CA3205018A1 - Method for producing a silicon-carbon anode and silicon-carbon anode obtainable by the method - Google Patents

Abstract

A pyrolytic production method for a silicon-carbon anode, in which the silicon-carbon anode obtained has a low degree of roughness, includes producing a pyrolyzable coating that is then applied to a substrate. The coating consists of a mixture of silicon particles, conductive additives, and a carbon-containing and pyrolyzable component. The silicon-carbon anode material is then produced by pyrolysis. According to a variant of the method, three different fractions of silicon particles are added to the mixture. According to another variant of the method, particles of a defined size are applied to the coating after pyrolysis.

Description

METHOD FOR PRODUCING A SILICON-CARBON ANODE AND SILICON-CARBON
ANODE OBTAINABLE BY THE METHOD
The invention relates to a method for producing a silicon-carbon anode and a silicon-carbon anode obtainable by the method.
Rechargeable lithium batteries have become a ubiquitous power source for mobile electronic devices. They are used in hybrid and electric vehicles and are an important part of energy storage solutions for renewable energies. To meet the ever-increasing energy demands of these applications, new electrode materials are needed that increase the energy density beyond currently available lithium batteries.
Secondary lithium-ion batteries are particularly attractive energy storage devices with high gravimetric and volumetric capacity and the ability to deliver a high output.
They have become ubiquitous power sources for electric and hybrid electric vehicles.
This has led to an intense interest in developing battery electrodes with high gravimetric and volumetric capacity to improve the energy density of the current generation of lithium batteries. The present application deals with specific anode materials that promise increased capacity.
Lithium metal is the best anode material from the point of view of energy density. However, the electrodeposition of dendritic lithium can cause a short circuit during charging, which raises significant safety concerns for lithium-metal anodes. The most common material used for commercial secondary lithium-ion battery anodes is graphite, which can intercalate a maximum of one lithium per six carbon atoms. The volumetric expansion during lithium intercalation between the planar graphite layers is slightly more than 10%, resulting in high reversibility and stable capacity under repeated cycles.
Nevertheless, the theoretical capacity of graphite is low compared to other potential anode materials, such as the lithium alloys of silicon or tin, which limits the power density.
Silicon is a promising alternative to high capacity graphite anodes. It has a low discharge potential (¨ 370 mV vs. Li/Li), which makes it suitable for high power applications in conjunction with common cathode materials such as LiCo02 or LiMn204. Abundant and non-toxic, it can be alloyed with up to 4.4 lithium atoms per silicon atom.
The theoretical Date Recue/Date Received 2023-06-28

- 2 -capacity of the fully lithiated alloy Li4.4Si is 4212 mAhg-1, which is an order of magnitude higher than graphite. However, the commercial use of silicon in lithium cells is limited by the low cycle stability of silicon. The large volume change during lithium intercalation leads to high internal stresses, pulverization of the electrode, and subsequent loss of electrical contact between the active material and the current collector. However, this challenge can be overcome by silicon nanostructures that allow for easy strain relaxation to counteract fragmentation of the electrode and that may offer the additional benefits of short lithium diffusion distances and enhanced mass transport.
Lithium batteries generally consist of electrochemical cells connected in parallel or in series to achieve the desired current and voltage characteristics. Each cell contains a positive electrode (cathode) and a negative electrode (anode), separated by an electrically insulating but lithium ion permeable separator. Ion conduction takes place by means of an electrolyte. The anode and cathode are connected to each other by means of an external circuit. During charging, electrons flow from the cathode to the anode through the external circuit, while lithium ions deintercalate from the cathode and migrate through the electrolyte to the anode to maintain charge neutrality. With a silicon anode, the lithium ions are alloyed with the silicon and the anode expands until it reaches the desired charge level. Discharge is simply the reverse of this process. The anode undergoes a volume contraction as lithium ions are released. The ions migrate back through the electrolyte and are intercalated at the cathode, while the electrons move through the external circuit to the cathode, performing useful work as they go.
Particle-based anodes, in which electrochemically active silicon nanoparticles are mixed with conductive additives and binders, have the advantage that the often simple particle syntheses are easily scalable. The capacity of particulate anodes containing conductive additives and Si-based composite nanoparticles increases with increasing silicon content.
Cycle stability can be improved by reducing the particle size. Most research in silicon composite anodes is focused on carbon matrices since carbon is abundant, its chemistry is well understood, and carbon has advantages over other possible matrix materials. For example, carbon is highly conductive, enabling efficient electron transport, and is also light and ductile, allowing it to accommodate the volume expansion of the active material.
Silicon-carbon composite materials are typically made by mechanical milling of the active and matrix materials or by pyrolysis of carbon and silicon precursors (special case) to Date Recue/Date Received 2023-06-28

