JPH11224664A - Lithium-ion secondary battery having high moisture resistance and high safety - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a safe lithium-ion secondary battery having high moisture- resistance where battery performance is prevented from decreasing caused by the effect of water on lithium containing complex oxide of a positive electrode material, and heat generation at the time of short-circuiting, etc., of the battery can be inhibited low. SOLUTION: This lithium-ion secondary battery has positive electrodes containing a positive electrode material made of particulates of lithium containing complex oxide, negative electrodes containing an active material enabling occlusion and emission of metal lithium, a lithium alloy and lithium ions, and an electrolyte. Here, at least one of surfaces of the lithium containing complex oxide partculates and surfaces of the positive electrodes have film made of a water-repellent material. At least on selected from among a fluorine containing macromolecular compound and an organosilicon compound are desirable as the water-repellent material.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lithium ion secondary battery having improved moisture resistance and improved safety.

[0002]

2. Description of the Related Art A lithium ion secondary battery has a higher volume energy density and a higher mass energy density than a nickel-cadmium battery or a nickel-metal hydride battery.
It is expected to develop as a power source for portable devices such as TRs and notebook computers. A lithium ion secondary battery has a positive electrode including a positive electrode material composed of lithium-containing composite oxide fine particles, a negative electrode including a metal lithium, a lithium alloy, or an active material capable of inserting and extracting lithium ions, and an electrolyte. Composite oxides such as lithium cobaltate, lithium nickelate or lithium manganate used as the cathode material for lithium ion secondary batteries are not only in the form of fine particles, but also in the air even after the cathode is formed. When left to stand, moisture in the air is adsorbed on the surface of the crystal particles. Such a positive electrode manufactured using a positive electrode material to which water is adsorbed or a positive electrode to which water is adsorbed after being manufactured using a positive electrode material to which no water is adsorbed does not adsorb water. Battery performance such as charge / discharge efficiency of a lithium ion secondary battery is lower than when a positive electrode is used. In particular, the above tendency is remarkable for lithium nickelate. Once moisture is adsorbed on the positive electrode material or the positive electrode, battery performance is inferior even if the adsorbed moisture is removed by, for example, drying treatment such as heating. For this reason, conventionally, a method for cutting off the contact with moisture, such as storing the positive electrode material in a dry gas atmosphere, has been adopted. In order to avoid contact with humid air as much as possible in the manufacturing process of the positive electrode, a method of working in a working room provided with a dehumidifying facility such as a dry room has been adopted.
In addition, the positive electrode itself must be protected from moisture until it is incorporated into the battery. Therefore, it is desired to improve the moisture resistance of the positive electrode material and the positive electrode to facilitate handling. In addition, in a lithium ion secondary battery using a composite oxide as a positive electrode material, when a large current flows due to a short circuit, misuse, or the like, the battery temperature may increase and generate heat. Various safety measures have been taken to ensure the safety of the battery in such a case, but further improvement in safety is desired.

[0003]

SUMMARY OF THE INVENTION The present invention prevents the lithium-containing composite oxide of the positive electrode material from deteriorating battery performance due to the influence of moisture and suppresses heat generation in the event of a battery short circuit or the like. It is an object of the present invention to provide a highly safe lithium-ion secondary battery capable of performing this.

[0004]

According to the present invention, there is provided a lithium ion secondary battery comprising: a cathode including a cathode material comprising lithium-containing composite oxide fine particles; and an active material capable of inserting and extracting lithium metal, a lithium alloy or lithium ions. In a lithium ion secondary battery having a negative electrode containing: and an electrolyte, at least one of the surface of the lithium-containing composite oxide fine particles and the surface of the positive electrode has a coating of a water-repellent substance. As the water-repellent substance, at least one selected from a fluorine-containing polymer compound and an organosilicon compound is preferable.

[0005] The lithium-containing composite oxide used in the present invention includes a composite oxide such as lithium cobalt oxide, lithium nickel oxide or lithium manganate used as a positive electrode material for a lithium ion secondary battery, or a cobalt atom. , A nickel oxide, and a composite oxide in which part of a manganese atom is replaced with another element. For example, in the crystal structure of lithium nickelate, Co, Mn, Fe, M
Composite lithium nickelate having a structure in which one or more metal elements such as g and Al are uniformly dissolved is used.
In this case, when the above metal elements other than lithium and nickel are represented by M, the respective atomic ratios are Ni / M = 70 /
30-95 / 5, Li / (Ni + M) = 0.95-1.
Complex lithium nickelates in the range of 30 are preferred.

