JP3060471B2 - Negative electrode for battery, method for producing the same, and nonaqueous electrolyte battery using the same - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a negative electrode for a battery using a carbonaceous material which is doped and dedoped with lithium, and a method for producing the same. The present invention relates to a nonaqueous electrolyte battery used as a negative electrode.

[Summary of the Invention]

The present invention provides a carbonaceous material having a large doping amount with respect to lithium by adding a boron compound when carbonizing an organic material into a carbonaceous material. It is intended to provide an electrolyte battery.

[Conventional technology]

Along with miniaturization of electronic equipment, higher energy density of batteries is required, and various new secondary batteries have been proposed to meet such demands. One of them is a non-aqueous electrolyte battery using lithium, and research is actively being conducted for practical use.

However, when the nonaqueous electrolyte battery is put into practical use, the following disadvantages associated with the use of metallic lithium for the negative electrode are particularly problematic.

That is, it requires 5 to 10 hours for charging, is inferior in quick chargeability, and has a short cycle life.

These are all caused by lithium itself, and are considered to be caused by morphological changes of the lithium negative electrode due to repeated charge and discharge, formation of dendrites (dendritic crystals), passivation of lithium, and the like.

As a method for solving the above-mentioned problem, it has been proposed to use metallic lithium as a negative electrode by doping it in a carbonaceous material, instead of using metallic lithium alone. This utilizes the fact that lithium intercalation compounds can be easily formed electrochemically.For example, when a carbonaceous material is used as a negative electrode and charged in a non-aqueous electrolyte, lithium in the positive electrode is electrochemically formed. Is doped between the layers of the negative electrode carbon. Then, the lithium-doped carbonaceous material acts as a lithium electrode. Lithium is undoped from the carbon layer with discharge, and returns to the positive electrode.

[Problems to be solved by the invention]

Incidentally, the electric capacity per unit weight of the carbonaceous material at this time is determined by the doping amount of lithium. Therefore, in order to increase the charge / discharge capacity of the battery, it is necessary to make the doping amount of lithium of the carbonaceous material as close as possible to the theoretical maximum capacity. For example, in graphite, a theoretical maximum capacity is obtained when one lithium atom is doped with respect to six carbon atoms.

Conventionally, as a carbonaceous material used for a negative electrode of this type of battery, for example, as described in JP-A-62-122066 or JP-A-62-90863, an organic material is carbonized. The resulting carbonaceous materials are known.

However, in the conventional carbonaceous materials, the doping amount of lithium is insufficient and only about half the theoretical value is obtained.

Therefore, the present invention has been proposed in view of the above-described conventional circumstances, and aims to develop a carbonaceous material having a large lithium doping amount and a method for manufacturing the same, whereby the charge and discharge capacity is large, An object is to provide a non-aqueous electrolyte battery having excellent cycle life characteristics.

[Means for solving the problem]

The present inventors have conducted intensive studies to achieve the above-mentioned object, and as a result, it has been found that adding a boron compound at the time of carbonization is very effective in increasing the doping amount of lithium in a carbonaceous material obtained. I found something. The present invention has been completed based on such findings.

That is, the battery negative electrode of the present invention is characterized in that the organic material is carbonized and contains a carbonaceous material containing 0.1 to 2.0% by weight of boron.

The method for producing a negative electrode for a battery according to the present invention includes the steps of: adding a boron compound in an amount of 0.15 to 2.5% by weight in terms of boron to an organic material or a carbonaceous material; carbonizing to obtain a carbonaceous material; A negative electrode for a battery is manufactured.

Further, the non-aqueous electrolyte battery of the present invention comprises a negative electrode containing an organic material carbonized and containing a carbonaceous material containing 0.1 to 2.0% by weight of boron, a positive electrode containing lithium, and a non-aqueous electrolyte. It is characterized by having.

In the present invention, the carbonaceous material used for the negative electrode for a battery is obtained by carbonizing an organic material by a method such as firing.

Organic materials used as starting materials include phenolic resins,
Acrylic resin, vinyl halide resin, polyamide imide resin, polyamide resin, polyacetylene, poly (p-
Any organic polymer compound such as a conjugated resin such as phenylene) and a cellulose resin can be used.

Further, furfuran resins composed of homopolymers or copolymers of furfuryl alcohol or furfural are also suitable. Specifically, furfuryl alcohol, furfuryl alcohol + dimethylol urea, furfuryl alcohol + formaldehyde, furfural + phenol,
Polymers composed of furfural + ketones are exemplified. The carbonaceous material obtained by carbonizing this furan resin is (00
2) The plane spacing d ₀₀₂ is 3.70Å or more, and the differential thermal analysis (D
In TA), it has no exothermic peak at 700 ° C. or higher, and exhibits very good characteristics as a negative electrode material of a battery.

