Improved particle coating method

Abstract

The present invention relates to a method for producing carbon coated particles or agglomerates of carbon coated particles, comprising: - providing a multitude of particles to be coated, - producing an intermediate molten pitch product, - dispersing the intermediate pitch product directly on the particles, - subsequently carbonizing the particles. Furthermore, the present invention relates to a method for producing battery electrodes comprising said method for producing said carbon coated particles or agglomerates of said carbon coated particles.

Description

[Technical field]

[0001] Technical Field The present invention relates generally to the production of carbon coated particles and agglomerates of carbon coated particles, and in particular to the production of battery electrodes, and more particularly lithium ion batteries. [Background technology]

[0002] background Commercially supplied anode materials have traditionally been graphite-based, but increasingly also include silicon oxide, silicon metal, silicon alloys, and composites of carbon or graphite with materials based on silicon, tin, and other elements.

[0003] Many of these anode materials are coated with a thin carbon coating using coal tar pitch and petroleum-based pitch as carbon precursors. To obtain a suitable coating, several processes are known. For example, a wet process can be used, which involves dissolving dried and ground pitch in a solvent, as described in US Pat. No. 9,096,473 B2 (CONOCO PHILLIPS). Another technique involves dispersing ground fine pitch powder in water, mixing the solution or suspension with the particles, drying the mixture, and then heat treating it at high temperatures, in both cases between 600 °C and 1300 °C, in an inert gas atmosphere, to carbonize the pitch coating. In addition, a dry coating process is also used, in which finely ground pitch is mixed with the electrode material particles with high shear energy. The mixture is then heated in an inert gas atmosphere to form a surface carbon layer, which is finally carbonized or graphitized as required.

[0004] A general problem with the above techniques is that grinding of coal tar and petroleum-based precursor materials is only feasible if the solid material is sufficiently brittle, usually at a softening point above 120° C., or lower if cryogenic grinding is applied. In addition to the cost that the grinding process adds to the product, the mechanical impact of the material on the equipment results in contamination of the carbon precursor and resulting electrode material with unwanted metallic impurities such as iron and stainless steel. Due to the potential generation of pitch dust, which is harmful to humans and the environment and prone to dust explosions when exposed to air, special care must be taken during grinding, e.g., the use of sealed casings (or containment vessels), pressure-resistant impact equipment, and / or grinding in a nitrogen atmosphere, thereby increasing production costs.

[0005] Coating methods that avoid the comminution of coal tar and petroleum-based precursor materials are based on chemical vapor deposition (CVD), where a hydrocarbon gas or vapor, such as methane, propane, acetylene or vaporized benzene, toluene and xylene, is mixed with a nitrogen gas flow and inserted into a fluidized bed of carbon particles at temperatures above 600 °C. To form a homogeneous coating, the surface of each particle needs to be surrounded by reactive gas. Therefore, good fluidization of the particles in the reactive gas / carrier gas mixture is essential, which is typically achieved in a fluidized bed process. CVD coating with hydrocarbon gas or vapor results in a more trapped carbon coating on the particle surface than coating with liquid or solid hydrocarbon precursors, although the carbon yield of gaseous precursors is usually low.

[0006] However, a drawback of CVD-based methods is that the targeted reduction of the BET specific surface area (BET SSA) by carbon coating is less efficient in the case of CVD compared to coating with pitch-based carbon precursors. Moreover, the type of carbon formed during the CVD process, the so-called pyrolytic carbon, turns out to be less compatible with the electrolytes used in batteries, so that increasing the carbon coating, which is usually required to reduce the BET SSA of the carbon powder, results in electrochemical performance reaching an optimum at a certain carbon concentration, but worsening again with increasing amounts of carbon. In addition, the scalability of CVD processes is limited, so industrial CVD processes, such as fluidized bed processes, usually add significant costs to the product.

[0007] Moreover, a problem particularly relevant to dry pitch coating is that the carbon coating is not necessarily homogeneously distributed on the electrode particle surface, and a relatively large amount of carbon, i.e. a relatively thick carbon film, is required to completely coat the particle surface, reducing the BET specific surface area, interfacial area, and reactivity of the graphite electrode to the electrolyte. Low surface area carbon coatings improve the electrochemical parameters of graphitic carbon particles by reducing charge loss and improving cell safety and charge-discharge cycle stability. However, thinner coatings are preferred, since the carbon formed on the particle surface contributes less to the reversible capacity of the electrode material compared to the graphite particle core, and the thickness of the carbon layer also affects the rate of lithium ion insertion in the bulk. Improved electrochemical performance with low surface area carbon coatings has also been reported for silicon-containing particulate electrode materials.

