JPH1064546A - Electrode and secondary battery using it - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrode for a secondary battery capable of ensuring safety in a nail piercing test by containing lignin and/or a lignin derivative in the electrode. SOLUTION: Lignin and/or a lignin derivative of 0.1wt% or more but 30wt% or less are/is contained in an electrode for a battery. As the lignin and/or lignin derivative, alkali lignin, lignin sulfonic acid and sulfonate, thiolignin, chlorolignin. nitrolignin, and Bjrkman lignin are listed, and they are used alone or as a mixture of two or more. By using the electrode as a positive electrode or negative electrode, a secondary battery capable of ensuring safety in a nail piercing test is obtained.

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 a secondary battery using the electrode.

[0002]

2. Description of the Related Art In recent years, with the spread of portable devices such as video cameras, mobile phones, and notebook computers, demand for small, lightweight, high-capacity secondary batteries has been increasing. Many of the secondary batteries currently used are nickel-cadmium batteries using an alkaline electrolyte, but it is difficult to increase the energy density because the average battery voltage is as low as 1.2V. Therefore, research on high energy secondary batteries using metallic lithium for the negative electrode has been conducted.

However, in a secondary battery using metallic lithium as a negative electrode, there is a danger that lithium may grow in dendrites by repeated charging and discharging, causing an internal short circuit and causing ignition. In addition, since highly active metal lithium is used, the risk is inherently high, and there are many problems in using it for consumer use. In recent years, lithium ion secondary batteries using various carbonaceous materials have been devised as a solution to such a safety problem and attaining high energy unique to a lithium electrode. This method utilizes that lithium ions are occluded (doped) in the carbonaceous material during charging and have the same potential as metallic lithium, and can be used as a negative electrode instead of metallic lithium. Further, at the time of discharging, the doped lithium ions are released (undoped) from the negative electrode and return to the original positive electrode material. like this,
When a carbonaceous material that can be doped with lithium ions is used as the negative electrode, the problem of dendrite formation is small, and since there is no metallic lithium, it is also excellent in safety, and active research is currently being conducted. .

A secondary battery using an electrode utilizing lithium ion doping of the above carbonaceous material includes:
JP-A-57-208079, JP-A-58-93176, JP-A-58-192266
, JP 62-90863, JP 62-122066, JP 2-66856
Etc. are known.

Conventionally, the electrodes used in these batteries are generally prepared by applying a paste prepared by dispersing a positive electrode active material or a negative electrode active material, a binder, a conductive material and the like in an organic solvent or water to a current collector. And dried.

As a binder for the electrode, JP-A-53-4173 is used.
2, JP-A-57-61267, JP-A-2-204963, etc., polyvinylidene fluoride (PVDF), methylcellulose (MC), carboxymethylcellulose (CMC), hydroxypropylcellulose (HPC), polyvinyl butyral (P
VB), polyethylene (PE), polyvinyl alcohol (PV
A), polytetrafluoroethylene (PTFE) and the like have been used alone or in combination.

[0007]

In recent years, with the spread of secondary batteries having a high energy density, safety requirements have been increasing. For example, as for the safety test of a lithium ion secondary battery, various tests such as an electrical test, a mechanical test, and an environmental test are described in the guideline for safety evaluation standard of lithium secondary battery (guideline of Japan Storage Battery Association of Japan, SBAG1101). There is. In addition, as an abuse test for mechanical tests and environmental tests,
Various tests such as nail penetration, crushing, heating, and dropping in water are also described. Because batteries are in the hands of ordinary consumers, it is essential to pass these misuse tests. One of the most severe tests is the nail penetration test. However, it has been difficult to secure safety during the nail penetration test with the combination of the binder, the active material, and the conductive material.

An object of the present invention is to solve the above-mentioned problems, and an object of the present invention is to provide a battery electrode excellent in safety and a secondary battery using the electrode.

[0009]

In order to achieve the above object, the present invention has the following arrangement.

"(1) An electrode for a battery comprising lignin and / or a lignin derivative.

(2) A secondary battery using the electrode of the above item (1). "

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The electrode of the present invention can be used as an electrode of any battery, and is particularly preferably used as a positive electrode or a negative electrode of a secondary battery. As a particularly preferred secondary battery, a secondary battery using a non-aqueous electrolyte containing an alkali metal salt can be exemplified.

In the present invention, lignin and / or lignin derivatives are essential components for improving safety.

