WO2020084631A1 - A method of preparing an electrode material for lithium-ion batteries - Google Patents

A method of preparing an electrode material for lithium-ion batteries Download PDF

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Publication number
WO2020084631A1
WO2020084631A1 PCT/IN2019/050730 IN2019050730W WO2020084631A1 WO 2020084631 A1 WO2020084631 A1 WO 2020084631A1 IN 2019050730 W IN2019050730 W IN 2019050730W WO 2020084631 A1 WO2020084631 A1 WO 2020084631A1
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lifep0
powder particles
niobium
precursors
mixture
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Srinivas Kumar ADAPAKA
Satyavani TRIUMALA VENKATA SESHA LAKSHMI
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Chairman Defence Research And Development Organisation (drdo)
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Priority to EP19874783.4A priority Critical patent/EP3870542A4/en
Priority to US17/288,694 priority patent/US11975986B2/en
Publication of WO2020084631A1 publication Critical patent/WO2020084631A1/en
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    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01G—COMPOUNDS CONTAINING METALS NOT COVERED BY SUBCLASSES C01D OR C01F
    • C01G49/00—Compounds of iron
    • C01G49/009—Compounds containing iron, with or without oxygen or hydrogen, and containing two or more other elements
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B25/00—Phosphorus; Compounds thereof
    • C01B25/16—Oxyacids of phosphorus; Salts thereof
    • C01B25/26—Phosphates
    • C01B25/45—Phosphates containing plural metal, or metal and ammonium
    • 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
    • H01M4/043—Processes of manufacture in general involving compressing or compaction
    • H01M4/0433—Molding
    • 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
    • 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
    • H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
    • H01M4/5825—Oxygenated metallic salts or polyanionic structures, e.g. borates, phosphates, silicates, olivines
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B82—NANOTECHNOLOGY
    • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
    • B82Y30/00—Nanotechnology for materials or surface science, e.g. nanocomposites
    • 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
    • C01P2004/00—Particle morphology
    • C01P2004/01—Particle morphology depicted by an image
    • C01P2004/03—Particle morphology depicted by an image obtained by SEM
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2004/00—Particle morphology
    • C01P2004/60—Particles characterised by their size
    • C01P2004/64—Nanometer sized, i.e. from 1-100 nanometer
    • 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
    • C01P2006/10—Solid density
    • 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
    • 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 Lithium-ion batteries and more particularly relates to electrode material of Lithium-ion batteries.
  • Battery technology is a core technology for all future-generation clean-energy vehicles such as fuel cell vehicles, electric vehicles, and plug-in hybrid vehicles. Promising for the future and still undergoing rapid development is the technology of reversible lithium cell. Lithium-ion battery technology has the potential to meet the requirements of high energy density and high-power density applications. Among all phosphates, lithium iron phosphate exhibits good reversible electrochemical lithium insertion/extraction reactions. Lithium iron phosphate lies within its tolerance range to overcharge/discharge, thereby less prone to thermal runaway.
  • LiFeP0 4 has a low intrinsic electronic conductivity and shows slow Li + diffusion across the LiFeP0 4 /FeP0 4 phase boundary during charge/discharge processes, limiting its performance rate.
  • the slow diffusion rate of Li + may be attributed to a variety of material properties such as large miscibility gap, dimensionality, and nature of defect sites.
  • a conventional method describes a method of preparation of metal-doped carbon coated lithium iron phosphate of microspheres of particle size of 15 ⁇ 40pm for enhancing the conductivity.
  • a preparation of a compound doped and cladded lithium-ion cell anode material LiFeP0 4 is described for enhancing the conductivity.
  • the method comprises the steps of mixing, pulping and drying raw materials to obtain a powdery precursor; pre-sintering the powdery precursor; performing secondary burdening and ball milling on the pre-sintered product, and sintering the mixture to obtain lithium-ion cell anode material LiFeP0 4 .
  • a method of preparing an electrode material for lithium-ion batteries comprises the steps of preparing a mixture of precursors taken in predefined stoichiometric ratios for synthesis of lithium iron phosphate (LiFeP0 4 ) and adding niobium pentoxide as a precursor for doping of niobium at Li+ site of LiFeP0 4 for synthesis of niobium doped LiFeP0 4 .