The method for producing such a lithium-containing composite oxide is not particularly limited, and those produced by a conventionally known method are used. For example, the above composite lithium nickelate is produced by the method described in Japanese Patent Application No. 8-284380 filed earlier by the present applicant. That is, an alkali is added to a mixed aqueous solution of a water-soluble nickel compound such as nickel nitrate and a water-soluble metal compound such as a nitrate of a third component metal to obtain a coprecipitate of the nickel compound and the third component metal compound. A powder obtained by drying and firing the coprecipitate is mixed with a lithium compound such as lithium hydroxide.
And obtained as fine particles.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In a first embodiment of the present invention, a lithium-containing composite oxide is treated with a water-repellent substance immediately after the production of fine particles of the lithium-containing composite oxide to form a film on the surface of the fine particles. Form. In the second embodiment,
Immediately after the production of fine particles of lithium-containing composite oxide, a positive electrode is formed and then treated with a water-repellent substance to form a coating on the positive electrode surface. The third embodiment is a combination of the first embodiment and the second embodiment, immediately after the production of fine particles of lithium-containing composite oxide, treated with a water-repellent substance to form a coating on the surface of the fine particles, A positive electrode is formed by using the same, and further treated with a water-repellent substance to form a film on the positive electrode surface. In any case, it is desirable to work in a work room provided with a dehumidifying facility such as a dry room in order to avoid contact with humid air as much as possible before treatment with a water-repellent substance. When the production of fine particles of the lithium-containing composite oxide and the production of the positive electrode are continuously performed at the same place, the second embodiment may be used. desirable.

The water-repellent substance used in the present invention includes:
In the first, second or third embodiment, occlusion and release of lithium ions at the positive electrode during charge / discharge are not hindered by the water-repellent substance, that is, those having lithium ion conductivity. There must be. Examples of such a water-repellent substance include a fluorine-containing polymer compound and an organosilicon compound, but are not particularly limited as long as the substance has lithium ion conductivity.
Specific compounds include a fluorine-based polymer compound such as polytetrafluoroethylene and polyvinylidene fluoride, a silicone-based polymer compound composed of a polycondensate of organochlorosilanes such as trichloromethylsilane and dichlorodimethylsilane, or Examples include silane coupling agents such as methoxysilane, tetraethoxysilane, and decyltrimethoxysilane.

Fine particles of lithium-containing composite oxide (cathode material)
Alternatively, the method for surface treatment of the positive electrode with a water-repellent substance is not particularly limited, but immersion or spraying is convenient. When the water-repellent substance is liquid, depending on its viscosity, it may be used as it is or dissolved in an appropriate organic solvent.If the water-repellent substance is solid, it may be dissolved in an appropriate organic solvent, for example, polyfluoroethylene. A water-repellent substance such as vinylidene fluoride dissolved in an organic solvent such as N-methylpyrrolidone is immersed or sprayed. Thereafter, by removing and drying the organic solvent, a coating of a water-repellent substance is formed on the surface of the positive electrode material or the positive electrode, and the desired positive electrode material or positive electrode made of a highly moisture-resistant lithium-containing composite oxide is obtained.

The method for forming the positive electrode from the positive electrode material may be a conventionally known method. Specifically, an ink (slurry) is prepared by kneading lithium-containing composite oxide fine particles with a conductive auxiliary such as acetylene black, a binder such as polyvinylidene fluoride, and an organic solvent such as N-methylpyrrolidone. After applying and drying this ink on the aluminum foil of the current collector, a method of obtaining a positive electrode by applying a roller press to improve the contact between the positive electrode material and the current collector while improving the contact between the positive electrode material and the current collector, There is a method in which acetylene black and polytetrafluoroethylene powder are sufficiently mixed in a positive electrode material, and then formed into a sheet by a roller press to obtain a positive electrode.

[0011] The lithium ion secondary battery according to the present invention comprises:
The positive electrode obtained as described above, lithium metal, a negative electrode made of a lithium alloy or an active material capable of inserting and extracting lithium ions, and an electrolyte and a separator, and manufactured by a known method using these. You. The shape of the battery is not particularly limited, and may be any shape such as a coin shape, a cylindrical shape, and a square shape.

