JP3427577B2 - Non-aqueous electrolyte secondary battery - Google Patents

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a non-aqueous electrolyte secondary battery using a carbonaceous material.

[0002]

2. Description of the Related Art In recent years, with the widespread use of portable devices such as video cameras and radio cassette recorders, there is an increasing demand for rechargeable secondary batteries instead of disposable primary batteries.

By the way, most of the secondary batteries used so far are nickel-cadmium batteries using an alkaline electrolyte.

However, since the battery voltage of this nickel-cadmium battery is about 1.2 V, it is difficult to improve the energy density of the battery. It also has a drawback that the self-discharge rate at room temperature is as high as 20% or more per month.

Therefore, a so-called non-aqueous electrolyte secondary battery using a non-aqueous solvent as an electrolytic solution and a light metal such as lithium for a negative electrode has been developed and studied. This non-aqueous electrolyte secondary battery has a high battery voltage of 3 V or higher, a high energy density, and a low self-discharge rate.

However, in a non-aqueous electrolyte secondary battery in which metallic lithium is used for the negative electrode, metallic lithium and the like used for the negative electrode grows in a dendrite form due to repeated charging and discharging and contacts the positive electrode. As a result, inside the battery. There is a problem that a short circuit is likely to occur, and it has a short life and is difficult to put into practical use.

In order to solve this, it has been attempted to alloy the negative electrode lithium with another metal, but in this case, by repeating charging and discharging, the alloy becomes fine particles and the life becomes short. There is a drawback that.

Under such circumstances, for example, Japanese Patent Laid-Open No. 62-
As disclosed in Japanese Patent No. 90863, etc., a novel non-aqueous electrolyte secondary battery using a carbonaceous material such as coke as a negative electrode active material has been proposed.

The non-aqueous electrolyte secondary battery using a carbonaceous material as the negative electrode does not have the above-mentioned drawbacks in the negative electrode, and therefore has excellent cycle life characteristics and uses lithium metal in terms of safety. It is much better than what it was. Then, by using the lithium composite oxide as the positive electrode active material, the battery life is improved, and a non-aqueous electrolyte secondary battery having a somewhat high energy density can be obtained.

[0010]

However, a non-aqueous electrolyte secondary battery using this carbonaceous material as a negative electrode active material has a high energy density, but a battery using metallic lithium or the like as a negative electrode active material. I have to say that it is considerably inferior to.

In a battery using a carbonaceous material as a negative electrode active material, as a method for eliminating such a defect, measures such as improving the packing density of the carbonaceous material can be considered, but this is also the limit. There is.

Therefore, the present invention provides a non-aqueous electrolyte secondary battery having excellent cycle life and safety and high energy density by using a carbonaceous material excellent in lithium ion doping / dedoping performance. To aim.

[0013]

As a result of earnest studies, the present inventors have developed a very high capacity carbonaceous material by using a certain carbonaceous raw material and heat-treating (calcining) it. Came to.

The non-aqueous electrolyte secondary battery of the present invention is a low expansion carbon binder having a carbon content of 90% or more, a softening start temperature of 300 ° C. or more, and a total expansion coefficient of 10% or less in a thermal expansion test. As a carbonaceous raw material, the carbonaceous raw material is fired at 700 ° C. to 1300 ° C. in an inert gas atmosphere or under a reduced pressure of 10 ⁻¹ torr or less, and has a true specific gravity of 1.5.
5 g / ml to 1.95 g / ml and a carbonaceous material having a lattice spacing of 002 planes of 3.58 angstroms to 3.74 angstroms as a negative electrode active material, and a lithium composite oxide as a positive electrode active material. , And further contains an organic electrolyte.

In the present invention, specific examples of the low-expansion carbon binder as a raw material include trade name LEC-1 (manufactured by Osaka Kasei Co.) and trade name LEC-2 (manufactured by Osaka Kasei Co.). It is possible to easily obtain a very excellent carbonaceous material by using these materials.

When firing the carbonaceous raw material, the temperature and the atmosphere are important. For example, the firing atmosphere is an inert gas atmosphere such as nitrogen or argon, or 10 ^-1 ton.
It is preferable that the pressure is reduced to rr or less. The latter is particularly preferable from the viewpoint of charge / discharge capacity. The firing temperature is preferably 700 ° C to 1300 ° C, more preferably 900 ° C to 1200 ° C.

