CA3069168A1 - Polycrystalline particulates for rechargeable battery electrodes - Google Patents
Polycrystalline particulates for rechargeable battery electrodes Download PDFInfo
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- CA3069168A1 CA3069168A1 CA3069168A CA3069168A CA3069168A1 CA 3069168 A1 CA3069168 A1 CA 3069168A1 CA 3069168 A CA3069168 A CA 3069168A CA 3069168 A CA3069168 A CA 3069168A CA 3069168 A1 CA3069168 A1 CA 3069168A1
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
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- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
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- Y02E60/10—Energy storage using batteries
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Abstract
Improved polycrystalline particulates and methods of preparation are disclosed, particularly for use as a lithium insertion cathode for a rechargeable lithium battery. The surface layer of the polycrystalline particulates is smoothed, for instance by mechanofusion. Coating layers that are desirably smoother can then be applied, also for instance by mechanofusion. Such polycrystalline particulates, both with and without coating layers, show improved performance in battery applications.
Description
Docket No.: Novonix003-CA
POLYCRYSTALLINE PARTICULATES FOR RECHARGEABLE BATTERY
ELECTRODES
Technical Field The present invention pertains to polycrystalline particulates, methods for modifying the surface of the particulates, and lithium insertion cathode and rechargeable lithium batteries comprising such particulates. In particular, the invention pertains to polycrystalline particulates whose surfaces have been modified by mechanofiision processing.
Background The development of rechargeable high energy density batteries, such as Li-ion batteries, is of great technological importance. Typically, commercial rechargeable Li-ion batteries use a lithium transition metal oxide cathode and a graphite anode. While batteries based on such materials are approaching their theoretical energy density limit, significant research and development continues in order to improve other important characteristics such as cycle life, efficiency, and cost.
Insertion compound transition metal oxide cathode materials for use in rechargeable batteries have the general formula AxMyNz02 in which x, y and z are numbers with x> 0, y? 0.5, and z? 0. A consists of one or more insertable alkali metals and in the case of Li ion batteries is lithium. For ease of manufacturing, an air stable version of the transition metal oxide is usually employed, e.g. with x typically being about equal to 1. M consists of one or more first row transition metal elements.
Optionally, the transition metal oxide may comprise other elements, e.g. in which N comprises a metal element other than an alkali metal or a first row transition metal element;
Such transition metal oxide cathode materials are often employed in the form of polycrystalline powders or particulates that are about 5 - 50 gm in size in which each powder particle consists of an aggregate of crystallites with grain sizes in the range of 0.2 - 1 gm. Such polycrystalline cathode particles contain surface features in the form of pits and valleys whose depth is on the order of the same size as their crystallite size. This results in the particles having a relatively high surface area, which in turn increases reactivity with electrolytes in battery applications, leading to reduced coulombic efficiency, impedance growth, and cell fade (i.e. loss of capacity on cycling).
As is known in the art, it can be advantageous to apply a coating layer, such as A1203, to cathode particles to create a more stable interface with battery electrolytes and to improve cycling performance. Such a coating layer should be very thin (e.g. comprising less than about 2 wt. % of the Docket No.: Novonix003-CA
cathode weight or ideally 0.5 wt. A of the cathode weight or less). Methods, such as atomic layer deposition (ALD) may be used to uniformly coat cathode particles, even if their surfaces are relatively rough. However, ALD is expensive and it would be much more desirable to coat particles using more economical, simpler methods if possible (e.g. mechanical methods). However, the presence of relatively large surface features on such cathode particles can make it difficult to uniformly coat the particle surfaces by dry mechanical methods, unless very thick coating layers (i.e. thicker than the size of the surface features) are applied to accommodate the surface roughness.
However, thick coating layers are not desirable because they reduce cathode specific capacity and increase cell impedance.
Physical methods that employ dry processing are environmentally friendly and advantageous for industrial use because of the elimination of the use of solvents. The mechanofusion (MF) process 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. .1., 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, ISM
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 0. 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.
Despite the continuing and substantial global effort directed at developing improved materials for use in rechargeable batteries, there remain a need for yet further improvement in materials, in the methods for making, and in the batteries made therewith. The present invention addressed such needs and provides further benefits as disclosed below.
Summary In the present invention, it was found that subjecting polycrystalline transition metal oxide particulate to mechanofusion results in a drastic reduction or even the elimination of surface features on the
POLYCRYSTALLINE PARTICULATES FOR RECHARGEABLE BATTERY
ELECTRODES
Technical Field The present invention pertains to polycrystalline particulates, methods for modifying the surface of the particulates, and lithium insertion cathode and rechargeable lithium batteries comprising such particulates. In particular, the invention pertains to polycrystalline particulates whose surfaces have been modified by mechanofiision processing.
Background The development of rechargeable high energy density batteries, such as Li-ion batteries, is of great technological importance. Typically, commercial rechargeable Li-ion batteries use a lithium transition metal oxide cathode and a graphite anode. While batteries based on such materials are approaching their theoretical energy density limit, significant research and development continues in order to improve other important characteristics such as cycle life, efficiency, and cost.
Insertion compound transition metal oxide cathode materials for use in rechargeable batteries have the general formula AxMyNz02 in which x, y and z are numbers with x> 0, y? 0.5, and z? 0. A consists of one or more insertable alkali metals and in the case of Li ion batteries is lithium. For ease of manufacturing, an air stable version of the transition metal oxide is usually employed, e.g. with x typically being about equal to 1. M consists of one or more first row transition metal elements.
Optionally, the transition metal oxide may comprise other elements, e.g. in which N comprises a metal element other than an alkali metal or a first row transition metal element;
Such transition metal oxide cathode materials are often employed in the form of polycrystalline powders or particulates that are about 5 - 50 gm in size in which each powder particle consists of an aggregate of crystallites with grain sizes in the range of 0.2 - 1 gm. Such polycrystalline cathode particles contain surface features in the form of pits and valleys whose depth is on the order of the same size as their crystallite size. This results in the particles having a relatively high surface area, which in turn increases reactivity with electrolytes in battery applications, leading to reduced coulombic efficiency, impedance growth, and cell fade (i.e. loss of capacity on cycling).
As is known in the art, it can be advantageous to apply a coating layer, such as A1203, to cathode particles to create a more stable interface with battery electrolytes and to improve cycling performance. Such a coating layer should be very thin (e.g. comprising less than about 2 wt. % of the Docket No.: Novonix003-CA
cathode weight or ideally 0.5 wt. A of the cathode weight or less). Methods, such as atomic layer deposition (ALD) may be used to uniformly coat cathode particles, even if their surfaces are relatively rough. However, ALD is expensive and it would be much more desirable to coat particles using more economical, simpler methods if possible (e.g. mechanical methods). However, the presence of relatively large surface features on such cathode particles can make it difficult to uniformly coat the particle surfaces by dry mechanical methods, unless very thick coating layers (i.e. thicker than the size of the surface features) are applied to accommodate the surface roughness.
However, thick coating layers are not desirable because they reduce cathode specific capacity and increase cell impedance.
Physical methods that employ dry processing are environmentally friendly and advantageous for industrial use because of the elimination of the use of solvents. The mechanofusion (MF) process 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. .1., 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, ISM
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 0. 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.
Despite the continuing and substantial global effort directed at developing improved materials for use in rechargeable batteries, there remain a need for yet further improvement in materials, in the methods for making, and in the batteries made therewith. The present invention addressed such needs and provides further benefits as disclosed below.
Summary In the present invention, it was found that subjecting polycrystalline transition metal oxide particulate to mechanofusion results in a drastic reduction or even the elimination of surface features on the
2 Docket No.: Novonix003-CA
particles in the particulate. This results in a significant reduction in surface area of the particles and leads to improved coulombic efficiency and improved cycling when used in Li-ion batteries.
In addition, it was found possible to further coat polycrystalline transition metal oxide particulate, which bad been processed by mechanofusion so as to reduce surface features on the particles, with thin, uniform coating layers of 2 wt.% of the particulate weight or less.
Therefore, mechanofusion processing of such particulate provides a desirable method by which the particles can be dry coated with thin layers of coating materials.
Specifically, polycrystalline particulate of the invention comprises aggregates of crystalline grains of a transition metal oxide in which the transition metal oxide has the general chemical formula A,M,Nz02 and in which x, y and z are numbers with x > 0, y? 0.5, and z? 0. Here, A
consists of one or more alkali metals. For use in Li-ion batteries, A is lithium and for manufacturing purposes, particulate is employed in which x is greater than 0.5 and typically about equal to 1. During cycling of such batteries however, x can vary over a wide range as lithium is inserted and extracted repeatedly from the material. Further, in this particulate, M consists of one or more first row transition metal elements (e.g. nickel, manganese, cobalt, etc.), and N comprises a metal element other than an alkali metal or a first row transition metal element (e.g. aluminum, magnesium). The average grain size of the transition metal oxide grains in the aggregate particulate is in the range of 0.2 to 1 gm. The average particle size of the particles in the polycrystalline particulate is in the range of 5 to 50 gm. The surfaces of the particles in the polycrystalline particulate of the invention are however much smoother than compositionally similar particulates of the prior art in that essentially all the depression depths are less than 50% of the average grain size of the transition metal oxide.
