon-based anodes for secondary batteries by depositing a silicon (Si) layer on a metal substrate that serves as an integral current collector, followed by flash lamp annealing. Flash lamp processes are typically used to rapidly and locally melt and crystallize silicon, for example for solar cells. However, this is not the purpose of the method described in patent document 1. Instead, flash lamp annealing is used as follows. Generally speaking, silicon can only be crystallized at around 700 °C. After flash lamp annealing, these Si atoms become free atoms and can diffuse along the grain boundaries of the metal substrate even at relatively low temperatures from about 200 °C, since the covalent bonds of the Si atoms at the interface with the metal are weakened. This has already been demonstrated in several metal / semiconductor systems (e.g. Au / a-Si and Ag / a-Si) and has proven to be energetically favorable, as described in non-patent document 1. Furthermore, crystallization of silicon can be achieved by introducing metal at relatively low temperatures. This is called metal-induced crystallization. Very simply, crystal growth can occur after the temperature drops below the melting point, which can be used as a criterion for phase transformation. Using the method described in US Pat. No. 5,999,436, multiphase silicon-metal structures can be fabricated that can accommodate the volume changes caused by delithiation and lithiation and provide stabilization of the entire material assembly. Lithiation refers to the intercalation of lithium ions into a host material (e.g., silicon or graphite).

[0016] The Si anodes that can be produced using the method known from US Pat. No. 5,999,393 are a mixture of silicon, pure metal and silicide, i.e. a microstructure is formed consisting of copper, copper silicide and silicon, when only copper (Cu) foil is used as substrate and a silicon layer is deposited on it. The advantage of the Si anodes produced in this way compared to those consisting of nanoparticles or nanowires is the higher electrical conductivity compared to pure silicon and conventional graphite, since the electrical conductivity of silicide is about two orders of magnitude better than that of graphite. Furthermore, the adhesion achieved between the Si layer as active material and the copper substrate is very good, and copper diffuses from the copper foil into the deposited Si layer as a result of flash lamp annealing. The active areas for lithium intercalation formed by pure silicon and the inactive areas formed by the silicide / metal in the matrix counterbalance the known detrimental volume expansion during charging. Another advantage is that due to the layered structure, only a small area forms a boundary layer with the electrolyte, which reduces electrolyte decomposition due to the small surface area compared to the case of nanostructured active materials.

[0017] However, the disadvantage of the method described in Patent Document 1 is that due to flash lamp annealing, the Si layer undergoes uncontrolled reactions to form copper silicide, and the conversion reaction always starts at the Cu-Si layer interface. As a result of the reaction, no silicon remains as active material for lithium intercalation, or if the input energy is very low, the reaction does not occur sufficiently, and the layer lacks sufficient stability in the operation of the battery, thus leading to capacity loss on the part of the battery. For sufficient target capacity in the production of lithium batteries, a sufficiently thick Si layer (up to 10 μm) is required. If the conversion reaction of Cu+Si to form copper silicide is caused uncontrolled by annealing methods, including flash lamp annealing, the entire copper substrate, e.g., copper foil, will completely react with silicon to form copper silicide, with the loss of the current collector of the lithium battery. Therefore, it is not possible to produce an anode with a stable structure and high areal storage density by the method described in Patent Document 1. [Prior art documents] [Patent documents]

[0018] [Patent Document 1] International Publication No. 2017 / 140581 [Non-patent literature]

[0019] [Non-Patent Document 1] 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) Summary of the Invention [Problem to be solved by the invention]

[0020] The object of the present invention is therefore to provide a method that allows to control the capacity of ion intercalation into functional layers for battery production. In particular for lithium-ion batteries, it should be possible to establish in a controlled manner the ratio of silicon to silicide and metal, i.e. a method for producing partially reacted silicon would be advantageous. The intention was to find a trade-off between a maximum proportion of amorphous or nanocrystalline pure silicon, which ideally must be available as active material for lithium intercalation, and at the same time a sufficient number of inactive regions to achieve stability and good electrical conductivity, providing a high capacity at a sufficient anode layer thickness with a high proportion of silicon. [Means for solving the problem]

[0021] This object is achieved by the method according to independent claim 1.

[0022] A method for producing partially reacted silicon for use in lithium batteries to control lithium intercalation capacity includes depositing a first silicon layer on a substrate, followed by accelerated annealing, applying a layer of silicon, metal and / or further material as a diffusion barrier according to the invention, followed by accelerated annealing, resulting in a layer of partially reacted silicon. The deposition and accelerated annealing are further repeated to form a multi-layer structure composed of partially reacted silicon.

