JP2015084273A - Positive electrode active material for lithium ion secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a positive electrode active material, usable even under a high voltage, excellent in battery performance such as discharge capacity, discharge average voltage, stability, volume capacity density, and charge/discharge cycle durability.SOLUTION: The positive electrode active material for a lithium ion secondary battery has phosphate on particle surfaces of a complex oxide containing lithium cobalt. A ratio D2/D1 of a phosphate crystallite diameter D2 to a lithium cobalt-containing complex oxide crystallite diameter D1 satisfies D2/D1≥0.45.

Description

  The present invention relates to a positive electrode active material used for a positive electrode material for a lithium ion secondary battery having a large volumetric capacity density and excellent charge / discharge cycle durability.

In recent years, as devices become more portable and cordless, demands for non-aqueous electrolyte secondary batteries such as lithium ion secondary batteries that are small, lightweight, and have high energy density are increasing. Examples of the positive electrode active material for the non-aqueous electrolyte secondary battery include LiCoO ₂ , LiNi _1/3 Co _1/3 Mn _1/3 O ₂ , LiNiO ₂ , LiNi _0.8 Co _0.2 O ₂ , LiMn _2. A composite oxide of lithium such as O ₄ and a transition metal (sometimes referred to as a lithium-containing composite oxide in the present invention) is known.

Among them, a lithium ion secondary battery using LiCoO ₂ as a positive electrode active material and a lithium alloy, or carbon such as graphite or carbon fiber as a negative electrode can obtain a high discharge voltage of 4 V class, and thus has a high energy density. This battery is excellent and widely used.

However, in the case of a lithium ion secondary battery using LiCoO ₂ as a positive electrode active material, the discharge capacity, the discharge average voltage, and the stability against heat during heating (in the present invention, it may be simply referred to as “safety”) Improvements are desired, and repeated charging / discharging cycles have problems of durability of charging / discharging cycles such as reduction in battery discharge capacity and swelling due to the reaction between the interface of the positive electrode active material and the electrolyte.
Further, when the charge / discharge voltage is set to a high voltage such as 4.5 V, there are problems such as remarkable deterioration of charge / discharge cycle durability and expansion of the battery due to generation of gas such as carbon dioxide due to decomposition of the electrolyte.

In order to solve these problems, for example, a lithium-containing composite oxide such as LiCoO ₂ , a phosphorus compound, and a solvent such as water or ethanol were mixed, dried and fired, and phosphoric acid was contained on the particle surface. It has been proposed to use a lithium-containing composite oxide (see Patent Documents 1 to 3).

  Further, a phosphorus compound is deposited on a lithium-containing composite oxide containing nickel (Ni), cobalt (Co) and aluminum (Al), or a lithium-containing composite oxide containing nickel, cobalt and manganese (Mn), and heated. It has been proposed to use a lithium-containing composite oxide containing a phosphorus compound on the surface of particles obtained by treatment (see Patent Documents 4 and 5).

  Furthermore, it has been proposed to use a lithium-containing composite oxide containing phosphorus obtained by mixing a lithium compound, a cobalt compound, a nickel compound, a manganese compound, and a phosphorus compound and then firing the mixture (patent) References 6 and 7).

International Publication No. 2006/85588 Special table 2008-530747 JP 2007-335331 A JP 2010-55777 A JP 2006-73482 A JP-A-5-36411 JP-A-5-47383

  As described above, various studies have been made so far, and lithium-containing composite oxides that satisfy all of the battery characteristics such as discharge capacity, discharge average voltage, stability, volume capacity density, and charge / discharge cycle durability. Is not obtained.

  For example, Example 7 of Patent Document 1 describes a positive electrode active material obtained by mixing phosphoric acid and a lithium-containing composite oxide. However, phosphoric acid and a lithium-containing composite oxide as a base material are mixed. The heat treatment temperature after the treatment is not described. As specific firing temperature, Example 2 only describes that heat treatment was performed at 500 ° C. in synthesizing a positive electrode active material containing boron. In this way, when the heat treatment temperature is low, the crystal growth of the phosphate and lithium-containing composite oxide is insufficient and the crystallinity is low, so the battery characteristics such as charge / discharge cycle durability and safety are insufficient. Therefore, further performance improvement is required.

Patent Document 2 describes a positive electrode active material obtained by bringing a lithium-containing composite oxide such as LiNi _0.5 Mn _1.5 O ₄ and LiCoO ₂ into contact with an aqueous solution containing phosphate ions. However, since the heat treatment temperature is 500 ° C. or less, the obtained positive electrode active material has insufficient crystal growth of phosphate and lithium-containing composite oxide, low crystallinity, charge / discharge cycle durability, safety In view of battery characteristics such as performance, the battery did not have a performance that could withstand practical use.

Patent Document 3 describes a positive electrode active material obtained by putting a lithium-containing composite oxide such as LiCoO ₂ into an aqueous solution containing a phosphorus compound, kneading and then drying. Crystal growth does not proceed under drying conditions such as drying at 130 ° C. and heat treatment at 900 ° C. for 3 hours specifically described in Patent Document 3, so that the crystallinity of the phosphate and lithium-containing composite oxide is low. In terms of battery characteristics such as charge / discharge cycle durability and safety, the battery characteristics were not practical.

  Patent Documents 4 and 5 disclose a positive electrode active material obtained by mixing a lithium-containing composite oxide containing Ni, Co, and Al or a lithium-containing composite oxide containing Ni, Co, and Mn and a phosphoric acid compound, and then performing a heat treatment. Is described. However, if a lithium-containing composite oxide containing Ni, Al, or Mn is used as a base material, the crystal growth of phosphate and lithium-containing composite oxide can be achieved even if the firing temperature is increased or the firing time is increased. However, since the crystallinity is lowered without progressing, the battery characteristics such as charge / discharge cycle durability and safety are poor, and it cannot be put into practical use.

  In a positive electrode active material obtained by firing a mixture of a lithium compound, a cobalt compound, and a phosphoric compound such as lithium phosphate or phosphoric acid described in Patent Documents 6 and 7, the phosphorous compound is dispersed inside the particles. Then, since the lithium compound, cobalt compound and phosphorus compound on the particle surface do not sufficiently react, the crystallinity of the phosphate and the lithium-containing composite oxide is lowered, and an excess lithium compound which does not react on the particle surface remains. The durability of the charge / discharge cycle was poor, and when charging / discharging was repeated for a long period of time, the deterioration progressed and the discharge capacity was significantly reduced.

  Therefore, the present invention is a positive electrode that can be used even under high voltage, has excellent battery performance such as discharge capacity, discharge average voltage, safety and charge / discharge cycle durability, and suppresses expansion of the battery due to charge / discharge. The purpose is to provide an active material.

The inventors of the present invention have intensively studied to achieve the above-mentioned problems, and have reached the present invention having the following configuration.
(1) In formula _{Li p Co x M y O z} F a ( where, M is at least one element selected transition metal elements other than Co, Al, from the group consisting of Sn and the second group element 0.9 ≦ p ≦ 1.2, 0.9 ≦ x ≦ 1, 0 ≦ y ≦ 0.1, 1.9 ≦ z ≦ 2.1, 0 ≦ a ≦ 0.05) A cathode active material having a phosphate on the particle surface of the cobalt-containing composite oxide, wherein a ratio D2 / D1 between the crystallite diameter D2 of the phosphate and the crystallite diameter D1 of the lithium cobalt-containing composite oxide is D2. /D1≧0.45, A positive electrode active material for a lithium ion secondary battery.
(2) The positive electrode active material according to (1), wherein the crystallite diameter D2 of the phosphate is D2 ≧ 40 nm.
(3) The positive electrode active material according to (1) or (2), wherein the content of phosphorus contained in the positive electrode active material is greater than 0.3 mol% with respect to the lithium cobalt-containing composite oxide.
(4) The positive electrode active material according to (3), wherein the content of phosphorus contained in the positive electrode active material is 0.5 to 2.0 mol% with respect to the lithium cobalt-containing composite oxide.
(5) The positive electrode active material according to any one of (1) to (4), wherein the phosphate is lithium phosphate.
(6) The positive electrode active material according to (5), wherein the crystal structure of lithium phosphate is orthorhombic.
(7) The positive electrode active material according to (5) or (6) above, wherein the half width β2 of the (210) plane of lithium phosphate is 0.25 rad or less.
(8) The ratio β2 / β1 between the half width β2 of the (210) plane of lithium phosphate and the half width β1 of the (003) plane of the lithium cobalt-containing composite oxide is β2 / β1 ≦ 2 above (5) -The positive electrode active material in any one of (7).
(9) The positive electrode active material according to any one of (1) to (8), wherein the M element is at least one element selected from the group consisting of Zr, Hf, Ti, Mg, and Al.
(10) The positive electrode active material according to any one of (1) to (9), wherein the M element contains Mg and Al, and Mg / Al, which is a molar ratio of Mg and Al, is 0.1 to 10.
(11) The atomic ratio Li / (Co + M) between lithium of the lithium-cobalt-containing composite oxide and cobalt and M is 0.99 ≦ Li / (Co + M) ≦ 1.10. The above (1) to (10) The positive electrode active material in any one.
(12) The positive electrode active material according to any one of the above (1) to (11), wherein the ratio of the lattice constant a to the lattice constant c of the positive electrode active material is c / a ≧ 4.992.
(13) A positive electrode comprising the positive electrode active material described in any of (1) to (12) above, a conductive agent, and a binder.
(14) A lithium ion secondary battery comprising the positive electrode described in (13) above, a negative electrode, a separator, and a nonaqueous electrolyte.

