JP2002279995A - Battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a battery capable of improving the characteristics by specifying a composition ratio of a negative electrode binder. SOLUTION: A negative electrode 22 has a negative electrode mix layer 22b composed of a negative electrode material, capable of occluding and removing lithium, a binding agent mainly composed of a styrene-butadiene copolymer, and a thickener composed mainly of a cellulose derivative. A composition ratio is defined, in such manner that a ratio of the binding agent to the negative electrode mix is 0.5 mass % or more to 4 mass % or less, a ratio of (weight ratio of binding agent to negative electrode mix)/(specific surface area of negative electrode material) is 0.25 or more to 4 or less, and the weight ratio of the thickener to the weight of the binding agent is 1/3 or more to 2 or less. Whereby the negative electrode mix is provided with proper viscosity, and the negative electrode material can be bound in the desired condition.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a battery provided with an electrolyte in addition to a positive electrode and a negative electrode, and more particularly to a battery in which the capacity of a negative electrode is the sum of a capacity component due to insertion and extraction of light metal and a capacity component due to precipitation and dissolution of light metal. For the battery represented by

[0002]

2. Description of the Related Art In recent years, portable electronic devices typified by a camera-integrated VTR (video tape recorder), a mobile phone and a laptop computer have become widespread, and there is a strong demand for long-time continuous driving thereof. Along with this, demands for higher capacity and higher energy density of secondary batteries as those portable power sources are increasing.

[0003] As a secondary battery capable of obtaining a high energy density, for example, a lithium ion secondary battery using a material capable of inserting and extracting lithium (Li) such as a carbon material for the negative electrode, or a negative electrode There is a lithium secondary battery using lithium metal. In particular, lithium secondary batteries have a theoretical electrochemical equivalent of lithium metal of 205.
Since it is as large as 4 mAh / cm ³ , corresponding to 2.5 times that of the graphite material used in the lithium ion secondary battery, it is expected that a higher energy density than the lithium ion secondary battery can be obtained. Until now, many researchers have been conducting research and development on the practical application of lithium secondary batteries (for example, Lithium Batteries, Jean-Paul
Gabano ed., Academic Press (1983)).

[0004]

However, the lithium secondary battery has a problem that the discharge capacity is greatly deteriorated when charging and discharging are repeated, and it is difficult to put the battery to practical use. This capacity deterioration is based on the fact that the lithium secondary battery utilizes the precipitation and dissolution reaction of lithium metal at the negative electrode, and the volume of the negative electrode corresponding to the lithium ions moving between the positive and negative electrodes during charging and discharging. Is greatly increased or decreased by the capacity, so that the volume of the negative electrode greatly changes, and the dissolution reaction and recrystallization reaction of the lithium metal crystal become difficult to reversibly proceed. In addition, the change in volume of the negative electrode increases as the energy density is increased, and the capacity deterioration further increases.

Therefore, the present inventors have newly developed a secondary battery in which the capacity of the negative electrode is represented by the sum of a capacity component due to insertion and extraction of lithium and a capacity component due to precipitation and dissolution of lithium. In this technology, a carbon material capable of inserting and extracting lithium is used for a negative electrode, and lithium is deposited on the surface of the carbon material during charging. According to this secondary battery, it is expected that charge / discharge cycle characteristics are improved while achieving high energy density. However, for practical use, it is necessary to further improve and stabilize the characteristics. For that purpose, since the characteristics of the battery reflect the electrode reaction,
In the negative electrode, an appropriate design of a binder for binding the negative electrode active materials to each other or the negative electrode active material and the current collector is required.

The present invention has been made in view of such a problem, and an object of the present invention is to provide a battery capable of defining the composition ratio of a negative electrode binder and improving characteristics.

[0007]

A battery according to the present invention comprises an electrolyte in addition to a positive electrode and a negative electrode. The capacity of the negative electrode is determined by a capacity component due to occlusion and desorption of light metal,
The negative electrode is represented by the sum of the capacity component due to the precipitation and dissolution of light metal. Including a negative electrode mixture composed of a viscous agent, the weight ratio of the binder to the negative electrode mixture is 0.5% by mass or more and 4% by mass or less, and the specific surface area of the negative electrode material (m ² / g)
Ratio of binder to negative electrode mixture (% by mass)
Is 0.25 or more and 4 or less, and the ratio of the weight of the thickener to the weight of the binder is 1/3 or more and 2 or less.

In the battery according to the present invention, the negative electrode includes, in addition to the negative electrode material, a negative electrode mixture mainly composed of a binder mainly composed of a styrene-butadiene copolymer and a thickener mainly composed of a carboxymethyl cellulose derivative. Since the composition ratio of these constituent materials is specified in the above ratio,
The binder binds the negative electrode material in a suitable state, and the cycle characteristics of the battery are further improved.

[0009]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 shows a sectional structure of a secondary battery according to an embodiment of the present invention. This secondary battery is a so-called cylindrical type. A wound electrode body 20 in which a band-shaped positive electrode 21 and a negative electrode 22 are wound via a separator 23 inside a substantially hollow cylindrical battery can 11. have. The battery can 11 is made of, for example, nickel-plated iron, and has one end closed and the other end open. Inside the battery can 11, a wound electrode body 20 is provided.
A pair of insulating plates 1 perpendicular to the winding peripheral surface so as to sandwich
2 and 13 are respectively arranged.

At the open end of the battery can 11, a battery cover 14 is provided.
And a safety valve mechanism 15 provided inside the battery lid 14.
And Positive Temperature Coefficie
nt; PTC element) 16 and caulked via a gasket 17, and the battery can 11
The inside is closed. The battery cover 14 is made of, for example, the same material as the battery can 11. The safety valve mechanism 15 is electrically connected to the battery cover 14 via the thermal resistance element 16, and when the internal pressure of the battery becomes higher than a certain level due to an internal short circuit or external heating, the disk plate 15a is inverted. Then, the electrical connection between the battery cover 14 and the spirally wound electrode body 20 is cut off. Thermal resistance element 1
Reference numeral 6 denotes an element for limiting the current by increasing the resistance value when the temperature rises and preventing abnormal heat generation due to a large current, and is made of, for example, a barium titanate-based semiconductor ceramic. The gasket 17 is made of, for example, an insulating material, and its surface is coated with asphalt.

The wound electrode body 20 is wound around, for example, a center pin 24. Positive electrode 2 of wound electrode body 20
1 is connected to a positive electrode lead 25 made of aluminum or the like, and the negative electrode 22 is connected to a negative electrode lead 26 made of nickel or the like. The positive electrode lead 25 is electrically connected to the battery cover 14 by being welded to the safety valve mechanism 15, and the negative electrode lead 26 is welded to and electrically connected to the battery can 11.

FIG. 2 is an enlarged view of a part of the spirally wound electrode body 20 shown in FIG. The positive electrode 21 has, for example, a structure in which a positive electrode mixture layer 21b is provided on both surfaces of a positive electrode current collector 21a having a pair of opposing surfaces. Although not shown, the positive electrode mixture layer 21b may be provided only on one side of the positive electrode current collector 21a. Positive electrode current collector 21a
Has a thickness of, for example, about 5 μm to 50 μm, and is made of a metal foil such as an aluminum foil, a nickel foil, or a stainless steel foil. The positive electrode mixture layer 21b has a thickness of, for example, 80 μm to 250 μm and includes a positive electrode material capable of inserting and extracting lithium as a light metal. When the positive electrode mixture layer 21b is provided on both surfaces of the positive electrode current collector 21a, the thickness of the positive electrode mixture layer 21b is the total thickness thereof.

As the positive electrode material capable of inserting and extracting lithium, for example, a lithium-containing compound such as lithium oxide, lithium sulfide, or an intercalation compound containing lithium is suitable. You may use it. In particular, to increase the energy density, a lithium composite oxide represented by the general formula Li _x MO ₂ or an intercalation compound containing lithium is preferable. In addition, M is preferably one or more transition metals. Specifically, cobalt (Co), nickel (Ni), manganese (Mn), iron (Fe), aluminum (Al), vanadium (V) and titanium ( At least one of Ti)
Species are preferred. x differs depending on the charge / discharge state of the battery, and is usually a value in the range of 0.05 ≦ x ≦ 1.10. In addition, LiM having a spinel type crystal structure is also used.
n ₂ O ₄ or LiF having an olivine type crystal structure
ePO _{4 is} also preferable because a high energy density can be obtained.

Incidentally, such a positive electrode material includes, for example, lithium carbonate, nitrate, oxide or hydroxide,
By mixing and pulverizing a transition metal carbonate, nitrate, oxide or hydroxide so as to have a desired composition, the mixture is fired in an oxidizing atmosphere at a temperature in the range of 600 ° C to 1000 ° C. Prepared.

The positive electrode mixture layer 21b also contains, for example, a conductive agent, and may further contain a binder, if necessary. Examples of the conductive agent include carbon materials such as graphite, carbon black and Ketjen black, and one or more of them are used in combination. Further, in addition to the carbon material, a metal material or a conductive polymer material may be used as long as the material has conductivity. Examples of the binder include synthetic rubbers such as styrene-butadiene rubber, fluorine rubber and ethylene propylene diene rubber, and polymer materials such as polyvinylidene fluoride, and one or more of them are mixed. Used as For example,
When the positive electrode 21 and the negative electrode 22 are wound as shown in FIG. 1, it is preferable to use a highly flexible styrene-butadiene-based rubber or a fluorine-based rubber as the binder.