[0023] Accelerated annealing specifically refers to flash lamp annealing and / or laser annealing. Flash lamp annealing has pulse durations or annealing times in the range of 0.3-20 ms and pulse energies in the range of 0.3-100 J / cm. 2 In the case of laser annealing, the intensity is in the range of 0.1 to 100 J / cm 2 To generate an energy density of 0.01 to 100 ms, the annealing time is established depending on the scanning speed of the local heating spot. The heating ramp rate achieved in accelerated annealing is 10 times faster than the required rate for this method. 4 ~10 7 Flash lamp annealing for this purpose utilizes the visible wavelength range of the spectrum, whereas laser annealing uses discrete wavelengths ranging from the infrared (IR) to the ultraviolet (UV) spectrum.

[0024] This sequence of layers produces an overall layer thickness of the partially reacted silicon multilayer of typically 4-15 μm, which is sufficient for the operation of the cell. Partially reacted silicon in the sense of the present invention refers to a layer that contains regions of pure silica, ideally amorphous or nanocrystalline, and regions of the corresponding silicide formed by partial or complete reaction with a metal.

[0025] A layer in the sense of the present invention refers to a sequence of layers of silicon, metal and / or further material acting as a diffusion barrier, which together produce a defined partially reacted silicon layer formed by accelerated annealing. A layer is therefore a sequence of layers which produce a defined partially reacted silicon / silicide layer. The diffusion barrier limits the amount of metal supplied from the outside that is supplied in the layer and is available for a defined reaction with silicon supplied in this layer. An additional diffusion barrier made of a further material other than metal is not absolutely necessary, since the formed silicide layer may already act as a sufficient diffusion barrier to prevent further reaction with silicon. In this case, the metal diffuses into the silicide slower than it diffuses into silicon.

[0026] In accelerated annealing, the diffusion and the formation of silicides in the layer can be controlled, so that the formation of silicides proceeds stepwise perpendicular to the surface. This is favorable for the adhesion of the Si layer to the copper foil, since the silicides are partially formed and still active silicon is available. The process control in accelerated annealing can be improved by using a suitable diffusion barrier. The retardation of diffusion when passing through the barrier allows for better process control in the time interval in which energy is introduced during accelerated annealing. Unlike conventional diffusion barriers, the aim is to weaken the diffusion of metal atoms, as opposed to their diffusion into silicon, only to the extent that a significant reduction in diffusion occurs in the time window in which energy is introduced during accelerated annealing. Correspondingly, in the method of the present invention, the architecture and thickness of the diffusion barrier are greatly simplified, which allows savings in terms of material and process time. At the same time, the diffusion of lithium is not reduced or only slightly, making it suitable for application in lithium-ion batteries. A suitable diffusion barrier is therefore understood to be one which locally weakens the diffusion of copper, particularly during accelerated annealing, and inhibits the formation of silicides, but at the same time allows the diffusion of lithium.

[0027] In one embodiment of the method of the present invention, the diffusion and reaction of metal with silicon in the case of flash lamp annealing is performed by flash lamp annealing with a pulse duration in the range of 0.3-20 ms and a pulse energy of 0.3-100 J / cm 2 The deposition is controlled by pulse energies ranging from 0.1 to 100 s, and preheating or cooling ranging from 4 °C to 200 °C, thus producing partially reacted silicon in each layer.

[0028] When laser annealing is used as accelerated annealing, the diffusion and reaction between metal and silicon depend on the scanning speed of the local heating area and the laser power of 0.1 to 100 J / cm2. 2 By establishing an energy density in the range of 0.1 - 100 ms, as well as a preheat or cooling in the range of 4 °C - 200 °C, the annealing time is controlled in the range of 0.01 - 100 ms, thus producing partially reacted silicon in each layer. The effect of external cooling is that the cooling of the substrate is more effectively controlled; otherwise, undesired reactions may occur outside the annealing area.

[0029] The metal may be copper from a copper substrate on which a multilayer structure is deposited to produce the active layer of an anode for lithium batteries. The diffusion of copper into the silicon layer can be controlled by adjustable pulse duration, pulse energy, and preheating or cooling in flash lamp annealing. A stepwise transition is possible without the entire layer reacting. In the area of ​​the Cu foil, a high concentration of copper can be measured, which gradually disappears until the surface of the deposited layer is reached. Thus, in the area of ​​the Cu foil, a large proportion reacts to form copper silicide. A chemical reaction of the interface area occurs, which significantly improves the adhesion of the layer. Due to the high proportion of silicide, little / no lithium is intercalated, therefore the volume expansion is small and the stress at the interface is significantly reduced. Due to the stepwise structure of the layer, the stress of the volume expansion during lithium intercalation is distributed homogeneously within the layer. The monolayer Si layer treated with accelerated annealing shows a significant improvement in the cycling stability compared to untreated layers, without a substantial change in the utilization of the Li storage capacity. A cycle refers to a complete charge and discharge of the battery. The number of cycles is related to the life of the battery. However, the drawback is that downstream annealing steps will cause the layers to react further, limiting the structure to only one annealing step or a few layers. By using a suitable diffusion barrier as an intermediate layer, this drawback can be avoided or the target thickness of the entire layer can be met. Suitable copper diffusion barriers are listed below:

[0030] In another embodiment of the method of the present invention, the diffusion and reaction of metal with silicon from the substrate is controlled by a pre-applied diffusion barrier.