Examples of the active material capable of inserting and extracting lithium ions include carbonaceous materials such as graphite and carbon black. Usually, a mixture of such a carbonaceous substance and a binder such as polyvinylidene fluoride is applied and fixed to a current collector such as a copper foil to form a negative electrode. As the electrolyte, a liquid electrolyte in which a lithium salt such as LiClO ₄ or LiPF ₆ is dissolved in an organic solvent such as propylene carbonate, ethylene carbonate, or 1,2-dimethoxyethane;
A solid electrolyte such as a polyethylene oxide-based polymer compound may be used.

Further, a separator made of a porous film of a polyolefin resin such as polyethylene is provided between the positive electrode and the negative electrode for separating the positive electrode and the negative electrode and preventing a short circuit while allowing the electrolyte and lithium ions to pass therethrough. Is good.

Hereinafter, the present invention will be described specifically with reference to Examples, but the present invention is not limited to the following Examples.

[0015]

Example 1 A mixed aqueous solution was prepared by dissolving 494.2 g of nickel nitrate (hexahydrate) and 89.1 g of cobalt nitrate (hexahydrate) in 2 L of pure water (solution A). In addition, an aqueous solution of sodium carbonate was prepared by dissolving 318.0 g of sodium carbonate in 1.8 L (liter) of pure water (Solution B). 80
The solution A and the solution B were simultaneously added to 1 L of hot water at a temperature of 0 ° C. and reacted. The obtained precipitate was filtered, washed and dried, and then calcined in air at 400 ° C. for 3 hours to obtain a composite oxide of Ni and Co (Ni: Co atomic ratio = 85: 15). In the composite oxide obtained above, the Li / (Ni + Co) atomic ratio = 0.
After adding and mixing lithium hydroxide powder so as to obtain 97, 1.03, and 1.10, the mixture is baked at 750 ° C. for 10 hours in an oxygen stream using a rotary kiln,
Composite lithium nickelate fine particles were obtained. Then, these were each added to a polytetrafluoroethylene solution (Asahi Glass Co., Ltd.)
After immersion in CYTOP, the solvent was evaporated by heating to obtain composite lithium nickelate fine particles (Samples 1, 2, and 3) having a water-repellent coating formed on the surface of each fine particle. After leaving each of Samples 1, 2, and 3 in the air for one week, acetylene black and polytetrafluoroethylene powder were sufficiently mixed in a weight ratio of 75: 20: 5, and then, the thickness was reduced to 0 by a roller press. .1mm, diameter 16mm
Was prepared. These positive electrodes, an electrolytic solution obtained by dissolving 1 mol / L LiClO ₄ in a mixed solution of propylene carbonate and dimethoxyethane (volume ratio 1: 1), a separator (trade name: Celgard), a metal lithium foil (0.2 mm thick) ) Was used to produce a test battery. A charge / discharge test was performed on these batteries. The charge and discharge conditions are a constant current and a current density of 0.5 mA / cm ² ,
Potential regulation was performed so that the charge potential was up to 4.3 V and the discharge potential was up to 3.0 V. Table 1 shows the results.

[0016]

Example 2 Under the same conditions as in Example 1, Li / (Ni +
Co) Composite lithium nickel oxide fine particles having an atomic ratio of 0.97 were prepared. The fine particles were immersed in a toluene solution of a polycondensate of dichlorodimethylsilane and then heated to evaporate the solvent, thereby obtaining composite lithium nickelate fine particles having a water-repellent coating on the surface (Sample 4). After the sample 4 was left in the air for one week, a positive electrode and a test battery were prepared in the same manner as in Example 1, and a charge / discharge test was performed under the same conditions as in Example 1. Table 1 shows the results.

[0017]

Embodiment 3 Under the same conditions as in Embodiment 1, Li / (Ni +
Co) Composite lithium nickel oxide fine particles having an atomic ratio of 0.97 were prepared. The fine particles were immersed in a xylene solution of tetraethoxysilane (concentration: 5% by weight), and then the solvent was evaporated to obtain composite lithium nickelate fine particles having a water-repellent coating on the surface (Sample 5). Place sample 5 in air
After standing for a week, a positive electrode and a test battery were prepared in the same manner as in Example 1, and a charge / discharge test was performed under the same conditions as in Example 1. Table 1 shows the results.

