Method for producing size selected particles

The invention provides a system for preparing specific sized particles, the system comprising a continuous stir tank reactor adapted to receive reactants; a centrifugal dispenser positioned downstream from the reactor and in fluid communication with the reactor; a particle separator positioned downstream of the dispenser; and a solution stream return conduit positioned between the separator and the reactor. Also provided is a method for preparing specific sized particles, the method comprising introducing reagent into a continuous stir reaction tank and allowing the reagents to react to produce product liquor containing particles; contacting the liquor particles with a centrifugal force for a time sufficient to generate particles of a predetermined size and morphology; and returning unused reagents and particles of a non-predetermined size to the tank.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a method for producing size selected particles, and more particularly this invention relates to a co-precipitation method for consistently producing particles within a predetermined size from a fluid containing relatively tiny and huge particles.

2. Background of the Invention

Certain sized particles as electrode active materials for secondary batteries, or as catalysts for chemical reactions, can optimize the performance associated with their applications. However, consistent generation of uniform sized particles, and the uniformed sized particles themselves remain elusive. This is because particles under one micron easily coagulate, aggregate, or associate with each other irregularly. Particle aggregation refers to formation of clusters in a colloidal suspension and represents the most frequent mechanism leading to unwanted particle growth. During this process, which normally occurs within short periods of time (seconds to hours), particles dispersed in the liquid phase stick to each other, and spontaneously form irregular particle clusters, flocs, or aggregates. As aggregation proceeds from early to later states, the aggregates grow to size of 1-100 micron, depending on the reagents used and the reaction method.

Efforts have been made to produce and maintain particles below 20 microns. Batch and continuous reactors have been part of these efforts.

Particle sizes of electrode active material precursor and electrode active material produced during co-precipitation using conventional continuous stirred tank reactor (CSTR) vary widely from a few nanometers to several dozen micrometers. This varying particle size lowers tap density and reduces the performance of lithium secondary batteries. For example, tiny particles (e.g., less than 500 nm in diameter) increase the total surface area of electrode active materials. This in turn leads to a decrease in the cycle life of the battery due to side reactions with electrolyte on the high surface area of the small particles.

Conversely, very large particles (e.g., more than 40 μm) cause problems with cathode coatings and create short circuits in the batteries.

Sieving processes have been used to produce specific sized particles. However, sieving does not eliminate particles at the small end of the spectrum. In addition, separated large particles are disposed of as an off-spec secondary waste stream.

Sedimentation methods have been employed to eliminate tiny particles, but these methods require time and several repetitions. Air-classification has also been used to separate dried particles in certain size ranges. These processes involve cycloning whereby dried powder materials are subjected to centrifugal force and therefore particle collision and rotor blade collision. This leads to particle loss and particle damage.

Batch reactors have been used to produce similar particle sizes. However, uniformity of particle sizes between batches is hit or miss. Specifically, average particle size, particle size distribution and quality of particles generated via batch processes fluctuate more than is acceptable.

A need exists in the art for a method to produce specific sized electrode active material precursor and electrode active material precursor without tiny and huge particles. The method should consistently produce uniform sized particles so as to optimize the tap density of the particles being produced. The method should incorporate common materials processing protocols.

SUMMARY OF INVENTION

An object of the invention is to provide a method for producing size selected particles that overcomes many of the drawbacks of the prior art.

Another object of the present invention is to produce size selected particles in a continuous process. A feature of the invention is the use of post-reactor particle polishing steps. An advantage of the invention is that it produces tight size-range particles and with desired morphologies. This invention provides a method and system for producing uniform spherical particles with high tap densities.

Another object of the invention is to provide a construct comprising different size selected particles. A feature of the invention is the use of a plurality of continuous stir reaction protocols to produce the different sized particles. An advantage of the invention is that the different sized particles are predetermined and substantially all of the reagents are utilized to continuously produce the particles in a co-precipitation protocol, such that reagents are recycled and reprocessed.

