JPH1173958A - Manufacture of positive electrode active material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a positive electrode active material superior in cycle characteristic with little deterioration of capacity under high-temperature environment by adding an alkali to a mixed aqueous solution of a cobalt salt and an aluminum salt to coprecipitate the cobalt-aluminum compound hydroxide, and adding lithium to the compound hydroxide followed by baking. SOLUTION: A lithium compound, such as lithium carbonate, is added to a coprecipitated cobalt-aluminum compound hydroxide and mixed therewith. The resulting mixture is baked to provide a lithium-cobalt-aluminum compound oxide. The compound oxide preferably has a composition represented by Lix Co(1-y) Aly O2 (wherein 0.05<=x<=1.10, 0.01<=y<=0.10). The baking temperature is preferably set within a range of 700 to 1100 deg.C under oxygen present atmosphere. As the lithium compound, lithium carbonate, lithium hydroxide, lithium nitrate and the like are included.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing a positive electrode active material used for a non-aqueous electrolyte secondary battery.

[0002]

2. Description of the Related Art Conventionally, in portable electronic devices and the like, a high energy density of a battery used as a power source of these electronic devices has been demanded because of high performance and miniaturization. To meet such demands, LiC
Lithium ion secondary batteries using oO ₂ as a cathode material and a carbon material capable of doping and dedoping lithium as a cathode material are used as power supplies for various portable electronic devices such as camcorders, mobile phones and notebook computers. ing.

[0003] In order to further improve the characteristics of the lithium ion secondary battery, improvement of LiCoO ₂ is being promoted.
For example, in order to exhibit excellent cycle characteristics at deep charge / discharge, in Japanese Unexamined Patent Publication No. Hei 4-253162, a part of LiCoO ₂ is converted into at least one element from Pb, Bi, and B. Used as the positive electrode active material. Here, a target positive electrode active material is obtained by firing a mixture obtained by pulverizing and mixing lithium carbonate, cobalt carbonate, lead dioxide, bismuth oxide, or boron oxide with a ball mill in the air. Further, Kokoku 4-24831, JP-A No. 7-176302 and JP-is Keep technique described in _{JP-A-7-176303, A x M y N z} O 2 ( where, A is an alkali metal At least one selected from the group consisting of M is a transition metal, N
Represents at least one selected from Al, In, and Sn, and x, y, and z are 0.05 ≦ x ≦ 1.10, 0.85
≤ y ≤ 1.00 and 0.001 ≤ z ≤ 0.10. )
It has been proposed to use a composite oxide represented by
As a specific example, Li _1.03 Co _0.95 Sn
_0.042 O ₂ , Li _1.01 Co _0.95 In _0.04 O ₂ , Li _1.02 C
o _0.96 In _0.04 O _{2 and the} like. Here, a target positive electrode active material is obtained by mixing lithium carbonate, cobalt oxide, stannic oxide, indium oxide, or aluminum oxide and firing in air.

[0004]

By the way, lithium ion secondary batteries are sometimes used for electronic equipment used not only in a normal temperature environment but also in various environments from a low temperature to a high temperature. In particular, lithium-ion rechargeable batteries used in electronic devices, such as notebook computers, whose internal temperature rises significantly with the speed of the central processing unit, are used for a long time in a high-temperature environment. However, it is required to maintain good battery characteristics.

[0005] The lithium ion secondary battery using the above-mentioned conventionally proposed lithium cobalt oxide as a positive electrode active material exhibits excellent cycle characteristics in deep charge and discharge, but is used or stored under a high temperature environment. In some cases, the battery has a characteristic that the battery capacity is relatively easily damaged.

Further, as described above, it is generally difficult for lithium cobalt oxide containing multiple elements to replace cobalt with another element and uniformly form a solid solution while maintaining a layered structure. The performance of the active material changes greatly depending on the mixing state of the starting raw materials and the like.

