JP2021180084A - Lithium ion secondary battery - Google Patents

Abstract

To provide a lithium ion secondary battery of which the expansion is suppressed and in which deterioration of a gas storage member is suppressed for a long period of time.SOLUTION: A lithium ion secondary battery is provided, comprising: a positive electrode including a positive electrode active material; a negative electrode including negative electrode active material; an electrolyte including lithium salt; and a gas storage member including a gas storage unit capable of storing gas, and a protective layer that covers at least a part of the gas storage unit, transmits the gas, and can suppresses contact between the gas storage unit and a component contained in the electrolyte.SELECTED DRAWING: Figure 1

Description

The present invention relates to a lithium ion secondary battery.

Lithium-ion secondary batteries, which are a type of non-aqueous electrolyte secondary batteries, are secondary batteries with high energy density, and are used as power sources for portable devices such as notebook computers and mobile phones by taking advantage of their characteristics.

In recent years, lithium-ion secondary batteries have been attracting attention as power supplies for electronic devices, power storage power supplies, power supplies for electric vehicles, etc., which are becoming smaller and smaller, and lithium-ion secondary batteries with even higher energy densities are required. There is.
As a means for improving the energy density, for example, there is a method of using a spinel-type lithium-nickel-manganese composite oxide showing a high working potential as a positive electrode active material. However, due to the high potential, in the conventional electrolytic solution using cyclic carbonate or chain carbonate, the cyclic carbonate or chain carbonate may be oxidatively decomposed at the contact portion between the positive electrode active material and the electrolytic solution. Further, the product produced by this oxidative decomposition may be deposited or deposited on the negative electrode side having a low potential to become a resistance, which may reduce the capacity of the lithium ion secondary battery. Due to these phenomena, there is a problem that a lithium ion secondary battery using a positive electrode active material showing a high operating potential cannot obtain sufficient charge / discharge cycle characteristics.
As a means for solving this, a lithium ion secondary using a negative electrode having a lithium titanium composite oxide as a negative electrode active material and an electrolytic solution containing a non-aqueous solvent having a diethyl carbonate (DEC) content of 80% by volume or more is used. Batteries have been proposed (see, for example, Patent Document 1).

Japanese Unexamined Patent Publication No. 2006-66341

Patent Document 1 mentions that diethyl carbonate contributes to the reduction of oxidative decomposition of non-aqueous solvents in the vicinity of the positive electrode. Therefore, according to Patent Document 1, it is considered that the deposition or precipitation of the product generated by the oxidative decomposition of the electrolytic solution on the negative electrode side can be suppressed.
However, there is a problem that the lithium-titanium composite oxide of the negative electrode acts catalytically to promote the reductive decomposition of non-aqueous solvents such as cyclic carbonate and chain carbonate, and to easily generate gas such as hydrogen gas. When a gas such as hydrogen gas is generated, a problem such as expansion of the battery occurs. Further, even when the electrolyte contains a solid electrolyte, there arises a problem that the battery expands due to the generation of carbon dioxide, sulfur oxide, hydrogen sulfide, etc. derived from the solid electrolyte.

The present disclosure has been made in view of the above problems, and an object of the present invention is to provide a lithium ion secondary battery in which expansion of the battery is suppressed and deterioration of the gas storage portion is suppressed for a long period of time.

Specific means for solving the above problems are as follows.
<1> A positive electrode containing a positive electrode active material and a positive electrode
Negative electrode containing negative electrode active material and negative electrode
Electrolytes containing lithium salts and
A protective layer that covers at least a part of the gas storage unit capable of storing gas and the gas storage unit, allows the gas to permeate, and suppresses contact between the gas storage unit and the components contained in the electrolyte. With the gas occlusion member
Lithium-ion secondary battery with.
<2> The lithium ion secondary battery according to <1>, wherein the protective layer is located between the gas storage unit and the electrolyte.
<3> The lithium ion II according to <1> or <2>, wherein the gas storage member is installed on at least a part of the inner wall surface of the positive electrode, the negative electrode, and the inner wall surface of the battery exterior in which the electrolyte is housed. Next battery.
<4> The lithium ion secondary battery according to any one of <1> to <3>, wherein the gas storage unit is capable of storing hydrogen gas.
<5> The ratio of the volume (mL) of the gas storage unit to the capacity (Ah) of the positive electrode or the capacity (Ah) of the negative electrode (volume of the gas storage unit / capacity of the positive electrode or capacity of the negative electrode) is 0.01. The lithium ion secondary battery according to any one of <1> to <4> described above.
<6> The gas storage unit has a metal layer and a catalyst layer located at least a part on the surface of the metal layer.
The lithium ion secondary battery according to any one of <1> to <5>, wherein the protective layer is located at least a part on the surface of the catalyst layer.
<7> The lithium according to any one of <1> to <6>, wherein the positive electrode active material contains an active material in which lithium ions are inserted and removed at a potential of 4.5 V or more with respect to the lithium potential. Ion secondary battery.
<8> The lithium according to any one of <1> to <7>, wherein the negative electrode active material contains an active material in which lithium ions are inserted and removed at a potential of 0.4 V or more with respect to the lithium potential. Ion secondary battery.
<9> Further, a separator interposed between the positive electrode and the negative electrode is provided.
The lithium ion secondary battery according to <1> to <8>, wherein the electrolyte contains a non-aqueous solvent.
<10> The lithium ion secondary battery according to <9>, wherein the separator has a porosity of 20% to 80%.
<11> The lithium ion secondary battery according to <1> to <8>, wherein the electrolyte contains a non-aqueous solvent and a polymer electrolyte impregnated with the non-aqueous solvent.
<12> The non-aqueous solvent is ethylene carbonate, diethyl carbonate, propylene carbonate, ethylmethylsulfone, vinylene carbonate, methylethyl carbonate, γ-butyrolactone, acetonitrile, 1,2-dimethoxyethane, dimethoxymethane, tetrahydrofuran, dioxolane, chloride. Does not contain any specific non-aqueous solvent selected from the group consisting of methylene, fluorinated ether and carboxylic acid ester (excluding carboxylic acid ester containing fluorine atom), or contains the total amount of the specific non-aqueous solvent. The lithium ion secondary battery according to any one of <9> to <11>, wherein the ratio is less than 30% by volume based on the total amount of the non-aqueous solvent.
<13> The lithium ion secondary battery according to any one of <9> to <12>, wherein the non-aqueous solvent contains a phosphoric acid ester containing a fluorine atom.
<14> The lithium ion secondary battery according to any one of <1> to <8>, wherein the electrolyte contains at least one of a sulfide-based inorganic solid electrolyte and an oxide-based inorganic solid electrolyte.
<15> The lithium salt is any one of <1> to <14>, which comprises at least one selected from the group consisting of lithium hexafluorophosphate, lithium tetrafluoroborate, and lithium bis (trifluoromethanesulfonyl) imide. The lithium ion secondary battery described in one.
<16> The lithium ion secondary according to any one of <1> to <15>, wherein the capacity ratio (negative electrode capacity / positive electrode capacity) between the negative electrode capacity of the negative electrode and the positive electrode capacity of the positive electrode is 1 or less. battery.

According to the present disclosure, it is possible to provide a lithium ion secondary battery in which expansion of the battery is suppressed and deterioration of the gas storage portion is suppressed for a long period of time.

It is a perspective view which shows an example of the lithium ion secondary battery of this disclosure. It is a perspective view which shows the positive electrode plate, the negative electrode plate, a separator and a gas storage member which make up an electrode group. It is sectional drawing which shows the other form of the lithium ion secondary battery of this disclosure. It is a schematic block diagram which shows the lithium ion secondary battery produced in the comparative example 1. FIG. In Comparative Example 1 and Comparative Example 3, it is a graph which shows the relationship between the number of charge / discharge cycles in a lithium ion secondary battery, and the amount of gas generation. In Comparative Example 2 and Comparative Example 4, it is a graph which shows the relationship between the number of charge / discharge cycles in a lithium ion secondary battery, and the amount of gas generation. In Comparative Example 3 and Comparative Example 4, it is a graph which shows the relationship between the number of charge / discharge cycles in a lithium ion secondary battery, and the discharge capacity retention rate. In Comparative Example 1 and Comparative Example 2, it is a graph which shows the relationship between the number of charge / discharge cycles in a lithium ion secondary battery, and the discharge capacity retention rate. In Comparative Example 1 and Comparative Example 2, it is a graph which shows the amount of each gas generated after charging and discharging a lithium ion secondary battery for 300 cycles.

Hereinafter, embodiments of the lithium ion secondary battery of the present invention will be described. However, the present invention is not limited to the following embodiments. In the following embodiments, the components (including element steps and the like) are not essential unless otherwise specified. The same applies to the numerical values and their ranges, and does not limit the present invention.
The numerical range indicated by using "~" in the present disclosure indicates a range including the numerical values before and after "~" as the minimum value and the maximum value, respectively.
In the numerical range described stepwise in the present disclosure, the upper limit value or the lower limit value described in one numerical range may be replaced with the upper limit value or the lower limit value of the numerical range described in another stepwise description. .. Further, in the numerical range described in the present disclosure, the upper limit value or the lower limit value of the numerical range may be replaced with the value shown in the examples.
Further, in the present disclosure, the content rate of each component means the total rate of the plurality of kinds of substances when there are a plurality of kinds of substances corresponding to each component, unless otherwise specified. Further, in the present disclosure, the particle size of each component means a value for a mixture of the plurality of types of particles when a plurality of types of particles corresponding to each component are present, unless otherwise specified.
In the present disclosure, the term "film" includes not only the configuration of a shape formed on the entire surface when observed as a plan view, but also the configuration of a shape partially formed.
In the present disclosure, the term "layer" includes not only the configuration of the shape formed on the entire surface but also the configuration of the shape partially formed when observed as a plan view. The term "laminated" refers to stacking layers, and two or more layers may be bonded or the two or more layers may be removable.
In the present disclosure, the "solid content" of the positive electrode mixture or the negative electrode mixture means the remaining components obtained by removing volatile components such as organic solvents from the positive electrode mixture or the negative electrode mixture.

[Lithium-ion secondary battery]
The lithium ion secondary battery of the present disclosure includes a positive electrode containing a positive electrode active material, a negative electrode containing a negative electrode active material, an electrolyte containing a lithium salt, a gas storage unit capable of storing gas, and at least one of the gas storage units. A gas storage member is provided, which covers a portion, allows the gas to permeate, and has a protective layer capable of suppressing contact between the gas storage portion and a component contained in the electrolyte.

