WO2020202307A1

WO2020202307A1 - Lithium ion secondary battery

Info

Publication number: WO2020202307A1
Application number: PCT/JP2019/014152
Authority: WO
Inventors: 由磨五行
Original assignee: 日立化成株式会社
Priority date: 2019-03-29
Filing date: 2019-03-29
Publication date: 2020-10-08
Also published as: JPWO2020202661A1; WO2020202661A1

Abstract

A lithium ion secondary battery which is provided with: a positive electrode that contains, as a positive electrode active material, an active material into which lithium ions are intercalated and deintercalated at a potential of 4.5 V or more with respect to the lithium potential; a negative electrode that contains, as a negative electrode active material, an active material into which lithium ions are intercalated and deintercalated at a potential of 0.4 V or more with respect to the lithium potential; a separator that is interposed between the positive electrode and the negative electrode; and an electrolyte solution that contains a lithium salt and a nonaqueous solvent. This lithium ion secondary battery is configured such that: the nonaqueous solvent contains a phosphoric acid ester that contains fluorine atoms; and the content of the phosphoric acid ester that contains fluorine atoms is more than 5% by volume with respect to the total amount of the nonaqueous solvent.

Description

Lithium ion secondary battery

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 laptop 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 and 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 precipitated 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 working 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 the non-aqueous solvent 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.

The present disclosure has been made in view of the above circumstances, and an object of the present disclosure is to provide a lithium ion secondary battery in which gas generation is suppressed.

Specific means for solving the above problems are as follows.
<1> A positive electrode containing 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 as a positive electrode active material, and
A negative electrode containing 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 as a negative electrode active material, and a negative electrode.
A separator interposed between the positive electrode and the negative electrode,
With an electrolytic solution containing a lithium salt and a non-aqueous solvent,
The non-aqueous solvent contains a phosphoric acid ester containing a fluorine atom, and the content of the phosphoric acid ester containing a fluorine atom is more than 5% by volume based on the total amount of the non-aqueous solvent.
<2> The lithium ion secondary battery according to <1>, wherein the content of the phosphoric acid ester containing a fluorine atom is 90% by volume or less based on the total amount of the non-aqueous solvent.
<3> The lithium ion secondary battery according to <1> or <2>, wherein the non-aqueous solvent further contains dimethyl carbonate.
<4> The lithium ion secondary battery according to <3>, wherein the content of the dimethyl carbonate is 5% by volume to 80% by volume with respect to the total amount of the non-aqueous solvent.
<5> The content volume ratio of the phosphoric acid ester containing a fluorine atom to the dimethyl carbonate (phosphoric acid ester containing a fluorine atom / dimethyl carbonate) is 0.05 to 2.5 <3> or <4>. The lithium ion secondary battery described in.
<6> The lithium ion secondary battery according to any one of <1> to <5>, wherein the phosphoric acid ester containing a fluorine atom contains tris phosphate (2,2,2-trifluoroethyl).
<7> The lithium ion secondary according to any one of <1> to <6>, wherein the capacity ratio (negative electrode capacity / positive electrode capacity) of the negative electrode capacity of the negative electrode to the positive electrode capacity of the positive electrode is 1 or less. battery.
<8> The lithium ion secondary battery according to any one of <1> to <7>, wherein the porosity of the separator is 20% to 80%.
<9> The non-aqueous solvent is ethylene carbonate, diethyl carbonate, propylene carbonate, ethyl methyl sulfone, vinylene carbonate, methyl ethyl carbonate, γ-butyrolactone, acetonitrile, 1,2-dimethoxyethane, dimethoxymethane, tetrahydrofuran, dioxolane, chloride. Free of any other non-aqueous solvent selected from the group consisting of methylene, methyl acetate, ethyl trifluoroacetate and 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether. Or, the lithium ion secondary according to any one of <1> to <8>, wherein the total content of the other non-aqueous solvent is less than 30% by volume based on the total amount of the non-aqueous solvent. battery.

According to the present disclosure, it is possible to provide a lithium ion secondary battery in which gas generation is suppressed.