As an illustration, in embodiments of the invention in which the average grain size of the transition metal oxide grains in the polycrystalline particulate is about 0.5 gm, essentially all the depression depths are less than 0.25 gm. However, as demonstrated in the following Examples, the depression depths may desirably be unmcasurably small. Preferably, essentially all the depression depths are at least less than 0.1 gm.
The surface of the particles in the polycrystalline particulate can comprise a surface layer in which the atomic ratio of A to M in the surface layer is essentially the same as that in the bulk particles. The surface layer in such embodiments however can have a lower electron density than that of the bulk particles. The thickness of such a surface layer can be less than about 100 urn.
For use as cathode materials in Li-ion battery applications, the polycrystalline particulate employed typically includes a transition metal oxide which is an insertion compound and in which A comprises
particles in the particulate. This results in a significant reduction in surface area of the particles and leads to improved coulombic efficiency and improved cycling when used in Li-ion batteries.
In addition, it was found possible to further coat polycrystalline transition metal oxide particulate, which bad been processed by mechanofusion so as to reduce surface features on the particles, with thin, uniform coating layers of 2 wt.% of the particulate weight or less.
Therefore, mechanofusion processing of such particulate provides a desirable method by which the particles can be dry coated with thin layers of coating materials.
Specifically, polycrystalline particulate of the invention comprises aggregates of crystalline grains of a transition metal oxide in which the transition metal oxide has the general chemical formula A,M,Nz02 and in which x, y and z are numbers with x > 0, y? 0.5, and z? 0. Here, A
consists of one or more alkali metals. For use in Li-ion batteries, A is lithium and for manufacturing purposes, particulate is employed in which x is greater than 0.5 and typically about equal to 1. During cycling of such batteries however, x can vary over a wide range as lithium is inserted and extracted repeatedly from the material. Further, in this particulate, M consists of one or more first row transition metal elements (e.g. nickel, manganese, cobalt, etc.), and N comprises a metal element other than an alkali metal or a first row transition metal element (e.g. aluminum, magnesium). The average grain size of the transition metal oxide grains in the aggregate particulate is in the range of 0.2 to 1 gm. The average particle size of the particles in the polycrystalline particulate is in the range of 5 to 50 gm. The surfaces of the particles in the polycrystalline particulate of the invention are however much smoother than compositionally similar particulates of the prior art in that essentially all the depression depths are less than 50% of the average grain size of the transition metal oxide.
As an illustration, in embodiments of the invention in which the average grain size of the transition metal oxide grains in the polycrystalline particulate is about 0.5 gm, essentially all the depression depths are less than 0.25 gm. However, as demonstrated in the following Examples, the depression depths may desirably be unmcasurably small. Preferably, essentially all the depression depths are at least less than 0.1 gm.
The surface of the particles in the polycrystalline particulate can comprise a surface layer in which the atomic ratio of A to M in the surface layer is essentially the same as that in the bulk particles. The surface layer in such embodiments however can have a lower electron density than that of the bulk particles. The thickness of such a surface layer can be less than about 100 urn.
For use as cathode materials in Li-ion battery applications, the polycrystalline particulate employed typically includes a transition metal oxide which is an insertion compound and in which A comprises
3 Docket No.: Novonix003-CA
lithium and in which 0 < x < 2, y I z is about 1, and y> 0.8 * z. Exemplary polycrystalline particulate for use as cathode materials include those in which M comprises nickel, manganese, and cobalt (e.g.
commercially available material known as NMC and/or precursor material employed in the following examples, namely Li iNit-MngCoh0,, where f, g and hare all greater than zero and f+ g + h = 1, e.g.
LiiNi0.6Mno.2Coo.202) and those in which M comprises nickel and cobalt, and N
comprises aluminum (e.g. commercially available material known as NCA).
Another aspect of the invention includes polycrystalline particulates which comprise a coating layer whose chemical composition is different from that of the grains of the underlying transition metal oxide. For instance, particulates with coating layers whose chemical composition is Al2O3 can be desirable for use as cathode materials in Li-ion battery applications.
Generally, the weight of suitable coating layers can be less than or about 2 % of the weight of the polycrystalline particulate.
The aforementioned polycrystalline particulates can be made using methods based on inexpensive, environmentally friendly mechanofusion dry processing methods. For instance, the surface of particles in such polycrystalline particulates can be smoothed simply by first obtaining a suitable amount of the polycrystalline particulate, and then mechanofusing that polycrystalline particulate in a mechanofusion system for a sufficient time to smooth the surface of the particles such that essentially all the depression depths are less than 50% of the average grain size of the transition metal oxide. In exemplary embodiments, mechanofusing times of greater than 5 minutes have proved to be sufficient.
Even longer times of up to 60 minutes or longer can be used to obtain an even smoother polycrystalline particulate surface.
Also for instance, mechanofusion dry processing methods can be used to uniformly coat the aforementioned polycrystalline particulates with a coating layer. In such a method, initially a suitable amount of the polycrystalline particulate is obtained and smoothed according to the mechanofusing method described above. Then, an amount of coating precursor powder having an average particle size less than 1 pm to the smoothed polycrystalline particulate is added, and the polycrystalline particulate and the coating precursor powder are mechanofused together in a mechanofusion system .. for a sufficient time to fuse the coating precursor powder to the surface of the particles, thereby forming the coating layer on the surface of the polycrystalline particulate.
In an exemplary embodiment, coating layers of Al2O3 in amounts less than or about 2% of the weight of the polycrystalline particulate may be successfully prepared in this way.
A mechanofusion system suitable for use in the inventive methods 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
lithium and in which 0 < x < 2, y I z is about 1, and y> 0.8 * z. Exemplary polycrystalline particulate for use as cathode materials include those in which M comprises nickel, manganese, and cobalt (e.g.
commercially available material known as NMC and/or precursor material employed in the following examples, namely Li iNit-MngCoh0,, where f, g and hare all greater than zero and f+ g + h = 1, e.g.
LiiNi0.6Mno.2Coo.202) and those in which M comprises nickel and cobalt, and N
comprises aluminum (e.g. commercially available material known as NCA).
Another aspect of the invention includes polycrystalline particulates which comprise a coating layer whose chemical composition is different from that of the grains of the underlying transition metal oxide. For instance, particulates with coating layers whose chemical composition is Al2O3 can be desirable for use as cathode materials in Li-ion battery applications.
Generally, the weight of suitable coating layers can be less than or about 2 % of the weight of the polycrystalline particulate.
The aforementioned polycrystalline particulates can be made using methods based on inexpensive, environmentally friendly mechanofusion dry processing methods. For instance, the surface of particles in such polycrystalline particulates can be smoothed simply by first obtaining a suitable amount of the polycrystalline particulate, and then mechanofusing that polycrystalline particulate in a mechanofusion system for a sufficient time to smooth the surface of the particles such that essentially all the depression depths are less than 50% of the average grain size of the transition metal oxide. In exemplary embodiments, mechanofusing times of greater than 5 minutes have proved to be sufficient.
Even longer times of up to 60 minutes or longer can be used to obtain an even smoother polycrystalline particulate surface.
Also for instance, mechanofusion dry processing methods can be used to uniformly coat the aforementioned polycrystalline particulates with a coating layer. In such a method, initially a suitable amount of the polycrystalline particulate is obtained and smoothed according to the mechanofusing method described above. Then, an amount of coating precursor powder having an average particle size less than 1 pm to the smoothed polycrystalline particulate is added, and the polycrystalline particulate and the coating precursor powder are mechanofused together in a mechanofusion system .. for a sufficient time to fuse the coating precursor powder to the surface of the particles, thereby forming the coating layer on the surface of the polycrystalline particulate.
In an exemplary embodiment, coating layers of Al2O3 in amounts less than or about 2% of the weight of the polycrystalline particulate may be successfully prepared in this way.
A mechanofusion system suitable for use in the inventive methods 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
4 Docket No.: Novonix003-CA
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 may be about 1400 rpm.
The inventive polycrystalline particulate, either with and without a coating layer, can be particularly suitable for use as lithium insertion cathode material in rechargeable lithium batteries, and particularly lithium ion batteries which comprise a lithium insertion cathode, a lithium cation conducting electrolyte, and a lithium insertion anode.
Brief Description of the Drawings Figure 1 shows a sketch of an overhead view of the mechanofusion dry process system used to prepare materials in the Examples.
Figures 2a, 2b, and 2c show various SEM images of a particle of comparative example CE1 from the Examples. Figure 2a is a SEM image of a particle from above. Figure 2b is a SEM image of a cross-section of a particle. Figure 2c is a backscatter SEM image at the surface of a cross-sectioned particle.
Figure 2d shows the voltage versus capacity curve obtained from a cell comprising comparative example CE1.
