JP2002279989A - Battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a battery capable of increasing safety by preventing heating from being produced by internal short circuiting. SOLUTION: A battery comprises a rolled electrode body 20, having a band- shaped positive electrode 21 and a negative electrode 22 rolled via a separator 23. The negative electrode 22 is so designed that lithium metal is deposited during charging. The capacity of the negative electrode 22 is expressed by the sum of a capacity component by the storage and release of lithium and a capacity component by the deposition and dissolution of the lithium metal. The positive electrode 21 contains, as positive electrode active material, phosphorus oxides such as LiFePO4 or LiFe0.5 Mn0.5 PO4 and oxides, such as LiCoO2 , LiNi0.8 CO0.2 O2 or LiMn2 O4 . Heating due to internal short circuiting is prevented by the phosphorus oxides, such as LiFePO4 to increase safety, and the capacity is increased by oxides, such as LiCoO2 .

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 the negative electrode is the sum of a capacity component due to insertion and extraction of lithium and a capacity component due to precipitation and dissolution of lithium. And a battery containing the same.

[0002]

2. Description of the Related Art In recent years, portable electronic devices typified by a camera-integrated VTR (video tape recorder), a cellular phone or a laptop computer have become widespread, and their miniaturization, weight reduction and continuous driving for a long time are strongly demanded. Have been. Along with this, demands for higher capacity and higher energy density of secondary batteries as those portable power sources are increasing.

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 a negative electrode, or There is a lithium secondary battery using lithium metal for the negative electrode. 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. In addition, in lithium secondary batteries, lithium metal tends to be non-uniformly deposited on the negative electrode and tends to be needle-like or powdery, so that it is necessary to provide more mechanisms for ensuring safety than others. There were also problems.

Accordingly, 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 method, 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. In addition, since the carbon material has a large specific surface area, lithium can be deposited relatively uniformly, and since the carbon material also functions as a heat sink, safety higher than that of the lithium secondary battery can be obtained.

However, in order to put this secondary battery into practical use,
Several safety mechanisms need to be provided. For example, a lithium ion secondary battery is also provided with a safety mechanism such as a shutdown mechanism for a separator, a safety valve, a current cutoff mechanism, or a thermal resistance element. Therefore, if the safety can be further improved by examining the electrode material and the like, these safety mechanisms can be simplified, and the safety can be more easily ensured. That is, the structure can be simplified, the manufacturing process can be simplified, and the cost can be reduced.

The present invention has been made in view of such a problem, and an object of the present invention is to provide a battery that can further improve safety.

[0008]

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 the capacity component due to insertion and extraction of lithium (Li), and the capacity of lithium deposition and separation. The positive electrode contains lithium as a positive electrode active material,
Iron (Fe), manganese (Mn) and cobalt (Co)
And at least one first element selected from the group consisting of: and a first oxide containing phosphorus.

In the battery according to the present invention, the positive electrode active material contains lithium, at least one first element selected from the group consisting of iron, manganese and cobalt, and a first oxide containing phosphorus. Therefore, heat generation due to an internal short circuit is suppressed, and safety is further improved.

[0010]

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 jelly-roll type battery. A band-shaped positive electrode 21 and a negative electrode 2 are provided inside a substantially hollow cylindrical battery can 11.
Electrode body 2 wound with a separator 2 via a separator 23
It has 0. 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 pair of insulating plates 12 and 13 are respectively arranged perpendicular to the winding peripheral surface so as to sandwich the winding electrode body 20.

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 16, 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 16 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 positive electrode active material. The positive electrode mixture layer 21b
Is the total thickness when the positive electrode mixture layer 21b is provided on both surfaces of the positive electrode current collector 21a.

The positive electrode material capable of inserting and extracting lithium includes lithium, at least one first element selected from the group consisting of iron, manganese, and cobalt;
One or more first oxides containing phosphorus are contained. As a result, in this secondary battery, excessive heat generation due to an internal short circuit can be suppressed, and safety can be improved. The first oxide is a phosphorus oxide having an olivine type crystal structure, and a chemical formula based on its stoichiometric composition is represented by, for example, Chemical Formula 1.

