JP2013182757A - Positive electrode active material for lithium secondary battery, manufacturing method thereof and lithium secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide: a positive electrode active material for a lithium secondary battery having high filling density and allowing improvement in safety property of a lithium secondary battery and also in cycle characteristics and operation voltage; an industrially advantageous manufacturing method thereof; and a lithium secondary battery using it, having a high capacity per volume and being excellent in safety property, cycle characteristics and also operation voltage.SOLUTION: A positive electrode active material for a lithium secondary battery is composed of a lithium cobalt composite oxide containing an Sr atom and a Ti atom which is obtained by calcination of a mixture comprising a lithium compound, a cobalt compound, and a strontium titanate.

Description

  The present invention relates to a positive electrode active material for a lithium secondary battery, a manufacturing method thereof, and a lithium secondary battery.

  In recent years, as home appliances are rapidly becoming portable and cordless, lithium ion secondary batteries have been put into practical use as power sources for small electronic devices such as laptop computers, mobile phones, and digital cameras. With regard to this lithium ion secondary battery, research and development on lithium cobalt composite oxide has been active since 1980 when Mizushima et al. Reported that lithium cobalt oxide was useful as a positive electrode active material for lithium ion secondary batteries. It is advanced to.

 With higher functionality of electronic devices, further increase in battery capacity is required. In order to increase the capacity of a battery having a predetermined volume, it has been proposed to use a positive electrode active material having a high packing density as a positive electrode.

  As a positive electrode active material having a high packing density, for example, in Patent Document 1 below, a lithium-cobalt composite oxide containing lithium transition metal composite oxide containing at least one of strontium, tungsten, and antimony and molybdenum is used. It has been proposed to be used as a positive electrode active material. Patent Document 2 below discloses a lithium transition metal composite oxide obtained by mixing and firing at least one compound of molybdenum, vanadium, tungsten, boron, and fluorine, a lithium raw material, and a transition metal raw material as a positive electrode active material. It has been proposed to be used as

  Patent Document 3 below proposes a positive electrode active material for a lithium secondary battery in which a lithium composite oxide is coated with strontium titanate. However, the positive electrode active material obtained in Patent Document 3 has a high packing density. Things are hard to get.

JP 2007-299668 A JP-A-2005-251716 JP 2003-17053 A

  In recent years, in addition to increasing the capacity of lithium secondary batteries, it has been desired to develop positive electrode active materials in consideration of safety.

  Accordingly, an object of the present invention is to provide a positive electrode active material for a lithium secondary battery, which has a high packing density and can improve the safety, further cycle characteristics and operating voltage of the lithium secondary battery, and its industrially advantageous production. It is an object of the present invention to provide a lithium secondary battery having a high capacity per volume using the method and excellent safety, cycle characteristics and operating voltage.

  As a result of intensive studies in view of the above circumstances, the present inventors have obtained a lithium cobalt composite oxide containing Sr atoms and Ti atoms obtained by firing a mixture containing a lithium compound, a cobalt compound, and strontium titanate. The lithium secondary battery using the lithium cobalt composite oxide as a positive electrode active material has a high capacity per volume and excellent safety, cycle characteristics and operating voltage. The headline and the present invention were completed.

  That is, the first invention to be provided by the present invention includes a lithium cobalt composite oxide containing Sr atoms and Ti atoms obtained by firing a mixture containing a lithium compound, a cobalt compound, and strontium titanate. This is a positive electrode active material for a lithium secondary battery.

  The second invention to be provided by the present invention is a raw material mixing step for obtaining a mixture containing a lithium compound, a cobalt compound, and strontium titanate, and then firing the mixture to produce a lithium cobalt composite oxide. It is a manufacturing method of the positive electrode active material for lithium secondary batteries characterized by including a process.

  A third invention to be provided by the present invention is a lithium secondary battery using the positive electrode active material for a lithium secondary battery according to the first invention.

The positive electrode active material for a lithium secondary battery of the present invention has a high packing density, and can improve the safety, cycle characteristics, operating voltage, and capacity per volume of the lithium secondary battery.
Moreover, according to the manufacturing method of this invention, this positive electrode active material for lithium secondary batteries can be provided by an industrially advantageous method.

It is a figure showing the quantity of the strontium atom in the depth direction of the positive electrode active material obtained in Example 3 and Example 4. FIG. It is a figure showing the quantity of the titanium atom in the depth direction of the positive electrode active material obtained in Example 3 and Example 4. FIG. The figure which shows the differential calorie | heat amount change of the positive electrode active material which extracted lithium from the positive electrode active material obtained in Example 7, Example 9, and Comparative Example 1, and was deintercalated. The figure which shows the differential calorie | heat amount change of the positive electrode active material which extracted lithium from the positive electrode active material obtained in Example 10, Example 11, Example 13, and the comparative example 1, and was deintercalated.

Hereinafter, the present invention will be described based on preferred embodiments.
The lithium secondary battery positive electrode active material according to the present invention (hereinafter sometimes simply referred to as “positive electrode active material”) is basically obtained by firing a mixture containing a lithium compound, a cobalt compound and strontium titanate. It consists of a lithium cobalt composite oxide containing Sr atoms and Ti atoms produced (hereinafter sometimes simply referred to as “lithium cobalt composite oxide”).

  The added amount of strontium titanate is 0.01 to 2 mol%, preferably 0.05 to 1 mol%, with respect to the produced lithium cobalt composite oxide. A lithium secondary battery using a lithium cobalt composite oxide as a positive electrode active material is preferable from the viewpoint of high capacity per volume and excellent cycle characteristics, operating voltage, and safety. The reason why the amount of strontium titanate added is within the above range is that when the amount of strontium titanate added is less than 0.01 mol%, the tap density of the positive electrode active material decreases, and the safety and cycle of the lithium secondary battery This is because the effect of improving the characteristics and operating voltage tends to be low, while when the amount of strontium titanate added is greater than 2 mol%, the capacity per weight tends to decrease.

