JPH0620679A - Battery electrode - Google Patents

Abstract

PURPOSE:To provide a battery electrode having a large capacity per unit volume, make a battery chargeable and dischargeable over a long period, and facilitate the manufacture by using the electrode. CONSTITUTION:In an electrode for battery using a composite of a polyacene organic polymer semiconductor and lithium cobalt oxide as an active material, the average particle size of lithium cobalt oxide is less than 1mum, and the pore volume less than 0.1 is 70% or more to the whole pore volume.

Description

Detailed Description of the Invention

[0001]

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

[0002]

2. Description of the Related Art In recent years, portable appliances and electronic appliances have been rapidly made into portable cords and cords. Along with this, compact and lightweight batteries with high performance have been demanded as power sources. At present, so-called primary batteries such as dry batteries and secondary batteries such as Ni-Cd batteries and lead batteries are used as power sources for the above devices. However, recently, secondary batteries, which have a short life and need to be replaced, and which can be repeatedly charged, have been widely used. Above all, Ni-Cd batteries are currently the mainstream as a power source for small devices, but in response to the needs for higher capacity, the improvement in performance is approaching the limit. In addition, discussions on global environmental issues have been active in the last few years, and public opinion about the harmfulness of Cd, which is an active material, is increasing. Therefore, there are great expectations for the development of a secondary battery that has higher performance than Ni-Cd batteries and that is reliable and safe.

The present applicant has previously used a secondary battery in which an insoluble and infusible substrate containing a polyacene-based skeleton, which is one of organic semiconductors, is doped with an electron donating substance or an electron accepting substance as an electrode active material. Has been proposed (Japanese Patent Laid-Open No. 60-170163). This battery is a promising secondary battery with high performance, possibility of thinning and weight saving, high oxidation stability of electrode active material, and easy molding. Further, the present applicant has proposed a secondary battery using a composite of the above polyacene-based organic semiconductor and a metal oxide as an active material (Japanese Patent Laid-Open No. 63-31475).
No. 9). This battery has a large capacity without losing the rapid charging property which is a feature of the battery using the polyacene-based organic semiconductor, but the capacity is not yet satisfactory.

[0004]

DISCLOSURE OF INVENTION Problems to be Solved by the Invention The inventors of the present invention have made extensive studies in view of the above problems, and have produced electrodes by various methods. As a result, the average particle size of lithium cobalt oxide (III) and the pore volume of electrodes are It has been found that the capacity per unit volume of this electrode remarkably increases when the electrode is controlled to a specific range, and the object of the present invention is to achieve a large capacity, particularly a large capacity per unit volume. To provide an electrode for a battery.

[0005]

The above-mentioned object is (a) a heat-treated product of an aromatic condensed polymer composed of carbon, hydrogen and oxygen, wherein the atomic ratio of hydrogen atoms / carbon atoms is 0.05.
BE having a polyacene-based skeleton structure of 0.5 to 0.5
A battery electrode comprising, as an active material, a composite of an insoluble infusible substrate having a specific surface area of 600 m ² / g or more as measured by the T method, and (b) lithium cobalt oxide, which comprises (1) The average particle size is 1 μm or less, and (2)
01. This is achieved by an electrode for a battery, characterized in that the pore volume having a pore diameter of μm or less occupies 70% or more of the total pore volume.

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

[Chemical 1] (Where x and y are independently 0.1 or 2)
Can be methylene bisphenols, or hydroxybiphenyls, hydroxynaphthalenes. Of these, phenols, particularly phenol, are suitable for practical use.

As the aromatic condensation polymer in the present invention, a part of the above-mentioned aromatic hydrocarbon compound having a phenolic hydroxyl group is an aromatic hydrocarbon compound having no phenolic hydroxyl group, for example, xylene, toluene, aniline and the like. It is also possible to use a substituted modified aromatic polymer such as a modified aromatic polymer which is a condensation product of phenol, xylene and formaldehyde, or a modified aromatic polymer substituted with melamine or urea. Furan resins are also suitable. Formaldehyde, acetaldehyde, furfural and the like can be used as the aldehyde, and formaldehyde is preferable. The phenol / aldehyde condensate may be a novolac type, a resol type or a complex thereof. A spherical phenolic resin (sphere diameter of about 100 μm or less) commercially available as Bellpearl R (trademark: 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.