[0016]

## STR1 ## LiMIPO in Equation _4, MI represents the first element.

Note that the first oxide does not have to have a stoichiometric composition, and may further contain an element other than the first element as a constituent element or an impurity. The first element preferably contains iron, and more preferably contains iron and manganese. This is because it is structurally stable. That is, the first oxide, expressed as a stoichiometric composition LiFePO ₄ or LiFe _h Mn _k PO ₄
(H + k = 1) and the like are preferable.

The positive electrode material capable of inserting and extracting lithium further includes a second material containing lithium and at least one second element selected from the group consisting of cobalt, nickel (Ni) and manganese. It is preferable to include at least one oxide. This is because a higher energy density can be obtained. The chemical formula of the second oxide is represented by, for example, Chemical Formula 2.

[0019]

Embedded image in Li _x MIIO ₂ expression, MII represents a second element, x is 0.4 <x <1.
It is preferably a value within the range of 1. The composition of oxygen is determined stoichiometrically, and may deviate from the stoichiometric composition.

The second oxide may further contain an element other than the second element as a constituent element or an impurity. The second element preferably contains cobalt, or cobalt and nickel, or manganese. This is because it is structurally stable. That is, as the second oxide, LiCoO ₂ ,
_{LiNi m Co n O 4 (m} + n = 1) or LiMn
₂ O _{4 and the} like are preferred.

The positive electrode material capable of inserting and extracting lithium may include one or more other materials in addition to the first oxide and the second oxide. The content of the first oxide in these positive electrode materials is
It is preferable that the content is 1% by mass or more based on the total mass of the positive electrode active material contained in 1. If the amount is less than this, the effect of preventing heat generation by mixing the first oxide cannot be sufficiently obtained.

Incidentally, such a positive electrode material includes, for example, lithium carbonate, nitrate, oxide or hydroxide,
It is prepared by mixing carbonates, nitrates, oxides or hydroxides of other constituent elements so as to have a desired composition, pulverizing, and firing in an oxygen atmosphere.

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 of negative electrode materials capable of inserting and extracting lithium, and if necessary, for example, the positive electrode mixture layer 21b And the same binder as described above. The thickness of the negative electrode mixture layer 22b is, for example, 80 μm to 2 μm.
50 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.

It should be noted that in the present specification, lithium storage and
Withdrawal means that lithium ions are electrochemically inserted and released without losing their ionicity. This includes not only the case where the stored lithium exists in a perfect ionic state but also the case where the stored lithium does not exist in a perfect ionic state. Examples of such cases include, for example, occlusion by electrochemical intercalation reaction of lithium ions with graphite. Another example is occlusion of lithium by forming an intermetallic compound or an alloy.

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 heating 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. Accordingly, the vacancies facilitate the progress of the insertion and extraction reaction of lithium, and also have the advantage of high industrial processing efficiency. In addition, as a raw material of the molded body, the moldability itself,
A filler having sinterability may be used. In this case, it is not necessary to use a binder pitch.

The non-graphitizable carbon has a (002) plane spacing of 0.37 nm or more and a true density of 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 a starting material, for example, furfuryl alcohol or furfural polymer or copolymer, or furan resin which is a copolymer of these polymers and 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 oxygen content of this compound is preferably at least 3%, more preferably at least 5% (see JP-A-3-25253). 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 treatment or the like.

As the non-graphitizable carbon, those produced using the above-mentioned organic materials as starting materials, and those described in
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 a metal or semiconductor capable of forming an alloy or compound with lithium, or an alloy or compound 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 an alloy or compound,
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, 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 in the charging process. 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 overcharged. For example, one of the guidelines set by the Japan Storage Battery Association (Battery Manufacturers Association) is “lithium”. 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
Fast charging characteristics and safety 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 the conventional lithium secondary battery, it is difficult to deposit lithium metal uniformly, which deteriorates cycle characteristics and lowers safety. Since possible anode materials generally have a large surface area, this secondary battery is capable of uniformly depositing lithium metal. 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, in this secondary battery, particles of the anode material capable of inserting and extracting lithium are used. Since the lithium metal precipitates also in the gaps between them, the volume change is small. Third
In the conventional lithium secondary battery,
The greater the amount of dissolution, the greater the above problem, but
In this secondary battery, the insertion and extraction of lithium by the negative electrode material capable of inserting and extracting lithium also contributes to the charge / discharge capacity. Therefore, 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. Fifth, in this secondary battery, a negative electrode material capable of inserting and extracting lithium can also function as a heat sink.

