Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M10/00—Secondary cells; Manufacture thereof
  • H01M10/05—Accumulators with non-aqueous electrolyte
  • H01M10/052—Li-accumulators
  • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M4/04—Processes of manufacture in general
  • H01M4/0402—Methods of deposition of the material
  • H01M4/0404—Methods of deposition of the material by coating on electrode collectors
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M4/04—Processes of manufacture in general
  • H01M4/0471—Processes of manufacture in general involving thermal treatment, e.g. firing, sintering, backing particulate active material, thermal decomposition, pyrolysis
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
  • H01M4/134—Electrodes based on metals, Si or alloys
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
  • H01M4/139—Processes of manufacture
  • H01M4/1395—Processes of manufacture of electrodes based on metals, Si or alloys
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M4/36—Selection of substances as active materials, active masses, active liquids
  • H01M4/38—Selection of substances as active materials, active masses, active liquids of elements or alloys
  • H01M4/386—Silicon or alloys based on silicon
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M4/64—Carriers or collectors
  • H01M4/66—Selection of materials
  • H01M4/661—Metal or alloys, e.g. alloy coatings
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
  • H01M2004/027—Negative electrodes
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
  • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
  • Y02E60/10—Energy storage using batteries

Definitions

• the invention relates to a silicon electrode suitable for use as an anode in a lithium-ion battery, comprising a current collector, preferably made of copper, an adhesive layer arranged on the current collector and a multilayer structure arranged on the adhesive layer.
• Electrochemical energy storage is an essential cornerstone of a global energy transition in order to temporarily store fluctuating renewable electricity and make it available for stationary and mobile applications.
• the rapid development in the field of electromobility and mobile communication devices also increases the demand for high storage capacities and high charging rates for energy storage devices. This is where the established technologies reach their limits.
• new materials are also required in addition to diversifying energy storage concepts.
• these should improve the technical performance of corresponding energy storage concepts (including capacity, energy density, service life), and on the other hand, they should also minimize manufacturing costs.
• the latter can be achieved in particular through the use of readily available chemical elements, such as silicon for which there is already a broad technology base.
• Batteries are electrochemical energy storage devices 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 called accumulators, on the other hand, are rechargeable electrochemical energy storage devices in which the chemical reaction that occurs is reversible, so that multiple use is possible. When charging, electrical energy is converted into chemical energy, and during discharging it is converted from chemical energy into electrical energy.
• Battery is the generic term for cells connected together.
• Cells are galvanic units consisting of two electrodes, electrolytes, separator and cell housing.
• Figure 1 shows an exemplary structure and the function of a lithium-ion cell during the discharging process. The components of a cell are briefly explained below.
• Each Li-ion cell consists of two different electrodes 7, 9, an electrode 7 that is negatively charged in the charged state and an electrode 9 that is positively charged in the charged state. Since during energy release, i.e. during discharge, ions migrate from the negatively charged electrode to the positively charged electrode, the positively charged electrode is called cathode 7 and the negatively charged electrode is called anode 9.
• the electrodes each consist of a current collector 2, 8 (also called a collector) and an active material applied to it together. Between the electrodes there is the ion-conducting electrolyte 4, which enables the necessary charge exchange, and the separator 5, which ensures the electrical separation of the electrodes.
• the cathode consists, for example, of mixed oxides that are 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 a collector and a layer of carbon as an active material. Natural or artificial graphite is usually used as the carbon compound because it has a low electrode potential and a low volume expansion during the charging and discharging process. During the charging process, lithium ions are reduced and stored in the graphite layers.
• the cathode In lithium-ion battery setups, the cathode typically supplies the lithium atoms for charging and discharging in the anode, so the battery capacity is limited by the cathode capacity.
• typical cathode materials used so far are e.g. b.
• Li (Ni, Co, Mn) O2 and LiFePO. ⁇ Due to the structure of the cathode using lithium metal oxides, an increase in capacity is only possible insignificantly.
