Sintered cathodes and methods of forming same

Abstract

A sintered cathode includes a first surface, a second surface opposite the first surface, a sintered polycrystalline material, a thickness greater than or equal to 5 µm, and a porosity less than 35%. The polycrystalline material includes a plurality of crystal grains having a layered rock-salt structure. A crystal direction of the plurality of crystal grains is random relative to a first surface and a second surface. A method of forming a sintered cathode includes mixing lithium-containing particles and cobalt-containing particles to form a LCO precursor powder including a LT-LCO phase, dispersing the LCO precursor powder in a binder and a solvent to form a slurry, tape casting the slurry to form a green tape including the LT-LCO, and sintering the green tape to form a sintered cathode including a HT-LCO phase and a random grain texture.

Description

SINTERED CATHODES AND METHODS OF FORMING SAMECross Reference to Related Application

[0001] This application claims the benefit of priority under 35 U.S.C. §119 of U.S. Provisional Application Serial No. 63 / 603299, filed on November 28, 2023, the content of which is relied upon and incorporated herein by reference in its entirety.Field

[0002] The present specification generally relates to sintered cathodes and, in particular, to methods of forming sintered cathodes having improved average diffusivity.Technical Background

[0003] Lithium-ion battery technology that is based on liquid carbonate electrolytes and intercalation electrodes is a method to power small electronic devices, such as cellular telephones, laptop computers, and cordless power tools. Lithium ion batteries are also used in larger-scale applications, such as hybrid and all electric vehicles and to stabilize electric grids at local and national levels under periods of high demand. Even with the success of lithium ion batteries, there is still demand for batteries with greater energy density and improved rate performance. The average diffusivity of lithium in the cathode may influence rate performance of a battery.

[0004] Accordingly, there is a need to improve the average diffusivity of the cathodes.SUMMARY

[0005] According to a first aspect A 1 , a method of forming a sintered cathode may comprise : mixing lithium-containing particles and cobalt-containing particles to form a LCO precursor powder comprising a LT-LCO phase; dispersing the LCO precursor powder in a binder and a solvent to form a slurry; tape casting the slurry to form a green tape comprising the LT-LCO phase; and sintering the green tape to form a sintered cathode comprising a HT-LCO phase and a random grain texture.

[0006] A second aspect A2 includes the method according to the first aspect Al, wherein a mean particle size of the LCO precursor powder is greater than or equal to 0. 1 pm and less than or equal to 1 .5 pm.

[0007] A third aspect A3 includes the method according to the first aspect Al or the second aspect A2, wherein the lithium-containing particles comprise lithium carbonate, lithium hydroxide, lithium hydroxide monohydrate, lithium nitrate, or combinations thereof.

[0008] A fourth aspect A4 includes the method according to any of the first through third aspects A1-A3, wherein the cobalt-containing particles comprise cobalt (II) carbonate, cobalt (II) oxide, cobalt (II, III) oxide spinel, cobalt (II) hydroxide, or combinations thereof.

[0009] A fifth aspect A5 includes the method according to any of the first through fourth aspects A1-A4, wherein the mixing comprises at least one of grinding and milling the lithium- containing particles and the cobalt-containing particles.

[0010] A sixth aspect A6 includes the method according to any of the first through fifth aspects A1-A5, wherein a thickness of the green tape is greater than or equal to 7 pm and less than or equal to 200 pm.

[0011] A seventh aspect A7 includes the method according to any of the first through sixth aspects A1-A6, wherein the binder comprises polyvinyl butyral, acrylic polymers, polyvinyl alcohol, polypropylene carbonate, or combinations thereof.

[0012] An eighth aspect A8 includes the method according to any of the first through seventh aspects A1-A7, wherein the solvent comprises methylethyl ketone, toluene, methoxypropyl acetate, ethanol, butanol, isopropanol, cyclohexanone, or combinations thereof.

[0013] A ninth aspect A9 includes the method according to any of the first through eighth aspects A1-A8, wherein the slurry comprises greater than or equal to 40 wt% and less than or equal to 70 wt% of the LCO precursor powder, greater than or equal to 1.5 wt% and less than or equal to 10 wt% of the binder, and greater than or equal to 25 wt% and less than or equal to 55 wt% of the solvent.

[0014] A tenth aspect A10 includes the method according to any of the first through ninth aspects A1-A9, wherein the sintering comprises a continuous sintering process.

[0015] An eleventh aspect Al l includes the method according to any of the first through tenth aspects A1-A10, wherein the sintering comprises heating the green tape at a sintering temperature greater than or equal to 900 °C and less than or equal to 1100 °C.

[0016] A twelfth aspect A 12 includes the method according to any of the first through eleventh aspects Al-Al 1, wherein a thickness of the sintered cathode is greater than or equal to 5 pm and less than or equal to 125 pm.

[0017] A thirteenth aspect A13 includes the method according to any of the first through twelfth aspects A1-A12, wherein a porosity of the sintered cathode is less than 35%.

[0018] A fourteenth aspect A 14 includes a battery comprising: a sintered cathode formed according to any of the first through thirteenth aspects Al -Al 3; and an electrolyte region penetrating a porous region of the sintered cathode, wherein the sintered cathode is a substrate of the battery.

[0019] According to a fifteenth aspect A15, a sintered cathode may comprise: a first surface; a second surface opposite the first surface; a sintered polycrystalline material comprising a plurality of crystal grains having a layered rock-salt structure, wherein a crystal direction of the plurality of crystal grains is random relative to the first surface and the second surface; a thickness from the first surface to the second surface greater than or equal to 5 pm; and a porosity less than 35%.

[0020] A sixteenth aspect A16 includes the sintered cathode according to the fifteenth aspect A 15, wherein the sintered poly crystalline material comprises LCO.

[0021] A seventeenth aspect A17 includes the sintered cathode according to the fifteenth aspect A15 or sixteenth aspect A 16, wherein the thickness of the sintered cathode is less than or equal to 125 pm.

[0022] An eighteenth aspect A18 includes the sintered cathode according to any of the fifteenth through seventeenth aspects Al 5-Al 7, wherein the porosity of the sintered electrode is greater than or equal to 0.1%.

[0023] A nineteenth aspect A19 includes the sintered cathode according to any of the fifteenth through eighteenth aspects A15-A18, wherein a width of the sintered cathode isgreater than or equal to 4 cm and a length of the sintered cathode is greater than or equal to 10 cm.

[0024] A twentieth aspect A20 includes the sintered cathode according to any of the fifteenth through nineteenth aspects A15-A19, wherein an average diffusivity of the sintered cathode is greater than or equal to 0.02 pm2 / s.

[0025] Additional features and advantages of the sintered cathodes and methods of forming same described herein will be set forth in the detailed description which follows, and in part will be readily apparent to those skilled in the art from that description or recognized by practicing the embodiments described herein, including the detailed description which follows, the claims, as well as the appended drawings.