Figures 3a, 3b, and 3c show various SEM images of a particle of inventive example 'El. Figure 3a is a SEM image of a particle from above. Figure 3b is a SEM image of a cross-section of a particle.
Figure 3c is a backscatter SEM image at the surface of a cross-sectioned particle.
Figure 3d shows the voltage versus capacity curve obtained from a cell comprising inventive example 1E1.
Figures 4a and 4b show SEM images of a particle of inventive example 1E2.
Figure 4a is a SEM
image of a particle from above. Figure 4b is a SEM image of a cross-section of a particle.
Figure 4c shows the voltage versus capacity curve obtained from a cell comprising inventive example 1E2.
Figure 5 compares the cycling performance (plotted as capacity retention versus cycle number at .. constant rate) of cells comprising electrodes of CE1, 1E1, and 1E2 material.
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 may be about 1400 rpm.
The inventive polycrystalline particulate, either with and without a coating layer, can be particularly suitable for use as lithium insertion cathode material in rechargeable lithium batteries, and particularly lithium ion batteries which comprise a lithium insertion cathode, a lithium cation conducting electrolyte, and a lithium insertion anode.
Brief Description of the Drawings Figure 1 shows a sketch of an overhead view of the mechanofusion dry process system used to prepare materials in the Examples.
Figures 2a, 2b, and 2c show various SEM images of a particle of comparative example CE1 from the Examples. Figure 2a is a SEM image of a particle from above. Figure 2b is a SEM image of a cross-section of a particle. Figure 2c is a backscatter SEM image at the surface of a cross-sectioned particle.
Figure 2d shows the voltage versus capacity curve obtained from a cell comprising comparative example CE1.
Figures 3a, 3b, and 3c show various SEM images of a particle of inventive example 'El. Figure 3a is a SEM image of a particle from above. Figure 3b is a SEM image of a cross-section of a particle.
Figure 3c is a backscatter SEM image at the surface of a cross-sectioned particle.
Figure 3d shows the voltage versus capacity curve obtained from a cell comprising inventive example 1E1.
Figures 4a and 4b show SEM images of a particle of inventive example 1E2.
Figure 4a is a SEM
image of a particle from above. Figure 4b is a SEM image of a cross-section of a particle.
Figure 4c shows the voltage versus capacity curve obtained from a cell comprising inventive example 1E2.
Figure 5 compares the cycling performance (plotted as capacity retention versus cycle number at .. constant rate) of cells comprising electrodes of CE1, 1E1, and 1E2 material.
5 Docket No.: Novonix003-CA
Figure 6 compares the rate capability (plotted as capacity retention versus cycle number at different discharge rates) of cells comprising electrodes of CE1, IE1, and 1E2 material.
Detailed Description Unless the context requires otherwise, throughout this specification and claims, the words "comprise", "comprising" and the like are to be construed in an open, inclusive sense. The words "a", "an", and the like are to be considered as meaning at least one and are not limited to just one.
In addition, the following definitions are to be applied throughout the specification:
Herein, "particulate" refers to a plurality of "particles" in which the "particles" are aggregates of smaller "grains" (also known in the art as crystallites).
The term "average grain size" refers to the grain size as deteimined by observation of the grains directly by SEM images of particle cross-sections.
The term "average particle size" refers to the particle size as determined by observation of the particles directly by SEM imaging.
The phrase "essentially all the depression depths are less than" an amount on the surface of certain particles refers to the depths of the numerous pits and valleys found on the surface of those particles and which are located between the plurality of grains in those particles. Thus these pits and valleys are local measurements (as determined from SEM images for instance) representing depths over local regions of order of the size of the grains in the particles. It does not for instance refer to depths over larger non-local regions. An example of a larger non-local region would be, for particles shaped like the sockets in typical ball-and-socket joints, the regions defined by the sockets. The term "essentially"
in this context is intended to include all practical embodiments in which the mere presence of a trivial number of larger depression depths present in a large supply of particulate does not materially affect the characteristics of the particulate.
In a like manner to the above, the term "essentially the same" in the context of atomic ratio is intended to include all practical embodiments in which a trivial difference in values determined by experimental methods does not materially affect those characteristics relating to atomic ratio.
Figure 6 compares the rate capability (plotted as capacity retention versus cycle number at different discharge rates) of cells comprising electrodes of CE1, IE1, and 1E2 material.
Detailed Description Unless the context requires otherwise, throughout this specification and claims, the words "comprise", "comprising" and the like are to be construed in an open, inclusive sense. The words "a", "an", and the like are to be considered as meaning at least one and are not limited to just one.
In addition, the following definitions are to be applied throughout the specification:
Herein, "particulate" refers to a plurality of "particles" in which the "particles" are aggregates of smaller "grains" (also known in the art as crystallites).
The term "average grain size" refers to the grain size as deteimined by observation of the grains directly by SEM images of particle cross-sections.
The term "average particle size" refers to the particle size as determined by observation of the particles directly by SEM imaging.
The phrase "essentially all the depression depths are less than" an amount on the surface of certain particles refers to the depths of the numerous pits and valleys found on the surface of those particles and which are located between the plurality of grains in those particles. Thus these pits and valleys are local measurements (as determined from SEM images for instance) representing depths over local regions of order of the size of the grains in the particles. It does not for instance refer to depths over larger non-local regions. An example of a larger non-local region would be, for particles shaped like the sockets in typical ball-and-socket joints, the regions defined by the sockets. The term "essentially"
in this context is intended to include all practical embodiments in which the mere presence of a trivial number of larger depression depths present in a large supply of particulate does not materially affect the characteristics of the particulate.
In a like manner to the above, the term "essentially the same" in the context of atomic ratio is intended to include all practical embodiments in which a trivial difference in values determined by experimental methods does not materially affect those characteristics relating to atomic ratio.
6 Docket No.: Novonix003-CA
The term "cathode" refers to the electrode at which reduction occurs when a metal-ion is discharged.
In a lithium ion cell, the cathode is the electrode that is lithiated during discharge and delithiated during charge.
The term "anode" refers to the electrode at which oxidation occurs when a metal-ion cell is discharged.
In a lithium ion cell, the anode is the electrode that is delithiated during discharge and lithiated during charge.
The term "metal-ion cell" or "metal-ion battery" refers to alkali metal ion cells, including lithium ion cells and sodium ion cells.
The term "half-cell" refers to a cell that has a working electrode and a metal counter/reference electrode. A lithium half-cell has a working electrode and a lithium metal counter/reference electrode.
The terms "cathode active material" or "cathode material" refer to an active material that is used to reversibly store metal ions in a cathode. In a Li-ion cell, cathode materials are lithiated during discharge and delithiated during charge at potentials greater than 2 V vs. Li.
In a Li half-cell, cathode materials are delithiated during charge and lithiated during discharge at potentials greater than 2 V vs.
Li.
The terms "anode active material" or "anode material" refer to an active material that is used to reversibly store metal ions in an anode. In a Li-ion cell, anode materials are lithiated during charge and delithiated during discharge at potentials less than 2 V vs. Li. In a Li half-cell, anode materials are delithiated during charge and lithiated during discharge at potentials less than 2 V vs. Li.
In a quantitative context, the term "about" should be construed as being in the range up to plus 10%
and down to minus 10%.
The present invention relates to polycrystalline particulates and coated polycrystalline particulates whose properties have been improved by smoothing relevant surfaces thereon.
The smoothing can be accomplished by special use of a dry mechanofusion process. When employed as electrode material in rechargeable batteries, the smoothed polycrystalline particulates can provide for performance improvement, particularly improved cycle life.
The polycrystalline particulates of the invention share many characteristics in common with conventional polycrystalline particulates and the former can be prepared by modifying the latter using simple mechnofusion techniques. Characteristics in common with conventional polycrystalline
The term "cathode" refers to the electrode at which reduction occurs when a metal-ion is discharged.
In a lithium ion cell, the cathode is the electrode that is lithiated during discharge and delithiated during charge.
The term "anode" refers to the electrode at which oxidation occurs when a metal-ion cell is discharged.
In a lithium ion cell, the anode is the electrode that is delithiated during discharge and lithiated during charge.
The term "metal-ion cell" or "metal-ion battery" refers to alkali metal ion cells, including lithium ion cells and sodium ion cells.
The term "half-cell" refers to a cell that has a working electrode and a metal counter/reference electrode. A lithium half-cell has a working electrode and a lithium metal counter/reference electrode.
The terms "cathode active material" or "cathode material" refer to an active material that is used to reversibly store metal ions in a cathode. In a Li-ion cell, cathode materials are lithiated during discharge and delithiated during charge at potentials greater than 2 V vs. Li.
In a Li half-cell, cathode materials are delithiated during charge and lithiated during discharge at potentials greater than 2 V vs.
Li.
The terms "anode active material" or "anode material" refer to an active material that is used to reversibly store metal ions in an anode. In a Li-ion cell, anode materials are lithiated during charge and delithiated during discharge at potentials less than 2 V vs. Li. In a Li half-cell, anode materials are delithiated during charge and lithiated during discharge at potentials less than 2 V vs. Li.
