JPH11167919A - Positive electrode material for highly stable lithium ion secondary battery, its manufacture and its usage - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a positive electrode material for a lithium ion secondary battery which is high in safety, large charging capacity, easy to handle, and made of composite lithium nickelate. SOLUTION: This positive electrode material consists of composite lithium nickelate fine particles containing lithium, nickel, a metal element other than lithium and nickel. In this case, at least a part of the surface of the composite lithium nickelate fine particle is covered with lithium carbonate, and the atomic ratio of nickel (Ni) to the metal element (M) other than lithium and nickel (Ni/M) in the composite lithium nickelate fine particles is specified to be in the range of 70/30 to 95/5.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a positive electrode material for a lithium ion secondary battery having a high charge capacity and excellent safety and a method for producing the positive electrode material for the lithium ion secondary battery. Furthermore, the present invention relates to a lithium ion secondary battery formed using a positive electrode including the above-described positive electrode material.

[0002]

BACKGROUND OF THE INVENTION Lithium-ion secondary batteries are characterized by higher energy density, smaller size and lighter weight than nickel-cadmium batteries and nickel-metal hydride batteries.
It is mounted as a power source for portable electronic devices such as a mobile phone, a camera-integrated VTR, and a notebook personal computer, and the demand has been rapidly increasing.

In such a lithium ion secondary battery,
Lithium cobalt oxide (LiCoO ₂ ) is used as a positive electrode material. Lithium cobaltate is a compound having a layered rock salt structure (α-NaFeO ₂ structure) and capable of reversibly storing and releasing lithium ions.

[0004] However, lithium cobalt oxide has a high
Material cost because of using a cobalt compound
Thus, the emergence of an inexpensive cathode material has been desired. For this reason,
As a pole material, the same layered rock salt structure as lithium cobalt oxide
Using nickel compounds that are
Lithium nickelate (LiNiO) _TwoExpectations have risen
I have.

[0005] However, lithium ion secondary batteries containing lithium nickelate as a positive electrode material have the disadvantage that the overvoltage is large and the discharge capacity is insufficient. This is because lithium nickelate, lithium (Li ⁺⁾ site, and is easy to occur substitution type nickel (Ni ²⁺⁾ enters, becomes a compound of lithium (Li ⁺⁾ nickel site (Ni ²⁺⁾ is present It is described that nickel (Ni ²⁺ ) inhibits diffusion of lithium ions and adversely affects charge / discharge characteristics.

For this reason, attempts have been made to improve the charge / discharge characteristics of batteries by substituting a part of nickel of lithium nickelate with another metal element.
No. 84380 proposes a composite lithium nickelate in which a part of nickel is replaced by another metal element as a positive electrode material for a lithium ion secondary battery.

[0007] In a lithium ion secondary battery, when a current flows due to a short circuit between the positive electrode and the negative electrode or due to misuse, the temperature of the battery may increase. Various safety measures have been taken to ensure the safety of the battery in such a case, but it is desired to improve the safety of lithium nickelate itself in order to further improve the safety.

[0008] Further, lithium nickelate reacts with the humidity in the air at room temperature and may degrade the battery performance. Therefore, it is necessary to keep a dry state during storage and it is difficult to handle. Was.

[0009]

SUMMARY OF THE INVENTION The object of the present invention is to solve the above-mentioned problems in the prior art, and to provide a high-quality lithium nickel nickelate which is excellent in safety, has a large charge capacity and is easy to handle. An object is to provide a positive electrode material for a stable lithium ion secondary battery.

[0010]

SUMMARY OF THE INVENTION A positive electrode material for a highly stable lithium ion secondary battery according to the present invention is a lithium ion secondary battery comprising fine particles of lithium composite nickelate containing lithium, nickel, and a metal element other than lithium and nickel. In the positive electrode material, at least a part of the surface of the composite lithium nickelate fine particles is coated with lithium carbonate, and
The atomic ratio (N) between nickel (Ni) of the composite lithium nickelate and a metal element (M) other than lithium and nickel
i / M) is in the range of 70/30 to 95/5.