  In addition to strontium titanate, the lithium cobalt composite oxide of the present invention can further contain Sr atoms and Ti atoms in addition to strontium titanate, but Sr atoms derived from strontium titanate The content is 0.01 to 1.80 mass%, preferably 0.04 to 0.90 mass% in terms of Sr atoms, and the content of Ti atoms derived from strontium titanate is 0.005 to 1 in terms of Ti atoms. The mass density, preferably 0.02 to 0.5 mass%, increases the packing density of the obtained lithium cobalt composite oxide and can provide a high capacity lithium secondary battery. This is preferable from the viewpoint of further improving the safety, cycle characteristics and operating voltage of the secondary battery.

One of the characteristics of the positive electrode active material according to the present invention is that Sr atoms derived from strontium titanate to be added are present at least on the particle surface of the lithium cobalt composite oxide.
According to the present inventors, by firing a mixture containing strontium titanate, Sr atoms exist both inside and on the particle surface of the lithium cobalt composite oxide, and Sr existing on the particle surface. It has been found that atoms exist as strontium compounds such as SrO, SrTiO ₃ , Sr ₃ Ti ₂ O ₇ , Sr ₄ Ti ₃ O _{10, and the} like. The added Sr atom particularly contributes to the improvement of the tap density. In addition, the synergistic effect of the strontium compound present on the particle surface, Sr atoms present inside the particles, and Ti atoms also contributes to the stabilization of the crystals both on the crystal surface and inside the lithium composite oxide. Therefore, the lithium secondary battery using the lithium cobalt composite oxide of the present invention as the positive electrode active material has excellent battery performance, particularly high capacity, safety, cycle performance, and operating voltage. Have guessed.

Sr atoms present on the particle surface of the lithium cobalt composite oxide include soluble strontium compounds such as SrO and hardly soluble strontium compounds such as SrTiO ₃ , Sr ₃ Ti ₂ O ₇ , and Sr ₄ Ti ₃ O _10. The Sr atoms present on the particle surface can be confirmed by the presence of at least a soluble strontium compound such as SrO.
The content of the soluble strontium compound is 0.002 to 0.25% by mass, preferably 0.005 to 0.1% by mass as Sr atoms, and the lithium secondary battery has a high capacity and excellent safety. It is preferable from the viewpoint of becoming a waste.

  In the present invention, the amount of the soluble strontium compound present on the particle surface of the lithium cobalt composite oxide is the amount of Sr that elutes when 5 g of lithium cobalt composite oxide is left in 50 ml of pure water at 25 ° C. for 5 minutes with stirring. Is determined by inductively coupled plasma optical emission spectrometer (ICP-AES).

  The amount of the soluble strontium compound contained in the lithium cobalt composite oxide is 2.0 to 30 with respect to the total amount of Sr atoms contained in the lithium cobalt composite oxide as Sr atoms in the soluble strontium compound. % By mass, preferably 5 to 25% by mass.

On the other hand, the Ti atom contained in the lithium cobalt composite oxide contributes to the improvement of the cycle characteristics of the lithium secondary battery, and further the operating voltage. The present inventors speculate that there are compounds existing as compounds such as SrTiO ₃ , Sr ₃ Ti ₂ O ₇ , and Sr ₄ Ti ₃ O _{10 on the} particle surface and those existing inside the particle.

It is presumed that Sr atoms and Ti atoms contained in the lithium cobalt composite oxide have an influence on the crystal structure of pure LiCoO ₂ . That is, the C-axis lattice constant of pure LiCoO ₂ is 14.050 to 14.053 angstroms, whereas the positive electrode active material of the present invention has a C-axis lattice constant of 14.053 to 14.065 angstroms. , Preferably 14.055 to 14.062 angstroms, which is larger than the lattice constant of the C axis of pure LiCoO ₂ .
The present inventors presume that this is an influence of Sr atoms and Ti atoms existing inside the particles of the lithium cobalt composite oxide.

The positive electrode active material according to the present invention has a tap density of 2.60 g / ml or more, preferably 2.6 to 3.1 g / ml. One of the characteristics is that the tap density is larger than that of pure LiCoO _2. It is. Since the positive electrode active material of the present invention has this large tap density, the packing density is increased and the capacity per volume of the lithium secondary battery can be increased.

  The tap density indicates a filling characteristic in a state where the positive electrode active material sample is naturally mixed without being particularly pressurized, and a sample of 50 to 70 g is placed in a graduated cylinder, Automatic T. It is set in the D measuring device, and the measurement conditions are determined as 500 times tapping, 3.2 mm tapping height, and 200 times / minute tapping pace (according to ASTM: B527-93, 85).

  In the positive electrode active material of the present invention, as other preferable physical properties, the average particle size determined by the laser light diffraction / scattering method is 10 to 30 μm, preferably 10 to 25 μm. From the viewpoint of the capacity of the lithium secondary battery, cycle characteristics, rate characteristics, safety, and slurry stability when the positive electrode active material is made into a paint.

The positive electrode active material of the present invention has a BET specific surface area of 0.05 to ¹ m ² / g, preferably 0.1 to 0.3 m ² / g, further improving the safety of the lithium secondary battery, Further, it is preferable from the viewpoint of cycle characteristics, rate characteristics, and slurry stability when the positive electrode active material is made into a paint.

  In the positive electrode active material of the present invention, the remaining lithium carbonate is 0.30% by mass or less, preferably 0.25% by mass or less, and the remaining lithium hydroxide is 0.15% by mass or less, preferably 0.8%. It is 10 mass% or less. When the remaining lithium carbonate and lithium hydroxide are in the above ranges, it is preferable from the viewpoint of the cycle characteristics of the lithium secondary battery and the slurry stability when the positive electrode active material is made into a paint.

  The positive electrode active material of the present invention further includes Mn, Ni, Mg, Zr, Al, Ti, Ca, Mo, W, Bi, Nb, and F for the purpose of improving various performances of the lithium secondary battery. 1 type (s) or 2 or more types of additional elements (M) chosen from these groups can be contained. Among these, when the additive element (M) is one or more selected from Mg, Zr, Ti, Al, and F, the capacity per volume of the lithium secondary battery, cycle characteristics, operating voltage, safety From the viewpoint of further improving the properties and rate characteristics, and particularly preferably, by including all the additive elements (M) of Mg, Zr, Ti, Al and F in combination, a lithium secondary battery It is preferable because these performances can be improved in a balanced manner.