• silicon instead of carbon in Li battery anodes.
• Silicon is a semiconductor with poor conductivity, very hard and brittle, the surface reacts with oxygen Silicon dioxide.
• silicon as an anode material has a high storage capacity of 3579 mAh/g at room temperature compared to conventional carbon-like materials such as.
• silicon has significantly reduced reactivity and prevents the formation of dendrite structures, especially at high surface currents. Dendrites are tree- or bush-like crystal structures that can pierce the separator and lead to short circuits in the battery and thus rapid cell death.
• Nanostructures of up to 100 nm for crystalline silicon and up to 1 pm for amorphous silicon are considered suitable. This allows the stress of volume expansion to be compensated for without the surface breaking up.
• this thickness is by far not sufficient to compete with the storage capacity of current lithium-ion batteries; for this purpose, structures made of at least 5 pm of pure silicon are necessary, which corresponds to an ideal capacity of 3.5 mAh/cm 2 .
• a layer of silicon particles with a carbon-containing binder is applied to a current collector. calendered.
• the binder ensures adhesion and electrical contact between the particles and to the current collector.
• SEI solid electrolyte interface
• the silicon-based anodes developed so far have the following problems: a high volume expansion when lithium is incorporated, the resulting pulverization of the material and a loss of electrical contact to the current collector, an unstable surface of the anode and poor intrinsic conductivity.
• the silicon electrode according to the invention which is designed and intended for use as an anode in a lithium-ion battery, comprises a current collector, preferably made of copper, an adhesive layer arranged on the current collector and a multilayer structure arranged on the adhesive layer, the multilayer structure as an active layer of the Si electrode is formed from at least one layer of a metal and silicon or is formed from a mixed system which consists of silicon mixed with at least one metal, the multilayer structure being subjected to a short-term tempering and a conductive one Metal-silicide matrix forms, the metal-silicide
• Matrix includes amorphous, nanocrystalline areas of silicon.
• the adhesive layer is formed from one or more of the materials titanium (Ti), silicon (Si), chromium (Cr), tantalum (Ta) and/or tungsten (W).
• the adhesive layer guarantees an extremely stable contact of the active layer of the anode with the current collector of the anode, on the one hand through a mechanical fixation using a roughened surface and on the other hand through a (partial) reaction with the substrate (chemisorption).
• Adhesive layers that can be used or used consist of titanium or chromium as adhesion promoters; With suitable diffusion barriers such as tungsten or carbon, silicon itself can also be used as an adhesive layer.
• the short-term annealing with a controllable and defined energy input into a silicon layer of the multilayer structure causes a partial reaction of the silicon with the copper current collector and the formation of a roughened surface, which creates an extremely strong adhesion between the multilayer structure and the current collector, which does not change weakens during battery operation.
• the multilayer structure as the active layer of the Si electrode is formed from at least one layer.
• a layer comprises a deposited layer of active material which is capable of storing lithium and one or more layers of metal.
• the thickness of the active layer ie the composite, can be made Active material and metal
• the electrode can be made up of one or more layers.
• the at least one layer can be formed from at least one metal and silicon.
• the silicon and the at least one metal are applied alternately through a separate layer deposition of the materials.
• a layer is thus formed from at least one layer of at least one metal and one layer of silicon, with several layers being formed in the multilayer structure in order to achieve the target thickness of the anode (FIG. 5).
• the at least one layer can also be formed by a mixing system, the mixing system made of silicon being mixed with at least one metal (FIG. 6).
• This homogeneous mixture of at least one metal and silicon can be produced from a sputtering target made of sintered powder (Fig. 8b) or it is deposited into a mixed layer by co-deposition (Fig. 8a) of the starting materials.
• the layer thickness for silicon is between 500 - 1000 nm, for metal the layer thickness is between 10 - 100 nm. This means that a multilayer structure of the active layer with a total thickness of 5pm can consist of up to 20 individual layers.