Specific examples of lignin and / or lignin derivatives include alkali lignin, ligninsulfonic acid and salts thereof, thiolignin, chlorlignin, nitrolignin, boujolguman lignin, dioxane lignin, hydrotropic lignin, alcohol lignin, phenol lignin. , Lignin acetate, lignin sulfate, lignin hydrochloride and the like, which may be used alone or
It can be used as a mixture of two or more. Among these, alkali lignin is preferably used from the viewpoints of being water-soluble from the viewpoint of environment and workability, being easily available, low in cost, and the like. The content of lignin and / or lignin derivative in the electrode is not particularly limited,
It is preferably 0.1% by weight or more and 30% by weight or less.
If it is less than 0.1% by weight, the effect of improving safety is poor, and if it exceeds 30% by weight, the battery capacity tends to decrease. More preferably, it is not less than 0.3% by weight and not more than 20% by weight.

In the present invention, a carbonaceous material is preferably used as part or all of the active material in the electrode.

The carbonaceous material is not particularly limited, and generally, a material obtained by firing an organic substance is used.
In addition, either crystalline or non-crystalline may be used. The form is not particularly limited, such as a powder form and a fibrous form. Specific examples include carbon fiber, artificial or natural graphite powder, and carbon fluoride.

In the present invention, carbon fibers are more preferably used. The carbon fiber used here is not particularly limited, but generally is obtained by firing an organic substance. Specifically, polyacrylonitrile (PAN
), Pitch-based carbon fibers obtained from pitch such as coal or petroleum, cellulosic carbon fibers obtained from cellulose, and vapor-grown carbon fibers obtained from low-molecular-weight organic gas. ,
In addition, carbon fibers obtained by firing polyvinyl alcohol, lignin, polyvinyl chloride, polyamide, polyimide, phenol resin, furfuryl alcohol, and the like are also preferably used. Among these carbon fibers, carbon fibers satisfying the characteristics are appropriately selected and used according to the characteristics of the electrode and the battery in which the carbon fibers are used. Among the carbon fibers, when used for a negative electrode of a secondary battery using a non-aqueous electrolyte containing an alkali metal salt such as lithium, PA
N-based carbon fibers and pitch-based carbon fibers are preferred. Among them, PAN-based carbon fibers are preferably used because alkali metal ions, particularly lithium ions, are preferably doped.

Although the diameter and length of the carbon fiber are not particularly limited, it is preferable to use milled carbon fiber from the viewpoint of easy application by a coater. The milled carbon fiber preferably has a diameter of 0.1 to 1000 μm, more preferably 3 to 10 μm, and an average length of 5 μm.
Or more, less than 1 mm, more preferably 7 μm or more, 100 μm
Less than. When milled carbon fibers are used, it is more preferable to perform high-temperature heat treatment in advance to improve cycle characteristics.

In the present invention, the amount of the carbonaceous material used is not particularly limited, but is preferably not less than 70% by weight,
% By weight or less. Less than 70% by weight, 99%
If the content exceeds% by weight, the battery capacity tends to decrease. More preferably, the content is 75% by weight or more and 90% by weight or less.

In the present invention, other paste thickeners,
It is also preferable to add a binder and the like, for example, polyvinylidene chloride, polyvinylidene fluoride, cellulose and
/ Or cellulose salt, polyethylene, polyvinyl alcohol, polyvinyl butyral, polyvinyl pyrrolidone, polytetrafluoroethylene, polyamide, polyimide, polysulfide, polyvinyl methyl ether,
Resins such as polyethylene glycol, polyethylene oxide, polypropylene oxide, epoxy resin, melamine resin, polyvinyl pyridine and higher alcohols, and salts thereof can also be used in combination. Among these resins, cellulose and / or cellulose salt are preferably used from the viewpoints of water solubility from the viewpoint of environment and workability, workability during paste application, paste stability and the like. The cellulose and / or cellulose salt is not particularly limited, but specific examples include hydroxypropyl cellulose, methyl cellulose, carboxymethyl cellulose, and their sodium and ammonium salts.

The amount of the thickener and binder used is not particularly limited, but is preferably 0.1% by weight or more, 30% by weight or less in the electrode.
% By weight or less. If the amount is less than 0.1% by weight, the paste coating properties may be insufficient, and if it exceeds 30% by weight, the battery capacity tends to decrease. More preferably, it is 0.5% by weight or more and 20% by weight or less.

