JP2744555B2 - Battery electrode - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrode for a battery, and more particularly to an electrode for a battery using, as an active material, a composite of an insoluble and infusible material having semiconductor properties and lithium cobalt oxide.

[0002]

2. Description of the Related Art In recent years, portable appliances and electronic devices have been rapidly becoming portable and cordless. Along with this, a small, lightweight and high-performance battery has been demanded as a power source. At present, a so-called primary battery such as a dry battery and a secondary battery such as a Ni-Cd battery or a lead battery are used as power supplies for the above-mentioned devices. However, recently, a secondary battery that can be repeatedly charged for a primary battery that has a short life and needs to be replaced has been frequently used. At present, Ni-Cd batteries are currently the mainstream as power supplies for small devices, but their performance improvement is approaching its limit in response to needs for higher capacity. In addition, discussions on global environmental issues have been active in recent years, and public opinion on the harmfulness of Cd, which is an active material, is increasing. Therefore, there is great expectation for the development of a secondary battery having performance higher than that of a Ni-Cd battery and having high reliability and safety.

The present applicant has previously disclosed a secondary battery using an insoluble and infusible substrate containing a polyacene-based skeleton structure, which is a kind of organic semiconductor, doped with an electron donating substance or an electron accepting substance as an electrode active material. (JP-A-60-170163). This battery is a promising secondary battery because it has high performance, has the potential of being thin and light, has high oxidation stability of the electrode active material, and is easy to mold. Further, the present applicant has proposed a secondary battery using a composite of the polyacene-based organic semiconductor and a metal oxide as an active material (Japanese Patent Application Laid-Open No. 63-31475).
No. 9). This battery has a large capacity without losing the rapid chargeability characteristic of the battery using the polyacene-based organic semiconductor, but the capacity is not yet satisfactory.

[0004]

SUMMARY OF THE INVENTION In view of the above problems, the present inventors have conducted intensive studies and prepared electrodes by various methods. As a result, the average particle size of lithium cobalt oxide (III) and the pore volume of the electrodes were determined. When the electrode is controlled to a specific range, this electrode finds that the capacity per unit volume is significantly increased, and completes the present invention, and the purpose is to increase the capacity, particularly the capacity per unit volume. An object of the present invention is to provide a battery electrode.

[0005]

The object of the present invention is to provide (a) a heat-treated aromatic condensed polymer comprising carbon, hydrogen and oxygen, wherein the ratio of the number of hydrogen atoms / carbon atoms is 0.05.
Having a polyacene skeleton structure of 0.5 to 0.5
An electrode for a battery comprising, as an active material, a composite of an insoluble and infusible substrate having a specific surface area of at least 600 m ² / g by a T method and (b) a lithium cobalt oxide. (2) having an average particle size of 1 μm or less;
01. This is achieved by a battery electrode characterized in that the pore volume having a pore diameter of not more than μm accounts for 70% or more of the total pore volume.

The insoluble and infusible substrate having a polyacene-based skeleton structure (hereinafter sometimes referred to as PAS) used in the present invention is disclosed in Japanese Patent Application Laid-Open No. 60-152 by the present applicant.
554 and JP-A-60-170163. Here, the aromatic condensation polymer is a condensate of an aromatic hydrocarbon compound having a phenolic hydroxyl group with an aldehyde. As the aromatic hydrocarbon compound, for example, so-called phenols such as phenol, cresol, and xylenol are suitable, but not limited thereto. For example, the following formula (Formula 1):

Embedded image (Where x and y are each independently 0.1 or 2)
Methylene bisphenols, or hydroxybiphenyls and hydroxynaphthalenes. Of these, phenols, particularly phenol, are practically preferred.

As the aromatic condensation polymer in the present invention, a part of the above-mentioned aromatic hydrocarbon compound having a phenolic hydroxyl group is converted into an aromatic hydrocarbon compound having no phenolic hydroxyl group, for example, xylene, toluene, aniline or the like. A substituted modified aromatic polymer, for example, a modified aromatic polymer which is a condensate of phenol, xylene and formaldehyde can be used, and a modified aromatic polymer substituted with melamine or urea can also be used. Furan resins are also suitable. As the aldehyde, formaldehyde, acetaldehyde, furfural and the like can be used, and formaldehyde is preferred. The phenol-aldehyde condensate may be any of a novolak type, a resol type, or a composite thereof. A spherical phenolic resin (sphere diameter of about 100 μm or less) commercially available as Bellpearl R (trade name, manufactured by Kanebo Co., Ltd.) can also be used. The PAS in the present invention is a heat-treated product of the aromatic compound as described above, and can be produced, for example, as follows.