The negative electrode 22 has, for example, a structure in which a negative electrode mixture layer 22b is provided on both surfaces of a negative electrode current collector 22a having a pair of opposing surfaces. Although not shown, the negative electrode mixture layer 22b may be provided only on one side of the negative electrode current collector 22a. The negative electrode current collector 22a is made of a metal foil such as a copper foil, a nickel foil, or a stainless steel foil having good electrochemical stability, electric conductivity, and mechanical strength. In particular, copper foil is most preferable because it has high electric conductivity. The thickness of the negative electrode current collector 22a is preferably, for example, about 6 μm to 40 μm. 6μ
If the thickness is smaller than m, the mechanical strength is reduced, the anode current collector 22a is easily broken in the manufacturing process, and the production efficiency is reduced. The volume ratio becomes larger than necessary,
This is because it becomes difficult to increase the energy density.

The negative electrode mixture layer 22b is composed of one or more negative electrode materials capable of inserting and extracting lithium, which is a light metal. -It contains a binder made of a butadiene copolymer and also contains a thickener mainly made of a cellulose derivative. The styrene-butadiene copolymer referred to herein is a copolymer obtained by emulsion polymerization of butadiene and styrene. The copolymer has a bound styrene content of 50% or less, and is composed of two components, styrene and butadiene. In addition, it may further include third, fourth or more components. Such a styrene-butadiene copolymer has a property of surface binding while polyvinylidene fluoride or the like, which has been conventionally used as a binder, is spot-bound. Therefore, the ratio of the binder in the negative electrode mixture layer 22b can be reduced. In particular, a styrene-butadiene copolymer having at least one of a carbonyl group and a cyano group is
The proportion of the negative electrode mixture can be reduced as compared with conventionally used polyvinylidene fluoride, which is preferable as a binder.

However, when this is mainly mixed with the negative electrode material, it is aggregated with the negative electrode material and the function as a binder is extremely lowered. Therefore, it is necessary to add a thickener and increase the viscosity of the solvent to improve the dispersibility of the binder and prevent aggregation. As such a thickener, a cellulose derivative is used, and specific examples thereof include an alkali metal salt or an ammonium salt of carboxymethyl cellulose. Particularly, an ammonium salt of carboxymethylcellulose is preferable, and further, the molecular weight is 100,000 or more and 20 or more.
It is preferably not more than 10,000. When the molecular weight is less than 100,000, it is difficult to obtain sufficient viscosity and dispersibility. When the molecular weight is more than 200,000, it is difficult to dissolve in water as a solvent, and there is a possibility that the preparation of the negative electrode mixture becomes difficult. .

Here, in order to maintain or improve the battery characteristics, the composition ratio of the binder and the thickener to the anode material is optimized. The optimization requirements are as follows. These are independent requirements,
Here, the material ratio is defined so as to satisfy all of them.

The weight ratio of the binder to the whole negative electrode mixture is 0.5% by mass or more and 4% by mass or less. That is,
When the weight ratio is less than 0.5% by mass, the binding property is insufficient, the formation of the negative electrode mixture layer 22b becomes difficult, and the negative electrode mixture layer 22b may peel off during use of the battery. is there. Conversely, if the weight ratio is greater than 4% by mass, the ratio of the binder covering the surface of the negative electrode material is too high, and the internal resistance of the negative electrode 22 may increase.

The ratio of the weight ratio of the binder to the entire negative electrode mixture relative to the specific surface area of the negative electrode material, that is, (weight ratio (% by mass) of the binder to the whole negative electrode mixture) / (ratio of negative electrode material) The value determined from the surface area (m ² / g) is
It is 0.25 or more and 4 or less. Since the styrene-butadiene copolymer is surface-bound, the relationship between the specific surface area of the negative electrode material and the weight ratio of the binder is also a factor that determines the bonding state of the negative electrode material in the negative electrode 22. Also in this requirement, when the amount of the binder is less than the specified range, the binding property is insufficient, and when it is more than the specified range, the internal resistance increases.

The ratio of the weight of the thickener to the weight of the binder is 1/3 or more and 2 or less. As described above, a thickener must be used in combination with the binder, but the ratio between the two needs to be optimized for more effective use. If this ratio is 1/3 or less, the viscosity of the negative electrode mixture is poor, and the dispersibility of the binder is low.
May be difficult to form, or the negative electrode mixture layer 22b may peel off during use of the battery. Conversely, if this ratio is greater than 2, the viscosity may be too high, and it may be difficult to form a coating film for the negative electrode mixture layer 22b.

Thus, since the negative electrode mixture layer 22b has an appropriate viscosity, it is easy to form a coating film and, at the same time, it is difficult for peeling after formation. Further, since the binder is sufficiently dispersed, the binding property of the negative electrode material is good, and peeling and increase in internal resistance are prevented. Therefore, the cycle characteristics of the battery are maintained and improved. The thickness of the negative electrode mixture layer 22b is, for example,
It is 80 μm to 250 μm. This thickness is the total thickness when the negative electrode mixture layer 22b is provided on both surfaces of the negative electrode current collector 22a.

[0025] In this specification, the term "storage and release of light metal" means that light metal ions are electrochemically stored and released without losing their ionicity. This includes not only the case where the occluded light metal exists in a perfect ionic state but also the case where the occluded light metal exists in a state that cannot be said to be a perfect ionic state. Such cases include, for example, occlusion by electrochemical intercalation reaction of light metal ions with respect to graphite. Further, occlusion of light metals by forming an intermetallic compound or an alloy can also be mentioned.

Examples of the negative electrode material capable of inserting and extracting lithium include carbon materials such as graphite, non-graphitizable carbon and graphitizable carbon. These carbon materials are preferable because a change in crystal structure that occurs during charge and discharge is very small, a high charge and discharge capacity can be obtained, and good charge and discharge cycle characteristics can be obtained. Particularly, graphite is preferable because it has a large electrochemical equivalent and can obtain a high energy density.

As the graphite, for example, the true density is 2.10
g / cm ³ or more, preferably 2.18 g / cm ³
The above is more preferable. In order to obtain such a true density, the C-axis crystallite thickness of the (002) plane must be 1
It is necessary to be 4.0 nm or more. Also, (00
2) The spacing between the surfaces is preferably less than 0.340 nm, and more preferably 0.335 nm or more and 0.337 nm or less.

The graphite may be natural graphite or artificial graphite.
In the case of artificial graphite, for example, it can be obtained by carbonizing an organic material, performing a high-temperature heat treatment, and pulverizing and classifying. The high-temperature heat treatment is performed by, for example, carbonizing at 300 ° C. to 700 ° C. in an inert gas stream such as nitrogen (N ₂ ) as necessary,
The temperature is raised from 900 ° C to 1500 ° C at a rate of 1 ° C to 100 ° C per minute, the temperature is maintained for about 0 hours to 30 hours, and calcined, and heated to 2000 ° C or more, preferably 2500 ° C or more. This is performed by maintaining the temperature for an appropriate time.

As the organic material used as a starting material, coal or pitch can be used. For the pitch, for example, tars obtained by pyrolyzing coal tar, ethylene bottom oil or crude oil at a high temperature, asphalt, etc. (vacuum distillation, normal pressure distillation or steam distillation), thermal polycondensation, extraction, Examples include those obtained by chemical polycondensation, those produced at the time of wood reflux, polyvinyl chloride resin, polyvinyl acetate, polyvinyl butyrate, and 3,5-dimethylphenol resin.
These coals or pitches have a maximum of 400
It exists as a liquid at about ℃, and aromatic rings are condensed and polycyclic by being held at that temperature, and it is in a laminated orientation state, and then becomes a solid carbon precursor at about 500 ° C. or higher, that is, semi-coke. (Liquid phase carbonization process).

Examples of the organic material include condensed polycyclic hydrocarbon compounds such as naphthalene, phenanthrene, anthracene, triphenylene, pyrene, perylene, pentaphen, and pentacene, and derivatives thereof (for example, carboxylic acids and carboxylic anhydrides of the above compounds). , Carboximides), or mixtures thereof. Further, condensed heterocyclic compounds such as acenaphthylene, indole, isoindole, quinoline, isoquinoline, quinoxaline, phthalazine, carbazole, acridine, phenazine, phenanthridine and derivatives thereof;
Alternatively, a mixture thereof can be used.

The pulverization may be performed before or after carbonization or calcination, or during the temperature raising process before graphitization. In these cases, heat treatment for graphitization is finally performed in a powder state. However, to obtain graphite powder with high bulk density and high breaking strength, heat treatment is performed after molding the raw material,
It is preferable to pulverize and classify the obtained graphitized molded body.

For example, in the case of producing a graphitized molded body, coke as a filler and binder pitch as a molding agent or a sintering agent are mixed and molded. And the pitch impregnating step of impregnating the sintered body with the melted binder pitch is repeated several times, followed by heat treatment at a high temperature. The impregnated binder pitch is carbonized and graphitized in the above heat treatment process. By the way, in this case,
Since filler (coke) and binder pitch are used as raw materials, it is graphitized as a polycrystal, and since sulfur and nitrogen contained in the raw materials are generated as a gas during heat treatment, minute holes are formed in the passage. It is formed. Thus, the vacancies facilitate the progress of the occlusion and desorption reactions of lithium, and also have the advantage of high industrial processing efficiency. As a raw material of the molded body, a filler having moldability and sinterability itself may be used. In this case, it is not necessary to use a binder pitch.