Inorganic substances such as zinc chloride, sodium phosphate, sodium hydroxide, potassium hydroxide or potassium sulfide are mixed in the aromatic condensation polymer. As a mixing method, the 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 meltable one such as novolac, it may be mixed under heating. The mixing ratio of the aromatic condensation polymer and the above-mentioned inorganic substance varies depending on the type and shape of the polymer and the inorganic substance to be mixed, but the weight ratio is 1
0/1 to 1/7 is preferable. Next, the mixture is cured into a film, plate, fiber, cloth, granule or a mixture thereof. The cured product thus obtained is then 350 to 800 ° C., preferably 350 to 7 in a non-acidic atmosphere.
It is heated to a temperature of 00 ° C, particularly preferably 400-600 ° C. The non-oxidizing atmosphere in which the heat treatment of the aromatic condensation polymer is performed is, for example, nitrogen, argon, helium, neon, carbon dioxide atmosphere, or vacuum, and nitrogen is preferably used. The non-oxidizing atmosphere may be stationary or flowing. By thoroughly washing the obtained heat-treated body with water, dilute hydrochloric acid or the like, the inorganic salt contained in the heat-treated body can be removed, and then, by drying this, PAS having a large specific surface area can be obtained.

Such a PAS used in the present invention has a hydrogen atom / carbon atom atomic 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 position of the main peak is 20.
It exists between 5 and 23.5 °, and in addition to this main peak, there is another broad peak between 41 and 46 °. That is, it is understood that the PAS is a polyacene-based benzene polycyclic structure uniformly and moderately developed among polyacene-based molecules. If the H / C ratio exceeds 0.5, the charge / discharge charge efficiency of the secondary battery using the composite of PAS and lithium cobalt oxide as an electrode becomes poor. On the other hand, if this value is less than 0.05, the battery capacity 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, it is necessary to increase the charging voltage in the battery using the battery electrode of the present invention, so that the energy efficiency is lowered and the electrolytic solution is deteriorated.

In the present invention, the PAS is 6 as described above.
Since it has a high specific surface area of 00 m ² / g or more, sufficient performance as an active material, that is, the capacity of PAS to be used can be sufficiently derived regardless of the particle size. However, if the PAS particle size is too large, the PAS
Since it becomes difficult to disperse lithium cobalt oxide, which is likely to be secondary aggregated, in the matrix, that is, between PAS particles,
Finally, it is desirable that the particle size is 1 μm or less.

In the electrode of the present invention, the above-mentioned LiCoO 2 is used.
The average particle size of ₂ needs to be 1 μm or less finally, that is, when it becomes an electrode. This is because PAS having a large surface area as described above can sufficiently bring out its capacity regardless of the particle size, whereas LiCoO ₂ can sufficiently bring out its capacity if the particle size is too large. This is because it will be 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 use of the electrode containing them, but is 90/10 to 10/90 (weight ratio), particularly 70/3.
It is preferably 0 to 30/70. Especially LiCoO
_{If 2} is increased too much, the rapid charging property, 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 crushing and mixing and, if necessary, a conductive agent and a binder are added to mold. At this time, the form of PAS and LiCoO ₂ may be a form in which powder, short fibers, etc. can be easily mixed, but the powder is practical. The conductive agent, binder, etc. used are not particularly limited in the present invention, and may be appropriately selected and used from those generally used for battery electrodes. P
AS and LiCoO ₂ may be individually pulverized to a predetermined particle size in advance and then mixed, or PAS and LiCoO ₂ may be pulverized and mixed simultaneously.

The crushing method is not particularly limited, but it is preferable to use a fine crusher represented by a ball mill such as a pot mill or a vibration mill. When a fine PAS and LiCoO ₂ having a small particle size are mixed to form an electrode, it is necessary to control the ratio of pores to be described later.
Difficult due to causes such as secondary aggregation of O ₂ (apparent particle size increase). Therefore, in order to disperse LiCoO ₂ uniformly in the matrix made by PAS, it is necessary to use PAS and Li
A method such as crushing and mixing CoO ₂ at the same time is desirable.
The molding method is not particularly limited, and a conventional molding method used for powder, such as a pressure molding method, can be used.

Lithium cobalt oxide can be easily obtained by a known method. As an example, for example, lithium carbonate (Li ₂ Co ₃ ) and cobalt carbonate (CoCO ₃ )
And 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 depending on its synthesis method and charge / discharge in the battery system. The lithium cobalt oxide (hereinafter abbreviated as LiCoO ₂ ) in the present invention is not particularly limited in the value of x.

In the battery electrode of the present invention, extremely fine LiCoO ₂ is homogeneously dispersed in the PAS matrix, and many electrodes have a small pore diameter.
A battery using this has a significantly large capacity and can be rapidly charged. The present invention will be specifically described below 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 It was poured into a mold of 10 cm × 10 cm × 1 cm, covered with a glass plate, and heated at 100 ° C. for 1 hour to be hardened while suppressing evaporation of water. This cured product was placed in a silicon knit electric furnace, heated in a nitrogen stream at a rate of 40 ° C./hour to 500 ° C., and heat treated.
Next, this 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
I got AS. The specific surface area of this PAS by the BET method is 2
It was an extremely large value of 000 m ² / g. In addition, elemental analysis revealed that the atomic ratio of hydrogen atoms / carbon atoms was 0.23. The PAS thus obtained was ground in a nylon ball mill for 10 minutes, 24 hours, and 48 hours with different grinding times, and the average particle size was 5.2.
PAS powders of μm, 0.7 μm, and 0.4 μm were obtained. The average particle size of the PAS powder was determined by electron microscopy (“powder”, edited by Teruichiro Kubo et al., Ed. 2nd edition of Showa 54, 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. In any case, LiCoO
_{The two} particles were secondarily aggregated, but they were measured by the size of the primary particles.

Example 2 PAS having an average particle size of 5.2 μm and L having an average particle size of 6.5 μm
iCoO ₂ was put into an alumina ball mill with PAS / LiCoO ₂ = 40/60 (weight ratio) and pulverized for 24 hours (Example 2a) and 48 hours (Example 2b). When the obtained composite of PAS and LiCoO ₂ was observed with an electron microscope, the average particle size of PAS was 0.5 μm and 0.4 μm, respectively. LiCoO ₂ is ground and P
It was difficult to measure the LiCO ₂ particle diameter accurately because the particles were homogeneously mixed with the AS particles, but the average particle diameter was about 0.5 μm in each case.

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 and kneaded, and then formed into a sheet by a roller. And thickness 7
An electrode sheet of 50 μm was obtained. The pore distribution of this electrode sheet was measured by a mercury porosimeter (Poresizer, manufactured by Shimadzu Corporation) (pore volume having a pore diameter of 0.006 μm or more and 0.1 μm or less) / (0.006 μm or more 10
The ratio of the volume of pores having a pore diameter of 0 μm or less) was 78% and 81%, respectively. This electrode sheet was punched out into 15 mmφ to make a positive electrode, and a battery as shown in FIG. 1 was assembled using a glass nonwoven fabric as a 1 M LiClO ₄ propylene carbonate solution separator in a lithium electrolyte as a negative electrode. The electromotive voltage was 2.90V. After charging this battery with a constant voltage of 4.1V for 2 hours, 2
The electrode performance was evaluated by discharging to 2.5 V with a current of mA and measuring the capacity. The results are shown in Table 1.

Example 3 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 nylon ball mill was used, PAS and LiC
There was no significant change in the particle size of oO ₂ . An electrode was produced 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. The results are shown in Table 1.

Example 4 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 with PAS / LiCoO ₂ = 40/60 (weight ratio) in a mortar to obtain a composite. Under these conditions, the particle size of PAS and LiCoO ₂ did not change significantly. 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.
The results are shown in Table 1.

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 using the obtained 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. The results are shown in Table 1.

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 using the obtained 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. The results are shown in Table 1.

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 using the obtained 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. The results are shown in Table 1.

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 using the obtained 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. The results are shown in Table 1.

Example 5 In Example 1b, PAS / LiCoO ₂ = 60/4
The electrodes were evaluated by the same method except that the weight ratio was 0.

Comparative Example 5 The electrodes were evaluated in the same manner as in Example 4, except that the mixing was performed using a mortar. Table 1 collectively shows the results of the electrode evaluation in the above Examples and Comparative Examples.

[0028]

[Table 1]

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

[0030]

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

[Brief description of drawings]

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

[Explanation 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

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Shizukuni Yada 2-6-13 Miyanishi, Harima-cho, Kako-gun, Hyogo Prefecture

Claims (2)

[Claims] 1. A heat-treated product of (a) an aromatic condensed polymer consisting of carbon, hydrogen and oxygen, wherein the atomic number ratio of hydrogen atoms / carbon atoms is 0.05 to 0.5. And has a specific surface area of 600 m according to the BET method.
A battery electrode comprising, as an active material, a composite of an insoluble and infusible substrate of ² / g or more and (b) lithium cobalt oxide, wherein (1) the average particle diameter of the lithium cobalt oxide is 1 μm.
And (2) the pore volume having a pore diameter of 0.1 μm or less in the electrode is 70 with respect to the total pore volume.
% Or more 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.