Yet another object of the present invention is to provide a system and method for continuously producing different sized materials and assembling those materials. A feature of the invention is the use of a plurality of continuous stir tank reactors and a plurality of centrifugal processing units each of the reactors and the processing units devoted to producing one particle size and morphology. An advantage of the invention is that tap densities of ensuing constructs are higher than what is produced in state of the art protocols, and this results in enhanced characteristics of the product comprised of the particles. For example, secondary batteries comprised of particles having high tap density results in those batteries having increased energy density.

Still another object of the present invention is to provide a method and a system for producing particles with optimal tap density (e.g., greater than 1.65 g/cc). A feature of the invention is the use of centrifugal force (e.g. centrifugal dispersers and dispensers) to remove tiny adherents from desired sized particles and simultaneously to polish the desired sized particles to a specific morphology (e.g., spherical shapes). An advantage of the invention is that it provides a polished particle and properly sized particle in one step.

A further object of the present invention is to provide a system of producing a uniform size distribution of metal particles that reduces the amount of deionized water used and, consequently, the amount of wastewater produced. A feature of the present invention is that the small particle return stream flows into a alkaline solution preparation tank where solid alkaline feed is added to the recycled water. This alkalinized solution then enters the reactor tank to mix with the metal reagent solution. An advantage of the present invention is that the same amount of product is created while halving the amount of deionized water used and wastewater produced.

Briefly, the invention provides a system for preparing specific sized particles, the system comprising a continuous stir tank reactor adapted to receive reactants; a centrifugal dispenser positioned downstream from the reactor and in fluid communication with the reactor; a particle separator positioned downstream of the dispenser; and a solution stream return conduit positioned between the separator and the reactor.

Also provided is a method for preparing specific sized particles, the method comprising continuously stirring the reagents to produce product liquor containing particles; contacting the liquor particles with a centrifugal force for a time sufficient to generate particles of a predetermined size and morphology; and returning particles of a non-predetermined size to the continuous stir venue, be that a continuous stir reaction tank, agitator or the like.

The invention further provides a system for preparing a plurality of specific sized particles, the system including a plurality of particle producing modules, each module comprising a continuous stir tank reactor adapted to receive reactants; a centrifugal dispenser positioned downstream from the reactor and in fluid communication with the reactor; a particle separator positioned downstream of the dispenser; and a solution stream return conduit positioned between the separator and the reactor.

DETAILED DESCRIPTION OF THE INVENTION

The foregoing summary, as well as the following detailed description of certain embodiments of the present invention, will be better understood when read in conjunction with the appended drawings.

FIG. 1is a schematic diagram of a system comprising a continuous stirred tank reactor1combined with a centrifugal disperser2and a particle size separator4. A salient feature depicted is the return of relatively small particles14to a continuous stirred tank reactor1for further growth. In an embodiment of the invention, agglomeration is used to form desired sized particles. For example, agglomeration of very tiny particles (e.g., under 1˜100 nm) is used to produce a growing particle (from 100 nm to the desired size such as 10 micron).

FIG. 1can be considered a module for producing particles of a single predetermined size. As such, a plurality of modules can be combined to generate particle streams, each of which has particles of predetermined size. Such a combination of modules is depicted inFIG. 11.

WhileFIG. 1is a module to generate a single sized particle,FIG. 11is a combination of modules to generate a sized particle from each module. For example, and as depicted inFIG. 12A, the multi-module system enables the production of cluster-shell type materials composed of primary seed particles, secondary seed particles and shells. The primary seed particles may be generated in the first reactor1depicted inFIG. 11, while the secondary particles may be generated in the second reactor20depicted inFIG. 11, and the shell particles may be generated in the third reactor30. As such, each of the reactor modules will have separate small particle return lines14,24and34to recycle unreacted reagent or too small of particles. Conduits33from each of the particle collectors4downstream of the first1and second20reactors direct first and second size selected particles to the third reactor30.