The lithium ion secondary battery of the present disclosure includes a gas storage member provided with a gas storage unit, so that when the electrolyte contains a non-aqueous solvent, the gas storage member contains a gas such as hydrogen gas generated by decomposition of the non-aqueous solvent. When the electrolyte contains a solid electrolyte, the gas storage member occludes gas such as carbon dioxide, sulfur oxide, and hydrogen sulfide generated by decomposition of the solid electrolyte, so that the expansion of the battery is suppressed. Further, since the gas storage member includes a protective layer that covers at least a part of the gas storage part, the reaction between the component contained in the electrolyte and the component contained in the gas storage part is contained in the gas storage part into the electrolyte. Deterioration of the gas storage portion due to dissolution, impregnation, etc. of the components is suppressed for a long period of time, and expansion of the battery is also suppressed for a long period of time.

Hereinafter, each configuration of the lithium ion secondary battery of the present disclosure will be described.

(Gas storage member)
The lithium ion secondary battery of the present disclosure covers at least a part of a gas storage unit capable of storing gas and the gas storage unit, allows the gas to pass through, and is a component contained in the gas storage unit and the electrolyte. A gas storage member having a protective layer capable of suppressing contact with the gas storage member is provided.

The gas storage unit may be any gas that can store gas generated by decomposition of a non-aqueous solvent, decomposition of a solid electrolyte, etc. For example, hydrogen gas, carbon monoxide gas, carbon dioxide gas, sulfur oxide gas, sulfide. Any gas such as hydrogen gas may be used as long as it can occlude gas. Above all, the gas storage unit is preferably capable of storing hydrogen gas, and more preferably a hydrogen storage metal, a hydrogen storage alloy, or the like. Examples of the hydrogen storage metal include metals such as titanium, and examples of the hydrogen storage alloy include alloys containing metals such as titanium.

The gas storage unit preferably has a metal layer and a catalyst layer located at least a part on the surface of the metal layer. Further, it is preferable that the protective layer is located at least a part on the surface of the catalyst layer, and it is more preferable that the protective layer covers the surface of the catalyst layer. By locating the protective layer on the surface of the catalyst layer, deterioration of the catalyst layer due to contact of the components contained in the electrolyte with the catalyst layer can be suppressed, and the gas storage unit has hydrogen gas, carbon dioxide, and sulfur for a long period of time. Gases such as oxides and hydrogen sulfide can be suitably stored. The catalyst layer may be, for example, a catalyst that acts as a catalyst for breaking the bonds of hydrogen molecules and the like.

The protective layer is a layer that covers at least a part of the gas storage portion. The protective layer is composed of a component that allows gas such as hydrogen gas, carbon dioxide, sulfur oxide, and hydrogen sulfide to permeate, and that does not easily react with a component contained in the electrolyte.

The material of the protective layer is a polyolefin such as polyimide, epoxy resin, polypropylene, etc. from the viewpoint of allowing gas such as hydrogen gas, carbon dioxide, sulfur oxide, hydrogen sulfide, etc. to permeate, reacting with components contained in the electrolyte, and being difficult to dissolve. Etc. are preferable.

The protective layer may be attached on the gas storage portion via an adhesive. Examples of the material of the pressure-sensitive adhesive include silicone-based pressure-sensitive adhesives, acrylic-based pressure-sensitive adhesives, and natural rubber-based pressure-sensitive adhesives. Further, from the viewpoint of suppressing the generation of gas for a long period of time, the material of the protective layer is preferably polyolefin such as polypropylene, and the pressure-sensitive adhesive is preferably an acrylic pressure-sensitive adhesive.

The gas storage member may be installed in a place where it does not come into contact with the electrolyte in the lithium ion secondary battery, a place where it is difficult to come into contact with the electrolyte in the lithium ion secondary battery, a place where the generated gas accumulates, or the like.

It is preferable that the protective layer is located between the gas storage portion and the electrolyte, and it is more preferable that the protective layer that covers the gas storage portion is provided. As a result, the gas storage section and the electrolyte come into contact with each other via the protective layer, so that the reaction between the components contained in the electrolyte and the components contained in the gas storage section and the dissolution of the components contained in the gas storage section in the electrolyte. , Deterioration of the gas storage portion due to impregnation and the like can be more preferably suppressed.

When the electrolyte contains a non-aqueous solvent, the gas storage member preferably stores gas such as hydrogen gas generated by decomposition of the non-aqueous solvent, and when the electrolyte contains a solid electrolyte, the gas storage member decomposes the solid electrolyte, etc. The gas occlusion member is installed on at least a part of the inner wall surface of the battery exterior body in which the positive electrode, the negative electrode and the electrolyte are accommodated, from the viewpoint of suitably storing the gas such as carbon dioxide, sulfur oxide and hydrogen sulfide generated by the occlusion. Is preferable.

The ratio of the volume (mL) of the gas storage unit to the capacity of the positive electrode (Ah) or the capacity of the negative electrode (Ah) (volume of the gas storage unit / capacity of the positive electrode or capacity of the negative electrode) is hydrogen gas, carbon dioxide, sulfur oxidation. From the viewpoint of occluding gas such as substances and hydrogen sulfide, it is preferably 0.01 or more, more preferably 0.08 or more, and from the viewpoint of miniaturization and cost reduction of the lithium ion secondary battery. Therefore, it is more preferably 0.08 to 2.9.

(Positive electrode active material)
The positive electrode active material used in the lithium ion secondary battery of the present disclosure is not particularly limited as long as it is a substance into which lithium ions are inserted and removed. As the positive electrode active material, lithium ions are inserted and desorbed at a potential of 4.5 V or more with respect to the lithium potential from the viewpoint of increasing the difference from the potential when the negative electrode active material inserts and desorbs lithium ions. It is preferable to contain an active material (hereinafter, may be referred to as “specific positive electrode active material”).

In the lithium ion secondary battery of the present disclosure, it is preferable that the specific positive electrode active material is used as the positive electrode active material. The content of the specific positive electrode active material in the positive electrode active material is preferably 50% by mass to 100% by mass. When the content of the specific positive electrode active material in the positive electrode active material is 50% by mass or more, the energy density of the lithium ion secondary battery tends to be further improved.
The content of the specific positive electrode active material in the positive electrode active material is more preferably 70% by mass to 100% by mass, further preferably 80% by mass to 100% by mass.

In the present disclosure, the specific positive electrode active material means that "the insertion reaction and the desorption reaction of lithium ions hardly occur at a potential lower than 4.5V with respect to the lithium potential, and 4.5V or more with respect to the lithium potential. It is an active material that is exclusively used by electric potential.
Specifically, "Activities in which a lithium ion insertion reaction and a desorption reaction are carried out at a potential of 4.5 V or more with respect to a lithium potential with an electrochemical capacity of at least 80 mAh / g or more per unit mass of the active material. It means "substance". For example, a spinel-type lithium-nickel-manganese composite oxide can be mentioned.

The spinel-type lithium-nickel-manganese composite oxide that can be used as the positive electrode active material of the lithium ion secondary battery of the present disclosure is represented by LiNi _X Mn _2-X O ₄ (0.3 <X <0.7). It is preferably a compound represented by LiNi _X Mn _2-X O ₄ (0.4 <X <0.6), more preferably LiNi _{0.5 from the viewpoint of stability.} It is more preferably Mn _1.5 O _4.

In order to make the crystal structure of the spinel-type lithium-nickel-manganese composite oxide more stable, a part of Mn, Ni or O-site of the spinel-type lithium-nickel-manganese composite oxide is replaced with another element. May be good.
Further, excess lithium may be present in the crystals of the spinel-type lithium-nickel-manganese composite oxide. Furthermore, a chemical substance having a defect in the O-site of the spinel-type lithium-nickel-manganese composite oxide can also be used.

Examples of the element capable of substituting the Mn or Ni site of the spinel-type lithium-nickel-manganese composite oxide include Ti, V, Cr, Fe, Co, Zn, Cu, W, Mg, Al and Ru. Can be mentioned. The Mn or Nisite of the spinel-type lithium-nickel-manganese composite oxide can be replaced with one or more of these metal elements. Of these substitutable elements, Ti is preferably used from the viewpoint of further stabilizing the crystal structure of the spinel-type lithium-nickel-manganese composite oxide.
Examples of the element capable of substituting the O-site of the spinel-type lithium-nickel-manganese composite oxide include F and B. The spinel-type lithium-nickel-manganese composite oxide Osite can be replaced with one or more of these elements. Of these substitutable elements, F is preferably used from the viewpoint of further stabilizing the crystal structure of the spinel-type lithium-nickel-manganese composite oxide.

From the viewpoint of high energy density, the spinel-type lithium-nickel-manganese composite oxide ^{preferably has a potential of 4.5 V to 5.1 V with respect to Li / Li +} in a charged state, and is preferably 4.6 V to 4.6 V. More preferably, it is 5.0 V.

The BET specific surface area of the spinel-type lithium-nickel-manganese composite oxide ^{is preferably less than 2.9 m 2} / g, and more preferably less than ^{2.8 m 2 / g, from the viewpoint of improving the storage characteristics.} It is more preferably less than 1.5 m ² / g, and particularly preferably less than ^{1.0 m 2 / g.} Further, the BET specific surface area of the spinel-type lithium-nickel-manganese composite oxide may be less than ^{0.3 m 2 / g.} In the viewpoint of improving the output characteristics, the BET specific surface area is preferably at 0.05 m ² / g or more, more preferably 0.08 m ² / g or more, 0.1 m ² / g or more It is more preferable to have.
BET specific surface area of the lithium-nickel-manganese composite oxide of the spinel is preferably less than 0.05 m ² / g or more ^{2.9m 2 / g, 0.05m 2 /} g or more 2.8 m ² / g It is more preferably less than, more preferably 0.08 m ² / g or more and ^{less than 1.5 m 2} / g, and particularly preferably 0.1 m ² / g or more and ^{less than 1.0 m 2} / g. Further, the BET specific surface area of the spinel-type lithium-nickel-manganese composite oxide may be 0.1 m ² / g or more and ^{less than 0.3 m 2} / g.

The BET specific surface area can be measured from the nitrogen adsorption capacity according to, for example, JIS Z 8830: 2013. As the evaluation device, for example, QUANTACHROME: AUTOSORB-1 (trade name) can be used. When measuring the BET specific surface area, it is considered that the water adsorbed on the sample surface and structure affects the gas adsorption capacity. Therefore, it is preferable to first perform a pretreatment for removing water by heating. ..
In the pretreatment, the measurement cell in which 0.05 g of the measurement sample is charged is depressurized to 10 Pa or less with a vacuum pump, kept at a temperature of 110 ° C. for 3 hours or more, and then kept at room temperature (reduced pressure). Naturally cool to 25 ° C). After performing this pretreatment, the evaluation temperature is set to 77K, and the evaluation pressure range is measured as a relative pressure (equilibrium pressure with respect to saturated vapor pressure) of less than 1.

Further, the median diameter D50 of the spinel-type lithium-nickel-manganese composite oxide particles (the median diameter D50 of the secondary particles when the primary particles are aggregated to form the secondary particles) is the dispersion of the particles. From the viewpoint of sex, it is preferably 0.5 μm to 100 μm, and more preferably 1 μm to 50 μm.
The median diameter D50 can be obtained from the particle size distribution obtained by the laser diffraction / scattering method. Specifically, a lithium-nickel-manganese composite oxide is added into pure water so as to be 1% by mass, dispersed by ultrasonic waves for 15 minutes, and then measured by a laser diffraction / scattering method.

