EP4626829A1 - Method for treating positive electrode active material particles, and positive electrode active material and nonaqueous electrolyte secondary battery employing same - Google Patents

Method for treating positive electrode active material particles, and positive electrode active material and nonaqueous electrolyte secondary battery employing same

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Publication number
EP4626829A1
EP4626829A1 EP23817967.5A EP23817967A EP4626829A1 EP 4626829 A1 EP4626829 A1 EP 4626829A1 EP 23817967 A EP23817967 A EP 23817967A EP 4626829 A1 EP4626829 A1 EP 4626829A1
Authority
EP
European Patent Office
Prior art keywords
compound
lithium
transition metal
positive electrode
metal element
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Pending
Application number
EP23817967.5A
Other languages
German (de)
French (fr)
Inventor
Junji KASHIWAGI
Daisuke Morita
Masatoshi Matsumoto
Kazumichi Koga
Kazutoshi Matsumoto
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
BASF SE
Original Assignee
BASF SE
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Filing date
Publication date
Application filed by BASF SE filed Critical BASF SE
Publication of EP4626829A1 publication Critical patent/EP4626829A1/en
Pending legal-status Critical Current

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Classifications

    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01G—COMPOUNDS CONTAINING METALS NOT COVERED BY SUBCLASSES C01D OR C01F
    • C01G53/00—Compounds of nickel
    • C01G53/40—Complex oxides containing nickel and at least one other metal element
    • C01G53/42—Complex oxides containing nickel and at least one other metal element containing alkali metals, e.g. LiNiO2
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01G—COMPOUNDS CONTAINING METALS NOT COVERED BY SUBCLASSES C01D OR C01F
    • C01G53/00—Compounds of nickel
    • C01G53/80—Compounds containing nickel, with or without oxygen or hydrogen, and containing one or more other elements
    • C01G53/82—Compounds containing nickel, with or without oxygen or hydrogen, and containing two or more other elements
    • 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
    • H01M4/36—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
    • H01M4/52—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron
    • H01M4/525—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron of mixed oxides or hydroxides containing iron, cobalt or nickel for inserting or intercalating light metals, e.g. LiNiO2, LiCoO2 or LiCoOxFy
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2002/00—Crystal-structural characteristics
    • C01P2002/80—Crystal-structural characteristics defined by measured data other than those specified in group C01P2002/70
    • C01P2002/85—Crystal-structural characteristics defined by measured data other than those specified in group C01P2002/70 by XPS, EDX or EDAX data
    • 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
    • C01P2004/50—Agglomerated particles
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2004/00—Particle morphology
    • C01P2004/80—Particles consisting of a mixture of two or more inorganic phases
    • C01P2004/82—Particles consisting of a mixture of two or more inorganic phases two phases having the same anion, e.g. both oxidic phases
    • C01P2004/84—Particles consisting of a mixture of two or more inorganic phases two phases having the same anion, e.g. both oxidic phases one phase coated with the other
    • 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
    • H01M2004/028—Positive electrodes
    • 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 method for treating positive electrode active material particles, and to a positive electrode active material and a nonaqueous electrolyte secondary battery employing same.
  • Nonaqueous secondary batteries which are compact, lightweight and have a high energy density are known as power sources for driving cellular telephones and notebook personal computers, etc.
  • power sources for driving cellular telephones and notebook personal computers, etc.
  • widespread use is made of lithium ion secondary batteries which have a large charging/discharging capacity and employ lithium cobaltate or a high-nickel material such as lithium nickelate in the positive electrode.
  • NCM nickel-cobalt-manganese
  • NCA nickel-cobalt-aluminum
  • it is currently feasible to obtain a high- capacity battery by using a positive electrode active material formed by a high-nickel layered compound with a nickel content of greater than 80 moll.
  • Patent Document 1 for example, a surface layer of a high-nickel positive electrode active material is coated with an oxide containing lithium and niobium, with the objective of preventing gas generation and improving battery output characteristics in a lithium ion secondary battery.
  • Patent Document 1 discloses a method for producing an active material composite powder, the method comprising: a spray drying step in which an active material such as lithium-nickel-manganese-cobalt (NMC) is sprayed with a solution containing a niobium peroxo complex and lithium while the solution is dried in parallel with this; and a heat treatment step in which the materials are heat treated after the spray drying step, wherein a heat treatment temperature is higher than 123°C and less than 350°C.
  • NMC lithium-nickel-manganese-cobalt
  • Patent Document 2 indicates that surfaces of positive electrode active material particles are coated with lithium niobate, and, for this purpose, a slurry obtained by dispersing Nb2Os in pure water is added to an aqueous solution of nickel-cobalt-manganese hydroxide, and dried and fired.
  • Patent Document 3 also indicates that surfaces of positive electrode active material particles are coated with lithium niobate, and, for this purpose, a positive electrode active material and niobium oxide are sprayed with 10 mass! of pure water while being mixed and stirred, after which the materials are heat treated.
  • step (3) a heat treatment step in which the cake-like compound obtained in the filter separation step is heat treated to obtain a dried lithium-nickel composite compound
  • the method further comprises, in at least one of step (1), step (2) and/or step (3), a step of mixing the aqueous solvent (used in step (1)), the slurry (of step (1)) or the cake-like compound (of step (2)) or the dried lithium-nickel composite compound (of step (3)) with (i) a compound comprising at least one type of transition metal element selected from the group consisting of Ti, V, Cr, Zr, Nb, Mo, Hf and Ta, and (ii) optionally with a lithium compound; where in case that said compound comprising at least one type of transition metal element is mixed with said dried lithium-nickel composite compound, mixing is carried out in the presence of an aqueous solvent; and where in the obtained product a compound containing lithium and the transition metal element, and the compound comprising a transition metal element are present on:
  • the transition metal element is at least one selected from the group consisting of Ti, V, Cr, Zr, Nb, Mo, Hf and Ta; and where the amount of residual lithium determined by means of neutralization titration is preferably 0.15 wt% or less.
  • FIG. 3 is a photograph obtained by means of scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX) of a cross section of a positive electrode active material produced by means of treatment method according to example 1-4.
  • the preferred embodiments apply both to the method of the invention, the positive electrode active material of the invention and the nonaqueous electrolyte secondary battery of the invention.
  • Patent Document 1 describes a method for producing active material particles having a lithium niobate (LiNbCh) coating layer on a surface layer, in which the active material particles are produced by spraying the active material with a solution containing a niobium peroxo complex and lithium and drying the solution in parallel with this.
  • the active material particles are produced by spraying the active material with a solution containing a niobium peroxo complex and lithium and drying the solution in parallel with this.
  • no treatment to reduce the amount of lithium is actively carried out, so excess Li is thought to remain on the surface layer of the active material particles.
  • the method for treating positive electrode active material particles constitutes a method for treating positive electrode active material particles comprising, preferably as a main component, a lithium-nickel composite compound which contains lithium (Li), nickel (Ni) and oxygen (0) and may contain another element besides Li, Ni and 0.
  • This treatment method then comprises the following steps (l)-(3), and further comprises, in at least one of step (1), step (2) and/or step (3), a step of mixing a compound comprising a transition metal element.
  • a slurry formation step in which the lithium-nickel composite compound is introduced into an aqueous solvent and stirred to prepare a slurry;
  • the step of mixing a compound comprising a transition metal element, the quantity of lithium eluted into the aqueous solvent from the lithiumnickel composite compound as a result of slurry formation, and the compound comprising a transition metal element which is mixed therewith are so minute that it is difficult to identify a primary particle size, and a very fine compound containing lithium and a transition metal element and a very fine compound comprising a transition metal element are thought to be deposited on the lithiumnickel composite compound.
  • the slurry of the lithium-nickel composite compound exhibits alkalinity with a pH of around 11-13, so it is thought that some of the transition metal element compound which has been mixed dissolves and penetrates, as transition metal element ions, into secondary particles of the lithiumnickel composite compound from grain boundary portions between primary particles that constitute the secondary particles, reacting with the excess lithium which is ultimately present on the primary particle surface portions.
  • the compound containing lithium and a transition metal element and the transition metal element compound can be deposited on the surface layer of the secondary particles and on the grain boundary portions between the primary particles of the very fine lithium-nickel composite compound by way of the filter separation step (2) and the heat treatment step (3).
  • the compound comprising a transition metal element is added to the cake-like compound obtained in step (2) or to the dried lithiumnickel composite compound obtained in step (3), as long as some moisture is present (the moisture (aqueous solvent) content being preferably at least 1% by weight (relative to the mixture obtained by mixing the lithiumnickel composite compound in the form in which it is respectively present (e.g.
  • the moisture content is more preferably at least 3% by weight, relative to the total weight of lithiumnickel composite compound and compound comprising a transition metal element (i.e. relative to the mixture obtained by mixing the lithium-nickel composite compound in the form in which it is respectively present ( e.g. in form of the slurry of step (1) or in form of the cake like compound of step (2)) with the compound comprising a transition metal element and optionally with said Li compound).
  • step (2) If the compound comprising a transition metal element is added to the cake-like compound obtained in step (2), addition of further moisture (i.e. of an aqueous solvent) is possible, but not necessary, since after filtration the filter cake generally is still sufficiently humid. If the compound comprising a transition metal element is added to the dried lithiumnickel composite compound obtained in step (3), unless drying is not complete (which generally is however not the case), some moisture has to be introduced to obtain the desired moisture content and to allow the desired reaction of lithium with the compound comprising a transition metal element.
  • further moisture i.e. of an aqueous solvent
  • the water content of the cakelike compound after filter separation is preferably 3 to 20 wt%, more preferably 3 to 10 wt%, and in particular 3 to 8 wt%, and is specifically 5 to 8% by weight, based on the total weight of the cake-like compound.
  • the moisture content of the slurry in the present invention is 65 wt% or less, and preferably 60 wt% or less, to take account of controlling the solidliquid ratio of the slurry to 750 g/L-2000 g/L.
  • “Moisture” means aqueous solvent.
  • the cake-like compound obtained in the filter separation step (2) is heat treated and dried to thereby obtain a dried lithiumnickel composite compound.
  • the temperature in the present invention is preferably set at 100°C-400°C, e.g. at 140 to 400°C, and more preferably at 200°C-350°C.
  • the temperature is lower than the lower limit value, sufficient drying is not easily achievable (generally only under high vacuum and/or after excessively long drying time) and, unless such measures are taken, a large amount of water remains in the lithium-nickel composite compound which is ultimately obtained.
  • the added transition metal element does not react sufficiently with the Li fraction, so an adequate effect cannot be achieved.
  • Li may separate from the crystal lattice of the lithium-nickel composite compound and elutes into the particle surface layer, so there is a risk of an increased amount of residual lithium in the lithium-nickel composite compound which is ultimately obtained.
  • the heat treatment may thus also serve for an annealing of the composite compound.
  • the drying method and treatment using a roller hearth kiln or a rotary kiln, or a vacuum drying treatment, etc. may be appropriately adopted, for example.
  • the atmosphere during the heat treatment needs to take account of the nickel content of the lithium-nickel composite compound which is dried, and the drying treatment is preferably carried out under an oxygen atmosphere, a vacuum atmosphere, an inert gas atmosphere, or decarbonized air having a carbon dioxide concentration of 100 ppm or less, for example.
  • the cake-like compound obtained in the filter separation step (2) is heat-treated in a first step at 100 to 195°C and in an optional second step at 200 to 400°C, and more preferably of 200 to 350°C.
  • the second step is carried out.
  • the first heat treatment is performed under reduced pressure, e.g. under a pressure of 0.1 to 100 mbar.
  • reduced pressure e.g. under a pressure of 0.1 to 100 mbar.
  • customary heatable vacuum drying apparatuses can be used.
  • the second heat treatment is performed under an oxygen-enriched atmosphere (such as oxygen-enriched air, oxygen-nitrogen mixtures with more than 20% by weight of oxygen, and oxygen, preference being given to oxygen mixtures containing at least 90% by weight of oxygen, based on the total weight of the mixture, or pure oxygen); and/or the second heat treatment is performed under an atmosphere with reduced CO2 content, preferably with a CO2 content of at most 100 ppm by volume (0.01% by volume), more preferably of at most 50 ppm by volume (0.005% by volume). More preferably, the second heat treatment is performed under an oxygen-enriched atmosphere which has simultaneously a reduced CO2 content, preferably a CO2 content of at most 100 ppm by volume, more preferably of at most 50 ppm by volume.
  • an oxygen-enriched atmosphere such as oxygen-enriched air, oxygen-nitrogen mixtures with more than 20% by weight of oxygen, and oxygen, preference being given to oxygen mixtures containing at least 90% by weight of oxygen, based on the total weight of the mixture, or pure oxygen
  • the second heat treatment is performed
  • the second heat treatment is carried out.
  • the separation into two heating steps is especially useful if the compound comprising a transition metal element is added in step (3).
  • it is expedient to carry out a first heating step in which the cake like compound obtained in step (2) is dried, then adding the compound comprising a transition metal element (and some moisture to allow reaction, and optionally said lithium compound) to the dried material, and then carrying out a second heating step, in which the obtained mixture is dried and, depending on the temperature, also annealed.
  • This embodiment further comprises, in at least one of step (1), step (2) and/or step (3), a step of mixing a compound comprising a transition metal element.
  • the compound comprising a transition metal element is mixed with the aqueous solvent or the slurry (formed from the aqueous solvent and the lithium-nickel composite compound) in step (1), or mixed with the cakelike compound in step (2), or mixed with the dried cakelike compound in step (3).
  • the lithium in the lithium-nickel composite compound reacts with the compound comprising a transition metal element which is mixed, and the surface layer of the particles can be coated with a compound containing lithium and a transition metal element, and the compound comprising a transition metal element.
  • the step of mixing the compound comprising a transition metal element may be performed in one or two or all three of step (1), step (2) and step (3).
  • the step of mixing the compound comprising a transition metal element is preferably performed before and/or after introduction of the lithium-nickel composite compound into the aqueous solvent in step (1), or performed with the cake-like compound obtained by filter separating the slurry in step (2).
  • mixing the compound comprising a transition metal element is performed in step (3).
  • mixing is carried out in the presence of an aqueous solvent.
  • this is carried out by using the compound comprising a transition metal element in form of an aqueous solution or suspension comprising said compound comprising a transition metal element and optionally said lithium compound.
  • an aqueous solution or suspension comprising said compound comprising a transition metal element and optionally said lithium compound is mixed with the lithium-nickel composite compound dried in step (3).
  • the compound containing lithium and a transition metal element and the compound comprising a transition metal element which are present on the surfaces or the grain boundary portions of the lithium-nickel composite compound may be present in the form of particles, and need not necessarily form a (coating) layer.
  • the compounds may form a layer and there is no particular limitation.
  • the coating condition and coating layer thickness afforded by the compound containing lithium and a transition metal element and the compound comprising a transition metal element may be investigated by using Auger electron spectroscopy (also referred to below as "AES”), scanning electron microscopy with energy dispersive X-ray spectroscopy (also referred to below as “SEM-EDX”), or transmission electron microscopy with energy dispersive X-ray spectroscopy (also referred to below as "TEM-EDX”), etc., for example.
  • Auger electron spectroscopy also referred to below as "AES”
  • SEM-EDX scanning electron microscopy with energy dispersive X-ray spectroscopy
  • TEM-EDX transmission electron microscopy with energy dispersive X-ray spectroscopy
  • a coating rate of the coating layer may be obtained by image analysis, for example.
  • the positive electrode active material according to the present invention should be formed by a lithium-nickel composite compound which contains Li, Ni and 0 and may contain another element besides Li, Ni and 0, and there is no particular limitation as to the composition thereof, but the lithium-nickel composite compound preferably has a composition represented by the following formula (I): Li a Ni 1-b-c Mn b M c 0 2 (I)
  • b is 0.05 to 0.2 and c is 0; the compound (I) being thus a compound of formula (1.1): Li a Ni 1-b Mn b 0 2 (1.1), where b is 0.05 to 0.2 and Ni is 0.80-0.95 (to be more precise, (1-b) is 0.80-0.95).
  • the positive electrode active material according to the present invention should comprise the lithium-nickel composite compound, while the A element compound may also be present on surfaces of the particles of the lithium-nickel composite compound, and the A element compound can be present in the form of a compound of lithium and the A element or in the form of an A element oxide, and the effects thereof may vary in some respects in the present invention.
  • the A element compound can be present in the form of a compound of lithium and the A element or in the form of an A element oxide, and the effects thereof may vary in some respects in the present invention.
  • an Al compound is present on the particle surfaces while an Nb compound is also present, it is possible to impart an effect of improving long-term cycle characteristics when a battery has been produced.
  • a element there is no particular limitation as to this A element, but examples thereof include: aluminum (Al), manganese (Mn), titanium (Ti), cobalt (Co), magnesium (Mg), zinc (Zn), niobium (Nb), tungsten (W), molybdenum (Mo), vanadium (V), chromium (Cr), calcium (Ca), iron (Fe), gallium (Ga), strontium (Sr), yttrium (Y), antimony (Sb), ruthenium (Ru), indium (In), tin (Sn), tantalum (Ta), bismuth (Bi), zirconium (Zr) and boron (B), etc.
  • an amount of residual lithium in the positive electrode active material according to the present invention as determined by neutralization titration is preferably 0.15 wt% or less, and more preferably 0.12 wt% or less. If the amount of residual lithium is above the upper limit value, this leads to gas generation, and there is also a risk of increasing reaction resistance in the lithium battery. It should be noted that the amount of residual lithium is the amount of Li derived from LiOH or Li2CC>3, for example, which is not included in the lithium-nickel composite compound or the coating layer (the compound containing lithium and a transition metal element).
  • the amount of residual lithium was calculated on the basis of the Warder method. Specifically, 20 g of a powder of particles of the lithium-nickel composite compound serving as positive electrode active material particles were added to 100 mL of water and stirred for 20 minutes at room temperature, after which solids were filter separated and removed to obtain a supernatant for which the amount of residual lithium was determined by titration using 0.2 N hydrochloric acid.
  • ⁇ Method for producing positive electrode active material> There is no particular limitation as to the method for producing the positive electrode active material according to the present invention, provided that the positive electrode active material particles are treated according to what is described above in the " ⁇ Method for treating positive electrode active material particles>" section, and the lithium-nickel composite compound constituting the positive electrode active material particles may be produced by a normal method.