In a quantitative context, the term "about" should be construed as being in the range up to plus 10%
and down to minus 10%.
The present invention relates to polycrystalline particulates and coated polycrystalline particulates whose properties have been improved by smoothing relevant surfaces thereon.
The smoothing can be accomplished by special use of a dry mechanofusion process. When employed as electrode material in rechargeable batteries, the smoothed polycrystalline particulates can provide for performance improvement, particularly improved cycle life.
The polycrystalline particulates of the invention share many characteristics in common with conventional polycrystalline particulates and the former can be prepared by modifying the latter using simple mechnofusion techniques. Characteristics in common with conventional polycrystalline
7 Docket No.: Novonix003-CA
particulates include the particles being aggregates of crystalline grains of a transition metal oxide in which the transition metal oxide has the chemical formula AxMyNzO, and in which x, y and z arc numbers with x > 0, y > 0.5, and z > 0. Further, A consists of one or more alkali metals, M consists of one or more first row transition metal elements, and N comprises a metal element other than an alkali metal or a first row transition metal element. Further still, the average grain size of the transition metal oxide grains in these particulates is in the range of 0.2 to 1 pm, and the average particle size of the polycrystalline particulate is in the range of 5 to 50 pm. The inventive particulates differ however in that the surface of the particles in the polycrystalline particulate is smoother, specifically such that essentially all the depression depths are less than 50% of the average grain size of the transition metal oxide. For example, in embodiments in which the average grain size of the transition metal oxide grains is about 0.5 pm, essentially all the depression depths would be less than 0.25 pm. At the lowest end of the grain size range (i.e. 0.2 gm), essentially all the depression depths are less than 0.1 pm. As is illustrated in the Examples below, this is markedly smoother than conventional particulate of this type.
In some embodiments, the surface of the particles comprises a surface layer in which the atomic ratio of A to M in the surface layer is essentially the same as that in the bulk particles, and the surface layer has a lower electron density than that of the bulk particles. The surface layer can be less than 100 nm thick, e.g. about 50 rim thick as found in an embodiment in the Examples.
Certain polycrystalline particulates of the invention are advantageous for use in rechargeable lithium batteries. The cycle life for instance can be improved by smoothing the particulate surface in accordance with, the invention. In particulates for this application, the transition metal oxide is an insertion compound and the insertable species A comprises lithium. The lithium may be inserted and removed typically over a range from about 0 to 2. The ratios y and z of transition metal (or metals) M
and any other metal (or metals) N respectively in the insertion compound is typically such that y z is about 1 and y> 0.8 * z. Exemplary such insertion compounds include those in which M comprises nickel, manganese, and cobalt (e.g. the common commercial material NMC which may have a chemical formula of Li INiiMngCoi,02, where f, g and h are all greater than zero and f + g + h = 1, e.g.
Li INi0.6Mno2Coo.202) or in which M comprises nickel and cobalt and N
comprises aluminum (e.g.
another common material NCA).
In another aspect of the invention, when preparing polycrystalline particulate with coating layers, initially smoothing the particulate surface in the aforementioned manner allows for the subsequent .. application of thinner, uniform coating layers. Otherwise, thicker, less uniform coating layers have to be applied in order to comprehensively coat the particulate. Advantageously, such thin, uniform coating layers can be applied to the particulate using mechanofusion methods too. To do so, an amount Docket No.: Novonix003-CA
of polycrystalline particulate which has already been smoothed is combined with an appropriate amount of coating precursor powder whose composition is that of the desired coating layer. The combination of particulate and precursor powder is then subjected to mechanofusion, thereby applying a coating layer derived from the precursor powder onto the surface of the particulate.
In certain applications, polycrystalline particulate with coating layers are desirably employed. In such applications, the chemical composition of the coating layer is generally something different from that of the grains of transition metal oxide in the particulate. In Li-ion battery applications, one such optional desirable coating layer comprises A1203 which can serve to reduce unwanted reactions between a particulate electrode and the battery electrolyte, and hence improve cycle life. However, a thin uniform coating layer is desirable in such a case, in part because Al2O3 is not electrically conductive.
It has been discovered that the aforementioned polycrystalline particulates and coated polycrystalline particulates can readily be prepared by modifying conventional particulate using mechanofusion (MF) dry processing methods. The MF process is relatively simple, inexpensive, and requires no solvents thereby making it potentially attractive for environmentally responsible commercial manufacture. In either case, the required steps merely include obtaining a suitable amount of conventional particulate and mechanofusing it under appropriate operating conditions for a sufficient time (typically of order of minutes) to suitably smooth the surface. To prepare coated polycrystalline particulate, the required steps involve preparing smoothed particulate from a conventional supply of particulate first, then adding an amount of a desired coating precursor powder (e.g. A1203 powder) having an average particle size less than 1 gm to the smoothed polycrystalline particulate, and mechanofusing the polycrystalline particulate and the coating precursor powder for a sufficient time to fuse the coating precursor powder to the surface of the particles (again typically of order of minutes). This results in a uniform coating layer on the polycrystalline particulate. The coating layers can be made desirably thin (e.g. in which the weight of the surface layer is less than or about 2% of the weight of the underlying polycrystalline particulate).
Figure 1 schematically shows a suitable MF system 1 for preparing particulate in accordance with the invention. It consists of rotating cylindrical chamber 2 in which fixed rounded press-head 3 and fixed scraper 4 are placed. The radius of press-head 3 is smaller than that of chamber 2 and the clearance space between press-head 3 and chamber wall 5 generally ranges from 1 to 5 mm.
The clearance between scraper 4 and chamber wall 5 is much smaller, usually around 0.5 mm.
Preferably these clearances are adjustable for optimization, depending on factors such as the chamber size, particle size, powder hardness, and so on.
Docket No.: Novonix003-CA
Operation of MF system 1 is simple, but the mechanism by which powder is processed within the chamber is complex (see W. Chen, R. N. Dave, R. Pfeffer and 0. Walton, Powder Technol., 2004, 146, 121-136). In use, powder 6 (comprising suitable amounts of polycrystalline particulate and optional coating precursor powder) is placed into the chamber and chamber 2 is sealed. When the chamber rotates, powder 6 is forced to chamber wall 5 by centrifugal action.
This also forces the powder to pass through the converging space between fixed press-head 3 and rotating chamber wall 5, establishing a high-shear field. In the case when optional coating precursor powder is included, as the particles come out of the diverging space of the press-head region, they adhere to each other and to the chamber wall. Scraper 4 serves to scrape off the powder attached to chamber wall 5. The sheared powder mixture is then re-dispersed into the chamber and moves towards the press-head region again.
The powder continuously undergoes this process of compression, frictional shearing, and de-agglomeration while chamber 2 is rotating. These interactions result in various effects, including smoothing, spheronization, and the coating of small or soft particles onto large particles. At the high rotation speeds typically utilized (>1000 rpm), these effects occur quickly, typically within minutes.
As those skilled in the art will appreciate, appropriate operating parameters for the MF system can be expected to vary according to the product desired and on the types and amounts of the powder materials employed. It is expected that those of ordinary skill will readily be able to determine appropriate operating parameters for a given situation based on guidance provided in the Examples below.
Once a suitable supply of particulate material has been prepared for a given application, electrodes and electrochemical devices employing this material may be prepared in numerous manners known to those in the art. For instance, the numerous optional designs and methods for making electrodes for rechargeable lithium batteries as well as the numerous optional designs and methods for making the batteries themselves have been documented extensively in the art. Particularly preferred applications for the present invention are for use as cathodes in rechargeable lithium ion batteries.
Without being bound by theory, it is hypothesized that, in addition to MF
providing a reduced surface area, the surface layer in which the atomic ratio of A to M in the surface layer is essentially the same as that in the bulk particles also resulting from the MF process further reduces electrolyte reactivity on cathode particles, leading to improved cycling performance.
The following examples are illustrative of certain materials and methods of the invention and demonstrate some of the advantages thereof. However, these examples should not be construed as limiting the invention in any way. Those skilled in the art will readily appreciate that many other variants are possible for the materials and methods disclosed herein.
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Examples Commercially available lithium nickel manganese cobalt oxide polycrystalline particulate material was obtained and particulate materials of the invention were prepared therefrom, both with and without an aluminum oxide coating layer, using mechanofusion as described below. Electrodes and electrochemical cells were prepared using these materials. Certain characteristics of the materials were determined and compared along with the cell performance results obtained from the electrochemical cells.
Preparatory and Analytical Methods employed Surface Area Analysis The specific surface areas of sample materials were determined by the single-point Brunauer-Enunett-Teller (BET) method using a Micromeritics Flowsorb 112300 surface area analyzer.
X-ray Diffraction X-ray diffraction (XRD) patterns were collected using a Rigaku Ultima 1V
diffractometer equipped with a Cu Ku. X-ray source, a diffracted beam monochromator and a scintillation detector. Each XRD
pattern was collected from 20 to 90 2-theta in 0.05 increments for 3 seconds per step.