  • the steps include ball milling of said mixture of precursors dry ground to obtain nano sized powder particles of niobium doped
  • LiFeP0 4 LiFeP0 4 . Then to said mixture, a precursor of carbon is added, and ball milled for synthesizing and obtaining carbon coated niobium doped LiFeP0 4 nano sized powder particles.
  • pellets of required size are prepared and sintered.
  • the obtained pellets are structurally characterized.
  • one or more compositions of Li l-x Nb x FeP0 4 /C, where x is equal to 0-0.15 are synthesized from solid state vacuum synthesis method.
  • a composition of Lio .g Nbo .i FePCVC is preferable and has a carbon content of about 8.8%.
  • Figure 2 (a) shows a scanning electron micrograph of LiNbFeP0 4 /C powder with an average particle size of 33 nm according to an embodiment of the present invention
  • Figure 2 (b) shows a scanning electron micrograph of Lio . 9Nbo . o5FePo 4 powder with an average particle size of 36 nm according to an embodiment of the present invention
  • Figure 2 (c) shows a scanning electron micrograph of Li 0. 9Nbo . oiFePo 4 powder with an average particle size of 47 nm according to an embodiment of the present invention.
  • Figure 2 (d) shows a scanning electron micrograph of Lio . 85Nbo .i5 FePo 4 powder with an average particle size of 62 nm according to an embodiment of the present invention.
  • a method of preparing an electrode material for lithium-ion batteries comprises the steps of preparing a mixture of lithium carbonate, iron oxalate and ammonium di-hydrogen phosphate precursors taken in predefined stoichiometric ratios for synthesis of lithium iron phosphate (LiFePCM), adding niobium pentoxide as a precursor for doping of niobium at Li+ site of LiFeP0 4 for synthesis of niobium doped LiFeP0 4 and ball milling said mixture of precursors dry ground to obtain nano sized powder particles of niobium doped LiFeP0 4 .
  • the steps includes adding and ball milling a precursor of carbon to said mixture of precursors for synthesizing and obtaining carbon coated niobium doped LiFeP0 4 nano sized powder particles.
  • said mixture of precursors are synthesized by solid state vacuum synthesis for obtaining one or more compositions of Li l-x Nb x FeP0 4 /C
  • a composition of Lio .g Nbo .i FePCVC is preferable and has a carbon content of about 8.8%.
  • pellets are prepared and sintered from said synthesized nano powder particles at a predetermined temperature for a predetermined time.
  • the steps further includes structurally characterizing said sintered pellets for identifying standard orthorhombic olivine type LiFeP04 structure.
  • the precursor of carbon is 10% of acetylene black.
  • a half-cell configuration of said Lio .9 Nbo .i FeP0 4 /C has a C-rate discharge of more than 1500 nos. of cycles with a retention capacity at 10C rate.
  • powder particles obtained during ball milling process are within the range of 39 nm to 47 nm size.
  • powder particles obtained during ball milling process are preferably of 42nm size.
  • each pellet has a diameter about 10 mm and a thickness of 1.5 mm.
  • the pellets are sintered at least at 10 bar vacuum and at said predetermined temperature in range of 650-800°C for said predetermined time of at least 10 hours to obtain a density of at least 3.6 g/cc.
  • the composition of Lio .9 Nbo .i FeP0 4 has a wider a channel for Li + diffusion, a minimum energy requirement for polaron and shows less resistance value.
  • the overall conductivity of the LiFeP0 4 cathode material is enhanced by adopting the techniques like reduction of particle size by ball milling of precursors, by providing carbon coating over LiNbFeP0 4 particles and by doping with different compositions of niobium in Lii -X Nb x FeP0 4 /C, where x is equal to 0-0.15.
  • Figure 1 illustrates the formation of a single phase without signatures of impurities. The existence of sharp and well- defined Bragg peaks confirms the presence of phase pure and crystalline products.
  • a mixture of (99.99% purity, Sigma Aldrich) lithium carbonate, iron oxalate and ammonium di-hydrogen phosphate precursors are taken in predefined stoichiometric ratios for synthesis of lithium iron phosphate (LiFeP04) by solid state vacuum synthesis method.
  • Niobium pentoxide is added as a precursor for doping of niobium at Li+ site of LiFeP0 4 for synthesis of niobium doped LiFeP0 4 .