  • an aqueous solution comprising a nickel compound aqueous solution and various types of aqueous solutions of compounds comprising an element other than Ni, according to the intended composition of the positive electrode active material are dripped into a reaction tank with stirring, using an alkaline aqueous solution such as a sodium hydroxide aqueous solution or an ammonia solution, for example, as a mother liquor, the pH is monitored and controlled to a suitable range while sodium hydroxide, etc. is also dripped, and the precursor composite compound is obtained by coprecipitation by means of a wet reaction.
  • the precursor composite compound which may be cited include hydroxides, oxides obtained by calcining said hydroxides, and carbonates, etc.
  • an inert gas, or nitrogen gas which is industrially preferred, is preferably used to set a nitrogen atmosphere inside the reaction tank so that the oxygen concentration inside the reaction tank system and in the solutions is as low as possible.
  • nickel compound there is no particular limitation as to the nickel compound, but examples which may be cited include: nickel sulfate, nickel oxide, nickel hydroxide, nickel nitrate, nickel carbonate, nickel chloride, nickel iodide, and metallic nickel, etc.
  • zinc compound there is no particular limitation as to the zinc compound, but examples which may be cited include: zinc sulfate, zinc oxide, zinc hydroxide, zinc nitrate, zinc carbonate, zinc chloride, zinc iodide, and metallic zinc, etc.
  • niobium compound there is no particular limitation as to the niobium compound, but examples which may be cited include: niobium oxide, niobium chloride, lithium niobate, and niobium iodide, etc.
  • tungsten compound there is no particular limitation as to the tungsten compound, and examples which may be cited include: tungsten oxide, sodium tungstate, ammonium paratungstate, tungsten hexacarbonyl, and tungsten sulfide, etc.
  • the proportions in which the nickel compound and the various types of compounds comprising an element other than Ni are blended should be appropriately adjusted while taking account of the intended composition of the positive electrode active material so that the amount of Ni and the amount of the various elements other than Ni reach the desired proportions.
  • the precursor composite compound obtained by means of a wet reaction as described above is preferably subjected to a washing treatment and then a drying treatment after dewatering.
  • washing treatment By performing the washing treatment, it is possible to rinse off impurities taken into agglomerated particles during the reaction, such as sulfate radicals and carbonate radicals adhering to a surface layer, and a sodium fraction.
  • Washing treatments which may be used include a process of Nutsche washing employing a Buchner funnel, provided that there is only a small amount of impurity, and a process of feeding a suspension after the reaction to a press filter, washing with water and dewatering.
  • the washing treatment may employ pure water, a sodium hydroxide aqueous solution, or a sodium carbonate aqueous solution, etc., but pure water is preferably used from an industrial point of view.
  • a sodium hydroxide aqueous solution which is pH-controlled according to the residual amount.
  • the precursor composite compound synthesized in this way and a lithium compound are then mixed in a predetermined ratio to prepare a mixture.
  • the mixing may be solventbased mixing in which the precursor composite compound and the lithium compound are each in the form of a solution, such as an aqueous solution, and the solutions are mixed in a predetermined ratio, or it may be nonsolvent-based mixing in which a powder of the precursor composite compound and a powder of the lithium compound are weighed out in predetermined proportions and mixed by a dry method.
  • the proportions in which the lithium compound and the precursor composite compound are blended should be appropriately adjusted while taking account of the intended composition of the positive electrode active material so that the total of the amount of Li, the amount of Ni, and the amounts of any of the various other elements reach the desired proportions.
  • the firing time during the firing is not particularly limited either, and it should be a time which likewise enables an adequate lithium formation reaction of the precursor composite compound and adequate crystal growth, and is preferably a time of 1 hour-15 hours, and more preferably 2 hours-10 hours, for example.
  • the positive electrode active material particles comprising a lithium-nickel composite compound obtained in this way are subjected to the treatment method according to an embodiment of the present invention, which comprises steps (l)-(3), and further comprises, in at least one of step (1), step (2) and step (3), a step of mixing a compound comprising a transition metal element, as described above, and as a result it is possible to obtain the positive electrode active material according to the present invention, in which the compound containing lithium and a transition metal element and the compound comprising a transition metal element are present on: (a) the surfaces of the secondary particles of the lithium-nickel composite compound, and (b) at least part of the grain boundary portions formed by adjacent primary particles located on the surfaces of the plurality of primary particles constituting the secondary particles .
  • negative electrode active materials such as lithium metal, graphite, and low-crystallinity carbon materials, for example, but also at least one non-metal or metal element selected from the group consisting of Si, Al, Sn, Pb, Zn, Bi and Cd, or alloys comprising same, or chalcogen compounds comprising same.
  • XRD diffraction data of the positive electrode active material was obtained under the following X-ray diffraction conditions using an X-ray diffraction apparatus [SmartLab, produced by Rigaku Corp.], after which a Rietveld analysis was performed using this XRD diffraction data, with reference to "R. A. Young, ed., "The Rietveld Method", Oxford University Press (1992)".
  • Samples of 0.2 g of the precursor composite compound and the positive electrode active material were each heated and dissolved in 25 mL of a 20% hydrochloric acid solution, and the materials were cooled then transferred to a 100 mL measuring flask, and pure water was introduced to prepare an adjusted liquid.
  • the elements in the adjusted liquid were quantitatively determined using ICP-AES (Optima 8300, produced by PerkinElmer, Inc.).
  • a 2032-type coin cell employing the positive electrode active material was produced by using a positive electrode, negative electrode and electrolytic solution produced by the following respective methods.
  • the coated aluminum foil was dried at 110°C to prepare a sheet which was punched to a diameter of 15 mm and then rolled so that the density of a composite material was 3.0 g/cm 3 , and this was used as the positive electrode.
  • a lithium foil having a thickness of 500 pm punched to a diameter of 16 mm was used as the negative electrode.
  • the initial charging/discharging efficiency was calculated on the basis of the following formula using the measured value of the initial charging capacity and the measured value of the initial discharging capacity.
  • the mixture was then fired over 5 hours at a maximum temperature of 750°C under an oxygen atmosphere (oxygen concentration: 97 vol%) using an electric furnace, and positive electrode active material particles 1 (lithiumnickel composite compound) (also referred to below as "NM") were obtained.
  • positive electrode active material particles 1 lithiumnickel composite compound
  • the mean particle size of primary particles in the positive electrode active material particles 1 was approximately 500 nm, and the mean particle size of secondary particles was approximately 12.8 pm .
  • the positive electrode active material particles 1 were introduced into pure water (water temperature 25°C) in a reaction tank (10 L capacity) and stirred over 10 minutes to prepare a slurry.
  • the ratio of the amount of positive electrode active material particles 1 to the amount of pure water was adjusted to 1250 g/L.
  • a niobium pentoxide hydrate (Nb2C>5-nH20) powder was admixed as a compound comprising a transition metal element with further stirring of the slurry, and stirring was performed over 10 minutes.
  • the added amount of niobium in the niobium pentoxide hydrate (Nb2Os-n ⁇ O) powder was 0.5 mol% with respect to the amount of metal element in the positive electrode active material particles 1. Furthermore, the pH of the slurry at this time was 12.2.
  • the mixed slurry was then filter separated using a Buchner funnel to obtain a cake-like compound.
  • a slurry was prepared in the same way as in example 1 and a niobium pentoxide hydrate (Nb2Os-nJbO) powder was admixed .
  • the slurry was filter separated in the same way as in example 1 to obtain a cake-like compound.
  • the characteristics of the resulting positive electrode active material were determined. The characteristics of the positive electrode active material and the conditions in the steps are shown in table 1.
  • Example 1-3 treatment of positive electrode active material particles 1 (production of positive electrode active material)> (1) Slurry formation step and step of mixing compound comprising a transition metal element
  • a slurry was prepared in the same way as in example 1 and 0.2 moll niobium pentoxide hydrate (Nb2Os-nJbO) powder was admixed .
  • the slurry was filter separated in the same way as in example 1 to obtain a cake-like compound.
  • the positive electrode active material particles 1 were introduced into pure water (water temperature 25°C) in a reaction tank (10 L capacity) and stirred over 10 minutes to prepare a slurry.
  • the ratio of the amount of positive electrode active material particles 1 to the amount of pure water was adjusted to 1250 g/L.
  • the pH of the slurry at this time was 12.1.
  • 0.1 moll niobium pentoxide hydrate (Nb2Os-n ⁇ O) powder was added, and the slurry obtained in the slurry formation step (1) was filter separated to obtain a cake-like compound.
  • the moisture content of the cake-like compound was 6.1 wtl.
  • 0.1 moll niobium pentoxide hydrate (Nb2C>5-nH20) powder was admixed with the resulting cakelike compound.
  • the positive electrode active material particles 1 were introduced into pure water (water temperature 25°C) in a reaction tank (10 L capacity) and stirred over 10 minutes to prepare a slurry.
  • the ratio of the amount of positive electrode active material particles 1 to the amount of pure water was adjusted to 1500 g/L.
  • the pH of the slurry at this time was 12.3.
  • the slurry obtained in the slurry formation step (1) was filter separated to obtain a cake-like compound.
  • the moisture content of the cake-like compound was 6 wt%.
  • Niobium pentoxide hydrate (Nb2Os-n ⁇ O) dissolved in an aqueous LiOH solution (Nb2Os-n ⁇ O was present in an amount of 0.2 mol% relative to the amount of all elements other than Li and 0 in the lithium-nickel composite compound) was admixed with the resulting cake-like compound.
  • the moisture content of the cake-like compound after mixing was 14.4 wt%.
  • the cake-like compound obtained in the filter separation step (2) was heat treated over 19 hours at 185°C using a vacuum drying apparatus. A heat treatment was then performed over 120 minutes at 300°C in an oxygen atmosphere (oxygen concentration: 97 vol%) using an electric furnace, and a dried lithium-nickel composite compound was obtained to produce the positive electrode active material.
  • the characteristics of the resulting positive electrode active material were determined. The characteristics of the positive electrode active material and the conditions in the steps are shown in table 1.
  • the positive electrode active material particles 1 were introduced into pure water (water temperature 25°C) in a reaction tank (10 L capacity) and stirred over 10 minutes to prepare a slurry.
  • the ratio of the amount of positive electrode active material particles 1 to the amount of pure water was adjusted to 1500 g/L.
  • the pH of the slurry at this time was 12.3.
  • the slurry obtained in the slurry formation step (1) was filter separated to obtain a cake-like compound.
  • the moisture content of the cake-like compound was 6.2 wt%.
  • a niobium pentoxide hydrate (Nb2Os-n ⁇ O) powder was mixed with the positive electrode active material particles 1 as a compound comprising a transition metal element, the mixture was heat treated over 120 minutes at 350°C in an oxygen atmosphere (oxygen concentration: 97 vol%) using an electric furnace, and the positive electrode active material was produced. The characteristics of the resulting positive electrode active material were determined. The characteristics of the positive electrode active material and the conditions in the steps are shown in table 1.
  • a powdery lithium niobate (LiNbCh) powder was mixed with the positive electrode active material particles 1 as a compound comprising a transition metal element, the mixture was heat treated over 120 minutes at 350°C in an oxygen atmosphere (oxygen concentration: 97 vol%) using an electric furnace, and the positive electrode active material was produced. The characteristics of the resulting positive electrode active material were determined. The characteristics of the positive electrode active material and the conditions in the steps are shown in table 1.
  • nonaqueous electrolyte secondary battery characteristics test> The initial charging capacity, initial discharging capacity, initial charging/discharging efficiency, initial reaction resistance, and resistance ratio (compared with comparative example 1-2) were obtained as characteristics of nonaqueous electrolyte secondary batteries in which the positive electrode active materials obtained in examples 1-1 to 1-5 and comparative examples 1-1 to 1-5 were used as the positive electrode. The results are shown in table 1.
  • the initial reaction resistance was then shown to be 59 Q in the battery employing the positive electrode active material according to example 1-1, in which the step of mixing Nb2Os-nJbO powder with the slurry, the filter separation step (2) and the heat treatment step (3) were performed, whereas the initial reaction resistance was shown to be 220 Q in the battery employing the positive electrode active material according to comparative example 1-2 in which the filter separation step (2) and the heat treatment step (3) were performed, without any addition to the slurry.
  • Li2MnO3 which is thought to be an unstable resistance component that impedes Li migration within the crystal structure, was formed as a domain in the crystal lattice by the Li fraction contained in excess, as a result of Mn, which is substituted with Ni in the positive electrode active material, reacting with Li when the positive electrode active material is synthesized, and therefore, during the heat treatment at 350°C in the heat treatment step in example 1-2, not only does the added Nb react with the eluted lithium, it is also thought to withdraw Li from the Li2MnO3 domain.
  • Li2MnO3 is eliminated in the resistance component because of a phase change to a crystal structure such as Lii- x NiyMnO2 or Li x Mn2O4- y , for example, which is therefore inferred to cause an increase in the Li capable of migrating within the crystal structure, and thus the battery capacity increased.
  • the method for treating positive electrode active material particles according to the examples which comprises the slurry formation step (l)-heat treatment step (3), and further comprises, in at least one of step (1), step (2) and step (3), a step of mixing a compound comprising a transition metal element, it is possible to provide positive electrode active material particles which achieve lower resistance by reducing a resistance component and higher battery capacity, while also reducing excess Li on surfaces of the primary particles and secondary particles of the lithium-nickel composite compound.
  • the SEM-EDX described in the embodiment above was performed for the positive electrode active material obtained in example 1-4, and a cross-sectional photograph of the positive electrode active material such as shown in fig. 3 was obtained. Detection locations (detection sites) were selected, Nb/(NiMnNb) (mol%) was calculated and these are shown in table 2 below, together with detection results.
  • the Nb detection results are denoted by 0 and X: an evaluation of 0 was given where the value of Nb/ (NiMnNb) was 0.10 mol% or greater, and an evaluation of X was given where the value was less than 0.10 mol%.
  • the amount of Nb in Nb/(NiMnNb) denotes the total amount of substance in compounds comprising Nb, and includes both the compound containing lithium and Nb and the compound comprising Nb. It should be noted that the numerical values of "039”, “040”, “041”, “042”, “043”, “044", “045", "046”, "047”, “048”, "049”,
  • the cake-like compound obtained in the filter separation step (2) was heat treated over 19 hours at 185°C using a vacuum drying apparatus, and a dried lithium-nickel composite compound was obtained to produce the positive electrode active material.
  • the amount of residual Li (the total amount of Li derived from LiOH and Li2CC>3) was determined for the resulting positive electrode active material. Furthermore, the treatment steps, added components, added amounts, and final heat treatment temperature (also referred to collectively below as “conditions in the steps") are also shown in table 3 below.
  • Step of mixing compound comprising a transition metal element and slurry formation step
  • a slurry was prepared in the same way as in example 2-1.
  • the slurry was filter separated in the same way as in example 1 to obtain a cake-like compound.
  • the cake-like compound obtained in the filter separation step (2) was heat treated over 19 hours at 185°C using a vacuum drying apparatus. A heat treatment was then performed over 120 minutes at 350°C in an oxygen atmosphere (oxygen concentration: 97 vol%) using an electric furnace, and a dried lithium-nickel composite compound was obtained to produce the positive electrode active material.
  • the characteristics of the resulting positive electrode active material were determined. The characteristics of the positive electrode active material and the conditions in the steps are shown in table 3.
  • the positive electrode active material particles 2 were introduced into pure water (water temperature 25°C) in a reaction tank (10 L capacity) and stirred over 10 minutes to prepare a slurry.
  • the ratio of the amount of positive electrode active material particles 2 to the amount of pure water was adjusted to 1250 g/L.
  • a vanadium pentoxide (V2O5) powder was admixed as a compound comprising a transition metal element with further stirring, and stirring was performed over 10 minutes.
  • the added amount of vanadium in the vanadium pentoxide (V2O5) powder was 0.2 mol% with respect to the amount of all elements other than Li and 0 in the positive electrode active material particles 2 (NCA).
  • the pH of the slurry at this time was 12.2.
  • the mixed slurry was then filter separated using a Buchner funnel to obtain a cake-like compound.
  • the cake-like compound obtained in the filter separation step (2) was heat treated over 19 hours at 185°C using a vacuum drying apparatus. A heat treatment was then performed over 120 minutes at 350°C in an oxygen atmosphere (oxygen concentration: 97 vol%) using an electric furnace, and a dried lithium-nickel composite compound was obtained to produce the positive electrode active material.
  • the characteristics of the resulting positive electrode active material were determined. The characteristics of the positive electrode active material and the conditions in the steps are shown in table 3.
  • Step of mixing compound comprising a transition metal element and slurry formation step
  • the cake-like compound obtained in the filter separation step (2) was heat treated over 19 hours at 185°C using a vacuum drying apparatus. A heat treatment was then performed over 120 minutes at 350°C in an oxygen atmosphere (oxygen concentration: 97 vol%) using an electric furnace, and a dried lithium-nickel composite compound was obtained to produce the positive electrode active material.
  • the slurry obtained in the slurry formation step (1) was filter separated using a Buchner funnel to obtain a cakelike compound.
  • the cake-like compound obtained in the filter separation step (2) was heat treated over 19 hours at 185°C using a vacuum drying apparatus. A heat treatment was then performed over 120 minutes at 350°C in an oxygen atmosphere (oxygen concentration: 97 vol%) using an electric furnace, and a dried lithium-nickel composite compound was obtained to produce the positive electrode active material.
  • the amount of residual Li was determined for the positive electrode active material particles 2 (positive electrode active material), without the positive electrode active material particles 2 (NCA) having undergone any of the slurry formation step (l)-heat treatment step (3) or the step of mixing a compound comprising a transition metal element. The results are shown in table 3.

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Abstract

The present invention relates to a method for treating positive electrode active material particles, in which residual lithium in excess in a particle surface layer of a lithium-nickel composite compound is reduced, and a balance is achieved between lower resistance as a result of reducing a resistance component, and higher battery capacity. The invention relates also to such positive electrode active material particles and to a nonaqueous electrolyte secondary battery comprising a positive electrode that contains such positive electrode active material.

Description

Method for treating positive electrode active material particles, and positive electrode active material and nonaqueous electrolyte secondary battery employing same
[Technical Field]
[0001]
The present invention relates to a method for treating positive electrode active material particles, and to a positive electrode active material and a nonaqueous electrolyte secondary battery employing same.