[0008] Solvent-based techniques are known to produce more uniform and thinner carbon coatings than dry processes, but are costly due to the need to handle the solvent, safety considerations especially due to the low flash points of most suitable solvents, and the need to dry and condense the evaporated solvent. Summary of the Invention [Problem to be solved by the invention]

[0009] In view of the above, it is a general object of the present invention to provide an alternative method for producing carbon coated particles which has reduced process costs and is more environmentally friendly.

[0010] In particular, it is an object of the present invention to provide a method for producing carbon coated particles having a thinner coating layer than typically achieved by dry coating techniques and avoiding the use of solvents. The particles to be coated are micron sized with an average particle size of 1-50 microns. Typical coating thicknesses are in the range of tens of nanometers, but as a general rule, the thinner the homogeneous coating with the minimum amount of carbon required to form a homogeneous coating, the better the electrochemical performance.

[0011] It is another object of the present invention to provide a method for producing carbon coated particles which results in an improved quality coating layer being formed.

[0012] Another general object of the present invention is to provide a method for producing carbon coated particles that results in similar processing and performance of targeted electrode materials in battery electrodes, particularly in lithium ion batteries.

[0013] Another general object is to provide a carbon precursor suitable for application in the coating method of the present invention.

[0014] It is yet a general object of the present invention to provide an alternative method for producing agglomerates of carbon coated particles which has reduced process costs and is more environmentally friendly. [Means for solving the problem]

[0015] overview The present invention relates to a method for producing carbon-coated particles, comprising the steps of: - providing a multiplicity of particles to be coated; - producing an intermediate melt pitch product; - dispersing intermediate melt (liquid) pitch products directly onto the particles; - Then, the particles are carbonized and The present invention relates to a method comprising the steps of:

[0016] In one embodiment of the invention, the amount of intermediate melt pitch product dispersed on the particles is at least 10% by weight, thereby resulting in agglomerates of said carbon coated particles.

[0017] Furthermore, the present invention relates to a method for producing a battery electrode comprising said method for producing the carbon-coated particles or said method for producing an agglomerate of carbon-coated particles. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] Detailed Description In the first embodiment of the present invention, - providing a multiplicity of particles to be coated; - producing an intermediate melt pitch product; - dispersing an intermediate molten pitch product directly onto the particles; - Then, the particles are carbonized and A method for producing carbon coated particles is provided, comprising:

[0019] In the context of the present invention, the particles to be coated may be all kinds of particles used in the field of manufacturing electrodes for batteries, such as batteries for household appliances, electric vehicles, energy storage devices for renewable electricity, in particular in the field of manufacturing negative electrodes for lithium-ion batteries. The particles to be coated may be carbonaceous or composite. The particulate material may be natural or synthetic graphite, silicon oxide, silicon metal, silicon alloys, and composites of carbon or graphite with materials based on silicon and tin. The average particle size is usually between 10 and 25 microns, the maximum particle size is usually up to 50 microns.

[0020] In one embodiment of the present invention, the particles to be coated may be preheated according to the needs of the process to ensure sufficient wettability of the intermediate molten pitch product.

[0021] In the context of the present invention, an intermediate molten pitch product is a freshly produced pitch product that is still in a molten state and can be any carbon residue-forming pitch product that is suitable for use as a carbon coating precursor and is suitable for being dispersed directly onto particles as produced, i.e., while still in a molten (liquid) state. Such intermediate molten pitch products are not solidified or melted (i.e., do not contain added solvents) and are not remelted before dispersion. In the context of the present invention, a freshly produced molten pitch product means that the pitch product produced from the raw materials is kept in a molten state and dispersed without undergoing intermediate process steps including solidification, granulation, grinding, dissolving or remelting.

[0022] In one embodiment of the present invention, dispersing the intermediate molten pitch product onto the particles to be coated may include spraying, e.g., airless spraying through a spray nozzle. Optionally, the particles may be fluidized during this by a suitable mixer, agitator, or gas flow. Alternatively, dispersing may include intensive mixing of the molten pitch product with the particles, e.g., intensive mixing by an intensive mixing unit. Optionally, the particles coated with the molten pitch product may be isolated by cooling the particle mixture to room temperature while stirring.

[0023] After dispersion, the molten pitch product dispersed on the particles is carbonized. In one embodiment, this method step includes one or more heat treatment steps between 550-1400°C in a nitrogen inert gas atmosphere while the particle mixture is still kept in motion by a mixer or agitator. Alternatively, the cooled particle mixture is carbonized in a furnace, which can be a tunnel furnace, roller kiln furnace, chamber furnace, or rotary kiln furnace.

[0024] Optionally, carbonization may be followed by graphitization at temperatures above 2000° C. in order to increase the crystallinity of the coating layer.