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 and a separator which constitute an electrode group. It is sectional drawing which shows the other form of the lithium ion secondary battery of this disclosure.

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 another numerical range described stepwise. .. 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 a shape structure formed on the entire surface but also a shape structure formed on a part thereof when observed as a plan view.
In the present disclosure, the term "layer" includes not only the shape structure formed on the entire surface but also the shape structure formed on a part thereof when observed as a plan view. The term "laminated" refers to stacking layers, with two or more layers bonded together and two or more layers detachable.
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]
In the lithium ion secondary battery of the present disclosure, 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 (hereinafter, may be referred to as a “specific positive electrode active material”) is used as a positive electrode. A positive electrode contained as an active material and 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 (hereinafter, may be referred to as “specific negative electrode active material”) are used as negative electrode active materials. A negative electrode containing a negative electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolytic solution containing a lithium salt and a non-aqueous solvent are provided, and the non-aqueous solvent contains a phosphoric acid ester containing a fluorine atom. The content of the phosphoric acid ester containing a fluorine atom is more than 5% by volume based on the total amount of the non-aqueous solvent.

In the lithium ion secondary battery of the present disclosure, since the negative electrode contains a negative electrode 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, the lithium of the present disclosure is disclosed. The ion secondary battery substantially operates as a "battery" when the potential of the negative electrode is 0.4 V or higher. For example, even if the negative electrode potential rises to 0.4 V or higher when a conventional lithium ion secondary battery mainly using graphite for the negative electrode is in an over-discharged state, such a battery Is, in reality, not a lithium ion secondary battery in which the negative electrode operates at a potential of 0.4 V or higher, and is excluded from the scope of the present invention. In the present invention, in order to say that the negative electrode contains a negative electrode active material into which lithium ions are inserted and removed at a potential of 0.4 V or more with respect to the lithium potential, a condition in which a lithium ion secondary battery is normally used is used. When discharging is performed underneath, it is required that at least 50% or more of the amount of discharged electricity is carried in correspondence with the negative electrode operating region having a negative electrode potential of 0.4 V or more. That is, it is substantially required that the operating potential of the negative electrode is 0.4 V or more with respect to Li / Li ⁺ .

In the lithium ion secondary battery of the present disclosure, since the non-aqueous solvent of the electrolytic solution contains more than 5% by volume of a phosphoric acid ester containing a fluorine atom, gas generation is suppressed. The reason is not clear, but it can be inferred as follows.
Since the phosphoric acid ester containing a fluorine atom has excellent oxidation resistance, it is not easily decomposed even when a high-potential positive electrode containing a spinel-type lithium-nickel-manganese composite oxide or the like as a positive electrode active material is used. Further, the phosphoric acid ester containing a fluorine atom is not easily reduced and decomposed because it is not subjected to the catalytic action of lithium titanium composite oxide (LTO) or the like. Therefore, it is considered that the non-aqueous solvent of the electrolytic solution contains a predetermined amount of the phosphoric acid ester containing a fluorine atom, so that the generation of gas due to the decomposition of the non-aqueous solvent is suppressed.

(Positive electrode active material)
In the lithium ion secondary battery of the present disclosure, 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, and 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 the insertion reaction and desorption reaction of lithium ions are carried out at a potential of 4.5 V or more with respect to the 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 preferable that the compound is LiNi _X Mn _2-X O ₄ (0.4 <X <0.6), and LiNi _0.5 is preferable 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.
In addition, 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 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. 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 containing 0.05 g of the measurement sample is decompressed 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 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 properties, 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 to 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 at least one element selected from the group consisting of B), Li _x Mn ₂ O ₄ and Li _x Mn. _2-y M ³ _y O ₄ (Li _x Mn _2-y M ³ _y O ₄ in 2, 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. 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 the other positive electrode active material can be measured by the same method as that of 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 are aggregated to form secondary particles). The median diameter D50) of the secondary particles is preferably 0.5 μm to 100 μm, and 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)
In the lithium ion secondary battery of the present disclosure, a negative electrode active material containing a specific negative electrode active material is used. 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, and 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 removed at a potential of 0.8 V or more 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 oxides 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 vanadate (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.

