JPH09289022A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce costs, decrease adverse effects on human body in a manufacturing process, and enhance stickiness by containing a water soluble polymer in an electrode mixture of a positive electrode or a negative electrode. SOLUTION: When an electrode sheet is manufactured by forming a thin mixture layer on both surfaces of a current collector of a metal foil (for example, an aluminum foil), a water soluble polymer is contained in an electrode mix of a positive electrode and/or a negative electrode. The binding capability to the current collector is enhanced, and since the solvent is water, the cost is reduced and the adverse effect on human body in a manufacturing process is decreased. Since a drying process is made at a relatively low temperature, heat damages to the materials constituting a mixture and a sheet electrode is minimized. As a result, energy density is enhanced, and the cycle life is lengthened.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-aqueous electrolyte secondary battery using a lithium ion conductive non-aqueous electrolyte as a positive electrode active material and a negative electrode active material which are capable of inserting and extracting lithium, and more particularly to a non-aqueous electrolyte secondary battery. The present invention relates to an electrode structure having high energy density, excellent high rate charge / discharge characteristics, and good long-term cycle characteristics.

[0002]

2. Description of the Related Art A non-aqueous electrolyte battery using lithium as a negative electrode active material has advantages such as high voltage, high energy density, small self-discharge, and excellent long-term reliability. It is already widely used as a power source for cameras and the like. With the recent remarkable development of portable electronic devices, communication devices, etc., a wide variety of devices that require a large current output for a battery as a power source have appeared,
From the viewpoints of economy, reduction in size and weight of equipment, and consideration for the environment, there is a strong demand for rechargeable / dischargeable secondary batteries having high energy density.

Therefore, as the negative electrode active material, a material represented by a carbon material capable of inserting and extracting lithium ions is used.
Research and development for promoting conversion of the non-aqueous electrolyte battery having high energy density into a secondary battery have been actively carried out, and it has been partially put into practical use as a “lithium ion secondary battery”. Energy density, charge / discharge cycle The service life and reliability are still insufficient.

The non-aqueous electrolyte used in the "lithium ion secondary battery" has a low ionic conductivity as compared with an aqueous electrolytic solution used in nickel-cadmium batteries or nickel-hydrogen batteries. For this reason, in order to obtain a high energy density, there is a structure in which an electrode sheet provided with a thin mixture layer on both sides of a current collector such as a metal foil is spirally wound in multiple layers to enlarge the battery reaction surface. It is common.

The mixture contains an active material, and if necessary, a conductive auxiliary agent and a binder. The properties required for a binder are to securely bind and hold the components that make up the mixture, to bind the mixture to the current collector, and to be chemically stable to the electrolyte (electrolyte) at a low cost. There are some things. In particular, when the above conditions are not satisfied, high rate performance and deterioration of battery performance such as cycle characteristics due to repeated charging and discharging are caused.

Conventionally, as a binder of a mixture used for a non-aqueous electrolyte secondary battery, a dispersion of polytetrafluoroethylene (PTFE) or a fluororesin such as polyvinylidene fluoride (PVDF) is used. It has been used a lot. Fluorine resin is stable to electrolyte,
It also has excellent heat resistance.

Among the fluororesins, PVDF, which is the only solution that can be used as a solution, has a good coating property and is often used in the process of manufacturing an electrode sheet in which a mixture slurry is coated on a current collector. (For example, JP-A-4-18
4872, JP-A-5-290854, JP-A6-1
11823, JP-A-6-349482).

[0008]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention As described above, PTFE dispersion and PV, which have been widely used as a binder,
DF and the like are good binders for binding the constituent substances in the mixture, but there is a problem that they are not optimal for binding to a current collector such as a metal foil. In addition, the fact that the fluororesin is expensive is also a problem in terms of battery manufacturing cost. In addition, N-methyl-2-pyrrolidone (NMP) and dimethylformamide (DMF), which are PVDF solvents, have the following problems.

Since it is an organic solvent which is expensive and increases the cost of the product, it is a high-boiling-point solvent which may affect the human body in the manufacturing process. When it is dried at a high temperature, PVDF is thermally decomposed and the binding property is deteriorated.

[0010]

In order to solve the above problems, the present invention provides a non-aqueous electrolyte composed of at least a positive electrode and a negative electrode capable of absorbing and releasing lithium ions, and a lithium ion conductive non-aqueous electrolyte. In the secondary battery, the water-soluble polymer is contained in the electrode mixture of the positive electrode and / or the negative electrode.

