WO2021250412A1 - Process for manufacturing doped lithium titanate - Google Patents

Process for manufacturing doped lithium titanate Download PDF

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Publication number
WO2021250412A1
WO2021250412A1 PCT/GB2021/051442 GB2021051442W WO2021250412A1 WO 2021250412 A1 WO2021250412 A1 WO 2021250412A1 GB 2021051442 W GB2021051442 W GB 2021051442W WO 2021250412 A1 WO2021250412 A1 WO 2021250412A1
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source
lithium
dopant
lanthanum
cerium
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PCT/GB2021/051442
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French (fr)
Inventor
Christopher R. HAWKINS
James Stevens
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Johnson Matthey Public Limited Company
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Publication of WO2021250412A1 publication Critical patent/WO2021250412A1/en

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/04—Processes of manufacture in general
    • H01M4/0471—Processes of manufacture in general involving thermal treatment, e.g. firing, sintering, backing particulate active material, thermal decomposition, pyrolysis
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01G—COMPOUNDS CONTAINING METALS NOT COVERED BY SUBCLASSES C01D OR C01F
    • C01G23/00—Compounds of titanium
    • C01G23/003—Titanates
    • C01G23/005—Alkali titanates
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/131—Electrodes based on mixed oxides or hydroxides, or on mixtures of oxides or hydroxides, e.g. LiCoOx
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/139—Processes of manufacture
    • H01M4/1391—Processes of manufacture of electrodes based on mixed oxides or hydroxides, or on mixtures of oxides or hydroxides, e.g. LiCoOx
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/485—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of mixed oxides or hydroxides for inserting or intercalating light metals, e.g. LiTi2O4 or LiTi2OxFy
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2002/00—Crystal-structural characteristics
    • C01P2002/50—Solid solutions
    • C01P2002/52—Solid solutions containing elements as dopants
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2002/00—Crystal-structural characteristics
    • C01P2002/70—Crystal-structural characteristics defined by measured X-ray, neutron or electron diffraction data
    • C01P2002/72—Crystal-structural characteristics defined by measured X-ray, neutron or electron diffraction data by d-values or two theta-values, e.g. as X-ray diagram
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2006/00—Physical properties of inorganic compounds
    • C01P2006/40—Electric properties
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
    • H01M2004/027—Negative electrodes
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H01M4/621—Binders
    • H01M4/622—Binders being polymers
    • H01M4/623—Binders being polymers fluorinated polymers
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H01M4/624—Electric conductive fillers
    • H01M4/625—Carbon or graphite
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/64—Carriers or collectors
    • H01M4/66—Selection of materials
    • H01M4/661—Metal or alloys, e.g. alloy coatings
    • 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
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Definitions

  • the present invention relates to a process for the manufacture of doped lithium titanate.
  • the doped lithium titanate prepared by the process finds use in anode materials in lithium secondary battery and related energy storage applications.
  • Lithium ion batteries are now ubiquitous in modern society, finding use not only in small, portable devices such as mobile phones and laptop computers but also increasingly in electric vehicles.
  • a lithium ion battery generally includes a graphite anode separated from a cathode by an electrolyte, through which lithium ions flow during charging and discharging cycles.
  • the cathode in a lithium ion battery may include a lithium transition metal oxide, for example a lithium nickel oxide, lithium cobalt oxide or lithium manganese oxide.
  • LiMnaCL lithium manganese spinels
  • olivine phosphate silicon-based materials
  • lithium titanate Li 4 TisOi 2
  • lithium titanate has shown promise due to its long lifetime, negligible structural change during lithium intercalation and de-intercalation, and increased safety. Despite this there have been challenges stemming from its lower specific capacity with respect to graphite and to its relatively poor electronic conductivity and Li-ion diffusion.
  • a first aspect of the invention is a method of making a doped lithium titanate material comprising: (a) preparing a liquid composition comprising a titanium source, a lithium source and a dopant source, wherein the dopant source comprises one or more of a lanthanum source and a cerium source;
  • This process is much simpler than existing manufacturing processes for lithium titanate materials. Furthermore, it has been found that through this process, a cerium- or lanthanum-doped lithium titanate material is prepared which shows an improvement in discharge capacity at higher discharge rates relative to materials prepared through alternative routes or containing alternative dopants.
  • the lanthanum-doped and cerium- doped materials made through the processes of the invention have been found to have discharge capacities in excess of 120 mAh/g at a 20C discharge rate, compared with capacities of around 90 mAh/g for known lithium titanate materials. This makes the material particularly suitable for use in batteries intended for high rate applications, such as in electric vehicles.
  • a second aspect of the invention is a doped lithium titanate material obtained or obtainable by a method according to the first aspect.
  • a third aspect of the invention is a negative active material comprising the material according to the second aspect.
  • a fourth aspect of the invention is a negative electrode comprising the negative active material according to the third aspect.
  • a fifth aspect of the invention is a method of making a spray-dried doped lithium titanate precursor material comprising:
  • Such a precursor material is useful as a precursor for the preparation of anode materials for lithium-ion batteries.
  • Figure 1 shows a plot of discharge capacity against discharge rate for various inventive and comparative materials.
  • Figure 2 shows a plot of discharge capacity against electrode loading at a 20C discharge rate for Comparative Example 8 and Example 3.
  • Figure 3 shows a plot of discharge capacity against electrode loading at a 30C discharge rate for Comparative Example 8 and Example 3.
  • Figure 4 shows a plot of discharge capacity against electrode loading at a 20C discharge rate for Comparative Example 8 and Example 4.
  • Figure 5 shows a plot of discharge capacity against electrode loading at a 30C discharge rate for Comparative Example 8 and Example 4.
  • Figure 6 shows an XRD pattern for a material prepared according to the processes of the invention.
  • Figure 7 shows an XRD pattern for a material prepared according to the processes of the invention.
  • a first aspect of the invention is a method of making a doped lithium titanate material comprising:
  • the first step of the method involves the preparation of a liquid composition comprising a titanium source, a lithium source and a dopant source.
  • the liquid composition consists of a titanium source, a lithium source and a dopant source in a liquid medium.
  • the liquid composition consists essentially of a titanium source, a lithium source and a dopant source in a liquid medium.
  • the liquid medium may be an aqueous medium, for example water.
  • the liquid composition is a slurry comprising a suspension of the titanium source in an aqueous solution, wherein at least a portion of the dopant source is dissolved in the aqueous solution.
  • the liquid composition is a slurry comprising a suspension of the titanium source in an aqueous solution, wherein the lithium source and dopant source are each at least partially dissolved in the aqueous solution. In some embodiments, the liquid composition is a slurry comprising a suspension of the titanium source in an aqueous solution, wherein the lithium source and dopant source are each fully dissolved in the aqueous solution.
  • the liquid composition may be a slurry comprising a solid component and a liquid component.
  • the solid component may comprise the titanium source (for example a particulate titanium source) and any undissolved portions of the lithium source and/or dopant source.
  • the liquid component may comprise an aqueous solution comprising the lithium source and dopant source dissolved in water.
  • the liquid composition may be prepared by mixing the titanium source, lithium source and dopant source into water, for example by adding the titanium source, lithium source and dopant source to a suitable quantity of water, in any order. Preparation of the liquid composition may comprise stirring, mixing or agitation of the mixture after the titanium source, lithium source and dopant source have been combined with the water.
  • the titanium source may be a titanium-containing compound, for example a titanium- containing inorganic compound.
