JP4813165B2 - Cathode active material for non-aqueous electrolyte secondary battery and method for producing the same - Google Patents

Description

  The present invention is a positive electrode active material for a non-aqueous electrolyte secondary battery such as a lithium secondary battery that can be used under a high voltage, has a high capacity, and is excellent in charge / discharge cycle characteristics, a method for producing the same, and the positive electrode active material. The present invention relates to a positive electrode for a lithium secondary battery and a lithium secondary battery.

In recent years, with the rapid development of information-related equipment and communication equipment such as personal computers and mobile phones, there has been an increasing demand for non-aqueous electrolyte secondary batteries such as lithium secondary batteries that are small, lightweight and have high energy density. Yes. As such positive electrode active materials for non-aqueous electrolyte secondary batteries, composite oxides of lithium and transition metals such as LiCoO ₂ , LiNiO ₂ , LiNi _0.8 Co _0.2 O ₂ and LiMn ₂ O ₄ are known. ing.

Among them, a lithium secondary battery using LiCoO ₂ as a positive electrode active material and carbon such as a lithium alloy, graphite, or carbon fiber as a negative electrode can obtain a high voltage of 4V, so that it has a high energy density. Widely used. However, LiCoO ₂ alone has a problem that it is difficult to meet the increasing demands for discharge capacity, safety, storage characteristics, and charge / discharge cycle characteristics. In order to solve these problems, Patent Documents 1 to 3 propose positive electrode active materials to which elements such as Zr, Hf, Ti, Mg, V, Cu, Zn, Fe, Ta, and Nb are added.

For example, Patent Document 1 describes a LiCoO ₂ positive electrode active material to which Zr and Mg are added so that Zr adheres to the particle surface and Mg diffuses uniformly in the particle. In the positive electrode active material, the charge / discharge cycle characteristics are slightly improved under the use of 4.4V high voltage using carbon for the negative electrode, but it is still insufficient and further improvement of the charge / discharge cycle characteristics is necessary. . In this method, zirconium contained in the positive electrode active material is not dissolved at all in LiCoO ₂ , so that it is considered that the effect of improving the charge / discharge cycle characteristics is insufficient.

Patent Document 2, after mixing the zirconium oxide LiCoO ₂ positive active material powder, by heating treatment, and to synthesize LiCoO ₂ positive active material containing zirconium. In the positive electrode active material, the charge / discharge cycle characteristics are slightly improved, but it is still insufficient and further improvement is required. In this method, zirconium is not added to the raw material but zirconium is added to the positive electrode active material, and since the heating temperature after addition of zirconium is 300 ° C., zirconium is not dissolved in LiCoO ₂ at all. Therefore, it is considered that the effect of improving the charge / discharge cycle characteristics is insufficient.

Patent Document 3 describes a LiCoO ₂ positive electrode active material in which one element selected from the group consisting of Zr, Nb, Ta, Ti and Hf is added, and the added element is completely dissolved in the crystal lattice. Has been. In the positive electrode active material, the charge / discharge cycle characteristics are slightly improved, but it is still insufficient and further improvement is required. In this positive electrode active material, the added zirconium is completely dissolved in the LiCoO ₂ crystal lattice to form a lithium composite oxide, and since the added zirconium is completely dissolved, the charge / discharge cycle characteristics are improved. The effect is considered insufficient.

In this way, the battery characteristics such as discharge capacity, safety and charge / discharge cycle characteristics are further improved, and those battery characteristics are fully satisfied at the same time, such as improvement of the battery characteristics under high voltage use. Not obtained.
Japanese Patent Laid-Open No. 2005-50779 JP 2003-221234 A Japanese Patent Publication No. 2001-27032

  In any of the above Patent Documents 1 to 3, it is considered that the effect of improving the charge / discharge cycle characteristics due to the addition of zirconium is insufficient, and the effect corresponding to the addition amount is not sufficiently achieved.