Therefore, the binding property to the current collector is good, and since the solvent is water, it is possible to solve the problems such as the above cost and the influence on the human body in the manufacturing process.
Further, since it can be dried at a relatively low temperature, it is possible to minimize thermal damage to the mixture and the material forming the sheet electrode.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION As the water-soluble polymer used in the present invention, various polymers such as natural product type polymers and synthetic resins can be used. For example, as a natural product type, starch type starch, modified starch, dextrin, cellulose type methyl cellulose, ethyl cellulose, hydroxyethyl cellulose, carboxymethyl cellulose (CMC), rubber type gum arabic, tragacanth gum, karaya gum, locust bean gum, guar gum, etc. can give. In the synthetic resin system, polyvinyl alcohol, polyacrylamide, polyethylene oxide, polyvinylpyrrolidone, vinyl acetate copolymer, acrylic acid polymer and the like can be used.

Among them, acrylic acid polymers, CMC and the like are preferable because they are excellent in binding property of metals such as aluminum and copper to current collectors. Further, it is effective to use a cross-linked acrylic acid polymer in order to enhance the binding property. Particularly, the content of carboxyl group in the cross-linked acrylic acid polymer is 50 to 7
It is preferably 0%.

These water-soluble polymers may be used alone or in a sufficient manner, but two or more kinds may be mixed and used. The composition of the water-soluble polymer of the present invention in the mixture should be limited to the minimum amount capable of maintaining the binding property of the mixture and the binding property to the current collector. If it is excessive, problems such as a decrease in battery capacity and an increase in impedance occur. If it is too small, the binding property cannot be maintained. In view of these, the water-soluble polymer composition in the mixture is 0.1% (w / w) or more and 20% (w / w).
w) The following is good.

The positive electrode active material used in the present invention includes:
Metal chalcogenides such as TiS ₂ , MoS ₂ and NbSe ₃ , as well as MnO ₂ and M
Metal oxides such as oO ₃ , V ₂ O ₅ , Li _x CoO ₂ , Li _x NiO ₂ and Li _x Mn ₂ O ₄ , conductive polymers such as polyaniline, polypyrrole, polyparaphenylene and polyacene, and graphite intercalation compounds Various substances capable of occluding and releasing lithium ions and / or anions can be used.

In particular, the electrode potential for metal lithium such as metal chalcogenide and metal oxide is 2 V or more, more preferably V ₂ O ₅ , MnO ₂ , Li _x CoO ₂ , Li _x NiO ₂ , and Li _x Mn _2. O ₄
Combining a (noble) active material having a high potential of 3 V to 4 V or more and a negative electrode using a (base) active material having a low potential of 1 V or less with respect to metallic lithium as described later. Thereby, a secondary battery having a high energy density can be obtained, which is more preferable.

[0017] As the negative electrode active material, metallic lithium, carbonaceous materials, LixSi, metal oxides, nitrides, silicides, _{carbides, Li x M y Si 1-} y M y O z (0 <x ≦ 6,0 ≦ y <1,0 <z <2, M is a metal other than alkali metal or a metal other than silicon) and various substances capable of occluding and releasing lithium ions and / or anions such as silicon oxide Can be used.

In particular, Li _x M _y Si _1-y M _y O _z (0 <x ≦ 6,0 ≦ y <
Silicon oxides such as 1,0 <z <2 and M is a metal except alkali metal or a metal other than silicon) have a large charge / discharge capacity in the region where the electrode potential with respect to metallic lithium is 1 V or less. Therefore, by combining with the positive electrode using the positive electrode active material, a secondary battery with high voltage and high energy density can be obtained, which is more preferable.

As the electrolyte, γ-butyrolactone, propylene carbonate, ethylene carbonate (E
C), butylene carbonate, dimethyl carbonate,
Diethyl carbonate, methyl formate, 1,2-
LiClO ₄ , LiP as a supporting electrolyte in a single or mixed nonaqueous organic solvent such as dimethoxyethane, tetrahydrofuran, dioxolan, dimethylformamide, etc.
An organic non-aqueous electrolyte in which lithium ion dissociable salts such as F ₆ , LiBF ₄ , LiCF ₃ SO ₃ , LiC (SO ₂ CF ₃ ) ₃ and LiN (SO ₂ CF ₃ ) ₂ are dissolved,
It is preferable to use a polymer solid electrolyte in which the lithium salt is solid-solved in a polymer such as polyethylene oxide or a crosslinked polyphosphazene, or a lithium ion conductive non-aqueous electrolyte such as an inorganic solid electrolyte such as Li ₃ N or LiI. it can.

