JPH10310432A - Lithium multiple oxide, its production and positive electrode active material for lithium ion secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a lithium multiple oxide adaptable to a positive electrode material for a lithium ion secondary battery, excellent in energy density and having stable characteristics. SOLUTION: Particles of an Ni salt or an Ni-Co salt and an Li salt are mixed and fired while blowing air having <=20 g/kg absolute humidity to produce the objective lithium multiple oxide represented by the formula, Lix Ni1-y Coy O2 (where 0<x<1.1 and 0<=y<=0.6) and having <=0.1 wt.% water content and/or having <=0.6 wt.% water content after it is allowed to stand at 30 deg.C and 60% relative humidity for 12 hr.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a lithium composite oxide, a method for producing the same, and a positive electrode active material for a lithium ion secondary battery having excellent energy density.

[0002]

[Technology] In recent years, home appliances have become portable,
With the rapid progress in cordless use, lithium ion secondary batteries have been put into practical use as power supplies for small electronic devices such as laptop computers, mobile phones, and video cameras. Regarding this lithium ion secondary battery, Mizushima et al. Reported in 1980 that lithium cobaltate was useful as a positive electrode active material for lithium ion secondary batteries ("Material Research Bulletin" vo115, P783-789 (1980)). Since then, research and development on lithium-based composite oxides have been actively promoted, and many proposals have been made on compounds such as lithium cobaltate, lithium nickelate and lithium manganate.

[0003] As lithium nickelate, for example, Li
_1-x NiO ₂ (where 0 ≦ x ≦ 1) (US Pat. No. 430)
2518), Li _y Ni _2-y O ₂ (Japanese Unexamined Patent Publication No.
No. 40861), Li _y Ni _x Co _1-x O ₂ (where 0 <x ≦ 0.75, y ≦ 1) (JP-A-63-29905)
No. 6) has been proposed as a composite oxide mainly containing lithium and a transition metal. Regarding physical properties, [0
03] LiNi _x Co _1-x O ₂ having a crystallite size of 50 angstroms and a lattice volume of 0.295 to 0.305
(JP-A-6-275274), the particle shape is spherical
3] The half width of the surface is 0.14 to 0.3 and Ni is 2.9 to
LiNi _x Co _1-x O _{2 in} the range of 3.1
JP-A-267539), LiNiO ₂ having a [003] plane / [104] plane strength of 1.5 or more (JP-A-6-215773), and a [003] plane / [104] plane having an intensity ratio of 1 .2
LiNiO ₂ (Japanese Patent Laid-Open No. 6-96769),
LiNi _x Co _1-x O having an average particle diameter of 10 to 35 μm
₂ (Japanese Patent Application Laid-Open No. 7-142056), polycrystalline powder LiNiO ₂ having an average particle diameter of 10 μm or less (Japanese Patent Application Laid-Open No. 7-149424).
Etc. have been proposed.

[0004]

Lithium nickelate has the advantage of being less expensive than lithium cobaltate, but tends to cause defects during use as a positive electrode material of a battery. Capacitance characteristics such as lack of properties are considered to be inferior to those of the cobalt type. Therefore, a lithium composite oxide in which part of LiNiO ₂ and nickel (Ni) having a stoichiometric ratio as close as possible is replaced by another transition metal, and a method of synthesizing the same are being studied. However,
As a positive electrode material for a lithium ion secondary battery, a material having sufficiently satisfactory characteristics has not yet been found, and it is desired to develop a lithium composite oxide having an excellent energy density suitable for the positive electrode material and having stable characteristics. It is rare.

Accordingly, an object of the present invention is to provide an excellent energy density suitable for a cathode material for a lithium ion secondary battery,
An object of the present invention is to provide a lithium composite oxide having stable characteristics and a method for producing the same.