- 3 -obtain silicon in a carbonaceous matrix. The uniform carbon deposition during pyrolysis or prolonged ball milling in many composites results in close contact between carbon and silicon. In particular, it is known that silicon-carbon composite materials can be produced by pyrolysis of organic starting materials mixed with nanoparticulate silicon or by direct pyrolysis of organosilicon starting materials. For example, nanocomposites with different polymers as the carbon source have been reported. Silicon-carbon composite materials, which are produced by pyrolysis and are used as anode material in lithium-ion batteries, are exemplified in US 2016/0365567 Al, US 2018/287129 Al, W02021/009031 Al, US

10673062 BI, US 11114660 BI, US 2022/0013782 Al, and US 2021/0384495 Al. What these processes have in common is that the prepolymer forms a porous carbon structure during pyrolysis. The disadvantage of the electrodes produced in this way has hitherto been a high degree of roughness of the electrodes obtained by pyrolysis, which leads to a high failure rate of the cells as a result of defects in the separator area, particularly in cyclic operation.
It is now the object of the invention to reduce the roughness of the silicon-carbon anode obtained by pyrolysis.
According to a first variant, this object is achieved by the method for producing a silicon-carbon anode with an active coating made of a silicon-carbon composite material. The method comprises the following steps:
al) producing a pyrolyzable coating on a current collector by applying a mixture which comprises a carbonaceous and pyrolyzable component, a conductive additive, and particles of an active material, wherein the active material is silicon or a silicon-containing compound, and the particles are present in at least 3 different fraction sizes determined by means of laser diffraction particle size analysis (LD) according to ISO 13320, of which a first fraction of the particles has the following particle size distribution:
mean diameter D5Om = 3 pm to 8 pm diameter D9Om = 1.5 x D5Om to 3 x D50m, a second fraction of the particles has the following particle size distribution:
mean diameter D5OT = 0.2 x D5Om to 0.25 x D5Om diameter D9OT = 1.5 x D5OT to 3 x D5OT and a third fraction of the particles has the following particle size distribution:
mean diameter D500 = 0.4 x D5Om to 0.45 x D5Om Date Recue/Date Received 2023-06-28

- 4 -diameter D900 = 1.5 x D500 to 3 x D500 wherein the following applies to the relative ratio of the particle numbers of the three fractions:
nT = 1.9 x nm to 2.1 x nm nT = 0.9 x nm to 1.1 x nm where nm = number of first fraction particles in a specified volume of active coating nT = number of second fraction particles in the same volume of active coating no = number of third fraction particles in the same volume of active coating;
and b1) pyrolysis of the coating.
The manufacturing process for the silicon-carbon anode accordingly provides for the application of a mixture containing a pyrolyzable, carbon-containing component which is converted into a carbon-containing matrix by pyrolysis. The mixture also contains at least particles of the active material (silicon or a silicon compound) as well as a conductive additive. In addition to the three essential ingredients mentioned, other components can optionally be present in the mixture. The mixture is applied to the current collector of the later anode and then pyrolysis takes place in a manner known per se, which leads to the formation of the active coating on the current collector. The active coating thus consists of a pyrolytically produced silicon-carbon composite material. The special feature of the method is that three different batches (or fractions) of particles of the active material are added to the mixture. The three fractions differ in their particle size distribution, wherein the particle sizes of the individual fractions are precisely matched to one another in such a way that the density of the active coating is increased. This is accompanied by a reduction in the roughness of the surface of the pyrolytically produced active coating of the anode.
Using laser diffraction particle size analysis (LD) according to ISO 13320, the particle sizes of the three added fractions of the active material can be determined.
The equivalent diameter of a non-spherical particle corresponds to the diameter of a spherical particle that has the same properties as the non-spherical particle under investigation. A first fraction of the particles has the following (volume-related) particle size distribution: mean diameter D5Om = 1 pm to 10 pm and diameter D9Om = 1.5xD5Om to 3x D50m. The particles of the first fraction have a significantly higher mean diameter D5Om than the particles of Date Recue/Date Received 2023-06-28

