WO2023147853A1

WO2023147853A1 - Hierarchically structured si/c agglomerates made by spray drying

Info

Publication number: WO2023147853A1
Application number: PCT/EP2022/052453
Authority: WO
Inventors: Stefan Bade; Julia Lyubina; Theresa WASSMER; Adil AMIN; Moritz LOEWENICH; Stefan Oliver KILIAN; Fatih ÖZCAN; Doris SEGETS; Hartmut Wiggers
Original assignee: Evonik Operations Gmbh; Universität Duisburg-Essen
Priority date: 2022-02-02
Filing date: 2022-02-02
Publication date: 2023-08-10
Also published as: TW202332653A

Abstract

The present invention relates to a method for making a micrometer-sized agglomerate powder for use as active anode material, a spray dried micrometer-sized agglomerate powder comprising nanometer-sized silicon-containing particles and a polymeric binder, a coating composition comprising the micrometer-sized agglomerate powder, a method for making an anode or an energy storage device comprising the step of applying the coating composition onto an anode substrate, and an anode or energy storage device comprising the micrometer-sized agglomerate powder.

Description

Hierarchically structured Si/C agglomerates made by spray drying

Lithium-ion batteries (LIBs) play a crucial part in non-stationary electric applications and the forthcoming energy transition, and the demand for them is ever increasing, due to e.g., the growth of applications such as electric vehicles and grid storage systems, personal electronic devices, and the like. For all these applications energy and power densities should be high, while manufacturing costs should be low and application safety should be given in order to allow broad commercial adoption.

At present, in LIBs the anode is typically made from graphite coated on copper foil. To further enhance the energy density of state-of-the-art LIBs, researchers have synthesized and optimized various new active materials. Among new electrode materials, silicon is the most promising one to replace graphite due to its high theoretical specific capacity and low electrochemical potential. However, in addition to intrinsic properties of the active material, its packing properties on the electrode also affect the energy density of the final battery, and the implementation of silicon is challenging due to its large volume expansion on lithiation, leading to fracturing, and hence a loss of electrical contact and a decrease in long-term stability.

To tackle these issues, structured composite particles have been synthesized by various processes. In order to reduce the surface-to-volume ratio, increase the achievable solids content of dispersions used for applying the material to anode substrates and achieve a dense packing on an electrode level while preserving the intrinsic properties of nanoscale materials, so-called hierarchically structured agglomerates have been synthesized wherein nanoscale structures are agglomerated to form an ordered micrometer-sized structure, which is often essentially spherical, while essentially maintaining the specific chemical properties of the nanoscale materials.

Spray drying is a well-known method for making spherical agglomerates which is used in various technical fields. For making active battery materials mainly reactive spray drying is reported in the literature. Herein a precursor compound is made by spray drying which is then processed using heat, and/or a chemical treatment to obtain the final active material. For instance, Si/C composites have been synthesized by spray drying a dispersion of silicon particles and polyvinyl alcohol (PVA) as a carbon precursor to first coat the silicon particles with a polymer layer which is then carbonized to obtain a carbon coating (C. Paireau et al. Electrochimica Acta 2015, 174, 361-368). Such approaches, however, are time-consuming and costly and often do not allow to precisely control the content of certain compounds in the active materials which may be electrochemically disadvantageous.

Other approaches for creating composite microstructures included spray pyrolysis of precursor compounds, ball milling of silicon in an inactive host material, or the chemical reaction of gels.

However, often poor cyclability is observed, the maximum obtainable amount of active material in the composite is still not high enough, processing times are rather long and in particular spray pyrolysis often does not allow to precisely control the structure, size and composition of the material obtained.

A. Amin et al. reported non-reactive spray drying of different silicon-based materials, including pure silicon, amorphous silicon nitride (SiN_x) and silicon/carbon (Si/C) composite nanoaggregates (A. Amin et al. 2021 ECS Meet. Abstr. MA2021-02 95). While SiN_x nanoaggregates could be successfully converted into micrometer-sized agglomerates by spray drying, this approach was unsuccessful for Si/C nanoaggregates. There remains a need for providing new active anode materials in an efficient manner in order to increase the energy density of batteries and other energy storage devices and to minimize irreversible capacity loss in both the initial and subsequent cycles.

This object has been solved by the methods, spray dried micrometer-sized agglomerate powder, coating composition, anode and energy storage device of the present invention, as defined in the appended claims.

It has surprisingly been found that mixing preformed nanometer-sized silicon-containing particles with a rather small amount of a polymeric binder in an aqueous medium to form a dispersion prior to spray drying said dispersion allows to make a micrometer-sized agglomerate powder for use as active anode material in a non-reactive spray drying process, i.e., without subjecting the dispersion or powder to a pyrolysis (carbonization step) during or after the spray drying step. In the process of the present invention the use of a binder enhances the structural stability of the particles and enables to achieve a high energy density in the anode material.

The present invention provides a post-synthetic spray drying process for producing hierarchically structured micrometer-sized agglomerates of preformed nanometer-sized aggregates. As used herein, the term "post-synthetic" refers to the fact that spray drying takes place after the Si/C nanoparticles have been formed, in contrast to the reactive spray drying processes known in the art. Further, no time- and energy-consuming process steps are necessary after the spray drying step to obtain the active anode material. The process and the micrometer-sized agglomerate powder obtained enable the making of densely packed electrodes of silicon-containing composite particles while preserving their nanoscale structure. The micrometer-sized agglomerates can easily be dispersed in a liquid medium to provide a coating composition to be applied onto an anode substrate, and the anodes obtained exhibit excellent specific discharge capacity compared to anodes coated with a dispersion comprising the preformed nanoaggregates which were not subjected to the process of the present invention for making a micrometer-sized agglomerate powder. This shows that the inner stress and the resulting cracking evolution in the electrodes can be well-relieved by the generated Si/C micrometer-sized agglomerates. Further, combining well- established industrial processes for nanoparticle synthesis in a hot-wall reactor with the post- synthetic, non-reactive spray drying process of the present invention enables the large-scale syntheses of highly dense active materials for LIBs with improved electrochemical properties.

Accordingly, the present invention relates to a method for making a micrometer-sized agglomerate powder for use as active anode material comprises the steps of: (i) mixing preformed nanometer-sized silicon-containing particles with a polymeric binder in an aqueous liquid to form a dispersion; and (ii) spray drying the dispersion and collecting the resulting micrometer-sized agglomerate powder without subjecting the dispersion or powder to a pyrolysis during or after step (ii).

As used herein, the term "micrometer-sized" generally refers to particles having a median particle size in the range of from 1 to 999 pm, determined by analytical centrifugation, as further described below.

