JP3506386B2 - Non-aqueous electrolyte secondary battery - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION This invention relates to a non-aqueous electrolyte secondary battery. More specifically, the present invention has good temperature characteristics and load characteristics by using a specific non-aqueous solvent,
The present invention relates to a non-aqueous electrolyte secondary battery having excellent redox resistance.

[0002]

2. Description of the Related Art Recently, a VTR with a built-in camera, a mobile phone,
Many new portable electronic devices such as laptop computers have appeared, and their size and weight have been reduced.
Therefore, a secondary battery has been attracting attention as a portable power source used in a portable electronic device, and a secondary battery capable of obtaining a high energy density is being developed. Among them, a lithium (secondary) battery has a large energy density as compared with a lead battery or a nickel-cadmium battery, which is an aqueous electrolyte secondary battery, and therefore, research is actively conducted.

A non-aqueous solvent is used as a solvent for an electrolyte in a lithium battery. As the non-aqueous solvent, a cyclic carbon such as propylene carbonate (PC) is used because it has a higher dielectric constant and is relatively stable than before. Acid esters are used. However, when this propylene carbonate is used as the sole solvent of the electrolytic solution, the load characteristics and the low temperature characteristics are remarkably inferior because the conductivity is relatively low, and the lithium charge / discharge efficiency is also low. Therefore, propylene carbonate is not used as the sole solvent of the electrolytic solution, and 1,2-dimethoxyethane (D
It is used as a mixed solvent combined with a low viscosity solvent such as ME).

[0004]

[Problems to be Solved by the Invention]
-When dimethoxyethane is used as an electrolyte, the oxidation resistance of 1,2-dimethoxyethane is not so large that the capacity deterioration and the cycle deterioration at high temperature when a lithium battery is stored in a charged state become large. was there.

For such a problem, it has been proposed to use a mixed solvent of propylene carbonate and diethyl carbonate (DEC) as an electrolytic solution. However, even if this mixed solvent is used, the conductivity cannot be sufficiently increased,
Therefore, there is a problem that the capacity under high load and the capacity at low temperature cannot be sufficiently improved.

In this mixed solvent, it has been proposed to use methyl ethyl carbonate (MEC) in place of diethyl carbonate to improve cycle characteristics and low temperature characteristics, but it has not been sufficiently improved.

The present invention is intended to solve such problems of the prior art, has found a non-aqueous solvent which can replace the conventional mixed solvent, and has a sufficiently high conductivity and good temperature characteristics and load characteristics. Moreover, it is an object of the present invention to provide a non-aqueous electrolyte secondary battery having excellent redox resistance.

[0008]

Means for Solving the Problems As a result of various studies to achieve the above object, the present inventors have found that propylene carbonate, ethylene carbonate and carbonic acid are used as a non-aqueous solvent in a non-aqueous electrolyte. It has been found that it is effective to use a mixed solvent containing three kinds of methylethyl solvents, and the present invention has been completed.

That is, according to the present invention, a negative electrode in which a negative electrode mixture layer composed of a negative electrode active material capable of doping and dedoping lithium and a binder is formed on both surfaces of the current collector in a band shape, and a current collector in a band shape. Bonding of the positive electrode active material that can be charged and discharged and the conductive agent on both sides of the
A positive electrode formed by forming a positive electrode mixture layer containing an agent, a wound electrode body that is wound a large number of times through a separator, and a non-aqueous electrolytic solution in which an electrolyte is dissolved in a non-aqueous solvent In the non-aqueous electrolyte secondary battery, the non-aqueous solvent of the non-aqueous electrolyte,
A non-aqueous electrolyte secondary battery comprising a mixed solvent containing 10 to 47% by volume of propylene carbonate, 3 to 40% by volume of ethylene carbonate and 30 to 70% by volume of methyl ethyl carbonate. provide.

The present invention will be described in detail below.

The present invention is characterized by containing three kinds of propylene carbonate, ethylene carbonate and methyl ethyl carbonate as the non-aqueous solvent of the electrolytic solution. Here, the mixing ratio of each solvent constituting the non-aqueous solvent is It is preferable that propylene carbonate is 10 to 75% by volume, ethylene carbonate is 3 to 50% by volume, and methyl ethyl carbonate is 10 to 80% by volume. In addition, the volume mixture ratio of the total of propylene carbonate and ethylene carbonate and methyl ethyl carbonate is 70:30 to 3
It is preferably set to 0:70 .

The electrolyte to be dissolved in such a non-aqueous solvent is not particularly limited and may be the same as the conventional lithium battery. For example, LiClO ₄ , LiAs
F ₆ , LiPF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , L
iN (CF ₃ SO ₂ ) ₂ or the like can be used, among which L
It is preferable to use iPF ₆ or LiBF ₄ .

The positive electrode is not particularly limited as long as it can be charged and discharged. For example, Li _x MO ₂ (wherein M represents one or more kinds of transition metals, and 0.05 ≦ x ≦ 1.10. is there)
A material composed of an active material mainly composed of is preferably used. In this case, especially as the transition metal M, Co,
It is preferable to use at least one of Ni and Mn. This makes it possible to increase the energy density.

On the other hand, the negative electrode is doped with lithium,
Use one that can be dedoped. Examples of such a negative electrode include pyrolytic carbons, cokes (pitch cokes, needle cokes, petroleum cokes, etc.), graphites, glassy carbons, organic polymer compound fired products (phenolic resins, furan resins, etc.). Carbon materials such as carbonized by firing at a suitable temperature), carbon fibers, activated carbon, and the like, or polymers such as metallic lithium, lithium alloys (for example, lithium-aluminum alloy), polyacetylene, polypyrrole, and the like can be used. In particular, it is preferable to use a carbon material that can be doped or dedoped with lithium because the cycle characteristics are improved.

The shape of the battery is also not particularly limited, and various shapes such as a cylindrical shape, a square shape, a coin shape and a button shape can be used.

[0016]

The non-aqueous electrolyte secondary battery according to the present invention is a mixed solvent of propylene carbonate and methyl ethyl carbonate, which has been proposed as a non-aqueous solvent for improving cycle characteristics and low temperature characteristics, and has a higher dielectric constant solvent. 3 blended with ethylene carbonate
Since it is a mixed solvent of the seeds, the electrolytic solution can simultaneously achieve high conductivity and low freezing point. Therefore, it becomes possible to sufficiently improve the load characteristics and low temperature characteristics of the battery.

[0017]

EXAMPLES The present invention will be specifically described below with reference to examples.

Examples 1 to 7 and Comparative Example 1 In each of the Examples and Comparative Examples, a battery having the structure shown in FIG. 1 was produced. This battery includes a separator 3 including a strip-shaped negative electrode 1 in which a negative electrode current collector 1a is coated with a negative electrode active material, and a strip-shaped positive electrode 2 formed by coating a positive electrode current collector 2a with a positive electrode active material.
The winding body is housed in the battery can 5 with the insulators 4 placed on the upper and lower ends thereof, and the upper portion of the winding body is caulked with the battery lid 7 via the sealing gasket 6. It is the one that has been sealed. Further, the negative electrode 1 is connected to the bottom of the battery via the negative electrode lead 9, and the positive electrode 2 is connected to the battery lid 7 via the positive electrode lead 10 so as to function as electrodes, respectively.

When manufacturing a battery having such a structure,
First, the negative electrode was manufactured as follows. As the negative electrode active material,
By using petroleum pitch as a starting material, introducing 10 to 20% of a functional group containing oxygen therein (so-called oxygen cross-linking), and then calcining at 1000 ° C. in an inert gas stream, it is possible to obtain properties similar to those of glassy carbon. A graphite carbon material was obtained. When X-ray diffraction of this non-graphite carbon material was conducted, the (002) plane spacing was 3.76 angstroms and the true specific gravity was 1.58 g.
It was / cm ^3. This non-graphite carbon material was pulverized into a powder having an average particle size of 10 μm, and 90 parts by weight of this powder was mixed with 10 parts by weight of polyvinylidene fluoride (PVDF) as a binder to prepare a negative electrode mixture. It was dispersed in methyl-2-pyrrolidone to form a slurry. Next, this slurry was uniformly applied to both surfaces of a strip-shaped copper foil having a thickness of 10 μm, which is a negative electrode current collector, dried, and compression-molded by a roll press machine to obtain strip-shaped negative electrode 1.

Next, a positive electrode was prepared as follows. As a positive electrode active material, lithium carbonate and cobalt carbonate were mixed at a ratio of 0.5 mol to 1 mol and fired in air at 900 ° C. for 5 hours to obtain LiCoO ₂ . LiCo thus obtained
91 parts by weight of O _2, 6 parts by weight of graphite as a conductive agent, and polyvinylidene fluoride (PVDF) 3 as a binder
Parts by weight to prepare a positive electrode mixture, which is mixed with N-methyl-
It was dispersed in 2-pyrrolidone to form a slurry. next,
This slurry was uniformly applied to both sides of a strip-shaped aluminum foil having a thickness of 20 μm, which is a positive electrode current collector, dried, and compression-molded with a roll press to obtain a strip-shaped positive electrode 2.

The positive electrode 2, the negative electrode 1 thus obtained, and the separator 3 made of a microporous polypropylene film having a thickness of 25 μm were laminated and spirally wound many times to prepare a wound body.

As the battery can 5, an iron can plated with nickel was prepared, the insulating plate 4 was inserted into the bottom of the can, and the wound body was housed. And in order to collect the current of the negative electrode,
One end of a negative electrode lead 9 made of nickel was pressure-bonded to the negative electrode 1, and the other end was welded to the battery can 5. Further, in order to collect current from the positive electrode, one end of a positive electrode lead 10 made of aluminum is attached to the positive electrode 2, and the other end is electrically connected to the battery lid 7 via a thin plate 8 for cutting off current according to the internal force of the battery. Connected to each other.

Next, into this battery can 5, an electrolytic solution in which 1 mol / l of LiPF ₆ was dissolved in the mixed solvent shown in Table 1 was injected. Then, the battery can 5 was caulked via the insulating sealing gasket 6 coated with Alfalto, the battery lid 7 was fixed, and a cylindrical nonaqueous electrolyte battery having a diameter of 18 mm and a height of 65 mm was produced.

Regarding the cylindrical non-aqueous electrolyte batteries of Examples 1 to 7 and Comparative Example 1 produced as described above, first, in order to evaluate the high load characteristics, the charging voltage was 4.
700V when charging at 2.5V at 1A for 2 hours
Nine cycles of discharging with a constant current of mA up to a final voltage of 2.5 V were performed, then recharging was performed under the same conditions, and discharging with a constant current of 1 A, which was a relatively high load, was performed, and the discharge capacity at that time was measured.

Further, in order to evaluate the low temperature characteristics, the same charge-discharge cycles and evaluation of high load characteristics, then -
Constant-current discharge of 1 A was performed at 20 ° C., and the discharge capacity at that time was measured.

Further, in order to evaluate the self-discharge characteristic,
Perform the same charge / discharge cycle as when evaluating high load characteristics and low temperature characteristics, then leave at 60 ° C for 15 hours, then at 20 ° C.
A constant current discharge of 1 A was performed and the self-discharge rate during that period was obtained.

The results are also shown in Table 1. Table 1
From the results of the above, the battery of the example of the present invention using the electrolytic solution containing three kinds of solvents of propylene carbonate, ethylene carbonate, and methyl ethyl carbonate is not only the normal cycle but also has high load characteristics, low temperature characteristics, and self-discharge characteristics. It is clear that it is also excellent.

[0028]

[Table 1] Non-aqueous solvent composition (vol%) High load characteristics Low temperature characteristics Self discharge rate PC: EC: MEC Discharge capacity (mAh ) Discharge capacity (mAh ) (%) Example 1 25:25:50 1026 780 9.4 Example 2 10:40:50 1030 765 8.7 Example 3 35:15:50 1019 751 9.7 Example 4 47: 3:50 1006 705 10.8 Example 5 30:30:40 1018 720 8.9 Implementation Example 6 35:35:30 1009 702 8.8 Example 7 15:15:70 1029 793 10.1 Comparative Example 1 50: 0: 50 995 697 11.5

[0029]

According to the present invention, the conductivity of the non-aqueous electrolyte secondary battery is sufficiently high, the temperature characteristics and the load characteristics are good, and the redox resistance is also excellent.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of batteries manufactured in Examples and Comparative Examples.

[Explanation of symbols]

1 negative electrode 1a Negative electrode current collector 2 positive electrode 2a Positive electrode current collector 3 separator 4 insulator 5 battery cans

─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-4-218270 (JP, A) JP-A-4-155775 (JP, A) JP-A-4-162370 (JP, A) JP-A-2- 148665 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) H01M 10/40

Claims (4)

(57) [Claims] 1. A negative electrode formed by forming a negative electrode mixture layer composed of a negative electrode active material capable of doping and dedoping lithium and a binder on both sides of a band-shaped current collector, and filling both sides of the band-shaped current collector. A positive electrode formed by forming a positive electrode mixture layer containing a dischargeable positive electrode active material, a conductive agent, and a binder, a wound electrode body formed by winding a large number of times through a separator, and a nonaqueous solvent. In a non-aqueous electrolyte secondary battery comprising a non-aqueous electrolyte solution in which an electrolyte is dissolved, the non-aqueous solvent of the non-aqueous electrolyte solution is 10 to 47% by volume propylene carbonate, 3 to 40% by volume ethylene carbonate and A non-aqueous electrolyte secondary battery, which is a mixed solvent containing 30 to 70% by volume of methyl ethyl carbonate. 2. The volume mixing ratio of the total of propylene carbonate and ethylene carbonate to methyl ethyl carbonate is 70: 30-3.
The non-aqueous electrolyte secondary battery according to claim 1, which is 0:70 . 3. The non-aqueous electrolytic solution according to claim 1, wherein the positive electrode comprises Li _x MO ₂ (wherein M represents one or more kinds of transition metals, and 0.05 ≦ x ≦ 1.10). Secondary battery. 4. The non-aqueous electrolyte secondary battery according to claim 3, wherein the negative electrode is made of a carbon material capable of being doped and dedoped with lithium.