WO2020194385A1

WO2020194385A1 - Electrode, battery and battery pack

Info

Publication number: WO2020194385A1
Application number: PCT/JP2019/012132
Authority: WO
Inventors: 祐輝渡邉; 佑介並木; 駿忠中澤; 哲郎鹿野
Original assignee: 株式会社東芝
Priority date: 2019-03-22
Filing date: 2019-03-22
Publication date: 2020-10-01
Also published as: JP7106748B2; JPWO2020194385A1

Abstract

Provided is an electrode according to one embodiment of the present invention. This electrode is provided with an active material-containing layer. The active material-containing layer includes active material particles, a binder, and a conductive agent. The binder covers the surfaces of the active material particles at a coverage of at least 80% but below 99%. In a cumulative volume distribution of micropores in the active material-containing layer, measured by mercury porosimetry, the volume of the pores is 0.035-0.050 mL/g in a region in which the diameter of the pores is 0.1 µ or less. The amount of carbon dioxide generated from the active material-containing layer is 9-10 mL/g according to pyrolysis gas chromatography at a temperature of 150-600ºC.

Description

Electrodes, batteries and battery packs

Embodiments of the present invention relate to electrodes, batteries and battery packs.

In recent years, for example, the development of lithium-ion batteries for automobiles to be installed in mild hybrid vehicles of 12 to 48 V is accelerating. Along with this, battery development aimed at improving input / output performance is progressing. As measures to improve the input / output performance, specifically, various measures such as reducing the particle size of the active material particles and increasing the amount of the conductive agent contained in the electrode mixture layer have been taken. It is being considered.

Japan Special Table 2013-510392 Japanese Patent Application Laid-Open No. 2016-104848 International Publication No. 2014/088070 International Publication No. 2016/068258 Japanese Patent Application Laid-Open No. 2014-194927 Japanese Patent Application Laid-Open No. 11-86846 International Publication No. 2012/111813 Japanese Patent Application Laid-Open No. 2012-174416

It is an object of the present invention to provide an electrode capable of realizing a battery capable of exhibiting excellent input / output performance and excellent life characteristics, a battery equipped with this electrode, and a battery pack provided with this battery.

According to the first embodiment, electrodes are provided. The electrode comprises an active material-containing layer. The active material-containing layer contains active material particles, a binder, and a conductive agent. The binder covers the surface of the active material particles with a coverage of 80% or more and less than 99%. In the integrated pore volume distribution of the active material-containing layer by the mercury intrusion method, the pore volume in the region where the pore diameter is 0.1 μm or less is 0.035 mL / g or more and 0.050 mL / g or less. The amount of carbon dioxide generated from the active material-containing layer by pyrolysis gas chromatography from 150 ° C. to 600 ° C. is 9 mL / g or more and 10 mL / g or less.

According to the second embodiment, batteries are provided. This battery includes an electrode according to the first embodiment as a positive electrode, a negative electrode, and an electrolyte.

According to the third embodiment, a battery pack is provided. This battery pack comprises the battery according to the second embodiment.

FIG. 1 is an integrated pore volume distribution of the active material-containing layer of the electrode of the example according to the first embodiment. FIG. 2 is a conceptual diagram showing a cross section of an active material-containing layer included in an example electrode according to the first embodiment. FIG. 3 is a conceptual diagram showing the outer peripheral portion of the active material particles in the active material-containing layer of FIG. 2 and the N atoms existing on the surface of the active material particles. FIG. 4 is a conceptual diagram showing the outer peripheral length of the portion of the surface of the active material particles in the active material-containing layer of FIG. 3 in which the N element is present. FIG. 5 is a schematic cross-sectional view of an example electrode according to the first embodiment. FIG. 6 is a schematic notched perspective view of the non-aqueous electrolyte battery of the first example according to the second embodiment. FIG. 7 is a schematic enlarged cross-sectional view of part A in FIG. FIG. 8 is a schematic notched perspective view of the non-aqueous electrolyte battery of the second example according to the second embodiment. FIG. 9 is a schematic exploded perspective view of an example battery pack according to the third embodiment. FIG. 10 is a block diagram showing an electric circuit of the battery pack of FIG.

Embodiment

The embodiment will be described below with reference to the drawings. In addition, the same reference numerals are given to common configurations throughout the embodiment, and duplicate description will be omitted. In addition, each figure is a schematic view for explaining the embodiment and promoting its understanding, and there are some differences in its shape, dimensions, ratio, etc. from the actual device, but these are described below and known techniques. The design can be changed as appropriate by taking into consideration.

(First Embodiment)
According to the first embodiment, electrodes are provided. The electrode comprises an active material-containing layer. The active material-containing layer contains active material particles, a binder, and a conductive agent. The binder covers the surface of the active material particles with a coverage of 80% or more and less than 99%. In the integrated pore volume distribution of the active material-containing layer by the mercury intrusion method, the pore volume in the region where the pore diameter is 0.1 μm or less is 0.035 mL / g or more and 0.050 mL / g or less. The amount of carbon dioxide generated from the active material-containing layer by pyrolysis gas chromatography from 150 ° C. to 600 ° C. is 9 mL / g or more and 10 mL / g or less.

If the amount of conductive agent is increased in order to improve the input / output performance of the battery, the impurities brought into the battery tend to increase. For example, during a battery charge / discharge cycle or during long-term tests such as battery storage, impurities may react with the active material, resulting in increased battery resistance. This problem is particularly remarkable in a battery containing a high nickel-based positive electrode active material having a large residual alkaline component.

As a method of suppressing the increase in resistance in the long-term test, for example, the surface of the active material particles may be coated with a binder at a coverage of 80% or more and less than 99%. By such measures, side reactions between the active material particles and the electrolytic solution or impurities can be suppressed.

On the other hand, when the coverage of the active material particles is 80% or more, the frequency of contact between the active material particles and the conductive agent in the active material-containing layer decreases. As a result, the initial resistance increases. In order to increase the contact frequency between the active material particles and the conductive agent, measures such as increasing the amount of the conductive agent or using a conductive agent having a large specific surface area can be considered. However, the conductive agent tends to aggregate due to the hydrophobic interaction of carbon. Therefore, even with such measures, the frequency of contact between the active material particles and the conductive agent does not actually increase as expected.

As a result of diligent research to solve such a problem, the inventors have realized the electrode according to the first embodiment.

An electrode in which the amount of carbon dioxide generated from the active material-containing layer by thermal decomposition gas chromatography from 150 ° C. to 600 ° C. is 9 mL / g or more and 10 mL / g or less can be hydrogen-bonded to the surface of the conductive agent. It can contain enough ingredients. Due to the presence of this component, the electrode according to the first embodiment can prevent the agglomeration of the conductive agent.

Further, the pore volume in the region where the pore diameter is 0.1 μm or less in the integrated pore volume distribution by the mercury injection method of the active material-containing layer is an index of the dispersed state of the conductive agent in the active material-containing layer. When the pore volume is 0.035 mL / g or more and less than 0.050 mL / g, it means that the conductive agent is sufficiently and uniformly dispersed around the active material particles.

As a result, in the electrode according to the first embodiment, the contact frequency between the active material particles and the conductive agent can be increased while showing a high coverage by the binder. Such electrodes can enhance electrical conduction between active material particles in the active material-containing layer. Further, in the electrode according to the first embodiment, since the contact frequency between the active material and the conductive agent is high, even if the active material particles expand and / or contract during charging and discharging, the active material cracks occur. It is possible to suppress the cutting of the conductive path by the conductive agent. As a result, the electrode according to the first embodiment can suppress deterioration of the active material particles due to expansion and / or contraction during charging / discharging. As a result, the electrode according to the first embodiment can prevent a local overvoltage from being generated in the active material-containing layer and deterioration of the active material particles.

For the reasons described above, the electrodes according to the first embodiment can realize excellent input / output performance and excellent life characteristics.

When the coverage of the binder on the surface of the active material particles is 99% or more, the contact probability between the active material particles and the conductive agent becomes low. Therefore, such an electrode cannot realize excellent input / output performance. An electrode having a binder coverage of less than 80% cannot sufficiently suppress side reactions between the active material particles and other components such as impurities. Therefore, such an electrode cannot exhibit excellent life characteristics. The coverage of the binder is preferably 85% or more and 95% or less, and more preferably 90% or more and 95% or less.

In the electrode where the pore volume is less than 0.035 mL / g in the region where the pore diameter is 0.1 μm or less in the integrated pore volume distribution, the conductive agent contained in the active material-containing layer is excessively aggregated, and the active material. Insufficient contact between the particles and the conductive agent. As a result, this electrode exhibits high resistance and cannot achieve excellent input / output performance. On the other hand, in the electrode in which the pore volume in the region where the pore diameter is 0.1 μm or less in the integrated pore volume distribution exceeds 0.050 mL / g, the conductive agent contained in the active material-containing layer is in a hyperdispersed state. In the active material-containing layer of such an electrode, the amount of isolated active material particles and the conductive agent is large, and the conductive path between the active material particles is cut off. Therefore, such an electrode exhibits high resistance and cannot realize excellent input / output performance. In the integrated pore volume distribution, the pore volume in the region where the pore diameter is 0.1 μm or less is preferably 0.037 mL / g or more and 0.047 mL / g or less, and 0.040 mL / g or more and 0.047 mL / g. It is more preferably g or less.

The component that generates carbon dioxide from the active material-containing layer by pyrolysis gas chromatography from 150 ° C. to 600 ° C. is, for example, a component containing a carbonyl group (C = O). That is, the active material-containing layer can contain a component containing a carbonyl group. For example, the binder can contain a carbonyl group. For example, the binder may contain polyvinylidene fluoride containing a carbonyl group. Alternatively, the active material particles may contain a carbonyl group on the surface. The carbonyl group may be attached to the surface of the active material particles. It can be said that such a carbonyl group modifies the surface of the active material particles, for example.

Electrodes that generate less than 9 mL / g of carbon dioxide from the active material-containing layer by pyrolysis gas chromatography from 150 ° C to 600 ° C do not sufficiently contain components that can hydrogen bond with the surface of the conductive agent. .. Therefore, such an electrode cannot sufficiently suppress the aggregation of the conductive agent. Electrodes that generate more than 10 mL / g of carbon dioxide contain too much carbon dioxide-generating component. Such an electrode generates a large amount of gas when stored at a high temperature, and its life characteristic is significantly deteriorated. The amount of carbon dioxide generated from the active material-containing layer is preferably 9.3 mL / g or more and 10 mL / g or less, and more preferably 9.4 mL / g or more and 9.8 mL / g or less.

Next, the electrodes according to the first embodiment will be described in more detail.

The electrode according to the first embodiment includes an active material-containing layer. The electrode according to the first embodiment may further include a current collector. The current collector can have, for example, a strip-shaped planar shape. The current collector can have, for example, a first surface and a second surface as the opposite surface of the first surface.

The active material-containing layer can be formed on one surface of the current collector or on both surfaces. For example, the active material-containing layer may be formed on either the first surface or the second surface of the current collector, or both the first surface and the second surface of the current collector. May be formed in. The current collector may include a portion that does not support the active material-containing layer. This portion can be used, for example, as a current collecting tab. Alternatively, the electrode according to the first embodiment may include a current collector tab separate from the current collector.

The active material-containing layer contains active material particles, a binder, and a conductive agent.
The active material particles and the binder that covers the surface of the active material particles can form, for example, a complex. That is, the active material-containing layer can include, for example, a composite containing active material particles and a binder that covers the surface of the active material particles with a coverage of 80% or more and less than 99%. In other words, the complex can include active material particles and a binder that covers the surface of some of the active material particles.