  In general, the charging voltage when lithium is used for the negative electrode active material is 4.3 V. In this case, only 50 to 60% of the positive electrode active material is used for charging and discharging. If this charging voltage can be increased, the amount of the positive electrode active material that can be used for charging and discharging increases. For example, if the charging voltage can be 4.5 V, about 70% of the positive electrode active material can be used, and the discharge capacity can be dramatically improved. However, when the charging voltage is increased, the charge / discharge cycle characteristics are significantly deteriorated at the same time. Therefore, improving the charge / discharge cycle characteristics in use under a high voltage is a major problem in the present application.

  In particular, Patent Document 2 and Patent Document 3 have poor charge / discharge cycle characteristics at a charge voltage of 4.3V, and charge / discharge cycle characteristics are further significantly deteriorated at a high voltage of charge voltage 4.5V. I can not expect at all.

  Therefore, in the present invention, by fully extracting the effect of improving the charge / discharge cycle characteristics commensurate with the amount of zirconium added, a lithium secondary battery having a high capacity and excellent charge / discharge cycle characteristics even under high voltage, etc. It aims at providing the positive electrode active material for nonaqueous electrolyte secondary batteries, its manufacturing method, the positive electrode for lithium secondary batteries containing the said positive electrode active material, and a lithium secondary battery.

The present inventor conducted intensive studies to achieve the above object, and found the following positive electrode active material for a lithium secondary battery having the above characteristics. That is, a LiCoO ₂ positive electrode active material obtained by firing a raw material mixed powder containing at least a lithium compound, a cobalt compound and a zirconium compound as raw materials, and 30 to 95 mol% of zirconium contained in the positive electrode active material is oxidized. A LiCoO ₂ positive electrode active material characterized in that it is zirconium and 5-70 mol% is a lithium composite oxide is used.

Thus, the present invention is based on the above novel findings and has the following configuration.
(1) A positive electrode active material for a non-aqueous electrolyte secondary battery containing a lithium atom, a cobalt atom and a zirconium atom, wherein 30 to 95 mol% of zirconium atoms contained in the positive electrode active material is zirconium oxide, and is 5 to 70 mol%. Is a positive electrode active material for a non-aqueous electrolyte secondary battery in which is present as a lithium composite oxide.
(2) The positive electrode active material for a nonaqueous electrolyte secondary battery according to (1), wherein the positive electrode active material contains 0.01 to 1.5 mol% of zirconium atoms with respect to cobalt atoms. material.
(3) The positive electrode active material for a non-aqueous electrolyte secondary battery according to (1) or (2), wherein the positive electrode active material further contains 0.05 to 3.0 mol% of magnesium atoms with respect to cobalt atoms.
(4) The positive electrode active material for a nonaqueous electrolyte secondary battery according to any one of (1) to (3), wherein the positive electrode active material further contains 0.05 to 3.0 mol% of aluminum atoms with respect to cobalt atoms. material.
(5) A method for producing a positive electrode active material containing lithium atoms, cobalt atoms and zirconium atoms by mixing a lithium compound, a cobalt compound and a zirconium compound, followed by firing. The non-aqueous electrolyte 2 is characterized in that there is a component that does not dissolve in the hydrochloric acid aqueous solution when it is brought into contact with an aqueous 18% hydrochloric acid solution, and the component contains 30 to 95 mol% of zirconium contained in the powder. A method for producing a positive electrode active material for a secondary battery.
(6) The method for producing a positive electrode active material for a nonaqueous electrolyte secondary battery according to (5), wherein the component not dissolved in the aqueous hydrochloric acid solution is zirconium oxide.
(7) A positive electrode for a lithium secondary battery including a positive electrode active material, a conductive material, and a binder, wherein the positive electrode active material is a positive electrode for a nonaqueous electrolyte secondary battery according to any one of (1) to (6) A positive electrode for a lithium secondary battery, comprising a positive electrode active material for a non-aqueous electrolyte secondary battery containing an active material.
(8) A lithium secondary battery comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte, wherein the positive electrode comprises the positive electrode according to (7).

  According to the present invention, the effect of improving the charge / discharge cycle characteristics by adding zirconium can be maximized. In addition, the charge / discharge cycle characteristics are good even under a high voltage, whereby a high-capacity lithium secondary battery can be realized.