The carbonaceous material obtained as described above has a true specific gravity of 1.55 g / ml or more and 1.95 g / ml or less, 00
The lattice spacing between the two surfaces is 3.58 angstroms to 3.7.
It is preferably 4 Å. More preferably, the true specific gravity is 1.80 g / ml or more and 1.89 g / ml.
The 002 plane has a lattice spacing of 3.60 angstroms to 3.68 angstroms.

The above-mentioned carbonaceous material is made into a negative electrode of a non-aqueous electrolyte secondary battery by, for example, being sintered together with a current collector.

At this time, the positive electrode has a general formula of Li _x MO ₂
(However, M is one or more kinds of transition metals, preferably Co,
Represents at least one of Ni and Fe, and 0.05 ≦ x ≦
It is 1.10. ) The active material containing the lithium composite oxide represented by Specific examples of such active material include LiCoO ₂ , LiNiO ₂ , and LiNi _y Co.
_{(1-y) O 2 (where,} 0 <y <1) composite oxide expressed by the like. Further, it is also possible to use LiMn ₂ O ₄ .

The above-mentioned composite oxide is obtained by mixing carbonates such as lithium, cobalt and nickel according to the composition and firing in a temperature range of 600 ° C. to 1000 ° C. in an oxygen atmosphere. The starting material at this time is not limited to the above-mentioned carbonate, and can be similarly synthesized from hydroxide or oxide.

Further, an electrolytic solution can be mentioned as a constituent element of the battery, and any known electrolytic solution can be used as long as it has an electrolyte dissolved in an organic solvent. Therefore, as the organic solvent, propylene carbonate, ethylene carbonate, esters such as γ-butyrolactone, diethyl ether, tetrahydrofuran, substituted tetrahydrofuran, dioxolane,
Pyran and its derivatives, ethers such as dimethoxyethane and diethoxyethane, 3-substituted-2-oxazolidinones such as 3-methyl-2-oxazolidinone, sulfolane, methylsulfolane, acetonitrile, propionitrile, and the like. Are used alone or in combination of two or more. Further, as the electrolyte, lithium perchlorate, lithium borofluoride, lithium phosphorus fluoride, lithium chloroaluminate, lithium halide, lithium trifluoromethanesulfonate, or the like can be used.

[0022]

Operation: Carbon content is 90% or more, softening start temperature is 30
The low expansion carbon binder having a total expansion coefficient of 10% or less in a thermal expansion test at 0 ° C. or higher easily becomes a carbonaceous material having excellent properties simply by firing.

The resulting carbonaceous material is excellent in lithium doping / dedoping performance. Therefore, by using this as a negative electrode active material for a non-aqueous electrolyte secondary battery, high energy density can be achieved.

[0024]

EXAMPLES Examples to which the present invention is applied will be described in detail below based on concrete experimental results.

(Comparative Example 1) First, a positive electrode pellet was prepared by the following procedure.

As the positive electrode compound, lithium carbonate 0.5
900 mol in air by mixing 1 mol of cobalt carbonate with 1 mol of cobalt carbonate
LiCoO ₂ was obtained by baking at 5 ° C. for 5 hours.
The LiCoO ₂ was pulverized with a bowl mill to obtain a powder having an average particle size of 10 μm. Then, this Li
91 parts by weight of CoO _2, 6 parts by weight of graphite as a conductive material, and 3 parts by weight of polyvinylidene fluoride as a binder were mixed, and N-methylpyrrolidone was added to this as a dispersant to prepare a paste. Then, this paste was dried and molded into a circular shape having a diameter of 15.5 mm under a pressure of 5 tons to obtain a positive electrode pellet. The volume density of this positive electrode pellet was 3.5 g / ml.

Next, a negative electrode pellet was prepared by the following procedure.

The carbonaceous material was obtained by milling pitch coke in a vibrating mill with stainless steel balls of diameter 12.7 mm for 15 minutes. The average particle size was 33 μm. The true density of the pitch coke used at this time was 2.03 g / ml, the spacing of 002 planes determined by X-ray diffraction according to the Japan Society for the Promotion of Science was 3.46 angstroms, and the crystal thickness Lc in the C-axis direction was Lc. Was 40 Å. Next, 90 parts by weight of this granular pitch coke and 10 parts by weight of polyvinylidene fluoride as a binder were mixed, and N-methylpyrrolidone was added to this as a dispersant to prepare a paste. Then, this paste was dried, formed into a circular shape having a diameter of 16 mm, and pressed onto a copper expanded metal serving as a current collector to obtain a negative electrode pellet.