[0020] In particular, Li _x M _y S described above as a negative electrode active material
i _1-y M _y O _z (0 <x ≦ 6,0 ≦ y <1,0 <z <2, M is a metal except alkali metal or a metal except silicon) When used, it is preferable to use a mixed solvent of an alkyl carbonate represented by Chemical formula 2 such as dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate and EC. EC and R1R2
More preferably, the volume mixing ratio of the type alkyl carbonate is in the range of about 3: 1 to about 1: 3.

[0021]

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The positive electrode current collector may be any substance that is stable with respect to the positive electrode active material potential, such as aluminum or its alloy, titanium or its alloy, or stainless. Examples of the form include foil, expanded metal, and the like.
The negative electrode current collector may be any material that is stable with respect to the potential of the negative electrode active material, such as copper or its alloy, nickel or its alloy, or stainless steel. Examples of the form include foil, expanded metal, and the like.

As a method for producing a sheet electrode, a mixture slurry prepared by mixing and dispersing a mixture constituent substance such as an active material in a solution of the water-soluble polymer of the present invention is prepared, and this mixture slurry is placed on a current collector. There is a method of coating and drying, and if necessary, rolling and fixing with a roll press. In addition, various methods such as a method in which the mixture layer formed into a sheet shape is pressure-bonded to the current collector or bonded to the current collector can be used. At this time, a conductive layer containing a carbon material or metal powder as a conductive filler may be provided between the current collector and the mixture layer. The electronic conductivity between the current collector and the mixture layer is improved, and an even higher performance battery is realized.

As a method for producing a coin-type or button-type electrode, a wet method in which a mixture slurry is prepared and dried in the same manner as described above, and then crushed and granulated to form a predetermined size,
It can be produced by various methods such as a dry method in which the mixture component material containing the water-soluble polymer of the present invention is uniformly mixed and then molded.

[0025]

EXAMPLES An example of the present invention will be described below with reference to examples. The present invention is not limited to this. As shown below, a prismatic battery was prepared and the charge / discharge characteristics were measured.

Example 1 LiB _0.03 Co as a positive electrode active material
85 parts by weight of a composite oxide of lithium, cobalt, and boron represented by _0.97 O ₂ and 8 parts by weight of graphite as a conductive agent were crushed and mixed in a mortar, and 7 parts by weight of PVDF as a binder were 51.3 parts by weight of NMP. Mixed and dispersed in a solution dissolved in
A positive electrode mixture slurry was prepared. This positive electrode mixture slurry is applied and dried on both sides of an aluminum foil having a thickness of 20 μm so that the mixture density after drying and rolling is 3.3 g / cm ³ and the mixture thickness on one side is 60 μm. It rolled using the press and produced the positive electrode sheet. The positive electrode sheet thus prepared is
A positive electrode plate was obtained by cutting into a size of 7.5 mm × 39 mm.

A negative electrode was prepared in the same manner. 45 parts by weight of commercially available silicon monoxide (SiO) as a negative electrode active material and 40 parts by weight of graphite as a conductive agent were pulverized and mixed in a mortar, and 15 parts by weight of a cross-linking acrylic acid polymer as a binder was added to 300 parts by weight of water. Was mixed and dispersed in a solution dissolved in a part to prepare a negative electrode mixture slurry. Thickness of this negative electrode mixture slurry is 1
Both sides of 0 μm copper foil have a mixture density of 1. after drying and rolling.
It was coated at 6 g / cm ^{3 so} that the mixture thickness on one side was 27 μm, dried, and then rolled using a roll press. The negative electrode sheet thus manufactured was cut into a size of 27.5 × 39 mm to obtain a negative electrode plate.

Fifteen positive electrode plates and sixteen negative electrode plates are alternately stacked with a separator, which is a lithium ion permeable porous film, interposed therebetween (the outermost negative electrode is a negative electrode coated with a mixture on only one side). The battery was inserted into the battery case, the lead was taken, the electrolytic solution was injected, and the battery was sealed to manufacture a prismatic battery.

The battery thus produced was subjected to three charge / discharge cycles under the conditions of a constant current of 20 mA, an end-of-charge voltage of 4.2 V and an end-of-discharge voltage of 2.7 V. After this, the charging voltage is 4.2V, the maximum charging current is 400mA, and the battery is charged at a constant current and constant voltage for 2.5 hours, and the discharging current is 400mA and 600mA.
3 at each current value under the condition of discharge constant voltage of 2.7V with constant current of
The charge and discharge characteristics were measured cycle by cycle. This discharge current 4
Discharge capacity 600mA for discharge capacity of 00mA
The discharge capacity ratio in the case of is shown in FIG. Further, the charging voltage is 4.2V, the maximum charging current is 400mA, and the constant current is constant voltage.
After charging for 5 hours, a charging / discharging cycle was performed under the conditions of a discharge current of 400 mA and a discharge end voltage of 2.7V. The cycle characteristics of this charge / discharge cycle are shown in FIG.