  In the positive electrode active material of the present invention, the content of the additive element (M) is preferably 0.03 to 5% by mass, particularly preferably 0.065 to 2.60% by mass with respect to the positive electrode active material. When the content of the additive element (M) is in the above range, it is possible to suppress a reduction in discharge capacity per weight and further improve battery performance such as cycle characteristics, rate characteristics, and safety.

  In addition, in the positive electrode active material of the present invention, when one or more selected from Mg, Zr, Ti, Al and F are added as the additive element (M), the content of Mg atoms is determined as the positive electrode active material. The content is preferably 0.005 to 1% by mass, particularly preferably 0.015 to 0.35% by mass. When the content of Mg atoms is in the above range, battery performance such as cycle characteristics and safety can be further improved.

  The Zr atom content is preferably 0.005 to 1.5 mass%, particularly preferably 0.009 to 1 mass%, based on the positive electrode active material. When the Zr atom content is in the above range, battery performance such as rate characteristics can be further improved.

  Further, the Ti atom content is preferably 0.005 to 0.5 mass%, particularly preferably 0.005 to 0.5 mass%, based on the positive electrode active material. When the content of Ti atoms is in the above range, battery performance such as rate characteristics and operating voltage can be further improved. The Ti atom of the additive element (M) does not originate from the added strontium titanate.

  Further, the content of Al atoms is preferably 0.005 to 1.2% by mass, particularly preferably 0.03 to 0.65% by mass, based on the positive electrode active material. When the Al atom content is in the above range, battery performance such as safety and cycle characteristics can be further improved.

  The F atom content is preferably 0.01 to 1% by mass, particularly preferably 0.01 to 0.25% by mass, based on the positive electrode active material. When the content of F atoms is in the above range, battery performance such as cycle characteristics can be further improved.

  These additive elements (M) may be present on the surface of the lithium cobalt composite oxide particles in the form of oxide, composite oxide, sulfate, phosphate, fluoride, etc. It may be present in the form of a solid solution within the particle, and may be present both inside the particle and on the particle surface.

Hereinafter, the manufacturing method of the positive electrode active material which concerns on this invention is demonstrated.
The method for producing a positive electrode active material of the present invention includes a raw material mixing step for obtaining a mixture containing a lithium compound, a cobalt compound and strontium titanate, and then a firing step for firing the mixture to produce a lithium cobalt composite oxide. It is a feature.

  The raw material mixing step is a step of obtaining a raw material mixture by mixing a lithium compound, a cobalt compound, and strontium titanate.

  The lithium compound related to the raw material mixing step is not particularly limited as long as it is a lithium compound that is usually used as a raw material for the production of a lithium cobalt composite oxide, and lithium oxide, hydroxide, carbonate, nitrate, and organic An acid salt etc. are mentioned, Among these, industrially cheap lithium carbonate is preferable.

  The average particle size of the lithium compound is particularly preferably 0.1 to 200 μm, preferably 2 to 50 μm, since the reactivity is good.

  The cobalt compound according to the raw material mixing step is not particularly limited as long as it is a cobalt compound that is usually used as a raw material for producing a lithium cobalt composite oxide, and is not limited to cobalt oxide, oxyhydroxide, hydroxide, carbonic acid. Examples thereof include salts, nitrates, and organic acid salts. Among these, cobalt oxide is preferable because it is industrially easily available and inexpensive. In addition, the cobalt compound has an average particle size of 0.5 to 40.0 μm, and preferably 2.0 to 35.0 μm, since the reactivity is good. In particular, it is preferable to use a cobalt compound having an average particle size of 10 to 25 μm, more preferably 15 to 25 μm, from the viewpoint of reducing the excess ratio of the lithium compound and reducing the remaining lithium compound.

  The strontium titanate related to the raw material mixing step is not particularly limited as long as it is industrially available, but strontium titanate has good reactivity when the average particle size is 0.05 to 5 μm. Particularly preferred.

  In the raw material mixing step, the mixing ratio of the lithium compound and the cobalt compound is such that the ratio of the number of moles of lithium in terms of atoms to the number of moles of cobalt in terms of atoms (Li / Co mixture mole ratio) is 0.990 to 1.100, The tap density of the positive electrode active material obtained to be preferably 1.000 to 1.080, particularly preferably 1.010 to 1.060 can be increased, particle size control, residual lithium carbonate and hydroxide It is preferable from the viewpoint of reducing lithium.

  Moreover, the mixing ratio of strontium titanate is 0.01 to 2 mol%, preferably 0.05 to 1 mol%, with respect to the lithium cobalt composite oxide to be produced. The reason for this is that, as described above, when the amount of strontium titanate added is less than 0.01 mol%, the tap density of the positive electrode active material decreases, and the safety, cycle characteristics, and rate characteristics of the lithium secondary battery are reduced. This is because the effect of improving the content tends to be low, while when the amount of strontium titanate added exceeds 2 mol%, the capacity per weight tends to decrease.

  Examples of the method of mixing the lithium compound, cobalt compound, and strontium titanate in the raw material mixing step include a mixing method using a ribbon mixer, a Henschel mixer, a super mixer, a nauter mixer, and the like.

  Further, in the raw material mixing step, in addition to the lithium compound, cobalt compound and strontium titanate, a compound containing an additional element (M) can be added and mixed. The compound containing the additive element (M) is a compound containing the additive element (M) described above. Specifically, the oxide, hydroxide, sulfate, carbonate, phosphoric acid of the additive element (M) Examples include salts, halides, and organic acid salts. The compound having the additive element (M) may be a compound containing two or more additive elements (M), and is not limited to one kind of compound with respect to one additive element (M). Different types of compounds may be used in combination. The compound containing the additive element (M) has an average particle size of 0.05 to 100 μm, preferably 0.1 to 90 μm, since the reactivity is particularly good.