[0026] It is to be understood that both the foregoing general description and the following detailed description describe various embodiments and are intended to provide an overview or framework for understanding the nature and character of the claimed subject matter. The accompanying drawings are included to provide a further understanding of the various embodiments, and are incorporated into and constitute a part of this specification. The drawings illustrate the various embodiments described herein, and together with the description serve to explain the principles and operations of the claimed subject matter.BRIEF DESCRIPTION OF THE DRAWINGS

[0027] FIG. 1 is a flow chart of a method of forming a sintered cathode, according to one or more embodiments described herein;

[0028] FIG. 2 is a photograph of a continuous sintering process, according to one or more embodiments described herein;

[0029] FIG. 3 is a schematic illustration of a battery comprising a sintered cathode, according to one or more embodiments described herein;

[0030] FIG. 4 is a plot of particle size distributions of comparative materials and example materials used to form sintered cathodes, accordingly to one or more embodiments described herein;

[0031] FIG. 5 are X-ray diffraction (XRD) spectra (y-axis: intensity (units: arbitrary units (an)); x-axis: 20 (units: degrees)) of a comparative raw material, tape, and sintered cathode;

[0032] FIG. 6 are XRD spectra (y-axis: intensity (units: arbitrary units (an)); x-axis: 20 (units: degrees)) of example raw materials, tapes, and sintered cathodes, according to one or more embodiments described herein;

[0033] FIG. 7 are XRD spectra (y-axis: intensity (units: arbitrary units (an)); x-axis: 20 (units: degrees)) of example raw materials, tapes, and sintered cathodes, according to one or more embodiments described herein;

[0034] FIG. 8 is a plot of measured capacity on discharge (y-axis (in mAh / g)) versus current density (x-axis (in mA / cm2)) of comparative sintered cathodes and exemplary cathodes, according to one or more embodiments described herein; and

[0035] FIG. 9 is a plot of potential start of discharge (y-axis (in V)) versus current density (x-axis (in mA / cm2)) of comparative sintered cathodes and exemplary cathodes, according to one or more embodiments described herein.DETAILED DESCRIPTION

[0036] Reference will now be made in detail to various embodiments of methods of forming sintered cathodes having improved average diffusivity. According to some embodiments, a sintered cathode includes a first surface, a second surface opposite the first surface, a sintered polycrystalline material, a thickness from the first surface to the second surface greater than or equal to 5 pm and a porosity less than 35%. The polycrystalline material includes a plurality of crystal grains having a layered rock-salt structure. A crystal direction of the plurality of crystal grains is random relative to a first surface and a second surface.

[0037] In other embodiments, a method of forming a sintered cathode includes mixing lithium-containing particles and cobalt-containing particles to form a lithium cobaltite (LCO) precursor powder including a low-temperature LCO (LT-LCO) phase, dispersing the LCO precursor powder in a binder and a solvent to form a slurry, tape casting the slurry to form a green tape including the LT-LCO phase, and sintering the green tape to form a sintered cathode including a high-temperature LCO (HT-LCO) phase and a random grain texture.

[0038] Various embodiments of sintered cathodes and methods of forming same will be described herein with specific reference to the appended drawings.

[0039] Ranges may be expressed herein as from “about” one particular value, and / or to “about” another particular value. When such a range is expressed, another embodiment includes from the one particular value and / or to the other particular value. Similarly, when values are expressed as approximations, by use of the antecedent “about,” it will be understood that the particular value forms another embodiment. It will be further understood that the endpoints of each of the ranges are significant both in relation to the other endpoint, and independently of the other endpoint.

[0040] Directional terms as used herein - for example up, down, right, left, front, back, top, bottom - are made only with reference to the figures as drawn and are not intended to imply absolute orientation.

[0041] Unless otherwise expressly stated, it is in no way intended that any method set forth herein be construed as requiring that its steps be performed in a specific order, nor that with any apparatus specific orientations be required. Accordingly, where a method claim does not actually recite an order to be followed by its steps, or that any apparatus claim does not actually recite an order or orientation to individual components, or it is not otherwise specifically stated in the claims or description that the steps are to be limited to a specific order, or that a specific order or orientation to components of an apparatus is not recited, it is in no way intended that an order or orientation be inferred, in any respect. This holds for any possible non-express basis for interpretation, including: matters of logic with respect to arrangement of steps, operational flow, order of components, or orientation of components; plain meaning derived from grammatical organization or punctuation, and; the number or type of embodiments described in the specification.

[0042] As used herein, the singular forms “a,” “an” and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to “a” component includes aspects having two or more such components, unless the context clearly indicates otherwise.

[0043] The term “cathode,” as used herein, refers to a positively charged electrode. The term “electrode,” as used herein, refers to a conductor that is used to make contact with a nonmetallic part of a circuit.

[0044] The term “rock-salt structure,” as used herein, refers to a sodium chloride (NaCl) structure.

[0045] The term “crystal direction,” as used herein, refers to the orientation of a grain with the layered rock-salt structure with respect to the two major faces of the cathode.

[0046] The type of texture of the sintered cathode is quantified from intensity of XRD peaks, using Cu Ka radiation, from the surfaces of the materials. “I” is the intensity of the peaks associated with the family of crystallographic planes of the layered rock-salt structure. The parameter IRI is defined, for this purpose, based upon intensity of (104) and (003) peaks from surface XRD traces as:The parameter IR2 is defined, for this purpose, based on intensity of (110) and (104) peaks from surface XRD traces:

[0047] The term “random grain texture,” as used herein, means that IRI is greater than 0.20 or IR2 is greater than 0.10. The Examples section herein includes XRD data analysis that exemplifies determining IRI and IR2.

[0048] The term “average diffusivity,” as used herein, refers to how quickly ions move through a battery’s electrode materials and for the purposes of this invention, within the sintered cathode. Average diffusivity is determined by fitting of discharge capacity measured under constant current conditions as a function of discharge rate to a diffusion model that includes the ohmic resistance of the cell and the average diffusivity. The model used herein is taken from “Thermodynamic and Mass Transport Properties of “LiAl,” J. Electrochem. Soc., 126 (1979) 2258-2266. The local concentration of lithium is related to local potential using open circuit voltage data published in the technical literature for LCO such as by Karthikeyan et al., “Thermodynamic model development for lithium intercalation electrodes,” Journal of Power Sources, 185 (2008) 1398-1407 and Bouwman, “Lithium Intercalculation in preferentially oriented submicron LiCoCh films,” Thesis, University of Twente (2002).

[0049] The term “ohmic resistance,” as used herein, refers to the sum ohmic contributors to cell resistance including ion conduction in the electrolyte, the resistance of the current collector, electronic transport in the electrodes, and charge transfer resistances at the electrodeelectrolyte interfaces Measurement of the ohmic resistance by current interruption or pulsing is described in “Determination of the Kinetic Parameters of Mixed Conducting Electrodes and Applications to the System LnSb. " J. Electrochem. Soc., 124 (1977) 1569-1579.

[0050] The size of the particles are measured using a Microtrac S3500. The term “dlO,” as used herein, refers to the point on a particle size distribution curve below which 10% of the particles fall. The term “d50,” as used herein, refers to the point on a particle size distribution curve below which 50% of the particles fall. The term “d50 particle size” and “mean particle size” may be used interchangeably herein. The term “d90,” as used herein, refers to the point on a particle size distribution curve below which 90% of the particles fall.

[0051] The term “porosity,” as used herein, refers to a measure of the void spaces in a material. Porosity of sintered cathodes is determined by laser cutting a disk or other shape with a quantifiable area from a sintered ribbon. The disk or other shape is weighed and then the thickness measured such as with a laser gauge or from a cross-section view under an optical or scanning electron microscope. The porosity is readily computed according to the equation, POR=100(l-m / (AtpL)) where A is the area, t is the thickness, m is the mass, and PL is the lattice density. Lattice density for LCO is 5.04 g / cm3, see J.N. Reimers and J.R. Dahn, "Electrochemical and In Situ X-Ray Diffraction Studies of Lithium Intercalation in LixCoO2," J. Electrochem. Soc., 139 (1992) 2091-2097, DOI: 10.1149 / 1.2221184. It is understood that in computation of porosity by this method for other cathode compositions that its lattice density should be utilized.