An inorganic substance such as zinc chloride, sodium phosphate, sodium hydroxide, potassium hydroxide or potassium sulfide is mixed into the above-mentioned aromatic condensation polymer. As a mixing method, an aromatic condensation polymer may be dissolved in a solvent such as methanol, acetone or water, and then the above-mentioned inorganic substance may be added and sufficiently mixed. Further, if the aromatic condensation polymer is a fusible one such as novolak, it may be mixed under heating. The mixing ratio of the aromatic condensed polymer and the above-mentioned inorganic substance varies depending on the type and shape of the polymer to be mixed and the inorganic substance.
0/1 to 1/7 are preferred. Next, the mixture is cured into a film, plate, fiber, cloth, granule, or a mixture thereof. The cured product thus obtained is then placed in a non-acidic atmosphere at 350 to 800 ° C., preferably at 350 to 7 ° C.
It is heated to a temperature of 00C, particularly preferably 400-600C. The non-oxidizing atmosphere in which the heat treatment of the aromatic condensation polymer is performed is, for example, a nitrogen, argon, helium, neon, carbon dioxide atmosphere, or a vacuum, and nitrogen is preferably used. Such a non-oxidizing atmosphere may be stationary or flowing. By sufficiently washing the obtained heat-treated body with water or dilute hydrochloric acid, the inorganic salt contained in the heat-treated body can be removed, and then dried to obtain PAS having a large specific surface area.

The PAS used in the present invention has a hydrogen atom / carbon atom number ratio (hereinafter referred to as H / C ratio) of 0.05 to 0.5, preferably 0.1 to 0.35. It has a polyacene skeleton structure. X-ray diffraction (CuKα)
According to the above, the position of the main peak is represented by 2θ.
There is another peak between 41 and 46 degrees apart from this main peak between 5 and 23.5 degrees. That is, it is understood that the PAS is a polyacene-based benzene polycyclic structure uniformly and appropriately developed between polyacene-based molecules. When the H / C ratio exceeds 0.5, the charge efficiency of charging and discharging of a secondary battery using a composite of PAS and lithium cobalt oxide as an electrode is deteriorated. On the other hand, if this value is less than 0.05, the capacity of the battery will decrease. BE of PAS used in the present invention
The specific surface area value by the T method is 600 m ² / g or more. 6
If it is less than 00 m ² / g, in the battery using the battery electrode of the present invention, it is necessary to increase the charging voltage, so that the energy efficiency is reduced and the electrolyte is deteriorated.

In the present invention, PAS is 6 as described above.
Since it has a high specific surface area of not less than 00 m ² / g, sufficient performance as an active material, that is, sufficient capacity of PAS to be used can be sufficiently obtained regardless of the particle size. However, if the particle size of PAS is too large, PAS
In the matrix, that is, between the PAS particles, it is difficult to disperse lithium cobalt oxide, which is liable to secondary aggregation,
Finally, it is desirable that the particle size is 1 μm or less.

In the electrode of the present invention, the above-mentioned LiCoO
The average particle size of ₂ needs to be 1 μm or less finally, that is, when it becomes an electrode. This is because the above-mentioned PAS having a large surface area can sufficiently draw out its possible capacity irrespective of the particle size, whereas in the case of LiCoO ₂ , if the particle size is too large, the capacity that can be held is sufficiently drawn out. Because it becomes difficult. That is, the particle size is 1
When LiCoO ₂ larger than μm is used, the capacity is not sufficient even if the pore distribution condition in the electrode described later is satisfied.