[0006]

Under such circumstances, the present inventors have conducted intensive studies and as a result, have found that lithium nickel oxide suitable as a positive electrode material for a lithium ion secondary battery can be produced using air blown during firing during production. Lithium nickelate produced by controlling the absolute humidity not only obtains an extremely small amount of water, but also obtains a compound that absorbs less moisture even under a humid atmosphere.
Further, they have found that this is the same for the lithium composite oxide containing cobalt, and have completed the present invention. That is, the present invention is represented by the following general formula (1): Li _x Ni _1-y Co _y O ₂ (1) (in the formula, 0 <x <1.1, 0 ≦ y ≦ 0.6). In the lithium composite oxide represented, the water content in the lithium composite oxide is 0.1% by weight or less and / or 30% by weight or less.
° C, relative humidity 60%, moisture content after standing for 12 hours is 0.
It is intended to provide a lithium composite oxide of not more than 6% by weight.

The present invention also provides a method for producing a lithium composite oxide by mixing a lithium salt with crystal particles of a nickel salt or crystal particles of a Ni—Co salt of nickel and cobalt, followed by firing. Absolute humidity 20g / k
An object of the present invention is to provide a method for producing a lithium composite oxide, which is produced while blowing air of g ′ or less into a furnace. Further, the present invention provides a positive electrode active material for a lithium ion secondary battery, comprising the lithium composite oxide as a main material.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The lithium composite oxide of the present invention
A compound represented by the general formula (1) Li _x Ni _1-y Co _y O ₂ (1) (where 0 <x <1.1, 0 ≦ y ≦ 0.6), It is characterized by a water content of 0.1% by weight or less, preferably 0.05% by moisture vaporization at 120 ° C. by Karl Fischer titration.
% By weight or less of lithium composite oxide. The water content of the compound after standing for 12 hours at 30 ° C. and a relative humidity of 60% is 0.6% by weight or less as measured by Karl Fischer titration at 120 ° C. water vaporization. The moisture measurement by the Karl Fischer titration at 120 ° C. is determined in accordance with JIS K0068 (method for measuring moisture in chemical products). The water content is 0.1% by weight and / or
Alternatively, if the water content after the specific moisture absorption exceeds 0.6% by weight is used as the positive electrode material, the electrolyte solution or the like is decomposed and the characteristics of the secondary battery are deteriorated, which is not preferable.

In the method for producing a lithium composite oxide according to the present invention, one of the starting materials is nickel (N
i) Salt crystal particles or nickel (Ni) and cobalt (C
o) and Ni-Co salt crystal particles. In the case of a Ni—Co salt, the atomic ratio (Ni: Co) is 1: 0 to 0.4:
0.6, preferably in the range of 1: 0 to 0.7: 0.3, and the Ni—Co salt may be simply mixed in a predetermined amount. Are preferably dissolved in a solid solution and / or coprecipitated and uniformly mixed in a predetermined amount.

As such Ni salt or Ni—Co salt,
It becomes a metal oxide when heated, and is a so-called precursor compound, and examples thereof include hydroxides, carbonates, oxides, organic acid salts such as oxalates, and the like. preferable.

The lithium (Li) salt as another raw material includes lithium hydroxide, lithium oxide, lithium carbonate, lithium nitrate, lithium acetate, lithium peroxide, lithium sulfate and the like. In the present invention, the lithium salt is preferably lithium hydroxide.

In the production method of the present invention, a predetermined amount of the above raw materials is mixed and fired. The firing conditions are not particularly limited, and any known conditions may be used. For example, firing is preferably performed in a multi-stage firing, and firing may be performed at a firing temperature of about 750 to 800 ° C. In addition, the firing rate of firing is preferably higher, and may be usually 1 ° C./min. Specifically, after sintering slowly in the range of about 200 to 400 ° C. at which the water contained in the raw material disappears, the temperature is rapidly raised to about 700 to 800 ° C. at a rate of 4 ° C./min. A method of firing at a temperature attained for several hours to 10 hours is particularly preferable.

It is necessary to calcine at a lower temperature as the y value of the general formula (1) is larger. However, if the mixture of Ni and Co is insufficient, for example, a lithium composite oxide with y = 0.5 may be used. Even if the synthesis is attempted, lithium oxides having different compositions are obtained, so that it is necessary to sufficiently mix the raw materials.