SEM and Cross-sectional SEM
Sample material and electrode morphology were studied with a TESCAN MIRA 3 LMU
Variable Pressure Schottky Field Emission Scanning Electron Microscope (SEM). Cross sections of sample material and electrode were prepared with a JEOL Cross-Polisher (JEOL Ltd., Tokyo, Japan) which sections samples by shooting argon ions at them. An energy dispersive spectroscopy (EDS) system (Oxford instrument X-max 80 mm2) with a silicon drift detector (SDD) was used for semi-quantitative analysis of atomic composition.
Electrode Preparation In all cases, sample electrodes were prepared from slurries made by mixing the selected polycrystalline particle, carbon black (Super C65, Imerys Graphite and Carbon) and polyvinylidene fluoride (PVDF) in a weight ratio of 86/7/7 in 1-methyl-2-pyrrolidone (NMP).
Slurries were mixed for 200 seconds with a Mazerustar mixer and then spread onto aluminum foil (Furukawa Electric, Japan) with a 0.006 inch gap coating bar. The coatings were then dried in air for 2 hours at 120 C, cut into 1.3 cm disks, and then heated under vacuum overnight at 120 C. The dried electrodes were not calendared.
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Cell Preparation To evaluate the various materials as cathode materials in Li-ion cells, laboratory test lithium half-cells were constructed and tested. Electrodes were assembled in 2325-type coin cells with a lithium foil (99.9%, Sigma Aldrich) counter/reference electrode. (Note: as is well known to those skilled in the art, results from these test lithium half-cells allow for reliable prediction of cathode materials performance in lithium ion batteries.) One layer of Celgard 2300 separator and one layer of blown microfiber (3M
company) were used as separator in each coin cell. 1M LiPF6 (BASF) in a solution of ethylene carbonate, diethyl carbonate and monofluoroethylene carbonate (volume ratio 3:6:1, all from BASF) was used as electrolyte. Cell assembly was carried out in an Ar-filled glove box. Cells were cycled galvanostatically at 30.0 0.1 C between 3.0 V and 4.4 V using a Maccor Series 4000 Automated Test System. All cells were cycled at a C/20 rate for the first cycle.
Thereafter, to test cycle life performance, certain cells were cycled at a constant C/2 rate with a 5 hour hold at the top of charge.
To test rate capability, other cells were cycled at various rates (C/20, C/10, C/5, C/2, 1C, and 5C), both charge and discharge with no hold, for 5 cycles respectively.
Comparative Example 1 (CE1) LiNi0.6Mno2Co0202 (CELLCORE HX12Th, commercially available NMC622 from Umicore, Korea) was used as received without any further treatment (hereafter denoted as particulate sample CE1). Figure 2a shows the SEM image of a particle of CE1. It consists of secondary particles with diameter of 5-50 gm which are aggregates of single crystal primary grains with a size of 0.2-1gm and an average grain size of about 0.5 pm. The surface area of the particulate measured by BET was 0.30 m2/g.
A cross-sectional SEM image of a particle of CE1 is shown in Figure 2b. The surface of the particle is characterized by features in the form of pits and valleys whose depression depths are on the order of the same size as the size of the grains making up the particle (average pit depth or depression depth of about 0.5 gm). This results in the particles having a relatively high surface area.
Figure 2c shows a backscatter SEM image at the surface of a cross-sectioned particle of CE1. The surface and bulk portions of the particle have the same composition and morphology, leading to the sharply contrasted particle edge seen in this image.
.. Figure 2d shows the voltage versus capacity curve obtained from the cell comprising an electrode of sample CE1. As expected, the voltage curve is characteristic of NMC622.
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Inventive Example 1 (IE1) A polycrystalline particulate with a smoothed surface was prepared in accordance with the invention using 135 g (50 mL tapped powder volume) of LiNi0.6Mno.2C00.202 (NMC622 as in CE1 above) and dry processing that using a mechanofusion system as shown in the sketch of Figure 1. Specifically, an AM-15F Mechanofusion System (Hosokawa Micron Corporation, Osaka, Japan) was used which had been modified by replacing the standard stainless steel chamber, scraper, and press head with identical hardened steel parts to reduce wear. Mechanofusion was conducted at 1400 rpm with a 0.5 mm scraper/wall gap, and a 1.4 mm press-head/wall gap for 60 mm. The processed sample here is denoted as particulate sample 1E1.
Figure 3a shows an SEM image of a particle of sample IEL The secondary particle size had not changed after the mechanofusion process and was essentially identical to that of unprocessed comparative sample CE1. However it is apparent that the surface had been markedly smoothed (appearing to have been smeared smoother) compared to that of CE1. This resulted in a significant reduction in surface area as evidenced by the surface area of IE1 as measured by BET was now only 0.13 m2/g.
A cross-sectional SEM image of a particle of sample TEl is shown in Figure 3b.
The surface of the particle has no apparent sharp pits or valleys. Therefore no depression depths could be determined from this image.
Figure 3c shows a backscatter SEM image at the surface of a cross-sectioned particle of sample IEL
An observable surface layer is apparent in this image and this layer has a different electron density than that of the bulk composition, resulting in a significant observed contrast in this backscatter SEM
image. The thickness of this surface layer is about 50 nm.
EDS compositional maps of the cross-section surface shown in Figure 3c were obtained for each of the elements Ni, Mn, and Co. It appeared that the surface layer had essentially the same transition metal composition as that of the bulk composition of the particle. However, it is believed that the surface layer has a different crystal structure and possibly less oxygen than the bulk particle, thereby resulting in the contrast seen in the backscatter SEM image of Figure 3c. The crystal structure of the surface film may be amorphous or may be like that of rocksalt.
The voltage versus capacity curve obtained from the cell comprising an electrode of sample TEl is shown in Figure 3d. The voltage curve is unchanged and still characteristic of NMC622.
Docket No.: Novonix003-CA
Inventive Example 2 (IE2) A polycrystalline particulate with an aluminum oxide coating layer was prepared in accordance with the invention by using 135 g (50 mL tapped powder volume) of the material from Inventive Example 1 above (IE1), adding 0.675 g of nano-A1203 (13 nm, from Sigma-Aldrich) thereto, and then dry processing using the aforementioned modified an AM-15F
Mechanofusion System. Mechanofusion was conducted at 1400 rpm with a 0.5 mm scraper/wall gap, and a 1.4 mm press-head/wall gap for 30 min. The processed sample here is denoted as particulate sample 1E2.
Figure 4a shows the SEM image of a particle of sample 1E2. The SEM image is very similar to that of sample TEL Again, the particle surface has been markedly smoothed compared to that of comparative sample CE1.
The cross-sectional SEM image of a particle of sample 1E2 is shown in Figure 4b. Similar to sample Ii, the surface of the particle has no apparent pits or valleys and thus any depression depths were too small to measure from this image. The size of the grains remained unchanged from that of CE1. A thin surface layer however is present at the surface of the particle.
The voltage versus capacity curve obtained from the cell comprising an electrode of sample IE2 is shown in Figure 4c. Here, the hysteresis seen is slightly larger than that seen for the electrodes of samples CE1 and IEl. This is believed to be due to the non-electrically conductive nature of an applied A1203 surface coating. It is otherwise believed that the particles of sample 1E2 are the same as sample 1E1 excepting that the former comprises an A1203 coating on top of the 50 nm surface layer of the latter.
Comparison of electrochemical performance in cells The capacity retention versus cycle number of cells comprising electrodes made from CE1, IE1, and 1E2 materials are compared in Figure 5. Compared to the CE1 based cell, improved cycling performance was observed for the IE1 based cell. This is ascribed to the reduced surface area of sample TEl and the thin coating on the surface of its particles. The capacity retention performance was further improved for the 1E2 based cell, which is ascribed to the presence of a thin A1203 surface layer.
The rate performance (plotted as capacity retention versus cycle number at different discharge rates) of cells comprising electrodes made from CE1, 1E1, and 1E2 materials are compared in Figure 6. All Docket No.: Novonix003-CA
cells showed acceptable and similar rate capability up to about C/2 rates and thus all were acceptable for practical applications. At even higher rates though, the 1E1 based cell showed the best rate performance, while the 1E2 based cell showed the worst rate performance, presumably due to the non-conductive nature of the A1203 surface coating.
The preceding examples demonstrate that mechanofusion can be used to make novel polycrystalline particulates, either with or without a coating layer, that are particularly suitable for use in positive electrodes for rechargeable batteries. Use of the method of the invention results in particulate with a smoother surface which in turn leads to improved perfolinance characteristics in such batteries.
Alone, the use of the mechanofusion process can improve cycling performance.
Further, an additional A1203 surface layer can be applied which can result in better cycle life, but at the detriment to rate capability.
All of the above U.S. patents, U.S. patent applications, foreign patents, foreign patent applications and non-patent publications referred to in this specification, are incorporated herein by reference in their entirety.