- 5 -the second and third fractions. The mean particle diameter D50m is preferably in the range from 3 pm to 8 pm, in particular in the range from 4 pm to 6 pm. D90m is preferably 1.5 x D50m to 2 x D50m, especially 1.5 x D50m.
The second added fraction of the particles has the following particle size distribution:
mean diameter D50T = 0.2 x D50m to 0.25 x D50m and diameter D90T = 1.5 x D50T
to 3 x D50T. In other words, the mean diameter of the particles of the second fraction is only 0.2 to 0.25 times the mean diameter of the particles of the first fraction. Even if the particles of the first fraction compactly abut one another in the active coating, the smaller particles of the second fraction can still occupy a place in the resulting tetrahedral voids of the compact arrangement. D90T is preferably 1.5 x D50T to 2 x D50T, in particular 1.5 x D50T.
The particles of the third fraction, which are slightly larger compared to the second fraction, have the following particle size distribution: mean diameter D500 =
0.4 x D5Om to 0.45 x D5Om and diameter D90o = 1.5 x D50o to 3 x D50o. In other words, the mean diameter of the particles of the third fraction is only 0.4 to 0.45 times the mean diameter of the particles of the first fraction. Even if the particles of the first fraction compactly abut one another in the active coating, the smaller particles of the third fraction can still occupy a place in the resulting octahedral voids of the compact arrangement. D90o is preferably 1.5 x D50o to 2 x D50o, in particular 1.5 x D50o.
In a specific volume of the active coating, there is a defined number nm of particles of the first fraction. The number of particles nm of the first fraction in turn determines the number of particles nT of the second fraction and the number of particles no of the third fraction.
The following relationship applies: nT = 1.9 x nm to 2.1 x nm and nT = 0.9 x nm to 1.1 x nm.
In the specified volume, the number of particles in the second fraction is therefore 1.8 to 2.1 times the number of particles in the first fraction and the number of particles in the third fraction is 0.9 to 1.1 times the number of particles in the first fraction. Overall, a particularly dense active coating can be achieved in this way, the roughness of which is reduced.
The silicon-containing compound may preferably be Si, SiC, SiOx, or SiN. The mixture can contain particles that consist of the same active material. However, it is also conceivable that particles with a different active material are used. For example, the active material of the individual fractions can differ from one another. However, it is also possible Date Recue/Date Received 2023-06-28

- 6 -to use different active materials within a fraction, provided they meet the criteria set for the fraction for the mean diameter D50 and the diameter D90.
The mixture for application in step al ) or the active coating contains a conductive additive.
The conductive additive can be a conductive carbon black and/or a carbon-based conductive material. Conductive carbon blacks are preferred. Conductive additives are well-known additives for lithium-ion batteries. Conductive carbon black (also known as conductive industrial soot, conductivity black, and carbon black) is a black specialty chemical available as a powder. It is manufactured using strictly controlled processes and contains more than 95% of pure carbon. Conductive carbon black has widely ramified aggregates that ensure electrical conductivity in the application. The shape of the aggregates can vary, and a distinction is made between spherical, elliptical, linear, and branched aggregates. Conductive carbon blacks with linear and branched aggregates are particularly preferred because they have higher electrical conductivity and can be dispersed more readily. Conductive carbon blacks are produced, among other things, by the furnace black method and by thermal cracking, such as the acetylene black method.
Carbon-based conductive materials comprise carbon nanotubes (CNT) and graphene.
Organic polymers such as, for example, polyvinyl alcohols, polyacrylates, and polyvinylamides can be used as carbon-containing and pyrolyzable components.
The mixture may also contain a binder or a solvent.
The mixture applied preferably has the following composition:
1 to 95% by weight of particles of silicon or a silicon-containing compound (total across all fractions), preferably 40 to 90% by weight;
0.01 to 15% by weight of conductive additive, preferably 0.5 to 5% by weight;
0.1 to 30% by weight of the carbonaceous and pyrolyzable component, preferably 1 to 20% by weight;
optionally, 0 to 20% by weight of a solvent;
optionally, 0 to 5% by weight of a binder; and less than 1% by weight of impurities.
The percentages are based on the total weight of the mixture. All percentages add up to 100% by weight.
In step bl ) of the method, the applied coating is converted into the desired silicon-carbon Date Recue/Date Received 2023-06-28