  According to the present invention, it can be used at a voltage higher than usual, that is, when a lithium or carbonaceous material is used for the negative electrode, 4.45V or more, particularly 4.5V or more. A positive electrode active material for a lithium ion secondary battery, which is excellent in battery performance such as safety and charge / discharge cycle durability and in which the expansion of the battery accompanying charge / discharge is suppressed, is provided.

  Although it is not necessarily clear why the positive electrode active material for lithium ion secondary batteries of the present invention exhibits excellent characteristics as a positive electrode for lithium ion secondary batteries as described above, it is estimated as follows. .

  The positive electrode active material of the present invention has a phosphate having high crystallinity in which D2 / D1 is in a specific range on the particle surface of the lithium cobalt-containing composite oxide. Since the reactivity with the electrolytic solution is low, the decomposition reaction of the electrolytic solution that occurs when charging and discharging are repeated and the decomposition reaction of the lithium cobalt-containing composite oxide that is the base material can be suppressed. When such a decomposition reaction proceeds in the battery, carbon dioxide and water are generated, leading to deterioration of the battery such as a decrease in capacity and a decrease in discharge voltage. On the other hand, in the positive electrode active material of the present invention, since the decomposition reaction thereof is suppressed, the expansion of the battery is suppressed even under a high voltage condition, and a good capacity retention rate, a high discharge average voltage and an excellent charge are obtained. It is estimated that the discharge cycle durability can be realized.

  The positive electrode active material of the present invention has a phosphate on at least the particle surface of the lithium cobalt-containing composite oxide, and the ratio D2 of the crystallite diameter D2 of the phosphate and the crystallite diameter D1 of the lithium cobalt-containing composite oxide. / D1 is D2 / D1 ≧ 0.45.

  The crystallite diameter D2 of the phosphate is preferably D2 ≧ 40 nm, especially. D2 ≧ 45 nm is more preferable, and D2 ≧ 50 nm is particularly preferable. Moreover, although an upper limit is not specifically limited, Especially D2 <= 100nm is preferable and D2 <= 80nm is more preferable. The crystallite diameter D1 of the lithium cobalt-containing composite oxide is not particularly limited, but is preferably D1 ≧ 50 nm, more preferably D1 ≧ 55 nm, and particularly preferably D1 ≧ 60 nm. Further, the upper limit is preferably D1 ≦ 150 nm, and more preferably D1 ≦ 120 nm. The ratio of D2 and D1 is D2 / D1 ≧ 0.45, and among them, D2 / D1 ≧ 0.50 is preferable, and D2 / D1 ≧ 0.60 is more preferable. Further, the upper limit of D2 / D1 is preferably D2 / D1 ≦ 1.50. When D2, D1, and D2 / D1 are in the above ranges, battery characteristics such as charge / discharge cycle durability tend to be particularly improved.

In the present invention, the crystallite diameters D2 and D1 are peak-searched by the powder X-ray diffraction method from the obtained X-ray diffraction spectrum using analysis software PDXL and database ICDD PDF-2 (manufactured by Rigaku Corporation). Thus, it is obtained by calculating the half width β.
The crystallite diameters D2 and D1 are obtained from the following formula (Scherrer formula).

(Equation 1)
D = K × λ / (β × cos θ)
D: Crystallite diameter [nm]
K: Scherrer coefficient
λ: X-ray wavelength [nm]
β: Half width [rad]
θ: Peak angle [rad]
Moreover, in the positive electrode active material of the present invention, the content of phosphorus is preferably 0.3 mol% or more, more preferably 0.5 to 3.0 mol% with respect to the lithium cobalt-containing composite oxide as a base material, 0.7 to 2.0 mol% is particularly preferable.

  As the phosphate, an alkali metal salt or alkaline earth metal salt of phosphoric acid is preferable, and among them, lithium phosphate, potassium phosphate, sodium phosphate, calcium phosphate, or magnesium phosphate is preferable, and lithium phosphate is particularly preferable. .

  When the phosphate is lithium phosphate, the full width at half maximum β2 of the (210) plane of lithium phosphate is preferably β2 ≦ 0.25 rad, more preferably β2 ≦ 0.20 rad, and in particular, β2 ≦ 0.16 rad. Particularly preferred. Further, β2 ≧ 0.090 rad is preferable.

  The half width β1 of the (003) plane of the lithium cobalt-containing composite oxide is preferably β1 ≦ 0.15 rad, more preferably β1 ≦ 0.13 rad, and particularly preferably β1 ≦ 0.12 rad. Further, β1 ≧ 0.07 rad is preferable.

The ratio β2 / β1 between the half width β2 of the (210) plane of lithium phosphate and the half width β1 of the (003) plane of the lithium cobalt-containing composite oxide is preferably β2 / β1 ≦ 2.0, β2 / β1 ≦ 1.6 is more preferable. Further, the lower limit of β2 / β1 is preferably β2 / β1 ≧ 1.0.
The crystal structure of lithium phosphate is preferably orthorhombic.

  The positive electrode active material of the present invention is preferably a particle having an average particle diameter D50 of 1 to 30 μm. In the present invention, the average particle size D50 is a particle size at which the particle size distribution is obtained on a volume basis and the cumulative curve is 50% in a cumulative curve where the total volume is 100%. It means the diameter (D50). The particle size distribution is obtained from a frequency distribution and a cumulative volume distribution curve measured with a laser scattering particle size distribution measuring apparatus. The particle size is measured by sufficiently dispersing the particles in an aqueous medium by ultrasonic treatment or the like and measuring the particle size distribution (for example, using Microtrack HRAX-100 manufactured by Nikkiso Co., Ltd.). Especially, 5-30 micrometers is more preferable and, as for the average particle diameter D50 of the positive electrode active material of this invention, 8-25 micrometers is especially preferable.

Moreover, the specific surface area of the positive electrode active material of the present invention is preferably 0.1 to 0.8 m ² / g. In the present invention, the specific surface area is measured by the BET method. Among them a specific surface area of the positive electrode active material of the present invention is more preferably ^{0.1~0.7m 2 / g, 0.15~0.60m 2 /} g is particularly preferred.

  The ratio c / a between the a-axis lattice constant a and the c-axis lattice constant c of the lithium cobalt-containing composite oxide as a base material is preferably c / a ≧ 4.992, and c / a ≧ 4.993 is satisfied. More preferred. The upper limit of the ratio c / a between the a-axis lattice constant a and the c-axis lattice constant c is preferably c / a ≦ 4.997.

Cathode active lithium-cobalt-containing composite oxide as the base material of the material of the present invention have the general formula _{Li p Co x M y O z} F a ( where, M is a transition metal element other than Co, Al, Sn, and the second At least one element selected from the group consisting of elements of the group: 0.9 ≦ p ≦ 1.2, 0.9 ≦ x ≦ 1, 0 ≦ y ≦ 0.1, 1.9 ≦ z ≦ 2. .1, 0 ≦ a ≦ 0.05).

  In the above general formula, p, x, y, z and a are as defined above. Among these, p is preferably 0.95 ≦ p ≦ 1.10, more preferably 0.95 ≦ p ≦ 1.07, and particularly preferably 0.97 ≦ p ≦ 1.04. x is preferably 0.93 ≦ y <1.0, more preferably 0.965 ≦ x ≦ 0.9995, and particularly preferably 0.995 ≦ x ≦ 0.999. y is preferably 0 <y ≦ 0.07, more preferably 0.0005 ≦ y ≦ 0.05, and particularly preferably 0.001 ≦ y ≦ 0.035. In this case, the balance of battery performance, that is, the balance of discharge capacity, safety, and charge / discharge cycle stability is good. In addition, when M element is included, the discharge capacity tends to decrease. Therefore, when importance is attached to the discharge capacity, a composition not including M element, that is, y = 0 is preferable. z is preferably 1.95 ≦ z ≦ 2.05, more preferably 1.97 ≦ z ≦ 2.03.