[0031] To prevent the multilayer structure applied to the substrate from reacting uncontrollably with a metal, e.g. copper, to form a silicide, a diffusion barrier can be applied to the substrate as a first layer, which has a sufficient barrier effect so that, for example, during flash lamp annealing, the diffusion and reaction of metal atoms from the substrate with silicon can be controlled by adapting the flash energy, the flash duration or a minimum thickness of the diffusion barrier layer.

[0032] In another embodiment of the method of the present invention, the layer is deposited by physical vapor deposition, for example by sputtering or evaporation, or by chemical vapor deposition.

[0033] Planar deposition, for example by sputtering or evaporation or by chemical vapor deposition, allows the diffusion barrier to be introduced layer by layer without increasing complexity and costs. In contrast to the diffusion barrier of conventional annealing processes, the requirements imposed on the diffusion barrier in the context of accelerated annealing are relatively minor, and diffusion, as mentioned above, does not have to be completely prevented but only sufficiently blocked. Thus, an extremely thin barrier of suitable elements and compounds, such as carbon, nitrides, oxides, metals, etc., is sufficient to allow a stable process control (stable process window) in the method of the invention. As a result, multiple annealing steps are possible with only minor changes in the layer structure. A layer in the method of the invention is understood to be synonymous with a layer stack of diffusion barriers composed of Si, metals and / or further materials, and therefore a layer in the sense of the invention is composed of partial layers of a layer stack. A plurality of layers forms a multilayer structure.

[0034] In a further embodiment of the method of the invention the diffusion barrier is applied 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 / or a mixture of these materials.

[0035] In another further embodiment of the method of the present invention, the volume expansion of the silicon in each layer of the multi-layer structure is controlled by partially reacted silicon, establishing a graded transition from a higher silicide concentration on the side of the multi-layer structure facing the substrate to a lower silicide concentration on the side of the multi-layer structure facing away from the substrate.

[0036] The graded transition is approximated stepwise by a multi-layer structure. For silicon and subsequent accelerated annealing in the multi-layer structure or in each layer of the multi-layer structure, the objective is to maximize the reaction of Si with the metal / copper present. As a result, the concentration of metal / copper decreases from layer to layer, building up substantially (<5%) metal-free / copper-free silicon as the last layer of the multi-layer structure.

[0037] In one embodiment of the method of the present invention, the reaction of metal with silicon to form silicide is controlled throughout the layers by introducing a diffusion barrier into the layers being deposited, allowing the frequency of accelerated annealing to be reduced as the number of layers increases.

[0038] After each silicon layer, a diffusion barrier is inserted. This corresponds to the conjunction "and" in independent claim 1. It is therefore possible to reduce the input energy by reducing the number of accelerated annealing operations. In this way, graded structures can also be generated and manufactured with the largest possible layer sequence, with only one accelerated annealing operation at the end of the multi-layer structure.

[0039] In one embodiment of the method of the present invention, for each layer of silicon, metal and diffusion barrier deposited, a controllable amount of metal, more specifically copper, nickel, aluminum, titanium, magnesium and / or tin, is inserted to produce partially reacted silicon throughout the multi-layer structure. The purpose and advantage of adding a controllable amount of metal to each layer of the multi-layer structure is the production of a conductive matrix in which the silicon is embedded.

[0040] Additionally, the metal also serves to enhance the electrical conductivity of silicon as a dopant. The reduction in lithium storage capacity is apparently a side effect of the partial reaction with silicon to form non-lithium reactive silicides / complexes, but this reduces the critical volume expansion of silicon upon lithium intercalation. If the first deposited layer of silicon, metal and / or diffusion barrier on the substrate is treated by accelerated annealing, there may not be any copper from the substrate available for the subsequent deposited layers to form silicides. Adjustable amounts of metal, more specifically Cu, Ni, Al, Ti, Mg and / or Sn, are added in the case of multiple layers to ensure partially reacted silicon at each layer. By varying the amount of metal through the amount of Si, graded structures can be produced as well. Accelerated annealing is performed after one or more deposited layers to ensure reaction at these layers.

[0041] For example, the deposited metals may include nickel, which reacts with silicon to form nickel silicide and simultaneously constitutes a diffusion barrier for copper. As a result, the manufacturing process can be simplified by reducing the number of individual steps. With nickel it is likewise possible to realize a graded structure of partially reacted silicon layers.

