JPS6196663A - Thin battery - Google Patents

Abstract

PURPOSE:To obtain a thin battery having good active material utilization factor by adding powder material having an apparent density of 1.2g/cm<3>, which is insoluble to organic solvent, to a negative mix. CONSTITUTION:Powder material is added to a negative mix 1. The amount to be added is decided by the kind and particle size of negative active material and the amount of binder, and normally the amount of 25% or less is preferable. Metal oxide, organic polymer, or carbon black having an apparent density of 1.2g/cm<3> can be used as the powder material. By adding the powder material, since the surface of the negative active material is exposed from organic polymer binder, the utilization factor of the negative active material is increased.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Field of Application> The present invention relates to a thin battery, and particularly to the use of a negative electrode mixture.

<Prior art> In recent years, as watches, calculators, cameras, toys, etc. have become more electronic, batteries have become smaller and thinner, and button-shaped batteries and flat batteries have become commercially available. .

Among them, thin batteries wrapped in plastic sheets are more flexible than metal AS button batteries, and have various advantages such as larger area and ease of manufacturing into arbitrary shapes. This is not only due to the need for miniaturization;
There are also great expectations for its integrated use with thin products such as displays, printed matter, and photographic film.

Conventionally, the negative electrode in batteries in this building has been prepared by combining negative active material powder with water-based polysaccharides such as etherified starch and hydroxyethyl cellulose, water such as polyacrylic modified sodium, polyvinyl alcohol, etc., fertile polymers, acrylic acid emulsions, acetic acid emulsions, etc. These emulsion resins were used as a binder and were applied to a negative electrode current collector by screen printing or sifting and then dried.

However, when a water-soluble polymer is used as a binder, the binder swells and dissolves in the electrolyte, and its adhesion with the current collector deteriorates over time, resulting in a gradual increase in battery internal resistance.

Further, when an emulsion resin is used as a binder, the adhesion between the negative electrode active material particles and the current collector is good, but the adhesion between the negative electrode active material particles is poor.

Furthermore, when the negative electrode active material powder is made into an ink using the above-mentioned various binders, since water is used as a solvent for the ink, the negative electrode active material is oxidized during the process of applying and drying the negative electrode active material, resulting in a decrease in battery capacity. It became.

'Furthermore, when applying oil to the negative electrode current collector by a printing method such as screen printing, the ink tends to aggregate, resulting in extremely poor printability.

Therefore, the present inventor created an electrode for a negative electrode by forming an ink from a negative electrode active material powder using a water-insoluble organic polymer binder and an organic solvent in which the binder can be commonly understood, and applying the ink to a negative electrode current collector and drying it.

However, if an ink is formed using an organic polymer binder that is insoluble in water and an organic solvent that can dissolve the binder, oxidation of the negative electrode active material during the process of applying and drying the negative electrode active material is extremely reduced, and furthermore, the negative electrode is created. When screen printing is performed, the printability is good, but the utilization rate of the negative electrode active material is extremely poor (which has become a practical problem).

<Problems to be Solved by the Invention> The present invention has been made in response to the above-mentioned current situation, and has a bulk density of 1.2. ! By using a negative electrode in which a powdery substance insoluble in the organic bath agent of i'/cril or less is added to the negative electrode mixture, a thin battery with an extremely high utilization rate of the active material is provided.

〈Means for solving problems〉 The present invention will be explained in detail below with reference to the drawings.

FIG. 1 is an explanatory diagram showing a cross section of a thin battery negative electrode in this example. According to the present invention, a powdery substance is added to the negative electrode mixture (11).The amount of the powdery substance added is determined by the type and particle size of the negative electrode active material and the amount of binder, but it is preferably 25% or less. Preferably, even if it is added in an amount of 25% or more, no further improvement in the utilization rate will be observed.

Furthermore, the type of powdered additive substance has a bulk density of 1.2M.
9/d or less, for example, ultrafine anhydrous alumina (Nippon Aerosil (mAERO8f La
luminarn oxide6 C) Ultrafine particulate anhydrous titanium oxide (Japan Aerosil @AERO8ILtita
metal oxides such as nium oxide P-25).

Organic polymer fine powders such as E11 ethylene fine particles and polytetrafluoroethylene fine particles, or carbon blacks such as acetylene black, graphite, and Ketjen black are effective.

This is because when the powder material is not added, the utilization rate of the covering active material is low because the organic polymer binder is the negative electrode active material particles. However, this is because the addition of the powder material makes the saturated polymer binder extending over the surface of the negative electrode active material incomplete, thereby improving the utilization rate of the active material. Furthermore, when the powder material has microscopic through-holes, the battery reaction proceeds through the through-holes, improving the active material utilization rate.