  • performing ball milling on said mixture of precursors dry ground obtains nano sized powder particles.
  • 10% of acetylene black is added as a precursor of carbon to said mixture of precursors and the ball milling operation is performed for synthesizing and obtaining carbon coated niobium doped LiFeP0 4 nano sized powder particles.
  • the carbon gets coated over each particle of niobium doped LiFeP04.
  • the carbon coating will be in a few nanometers which can be confirmed by TEM.
  • the carbon coating on the surface of LiFeP04 may be confirmed from Selected Area Diffraction Pattern (SADP) of TEM and with the help of carbon analyzer.
  • SADP Selected Area Diffraction Pattern
  • pellets are prepared and sintered from said synthesized nano powder particles at a predetermined temperature for a predetermined time.
  • the resultant sintered pellets may be structurally characterized by XRD, FTIR, SEM and EDS for identifying standard orthorhombic olivine type LiFeP04 structure.
  • a composition of Lio .9 Nbo .i FeP0 4 /C is preferable from one or more synthesized compositions of Li l-x Nb x FeP0 4 /C, where x is equal to 0 - 0.15.
  • a composition of Lio .9 Nbo .i FeP0 4 /C is preferable and has a carbon content of about 8.8%.
  • powder particles obtained during ball milling process are within the range of 39 nm to 47 nm size.
  • the pellets are sintered at least at 10 2 bar vacuum and at said predetermined temperature in range of 650-800°C for said predetermined time of at least 10 hours to obtain a density of at least 3.6 g/cc.
  • the presence of well-defined fine spherical particles is shown in Fig. 2 (a), (b), (c) and (d), wherein the particle size is seen to be increasing with an increase in doping proportion of niobium.
  • a high energy centrifugal ball mill (Model SFM-3, 030756) was used (1200 rpm) for dry grounding the mixture of precursors for different time intervals of 5, 10, 15 and 20 hours to obtain nano sized powder particles. It was observed that the particle size reduced from 350 nm to 183 nm after 5 hours of ball milling of said mixture of precursors, reduced to 108 nm after 10 hours, reduced to 42 nm after 15 hours and reduced to 39 nm after 20 hours. Particle sizes was measured with particle size analyzer, dynamic light scattering instrument model no.SZ-lOO, Horiba Instruments.
  • the ball milling time to obtain nano sized powder particles may depend on the type of ball mill used i.e. when a ball mill of low capacity is used it may take more time for obtaining nano sized powder particle.
  • Sintered pellets were prepared from synthesized nano powder particles at predetermined temperatures for predetermined time. The density of the pellet was found using Archimedes principle. Accordingly, 0.2 grams of synthesized material was taken in a mortar and a Polyvinyl alcohol was used as a binder. 5 grams of binder was mixed 100 ml of water and heated at l00°C for 20 minutes. 2 to 3 drops of the binder was added to synthesized material and ground thoroughly. The grounded mixture was pressed into pellets of dimensions, 10 mm diameter and 1.5 mm thickness in a mold at 3 bar pressure for two minutes dwell time. The pellets were kept in a vacuum furnace at 10 bar vacuum for sintering.
  • One or more synthesized compositions of Lii -x Nb x FeP0 4 /C, where x is equal to 0- 0.15 were synthesized by solid-state vacuum synthesis method. Both material and electrochemical characterization of the synthesized powder was done. The powder was structurally characterized by XRD, FTIR, SEM, and EDS. Pellets prepared from synthesized powder were sintered and used to calculate dc conductivity and activation energy.
  • the supervalent dopants which are successfully doped in the olivine structure without affecting the structural stability decrease the grain size due to cation vacancies created during charge compensation and also the presence of the dopant increases the size of the channel for Li+ diffusion, resulting in faster Li+ diffusion. It was observed that due to the lower electrical resistivity and higher ionic radius of niobium, the widening of the channel for Li+ diffusion is also more in the case of niobium which resulted in faster Li+ ion diffusion and in turn higher conductivity, and diffusion coefficient.
  • the ac impedances were measured and diffusion coefficients were calculated for the cells in half-cell configuration. It was observed that the values of RQ, Rf and Ret reduced when doped with niobium as compared to LiFeP0 4 /C, suggesting that the overall resistance decreased and Li+ migration improved.
  • Lio .9 Nbo .i FeP0 4 /C showed minimum resistance values.
