WO2013146723A1 - リチウムイオン二次電池用活物質及びリチウムイオン二次電池 - Google Patents
リチウムイオン二次電池用活物質及びリチウムイオン二次電池 Download PDFInfo
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- WO2013146723A1 WO2013146723A1 PCT/JP2013/058665 JP2013058665W WO2013146723A1 WO 2013146723 A1 WO2013146723 A1 WO 2013146723A1 JP 2013058665 W JP2013058665 W JP 2013058665W WO 2013146723 A1 WO2013146723 A1 WO 2013146723A1
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/13—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
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/36—Selection of substances as active materials, active masses, active liquids
- H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
- H01M4/485—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of mixed oxides or hydroxides for inserting or intercalating light metals, e.g. LiTi2O4 or LiTi2OxFy
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/05—Accumulators with non-aqueous electrolyte
- H01M10/052—Li-accumulators
- H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/36—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
- H01M4/50—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese
- H01M4/505—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese of mixed oxides or hydroxides containing manganese for inserting or intercalating light metals, e.g. LiMn2O4 or LiMn2OxFy
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/36—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
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
- H01M2004/028—Positive electrodes
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- 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 an active material for a lithium ion secondary battery and a lithium ion secondary battery.
- a so-called solid solution positive electrode has been studied as a positive electrode material (positive electrode active material) that may meet this demand.
- a solid solution (so-called Li-excess layered positive electrode material) of electrochemically inactive layered Li 2 MnO 3 and electrochemically active layered LiAO 2 (A is a transition metal such as Co and Ni) ) Is expected as a candidate for a high-capacity positive electrode material that can exhibit a large electric capacity exceeding 200 mAh / g (see Patent Document 1 below).
- the solid solution positive electrode using Li 2 MnO 3 described in Patent Document 1 has a problem that the cycle characteristics are easily deteriorated by repeated charge and discharge, although the discharge capacity is large. Further, although using a Li [Li q Co x Ni y Mn z] O 2 positive electrode of the solid solution system also in Patent Document 2, although the cycle characteristic is excellent for the item, a problem initial discharge capacity is low .
- the present invention has been made in view of the above-described problems of the prior art, and an object thereof is to provide an active material having a high capacity and excellent cycle characteristics, and a lithium ion secondary battery.
- an active material according to the present invention has a layered crystal structure and is represented by the following composition formula (1): Li y Ni a Co b Mn c M d O x (1)
- the element M is at least one element selected from the group consisting of Al, Si, Zr, Ti, Fe, Mg, Nb, Ba and V, and 1.9 ⁇ (a + b + c + d + y) ⁇ 2 0.1, 1.05 ⁇ y ⁇ 1.35, 0 ⁇ a ⁇ 0.3, 0 ⁇ b ⁇ 0.25, 0.3 ⁇ c ⁇ 0.7, 0 ⁇ d ⁇ 0.1, 1.9 ⁇ x ⁇ 2.1, and when the Ni composition amount in the center of the active material primary particles is Ni ⁇ near the Ni ⁇ surface, 0.69 ⁇ Ni ⁇ / Ni ⁇ ⁇ 0.85 It is characterized by being.
- the active material of the present invention having the above characteristics is used, it is considered that lithium is smoothly desorbed and inserted during charge and discharge.
- a general nickel, cobalt, or manganese-based positive electrode active material has a layered crystal structure, and a lithium layer and a transition metal layer are alternately stacked.
- an active material having the composition of the present invention is Part of the transition metal layer is replaced with lithium.
- the structural feature of 0.69 ⁇ Ni ⁇ / Ni ⁇ ⁇ 0.85 of the active material in the present invention is that the Ni composition amount on the primary particle surface is small, so that lithium tends to enter the transition metal layer on the primary particle surface, or the transition It is considered that the metal layer easily moves into the electrolytic solution. That is, it is presumed that high capacity and excellent cycle characteristics can be exhibited by facilitating the movement of lithium accompanying charging and discharging.
- the element M is preferably Fe or V, and d is preferably 0 ⁇ d ⁇ 0.1.
- a lithium ion secondary battery includes a positive electrode current collector, a positive electrode active material layer including a positive electrode active material, a negative electrode current collector, and a negative electrode active material layer including a negative electrode active material, And a separator located between the positive electrode active material layer and the negative electrode active material layer, a negative electrode, a positive electrode, and an electrolyte in contact with the separator. Contains substances.
- the lithium ion secondary battery of the present invention containing the active material of the present invention in the positive electrode active material layer has a high capacity and excellent cycle characteristics.
- the present invention it is possible to provide an active material having a high capacity and excellent cycle characteristics, and a lithium ion secondary battery.
- FIG. 1 is a schematic cross-sectional view of a lithium ion secondary battery including a positive electrode active material layer including an active material formed from a precursor according to an embodiment of the present invention.
- FIG. 2A is a photograph of the active material primary particles of Example 1 taken with a scanning transmission electron microscope (STEM), and the + portion in the photograph is an energy dispersive X-ray spectrometer (EDS) attached to the STEM. ) Is the part of the point analysis.
- FIG. 2B is a photograph of the active material primary particles of Comparative Example 1 taken with a scanning transmission electron microscope (STEM), and the + portion in the photograph is an energy dispersive X-ray spectrometer (attached to the STEM) ( This is the part of the point analysis by EDS).
- FIG. 2A is a photograph of the active material primary particles of Example 1 taken with a scanning transmission electron microscope (STEM), and the + portion in the photograph is an energy dispersive X-ray spectrometer (attached to the STEM)
- FIG. 3 is a distribution diagram showing the relationship between Ni ⁇ / Ni ⁇ and cycle characteristics of Examples 1 to 10 and Comparative Examples 1 and 2 of the active material of the present invention.
- FIG. 4 is a distribution diagram showing the relationship between the initial discharge capacity and the cycle characteristics of Examples 11 to 19 of the active material of the present invention.
- the active material of the present embodiment is a lithium-containing composite oxide having a layered crystal structure and represented by the following composition formula (1).