As the non-graphitizable carbon, the (002) plane spacing is 0.37 nm or more, and the true density is 1.70 g / cm.
With less than ^3, differential thermal analysis in air (Differen
Those which do not show an exothermic peak above 700 ° C. in tial thermal analysis (DTA) are preferred.

Such non-graphitizable carbon can be obtained, for example, by subjecting an organic material to a heat treatment at about 1200 ° C., followed by pulverization and classification. The heat treatment is, for example, 3
After carbonization at 00 ° C to 700 ° C (solid carbonization process),
The temperature is raised from 900 ° C. to 1300 ° C. at a rate of 1 ° C. to 100 ° C. per minute, and the temperature is maintained for about 0 to 30 hours. The pulverization may be performed before or after carbonization, or during the heating process.

As the organic material used as the starting material, for example, a furfuryl alcohol or furfural polymer or copolymer, or a furan resin which is a copolymer of these polymers with other resins can be used. . Also,
Phenol resin, acrylic resin, vinyl halide resin, polyimide resin, polyamide imide resin, polyamide resin, conjugated resin such as polyacetylene or polyparaphenylene, cellulose or derivatives thereof, coffee beans, bamboo, shellfish including chitosan, bacteria Biocelluloses utilizing the same can also be used. Furthermore, the atomic ratio H / of hydrogen atoms (H) and carbon atoms (C)
A compound in which a functional group containing oxygen (O) is introduced (so-called oxygen cross-linking) into petroleum pitch in which C is, for example, 0.6 to 0.8 can also be used.

The content of oxygen in this compound is preferably at least 3%, more preferably at least 5% (see Japanese Patent Application Laid-Open No. 3-252053). The oxygen content affects the crystal structure of the carbon material, and at a higher content, the physical properties of the non-graphitizable carbon can be increased.
This is because the capacity of the negative electrode 22 can be improved.
Incidentally, petroleum pitch is, for example, coal tar, tar bottoms obtained by pyrolyzing ethylene bottom oil or crude oil at high temperature, or asphalt,
It is obtained by distillation (vacuum distillation, normal pressure distillation or steam distillation), thermal polycondensation, extraction or chemical polycondensation. Examples of the oxidative crosslinking method include nitric acid,
A wet method in which an aqueous solution of sulfuric acid, hypochlorous acid, or a mixed acid thereof is reacted with petroleum pitch, a dry method in which an oxidizing gas such as air or oxygen is reacted with petroleum pitch, or sulfur, ammonium nitrate, ammonium persulfate, A method of reacting a solid reagent such as ferric chloride with petroleum pitch can be used.

The organic material used as a starting material is not limited to these, and any other organic material may be used as long as it is an organic material that can be made non-graphitizable carbon through a solid phase carbonization process by oxygen crosslinking or the like.

Examples of the non-graphitizable carbon include those produced using the above-mentioned organic materials as starting materials, and those described in JP-A-3-3-1.
A compound containing phosphorus (P), oxygen and carbon as main components described in 37010 is also preferable because it shows the above-mentioned physical property parameters.

Examples of the negative electrode material capable of inserting and extracting lithium include metals and semiconductors capable of forming alloys and compounds with lithium, and alloys and compounds thereof. These are preferable because a high energy density can be obtained, and it is more preferable to use them together with a carbon material because a high energy density can be obtained and excellent cycle characteristics can be obtained.

As such a metal or semiconductor,
For example, tin (Sn), lead (Pb), aluminum (A
l), indium (In), silicon (Si), zinc (Z
n), antimony (Sb), bismuth (Bi), gallium (Ga), germanium (Ge), arsenic (As), silver (Ag), hafnium (Hf), zirconium (Zr)
And yttrium (Y). These alloys or compounds, e.g., chemical formula Ma _s Mb _t
Li _u, or include those represented by the chemical formula Ma _p Mc _q Md _r. In these chemical formulas, Ma represents at least one of a metal element and a semiconductor element capable of forming an alloy or a compound with lithium; Mb represents at least one of a metal element and a semiconductor element other than lithium and Ma; Represents at least one kind of non-metallic element, and Md represents at least one kind of metallic element and semiconductor element other than Ma. Also, s, t, u,
The values of p, q and r are s> 0, t ≧ 0, u ≧
0, p> 0, q> 0, r ≧ 0.

Among them, a metal element or a semiconductor element of group 4B, or an alloy or compound thereof is preferable.
Particularly preferred are silicon or tin, or alloys or compounds thereof. These may be crystalline or amorphous.

For such alloys or compounds,
To give an example, LiAl, AlSb, CuMgS
b, SiB_Four, SiB₆, Mg_TwoSi, Mg_TwoSn, N
i_TwoSi, TiSi_Two, MoSi_Two, CoSi_Two, Ni
Si_Two, CaSi_Two, CrSi_Two, Cu_FiveSi, FeS
i_Two, MnSi_Two, NbSi_Two, TaSi_Two, VS
i _Two, WSi_Two, ZnSi_Two, SiC, Si_ThreeN_Four, S
i_TwoN_TwoO, SiO_v(0 <v ≦ 2), SnO_w(0 <
w ≦ 2), SnSiO_Three, LiSiO or LiSn
O and the like.

The negative electrode material capable of inserting and extracting lithium further includes other metal compounds or polymer materials. Examples of other metal compounds include oxides such as iron oxide, ruthenium oxide, and molybdenum oxide, and LiN _3. Examples of polymer materials include polyacetylene, polyaniline, and polypyrrole.

In this secondary battery, during the charging process, lithium metal starts to precipitate on the negative electrode 22 when the open circuit voltage (that is, the battery voltage) is lower than the overcharge voltage. That is, when the open circuit voltage is lower than the overcharge voltage, lithium metal is deposited on the negative electrode 22, and the capacity of the negative electrode 22 is based on the capacity component due to insertion and extraction of lithium and the capacity component due to deposition and dissolution of lithium metal. And the sum of Therefore, in this secondary battery, both the negative electrode material capable of inserting and extracting lithium and the lithium metal function as the negative electrode active material, and the negative electrode material capable of inserting and extracting lithium is the base material when the lithium metal is deposited. It has become.

The overcharge voltage refers to an open circuit voltage when the battery is in an overcharged state, and is, for example, one of the guidelines set by the Japan Storage Battery Association (Battery Manufacturers Association). Guideline for Secondary Battery Safety Evaluation Standards ”(S
"Full charge" as defined and defined in BA G1101)
Refers to a voltage higher than the open circuit voltage of the battery. In other words, it refers to a voltage higher than the open circuit voltage after charging using the charging method, the standard charging method, or the recommended charging method used to determine the nominal capacity of each battery. Specifically, in this secondary battery, for example, the battery is fully charged when the open circuit voltage is 4.2 V, and the negative electrode capable of inserting and extracting lithium in a part of the open circuit voltage in the range of 0 V or more and 4.2 V or less. Lithium metal is deposited on the surface of the material.

Thus, in this secondary battery, a high energy density can be obtained, and the cycle characteristics and the rapid charging characteristics can be improved. This is similar to a conventional lithium secondary battery using lithium metal or a lithium alloy for the negative electrode in that lithium metal is deposited on the negative electrode 22, but lithium metal is deposited on a negative electrode material capable of inserting and extracting lithium. This is considered to be because the following advantages are brought about by performing the operation.

First, in conventional lithium secondary batteries, it is difficult to deposit lithium metal uniformly, which causes deterioration of cycle characteristics. However, negative electrode materials capable of inserting and extracting lithium are generally used. In this secondary battery, lithium metal can be uniformly deposited because of its large surface area. Second, in the conventional lithium secondary battery, the volume change accompanying the precipitation and elution of lithium metal was large, which also deteriorated the cycle characteristics. However, this secondary battery is capable of inserting and extracting lithium. The lithium metal precipitates also in the gaps between the particles of the negative electrode material, so that the volume change is small. Third, in a conventional lithium secondary battery, the larger the amount of lithium metal deposited / dissolved, the greater the above problem. However, in this secondary battery, lithium storage / removal by a negative electrode material capable of storing / removing lithium is performed. Since the detachment also contributes to the charge / discharge capacity, the amount of lithium metal deposited and dissolved is small in spite of the large battery capacity. Fourth, in a conventional lithium secondary battery, when rapid charging is performed, lithium metal precipitates more unevenly, so that cycle characteristics are further deteriorated. However, in this secondary battery, lithium is occluded in the initial stage of charging. -Fast charging is possible because lithium is occluded in the detachable negative electrode material.

In order to obtain these advantages more effectively, for example, the maximum deposition capacity of lithium metal deposited on the negative electrode 22 at the maximum voltage before the open circuit voltage becomes the overcharge voltage is determined as follows. It is preferable that the charge capacity is 0.05 times or more and 3.0 times or less of the charge capacity of the detachable negative electrode material. If the amount of lithium metal deposited is too large, a problem similar to that of a conventional lithium secondary battery occurs, and if the amount is too small, the charge / discharge capacity cannot be sufficiently increased. Also, for example, the discharge capacity of the negative electrode material capable of inserting and extracting lithium is preferably 150 mAh / g or more. This is because the greater the ability to insert and extract lithium, the smaller the amount of lithium metal deposited. As for the capacity component due to the insertion and extraction of lithium, the charge capacity of the negative electrode material is, for example, constant current / constant until the potential becomes 0 V for the negative electrode using lithium metal as a counter electrode and using this negative electrode material as a negative electrode active material. It is obtained from the amount of electricity when charged by the voltage method. The discharge capacity capacity of the negative electrode material is determined, for example, from the quantity of electricity when the negative electrode is discharged until the potential of the negative electrode reaches 2.5 V over 10 hours or more by a constant current method.