  When the lithium cobalt-containing composite oxide contains fluorine, the heat generation start temperature is improved, and the safety is further improved. Therefore, when safety is important, a is preferably 0 <a ≦ 0.03, more preferably 0.0005 ≦ a ≦ 0.02, and particularly preferably 0.001 ≦ a ≦ 0.01. On the other hand, when a = 0, that is, when the lithium cobalt-containing composite oxide does not contain fluorine, the discharge capacity tends to increase. Therefore, a = 0 is preferable when importance is attached to the capacity.

  The M element in the above general formula is at least one element selected from the group consisting of transition metal elements other than Co, Al, Sn, and Group 2 elements. Here, the transition metal element represents a transition metal of Group 4, Group 5, Group 6, Group 7, Group 8, Group 9, Group 10, or Group 11 of the Periodic Table. Among these, the M element is preferably at least one element selected from the group consisting of Zr, Hf, Ti, Nb, Ta, Mg, Cu, Sn, Zn, and Al. In particular, at least one element selected from the group consisting of Zr, Hf, Ti, Mg, and Al is more preferable from the viewpoint of capacity development, safety, cycle durability, and the like. The M element contains Mg and Al, and Mg / Al, which is the molar ratio of Mg to Al, is preferably 0.1 to 10.

  Further, for the lithium cobalt-containing composite oxide, the atomic ratio Li / (Co + M) of Li to the total of Co and M elements is preferably 0.99 ≦ Li / (Co + M) ≦ 1.1, and 0.995 ≦ Li / (Co + M) ≦ 1.05 is more preferable.

  Although the manufacturing method of the positive electrode active material of this invention is not specifically limited, Specifically, it can manufacture by the following method.

In the present invention, the composition of the lithium cobalt-containing composite oxide can be measured and analyzed with an ICP analysis (high frequency inductively coupled plasma emission spectroscopy) apparatus.
For example, it can be manufactured by mixing a lithium cobalt-containing composite oxide and a phosphorus compound and then heat-treating the obtained mixture under predetermined conditions. In addition, a mixture containing at least a cobalt compound and a lithium compound is calcined under a predetermined condition to synthesize a calcined powder, and then the calcined powder and the phosphorus compound are mixed, and then the obtained mixture is heat-treated under a predetermined condition. Can be manufactured.

  The phosphorus compound used in the present invention is not particularly limited, but phosphoric acid, pyrophosphoric acid, phosphorous acid, hypophosphorous acid, hexametaphosphoric acid, tripolyphosphoric acid, tetrapolyphosphoric acid, polyphosphoric acid, lithium phosphate, ammonium phosphate, Diammonium hydrogen phosphate, ammonium dihydrogen phosphate, ammonium phosphate ester and the like can be used. Among them, phosphoric acid, pyrophosphoric acid, phosphorous acid, hypophosphorous acid, tripolyphosphoric acid, tetrapolyphosphoric acid, polyphosphoric acid, lithium phosphate, ammonium phosphate, diammonium hydrogen phosphate, ammonium dihydrogen phosphate, guanidine phosphate And one selected from the group consisting of choline phosphate. Among them, there is a tendency to further improve the battery performance, which is considered to have an effect of suppressing the reaction with the electrolytic solution, phosphoric acid, pyrophosphoric acid, hypophosphorous acid, polyphosphoric acid, lithium phosphate, ammonium phosphate, One type selected from the group consisting of diammonium hydrogen phosphate, ammonium dihydrogen phosphate and guanidine phosphate is more preferable. Furthermore, at least one selected from the group consisting of phosphoric acid, pyrophosphoric acid, ammonium phosphate, diammonium hydrogen phosphate, and ammonium dihydrogen phosphate, which are remarkably effective and inexpensive and easily available, is particularly preferable.

In addition, the lithium cobalt-containing composite oxide used as a raw material in the present invention is not particularly limited, and a lithium cobalt-containing composite oxide synthesized by a known method can be used. Among these, the above general formula Li _p Co _x M _y O _z F lithium cobalt-containing complex oxide having a composition represented by _a is preferable. In general, a lithium-cobalt-containing composite oxide is obtained by firing a mixture containing at least a lithium compound and a cobalt compound, and optionally containing an M element compound and a fluorine compound in the range of 700 to 1100 ° C. It is done.

  Although it does not specifically limit as a cobalt compound, It is preferable to use a cobalt hydroxide, a cobalt oxyhydroxide, a cobalt oxide, a cobalt carbonate, a cobalt sulfate, or a cobalt nitrate, Especially, a cobalt hydroxide, a cobalt oxyhydroxide, or an oxidation. Cobalt is more preferred, and cobalt oxyhydroxide is particularly preferred.

  Although it does not specifically limit as a lithium compound, It is preferable to use lithium carbonate or lithium hydroxide, and lithium carbonate is more preferable especially.

  Further, the M element compound is not particularly limited, but is an inorganic salt such as oxide, hydroxide, nitrate, sulfate, carbonate, acetate, oxalate, citrate, maleic acid, lactate, tartaric acid. It is preferable to use an organic acid salt such as a salt, malate or malonate, an organic metal chelate complex, or a compound obtained by stabilizing a metal alkoxide with a chelate or the like.

  Furthermore, although it does not specifically limit as a fluorine compound, It is preferable to use a metal fluoride, and lithium fluoride, magnesium fluoride, or aluminum fluoride is more preferable especially from a viewpoint of a safety improvement.

  The M element compound and the fluorine compound may be added when the lithium cobalt-containing composite oxide and the phosphorus compound are mixed, or may be added to the raw material when the lithium cobalt-containing composite oxide is synthesized. It may be added to the calcined powder.

  When the lithium cobalt-containing composite oxide and the phosphorus compound are mixed and then the resulting mixture is heat-treated to synthesize a positive electrode active material, the heat treatment temperature of the mixture of the lithium cobalt-containing composite oxide and the phosphorus compound is 600 to 1080 ° C. Among them, 650 to 1080 ° C is more preferable, and 700 to 1050 ° C is particularly preferable.

Also, a mixture containing a cobalt compound and a lithium compound is calcined to synthesize calcined powder, and then the calcined powder and phosphorus compound are mixed, and then the resulting mixture is heat treated to synthesize a positive electrode active material. In this case, the calcination temperature is preferably 300 to 600 ° C, more preferably 350 to 600 ° C, particularly preferably 400 to 550 ° C. Furthermore, the heat treatment temperature of the mixture of calcined powder and phosphorus compound is preferably 800 to 1080 ° C, more preferably 900 to 1080 ° C, particularly preferably 950 to 1050 ° C.
Moreover, the atmosphere of calcination and heat treatment is preferably in the air. The specific oxygen concentration during calcination and heat treatment is preferably 10 to 60% by volume, and more preferably 15 to 40% by volume.

  The ratio D2 / D1 between D2 and D1 can be controlled by controlling the temperature and time of the heat treatment. It is preferable to increase the heat treatment temperature or lengthen the heat treatment time because D2 / D1 tends to increase and the battery performance is further improved.

  When the positive electrode active material obtained in the present invention is used as a positive electrode material to produce a positive electrode for a lithium ion secondary battery, first, carbon such as acetylene black, graphite, ketjen black, etc. is used as the positive electrode active material powder. Mix the conductive material and binder. As the binder, polyvinylidene fluoride, polytetrafluoroethylene, polyamide, carboxymethyl cellulose, acrylic resin, or the like is preferably used. The positive electrode active material powder, conductive material and binder obtained by the present invention are made into a slurry or a kneaded product using a solvent or a dispersion medium. This is supported on a positive electrode current collector such as an aluminum foil by coating or the like to produce a positive electrode for a lithium ion secondary battery.

  In the lithium ion secondary battery using the positive electrode active material obtained in the present invention as the positive electrode material, a porous polyethylene film, a porous polypropylene film, or the like is used as the separator. Various solvents can be used as the solvent for the electrolyte solution of the battery, and among them, carbonate ester is preferable. The carbonate ester can be either cyclic or chain. Examples of the cyclic carbonate include propylene carbonate and ethylene carbonate (EC). Examples of the chain carbonate include dimethyl carbonate, diethyl carbonate (DEC), ethyl methyl carbonate (EMC), methyl propyl carbonate, methyl isopropyl carbonate, and the like.

  In this invention, the said carbonate ester can be used individually or in mixture of 2 or more types. Moreover, you may mix and use with another solvent. Moreover, 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, cycle durability, and charge / discharge efficiency may be improved.

Further, in a lithium ion secondary battery using the positive electrode active material obtained in the present invention as the positive electrode material, a vinylidene fluoride-hexafluoropropylene copolymer (for example, trade name Kyner manufactured by Atchem Co.) or vinylidene fluoride- A gel polymer electrolyte containing a perfluoropropyl vinyl ether copolymer may be used as the electrolyte. Solutes added to the electrolyte solvent or polymer electrolyte include ClO ₄ ⁻ , CF ₃ SO ₃ ⁻ , BF ₄ ⁻ , PF ₆ ⁻ , AsF ₆ ⁻ , SbF ₆ ⁻ , CF ₃ CO ₂ ⁻ , (CF ₃ Any one or more of lithium salts having SO ₂ ) ₂ N ^— or the like as an anion is preferably used. The concentration of the lithium salt contained in the electrolyte solvent or polymer electrolyte is preferably 0.2 to 2.0 mol / l (liter), particularly preferably 0.5 to 1.5 mol / l. In this concentration range, the ionic conductivity is large, and the electrical conductivity of the electrolyte is increased.

