JP2961745B2 - Non-aqueous electrolyte secondary battery - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a non-aqueous electrolyte secondary battery using a carbonaceous material as a negative electrode active material, and more particularly to an improvement in self-discharge characteristics and a filling factor of the battery. It is.

[Summary of the Invention]

The present invention provides a nonaqueous electrolyte secondary battery using a carbonaceous material as a negative electrode active material, wherein the carbonaceous material having a particle size of 5 μm or less is 3% or less by volume relative to the entire carbonaceous material,
The average particle size of the carbonaceous material is 25-50 μm, preferably 30
By setting the thickness to μ50 μm, the self-discharge characteristics and the filling rate of the battery are improved.

[Conventional technology]

2. Description of the Related Art In recent years, with the spread of portable devices such as video cameras and boomboxes, demand for secondary batteries that can be used repeatedly instead of disposable primary batteries has been increasing.

Most of the secondary batteries currently used are nickel cadmium batteries using an alkaline electrolyte. However, since the voltage of this battery is about 1.2 V, it is difficult to improve the energy density of the battery. Another drawback is that the self-discharge rate at room temperature is as high as 20% or more in one month.

Therefore, by using a non-aqueous solvent for the electrolyte and using a light metal such as lithium for the negative electrode, the secondary battery has a high energy density of 3 V or more and a low self-discharge rate. Batteries have been considered. However, such a secondary battery has a disadvantage that lithium metal or the like used for the negative electrode grows in a dendrite shape by repeated charge and discharge and comes into contact with the positive electrode, and as a result, a short circuit easily occurs inside the battery.

Therefore, a non-aqueous electrolyte secondary battery in which lithium or the like is alloyed with another metal and this alloy is used for the negative electrode has been studied. However, in this case, it is also difficult to put the alloy into practical use because of the disadvantage that the alloy is liable to become particles due to repeated charging and discharging.

Then, as disclosed in, for example, JP-A-62-90863, a non-aqueous electrolyte secondary battery using a carbonaceous material such as coke as a negative electrode active material has been proposed. Since this secondary battery does not have the above-described disadvantages of the negative electrode, it has excellent cycle life characteristics. As the positive electrode active material, Li _x MO ₂ (M represents one or more transition metals, as proposed by the inventor of the present application in Japanese Patent Application No. 63-135099, and 0.05 <x < Using 1.10) improves the battery capacity, and can provide a high-energy-density nonaqueous electrolyte secondary battery.

[Problems to be solved by the invention]

However, non-aqueous electrolyte secondary batteries using a carbonaceous material as the negative electrode active material have the disadvantage that the self-discharge rate is extremely high and their storage stability is poor compared to batteries using lithium metal or the like as the negative electrode active material. Have. In order to improve such disadvantages, for example, in Japanese Patent Application Laid-Open No.
It is disclosed that a carbonaceous material having a particle size distribution of 90% or more by volume in the range of 1 to 50 μm is used.

However, the inventor of the present application has found that the use of the carbonaceous material as described above does not necessarily improve the self-discharge characteristics.

The present invention uses a carbonaceous material as the negative electrode active material,
An object of the present invention is to provide a non-aqueous electrolyte secondary battery having excellent self-discharge characteristics and a filling factor.

[Means for solving the problem]

In order to achieve the above object, the present invention provides a non-aqueous electrolyte secondary battery using a carbonaceous material as a negative electrode active material,
The carbonaceous material having a particle size of 5 μm or less is 3% by volume or less based on the entire carbonaceous material, and the average particle size of the carbonaceous material is in the range of 25 to 50 μm, preferably 30 to 50 μm. It was done.

As the carbonaceous material, lithium can be doped and dedoped, and pyrolytic carbons, cokes (pitch coke, needle coke, petroleum coke, etc.),
Graphites, glassy carbons, fired bodies of organic polymer compounds (fired phenol resin, furan resin, etc. at an appropriate temperature), carbon fibers, activated carbon, and the like can be used.

As the electrolytic solution, any conventionally known one can be used as long as the electrolyte is dissolved in an organic solvent. Therefore, as the organic solvent, propylene carbonate,
Esters such as ethylene carbonate and γ-butyrolactone, ethers such as diethyl ether, tetrahydrofuran, substituted tetrahydrofuran, dioxolan, pyran and derivatives thereof, dimethoxyethane and diethoxyethane, and trisubstituted such as 3-methyl-2-oxazolidinone Examples thereof include -2-oxazolidinones, sulfolane, methylsulfolane, acetonitrile, propionitrile, and the like, and these are used alone or in combination of two or more. Further, as the electrolyte, lithium perchlorate, lithium borofluoride, lithium phosphofluoride, lithium aluminate, lithium halide, lithium trifluoromethanesulfonate and the like can be used.

In the present invention, the average particle diameter is an average volume diameter (also referred to as a volume-weighted average particle diameter), and is represented by the following formula: (Σnd ³ / Σn) ^1/3 (I) n represents the number of particles, and d represents the particle size). Therefore, for example, by using a Microtrac particle size analyzer and measuring the number n of particles and the diameter d of one particle by scattering of laser light,
The average volume diameter can be calculated according to the above equation.