[0025] A general advantage of the present invention is that by dispersing an intermediate pitch product in the molten state directly onto the particles without intermediate cooling and solidification, granulation, grinding, melting or remelting, many process steps in the manufacture of conventional carbon coated particles are streamlined, resulting in a significant reduction in process costs, safety issues and environmental impacts.

[0026] Another advantage of the method according to the invention is that the coating method provides good coverage of the particle surface and forms a homogeneous carbon film of several tens of nanometers, which can reduce the BET specific surface area and improve the electrode performance compared to other coating techniques. In addition, the use of organic solvents such as tetrahydrofuran or toluene used in solvent-based coating techniques can be avoided, which can eliminate the need for dissolving pitch in the solvent, the drying process after mixing the pitch solution with the particle mass to be coated, and the solvent recovery process. This makes the installation of the coating process easier and reduces costs.

[0027] In one embodiment of the present invention, the intermediate melt pitch product is coal tar and / or petroleum based.

[0028] In an embodiment according to the invention, the intermediate melt pitch products used in the present invention may have a Mettler softening point of less than 260° C., preferably less than 150° C., and most preferably less than 120° C., thereby allowing for lower processing temperatures.

[0029] Additionally, the intermediate melt pitch product may have a melt viscosity of 10 to 3000 mPa·s at the use temperature, or preferably 50 to 1000 mPa·s at the use temperature, to allow for efficient dispersion.

[0030] In another embodiment according to the present invention, the intermediate melt pitch product further has the following characteristics: - 30~70% Alkane Coke Number - Flash point above 200°C, preferably above 250°C - Quinoline insolubles less than 2%, preferably less than 1% The present invention may have one or more of the following:

[0031] A sufficiently high flash point is known to limit safety issues, while a sufficiently low quinoline insoluble content avoids clogging of spray nozzles when the intermediate molten pitch product is dispersed by spraying.

[0032] Preferably, the molten intermediate pitch product used in the present invention has a low viscosity at low temperatures and can have a low softening point combined with a high coking yield and flash point. These parameters contribute to improved carbonization, reduced safety issues, a combination of low processing temperatures combined with easy processing in the molten state, high coverage, and good wettability of the particle surface, resulting in a significant reduction in the BET specific surface area of ​​the coated particles. Furthermore, the production cost of carbon-coated particles is significantly reduced. Furthermore, the coating process is carried out in a closed reactor, avoiding the solid pitch dust generated by pitch grinding to micron-sized particles, thus reducing the environmental impact.

[0033] In a preferred embodiment, the intermediate melt pitch product used may have a Mettler softening point of less than 120°C; a melt viscosity of less than 1000 mPa·s at 140°C; an Alcan coke value of 30-70%; a flash point of greater than 250°C; and a quinoline insoluble content of less than 1%.

[0034] In certain embodiments of the present invention, the intermediate melt pitch product used may be based on a petroleum-based feedstock. More specifically, the pitch product may be characterized by a flash point greater than 250° C. and a Mettler softening point between 100 and 200° C., more preferably between 120 and 180° C. Such pitches may have high flash points and coke numbers similar to coal tar-based pitches with significantly reduced carcinogenic benzo[a]pyrene (B[a]P) content, as well as low viscosities to meet the requirements of melt coating materials.

[0035] In another particular embodiment according to the invention, the intermediate melt pitch product used may be a coal tar-based or petroleum-based distillation residue, or a blend thereof, or preferably a distillation residue based on the heavy fractions of coal tar or petroleum distillation, or a blend thereof.

[0036] More specifically, the distillation residues of coal tar or heavy fractions of petroleum distillation may have a Mettler softening point of 70-120° C. and a coking number of 40-59% or 44-59% (ALCAN). Such coating materials contain very little or are substantially free of solid particles, which is advantageous in spraying processes, since it not only avoids nozzle clogging, but also aids in the formation of a homogeneous thin layer coating on the particle surface.

[0037] Optionally, such distillation residue of coal tar or heavy end fraction of petroleum distillation may further comprise a petroleum-based pitch having a Mettler softening point of 110-270° C., preferably 130-180° C. The petroleum-based pitch reduces the B[a]P content of the coal tar pitch-containing blend.

[0038] In an additional embodiment of the invention, the amount of intermediate molten pitch product dispersed on the particles is at least 10% by weight, thereby resulting in agglomerates of carbon-coated particles. The amount of dispersed molten pitch product can determine whether the particles are coated or coated and agglomerated. For coated agglomerated particles, the amount of dispersed molten pitch required is at least 10% by weight, or at least 12% by weight, preferably 15-20% by weight, of the carbon-coated particles. As a result, for particles that are coated but not agglomerated, the amount of dispersed molten pitch required may be less than 12% by weight, or less than 10% by weight, or even less than 8% by weight, of the carbon-coated particles. If the amount of molten pitch exceeds, preferably, 10% by weight, the particles may agglomerate to a larger particle size and result in agglomerates of coated particles. Particles finer than the typical average particle size are prone to agglomeration and may result in agglomerates of coated particles of a typical particle size.