[0018]

Comparative Example 1 Li / (Ni + C) under the same conditions as in Example 1.
o) Composite lithium nickelate fine particles (Samples 6, 7, and 8) having atomic ratios of 0.97, 1.03, and 1.10. After being left in the air for one week without treatment with a water-repellent substance, a test positive electrode and a test electrode were prepared in the same manner as in Example 2, and the same charge / discharge test was performed. Table 1 shows the results.

[0019]

Comparative Example 2 Li / (Ni + C) under the same conditions as in Example 1.
o) Composite lithium nickelate fine particles (Sample 9) having an atomic ratio of 0.97 were prepared. A test positive electrode and a test battery were immediately prepared in the same manner as in Example 2 in a dry air atmosphere (dew point: -50 ° C.), and the same charge / discharge test was performed. Table 1 shows the results.

[0020]

[Table 1]

Table 1 shows that the positive electrode material treated with the water-repellent substance hardly deteriorates in charge capacity, discharge capacity and charge / discharge efficiency even when left in the air for one week. The charge capacity, discharge capacity and charge / discharge efficiency of a battery using a positive electrode containing a positive electrode material treated with these water-repellent materials were measured in a dry atmosphere after preparation of the positive electrode material. Even when compared with a battery using, the battery performance is not reduced even if the positive electrode material is subjected to the water-repellent treatment.

[0022]

Embodiment 4 Li / (Ni + C) under the same conditions as in Embodiment 1.
o) Composite lithium nickelate fine particles having an atomic ratio of 0.97 and 1.10. Then immediately acetylene black and polytetrafluoroethylene powder were added to them at 75: 2.
After sufficient mixing at a weight ratio of 0: 5, the mixture was molded by a roller press to prepare a positive electrode having a thickness of 0.1 mm and a diameter of 16 mm.
Each of these positive electrodes was immersed in a polytetrafluoroethylene solution (Cytop manufactured by Asahi Glass Co., Ltd.), and then heated to evaporate the solvent, and a test positive electrode having a water-repellent film formed on the positive electrode surface (sample 10) , 11). After leaving these test cathodes in the air for one week, a mixed solution of propylene carbonate and dimethoxyethane (volume ratio 1: 1)
A test battery was prepared using an electrolyte solution in which 1 mol / L of LiClO ₄ was dissolved, a separator (trade name: Celgard), and a metal lithium foil (thickness: 0.2 mm). These batteries were subjected to a charge / discharge test. The charge and discharge conditions were a constant current and a current density of 0.5 mA / cm ² , and the charge potential was regulated to 4.3 V and the discharge potential was regulated to 3.0 V. Table 2 shows the results.

[0023]

Embodiment 5 Li / (Ni + C) under the same conditions as in Embodiment 1.
o) Composite lithium nickelate fine particles having an atomic ratio of 0.97 were prepared, and a positive electrode was prepared using the fine particles in the same manner as in Example 4. Next, this positive electrode was immersed in a toluene solution of dichlorodimethylsilane polycondensate, and then the solvent was evaporated to obtain a positive electrode for testing (sample 12) having a water-repellent film formed on the surface. After leaving the sample 12 in the air for one week, a test battery was prepared in the same manner as in Example 4, and the results of a charge / discharge test performed under the same conditions as in Example 4 are shown in Table 2.

[0024]

Embodiment 6 Li / (Ni + C) under the same conditions as in Embodiment 1.
o) Composite lithium nickelate fine particles having an atomic ratio of 0.97 were prepared, and a positive electrode was prepared using the fine particles in the same manner as in Example 4. Next, the positive electrode was immersed in a xylene solution of tetraethoxysilane (concentration: 5% by weight), and then the solvent was evaporated to form a test positive electrode having a water-repellent coating on the surface (sample 1).
3) was obtained. After the sample 13 was left in the air for one week, a test battery was prepared in the same manner as in Example 4, and a charge / discharge test was performed under the same conditions as in Example 4. Table 2 shows the results.

[0025]

COMPARATIVE EXAMPLE 3 Composite lithium nickel oxide fine particles were prepared under the same conditions as in Example 1, and the same procedure as in Example 4 was carried out except that the treatment with the water-repellent substance was not performed.
15) was obtained. After these test positive electrodes were left in the air for one week, a test battery was prepared in the same manner as in Example 4, and a charge / discharge test was performed. Table 2 shows the results.

