JP2002025530A - Thin battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a thin battery which is superior in safety by adhering an electrode and a separator with an adhesive resin layer and by finding the optimum filler material contained in the resin layer. SOLUTION: In the thin battery that is equipped with the first and the second electrode, which respectively has active substances and one of which becomes a positive electrode and the other becomes a negative electrode, and with a separator which is between those electrodes and which retains an electrolyte, at least one of the first and the second electrode and the separator are adhered with the adhesive resin layer containing a filler composed of polypropylene.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thin battery, particularly a nonaqueous electrolyte thin battery excellent in safety.

[0002]

2. Description of the Related Art By adhering a positive electrode, a negative electrode and a separator with an adhesive resin layer, even if these electric storage elements are stored not in a fixed container made of a rigid material but in a bag made of a flexible material, a constant electrode spacing can be obtained. (PCT / JP98 / 00152) is known. This has made it possible to make batteries even thinner. Since the adhesive resin layer in the battery described in the above publication is insulative, it is manufactured by adding a filler made of ceramic or the like into it so that it does not block ionic conduction between the electrodes. At the same time, battery characteristics are obtained while maintaining adhesive strength by providing porosity while preventing the adhesive from penetrating into the electrode plate.

[0003]

However, the battery described in the above publication focuses only on the porosity of the adhesive resin layer, and suggests an optimum material as a filler for the adhesive resin layer of a thin battery. Not. Therefore, the object of the present invention is to
It is an object of the present invention to find a suitable filler material unlike the above-mentioned publication and to provide a thin battery having a novel safety mechanism and excellent safety.

[0004]

In order to solve the problem, a thin battery according to the present invention comprises a first electrode and a second electrode each having a positive electrode and the other being a negative electrode, each of which has an active material, and an electrode between the electrodes. In a thin battery including a separator that holds an electrolyte interposed therebetween, at least one of the first and second electrodes and the separator are bonded by an adhesive resin layer containing a filler made of polypropylene. And

[0005] Polypropylene begins to soften at a lower temperature than other organic polymers, but has excellent insulating properties after softening.
Therefore, when the temperature of the battery rises abnormally due to an internal short circuit or a high-temperature environment, the battery is quickly softened, closes the holes of the adhesive resin layer, insulates the electrodes, and suppresses the temperature rise. This point is significantly different from a ceramic filler which does not soften even at high temperatures.

The above-mentioned adhesive resin layer may be present between any of the positive and negative electrodes and the separator. At the time of overcharging, it is considered that the electrolyte and the negative electrode react first to generate heat, and then the electrolyte and the positive electrode react and lead to thermal runaway, so that the reaction between the electrolyte and any of the electrodes is suppressed. This is because if it can be performed, the safety is improved as compared with the case where the adhesive resin layer is not present at all.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The resin used for the above-mentioned adhesive resin layer is usually a thermoplastic resin, for example, a copolymer of polyvinylidene fluoride (PVdF) emulsion-polymerized with hexafluoropropylene, PVdF alone. , Polyethylene oxide (PEO), polyacrylonitrile (PAN) and the like. The average particle size of the filler is preferably in the range of 0.5 to 5 μm.

[0008]

EXAMPLES - as Example 1 storage element, lithium cobalt complex oxide on both sides of the current collector made of aluminum foil LiCoO ₂ 90 wt%
A positive electrode plate having an active material layer formed thereon, a negative electrode plate having a 90% by weight carbon active material layer formed on both surfaces of a current collector made of copper foil, and an air permeability (25 ° C.) 20 made of a polyethylene sheet.
A 0 second / 100 cc separator was prepared. The weight of each of the positive electrode active material layer and the negative electrode active material layer on one surface of the current collector was 1 g / 100 cm ² , and the porosity was 35%.

Then, a mixture of PVdF and a filler having an average particle diameter of 1.5 μm described below is applied to both surfaces of the negative electrode plate to form an adhesive resin layer, and the separator is attached to almost the entire surface of the negative electrode plate to form a separator / separator. A laminate composed of the negative electrode plate / separator was produced. In the adhesive resin layer, PVdF is microscopically adhered to the periphery of the solid filler, and porosity is obtained by the gap between the solid fillers, and at the same time, the adhesive property is provided by the PVdF.

[0010] Separately, an adhesive resin layer is formed on both sides of the positive electrode plate and kept in a standby state, and a positive electrode plate with an adhesive resin layer is laminated on the outside of the laminate to form a metal core together with the laminate. It was spirally wound around the circumference. After the winding, the core was removed by axially pulling or pushing the core from the electricity storage element.

Thereafter, the storage element was housed in a bag-shaped battery container made of a metal resin laminated film, an electrolyte was injected, and the battery was sealed to complete a thin battery. The injected electrolyte was mixed with a 1: 1 mixed solvent of ethylene carbonate (EC) and diethyl carbonate (DEC) at 1M.
This is a solution in which a concentration of LiPF ₆ is dissolved.

This battery was charged at a constant current and a constant voltage of 1 A and 4.1 V for 2 hours, and then the internal resistance was measured in a discharged state. Separately, a 25 μm thick film of the same material as the filler contained in the adhesive resin layer was subjected to differential scanning calorimetry (D
SC) The softening start temperature was measured in advance by using an apparatus. The standard material for DSC was polystyrene. And
The battery was kept at a temperature 20 ° C. higher than the softening start temperature, and the internal resistance was measured after 5 seconds. Table 1 shows the results.

[0013]

[Table 1] As can be seen in Table 1, the filler made of polypropylene begins to soften at a temperature lower than the temperature at which thermal runaway of the battery is expected to occur. Moreover, the internal resistance after softening is rapidly increased to insulate the electrodes. Therefore, a thin battery using this filler is safe.

Example 2 In Example 1, each electrode was bonded to the separator with an adhesive resin layer containing various fillers interposed between the positive electrode and the separator and between the negative electrode and the separator. The battery No. of Example 1 An overcharge test of charging 1 to 1 V at 1 A was performed, and the state of the battery was observed thereafter.

Battery No. 1 except that no adhesive resin layer was present between the negative electrode and the separator. Batteries of the same type and quality as
o. Battery No. 5) except that no adhesive resin layer was present between the positive electrode and the separator. Batteries of the same shape and quality as No. 1 (referred to as No. 6), except that an alumina filler was used in place of the polypropylene filler. A similar overcharge test was performed on a battery of the same shape and the same quality as No. 1 (referred to as No. 7). Table 2 shows the observation results.

[0016]

[Table 2] From Table 2, between any of the positive and negative electrodes and the separator,
It is clear that the safety is improved by interposing the adhesive resin layer containing the PP filler.

[0017]

As described above, according to the thin battery of the present invention, not only can the electrode interval be kept constant even when the storage element is housed in a bag-like container, and the safety at high temperatures is excellent. It is useful as a power source for small electronic devices such as mobile phones.

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Claims (1)

[Claims] 1. A thin battery comprising a positive electrode and a negative electrode, each having a first electrode and a second electrode each having an active material, and a separator interposed between the electrodes to hold an electrolyte. A thin battery, wherein at least one of the second electrodes and the separator are bonded with an adhesive resin layer containing a filler made of polypropylene.