  In the lithium ion secondary battery using the positive electrode active material obtained in the present invention as the positive electrode material, a material capable of inserting and extracting lithium ions is used as the negative electrode active material. The material for forming the negative electrode active material is not particularly limited. For example, lithium metal, lithium alloy, carbon material, periodic table 14 or group 15 metal oxide, carbon compound, silicon carbide compound, silicon oxide compound, Examples thereof include titanium sulfide and boron carbide compounds. As the carbon material, those obtained by pyrolyzing an organic substance under various pyrolysis conditions, artificial graphite, natural graphite, soil graphite, expanded graphite, flake 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. Such a negative electrode is preferably produced by kneading the active material with an organic solvent to form a slurry, and applying the slurry to a metal foil current collector, drying, and pressing.

  The shape of the lithium battery using the positive electrode active material obtained in the present invention as the positive electrode material is not particularly limited. A sheet shape, a 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 should not be construed as being limited to these examples. The following Examples 1 to 14 are examples of the present invention, and Examples 15 to 18 are comparative examples.
[Example 1]
1.73 g of magnesium carbonate, 20.83 g of aluminum maleate having an Al content of 2.65% by mass, 1.327 g of basic ammonium zirconium carbonate having a Zr content of 14.07% by mass and 6.02 g of citric acid monohydrate An aqueous solution was prepared by dissolving in 24.5 g of water. This aqueous solution was mixed with 196.72 g of cobalt oxyhydroxide having an average particle size of 13 μm and a cobalt content of 60.0% by mass, and then dried to obtain a dry powder.
The obtained dry powder was mixed with 78.97 g of lithium carbonate having an average particle size of 5.6 μm and a lithium content of 18.7% by mass in a mortar, and calcined at 1000 ° C. for 10 hours in the atmosphere. A composite oxide powder was obtained. The composition of the obtained lithium cobalt-containing composite oxide was Li _1.02 (Co _0.979 Mg _0.01 Al _0.01 Zr _0.001 ) _0.98 O ₂ . Li / (Co + M) was 1.04.

  Subsequently, an aqueous solution in which diammonium hydrogen phosphate is dissolved is sprayed on the obtained lithium cobalt-containing composite oxide so that phosphorus is 1 mol%, and then the mixture obtained by mixing is mixed in the atmosphere. A positive electrode active material was obtained by heat treatment at 12 ° C. for 12 hours.

As a result of measuring the particle size distribution of the obtained positive electrode active material in an aqueous solvent using a laser scattering particle size distribution measuring apparatus, the average particle size D50 was 14.6 μm. The specific surface area of the positive electrode active material measured by the BET method was 0.29 m ² / g.

Further, with respect to this positive electrode active material, an X-ray diffraction spectrum was obtained by a powder X-ray diffraction method. For the measurement, CuKα radiation having a wavelength of 1.54 mm was used. The measurement range was 2θ = 10 to 90 °. For the measurement, a RINT2100 type X-ray diffractometer manufactured by Rigaku Corporation was used. About the obtained data, peak search was performed using analysis software PDXL made by Rigaku and PDF-2 made by database ICDD. In addition, an elemental analysis of the particle cross section of the positive electrode active material was performed using an electron beam microanalyzer (also referred to as EPMA in the present invention). As a result, it was confirmed that orthorhombic lithium phosphate having a composition of Li ₃ PO ₄ was present on the particle surface of the lithium cobalt-containing composite oxide as a base material.

  Next, Rietveld analysis was performed on the obtained X-ray diffraction spectrum in the range of 2θ = 10 to 90 ° using RIETA-FP. As a result, the half width β1 of the fitting (003) plane peak of the lithium cobalt-containing composite oxide was 0.080 rad, and the half width β2 of the fitting (210) plane peak of lithium phosphate was 0.112 rad. . The half width ratio β2 / β1 at this time was 1.40. In addition, the crystallite diameter D1 of the lithium cobalt-containing composite oxide was 100.43 nm, the crystallite diameter D2 of lithium phosphate was 72.56 nm, and the ratio D2 / D1 of the crystallite diameter was 0.72. . The ratio c / a between the lattice constant of the a axis and the lattice constant of the c axis was 4.993.

  Next, the obtained positive electrode active material, acetylene black, and polyvinylidene fluoride were mixed at a mass ratio of 80/12/8, N-methylpyrrolidone was added to prepare a slurry, and aluminum having a thickness of 20 μm. The foil was coated on one side using a doctor blade. This was dried and roll press rolled to produce a positive electrode sheet for a lithium battery.

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

The assembled battery is charged to 4.5 V at a load current of 180 mA per 1 g of the positive electrode active material at 25 ° C. and discharged to 2.75 V at a load current of 75 mA per 1 g of the positive electrode active material. Asked. Further, this battery was subsequently subjected to 50 charge / discharge cycle tests.
As a result, the initial discharge capacity was 181 mAh / g, the initial discharge average voltage was 3.99 V, the capacity retention rate after 50 charge / discharge cycles was 95.3%, and the discharge average voltage after 50 charge / discharge cycles was 3 .93V.

  Similarly, another battery was assembled, charged at 4.3 ° C. for 10 hours at 25 ° C., then disassembled in an argon atmosphere glove box, taken out of the charged positive electrode sheet, and the positive electrode sheet was removed by DEC. After cleaning, the punch is punched out to a diameter of 3 mm, put into an aluminum sealed container together with EC, and heated by a differential scanning calorimeter DSC (DSC6200 manufactured by SII Nanotechnology) at a heating rate of 5 ° C./min. As a result of measuring the behavior, the heat generation start temperature was 158 ° C.

[Example 2]
A positive electrode active material was synthesized in the same manner as in Example 1 except that the heat treatment temperature of the mixture of the lithium cobalt-containing composite oxide and diammonium hydrogen phosphate was 900 ° C.
D50 of the obtained positive electrode active material was 15.5 micrometers, and the specific surface area was 0.20 m < ² > / g.
About the obtained positive electrode active material, the X-ray-diffraction spectrum measured like Example 1 was analyzed using the powder X-ray diffraction method, and the elemental analysis of the particle | grain cross section of the positive electrode active material was performed using EPMA. As a result, it was confirmed that orthorhombic lithium phosphate having a composition of Li ₃ PO ₄ was present on the particle surface of the lithium cobalt-containing composite oxide as a base material.

  Further, as a result of Rietveld analysis of the obtained positive electrode active material in the same manner as in Example 1, the half width β1 of the (003) plane peak of the lithium cobalt-containing composite oxide was 0.096 rad, and ( 210) The half-value width β2 of the plane peak was 0.131 rad, and the ratio of the half-value widths β2 / β1 was 1.36. Further, the crystallite diameter D1 of the lithium cobalt-containing composite oxide was 84.34 nm, the crystallite diameter D2 of lithium phosphate was 61.68 nm, and the ratio D2 / D1 of the crystallite diameter was 0.73. . The ratio c / a between the lattice constant of the a axis and the lattice constant of the c axis was 4.992.

  Further, using the obtained positive electrode active material, a battery was evaluated in the same manner as in Example 1. As a result, the initial discharge capacity was 183 mAh / g, the initial discharge average voltage was 3.99 V, the capacity retention rate after 50 charge / discharge cycles was 97.5%, and the discharge average voltage after 50 charge / discharge cycles was 3 90V. The heat generation starting temperature was 157 ° C.

[Example 3]
A positive electrode active material was synthesized in the same manner as in Example 1 except that the heat treatment temperature of the mixture of the lithium cobalt-containing composite oxide and diammonium hydrogen phosphate was 800 ° C.
D50 of the obtained positive electrode active material was 13.4 micrometers, and the specific surface area was 0.28 m < ² > / g.
About the obtained positive electrode active material, the X-ray-diffraction spectrum measured like Example 1 was analyzed using the powder X-ray diffraction method, and the elemental analysis of the particle | grain cross section of the positive electrode active material was performed using EPMA. As a result, it was confirmed that orthorhombic lithium phosphate having a composition of Li ₃ PO ₄ was present on the particle surface of the lithium cobalt-containing composite oxide as a base material.

  Further, as a result of Rietveld analysis of the obtained positive electrode active material in the same manner as in Example 1, the half width β1 of the (003) plane peak of the lithium cobalt-containing composite oxide was 0.096 rad, and ( 210) The half-value width β2 of the plane peak was 0.146 rad, and the ratio of the half-value widths β2 / β1 was 1.52. Further, the crystallite diameter D1 of the lithium cobalt-containing composite oxide was 84.34 nm, the crystallite diameter D2 of lithium phosphate was 55.47 nm, and the ratio D2 / D1 of the crystallite diameter was 0.66. . The ratio c / a between the lattice constant of the a axis and the lattice constant of the c axis was 4.993.