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. The charge capacity of the negative electrode material is obtained, for example, from the amount of electricity when a negative electrode using lithium metal as a counter electrode and using the negative electrode material as a negative electrode active material is charged to 0 V by a constant current / constant voltage method. The discharge capacity capacity of the negative electrode material is obtained, for example, from the quantity of electricity when the battery is discharged to 2.5 V over 10 hours or more by the constant current method.

The separator 23 is composed of, for example, a porous film made of a synthetic resin such as polytetrafluoroethylene, polypropylene or polyethylene, or a porous film made of ceramic. The structure may be modified. 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 100
Since the shutdown effect can be obtained in the range of not less than 160 ° C. and the electrochemical stability is excellent, it is preferable as the material forming the separator 23. In addition, polypropylene is also preferable, and any other resin having chemical stability can be used by copolymerizing or blending with polyethylene or polypropylene.

The porous film made of polyolefin is prepared, for example, by kneading a liquid polyolefin composition in a molten state with a low-volatility solvent in a liquid state in a molten state 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 performed by biaxial stretching, for example, by heating the gel-like sheet and using 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, it is preferable to wash the stretched film 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 is impregnated with an electrolytic solution which is a liquid electrolyte. The electrolyte is a liquid solvent,
For example, it contains a non-aqueous solvent such as an organic solvent and a lithium salt which is an electrolyte salt dissolved in the non-aqueous solvent. The liquid non-aqueous solvent is, for example, composed of one or more non-aqueous compounds and has an intrinsic viscosity at 25 ° C. of 10.0 mPa ·
say s In addition, the intrinsic clay in a state in which the electrolyte salt is dissolved may be 10.0 mPa · s or less,
When a plurality of non-aqueous compounds are mixed to form a solvent, the intrinsic clay in the 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, propylene carbonate, butylene carbonate, vinylene carbonate, γ-butyrolactone, γ-valerolactone, 1,2-dimethoxyethane, tetrahydrofuran,
2-methyltetrahydrofuran, 1,3-dioxolan, 4-methyl-1,3-dioxolan, methyl acetate,
Methyl propionate, ethyl propionate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, acetonitrile, glutaronitrile, adiponitrile, methoxyacetonitrile, 3-methoxypropyronitrile, N, N-dimethylformamide, N-
Methylpyrrolidinone, N-methyloxazolidinone,
N, 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 a fluorine group are exemplified.
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, LiBr and the like.
Species or a mixture of two or more species is used. The content (concentration) of the lithium salt with respect to the solvent is preferably 3.0 mol / kg or less, more preferably 0.5 mol / kg or more. This is because the ionic conductivity of the electrolytic solution can be increased within this range.

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-pyrrolidone or the like. To a paste-like positive electrode mixture slurry. The positive electrode mixture slurry is applied to the positive electrode current collector 21a, the solvent is dried, and then compression-molded by a roll press or the like to form the positive electrode mixture layer 21b, and the positive electrode 21 is manufactured.

Next, for example, a negative electrode mixture is prepared by mixing a negative electrode material capable of inserting and extracting lithium and a binder, and this negative electrode mixture is dispersed in a solvent such as N-methyl-2-pyrrolidone. To form a paste-like negative electrode mixture slurry.
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.

Subsequently, the positive electrode lead 2 is connected to the positive electrode current collector 21a.
5 is attached by welding or the like.
The negative electrode lead 26 is attached to “a” by welding or the like. After that, the positive electrode 21 and the negative electrode 22 are wound via the separator 23, 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 positive electrode 21 and the negative electrode 22 sandwiched between the pair of insulating plates 12 and 13 are housed inside the battery can 11. After housing the positive electrode 21 and the negative electrode 22 inside the battery can 11, an electrolyte is injected into the inside of the battery can 11,
3 impregnated. 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 through the gasket 16. 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
First, the negative electrode mixture layer 22
The lithium contained in b is stored in a negative electrode material that can be inserted and extracted. When charging is further continued, in the state where the open circuit voltage is lower than the overcharge voltage, the charge capacity exceeds the charge capacity capacity of the negative electrode material capable of inserting and extracting lithium, and the surface of the negative electrode material capable of inserting and extracting lithium is charged. Lithium metal begins to precipitate. Thereafter, lithium metal continues to be deposited on the negative electrode 22 until charging is completed. As a result, the appearance of the negative electrode mixture layer 22b changes from black to golden, and further to white silver when, for example, a carbon material is used as the 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. Therefore, in this secondary battery, the characteristics of both the conventional so-called lithium secondary battery and lithium ion secondary battery, that is, high energy density and good charge / discharge cycle characteristics are obtained.