The metal elements other than lithium and nickel are preferably 0.8 to 1.5 times the ionic radius of nickel. The method for producing a positive electrode material for a highly stable lithium ion secondary battery according to the present invention includes the steps of: mixing a mixture containing a lithium compound, a nickel compound, and a compound of a metal other than lithium and nickel in an oxygen-containing gas atmosphere under an oxygen-containing gas atmosphere;
It is characterized by firing at ~ 850 ° C and then contacting with carbon dioxide gas at 400 ° C or less.

[0012] The lithium ion secondary battery according to the present invention comprises:
(i) a positive electrode composed of the positive electrode material for a lithium ion secondary battery, (ii) a negative electrode containing a lithium metal, a lithium alloy or a material capable of occluding and releasing lithium ions as a negative electrode active material, and (iii) a liquid. Alternatively, a solid electrolyte is included.

[0013]

DETAILED DESCRIPTION OF THE INVENTION Hereinafter, the cathode material for a highly stable lithium ion secondary battery according to the present invention and a method for producing the same will be described in detail.

[Positive Electrode Material for Highly Stable Lithium Ion Secondary Battery] The positive electrode material for a highly stable lithium ion secondary battery according to the present invention comprises lithium, nickel, and a metal element other than lithium and nickel (hereinafter, referred to as a lithium-ion secondary battery). Trimetallic element).

The third metal element has an ionic radius of Ni
0.8 to 1.5 times, preferably 0.9 to 1.5 times the ion radius of
It is preferably in the range of 1.3 times, specifically, Mn,
Fe, Co, Mg, Al and the like. In the present invention, one or more of these third metal elements are uniformly dissolved in the crystal structure of lithium nickelate.

The atomic ratio (Ni / M) between nickel (Ni) and the third metal element (M) of the composite lithium nickelate
Is 70/30 to 95/5, preferably 80/20 to 9
Desirably, it is 0/10. If Ni / M is larger than 95/5, the cycle characteristics of the battery may be deteriorated, and if Ni / M is smaller than 70/30, the charge capacity may be reduced.

Further, lithium (Li) of the composite lithium nickelate, nickel and a third metal element (Ni + M)
The atomic ratio (Li / (Ni + M)) is preferably in the range of 0.95 to 1.3, more preferably 0.97 to 1.05.
When the atomic ratio is less than 0.95, the lithium in the composite lithium nickelate is small, so that the discharge capacity of the battery is reduced and the amount of lithium carbonate coated on the surface of the fine particles is reduced.
Further, even if the atomic ratio is more than 1.3, the effect of improving the discharge capacity is small, and the effect of covering with carbon dioxide gas described later is also small.

In the present invention, at least a portion of the surface of the composite lithium nickelate fine particles is coated with lithium carbonate. Compounds other than lithium carbonate, such as lithium oxide, may be present on the surface of the composite lithium nickelate fine particles, but most surfaces of the composite lithium nickelate fine particles are coated with lithium carbonate. It is desirable to have been.

In the cathode material for a highly stable lithium ion secondary battery according to the present invention, a lithium compound, a nickel compound, and a compound of a third metal element are mixed at a predetermined ratio. The mixture is calcined in an oxygen-containing gas atmosphere at 600 to 850 ° C, preferably 700 to 750 ° C, and then 400 ° C or less, preferably 200 to 300 ° C.
It can be obtained by contacting carbon dioxide gas at a temperature of ° C.

As the lithium compound, lithium carbonate,
Examples include lithium peroxide, lithium hydroxide, lithium nitrate, lithium acetate, lithium citrate and the like. Examples of the nickel compound include nickel metal, nickel oxide, nickel hydroxide, nickel carbonate, nickel nitrate, nickel sulfate, nickel acetate, nickel citrate and the like. Of these, water-soluble nickel sulfate and nickel nitrate are particularly desirable.

As the compound of the third metal element, carbonate,
Nitrate, hydroxide, oxide and the like can be mentioned. In particular, water-soluble salts are preferred. Specific examples of the method for producing such a positive electrode material for a lithium ion secondary battery include the following methods.