As used herein, the term "preformed nanometer-sized silicon-containing particles" refers to particles comprising silicon, which have a primary particle size, as determined by SEM, and a median particle size in aggregated form, determined by analytical centrifugation, as further described below, both being in the range of from 1 to 999 nm. The preformed nanometer-sized silicon-containing particles are not formed during or after the spray drying step of the method of the present invention, but have been previously formed by a separate method. They may comprise or consist essentially of elemental silicon in amorphous or crystalline form, i.e., comprise other elements in a total amount of less than, such as less 5 wt.-%, preferably less than 2 wt.-%, and more preferably less than 1 wt.-%, based on the total weight of nanometer-sized silicon-containing particles, and can be made by various processes known in the art, including e.g., gas-phase reactions, milling etching, etc. The preformed nanometer-sized silicon-containing particles may preferably comprise silicon and carbon in elemental form, and in this instance may also be referred to as "preformed nanometer-sized silicon-carbon composite particles". They may preferably consist essentially of silicon and carbon, i.e., comprise other elements in a total amount of less than, such as less 5 wt.-%, preferably less than 2 wt.-%, and more preferably less than 1 wt.-%, based on the total weight of nanometer-sized silicon-containing particles. Suitable nanometer-sized silicon-carbon composite particles may be produced by gas-phase synthesis in a hot wall reactor using e.g., the process described in EP 3415469 Al or the process described by H. Orthner et al. (Journal of Alloys and Compounds 2021, 870, 159315). EP 3415469 Al describes a process of producing a silicon-carbon composite powder, wherein a first gas stream containing at least one silane selected from Sil- , SiaHg and/or SiaHg and at least one hydrocarbon selected from ethene and/or acetylene, and a coaxial second gas stream containing hydrogen or argon are fed into a hot wall reactor, wherein the second gas stream forms the jacket stream with respect to the first gas stream, wherein at least the first gas stream is reacted at a temperature of 600 °C to 1100 °C, and wherein subsequently at the outlet of the hot wall reactor the reaction mixture is cooled or allowed to cool and the pulverulent reaction product is separated from gaseous materials. Suitable nanometer-sized silicon-carbon composite particles are also commercially available as Siridion® Black from Evonik Industries (Essen, Germany).

As used herein, the term "aqueous liquid" refers to a medium which is liquid at room temperature (23 °C) and comprises water. The aqueous liquid may comprise water in an amount of more than 50 wt.-%, preferably in an amount of at least 75 wt.-%, more preferably in an amount of at least 85 wt.-%, even more preferably in an amount of at least 90 wt.-%, and still even more preferably in an amount of at least 95 wt.-%, based on the combined weight of solvents in the medium. Organic solvents, such as alcohols, may be present in the aqueous liquid, but most preferably the aqueous liquid consists of water as the sole solvent.

In the method of the present invention, preformed nanometer-sized silicon-containing particles are used, so that there is no need to subject the dispersion to be spray dried or the powder obtained after spray drying to a pyrolysis or carbonization step in order to thermally decompose organic carbon-containing precursors to form elemental carbon, as it is the case in many processes of the prior art which make use of a spray drying step. Preferably, the dispersion to be spray dried and the powder obtained after spray drying are not subjected to temperatures exceeding 200 °C during or after carrying out the method of the present invention. It will be understood that using the method of the present invention, the organic nature of the polymeric binder is essentially retained, except for some possible condensation or crosslinking reactions between functional groups in the binder, as described below.

The content of silicon in the preformed nanometer-sized silicon-containing particles may be 80 wt.-% or more, preferably 85 wt.-% or more, more preferably 90 wt.-% or more, and most preferably 95 wt.-% or more, based on the total weight of the preformed nanometer-sized silicon-containing particles. The content of silicon in the preformed nanometer-sized sil iconcontaining particles may be 99.5 wt.-% or less, preferably 99 wt.-% or less, more preferably 98 wt.-% or less, even more preferably 97 wt.-% or less, and most preferably 96 wt.-% or less, based on the total weight of the preformed nanometer-sized silicon-containing particles. Accordingly, the content of silicon in the preformed nanometer-sized silicon-containing particles may be in the range of from 80 to 99.5 wt.-%, preferably of from 85 to 99 wt.-%, more preferably of from 90 to 98 wt.-%, even more preferably of from 90 to 97 wt.-%, and most preferably of from 95 to 96 wt.- %, based on the total weight of the preformed nanometer-sized silicon-containing particles.

The content of elemental carbon in the preformed nanometer-sized silicon-containing particles may be 20 wt.-% or less, preferably 15 wt.-% or less, more preferably 10 wt.-% or less, and most preferably 5 wt.-% or less, based on the total weight of the preformed nanometer-sized silicon- containing particles. The content of elemental carbon in the preformed nanometer-sized silicon- containing particles may be 0.5 wt.-% or more, preferably 1 wt.-% or more, more preferably 2 wt.-% or more, even more preferably 3 wt.-% or more, and most preferably 4 wt.-% or more, based on the total weight of the preformed nanometer-sized silicon-containing particles. Accordingly, the content of elemental carbon in the preformed nanometer-sized silicon- containing particles may be in the range of from 0.5 to 20 wt.-%, preferably of from 1 to 15 wt.- %, more preferably of from 2 to 10 wt.-%, even more preferably of from 3 to 5 wt.-%, and most preferably of from 4 to 5 wt.-%, based on the total weight of the preformed nanometer-sized silicon-containing particles.

While other elements may be present in the preformed nanometer-sized silicon-containing particles, the preformed nanometer-sized silicon-containing particles preferably consist essentially of silicon and carbon and contains other elements only in a maximum amount of 5 wt.-% or less, preferably 2 wt.-% or less and more preferably 1 wt.-% or less, based on the total weight of the preformed nanometer-sized silicon-containing particles. Most preferably the preformed nanometer-sized silicon-containing particles consist of silicon and carbon, i.e., their respective contents in the preformed nanometer-sized silicon-containing particle add up to 100 wt.-%, based on the total weight of the preformed nanometer-sized silicon-containing particles. The content of silicon in the micrometer-sized agglomerate powder may be 77 wt.-% or more, preferably 82 wt.-% or more, more preferably 87 wt.-% or more, and most preferably 92 wt.-% or more, based on the total weight of the micrometer-sized agglomerate powder. The content of silicon in the micrometer-sized agglomerate powder may be 98 wt.-% or less, preferably 97 wt.-% or less, more preferably 96 wt.-% or less, even more preferably 95 wt.-% or less, and most preferably 94 wt.-% or less, based on the total weight of the micrometer-sized agglomerate powder. Accordingly, the content of silicon in the micrometer-sized agglomerate powder may be in the range of from 77 to 98 wt.-%, preferably of from 82 to 97 wt.-%, more preferably of from 87 to 96 wt.-%, even more preferably of from 87 to 95 wt.-%, and most preferably of from 92 to 95 wt.-%, based on the total weight of the micrometer-sized agglomerate powder.

The content of elemental carbon in the micrometer-sized agglomerate powder may be 20 wt.-% or less, or 15 wt.-% or less, or 10 wt.-% or less, or 5 wt.-% or less, based on the total weight of the micrometer-sized agglomerate powder. The content of elemental carbon in the micrometer-sized agglomerate powder may be 0.5 wt.-% or more, preferably 1 wt.-% or more, more preferably 2 wt.-% or more, even more preferably 3 wt.-% or more, and most preferably 4 wt.-% or more, based on the total weight of the micrometer-sized agglomerate powder. Accordingly, the content of elemental carbon in the micrometer-sized agglomerate powder may be in the range of from 0.5 to 20 wt.-%, preferably of from 1 to 15 wt.-%, more preferably of from 2 to 10 wt.-%, even more preferably of from 3 to 5 wt.-%, and most preferably of from 4 to 5 wt.-%, based on the total weight of the micrometer-sized agglomerate powder. As used herein, the term "elemental carbon" does not include the organic carbon being present in the polymeric organic binder.