The electrodes according to the first embodiment can be used in a battery. The electrode according to the first embodiment can be used as, for example, a positive electrode in a battery. The battery can be, for example, a secondary battery that can be repeatedly charged and discharged. An example of a secondary battery is a non-aqueous electrolyte battery. A non-aqueous electrolyte battery contains a non-aqueous electrolyte, and a non-aqueous electrolyte contains an electrolyte. As another example of the secondary battery, a battery containing an electrolytic solution containing an aqueous solvent and an electrolyte dissolved in the aqueous solvent can be mentioned.

Next, an example of a material that can be used in the electrode according to the first embodiment will be specifically described.

(Current collector)
As the current collector, a sheet containing a material having high electrical conductivity can be used. For example, an aluminum foil or an aluminum alloy foil can be used as the current collector. When an aluminum foil or an aluminum alloy foil is used, the thickness thereof is, for example, 20 μm or less, preferably 15 μm or less. The aluminum alloy foil can include magnesium, zinc, silicon and the like. Further, the content of transition metals such as iron, copper, nickel and chromium contained in the aluminum alloy foil is preferably 1% or less.

(Active material particles)
The active material particles are, for example, positive electrode active material particles. Examples of the positive electrode active material include lithium cobalt composite oxide (lithium cobalt oxide; LCO), lithium nickel cobalt manganese composite oxide (NCM), lithium nickel cobalt aluminum composite oxide (NCA), and lithium manganese having a layered rock salt structure. Composite oxide (lithium manganate; LMO), lithium nickel-manganese composite oxide (LNMO), lithium iron phosphate (LFP) having an olivine-type crystal structure, manganese-containing iron lithium phosphate (LMP), lithium nickel composite oxidation Things (LNO), lithium nickel cobalt composite oxide (LNCO) and lithium manganese cobalt composite oxide (LMCO) can be mentioned. The active material particles preferably contain at least one selected from the group consisting of these composite oxides.

The lithium cobalt composite oxide can have, for example, a composition represented by the general formula Li _a CoO ₂ (the subscript a is in the range of 0.9 ≦ a ≦ 1.2). Lithium-nickel-cobalt-manganese composite oxide, for example, the general formula _{_{_{_{Li b Ni x Co y Mn z}}}} O 2 ( subscripts x and y satisfy the x + y + z = 1, the subscript b is a 0.9 ≦ b ≦ 1.2 It can have a composition represented by) (within the range). Lithium-nickel-cobalt-aluminum composite oxide, for example, the general formula _{_{_{_{Li c Ni x Co y Al z}}}} O 2 ( subscripts x and y satisfy the x + y + z = 1, the subscript c is a 0.9 ≦ c ≦ 1.2 It can have a composition represented by) (within the range). Lithium manganese composite oxide, for example, the general formula _Li d Mn ₂ O ₄ or _Li e MnO ₂ (subscript d is in the range of 0.9 ≦ d ≦ 1.2, the subscript e is 0.9 ≦ It can have a composition represented by (within the range of e ≦ 1.2). Lithium-manganese composite oxide having a composition represented by the general formula Li _d Mn ₂ O _4, for example, it may have a spinel structure. The lithium nickel-manganese composite oxide is, for example, the general formula Li _f Ni _1-x Mn _x O ₂ (the subscript x satisfies 0 <x <1, and the subscript f is within the range of 0.9 ≦ f ≦ 1.2. Can have a composition represented by). Lithium iron phosphate, for example, the general formula _Li g FePO ₄ (subscript g is in the range of 0.9 ≦ g ≦ 1.2) can have a composition represented by. The manganese-containing iron phosphate is, for example, the general formula Li _h Mn _x Fe _1-x PO ₄ (LFP): the subscript h is in the range of 0.9 ≦ h ≦ 1.2, and the subscript x is 0 <. It can have a composition represented by (within the range of x <1). The lithium nickel composite oxide can have, for example, a composition represented by the general formula Li _i NiO ₂ (the subscript i is in the range of 0.9 ≦ i ≦ 1.2). The lithium nickel-cobalt composite oxide is, for example, the general formula Li _j Ni _1-x Co _x O ₂ (the subscript j is in the range of 0.9 ≦ j ≦ 1.2, and the subscript x is 0 <x <. It can have a composition represented by (within the range of 1). The lithium manganese-cobalt composite oxide is, for example, the general formula Li _k Mn _x Co _1-x O ₂ (the subscript k is in the range of 0.9 ≦ k ≦ 1.2, and the subscript x is 0 <x <. It can have a composition represented by (within the range of 1).

The content of nickel in the transition metal in the active material particles is preferably 40 mol% or more. Although such active material particles can realize a high charge / discharge capacity, they can avoid deterioration due to expansion and / or contraction during charge / discharge for the reason described above, and have excellent input / output performance. Life characteristics and can be maintained. The content of nickel in the transition metal in the active material particles is, for example, 95 mol% or less.

The active material particles may exist as primary particles, or may be secondary particles formed by agglomeration of primary particles. Alternatively, it may be a mixture of primary particles and secondary particles.

The average primary particle size of the active material particles is preferably 0.05 μm or more and 1 μm or less, and more preferably 0.1 μm or more and 0.5 μm or less. The average secondary particle diameter of the active material particles is preferably 3 μm or more and 12 μm or less, and more preferably 3 μm or more and 6 μm or less.

In one embodiment, the active material particles contain a carbonyl group on the surface. For example, the carbonyl group may be attached to the surface of the active material particles, such as a portion of the surface. When the active material particles contain secondary particles, the carbonyl group may be attached to the surface of the secondary particles, or may be attached to the surface of at least some of the primary particles constituting the secondary particles. Good. The method for producing an electrode containing active material particles containing a carbonyl group on the surface will be described in detail later.

(Conducting agent)
The conductive agent can play a role of assisting electrical conduction between the active material particles and a role of assisting electrical conduction from the active material particles to the current collector, for example, in the active material-containing layer.

The conductive agent can contain a carboxyl group and / or a hydroxyl group. Carboxyl groups and / or hydroxyl groups can be included, for example, on the surface of the conductive agent. For example, the carboxyl group and / or the hydroxyl group can be introduced into the conductive agent by the treatment with a strong acid described later. The carbonyl group that can be contained on the surface of the active material particles can also be hydrogen bonded to the carboxyl group and / or the hydroxyl group that can be contained in the conductive agent.

As the conductive agent, for example, a carbon substance such as acetylene black, ketjen black, lamp black, furnace black, graphite, carbon fiber, graphene can be used. The conductive agent preferably contains Ketjen Black. Ketjen Black can have, for example, a specific surface area of 200 m ² / g or more and 500 m ² / g or less. By using Ketjen black, the frequency of contact with the active material particles can be further increased. As the conductive agent, one of the above-mentioned materials may be used, or a mixture of two or more kinds may be used.

The average particle size of the conductive agent is, for example, 20 nm or more and 50 nm or less.

(Binder)
The binder can exhibit the function of binding the active material and the current collector. Examples of binders are mainly polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), fluororubber, styrene-butadiene rubber (SBR), polypropylene (PP), polyethylene (PE), and acrylic copolymers. Examples of the binder (for example, polyacrylonitrile (PAN)) and carboxymethyl cellulose (CMC) as components can be mentioned.

In one embodiment, the binder comprises PVdF containing a carbonyl group and / or an acrylic copolymer containing a carbonyl group. The carbonyl group is included, for example, in the functional group of each binder.

The binder may be, for example, one of the materials listed above, or a mixture of two or more. For example, the binder may include a first binder that covers the active material particles and a second binder that is different from the first binder. The second binder can bind the composites containing the active material particles and the first binder to each other, and can also bind these composites to the current collector. Alternatively, the second binder may contain the same material as the material of the first binder.

(Mixing ratio in active material-containing layer)
The ratio (blending ratio) of the active material particles, the conductive agent and the binder in the active material-containing layer is 75% by weight or more and 96% by weight or less, 3% by weight or more and 15% by weight or less, and 1% by weight or more and 10% by weight or less, respectively. It is preferably 90% by weight or more and 95% by weight or less, 3% by weight or more and 5% by weight or less, and 2% by weight or more and 5% by weight or less.

[Example of manufacturing method]
The electrode according to the first embodiment can be manufactured, for example, by the method described below.

(First example)
As a first example, an example of a method for manufacturing an electrode containing a binder containing a carbonyl group will be described.

[Preparation of electrode paint]
<Preparation of pre-dispersion liquid A>
Prepare the active material particles and a binder containing a carbonyl group. These are added to a suitable solvent, such as N-methylpyrrolidone, to give a mixture.
The resulting mixture is further mixed in a disperser capable of applying a high shear force. Examples of such a disperser include a disperser using media. Examples of the disperser using the media include a ball mill and a bead mill. By such dispersion, the pre-dispersion liquid A is obtained. The pre-dispersion liquid A contains a complex containing the active material particles and a binder covering the surface of the active material particles.

<Preparation of pre-dispersion liquid B>
Prepare the conductive agent and the binder.
As the conductive agent, one treated with a strong acid is used. Examples of the strong acid include concentrated sulfuric acid. Treatment with a strong acid allows sufficient introduction of carboxyl groups and / or hydroxyl groups on the surface of the conductive agent.

The binder prepared here may or may not contain a carbonyl group.
These are then charged into a suitable solvent, such as N-methylpyrrolidone, to give a mixture.
The resulting mixture is further mixed, for example, in a bead mill disperser. Thus, the pre-dispersion liquid B is obtained.

<Preparation of electrode paint>
Next, the pre-dispersion liquid A and the pre-dispersion liquid B are mixed. The resulting mixture is further mixed and dispersed, for example in a roll mill device. Thus, an electrode paint is obtained.

The reason why the pre-dispersion liquid A containing the active material particles and the pre-dispersion liquid B containing the conductive agent are separately first dispersed will be described below.
When an active material particle having a large particle size and a large amount and a conductive agent having a small particle size and a small amount as compared with the active material particle are dispersed together with a binder, the active material particle having a large volume becomes conductive with a small volume. Inhibits the dispersion of the agent. On the other hand, when the conductive agent is dispersed together with the binder before being mixed with the active material particles, the factors that hinder the dispersion of the conductive agent can be reduced. Therefore, the pre-dispersion liquid B obtained by pre-dispersing the conductive agent is excellent in the dispersed state of the conductive agent. By further dispersing the pre-dispersion liquid B having an excellent dispersion state of the conductive agent together with the pre-dispersion liquid A containing the active material particles, an electrode coating material having an excellent dispersion of the conductive agent can be prepared.

However, when the total specific surface area of the conductive agent is large, it may be difficult to prevent the conductive agent from agglomerating only by the above-mentioned prior dispersion.

On the other hand, in the production method of this example, the pre-dispersion liquid B containing the conductive agent subjected to the strong acid treatment is prepared. The carboxyl group and / or hydroxyl group contained in this conductive agent can be hydrogen-bonded to the carbonyl group of the complex contained in the pre-dispersion liquid A when the pre-dispersion liquid A and the pre-dispersion liquid B are mixed. This hydrogen bond helps prevent agglomeration of the conductive agent. In the production method of this example, a sufficient amount of carboxyl groups and / or hydroxyl groups can be introduced into the conductive agent by the strong acid treatment, so that aggregation of the conductive agent can be more sufficiently prevented. As a result, in the production method of this example, the conductive agent can be more uniformly dispersed around the active material particles.