Each of the reactors may accommodate different reactant streams, for example reactor1accommodating a first reactant stream11, reactor20accommodating a second reactor stream21and reactor30accommodating a third reactor stream31. It should be understood that the system is not limited to the three reactors depicted inFIG. 11.

The multi-module scenario depicted inFIG. 11enables the continuous production of cluster shell morphology cathode materials. The cluster shell may comprise a plurality (e.g. two) of different seed precursors encapsulated in a shell material.

FIG. 12Bdepicts SEM micrographs of seed clusters featuring two seed types. The primary seed material was CoCO3. The micrographs on the far left of the graph contain only CoCO3, (thus the 1:0 ratio). The micrographs depicted to the right of the first micrograph all contain varying amounts of Ni0.33Mn0.67CO3secondary seeds (i.e., from weight ratios ranging from 1:1 to 1:6).

As depicted on the second row of higher definition micrographs, the more secondary seed material that is added, the more the seed clusters begin to approach a spherical morphology and act as a shell composition. The addition of secondary seed material provides a means for encapsulating smaller particles, i.e., enabling the development of a shell around smaller particles contained within it.

The aforementioned module, either alone (e.g.,FIG. 1) or in combination with other modules (e.g.,FIG. 11), can operate at a myriad of temperature and pressures. For example, the system can operate at between approximately 1 and approximately 100 bar and between about 0 and about 450° C. Absent the need for operation in adverse conditions, the system is generally operated at about 1 bar (atmospheric pressure) and about 50° C.

Centrifugal Polishing Detail

The inventors found that imparting centrifugal forces on particles produced in the first steps of the invented process provides a means for tailoring particle morphology and size. Suitable centrifugal based equipment generates the shearing force necessary to produce targeted particle sizes and morphologies. For example, a centrifugal dispenser coupled to a transfer pump is a means for providing tailored particle sizes and morphologies, particularly for materials having high tap densities of about 1.65 g/cc or greater. (For a given material composition, tap density has a strong relation with particle morphology and size which are determined by synthesis processes. Higher tap density is desired to reduce the volume of batteries.) Generally, tap densities range from between about 1.5 and about 3.0 g/cc are obtained with the invented process. For example, in one embodiment, tap densities of about 1.71 g/cc or greater have been achieved.

This invention provides high tap densities above 1.65 g/cc in case of lithium-rich and manganese-rich electrode active materials (Li1.37Ni1/3Mn2/3OyinFIG. 13). Typically, the invented process and system provides about a 20 percent increase in tap density for same material composition (See density increase inFIG. 13, to wit: from 1.41 to 1.7 g/cc). These improved materials are depicted inFIG. 13as second sample 120905. This compares to lower tap densities (of about 1.41 g/cc) for materials produced using conventional CSTR, those materials depicted inFIG. 13as first sample 101217B. Such a dispenser provides strong agitation combined with a transfer pump

Alternatively, a centrifugal disperser is utilized to produce particles having higher hardness values. Such a disperser is a centrifugal pump comprising a centrifugal impeller. Centrifugal dispersers are more efficient than dispensers for size control and sphericalization of precursor material and active material. The inventors found that centrifugal dispersers causes more frequent collisions between particles, particularly along the peripheral regions of the disperser, where the impeller blades terminate and therefore travel at the highest velocity compared to other regions of the blades.

A centrifugal disperser2provides a means for creating size control and desired morphologies of the particles being processed. The disperser utilizes centrifugal force by rotation to create shear stress and fluid flow velocity and particle collisions with each other and with impellers3(depicted in phantom inFIG. 1) of the disperser2.

The system depicted inFIG. 1includes a reactant feed stream11in fluid communication with the CSTR1. A first end of a conduit12provides egress of particles out of the CSTR, while a second end of the conduit12provides particle ingress to the centrifugal disperser2. In the embodiment shown the first end of the conduit is positioned at approximately the center of the depending end of the CSTR1.