Accordingly, the present invention has been proposed with the object of providing a method for producing a positive electrode active material which achieves high capacity with little deterioration in capacity even when used or stored in a high temperature environment. .

[0008]

In order to achieve the above object, a method for producing a positive electrode active material according to the present invention comprises the steps of: adding an aqueous alkali solution to a mixed aqueous solution of a cobalt salt and an aluminum salt; A hydroxide is coprecipitated, a lithium compound is added to and mixed with the cobalt / aluminum composite hydroxide, and the mixture is calcined to obtain a lithium / cobalt / aluminum composite oxide.

In the present invention, since a cobalt-aluminum composite hydroxide having a crystal structure similar to that of lithium-cobalt oxide is used as a raw material, the stability of the crystal structure can be improved. Furthermore, since this synthesis is performed by a coprecipitation reaction, it is possible to obtain a uniform positive electrode active material in which cobalt and aluminum are not ubiquitous as compared with physical mixing, improve the charge / discharge capacity, and The stability of the crystal structure can be further improved.

Therefore, when a non-aqueous electrolyte secondary battery is constructed, the positive electrode active material obtained by such a production method can obtain a high capacity and at the same time suppress the capacity deterioration at high temperatures. The capacity retention rate is high.

The lithium-cobalt-aluminum composite oxide is Li _x Co _(1-y) Al _y O ₂ (provided that
0.05 ≦ x ≦ 1.10 and 0.01 ≦ y ≦ 0.10. ) Is preferable. If the ratio of aluminum is less than 0.01, the effect of improving the capacity retention ratio is small, and if the ratio of aluminum is more than 0.1, the initial capacity is undesirably reduced.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION The method for producing a positive electrode active material according to the present invention comprises the steps of:
An aqueous alkali solution is added to coprecipitate the cobalt / aluminum composite hydroxide, a lithium compound is added to the cobalt / aluminum composite hydroxide and mixed, and the mixture is calcined to form the lithium / cobalt / aluminum composite oxide. obtain.

LiCoO ₂ has a crystal structure having a hexagonal layered structure, but when aluminum is not dissolved in a solid state, it is in a charged state, that is, in a state in which lithium is dedoped from the positive electrode active material. The crystal itself becomes unstable. Therefore, when LiCoO ₂ is repeatedly subjected to such a state, that is, during a charge / discharge cycle or when subjected to a thermal stress in a charged state, for example, the crystal structure is destroyed during high-temperature storage, and lithium doping / undoping is normal. And the performance as a positive electrode active material is impaired.
In contrast, the lithium composite oxide of aluminum is solid-solved in the present invention _{(Li x Co (1-y} ) Al y O 2) is well under normal temperature environment, a lithium doped and dedoped in a high-temperature environment Even when this is performed, the performance as the positive electrode active material is stably maintained. This is because the solid solution of aluminum stabilizes the hexagonal crystal structure during charging,
This is because the crystal structure is maintained even in a high temperature environment.

There are three types of crystal structures of aluminum oxide containing lithium (LiAlO ₂ ).
Those having a crystal structure similar to iCoO ₂ are α-LiAl
O ₂ . Therefore, it is desirable synthesis from the alpha-LiAlO easily generate ₂ Al (OH) _3. Therefore, a cobalt-aluminum composite hydroxide is synthesized by adding an alkaline solution to a mixed aqueous solution of an Al salt and a Co salt and coprecipitating the mixed solution. Thus, the stability of the crystal structure is improved as compared with the one synthesized using Al ₂ O ₃ . Furthermore, the mixed state of the cobalt-aluminum composite hydroxide, which is a coprecipitate, is overwhelmingly superior to that obtained by physical mixing, and a uniform positive electrode activity without ubiquity of Co and Al. Substance can be obtained. As a result, in this positive electrode active material, the charge capacity is increased, and the stability of the crystal structure is further improved.

The positive electrode active material obtained by such a manufacturing method can obtain a high capacity when a non-aqueous electrolyte secondary battery is constructed, and at the same time, suppresses capacity deterioration at a high temperature to maintain the capacity. The rate will be high.

