Again published on 6th July 2022:
NOVONIX BATTERY TECH SOLUTIONS INCIMPROVED MICROGRANULATION METHODS AND PRODUCT PARTICLES
THEREFROM
Technical Field
The present invention pertains to improved microgranulation methods for aggregating precursor particles into larger product particles with improved properties and, in some instances, novel structures. The product particles are useful as electrode materials in lithium batteries and other applications.
Background
Numerous applications require powders consisting of dense particles in the micron size range (e.g. 1- 100 pm) with narrow particle size distributions (e.g. active powders for battery electrodes, fertilizers, pharmaceuticals, toners, pigments, fillers, catalysts, etc.). In some of these applications spherical or rounded particles are desired. However, the manufacture of particles of uniform shape and size in the micron size range is difficult.
For instance, it can be desirable for the particles used in the manufacture of electrodes for rechargeable high energy density batteries, such as Li-ion batteries, to be spherical in shape and of uniform size. And given the substantial demand for these batteries, it is also of great importance to be able to provide significant and economic supplies of such materials. At present, the cathode particles for Li- ion batteries (e.g. lithium nickel manganese cobalt oxides or NMC) are often made by a co precipitation process in a continuous flow tank reactor. This results in a broad particle size distribution because of the variable particle residence time of the particles in the reactor. In addition, careful process control and various chemical additives are required (e.g. chelating agents) in order to maintain an even precipitation rate of the different metal salts and to achieve a uniform spherical particle shape. Furthermore, after the co-precipitation process, the particles need to be separated from their mother liquor by filtration, washing, drying and blending with a lithium source prior to sintering, creating additional processing steps and energy, chemical, and water waste. The anode particles for Li-ion batteries are typically carbonaceous, e.g. graphite particles. Typically, to make battery-grade graphite from natural graphite, the natural graphite is first ground and classified in order to obtain a powder with the desired size distribution (-10-20 pm in diameter). The sized powders are then spheronized using a spheronizer. However, the spheronizing process is typically only 50-60% efficient, producing a mixture of the desired spheronized particles and fine particles less than 5 pm in diameter. The resulting mixture requires an additional classification step to separate the desired particles from the fine particles, which are typically disposed of as waste. Obviously then, a significant amount of the starting natural graphite is lost as a result.
Granulation is a method in which small particles may be aggregated into larger particles. Granulation methods include both wet and dry methods. Wet granulation methods include fluid bed, disc, drum, and mixer (e.g. via the use of pins, paddles and/or blades) methods. Such wet methods require the separation of the product particles from liquids and may require additional binders or dispersing agents. Dry granulation methods include roll pressing, tableting, ram/piston extrusion, pelleting mills, radial extrusion, and axial exclusion. However both wet and dry methods of granulation have difficulty in making uniform product particles less than 100 pm in diameter and the resulting product particles can often contain internal voids.
Other methods of producing micron-sized spherical or rounded particles including spray drying and prilling. During spray drying, a fluid comprising a liquid (typically water) and suspended particulates and/or dissolved species are sprayed through a nozzle to produce droplets. The fluid can further contain additives, such as wetting agents and binders. The droplets emitted from the spray nozzle are dried (e.g. by a flow of air) while still airborne and captured in a filter. This method can be expensive and wasteful, as it is typically energy intensive to remove the liquid during the drying step and the liquid is often lost as waste. The resulting powders are often porous and may need further processing (e.g. washing and filtering). Prilling is a method in which a molten liquid spray is solidified in-flight. This method is only applicable for materials that can form a molten state.
There is a need then for a dry granulation method at the micro-scale (i.e. microgranulation) in which small particles (e.g. ~1 pm or less) may be aggregated to form larger, dense, and uniform micron-sized particles that are spherical or rounded and where the method does not form a significant amount of waste fine particles. However, according to US 9,132,482: "The extremely poor amount of literature on granulation of inorganic nanopowders demonstrates the difficulty in conditioning them in the form of granules."
Physical methods that employ dry processing are environmentally friendly and advantageous for industrial use because of the elimination of the use of solvents. The mechanofiision (MF) process was developed in Japan in the mid-1980s and is based on using a high shear field to spheronize or dry -coat powders without using any liquids (see T. Yokoyania, K. Urayama and T. Yokoyama, KONA Powder Part. J, 1983, 1, 53-63). In the Li-ion battery field, MF is commonly used to spheronize natural graphite for use in negative electrodes (e.g. US 9,142,832 or US patent application number 14/431,398). Despite its usefulness in industry, MF has rarely been published in the literature. One reason for this may be because the parameters for the use of MF equipment are not widely known. Nonetheless, several publications describe particles that have been spheronized or coated with 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). Still, few publications sufficiently describe the conditions under which such engineered particles were made.