[Background Art] [0002]
Nonaqueous secondary batteries which are compact, lightweight and have a high energy density are known as power sources for driving cellular telephones and notebook personal computers, etc. Among these, widespread use is made of lithium ion secondary batteries which have a large charging/discharging capacity and employ lithium cobaltate or a high-nickel material such as lithium nickelate in the positive electrode.
[0003]
Examples of positive electrode active materials which are used for lithium ion secondary batteries include high- nickel positive electrode active materials such as nickel-cobalt-manganese (NCM)-based positive electrode active materials in which a portion of the nickel is substituted with cobalt, and manganese is introduced, and nickel-cobalt-aluminum (NCA)-based positive electrode active materials in which a portion of the nickel is substituted with cobalt, and aluminum is introduced. In particular, it is currently feasible to obtain a high- capacity battery by using a positive electrode active material formed by a high-nickel layered compound with a nickel content of greater than 80 moll. However, when a lithium ion secondary battery employing this kind of positive electrode active material is repeatedly used over a long period of time, the lithium ion secondary battery generates gas, and there is also a rise in reaction resistance which causes a drop in battery output characteristics and cycle characteristics.
[0004]
The effect of the lithium component remaining on the surface of positive electrode active material particles is thought to be one of the causes of the problems above. In order to obtain positive electrode active material particles having a favorable crystal state in a high- nickel-content positive electrode active material such as described above, it is necessary to set the molar amount of lithium slightly greater than a metal component in a precursor composite compound when a lithium compound and the precursor composite compound are mixed, that is, the ratio Li/(metal component in precursor composite compound) needs to be slightly greater than 1.0, and as a result, excess lithium remains on the particle surfaces of the lithium-nickel composite compound which is obtained via a firing step. Attempts are being made to reduce the amount of residual lithium by water washing and heat treating the lithium-nickel composite compound after the firing step, and although the excess lithium can be reduced when a temperature of around 100°C is used in a drying step for the heat treatment, it is not possible to eliminate proton exchange to Li sites in particle surface layer portions due to the water washing, and a resistance component is formed. Furthermore, when a temperature of 450°C or greater is used, lithium separates from the crystal lattice within the particles during the heat treatment and elutes into the particle surface layer, and the excess lithium is ultimately formed on the particle surface layer. For this reason, attempts are being made to reduce the resistance component resulting from proton exchange to the Li sites, while reducing excess lithium remaining on the particle surfaces. [0005]
In Patent Document 1, for example, a surface layer of a high-nickel positive electrode active material is coated with an oxide containing lithium and niobium, with the objective of preventing gas generation and improving battery output characteristics in a lithium ion secondary battery. Specifically, Patent Document 1 discloses a method for producing an active material composite powder, the method comprising: a spray drying step in which an active material such as lithium-nickel-manganese-cobalt (NMC) is sprayed with a solution containing a niobium peroxo complex and lithium while the solution is dried in parallel with this; and a heat treatment step in which the materials are heat treated after the spray drying step, wherein a heat treatment temperature is higher than 123°C and less than 350°C.
[0006]
Furthermore, Patent Document 2 indicates that surfaces of positive electrode active material particles are coated with lithium niobate, and, for this purpose, a slurry obtained by dispersing Nb2Os in pure water is added to an aqueous solution of nickel-cobalt-manganese hydroxide, and dried and fired.
[0007]
Furthermore, Patent Document 3 also indicates that surfaces of positive electrode active material particles are coated with lithium niobate, and, for this purpose, a positive electrode active material and niobium oxide are sprayed with 10 mass! of pure water while being mixed and stirred, after which the materials are heat treated.
[0008]
Furthermore, Patent Document 4 describes a positive electrode active material in which primary particle surfaces contain calcium, and secondary particle surfaces contain niobium, and in order to obtain this kind of positive electrode active material, calcium-containing positive electrode active material particles are washed with water, after which niobium hydroxide is admixed, and the mixture is heat-treated.
[Prior Art Documents]
[Patent Document]
[0009]
[Patent Document 1] JP 2015-056307 A
[Patent Document 2] JP 2019-139862 A
[Patent Document 3] WO 2021/054468 Al
[Patent Document 4] WO 2021/241078 Al
[Non-Patent Documents] [0010]
[Non-Patent Document 1] Analele Universitatii din Bucuresti-Chimie, Anul XIV (serie noua), vol. I-II, pp. 65-72
[Summary of the Invention]
[Problems to be Solved by the Invention] [0011]
As indicated above, Patent Document 1 describes production of active material particles in which, when the active material is sprayed with a solution containing a niobium peroxo complex and lithium and the solution is dried in parallel with this, a lithium niobate (LiNbCh) coating layer is formed on the surface layer of the active material. This lithium niobate coating layer allows a lithium ion-conductive oxide layer to be interposed at an interface between a sulfide-based solid electrolyte and a positive electrode active material, and improved battery characteristics are anticipated as a result. Patent Document 1 furthermore indicates that the lithium niobate coating layer formed in this way has a small number of voids and therefore has high lithium ion conductivity, making it possible to produce active material particles for a lithium battery with a reduced resistance component.
[0012]
However, no special operations are performed to reduce the amount of lithium in the active material particles produced in this way, and excess lithium is thought to remain on the surface layer of the active material particles. When these active material particles are actually used as a positive electrode active material, there are thus problems in the lithium secondary battery in that gas is generated due to the residual lithium, and the reduction in the resistance component is also inadequate .
[0013]
Furthermore, in Patent Documents 2-4, the particles are washed with water (formed into a slurry) or the surfaces of the positive electrode active material particles are coated with lithium niobate, whereby it is thought possible to limit the effects of the excess lithium on the particle surfaces to a certain extent.
[0014]
However, none of the treatment methods in the documents above is properly suited to reducing the excess lithium on the particle surfaces of the positive electrode active material, and there is a risk that it will not be possible to sufficiently reduce the excess lithium. Additionally, the excess lithium may cause gelling of the slurry during battery production and gas generation after the battery has been produced. Additionally, as a result of the step of water washing (forming a slurry), it is feasible that the resistance component resulting mainly from proton exchange with Li in the particle surface layer will increase, and even though the intention may be to achieve higher battery capacity by performing the heat treatment to remove the excess lithium, problems may still arise in the long term lifespan of the battery because of the resistance component.
[0015]
In light of these matters, there is a need for a material which is capable of achieving a balance between lower resistance and higher battery capacity, while also reducing residual lithium which is in excess.
[0016]
The present invention has been devised in light of the problems of the prior art as described above, and the objective thereof lies in providing a method for treating positive electrode active material particles, in which residual lithium in excess in a particle surface layer of a lithium-nickel composite compound is reduced, and a balance is achieved between lower resistance as a result of reducing a resistance component, and higher battery capacity, and also in providing a positive electrode active material and a nonaqueous electrolyte secondary battery employing same.
[Means for Solving the Problems]
[0017]
In order to achieve this objective, the present invention provides a method for treating positive electrode active material particles in which formation of a slurry of a lithium-nickel composite compound, which also constitutes a water washing step, and mixing of a transition metal compound are suitably performed so as to reduce excess lithium in a surface layer of the positive electrode active material particles, and to achieve a balance between lower resistance and higher battery capacity in the positive electrode active material particles after heat treatment. Furthermore, this treatment method achieves the objective above by virtue of the fact that a compound containing lithium and a transition metal element, and a compound comprising a transition metal element are also present on surfaces of secondary particles of the positive electrode active material and on at least part of a grain boundary portion (interface between primary particles) formed by adjacent primary particles located on surfaces of the plurality of primary particles constituting the secondary particles
[0018]
Specifically, the present invention provides a method for treating positive electrode active material particles comprising a lithium-nickel composite compound which contains lithium, nickel and oxygen and may contain another element besides lithium, nickel and oxygen, the method being characterized by comprising:
(1) a slurry formation step in which the lithium-nickel composite compound is introduced into an aqueous solvent and stirred to prepare a slurry;
(2) after the slurry formation step, a filter separation step in which the slurry is filter separated to obtain a cake-like compound; and
(3) a heat treatment step in which the cake-like compound obtained in the filter separation step is heat treated to obtain a dried lithium-nickel composite compound, wherein the method further comprises, in at least one of step (1), step (2) and/or step (3), a step of mixing the aqueous solvent (used in step (1)), the slurry (of step (1)), the cake-like compound (of step (2)) and/or the dried lithium-nickel composite compound (of step (3)) with (i) a compound comprising at least one type of transition metal element selected from the group consisting of Ti, V, Cr, Zr, Nb, Mo, Hf and Ta, and (ii) optionally with a lithium compound; where in case that said compound comprising at least one type of transition metal element is mixed with said dried lithium-nickel composite compound (of step (3)), mixing is carried out in the presence of an aqueous solvent; and where in the obtained product a compound containing lithium and the transition metal element, and the compound comprising a transition metal element are present on:
(a) surfaces of secondary particles of the dried lithiumnickel composite compound, and
(b) at least part of a grain boundary portion (interface between primary particles) formed by adjacent primary particles located on surfaces of the plurality of primary particles constituting the secondary particles.
[0019]
The present method can alternatively be worded as a method for preparing positive electrode active material particles comprising a lithium-nickel composite compound which contains lithium, nickel and oxygen and may contain another element besides lithium, nickel and oxygen, the method being characterized by the same step as outlined above, namely by comprising:
(1) a slurry formation step in which the lithium-nickel composite compound is introduced into an aqueous solvent and stirred to prepare a slurry;
(2) after the slurry formation step, a filter separation step in which the slurry is filter separated to obtain a cake-like compound; and
(3) a heat treatment step in which the cake-like compound obtained in the filter separation step is heat treated to obtain a dried lithium-nickel composite compound, wherein the method further comprises, in at least one of step (1), step (2) and/or step (3), a step of mixing the aqueous solvent (used in step (1)), the slurry (of step (1)) or the cake-like compound (of step (2)) or the dried lithium-nickel composite compound (of step (3)) with (i) a compound comprising at least one type of transition metal element selected from the group consisting of Ti, V, Cr, Zr, Nb, Mo, Hf and Ta, and (ii) optionally with a lithium compound; where in case that said compound comprising at least one type of transition metal element is mixed with said dried lithium-nickel composite compound, mixing is carried out in the presence of an aqueous solvent; and where in the obtained product a compound containing lithium and the transition metal element, and the compound comprising a transition metal element are present on:
(a) surfaces of secondary particles of the dried lithiumnickel composite compound, and
(b) at least part of a grain boundary portion (interface between primary particles) formed by adjacent primary particles located on surfaces of the plurality of primary particles constituting the secondary particles.
[0020]
The remarks made below to the "treatment method" of the invention apply mutatis mutandis to the "method of preparing" wording.
[0021]
The present invention relates also to a positive electrode active material obtainable by the method according to the invention; as well as to a positive electrode active material comprising a lithium-nickel composite compound which contains lithium, nickel and oxygen and may contain another element besides lithium, nickel and oxygen, where a compound containing lithium and a transition metal element, and a compound comprising the transition metal element are present on:
(a) surfaces of secondary particles of the lithium-nickel composite compound, and
(b) at least part of a grain boundary portion (interface between primary particles) formed by adjacent primary particles located on surfaces of the plurality of primary particles constituting the secondary particles; where the transition metal element is at least one selected from the group consisting of Ti, V, Cr, Zr, Nb, Mo, Hf and Ta; and where the amount of residual lithium determined by means of neutralization titration is preferably 0.15 wt% or less.
[0022]
The present invention relates moreover to a nonaqueous electrolyte secondary battery comprising a positive electrode containing the positive electrode active material of the invention.
[0023]
According to the present invention, by controlling the excess amount of lithium resulting from the slurry formation step, and by introducing the transition metal element which reacts with this excess amount of lithium, not only does this reduce the excess amount of lithium ultimately remaining, the locations where the compound of lithium and transition metal element is present and the amount in which it is present are effectively controlled, so a balance between high battery capacity and low resistance is achieved.
[Advantage of the Invention]
[0024]
The present invention makes it possible to provide a method for treating positive electrode active material particles in which formation of a slurry of a lithiumnickel composite compound, which also constitutes a water washing step, and mixing of a transition metal compound are suitably performed so as to reduce excess lithium in a surface layer of the positive electrode active material particles, and to achieve a balance between lower resistance and higher battery capacity in the positive electrode active material particles after heat treatment, and also to provide a positive electrode active material and a nonaqueous electrolyte secondary battery employing same.
[Brief Description of the Figures]
[0025]
[Fig. 1] is a schematic view in longitudinal section of a surface layer of a secondary particle of a lithiumnickel composite compound when a coating layer of a compound containing lithium and a transition metal element and a compound comprising the transition metal element is formed by means of a method for treating positive electrode active material particles according to the embodiment.
[Fig. 2] is a schematic view in transverse section of a secondary particle of a lithium-nickel composite compound when a coating layer of a compound containing lithium and a transition metal element and a compound comprising the transition metal element is formed by means of the method for treating positive electrode active material particles according to the embodiment.
[Fig. 3] is a photograph obtained by means of scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX) of a cross section of a positive electrode active material produced by means of treatment method according to example 1-4.
[Embodiment of the Invention]
[0026]
Embodiments of the present invention will be described below with reference to the drawings. The following description of preferred embodiments is merely an illustration in essence, and is not intended to limit the present invention, methods of application thereof or usages thereof.
As far as applicable, the preferred embodiments apply both to the method of the invention, the positive electrode active material of the invention and the nonaqueous electrolyte secondary battery of the invention. [0027]
<Method for treating positive electrode active material particles>
As indicated above, Patent Document 1 describes a method for producing active material particles having a lithium niobate (LiNbCh) coating layer on a surface layer, in which the active material particles are produced by spraying the active material with a solution containing a niobium peroxo complex and lithium and drying the solution in parallel with this. In the production method of Patent Document 1, however, no treatment to reduce the amount of lithium is actively carried out, so excess Li is thought to remain on the surface layer of the active material particles. Furthermore, in the production method of Patent Document 1, a coating layer is formed on the surface layer of the active material by simply spraying a niobium compound-containing solution, and when active material particles such as these are actually used as a positive electrode active material, there are problems with the lithium secondary battery in that gelling of a paste occurs when a coating is formed because of the excess lithium, a gas is generated after the battery has been produced, and a resistance component is insufficiently reduced.
[0028]
As a method for reducing the excess lithium on the surface layer of a lithium-nickel composite compound and achieving lower resistance and higher battery capacity by reducing the resistance component, the present invention therefore elucidates a step of further mixing a compound comprising at least one type of transition metal element selected from the group consisting of Ti, V, Cr, Zr, Nb, Mo, Hf and Ta in at least one of a slurry formation step, a filter separation step and heating step, in addition to water washing (slurry formation) of the lithium-nickel composite compound in order to remove excess lithium.
[0029]
The method for treating positive electrode active material particles according to an embodiment of the present invention constitutes a method for treating positive electrode active material particles comprising, preferably as a main component, a lithium-nickel composite compound which contains lithium (Li), nickel (Ni) and oxygen (0) and may contain another element besides Li, Ni and 0. This treatment method then comprises the following steps (l)-(3), and further comprises, in at least one of step (1), step (2) and/or step (3), a step of mixing a compound comprising a transition metal element.
(1) A slurry formation step in which the lithium-nickel composite compound is introduced into an aqueous solvent and stirred to prepare a slurry;
(2) after the slurry formation step, a filter separation step in which the slurry is filter separated to obtain a cake-like compound; and
(3) a heat treatment step in which the cake-like compound obtained in the filter separation step is heat treated to obtain a dried lithium-nickel composite compound.
[0030]
In the treatment method comprising the steps (l)-(3) above, and further comprising, in at least one of steps
(1), (2) and/or (3), the step of mixing a compound comprising a transition metal element, the quantity of lithium eluted into the aqueous solvent from the lithiumnickel composite compound as a result of slurry formation, and the compound comprising a transition metal element which is mixed therewith are so minute that it is difficult to identify a primary particle size, and a very fine compound containing lithium and a transition metal element and a very fine compound comprising a transition metal element are thought to be deposited on the lithiumnickel composite compound.
[0031]
In the slurry formation step (1) in particular, when the aqueous solvent or the slurry is mixed with the compound comprising a transition metal element, the slurry of the lithium-nickel composite compound exhibits alkalinity with a pH of around 11-13, so it is thought that some of the transition metal element compound which has been mixed dissolves and penetrates, as transition metal element ions, into secondary particles of the lithiumnickel composite compound from grain boundary portions between primary particles that constitute the secondary particles, reacting with the excess lithium which is ultimately present on the primary particle surface portions. As a result, the compound containing lithium and a transition metal element and the transition metal element compound can be deposited on the surface layer of the secondary particles and on the grain boundary portions between the primary particles of the very fine lithium-nickel composite compound by way of the filter separation step (2) and the heat treatment step (3).
[0032]
That is to say, the compound containing lithium and a transition metal element and the compound comprising a transition metal element are present on the surfaces of the secondary particles of the lithium-nickel composite compound and on the grain boundary portions (primary particle surfaces) between the primary particles constituting the secondary particles, and, as a result, excess lithium remaining on the particle surface layer of the lithium-nickel composite compound can be effectively reduced, and it is possible to achieve an effect of a balance between lower resistance as a result of reducing a reaction resistance component, and higher battery capacity, by virtue of the effect of improving lithium ion conductivity by means of the compound containing lithium and a transition metal element which is synthesized by further mixing the transition metal element compound.
