Improved microgranulation methods and product particles therefrom

Abstract

To provide simple, material-efficient microgranulation methods for aggregating precursor particles into larger product particles with improved properties and, in some instances, novel structures, where the product particles are useful in applications requiring uniform, smooth, spherical or rounded particles, e.g., for electrode materials in lithium batteries, and other applications.SOLUTION: A microgranulation method of aggregating precursor particles comprises: obtaining an amount of precursor particles having an average particle size less than 1000 μm; obtaining an amount of templating media having an average particle size less than 500 μm and a hardness greater than that of the precursor particles; preparing a mixture comprising the amounts of precursor particles and templating media; and subjecting the mixture to a high shear and high pressure field thereby aggregating the precursor particles into product particles.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] Technical Field The present invention relates to an improved microgranulation method for aggregating precursor particles into larger product particles having improved properties and, in some instances, a novel structure. The product particles are useful as electrode materials for lithium batteries and for other applications.

Background Art

[0002] Background In many applications, powders consisting of high-density particles in the micron size range (e.g., 1 - 100 μm) having a narrow particle size distribution (e.g., active powders for battery electrodes, fertilizers, pharmaceuticals, toners, pigments, fillers, catalysts, etc.) are required. In some of these applications, spherical or round particles are desirable. However, it is difficult to produce particles of uniform shape and size in the micron size range.

[0003] For example, with respect to particles used in the manufacture of electrodes for rechargeable high energy density batteries such as lithium ion batteries, it may be desirable for the particles to be spherical in shape and of uniform diameter. When there are substantial requirements for such batteries, it is also very important that a significant and economical supply of such materials can be provided. At present, cathode particles for lithium ion batteries (e.g., lithium nickel manganese cobalt oxide or NMC) are often produced by a co-precipitation process in a continuous flow tank reactor. This results in a wide particle size distribution due to the various particle residence times of the particles in the reactor. In addition, careful process control and various chemical additives (e.g., chelating reagents) are required to maintain a uniform precipitation rate of the different metal salts and to achieve a uniform spherical particle shape. Furthermore, after the co-precipitation process and prior to sintering, the particles need to be separated from their mother liquor by filtration, washing, drying and blending with a lithium source, thereby resulting in additional processing steps and energy, chemicals and waste water. Anode particles for lithium ion batteries are typically carbonaceous, e.g., graphite particles. Typically, to produce battery grade graphite from natural graphite, the natural graphite is first crushed and classified to obtain a powder with a desired particle size distribution (diameter of about 10 - 20 μm). Then, a spheronizer is used to spheronize the sized powder. However, the spheronizing process is typically only 50 - 60% efficient, resulting in a mixture of the desired spheronized particles and fine particles less than 5 μm in diameter. The resulting mixture requires an additional classification step to separate the desired particles from the fine particles, and the fine particles are typically discarded as waste. Clearly, then, a significant amount of the starting natural graphite is lost as a result.

[0004] Granulation is a method by which small particles can aggregate into larger particles. Granulation methods include both wet and dry methods. Wet granulation methods include fluidized bed, disk, drum, and mixer (e.g., by use of pins, paddles, and / or blades) methods. Such wet methods require separation of product particles from a liquid and may require additional binders or dispersing aids. Dry granulation methods include roll pressing, tableting, ram / piston extrusion, pelletizing mills, radial extrusion, and axial exclusion. However, both wet and dry methods of granulation have problems in producing uniform product particles less than 100 μm in diameter, and the resulting product particles may often contain internal voids.

[0005] Other methods for producing micron-sized spherical or rounded particles include spray drying and prilling. During spray drying, a fluid containing a liquid (typically water) and suspended fine particles and / or dissolved seeds is sprayed through a nozzle to produce droplets. The fluid can further contain additives such as wetting agents and binders. The droplets released from the spray nozzle are dried while in the air (e.g., by an air flow) and captured by a filter. This method can be expensive and wasteful because removing the liquid during the drying step is typically energy-intensive and often results in loss of the liquid as waste. The resulting powder is often porous and may require further processing (e.g., washing and filtering). Prilling is a method in which a molten liquid spray solidifies during flight. This method is applicable only to materials capable of forming a molten state.

[0006] Smaller particles (e.g., less than about 1 μm) can be aggregated to form larger, high-density, and uniform micron-sized particles that are spherical or rounded and do not form a significant amount of waste fine particles, and there is a need for a method for dry granulation (i.e., micro granulation) on a micro scale. However, according to U.S. Patent No. 9,132,482, "The extremely insufficient amount of literature on the granulation of inorganic nano powders demonstrates the problems of conditioning them in the form of granules."

[0007] Physical methods that utilize dry processes are environmentally friendly and advantageous for industrial applications because they eliminate the use of solvents. The mechanofusion (MF) process was developed in Japan in the mid-1980s and is based on using a high-shear field to spheronize and size powders or to apply a dry coating without using any liquids (see T. Yokoyania, K. Urayama and T. Yokoyama, KONA Powder Part. J., 1983, 1, 53-63). In the field of lithium-ion batteries, MF is commonly used to spheronize and size natural graphite for use in the negative electrode (e.g., U.S. Patent No. 9,142,832 or U.S. Patent Application No. 14 / 431,398).

[0008] Despite its industrial usefulness, MF has been scarcely published in the literature. One of the reasons for this may be that the parameters of the use of MF devices are not widely known. Nevertheless, some publications describe particles spheroidized and sized or coated by another phase by the MF method (e.g., M. Naito, M. Yoshikawa, T. Tanaka and A. Kondo, KONA Powder Part. J., 1993, 11, 229-234, N. Product and M. Features, 1999, 17, 244-250, M. Alonso, M. Satoh and K. Miyanami, Powder Technol., 1989, 59, 45-52, M. Naito, A. Kondo and T. Yokoyama, ISIJ Int., 1993, 33, 915-924, R. Pfeffer, R. N. Dave, D. Wei and M. Ramlakhan, Powder Technol., 2001, 117, 40-67, W. Chen, R. N. Dave, R. Pfeffer and O. Walton, Powder Technol., 2004, 146, 121-136, and C.-S. Chou, C.-H. Tsou and C.-I. Wang, Adv. Powder Technol., 2008, 19, 383-396). However, most publications do not adequately describe the conditions under which such designed particles are manufactured.

[0009] An interesting type of graphite material known as "onion graphite" has been observed in the art. According to some, onion graphite refers to spherical or oval graphite particles in which the graphite basal planes are arranged in concentric, nested, smooth, oval or spherical layers centered around a common point at the core of the particle, and the arrangement of the ends of the graphite sheets does not spread radially (among other things) from the central nucleus (onion graphite means only a completely nested buckyball). In other words, the graphene layers in onion graphite are randomly arranged on the surface of concentric, nested spheres or ovals, except that they are oriented such that their basal planes are tangential to the concentric, nested spheres or ovals. Onion graphite is distinguishable from the graphite spheres of cast iron, which are known to have a microstructure in which the graphite basal planes are concentrically arranged but the ends of the planes spread radially from the central core (as shown, for example, in Figure 6-4 of "Mesomolecules: From Molecules to Materials" SEARCH Series, Volume 1, G. David Mendenhall, Arthur Greenberg, and Jeol F. Liebman, eds., Chapman & Hall, New York, 1995). Conventionally, onion graphite has only been observed with diameters up to 2 μm. They have been found to form in interplanetary space, as evidenced by their presence in meteorites. Conventionally, nano-sized graphite onions have been produced in small amounts by synthetic means, for example, by high electron irradiation of carbon particles, annealing of nanodiamonds, arc discharge between two graphite electrodes submerged in water, or carbon ion implantation into a silver or copper substrate (see, for example, V.D. Blank, B.A. Kulnitskiy and I.A. Perezhogin, Scripta Materialia, 60 (2009) 407-410).None of these methods can produce particles larger than 2 μm in diameter, by volume (i.e., greater than 1 gram), in a highly graphitized state, and in an economically practical way. For example, U.S. Patent Application Publication No. 2013 / 0189178A1 describes a method for producing onion-like carbon, but the maximum diameter of the achieved carbon onions is only 6 nm. Furthermore, the level of graphitization achieved is not described.

SUMMARY OF THE INVENTION

PROBLEMS TO BE SOLVED BY THE INVENTION

[0010] Despite such continuous and substantial overall efforts related to developing improved manufacturing methods for such materials, further improvements are needed. As disclosed below, the present invention addresses these needs and provides further advantages.

MEANS FOR SOLVING THE PROBLEMS

[0011] SUMMARY It has been discovered that specific high shear and high pressure field processes, such as dry mechanical fusion (MF), can be used to prepare desirable aggregates from various precursor particles in a simple manner and with efficient utilization of the precursor particles. Aggregated precursor particles (“product particles”) can be desirably produced with a narrow particle size distribution and in a smooth spherical or rounded shape without cavities. In some embodiments, it is possible for the product particles to contain cavities.