In addition, naphthalene, phenanthrene, anthracene, triphenylene, pyrene, chrysene, naphthacene,
Condensed polycyclic hydrocarbon compounds such as picene, perylene, pentaphene and pentacene, derivatives thereof (for example, carboxylic acids, carboxylic anhydrides, carboxylic imides, etc. of the above compounds), and various pitches containing as a main component a mixture of the above compounds Also, condensed heterocyclic compounds such as indole, isoindole, quinoboron, isoquinoboron, quinoxaboron, phthalazine, carbazole, acridine, phenazine, phenanthridine, and derivatives thereof can be used.

These organic materials are carbonized by a heat treatment such as firing. The carbonization temperature varies depending on the starting materials, but is usually 500 to 3000 ° C.

In the present invention, by adding a boron compound during the carbonization, the amount of doping of the resulting carbonaceous material with respect to lithium is increased.

Examples of the boron compound include boron oxides such as diboron dioxide, diboron trioxide (so-called boron oxide), tetraboron trioxide, and tetraboron pentoxide, and orthoboric acid (so-called boric acid), metaboric acid, and tetraboric acid. And oxo acids of boron such as hypoboric acid and salts thereof. Any of these boron compounds can be added to a reaction system for carbonization in the form of an aqueous solution.

In the present invention, the amount of the boron compound added during the carbonization of the organic material is 0.15 to 2.5% by weight in terms of boron with respect to the organic material or the carbonaceous material, and the content of boron in the carbonaceous material is 0.1 to 2.0% by weight. These ranges have been determined based on the following preliminary experiments performed by the present inventors.

First, FIG. 1 shows the relationship between the amount of boron charged when boric acid is added during firing of a fired body of polyfurfuryl alcohol resin (maleic anhydride catalyst) and the amount of boron remaining in the fired body. The remaining amount of boron was quantified by inductively coupled plasma emission spectroscopy. Further, the charged amount of boron is calculated from the added amount of boric acid. From this, it can be seen that the remaining amount of boron increases almost in proportion to the charged amount of boron.

FIG. 2 shows a change in the amount of electricity that can be continuously charged and discharged according to the charged amount of boron in a battery using such a fired body as a negative electrode. This indicates that the addition of boron during firing is effective in increasing the charge / discharge capacity, but the change pattern has a maximum value. That is, it cannot be said that the larger the amount of boron remaining in the negative electrode, the better.

Generally, it is considered that the electrical conductivity is reduced when a carbon atom in a carbonaceous material is replaced with a boron atom. Then, when the relationship between the charged amount of boron and the internal resistance of the battery was examined, the internal resistance was increased as the charged amount of boron was increased, as shown in FIG.

Therefore, the charged amount and the remaining amount of boron need to be defined in the optimum range in consideration of the practical performance of the battery,
The above ranges have been determined. If the amount of the boron compound is less than the above range, and as a result the proportion of boron in the carbonaceous material is too small, the doping amount of lithium cannot be effectively increased. Conversely, if the amount of the boron compound is larger than the above range, and as a result, the proportion of boron in the carbonaceous material becomes too large, the internal resistance increases and the carbon substantially involved in lithium doping is added. There is a risk of reducing the proportion of quality material.

When the above-mentioned carbonaceous material is used as a negative electrode of a nonaqueous electrolyte battery, it is preferable to use a material containing a sufficient amount of lithium as a positive electrode material, and a general formula LiMO ₂ (where M
Represents at least one of Co and Ni. ), An intermetallic compound containing lithium, or the like. In particular, good characteristics are exhibited when LiCoO ₂ or LiCo _0.8 Ni _0.2 O ₂ is used.

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,
3-dioxolan, 4-methyl-1,3-dioxolan, diethyl ether, sulfolane, methylsulfolane, acetonitrile, propionitrile, anisole and the like.

As electrolytes, LiClO ₄ , LiAsF ₆ , LiPF ₆ , LiBF ₄ , Li
B (C ₆ H ₅ ) ₄ , CH ₃ SO ₃ Li, CF ₃ SO ₃ Li, LiCl, LiBr and the like.

[Action]

When a boron compound such as boric acid is added when carbonizing an organic material into a carbonaceous material, the doping amount of lithium becomes large, and the charge / discharge efficiency expressed by the undoped amount / doped amount also increases. It will be big.

When the carbonaceous material having a large lithium doping amount is used as the negative electrode of the nonaqueous electrolyte battery, the charge / discharge capacity is increased, and deterioration due to repetition of the charge / discharge operation is suppressed.

〔Example〕

Hereinafter, the present invention will be described based on specific experimental results.