- 7 -composite material by pyrolysis and forms the anode. The composite material is formed in the course of the thermochemical conversion of the mixture of substances.
Pyrolysis preferably takes place in an oxygen-free atmosphere and at a temperature in the range from 200 C to 1000 C, preferably from 250 C to 900 C.
A silicon-carbon anode with an active coating of a silicon-carbon composite material is obtainable by the method, wherein the silicon-carbon composite material comprises the following components:
(i) a pyrolytically produced carbonaceous matrix;
(ii) a conductive additive; and (iii) particles of an active material, wherein the active material is silicon or a silicon-containing compound and the particles are present in at least 3 different fraction sizes determined by means of laser diffraction particle size analysis (LD) according to ISO
13320, of which a first fraction of the particles has the following particle size distribution:
mean diameter D5Om = 1 pm to 10 pm diameter D9Om = 1.5 x D5Om to 3 x D5Om a second fraction of the particles has the following particle size distribution:
mean diameter D5OT = 0.2 x D5Om to 0.25 x D5Om diameter D9OT = 1.5 x D5OT to 3 x D5OT and a third fraction of the particles has the following particle size distribution:
mean diameter D500 = 0.4 x D5Om to 0.45 x D5Om diameter D90o = 1 .5 x D50o to 3 x D50o wherein the following applies to the relative ratio of the particle numbers of the three fractions:
nT = 1.9 x nm to 2.1 x nm nT = 0.9 x nm to 1.1 x nm where nm = number of first fraction particles in a specified volume of active coating nT = number of second fraction particles in said volume of active coating no = number of third fraction particles in said volume of active coating.
According to a second variant, the object mentioned above is achieved by the method for producing a silicon-carbon anode with an active coating made of a silicon-carbon composite material. For this purpose, said method comprises the following steps:
Date Recue/Date Received 2023-06-28

- 8 -a2) producing a pyrolyzable coating on a current collector by applying a mixture containing a carbonaceous and pyrolyzable component, a conductive additive, and particles of silicon or a silicon-containing compound;
b2) pyrolysis of the coating; and c2) applying compensating particles made of an active material to the active coating resulting from step b2), wherein the active material is selected from the group consisting of graphite, graphene, silicon, and silicon-containing compounds and the compensating particles have a mean diameter D50 of 5 pm to 20 pm, wherein the mean diameter D50 is determined using laser diffraction particle size analysis (LD) according to ISO 13320.
The manufacturing method for the silicon-carbon anode according to the second variant thus provides for the application of a mixture containing a pyrolyzable, carbon-containing component which is converted into a carbon-containing matrix by pyrolysis. The mixture also contains at least particles of the active material (silicon or a silicon compound) as well as a conductive additive. In addition to the three essential ingredients mentioned, further components can optionally be present in the mixture. The mixture is applied to the current collector of the later anode and then pyrolysis takes place in a manner known per se, which leads to the formation of a coating on the current collector. This coating thus consists of a pyrolytically produced silicon-carbon composite material. The special feature of the method is that the relatively rough coating obtained through pyrolysis is then leveled by applying particles of an active material. The particle size is chosen so that applied compensating particles can fill depressions in the surface of the pyrolytically produced coating. As a result, the surface is smoothed so that the roughness of the surface of the pyrolytically produced active coating of the anode is reduced.
The compensating particles used in step c2) have a mean diameter D50 of 5 pm to 20 pm, preferably 8 pm to 12 pm, wherein the mean diameter D50 is determined using laser diffraction particle size analysis (LD) according to ISO 13320. It has been shown that this particle size is particularly suitable for smoothing the rough surface of the coating produced by pyrolysis.
The silicon-containing compound of the particles or compensating particles can preferably be Si, SiC, SiOx, or SiN.
Date Recue/Date Received 2023-06-28

