JPH08236115A - Secondary battery - Google Patents

Abstract

PURPOSE: To enhance balance of safety performance with battery performance by using a lithium-containing compound capable of performing electrical oxidation-reduction reaction in accordance with releasing of a lithium ion as a positive active material and CuFeO2 in a negative electrode as a negative active material. CONSTITUTION: An aluminium foil 10 is put on the bottom of a battery can 4, and a gasket 6 is fit to the battery can 4. A negative electrode 1 using CuFeO2 as a negative active material and a positive electrode 2 using a lithium- containing compound capable of performing electrical oxidation-reduction reaction in accordance with releasing of a lithium ion as a positive active material are faced with a separator 3 interposed and housed in the center of the battery can 4, then a nonaqueous electrolyte is poured thereon. An electrode pressing plate 7 is put on the negative electrode 1, and a battery cover 5 is put thereon, then the battery can 4 is crimped through the gasket 6.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to improving the safety of non-aqueous electrolyte secondary batteries.

[0002]

2. Description of the Related Art As electronic devices are becoming smaller and lighter, there is a growing demand for high energy density secondary batteries as their power sources. Non-aqueous electrolyte secondary batteries are the most promising candidates for high-performance secondary batteries, and their practical application has been tried for a long time. In the conventional aqueous electrolyte solution, a substance having a base potential lower than that of metallic zinc decomposes water and thus cannot be used as a negative electrode active material. However, in the non-aqueous electrolytic solution, even lithium metal having the most base potential can be used as the negative electrode active material, and thus a non-aqueous electrolytic solution secondary battery can be produced with a high voltage in unit cell unit. In addition, many positive electrode active materials that could not be used as active materials because they are conventionally soluble in aqueous electrolytes are not soluble in non-aqueous electrolytes, and many types of substances are non-aqueous electrolyte batteries. Can be a positive electrode active material candidate. So far, more than 100 kinds of major substances have been studied as active materials for non-aqueous electrolyte secondary batteries. However, a non-aqueous electrolyte secondary battery that can be used practically did not appear except for a coin-type battery having a small capacity. The reason is that practical batteries are required to have not only electrical characteristics but also various other necessary and indispensable conditions (for example, size and shape, safety, material cost, storage performance, etc.). This is because if it is fatally bad, it will not be a practical battery. In particular, ensuring safety must be a top priority. It is impossible to infer the feasibility of a practical battery by analogy with any known combination of elemental technologies.In the end, it is possible to make a battery in a size and shape that matches the practical purpose and to put it into practical use. There is no way to complete it, except to confirm it. In particular, safety is an important item for practical application, and many of safety are one of the characteristics that cannot be theoretically inferred. 199 for non-aqueous electrolyte secondary batteries
Only one AA size non-aqueous electrolyte secondary battery using metallic lithium as the negative electrode active material and molybdenum disulfide as the positive electrode active material was the only one that was attempted to be put into practical use before 0 years.
Eventually, this battery caused an accident that it ignited while being used in a mobile phone, and its practical application was abandoned. Only recently, a non-aqueous electrolyte secondary battery having a carbon electrode as a negative electrode, which utilizes the inflow and outflow of lithium ions into carbon, has been developed, and finally the non-aqueous electrolyte secondary battery has also entered the stage of practical application. This battery was named by the present inventors as a lithium ion secondary battery, and was named in 1990 (Magazine Prog.
less in Batteries & Solar
Cells, Vol. 9, P.I. 209), and the positive electrode active material is a lithium-containing compound (for example, LiCoO ₂ or LiMn ₂ O) that is capable of electrochemical redox reaction with desorption of lithium ions.
₄ etc.) and a carbonaceous material is used for the negative electrode. At present, the battery industry and academic societies have recognized it under the name of lithium-ion secondary battery, and even though it is said to be the next-generation secondary battery, it has attracted a lot of attention, but the carbon material (US Pat.
4,423,125) and LiCoO ₂ (USP).
at. 4, 302, 518) or LiMn ₂ O
No. ₄ (see US Pat. _4, 312, 930) as an electrode active material for a non-aqueous electrolyte battery is a known fact already proposed in the early 1980s. It was The point of practical application of the lithium ion secondary battery by the present inventors is to combine the individual proposals, create a battery with a size and shape that match the practical purpose, and confirm whether it is practical or not. is there. Needless to say, a big confirmation item was whether or not sufficient safety was secured for practical use. However, the lithium ion secondary battery using a carbon material as the negative electrode active material is not safe under any circumstances. If the battery temperature is 150 ℃
When the above is reached, the battery heats up violently and smokes or ignites. Therefore, the practical use of the lithium ion secondary battery is possible only in a small battery (1 to 1.5 Ah or less) whose battery temperature does not exceed 150 ° C. due to self-heating in the event of an internal short circuit or an external short circuit. It was. In a lithium ion secondary battery using a carbon material as a negative electrode active material, lithium ions are extracted from the positive electrode by charging, and the lithium ions intercalate in the carbon of the negative electrode. Carbon intercalated with lithium ions is a relatively stable compound,
After all, it has quite a monopolar potential close to that of metallic lithium, so it is quite active and basically reacts with the electrolyte. However, at room temperature, the reaction product with the electrolytic solution covers the carbon surface, and this acts to suppress the reaction with the electrolytic solution, so that at room temperature it somehow functions safely. However, it is considered that the reaction with the electrolytic solution becomes vigorous at high temperature, and eventually thermal runaway occurs at 150 ° C or higher. The internal temperature of the battery rises considerably due to internal heat generation when the current drawn is large, so current lithium-ion secondary batteries should not be used for applications that draw large currents, and large-sized lithium-ion secondary batteries should not be used. If an internal short circuit or an external short circuit occurs, the short-circuit current will increase in proportion to the battery capacity, and the heat generation amount inside the battery will increase in proportion to the square of the short-circuit current. It is a danger. In order to make a lithium-ion secondary battery a safer battery, it is a good idea to use a substance whose electrode potential in a state in which lithium ions are intercalated is nobler than that of a carbon material, as the negative electrode active material. There are two ways. However, of course, the noble negative electrode potential lowers the battery voltage, so that the energy density is lowered although the safety is improved. Therefore, a good balance between safety and energy density is important, and the discovery of new negative electrode materials is an important key to achieving this. US Patent 4,98
3 and 476 have positive electrode active materials such as LiCoO ₂ and LiF.
Using the eO _2, LiMnO _2, LiCrO lithium-containing compound such as _2, a negative electrode _{TiS 2,} VS 2, Cd
S _{2, NbS} 2, although the secondary battery using the FeS sulfide of a transition metal such as ₂ have been proposed, the battery voltage is 1.2
V and the energy density is 100 wh /
It becomes 1 or less. This is less than the value of the existing secondary battery, and is not satisfactory in terms of energy density. The energy density of the existing nickel-cadmium secondary battery is 100 to 150 wh / l, and although the lithium ion secondary battery is strongly required to have high safety, its energy density is 150 wh / l or more, preferably 18 wh / l.
If it does not achieve 0 wh / l, it cannot replace the existing battery.