- the element M is at least one element selected from the group consisting of Al, Si, Zr, Ti, Fe, Mg, Nb, Ba and V, and 1.9 ⁇ (a + b + c + d + y) ⁇ 2 0.1, 1.05 ⁇ y ⁇ 1.35, 0 ⁇ a ⁇ 0.3, 0 ⁇ b ⁇ 0.25, 0.3 ⁇ c ⁇ 0.7, 0 ⁇ d ⁇ 0.1, 1.9 ⁇ x ⁇ 2.1, where Ni ⁇ in the central part of the active material primary particles is Ni ⁇ and Ni composition in the vicinity of the surface is Ni ⁇ , 0.69 ⁇ Ni ⁇ / Ni ⁇ ⁇ 0. 85.
- the vicinity of the surface typically means, for example, a region from the surface of the active material up to about 30 nm in the depth direction, and indicates a region having a width of 30 nm from the surface when a cross section of the active material is viewed with a microscope.
- the primary particle diameter of the active material it means a depth region of about 15% from the surface to the primary particle diameter.
- the composition range of Li is preferably 1.10 ⁇ y ⁇ 1.35, more preferably 1.15 ⁇ y ⁇ 1.35, and even more preferably 1.20 ⁇ y ⁇ 1.35. is there. If the value of Ni ⁇ / Ni ⁇ is too low, the stress on the crystal structure will increase, so the range is preferably 0.69 ⁇ Ni ⁇ / Ni ⁇ ⁇ 0.80, preferably 0.8. 69 ⁇ Ni ⁇ / Ni ⁇ ⁇ 0.76 is preferable.
- the average particle size of the active material primary particles is preferably in the range of 0.2 to 1.0 ⁇ m, more preferably in the range of 0.2 to 0.5 ⁇ m. Furthermore, it is preferable that there are no coarse particles of 10 ⁇ m or more.
- Fe or V having various valence forms is preferably added.
- Fe or V is preferably such that d is 0 ⁇ d ⁇ 0.1 in the above-described composition formula (1).
- the peak half-value width FWHM (003) of (003) in the X-ray diffraction pattern is FWHM (003) ⁇ 0.13
- the peak half-value width FWHM (010) of (010) is FWHM (010) ⁇
- the peak half-value width FWHM (104) of (104) is FWHM (104) ⁇ 0.20
- further FWHM (003) / FWHM (104) is 0.57 ° or less. More preferably.
- the layered crystal structure here is generally expressed as LiAO 2 (A is a transition metal such as Co, Ni, and Mn), and is a structure in which a lithium layer, a transition metal layer, and an oxygen layer are laminated in a uniaxial direction. is there.
- Typical examples include those belonging to the ⁇ -NaFeO 2 type such as LiCoO 2 and LiNiO 2 , which are rhombohedral, and are attributed to the space group R ( ⁇ 3) m due to their symmetry.
- LiMnO 2 is orthorhombic and is attributed to the space group Pm2m due to its symmetry.
- Li 2 MnO 3 can also be expressed as Li [Li 1/3 Mn 2/3 ] O 2 , which is monoclinic Although it is space group C2 / m, it is a layered compound in which a Li layer, a [Li 1/3 Mn 2/3 ] layer, and an oxygen layer are stacked.
- the active material of this embodiment is a solid solution of a lithium transition metal composite oxide represented by LiAO 2 and is a system that also allows Li as a metal element occupying the transition metal site. is there.
- solid solution is distinguished from a mixture of compounds. For example, even if a mixture such as LiNi 0.5 Mn 0.5 O 2 powder or LiNi 0.33 Co 0.33 Mn 0.34 O 2 powder apparently satisfies the composition formula (1), “ It is not included in the “solid solution”.
- the peak position corresponding to each lattice constant observed when X-ray diffraction measurement is performed is different, so that one peak splits into two or three.
- the “solid solution” and the mixture can be distinguished by the presence or absence of the split of the peak of the X-ray diffraction measurement.
- the layered crystal structure is assumed to be a rhombohedral system and a space group R (-3) m structure.
- an active material precursor is first prepared.
- the precursor has a composition corresponding to the following composition formula (1).
- the element M is at least one element selected from the group consisting of Al, Si, Zr, Ti, Fe, Mg, Nb, Ba and V, and 1.9 ⁇ (a + b + c + d + y) ⁇ 2 0.1, 1.05 ⁇ y ⁇ 1.35, 0 ⁇ a ⁇ 0.3, 0 ⁇ b ⁇ 0.25, 0.3 ⁇ c ⁇ 0.7, 0 ⁇ d ⁇ 0.1, 1.9 ⁇ x ⁇ 2.1.
- the precursor of this embodiment includes, for example, Li, Ni, Co, Mn, M (M is the same as described above) and O, and Li, Ni, Co, Mn, M, as in the above composition formula (1). And a substance having a molar ratio of O and O of y: a: b: c: d: x.
- a compound containing each of Li, Ni, Co, Mn, and M for example, a salt
- a compound containing O are mixed so as to satisfy the above molar ratio, and mixed and heated as necessary.
- One of the compounds contained in the precursor may be composed of a plurality of elements selected from the group consisting of Li, Ni, Co, Mn, M, and O.
- the molar ratio of O in the precursor may be outside the numerical value range of x.
- the precursor is obtained by blending the following compounds so as to satisfy the molar ratio shown in the composition formula (1).
- the precursor can be produced from the following compound by a method such as pulverization / mixing, thermal decomposition mixing, precipitation reaction, or hydrolysis.
- a method of mixing, stirring, and heat-treating a liquid raw material in which a manganese compound, a nickel compound, a cobalt compound, and a lithium compound are dissolved in a solvent such as water is preferable. By drying this, it becomes easy to produce a complex oxide (precursor) having a uniform composition and being easily crystallized at a low temperature.
- lithium compound examples include lithium acetate dihydrate, lithium hydroxide monohydrate, lithium carbonate, lithium nitrate, and lithium chloride.
- Nickel compounds include nickel acetate tetrahydrate, nickel sulfate hexahydrate, nickel nitrate hexahydrate, nickel chloride hexahydrate and the like.
- Cobalt compounds include cobalt acetate tetrahydrate, cobalt sulfate heptahydrate, cobalt nitrate hexahydrate, cobalt chloride hexahydrate and the like.
- Manganese compounds include manganese acetate tetrahydrate, manganese sulfate pentahydrate, manganese nitrate hexahydrate, manganese chloride tetrahydrate, manganese acetate tetrahydrate, and the like.