[0042] By multiple accelerated annealing, thick layers of active layers with silicon for high lithium intercalation capacity can be built. By controlling the diffusion with the help of layered structures, completely new variations of layered structures are possible. Any desired functional layer can be built and by accelerated annealing the properties required for stable battery operation can be targeted. For example, sputtered carbon can be used to suppress the diffusion of Cu into silicon, while deposited Cu3Si can also promote the diffusion of Cu into silicon. Optimization for other uses, such as other types of batteries (such as aluminum-ion (Al), sodium (Na) or magnesium (Mg) batteries) or even thermoelectric systems, is likewise possible as a result of the high flexibility.

[0043] The method of the invention can therefore be advantageously used to manufacture functional layers of aluminium ion batteries, thermoelectric systems and / or sodium or magnesium batteries.

[0044] By multiple accelerated annealing, metals, e.g. copper, can be mixed in a targeted manner into silicon, so that layers with defined concentrations can be produced by targeted silicide formation, and the amount of lithium incorporated into silicon can be adjusted. Other metals, e.g. Ti, Ni, Sn, Al, W, Mo, C and / or mixtures thereof, are possible as required, so that a layer-by-layer graded structure is possible.

[0045] The object of the invention is likewise achieved by an anode according to the invention.

[0046] The anode is suitable for use in a lithium battery and is produced by the method according to the method claims. The anode of the invention comprises a current collector, preferably of copper, and a multilayer structure deposited on the current collector, forming the active layer of the anode, the multilayer structure being formed from at least a first partially reacted silicon layer made of silicon, metal and / or further materials, which is subjected to accelerated annealing, and a second partially reacted silicon layer made of silicon, metal and / or further materials, which is also subjected to accelerated annealing.

[0047] The first applied silicon layer, which is subsequently subjected to accelerated annealing, can advantageously act as an adhesion layer, which reacts completely with the copper of the current collector to form a copper silicide, resulting in an increased roughness and high adhesion of the current collector, e.g. a Cu foil, and the silicon layer reacted with copper acts as an adhesion layer for further layer structures. Since the copper silicide layer reacts completely, the application of a diffusion barrier consisting of a further material, e.g. carbon, ensures a sufficiently stable diffusion barrier also for subsequent processing steps. This diffusion barrier is necessary to prevent the silicon in the copper from reacting to form copper silicide during further accelerated annealing, in particular flash lamp annealing and / or laser annealing. The further materials subsequently applied in sequence, further Si, metal and / or diffusion barrier layers, are then stabilized by further accelerated annealing. The anode for a lithium battery according to the invention has a maximum current density of up to 4 mAh / cm 2 , and even up to 6mAh / cm 2 It has a high storage capacity.

[0048] In one embodiment of the anode of the present invention, the volume expansion of the silicon in the multilayer structure upon lithium intercalation can be controlled by the partially reacted silicon layer, resulting in a gradual transition 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 anode active layer facing away from the current collector, and the proportion of metal in the multilayer structure results in high electrical conductivity in the anode active layer. Good electrical conductivity is achieved when the resistivity of graphite is greater than 3*10 -3 High conductivity refers to a resistivity in the ohm-cm range, lower than that of graphite and (10~50)*10 of pure copper silicide. -6 This refers to ohms / cm.

[0049] The gradual progression of layers is approximated stepwise by a multi-layer structure. The purpose of each layer of Si and subsequent accelerated annealing is to maximize the reaction of the Si with the metals present, e.g. copper. As a result, the concentration of copper decreases with each layer, and the final layer built up is silicon that is essentially (<5%) copper-free.

[0050] In each deposited layer of silicon, metal and diffusion barrier, the amount of metal (which may be copper, nickel, aluminum, titanium, magnesium and / or tin, more specifically) can be adjusted to produce partially reacted silicon throughout the multi-layer structure. The purpose and advantage of adjustable amounts of metal added to each layer of the multi-layer structure is the production of a conductive matrix in which silicon is embedded. The adjusted amount of metal serves to enhance the conductivity of silicon as a dopant. The reduction in lithium storage capacity is apparently a result of partial reaction with silicon to form non-lithium reactive silicides / complexes, which reduces the critical volume expansion of silicon upon lithium intercalation.

[0051] In a further embodiment of the anode of the invention, a further material forms the diffusion barrier, which is formed from one of the following materials: titanium (Ti), nickel (Ni), aluminium (Al), tin (Sn), gold (Au), silver (Ag), molybdenum (Mo), tungsten (W), carbon (C), and their nitrides and silicides, and / or mixtures of these materials.

[0052] The anode of the invention may have a diffusion barrier after each silicon layer. It is therefore possible to reduce the input energy by reducing the number of accelerated annealing operations in the manufacture of the anode. In this way, it is likewise possible to manufacture a graded structure of the active layer of the anode with the maximum possible layer sequence with only one accelerated annealing operation. For example, nickel can be used as a diffusion barrier. Nickel reacts with silicon to form nickel silicide, which at the same time constitutes a diffusion barrier for copper. Anodes constructed in this way can be manufactured from fewer individual steps.