The content of binder in the micrometer-sized agglomerate powder may be in the range of from 15 to 0.5 wt.-%, preferably of from 12 to 1 wt.-%, more preferably from 10 to 2.5 wt.-%, even more preferably from 7.5 to 2.5 wt.-%, still even more preferably from 5 to 2.5 wt.-%, and most preferably 3 wt.-%, based on the total weight of the micrometer-sized agglomerate powder.

The preformed nanometer-sized silicon-containing particles may be unsintered or partially sintered amorphous particles produced by gas phase synthesis in a hot-wall reactor, as described in the above cited references. While unsintered amorphous particles are merely associated by physical forces, sintered particles are also chemically bound to each other and may form e.g. chain or ring containing structures. The preformed nanometer-sized silicon-containing particles may comprise primary particles which are substantially spherical. For instance, the particles may have a sphericity factor (S80) of at least 0.8, as determined by the method described in US 2020/206107 Al, wherein an SEM image of the particle sample is magnified 20,000 times, which is representative of the particle sample, and is imported into a photo imaging software, and the outline of each particle (two-dimensionally) is traced. Particles that are close in proximity to one another but not attached to one another should be considered separate particles for this analysis. The outlined particles are then filled in with color, and the image is imported into a particle characterization software (e.g., IMAGE-PRO PLUS available from Media Cybernetics, Inc., Bethesda, Md.) capable of determining the perimeter and area of the particles. Sphericity of the particles can then be calculated according to the equation, Sphericity = (perimeter)² divided by (4n x area), wherein perimeter is the software measured perimeter derived from the outlined trace of the particles, and wherein area is the software measured area within the traced perimeter of the particles. The sphericity calculation is performed for each particle that fits entirely within the SEM image. These values are then sorted by value, and the lowest 20% of these values are discarded. The remaining 80% of these values are averaged to obtain the sphericity factor (S80).

The preformed nanometer-sized silicon-containing particles may comprise primary particles which have a gradient concentration of carbon which increases from the inside of the particle towards the outside, i.e., the particles are poor in carbon at the center of the particle and richer in carbon closer to the particle surface due to the initial nucleation of pure silicon nanoparticles in the gas phase.

The preformed nanometer-sized silicon-containing particles may have a primary particle size in the range of from 50 to 350 nm, as determined by SEM. They may be present in the form of aggregates having a median particle size in the range of from 550 to 950 nm, preferably of from 600 to 900 nm, more preferably of from 650 to 850 nm, and most preferably from 700 to 800 nm, determined by analytical centrifugation. The micrometer-sized agglomerate powder may have a median particle size in the range of from 2 to 7.5 pm, preferably of from 3 to 6.5 pm, more preferably of from 4 to 5.5 pm, and most preferably of from 4.5 to 5.0 pm, as determined by analytical centrifugation.

The powder particles of the micrometer-sized agglomerate powder may be substantially spherical. For instance, they may have a sphericity factor (S80) of at least 0.8, as determined by the method described above.

The preformed nanometer-sized silicon-containing particles have a specific surface area in the range of from 4 to 30 m²/g, preferably of 4 to 16 m²/g, more preferably of 4 to 12 m²/g, even more preferably of from 4 to 10 m²/g, still even more preferably of from 4.5 to 9.5 m²/g, still even more preferably of from 5.5 to 8.5 m²/g, ad most preferably of from 6.5 to 7.5 m²/g, as determined by the BET method in accordance with DIN ISO 9277:2014-01 using the "Static manometric (volumetric) method" according to chapter 6.3.1 of this norm.

The micrometer-sized agglomerate powder may have a specific surface area in the range of from 2 to 6 m²/g, preferably of from 3 to 5 m²/g, and most preferably of from 3.5 to 4.5 m²/g, as determined by the BET method in accordance with DIN ISO 9277:2014-01 using the "Static manometric (volumetric) method" according to chapter 6.3.1 of this norm.

The polymeric binder may comprise a polymer having pendant acid and/or anhydride groups, preferably a polymer having pendant carboxylic acid and/or anhydride groups, and more preferably a poly(meth)acrylic acid and/or an anhydride thereof. Most preferably the binder is a polyacrylic acid. During spray drying, the acid groups in the polymeric binder may condense forming anhydride groups. However, FTIR analysis of the micrometer-sized agglomerate powder suggests that no chemical reaction between these particles and the binder takes place and the inherent surface chemistry of these particles remains substantially unchanged.

In step (i) of the method of the present invention a solution or suspension of the polymer in an aqueous liquid may be combined with the preformed nanometer-sized silicon-containing particles in additional aqueous liquid to form the dispersion of step (i) of the method of the present invention. The dispersion should be thoroughly mixed prior to spray drying without, however, breaking the micrometer-sized agglomerate particles. For instance, the dispersion may be mixed for at least 1 hour, preferably at least 2 hours, more preferably at least 6 hours, even more preferably at least 12 hours, for instance for 24 hours, e.g., using a magnetic stirrer at a velocity being in the range of from 250 to 750 rpm, e.g., of 500 rpm, prior to being subjected to step (ii).

The concentration of the preformed nanometer-sized silicon-containing particles in the dispersion of step (i) may be is in the range of from 0.5 to 10 wt.-%, preferably of from 1 to 5% wt.-%, based on the total weight of the dispersion.

While further additives can be present in the dispersion to be spray dried, the dispersion may also consist of the preformed nanometer-sized silicon-containing particles, the polymeric binder and the aqueous liquid.

In step (ii) of the method of the present invention, the dispersion is spray dried using an inert spray gas and a drying gas having an inlet temperature being in the range of from 120 to 200 °C, preferably of from 130 to 170 °C, more preferably of from 140 to 160 °C, and most preferably of from 145 to 155 °C.

While in the appended experimental section most examples were carried out using a laboratoryscale spray drying apparatus, additional experiments showed that up-scaling to technical spray drying apparatus is possible using the same gas flow scheme and ratios of feed, drying gas and spraying gas, exchanging the nozzle used in the laboratory-scale apparatus by a rotary atomizer. For instance, the ratio of spraying gas flow to drying gas flow may be in the range of from 1:20 to 1:1000, preferably of from 1:50 to 1:500, and most preferably of from 1:75 to 1:250. The ratio of feed (dispersion) flow to spraying gas flow may be in the range of from 1:200 to 1:10000, preferably of from 1:500 to 1:5000, and most preferably of from 1:750 to 1:2500. The present invention further relates to a spray dried micrometer-sized agglomerate powder comprising nanometer-sized silicon-containing particles and a polymeric binder. Herein, the spray dried micrometer-sized agglomerate powder is formed by spray drying a dispersion comprising a nanometer-sized silicon-containing particles and a polymeric binder, and the term does not cover micrometer-sized agglomerate powder wherein the polymeric binder had not been subjected to a spray drying step, such as, for instance, powders made by simply mixing nanometer-sized silicon-containing particles with a polymeric binder without subjecting said mixture to a spray drying step.

In said micrometer-sized agglomerate powder, the nanometer-sized silicon-containing particles and/or the polymeric binder preferably may be those already described above.

Preferably, the micrometer-sized agglomerate powder may be made by the method of the present invention described above.