  • the composition of Lio .9 Nbo .i FeP0 4 /C was observed to have a diffusion coefficient of 16.21
  • a chart of diffusion coefficient of solid vacuum synthesized Lii -x Nb x FeP0 4 /C (x
  • the improved electrochemical properties due to niobium doping was attributed to the shortened diffusion path distance and improved electrical conductivity.
  • the coin cells with Lio .9 Nbo .i FeP0 4 /C cathodes were cycled in CR2032 half-cell configuration at different C-rates.
  • the coin cells when discharged at C/10, 1C, 5C, 10C, 15C and 20C yielded maximum specific capacities of 168.5 mAhg-l,l43 mAhg-l, 128 mAhg-l, 110 mAhg-l, 85 mAhg-l and 50 mAhg-l respectively. It was observed that
  • Lio .9 Nbo .i FeP0 4 /C based half cells yielded more than 1500 nos. of cycles at a 10C rate with reasonable capacity retention.
  • LiFeP0 4 cathode material is enhanced by adopting the techniques like reduction of particle size by ball milling of precursors, by providing carbon coating over LiFeP0 4 particles and by doping with different compositions of niobium in Lii -X Nb x FeP0 4 /C.
  • the room temperature dc conductivity LiFeP0 4 cathode material is improved by Nb doping when compared to LiFeP0 4 /C.
  • the diffusion coefficients LiFeP0 4 cathode material are improved by Nb doping when compared to LiFeP0 4 /C.

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Abstract

The present invention discloses a method of preparing an electrode material for lithium-ion batteries comprising the steps of preparing a mixture of precursors taken in predefined stoichiometric ratios for synthesis of lithium iron phosphate (LiFePO4), adding niobium pentoxide as a precursor for doping of niobium at Li+ site of LiFePO4 for synthesis of niobium doped LiFePO4 and ball milling operation provides nano sized powder particles. Now, a precursor of carbon is added to said mixture of precursors for synthesizing and obtaining carbon coated niobium doped LiFePO4 nano sized powder particles. Pellets of required size are prepared and sintered. The obtained pellets are structurally characterized.

Description

A METHOD OF PREPARING AN ELECTRODE MATERIAL FOR
LITHIUM-ION BATTERIES
TECHNICAL FIELD OF THE INVENTION
The present invention relates to Lithium-ion batteries and more particularly relates to electrode material of Lithium-ion batteries. BACKGROUD OF THE INVENTION
Battery technology is a core technology for all future-generation clean-energy vehicles such as fuel cell vehicles, electric vehicles, and plug-in hybrid vehicles. Promising for the future and still undergoing rapid development is the technology of reversible lithium cell. Lithium-ion battery technology has the potential to meet the requirements of high energy density and high-power density applications. Among all phosphates, lithium iron phosphate exhibits good reversible electrochemical lithium insertion/extraction reactions. Lithium iron phosphate lies within its tolerance range to overcharge/discharge, thereby less prone to thermal runaway. However, LiFeP04 has a low intrinsic electronic conductivity and shows slow Li+ diffusion across the LiFeP04/FeP04 phase boundary during charge/discharge processes, limiting its performance rate. The slow diffusion rate of Li+ may be attributed to a variety of material properties such as large miscibility gap, dimensionality, and nature of defect sites.
A conventional method describes a method of preparation of metal-doped carbon coated lithium iron phosphate of microspheres of particle size of 15 ~ 40pm for enhancing the conductivity. In yet another conventional method a preparation of a compound doped and cladded lithium-ion cell anode material LiFeP04 is described for enhancing the conductivity. The method comprises the steps of mixing, pulping and drying raw materials to obtain a powdery precursor; pre-sintering the powdery precursor; performing secondary burdening and ball milling on the pre-sintered product, and sintering the mixture to obtain lithium-ion cell anode material LiFeP04.
However, with the compositions obtained thereof, or the methods adopted, the limitation of low intrinsic electronic conductivity and slow Li+ diffusion still exists and therefore conventional methods tends to be ineffective in solving the problem.