[0053] In different embodiments of the anode of the invention, the anode exhibits a graded transition of 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 anode active layer facing away from the current collector. The non-active regions in the heterogeneous structure throughout the layer contain concentrations of at least copper-3 silicide (Cu3Si) through Cu7Si to pure copper. Below a concentration of Cu3Si, the silicon is said to have a high to very high concentration of copper. As a lower limit for metal-rich silicon, a value typical of metallurgical silicon with a metal content of about 3% is taken. With values ​​below 0.1% metal in silicon, the silicon is said to be metal-poor.

[0054] In yet another embodiment of the anode of the invention, the anode comprises a graded transition of metal concentration in the layers of the multi-layer structure, where the regions of high silicide concentration provide adhesion and stability to the active layer, and the regions of low silicide concentration and high silicon fraction provide high lithium intercalation capacity, where high silicide concentration refers to a silicide fraction greater than 50% in the layer, and low silicide concentration refers to a silicide fraction less than 10% in the layer.

[0055] The invention is explained in more detail below using exemplary embodiments. [Brief description of the drawings]

[0056] [Figure 1] FIG. 1 illustrates an exemplary structure and function of a lithium-ion cell during discharge. [Figure 2a] FIG. 2 shows the effect of input temperature on silicide formation in silicon anodes in a conventional oven process (prior art). [Figure 2b] FIG. 1 shows the effect of input temperature on the formation of silicide in silicon anodes, by accelerated annealing, more specifically flash lamp annealing. [Figure 3a] FIG. 1 is a process flow diagram of the method of the present invention. [Figure 3b]FIG. 1 is a schematic diagram of a method of the present invention for controlling lithium intercalation capacity by targeted accelerated annealing, more specifically flash lamp annealing, of functional layers for battery fabrication. [Figure 3c] 1A-1C are diagrams showing the stepwise progression of silicide formation according to the method of the present invention; [Figure 4] 1A-1D are schematic diagrams of multilayer structures according to the method of the present invention for producing partially reacted silicon for controlling lithium intercalation capacity. a) Single layer and multilayer structures consisting of multiple layers of silicon, metal and diffusion barrier are shown, and b) the effect of accelerated annealing process parameters and diffusion barrier thickness on the gradual progression of silicon / silicide concentration within the layers. [Diagram 5] a) is a schematic diagram of a multilayer structure as an active layer of an anode of the present invention; b) shows the stepwise progression of silicide concentration established by controlled addition of a metal, e.g. copper, to each layer of the multilayer structure separated by a diffusion barrier; c) shows the stepwise progression of metal concentration in each layer of the multilayer structure without a diffusion barrier. [Figure 6] Schematic diagram of a) graded transition within individual layers, b) graded transition without diffusion barrier between individual layers, and c) graded transition with diffusion barrier between individual layers of silicon concentration / metal concentration / silicide concentration on a copper substrate. [Figure 7] 1 is a SEM micrograph of a multilayer structure without a diffusion barrier. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0057] Figure 2b) shows the effect of accelerated annealing, more specifically flash lamp annealing, on the formation of silicides in a copper-silicon layer system. Due to the very short flash pulses in the range of 0.1-10 ms, the reaction between silicon and copper to form copper silicide is incomplete. Flash lamp annealing leaves pure amorphous or nanocrystalline silicon available as active material for lithium intercalation, while at the same time there is a sufficient number of inactive regions to ensure stability and good electrical conductivity.

[0058] FIG. 3a) shows the method steps of the invention in a flow diagram, while FIG. 3b) shows the flow of the method steps for the generated anode structure in comparison with a conventional oven process in the left part of FIG. 3c). The substrate 14, which simultaneously serves as the current collector of the LIB (Lithium Ion Battery), is subjected to a pre-cleaning 13 under vacuum conditions in a plasma atmosphere. This cleaning is necessary because in air an oxide layer 15 forms on the substrate 14, which prevents the reaction between the subsequently applied silicon layer 16 and the copper substrate 14 in a flash lamp annealing operation (FLA flash lamp annealing), meaning that the silicon layer 16 therefore no longer adheres to the Cu substrate. Following this, a first silicon layer 16 is deposited, for example by sputtering. This first silicon layer 16 reacts with the Cu substrate 14 in the transition region to form a copper silicide 17, which increases the roughness of the substrate 14, for example a Cu foil, and the copper-containing silicon layer serves as a kind of adhesion layer for further layer structures. Since the copper silicide layer 17 is completely inert in the cell, in a subsequent step a diffusion barrier 18, for example made of carbon, is applied first. This diffusion barrier 18 is necessary to prevent the silicon in the copper from reacting to form copper silicide during further flash lamp annealing. Subsequently, a further Si layer 19 may be applied, each layer formed from silicon and the diffusion barrier layer being stabilized by a flash lamp annealing 11. The advantage of repeating the Si deposition and the subsequent flash lamp annealing 11 is that with each sequence a stable ("reaction neutralized") layer with sealed interfaces is formed, which acts as an intermediate layer for the subsequent layers. This is favorable for the adhesion of the Si layer to the copper foil, since the copper silicide is partially formed and still active silicon is available. The inventive method described thus results in a further roughening of the surface, forming a good adhesion for further layers. The growth of columnar structures is promoted as well, so that the ionic conductivity is improved and the copper percentage can be easily controlled for downstream processes.