[0012] In particular, the product particles are manufactured using a micro-granulation method that includes the following steps: obtaining an amount of precursor particles having an average particle size of less than 1000 μm, obtaining an amount of templating media having an average particle size of less than 500 μm and a hardness higher than that of the precursor particles, and preparing a mixture containing the amount of precursor particles and the templating media. The mixture is then subjected to an appropriate high shear and high pressure field such as obtained by mechanofusion so that the precursor particles aggregate into the desired product particles. The product particles can then be separated from the templating media if desired for the intended application.

[0013] The method can be successfully used with a large number of types of precursor particles having a wide range of properties. This includes precursor particles having an average diameter of less than 50 μm, particularly less than 10 μm. Suitable types of precursor particles include powders intended for use (either directly or after subsequent processing) in battery electrodes, fertilizers, pharmaceuticals, toners, pigments, fillers or catalysts. As demonstrated in the examples below, suitable precursor particles include carbonaceous powders, mixed metal oxide powders or metal carbonate powders, such as carbon, graphite flakes or LiNi 1 / 3 Mn 1 / 3 Co 1 / 3 O2 powders. Advantageously, the mixed metal oxide powders used as precursor particles may be manufactured by an all-solid-state method that includes ball milling an amount of metal oxide raw material powder for manufacturing the precursor particles. (Note that, for example, the precursor particles themselves used in the examples below are not suitable for use in battery electrodes, but can be made suitable for such use by micro-granulation processing and optionally subsequent processing steps, such as heating.) Further, and generally, at least a portion of such an amount of precursor particles may be treated in some suitable manner (including ball milling or heating) prior to preparing the mixture.

[0014] The method of the present invention preferably produces spherical and / or rounded aggregates, although the starting precursor particles can be powders that are very irregularly shaped. In addition, the method of the present invention preferably produces powders with a narrow particle size distribution, although the particle size distribution of the starting precursor particles can be very large.

[0015] The resulting characteristics of the resulting product particles are, in part, the effect of the characteristics of the mold medium utilized. As described above, the hardness of the mold medium is greater than the hardness of the precursor particles so as not to break the former. Accordingly, a suitable mold medium can be selected from the group consisting of zirconium oxide, tungsten carbide, tungsten, silicon oxide, aluminum oxide, silicon nitride, hardened steel, stainless steel, and quartz. A mold medium with an average diameter of 100 μm or less can be utilized to yield product particles of the desired diameter and shape. Further, the surface of the mold medium can desirably be smooth and can be spherical. In addition, it is desirable that the diameter distribution of the mold medium be uniform, such as (D90-D10) / D50 < 2, preferably (D90-D10) / D50 < 1, or more preferably (D90-D10) / D50 < 0.7. Further, it may be desirable that the bulk volume of such an amount of the mold medium utilized be higher than the bulk volume of such an amount of the precursor particles utilized, particularly 3 times or more the bulk volume of such an amount of the precursor particles.

[0016] A mechanofusion system suitable for use in the method of the present invention can include a chamber, a rotating wall portion within the chamber, a scraper within the rotating wall portion, and a press head within the rotating wall portion. A representative spacing between the scraper and the rotating wall portion can be about 0.5 mm. A representative spacing between the press head and the rotating wall portion can be about 1.4 mm. And a representative speed for rotating the rotating wall portion is one that provides a wall surface speed of about 8 m / sec. In some embodiments, a mechanofusion time of about 12 hours or more has been demonstrated to be a favorable result. Shorter processing times can be achieved when a mold medium already coated with a precursor from a previous synthesis is reused in a new synthesis. The system manufactures products in batch form, but advantageously, mechanofusion can also be performed in a continuous mode (e.g., appropriate modifications are made to such a system).

[0017] In an exemplary embodiment, product particles having an average diameter of 10 to 100 μm can be produced. Further, the particle size distribution of the exemplary product particles can be sufficiently uniform such that (D90 - D10) / D50 < 2. Further, the surface of the product particles can desirably be smooth. In some aspects of the present invention, the product particles include particles having a roughness less than 0.02, less than 0.01, less than 0.006, or even smaller (as defined below). In some aspects of the present invention, all product particles essentially have a roughness value less than 0.02, less than 0.01, less than 0.006, or even smaller. In some aspects of the present invention, the product particles include particles that essentially do not contain cavities. In some aspects of the present invention, all product particles essentially do not contain cavities. And as demonstrated in the following examples, spherical or tetrahedral product particles can be produced.

[0018] Optionally, the complete preparation of the product particles can additionally include an annealing step at a high temperature (e.g., to recrystallize the particles following mechanofusion).

[0019] The product particles produced by the method of the present invention can be considered for use in a number of commercial applications, including as battery electrodes, fertilizers, pharmaceuticals, toners, pigments, fillers or catalysts. They can be particularly suitable for use as anode or cathode electrodes in rechargeable lithium batteries such as lithium-ion batteries.

[0020] It has further been found that the method can be used to prepare novel structures of graphite microparticles, lithium nickel manganese cobalt oxide microparticles, and lithium transition metal oxide microparticles.

[0021] In one aspect, the novel graphite microparticles include graphite particles in which the graphite particles are shaped as spheres or ovals and which contain concentric nested spherical or oval shapes of graphene layers. These graphene layers are randomly arranged on the surface of the concentric nested spherical or oval shape, except that the graphene layers are oriented such that their basal planes are tangential to the concentric nested spherical or oval shape. The graphite particles further have an average particle size greater than 2 μm and an average d 002 spacing of less than 3,400 Å. In some embodiments, the graphite particles in the microparticles include porous concentric layers having a hollow or void near their core. In some embodiments, the graphite particles have an average particle size of 5 μm to 50 μm and a particle size distribution of (D90 - D10) / D50 < 2.

[0022] In one aspect, the novel lithium mixed metal oxide microparticles include particles having a core of randomly oriented lithium nickel manganese cobalt crystallites having an average diameter of about 1 μm, coated with smaller randomly oriented lithium nickel manganese cobalt crystallites having an average diameter of about 0.3 μm.

[0023] The above-mentioned new lithium transition metal oxide microparticles include particles having at least two transition metals present in the group consisting of Mn, Ni, and Co. Further, the particles have an O3 structure, an average particle size in the range of 1 to 50 μm, and they contain crystallites whose shape and diameter vary randomly throughout their interior. In certain embodiments, the crystallites have an average diameter greater than 0.5 μm, and the average particle size of the particles is more than 5 times greater than the average crystallite diameter. In certain embodiments, the composition of one of the two transition metals can vary by at least 5 atomic % from the core of the particle to the shell of the particle.

[0024] This method can be used to produce product particles having a uniform composition, but can also be used to produce product particles having a composition different near their core than near their surface. The precursor particles utilized may be single-phase, or they may consist of a mixture of particles having different characteristics. For example, the precursor particles can consist of a mixture of first particles of a first composition and second particles of a second composition, where the first and second compositions are different and / or the first and second particles have different average crystallite diameters (e.g., the average crystallite diameter of the first precursor particles is at least 10% different from the average crystallite diameter of the second precursor particles).

[0025] Suitable precursor particles for the formation of graphite product particles include graphitizable carbon such as natural graphite, coke, and soft carbon. Suitable precursor particles for the formation of product particles useful as cathode materials for lithium ion batteries include hydroxides, oxides, sulfates, nitrates, and carbonates of lithium, aluminum, magnesium, transition metals, and mixtures thereof. In the case of lithium nickel manganese cobalt oxide product particles, suitable precursor particles are lithium nickel manganese cobalt oxide particles. In the case of lithium transition metal oxide product particles, suitable precursor particles are lithium transition metal oxide particles.

Brief Description of the Drawings

[0026] Brief Description of the Drawings

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Mode for Carrying Out the Invention

[0027] Detailed Description Unless the context requires otherwise, throughout this specification and the claims, terms such as "comprise", "comprising", etc. are to be construed in a non-limiting, inclusive sense. Terms such as "a", "an", etc. are considered to mean at least one and are not limited to only one.

[0028] In addition, throughout this specification, the following definitions apply.

[0029] In this specification, the term "high shear and high pressure field" means shear and pressure conditions similar to those experienced during a typical mechanofusion process.

[0030] With respect to a plurality of particles, the term "formed irregularly" is intended to mean not only individual particles of irregular shape but also mixtures of particles of irregular shape in other ways that do not have a common shape.

[0031] The particle size distribution of a given sample is quantified herein by its "Dn" diameter. This is defined, as usual, as the diameter at which n% of the mass of the sample has a smaller particle size.

[0032] Therefore, the term "average diameter" of a group of particles is defined as its D50 diameter.

[0033] The term "projected area diameter" of a particle is the diameter of a circle having the same area as the projected image of the particle (i.e., its silhouette), or the cross-section of the particle passing near the center of mass of the particle.

[0034] The term "cavity" is used to mean a depression on the surface of a particle having a relative depth in the range of 0.02 to 0.1 and a relative aspect ratio greater than 0.2. The method for quantifying the relative depth and relative aspect ratio is presented in the characterization of the materials of the following examples.