While particular elements, embodiments and applications of the present invention have been shown and described, it will be understood, of course, that the invention is not limited thereto since modifications may be made by those skilled in the art without departing from the spirit and scope of the present disclosure, particularly in light of the foregoing teachings. For instance, while the examples focussed on lithium transition metal oxide materials and on their expected performance as cathodes in lithium ion batteries, it is expected that similarly useful materials based on other alkali metals or mixtures thereof may be made using similar methods. Further, such materials may find use in other batteries or electrochemical devices. Such modifications are to be considered within the purview and scope of the claims appended hereto.
particulates include the particles being aggregates of crystalline grains of a transition metal oxide in which the transition metal oxide has the chemical formula AxMyNzO, and in which x, y and z arc numbers with x > 0, y > 0.5, and z > 0. Further, A consists of one or more alkali metals, M consists of one or more first row transition metal elements, and N comprises a metal element other than an alkali metal or a first row transition metal element. Further still, the average grain size of the transition metal oxide grains in these particulates is in the range of 0.2 to 1 pm, and the average particle size of the polycrystalline particulate is in the range of 5 to 50 pm. The inventive particulates differ however in that the surface of the particles in the polycrystalline particulate is smoother, specifically such that essentially all the depression depths are less than 50% of the average grain size of the transition metal oxide. For example, in embodiments in which the average grain size of the transition metal oxide grains is about 0.5 pm, essentially all the depression depths would be less than 0.25 pm. At the lowest end of the grain size range (i.e. 0.2 gm), essentially all the depression depths are less than 0.1 pm. As is illustrated in the Examples below, this is markedly smoother than conventional particulate of this type.
In some embodiments, the surface of the particles comprises a surface layer in which the atomic ratio of A to M in the surface layer is essentially the same as that in the bulk particles, and the surface layer has a lower electron density than that of the bulk particles. The surface layer can be less than 100 nm thick, e.g. about 50 rim thick as found in an embodiment in the Examples.
Certain polycrystalline particulates of the invention are advantageous for use in rechargeable lithium batteries. The cycle life for instance can be improved by smoothing the particulate surface in accordance with, the invention. In particulates for this application, the transition metal oxide is an insertion compound and the insertable species A comprises lithium. The lithium may be inserted and removed typically over a range from about 0 to 2. The ratios y and z of transition metal (or metals) M
and any other metal (or metals) N respectively in the insertion compound is typically such that y z is about 1 and y> 0.8 * z. Exemplary such insertion compounds include those in which M comprises nickel, manganese, and cobalt (e.g. the common commercial material NMC which may have a chemical formula of Li INiiMngCoi,02, where f, g and h are all greater than zero and f + g + h = 1, e.g.
Li INi0.6Mno2Coo.202) or in which M comprises nickel and cobalt and N
comprises aluminum (e.g.
another common material NCA).
In another aspect of the invention, when preparing polycrystalline particulate with coating layers, initially smoothing the particulate surface in the aforementioned manner allows for the subsequent .. application of thinner, uniform coating layers. Otherwise, thicker, less uniform coating layers have to be applied in order to comprehensively coat the particulate. Advantageously, such thin, uniform coating layers can be applied to the particulate using mechanofusion methods too. To do so, an amount Docket No.: Novonix003-CA
of polycrystalline particulate which has already been smoothed is combined with an appropriate amount of coating precursor powder whose composition is that of the desired coating layer. The combination of particulate and precursor powder is then subjected to mechanofusion, thereby applying a coating layer derived from the precursor powder onto the surface of the particulate.
In certain applications, polycrystalline particulate with coating layers are desirably employed. In such applications, the chemical composition of the coating layer is generally something different from that of the grains of transition metal oxide in the particulate. In Li-ion battery applications, one such optional desirable coating layer comprises A1203 which can serve to reduce unwanted reactions between a particulate electrode and the battery electrolyte, and hence improve cycle life. However, a thin uniform coating layer is desirable in such a case, in part because Al2O3 is not electrically conductive.
It has been discovered that the aforementioned polycrystalline particulates and coated polycrystalline particulates can readily be prepared by modifying conventional particulate using mechanofusion (MF) dry processing methods. The MF process is relatively simple, inexpensive, and requires no solvents thereby making it potentially attractive for environmentally responsible commercial manufacture. In either case, the required steps merely include obtaining a suitable amount of conventional particulate and mechanofusing it under appropriate operating conditions for a sufficient time (typically of order of minutes) to suitably smooth the surface. To prepare coated polycrystalline particulate, the required steps involve preparing smoothed particulate from a conventional supply of particulate first, then adding an amount of a desired coating precursor powder (e.g. A1203 powder) having an average particle size less than 1 gm to the smoothed polycrystalline particulate, and mechanofusing the polycrystalline particulate and the coating precursor powder for a sufficient time to fuse the coating precursor powder to the surface of the particles (again typically of order of minutes). This results in a uniform coating layer on the polycrystalline particulate. The coating layers can be made desirably thin (e.g. in which the weight of the surface layer is less than or about 2% of the weight of the underlying polycrystalline particulate).
Figure 1 schematically shows a suitable MF system 1 for preparing particulate in accordance with the invention. It consists of rotating cylindrical chamber 2 in which fixed rounded press-head 3 and fixed scraper 4 are placed. The radius of press-head 3 is smaller than that of chamber 2 and the clearance space between press-head 3 and chamber wall 5 generally ranges from 1 to 5 mm.
The clearance between scraper 4 and chamber wall 5 is much smaller, usually around 0.5 mm.
Preferably these clearances are adjustable for optimization, depending on factors such as the chamber size, particle size, powder hardness, and so on.
Docket No.: Novonix003-CA
Operation of MF system 1 is simple, but the mechanism by which powder is processed within the chamber is complex (see W. Chen, R. N. Dave, R. Pfeffer and 0. Walton, Powder Technol., 2004, 146, 121-136). In use, powder 6 (comprising suitable amounts of polycrystalline particulate and optional coating precursor powder) is placed into the chamber and chamber 2 is sealed. When the chamber rotates, powder 6 is forced to chamber wall 5 by centrifugal action.
This also forces the powder to pass through the converging space between fixed press-head 3 and rotating chamber wall 5, establishing a high-shear field. In the case when optional coating precursor powder is included, as the particles come out of the diverging space of the press-head region, they adhere to each other and to the chamber wall. Scraper 4 serves to scrape off the powder attached to chamber wall 5. The sheared powder mixture is then re-dispersed into the chamber and moves towards the press-head region again.
The powder continuously undergoes this process of compression, frictional shearing, and de-agglomeration while chamber 2 is rotating. These interactions result in various effects, including smoothing, spheronization, and the coating of small or soft particles onto large particles. At the high rotation speeds typically utilized (>1000 rpm), these effects occur quickly, typically within minutes.
As those skilled in the art will appreciate, appropriate operating parameters for the MF system can be expected to vary according to the product desired and on the types and amounts of the powder materials employed. It is expected that those of ordinary skill will readily be able to determine appropriate operating parameters for a given situation based on guidance provided in the Examples below.
Once a suitable supply of particulate material has been prepared for a given application, electrodes and electrochemical devices employing this material may be prepared in numerous manners known to those in the art. For instance, the numerous optional designs and methods for making electrodes for rechargeable lithium batteries as well as the numerous optional designs and methods for making the batteries themselves have been documented extensively in the art. Particularly preferred applications for the present invention are for use as cathodes in rechargeable lithium ion batteries.
Without being bound by theory, it is hypothesized that, in addition to MF
providing a reduced surface area, the surface layer in which the atomic ratio of A to M in the surface layer is essentially the same as that in the bulk particles also resulting from the MF process further reduces electrolyte reactivity on cathode particles, leading to improved cycling performance.
The following examples are illustrative of certain materials and methods of the invention and demonstrate some of the advantages thereof. However, these examples should not be construed as limiting the invention in any way. Those skilled in the art will readily appreciate that many other variants are possible for the materials and methods disclosed herein.
Docket No.: Novonix003-CA
Examples Commercially available lithium nickel manganese cobalt oxide polycrystalline particulate material was obtained and particulate materials of the invention were prepared therefrom, both with and without an aluminum oxide coating layer, using mechanofusion as described below. Electrodes and electrochemical cells were prepared using these materials. Certain characteristics of the materials were determined and compared along with the cell performance results obtained from the electrochemical cells.
Preparatory and Analytical Methods employed Surface Area Analysis The specific surface areas of sample materials were determined by the single-point Brunauer-Enunett-Teller (BET) method using a Micromeritics Flowsorb 112300 surface area analyzer.
X-ray Diffraction X-ray diffraction (XRD) patterns were collected using a Rigaku Ultima 1V
diffractometer equipped with a Cu Ku. X-ray source, a diffracted beam monochromator and a scintillation detector. Each XRD
pattern was collected from 20 to 90 2-theta in 0.05 increments for 3 seconds per step.