  Further, using the obtained positive electrode active material, a battery was evaluated in the same manner as in Example 1. As a result, the initial discharge capacity was 180 mAh / g, the initial discharge average voltage was 4.00 V, the capacity retention rate after 50 charge / discharge cycles was 96.9%, and the discharge average voltage after 50 charge / discharge cycles was 3 .88V. The heat generation starting temperature was 159 ° C.

[Example 4]
A positive electrode active material in the same manner as in Example 2, except that an aqueous solution in which diammonium hydrogen phosphate was dissolved was sprayed on the lithium cobalt-containing composite oxide as a base material so that phosphorus was 0.8 mol%. Was synthesized.
D50 of the obtained positive electrode active material was 14.9 micrometers, and the specific surface area was 0.22 m < ² > / g.
About the obtained positive electrode active material, the X-ray-diffraction spectrum measured like Example 1 was analyzed using the powder X-ray diffraction method, and the elemental analysis of the particle | grain cross section of the positive electrode active material was performed using EPMA. As a result, it was confirmed that orthorhombic lithium phosphate having a composition of Li ₃ PO ₄ was present on the particle surface of the lithium cobalt-containing composite oxide as a base material.

  In addition, as a result of Rietveld analysis of the obtained positive electrode active material in the same manner as in Example 1, the half width β1 of the (003) plane peak of the lithium cobalt-containing composite oxide was 0.089 rad, and ( 210) The full width at half maximum β2 of the surface peak was 0.165 rad, and the ratio of the full width at half maximum β2 / β1 was 1.85 at β2 / β1. Further, the crystallite diameter D1 of the lithium cobalt-containing composite oxide was 90.50 nm, the crystallite diameter D2 of lithium phosphate was 48.9 nm, and the crystallite diameter ratio D2 / D1 was 0.54. . The ratio c / a between the lattice constant of the a axis and the lattice constant of the c axis was 4.992.

  Further, using the obtained positive electrode active material, a battery was evaluated in the same manner as in Example 1. As a result, the initial discharge capacity was 182 mAh / g, the initial discharge average voltage was 4.02 V, the capacity retention rate after 50 charge / discharge cycles was 85.4%, and the discharge average voltage after 50 charge / discharge cycles was 3 .91V. The heat generation starting temperature was 157 ° C.

[Example 5]
A positive electrode active material in the same manner as in Example 2 except that an aqueous solution in which diammonium hydrogen phosphate was dissolved was sprayed so that phosphorus was 0.5 mol% with respect to the lithium cobalt-containing composite oxide as a base material. Was synthesized.
D50 of the obtained positive electrode active material was 13.7 micrometers, and the specific surface area was 0.22 m < ² > / g.
About the obtained positive electrode active material, the X-ray-diffraction spectrum measured like Example 1 was analyzed using the powder X-ray diffraction method, and the elemental analysis of the particle | grain cross section of the positive electrode active material was performed using EPMA. As a result, it was confirmed that orthorhombic lithium phosphate having a composition of Li ₃ PO ₄ was present on the particle surface of the lithium cobalt-containing composite oxide as a base material.

  Further, as a result of Rietveld analysis of the obtained positive electrode active material in the same manner as in Example 1, the half width β1 of the (003) plane peak of the lithium cobalt-containing composite oxide was 0.090 rad, and ( 210) The half-value width β2 of the plane peak was 0.169 rad, and the ratio of the half-value widths β2 / β1 was 1.88. Further, the crystallite diameter D1 of the lithium cobalt-containing composite oxide was 90.47 nm, the crystallite diameter D2 of lithium phosphate was 47.43 nm, and the ratio D2 / D1 of the crystallite diameter was 0.52. . The ratio c / a between the lattice constant of the a axis and the lattice constant of the c axis was 4.992.

  Further, using the obtained positive electrode active material, a battery was evaluated in the same manner as in Example 1. As a result, the initial discharge capacity was 182 mAh / g, the initial discharge average voltage was 4.03 V, the capacity retention rate after 50 charge / discharge cycles was 82.3%, and the discharge average voltage after 50 charge / discharge cycles was 3 .91V. The heat generation starting temperature was 158 ° C.

[Example 6]
A positive electrode active material was synthesized in the same manner as in Example 2 except that ammonium dihydrogen phosphate was used in place of diammonium hydrogen phosphate as the phosphorus compound.
D50 of the obtained positive electrode active material was 15.8 micrometers, and the specific surface area was 0.22 m < ² > / g.
About the obtained positive electrode active material, the X-ray-diffraction spectrum measured like Example 1 was analyzed using the powder X-ray diffraction method, and the elemental analysis of the particle | grain cross section of the positive electrode active material was performed using EPMA. As a result, it was confirmed that orthorhombic lithium phosphate having a composition of Li ₃ PO ₄ was present on the particle surface of the lithium cobalt-containing composite oxide as a base material.

  Further, as a result of Rietveld analysis of the obtained positive electrode active material in the same manner as in Example 1, the half width β1 of the (003) plane peak of the lithium cobalt-containing composite oxide was 0.112 rad, and ( 210) The full width at half maximum β2 of the plane peak was 0.125 rad, and the ratio of the full width at half maximum β2 / β1 was 1.12. Further, the crystallite diameter D1 of the lithium cobalt-containing composite oxide was 72.17 nm, the crystallite diameter D2 of lithium phosphate was 64.99 nm, and the ratio D2 / D1 of the crystallite diameter was 0.90. . The ratio c / a between the lattice constant of the a axis and the lattice constant of the c axis was 4.993.

  Further, using the obtained positive electrode active material, a battery was evaluated in the same manner as in Example 1. As a result, the initial discharge capacity was 182 mAh / g, the initial discharge average voltage was 4.01 V, the capacity retention rate after 50 charge / discharge cycles was 94.9%, and the discharge average voltage after 50 charge / discharge cycles was 3 .94V. The heat generation starting temperature was 158 ° C.

[Example 7]
1.73 g of magnesium carbonate, 20.83 g of aluminum maleate having an Al content of 2.65% by mass, 1.327 g of basic ammonium zirconium carbonate having a Zr content of 14.07% by mass and 6.02 g of citric acid monohydrate An aqueous solution was prepared by dissolving in 24.5 g of water. This aqueous solution was mixed with 196.72 g of cobalt oxyhydroxide having an average particle diameter of 15 μm and a cobalt content of 60.0% by mass, followed by drying to obtain a dry powder. The obtained dry powder and 78.21 g of lithium carbonate having an average particle size of 5.6 μm having a lithium content of 18.7% by mass were mixed in a mortar and calcined at 400 ° C. for 10 hours in the atmosphere. Baked powder was obtained.
Next, 30 g of an aqueous solution having a diammonium hydrogen phosphate content of 15% by mass in which 4.5 g of diammonium hydrogen phosphate was dissolved in 25.5 g of ion-exchanged water was prepared. The prepared aqueous solution was sprayed so as to contain 1 mol% of phosphorus with respect to 100 g of the calcined powder obtained above, and then dried and mixed to obtain a mixture. This mixture was heat-treated at 1010 ° C. for 14 hours in the air to obtain a positive electrode active material powder.

The composition of the lithium cobalt-containing composite oxide that is the base material of the obtained positive electrode active material was Li _1.015 (Co _0.979 Mg _0.01 Al _0.01 Zr _0.001 ) _0.985 O ₂ . . Li / (Co + M) was 1.03.
D50 of the obtained positive electrode active material was 17.4 micrometers, and the specific surface area was 0.26 m < ² > / g.
About the obtained positive electrode active material, the X-ray-diffraction spectrum measured like Example 1 was analyzed using the powder X-ray diffraction method, and the elemental analysis of the particle | grain cross section of the positive electrode active material was performed using EPMA. As a result, it was confirmed that orthorhombic lithium phosphate having a composition of Li ₃ PO ₄ was present on the particle surface of the lithium cobalt-containing composite oxide as a base material.

  In addition, the obtained positive electrode active material was subjected to Rietveld analysis in the same manner as in Example 1. As a result, the half value width β1 of the (003) plane peak of the lithium cobalt-containing composite oxide was 0.101 rad, and ( 210) The half-value width β2 of the plane peak was 0.179 rad, and the ratio of the half-value widths β2 / β1 was 1.77. Further, the crystallite diameter D1 of the lithium cobalt-containing composite oxide was 79.44 nm, the crystallite diameter D2 of lithium phosphate was 45.53 nm, and the ratio D2 / D1 of the crystallite diameter was 0.57. . The ratio c / a between the lattice constant of the a axis and the lattice constant of the c axis was 4.992.