The positive electrode active material in the lithium ion secondary battery of the present disclosure may contain other positive electrode active materials other than the spinel-type lithium-nickel-manganese composite oxide.
Other positive-electrode active material other than the lithium-nickel-manganese composite oxide, for _{example, Li x CoO 2, Li x} NiO 2, Li x MnO 2, Li x Co y Ni 1-y O 2, Li x Co y M ¹ in _{1-y O z (Li x} Co y M 1 1-y O z, M 1 is Na, Mg, Sc, Y, Mn, Fe, Cu, Zn, Al, Cr, Pb, Sb, V and Indicates at least one element selected from the group consisting of B), Li _x Ni _1-y M ² _{y Oz} (in Li _x Ni _1-y M ² _{y Oz} , M ² is Na, Mg, Sc. , Y, Mn, Fe, Co, Cu, Zn, Al, Cr, Pb, Sb, V and B.), Li _x Mn ₂ O ₄ and Li _x Mn. _2-y M ³ _y O ₄ (In Li _x Mn _2-y M ³ _y O ₄ , M ³ is Na, Mg, Sc, Y, Fe, Co, Cu, Zn, Al, Cr, Pb, Sb, V. And at least one element selected from the group consisting of B). Here, x is in the range of 0 <x ≦ 1.2, y is in the range of 0 to 0.9, and z is in the range of 2.0 to 2.3. Further, the x value indicating the molar ratio of lithium increases or decreases depending on charging and discharging.

When the positive electrode active material contains other positive electrode active materials other than the spinel-type lithium-nickel-manganese composite oxide, the BET specific surface area of the other positive electrode active materials is 2.9 m ^{2 from the viewpoint of improving the storage characteristics.} It is preferably less than / g, more preferably less than ^{2.8 m 2} / g, even more preferably less than ^{1.5 m 2} / g, and particularly preferably less than ^{1.0 m 2 / g.} .. Further, the BET specific surface area of the other positive electrode active material may be less than ^{0.3 m 2 / g.} In the viewpoint of improving the output characteristics, the BET specific surface area is preferably at 0.05 m ² / g or more, more preferably 0.08 m ² / g or more, 0.1 m ² / g or more It is more preferable to have.
BET specific surface area of the other of the positive electrode active material is preferably less than 0.05 m ² / g or more 2.9 m ² / g, more is less than 0.05 m ² / g or more 2.8 m ² / g It is more preferably 0.08 m ² / g or more and ^{less than 1.5 m 2} / g, and particularly preferably 0.1 m ² / g or more and ^{less than 1.0 m 2} / g. Further, the BET specific surface area of the other positive electrode active material ^{may be 0.1 m 2} / g or more and ^{less than 0.3 m 2} / g.
The BET specific surface area of other positive electrode active materials can be measured by the same method as the spinel-type lithium-nickel-manganese composite oxide.

When the positive electrode active material contains other positive electrode active materials other than the spinel-type lithium-nickel-manganese composite oxide, the median diameter D50 of the particles of the other positive electrode active materials (primary particles aggregate and secondary particles). The median diameter D50) of the secondary particles is preferably 0.5 μm to 100 μm, more preferably 1 μm to 50 μm, from the viewpoint of particle dispersibility. The median diameter D50 of the other positive electrode active material can be measured by the same method as the spinel-type lithium-nickel-manganese composite oxide.

(Negative electrode active material)
The negative electrode active material used in the lithium ion secondary battery of the present disclosure is not particularly limited as long as it is a substance into which lithium ions are inserted and removed. As the negative electrode active material, from the viewpoint of suppressing the precipitation of lithium at the negative electrode, an active material in which lithium ions are inserted and desorbed at a potential of 0.4 V or more with respect to the lithium potential (hereinafter, “specific negative electrode active material””. It may be referred to as).

In the lithium ion secondary battery of the present disclosure, it is preferable to use a negative electrode active material containing a specific negative electrode active material. The content of the specific negative electrode active material in the negative electrode active material is preferably 50% by mass to 100% by mass. When the content of the specific negative electrode active material in the negative electrode active material is 50% by mass or more, the energy density of the lithium ion secondary battery tends to be further improved.
The content of the specific negative electrode active material in the negative electrode active material is more preferably 70% by mass to 100% by mass, further preferably 80% by mass to 100% by mass.

In the present disclosure, the specific negative electrode active material means that "the insertion reaction and the desorption reaction of lithium ions hardly occur at a potential lower than 0.4 V with respect to the lithium potential, and 0.4 V or more with respect to the lithium potential. It is an active material that is exclusively used by electric potential.
Specifically, "Activities in which a lithium ion insertion reaction and a desorption reaction are carried out at a potential of 0.4 V or more with respect to a lithium potential with an electrochemical capacity of at least 100 mAh / g or more per unit mass of the active material. It means "substance".

The specific negative electrode active material is a negative electrode active material in which lithium ions are inserted and desorbed at a potential of 0.8 V or higher with respect to the lithium potential in the charged state from the viewpoint of suppressing the precipitation of lithium at the negative electrode. It may be a negative electrode active material in which lithium ions are inserted and removed at a potential of 1.0 V or higher, or a negative electrode active material in which lithium ions are inserted and removed at a potential of 1.2 V or higher. You may.

Examples of the specific negative electrode active material include _{lithium titanium composite oxide such as Li 4} Ti ₅ O ₁₂ , molybdenum oxide, niobium pentoxide, iron sulfide, titanium sulfide, titanium dioxide, titanium niobium oxide (TiNb ₂ O ₇ ), and oxidation. Examples include iron (Fe ₂ O ₃ ), lithium vanadium (Li ₃ VO ₄ ), tungsten oxide (WO ₃ ), manganese oxide (Mn ₂ O ₃ ) and Y ₂ Ti ₂ O ₅ S ₂ . Among these, lithium titanium composite oxide (LTO) is preferable. Examples of the lithium-titanium composite oxide include lithium titanate.

Since the lithium ion insertion reaction and desorption reaction of the specific negative electrode active material almost occur at a potential of 0.4 V or more with respect to the lithium potential, the operating potential is higher than that of the carbon-based negative electrode active material, and lithium at the negative electrode is used. Precipitation is suppressed. Furthermore, unlike when a carbon-based negative electrode active material is used, the SEI (solid electrolyte) film that suppresses the subsequent decomposition of the non-aqueous solvent is not formed on the surface of the negative electrode during the initial charging, and the non-aqueous solvent is decomposed. Is also different. Therefore, the specific negative electrode active material has a significantly different action from the carbon negative electrode active material such as graphite, and the lithium ion secondary battery using the specific negative electrode active material and the lithium ion secondary battery using the carbon negative electrode active material are different. , The type of battery is also very different.

The lithium titanium composite oxide that can be used as the negative electrode active material of the lithium ion secondary battery of the present disclosure is preferably a spinel-type lithium titanium composite oxide. The basic formula of the spinel-type lithium-titanium composite oxide _is represented by _{Li [Li 1/3 Ti 5/3] O} 4.
In order to further stabilize the crystal structure of the spinel-type lithium-titanium composite oxide, a part of Li, Ti or O-site of the spinel-type lithium-titanium composite oxide may be replaced with another element.
In addition, excess lithium may be present in the crystals of the spinel-type lithium-titanium composite oxide. Furthermore, a chemical substance having a defect in the O-site of the spinel-type lithium-titanium composite oxide can also be used.

Elements that can replace the Li or Ti sites of the spinel-type lithium-titanium composite oxide include, for example, Nb, V, Mn, Ni, Cu, Co, Zn, Sn, Pb, Al, Mo, Ba, Sr. , Ta, Mg and Ca. The Li or Ti sites of the spinel-type lithium-titanium composite oxide can be replaced with one or more of these elements. Among these substitutable elements, it is preferable to use Al from the viewpoint of further stabilizing the crystal structure of the spinel-type lithium titanium composite oxide.
Examples of the element capable of substituting the O-site of the spinel-type lithium-titanium composite oxide include F and B. The Osite of the spinel-type lithium-titanium composite oxide can be replaced with one or more of these elements. Of these substitutable elements, F is preferably used from the viewpoint of further stabilizing the crystal structure of the spinel-type lithium titanium composite oxide.

The BET specific surface area of the negative electrode active material is preferably less than ^{40 m 2 / g, more preferably less than 30 m 2} / g, and further preferably less than ^{20 m 2 / g from the viewpoint of improving the storage characteristics.} It is preferably ^{less than 15 m 2} / g, particularly preferably less than 15 m 2 / g. From the viewpoint of improving the input / output characteristics, the BET specific surface area is ^{preferably 0.1 m 2} / g or more, more preferably 0.5 m ² / g or more, and 1.0 m ² / g or more. It is more preferable to have it, and it is particularly preferable that it is ^{2.0 m 2 / g or more.} Further, the BET specific surface area of the negative electrode active material may be ^{less than 2.9 m 2} / g, less than 2.8 m ² / g, or less than 1.5 m ² / g. It may be less than 0.3 m ^{2 / g.} On the other hand, BET specific surface area of the negative electrode active material may also be 0.05 m ² / g or more, may also be 0.08 m ² / g or more, it may be 0.1 m ² / g or more.
BET specific surface area of the negative electrode active material is preferably less than 0.1 m ² / g or more ^{40 m} 2 / g, more preferably less than 0.5 m ² / g or more ^{30m 2} / g, 1.0m 2 It is more preferably more than / g and less than 20 m ^{2 / g, and particularly preferably 2.0 m 2} / g or more and ^{less than 15 m 2} / g. Further, BET specific surface area of the negative electrode active material may be less than 0.05 m ² / g or more 2.9 m ² / g may be less than ² / g 0.05m ² / g or more 2.8m may be less than 0.08 m ² / g or more 1.5 m ² / g, may be less than 0.1 m ² / g or more 0.3 m ² / g.
The BET specific surface area of the negative electrode active material can be measured by the same method as the spinel-type lithium-nickel-manganese composite oxide.

Further, the median diameter D50 of the particles of the negative electrode active material (the median diameter D50 of the secondary particles when the primary particles are aggregated to form the secondary particles) is 0.5 μm from the viewpoint of particle dispersibility. It is preferably ~ 100 μm, more preferably 1 μm to 50 μm.
The median diameter D50 of the negative electrode active material can be measured by the same method as the spinel-type lithium-nickel-manganese composite oxide.

(Positive electrode)
The lithium ion secondary battery of the present disclosure includes a positive electrode containing a positive electrode active material. The positive electrode (positive electrode plate) of the present disclosure has a current collector and a positive electrode mixture formed on both sides or one side thereof. The positive electrode mixture contains the above-mentioned positive electrode active material.

