Method for producing isotropic carbonaceous precursor aggregate

Abstract

The present invention relates to a process for producing isotropic carbonaceous precursor agglomerates comprising the steps of: i. Providing an average particle size lt; coke particles of 50 m, and the volatile content (VM) of the particles is between 4% and 20%. The present invention relates to a method for producing coke particles, comprising the steps of: i. Drying the coke particles, ii. Mixing the coke particles with water and a water-soluble temporary binder, thereby agglomerating the coke particles within the mixture, iii. At least partially drying the mixture, iv. Carbonizing the mixture. Furthermore, the invention relates to a method for producing an isotropic graphite electrode material for a battery electrode, in particular for a lithium ion battery, comprising a method for producing an isotropic carbonaceous precursor aggregate according to the invention and for further graphitizing said aggregate into an electrode material.

Description

TECHNICAL FIELD

[0001] The present invention generally relates to a process for producing carbonaceous precursor agglomerates, in particular isotropic carbonaceous precursor agglomerates. These agglomerates can be particularly suitable as precursors for isotropic graphites.

[0002] Furthermore, the present invention also relates to a process for manufacturing isotropic graphite electrode material for use in battery electrodes, in particular for use in lithium-ion batteries and EV (electric vehicle) batteries. BACKGROUND

[0003] The anode of a lithium-ion battery mainly contains isotropic natural graphite and / or synthetic graphite. Isotropic synthetic graphite material is considered to be a high-quality anode material, especially in lithium-ion batteries, because isotropic synthetic graphite is capable of improving the charge-discharge performance and cycle stability.

[0004] Furthermore, in order to increase the energy density of the battery cell, silicon, silicon oxide or silicon alloy particles are usually added to the battery anode in the form of a secondary particle composite with graphite or carbon.

[0005] Conventionally, in order to obtain a favorable structure of the porous electrode material, fine graphite primary particles are agglomerated to form equidistantly shaped agglomerates. These isotropic synthetic graphite agglomerates are produced from coke by agglomeration of fine coke with molten coal tar pitch and / or petroleum pitch. The carbon components are uniformly mixed with a finely ground solid pitch binder and the mixture is further treated in a high-temperature reactor, in which the molten pitch agglomerates the coke particles.

[0006] A general disadvantage of the high-temperature agglomeration process is the need for a complex high-temperature reactor and the possibility of scale-up to only a certain limit. Due to the long residence time of the heat treatment step, scale-up requires several reactors to be operated in parallel to achieve an industrially relevant throughput, since the agglomeration and the initial heat treatment step are carried out in the same device and are not separated from each other. Obviously, this scale-up significantly increases the cost of the agglomerate product. In addition, for large thermal batch reactors, in which the powder is fluidized by means of a screw-type ore masterbatch mixer, the high-temperature gradient and the temperature homogeneity become a problem.

[0007] A second disadvantage of the conventional process is that the pitch binder needs to be finely ground, and since some of the polycyclic aromatic hydrocarbons contained therein are carcinogenic, special measures need to be taken for the handling and control of the pitch dust.

[0008] Another conventional method for producing equidistant graphite particle agglomerates is spray granulation (as described in US Patent US2018 / 0183060 A1). However, this method is less popular due to its high cost. Furthermore, the particles formed during spray drying are typically hollow and exhibit relatively low density and mechanical strength during compression.

[0009] In summary, the overall objective of this invention is to provide a method for producing isotropic carbonaceous precursor aggregates, which requires relatively simple equipment and processing, and has low processing costs.

[0010] Another objective of this invention is to provide a method for producing isotropic carbonaceous precursor aggregates that is more easily scaled up to an industrial scale.

[0011] Another objective of the present invention is to provide a method for producing isotropic carbonaceous precursor aggregates, wherein the method poses a lower risk regarding the carcinogenic properties of polycyclic aromatic hydrocarbons contained in asphalt adhesives.

[0012] Furthermore, another objective of the present invention is to provide an advantageous method for manufacturing isotropic graphite electrode materials for battery electrodes, particularly porous electrode materials, and even more particularly for lithium-ion batteries, EV (electric vehicle) batteries, and stationary batteries for battery energy storage. Summary of the Invention

[0013] This invention provides a method for producing isotropic carbonaceous precursor aggregates, comprising the following steps: i. Provide coke particles with an average particle size <50 µm, and the volatile matter (VM) content of said particles is between 4 wt.% and 20 wt.%. ii. The coke particles are mixed with water and a water-soluble temporary binder, thereby causing the coke particles in the mixture to agglomerate. iii. Dry the mixture at least partially. iv. Carbonize the mixture.

