CN1665052B - Lithium cobalt dioxide, preparing method thereof and non-aqueous electrolyte secondary battery - Google Patents

Abstract

The invention provides a lithium cobalt oxide for a non-aqueous electrolyte secondary battery with excellent initial capacity and capacity retention rate and a preparation method thereof. The bulk density of lithium cobaltate is 1.8 g/cm ³ or more, and the pressed density is 3.5 to 4.0 g/cm ³ . Mix lithium cobalt oxide (A) with a bulk density of 1.7 to 3.0 g/cm ³ and lithium cobalt oxide (B) with a bulk density of 1.0 to 2.0 g/cm ³ to make lithium cobalt oxide (A) and lithium cobalt oxide (B) The above-mentioned method for producing lithium cobaltate whose bulk density difference is 0.20 g/cm ³ or more.

Description

Lithium cobaltate, its preparation method and non-aqueous electrolyte secondary battery

technical field

The invention relates to lithium cobaltate, its preparation method and a non-aqueous electrolyte secondary battery equipped with a positive plate using the lithium cobaltate as a positive active material.

Background technique

In recent years, along with the rapid development of portable household appliances and batteries, lithium-ion secondary batteries and other non-aqueous electrolyte secondary batteries have been used as power sources for portable micro personal computers, mobile phones, video recorders and other small appliances.

Regarding the lithium-ion secondary battery, since lithium cobaltate can be used as the positive electrode active material of the lithium-ion secondary battery, research involving lithium-based composite oxides has been developed every time. Previously, as the positive electrode active material, cobalt Various proposals have been made for compounds such as lithium oxide, lithium nickel oxide, and lithium manganate.

Various proposals have been made to improve the performance of these positive electrode active materials, and various techniques have been disclosed regarding apparent density, pressurized density, and the like as important conditions.

For example, some proposals propose to calcinate a granular composition composed of two or more _starting materials with different average particle diameters to make a positive electrode active material with a bulk density of _LiPMO2 of 2.65 g/cm3 ^{or more} (For example, refer to Patent Document 1).

In addition, in the positive electrode active material for a non-aqueous electrolyte secondary battery using lithium cobaltate represented by LiCoO ₂ , the projected pattern of lithium cobaltate observed by SEM has a diameter of 0.1 to 4 μm and an average particle diameter of 2 μm. The primary particles of the following small crystals are composed of multiple secondary particles aggregated into spherical or ellipsoidal shapes, and the bulk density of the lithium cobaltate is 2.2 g/cm3 ^or more. The positive electrode of the non-aqueous electrolyte secondary battery Active substances have been proposed (for example, refer to Patent Document 2).

In addition, it has been proposed to use the following lithium cobaltate as the positive electrode active material of the non-aqueous electrolyte secondary battery: it is essentially composed of secondary particles of lithium cobaltate represented by _LiCoO2 , which are aggregated by a plurality of tiny primary particles. Yes, the secondary particles have a plurality of fine gaps through which the electrolyte can permeate, and have a bulk density of 2.2 g/cm ³ or more (for example, refer to Patent Document 3).

[Patent Document 1] JP-A-2001-85009 Gazette (Page 1)

[Patent Document 2] Japanese Unexamined Publication No. 2001-135313 (Page 1)

[Patent Document 3] Japanese Unexamined Publication No. 2001-155729 (Page 1)

Contents of the invention

However, there is no non-aqueous electrolyte secondary battery using the above-mentioned lithium cobaltate as the positive electrode active material that satisfies both discharge capacity and rapid charge-discharge performance. Therefore, various tests have been conducted. For example, attempts have been made to increase the electrode density by changing the particle size and particle shape of lithium cobaltate, thereby improving battery capacity and rapid charge-discharge performance, but sufficient results have not yet been obtained.

In view of the above-mentioned problems in the prior art, the object of the present invention is to provide a lithium cobaltate having excellent powder physical properties, high electrode density, large discharge capacity and excellent fast charge and discharge performance when used in a battery, and its Preparation method and non-aqueous electrolyte secondary battery using it.

The present inventors have found that when lithium composite oxide particles are used as the positive electrode active material, not only the particle characteristics of the lithium composite oxide, but also the properties of the particles can be brought into full play by blending lithium composite oxide particles with different particle sizes. characteristics, thereby completing the present invention.

That is, the present invention relates to lithium cobaltate characterized in that it has a bulk density of 1.8 g/cm ³ or more and a pressed density of 3.5 to 4.0 g/cm ³ .

In addition, the lithium cobaltate of the present invention is preferably composed of a mixture of primary particle monodispersed lithium cobaltate (A) and primary particle aggregated lithium cobaltate (B), and the bulk density of the mixture is 1.8 g/cm ³ or above, and the pressed density is 3.5-4.0 g/cm ³ .

In addition, the present invention relates to the following preparation method of lithium cobaltate, characterized in that lithium cobaltate (A) with a bulk density of 1.7 to 3.0 g/ ^cm and lithium cobaltate with a bulk density of 1.0 to ^2.0 g/cm (B) Mixing such that the difference in bulk density between the above-mentioned lithium cobaltate (A) and the above-mentioned lithium cobaltate (B) is 0.20 g/cm ³ or more.

Preferably, the above-mentioned lithium cobaltate (A) and lithium cobaltate (B) are mixed at a ratio of (A):(B)=95:5 to 60:40 by weight.

The above-mentioned lithium cobaltate (A) is preferably monodispersed with primary particles, and the above-mentioned lithium cobaltate (B) is preferably aggregated with primary particles.

Preferably, the lithium cobaltate (A) has an average particle diameter of 5 to 30 μm, and the lithium cobaltate (B) has an average particle diameter of 0.1 to 10 μm.

Also, the present invention relates to a nonaqueous electrolyte secondary battery characterized by comprising a positive electrode plate composed of the aforementioned lithium cobaltate as a positive electrode active material.

Brief description of the drawings

Fig. 1 shows the SEM photo (magnification × 3000) of the particle structure of lithium cobaltate (A) in which the primary particles are neatly and monodispersed in Preparation Example 1.