[0033]
This works however also if the compound comprising a transition metal element is added to the cake-like compound obtained in step (2) or to the dried lithiumnickel composite compound obtained in step (3), as long as some moisture is present (the moisture (aqueous solvent) content being preferably at least 1% by weight (relative to the mixture obtained by mixing the lithiumnickel composite compound in the form in which it is respectively present ( e.g. in form of the slurry of step (1) or in form of the cake-like compound of step (2) or in form of the dried compound of step (3)) with the compound comprising a transition metal element and optionally with said Li compound), where in the slurry of step (1) and in the cake-like compound obtained in step (2) the moisture content is more preferably at least 3% by weight, relative to the total weight of lithiumnickel composite compound and compound comprising a transition metal element (i.e. relative to the mixture obtained by mixing the lithium-nickel composite compound in the form in which it is respectively present ( e.g. in form of the slurry of step (1) or in form of the cake like compound of step (2)) with the compound comprising a transition metal element and optionally with said Li compound). If the compound comprising a transition metal element is added to the cake-like compound obtained in step (2), addition of further moisture (i.e. of an aqueous solvent) is possible, but not necessary, since after filtration the filter cake generally is still sufficiently humid. If the compound comprising a transition metal element is added to the dried lithiumnickel composite compound obtained in step (3), unless drying is not complete (which generally is however not the case), some moisture has to be introduced to obtain the desired moisture content and to allow the desired reaction of lithium with the compound comprising a transition metal element. This can for example be done by remoistening the dried filter cake or, more simply and thus preferably, by providing the compound comprising a transition metal element in form of an aqueous solution; or also by mixing simultaneously the dried filter cake, the compound comprising a transition metal element and an aqueous solvent.
[0034]
"Solution" in terms of the present invention is not restricted to solutions in the proper sense (a solution in the proper sense being a monophasic, homogeneous mixture of two or more substances, where the particles of solute cannot be seen by the naked eye; a solution does not cause beams of light to scatter), but also encompasses suspensions and emulsions. Analogously, the term "solvent" does not require that a solution in the proper sense be formed, but means any liquid medium in which solid particles can be distributed, thus also in form of suspensions.
[0035]
The steps will be described in order below.
[0036]
(1) Slurry formation step
In the slurry formation step (1), the lithium-nickel composite compound is introduced into an aqueous solvent and stirred to prepare a slurry of the lithium-nickel composite compound. In the treatment method of the present invention, one objective of this step is also to remove excess lithium remaining in the lithium-nickel composite compound, but, in addition to minimizing damage to the particles caused by water washing of the lithium- nickel composite compound, an objective at the same time is also to deposit the compound containing lithium and a transition metal element on the surfaces of particles of the lithium-nickel composite compound by causing a reaction with the transition metal element compound which is added, and therefore it is necessary to control the amount of Li eluted into the slurry. This step is therefore not aimed solely at reducing the amount of excess lithium remaining.
[0037]
This slurry formation step (1) is an especially important step considering that: it achieves a sufficient effect of reducing excess lithium in the lithium-nickel composite compound, as described above; it exercises control to restrict proton exchange in the particle surface layer caused by excessive water washing; and it also causes deposition of the compound containing lithium and a transition metal element on surfaces of particles of the lithium-nickel composite compound by causing a reaction between the transition metal element and the lithium eluted into the slurry.
[0038]
Furthermore, in one of the alternatives of introducing the compound comprising a transition metal element, the latter is preferably mixed before and/or after introduction of the lithium-nickel composite compound into the aqueous solvent with stirring in order to prepare the slurry, although this will be described in detail later.
[0039]
The lithium-nickel composite compound which is used in the present invention contains Li, Ni and 0 and may contain another element besides Li, Ni and 0. There is no particular limitation as to the lithium-nickel composite compound, and it may be modified as appropriate Furthermore, the lithium-nickel composite compound preferably has a composition having a layered rock-salt structure and is represented by the following formula (I):
LiaNi1-b-cMnbMcO2 (I)
(in the formula, M is one or more different elements other than Li, Ni, Mn or 0; 0.95<adl.l5, 0<bd0.20, 0<cd0.20, and Ni is 0.80-0.98 (to be more precise, (1—b— c) is 0.80-0.98)).
When there is a high content of Ni in the lithium-nickel composite compound, this achieves a high battery capacity while also causing a problem in that a large amount of excess lithium is present when the lithium-nickel composite compound is synthesized, but this can be solved by using the treatment method according to this embodiment .
[0040]
Examples of the element M other than Li, Ni, Mn and 0 are Al, Ti, Co, Mg, Zn, Nb, W, Mo, Sb, V, Cr, Ca, Fe, Ga, Sr, Y, Ru, In, Sn, Ta, Bi, Zr, Si, P and B, etc., where M can also be two or more different elements. In a specific embodiment, M is one or both of Al and/or Co.
[0041]
In a preferred embodiment, b is 0.05 to 0.2 and c is 0; the compound (I) being thus a compound of formula (1.1): LiaNi1-bMnbO2 (1.1), where b is 0.05 to 0.2 and Ni is 0.80-0.95 (to be more precise, (1-b) is 0.80-0.95).
[0042]
In another preferred embodiment, the lithium-nickel composite compound is represented by the following formula (1.2): LiaNii-c1-C2CociAlC202 (1.2)
(in the formula, 0.95<adl.l5, 0<cld0.20, 0<c2<0.20, and Ni is 0.80-0.98 (to be more precise, (l-cl-c2) is 0.80- 0.98), where preferably 0.95<adl.l5, 0<cl<0.20, 0<c2<0.20, and Ni is 0.80-0.98 (to be more precise, (1- cl-c2) is 0.80-0.98), and where more preferably 0.01<cl<0.09 and 0.01<c2<0.09).
[0043]
The slurry is prepared, for example, by introducing an aqueous solvent comprising a predetermined amount of pure water, etc. into a reaction tank, introducing the lithium-nickel composite compound into the aqueous solvent, and then stirring the materials. It should be noted that there is no particular limitation as to the aqueous solvent, and it may equally comprise an organic solvent. Suitable organic solvents are water-miscible (preferably having a miscibility with water at 25°C in any mixing ratio), examples being Ci-Cs-alkanols (i.e. methanol, ethanol, n-propanol, isopropanol), diols, in particular ethylene glycol and propylene glycol, and cyclic ethers, in particular tetrahydrofuran and 1,4- dioxane. Preferably, the aqueous solvent is water; more preferably deionized water. Here, the ratio of the amount of lithium-nickel composite compound introduced to the amount of aqueous solvent (also referred to below as the "solid-liquid ratio") may be adjusted to a suitable range
[0044]
The amount of lithium eluted from the lithium-nickel composite compound is determined by controlling the solid-liquid ratio, and this lithium reacts with the transition metal element in the compound comprising a transition metal element, which is mixed at a suitable time, to form a compound containing lithium and a transition metal element, whereby the amount of residual lithium in the positive electrode active material which is the final target product can be appropriately controlled .
[0045] That is to say, in the slurry formation step (1), the ratio (solid-liquid ratio) of the amount of lithiumnickel composite compound to the amount of aqueous solvent is preferably adjusted to 750 g/L-2000 g/L, and more preferably to 800 g/L-1800 g/L, the volume referring to the volume of the solvent used (and not of the solution formed; i.e. the solid-liquid ratio is preferably adjusted to 750-2000 g of lithium-nickel composite compound per liter of aqueous solvent, and more preferably to 800-1800 g of lithium-nickel composite compound per liter of aqueous solvent). The volume refers to the volume of the solvent at room temperature (25°C). If the solid-liquid ratio is below the lower limit value, there may be an excessively large amount of the aqueous solvent, which may cause excessive Li elution from within the particles of the lithium-nickel composite compound, and there is a risk of this leading to a drop in quality of the positive electrode active material which is the final target product. Furthermore, if the solid-liquid ratio is above the upper limit value, there may be an insufficient amount of the aqueous solvent and the amount of residual lithium in the surface layer of the secondary particles may be greater than necessary, making it difficult to appropriately control the amount of residual lithium in the positive electrode active material which is the final target product. In this embodiment, the amount of lithium eluted into the slurry is controlled by controlling the solid-liquid ratio to the range above, and therefore the pH of the slurry is preferably controlled to 11-13 (see also reaction a below).
[0046]
Furthermore, the slurry is prepared by introducing the lithium-nickel composite compound into the aqueous solvent and stirring the materials, but it is possible to cause a sufficiently large amount of Li to elute into the slurry from the secondary particles of the lithium- nickel composite compound by adjusting the stirring time, and this enables greater stability.
[0047]
That is to say, in the slurry formation step (1), the slurry is prepared by performing the stirring with the stirring time preferably adjusted to 3 minutes-30 minutes, and more preferably 5 minutes-25 minutes. If the stirring time is below the lower limit value, the amount of Li expected to elute from the secondary particles of the lithium-nickel composite compound decreases, and there is a risk of a greater amount of residual lithium. Furthermore, if the stirring time is above the upper limit value, there is no further improvement in the effect relating to preparation of the slurry, and therefore a drop in productivity.
[0048]
It should be noted that there is no particular limitation as to the temperature of the aqueous solvent into which the lithium-nickel composite compound is introduced, but the temperature of the aqueous solvent is preferably adjusted to around 15°C-35°C, for example, in order to prepare an appropriate slurry as described above.
[0049]
In the slurry formation step (1), the following [reaction a] progresses when the lithium-nickel composite compound is represented by the formula: LixNiO2, for example. [Reaction a] LixNiO2 Lix-yNiO2+yLiOHaq
[0050]
(2) Filter separation step
In the filter separation step (2), after the end of the slurry formation step (1), the slurry is filter-separated using a filtration device, etc. such as a Buchner funnel or a filter press, to obtain a cake-like compound. [0051]
This kind of filter separation step (2) makes it possible to adjust the water content of the cake-like compound to a suitable amount, which further improves the quality of the positive electrode active material particles which are ultimately obtained. There is no particular limitation as to the water content of the cake-like compound after filter separation, but it is 20 wt% or less, preferably 10 wt% or less, and more preferably 8 wt% or less. However, the water content of the cake-like compound after filter separation is preferably 3 wt% or greater. Thus, preferably, the water content of the cakelike compound after filter separation is preferably 3 to 20 wt%, more preferably 3 to 10 wt%, and in particular 3 to 8 wt%, and is specifically 5 to 8% by weight, based on the total weight of the cake-like compound.
[0052]
It should be noted that the moisture content of the slurry in the present invention is 65 wt% or less, and preferably 60 wt% or less, to take account of controlling the solidliquid ratio of the slurry to 750 g/L-2000 g/L.
[0053]
"Moisture" means aqueous solvent.
[0054]
(3) Heat treatment step
In the heat treatment step (3), the cake-like compound obtained in the filter separation step (2) is heat treated and dried to thereby obtain a dried lithiumnickel composite compound. When the heat treatment is performed, reference may be made to Non-Patent Document 1, for example, but the temperature in the present invention is preferably set at 100°C-400°C, e.g. at 140 to 400°C, and more preferably at 200°C-350°C. When the temperature is lower than the lower limit value, sufficient drying is not easily achievable (generally only under high vacuum and/or after excessively long drying time) and, unless such measures are taken, a large amount of water remains in the lithium-nickel composite compound which is ultimately obtained. Furthermore, the added transition metal element does not react sufficiently with the Li fraction, so an adequate effect cannot be achieved. When the temperature is higher than the upper limit value, on the other hand, Li may separate from the crystal lattice of the lithium-nickel composite compound and elutes into the particle surface layer, so there is a risk of an increased amount of residual lithium in the lithium-nickel composite compound which is ultimately obtained. The heat treatment may thus also serve for an annealing of the composite compound.
[0055]
Furthermore, there is no particular limitation as to the drying method, and treatment using a roller hearth kiln or a rotary kiln, or a vacuum drying treatment, etc. may be appropriately adopted, for example. Additionally, the atmosphere during the heat treatment needs to take account of the nickel content of the lithium-nickel composite compound which is dried, and the drying treatment is preferably carried out under an oxygen atmosphere, a vacuum atmosphere, an inert gas atmosphere, or decarbonized air having a carbon dioxide concentration of 100 ppm or less, for example.
[0056]
In a preferred embodiment of the heat treatment step (3), the cake-like compound obtained in the filter separation step (2) is heat-treated in a first step at 100 to 195°C and in an optional second step at 200 to 400°C, and more preferably of 200 to 350°C. Preferably, the second step is carried out.
[0057] Preferably, the first heat treatment is performed under reduced pressure, e.g. under a pressure of 0.1 to 100 mbar. For this purpose, customary heatable vacuum drying apparatuses can be used.
[0058]
Preferably, the second heat treatment is performed under an oxygen-enriched atmosphere (such as oxygen-enriched air, oxygen-nitrogen mixtures with more than 20% by weight of oxygen, and oxygen, preference being given to oxygen mixtures containing at least 90% by weight of oxygen, based on the total weight of the mixture, or pure oxygen); and/or the second heat treatment is performed under an atmosphere with reduced CO2 content, preferably with a CO2 content of at most 100 ppm by volume (0.01% by volume), more preferably of at most 50 ppm by volume (0.005% by volume). More preferably, the second heat treatment is performed under an oxygen-enriched atmosphere which has simultaneously a reduced CO2 content, preferably a CO2 content of at most 100 ppm by volume, more preferably of at most 50 ppm by volume.
[0059]
Preferably, the second heat treatment is carried out. The separation into two heating steps is especially useful if the compound comprising a transition metal element is added in step (3). In this case, it is expedient to carry out a first heating step, in which the cake like compound obtained in step (2) is dried, then adding the compound comprising a transition metal element (and some moisture to allow reaction, and optionally said lithium compound) to the dried material, and then carrying out a second heating step, in which the obtained mixture is dried and, depending on the temperature, also annealed.
[0060]
<Step of mixing the compound comprising a transition metal element> This embodiment further comprises, in at least one of step (1), step (2) and/or step (3), a step of mixing a compound comprising a transition metal element. Specifically, the compound comprising a transition metal element is mixed with the aqueous solvent or the slurry (formed from the aqueous solvent and the lithium-nickel composite compound) in step (1), or mixed with the cakelike compound in step (2), or mixed with the dried cakelike compound in step (3). By this means, the lithium in the lithium-nickel composite compound reacts with the compound comprising a transition metal element which is mixed, and the surface layer of the particles can be coated with a compound containing lithium and a transition metal element, and the compound comprising a transition metal element.
[0061]
The step of mixing the compound comprising a transition metal element may be performed in one or two or all three of step (1), step (2) and step (3). Specifically, the step of mixing the compound comprising a transition metal element is preferably performed before and/or after introduction of the lithium-nickel composite compound into the aqueous solvent in step (1), or performed with the cake-like compound obtained by filter separating the slurry in step (2). In another preferred embodiment, mixing the compound comprising a transition metal element is performed in step (3). As already explained, in this case, mixing is carried out in the presence of an aqueous solvent. Preferably, this is carried out by using the compound comprising a transition metal element in form of an aqueous solution or suspension comprising said compound comprising a transition metal element and optionally said lithium compound. Thus, in this alternative, preferably, an aqueous solution or suspension comprising said compound comprising a transition metal element and optionally said lithium compound is mixed with the lithium-nickel composite compound dried in step (3). In this alternative, it is preferred to use an aqueous solution or suspension comprising said compound comprising a transition metal element and said lithium compound.
Also when mixing is carried out with the cake-like compound obtained in step (2), the compound comprising a transition metal element is preferably used in form of an aqueous solution or suspension comprising said compound comprising a transition metal element and optionally said lithium compound.
[0062]
Furthermore, as described above, the compound comprising a transition metal element may further be mixed in step (2) also, after the compound comprising a transition metal element has been mixed in step (1). Additionally, different transition metal element compounds may be added in step (1) and step (2).
[0063]
That is to say, when the step of mixing the compound comprising a transition metal element is performed in step (1) and/or step (2), at least a small amount of the compound comprising a transition metal element can dissolve because the pH in the slurry is around 11-13 and the cake-like compound likewise also has a pH of around 11-13, and it is hypothesized that the lithium and the dissolved transition metal element also penetrate into the grain boundary portions formed by adjacent primary particles located on surfaces of the plurality of primary particles constituting the secondary particles of the lithium-nickel composite compound as a result, and these grain boundary portions can therefore be coated with the compound containing lithium and a transition metal element and the compound comprising a transition metal element .
[0064] When the heat treatment step (3) is performed in this state, a reaction between the excess lithium remaining on the surfaces of the primary particles of the lithiumnickel composite compound and the transition metal element is also further promoted, and formation of the compound containing lithium and a transition metal element can be promoted. The compound containing lithium and a transition metal element is as described above, but it is thought to be capable of restricting formation of a resistance component without reducing battery characteristics .
[0065]
Alternatively, the compound comprising a transition metal element may further be mixed in step (3) also, after the compound comprising a transition metal element has been mixed in step (1) and/or step (2). Additionally, different transition metal element compounds may be added in step (l)/step (2) and step (3).
[0066]
The transition metal element is preferably used in form of a transition metal oxide, hydroxide, mixed oxidehydroxide, sulfate, oxalate or a hydrate of the abovelisted forms. Preference is given to the oxides and oxide hydrates .
[0067]
There is no particular limitation as to the transition metal element, but it is preferably at least one type of transition metal element selected from the group consisting of Ti, V, Cr, Zr, Nb, Mo, Hf and Ta. More preferably, the transition metal element is at least one selected from the group consisting of V and Nb, and is specifically Nb. Furthermore, when the transition metal element is Nb, for example, the compound comprising a transition metal element is preferably niobium pentoxide (Nb2Os) or niobium pentoxide hydrate (Nb2Os-nfbO). Also when the transition metal element is V, the compound comprising a transition metal element is preferably vanadium pentoxide (V2O5).
[0068]
Furthermore, by suitably adjusting the amount of the compound comprising a transition metal element which is mixed, the surfaces of the secondary particles and at least part of the grain boundary portions (interfaces between primary particles) formed by adjacent primary particles located on surfaces of the plurality of primary particles constituting the secondary particles can be coated with the compound containing lithium and a transition metal element and the compound comprising a transition metal element.
[0069]
That is to say, in the step of mixing the compound comprising a transition metal element, the amount of the compound comprising a transition metal element which is mixed is preferably set at an amount of compound such that the transition metal element is at 0.01 mol%-1.5 moll with respect to the total amount of all elements in the lithium-nickel composite compound except lithium and oxygen. If the amount of the compound comprising a transition metal element which is mixed is below the lower limit value, there is a risk of increasing the amount of the compound containing lithium and the transition metal element which is incapable of coating the secondary particles of the lithium-nickel composite compound. Furthermore, if the amount of the compound comprising a transition metal element which is mixed is above the upper limit value, the compound is present in an excessively large amount on the secondary particle surface layer, and there is a risk of the resistance component being excessively large. There are additional risks that the amount of excess lithium for the reaction will be insufficient, Li will be drawn out from the lithium-nickel composite compound, and the resistance component will in any case become larger. The amount of the compound comprising a transition metal element which is mixed is more preferably an amount of compound such that the transition metal element is at 0.1 mol%-1.2 moll
[0070]
When the step of mixing the compound comprising a transition metal element is carried out in step (1), the slurry with which the compound comprising a transition metal element is mixed is preferably alkaline so that more than a fixed amount of the compound comprising a transition metal element does not precipitate in the aqueous solvent or in the slurry, and the pH is preferably 11-13 to be specific. At least some of the compound comprising a transition metal element thus dissolves, so the transition metal element and the compound comprising a transition metal element are also able to permeate into the secondary particles and react not only with the excess lithium on the surface layer of the secondary particles of the lithium-nickel composite compound, but also on the surface layer of the primary particles so that the amount of excess lithium remaining in the lithium-nickel composite compound which is ultimately obtained can be reduced.