[0052] As mentioned herein, there is a demand for lithium-ion batteries with improved rate performance, which is related to energy density. Two ways to increase energy density of a lithium-based battery are to use lithium metal as the anode and to minimize the amount of inactive materials. A cathode -supported battery architecture based upon a sintered cathode accomplishes both. The sintered cathode acts as a mechanical support on which other components of the battery are built including a solid electrolyte like lithium phosphooxynitride (LiPON) originally developed for thin-film micro-batteries. It also eliminates binder and carbon conductor material in the electrode . Energies densities for this architecture may exceed 1500 Wh / L.

[0053] Layered rock-salt materials like lithium cobaltite (LCO) and its relatives like lithium nickel manganese cobalt oxide (NMC) and lithium nickel cobalt aluminum oxide (NCA) that are used in conventional, foil-supported electrodes may also be sintered to make a cathodesupport on which to build a cathode-supported battery. In addition to energy density, a battery should also provide power while preserving as much of the stated energy density as possible and be capable of fast charging. This is the so-called rate performance of the battery. The electrochemical performance of the battery may be strongly influenced by the microstructure, specifically grain texture, of the sintered cathode.

[0054] A sintered cathode is made by first preparing a tape that can be sintered. Tape casting of cathode materials as inputs to a continuous sintering process typically starts with a powder of desired phase and composition, like lithium cobaltite (LCO). LCO has a layered rock-salt structure with lithium and cobalt residing on alternate planes of the rock-salt structure. Because of the layered crystal structure, particles cleave along the planes to give smaller particles with a plate-like morphology. The particles are said to exfoliate. The shearing action (i.e., exfoliation) of tape casting a slurry and consolidation normal to the carrier during drying may lead to parallel alignment of the plate-shaped cathode grains relative to a major plane of the tape. However, the parallel grain texture of the resulting sintered LCO cathode may have a detrimental impact on average diffusivity. Lithium diffuses relatively easily within the plane of the layered rock-salt structure; however, crossing between planes is slow as the path is blocked by layers of cobalt or other transition metals due to the parallel alignment of the grains.

[0055] Disclosed herein are methods of forming sintered cathodes which may mitigate the aforementioned problems. Specifically, methods of forming sintered cathodes disclosed herein involve a reactive sintering process that mitigates the impact of exfoliation on grain texture of sintered cathodes with a layered rock-salt structure. In these methods, lithium and cobalt- containing raw materials are reacted to produce a LCO precursor powder comprising a low- temperature LCO (LT-LCO) phase, which does not have a layered rock-salt structure. As such, exfoliation during tape casting is mitigated or eliminated, resulting in a green tape having the LT-LCO phase. During sintering of the green tape to form a sintered cathode, the LT-LCO phase is converted to a high-temperature LCO (HT-LCO) phase having the layered rock-salt structure suitable for use in a battery. The sintered cathode has a random grain texture such that lithium is not blocked by layers of cobalt or other transition metals, leading to increased average diffusivity.

[0056] Referring now to FIG. 1, a method of forming a sintered cathode is shown at 150. The method 150 begins at block 152 with mixing lithium-containing particles and cobalt- containing particles to form a LCO precursor powder comprising a LT-LCO phase. “LT-LCO” refers to the polymorph of LCO that has a cubic structure (i.e., does not have a layered rocksalt structure). “HT-LCO” refers to the polymorph of LCO that has a layered rock-salt structure.

[0057] A relatively small particle size (e.g., mean particle size less than or equal to 1.5 pm) and shape of the particles (e.g., spherical) of the LCO precursor powder leads to random grain texture and decreased porosity in the resulting sintered cathode (e.g. less than 35%), thereby improving average diffusivity. Moreover, if a HT-LCO phase is present in the LCO precursor powder as described herein, a relatively smaller particle size helps to mitigate exfoliation during tape casting. Additionally, a mean particle size greater than or equal to 0. 1 pm and less than or equal to 1.5 pm may allow the particles to be dispersible into a slurry for tape casting and sintering to form a sintered cathode. As such, grinding of the particles may not be necessary, such grinding potentially inducing exfoliation if a layered rock-salt phase is present.

[0058] In embodiments, a mean particle size of the LCO precursor powder may be greater than or equal to 0. 1 pm and less than or equal to 1.5 pm. In embodiments, the mean particle size of LCO precursor powder may be greater than or equal to 0. 1 pm, greater than or equal to 0.3 pm, or even greater than or equal to 0.5 pm. In embodiments, the mean particle size of the LCO precursor powder may be less than or equal to 1.5 pm, less than or equal to 1.3 pm, or even less than or equal to 1.0 pm. In embodiments, the mean particle size of LCO precursor powder may be greater than or equal to 0. 1 pm and less than or equal to 1.5 pm, greater than or equal to 0.1 pm and less than or equal to 1.3 pm, greater than or equal to 0.1 pm and less than or equal to 1.0 pm, greaterthan orequal to 0.3 pm and less than or equal to 1.5 pm, greater than or equal to 0.3 pm and less than or equal to 1.3 pm, greater than or equal to 0.3 pm and less than or equal to 1.0 pm, greater than or equal to 0.5 pm and less than or equal to 1.5 pm, greater than or equal to 0.5 pm and less than or equal to 1.3 pm, or even greater than or equal to 0.5 pm and less than or equal to 1.0 pm, or any and all sub-ranges formed from any of these endpoints.

[0059] In embodiments, the lithium-containing particles may comprise lithium carbonate, lithium hydroxide, lithium hydroxide monohydrate, lithium nitrate, or combinations thereof.In embodiments, the cobalt-containing particles may comprise cobalt (II) carbonate, cobalt (II) oxide, cobalt (II, III) oxide spinel, cobalt (II) hydroxide, or combinations thereof.

[0060] In embodiments, the mixing of block 152 may comprise at least one of grinding and milling the lithium -containing particles and the cobalt-containing particles. Grinding may ensure that the resulting LCO precursor powder has the desired mean particle size. Regarding milling, the lithium-containing and cobalt-containing particles react to produce the LCO precursor powder, which may include both LT-LCO and HT-LCO phases. Milling may ensure that the lithium-containing particles and cobalt-containing particles are thoroughly mixed such that the reaction favors the formation of a LT-LCO phase. If an HT-LCO phase is present in the LCO precursor powder, the amount of HT-LCO should be limited so as to avoid exfoliation. Milling also helps to break of agglomerates of particles.

[0061] In embodiments, the mixing may be followed by reaction of the mixed lithium- containing particles and the cobalt-containing particles at a temperature greater than or equal to 450 °C and less than or equal to 600 °C for a time period greater than or equal to 1 hour and less than or equal to 24 hours under a dry (e.g., less than 5 ppm H2O) and oxidizing atmosphere (e.g., 20% oxygen) to form the LCO precursor powder or prepare the powder for tape casting.

[0062] Referring back to FIG. 1, the method 150 continues at block 154 with dispersing the LCO precursor in a binder and a solvent to form a slurry. The slurry may be formed by dispersing the LCO precursor powder into the solvent and any additives using, for example, ball milling. The binder may be added in a second step with time provided for homogenization.