In the specific negative electrode active material, the insertion reaction and the desorption reaction of lithium ions almost occur at a potential of 0.4 V or more with respect to the lithium potential, so that the operating potential is higher than that of the carbon-based negative electrode active material, and lithium in the negative electrode is used. Precipitation is suppressed. Further, unlike the case where 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 at the time of 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.

Examples of the element capable of substituting the Li or Ti site of the spinel-type lithium titanium composite oxide include Nb, V, Mn, Ni, Cu, Co, Zn, Sn, Pb, Al, Mo, Ba, and 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. Of these substitutable elements, Al is preferably used 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 O-site 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 storage characteristics. It is preferably less than 15 m ² / g, especially 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 that the amount 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. The thickness is preferably from 100 μm, more preferably from 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.

<Overall configuration of lithium-ion secondary battery>
(Positive electrode)
The lithium ion secondary battery of the present disclosure has the following positive electrodes applicable to the lithium ion secondary battery. 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 specific 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 an 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 composed of the above components, the positive electrode mixture contains known olivine-type lithium salts, chalcogen compounds, 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 It is more preferably ² to 200 g / m ² , and even more preferably 130 g / m ² to 170 g / 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 It is more preferably about 3.2 g / cm ³ , and even more preferably 2.2 g / cm ³ to 3.1 g / cm ³ .

(Negative electrode)
The lithium ion secondary battery of the present disclosure has the following negative electrodes applicable to the lithium ion secondary battery. The negative electrode (negative electrode plate) of the present disclosure includes 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 containing a specific negative electrode active material such as lithium titanium composite oxide and a conductive agent were mixed, and an appropriate binder and solvent were added as necessary to prepare a paste-like negative electrode mixture. It can be formed by applying and drying the material on the surface of a current collector of a metal foil such as copper, and then 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 It is more preferably ² to 200 g / m ² , and even more preferably 80 g / m ² to 160 g / m ² .
Density 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 1.0g / cm 3 ~ 3.3g / cm 3, 1.2g / cm 3 It is more preferably ~ 3.2 g / cm ³ , and even more preferably 1.4 g / cm ³ to 2.8 g / cm ³ .

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, and reduced graphene oxide.

Further, 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-based polymers such as polyethylene, polypropylene, polyethylene terephthalate, polymethyl methacrylate, polyimide, aromatic polyamide, cellulose, and nitrocellulose; SBR (styrene-butadiene rubber), NBR (acrylonitrile-butadiene rubber), fluorine. Rubber-like polymers such as rubber, isoprene rubber, butadiene rubber, ethylene-propylene rubber; styrene-butadiene-styrene block copolymer or hydrogen additive thereof, EPDM (ethylene-propylene-diene ternary copolymer), styrene- Thermoplastic elastomeric polymers such as isoprene-styrene block copolymers or hydrogenated products thereof; syndiotactic-1,2-polybutadiene, polyvinyl acetate, ethylene-vinyl acetate copolymers, propylene-α-olefin copolymers Soft resinous polymers such as coalesced; polyvinylidene fluoride (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 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, and further 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.

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

(Current collector)
A current collector is used for the positive electrode and the negative electrode. The material of the current collector may be aluminum, titanium, stainless steel, nickel, conductive polymer, etc., as well as aluminum, copper, etc. for the purpose of improving adhesiveness, conductivity, and oxidation resistance. A material that has been treated to adhere carbon, nickel, titanium, silver, etc. to the surface can be used.
As the negative electrode 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 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, a nylon, or the like is 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 of 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 in which the above-mentioned inorganic substance in the form of fibers or particles is attached 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 base material, a base material 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 obtained by forming a composite porous layer of the above-mentioned inorganic substance having a fiber shape or a particle shape 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 in which alumina particles having a 90% particle size (D90) of less than 1 μm are bound 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. Further, since 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 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 deterioration of 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 mercury porosimeter measurement. The conditions for measuring the mercury porosimeter are as follows.
・ Equipment: Shimadzu Corporation Autopore IV 9500
・ Mercury press-fitting 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: 13.535 g / mL