[0071]
As indicated above, the treatment method comprises step (l)-step (3) and further comprises, in at least one of step (1), step (2) and step (3), a step of mixing the compound comprising a transition metal element, and, by this means, the compound containing lithium and a transition metal element and the compound comprising a transition metal element can be present on the surface layer of the secondary particles of the lithium-nickel composite compound.
[0072] Furthermore, in step (l)-step (3), an A element compound may also optionally be mixed. By mixing an A element compound such as this, the A element compound can be present on the surface of the particles of the lithium- nickel composite compound in the form of a compound of lithium and the A element, or in the form of the A element compound, and effects based on the A element compound can be achieved. There is no particular limitation as to this A element, but examples thereof include: aluminum (Al), manganese (Mn), titanium (Ti), cobalt (Co), magnesium (Mg), zinc (Zn), niobium (Nb), tungsten (W), molybdenum (Mo), vanadium (V), chromium (Cr), calcium (Ca), iron (Fe), gallium (Ga), strontium (Sr), yttrium (Y), antimony (Sb), ruthenium (Ru), indium (In), tin (Sn), tantalum (Ta), bismuth (Bi), zirconium (Zr) and boron (B), etc.
[0073]
In the treatment method of the present invention, the part where the compound containing lithium and a transition metal element and the compound comprising the transition metal element are present on the surface of the lithium-nickel composite compound constitutes the surface of the particles of the lithium-nickel composite compound, and said compound may be present on the following portions (a) and (b):
(a) at least part of the surfaces of the secondary particles of the lithium-nickel composite compound, and
(b) at least part of the grain boundary portions (interfaces between primary particles) formed by adjacent primary particles located on the surfaces of the plurality of primary particles constituting the secondary particles .
[0074]
Furthermore, when the A element compound has been optionally added in abovementioned step (l)-step (3), the A element compound can be present on the surface of the lithium-nickel composite compound. For example, the A element compound is a compound of lithium and the A element, or an A element oxide, etc. Furthermore, the type of A element is as described above.
[0075]
The type of lithium compound (ii) optionally mixed with the aqueous solvent (used in step (1)), the slurry (of step (1)), the cake-like compound (of step (2)) or the dried lithium-nickel composite compound (of step (3)) is not particularly limited, but is preferably LiOH.
[0076]
Fig. 1 is a schematic view in longitudinal section of a surface layer of a secondary particle of a lithium-nickel composite compound when a coating layer of a compound containing lithium and a transition metal element and a compound comprising the transition metal element is formed by means of the treatment method of the present invention .
[0077]
As shown in the longitudinal section of fig. 1, a coating layer 3 of the compound containing lithium and a transition metal element and a compound comprising the transition metal element is formed not only on a surface
2 of a secondary particle 1 formed by a plurality of primary particles 11, 12, 13, 14..., but the coating layer
3 of the compound containing lithium and a transition metal element and the compound comprising a transition metal element is also formed on parts of grain boundary portions 4 formed by adjacent primary particles 11, 12; 12, 13; 13, 14... located on an uppermost surface. For the example in fig. 1, a description has been given of a case in which the compound containing lithium and a transition metal element and the compound comprising a transition metal element form the coating layer, but a layer need not necessarily be formed, and the compounds may be present in the form of particles, as will be described later.
[0078]
Fig. 2 is a schematic view in transverse section of the surface layer of a secondary particle of a lithium-nickel composite compound when a coating layer formed by a compound containing lithium and a transition metal element and a compound comprising the transition metal element is formed by means of the treatment method of the present invention. Specifically, fig. 2 is a schematic view in transverse section cut close to the height of the grain boundary portions 4 of the secondary particle 1.
[0079]
The transverse section of fig. 2 shows a state in which the coating layer 3 of the compound containing lithium and a transition metal element and the compound comprising a transition metal element is also formed on parts of the grain boundary portions 4 formed by the plurality of primary particles 11, 12, 13, 14... constituting the secondary particle 1, as described above It should be noted that in fig. 2, the bold line denotes grain boundary portions 4 on which the coating layer 3 is not formed. Furthermore, a partial transverse section of the secondary particle 1 is shown in fig. 2, and a large number of primary particles are present at ends of the secondary particle 1 in fig. 2, although these are not depicted.
[0080]
<Positive electrode active material>
The positive electrode active material according to the present invention comprises, preferably as a main component, a lithium-nickel composite compound which contains Li, Ni and 0 and may contain another element besides Li, Ni and 0. As indicated above, the compound containing lithium and a transition metal element and the compound comprising a transition metal element are present on predetermined parts of this nickel-lithium composite compound, i.e. on the following (a) and (b):
(a) surfaces of the secondary particles of the lithiumnickel composite compound, and
(b) at least part of the grain boundary portions (interfaces between primary particles) formed by adjacent primary particles located on the surfaces of the plurality of primary particles constituting the secondary particles.
[0081]
"Part of the grain boundary portions", as the phrase indicates, means a part of the grain boundary portions rather than the entire surface thereof. The length of the entire surface of the grain boundary portions differs according to the size of the primary particles constituting the secondary particles and is not particularly limited, but is around 80 nm-800 nm, taking account of a minor axis portion in the shape of the primary particles constituting the secondary particles, for example.
[0082]
In the present specification, the average particle size is a value obtained by using a scanning electron microscope SEM-EDS (field emission scanning electron microscope JS-7100F: produced by JEOL Ltd.) with an acceleration voltage of 10 kV, and is based on scanning electron microscope photographs (SEM photographs) of the primary particles or the secondary particles of the lithium-nickel composite compound imaged so that grain boundaries of the primary particles can be confirmed.
[0083]
The compound containing lithium and a transition metal element is formed by compounding of excess lithium in the primary particles and the secondary particles of the lithium-nickel composite compound with the compound comprising a transition metal element, and therefore has the effect of reducing excess lithium by formation of the compound containing lithium and a transition metal element. For example, when the compound comprising a transition metal element is niobium pentoxide (Nb2Os) or niobium pentoxide hydrate (Nb2Os-nJbO), the compound containing lithium and a transition metal element is thought to be formed by LiNbCh or Li3NbO4, etc. Furthermore, there is no particular limitation as to the ratio of Li and the transition metal element in the compound containing lithium and the transition metal element, and it may be such that Li/transition metal element = 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, etc., for example.
[0084]
The compound comprising a transition metal element is preferably an oxide comprising a transition metal element For example, when Nb is selected as the transition metal element, the compound comprising a transition metal element is preferably an oxide such as Nb2Os or Nb2Os-nH2O.
[0085]
The compound containing lithium and a transition metal element and the compound comprising a transition metal element which are present on the surfaces or the grain boundary portions of the lithium-nickel composite compound may be present in the form of particles, and need not necessarily form a (coating) layer. However, the compounds may form a layer and there is no particular limitation. There is also no particular limitation as to the thickness of the layer when a layer is formed, and it may have any thickness.
[0086]
In the present specification, the coating condition and coating layer thickness afforded by the compound containing lithium and a transition metal element and the compound comprising a transition metal element may be investigated by using Auger electron spectroscopy (also referred to below as "AES"), scanning electron microscopy with energy dispersive X-ray spectroscopy (also referred to below as "SEM-EDX"), or transmission electron microscopy with energy dispersive X-ray spectroscopy (also referred to below as "TEM-EDX"), etc., for example.
[0087]
There is no particular limitation as to a coefficient of variation of the amount of transition metal element which is present in the coating layer of the compound containing lithium and a transition metal element and the compound comprising a transition metal element, and it may have any value.
[0088]
In the present specification, the coefficient of variation of the amount of transition metal element which is present on the surfaces of the particles may be determined by using the abovementioned AES, SEM-EDX or TEM-EDX, etc., for example.
[0089]
For example, when the abovementioned SEM-EDX is used, the coefficient of variation may be determined by means of point analysis of the SEM-EDX from the results at five randomly selected locations (N = 5) in the coating layer using the standard deviation and mean value of numerical values obtained after confirming the presence of the transition metal element, on the basis of the following formula.
Coefficient of variation (%) (standard deviation/mean value) xl00
[0090] In the present specification, a coating rate of the coating layer may be obtained by image analysis, for example.
[0091]
The positive electrode active material according to the present invention should be formed by a lithium-nickel composite compound which contains Li, Ni and 0 and may contain another element besides Li, Ni and 0, and there is no particular limitation as to the composition thereof, but the lithium-nickel composite compound preferably has a composition represented by the following formula (I): LiaNi1-b-cMnbMc02 (I)
(in the formula, M is an element other than Li, Ni, Mn or 0; 0.95<adl.l5, 0<bd0.20, 0<cd0.20, and Ni is 0.80- 0.98 (to be more precise, (1-b-c) is 0.80-0.98)).
[0092]
In formula (I) above, there is no particular limitation as to the element M other than Li, Ni and 0, but examples thereof include: aluminum (Al), titanium (Ti), cobalt (Co), magnesium (Mg), zinc (Zn), niobium (Nb), tungsten (W), molybdenum (Mo), vanadium (V), chromium (Cr), calcium (Ca), iron (Fe), gallium (Ga), strontium (Sr), yttrium (Y), antimony (Sb), ruthenium (Ru), indium (In), tin (Sn), tantalum (Ta), bismuth (Bi), zirconium (Zr), silicon (Si), phosphorus (P) and boron (B), etc. In a specific embodiment, M is one or both of Al and/or Co.
[0093]
In a preferred embodiment, b is 0.05 to 0.2 and c is 0; the compound (I) being thus a compound of formula (1.1): LiaNi1-bMnb02 (1.1), where b is 0.05 to 0.2 and Ni is 0.80-0.95 (to be more precise, (1-b) is 0.80-0.95).
[0094] In another preferred embodiment, the lithium-nickel composite compound is represented by the following formula (1.2):
LiaNii-ci-C2CociAlC202 (1.2)
(in the formula, 0.95<adl.l5, 0<cld0.20, 0<c2<0.20, and Ni is 0.80-0.98 (to be more precise, (l-cl-c2) is 0.80- 0.98), where preferably 0.95<adl.l5, 0<cl<0.20, 0<c2<0.20, and Ni is 0.80-0.98 (to be more precise, (1- cl-c2) is 0.80-0.98), and where more preferably 0.01<cl<0.09 and 0.01<c2<0.09).
[0095]
Furthermore, the positive electrode active material according to the present invention should comprise the lithium-nickel composite compound, while the A element compound may also be present on surfaces of the particles of the lithium-nickel composite compound, and the A element compound can be present in the form of a compound of lithium and the A element or in the form of an A element oxide, and the effects thereof may vary in some respects in the present invention. For example, when an Al compound is present on the particle surfaces while an Nb compound is also present, it is possible to impart an effect of improving long-term cycle characteristics when a battery has been produced. There is no particular limitation as to this A element, but examples thereof include: aluminum (Al), manganese (Mn), titanium (Ti), cobalt (Co), magnesium (Mg), zinc (Zn), niobium (Nb), tungsten (W), molybdenum (Mo), vanadium (V), chromium (Cr), calcium (Ca), iron (Fe), gallium (Ga), strontium (Sr), yttrium (Y), antimony (Sb), ruthenium (Ru), indium (In), tin (Sn), tantalum (Ta), bismuth (Bi), zirconium (Zr) and boron (B), etc.
[0096]
Furthermore, an amount of residual lithium in the positive electrode active material according to the present invention as determined by neutralization titration is preferably 0.15 wt% or less, and more preferably 0.12 wt% or less. If the amount of residual lithium is above the upper limit value, this leads to gas generation, and there is also a risk of increasing reaction resistance in the lithium battery. It should be noted that the amount of residual lithium is the amount of Li derived from LiOH or Li2CC>3, for example, which is not included in the lithium-nickel composite compound or the coating layer (the compound containing lithium and a transition metal element).
[0097]
In the present specification, the amount of residual lithium was calculated on the basis of the Warder method. Specifically, 20 g of a powder of particles of the lithium-nickel composite compound serving as positive electrode active material particles were added to 100 mL of water and stirred for 20 minutes at room temperature, after which solids were filter separated and removed to obtain a supernatant for which the amount of residual lithium was determined by titration using 0.2 N hydrochloric acid. Two points where the gradient was greatest on a pH curve drawn by plotting titration amount (mL) on the horizontal axis and supernatant pH on the vertical axis were taken as a first titration point and a second titration point, from the point where the titration amount was smaller, and the amount of residual lithium is the value obtained from the titration amounts at these points by calculation using a calculation formula.
[0098]
<Method for producing positive electrode active material> There is no particular limitation as to the method for producing the positive electrode active material according to the present invention, provided that the positive electrode active material particles are treated according to what is described above in the "<Method for treating positive electrode active material particles>" section, and the lithium-nickel composite compound constituting the positive electrode active material particles may be produced by a normal method.
[0099]
That is to say, it is possible to adopt a method in which a precursor composite compound containing at least Ni is synthesized, and the precursor composite compound and a lithium compound are mixed to obtain a mixture, after which the mixture is fired, for example, or another method may be adopted.
[0100]
There is no particular limitation as to the method for synthesizing the precursor composite compound, and, for example, an aqueous solution comprising a nickel compound aqueous solution and various types of aqueous solutions of compounds comprising an element other than Ni, according to the intended composition of the positive electrode active material, are dripped into a reaction tank with stirring, using an alkaline aqueous solution such as a sodium hydroxide aqueous solution or an ammonia solution, for example, as a mother liquor, the pH is monitored and controlled to a suitable range while sodium hydroxide, etc. is also dripped, and the precursor composite compound is obtained by coprecipitation by means of a wet reaction. Examples of the precursor composite compound which may be cited include hydroxides, oxides obtained by calcining said hydroxides, and carbonates, etc.
[0101]
It should be noted that, once the alkaline aqueous solution serving as the mother liquor has been prepared for the reaction relating to the synthesis, an inert gas, or nitrogen gas which is industrially preferred, is preferably used to set a nitrogen atmosphere inside the reaction tank so that the oxygen concentration inside the reaction tank system and in the solutions is as low as possible.
[0102]
There is no particular limitation as to the nickel compound, but examples which may be cited include: nickel sulfate, nickel oxide, nickel hydroxide, nickel nitrate, nickel carbonate, nickel chloride, nickel iodide, and metallic nickel, etc.
[0103]
There is no particular limitation as to the element other than Ni constituting the positive electrode active material, but examples thereof include Mn, and also Al, Ti, Co, Mg, Zn, Nb, W, Mo, Sb, V, Cr, Ca, Fe, Ga, Sr, Y, Ru, In, Sn, Ta, Bi, Zr, Si, P and B, etc., which were given as examples of the element M other than Li, Ni, Mn and 0, in formula (I) above.
[0104]
There is no particular limitation as to the compound comprising an element other than Ni, but examples thereof include a cobalt compound, aluminum compound, manganese compound, titanium compound, magnesium compound, zinc compound, niobium compound, and tungsten compound, etc.
[00105]
There is no particular limitation as to the cobalt compound, but examples which may be cited include: cobalt sulfate, cobalt oxide, cobalt hydroxide, cobalt nitrate, cobalt carbonate, cobalt chloride, cobalt iodide, and metallic cobalt, etc.
[00106]
There is no particular limitation as to the aluminum compound, but examples which may be cited include: aluminum sulfate, aluminum oxide, aluminum hydroxide, aluminum nitrate, aluminum carbonate, aluminum chloride, aluminum iodide, sodium aluminate, and metallic aluminum, etc.
[0107]
There is no particular limitation as to the manganese compound, but examples which may be cited include: manganese sulfate, manganese oxide, manganese hydroxide, manganese nitrate, manganese carbonate, manganese chloride, manganese iodide, and metallic manganese, etc.
[0108]
There is no particular limitation as to the titanium compound, but examples which may be cited include: titanyl sulfate, titanium oxide, titanium hydroxide, titanium nitrate, titanium carbonate, titanium chloride, titanium iodide, and metallic titanium, etc.
[0109]
There is no particular limitation as to the magnesium compound, but examples which may be cited include: magnesium sulfate, magnesium oxide, magnesium hydroxide, magnesium nitrate, magnesium carbonate, magnesium chloride, magnesium iodide, and metallic magnesium, etc.
[0110]
There is no particular limitation as to the zinc compound, but examples which may be cited include: zinc sulfate, zinc oxide, zinc hydroxide, zinc nitrate, zinc carbonate, zinc chloride, zinc iodide, and metallic zinc, etc.
[0111]
There is no particular limitation as to the niobium compound, but examples which may be cited include: niobium oxide, niobium chloride, lithium niobate, and niobium iodide, etc.
[0112] There is no particular limitation as to the tungsten compound, and examples which may be cited include: tungsten oxide, sodium tungstate, ammonium paratungstate, tungsten hexacarbonyl, and tungsten sulfide, etc.
[0113]
The proportions in which the nickel compound and the various types of compounds comprising an element other than Ni are blended should be appropriately adjusted while taking account of the intended composition of the positive electrode active material so that the amount of Ni and the amount of the various elements other than Ni reach the desired proportions.
[0114]
The appropriate range to which the pH is controlled when the precursor composite compound is synthesized may be determined so as to achieve a desired secondary particle size and coarseness/fineness, and the pH is generally in the range of around 10 to around 13.
[0115]
The precursor composite compound obtained by means of a wet reaction as described above is preferably subjected to a washing treatment and then a drying treatment after dewatering.