Fig. 2 shows the SEM photo (magnification × 3000) of the lithium cobaltate (B) particle structure of the first-stage particles aggregated in Preparation Example 7.

FIG. 3 is a diagram showing the safety evaluation of secondary batteries using lithium cobaltate in Example 2 and Comparative Example 1 as positive electrode active materials.

Fig. 4 is a graph showing the rapid charge and discharge test results of the secondary battery using the lithium cobaltate of Example 2 and Comparative Example 1 as the positive electrode active material.

embodiment of the invention

The present invention will be described more specifically below.

The lithium cobaltate of the present invention is characterized in that the bulk density is 1.8 g/cm ³ or more, and the pressed density is 3.5-4.0 g/cm ³ .

The lithium cobaltate is composed of a mixture of at least two compounds selected from the compounds represented by Li _a CoO ₂ (where a represents a number within the range of 0.2≤a≤1.2) of the general formula (1), or, By the compound represented by Li _a CoO ₂ of general formula (1) and the compound represented by Li _a Co _1-y M _y O _2-z of general formula (2) (in the formula, M represents the transition selected from except Co At least one element among metal elements or elements with an atomic number of 9 or more, a represents a number within the range of 0.2≤a≤1.2, y represents a number within the range of 0<y≤0.4, z represents 0≤z≤1.0 The number within the range) is composed of a mixture.

Specifically, Li _a CoO ₂ or a part of Co in Li _a CoO ₂ may also be replaced by other metal elements (M). The substituted metal element (M) may be at least one element selected from transition metal elements other than Co or elements with an atomic number of 9 or more, such as Na, Mg, Al, Ca, Ti, V, At least one of Cr, Mn, Fe, Ni, Zn, Si, Ga, Zr, Nb, W, and Mo.

In addition, the surface of lithium cobalt oxide in which part of Co in Li _a CoO ₂ or Li _a CoO ₂ is replaced with other metal elements can also be coated with sulfate.

In general, bulk density represents the packing characteristics of a powder that is not particularly pressurized, and where coarse and fine particles are naturally mixed. Pressed density represents the characteristic of how coarse and fine particles are packed under pressurization. The present invention found that when lithium cobaltate is used as a positive electrode active material of a non-aqueous electrolyte secondary battery, lithium cobaltate having a bulk density and a pressurized density within a specific range is important.

That is, the bulk density of the lithium cobaltate of the present invention is 1.8 g/cm ³ or more, preferably 2.0 g/cm ³ or more, and more preferably 2.5 to 3.5 g/cm ³ .

In addition, the pressed density of the lithium cobaltate of the present invention is 3.5-4.0 g/cm ³ , preferably 3.6-4.0 g/cm ³ , more preferably 3.7-4.0 g/cm ³ .

The lithium cobaltate of the present invention has excellent characteristics as a positive electrode active material because the bulk density and the pressed density are within the above-mentioned specific ranges.

Next, the preparation method of lithium cobaltate of the present invention will be described.

The preparation method of the lithium cobaltate of the present invention is prepared by dry mixing two or more kinds of lithium cobaltate with different bulk densities.

Specifically, the preparation method of lithium cobaltate of the present invention is characterized in that lithium cobaltate (A) with a bulk density of 1.7 to 3.0 g/ ^cm and lithium cobaltate (A) with a bulk density of 1.0 to ^2.0 g/cm B) Selectively mixed so that the difference in bulk density between the lithium cobaltate (A) and the lithium cobaltate (B) is 0.20 g/cm ³ or more.

The mixing ratio of lithium cobaltate (A) and lithium cobaltate (B) is (A):(B)=95:5˜60:40 by weight, preferably 90:10˜80:20.

The bulk density of lithium cobaltate (A) is 1.7-3.0 g/cm ³ , preferably 2.0-3.0 g/cm ³ .

The bulk density of lithium cobaltate (B) is 1.2-2.0 g/cm ³ , preferably 1.0-1.7 g/cm ³ .

These lithium cobaltate (A) and lithium cobaltate (B) are preferably those having different bulk densities, and the difference in bulk density between these lithium cobaltate (A) and lithium cobaltate (B) is 0.20 or more, preferably 0.30 or more.

In addition, lithium cobaltate (A) preferably has primary particles monodispersed. The so-called first-order particle monodispersity means the existence of the smallest particles scattered separately, which can be confirmed by photographic observation with SEM (scanning electron microscope). A monodisperse powder that is more than 80% of the field of view of the SEM is regarded as a monodisperse powder. Fig. 1 shows the SEM photo (magnification × 3000) of the particle structure of lithium cobaltate (A) in which the primary particles are neatly and monodispersed in Preparation Example 1.

The average particle size of the lithium cobaltate (A) is in the range of 5-30 μm, preferably 10-20 μm. Lithium cobaltate (A) has coarser particles than lithium cobaltate (B).

In addition, lithium cobaltate (B) is preferably lithium cobaltate in which primary particles are aggregated to form secondary particles. The so-called aggregation of primary particles to form secondary particles refers to the state in which the smallest particles are aggregated by the attraction of van der Waals force and surface charge force to form particle shapes, which can be confirmed by SEM photographic observation. Powders that aggregate more than 80% of the SEM field of view are also referred to as aggregated powders. Fig. 2 shows the SEM photo (magnification × 3000) of the lithium cobaltate (B) particle structure of the first-stage particle aggregation of Preparation Example 5.

The average particle size of the lithium cobaltate (B) is in the range of 0.1-10 μm, preferably 2.0-8.0 μm.

The average particle diameter in the present invention represents the value of the cumulative 50% (D ₅₀ ) of the particle size distribution obtained by a laser scattering particle size distribution measuring device.

In the present invention, when lithium cobaltate (B) which is aggregated into primary particles and monodisperse lithium cobaltate (A) are mixed as the positive active material of the non-aqueous electrolyte secondary battery, it shows excellent performance. battery characteristics. The reason for this is unclear, but such a particle mixture not only increases the packing density on the positive electrode plate, but also provides excellent rapid charge and discharge with aggregated particles, and high safety characteristics with monodispersed particles.

In addition, in the preparation method of the present invention, the lithium cobaltate (A) is preferably a compound represented by Li _a CoO ₂ (where a represents a number in the range of 0.2≤a≤1.2) of the general formula (1) . In addition, the lithium cobaltate (B) adopts the compound represented by the above general formula (1) or the Li _a Co _1-y M _y O _2-z of the general formula (2) (in the formula, M represents Other transition metal elements or at least one element among elements with an atomic number of 9 or more, a represents a number within the range of 0.2≤a≤1.2, y represents a number within the range of 0<y≤0.4, z represents 0≤z≤ Compounds represented by numbers within the range of 1.0) are preferred.

The lithium cobalt oxide of the present invention can be obtained by uniformly mixing two or more lithium cobalt oxides with different bulk densities and average particle diameters, and the method of uniform mixing is not required as long as it is an industrially implementable method. limited. For example, rotary mixers using horizontal cylindrical, V-shaped, double-conical containers, ribbon-shaped, horizontal spiral, paddle-shaped, vertical belt-shaped, grinder-shaped, star-shaped, static mixer , uniaxial roll, Henschel mixer, flow jet mixer and other container fixed mixer methods.

The nonaqueous electrolyte secondary battery of the present invention is composed of a positive electrode, a negative electrode, a separator, a nonaqueous electrolyte (for example, an electrolyte containing a lithium salt), and the like.

The positive electrode is made by coating a positive electrode mixture containing a positive electrode active material, a conductive agent, and a binder on a positive electrode plate (positive electrode current collector: such as an aluminum plate). The non-aqueous electrolyte secondary battery of the present invention uses the positive electrode active material composed of the above-mentioned lithium cobaltate as the positive electrode active material constituting the positive electrode plate. Also, instead of preparing the positive electrode active material in advance, the lithium cobaltate of the present invention, which satisfies the conditions of the positive electrode active material, can be blended and uniformly mixed when preparing the positive electrode mixture.

In the positive electrode mixture, in addition to the positive electrode active material, conductive agents, binders and fillers can also be added.

As the conductive agent, for example, one selected from metal powder conductive materials such as natural graphite (flaky graphite, flaky graphite, amorphous graphite, etc.), artificial graphite, carbon black, acetylene black, carbon fiber, nickel powder, or the like can be used. 2 or more. Among them, the combined use of graphite and alkyne black as the conductive agent is preferable. In addition, the blending amount of the conductive agent in the positive electrode mixture is 1 to 50% by weight, preferably in the range of 2 to 30% by weight.

In addition, as a binder, for example, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, regenerated cellulose, diacetyl cellulose, polyvinyl pyrrolidone, ethylene-propylene-diene terpolymer, Copolymer (EPDM), sulfonated EPDM, polysaccharides such as styrene-butadiene rubber, fluororubber, polyethylene oxide, thermoplastic resin, polymer with rubber elasticity, etc. 1 or more. It is preferable that the blending amount of the binder in the positive electrode mixture is in the range of 2 to 30% by weight.

Any fibrous material that does not cause chemical changes in the non-aqueous electrolyte secondary battery can be used as the filler, but fibers such as olefin polymers such as polypropylene and polyethylene, glass fibers, and carbon fibers are generally used. The compounding amount of the filler in the positive electrode mixture is not particularly limited, but is preferably in the range of 0 to 30% by weight.

In addition, the blending amount of the positive electrode active material composed of lithium cobaltate in the positive electrode mixture of the present invention is not particularly limited, but is preferably 60 to 95% by weight, particularly preferably within the range of 70 to 94% by weight.

The negative electrode material used in the negative electrode of the nonaqueous electrolyte secondary battery of the present invention is not particularly limited, and examples thereof include carbonaceous materials, metal composite oxides, lithium metal, or lithium alloys. Examples of the carbonaceous material include hard-to-graphitize carbonaceous materials, graphite-based carbonaceous materials, and the like. Metal composite oxides can include SnM ¹ _1-x M ² _y O _z (wherein M ¹ represents one or more elements selected from Mn, Fe, Pb or Ge, and M ² represents elements selected from Al, B, P, Si, two or more elements from Group 1, Group 2, Group 3 or halogen elements of the periodic table, x represents a number within the range of 0<x≤1, and y represents 1≤y≤ 3, z represents a number within the range of 1≤z≤8) and other compounds.

In addition, the nonaqueous electrolytic solution used in the nonaqueous electrolyte secondary battery, for example, is made of propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, γ-butyrolactone, 1 , 2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dimethylsulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, Nitromethane, methyl formate, methyl acetate, phosphate triester, trimethoxymethane, dioxolane derivatives, sulfolane, 3-methyl-2-oxazolidinone (Oxazolidinone), propylene carbonate Mixed solvents of at least one kind of aprotic organic solvents such as derivatives, tetrahydrofuran derivatives, diethyl ether, 1,3-propansolton, and lithium salts dissolved in the solvent, such as LiClO ₄ , LiBF ₄ , LiPF ₆ , LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , LiAsF ₆ , LiSbF ₆ , LiB ₁₀ Cl ₁₀ , LiAlCl ₄ , lithium chloroborane, lower aliphatic lithium carboxylate, lithium tetraphenyl borate, etc., and one or more composed of lithium salts.

In addition, in addition to the aqueous electrolyte, an organic solid electrolyte can also be used. For example, a polyethylene derivative or a polymer containing it, a polypropylene oxide derivative or a polymer containing it, a phosphate ester polymer, etc. are mentioned.

The current collector of the electrode is not particularly limited as long as it is an electrical conductor that does not cause chemical changes in the non-aqueous electrolyte secondary battery formed, but the positive electrode can be made of, for example, stainless steel, nickel, aluminum, titanium, calcined carbon, Aluminum or stainless steel surface treated with carbon, nickel, copper, titanium or silver. In addition to stainless steel, nickel, copper, titanium, aluminum, calcined carbon, etc., the negative electrode can also be a product of copper or stainless steel surface treated with carbon, nickel, titanium or silver, Al-Cd alloy, etc.

The shape of the non-aqueous electrolyte secondary battery may be coin-shaped, button-shaped, sheet-shaped, cylindrical, or square.

The purposes of the non-aqueous electrolyte secondary battery of the present invention are not particularly limited, for example, can enumerate electrical appliances such as notebook computer, portable miniature personal computer, pocket word processor, portable telephone, cordless telephone, portable CD, radio radio, automobile, tram , game consoles and other civilian appliances.

Example

Examples are given below to illustrate the present invention more specifically.

The positive electrode active material and the nonaqueous electrolyte secondary battery of the present invention will be described by way of examples.

(1) Determination method of bulk density

Dry the graduated cylinder completely and measure the weight of the empty graduated cylinder. Weigh about 70 g of the sample and put it on the medicine-packed paper. Use the funnel to transfer the sample into the graduated cylinder. Fix the measuring cylinder on the automatic T·D measuring device (manufactured by Yuasa Ionix Co., Ltd., DUALUO TOTAPP), adjust the number of tapping (tapping) to 500, perform tapping, and read the scale on the sample surface , Measure the weight of the graduated cylinder in which the sample is put, and calculate the bulk density. The tapping height is 3.2 mm, and the tapping speed is 200 times/min (according to ASTM: B527-93, 85).

(2) Determination method of pressurized density

Put the sample into a metal mold with a diameter of 15 mm, and pressurize it with a 1.96×10 ⁸ Pa (2 tons/cm ² ) press (Hand Press, manufactured by Toyo Shoko Co., Model No.: WPN-10) for 1 minute to obtain small ball. Then, the weight and volume of the pellets were measured, and the pellet density was calculated as the pressurized density.

Preparation Example 1

Lithium carbonate and cobalt oxide were weighed so that the Li/Co atomic ratio reached 1.02, and they were thoroughly mixed in a mortar to form a homogeneous mixture. Then, put the mixture into an alumina crucible, place it in an electric heating furnace to raise the temperature in the atmosphere, and keep it at a temperature of 700°C to 1000°C for 10 hours for calcination treatment, and the obtained calcined product is cooled in the atmosphere and then pulverized and classified Lithium cobaltate (LiCoO ₂ ) with an average particle size of 15.5 μm, a bulk density of 2.80 g/cm ³ , and a pressed density of 3.45 g/cm ³ was obtained.

This lithium cobaltate is a lithium cobaltate (A-1) in which primary particles are uniformly and monodispersed.

Preparation example 2

As in Preparation Example 1, lithium carbonate and cobalt oxide were mixed so that the Li/Co atomic ratio reached 1.04 to make a homogeneous mixture, which was calcined at a temperature of 1000°C to 1050°C for 10 hours to obtain an average particle size of 12.3 Lithium cobaltate (LiCoO ₂ ) having a micrometer, a bulk density of 2.50 g/cm ³ , and a pressed density of 3.48 g/cm ³ .

The SEM image of this lithium cobaltate is lithium cobaltate (A-2) in which primary particles are uniformly and monodispersed.

Preparation example 3

As in Preparation Example 1, lithium carbonate and cobalt oxide were mixed so that the Li/Co atomic ratio reached 1.02 to make a homogeneous mixture, which was calcined at a temperature of 1000°C to 1050°C for 10 hours to obtain an average particle size of 7.8 Lithium cobaltate with μm, bulk density of 1.90g/cm ³ , and pressurized density of 3.41g/cm ³ .

This lithium cobaltate is a lithium cobaltate (A-3) in which primary particles are uniformly and monodispersed.

Preparation Example 4

As in Preparation Example 1, lithium carbonate and cobalt oxide were mixed so that the Li/Co atomic ratio reached 1.00 to make a homogeneous mixture, which was calcined at a temperature of 900° C. to 1000° C. for 10 hours to obtain an average particle size of 7.4 Lithium cobaltate (LiCoO ₂ ) with μm, bulk density of 1.80g/cm3 ^{, and} pressurized density of 3.20g/ ^cm3 .

This lithium cobaltate is lithium cobaltate (B-1) in which primary particles are aggregated.

Preparation Example 5

As in Preparation Example 1, lithium carbonate and cobalt oxide were mixed so that the Li/Co atomic ratio reached 1.00 to make a homogeneous mixture, which was calcined at a temperature of 900° C. to 1000° C. for 10 hours to obtain an average particle size of 5.2 Lithium cobaltate (LiCoO ₂ ) having a μm of 1.50 g/cm ³ bulk density and 3.15 g/cm ³ pressed density.

This lithium cobaltate is lithium cobaltate (B-2) in which primary particles are aggregated.

Preparation Example 6

As in Preparation Example 1, lithium carbonate and cobalt oxide were mixed so that the Li/Co atomic ratio reached 1.00 to make a homogeneous mixture, which was calcined at a temperature of 800°C to 900°C for 10 hours to obtain an average particle size of 3.2 Lithium cobaltate (LiCoO ₂ ) having a micrometer, a bulk density of 1.20 g/cm ³ , and a pressed density of 3.21 g/cm ³ .

The SEM image of this lithium cobaltate is lithium cobaltate (B-3) in which primary particles are gathered.

Preparation Example 7

In the same manner as in Preparation Example 1, 2 mol % of Al was added to Co to synthesize LiCo _0.98 Al _0.02 O ₂ . The calcining method _is the same as that of Preparation Example 1. When mixing in a mortar, Al(OH) is mixed so that the relative Co reaches 2 mol%, and the calcining is carried out at a temperature of 800° C. to 900° C. to obtain lithium cobaltate (LiCo _0.98 Al _0.02 O ₂ ).

The lithium cobaltate had an average particle diameter of 2.8 μm, a bulk density of 1.18 g/cm ³ , and a pressed density of 3.19 g/cm ³ .

The SEM image of this lithium cobaltate is lithium cobaltate (B-4) in which primary particles are aggregated.

Fig. 1 is a SEM photograph (magnification × 3000) showing the particle structure of lithium cobaltate (A) in which primary particles are neatly and monodispersed in Preparation Example 1.

Fig. 2 is a SEM photograph (magnification × 3000) showing the particle structure of aggregated lithium cobaltate (B) in Preparation Example 7.

Table 1 summarizes the lithium cobaltate (A) and lithium cobaltate (B) obtained in Preparation Examples 1 to 7 above.

Table 1

(Note) (A) in the table represents lithium cobaltate (A), and (B) represents lithium cobaltate (B).

The pressed density of lithium cobaltate (A) in the present invention is 3.3-3.7 g/cm ³ , preferably 3.5-3.7 g/cm ³ . In addition, the pressed density of lithium cobaltate (B) in the present invention is 3.1 to 3.5 g/cm ³ , preferably 3.1 to 3.3 g/cm ³ .

The pressed density difference between lithium cobaltate (A) and lithium cobaltate (B) in the present invention is 0.2 g/cm ³ or more, preferably 0.8 to 1.5 g/cm ³ .

Example 1

The average particle diameter that obtains in preparation example 1 is 15.5 μ m, bulk ^density is 2.80g/cm 5 parts by weight of lithium cobaltate (B-3) of 1.20 g/cm ³ were uniformly mixed with a small ribbon mixer to prepare lithium cobaltate. The obtained lithium cobaltate had an average particle diameter of 15.0 μm, a bulk density of 2.75 g/cm ³ , and a pressed density of 3.65 g/cm ³ .

Example 2

The average particle diameter obtained in Preparation Example 1 is 15.5 μm, bulk ^density is 2.80g/cm Lithium cobaltate was prepared by uniformly mixing 30 parts by weight of lithium cobaltate (B-3) of 1.20 g/cm ³ . The obtained lithium cobaltate had an average particle diameter of 11.9 μm, a bulk density of 2.40 g/cm ³ , and a pressed density of 3.92 g/cm ³ .

Example 3

The average particle diameter that obtains in preparation example 1 is 15.5 μ m, bulk ^density is 2.80g/cm Lithium cobaltate was prepared by uniformly mixing 30 parts by weight of lithium cobaltate (B-2) of 1.50 g/cm ³ . The obtained lithium cobaltate had an average particle diameter of 12.8 μm, a bulk density of 2.53 g/cm ³ , and a pressed density of 3.82 g/cm ³ .

Example 4

The average particle diameter that obtains in preparation example 2 is that 12.3 μm, bulk ^density are 2.50g/cm Lithium cobaltate was prepared by uniformly mixing 20 parts by weight of lithium cobaltate (B-2) of 1.50 g/cm ³ . The obtained lithium cobaltate had an average particle diameter of 10.5 μm, a bulk density of 2.40 g/cm ³ , and a pressed density of 3.75 g/cm ³ .

Example 5

The average particle diameter obtained in Preparation Example 2 is 12.3 μm, bulk ^density is 2.50g/cm Lithium cobaltate was prepared by uniformly mixing 40 parts by weight of lithium cobaltate (B-1) of 1.80 g/cm ³ . The obtained lithium cobaltate had an average particle diameter of 10.1 μm, a bulk density of 2.35 g/cm ³ , and a pressed density of 3.65 g/cm ³ .

Example 6

The average particle diameter that obtains in preparation example ³ is 7.8 μ m, bulk density is 1.90g/cm Lithium cobaltate was prepared by uniformly mixing 15 parts by weight of lithium cobaltate (B-3) of 1.20 g/cm ³ . The obtained lithium cobaltate had an average particle diameter of 7.0 μm, a bulk density of 1.83 g/cm ³ , and a pressed density of 3.55 g/cm ³ .

Example 7

The average particle diameter that obtains in preparation example 1 is that 15.5 μ m, bulk ^density are 2.80g/cm Lithium cobaltate was prepared by uniformly mixing 40 parts by weight of lithium cobaltate (B-3) of 1.20 g/cm ³ . The obtained lithium cobaltate had an average particle diameter of 7.8 μm, a bulk density of 1.88 g/cm ³ , and a pressed density of 3.50 g/cm ³ .

Example 8

The average particle diameter obtained in Preparation Example 1 is 15.5 μm, bulk density is 2.80g/cm The average particle diameter that obtains in Preparation Example 7 is 2.8 μm, ^bulk density Lithium cobaltate was prepared by uniformly mixing 30 parts by weight of Al-added lithium cobaltate (LiCo _0.98 Al _0.02 O ₂ ) (B-4) of 1.18 g/cm ³ . The obtained lithium cobaltate had an average particle diameter of 7.7 μm, a bulk density of 2.38 g/cm ³ , and a pressed density of 3.89 g/cm ³ .

Example 9

The average particle diameter obtained in Preparation Example 1 is 15.5 μm, bulk ^density is 2.80g/cm Lithium cobaltate was prepared by uniformly mixing 10 parts by weight of lithium cobaltate (B-3) of 1.20 g/cm ³ . The obtained lithium cobaltate had an average particle diameter of 13.8 μm, a bulk density of 2.65 g/cm ³ , and a pressed density of 3.72 g/cm ³ .

Example 10

The average particle diameter obtained in Preparation Example 1 is 15.5 μm, bulk ^density is 2.80g/cm Lithium cobaltate was prepared by uniformly mixing 10 parts by weight of lithium cobaltate (B-1) of 1.80 g/cm ³ . The obtained lithium cobaltate had an average particle diameter of 14.8 μm, a bulk density of 2.70 g/cm ³ , and a pressed density of 3.60 g/cm ³ .

Example 11

The average particle diameter obtained in Preparation Example 1 is 15.5 μm, bulk density is 2.80g/cm The average particle diameter 3.2 μm obtained in Preparation ^Example 6 and the average particle diameter 3.2 μm, bulk density of 2.80g/cm 20 parts by weight of lithium cobaltate (B-3) of 1.20 g/ ^cm3 were uniformly mixed to prepare lithium cobaltate. The obtained lithium cobaltate had an average particle diameter of 13.2 μm, a bulk density of 2.85 g/cm ³ , and a pressed density of 3.74 g/cm ³ .

Example 12

The average particle diameter obtained in Preparation Example 1 is 15.5 μm, bulk density is 2.80g/cm ⁸⁰ weight parts of lithium cobaltate (A-1) and the average particle diameter obtained in Preparation Example 4 is 7.4 μm, bulk density Lithium cobaltate was prepared by uniformly mixing 20 parts by weight of lithium cobaltate (B-1) of 1.80 g/cm ³ . The obtained lithium cobaltate had an average particle diameter of 13.8 μm, a bulk density of 2.62 g/cm ³ , and a pressed density of 3.58 g/cm ³ .

Table 2 and Table 3 summarize the lithium cobaltate obtained by mixing lithium cobaltate (A) and (B) in the above-mentioned Examples 1 to 12.

Table 2

(A) Bulk density (g/cm ³ ) (B) Bulk density (g/cm ³ ) Bulk density (g/cm ³ ) Mixing ratio A: B Mixed density (g/cm ³ ) Average particle size (μm) Example 1 2.80(A-1) 1.20(B-3) 1.60 95:5 2.75 15.0 Example 2 2.80(A-1) 1.20(B-3) 1.60 70:30 2.40 11.9 Example 3 2.80(A-1) 1.50(B-2) 1.30 70:30 2.53 12.8 Example 4 2.50(A-2) 1.50(B-2) 1.00 80:20 2.40 10.5 Example 5 2.50(A-2) 1.80(B-1) 0.70 60:40 2.35 10.1 Example 6 1.90(A-3) 1.20(B-3) 0.70 85:15 1.83 7.0 Example 7 2.80(A-1) 1.20(B-3) 1.60 60:40 1.88 7.8 Example 8 2.80(A-1) 1.18(B-4) 1.62 70:30 2.38 7.7 Example 9 2.80(A-1) 1.20(B-3) 1.60 90:10 2.65 13.8 Example 10 2.80(A-1) 1.80(B-1) 1.00 90:10 2.70 14.8 Example 11 2.80(A-1) 1.20(B-3) 1.60 80:20 2.58 13.2 Example 12 2.80(A-1) 1.80(B-1) 1.00 80:20 2.62 13.8

table 3

(A) Density under pressure (g/cm ³ ) (B) Density under pressure (g/cm ³ ) Density difference under pressure (g/cm ³ ) Mixing ratio A: B Mixed press density (g/cm ³ ) Average particle size (μm) Example 1 3.45(A-1) 3.21(B-3) 0.24 95:5 3.65 15.0 Example 2 3.45(A-1) 3.21(B-3) 0.24 70:30 3.95 11.9 Example 3 3.45(A-1) 3.15(B-2) 0.30 70:30 3.82 12.8 Example 4 3.48(A-2) 3.15(B-2) 0.33 80:20 3.75 10.5 Example 5 3.48(A-2) 3.20(B-1) 0.28 60:40 3.65 10.1 Example 6 3.41(A-3) 3.21(B-3) 0.20 85:15 3.55 7.0 Example 7 3.45(A-1) 3.21(B-3) 0.24 60:40 3.50 7.8 Example 8 3.45(A-1) 3.19(B-4) 0.26 70:30 3.89 7.7 Example 9 3.45(A-1) 3.21(B-3) 0.24 90:10 3.72 13.8 Example 10 3.45(A-1) 3.20(B-1) 0.25 90:10 3.60 14.8 Example 11 3.45(A-1) 3.21(B-3) 0.24 80:20 3.74 13.2 Example 12 3.45(A-1) 3.20(B-1) 0.25 80:20 3.58 13.8

(Note) In the table (A) represents lithium cobaltate (A), and (B) represents lithium cobaltate (B).

Comparative example 1

Lithium cobaltate (LiCoO ₂ ) obtained in Preparation Example 2 with an average particle size of 12.3 μm, a bulk density of 2.50 g/cm ³ , and a pressed density of 3.48 g/cm ³ was used as a comparative example.

The SEM image of this lithium cobaltate is a monodisperse lithium cobaltate (A) with orderly primary particles.

Next, comparative examples of lithium cobaltate obtained when the mixture of lithium cobaltate (A) and lithium cobaltate (B) of the present invention are changed are shown.

Preparation example 8 (comparative preparation example)

Mix lithium carbonate and cobalt oxide so that the Li/Co atomic ratio reaches 1.00 to make a homogeneous mixture, and keep it at a temperature of 1000 ° C to 1050 ° C for 10 hours for calcination treatment, and the obtained calcined product is crushed and classified in the atmosphere Lithium cobaltate (LiCoO ₂ ) with an average particle size of 4.5 μm, a bulk density of 1.60 g/cm ³ , and a pressed density of 3.25 g/cm ³ was obtained.

This lithium cobaltate is lithium cobaltate (C-1) in which primary particles are monodispersed.

Preparation example 9 (comparative preparation example)

Mix lithium carbonate and cobalt oxide so that the Li/Co atomic ratio reaches 1.00 to make a homogeneous mixture, and keep it at a temperature of 800°C to 850°C for 10 hours for calcination treatment, and the obtained calcined product is crushed and classified in the atmosphere Lithium cobaltate (LiCoO ² ) with an average particle size of 11.0 μm, a bulk density of 2.20 g/cm ³ , and a pressed density of 3.30 g/cm ³ was obtained.

This lithium cobaltate is lithium cobaltate (C-2) in which primary particles are aggregated.

Preparation example 10 (comparative preparation example)

Mix lithium carbonate and cobalt oxide so that the Li/Co atomic ratio reaches 1.00 to make a homogeneous mixture, and keep it at a temperature of 1000 ° C to 1050 ° C for 10 hours for calcination treatment, and the obtained calcined product is crushed and classified in the atmosphere Lithium cobaltate (LiCoO ² ) with an average particle size of 5.0 μm, a bulk density of 1.32 g/cm ³ , and a pressed density of 3.12 g/cm ³ was obtained.

This lithium cobaltate is lithium cobaltate (C-3) in which primary particles are monodispersed.

Comparative example 2

80 parts by weight of lithium cobaltate (C-1) obtained in Preparation Example 8 and 20 parts by weight of lithium cobaltate (B-3) obtained in Preparation Example 6 were uniformly mixed with a small ribbon mixer to prepare lithium cobaltate.

The obtained lithium cobaltate had an average particle diameter of 3.5 μm, a bulk density of 1.32 g/cm ³ , and a pressed density of 3.22 g/cm ³ .

Comparative example 3

80 parts by weight of lithium cobaltate (C-2) obtained in Preparation Example 9 and 20 parts by weight of lithium cobaltate (B-3) obtained in Preparation Example 6 were uniformly mixed with a small ribbon mixer to prepare lithium cobaltate.

The obtained lithium cobaltate had an average particle diameter of 11.2 μm, a bulk density of 2.15 g/cm ³ , and a pressed density of 3.45 g/cm ³ .

Comparative example 4

80 parts by weight of lithium cobaltate (A-1) obtained in Preparation Example 1 and 20 parts by weight of lithium cobaltate (C-2) obtained in Preparation Example 9 were uniformly mixed with a small ribbon mixer to prepare lithium cobaltate.

The obtained lithium cobaltate had an average particle diameter of 11.2 μm, a bulk density of 2.56 g/cm ³ , and a pressed density of 3.37 g/cm ³ .

Comparative Example 5

80 parts by weight of lithium cobaltate (A-1) obtained in Preparation Example 1 and 20 parts by weight of lithium cobaltate (C-3) obtained in Preparation Example 10 were uniformly mixed with a small ribbon mixer to prepare lithium cobaltate.

The obtained lithium cobaltate had an average particle diameter of 13.4 μm, a bulk density of 2.62 g/cm ³ , and a pressed density of 3.40 g/cm ³ .

Comparative example 6

50 parts by weight of lithium cobaltate (A-1) obtained in Preparation Example 1 and 50 parts by weight of lithium cobaltate (B-3) obtained in Preparation Example 6 were uniformly mixed with a small ribbon mixer to prepare lithium cobaltate.

The obtained lithium cobaltate had an average particle diameter of 9.5 μm, a bulk density of 1.71 g/cm ³ , and a pressed density of 3.42 g/cm ³ .

Table 4

table 5

(A) Bulk density (g/cm ³ ) (B) Bulk density (g/cm ³ ) Bulk density difference (g/cm ³ ) Mixing ratio A: B Mixed bulk density (g/cm ³ ) Average particle size (μm) Comparative example 1 2.50(A-2) - - 100 2.50 12.3 Comparative example 2 1.60(C-1) 1.20(B-3) 0.40 80:20 1.32 3.5 Comparative example 3 2.20(C-2) 1.20(B-3) 1.00 80:20 2.15 11.2 Comparative example 4 2.80(A-1) 2.20(C-2) 0.60 80:20 2.56 11.2 Comparative Example 5 2.80(A-1) 1.32(C-3) 1.48 80:20 2.62 13.4 Comparative example 6 2.80(A-1) 1.20(B-3) 1.60 50:50 1.71 9.5

Table 6

(A) Density under pressure (g/cm ³ ) (B) Density under pressure (g/cm ³ ) Density difference under pressure (g/cm ³ ) Mixing ratio A: B Mixed press density (g/cm ³ ) Average particle size (μm) Comparative Example 1 3.48(A-2) - - 100 3.48 12.3 Comparative example 2 3.25(C-1) 3.21(B-3) 0.04 80:20 3.22 3.5 Comparative example 3 3.30(C-2) 3.21(B-3) 0.09 80:20 3.45 11.2 Comparative example 4 3.45(A-1) 3.30(C-2) 0.15 80:20 3.37 11.2 Comparative Example 5 3.45(A-1) 3.12(C-3) 0.33 80:20 3.40 13.4 Comparative example 6 3.45 3.21 0.24 50:50 3.42 9.5

(A-1) (B-3)

The safety evaluation and rapid charge and discharge test results of the secondary battery using the lithium cobaltate of the present invention as the positive electrode active material are given below.

Safety Evaluation

The lithium cobaltate of Example 2 and the lithium cobaltate (A) of Comparative Example 1 were respectively used as positive electrode active materials. The positive electrode active material is coated on the aluminum foil, and the positive electrode plate is used to make a lithium-ion secondary battery using separators, negative electrodes, positive electrodes, current collectors, jigs for assembly, external terminals, and electrolyte. Wherein, metal lithium is used as the negative electrode, and a solution of 1 mole of LiPF ₆ dissolved in 1 liter of a 1:1 mixed solution of EC (ethylene carbonate) and MEC (ethyl methyl carbonate) is used as the electrolyte. After the battery was fabricated, it was charged with Li/Li ⁺ 4.3V, washed thoroughly with acetone and dried. This electrode and a 1:1 mixed solution of electrolytic solution EC (ethylene carbonate) and MEC (ethyl methyl carbonate) were sealed in a sealed container, and then a thermal stability test was performed by DSC measurement. The results are shown in Figure 3.

It can be seen from the results in Fig. 3 that the first exothermic peak of Example 2 (the low temperature side is near 180°C) is lower than the first exothermic peak of Comparative Example 1 (the low temperature side is near 180°C), and the calorific value is small. It can also be seen that the safety of the active material of Example 2 is higher than that of the active material of Comparative Example 1. In general, microparticles have a large specific surface area, high reactivity, and poor safety. However, it can be inferred that the lithium cobaltate of Example 2 coexists with the coarse particles (lithium cobaltate (A), and the safety of the coarse particles is high, showing the effect of suppressing the deterioration of the safety of the fine particles (lithium cobaltate (B).

Rapid charge and discharge test

The lithium cobaltate of Example 2 and the lithium cobaltate (A) of Comparative Example 1 were respectively used as positive electrode active materials. The positive electrode active material is coated on an aluminum foil, and the positive electrode plate is used to manufacture a lithium ion secondary battery using various components such as a separator, a negative electrode, a positive electrode, a current collector, jigs for assembly, external terminals, and an electrolyte. Wherein, metal lithium is used as the negative electrode, and a solution of 1 mol of LiPF ₆ dissolved in 1 liter of a 1:1 mixed solution of EC (ethylene carbonate) and MEC (ethyl methyl carbonate) is used as the electrolyte.

A constant current charge and discharge test was carried out at 2.7V to 4.3V (for Li/Li ⁺ ), and the charge and discharge curves are shown in FIG. 4 . In this case, the current value was increased by 0.2C→0.5C→1.0C→2.0C (1.0C→discharge for 1 hour, 2.0C→discharge for 0.5 hour), and the rapid charge and discharge performance was tested. Positive and negative electrodes: metal Li, electrolyte: 1M LiPF ₆ /EC+NEC, charging method: CCCV (0.5C, 5H), scanning potential: 2.7V, 4.3V.

As can be seen from the results in FIG. 4 , the discharge capacity of Example 2 is larger than that of Comparative Example 1. It is considered that the fine particles (lithium cobaltate (B)) contained in the lithium cobaltate of Example 2 are excellent in rapid charge and discharge and exhibit good characteristics.

Large particles endow high safety, small particles enter the gaps of large particles, and due to the increase in conductivity between powders, high rapid charge and discharge performance can be obtained. However, when the pressing density is too high (4.0 or more), the electrode density is too high when the electrode is produced, the electrolyte solution impregnates the electrode insufficiently, and the rapid charge and discharge performance deteriorates, which is not suitable. In addition, when the pressing density and bulk density are inappropriate values, sufficient electrode density cannot be obtained.

Next, the pressed density of the lithium cobaltate of the present invention will be described.

The lithium cobaltate of the present invention is composed of a mixture of primary particle monodispersed lithium cobaltate (A) and primary particle aggregated lithium cobaltate (B), and the bulk density of the mixture is 1.8g/ ^cm3 or above , and the pressed density is 3.5-4.0 g/cm ³ .

As a preferred embodiment of the above-mentioned lithium cobaltate of the present invention, lithium cobaltate (A) with a bulk density of 1.7 to 3.0 g/cm ³ and a pressurized density of 3.4 to 3.7 g/cm ³ and a bulk density of 1.0 to 2.0 g /cm ³ , a mixture of lithium cobalt oxide (B) with a press density of 3.1 to 3.5 g/cm ³ , and the bulk density difference between lithium cobalt oxide (A) and lithium cobalt oxide (B) is 0.10 g/cm Lithium cobaltate of ³ or more is preferable.

The effect of the invention

As mentioned above, the lithium cobaltate of the present invention can obtain high pressurized density and appropriate bulk density by mixing two different kinds of lithium cobaltate. When it is used as the positive electrode active material for the positive plate, it can obtain The effect of increased electrode density.

In addition, lithium cobalt oxide which can be used as positive electrode active material can be easily obtained by adopting the preparation method of the present invention.

Also, according to the present invention, it is effective to use the above-mentioned lithium cobaltate as the positive electrode active material, and a nonaqueous electrolyte secondary battery excellent in safety and rapid charge and discharge can be obtained.

Claims (7)

1. Lithium cobaltate, characterized in that the bulk density is 1.8g/cm ³ or above, and the pressurized density is 3.5-4.0g/cm ³ , the lithium cobaltate includes lithium cobaltate (A) and lithium cobaltate (B), the lithium cobaltate (A) is a monodisperse primary particle, and the lithium cobaltate (B) is an aggregation of primary particles, and, compared with the average particle diameter of lithium cobaltate (B), cobalt Lithium acid (A) is a coarse particle. 2. according to the preparation method of the lithium cobalt oxide of claim 1, it is characterized in that, be that bulk density is 1.7～3.0g/cm The cobalt oxide lithium ( ^A ) and bulk density are 1.0～ ^2.0g /cm Cobalt acid Lithium (B) is mixed so that the bulk density difference between the lithium cobaltate (A) and the lithium cobaltate (B) is 0.20 g/ ^cm3 or more, and the lithium cobaltate (A) is a monodisperse primary particle , the lithium cobaltate (B) is a primary particle aggregate, and compared with the average particle diameter of the lithium cobaltate (B), the lithium cobaltate (A) is a coarser particle. 3. according to the preparation method of lithium cobaltate described in claim 2, it is characterized in that, above-mentioned lithium cobaltate (A) and lithium cobaltate (B) with weight ratio (A): (B)=95: 5～60 : 40 ratio to be mixed. 4. according to the preparation method of lithium cobaltate according to claim 2, it is characterized in that, the average particle diameter of described lithium cobaltate (A) is 5～30 μ m, the average particle diameter of described lithium cobaltate (B) is 0.1 ~10 μm. 5. according to the preparation method of lithium cobaltate according to claim 3, it is characterized in that, the average particle diameter of described lithium cobaltate (A) is 5～30 μ m, the average particle diameter of described lithium cobaltate (B) is 0.1 ~10 μm. 6. according to the preparation method of lithium cobaltate described in any one in claim 2～5, it is characterized in that, described lithium cobaltate (A) is the compound represented by general formula (1), described lithium cobaltate ( B) is a compound represented by general formula (1) or a compound represented by general formula (2), General formula of Li _a CoO ₂ (1) In the general formula (1), a represents a number within the range of 0.2≤a≤1.2, Li _a Co _1-y M _y O _2-z general formula (2) In the general formula (2), M represents at least one element selected from a transition metal element other than Co or an element with an atomic number of 9 or more, a represents a number in the range of 0.2≤a≤1.2, and y represents A number within the range of 0<y≤0.4, and z represents a number within the range of 0≤z≤1.0. 7. A non-aqueous electrolyte secondary battery comprising a positive electrode plate using the lithium cobaltate described in claim 1 as a positive electrode active material.

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