As the compound containing the additive element (M), a compound having a magnesium atom, a compound having a titanium atom, a compound having a zirconium atom, a compound having an aluminum atom, and a compound having a fluorine atom are preferable, and MgF ₂ , MgO, By using one or more selected from TiO ₂ , ZrO ₂ , Al (OH) ₃ and AlF ₃ , various battery performances can be further improved. For example, MgF ₂ is the capacity retention rate of the lithium secondary battery, MgO is the safety of the lithium secondary battery, TiO ₂ is the average operating voltage of the lithium secondary battery, ZrO ₂ is the safety and rate characteristics of the lithium secondary battery, Al (OH) ₃ can effectively improve the safety of the lithium secondary battery, and AlF ₃ can effectively improve the capacity maintenance rate of the lithium secondary battery.

In the present invention, the compound containing the additive element (M) is a combination of MgF ₂ , MgO, TiO ₂ , ZrO ₂ , Al (OH) _3, and AlF ₃ used in combination. This is preferable from the viewpoint of improving the performance in a balanced manner.

  In the raw material mixing step, when the compound containing the additive element (M) is mixed, the amount of the compound containing the additive element (M) is such that the additive element (M) is based on the lithium cobalt composite oxide produced. A mixing amount of 0.03 to 5% by mass is preferable, and a mixing amount of 0.065 to 2.6% by mass is particularly preferable. When the amount of the compound containing the additive element (M) is within the above range, the reduction of the discharge capacity per weight of the lithium secondary battery is suppressed, and the capacity maintenance rate, operating voltage, rate characteristics, safety, etc. This is preferable from the viewpoint of improving battery performance.

Incidentally, as the compound containing the additive element _(M), in the case of using a _{MgF 2, MgO, TiO 2,} ZrO 2, Al (OH) 1 , two or more selected from ₃ and AlF ₃ are of MgF ₂ The addition amount is 0.01 to 1 mol%, preferably 0.01 to 0.25 mol%, with respect to the lithium cobalt composite oxide to be produced. The addition amount of MgO is relative to the lithium cobalt composite oxide to be produced. And 0.01 to 2.50 mol%, preferably 0.05 to 1.00 mol%. Further, the lithium-cobalt composite oxide addition amount of TiO ₂ is for generating, 0.01 mol%, preferably from 0.01 to 1 mol%, lithium-cobalt composite amount of ZrO ₂ is to generate It is 0.01-1.50 mol% with respect to an oxide, Preferably it is 0.10-1 mol%. The addition amount of Al (OH) ₃ is 0.01 to 3 mol%, preferably 0.1 to 2 mol%, with respect to the lithium cobalt composite oxide to be produced, and the addition amount of AlF ₃ is lithium cobalt to be produced. It is 0.01-1 mol% with respect to complex oxide, Preferably it is 0.01-0.25 mol%.

  The raw material lithium compound, cobalt compound, strontium titanate, and the compound containing the additive element (M) added if necessary do not have any manufacturing history, but to produce a high purity lithium cobalt composite oxide powder. In addition, it is preferable that the impurity content is as low as possible.

  The firing step according to the method for producing a positive electrode active material of the present invention is a raw material of a compound containing an additive element (M) mixed in a lithium compound, a cobalt compound, and strontium titanate obtained in the raw material mixing step. In this step, the mixture is fired to obtain a lithium cobalt composite oxide.

In the firing step, the firing temperature when firing the raw material mixture and reacting the lithium compound, cobalt compound and strontium titanate with the compound containing the additive element (M) mixed as necessary is 1000 to 1100 ° C., Preferably it is 1050-1080 degreeC. The reason for this is that when the firing temperature is less than 1000 ° C., the tap density of the lithium cobalt composite oxide tends to decrease. On the other hand, when the firing temperature is higher than 1100 ° C., the sintered product obtained is strongly sintered and has a very high hardness. This is because it tends to be hard and difficult to crush and crush.
The reaction time is 1 to 30 hours, preferably 5 to 20 hours. The firing atmosphere is an oxidizing atmosphere such as in air or oxygen gas.

  The lithium cobalt composite oxide containing Sr atoms and Ti atoms obtained in this manner may be subjected to a plurality of firing steps as necessary.

  After firing, the lithium cobalt composite oxide containing Sr atoms and Ti atoms obtained is crushed and / or pulverized as necessary, and further classified to obtain a positive electrode active material for a lithium secondary battery. To do.

  Thus, the obtained positive electrode active material of the present invention is composed of a lithium cobalt composite oxide containing Sr atoms and Ti atoms, and preferable physical properties include an average particle of 10 to 30 μm, preferably 10 to 25 μm, and a tap density. It is 2.6 g / ml or more, preferably 2.6 to 3.1 g / ml, and Sr atoms are present at least on the particle surface of the lithium cobalt composite oxide.

  Moreover, the lithium secondary battery of this invention uses the positive electrode active material of this invention, and this lithium secondary battery consists of a nonaqueous electrolyte containing a positive electrode, a negative electrode, a separator, and lithium salt.

  The positive electrode according to the lithium secondary battery of the present invention is formed, for example, by applying and drying a positive electrode mixture on a positive electrode current collector. The positive electrode mixture includes a positive electrode active material, a conductive agent, a binder, and a filler that is added as necessary. In the lithium secondary battery of the present invention, the positive electrode active material for a lithium secondary battery of the present invention is uniformly applied to the positive electrode. For this reason, the lithium secondary battery of the present invention has high battery performance, particularly high capacity and high safety.

The content of the positive electrode active material contained in the positive electrode mixture according to the lithium secondary battery of the present invention is 70 to 100% by mass, preferably 90 to 98% by mass.
The positive electrode current collector according to the lithium secondary battery of the present invention is not particularly limited as long as it is an electronic conductor that does not cause a chemical change in the constituted battery. For example, stainless steel, nickel, aluminum, titanium , Carbon, nickel, titanium, and silver surface treated with baked carbon, aluminum or stainless steel. The surface of these materials may be oxidized and used, or the current collector surface may be provided with irregularities by surface treatment. Examples of the current collector include foils, films, sheets, nets, punched ones, lath bodies, porous bodies, foam bodies, fiber groups, nonwoven fabric molded bodies, and the like. The thickness of the current collector is not particularly limited, but is preferably 1 to 500 μm.