(Example 2) In Example 1, 45 parts by weight of commercially available silicon monoxide (SiO) as a negative electrode active material,
40 parts by weight of graphite as a conductive agent was crushed and mixed in a mortar, and 15 parts by weight of PVDF as a binder was used as NMP110.
A prismatic battery was prepared in the same manner except that a negative electrode mixture slurry was prepared by mixing and dispersing it in a solution dissolved in parts by weight, and the same charge and discharge test was conducted. As a result, the discharge current is 600 m with respect to the discharge capacity when the discharge current is 400 mA.
The discharge capacity ratio in the case of A is shown in FIG. 1, and the cycle characteristics are shown in FIG.

As is apparent from FIGS. 1 and 2, the use of the water-soluble polymer of the present invention as a binder reduced the capacity decrease during high rate discharge. It is considered that this is because the impedance decreased due to the improvement in the adhesion between the mixture and the adhesion between the mixture and the current collector. Further, since the cycle characteristics are remarkably improved, by using the water-soluble polymer of the present invention as a binder, the adhesiveness between the mixture and the mixture and the current collector can be maintained even after the charge / discharge cycle. It is a result that reflects what can be done.

Needless to say, the performance of the battery is further improved by containing the water-soluble polymer as the binder of the positive electrode mixture.

[0033]

INDUSTRIAL APPLICABILITY As described above, the present invention provides a positive electrode and / or negative electrode in a non-aqueous electrolyte secondary battery which is composed of at least a positive electrode and a negative electrode capable of absorbing and desorbing lithium ions, and a lithium ion conductive non-aqueous electrolyte. Alternatively, the electrode mixture of the negative electrode contains a water-soluble polymer to reduce the battery impedance and enable high-rate discharge. Adhesion between the mixture after a charge / discharge cycle or between the mixture and the current collector Property can be maintained and battery deterioration can be significantly suppressed.

The drying temperature of the mixture slurry can be lowered, and thermal damage to the active material and the like can be suppressed. Since the solvent is water, it has little effect on the human body in the battery manufacturing process. And the like. As a result, a high-quality secondary battery having high energy density and good cycle characteristics can be obtained.

[Brief description of drawings]

FIG. 1 is an explanatory diagram comparing the ratio of the discharge capacity at a discharge current of 600 mA to the discharge capacity at a discharge current of 400 mA of the prismatic batteries manufactured in Example 1 and Example 2 according to the present invention. .

FIG. 2 is an explanatory diagram comparing the charge / discharge cycle characteristics of the prismatic batteries manufactured in Example 1 and Example 2 carried out in the present invention.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁶ Identification number Reference number within the agency FI Technical display location H01M 10/40 H01M 10/40 Z (72) Inventor Hideo Sakamoto 1-chome, Nakase, Mihama-ku, Chiba-shi 8 Seiko Electronics Co., Ltd. (72) Inventor Shinichi Takasugi 1-8 Nakase, Mihama-ku, Chiba, Chiba Seiko Electronics Co., Ltd. (72) Inventor, Tsuneaki Tamachi Nakase, Mihama-ku, Chiba 1-8, Seiko Electronics Co., Ltd.

Claims (5)

[Claims] 1. A non-aqueous electrolyte secondary battery comprising a positive electrode and a negative electrode capable of occluding and releasing lithium ions, and a lithium ion conductive non-aqueous electrolyte, wherein a water-soluble polymer is contained in an electrode mixture of the positive electrode or the negative electrode. Non-aqueous electrolyte secondary battery. 2. The non-aqueous electrolyte secondary battery according to claim 1, wherein the water-soluble polymer is a polymer selected from acrylic acid polymers, polyvinyl alcohol, and carboxymethyl cellulose. 3. The non-aqueous electrolyte secondary battery according to claim 1, wherein the positive electrode active material of the positive electrode mixture has a composite transition metal oxide containing lithium. 4. The non-aqueous electrolyte secondary battery according to claim 1, wherein the negative electrode active material of the negative electrode mixture contains a carbonaceous material or an oxide of silicon. 5. The non-aqueous electrolyte secondary battery according to claim 1, wherein the non-aqueous electrolyte contains propylene carbonate or ethylene carbonate and an alkyl carbonate represented by Chemical formula 1. Embedded image