  Further, using the obtained positive electrode active material, a battery was evaluated in the same manner as in Example 1. As a result, the initial discharge capacity was 179 mAh / g, the initial discharge average voltage was 4.02 V, the capacity retention rate after 50 charge / discharge cycles was 82.5%, and the discharge average voltage after 50 charge / discharge cycles was 3 .91V. The heat generation starting temperature was 159 ° C.

[Example 8]
In the same manner as in Example 7, except that an aqueous solution in which diammonium hydrogen phosphate was dissolved was sprayed on the base material lithium cobalt-containing composite oxide so that phosphorus was 1.5 mol%. The material was synthesized.
D50 of the obtained positive electrode active material was 20.1 micrometers, and the specific surface area was 0.33 m < ² > / g.
About the obtained positive electrode active material, the X-ray-diffraction spectrum measured like Example 1 was analyzed using the powder X-ray diffraction method, and the elemental analysis of the particle | grain cross section of the positive electrode active material was performed using EPMA. As a result, it was confirmed that orthorhombic lithium phosphate having a composition of Li ₃ PO ₄ was present on the particle surface of the lithium cobalt-containing composite oxide as a base material.

  In addition, as a result of Rietveld analysis of the obtained positive electrode active material in the same manner as in Example 1, the half width β1 of the (003) plane peak of the lithium cobalt-containing composite oxide was 0.106 rad, and ( 210) The full width at half maximum β2 of the plane peak was 0.133 rad, and the ratio of the full width at half maximum β2 / β1 was 1.25. Further, the crystallite diameter D1 of the lithium cobalt-containing composite oxide was 71.07 nm, the crystallite diameter D2 of lithium phosphate was 58.9 nm, and the ratio D2 / D1 of the crystallite diameter was 0.83. . The ratio c / a between the lattice constant of the a axis and the lattice constant of the c axis was 4.994.

  Further, using the obtained positive electrode active material, a battery was evaluated in the same manner as in Example 1. As a result, the initial discharge capacity was 176 mAh / g, the initial discharge average voltage was 4.00 V, the capacity retention rate after 50 charge / discharge cycles was 96.8%, and the discharge average voltage after 50 charge / discharge cycles was 3 It was .98V. The heat generation starting temperature was 157 ° C.

[Example 9]
In the same manner as in Example 7, except that an aqueous solution in which diammonium hydrogen phosphate was dissolved was sprayed on the lithium cobalt-containing composite oxide as a base material so that phosphorus was 2.0 mol%. The material was synthesized.
D50 of the obtained positive electrode active material was 18.0 micrometers, and the specific surface area was 0.35 m < ² > / g.
About the obtained positive electrode active material, the X-ray-diffraction spectrum measured like Example 1 was analyzed using the powder X-ray diffraction method, and the elemental analysis of the particle | grain cross section of the positive electrode active material was performed using EPMA. As a result, it was confirmed that orthorhombic lithium phosphate having a composition of Li ₃ PO ₄ was present on the particle surface of the lithium cobalt-containing composite oxide as a base material.

  Further, as a result of Rietveld analysis of the obtained positive electrode active material in the same manner as in Example 1, the half value width β1 of the (003) plane peak of the lithium cobalt-containing composite oxide was 0.116 rad, and ( 210) The half-value width β2 of the plane peak was 0.131 rad, and the ratio of the half-value widths β2 / β1 was 1.13. Further, the crystallite diameter D1 of the lithium cobalt-containing composite oxide was 69.62 nm, the crystallite diameter D2 of lithium phosphate was 62.00 nm, and the ratio D2 / D1 of the crystallite diameter was 0.89. . The ratio c / a between the lattice constant of the a axis and the lattice constant of the c axis was 4.995.

  Further, using the obtained positive electrode active material, a battery was evaluated in the same manner as in Example 1. As a result, the initial discharge capacity was 174 mAh / g, the initial discharge average voltage was 4.00 V, the capacity retention rate after 50 charge / discharge cycles was 94.6%, and the discharge average voltage after 50 charge / discharge cycles was 3 97V. The heat generation starting temperature was 158 ° C.

[Example 10]
A positive electrode active material was synthesized in the same manner as in Example 7 except that the amount of lithium carbonate to be mixed was changed to 75.93 g and the composition of the lithium cobalt-containing composite oxide as a base material was changed.
The composition of the lithium cobalt-containing composite oxide that is the base material of the obtained positive electrode active material was Li (Co _0.979 Mg _0.01 Al _0.01 Zr _0.001 ) O ₂ containing phosphate. . Li / (Co + M) was 1.00.
D50 of the obtained positive electrode active material was 19.4 micrometers, and the specific surface area was 0.34 m < ² > / g.
About the obtained positive electrode active material, the X-ray-diffraction spectrum measured like Example 1 was analyzed using the powder X-ray diffraction method, and the elemental analysis of the particle | grain cross section of the positive electrode active material was performed using EPMA. As a result, it was confirmed that orthorhombic lithium phosphate having a composition of Li ₃ PO ₄ was present on the particle surface of the lithium cobalt-containing composite oxide as a base material.

  In addition, as a result of Rietveld analysis of the obtained positive electrode active material in the same manner as in Example 1, the half width β1 of the (003) plane peak of the lithium cobalt-containing composite oxide was 0.113 rad, and ( 210) The half-value width β2 of the plane peak was 0.156 rad, and the ratio of the half-value widths β2 / β1 was 1.38. Further, the crystallite diameter D1 of the lithium cobalt-containing composite oxide was 71.53 nm, the crystallite diameter D2 of lithium phosphate was 51.78 nm, and the ratio D2 / D1 of the crystallite diameter was 0.72. . The ratio c / a between the lattice constant of the a axis and the lattice constant of the c axis was 4.995.

  Further, using the obtained positive electrode active material, a battery was evaluated in the same manner as in Example 1. As a result, the initial discharge capacity was 177 mAh / g, the initial discharge average voltage was 3.99 V, the capacity retention rate after 50 charge / discharge cycles was 96.6%, and the discharge average voltage after 50 charge / discharge cycles was 3 It was .98V. The heat generation starting temperature was 156 ° C.

[Example 11]
A positive electrode active material was synthesized in the same manner as in Example 7 except that the amount of lithium carbonate to be mixed was changed to 77.45 g and the composition of the lithium cobalt-containing composite oxide as a base material was changed.
The composition of the lithium cobalt-containing composite oxide that is the base material of the obtained positive electrode active material was Li _1.01 (Co _0.979 Mg _0.01 Al _0.01 Zr _0.001 ) _0.99 O ₂ . . Li / (Co + M) was 1.02.
D50 of the obtained positive electrode active material was 19.9 micrometers, and the specific surface area was 0.33 m < ² > / g.
About the obtained positive electrode active material, the X-ray-diffraction spectrum measured like Example 1 was analyzed using the powder X-ray diffraction method, and the elemental analysis of the particle | grain cross section of the positive electrode active material was performed using EPMA. As a result, it was confirmed that orthorhombic lithium phosphate having a composition of Li ₃ PO ₄ was present on the particle surface of the lithium cobalt-containing composite oxide as a base material.

  In addition, the obtained positive electrode active material was subjected to Rietveld analysis in the same manner as in Example 1. As a result, the half width β1 of the (003) plane peak of the lithium cobalt-containing composite oxide was 0.105 rad, and ( 210) The half-value width β2 of the plane peak was 0.151 rad, and the half-value width ratio β2 / β1 was 1.44. Furthermore, the crystallite diameter D1 of the lithium cobalt-containing composite oxide was 91.17 nm, the crystallite diameter D2 of lithium phosphate was 67.47 nm, and the ratio D2 / D1 of the crystallite diameter was 0.74. . The ratio c / a between the lattice constant of the a axis and the lattice constant of the c axis was 4.992.

  Further, using the obtained positive electrode active material, a battery was evaluated in the same manner as in Example 1. As a result, the initial discharge capacity was 179 mAh / g, the initial discharge average voltage was 4.01 V, the capacity retention rate after 50 charge / discharge cycles was 95.4%, and the discharge average voltage after 50 charge / discharge cycles was 3 It was .98V. The heat generation starting temperature was 158 ° C.

[Example 12]
A positive electrode active material was synthesized in the same manner as in Example 7 except that the amount of lithium carbonate to be mixed was changed to 78.97 g and the composition of the lithium cobalt-containing composite oxide as a base material was changed.
The composition of the lithium cobalt-containing composite oxide that is the base material of the obtained positive electrode active material was Li _1.02 (Co _0.979 Mg _0.01 Al _0.01 Zr _0.001 ) _0.98 O ₂ . . Li / (Co + M) was 1.04.
D50 of the obtained positive electrode active material was 17.1 μm, and the specific surface area was 0.23 m ² / g.
About the obtained positive electrode active material, the X-ray-diffraction spectrum measured like Example 1 was analyzed using the powder X-ray diffraction method, and the elemental analysis of the particle | grain cross section of the positive electrode active material was performed using EPMA. As a result, it was confirmed that orthorhombic lithium phosphate having a composition of Li ₃ PO ₄ was present on the particle surface of the lithium cobalt-containing composite oxide as a base material.