The present invention further relates to a coating composition comprising said micrometer-sized agglomerate powder and an additional binder, i.e., an amount of binder in addition to that being present in the micrometer-sized agglomerate powder. Said additional binder the same or different from the binder used to make the micrometer-sized agglomerate powder. The use of the above-described binders may be preferred, and the additional binder may be the same used to make the micrometer-sized agglomerate powder.

The coating composition of the present invention may optionally further comprise additional conductive particles. These additional conductive particles preferably may include carbon containing particles, more preferably carbon containing particles selected from the groups containing graphite, graphene, and carbon black, and even more preferably carbon black. Suitable conductive particles are commercially available, e.g. as C-NERGY conductive carbon blacks from Imerys (Paris, France). In the coating composition of the present invention the weight ratio of the micrometer-sized agglomerate powder to the additional binder may be in the range of from 1:1 to 10:1, preferably of from 2:1 to 9:1, more preferably of from 3:1 to 8:1, and most preferably of from 4:1 to 6:1.

The weight ratio of the micrometer-sized agglomerate powder to the additional conductive particles, if present, may be in the range of from 4:1 to 28:1, preferably from 10:1 to 22:1, and most preferably of from 14:1 to 18:1.

The weight ratio of the additional binder to the additional conductive particles, if present, may be in the range of from 0.5:1 to 10:1, preferably of from 1:1 to 5:1, and most preferably of from 2:1 to 4:1.

The coating composition of the present invention may be a waterborne composition, i.e., composition comprising water in an amount of more than 50 wt.-%, preferably in an amount of at least 75 wt.-%, more preferably in an amount of at least 85 wt.-%, even more preferably in an amount of at least 90 wt.-%, and still even more preferably in an amount of at least 95 wt.-%, based on the combined weight of solvents in the compositions. Organic solvents, such as alcohols, may be present in the aqueous liquid, but most preferably the waterborne composition contains water as the sole solvent.

The coating composition of the present invention may have a solids content in the range of from 20 to 60 wt.-%, preferably in the range of from 25 to 55 wt.-%, more preferably of from 30 to 50 wt.-%, and most preferably of from 35 to 45 wt.-%, based on the total weight of the coating composition.

The coating composition of the present invention may have a shear thinning behavior, and may have a dynamic viscosity at room temperature in the range from about 500 mPa-s at 1000 s’¹ to 50000 mPa-s at 0.1 s’¹. The present invention further relates to a method for making an anode or an energy storage device comprising said anode, comprising the steps of applying the coating composition of the present invention onto an anode substrate, and drying the coating.

The anode substrate may be a film or foil, preferably a conductive metal containing foil, more preferably copper foil. The film or foil may have a thickness in the range of from 10 to 30 pm, preferably of from 15 to 25 pm.

The coating may be applied at a wet coating thickness in the range of from 25 to 75 pm, preferably of from 30 to 70 pm, more preferably of from 35 to 65 pm, even more preferably of from 40 to 60 pm, and most preferably of from 45 to 55 pm.

The dry coating thickness may be in the range of from 7 to 30 pm, preferably of from 10 to 27 pm, more preferably of from 12 to 25 pm, even more preferably of from 15 to 22 pm, and most preferably of from 17 to 20 pm.

In the dried coating the mass loading of silicon on the substrate may be higher than 0.5 mg/cm², and preferably may be in the range of from 1 to 5 mg/cm², more preferably in the range of from 1.0 to 2.5 mg/cm², and most preferably in the range of from 1.25 to 1.75 mg/cm².

The dense packing of the nanometer-sized silicon-containing particles within the micrometersized agglomerate powder of the present invention and the possibility of applying thick coatings per unit area allow to increase in mass loading of silicon on the anode.

The present invention further relates to an anode comprising the micrometer-sized agglomerate powder of the present invention as an active material or an energy storage device comprising said anode. Said anode or energy storage device may comprise the micrometer-sized agglomerate powder applied to an anode substrate in form of a coating, preferably a coating formed from the coating composition according to the present invention as described above. Herein, the above-described method for making an anode or an energy storage device comprising said anode may be used.

An energy storage device typically comprises an anode, a cathode, an electrolyte and optionally a separator. The energy storage device of the present invention may be a lithium-ion containing energy storage device. It may, for instance, be a battery, a cell, a secondary battery, a battery pack, a pseudocapacitor, a capacitor, or a supercapacitor, such as a lithium-ion battery or battery pack.

The following clauses summarizes some aspects of the present invention:

In a first aspect the present invention relates to a method for making a micrometer-sized agglomerate powder for use as active anode material, the method comprising the steps of: (i) mixing preformed nanometer-sized silicon-containing particles with a polymeric binder in an aqueous liquid to form a dispersion; and (ii) spray drying the dispersion and collecting the resulting micrometer-sized agglomerate powder without subjecting the dispersion or powder to a pyrolysis during or after step (ii).

In a second aspect the present invention relates to the method of the first aspect, wherein the content of silicon in the preformed nanometer-sized silicon-containing particles is 80 wt.-% or more, preferably 85 wt.-% or more, more preferably 90 wt.-% or more, and most preferably 95 wt.-% or more, based on the total weight of the preformed nanometer-sized silicon-containing particles.

In a third aspect the present invention relates to the method of the first or second aspect, wherein the content of silicon in the micrometer-sized agglomerate powder is 77 wt.-% or more, preferably 82 wt.-% or more, more preferably 87 wt.-% or more, and most preferably 92 wt.-% or more, based on the total weight of the micrometer-sized agglomerate powder. In a fourth aspect the present invention relates to the method of any one of the preceding aspects, wherein the content of elemental carbon in the preformed nanometer-sized sil iconcontaining particles and/or the micrometer-sized agglomerate powder is 20 wt.-% or less, preferably 15 wt.-% or less, more preferably 10 wt.-% or less, and most preferably 5 wt.-% or less, based on the total weight of the preformed nanometer-sized silicon-containing particles or the micrometer-sized agglomerate powder, respectively.

In a fifth aspect the present invention relates to the method of any one of the preceding aspects, wherein the content of binder in the micrometer-sized agglomerate powder is in the range of from 15 to 0.5 wt.-%, preferably of from 12 to 1 wt.-%, more preferably from 10 to 2.5 wt.-%, even more preferably of from 7.5 to 2.5 wt.-%, still even more preferably of from 5 to 2.5 wt.-%, and most preferably 3 wt.-%, based on the total weight of the micrometer-sized agglomerate powder.

In a sixth aspect the present invention relates to the method of any one of the preceding aspects, wherein the preformed nanometer-sized silicon-containing particles are unsintered or partially sintered amorphous particles produced by gas phase synthesis in a hot-wall reactor and preferably comprise primary particles which are substantially spherical and/or have a gradient concentration of carbon which increases from the inside out.

In a seventh aspect the present invention relates to the method of any one of the preceding aspects, wherein the preformed nanometer-sized silicon-containing particles have a primary particle size in the range of from 50 to 350 nm, as determined by SEM.