[0026]

Example 7 The test positive electrode 10 obtained in Examples 4 to 6,
With respect to 11, 12, and 13, batteries similar to those of Example 4 were produced immediately without being left in the air. A charge / discharge test was performed on these batteries. Table 2 shows the results.

[0027]

COMPARATIVE EXAMPLE 4 Test Positive Electrodes 14, 15 Obtained in Comparative Example 3
For, a battery similar to that of Example 4 was immediately prepared without leaving it in the air. A charge / discharge test was performed on these batteries. Table 2 shows the results.

[0028]

[Table 2]

As is clear from Table 2, both the positive electrode subjected to the water-repellent treatment and the positive electrode not subjected to the water-repellent treatment have almost the same battery performance when the batteries are immediately prepared without being left in the air. It is not allowed. However, the water-repellent positive electrode was not affected by moisture even after being left in the air for one week, and the battery performance was hardly reduced. When left unattended, the battery performance is greatly reduced.

[0030]

Example 8 As a safety test of a lithium ion secondary battery, the following heat generation test was performed using a differential thermal balance. Samples 10, 11, 12, 1 prepared in the same manner as in Examples 4 to 6.
3 was used to form a battery, and after initial charging was performed up to 4.3 V, a positive electrode was taken out of the battery and vacuum degassed to prepare a measurement sample. Ethylene carbonate (EC) was mixed with the mixture at a ratio of 1: 1 (weight ratio), and the mixture was heated in an air atmosphere using a differential thermobalance, and the calorific value was measured. Heat value is EC
Since the heat absorption due to the evaporation and the heat generation due to the combustion proceed in parallel, the heat absorption due to the evaporation of the EC was subtracted to obtain the heat generation. As a result, the calorific value of Sample 14 of Comparative Example 5 was 1
Table 3 shows the relative calorific value determined as 00.

[0031]

Comparative Example 5 A similar heat generation test was performed using samples 14 and 15 in the same manner as in Example 8. The results are shown in Table 3 as relative heat values with the heat value of Sample 14 taken as 100.

[0032]

[Table 3]

From Table 3, it can be seen that the positive electrode taken out of the battery using the positive electrode subjected to the water repellent treatment after charging was suppressed in heat generation as compared with the positive electrode taken out of the battery using the positive electrode not subjected to the water repellent treatment after charging. You can see that it is.

[0034]

The positive electrode material and / or the positive electrode used in the lithium ion secondary battery according to the present invention is treated with a water-repellent substance. Therefore, since the positive electrode material and the positive electrode have excellent moisture resistance, there is no adsorption of moisture in the air, and there is no decrease in battery performance due to the adsorption of moisture. Further, the lithium-containing composite oxide serving as the positive electrode material does not come into direct contact with the electrolytic solution.
Therefore, even if the positive electrode and the negative electrode are short-circuited, heat generation is suppressed, and safety is improved.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Takayuki Fujita 1-26 Takiya Honmachi Niigata Niigata Pref. Inside the R & D Laboratories (72) Inventor Koji Mizusawa 1-26 Takitani Honmachi Niigata Niigata Nikki Chemical Co., Ltd. Inside the Research Laboratory (72) Inventor Masaharu Sakai 1-26 Takiya Honmachi, Niitsu City, Niigata Prefecture JGC Chemicals R & D Laboratories (72) Inventor Yoshio Fujii 1-26 Takiya Honmachi, Niitsu City, Niigata Prefecture JGC Chemicals R & D Laboratory ( 72) Inventor Masami Sakaguchi 1-26 Takiya Honcho, Niitsu City, Niigata Pref.

Claims (2)

[Claims] 1. A lithium ion secondary battery comprising: a positive electrode including a positive electrode material composed of lithium-containing composite oxide fine particles; a negative electrode including metallic lithium, a lithium alloy or an active material capable of inserting and extracting lithium ions; and an electrolyte. A lithium ion secondary battery, wherein at least one of the surface of the lithium-containing composite oxide fine particles and the surface of the positive electrode has a coating of a water-repellent substance. 2. The water-repellent substance is at least one selected from a fluorine-containing polymer compound and an organosilicon compound.
The lithium ion secondary battery according to claim 1, which is a seed.