[0035] The term "roughness" is used to mean the coefficient of variation determined by the spline deformation method described in the characterization of the materials of the following examples.

[0036] The term "smooth" means a particle having a roughness less than 0.02.

[0037] The term "spherical" is used to mean a particle whose surface varies by no more than 25% at the distance from the center of mass of the particle.

[0038] The term "fine particles" means a plurality of particles or aggregated particles.

[0039] In a quantitative relationship, the term "about" shall be construed to be in the range of plus 10% and minus 10%.

[0040] The term "anode" means the electrode at which oxidation occurs when the metal ion cell is discharged. In a lithium ion cell, the anode is the electrode that is de-lithiated during discharge and lithiated during charge.

[0041] The term "cathode" means an electrode where reduction occurs when metal ions are discharged. In a lithium-ion cell, the cathode is the electrode that is lithiated during discharge and delithiated during charging.

[0042] The term "metal-ion cell" or "metal-ion battery" means an alkali metal-ion cell including a lithium-ion cell and a sodium-ion cell.

[0043] The term "half cell" means a cell having a working electrode and a metal couple / reference electrode. A lithium half cell has a working electrode and a lithium metal couple / reference electrode.

[0044] The term "active material" means a material that can reversibly store metal ions in an anode or a cathode.

[0045] The term "anode active material" or "anode material" means an active material used to reversibly store metal ions in an anode. In a lithium-ion cell, the anode material is lithiated during charging and delithiated during discharge at a potential less than 2 V versus Li. In a Li half cell, the anode material is delithiated during charging and lithiated during discharge at a potential less than 2 V versus Li.

[0046] The term "cathode active material" or "cathode material" means an active material used to reversibly store metal ions in a cathode. In a lithium-ion cell, the cathode material is lithiated during discharge and delithiated during charging at a potential less than 2 V versus Li. In a Li half cell, the cathode material is delithiated during charging and lithiated during discharge at a potential less than 2 V versus Li.

[0047] It is understood that the term "cross section" means a cross section passing near the mass center of the particle.

[0048] The term "average crystallite size" means the grain size of the phase determined by the Scherrer crystallite size determination method, as detailed below. (Note: In principle, the average crystallite size can be determined not only by X-ray diffraction techniques but also from SEM images. In the former, known as the Scherrer grain size determination method, the Scherrer equation is applied to the FWHM of any one of the X-ray powder diffraction peaks of the phase between 20° and 60° 2-theta under incident CuKα1 radiation. An explanation of the Scherrer equation can be found in "X-ray Diffraction" by B.E. Warren, Dover Publications (1990). In the latter, the average crystallite size is determined from the average of the crystallite sizes of randomly extracted crystallites observed by scanning electron microscopy.)

[0049] As used herein, the term "O3 phase" means a phase having an α-NaFeO2-type structure, as described in C. Delmas, C. Fouassier, and P. Hagenmuller, Physica, 99B (1980) 81-85. As an example, LiCoO2, which is widely used as an active cathode material in commercially available lithium-ion batteries, has an O3 structure. X-ray diffraction may be used to determine the structure of the phases in a sample, including whether the material contains a phase having an O3 structure or a phase having a graphite structure.

[0050] It has been discovered that high shear and high pressure fields associated with the mechanofusion (MF) dry process method can be utilized to produce uniform aggregates from various precursor particles. The MF process is relatively simple and inexpensive. Most of the precursor particles are incorporated into the product particles, and thus the precursor particles are efficiently utilized. Further, the MF process is a dry process and does not require solvents, making it potentially attractive for environmentally reliable commercial manufacturing. The steps required simply include obtaining appropriate amounts of precursor particles and a templating medium and mechanofusing a mixture of these amounts for a sufficient time to appropriately produce aggregate microparticles. After the mechanofusion process, the product particles may be separated from the templating medium by known air classification, sieving, cyclones, washing, sedimentation, hydrocyclones, or other wet or dry methods for separating particles based on diameter, shape, or density.

[0051] Figure 1 schematically shows a suitable MF system 1 for preparing microparticles by the method of the present invention. It consists of a rotating cylindrical chamber 2, in which a fixed round press head 3 and a fixed scraper 4 are arranged. The radius of the press head 3 is smaller than the radius of the chamber 2, and the clearance space between the press head 3 and the chamber wall 5 is generally in the range of 1 to 5 mm. The clearance between the scraper 4 and the chamber wall portion 5 is smaller (usually about 0.5 mm). Preferably, these clearances are adjustable for optimization depending on factors such as the diameter of the chamber, particle size, powder hardness, etc.

[0052] The operation of the MF system 1 is simple, but the mechanism by which the powder is processed in the chamber is complex (see W. Chen, R. N. Dave, R. Pfeffer and O. Walton, Powder Technol., 2004, 146, 121-136). During use, a powder mixture 6 (containing an appropriate amount of precursor particles and a templating medium) is placed in the chamber, and the chamber 2 is sealed. As the chamber rotates, the powder mixture 6 is pressed against the chamber wall 5 by centrifugal action. This causes the powder mixture to be forced through the converging space between the fixed press head 3 and the rotating chamber wall 5, and a high shear and high pressure field is established. As the powder particles exit the diverging space in the press head region, they adhere to each other and to the chamber wall. The spatula 4 is useful for scraping off the powder adhering to the chamber wall 5. The sheared powder mixture is then redispersed in the chamber and moved back towards the press head region. While the chamber 2 is rotating, the powder continuously undergoes this process of compression, frictional shearing and deaggregation. These interactions result in various effects including spheroidization, coating of small or soft particles onto larger particles, and encapsulation of small particles within larger particles. These effects occur rapidly at high rotational speeds (wall surface speeds > 1000 rpm or greater than about 8 m / s) typically utilized.

[0053] As will be appreciated by those skilled in the art, the appropriate operating parameters of the MF system are expected to vary depending on the desired product particles and the type and amount of precursor particles and templating medium utilized. It is expected that those skilled in the art will be able to readily determine the appropriate operating parameters for a given situation based on the guidance presented in the following examples.

[0054] The method of the present invention can be used to agglomerate various types of precursor particles into largely uniform product particles. In principle, any amount of precursor particles having an average particle size of less than 1000 μm can be agglomerated. [Note: In principle, since their diameters are expected to decrease during processing, it is possible to start with initially larger particles up to a maximum of 1000 μm. Thus, precursor particles larger than the mold medium may be utilized. Such particles can be ground in situ to smaller diameters during processing.] This method is particularly suitable for producing product particles with an average diameter of less than 100 μm and smaller (e.g., less than 50 μm or less than 10 μm).

[0055] As demonstrated in the following examples, the powders used in battery electrodes may be agglomerated by the method of the present invention. Such precursor powders include carbonaceous powders (e.g., graphite flakes) or conventional mixed metal oxide powders (e.g., NMC or LiNi 1 / 3 Mn 1 / 3 Co 1 / 3 O2) powders and other anode-active and cathode-active materials. Suitable precursor powders include mixed metal oxide powders prepared without being constrained by convention, for example, those prepared using a novel all-solid method in which an appropriate mixture of metal oxide raw material powders is ball-milled to produce mixed metal oxide precursor particles. However, in addition to this, it is expected that similar aggregates of powders generally intended to be used as fertilizers, pharmaceuticals, toners, pigments, fillers, or catalysts for other industrial applications can be readily prepared in a similar manner. A useful feature of the method of the present invention is that no special shape or particle size distribution of the starting precursor particles is required to obtain the desired end product. The precursor particles can have a regular shape or, alternatively, can be powders shaped irregularly and can have a narrow, or wide, or multimodal diameter distribution.

[0056] The microgranulation method of the present invention generally involves preparing a mixture of a selected amount of precursor particles and an appropriate amount of a template medium. The template medium generally has an average particle size of less than 500 μm and is selected to have a hardness higher than that of the precursor particles. Thus, the template medium does not break itself under the high shear and pressure conditions associated with the method. Options for suitable materials for the template medium include zirconium oxide, tungsten carbide, tungsten, silicon oxide, aluminum oxide, silicon nitride, hardened steel, stainless steel, and quartz. In still other cases, the template medium is preferably regular, smooth, and spherical because it will probably break during processing and ultimately decompose into spherical shapes, thereby contaminating the target product.