[0014] In addition, the present invention provides a method for manufacturing an isotropic graphite electrode material for battery electrodes, particularly for lithium-ion batteries, the method comprising producing an isotropic carbonaceous precursor aggregate according to the present invention, and a method for further graphitizing the aggregate into an electrode material. Detailed Implementation

[0015] This invention relates to the production of carbonaceous precursor aggregates with an average particle size of less than 2000 micrometers, preferably less than 1000 micrometers, and possessing high isotropy, high density, low BET specific surface area, and low porosity. These aggregates can be used as precursors for manufacturing lithium-ion batteries, particularly isotropic graphite electrode materials used in batteries for electric vehicles (EVs) or battery energy storage applications. The carbonaceous aggregates consist of primary coke particles randomly oriented in a secondary particle structure.

[0016] In the context of this invention, isotropic aggregates are understood as aggregates of primary particles with random orientation, resulting in high isotropy within the aggregates and thus high uniformity of the physical properties and characteristics of the aggregates in all directions.

[0017] According to the present invention, a method for producing isotropic carbonaceous precursor aggregates includes the following steps: i. Provide coke particles with an average particle size <50 µm, and the volatile matter (VM) content of said particles is between 4 wt.% and 20 wt.%. ii. The coke particles are mixed with water and a water-soluble temporary binder, thereby causing the coke particles in the mixture to agglomerate. iii. Dry the mixture at least partially. iv. Carbonize the mixture.

[0018] Coke particles with an average particle size of <50 µm can be obtained through a grinding step. Preferably, the average particle size of the coke particles is between 1 and 20 µm.

[0019] According to the present invention, the coke particles may be uncalcined coke particles.

[0020] In one embodiment, the coke particles can be raw needle coke or other forms of raw petroleum coke, preferably raw petroleum coke with a sulfur content of less than 2 wt.%, or pitch coke. In addition to being used in a raw or uncalcined state, needle coke, petroleum coke, or pitch coke can also be used in a calcined form in a certain amount.

[0021] In another embodiment of the invention, the coke particles may be mixed with other carbonaceous materials, such as natural or synthetic graphite, calcined petroleum coke powder, carbonaceous additives, carbonaceous waste, recycled materials, or combinations thereof. Recycled materials may include recycled graphite.

[0022] In one embodiment of the invention, the concentration of uncalcined coke particles in the total primary particle mixture may be at least 40% by weight, preferably at least 50% by weight, and more preferably at least 60% by weight. Those skilled in the art will understand that the minimum required concentration of uncalcined coke particles in the primary particle mixture depends on its VM content.

[0023] Other additives may be nano- and micro-sized silicon metal, silicon dioxide, tin or aluminum metal particles, or combinations thereof.

[0024] Preferably, the ash content of the coke particles is less than 5000 ppm, more preferably less than 2000 ppm.

[0025] Preferably, the volatile matter content (VM) of the coke particles, particularly uncalcined coke particles, can be from 4 wt.% to 20 wt.%, more preferably from 5 wt.% to 18 wt.%, and even more preferably from 6 wt.% to 15 wt.%. Comparing the carbon content of the coke particles with that of bitumen-based products, those skilled in the art will understand that a VM level of 4 wt.% to 20 wt.% corresponds to a coking value of 80-95 wt.% ALCAN.

[0026] In one embodiment, the water-soluble temporary binder added during the mixing and agglomeration steps may comprise any suitable water-soluble natural or synthetic polymer, such as starch, sugar, lignin sulfonate, humic substances, polyvinyl acetate (PVA), carboxymethyl cellulose (CMC), carboxymethyl cellulose (CMC) reacted with citric acid, methyl cellulose, or hemicellulose or derivatives thereof.

[0027] In the context of this invention, those skilled in the art will understand that the term "temporary" refers to a water-soluble temporary adhesive selected based on its ability to volatilize (at least partially volatilize, preferably substantially completely volatilize) during the carbonization step. Volatilization refers to the process of evaporating the temporary adhesive (at least partially), which contradicts the use of non-temporary adhesives, where de-volatilization during the carbonization step refers to the removal of volatile components from the non-temporary adhesive material.

[0028] In addition to water-soluble temporary binders, asphalt products, or combinations of asphalt products and dispersants, or asphalt product-water slurries, or asphalt product emulsions containing asphalt product particles dispersed in water in the presence of an emulsifier (such as a fatty acid or resin acid) may be added to the mixture. The asphalt product may be coal tar-based or petroleum-based, or a derivative thereof, or a combination thereof. Adding asphalt products to the mixture can enhance agglomeration.

[0029] The amount of water-soluble temporary adhesive used can be 0 to 50% by weight of the mixture of water and water-soluble temporary adhesive, preferably 0 to 30% by weight of the mixture of water and water-soluble temporary adhesive, and even more preferably 0 to 15% by weight of the mixture of water and water-soluble temporary adhesive.

[0030] The amount of water and water-soluble temporary adhesive mixture can be 0 to 50% by weight of the total mixture of primary particles, water and water-soluble temporary adhesive, preferably 0 to 45% by weight, more preferably 0 to 30% by weight.

[0031] Following the agglomeration step, the mixture is at least partially dried. In a preferred embodiment, the dried mixture contains less than 2% by weight, preferably less than 1% by weight, of water.

[0032] In one embodiment, after the drying step and before the carbonization of the mixture, the dried mixture may contain 0 to 10% by weight, or 0 to 8% by weight, or 1 to 4% by weight of a water-soluble temporary binder in the agglomerates.

[0033] In one embodiment of the method of the present invention, the mixing and agglomeration of coke particles with water and a water-soluble temporary binder are carried out at a temperature below 70°C, more preferably below 50°C, and most preferably at room temperature. The advantage of the method according to the invention is that it is carried out at a lower processing temperature, preferably even at room temperature, thus eliminating the need for a high-temperature reactor, and significantly reducing occupational health and safety risks when using the method.

[0034] The mixing and agglomeration steps can be carried out in any type of mixing equipment capable of mixing and agglomerating at room temperature, preferably a high-shear mixer, a high-intensity mixer, or a granulating mixer. Disc granulators, pin mixers, or pin agglomerators may also be used.

[0035] Using a combination of water-soluble temporary binders and volatiles from coke particles as a binder, instead of conventional high-temperature binders based on coal tar or petroleum bitumen precursors, can result in a denser structure with a lower BET specific surface area (BET SSA) and reduced porosity due to the reduction of volatiles in the pre-carbonized aggregates. Furthermore, the agglomeration step can be carried out at room temperature, avoiding the complexities of high-temperature agglomeration processes using conventional, potentially harmful bitumen binder materials.

[0036] To generate an agglomerated structure, a water-soluble temporary binder is used to initially (mechanically) agglomerate primary particles (e.g., finely ground raw coke from different sources, such as petroleum coke or pitch coke, mixed with other types of particles, such as silica, graphite, or metal particles), said particles having a particle size of less than 50 micrometers, a volatile matter (VM) content of at least 5 wt.%, and preferably, an ash content of less than 5000 ppm and a sulfur content of less than 2%.

[0037] During the subsequent carbonization process, the temporary binder largely or preferably substantially completely decomposes into gaseous products, i.e., at least partially or preferably substantially completely volatilizes, while the inherent VM in the coke particles (especially uncalcined coke particles) undergoes devolatization and coking, i.e., the VM is activated and then carbonized, forming an in-situ binder that bonds the primary particles ((uncalcined) coke particles, or, where applicable, a mixture of coke particles and other types of particles) together, forming dense aggregates with sizes less than 2000 micrometers, less than 1000 micrometers, less than 500 micrometers, preferably less than 100 micrometers, exhibiting low porosity and low BET specific surface area. For sufficient bonding effect, the VM content of the coke particles used needs to be higher than 5 wt.%. In the early stages of carbonization, the volatile components form tar-like binder active components, which act similarly to glue, binding the primary particles together. Unwilling to be bound by any theory, an aqueous system using a water-soluble temporary binder material dissolved in water was employed. The aqueous component supported particle agglomeration, and the water-soluble temporary binder material then stabilized the agglomerates after a drying step. However, during the subsequent carbonization process, the temporary binder, typically used at low concentration levels, was largely decomposed. The VM of the coke particles acted as the actual binder for the agglomerates. Due to the excellent graphitization ability of the resulting carbon, a higher degree of graphitization could be obtained during subsequent graphitization of the carbonized particles.

[0038] Depending on the target size of the carbonaceous precursor agglomerates, the particle size of the agglomerates can be adjusted for further utilization through gentle mechanical grinding, sieving, and / or classification.

[0039] The carbonaceous precursor aggregates produced by the method of this invention are highly suitable for use as precursors for isotropic graphite. In another embodiment of the invention, the method may include further coating and bonding the generated isotropic carbonaceous precursor aggregates, and further impregnation and graphitization, thereby obtaining isotropic graphite electrode materials for battery electrodes (particularly lithium-ion batteries and EV batteries).

[0040] The BET SSA of isotropic carbonaceous precursor aggregates produced by the method of this invention can reach 0.5-4 m. 2 Within the range of / g.

[0041] In addition, the aggregate size distribution of the final aggregated product can be d50: 1 to 50 micrometers, and / or d90: 15 to 75 micrometers, and / or d100: less than 100 micrometers.

[0042] Furthermore, the tap density of the graded agglomerates can be in the range of 0.7-1.4 g / cm3, preferably 0.9-1.4 g / cm3.