[Preparation of electrodes]
Next, the electrode paint thus obtained is applied to the surface of the current collector. The coating is then dried. Next, the coating film is pressed together with the current collector. The electrode density after pressing (density of the active material-containing layer that does not include the current collector) is, for example, 2.5 g / cm ³ or more and 3.5 g / cm ³ or less. The density is preferably 2.8 g / cm ³ or more and 3.3 g / cm ³ or less, and more preferably 3.0 g / cm ³ or more and 3.3 g / cm ³ or less. Thus, an example electrode according to the first embodiment is obtained.

The specific surface area of the conductive agent differs depending on the type. In addition, the integrated pore volume distribution also changes depending on the pressing conditions. Therefore, for example, the type of the conductive agent (particularly the specific surface area), the dispersion condition of the pre-dispersion liquid, the dispersion condition of the electrode coating material, the compounding ratio of the active material particles, the conductive agent and the binder, and the pressing condition of the coating film are combined and adjusted. Thereby, the integrated pore volume distribution can be adjusted. Specific examples of combinations of these conditions will be shown in the subsequent examples.

Further, in the production method of the first example, for example, the amount of the binder containing a carbonyl group used in the preparation of the electrode coating material and the content of the carbonyl group contained in the binder are combined and adjusted. The amount of carbon dioxide generated from the active material-containing layer of the obtained electrode can be adjusted. Specific examples of combinations of these conditions will be shown in the subsequent examples.

(Second example)
As a second example, an example of a method for manufacturing an electrode containing active material particles containing a carbonyl group on the surface will be described.

The production method of the second example is the same as the production method of the first example except for the method of preparing the pre-dispersion liquid A.

In the second example, as the active material particles, active material particles stored for 24 hours or more in an atmospheric environment where the dew point is not controlled are used. Such active material particles can contain lithium carbonate (Li ₂ CO ₃ ) on the surface. That is, such active material particles can contain a carbonyl group on the surface. Storage in an air environment is preferably 12 hours or more and 48 hours or less, and more preferably 24 hours or more and 36 hours or less.

Note that a binder containing a carbonyl group may or may not be used in the preparation of the pre-dispersion liquid A and / or the pre-dispersion liquid B.

In the production method of the second example, for example, the amount of carbon dioxide generated from the active material-containing layer of the obtained electrode is adjusted by adjusting the composition of the active material particles and the storage time in an atmospheric environment in combination. can do. When a binder containing a carbonyl group is used in the preparation of the pre-dispersion liquid A and / or the pre-dispersion liquid B, in addition to the above conditions, the amount of the binder containing the carbonyl group and the carbonyl group contained in the binder The content is also adjusted in combination. Specific examples of combinations of these conditions will be shown in the subsequent examples.
(Third example)
As a third example, another example of a method for producing an electrode containing active material particles containing a carbonyl group on the surface will be described.

The production method of the third example is the same as the production method of the first example except for the method of preparing the pre-dispersion liquid A.

In the production method of the third example, an additive is further used when preparing the pre-dispersion liquid A. Examples of the additive include substances containing a carboxyl group such as acetic acid, oxalic acid, phthalic acid, and maleic acid.

By leaving the prepared pre-dispersion liquid A in the state of a coating liquid for one day, the reaction between the surface of the active material particles and the additive proceeds, and a carbonyl group can be bonded to the surface of the active material particles. The atmosphere of the predisperse A is preferably an air atmosphere at normal temperature and pressure. It is more preferable to leave it while stirring in this atmosphere.

Further, in the production method of the third example, as in the production method of the second example, when the pre-dispersion liquid A is prepared, the active material particles are used as active material particles for 24 hours or more in an air environment where dew point control is not performed. Stored active material particles can also be used.

In the production method of the third example, for example, the type and amount of the electrode additive and the leaving time of the pre-dispersion liquid A for reacting the additive with the surface of the active material particles are adjusted in combination. The amount of carbon dioxide generated from the active material-containing layer of the electrode to be formed can be adjusted. When a binder containing a carbonyl group is used in the preparation of the pre-dispersion liquid A and / or the pre-dispersion liquid B, in addition to the above conditions, the amount of the binder containing the carbonyl group and the carbonyl group contained in the binder The content is also adjusted in combination. Similarly, when active material particles stored for 24 hours or more in an air environment without dew point control are used as the active material particles, the composition of the active material particles and the storage time in the air environment are also adjusted in combination. Specific examples of combinations of these conditions will be shown in the subsequent examples.

The electrodes obtained as described above may be cut to a predetermined size. Further, a current collector tab separate from the current collector may be connected to the current collector by welding, for example.

[Analysis method]
Next, various analysis methods will be described.
(A) Pretreatment The electrodes incorporated in the non-aqueous electrolyte battery are pretreated according to the following procedure.
First, the non-aqueous electrolyte battery is disassembled in a glove box filled with argon, and the electrode to be measured is taken out from the non-aqueous electrolyte battery. The removed electrodes are then washed with methyl ethyl carbonate (MEC). The washed electrodes are then dried in an atmosphere of 25 ° C. and a gauge pressure of −90 Pa. The dried electrodes are the subject of each analysis described below. Hereinafter, the electrode to be measured is simply referred to as an “electrode”.

(B) Method of Obtaining Integrated Pore Volume Distribution of Active Material-Containing Layer by Mercury Intrusion Method The procedure for obtaining the integrated pore volume distribution of the active material-containing layer by the mercury injection method is shown below.

As the pore distribution measuring device, for example, Shimadzu Autopore 9520 type can be used. At the time of measurement, one tip sample is cut into a size of about 25 mm width, folded, taken in a standard cell, and inserted into a measuring chamber. The measurement is performed under the conditions of an initial pressure of 20 kPa (about 3 psia, equivalent to a pore diameter of about 60 μm) and a final pressure of 414000 kPa (about 60,000 psia, equivalent to a pore diameter of about 0.003 μm). The average value of the three samples is used as the measurement result. In organizing the data, the pore specific surface area is calculated by assuming that the shape of the pore is a cylinder. The analysis principle of the mercury intrusion method is based on Washburn's formula: D = -4γcosθ / P. Here, P is the applied pressure, D is the pore diameter, γ is the surface tension of mercury (480 dyne · cm ^-1 ), and θ is the contact angle between mercury and the wall surface of the pores, which is 140 °. Since γ and θ are constants, the relationship between the applied pressure P and the pore diameter D can be obtained from the Washburn equation, and the pore diameter and its volume distribution can be derived by measuring the mercury intrusion volume at that time. Can be done. For details of the measurement method, principle, etc., refer to

Non-Patent Documents

1 and 2.

By this measurement, the integrated pore volume distribution of the active material-containing layer can be obtained. The integrated pore volume distribution obtained by the above procedure reflects not only the pore diameter of the active material-containing layer but also the pore diameter of the current collector. However, the pore diameter of the current collector is sufficiently smaller than the pore diameter of the active material-containing layer, and the abundance ratio is small, so that it can be ignored. From the obtained distribution, the pore volume (mL / g) of the region where the pore diameter is 0.1 μm or less can be determined. The reference weight here is the weight (g) of the active material-containing layer used for the measurement.

FIG. 1 shows the integrated pore volume distribution of the active material-containing layer of the electrode of the example according to the first embodiment. The integrated pore volume distribution shown in FIG. 1 is the integrated pore volume distribution for the electrode of Example 6 shown in the latter part. In the integrated pore volume distribution shown in FIG. 1, the pore volume in the region where the pore diameter is 0.1 μm or less is 0.047 mL / g.

(C) Analysis Using Pyrolysis Chromatography Next, the procedure for analyzing the amount of carbon dioxide generated from the active material-containing layer by pyrolysis chromatography will be described.

Prior to the analysis, the weight of the electrodes to be analyzed is measured.
A pyrolysis gas chromatography mass spectrometer (Pyro-GC / MS) is used for the analysis. For example, a pyrolyzer manufactured by Frontier Lab Co., Ltd. can be used. In this device, the pyrolyzer holds the electrodes at 40 ° C. for 8 minutes. The electrode is then heated to 600 ° C. at a rate of 5 ° C./min. By this treatment, among the components contained in the active material-containing layer, the components that decompose at a temperature of 600 ° C. can be thermally decomposed. Then, by using the gas chromatograph mass spectrometer of this apparatus, it is possible to identify the components generated by thermal decomposition. In this analysis, the temperature of the gas chromatograph mass spectrometer is controlled to be constant at 250 ° C.

After the analysis, the active material-containing layer is peeled off from the current collector. The weight of the current collector thus obtained is measured. The weight of the current collector is subtracted from the weight of the electrode measured earlier to obtain the weight of the active material-containing layer.

By dividing the amount of carbon dioxide generated between 150 ° C. and 600 ° C. by the weight of the active material-containing layer in this analysis, pyrolysis gas chromatography from 150 ° C. to 600 ° C. was performed from the active material-containing layer. The amount of carbon dioxide generated (mL / g) can be calculated. That is, the amount of carbon dioxide generated is the amount of carbon dioxide generated per 1 g of the active material-containing layer.

(D) Method for Confirming Active Material-Containing Layer, Conductive Agent and Binder The shape of the active material particles and conductive agent contained in the active material-containing layer is determined by the field emission scanning electron microscope (FE-). It can be confirmed using SEM). Further, the distribution of the active material particles, the conductive agent and the binder contained in the active material-containing layer can be discriminated by energy dispersive X-ray spectrometry (EDX).

The method for confirming the active material particles, the conductive agent and the binder contained in the active material-containing layer will be specifically described below.

First, obtain the cross section of the electrode. The method for producing the cross section for observation is not limited as long as the cross section can be obtained, and is appropriately selected depending on the ease of processing the electrode. At this time, the electrode may be processed as it is, or if necessary, the electrode may be processed in which the pores of the active material-containing layer are filled with a filler such as resin. These electrodes are cut to obtain a sample with the cut surface exposed. Examples of the cutting method include cutting with a razor or a microtome, cutting in liquid nitrogen, cutting with an Ar ion beam or a Ga ion beam, and the like.

Next, paste the sample on the sample table of FE-SEM. At this time, treatment is performed using a conductive tape or the like so that the sample does not come off or float from the sample table. If necessary, the sample may be cut to a size suitable for attaching to the sample table. In the measurement, the sample is introduced into the sample chamber while being maintained in an inert atmosphere. For the sample prepared as described above, the cross section of the active material-containing layer is observed by FE-SEM at a magnification of 30,000 times.

Furthermore, elemental analysis by EDX will be carried out for the same analysis range. As a result, among the constituent elements of the active material particles, the conductive agent and the binder contained in the cross section of the active material-containing layer projected on the FE-SEM image, the elements from boron B to uranium U in the periodic table are confirmed. can do.

Next, from the elemental analysis results by EDX, mapping images of constituent elements peculiar to the active material particles, such as metal elements such as Ni, Mn, Co and Fe, are obtained. Similarly, from the elemental analysis results by EDX, a mapping image for a binder-specific constituent element, for example, an element of F (for example, polyvinylidene fluoride) or N (for example, polyacrylonitrile) is obtained. Images can be obtained by staining styrene-butadiene rubber (SBR) with osmium tetroxide (OsO ₄ ) and mapping for the elements of Os.

Next, among the active material particles confirmed by SEM observation and EDX analysis of the sample cross section, the largest particles and the smallest particles are excluded. For the remaining active material particles, the mapping image of the constituent elements of the binder in the outer peripheral portion of the particles is binarized, and the abundance ratio of the elements is obtained. The value obtained as a result is defined as the binder coverage (%) on the surface of the active material particles. An example of a specific calculation method will be described later.

