JP2812324B2 - Non-aqueous electrolyte secondary battery - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-aqueous electrolyte secondary battery, and more particularly to an improvement in its cycle characteristics.

[0002]

2. Description of the Related Art Along with the miniaturization of electronic equipment, a higher energy density of a battery is required, and various non-aqueous electrolyte batteries such as a so-called lithium battery have been proposed to meet the demand.

[0003] However, for example, a battery using a lithium metal for the negative electrode has the following drawbacks, especially when a secondary battery is used. That is, charging usually requires 5 to 10 hours, which is inferior in quick chargeability, short in cycle life, and the like.

These are all caused by lithium metal itself, and are caused by changes in lithium form, formation of dendritic lithium, irreversible change of lithium, etc. which occur with repeated charge and discharge. .

[0005] In order to solve these problems, it has been proposed to use a carbonaceous material for the negative electrode. This is based on the fact that the lithium carbon intercalation compound can be easily formed electrochemically, for example,
When charging is performed in a non-aqueous electrolyte using carbon as a negative electrode, lithium in the positive electrode is electrochemically doped between layers of the negative electrode carbon. Then, the lithium-doped carbon acts as a lithium electrode, and the lithium is undoped from the carbon layer upon discharge, and returns to the positive electrode.

[0006]

The performance of this type of battery is determined by the amount of lithium doped in the negative electrode carbonaceous material and the like.
The fact is that there is a limit.

Accordingly, the present invention has been proposed in view of the above-mentioned conventional circumstances, and has as its object to provide a non-aqueous electrolyte battery having excellent cycle life characteristics and a large discharge capacity as compared with the conventional one. Aim.

[0008]

SUMMARY OF THE INVENTION The present invention has been completed as a result of long-term studies to achieve the above-mentioned objects, and comprises a negative electrode made of a carbonaceous material and a positive electrode containing Li. And a non-aqueous electrolyte. The carbonaceous material has a (002) plane spacing of 3.70 ° or more, a true density of less than 1.70 g / cm ³ , and a differential thermal analysis. 700
The positive electrode contains Li corresponding to a charge / discharge capacity of 250 mAH or more per gram of the negative carbonaceous material, and has a charge amount of 350 mAH.
/ G and the charge / discharge cycle is repeated 50 times, and the utilization rate represented by the following equation is 95% or more.

Utilization rate = (discharge amount / charge amount) × 100 (%) As described above, in the high charge amount region of 350 mAH / g, the non-aqueous electrolyte solution whose utilization ratio after 50 cycles exceeds 95%. Secondary batteries have not been reported.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS As described above, the battery of the present invention has a negative electrode made of a carbonaceous material, a positive electrode containing Li, and a non-aqueous electrolyte, and has a reduced charge amount. 350mAH /
g, and the utilization rate represented by the following equation after repeating charge / discharge for 50 cycles is 95% or more.

Utilization rate = (discharge amount / charge amount) × 100 (%) The above characteristics can be obtained by selecting, for example, a carbonaceous material. .
A carbonaceous material having a true density of 70 ° or more, a true density of less than 1.70 g / cm ³ , and having no exothermic peak at 700 ° C. or more in differential thermal analysis may be used.

(002) of the carbonaceous material used for the negative electrode
If the plane spacing is less than 3.70 °, the discharge capacity decreases and the cycle life deteriorates to the same extent as the conventional one.

Similarly, even when the true density exceeds 1.70 g / cm ³ , the discharge capacity and the cycle life deteriorate.

Further, as a result of repeating various experiments, it was found that the result of the differential thermal analysis had a large effect on the battery characteristics, and that it was necessary to have no exothermic peak at 700 ° C. or higher.

As a carbonaceous material having such characteristics,
One obtained by calcining a furan resin at a temperature of less than 1500 ° C. and carbonizing the same. Even if a furan resin (for example, a polymer of furfuryl alcohol) is used as a raw material, the temperature at the time of calcination is set to 15
When the temperature is higher than 00 ° C. (for example, 1500 ° C.), an exothermic peak appears at 700 ° C. or higher (743 ° C.) in the differential thermal analysis, and the spacing between (002) planes is 3.69 °, so that a good carbonaceous material cannot be obtained. .

The furan resin used as a starting material is a furfuryl alcohol or furfural homopolymer or copolymer, specifically, furfural + phenol, furfuryl alcohol + dimethylol urea,
Furfuryl alcohol multimer, Furfuryl alcohol +
Polymers composed of formaldehyde, furfural + ketones and the like can be mentioned.