A means of egress16is provided for the particles from the disperser2. This egress means16, (.e.g, a conduit such as a pipe or channel) defines a particle size separator inlet stream into a particle size separator4. Suitable size separators include, but are not limited to centrifugal separators, hydrocyclones, filters separators, sedimentation tanks and combinations thereof. The separator4bifurcates the inlet stream13into a desired-size particle solution outlet stream15and a particle solution return stream14for particles which are smaller in size than the sizes of the desired particles. A suitable particle sized separator is a hydrocyclone from which the flow rate of desired-size particle solution outlet stream is about 5 to about 200 percent of the flow rate of the tiny particle (smaller than about 1 micron) solution return stream, and preferably 10 to 75 percent.

Another suitable particle size separator is a settling tank whereby natural sedimentation methods are utilized.

Reagent and Product Detail

In operation, initially, the metal reagents and the alkalinizing agents are dissolved in liquid solutions prior to entering the tank reactor1. The metal reagents are dissolved in acidic solutions derived from inter alia chlorides, nitrates, sulfates, and phosphates. The alkalinizing agents are typically dissolved in deionized water. (.e.g, for the synthesis of Ni0.33Mn0.67CO3, 0.165˜0.66 M NiSO4(H2O)6and 0.335˜1.34 M MnSO4(H2O) were used for the metal reagents and 0.01˜25 M NH4OH and 0.5˜2 M Na2CO3and were used for the alkalinizing agents).

In the embodiment depicted inFIG. 1, each liquid reagent solution is introduced to the tank reactor1independently (feed stream11). In another embodiment, the metal reagents enter the reactor after pre-combination, followed by the alkalinizing agents after pre-combination.

In another embodiment (FIG. 14) discussed below, solid or liquid alkalinizing agents are mixed with the recycled solution from the particle solution return line14. This newly mixed alkalinizing solution is then introduced to the reactor tank1via an ingress line19separate from the feed stream11. The feed stream11in this embodiment only contains the liquid, metal-containing solution. The advantages of this embodiment are decreasing fresh deionized water (DI) water usage for alkalinizing agent preparation, reusing unreacted alkalinizing agents, reducing wastewater generation, and lowering the operation cost by the usage of hot recycled solution from the particle solution return line14.

The reactants remain in the CSTR for a time and at a temperature sufficient to cause particles of a target size to be generated. Suitable residence time in the CSTR at room temperature range from between about 2 hours and about 20 hours. Suitable temperatures range from between about 0° C. and about 250° C. at the pressure of between about 1 bar and about 50 bar.

After a suitable dwell time in the reactor, the formed particles are directed to the particle polishing means, such as the centrifugal devices described supra. RPM values between about 300 and about 5000 are suitable, when temperatures between about 0° C. and about 250° C. are present. Suitable internal pressures in which the invented system operates are between about 1 bar and about 50 bar.

The systems depicted inFIGS. 1 and 14are operated continuously but also can be operated as batch processes at the reaction pressure of between about 1 bar and about 50 bar. For continuous operation, suitable feed flow rates of the metal reagents and alkalinizing agents are selected to keep the residence time in the CSTR range from between about 2 hours and about 20 hours, and preferably between about 5 hours and about 8 hours. (e.g., for 20 L CSTR, the feed flow rate of pre-combined metal reagents is 3.3 L/hr and the feed flow rate of pre-combined alkalinizing agents is 3.3 L/hr to make the residence time in the CSTR about 3-4 hrs, generally and about 3 hours typically).

The inventors have generated electrode active material precursors and electrode active materials for secondary batteries via the invented system and method. For example, Mn CO3, Ni0.15Mn0.85CO3, Ni0.25Mn0.75CO3, Ni0.35Mn0.65CO3, Ni1/3Mn2/3CO3, Ni1/3Mn2/3(OH)2, Ni0.16Mn0.71Co0.13(OH)2, Li2Mn O3, Li1.65N0.15Mn0.85Oy, Li1.46N0.25Mn0.75Oy, Li1.23N0.35Mn0.65Oy, Li1.39N1/3Mn2/3Oy, and Li1.57Ni0.16Mn0.71Co0.13Oyhave been produced using metal feed reagents and hydroxide or carbonate feed reagents. Reactor volumes of between about 4 L and 20 L have been realized.