The binarization threshold is set as follows. In the case of the F element mapping image, it is determined that the F element is present at a position where the fluorine concentration obtained from the F—Ka spectrum of SEM-EDX is 1.5% by weight or more and 3% by weight or less. In the case of the N element mapping image, it is determined that the N element is present at a position where the nitrogen concentration obtained from the N-Ka spectrum of SEM-EDX is 1.5% by weight or more and 5% by weight or less.

Next, the state of coating the surface of the active material particles with the binder in the active material-containing layer of the electrode of the example according to the first embodiment will be described with reference to the schematic diagram.

FIG. 2 is a conceptual diagram showing a cross section of the active material-containing layer included in the electrode of the example according to the first embodiment. FIG. 3 is a conceptual diagram showing the outer peripheral portion of the active material particles in the active material-containing layer of FIG. 2 and the N atoms existing on the surface of the active material particles. FIG. 4 is a conceptual diagram showing the outer peripheral length of the portion of the surface of the active material particles in the active material-containing layer of FIG. 3 in which the N element is present.

FIG. 2 schematically shows the active material particles 10 and the binder molecules 11 confirmed when the cross section of the active material-containing layer is observed by the FE-SEM measurement described above. Further, FIG. 2 more schematically shows the N element 12 confirmed from the mapping image of the nitrogen (N) element obtained by subjecting the cross section of the active material-containing layer to the EDX analysis described above. The active material-containing layer of the electrode of this example contains a first binder containing N atoms. Therefore, in FIG. 2, the distribution of the binder molecule 11 and the distribution of the N element 12 overlap. Further, for simplification of the description, in FIG. 2, all the active material particles 10 are represented as primary particles. On the other hand, the conductive agent is not shown.

In FIG. 3, the N element 12 existing (adjacent) on the outer peripheral portion 10a and the outer peripheral portion 10a of the surface of the active material particle 10 is extracted from the cross section shown in FIG. FIG. 4 shows an N-adjacent outer peripheral portion 10b, which is a portion of the outer peripheral portion 10a shown in FIG. 3 to which the N element 12 is adjacent. For example, the length of the N-adjacent outer peripheral portion 10b can be calculated based on the number of points of the N element 12 shown in FIG. By substituting the length of the outer peripheral portion 10a in FIG. 3 and the length of the N adjacent outer peripheral portion 10b obtained from FIG. 4 into the following equation, the coverage of the active material particles with a binder, for example, a nitrogen atom can be calculated.

Coverage (%) = (length of outer peripheral portion 10b adjacent to N on the surface of active material particles 10) / (length of outer peripheral portion 10a on the surface of active material particles 10) × 100%
(E) Average particle diameters of active material particles and conductive agent 30 active materials and conductive agents are arbitrarily searched from the SEM images of a plurality of fields of view obtained at the same time during the SEM observation and EDX analysis described above. The average value of the particle diameters of these particles is taken as the average particle diameter.

Next, the electrodes according to the first embodiment will be specifically described with reference to the drawings.
FIG. 5 is a schematic cross-sectional view of an example electrode according to the first embodiment.
The positive electrode 3 shown in FIG. 5 includes a current collector 3a and an active material-containing layer 3b formed on the surfaces of both the current collectors 3a. Although not shown, the current collector 3a has a band shape. The current collector 3a includes a portion that does not support the active material-containing layer 3b on any surface. This part can act as a current collector tab.

The active material-containing layer included in the electrode according to the first embodiment contains active material particles, a binder, and a conductive agent. The binder covers the surface of the active material particles with a coverage of 80% or more and less than 99%. In the integrated pore volume distribution of the active material-containing layer by the mercury intrusion method, the pore volume in the region where the pore diameter is 0.1 μm or less is 0.035 mL / g or more and 0.050 mL / g or less. The amount of carbon dioxide generated from the active material-containing layer by pyrolysis gas chromatography from 150 ° C. to 600 ° C. is 9 mL / g or more and 10 mL / g or less. In this active material-containing layer, the binder covers the surface of the active material particles with a high coverage, but the conductive agent can be uniformly present around the active material particles in a sufficient amount. Therefore, in this active material-containing layer, the active material particles and the conductive agent can exhibit a high contact frequency. As a result, the electrode according to the first embodiment can realize a battery capable of exhibiting excellent input / output performance and excellent life characteristics.

(Second Embodiment)
According to the second embodiment, batteries are provided. This battery includes an electrode according to the first embodiment as a positive electrode, a negative electrode, and an electrolyte.

Since the battery according to the second embodiment includes the electrodes according to the first embodiment, it can exhibit excellent input / output performance and excellent life characteristics.

The battery according to the second embodiment can be repeatedly charged and discharged, for example. Therefore, the battery according to the second embodiment can be said to be a secondary battery.

The battery according to the second embodiment is, for example, a non-aqueous electrolyte battery. A non-aqueous electrolyte battery contains a non-aqueous electrolyte, and a non-aqueous electrolyte contains an electrolyte. Alternatively, the battery according to the second embodiment may be a battery containing an electrolytic solution containing an aqueous solvent and an electrolyte dissolved in the aqueous solvent.

Next, the battery according to the second embodiment will be described in more detail.

The battery according to the second embodiment includes an electrode according to the first embodiment as a positive electrode. Therefore, the positive electrode included in the battery according to the second embodiment includes the active material-containing layer provided by the electrode according to the first embodiment. Further, the positive electrode can be provided with a current collector that can be provided by the electrode according to the first embodiment. Hereinafter, in order to distinguish from the member of the negative electrode, the current collector, the active material-containing layer, the current collecting tab, and the active material particles, which can be provided by the electrode according to the first embodiment, are each subjected to positive electrode current collection. It is called a body, a positive electrode active material-containing layer, a positive electrode current collecting tab, and a positive electrode active material particle. For details on the positive electrode, refer to the description of the electrode according to the first embodiment.

The battery according to the second embodiment further includes a negative electrode.
The negative electrode can include, for example, a negative electrode current collector and a negative electrode active material-containing layer formed on the negative electrode current collector.
The negative electrode active material-containing layer may be provided on the surface of either one of the negative electrode current collectors, or may be provided on both surfaces.

The negative electrode active material-containing layer can contain a negative electrode active material, a conductive auxiliary agent, and a binder.

The negative electrode current collector can also include a portion that does not support a negative electrode active material-containing layer on the surface. This portion can also serve, for example, as a negative electrode current collector tab. Alternatively, the negative electrode may include a negative electrode current collector tab that is separate from the negative electrode current collector.

The negative electrode can be manufactured by the following procedure, for example. First, the negative electrode active material, the conductive agent and the binder are dissolved in a suitable solvent such as N-methylpyrrolidone and mixed. The resulting mixture is subjected to dispersion with a bead mill to prepare a paste-like negative electrode paint. This negative electrode paint is applied to a band-shaped negative electrode current collector, and the coating film is dried. Then, the dried coating film is pressed together with the negative electrode current collector. Thus, a negative electrode can be obtained. The obtained negative electrode may be cut to a predetermined size. Further, a negative electrode current collector tab separate from the negative electrode current collector may be connected to the negative electrode current collector by welding, for example.

The positive electrode and the negative electrode can be arranged so that the positive electrode active material-containing layer and the negative electrode active material-containing layer face each other to form an electrode group. A member that allows lithium ions to permeate but does not conduct electricity, such as a separator, can be arranged between the positive electrode active material-containing layer and the negative electrode active material-containing layer.

The electrode group can have various structures. The electrode group may have a stack type structure or a wound type structure. The stack type structure has, for example, a structure in which a plurality of negative electrodes and a plurality of positive electrodes are laminated with a separator sandwiched between the negative electrode and the positive electrode. The electrode group of the wound type structure may be, for example, a can-shaped structure in which a negative electrode and a positive electrode are laminated with a separator sandwiched between them, or by pressing the can-shaped structure. The obtained flat structure may be used.

The battery according to the second embodiment may further include a positive electrode terminal and a negative electrode terminal. The positive electrode current collector tab can be electrically connected to the positive electrode terminal. Similarly, the negative electrode current collector tab can be electrically connected to the negative electrode terminal. The positive electrode terminal and the negative electrode terminal can extend from the electrode group.

In the non-aqueous electrolyte battery, which is an example of the battery according to the second embodiment, the non-aqueous electrolyte can be held, for example, in a state of being impregnated in the electrode group. Alternatively, in the battery of another example according to the second embodiment, the electrolytic solution containing the electrolyte can be held, for example, in a state of being impregnated in the electrode group.

The battery according to the second embodiment may further include an exterior member. The exterior member can accommodate, for example, a group of electrodes and an electrolyte.

The exterior member may have a structure capable of extending a part of the positive electrode terminal and a part of the negative electrode terminal to the outside thereof. Alternatively, the exterior member may include two external terminals, each of which is electrically connected to each of the positive electrode terminal and the negative electrode terminal. Alternatively, the exterior member itself can act as either a positive electrode terminal or a negative electrode terminal.

Next, each member that can be included in the non-aqueous electrolyte battery, which is an example of the battery according to the second embodiment, will be described in more detail.

(Positive electrode)
For the positive electrode, refer to the description of the electrode according to the first embodiment.

(Negative electrode)
As the negative electrode current collector, a sheet containing a material having high electrical conductivity and capable of suppressing corrosion in the working potential range of the negative electrode can be used. For example, an aluminum foil or an aluminum alloy foil can be used as the negative electrode current collector. When an aluminum foil or an aluminum alloy foil is used, the thickness thereof is, for example, 20 μm or less, preferably 15 μm or less. The aluminum alloy foil can include magnesium, zinc, silicon and the like. Further, the content of transition metals such as iron, copper, nickel and chromium contained in the aluminum alloy foil is preferably 1% or less.

As the negative electrode active material, for example, a metal, a metal alloy, a metal oxide, a metal sulfide, a metal nitride, a graphitic material, a carbonaceous material, or the like can be used. Examples of the metal oxide include compounds containing titanium such as titanium dioxide having a monoclinic crystal structure (for example, TiO ₂ (B)) and lithium titanium composite oxide. Examples of the metal sulfide include titanium sulfide such as TiS ₂ , molybdenum sulfide such as MoS ₂ , FeS, FeS ₂ , and Li _l FeS ₂ (subscript h is 0.9 ≦ l ≦ 1.2). Such as iron sulfide. Examples of the graphitic material and the carbonaceous material include natural graphite, artificial graphite, coke, vapor-grown carbon fiber, mesophase pitch-based carbon fiber, spherical carbon, and resin calcined carbon. It is also possible to mix and use a plurality of different negative electrode active materials.

As a more specific example of the compound containing titanium, for example, spinel-type lithium titanate (lithium titanate having a spinel-type crystal structure) can be mentioned. This compound has a composition represented by the general formula Li _{4 + w} Ti ₅ O ₁₂ , 0 ≦ w ≦ 3, and has a spinel-type crystal structure. The spinel-type lithium titanate exhibits electron conductivity in a state where lithium is inserted (w> 0), and the electron conductivity improves as the amount of lithium inserted increases.

Other specific examples of the lithium titanium composite oxide include a niobium titanium composite oxide having a monoclinic crystal structure and a titanium-containing composite oxide having an orthorhombic crystal structure. Can be mentioned.