(Electrolytic solution)
The electrolytic solution of the present disclosure contains a lithium salt which is an electrolyte and a non-aqueous solvent which dissolves the lithium salt.
The non-aqueous solvent used in the present disclosure includes a phosphate ester containing a fluorine atom. Since a phosphoric acid ester containing a fluorine atom has a relatively low melting point, it is considered that it is easy to secure battery characteristics in a wide temperature range.

The content of the phosphoric acid ester containing a fluorine atom may exceed 5% by volume, preferably 7% by volume or more, and more preferably 10% by volume or more with respect to the total amount of the non-aqueous solvent. , 15% by volume or more is more preferable, and 20% by volume or more is particularly preferable. When the content of the phosphoric acid ester containing a fluorine atom is 10% by volume or more, the melting point of the electrolytic solution 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 60% by volume, based on the total amount of the non-aqueous solvent. It is more preferably% or less, and particularly preferably 50% by volume or less.

A 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 or 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 ( 2,2,3,3,4,5,5-octafluoropentyl), tris phosphate (2,2,3,3,4,5,5,5-nonafluoropentyl), phosphoric acid Tris (3,3,4,5,5,6,6,6-nonafluorohexyl), bis (2,2,2-trifluoroethyl) methyl phosphate, 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 further 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 electrolytic solution.

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, further 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% 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 electrolytic solution 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), ethyl methyl sulfone (EMS), vinylene carbonate (VC), methyl ethyl carbonate, γ-butyrolactone, acetonitrile, 1 , 2-Dimethoxyethane, dimethoxymethane, tetrahydrofuran, dioxolane, methylene chloride, methyl acetate, ethyl acetate, methyl difluoroacetate, ethyl trifluoroacetate, methyl propionate, ethyl propionate, methyl butyrate and other carboxylic acid esters and 1,1 , 2,2-Tetrafluoroethyl 2,2,3,3-Tetrafluoropropyl ether may be selected from the group.

When the electrolytic solution contains other non-aqueous solvent, the total content of the other non-aqueous solvent is preferably less than 30% by volume, preferably 25% by volume or less, based on the total amount of the non-aqueous solvent. 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, etc. I hope there is.
When the electrolytic solution contains other non-aqueous solvent, the other non-aqueous solvent may be used alone or in combination of two or more. In the case of one type alone, the total content of the other non-aqueous solvents described above shall be read as the content of the other non-aqueous solvents.
The electrolytic solution can be made safe by using a solvent having a high flash point such as EC or 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.

The lithium salt, LiPF ₆ (lithium _{hexafluorophosphate),} LiBF 4, LiFSI (lithium bisfluorosulfonylimide), LiTFSI (lithium _{_{_{_{bistrifluoromethanesulfonylimide), LiClO 4, LiB (C}}}} 6 H 5) 4, LiCH Examples thereof include ₃ SO ₃ , LiCF ₃ SO ₃ , and LiN (SO ₂ CF ₂ CF ₃ ) ₂ . These lithium salts may be used alone or in combination of two or more.
Among these, the lithium salt is lithium hexafluorophosphate when comprehensively judging the solubility in a solvent, charge / discharge characteristics in the case of a lithium ion secondary battery, input / discharge characteristics, charge / discharge cycle characteristics, etc. preferable.

From the viewpoint of safety, the concentration of the lithium salt in the electrolytic solution is preferably 0.8 mol / L to 4.0 mol / L, more preferably 1.0 mol / L to 3.0 mol / L. It is more preferably 1.2 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 electrolytic solution can be made safer.