In particular, in this embodiment, since the positive electrode material contains the first oxide containing lithium, the first element, and phosphorus, excessive heat generation is prevented even if an internal short circuit occurs. You.

As described above, according to the present embodiment, since the positive electrode 22 contains the first oxide containing lithium, the first element, and phosphorus, excessive heat generation due to an internal short circuit is prevented. And safety can be further improved. Therefore, the safety mechanism can be simplified.

In particular, if the positive electrode 22 contains a second oxide containing lithium and a second element in addition to the first oxide, the safety can be improved and High energy density can be obtained.

[0072]

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

Examples 1 to 6 First, iron oxalate dihydrate (Fe ₂ CO ₄ .2H ₂ O), ammonium dihydrogen phosphate (NH ₄ H ₂ PO ₄ ) and lithium carbonate (Li ₂ C)
O ₃ ) and Fe ₂ CO ₄ .2H ₂ O: NH ₄ H ₂ PO
₄ : Li ₂ CO ₃ = 2: 2: 1 (molar ratio), sufficiently mixed, and calcined in a nitrogen atmosphere at 300 ° C. for 12 hours to obtain a reaction precursor. Thereafter, the reaction precursor was calcined at 600 ° C. for 24 hours in a nitrogen atmosphere to synthesize lithium iron phosphate (LiFePO ₄ ) as a first oxide.

Further, lithium carbonate (Li ₂ CO ₃ ) and cobalt carbonate (CoCO ₃ ) are converted into Li ₂ CO ₃ : CoC
O ₃ was mixed at a ratio of 0.5: 1 (molar ratio) and calcined in air at 900 ° C. for 5 hours to obtain a lithium-cobalt composite oxide (LiCoO ₂ ) as a _second oxide. Next, the lithium-cobalt composite oxide and the lithium iron phosphate were used as a positive electrode active material, 99 parts by mass of the positive electrode active material, 6 parts by mass of graphite as a conductive agent, and 3 parts by mass of polyvinylidene fluoride as a binder To prepare a positive electrode mixture. At that time, the content of lithium iron phosphate in the positive electrode active material was determined in Examples 1 to 6 according to Table 1.
Was changed as shown in FIG.

[0075]

[Table 1]

Subsequently, this positive electrode mixture is dispersed in N-methyl-2-pyrrolidone as a solvent to form a positive electrode mixture slurry, and is uniformly applied to both surfaces of a positive electrode current collector 21a made of a 20 μm-thick strip-shaped aluminum foil. The mixture was dried and compression-molded with a roll press to form a positive electrode mixture layer 21b, thereby preparing a positive electrode 21 having a thickness of 174 μm. After that, a positive electrode lead 25 made of aluminum was attached to one end of the positive electrode current collector 21a.

The (002) plane spacing is 0.335.
A granular artificial graphite powder of 8 nm was prepared as a negative electrode material, and 90 parts by mass of the granular artificial graphite powder and 10 parts by mass of polyvinylidene fluoride as a binder were mixed to prepare a negative electrode mixture. Next, this negative electrode mixture was mixed with N-methyl-
After dispersing in 2-pyrrolidone to form a slurry, the mixture is uniformly applied to both sides of a negative electrode current collector 22a made of a 10 μm-thick strip-shaped copper foil, dried, and compression-molded by a roll press to form a negative electrode mixture layer 22b Was formed to produce a negative electrode 22 having a thickness of 130 μm. Subsequently, a negative electrode lead 26 made of nickel was attached to one end of the negative electrode current collector 22a.