First, a mixed aqueous solution in which a water-soluble nickel compound and a water-soluble compound of a third metal element are dissolved is prepared, and an aqueous alkali solution such as sodium carbonate is added to this aqueous solution to form a mixture of the nickel compound and the third metal element. The co-precipitate with the compound precipitates.

After filtering and washing the obtained coprecipitate,
By firing at 300 to 500 ° C., composite oxide fine particles are obtained. The obtained composite oxide fine particles are mixed with a lithium compound such as lithium hydroxide, and mixed under an oxygen-containing gas atmosphere.
Firing at 00 to 850 ° C, preferably 700 to 750 ° C, prepares fine particles composed of composite lithium nickelate crystal particles or an aggregate of crystal particles.

The prepared composite lithium nickelate fine particles are heated to 400 ° C. or lower, preferably 200 to 300 ° C. while supplying carbon dioxide, to form a lithium carbonate layer on the surface of the composite lithium nickelate fine particles.

The reason why a lithium carbonate layer is formed on the surface of the composite lithium nickel oxide fine particles by heating in such a carbon dioxide gas atmosphere is considered as follows.

[0026] Lithium nickelate or composite lithium nickelate is usually baked at a high temperature to produce and grow these crystals to obtain crystal grains of a certain size. It is believed that some migrate to the surface of the crystal grains. The lithium transferred to the surface is oxidized to lithium oxide, so that the crystal particles of the composite lithium nickel oxide after firing and the fine particles in which these crystal particles are aggregated are in a state where the surface is coated with lithium oxide. It is thought that it is.

When the composite lithium nickel oxide fine particles whose surface is coated with lithium oxide are treated with carbon dioxide gas, at least a part of the lithium oxide is changed to lithium carbonate, and the surface according to the present invention is carbonated. It is considered that composite lithium nickelate fine particles coated with lithium can be obtained.

The positive electrode material for a highly stable lithium ion secondary battery according to the present invention may further comprise, in addition to the above method, a mixture of composite lithium nickel oxide fine particles and lithium carbonate powder after firing.
It can also be obtained by heating to 700 to 750 ° C. while rolling to melt the lithium carbonate, and coating the surface of the composite lithium nickel oxide fine particles with lithium carbonate powder.

In such a positive electrode material for a lithium ion secondary battery, since a lithium carbonate layer is formed on the surface, the composite lithium nickel oxide of the positive electrode material and the electrolytic solution are in contact via the lithium carbonate layer. . Therefore, it is considered that the heat generation of the positive electrode in the case of a short circuit or the like is suppressed. In addition, by the lithium carbonate layer on the surface of the composite lithium nickelate fine particles,
Adsorption of moisture in the atmosphere can be suppressed.

Therefore, the use of the highly stable cathode material for a lithium ion secondary battery according to the present invention makes it possible to produce a lithium ion secondary battery having excellent safety and moisture resistance.

[Lithium ion secondary battery] The lithium ion secondary battery according to the present invention comprises (i) a positive electrode composed of the above-mentioned positive electrode material for a lithium ion secondary battery, and (ii) a lithium ion secondary battery capable of inserting and extracting lithium ions. A negative electrode containing a suitable material or a lithium metal or a lithium alloy as a negative electrode active material; (iii) a liquid or solid electrolyte; and (iv) a separator for separating the positive electrode from the negative electrode.

The positive electrode is composed of the positive electrode material for a lithium ion secondary battery, a conductive material and a binder. As the conductive material, a carbonaceous material such as natural graphite, artificial graphite, coke, and carbon black is used. As the binder, a fluororesin such as polytetrafluoroethylene is used.

Such a positive electrode can be obtained by rolling a mixture of the positive electrode material for a lithium ion secondary battery, a conductive material and a binder. Further, it can also be obtained by applying a mixture comprising the positive electrode material for a lithium ion secondary battery, a conductive material and a binder, and, if necessary, a solvent to a current collector such as Al, Ni or stainless steel.