[0057] The diameter, uniformity, and amount of the template medium used can also be important with respect to the characteristics of the desired target product microparticles. Agglomerated target product particles are expected to be somewhat smaller but on the order of the diameter of the template medium used. Thus, for smaller agglomerates, it may be desirable for the average particle size of the template medium to be less than 100 μm. Further, the uniformity of the target product microparticles is expected to be approximately similar to the uniformity of the template medium used. Thus, for a preferably uniform final product, it may be desirable for the diameter distribution of the template medium to be sufficiently uniform such that (D90-D10) / D50 < 2, preferably (D90-D10) / D50 < 1, more preferably (D90-D10) / D50 < 0.7, or such that (D90-D10) / D50 is even smaller. Further, a sufficient amount of the template medium must be utilized in the method such that all of the precursor particles present are completely and successfully processed. In this regard, in some embodiments, the bulk volume of the amount of the template medium is desirably greater than the bulk volume of the amount of the precursor particles. More specifically, when utilizing a uniform spherical template medium, the relevant amounts of the mixture are preferably selected such that the volume of the precursor particles can fit into the void volume (which is approximately 1 / 3 of the bulk volume of the spheres) that exists between randomly packed spherical template medium. Thus, a bulk volume ratio of 1:3 of small precursor particles to template medium may be preferred (i.e., the bulk volume of the amount of the template medium is preferably at least about 3 times the bulk volume of the amount of the precursor particles).

[0058] The microgranulation process itself involves subjecting a suitable mixture containing an amount of precursor particles and a templating medium to mechanofusion or other equivalent high shear and high pressure fields. This step is useful for aggregating the precursor particles into product particles. Mechanofusion can be carried out, for example, in the mechanofusion system of FIG. 1. Representative settings for the process include a gap of about 0.5 mm between the scraper and the rotating wall and a gap of about 1.4 mm between the press head and the rotating wall. Representative rotational speeds are in the order of 1000 rpm and above, resulting in a wall surface speed of about 8 m / s or more. A mechanofusion process time of about 12 hours or more has been shown to be sufficient. Shorter process times can be achieved when different sample volumes, rotational speeds, powder ratios are used, or when the templating medium is recycled.

[0059] In the mechanofusion process, the precursor particles and the templating particles are in a vacuum or fluid environment, typically a gas atmosphere. In a simple embodiment, the gas atmosphere is air. However, in other embodiments, the gas atmosphere can be an inert gas, such as argon or nitrogen. Further, the gas atmosphere may be reduced and may contain hydrogen or ammonia, for example, a mixture of 5% hydrogen gas and 95% nitrogen gas. Additionally, the gas atmosphere may be oxidized and may contain an oxidizing gas such as oxygen or carbon dioxide.

[0060] The mechanofusion system shown in FIG. 1 and discussed above is used to prepare product particles in a batch process, but it is possible to modify the apparatus so that the preparation can be carried out continuously instead. For example, during mechanofusion, the particles may be continuously sucked in from the mechanofusion machine in a particle stream. Then, by a continuous classification process, the desired product particles can be separated from the particle stream and collected. The raw precursor particles and the template medium remaining in the particle stream may then be returned to the mechanofusion machine. Additional precursor particles may be continuously added to the mechanofusion machine to replace the product particles removed by classification. In this way, the product particles can be continuously manufactured and collected.

[0061] After the mechanofusion or equivalent process step is completed, the product particles are separated from the template medium. This may be accomplished in a variety of conventional manners. For example, if the product particles and the template medium are sufficiently uniform but have different diameters, appropriate separation can be achieved simply by sieving. Alternatively, if the densities of the product particles and the template medium are sufficiently different, density separation techniques may be utilized (as demonstrated, for example, in an embodiment where high-density ZrO2 microspheres are used as the template medium and then easily separated from the significantly lower-density product particles using density separation techniques). Methods for separating product particles from the template medium include air classification, sieving, cyclones, washing, sedimentation, hydrocyclones, or other wet or dry methods known for separating particles based on diameter, shape, or density.

[0062] It has been observed that some loss of crystallinity associated with the precursor particles can occur as a result of the mechanical processing associated with this method. If desired and / or necessary, this loss can be easily corrected by annealing (heating) the product particles at an elevated temperature and in an appropriate environment for the materials involved (e.g., an inert atmosphere for carbonaceous powders or air for oxide powders).

[0063] In some embodiments, the synthesis of the precursor particles may include a step of reducing the average particle size, for example, by grinding including ball milling or classification. In some embodiments, the synthesis of the precursor particles may include a step of reducing the crystallite size, including ball milling. In some embodiments, the synthesis of the precursor particles may include a step of increasing the crystallite size, including a heating step or a classification step. In some embodiments, the synthesis of the precursor particles may include a step of reacting two or more components together, including co-precipitation, heating, ball milling, or other known methods. In some embodiments, the synthesis of the precursor particles may include a step of combining particles having different average crystallite sizes and different compositions together.

[0064] In some embodiments, by applying the above micro-granulation method to the template particles and the precursor particles including a mixture of precursor particles having different crystallite sizes, on average, product particles are obtained that have larger precursor particle crystallites near the product particle core and smaller precursor particle crystallites near the product particle surface. Further, in some embodiments, when a mixture of precursor particles of different chemical compositions is used that contains precursor particles of one composition having an average crystallite size larger than the average crystallite size of precursor particles of another composition, the product particle core has a composition closer to and similar to the composition of the precursor particles having the larger crystallite size, and the product particle surface has a composition closer to and similar to the composition of the precursor particles having the smaller crystallite size, and product particles are obtained. Theoretically, product particles having a continuously varying composition can be produced by applying the above method to the template particles and the precursor particles including a mixture of precursor particles having different compositions and average crystallite sizes such that the composition of the product particles varies from their surface to their core in the order of increasing average crystallite size of the respective precursor particle powders.

[0065] The precursor particles can also include particles having different compositions such that composite product particles are produced that include an agglomerated mixture of precursor particles having different compositions. In some embodiments, the composite product particles can be heated such that the component precursor particles react with each other.

[0066] The product particles can be prepared in a manner such that the average diameter is from 10 to 100 μm. Further, the product particles can have a narrow particle size distribution similar to the template medium utilized and can be very uniform in diameter. For example, the particle size distribution of the product particles can be uniform such that (D90 - D10) / D50 < 2, (D90 - D10) / D50 < 1, (D90 - D10) / D50 < 0.7, or even smaller. Further, the product particles can desirably be smooth and can be formed into regular rounded shapes such as spheres and rounded tetrahedrons. The product particles may not further contain features having both a relative depth in the range of 0.1 - 0.2 and a relative aspect ratio greater than 0.2.

[0067] Once prepared in the manner described above, the product particles are generally immediately available for conventional use in their intended applications. In battery applications, electrodes and electrochemical devices utilizing the product particles can be prepared in a number of manners known to those skilled in the art. For example, there are numerous optional designs and methods for manufacturing electrodes for rechargeable lithium ion batteries as well as for manufacturing the batteries themselves, and these are extensively documented in the art.

[0068] The mechanofusion method has been found to be effective in preparing uniform round aggregates in such a manner, while other conventional granulation methods such as automatic grinding and ball milling processes are not effective. Without being bound by theory, in this method, it is considered that the precursor particles first coat the mold medium. However, due to the smoothness of the mold medium, the precursor particles adhere insufficiently to the mold medium. Therefore, after reaching a specific thickness, the layer of precursor particles breaks away from the mold medium. This results in the formation of intermediate particles of relatively uniform volume. These intermediate particles are then spheronized and sized to form product particles. Therefore, this process depends on the ability of the mechanofusion process to form a high-density coating on the particles. This is only possible in the high shear and high compression fields that exist during the mechanofusion process. Other processes such as grinding, milling, and high shear mixing have been found not to have this characteristic and thus did not produce equivalent product particles.

[0069] An additional discovery related to this method is that some of the product particles that can be prepared are characterized by novel potentially useful structures. These include graphite product particles, lithium mixed metal oxide product particles, and lithium transition metal oxide product particles characterized by unique structures. For example, it is possible to prepare graphite microparticles that include graphite particles shaped as spheres or ovals and include concentric nested spherical or oval shapes of graphene layers. These graphene layers are randomly arranged on the surface of the concentric nested spherical or oval shapes, but the graphene layers are oriented such that their basal planes are tangential to the concentric nested spherical or oval shapes. Further, the graphite particles have an average particle size greater than 2 μm and an average d 002 spacing of less than 3,400 Å. In some embodiments, the microparticle graphite particles include a porous concentric layer having a hollow or void near its core. In some embodiments, the graphite particles have an average particle size of 5 μm to 50 μm and a particle size distribution of (D90 - D10) / D50 < 2.

[0070] The above-mentioned graphite microparticles and highly graphitized onion graphite are expected to be advantageous as active anode materials in lithium-ion batteries. It is well-known that the basal plane of graphite is a highly reactive site with respect to lithium-ion battery electrolytes. Therefore, natural graphite is typically spheronized and sized to reduce the surface area of the basal plane in contact with the electrolyte, as discussed in M. Yoshio et al., J. Mater. Chem. 14 (3005) 1754-1758. However, in conventional spheronization methods, graphite planes that are coiled in a helical manner, as in the same arrangement as a jelly roll or as described by M. Yoshio et al. as "spherical natural graphite particles appear like a tightly clenched fist," are formed. In other words, the graphite layers of conventionally spheronized and sized natural graphite particles are arranged concentrically around the central axis (i.e., concentric cylinders in a nested state) rather than concentrically around a single point (i.e., nested spherical or oval shapes as in the case of onion graphite). The arrangement of the graphite basal planes of spherical natural graphite reduces the amount of graphite basal planes exposed to the electrolyte, but the graphite basal planes remain exposed at either end of the "jelly roll." To reduce the reactivity of the exposed basal planes, spherical natural graphite is typically carbon-coated, as described by M. Yoshio et al. In contrast, the microstructure of onion graphite has no basal planes exposed to the electrolyte and is therefore expected to have improved performance as an anode material in lithium-ion batteries.Onion graphite is expected to be superior to the types of graphite spheres found in cast iron, which are known to have a microstructure in which the graphite basal planes are concentrically arranged but the planes radiate out from a central core (as shown, for example, in Figure 6-4 of "Mesomolecules: From Molecules to Materials" SEARCH Series, Volume 1, G. David Mendenhall, Arthur Greenberg, and Jeol F. Liebman, eds., Chapman & Hall, New York, 1995). In this structure, the electrolyte is expected to approach the graphite basal planes along radial lines that separate the basal planes extending from the particle core to the surface. For practical use in lithium-ion battery applications, the diameter of the onion graphite should be greater than 5 μm, more preferably between 10 μm and 50 μm. In addition, the onion graphite should have a high level of graphitization. This is known to improve the reversible capacity and reduce cell polarization. When measured by X-ray diffraction, the measurement of the graphitization level is the d-spacing of graphite, and the lower the value of the d-spacing, the higher the degree of graphitization. The preferred level of graphitization is indicated by a d-spacing of less than 3.400 Å, more preferably less than 3.360 Å, or more preferably less than 3.350 Å. 002 spacing, and d 002 The lower the value of the d-spacing, the higher the degree of graphitization. The preferred level of graphitization is less than 3.400 Å, or more preferably less than 3.360 Å, or more preferably less than 3.350 Å of the d-spacing. 002 spacing.

[0071] For example, lithium mixed metal oxide fine particles can be prepared that include particles having a core of randomly oriented lithium nickel manganese cobalt crystallites with an average diameter of about 1 μm, coated with smaller randomly oriented lithium nickel manganese cobalt crystallites having an average diameter of about 0.3 μm. In some embodiments, the lithium mixed metal oxide product particles are smooth tetrahedrons.

[0072] Furthermore, for example, lithium transition metal oxide fine particles can be prepared that include particles having at least two transition metals present in the group consisting of Mn, Ni, and Co. These particles have an O3 structure, an average particle size in the range of 1 to 50 μm, and they include crystallites whose shape and diameter vary randomly throughout their interior. In certain embodiments, the crystallites have an average diameter greater than 0.5 μm, and the average particle size of the particles is more than 5 times greater than the average crystallite diameter. In certain embodiments, the composition of one of the two transition metals can vary by at least 5 atomic % from the core to the shell of the particle.

[0073] The following examples are illustrative of specific aspects of the invention and should not be construed as limiting the invention in any way. Those skilled in the art will readily recognize that other variations are possible with respect to the methods and materials produced herein.

Examples

[0074] Examples To agglomerate precursor particles according to the present invention, mechano-fusion was used to prepare exemplary fine particles. Other fine particles were also prepared for comparison purposes. Various characteristics of these fine particles were determined and are presented below. In addition, some of these fine particles were used to prepare electrodes and electrochemical cells. The results of the cell performance obtained from the electrochemical cells are also presented below.

[0075] Micro-granulation method (mechano-fusion) As schematically shown in Figure 1 below, micro granulation was achieved using an AM-15F Mechanofusion System (Hosokawa Micron Corporation, Osaka, Japan). To reduce wear, the device was modified by replacing the standard stainless steel chamber, scraper, and press head with parts made of the same hardened steel. The chamber had an inner diameter of 15 cm. Unless otherwise specified, mechanofusion was carried out at high rpm using a 0.5 mm scraper / wall spacing and a 1.4 mm press head / wall spacing. After a given process time, samples were collected from several different regions of the chamber. Unless otherwise specified, the gas atmosphere used during the mechanofusion process was air.

[0076] Characterization of Materials The particle size distribution of the fine particle samples was obtained using a Horiba Partica LA-950V2 laser dispersion particle size distribution analyzer.

[0077] X-ray diffraction (XRD) patterns were collected using a Rigaku Ultima IV diffractometer equipped with a Cu Kα X-ray source, a diffracted beam graphite monochromator, and a scintillation detector.

[0078] Unless otherwise specified, the average crystallite size of the different phases was determined by applying the Scherrer equation to the maximum XRD peak of the phase in question.

[0079] SEM and cross-section SEM were used to study the sample morphology. For this purpose, a TESCAN MIRA 3 LMU Variable Pressure Schottky Field Emission Scanning Electron Microscope (SEM) was used. The cross-sections of the samples were prepared by a JEOL Cross-Polisher (JEOL Ltd., Tokyo, Japan) that sections the samples by emitting argon ions at them.

[0080] To characterize the particle surface cavities, the relative depth and relative aspect of the indentations on the particle surface are measured from the particle cross-section or projection area (i.e., silhouette) as follows. As shown in Fig. 19, line AB is created above the indentation on the particle surface and has both ends in contact with the particle surface. The longest distance (line GC) measured vertically from line AB to the particle surface is described as the characteristic depth, d. Two lines are drawn from point C (lines EC and CF in Fig. a) such that they contact the surface contact line AB and have the maximum possible acute angle between them without passing through the particle volume. The relative depth of the particle is defined as d / D, where D is the projected area diameter. The relative aspect is defined as {(EC + FC) / EF - 1}. The surface cavities are those features having a relative depth in the range of 0.02 to 0.1 and a relative aspect greater than 0.2.

[0081] To determine the particle roughness, the spline deformation method is used. By this method, the particle roughness is determined by quantifying the deformation at the radius of the surface when measured from the mass center. In this method, a scanning electron microscope (SEM) digital image of a cross-section or the silhouette of the desired particle with a minimum image resolution such that at least 1000 pixels are in the periphery of the particle is obtained. After more than 1000 outline pixels of the SEM image are determined, the mass center of this outline silhouette is found. Next, the distance from each point of the outline silhouette to the mass center is measured ("radial segment value"). Then, the radial segment values are plotted as a function of the angle around the mass center from 0° to 360°, and this plot is fitted to a smoothing spline function.

Number

[0082] Electrode preparation The sample electrodes for laboratory tests were prepared from a slurry prepared by mixing microparticles, carbon black (Super C65, Imerys Graphite and Carbon), and lithium polyacrylate (LiPAA, provided in a 10 wt% aqueous solution produced by neutralizing a polyacrylic acid solution (Sigma-Aldrich, average molecular weight of about 250,000 g / mol, 35 wt% in H2O) with LiOH·H2O (Sigma Aldrich, 98%) in distilled water) in a volume ratio of 70 / 5 / 25 active particles / carbon black / LiPAA based on the bulk density. The slurry was mixed at 100 rpm for 1 hour using a Retsch PM200 planetary mill equipped with three 13 mm tungsten carbide balls and then spread onto metal foils (copper or aluminum for anode active and cathode active materials, respectively) using a 0.004-inch gap coating bar. The coating was then air-dried at 120 °C for 1 hour, cut into 1.3 cm disks, and then heated under vacuum at 120 °C for 1 hour without further air exposure. The resulting electrode loading was about 2 - 2.5 mg / cm 2 was obtained.

[0083] Cell Preparation To evaluate various materials as electrode materials in lithium-ion cells, test lithium half-cells were constructed and tested. The electrodes were assembled into 2325-type coin lithium half-cells with lithium foil (99.9%, Sigma Aldrich) counter / reference electrodes (Note: As is well known to those skilled in the art, the results from these test lithium half-cells enable a reliable prediction of the electrode material performance in lithium-ion batteries). A two-layer Celgard 2300 separator was used in each coin lithium half-cell. A 1 M LiPF6 (BASF) in a solution of ethylene carbonate, diethyl carbonate, and monofluoroethylene carbonate (volume ratio 3:6:1, all from BASF) was used as the electrolyte. Cell assembly was performed in an Ar-filled glove box. The cells were cycled at a constant current at 30.0 ± 0.1 °C.

[0084] Example 1 of the present invention - Microgranulation of graphite flakes Zirconium oxide (ZrO2) microspheres (Glen Mills Inc.) with an average diameter (diameter) of 57 μm were used as a mold medium, and graphite flake precursor particles were aggregated into graphite product particles. Figures 2a and 2b show SEM images of the ZrO2 mold medium at two different magnifications. Figure 2c shows a cross-section of the ZrO2 particle showing its peripheral part and mass center. Figure 2d shows the interpolated radial segment values and the remaining plot of the interpolated f(x) values, a function of x. From this data, the roughness was determined. The ZrO2 mold medium is smooth and has a roughness of only 0.0022 and no cavities. Figure 3 shows the uniform particle size distribution of the ZrO2 mold medium with a D50 of 57.35 μm and (D90 - D10) / D50 = 0.61.

[0085] Natural graphite flakes (230U, Asbury Graphite Mills Inc.) were used as the graphite precursor particles. Figures 4a and 4b show SEM images of these precursor particles at two different magnifications. As is evident from these images, the graphite flakes are irregularly shaped particles with a layered structure and very different particle diameters. Many of the particles have jagged surface features, which are large cavities.

[0086] A mixture containing approximately 225 g of ZrO2 microsphere mold medium and approximately 25 g of graphite precursor particles (total powder volume of approximately 50 mL) was prepared and then subjected to the high shear and high pressure fields provided by the above-mentioned mechanofusion system. The system was operated at 1500 rpm (wall velocity of 12 m / s) for 12 hours. Figures 5a and 5b show SEM images of the product obtained after this mechanofusion at two different magnifications. In these images, the ZrO2 microspheres appear to be partially coated with a thin layer of graphite. Also, it is evident that the graphite spheres (product particles) have a diameter slightly smaller than that of the ZrO2 microspheres.

[0087] Next, (between ZrO2 of 5.68 g / cm 3 and graphite of 2.23 g / cm 3 ), methylene iodide (MI-GEE, GEO Liquids, Inc., Prospect Heights, IL) having a density of 3.32 g / cm 3 was used to separate graphite spherical product particles from ZrO2 microspheres by density. FIGS. 6a and 6b show SEM images of the graphite spherical product particles at two different magnifications after separation and drying with methylene iodide. Almost all of the ZrO2 was removed, and thus most of the remaining particles were graphite spheres.

[0088] XRD patterns of graphite were obtained before and after the mechanofusion process. Based on the obtained XRD patterns, the mechanofusion process appeared to somewhat disrupt the crystal structure of graphite, causing some loss of crystallinity. This was evident from the broadening of the peaks and the amorphous characteristics in the XRD pattern. The pattern also showed the presence of a small amount of ZrO2 impurities remaining in the sample (it is expected that such impurities can be easily removed on an industrial scale using better separation techniques). Therefore, the graphite spherical product particles were recrystallized by annealing (heating) at 3000 °C for 3 hours in argon. The subsequent XRD pattern of the annealed product particles was obtained. At this stage, all the peaks were sharp, indicating good crystallinity. The d 002 spacing based on the position of the (002) X-ray diffraction peak was determined to be 3.355 Å for the annealed product particles, indicating a high degree of graphitization. Perhaps due to the reduction of ZrO2 by carbon at high temperature in argon, a small amount of ZrC was present in the XRD pattern. FIGS. 7a, 7b, and 7c show these various XRD patterns, namely, the XRD pattern of the graphite flake precursor particles before mechanofusion, the XRD pattern of the graphite spherical product particles after mechanofusion and separation from the template medium, and the XRD pattern of the graphite spherical product particles after annealing, respectively.

[0089] Figure 8 shows the particle size distribution of the graphite spherical product particles after annealing. For comparison, the particle size distribution of the ZrO2 mold medium is also shown (dotted line). The graphite spherical product particles have an average diameter of about 41 μm, and it can be seen that the diameter is very uniform.

[0090] Using these graphite spherical product particles as the anode active material, electrodes were prepared, and lithium half-cells containing such electrodes were manufactured and tested. The cells were cycled at 0.005 V to 0.9 V. For the first cycle, the cells were cycled at C / 10 and at a lower potential, and the cells were held at a constant potential until the current decreased to a value of C / 20 before the next cycle started. For subsequent cycles, the cells were cycled at C / 5, and the cells were held at a lower potential limit respectively until the current decreased to a value of C / 10 before the next cycle started. Figures 9a, 9b, and 9c show the electrochemical performance of this cell. In these figures, the voltage curve, the corresponding differential capacitance curve, and the cycling performance are shown respectively. The voltage curve is typical for graphite, and the staging expected in the differential capacitance curve can be clearly observed. Due to the good cycling performance, a reversible capacity of about 275 mAh / g is obtained.

[0091] To further analyze the structure of these graphite spherical product particles, as detailed above, representative particles were cross-sectioned and imaged using SEM. Figures 10a, 10b, and 10c show some of the resulting SEM images. Figure 10a shows the entire portion of the product particle, and Figures 10b and 10c show different portions of the product particle at a higher magnification. Some of the product particles contain void space (i.e., a hollow core) near the center of the particle. In addition, porosity arranged in concentric layers is observed throughout the particle. Thus, the product particles appear to be characterized by a novel concentric structure. The product particles contain concentric layers of graphene sheets. Figure 10d shows a cross-section of a product particle showing its periphery and mass center. Figure 10e shows the interpolated radial segment values and the remaining plot of the interpolated f(x) values, a function of x. The roughness was determined from this data. The graphite product particles are smooth and have a roughness of only 0.0052 and no cavities.

[0092] Example 2 of the present invention - Microgranulation of Lithium Transition Metal Oxide Powder Zirconium oxide (ZrO2) microspheres similar to the above examples were used as a template medium, and submicron irregularly shaped precursor NMC particles were aggregated into larger regularly shaped NMC product particles.

[0093] Using the all-solid method, the formula LiNi 1 / 3 Mn 1 / 3 Co 1 / 3NMC precursor particles with O2 were prepared. In particular, using a SPEX 8000 mixer, by high-energy ball milling, the stoichiometric amounts of NiO (Sigma-Aldrich, 99%), MnO (Aldrich, 99%), Co3O4 (Alfa Aesar, 99.7%) and Li2CO3 (Alfa Aesar, 99%) with a 10% excess of Li2CO3 were mixed together. A sample diameter of about 2.4 g was milled for 4 hours using 180 g of 1.6 mm stainless steel balls (Thomson Linear Motion). The resulting ball-milled mixture was then pelletized and heated in air at 900 °C for 3 hours. Finally, the pellets were crushed into fine powder to produce NMC precursor particles. Figures 11a and 11b show SEM images of these NMC precursor particles at two different magnifications. Aggregation of submicron NMC particles can be observed irregularly.

[0094] A mixture containing about 225 g of ZrO2 microsphere casting media and about 15 g of NMC precursor particles (total powder volume of about 50 mL) was prepared and then subjected to mechanofusion as described above. The system was operated for 24 hours at 1000 rpm (wall velocity of about 8 m / s). Figures 12a and 12b show SEM images of the product obtained after this mechanofusion at two different magnifications. In these images, the ZrO2 microspheres appear to be partially coated by a thin layer of NMC. Also, it is clear that the NMC tetrahedra (product particles) have a diameter slightly smaller than the ZrO2 microspheres but larger than the NMC precursor particles.

[0095] Subsequently, 400-mesh sieves were used to separate the NMC tetrahedron product particles from the ZrO2 microspheres. Figures 13a and 13b show SEM images of the tetrahedral NMC product particles at two different magnifications after separation in this manner. The product particles are smooth. Again, almost all of the ZrO2 was removed.

[0096] XRD patterns of the NMC product particles were obtained before and after the mechanofusion process. Again, the mechanofusion process appeared to somewhat disrupt the crystal structure of the product particles, causing some loss of crystallinity. This was evident from the broadening of the peaks and amorphous features in the XRD pattern. The pattern also showed the presence of a small amount of ZrO2 impurities remaining in the sample (again, it is expected that on an industrial scale, such impurities can be easily removed using better separation techniques). Therefore, the NMC product particles were recrystallized by annealing in air at 900 °C. The subsequent XRD pattern of the annealed product particles was obtained. At this stage, all the peaks were sharp, indicating good crystallinity. A small amount of ZrO2 was still present in the XRD pattern. Figures 14a, 14b, and 14c show these various XRD patterns, namely, the XRD pattern of the NMC precursor particles before mechanofusion, the NMC tetrahedral product particles after mechanofusion and separation from the template medium, and the XRD pattern of the NMC product particles after annealing, respectively.

[0097] Figure 15 shows the particle size distribution of the NMC product particles after annealing. For comparison, the particle size distribution of the ZrO2 template medium is also shown (dotted line). The NMC product particles have an average diameter (D50) of about 28 μm and a narrow distribution with (D90 - D10) / D50 = 0.66, indicating that the diameters are very uniform.

[0098] Using these NMC product particles as the cathode active material, electrodes were prepared, and lithium half-cells containing such electrodes were fabricated and tested. For the first cycle, the cells were cycled at 3.0 V - 4.2 V at C / 10. For the remaining cycles, the cells were cycled at C / 4 and held at the upper cutoff potential until the current decreased to C / 10 before starting the next cycle. Figures 16a and 16b show the electrochemical performance of this cell. In these figures, the voltage curve and the cycling performance are shown respectively. The voltage curve is typical for NMC, and a reversible capacity of about 90 mAh / g is obtained.