An example of the niobium-titanium composite oxide having a monoclinic-type crystal structure (monoclinic-type niobium-titanium composite oxide) is the general formula Li _m Ti _1-n M1 _n Nb _2-o M2 _o O _{7 + δ} . Examples include the compounds represented. Here, M1 is at least one selected from the group consisting of Zr, Si and Sn. M2 is at least one selected from the group consisting of V, Ta and Bi. Each subscript in the general formula is 0 ≦ m ≦ 5, 0 ≦ n <1, 0 ≦ o <2, −0.3 ≦ δ ≦ 0.3. Specific examples of the monoclinic niobium titanium composite oxide can include a composite oxide having a composition represented by the general formula _{_{_{Li m Nb 2 TiO 7 (0}}} ≦ m ≦ 5).

Other examples of monoclinic niobium titanium composite oxide, a compound represented by the general formula _{_{Li p Ti 1-q M3 q}} + r Nb 2-r O 7-δ and the like. Here, M3 is at least one selected from Mg, Fe, Ni, Co, W, Ta, and Mo. Each subscript in the composition formula is 0 ≦ p ≦ 5, 0 ≦ q <1, 0 ≦ r <2, −0.3 ≦ δ ≦ 0.3.

An example of a titanium-containing composite oxide having an orthorhombic crystal structure (orthorhombic titanium-containing composite oxide) is the general formula Li _{2 + s} M (I) _2-t Ti _6-u M (II) _v. Examples thereof include compounds represented by O _{14 + σ} . Here, M (I) is at least one selected from the group consisting of Sr, Ba, Ca, Mg, Na, Cs, Rb and K. M (II) is at least one selected from the group consisting of Zr, Sn, V, Nb, Ta, Mo, W, Y, Fe, Co, Cr, Mn, Ni and Al. Each subscript in the composition formula is 0 ≦ s ≦ 6, 0 ≦ t <2, 0 ≦ u <6, 0 ≦ v <6, −0.5 ≦ σ ≦ 0.5. Specific examples of the orthorhombic titanium-containing composite oxide include compounds having a composition represented by the general formula Li _{2 + s} Na ₂ Ti ₆ O ₁₄ (0 ≦ s ≦ 6).

As the negative electrode active material, it is preferable to use a titanium-containing oxide having a small expansion and contraction of the active material during charging and discharging. It is more preferable that the negative electrode active material contains lithium titanate having a composition represented by the composition formula Li ₄ Ti ₅ O ₁₂ , which has the characteristic of being distortion-free without expansion and contraction of the active material during charging and discharging. By using an active material having a small expansion and contraction during charging and discharging as the negative electrode active material, it is possible to suppress cracking of the active material particles due to expansion and contraction during charging and discharging of the negative electrode active material.

The conductive agent can play a role of assisting electrical conduction between the negative electrode active materials and a role of assisting electrical conduction from the negative electrode active material to the negative electrode current collector, for example, in the negative electrode active material-containing layer.

As the conductive agent for the negative electrode, for example, carbon black such as acetylene black or a carbon substance such as graphite, carbon fiber or graphene can be used.

The binder can show the function of binding the active material and the current collector. As the binder of the negative electrode, for example, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), or fluorine-based rubber can be used.

The proportions (blending ratio) of the negative electrode active material, the conductive agent, and the binder contained in the negative electrode active material-containing layer are preferably 70 to 95% by weight, 0 to 25% by weight, and 2 to 10% by weight, respectively. More preferably, it is 85 to 95% by weight, 3 to 10% by weight and 2 to 5% by weight.

(Separator)
The separator is not particularly limited as long as it has insulating properties. For example, as the separator, a porous film or non-woven fabric made of a polymer such as polyolefin, cellulose, polyethylene terephthalate, polyamide, polyamideimide and vinylon can be used. The material of the separator may be one kind, or two or more kinds may be used in combination.

(Non-aqueous electrolyte)
The non-aqueous electrolyte contains a non-aqueous solvent and an electrolyte (electrolyte salt) dissolved in the non-aqueous solvent.

As the electrolyte, for example, lithium hexafluorophosphate (LiPF ₆ ), lithium tetrafluoroborate (LiBF ₄ ), lithium perchlorate (LiClO ₄ ) and the like can be used. Non-aqueous solvents include, for example, propylene carbonate (PC), ethylene carbonate (EC), 1,2-dimethoxyethane (DME), γ-butyrolactone (GBL), tetrahydrofuran (THF), 2-methyltetrahydrofuran (2-MeHF), 1,3-Dioxolane, sulfolane, acetonitrile (AN), diethyl carbonate (DEC), dimethyl carbonate (DMC), methyl ethyl carbonate (MEC) can be used.

(Negative electrode current collecting tab, positive electrode current collecting tab, negative electrode terminal and positive electrode terminal)
The negative electrode current collecting tab, the positive electrode current collecting tab, the negative electrode terminal, and the positive electrode terminal are preferably formed of a material having high electrical conductivity. When connected to a current collector, these members are preferably made of the same material as the current collector in order to reduce contact resistance.

(Exterior member)
As the exterior member, for example, a metal container or a laminated film container can be used, but is not particularly limited.

By using a metal container as the exterior member, it is possible to realize a battery with excellent impact resistance and long-term reliability. By using a container made of a laminated film as the exterior member, it is possible to realize a battery having excellent corrosion resistance and to reduce the weight of the battery.

As the metal container, for example, a container having a wall thickness within the range of 0.2 to 5 mm can be used. It is more preferable that the wall thickness of the metal container is 0.5 mm or less.

The metal container preferably contains at least one selected from the group consisting of Fe, Ni, Cu, Sn and Al. The metal container can be made of, for example, aluminum or an aluminum alloy. The aluminum alloy is preferably an alloy containing elements such as magnesium, zinc and silicon. When the alloy contains a transition metal such as iron, copper, nickel, and chromium, the content thereof is preferably 1% by weight or less. As a result, long-term reliability and impact resistance in a high temperature environment can be dramatically improved.

The container made of a laminated film can be produced, for example, by using a laminated film having a thickness in the range of 0.1 to 2 mm. The thickness of the laminated film is more preferably 0.2 mm or less.
As the laminate film, a multilayer film including a metal layer and a resin layer sandwiching the metal layer is used. The metal layer preferably contains a metal containing at least one selected from the group consisting of Fe, Ni, Cu, Sn and Al. The metal layer is preferably an aluminum foil or an aluminum alloy foil for weight reduction. As the resin layer, for example, a polymer material such as polypropylene (PP), polyethylene (PE), nylon, or polyethylene terephthalate (PET) can be used. The laminated film can be sealed into the shape of an exterior member by heat fusion.

Examples of the shape of the exterior member include a flat type (thin type), a square type, a cylindrical type, a coin type, and a button type. The exterior member can have various dimensions depending on the application. For example, when the battery according to the second embodiment is used for a portable electronic device, the exterior member can be made smaller according to the size of the mounted electronic device. Alternatively, in the case of a non-aqueous electrolyte battery loaded on a two-wheeled to four-wheeled automobile or the like, the container may be a container for a large battery.

Next, an example of the battery according to the second embodiment will be described in more detail with reference to the drawings.

FIG. 6 is a schematic notched perspective view of the battery of the first example according to the second embodiment. FIG. 7 is a schematic enlarged cross-sectional view of part A in FIG.

The battery 100 shown in FIGS. 6 and 7 includes a flat electrode group 1. The flat electrode group 1 includes a negative electrode 2, a positive electrode 3, and a separator 4.

As shown in FIG. 7, the negative electrode 2 includes a negative electrode current collector 2a and a negative electrode active material-containing layer 2b supported on the negative electrode current collector 2a. In the outermost portion of the negative electrode 2, the negative electrode active material-containing layer 2b is provided only on one surface of the negative electrode current collector 2a. In other parts, the negative electrode active material-containing layer 2b is provided on both surfaces of the negative electrode current collector 2a. As shown in FIG. 7, the positive electrode 3 includes a positive electrode current collector 3a and a positive electrode active material-containing layer 3b supported on the surfaces of both the positive electrode current collectors 3a. That is, the positive electrode 3 has the same structure as the electrode 3 of the example according to the first embodiment shown in FIG.

In the electrode group 1, as shown in FIG. 7, the negative electrode 2 and the positive electrode 3 are laminated with the separator 4 interposed between the negative electrode active material-containing layer 2b and the positive electrode active material-containing layer 3b. Such an electrode group 1 can be obtained by the following procedure. First, one flat plate-shaped negative electrode 2 and one flat plate-shaped positive electrode 3 are laminated with a separator 4 interposed therebetween. Next, another separator 4 is laminated on the positive electrode active material-containing layer 3b that does not face the negative electrode 2 to form a laminated body. This laminate is wound with the negative electrode 2 on the outside. Then, after pulling out the winding core, press it to make it flat. Thus, the electrode group 1 shown in FIGS. 6 and 7 can be obtained.

A band-shaped negative electrode terminal 5 is electrically connected to the negative electrode 2. A band-shaped positive electrode terminal 6 is electrically connected to the positive electrode 3.

The battery 100 shown in FIGS. 6 and 7 further includes an outer bag 7 made of a laminated film as a container.

The electrode group 1 is housed in an outer bag 7 made of a laminated film in a state in which the ends of the negative electrode terminal 5 and the positive electrode terminal 6 extend from the outer bag 7.

A non-aqueous electrolyte (not shown) is housed in the laminated film outer bag 7. That is, the battery 100 shown in FIGS. 6 and 7 is a non-aqueous electrolyte battery. The non-aqueous electrolyte is impregnated in the electrode group 1. The peripheral portion of the outer bag 7 is heat-sealed, thereby sealing the electrode group 1 and the non-aqueous electrolyte.

Next, a second example of the battery according to the second embodiment will be described in detail with reference to FIG.

FIG. 8 is a partially cutaway perspective view of the battery of the second example according to the second embodiment.

The battery 100 shown in FIG. 8 is significantly different from the battery 100 of the first example in that the exterior material is composed of the metal container 7a and the sealing plate 7b.

The battery 100 shown in FIG. 8 includes an electrode group 1 similar to the electrode group 1 of the battery 100 of the first example. The difference from the first example is that in the second example shown in FIG. 8, the member 5a used as the negative electrode terminal 5 in the first example is used as the negative electrode lead, and the positive electrode in the first example. The point is that the member 6a used as the terminal 6 is used as the positive electrode lead.

In the battery 100 shown in FIG. 8, such an electrode group 1 is housed in a metal container 7a. The metal container 7a further houses the non-aqueous electrolyte. The metal container 7a is sealed by a metal sealing plate 7b.

The sealing plate 7b is provided with a negative electrode terminal 5 and a positive electrode terminal 6. An insulating member 7c is arranged between the positive electrode terminal 6 and the sealing plate 7b. As a result, the positive electrode terminal 6 and the sealing plate 7b are electrically insulated.

The negative electrode terminal 5 is connected to the negative electrode lead 5a as shown in FIG. Similarly, the positive electrode terminal 6 is connected to the positive electrode lead 6a.

(Third Embodiment)
According to a third embodiment, a battery pack is provided. This battery pack comprises the battery according to the second embodiment.

The battery pack according to the third embodiment may include a plurality of batteries. Multiple batteries can be electrically connected in series or electrically in parallel. Alternatively, a plurality of batteries can be connected in series and in parallel.

For example, the battery pack according to the third embodiment may include a plurality of batteries according to the second embodiment. These batteries can be connected in series. Further, the batteries connected in series can form an assembled battery. That is, the battery pack according to the third embodiment may also include an assembled battery.

The battery pack according to the third embodiment can include a plurality of assembled batteries. A plurality of assembled batteries can be connected in series, in parallel, or in a combination of series and parallel.

An example of the battery pack according to the third embodiment will be described in detail with reference to FIGS. 9 and 10. The battery pack 20 shown in FIGS. 9 and 10 includes a plurality of cell cells 21. The battery shown in FIG. 8 can be used as the cell 21.