As the negative electrode active material constituting the negative electrode, any of a carbon-based material such as graphite capable of occluding and releasing lithium ions, metallic lithium, and a lithium alloy can be used.

In the lithium ion secondary battery according to the present invention, a liquid or solid electrolyte is used as the electrolyte. As the liquid electrolyte, a non-aqueous electrolyte obtained by dissolving a lithium salt in an organic solvent is usually used.

As the lithium salt, LiPF ₆ , LiB
F ₄ , LiClO ₄ , LiAsF ₆ , LiOSO ₂ CF ₃ ,
LiAlCl ₄ , LiN (SO ₂ CF ₃ ) ₂ , LiC (SO ₂ C
F ₃ ), LiOSO ₂ C ₄ F _{9 and the} like.

As the organic solvent, ethylene carbonate, propylene carbonate, dimethyl carbonate,
Carbonates such as methyl ethyl carbonate, diethyl carbonate, methyl isopropyl carbonate,
Esters such as γ-butyrolactone, methyl formate, methyl acetate and the like.

Examples of the solid electrolyte include a polyethylene oxide polymer, a polymer containing a polyorganosiloxane chain or a polyoxyalkylene chain, Li ₂ S—SiS ₂ , Li ₂
Such as _{S-GeS 2, Li 2 S} -P 2 S 5, Li 2 S-B 2 S 3 and the like. Further, a gel-like material in which the above-mentioned non-aqueous solvent is held in a polyethylene oxide-based polymer can also be used.

As the separator, a porous film made of a polyolefin resin or the like is used. The shape of the lithium ion secondary battery according to the present invention is not particularly limited, and may be any of a paper type, a coin type, a cylindrical type, a square type, and the like.

[0040]

The positive electrode material for a lithium ion secondary battery according to the present invention is excellent in safety, discharge capacity and cycle because at least a part of the surface of the composite lithium nickel oxide fine particles is coated with lithium carbonate. A lithium ion secondary battery having excellent characteristics can be obtained.

Further, the positive electrode material for a lithium ion secondary battery according to the present invention is excellent in moisture resistance, so that it does not adsorb moisture in the air, and has the same characteristics as a conventional positive electrode material. No performance degradation. Therefore, there is no need for a dehumidifying facility as in the case of handling a conventional positive electrode material using lithium nickelate.

[0042]

EXAMPLES Hereinafter, the present invention will be described with reference to examples, but the present invention is not limited to these examples.

[0043]

Production Example An aqueous solution was prepared by dissolving 494.2 g of nickel nitrate and 89.1 g of cobalt nitrate in 2 liters of pure water (Solution A). Further, an aqueous solution prepared by dissolving 318.0 g of sodium carbonate in 1.8 liter of pure water was prepared (B
liquid). One liter of 80 ° C. hot water and the above-mentioned solution A and solution B were poured and reacted. The obtained precipitate is filtered, washed,
After drying, the mixture is calcined in air at 400 ° C. for 3 hours to obtain a composite oxide of Ni and Co (Ni: Co = 85: 15).
I got

The obtained composite oxide was added with Li / (Ni + Co)
And lithium hydroxide powder were mixed and baked at 750 ° C. for 10 hours in an oxygen stream using a rotary kiln to obtain composite lithium nickelate fine particles (Sample A). I got

Then, the mixture was heated at 200 ° C. for 3 hours while supplying carbon dioxide to the rotary kiln containing sample A, to obtain composite lithium nickelate fine particles (sample B) coated with lithium carbonate.

[0046]

Example 1 Sample B, conductive additive (acetylene black)
And binder (polytetrafluoroethylene powder)
The mixture was mixed at a ratio of 5: 20: 5 (weight ratio), kneaded and rolled to prepare a test battery positive electrode, and a charge / discharge test and a safety test were performed.

After the sample B was left in the air at room temperature for one week, acetylene black and polytetrafluoroethylene powder were similarly added, kneaded and rolled to prepare a test battery positive electrode, and a moisture resistance test was performed. Was done.