In the present invention, it is preferable to add various conductive materials to improve the conductivity of the electrode. The conductive material that can be used is not particularly limited, such as a carbon material and a metal powder, but particularly preferable conductive materials include various carbon blacks.

Specific examples of carbon black include gas black, oil black, acetylene black, and the like. Creosote oil, petroleum heavy oil, natural gas, naphthalene, pitch oil, acetylene gas, etc. are used as raw materials.
Those manufactured by a furnace method, a contact method, a thermal method, or the like can be used.

Among the carbon blacks, acetylene black or Ketjen black, which have a very low hydrogen content and a high carbon content, are preferably used from the viewpoint of conductivity. In addition, from the viewpoints of further improving conductivity and improving electrode characteristics, it is also possible to use natural graphite, artificial graphite and the like in combination.

In order to improve the conductivity by adding a conductive material, the optimum particle size and the amount to be added should be determined experimentally according to the material, shape and particle size of the active material, and the kind and amount of the binder. However, usually the primary particle diameter is 0.001 μm to 100 μm
More preferably, fine particles of 0.005 μm to 20 μm are used, and the addition amount is 0.1 to 20% by weight, more preferably 0.5 to 10% by weight. Primary particle size 0.00
If it is less than 1 μm, stable production is difficult, and if it is more than 100 μm, the effect of addition tends to be small. On the other hand, if the addition amount is less than 0.1 wt%, the effect of addition is small, and if it exceeds 20 wt%, the capacity per unit weight of the electrode tends to decrease.

The electrode of the present invention can be used as either a positive electrode or a negative electrode. When used as a negative electrode, a Li composite oxide is preferably used as a positive electrode active material. Especially LiCoO ₂ , LiNiO ₂ , LiMn ₂ O ₄ , Li _y Ni
_1-x Me _x O ₂ (Me: Ti, V, Mn, Fe), Li _1-xa A
_x Ni _1-yb B _y O ₂ (where A is at least one alkali or alkaline earth metal element, B is at least one transition metal element) It is preferably used. Especially,
In Li _1-xa A _x Ni _1-yb B _y O ₂ , 0 <x ≦ 0.
1, 0 ≤ y ≤ 0.3, -0.1 ≤ a ≤ 0.1, -0.15 ≤ b ≤ 0.15
(However, when A and B consist of two or more elements, x
Is an alkali or alkaline earth metal excluding Li, and y is
When the total number of moles of all transition metal elements excluding Ni, y = 0, A contains at least one or more alkaline earth metal elements. ), A positive electrode material having excellent characteristics can be obtained. Particularly preferred examples of A include Mg, Sr, and B include Co and Fe.

As the positive electrode active material, in addition to the Li composite oxide, a transition metal oxide containing an alkali metal, an inorganic compound such as a transition metal chalcogen, polyacetylene, polyparaphenylene, polyphenylenevinylene, polyaniline, polypyrrole, polythiophene Conjugated polymers such as
Examples include a crosslinked polymer having a disulfide bond, thionyl chloride, and the like. Among these, in the case of a secondary battery using a non-aqueous electrolyte containing a lithium salt as an electrolyte, cobalt, nickel, manganese, molybdenum, vanadium,
Transition metal oxides such as chromium, iron, copper and titanium and transition metal compounds such as transition metal chalcogens are preferably used.

The electrode in the present invention is preferably produced by providing an electrode material on one or both sides of the current collector.

The current collector in the present invention is preferably a metal,
The metal can be used in the form of a foil, a net, a lath, or the like, but these are not particularly limited.

The method for preparing the electrode by applying the electrode material to the current collector is not particularly limited, and a liquid obtained by dissolving and dispersing the electrode material in a solvent together with a binder, a conductive material, and the like is used. Can be prepared by coating on one side or both sides and drying. It is also preferable that the electrode sheet after application and drying is subjected to a treatment such as a heat treatment or a press, if necessary. When the electrode material is applied to one side of the current collector, the two uncoated surfaces are overlapped,
It is preferable to take the same form as when applied on both sides.
However, in the case of single-sided application, it is difficult to perform heat treatment or pressing of the electrode sheet, and when manufacturing a spirally wound electrode body, it is easy to cause winding deviation. It is preferable to apply.

The form of the battery using the electrode produced in the present invention is not particularly limited, but a battery using an electrode body in which a positive electrode sheet, a negative electrode sheet, and a separator are spirally wound is used as an electrode unit. This is preferable because the current per area is small and the battery can be used under heavy load. Also, the form is not particularly limited, such as a cylindrical shape, a square shape, a coin shape, a sheet shape, and the like.