After producing the positive electrode 21 and the negative electrode 22, respectively, a separator 23 made of a stretched microporous polyethylene film having a thickness of 25 μm is prepared, and the negative electrode 22, the separator 23, the positive electrode 21, and the separator 23 are laminated in this order. Was spirally wound many times to produce a wound electrode body 20.

After the wound electrode body 20 has been 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. After that, the electrolytic solution was injected into the battery can 11. The electrolytic solution contained 35% by mass of ethylene carbonate, 50% by mass of dimethyl carbonate, and 15% by mass of ethyl methyl carbonate.
And LiPF ₆ as an electrolyte salt in a solvent mixed with
Was dissolved in a solvent at a content of 1.2 mol / kg.

After injecting the electrolytic solution into the battery can 11, the battery lid 14 was caulked to the battery can 11 via a gasket 16 coated with asphalt on the surface, whereby the diameters of Examples 1 to 6 were 14 mm and the height was 14 mm. A jelly roll type secondary battery having a thickness of 65 mm was obtained. The PTC 16 was not interposed between the safety valve mechanism 15 and the battery cover 14.

The obtained secondary batteries of Examples 1 to 6 were subjected to a charge / discharge test to determine the rated discharge capacity of the batteries.
At that time, charging was performed at a constant current of 400 mA and a battery voltage of 4.
After the operation was performed until the voltage reached 2 V, the charging was performed at a constant voltage of 4.2 V until the total charging time reached 4 hours. The voltage between the positive electrode 21 and the negative electrode 22 immediately before the end of charging was 4.2 V, and the current value was 5 mA or less. On the other hand, discharging was performed at a constant current of 400 mA until the battery voltage reached 2.75 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 rated discharge capacity is 2
The discharge capacity at the cycle was used. Table 1 shows the results.

Further, regarding the secondary batteries of Examples 1 to 6,
After performing one cycle of charge and discharge under the conditions described above, the battery that was fully charged again was disassembled, visually inspected and By 7Li nuclear magnetic resonance spectroscopy, it was examined whether or not lithium metal was deposited on the negative electrode mixture layer 22b. Further, two cycles of charge and discharge were performed under the above-described conditions, and the completely discharged battery was disassembled, and similarly, it was examined whether or not lithium metal had precipitated on the negative electrode mixture layer 22b. The results are also shown in Table 1.

Further, regarding the secondary batteries of Examples 1 to 6,
An overcharge nail penetration test was performed as follows to examine heat generation due to an internal short circuit. First, after fully charging under the above-described conditions, a constant current charge of 400 mA was performed with a battery voltage of 4.4 V.
, And then constant voltage charging at 4.4 V was performed until the total charging time reached 4 hours, to obtain an overcharged state. The voltage between the positive electrode 21 and the negative electrode 22 immediately after the end of the overcharge was 4.4V. After that, the center of the overcharged battery was penetrated with a nail having a thickness of 3 mm to cause an internal short circuit, and the temperature of the battery can 11 at that time was measured. At that time, if the temperature of the battery can 11 was 200 ° C. or lower, it was determined that there was an effect of preventing heat generation, and if it exceeded 200 ° C., it was determined that there was no effect of preventing heat generation. The results are also shown in Table 1. In addition,
In Table 1, when there is an effect of preventing heat generation, it is represented by O, and when it is not, it is represented by X.

As Comparative Examples 1 to 3 with respect to this example, secondary batteries were fabricated in the same manner as in this example, using only the lithium-cobalt composite oxide as the positive electrode active material. In addition,
In Comparative Example 1, the other conditions were the same as in the present Example, and Comparative Example 2
In this example, the rest was the same as the present example except that a thermal resistance element was provided. Comparative Example 3 was the same as the present example except that a thermosensitive resistor was provided, the thickness of the negative electrode was set to 180 μm, and the amount of the negative electrode material was increased so that lithium metal was not deposited during charging. And Comparative Examples 1-3
The secondary battery was also subjected to a charge / discharge test in the same manner as in Examples 1 to 6, to check the rated discharge capacity of the battery and the presence / absence of lithium metal deposition in the fully charged state and the completely discharged state, and to determine the overcharge. A nail penetration test was performed. Table 1 shows the obtained results.