[0003]

DISCLOSURE OF THE INVENTION The present invention is intended to complete a non-aqueous electrolyte secondary battery which secures energy density higher than that of existing batteries and has high safety.

[0004]

As a means for solving the problems, a lithium-containing compound is used as the positive electrode active material and CuFeO ₂ is used as the negative electrode active material.

[0005]

The energy density (wh / l) of the battery is given by the product of the current capacity density (Ah / l) and the battery voltage (v).
A lithium ion secondary battery using a lithium-containing compound for the positive electrode can obtain a current capacity density of about 75 to 85 Ah / l. Therefore, a lithium ion secondary battery having an energy density of 180 wh / l needs to operate at an average discharge voltage of 2.4 V or higher. Further, since it is preferable that the battery voltage is low from the viewpoint of improving safety, the present inventor sets a target of the battery voltage in the range of 2.4 to 3.5 V, and uses various compounds as negative electrode materials. As a result of diligent examination of the possibility, it was found that CuFeO _{2, which} is known as a delafossite compound, can be a good negative electrode material that meets the purpose, and the present invention has been completed. The negative electrode material CuFeO ₂ in the present invention is a plate-like crystal particle, and has a basic crystal structure in which oxygen molecules are stacked between metal molecules composed of Cu and Fe, and is a semiconductor in electric conductivity, It is a convenient material for the negative electrode active material.
When CuFeO ₂ is used as the negative electrode active material, a battery using LiCoO ₂ as the positive electrode active material has an open circuit voltage of about 3 V after charging and an average discharge voltage of 2.4 V or more. Further, in the battery using LiMn ₂ O ₄ as the positive electrode active material, the open circuit voltage after charging is about 3.2V, and the battery can be operated at the average discharge voltage of 2.4V or more.