The electrolytic solution may contain an additive if necessary.
The additive is not particularly limited as long as it is an additive for an electrolytic solution of a lithium ion secondary battery, and is, for example, a nitrogen-containing heterocyclic compound, a sulfur-containing heterocyclic compound, and a nitrogen- and sulfur-containing heterocycle compound. Examples thereof include ring compounds, cyclic carboxylic acid esters, fluorine-containing cyclic carbonates, fluorine-containing boric acid 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.

By containing additives in the electrolytic solution, it is possible to improve storage characteristics at high temperatures, charge / discharge cycle characteristics, and input / output characteristics.

(Capacity ratio of negative electrode capacity of negative electrode to positive electrode capacity of 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 volume 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 volumetric 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 volumetric 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 [the discharge capacity of the negative electrode], and the positive electrode capacity indicates [the 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 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 0.37mA 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, it is possible to adjust the capacity ratio (negative electrode capacity / positive electrode capacity) of the lithium ion secondary battery of the present disclosure 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. Regardless of the shape, a separator is interposed between the positive electrode and the negative electrode to form an electrode body, and the area 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 collected. A lithium ion secondary battery is completed by connecting using an electric lead or the like and sealing this electrode body together with an electrolytic solution in a battery case.
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, and a separator constituting the electrode group.
The size of the members in each figure is conceptual, and the relative relationship between the members is not limited to this. Further, members having substantially the same function may be given the same reference numerals throughout the drawings, and duplicate 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 has a positive electrode current collecting tab 2 and a negative electrode current collecting tab 4 in the battery exterior body 6. I try to take it out.

Then, as shown in FIG. 2, the electrode group 20 is a stack of a positive electrode plate 1 to which the positive electrode current collecting tab 2 is attached, a separator 5, and a negative electrode plate 3 to which the negative electrode current collecting tab 4 is attached.
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 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. A cylindrical lithium ion secondary battery can be mentioned.
FIG. 3 is a cross-sectional view showing another form 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 above the electrode group 15 and is ultrasonically bonded to the lower surface of the disk-shaped battery lid that serves as the positive electrode external terminal. On the other hand, on the lower end surface of the electrode group 15, a ribbon-shaped negative electrode tab terminal made of nickel whose one end is 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 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 provided 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, an electrolytic solution (not shown) is injected into the battery exterior body 16.
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 the 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). Was mixed by 2 parts by mass, 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, so as to have a solid content of 145 g / m ² of the positive electrode mixture substantially evenly and uniformly. Then, it was dried to obtain a dry coating film. This dried coating film was compacted 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. Li400, Denka Co., Ltd.) is mixed by 4 parts by mass, and polyvinylidene fluoride (KF polymer # 9130, Kureha Co., Ltd.) is mixed by 5 parts by mass as a binder, and an appropriate amount of N-methyl-2-pyrrolidone is added and kneaded. 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 dried to obtain a dry coating film. This dried coating film was compacted 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 ( A 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 collected wet precipitate was washed 3 times with 1800 g of purified water and then vacuum-dried at 80 ° C. for 10 hours to isolate and purify 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 (vacancy ratio 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 electrolyte)
The electrolyte, LiPF ₆ , was dissolved in the non-aqueous solvent shown in Table 1 below at a concentration of 1.0 mol / L to prepare an electrolytic solution. In addition, EC in Table 1 represents ethylene carbonate, TFEP represents tris phosphate (2,2,2-trifluoroethyl), and DMC represents dimethyl carbonate.

(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 laminate 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 so as to take out the electric tab to the outside. The aluminum laminate film is a laminate 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 for 3 cycles in a voltage range of 2.0 V to 3.5 V at 40 ° C. and a current value of 0.2 C.