  The conductive agent according to the lithium secondary battery of the present invention is not particularly limited as long as it is an electron conductive material that does not cause a chemical change in the constituted battery. For example, graphite such as natural graphite and artificial graphite, carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, carbon black such as thermal black, conductive fibers such as carbon fiber and metal fiber, Examples include metal powders such as carbon fluoride, aluminum and nickel powder, conductive whiskers such as zinc oxide and potassium titanate, conductive metal oxides such as titanium oxide, and conductive materials such as polyphenylene derivatives. Examples of graphite include scaly graphite, scaly graphite, and earthy graphite. These can be used alone or in combination of two or more. The compounding ratio of the conductive agent is 1 to 50% by mass, preferably 2 to 30% by mass in the positive electrode mixture.

Examples of the binder according to the lithium secondary battery of the present invention include starch, polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, regenerated cellulose, diacetyl cellulose, polyvinyl pyrrolidone, tetrafluoroethylene, polyethylene, and polypropylene. , Ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene butadiene rubber, fluoro rubber, tetrafluoroethylene-hexafluoroethylene copolymer, tetrafluoroethylene-hexafluoropropylene copolymer, tetrafluoroethylene-par Fluoroalkyl vinyl ether copolymer, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-chlorotrifluoroethylene Copolymer, ethylene-tetrafluoroethylene copolymer, polychlorotrifluoroethylene, vinylidene fluoride-pentafluoropropylene copolymer, propylene-tetrafluoroethylene copolymer, ethylene-chlorotrifluoroethylene copolymer, fluorine Vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer, vinylidene fluoride-perfluoromethyl vinyl ether-tetrafluoroethylene copolymer, ethylene-acrylic acid copolymer or its (Na ⁺ ) ion crosslinked product, ethylene-methacrylic acid An acid copolymer or its (Na ⁺ ) ion crosslinked product, an ethylene-methyl acrylate copolymer or its (Na ⁺ ) ion crosslinked product, an ethylene-methyl methacrylate copolymer or its (Na ⁺ ) ion crosslinked product, Polyethylene Polysaccharides such as Sid, thermoplastic resins, polymers having rubber elasticity, and these may be used individually or in combination. In addition, when using the compound containing a functional group which reacts with lithium like a polysaccharide, it is preferable to add the compound like an isocyanate group and to deactivate the functional group, for example. The blending ratio of the binder is 1 to 50% by mass, preferably 5 to 15% by mass in the positive electrode mixture.

  The filler relating to the lithium secondary battery of the present invention suppresses the volume expansion of the positive electrode in the positive electrode mixture, and is added as necessary. As the filler, any fibrous material can be used as long as it does not cause a chemical change in the constructed battery. For example, olefinic polymers such as polypropylene and polyethylene, and fibers such as glass and carbon are used. Although the addition amount of a filler is not specifically limited, 0-30 mass% is preferable in a positive mix.

  The negative electrode according to the lithium secondary battery of the present invention is formed by applying and drying a negative electrode material on a negative electrode current collector. The negative electrode current collector according to the lithium secondary battery of the present invention is not particularly limited as long as it is an electronic conductor that does not cause a chemical change in the constructed battery. For example, stainless steel, nickel, copper, titanium , Aluminum, baked carbon, copper or stainless steel surface treated with carbon, nickel, titanium, silver, and an aluminum-cadmium alloy. Further, the surface of these materials may be used after being oxidized, or the surface of the current collector may be used with surface roughness by surface treatment. Examples of the current collector include foils, films, sheets, nets, punched ones, lath bodies, porous bodies, foam bodies, fiber groups, nonwoven fabric molded bodies, and the like. The thickness of the current collector is not particularly limited, but is preferably 1 to 500 μm.

The negative electrode material according to the lithium secondary battery of the present invention is not particularly limited, and examples thereof include carbonaceous materials, metal composite oxides, lithium metals, lithium alloys, silicon alloys, tin alloys, metal oxides. Materials, conductive polymers, chalcogen compounds, Li—Co—Ni based materials, Li ₄ Ti ₅ O _{12 and the} like. Examples of the carbonaceous material include non-graphitizable carbon materials and graphite-based carbon materials. As the metal complex oxide, for example, Sn _p (M ¹ ) _1-p (M ² ) _{q Or} (wherein M ¹ represents one or more elements selected from Mn, Fe, Pb and Ge, M ² represents one or more elements selected from Al, B, P, Si, Group 1, Group 2, Group 3 and a halogen element in the periodic table, and 0 <p ≦ 1, 1 ≦ q ≦ 3 1 ≦ r ≦ 8), Li _t Fe ₂ O ₃ (0 ≦ t ≦ 1), Li _t WO ₂ (0 ≦ t ≦ 1), and the like. As the metal _{oxide, GeO, GeO 2, SnO,} SnO 2, PbO, PbO 2, Pb 2 O 3, Pb 3 O 4, Sb 2 O 3, Sb 2 O 4, Sb 2 O 5, Bi 2 O 3 Bi ₂ O ₄ , Bi ₂ O _{5 and the} like. Examples of the conductive polymer include polyacetylene and poly-p-phenylene.

  As the separator according to the lithium secondary battery of the present invention, an insulating thin film having a large ion permeability and a predetermined mechanical strength is used. Sheets and non-woven fabrics made of olefin polymers such as polypropylene, glass fibers or polyethylene are used because of their organic solvent resistance and hydrophobicity. The pore diameter of the separator may be in a range generally useful for batteries, and is, for example, 0.01 to 10 μm. The thickness of the separator may be in a range for a general battery, for example, 5 to 300 μm. When a solid electrolyte such as a polymer is used as the electrolyte described later, the solid electrolyte may also serve as a separator.

  The nonaqueous electrolyte containing a lithium salt according to the lithium secondary battery of the present invention is composed of a nonaqueous electrolyte and a lithium salt. As the non-aqueous electrolyte according to the lithium secondary battery of the present invention, a non-aqueous electrolyte, an organic solid electrolyte, or an inorganic solid electrolyte is used. Examples of the non-aqueous electrolyte include N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, γ-butyrolactone, 1,2-dimethoxyethane, tetrahydroxyfuran, and 2-methyl. Tetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, phosphoric acid triester, trimethoxymethane, dioxolane derivatives, sulfolane, methylsulfolane, 3-methyl -2-oxazolidinone, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivative, tetrahydrofuran derivative, diethyl ether, 1,3- Ropansaruton, methyl propionate, and a solvent obtained by mixing one or more aprotic organic solvents such as ethyl propionate.

  Examples of the organic solid electrolyte according to the lithium secondary battery of the present invention include polyethylene derivatives, polyethylene oxide derivatives or polymers containing the same, polypropylene oxide derivatives or polymers containing the same, phosphate ester polymers, polyphosphazenes, polyaziridines, and polyethylenes. Examples thereof include a polymer containing an ionic dissociation group such as sulfide, polyvinyl alcohol, polyvinylidene fluoride, and polyhexafluoropropylene, and a mixture of a polymer containing an ionic dissociation group and the non-aqueous electrolyte.

As the inorganic solid electrolyte according to the lithium secondary battery of the present invention, Li nitride, halide, oxyacid salt, sulfide, and the like can be used. For example, Li ₃ N, LiI, Li ₅ NI ₂ , Li ₃ N-LiI-LiOH, LiSiO ₄ , LiSiO ₄ -LiI-LiOH, Li ₂ SiS ₃ , Li ₄ SiO ₄ , Li ₄ SiO ₄ -LiI-LiOH, P ₂ S ₅ , Li ₂ S or Li ₂ S-P ₂ S ₅ , Li ₂ S—SiS ₂ , Li ₂ S—GeS ₂ , Li ₂ S—Ga ₂ S ₃ , Li ₂ S—B ₂ S ₃ , Li ₂ S—P ₂ S ₅ —X, Li ₂ S _{-SiS 2 -X, Li 2 S-} GeS 2 -X, Li 2 S-Ga 2 S 3 -X, Li 2 S-B 2 S 3 -X, ( wherein, X is LiI, B ₂ S _3, Or at least one selected from Al ₂ S ₃ ).
Further, when the inorganic solid electrolyte is amorphous (glass), lithium phosphate (Li ₃ PO ₄ ), lithium oxide (Li ₂ O), lithium sulfate (Li ₂ SO ₄ ), phosphorus oxide (P ₂ O ₅₎ ), Oxygen-containing compounds such as lithium borate (Li ₃ BO ₃ ), Li ₃ PO _4-u N _{2u / 3} (u is 0 <u <4), Li ₄ SiO _4-u N _{2u / 3} (u is Nitrogen such as 0 <u <4), Li ₄ GeO _4-u N _{2u / 3} (u is 0 <u <4), Li ₃ BO _3-u N _{2u / 3} (u is 0 <u <3) The compound to be contained can be contained in the inorganic solid electrolyte. By adding the compound containing oxygen or the compound containing nitrogen, the gap between the formed amorphous skeletons can be widened, the hindrance to movement of lithium ions can be reduced, and ion conductivity can be further improved.

As the lithium salt according to the lithium secondary battery of the present invention, those dissolved in the non-aqueous electrolyte are used, for example, LiCl, LiBr, LiI, LiClO ₄ , LiBF ₄ , LiB ₁₀ Cl ₁₀ , LiPF ₆ , LiCF _3. SO ₃ , LiCF ₃ CO ₂ , LiAsF ₆ , LiSbF ₆ , LiB ₁₀ Cl ₁₀ , LiAlCl ₄ , CH ₃ SO ₃ Li, CF ₃ SO ₃ Li, (CF ₃ SO ₂ ) ₂ NLi, chloroborane lithium, lower aliphatic Examples thereof include a salt obtained by mixing one or more of lithium carboxylate, lithium tetraphenylborate, imides and the like.

  Moreover, the compound shown below can be added to a nonaqueous electrolyte for the purpose of improving discharge, a charge characteristic, and a flame retardance. For example, pyridine, triethyl phosphite, triethanolamine, cyclic ether, ethylenediamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivative, sulfur, quinoneimine dye, N-substituted oxazolidinone and N, N-substituted imidazolidine, ethylene glycol dialkyl ether , Ammonium salt, polyethylene glycol, pyrrole, 2-methoxyethanol, aluminum trichloride, conductive polymer electrode active material monomer, triethylenephosphonamide, trialkylphosphine, morpholine, aryl compounds with carbonyl group, hexamethylphosphine Examples include hollic triamide and 4-alkylmorpholine, bicyclic tertiary amines, oils, phosphonium salts and tertiary sulfonium salts, phosphazenes, and carbonates. That. In order to make the electrolyte nonflammable, a halogen-containing solvent such as carbon tetrachloride or ethylene trifluoride can be included in the electrolyte. In addition, carbon dioxide gas can be included in the electrolytic solution in order to make it suitable for high-temperature storage.

  The lithium secondary battery of the present invention is a lithium secondary battery having a high capacity per volume and excellent in safety, cycle characteristics and operating voltage. The shape of the battery is a button, a sheet, a cylinder, a corner, a coin type, etc. Any shape may be sufficient.

  Although the use of the lithium secondary battery of the present invention is not particularly limited, for example, a notebook computer, a laptop computer, a pocket word processor, a mobile phone, a cordless cordless handset, a portable CD player, a radio, an LCD TV, a backup power source, an electric shaver, Examples include electronic devices such as memory cards and video movies, and consumer electronic devices such as automobiles, electric vehicles, game machines, and electric tools.

EXAMPLES Hereinafter, although an Example demonstrates this invention in detail, this invention is not limited to these Examples.
{Examples 1-9}
Tricobalt tetroxide (average particle size 25.0 μm) and lithium carbonate (average particle size 7.0 μm) were weighed so that the molar ratio of Co atom to Li atom shown in Table 1 was obtained, and strontium titanate (average particle size) 0.9 μm) was thoroughly mixed for 60 seconds using a household mixer in a dry manner so that the ratio shown in Table 1 was obtained to obtain a raw material mixture. Next, the obtained raw material mixture was baked in the atmosphere at a temperature and time shown in Table 1 in an alumina pot. After firing, the fired product was pulverized and classified to obtain a lithium cobalt composite oxide containing Sr atoms and Ti atoms, which was used as a positive electrode active material sample.