The plurality of cell cells 21 composed of the battery 100 shown in FIG. 8 described above are laminated so that the negative electrode terminals 5 and the positive electrode terminals 6 extending to the outside are aligned in the same direction, and are fastened with adhesive tape 22. It constitutes the assembled battery 23. As shown in FIG. 10, these cell cells 21 are electrically connected in series with each other.

The printed wiring board 24 is arranged so as to face the side surface of the cell 21 on which the negative electrode terminal 5 and the positive electrode terminal 6 extend. As shown in FIG. 10, the printed wiring board 24 is equipped with a thermistor 25, a protection circuit 26, and a terminal 27 for energizing an external device. An insulating plate (not shown) is attached to the surface of the printed wiring board 24 facing the assembled battery 23 in order to avoid unnecessary connection with the wiring of the assembled battery 23.

The positive electrode side lead 28 is connected to the positive electrode terminal 6 located at the bottom layer of the assembled battery 23, and the tip thereof is inserted into the positive electrode side connector 29 of the printed wiring board 24 and electrically connected. The negative electrode side lead 30 is connected to the negative electrode terminal 5 located on the uppermost layer of the assembled battery 23, and the tip thereof is inserted into the negative electrode side connector 31 of the printed wiring board 24 and electrically connected. These

connectors

29 and 31 are connected to the protection circuit 26 through the

wirings

32 and 33 formed on the printed wiring board 24.

The thermistor 25 detects the temperature of the cell 21 and the detection signal is transmitted to the protection circuit 26. The protection circuit 26 can cut off the positive side wiring 34a and the negative side wiring 34b between the protection circuit 26 and the energizing terminal 27 to the external device under predetermined conditions. The predetermined condition is, for example, when the detection temperature of the thermistor 25 becomes equal to or higher than the predetermined temperature. Further, the predetermined condition is when overcharge, overdischarge, overcurrent, etc. of the cell 21 are detected. The detection of overcharging or the like is performed for each individual cell 21 or the entire assembled battery 23. When detecting the individual cell 21, the battery voltage may be detected, or the positive electrode potential or the negative electrode potential may be detected. In the latter case, a lithium electrode used as a reference electrode is inserted into each cell 21. In the case of FIGS. 9 and 10, a wiring 35 for voltage detection is connected to each of the cell 21s, and a detection signal is transmitted to the protection circuit 26 through these wirings 35.

A protective sheet 36 made of rubber or resin is arranged on each of the three side surfaces of the assembled battery 23 except for the side surface on which the positive electrode terminal 6 and the negative electrode terminal 5 protrude.

The assembled battery 23 is stored in the storage container 37 together with the protective sheet 36 and the printed wiring board 24. That is, the protective sheet 36 is arranged on both inner side surfaces in the long side direction and the inner side surface in the short side direction of the storage container 37, and the printed wiring board 24 is arranged on the inner side surface on the opposite side in the short side direction. The assembled battery 23 is located in a space surrounded by the protective sheet 36 and the printed wiring board 24. The lid 38 is attached to the upper surface of the storage container 37.

A heat-shrinkable tape may be used instead of the adhesive tape 22 to fix the assembled battery 23. In this case, protective sheets are arranged on both side surfaces of the assembled battery, the heat-shrinkable tape is circulated, and then the heat-shrinkable tape is heat-shrinked to bind the assembled battery.

Although the cells 21 are connected in series in FIGS. 9 and 10, they may be connected in parallel in order to increase the battery capacity. The assembled battery packs can also be connected in series and / or in parallel.

Further, the mode of the battery pack according to the third embodiment is appropriately changed depending on the intended use. The battery pack according to the third embodiment is suitably used for applications in which excellent cycle characteristics are required when a large current is taken out. Specifically, it is used as a power source for a digital camera, or as an in-vehicle battery for vehicles such as trains, two-wheeled to four-wheeled hybrid electric vehicles, two-wheeled to four-wheeled electric vehicles, and assisted bicycles. In particular, it is suitably used as an in-vehicle battery.

Since the battery pack according to the third embodiment includes the battery according to the second embodiment, it can exhibit excellent input / output performance and excellent life characteristics.

[Example]
Examples will be described below, but the present invention is not limited to the examples described below as long as the gist of the present invention is not exceeded.

[Preparation of electrodes]
(Example 1)
In Example 1, an electrode was produced by the following procedure.

(Preparation of pre-dispersion liquid A)
First, as active material particles, particles of a lithium-containing nickel-cobalt-manganese composite oxide having a composition represented by the formula LiNi _0.6 Co _0.2 Mn _0.2 O ₂ were prepared. The particles were stored for 30 hours in an air environment with no dew point control. The particles obtained were a mixture of primary and secondary particles. The average primary particle size was 0.5 μm, and the average secondary particle size was 7 μm.

In addition, polyvinylidene fluoride was prepared as a binder.

Next, the active material particles and the binder were added to N-methylpyrrolidone at a weight ratio of 99: 1 to obtain a mixture. The resulting mixture was then stirred in a ball mill for 60 minutes. Thus, a paste-like pre-dispersion liquid A was obtained.

(Preparation of pre-dispersion liquid B)
First, acetylene black was prepared as a conductive agent. This acetylene black was heated in concentrated sulfuric acid at 200 ° C. By this treatment, the amount of functional groups on the surface of the conductive agent can be increased. In fact, the obtained conductive agent had a hydroxyl group and a carboxyl group on the surface. The average particle size of the conductive agent was 40 nm.

In addition, polyvinylidene fluoride was prepared as a binder.

Next, the conductive agent and the binder were added to N-methylpyrrolidone at a weight ratio of 70:30 to obtain a mixture. The resulting mixture was then stirred in a ball mill for 60 minutes. Thus, a paste-like pre-dispersion liquid B was obtained.

(Preparation of electrode paint C)
Next, the pre-dispersion liquid A and the pre-dispersion liquid B were mixed so that the weight ratio of the active material particles: the conductive agent: the binder was 85:10: 5 to obtain a mixture. The resulting mixture was then stirred on a roll mill for 60 minutes. Thus, a paste-like electrode paint C was obtained.

(Completion of electrode)
Next, the electrode paint C was uniformly applied to both surfaces of the current collector made of strip-shaped aluminum foil. Next, the coating film was dried to obtain a strip containing a current collector and an active material-containing layer provided on the surface of the current collector. Then, the strip containing the current collector and the active material-containing layer was subjected to a press.

After pressing, the strip was cut and the current collector tab was welded to the current collector. Thus, the electrode of Example 1 was obtained.

(Example 2)
In Example 2, the electrode was prepared by the same procedure as in Example 1 except that the pre-dispersion liquid A was prepared by the following procedure and the electrode coating material C was prepared by the following procedure.

In this example, as the active material particles, particles of a lithium-containing nickel-cobalt-manganese composite oxide having a composition represented by the formula LiNi _0.6 Co _0.2 Mn _0.2 O ₂ were prepared. The particles were stored in a dry room and removed from the dry room immediately before use. The particles were a mixture of primary and secondary particles. The average primary particle size was 0.7 μm, and the average secondary particle size was 8 μm.

In addition, oxalic acid as an electrode additive and polyvinylidene fluoride as a binder were prepared.

Next, the active material particles, the electrode additive and the binder were added to N-methylpyrrolidone at a weight ratio of 98: 1: 1 to obtain a mixture. Next, the obtained mixture was stirred with a ball mill for 60 minutes under an air atmosphere of normal temperature and pressure. Thus, a paste-like pre-dispersion liquid A was obtained. The obtained paste was stored in a state of being allowed to stand for 36 hours.

On the other hand, the pre-dispersion liquid B was obtained by the same procedure as in Example 1. Next, the pre-dispersion liquid A and the pre-dispersion liquid B were mixed so that the weight ratio of the active material particles: conductive agent: binder: electrode additive was 85: 9: 5: 1 to obtain a mixture. The resulting mixture was then stirred in a ball mill for 60 minutes. Thus, a paste-like electrode paint C was obtained.

(Example 3)
In Example 3, an electrode was prepared by the same procedure as in Example 1 except that the pre-dispersion liquid A was prepared by the following procedure.

In this example, the same lithium-containing nickel-cobalt-manganese composite oxide particles used in Example 2 were prepared as the active material particles. In addition, as a binder, polyvinylidene fluoride containing a functional group containing a carbonyl group in the side chain was prepared. The ratio of the molecular weight of the carbonyl group portion to the total molecular weight of this polyvinylidene fluoride was 3%.

(Example 4)
In Example 4, an electrode was prepared by the same procedure as in Example 1 except that the pre-dispersion liquid A was prepared by the following procedure.

In this example, the same lithium-containing nickel-cobalt-manganese composite oxide particles used in Example 2 were prepared as the active material particles. In addition, as a binder, a polyacrylonitrile binder containing a functional group containing a carbonyl group in the side chain was prepared. The ratio of the molecular weight of the carbonyl group portion to the total molecular weight of this polyacrylonitrile was 3%.

(Example 5)
In Example 5, an electrode was prepared by the same procedure as in Example 3 except that the pre-dispersion liquid B was prepared by the following procedure.

In this example, Ketjen Black was prepared as a conductive agent. This Ketjen black was heated in concentrated sulfuric acid at 200 ° C. By this treatment, the amount of functional groups on the surface of the conductive agent can be increased. In fact, the obtained conductive agent had a hydroxyl group and a carboxyl group on the surface. The average particle size of the conductive agent was 35 nm.

Also, as a binder, the same polyvinylidene fluoride as that used in Example 3 was prepared.

(Example 6)
In Example 6, an electrode was prepared by the same procedure as in Example 5 except that the pre-dispersion liquid B was prepared by the following procedure.

In this example, the same Ketjen black used in Example 5 was prepared as the conductive agent. This Ketjen black was treated with concentrated sulfuric acid in the same procedure as in Example 5.

Next, the conductive agent and the binder were added to N-methylpyrrolidone at a weight ratio of 70:30 to obtain a mixture. Next, the obtained mixture was put into a bead type wet fine particle dispersion crusher "sand grinder" which is a bead mill disperser. Dispersion was carried out in this bead mill disperser for 60 minutes. For dispersion, glass beads having a diameter of 2 mm were used as the dispersion medium. Moreover, the rotation speed of the wing was set to 800 rpm. Thus, a paste-like pre-dispersion liquid B was obtained.

(Examples 7 and 8)
In Examples 7 and 8, electrodes were produced by the same procedure as in Example 1 except that the electrode coating material C was prepared by the following procedure, respectively.

In Example 7, the pre-dispersion liquid A and the pre-dispersion liquid B were mixed so that the weight ratio of the active material particles: the conductive agent: the binder was 85: 8: 7 to obtain a mixture. The resulting mixture was then treated in the same manner as in Example 1. Thus, a paste-like electrode paint C was obtained.

In Example 8, the pre-dispersion liquid A and the pre-dispersion liquid B were mixed so that the weight ratio of the active material particles: the conductive agent: the binder was 85: 5: 10 to obtain a mixture. The resulting mixture was then treated in the same manner as in Example 1. Thus, a paste-like electrode paint C was obtained.

(Example 9)
In Example 9, an electrode was prepared by the same procedure as in Example 1 except that the pre-dispersion liquid A was prepared by the following procedure.

First, as active material particles, particles of a lithium-containing manganese composite oxide having a spinel-type crystal structure having a composition represented by the formula LiMn ₂ O ₄ were prepared. The particles were stored for 36 hours in an air environment with no dew point control. The particles obtained were a mixture of primary and secondary particles. The average primary particle size was 1 μm, and the average secondary particle size was 10 μm.