[0116]
By performing the washing treatment, it is possible to rinse off impurities taken into agglomerated particles during the reaction, such as sulfate radicals and carbonate radicals adhering to a surface layer, and a sodium fraction. Washing treatments which may be used include a process of Nutsche washing employing a Buchner funnel, provided that there is only a small amount of impurity, and a process of feeding a suspension after the reaction to a press filter, washing with water and dewatering. It should be noted that the washing treatment may employ pure water, a sodium hydroxide aqueous solution, or a sodium carbonate aqueous solution, etc., but pure water is preferably used from an industrial point of view. However, when there is a large quantity of residual sulfate radicals, it is also possible to perform the washing treatment using a sodium hydroxide aqueous solution which is pH-controlled according to the residual amount.
[0117]
The precursor composite compound synthesized in this way and a lithium compound are then mixed in a predetermined ratio to prepare a mixture. The mixing may be solventbased mixing in which the precursor composite compound and the lithium compound are each in the form of a solution, such as an aqueous solution, and the solutions are mixed in a predetermined ratio, or it may be nonsolvent-based mixing in which a powder of the precursor composite compound and a powder of the lithium compound are weighed out in predetermined proportions and mixed by a dry method.
[0118]
There is no particular limitation as to the lithium compound, and various types of lithium salts may be used. Examples of the lithium compound which may be cited include: anhydrous lithium hydroxide, lithium hydroxide hydrate, lithium nitrate, lithium carbonate, lithium acetate, lithium bromide, lithium chloride, lithium citrate, lithium fluoride, lithium iodide, lithium lactate, lithium oxalate, lithium phosphate, lithium pyruvate, lithium sulfate, and lithium oxide, etc. Among these, lithium carbonate, anhydrous lithium hydroxide, and lithium hydroxide hydrate are preferred.
[0119]
The proportions in which the lithium compound and the precursor composite compound are blended should be appropriately adjusted while taking account of the intended composition of the positive electrode active material so that the total of the amount of Li, the amount of Ni, and the amounts of any of the various other elements reach the desired proportions.
[0120]
There is no particular limitation as to the firing temperature when the mixture of the precursor composite compound and the lithium compound is fired, but it is preferably around 700°C-950°C, and more preferably around 720°C-930°C, for example. If the firing temperature is below the lower limit value, there is a risk of difficulty in obtaining the desired crystals. Furthermore, if the firing temperature is above the upper limit value, crystal growth progresses excessively and there is a risk of reduced energy density.
[0121]
The atmosphere during the firing is not particularly limited either, and it should be an atmosphere which enables an adequate lithium formation reaction of the precursor composite compound and adequate crystal growth, and which furthermore has an oxygen partial pressure such that Ni contained in the mixture being fired does not reduce, and an oxidizing gas atmosphere or an oxygen atmosphere is preferably used, for example.
[0122]
The firing time during the firing is not particularly limited either, and it should be a time which likewise enables an adequate lithium formation reaction of the precursor composite compound and adequate crystal growth, and is preferably a time of 1 hour-15 hours, and more preferably 2 hours-10 hours, for example.
[0123] The positive electrode active material particles comprising a lithium-nickel composite compound obtained in this way are subjected to the treatment method according to an embodiment of the present invention, which comprises steps (l)-(3), and further comprises, in at least one of step (1), step (2) and step (3), a step of mixing a compound comprising a transition metal element, as described above, and as a result it is possible to obtain the positive electrode active material according to the present invention, in which the compound containing lithium and a transition metal element and the compound comprising a transition metal element are present on: (a) the surfaces of the secondary particles of the lithium-nickel composite compound, and (b) at least part of the grain boundary portions formed by adjacent primary particles located on the surfaces of the plurality of primary particles constituting the secondary particles .
[0124]
<Nonaqueous electrolyte secondary battery>
A nonaqueous electrolyte secondary battery according to the present invention comprises a positive electrode containing the positive electrode active material of the present invention produced in the manner described above, for example, and the nonaqueous electrolyte secondary battery comprises the abovementioned positive electrode, a negative electrode, and an electrolytic solution comprising an electrolyte.
[0125]
When the positive electrode is produced, a conductive agent and a binder are admixed with the positive electrode active material of the present invention by means of a normal process. Acetylene black, carbon black, and graphite, etc. are preferred as conductive agents, for example. Polytetrafluoroethylene and polyvinylidene fluoride, etc. are preferred as binders, for example. [0126]
For the negative electrode, it is possible to use not only negative electrode active materials such as lithium metal, graphite, and low-crystallinity carbon materials, for example, but also at least one non-metal or metal element selected from the group consisting of Si, Al, Sn, Pb, Zn, Bi and Cd, or alloys comprising same, or chalcogen compounds comprising same.
[0127]
Examples of solvents of the electrolytic solution that may be used include organic solvents comprising at least one type of carbonate such as ethylene carbonate, propylene carbonate, dimethyl carbonate and diethyl carbonate, or at least one type of ether such as dimethoxyethane .
[0128]
Other than lithium hexafluorophosphate (LiPFg), at least one type of lithium salt such as lithium perchlorate or lithium tetrafluoroborate, for example, may be dissolved in the solvent for use as the electrolyte.
[0129]
<Action>
By virtue of the method for treating positive electrode active material particles, the amount of excess lithium remaining in the positive electrode active material is sufficiently reduced and the resistance component is also reduced, and therefore it is possible to provide a positive electrode active material which suppresses gas generation in a lithium battery while also achieving lower resistance and higher battery capacity in a nonaqueous electrolyte secondary battery employing this positive electrode active material in the positive electrode thereof. [Examples]
[0130]
Representative examples of the present invention and comparative examples will be given below to describe the present invention in specific terms, but the present invention is not limited to these examples. It should be noted that physical properties and methods for obtaining characteristics, etc. are as given below.
[0131]
<XRD diffraction>
XRD diffraction data of the positive electrode active material was obtained under the following X-ray diffraction conditions using an X-ray diffraction apparatus [SmartLab, produced by Rigaku Corp.], after which a Rietveld analysis was performed using this XRD diffraction data, with reference to "R. A. Young, ed., "The Rietveld Method", Oxford University Press (1992)".
(X-ray diffraction conditions)
Radiation source: Cu-Ka
Acceleration voltage and current: 45 kV and 200 mA Sampling width: 0.02 deg.
Scanning width: 15 deg.-122 deg.
Scan speed: 1.0 steps/second
Divergence slit: 2/3 deg.
Receiving slit width: 0.15 mm Scattering slit: 2/3 deg.
[0132]
C omposition of precursor composite compound and positive electrode active material>
Samples of 0.2 g of the precursor composite compound and the positive electrode active material were each heated and dissolved in 25 mL of a 20% hydrochloric acid solution, and the materials were cooled then transferred to a 100 mL measuring flask, and pure water was introduced to prepare an adjusted liquid. The elements in the adjusted liquid were quantitatively determined using ICP-AES (Optima 8300, produced by PerkinElmer, Inc.).
[0133]
<Coin cell employing positive electrode active material> A 2032-type coin cell employing the positive electrode active material was produced by using a positive electrode, negative electrode and electrolytic solution produced by the following respective methods.
(Positive electrode)
Using acetylene black and graphite as the conductive agent at a weight ratio of acetylene black:graphite=l:1, and using polyvinylidene fluoride as the binder, the positive electrode active material, conductive agent and binder were blended to achieve a weight ratio of positive electrode active material:conductive agent:binder=90:6:4, and a slurry obtained by mixing these materials with N- methylpyrrolidone was coated on an aluminum foil. The coated aluminum foil was dried at 110°C to prepare a sheet which was punched to a diameter of 15 mm and then rolled so that the density of a composite material was 3.0 g/cm3, and this was used as the positive electrode.
(Negative electrode)
A lithium foil having a thickness of 500 pm punched to a diameter of 16 mm was used as the negative electrode.
(Electrolytic solution)
A mixed solvent of ethylene carbonate (EC) and dimethyl carbonate (DMC) was prepared at a volume ratio of EC:DMC=1:2, and a solution obtained by mixing a IM LiPFg electrolyte therewith was used as the electrolytic solution .
[0134]
<Nonaqueous electrolyte secondary battery characteristics> (1) Initial charging capacity, initial discharging capacity, and initial charging/discharging efficiency Using the coin cell produced by the method above, after constant current charging at a current density of 20 mA/g to 4.30 V (upper limit voltage) under a 25°C environment, constant voltage charging was performed until the current reached 2 mA/g. The capacity at this time was taken as the initial charging capacity (mAh/g).
[0135]
After a pause of 5 minutes, constant current discharging was performed at a current density of 20 mA/g to 3.00 V under the same environment, and the initial discharging capacity (mAh/g) was measured after a 5 minute pause.
[0136]
The initial charging/discharging efficiency was calculated on the basis of the following formula using the measured value of the initial charging capacity and the measured value of the initial discharging capacity.
Initial charging/discharging efficiency (%) = (initial discharging capacity/initial charging capacity) x 100
[0137]
(2) Initial reaction resistance
Measurements were taken under a 25°C environment and the conditions indicated below using a coin cell produced by the method above.
First cycle:
0.1 C charging (4.3 V cc-cv)
5 minute pause
0.1 C charging (2.5 V cc)
5 minute pause
Second cycle:
0.1 C charging (4.3 V cc-cv)
The impedance was measured under 25°C environment and the conditions indicated below using a cell for which the second cycle of charging had been completed. The result thereof was used as the impedance measurement result for the second cycle (reaction resistance of the second cycle (initial reaction resistance)).
Frequency range: 300 k-0.01 Hz (76 points)
Amplitude: 10 mV
[0138]
<Production example 1: production of positive electrode active material particles 1>
A nickel sulfate aqueous solution and a manganese sulfate aqueous solution were mixed so that the proportions (molar ratio) of Ni and Mn were Ni:Mn=88:12, and a mixed aqueous solution was obtained. 10 L of pure water to which 300 g of a sodium hydroxide aqueous solution and 500 g of ammonia water had been added was prepared in advance as a mother liquor in a reaction tank, a nitrogen atmosphere was set inside the reaction tank by means of nitrogen gas at a flow rate of 0.7 L/min, and the reaction was also carried out under a nitrogen atmosphere.
[0139]
After this, the mixed aqueous solution, sodium hydroxide aqueous solution and ammonia water were simultaneously dripped at a predetermined rate while a stirring blade was rotated at 1000 rpm, and, by means of a crystallization reaction in which the dripping amount of alkaline solution was adjusted to achieve a pH of 11.7, the Ni and Mn crystallized and coprecipitated so that agglomerated particles were formed, and a coprecipitate was obtained.
[0140]
After this, the slurry inside the reactor was subjected to solid-liquid separation and further washed with pure water to thereby reduce residual impurities, after which the coprecipitate in a caked state was dried for 12 hours at 110°C under the atmosphere to obtain precursor composite compound 1.
[0141]
The precursor composite compound 1 and anhydrous lithium hydroxide were weighed out so that the proportions (molar ratio) of the total amount of Li, Ni and Mn were Li/ (Ni+Mn)=1.040, and the materials were mixed using a mixer to prepare a mixture.
[0142]
The mixture was then fired over 5 hours at a maximum temperature of 750°C under an oxygen atmosphere (oxygen concentration: 97 vol%) using an electric furnace, and positive electrode active material particles 1 (lithiumnickel composite compound) (also referred to below as "NM") were obtained. The mean particle size of primary particles in the positive electrode active material particles 1 was approximately 500 nm, and the mean particle size of secondary particles was approximately 12.8 pm .
[0143]
<Production example 2: production of positive electrode active material particles 2>
A nickel sulfate aqueous solution, cobalt sulfate aqueous solution and aluminum sulfate aqueous solution were mixed so that the proportions (molar ratio) of Ni, Co and Al were Ni:Co:Al=90:5:5, and a mixed aqueous solution was obtained. 10 L of pure water to which 300 g of a sodium hydroxide aqueous solution and 500 g of ammonia water had been added was prepared in advance as a mother liquor in a reaction tank, a nitrogen atmosphere was set inside the reaction tank by means of nitrogen gas at a flow rate of 0.7 L/min, and the reaction was also carried out under a nitrogen atmosphere.
[0144] After this, the mixed aqueous solution, sodium hydroxide aqueous solution and ammonia water were simultaneously dripped at a predetermined rate while a stirring blade was rotated at 1000 rpm, and, by means of a crystallization reaction in which the amount of alkaline solution dripped was adjusted to achieve a pH of 11, the Ni, Co and Al crystallized and coprecipitated so that agglomerated particles were formed, and a coprecipitate was obtained.
[0145]
After this, the slurry inside the reactor was subjected to solid-liquid separation and further washed with pure water to thereby reduce residual impurities, after which the coprecipitate in a caked state was dried for 12 hours at 110°C under the atmosphere to obtain precursor composite compound 2.
[0146]
The precursor composite compound 2 and anhydrous lithium hydroxide were weighed out so that the proportions (molar ratio) of the total amount of Li, Ni and Al were Li/ (Ni+Co+Al)=1.020, and the materials were mixed using a mixer to prepare a mixture. It should be noted that coarse anhydrous lithium hydroxide particles having a particle size of greater than 500 pm were crushed before use so that the mixture did not contain such coarse particles .
[0147]
The mixture was then fired over 5 hours at a maximum temperature of 740°C under an oxygen atmosphere (oxygen concentration: 97 vol%) using an electric furnace, and positive electrode active material particles 2 (lithiumnickel composite compound) (also referred to below as "NCA") were obtained. The mean particle size of primary particles in the positive electrode active material particles 2 was approximately 280 nm, and the mean particle size of secondary particles was approximately 11.3 pm .
[0148]
<Example 1-1: treatment of positive electrode active material particles 1 (production of positive electrode active material)>
(1) Slurry formation step and step of mixing compound comprising a transition metal element
The positive electrode active material particles 1 (NM) were introduced into pure water (water temperature 25°C) in a reaction tank (10 L capacity) and stirred over 10 minutes to prepare a slurry. Here, the ratio of the amount of positive electrode active material particles 1 to the amount of pure water (solid-liquid ratio) was adjusted to 1250 g/L. After this, a niobium pentoxide hydrate (Nb2C>5-nH20) powder was admixed as a compound comprising a transition metal element with further stirring of the slurry, and stirring was performed over 10 minutes. It should be noted that the added amount of niobium in the niobium pentoxide hydrate (Nb2Os-n^O) powder was 0.5 mol% with respect to the amount of metal element in the positive electrode active material particles 1. Furthermore, the pH of the slurry at this time was 12.2.
(2) Filter separation step
The mixed slurry was then filter separated using a Buchner funnel to obtain a cake-like compound.
(3) Heat treatment step
The cake-like compound obtained in the filter separation step (2) was heat treated over 19 hours at 155°C using a vacuum drying apparatus, and a dried lithium-nickel composite compound was obtained to produce the positive electrode active material.
[0149]
The amount of residual Li (the total amount of Li derived from LiOH and Li2CC>3) was determined for the resulting positive electrode active material. Furthermore, the treatment steps, added components, added amounts, and final heat treatment temperature (also referred to collectively below as "conditions in the steps") are also shown in table 1 below.
[0150]
<Example 1-2: treatment of positive electrode active material particles 1 (production of positive electrode active material)>
(1) Slurry formation step and step of mixing compound comprising a transition metal element
A slurry was prepared in the same way as in example 1 and a niobium pentoxide hydrate (Nb2Os-nJbO) powder was admixed .
(2) Filter separation step
The slurry was filter separated in the same way as in example 1 to obtain a cake-like compound.
(3) Heat treatment step
The cake-like compound obtained in the filter separation step (2) was heat treated over 19 hours at 185°C using a vacuum drying apparatus. A heat treatment was then performed over 120 minutes at 350°C in an oxygen atmosphere (oxygen concentration: 97 vol%) using an electric furnace, and a dried cake-like compound was obtained to produce the positive electrode active material .
[0151]
The characteristics of the resulting positive electrode active material were determined. The characteristics of the positive electrode active material and the conditions in the steps are shown in table 1.
[0152]
<Example 1-3: treatment of positive electrode active material particles 1 (production of positive electrode active material)> (1) Slurry formation step and step of mixing compound comprising a transition metal element
A slurry was prepared in the same way as in example 1 and 0.2 moll niobium pentoxide hydrate (Nb2Os-nJbO) powder was admixed .
(2) Filter separation step
The slurry was filter separated in the same way as in example 1 to obtain a cake-like compound.
(3) Heat treatment step
The cake-like compound obtained in the filter separation step (2) was heat treated over 19 hours at 185°C using a vacuum drying apparatus. A heat treatment was then performed over 120 minutes at 350°C in an oxygen atmosphere (oxygen concentration: 97 vol%) using an electric furnace, and a dried lithium-nickel composite compound was obtained to produce the positive electrode active material.
[0153]
The characteristics of the resulting positive electrode active material were determined. The characteristics of the positive electrode active material and the conditions in the steps are shown in table 1.
[0154]
<Example 1-4: treatment of positive electrode active material particles 1 (production of positive electrode active material)>
(1) Slurry formation step and step of mixing compound comprising a transition metal element
A slurry was prepared in the same way as in example 1 and 1.0 moll niobium pentoxide hydrate (Nb2Os-n^O) powder was admixed .
(2) Filter separation step
The slurry was filter separated in the same way as in example 1 to obtain a cake-like compound.
(3) Heat treatment step The cake-like compound obtained in the filter separation step (2) was heat treated over 19 hours at 185°C using a vacuum drying apparatus. A heat treatment was then performed over 120 minutes at 350°C in an oxygen atmosphere (oxygen concentration: 97 voll) using an electric furnace, and a dried lithium-nickel composite compound was obtained to produce the positive electrode active material.
[0155]
The characteristics of the resulting positive electrode active material were determined. The characteristics of the positive electrode active material and the conditions in the steps are shown in table 1.
[0156]
<Example 1-5: treatment of positive electrode active material particles 1 (production of positive electrode active material)>
(1) Slurry formation step
The positive electrode active material particles 1 (NM) were introduced into pure water (water temperature 25°C) in a reaction tank (10 L capacity) and stirred over 10 minutes to prepare a slurry. Here, the ratio of the amount of positive electrode active material particles 1 to the amount of pure water (solid-liquid ratio) was adjusted to 1250 g/L. The pH of the slurry at this time was 12.1.