For the positive electrode of a lithium ion secondary battery, a positive electrode active material and a conductive agent are mixed, and an appropriate binder and solvent are added as necessary to prepare a paste-like positive electrode mixture, such as aluminum foil. It can be formed by applying and drying the metal foil on the surface of the current collector, and then increasing the density of the positive electrode mixture by pressing or the like, if necessary.
Although the positive electrode mixture can be formed by using the above components, the positive electrode mixture contains a known olivine-type lithium salt, a chalcogen compound, manganese dioxide, etc. for the purpose of improving the characteristics of the lithium ion secondary battery. You may let me.

Single-side coating of the current collector of the positive electrode mixture, from the viewpoint of energy density and output characteristics, it is preferable that the solid content of the positive electrode ^mixture, a ^{100g / m 2 ~250g / m 2} , 110g / m more preferably ^{2 ~200g} / ^{m 2,} further preferably ^{130g / m 2 ~170g / m 2} .
Density of the positive electrode mixture, from the viewpoint of energy density and output characteristics, it is preferable that the solid content of the positive electrode mixture ^{is 1.8g / cm 3 ~3.3g / cm 3} , 2.0g / cm 3 more preferably ~3.2g / cm ^3, further preferably ^{2.2g / cm 3 ~3.1g / cm 3} .

(Negative electrode)
The lithium ion secondary battery of the present disclosure includes a negative electrode containing a negative electrode active material. The negative electrode (negative electrode plate) of the present disclosure preferably has a current collector and a negative electrode mixture formed on both sides or one side thereof. The negative electrode mixture contains the above-mentioned negative electrode active material.

For the negative electrode, a negative electrode active material and a conductive agent are mixed, and an appropriate binder and solvent are added as necessary to prepare a paste-like negative electrode mixture, which is the surface of a current collector of a metal foil such as copper. After that, it can be formed by increasing the density of the negative electrode mixture by pressing or the like, if necessary.
Although the negative electrode mixture can be formed by using the above components, the negative electrode mixture may contain a known carbon material or the like for the purpose of improving the characteristics of the lithium ion secondary battery.

Single-side coating of the current collector of the negative electrode mixture, from the viewpoint of energy density and output characteristic, as a solid of the negative electrode mixture component ^is preferably ^{10g / m 2 ~225g / m 2} , 50g / m more preferably ^{2 ~200g} / ^{m 2,} further preferably ^{80g / m 2 ~160g / m 2} .
Density of the negative electrode mixture, from the viewpoint of energy density and output characteristics, it is preferable that a solid of the negative electrode mixture component ^{is 1.0g / cm 3 ~3.3g / cm 3} , 1.2g / cm 3 more preferably ~3.2g / cm ^3, further preferably ^{1.4g / cm 3 ~2.8g / cm 3} .

(Conducting agent)
The conductive agent used for the positive electrode (hereinafter referred to as the positive electrode conductive agent) is preferably acetylene black from the viewpoint of further improving the input / output characteristics. From the viewpoint of input / output characteristics, the content of the positive electrode conductive agent is preferably 4% by mass or more, more preferably 5% by mass or more, based on the total solid content of the positive electrode mixture, 5.5. It is more preferably mass% or more. From the viewpoint of battery capacity, the upper limit is preferably 10% by mass or less, more preferably 9% by mass or less, and further preferably 8.5% by mass or less.
The content of the positive electrode conductive agent is preferably 4% by mass to 10% by mass, more preferably 5% by mass to 9% by mass, based on the total solid content of the positive electrode mixture, and is 5.5% by mass. It is more preferably% to 8.5% by mass.

From the viewpoint of further suppressing the generation of gas, the positive electrode conductive agent may contain graphite. Examples of graphite include artificial graphite, thermally decomposed graphite, natural graphite, spheroidal graphite, flaky graphite, scaly graphite, scaly graphite, massive graphite, vapor phase carbon fiber, carbon nanotube, graphene, reduced graphene oxide and the like.

The conductive agent used for the negative electrode (hereinafter referred to as the negative electrode conductive agent) is preferably acetylene black from the viewpoint of further improving the input / output characteristics. From the viewpoint of input / output characteristics, the content of the negative electrode conductive agent is preferably 1% by mass or more, more preferably 4% by mass or more, and 6% by mass, based on the total solid content of the negative electrode mixture. The above is more preferable. From the viewpoint of battery capacity, the upper limit is preferably 15% by mass or less, more preferably 12% by mass or less, and further preferably 10% by mass or less.
The content of the negative electrode conductive agent is preferably 1% by mass to 15% by mass, more preferably 4% by mass to 12% by mass, and 6% by mass to 6% by mass, based on the total solid content of the negative electrode mixture. It is more preferably 10% by mass.

(Binder)
The binder is not particularly limited, and a material having good solubility or dispersibility in the solvent used for preparing the paste-like positive electrode mixture or negative electrode mixture is selected. Specific examples include resin polymers such as polyethylene, polypropylene, polyethylene terephthalate, polymethylmethacrylate, polyimide, aromatic polyamide, cellulose, and nitrocellulose; SBR (styrene-butadiene rubber), NBR (acrylonitrile-butadiene rubber), and fluorine. Rubber-like polymers such as rubber, isoprene rubber, butadiene rubber, ethylene-propylene rubber; styrene-butadiene-styrene block copolymer or its hydrogen additive, EPDM (ethylene-propylene-diene ternary copolymer), styrene- Thermoplastic elastomeric polymers such as isoprene-styrene block copolymers or hydrogenated products thereof; syndiotactic-1,2-polybutadiene, polyvinylacetate, ethylene-vinyl acetate copolymer, propylene-α-olefin copolymer. Soft resinous polymers such as coalesced; polyfluorovinylidene (PVdF), polytetrafluoroethylene, fluorinated polyvinylidene fluoride, polytetrafluoroethylene-ethylene copolymer, polytetrafluoroethylene-vinylidene fluoride copolymer, etc. Examples thereof include a fluoropolymer, a copolymer in which an acrylic acid and a linear ether group are added to a polyacrylonitrile skeleton; and a polymer composition having ionic conductivity of alkali metal ions (particularly lithium ions). Of these, one type may be used alone, or two or more types may be used in combination. From the viewpoint of high adhesion, it is preferable to use polyvinylidene fluoride (PVdF) or a copolymer in which acrylic acid and a linear ether group are added to the polyacrylonitrile skeleton for both the positive and negative electrodes, further improving the charge / discharge cycle characteristics. From the viewpoint of the above, a copolymer in which acrylic acid and a linear ether group are added to a polyacrylonitrile skeleton is more preferable.

Regarding the content of the binder, the range of the content of the binder based on the total solid content of the positive electrode mixture is as follows. The lower limit of the range is 0.1% by mass or more from the viewpoint of sufficiently binding the positive electrode active material to obtain sufficient mechanical strength of the positive electrode and stabilizing battery performance such as charge / discharge cycle characteristics. It is preferably 1% by mass or more, more preferably 2% by mass or more. The upper limit is preferably 30% by mass or less, more preferably 20% by mass or less, and further preferably 10% by mass or less from the viewpoint of improving the battery capacity and conductivity.
The content of the binder based on the total solid content of the positive electrode mixture is preferably 0.1% by mass to 30% by mass, more preferably 1% by mass to 20% by mass, and 2% by mass. It is more preferably% to 10% by mass.
The content of the binder based on the total solid content of the negative electrode mixture is as follows. The lower limit of the range is 0.1% by mass or more from the viewpoint of sufficiently binding the negative electrode active material to obtain sufficient mechanical strength of the negative electrode and stabilizing battery performance such as charge / discharge cycle characteristics. It is more preferably 0.5% by mass or more, and even more preferably 1% by mass or more. The upper limit is preferably 40% by mass or less, more preferably 25% by mass or less, still more preferably 15% by mass or less, from the viewpoint of improving the battery capacity and conductivity.
The content of the binder based on the total solid content of the negative electrode mixture is preferably 0.1% by mass to 40% by mass, more preferably 0.5% by mass to 25% by mass. It is more preferably 1% by mass to 15% by mass.

As a solvent for dissolving or dispersing these active substances, conductive agents, binders and the like, an organic solvent such as N-methyl-2-pyrrolidone can be used.

(Current collector)
It is preferable that a current collector is used for the positive electrode and the negative electrode. As the material of the current collector, as the positive current collector, in addition to aluminum, titanium, tantalum, nickel, alloys thereof, stainless steel, conductive polymer, etc., for the purpose of improving adhesiveness, conductivity and oxidation resistance. , Aluminum, copper and other materials that have been treated to adhere carbon, nickel, titanium, silver, etc. to the surface can be used.
As the negative current collector, the material of the current collector is copper, stainless steel, nickel, aluminum, titanium, conductive polymer, aluminum-cadmium alloy, etc., as well as improving adhesiveness, conductivity, and reduction resistance. For the purpose, a material such as copper or aluminum that has been treated to adhere carbon, nickel, titanium, silver or the like to the surface can be used.

(Separator)
The lithium ion secondary battery of the present disclosure further includes a separator interposed between the positive electrode and the negative electrode, and the electrolyte may be an electrolytic solution containing a non-aqueous solvent described later. The separator is not particularly limited as long as it electronically insulates between the positive electrode and the negative electrode, has ion permeability, and has resistance to oxidizing property on the positive electrode side and reducing property on the negative electrode side. .. As the material (material) of the separator satisfying such characteristics, a resin, an inorganic substance, or the like is used.

As the resin, an olefin polymer, a fluoropolymer, a cellulosic polymer, a polyimide, nylon and the like are used. Specifically, it is preferable to select from materials that are stable to the electrolytic solution and have excellent liquid retention properties, and it is preferable to use a porous sheet or non-woven fabric made from a polyolefin such as polyethylene or polypropylene.

As the inorganic substance, oxides such as alumina and silicon dioxide, nitrides such as aluminum nitride and silicon nitride, sulfates such as barium sulfate and calcium sulfate, and glass are used. For example, a sheet obtained by adhering the above-mentioned inorganic substance in the form of fibers or particles to a thin film-shaped base material such as a non-woven fabric, a woven fabric, or a microporous film can be used as a separator.
As the thin film-shaped substrate, a substrate having a pore diameter of 0.01 μm to 1 μm and a thickness of 5 μm to 50 μm is preferably used. Further, for example, a sheet in which the above-mentioned inorganic substance having a fiber shape or a particle shape is made into a composite porous layer by using a binder such as a resin can be used as a separator. Further, this composite porous layer may be formed on the surface of the positive electrode or the negative electrode to serve as a separator. Alternatively, this composite porous layer may be formed on the surface of another separator to form a multilayer separator. For example, a composite porous layer obtained by binding alumina particles having a 90% particle size (D90) of less than 1 μm using a fluororesin as a binder may be formed on the surface of the positive electrode or the surface of the separator facing the positive electrode. ..