[0043] The hierarchical isotropic carbonaceous precursor aggregates produced by the method of this invention exhibit low BET specific surface area and high tap density, and can be used as a favorable precursor for producing high-quality isotropic graphite through subsequent graphitization methods in the manufacturing of lithium-ion battery anode materials.

[0044] Graphite electrodes produced from isotropic carbonaceous precursor aggregates by the method of the present invention can have the following characteristics: - The graphite aggregates have a particle size distribution of d50: 3-30 micrometers and / or d90: 20-80 micrometers. - Crystallinity: d002 is between 0.3354 and 0.3370 micrometers and / or Lc is between 20 and 500 nanometers. -BET SSA range is between 1 and 4 m 2 / g - Tap density ranges from 0.8 to 1.4 g / cm³ 3 - The actual density ranges from 2.22 to 2.67 g / cm³. 3 - Reversible capacity ranges from 320-370 mAh / g In addition to using the resulting aggregates as carbonaceous precursor products for battery electrodes, these aggregates can also be used as carbon or graphite spheres in fluidized bed technologies, for example, in purification steps.

[0045] Example of the method according to the present invention: Isotropic carbon precursor 1 was produced using raw petroleum coke (GPC) with a VM content of 11.7%. The material was milled to a particle size d50 of 7 µm. The milled GPC was then agglomerated in a high-intensity mixer using an aqueous binder system (lignin sulfonate) until microspheres were formed. These were removed from the mixer and subsequently dried. The resulting microspheres were then carbonized to 1100°C under a nitrogen flow. The material was further gently milled to the desired particle size shown below.

[0046] Isotropic carbon precursor 2 was produced from raw coke with a d50 particle size of 6.2 µm and a VM content of 10.8%. The milled material was then agglomerated in a high-intensity mixer using an aqueous binder system, followed by drying. The resulting microspheres were carbonized to 1050 °C under a nitrogen flow and further finely milled to the desired particle size (as shown below).

[0047] Calcined petroleum coke 1-3 are examples of raw milled and graded calcined petroleum coke that have not undergone any granulation process. Those skilled in the art will understand that the isotropic carbon precursor produced according to the present invention exhibits a higher tap density and a relatively lower surface area than raw milled and graded calcined petroleum coke.

[0048]

[0049] The analysis procedure for the product parameters used in this article is listed below: - Particle size distribution (µm): Laser diffraction, Malvern 3000 (dry dispersion) - VM (%): ASTM D7582 - Actual density (g / cm³) 3 ): ASTM D2638 - Sulfur (%): ASTM D6376 - BET surface area (m²) 2 / g): ISO 9277 - Tap density (g / cm³) 3 ): According to the internal method of DIN 51916.

Claims

1. A method for producing isotropic carbonaceous precursor aggregates, comprising the following steps: i. Provide coke particles with an average particle size < 50 µm, and the volatile matter (VM) content of said particles is between 4% and 20%. ii. The coke particles are mixed with water and a water-soluble temporary binder, thereby causing the coke particles in the mixture to agglomerate. iii. Dry the mixture at least partially. iv. Carbonize the mixture.

2. The method of claim 1, wherein the average particle size of the coke particles is 1-20 µm.

3. The method of claim 1, wherein the ash content of the coke particles is less than 5000 ppm.

4. The method of claim 1, wherein the coke particles comprise at least 40% by weight of uncalcined coke particles.

5. The method of claim 1, wherein the coke particles are needle coke and / or other forms of raw petroleum coke or pitch coke.

6. The method of claim 4 or 5, wherein natural or synthetic graphite, calcined petroleum coke powder, carbonaceous additives, carbonaceous waste, nano- and micro-sized silicon metal, silicon dioxide, tin or aluminum metal particles, recycled materials, or combinations thereof are added to the mixture.

7. The method of claim 6, wherein the recycled material comprises recycled graphite.

8. The method of claim 1, wherein the mixing and agglomeration are performed by a high-shear mixer, a high-intensity mixer, or a granulation mixer.

9. The method of claim 1, wherein the mixing and agglomeration are carried out at a temperature below 70°C.

10. The method of claim 1, wherein the water-soluble temporary binder is starch, sugar, lignin sulfonate, PVA, CMC, CMC reacted with citric acid, humic substances, methylcellulose or hemicellulose, or derivatives thereof.

11. The method of claim 1, wherein, In addition to the water-soluble temporary binder, a composition comprising asphalt products and dispersants, or an asphalt product-water slurry, or an emulsion of asphalt products is added to the mixture.

12. A method for manufacturing an isotropic graphite electrode material for battery electrodes, particularly for lithium-ion batteries, the method comprising producing an isotropic carbonaceous precursor aggregate according to any one of the preceding claims, and a method for further graphitizing the aggregate into an electrode material.

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