- M compound examples include Al source, Si source, Zr source, Ti source, Fe source, Mg source, Nb source, Ba source, oxide consisting of V source, fluoride, and the like.
- Japanese compounds such as aluminum fluoride, iron sulfate heptahydrate, silicon dioxide, zirconium nitrate dihydrate, titanium sulfate hydrate, magnesium nitrate hexahydrate, niobium oxide, barium carbonate, vanadium oxide, etc. Is mentioned. By adjusting the blending amount of these raw materials, an active material with a low nickel concentration on the surface can be produced.
- the raw material mixture prepared by adding a complexing agent to a solvent in which the above compound is dissolved may be further mixed, stirred and heat-treated. If necessary, an acid may be added to the raw material mixture in order to adjust the pH.
- the type of complexing agent is not limited, but citric acid, malic acid, tartaric acid, lactic acid and the like are preferable in view of availability and cost.
- the specific surface area of the precursor is preferably 0.5 to 6.0 m 2 / g. Thereby, crystallization (sintering) of the precursor easily proceeds and the cycle characteristics are easily improved.
- the specific surface area of the precursor is smaller than 0.5 m 2 / g, the particle size of the precursor after firing (particle size of the lithium transition metal oxide) becomes large, and the composition distribution of the finally obtained active material is not good. May be uniform.
- the specific surface area of a precursor is larger than 6.0 m ⁇ 2 > / g, the water absorption amount of a precursor increases and a baking process becomes difficult. When the water absorption amount of the precursor is large, it is necessary to prepare a dry environment, which increases the cost of manufacturing the active material.
- the specific surface area can be measured with a known BET type powder specific surface area measuring device.
- the specific surface area of the precursor is outside the above range, the temperature at which the precursor crystallizes tends to increase.
- the specific surface area of the precursor can be adjusted by the grinding method, the grinding media, the grinding time, and the like.
- the precursor produced by the above method is fired.
- a solid solution (active material) of a lithium transition metal oxide having a layered crystal structure and represented by the following composition formula (1) can be obtained.
- the element M is at least one element selected from the group consisting of Al, Si, Zr, Ti, Fe, Mg, Nb, Ba and V, and 1.9 ⁇ (a + b + c + d + y) ⁇ 2 0.1, 1.05 ⁇ y ⁇ 1.35, 0 ⁇ a ⁇ 0.3, 0 ⁇ b ⁇ 0.25, 0.3 ⁇ c ⁇ 0.7, 0 ⁇ d ⁇ 0.1, 1.9 ⁇ x ⁇ 2.1.
- the firing temperature of the precursor is preferably 800 to 1100 ° C, more preferably 850 to 1050 ° C.
- the firing temperature of the precursor is less than 500 ° C.
- the sintering reaction of the precursor does not proceed sufficiently, and the resulting lithium transition metal oxide has low crystallinity, which is not preferable.
- the firing temperature of the precursor exceeds 1100 ° C.
- the amount of lithium evaporation increases.
- the temperature exceeds 1100 ° C. the primary particles are sintered and the specific surface area is remarkably reduced, which is not preferable.
- the firing atmosphere of the precursor is preferably an atmosphere containing oxygen.
- Specific examples of the atmosphere include a mixed gas of an inert gas and oxygen, and an atmosphere containing oxygen such as air.
- the firing time of the precursor is preferably 3 hours or longer, and more preferably 5 hours or longer.
- the structural features of the present invention can also be made by further adding lithium carbonate after completion of the precursor and calcining, adjusting the oxygen content during calcining, or combining them.
- the average particle diameter of the positive electrode active material powder is preferably in the range of 0.2 to 1.0 ⁇ m, more preferably in the range of 0.2 to 0.5 ⁇ m. More preferably, there are no coarse particles of 10 ⁇ m or more.
- the average particle size of the negative electrode active material powder is preferably 100 ⁇ m or less.
- a pulverizer or a classifier is used.
- a mortar, a ball mill, a bead mill, a sand mill, a vibrating ball mill, a planetary ball mill, a jet mill, a counter jet mill, a swirling air flow type jet mill, a sieve, or the like is used.
- wet pulverization in which an organic solvent such as water or hexane coexists can be used.
- the classification method is not particularly limited, and a sieve, an air classifier, or the like is used as needed for both dry and wet methods.
- a lithium ion secondary battery 100 As shown in FIG. 1, a lithium ion secondary battery 100 according to the present embodiment is disposed adjacent to each other between a plate-like negative electrode 20 and a plate-like positive electrode 10 facing each other, and the negative electrode 20 and the positive electrode 10.
- a negative electrode lead 62 whose other end protrudes outside the case, and a positive electrode lead 60 whose one end is electrically connected to the positive electrode 10 and whose other end protrudes outside the case are provided. .
- the negative electrode 20 has a negative electrode current collector 22 and a negative electrode active material layer 24 formed on the negative electrode current collector 22.
- the positive electrode 10 includes a positive electrode current collector 12 and a positive electrode active material layer 14 formed on the positive electrode current collector 12.
- the separator 18 is located between the negative electrode active material layer 24 and the positive electrode active material layer 14.
- the positive electrode active material contained in the positive electrode active material layer 14 has a layered crystal structure and is represented by the composition formula (1).
- any material that can deposit or occlude lithium ions may be selected.
- titanium-based materials such as lithium titanate having a spinel crystal structure represented by Li [Li 1/3 Ti 5/3 ] O 4
- alloy-based materials such as Si, Sb, and Sn-based lithium metal
- lithium alloys Lithium metal-containing alloys such as lithium-silicon, lithium-aluminum, lithium-lead, lithium-tin, lithium-aluminum-tin, lithium-gallium, and wood alloys
- lithium composite oxide lithium-titanium
- silicon oxide silicon oxide
- an alloy capable of inserting and extracting lithium a carbon material (for example, graphite, hard carbon, low-temperature fired carbon, amorphous carbon, etc.) can be used.
- the positive electrode active material layer 14 and the negative electrode active material layer 24 may contain a conductive auxiliary agent, a binder, a thickener, a filler, and the like as other constituent components in addition to the main constituent components described above.
- the conductive auxiliary agent is not limited as long as it is an electron conductive material that does not adversely affect the battery performance.
- natural graphite scale-like graphite, scale-like graphite, earth-like graphite, etc.