[0059] Thus, after repeated deposition of silicon, metal and / or diffusion barriers made of different materials followed by accelerated annealing, more specifically flash lamp annealing, it is possible to control the diffusion and formation of silicides in the layers, so that a stepwise progression of silicide formation perpendicular to the surface can be established. This is shown in comparison with a conventional oven process in FIG. 3c). In the oven process, the Cu substrate 14 is heated together with the deposited Si layers 16, 19 and the diffusion barrier 18. As the diffusion barrier 18 made of, for example, carbon or nickel does not have a sufficient barrier effect, the whole silicon reacts with the copper to form copper silicide 17.

[0060] This situation is different when the layer undergoes accelerated annealing by flash lamp or laser. The process control during flash lamp or laser annealing can be significantly improved by introducing a suitable diffusion barrier 18. The formation of copper silicide can be adjusted stepwise by adjusting the flash lamp energy, flash lamp duration and / or annealing time, by adjusting the scanning speed and energy density of the local heating spot by the laser and / or by adapting the minimum thickness of the deposited silicon layer or diffusion barrier, which is shown on the right side of FIG. 3c). The use of a diffusion barrier 18 in conjunction with accelerated annealing, more specifically flash lamp annealing and / or laser annealing 11, is suitable for controlling the intercalation of ions in the production of batteries.

[0061] A further exemplary embodiment is shown in Fig. 4. Fig. 4a) shows an individual layer 21, composed on top of a copper layer or generally a metal layer 20, a silicon layer 16 and a diffusion barrier 18. Each layer 21 may be treated by accelerated annealing 11, whereby the silicon 16 and the metal 20 are converted into a silicide 17, and by adjusting the parameters of the accelerated annealing process 11 a graded profile of silicide / silicon concentration within the layer is generated. Several layers 21 form a multi-layer structure 22.

[0062] The gradual progression of the silicide / silicon concentration in the layer 21 can be adjusted both by the selected process parameters of the accelerated annealing process 11 and by the thickness of the deposited diffusion barrier 18. This is shown diagrammatically in FIG. 4b). The higher the selected input energy, for example by the flash lamp or laser 11, the more metal atoms can diffuse into the silicon layer 19 during the accelerated annealing process and therefore the smaller the gradient of the silicide / silicon concentration in the layer (compare FIG. 4b, left and center diagrams). A small gradient is synonymous with a gradual decrease in the concentration of silicide in the layer or anode active layer 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. A large gradient means a rapid decrease in the silicide concentration. If the thickness of the diffusion barrier 18 is increased without changing the parameters of the accelerated annealing process, fewer metal atoms can diffuse through the diffusion barrier 18 into the deposited layer during the accelerated annealing operation, so the gradient in the deposited layer increases and therefore the concentration decreases over a short distance perpendicular to the surface of the layer / active layer. A high silicide concentration forms on the lower side of the layer and decreases rapidly, leaving only silicon on the upper side, i.e. the side of the layer / active layer facing away from the current collector. Pure silicon is available for lithium intercalation, but the formation of silicide improves the electrical conductivity.

[0063] For example, a stepwise transition of the copper concentration in a silicon layer with a copper layer is established by adapting the pulse duration, the preheating or cooling of the layered structure, and the thickness of the deposited layer, in other words by adapting the input energy (over time and temperature) and the thickness ratio of the silicon layer to the copper layer, so that the average reaction depth (diffusion length) should be smaller than the thickness of the silicon layer in order to provide enough unreacted silicon for lithium intercalation.

[0064] Figure 5 shows a schematic diagram of a multilayer structure as active layer of an anode of the invention in different exemplary embodiments. In figure 5a) a layer 21 is made up of silicon 16, 19, metals 20, 23 and a diffusion barrier 18. This layer is subjected to an accelerated annealing 11. Several layers 21 and several accelerated annealing operations 11 form a multilayer structure 22, which layers are separated by a diffusion barrier 18 made for example of carbon, and a further metal 20 is introduced in a further layer. Each layer is subsequently subjected to an accelerated annealing 11. Starting from the metal layer 20, a stepwise transition of the silicide concentration in each layer is clearly visible.