{Comparative Examples 1-2}
Weigh tricobalt tetroxide (average particle size 25.0 μm) and lithium carbonate (average particle size 7.0 μm) so that the molar ratio of Co atom and Li atom shown in Table 1 is obtained, and use a dry-type home mixer. Mix well for 60 seconds to obtain a raw material mixture. Next, the obtained raw material mixture was baked in the atmosphere at a temperature and time shown in Table 1 in an alumina pot. After firing, the fired product was pulverized and classified to obtain a lithium transition metal composite oxide, which was used as a positive electrode active material sample.

注）ＳｒＴｉＯ_３の添加量は、生成されるリチウムコバルト複合酸化物に対するモル％を示す。

Note) The amount of SrTiO ₃ added indicates mol% with respect to the produced lithium cobalt composite oxide.

<Evaluation of physical properties of positive electrode active material sample>
For the positive electrode active material samples obtained in Examples and Comparative Examples, the average particle size, BET specific surface area, tap density, strontium amount eluted in water, C-axis lattice constant, and residual LiOH and Li ₂ CO ₃ contents Asked. The results are shown in Table 2.

<Average particle size>
The average particle size was measured by a laser diffraction / scattering method.

<Tap density>
Based on the apparent density or apparent specific volume method described in JIS-K-5101, the tap density is set in a dual automatic tap device manufactured by Yuasa Ionics Co., Ltd. Then, tapping was performed 500 times with a tapping height of 3.2 mm, the capacity was read, and the apparent density was calculated to obtain the tap density.

<C-axis lattice constant size>
The lattice constant was obtained by refining the lattice constant and structural parameters by performing Rietveld analysis using a diffraction pattern obtained by X-ray diffraction (XRD) analysis using CuKα rays with a positive electrode active material sample as a radiation source. Rietveld analysis uses an X-ray diffraction pattern, and in order to extract the information contained therein, fitting the diffraction pattern obtained by actual measurement and the diffraction pattern expected from the crystal structure model This is a method for refining the parameters related to the crystal structure.

<Evaluation of the amount of Sr eluted in water>
5 g of a positive electrode active material sample was dispersed in 100 ml of pure water for 5 minutes at 25 ° C., Sr atoms were eluted from the particle surface, and the amount of Sr in the solution was quantified with an inductively coupled plasma emission spectrometer (ICP-AES). .

<Evaluation of remaining LiOH and Li ₂ CO ₃ contents)
15 g of a positive electrode active material sample and 100 g of pure water are measured in a beaker and dispersed for 5 minutes using a magnetic stirrer. Next, this dispersion was filtered, and 30 ml of the filtrate was titrated with 0.1 N HCl with an automatic titrator (model COMMITE-2500) to calculate residual LiOH and Li ₂ CO ₃ .

<XPS measurement>
The positive electrode active material samples obtained in Example 3 and Example 4 were subjected to X-ray photoelectron spectroscopy (XPS) analysis, the surface was etched with argon, and the Sr peak and Ti peak were measured in the depth direction. 1 and FIG.
The etching conditions are as follows.
Etching conditions Ion gun used; Low energy differential exhaust type floating ion gun with neutral particle removal mechanism
Ion species; Ar ⁺ ions
Extractor current: 2μA
Acceleration voltage: 5.0 kV
Etching rate: 1.84 nm / min (SiO ₂ conversion)

{Example 10}
Tricobalt tetroxide (average particle size 25.0 μm) and lithium carbonate (average particle size 7.0 μm) were weighed so that the molar ratio of Co atom to Li atom shown in Table 3 was obtained, and strontium titanate (average particle size) 0.9 μm), TiO ₂ (average particle size 0.2 μm), and ZrO ₂ (average particle size 0.5 μm) were mixed thoroughly for 60 seconds using a home mixer in a dry type so as to have the ratio shown in Table 3. Got. Subsequently, the obtained raw material mixture was baked in the atmosphere at 1080 ° C. for 5 hours in an alumina pot. After firing, the fired product was pulverized and classified to obtain a lithium cobalt composite oxide containing Sr atoms and Ti atoms, which was used as a positive electrode active material sample.

{Examples 11 to 13}
Tricobalt tetroxide (average particle size 25.0 μm) and lithium carbonate (average particle size 7.0 μm) were weighed so that the molar ratio of Co atom to Li atom shown in Table 3 was obtained, and strontium titanate (average particle size) 0.9 μm), MgF ₂ (average particle size 22.6 μm), MgO (average particle size 3.1 μm), TiO ₂ (average particle size 0.2 μm), ZrO ₂ (average particle size 0.5 μm), Al (OH) ₃ (average) A raw material mixture was obtained by thoroughly mixing AlF ₃ (average particle diameter: 82.2 μm) and 60% for 60 seconds using a household mixer in a dry manner so as to have the ratio shown in Table 3. Subsequently, the obtained raw material mixture was baked in the atmosphere at 1080 ° C. for 5 hours in an alumina pot. After firing, the fired product was pulverized and classified to obtain a lithium cobalt composite oxide containing Sr atoms and Ti atoms, which was used as a positive electrode active material sample.

<Evaluation of physical properties of lithium cobalt composite oxide>
Lithium cobalt composite oxides obtained in Examples 10-13, the average particle diameter, tap density, the LiOH and Li ₂ CO ₃ content to strontium amount and remaining eluted in water was determined by the method described above. The results are shown in Table 4.

The battery performance test was conducted as follows.
<Production of lithium secondary battery>
A positive electrode agent was prepared by mixing 96% by mass of the positive electrode active material obtained in Examples 7 and 9-13 and Comparative Example 1, 2% by mass of graphite powder, and 2% by mass of polyvinylidene fluoride. A kneaded paste was prepared by dispersing in pyrrolidinone. The kneaded paste was applied to an aluminum foil, dried, pressed and punched into a disk with a diameter of 15 mm to obtain a positive electrode plate.
Using this positive electrode plate, a coin-type lithium secondary battery was manufactured using each member such as a separator, a negative electrode, a positive electrode, a current collector plate, a mounting bracket, an external terminal, and an electrolytic solution. Among these, a metal lithium foil was used for the negative electrode, and 1 mol of LiPF ₆ was dissolved in 1 liter of a 1: 1 kneaded solution of ethylene carbonate and methyl ethyl carbonate as the electrolyte.
Subsequently, performance evaluation of the obtained lithium secondary battery was performed. The results are shown in Table 5.