The separator 23 is provided to prevent a short circuit between the positive electrode 21 and the negative electrode 22. For example, a porous film made of a synthetic resin such as polytetrafluoroethylene, polyvinylidene fluoride, polypropylene or polyethylene, or a porous film made of ceramic is used. And two or more of these porous films are stacked. Above all, a polyolefin porous film is preferable because it has an excellent short-circuit prevention effect and can improve battery safety by a shutdown effect. In particular, polyethylene is preferable as a material forming the separator 23 because it can obtain a shutdown effect in a range of 100 ° C. or more and 160 ° C. or less and has excellent electrochemical stability.
Polypropylene is also preferable, and any other resin having chemical stability can be used by copolymerizing or blending with polyethylene or polypropylene.

The polyolefin porous membrane is prepared, for example, by kneading a molten low-volatile solvent with a molten polyolefin composition to form a uniform high-concentration solution of the polyolefin composition. Molded by
It is obtained by cooling into a gel-like sheet and stretching.

As the low volatile solvent, for example, nonane,
Low volatile aliphatic or cyclic hydrocarbons such as decane, decalin, p-xylene, undecane or liquid paraffin can be used. The mixing ratio of the polyolefin composition and the low-volatile solvent is 100% by mass of the total of both.
The content of the polyolefin composition is preferably from 10% by mass to 80% by mass, and more preferably from 15% by mass to 70% by mass. If the amount of the polyolefin composition is too small, swelling or neck-in becomes large at the die exit during molding, and sheet molding becomes difficult. on the other hand,
If the amount of the polyolefin composition is too large, it is difficult to prepare a uniform solution.

When a high-concentration solution of the polyolefin composition is molded with a die, in the case of a sheet die, the gap is preferably, for example, 0.1 mm or more and 5 mm or less. Further, the extrusion temperature is preferably from 140 ° C. to 250 ° C., and the extrusion speed is preferably from 2 cm / min to 30 cm / min.

The cooling is performed to at least the gelling temperature or lower. As a cooling method, a method of directly contacting with cold air, cooling water, or another cooling medium, a method of contacting with a roll cooled by a refrigerant, or the like can be used. The high-concentration solution of the polyolefin composition extruded from the die may be taken at a take-up ratio of 1 to 10 and preferably 1 to 5 before or during cooling. If the take-up ratio is too large, neck-in becomes large, and breakage tends to occur during stretching, which is not preferable.

The stretching of the gel-like sheet is preferably carried out by biaxial stretching, for example, by heating this gel-like sheet and employing a tenter method, a roll method, a rolling method or a combination thereof. At that time, either vertical or horizontal simultaneous stretching or sequential stretching may be used, but simultaneous secondary stretching is particularly preferable.
The stretching temperature is preferably equal to or lower than the temperature obtained by adding 10 ° C. to the melting point of the polyolefin composition, and more preferably equal to or higher than the crystal dispersion temperature and lower than the melting point. If the stretching temperature is too high, an effective molecular chain orientation due to stretching cannot be performed due to melting of the resin, which is not preferable.If the stretching temperature is too low, the softening of the resin becomes insufficient and the film breaks during stretching. This is because it is easy to perform stretching at a high magnification.

After stretching the gel-like sheet, the stretched film is preferably washed with a volatile solvent to remove the remaining low-volatile solvent. After washing, the stretched film is dried by heating or blowing, and the washing solvent is volatilized. As the cleaning solvent, for example, pentane, hexane,
A volatile substance such as a hydrocarbon such as hebutane, a chlorinated hydrocarbon such as methylene chloride or carbon tetrachloride, a fluorocarbon such as ethane trifluoride, or an ether such as diethyl ether or dioxane is used. The washing solvent is selected according to the low-volatile solvent used, and used alone or in combination. The washing can be performed by a method of immersing in a volatile solvent for extraction, a method of sprinkling with a volatile solvent, or a method of combining these. This washing is performed until the residual low-volatile solvent in the stretched film becomes less than 1 part by mass with respect to 100 parts by mass of the polyolefin composition.

The separator 23 has a thickness of 15 μm.
It is desirable to set it to about 30 μm. If the thickness is 15 μm or less, the yield of the battery may decrease, and if it is 30 μm or more, the energy density of the battery may decrease.

The separator 23 is impregnated with an electrolytic solution which is a liquid electrolyte. The electrolyte is a liquid solvent,
For example, a lithium salt is dissolved as an electrolyte salt in a non-aqueous solvent such as an organic solvent. The liquid non-aqueous solvent is, for example, one composed of one or more non-aqueous compounds and having an intrinsic viscosity at 25 ° C. of 10.0 mPa · s or less. In addition, the intrinsic clay in a state where the electrolyte salt is dissolved is 1
It may be 0.0 mPa · s or less, and when a plurality of types of non-aqueous compounds are mixed to form a solvent, the intrinsic clay in a mixed state may be 10.0 mPa · s or less. . As such a non-aqueous solvent, for example, a mixture of one or more compounds represented by a cyclic carbonate or a chain carbonate is preferable.

Specifically, ethylene carbonate (E
C), propylene carbonate (PC), butylene carbonate (BC), vinylene carbonate, γ-butyrolactone (GBL), γ-valerolactone, 1,2-dimethoxyethane (DME), tetrahydrofuran,
Methyltetrahydrofuran, 1,3-dioxolane, 4
-Methyl-1,3-dioxolane, methyl acetate, methyl propionate, dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), ethyl propyl carbonate (EP
C), acetonitrile, glutaronitrile, adiponitrile, methoxyacetonitrile, 3-methoxypropyronitrile, N, N-dimethylformamide, N-methylpyrrolidinone, N-methyloxazolidinone,
N'-dimethylimidazolidinone, nitromethane, nitroethane, sulfolane, dimethyl sulfoxide, trimethyl phosphate, and those obtained by substituting a part or all of the hydroxyl groups of these compounds with fluorine groups. In particular, in order to realize excellent charge / discharge capacity characteristics and charge / discharge cycle characteristics, it is preferable to use at least one of ethylene carbonate, propylene carbonate, vinylene carbonate, dimethyl carbonate, and ethyl methyl carbonate.

As the lithium salt, for example, LiAsF
₆ , LiPF ₆ , LiBF ₄ , LiClO ₄ , LiB
(C ₆ H ₅ ) ₄ , LiCH ₃ SO ₃ , LiCF ₃ S
O ₃ , LiN (SO ₂ CF ₃ ) ₂ , LiC (SO ₂ CF
₃ ) ₃ , LiAlCl ₄ , LiSiF ₆ , LiCl, L
Examples thereof include iBr, LiI, and LiSCN, and any one or more of these are used in combination. Note that the lithium salt may be in any concentration as long as it can be dissolved in a solvent, and particularly, 0.2 mol / l to 2.0 mol / l.
mol / l, preferably 0.6 mol / l.
More preferably, it is in the range of 1 / l to 1.5 mol / l. If the concentration is lower than this range, the ionic conductivity of the electrolyte decreases. If the concentration is higher than this range, the viscosity of the electrolyte increases, so that the mobility of lithium decreases and a theoretical capacity cannot be obtained.

In place of the electrolyte, a gel electrolyte in which the electrolyte is held by a host polymer compound may be used. The gel electrolyte has an ionic conductivity of 1 mS /
cm or more, and there is no particular limitation on the composition and the structure of the host polymer compound. The electrolytic solution (that is, the liquid solvent and the electrolyte salt) is as described above. As the host polymer compound, for example, polyacrylonitrile, polyvinylidene fluoride, a copolymer of polyvinylidene fluoride and polyhexafluoropropylene, polytetrafluoroethylene, polyhexafluoropropylene, polyethylene oxide, polypropylene oxide, polyphosphazene, poly Examples include siloxane, polyvinyl acetate, polyvinyl alcohol, polymethyl methacrylate, polyacrylic acid, polymethacrylic acid, styrene-butadiene rubber, nitrile-butadiene rubber, polystyrene and polycarbonate. In particular, from the viewpoint of electrochemical stability, it is desirable to use a polymer compound having a structure of polyacrylonitrile, polyvinylidene fluoride, polyhexafluoropropylene, or polyethylene oxide. The amount of the host polymer compound added to the electrolyte varies depending on the compatibility of both,
Usually, it is preferable to add a host polymer compound corresponding to 5% by mass to 50% by mass of the electrolytic solution.

The content of the lithium salt is preferably not more than 3.0 mol / kg, more preferably not less than 0.5 mol / kg, based on the solvent, as in the case of the electrolytic solution. However, the term “solvent” used herein is not limited to a liquid solvent alone, but is a concept that broadly includes a solvent capable of dissociating an electrolyte salt and having ion conductivity.
Therefore, when a host polymer having ion conductivity is used, the host polymer is also included in the solvent.

This secondary battery can be manufactured, for example, as follows.