SUMMARY OF THE INVENTION
According to an embodiment of the invention, a method of preparing an electrode material for lithium-ion batteries comprises the steps of preparing a mixture of precursors taken in predefined stoichiometric ratios for synthesis of lithium iron phosphate (LiFeP04) and adding niobium pentoxide as a precursor for doping of niobium at Li+ site of LiFeP04 for synthesis of niobium doped LiFeP04. According to the embodiment, the steps include ball milling of said mixture of precursors dry ground to obtain nano sized powder particles of niobium doped
LiFeP04. Then to said mixture, a precursor of carbon is added, and ball milled for synthesizing and obtaining carbon coated niobium doped LiFeP04 nano sized powder particles.
According to the embodiment, pellets of required size are prepared and sintered. The obtained pellets are structurally characterized.
According to the embodiment, one or more compositions of Lil-xNbxFeP04/C, where x is equal to 0-0.15 are synthesized from solid state vacuum synthesis method. According to the embodiment, a composition of Lio.gNbo.iFePCVC is preferable and has a carbon content of about 8.8%.
BRIEF DESCRIPTION OF THE DRAWINGS
The various aspects, features, and advantages of the embodiment of the present invention, hereinafter more particularly described, will be more apparent from the following description taken in conjunction with the drawings, in which:
Figure 1 shows an X-Ray diffraction pattern of one or more synthesized compositions of Lii-xNbxFeP04/C (x=0.05, 0.1, 0.15, 0.16) according to an embodiment of the present invention; Figure 2 (a) shows a scanning electron micrograph of LiNbFeP04/C powder with an average particle size of 33 nm according to an embodiment of the present invention;
Figure 2 (b) shows a scanning electron micrograph of Lio.9Nbo.o5FePo4 powder with an average particle size of 36 nm according to an embodiment of the present invention;
Figure 2 (c) shows a scanning electron micrograph of Li0.9Nbo.oiFePo4 powder with an average particle size of 47 nm according to an embodiment of the present invention; and
Figure 2 (d) shows a scanning electron micrograph of Lio.85Nbo.i5FePo4 powder with an average particle size of 62 nm according to an embodiment of the present invention.
DETAILED DESCRIPTION OF THE EMBODIMENTS OF THE INVENTION
The embodiments herein are explained more fully with reference to the accompanying drawings and detailed in the following description. The examples used herein drawings are intended merely to facilitate an understanding of ways in which the embodiment herein can be practiced by those skilled in the art and should not be construed as limiting the scope of the embodiment herein. According to an embodiment of the invention, a method of preparing an electrode material for lithium-ion batteries comprises the steps of preparing a mixture of lithium carbonate, iron oxalate and ammonium di-hydrogen phosphate precursors taken in predefined stoichiometric ratios for synthesis of lithium iron phosphate (LiFePCM), adding niobium pentoxide as a precursor for doping of niobium at Li+ site of LiFeP04 for synthesis of niobium doped LiFeP04 and ball milling said mixture of precursors dry ground to obtain nano sized powder particles of niobium doped LiFeP04. According to the embodiment of the invention, the steps includes adding and ball milling a precursor of carbon to said mixture of precursors for synthesizing and obtaining carbon coated niobium doped LiFeP04 nano sized powder particles.
According to the embodiment, said mixture of precursors are synthesized by solid state vacuum synthesis for obtaining one or more compositions of Lil-xNbxFeP04/C
(where x is equal to 0 to 0.15) nano sized powder particles.
According to the embodiment of the invention, a composition of Lio.gNbo.iFePCVC is preferable and has a carbon content of about 8.8%.
According to the embodiment, pellets are prepared and sintered from said synthesized nano powder particles at a predetermined temperature for a predetermined time. According to the embodiment of the invention, the steps further includes structurally characterizing said sintered pellets for identifying standard orthorhombic olivine type LiFeP04 structure.
According to the embodiment of the invention, the precursor of carbon is 10% of acetylene black.
According to the embodiment of the invention, a half-cell configuration of said Lio.9Nbo.iFeP04/C has a C-rate discharge of more than 1500 nos. of cycles with a retention capacity at 10C rate.
According to the embodiment of the invention, powder particles obtained during ball milling process are within the range of 39 nm to 47 nm size.
According to the embodiment of the invention, powder particles obtained during ball milling process are preferably of 42nm size.
According to the embodiment of the invention, each pellet has a diameter about 10 mm and a thickness of 1.5 mm.