- artificial graphite carbon black, acetylene black
- conductive materials such as ketjen black, carbon whisker, carbon fiber, metal (copper, nickel, aluminum, silver, gold, etc.) powder, metal fiber, and conductive ceramic material.
- These conductive assistants may be used alone or a mixture thereof may be used.
- acetylene black is preferable from the viewpoints of electronic conductivity and coatability.
- the addition amount of the conductive assistant is preferably 0.1% by weight to 50% by weight, and more preferably 0.5% by weight to 30% by weight with respect to the total weight of the positive electrode active material layer or the negative electrode active material layer.
- These mixing methods are physical mixing, and the ideal is uniform mixing. Therefore, powder mixers such as V-type mixers, S-type mixers, crackers, ball mills, and planetary ball mills can be mixed dry or wet.
- thermoplastic resins such as polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyethylene, polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene butadiene rubber are usually used.
- a polymer having rubber elasticity such as (SBR) or fluororubber can be used as one kind or a mixture of two or more kinds.
- the amount of the binder added is preferably 1 to 50% by weight and more preferably 2 to 30% by weight with respect to the total weight of the positive electrode active material layer or the negative electrode active material layer.
- the thickener polysaccharides such as carboxymethyl cellulose and methyl cellulose can be used usually as one kind or a mixture of two or more kinds. Moreover, it is preferable that the thickener which has a functional group which reacts with lithium like a polysaccharide deactivates the functional group by methylation etc., for example.
- the addition amount of the thickener is preferably 0.5 to 10% by weight, more preferably 1 to 2% by weight, based on the total weight of the positive electrode active material layer or the negative electrode active material layer.
- any material that does not adversely affect battery performance may be used.
- olefin polymers such as polypropylene and polyethylene, amorphous silica, alumina, zeolite, glass, carbon and the like are used.
- the addition amount of the filler is preferably 30% by weight or less with respect to the total weight of the positive electrode active material layer or the negative electrode active material layer.
- the positive electrode active material layer or the negative electrode active material layer is obtained by kneading main constituent components (positive electrode active material or negative electrode active material) and other materials (conductive aid, binder, thickener, filler, etc.).
- the mixture was mixed with an organic solvent such as N-methylpyrrolidone or toluene, and the resulting mixture was applied onto a current collector or pressure-bonded at a temperature of about 50 ° C. to 250 ° C. It is preferably produced by heat treatment for about an hour.
- the application method for example, it is preferable to apply to any thickness and any shape using means such as roller coating such as applicator roll, screen coating, doctor blade method, spin coating, bar coater, etc. Is not to be done.
- the electrode current collector iron, copper, stainless steel, nickel and aluminum can be used. Moreover, a sheet
- the electrolyte solution containing lithium ions is a non-aqueous electrolyte, and non-aqueous electrolytes that are generally proposed for use in lithium batteries and the like can be used.
- the nonaqueous solvent used for the nonaqueous electrolyte include cyclic carbonates such as propylene carbonate, ethylene carbonate, butylene carbonate, chloroethylene carbonate, and vinylene carbonate; cyclic esters such as ⁇ -butyrolactone and ⁇ -valerolactone; dimethyl carbonate, Chain carbonates such as diethyl carbonate and ethyl methyl carbonate; chain esters such as methyl formate, methyl acetate and methyl butyrate; tetrahydrofuran or derivatives thereof; 1,3-dioxane, 1,4-dioxane, 1,2-dimethoxy Ethers such as ethane, 1,4-dibutoxyethane and methyldiglyme; Nitriles such as acet
- the solid electrolyte can be used as the solid electrolyte.
- a crystalline or amorphous inorganic solid electrolyte can be used.
- Amorphous inorganic solid electrolytes include LiI—Li 2 O—B 2 O 5 series, Li 2 O—SiO 2 series, LiI—Li 2 S—B 2 S 3 series, LiI—Li 2 S—SiS 2.
- a Li 2 S—SiS 2 —Li 3 PO 4 system or the like can be used.
- electrolyte salt used for the non-aqueous electrolyte examples include LiClO 4 , LiBF 4 , LiAsF 6 , LiPF 6 , LiSCN, LiBr, LiI, Li 2 SO 4 , Li 2 B 10 Cl 10 , NaClO 4 , NaI, NaSCN, NaBr , KClO 4 , KSCN, and other inorganic ion salts containing one of lithium (Li), sodium (Na), or potassium (K), LiCF 3 SO 3 , LiN (CF 3 SO 2 ) 2 , LiN (C 2 F 5 (SO 2 ) 2 , LiN (CF 3 SO 2 ) (C 4 F 9 SO 2 ), LiC (CF 3 SO 2 ) 3 , LiC (C 2 F 5 SO 2 ) 3 , (CH 3 ) 4 NBF 4 , ( CH 3 ) 4 NBr, (C 2 H 5 ) 4 NClO 4 , (C 2 H 5 ) 4 NI, (C 2
- ionic compounds can be used alone or in admixture of two or more.
- the active material of the present embodiment is difficult to chemically react with an electrolyte salt containing F such as LiBF 4 , LiAsF 6 , and LiPF 6 and has high durability.
- LiPF 6 LiPF 6
- a lithium salt having a perfluoroalkyl group such as LiN (C 2 F 5 SO 2 ) 2 .
- the viscosity of the electrolyte can be further reduced, so that the low-temperature characteristics can be further improved and self-discharge can be suppressed.
- the room temperature molten salt or ionic liquid may be used for the non-aqueous electrolyte.
- the concentration of the electrolyte salt in the nonaqueous electrolyte is preferably 0.1 mol / l to 5 mol / l, more preferably 0.5 mol / l to 2.5 mol / l.
- a separator for a lithium ion secondary battery it is preferable to use a porous film or a non-woven fabric exhibiting excellent high rate discharge performance alone or in combination.
- the material constituting the separator for a lithium ion secondary battery include polyolefin resins typified by polyethylene and polypropylene, polyester resins typified by polyethylene terephthalate and polybutylene terephthalate, polyvinylidene fluoride, and vinylidene fluoride.
- the porosity of the lithium ion secondary battery separator is preferably 98% by volume or less from the viewpoint of strength. Further, the porosity is preferably 20% by volume or more from the viewpoint of charge / discharge characteristics.
- a polymer gel composed of a polymer such as acrylonitrile, ethylene oxide, propylene oxide, methyl methacrylate, vinyl acetate, vinyl pyrrolidone, and polyvinylidene fluoride and an electrolyte may be used.
- a nonaqueous electrolyte in a gel state has an effect of preventing leakage.
- the shape of the lithium ion secondary battery is not limited to that shown in FIG.
- the shape of the lithium ion secondary battery may be a square, an ellipse, a coin, a button, a sheet, or the like.
- the active material of this embodiment can also be used as an electrode material for electrochemical elements other than lithium ion secondary batteries.
- an electrochemical element other than lithium ion secondary batteries such as a metal lithium secondary battery (an electrode containing an active material obtained by the present invention is used as a positive electrode and metal lithium is used as a negative electrode).
- Examples include secondary batteries and electrochemical capacitors such as lithium ion capacitors.
- These electrochemical elements can be used for power sources such as self-propelled micromachines and IC cards, and distributed power sources arranged on or in a printed circuit board.
- Example 1 [Precursor preparation] Lithium acetate dihydrate 37.10 g, cobalt acetate tetrahydrate 8.30 g, manganese acetate tetrahydrate 40.11 g, nickel acetate tetrahydrate 11.43 g are dissolved in distilled water and citric acid is added. Then, the reaction was allowed to proceed for 10 hours while heating and stirring. This precursor reaction product was dried at 120 ° C. for 24 hours, and after removing moisture, heat treatment was performed at 500 ° C. for 5 hours to remove organic components, whereby a brown-colored powder (precursor of Example 1) was obtained. .
- lithium, nickel, cobalt contained in the precursor and the amount of lithium acetate dihydrate, nickel acetate tetrahydrate, manganese acetate tetrahydrate and cobalt acetate tetrahydrate in the raw material mixture are adjusted
- the number of moles of manganese was adjusted to correspond to 0.30 mol of Li 1.20 Ni 0.15 Co 0.11 Mn 0.54 O 2 . That is, the number of moles of each element in the raw material mixture was adjusted so that 0.30 mol of Li 1.20 Ni 0.15 Co 0.11 Mn 0.54 O 2 was generated from the precursor of Example 1. .
- Citric acid as a complexing agent was added in an equivalent number of moles, that is, 0.30 moles relative to 0.30 moles of the active material obtained from the precursor of Example 1.
- the lithium transition metal oxide (active material) of Example 1 was calcined at 950 ° C. for 10 hours at an oxygen concentration of 50 vol%. Obtained.
- the crystal structure of the lithium transition metal oxide of Example 1 was analyzed by powder X-ray diffraction.
- the active material of Example 1 was confirmed to have a rhombohedral crystal, space group R (-3) m structure main phase. Further, in the X-ray diffraction pattern of the active material of Example 1, a diffraction peak peculiar to the Li 2 MnO 3 type monoclinic space group C2 / m structure was observed at 2 ⁇ of around 20 to 25 °.
- composition of the lithium transition metal oxide (active material) of Example 1 is Li 1.28 Ni 0.15 Co 0.11 Mn 0.54 O 2 . It was confirmed that there was. It was confirmed that the molar ratio of each metal element in the active material of Example 1 coincided with the molar ratio of each metal element in the precursor of Example 1. That is, it was confirmed that the composition of the lithium transition metal oxide (active material) obtained from the precursor can be accurately controlled by adjusting the molar ratio of the metal element in the precursor.
- FIG. 2A shows a TEM image of Example 1.
- +001 is the Ni composition amount Ni ⁇ near the particle surface
- the point +003 is the Ni composition amount Ni ⁇ in the center of the particle.
- the positive electrode paint was prepared by mixing the lithium transition metal oxide (active material) of Example 1, a conductive additive, and a solvent containing a binder.
- the positive electrode coating material was applied to an aluminum foil (thickness 20 ⁇ m) as a positive electrode current collector by a doctor blade method, dried at 100 ° C., and rolled. This obtained the positive electrode comprised from the layer of lithium transition metal oxide (active material) and a positive electrode electrical power collector. Carbon black and graphite were used as the conductive assistant.
- the solvent containing the binder N-methyl-2-pyrrolidone in which PVDF was dissolved was used.
- a negative electrode paint was prepared in the same manner as the positive electrode paint except that natural graphite was used in place of the active material of Example 1 and only carbon black was used as the conductive additive.
- the negative electrode coating material was applied to a copper foil (thickness 16 ⁇ m) as a negative electrode current collector by a doctor blade method, dried at 100 ° C., and rolled. This obtained the negative electrode comprised from a negative electrode active material layer and a negative electrode electrical power collector.
- An aluminum foil (width 4 mm, length 40 mm, thickness 100 ⁇ m) and nickel foil (width 4 mm, length 40 mm, thickness 100 ⁇ m) were ultrasonically welded to the positive electrode and the negative electrode, respectively, as external lead terminals.
- Polypropylene (PP) grafted with maleic anhydride was wrapped around this external lead terminal and thermally bonded. This is to improve the sealing performance between the external terminal and the exterior body.
- An aluminum laminate material composed of a PET layer, an Al layer, and a PP layer was used as a battery outer package enclosing a battery element in which a positive electrode, a negative electrode, and a separator were stacked.
- the thickness of the PET layer was 12 ⁇ m.
- the thickness of the Al layer was 40 ⁇ m.
- the thickness of the PP layer was 50 ⁇ m.
- PET is an abbreviation for polyethylene terephthalate
- PP is an abbreviation for polypropylene.
- the PP layer was arranged inside the outer package. A battery element was placed in the outer package, an appropriate amount of electrolyte was injected, and the outer package was vacuum-sealed. Thus, a lithium ion secondary battery using the lithium transition metal oxide of Example 1 was completed.
- the initial discharge capacity is the charge / discharge data for the second time, that is, the discharge capacity when the battery is charged at a constant current up to 4.8V and then discharged at a constant current down to 2.0V.
- a high cycle characteristic indicates that the battery is excellent in the cycle characteristic.
- a battery having an initial discharge capacity of 190 mAh / g or more and a cycle characteristic of 85% or more is evaluated as “A”.
- a battery having an initial discharge capacity of less than 190 mAh / g or a cycle characteristic of less than 85% is evaluated as “F”.
- lithium transition metal oxides were prepared by adjusting the amount of lithium carbonate added to the precursor.
- Example 2 lithium carbonate equivalent to 0.04 mol% was added to the precursor adjusted so that the composition amount was Li 1.20 Ni 0.15 Co 0.11 Mn 0.54 O 2 and mixed for 30 minutes. Thereafter, it was calcined at 950 ° C. for 10 hours at an oxygen concentration of 50% by volume to obtain a lithium transition metal oxide.
- Example 3 lithium carbonate equivalent to 0.12 mol% was added to the precursor adjusted to have a composition amount of Li 1.20 Ni 0.15 Co 0.11 Mn 0.54 O 2 and mixed for 30 minutes. Thereafter, it was calcined at 950 ° C. for 10 hours at an oxygen concentration of 50% by volume to obtain a lithium transition metal oxide.
- Example 4 lithium carbonate equivalent to 0.15 mol% was added to the precursor adjusted to have a composition amount of Li 1.20 Ni 0.15 Co 0.11 Mn 0.54 O 2 and mixed for 30 minutes. Thereafter, it was calcined at 950 ° C. for 10 hours at an oxygen concentration of 50% by volume to obtain a lithium transition metal oxide.
- Comparative Example 1 the precursor adjusted to have a composition amount of Li 1.20 Ni 0.15 Co 0.11 Mn 0.54 O 2 was added at 950 ° C. for 10 hours without adding lithium carbonate.
- the lithium transition metal oxide was obtained by firing at a concentration of 50% by volume.
- FIG. 2B shows a TEM image of Comparative Example 1.
- +004 is the Ni composition amount Ni ⁇ near the particle surface
- the point +005 is the Ni composition amount Ni ⁇ in the center of the particle.
- the composition formula Li y Ni a Co b Mn c M d O x in Comparative Example 1 are within the scope of the present invention, the Ni composition amount Ni beta / Ni alpha is outside the scope of the present invention.
- Comparative Example 2 a precursor adjusted to have a composition amount of Li 1.30 Ni 0.15 Co 0.11 Mn 0.54 O 2 was fired at 950 ° C. for 10 hours at an oxygen concentration of 50 vol%. Thus, a lithium transition metal oxide was obtained.
- Example 5 to 10 Comparative Examples 3 to 5
- Example 5 to 10 and Comparative Examples 3 to 5 after adjusting the amounts of the Co source, Ni source, and Mn source in the precursor raw material mixture, 0.08 mol% of lithium carbonate was added and mixed for 30 minutes.
- a lithium transition metal oxide was produced by firing at 50 ° C. for 10 hours at a temperature of 50 ° C.
- the Ni composition amount Ni ⁇ / Ni ⁇ is within the scope of the present invention, but the composition formula Li y Ni a Co b Mn c M d O x is outside the scope of the present invention.
- Example 11 to 19 In Examples 11 to 19, after adjusting the composition of the precursor raw material mixture as follows, 0.08 mol% of lithium carbonate was added and mixed for 30 minutes, and the mixture was mixed at 950 ° C. for 10 hours with an oxygen concentration of 50 volumes.
- the lithium transition metal oxide was obtained by baking at%. That is, as the source of M represented by the formula (1), in Example 11, aluminum nitrate nonahydrate was used as the Al source in the precursor raw material mixture. In Example 12, vanadium oxide was used as a V source in the precursor raw material mixture. In Example 13, silicon dioxide was used as the Si source in the precursor raw material mixture. In Example 14, magnesium nitrate hexahydrate was used as the Mg source in the precursor raw material mixture.
- Example 15 zirconium oxide dihydrate was used as a Zr source in the precursor raw material mixture.
- titanium sulfate hydrate was used as a Ti source in the precursor raw material mixture.
- iron sulfate heptahydrate was used as the Fe source in the precursor raw material mixture.
- barium carbonate was used as the Ba source in the precursor raw material mixture.
- niobium oxide was used as the Nb source in the precursor raw material mixture.
- Example 1 In the same manner as in Example 1, the initial discharge capacities and cycle characteristics of the batteries of Examples 2 to 19 and Comparative Examples 1 to 5 were evaluated. The results are shown in Table 1. In the table below, a battery having a capacity of 190 mAh / g or more and a cycle characteristic of 85% or more and excellent in charge / discharge cycle characteristics is evaluated as “A”. A battery having a capacity of less than 190 mAh / g or a cycle characteristic of less than 85% is evaluated as “F”.
- FIG. 3 shows the relationship between Ni ⁇ / Ni ⁇ and the cycle characteristics in Examples 1 to 10 and Comparative Examples 1 and 2.
- FIG. 4 shows the relationship between the initial discharge capacity and the cycle characteristics of Examples 11 to 19.
- the present invention contributes to the manufacture and use of not only an active material having a high capacity and excellent cycle characteristics but also an electrochemical element such as a lithium ion secondary battery, and thus has industrial applicability.
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Abstract
Description
また、特許文献2においてもLi[LiqCoxNiyMnz]O2固溶体系の正極を用いているが、こちらについてはサイクル特性が良好であるものの、初期放電容量が低いという問題がある。
LiyNiaCobMncMdOx (1)
上記式(1)中、元素MはAl,Si,Zr,Ti,Fe,Mg,Nb,Ba及びVからなる群から選ばれる少なくとも1種の元素であり、1.9≦(a+b+c+d+y)≦2.1、1.05≦y≦1.35、0<a≦0.3、0<b≦0.25、0.3≦c≦0.7、0≦d≦0.1、1.9≦x≦2.1であって、活物質一次粒子の中心部のNi組成量をNiα表面近傍のNi組成量をNiβとした場合、0.69≦Niβ/Niα≦0.85であることを特徴とする。
本実施形態の活物質は、層状の結晶構造を有し、下記組成式(1)で表されるリチウム含有複合酸化物である。
LiyNiaCobMncMdOx (1)
上記式(1)中、元素MはAl,Si,Zr,Ti,Fe,Mg,Nb,Ba及びVからなる群から選ばれる少なくとも1種の元素であり、1.9≦(a+b+c+d+y)≦2.1、1.05≦y≦1.35、0<a≦0.3、0<b≦0.25、0.3≦c≦0.7、0≦d≦0.1、1.9≦x≦2.1であって、活物質一次粒子の中心部のNi組成量をNiα、表面近傍のNi組成量をNiβとした場合、0.69≦Niβ/Niα≦0.85であることを特徴とする。
詳細に説明するため、以下層状の結晶構造を菱面体晶系、空間群R(-3)m構造に仮定して説明する。
活物質の製造では、まず活物質の前駆体を調製する。前駆体は、下記組成式(1)に対応する組成を有する。
LiyNiaCobMncMdOx (1)
上記式(1)中、元素MはAl,Si,Zr,Ti,Fe,Mg,Nb,Ba及びVからなる群から選ばれる少なくとも1種の元素であり、1.9≦(a+b+c+d+y)≦2.1、1.05≦y≦1.35、0<a≦0.3、0<b≦0.25、0.3≦c≦0.7、0≦d≦0.1、1.9≦x≦2.1。
リチウム化合物は、酢酸リチウム二水和物、水酸化リチウム一水和物、炭酸リチウム、硝酸リチウム、塩化リチウム等。
ニッケル化合物は、酢酸ニッケル四水和物、硫酸ニッケル六水和物、硝酸ニッケル六水和物、塩化ニッケル六水和物等。
コバルト化合物は、酢酸コバルト四水和物、硫酸コバルト七水和物、硝酸コバルト六水和物、塩化コバルト六水和物等。
マンガン化合物は、酢酸マンガン四水和物、硫酸マンガン五水和物、硝酸マンガン六水和物、塩化マンガン四水和物、酢酸マンガン四水和物、等が挙げられ、
M化合物は、Al源、Si源、Zr源、Ti源、Fe源、Mg源、Nb源、Ba源、V源からなる酸化物、またはフッ化物等が挙げられ、、例えば、硝酸アルミニウム九水和物、フッ化アルミニウム、硫酸鉄七水和物、二酸化ケイ素、硝酸酸化ジルコニウム二水和物、硫酸チタン水和物、硝酸マグネシウム六水和物、酸化ニオブ、炭酸バリウム、酸化バナジウム、等の化合物が挙げられる。これらの原料の配合量を調整することによって表面のニッケル濃度が少ない活物質を作製できる。
LiyNiaCobMncMdOx (1)
上記式(1)中、元素MはAl,Si,Zr,Ti,Fe,Mg,Nb,Ba及びVからなる群から選ばれる少なくとも1種の元素であり、1.9≦(a+b+c+d+y)≦2.1、1.05≦y≦1.35、0<a≦0.3、0<b≦0.25、0.3≦c≦0.7、0≦d≦0.1、1.9≦x≦2.1となるものである。
図1に示すように、本実施形態に係るリチウムイオン二次電池100は、互いに対向する板状の負極20及び板状の正極10と、負極20と正極10との間に隣接して配置される板状のセパレータ18と、を備える発電要素30と、リチウムイオンを含む電解質溶液と、これらを密閉した状態で収容するケース50と、負極20に一方の端部が電気的に接続されると共に他方の端部がケースの外部に突出される負極リード62と、正極10に一方の端部が電気的に接続されると共に他方の端部がケースの外部に突出される正極リード60とを備える。
[前駆体の作製]
酢酸リチウム二水和物37.10g、酢酸コバルト四水和物8.30g、酢酸マンガン四水和物40.11g、酢酸ニッケル四水和物11.43gを蒸留水に溶解させ、クエン酸を添加した後、加温・攪拌しながら10hr反応させた。この前駆体反応物を120℃、24hr乾燥させ、水分を除去した後に500℃、5hr熱処理し、有機成分を除去することにより、茶渇色の粉末(実施例1の前駆体)が得られた。なお、原料混合物における酢酸リチウム二水和物、酢酸ニッケル四水和物、酢酸マンガン四水和物及び酢酸コバルト四水和物の配合量の調整により、前駆体が含有するリチウム,ニッケル,コバルト及びマンガンのモル数を、0.30molのLi1.20Ni0.15Co0.11Mn0.54O2に相当するように調整した。つまり、実施例1の前駆体から、0.30molのLi1.20Ni0.15Co0.11Mn0.54O2が生成するように、原料混合物中の各元素のモル数を調整した。錯化剤としてのクエン酸は、実施例1の前駆体から得られる活物質のモル数0.30molに対して、同等のモル数すなわち0.30mol添加した。
前駆体に0.08mol%相当の炭酸リチウムを添加して30分混合した後、950℃で10時間、酸素濃度50容量%において焼成して実施例1のリチウム遷移金属酸化物(活物質)を得た。実施例1のリチウム遷移金属酸化物の結晶構造を粉体X線回折法により解析した。実施例1の活物質は、菱面体晶系、空間群R(-3)m構造の主相を有することが確認された。また、実施例1の活物質のX線回折パターンにおいて2θが20~25°付近に、Li2MnO3型の単斜晶系の空間群C2/m構造に特有の回折ピークが観察された。
誘導結合プラズマ法(ICP法)による組成分析の結果、実施例1のリチウム遷移金属酸化物(活物質)の組成は、Li1.28Ni0.15Co0.11Mn0.54O2であることが確認された。実施例1の活物質中の各金属元素のモル比は、実施例1の前駆体における各金属元素のモル比に一致していることが確認された。つまり、前駆体中の金属元素のモル比の調整により、前駆体から得られるリチウム遷移金属酸化物(活物質)の組成が正確に制御できることが確認された。
〈一次粒子の組成分析〉
実施例1のリチウム遷移金属酸化物(活物質)の一次粒子を透過型電子顕微鏡(TEM)を用いて観察し、TEMに付属のエネルギー分散型X線分光装置(EDS)を用いて、一次粒子中央部における点分析と粒子表面付近(表面から30nm以内の範囲)の点分析を行い、元素の含有比率を算出する。なお、測定点の数は特に制限されないが、5点以上であることが好ましい。図2(a)に実施例1のTEM像を示す。この場合、+001が粒子表面近傍のNi組成量Niβであり、ポイント+003が粒子中央部におけるNi組成量Niαである。
実施例1のリチウム遷移金属酸化物(活物質)と、導電助剤と、バインダーを含む溶媒とを混合して、正極用塗料を調製した。正極用塗料を正極集電体であるアルミニウム箔(厚み20μm)にドクターブレード法で塗布後、100℃で乾燥し、圧延した。これにより、リチウム遷移金属酸化物(活物質)の層及び正極集電体から構成される正極を得た。導電助剤としては、カーボンブラック及び黒鉛を用いた。バインダーを含む溶媒としては、PVDFを溶解したN-メチル-2-ピロリドンを用いた。
実施例1の活物質の代わりに天然黒鉛を用い、導電助剤としてカーボンブラックだけを用いたこと以外は、正極用塗料と同様の方法で、負極用塗料を調製した。負極用塗料を負極集電体である銅箔(厚み16μm)にドクターブレード法で塗布後、100℃で乾燥し、圧延した。これにより、負極活物質層及び負極集電体から構成される負極を得た。
上述したとおり準備した正極、及び負極と、セパレータ(ポリオレフィン製の微多孔質膜)とを所定の寸法に切断した。正極、負極には、外部引き出し端子を溶接するために電極用塗料を塗布しない部分を設けておいた。そして、正極、負極、セパレータをこの順序で積層した。積層する際には、正極、負極、セパレータがずれないようにホットメルト接着剤(エチレン-メタアクリル酸共重合体、EMAA)を少量塗布し固定した。正極、負極には、それぞれ、外部引き出し端子としてアルミニウム箔(幅4mm、長さ40mm、厚み100μm)、ニッケル箔(幅4mm、長さ40mm、厚み100μm)を超音波溶接した。この外部引き出し端子に、無水マレイン酸をグラフト化したポリプロピレン(PP)を巻き付け熱接着させた。これは外部端子と外装体とのシール性を向上させるためである。正極、負極、セパレータを積層した電池要素を封入する電池外装体として、PET層、Al層及びPP層から構成されるアルミニウムラミネート材料を用いた。PET層の厚さは12μmであった。Al層の厚さは40μmであった。PP層の厚さは50μmであった。なお、PETはポリエチレンテレフタレート、PPはポリプロピレンの略称である。電池外装体の作製では、PP層を外装体の内側に配置させ作製した。この外装体の中に電池要素を入れ電解液を適当量注入し、外装体を真空密封した。こうして、実施例1のリチウム遷移金属酸化物を用いたリチウムイオン二次電池を完成させた。なお、電解液としては、エチレンカーボンネート(EC)とジメチルカーボネート(DMC)の混合溶媒にLiPF6を濃度1M(1mol/L)で溶解させたものを用いた。混合溶媒におけるECとDMCとの体積比は、EC:DMC=30:70とした。
上記実施例1の電池を、1度充放電した後、電流値として30mA/gにて4.8Vまで低電流で充電した後、電流値として30mA/gにて2.0Vまで定電流放電した。実施例1の初期放電容量は211mAh/gであった。この充放電サイクルを50サイクル繰返すサイクル試験を行った。試験は25℃で行った。実施例1の電池の初期放電容量を100%とすると、50サイクル後の放電容量は96%であった。以降、初期放電容量を100%としたときの、50サイクル後の放電容量の割合をサイクル特性と呼ぶことにする。初期放電容量とは2回目の充放電データ、すなわち1度充放電した後、4.8Vまで定電流充電し、次いで2.0Vまで定電流放電した際の放電容量をいう。サイクル特性が高いことは、電池がサイクル特性に優れていることを示す。なお、初期放電容量が190mAh/g以上であり、且つサイクル特性が85%以上である電池を「A」と評価する。初期放電容量が190mAh/g未満である電池、又はサイクル特性が85%未満である電池を「F」と評価する。
実施例2、3は前駆体へ添加する炭酸リチウム量を調整してリチウム遷移金属酸化物を作製した。
実施例5~10並びに比較例3~5は前駆体原料混合物のCo源、Ni源、Mn源の量を調整した後、0.08mol%相当の炭酸リチウムを添加して30分混合し、950℃で10時間、酸素濃度50容量%において焼成することによりリチウム遷移金属酸化物を作製した。なお、比較例3~5はNi組成量Niβ/Niαは本発明の範囲内であるが、組成式LiyNiaCobMncMdOxは本発明の範囲外である。
実施例11~19では、前駆体の原料混合物の組成を以下のように調整した後、0.08mol%相当の炭酸リチウムを添加して30分混合し、950℃で10時間、酸素濃度50容量%において焼成することによりリチウム遷移金属酸化物を得た。すなわち式(1)で表されるMの源として、実施例11では前駆体の原料混合物にAl源として硝酸アルミニウム九水和物を用いた。実施例12では前駆体の原料混合物にV源として酸化バナジウムを用いた。実施例13では前駆体の原料混合物にSi源として二酸化ケイ素を用いた。実施例14では前駆体の原料混合物にMg源として硝酸マグネシウム六水和物を用いた。実施例15では前駆体の原料混合物にZr源として硝酸酸化ジルコニウム二水和物を用いた。実施例16では前駆体の原料混合物にTi源として硫酸チタン水和物を用いた。実施例17では前駆体の原料混合物にFe源として硫酸鉄七水和物を用いた。実施例18では前駆体の原料混合物にBa源として炭酸バリウムを用いた。実施例19では前駆体の原料混合物にNb源として酸化ニオブを用いた。
Claims (3)
- 層状の結晶構造を有し、下記組成式(1)で表される、活物質であり、
LiyNiaCobMncMdOx (1)
[上記式(1)中、元素MはAl,Si,Zr,Ti,Fe,Mg,Nb,Ba及びVからなる群から選ばれる少なくとも1種の元素であり、1.9≦(a+b+c+d+y)≦2.1、1.05≦y≦1.35、0<a≦0.3、0<b≦0.25、0.3≦c≦0.7、0≦d≦0.1、1.9≦x≦2.1]、
活物質の一次粒子の中心部のNi組成量をNiα、表面近傍のNi組成量をNiβとした場合、0.69≦Niβ/Niα≦0.85であることを特徴とするリチウムイオン二次電池用活物質。 - 前記元素Mが、FeまたはVであり、dが0<d≦0.1であることを特徴とする請求項1記載のリチウムイオン二次電池。
- 正極集電体と、正極活物質を含む正極活物質層と、を有する正極と、
負極集電体と、負極活物質を含む負極活物質層と、を有する負極と、
前記正極活物質層と前記負極活物質層との間に位置するセパレータと、
前記負極、前記正極、及び前記セパレータに接触している電解質と、を備え、
前記正極活物質が請求項1~2に記載の活物質を含むことを特徴とするリチウムイオン二次電池。
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