In addition, polyvinylidene fluoride was prepared as a binder.

(Example 10)
In Example 10, an electrode was prepared by the same procedure as in Example 1 except that the pre-dispersion liquid A was prepared by the following procedure.

First, as active material particles, particles of lithium iron phosphate having an olivine-type crystal structure having a composition represented by the formula LiFePO ₄ were prepared. The particles were stored for 36 hours in an air environment with no dew point control. The particles obtained were a mixture of primary and secondary particles. The average primary particle size was 0.2 μm, and the average secondary particle size was 3 μm.

In addition, polyvinylidene fluoride was prepared as a binder.

(Example 11)
In Example 11, electrodes were produced in the same procedure as in Example 1.

(Comparative Example 1)
In Comparative Example 1, the electrode was prepared in the same procedure as in Example 1 except that the pre-dispersion liquid A was prepared by the following procedure and the pre-dispersion liquid B was prepared by the following procedure.

In this example, as the active material particles, particles of a lithium-containing nickel-cobalt-manganese composite oxide having a composition represented by the formula LiNi _0.6 Co _0.2 Mn _0.2 O ₂ were prepared. The particles were stored in a dry room and removed from the dry room immediately before use. The particles were a mixture of primary and secondary particles. The average primary particle size was 0.7 μm, and the average secondary particle size was 8 μm. That is, in this example, the same active material particles as those used in Example 2 were used.

In addition, polyvinylidene fluoride was prepared as a binder.

Next, the active material particles and the binder were added to N-methylpyrrolidone at a weight ratio of 70:30 to obtain a mixture. The resulting mixture was then treated in the same manner as in Example 1. Thus, a paste-like pre-dispersion liquid A was obtained.

In this example, acetylene black was prepared as a conductive agent. However, unlike Examples 1 to 4 and 7 to 11, the prepared acetylene black was not subjected to treatment with concentrated sulfuric acid. The average particle size of the conductive agent was 40 nm. In this example, the pre-dispersion liquid B was prepared by the same procedure as in Example 1 except that this conductive agent was used.

(Comparative Example 2)
In Comparative Example 2, an electrode was prepared by the same procedure as in Comparative Example 1 except that the pre-dispersion liquid B was prepared by the following procedure.

In this example, Ketjen Black was prepared as a conductive agent. However, unlike Examples 5 and 6, the prepared Ketjen black was not treated with concentrated sulfuric acid. The average particle size of the conductive agent was 35 nm.

In addition, polyvinylidene fluoride was prepared as a binder.

(Comparative Examples 3 and 4)
In Comparative Examples 3 and 4, electrodes were produced by the same procedure as in Comparative Example 2 except that the electrode coating material C was prepared by the following procedure, respectively.

In Comparative Example 3, the pre-dispersion liquid A and the pre-dispersion liquid B were mixed so that the weight ratio of the active material particles: conductive agent: binder was 94: 1: 5 to obtain a mixture. The resulting mixture was then treated in the same manner as in Example 1. Thus, a paste-like electrode paint C was obtained.

In Comparative Example 4, the pre-dispersion liquid A and the pre-dispersion liquid B were mixed so that the weight ratio of the active material particles: the conductive agent: the binder was 75:20: 5 to obtain a mixture. The resulting mixture was then treated in the same manner as in Example 1. Thus, a paste-like electrode paint C was obtained.

(Comparative Example 5)
In Comparative Example 5, an electrode was produced by the same procedure as in Example 1 except that the electrode paint D prepared in the following procedure was used instead of the electrode paint C.

In this example, first, as the active material particles, particles of a lithium-containing nickel-cobalt-manganese composite oxide having a composition represented by the formula LiNi _0.6 Co _0.2 Mn _0.2 O ₂ were prepared. The particles were stored for 30 hours in an air environment with no dew point control. The particles obtained were a mixture of primary and secondary particles. The average primary particle size was 0.5 μm, and the average secondary particle size was 7 μm. That is, active material particles similar to those used in Example 1 were prepared.

Next, as a conductive agent, the same acetylene black used in Comparative Example 1 was prepared. That is, in this example, acetylene black, which has not been treated with concentrated sulfuric acid, was used as the conductive agent. Further, as a binder, the same polyvinylidene fluoride as that used in Example 1 was prepared.

Next, these were mixed so that the weight ratio of active material particles: conductive agent: binder was 85:10: 5 to obtain a mixture. The resulting mixture was then charged into N-methylpyrrolidone to give a suspension.

Next, this suspension was put into a bead type wet fine particle dispersion crusher "sand grinder" which is a bead mill disperser. Dispersion was carried out in this bead mill disperser for 60 minutes. For dispersion, glass beads having a diameter of 2 mm were used as the dispersion medium. Moreover, the rotation speed of the wing was set to 800 rpm. Thus, a paste-like electrode coating material D was obtained.

(Comparative Example 6)
In Comparative Example 6, the electrode was prepared in the same procedure as in Example 9 except that the pre-dispersion liquid A was prepared by the following procedure and the pre-dispersion liquid B was prepared by the following procedure.

First, as active material particles, particles of a lithium-containing manganese composite oxide having a spinel-type crystal structure having a composition represented by the formula LiMn ₂ O ₄ were prepared. The particles were stored in a dry room and removed from the dry room immediately before use. The particles were a mixture of primary and secondary particles. The average primary particle size was 1 μm, and the average secondary particle size was 10 μm.

In addition, polyvinylidene fluoride was prepared as a binder.

On the other hand, in this example, the same acetylene black used in Comparative Example 1 was prepared as the conductive agent. That is, in this example, acetylene black, which has not been treated with concentrated sulfuric acid, was used as the conductive agent. In this example, the pre-dispersion liquid B was prepared by the same procedure as that of Comparative Example 1 except that this conductive agent was used.

(Comparative Example 7)
In Comparative Example 7, the electrode was prepared by the same procedure as in Example 10 except that the pre-dispersion liquid A was prepared by the following procedure and the pre-dispersion liquid B was prepared by the following procedure.

First, as active material particles, particles of lithium iron phosphate having an olivine-type crystal structure having a composition represented by the formula LiFePO ₄ were prepared. The particles were stored in a dry room and removed from the dry room immediately before use. The particles were a mixture of primary and secondary particles. The average primary particle size was 0.2 μm, and the average secondary particle size was 3 μm.

In addition, polyvinylidene fluoride was prepared as a binder.

(Comparative Example 8)
In Comparative Example 8, an electrode was produced in the same procedure as in Comparative Example 1.

(Comparative Example 9)
In Comparative Example 9, an electrode was produced by the following procedure.

First, as active material particles, particles of a lithium-containing nickel-cobalt-manganese composite oxide having a composition represented by the formula LiNi _0.6 Co _0.2 Mn _0.2 O ₂ were prepared. The particles were stored in a dry room and removed from the dry room immediately before use. The particles were a mixture of primary and secondary particles. The average primary particle size was 0.7 μm, and the average secondary particle size was 8 μm. That is, in this example, the same active material particles as those used in Example 2 were used.
In addition, Ketjen Black was prepared as a conductive agent. No acid treatment was performed on this Ketjen black. The average particle size of this conductive agent was 35 nm.

Further, as a binder, polyvinylidene fluoride similar to that used in Comparative Example 1 and polyacrylonitrile containing no carbonyl group were prepared. That is, the binder prepared in this example did not contain a carbonyl group.

Next, these were mixed so that the weight ratio of active material particles: conductive agent: polyvinylidene fluoride: polyacrylonitrile was 96: 2: 1.6: 0.4 to obtain a mixture. The resulting mixture was then charged into N-methylpyrrolidone to give a suspension. This suspension was stirred with a planetary mixer to obtain a paste-like electrode coating material E. Stirring with a planetary mixer was a condition of 50 rpm for 60 minutes.

Next, the electrode paint E was uniformly applied to both surfaces of the current collector made of strip-shaped aluminum foil. Next, the coating film was dried to obtain a strip containing a current collector and an active material-containing layer provided on the surface of the current collector. Then, the strip containing the current collector and the active material-containing layer was subjected to a press.

After pressing, the strip was cut and the current collector tab was welded to the current collector. Thus, an electrode was obtained.

[Battery production]
(Examples 1 to 10, Comparative Examples 1 to 7, Comparative Example 9)
In each of Examples 1 to 10, Comparative Examples 1 to 7, and Comparative Example 9, the batteries of each example were produced by the following procedure. In the following description, the electrodes of Examples 1 to 10, Comparative Examples 1 to 7, and Comparative Example 9 are referred to as "positive electrodes".

(Preparation of negative electrode)
First, as a negative electrode active material, lithium titanate having a spinel-type crystal structure and a composition represented by the formula Li ₄ Ti ₅ O ₁₂ was prepared. In addition, graphite as a conductive agent and polyvinylidene fluoride as a binder were prepared. These were added to N-methylpyrrolidone and mixed so that the weight ratio of the negative electrode active material, the conductive agent and the binder was 90: 5: 5. Thus, a paste-like negative electrode paint was prepared.

This paste-like negative electrode paint was uniformly applied to both surfaces of the negative electrode current collector made of strip-shaped aluminum foil. Next, the coating film was dried to obtain a strip containing a negative electrode current collector and a negative electrode active material-containing layer provided on the surface of the negative electrode current collector. Next, a strip containing the negative electrode current collector and the negative electrode active material-containing layer was subjected to a press.

After pressing, the strip was cut and the negative electrode current collector tab was welded to the negative electrode current collector. Thus, a negative electrode was obtained.

(Preparation of electrode group)
Two polyethylene resin separators were prepared. Next, one separator, a positive electrode, another separator, and a negative electrode were laminated in this order to form a laminate. Next, the laminate thus obtained was spirally wound so that the negative electrode was located on the outermost circumference. Then, the winding core was pulled out from the winding body. Then, the wound body was pressed while being heated. Thus, a flat-shaped wound electrode group was produced.

(Preparation of non-aqueous electrolyte)
Ethylene carbonate and propylene carbonate were mixed at a volume ratio of 1: 2 to prepare a non-aqueous solvent. Lithium hexafluorophosphate LiPF ₆ as an electrolyte was dissolved in this non-aqueous solvent at a concentration of 1.0 mol / L. Thus, a non-aqueous electrolyte was prepared.

(Battery assembly)
Terminals were connected to the positive electrode and the negative electrode of the wound electrode group obtained as described above, respectively. Next, the electrode group was housed in a square container (exterior member) made of aluminum. The above-mentioned non-aqueous electrolyte was injected into this container. Thus, the batteries of each example were obtained.

(Example 11 and Comparative Example 8)
In each of Example 11 and Comparative Example 8, the same procedure as in Example 1 was performed except that the negative electrode was prepared by the following procedure and each electrode of Example 11 and Comparative Example 8 was used as the positive electrode. A battery was manufactured.

In these examples, as the negative electrode active material, a niobium-titanium composite oxide having a monoclinic crystal structure and a composition represented by the formula TiNb ₂ O ₇ was prepared. In these examples, a negative electrode was prepared by the same procedure as in Example 1 except that this niobium-titanium composite oxide was used as the negative electrode active material.

Tables 1 and 2 below show the manufacturing conditions for the batteries of each example.

[Evaluation of battery performance]
Each of the batteries of Examples and Comparative Examples was evaluated by the following procedure. In the following description, each battery is simply referred to as a battery.