In an eighth aspect the present invention relates to the method of any one of the preceding aspects, wherein the preformed nanometer-sized silicon-containing particles are present in the form of aggregates having a median particle size in the range of from 550 to 950 nm, preferably of from 600 to 900 nm, more preferably of from 650 to 850 nm, and most preferably from 700 to 800 nm, as determined by analytical centrifugation. In a ninth aspect the present invention relates to the method of any one of the preceding aspects, wherein the micrometer-sized agglomerate powder has a median particle size in the range of from 2 to 7.5 pm, preferably of from 3 to 6.5 pm, more preferably of from 4 to 5.5 pm, and most preferably of from 4.5 to 5.0 pm, as determined by analytical centrifugation.

In a tenth aspect the present invention relates to the method of any one of the preceding aspects, wherein the powder particles of the micrometer-sized agglomerate powder are substantially spherical.

In an eleventh aspect the present invention relates to the method of any one of the preceding aspects, wherein the preformed nanometer-sized silicon-containing particles have a specific surface area in the range of from 4 to 30 m²/g, preferably of from 4 to 16 m²/g, more preferably of 4 to 12 m²/g, even more preferably of from 4 to 10 m²/g, still even more preferably of from 4.5 to 9.5 m²/g, still even more preferably of from 5.5 to 8.5 m²/g, and most preferably of from 6.5 to

7.5 m²/g, as determined by the BET method.

In a twelfth aspect the present invention relates to the method of any one of the preceding aspects, wherein the micrometer-sized agglomerate powder has a specific surface area in the range of from 2 to 6 m²/g, preferably of from 3 to 5 m²/g, and most preferably of from 3.5 to

4.5 m²/g, as determined by the BET method.

In a thirteenth aspect the present invention relates to the method of any one of the preceding aspects, wherein the binder comprises a polymer having pendant acid and/or anhydride groups, preferably a polymer having pendant carboxylic acid and/or anhydride groups, more preferably a poly(meth)acrylic acid and/or an anhydride thereof and wherein most preferably the binder used in step (i) is a polyacrylic acid.

In a fourteenth aspect the present invention relates to the method of any one of the preceding aspects, wherein in step (i) a solution or suspension of the polymer in an aqueous liquid is combined with the preformed nanometer-sized silicon-containing particles in additional aqueous liquid to form the dispersion of step (i), which dispersion is then preferably mixed for at least 1 hour, preferably at least 2 hours, more preferably at least 6 hours and most preferably at least 12 hours, prior to being subjected to step (ii).

In a fifteenth aspect the present invention relates to the method of any one of the preceding aspects, wherein the concentration of the preformed nanometer-sized silicon-containing particles in the dispersion of step (i) is in the range of from 0.5 to 10 wt.-%, more preferably of from 1 to 5% wt.-%, based on the total weight of the dispersion.

In a sixteenth aspect the present invention relates to the method of any one of the preceding aspects, wherein in step (ii) the dispersion is spray dried using an inert spray gas and a drying gas having an inlet temperature being in the range of from 120 to 200 °C, preferably of from 130 to 170 °C, more preferably of from 140 to 160 °C, and most preferably of from 145 to 155 °C.

In a seventeenth aspect the present invention relates to a spray dried micrometer-sized agglomerate powder comprising nanometer-sized silicon-containing particles and a polymeric binder.

In an eighteenth aspect the present invention relates to the micrometer-sized agglomerate powder of the ninth aspect, wherein the micrometer-sized agglomerate powder, the nanometersized silicon-containing particles and/or the polymeric binder are as further defined in any one of the second to thirteenth aspects; and/or wherein the micrometer-sized agglomerate powder is made by the method of any one of the first to sixteenth aspects.

In a nineteenth aspect the present invention relates to a coating composition comprising (i) the micrometer-sized agglomerate powder of any one of the seventeenth or eighteenth aspects and (ii) an additional binder, which may be the same or different from the binder used to make the micrometer-sized agglomerate powder. In a twentieth aspect the present invention relates to the coating composition of the nineteenth aspect, which further comprises (iii) additional conductive particles, which preferably include carbon containing particles, more preferably carbon containing particles selected from the groups containing graphite, graphene, and carbon black, and even more preferably carbon black.

In a twenty-first aspect present invention relates to the coating composition of the nineteenth or twentieth aspect, wherein the weight ratio of (i) the micrometer-sized agglomerate powder to (ii) the additional binder is in the range of from 1:1 to 10:1, preferably of from 2:1 to 9:1, more preferably of from 3:1 to 8:1, and most preferably of from 4:1 to 6:1.

In a twenty-second aspect present invention relates to the coating composition of any one of the nineteenth to twenty-first aspect, wherein the weight ratio of (i) the micrometer-sized agglomerate powder to (iii) the additional conductive particles, if present, is in the range of from 4:1 to 28:1, preferably of from 10:1 to 22:1, and most preferably of from 14:1 to 18:1.

In a twenty-third aspect present invention relates to the coating composition of any one of the nineteenth to twenty-second aspect, wherein the weight ratio of (ii) the additional binder to (iii) the additional conductive particles, if present, is in the range of from 0.5:1 to 10:1, preferably of from 1:1 to 5:1, and most preferably of from 2:1 to 4:1.

In a twenty-fourth aspect the present invention relates to the coating composition of any one of the nineteenth to twenty-third aspect, wherein the coating composition is a waterborne composition, which preferably has a solids content in the range of from 20 to 60 wt.-%, preferably in the range of from 25 to 55 wt.-%, more preferably of from 30 to 50 wt.-%, and most preferably of from 35 to 45 wt.-%, based on the total weight of the coating composition.

In a twenty-fifth aspect the present invention relates to the coating composition of any one of the nineteenth to twenty-fourth aspect, wherein the coating composition has a shear thinning behavior. In a twenty-sixth aspect the present invention relates to a method for making an anode or an energy storage device comprising said anode, comprising the steps of: (i) applying the coating composition of any one of the nineteenth to twenty-fifth aspects onto an anode substrate; and (ii) drying the coating.

In a twenty-seventh aspect the present invention relates to the method of the twenty-sixth aspect, wherein the substrate is a film or foil, preferably a conductive metal containing foil, more preferably copper foil, wherein the film or foil preferably has a thickness in the range of from 10 to 30 pm, preferably of from 15 to 25 pm.

In a twenty-eighth aspect the present invention relates to the method of the twenty-sixth or twenty-seventh aspect, wherein the coating is applied at a wet coating thickness in the range of from 25 to 75 pm, preferably of from 30 to 70 pm, more preferably of from 35 to 65 pm, even more preferably of from 40 to 60 pm, and most preferably of from 45 to 55 pm.

In a twenty-ninth aspect the present invention relates to the method of any one of the twentysixth to twenty-eighth aspect, wherein the coating is applied at a dry coating thickness in the range of from 7 to 30 pm, preferably of from 10 to 27 pm, more preferably of from 12 to 25 pm, even more preferably of from 15 to 22 pm, and most preferably of from 17 to 20 pm.

In a thirtieth aspect the present invention relates to the method of any one of the twenty-sixth to twenty-ninth aspect, wherein in the dried coating the mass loading of silicon on the substrate is higher than 0.5 mg/cm², and preferably in the range of from 1 to 5 mg/cm², more preferably in the range of from 1.0 to 2.5 mg/cm², and most preferably in the range of from 1.25 to 1.75 mg/cm².