  The positive electrode active material of the present invention is a positive electrode active material for a non-aqueous electrolyte secondary battery containing at least lithium, cobalt, and zirconium, and 30 to 95 mol% of zirconium contained in the positive electrode active material is zirconium oxide, and 5 to 70 mol % Is a lithium composite oxide.

  In the present invention, the mechanism by which the positive electrode active material having excellent characteristics as described above is obtained is not necessarily clear, but can be estimated as follows. That is, it is considered that 30 to 95 mol% of the added zirconium is zirconium oxide, and a part of the zirconium oxide is present on the surface of the positive electrode active material. As a result, the area where the electrolyte solution and the positive electrode active material are in direct contact is reduced, so that the decomposition reaction of the electrolyte solution that occurs during charging and discharging is suppressed, and dryout (electrolyte depletion) can be prevented. Since the amount of elution of metal elements such as lithium and cobalt from the active material into the electrolytic solution is reduced, it is considered that the charge / discharge cycle characteristics are improved. Further, as a result of the presence of 5 to 70 mol% as a lithium composite oxide, the surface layer of the positive electrode material is modified to further reduce the dissolution of the metal element in the electrolytic solution, and at the same time, the positive electrode active material crystals that are caused by repeated charge and discharge Since the collapse of the structure is suppressed, it seems that the charge / discharge cycle characteristics are improved. Due to these synergistic effects, it is considered that the positive electrode active material of the present invention exhibits extremely excellent charge / discharge cycle characteristics. This synergistic effect is particularly noticeable when charging and discharging are performed under a high voltage of 4.5 V where a large amount of lithium is extracted from the positive electrode and the crystal structure becomes unstable.

  A preferable range of the amount of zirconium oxide is preferably 30 to 90 mol%, more preferably 45 to 85 mol%, and particularly preferably 60 to 80 mol% with respect to zirconium contained in the positive electrode active material. Similarly, the preferable range of the amount of the lithium composite oxide is preferably 10 to 70 mol%, more preferably 15 to 55 mol%, and particularly preferably 20 to 40 mol% with respect to zirconium contained in the positive electrode active material. In the case where the amount of zirconium oxide or lithium composite oxide is in the above range, in particular, it is possible to expect an even better effect of improving charge / discharge cycle characteristics, and in addition, an effect of improving storage characteristics can be obtained. It is preferable because it can be pulled out efficiently.

Zirconium oxide as used in the present application is an oxide of at least zirconium, and remains dissolved as a residue without being dissolved even when heated in a sealed state at 225 ° C. for 20 minutes in a 18% hydrochloric acid aqueous solution. One example is ZrO ₂ . On the other hand, the lithium composite oxide referred to in the present application is considered to be caused by the solid solution of zirconium in lithium cobalt oxide. Specifically, the lithium composite oxide is a solid solution of zirconium in a lithium cobalt composite oxide or a composite of lithium and zirconium. Presumed to be an oxide. In addition, it has a property of being dissolved when heated in a sealed state at 225 ° C. for 20 minutes by microwave in at least 18% hydrochloric acid aqueous solution. For example, Li ₂ ZrO ₃ , LiCoO ₂ in which zirconium is dissolved, etc. Can be mentioned.

  The 18% hydrochloric acid aqueous solution according to the present invention is an aqueous solution prepared by mixing commercially available about 36% concentrated hydrochloric acid with pure water at a volume ratio of 1: 1, not strictly an 18% concentration hydrochloric acid aqueous solution, About 18% is sufficient. The percentage of hydrochloric acid is based on weight.

  The storage characteristics referred to in the present application are measured by observing the amount of gas such as carbon dioxide generated when left at 20 to 100 ° C. for 1 to 20 days with a high voltage applied to the prepared battery. Can do. As a result of being left in this charged state, the smaller the amount of gas generated, the more the positive electrode active material has better storage characteristics. A positive electrode active material having excellent storage characteristics is preferred because it is expected that the battery container will not swell when used as a battery.