The lithium-cobalt-aluminum composite oxide is Li _x Co _(1-y) Al _y O ₂ (provided that
0.05 ≦ x ≦ 1.10 and 0.01 ≦ y ≦ 0.10. ) Is preferable. If the ratio of aluminum is less than 0.01, the effect of improving the capacity retention ratio is small, and if the ratio of aluminum is more than 0.1, the initial capacity is undesirably reduced.

The firing temperature for the mixture of the cobalt / aluminum composite oxide and the lithium compound is preferably in the range of 700 to 1100 ° C. in an atmosphere containing oxygen. If the firing temperature exceeds 1100 ° C., the lithium composite oxide itself is undesirably decomposed.

Examples of the lithium compound include lithium carbonate, lithium hydroxide, lithium nitrate, lithium sulfate, lithium acetate and the like. In particular, lithium carbonate and lithium hydroxide are preferable.

When a non-aqueous electrolyte secondary battery is constructed using the above-described positive electrode active material, the negative electrode active material may be any material capable of doping and undoping lithium ions. A lithium alloy with lead, indium, or the like, another carbon material capable of doping / dedoping lithium, or a polymer such as polyacetylene or polypyrrole is suitably used.

The carbon material used for the negative electrode is not particularly limited, but includes pyrolytic carbons, pitch cokes, needle cokes, cokes such as petroleum cokes, graphites, glassy carbons, phenolic resins, and the like. An organic polymer compound fired body obtained by firing a furan resin or the like at an appropriate temperature, carbon fiber, activated carbon, or the like can be used.

Particularly, non-graphitizable carbons are preferably used because of their high charge / discharge capacity per weight and excellent cycle characteristics. Among them, the (002) plane spacing is 0.370 nm or more, and the true density is 1.70 g / cm ^3.
And in differential thermal analysis in an air stream of 70
A carbonaceous material having no exothermic peak at 0 ° C. or higher is used.

Examples of the material having such properties include a carbonaceous material obtained by carbonizing an organic material by a method such as calcination. As a starting material for carbonization, furfuryl alcohol or furfural homopolymer, Furan resins consisting of copolymers are preferred. In particular,
Furfural + phenol, furfuryl alcohol + dimethylol urea, furfuryl alcohol, furfuryl alcohol + formaldehyde, furfuryl alcohol +
Polymers composed of furfural, furfural + ketones and the like are preferably used.

Alternatively, a hydrogen / carbon atomic ratio of 0.6
Using a petroleum pitch of ~ 0.8, a functional group containing oxygen is introduced into this, and a so-called oxygen cross-link is applied to obtain an oxygen content of 10 ~
A carbonaceous material obtained by baking after forming a precursor of 20% by weight is also suitable.

Further, a carbonaceous material having a large doping amount with respect to lithium by adding a phosphorus compound or a boron compound when carbonizing the above-mentioned furan resin or petroleum pitch can be used.

The graphite material needs to have a true specific gravity of at least 2.10 g / cm ³ , and preferably at least 2.18 g / cm ^{3 in} order to obtain a higher negative electrode mixture filling property. Used for In order to obtain such a true specific gravity, the plane spacing obtained by the X-ray diffraction method needs to be 0.335 nm or more and 0.34 nm or less.
More preferably, it is 35 nm or more and 0.337 nm or less. The crystal thickness in the c-axis direction is preferably at least 16.0 nm, more preferably at least 24.0 nm.

Further, the following components can be used as other components constituting the above-mentioned non-aqueous electrolyte secondary battery, for example, a non-aqueous electrolyte, a separator and the like.