• a further layer of silicon or the mixed system and/or a protective layer which forms a planar surface is arranged on the multilayer structure.
• the deposition technology used for the multilayer structure creates a planar surface.
• a layer of silicon, or the mixed system of silicon and one or more metals can be arranged up to a desired layer thickness and / or a protective layer.
• the planar layer structure has only a small surface area that does not change during battery operation.
• a boundary layer and/or a solid electrolyte is therefore arranged on the planar multilayer structure.
• planar layer structure of the multilayer structure simultaneously offers the possibility of building an artificial protective layer (artificial SEI) through to the application of a solid electrolyte for battery optimization and is therefore suitable for new cell concepts.
• artificial SEI artificial protective layer
• the multilayer structure has an active layer thickness of 10pm.
• the multilayer structure has a specific capacity of >1500mAh/g, preferably >2000mAh/g.
• the active layer can be used in a multi-layer structure or in the multilayer structure, both terms are used synonymously, with various materials and silicon or in the manner of a mixed system made of silicon and one or more metals to produce a specific capacity of over 1500mAh/g, preferably over 2000 mAh/g .
• the specific capacity of pure silicon of 3579 mAh/g the capacity of the Si electrode according to the invention reaches more than 50%.
• the multilayer structure has an area capacity of 2mAh/cm 2 to 6mAh/cm 2 . Larger surface capacities do not make sense because the cost of production increases with increasing layer thickness.
• the multilayer structure can be produced alternately in multilayers by separate layer deposition of the silicon and the at least one metal.
• the advantage of a layered structure over a mixed system is that you can vary each layer in each layer and thus create a customized structure with advantageous properties. For example, to control the volume expansion, a gradual build-up can be created in which an increased metal silicide is present in the area close to the substrate Portion is inserted, whereas in the one near the surface
• a silicon-rich structure can be selected.
• the metal provided in the active layer is made of at least one of the materials titanium (Ti), nickel (Ni), iron (Fe), manganese (Mn), aluminum (Al), tin (Sn). , gold (Au) and / or silver (Ag) and / or a mixture of these materials.
• the short-term annealing is a flash lamp annealing, which is carried out using a flash lamp with a flash duration in the range of 0.2 to 20 ms and an energy density in the range of 0.3 to 160 J/cm 2 and/or preheating or cooling can be carried out in the range from 4 °C to 200 °C.
• the short-term annealing is a laser annealing, which is carried out using a laser with an annealing time in the range from 0.01 to 100 ms by setting a scanning speed of a local heating point and an energy density in the range from 0.1 to 100J/cm 2 and / or can be carried out with preheating or cooling in the range from 4°C to 200°C.
• the temperature range from 4°C to 200°C this refers to the surface temperature of the substrate or the layer to be tempered.
• Ti silicide is formed, which can be Li-storable in the right phase (see: Xu, J. et al. Preparation of TiSi2 Powders with Enhanced Lithium-Ion Storage via Chemical Oven Self-Propagating High-Temperature Synthesis . Nanomaterials 11, 2279 (2021) ) .
• This has the advantage that there is no clear Li-active-inactive interface and therefore good electrical contact also exists during cycling.
• Other metals such as aluminum do not form a compound with silicon, i.e. no silicides. The consequence is that these metals mix in silicon and the electrical conductivity is increased.
• the short-term annealing step the morphology and hardness of the silicon-metal layer can also improve compared to the hard pure silicon.
• the reactions between the silicon particles and the metal particles forced by the short-term tempering are non-equilibrium processes that can only be realized in the ms range and therefore require the use of a flash lamp or a laser.
• the heating ramps achieved in short-term tempering are in for the range of 10 4 - 10 7 K/s required in the process.
• Flash lamp annealing uses a spectrum in the visible wavelength range, whereas laser annealing uses discrete wavelengths in the infrared (IR) to ultraviolet (UV) spectrum.