The porosity of the separator is preferably 20% or more, more preferably 20% to 80%, further preferably 25% to 70%, and particularly preferably 30% to 70%. preferable.
When the porosity of the separator is 20% or more, the permeability of the electrolytic solution is improved and a large amount of the electrolytic solution can be injected, so that the cycle characteristics tend to be improved. Furthermore, since an active material in which lithium ions are inserted and removed at a potential of 0.4 V or higher with respect to the lithium potential is used as the negative electrode active material, lithium in the negative electrode is used even when the porosity of the separator is high. Precipitation tends to be suppressed. Further, even when a phosphoric acid ester containing a fluorine atom having a relatively high viscosity is used, it is considered that the deterioration of the input / output characteristics can be suppressed by increasing the porosity of the separator.
When the porosity of the separator is 80% or less, the occurrence of a short circuit tends to be suppressed.
The porosity of the separator is a value obtained from the mercury porosity measurement. The conditions for measuring the mercury porosimeter are as follows.
・ Equipment: Shimadzu Corporation Autopore IV 9500
・ Mercury press pressure: 0.51 psia
・ Pressure holding time at each measured pressure: 10s
・ Contact angle between sample and mercury: 140 °
・ Surface tension of mercury: 485 days / cm
-Mercury density: 13.535g / mL

(Electrolytes)
The electrolytes of the present disclosure include lithium salts. Further, the electrolyte of the present disclosure may further contain a non-aqueous solvent, a polymer electrolyte impregnated with a non-aqueous solvent and a non-aqueous solvent, or a sulfide-based inorganic solid electrolyte and oxidation. It may further contain at least one of the physical inorganic solid electrolytes.
In particular, when the positive electrode contains a specific positive electrode active material and the negative electrode contains a specific negative electrode active material, carbon dioxide and sulfur oxidation due to decomposition of solid electrolytes such as polymer electrolytes, sulfide-based inorganic solid electrolytes, and oxide-based inorganic solid electrolytes. The generation of substances, hydrogen sulfide, etc. makes it easier for the battery to expand. On the other hand, in the lithium ion secondary battery of the present disclosure, the gas storage member stores gas such as carbon dioxide, sulfur oxide, and hydrogen sulfide generated by decomposition of the solid electrolyte, so that the expansion of the battery is suitably suppressed. ..

Examples of the polymer electrolyte include polyethylene oxide, polyvinylidene fluoride, polyvinylidene fluoride-polyhexafluoropropylene copolymer, polyester, polyethylene carbonate and the like.

The sulfide-based inorganic solid electrolyte is not particularly limited as long as it contains a sulfur atom (S), has lithium ion conductivity, and has electron insulation. For example, a lithium ion conductive inorganic solid electrolyte satisfying the composition represented by the following formula (A) can be mentioned.
Li _a M _b P _c S _d A _e ... (A)
In the formula (A), M is one or more elements selected from the group consisting of B, Zn, Sn, Si, Cu, Ga, Sb, Al and Ge, and among them, B, Sn, Si, Al or Ge is preferable, Sn, Al or Ge is more preferable. A is one or more elements selected from the group consisting of I, Br, Cl and F, and among them, I or Br is preferable, and I is more preferable. a to e indicate the composition ratio of each element, and a: b: c: d: e satisfies 1 to 12:00 to 1: 1: 2 to 12:00 to 5. a is preferably 1 to 9, more preferably 1.5 to 4. b is preferably 0 to 0.5. d is preferably 3 to 7, more preferably 3.25 to 4.5. e is preferably 0 to 3, more preferably 0 to 2.

The oxide-based inorganic solid electrolyte is not particularly limited as long as it contains an oxygen atom (O), has lithium ion conductivity, and has electron insulation.
For example, Li _xa La _ya TiO ₃ [xa satisfies 0.3 ≦ xa ≦ 0.7, and ya satisfies 0.3 ≦ ya ≦ 0.7. ] (LLT);
Li _xb La _yb Zr _zb M ^bb _{mb Onb} (M ^bb is one or more elements selected from the group consisting of Al, Mg, Ca, Sr, V, Nb, Ta, Ti, Ge, In and Sn. xb satisfies 5 ≦ xb ≦ 10, yb satisfies 1 ≦ yb ≦ 4, zb satisfies 1 ≦ zb ≦ 4, mb satisfies 0 ≦ mb ≦ 2, and nb satisfies 5 ≦ nb ≦ 20. );
Li _{xc Byc} M ^cc _{zc Onc} (M ^cc is one or more elements selected from the group consisting of C, S, Al, Si, Ga, Ge, In and Sn, and xc is 0 ≦ xc ≦ 5. Satisfaction, yc satisfies 0 ≦ yc ≦ 1, zc satisfies 0 ≦ zc ≦ 1, nc satisfies 0 ≦ nc ≦ 6);
_{Li xd (Al, Ga) yd} (Ti, Ge) zd Si ad P md O nd (xd satisfies 1 ≦ xd ≦ 3, yd satisfies 0 ≦ yd ≦ 1, zd satisfies 0 ≦ zd ≦ 2 , Ad satisfies 0 ≦ ad ≦ 1, md satisfies 1 ≦ md ≦ 7, and nd satisfies 3 ≦ nd ≦ 13.);
^{_{Li (3-2xe) M ee xe D}} ee O (xe represents a number of 0 to ^{0.1, M ee} is ^{.D ee} representing the divalent metal atom one halogen atom or two or more of Represents a combination of halogen atoms.);
Li _xf Si _{yf Ozf} (xf satisfies 1≤xf≤5, yf satisfies 0 <yf≤3, zf satisfies 1≤zf≤10);
Li _xg S _yg O _{zg (xg} satisfies 1 ≦ xg ≦ 3, yg satisfies 0 <yg ≦ 2, zg satisfies 1 ≦ zg ≦ 10.);
Li ₃ BO ₃ ;
Li ₃ BO _{3- Li 2} SO ₄ ;
Li ₂ O-B ₂ O _3- P ₂ O ₅ ;
Li ₂ O-SiO ₂ ;
Li ₆ BaLa ₂ Ta ₂ O ₁₂ ;
Li ₃ PO _{(4-3 / 2w)} N _w (w is w <1);
_{Li 3.5} Zn _0.25 GeO ₄ with a Lithium (Lithium super ionic controller) type crystal structure;
_{La 0.55} Li _0.35 TiO ₃ with a perovskite-type crystal structure;
_{LiTi 2} P ₃ O ₁₂ , Li _{1 + xh + yh} (Al, Ga) _xh (Ti, Ge) _2-xh Si _yh P _3-yh O ₁₂ (xh is 0 ≦ xh ≦) having a NASION (Naturium super ionic controller) type crystal structure. 1 is satisfied, and yh satisfies 0 ≦ yh ≦ 1);
_{Examples thereof include Li 7} La ₃ Zr ₂ O ₁₂ having a garnet-type crystal structure.

From the viewpoint of suppressing the generation of gas due to the decomposition of the non-aqueous solvent, the non-aqueous solvent preferably contains a phosphoric acid ester containing a fluorine atom. Since the phosphoric acid ester containing a fluorine atom has a relatively low melting point, it is considered that it is easy to secure the battery characteristics in a wide temperature range.

When the non-aqueous solvent contains a phosphoric acid ester containing a fluorine atom, the content of the phosphoric acid ester containing a fluorine atom preferably exceeds 5% by volume, preferably 7% by volume or more, based on the total amount of the non-aqueous solvent. It is more preferably 10% by volume or more, particularly preferably 15% by volume or more, and even more preferably 20% by volume or more. When the content of the phosphoric acid ester containing a fluorine atom is 10% by volume or more, the melting point of the non-aqueous solvent is lowered, and the effect of excellent low temperature characteristics can be obtained.
From the viewpoint of input / output characteristics, the content of the phosphoric acid ester containing a fluorine atom is preferably 90% by volume or less, more preferably 80% by volume or less, and more preferably 60% by volume with respect to the total amount of the non-aqueous solvent. It is more preferably% or less, and particularly preferably 50% by volume or less.

The phosphoric acid ester containing a fluorine atom has a structure in which all three hydrogen atoms of phosphoric acid are substituted with organic groups, and is not particularly limited as long as at least one of the three organic groups contains a fluorine atom. ..
Examples of the organic group containing a fluorine atom include a group in which at least one hydrogen atom such as an alkyl group, an alkenyl group, an aralkyl group, an aryl group, a heteroaryl group, an aralkyl group and a heteroaralkyl group is substituted with a fluorine atom. ..
Examples of the organic group containing no fluorine atom include an alkyl group, an alkenyl group, an aralkyl group, an aryl group, a heteroaryl group, an aralkyl group, and a heteroaralkyl group.

Specific examples of the phosphate ester containing a fluorine atom include tris phosphate (trifluoromethyl), tris phosphate (2,2-difluoroethyl), and tris phosphate (2,2,2-trifluoroethyl). , Tris phosphate (2,2,3,3-tetrafluoropropyl), Tris phosphate (2,2,3,3,3-pentafluoropropyl), Tris phosphate (hexafluoroisopropyl), Tris phosphate (2,2,3,3-pentafluoropropyl) 2,2,3,3,4,5,5-octafluoropentyl), Tris phosphate (2,2,3,3,4,5,5,5-nonafluoropentyl), phosphoric acid Tris (3,3,4,4,5,5,6,6,6-nonafluorohexyl), bis phosphate (2,2,2-trifluoroethyl) methyl, bis phosphate (2,2,2) -Trifluoroethyl) ethyl, bis phosphate (2,2,2-trifluoroethyl) 2,2-difluoroethyl, bis phosphate (2,2,2-trifluoroethyl) 2,2,3,3- Tetrafluoropropyl, bis phosphate (2,2,3,3-tetrafluoropropyl) 2,2,2-trifluoroethyl and bis phosphate (2,2,2-trifluoroethyl) (2,2,3) , 3-Tetrafluoropropyl) and the like. Of these, tris phosphate (2,2,2-trifluoroethyl) is preferable because it is not particularly affected by the catalytic action of lithium-titanium composite oxide (LTO) or the like. As the phosphoric acid ester containing these fluorine atoms, one type may be used alone or two or more types may be used in combination.

The non-aqueous solvent preferably contains dimethyl carbonate. Dimethyl carbonate is excellent in oxidation resistance and reduction resistance, and it is presumed that the charge / discharge cycle characteristics of the lithium ion secondary battery are improved by adding it to the electrolyte.

When the non-aqueous solvent contains dimethyl carbonate, the content of dimethyl carbonate is preferably 5% by volume or more, preferably 15% by volume or more, based on the total amount of the non-aqueous solvent from the viewpoint of charge / discharge cycle characteristics. More preferably, it is more preferably 30% by volume or more, and particularly preferably 50% by volume or more. Further, from the viewpoint of low temperature characteristics, it is preferably 80% by volume or less, more preferably 70% by volume or less, still more preferably 65% by volume or less, and 55 by volume, based on the total amount of the non-aqueous solvent. It is particularly preferable that the volume is 0% or less.