[0063] A sufficient amount of the LCO precursor powder (e.g., greater than or equal to 40 wt%) may be included in the slurry to ensure that the resulting sintered cathode has a desired thickness (e.g., greater than or equal to 5 pm) and porosity (e.g., less than 35%). The amount of the LCO precursor powder may be limited (e.g., less than or equal to 70%) to ensure enough binder is present to maintain mechanical integrity during tape casting and sintering. In embodiments, the slurry may comprise greater than or equal to 40 wt% and less than or equal to 70 wt% of the LCO precursor powder. In embodiments, the amount of the LCO precursor powder in the slurry may be greater than or equal to 40 wt%, greater than or equal to 45 wt%, or even greater than or equal to 50 wt%. In embodiments, the amount of the LCO precursor powder in the slurry may be less than or equal to 70 wt%, less than or equal to 65 wt%, or even less than or equal to 60 wt%. In embodiments, the amount of the LCO precursor powder in theslurry may be greater than or equal to 40 wt% and less than or equal to 70 wt%, greater than or equal to 40 wt% and less than or equal to 65 wt%, greater than or equal to 40 wt% and less than or equal to 60 wt%, greater than or equal to 45 wt% and less than or equal to 70 wt%, greater than or equal to 45 wt% and less than or equal to 65 wt%, greater than or equal to 45 wt% and less than or equal to 60 wt%, greater than or equal to 50 wt% and less than or equal to 70 wt%, greater than or equal to 50 wt% and less than or equal to 65 wt%, or even greater than or equal to 50 wt% and less than or equal to 60 wt%, or any and all sub-ranges formed from any of these endpoints.

[0064] In embodiments, the binder may comprise polyvinyl butyral, acrylic polymers, polyvinyl alcohol, polypropylene carbonate, or combinations thereof.

[0065] A sufficient amount of binder (e.g., greater than or equal to 1.5 wt%) may be included in the slurry to ensure mechanical integrity is maintained during tape casting and sintering. The amount of binder may be limited (e.g., less than or equal to 10 wt%) to ensure a sufficient amount of LCO precursor is present to form a sintered cathode having desirable properties (e.g., a thickness greater than or equal to 5 pm and a porosity less than 35%). In embodiments, the slurry may comprise greater than or equal to 1.5 wt% and less than or equal to 10 wt% of the binder. In embodiments, the amount of the binder in the slurry may be greater than or equal to 1.5 wt% or even greater than or equal to 2 wt%. In embodiments, the amount of the binder in the slurry may be less than or equal to 10 wt%, less than or equal to 7 wt%, less than or equal to 5 wt%, or even less than or equal to 3 wt%. In embodiments, the amount of the binder in the slurry may be greater than or equal to 1.5 wt% and less than or equal to 10 wt%, greater than or equal to 1.5 wt% and less than or equal to 7 wt%, greater than or equal to 1.5 wt% and less than or equal to 5 wt%, greater than or equal to 1.5 wt% and less than or equal to 3 wt%, greater than or equal to 2 wt% and less than or equal to 10 wt%, greater than or equal to 2 wt% and less than or equal to 7 wt%, greater than or equal to 2 wt% and less than or equal to 5 wt%, or even greater than or equal to 2 wt% and less than or equal to 3 wt%, or any and all subranges formed from any of these endpoints.

[0066] In embodiments, the solvent may comprise methylethyl ketone, toluene, methoxypropyl acetate, ethanol, butanol, isopropanol, cyclohexanone, or combinations thereof.

[0067] In embodiments, the slurry may comprise greater than or equal to 25 wt% and less than or equal to 55 wt% of the solvent. In embodiments, the amount of the solvent in the slurrymay be greater than 25 wt%, greater than or equal to 30 wt%, or even greater than or equal to 35 wt%. In embodiments, the amount of the solvent in the slurry may be less than or equal to 55 wt%, less than or equal to 50 wt%, or even less than or equal to 45 wt%. In embodiments, the amount of the solvent in the slurry may be greater than or equal to 25 wt% and less than or equal to 55 wt%, greater than or equal to 25 wt% and less than or equal to 50 wt%, greater than or equal to 25 wt% and less than or equal to 45 wt%, greater than or equal to 30 wt% and less than or equal to 55 wt%, greater than or equal to 30 wt% and less than or equal to 50 wt%, greater than or equal to 30 wt% and less than or equal to 45 wt%, greater than or equal to 35 wt% and less than or equal to 55 wt%, greater than or equal to 35 wt% and less than or equal to 50 wt%, or even greater than or equal to 35 wt% and less than or equal to 45 wt%, or any and all sub-ranges formed from any of these endpoints.

[0068] The slurry may further include additives, such as a dispersant and a plasticizer.

[0069] In embodiments, the dispersant may comprise fish oil, polyester-polyamines (e.g., Hypermer KD-1), polysorbates (e.g., Tween), or combinations thereof. In embodiments, In embodiments, the amount of the dispersant in the slurry may be greater than or equal to 0.1 wt% and less than or equal to 5 wt%, greater than or equal to 0. 1 wt% and less than or equal to 3 wt%, greater than or equal to 0. 1 wt% and less than or equal to 1 wt%, greater than or equal to 0.5 wt% and less than or equal to 5 wt%, greater than or equal to 0.5 wt% and less than or equal to 3 wt%, or even greater than or equal to 0.5 wt% and less than or equal to 1 wt%, or any and all sub-ranges formed from any of these endpoints.

[0070] In embodiments, the plasticizer may comprise dibutyl phthalate, dibutyl adipate, dibutyl maleate, and non-phthalates (e.g., polyoxyethylene, such as Pycal 94), or combinations thereof. In embodiments, the amount of the plasticizer in the slurry may be greater than or equal to 0.1 wt% and less than or equal to 5 wt%, greater than or equal to 0.1 wt% and less than or equal to 3 wt%, greater than or equal to 0. 1 wt% and less than or equal to 1 wt%, greater than or equal to 0.5 wt% and less than or equal to 5 wt%, greater than or equal to 0.5 wt% and less than or equal to 3 wt%, or even greater than or equal to 0.5 wt% and less than or equal to 1 wt%, or any and all sub-ranges formed from any of these endpoints.

[0071] Referring back to FIG. 1, the method 150 continues at block 156 with tape casting the slurry to form a green tape comprising the LT-LCO phase. As described herein, exfoliation during tape casting is mitigated or eliminated because the LCO precursor powder includes aLT-LCO phase, which does not have a layered rock-salt structure. The resulting green tape has the LT-LCO phase.

[0072] In embodiments, the slurries may be tape cast onto a carrier (e.g., a Mylar carrier with a silicon release layer) to form the green tape.

[0073] The green tape may shrink during sintering when forming the sintered cathode such that the thickness of the green tape is greater than the sintered cathode formed therefrom. As such, the thickness of the green tape may be adjusted to account for this shrinkage in forming a sintered cathode having a desired thickness. In embodiments, a thickness of the green tape may be greater than or equal to 7 pm and less than or equal to 200 pm. In embodiments, the thickness of the green tape may be greater than or equal to 7 pm, greater than or equal to 10 pm, greater than or equal to 15 pm, greater than or equal to 20 pm, or even greater than or equal to 25 pm. In embodiments, the thickness of the green tape may be less than or equal to 200 pm, less than or equal to 150 pm, less than or equal to 100 pm, or even less than or equal to 50 pm. In embodiments, a thickness of the green tape may be greater than or equal to 7 pm and less than or equal to 200 pm, greater than or equal to 7 pm and less than or equal to 150 pm, greater than or equal to 7 pm and less than or equal to 100 pm, greater than or equal to 7 pm and less than or equal to 50 pm, greater than or equal to 10 pm and less than or equal to 200 pm, greater than or equal to 10 pm and less than or equal to 150 pm, greater than or equal to 10 pm and less than or equal to 100 pm, greater than or equal to 10 pm and less than or equal to 50 pm, greater than or equal to 15 pm and less than or equal to 200 pm, greater than or equal to 15 pm and less than or equal to 150 pm, greater than or equal to 15 pm and less than or equal to 100 pm, greater than or equal to 15 pm and less than or equal to 50 pm, greater than or equal to 20 pm and less than or equal to 200 pm, greater than or equal to 20 pm and less than or equal to 150 pm, greater than or equal to 20 pm and less than or equal to 100 pm, greater than or equal to 20 pm and less than or equal to 50 pm, greater than or equal to 25 pm and less than or equal to 200 pm, greater than or equal to 25 pm and less than or equal to 150 pm, greater than or equal to 25 pm and less than or equal to 100 pm, or even greater than or equal to 25 pm and less than or equal to 50 pm, or any and all sub-ranges formed from any of these endpoints.