In the electrode of the present invention, PAS / LiCo
The ratio of O ₂ may vary depending on the application of the electrode containing them, but it is 90/10 to 10/90 (weight ratio), especially 70/3.
It is preferably 0 to 30/70. Especially LiCoO
_{If the} number ₂ is too large, the rapid chargeability, which is a feature of the composite, tends to be lost. The battery electrode of the present invention using a composite of PAS and LiCoO ₂ as an active material can be manufactured, for example, as follows. That is, PAS and LiCoO ₂
After pulverizing and mixing, a conductive agent and a binder are added if necessary, and then molded. At this time, the form of PAS and LiCoO ₂ may be any form in which powder, short fibers and the like are easily mixed, but the powder is practical. The conductive agent, binder, and the like used are not particularly limited in the present invention, and may be appropriately selected from those generally used for battery electrodes. P
AS and LiCoO ₂ may be individually pulverized to a predetermined particle size and then mixed, or PAS and LiCoO ₂ may be pulverized and mixed simultaneously.

The pulverizing method is not particularly limited, but it is preferable to use a fine pulverizer represented by a ball mill such as a pot mill and a vibration mill. When an electrode is produced by mixing fine PAS and small particle size LiCoO ₂ by mixing, controlling the pore ratio described later requires LiCo
Difficult due to secondary aggregation of O ₂ (apparent increase in particle size) and the like. Therefore, to uniformly disperse LiCoO ₂ in a matrix made by PAS, PAS and Li
A method of simultaneously pulverizing and mixing CoO ₂ and the like is desirable.
The molding method is not particularly limited, and a conventional molding method used for powders, for example, a pressure molding method or the like can be used.

[0014] Lithium cobalt oxide can be easily obtained by a known appropriate method. As an example, for example, lithium carbonate (Li ₂ Co ₃ ) and cobalt carbonate (CoCO ₃ )
Are heated at 900 ° C. Cobalt lithium oxide is generally represented as LixCoO ₂ , but the value of x is in the range of 0 ≦ x ≦ 1 due to its synthesis method and charge / discharge in a battery system. The lithium cobalt oxide (hereinafter abbreviated as LiCoO ₂ ) in the present invention is not particularly limited with respect to the value of x.

In the battery electrode of the present invention, very fine LiCoO ₂ is homogeneously dispersed in the PAS matrix, and the electrode has many small pore diameters.
The battery using this has a remarkably large capacity and can be rapidly charged. Hereinafter, the present invention will be described specifically with reference to examples.

[0016]

【Example】

Example 1 PAS and LiCoO ₂ in producing: - a (1) producing a water-soluble resol-type phenolic resin (about 60% strength) of PAS / zinc chloride / water mixed in a ratio of 10/25/5 by weight slurry The mixture was poured into a mold having a size of 10 cm × 10 cm × 1 cm, and a glass plate was placed on the mold, followed by heating at 100 ° C. for 1 hour while suppressing the evaporation of water to cure. This cured product was placed in a siliconite electric furnace, heated in a nitrogen stream at a rate of 40 ° C./hour, heated to 500 ° C., and heat-treated.
Next, the heat-treated product is washed with dilute hydrochloric acid to remove zinc chloride, washed with water, and then dried to obtain a plate-shaped P.
AS was obtained. The specific surface area of this PAS by the BET method is 2
It was an extremely large value of 000 m ² / g. Elemental analysis revealed that the ratio of the number of hydrogen atoms to the number of carbon atoms was 0.23. The PAS thus obtained was pulverized in a nylon ball mill for 10 minutes, 24 hours, and 48 hours while changing the pulverization time to 5.2 particles each having an average particle size of 5.2.
μm, 0.7 μm, and 0.4 μm PAS powders were obtained. The average particle size of the PAS powder was determined by electron microscopy ("powder", edited by Kuichiro Teruichiro et al., 1979 revised version 2 Maruzen Co., Ltd.).

[0017] (2) LiCoO ₂ in producing commercially available LiCoO ₂ the grinding time 10 minutes using a ball mill made of alumina for 48 hours, then milled for 72 hours, an average particle diameter of each of 6.5 [mu] m, 0.6 .mu.m, 0. 4 μm L
iCoO ₂ powder was obtained. The average particle size was measured by electron microscopy as in PAS. LiCoO in each case
_{Although the two} particles were secondary aggregated, they were measured by the size of the primary particles.