As shown in Table 1, in Examples 1 to 6 and Comparative Examples 1 and 2, in the fully charged state, the negative electrode mixture layer 2
2b, a silvery white precipitate is seen, 7Li nuclear magnetic resonance spectroscopy gave a peak attributed to lithium metal. That is, deposition of lithium metal was observed. In a fully charged state, By 7Li nuclear magnetic resonance spectroscopy, a peak attributed to lithium ions was also obtained, and the negative electrode mixture layer 22b
It was confirmed that lithium ions were occluded between graphite layers. On the other hand, in the completely discharged state, the negative electrode mixture layer 22b does not show black and silvery precipitates, 7Li nuclear magnetic resonance spectroscopy did not show any peak attributed to lithium metal. Further, the peak attributed to lithium ions was slightly recognized. That is, it was confirmed that the capacity of the negative electrode 22 was represented by the sum of the capacity component due to precipitation and dissolution of lithium metal and the capacity component due to occlusion and release of lithium.

On the other hand, in Comparative Example 3, no silver-white precipitate was observed in the fully charged state, and the deposit was golden. By 7Li nuclear magnetic resonance spectroscopy, no peak attributed to lithium metal was observed, and only a peak attributed to lithium ion was obtained. On the other hand, in a completely discharged state, it is black, By 7Li nuclear magnetic resonance spectroscopy, no peak attributed to lithium metal was observed, and a slight peak attributed to lithium ion was observed. In other words, the capacity of the negative electrode is represented by the capacity of inserting and extracting lithium,
Comparative Example 3 was confirmed to be an existing lithium ion secondary battery.

Further, as can be seen from Table 1, in Examples 1 to 6 in which lithium iron phosphate was mixed, the effect of preventing heat generation was observed in the overcharge nail penetration test, whereas lithium iron phosphate was mixed. In Comparative Example 1 where no heat was generated, no heat generation preventing effect was observed. Further, in Comparative Example 2 provided with a thermal resistance element without mixing lithium iron phosphate, an effect of preventing heat generation was observed. That is, it was found that if the positive electrode 22 contains lithium iron phosphate, heat generation due to an internal short circuit can be effectively prevented, and safety can be ensured even if the safety mechanism is simplified.

This effect of preventing heat generation was also observed in Example 1 in which the content of lithium iron phosphate in the positive electrode active material was 1% by mass. That is, it was found that safety can be ensured when the content of lithium iron phosphate is 1% by mass or more of the total mass of the positive electrode active material.

The rated discharge capacity of each of Examples 1 to 6 was larger than that of Comparative Example 3 which is a conventional lithium ion secondary battery, but the content of lithium iron phosphate was increased. The tendency was to decrease. That is, if it is used by mixing with the lithium-cobalt composite oxide, the safety can be improved,
It has been found that a larger capacity can be obtained.

(Examples 7 to 9) First oxide or second oxide
A secondary battery was fabricated in the same manner as in Example 3, except that the oxide was changed as shown in Table 2. Incidentally, LiFe _0.5 the first oxide in Example 7 Mn _0.5 instead of PO _4, LiNi the second oxide Example 8 _{0. 8} Co
_{Instead of 0.2} O ₂ , in Example 9, the second oxide was LiMn.
_It was replaced by ₂ O ₄ . Also in Examples 7 to 9, a charge / discharge test was performed in the same manner as in Example 3 to check the rated discharge capacity of the battery and the presence / absence of lithium metal deposition in a fully charged state and a completely discharged state. A stab test was performed. The results obtained are shown in Table 2 together with the results of Example 3 and Example 6.

[0091]

[Table 2]

As can be seen from Table 2, in Example 7 in which the first oxide was replaced, the effect of preventing heat generation was recognized as in Example 3. Also, in Examples 8 and 9 in which the second oxide was replaced, as in Examples 1 to 5, a larger rated discharge capacity was obtained than in Example 6 not including the second oxide.

That is, if the first oxide containing lithium, the first element, and phosphorus is contained as the positive electrode active material, the safety can be improved. It has been found that a larger discharge capacity can be obtained if the second oxide containing the element is contained.

In the above embodiment, some specific examples of the first oxide have been described. However, it is considered that the heat generation preventing effect of the first oxide is caused by its crystal structure. Therefore, a similar result can be obtained even if another first oxide is used. Further, similar results can be obtained even if another second oxide is used.