[0099] To further analyze the structure of these NMC product particles, as described above, representative particles were sectioned and imaged using SEM. Figures 17a, 17b, 17c, and 17d show some of the obtained SEM images. Figure 17a shows the entire part of the product particle, and Figures 17b, 17c, and 17d show different parts of the product particle at some higher magnifications. The product particles appear to be smooth and tetrahedral in shape with rounded corners. They contain a core of randomly oriented crystallites with an average diameter of about 1 μm, coated with smaller randomly oriented crystallites having an average diameter of about 0.3 μm. Thus, the aggregated NMC product particles appear to be characterized by a novel structure.

[0100] Figure 17e shows a cross-section of the product particle, indicating its peripheral part and the center of mass. Figure 17f shows the interpolated radial segment values and the remaining plots of the interpolated f(x) values, which are functions of x. The roughness was determined from this data. The NMC product particles are smooth and have a roughness of only 0.0094 and no cavities.

[0101] Comparative Example - Attempts at Microgranulation of Lithium Transition Metal Oxides Using an Automatic Grinding Process Zirconium oxide (ZrO2) microspheres and NMC precursor particles similar to those in the above examples were used. A mixture containing the same ratio of ZrO2 and NMC was mixed in a Brinkmann Retsch automatic grinder. The automatic grinder was set to operate at about 120 rpm for two weeks. Figures 18a and 18b show the SEM images obtained for this sample undergoing automatic grinding. The SEM images show that all the ZrO2 microspheres are loosely coated with NMC, but little granulation of NMC can be observed. This comparative example shows that very long-term automatic grinding does not provide the inherent advantages of the mechanofusion process.

[0102] Example 3 of the Present Invention - Microgranulation of a Mixture of Precursor Particles Having Different Compositions and Different Average Crystallite Sizes Zirconium oxide (ZrO2) microspheres similar to the above examples were used as the template medium, and several types of precursor particles with different compositions and average crystallite sizes were aggregated.

[0103] A mixture containing about 180 g of ZrO2 microsphere template medium, 6.94 g of NiO (Sigma-Aldrich, 99%), 2.20 g of MnO (Aldrich, 99%), 2.48 g of Co3O4 ((Alfa Aesar, 99.7%) and 6.29 g of Li2CO3 (Alfa Aesar, 99%) was prepared. As determined by observation of single-crystalline crystallites by SEM, the average crystallite size of Co3O4 was 0.3 μm, and the average crystallite size of NiO was 2 μm. The mixture was then subjected to the above-mentioned mechanofusion at 1000 rpm (wall velocity of about 8 m / sec) for 18 hours. The product particles were then separated from the ZrO2 microspheres using a 400 mesh sieve. Figures 20a and 20b show SEM images of cross-sections of the product particles at two different magnifications. The product particles are smooth, and most particles have a diameter of 5 - 10 μm. In the cross-section, the particles can be seen to have a core-shell structure. The brightness is different for the particle core and for the particle shell, and different elemental compositions are shown for the core and the shell. Figure 21 shows a cross-sectional image of the particles according to the positions of five data points shown as spectra 1 - 5. The elemental composition of each point is listed in Table 1 below according to EDS determination. Co is rich in the core, while Mn and Ni are rich in the shell.

[0104]

Table 1

[0105] Example 4 of the present invention has 4 - x + y + z = 1 and contains particles having a higher Ni content in their cores than in their shells, O3-phase LiNi x Mn y Co z Synthesis of O2 powder As an Mn-rich particle shell, LiNi 1 / 3 Mn1 / 3 Co 1 / 3 The target composition of CoO2(NMC111) was selected. 12.88 g of NiO (Sigma-Aldrich, 99%), 12.24 g of MnO (Aldrich, 99%), 13.85 g of Co3O4 (Alfa Aesar, 99.7%), 21.03 g of Li2CO3 (Alfa Aesar, 99%) (equivalent to 10% excess Li2CO3 according to the formula LiNi 1 / 3 Mn 1 / 3 Co 1 / 3 O2) and 10 kg of 0.5-inch stainless steel balls were sealed in a 5 L stainless steel jar mill (US Stoneware) and milled at 85 rpm for one week to produce the shell precursor powder. The XRD pattern of the obtained shell precursor powder is shown in Figure 22. It contains a mixture of Li2CO3, Co3O4, NiO, and MnO phases. The SEM image of the obtained shell precursor powder is shown in Figure 23. It contains crystallites with a diameter of less than 0.1 μm.

[0106] As a Ni-rich particle core, LiNi 0.6 Mn 0.2 Co 0.2 The target composition of O2(NMC622) was selected. In air, 41.61 g of NiO (Sigma-Aldrich, 99%), 13.18 g of MnO (Aldrich, 99%), 14.90 g of Co3O4 (Alfa Aesar, 99.7%) and 10 kg of 0.5-inch stainless steel balls were sealed in a 5 L stainless steel jar mill (US Stoneware) and milled at 85 rpm for one week to produce the core precursor powder (described as Intermediate A). Figure 24 shows the XRD pattern of Intermediate A corresponding to a single-phase rock salt-type structure. The SEM image of Intermediate A is shown in Figure 25. Intermediate A consists of crystallites with a diameter of less than 0.1 μm. Using a mortar and pestle until a homogeneous mixture is obtained (about 10 minutes), 15 g of Intermediate A was mixed with the formula LiNi 0.6 Mn 0.2 Co 0.2According to O2, 7.83 g of Li2CO3 (Alfa Aesar, 99%) corresponding to a 5% excess of Li2CO3 was mixed. The mixture was placed in an alumina crucible and heated in a box furnace in air at 900 °C for 3 hours, and core precursor particles were obtained. The purpose of this heating step is to increase the crystallite size of the core precursor particles such that they are more than 10% larger than the crystallite size of the shell precursor particles. Figure 26 shows the SEM image of the obtained core precursor particles. They have an average crystallite size of about 2 μm. Figure 27 shows the XRD pattern of the core precursor particles. It corresponds to phase-pure O3-phase NMC622.

[0107] A mixture was prepared containing about 180 g of ZrO2 microsphere casting medium, 13.33 g of shell precursor particles and 6.67 g of core precursor particles. The mixture was then subjected to the above-mentioned mechanofusion at 1000 rpm (wall velocity of about 8 m / s) for 20 hours. The product particles were then separated from the ZrO2 microspheres using a 400 mesh sieve.

[0108] Figures 28a and 28b show SEM images of the cross-section of the product particles at two different magnifications. Most of the product particles have a diameter of 5 - 20 μm. In the cross-section, the particles can be seen to have a core-shell structure. The brightness is different for the particle core and for the particle shell, and different elemental compositions are shown for the core and the shell. The core consists of randomly oriented crystallites having the same average crystallite size as the core precursor particles, and the shell consists of randomly oriented crystallites having the same average crystallite size as the shell precursor particles. The core and the shell contain porosity. Figure 29 shows the cross-section SEM image according to the positions of five data points shown as Spectra 1 - 5. The elemental composition of each point is listed in Table 2 below according to the determination by EDS. The core is about 13% richer in Ni than the shell.

[0109]

Table 2

[0110] Figure 30a shows a cross-sectional image of the product particles, and Figure 30b shows the EDS Ni-mapping of the same product particles. The intensity of the Ni signal from the core is stronger than that from the shell, and it is confirmed that the product particles consist of a Ni-rich core and the shell is rich in Co and Mn. Figure 31 shows the XRD pattern of the product particles. The XRD pattern corresponds to that of a mixture of the product particles and the core particles.

[0111] The product particles were placed in an alumina crucible and heated in air in a box furnace at 900 °C for 3 hours to cause the reaction of the components of the product particles to form layered lithium nickel manganese cobalt oxide with the overall composition of LiNi 0.4 Mn 0.3 Co 0.3 O2. Figure 32 shows the XRD pattern of the heated product particles. The XRD pattern contains peaks corresponding only to the O3 phase of LiNi x Mn y Co z O2 with x + y + z = 1. Figure 33 shows the SEM image of the cross-section of the heated product particles. The diameter of the heated product particles was the same as that of the product particles before heating. The heated product particles had an average diameter of 2 μm, were randomly shaped, and contained randomly oriented crystallites. Some of the heated product particles contained voids while others did not.

[0112] Figure 34 shows the cross-sectional image of the heated product particles at the positions of six data points shown as Spectra 1 - 6. The elemental composition of each point is listed in Table 3 below according to the determination by EDS. A concentration gradient is generated by the diffusion of transition metals during the high-temperature heating process. The Ni content gradually increases from the shell to the core, and the Mn content increases from the core to the shell. Figure 35 shows the variation of the transition metal composition as a function of the distance from the surface of the heated product particles determined from Spectra 1 - 6 in Figure 34. The Ni concentration near the core is about 9% higher than that in the shell.