2
According to the embodiment of the invention, the pellets are sintered at least at 10 bar vacuum and at said predetermined temperature in range of 650-800°C for said predetermined time of at least 10 hours to obtain a density of at least 3.6 g/cc.
According to the embodiment of the invention, the composition of Lio.9Nbo.iFeP04 has a wider a channel for Li+ diffusion, a minimum energy requirement for polaron and shows less resistance value.
The overall conductivity of the LiFeP04 cathode material is enhanced by adopting the techniques like reduction of particle size by ball milling of precursors, by providing carbon coating over LiNbFeP04 particles and by doping with different compositions of niobium in Lii-X NbxFeP04/C, where x is equal to 0-0.15.
Referring Figure 1 shows XRD pattern of Lii-xNbxFeP04/C (x=0 to 0.16). The synthesized Lii-xNbxFeP04/C (x=0.05, 0.1, 0.15, 0.16) composites may be structurally characterized using X-ray diffraction by Panalyti calx’ pert pro X-ray diffractometer to identify orthorhombic formation. Figure 1 illustrates the formation of a single phase without signatures of impurities. The existence of sharp and well- defined Bragg peaks confirms the presence of phase pure and crystalline products. Lii-xNbxFeP04/C (x = 0.05, 0.1, 0.15) composites exhibits standard orthorhombic olivine-type LiFeP04 structure (JCPDS 83-2092, a=l0.33 A, b= 5.98 A, c= 4.69 A).
It was seen that olivine structure of LiFeP04 is maintained and formation of a solid solution is possible only up to niobium doping of x= 0.15. At niobium doping of x= 0.16, the structure has deviated from LiFeP04 to Fe2Nb i.e. unformed LFP.
According to an embodiment, a mixture of (99.99% purity, Sigma Aldrich) lithium carbonate, iron oxalate and ammonium di-hydrogen phosphate precursors are taken in predefined stoichiometric ratios for synthesis of lithium iron phosphate (LiFeP04) by solid state vacuum synthesis method. Niobium pentoxide is added as a precursor for doping of niobium at Li+ site of LiFeP04 for synthesis of niobium doped LiFeP04. According to an embodiment, performing ball milling on said mixture of precursors dry ground obtains nano sized powder particles. Now, 10% of acetylene black is added as a precursor of carbon to said mixture of precursors and the ball milling operation is performed for synthesizing and obtaining carbon coated niobium doped LiFeP04 nano sized powder particles.
According to an embodiment, when the ball milled mixture of precursors undergoes pre-calcination and final calcination, the carbon gets coated over each particle of niobium doped LiFeP04. The carbon coating will be in a few nanometers which can be confirmed by TEM. The carbon coating on the surface of LiFeP04 may be confirmed from Selected Area Diffraction Pattern (SADP) of TEM and with the help of carbon analyzer. According to the embodiment, pellets are prepared and sintered from said synthesized nano powder particles at a predetermined temperature for a predetermined time.
According to an embodiment, the resultant sintered pellets may be structurally characterized by XRD, FTIR, SEM and EDS for identifying standard orthorhombic olivine type LiFeP04 structure. A composition of Lio.9Nbo.iFeP04/C is preferable from one or more synthesized compositions of Lil-xNbxFeP04/C, where x is equal to 0 - 0.15. According to the embodiment of the invention, a composition of Lio.9Nbo.iFeP04/C is preferable and has a carbon content of about 8.8%.
According to the embodiment of the invention, powder particles obtained during ball milling process are within the range of 39 nm to 47 nm size.
According to the embodiment of the invention, the pellets are sintered at least at 10 2 bar vacuum and at said predetermined temperature in range of 650-800°C for said predetermined time of at least 10 hours to obtain a density of at least 3.6 g/cc.