First, for example, a positive electrode material is prepared by mixing a positive electrode material capable of inserting and extracting lithium, a conductive agent and a binder, and this positive electrode mixture is mixed with N-methyl-2. −
It is dispersed in a solvent such as pyrrolidone to form a paste-like positive electrode mixture slurry. This positive electrode mixture slurry is mixed with the positive electrode current collector 2
After coating on 1a and drying the solvent, compression molding is performed by a roll press machine or the like to form a positive electrode mixture layer 21b, and the positive electrode 21 is produced.

Next, for example, a negative electrode material capable of inserting and extracting lithium, a binder mainly composed of a styrene-butadiene copolymer, and a thickener mainly composed of a cellulose derivative are combined with the above-mentioned optimum requirements. A negative electrode mixture is prepared by mixing at a ratio satisfying the following, and this negative electrode mixture is dispersed in a solvent such as distilled water to obtain a paste-like negative electrode mixture slurry. The slurry for the negative electrode mixture contains a binder in an amount necessary for binding the negative electrode material and a thickener in an amount necessary for dispersing the binder. Therefore,
The negative electrode mixture slurry has an appropriate viscosity so that the coating can be easily performed and the binder is well dispersed. The negative electrode mixture slurry is applied to the negative electrode current collector 22a, the solvent is dried, and then compression-molded by a roll press or the like to form the negative electrode mixture layer 22b, thereby producing the negative electrode 22. As a result, the negative electrode material is uniformly bonded without containing a large amount of the binder, and an increase in the internal resistance and peeling of the formed negative electrode mixture layer 22b are prevented.

Subsequently, the cathode lead 25 is attached to the cathode current collector by welding or the like, and the anode lead 26 is attached to the anode current collector 22a by welding or the like. after that,
The positive electrode 21 and the negative electrode 22 are wound with the separator 23 interposed therebetween, and the tip of the positive electrode lead 25 is welded to the safety valve mechanism 15, and the tip of the negative electrode lead 26 is welded to the battery can 11. The negative electrode 22 is sandwiched between the pair of insulating plates 12 and 13 and housed inside the battery can 11. Positive electrode 2
After storing the first and negative electrodes 22 inside the battery can 11,
The electrolyte is injected into the battery can 11 and impregnated in the separator 23. After that, the battery lid 14, the safety valve mechanism 15, and the thermal resistance element 16 are fixed to the open end of the battery can 11 by caulking via the gasket 17. Thereby, the secondary battery shown in FIG. 1 is formed.

This secondary battery operates as follows.

In this secondary battery, when charged, lithium ions are released from the positive electrode mixture layer 21b, and the separator 2
The lithium in the negative electrode mixture layer 22b reaches the negative electrode material capable of occluding and releasing lithium through the electrolytic solution impregnated in 3, and is initially absorbed therein during charging. When charging is further continued, at the time when the open circuit voltage is lower than the overcharge voltage, the capacity exceeds the chargeable capacity by the occlusion / desorption reaction in the negative electrode 22, and lithium ions begin to precipitate as lithium metal on the surface of the negative electrode material. As a result, charging is continued, and lithium metal continues to be deposited on the negative electrode 22 until charging is completed. In addition, the appearance of the negative electrode mixture layer 22b changes from black to golden and further to white silver with charging when, for example, a carbon material is used as a negative electrode material capable of inserting and extracting lithium.

Next, when the discharge is performed, first, the lithium metal deposited on the negative electrode 22 is eluted as ions, and is passed through the electrolyte impregnated in the separator 23.
b. When the discharge is further continued, the negative electrode mixture layer 22
The lithium ions occluded in the negative electrode material capable of occluding and releasing lithium in b are released and occluded in the positive electrode mixture layer 21b via the electrolytic solution. Thus, in this secondary battery, charging and discharging are performed based on the operation principles of both the conventional so-called lithium secondary battery and lithium ion secondary battery, and a high energy density and good charge / discharge cycle characteristics can be obtained. .

In particular, the negative electrode 22 is composed of a negative electrode material capable of inserting and extracting lithium, a binder mainly composed of a styrene-butadiene copolymer, and a thickener mainly composed of a cellulose derivative. Since it contains in a ratio that satisfies the optimal requirements, the negative electrode material is uniformly bound inside without containing a large amount of the binder, and the electrode reaction itself in the above-described negative electrode 22 is inhibited or during use. Peeling is prevented.

As described above, according to the present embodiment, the negative electrode 2
No. 2 satisfies the above-mentioned optimum requirements of a negative electrode material capable of inserting and extracting lithium, a binder mainly composed of a styrene-butadiene copolymer, and a thickener mainly composed of a cellulose derivative. Since it is included in the ratio, the battery can be easily manufactured and the cycle characteristics of the battery can be further maintained and improved.

(Modification) In the above embodiment, a cylindrical battery has been described. However, batteries having other shapes and structures can be manufactured. In this modification, a card-type secondary battery will be described as an example. Here, the same components as those in the above embodiment are denoted by the same reference numerals, and description thereof will be omitted.

FIG. 3 shows an exploded structure of the secondary battery, and FIG. 4 shows a sectional structure of the spirally wound electrode body 20 shown in FIG. This secondary battery has a positive electrode lead wire 2
5 and a wound electrode body 20 to which a negative electrode lead wire 26 is attached in parallel is sealed in a film-shaped exterior member 30. In this case, the wound electrode body 20 is formed by winding the positive electrode 21, the separator 23, and the negative electrode 22 of the wound electrode body 20 in the above-described embodiment via, for example, a gel electrolyte layer 27 therebetween. I have. The negative electrode 2
2 is protected by a protective tape (not shown).

The positive electrode 21 is, for example, a positive electrode current collector layer 21a.
And a positive electrode mixture layer 21b provided on both surfaces or one surface of the positive electrode current collector layer 21a. The positive electrode current collector layer 21a has a portion where the positive electrode mixture layer 21b is not provided at one end in the longitudinal direction and the positive electrode current collector layer 21a is exposed. 11 is attached.

The negative electrode 22 is, for example, similar to the positive electrode 21,
It has a negative electrode current collector layer 22a and a negative electrode mixture layer 22b provided on both surfaces or one surface of the negative electrode current collector layer 22a. Also in this case, the negative electrode mixture layer 22b includes, together with the negative electrode material, a binder mainly composed of a styrene-butadiene copolymer, and a thickener mainly composed of a cellulose derivative.
It is included in a ratio that satisfies the optimal requirements described in the above embodiment. The negative electrode current collector layer 22a has a portion where the negative electrode mixture layer 22b is not provided at one end in the longitudinal direction and the negative electrode current collector layer 22a is exposed. 12 are attached.

The electrolyte layer 27 includes, for example, a lithium salt,
It is a gel electrolyte composed of a non-aqueous solvent that dissolves this lithium salt and a polymer material. The gel electrolyte refers to an electrolyte in which a solvent is dispersed in a polymer matrix, and the amount of the dispersed electrolyte is not limited. As the lithium salt, the nonaqueous solvent, and the polymer material, those described in the above embodiment can be used, and those other than those described above are confirmed to be compatible with the electrolytic solution to form a gel. Can be used. In addition, the exterior member 3
When a laminated film described later is used as 0, ethylene carbonate, propylene carbonate, butylene carbonate, γ-butyl lactone, 2,4-difluoroanisole, 2,6-difluoroanisole or 4-bromoveratrol is used as a nonaqueous solvent. It is preferable to use one having a boiling point of 150 ° C. or higher. This is because if vaporized easily, the exterior member 30 swells and the outer shape becomes defective. Further, in such a battery, the thickness of the solid electrolyte layer 27 is desirably 5 μm or more and 15 μm or less. If it is less than 5 μm, it is too thin and short circuit easily occurs.
If the thickness is larger than m, the high-load characteristics of the battery may be degraded and the volume energy density may be reduced.

For the separator 23, the materials described in the above embodiment can be used. In such a battery, the thickness of the separator 23 is 5 μm to 15 μm.
It is desirable to set it to about μm. If the thickness is less than 5 μm, the yield of the battery decreases, and if the thickness is more than 15 μm, the energy density of the battery may decrease. Here, since the electrolyte layer 27 prevents a short circuit between the electrodes, the separator 23 need not be provided.

The exterior member 30 has a thickness of, for example, 90 μm or less.
It is composed of two rectangular films of about 110 μm, and the respective outer edges are adhered to each other by fusion bonding or an adhesive. The exterior member 30 includes at least an aluminum layer and a heat-sealing polymer layer, and is, for example, a laminate film shown in FIG.
a, an aluminum film 30b, a polyethylene terephthalate (PET) film 30c, and an unstretched polypropylene (CPP) film 30d are laminated as a multilayer film in this order. Among them, the aluminum film 30b has a moisture-proof property for preventing the invasion of the outside air, and the PET film 30c and the CPP
The film 30d has good heat-sealing properties. In addition, nylon, linear low density polyethylene (LLDPE), high density polyethylene (H
DPE), and their copolymers. Such an exterior member 30 is provided so that the CPP film 30d and the wound electrode body 20 face each other. Note that the exterior member 30 may be made of a laminated film having another structure, a polymer film such as polypropylene, or a metal film instead of the above-described laminated film.