As the non-aqueous electrolyte, for example, a non-aqueous electrolyte in which a lithium salt is used as an electrolyte and this is dissolved in an organic solvent is used. As the organic solvent, although not particularly limited, propylene carbonate, ethylene carbonate, 1,2-dimethoxyethane, γ-butyrolactone,
Diethyl ether, tetrahydrofuran, 2-methyl-
A single solvent or a mixture of two or more solvents such as tetrahydrofuran, 1,3-dioxolan, sulfolane, acetonitrile, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, methyl ethyl carbonate, methyl propyl carbonate and the like are used.

Examples of the separator include, but are not particularly limited to, woven fabric, nonwoven fabric, and synthetic resin microporous membrane. In particular, a synthetic resin microporous membrane is preferably used,
Among them, a polyolefin-based microporous film is suitably used in terms of thickness, film strength, film resistance and the like. Specifically, a microporous membrane made of polyethylene and polypropylene or a microporous membrane obtained by combining these is used.

The shape of the current collector of the electrode is not particularly limited, but a foil shape or a mesh shape such as a mesh or expanded metal is used. As a material used for the positive electrode current collector, for example, aluminum, stainless steel, nickel, or the like is preferably used. A thickness of 10 to 50 μm is suitably used. As a material used for the negative electrode current collector, for example, copper, stainless steel, nickel, or the like is preferably used. A thickness of 5 to 30 μm is preferably used.

Further, in order to obtain a sealed non-aqueous electrolyte secondary battery having higher safety, a device such as a safety valve which operates by an increase in battery internal pressure and shuts off current when an abnormality such as overcharging occurs is provided. It is desirable that

[0031]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, specific embodiments to which the present invention is applied will be described.

The present invention is not limited at all by the embodiments described below, and can be implemented by appropriately changing the scope of the invention without changing the gist of the invention.

Example 1 First, as shown in FIG. 1, a positive electrode 1 is manufactured as follows. Commercially available cobalt sulfate and aluminum sulfate are weighed so that the molar ratio becomes Co / Al = 0.97 / 0.03,
The concentration is adjusted by adding water, and the mixture is stirred to prepare a mixed aqueous solution of cobalt sulfate and Al sulfate. Then, sodium hydroxide is gradually added to the mixed aqueous solution to precipitate (coprecipitate) hydroxides of cobalt and aluminum. The coprecipitate was filtered and washed with pure water while checking the pH.
Dry at 0 ° C.

Elemental analysis of the thus obtained cobalt-aluminum composite hydroxide showed that the composition ratio was almost the same as the measurement ratio. Further, the powder X-ray diffraction pattern of the cobalt / aluminum composite hydroxide is close to a single phase.

Then, lithium carbonate was added to the cobalt / aluminum composite hydroxide in a molar ratio of Li / (Co + A).
l) = 1.01 / 1.00, and mix with a ball mill. In addition, this mixture is
After calcination at 1 ° C. for 1 hour, the mixture is further baked at 900 ° C. for 10 hours to synthesize a cathode active material.

Next, after pulverizing the positive electrode active material, 91% by weight of the positive electrode active material, 6% by weight of graphite as a conductive agent, and 3% by weight of polyvinylidene fluoride as a binder were mixed to form a positive electrode. A positive electrode mixture slurry is obtained by preparing an agent and dispersing it in N-methyl-2-pyrrolidone. The positive electrode mixture slurry is applied to an aluminum foil serving as the positive electrode current collector 10, dried, and then compression-molded by a roller press to produce a belt-shaped positive electrode 1.

Next, the negative electrode 2 is manufactured as follows. Petroleum pitch is used as a starting material, and oxygen-containing functional groups are added to this.
After introducing 0 to 20% (oxygen crosslinking), the mixture was calcined in an inert gas at a temperature of 1000 ° C. to obtain a negative electrode active material. The obtained negative electrode active material is a non-graphitizable carbon material close to a glassy carbon material. 90% by weight of this carbonaceous material and 10% by weight of polyvinylidene fluoride as a binder are mixed to prepare a negative electrode mixture, which is dispersed in N-methyl-2-pyrrolidone to obtain a negative electrode mixture slurry. The negative electrode mixture slurry is applied to both surfaces of a copper foil serving as the negative electrode current collector 11, dried, and then compression-molded by a roll press to form a strip-shaped negative electrode 2.