PAS having an average particle size of 5.2 μm and LiCoO ₂ having an average particle size of 6.5 μm were converted into PAS / LiCoO ₂ = 4.
0/60 (weight ratio), put in an alumina ball mill,
Milling for 4 hours (Example 1a) and 48 hours (Example 1b) . Observation of the obtained composite of PAS and LiCoO ₂ with an electron microscope revealed that the average particle size of PAS was 0.5 μm and 0.4 μm, respectively. Since LiCoO ₂ was ground and homogeneously mixed with the PAS particles,
Although accurate measurement of LiCoO ₂ particle diameter was difficult,
In each case, the average particle size was about 0.5 μm.

To 100 parts by weight of the obtained composite, 75 parts by weight of carbon black as a conductive agent and 8 parts by weight of polytetrafluoroethylene as a binder were added, mixed in a mortar, kneaded, and then formed into a sheet by a roller. To a thickness of 7
An electrode sheet of 50 μm was obtained. The pore distribution of this electrode sheet was measured by a mercury porosimeter (Pore Sizer, manufactured by Shimadzu Corporation) (pore volume having a pore diameter of 0.006 μm to 0.1 μm) / (0.006 μm to 10 μm).
The ratio of pore volume having a pore diameter of 0 μm or less was 78% and 81%, respectively. This electrode sheet was punched into 15 mmφ to form a positive electrode, lithium was used as a negative electrode, and a glass nonwoven fabric was used as a 1 M LiClO ₄ propylene carbonate solution separator as an electrolyte.
A battery as shown in FIG. The electromotive voltage was 2.90V. The battery was charged at a constant voltage of 4.1 V for 2 hours, then discharged at a current of 2 mA to 2.5 V, and the capacity was measured to evaluate the electrode performance. Table 1 shows the results.

Example 2 PAS having an average particle size of 0.4 μm and L having an average particle size of 0.4 μm
iCoO ₂ was mixed with PAS / LiCoO ₂ = 40/60 (weight ratio) in a nylon ball mill for 1 hour. Since a nylon ball mill was used, PAS and LiC
There was no significant change in the particle size of oO ₂ . Using this composite, an electrode was manufactured in the same manner as in Example 1, and then a battery was assembled. The electrodes of this battery were evaluated in the same manner as in Example 1. Table 1 shows the results.

Example 3 PAS having an average particle size of 0.7 μm and L having an average particle size of 0.6 μm
iCoO ₂ was mixed in a mortar with PAS / LiCoO ₂ = 40/60 (weight ratio) to obtain a composite. Under these conditions, there was no significant change in the particle size of PAS and LiCoO ₂ . An electrode was manufactured using this composite in the same manner as in Example 1, and then a battery was assembled. The electrodes of this battery were evaluated in the same manner as in Example 1.
Table 1 shows the results.

Comparative Example 1 PAS having an average particle size of 5.2 μm and L having an average particle size of 6.5 μm
iCoO ₂ was mixed in a mortar with PAS / LiCoO ₂ = 40/60 (weight ratio). An electrode was manufactured in the same manner as in Example 1 using the obtained composite, and then a battery was assembled. The electrodes of this battery were evaluated in the same manner as in Example 1. Table 1 shows the results.

Comparative Example 2 PAS having an average particle size of 0.4 μm and L having an average particle size of 6.5 μm
iCoO ₂ was mixed in a mortar with PAS / LiCoO ₂ = 40/60 (weight ratio). An electrode was manufactured in the same manner as in Example 1 using the obtained composite, and then a battery was assembled. The electrodes of this battery were evaluated in the same manner as in Example 1. Table 1 shows the results.

Comparative Example 3 PAS having an average particle size of 0.4 μm and L having an average particle size of 0.6 μm
iCoO ₂ was mixed with PAS / LiCoO ₂ = 40/60 (weight ratio) in a nylon ball mill for 1 hour. An electrode was manufactured in the same manner as in Example 1 using the obtained composite, and then a battery was assembled. The electrodes of this battery were evaluated in the same manner as in Example 1. Table 1 shows the results.