[0006]

EXAMPLES Examples of lithium ion secondary batteries using CuFeO ₂ as a negative electrode active material according to the present invention will be described below with reference to the drawings.

Example 1 An example applied to a coin-type battery using a spinel type lithium manganese composite oxide as a positive electrode active material will be shown. A coin type non-aqueous electrolyte secondary battery having the battery structure shown in FIG. 2 is prepared. First, the negative electrode was prepared as follows. Mixing cuprous oxide and iron oxyhydroxide at a molar ratio of 1: 1,
After adding and mixing this to a 1.5 N caustic soda solution,
Hydrothermal treatment (350 ° C., 12 hours) and cooling to room temperature. After that, rinse well with distilled water and in the air at 80 ° C-1
It was dried at 00 ° C. to obtain CuFeO ₂ fine particles (0.1 to ₂ μm). The microparticles in the hexagonal According to x-ray _analysis, a o = _3.05Å, was c o = 17.16Å. The fine powder of CuFeO ₂ thus obtained was added with 3 parts by weight of acetylene black and 6 parts by weight of graphite to 88 parts by weight of the powder and mixed well, and further 4 parts by weight of polyvinylidene fluoride as a binder and N-methyl-solvent. 2-Pyrrolidone was added and wet mixed to prepare a negative electrode mixture paste. This negative electrode mixture paste was uniformly applied to one surface of a 0.02 mm-thick aluminum foil serving as the negative electrode current collector (8), dried and then pressure-molded with a roller press machine to obtain a sheet-shaped electrode. 15.5 mm diameter from this sheet electrode
The disc was punched out to prepare a negative electrode (1) for a coin-type battery, which was dried in a vacuum dryer at a temperature of 100 ° C. for 12 hours.

Next, as a lithium-containing compound used as a positive electrode active material, spinel type lithium manganese oxide (LiMn
₂ O ₄ ) was synthesized. Manganese dioxide (MnO ₂ ) and lithium carbonate (Li ₂ CO ₃ ) were mixed well in a molar ratio of 1: 0.27, and the mixture was calcined in air at 850 ° C. for 12 hours, and when the temperature dropped to room temperature, , Average particle size 2
A lithium manganese oxide (LiMn ₂ O ₄ ) was prepared as a positive electrode active material after being prepared as a powder of 5 μm. However, the lithium manganese oxide synthesized here has a good agreement with the diffraction pattern of spinel type LiMn ₂ O _{4 in} X-ray diffraction, but it was judged from the valence analysis of manganese that
More precisely, L in which a part of manganese is replaced with lithium
It is considered to be i _1.05 Mn _1.95 O ₄ . 90 parts by weight of the prepared lithium manganese oxide together with 3 parts by weight of carbon black, 4 parts by weight of graphite and 4 parts by weight of polyvinylidene fluoride as a binder, N- which is a solvent.
Wet mix with methyl-2-pyrrolidone to form a slurry (paste form). This slurry was uniformly applied to one surface of a 0.02 mm-thick aluminum foil serving as the positive electrode current collector (9), dried and then pressure-molded with a roller press machine to obtain a sheet-shaped electrode. 15.5m in diameter from this sheet electrode
Positive electrode for coin-type battery stamped into m disk (2)
And set the temperature to 100 ° C in a vacuum dryer and
Dried for hours.

Preparation of Battery (A) As shown in FIG. 2, an aluminum foil (10) was laid on the bottom of a battery can (4), a gasket (6) was installed, and the prepared negative electrode (1) and positive electrode (2) were formed. ), A non-woven polypropylene separator (3) is sandwiched between the active material layers so as to face each other and are housed in the center of the battery can (4). A mixed solution of ethylene carbonate (EC) in which LiPF ₆ is dissolved and diethyl carbonate (DEC) is injected. After that, the electrode pressing plate (7) is installed, the battery lid (5) is overlaid, and the battery can and the battery lid are caulked via the gasket (6) to seal and seal the battery, and then the battery shown in FIG. A battery (A) having the structure was prepared.