The separator in the present invention is not particularly limited as long as it can prevent a short circuit between the positive electrode and the negative electrode. In addition, the electrolyte has good permeability,
It is desirable not to cause electron and ion migration resistance, and typical materials include polyolefin, polyester,
Polyamide, polyacrylate, polymethacrylate,
Polysulfone, polycarbonate, polytetrafluoroethylene and the like can be mentioned. Among them, polyethylene, polypropylene, polysulfone and the like are particularly preferred because of their excellent strength and safety. Examples of the shape of the separator generally include a porous film and a nonwoven fabric, but a porous film is preferable because the filling rate in the battery can is easily increased. Further, the porous membrane is generally a symmetric membrane or an asymmetric membrane, but may be a composite membrane in which a plurality of types of membranes are laminated in order to improve strength and safety. The porosity of the porous film is preferably as high as possible in order to increase the permeability of electrons and ions, but there is a risk of causing a decrease in the strength of the film, so it should be determined according to the material and the film thickness. is there. Generally, it is desirable that the film thickness be 20 to 100 μm and the porosity be 30 to 80%.
Further, the diameter of the holes is desirably in a range that does not allow the active material, the binder, and the conductive material detached from the electrode sheet to pass therethrough. Specifically, the average hole diameter is preferably 0.01 to 1 μm.

In the case of a spirally wound electrode body, the shape thereof is not necessarily required to be a perfect cylindrical shape.
A long cylindrical shape having an elliptical spiral cross section or a prism having a rectangular cross section such as a rectangle may be used. In this case, the battery can can also take a shape corresponding to the shape of the electrode body. Typical usage patterns include:
The most common form is a spiral-shaped electrode body and electrolyte loaded in a cylindrical bottom battery can, and the lead taken out of the electrode sheet is sealed with the cap and the battery can welded together. However, the present invention is not particularly limited to this mode.

The battery can in which the spiral electrode body is loaded is not particularly limited, but a battery can in which iron is plated with a metal such as Ni, a stainless steel battery can, and the like have strength, corrosion resistance, and the like. It is preferable because of excellent workability. Further, it is possible to reduce the weight by using an aluminum alloy or various engineering plastics, and it is also possible to use various engineering plastics and metals in combination.

The solvent used for the electrolyte in the present invention is not particularly limited, and a conventional solvent can be used. For example, an acid or alkali aqueous solution, a non-aqueous solvent and the like can be mentioned. Among them, as the solvent of the electrolyte of the secondary battery comprising the non-aqueous electrolyte containing the above-described alkali metal salt, ethylene carbonate, propylene carbonate, diethyl carbonate, dimethyl carbonate, γ
-Butyrolactone, N-methyl-2-pyrrolidone, acetonitrile, N, N-dimethylformamide, dimethyl sulfoxide, tetrahydrofuran, 1,3-dioxolan, methyl formate, sulfolane, thionyl chloride, 1,2-dimethoxyethane, diethylene carbonate And their derivatives and mixtures are preferably used.

The electrolyte contained in the electrolytic solution of the present invention may be an alkali metal, especially a halide of lithium,
Perchlorate, thiocyanate, borofluoride, phosphorous fluoride, arsenic fluoride, aluminum fluoride, trifluoromethyl sulfate and the like are preferably used. Particularly, lithium salt has the lowest standard electrode potential and can obtain a large potential difference, and thus is more preferably used as an electrolyte contained in an electrolytic solution.

According to the present invention, a battery electrode having excellent safety and a secondary battery using the electrode can be provided.

[0038]

The present invention will be described in more detail with reference to the following examples. The present invention is not limited to these examples.

The nail penetration test was carried out according to the method described in Guidelines for Evaluation of Safety of Lithium Secondary Batteries (Guideline of Japan Storage Battery Association SBAG1101).

Example 1 90 wt% of LiCoO ₂ as a positive electrode active material, polyvinylidene fluoride as a binder: 5 wt% of “KF Polymer” # 1000 (manufactured by Kureha Chemical Industry Co., Ltd.), and acetylene black as a conductive material:
5% by weight of "DENKA BLACK" (manufactured by Denki Kagaku Kogyo KK) was mixed, and this mixture was dispersed in N-methyl-2-pyrrolidone to form a slurry. Then, this slurry is uniformly applied to both sides of a 20 μm thick aluminum foil as a current collector,
After drying, a positive electrode sheet was obtained by performing a roll press.