[0065] Figure 5b) shows, in addition to figure 5a), a gradation of the silicide concentration in the layers of the multi-layer structure 22 separated by a diffusion barrier 18, for example made of carbon. Furthermore, in the layers, a further layer of metal 23, for example aluminum, is introduced, which allows to further improve the gradation in the layers and the reaction of the metal with silicon.

[0066] Figure 5c) shows the same structure of the multilayer structure 22 as in figure 5b), with the difference that this multilayer structure 22 does not have a diffusion barrier 18 separating the individual layers 21 from each other. The gradation is controlled by the thickness of the inserted metal layers 20 and 23. An SEM micrograph showing an exemplary Si / Cu / Si / Al / Si / Cu / Si / Al / Si structure is shown in figure 5d). The intermediate layers are no longer clearly visible and after flash lamp annealing, the copper has reacted with the silicon to form CuSi x The aluminum "dissolves" into the silicon. The result is a stable multi-layer structure with high silicon content, good electrical conductivity, and high battery capacity. CuSi with carbon x An adhesion layer 24 is formed on the copper substrate 14 to ensure continuous electrical contact.

[0067] FIG. 6 shows a schematic diagram of the creation of a stepwise transition of silicon or metal or silicide concentration on a copper substrate. FIG. 6a) shows a monolayer of silicon with a thickness of Si, where the reaction of silicon with metal to form silicide is still controllable by the choice of flash lamp process parameters. The layer thickness here is limited to the maximum thickness of silicon that is process-wise stable before flash lamp annealing, typically 1 μm. FIG. 6b) shows the creation of a stepwise transition starting from a copper substrate with a monolayer of silicon, which reacts completely to form copper silicide after flash lamp annealing 11 (FIG. 6b-1), followed by the deposition of an additional silicon layer 19 (FIG. 6a-2), which subsequently reacts after flash lamp annealing 11 to form a less pronounced silicide layer (FIG. 6a-3), where a concentration gradient is already visible. After further deposition of a silicon layer and a flash lamp annealing operation 11, a substantially stepwise transition is created in the multilayer structure (FIG. 6a-4).

[0068] FIG. 6c) shows the creation of a graded transition of silicon or metal or silicide concentration on a copper substrate with a diffusion barrier 18, several silicon layers 19, and flash lamp annealing 11 between each individual layer. Here, compared to FIG. 6b), both the degree and amount of reaction and silicidation can be controlled more targetedly in each layer to create a graded structure. With increasing distance in the active layer perpendicular to the surface of the copper substrate 14, the concentration of silicon increases and the concentration of silicide decreases. By establishing and adapting the parameters of the flash lamp annealing process, a gradient can be established targeted, starting with one or several layers of silicon. In contrast to FIG. 6a), the multilayer structures of FIG. 6b)-4 and FIG. 6c)-3 have the advantage of better control of the transition from silicide 17 to silicon 19, allowing structures with larger layer thicknesses.

[0069] 7 shows an SEM micrograph of a multi-layer structure 22 composed of eg Si / Cu / Si / Cu without any diffusion barriers 18 between the individual layers. As an adhesion layer only a thin diffusion barrier was applied to the substrate. [Explanation of symbols]

[0070] 1 Lithium-ion battery 2 Anode side current collector 3 SEI-Solid Electrolyte Interphase 4 Electrolytes 5. Separator 6 Contact phase 7 Cathode, positive electrode 8 Cathode side current collector 9 Anode, negative electrode 10. Sputtering of Si layer 11 Flash lamp annealing 12 Repeating the Process Steps 13 Plasma pre-cleaning 14 Substrate 15 Oxide layer 16 First silicon layer 17 Copper silicide, metal silicide 18 Diffusion Barrier 19 More Silicon Layers 20 metal layer 21 Single layer 22 Multilayer structures, structures 23 More Metal Layers 24 Adhesive layer

Claims

1. A method for producing partially reacted silicon for use in lithium batteries to control lithium intercalation capacity, comprising depositing a first silicon layer (16) on a substrate (14) followed by accelerated annealing (11), applying a layer (21) of silicon, metal and / or further material as a diffusion barrier (18) followed by a subsequent accelerated annealing (11); The diffusion and reaction between the metal (20, 23) and the silicon (16, 19) in the flash lamp annealing (11) is controlled 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 temperature in the range of 4°C to 200°C in the flash lamp annealing (11); or The diffusion and reaction between the metal (20, 23) and the silicon (16, 19) in the laser annealing (11) is controlled by the annealing time in the range of 0.01 to 100 ms by establishing the scanning speed of the local heating point in the laser annealing (11), the energy density in the range of 0.1 to 100 J / cm 2 , and the preheating or cooling in the range of 4°C to 200°C; thereby producing partially reacted silicon in each layer (21); The partially reacted silicon refers to a layer containing regions of pure silica, ideally amorphous or nanocrystalline, and regions of corresponding silicide formed by partial to complete reaction with the metal.

2. 2. The method for producing partially reacted silicon for controlling lithium intercalation capacity according to claim 1, characterized in that the deposition and the accelerated annealing (11) are subsequently repeated further to form a multilayer structure (22) composed of partially reacted silicon.

3. 2. The method for producing partially reacted silicon for controlling lithium intercalation capacity according to claim 1, characterized in that the diffusion and reaction of metals (20, 23) from the substrate (14) with the silicon (16, 19) is controlled by a pre-applied diffusion barrier (18).

4. 2. A method for producing partially reacted silicon for controlling lithium intercalation capacity according to claim 1, characterized in that said layer (21) is deposited by physical and / or chemical vapor deposition.

5. 2. The method for producing partially reacted silicon for controlling lithium intercalation capacity according to claim 1, wherein the diffusion barrier (18) is formed from one of the following materials: titanium (Ti), nickel (Ni), aluminum (Al), tin (Sn), gold (Au), silver (Ag), molybdenum (Mo), tungsten (W), carbon (C), nitrides and silicides thereof, and / or mixtures of these materials.

6. 2. The method for producing partially reacted silicon for controlling lithium intercalation capacity as recited in claim 1, wherein said diffusion barrier (18) allows diffusion of lithium.

7. 2. The method for producing partially reacted silicon for controlling lithium intercalation capacity according to claim 1, characterized in that the volume expansion of the silicon in the layer (21) of the multilayer structure (22) is controlled by the partially reacted silicon to silicide, and a gradual transition is established from a high silicide concentration on the side of the multilayer structure (22) facing the substrate (14) to a low silicide concentration on the side of the multilayer structure (22) facing away from the substrate (14).

8. 2. A method for producing partially reacted silicon for controlling lithium intercalation capacity according to claim 1, characterized in that the reaction of metal (20, 23) with silicon (16, 19) to form silicide is controlled throughout the layers by the introduction of a diffusion barrier (18), and the frequency of said accelerated annealing (11) decreases as the number of layers increases.

9. 2. The method for producing partially reacted silicon to control lithium intercalation capacity according to claim 1, characterized in that for each layer of deposited silicon (16, 19), metal (20, 23) and diffusion barrier (18), an adjustable amount of metal (23), more specifically copper (Cu), nickel (Ni), aluminum (Al), titanium (Ti), magnesium (Mg) and / or tin (Sn), is inserted to produce partially reacted silicon throughout the multilayer structure (22).

10. 1. An anode suitable for use in a lithium battery, comprising an anode (9) comprising a current collector (2), preferably made of copper, and a multilayer structure (22) deposited on the current collector (2) and forming the active layer of the anode, characterized in that the multilayer structure (22) is formed from at least one first partially reacted silicon layer made of silicon, metal and / or further materials and having a microstructure characteristic of accelerated annealing (11) based on silicon, metal and / or further materials, and a second partially reacted silicon layer made of silicon, metal and / or further materials and also having a microstructure characteristic of accelerated annealing (11) based on silicon, metal and / or further materials.

11. 11. The anode of claim 10, wherein the volume expansion of the silicon in the multilayer structure (22) upon lithium intercalation is controllable by the partially reacted silicon layer, resulting in a gradual transition from a high silicide concentration on the side of the active layer facing the current collector (2) to a low silicide concentration on the side of the anode active layer facing away from the current collector (2), and wherein the proportion of metal in the multilayer structure (22) results in high electrical conductivity of the anode active layer.

12. 11. The anode according to claim 10, characterized in that the further material forms a diffusion barrier (18), the diffusion barrier (18) being made of one of the following materials: titanium (Ti), nickel (Ni), aluminum (Al), tin (Sn), gold (Au), silver (Ag), molybdenum (Mo), tungsten (W), carbon (C), nitrides and silicides thereof, and / or mixtures of these materials.

13. 11. The anode according to claim 10, wherein the anode active layer has a thickness of 4 to 15 μm.

14. 11. The anode of claim 10, characterized in that the anode comprises a graded transition of metal concentration in the active layer from a higher metal concentration on a side of the active layer facing the current collector (2) to a lower metal concentration on a side of the anode active layer facing away from the current collector (2).

15. 15. The anode of claim 14, wherein the anode comprises a graded transition of metal concentrations in the layers (21) of the multilayer structure (22), with regions of high silicide concentration providing adhesion and stability of the active layer and regions of low silicide concentration and high silicon fraction exhibiting a high lithium intercalation capacity.

16. Use of the method for producing partially reacted silicon for controlling the lithium intercalation capacity according to any one of claims 1 to 9 for a functional layer of an aluminum-ion battery.

17. 10. Use of the method for producing partially reacted silicon for controlling the lithium intercalation capacity according to any one of claims 1 to 9 for a thermoelectric system.

18. Use of the method for producing partially reacted silicon to control the lithium intercalation capacity according to any one of claims 1 to 9 for sodium or magnesium batteries.

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