On the other hand, the positive electrode must contain a sufficient amount of Li, and if the amount of Li is equivalent to the charge / discharge capacity and is less than 250 mAH per gram of the negative carbonaceous material, it is difficult to secure a high capacity. . Conversely, the present invention has a great effect when applied to such a large-capacity battery, and the provision that the present invention contains Li corresponding to a charge / discharge capacity of 250 mAH or more per gram of the negative electrode carbonaceous material is that the present invention This stipulates the regulation on the positive electrode side in the target battery.

Therefore, as a positive electrode material, the general formula Li
A composite metal oxide represented by MO ₂ (where M represents at least one of Co and Ni), an intercalation compound containing Li, and the like are preferable. Particularly, when LiCoO ₂ is used, good characteristics are obtained. Demonstrate.

The non-aqueous electrolyte is prepared by appropriately combining an organic solvent and an electrolyte, and any of these organic solvents and electrolytes can be used as long as they are used for this type of battery.

For example, as the organic solvent, propylene carbonate, ethylene carbonate, 1,2-dimethoxyethane, 1,2-diethoxyethane, γ-butyrolactone, tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolan, 4-methyl-1,
3-dioxolane, diethyl ether, sulfolane, methylsulfolane, acetonitrile, propionitrile,
Anisole and the like.

As the electrolyte, LiClO ₄ , LiAs
F ₆ , LiPF ₆ , LiBF ₄ , LiB (C ₆ H ₅ ) ₄ , Li
Cl, LiBr, CH ₃ SO ₃ Li, CF ₃ SO ₃ Li and the like.

[0022]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, specific embodiments of the present invention will be described.

Example 500 parts by weight of furfuryl alcohol, 85% phosphoric acid
A mixture of 5 parts by weight and 50 parts by weight of water was heated on a hot water bath for 5 hours to obtain a viscous polymer.

Next, 1N NaOH was added to the reaction
After neutralization to H5, residual water and unreacted alcohol were removed by vacuum distillation.

Further, the obtained polymer was heated at 500 ° C. for 5 hours.
After carbonization in a nitrogen stream for an hour, the temperature was further raised to 1100 ° C. and heat-treated for 1 hour.

The carbon thus obtained had a turbostratic structure, and as a result of X-ray diffraction, the (002) plane spacing d ₀₀₂ was 3.80 °. The true density ρ is 1.55 g / cm
^{Was 3} .

Here, the result of d ₀₀₂ is the atomic scattering factor, the Lorentz factor (Lore
The tangent was drawn to the diffraction line at the peak position without performing correction by ntz factor) or the like, and the intersection was determined by a simple method with 2θ (diffraction angle). (Refer to FIG. 5) The true density was determined by a floating / sedimentation method using a mixture of CCl ₄ , CHBr ₃ , and benzene for a sample pulverized to 200 mesh or less.

Further, when a differential thermal analysis was performed in an air stream, an exothermic peak appeared at 671 ° C.

The conditions of the differential thermal analysis were as follows: 10 mg of a sample pulverized to a size of 200 mesh or less, and an air flow rate of 100 mg.
ml / min, and the heating rate was 10 ° C./min.

The following battery was constructed using this carbon.

First, carbon was pulverized in a mortar and classified by a sieve and used was 390 mesh or less. To 90 parts by weight of the classified carbon, 10 parts by weight of polyvinylidene fluoride as a binder was added, and a paste was formed using dimethylformamide.
Crimping was performed at a pressure of t / cm ² . After drying, it was punched into an appropriate shape and used as a negative electrode.

On the other hand, the positive electrode was prepared as follows. That is, a mixture composed of 91 parts by weight of LiNi _0.2 Co _0.8 O ₂ , 6 parts by weight of graphite, and 3 parts by weight of a polytetrafluoroethylene resin was put into a molding die, compression-molded at a pressure of ² t / cm ² , and formed into a disk-shaped electrode. did.

Using the positive electrode and the negative electrode thus obtained, an electrolyte prepared by adding 1 mol / dm ³ LiClO ₄ to a mixed solvent of propylene carbonate-dimethoxyethane (1: 1 by volume) as an electrolytic solution was used. , A charge / discharge test was performed.

The amount of the active material used in the battery was such that the positive electrode >> the negative electrode as an electrochemical equivalent, and the battery capacity was regulated to the negative electrode. Both charging and discharging were performed at a current density of 0.53 mA / cm ² .