The content volume ratio of the phosphoric acid ester containing a fluorine atom to the dimethyl carbonate (phosphate containing a fluorine atom / dimethyl carbonate) is 0.05 to 2.5 from the viewpoint of charge / discharge cycle characteristics and suppression of gas generation. It is preferably 0.05 to 1.5, more preferably 0.1 to 1.4, and particularly preferably 0.15 to 1.2.

The electrolyte of the present disclosure may or may not contain a phosphoric acid ester containing a fluorine atom and other non-aqueous solvents other than dimethyl carbonate.
Other non-aqueous solvents include ethylene carbonate (EC), diethyl carbonate (DEC), propylene carbonate (PC), ethylmethylsulfone (EMS), vinylene carbonate (VC), methylethyl carbonate, γ-butyrolactone, acetonitrile, 1, Fluorinated ethers such as 2-dimethoxyethane, dimethoxymethane, tetrahydrofuran, dioxolane, methylene chloride, 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether, and methyl acetate, ethyl acetate. , Even a non-aqueous solvent selected from the group consisting of carboxylic acid esters (excluding carboxylic acid esters containing a fluorine atom) such as methyl difluoroacetate, ethyl trifluoroacetate, methyl propionate, ethyl propionate, and methyl butyrate. good.

When the electrolyte contains other non-aqueous solvents, the total content of the other non-aqueous solvents is preferably less than 30% by volume and more preferably 25% by volume or less with respect to the total amount of the non-aqueous solvents. It is more preferably 15% by volume or less, and particularly preferably 10% by volume or less. The total content of the other non-aqueous solvents may be 0% by volume with respect to the total amount of the non-aqueous solvent, but it should be 5% by volume or more from the viewpoint of improving safety, input / output characteristics, low temperature characteristics and the like. It would be nice to have it.
When the electrolyte contains other non-aqueous solvents, the other non-aqueous solvents may be used alone or in combination of two or more. In the case of one type alone, the total content of the above-mentioned other non-aqueous solvents shall be read as the content of other non-aqueous solvents.
The electrolyte can be made safe by using a solvent having a high flash point such as EC and EMS, but these compounds may be inferior in reduction resistance. Therefore, when another non-aqueous solvent is used, if the content of the other non-aqueous solvent with respect to the total amount of the non-aqueous solvent is less than 30% by volume, the deterioration of the charge / discharge cycle characteristics tends to be suppressed.
By using a carboxylic acid ester having a low melting point such as methyl acetate as a solvent, the low temperature characteristics can be improved.
Input / output characteristics can be improved by using a solvent having a low viscosity such as 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether.

Examples of the lithium salt include LiPF ₆ (lithium hexafluorophosphate), LiBF ₄ (lithium tetrafluoroborate), LiFSI (lithium bis (fluorosulfonyl) imide), LiTFSI (lithium bis (trifluoromethanesulfonyl) imide), LiClO _4. , LiB (C ₆ H ₅ ) ₄ , LiCH ₃ SO ₃ , LiCF ₃ SO ₃ , LiN (SO ₂ CF ₂ CF ₃ ) _{2, and the} like. These lithium salts may be used alone or in combination of two or more.
Among these, when comprehensively judging the solubility in a solvent, charge / discharge characteristics, input / output characteristics, charge / discharge cycle characteristics, etc. in the case of a lithium ion secondary battery, the lithium salts are lithium hexafluorophosphate and tetrafluoro. It preferably contains at least one of lithium borate and lithium bis (trifluoromethanesulfonyl) imide, and more preferably contains at least one of lithium hexafluorophosphate and lithium tetrafluoroborate.

From the viewpoint of safety, the concentration of the lithium salt in the electrolyte is preferably 0.8 mol / L to 4.0 mol / L, more preferably 1.0 mol / L to 3.0 mol / L, and 1 It is more preferably .2 mol / L to 2.5 mol / L. By increasing the concentration of the lithium salt to 1.2 mol / L to 2.0 mol / L, the flash point can be raised and the electrolyte can be made safer.

The electrolyte may contain additives as needed.
The additive is not particularly limited as long as it is an additive for an electrolyte of a lithium ion secondary battery, and is, for example, a heterocyclic compound containing nitrogen, a heterocyclic compound containing sulfur, or a heterocycle containing nitrogen and sulfur. Examples thereof include compounds, cyclic carboxylic acid esters, fluorine-containing cyclic carbonates, fluorine-containing borate esters, and other compounds having unsaturated bonds in the molecule. In addition to the above additives, other additives such as an overcharge inhibitor, a negative electrode film forming agent, a positive electrode protective agent, and a high input / output agent may be used depending on the required function.

When the electrolyte contains an additive, it is possible to improve the storage characteristics at high temperatures, the charge / discharge cycle characteristics, and the input / output characteristics.

(Capacity ratio between the negative electrode capacity of the negative electrode and the positive electrode capacity of the positive electrode)
In the present disclosure, the capacity ratio (negative electrode capacity / positive electrode capacity) is preferably 1 or less from the viewpoint of charge / discharge cycle characteristics and energy density. For example, when the capacity ratio (negative electrode capacity / positive electrode capacity) is 1 or less, an increase in the positive electrode potential can be suppressed, so that the decomposition reaction of a non-aqueous solvent such as dimethyl carbonate can be suppressed, and the charge / discharge cycle characteristics are improved. There is a tendency. Further, by using a phosphoric acid ester containing a fluorine atom as a non-aqueous solvent as described above, gas generation on the negative electrode side can be suppressed.

The capacity ratio (negative electrode capacity / positive electrode capacity) is preferably 0.6 or more and less than 1. When the capacity ratio is 0.6 or more, the battery capacity tends to be improved and the volume energy density tends to be improved. The capacity ratio (negative electrode capacity / positive electrode capacity) is more preferably 0.7 to 0.98, and further preferably 0.75 to 0.95 from the viewpoint of volume energy density and input characteristics.

The "positive electrode capacity" and "negative electrode capacity" are the maximum capacities that can be reversibly obtained when a constant current charge-constant current discharge is performed by forming an electrochemical cell whose counter electrode is metallic lithium, respectively. Means.
Further, the negative electrode capacity indicates [discharge capacity of the negative electrode], and the positive electrode capacity indicates [discharge capacity of the positive electrode].
Here, the [discharge capacity of the negative electrode] is defined as being calculated by the charging / discharging device when the lithium ions inserted in the negative electrode active material are desorbed. Further, [discharge capacity of the positive electrode] is defined as being calculated by the charging / discharging device when lithium ions are inserted into the positive electrode active material.
For example, when a spinel-type lithium-nickel-manganese composite oxide is used as the positive electrode active material and LTO is used as the negative electrode active material, the “positive electrode capacity” and the “negative electrode capacity” are in the voltage range in the above-mentioned electrochemical cell. 4.95V to 3.5V and 1.0V to 2.0V, respectively, and the current density during constant current charging and constant current discharging is 0.37mA / cm ^{2 for} the positive electrode capacity and 0.30mA for the negative electrode capacity. The capacity is defined as / cm ² and is the capacity obtained when evaluated by performing the above charging and discharging.
In the electrochemical cell, the direction in which lithium ions are inserted from the negative electrode active material such as lithium titanium composite oxide is defined as charging, and the direction in which lithium ions are desorbed is defined as discharging. Further, in the electrochemical cell, the direction in which lithium ions are desorbed from the lithium-nickel-manganese composite oxide which is the positive electrode active material is defined as charging, and the direction in which lithium ions are inserted is defined as discharging.

In the present disclosure, the positive electrode capacity tends to increase by increasing the amount of the positive electrode active material contained in the positive electrode, and tends to decrease by decreasing the amount. The negative electrode capacity, like the positive electrode capacity, increases or decreases depending on the amount of the negative electrode active material. By adjusting the positive electrode capacity and the negative electrode capacity, the capacity ratio (negative electrode capacity / positive electrode capacity) of the lithium ion secondary battery of the present disclosure can be adjusted to 1 or less.

The shape of the lithium ion secondary battery of the present disclosure can be various shapes such as a cylindrical type, a laminated type, a coin type, and a laminated type. When the electrolyte is an electrolytic solution containing a non-aqueous solvent, a separator is interposed between the positive electrode and the negative electrode to form an electrode body, and the space between the positive electrode current collector and the negative electrode current collector and the positive electrode terminal and the negative electrode terminal leading to the outside is , Connect using a lead for collecting electricity, etc., and seal this electrode body together with the electrolytic solution in the battery exterior to complete the lithium ion secondary battery.
Hereinafter, a laminated lithium ion secondary battery in which a positive electrode plate and a negative electrode plate are laminated via a separator will be described, but the present disclosure is not limited thereto.

FIG. 1 is a perspective view showing an example of the lithium ion secondary battery of the present disclosure. Further, FIG. 2 is a perspective view showing a positive electrode plate, a negative electrode plate, a separator, and a gas storage member constituting the electrode group.
It should be noted that the size of the members in each figure is conceptual, and the relative relationship between the sizes of the members is not limited to this. In addition, members having substantially the same function may be given the same reference numerals throughout the drawings, and overlapping description may be omitted.
The lithium ion secondary battery 10 of FIG. 1 contains an electrode group 20 and an electrolytic solution in a battery exterior body 6 of a laminated film, and a positive electrode current collecting tab 2 and a negative electrode current collecting tab 4 are housed in the battery exterior body 6. I try to take it out. Further, the gas storage member 7 is arranged in the battery exterior body 6 of the laminated film.

Then, as shown in FIG. 2, the electrode group 20 is formed by laminating a positive electrode plate 1 to which a positive electrode current collecting tab 2 is attached, a gas storage member 7, a separator 5, and a negative electrode plate 3 to which a negative electrode current collecting tab 4 is attached. be.
The size, shape, etc. of the positive electrode plate, negative electrode plate, separator, electrode group, gas occlusion member, and battery can be arbitrary, and are not limited to those shown in FIGS. 1 and 2. ..
Examples of the material of the battery exterior 6 include a laminated film made of aluminum, SUS, aluminum, copper, stainless steel and the like.