  The ratio of zirconium oxide or lithium composite oxide to zirconium contained in the positive electrode active material according to the present invention is measured as follows. However, the measurement method of the ratio of the following zirconium oxide or lithium composite oxide is an example of a suitable one, and the measurement method is not particularly limited thereto.

  First, about 1.0000 g of the positive electrode active material powder is weighed and transferred to a pressure-sealing container made of plastic and made of PTFE resin. Next, about 10 ml of 18% hydrochloric acid aqueous solution was added, the container was sealed, and most of the positive electrode active material was heated by microwave at 225 ° C. for 20 minutes using MICROWAVE LABORATORY SYSTEM LAB Terminal 800 manufactured by Milestone. A dissolved aqueous hydrochloric acid solution is obtained. At this time, there are components that do not dissolve in the aqueous hydrochloric acid solution, and they remain undissolved as a residue. The aqueous solution and the residue are transferred to a 100 ml volumetric flask and made up, and then the residue is allowed to settle. The amount of the lithium composite oxide (mol) can be determined by separating the supernatant and examining the composition of the dissolved component by ICP measurement.

  Further, the residue obtained by centrifuging the mixture of the remaining aqueous solution and the residue is washed and then dried. The residue after drying was a white powder. With respect to this residue, an X-ray diffraction spectrum is measured using an X-ray diffractometer (RINT2100 type, manufactured by Rigaku Corporation). Specifically, by high-sensitivity powder X-ray diffraction using CuKα rays, an applied voltage of 50 KV, an acceleration current of 250 mA, a scanning speed of 1 ° / min, a step angle of 0.02 °, a divergence slit of 1 °, a scattering slit of 1 °, An X-ray diffraction spectrum was measured under the conditions of a light receiving slit of 0.3 mm and monochrome monochromation. From this measurement, it was found that the residue was zirconium oxide.

  Next, 0.5000 g of the positive electrode active material powder is newly weighed and transferred to a pressure sealed container whose inside is made of PTFE resin. About 5 ml of sulfuric acid aqueous solution in which concentrated sulfuric acid and pure water are mixed at a volume ratio of 1: 1 is added, 5 drops of hydrogen peroxide is dropped, the container is sealed, placed in an oven at 230 ° C., and heated for 12 hours. When the sealed container was opened, a red precipitate remained. Then, about 10 ml of 18% hydrochloric acid aqueous solution was added and heated to dissolve completely. The solution thus obtained is analyzed by ICP, and the total amount (mol) of zirconium contained in the positive electrode active material is measured.

  By multiplying the value obtained by dividing the amount (mol) of the lithium composite oxide obtained as described above by the total amount (mol) of zirconium by 100, the ratio of the lithium composite oxide to the total amount of zirconium contained in the positive electrode active material ( mol%) can be obtained.

  Also, subtracting the amount (mol) of the lithium composite oxide from the total amount (mol) of zirconium gives the amount (mol) of the component that does not dissolve in the hydrochloric acid aqueous solution, and further dividing this by the total amount (mol) of zirconium. By multiplying by 100, the ratio (mol%) of the amount of the component not dissolved in the hydrochloric acid aqueous solution with respect to zirconium contained in the positive electrode active material can be obtained.

  Conventionally, in order to examine the charge / discharge cycle characteristics of the positive electrode active material, a method of actually manufacturing a lithium secondary battery and repeatedly testing it by charging / discharging has been adopted. Similarly, in order to investigate the storage characteristics, a method of actually manufacturing a lithium secondary battery and storing and testing it for a long period of time has been adopted. These methods required a long time, a lot of labor and a lot of cost. However, by using the above analysis method, it is possible to judge the quality of charge / discharge cycle characteristics and storage characteristics easily and inexpensively in a significantly shorter period of time (hereinafter referred to as this analysis method). Zirconium simplified analysis method).