(2) Filter separation step and step of mixing a compound comprising a transition metal element
0.1 moll niobium pentoxide hydrate (Nb2Os-n^O) powder was added, and the slurry obtained in the slurry formation step (1) was filter separated to obtain a cake-like compound. The moisture content of the cake-like compound was 6.1 wtl. 0.1 moll niobium pentoxide hydrate (Nb2C>5-nH20) powder was admixed with the resulting cakelike compound.
(3) Heat treatment step The cake-like compound obtained in the filter separation step (2) was heat treated over 19 hours at 185°C using a vacuum drying apparatus. A heat treatment was then performed over 120 minutes at 250°C in an oxygen atmosphere (oxygen concentration: 97 vol%) using an electric furnace, and a dried lithium-nickel composite compound was obtained to produce the positive electrode active material.
[0157]
The characteristics of the resulting positive electrode active material were determined. The characteristics of the positive electrode active material and the conditions in the steps are shown in table 1.
[0158]
<Example 1-6: treatment of positive electrode active material particles 1 (production of positive electrode active material)>
(1) Slurry formation step and step of mixing compound comprising a transition metal element
A slurry was prepared in the same way as in example 1, where however the ratio of the amount of positive electrode active material particles 1 to the amount of pure water (solid-liquid ratio) was adjusted to 1500 g/L. Then 0.2 mol% niobium pentoxide hydrate (Nb2Os-nJbO) powder was admixed.
(2) Filter separation step
The slurry was filter separated in the same way as in example 1 to obtain a cake-like compound.
(3) Heat treatment step
The cake-like compound obtained in the filter separation step (2) was heat treated over 19 hours at 185°C using a vacuum drying apparatus. A heat treatment was then performed over 120 minutes at 300°C in an oxygen atmosphere (oxygen concentration: 97 vol%) using an electric furnace, and a dried lithium-nickel composite compound was obtained to produce the positive electrode active material.
[0159]
The characteristics of the resulting positive electrode active material were determined. The characteristics of the positive electrode active material and the conditions in the steps are shown in table 1.
[0160]
<Example 1-7: treatment of positive electrode active material particles 1 (production of positive electrode active material)>
(1) Slurry formation step
The positive electrode active material particles 1 (NM) were introduced into pure water (water temperature 25°C) in a reaction tank (10 L capacity) and stirred over 10 minutes to prepare a slurry. Here, the ratio of the amount of positive electrode active material particles 1 to the amount of pure water (solid-liquid ratio) was adjusted to 1500 g/L. The pH of the slurry at this time was 12.3.
(2) Filter separation step and step of mixing a compound comprising a transition metal element
The slurry obtained in the slurry formation step (1) was filter separated to obtain a cake-like compound. The moisture content of the cake-like compound was 6 wt%. Niobium pentoxide hydrate (Nb2Os-n^O) dissolved in an aqueous LiOH solution (Nb2Os-n^O was present in an amount of 0.2 mol% relative to the amount of all elements other than Li and 0 in the lithium-nickel composite compound) was admixed with the resulting cake-like compound. The moisture content of the cake-like compound after mixing was 14.4 wt%.
(3) Heat treatment step
The cake-like compound obtained in the filter separation step (2) was heat treated over 19 hours at 185°C using a vacuum drying apparatus. A heat treatment was then performed over 120 minutes at 300°C in an oxygen atmosphere (oxygen concentration: 97 vol%) using an electric furnace, and a dried lithium-nickel composite compound was obtained to produce the positive electrode active material.
[0161]
The characteristics of the resulting positive electrode active material were determined. The characteristics of the positive electrode active material and the conditions in the steps are shown in table 1.
[0162]
<Example 1-8: treatment of positive electrode active material particles 1 (production of positive electrode active material)>
(1) Slurry formation step
The positive electrode active material particles 1 (NM) were introduced into pure water (water temperature 25°C) in a reaction tank (10 L capacity) and stirred over 10 minutes to prepare a slurry. Here, the ratio of the amount of positive electrode active material particles 1 to the amount of pure water (solid-liquid ratio) was adjusted to 1500 g/L. The pH of the slurry at this time was 12.3.
(2) Filter separation step and step of mixing a compound comprising a transition metal element
The slurry obtained in the slurry formation step (1) was filter separated to obtain a cake-like compound. The moisture content of the cake-like compound was 6.2 wt%.
(3) Heat treatment step
The cake-like compound obtained in the filter separation step (2) was heat treated over 19 hours at 185°C using a vacuum drying apparatus. The dried cake-like compound was mixed with niobium pentoxide hydrate (Nb2Os-n^O) dissolved in an aqueous LiOH solution (Nb2Os-n^O was present in an amount of 0.2 mol% relative to the amount of all elements other than Li and 0 in the lithium-nickel composite compound), which enhanced the moisture content to 8.2 wt%. Another heat treatment was then performed over 120 minutes at 300°C in an oxygen atmosphere (oxygen concentration: 97 vol%) using an electric furnace.
[0163]
The characteristics of the resulting positive electrode active material were determined. The characteristics of the positive electrode active material and the conditions in the steps are shown in table 1.
[0164]
<Example 1-9: treatment of positive electrode active material particles 1 (production of positive electrode active material)>
The procedure was analogous to that of example 1-8, only that the moisture content after the treatment of the dried cake-like compound with niobium pentoxide hydrate (Nb2C>5-nfbO) dissolved in an aqueous LiOH solution was lower (only 1.2%) than in example 1-8. The characteristics of the positive electrode active material and the conditions in the steps are shown in table 1.
[0165]
C omparative example 1-1: production of positive electrode active material>
The amount of residual Li was determined for the positive electrode active material particles 1 (positive electrode active material), without the positive electrode active material particles 1 having undergone any of the slurry formation step (l)-heat treatment step (3) or the step of mixing a compound comprising a transition metal element. The results are shown in table 1.
[0166]
C omparative example 1-2: production of positive electrode active material>
(1) Slurry formation step
A slurry was prepared in the same way as in example 1.
(2) Filter separation step The slurry obtained in the slurry formation step (1) was filter separated using a Buchner funnel to obtain a cakelike compound. The moisture content of the cake-like compound was 5.7 wt%.
(3) Heat treatment step
The cake-like compound obtained in the filter separation step (2) was heat treated over 19 hours at 185°C using a vacuum drying apparatus. The heat treatment step was performed and a dried cake-like compound was obtained to produce the positive electrode active material.
[0167]
The characteristics of the resulting positive electrode active material were determined. The characteristics of the positive electrode active material and the conditions in the steps are shown in table 1.
[0168]
C omparative example 1-3: production of positive electrode active material>
A niobium pentoxide hydrate (Nb2Os-n^O) powder was mixed with the positive electrode active material particles 1 as a compound comprising a transition metal element, the mixture was heat treated over 120 minutes at 350°C in an oxygen atmosphere (oxygen concentration: 97 vol%) using an electric furnace, and the positive electrode active material was produced. The characteristics of the resulting positive electrode active material were determined. The characteristics of the positive electrode active material and the conditions in the steps are shown in table 1.
[0169]
C omparative example 1-4: production of positive electrode active material>
A powdery lithium niobate (LiNbCh) powder was mixed with the positive electrode active material particles 1 as a compound comprising a transition metal element, the mixture was heat treated over 120 minutes at 350°C in an oxygen atmosphere (oxygen concentration: 97 vol%) using an electric furnace, and the positive electrode active material was produced. The characteristics of the resulting positive electrode active material were determined. The characteristics of the positive electrode active material and the conditions in the steps are shown in table 1.
[0170]
C omparative example 1-5: production of positive electrode active material>
(1) Slurry formation step
A slurry was prepared in the same way as in example 1.
(2) Filter separation step
The slurry obtained in the slurry formation step (1) was filter separated using a Buchner funnel to obtain a cakelike compound. The moisture content of the cake-like compound was 5.9 wt%.
(3) Heat treatment step
The cake-like compound obtained in the filter separation step (2) was heat treated over 19 hours at 185°C using a vacuum drying apparatus. A heat treatment was then performed over 120 minutes at 350°C in an oxygen atmosphere (oxygen concentration: 97 vol%) using an electric furnace and a dried lithium-nickel composite compound was obtained to produce the positive electrode active material.
[0171]
The characteristics of the resulting positive electrode active material were determined. The characteristics of the positive electrode active material and the conditions in the steps are shown in table 1.
[0172]
<Test example: nonaqueous electrolyte secondary battery characteristics test> The initial charging capacity, initial discharging capacity, initial charging/discharging efficiency, initial reaction resistance, and resistance ratio (compared with comparative example 1-2) were obtained as characteristics of nonaqueous electrolyte secondary batteries in which the positive electrode active materials obtained in examples 1-1 to 1-5 and comparative examples 1-1 to 1-5 were used as the positive electrode. The results are shown in table 1.
[0174]
As shown in the columns for examples 1-1 and 1-2, and comparative examples 1-2 and 1-5 in table 1, it was first of all confirmed that the amount of residual Li in the positive electrode active material was smaller when the slurry formation step (1) was performed in the production of the positive electrode active material. Meanwhile, as shown in the columns for comparative examples 1-3 and 1- 4 in table 1, it was confirmed that there was no reduction in the amount of residual Li in the positive electrode active material, even in comparison with comparative example 1-1 in which no treatments at all were performed, when the slurry formation step (1) was not performed in the production of the positive electrode active material.
[0175]
As shown in the columns for example 1-1 and comparative example 1-2 in table 1, the initial reaction resistance was then shown to be 59 Q in the battery employing the positive electrode active material according to example 1-1, in which the step of mixing Nb2Os-nJbO powder with the slurry, the filter separation step (2) and the heat treatment step (3) were performed, whereas the initial reaction resistance was shown to be 220 Q in the battery employing the positive electrode active material according to comparative example 1-2 in which the filter separation step (2) and the heat treatment step (3) were performed, without any addition to the slurry.
[0176]
Based on the matters above, it is thought that a compound comprising Li and Nb is formed on the surfaces of the particles, as shown in fig. 1, as a result of heat treating the eluted lithium and added elemental Nb, because the treatment method passes through the step of mixing Nb2Os-nJbO powder with the slurry, the filter separation step (2) and the heat treatment step (3), and therefore the initial reaction resistance decreased due to the effect of improving lithium ion conductivity. Furthermore, it is thought that the amount of residual Li decreased because the amount of excess lithium was reduced by the formation of the compound comprising Li and Nb.
[0177]
Furthermore, the same effect was also confirmed when the temperature of the heat treatment step with respect to the abovementioned matters was 350°C, as in example 1-2 and comparative example 1-5, and the initial battery capacity increased. From this, it is inferred that Li2MnO3, which is thought to be an unstable resistance component that impedes Li migration within the crystal structure, was formed as a domain in the crystal lattice by the Li fraction contained in excess, as a result of Mn, which is substituted with Ni in the positive electrode active material, reacting with Li when the positive electrode active material is synthesized, and therefore, during the heat treatment at 350°C in the heat treatment step in example 1-2, not only does the added Nb react with the eluted lithium, it is also thought to withdraw Li from the Li2MnO3 domain. It is thought that, as a result of this, Li2MnO3 is eliminated in the resistance component because of a phase change to a crystal structure such as Lii-xNiyMnO2 or LixMn2O4-y, for example, which is therefore inferred to cause an increase in the Li capable of migrating within the crystal structure, and thus the battery capacity increased.
[0178]
Moreover, it is speculated that the phenomenon described above is manifested in positive electrode active materials in which Mn is substituted with Ni, and it is thought possible for this phenomenon to be resolved by implementing the treatment method according to the present invention. [0179]
Meanwhile, when Nb2Os-nfbO powder was added directly to the powdered positive electrode active material, as shown in the column for comparative example 1-3 in table 1, and when the powdery lithium niobium oxide (LiNbCh) powder was added to the positive electrode active material, as shown in the column for comparative example 1-4 in table 1, residual Li did not decrease, despite the heat treatment step (3) being performed at a final heat treatment temperature of 350°C, and there was confirmed to be no increase in the battery capacity, such as the initial charging capacity and the initial discharging capacity .
[0180]
These results showed that, in order to achieve higher battery capacity, it is not sufficient simply to carry out the heat treatment step (3), it is also important to implement the step of mixing the compound comprising a transition metal element, in a state in which the moisture content of the positive electrode active material is 3 wt% or greater, through the slurry formation step (1) and the filter separation step (2) or the treatment of the dried cake-like compound with the compound comprising a transition metal element in the presence of some moisture during the heat treatment step (3), where the moisture content can even be as low as 1 wt%. This is inferred to be because of a state in which the added transition metal element compound partially dissolves in the positive electrode active material having a moisture content of 3 wt% or greater and is readily deposited in a very fine state on the secondary particles surfaces and grain boundary portions thereof, and additionally because of a state in which the lithium fraction also has a high moisture content, therefore partially dissolving and readily migrating, and, as a result, the transition metal element and the eluted Li and excess Li on the particle surfaces can react, and it is thought that forms such as in fig. 1 and 2 can be achieved.
[0181]
It can be understood from the results above that, by virtue of the method for treating positive electrode active material particles according to the examples, which comprises the slurry formation step (l)-heat treatment step (3), and further comprises, in at least one of step (1), step (2) and step (3), a step of mixing a compound comprising a transition metal element, it is possible to provide positive electrode active material particles which achieve lower resistance by reducing a resistance component and higher battery capacity, while also reducing excess Li on surfaces of the primary particles and secondary particles of the lithium-nickel composite compound.
[0182]
C onfirmation of sites where the compound containing lithium and Nb and the compound comprising Nb were present in the positive electrode active material>
The SEM-EDX described in the embodiment above was performed for the positive electrode active material obtained in example 1-4, and a cross-sectional photograph of the positive electrode active material such as shown in fig. 3 was obtained. Detection locations (detection sites) were selected, Nb/(NiMnNb) (mol%) was calculated and these are shown in table 2 below, together with detection results. The Nb detection results are denoted by 0 and X: an evaluation of 0 was given where the value of Nb/ (NiMnNb) was 0.10 mol% or greater, and an evaluation of X was given where the value was less than 0.10 mol%. Furthermore, the amount of Nb in Nb/(NiMnNb) denotes the total amount of substance in compounds comprising Nb, and includes both the compound containing lithium and Nb and the compound comprising Nb. It should be noted that the numerical values of "039", "040", "041", "042", "043", "044", "045", "046", "047", "048", "049",
"050", and "051" in fig. 3 denote the detection locations in the positive electrode active material, and correspond to the detection locations in table 2 below.
[0183]
[0184]
As shown in fig. 3 and table 2, it was first of all confirmed that the compound containing lithium and Nb and the compound comprising Nb were present in the positive electrode active material obtained in example 1-4 on the surfaces of the secondary particles of the positive electrode active material particles (detection locations 045-047). It was furthermore confirmed that the compound containing lithium and Nb and the compound comprising Nb were also present on the grain boundary portions formed by adjacent primary particles located on the surfaces of the plurality of positive electrode active material particles constituting the secondary particles (detection positions 039-044 and 051). Meanwhile, it was confirmed that the compound containing lithium and Nb and the compound comprising Nb were largely absent within the primary particles of the positive electrode active material (detection locations 048-050).
[0185]
These results confirmed that the compound containing lithium and Nb and the compound comprising Nb were present in the positive electrode active material according to the present invention on the surfaces of the secondary particles of the lithium-nickel composite compound and on at least part of the grain boundary portions (interfaces between primary particles) formed by adjacent primary particles located on surfaces of the plurality of primary particles constituting the secondary particles .
[0186]
<Example 2-1: treatment of positive electrode active material particles 2 (production of positive electrode active material)>
(1) Step of mixing compound comprising a transition metal element and slurry formation step
A niobium pentoxide hydrate (Nb2Os-nJbO) powder was added as a compound comprising a transition metal element into pure water (water temperature 25°C) in a reaction tank (10 L capacity) and stirred. It should be noted that the added amount of niobium in the niobium pentoxide hydrate (Nb2C>5-nfbO) powder was 0.5 mol% with respect to the amount of all elements other than Li and 0 in the positive electrode active material particles 2 (NCA). After this, the positive electrode active material particles 2 (NCA) were introduced and stirred over 10 minutes to prepare a slurry. Here, the ratio of the amount of positive electrode active material particles 2 to the amount of pure water (solid-liquid ratio) was adjusted to 1250 g/L. Furthermore, the pH of the slurry at this time was 12.2.
(2) Filter separation step The slurry obtained in the slurry formation step (1) was filter separated using a Buchner funnel to obtain a cakelike compound.
(3) Heat treatment step
The cake-like compound obtained in the filter separation step (2) was heat treated over 19 hours at 185°C using a vacuum drying apparatus, and a dried lithium-nickel composite compound was obtained to produce the positive electrode active material.
[0187]
The amount of residual Li (the total amount of Li derived from LiOH and Li2CC>3) was determined for the resulting positive electrode active material. Furthermore, the treatment steps, added components, added amounts, and final heat treatment temperature (also referred to collectively below as "conditions in the steps") are also shown in table 3 below.
[0188]
<Example 2-2: treatment of positive electrode active material particles 2 (production of positive electrode active material)>
(1) Step of mixing compound comprising a transition metal element and slurry formation step
A slurry was prepared in the same way as in example 2-1.
(2) Filter separation step
The slurry was filter separated in the same way as in example 1 to obtain a cake-like compound.
(3) Heat treatment step
The cake-like compound obtained in the filter separation step (2) was heat treated over 19 hours at 185°C using a vacuum drying apparatus. A heat treatment was then performed over 120 minutes at 350°C in an oxygen atmosphere (oxygen concentration: 97 vol%) using an electric furnace, and a dried lithium-nickel composite compound was obtained to produce the positive electrode active material. [0189]
The characteristics of the resulting positive electrode active material were determined. The characteristics of the positive electrode active material and the conditions in the steps are shown in table 3.
[0190]
<Example 2-3: treatment of positive electrode active material particles 2 (production of positive electrode active material)>
(1) Slurry formation step and step of mixing compound comprising a transition metal element
The positive electrode active material particles 2 (NCA) were introduced into pure water (water temperature 25°C) in a reaction tank (10 L capacity) and stirred over 10 minutes to prepare a slurry. Here, the ratio of the amount of positive electrode active material particles 2 to the amount of pure water (solid-liquid ratio) was adjusted to 1250 g/L. After this, a vanadium pentoxide (V2O5) powder was admixed as a compound comprising a transition metal element with further stirring, and stirring was performed over 10 minutes. It should be noted that the added amount of vanadium in the vanadium pentoxide (V2O5) powder was 0.2 mol% with respect to the amount of all elements other than Li and 0 in the positive electrode active material particles 2 (NCA). Furthermore, the pH of the slurry at this time was 12.2.