FIG. 1 shows the result of the cycle test, and FIG. 2 shows the discharge curve. The cycle test is 320 mAH / g
Was charged, and discharging was performed by cutting at 1.5V.

As a result, it was found that the battery of this example had a utilization rate (discharge amount / charge amount × 100) of 97% and did not deteriorate even after more than 60 cycles.

Then, the cycle life was further examined by setting the charge amount to 350 mAH / g. The results are shown in FIG.

In this case as well, the utilization is as good as 95%, and 5%.
Although the capacity slightly deteriorated after the 0th cycle, excellent cycle characteristics were exhibited.

Comparative Example 1 As a conventional example, a battery using petroleum pitch-based coke was also tested for comparison.

The (002) plane distance d ₀₀₂ is 3.46.
Å, using a coke with a true density ρ of 2.03 g / cm ³ ,
Otherwise, a battery was manufactured in the same manner as in the previous example.

The exothermic peak of the carbon in the air flow of the differential thermal analysis appeared at 745 ° C.

A cycle test was performed on the obtained battery in the same manner as in the example. In this example, the charge amount was 216 mAH /
g, 1.5 V, and the discharge was cut. FIG. 4 shows the results.

As shown by the curve A in FIG. 4, the utilization rate of the battery of this example was as high as 97%, but the cycle life was short, and the discharge capacity began to decrease after about 20 cycles.

When the charge amount is further increased to 247 mAH / g, the curve B in FIG.
%, And the cycle life became severely degraded after the second and third cycles.

Comparative Example 2 Carbon was obtained in the same manner as in Example except that the heat treatment temperature was changed from 1100 ° C. to 1500 ° C. The morphological parameters of the obtained carbon were as follows: interplanar spacing d ₀₀₂ = 3.69 °, true density ρ = 1.60 g
/ Cm ³ .

The exothermic peaks of the differential thermal analysis in the air stream appeared at 679 ° C. and 743 ° C.

A battery was produced in the same manner as in the example except that the obtained carbon was used.

When the same cycle test (320 mAH / g charge, 1.5 V discharge cut) was performed on this battery, as shown in FIG.
Deterioration started after 15 cycles.

As can be seen from the results of these Examples and Comparative Examples, in the battery to which the present invention is applied, the discharge capacity can be greatly improved, and the cycle deterioration is much smaller than that of the conventional battery.

Also, as can be seen from a comparison between the example and comparative example 2, even if carbon is obtained by firing from the same raw material, the discharge capacity decreases as the carbon interlayer distance decreases, and the cycle time increases. The service life has also deteriorated to the level of the conventional example.

[0051]

As is apparent from the above description, according to the present invention, it is possible to provide a non-aqueous electrolyte battery having a large discharge capacity and a long cycle life.

Further, since the battery of the present invention uses the carbonaceous material as the negative electrode, the feature that the charging time is short is maintained, and from this point of view, a highly practical battery can be provided.

[Brief description of the drawings]

FIG. 1 is a characteristic diagram showing cycle life characteristics of an example battery to which the present invention is applied, in comparison with that of a comparative example.

FIG. 2 is a characteristic diagram showing a discharge curve of an example battery.

FIG. 3 is a characteristic diagram showing cycle life characteristics when charged at 350 mAH / g.

FIG. 4 is a characteristic diagram showing cycle life characteristics of a battery using petroleum-based pitch coke.

FIG. 5 is a characteristic diagram illustrating a method of obtaining a diffraction angle by a simple method.

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H01M 10/40

Claims (2)

(57) [Claims] 1. A negative electrode comprising a carbonaceous material, a positive electrode containing Li, and a non-aqueous electrolyte, wherein the carbonaceous material has a (002) plane spacing of 3.70 °.
As described above, the carbonaceous material having a true density of less than 1.70 g / cm ³ and having no exothermic peak at 700 ° C. or higher in differential thermal analysis. The positive electrode has a charge / discharge of 250 mAH or more per gram of the carbonaceous material of the negative electrode. A non-aqueous electrolyte secondary battery comprising Li equivalent to the capacity, and having a charge rate of 350 mAH / g and a charge / discharge cycle of 50 cycles, the utilization of which is represented by the following formula is 95% or more. Utilization rate = (discharge amount / charge amount) x 100 (%) 2. The non-electrode according to claim 1, wherein the positive electrode is a composite metal oxide represented by a general formula LiMO ₂ (where M represents at least one of Co and Ni). Water electrolyte secondary battery.