  • the titanium source may be insoluble in water or have poor solubility in water such that it remains at least partially in suspension when added to the liquid composition.
  • the titanium source comprises titanium dioxide (titania).
  • the titanium source may comprise a particulate titanium source, such as particulate titanium dioxide.
  • soluble denotes a solubility of at least 5 g/100 ml_, for example at least 10 g/100 ml_ at 25 °C in the specified solvent.
  • insoluble denotes a solubility of less than 0.10 g/100 mL, for example less than 0.05 g/100 ml_, for example less than 0.02 g/100 mL at 25 °C in the specified solvent.
  • the titania may be in the form of nanoparticles (i.e. a particulate material with an average particles diameter less than 100 nm, for example less than 50 nm, for example less than 25 nm).
  • the slurry comprises from 5 to 25 wt% titanium source based on the total weight of the slurry, for example from 5 to 15 wt%, from 5 to 12 wt%, from 6 to 12 wt%, from 6 to 10 wt% or from 7 to 9 wt%.
  • the dopant source which is present in the liquid composition comprises one or more of a lanthanum source and a cerium source. In some embodiments, the dopant source comprises only one of a lanthanum source and a cerium source. In some embodiments, the dopant source comprises or consists of a lanthanum source. In some embodiments, the dopant source comprises or consists of a cerium source.
  • the dopant source is a dopant-containing compound, such as a dopant-containing inorganic compound.
  • the compound may be at least partially soluble in the liquid of the liquid composition such that the liquid composition contains dissolved dopant species.
  • the dopant-containing compound may be selected from oxides, hydroxides, carbonates, nitrates, acetates and hydrated forms thereof.
  • the dopant-containing compound is a dopant-containing acetate.
  • the dopant source is a cerium-containing compound, such as a cerium-containing inorganic compound. In some embodiments, the dopant source is a lanthanum-containing compound, such as a lanthanum-containing inorganic compound.
  • the dopant source comprises or consists of a lanthanum-containing compound, such as a lanthanum oxide, hydroxide, carbonate, nitrate, acetate or hydrated form thereof.
  • the dopant source comprises or consists of a cerium- containing compound, such as a cerium oxide, hydroxide, carbonate, nitrate, acetate or hydrated form thereof.
  • the liquid composition comprises or consists of one or more of dissolved lanthanum species and dissolved cerium species. In some embodiments, the liquid composition comprises only one of dissolved lanthanum species and dissolved cerium species. In some embodiments, the liquid composition comprises dissolved dopant species which consist of dissolved lanthanum species. In some embodiments, the liquid composition comprises dissolved dopant species which consist of dissolved cerium species.
  • the dissolved lanthanum species comprises or consists of La 3+ and the dissolved cerium species comprises or consists of Ce 3+ .
  • the aqueous solution comprises from 5 to 40 mM dissolved lanthanum species, for example from 5 to 20 mM, from 5 to 15 mM, from 6 to 15 mM, from 8 to 15 mM or from 10 to 15 mM dissolved lanthanum species.
  • the aqueous solution comprises from 5 to 20 mM La 3+ , for example from 5 to 15 mM, from 6 to 15 mM, from 8 to 15 mM or from 10 to 15 mM La 3+ .
  • the aqueous solution comprises from 5 to 40 mM dissolved cerium species, for example from 5 to 20 mM, from 5 to 15 mM, from 6 to 15 mM, from 8 to 15 mM or from 10 to 15 mM dissolved cerium species.
  • the aqueous solution comprises from 5 to 20 mM Ce 3+ , for example from 5 to 15 mM, from 6 to 15 mM, from 8 to 15 mM or from 10 to 15 mM Ce 3+ .
  • the dopant source consists of a lanthanum source.
  • the lanthanum source may comprise a lanthanum-containing compound.
  • the lanthanum-containing compound may be selected from a soluble or partially-soluble compound (e.g. salt) of lanthanum, or a hydrated form thereof.
  • the lanthanum-containing compound may be selected from lanthanum oxide (l_a2C>3), lanthanum hydroxide (La(OH)3), lanthanum carbonate (l_a2(CC>3)3), lanthanum acetate (La(OAc)3), lanthanum nitrate (La(NC>3)3) and hydrated forms thereof.
  • the dopant source consists of lanthanum acetate or a hydrated form thereof.
  • the dopant source consists of a cerium source.
  • the cerium source may comprise a cerium-containing compound.
  • the cerium-containing compound may be selected from a soluble or partially-soluble compound (e.g. salt) of cerium, or a hydrated form thereof.
  • the cerium-containing compound may be selected from cerium oxide (Ce2C>3), cerium hydroxide (Ce(OH)3), cerium carbonate (Ce2(CC>3)3), cerium acetate (Ce(OAc)3), cerium nitrate (Ce(NC>3)3) and hydrated forms thereof.
  • the dopant source consists of cerium acetate or a hydrated form thereof.
  • the dopant source comprises or consists of one or more of lanthanum acetate and cerium acetate. In some embodiments, the dopant source comprises or consists of lanthanum acetate. In some embodiments, the dopant source comprises or consists of cerium acetate.
  • the lithium source may comprise a lithium-containing compound, such as a lithium- containing inorganic compound.
  • the lithium-containing compound may be at least partially soluble in the liquid of the liquid composition, such that the liquid composition contains dissolved lithium species.
  • the lithium source comprises one or more of lithium acetate and lithium hydroxide.
  • the lithium source consists of one or more of lithium acetate and lithium hydroxide.
  • the lithium source consists of lithium acetate.
  • the lithium source consists of lithium hydroxide.
  • the liquid composition comprises a lithium source, for example a lithium-containing compound.
  • the liquid composition may comprise a single type of lithium-containing compound or two or more different types of lithium-containing compound.
  • the lithium- containing compound may be selected from a soluble or partially-soluble compound (e.g. salt) of lithium.
  • the lithium-containing compound is selected from lithium hydroxide (e.g. LiOH or UOH.H 2 O), lithium carbonate (U 2 CO 3 ), lithium acetate, lithium nitrate (UNO 3 ) and hydrated forms thereof.
  • the lithium- containing compound is selected from lithium hydroxide and lithium acetate.
  • the liquid composition comprises dissolved lithium species which provide a total concentration of Li + in the liquid composition of from 0.5 to 2.5 M, for example from 0.5 to 2 M, from 0.5 to 1.5 M, from 0.5 to 1.4 M, from 0.6 to 1.4 M, from 0.7 to 1.4 M, from 0.7 to 1.3 M, from 0.8 to 1.4 M, from 0.8 to 1.3 M, from 0.8 to 1.2 M or about 1.0 M.
  • step (a) comprises preparing a liquid composition comprising a titanium-containing compound, a lithium-containing compound and a dopant-containing compound, wherein the dopant-containing compound comprises one or more of a lanthanum-containing compound and a cerium-containing compound.
  • the liquid composition may be a slurry comprising an aqueous composition which contains dissolved lithium species and one or more of dissolved lanthanum species and dissolved cerium species, wherein the slurry comprises a suspended particulate titanium-containing compound.
  • step (a) comprises preparing a liquid composition comprising titanium dioxide, one or more of lithium hydroxide and lithium acetate, and one or more of lanthanum acetate and cerium acetate.
  • step (a) comprises preparing an aqueous slurry comprising titanium dioxide, one or more of lithium hydroxide and lithium acetate, and one or more of lanthanum acetate and cerium acetate, in an aqueous solution.