As another embodiment of the lithium ion secondary battery, for example, an electrode group obtained by winding a laminate formed by laminating a positive electrode plate and a negative electrode plate via a separator is enclosed in a cylindrical battery exterior. , Cylindrical battery A cylindrical lithium ion secondary battery in which a gas storage member is arranged inside the exterior can be mentioned.
FIG. 3 is a cross-sectional view showing another embodiment of the lithium ion secondary battery of the present disclosure.
As shown in FIG. 3, the lithium ion secondary battery 11 has a battery exterior body 16 made of nickel-plated steel and having a bottomed cylindrical shape. The electrode group 15 is housed in the battery exterior body 16. In the electrode group 15, the strip-shaped positive electrode plate 12 and the negative electrode plate 13 are wound in a spiral cross section via a separator 14 of a porous sheet made of polyolefin such as polyethylene or polypropylene. The separator 14 is set to, for example, a width of 58 mm and a thickness of 20 μm. On the upper end surface of the electrode group 15, a ribbon-shaped positive electrode tab terminal made of aluminum whose one end is fixed to the positive electrode plate 12 is led out. The other end of the positive electrode tab terminal is arranged on the upper side of the electrode group 15 and is joined to the lower surface of the disk-shaped battery lid serving as the positive electrode external terminal by ultrasonic welding. On the other hand, on the lower end surface of the electrode group 15, a ribbon-shaped negative electrode tab terminal made of nickel having one end fixed to the negative electrode plate 13 is led out. The other end of the negative electrode tab terminal is joined to the inner bottom of the battery exterior 16 by resistance welding. Therefore, the positive electrode tab terminal and the negative electrode tab terminal are led out to the opposite sides of both end faces of the electrode group 15, respectively. The entire circumference of the outer peripheral surface of the electrode group 15 is covered with an insulating coating (not shown). The battery lid is caulked and fixed to the upper part of the battery exterior 16 via an insulating resin gasket. Therefore, the inside of the lithium ion secondary battery 11 is sealed. Further, a gas storage member (not shown) is arranged in the battery exterior body 16, and an electrolytic solution (not shown) is injected. In the lithium ion secondary battery 11, the arrangement of the gas storage member is not particularly limited.
The size, shape, and the like of the positive electrode plate, the negative electrode plate, the separator, the electrode group, and the battery can be arbitrary, and are not limited to those shown in FIG.

Hereinafter, the present disclosure will be described in more detail based on examples. The present invention is not limited to the following examples.

[Comparative Example 1]
The positive electrode is a spinel-type lithium-nickel-manganese composite oxide (LiNi _0.5 Mn _1.5 O ₄ , BET specific surface area: 0.31 m ² / g, median diameter D50: 16.9 μm), which is a positive electrode active material. 93 parts by mass, 5 parts by mass of acetylene black (Denka Co., Ltd.) as a conductive agent, and a copolymer in which acrylic acid and a linear ether group are added to a polyacrylonitrile skeleton as a binder (binder resin composition of Synthesis Example 1 described later). 2 parts by mass of the product) was mixed, an appropriate amount of N-methyl-2-pyrrolidone was added, and the mixture was kneaded to obtain a paste-like positive electrode mixture slurry. This slurry was applied to one side of an aluminum foil having a thickness of 15 μm, which is a current collector for the positive electrode, substantially evenly and uniformly so as to have a solid content of 145 g / m ² of the positive electrode mixture. Then, it was subjected to a drying treatment, and a dry coating film was obtained. ^{This dry coating film was consolidated by pressing until the density became 2.3 g / cm 3} as the solid content of the positive electrode mixture to prepare a sheet-shaped positive electrode. The thickness of the layer containing the positive electrode mixture was 63 μm. This was cut into a width of 30 mm and a length of 45 mm to obtain a positive electrode plate, and as shown in FIG. 2, a positive electrode current collecting tab was attached to this positive electrode plate.

^{For the negative electrode, 91 parts by mass of lithium titanate (BET specific surface area: 6.5 m 2} / g, median diameter D50: 7.3 μm), which is a kind of lithium titanium composite oxide, as the negative electrode active material, and acetylene black (acetylene black) as the conductive agent. Mix 4 parts by mass of Li400 (Denka Co., Ltd.) and 5 parts by mass of polyvinylidene fluoride (KF polymer # 9130, Kureha Co., Ltd.) as a binder, add an appropriate amount of N-methyl-2-pyrrolidone, and knead. As a result, a paste-like negative electrode mixture slurry was obtained. This slurry was applied to one side of an aluminum foil having a thickness of 15 μm, which is a current collector for the negative electrode, so as to have a solid content of 100 g / m ^{2 of the negative electrode mixture.} Then, it was subjected to a drying treatment, and a dry coating film was obtained. This dry coating film was consolidated by pressing until the density became 2.0 g / cm ³ as the solid content of the negative electrode mixture to prepare a sheet-shaped negative electrode. The thickness of the layer containing the negative electrode mixture was 50 μm. This was cut into a width of 30 mm and a length of 45 mm to obtain a negative electrode plate, and as shown in FIG. 2, a negative electrode current collecting tab was attached to this negative electrode plate.

An example of synthesizing the binder used for the positive electrode is shown below.

<Synthesis example 1>
1804 g of purified water was placed in a 3 liter separable flask equipped with a stirrer, a thermometer, a cooling tube and a nitrogen gas introduction tube, and the temperature was raised to 74 ° C. while stirring under the condition of a nitrogen gas aeration rate of 200 ml / min. After that, the ventilation of nitrogen gas was stopped. Next, an aqueous solution prepared by dissolving 0.968 g of ammonium persulfate as a polymerization initiator in 76 g of purified water was added, and immediately, 183.8 g of acrylonitrile as a nitrile group-containing monomer and 9.7 g of acrylic acid as a carboxyl group-containing monomer were added. (Ratio of 0.039 mol to 1 mol of acrylonitrile) and 6.5 g of monomeric methoxytriethylene glycol acrylate (Shin-Nakamura Chemical Industry Co., Ltd., trade name: NK ester AM-30G) (to 1 mol of acrylonitrile) The mixed solution (at a ratio of 0.0085 mol) was added dropwise over 2 hours while maintaining the temperature of the reaction system at 74 ± 2 ° C. Subsequently, an aqueous solution prepared by dissolving 0.25 g of ammonium persulfate in 21.3 g of purified water was added to the suspended reaction system, the temperature was raised to 84 ° C., and then the temperature of the reaction system was maintained at 84 ± 2 ° C. The reaction proceeded for 2.5 hours. Then, after cooling to 40 ° C. over 1 hour, stirring was stopped and the mixture was allowed to cool overnight at room temperature to obtain a reaction solution in which the binder resin composition was precipitated. The reaction solution was suction-filtered, and the recovered wet precipitate was washed 3 times with 1800 g of purified water and then vacuum dried at 80 ° C. for 10 hours for isolation and purification to obtain a binder resin composition.

(Preparation of electrode group)
The prepared positive electrode plate and the negative electrode plate were opposed to each other via a separator made of a polypropylene single layer film (porosity 50%) having a thickness of 15 μm, a width of 35 mm, and a length of 50 mm to prepare a laminated electrode group.

(Preparation of electrolytic solution)
An electrolytic solution was prepared by dissolving _{LiPF 6} , which is an electrolyte, in a non-aqueous solvent shown in Table 1 below at a concentration of 1.0 mol / L.

(Manufacturing of lithium-ion secondary battery)
As shown in FIG. 1, the electrode group is housed in a battery exterior body made of an aluminum laminated film, and after injecting an electrolytic solution into the battery exterior body, the positive electrode current collecting tab and the negative electrode collection are described. The lithium ion secondary battery of Comparative Example 1 was produced by closing the opening of the battery container by taking out the electric tab to the outside. The aluminum laminated film is a laminated body of polyethylene terephthalate (PET) film / aluminum foil / sealant layer (polypropylene or the like).
The prepared lithium ion secondary battery was left at room temperature for half a day, and then subjected to constant current charging and constant current discharging in a voltage range of 2.0 V to 3.5 V at 40 ° C. and a current value of 0.2 C for 3 cycles.

(Measurement of positive electrode capacity and negative electrode capacity)
-Measurement of positive electrode capacity-
A lithium foil having a thickness of 0.5 mm cut into a width of 31 mm and a length of 46 mm was attached to a copper mesh cut into a width of 31 mm and a length of 46 mm, and used as a counter electrode. A current collector tab was attached to the opposite pole. The prepared positive electrode plate and the counter electrode were opposed to each other via a separator made of a polypropylene single-layer film (porosity 50%) having a thickness of 15 μm, a width of 35 mm, and a length of 50 mm to prepare a laminated electrode group. As shown in FIG. 1, this electrode group is housed in a battery exterior body made of an aluminum laminated film, and after injecting an electrolytic solution into the battery exterior body, a positive electrode current collecting tab and a counter electrode current collecting tab are used. A lithium ion secondary battery was manufactured by sealing the opening of the battery exterior body by taking out the battery to the outside. The aluminum laminated film is a laminated body of polyethylene terephthalate (PET) film / aluminum foil / sealant layer (polypropylene or the like). As the electrolytic solution, _{an EC / DMC mixed solvent having a LiPF 6} concentration of 1.2 mol / L (EC: DMC: 3: 7 by volume) was used. The positive electrode capacity is the discharge capacity obtained when evaluated by charging / discharging with a voltage range of 4.95 V to 3.5 V and a current density of 0.37 mA / cm ^{2 during constant current charging and constant current discharge.} bottom.
As a result of the measurement, the capacity of the positive electrode for Comparative Example 1 was 25 mAh.

-Measurement of negative electrode capacity-
In the measurement of the positive electrode capacity, a negative electrode plate is used instead of the prepared positive electrode plate, the voltage range is 1.0V to 2.0V, and the current density during constant current charging and constant current discharging is 0.30 mA / cm ^2. The negative electrode capacity was measured in the same manner as the positive electrode capacity measurement except that the evaluation was performed by discharging.
As a result of the measurement, the capacity of the negative electrode for Comparative Example 1 was 21 mAh.
The capacity ratio (negative electrode capacity / positive electrode capacity) was calculated to be 0.85 from the positive electrode capacity and the negative electrode capacity of Comparative Example 1.

(Measurement of gas generation amount)
The volume of the lithium ion secondary battery of Comparative Example 1 was measured with a hydrometer (MDS-300, Alpha Mirage Co., Ltd.) (initial volume).
Next, the above lithium ion secondary battery is charged with a constant current at 50 ° C. at a current value of 1C and a charge termination voltage of 3.5V using a charging / discharging device (BATTERY TEST UNIT, IEM Co., Ltd.), and is paused for 15 minutes. After that, constant current discharge was performed with a current value of 1C and a discharge termination voltage of 2.6V. In addition, C used as a unit of a current value means "current value (A) / battery capacity (Ah)". After repeating this operation 100 times, 300 times or 500 times, the volume of the lithium ion secondary battery was measured using the above-mentioned hydrometer (volume after 100 cycles, volume after 300 cycles or after 500 cycles). volume).
From the following formulas, the amount of gas generated after 100 cycles, the amount of gas generated after 300 cycles, and the amount of gas generated after 500 cycles were calculated. The obtained results are shown in Table 1 and FIG.
Amount of gas generated after each cycle (mL) = (volume after each cycle)-(initial volume)

(Evaluation of cycle characteristics)
Charging and discharging are repeated under the same conditions as described above (measurement of gas generation amount), and this charging and discharging is performed for 700 cycles, and the discharge capacity is determined after 100 cycles, 300 cycles, 500 cycles, and 700 cycles, respectively. It was measured. Then, the discharge capacity retention rate (%) was calculated from the following formula. The obtained results are shown in FIG.
Discharge capacity retention rate (%) = (Discharge capacity after each cycle / Discharge capacity in the first cycle) x 100

[Comparative Example 2]
A lithium ion secondary battery was produced in the same manner as in Comparative Example 1 except that the composition of the non-aqueous solvent was changed as shown in Table 1, and the evaluation was carried out in the same manner as in Comparative Example 1. The obtained evaluation results are shown in Table 1, FIG. 6 and FIG.