In a thirty-first aspect the present invention relates to an anode comprising the micrometer-sized agglomerate powder of any one of the seventeenth or eighteenth aspects as an active material or an energy storage device comprising said anode. In a thirty-second aspect the present invention relates to the anode or energy storage device of the thirty-first aspect, comprising the micrometer-sized agglomerate powder applied to an anode substrate in form of a coating, preferably a coating formed from a coating composition according to any one of the nineteenth to twenty-fifth aspects, more preferably by a method according to any one of twenty-sixth or thirtieth aspects.

Figures

Figure 1 shows the dynamic viscosity of a coating composition in accordance with the present invention (squares) and a comparative coating composition (diamonds) not comprising the micrometer-sized agglomerate powder as a function of shear rate, as further described in Example 1.

Figures 2 and 3 show the results of evaluating a coating obtained from a composition in accordance with the present invention by atomic force microscopy (AFM), as further described in Example 1.

Figures 4, 8 and 9 shows scanning electron microscopy (SEM) images of a coating obtained from a composition in accordance with the present invention, as further described in Example 1.

Figures 5 and 6 show the results of evaluating a coating obtained from a comparative composition not comprising the micrometer-sized agglomerate powder of the present invention by AFM, as further described in Example 1.

Figure 7, 10 and 11 show scanning electron microscopy (SEM) images of a coating obtained from the comparative composition in accordance with the present invention, as further described in Example 1. Figure 12 shows the electrochemical performance of an energy storage device in accordance with the present invention (upper curve) in comparison to one not comprising the micrometer-sized agglomerate powder of the present invention.

Examples

Example 1

Preparation of dispersion for spray drying

To 9.25 g of Millipore-Q water (18.2 MQ-cm) 0.75 g of a 25 wt.-% suspension of poly(acrylic acid) (PAA) in water (having an average molecular weight (M_w) of 240000 g/mol which is commercially available from Alfa Aesar, Ward Hill, MA, USA under the product number 44669) was added. The resulting mixture was stirred at 500 rpm for 10 min using a magnetic stirrer. To this mixture 6 g of preformed nanometer-sized silicon-carbon composite (Si/C) particles were added, the particles having a primary particle size in the range of from 100 to 250 nm, as determined by scanning electron microscopy (SEM), a median aggregate particle size of 749 nm, as determined by analytical centrifugation using a LUMiSizer® analytical centrifuge (LUM GmbH, Berlin, Germany) in accordance with ISO 13318-2 using water as the dispersing solvent at a sample concentration of 0.17 mg/mL, a measurement temperature of 7 °C, a measurement wavelength of 870 nm, and a total of 1000 profiles with the first 600 profiles being taken at an 5 s interval, and the remaining 400 profiles being taken at a 15 s interval, to determine the volume weighted particle size distribution Q3(x), with 10% of the particles having a particle size of 450 nm or less, and 90% of the particles having a size of 1461 nm or less, a specific surface area of 6.85 m²/g, as determined by the BET method, and a carbon content of about 4.65 wt.-%, based on the total weight of the siliconcarbon composite particles, as determined by elemental analysis. Another 184 g of Millipore-Q. water was then, so that the resulting dispersion had a content of 3 wt.-% of nanometer-sized Si/C particles, based on the total weight of the dispersion, and contained 3.1 wt.-% PAA, based on the dry powder mass of the nanometer-sized Si/C particles. The dispersion was left to stir at 500 rpm for 24 h using a magnetic stirrer before being subjected to spray drying. Spray-Drying

A laboratory scale spray dryer (Mini Spray Dryer B-290, available from BUCHI Labortechnik GmbH, Essen, Germany) having an electric heater for heating the compressed spraying gas, an integrated two-fluid nozzle gas inlet for dispersing the dispersion into fine droplets using the spraying gas having a nozzle tip diameter of 0.7 mm, a spray cylinder (tower) for conductive heat exchange between a drying gas and the droplets, and a cyclone for separating the solid particles formed was used. The spray cylinder (tower) of this spray drying apparatus is made of borosilicate glass and has a length of 55 cm and an inner diameter of 50 cm, with the outlet having an inner diameter of 3.5 cm and being located 42 cm from the top. Illustrations of the general set-up and flow in the Mini Spray Dryer B-290 are available from the manufacturer. During spray drying, the dispersion feed was continuously stirred at 500 rpm to avoid particle sedimentation. Nitrogen was used as the spray gas at a velocity of 357 L/h. Air was used as the drying gas at a flow rate of about 35 m³/h, resulting in a residence time of the drying gas and the feed in the spray cylinder of about 1 to 2 seconds. The temperature of the drying gas at the inlet was was set to 150 °C. The feed flow rate was about 5 mL/min.

A yield of 89.4 wt.-% of micrometer-sized agglomerate powder was obtained which was characterized as described below.

Repeating the above-described spray drying procedure in a technical spray drying apparatus equipped with a spray tower having both an inner diameter and a length of 6 m using a rotary atomizer instead of the above two-fluid nozzle gas inlet, at the same ratios of (i) spray gas flow rate to drying gas flow rate and (ii) feed flow rate to spray gas flow rate as described above, both in cocurrent and counter-current modus, gave similar results.

Characterization of the micrometer-sized agglomerate powder

FTIR spectroscopy of the obtained micrometer-sized agglomerate powder showed that during spray drying the acid groups in the polymeric binder were at least partially condensed to form anhydride groups, whereas the peak characterizing the preformed nanometer-sized silicon-carbon composite particles remained substantially unchanged, suggesting that no chemical reaction between these particles and the binder took place and the inherent surface chemistry of these particles remained substantially unchanged.

The micrometer-sized agglomerate powder had a specific surface area of 3.9 m²/g, as determined by the BET (Brunauer-Emmett-Teller) method in accordance with DIN ISO 9277:2014-01 using the "Static manometric (volumetric) method" according to chapter 6.3.1. The analysis was carried out with a Micromeritics Adsorption-Analyzer "ASAP2420" (Micromeritics Instrument Corporation, Norcross, GA, USA) using the software ASAP2420 V2.09. The gases used, helium 5.0 and nitrogen 5.0, had a purity of 99.999%. The samples were treated prior to the measurement for 1 h at 200 °C under vacuum. The analysis was carried out as a multi-point determination (6 points) in the pressure range p/pO = 0.03 - 0.22, the data evaluation corresponding to DIN ISO 9277:2014-01 Chapter 7.2.

The micrometer-sized agglomerate powder had a median particle size of 4.76 ± 0.11 pm, as determined by analytical centrifugation using a LUMiSizer® analytical centrifuge (LUM GmbH, Berlin, Germany) in accordance with ISO 13318-2 following the procedure described above, except that isopropanol was used as the dispersing solvent at room temperature (23 °C), to determine the volume weighted particle size distribution Q3(x), with 10% of the particles having a particle size of 1.81 pm or less, and 90% of the particles having a size of 6.64 pm or less.