The spirally wound electrode body is formed by laminating the positive electrode 1 and the negative electrode 2 prepared as described above in order through a separator 3 made of a microporous polypropylene film having a thickness of 25 μm and winding a number of times. In this spiral electrode body, the negative electrode 2 is formed so as to be larger in both width and length than the positive electrode 1.

The spirally wound electrode body thus manufactured is housed in a nickel-plated iron battery can 5 and insulating plates 4 are arranged on both upper and lower surfaces of the spirally wound electrode body. Then, in order to collect the current of the positive electrode 1 and the negative electrode 2, the aluminum lead 12 is led out from the positive electrode current collector 10, and the battery cover 7 and the PTC
The battery can 5 is welded to the safety valve device 8 connected via the element 9, the nickel lead 13 is led out from the negative electrode current collector 11, and
To weld. Then, into the battery can 5, an electrolyte obtained by dissolving 1 mol of LiPF _{6 in} a mixed solvent of 50% by volume of propylene carbonate and 50% by volume of diethyl carbonate is injected. Next, the battery cover 7 is fixed by caulking the battery cover 7 and the battery can 5 through the sealing gasket 6 coated with asphalt, so that the diameter is 18 mm as shown in FIG. 1 and the height is 65 mm. A cylindrical battery is made.

Example 2 In Example 2 according to the present invention, cobalt sulfate and aluminum sulfate were configured so that the molar ratio was Co / Al = 0.99 / 0.01. Example 1 described above
A positive electrode active material is synthesized in the same manner as described above to produce a cylindrical battery.

Example 3 In Example 3 according to the present invention, cobalt sulfate and aluminum sulfate were configured so that the molar ratio was Co / Al = 0.95 / 0.05. Example 1 described above
A positive electrode active material is synthesized in the same manner as described above to produce a cylindrical battery.

Embodiment 4 Embodiment 4 according to the present invention is configured so that cobalt sulfate and aluminum sulfate are in a molar ratio of Co / Al = 0.93 / 0.07. Example 1 described above
A positive electrode active material is synthesized in the same manner as described above to produce a cylindrical battery.

Embodiment 5 Embodiment 5 according to the present invention is configured so that cobalt / aluminum sulfate has a molar ratio of Co / Al = 0.90 / 0.10. Example 1 described above
A positive electrode active material is synthesized in the same manner as described above to produce a cylindrical battery.

Comparative Example 1 Here, as Comparative Example 1, lithium carbonate, cobalt oxide, and aluminum oxide were used in a molar ratio of Li / Co / Al.
= 1.01 / 0.97 / 0.03, mixed in a ball mill, calcined in air at 600 ° C. for 1 hour, and then calcined at 900 ° C. for 10 hours to synthesize a positive electrode active material. Then, using this positive electrode active material, a cylindrical battery is manufactured in the same manner as in Example 1 except for the above.

Experimental Example 1 Further, as Experimental Example 1, Co / Al = 0.959 / 0.00 in a molar ratio of cobalt sulfate and aluminum sulfate.
A positive electrode active material was synthesized in the same manner as in Example 1 except that the weight was adjusted to 5 to produce a cylindrical battery.

Experimental Example 2 Further, as Experimental Example 2, Co / Al = 0.88 / 0.1 in a molar ratio of cobalt sulfate and aluminum sulfate.
A positive electrode active material was synthesized in the same manner as in Example 1 except that the weight was adjusted to 2 to produce a cylindrical battery.

Examples, comparative examples,
And about the cylindrical battery of an experimental example, the initial capacity and the capacity maintenance rate under high temperature environment were measured.

Note that the initial capacity is a charging voltage of 4.20 V,
After charging for 2.5 hours under the condition of a charging current of 1 A and then discharging under a condition of a discharging current of 250 mA and a cut-off voltage of 2.50 V, a charge-discharge cycle of two cycles is repeated.
The discharge capacity at the cycle is shown. The capacity retention rate in a high-temperature environment is calculated by measuring the discharge capacity when the battery whose initial capacity has been investigated is further repeated 200 cycles in an environment of 60 ° C., and dividing the discharge capacity at the 200th cycle by the initial capacity. Is the ratio of

Table 1 shows the results of Examples, Comparative Examples and Experimental Examples.
And Table 2.

[0050]

[Table 1]

[0051]

[Table 2]

As shown in Table 1, the cylindrical battery of Example 1 in which a positive electrode active material was synthesized from a coprecipitated composite hydroxide of cobalt and aluminum was obtained by dry mixing oxidation of aluminum oxide and cobalt oxide by a conventional method. Compared with the cylindrical battery of Comparative Example 1 in which the positive electrode active material was synthesized from the material, the initial capacity was increased, and the capacity retention under a high temperature environment was improved.

Examples 1 to 5 and Experimental Examples 1 to 5
As can be seen from the results of Experimental Example 2, the lithium-cobalt-aluminum composite oxide was Li _x Co _(1-y) Al _y O ₂
Is preferably 0.01 ≦ y ≦ 0.10. When the ratio of aluminum is less than 0.01 as in Experimental Example 1, the effect of improving the capacity retention ratio decreases. As in Experimental Example 2, when the ratio of aluminum exceeds 0.1, the initial capacity decreases.

As described above, the lithium composite oxide Li _x obtained by firing the mixture of the cobalt / aluminum composite hydroxide obtained by the coprecipitation reaction and the lithium compound.
Co _(1-y) Al _y O ₂ (provided that 0.05 ≦ x ≦ 1.10.
0.01 ≦ y ≦ 0.10) is a positive electrode active material having a high capacity and an excellent capacity retention rate in a high-temperature environment.

In this embodiment, lithium carbonate is used as the lithium salt used in the synthesis. However, similar results can be obtained with other lithium salts such as lithium hydroxide and lithium nitrate. Furthermore, in this example, cobalt sulfate was used as the cobalt salt used for the synthesis, and aluminum sulfate was used as the aluminum salt. However, similar results can be obtained as long as the cobalt salt or aluminum salt can be made into a solution.

In this embodiment, the case where the present invention is applied to a cylindrical battery has been described. However, the shape is not particularly limited, and the present invention is applicable to a square type, an elliptical type, a coin type, and a button type. And non-aqueous electrolyte secondary batteries of various shapes such as a paper type battery.

[0057]

As is clear from the above description, according to the present invention, when a lithium composite oxide is obtained, a cobalt-aluminum composite hydroxide obtained by a coprecipitation reaction is used. A positive electrode active material having a high capacity and excellent cycle characteristics under a high temperature environment can be obtained.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view showing a cylindrical battery to which the present invention is applied.

[Explanation of symbols]

1 positive electrode, 2 negative electrode, 3 separator, 4 insulating plate, 5
Battery can, 6 Seal gasket, 7 Battery lid, 8 Safety valve device, 9 PTC element, 10 Positive current collector, 11 Negative current collector, 12 Positive electrode lead, 13 Negative electrode lead

Claims (2)

[Claims] An alkaline aqueous solution is added to a mixed aqueous solution of a cobalt salt and an aluminum salt to coprecipitate a cobalt / aluminum composite hydroxide, and a lithium compound is added to the cobalt / aluminum composite hydroxide and mixed. A method for producing a positive electrode active material, wherein the mixture is fired to obtain a lithium-cobalt-aluminum composite oxide. 2. The lithium-cobalt-aluminum composite oxide is Li _x Co _(1-y) Al _y O ₂ (provided that 0.0
5 ≦ x ≦ 1.10 and 0.01 ≦ y ≦ 0.10. )
The method for producing a positive electrode active material according to claim 1, wherein