Referring Figure 2 through Figures 2(a-d), shows the scanned electron micrograph (SEM) images of LiFeP04/C powder with an average particle size 33 nm,
Lio.95Nbo.o5FeP04 powder with an average particle size 36 nm, Lio.9Nbo.iFeP04 powder with average particle size 47nm, and Lio.ssNbo.isFePCE powder with average particle 62 nm. The presence of well-defined fine spherical particles is shown in Fig. 2 (a), (b), (c) and (d), wherein the particle size is seen to be increasing with an increase in doping proportion of niobium. Example 1
A high energy centrifugal ball mill (Model SFM-3, 030756) was used (1200 rpm) for dry grounding the mixture of precursors for different time intervals of 5, 10, 15 and 20 hours to obtain nano sized powder particles. It was observed that the particle size reduced from 350 nm to 183 nm after 5 hours of ball milling of said mixture of precursors, reduced to 108 nm after 10 hours, reduced to 42 nm after 15 hours and reduced to 39 nm after 20 hours. Particle sizes was measured with particle size analyzer, dynamic light scattering instrument model no.SZ-lOO, Horiba Instruments. The ball milling time to obtain nano sized powder particles may depend on the type of ball mill used i.e. when a ball mill of low capacity is used it may take more time for obtaining nano sized powder particle.
Example 2
Sintered pellets were prepared from synthesized nano powder particles at predetermined temperatures for predetermined time. The density of the pellet was found using Archimedes principle. Accordingly, 0.2 grams of synthesized material was taken in a mortar and a Polyvinyl alcohol was used as a binder. 5 grams of binder was mixed 100 ml of water and heated at l00°C for 20 minutes. 2 to 3 drops of the binder was added to synthesized material and ground thoroughly. The grounded mixture was pressed into pellets of dimensions, 10 mm diameter and 1.5 mm thickness in a mold at 3 bar pressure for two minutes dwell time. The pellets were kept in a vacuum furnace at 10 bar vacuum for sintering. Sintering was carried out at 650°C, 700°C, 750°C and 800°C for different durations. The compactness of the pellet was checked by fracturing the pellet. The bulk density of the sintered pellet was determined by weighing them in the air and after immersing them in water. It was found that sintering carried out at 700°C sintering temperature for a duration of 12 hours resulted in a density of the pellet which is 3.6 g/cc, the density of LiFePCM.
Example 3
One or more synthesized compositions of Lii-xNbxFeP04/C, where x is equal to 0- 0.15 were synthesized by solid-state vacuum synthesis method. Both material and electrochemical characterization of the synthesized powder was done. The powder was structurally characterized by XRD, FTIR, SEM, and EDS. Pellets prepared from synthesized powder were sintered and used to calculate dc conductivity and activation energy.
In general, the supervalent dopants which are successfully doped in the olivine structure without affecting the structural stability decrease the grain size due to cation vacancies created during charge compensation and also the presence of the dopant increases the size of the channel for Li+ diffusion, resulting in faster Li+ diffusion. It was observed that due to the lower electrical resistivity and higher ionic radius of niobium, the widening of the channel for Li+ diffusion is also more in the case of niobium which resulted in faster Li+ ion diffusion and in turn higher conductivity, and diffusion coefficient.
It was observed that the room temperature dc conductivity of Lii-xNbxFeP04/C (x=0.05, 0.1, 0.15) was improved by Niobium (Nb) doping when compared to LiFeP04/C and for Lio.9Nbo.iFeP04/C it was observed to be 5l.6xl0 2 Son 1. It was also observed that the activation energy which is the energy required for polaron hopping was also minimum for Lio.9Nbo.iFeP04/C.
To understand the effect the of niobium doping in detail, ac impedance measurement was carried out by fabricating coin cells in half-cell configuration containing solid state vacuum synthesized Lii-xNbxFeP04/C (x=0.an 05, 0.1, 0.15) and compared with that of the respective LiFeP04/C composites. The ac impedances were measured and diffusion coefficients were calculated for the cells in half-cell configuration. It was observed that the values of RQ, Rf and Ret reduced when doped with niobium as compared to LiFeP04/C, suggesting that the overall resistance decreased and Li+ migration improved. The composition of Lio.9Nbo.iFeP04/C showed minimum resistance values. Li+ diffusion coefficients (DLi+) was determined for LiFeP04/C and Lii-xNbxFeP04/C (x=0.05, 0.1, 0.15) using Warburg coefficients (W) which were obtained from ac impedance measurements. The composition of Lio.9Nbo.iFeP04/C was observed to have a diffusion coefficient of 16.21
Figure imgf000015_0001
A chart of diffusion coefficient of solid vacuum synthesized Lii-xNbxFeP04/C (x=
0.05, 0.1, and 0.15) is as follows:
Figure imgf000015_0002
Example 4
The improved electrochemical properties due to niobium doping was attributed to the shortened diffusion path distance and improved electrical conductivity. The coin cells with Lio.9Nbo.iFeP04/C cathodes were cycled in CR2032 half-cell configuration at different C-rates. The coin cells when discharged at C/10, 1C, 5C, 10C, 15C and 20C yielded maximum specific capacities of 168.5 mAhg-l,l43 mAhg-l, 128 mAhg-l, 110 mAhg-l, 85 mAhg-l and 50 mAhg-l respectively. It was observed that
Lio.9Nbo.iFeP04/C based half cells yielded more than 1500 nos. of cycles at a 10C rate with reasonable capacity retention. ADVANTAGES
1. The overall conductivity of LiFeP04 cathode material is enhanced by adopting the techniques like reduction of particle size by ball milling of precursors, by providing carbon coating over LiFeP04 particles and by doping with different compositions of niobium in Lii-X NbxFeP04/C.