  In addition, as a result of Rietveld analysis of the obtained positive electrode active material in the same manner as in Example 1, the half width β1 of the (003) plane peak of the lithium cobalt-containing composite oxide was 0.108 rad, and ( 210) The half-value width β2 of the plane peak was 0.186 rad, and the ratio of the half-value widths β2 / β1 was 1.72. Furthermore, the crystallite diameter D1 of the lithium cobalt-containing composite oxide was 84.58 nm, the crystallite diameter D2 of lithium phosphate was 46.53 nm, and the ratio D2 / D1 of the crystallite diameter was 0.55. . The ratio c / a between the lattice constant of the a axis and the lattice constant of the c axis was 4.992.

  Further, using the obtained positive electrode active material, a battery was evaluated in the same manner as in Example 1. As a result, the initial discharge capacity was 178 mAh / g, the initial discharge average voltage was 4.01 V, the capacity retention rate after 50 charge / discharge cycles was 81.5%, and the discharge average voltage after 50 charge / discharge cycles was 3 .88V. The heat generation starting temperature was 160 ° C.

[Example 13]
196.72 g of cobalt oxyhydroxide having an average particle size of 13 μm having a Co content of 60.0% by mass, 75.17 g of lithium carbonate having an average particle size of 5.6 μm having an Li content of 18.7% by mass, 0.60 g of magnesium hydroxide with an Mg content of 41.14% by mass, 0.79 g of aluminum hydroxide with an Al content of 34.45% by mass, and 0.18 g of titanium oxide with a Ti content of 55.14% by mass The resulting mixture was baked at 1000 ° C. for 10 hours in the air to obtain a lithium cobalt-containing composite oxide powder. The composition of the obtained lithium cobalt-containing composite oxide was Li (Co _0.989 Mg _0.005 Al _0.005 Ti _0.001 ) O ₂ . Li / (Co + M) was 1.00.
Then, after spraying the aqueous solution which melt | dissolved diammonium hydrogenphosphate so that phosphorus might be 1 mol% with respect to the obtained lithium cobalt containing complex oxide, the mixture obtained by mixing is 900 degreeC at 12 degreeC. A positive electrode active material was obtained by heat treatment for a period of time.
D50 of the obtained positive electrode active material was 13.5 micrometers, and the specific surface area was 0.27 m < ² > / g.

About the obtained positive electrode active material, the X-ray-diffraction spectrum measured like Example 1 was analyzed using the powder X-ray diffraction method, and the elemental analysis of the particle | grain cross section of the positive electrode active material was performed using EPMA. As a result, it was confirmed that orthorhombic lithium phosphate having a composition of Li ₃ PO ₄ was present on the particle surface of the lithium cobalt-containing composite oxide as a base material.

  Further, as a result of Rietveld analysis of the obtained positive electrode active material in the same manner as in Example 1, the half-value width β1 of the (003) plane peak of the lithium cobalt-containing composite oxide was 0.107 rad, and ( 210) The half-value width β2 of the plane peak was 0.136 rad, and the half-value width ratio β2 / β1 was 1.27. Further, the crystallite diameter D1 of the lithium cobalt-containing composite oxide was 77.55 nm, the crystallite diameter D2 of lithium phosphate was 67.47 nm, and the crystallite diameter ratio D2 / D1 was 0.87. . The ratio c / a between the lattice constant of the a axis and the lattice constant of the c axis was 4.993.

Next, using the obtained composite oxide, an electrode and a battery were produced in the same manner as in Example 1 and evaluated.
Further, using the obtained positive electrode active material, a battery was evaluated in the same manner as in Example 1. As a result, the initial discharge capacity was 180 mAh / g, the initial discharge average voltage was 4.03 V, the capacity retention rate after 50 charge / discharge cycles was 96.2%, and the discharge average voltage after 50 charge / discharge cycles was 3 .91V. The heat generation starting temperature was 155 ° C.

[Example 14]
196.72 g of cobalt oxyhydroxide having an average particle size of 13 μm having a Co content of 60.0% by mass, 74.71 g of lithium carbonate having an average particle size of 5.6 μm having an Li content of 18.7% by mass, 0.79 g of aluminum hydroxide having an Al content of 34.45% by mass and 0.10 g of lithium fluoride were mixed in a mortar, and the resulting mixture was calcined in the atmosphere at 1000 ° C. for 10 hours to obtain lithium. A cobalt-containing composite oxide powder was obtained. The composition of the obtained lithium cobalt-containing composite oxide was LiCo _0.995 Al _0.005 O _1.998 F _0.002 . Li / (Co + M) was 1.00.

Then, after spraying the aqueous solution which melt | dissolved diammonium hydrogenphosphate so that phosphorus might be 1 mol% with respect to the obtained lithium cobalt containing complex oxide, the mixture obtained by mixing is 900 degreeC at 12 degreeC. A positive electrode active material was obtained by heat treatment for a period of time.
D50 of the obtained positive electrode active material was 14.3 micrometers, and the specific surface area was 0.22 m < ² > / g.
About the obtained positive electrode active material, the X-ray-diffraction spectrum measured like Example 1 was analyzed using the powder X-ray diffraction method, and the elemental analysis of the particle | grain cross section of the positive electrode active material was performed using EPMA. As a result, it was confirmed that orthorhombic lithium phosphate having a composition of Li ₃ PO ₄ was present on the particle surface of the lithium cobalt-containing composite oxide as a base material.

  Further, as a result of Rietveld analysis of the obtained positive electrode active material in the same manner as in Example 1, the half-value width β1 of the (003) plane peak of the lithium cobalt-containing composite oxide was 0.107 rad, and ( 210) The full width at half maximum β2 of the plane peak was 0.155 rad, and the ratio of the full width at half maximum β2 / β1 was 1.45. Further, the crystallite diameter D1 of the lithium cobalt-containing composite oxide was 85.81 nm, the crystallite diameter D2 of lithium phosphate was 55.78 nm, and the ratio D2 / D1 of the crystallite diameter was 0.65. . The ratio c / a between the lattice constant of the a axis and the lattice constant of the c axis was 4.994.

  Further, using the obtained positive electrode active material, a battery was evaluated in the same manner as in Example 1. As a result, the initial discharge capacity was 178 mAh / g, the initial discharge average voltage was 3.98 V, the capacity retention rate after 50 charge / discharge cycles was 97.3%, and the discharge average voltage after 50 charge / discharge cycles was 3 .88V. The heat generation starting temperature was 167 ° C.

Example 15 Comparative Example A positive electrode active material was synthesized in the same manner as in Example 1 except that the heat treatment temperature of the mixture of the lithium cobalt-containing composite oxide and diammonium hydrogen phosphate was 500 ° C.
D50 of the obtained positive electrode active material was 16.0 micrometers, and the specific surface area was 0.41 m < ² > / g.
About the obtained positive electrode active material, the X-ray-diffraction spectrum measured like Example 1 was analyzed using the powder X-ray diffraction method, and the elemental analysis of the particle | grain cross section of the positive electrode active material was performed using EPMA. As a result, it was confirmed that orthorhombic lithium phosphate having a composition of Li ₃ PO ₄ was present on the particle surface of the lithium cobalt-containing composite oxide as a base material.

  In addition, as a result of Rietveld analysis of the obtained positive electrode active material in the same manner as in Example 1, the half width β1 of the (003) plane peak of the lithium cobalt-containing composite oxide was 0.106 rad, and ( 210) The half-value width β2 of the plane peak was 0.261 rad, and the ratio of the half-value widths β2 / β1 was 2.46. Further, the crystallite diameter D1 of the lithium cobalt-containing composite oxide was 76.06 nm, the crystallite diameter D2 of lithium phosphate was 31.00 nm, and the ratio D2 / D1 of the crystallite diameter was 0.41. . The ratio c / a between the lattice constant of the a axis and the lattice constant of the c axis was 4.991.

  Further, using the obtained positive electrode active material, a battery was evaluated in the same manner as in Example 1. As a result, the initial discharge capacity was 172 mAh / g, the initial discharge average voltage was 4.00 V, the capacity retention rate after 50 charge / discharge cycles was 75.6%, and the discharge average voltage after 50 charge / discharge cycles was 3 .68V. The heat generation starting temperature was 157 ° C.

[Example 16] Comparative Example A positive electrode active material was synthesized in the same manner as in Example 1 except that the heat treatment temperature of the mixture of the lithium cobalt-containing composite oxide and diammonium hydrogen phosphate was 400 ° C.
D50 of the obtained positive electrode active material was 12.5 micrometers, and the specific surface area was 0.60 m < ² > / g.
About the obtained positive electrode active material, the X-ray-diffraction spectrum measured like Example 1 was analyzed using the powder X-ray diffraction method, and the elemental analysis of the particle | grain cross section of the positive electrode active material was performed using EPMA. As a result, it was confirmed that orthorhombic lithium phosphate having a composition of Li ₃ PO ₄ was present on the particle surface of the lithium cobalt-containing composite oxide as a base material.