In the manufacturing method of the present invention, it is necessary to blow air having an absolute humidity of 20 g / kg 'or less during the firing. The absolute humidity means humidity on a weight basis, and indicates the weight (g / kg ′ (dry air)) of water vapor accompanying 1 kg of dry air. The humidity in the air blown during firing is
It is preferable that the temperature is as low as possible.
g 'or less, and more preferably 5 g / kg' or less in absolute humidity. When a lithium-ion secondary battery was prepared using a lithium composite oxide fired in air having an absolute humidity of more than 20 g / kg 'as a positive electrode material of the lithium-ion secondary battery, the initial discharge capacity and the capacity retention were reduced. Low batteries are created, which is undesirable.

In the production method of the present invention, after the calcination, a lithium composite oxide powder is obtained through a step of cooling and pulverizing and classifying. Even in the step of cooling and pulverizing, the absolute humidity is 20 g / kg. 'It is preferable to blow the following air.

The lithium composite oxide obtained by the above production method is represented by the above general formula (1), and its compounding ratio is such that the atomic ratio of lithium (Li), nickel (Ni) and cobalt (Co) is x (Li), 1-y (Ni) and y (Co) (provided that 0 <x <1.1 and 0 ≦ y ≦ 0.6). For example, if the mixing ratio is L
The ratio of i / (total amount of Ni or Ni and Co) is set to around 1, but depending on the properties of the raw materials and the sintering conditions, it is permissible that the blending ratio has a certain width around 1. A preferred compounding ratio is in the range of 0.99 to 1.10.

The preferred form of the mixture of Ni—Co in the general formula (1) is not a mixture of both metals, but a solid solution compound in which a part of nickel in the crystal structure is replaced by cobalt. The lithium ion secondary battery has a high practicality as a positive electrode material for a lithium ion secondary battery because the lithium ion intercalation and deintercalation reactions can be performed more smoothly in a higher potential range.

The lithium composite oxide of the present invention is useful as a positive electrode active material for a lithium secondary battery, and is prepared by coating a conductive substrate with a positive electrode active material for a lithium secondary battery containing the compound as a main component. A positive electrode plate for a secondary battery can be obtained, and a lithium secondary battery can be provided by using the positive electrode plate.

Next, an example of the basic structure of the lithium secondary battery according to the present invention will be described. That is, the lithium composite oxide obtained as described above is used as a main component, and a graphite powder, polyvinylidene fluoride, or the like is mixed and processed to form a positive electrode material (a positive electrode active material for a lithium secondary battery). To prepare a kneaded paste. After applying the kneading paste to a conductive substrate such as an aluminum foil, drying,
The positive electrode plate is obtained by pressing and cutting into an appropriate shape. Using this positive electrode plate, each member constituting the lithium secondary battery is laminated to manufacture a lithium secondary battery.

[0020]

By using the lithium composite oxide of the present invention as a positive electrode material for a lithium ion secondary battery, a lithium ion secondary battery having high energy density and stable performance can be obtained. Further, according to the method for producing a lithium composite oxide of the present invention, a positive electrode active material for a lithium ion secondary battery exhibiting excellent performance can be obtained in a simple manner.

[0021]

EXAMPLES Next, the present invention will be described more specifically with reference to examples, but this is merely an example and does not limit the present invention.

Example 1 Ni-Co hydroxide and lithium hydroxide in a coprecipitated state of nickel and cobalt having an atomic ratio of 8: 2 were replaced with lithium and a transition metal (Ni.Co) having an atomic ratio of 1.03: It was weighed to 1.00 and mixed uniformly. This mixture is
After calcination at ° C, the temperature was raised to 720 ° C at 4 ° C / minute, and then to 770 ° C at 1 ° C / minute and held for 7 hours. During firing, air having an absolute humidity of 0.5 g / kg 'was blown into the furnace. After the completion of the calcination, the mixture was pulverized and classified to obtain a lithium composite oxide.