SEM and Cross-sectional SEM
Sample material and electrode morphology were studied with a TESCAN MIRA 3 LMU
Variable Pressure Schottky Field Emission Scanning Electron Microscope (SEM). Cross sections of sample material and electrode were prepared with a JEOL Cross-Polisher (JEOL Ltd., Tokyo, Japan) which sections samples by shooting argon ions at them. An energy dispersive spectroscopy (EDS) system (Oxford instrument X-max 80 mm2) with a silicon drift detector (SDD) was used for semi-quantitative analysis of atomic composition.
Electrode Preparation In all cases, sample electrodes were prepared from slurries made by mixing the selected polycrystalline particle, carbon black (Super C65, Imerys Graphite and Carbon) and polyvinylidene fluoride (PVDF) in a weight ratio of 86/7/7 in 1-methyl-2-pyrrolidone (NMP).
Slurries were mixed for 200 seconds with a Mazerustar mixer and then spread onto aluminum foil (Furukawa Electric, Japan) with a 0.006 inch gap coating bar. The coatings were then dried in air for 2 hours at 120 C, cut into 1.3 cm disks, and then heated under vacuum overnight at 120 C. The dried electrodes were not calendared.
Docket No.: Novonix003-CA
Cell Preparation To evaluate the various materials as cathode materials in Li-ion cells, laboratory test lithium half-cells were constructed and tested. Electrodes were assembled in 2325-type coin cells with a lithium foil (99.9%, Sigma Aldrich) counter/reference electrode. (Note: as is well known to those skilled in the art, results from these test lithium half-cells allow for reliable prediction of cathode materials performance in lithium ion batteries.) One layer of Celgard 2300 separator and one layer of blown microfiber (3M
company) were used as separator in each coin cell. 1M LiPF6 (BASF) in a solution of ethylene carbonate, diethyl carbonate and monofluoroethylene carbonate (volume ratio 3:6:1, all from BASF) was used as electrolyte. Cell assembly was carried out in an Ar-filled glove box. Cells were cycled galvanostatically at 30.0 0.1 C between 3.0 V and 4.4 V using a Maccor Series 4000 Automated Test System. All cells were cycled at a C/20 rate for the first cycle.
Thereafter, to test cycle life performance, certain cells were cycled at a constant C/2 rate with a 5 hour hold at the top of charge.
To test rate capability, other cells were cycled at various rates (C/20, C/10, C/5, C/2, 1C, and 5C), both charge and discharge with no hold, for 5 cycles respectively.
Comparative Example 1 (CE1) LiNi0.6Mno2Co0202 (CELLCORE HX12Th, commercially available NMC622 from Umicore, Korea) was used as received without any further treatment (hereafter denoted as particulate sample CE1). Figure 2a shows the SEM image of a particle of CE1. It consists of secondary particles with diameter of 5-50 gm which are aggregates of single crystal primary grains with a size of 0.2-1gm and an average grain size of about 0.5 pm. The surface area of the particulate measured by BET was 0.30 m2/g.
A cross-sectional SEM image of a particle of CE1 is shown in Figure 2b. The surface of the particle is characterized by features in the form of pits and valleys whose depression depths are on the order of the same size as the size of the grains making up the particle (average pit depth or depression depth of about 0.5 gm). This results in the particles having a relatively high surface area.
Figure 2c shows a backscatter SEM image at the surface of a cross-sectioned particle of CE1. The surface and bulk portions of the particle have the same composition and morphology, leading to the sharply contrasted particle edge seen in this image.
.. Figure 2d shows the voltage versus capacity curve obtained from the cell comprising an electrode of sample CE1. As expected, the voltage curve is characteristic of NMC622.
Docket No.: Novonix003-CA
Inventive Example 1 (IE1) A polycrystalline particulate with a smoothed surface was prepared in accordance with the invention using 135 g (50 mL tapped powder volume) of LiNi0.6Mno.2C00.202 (NMC622 as in CE1 above) and dry processing that using a mechanofusion system as shown in the sketch of Figure 1. Specifically, an AM-15F Mechanofusion System (Hosokawa Micron Corporation, Osaka, Japan) was used which had been modified by replacing the standard stainless steel chamber, scraper, and press head with identical hardened steel parts to reduce wear. Mechanofusion was conducted at 1400 rpm with a 0.5 mm scraper/wall gap, and a 1.4 mm press-head/wall gap for 60 mm. The processed sample here is denoted as particulate sample 1E1.
Figure 3a shows an SEM image of a particle of sample IEL The secondary particle size had not changed after the mechanofusion process and was essentially identical to that of unprocessed comparative sample CE1. However it is apparent that the surface had been markedly smoothed (appearing to have been smeared smoother) compared to that of CE1. This resulted in a significant reduction in surface area as evidenced by the surface area of IE1 as measured by BET was now only 0.13 m2/g.
A cross-sectional SEM image of a particle of sample TEl is shown in Figure 3b.
The surface of the particle has no apparent sharp pits or valleys. Therefore no depression depths could be determined from this image.
Figure 3c shows a backscatter SEM image at the surface of a cross-sectioned particle of sample IEL
An observable surface layer is apparent in this image and this layer has a different electron density than that of the bulk composition, resulting in a significant observed contrast in this backscatter SEM
image. The thickness of this surface layer is about 50 nm.
EDS compositional maps of the cross-section surface shown in Figure 3c were obtained for each of the elements Ni, Mn, and Co. It appeared that the surface layer had essentially the same transition metal composition as that of the bulk composition of the particle. However, it is believed that the surface layer has a different crystal structure and possibly less oxygen than the bulk particle, thereby resulting in the contrast seen in the backscatter SEM image of Figure 3c. The crystal structure of the surface film may be amorphous or may be like that of rocksalt.
The voltage versus capacity curve obtained from the cell comprising an electrode of sample TEl is shown in Figure 3d. The voltage curve is unchanged and still characteristic of NMC622.
Docket No.: Novonix003-CA
Inventive Example 2 (IE2) A polycrystalline particulate with an aluminum oxide coating layer was prepared in accordance with the invention by using 135 g (50 mL tapped powder volume) of the material from Inventive Example 1 above (IE1), adding 0.675 g of nano-A1203 (13 nm, from Sigma-Aldrich) thereto, and then dry processing using the aforementioned modified an AM-15F
Mechanofusion System. Mechanofusion was conducted at 1400 rpm with a 0.5 mm scraper/wall gap, and a 1.4 mm press-head/wall gap for 30 min. The processed sample here is denoted as particulate sample 1E2.
Figure 4a shows the SEM image of a particle of sample 1E2. The SEM image is very similar to that of sample TEL Again, the particle surface has been markedly smoothed compared to that of comparative sample CE1.
The cross-sectional SEM image of a particle of sample 1E2 is shown in Figure 4b. Similar to sample Ii, the surface of the particle has no apparent pits or valleys and thus any depression depths were too small to measure from this image. The size of the grains remained unchanged from that of CE1. A thin surface layer however is present at the surface of the particle.
The voltage versus capacity curve obtained from the cell comprising an electrode of sample IE2 is shown in Figure 4c. Here, the hysteresis seen is slightly larger than that seen for the electrodes of samples CE1 and IEl. This is believed to be due to the non-electrically conductive nature of an applied A1203 surface coating. It is otherwise believed that the particles of sample 1E2 are the same as sample 1E1 excepting that the former comprises an A1203 coating on top of the 50 nm surface layer of the latter.
Comparison of electrochemical performance in cells The capacity retention versus cycle number of cells comprising electrodes made from CE1, IE1, and 1E2 materials are compared in Figure 5. Compared to the CE1 based cell, improved cycling performance was observed for the IE1 based cell. This is ascribed to the reduced surface area of sample TEl and the thin coating on the surface of its particles. The capacity retention performance was further improved for the 1E2 based cell, which is ascribed to the presence of a thin A1203 surface layer.
The rate performance (plotted as capacity retention versus cycle number at different discharge rates) of cells comprising electrodes made from CE1, 1E1, and 1E2 materials are compared in Figure 6. All Docket No.: Novonix003-CA
cells showed acceptable and similar rate capability up to about C/2 rates and thus all were acceptable for practical applications. At even higher rates though, the 1E1 based cell showed the best rate performance, while the 1E2 based cell showed the worst rate performance, presumably due to the non-conductive nature of the A1203 surface coating.
The preceding examples demonstrate that mechanofusion can be used to make novel polycrystalline particulates, either with or without a coating layer, that are particularly suitable for use in positive electrodes for rechargeable batteries. Use of the method of the invention results in particulate with a smoother surface which in turn leads to improved perfolinance characteristics in such batteries.
Alone, the use of the mechanofusion process can improve cycling performance.
Further, an additional A1203 surface layer can be applied which can result in better cycle life, but at the detriment to rate capability.
All of the above U.S. patents, U.S. patent applications, foreign patents, foreign patent applications and non-patent publications referred to in this specification, are incorporated herein by reference in their entirety.
While particular elements, embodiments and applications of the present invention have been shown and described, it will be understood, of course, that the invention is not limited thereto since modifications may be made by those skilled in the art without departing from the spirit and scope of the present disclosure, particularly in light of the foregoing teachings. For instance, while the examples focussed on lithium transition metal oxide materials and on their expected performance as cathodes in lithium ion batteries, it is expected that similarly useful materials based on other alkali metals or mixtures thereof may be made using similar methods. Further, such materials may find use in other batteries or electrochemical devices. Such modifications are to be considered within the purview and scope of the claims appended hereto.