Thermogravimetric analysis under argon atmosphere showed that the binder, predominantly being present in the form of poly(acrylic anhydride) in the micrometer-sized agglomerate powder obtained from spray drying, is stable to temperatures of up to 200 °C and more, decomposing in two steps, at around 220 °C and 420 °C, respectively. Preparation of the coating composition (slurry)

To a dispersion cell 0.2 g of carbon black (C-NERGY SUPER C65 from Imerys, Paris, France), 2.5 g of a 25 wt.-% suspension of PAA in water and 1.2 g of Millipore-Q water were added, and the resulting mixture was mixed at 4,000 rpm for 3 min using zirconia beads having a diameter of 5 mm and an Ultra-Turrax tube drive disperser (IKA®-Werke GmbH & Co. KG, Staufen, Germany). 3.2 g of the above micrometer-sized agglomerate powder and additional 3 g of Millipore-Q. water were then added, and the resulting mixture was again mixed for 3 min at 4,000 rpm using the Ultra-Turrax tube drive. The final slurry had a total solids content of 40 wt.-%, based on the total weight of the composition, the solids being composed of 78.4 wt.-% Si/C active particles (excluding the PAA present in the agglomerate powder), 5 wt.-% carbon black, and a total of 16.6 wt.-% PAA (15 wt.- % being added to the slurry in form of an aqueous suspension and 1.6 wt.-% being present in the agglomerate powder).

As a comparative example, a coating slurry was prepared as described above, replacing the micrometer-sized agglomerate powder by the same amount of the above-described nanometersized silicon-carbon composite (Si/C) particles which were not agglomerated by spray drying in accordance with the present invention, but are still present as nanometer-sized aggregates. The final slurry had the same total solids content of 40 wt.-%, based on the total weight of the composition, with the solids being composed of 80 wt.-% Si/C active particles, 5 wt.-% carbon black, and 15 wt.-% PAA.

Dynamic viscosity of both compositions was studied at room temperature using a rheometer (Anton Paar GmbH, Graz, Austria), and the results are shown in Fig. 1. It can be seen from Fig. 1 that both compositions are shear thinning and have a similar dynamic viscosity at the application shear used for doctor blading in the following experiments (1000 s'¹) with the inventive composition yielding lower viscosities at low shear rates (up to about 20 s ¹). Application of the coating composition to copper foil

The above coating compositions were applied to copper foil having a thickness of 18 pm (Carl SCHLENK AG, Roth, Germany) using a doctor-blade (Zehntner GmbH, Sissach, Switzerland) and an automatic film applicator (TQ.C Sheen, Capelle aan den Ussel, The Netherlands) at a coating speed of 50 mm/s to obtain a wet coating thickness of 50 pm.

After drying the coating at 60 °C for 16 h, the morphology of the coatings was evaluated by atomic force microscopy (AFM) using a Tosca 400 (Anton Paar GmbH, Graz, Austria) in contact mode. The results are shown in Fig. 2 and 3 (coating obtained from the composition in accordance with the present invention) and Fig. 5 and 6 (coating obtained from the comparative composition). Also shown are SEM images of the coatings, Fig. 4 showing the coating obtained from the composition in accordance with the present invention and Fig. 7 showing the coating obtained from the comparative composition, obtained using an accelerating voltage of 25.0 kV, a spot size of 1.5 nm, and a working distance (WD) of 8.7 mm (Fig. 4) or 8.5 mm (Fig. 7), respectively. Magnification was 1000X. It can be seen that the coating obtained from the composition in accordance with the present invention was wavy and rough in comparison to the comparative example.

Further SEM images of the coatings obtained from the composition in accordance with the present invention are shown in Fig. 8 and 9 and from the comparative composition in Fig. 10 and 11. For obtaining these images, an accelerating voltage of 25.0 kV, a spot size of 2.0 nm, and a working distance (WD) of 8.0 mm (Fig. 8 and 9) or 8.4 mm (Fig. 10 and 11) were used. Magnification was 1000X in Fig. 9 and 11, 2500X in Fig. 8, and 5000X in Fig. 11.

Both AFM and SEM images confirm that the micrometer-sized agglomerates are stable even after the doctor blading process.

Mass loading (i.e., the mass of silicon on the current collector per unit area) and dry coating thickness were determined from the SEM images using the Image J software. The inventive sample had a dry layer thickness of 18.5 pm, whereas the comparative sample had a dry layer thickness of 12.1 pm. The dense packing of the nanometer-sized silicon-carbon composite particles within the micrometer-sized agglomerate powder of the present invention and the possibility of applying thick coatings per unit area led to a significant increase in mass loading. In the inventive sample mass loading was 1.52 mg/cm², whereas in the comparative sample mass loading was 1.18 mg/cm², corresponding to an increase of about 29%.

Electrochemical performance

The above samples were tested for discharge capacity, and the results are shown in Fig. 12. In these tests, lithium foil was used as the counter and reference electrode. In a glovebox, the electrodes were mounted in Swagelok T-cells. A mixture of 1 M LiPFg, ethylene carbonate (EC), dimethyl carbonate (DMC) and 5 wt.-% fluoroethylene carbonate (FEC) was used as the electrolyte. Glass fiber material was used as a separator. All electrochemical measurements were performed at 25 °C and with a specific current corresponding to 0.05 C, 0.1 C and 0.5 C using a 4000 Battery Tester (Maccor Inc., Tulsa, OK, USA). In the inventive sample, less capacity loss is observed during the initial lithiation cycles (initial specific capacity 2316 mAh/g) as compared to the comparative sample (1168 mAh/g). Further, in the inventive sample 82.9% capacity was retained after 100 cycles, whereas in the comparative sample capacity retention was only 11.5% after 100 cycles, even though the comparative sample contains 1.6 wt.-% more active Si/C-particles in the coating.

A further comparative sample was prepared using a reduced wet layer thickness of 25 pm having twice the amount of carbon black in the coating composition (10 wt.-%). However, capacity retention still was only 25.9% after 100 cycles. In addition, thinner coatings are less favorable in terms of energy density.

Examples 2 to 4

Additional dispersions were prepared, spray dried to obtain micrometer-sized agglomerate powders, these powders then being formulated into a coating composition which was coated onto copper foil to obtain electrodes tested for electrochemical performance as described above except 1 that the amount of poly(acrylic acid) in the dispersion for spray drying was varied: Example 2 contained 1 wt.-% PAA, based on the dry powder mass of the nanometer-sized Si/C particles, and Example 3 contained 2 wt.-% PAA, based on the dry powder mass of the nanometer-sized Si/C particles. Example 4 contained 1 wt.-% PAA, based on the dry powder mass of the nanometer-sized Si/C particles, but the step of thoroughly mixing the dispersion for 24 h at 500 rpm prior to spray drying was omitted.

SEM analysis showed that this premixing step significantly enhances the homogeneity and quality of the micrometer-sized agglomerate powders obtained after spray drying, and the coating obtained from Example 4 peeled off from the copper foil after doctor blade coating. The coatings obtained from Examples 2 and 3 were visually good.

The coating compositions obtained from Examples 2 and 3 had a shear-thinning behavior similar to that of the inventive sample of Example 1.

In the coatings obtained from Examples 2 and 3 mass loading was 1.28 mg/cm², and 1.44 mg/cm², respectively. The coating obtained from Examples 2 had a dry layer thickness of 12.2 pm, and the coating obtained from Examples 3 had a dry layer thickness of 16.8 pm.

AFM analysis of the coatings obtained from Examples 2 and 3 suggested that at this lower binder content the micrometer-sized agglomerate particles are at least partially broken during processing of the coating composition (ball-assisted milling and doctor blading). While in the coating obtained from Example 2 broken agglomerates of similar aspects were observed, in Example 3 a mixture of micrometer-sized agglomerate particles and broken particles were observed. The electrochemical performance of Examples 2 and 3 were worse than that of Example 1 with the cells of Example 3 dying during cycling presumably due to the inhomogeneity of the coating.