[Action]

When the volume ratio of the carbonaceous material having a particle diameter of 5 μm or less is 3% or more and the average particle diameter of the carbonaceous material is 25 μm or more, the specific surface area of the particles does not unnecessarily increase, and the carbonaceous material that is more active than necessary is required. Since there are few materials, self-discharge is suppressed. Further, when the average particle size is 50 μm or less, the bulk density of the carbonaceous material does not become too small, and the filling rate as an active material does not decrease.

〔Example〕

Hereinafter, an embodiment to which the present invention is applied will be described with reference to FIGS. 1 to 3 and Tables 1 to 4.

First, the positive electrode plate 1 was made as follows. The positive electrode compound is obtained by mixing 1 mol of lithium carbonate and 1 mol of cobalt carbonate and calcining the mixture in air at 900 ° C. for 5 hours.
₂ was obtained by grinding this LiCoO ₂ in a bowl mill. Next, 91 parts by weight of this LiCoO _2, 6 parts by weight of graphite as a conductive agent, and 3 parts by weight of polyvinylidene fluoride as a binder were mixed, and N-methylpyrrolidone was added as a dispersant, and the paste was added. I made it. And
This paste was uniformly applied to both sides of a 30 μm-thick aluminum foil current collector, dried, and then subjected to roller pressing, whereby positive electrode plate 1 was obtained. The positive electrode plate 1 was a plate having a width of 35 mm, a length of 300 mm, and a thickness of 0.18 mm. An aluminum lead wire 7 was attached to an end of the positive electrode plate 1 by welding.

Next, the negative electrode plate 2 was produced as follows. The negative electrode active material was obtained by grinding pitch coke in a vibrating mill together with stainless steel balls having a diameter of 12.7 mm for 2 minutes. The true density of this pitch coke was 2.03 g / cm ³ , the spacing between 002 planes determined by X-ray diffraction according to the Japan Society for the Promotion of Science was 3.46 °, and the crystal thickness in the C-axis direction was 40 °. Next, 90 parts by weight of the granular pitch coke and 10 parts by weight of polyvinylidene fluoride as a binder were mixed.
-Methylpyrrolidone was added as a dispersant to make a paste. Then, as shown in FIG. 2, this paste is uniformly applied to both surfaces of a current collector 5 made of copper foil having a thickness of 10 μm to form active material layers 6a and 6b. As a result, a negative electrode plate 2 was obtained. The negative electrode plate 2 was a plate having a width of 35 mm, a length of 300 mm, and a thickness of 0.2 mm. A nickel lead wire (not shown) was attached to an end of the negative electrode plate 2 by welding.

Using the positive electrode plate 1, the negative electrode plate 2, and a pair of thin plate separators 3a and 3b made of polypropylene, the negative electrode plate 2, the separator 3a, the positive electrode plate 1, and the separator 3b are laminated in this order, Wound around the mold. Then, the wound body was housed in a nickel-plated iron can 4.
In this case, the above-mentioned lead wire was welded to the can 4 and the battery lid 9. As an electrolytic solution, a mixed solution of propylene carbonate in which lithium hexafluorophosphate was dissolved at 1 mol / mol and 1.2-dimethoxyethane was used. Then, this mixed solution is added to the can 4
After that, the gasket 8 made of polypropylene and the battery lid 9 are inserted into the upper portion of the can 4, and the battery is sealed by caulking the upper portion of the can 4, as shown in FIG. A cylindrical non-aqueous electrolyte secondary battery having an outer diameter of 13.8 mm and a height of 45 mm was produced. This secondary battery is referred to as Example 1. Table 1 shows the particle size distribution of the granular pitch coke used in this case.

In order to confirm the effects of the present invention, as Example 2 and Example 3, as shown in Table 1, the diameter of steel balls and / or
Alternatively, a nonaqueous electrolyte secondary battery was produced in the same manner as described above using pitch coke whose particle size distribution was changed by changing the grinding time. In addition, in the same table, the pulverization time was made longer than that in the case of Examples 1 to 3 so that the particle size was 5 μm.
Comparative examples 1 to 5 containing the following pitch coke in a volume ratio of more than 3% are also shown. Further, the particle size distribution in Table 1 is represented by a volume ratio (%).

The non-aqueous electrolyte secondary batteries of Examples 1 to 3 and Comparative Examples 1 to 5 were charged at a constant current of 100 mA and a final voltage of 4 V, and then discharged at a current of 100 mA.
Charge / discharge such as performing constant current discharge up to a final voltage of 2.5V
The discharge was repeated 20 times, and the discharge capacity (hereinafter, referred to as “capacity before storage”) was measured at the time of the 20th discharge. Next, after refilling under the same conditions as above, these secondary batteries are
It was left at a temperature of 24 ° C. for 30 days (720 hours). After this standing, the battery was discharged only once under the same conditions as described above, and the discharge capacity (hereinafter referred to as “capacity after storage”) was measured.
The self-discharge rate was calculated in comparison with the 20th discharge capacity.
Table 2 shows the results.