Next, as the negative electrode active material, PAN-based carbon fiber:
80% by weight of shortened “Treca” T-300 (Toray Co., Ltd.), 10% by weight of alkaline lignin (special grade reagent of Wako Pure Chemical Industries, Ltd.) as binder, and carboxy as thickener Sodium methylcellulose: "CMC Daicel"# 129
5% by weight (made by Daicel Chemical Industries, Ltd.) and 5% by weight of acetylene black: "Denka Black" (made by Denki Kagaku Kogyo Co., Ltd.) as a conductive material were mixed in water to form a slurry. . Then, this slurry was uniformly applied to both surfaces of a copper foil having a thickness of 16 μm as a current collector, dried, and then roll-pressed to obtain a negative electrode sheet.

Next, a positive electrode sheet having a thickness of 100 μm and a width of 3 m
m aluminum plate is welded to the negative electrode sheet using a 100 μm-thick nickel plate as a lead, and then the positive electrode sheet is inserted through a porous polyethylene film: “SETELA” E25MMO (manufactured by Tonen Chemical Co., Ltd.) as a separator. And spirally wound to obtain a spiral electrode body. Similarly, a total of 100 electrode bodies were produced.

Next, the electrode body was loaded into a cylindrical battery can having a diameter of 18 mm and a length of 65 mm, and propylene carbonate and dimethyl carbonate containing 1M-lithium phosphide were used as an electrolyte.
A battery using a 1: 1 mixture was prepared. This battery was charged at a constant current and a constant voltage with a charging current of 1 A, a constant voltage value of 4.2 V and a charging time of 2.5 hours, and a capacity test was performed at a discharge current of 200 mA and a discharge end voltage of 2.5 V.

Next, the battery was subjected to a nail penetration test. The results are shown in Table 1.

Comparative Example 1 In Example 1, PAN-based carbon fiber was used as the negative electrode active material:
80% by weight of "Treca" T-300 (manufactured by Toray Industries, Inc.), 80% by weight, polyvinylidene fluoride as binder: "KF Polymer"# 1000 (15% by weight, manufactured by Kureha Chemical Industry Co., Ltd.), conductive As a material, 5 wt% of acetylene black: "DENKA BLACK" (manufactured by Denki Kagaku Kogyo KK) was mixed, and this mixture was dispersed in N-methyl-2-pyrrolidone to form a slurry. Then, the slurry was uniformly applied to both surfaces of a copper foil having a thickness of 16 μm as a current collector, dried, and then roll-pressed to obtain a negative electrode sheet in the same manner as in Example 1 except that a negative electrode sheet was obtained. A battery production, capacity test, and nail penetration test were performed. The results are shown in Table 1.

[0046]

[Table 1]

[0047]

According to the present invention, it is possible to provide a battery electrode excellent in safety and a secondary battery using the electrode.

Claims (14)

[Claims] 1. A battery electrode comprising lignin and / or a lignin derivative. 2. The battery electrode according to claim 1, wherein part or all of the active material in the electrode is a carbonaceous material. 3. The battery electrode according to claim 1, wherein said carbonaceous material is carbon fiber. 4. The battery electrode according to claim 1, wherein said carbon fiber is obtained from polyacrylonitrile. 5. The battery electrode according to claim 1, wherein said carbon fibers are milled carbon fibers. 6. The battery electrode according to claim 1, further comprising a thickener. 7. The battery electrode according to claim 1, wherein the thickener is cellulose and / or a cellulose salt. 8. The battery electrode according to claim 1, further comprising a conductive material. 9. The battery electrode according to claim 1, wherein said conductive material is carbon black. 10. The battery electrode according to claim 1, wherein said electrode contains 0.1 to 30% by weight of said lignin and / or lignin derivative. 11. The electrode according to claim 10, wherein the carbonaceous material is 70 to 99% by weight.
The battery electrode according to any one of claims 2 to 10, wherein the electrode is contained. 12. The battery electrode according to claim 7, wherein said electrode contains 0.1 to 30% by weight of said cellulose and / or cellulose salt. 13. The method according to claim 13, wherein the carbon black is 0.1 to
The battery electrode according to any one of claims 9 to 12, comprising 20% by weight. 14. A secondary battery using the electrode according to claim 1.