[Comparative Example 3]
In the production of the lithium ion secondary battery of Comparative Example 1, a 125 μm-thick hydrogen storage metal material (material: titanium-based metal compound, 1 cm square) was installed at the position shown in FIG. 4 inside the battery exterior, and the hydrogen storage metal material was placed. A lithium ion secondary battery was produced in the same manner as in Comparative Example 1 except that one side was fixed to the battery exterior with a resin, and evaluated in the same manner as in Comparative Example 1. The obtained evaluation results are shown in Table 1, FIG. 5 and FIG. 7.

[Comparative Example 4]
A lithium ion secondary battery was produced in the same manner as in Comparative Example 3 except that the composition of the non-aqueous solvent was changed as shown in Table 1, and the evaluation was carried out in the same manner as in Comparative Example 3. The obtained evaluation results are shown in Table 1, FIG. 6 and FIG.

[Example 1]
The sheet-shaped positive electrode plate and the negative electrode plate in Comparative Example 1 are each cut to a predetermined size, and the positive electrode and the negative electrode obtained by cutting are sandwiched between them and rolled with a polypropylene microporous film having a thickness of 15 μm. It was turned to prepare a roll-shaped electrode group. The length of the positive electrode was 74 cm, the length of the negative electrode was 78 cm, and the length of the separator was 85 cm. The width of the positive electrode was 6.4 cm, the width of the negative electrode was 5.6 cm, and the width of the separator was 5.85 cm. The porosity of the separator was 50%.
A current collecting lead is attached to this electrode group, the electrode group is inserted into the battery exterior, and 125 μm thick hydrogen storage is covered with 50 μm polypropylene tape (adhesive; acrylic adhesive) above and below the positive and negative electrodes. After installing a metal object (material: titanium-based metal compound, 1 cm square) and fixing one side of the hydrogen-storing metal object to the battery exterior with resin, the non-aqueous electrolyte solution shown in Table 1 is placed inside the cylindrical battery exterior. 8 mL was injected. Finally, the battery exterior was sealed to complete the lithium-ion secondary battery.
In Example 1, the ratio of the volume (mL) of the hydrogen storage metal to the capacity (Ah) of the positive electrode (volume of the hydrogen storage metal / capacity of the positive electrode) is 0.25. The object was installed on the battery exterior.

In Example 1, charging / discharging is repeated under the same conditions as described above (evaluation of cycle characteristics), this charging / discharging is performed for 1000 cycles, the discharge capacity after 1000 cycles is measured, and the discharge capacity retention rate (%) is determined. As a result of calculation, a discharge capacity retention rate of 90% or more was shown after 1000 cycles.

[Comparative Example 5]
A lithium ion secondary battery was completed in the same manner as in Example 1 except that the hydrogen storage metal covered with polypropylene tape was not installed on the battery exterior, and the cycle characteristics were evaluated. In Comparative Example 5, the discharge capacity retention rate was 20% or less after 1000 cycles, and the cycle characteristics were significantly deteriorated as compared with Example 1.

[Example 2]
A lithium ion secondary battery was produced in the same manner as in Example 1 except that the non-aqueous solvent was changed to the same composition as in Comparative Example 1, and the amount of gas generated was evaluated in the same manner as in Example 1. The obtained evaluation results are shown in Table 1.

In Comparative Examples 2 to 4 and Example 1, the one-sided coating amount of the positive electrode mixture and the density of the positive electrode mixture were fixed so that the capacity ratio (negative electrode capacity / positive electrode capacity) was 0.85, and then the mixture was fixed. The amount of one-sided coating of the negative electrode mixture and the density of the negative electrode mixture were changed.

In Table 1, EC represents ethylene carbonate, TFEP represents tris phosphate (2,2,2-trifluoroethyl), and DMC represents dimethyl carbonate.

As shown in FIG. 5, when Comparative Example 1 and Comparative Example 3 using the same non-aqueous solvent are compared, as shown in Table 1, Comparative Example 3 including a gas occlusion member is measured more than Comparative Example 1. It was confirmed that the amount of gas generated was small and the expansion of the battery was suppressed. Further, in Comparative Example 3, deterioration of the gas storage member due to the electrolytic solution was not confirmed after 300 cycles.

As shown in FIG. 6, when Comparative Example 2 and Comparative Example 4 using the same non-aqueous solvent are compared, as shown in Table 1, Comparative Example 4 including a gas occlusion member is measured more than Comparative Example 2. It was confirmed that the amount of gas generated was small and the expansion of the battery was suppressed. Further, in Comparative Example 4, deterioration of the gas storage member due to the electrolytic solution was not confirmed after 500 cycles. Further, in Comparative Example 4 in which the electrolytic solution contained TFEP, the measured amount of gas generated was smaller than that in Comparative Example 3.

As shown in FIGS. 7 and 8, it was confirmed that in Comparative Example 3 and Comparative Example 4, the value of the discharge capacity retention rate was higher than that of Comparative Example 1 and Comparative Example 2, and the cycle characteristics were excellent.

(Analysis of generated gas ratio)
For Comparative Example 1 and Comparative Example 2, the amount of each gas generated after the cell was allowed to stand in an environment of 50 ° C. for 30 days after being fully charged was analyzed using a GC-MS (gas chromatograph mass spectrometer). A GC7100 type gas chromatograph manufactured by J-Science Labs Co., Ltd. was used for the measurement of hydrogen gas, a Molecular Sieve 5A was used for the column, and the column temperature was set to 70 ° C. A thermal conductivity detector was used as the detector. A G3810 type gas chromatograph manufactured by Yanagimoto Seisakusho Co., Ltd. was used for the measurement of carbon monoxide gas and carbon dioxide gas, activated carbon was used for the column, and the column temperature was set to 80 ° C. A hydrogen flame ionization detector was used as the detector. The cell that had been allowed to stand under the above test conditions was sealed in a gas bag together with 1000 mL of argon, and the gas in the cell was released into the bag in a closed environment. This gas was used as a sample for GC-MS.
The results are shown in FIG. As shown in FIG. 9, in Comparative Example 2 in which the non-aqueous solvent contains a phosphoric acid ester containing a fluorine atom, the amount of hydrogen gas generated is significantly reduced after the cell is allowed to stand for 30 days as compared with Comparative Example 1. It was confirmed that there was. From this, it was found that the generation of hydrogen gas can be particularly suppressed by using a non-aqueous solvent containing a phosphoric acid ester containing a fluorine atom.

1, 12 ... Positive electrode plate, 2 ... Positive electrode current collecting tab, 3, 13 ... Negative electrode plate, 4 ... Negative electrode collecting tab, 5, 14 ... Separator, 6, 16 ... Battery exterior, 7 ... Gas storage member, 10, 11 ... Lithium ion secondary battery, 15, 20 ... Electrode group

Claims (16)

A positive electrode containing a positive electrode active material and a positive electrode
Negative electrode containing negative electrode active material and negative electrode
Electrolytes containing lithium salts and
A protective layer that covers at least a part of the gas storage unit capable of storing gas and the gas storage unit, allows the gas to permeate, and suppresses contact between the gas storage unit and the components contained in the electrolyte. With the gas occlusion member
Lithium-ion secondary battery with. The lithium ion secondary battery according to claim 1, wherein the protective layer is located between the gas storage unit and the electrolyte. The lithium ion secondary battery according to claim 1 or 2, wherein the gas storage member is installed on at least a part of the inner wall surface of the battery exterior containing the positive electrode, the negative electrode, and the electrolyte. The lithium ion secondary battery according to any one of claims 1 to 3, wherein the gas storage unit is capable of storing hydrogen gas. The ratio of the volume (mL) of the gas storage unit to the capacity (Ah) of the positive electrode or the capacity (Ah) of the negative electrode (volume of the gas storage unit / capacity of the positive electrode or capacity of the negative electrode) is 0.01 or more. The lithium ion secondary battery according to any one of claims 1 to 4. The gas storage unit has a metal layer and a catalyst layer located at least a part on the surface of the metal layer.
The lithium ion secondary battery according to any one of claims 1 to 5, wherein the protective layer is located on at least a part of the surface of the catalyst layer. The lithium ion secondary according to any one of claims 1 to 6, wherein the positive electrode active material contains an active material in which lithium ions are inserted and removed at a potential of 4.5 V or more with respect to the lithium potential. battery. The lithium ion secondary according to any one of claims 1 to 7, wherein the negative electrode active material contains an active material in which lithium ions are inserted and removed at a potential of 0.4 V or more with respect to the lithium potential. battery. Further, a separator interposed between the positive electrode and the negative electrode is provided.
The lithium ion secondary battery according to claim 1 to claim 8, wherein the electrolyte contains a non-aqueous solvent. The lithium ion secondary battery according to claim 9, wherein the separator has a porosity of 20% to 80%. The lithium ion secondary battery according to claim 1 to claim 8, wherein the electrolyte includes a non-aqueous solvent and a polymer electrolyte impregnated with the non-aqueous solvent. The non-aqueous solvent is ethylene carbonate, diethyl carbonate, propylene carbonate, ethylmethylsulfone, vinylene carbonate, methylethyl carbonate, γ-butyrolactone, acetonitrile, 1,2-dimethoxyethane, dimethoxymethane, tetrahydrofuran, dioxolane, methylene chloride, fluorine. It does not contain any of the specific non-aqueous solvents selected from the group consisting of the modified ether and the carboxylic acid ester (excluding the carboxylic acid ester containing a fluorine atom), or the total content of the specific non-aqueous solvent is the total content of the specific non-aqueous solvent. The lithium ion secondary battery according to any one of claims 9 to 11, wherein the amount is less than 30% by volume based on the total amount of the non-aqueous solvent. The lithium ion secondary battery according to any one of claims 9 to 12, wherein the non-aqueous solvent contains a phosphoric acid ester containing a fluorine atom. The lithium ion secondary battery according to any one of claims 1 to 8, wherein the electrolyte contains at least one of a sulfide-based inorganic solid electrolyte and an oxide-based inorganic solid electrolyte. The one according to any one of claims 1 to 14, wherein the lithium salt contains at least one selected from the group consisting of lithium hexafluorophosphate, lithium tetrafluoroborate and lithium bis (trifluoromethanesulfonyl) imide. The lithium ion secondary battery described. The lithium ion secondary battery according to any one of claims 1 to 15, wherein the capacity ratio (negative electrode capacity / positive electrode capacity) between the negative electrode capacity of the negative electrode and the positive electrode capacity of the positive electrode is 1 or less.

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