(2) Filter separation step
The mixed slurry was then filter separated using a Buchner funnel to obtain a cake-like compound.
(3) Heat treatment step
The cake-like compound obtained in the filter separation step (2) was heat treated over 19 hours at 185°C using a vacuum drying apparatus. A heat treatment was then performed over 120 minutes at 350°C in an oxygen atmosphere (oxygen concentration: 97 vol%) using an electric furnace, and a dried lithium-nickel composite compound was obtained to produce the positive electrode active material.
[0191]
The characteristics of the resulting positive electrode active material were determined. The characteristics of the positive electrode active material and the conditions in the steps are shown in table 3.
[0192]
<Example 2-4: treatment of positive electrode active material particles 2 (production of positive electrode active material)>
(1) Step of mixing compound comprising a transition metal element and slurry formation step
A niobium pentoxide (Nb2Os) powder was added as a compound comprising a transition metal element into pure water (water temperature 25°C) in a reaction tank (10 L capacity) and stirred. It should be noted that the added amount of niobium in the niobium pentoxide (Nb2Os) powder was 0.5 mol% with respect to the amount of all elements other than Li and 0 in the positive electrode active material particles 2 (NCA). After this, the positive electrode active material particles 2 (NCA) were introduced and stirred over 10 minutes to prepare a slurry. Here, the ratio of the amount of positive electrode active material particles 2 to the amount of pure water (solid-liquid ratio) was adjusted to 800 g/L.
(2) Filter separation step
The slurry obtained in the slurry formation step (1) was filter separated using a Buchner funnel to obtain a cakelike compound.
(3) Heat treatment step
The cake-like compound obtained in the filter separation step (2) was heat treated over 19 hours at 185°C using a vacuum drying apparatus. A heat treatment was then performed over 120 minutes at 350°C in an oxygen atmosphere (oxygen concentration: 97 vol%) using an electric furnace, and a dried lithium-nickel composite compound was obtained to produce the positive electrode active material.
[0193]
The characteristics of the resulting positive electrode active material were determined. The characteristics of the positive electrode active material and the conditions in the steps are shown in table 3.
[0194]
<Example 2-5: treatment of positive electrode active material particles 2 (production of positive electrode active material)>
(1) Step of mixing compound comprising a transition metal element and slurry formation step
A niobium pentoxide (Nb2Os) powder was added as a compound comprising a transition metal element into pure water (water temperature 25°C) in a reaction tank (10 L capacity) and stirred. It should be noted that the added amount of niobium in the niobium pentoxide (Nb2Os) powder was 0.5 mol% with respect to the amount of all elements other than Li and 0 in the positive electrode active material particles 2 (NCA). After this, the positive electrode active material particles 2 (NCA) were introduced and stirred over 10 minutes to prepare a slurry. Here, the ratio of the amount of positive electrode active material particles 2 to the amount of pure water (solid-liquid ratio) was adjusted to 1800 g/L. The pH of the slurry at this time was 12.5.
(2) Filter separation step
The slurry obtained in the slurry formation step (1) was filter separated using a Buchner funnel to obtain a cakelike compound.
(3) Heat treatment step
The cake-like compound obtained in the filter separation step (2) was heat treated over 19 hours at 185°C using a vacuum drying apparatus. A heat treatment was then performed over 120 minutes at 350°C in an oxygen atmosphere (oxygen concentration: 97 vol%) using an electric furnace, and a dried lithium-nickel composite compound was obtained to produce the positive electrode active material.
[0195]
C omparative example 2-1: production of positive electrode active material>
The amount of residual Li was determined for the positive electrode active material particles 2 (positive electrode active material), without the positive electrode active material particles 2 (NCA) having undergone any of the slurry formation step (l)-heat treatment step (3) or the step of mixing a compound comprising a transition metal element. The results are shown in table 3.
[0196]
C omparative example 2-2: production of positive electrode active material>
(1) Slurry formation step
The positive electrode active material particles 2 (NCA) were introduced into pure water (water temperature 25°C) in a reaction tank (10 L capacity) and stirred over 10 minutes to prepare a slurry. Here, the ratio of the amount of positive electrode active material particles 2 to the amount of pure water (solid-liquid ratio) was adjusted to 1250 g/L.
(2) Filter separation step
The slurry obtained in the slurry formation step (1) was filter separated using a Buchner funnel to obtain a cakelike compound. The moisture content of the cake-like compound was 5.5 wt%.
(3) Heat treatment step
The cake-like compound obtained in the filter separation step (2) was heat treated over 19 hours at 185°C using a vacuum drying apparatus. The heat treatment step was performed and a dried cake-like compound was obtained to produce the positive electrode active material.
[0197]
The characteristics of the resulting positive electrode active material were determined. The characteristics of the positive electrode active material and the conditions in the steps are shown in table 3.
[0198]
C omparative example 2-3: production of positive electrode active material>
(1) Slurry formation step
The positive electrode active material particles 2 (NCA) were introduced into pure water (water temperature 25°C) in a reaction tank (10 L capacity) and stirred over 10 minutes to prepare a slurry. Here, the ratio of the amount of positive electrode active material particles 2 to the amount of pure water (solid-liquid ratio) was adjusted to 1250 g/L.
(2) Filter separation step
The slurry obtained in the slurry formation step (1) was filter separated using a Buchner funnel to obtain a cakelike compound. The moisture content of the cake-like compound was 5.9 wt%.
(3) Heat treatment step
The cake-like compound obtained in the filter separation step (2) was heat treated over 19 hours at 185°C using a vacuum drying apparatus. A heat treatment was then performed over 120 minutes at 350°C in an oxygen atmosphere (oxygen concentration: 97 vol%) using an electric furnace, and a dried lithium-nickel composite compound was obtained to produce the positive electrode active material.
[0199]
The characteristics of the resulting positive electrode active material were determined. The characteristics of the positive electrode active material and the conditions in the steps are shown in table 3.
[0201]
As shown in the columns for examples 2-1 and 2-2, and comparative examples 2-2 and 2-3 in table 3, it was first of all confirmed that the amount of residual Li in the positive electrode active material was smaller when the slurry formation step (1) was performed in the production of the positive electrode active material, in the same way as in table 1. Furthermore, it was confirmed from the results that the positive electrode active material particles are not limited to NM, and an effect such as can be seen in the present invention was also apparent for NCA. Additionally, the same effect was also achieved in example 2-3 where the transition metal element was V.
[0202]
Furthermore, it was confirmed from the results of examples 2-1 and 2-2 that an effect such as can be seen in the present invention was also apparent when the transition metal element compound was added before the slurry was formed.
[0203]
The columns for examples 2-4 and 2-5 are cases where the solid-liquid ratios during slurry formation were different, but the results for residual Li and battery characteristics were different. These results show the importance in the present invention of adjusting the amount of lithium which is eluted by adjusting the solidliquid ratio during slurry formation and of controlling the reaction with the transition metal element, as described above, and it could be confirmed that the impact of the positive electrode active material which is ultimately obtained on the residual Li and battery characteristics must be taken into account.
[Industrial Applicability]
[0204] The positive electrode active material according to the present invention makes it possible to provide positive electrode active material particles which achieve lower resistance by reducing a resistance component and higher battery capacity, while also reducing excess Li on surfaces of primary particles and secondary particles of a lithium-nickel composite compound, and is therefore suitable for a positive electrode of a nonaqueous electrolyte secondary battery.
[Key to Symbols]
[0205]
1... Secondary particle
2... Surface
3... Coating layer of compound containing lithium and a transition metal element and compound comprising a transition metal element
4... Grain boundary portion
11, 12, 13, 14... Primary particle

Claims

CLAIMS [Claim 1] A method for treating positive electrode active material particles comprising a lithium-nickel composite compound which contains lithium, nickel and oxygen and may contain another element besides lithium, nickel and oxygen, the method being characterized by comprising:
(1) a slurry formation step in which the lithium-nickel composite compound is introduced into an aqueous solvent and stirred to prepare a slurry;
(2) after the slurry formation step (1), a filter separation step in which the slurry is filter separated to obtain a cake-like compound; and
(3) a heat treatment step in which the cake-like compound obtained in the filter separation step (2) is heat treated to obtain a dried lithium-nickel composite compound, wherein the method further comprises, in at least one of step (1), step (2) and/or step (3), a step of mixing the aqueous solvent (used in step (1)), the slurry (of step (1)), the cake-like compound (of step (2)) and/or the dried lithium-nickel composite compound (of step (3)) with (i) a compound comprising at least one type of transition metal element selected from the group consisting of Ti, V, Cr, Zr, Nb, Mo, Hf and Ta, and (ii) optionally with a lithium compound; where in case that said compound comprising at least one type of transition metal element is mixed with said dried lithium-nickel composite compound (of step (3)), mixing is carried out in the presence of an aqueous solvent; and where in the obtained product a compound containing lithium and the transition metal element, and the compound comprising a transition metal element are present on:
(a) surfaces of secondary particles of the dried lithium- nickel composite compound, and (b) at least part of a grain boundary portion (interface between primary particles) formed by adjacent primary particles located on surfaces of the plurality of primary particles constituting the secondary particles.
[Claim 2]
The method as claimed in claim 1, wherein the step of mixing the compound comprising a transition metal element is performed before and/or after introduction of the lithium-nickel composite compound into the aqueous solvent in step (1).
[Claim 3]
The method as claimed in claim 1, wherein said compound comprising a transition metal element and optionally said lithium compound is mixed with the cake-like compound of step (2), where said compound comprising a transition metal element and optionally said lithium compound are preferably used as an aqueous solution or suspension comprising said compound comprising a transition metal element and optionally said lithium compound.
[Claim 4]
The method as claimed in claim 1, wherein an aqueous solution or suspension comprising said compound comprising a transition metal element and optionally said lithium compound is mixed with the dried lithium-nickel composite compound of step (3).
[Claim 5]
The method as claimed in any of the preceding claims, wherein the transition metal element is used in form of a transition metal oxide, hydroxide, mixed oxidehydroxide, sulfate, oxalate or a hydrate of the aforementioned forms.
[Claim 6] The method as claimed in any of the preceding claims, wherein the transition metal element is at least one selected from the group consisting of Ti, V, Zr, Nb and Mo.
[Claim 7]
The method as claimed in claim 6, wherein the transition metal element is at least one selected from the group consisting of V and Nb.
[Claim 8]
The method as claimed in claim 7, wherein the transition metal element is Nb, where the compound comprising Nb is preferably Nb2Os or a hydrate thereof.
[Claim 9]
The method as claimed in any of the preceding claims, wherein the lithium compound optionally mixed with the aqueous solvent (used in step (1)), the slurry (of step (1)), the cake-like compound (of step (2)) or the dried lithium-nickel composite compound (of step (3)) is LiOH.
[Claim 10]
The method as claimed in any of the preceding claims, wherein the lithium-nickel composite compound is introduced in the slurry formation step (1) with a ratio (solid-liquid ratio) of the amount of the lithium-nickel composite compound to the amount of the aqueous solvent adjusted to 750 g -2000 g per liter of the aqueous solvent
[Claim 11]
The method as claimed in any of the preceding claims, wherein the added amount of the transition metal element is 0.01 mol%-1.5 moll with respect to the total amount of all elements except lithium and oxygen in the lithium- nickel composite compound.
[Claim 12] The treatment method as claimed in any of the preceding claims, wherein the content of the aqueous solvent, preferably of water, of the lithium-nickel composite compound is 1 wt% or greater, preferably 3 wt% or greater when the compound comprising a transition metal element is mixed.
[Claim 13]
The method as claimed in claim 12, where in case that the cake-like compound of step (2) is mixed with said compound comprising a transition metal element and optionally with said lithium compound, the total content of aqueous solvent, preferably of water, in the mixture obtained by mixing said cake-like compound, said compound comprising a transition metal element and optionally said lithium compound is 3 wt% or greater, based on the total weight of said obtained mixture; and/or where in case that the dried lithium-nickel composite compound of step (3) is mixed with said compound comprising a transition metal element and optionally with said lithium compound, the total content of aqueous solvent, preferably of water, in the mixture obtained by mixing said dried lithium-nickel composite compound with said compound comprising a transition metal element and optionally said lithium compound is 1 wt% or greater, based on the total weight of said obtained mixture; where in the latter case the desired content of aqueous solvent is preferably obtained by mixing the dried lithium-nickel composite compound of step (3) with an aqueous solution or suspension comprising said compound comprising a transition metal element and optionally said lithium compound.
[Claim 14]
The method as claimed in any of the preceding claims, wherein the heat treatment is performed at 100°C-400°C in the heat treatment step (3).
[Claim 15]
The method as claimed in claim 14, where in the heat treatment step (3) the cake-like compound obtained in the filter separation step (2) is heat-treated in a first step at 100 to 195°C and in an optional second step at 200 to 400°C.
[Claim 16]
The method as claimed in claim 15, wherein the second heat treatment is performed, where the second heat treatment is preferably performed at 200°C-350°C.
[Claim 17]
The method as claimed in any of claims 15 or 16, wherein one or two or all three of the following conditions (a), (b) and/or (c) apply:
(a) the first heat treatment is performed under reduced pressure; and/or
(b) the second heat treatment is performed under an oxygen-enriched atmosphere (such as oxygen-enriched air, oxygen-nitrogen mixtures with more than 20% by volume of oxygen, and oxygen); and/or
(c) the second heat treatment is performed under an atmosphere with reduced CO2 content, preferably with CO2 content of at most 100 ppm by volume, more preferably of at most 50 ppm by volume.
[Claim 18]
The method as claimed in any of the preceding claims, wherein the lithium-nickel composite compound has a composition having a layered rock-salt structure and represented by the following formula (I): LiaNi1-b-cMnbMcO2 (I)
(in the formula, M is one or more elements other than Li, Ni, Mn or 0; 0.95<adl.l5, 0<bd0.20, 0<cd0.20, and Ni is 0.80-0.98).
[Claim 19]
The method as claimed in claim 18, where M is one or more elements selected from the group consisting of Al, Ti, Co, Mg, Zn, Nb, W, Mo, Sb, V, Cr, Ca, Fe, Ga, Sr, Y, Ru, In, Sn, Ta, Bi, Zr, Si, P and B; where M is specifically Al and/or Co.
[Claim 20]
The method as claimed in claim 18, where b is 0.05 to 0.2 and c is 0.
[Claim 21]
The method as claimed in any of claims 18 or 19, wherein the lithium-nickel composite is represented by the following formula (1.2):
LiaNii-ci-C2CociAlC202 (1.2)
(in the formula, 0.95<adl.l5, 0<cld0.20, 0<c2<0.20, and Ni is 0.80-0.98; where preferably 0.95<adl.l5, 0<cl<0.20, 0<c2<0.20, and Ni is 0.80-0.98; where more preferably 0.01<cl<0.09 and 0.01<c2<0.09).
[Claim 22]
A positive electrode active material, obtainable by the method as claimed in any of claims 1 to 21.
[Claim 23]
A positive electrode active material comprising a lithium-nickel composite compound which contains lithium, nickel and oxygen and may contain another element besides lithium, nickel and oxygen, wherein: a compound containing lithium and a transition metal element, and a compound comprising the transition metal element are present on:
(a) surfaces of secondary particles of the lithium-nickel composite compound, and
(b) at least part of a grain boundary portion (interface between primary particles) formed by adjacent primary particles located on surfaces of the plurality of primary particles constituting the secondary particles; the transition metal element is at least one selected from the group consisting of Ti, V, Cr, Zr, Nb, Mo, Hf and Ta; and an amount of residual lithium determined by means of neutralization titration is preferably 0.15 wt% or less.
[Claim 24]
The positive electrode active material as claimed in claim 23, wherein the transition metal element is at least one selected from the group consisting of Ti, V, Zr, Nb and Mo, preferably from V and Nb, and is in particular Nb.
[Claim 25]
The positive electrode active material as claimed in any of claims 23 or 24, wherein the lithium-nickel composite compound has a composition having a layered rock-salt structure and represented by the following formula (I): LiaNi1-b-cMnbMcO2 (I)
(in the formula, M is one or more elements other than Li, Ni, Mn or 0;
0.95<a<1.15, 0<b<0.20, 0<c<0.20, and Ni is 0.80-0.98; where M is preferably one or more elements selected from the group consisting of Al, Ti, Co, Mg, Zn, Nb, W, Mo, Sb, V, Cr, Ca, Fe, Ga, Sr, Y, Ru, In, Sn, Ta, Bi, Zr, Si, P and B; and more preferably from the group consisting of Ti, Mg, Zn, Nb, W, Mo, V, Cr, Ca, Fe, Ga, Sr, Y, Sb, Ru, In, Sn, Ta, Bi, Zr, Si, P and B; and is specifically Al and/or Co).
[Claim 26]
The positive electrode active material as claimed in claim 25, wherein in the lithium-nickel composite compound b is 0.05 to 0.2 and c is 0; or the lithium-nickel composite compound is represented by the following formula (1.2):
LiaNii-ci-C2CociAlC202 (1.2)
(in the formula, 0.95<adl.l5, 0<cld0.20, 0<c2<0.20, and Ni is 0.80-0.98; where preferably 0.95<adl.l5, 0<cl<0.20, 0<c2<0.20, and Ni is 0.80-0.98; where more preferably 0.01<cl<0.09 and 0.01<c2<0.09).
[Claim 27] A nonaqueous electrolyte secondary battery comprising a positive electrode that contains the positive electrode active material as claimed in any one of claims 23 to 26.
EP23817967.5A 2022-11-30 2023-11-30 Method for treating positive electrode active material particles, and positive electrode active material and nonaqueous electrolyte secondary battery employing same Pending EP4626829A1 (en)

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JP5987401B2 (en) * 2012-03-28 2016-09-07 住友金属鉱山株式会社 Cathode active material for non-aqueous electrolyte secondary battery, method for producing the same, and secondary battery
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US10374227B2 (en) * 2014-12-05 2019-08-06 Lg Chem, Ltd. Positive electrode active material, method for preparing the same and lithium secondary battery including the same
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