Incidentally, the positive electrode lead wire 25, the negative electrode lead wire 26 and the exterior member 30 are sufficiently adhered to each other through, for example, an adhesive film 31 so as to prevent the invasion of the outside air. The adhesive film 31 is made of a material having adhesiveness to the positive electrode lead wire 11 and the negative electrode lead wire 12. For example, when the positive electrode lead wire 11 and the negative electrode lead wire 12 are made of the above-described metal material, ,
It is preferable to be composed of a polyolefin resin such as polyethylene, polypropylene, modified polyethylene or modified polypropylene.

The secondary battery having such a configuration can be manufactured, for example, as follows.

First, the same positive electrode material as in the above embodiment, a conductive agent and a binder are mixed to prepare a positive electrode mixture, and the mixture is dispersed in a solvent such as N-methyl-2-pyrrolidone to form a positive electrode mixture. Prepare an agent slurry. Next, this positive electrode mixture slurry is applied to both surfaces or one surface of the positive electrode current collector layer 21a, dried, and compression molded to form a positive electrode mixture layer 21b,
The positive electrode 21 is manufactured. At this time, the positive electrode mixture is not applied to one end of the positive electrode current collector layer 21a, and the end is exposed.

Next, for example, a negative electrode material capable of inserting and removing lithium, a binder mainly composed of a styrene-butadiene copolymer, and a thickener mainly composed of a cellulose derivative satisfy the above-mentioned optimum requirements. A negative electrode mixture is prepared by mixing at a ratio, and this negative electrode mixture is dispersed in a solvent such as distilled water to obtain a paste-like negative electrode mixture slurry.
The slurry for the negative electrode mixture contains a binder in an amount necessary for binding the negative electrode material and a thickener in an amount necessary for dispersing the binder. Therefore, the negative electrode mixture slurry has an appropriate viscosity so that the coating can be easily performed and the binder is well dispersed. The negative electrode mixture slurry is applied to the negative electrode current collector 22a, the solvent is dried, and then compression-molded by a roll press or the like to form the negative electrode mixture layer 22b, thereby producing the negative electrode 22. As a result, the negative electrode material is uniformly bonded without containing a large amount of the binder, and an increase in the internal resistance and peeling of the formed negative electrode mixture layer 22b are prevented. At this time, the negative electrode mixture is not applied to one end of the negative electrode current collector layer 22a, and the end is exposed.

Subsequently, a cathode lead wire 25 is attached to the exposed portion of the cathode current collector layer 21a by resistance welding or ultrasonic welding, and an electrolyte is applied on the cathode mixture layer 21b to form an electrolyte layer 27, for example. Form. The negative electrode lead wire 26 is attached to the exposed portion of the negative electrode current collector layer 22a by resistance welding or ultrasonic welding, and an electrolyte is applied on the negative electrode mixture layer 22b, for example, to form an electrolyte layer 27. After that, for example, the separator 23,
The positive electrode 21 on which the electrolyte layer 27 is formed, the separator 23,
The negative electrode 22 on which the electrolyte layer 27 is formed is sequentially laminated and wound, and a protective tape is adhered to the outermost peripheral portion, for example, to form the wound electrode body 20.

When the electrolyte layer 27 is formed, for example, the raw material of the electrolyte stored in a dry atmosphere (ie, a mixture of a lithium salt, a non-aqueous solvent, and a polymer material) is heated to about 70 ° C. The polymer is heated and polymerized, and the temperature is maintained to apply onto the positive electrode mixture layer 21b or the negative electrode mixture layer 22b. This prevents the generation of free acid.

Next, for example, two exterior members 30 are prepared, the wound electrode body 20 is sandwiched therebetween, and the exterior member 30 is pressed against the wound electrode body 20 in a reduced pressure atmosphere, The outer edges are brought into close contact with each other by heat fusion or the like. At the end of the exterior member 30 from which the positive lead wire 25 and the negative lead wire 26 are led out, adhesive films 31 are arranged so as to sandwich the positive lead wire 25 and the negative lead wire 26, respectively. The outer edges are brought into close contact with each other. Thereby, the battery shown in FIG. 3 is completed.

In this secondary battery, the same electrode reaction as in the above embodiment occurs. Therefore, also in this modification, the same effect as in the above embodiment can be obtained.

[0086]

FIG. 1 shows a specific embodiment of the present invention.
This will be described in detail with reference to FIG.

Example 1 First, lithium carbonate (Li ₂
CO ₃ ) and cobalt carbonate (CoCO ₃ ) are mixed such that lithium atoms and cobalt atoms have a composition ratio of 1: 1 and calcined in air at 900 ° C. for 5 hours to obtain a lithium-cobalt composite oxide. (LiCoO ₂ ) was obtained. X-ray diffraction measurement of the obtained lithium-cobalt composite oxide showed a good agreement with the peak of LiCoO ₂ registered in the JCPDS file. Next, this lithium-cobalt composite oxide was pulverized to obtain a powdery positive electrode material.

Subsequently, 95% by mass of the lithium-cobalt composite oxide powder was used, and KS having an average particle size of 7 μm was used as a conductive agent.
-15 graphite (manufactured by Lonza) 2% by mass, and
A cathode mixture was prepared by mixing 3% by mass of polyvinylidene fluoride as a binder. This positive electrode mixture is dispersed in N-methyl-2-pyrrolidone as a solvent to form a positive electrode mixture slurry, which is uniformly applied to both surfaces of a positive electrode current collector 21a made of a strip-shaped aluminum foil having a thickness of 20 μm and a width of 58 mm and dried. Then, the positive electrode mixture layer 21b was formed by compression molding with a roll press machine to form the positive electrode 21. After that, the positive electrode current collector 2
A positive electrode lead 25 made of aluminum was attached to one end of 1a.

Further, a pitch coke having a specific surface area of 2 g / m ² after pulverization was used as a negative electrode material, and 96 mass% of the pitch coke was used as a binder. A negative electrode mixture was prepared by mixing 2% by mass of a styrene-butadiene polymer having a group and 2% by mass of carboxymethylcellulose ammonium having a molecular weight of 150,000 (hereinafter simply referred to as carboxymethylcellulose ammonium) as a thickener. In all the examples and comparative examples described below, the styrene-butadiene polymer used as the binder refers to the above. Subsequently, the negative electrode mixture was dispersed in distilled water to form a slurry, and then a thickness of 10 μm and a width of 59 m
The negative electrode current collector 22a made of a copper foil of m was uniformly coated on both sides, dried, and compression-molded with a roll press to produce a strip-shaped negative electrode 22. Thereafter, a negative electrode lead 26 made of nickel was attached to one end of the negative electrode current collector 22a.

After each of the positive electrode 21 and the negative electrode 22 was prepared, a separator 23 made of a microporous stretched polyethylene film was prepared.
1, the separator 23 was laminated in this order, and the laminate was spirally wound many times to produce a wound electrode body 20.

After the wound electrode body 20 is manufactured, the wound electrode body 20 is sandwiched between a pair of insulating plates 12 and 13, and the negative electrode lead 2 is formed.
6 was welded to the battery can 11, the positive electrode lead 25 was welded to the safety valve mechanism 15, and the wound electrode body 20 was housed inside the nickel-plated iron battery can 11 having an inner diameter of 13.3 mm. After that, the electrolytic solution was injected into the battery can 11 by a reduced pressure method. The electrolyte contains L as an electrolyte salt.
A mixture of propylene carbonate in which iPF ₆ was dissolved at a concentration of 1 mol / l and 1,2-dimethoxyethane was used.

After injecting the electrolytic solution into the battery can 11, the battery cover 14 is caulked to the battery can 11 via a gasket 17 coated with asphalt on the surface, thereby forming a cylindrical mold 14 mm in diameter and 65 mm in height. The following battery was obtained.

The obtained secondary battery was subjected to a charge / discharge test, and the initial capacity and the discharge capacity retention of the battery were determined. At that time, charging was performed at a constant current and constant voltage of 600 mA and 4.2 V, and discharging was performed at a constant current of 400 mA until the battery voltage reached 3.0 V. By the way, when charging and discharging are performed under the conditions shown here, a fully charged state and a completely discharged state are obtained. The discharge capacity retention ratio is the ratio of the discharge capacity at the 100th cycle when the discharge capacity at the second cycle is 100%, that is, (discharge capacity at the 100th cycle /
The discharge capacity at the second cycle) × 100 was calculated.

(Example 2) 96% by mass of pitch coke,
A secondary battery was prepared and evaluated in the same manner as in Example 1, except that 3% by mass of a styrene-butadiene polymer and 1% by mass of carboxymethylcellulose ammonium were mixed to prepare a negative electrode mixture.

(Example 3) 94% by mass of pitch coke,
A secondary battery was prepared and evaluated in the same manner as in Example 1 except that a negative electrode mixture was prepared by mixing 4% by mass of a styrene-butadiene polymer and 2% by mass of carboxymethylcellulose ammonium.

Example 4 92% by mass of pitch coke
A secondary battery was prepared and evaluated in the same manner as in Example 1, except that 4% by mass of a styrene-butadiene polymer and 4% by mass of carboxymethylcellulose ammonium were mixed to prepare a negative electrode mixture.

Example 5 92% by mass of pitch coke,
A secondary battery was prepared in the same manner as in Example 1, except that 8/3% by mass of a styrene-butadiene polymer and 16/3% by mass of carboxymethylcellulose ammonium were mixed to prepare a secondary battery, and the characteristics were evaluated. went.