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-described embodiments and examples, the case where the occlusion / desorption reaction of lithium and the precipitation / dissolution reaction of lithium are used has been described. However, when lithium is precipitated, an alloy may be formed. . In that case, a substance capable of forming an alloy with lithium is present in the electrolyte, and an alloy may be formed at the time of deposition. At this time, an alloy may be formed.

Further, in the above embodiments and examples, the case where lithium is used as the electrode reactive species has been described, but other reactive species may be further included. Other reactive species include, for example, other alkali metals such as sodium (Na) or potassium (K), alkaline earth metals such as magnesium (Mg) or calcium (Ca), or other alkali metals such as aluminum (Al). Light metal.

Further, in the above embodiments and examples, the case where the gel electrolyte which is one kind of the electrolyte or the solid electrolyte is used is described, 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, a cylindrical secondary battery having a wound structure has been described. However, the present invention relates to an elliptical or polygonal secondary battery having a wound structure. Alternatively, the present invention can be similarly applied to 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 a secondary battery such as a coin type, a button type, and a card type. Further, the invention is not limited to the secondary battery, and can be applied to a primary battery.

[0099]

As described above, according to the battery according to any one of the first to fourteenth aspects, the positive electrode comprises the first oxide containing lithium, the first element, and phosphorus. , Excessive heat generation due to an internal short circuit can be prevented, and safety can be further improved. Therefore, the safety mechanism can be simplified.

According to the battery of any one of claims 4 to 8, the positive electrode comprises the second oxide containing lithium and the second element in addition to the first oxide. , The safety can be improved and a higher energy density 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.

[Explanation of symbols]

11 ... battery can, 12, 13 ... insulating plate, 14 ... battery lid, 1
Reference numeral 5: safety valve mechanism, 15a: disk plate, 16: thermal resistance 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 electrode lead, 26 ... Negative electrode lead

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Momoe Adachi 6-7-35 Kita-Shinagawa, Shinagawa-ku, Tokyo Inside Sony Corporation (72) Inventor Goro Shibamoto 6-35-35 Kita-Shinagawa, Shinagawa-ku, Tokyo Sony Corporation F-term (reference) CB08 CB11 CB12 CB13 CB14 CB15 CB20 CB21 CB22 CB29 EA02 EA09 EA24 FA05 HA01 HA19

Claims (14)

[Claims] 1. A battery provided with an electrolyte together with a positive electrode and a negative electrode, wherein the capacity of the negative electrode includes a sum of a capacity component due to insertion and extraction of lithium (Li) and a capacity component due to precipitation and dissolution of lithium. The positive electrode has lithium and iron (F) as positive electrode active materials.
e) a battery comprising a first oxide containing at least one first element selected from the group consisting of manganese (Mn) and cobalt (Co), and phosphorus. 2. The battery according to claim 1, wherein the first oxide contains iron as a first element. 3. The battery according to claim 1, wherein the first oxide contains iron and manganese as the first elements. 4. The positive electrode as a positive electrode active material, further comprising:
2. The semiconductor device according to claim 1, further comprising a second oxide containing lithium and at least one second element selected from the group consisting of cobalt, nickel (Ni) and manganese.
The battery as described. 5. The battery according to claim 4, wherein the second oxide contains cobalt as a second element. 6. The second oxide according to claim 4, wherein the second oxide contains cobalt and nickel as the second elements.
The battery as described. 7. The battery according to claim 4, wherein the second oxide contains manganese as a second element. 8. The battery according to claim 4, wherein the content of the first oxide is 1% by mass or more based on the total mass of the positive electrode active material contained in the positive electrode. 9. The battery according to claim 1, wherein the negative electrode includes a negative electrode material capable of inserting and extracting lithium. 10. The battery according to claim 9, wherein the negative electrode contains a carbon material. 11. The battery according to claim 10, wherein the negative electrode includes at least one member selected from the group consisting of graphite, graphitizable carbon, and non-graphitizable carbon. 12. The battery according to claim 11, wherein the negative electrode contains graphite. 13. The battery according to claim 9, 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 lithium. . 14. 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 13, wherein: