WO2018181158A1 - リチウム二次電池用正極活物質、リチウム二次電池用正極及びリチウム二次電池 - Google Patents
リチウム二次電池用正極活物質、リチウム二次電池用正極及びリチウム二次電池 Download PDFInfo
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- C01G53/00—Compounds of nickel
- C01G53/40—Nickelates
- C01G53/42—Nickelates containing alkali metals, e.g. LiNiO2
- C01G53/44—Nickelates containing alkali metals, e.g. LiNiO2 containing manganese
- C01G53/50—Nickelates containing alkali metals, e.g. LiNiO2 containing manganese of the type [MnO2]n-, e.g. Li(NixMn1-x)O2, Li(MyNixMn1-x-y)O2
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- H01M4/02—Electrodes composed of, or comprising, active material
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- 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
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- H01M4/36—Selection of substances as active materials, active masses, active liquids
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- H—ELECTRICITY
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- 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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- 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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- C01G53/42—Nickelates containing alkali metals, e.g. LiNiO2
- C01G53/44—Nickelates containing alkali metals, e.g. LiNiO2 containing manganese
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- C01P2004/60—Particles characterised by their size
- C01P2004/61—Micrometer sized, i.e. from 1-100 micrometer
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- C01P2006/16—Pore diameter
- C01P2006/17—Pore diameter distribution
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- C—CHEMISTRY; METALLURGY
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- H—ELECTRICITY
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- 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
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- 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 positive electrode active material for a lithium secondary battery, a positive electrode for a lithium secondary battery, and a lithium secondary battery.
- the lithium composite oxide is used as a positive electrode active material for non-aqueous electrolyte secondary batteries (hereinafter sometimes referred to as “positive electrode active material”).
- Lithium secondary batteries have already been put into practical use not only for small power sources for mobile phones and notebook computers, but also for medium and large power sources for automobiles and power storage.
- cited reference 1 describes a positive electrode active material powder in which two kinds of particle powders having different compressive fracture strengths are mixed.
- volume capacity density means the battery capacity per unit volume (the amount of power that can be stored). The larger the volume capacity density value, the more suitable for a small battery.
- the positive electrode active material for a lithium secondary battery as described in Patent Document 1 has room for improvement from the viewpoint of improving the volume capacity density.
- the present invention has been made in view of the above circumstances, and has a high volume capacity density positive active material for a lithium secondary battery, a positive electrode for a lithium secondary battery using the positive active material for a lithium secondary battery, and the lithium It is an object of the present invention to provide a lithium secondary battery having a positive electrode for a secondary battery.
- a positive electrode active material for a lithium secondary battery which is an active material powder containing secondary particles obtained by agglomerating primary particles that can be doped and dedoped with lithium ions, and secondary particles having voids inside the particles
- a positive electrode active material for a lithium secondary battery that satisfies the following requirements (1) and (2) in a pore distribution measured by a mercury intrusion method of the positive electrode active material for a lithium secondary battery: (1) A pore peak has a pore radius in the range of 10 nm to 200 nm. (2) It has three or more inflection points of the cumulative pore volume in the range where the pore radius is 10 nm or more and 3000 nm or less.
- the positive electrode active material for a lithium secondary battery according to [1] which has three inflection points of the cumulative pore volume in the range of 10 nm to 1500 nm in the requirement (2).
- the positive electrode active material for a lithium secondary battery according to [1] or [2], wherein the positive electrode active material for a lithium secondary battery is represented by the following composition formula (I).
- M is one or more metal elements selected from the group consisting of Fe, Cu, Ti, Mg, Al, W, B, Mo, Nb, Zn, Sn, Zr, Ga and V, and 0 ⁇ x ⁇ 0.2, 0 ⁇ y ⁇ 0.4, 0 ⁇ z ⁇ 0.4, and 0 ⁇ w ⁇ 0.1 are satisfied.
- the positive electrode active material for a lithium secondary battery according to any one of [1] to [3], wherein an average particle size of the secondary particles is 1 ⁇ m or more and 30 ⁇ m or less.
- the active material powder includes secondary particles A having an average secondary particle diameter of 1 ⁇ m to 10 ⁇ m and secondary particles B having an average secondary particle diameter of 5 ⁇ m to 30 ⁇ m, and the secondary particles A
- the positive electrode active material for a lithium secondary battery according to [5] wherein the mixing ratio (mass ratio) of the secondary particles B is 20:80 to 50:50.
- the positive electrode active material for a lithium secondary battery having a high volume capacity density the positive electrode for a lithium secondary battery using the positive electrode active material for the lithium secondary battery, and the lithium secondary battery having the positive electrode for the lithium secondary battery.
- a secondary battery can be provided.
- 4 is a graph showing the inflection point of the cumulative pore volume in the range where the pore radius of the positive electrode active material for a lithium secondary battery of Example 1 is 10 nm or more and 3000 nm or less.
- 6 is a graph showing the inflection point of the cumulative pore volume when the pore radius of the positive electrode active material for a lithium secondary battery of Comparative Example 2 is in the range of 10 nm to 3000 nm.
- the positive electrode active material for a lithium secondary battery according to one embodiment of the present invention includes an active material powder containing secondary particles obtained by agglomerating primary particles that can be doped and dedoped with lithium ions. It is a substance.
- the positive electrode active material for a lithium secondary battery according to one embodiment of the present invention includes secondary particles having voids inside the particles, and the pore distribution measured by the mercury intrusion method includes the following requirements (1) and (2 Is satisfied. (1)
- a pore peak has a pore radius in the range of 10 nm to 200 nm.
- the secondary particles having voids inside the particles are voids located between a plurality of primary particles forming the secondary particles, and the voids where the secondary particle surface communicates with the inside of the secondary particles (hereinafter referred to as “ Secondary particle having a fine void in the secondary particle).
- the positive electrode active material for a lithium secondary battery according to the present embodiment has a pore peak in a pore radius range of 10 nm to 200 nm.
- the pore peak in this range is a pore peak derived from the fine voids in the secondary particles possessed by the secondary particles, and means that secondary particles having fine voids in the secondary particles are included.
- the pore peak means a peak including a maximum in a pore distribution curve measured by mercury porosimetry.
- the positive electrode active material for a lithium secondary battery of the present embodiment has three or more inflection points of the cumulative pore volume in the range where the pore radius is 10 nm or more and 3000 nm or less.
- the “inflection point” means a point where the sign of the second-order derivative changes.
- the three inflection points of requirement (2) are calculated by the following method. First, 71 points of data are measured by pore distribution measurement so that the pore radius is equidistant between 0.0018 ⁇ m and 246.9 ⁇ m when the pore radius is a logarithmic axis and a horizontal axis. The cumulative pore volume is calculated from each data plot, and the point where the sign of the second-order derivative changes is counted as the inflection point. In this embodiment, it is preferable to carry out the pore distribution measurement a plurality of times and confirm that the inflection point appears with good reproducibility. In addition, it is determined that a portion having no reproducibility is derived from a noise peak and is not counted as an inflection point.
- the at least three inflection points of requirement (2) are in addition to the first inflection point derived from the fine voids of the secondary particles having voids inside, that is, the fine voids in the secondary particles, and between the secondary particles.
- the secondary particle gap is a gap formed between secondary particles having a large average secondary particle diameter (hereinafter sometimes referred to as secondary particles B), a secondary particle having a large average secondary particle diameter, and A gap formed between secondary particles having a small average secondary particle diameter (hereinafter sometimes referred to as secondary particle A) and a gap formed between secondary particles having a small average secondary particle diameter are categorized.
- the two or more inflection points due to the secondary particle gap include one or more inflection points derived from the gap between the secondary particles having a large average secondary particle diameter and a secondary having a small average secondary particle diameter.
- one or more inflection points derived from the gap between the particles and from the gap formed between the secondary particles having a large average secondary particle diameter and the secondary particles having a small average secondary particle diameter An inflection point derived from a gap between one or more inflection points and a secondary particle having a large average secondary particle diameter and a gap between secondary particles having a small average secondary particle diameter
- the average secondary particle diameter refers to a value measured by the following method (laser diffraction scattering method).
- a laser diffraction particle size distribution analyzer manufactured by HORIBA, Ltd., model number: LA-950
- 0.1 g of secondary particles to be measured is put into 50 ml of a 0.2 mass% sodium hexametaphosphate aqueous solution, A dispersed dispersion is obtained.
- the particle size distribution of the obtained dispersion is measured to obtain a volume-based cumulative particle size distribution curve.
- the value of the particle diameter (D50) viewed from the fine particle side when 50% is accumulated is defined as the average particle diameter of the positive electrode active material powder for a lithium secondary battery.
- the average secondary particle diameter of secondary particles having a small average secondary particle diameter is smaller than the average secondary particle diameter of secondary particles having a large average secondary particle diameter (secondary particles B).
- the average secondary particle diameter of the secondary particles A is usually 1 ⁇ m or more and 10 ⁇ m or less.
- the average secondary particle diameter of the secondary particles B is usually defined as secondary particles having a size of 5 ⁇ m or more and 30 ⁇ m or less.
- This embodiment that satisfies the requirement (2) by realizing a state in which there are voids inside the secondary particles, that is, fine voids in the secondary particles, and large secondary particles and small secondary particles coexist.
- the positive electrode active material for lithium secondary batteries can be obtained.
- the method for controlling the requirements (1) and (2) within the scope of the present invention will be described in detail later, and specifically, there is a method of broadening the particle size distribution.
- a method of mixing powders having different average secondary particle diameters is preferable.
- a cumulative particle size distribution curve measured by a laser diffraction scattering method of a mixture of powders having different average secondary particle diameters may have at least two peaks.
- the pore radius is 10 nm or more and 1500 nm or less.
- the pore peak of the above requirement (1) and the cumulative pore volume of (2) can be calculated from the pore distribution obtained by the mercury intrusion method.
- the pore distribution measurement by the mercury intrusion method is performed by the following method.
- the container is filled with mercury.
- Mercury has a high surface tension, and as it is, mercury does not enter the pores on the surface of the positive electrode active material.
- the pores with smaller diameters increase in order from the larger diameter. Mercury gradually penetrates into the pores. If the amount of mercury intrusion is detected while continuously increasing the pressure, a mercury intrusion curve can be obtained from the relationship between the pressure applied to mercury and the amount of mercury intrusion.
- the volume increase dV in a certain pore diameter range is due to a cylindrical pore having a certain average pore diameter
- the pore specific surface area ⁇ A is calculated.
- the lower limit is about 2 nm and the upper limit is about 200 ⁇ m.
- Measurement by the mercury intrusion method can be performed using an apparatus such as a mercury porosimeter.
- Specific examples of the mercury porosimeter include Autopore III9420 (manufactured by Micromeritics).
- the measurement conditions were a measurement temperature of 25 ° C., a measurement pressure of 0.432 psia to 59245.2 psia (2.98 kPaA to 408.391 MPaA), a mercury surface tension of 480 dynes / cm, and a contact angle between mercury and the sample.
- An example of the condition is 140 °.
- the positive electrode active material for a lithium secondary battery of the present embodiment includes secondary particles having voids inside the particles.
- the density of the positive electrode active material for a lithium secondary battery tends to decrease and the volume capacity density tends to decrease. According to the present embodiment, even when secondary particles having voids are included inside the particles, the positive electrode active for lithium secondary batteries having a high volume capacity density is satisfied by satisfying the requirements (1) and (2). Can provide material.
- the positive electrode active material for a lithium secondary battery according to this embodiment is preferably represented by the following composition formula (I).
- M is one or more metal elements selected from the group consisting of Fe, Cu, Ti, Mg, Al, W, B, Mo, Nb, Zn, Sn, Zr, Ga and V, and 0 ⁇ x ⁇ 0.2, 0 ⁇ y ⁇ 0.4, 0 ⁇ z ⁇ 0.4, and 0 ⁇ w ⁇ 0.1 are satisfied.
- x in the composition formula (I) is preferably more than 0, more preferably 0.01 or more, and further preferably 0.02 or more. . Further, from the viewpoint of obtaining a lithium secondary battery having higher initial Coulomb efficiency, x in the composition formula (I) is preferably 0.1 or less, more preferably 0.08 or less, and 0.06. More preferably, it is as follows. The upper limit value and the lower limit value of x can be arbitrarily combined. For example, x is preferably more than 0 and 0.1 or less, more preferably 0.01 or more and 0.08 or less, and further preferably 0.02 or more and 0.06 or less.
- y in the composition formula (I) is preferably 0.005 or more, more preferably 0.01 or more, and 0.05 or more. More preferably it is. Further, from the viewpoint of obtaining a lithium secondary battery having high thermal stability, y in the composition formula (I) is more preferably 0.35 or less, and further preferably 0.33 or less.
- the upper limit value and the lower limit value of y can be arbitrarily combined. For example, y is preferably 0.005 or more and 0.35 or less, more preferably 0.01 or more and 0.33 or less, and further preferably 0.05 or more and 0.33 or less.
- z in the composition formula (I) is preferably 0 or more, more preferably 0.03 or more, and 0.1 or more. Is more preferable. Further, from the viewpoint of obtaining a lithium secondary battery having high storage characteristics at a high temperature (for example, at 60 ° C.), z in the composition formula (I) is preferably 0.4 or less, and is 0.38 or less. Is more preferable, and it is still more preferable that it is 0.35 or less.
- the upper limit value and lower limit value of z can be arbitrarily combined. For example, z is preferably 0 or more and 0.4 or less, more preferably 0.03 or more and 0.38 or less, and further preferably 0.1 or more and 0.35 or less.
- w in the composition formula (I) is preferably more than 0, more preferably 0.0005 or more, and 0.001 or more. Further preferred. Further, from the viewpoint of obtaining a lithium secondary battery having a high discharge capacity at a high current rate, w in the composition formula (I) is preferably 0.09 or less, more preferably 0.08 or less, and 0 More preferably, it is 0.07 or less.
- the upper limit value and the lower limit value of w can be arbitrarily combined. For example, it exceeds 0 and is preferably 0.09 or less, more preferably 0.0005 or more and 0.08 or less, and further preferably 0.001 or more and 0.07 or less.
- M in the composition formula (I) represents one or more metals selected from the group consisting of Fe, Cu, Ti, Mg, Al, W, B, Mo, Nb, Zn, Sn, Zr, Ga, and V. .
- M in the composition formula (I) is one or more metals selected from the group consisting of Ti, Mg, Al, W, B, and Zr. From the viewpoint of obtaining a lithium secondary battery with high thermal stability, it is preferably one or more metals selected from the group consisting of Al, W, B, and Zr.
- the average secondary particle size of the positive electrode active material for lithium secondary batteries is preferably 1 ⁇ m or more, and preferably 4 ⁇ m or more. More preferably, it is more preferably 5 ⁇ m or more. From the viewpoint of obtaining a lithium secondary battery having a high discharge capacity at a high current rate, it is preferably 30 ⁇ m or less, more preferably 20 ⁇ m or less, and even more preferably 10 ⁇ m or less.
- the upper limit value and lower limit value of the average secondary particle diameter can be arbitrarily combined.
- the average secondary particle diameter of the positive electrode active material for a lithium secondary battery is preferably 1 ⁇ m or more and 30 ⁇ m or less, more preferably 4 ⁇ m or more and 20 ⁇ m or less, and further preferably 5 ⁇ m or more and 10 ⁇ m or less.
- the “average secondary particle diameter” of the positive electrode active material powder for a lithium secondary battery refers to a value measured by the laser diffraction scattering method described above.
- the positive electrode active material for a lithium secondary battery preferably contains an active material powder containing two or more types of secondary particles having different average secondary particle diameters.
- the active material powder is preferably mixed with secondary particles A having an average secondary particle diameter of 1 ⁇ m to 10 ⁇ m and secondary particles B having an average secondary particle diameter of 5 ⁇ m to 30 ⁇ m.
- either the secondary particle A or the secondary particle B is a secondary particle having a fine void in the secondary particle.
- the mixing ratio is preferably 20:80 to 50:50. Whether or not the mixed active material is a mixture of the secondary particles A and the secondary particles B is measured by measuring the particle size distribution and observing the peak caused by the secondary particles A and the peak caused by the secondary particles B. This can be confirmed.
- the crystal structure of the positive electrode active material for a lithium secondary battery is a layered structure, and more preferably a hexagonal crystal structure or a monoclinic crystal structure.
- the hexagonal crystal structures are P3, P31, P32, R3, P-3, R-3, P312, P321, P3112, P3121, P3212, P3221, R32, P3m1, P31m, P3c1, P31c, R3m, R3c, P-31m, P-31c, P-3m1, P-3c1, R-3m, R-3c, P6, P61, P65, P62, P64, P63, P-6, P6 / m, P63 / m, P622, P6122, P6522, P6222, P6422, P6322, P6mm, P6cc, P63cm, P63mc, P-6m2, P-6c2, P-62m, P-62c, P6 / mmm, P6 / mcc, P63 / mcm, and P63 / mmc Belonging to any one space group selected from the group consisting of
- the monoclinic crystal structure is from P2, P21, C2, Pm, Pc, Cm, Cc, P2 / m, P21 / m, C2 / m, P2 / c, P21 / c, and C2 / c. It belongs to any one space group selected from the group.
- the crystal structure is a hexagonal crystal structure belonging to the space group R-3m or a monoclinic crystal belonging to C2 / m.
- a crystal structure is particularly preferred.
- a metal other than lithium that is, an essential metal composed of Ni, Co, and Mn is included, and optionally Fe, Cu, Ti, Mg , Al, W, B, Mo, Nb, Zn, Sn, Zr, Ga, and V
- a metal composite compound containing any one or more arbitrary metals is prepared, and the metal composite compound is mixed with an appropriate lithium compound After that, it is preferable to fire the resulting mixture.
- a metal complex compound a metal complex hydroxide or a metal complex oxide is preferable.
- the metal complex compound can be usually produced by a known batch coprecipitation method or continuous coprecipitation method.
- the manufacturing method will be described in detail by taking a metal composite hydroxide containing nickel, cobalt, and manganese as an example.
- the metal complex hydroxide is co-precipitation, in particular by a continuous method described in 2002-201028 JP-nickel salt solution, cobalt salt solution, is reacted manganese salt solution and a complexing agent, Ni 1 -y-z Co y Mn z ( OH) 2 ( wherein, 0 ⁇ y ⁇ 0.4,0 ⁇ z ⁇ 0.4) can be produced a metal complex hydroxide represented by.
- nickel salt which is the solute of the said nickel salt solution For example, any one of nickel sulfate, nickel nitrate, nickel chloride, and nickel acetate can be used.
- cobalt salt that is the solute of the cobalt salt solution for example, any one of cobalt sulfate, cobalt nitrate, cobalt chloride, and cobalt acetate can be used.
- manganese salt that is the solute of the manganese salt solution for example, any of manganese sulfate, manganese nitrate, manganese chloride, and manganese acetate can be used.
- More metal salts are used in proportions corresponding to the composition ratio of the Ni 1-y-z Co y Mn z (OH) 2. That is, each of the molar ratios of nickel, cobalt, and manganese in the mixed solution containing the metal salt corresponds to (1-yz): y: z in the composition formula (I) of the lithium composite metal compound. Define the amount of metal salt. Moreover, water is used as a solvent.
- the complexing agent can form a complex with nickel, cobalt, and manganese ions in an aqueous solution.
- an ammonium ion supplier ammonium hydroxide, ammonium sulfate, ammonium chloride, ammonium carbonate, ammonium fluoride, etc.
- Hydrazine ethylenediaminetetraacetic acid, nitrilotriacetic acid, uracil diacetic acid, and glycine.
- the complexing agent may not be included if desired.
- the complexing agent contained in the mixed solution containing the nickel salt solution, the cobalt salt solution, the manganese salt solution, the M salt solution and the complexing agent is included.
- the amount of the agent is, for example, a molar ratio with respect to the total number of moles of the metal salt greater than 0 and 2.0 or less.
- an alkali metal hydroxide for example, sodium hydroxide or potassium hydroxide
- an alkali metal hydroxide for example, sodium hydroxide or potassium hydroxide
- Ni 1-yz Co y Mn z. (OH) 2 when a complexing agent is continuously supplied to the reaction tank, nickel, cobalt, and manganese react to form Ni 1-yz Co y Mn z. (OH) 2 is produced.
- the temperature of the reaction vessel is controlled within a range of 20 ° C. or more and 80 ° C. or less, preferably 30 ° C. or more and 70 ° C.
- the pH value in the reaction vessel is, for example, pH 9 or more and pH 13 or less when measured at 40 ° C.
- the pH is controlled within the range of 11 to 13, and the substance in the reaction vessel is appropriately stirred.
- the reaction vessel is of a type that causes the formed reaction precipitate to overflow for separation.
- the secondary particle diameter of the lithium metal composite oxide finally obtained in the following steps by appropriately controlling the concentration of metal salt to be supplied to the reaction tank, the stirring speed, the reaction temperature, the reaction pH, the firing conditions described later, etc.
- Various physical properties such as pore radius can be controlled.
- various gases such as nitrogen, argon, carbon dioxide and other inert gases that promote the reduction state, air that promotes the oxidation state, oxidizing gases such as oxygen, or a mixture of these gases are reacted. You may supply in a tank.
- oxidants such as hydrogen peroxide and other peroxide salts, permanganate and other peroxide salts, perchlorate, hypochlorite, nitric acid, halogen, and ozone are used. be able to.
- organic acids such as oxalic acid and formic acid, sulfites, hydrazine and the like can be used to promote the reduced state.
- reaction pH in the reaction vessel when the reaction pH in the reaction vessel is increased, a metal composite compound having a small secondary particle size is easily obtained. On the other hand, when the reaction pH is lowered, a metal composite compound having a large secondary particle size is easily obtained. Moreover, when the oxidation state in the reaction vessel is increased, a metal composite compound having many voids is easily obtained. On the other hand, when the oxidation state is lowered, a dense metal composite compound is easily obtained. Since the reaction conditions depend on the size of the reaction tank used, the reaction conditions may be optimized while monitoring various physical properties of the finally obtained lithium composite oxide.
- the obtained reaction precipitate is washed with water and then dried to isolate the nickel cobalt manganese metal composite hydroxide as the nickel cobalt manganese metal composite compound. Moreover, you may wash
- nickel cobalt manganese metal composite hydroxide is manufactured, but nickel cobalt manganese metal composite oxide may be prepared.
- the metal composite oxide or hydroxide is dried and then mixed with a lithium compound.
- the drying conditions are not particularly limited, but, for example, conditions in which the metal composite oxide or hydroxide is not oxidized and reduced (that is, the oxide is maintained as an oxide, the hydroxide is maintained as a hydroxide).
- Conditions conditions under which the metal composite hydroxide is oxidized (ie, conditions under which the hydroxide is oxidized into oxide), conditions under which the metal composite oxide is reduced (ie under conditions under which the oxide is reduced into hydroxide) Any of the above conditions may be used.
- an inert gas such as nitrogen, helium and argon may be used.
- a reducing agent such as hydrazine or sodium sulfite may be used in an inert gas atmosphere.
- the lithium compound include lithium carbonate, lithium nitrate, lithium sulfate, lithium acetate, lithium hydroxide, lithium hydroxide hydrate, lithium oxide, lithium chloride, and lithium fluoride, or two or more. Can be used in combination. Classification may be appropriately performed after the metal composite oxide or hydroxide is dried. The lithium compound and the metal composite oxide or hydroxide are used in consideration of the composition ratio of the final target product.
- the lithium compound and the metal composite hydroxide are Li x Ni (1-yz) Co y Mn z O 2 (where 0 ⁇ x ⁇ 0 .2, 0 ⁇ y ⁇ 0.4, 0 ⁇ z ⁇ 0.4).
- a lithium-nickel cobalt manganese metal composite oxide is obtained by firing a mixture of a nickel cobalt manganese metal composite hydroxide and a lithium compound. For the firing, dry air, an oxygen atmosphere, an inert atmosphere, or the like is used according to a desired composition, and a plurality of heating steps are performed if necessary.
- the firing temperature of the metal composite oxide or hydroxide and lithium compounds such as lithium hydroxide and lithium carbonate is not particularly limited.
- the temperature is preferably 600 ° C. or higher and 1100 ° C. or lower, more preferably 750 ° C. or higher and 1050 ° C. or lower, and further preferably 800 ° C. or higher and 1025 ° C. or lower.
- the firing time is preferably 3 hours to 50 hours. When the firing time is 50 hours or less, the volatilization of Li can be suppressed, and deterioration of battery performance can be prevented. If the firing time is 3 hours or longer, the crystal development tends to proceed well. In addition, it is also effective to perform temporary baking before the above baking.
- the temperature for such preliminary firing is preferably in the range of 300 to 850 ° C. for 1 to 10 hours.
- the time from the start of the temperature rise to the firing temperature is preferably 0.5 hours or more and 20 hours or less. When the time from the start of temperature rise to the firing temperature is within this range, a more uniform lithium nickel composite oxide can be obtained.
- the time from reaching the firing temperature to the end of the temperature holding is 0.5 hours or more and 20 hours or less.
- the time from reaching the firing temperature to the end of the temperature holding is within this range, the development of crystals progresses better, and the battery performance can be further improved.
- the lithium metal composite oxide obtained by firing is appropriately classified after pulverization, and is used as a positive electrode active material applicable to a lithium secondary battery.
- at least one of the secondary particles A or the secondary particles B is a secondary particle having fine voids in the secondary particles.
- the mixing ratio is preferably 20:80 to 50:50.
- the requirements (1) and (2) may be controlled within the desired range of the present invention.
- the particle size distribution for example, in the production process of the metal composite hydroxide, the state in which crystals tend to grow and the state in which nuclei are likely to be generated change with time by raising and lowering the reaction pH. A wide lithium metal composite oxide can be obtained.
- reaction pH is lowered in the first-stage reaction tank, and 1 in the second-stage reaction tank.
- a lithium metal composite oxide having a wide particle size distribution can be obtained by making the reaction pH higher than that in the stage reaction vessel.
- the pulverization step after firing there is a method of appropriately adjusting the pulverization time, the rotational speed of the pulverization mill, and the pulverization process type (dry pulverization or wet pulverization).
- An example of the lithium secondary battery of the present embodiment includes a positive electrode and a negative electrode, a separator sandwiched between the positive electrode and the negative electrode, and an electrolytic solution disposed between the positive electrode and the negative electrode.
- FIG. 1A and 1B are schematic views showing an example of the lithium secondary battery of the present embodiment.
- the cylindrical lithium secondary battery 10 of this embodiment is manufactured as follows.
- a pair of separators 1 having a strip shape, a strip-like positive electrode 2 having a positive electrode lead 21 at one end, and a strip-like negative electrode 3 having a negative electrode lead 31 at one end, a separator 1, a positive electrode 2, and a separator 1 and negative electrode 3 are laminated in this order and wound to form electrode group 4.
- the lithium secondary battery 10 can be manufactured by sealing the upper part of the battery can 5 with the top insulator 7 and the sealing body 8.
- a columnar shape in which the cross-sectional shape when the electrode group 4 is cut in a direction perpendicular to the winding axis is a circle, an ellipse, a rectangle, or a rectangle with rounded corners. Can be mentioned.
- a shape of the lithium secondary battery having such an electrode group 4 a shape defined by IEC 60086 or JIS C 8500 which is a standard for a battery defined by the International Electrotechnical Commission (IEC) can be adopted. .
- IEC 60086 or JIS C 8500 which is a standard for a battery defined by the International Electrotechnical Commission (IEC)
- cylindrical shape, square shape, etc. can be mentioned.
- the lithium secondary battery is not limited to the above-described wound type configuration, and may have a stacked type configuration in which a stacked structure of a positive electrode, a separator, a negative electrode, and a separator is repeatedly stacked.
- Examples of the stacked lithium secondary battery include so-called coin-type batteries, button-type batteries, and paper-type (or sheet-type) batteries.
- the positive electrode of this embodiment can be manufactured by first adjusting a positive electrode mixture containing a positive electrode active material, a conductive material and a binder, and supporting the positive electrode mixture on a positive electrode current collector.
- a carbon material As the conductive material included in the positive electrode of the present embodiment, a carbon material can be used.
- the carbon material include graphite powder, carbon black (for example, acetylene black), and a fibrous carbon material. Since carbon black is fine and has a large surface area, by adding a small amount to the positive electrode mixture, the conductivity inside the positive electrode can be improved and the charge / discharge efficiency and output characteristics can be improved. Both the binding force between the positive electrode mixture and the positive electrode current collector and the binding force inside the positive electrode mixture are reduced, which causes an increase in internal resistance.
- the proportion of the conductive material in the positive electrode mixture is preferably 5 parts by mass or more and 20 parts by mass or less with respect to 100 parts by mass of the positive electrode active material.
- a fibrous carbon material such as graphitized carbon fiber or carbon nanotube is used as the conductive material, this ratio can be lowered.
- thermoplastic resin As the binder included in the positive electrode of the present embodiment, a thermoplastic resin can be used.
- the thermoplastic resin include polyvinylidene fluoride (hereinafter sometimes referred to as PVdF), polytetrafluoroethylene (hereinafter sometimes referred to as PTFE), tetrafluoroethylene, hexafluoropropylene, and vinylidene fluoride.
- fluororesins such as copolymers, propylene hexafluoride / vinylidene fluoride copolymers, tetrafluoroethylene / perfluorovinyl ether copolymers; polyolefin resins such as polyethylene and polypropylene.
- thermoplastic resins may be used as a mixture of two or more.
- a fluororesin and a polyolefin resin as a binder, the ratio of the fluororesin to the total positive electrode mixture is 1% by mass or more and 10% by mass or less, and the ratio of the polyolefin resin is 0.1% by mass or more and 2% by mass or less.
- a positive electrode mixture having both high adhesion to the current collector and high bonding strength inside the positive electrode mixture can be obtained.
- a band-shaped member made of a metal material such as Al, Ni, and stainless steel can be used as the positive electrode current collector included in the positive electrode of the present embodiment.
- a material that is made of Al and formed into a thin film is preferable because it is easy to process and inexpensive.
- Examples of the method of supporting the positive electrode mixture on the positive electrode current collector include a method of pressure-molding the positive electrode mixture on the positive electrode current collector. Also, the positive electrode mixture is made into a paste using an organic solvent, and the resulting positive electrode mixture paste is applied to at least one surface side of the positive electrode current collector, dried, pressed and fixed, whereby the positive electrode current collector is bonded to the positive electrode current collector. A mixture may be supported.
- usable organic solvents include amine solvents such as N, N-dimethylaminopropylamine and diethylenetriamine; ether solvents such as tetrahydrofuran; ketone solvents such as methyl ethyl ketone; methyl acetate And amide solvents such as dimethylacetamide and N-methyl-2-pyrrolidone (hereinafter sometimes referred to as NMP).
- amine solvents such as N, N-dimethylaminopropylamine and diethylenetriamine
- ether solvents such as tetrahydrofuran
- ketone solvents such as methyl ethyl ketone
- amide solvents such as dimethylacetamide and N-methyl-2-pyrrolidone (hereinafter sometimes referred to as NMP).
- Examples of the method of applying the positive electrode mixture paste to the positive electrode current collector include a slit die coating method, a screen coating method, a curtain coating method, a knife coating method, a gravure coating method, and an electrostatic spray method.
- a positive electrode can be manufactured by the method mentioned above.
- the negative electrode included in the lithium secondary battery of this embodiment is only required to be able to dope and dedope lithium ions at a lower potential than the positive electrode, and the negative electrode mixture containing the negative electrode active material is supported on the negative electrode current collector. And an electrode composed of the negative electrode active material alone.
- Negative electrode active material examples of the negative electrode active material possessed by the negative electrode include carbon materials, chalcogen compounds (oxides, sulfides, etc.), nitrides, metals, and alloys that can be doped and dedoped with lithium ions at a lower potential than the positive electrode. It is done.
- Examples of carbon materials that can be used as the negative electrode active material include graphite such as natural graphite and artificial graphite, cokes, carbon black, pyrolytic carbons, carbon fibers, and organic polymer compound fired bodies.
- the oxide can be used as an anode active material, (wherein, x represents a positive real number) SiO 2, SiO, etc. formula SiO x oxides of silicon represented by; TiO 2, TiO, etc. formula TiO x (wherein , X is a positive real number); oxide of titanium represented by formula VO x (where x is a positive real number) such as V 2 O 5 and VO 2 ; Fe 3 O 4 , Fe 2 O 3 , FeO, etc. Iron oxide represented by the formula FeO x (where x is a positive real number); SnO 2 , SnO, etc.
- Examples of sulfides that can be used as the negative electrode active material include titanium sulfides represented by the formula TiS x (where x is a positive real number) such as Ti 2 S 3 , TiS 2 , and TiS; V 3 S 4 , VS 2, VS and other vanadium sulfides represented by the formula VS x (where x is a positive real number); Fe 3 S 4 , FeS 2 , FeS and other formulas FeS x (where x is a positive real number) Iron sulfide represented; Mo 2 S 3 , MoS 2 and the like MoS x (where x is a positive real number) Molybdenum sulfide; SnS 2, SnS and other formula SnS x (where, a sulfide of tin represented by x is a positive real number; a sulfide of tungsten represented by a formula WS x (where x is a positive real number) such as WS 2
- Examples of the nitride that can be used as the negative electrode active material include Li 3 N and Li 3-x A x N (where A is one or both of Ni and Co, and 0 ⁇ x ⁇ 3). And lithium-containing nitrides.
- These carbon materials, oxides, sulfides and nitrides may be used alone or in combination of two or more. These carbon materials, oxides, sulfides and nitrides may be crystalline or amorphous.
- examples of the metal that can be used as the negative electrode active material include lithium metal, silicon metal, and tin metal.
- Alloys that can be used as the negative electrode active material include lithium alloys such as Li—Al, Li—Ni, Li—Si, Li—Sn, and Li—Sn—Ni; silicon alloys such as Si—Zn; Sn—Mn, Sn -Tin alloys such as Co, Sn-Ni, Sn-Cu, Sn-La; alloys such as Cu 2 Sb, La 3 Ni 2 Sn 7 ;
- These metals and alloys are mainly used alone as electrodes after being processed into a foil shape, for example.
- carbon materials containing graphite as a main component such as natural graphite and artificial graphite, are preferably used.
- the shape of the carbon material may be any of a flake shape such as natural graphite, a spherical shape such as mesocarbon microbeads, a fibrous shape such as graphitized carbon fiber, or an aggregate of fine powder.
- the negative electrode mixture may contain a binder as necessary.
- the binder include thermoplastic resins, and specific examples include PVdF, thermoplastic polyimide, carboxymethyl cellulose, polyethylene, and polypropylene.
- the negative electrode current collector of the negative electrode examples include a band-shaped member made of a metal material such as Cu, Ni, and stainless steel. In particular, it is preferable to use Cu as a forming material and process it into a thin film from the viewpoint that it is difficult to make an alloy with lithium and it is easy to process.
- Examples of the separator included in the lithium secondary battery of the present embodiment include a porous film, a nonwoven fabric, a woven fabric, and the like made of a material such as a polyolefin resin such as polyethylene and polypropylene, a fluororesin, and a nitrogen-containing aromatic polymer. A material having the following can be used. Moreover, a separator may be formed by using two or more of these materials, or a separator may be formed by laminating these materials.
- the separator allows the electrolyte to permeate well when the battery is used (during charging / discharging). Therefore, the air resistance according to the Gurley method defined in JIS P 8117 is 50 seconds / 100 cc or more, 300 seconds / 100 cc. Or less, more preferably 50 seconds / 100 cc or more and 200 seconds / 100 cc or less.
- the porosity of the separator is preferably 30% by volume or more and 80% by volume or less, more preferably 40% by volume or more and 70% by volume or less with respect to the volume of the separator.
- the separator may be a laminate of separators having different porosity.
- the electrolyte solution included in the lithium secondary battery of this embodiment contains an electrolyte and an organic solvent.
- the electrolyte contained in the electrolyte includes LiClO 4 , LiPF 6 , LiAsF 6 , LiSbF 6 , LiBF 4 , LiCF 3 SO 3 , LiN (SO 2 CF 3 ) 2 , LiN (SO 2 C 2 F 5 ) 2 , LiN (SO 2 CF 3 ) (COCF 3 ), Li (C 4 F 9 SO 3 ), LiC (SO 2 CF 3 ) 3 , Li 2 B 10 Cl 10 , LiBOB (where BOB is bis (oxalato) borate LiFSI (where FSI is bis (fluorosulfonyl) imide), lithium compounds such as lower aliphatic lithium carboxylate compounds and LiAlCl 4, and mixtures of these two or more May be used.
- the electrolyte at least selected from the group consisting of LiPF 6 , LiAsF 6 , LiSbF 6 , LiBF 4 , LiCF 3 SO 3 , LiN (SO 2 CF 3 ) 2 and LiC (SO 2 CF 3 ) 3 containing fluorine. It is preferable to use one containing one kind.
- Examples of the organic solvent contained in the electrolyte include propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, 4-trifluoromethyl-1,3-dioxolan-2-one, and 1,2-di- Carbonates such as (methoxycarbonyloxy) ethane; 1,2-dimethoxyethane, 1,3-dimethoxypropane, pentafluoropropyl methyl ether, 2,2,3,3-tetrafluoropropyl difluoromethyl ether, tetrahydrofuran, 2- Ethers such as methyltetrahydrofuran; Esters such as methyl formate, methyl acetate and ⁇ -butyrolactone; Nitriles such as acetonitrile and butyronitrile; N, N-dimethylformamide, N, N-dimethyla Amides such as toamide; Carbamates such as 3-methyl-2-oxazolidone;
- a mixed solvent containing carbonates is preferable, and a mixed solvent of cyclic carbonate and acyclic carbonate and a mixed solvent of cyclic carbonate and ethers are more preferable.
- a mixed solvent of a cyclic carbonate and an acyclic carbonate a mixed solvent containing ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate is preferable.
- the electrolyte using such a mixed solvent has a wide operating temperature range, hardly deteriorates even when charged and discharged at a high current rate, hardly deteriorates even when used for a long time, and natural graphite as an active material of the negative electrode. Even when a graphite material such as artificial graphite is used, it has many features that it is hardly decomposable.
- an electrolytic solution containing a lithium compound containing fluorine such as LiPF 6 and an organic solvent having a fluorine substituent because the safety of the obtained lithium secondary battery is increased.
- a mixed solvent containing ethers having fluorine substituents such as pentafluoropropyl methyl ether and 2,2,3,3-tetrafluoropropyl difluoromethyl ether and dimethyl carbonate is capable of capacity even when charging / discharging at a high current rate. Since the maintenance rate is high, it is more preferable.
- a solid electrolyte may be used instead of the above electrolytic solution.
- the solid electrolyte for example, an organic polymer electrolyte such as a polyethylene oxide polymer compound, a polymer compound containing at least one of a polyorganosiloxane chain or a polyoxyalkylene chain can be used.
- maintained the non-aqueous electrolyte in the high molecular compound can also be used.
- Li 2 S—SiS 2 , Li 2 S—GeS 2 , Li 2 S—P 2 S 5 , Li 2 S—B 2 S 3 , Li 2 S—SiS 2 —Li 3 PO 4 , Li 2 S—SiS 2 -Li 2 SO 4, Li 2 S-GeS 2 -P 2 S 5 inorganic solid electrolytes containing a sulfide, and the like, may be used a mixture of two or more thereof. By using these solid electrolytes, the safety of the lithium secondary battery may be further improved.
- the solid electrolyte when a solid electrolyte is used, the solid electrolyte may serve as a separator, and in that case, the separator may not be required.
- the life of the lithium secondary battery using the positive electrode active material can be extended.
- the positive electrode having the above-described configuration has the above-described positive electrode active material for a lithium secondary battery according to this embodiment, the life of the lithium secondary battery can be extended.
- the lithium secondary battery having the above-described configuration has the above-described positive electrode, it becomes a lithium secondary battery having a longer life than before.
- evaluation of a positive electrode active material for a lithium secondary battery and production evaluation of a positive electrode for a lithium secondary battery and a lithium secondary battery were performed as follows.
- (1) Evaluation of positive electrode active material for lithium secondary battery / Measurement of average secondary particle diameter 0.1 g of positive electrode active material powder for lithium secondary battery to be measured was put into 50 ml of 0.2% by mass sodium hexametaphosphate aqueous solution. A dispersion in which the powder was dispersed was obtained. The particle size distribution of the obtained dispersion was measured using a laser diffraction / scattering particle size distribution measuring apparatus (manufactured by Horiba, Ltd., model number: LA-950) to obtain a volume-based cumulative particle size distribution curve. In the obtained cumulative particle size distribution curve, the value of the particle diameter (D 50 ) viewed from the fine particle side at 50% accumulation was taken as the average secondary particle diameter.
- the number of powders having different average secondary particle diameters contained in the positive electrode active material powder for lithium secondary batteries can be determined. If two or more kinds of powders having different average secondary particle diameters contained in the positive electrode active material powder for a lithium secondary battery, two or more peak tops are observed.
- Measurement of particle size distribution of positive electrode active material for lithium secondary battery 0.1 g of positive electrode active material powder for lithium secondary battery to be measured was put into 50 ml of 0.2 mass% sodium hexametaphosphate aqueous solution, and the powder was dispersed. A dispersion was obtained. The particle size distribution of the obtained dispersion was measured using a laser diffraction scattering particle size distribution measuring apparatus (manufactured by Horiba, Ltd., model number: LA-950).
- composition analysis of the positive electrode active material powder for lithium secondary battery produced by the method described below is performed by dissolving the obtained positive electrode active material powder for lithium secondary battery in hydrochloric acid and then performing inductively coupled plasma emission spectrometry. The measurement was performed using an apparatus (SPS3000, manufactured by SII Nano Technology).
- Measurement conditions Measurement temperature: 25 ° C Measurement pressure: 0.432 psia to 59245.2 psia
- the data measurement points in the pore distribution measurement were 71 points, and when the pore radius was a logarithmic axis and a horizontal axis, the pore radius was set to be equally spaced between 0.0018 ⁇ m and 246.9 ⁇ m.
- the cumulative pore volume was calculated from each data plot, and the point at which the sign of the second-order derivative changed was counted as the inflection point.
- the pore distribution measurement was performed several times, and it was confirmed that the inflection point appeared with good reproducibility. It was decided that the places without restrictions were derived from noise peaks and were not counted as inflection points.
- a positive electrode active material for lithium secondary battery, a conductive material (acetylene black), and a binder (PVdF) obtained by the production method described later are used as a positive electrode active material for lithium secondary battery:
- N-methyl-2-pyrrolidone was used as the organic solvent.
- the obtained positive electrode mixture was applied to an Al foil having a thickness of 40 ⁇ m serving as a current collector and vacuum-dried at 150 ° C. for 8 hours to obtain a positive electrode for a lithium secondary battery.
- the electrode area of the positive electrode for the lithium secondary battery was 1.65 cm 2 .
- the obtained negative electrode mixture was applied to a 12 ⁇ m thick Cu foil serving as a current collector and vacuum dried at 100 ° C. for 8 hours to obtain a negative electrode for a lithium secondary battery.
- the electrode area of this negative electrode for a lithium secondary battery was 1.77 cm 2 .
- the electrolytic solution was ethylene carbonate (hereinafter sometimes referred to as EC), dimethyl carbonate (hereinafter sometimes referred to as DMC), and ethyl methyl carbonate (hereinafter sometimes referred to as EMC) 30:35.
- 35 (volume ratio) used was a solution in which LiPF 6 was dissolved to 1.0 mol / l (hereinafter sometimes referred to as LiPF 6 / EC + DMC + EMC).
- LiPF 6 / EC + DMC + EMC lithium metal as the negative electrode
- the negative electrode is placed on the upper side of the laminated film separator, covered with a gasket, and then caulked with a caulking machine to form a lithium secondary battery (coin type half cell R2032, hereinafter "half cell”).
- coin type half cell R2032 hereinafter "half cell”
- volume Capacity Density Test Using the half cell produced in “(4) Production of lithium secondary battery (coin-type half cell)”, a charge / discharge test was carried out under the following conditions to calculate the volume capacity density.
- ⁇ Charge / discharge test> Test temperature 25 ° C Charge maximum voltage 4.3V, charge time 6 hours, charge current 1.0CA, constant current constant voltage charge discharge minimum voltage 2.5V, discharge time 5 hours, discharge current 1.0CA, constant current discharge ⁇ volume capacity density calculation > From the discharge capacity discharged to 1.0 C and the mass per unit volume of the positive electrode material, the volume capacity density was determined based on the following calculation formula.
- Volume capacity density (mAh / cm 3 ) specific capacity of positive electrode material (mAh / g) ⁇ electrode density (g / cm 3 )
- a nickel sulfate aqueous solution, a cobalt sulfate aqueous solution, and a manganese sulfate aqueous solution were mixed so that the atomic ratio of nickel atoms, cobalt atoms, and manganese atoms was 55:21:24 to prepare a mixed raw material solution.
- the mixed raw material solution and the aqueous ammonium sulfate solution were continuously added as a complexing agent in the reaction vessel, and nitrogen gas was continuously passed through.
- a sodium hydroxide aqueous solution is dropped in a timely manner so that the pH of the solution in the reaction vessel (when measured at 40 ° C.) is 13.0 to obtain nickel cobalt manganese composite hydroxide particles, washed, and then dehydrated with a centrifuge. Then, washing, dehydration, isolation, and drying at 105 ° C. yielded nickel cobalt manganese metal composite hydroxide 1.
- a nickel sulfate aqueous solution, a cobalt sulfate aqueous solution, and a manganese sulfate aqueous solution were mixed so that the atomic ratio of nickel atoms, cobalt atoms, and manganese atoms was 55:21:24 to prepare a mixed raw material solution.
- the mixed raw material solution and the aqueous ammonium sulfate solution were continuously added as a complexing agent in the reaction vessel, and nitrogen gas was continuously passed through.
- a sodium hydroxide aqueous solution is dropped in a timely manner so that the pH of the solution in the reaction vessel (when measured at 40 ° C.) is 11.9 to obtain nickel cobalt manganese composite hydroxide particles, washed, and then dehydrated with a centrifuge. Then, washing, dehydration, isolation and drying at 105 ° C. yielded nickel cobalt manganese composite hydroxide 2.
- a nickel sulfate aqueous solution, a cobalt sulfate aqueous solution, and a manganese sulfate aqueous solution were mixed so that the atomic ratio of nickel atoms, cobalt atoms, and manganese atoms was 55:21:24 to prepare a mixed raw material solution.
- this mixed raw material solution and ammonium sulfate aqueous solution were continuously added as a complexing agent to the reaction vessel, and air was mixed with nitrogen gas so that the oxygen concentration was 3.7%.
- An oxygen-containing gas was continuously vented.
- a sodium hydroxide aqueous solution is dropped in a timely manner so that the pH of the solution in the reaction vessel (when measured at 40 ° C.) is 12.5 to obtain nickel cobalt manganese composite hydroxide particles, washed, and then dehydrated with a centrifuge. Washing, dehydration, isolation and drying at 105 ° C. yielded a nickel cobalt manganese composite hydroxide 3.
- a nickel sulfate aqueous solution, a cobalt sulfate aqueous solution, and a manganese sulfate aqueous solution were mixed so that the atomic ratio of nickel atoms, cobalt atoms, and manganese atoms was 55:21:24 to prepare a mixed raw material solution.
- this mixed raw material solution and ammonium sulfate aqueous solution were continuously added as a complexing agent to the reaction vessel, and air was mixed with nitrogen gas so that the oxygen concentration was 8.6%.
- An oxygen-containing gas was continuously vented.
- a sodium hydroxide aqueous solution is dropped in a timely manner so that the pH of the solution in the reaction vessel (when measured at 40 ° C.) is 12.0 to obtain nickel cobalt manganese composite hydroxide particles, washed, and then dehydrated with a centrifuge. Then, washing, dehydration, isolation and drying at 105 ° C. yielded nickel cobalt manganese composite hydroxide 4.
- Example 1 Production of positive electrode active material 1 for lithium secondary battery Lithium nickel cobalt manganese composite oxide 3 produced in Production Example 3 as secondary particles A, and lithium nickel cobalt manganese composite oxide 2 produced in Production Example 2 as secondary particles B was mixed at a mixing ratio of secondary particles A and secondary particles B of 25/75 to obtain a positive electrode active material 1 for a lithium secondary battery.
- the positive electrode active material 1 for a lithium secondary battery had a pore peak in the range of 10 nm to 100 nm (requirement (1)) in the pore distribution obtained by the mercury intrusion method. Moreover, it had three inflection points of cumulative pore volume in the range whose pore radius is 10 nm or more and 1500 nm or less (requirement (2)). The volume capacity density (mAh / cm 3) was 457mAh / cm 3.
- Example 2 Production of cathode active material 2 for lithium secondary battery Lithium nickel cobalt manganese composite oxide 3 produced in Production Example 3 as secondary particles A, and lithium nickel cobalt manganese composite oxide 2 produced in Production Example 2 as secondary particles B And mixing the secondary particles A and the secondary particles B at a mixing ratio of 50/50 to obtain a positive electrode active material 2 for a lithium secondary battery.
- the positive electrode active material 2 for a lithium secondary battery had a pore peak in the range of 10 nm to 100 nm (requirement (1)) in the pore distribution obtained by the mercury intrusion method. Moreover, it had three inflection points of cumulative pore volume in the range whose pore radius is 10 nm or more and 1500 nm or less (requirement (2)). The volume capacity density (mAh / cm 3) was 455mAh / cm 3.
- the positive electrode active material 3 for a lithium secondary battery had a pore peak in the range of 10 nm to 100 nm (requirement (1)) in the pore distribution obtained by the mercury intrusion method. Moreover, it had three inflection points of cumulative pore volume in the range whose pore radius is 10 nm or more and 1500 nm or less (requirement (2)).
- the volume capacity density (mAh / cm 3) was 434mAh / cm 3.
- Example 4 Production of cathode active material 4 for lithium secondary battery Lithium nickel cobalt manganese composite oxide 3 produced in Production Example 3 as secondary particles A, and lithium nickel cobalt manganese composite oxide 2 produced in Production Example 4 as secondary particles B Were mixed at a mixing ratio of secondary particles A and secondary particles B of 50/50 to obtain a positive electrode active material 4 for a lithium secondary battery.
- the positive electrode active material 4 for a lithium secondary battery had a pore peak in the range of 10 nm to 100 nm (requirement (1)) in the pore distribution obtained by the mercury intrusion method. Moreover, it had three inflection points of the cumulative pore volume in the range where the pore radius was 10 nm or more and 1500 nm or less (requirement (2)). The volume capacity density (mAh / cm 3) was 438mAh / cm 3.
- the positive electrode active material 5 for a lithium secondary battery does not have a pore peak in the range of 10 nm to 200 nm in the pore distribution obtained by the mercury intrusion method, and the pore radius is 300 nm to 2000 nm as shown in FIG. Only the following ranges had inflection points of the cumulative pore volume.
- the volume capacity density (mAh / cm 3) was 432mAh / cm 3.
- the positive electrode active material 6 for a lithium secondary battery has a pore peak in the range of 10 nm to 100 nm in the pore distribution obtained by the mercury intrusion method, and the pore radius is 10 nm to 100 nm as shown in FIG. Each had an inflection point of the cumulative pore volume in the range and in the range of 200 nm to 1500 nm.
- the volume capacity density (mAh / cm 3) was 417mAh / cm 3.
- the positive electrode active material 7 for a lithium secondary battery has a pore peak in the range of 10 nm to 100 nm in the pore distribution obtained by the mercury intrusion method, the pore radius is in the range of 10 nm to 100 nm, and 150 nm or more. Each had an inflection point of the cumulative pore volume in the range of 1000 nm or less.
- the volume capacity density (mAh / cm 3) was 431mAh / cm 3.
- the positive electrode active material 8 for a lithium secondary battery has no pore peak in the pore distribution obtained by the mercury intrusion method, and has two cumulative pore volumes in the range of the pore radius of 100 nm to 1500 nm. Had inflection points.
- the volume capacity density (mAh / cm 3) was 420 mAh / cm 3.
- Examples 1 to 4 to which the present invention was applied had higher volume capacity density than Comparative Examples 1 to 4 to which the present invention was not applied.
- FIG. 5 shows the particle size distribution measurement results of Examples 1 and 2 and Comparative Examples 1 and 3.
- Examples 1 and 2 peaks attributable to the mixed metal oxides could be confirmed.
- Comparative Examples 1 and 3 only one peak was confirmed.
- a positive electrode active material for a lithium secondary battery having a high volumetric capacity density can be provided.
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Abstract
Description
本願は、2017年3月31日に、日本に出願された特願2017-072869号に基づき優先権を主張し、その内容をここに援用する。
しかしながら、前記特許文献1に記載のようなリチウム二次電池用正極活物質においては、体積容量密度を向上させる観点から改良の余地がある。
本発明は上記事情に鑑みてなされたものであって、体積容量密度が高いリチウム二次電池用正極活物質、前記リチウム二次電池用正極活物質を用いたリチウム二次電池用正極及び前記リチウム二次電池用正極を有するリチウム二次電池を提供することを課題とする。
[1]リチウムイオンをドープ及び脱ドープ可能な一次粒子が凝集してなる二次粒子を含む活物質粉末であるリチウム二次電池用正極活物質であって、粒子内部に空隙を有する二次粒子を含み、前記リチウム二次電池用正極活物質の水銀圧入法によって測定された細孔分布において、下記要件(1)及び(2)を満たすリチウム二次電池用正極活物質。
(1)細孔半径が10nm以上200nm以下の範囲に細孔ピークを有する。
(2)細孔半径が10nm以上3000nm以下の範囲における、累積細孔容積の変曲点を3つ以上有する。
[2]前記要件(2)において、10nm以上1500nm以下の範囲に累積細孔容積の3つの変曲点を有する[1]に記載のリチウム二次電池用正極活物質。
[3]前記リチウム二次電池用正極活物質が、以下組成式(I)で表される、[1]又は[2]に記載のリチウム二次電池用正極活物質。
Li[Lix(Ni(1-y-z-w)CoyMnzMw)1-x]O2 (I)
(ただし、MはFe、Cu、Ti、Mg、Al、W、B、Mo、Nb、Zn、Sn、Zr、Ga及びVからなる群より選択される1種以上の金属元素であり、0≦x≦0.2、0<y≦0.4、0<z≦0.4、0≦w≦0.1を満たす。)
[4]前記二次粒子の平均粒子径が、1μm以上30μm以下である、[1]~[3]のいずれか1つに記載のリチウム二次電池用正極活物質。
[5]前記活物質粉末は、平均二次粒子径の異なる二種類以上の二次粒子を含む、[1]~[4]のいずれか1つに記載のリチウム二次電池用正極活物質。
[6]前記活物質粉末は、平均二次粒子径が1μm以上10μm以下の二次粒子Aと、平均二次粒子径が5μm以上30μm以下の二次粒子Bとを含み、前記二次粒子Aと前記二次粒子Bの混合割合(質量比)が、20:80~50:50である[5]に記載のリチウム二次電池用正極活物質。
[7][1]~[6]のいずれか1つに記載のリチウム二次電池用正極活物質を有するリチウム二次電池用正極。
[8][7]に記載のリチウム二次電池用正極を有するリチウム二次電池。
本発明の一態様におけるリチウム二次電池用正極活物質は、リチウムイオンをドープ及び脱ドープ可能な一次粒子が凝集してなる二次粒子を含む活物質粉末を含有するリチウム二次電池用正極活物質である。また、本発明の一態様におけるリチウム二次電池用正極活物質は、粒子内部に空隙を有する二次粒子を含み、水銀圧入法によって測定された細孔分布において、下記要件(1)及び(2)を満たす。
(1)細孔半径が10nm以上200nm以下の範囲に細孔ピークを有する。
(2)細孔半径が10nm以上3000nm以下の範囲における、累積細孔容積の変曲点を3つ以上有する。
ここで粒子内部に空隙を有する二次粒子とは、二次粒子を形成する複数の一次粒子間に位置する空隙であり、二次粒子表面と二次粒子内部とが連通する空隙(以下、「二次粒子内微細空隙」と記載することがある)を有する二次粒子であることを意味する。
本実施形態のリチウム二次電池用正極活物質は、細孔半径が10nm以上200nm以下の範囲に細孔ピークを有する。この範囲の細孔ピークは、二次粒子の有する、二次粒子内微細空隙に由来する細孔ピークであり、二次粒子内微細空隙を有する二次粒子を含むことを意味する。
ここで細孔ピークとは、水銀圧入法にて測定された細孔分布曲線における極大を含むピークを意味する。
本実施形態のリチウム二次電池用正極活物質は、細孔半径が10nm以上3000nm以下の範囲における、累積細孔容積の変曲点を3つ以上有する。
本実施形態において、「変曲点」とは、二階の導関数の符号が変化する点を意味する。
まず、細孔分布測定により、細孔半径を対数軸で横軸としたときに、細孔半径が0.0018μm~246.9μmの間で等間隔となるように71点のデータを測定する。
各データプロットから累積細孔容積を算出し、二階の導関数の符号が変化する点を変曲点として計上する。
本実施形態においては、細孔分布測定は複数回実施し、再現性の良く変曲点が現れることを確認することが好ましい。また、再現性がない箇所に関しては、ノイズピークに由来すると判断し、変曲点とは計上しないこととする。
上記要件(1)の細孔ピーク、及び、(2)の累積細孔容積は、水銀圧入法によって得られた細孔分布から算出できる。
本実施形態において、水銀圧入法による細孔分布測定は下記のような方法で行う。
ここで、細孔の形状を円筒状と仮定し、水銀に加えられた圧力をP、その細孔径(細孔直径)をD、水銀の表面張力をσ、水銀と試料との接触角をθとすると、細孔径は、下記式(A)で表される。
D=-4σ×cosθ/P ・・・(A)
V=πD2L/4 ・・・(B)
円筒の側面積S=πDLのため、S=4V/Dと表すことができる。ここで、ある細孔径の範囲での体積増加dVが、あるひとつの平均細孔径を有する円筒細孔によるものと仮定すれば、その区間で増加した比表面積はdA=4dV/Dav (Davは平均細孔径)と求めることができ、細孔比表面積ΣAが算出される。なお、水銀圧入法による細孔径のおおよその測定限界は、下限が約2nm、上限が約200μmである。水銀圧入法による測定は、水銀ポロシメータ等の装置を用いて行うことができる。水銀ポロシメータの具体例としては、オートポアIII9420(Micromeritics 社製)等が挙げられる。測定条件としては、測定温度25℃下において、測定圧力が0.432psia~59245.2psia(2.98kPaA~408.391MPaA)の範囲、水銀の表面張力が480dynes/cm、水銀と試料の接触角が140°の条件が挙げられる。
Li[Lix(Ni(1-y-z-w)CoyMnzMw)1-x]O2 (I)
(ただし、MはFe、Cu、Ti、Mg、Al、W、B、Mo、Nb、Zn、Sn、Zr、Ga及びVからなる群より選択される1種以上の金属元素であり、0≦x≦0.2、0<y≦0.4、0≦z≦0.4、0≦w≦0.1を満たす。)
xの上限値と下限値は任意に組み合わせることができる。例えば、xは0を超え0.1以下であることが好ましく、0.01以上0.08以下であることがより好ましく、0.02以上0.06以下であることがさらに好ましい。
yの上限値と下限値は任意に組み合わせることができる。例えば、yは0.005以上0.35以下であることが好ましく、0.01以上0.33以下であることがより好ましく、0.05以上0.33以下であることがさらに好ましい。
zの上限値と下限値は任意に組み合わせることができる。例えば、zは0以上0.4以下であることが好ましく、0.03以上0.38以下であることがより好ましく、0.1以上0.35以下であることがさらに好ましい。
wの上限値と下限値は任意に組み合わせることができる。例えば、0を超え、0.09以下であることが好ましく、0.0005以上0.08以下であることがより好ましく、0.001以上0.07以下であることがさらに好ましい。
平均二次粒子径の上限値と下限値は任意に組み合わせることができる。例えば、リチウム二次電池用正極活物質の平均二次粒子径は、1μm以上30μm以下であることが好ましく、4μm以上20μm以下であることがより好ましく、5μm以上10μm以下であることがさらに好ましい。
本発明において、リチウム二次電池用正極活物質粉末の「平均二次粒子径」とは、前述のレーザー回折散乱法によって測定される値を指す。
リチウム二次電池用正極活物の結晶構造は、層状構造であり、六方晶型の結晶構造又は単斜晶型の結晶構造であることがより好ましい。
本発明のリチウム二次電池用正極活物質を製造するにあたって、まず、リチウム以外の金属、すなわち、Ni、Co及びMnから構成される必須金属を含み、並びに、所望によりFe、Cu、Ti、Mg、Al、W、B、Mo、Nb、Zn、Sn、Zr、Ga及びVのうちいずれか1種以上の任意金属を含む金属複合化合物を調製し、当該金属複合化合物を適当なリチウム化合物と混合した後、得られる混合物を焼成することが好ましい。金属複合化合物としては、金属複合水酸化物又は金属複合酸化物が好ましい。以下に、正極活物質の製造方法の一例を、金属複合化合物の製造工程と、リチウム金属複合酸化物の製造工程とに分けて説明する。
金属複合化合物は、通常、公知のバッチ共沈殿法又は連続共沈殿法により製造することが可能である。以下、金属として、ニッケル、コバルト及びマンガンを含む金属複合水酸化物を例に、その製造方法を詳述する。
また、溶媒として水が使用される。
なお、上記の例では、ニッケルコバルトマンガン金属複合水酸化物を製造しているが、ニッケルコバルトマンガン金属複合酸化物を調製してもよい。
上記金属複合酸化物又は水酸化物を乾燥した後、リチウム化合物と混合する。乾燥条件は、特に制限されないが、例えば、金属複合酸化物又は水酸化物が酸化及び還元されない条件(すなわち酸化物が酸化物のまま維持される、水酸化物が水酸化物のまま維持される条件)、金属複合水酸化物が酸化される条件(すなわち水酸化物が酸化物に酸化される条件)、金属複合酸化物が還元される条件(すなわち酸化物が水酸化物に還元される条件)のいずれの条件でもよい。酸化及び還元がされない条件のためには、窒素、ヘリウム及びアルゴン等の不活性ガスを使用すれば良い。水酸化物が酸化される条件では、酸素又は空気を使用すれば良い。また、金属複合酸化物が還元される条件としては、不活性ガス雰囲気下、ヒドラジン、亜硫酸ナトリウム等の還元剤を使用すれば良い。リチウム化合物としては、炭酸リチウム、硝酸リチウム、硫酸リチウム、酢酸リチウム、水酸化リチウム、水酸化リチウム水和物、酸化リチウム、塩化リチウム、及びフッ化リチウムのうち何れか一つ、又は、二つ以上を混合して使用することができる。
金属複合酸化物又は水酸化物の乾燥後に、適宜分級を行っても良い。以上のリチウム化合物と金属複合酸化物又は水酸化物とは、最終目的物の組成比を勘案して用いられる。例えば、ニッケルコバルトマンガン金属複合水酸化物を用いる場合、リチウム化合物と当該金属複合水酸化物は、LixNi(1-y-z)CoyMnzO2(式中、0≦x≦0.2、0<y≦0.4、0≦z≦0.4)の組成比に対応する割合で用いられる。ニッケルコバルトマンガン金属複合水酸化物及びリチウム化合物の混合物を焼成することによって、リチウム-ニッケルコバルトマンガン金属複合酸化物が得られる。なお、焼成には、所望の組成に応じて乾燥空気、酸素雰囲気、不活性雰囲気等が用いられ、必要ならば複数の加熱工程が実施される。
昇温開始から焼成温度に達するまでの時間は、0.5時間以上20時間以下であることが好ましい。昇温開始から焼成温度に達するまでの時間がこの範囲であると、より均一なリチウムニッケル複合酸化物を得ることができる。また、焼成温度に達してから温度保持が終了するまでの時間は、0.5時間以上20時間以下であることが好ましい。焼成温度に達してから温度保持が終了するまでの時間がこの範囲であると、結晶の発達がより良好に進行し、電池性能をより向上させることができる。
本実施形態においては、上記の方法により得られたリチウム金属複合酸化物のうち、二次粒子内微細空隙を有し、かつ、平均二次粒子径が小さいリチウム金属複合酸化物と平均二次粒子径が大きいリチウム金属複合酸化物とを混合することによって、前記要件(1)及び(2)を満たすリチウム二次電池用正極活物質を得ることができる。
また、本実施形態においては、上記の方法により得られたリチウム金属複合酸化物のうち、二次粒子の粒度分布が広い材料(粒度分布がブロードである材料)を用いることにより、要件(1)及び要件(2)を本発明の所望の範囲に制御してもよい。 粒度分布を広くするためには、例えば、金属複合水酸化物の製造工程において、反応pHを上下させることで結晶が成長しやすい状態と核発生しやすい状態が時間的に変化するため、粒度分布が広いリチウム金属複合酸化物を得ることができる。
次いで、リチウム二次電池の構成を説明しながら、本発明の二次電池用正極活物質を、リチウム二次電池の正極活物質として用いた正極、及びこの正極を有するリチウム二次電池について説明する。
(正極)
本実施形態の正極は、まず正極活物質、導電材及びバインダーを含む正極合剤を調整し、正極合剤を正極集電体に担持させることで製造することができる。
本実施形態の正極が有する導電材としては、炭素材料を用いることができる。炭素材料として黒鉛粉末、カーボンブラック(例えばアセチレンブラック)、繊維状炭素材料などを挙げることができる。カーボンブラックは、微粒で表面積が大きいため、少量を正極合剤中に添加することにより正極内部の導電性を高め、充放電効率及び出力特性を向上させることができるが、多く入れすぎるとバインダーによる正極合剤と正極集電体との結着力、及び正極合剤内部の結着力がいずれも低下し、かえって内部抵抗を増加させる原因となる。
本実施形態の正極が有するバインダーとしては、熱可塑性樹脂を用いることができる。
この熱可塑性樹脂としては、ポリフッ化ビニリデン(以下、PVdFということがある。)、ポリテトラフルオロエチレン(以下、PTFEということがある。)、四フッ化エチレン・六フッ化プロピレン・フッ化ビニリデン系共重合体、六フッ化プロピレン・フッ化ビニリデン系共重合体、四フッ化エチレン・パーフルオロビニルエーテル系共重合体などのフッ素樹脂;ポリエチレン、ポリプロピレンなどのポリオレフィン樹脂;を挙げることができる。
本実施形態の正極が有する正極集電体としては、Al、Ni、ステンレスなどの金属材料を形成材料とする帯状の部材を用いることができる。なかでも、加工しやすく、安価であるという点でAlを形成材料とし、薄膜状に加工したものが好ましい。
(負極)
本実施形態のリチウム二次電池が有する負極は、正極よりも低い電位でリチウムイオンのドープかつ脱ドープが可能であればよく、負極活物質を含む負極合剤が負極集電体に担持されてなる電極、及び負極活物質単独からなる電極を挙げることができる。
負極が有する負極活物質としては、炭素材料、カルコゲン化合物(酸化物、硫化物など)、窒化物、金属又は合金で、正極よりも低い電位でリチウムイオンのドープかつ脱ドープが可能な材料が挙げられる。
負極が有する負極集電体としては、Cu、Ni、ステンレスなどの金属材料を形成材料とする帯状の部材を挙げることができる。なかでも、リチウムと合金を作り難く、加工しやすいという点で、Cuを形成材料とし、薄膜状に加工したものが好ましい。
本実施形態のリチウム二次電池が有するセパレータとしては、例えば、ポリエチレン、ポリプロピレンなどのポリオレフィン樹脂、フッ素樹脂、含窒素芳香族重合体などの材質からなる、多孔質膜、不織布、織布などの形態を有する材料を用いることができる。また、これらの材質を2種以上用いてセパレータを形成してもよいし、これらの材料を積層してセパレータを形成してもよい。
本実施形態のリチウム二次電池が有する電解液は、電解質及び有機溶媒を含有する。
(1)リチウム二次電池用正極活物質の評価
・平均二次粒子径の測定
測定するリチウム二次電池用正極活物質粉末0.1gを、0.2質量%ヘキサメタリン酸ナトリウム水溶液50mlに投入し、前記粉末を分散させた分散液を得た。得られた分散液についてレーザー回折散乱粒度分布測定装置(株式会社堀場製作所製、型番:LA-950)を用いて、粒度分布を測定し、体積基準の累積粒度分布曲線を得た。得られた累積粒度分布曲線において、50%累積時の微小粒子側から見た粒子径(D50)の値を、平均二次粒子径とした。
測定するリチウム二次電池用正極活物質粉末0.1gを、0.2質量%ヘキサメタリン酸ナトリウム水溶液50mlに投入し、前記粉末を分散させた分散液を得た。得られた分散液についてレーザー回折散乱粒度分布測定装置(株式会社堀場製作所製、型番:LA-950)を用いて、粒度分布を測定した。
後述の方法で製造されるリチウム二次電池用正極活物質粉末の組成分析は、得られたリチウム二次電池用正極活物質の粉末を塩酸に溶解させた後、誘導結合プラズマ発光分析装置(エスアイアイ・ナノテクノロジー株式会社製、SPS3000)を用いて行った。
前処理としてリチウム二次電池用正極活物質を120℃、4時間、恒温乾燥した。水銀ポロシメータ(Micromeritics 社製、オートポアIII9420)を用いて、下記の測定条件にて細孔分布測定を実施した。なお水銀の表面張力は480dynes/cm、水銀と試料の接触角は140°とした。
測定温度 : 25℃
測定圧力 : 0.432psia~59245.2psia
制限性がない箇所に関しては、ノイズピークに由来すると判断し、変曲点とは計上しないこととした。
後述する製造方法で得られるリチウム二次電池用正極活物質と導電材(アセチレンブラック)とバインダー(PVdF)とを、リチウム二次電池用正極活物質:導電材:バインダー=92:5:3(質量比)の組成となるように加えて混練することにより、ペースト状の正極合剤を調製した。正極合剤の調製時には、N-メチル-2-ピロリドンを有機溶媒として用いた。
次に、負極活物質として人造黒鉛(日立化成株式会社製、MAGD)と、バインダーとしてCMC(第一工業薬製株式会社製)とSBR(日本エイアンドエル株式会社製)とを、負極活物質:CMC:SRR=98:1:1(質量比)の組成となるように加えて混練することにより、ペースト状の負極合剤を調製した。負極合剤の調製時には、溶媒としてイオン交換水を用いた。
以下の操作を、アルゴン雰囲気のグローブボックス内で行った。
「(2)リチウム二次電池用正極の作製」で作製したリチウム二次電池用正極を、コイン型電池R2032用のパーツ(宝泉株式会社製)の下蓋にアルミ箔面を下に向けて置き、その上に積層フィルムセパレータ(ポリエチレン製多孔質フィルムの上に、耐熱多孔層を積層(厚み16μm))を置いた。ここに電解液を300μl注入した。電解液は、エチレンカーボネート(以下、ECと称することがある。)とジメチルカーボネート(以下、DMCと称することがある。)とエチルメチルカーボネート(以下、EMCと称することがある。)の30:35:35(体積比)混合液に、LiPF6を1.0mol/lとなるように溶解したもの(以下、LiPF6/EC+DMC+EMCと表すことがある。)を用いた。
次に、負極として金属リチウムを用いて、前記負極を積層フィルムセパレータの上側に置き、ガスケットを介して上蓋をし、かしめ機でかしめてリチウム二次電池(コイン型ハーフセルR2032。以下、「ハーフセル」と称することがある。)を作製した。
「(4)リチウム二次電池(コイン型ハーフセル)の作製」で作製したハーフセルを用いて、以下に示す条件で充放電試験を実施し、体積容量密度を算出した。
<充放電試験>
試験温度25℃
充電最大電圧4.3V、充電時間6時間、充電電流1.0CA、定電流定電圧充電
放電最小電圧2.5V、放電時間5時間、放電電流1.0CA、定電流放電
<体積容量密度の算出>
1.0Cまで放電した放電容量と、正極材の単位体積あたりの質量とから、下記の計算式に基づいて体積容量密度を求めた。
体積容量密度(mAh/cm3)=正極材の比容量(mAh/g)×電極密度(g/cm3)
1.リチウムニッケルコバルトマンガン金属複合酸化物1の製造
攪拌器及びオーバーフローパイプを備えた反応槽内に水を入れた後、水酸化ナトリウム水溶液を添加し、液温を30℃に保持した。
1.リチウムニッケルコバルトマンガン金属複合酸化物2の製造
攪拌器及びオーバーフローパイプを備えた反応槽内に水を入れた後、水酸化ナトリウム水溶液を添加し、液温を60℃に保持した。
1.リチウムニッケルコバルトマンガン複合酸化物3の製造
攪拌器及びオーバーフローパイプを備えた反応槽内に水を入れた後、水酸化ナトリウム水溶液を添加し、液温を50℃に保持した。
1.リチウムニッケルコバルトマンガン複合酸化物4の製造
攪拌器及びオーバーフローパイプを備えた反応槽内に水を入れた後、水酸化ナトリウム水溶液を添加し、液温を50℃に保持した。
1.リチウム二次電池用正極活物質1の製造
二次粒子Aとして製造例3で作製したリチウムニッケルコバルトマンガン複合酸化物3、二次粒子Bとして製造例2で作製したリチウムニッケルコバルトマンガン複合酸化物2を用い、二次粒子Aと二次粒子Bとの混合比を25/75で混合し、リチウム二次電池用正極活物質1を得た。
リチウム二次電池用正極活物質1の組成分析を行い、組成式(I)に対応させたところ、x=0.029、y=0.207、z=0.239、w=0であった。平均二次粒子径は、9.6μmであった。
また、体積容量密度(mAh/cm3)が457mAh/cm3であった。
1.リチウム二次電池用正極活物質2の製造
二次粒子Aとして製造例3で作製したリチウムニッケルコバルトマンガン複合酸化物3、二次粒子Bとして製造例2で作製したリチウムニッケルコバルトマンガン複合酸化物2を用い、二次粒子Aと二次粒子Bとの混合比を50/50で混合し、リチウム二次電池用正極活物質2を得た。
リチウム二次電池用正極活物質1の組成分析を行い、組成式(I)に対応させたところ、x=0.031、y=0.208、z=0.340、w=0であった。平均二次粒子径は、7.6μmであった。
また、体積容量密度(mAh/cm3)が455mAh/cm3であった。
1.リチウム二次電池用正極活物質3の製造
二次粒子Aとして製造例3で作製したリチウムニッケルコバルトマンガン複合酸化物3、二次粒子Bとして製造例4で作製したリチウムニッケルコバルトマンガン複合酸化物2を用い、二次粒子Aと二次粒子Bとの混合比を25/75で混合し、リチウム二次電池用正極活物質3を得た。
2.リチウム二次電池用正極活物質3の評価
リチウム二次電池用正極活物質3の組成分析を行い、組成式(I)に対応させたところ、x=0.038、y=0.208、z=0.244、w=0であった。平均二次粒子径は、7.6μmであった。
また、体積容量密度(mAh/cm3)が434mAh/cm3であった。
1.リチウム二次電池用正極活物質4の製造
二次粒子Aとして製造例3で作製したリチウムニッケルコバルトマンガン複合酸化物3、二次粒子Bとして製造例4で作製したリチウムニッケルコバルトマンガン複合酸化物2を用い、二次粒子Aと二次粒子Bとの混合比を50/50で混合し、リチウム二次電池用正極活物質4を得た。
リチウム二次電池用正極活物質4の組成分析を行い、組成式(I)に対応させたところ、x=0.037、y=0.209、z=0.243、w=0であった。平均二次粒子径は、6.3μmであった。
また、体積容量密度(mAh/cm3)が438mAh/cm3であった。
1.リチウム二次電池用正極活物質5の製造
製造例2で作製したリチウムニッケルコバルトマンガン複合酸化物2をリチウム二次電池用正極活物質5とした。
リチウム二次電池用正極活物質5の組成分析を行い、組成式(I)に対応させたところ、x=0.027、y=0.206、z=0.237、w=0であった。平均二次粒子径は、11.6μmであった。
また、体積容量密度(mAh/cm3)が432mAh/cm3であった。
1.リチウム二次電池用正極活物質6の製造
製造例4で作製したリチウムニッケルコバルトマンガン複合酸化物4をリチウム二次電池用正極活物質6とした。
2.リチウム二次電池用正極活物質6の評価
リチウム二次電池用正極活物質6の組成分析を行い、組成式(I)に対応させたところ、x=0.034、y=0.208、z=0.245、w=0であった。平均二次粒子径は、8.9μmであった。
また、体積容量密度(mAh/cm3)が417mAh/cm3であった。
1.リチウム二次電池用正極活物質7の製造
製造例3で作製したリチウムニッケルコバルトマンガン複合酸化物3をリチウム二次電池用正極活物質7とした。
リチウム二次電池用正極活物質7の組成分析を行い、組成式(I)に対応させたところ、x=0.035、y=0.210、z=0.242、w=0であった。平均二次粒子径は、3.6μmであった。
また、体積容量密度(mAh/cm3)が431mAh/cm3であった。
1.リチウム二次電池用正極活物質8の製造
二次粒子Aとして製造例1で作製したリチウムニッケルコバルトマンガン複合酸化物3、二次粒子Bとして製造例2で作製したリチウムニッケルコバルトマンガン複合酸化物2を用い、二次粒子Aと二次粒子Bとの混合比を25/75で混合し、リチウム二次電池用正極活物質8を得た。
リチウム二次電池用正極活物質8の組成分析を行い、組成式(I)に対応させたところ、x=0.028、y=0.207、z=0.237、w=0であった。平均二次粒子径は、9.9μmであった。
また、体積容量密度(mAh/cm3)が420mAh/cm3であった。
図5に、実施例1~2、比較例1及び3の粒度分布測定の結果を記載する。実施例1~2は、混合した金属酸化物それぞれに起因するピークが確認できた。これに対し、比較例1及び3は、ピークは1つのみ確認された。
Claims (7)
- リチウムイオンをドープ及び脱ドープ可能な一次粒子が凝集してなる二次粒子を含む活物質粉末を含有するリチウム二次電池用正極活物質であって、粒子内部に空隙を有する二次粒子を含み、前記リチウム二次電池用正極活物質の水銀圧入法によって測定された細孔分布において、下記要件(1)及び(2)を満たすリチウム二次電池用正極活物質。
(1)細孔半径が10nm以上200nm以下の範囲に細孔ピークを有する。
(2)細孔半径が10nm以上3000nm以下の範囲における、累積細孔容積の変曲点を3つ以上有する。 - 前記要件(2)において、10nm以上1500nm以下の範囲に累積細孔容積の3つの変曲点を有する請求項1に記載のリチウム二次電池用正極活物質。
- 前記リチウム二次電池用正極活物質が、以下組成式(I)で表される、請求項1又は2に記載のリチウム二次電池用正極活物質。
Li[Lix(Ni(1-y-z-w)CoyMnzMw)1-x]O2 (I)
(ただし、MはFe、Cu、Ti、Mg、Al、W、B、Mo、Nb、Zn、Sn、Zr、Ga及びVからなる群より選択される1種以上の金属元素であり、0≦x≦0.2、0<y≦0.4、0<z≦0.4、0≦w≦0.1を満たす。) - 前記二次粒子の平均粒子径が、1μm以上30μm以下である、請求項1~3のいずれか1項に記載のリチウム二次電池用正極活物質。
- 前記活物質粉末は、平均二次粒子径の異なる二種類以上の二次粒子を含む、請求項1~4のいずれか1項に記載のリチウム二次電池用正極活物質。
- 前記活物質粉末は、平均二次粒子径が1μm以上10μm以下の二次粒子Aと、平均二次粒子径が5μm以上30μm以下の二次粒子Bとを含み、前記二次粒子Aと前記二次粒子Bの混合割合(質量比)が、20:80~50:50である請求項5に記載のリチウム二次電池用正極活物質。
- 請求項1~6のいずれか1項に記載のリチウム二次電池用正極活物質を有するリチウム二次電池用正極。
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