[0074] Referring back to FIG. 1, the method 150 continues at block 158 with sintering the green tape to form a sintered cathode comprising a HT-LCO phase and a random grain texture. As described herein, during sintering of the green tape to form the sintered cathode, the LT-LCO phase is converted to a HT-LCO phase having the layered rock-salt structure suitable for use in a battery. The sintered cathode has a random grain texture such that lithium is not blocked by layers of cobalt or other transition metals, leading to increased average diffusivity

[0075] In embodiments, the sintering comprises a continuous sintering process. Referring now to FIG. 2, in embodiments, the continuous sintering process may comprise roll-to-roll sintering. In roll-to-roll sintering, the green tape (not shown) is drawn from a first drum (not shown) into a furnace 202 to sinter the green tape and form sintered cathode 204. The sintered cathode 204 is then advanced toward a second drum 206 for winding.

[0076] In embodiments, the sintering may comprise heating the green tape at a sintering temperature. “Sintering temperature,” as used herein, refers to the temperature of the furnace to which the green tape is exposed. In embodiments, the sintering temperature may be greater than or equal to 900 °C and less than or equal to 1100 °C. In embodiments, the sintering temperature may be greater than or equal to 900 °C, greater than or equal to 950 °C, or even greater than or equal to 1000 °C. In embodiments, the sintering temperature may be less than or equal to 1100 °C. In embodiments, the sintering temperature may be greater than or equal to 900 °C and less than or equal to 1100 °C, greater than or equal to 950 °C and less than or equal to 1100 °C, or even greater than or equal to 1000 °C and less than or equal to 1100 °C, or any and all sub-ranges formed from any of these endpoints.

[0077] Referring now to FIG. 3, the sintered cathode 300 comprises a first surface 302, a second surface 304 opposite the first surface 302, and a sintered poly crystalline material 306. The sintered polycrystalline material 306 comprises a plurality of crystal grains having a layered rock-salt structure (e.g., a HT-LCO phase). In embodiments, the sintered poly crystalline material comprises LCO. The crystal direction of the plurality of crystal grains is random relative to the first surface 302 and the second surface 304 of the sintered cathode 300.

[0078] The continuous sintering process may allow for relatively thicker sintered cathodes (e.g., greater than or equal to 5 pm), thereby increasing the average diffusivity thereof. In embodiments, a thickness t of the sintered cathode 300 from the first surface 302 to the second surface 304 may be greater than or equal to 5 pm. In embodiments, the thickness t of the sintered cathode 300 may be greater than or equal to 5 pm and less than or equal to 125 pm. In embodiments, the thickness t of the sintered cathode 300 may be greater than or equal to 5qm, greater than or equal to 10 qm, greater than or equal to 15 qm. or even greater than or equal to 20 qm. In embodiments, the thickness t of the sintered cathode 300 may be less than or equal to 125 qm, less than or equal to 100 qm, less than or equal to 75 qm, or even less than or equal to 50 qm. In embodiments, the thickness t of the sintered cathode 300 may be greater than or equal to 5 qm and less than or equal to 125 qm, greater than or equal to 5 qm and less than or equal to 100 qm, greater than or equal to 5 qm and less than or equal to 75 qm, greater than or equal to 5 qm and less than or equal to 50 qm, greater than or equal to 10 qm and less than or equal to 125 qm, greater than or equal to 10 qm and less than or equal to 100 qm, greater than or equal to 10 qm and less than or equal to 75 qm, greater than or equal to 10 qm and less than or equal to 50 qm, greater than or equal to 15 qm and less than or equal to 125 qm, greater than or equal to 15 qm and less than or equal to 100 qm, greater than or equal to 15 qm and less than or equal to 75 qm, greater than or equal to 15 qm and less than or equal to 50 qm, greater than or equal to 20 qm and less than or equal to 125 qm, greater than or equal to 20 qm and less than or equal to 100 qm, greater than or equal to 20 qm and less than or equal to 75 qm, or even greater than or equal to 20 qm and less than or equal to 50 qm, or any and all sub-ranges formed from any of these endpoints.

[0079] In embodiments, a width of the sintered cathode 300 may be greater than or equal to 4 cm and a length of the sintered cathode may be greater than or equal to 10 cm. In embodiments, a width of the sintered cathode 300 may be greater than or equal to 4 cm, greater than or equal to 6 cm, greater than or equal to 8 cm, or even greater than or equal to 10 cm. In embodiments, a length of the sintered cathode greater than or equal to 10 cm, greater than or equal to 25 cm, greater than or equal to 50 cm, or even greater than or equal to 100 cm.

[0080] Decreasing a porosity of the sintered cathode 300 may help to increase the average diffusivity thereof. Accordingly, in embodiments, the sintered cathode 300 may have a porosity less than 35%. In embodiments, a porosity of the sintered cathode 300 may be greater than or equal to 0.1% and less than or equal to 35%. In embodiments, the porosity of the sintered cathode 300 may be greater than or equal to 0.1%, greater than or equal to 0.5%, greater than or equal to 3%, or even greater than or equal to 5%. In embodiments, the porosity of the sintered cathode 300 may be less than or equal to 35%, less than or equal to 25%, less than or equal to 15%, or even less than or equal to 5%. In embodiments, the porosity of the sintered cathode 300 may be greater than or equal to 0. 1% and less than or equal to 35%, greater than or equal to 0. 1% and less than or equal to 25%, greater than or equal to 0. 1% and less thanor equal to 15%, greater than or equal to 0.1% and less than or equal to 5%, greater than or equal to 0.5% and less than or equal to 35%, greater than or equal to 0.5% and less than or equal to 25%, greater than or equal to 0.5% and less than or equal to 15%, greater than or equal to 0.5% and less than or equal to 5%, greater than or equal to 1% and less than or equal to 35%, greater than or equal to 1% and less than or equal to 25%, greater than or equal to 1% and less than or equal to 15%, greater than or equal to 1% and less than or equal to 5%, greater than or equal to 3% and less than or equal to 35%, greater than or equal to 3% and less than or equal to 25%, greater than or equal to 3% and less than or equal to 15%, greater than or equal to 3% and less than or equal to 5%, greater than or equal to 5% and less than or equal to 35%, greater than or equal to 5% and less than or equal to 25%, or even greater than or equal to 5% and less than or equal to 15%, or any and all sub-ranges formed from any of these endpoints.

[0081] In embodiments, an average diffusivity of the sintered cathode may be greater than or equal to 0.02 pm2 / s, greater than or equal to 0.03 pm2 / s, or even greater than or equal to 0.04 pm2 / s.

[0082] Referring back to FIG. 3, the sintered cathode 300 may be included in a battery 310. The battery 310 may comprise the sintered cathode 300, an electrolyte region 312 penetrating a porous region of the sintered cathode 300, and an anode 314. The cathode 300 may be a substrate of the battery 310. The battery 310 may also include a first current collector 316 disposed on the second surface 304 of the battery 310. The first current collector 316 may comprise a cathode current collector made of a metal, such as aluminum. The battery 310 may include a second current collector 318 disposed on the anode 314. The second current collector 318 may comprise an anode current collector made of a metal, such as copper. The battery 310 may be encased in a protective coating 320, such as parylene.