• the aforementioned reaction is made possible by the defined energy input into one or more layers of particles by means of short-term annealing. There is a sufficient reaction between metal and silicon without the silicon reacting completely. Only insufficient active material remains. More metal means more reaction options but less active material. More energy means more adhesion but less active material. An optimal result depends on the materials used and particle sizes.
• Fig. 1 Example of structure and function of a lithium-ion cell during the discharging process
• Fig. 2 Influence of a temperature input on the silicide formation in a silicon anode a) in a classic furnace process (state of the art) b) with short-term annealing, in particular flash lamp annealing;
• FIG. 3 Schematic representation of the planar Si anode according to the invention
• Fig. 4 Schematic representation of the process for producing an adhesive layer made of silicon
• FIG. 5 Schematic representation of a method for producing a multilayer structure made of silicon and metal
• Fig. 6 Schematic representation of a heterogeneous multilayer structure according to a variant of the Si electrode according to the invention.
• Fug. 7 Schematic representation of a multilayer structure, which is formed from a mixed system, according to a further variant of the Si electrode according to the invention.
• Fig. 8 Possible production variants of the Si electrode according to the invention a) co-deposition of different materials, b) deposition of a mixed target;
• FIG. 9 Schematic representation of a method for producing a mixing system with gradients.
• Figure 2b shows the influence of the short-term annealing 13, in particular flash lamp annealing, on the silicid formation 12 at the contact point in a layer system made of copper 10 and silicon 11. Due to the very short lightning pulse in the range of 0.1 to 10 ms, the silicon 11 does not react completely with the copper 10 to form copper silicide 12. Through the flash lamp annealing 13, pure amorphous or nanocrystalline silicon 11 remains, which is available as an active material for lithium storage, while at the same time there are a sufficient number of inactive areas that ensure stability and good electrical conductivity.
• FIG. 3 shows the schematic representation of the planar Si anode according to the invention.
• An adhesive layer 14 is arranged on a copper substrate 10, on which the multilayer structure 15 is applied as the active layer of the Si anode.
• a protective layer 16 or artificial SEI trained is also provided.
• Figure 4 shows process steps for producing an adhesive layer 14 on the copper substrate 10 for the subsequent construction of the active layer 15 of the Si anode.
• a substrate 10 which also serves as a current collector in a LIB (lithium-ion battery), undergoes a pre-cleaning 17 under vacuum conditions in a plasma atmosphere. This cleaning is necessary because an oxidation layer 18 forms on the substrate 10 in air, which would prevent a reaction between a subsequently applied silicon layer 11 with the copper substrate 10 during flash lamp annealing 13 (FLA - flash lamp annealing) and the silicon layer 11 thus would not adhere to the Cu substrate 10.
• a first silicon layer 11 is then deposited, e.g. B. by sputtering.
• This first silicon layer 11 reacts with the Cu substrate 10 in a transition region to copper silicide 12, thereby increasing the roughness of the substrate 10, e.g. B. a Cu foil, is increased and the silicon layer reacted with the copper serves as a kind of adhesive layer for the further layer structure.
• the copper silicide layer 12 is completely inactive in a battery, so that in a following step a diffusion barrier 19, e.g. B. is applied from carbon.
• This diffusion barrier 19 is necessary in order to prevent the reaction of silicon 11 in copper 10 to form copper silicide 12 during further short-term tempering 13.
• Further Si layers 11, 31 can then be applied sequentially, the layers being able to be stabilized by flash lamp annealing 13 (FIG. 5).
• the advantage of repeated Si -Ab separation and subsequent flash lamp annealing 13 is that with each sequence a stable ("reacted") layer with a closed interface is formed, which acts as an intermediate layer (interface) for the subsequent layers.
• This is advantageous for the adhesion of the Si layer to copper foil, since copper silicide 12 is partially formed and active silicon 11 is still available.
• the method according to the invention described thus also causes a roughening of the surface, so that good adhesion is created for further layers.
• the growth of column structures is also promoted, so that better ion conductivity can be achieved and the copper content can be well controlled for subsequent processes.
• a protective layer 16 is applied to the multilayer structure 15.
• the diffusion and silicide formation 30 can be controlled in a layer, so that a gradual course of silicide formation can be set perpendicular to the surface.
• the copper silicide formation 12, 30 can be gradually adjusted by adjusting the flash lamp energy, the flash lamp duration or the annealing time, by adjusting a scanning speed of a local heating point and an energy density using a laser and/or by minimally adjusting the thickness of the deposited silicon layer 11.
• Figure 6 shows a schematic representation of a heterogeneous structure of a multilayer structure 15, which is formed from layers that are made of silicon 11 and one or more metals 21. Due to the short-term tempering 13, dendrites 23 and nanoparticles 24 are formed in the layers due to diffusion and segregation processes, which form a silicide matrix with large proportions of amorphous silicon 11, which, as a high-capacity electrode material, is ideally suited to cushioning the volume expansion of silicon due to lithium incorporation. At the same time, the conductive silicide matrix forms a stable framework of dendrites 23 to ensure solid electrical contact with the current collector and thus enable continuous battery operation.
• Cavity structures can form because the diffusion rate of Cu in Si is significantly higher than that of Si in Cu, the following applies: D Cu in s ⁇ >> D si in Cu - In the thermal equilibrium state the following applies: D Cu in si ⁇ D VO ids + D si in Cu - Figure 7 shows the influence of the short-term tempering 13 on a mixing system 22.
• a heterogeneous layer 25 can be formed uniformly from a framework of conductive dendrites 23 with an amorphous matrix of the active material 11 through separation processes. Due to supersaturation, nanoparticles (nano droplets) 24 can also form through condensation due to the partial separation of the starting materials.
• the gradual progression e.g. B. the copper concentration in a silicon layer with a copper layer is adjusted by adjusting the pulse duration, the preheating or cooling of the layer structure and a layer thickness of the deposited layers, i.e. 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 the lithium incorporation.
• the overall structure of the silicon electrode according to the invention as an anode in a lithium-ion battery is as follows:
• the active layer was deposited in the multilayer structure 15 with various materials (metals and silicon) or as a mixed system 22 made of at least one metal and silicon and has a specific capacity of over 1500 mAh/g, preferably greater than 2000 mAh/g.
• a further layer of silicon or the mixing system and/or a protective layer or optionally a boundary layer up to a structure of a solid electrolyte is deposited, which has a planar surface.
• an active layer thickness of the active material of the anode of 10 pm is achieved, which enables a surface capacity of 4 mAh/cm 2 with a specific total capacity of 2000 mAh/g.
• This layer structure enables excellent lithium diffusion as well as high electrical conductivity and is suitable for battery operation without the active layer 15 pulverizing.
• the active layer 15 of the anode has an electrical conductivity that is up to 100 times higher than graphite of up to 5*10 4 S/cm due to the heterogeneous formation of a silicide framework. Due to the low resistance, less waste heat is generated during charging/discharging and a more compact design of the entire cell is possible with less cooling.
• planar surface limits the build-up of SEI to an absolute minimum and only the smallest amounts of additives are necessary for SEI control. This also results in low electrolyte consumption and a long service life for anodes constructed in this way.
• Lithium ion battery Collector on anode side SEI -Solid-Electrolyte- Interphase Electrolyte Separator Conductive intermediate phase Cathode, positive electrode Collector on cathode side Anode, negative electrode Copper substrate Silicon Copper silicide, metal silicide
• Short-term tempering e.g. B. Flash lamp tempering adhesive layer multi-layer structure protective layer or SEI plasma pre-cleaning oxidation layer diffusion barrier

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• 2023
  • 2023-02-08 EP EP23706702.0A patent/EP4540871A1/de active Pending
  • 2023-02-08 CN CN202380046838.1A patent/CN119365981A/zh active Pending
  • 2023-02-08 JP JP2024569076A patent/JP2025520280A/ja active Pending
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