As the electrolytic solution, a mixed solution of ethylene carbonate and diethyl carbonate is used, and lithium phosphorus fluoride L is added.
iPF ₆ was used after dissolved in a proportion of 1 mole / liter.

Using the above-mentioned carbon material negative electrode pellet, positive electrode pellet, polypropylene thin film separator, electrolytic solution, negative electrode cup, positive electrode can and gasket, the positive electrode pellet, separator and negative electrode pellet were laminated in this order and the electrolytic solution was injected. After that, they were caulked to prepare a lithium ion coin type battery having a diameter of 20 mm and a thickness of 2.5 mm. This secondary battery is referred to as Comparative Example 1.

Example 1 A coin-type battery was prepared in the same manner as in Comparative Example 1 except that the sintered composite material prepared as follows was used for the negative electrode.

Preparation of Sintered Composite Low expansion carbon binder (trade name LEC-1) manufactured by Osaka Kasei Co., Ltd. (Physical properties are shown in Tables 1 and 2).
Shown in. ) Was calcinated in an inert gas at a temperature of 900 ° C. for 1 hour, and the calcinated body obtained was pulverized to 250 mesh or less.

This calcinated body and the uncalcined low expansion carbon binder LEC-1 were mixed at a ratio of 1: 1 and the mixed powder was tentatively molded into pellets.

Next, a copper expanded metal was inserted as a current collector into the center of this mixed powder, and the mixture was compression-molded into pellets having a diameter of 16.5 mm at 3 tons. The copper expanded metal used here has a thickness of 0.1 mm and an opening shape of 1 × 2 mm.

Then, this molded body was fired in an inert gas at a temperature of 1000 ° C. for 3 hours to obtain a sintered composite body of a carbon sintered body having a diameter of 16.0 mm and a current collector. The volume density of the carbonaceous portion of the sintered composite excluding the collector portion is 1.2 g / m.
It was l.

The true specific gravity of the carbonaceous portion is 1.81 g /
ml, and the interplanar spacing d0 of the 002 plane by powder X-ray diffraction
02 was 3.66 Angstroms. The true specific gravity was obtained by finely pulverizing the obtained sintered body or powder in an agate mortar and filling about 5 g in a glass bottle for measurement, manufactured by Seishin Co., Ltd. under the trade name AUTO TRUE DENSER MA.
The measurement was performed using butanol using T-5000. For powder X-ray diffraction, the obtained sintered body or powder is finely pulverized in an agate mortar and loaded on a glass plate for measurement to a thickness of about 1 mm, and manufactured by Rigaku Geiger Flex Co., Ltd. under the product name RAD-IIC. Was measured using a Cu target. The lattice plane spacing was calculated without correction as it was measured, by drawing a baseline on the curve on the chart and determining the peak top by drawing.

Example 2 A coin-type battery was prepared in the same manner as in Comparative Example 1 except that the sintered composite material prepared as described below was used for the negative electrode.

Preparation of Sintered Composites Low expansion carbon binder (trade name LEC-2) manufactured by Osaka Kasei Co., Ltd. (Physical properties are shown in Tables 1 and 2).
Shown in. ) Was calcinated in an inert gas at a temperature of 900 ° C. for 1 hour, and the calcinated body obtained was pulverized to 250 mesh or less.

The calcinated body and the uncalcined low expansion carbon binder LEC-2 were mixed at a ratio of 1: 1 and the mixed powder was tentatively molded into pellets.

Next, a copper expanded metal was inserted as a current collector into the center of the mixed powder, and the mixture was compression-molded into a pellet having a diameter of 16.5 mm at 3 tons. The copper expanded metal used here has a thickness of 0.1 mm and an opening shape of 1 × 2 mm.

Then, this molded body was fired in an inert gas at a temperature of 1000 ° C. for 3 hours to obtain a sintered composite body of a carbon sintered body having a diameter of 16.0 mm and a current collector. The volume density of the carbonaceous portion of the sintered composite excluding the collector portion is 1.2 g / m.
It was l.

The true specific gravity of the carbonaceous portion is 1.82 g /
ml and the interplanar spacing d0 of the 002 plane by powder X-ray diffraction
02 was 3.67 Angstroms.