An interesting type of graphitic material, known as “onion graphite”, has been observed in the art. According to some, onion graphite refers to spherical or ovoid graphite particles where the graphite basal planes are arranged in nested ovoid or spherical smooth concentric layers centered around a common point in the core of the particle, and where the alignment of the edges of graphite sheets does not radiate from a central nucleus (to others, onion graphite refers to only to perfect nested buckyballs). In other words, the graphene layers in onion graphite are randomly positioned on the surface of the concentric nested spheres or ovoids, excepting that they are oriented such that their basal planes are tangential to the concentric nested spheres or ovoids. Onion graphite can be differentiated from graphite spheres in cast irons, which are known to have a micro structure in which the graphite basal planes are arranged concentrically, however the edges of the planes radiate from a central core (e.g. as shown 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.). Onion graphites have previously only been observed in sizes up to 2 pm. They have been found to form in interstellar space, as evidenced by their presence in meteorites. Nano-sized graphite onions have only been made previously in small quantities by synthetic means, for instance by the high electron irradiation of carbon particles, the annealing of nanodiamonds, an arc discharge between two graphite electrodes submerged in water, the carbon-ion implantation of silver or copper substrates (e.g. see V.D. Blank, B.A. Kulnitskiy and I.A. Perezhogin, Scripta Materialia, 60 (2009) 407-410.) None of these methods can make particles above 2 pm in size, in bulk (i.e. greater than 1 gram quantities), in a high state of graphitization, and in a way that is economically practical. For instance, US patent application 2013/0189178 A1 describes a method to manufacture onion-like carbon, however the maximum size of the carbon onions achieved is only 6 nm. Furthermore, the level of graphitization achieved is not mentioned. Despite this continuing and substantial global effort directed at developing improved methods of manufacture of such materials, there remain a need for further improvement. The present invention addressed these needs and provides further benefits as disclosed below.
Summary
It has been discovered that certain high shear and high pressure field processes, such as dry mechanofusion (MF), can be used to prepare desirable aggregates from a variety of precursor particles in a simple manner and with efficient use of the precursor particles. The aggregated precursor particles ("product particles") can desirably be made in narrow particle size distributions and in smooth, spherical or rounded shapes that are free from cavities. In some aspects, cavities can be included within the product particles.
Specifically, the product particles are made using a microgranulation method involving the steps of: obtaining an amount of precursor particles having an average particle size less than 1000 pm, obtaining an amount of templating media having an average particle size less than 500 pm and a hardness greater than that of the precursor particles, and then preparing a mixture comprising the amounts of precursor particles and templating media. This mixture is then subjected to an appropriate high shear and high pressure field, such as that obtained via mechanofusion, such that the precursor particles are aggregated into desirable product particles. The product particles can then be separated from the templating media if desired for an intended application.
The aforementioned method can be successfully used on numerous types of precursor particles having a wide range of properties. This includes precursor particles with an average size of less than 50 pm, and particularly less than 10 pm. 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, e.g. a carbon, graphite flakes or LiNiiaMniaComCE powder. Advantageously, mixed metal oxide powders used as precursor particles may be made by an all -solid-state method comprising ball milling an amount of metal oxide raw material powders to produce the precursor particles. (Note for instance that the precursor particles used in the following Examples were not suitable for use per se in battery electrodes but can be made suitable for such use by microgranulation processing and optionally by subsequent processing steps, e.g. by heating.) Further and in general, at least a portion of the amount of precursor particles may be processed in some suitable manner prior to preparing the mixture (including ball milling or heating). While the inventive method desirably produced spherical and/or rounded aggregate, the starting precursor particles can be quite irregularly shaped powders. In addition, while the inventive method desirably produces powders with a narrow particle size distribution, the particle size distribution of the starting precursor particles can be quite large.
The resulting characteristics of the product particles obtained are in part a function of those of the templating media employed. As mentioned, the hardness of the templating media is greater than that of the precursor particles so as not to break down the former. Suitable templating media may thus be selected from the group consisting of zirconium oxide, tungsten carbide, tungsten, silicon oxide, aluminum oxide, silicon nitride, hardened steel, stainless steel, and agate. To produce product particles of desirable size and shape, templating media whose average size is 100 pm or smaller may be employed. Further, the surface of the templating media may desirably be smooth and spherically shaped. In addition, it is desirable for the size distribution of the templating media to be uniform, e.g. such that (D90-D10)/D50 < 2, preferably (D90-D10)/D50 < 1 or more preferably (D90-D10)/D50 < 0.7. Further, it can be desirable for the bulk volume of the amount of templating media employed to be greater than that of the bulk volume of the amount of precursor particles employed, and particularly greater than or about three times that of the bulk volume of the amount of precursor particles.