  As a result of Rietveld analysis of the obtained positive electrode active material in the same manner as in Example 1, the half width β1 of the (003) plane peak of the lithium cobalt-containing composite oxide was 0.102 rad, and ( 210) The half-value width β2 of the plane peak was 0.321 rad, and the ratio of the half-value widths β2 / β1 was 3.14. Further, the crystallite diameter D1 of the lithium cobalt-containing composite oxide is 78.89 nm, the crystallite diameter D2 of lithium phosphate is 25.23 nm, and the ratio D2 / D1 of the crystallite diameter is 0.2. 32. The ratio c / a between the lattice constant of the a axis and the lattice constant of the c axis was 4.990.

  Further, using the obtained positive electrode active material, a battery was evaluated in the same manner as in Example 1. As a result, the initial discharge capacity was 161 mAh / g, the initial discharge average voltage was 4.00 V, the capacity retention rate after 50 charge / discharge cycles was 32.2%, and the discharge average voltage after 50 charge / discharge cycles was 3 .32V. The heat generation starting temperature was 158 ° C.

[Example 17] Comparative Example Example 2 except that an aqueous solution in which diammonium hydrogen phosphate was dissolved was sprayed so that phosphorus was 0.2 mol% with respect to the lithium cobalt-containing composite oxide as a base material. Similarly, a positive electrode active material was synthesized.
D50 of the obtained positive electrode active material was 14.6 micrometers, and the specific surface area was 0.30 m < ² > / g.
About the obtained positive electrode active material, the X-ray-diffraction spectrum measured like Example 1 was analyzed using the powder X-ray diffraction method, and the elemental analysis of the particle | grain cross section of the positive electrode active material was performed using EPMA. As a result, it was confirmed that orthorhombic lithium phosphate having a composition of Li ₃ PO ₄ was present on the particle surface of the lithium cobalt-containing composite oxide as a base material.

  In addition, as a result of Rietveld analysis of the obtained positive electrode active material in the same manner as in Example 1, the half width β1 of the (003) plane peak of the lithium cobalt-containing composite oxide was 0.106 rad, and ( 210) The full width at half maximum β2 of the plane peak was 0.305 rad, and the ratio of the full width at half maximum β2 / β1 was 2.88. Further, the crystallite diameter D1 of the lithium cobalt-containing composite oxide was 88.24 nm, the crystallite diameter D2 of lithium phosphate was 33.53 nm, and the ratio D2 / D1 of the crystallite diameter was 0.38. . The ratio c / a between the lattice constant of the a axis and the lattice constant of the c axis was 4.991.

  Further, using the obtained positive electrode active material, a battery was evaluated in the same manner as in Example 1. As a result, the initial discharge capacity was 176 mAh / g, the initial discharge average voltage was 4.03 V, the capacity retention rate after 50 charge / discharge cycles was 74.1%, and the discharge average voltage after 50 charge / discharge cycles was 3 .62V. The heat generation starting temperature was 156 ° C.

[Example 18] Comparative Example A positive electrode active material was prepared in the same manner as in Example 7 except that the amount of lithium carbonate to be mixed was changed to 79.73 g and the composition of the lithium cobalt-containing composite oxide as a base material was changed. Synthesized.
The composition of the lithium cobalt-containing composite oxide that is the base material of the obtained positive electrode active material was Li _1.025 (Co _0.979 Mg _0.01 Al _0.01 Zr _0.001 ) _0.975 O ₂ . . Li / (Co + M) was 1.05.
D50 of the obtained positive electrode active material was 17.4 micrometers, and the specific surface area was 0.22 m < ² > / g.

About the obtained positive electrode active material, the X-ray-diffraction spectrum measured like Example 1 was analyzed using the powder X-ray diffraction method, and the elemental analysis of the particle | grain cross section of the positive electrode active material was performed using EPMA. As a result, it was confirmed that orthorhombic lithium phosphate having a composition of Li ₃ PO ₄ was present on the particle surface of the lithium cobalt-containing composite oxide as a base material.

  As a result of Rietveld analysis of the obtained positive electrode active material in the same manner as in Example 1, the half width β1 of the (003) plane peak of the lithium cobalt-containing composite oxide was 0.102 rad, and ( 210) The half-value width β2 of the plane peak was 0.324 rad, and the ratio of the half-value widths β2 / β1 was 3.18. Furthermore, the crystallite diameter D1 of the lithium cobalt-containing composite oxide was 78.89 nm, the crystallite diameter D2 of lithium phosphate was 23.16 nm, and the crystallite diameter ratio D2 / D1 was 0.29. . The ratio c / a between the lattice constant of the a axis and the lattice constant of the c axis was 4.991.

  Further, using the obtained positive electrode active material, a battery was evaluated in the same manner as in Example 1. As a result, the initial discharge capacity was 177 mAh / g, the initial discharge average voltage was 4.02 V, the capacity retention rate after 50 charge / discharge cycles was 49.2%, and the discharge average voltage after 50 charge / discharge cycles was 3 .41V. The heat generation starting temperature was 159 ° C.

[Contrast between Example and Comparative Example]
Each of the lithium cobalt-containing composite oxides of Examples 1 to 14 which is an example has a capacity retention ratio of 82.3 to 97.5 after 50 charge / discharge cycles at 4.5 V charge under high voltage conditions. It can be seen that the discharge average voltage is as high as 3.88 to 3.98 V.
On the other hand, in the batteries using the lithium cobalt-containing composite oxides of Examples 15 to 18 as comparative examples, it can be seen that both the capacity maintenance ratio and the discharge average voltage cannot be increased simultaneously.

  The positive electrode active material of the present invention can be used even under a high voltage, is excellent in discharge capacity, discharge average voltage and safety, in particular, is excellent in charge / discharge cycle durability, and is positive electrode active for a lithium secondary battery positive electrode. As a substance, it can be used in a wide range.

Claims (14)

Formula _{Li p Co x M y O z} F a ( where, M is at least one element selected transition metal elements other than Co, Al, from the group consisting of Sn and the second group element .0. 9 ≦ p ≦ 1.2, 0.9 ≦ x ≦ 1, 0 ≦ y ≦ 0.1, 1.9 ≦ z ≦ 2.1, 0 ≦ a ≦ 0.05) A positive electrode active material having a phosphate on the surface of oxide particles, wherein the ratio D2 / D1 between the crystallite diameter D2 of the phosphate and the crystallite diameter D1 of the lithium cobalt-containing composite oxide is D2 / D1 ≧ A positive electrode active material for a lithium ion secondary battery, wherein the positive electrode active material is 0.45.   The positive electrode active material according to claim 1, wherein a crystallite diameter D2 of the phosphate is D2 ≧ 40 nm.   The positive electrode active material according to claim 1 or 2, wherein a content of phosphorus contained in the positive electrode active material is larger than 0.3 mol% with respect to the lithium cobalt-containing composite oxide.   The positive electrode active material according to claim 3, wherein a content of phosphorus contained in the positive electrode active material is 0.5 to 2.0 mol% with respect to the lithium cobalt-containing composite oxide.   The positive electrode active material according to claim 1, wherein the phosphate is lithium phosphate.   The positive electrode active material according to claim 5, wherein the crystal structure of lithium phosphate is orthorhombic.   7. The positive electrode active material according to claim 5, wherein a half-value width β2 of the (210) plane of lithium phosphate is 0.25 rad or less.   The ratio β2 / β1 of the half width β2 of the (210) plane of lithium phosphate and the half width β1 of the (003) plane of the lithium cobalt-containing composite oxide is β2 / β1 ≦ 2. A positive electrode active material according to claim 1.   The positive electrode active material according to claim 1, wherein the M element is at least one element selected from the group consisting of Zr, Hf, Ti, Mg, and Al.   The positive electrode active material according to any one of claims 1 to 9, wherein the M element contains Mg and Al, and Mg / Al, which is a molar ratio of Mg and Al, is 0.1 to 10.   11. The positive electrode according to claim 1, wherein an atomic ratio Li / (Co + M) between lithium and cobalt and M in the lithium-cobalt-containing composite oxide is 0.99 ≦ Li / (Co + M) ≦ 1.10. Active material.   The positive electrode active material according to claim 1, wherein the ratio of the lattice constant a to the lattice constant c of the positive electrode active material is c / a ≧ 4.992.   A positive electrode comprising the positive electrode active material according to claim 1, a conductive agent, and a binder.   A lithium ion secondary battery comprising the positive electrode according to claim 13, a negative electrode, a separator, and a nonaqueous electrolyte.