[0043]

[Table 1]

[0044]

[Table 2]

(Examples 3 to 9 and Comparative Example 2) With the same structure and procedure as in Example 1, only the final firing temperature was changed to prepare various secondary batteries. The final firing temperature was changed from 600 ° C to 1200 ° C.

With respect to each of the batteries of Examples and Comparative Examples described above, the physical properties of the carbonaceous material of the negative electrode were measured, and the battery characteristics were investigated by charging and discharging under the following conditions. The results are shown in Tables 3 and 4.

Charging conditions Charging voltage 4.2 Vmax, charging current 1 mA Discharging conditions Discharge cutoff 3.0 V, discharging current 5
mA

[0048]

[Table 3]

[0049]

[Table 4]

From these results, it is clear that each of the batteries of Examples has excellent discharge capacity and low internal resistance as compared with the batteries of Comparative Example. It is considered that this is because the conductivity was improved by using the sintered body, and the reaction efficiency was improved by adding no binder.

(Example 10) Next, the sintered body was pulverized to prepare a powder, and the powder was evaluated.

That is, the carbonaceous portion of the sintered composite body prepared in Example 1 was separated from the current collector and pulverized to 250 mesh or less.

A binder was added to this carbon powder in the same manner as in Comparative Example 1, and a current collector was pressed again to prepare pellets.
A battery was formed in the same manner as in Comparative Example 1.

When the battery characteristics of the obtained battery were evaluated under the same conditions, the results shown in Table 5 were obtained.

[0055]

[Table 5]

From these results, it can be judged that the characteristics are inferior to those of Example 1 (using the sintered body), but are superior to Comparative Example 1 (using the pitch coke). Therefore, the effect of the present invention is maximized when it is made into a sintered body, but it is recognized to some extent even in a pulverized state, and the low expansion carbon binders LEC-1 and LE
It was confirmed that the product obtained by firing C-2 was a very excellent negative electrode active material.

(Examples 11 and 12) Next, the raw material (LEC-1) of Example 1 was calcined under a reduced pressure instead of an inert gas.

That is, the pellets (compression molded together with the current collector) in Example 1 were fired at 1000 ° C. for 3 hours under reduced pressure of 10 ⁻¹ torr or less and 10 ⁻² torr or less.

When the battery characteristics of the obtained battery were evaluated under the same conditions, the results shown in Table 6 were obtained.

[0060]

[Table 6]

As a result, although the physical properties were the same as in Example 1, the charge / discharge capacity increased. It is presumed that the reason for the improved characteristics is that the volatile components were volatilized under reduced pressure rather than under an inert gas flow of nitrogen or argon.

The specific embodiments to which the present invention is applied have been described above, but it goes without saying that the present invention should not be construed as being limited to these embodiments. For example,
In the above-mentioned embodiment, the low expansion carbon binder L is used as the carbonaceous raw material.
Although EC-1 and LEC-2 are used, any carbonaceous raw material can be used as long as it has physical properties equivalent to these.

[0063]

As is clear from the above description, the carbonaceous material of the present invention is very excellent in lithium doping / dedoping performance. Therefore, this carbonaceous material is used in a non-aqueous electrolyte battery. By using it as a negative electrode active material, it is possible to provide a non-aqueous electrolyte secondary battery having excellent cycle life, safety, and high energy density.

─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-6-145669 (JP, A) JP-A-5-101818 (JP, A) JP-A-5-174820 (JP, A) JP-A-5- 325948 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) H01M 4/00-4/62 C01B 31/02 C04B 35/52

Claims (2)

(57) [Claims] 1. A carbon content of 90% or more, a softening start temperature of 300 ° C. or more, and a total expansion coefficient in a thermal expansion test of 10%.
The low expansion carbon caking and carbonaceous material is less, the
The carbonaceous raw material is in an inert gas atmosphere, or 10 ⁻¹ to
Baked at 700 ° C to 1300 ° C under reduced pressure of rr or less
The true specific gravity is 1.55g / ml-1.95g / ml
And the lattice spacing of the 002 plane is 3.58 angstroms.
Negative carbonaceous material that is ~ 3.74 angstroms
In addition to using it as an active material, use lithium composite oxide as a positive electrode active material.
Characterized by containing an organic electrolyte as a substance
Non-aqueous electrolyte secondary battery. 2. The non-aqueous electrolyte secondary battery according to claim 1, wherein the carbonaceous material is sintered together with a current collector to form a sintered composite body, and the sintered composite body serves as a negative electrode. .