  The amount of zirconium contained in the positive electrode active material according to the present invention is preferably in the range of 0.01 to 1.5 mol% with respect to cobalt, and more preferably in the range of 0.02 to 1.0 mol%. Is preferable, and is particularly preferably in the range of 0.05 to 0.75 mol%. When the amount of zirconium is in the above range, the balance between charge / discharge cycle characteristics and discharge capacity is good, which is preferable. That is, the possibility of obtaining a positive electrode active material having sufficient charge / discharge cycle characteristics and high discharge capacity is increased.

Furthermore, the positive electrode active material of the present invention preferably contains aluminum and / or magnesium. These elements have the effect of further improving safety.
0.05-3.0 mol% is preferable with respect to cobalt, and, as for the quantity of aluminum contained in the positive electrode active material of this invention, 0.1-2.0 mol% is more preferable. Similarly, the amount of magnesium is preferably 0.05 to 3.0 mol%, more preferably 0.1 to 2.0 mol%.

  When the amount of aluminum or magnesium contained in the positive electrode active material is within the above range, the balance between charge / discharge cycle characteristics, discharge capacity, and safety is very good, which is preferable. That is, it is preferable because it is likely to be a positive electrode active material having sufficient charge / discharge cycle characteristics, high discharge capacity, and high safety.

  In addition, when the positive electrode active material according to the present invention is a positive electrode active material having 0.1 to 3.0 mol% of aluminum and magnesium with respect to cobalt, the positive electrode active material is significantly more excellent. It exhibits charge / discharge cycle characteristics, discharge capacity and safety, and also has a very good balance, and at the same time has excellent storage characteristics, which is very preferable.

  In addition, in the measurement of the amount of zirconium, aluminum, magnesium and cobalt contained in the positive electrode active material, the above-mentioned high frequency plasma emission analysis (ICP), X-ray diffraction method (XRD), energy dispersive X-ray spectroscopy (EDX) X-ray photoelectron analysis (ESCA), electron probe microanalysis (EPMA), or the like can be used.

  Value obtained by dividing the amount of lithium (mol) contained in the positive electrode active material according to the present invention by the total amount (mol) of other metals (eg, zirconium, aluminum, magnesium, cobalt) other than lithium contained in the positive electrode active material The preferable range (hereinafter referred to as Li / Me ratio) is 0.97 to 1.03, and more preferably 0.98 to 1.00.

  When producing the positive electrode active material of the present invention, when the Li / Me ratio is in the above range, the positive electrode active material of the present invention tends to be stably produced and it is difficult to produce a defective product lot. The Li / Me ratio is preferably in the above range.

  If the total amount of zirconium, aluminum and magnesium contained in the positive electrode active material of the present invention is too large relative to cobalt in the positive electrode active material, the discharge capacity may decrease, and the charge / discharge cycle characteristics may deteriorate. The total amount of zirconium, aluminum and magnesium with respect to cobalt is preferably 0.1 to 3.5 mol%.

  The manufacturing method of the positive electrode active material of this invention is not necessarily restrict | limited, It can manufacture by a known method. For example, the cobalt raw material is not particularly limited, but cobalt hydroxide, cobalt oxide, cobalt oxyhydroxide, cobalt sulfate, and cobalt nitrate can be used, and cobalt hydroxide and cobalt oxyhydroxide are particularly preferable.

Although it does not specifically limit as a lithium raw material, Lithium carbonate and lithium hydroxide can be used, and lithium carbonate and lithium hydroxide are especially preferable.
Although it does not specifically limit as a zirconium raw material, an aluminum raw material, or a magnesium raw material, The organic acid salt containing an oxide, a hydroxide, nitrate, a sulfate, and acetate can be used, and an oxide and a hydroxide are especially preferable.

  The raw material mixed powder according to the present invention is preferably fired at a temperature of 800 to 1100 ° C. in an oxygen-containing atmosphere for 5 to 24 hours. If the calcination temperature is lower than 800 ° C., the reaction may be incomplete and unreacted raw materials may remain in the product positive electrode active material, and if it exceeds 1100 ° C., the product positive electrode active material is partially decomposed. There is a possibility that charge / discharge cycle characteristics and discharge capacity may be deteriorated. Further, the firing temperature is more preferably in the range of 900 to 1050 ° C. The obtained fired product is cooled, pulverized and classified to obtain the positive electrode active material powder of the present invention.