- 9 -The compensating particles can consist of the same active material as the particles already present in the coating. However, it is also conceivable that the compensating particles consist of a different active material. However, it is also possible to use compensating particles made from different active materials, provided they meet the criterion set for the mean diameter D50.
According to a preferred variant of the method, the compensating particles made of the active material are applied in the form of a paste. A paste is a solid-liquid mixture (suspension) having a high solids content. Pastes are no longer flowable, but spreadable.
Application of the paste is particularly easy to implement in terms of process engineering.
The paste can be in the form of an aqueous suspension, for example. In addition to the compensating particles from the active material, the paste can contain other components, such as conductive additives and binders.
The mixture for application in step a2) or the coating produced in step b2) contains a conductive additive. Likewise, the paste with the compensating particles can contain a conductive additive. The conductive additive can be a conductive carbon black and/or a carbon-based conductive material. Conductive carbon blacks are preferred.
Conductive additives are well-known additives for lithium-ion batteries. Conductive carbon black (also known as conductive industrial soot, conductivity black, and carbon black) is a black specialty chemical available as a powder. It is manufactured using strictly controlled processes and contains more than 95% of pure carbon. Conductive carbon black has widely ramified aggregates that ensure electrical conductivity in the application. The shape of the aggregates can vary, and a distinction is made between spherical, elliptical, linear, and branched aggregates. Conductive carbon blacks with linear and branched aggregates are particularly preferred because they have higher electrical conductivity and can be dispersed more readily. Conductive carbon blacks are produced, among other things, by the furnace black method and by thermal cracking, such as the acetylene black method. Carbon-based conductive materials comprise carbon nanotubes (CNT) and graphene.
Organic polymers such as, for example, polyvinyl alcohols, polyacrylates, and polyvinylamides can be used as carbon-containing and pyrolyzable components.
The mixture may also contain a binder or a solvent.
Date Recue/Date Received 2023-06-28

- 10 -The mixture applied from step a2) preferably has the following composition:
1 to 95% by weight of particles of silicon or a silicon-containing compound, preferably 40 to 90% by weight;
0.01 to 15% by weight of conductive additive, preferably 0.5 to 5% by weight;
0.1 to 30% by weight of the carbonaceous and pyrolyzable component, preferably 1 to 20% by weight;
optionally, 0 to 20% by weight of a solvent;
optionally, 0 to 5% by weight of a binder; and less than 1% by weight of impurities.
The percentages are based on the total weight of the mixture. All percentages add up to 100% by weight.
In step b2) of the method, the applied coating is converted into the desired silicon-carbon composite material by pyrolysis and forms the anode. The composite material is formed in the course of the thermochemical conversion of the mixture of substances.
Pyrolysis preferably takes place in an oxygen-free atmosphere and at a temperature in the range from 200 C to 1000 C, preferably from 250 C to 900 C.
Preferred refinements of the invention will be apparent from the other features mentioned in the dependent claims and from the following description.
The various embodiments of the invention mentioned in this application can be combined with one another, unless stated otherwise in an individual case.
The invention is explained below in exemplary embodiments with reference to the associated drawings. Wherein:
Figure 1 shows a schematic structure of a rechargeable lithium-ion battery.
Figure 2 shows a flowchart for the production method according to the invention of a silicon-carbon anode according to a first variant.
Figure 3 shows a flowchart for the production method according to the invention of a silicon-carbon anode according to a second variant.
Date Recue/Date Received 2023-06-28

-11 -Figure 1 shows a highly schematic sectional view of the basic structure of a rechargeable lithium-ion battery 10. The lithium-ion battery 10 includes a positive electrode (cathode