[0083] Ohmic resistance of the battery 310 may be indicative of improved rate performance. In embodiments, an ohmic resistance of the battery 310 may greater than or equal to 0.5 Qcm2and less than or equal to 200 Qcm2. In embodiments, an ohmic resistance of the battery 310 may be greater than or equal to 0.5 Qcm2, greater than or equal to 1 Qcm2, greater than or equal to 5 Qcm2, greater than or equal to 10 Qcm2, or even greater than or equal to 25 Qcm2. In embodiments, the ohmic resistance of the battery 310 may be less than or equal to 200 Qcm2, less than or equal to 150 Qcm2, less than or equal to 100 Qcm2, or even less than or equal to 50 Qcm2. In embodiments, an ohmic resistance of the battery may greater than or equal to 0.5 Qcm2and less than or equal to 200 Qcm2, greater than or equal to 0.5 Qcm2and less than orequal to 150 Qcm2, greater than or equal to 0.5 Qcm2and less than or equal to 100 Qcm2, greater than or equal to 0.5 Qcm2and less than or equal to 50 Qcm2, greater than or equal to 1 Qcm2and less than or equal to 200 Qcm2, greater than or equal to 1 Qcm2and less than or equal to 150 Qcm2, greater than or equal to 1 Qcm2and less than or equal to 100 Qcm2, greater than or equal to 1 Qcm2and less than or equal to 50 Qcm2, greater than or equal to 5 Qcm2and less than or equal to 200 Qcm2, greater than or equal to 5 Qcm2and less than or equal to 150 Qcm2, greater than or equal to 5 Qcm2and less than or equal to 100 Qcm2, greater than or equal to 5 Qcm2and less than or equal to 50 Qcm2, greater than or equal to 10 Qcm2and less than or equal to 200 Qcm2, greater than or equal to 10 Qcm2and less than or equal to 150 Qcm2, greater than or equal to 10 Qcm2and less than or equal to 100 Qcm2, greater than or equal to 10 Qcm2and less than or equal to 50 Qcm2, greater than or equal to 25 Qcm2and less than or equal to 200 Qcm2, greater than or equal to 25 Qcm2and less than or equal to 150 Qcm2, greater than or equal to 25 Qcm2and less than or equal to 100 Qcm2, or even greater than or equal to 25 Qcm2and less than or equal to 50 Qcm2, or any and all sub-ranges formed from any of these endpoints.Examples

[0084] In order that various embodiments be more readily understood, reference is made to the following examples, which are intended to illustrate various embodiments of the sintered cathodes described herein.

[0085] Raw Materials

[0086] Table 1 lists and provides the attributes and properties of Comparative Raw Material CR1 and Example Raw Materials R1-R3.

[0087] Table 1Raw Material CR1 R1 R2 R3T. , . , , . Lithium Cobalt (II) Cobalt oxideLithium cobaltite, , , . ,Composition carbonate, carbonate, spinel,Li2CO3CoCOs CO3O4Alf* AGS T*Source NEI Corporation Rockwood Alfa Aesar, 99%99 ?0 / ’Li2O (%) 14.5 39.9Co3O4(%) 79.3 - 61.1 99.5 dw (pm) 7.3 3.0 3.0 3.0 d50(pm) 13.3 216.0 15.2 5.4 dgo (pm) 23.2 792.0 29.3 9.0

[0088] Table 2 lists the formulations of Example Mixed Raw Materials MR1 and MR2. Example Mixed Raw Materials MR1 and MR2 were formed by reacting the raw materials in alumina crucibles with approximately 2 liters (L) volume in a furnace with atmosphere control. The charge of powders into the crucibles was about 125 g when cobalt (II) carbonate was used as a reactant and about 300 grams (g) when cobalt spinel was the source of cobalt. Air was flowed into the furnace at a rate of 400 milliliters / minute (mL / min) to provide oxygen for oxidation of cobalt and to sweep away carbon dioxide. The change in weight of the product was monitored and was consistent with release of carbon dioxide and oxidation of cobalt to a valence of 3+. The particle sizes and the phases gauged by x-ray diffraction (XRD) of Example Mixed Raw Materials MR1 and MR2 are shown in Table 2. As shown, the Example Mixed Raw Materials MR1 and MR2 both included LT-LCO and HT-LCO phases, with Example Mixed Raw Material MR2 including more LT-LCO than HT-LCO, as described in more detail below.

[0089] Table 2Mixed Raw Materials MR1 MR2R1 (wt%) 42.6 31.5R2 (wt%) 57.4R3 (wt%) 68.5Reaction ConditionsReaction temperature (°C) 500 550Reaction time (h) 6 6Weight loss (%) 38.5 16.9PhasesPhases by XRD HT-LCO > LT-LCO LT-LCO > HT-LCO

[0090] Milling

[0091] Comparative Raw Material CR1 and Example Mixed Raw Materials MR1 and MR2 were simultaneously ground and mixed in an attrition mill from Union Process. Milling was conducted using a 1 L tank fdled with 2600 g of stabilized zirconia milling media measuring 1 millimeters (mm) in diameter and 420 g of isopropyl alcohol. The charge of inorganics into the mill was nominally 79 cm3. Milling was conducted for 3 hours (h) at a speed of 2000 revolutions per minute (rpm). The media and charge were dried together and then separated using a metal sieve screen. Particle sizes of the resulting Comparative Milled Material CM1 and Example Mixed Milled Materials MM1 and MM2 are shown in Table 3. The particle size distributions of Comparative Raw Material CR1, Comparative Milled Material CM1, Example Mixed Raw Materials MR1 and MR2, and Example Mixed Milled Materials MM1 and MM2, as measured by laser light scattering is shown in FIG. 4.

[0092] Table 3Milled materials CM1 MM1 MM2Raw material CR2 MR1 MR2 dio (pm) 0.3 0.2 0.2 d5o (pm) 0.5 0.3 0.3 doo (pm) 1.1 0.4 0.5

[0093] As shown in Table 2, the mean particle sizes (i.e., dso) of Mixed Raw Materials MR1 and MR2 were 0.6 micrometeres (pm) and 1.2 pm, respectively, which were smaller than the 13.3 pm mean particle size of Comparative Raw Material CR1. As such, grinding of the particles of Mixed Raw Materials MR1 and MR2 may not be necessary prior to tape casting, such grinding potentially inducing exfoliation if a layered rock-salt phase is present.

[0094] As shown by a comparison between Tables 2 and 3, the mean particle sizes of Example Mixed Raw Materials MR1 and MR2 showed a relatively small reduction in forming Example Mixed Milled Materials MM1 and MM2. The mean particle size of Comparative Raw Material CR1 was reduced from 13.3 pm to 0.5 pm in Comparative Milled Material CM1, which was similar to the mean particle size of Example Mixed Raw Materials MR1.

[0095] Tape Casting

[0096] Comparative Milled Material CM1, Example Mixed Raw Materials MR1 and MR2, and Example Mixed Milled Materials MM1 and MM2 were tape cast. The slurry formulations for Comparative Tape CT1, Example Raw Tapes RT1 and RT2, and Example Milled Tapes MT1 and MT2 are shown in Table 4, in weight percentages. The slurries were prepared by first dispersing the powders into a mixture of the solvent and additives using ball mill. Binder was added in a second step with time provided for homogenization. The slurries were cast onto a Mylar carrier coated with a silicone release layer at a speed of 50.8 centimeteres / minute (cm / min). The thicknesses of the resulting green tapes are shown in Table 4.