A mechanofusion system suitable for use in the inventive method can comprise a chamber, a rotating wall within the chamber, a scraper within the rotating wall, and a press-head within the rotating wall. A representative gap between the scraper and the rotating wall may be about 0.5 mm. A representative gap between the press-head and the rotating wall may be about 1.4 mm. And a representative speed for rotating the rotating wall is one that results in wall surface speeds of about 8 m/s. In some embodiments, mechanofusing times of greater than or about 12 hours have proved to be successful. Shorter processing times may be achieved if the templating media already coated with precursor from a previous synthesis are reused in a new synthesis. While the aforementioned system produces product in batch form, advantageously mechanofusion can also be performed in a continuous manner (for instance with suitable modifications to such a system).
In exemplary embodiments, product particles can be produced whose average size is between 10 and 100 pm. Further, the size distribution of exemplary product particles can be sufficiently uniform such that (D90-D10)/D50 < 2. Further still, the surface of the product particles may desirably be smooth. In some aspects of the invention the product particles comprise particles having a roughness (as defined below) less than 0.02, less than 0.01, less than 0.006 or even smaller. In some aspects of the invention all the product particles essentially have roughness values less than 0.02, less than 0.01, less than 0.006 or even smaller. In some aspects of the invention, the product particles comprise particles that are essentially free from cavities. In some aspects of the invention, all the product particles are essentially free from cavities And as demonstrated in the Examples below, product particles can be made that are spherically shaped or tetrahedrally shaped.
Optionally, the complete preparation of product particles may additionally comprise an annealing step at an elevated temperature (for instance to recrystallize the particles following mechanofusion).
The product particles made according to the inventive method may be considered for use in numerous commercial applications including as a battery electrode, a fertilizer, a pharmaceutical, a toner, a pigment, a fdler, or a catalyst. They can be particularly suitable for use in anode or cathode electrodes in rechargeable lithium batteries, e.g. lithium ion batteries.
It has further been discovered that the aforementioned methods can be used to prepare novel structures of graphite particulate, lithium nickel manganese cobalt oxide particulate, and lithium transition metal oxide particulate.
In one aspect, a novel graphite particulate comprises graphite particles in which the graphite particles are shaped as spheres or ovoids and they comprise concentric nested spheres or ovoids of graphene layers. These graphene layers are randomly positioned on the surface of the concentric nested spheres or ovoids, except that the graphene layers are oriented such that their basal planes are tangential to the concentric nested spheres or ovoids. The graphite particles further have an average particle size greater than 2 pm and an average doo2 spacing of less than 3.400 A. In some embodiments, the graphite particles in the particulate comprise concentric layers of porosity with a void or hollow near its core. In some embodiments, the graphite particles have an average particle size between 5 pm and 50 pm and a size distribution of (D90-D10)/D50 < 2.
In one aspect, a novel lithium mixed metal oxide particulate comprises particles having a core of lithium nickel manganese cobalt oxide crystallites that are randomly oriented and have an average size of about 1 pm coated with smaller randomly oriented lithium nickel manganese cobalt oxide crystallites that have an average size of about 0.3 pm.
The preceding novel lithium transition metal oxide particulate comprises particles having at least two transition metals present from the group consisting of Mn, Ni, and Co. Further, the particles have an 03 structure, an average particle size ranging from 1 to 50 pm, and they comprise crystallites that vary randomly in shape and size throughout their interior. In certain embodiments, the crystallites have an average size greater than 0.5 pm and the average particle size of the particles is more than 5 times larger than the average crystallite size. In certain embodiments, the composition of one of the two transition metals can vary from the core of the particles to the shell of the particles by at least 5 atomic %.
The method can be used to make product particles of uniform composition but also can be used to make product particles having different compositions near their core than near their surface. The precursor particles employed may be a single phase or they may consist of a mixture of particles having different characteristics. For instance, the precursor particles may consist of a mixture of first particles of a first composition and second particles of a second composition in which the first and second compositions are different and/or in which the first and second particles have comprise crystallites with different average crystallite sizes (e.g. in which the average crystallite size of the first precursor particles differs from the average crystallite size of the second precursor particles by at least 10%).
Suitable precursor particles for the formation of graphite product particles include graphitizable carbons, such as natural graphite, coke, and soft carbons. Suitable precursor particles for the formation of product particles useful as cathode materials in Li-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.
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