<Battery performance evaluation>
The produced coin-type lithium secondary battery was operated at room temperature under the following test conditions, and the following battery performance was evaluated.
(Evaluation A)
(1) Test conditions for cycle characteristic evaluation First, constant current / constant voltage charging (CCCV charging) is performed in which charging is performed over 2 hours at 0.5 C to 4.45 V, and voltage is further maintained at 4.45 V for 3 hours. went. Thereafter, charging and discharging were performed at a constant current discharge (CC discharge) to 2.7 V at 0.2 C, and these operations were taken as one cycle, and the discharge capacity was measured every cycle. This cycle was repeated 20 cycles.
(2) Initial discharge capacity (per weight)
The discharge capacity at the first cycle in the cycle characteristic evaluation was defined as the initial discharge capacity.
(3) Initial discharge capacity (per volume)
Calculation was performed by the product of the electrode density measured at the time of producing the positive electrode plate and the initial discharge capacity (per weight).
(4) Capacity maintenance rate From each discharge capacity (per weight) of the 1st cycle and 20th cycle in cycle characteristic evaluation, the capacity maintenance rate was computed by the following formula.
Capacity maintenance ratio (%) = (discharge capacity at 20th cycle / discharge capacity at 1st cycle) × 100
(5) Average operating voltage The average operating voltage at the 20th cycle in the cycle characteristics evaluation was defined as the average operating voltage.

(Evaluation B: Safety evaluation)
Soseki, Kita, Wada (November 21-23, 2001, 42nd Battery Symposium, Abstracts, 462-463), Ota, Oiwa, Ishigaki et al. (November 21-23, 2001) Based on the battery thermal stability evaluation methods disclosed in the 42nd Battery Discussion Meeting, 470-471), JP 2002-158008A and JP 2003-221235A, in Examples and Comparative Examples The lithium secondary battery using the prepared positive electrode active material was charged to 4.45 V at 0.5 C for 5 hours by constant current voltage (CCCV) charging with respect to the positive electrode, and then lithium secondary battery in an argon atmosphere. The battery was disassembled, and the positive electrode plate containing the positive electrode active material which was extracted and deintercalated with lithium was taken out. Next, 5.0 mg of the positive electrode active material was scraped from each of the taken-out positive plates, and differential scanning calorimetry was performed together with 5.0 μml of a solution of 1 mol of LiPF in 1 liter of a 1: 1 kneaded solution of ethylene carbonate and methyl ethyl carbonate ( DSC) was enclosed in a closed cell (SUS cell), and the change in differential calorific value was measured with a differential scanning calorimeter (model DSC6200, manufactured by SII Epolide Service Co., Ltd.) at a heating rate of 2 ° C./min. Further, the total calorific value S (J / g) in the range of 180 ° C. to 220 ° C. was obtained. A smaller value of the total heat generation S (J / g) indicates better thermal stability, that is, battery safety. The result of the differential calorific value change of Example 7, Examples 9-11, and Example 13 is shown in FIGS. The calorific value on the vertical axis in FIGS. 1 and 2 was a value divided by the weight of the measured positive electrode active material.

The positive electrode active material for a lithium secondary battery of the present invention has a high packing density, and can improve the safety, cycle characteristics, operating voltage, and capacity per volume of the lithium secondary battery.
Moreover, according to the manufacturing method of this invention, this positive electrode active material for lithium secondary batteries can be provided by an industrially advantageous method.

Claims (11)

  A positive electrode active material for a lithium secondary battery, comprising a lithium cobalt composite oxide containing Sr atoms and Ti atoms obtained by firing a mixture containing a lithium compound, a cobalt compound, and strontium titanate .   2. The positive electrode active material for a lithium secondary battery according to claim 1, wherein the average particle diameter is 10 to 30 μm and the tap density is 2.60 g / ml or more.   The positive electrode active material for a lithium secondary battery according to claim 1 or 2, wherein Sr atoms are present at least on the particle surfaces of the lithium cobalt composite oxide.   4. The positive electrode active material for a lithium secondary battery according to claim 1, wherein the content of the soluble strontium compound existing on the particle surface is 0.005 to 0.100 mass% in terms of Sr atoms.   Furthermore, it is characterized by containing one or more additive elements (M) selected from the group consisting of Mn, Ni, Mg, Zr, Al, Ti, Ca, Mo, W, Bi, Nb and F. The positive electrode active material for a lithium secondary battery according to any one of claims 1 to 4.   The positive electrode active material for a lithium secondary battery according to claim 5, wherein the additive element (M) is one or more selected from Mg, Zr, Ti, Al and F.   A positive electrode for a lithium secondary battery, comprising: a raw material mixing step for obtaining a mixture containing a lithium compound, a cobalt compound, and strontium titanate; and then a firing step for firing the mixture to form a lithium cobalt composite oxide. A method for producing an active material.   The method for producing a positive electrode active material for a lithium secondary battery according to claim 7, wherein the addition amount of strontium titanate is 0.01 to 2 mol% with respect to the lithium cobalt composite oxide produced.   In the raw material mixing step, one or more compounds containing one or more additional elements (M) selected from the group of Mn, Ni, Mg, Zr, Ti, Al and F are added. The manufacturing method of the positive electrode active material for lithium secondary batteries of Claim 7 or 8 characterized by the above-mentioned. Compounds containing an additive element (M) _{is, MgF 2, MgO, TiO 2} , ZrO 2, Al (OH) 3 and characterized in that it is selected from AlF _3, a positive electrode for a lithium secondary battery according to claim 9, wherein A method for producing an active material. A lithium secondary battery using the positive electrode active material for a lithium secondary battery according to any one of claims 1 to 6.

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