A salient feature of the invention is that it enables carbonate and hydroxide chemistry resulting in uniform spherical particles with high tap density. This differs from state of the art carbonate protocols which generate tiny (smaller than about 1 micron) and huge (bigger than about 30 micron) particles with low tap density. As such, the invention enables the creation of materials having high crack resistance. This invention enables the production of crack-resistant materials inasmuch as it eliminates loose contact between particles. Conversely the invention maximizes surface to surface contact between particles, by facilitating high tap densities.

FIG. 13provides a chart of electrode active materials produced with both carbonate and hydroxide reagents using the invented method and system.

FIGS. 2 and 3are scanning electron micrograph images (×3000) of agglomerated precursor produced during co-precipitation using a continuous stirred tank reactor without centrifugal disperser. Both figures depict particles of varying sizes, and agglomerations. Both images show agglomeration and cluster formation which occurred during co-precipitation using batch or continuous stirred tank reactor conditions. As discussed supra, these conditions by themselves must be avoided to provide higher quality electrode active material.

Surprisingly and unexpectedly, the agglomeration and widely variable morphologies seen inFIGS. 2 and 3are avoided when centrifugal dispersers and particle size separators are combined with CSTR. The size control effect is verified by the results shown in the particle graph ofFIG. 4. The inventors discovered that by adjusting the revolutions per minute (RPM) of the centrifugal disperser2, mean particle size can be decreased by two-thirds. For example, mean particle size in the example shown decreased from 45 μm to 15 μm, when RPMs changed from about 500 RPMs to about 2000 RPMs.

FIGS. 5 and 6confirm that the invented method results in no agglomeration of precursor particles. The photomicrographs further show that morphology of the particles is relegated to spheres. As discussed supra, spherical particles exhibit increased tap density compared to non-spherical particles. Further, the inventors found that small spherical particles (e.g., between 5 and 15 μm) provides better safety and electrochemical performance for batteries that large spherical particles (e.g., between 15 and 30 μm).

FIG. 7is a graph which shows that particle size of both electrode active material precursor and electrode active material decreases when RPMs of the centrifugal disperser is increase.

FIGS. 8-10show that size-controlled spherical electrode active materials are produced using the invented method and apparatus.

A metal solution prepared using nickel sulfate and manganese sulfate, sodium carbonate solution and ammonia solution were fed into a 20 L CSTR with centrifugal disperser and hydrocyclone. The molar flow rate of NiSO4, MnSO4, Na2CO3, and NH4OH are 3.25 mol/hr, 6.5 mol/hr, 10.8 mol/hr, and 1.1 mol/hr, respectively. The ratio of metal solution to alkaline solution is approximately 1:1.2. The residence time in the reactor was approximately 2 hours and reaction temperature was approximately 50° C. This shows that the invention generates size- and morphology-controlled particles (uniform, small and spherical) in the same amount of residence time that state of the art systems take to produce inferior particles (i.e., particles exhibiting varying sizes and morphologies) with the same starting materials. Flow rate of the centrifugal disperser inlet stream was about 1 L/min and the flow rate of desired-size particle solution outlet stream was 25 percent of the tiny particle solution return stream.

Average particle sizes of nickel manganese carbonate produced was 45 pm with a continuous operation time of about 10 hours when 500 RPM was applied for the centrifugal disperser. When a 2000 RPM was applied for the centrifugal disperser, average particle size of the nickel manganese carbonate was about 15 μm with a continuous operation time of about 24 hours. These results are shown by the graph inFIG. 4.

Rotation speed of the centrifugal disperser was varied while all other operations variables maintained as in Example 1. When 1000 RPM was applied to the centrifugal disperser, the average particle size of nickel manganese carbonates produced was about 22 μm. Then the rotation speed was increased to 2000 RPM, the average particle size was about 15 μm. When the rotation speed was increased to 3000 RPM, the average particle size was about 8 μm

A density of distribution graph of nickel manganese carbonates produced by the CSTR when the centrifugal disperser's speeds are varied between 1000 and 3000 RPM is illustrated inFIG. 7. SEM images of the electrode active materials which results for the lithium secondary battery by 20 L CSTR with centrifugal disperser and hydrocyclone using these precursors are shown inFIGS. 8-10.

Reduced Wastewater

Embodiment

In the first embodiment of the presently invented system as depicted in

FIG. 1and discussed above, the tank reactor1is fed by feed stream11and by the small particle return line14. The feed stream11and particle return line14supply the reactor tank in about a 1:1 ratio. The feed stream11contains a metal solution and an alkaline solution. The total contributions from each the feed stream11and the return line14include 1 part metal solution and 1 part alkaline solution from the feed stream11and 2 parts small particle return from the return line14.

An alternate embodiment reduces the amount of deionized water needed for the alkaline solution. By reducing the deionized water input, the amount of wastewater in the product stream is reduced as well. In this embodiment as depicted inFIG. 14, the particle return line14does not supply the reactor tank1directly. Instead, the particle return line14supplies an alkaline solution preparation tank17. The alkaline solution preparation tank17is also supplied by alkaline solid feed line18. In this way, solid feed provided by line18homogeneously combines with the fluid contained in the particle return line14to produce the alkaline solution for reaction with the metal solution. The alkaline solution created in the alkaline solution preparation tank17is delivered to reactor tank1via ingress line19.

By using the fluid in the particle return line14to prepare the alkaline solution, the incoming feed stock is reduced by half while still producing the same amount of solid product. Thus, the amount of deionized water needed to create the alkaline solution is halved, which also halves the amount of wastewater in the product stream. Further, the excess alkaline feed can be recycled, and the recycled liquid will already be heated to the operating temperature. An example of the reduced wastewater embodiment is provided in Example 3 below.

The multi-module embodiment ofFIG. 11is also accomplished by using multiple modules of the reduced waste water embodiment. Intermediate of the return line14,24,34and the reactor tank1,20,30will be an alkaline solution preparation tank, a solid feed line, and an ingress line. Because the volumetric inputs and outputs of each module are halved, the ultimate product stream will also be halved.

The reactor tank1is fed by a 1 M metal solution from feed stream11at about 1 L/min and by a 0.6 M alkaline solution at 2 L/min from ingress line19. The ratio of metal solution to alkaline solution is maintained at about 1:1.2. The solutions are mixed in the reactor tank1and delivered to the centrifugal dispenser2via conduit12. The mixture leaves the reactor tank1at a volumetric rate of 3 L/min as opposed to the 4 L/min of the previous embodiment; however, the total number of moles of reactants is the same.

The mixture from the centrifugal dispenser2is provided to the particle separator4. Like the previous embodiment, a solution containing small particles is returned via return line14at a rate of 2 L/min. Thus, the product solution is provided at a rate of 1 L/min, but the solution contains a greater density of the desired size particles. Because a lesser amount of product solution is created, less water is wasted in the recovery of the desired particles.

The return line14supplies the return solution to the alkaline solution preparation tank17. Alkaline solid feed, such as NaOH or Na2CO3, is mixed with the return solution to recreate the 0.6M alkaline solution for reaction in the reactor tank.

One skilled in the art will also readily recognize that where members are grouped together in a common manner, such as in a Markush group, the present invention encompasses not only the entire group listed as a whole, but each member of the group individually and all possible subgroups of the main group. Accordingly, for all purposes, the present invention encompasses not only the main group, but also the main group absent one or more of the group members. The present invention also envisages the explicit exclusion of one or more of any of the group members in the claimed invention.