The positive electrode active material powder of the present invention thus obtained has an average particle size of preferably 10 to 25 μm, more preferably 12 to 20 μm, and a specific surface area of preferably 0.15 to 0.60 m ² / g, particularly preferably 0.18 to 0.50 m ² / g.

  The average particle size in the present invention means a cumulative 50% value of the volume particle size distribution obtained by a laser scattering particle size distribution measuring apparatus (for example, using Microtrack HRAX-100 manufactured by Lees & Northrup). The specific surface area was determined by the BET method.

  The (110) plane diffraction peak integral width of 2θ = 66.5 ± 1 ° measured by X-ray diffraction using a CuKα radiation source (manufactured by Rigaku Corporation, using RINT2100 type) is preferably 0.09-0. .13 °.

  If the average particle diameter, specific surface area or (110) plane diffraction peak integral width of the positive electrode active material powder is not within the above range, the current collector characteristics of the positive electrode, self-discharge characteristics and safety are reduced. It may be difficult to uniformly apply to the body, which is not preferable.

A method for obtaining a positive electrode for a lithium secondary battery using the positive electrode active material according to the present invention can be carried out according to a conventional method. For example, the positive electrode mixture is formed by mixing the positive electrode active material powder of the present invention with a carbon-based conductive material such as acetylene black, graphite, or ketjen black and a binder. As the binder, polyvinylidene fluoride, polytetrafluoroethylene, polyamide, carboxymethyl cellulose, acrylic resin, or the like is used.
A slurry in which the above positive electrode mixture is dispersed in a dispersion medium such as N-methylpyrrolidone is applied to a positive electrode current collector such as an aluminum foil, dried and press-rolled to form a positive electrode active material layer on the positive electrode current collector Form.

In the lithium secondary battery using the positive electrode active material of the present invention for the positive electrode, the solute of the electrolyte solution is ClO ₄ ⁻ , CF ₃ SO ₃ ⁻ , BF ₄ ⁻ , PF ₆ ⁻ , AsF ₆ ⁻ , SbF ₆ ⁻ , It is preferable to use at least one of lithium salts having CF ₃ CO ₂ ⁻ , (CF ₃ SO ₂ ) ₂ N ⁻ or the like as an anion. In the above electrolyte solution or polymer electrolyte, an electrolyte composed of a lithium salt is preferably added to the solvent or the solvent-containing polymer at a concentration of 0.2 to 2.0 mol / L. If it deviates from this range, the ionic conductivity is lowered and the electrical conductivity of the electrolyte is lowered. More preferably, 0.5 to 1.5 mol / L is selected. For the separator, porous polyethylene or porous polypropylene film is used.

  Further, as the solvent of the electrolyte solution, a carbonate ester is preferable. The carbonate ester can be either cyclic or chain. Examples of cyclic carbonates include propylene carbonate and ethylene carbonate (EC). Examples of the chain carbonate include dimethyl carbonate, diethyl carbonate (DEC), ethyl methyl carbonate, methyl propyl carbonate, methyl isopropyl carbonate and the like.

  The carbonate ester may be used alone or in combination of two or more. Moreover, you may mix and use with another solvent. Further, depending on the material of the negative electrode active material, when a chain carbonate ester and a cyclic carbonate ester are used in combination, discharge characteristics, charge / discharge cycle characteristics, and charge / discharge efficiency may be improved.

  Further, by adding a vinylidene fluoride-hexafluoropropylene copolymer (for example, Kyner manufactured by Atchem Co.) or a vinylidene fluoride-perfluoropropyl vinyl ether copolymer to these organic solvents, and adding the following solute, the gel polymer electrolyte is added. It is also good.

  The negative electrode active material of a lithium battery using the positive electrode active material of the present invention for the positive electrode is a material that can occlude and release lithium ions. The material for forming the negative electrode active material is not particularly limited. For example, lithium metal, lithium alloy, carbon material, carbon compound, silicon carbide compound, silicon oxide compound, titanium sulfide, boron carbide compound, periodic table 14, and group 15 metal are used. The main oxides are listed.