In particular, by adding a conductive agent such as carbon black such as acetylene black or Ketjen black to the negative electrode mixture, the utilization rate of the active material is improved and the electronic conductivity between the negative electrode active material and the current collector is improved. Therefore, the internal resistance of the battery becomes extremely low.

<Example> The negative electrode mixture ink composition used in this example is shown below.

Negative electrode active material powder Zinc powder 100 (
Part by weight) Organic polymer binder ethyl cellulose
1 (η) Powdered additive TiO2+C^03
．． 1 to 10 (tt) Organic solvent: butyl cellosolve 20 (//) The above composition was kneaded to prepare a negative electrode mixture ink.

The negative electrode current collector (4) was printed with a thickness of 20 μm by screen printing to obtain a negative electrode 1.1) as shown in FIG.

The negative electrode current collector (4) is made of a conductive plastic film (2) made by kneading a conductive agent with brass foil or plastic resin. A current collector was used in which a conductive film (2) and an AA foil (3) were laminated with ~40 wt% crosstalk.

In the above composition, 200 mesh pass zinc powder was used as the negative electrode active material powder. In addition, as an organic solvent, it is electrochemically stable to zinc, which is the negative electrode active material, and chemically stable to the current collector. Various polymer binders can be used depending on the type of negative electrode active material and the type of organic solvent. Ethyl i that can be dissolved in the solvent butyl cellosolve and has a viscosity suitable for screen printing.
cellulose? Using.

The powdered additive substance may be one having a bulk density of 1.297 or less, but fine powder titanium oxide (Japan Aerosil @ KEROSIL Tituniumo2<ide P-25) with a bulk density of 0.08 g /c
r! , Addition amount to zinc powder: 10wt% Graphite (LON2A LTD, KS-1s) Bulk density: 0.
Amount added to 1g/cn zinc powder: 5wt% Acetylene plastic (Electrochemical 1.Kiku, Denka Black) Bulk density: 0,
Addition amount to os2i/crd zinc powder: 1.0 w
Six kinds of t% were used.

Table 1 below shows the utilization of the three types of negative electrodes constructed in this manner and the thin batteries having the same composition except that no additives were added.

Table 1 As is clear from Table 1, the battery of the present invention containing powdered additives has a significantly improved battery utilization rate compared to conventional products (without the addition of additives). '-I see. In particular, when only i wt% of acetylene black is added to the negative electrode active material, the utilization rate reaches nearly ioo%.

Next, an example of the structure of a thin battery using the negative electrode of the present invention will be explained with reference to FIG. A negative electrode mixture (1) is applied onto a negative electrode current collector (4) consisting of a conductive plastic film (2) laminated with aluminum foil (3) on one side. A positive electrode mixture (5) consisting of manganese dioxide, acetylene black and an emulsion binder is coated on a positive electrode current collector (8) having the same structure as the negative electrode current collector, and 2M lead perchlorate It is sealed to the negative electrode current collector side via a separator (3) made of a polyester nonwoven fabric impregnated with a water-soluble resin. Further, a sealing frame (7) is provided at the shoulder edge of the battery and is sealed with the positive electrode current collector (8) and the negative electrode current collector (4) by thermal fusion.

<Effects of the Invention> As described above, in a thin battery having a negative electrode formed by forming a negative electrode mixture consisting of a powdered negative electrode active material and an organic polymer binder into an ink with an organic solvent, applying it to a negative electrode current collector, and then drying it. , the density of the negative electrode mixture is 1.2 g/(ffl
By adding an insoluble powder substance to the following several solvents, a thin battery with a dramatically improved battery utilization rate can be produced, which is extremely valuable in terms of industrial value.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of a negative electrode obtained according to an example of the present invention;
Figure 2 is an explanatory diagram showing the cross section of a thin battery, (1)...
Negative electrode mixture (2)...Conductive plastic film f3J...Aluminum foil (4)...
Negative electrode current collector (5)... Positive electrode mixture (61... Separator (force)... Seal frame (8)... Positive electrode current collector

Claims (1)

[Scope of Claims] 1) A negative electrode mixture consisting of a powdered negative electrode active material and an organic polymer binder is made into an ink using an organic solvent, and the inked negative electrode mixture is applied onto a negative electrode current collector and then dried. 1. A thin battery having a negative electrode comprising: a powder additive material insoluble in the organic solvent having a bulk density of 1.2 g/cm^3 or less is added to the negative electrode mixture. 2) The amount of the powder additive material is 25% by weight based on the negative electrode mixture.
The thin battery according to claim 1, characterized in that the following is added: 3) The thin battery according to claims 1 and 2, wherein the powder additive material is carbon black.