In addition, the same nonaqueous electrolyte secondary as Examples 4 to 7 and Comparative Examples 6 to 9 was obtained by using needle coke having a particle size distribution as shown in Table 3 instead of the pitch coke described above. A battery was prepared, and a test similar to that described above was performed.

The true density of this needle coke is 2.12 g / cm ³ ,
The spacing between the 002 planes determined by X-ray diffraction according to the Japan Society for the Promotion of Science was 3.44Å, and the crystal thickness in the C-axis direction was 65Å.

 Table 4 shows the results.

From Tables 1 to 4, it can be said that what has a bad influence on self-discharge is relatively fine coke having a particle size of 5 μm or less. This is considered to be because coke having a small particle diameter is more active than necessary and easily self-discharges, as is apparent from the following points. That is, as shown in Examples 1 to 7, when the abundance ratio of coke having a particle diameter of 5 μm or less is as low as 3% or less by volume, the self-discharge rate is 73% or less. Has become. Comparative Example 3
In Comparative Example 4 and Comparative Example 4, the self-discharge rate of the latter is considerably larger than that of the former, although the abundance ratio of coke having a particle size of 30 μm or less is the same as 80%. Furthermore, in Comparative Examples 2 and 4, the particle size was 50 μm.
The same is true for those below m.

FIG. 3 shows the relationship between the average particle size, the particle size distribution (volume ratio to the whole), and the self-discharge rate when the average particle size of pitch coke is variously changed in the nonaqueous electrolyte secondary battery shown in FIG. An example is shown. In the case of the example shown in FIG. 3,
It can be seen that the average particle size of coke having a particle size of 5 μm or less and having an abundance ratio of 3% or less by volume is about 28.5 μm or more. Further, in the case of the example shown in FIG. 3, when coke having an average particle size of 30 μm or more is used,
It can be seen that the self-discharge rate is very small. If the average particle size exceeds 50 μm, the bulk density of coke becomes small and the filling rate becomes low even though the self-discharge rate is good.
Therefore, from this point of view, the average particle size is 50
It needs to be less than μm.

As described above, those having a particle size of 5 μm or less have a volume ratio of 3
% And an average particle diameter in the range of 25 to 50 μm, a secondary battery having excellent self-discharge rate and filling rate can be obtained.

In the present embodiment, two types of carbonaceous materials are used, but other types of carbonaceous materials may be used. Further, as the positive electrode active material, Li _x MO ₂ as described above
(M is one or more transition metals). The shape of the battery is also cylindrical in this embodiment,
It may be a square, coin, button or the like. The non-aqueous electrolyte may be a solid, and in this case, a conventionally known solid electrolyte can be used.

〔The invention's effect〕

As described above, the present invention relates to a nonaqueous electrolyte secondary battery using a carbonaceous material as a negative electrode active material, wherein the carbonaceous material having a particle size of 5 μm or less is 3% by volume in the entire carbonaceous material.
Since the average particle size of the carbonaceous material is 25 μm or more, the specific surface area of the carbonaceous material particles does not become unnecessarily large, and the number of unnecessarily active carbonaceous material particles is small. For this reason, the self-discharge characteristics are very excellent, and the average particle size of the carbonaceous material is set to 50 μm or less, so that the bulk density of the carbonaceous material becomes too small, and as a negative electrode active material, The filling rate does not decrease, and therefore, a nonaqueous electrolyte secondary battery having a very excellent filling rate can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic front view of a half of a nonaqueous electrolyte secondary battery according to an embodiment of the present invention, and FIG.
FIG. 3 is a perspective view of a partially cutaway portion of the negative electrode plate shown in FIG. 3, and FIG. 3 is an average particle size and particle size distribution when the average particle size of coke is variously changed in the nonaqueous electrolyte secondary battery shown in FIG. FIG. 5 is a diagram showing an example of a relationship between the discharge rate and the self-discharge rate. In addition, in the code | symbol used for drawing, 1 ... Positive electrode plate 2 ... Negative electrode plate 3a, 3b ... Separator.

Continuation of the front page (56) References JP-A-1-292753 (JP, A) JP-A-1-204361 (JP, A) JP-A-1-130470 (JP, A) JP-A-64-54722 (JP) JP-A-64-14881 (JP, A) JP-A-63-218159 (JP, A) JP-A-63-193463 (JP, A) JP-A-63-121248 (JP, A) 63-110622 (JP, A) JP-A-63-102166 (JP, A) JP-A-58-5967 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) H01M 4/58 H01M 4/02 H01M 10/40

Claims (1)

(57) [Claims] 1. A non-aqueous electrolyte secondary battery using a carbonaceous material as a negative electrode active material, wherein the volume ratio of the carbonaceous material having a particle size of 5 μm or less to the entire carbonaceous material is 3% or less. A non-aqueous electrolyte secondary battery, wherein the average particle size of the carbonaceous material is in the range of 25 to 50 μm.