  As the carbon material, those obtained by pyrolyzing organic substances under various pyrolysis conditions, artificial graphite, natural graphite, soil graphite, expanded graphite, scale-like graphite, and the like can be used. As the oxide, a compound mainly composed of tin oxide can be used. As the negative electrode current collector, a copper foil, a nickel foil or the like is used.

  There is no restriction | limiting in particular in the shape of the lithium secondary battery which uses the positive electrode active material in this invention. A sheet shape (so-called film shape), a folded shape, a wound-type bottomed cylindrical shape, a button shape, or the like is selected depending on the application.

EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.
(Example 1)
Lithium carbonate with a lithium content of 18.7% by weight, zirconium oxide with a zirconium content of 74.0% by weight, magnesium hydroxide with a magnesium content of 41.6% by weight, aluminum hydroxide with an aluminum content of 34.6% by weight and cobalt content 59. Cobalt oxyhydroxide powder having an average particle diameter D50 of 12.3 μm and a weight ratio of Li: Zr: Mg: Al: Co is 1: 0.002: 0.005: 0.005: 0.988. The raw material mixed powder was prepared by mixing so that Subsequently, this raw material mixed powder was fired at 1000 ° C. for 15 hours in the air. After firing, the mixture was pulverized to obtain a positive electrode active material powder.

  In order to measure the amount of zirconium oxide contained in the positive electrode active material powder, analysis was performed using the above-described simple zirconium analysis method. As a result, 31 mol% of the added zirconium was zirconium oxide, and 69 mol% was a lithium composite oxide. Met.

With respect to this positive electrode active material powder, the specific surface area determined by the BET method was 0.32 m ² / g, and the average particle diameter D50 determined by a laser scattering particle size distribution meter was 12.3 μm.

  Further, an X-ray diffraction spectrum was obtained using an X-ray diffractometer (RINT2100, manufactured by Rigaku Corporation). In powder X-ray diffraction using CuKα ray, the (110) plane diffraction peak integration width at 2θ = 66.5 ± 1 ° was 0.121 °.

  Next, the positive electrode active material powder, acetylene black, and polyvinylidene fluoride powder were mixed at a weight ratio of 90/5/5, N-methylpyrrolidone was added to prepare a slurry, and an aluminum foil having a thickness of 20 μm One side coating was performed using a doctor blade. Subsequently, it dried and roll-press-rolled to produce the positive electrode sheet for lithium batteries.

The positive electrode sheet is punched out as a positive electrode, a metal lithium foil having a thickness of 500 μm is used as a negative electrode, a nickel foil of 20 μm is used as a negative electrode current collector, and a porous polypropylene having a thickness of 25 μm is used as a separator. Further, the electrolytic solution used is a LiPF ₆ / EC + DEC (1: 1) solution having a concentration of 1 M (meaning a mixed solution of EC and DEC in volume ratio (1: 1) containing LiPF ₆ as a solute. Solvents described later). The stainless steel simple sealed cell type lithium battery was assembled in an argon glove box.

  The assembled battery is charged at 4.3 V for 10 hours, disassembled in an argon glove box, the positive electrode sheet after charging is taken out, the positive electrode sheet is washed, punched to a diameter of 3 mm, and aluminum together with EC. It sealed in the capsule made from a product, and heated at a rate of 5 ° C./min with a scanning differential calorimeter to measure the heat generation start temperature. As a result, the heat generation start temperature of the 4.3V charged product was 161 ° C.

  Moreover, the same battery was further produced, and the evaluation at the time of high voltage use was performed as follows. At 25 ° C., the battery was charged to 4.5 V with a load current of 75 mA per 1 g of the positive electrode active material, and discharged to 2.5 V with a load current of 75 mA per 1 g of the positive electrode active material. The initial discharge capacity at this time was 189 mAh / g. The volume capacity density was determined from the density of the electrode layer and the capacity per weight. Further, the charge / discharge cycle test was performed 50 times. As a result, the capacity retention rate after 50 charge / discharge cycles at 25 ° C. was 94.8%.