Example 1 Furfuryl alcohol 500 g, maleic anhydride 1 g, pure water 20
Then, the mixture was refluxed for 2 hours on a hot water bath to obtain a red-black viscous polymer.

After removing unreacted alcohol and residual water by vacuum distillation, an aqueous solution in which 5 g of boric acid (0.87 g in terms of boron) was dissolved in 50 g of pure water was added to 100 g of the obtained polymer.

This mixture was carbonized while being kept at 500 ° C. for 5 hours in a nitrogen stream, and then heated to 1200 ° C. and heat-treated for 1 hour. The properties of the carbonaceous material obtained in this way are as follows:
5Å, true density 1.55g / cm ³ , exothermic peak in DTA 595 ℃,
The boron content was 0.45% by weight.

Next, a coin-type nonaqueous electrolyte battery was formed using the carbonaceous material.

First, the above carbonaceous material was pulverized in a mortar and then classified by a sieve, and a material having a size of 390 mesh or less was collected.

100 mg of polyvinylidene fluoride as a binder was added to 1 g of the classified carbonaceous material, and a paste was formed using dimethylformamide.
Crimping was performed at a pressure of m ² . This was punched out into an appropriate shape to obtain a negative electrode.

The positive electrode was prepared as follows using LiNi _0.2 Co _0.8 O ₂ as an active material.

600 mg of graphite and 300 mg of polytetrafluoroethylene were added to 9.1 g of LiNi _0.2 Co _0.8 O ₂ and mixed, and then 1 g of the mixture was placed in a mold, compression-molded at a pressure of ² t / cm ² , and a disc-shaped positive electrode was formed. And

Using the above positive electrode and negative electrode, a solution prepared by dissolving LiClO ₄ at a ratio of 1 mol / in a 1: 1 (volume ratio) mixed solvent of propylene carbonate and 1,2-dimethoxyethane as an electrolytic solution, and polypropylene as a separator A coin-type battery was prepared using the nonwoven fabric. At this time, the amount of the active material used in both electrodes was set so that the positive electrode was sufficiently larger than the negative electrode when compared in terms of electrochemical equivalent, and thus the battery capacity was regulated to the negative electrode.

A charge / discharge cycle test was performed on this battery. Both charging and discharging were performed at a constant current of 0.53 mA / cm ² , and the discharge end voltage was 1.5 V. FIG. 4 shows the results of a charge / discharge cycle test in which the charge amount was 380 mAH / g (the charge amount per gram of the carbonaceous material; the same applies hereinafter). In the figure, the vertical axis represents the discharge capacity (mAH / g), the horizontal axis represents the number of cycles (times), and the result of the present embodiment is represented by a curve I. As is clear from these results, the battery according to the present example stably maintains a high discharge capacity even after 90 cycles, and the theoretical maximum capacity when graphite was used as the negative electrode (37
It can be seen that charge / discharge is possible with a charge amount equal to or greater than 2 mAH / g).

FIG. 5 shows a discharge curve when the charge amount is 380 mAH / g. In the figure, the vertical axis represents the discharge voltage (V), the horizontal axis represents the discharge capacity (mAH / g), and the result of the present embodiment is represented by a solid line.
The charge / discharge efficiency at this time was as good as 98.3%.

Comparative Example 1 After a polymer was obtained in the same manner as in Example 1, heat treatment was performed without adding a boric acid aqueous solution to obtain a carbonaceous material.

Using this carbonaceous material, a battery similar to that of Example 1 was prepared, and a charge / discharge cycle test was performed under the same conditions. However, the charge amount was changed to 320, 350, 380 mAH / g. The results are shown in FIG. 4 described above. In the figure, curve II shows the charge amount of 32.
If 0 mAH / g, curve III is 350 mAH / g, curve IV is 380 mA
H / g corresponds to each case. As a result, stable charge / discharge characteristics can be obtained only when the charge amount is 320 mAH /
It was found that it was limited to the case of low g.

In addition, in FIG. 5 described above, a discharge curve when the charge amount is set to 320 mAH / g is shown by a broken line. At this time, the charge / discharge efficiency was 97.0%.

Example 2 10 g of poly-p-phenylene terephthalamide fiber was
After moistening in a solution of 500 mg of boric acid (87.5 mg in terms of boron) dissolved in 15 g of pure water, carbonization was carried out at 500 ° C. for 5 hours in a nitrogen stream, and the temperature was further raised to 1200 ° C. for 1 hour. Time heat treatment was performed. The properties of the carbonaceous material obtained in this manner have a true density of 1.35 g / cm ³ and an exothermic peak 610 in DTA.
° C, the boron content was 0.45% by weight.

Using the above carbonaceous material, a battery similar to that of Example 1 was produced.