12) and a negative electrode (anode 14), which are separated from one another by an electrically insulating but lithium ion permeable separator 16. Ion conduction takes place by means of a liquid electrolyte. The anode 14 and cathode 12 are connected to each other by means of an external circuit. During charging, electrons flow from the cathode 12 to the anode 14 through the external circuit, while lithium ions deintercalate from the cathode 12 and migrate through the electrolyte to the anode 14 to maintain charge neutrality. Discharge is simply the reverse of this process. The anode 14 undergoes a volume contraction as lithium ions are released. The ions migrate back through the electrolyte and are intercalated at the cathode 12, while the electrons move through the external circuit to the cathode 12, performing useful work as they go (load 20).
The anode 14 is a silicon-carbon anode and, according to the exemplary embodiment, contains silicon particles embedded in an electrically conductive carbon matrix.
First variant of the production method The silicon-carbon anode is produced using a pyrolytic method, the method steps of which are illustrated in FIG. 2 using an exemplary embodiment.
In step S100 of the method, a mixture is produced of silicon particles, conductive additive, a carbon-containing and pyrolyzable component, and a solvent. For this purpose, the ingredients can be mixed with one another using conventional mechanical methods. The aim is to obtain a mixture with the most homogeneous distribution of the components possible.
When preparing the mixture, three different fractions of silicon particles are used. A first fraction contains particles with a mean diameter D5Om of 5 pm and a diameter D9Om of 9 pm. The second fraction contains particles with a mean diameter D5OT of 1 pm and a diameter D9OT of 2 pm. The third fraction contains particles with a mean diameter D50o of 2 pm and a diameter D90o of 4 pm. The proportions of the fractions are measured in such a way that the number of particles in the first and third fractions is the same and twice as many particles are present in the second fraction compared to the number of particles of the first fraction in the mixture.
Date Recue/Date Received 2023-06-28 Water is used as the solvent, wherein the conductive additive is a conductive carbon black and the pyrolyzable component is a polyvinyl alcohol. The mixture contains 50%
by weight of silicon particles or particles of silicon or a silicon-containing compound, 25% by weight of the pyrolyzable component, 20% by weight of water and 5% by weight of conductive additive.
In step S110, the homogeneous mixture produced is applied to a current collector. The current collector can be a metal foil, for example. Common mechanical coating techniques can also be used for this method step. Pastes can be applied, for example, by roll coating, thermal spraying, slot coating, spray coating, or knife coating.
In step S120, the coated substrate is heated such that the carbonaceous and pyrolyzable component is thermally decomposed into carbon. Accordingly, the process conditions necessary for the pyrolysis of the respective component prevail in this method step. This is usually a low-oxygen or oxygen-free atmosphere and temperatures above 200 C. At the end of the pyrolysis and after cooling, the silicon-carbon anode obtained in this way is available for the further method steps in the production of lithium-ion batteries.
Second variant of the production method Figure 3 illustrates the production of a silicon-carbon anode according to another variant of the method in a flow chart.
In step S200 of the method, a mixture is produced of silicon particles, conductive additive, a carbon-containing and pyrolyzable component, and a solvent. For this purpose, the ingredients can be mixed with one another using conventional mechanical methods. The aim is to obtain a mixture with the most homogeneous distribution of the components possible.
Water is used as the solvent, the conductive additive is a conductive carbon black, and the pyrolyzable component is a polyvinyl alcohol. The mixture contains 50% by weight of silicon particles, 25% by weight of the pyrolyzable component, 20% by weight of water, and 5% by weight of conductive additive.
Date Recue/Date Received 2023-06-28

- 13 -In step S210, the homogeneous mixture produced is applied to a current collector. The current collector can be a metal foil, for example. Common mechanical coating techniques can also be used for this method step. Pastes can be applied, for example, by roll coating, thermal spraying, slot coating, spray coating, or knife coating.
In step S220, the coated substrate is heated such that the carbonaceous and pyrolyzable component is thermally decomposed into carbon. Accordingly, the process conditions necessary for the pyrolysis of the respective component prevail in this method step. This is usually a low-oxygen or oxygen-free atmosphere and temperatures above 200 C.
In step S230 of the method, a paste is prepared from silicon particles or particles of silicon or a silicon-containing compound (as compensating particles), a conductive additive, a binder, and a solvent. For this purpose, the ingredients can be mixed with one another using conventional mechanical methods. The aim is to obtain a mixture with the most homogeneous distribution of the components possible.
The compensation particles have a mean diameter D50 of 10 pm and are made of silicon.
Water is used as the solvent, and the conductive additive is a conductive carbon black.
The paste contains 80% by weight of silicon particles, 15% by weight of water, and 5%
by weight of conductive additive.
In a step S240, the paste is applied to the coating produced in step S200.
Common mechanical coating techniques can also be used for this method step. Pastes can be applied, for example, by roll coating, thermal spraying, slot coating, spray coating, or knife coating.
After the paste has dried, the active coating of the silicon-carbon anode is complete and the anode obtained in this way is available for the further method steps in the production of lithium-ion batteries.
Date Recue/Date Received 2023-06-28