[0097] Table 4Green Tapes CT1 RT1 MT1 RT2 MT2CM1 59.74 . . . .MR1 59.81 MM149.66MR2 62.93 MM2 52.43 Binder (polyvinyl butyral 2.75 2.75 2.25 2.92 2.41 (Butvar B-76)) Solvent24.50 24.57 32.23 22.10 30.10 (methylethyl ketone) Solvent (cyclohexanone) 0.89 0.79 0.72 0.86 0.71 Solvent10.50 10.53 13.81 9.47 12.91 (toluene) Dispersant0.82 0.74 0.67 0.86 0.72 (Hypermer KD-1) Plasticizer0.82 0.82 0.67 0.87 0.72 (dibutyl phthalate) Thickness (pm) 37 36 35 38 34

[0098] Sintering

[0099] Comparative Tape CT1, Example Raw Tapes RT1 and RT2, and Example Milled Tapes MT1 and MT2 were sintered at a temperature of 1090 °C. During processing, the tapes were fed through a binder bum-out zone and then into a furnace for sintering at pull speeds ranging between 2.5 and 5 inches / minute (in / min) (i.e., between 1.1 and 2.2 millimeters / second (mm / s)) to produce Comparative Sintered Cathode CC1 (from Comparative Tape CT1), Example Raw Sintered Cathodes RC1 and RC2 (from Example Raw Tapes RT1 and RT2, respectively), and Example Milled Sintered Cathodes MCI and MC2 (from Example Milled Tapes MT1 and MT2, respectively).

[0100] XRD Data Analysis

[0101] FIGS. 5-7 include the XRD spectra of the comparative and example raw materials, milled materials, green tapes, and sintered cathodes described herein. FIG. 5 includes the spectra of Comparative Raw Material CR1, Comparative Tape CT1, and Comparative Sintered Cathode CC1. FIG. 6 includes the spectra of Example Raw Material Rl, Example Raw Tape RT1, Example Raw Sintered Cathode RC1, Example Milled Tape MT1, and Example MilledSintered Cathode MCI. FIG. 7 includes the spectra of Example Raw Material R2, Example Raw Tape RT2, Example Raw Sintered Cathode RC2, Example Milled Tape MT2, and Example Milled Sintered Cathode MC2.

[0102] The type of texture imparted was quantified from intensity of XRD peaks from the surfaces of the materials. Note that neither IRI nor IR2 was calculated for example raw materials and tapes, as IRI and IR2 are defined based on peaks and peak intensities from the HT-LCO phase. The example raw materials and tapes described herein included substantial quantities of LT-LCO. Thus, the IRI and IR2 definitions did not apply. Hence, changes in peak intensities between the raw materials and the resulting tapes were used to judge exfoliation. Little to no change in peak intensity was indicative of an absence in exfoliation.

[0103] A number within parentheses (e.g., 003) included in the XRD spectra of FIGS. 5-7 refer to a family of planes. The number and the parentheses within which the number is (e.g., (003)) refers to a family of planes of a certain structure. This combination of parenthesis with three included numbers when used to refer to crystallographic planes are known as “Miller Indices.” The peaks are labeled for the purposes of the discussion herein. However, peaks identified with respect to one spectrum in a figure may apply to other spectrum in the figure.

[0104] Regarding the raw materials, referring to FIG. 6, the shoulder in the peak at about 19° in the Example Raw Material R1 spectrum was the (111) peak from a LT-LCO phase. Referring to the Example Raw Material R2 spectrum in FIG. 7, the (003) peak of a HT-LCO phase and the (111) peak of a LT-LCO phase were separated and of similar intensity, indicating similar relative amounts. It can also be seen in the Example Raw Material R2 spectrum that the (440) peak of a LT-LCO phase at 66.2° was larger than the (018) and (110) peaks from a HT-LCO phase at 65.3° and 66.23°, respectively. In contrast, all peaks in the Comparative Raw Material CR1 spectrum in FIG. 5 were assignable to a HT-LCO phase; no detectable LT- LCO was present.

[0105] Regarding the green tapes, the Comparative Tape CT1 spectrum in FIG. 5 showed a strong (003) peak of aHT-LCO phase. The (104) peak of aHT-LCO phase ofthe Comparative Tape CT1 spectrum was strongly suppressed relative to the Comparative Raw Material CR1 spectrum. This indicated that exfoliation of HT-LCO occurred during grinding and / or subsequent alignment during casting. The IR of Comparative Raw Material CR1 was 0.299 dropped to 0.017 in Comparative Tape CT1. In contrast, the spectra of example raw and milledtapes showed little to no indication of exfoliation. In FIG. 6, the XRD spectra of Example Raw Tape RT1 and Example Milled Tape RM1 had peak intensities similar to that of Example Raw Material Rl. The same may be seen in FIG. 7, for Example Raw Tape RT2 and Example Milled Tape RM2; their peak intensities were even more similar to Example Raw Material R2.

[0106] The IRI and IR2 values of Comparative Sintered Cathode CC1, Example Raw Sintered Cathodes RC1 and RC2, and Example Milled Sintered Cathodes MCI and MC2 are listed in Table 5.

[0107] Table 5Sintered Cathodes CCl RC1 MCI RC2 MC2IRI 0.001 0.216 0.242 0.295 0.275IR2 0.001 0.164 0.135 0.166 0.176

[0108] Regarding the sintered cathodes, the (003) peak of a HT-LCO phase of Comparative Sintered Cathode CC1 intensified after sintering, as shown in FIG. 5 The (104) peak of a HT- LCO phase of the Comparative Sintered Cathode CC1 was perceptibly less than in Comparative Tape CT1, and IR drops from 0.016 to 0.001. The example sintered cathodes had random grain textures. The XRD spectra for Example Raw Sintered Cathode RC1 and Example Raw Milled Cathode MCI shown in FIG. 6 had intense and well-developed (104) peaks. The intensity of the (104) peak on a relative basis was comparable to Comparative Raw Material CR1 shown in FIG. 5. IRI and IR2 values for Example Raw Sintered Cathode RC1 and Example Raw Milled Cathode MCI were both above 0.20 and 0.10, respectively, and reflective of a random grain texture. The same statements apply to as shown in Example Raw Sintered Cathode RC2 and Example Raw Milled Cathode MC2 their respective XRD spectra in FIG. 7.

[0109] As exemplified by the XRD analysis, the methods described herein produce a LCO precursor powder having a LT-LCO phase, a green tape having the LT-LCO phase, and a sintered cathode having a HT-LCO phase and a random grain texture.

[0110] Average Diffusivity and Rate Performance

[0111] Sintered cathode disks measuring 12.3 mm in diameter were harvested from Comparative Sintered Cathode CC1, Example Raw Sintered Cathodes RC1 and RC2, andExample Milled Sintered Cathodes MCI and MC2 by laser cutting. The weights and thicknesses of the cut cathodes are shown in Table 6.

[0112] Following handling for laser cutting, the cathode disks were heated to 800 °C for 10 min to pyrolyze the surfaces and to oxide the LCO. The carrier side of the cathodes was coated with a thin layer of gold by sputtering to provide a low resistance electric contact. The cathodes were built into 2032-type coin cells using components from MTI Corporation. The cell assemblies consisted of the following components in sequence of stacking: an anode cap; a wave spring, 1.5 mm in height in the uncompressed state; a 15 mm diameter and 0.5 mm thick stainless steel separator; a 14 mm diameter and 0.3 mm thick chip of lithium as the anode; a 17 mm diameter and 90% porous Whatman glass fiber separator (GF / A 1820-915); the sintered cathode disk coated with a gold metallization, uncoated side facing the separator; a 15 mm diameter and 0.3 mm thick stainless steel spacer; and a cathode cap. The electrolyte used in the cells was a 1 molar (M) solution of LiPFe in a 1: 1 mixture of ethylene carbonate and dimethyl carbonate solution. The electrolyte was applied to the fiber separator with an automated pipette in three 50 pL shots.