As a result of conducting a charge / discharge cycle test with various charge / discharge amounts,
It was found that stable charge and discharge can be performed even at a high charge amount of 380 mAH / g.

The discharge curve when the charge amount is 380 mAH / g is shown by a solid line in FIG. At this time, the charge / discharge efficiency was 98.5%. Comparative Example 2 A battery was prepared in exactly the same manner as in Example 2 except that boric acid was not added to the poly-p-phenylene terephthalamide fiber. A charge / discharge cycle test was performed.

As a result, stable charge / discharge is performed only when the charge amount is 36
It turned out that it is limited to the case of about 0 mAH / g.

When the charge amount is set to 360 mAH / g,
This is indicated by a broken line in the figure. At this time, the charge / discharge efficiency was 98.0%.

As is clear from the above Examples and Comparative Examples, by coexisting boron when carbonizing and heat-treating an organic material, a carbonaceous material with improved charge / discharge capacity as compared with the related art can be obtained. In particular, as shown in each Example, a carbonaceous material having a charge / discharge capacity exceeding the theoretical maximum capacity when graphite is used as the negative electrode can be obtained by appropriately selecting the starting material.

Although specific embodiments to which the present invention is applied have been described above, the present invention is not limited to these embodiments, and various modifications can be made without departing from the gist of the present invention.

〔The invention's effect〕

As is clear from the above description, since the carbonaceous material used for the negative electrode for a battery in the present invention contains boron, it is possible to provide a carbonaceous material having a large doping amount with respect to lithium.

Further, according to the production method of the present invention, a carbonaceous material having excellent characteristics can be produced by a simple operation, and particularly a carbonaceous material having a large lithium doping amount and a large charge / discharge efficiency (dedoping amount / doping amount). It is possible to produce the material.

Further, in the nonaqueous electrolyte battery of the present invention, since the carbon material having a large lithium doping amount and charge / discharge efficiency is used as the negative electrode, a charge / discharge capacity that exceeds the theoretical maximum capacity when graphite is used as the negative electrode is realized. It is possible to provide a battery having excellent cycle characteristics and charge / discharge efficiency.

[Brief description of the drawings]

FIG. 1 is a characteristic diagram showing the relationship between the amount of boron charged during firing of a polyfurfuryl alcohol resin and the remaining amount of boron in the obtained fired body. FIG. 2 is a characteristic diagram showing the relationship between the amount of boron charged in sintering a polyfurfuryl alcohol resin and the amount of electricity that can be continuously charged and discharged in a battery having the obtained fired body as a negative electrode. FIG. 3 is a characteristic diagram showing the relationship between the charged amount of boron and the internal resistance of a battery having the obtained fired body as a negative electrode. FIG. 4 shows the charge / discharge cycle characteristics of a nonaqueous electrolyte secondary battery using a carbonaceous material prepared by adding boric acid to polyfurfuryl alcohol resin as a negative electrode. FIG. 5 is a characteristic diagram shown in comparison with that of the battery of FIG. FIG. 5 shows a discharge curve of a nonaqueous electrolyte secondary battery using a carbonaceous material prepared by adding boric acid to a polyfurfuryl alcohol resin as a negative electrode. A carbonaceous material prepared without adding boric acid was used as a negative electrode. FIG. 3 is a characteristic diagram shown in comparison with that of a battery. FIG. 6 shows a discharge curve of a non-aqueous electrolyte secondary battery using a carbonaceous material prepared by adding boric acid to poly-p-phenylene terephthalamide fiber as a negative electrode. FIG. 4 is a characteristic diagram shown in comparison with that of a battery having a negative electrode.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-57-191328 (JP, A) JP-A-61-163562 (JP, A) Aso Oya et al. , "Catalytic graphitization of carbons by borons", FUEL, 1979, Vol. 158, July, p. 495-500 (58) Field surveyed (Int.Cl. ⁷ , DB name) H01M 4/02-4/04 H01M 4/58 H01M 10/40 C01B 31/00-31/36

Claims (3)

(57) [Claims] (1) An organic material is carbonized, and boron is added to 0.1%.
A negative electrode for a battery, comprising a carbonaceous material containing 1 to 2.0% by weight. 2. A method for producing a negative electrode for a battery by adding a boron compound in an amount of 0.15 to 2.5% by weight in terms of boron to an organic material or a carbonaceous material and carbonizing to obtain a carbonaceous material. A method for producing a negative electrode for a battery. (3) The organic material is carbonized, and boron is added to the material in an amount of 0.
A non-aqueous electrolyte battery comprising a negative electrode containing a carbonaceous material containing 1 to 2.0% by weight, a positive electrode containing lithium, and a non-aqueous electrolyte.