Example 6 Example 1 was repeated except that 98.5% by weight of pitch coke, 0.5% by weight of a styrene-butadiene polymer and 1% by weight of carboxymethylcellulose ammonium were mixed to prepare a negative electrode mixture. In the same manner as in the above, a secondary battery was produced and its characteristics were evaluated.

(Example 7) 99% by mass of pitch coke,
A secondary battery was prepared in the same manner as in Example 1, except that 1/3% by mass of a styrene-butadiene polymer and 2/3% by mass of carboxymethylcellulose ammonium were mixed to prepare a secondary battery, and the characteristics were evaluated. went.

As comparative examples with respect to Examples 1 to 7, secondary batteries of Comparative Examples 1 to 8 were produced, and their characteristics were evaluated.

Comparative Example 1 90% by mass of pitch coke
A secondary battery was prepared and evaluated in the same manner as in Example 1, except that 10% by mass of polyvinylidene fluoride was mixed as a binder to prepare a negative electrode mixture.

Comparative Example 2 95.5% by mass of pitch coke, 4% by mass of a styrene-butadiene polymer and 0.5% by mass of carboxymethylcellulose ammonium were mixed to obtain a negative electrode mixture. Except for this, the production of the negative electrode 22 was attempted in the same manner as in Example 1. However, the binder aggregated on the negative electrode material and could not be coated, and thus the negative electrode 22 could not be produced.

Comparative Example 3 93% by mass of pitch coke
A secondary battery was prepared and evaluated in the same manner as in Example 1, except that 6% by mass of a styrene-butadiene polymer and 1% by mass of carboxymethylcellulose ammonium were mixed to prepare a negative electrode mixture.

(Comparative Example 4) 91% by mass of pitch coke,
A secondary battery was prepared and evaluated in the same manner as in Example 1, except that 6% by mass of a styrene-butadiene polymer and 3% by mass of carboxymethylcellulose ammonium were mixed to prepare a negative electrode mixture.

(Comparative Example 5) 91% by mass of pitch coke,
A secondary battery was prepared and evaluated in the same manner as in Example 1, except that 4% by mass of a styrene-butadiene polymer and 5% by mass of carboxymethylcellulose ammonium were mixed to prepare a negative electrode mixture.

Comparative Example 6 92% by mass of pitch coke
A secondary battery was prepared and evaluated in the same manner as in Example 1, except that a negative electrode mixture was prepared by mixing 1% by mass of a styrene-butadiene polymer and 7% by mass of carboxymethylcellulose ammonium.

(Comparative Example 7) 95% by mass of pitch coke,
A secondary battery was prepared and evaluated in the same manner as in Example 1, except that 1% by mass of a styrene-butadiene polymer and 4% by mass of carboxymethylcellulose ammonium were mixed to prepare a negative electrode mixture.

Comparative Example 8 A negative electrode mixture was prepared by mixing 99.5% by mass of pitch coke, 0.25% by mass of a styrene-butadiene polymer, and 0.25% by mass of carboxymethylcellulose ammonium. An attempt was made to produce the negative electrode 22 in the same manner as in Example 1. However, the binder was not able to form a coating film due to the aggregation of the binder on the negative electrode material, and thus the negative electrode 22 could not be produced.

Table 1 shows the evaluation results of the battery characteristics in Examples 1 to 7 and Comparative Examples 1 to 8.

[0110]

[Table 1]

As is clear from Table 1, the initial capacity is almost the same in both the example and the comparative example, but the discharge capacity retention ratio is higher in the example than in the comparative example. FIG. 6 is a graph in which the discharge capacity retention rates of Examples 1 to 7 and Comparative Examples 2 to 8 are plotted in a ternary composition diagram showing the material composition ratio of the negative electrode mixture. In the figure, the region surrounded by the thick line simultaneously satisfies the optimal requirements described in the above-described embodiment, and the shape of the contour line of the discharge capacity retention rate substantially matches the shape of this region. Understand.

In Comparative Examples 2 and 8, the negative electrode 22
It was difficult to fabricate this. Thus, it is suggested that the absolute amount of the binder itself, and the composition system in which the thickener is smaller than the binder, has insufficient dispersibility of the binder and makes it difficult to form a coating film. . Further, it is suggested that in a composition system in which the absolute amount of the binder, that is, the binder and the thickener is small, the amount of the binder is insufficient and the formation of the coating film becomes difficult. Therefore,
It can be seen that not only by using these binders and thickeners, but also by defining the composition ratio, the negative electrode material can be bound in a suitable state, and higher cycle characteristics can be obtained.

Further, an embodiment of the present invention will be described in detail with reference to FIG.

Example 8 First, a positive electrode mixture slurry was prepared in the same manner as in Example 1, and then the thickness was 20 μm and the width was 4 μm.
Positive electrode collector 21a made of 9 mm strip-shaped aluminum foil
Was uniformly coated on both sides of the substrate, dried, and compression-molded with a roll press to form a positive electrode mixture layer 21b, thereby producing a positive electrode 21. Thereafter, a rod-shaped positive electrode lead 25 made of aluminum was attached to one end of the positive electrode current collector 21a by spot welding.

Also, a negative electrode mixture was prepared by using the same material as in Example 1 except that pulverized mesocarbon microbeads having a specific surface area of 2 g / m ² were used as the negative electrode material. did. After this was turned into a slurry, a negative electrode current collector 22a made of copper foil having a thickness of 10 μm and a width of 51 mm was used.
Was uniformly coated on both sides of the film, dried, and compression-molded with a roll press to produce a strip-shaped negative electrode 22. Then, a rod-shaped nickel negative electrode lead 2 is attached to one end of the negative electrode current collector 22a.
6 was mounted by spot welding.

Next, PVdF and EC, P as a solvent were used.
C, DMC, and LiAsF ₆ as lithium salts at 5.8 wt%, 25.8 wt%, 17.2 wt%, and 4 wt%, respectively.
7.3 wt% and 3.9 wt% were mixed and stirred at 80 ° C. to prepare a sol electrolyte solution.
This mixed solution was applied to both surfaces of the positive electrode 21 and the negative electrode 22 in a liquid state by a doctor blade method.
It was dried in a 5 ° C. thermostat for 3 minutes to form an electrolyte layer 27 having a thickness of 10 μm.

Next, the positive electrode 21, the negative electrode 22, and the separator 23 each having the electrolyte layer 27 formed on the surface thereof were superposed and wound in the order shown in FIG. 4 to form a wound electrode body 20 having a size of 30 mm × 53 mm × 5 mm. . This was sealed with an exterior member 30 made of a moisture-proof multilayer film having a thickness of 100 μm.
Was obtained.

The obtained secondary battery was subjected to a charge / discharge test to determine the initial capacity and the discharge capacity retention of the battery. At that time, charging was performed at a constant current and constant voltage of 400 mA and 4.2 V, and discharging was performed at a constant current of 200 mA until the battery voltage reached 3.0 V.

Example 9 A secondary battery was manufactured in the same manner as in Example 8, except that mesocarbon microbeads were used as a negative electrode material and mixed at the same composition ratio as in Example 2 to prepare a negative electrode mixture. Was fabricated and characteristics were evaluated.

Example 10 A secondary battery was manufactured in the same manner as in Example 8, except that mesocarbon microbeads were used as a negative electrode material and mixed at the same composition ratio as in Example 3 to prepare a negative electrode mixture. Was fabricated and characteristics were evaluated.

Example 11 A secondary battery was produced in the same manner as in Example 8, except that mesocarbon microbeads were used as a negative electrode material and mixed at the same composition ratio as in Example 4 to prepare a negative electrode mixture. Was fabricated and characteristics were evaluated.

Example 12 A secondary battery was produced in the same manner as in Example 8, except that mesocarbon microbeads were used as a negative electrode material and mixed at the same composition ratio as in Example 5 to prepare a negative electrode mixture. Was fabricated and characteristics were evaluated.

Example 13 A secondary battery was produced in the same manner as in Example 8, except that mesocarbon microbeads were used as a negative electrode material and mixed at the same composition ratio as in Example 6 to prepare a negative electrode mixture. Was fabricated and characteristics were evaluated.

Example 14 A secondary battery was manufactured in the same manner as in Example 8, except that mesocarbon microbeads were used as a negative electrode material and mixed at the same composition ratio as in Example 7 to prepare a negative electrode mixture. Was fabricated and characteristics were evaluated.

As comparative examples with respect to Examples 8 to 14, secondary batteries of Comparative Examples 9 to 16 were produced, and their characteristics were evaluated.

Comparative Example 9 A secondary battery was manufactured in the same manner as in Example 8, except that mesocarbon microbeads were used as a negative electrode material and mixed at the same composition ratio as in Comparative Example 1 to prepare a negative electrode mixture. Was fabricated and characteristics were evaluated.

Comparative Example 10 A secondary battery was prepared in the same manner as in Example 8, except that mesocarbon microbeads were used as a negative electrode material and mixed at the same composition ratio as in Comparative Example 2 to prepare a negative electrode mixture. Was fabricated and characteristics were evaluated.

Comparative Example 11 A secondary battery was manufactured in the same manner as in Example 8, except that mesocarbon microbeads were used as a negative electrode material and mixed at the same composition ratio as in Comparative Example 3 to prepare a negative electrode mixture. Was fabricated and characteristics were evaluated.

(Comparative Example 12) A secondary battery was manufactured in the same manner as in Example 8, except that mesocarbon microbeads were used as a negative electrode material and mixed at the same composition ratio as in Comparative Example 4 to prepare a negative electrode mixture. Was fabricated and characteristics were evaluated.

(Comparative Example 13) A secondary battery was manufactured in the same manner as in Example 8, except that mesocarbon microbeads were used as a negative electrode material and mixed at the same composition ratio as in Comparative Example 5 to prepare a negative electrode mixture. Was fabricated and characteristics were evaluated.

Comparative Example 14 A secondary battery was produced in the same manner as in Example 8, except that mesocarbon microbeads were used as a negative electrode material and mixed at the same composition ratio as in Comparative Example 6 to prepare a negative electrode mixture. Was fabricated and characteristics were evaluated.

Comparative Example 15 A secondary battery was produced in the same manner as in Example 8, except that mesocarbon microbeads were used as a negative electrode material and mixed at the same composition ratio as in Comparative Example 7 to prepare a negative electrode mixture. Was fabricated and characteristics were evaluated.

(Comparative Example 16) A secondary battery was manufactured in the same manner as in Example 8 except that mesocarbon microbeads were used as a negative electrode material and mixed at the same composition ratio as in Comparative Example 8 to prepare a negative electrode mixture. Was fabricated and characteristics were evaluated.

Examples 8 to 14 and Comparative Examples 9 to
Table 2 shows the evaluation results of the battery characteristics of No. 16.

[0135]

[Table 2]

As is clear from Table 2, the initial capacity is almost the same in both the example and the comparative example, but the discharge capacity retention ratio is higher in the example than in the comparative example. The discharge capacity retention rates of these Examples 8 to 14 simultaneously satisfy the optimum requirements described in the above-described embodiment, and are not shown, but are similar to Examples 1 to 7 in terms of the material composition ratio of the negative electrode mixture. It belongs to the region where the discharge capacity retention ratio is high.

In Comparative Examples 10 and 16, it was difficult to produce the negative electrode 22 itself. Therefore, even when the negative electrode of the present invention is applied to the battery shown in FIG. 3, the absolute amount of the binder itself, and the dispersibility of the binder in a composition system in which the thickener is smaller than the binder, are used. Is not sufficient, and it is suggested that coating film formation becomes difficult. Also, the binder,
It is suggested that in a composition system in which the absolute amounts of the binder and the thickener are small, the amount of the binder is insufficient and the formation of a coating film becomes difficult.

From the above results, not only these binders and thickeners are used, but also by defining the composition ratio, the negative electrode material can be bound in a suitable state and higher cycle characteristics can be obtained. This shows that these effects are exhibited regardless of the shape of the battery.

Although the present invention has been described with reference to the embodiments and examples, the present invention is not limited to the above-described embodiments and examples, and can be variously modified. For example, in the above embodiments and examples, the case where lithium is used as the light metal has been described. However, another alkali metal such as sodium (Na) or potassium (K), or magnesium (Mg) or calcium (Ca) is used. The present invention can also be applied to the case where an alkaline earth metal, other light metal such as aluminum (Al), lithium or an alloy thereof is used, and the same effect can be obtained. At this time, a negative electrode material, a positive electrode material, a non-aqueous solvent, an electrolyte salt, or the like capable of inserting and extracting a light metal is selected according to the light metal. However, it is preferable to use lithium or an alloy containing lithium as the light metal because voltage compatibility with lithium ion secondary batteries currently in practical use is high. When an alloy containing lithium is used as the light metal, a substance capable of forming an alloy with lithium exists in the electrolyte, and an alloy may be formed at the time of deposition. There is a possible substance,
An alloy may be formed during precipitation. Incidentally, as the substance capable of forming an alloy with lithium, specifically, aluminum, zinc (Zn), lead (Pb), tin (Sn), antimony (Sb), bismuth (Bi), cadmium (C
d) and the like.

Further, in the above embodiments and examples, the case where a gel electrolyte which is one kind of an electrolyte or a solid electrolyte is used, but another electrolyte may be used. Other electrolytes include, for example, an organic solid electrolyte in which an electrolyte salt is dispersed in a polymer compound having ion conductivity, an ion conductive ceramic,
Inorganic solid electrolytes made of ion-conductive glass or ionic crystals, or mixtures of these inorganic solid electrolytes and electrolytes, or mixtures of these inorganic solid electrolytes and gel electrolytes or organic solid electrolytes Is mentioned.

Further, in the above embodiments and examples, the cylindrical type and the card type among the secondary batteries having the wound structure have been described. However, the present invention is not limited to the polygon type having the wound structure. The present invention can be similarly applied to a secondary battery of another shape or a secondary battery having a structure in which a positive electrode and a negative electrode are folded or stacked. In addition, the present invention can be applied to so-called coin-type and button-type secondary batteries, and can be applied not only to secondary batteries but also to primary batteries.

[0142]

As described above, according to the battery of the present invention, the negative electrode comprises a negative electrode material capable of inserting and extracting a light metal, a binder mainly composed of a styrene-butadiene copolymer, and a carboxymethyl cellulose derivative. Including a negative electrode mixture composed of a thickening agent consisting of, a necessary amount of binder to bind the negative electrode material, and a necessary amount of thickener to disperse the binder are contained Since the composition ratio is defined as such, the negative electrode mixture can be easily coated and has a suitable viscosity such that the binder is well dispersed, and the negative electrode material can be used without containing a large amount of the binder. It is uniformly bonded, and increases in internal resistance and peeling of the negative electrode are prevented. Therefore, good cycle characteristics can be obtained.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating a configuration of a secondary battery according to an embodiment of the present invention.

FIG. 2 is an enlarged cross-sectional view showing a part of a wound electrode body in the secondary battery shown in FIG.

FIG. 3 is a cross-sectional view illustrating a configuration of a secondary battery according to a modified example of the invention.

FIG. 4 is a cross-sectional view illustrating a part of a wound electrode body in the secondary battery illustrated in FIG. 3 in an enlarged manner.

5 is a cross-sectional view of an exterior member in the secondary battery shown in FIG.

FIG. 6 is a diagram showing a discharge capacity retention ratio with respect to a material composition ratio of a negative electrode mixture in Examples and Comparative Examples of the present invention.

[Explanation of symbols]

11 ... battery can, 12, 13 ... insulating plate, 14 ... battery lid, 1
5 safety valve mechanism, 16 thermosensitive resistor element, 17 gasket, 20 wound electrode body, 21 positive electrode, 21a positive electrode current collector, 21b positive electrode mixture layer, 22 negative electrode, 22a negative electrode current collector , 22b ... negative electrode mixture layer, 23 ... separator, 24 ...
Center pin, 25: positive lead, 26: negative lead,
27: electrolyte layer, 30: exterior member, 31: adhesive film

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5H029 AJ05 AK03 AL06 AL07 AL08 AM03 AM05 AM07 BJ02 BJ14 DJ08 EJ12 HJ01 HJ07 5H050 AA07 CA07 CA08 CA09 CB07 CB08 CB09 CB11 CB13 CB14 CB15 DA11 EA23 HA01 HA07

Claims (10)

[Claims] 1. A battery provided with an electrolyte together with a positive electrode and a negative electrode, wherein the capacity of the negative electrode is represented by the sum of a capacity component due to occlusion and desorption of light metal and a capacity component due to precipitation and dissolution of light metal. The negative electrode includes a negative electrode material capable of inserting and extracting a light metal, a binder mainly composed of a styrene-butadiene copolymer, and a negative electrode mixture mainly composed of a thickener composed of a carboxymethylcellulose derivative. The weight ratio of the binder in the negative electrode mixture is 0.5% by mass or more and 4% by mass or less, and the weight ratio of the binder in the negative electrode mixture with respect to the specific surface area (m ² / g) of the negative electrode material (Mass%) is 0.25 or more and 4 or less, and the ratio of the weight of the thickener to the weight of the binder is 1/3 or more and 2 or less. 2. The battery according to claim 1, wherein the cellulose derivative is an alkali metal salt of carboxymethyl cellulose or an ammonium salt of carboxymethyl cellulose. 3. The battery according to claim 2, wherein the cellulose derivative has a molecular weight of 100,000 to 200,000. 4. The styrene-butadiene copolymer,
The battery according to claim 1, wherein the battery has at least one of a carbonyl group and a cyano group. 5. The battery according to claim 4, wherein the negative electrode contains a carbon material. 6. The battery according to claim 5, wherein the negative electrode includes at least one member selected from the group consisting of graphite, graphitizable carbon, and non-graphitizable carbon. 7. The battery according to claim 6, wherein the negative electrode contains graphite. 8. The method according to claim 4, wherein the negative electrode includes at least one selected from the group consisting of metals, semiconductors, alloys and compounds capable of forming an alloy or a compound with the light metal. battery. 9. The negative electrode comprises tin (Sn), lead (P)
b), aluminum (Al), indium (In), silicon (Si), zinc (Zn), antimony (Sb), bismuth (Bi), cadmium (Cd), magnesium (Mg), boron (B), gallium ( Ga), germanium (Ge), arsenic (As), silver (Ag), hafnium (Hf), zirconium (Zr) and yttrium (Y), and at least one of the group consisting of alloys and compounds. The battery according to claim 8, wherein: 10. The battery according to claim 1, wherein the light metal includes lithium (Li).