Comparative Example 4 PAS having an average particle size of 5.2 μm and L having an average particle size of 0.6 μm
iCoO ₂ was mixed with PAS / LiCoO ₂ = 40/60 (weight ratio) in a nylon ball mill for 1 hour. An electrode was manufactured in the same manner as in Example 1 using the obtained composite, and then a battery was assembled. The electrodes of this battery were evaluated in the same manner as in Example 1. Table 1 shows the results.

Example 4 In Example 1b, PAS / LiCoO ₂ = 60/4
The electrode was evaluated in the same manner except that it was set to 0 (weight ratio).

Comparative Example 5 An electrode was evaluated in the same manner as in Example 4 except that a mortar was used for mixing. Table 1 summarizes the results of the electrode evaluation in the above Examples and Comparative Examples.

[0028]

[Table 1] ┌──────┬────┬──────┬───────┬─────┐ │ │ PAS │ LiCoO ₂ │ 0.1 μm │ battery │ │ │Average particle size│Average particle size│Pore ratio below│││││ (μm) │ (μm) │ (%) │ (mAh) │ ├──────┼────┼ ──────┼───────┼─────┤ │Example 1a│ 0.5 │ 0.5 │ 78 │ 8.0 │ ├──────┼── │ Example 1b│ 0.4│ 0.5 │ 81 │ 8.0 │ ├────── │ │ Example 2 │ 0.4 │ 0.4 │ 83 │ 8.2 │ ├─── │ │ Example 3 │ 0.7 │ 7.6 | 76 | 7.7 | ７ | Comparative Example 1 | 2│ 6.5 │ 53 │ 6.0 │ ├──────┼────┼──────┼───────┼─────┤ │ │ Comparative Example 2 │ 0.4│ 6.5 │ 74 │ 6.4 │ ├──────┼────┼──────┼───────┼─────┤ │ Comparative Example 3│0.4│0.6│68│7.2│├──────┼────┼──────┼───────┼──── │ │ Comparative Example 4 │ 5.2 │ 0.6 │ 64 │ 6.6 │ ├──────┼────┼──────┼───────┼─ │ │ Example 4 │ 0.4 │ 0.5 │ 83 │ 6.2 │ ├──────┼────┼──────┼────── ─ │ │ Comparative Example 5 │ 0.4 │ 0.5 │ 68 │ 5.1 │ └──────┴────┴──────┴───── ──┴─────┘

It is clear that all the examples in which the average particle size of LiCoO ₂ is 1 μm or less and the proportion of pores of 0.1 μm or less in the electrode is 70% or more have a high battery capacity. In Comparative Example 2, the capacity of the battery was low because the average particle size of LiCoO ₂ was large even though the pore ratio was 74%.

[0030]

According to the present invention, a battery electrode having a large capacity per unit volume can be provided. The battery using the electrode of the present invention can be charged and discharged for a long time, and is easy and economical to manufacture.

[Brief description of the drawings]

FIG. 1 shows a basic configuration of a battery according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Positive electrode 2 Negative electrode 3 Current collector 3 'Current collector 4 Electrolyte 5 Separator 6 Battery case 7 External terminal 7' External terminal

 ────────────────────────────────────────────────── ─── Continuation of the front page Examiner Kazuhiro Itaya (56) References JP-A-2-214762 (JP, A) JP-A-2-230668 (JP, A) JP-A-61-80774 (JP, A) Kaisho 59-3806 (JP, A)

Claims (2)

(57) [Claims] 1. A heat-treated aromatic condensed polymer comprising carbon, hydrogen and oxygen, wherein the polyacene skeleton structure has a hydrogen atom / carbon atom number ratio of 0.05 to 0.5. And the specific surface area by the BET method is 600 m
An electrode for a battery comprising a composite of (b) lithium cobalt oxide as an active material and an insoluble infusible substrate of ² / g or more, wherein (1) the lithium cobalt oxide has an average particle size of 1 μm
And (2) a pore volume having a pore diameter of 0.1 μm or less in the electrode is 70% of the total pore volume.
% Of the battery electrode. 2. The battery electrode according to claim 1, wherein the insoluble and infusible substrate comprises particles having an average particle size of 1 μm or less.