2. The room temperature dc conductivity LiFeP04 cathode material is improved by Nb doping when compared to LiFeP04/C.
3. The diffusion coefficients LiFeP04 cathode material are improved by Nb doping when compared to LiFeP04/C.
4. One or more compositions of Lil-xNbxFeP04/C (x= 0.05, 0.1, and 0.15) half cells have shown higher specific capacities than LiFeP04/C.
There have been described and illustrated herein embodiments for a method of preparation of an electrode material for lithium-ion batteries. While particular embodiments of the invention have been described, it is not intended that the invention be limited thereto, as it is intended that the invention be as broad in scope as the art will allow and that the specification be read likewise. Thus, while particular types of compositions, particle sizes, structural characterization techniques, temperatures and time periods have been disclosed, it will be appreciated that other compositions, particle sizes, structural characterization techniques, temperatures and time periods may also be used. Many modifications may be made without departing from the basic spirit of the present invention. Accordingly, it will be appreciated by those skilled in the art that the invention may be practiced other than has been specifically described herein.

Claims

Claims :
1. A method of preparing an electrode material for lithium-ion batteries comprising the steps of:
a) preparing a mixture of lithium carbonate, iron oxalate and ammonium di hydrogen phosphate precursors taken in predefined stoichiometric ratios for synthesis of lithium iron phosphate (LiFeP04);
b) adding niobium pentoxide as a precursor for doping of niobium at Li+ site of LiFeP04 for synthesis of niobium doped LiFeP04;
c) ball milling said mixture of precursors dry ground to obtain nano sized powder particles of niobium doped LiFeP04;
d) adding and ball milling a precursor of carbon to said mixture of precursors for synthesizing and obtaining carbon coated niobium doped LiFeP04 nano sized powder particles; and
e) preparing and sintering pellets from said synthesized nano powder particles at a predetermined temperature for a predetermined time.
2. The method as claimed in claim 1, wherein said mixture of precursors are synthesized by solid state vacuum synthesis for obtaining one or more compositions of Lii-xNbxFeP04/C (where x is equal to 0 to 0.15) nano sized powder particles.
3. The method as claimed in claim 1 or 2, wherein a preferable composition is
Lio.9Nbo.iFeP04/C, having a carbon content of about 8.8%.
4. The method as claimed in claim 1, wherein said sintered pellets are structurally characterized for identifying standard orthorhombic olivine type LiFeP04 structure.
5. The method as claimed in claim 1, wherein said precursor of carbon is 10% of acetylene black.
6. The method as claimed in claim 1, wherein a half-cell configuration of said composition of Lio.9Nbo.iFeP04/C has a C-rate discharge of more than 1500 nos. of cycles with a retention capacity at 10C rate.
7. The method as claimed in claim 1, wherein said powder particles obtained during ball milling process are within the range 39 nm to 47 nm of size.
8. The method as claimed in claim 1 or 7, wherein said powder particles obtained during ball milling process are preferably 42nm of size.
9. The method as claimed in claim 1, wherein each pellet has a diameter of about 10 mm and a thickness of about 1.5 mm.
2
10. The method as claimed in claim 1, wherein said pellets are sintered at least at 10 bar vacuum and at said predetermined temperature in range of 650-800°C for said predetermined time of at least 10 hours to obtain a density of at least 3.6 g/cc.
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CN114824253A (en) * 2022-04-24 2022-07-29 中南大学 Method for granulating spherical particles of lithium ion battery cathode material
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