  • step (a) comprises preparing an aqueous slurry by combining the following components:
  • step (a) comprises first combining the water, the lithium acetate and one of the lanthanum acetate or the cerium acetate to produce a lithium/dopant aqueous solution, followed by combining the lithium/dopant aqueous solution with the titania to produce a slurry.
  • the titania may be in the form of particulate titania.
  • the titania may be in the form of nanoparticles (i.e. a particulate material with an average particles diameter less than 100 nm, for example less than 50 nm, for example less than 25 nm).
  • step (a) comprises mixing a solution comprising the dopant source with the titanium source and optionally stirring.
  • the slurry may be stirred, mixed or agitated for at least 10 mins, for example at least 15 mins, at least 20 mins, at least 25 mins, at least 30 mins, at least 45 mins or at least an hour to ensure dissolution and homogeneous dispersion of components.
  • the liquid composition is prepared by first dissolving the dopant source in water to form a dopant source solution, followed by the addition of the lithium source to the dopant source solution to form a dopant and lithium source solution, followed by mixing the dopant and lithium source solution with the titanium source.
  • Step (b) of the method of making a doped lithium titanate material comprises spray-drying the liquid composition to provide a spray-dried composition. Drying through spray-drying provides a material with improved high-rate discharge capacity.
  • the spray-dried composition is a particulate spray-dried composition.
  • spray drying is carried out with an inlet temperature of at least 120 °C, for example from 120 °C to 300 °C, from 120 °C to 250 °C, or from 200 to 250 °C.
  • One example of a suitable spray dryer is the Buchi B290.
  • annealing is performed at a temperature of at least 500 °C, for example at least 550 °C, at least 600 °C, at least 650 °C, at least 700 °C, at least 750 °C or at least 800 °C.
  • the annealing may be performed at a temperature of up to 1200 °C, for example up to 1150 °C, up to 1100 °C, up to 1050 °C, up to 1000 °C, up to 950 °C, up to 900 °C or up to 850 °C.
  • annealing is performed at a temperature of from 500 °C to 1200 °C, for example from 500 °C to 1150 °C, from 550 °C to 1150 °C, from 550 °C to 1100 °C, from 600 °C to 1000 °C, from 650 °C to 1000 °C, from 650 °C to 950 °C, from 700 °C to 900 °C or about 800 °C.
  • Any furnace which provides a stable temperature in the required range would be suitable for use in the annealing step.
  • One suitable furnace is the Carbolite muffle furnace GPC12/36.
  • Annealing may be carried out by increasing the temperature from ambient temperature up to a temperature Ti at a ramping rate Ri, followed by increasing the temperature from temperature Ti up to a temperature T2 at a ramping rate R2. The temperature may then be held at T2 for a predetermined annealing time ti.
  • Ti is from 300 °C to 700 °C, for example from 350 °C to 650 °C, from 400 °C to 600 °C, from 420 °C to 580 °C, from 450 °C to 550 °C or about 500 °C.
  • T2 is from 500 °C to 1200 °C, for example from 500 °C to 1150 °C, from 550 °C to 1150 °C, from 550 °C to 1100 °C, from 600 °C to 1000 °C, from 650 °C to 1000 °C, from 650 °C to 950 °C, from 700 °C to 900 °C or about 800 °C.
  • Ri may be from 2-8 °C/min, for example from 2.5-7.5 °C/min, from 3-7 °C/min, from 3.5-6.5 °C/min, from 4-6 °C/min, from 4.5-6.5 °C/min or about 5 °C/min.
  • R2 may be from 0.5-3.5 °C/min, for example from 1-3 °C/min, from 1.5-2.5 °C/min or about 2 °C/min. In some embodiments, R I >R2.
  • the annealing time ti may be from 2 to 15 hours, for example from 3 to 12 hours, from 5 to 10 hours, from 6 to 10 hours or about 8 hours.
  • the material may be left to cool.
  • the material may be left under ambient temperature to cool.
  • the furnace is allowed to cool under ambient conditions or may be allowed to cool under a controlled ramp rate.
  • step (c) annealing is performed at a temperature of at least 700 °C for at least 2 hours.
  • step (c) annealing is performed at a temperature of at least 770 °C, for example at least 775 °C, at least 780 °C, at least 785 °C, at least 790 °C, at least 795 °C or at least 800 °C. It has been found that at such annealing temperatures the effects of the invention in providing a material having a higher capacity at high discharge rates are more pronounced.
  • annealing is performed at a temperature of from 770 °C to 820 °C, for example from 780 °C to 820 °C, from 790 °C to 820 °C, from 790 °C to 810 °C, or at about 800 °C.
  • the annealing may include placing the spray-dried composition in a suitable container for annealing, for example an alumina crucible.
  • the method comprises deagglomerating the material after annealing, for example by grinding or milling.
  • the deagglomerating may include sieving to a suitable size fraction with optional additional milling or grinding of the oversize fraction.
  • the method may comprise further annealing steps after the annealing in step (c).
  • the doped lithium titanate material has the formula LLTis- x M x Oia wherein M is selected from one or more of La and Ce, and 0.02 £ x £ 0.1. In some embodiments, 0.05 £ x £ 0.1.
  • a second aspect of the invention is a doped lithium titanate material obtained or obtainable by a method according to the first aspect.
  • a third aspect of the invention is a negative active material comprising the material according to the second aspect.
  • a fourth aspect of the invention is a negative electrode comprising the negative active material according to the third aspect.
  • the negative electrode comprises the negative active material at an electrode loading of at least 4.8 mg/cm 2 , for example at least 4.9 mg/cm 2 , at least 5.0 mg/cm 2 , at least 5.2 mg/cm 2 or at least 5.4 mg/cm 2 .
  • the negative electrode comprises the negative active material at an electrode loading of from 4.8 mg/cm 2 to 7.0 mg/cm 2 , for example from 4.8 mg/cm 2 to 6.5 mg/cm 2 , from 4.8 mg/cm 2 to 6.0 mg/cm 2 or from 5.0 mg/cm 2 to 6.0 mg/cm 2 .
  • a fifth aspect of the invention is a method of making a spray-dried doped lithium titanate precursor material comprising:
  • a lithium solution was prepared by adding 200 mmol of a lithium salt to 200 ml_ of distilled water.
  • a lithium/dopant solution was prepared by first adding 2.5 mmol of dopant salt to 200 ml_ of distilled water to form a dopant solution, followed by adding 200 mmol of a lithium salt to the dopant solution.
  • the lithium solution (or lithium/dopant solution) was then added to the titania in the Schott bottle to form a suspension which was stirred for 1 hour with a magnetic stirrer.
  • the suspension was then spray dried using a Buchi B290 spray dryer using 220 °C inlet temperature, 100% aspirator, 50% pump and 600 L/h air flow. Spray-dried powder was collected in a collection vessel. 7 g of this powder was placed in an alumina boat and placed in a Carbolite retorted furnace. The temperature was increased from ambient to 500 °C at a rate of 5 °C/min, then increased from 500 °C to 800 °C at a rate of 2 °C/min. The sample was then held at 800 °C for 8 hours for annealing.
  • a solution was prepared by combining 4.48 mol of UOH.H2O with 1.5 L of distilled water, then 443 g of T1O2 was added to the solution along with 0.056 mol of La(0Ac) 3 .1.5H 2 0. This suspension was stirred for 1 h using a high shear mixer (disperser head). This suspension was transferred to an autoclave with further 0.5 L water and treated for 12 h at 160°C.
  • Example 4 The suspension was then spray dried using 220 °C inlet temperature, 100% aspirator, 50% pump and 600 L/h air flow. Spray-dried powder was collected in a collection vessel. 20 g of this powder was placed in an alumina boat and placed in a Carbolite retorted furnace. The temperature was increased from ambient to 760 °C at a rate of 5 °C/min. The sample was then held at 760 °C for 6 hours for annealing.
  • Example 4 Example 4
  • a sample was prepared in the same way as Example 3, except that in the Carbolite retorted furnace the temperature was increased from ambient to 800 °C at a rate of 5 °C/min. The sample was then held at 800 °C for 6 hours for annealing.
  • a sample was prepared by a method involving hydrothermal treatment in an autoclave followed by spray-drying and calcination in a similar way to Example 3, but without the presence of any dopant salt.
  • Inks were then prepared containing each of the above materials which were printed to form anodes for testing.
  • To prepare the ink 0.32 g of C65 carbon black, 3.36 g of active material from one of the above Examples or Comparative Examples, 3.2 g of 10% PVdF (Solvay 5300) in NMP binder solution and a further 2.72 g of N-methyl-2-pyrrolidone (NMP) were sequentially added to a 58 ml PVP pot.
  • a Thinky mixer was then used to thoroughly mix the ingredients.
  • a rectangular sheet of aluminium foil (20 x 25 cm) was cleaned with acetone followed by isopropanol.
  • the edge of the print blade was lubricated with a drop of NMP and printing was carried out at a wet thickness of 200 pm using a print speed of 20 mm/s.
  • the printed composition was dried in a vented oven at 120 °C for 12 hours.
  • All electrodes were roller calendared to achieve an electrode density of 2.0 g/cm 3 .
  • Coin cells (CR 2032) were prepared in half cell configuration vs Lithium metal (Alfa Aesar) with 85 pL of LP30 electrolyte. Electrochemical testing was performed at 23 °C by use of a Maccor4000 apparatus. The cells were cycled asymmetrically between 1 and 50 C, using constant current constant voltage in the voltage range of 1.25 V-2.5 V.
  • Figure 1 shows the results of the testing for some of the examples and comparative examples.
  • Example 1 maintains a capacity of over 120 mAh/g at a D- rate as high as 20C.
  • Example 2 also demonstrates a high capacity in excess of 80 mAh/g at 20C.
  • Comparative Examples demonstrate relatively high capacities at lower D-rates, these quickly drop off as D-rate increases.
  • Comparative Examples 2 and 4 demonstrate capacities above 140 mAh/g at a discharge rate of 10C, but at 20C the capacities have fallen to lower than 60 mAh/g, making them unsuitable for use in applications where a high capacity is required even at higher discharge rates.
  • Figure 2 provides a plot of discharge capacity against electrode loading for Example 3 and Comparative Example 8 at a constant D-rate of 20C. The results show that doping the material with La leads to an increased capacity at a high D-rate (20C), which is particularly evident at electrode loadings in excess of 5 mg/cm 2 .
  • Figure 3 provides a plot of discharge capacity against electrode loading for Example 3 and Comparative Example 8 at a constant D-rate of 30C. The results show that doping the material with La leads to an increased capacity at a high D-rate (30C), which is particularly evident at electrode loadings in excess of 5 mg/cm 2 .
  • Figure 4 provides a plot of discharge capacity against electrode loading for Example 4 and Comparative Example 8 at a constant D-rate of 20C. The results show that doping the material with La leads to a significantly increased capacity at a high D-rate (20C), which is particularly evident at electrode loadings in excess of 5 mg/cm 2 .
  • Figure 5 provides a plot of discharge capacity against electrode loading for Example 4 and Comparative Example 8 at a constant D-rate of 30C. The results show that doping the material with La leads to a significantly increased capacity at a high D-rate (30C), which is particularly evident at electrode loadings in excess of 5 mg/cm 2 .
  • the materials of the invention are therefore highly suitable for use in high-end applications requiring large capacity at a high discharge rate, such as Li-ion batteries for electric vehicles.
  • X-ray diffraction patterns were collected for the materials of Examples 1 and 2.
  • a Bruker D8 Advance diffractometer was used to collect the data, fitted with a 90-position sample changer for measurements in reflection mode.
  • the tube voltage was 40 kV and the current was 40 mA.
  • the measurements were taken at ambient temperature.
  • a Lynxeye-XE PSD detector was used with a 0.0125° Ni filter.
  • Bruker AXS Diffrac Eva V4 software (2010-2016) and the PDF-4+ database, release 2016, were used for phase identification.
  • Figure 6 shows the XRD pattern for the material of Example 1 , showing that it contains predominantly the lithium titanate spinel phase with minor amounts of a lanthanum titanate phase.
  • Figure 7 shows the XRD pattern for the material of Example 2, showing that it contains predominantly the lithium titanate spinel phase with minor amounts of a cerium oxide phase.

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Abstract

A process for making a doped lithium titanate material which includes preparing a liquid composition comprising a titanium source, a lithium source and a dopant source, wherein the dopant source comprises one or more of a lanthanum source and a cerium source, spray drying the liquid composition to provide a spray-dried composition; and annealing the spray-dried composition. The resultant doped lithium titanate may find use in a negative active material for use in negative electrodes.

Description

Process for manufacturing doped lithium titanate
Field of the Invention
The present invention relates to a process for the manufacture of doped lithium titanate. The doped lithium titanate prepared by the process finds use in anode materials in lithium secondary battery and related energy storage applications.
Background of the Invention
Lithium ion batteries are now ubiquitous in modern society, finding use not only in small, portable devices such as mobile phones and laptop computers but also increasingly in electric vehicles.
A lithium ion battery generally includes a graphite anode separated from a cathode by an electrolyte, through which lithium ions flow during charging and discharging cycles. The cathode in a lithium ion battery may include a lithium transition metal oxide, for example a lithium nickel oxide, lithium cobalt oxide or lithium manganese oxide.
The traditional use of a graphite anode in lithium anode batteries is associated with the potentially dangerous formation of lithium dendrites, and several promising alternative materials have been developed including lithium manganese spinels (LiMnaCL), olivine phosphate, silicon-based materials and lithium titanate (Li4TisOi2).
Of these, lithium titanate has shown promise due to its long lifetime, negligible structural change during lithium intercalation and de-intercalation, and increased safety. Despite this there have been challenges stemming from its lower specific capacity with respect to graphite and to its relatively poor electronic conductivity and Li-ion diffusion.
There is an ongoing need to provide improved anode materials for lithium ion batteries which offer enhanced performance, for example through improved electrochemical properties. In particular, there is a need for alternative processes which provide simple and efficient means to prepare lithium titanate materials having improved electrochemical properties.
Summary of the Invention
A first aspect of the invention is a method of making a doped lithium titanate material comprising: (a) preparing a liquid composition comprising a titanium source, a lithium source and a dopant source, wherein the dopant source comprises one or more of a lanthanum source and a cerium source;
(b) spray drying the liquid composition to provide a spray-dried composition; and
(c) annealing the spray-dried composition.
This process is much simpler than existing manufacturing processes for lithium titanate materials. Furthermore, it has been found that through this process, a cerium- or lanthanum-doped lithium titanate material is prepared which shows an improvement in discharge capacity at higher discharge rates relative to materials prepared through alternative routes or containing alternative dopants. The lanthanum-doped and cerium- doped materials made through the processes of the invention have been found to have discharge capacities in excess of 120 mAh/g at a 20C discharge rate, compared with capacities of around 90 mAh/g for known lithium titanate materials. This makes the material particularly suitable for use in batteries intended for high rate applications, such as in electric vehicles.
A second aspect of the invention is a doped lithium titanate material obtained or obtainable by a method according to the first aspect.
A third aspect of the invention is a negative active material comprising the material according to the second aspect.
A fourth aspect of the invention is a negative electrode comprising the negative active material according to the third aspect.
A fifth aspect of the invention is a method of making a spray-dried doped lithium titanate precursor material comprising:
(a) preparing a liquid composition comprising a titanium source, a lithium source and a dopant source, wherein the dopant source comprises one or more of a lanthanum source and a cerium source; and
(b) spray drying the liquid composition to provide a spray-dried composition.
Such a precursor material is useful as a precursor for the preparation of anode materials for lithium-ion batteries. Brief Description of the Drawings
Figure 1 shows a plot of discharge capacity against discharge rate for various inventive and comparative materials.
Figure 2 shows a plot of discharge capacity against electrode loading at a 20C discharge rate for Comparative Example 8 and Example 3.
Figure 3 shows a plot of discharge capacity against electrode loading at a 30C discharge rate for Comparative Example 8 and Example 3.
Figure 4 shows a plot of discharge capacity against electrode loading at a 20C discharge rate for Comparative Example 8 and Example 4.
Figure 5 shows a plot of discharge capacity against electrode loading at a 30C discharge rate for Comparative Example 8 and Example 4.
Figure 6 shows an XRD pattern for a material prepared according to the processes of the invention.
Figure 7 shows an XRD pattern for a material prepared according to the processes of the invention.
Detailed Description
Preferred and/or optional features of the invention will now be set out. Any aspect of the invention may be combined with any other aspect of the invention unless the context demands otherwise. Any of the preferred and/or optional features of any aspect may be combined, either singly or in combination, with any aspect of the invention unless the context demands otherwise.
A first aspect of the invention is a method of making a doped lithium titanate material comprising:
(a) preparing a liquid composition comprising a titanium source, a lithium source and a dopant source, wherein the dopant source comprises one or more of a lanthanum source and a cerium source;
(b) spray drying the liquid composition to provide a spray-dried composition; and
(c) annealing the spray-dried composition. The first step of the method involves the preparation of a liquid composition comprising a titanium source, a lithium source and a dopant source. In some embodiments, the liquid composition consists of a titanium source, a lithium source and a dopant source in a liquid medium. In some embodiments, the liquid composition consists essentially of a titanium source, a lithium source and a dopant source in a liquid medium. The liquid medium may be an aqueous medium, for example water. In some embodiments, the liquid composition is a slurry comprising a suspension of the titanium source in an aqueous solution, wherein at least a portion of the dopant source is dissolved in the aqueous solution. In some embodiments, the liquid composition is a slurry comprising a suspension of the titanium source in an aqueous solution, wherein the lithium source and dopant source are each at least partially dissolved in the aqueous solution. In some embodiments, the liquid composition is a slurry comprising a suspension of the titanium source in an aqueous solution, wherein the lithium source and dopant source are each fully dissolved in the aqueous solution.
The liquid composition may be a slurry comprising a solid component and a liquid component. The solid component may comprise the titanium source (for example a particulate titanium source) and any undissolved portions of the lithium source and/or dopant source. The liquid component may comprise an aqueous solution comprising the lithium source and dopant source dissolved in water.
The liquid composition may be prepared by mixing the titanium source, lithium source and dopant source into water, for example by adding the titanium source, lithium source and dopant source to a suitable quantity of water, in any order. Preparation of the liquid composition may comprise stirring, mixing or agitation of the mixture after the titanium source, lithium source and dopant source have been combined with the water.
The titanium source may be a titanium-containing compound, for example a titanium- containing inorganic compound. The titanium source may be insoluble in water or have poor solubility in water such that it remains at least partially in suspension when added to the liquid composition. In some embodiments, the titanium source comprises titanium dioxide (titania). The titanium source may comprise a particulate titanium source, such as particulate titanium dioxide.
Herein, “soluble” denotes a solubility of at least 5 g/100 ml_, for example at least 10 g/100 ml_ at 25 °C in the specified solvent. Herein, “insoluble” denotes a solubility of less than 0.10 g/100 mL, for example less than 0.05 g/100 ml_, for example less than 0.02 g/100 mL at 25 °C in the specified solvent.
The titania may be in the form of nanoparticles (i.e. a particulate material with an average particles diameter less than 100 nm, for example less than 50 nm, for example less than 25 nm).
In some embodiments, the slurry comprises from 5 to 25 wt% titanium source based on the total weight of the slurry, for example from 5 to 15 wt%, from 5 to 12 wt%, from 6 to 12 wt%, from 6 to 10 wt% or from 7 to 9 wt%.
The dopant source which is present in the liquid composition comprises one or more of a lanthanum source and a cerium source. In some embodiments, the dopant source comprises only one of a lanthanum source and a cerium source. In some embodiments, the dopant source comprises or consists of a lanthanum source. In some embodiments, the dopant source comprises or consists of a cerium source.
In some embodiments, the dopant source is a dopant-containing compound, such as a dopant-containing inorganic compound. The compound may be at least partially soluble in the liquid of the liquid composition such that the liquid composition contains dissolved dopant species. The dopant-containing compound may be selected from oxides, hydroxides, carbonates, nitrates, acetates and hydrated forms thereof. In some embodiments, the dopant-containing compound is a dopant-containing acetate.
In some embodiments, the dopant source is a cerium-containing compound, such as a cerium-containing inorganic compound. In some embodiments, the dopant source is a lanthanum-containing compound, such as a lanthanum-containing inorganic compound.
In some embodiments, the dopant source comprises or consists of a lanthanum-containing compound, such as a lanthanum oxide, hydroxide, carbonate, nitrate, acetate or hydrated form thereof. In some embodiments, the dopant source comprises or consists of a cerium- containing compound, such as a cerium oxide, hydroxide, carbonate, nitrate, acetate or hydrated form thereof.
In some embodiments, the liquid composition comprises or consists of one or more of dissolved lanthanum species and dissolved cerium species. In some embodiments, the liquid composition comprises only one of dissolved lanthanum species and dissolved cerium species. In some embodiments, the liquid composition comprises dissolved dopant species which consist of dissolved lanthanum species. In some embodiments, the liquid composition comprises dissolved dopant species which consist of dissolved cerium species.
In some embodiments, the dissolved lanthanum species comprises or consists of La3+ and the dissolved cerium species comprises or consists of Ce3+.
In some embodiments, the aqueous solution comprises from 5 to 40 mM dissolved lanthanum species, for example from 5 to 20 mM, from 5 to 15 mM, from 6 to 15 mM, from 8 to 15 mM or from 10 to 15 mM dissolved lanthanum species. In some embodiments, the aqueous solution comprises from 5 to 20 mM La3+, for example from 5 to 15 mM, from 6 to 15 mM, from 8 to 15 mM or from 10 to 15 mM La3+.
In some embodiments, the aqueous solution comprises from 5 to 40 mM dissolved cerium species, for example from 5 to 20 mM, from 5 to 15 mM, from 6 to 15 mM, from 8 to 15 mM or from 10 to 15 mM dissolved cerium species. In some embodiments, the aqueous solution comprises from 5 to 20 mM Ce3+, for example from 5 to 15 mM, from 6 to 15 mM, from 8 to 15 mM or from 10 to 15 mM Ce3+.
In some embodiments the dopant source consists of a lanthanum source. The lanthanum source may comprise a lanthanum-containing compound. The lanthanum-containing compound may be selected from a soluble or partially-soluble compound (e.g. salt) of lanthanum, or a hydrated form thereof. The lanthanum-containing compound may be selected from lanthanum oxide (l_a2C>3), lanthanum hydroxide (La(OH)3), lanthanum carbonate (l_a2(CC>3)3), lanthanum acetate (La(OAc)3), lanthanum nitrate (La(NC>3)3) and hydrated forms thereof. In some embodiments the dopant source consists of lanthanum acetate or a hydrated form thereof.
In some embodiments the dopant source consists of a cerium source. The cerium source may comprise a cerium-containing compound. The cerium-containing compound may be selected from a soluble or partially-soluble compound (e.g. salt) of cerium, or a hydrated form thereof. The cerium-containing compound may be selected from cerium oxide (Ce2C>3), cerium hydroxide (Ce(OH)3), cerium carbonate (Ce2(CC>3)3), cerium acetate (Ce(OAc)3), cerium nitrate (Ce(NC>3)3) and hydrated forms thereof. In some embodiments the dopant source consists of cerium acetate or a hydrated form thereof. In some embodiments, the dopant source comprises or consists of one or more of lanthanum acetate and cerium acetate. In some embodiments, the dopant source comprises or consists of lanthanum acetate. In some embodiments, the dopant source comprises or consists of cerium acetate.
The lithium source may comprise a lithium-containing compound, such as a lithium- containing inorganic compound. The lithium-containing compound may be at least partially soluble in the liquid of the liquid composition, such that the liquid composition contains dissolved lithium species. In some embodiments, the lithium source comprises one or more of lithium acetate and lithium hydroxide. In some embodiments, the lithium source consists of one or more of lithium acetate and lithium hydroxide. In some embodiments, the lithium source consists of lithium acetate. In some embodiments, the lithium source consists of lithium hydroxide.
The liquid composition comprises a lithium source, for example a lithium-containing compound. The liquid composition may comprise a single type of lithium-containing compound or two or more different types of lithium-containing compound. The lithium- containing compound may be selected from a soluble or partially-soluble compound (e.g. salt) of lithium. In some embodiments, the lithium-containing compound is selected from lithium hydroxide (e.g. LiOH or UOH.H2O), lithium carbonate (U2CO3), lithium acetate, lithium nitrate (UNO3) and hydrated forms thereof. In some embodiments the lithium- containing compound is selected from lithium hydroxide and lithium acetate.
In some embodiments, the liquid composition comprises dissolved lithium species which provide a total concentration of Li+ in the liquid composition of from 0.5 to 2.5 M, for example from 0.5 to 2 M, from 0.5 to 1.5 M, from 0.5 to 1.4 M, from 0.6 to 1.4 M, from 0.7 to 1.4 M, from 0.7 to 1.3 M, from 0.8 to 1.4 M, from 0.8 to 1.3 M, from 0.8 to 1.2 M or about 1.0 M.
In some embodiments, step (a) comprises preparing a liquid composition comprising a titanium-containing compound, a lithium-containing compound and a dopant-containing compound, wherein the dopant-containing compound comprises one or more of a lanthanum-containing compound and a cerium-containing compound. The liquid composition may be a slurry comprising an aqueous composition which contains dissolved lithium species and one or more of dissolved lanthanum species and dissolved cerium species, wherein the slurry comprises a suspended particulate titanium-containing compound. In some embodiments, step (a) comprises preparing a liquid composition comprising titanium dioxide, one or more of lithium hydroxide and lithium acetate, and one or more of lanthanum acetate and cerium acetate. In some embodiments, step (a) comprises preparing an aqueous slurry comprising titanium dioxide, one or more of lithium hydroxide and lithium acetate, and one or more of lanthanum acetate and cerium acetate, in an aqueous solution.
In some embodiments, step (a) comprises preparing an aqueous slurry by combining the following components:
(i) water;
(ii) titania (Ti02);
(iii) lithium acetate (LiOAc or CH3COOU); and
(iv) one of lanthanum acetate (La(OAc)3) and cerium acetate (Ce(OAc)3); and optionally stirring the mixture. In some embodiments step (a) comprises first combining the water, the lithium acetate and one of the lanthanum acetate or the cerium acetate to produce a lithium/dopant aqueous solution, followed by combining the lithium/dopant aqueous solution with the titania to produce a slurry. The titania may be in the form of particulate titania. The titania may be in the form of nanoparticles (i.e. a particulate material with an average particles diameter less than 100 nm, for example less than 50 nm, for example less than 25 nm).
In some embodiments, step (a) comprises mixing a solution comprising the dopant source with the titanium source and optionally stirring.
After combining the components to form the slurry, the slurry may be stirred, mixed or agitated for at least 10 mins, for example at least 15 mins, at least 20 mins, at least 25 mins, at least 30 mins, at least 45 mins or at least an hour to ensure dissolution and homogeneous dispersion of components.
In some embodiments, the liquid composition is prepared by first dissolving the dopant source in water to form a dopant source solution, followed by the addition of the lithium source to the dopant source solution to form a dopant and lithium source solution, followed by mixing the dopant and lithium source solution with the titanium source.
Step (b) of the method of making a doped lithium titanate material comprises spray-drying the liquid composition to provide a spray-dried composition. Drying through spray-drying provides a material with improved high-rate discharge capacity. In some embodiments the spray-dried composition is a particulate spray-dried composition. In some embodiments, in step (b), spray drying is carried out with an inlet temperature of at least 120 °C, for example from 120 °C to 300 °C, from 120 °C to 250 °C, or from 200 to 250 °C.
One example of a suitable spray dryer is the Buchi B290.
In some embodiments, in step (c), annealing is performed at a temperature of at least 500 °C, for example at least 550 °C, at least 600 °C, at least 650 °C, at least 700 °C, at least 750 °C or at least 800 °C. The annealing may be performed at a temperature of up to 1200 °C, for example up to 1150 °C, up to 1100 °C, up to 1050 °C, up to 1000 °C, up to 950 °C, up to 900 °C or up to 850 °C.
In some embodiments, in step (c), annealing is performed at a temperature of from 500 °C to 1200 °C, for example from 500 °C to 1150 °C, from 550 °C to 1150 °C, from 550 °C to 1100 °C, from 600 °C to 1000 °C, from 650 °C to 1000 °C, from 650 °C to 950 °C, from 700 °C to 900 °C or about 800 °C.
Any furnace which provides a stable temperature in the required range would be suitable for use in the annealing step. One suitable furnace is the Carbolite muffle furnace GPC12/36.
Annealing may be carried out by increasing the temperature from ambient temperature up to a temperature Ti at a ramping rate Ri, followed by increasing the temperature from temperature Ti up to a temperature T2 at a ramping rate R2. The temperature may then be held at T2 for a predetermined annealing time ti.
In some embodiments, Ti is from 300 °C to 700 °C, for example from 350 °C to 650 °C, from 400 °C to 600 °C, from 420 °C to 580 °C, from 450 °C to 550 °C or about 500 °C.
In some embodiments, T2 is from 500 °C to 1200 °C, for example from 500 °C to 1150 °C, from 550 °C to 1150 °C, from 550 °C to 1100 °C, from 600 °C to 1000 °C, from 650 °C to 1000 °C, from 650 °C to 950 °C, from 700 °C to 900 °C or about 800 °C.
Ri may be from 2-8 °C/min, for example from 2.5-7.5 °C/min, from 3-7 °C/min, from 3.5-6.5 °C/min, from 4-6 °C/min, from 4.5-6.5 °C/min or about 5 °C/min. R2 may be from 0.5-3.5 °C/min, for example from 1-3 °C/min, from 1.5-2.5 °C/min or about 2 °C/min. In some embodiments, RI>R2. The annealing time ti may be from 2 to 15 hours, for example from 3 to 12 hours, from 5 to 10 hours, from 6 to 10 hours or about 8 hours.
After annealing the material may be left to cool. In some embodiments, the material may be left under ambient temperature to cool. In some embodiments, the furnace is allowed to cool under ambient conditions or may be allowed to cool under a controlled ramp rate.
In some embodiments, in step (c), annealing is performed at a temperature of at least 700 °C for at least 2 hours.
In some embodiments, in step (c), annealing is performed at a temperature of at least 770 °C, for example at least 775 °C, at least 780 °C, at least 785 °C, at least 790 °C, at least 795 °C or at least 800 °C. It has been found that at such annealing temperatures the effects of the invention in providing a material having a higher capacity at high discharge rates are more pronounced. In some embodiments, in step (c), annealing is performed at a temperature of from 770 °C to 820 °C, for example from 780 °C to 820 °C, from 790 °C to 820 °C, from 790 °C to 810 °C, or at about 800 °C.
The annealing may include placing the spray-dried composition in a suitable container for annealing, for example an alumina crucible.
In some embodiments, the method comprises deagglomerating the material after annealing, for example by grinding or milling. The deagglomerating may include sieving to a suitable size fraction with optional additional milling or grinding of the oversize fraction.
The method may comprise further annealing steps after the annealing in step (c).
The methods described herein are applicable to a wide variety of doped lithium titanate materials and the exact composition of the material is therefore not limited.
In some embodiments, the doped lithium titanate material has the formula LLTis-xMxOia wherein M is selected from one or more of La and Ce, and 0.02 £ x £ 0.1. In some embodiments, 0.05 £ x £ 0.1.
A second aspect of the invention is a doped lithium titanate material obtained or obtainable by a method according to the first aspect. A third aspect of the invention is a negative active material comprising the material according to the second aspect.
A fourth aspect of the invention is a negative electrode comprising the negative active material according to the third aspect.
In some embodiments, the negative electrode comprises the negative active material at an electrode loading of at least 4.8 mg/cm2, for example at least 4.9 mg/cm2, at least 5.0 mg/cm2, at least 5.2 mg/cm2 or at least 5.4 mg/cm2. In some embodiments, the negative electrode comprises the negative active material at an electrode loading of from 4.8 mg/cm2 to 7.0 mg/cm2, for example from 4.8 mg/cm2 to 6.5 mg/cm2, from 4.8 mg/cm2 to 6.0 mg/cm2 or from 5.0 mg/cm2 to 6.0 mg/cm2.
A fifth aspect of the invention is a method of making a spray-dried doped lithium titanate precursor material comprising:
(a) preparing a liquid composition comprising a titanium source, a lithium source and a dopant source, wherein the dopant source comprises one or more of a lanthanum source and a cerium source; and
(b) spray drying the liquid composition to provide a spray-dried composition.
All of the options and preferences set out above in the context of the first aspect apply equally to the fifth aspect.
Examples
General method for preparing lithium titanate
The following method was used to prepare both doped and un-doped lithium titanate material.
19.77 g of T1O2 (NanoArc) was weighed in a Schott bottle. For the preparation of un-doped samples, a lithium solution was prepared by adding 200 mmol of a lithium salt to 200 ml_ of distilled water. For the preparation of doped samples, a lithium/dopant solution was prepared by first adding 2.5 mmol of dopant salt to 200 ml_ of distilled water to form a dopant solution, followed by adding 200 mmol of a lithium salt to the dopant solution.
The lithium solution (or lithium/dopant solution) was then added to the titania in the Schott bottle to form a suspension which was stirred for 1 hour with a magnetic stirrer. The suspension was then spray dried using a Buchi B290 spray dryer using 220 °C inlet temperature, 100% aspirator, 50% pump and 600 L/h air flow. Spray-dried powder was collected in a collection vessel. 7 g of this powder was placed in an alumina boat and placed in a Carbolite retorted furnace. The temperature was increased from ambient to 500 °C at a rate of 5 °C/min, then increased from 500 °C to 800 °C at a rate of 2 °C/min. The sample was then held at 800 °C for 8 hours for annealing.
The following materials were prepared according to this method:
Figure imgf000014_0001
Figure imgf000014_0002
Example 3
A solution was prepared by combining 4.48 mol of UOH.H2O with 1.5 L of distilled water, then 443 g of T1O2 was added to the solution along with 0.056 mol of La(0Ac)3.1.5H20. This suspension was stirred for 1 h using a high shear mixer (disperser head). This suspension was transferred to an autoclave with further 0.5 L water and treated for 12 h at 160°C.
The suspension was then spray dried using 220 °C inlet temperature, 100% aspirator, 50% pump and 600 L/h air flow. Spray-dried powder was collected in a collection vessel. 20 g of this powder was placed in an alumina boat and placed in a Carbolite retorted furnace. The temperature was increased from ambient to 760 °C at a rate of 5 °C/min. The sample was then held at 760 °C for 6 hours for annealing. Example 4
A sample was prepared in the same way as Example 3, except that in the Carbolite retorted furnace the temperature was increased from ambient to 800 °C at a rate of 5 °C/min. The sample was then held at 800 °C for 6 hours for annealing.
Comparative Example 8
A sample was prepared by a method involving hydrothermal treatment in an autoclave followed by spray-drying and calcination in a similar way to Example 3, but without the presence of any dopant salt.
Preparation of cells for testing
Inks were then prepared containing each of the above materials which were printed to form anodes for testing. To prepare the ink, 0.32 g of C65 carbon black, 3.36 g of active material from one of the above Examples or Comparative Examples, 3.2 g of 10% PVdF (Solvay 5300) in NMP binder solution and a further 2.72 g of N-methyl-2-pyrrolidone (NMP) were sequentially added to a 58 ml PVP pot. A Thinky mixer was then used to thoroughly mix the ingredients.
To print the anodes, a rectangular sheet of aluminium foil (20 x 25 cm) was cleaned with acetone followed by isopropanol. The edge of the print blade was lubricated with a drop of NMP and printing was carried out at a wet thickness of 200 pm using a print speed of 20 mm/s. The printed composition was dried in a vented oven at 120 °C for 12 hours.
All electrodes were roller calendared to achieve an electrode density of 2.0 g/cm3.
Coin cells (CR 2032) were prepared in half cell configuration vs Lithium metal (Alfa Aesar) with 85 pL of LP30 electrolyte. Electrochemical testing was performed at 23 °C by use of a Maccor4000 apparatus. The cells were cycled asymmetrically between 1 and 50 C, using constant current constant voltage in the voltage range of 1.25 V-2.5 V.
Figure 1 shows the results of the testing for some of the examples and comparative examples.
The plot in Figure 1 shows that the materials of Examples 1 and 2 have high discharge capacity at high discharge rates. Example 1 maintains a capacity of over 120 mAh/g at a D- rate as high as 20C. Example 2 also demonstrates a high capacity in excess of 80 mAh/g at 20C. By contrast, although some of the Comparative Examples demonstrate relatively high capacities at lower D-rates, these quickly drop off as D-rate increases. For example, Comparative Examples 2 and 4 demonstrate capacities above 140 mAh/g at a discharge rate of 10C, but at 20C the capacities have fallen to lower than 60 mAh/g, making them unsuitable for use in applications where a high capacity is required even at higher discharge rates.
Figure 2 provides a plot of discharge capacity against electrode loading for Example 3 and Comparative Example 8 at a constant D-rate of 20C. The results show that doping the material with La leads to an increased capacity at a high D-rate (20C), which is particularly evident at electrode loadings in excess of 5 mg/cm2.
Figure 3 provides a plot of discharge capacity against electrode loading for Example 3 and Comparative Example 8 at a constant D-rate of 30C. The results show that doping the material with La leads to an increased capacity at a high D-rate (30C), which is particularly evident at electrode loadings in excess of 5 mg/cm2.
Figure 4 provides a plot of discharge capacity against electrode loading for Example 4 and Comparative Example 8 at a constant D-rate of 20C. The results show that doping the material with La leads to a significantly increased capacity at a high D-rate (20C), which is particularly evident at electrode loadings in excess of 5 mg/cm2.
Figure 5 provides a plot of discharge capacity against electrode loading for Example 4 and Comparative Example 8 at a constant D-rate of 30C. The results show that doping the material with La leads to a significantly increased capacity at a high D-rate (30C), which is particularly evident at electrode loadings in excess of 5 mg/cm2.
A comparison of the results in Figures 2 and 3 with Figures 4 and 5 shows that the observed improvement in capacity at higher D-rates is further amplified when the peak annealing temperature during preparation of the material is increased from 760 °C (Example 8) to 800 °C (Example 9).
The materials of the invention are therefore highly suitable for use in high-end applications requiring large capacity at a high discharge rate, such as Li-ion batteries for electric vehicles.
X-Ray Diffraction
X-ray diffraction patterns were collected for the materials of Examples 1 and 2. A Bruker D8 Advance diffractometer was used to collect the data, fitted with a 90-position sample changer for measurements in reflection mode. The radiation used was Cu Ka (l = 1.5406 + 1.54439 A) with a scan range of 10-130° 2Q and a step size of 0.02°. The tube voltage was 40 kV and the current was 40 mA. The measurements were taken at ambient temperature. A Lynxeye-XE PSD detector was used with a 0.0125° Ni filter.
Bruker AXS Diffrac Eva V4 software (2010-2016) and the PDF-4+ database, release 2016, were used for phase identification. Bruker-AXS TOPAS 5 software (1999-2014) was used for crystallite size and lattice parameter measurements.
For sample preparation, powdered samples with <50 pm particle size were packed in a flat plate sample holder.
Figure 6 shows the XRD pattern for the material of Example 1 , showing that it contains predominantly the lithium titanate spinel phase with minor amounts of a lanthanum titanate phase.
Figure 7 shows the XRD pattern for the material of Example 2, showing that it contains predominantly the lithium titanate spinel phase with minor amounts of a cerium oxide phase.

Claims

Claims
1. A method of making a doped lithium titanate material comprising:
(a) preparing a liquid composition comprising a titanium source, a lithium source and a dopant source, wherein the dopant source comprises one or more of a lanthanum source and a cerium source;
(b) spray drying the liquid composition to provide a spray-dried composition; and
(c) annealing the spray-dried composition.
2. A method according to claim 1 wherein the liquid composition is a slurry comprising a suspension of the titanium source in an aqueous solution, wherein at least a portion of the dopant source is dissolved in the aqueous solution.
3. A method according to claim 2 wherein the titanium source comprises titanium dioxide.
4. A method according to claim 2 or 3 wherein the slurry comprises from 5 to 25 wt% titanium source based on the total weight of the slurry.
5. A method according to any one of claims 2 to 4 wherein the aqueous solution comprises one or more of dissolved lanthanum species and dissolved cerium species.
6. A method according to claim 5 wherein the dissolved lanthanum species comprises La3+ and the dissolved cerium species comprises Ce3+.
7. A method according to claim 6 wherein the aqueous solution comprises from 5 to 25 mM La3+ or from 5 to 20 mM Ce3+.
8. A method according to any one of claims 1 to 7 wherein the dopant source comprises only one of a lanthanum source and a cerium source.
9. A method according to any one of claims 1 to 8 wherein the dopant source comprises one or more of lanthanum acetate and cerium acetate, or a hydrated form thereof.
10. A method according to any one of claims 1 to 9 wherein the lithium source comprises one or more of lithium acetate and lithium hydroxide, or a hydrated form thereof.
11. A method according to any one of claims 1 to 10 wherein the liquid composition comprises dissolved lithium species which provide a total concentration of Li+ in the liquid composition of from 0.5 to 2.5 M.
12. A method according to any one of claims 1 to 11 wherein step (a) comprises mixing a solution comprising the dopant source with the titanium source and optionally stirring.
13. A method according to any one of claims 1 to 12 wherein the liquid composition is prepared by first dissolving the dopant source in water to form a dopant source solution, followed by the addition of the lithium source to the dopant source solution to form a dopant and lithium source solution, followed by mixing the dopant and lithium source solution with the titanium source.
14. A method according to any one of claims 1 to 13 wherein in step (b), spray drying is carried out with an inlet temperature of from 200 to 250 °C.
15. A method according to any one of claims 1 to 14 wherein in step (c), annealing is performed at a temperature of at least 700 °C for at least 2 hours.
16. A method according to any one of claims 1 to 14 wherein in step (c), annealing is performed at a temperature of at least 770 °C.
17. A method according to any one of claims 1 to 16 wherein the doped lithium titanate material has the formula LLTis-xMxOia wherein M is selected from one or more of La and Ce, and 0.02 £ x £ 0.1.
18. A doped lithium titanate material obtained or obtainable by a method according to any one of claims 1 to 17.
19. A doped lithium titanate material according to claim 18, wherein the doped lithium titanate material has the formula LLTis-xMxOia wherein M is selected from one or more of La and Ce, and 0.02 £ x £ 0.1.
20. A negative active material comprising the material according to claim 18 or 19.
21. A negative electrode comprising the negative active material according to claim 20.
22. A negative electrode according to claim 21, wherein the negative electrode comprises the negative active material at an electrode loading of at least 4.8 mg/cm2.
23. A method of making a spray-dried doped lithium titanate precursor material comprising:
(a) preparing a liquid composition comprising a titanium source, a lithium source and a dopant source, wherein the dopant source comprises one or more of a lanthanum source and a cerium source; and (b) spray drying the liquid composition to provide a spray-dried composition.
24. A spray dried composition comprising lithium titanate doped with one or more of cerium and lanthanum, obtained or obtainable by a method according to claim 23.
PCT/GB2021/051442 2020-06-11 2021-06-10 Process for manufacturing doped lithium titanate WO2021250412A1 (en)

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US20170250405A1 (en) * 2014-07-30 2017-08-31 Central Glass Co., Ltd. Precursor of Lithium Titanate Composite Product and Method for Producing Same

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KR20120017991A (en) * 2010-08-20 2012-02-29 삼성에스디아이 주식회사 Negative active material for rechargeable lithium battery, method of preparing same, and rechargeable lithium battery including same

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CN104282883B (en) * 2014-10-14 2016-11-30 秦皇岛中科远达电池材料有限公司 Composite negative electrode material of lithium ion battery and preparation method thereof, anode plate for lithium ionic cell and lithium ion battery
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