Charge / Discharge Test The positive electrode, a non-aqueous electrolyte (LiCl ₄ dissolved in a mixed solvent of ethylene carbonate and dimethyl carbonate at a volume ratio of 1: 1 at 1 mol / liter), a diaphragm,
A charge / discharge test battery was prepared using the negative electrode (metal lithium), and the battery was charged to a potential of 4.3 V at a constant current and a current density of 0.5 mA / cm ² , and then discharged to 3.0 V. Then, the discharge efficiency of the battery was measured.

Safety test After the test battery was charged to a potential of 4.3 V, the positive electrode was taken out of the battery and degassed under vacuum. This positive electrode and ethylene carbonate were mixed at a weight ratio of 1: 1 to prepare a safety test sample.

This sample was placed on a differential thermobalance and heated in air to measure the calorific value. Moisture resistance test The above-described battery for charge / discharge test was prepared using a positive electrode using Sample B that had been left in the air at room temperature for one week.
After charging the battery to 4.3 V at a current density of 5 mA / cm ² , the discharge capacity of the battery when discharged to 3.0 V was measured.

Table 1 shows the results.

[0052]

Comparative Example 1 A charge / discharge test, a safety test, and a moisture resistance test were conducted in the same manner as in Example 1, except that Sample A in which the surface of the fine particles was not coated with lithium carbonate was used instead of Sample B.

Table 1 shows the results.

[0054]

[Table 1]

As can be seen from the results in Table 1, the positive electrode including the positive electrode material using the composite lithium nickelate whose surface was coated with lithium carbonate was the same as the positive electrode material using the composite lithium nickelate not coated with lithium carbonate. The calorific value is lower than that of the positive electrode containing, and the safety of the battery is improved. Further, in such a positive electrode material, even if the positive electrode is formed after being left in the air for one week, the discharge capacity does not change, the performance degradation due to moisture in the air is suppressed, and the moisture resistance is improved. ing.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Takayuki Fujita 1-26 Takiya Honmachi, Niitsu City, Niigata Prefecture Inside of JGC Chemicals Research Laboratory (72) Inventor Koji Mizusawa 1-Takiya Honmachi, Niitsu City, Niigata Prefecture 26 Inside JGC Chemicals Development Laboratory (72) Masaharu Sakai Inventor 1-26 Takiya Honcho, Niitsu City, Niigata Prefecture Inside (72) Inventor Yoshio Fujii, Takiya Honmachi Niigata City, Niigata Prefecture 1-26 Inside JGC Chemicals Development Laboratory (72) Inventor Masami Sakaguchi 1-26 Takiya Honcho, Niitsu City, Niigata Prefecture Inside JGC Chemicals Development Laboratory

Claims (4)

[Claims] 1. A positive electrode material for a lithium ion secondary battery comprising lithium composite nickel fine particles containing lithium, nickel, and a metal element other than lithium and nickel, wherein at least a part of the surface of the composite lithium nickel oxide fine particles is provided. , Coated with lithium carbonate, and nickel (Ni) of composite lithium nickelate;
A cathode material for a highly stable lithium ion secondary battery, wherein the atomic ratio (Ni / M) to a metal element (M) other than lithium and nickel is in the range of 70/30 to 95/5. 2. The highly stable lithium ion secondary battery according to claim 1, wherein the metal element other than lithium and nickel has an ionic radius of 0.8 to 1.5 times the ionic radius of nickel. Positive electrode material. 3. A mixture containing a lithium compound, a nickel compound, and a compound of a metal other than lithium and nickel, is calcined at 600 to 850 ° C. in an oxygen-containing gas atmosphere, and then with a carbon dioxide gas at 400 ° C. or lower. A method for producing a positive electrode material for a highly stable lithium ion secondary battery comprising a composite lithium nickelate, characterized by contacting with a nickel. 4. A positive electrode comprising (i) a positive electrode material for a lithium ion secondary battery according to claim 1 or 2; and (ii) a negative electrode comprising lithium metal, a lithium alloy, or a material capable of occluding and releasing lithium ions. A lithium ion secondary battery comprising: a negative electrode containing an active material; and (iii) a liquid or solid electrolyte.