(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 to serve as a counter electrode. A current collecting 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 (vacancy ratio 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 outer body made of an aluminum laminated film, and after injecting an electrolytic solution into the battery outer body, a positive electrode current collecting tab and a counter electrode current collecting tab are used. A lithium ion secondary battery was produced by sealing the opening of the battery exterior body so as to take out the battery to the outside. The aluminum laminate film is a laminate 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 has a volume ratio of 3: 7) 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 discharging. did.
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 produced 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 in 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 constantly charged at 50 ° C. with 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 paused for 15 minutes. After that, constant current discharge was performed with a current value of 1C and a discharge end 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, the volume of the lithium ion secondary battery was measured using the above hydrometer (volume after 100 cycles).
The amount of gas generated after 100 cycles was calculated from the following formula. The results obtained are shown in Table 1 and FIG.
Gas generation amount (mL) = (volume after 100 cycles)-(initial volume)

[Examples 1 to 11, Comparative Example 2]
Lithium-ion secondary batteries of Examples 1 to 11 and Comparative Example 2 were 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 same as in Comparative Example 1. evaluated. The obtained evaluation results are shown in Table 1.
In Examples 1 to 11 and Comparative Example 2, the one-sided coating amount of the positive electrode mixture and the density of the positive electrode mixture were fixed so that the volume ratio (negative electrode capacity / positive electrode capacity) was 0.85. The single-sided coating amount of the negative electrode mixture and the density of the negative electrode mixture were changed.

In Examples 1 to 11 in which the electrolytic solution contains more than 5% by volume of TFEP, the amount of gas generated is 0.3 mL or less, and Comparative Example 1 in which the electrolytic solution contains 5% by volume of TFEP and the comparison in which the electrolytic solution does not contain TFEP. The amount of gas generated was suppressed as compared with Example 2.

All documents, patent applications, and technical standards described herein are to the same extent as if the individual documents, patent applications, and technical standards were specifically and individually stated to be incorporated by reference. Incorporated herein by reference.

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

Claims

A positive electrode containing an active material in which lithium ions are inserted and removed at a potential of 4.5 V or higher with respect to the lithium potential as a positive electrode active material, and
A negative electrode containing 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 as a negative electrode active material, and a negative electrode.
A separator interposed between the positive electrode and the negative electrode,
With an electrolytic solution containing a lithium salt and a non-aqueous solvent,
The non-aqueous solvent contains a phosphoric acid ester containing a fluorine atom, and the content of the phosphoric acid ester containing a fluorine atom is more than 5% by volume based on the total amount of the non-aqueous solvent.
The lithium ion secondary battery according to claim 1, wherein the content of the phosphoric acid ester containing a fluorine atom is 90% by volume or less based on the total amount of the non-aqueous solvent.
The lithium ion secondary battery according to claim 1 or 2, wherein the non-aqueous solvent further contains dimethyl carbonate.
The lithium ion secondary battery according to claim 3, wherein the content of the dimethyl carbonate is 5% by volume to 80% by volume with respect to the total amount of the non-aqueous solvent.
The third or fourth claim, wherein the content volume ratio of the phosphoric acid ester containing a fluorine atom to the dimethyl carbonate (phosphoric acid ester containing a fluorine atom / dimethyl carbonate) is 0.05 to 2.5. Lithium-ion secondary battery.
The lithium ion secondary battery according to any one of claims 1 to 5, wherein the phosphoric acid ester containing a fluorine atom contains tris phosphate (2,2,2-trifluoroethyl).
The lithium ion secondary battery according to any one of claims 1 to 6, wherein the capacity ratio (negative electrode capacity / positive electrode capacity) of the negative electrode capacity of the negative electrode to the positive electrode capacity of the positive electrode is 1 or less.
The lithium ion secondary battery according to any one of claims 1 to 7, wherein the porosity of the separator is 20% to 80%.
The non-aqueous solvent is ethylene carbonate, diethyl carbonate, propylene carbonate, ethyl methyl sulfone, vinylene carbonate, methyl ethyl carbonate, γ-butyrolactone, acetonitrile, 1,2-dimethoxyethane, dimethoxymethane, tetrahydrofuran, dioxolane, methylene chloride, acetic acid. It does not contain any of the other non-aqueous solvents selected from the group consisting of methyl, ethyl trifluoroacetate and 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether, or The lithium ion secondary battery according to any one of claims 1 to 8, wherein the total content of the other non-aqueous solvent is less than 30% by volume based on the total amount of the non-aqueous solvent.