- 14 -List of reference numerals lithium-ion battery 12 cathode 5 14 anode 16 separator load S100 - S120 method steps according to a first variant S200 - S240 method steps according to a second variant Date Recue/Date Received 2023-06-28

Claims (6)

What is claimed is:

1. A method of producing a silicon-carbon anode having an active coating of a silicon-carbon composite, wherein the method comprises the steps of:
al) producing a pyrolyzable coating on a current collector by applying a mixture which comprises a carbonaceous and pyrolyzable component, a conductive additive, and particles of an active material, wherein the active material is silicon or a silicon-containing compound, and the particles are present in at least 3 different fraction sizes determined by means of laser diffraction particle size analysis (LD) according to ISO 13320, of which a first fraction of the particles has the following particle size distribution:
mean diameter D5Orvi = 3 pm to 8 pm diameter D9Orvi = 1.5 x D5Orvi to 3 x D5Orvi a second fraction of the particles has the following particle size distribution:
mean diameter D5OT = 0.2 x D5Orvi to 0.25 x D5Orvi diameter D9OT = 1.5 x D5OT to 3 x D5OT and a third fraction of the particles has the following particle size distribution:
mean diameter D50o = 0.4 x D5Onn to 0.45 x D5Onn diameter D90o = 1.5 x D50o to 3 x D50o, wherein the following applies to the relative ratio of the particle numbers of the three fractions:
nT = 1.9 x nivi to 2.1 x rim nT = 0.9 x nivi to 1.1 x rim where rim = number of first fraction particles in a specified volume of active coating nT = number of second fraction particles in the same volume of active coating no = number of third fraction particles in the same volume of active coating;
and bl) pyrolysis of the coating.

2. A silicon-carbon anode with an active coating of a silicon-carbon composite material, wherein the silicon-carbon composite material comprises the following com ponents:
(i) a pyrolytically produced carbonaceous matrix;

(ii) a conductive additive; and (iii) particles of an active material, wherein the active material is silicon or a silicon-containing compound and the particles are present in at least 3 different fraction sizes determined by means of laser diffraction particle size analysis (LD) according to ISO 13320, of which a first fraction of the particles has the following particle size distribution:
mean diameter D5Orvi = 1 pm to 10 pm diameter D9Onn = 1.5 x D5Onn to 3 x D5Onn a second fraction of the particles has the following particle size distribution:
mean diameter D5OT = 0.2 x D5Orvi to 0.25 x D5Orvi diameter D9OT = 1.5 x D5OT to 3 x D5OT and a third fraction of the particles has the following particle size distribution:
mean diameter D50o = 0.4 x D5Onn to 0.45 x D5Onn diameter D90o = 1.5 x D50o to 3 x D50o, wherein the following applies to the relative ratio of the particle numbers of the three fractions:
nT = 1.9 x nivi to 2.1 x rim nT = 0.9 x rim to 1.1 x rim where rim = number of first fraction particles in a specified volume of active coating nT = number of second fraction particles in said volume of active coating no = number of third fraction particles in said volume of active coating.

3. A silicon-carbon anode according to claim 2, wherein the silicon-containing compound is SiC, SiOx, or SiN.

4. A method of producing a silicon-carbon anode having an active coating of a silicon-carbon composite, wherein the method comprises the steps of:
a2) producing a pyrolyzable coating on a current collector by applying a mixture containing a carbonaceous and pyrolyzable component, a conductive additive, and particles of silicon or a silicon-containing compound;
b2) pyrolysis of the coating; and c2) applying compensating particles made of an active material to the active coating produced by step b2), wherein the active material is selected from the group consisting of graphite, graphene, silicon, and silicon-containing compounds, and the compensation particles have a mean diameter D50 of 5 pm to 20 pm, wherein the mean diameter D50 is determined using laser diffraction particle size analysis (LD) in accordance with ISO 13320.

5. The method according to claim 4, wherein the compensating particles from the active material are applied in the form of a paste.

6. The method according to claim 5, wherein the paste is present in the form of an aqueous suspension.