[0113]

Table 3

[0114] Example 5 of the Invention - Microgranulation of Graphite Flakes Graphite product particles were produced using the same method as in Example 1 of the present invention, except that the product particles were separated from the ZrO2 mold medium by passing the product particle / mold medium mixture through a 38 μm sieve after the mechanofusion process. The product particles were then heated to 2840 °C under argon gas for 90 minutes to produce graphite spheres. Presumably because diiodomethane was not used during the process, the annealed product particle spheres had the same shape and average particle size as those of Example 1 of the present invention, but were less porous. It is thought that diiodomethane penetrates between the graphite layers during heating, creating concentric porosity and void spaces. Figure 36 shows a SEM cross-sectional image of some of the annealed product particles of Example 5 of the present invention. Some of the annealed product particles contained little or no porosity, some contained concentric porosity, and some contained central void spaces. All of the annealed product particles contained layers of graphite concentrically arranged in nested ovoid or spherical shells, with the basal plane ends not radiating radially from the center point to the outside of the particle.

[0115] Example 6 of the Invention - Microgranulation of Petroleum Coke 30 g of petroleum coke in the form of flakes having an average flake thickness of 2 μm and an average flake width of 10 μm; and 330 g of ZrO2 spheres of the same type as those used in Example 1 of the present invention were subjected to the high shear and high pressure fields described in Example 1 for 32 hours. A 400 mesh sieve was used to separate the resulting product particles from the ZrO2 spheres. The resulting product particles had a nodular shape, but were round, smooth, and had an average diameter of 20 μm.

[0116] The above examples demonstrate that mechanofusion can be used to simply and efficiently agglomerate various precursor particles into larger product particles. The product particles can be uniform and desirably smooth and can be spherical or rounded. In some examples, microparticles having novel structures can be produced by the method. And as demonstrated in laboratory test cells, the present invention can be used to produce suitable microparticles for electrode materials in lithium batteries.

[0117] All of the above U.S. patents, U.S. patent applications, foreign patents, foreign patent applications, and non-patent publications described herein are hereby incorporated by reference in their entirety.

[0118] Although specific elements, embodiments, and applications of the invention have been shown and described, of course, it will be understood that the invention is not limited thereto, as it may be modified by those skilled in the art without departing from the spirit and scope of the disclosure, particularly in view of the above teachings. For example, it is expected that similar uniform product microparticles can be provided by other methods that can provide shear and pressure field conditions similar to those provided by mechanofusion. Such modifications are considered to be within the scope of the claims appended hereto.

Claims

1. obtaining an amount of precursor particles having an average particle size of less than 1000 μm; obtaining an amount of a mold medium having an average particle size of less than 500 μm and a hardness higher than that of the precursor particles; preparing a mixture comprising the amount of precursor particles and the mold medium; subjecting the mixture to a high shear and high pressure field to agglomerate the precursor particles into product particles A microgranulation method for agglomerating precursor particles, comprising:

2. The method according to claim 1, wherein the step of subjecting the mixture to a high shear and high pressure field comprises mechanofusing the mixture.

3. The method according to claim 1, wherein the average diameter of the precursor particles is less than 50 μm.

4. The method according to claim 3, wherein the average diameter of the precursor particles is less than 10 μm.

5. The method according to claim 1, wherein the precursor particles are powders for use in battery electrodes, fertilizers, pharmaceuticals, toners, pigments, fillers or catalysts.

6. The method according to claim 5, wherein the precursor particles are carbonaceous powders, or mixed metal oxide powders, or metal carbonate powders.

7. The method according to claim 6, wherein the precursor particles contain carbon.

8. The precursor particles are graphite flakes or LiNi １／３ Mn １／３ Co １／３ O ２ powder, and the method according to claim 6.

9. wherein the precursor particles are mixed metal oxide powders, and the step of obtaining the amount of precursor particles comprises obtaining a metal oxide raw material powder; ball-milling the metal oxide raw material powder to produce the precursor particles The method according to claim 6, comprising:

10. The method according to claim 1, comprising ball-milling at least a portion of the amount of precursor particles before preparing the mixture.

11. The method according to claim 1, comprising heating at least a portion of the amount of precursor particles before preparing the mixture.

12. The method according to claim 1, wherein the precursor particles are irregularly shaped powders.

13. The method according to claim 1, wherein the average diameter of the mold medium is 100 μm or less.

14. The method according to claim 1, wherein the mold medium is selected from the group consisting of zirconium oxide, tungsten carbide, tungsten, silicon oxide, aluminum oxide, silicon nitride, hardened steel, stainless steel and quartz.

15. The method according to claim 1, wherein the surface of the mold medium is smooth.

16. The method according to claim 15, wherein the mold medium is spherical.

17. The method according to claim 1, wherein the particle size distribution of the mold medium is uniform such that (D90 - D10) / D50 < 2.

18. The method according to claim 1, wherein the bulk volume of the amount of mold medium is greater than the bulk volume of the amount of precursor particles.

19. The method according to claim 1, wherein the bulk volume of the amount of mold medium is greater than 10% of the bulk volume of the amount of precursor particles.

20. The method according to claim 19, wherein the bulk volume of the amount of mold medium is about three times or more the bulk volume of the amount of precursor particles.

21. The method according to claim 2, wherein the mechanofusion is carried out in a mechanofusion system including a chamber, a rotating wall portion within the chamber, a scraper within the rotating wall portion, and a press head within the rotating wall portion.

22. The mechanofusion sets a gap of about 0.5 mm between the scraper and the rotating wall portion, sets a gap of about 1.4 mm between the press head and the rotating wall portion, and rotates the wall surface at a speed of about 8 m / s or more. The method according to claim 21, comprising:

23. The method according to claim 1, wherein the average particle size of the product particles is 10 to 100 μm.

24. The method according to claim 1, wherein the particle size distribution of the product particles is uniform such that (D90 - D10) / D50 < 2.

25. The method according to claim 2, wherein the surface of the product particles is smooth.

26. The method according to claim 2, wherein the surface of the product particles does not contain cavities.

27. The method according to claim 2, wherein the product particles have a roughness of less than 0.

02.

28. The method according to claim 25, wherein the product particles are spherical.

29. The method according to claim 25, wherein the product particles are tetrahedral.

30. The method according to claim 2, further comprising annealing the product particles at a high temperature.

31. Use of product particles produced according to the method according to claim 1 as battery electrodes, fertilizers, pharmaceuticals, toners, pigments, fillers or catalysts.

32. A rechargeable battery including an anode electrode and a cathode electrode, wherein at least one of the anode and cathode electrodes includes product particles produced according to the method according to claim 1.

33. Graphite microparticles including graphite particles, wherein the graphite particles are spherical or oval, The graphite particles include concentric nested spherical or oval shapes of graphene layers, The graphene layers are randomly arranged on the surface of the concentric nested spherical or oval shape, except that the basal planes of the graphene layers are oriented tangentially to the concentric nested spherical or oval shape, The graphite particles have an average particle size greater than 2 μm, The graphite particles having an average d of less than 3,400 Å ００２ Graphite fine particles having an interval.

34. The graphite fine particles according to claim 33, wherein the graphite particles include a porous and concentric layer of a hollow core.

35. The graphite fine particles according to claim 33, wherein the graphite particles have an average particle size in the range of 5 μm to 50 μm and a particle size distribution of (D90 - D10) / D50 < 2.

36. An agglomerated graphite fine particle including an agglomerate of graphite particles produced according to the method of claim 1, wherein the precursor particles are graphite particles and the product particles are graphite fine particles.

37. Lithium mixed metal oxide fine particles including particles having a core of randomly oriented lithium nickel manganese cobalt crystallites having an average diameter of about 1 μm and coated with smaller randomly oriented lithium nickel manganese cobalt crystallites having an average diameter of about 0.3 μm.

38. Lithium nickel manganese cobalt fine particles including an agglomerate of lithium nickel manganese cobalt particles produced according to the method of claim 1, wherein the precursor particles are lithium nickel manganese cobalt particles and the product particles are lithium nickel manganese cobalt fine particles.

39. The method of claim 1, wherein the amount of precursor particles includes a mixture of first particles of a first composition and second particles of a second composition, and the first and second compositions are different.

40. The method of claim 39, wherein the average crystallite diameter of the first precursor particles differs by at least 10% from the average crystallite diameter of the second precursor particles.

41. Lithium transition metal oxide fine particles including particles of a lithium transition metal oxide, The particles include at least two transition metals from the group consisting of Mn, Ni, and Co, The particles have an O3 structure, The particles have an average particle size in the range of 1 to 50 μm, The lithium transition metal oxide fine particles, wherein the particles include crystallites whose shape and diameter vary randomly throughout their interior.

42. The lithium transition metal oxide fine particles according to claim 41, wherein the crystallites have an average diameter larger than 0.5 μm, and the average particle diameter of the particles is at least five times larger than the average crystallite diameter.

43. The lithium transition metal oxide fine particles according to claim 41, wherein the composition of at least one of the at least two transition metals varies by at least 5% atomically from the core of the particles to the shell of the particles.

44. Lithium transition metal oxide fine particles containing lithium transition metal oxide particles produced according to the method according to claim 1, wherein the precursor particles are lithium transition metal oxide particles and the product particles are lithium transition metal oxide fine particles.

45. The method according to claim 1, comprising separating the product particles from the mold medium after aggregating the precursor particles into product particles.

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