Claims

Claims A method for making a micrometer-sized agglomerate powder for use as active anode material, the method comprising the steps of:

(i) mixing preformed nanometer-sized silicon-containing particles with a polymeric binder in an aqueous liquid to form a dispersion; and

(ii) spray drying the dispersion and collecting the resulting micrometer-sized agglomerate powder without subjecting the dispersion or powder to a pyrolysis during or after step (ii). The method of claim 1, wherein the content of silicon in the preformed nanometer-sized silicon-containing particles is 80 wt.-% or more, preferably 85 wt.-% or more, more preferably 90 wt.-% or more, and most preferably 95 wt.-% or more, based on the total weight of the preformed nanometer-sized silicon-containing particles, and/or wherein the content of silicon in the micrometer-sized agglomerate powder is 77 wt.-% or more, preferably 82 wt.-% or more, more preferably 87 wt.-% or more, and most preferably 92 wt.-% or more, based on the total weight of the micrometer-sized agglomerate powder, and/or wherein the content of elemental carbon in the preformed nanometer-sized silicon-containing particles and/or the micrometer-sized agglomerate powder is 20 wt.-% or less, preferably 15 wt.-% or less, more preferably 10 wt.-% or less, and most preferably 5 wt.-% or less, based on the total weight of the preformed nanometer-sized silicon- containing particles or the micrometer-sized agglomerate powder, respectively, and/or wherein the content of binder in the micrometer-sized agglomerate powder is in the range of from 15 to 0.5 wt.-%, preferably of from 12 to 1 wt.-%, more preferably from 10 to 2.5 wt.-%, even more preferably of from 7.5 to 2.5 wt.-%, still even more preferably of from 5 to 2.5 wt.-%, and most preferably 3 wt.-%, based on the total weight of the micrometer-sized agglomerate powder. The method of any one of claims 1 or 2, wherein the preformed nanometer-sized silicon- containing particles are unsintered or partially sintered amorphous particles produced by gas phase synthesis in a hot-wall reactor and preferably comprise primary particles which are substantially spherical and/or have a gradient concentration of carbon which increases from the inside out. The method of any one of the preceding claims, wherein the preformed nanometer-sized silicon-containing particles have a primary particle size in the range of from 50 to 350 nm, as determined by SEM, and/or are present in the form of aggregates having a median particle size in the range of from 550 to 950 nm, preferably of from 600 to 900 nm, more preferably of from 650 to 850 nm, and most preferably of from 700 to 800 nm, as determined by analytical centrifugation, and/or wherein the micrometer-sized agglomerate powder has a median particle size in the range of from 2 to 7.5 pm, preferably of from 3 to 6.5 pm, more preferably of from 4 to 5.5 pm, and most preferably of from 4.5 to 5.0 pm, as determined by analytical centrifugation, and/or wherein the powder particles of the micrometer-sized agglomerate powder are substantially spherical. The method of any one of the preceding claims, wherein the preformed nanometer-sized silicon-containing particles have a specific surface area in the range of from 4 to 30 m²/g, preferably of from 4 to 16 m²/g, more preferably of 4 to 12 m²/g, even more preferably of from 4 to 10 m²/g, still even more preferably of from 4.5 to 9.5 m²/g, still even more preferably of from 5.5 to 8.5 m²/g, and most preferably of from 6.5 to 7.5 m²/g, as determined by the BET method, and/or wherein the micrometer-sized agglomerate powder has a specific surface area in the range of from 2 to 6 m²/g, preferably of from 3 to 5 m²/g, and most preferably of from 3.5 to 4.5 m²/g, as determined by the BET method. The method of any one of the preceding claims, wherein the binder comprises a polymer having pendant acid and/or anhydride groups, preferably a polymer having pendant carboxylic acid and/or anhydride groups, more preferably a poly(meth)acrylic acid and/or an anhydride thereof and wherein most preferably the binder used in step (i) is a polyacrylic acid.

7. The method of any one of the preceding claims, wherein in step (i) a solution or suspension of the polymer in an aqueous liquid is combined with the preformed nanometer-sized silicon-containing particles in additional aqueous liquid to form the dispersion of step (i), which dispersion is then preferably mixed for at least 1 hour, preferably at least 2 hours, more preferably at least 6 hours and most preferably at least 12 hours, prior to being subjected to step (ii), wherein the concentration of the preformed nanometer-sized silicon-containing particles in the dispersion of step (i) preferably is in the range of from 0.5 to 10 wt.-%, more preferably of from 1 to 5% wt.-%, based on the total weight of the dispersion.

8. The method of any one of the preceding claims, wherein in step (ii) the dispersion is spray dried using an inert spray gas and a drying gas having an inlet temperature being in the range of from 120 to 200 °C, preferably of from 130 to 170 °C, more preferably of from 140 to 160 °C, and most preferably of from 145 to 155 °C.

9. A spray dried micrometer-sized agglomerate powder comprising nanometer-sized silicon- containing particles and a polymeric binder.

10. The micrometer-sized agglomerate powder of claim 9, wherein the micrometer-sized agglomerate powder, the nanometer-sized silicon-containing particles and/or the polymeric binder are as further defined in any one of claims 2 to 6; and/or wherein the micrometer-sized agglomerate powder is made by the method of any one of claims 1 to 8. A coating composition comprising (i) the micrometer-sized agglomerate powder of any one of claims 9 or 10 and (ii) an additional binder, which may be the same or different from the binder used to make the micrometer-sized agglomerate powder. The coating composition of claim 11, optionally further comprising

(iii) additional conductive particles, which preferably include carbon containing particles, more preferably carbon containing particles selected from the groups containing graphite, graphene, and carbon black, and even more preferably carbon black, wherein the weight ratio of (i) the micrometer-sized agglomerate powder to (ii) the additional binder is in the range of from 1:1 to 10:1, preferably of from 2:1 to 9:1, more preferably of from 3:1 to 8:1, and most preferably of from 4:1 to 6:1, and/or wherein the weight ratio of (i) the micrometer-sized agglomerate powder to (iii) the additional conductive particles, if present, is in the range of from 4:1 to 28:1, preferably of from 10:1 to 22:1, and most preferably of from 14:1 to 18:1, and/or wherein the weight ratio of (ii) the additional binder to (iii) the additional conductive particles, if present, is in the range of from 0.5:1 to 10:1, preferably of from 1:1 to 5:1, and most preferably of from 2:1 to 4:1. The coating composition of any one of claims 11 or 12, wherein the coating composition is a waterborne composition, which preferably has a solids content in the range of from 20 to 60 wt.-%, preferably in the range of from 25 to 55 wt.-%, more preferably of from 30 to 50 wt.-%, and most preferably of from 35 to 45 wt.-%, based on the total weight of the coating composition, and/or wherein the coating composition has a shear thinning behavior. A method for making an anode or an energy storage device comprising said anode, comprising the steps of:

(i) applying the coating composition of any one of claims 11 to 13 onto an anode substrate; and

(ii) drying the coating. anode comprising the micrometer-sized agglomerate powder of any one of claims 9 or as an active material or an energy storage device comprising said anode.