Claims (28)
1. A polycrystalline particulate comprising aggregates of crystalline grains of a transition metal oxide wherein:
the transition metal oxide has the chemical formula A x M y N z O2 wherein x, y and z are numbers with x >= 0, y >= 0.5, and z >= 0;
A consists of one or more alkali metals;
M consists of one or more first row transition metal elements;
N comprises a metal element other than an alkali metal or a first row transition metal element;
the average grain size of the transition metal oxide grains is in the range of 0.2 to 1 µm; and the average particle size of the polycrystalline particulate is in the range of 5 to 50 µm;
characterized in that the surface of the particles in the polycrystalline particulate is smooth such that essentially all the depression depths are less than 50% of the average grain size of the transition metal oxide.
the transition metal oxide has the chemical formula A x M y N z O2 wherein x, y and z are numbers with x >= 0, y >= 0.5, and z >= 0;
A consists of one or more alkali metals;
M consists of one or more first row transition metal elements;
N comprises a metal element other than an alkali metal or a first row transition metal element;
the average grain size of the transition metal oxide grains is in the range of 0.2 to 1 µm; and the average particle size of the polycrystalline particulate is in the range of 5 to 50 µm;
characterized in that the surface of the particles in the polycrystalline particulate is smooth such that essentially all the depression depths are less than 50% of the average grain size of the transition metal oxide.
2. The polycrystalline particulate of claim 1 wherein the surface of the particles comprises a surface layer wherein:
the atomic ratio of A to M in the surface layer is essentially the same as that in the bulk particles; and the surface layer has a lower electron density than that of the bulk particles.
the atomic ratio of A to M in the surface layer is essentially the same as that in the bulk particles; and the surface layer has a lower electron density than that of the bulk particles.
3. The polycrystalline particulate of claim 2 wherein the surface layer is less than 100 nm thick.
4. The polycrystalline particulate of claim 1 wherein:
the transition metal oxide is an insertion compound;
A comprises lithium;
0 <= x <= 2;
y + z is about 1; and y > 0.8 * z.
the transition metal oxide is an insertion compound;
A comprises lithium;
0 <= x <= 2;
y + z is about 1; and y > 0.8 * z.
5. The polycrystalline particulate of claim 4 wherein M comprises nickel, manganese, and cobalt.
6. The polycrystalline particulate of claim 5 wherein the transition metal oxide has the chemical formula Li1Ni0.6Mn0.2Co0.2O2.
7. The polycrystalline particulate of claim 5 wherein the average grain size of the transition metal oxide grains is about 0.5 µm and essentially all the depression depths are less than 0.25 µm.
8. The polycrystalline particulate of claim 5 wherein essentially all the depression depths are less than 0.1 µm.
9. The polycrystalline particulate of claim 4 wherein M comprises nickel and cobalt, and N
comprises aluminum.
comprises aluminum.
10. The polycrystalline particulate of claim 1 wherein the particles in the polycrystalline particulate comprise a coating layer wherein the chemical composition of the coating layer is different from that of the grains of transition metal oxide.
11. The polycrystalline particulate of claim 4 wherein the particles in the polycrystalline particulate comprise a coating layer wherein the chemical composition of the coating layer is Al2O3.
12. The polycrystalline particulate of claim 10 wherein the weight of the coating layer is less than or about 2 % of the weight of the polycrystalline particulate.
13. A lithium insertion cathode for a rechargeable lithium battery comprising the polycrystalline particulate of claim 4.
14. A rechargeable lithium battery comprising the lithium insertion cathode of claim 13.
15. A lithium insertion cathode for a rechargeable lithium battery comprising the polycrystalline particulate of claim 11.
16. A rechargeable lithium battery comprising the lithium insertion cathode electrode of claim 15.
17. A method of smoothing the surface of particles in a polycrystalline particulate, the polycrystalline particles comprising aggregates of crystalline grains of transition metal oxide wherein the transition metal oxide has the chemical formula A x M y N z O 2 wherein x, y and z are numbers with x >= 0, y >= 0.5, and z >= 0, A consists of one or more alkali metals, M consists of one or more first row transition metal elements, N comprises a metal element other than an alkali metal or a first row transition metal element, the average grain size of the transition metal oxide grains is in the range of 0.2 to 1 µm, and the average particle size of the polycrystalline particulate is in the range of 5 to 50 µm, the method comprising:
obtaining an amount of the polycrystalline particulate; and mechanofusing the polycrystalline particulate in a mechanofusion system for a sufficient time to smooth the surface of the particles such that essentially all the depression depths are less than 50% of the average grain size of the transition metal oxide.
obtaining an amount of the polycrystalline particulate; and mechanofusing the polycrystalline particulate in a mechanofusion system for a sufficient time to smooth the surface of the particles such that essentially all the depression depths are less than 50% of the average grain size of the transition metal oxide.
18. The method of claim 17 wherein the mechanofusing is performed for greater than 5 minutes.
19. The method of claim 17 wherein the mechanofusion system comprises a chamber, a rotating wall within the chamber, a scraper within the rotating wall, and a press-head within the rotating wall.
20. The method of claim 19 wherein the mechanofusing step comprises:
setting a gap of about 0.5 mm between the scraper and the rotating wall;
setting a gap of about 1.4 mm between the press-head and the rotating wall;
and rotating the rotating wall at about 1400 rpm.
setting a gap of about 0.5 mm between the scraper and the rotating wall;
setting a gap of about 1.4 mm between the press-head and the rotating wall;
and rotating the rotating wall at about 1400 rpm.
21. The method of claim 17 wherein:
the transition metal oxide is an insertion compound;
A comprises lithium;
0<= x<= 2;
y + z is about 1; and y > 0.8 * z.
the transition metal oxide is an insertion compound;
A comprises lithium;
0<= x<= 2;
y + z is about 1; and y > 0.8 * z.
22. A method of uniformly coating a polycrystalline particulate with a coating layer, the polycrystalline particles comprising aggregates of crystalline grains of transition metal oxide wherein the transition metal oxide has the chemical formula A x M y N z O2 wherein x, y and z are numbers with x >= 0, y >= 0.5, and z >= 0, A consists of one or more alkali metals, M consists of one or more first row transition metal elements, N comprises a metal element other than an alkali metal or a first row transition metal element, the average grain size of the transition metal oxide grains is in the range of 0.2 to 1 µm, the average particle size of the polycrystalline particulate is in the range of 5 to 50 and wherein the chemical composition of the coating layer is different from that of the grains of transition metal oxide, the method comprising:
obtaining an amount of the polycrystalline particulate;
smoothing the surface of particles in the polycrystalline particulate according to the method of claim 17;
adding an amount of coating precursor powder having an average particle size less than 1 µm to the smoothed polycrystalline particulate; and mechanofusing the polycrystalline particulate and the coating precursor powder in a mechanofusion system for a sufficient time to fuse the coating precursor powder to the surface of the particles, thereby forming the coating layer on the surface of the polycrystalline particulate.
obtaining an amount of the polycrystalline particulate;
smoothing the surface of particles in the polycrystalline particulate according to the method of claim 17;
adding an amount of coating precursor powder having an average particle size less than 1 µm to the smoothed polycrystalline particulate; and mechanofusing the polycrystalline particulate and the coating precursor powder in a mechanofusion system for a sufficient time to fuse the coating precursor powder to the surface of the particles, thereby forming the coating layer on the surface of the polycrystalline particulate.
23. The method of claim 22 wherein the amount of coating precursor powder is less than or about 2% of the weight of the polycrystalline particulate.
24. The method of claim 22 wherein the coating precursor powder is Al2O3 powder and the polycrystalline particulate comprises a coating layer of Al2O3.
25. A lithium insertion cathode for a rechargeable lithium battery comprising a polycrystalline particulate wherein the surfaces of the particles in the polycrystalline particulate have been smoothed according to the method of claim 17.
26. A rechargeable lithium battery comprising the lithium insertion cathode of claim 25.
27. A lithium insertion cathode for a rechargeable lithium battery comprising a polycrystalline particulate comprising a coating layer wherein the coating layer has been uniformly coated onto the surfaces of the particles in the polycrystalline particulate according to the method of claim 22.
28. A rechargeable lithium battery comprising the lithium insertion cathode of claim 27.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US201962824506P | 2019-03-27 | 2019-03-27 | |
| US62/824,506 | 2019-03-27 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA3069168A1 true CA3069168A1 (en) | 2020-05-18 |
Family
ID=70768715
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA3069168A Abandoned CA3069168A1 (en) | 2019-03-27 | 2020-01-22 | Polycrystalline particulates for rechargeable battery electrodes |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA3069168A1 (en) |
-
2020
- 2020-01-22 CA CA3069168A patent/CA3069168A1/en not_active Abandoned
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