Test Results The battery (A) thus prepared was charged for 8 hours after the aging period of 12 hours had elapsed for the purpose of stabilizing the inside of the battery, then the charging voltage was set to 3.25V. The open circuit voltage of the battery (A) after completion of charging was 3.2 V on average (N = 5). In addition, FIG. 1 shows a charge / discharge curve of this battery (A).

Example 2 As a positive electrode active material, a lithium cobalt composite oxide (LiCo
An example using O ₂ ) will be described. The lithium cobalt composite oxide (LiCoO ₂ ) was prepared as follows. Commercially available lithium carbonate (Li ₂ CO ₃ ) and cobalt carbonate (CoCO ₃ ) have an atomic ratio of Li and Co of 1.03: 1.
Mix so that the composition ratio is about 900 ° C in air at about 10
LiCoO ₂ is obtained by firing for a time. LiCoO after firing
_{Since 2} is obtained as a very hard mass, it is ground into a powder with an average particle size of 10 microns. 91 parts by weight of this powdery LiCoO ₂ , 6 parts by weight of graphite as a conductive agent, and 3 parts by weight of polyvinylidene fluoride as a binder were wet-mixed with N-methyl-2-pyrrolidone as a solvent to form a slurry (paste). To do. Next, this slurry was uniformly applied to one side of a 0.02 mm-thick aluminum foil serving as a positive electrode current collector, dried, and pressure-molded with a roller press machine to obtain a sheet-shaped electrode. A disk having a diameter of 15.5 mm was punched from the sheet-like electrode to prepare a positive electrode (2b) for a coin-type battery, which was dried in a vacuum dryer at 100 ° C. for 12 hours.

Preparation of Battery (B) The negative electrode used was the same as the negative electrode (1) prepared in Example 1, and the same procedure as in Example 1 except that the positive electrode (2b) was used. A battery (B) was prepared with the battery structure shown in.

Test Results The prepared battery (B) was subjected to an aging period of 12 hours for the purpose of stabilizing the inside of the battery, and then the charging voltage was 3.10.
It was set to V and charged for 8 hours. The open circuit voltage of the battery (B) after completion of charging was 3.05 V on average (N = 5). Further, FIG. 3 shows a charge / discharge curve of this battery (B).

Example 3 An example in which a spinel-type lithium manganese composite oxide was used as a positive electrode active material and applied to a cylindrical battery will be described. Figure 5
A cylindrical non-aqueous electrolyte secondary battery (C) having the structure shown in was prepared as follows. A negative electrode mixture paste containing CuFeO ₂ as an active material, which was prepared by the same procedure as in Example 1, was uniformly applied to both sides of an aluminum foil having a thickness of 0.02 mm, dried and then pressure-molded with a roller press. A sheet-shaped electrode was used. The sheet-shaped electrode was adjusted to have an electrode width of 54 mm to form a strip-shaped negative electrode (11), which was placed in a vacuum dryer for 10
It was dried at 0 ° C. for 12 hours.

Also in the production of the positive electrode, the positive electrode mixture paste prepared by using lithium manganese oxide as an active material was applied in exactly the same procedure as in Example 1 evenly on both sides of an aluminum foil having a thickness of 0.02 mm, and after drying. A sheet-shaped electrode was formed by pressure molding with a roller press. This sheet-shaped electrode was also adjusted to have an electrode width of 54 mm to prepare a strip-shaped positive electrode (12) and dried in a vacuum dryer at 100 ° C. for 12 hours.

The strip-shaped negative electrode (11) and the positive electrode (12) are wound into a roll with a strip-shaped porous polypropylene separator (13) having a width of 58 mm sandwiched between them to form a roll as shown in FIG. Outer diameter 17.1 mm, height 58
A mm battery element was prepared. Next, the insulating sheet (24) is placed on the bottom of the aluminum battery can (14) to house the battery element. The negative electrode lead (15) taken out from the battery element was welded to the bottom of the battery can, and 1 mol / l of LiPF ₆ was dissolved as an electrolytic solution in the battery can to obtain ethylene carbonate (EC) and diethyl carbonate (DEC). Inject the mixed solution. After that, the insulating sheet (24) is also installed on the upper part of the battery element, and the gasket (1
6) is fitted and the explosion-proof valve (18) is installed inside the battery as shown in FIG. Positive electrode lead (1
7) is welded before injecting the electrolytic solution into this explosion-proof valve. On the explosion-proof valve, a closing lid (1
9) were piled up and the edge of the battery can was caulked to prepare a battery (C) having an outer diameter of 18.1 mm and a height of 65 mm with the battery structure shown in FIG.