[0113] The coin cells were tested following a laddered charge-discharge cycling protocol to quantify the rate dependence of capacity. A sequence of progressively higher current densities were selected and three charge-discharge cycles were applied at each. Cut-off potentials versus Li in these examples were 3.0 and 4.3 volts (V). Charging was performed first in a constant current mode and then at a constant potential until the current attenuated to 10% of the constant current value. Discharge was conducted at the same current density as for charging. The third cycle was taken as representative of steady-state behavior and use in analysis.

[0114] Table 6Sintered Cathodes CC1 RC1 MCI RC2 MC2Weight (g) 0.0137 0.0149 0.0131 0.0171 0.0125 Thickness (ym) 22.8 24.8 21.8 28.4 20.8 Average diffusivity (ym2 / s) 0.0076 0.041 0.085 0.063 0.089 Ohmic resistance at start of657.0 97.0 48.1 73.0 51.5 discharge (Clem2) Statistical coefficient of0.98 >0.99 >0.99 >0.99 >0.99 determination, R2

[0115] Referring now to FIG. 8, capacities on discharge of the cells with the sintered cathodes were plotted as a function of current density. Capacity of the cells made from Example Raw Sintered Cathodes RC 1 and RC2 and Example Milled Sintered Cathodes MC 1 and MC2 were greater than the cell made from Comparative Sintered Cathode CC1 at all current densities. While not wishing to be bound by theory, the increased capacity of the cells is believed attributable to grain texture.

[0116] In particular, referring now to FIG. 9, the ohmic resistance was estimated from the dependence of the potential at the start of discharge on current density. The ohmic resistance of each cell was determined from a least-squares fit and is listed in Table 6. The ohmic resistances of cells with Example Raw Sintered Cathodes RC1 and RC2 and Example Milled Sintered Cathodes MCI and MC2 were lower by between a factor of 6.7 and 13.6 times than the cell with Comparative Sintered Cathode CC1. The cells were otherwise identical, so the sintered cathodes were identified as being responsible for the difference. The lower ohmic resistance of Example Raw Sintered Cathodes RC1 and RC2 and Example Milled Sintered Cathodes MCI and MC2 may be explained in terms of the random grain texture. As exemplified by Table 6 and FIG. 9, supply of lithium ions to or removal from the interface of the LCO cathode for charge transfer is more facile for a random grain texture as described herein than at the surfaces in cathodes made a comparative powder.

[0117] The other contributing factor to the greater capacity of cells was diffusivity. An average diffusivity within the cathode for each cell was estimated by fitting discharge capacities to a galvanostatic model. Average diffusivities of the cathodes for Example Raw Sintered Cathodes RC1 and RC2 and Example Milled Sintered Cathodes MCI and MC2, also provided in Table 6, were more than a factor of five-fold higher than the cell made from Comparative Sintered Cathode CC1. The strong (003) peak attributable to a HT-LCO phase of Comparative Sintered Cathode CC1 was unfavorable for lithium diffusion in the direction of current flow within the cell.

[0118] As indicated by the ohmic resistance and average diffusivity shown in FIGS. 8 and 9 and listed in Table 6, performance of a battery with a sintered cathode may be improved with a random grain texture. The faster transport kinetics, both ohmic such as through reduced charge transfer resistance and faster diffusivity, allow a relatively thicker sintered cathode to be utilized.

[0119] It will be apparent to those skilled in the art that various modifications and variations may be made to the embodiments described herein without departing from the spirit and scope of the claimed subject matter. Thus, it is intended that the specification cover the modifications and variations of the various embodiments described herein provided such modification and variations come within the scope of the appended claims and their equivalents.

Claims

CLAIMS1 . A method of forming a sintered cathode, the method comprising: mixing lithium-containing particles and cobalt-containing particles to form a LCO precursor powder comprising a LT-LCO phase; dispersing the LCO precursor powder in a binder and a solvent to form a slurry; tape casting the slurry to form a green tape comprising the LT-LCO phase; and sintering the green tape to form a sintered cathode comprising a HT-LCO phase and a random grain texture.

2. The method of claim 1, wherein a mean particle size of the LCO precursor powder is greater than or equal to 0. 1 pm and less than or equal to 1.5 pm.

3. The method of claim 1, wherein the lithium-containing particles comprise lithium carbonate, lithium hydroxide, lithium hydroxide monohydrate, lithium nitrate, or combinations thereof.

4. The method of claim 1, wherein the cobalt-containing particles comprise cobalt (II) carbonate, cobalt (II) oxide, cobalt (II, III) oxide spinel, cobalt (II) hydroxide, or combinations thereof.

5. The method of claim 1, wherein the mixing comprises at least one of grinding and milling the lithium-containing particles and the cobalt-containing particles.

6. The method of claim 1, wherein a thickness of the green tape is greater than or equal to 7 pm and less than or equal to 200 pm.

7. The method of claim 1, wherein the binder comprises polyvinyl butyral, acrylic polymers, polyvinyl alcohol, polypropylene carbonate, or combinations thereof.

8. The method of claim 1, wherein the solvent comprises methylethyl ketone, toluene, methoxypropyl acetate, ethanol, butanol, isopropanol, cyclohexanone, or combinations thereof.

9. The method of claim 1, wherein the slurry comprises greater than or equal to 40 wt% and less than or equal to 70 wt% of the LCO precursor powder, greater than or equal to 1.5 wt% and less than or equal to 10 wt% of the binder, and greater than or equal to 25 wt% and less than or equal to 55 wt% of the solvent.

10. The method of claim 1, wherein the sintering comprises a continuous sintering process.

11. The method of claim 1, wherein the sintering comprises heating the green tape at a sintering temperature greater than or equal to 900 °C and less than or equal to 1100 °C.

12. The method of claim 1, wherein a thickness of the sintered cathode is greater than or equal to 5 pm and less than or equal to 125 pm.

13. The method of claim 1, wherein a porosity of the sintered cathode is less than 35%.

14. A battery comprising: a sintered cathode formed according to the method of claim 1 ; and an electrolyte region penetrating a porous region of the sintered cathode, wherein the sintered cathode is a substrate of the battery.

15. A sintered cathode comprising: a first surface; a second surface opposite the first surface; a sintered polycrystalline material comprising a plurality of crystal grains having a layered rock-salt structure, wherein a crystal direction of the plurality of crystal grains is random relative to the first surface and the second surface; a thickness from the first surface to the second surface greater than or equal to 5 pm; and a porosity less than 35%.

16. The sintered cathode of claim 15, wherein the sintered poly crystalline material comprises LCO.

17. The sintered cathode of claim 15, wherein the thickness of the sintered cathode is less than or equal to 125 pm.

18. The sintered cathode of claim 15, wherein the porosity of the sintered electrode is greater than or equal to 0. 1%.

19. The sintered cathode of claim 15, wherein a width of the sintered cathode is greater than or equal to 4 cm and a length of the sintered cathode is greater than or equal to 10 cm.

20. The sintered cathode of claim 15, wherein an average diffusivity of the sintered cathode is greater than or equal to 0.02 pm2 / s.

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