(Examples 2-4, Comparative Examples 1-2)
Except that the amount of lithium carbonate, zirconium oxide, magnesium hydroxide, aluminum hydroxide, and cobalt oxyhydroxide powders as raw materials was appropriately changed, and a positive electrode active material having a composition as shown in Table 1 below was synthesized, the above implementation was carried out. In the same manner as in Example 1, a positive electrode active material powder was obtained. In Table 1, Li, Zr, Mg, Al, and Co are molar ratios of each element contained in the positive electrode active material. Further, the ratio (mol%) of zirconium oxide or lithium composite oxide in zirconium in the positive electrode active material is also described.

(Comparative Example 3)
Adjusting the amount of the raw material lithium carbonate, zirconium oxide, magnesium hydroxide, aluminum hydroxide and cobalt content of 60.2% by weight and the average particle size D50 of 12.4 μm cobalt oxyhydroxide powder; The same as Example 1 except that the positive electrode active material was synthesized so that the molar ratio of Li: Zr: Mg: Al: Co was 1: 0.002: 0.005: 0.005: 0.988. Thus, a positive electrode active material powder was obtained. Table 1 also shows the ratio (mol%) of zirconium oxide or lithium composite oxide in zirconium in the positive electrode active material.

  Next, the positive electrode active material powders obtained in Examples 2 to 4 or Comparative Examples 1 to 3 were measured in the same manner as in Example 1 to measure the powder characteristics and battery characteristics of the positive electrode active material. The results are shown in Table 2 below together with Example 1.

  Table 3 collectively shows the amount (mol%) of zirconium, magnesium or aluminum contained in the positive electrode active materials obtained in Examples 1 to 4 and Comparative Examples 1 to 3 with respect to cobalt.

  As described above, according to the present invention, there is provided a positive electrode active material for a lithium secondary battery that has excellent charge / discharge cycle characteristics that are useful for a lithium secondary battery, has a high capacity, and can be used for high voltage applications. Provided.

Claims (8)

  A positive electrode active material for a non-aqueous electrolyte secondary battery containing a lithium atom, a cobalt atom and a zirconium atom, wherein 30 to 95 mol% of zirconium atoms contained in the positive electrode active material is zirconium oxide, and 5 to 70 mol% is a lithium composite A positive electrode active material for a non-aqueous electrolyte secondary battery that exists as an oxide.   The positive electrode active material for a nonaqueous electrolyte secondary battery according to claim 1, wherein the positive electrode active material contains 0.01 to 1.5 mol% of zirconium atoms with respect to cobalt atoms.   The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, wherein the positive electrode active material further contains 0.05 to 3.0 mol% of magnesium atoms with respect to cobalt atoms.   The positive electrode active material for a non-aqueous electrolyte secondary battery according to any one of claims 1 to 3, wherein the positive electrode active material further contains 0.05 to 3.0 mol% of aluminum atoms with respect to cobalt atoms.   A method for producing a positive electrode active material containing lithium atoms, cobalt atoms and zirconium atoms by mixing a lithium compound, a cobalt compound and a zirconium compound, followed by firing, wherein the powder obtained after firing is 18% at 225 ° C. For a non-aqueous electrolyte secondary battery characterized in that there is a component that does not dissolve in the aqueous hydrochloric acid solution when it is brought into contact with the aqueous hydrochloric acid solution, and the component contains 30 to 95 mol% of zirconium contained in the powder. Method for producing positive electrode active material   The method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 5, wherein the component not dissolved in the hydrochloric acid aqueous solution is zirconium oxide.   It is a positive electrode for lithium secondary batteries containing a positive electrode active material, a electrically conductive material, and a binder, The said positive electrode active material contains the positive electrode active material for nonaqueous electrolyte secondary batteries in any one of Claims 1-4. A positive electrode for a lithium secondary battery, comprising a positive electrode active material for a water electrolyte secondary battery.   A lithium secondary battery comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte, wherein the positive electrode comprises the positive electrode according to claim 7.