Results of safety test The battery (C) thus prepared was charged for 8 hours after the aging period of 12 hours had elapsed for the purpose of stabilizing the inside of the battery, then the charging voltage was set to 3.25V. It was The open-circuit voltage after completion of charging is the same as that of the coin-type battery of Example 1, 3.
It was 2V. The battery (C) after charging was discharged at a constant current of 100 mA to a voltage of 2.0 V from beginning to end.
The capacity of 50mAh is obtained and the energy density is 186W.
It was h / l. After that, the same charge and discharge was repeated three times. The charge voltage, the discharge voltage, the charge capacity, and the discharge capacity were hardly changed in the three charge / discharge cycles. After that, a safety test was performed at high temperature. The battery (C) in a fully charged state, which has been charged under the same charging conditions as described above, is placed in an oven, the temperature of the oven is gradually raised, and after the oven temperature reaches 180 ° C, the oven temperature is set to 180 ° C. Hold at 5 ° C for 5 hours. The battery (C) did not emit smoke or ignite.

On the other hand, for comparison with the battery according to the present invention, a commercially available lithium-ion secondary battery (X) having almost the same size as the battery (C) was obtained, and the same safety test at high temperature was carried out. . The battery (X) uses a carbon material as the negative electrode active material. First, this battery (X) was charged at a charging voltage of 4.2 V for 8 hours. The open circuit voltage after charging was 4.15V, which was about 1V higher than that of the battery according to the present invention. The battery (X) after charging has a constant current of 100 mA and a voltage of 2.0 V throughout.
When discharged up to, a capacity of about 1200 mAh was obtained. After that, the same charging / discharging was repeated 3 times, but in this battery (X) as well, the charging voltage, the discharging voltage, the charging capacity, and the discharging capacity were not significantly changed after the 3 times charging / discharging. After that, a safety test was performed at high temperature. A fully charged battery (X) charged under the same charging conditions as above (charging voltage of 4.2 V and charging time of 8 hours) was placed in the oven, and the temperature of the oven was gradually raised. When the temperature reached 155 ° C, the battery (X) ignited and smoked violently.

[0019]

As described above, the commercially available lithium ion secondary battery ignites at 155 ° C, whereas the battery according to the present invention is safe even at 180 ° C. In a lithium-ion secondary battery that uses a lithium-containing compound such as lithium manganese oxide or lithium cobalt oxide as a positive electrode active material, CuFeO ₂ is used as a negative electrode active material so that a conventional carbon material is used as a negative electrode active material. Since the discharge voltage is about 1 V lower than that of the lithium-ion secondary battery, the safety at high temperature is high. Moreover, since an energy density of 180 wh / l or more is ensured, the present invention realizes a lithium ion secondary battery in which safety performance and battery performance are well balanced. As a result, safety is ensured even with a large capacity battery, and a high capacity battery that can be used in a wide range of applications can be provided, and its industrial value is great.

[Brief description of drawings]

FIG. 1 is a battery charge / discharge curve.

FIG. 2 is a schematic cross-sectional view of a coin battery.

FIG. 3 shows a charge / discharge curve of a battery.

FIG. 4 is a cross-sectional view of a battery element having a wound electrode structure.

FIG. 5 is a schematic cross-sectional view of a cylindrical battery.

[Explanation of symbols]

1 and 11 are negative electrodes, 2 and 12 are positive electrodes, 3 and 1
3 is a separator, 4 and 14 are battery cans, 5 and 19
Is a lid, 6 and 16 are gaskets, 7 is an electrode pressing plate, 10 is an aluminum foil, 15 is a negative electrode lead, 17 is a positive electrode lead, 18 is an explosion-proof valve, and 20 is an insulating sheet.

Claims (1)

[Claims] 1. In a non-aqueous electrolyte secondary battery using a lithium-containing compound capable of an electrochemical redox reaction with desorption of lithium ions as a positive electrode active material, CuFeO ₂ is used as the negative electrode in the negative electrode active material. A non-aqueous electrolyte secondary battery characterized by being used as.