(First charge / discharge)
The battery was charged at a constant current value of 0.2 C under a temperature environment of 25 ° C. until the voltage reached 2.8 V. The battery was then charged at a constant voltage until the current value reached a current value of 0.01C. That is, the battery was subjected to constant current constant voltage charging (CC-CV charging). Next, the batteries stored at a high temperature of 50 ° C. or higher were stored for 5 hours in a temperature environment of 25 ° C. The battery was then discharged at a constant current value of 1C until the voltage reached 1.5V. The capacity obtained by this discharge was used as the inspection capacity.

(Output test)
The battery was discharged at a current value of 1 C from a state of a charge rate of 100% (SOC 100%) to a charge rate of 0% (SOC 0%) in a temperature environment of 25 ° C. Next, the battery was subjected to constant current and constant voltage charging under the same conditions as above under a temperature environment of 25 ° C. Next, the battery was discharged at a current value of 10 C from a state of a charge rate of 100% (SOC 100%) to a charge rate of 0% (SOC 0%) in a temperature environment of 25 ° C. The ratio C (10C) / C (1C) of the discharge capacity obtained when discharging at each current value was determined as the rate capacity retention rate. The rate capacity retention rate is an index of output performance. A battery having a high rate capacity retention rate can exhibit excellent output performance. Further, a battery capable of exhibiting excellent output performance can also exhibit excellent input performance because the internal resistance of the battery is low.

(Life test)
The batteries were subjected to a life test according to the following procedure.
First, the battery was placed in a temperature environment of 25 ° C. Under this environment, the battery was set to a state of a charge rate of 50% (SOC 50%). The open circuit voltage (OCV) of the battery in this state was measured and set to the open circuit voltage V ₀ before the start of discharge. Next, the battery was discharged at a current value of 10 C for 10 seconds, and the voltage was measured. This voltage was defined as the voltage V ₁₀ after discharging for 10 seconds. The pre-cycle resistance value R ₀ was calculated from the difference between the voltage V ₀ and the voltage V ₁₀ . Specifically, R ₀ was obtained by substituting the values of V ₀ and V ₁₀ into the following equation. R ₀ = (V _0- V ₁₀ ) / 10C.

Next, the battery was placed in a temperature environment of 45 ° C. Here, the battery was charged with a constant current value of 2C until the battery voltage reached 2.8V. The battery was then discharged at a constant current value of 2C until the battery voltage reached 1.5V. This charge / discharge set was regarded as one charge / discharge cycle. The battery was then subjected to 500 charge / discharge cycles.

Next, the resistance value R ₅₀₀ after 500 cycles of the battery was calculated by the same procedure as the measurement of the resistance value R1 before the cycle.

By dividing the resistance value R ₅₀₀ by the resistance value R ₀ , the resistance increase rate by 500 charge / discharge cycles was obtained.

The resistance increase rate is an index of battery life performance. A battery having a low rate of increase in resistance can exhibit excellent life characteristics.

Table 3 below shows the rate capacity maintenance rate and resistance increase rate of each battery.

(Measurement of binder coverage on active material particles)
The coverage of the binder with respect to the active material particles (positive electrode active material particles) contained in the positive electrode of each battery was measured by the procedure described above. The results are shown in Table 4 below.

(Measurement of integrated pore volume distribution of active material-containing layer)
The integrated pore volume distribution of the positive electrode active material-containing layer (positive electrode active material-containing layer) of each battery was obtained by the procedure described above. The pore volume in the region where the pore diameter is 0.1 μm or less in the integrated pore volume distribution obtained for each battery is shown in Table 4 below.

(Measurement of carbon dioxide generation from active material-containing layer)
The positive electrode active material-containing layer (positive electrode active material-containing layer) of each battery was subjected to analysis by thermal decomposition chromatography according to the procedure described above. The amount of carbon dioxide generated from the active material-containing layer obtained by this analysis is shown in Table 4 below.

From the results shown in Table 3, it can be seen that the electrodes of Examples 1 to 11 were able to realize a battery capable of exhibiting excellent output performance and excellent life characteristics. Further, from the comparison between Example 1 and Examples 9 and 10, the electrodes of these Examples have different positive electrode active materials, but similarly exhibit excellent output performance and excellent life characteristics. It can be seen that the battery that was made was realized. Further, from the comparison between Example 1 and Example 11, although the batteries of these Examples have different negative electrode active materials, they were also able to show excellent output performance and excellent life characteristics. You can see that.

On the other hand, the batteries of Comparative Example 1 had lower output performance than the batteries of Examples 1 to 11. It is probable that at the positive electrode of the battery of Comparative Example 1, the conductive agent was aggregated and could not be uniformly dispersed around the active material particles. Therefore, it is considered that the active material particles and the conductive agent could not sufficiently contact each other at the positive electrode of the battery of Comparative Example 1, and as a result, the battery of Comparative Example 1 showed poor output performance.

The electrode of Comparative Example 2 is different from Comparative Example 1 in that Ketjen Black is used instead of acetylene black as the conductive agent. From the results of Comparative Examples 1 and 2, even if Ketjen Black having a small particle diameter, that is, a large specific surface area was used in the electrode of Comparative Example 1, the contact frequency between the active material particles and the conductive agent was sufficiently improved. I know I can't.

The batteries of Comparative Example 3 had lower output performance than the batteries of Examples 1 to 11. It is considered that the conductive agent was not sufficiently present around the active material particles in the positive electrode of the battery of Comparative Example 3. Therefore, it is considered that the active material particles and the conductive agent could not sufficiently contact each other at the positive electrode of the battery of Comparative Example 3, and as a result, the battery of Comparative Example 3 showed poor output performance. From this result, even if the amount of carbon dioxide generated from the active material-containing layer by thermal decomposition gas chromatography from 150 ° C. to 600 ° C. is 9 mL / g or more and 10 mL / g or less, mercury injection of the active material-containing layer is performed. It can be seen that if the pore volume in the region where the pore diameter is 0.1 μm or less in the integrated pore volume distribution by the method is less than 0.035 mL / g, excellent output performance cannot be realized.

On the other hand, the batteries of Comparative Example 4 were inferior in life characteristics to the batteries of Examples 1 to 11. In the positive electrode of the battery of Comparative Example 4, it is considered that the coverage of the binder with respect to the active material particles was too low, and the side reaction between the active material and the non-aqueous electrolyte, impurities, etc. could not be suppressed.

The batteries of Comparative Example 5 had lower output performance than the batteries of Examples 1 to 11. It is considered that the conductive agent was not uniformly present around the active material particles in the positive electrode of the battery of Comparative Example 5. Therefore, it is considered that the active material particles and the conductive agent could not sufficiently come into contact with each other at the positive electrode of the battery of Comparative Example 5, and as a result, the battery of Comparative Example 5 showed poor output performance. From this result, even if the amount of carbon dioxide generated from the active material-containing layer by thermal decomposition gas chromatography from 150 ° C. to 600 ° C. is 9 mL / g or more and 10 mL / g or less, mercury injection of the active material-containing layer is performed. It can be seen that if the pore volume in the region where the pore diameter is 0.1 μm or less in the integrated pore volume distribution by the method is less than 0.035 mL / g, excellent output performance cannot be realized.

The batteries of Comparative Examples 6 and 7 were also inferior in output performance as the batteries of Comparative Example 1. Comparative Examples 1, 6 and 7 are examples in which the positive electrode active materials are different from each other. From the results of these Comparative Examples, it can be seen that the poor output performance of the batteries of Comparative Examples 1, 6 and 7 does not depend on the type of the positive electrode active material. Further, the set of Example 1 and Comparative Example 1, the set of Example 9 and Comparative Example 6, and the set of Example 10 and Comparative Example 7 have the same composition of the prepared positive electrode active material, respectively. From the results of these examples, it can be seen that the batteries of each example were able to exhibit superior output performance and superior life characteristics as compared with the batteries of the corresponding comparative examples.

Further, the battery of Comparative Example 8 was inferior in output performance like the battery of Comparative Example 1. The positive electrode of the battery of Comparative Example 8 is the same as that of Comparative Example 1. From the comparison of the results of Comparative Examples 1 and 8, it can be seen that the poor output performance of the battery of Comparative Example 8 does not depend on the type of the negative electrode active material. Further, from the results shown in Table 3, it can be seen that the battery of Example 11 was superior in output performance to the battery of Comparative Example 8 having the same negative electrode active material.

The battery of Comparative Example 9 was inferior in output performance like the battery of Comparative Example 1. In the active material-containing layer of the positive electrode of the battery of Comparative Example 9, the coverage of the binder with respect to the active material particles was, for example, the same as that of Example 1. Further, Ketjen Black, which is the conductive agent used in Comparative Example 9, had a smaller average particle diameter, that is, a larger specific surface area than the conductive agent used in Example 1. However, in the active material-containing layer of the positive electrode of the battery of Comparative Example 9, the amount of carbon dioxide generated from the active material-containing layer was less than 9 mL / g, so that the conductive agent was aggregated. This is also clear from the fact that the pore volume of the region where the pore diameter is 0.1 μm or less in the integrated pore volume distribution by the mercury intrusion method of the active material-containing layer was less than 0.035 mL / g. That is, in the battery of Comparative Example 9, 85% of the surface of the positive electrode active material particles was covered with a binder, and the conductive additive was aggregated. Therefore, in the active material-containing layer of the positive electrode of the battery of Comparative Example 9, the contact frequency between the active material particles and the conductive agent was low. As a result, it is considered that the battery of Comparative Example 9 showed poor output performance.

The electrodes of at least one of these embodiments or examples include an active material-containing layer. This active material-containing layer contains active material particles, a binder, and a conductive agent. The binder covers the surface of the active material particles with a coverage of 80% or more and less than 99%. In the integrated pore volume distribution of the active material-containing layer by the mercury intrusion method, the pore volume in the region where the pore diameter is 0.1 μm or less is 0.035 mL / g or more and 0.050 mL / g or less. The amount of carbon dioxide generated from the active material-containing layer by pyrolysis gas chromatography from 150 ° C. to 600 ° C. is 9 mL / g or more and 10 mL / g or less. In this active material-containing layer, the binder covers the surface of the active material particles with a high coverage, but the conductive agent can be uniformly present around the active material particles in a sufficient amount. Therefore, in this active material-containing layer, the active material particles and the conductive agent can exhibit a high contact frequency. As a result, this electrode can realize a battery capable of exhibiting excellent input / output performance and excellent life characteristics.

Although some embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other embodiments, and various omissions, replacements, and changes can be made without departing from the gist of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention as well as the invention described in the claims and the equivalent scope thereof.

Claims

Active material particles and
A binder that covers the surface of the active material particles with a coverage of 80% or more and less than 99%.
A layer containing an active material containing a conductive agent is provided.
In the integrated pore volume distribution of the active material-containing layer by the mercury intrusion method, the pore volume in the region where the pore diameter is 0.1 μm or less is 0.035 mL / g or more and 0.050 mL / g or less.
An electrode in which the amount of carbon dioxide generated from the active material-containing layer by thermal decomposition gas chromatography from 150 ° C. to 600 ° C. is 9 mL / g or more and 10 mL / g or less.
The electrode according to claim 1, wherein the binder contains a carbonyl group.
The electrode according to claim 1 or 2, wherein the binder contains polyvinylidene fluoride containing a carbonyl group.
The electrode according to any one of claims 1 to 3, wherein the active material particles contain a carbonyl group on the surface.
The electrode according to any one of claims 1 to 4, wherein the conductive agent contains Ketjen black.
The electrode according to any one of claims 1 to 5 as a positive electrode and
With the negative electrode
A battery equipped with an electrolyte.
A battery pack including the battery according to claim 6.