Example 2 Nickel hydroxide and cobalt oxide were uniformly mixed such that the atomic ratio of nickel to cobalt was 8: 2, and the atomic ratio of this mixture to lithium and transition metal was 1.03: 1.00. Were weighed so as to be mixed uniformly. 35 of this mixture
After calcination at 0 ° C., the temperature was raised to 720 ° C. at 4 ° C./min, and then to 770 ° C. at 1 ° C./min and held for 7 hours. During firing, air having an absolute humidity of 0.5 g / kg 'was blown into the furnace. After the completion of the firing, pulverization and classification were performed to obtain a lithium oxide.

Example 3 Ni-Co hydroxide and lithium hydroxide in a co-precipitated state with an atomic ratio of nickel and cobalt of 8: 2 were replaced with an atomic ratio of lithium and a transition metal (Ni.Co) of 1.03: It was weighed to 1.00 and mixed uniformly. This mixture is
After calcination at ° C, the temperature was raised to 720 ° C at 4 ° C / minute, and then to 770 ° C at 1 ° C / minute and held for 7 hours. During firing, air having an absolute humidity of 10 g / kg 'was blown into the furnace. After the completion of the calcination, the mixture was pulverized and classified to obtain a lithium composite oxide.

COMPARATIVE EXAMPLE 1 Ni-Co hydroxide and lithium hydroxide in a coprecipitated state of nickel and cobalt having an atomic ratio of 8: 2 were replaced with lithium and a transition metal (Ni.Co) having an atomic ratio of 1.03: It was weighed to 1.00 and mixed uniformly. This mixture is
After calcination at ° C, the temperature was raised to 720 ° C at 4 ° C / minute, and then to 770 ° C at 1 ° C / minute and held for 7 hours. During firing, air having an absolute humidity of 25 g / kg 'was blown into the furnace. After the completion of the calcination, the mixture was quickly taken out of the furnace, allowed to cool in the air, and pulverized and classified to obtain a lithium composite oxide.

The moisture content (before moisture absorption) and the moisture content (after moisture absorption) of the above Examples 1 to 3 and Comparative Example 1 after standing for 12 hours at 30 ° C. and a relative humidity of 60% were measured at 120 ° C. by Karl Fischer titration. It was measured by the moisture vaporization method. Table 1 shows the results
It was shown to.

(Evaluation of Battery Performance) Using the lithium composite oxides obtained in the above Examples and Comparative Examples as a positive electrode active material, lithium ion secondary batteries were manufactured. Next, the produced lithium secondary battery was operated, the initial discharge capacity and the capacity retention were measured, and the battery performance was evaluated. The results are shown in Table 1.

Measurement of Discharge Capacity The discharge capacity is measured by repeating charging and discharging of the positive electrode at 1 mA / cm ² to 4.2 V and then discharging to 2.7 V. From the result of repeating the discharge, it was calculated by the following equation.

[0029]

[Table 1]

According to Table 1, during firing, the absolute humidity was 20 g / kg '.
Examples 1 to 3 obtained by blowing the following air
All had excellent initial discharge capacity and capacity retention.

Claims (3)

[Claims] 1. A compound represented by the following general formula (1): Li _x Ni _{1 -y} Co _y O ₂ (1) (where 0 <x <1.1, 0 ≦ y ≦ 0.6) In the lithium composite oxide to be produced, the water content in the lithium composite oxide is 0.1% by weight or less and / or 30% by weight.
° C, relative humidity 60%, moisture content after standing for 12 hours is 0.
A lithium composite oxide, which is not more than 6% by weight. 2. A method for producing a lithium composite oxide by mixing nickel salt crystal particles or Ni-Co salt crystal particles of nickel and cobalt with a lithium salt, followed by firing to produce a lithium composite oxide. / Kg 'or less while blowing into the furnace. 3. A positive electrode active material for a lithium ion secondary battery, comprising the lithium composite oxide according to claim 1 as a main material.