[0039] Additionally, there is provided a method of making a battery electrode, comprising the method of making the carbon coated particles as described throughout this specification. Such a method may include providing a number of particles to be coated, coating the particles according to the method of making the carbon coated particles described throughout this specification, bonding the coated particles, and further forming and graphitizing to form a battery electrode. These electrodes may be suitable electrodes for use in batteries for consumer electronics, electric vehicles, and renewable power storage devices, particularly as negative electrodes in lithium ion batteries.

[0040] The following Examples 1 and 2 each illustrate one embodiment of a method according to the present invention. EXAMPLES

[0041] Example 1: 446 g of a medium-heat liquid pitch product having a Mettler softening point of 87.4° C. was mixed with preheated spherical graphite (6 m) in a heated intensive mixer. 2 The mixture was added to 4.5 kg of 1000g of BET SSA (100% / g). Both materials were mixed at high intensity for 5 minutes at a temperature of 170°C, after which the mixing intensity was reduced and the mixer was cooled until the material temperature was 20°C below the softening point of the pitch product used. The materials were removed and cooled to room temperature before being transferred to a crucible and carbonized at 1100°C for 5 hours with a heating rate of 100°C / h.

[0042] The coating method described herein allows the initial BET SSA of the initial spheroidal graphite to be reduced to 6m 2 / g of the coated spheroidal graphite at 2.3m 2 / g.

[0043] [Table 1]

[0044] [Table 2]

[0045] Example 2: The following table shows product parameters for certain embodiments of the intermediate pitch products used in the present invention.

[0046] [Table 3]

[0047] The following table outlines the analytical procedures for the product parameters used herein.

[0048] [Table 4]

Claims

1. A method for producing carbon-coated particles, comprising: providing a number of particles to be coated; - Producing an intermediate pitch product, which is a freshly produced pitch product that is maintained in a molten state; - dispersing the intermediate pitch product in the molten state directly onto the particles; - then carbonizing said particles; A method comprising:

2. 10. The method of claim 1, wherein the intermediate pitch product is not solidified, dissolved, or re-dissolved prior to dispersion.

3. The intermediate pitch product further has the following characteristics: Melt viscosity: 10 to 3000 mPas at the processing temperature, measured according to DIN 53019 Mettler softening point <200°C when measured according to ASTM D3104 2. The method of claim 1, comprising:

4. The intermediate pitch product further has the following characteristics: Alkane coke number 30-70% as measured according to ASTM D4715 Flash point >200°C when measured according to ISO 3679 - less than 2% by weight of quinoline insolubles, determined according to DIN 51921 4. The method of claim 3, comprising:

5. 10. The method of claim 1, wherein the intermediate pitch product is based on a petroleum-based feedstock.

6. 6. The method of claim 5, wherein the intermediate pitch product is characterized by a flash point greater than 250°C and a Mettler softening point between 100 and 200°C.

7. 10. The method of claim 1, wherein the intermediate pitch product is a coal tar-based or petroleum-based distillation residue, or a blend thereof, or a blend of a distillation residue and a petroleum-based pitch having a Mettler softening point of 130 to 300°C.

8. 8. The method of claim 7, wherein the distillation residue is based on coal tar distillation residue or petroleum distillation residue and has a Mettler softening point of 70 to 120°C and a coking value of 40 to 59% (ALCAN).

9. 8. The method of claim 7, wherein the pitch further comprises a petroleum-based pitch having a Mettler softening point of 110 to 270°C.

10. The method of claim 7, wherein the distillation residue is based on coal tar distillation residue or petroleum distillation residue and has a Mettler softening point of 70 to 120°C and a coking value of 40 to 59% (ALCAN), and the pitch further comprises a petroleum-based pitch having a Mettler softening point of 110 to 270°C.

11. 10. The method of claim 1, wherein dispersing comprises spraying the intermediate pitch product onto the particles while they are being fluidized, or dispersing comprises mixing the molten intermediate pitch product with the particles by intensive mixing.

12. 2. The method of claim 1, wherein the carbonization is carried out by heat treatment in an inert gas atmosphere at a temperature of 550 to 1400°C.

13. 10. The method of claim 1, wherein the amount of intermediate pitch product dispersed on the particles is at least 10% by weight, thereby resulting in agglomerates of carbon coated particles.

14. providing a number of particles to be coated; - coating the particles according to the method of any one of claims 1 to 13, - binding the coated particles; - Further shaping and graphitization to form battery electrodes A method for manufacturing a battery electrode, comprising: