WO2016171276A1

WO2016171276A1 - Lithium ion cell

Info

Publication number: WO2016171276A1
Application number: PCT/JP2016/062835
Authority: WO
Inventors: 由磨五行
Original assignee: 日立化成株式会社
Priority date: 2015-04-24
Filing date: 2016-04-22
Publication date: 2016-10-27
Also published as: JPWO2016171276A1

Abstract

The purpose of the present invention is to provide a lithium ion cell that has excellent charge-discharge cycle properties in spite of using a conventional lithium ion cell electrolyte solution. This lithium ion cell is provided, inside a cell outer casing, with the following: a positive electrode containing a spinel-type lithium-nickel-manganese composite oxide as the positive electrode active substance; a negative electrode containing a negative electrode active substance capable of absorbing lithium ions; a separator for insulating the positive electrode and the negative electrode; and an electrolyte solution. The ratio (Y/X) of the volume Y occupied by the electrolyte solution to the volume X inside the cell outer casing is 0.2 or greater.

Description

Lithium ion battery

The present invention relates to a lithium ion battery.

Lithium ion batteries are high energy density secondary batteries, and are used as power sources for portable devices such as notebook computers and mobile phones, taking advantage of their characteristics.

In recent years, lithium ion batteries have attracted attention as power supplies for electronic devices, power storage power supplies, and electric vehicle power supplies that are becoming smaller in size, and lithium ion batteries that are further excellent in high energy density are required.
As a means for improving the energy density, for example, there is a method of using, as a positive electrode active material, a spinel type lithium / nickel / manganese composite oxide showing a high operating voltage. However, due to the high potential, in conventional electrolytes using cyclic carbonates and chain monocarbonates, the decomposition reaction of the electrolyte solution tends to occur at the contact portion between the positive electrode active material and the electrolyte solution, and sufficient cycle characteristics are obtained. There was a problem that it was not possible.
As means for solving this problem, Japanese Patent Application Laid-Open No. 2004-79426 proposes a method using alkylene biscarbonate as an electrolytic solution.

However, the alkylene biscarbonate described in JP-A-2004-79426 is expensive and not economical.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a lithium ion battery having excellent charge / discharge cycle characteristics even when a conventional electrolyte for a lithium ion battery is used.

Specific means for achieving the above object are as follows.
By configuring the lithium ion battery as follows, the lithium ion battery is excellent in charge / discharge cycle characteristics.
<1> A positive electrode including a spinel type lithium / nickel / manganese composite oxide as a positive electrode active material, a negative electrode including a negative electrode active material capable of occluding lithium ions, a separator for insulating the positive electrode and the negative electrode, and electrolysis A battery and a battery exterior body,
A lithium ion battery in which a ratio (Y / X) of a volume Y occupied by the electrolytic solution to a volume X in the battery outer body is 0.2 or more.
<2> The lithium ion battery according to <1>, wherein the electrolytic solution contains a non-aqueous solvent and a lithium salt, and a content of chain monocarbonate in a total amount of the non-aqueous solvent exceeds 70% by volume.
<3> The lithium ion battery according to <2>, wherein the chain monocarbonate contains dimethyl carbonate.
<4> The lithium ion battery according to any one of <1> to <3>, wherein the electrolytic solution contains a fluorine-containing borate ester.
<5> The lithium ion battery according to any one of <1> to <4>, wherein the ratio (Y / X) is 0.8 or less.
<6> The lithium ion battery according to any one of <1> to <5>, wherein the separator has a porosity of 20% or more.
<7> The lithium ion battery according to any one of <1> to <6>, wherein the negative electrode active material capable of storing lithium ions contains a lithium titanium composite oxide.
<8> The spinel-type lithium / nickel / manganese composite oxide contains a compound represented by LiNi _X Mn _2-X O ₄ (0.3 <X <0.7) <1> to <7 > The lithium ion battery of any one of>.

According to the present invention, it is possible to provide a lithium ion battery excellent in charge / discharge cycle characteristics even when a conventional electrolyte for a lithium ion battery is used.

It is a perspective view which shows one form of the lithium ion battery of this embodiment. It is a perspective view which shows the positive electrode plate, negative electrode plate, and separator which comprise an electrode group. It is sectional drawing which shows the other form of the lithium ion battery of this embodiment.

Hereinafter, the form for implementing the lithium ion battery of this invention is demonstrated in detail.
In this specification, the term “process” includes a process that is independent of other processes and includes the process if the purpose of the process is achieved even if it cannot be clearly distinguished from the other processes. It is.
In the present specification, numerical values indicated by using “to” include numerical values described before and after “to” as the minimum value and the maximum value, respectively.
In the numerical ranges described stepwise in this specification, 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. Good. Further, in the numerical ranges described in this specification, the upper limit value or the lower limit value of the numerical range may be replaced with the values shown in the examples.
In this specification, the content rate or content of each component means the total content rate or content of the plurality of types of substances when there are a plurality of types of substances corresponding to each component, unless otherwise specified.
In the present specification, the particle diameter of each component means a value for a mixture of the plurality of types of particles when there are a plurality of types of particles corresponding to each component, unless otherwise specified.
In this specification, the term “layer” or “film” refers to a part of the region in addition to the case where the layer or the film is formed when the region where the layer or film exists is observed. It is also included when it is formed only.
In this specification, the term “lamination” indicates that layers are stacked, and two or more layers may be combined, or two or more layers may be detachable.
In addition, the magnitude | size of the member in each figure is notional, The relative relationship of the magnitude | size between members is not limited to this. Moreover, the same code | symbol is provided to the member which has the substantially same function through all the drawings, and the overlapping description may be abbreviate | omitted.

The lithium ion battery of this embodiment includes a positive electrode including a spinel-type lithium / nickel / manganese composite oxide as a positive electrode active material, a negative electrode including a negative electrode active material capable of occluding lithium ions, the positive electrode, and the negative electrode. A separator to be insulated and an electrolytic solution are provided in the battery outer package, and a ratio (Y / X) of a volume Y occupied by the electrolytic solution to a volume X in the battery outer package is 0.2 or more.
Hereinafter, embodiments of the lithium ion battery of the present invention will be described in the order of a spinel type lithium / nickel / manganese composite oxide serving as a positive electrode active material, a negative electrode active material capable of occluding lithium ions, and an overall configuration of the lithium ion battery. To do.

<Lithium / nickel / manganese composite oxide>
A lithium ion battery has the following positive electrode applicable to a lithium ion battery. The positive electrode (positive electrode plate) used in the present embodiment has a current collector and a positive electrode mixture layer formed on both surfaces or one surface thereof. The positive electrode mixture layer contains a spinel type lithium / nickel / manganese composite oxide as a positive electrode active material.
The spinel-type lithium / nickel / manganese composite oxide serving as the positive electrode active material of the lithium ion battery according to the present embodiment is a compound represented by LiNi _X Mn _2-X O ₄ (0.3 <X <0.7). Preferably, it is a compound represented by LiNi _X Mn _2-X O ₄ (0.4 <X <0.6). From the viewpoint of stability, LiNi _0.5 Mn _1.5 More preferably, it is a compound represented by O ₄ . In order to further stabilize the crystal structure of the spinel type lithium / nickel / manganese composite oxide, the site selected from the group consisting of Mn sites, Ni sites and O sites of the spinel type lithium / nickel / manganese composite oxides What substituted a part with other elements can also be used as a positive electrode active material.
Further, excess lithium may be present in the crystal of the spinel type lithium / nickel / manganese composite oxide. Further, a spinel-type lithium / nickel / manganese composite oxide in which defects are generated at the O site can also be used.
Examples of other elements (metal elements) that can substitute at least one of the Mn site and the Ni site include Ti, V, Cr, Fe, Co, Zn, Cu, W, Mg, Al, and Ru. Can do. Mn sites and Ni sites can be substituted with one or more of these metal elements. Of these substitutable metal elements, Ti is preferably used as the substitution element from the viewpoint of stabilizing the crystal structure.
Examples of the element that can replace the O site of the spinel type lithium / nickel / manganese composite oxide include F and B. The O site of the spinel type lithium-nickel-manganese composite oxide can be substituted 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.

The spinel-type lithium / nickel / manganese composite oxide preferably has a potential in a fully charged state of 4.5 V to 5 V with respect to Li / Li ⁺ from the viewpoint of high energy density, and is preferably 4.6 V to 4 V. More preferably, it is 9V. The fully charged state means a state where the SOC (state of charge) is 100%.

The positive electrode active material in the lithium ion battery of this embodiment may contain other positive electrode active materials other than the spinel type lithium / nickel / manganese composite oxide.
Other positive electrode active materials other than the spinel type lithium / nickel / manganese composite oxide include, 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 _1-y O _z (in 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 And at least one element selected from the group consisting of V and B), Li _x Ni _1-y M ² _y O _z (in Li _x Ni _1-y M ² _y O _z , M ² is Na, And at least one element selected from the group consisting of 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 (Li Among _{^{_{_{Mn 2-y M 3 y O}}}} 4, M 3 at least one is of Na, Mg, Sc, Y, Fe, Co, Cu, Zn, Al, Cr, Pb, Sb, selected from the group consisting of V and B Element).). Here, x is in the range of 0 to 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 due to charge / discharge.

The BET specific surface area of the spinel type lithium / nickel / manganese composite oxide is preferably less than 2.9 m ² / g, preferably less than 2.8 m ² / g, from the viewpoint of further improving the storage characteristics. More preferably, 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 More preferably it is.
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 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.
A BET specific surface area can be measured from nitrogen adsorption capacity according to JIS Z 8830: 2013, for example. As the evaluation apparatus, for example, trade name: AUTOSORB-1 manufactured by QUANTACHROME can be used. When measuring the BET specific surface area, it is considered that the moisture adsorbed on the sample surface and structure affects the gas adsorption capacity. Therefore, it is preferable to first perform pretreatment for moisture removal by heating. . In the pretreatment, a measurement cell charged with 0.05 g of a measurement sample is depressurized to 10 Pa or less with a vacuum pump, heated at 110 ° C. and held for 3 hours or more, and then kept at a normal temperature ( Cool to 25 ° C). After this pretreatment, the evaluation temperature is 77 K (−196 ° C.), and the evaluation pressure range is measured as a relative pressure (equilibrium pressure with respect to the saturated vapor pressure) of less than 1.

When other positive electrode active materials other than spinel type lithium / nickel / manganese composite oxide are included as the positive electrode active material, the BET specific surface area of the other positive electrode active material is 2.9 m ² from the viewpoint of improving storage characteristics. Is preferably less than 2.8 m ² / g, more preferably less than 1.5 m ² / g, and particularly preferably less than 1.0 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 More preferably it is.
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 other positive electrode active materials can be measured by the same method as for spinel type lithium / nickel / manganese composite oxide.

In the present embodiment, a spinel type lithium / nickel / manganese composite oxide is used as a main positive electrode active material.
The content of the spinel-type lithium / nickel / manganese composite oxide is preferably 60% by mass to 100% by mass, and preferably 70% by mass to 100% by mass, based on the total amount of the positive electrode active material, from the viewpoint of improving battery capacity. %, More preferably 85% by mass to 100% by mass.

The median diameter D50 of the spinel-type lithium / nickel / manganese composite oxide particles (when the primary particles are aggregated to form secondary particles, the median diameter D50 of the secondary particles) is a mixture slurry. From the viewpoint of dispersibility, the thickness is preferably 0.5 μm to 100 μm, 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.

Further, when the positive electrode active material includes 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 material (the primary particles are aggregated to form secondary particles). Is formed, 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 dispersibility of the mixture slurry.

<Anode active material capable of occluding lithium ions>
A lithium ion battery has the following negative electrode applicable to a lithium ion battery. The negative electrode (negative electrode plate) used in this embodiment has a current collector and a negative electrode mixture layer formed on both sides or one side thereof. The negative electrode mixture layer contains a negative electrode active material capable of electrochemically inserting and extracting lithium ions.

As the negative electrode active material used in the present embodiment, a carbon material, a lithium titanium composite oxide, or the like is preferable.

[Carbon material]
Carbon materials are roughly classified into graphite-based carbon materials having a uniform crystal structure and non-graphite-based carbon materials having a disordered crystal structure. Examples of the graphite-based carbon material include natural graphite and artificial graphite. Non-graphite-based carbon materials include amorphous carbon and the like, and although the crystal structure is disordered, graphitizable carbon (or graphitizable carbon) that easily becomes graphite when heated at 2000 ° C. to 3000 ° C. ) And non-graphitizable carbon (or non-graphitizable carbon) that is difficult to become graphite. Amorphous carbon can be produced by heat-treating petroleum pitch, polyacene, polyparaphenylene, polyfurfuryl alcohol, polysiloxane, etc., and can be made non-graphitizable carbon by changing the treatment temperature. Graphitized carbon can be used. For example, a treatment temperature of about 500 ° C. to 800 ° C. is suitable for producing non-graphitizable carbon, and a treatment temperature of about 800 ° C. to 1000 ° C. is suitable for producing graphitizable carbon. The non-graphitizable carbon is defined as having a plane spacing d002 value in the C-axis direction obtained by a wide-angle X-ray diffraction method of 0.36 nm to 0.40 nm.

Graphitizable carbon is defined as having a surface spacing d002 value in the C-axis direction obtained by a wide-angle X-ray diffraction method of 0.34 nm or more and less than 0.36 nm.
The graphitizable carbon preferably has a C-axis direction spacing d002 value of 0.341 nm or more and 0.355 nm or less obtained by wide-angle X-ray diffraction, and is 0.342 nm or more and 0.35 nm or less. It is more preferable.

In the present embodiment, when amorphous carbon is used as the negative electrode active material, the content of amorphous carbon is preferably 55% by mass or more and 70% by mass or more with respect to the total amount of the negative electrode active material. More preferably, it is more preferably 90% by mass or more. As the amorphous carbon, graphitizable carbon is preferably used from the viewpoint of battery characteristics. As the amorphous carbon, easily graphitizable carbon and non-graphitizable carbon may be used in combination.

[Lithium titanium composite oxide]
The lithium titanium composite oxide (LTO) serving as the negative electrode active material of the lithium ion battery of this embodiment is preferably a lithium titanium composite oxide having a spinel structure. The basic composition formula of the spinel-structure lithium-titanium composite oxide is represented by Li [Li _1/3 Ti _5/3 ] O ₄ , and in order to further stabilize the crystal structure, the spinel-structure lithium-titanium composite oxide It is also possible to use a material in which a part of the Li site or Ti site of the product is replaced with another metal, a material in which excess lithium is present in the crystal, or a part of the O site is replaced with another element. . Other elements that can replace the Li site or Ti site include, for example, F, B, Nb, V, Mn, Ni, Cu, Co, Zn, Sn, Pb, Al, Mo, Ba, Sr, Ta , Mg, and Ca. The Li site or Ti site can be substituted with one or more of these elements.
Examples of the element that can replace the O site include F and B. The O site can be substituted with one or more of these elements.

The potential in the fully charged state of the lithium titanium composite oxide is preferably 1 V to 2 V with respect to Li / Li ⁺ .

The negative electrode active material in the lithium ion battery of the present embodiment may include a negative electrode active material other than a carbon material and a lithium titanium composite oxide.

The negative electrode active material capable of occluding lithium ions preferably contains a lithium titanium composite oxide from the viewpoint of cycle characteristics.

In the case of using a lithium titanium composite oxide as a negative electrode active material capable of occluding lithium ions, the content is preferably 70% by mass to 100% by mass in the total amount of the negative electrode active material from the viewpoint of improving battery capacity. 80% by mass to 100% by mass is more preferable, and 90% by mass to 100% by mass is even more preferable.

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 even more preferably less than 20 m ² / g from the viewpoint of improving storage characteristics. Preferably, it is 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 m ² / g or more. Is more preferable.
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 0.1 m ² / g or more ^30m ² / g, 0.5m 2 more preferably less than / g or more ^{20 m} 2 / g, and particularly preferably less than ^{1 m} 2 / g or more ^{15 m} 2 / g.
The BET specific surface area of the negative electrode active material can be measured by the same method as for the spinel type lithium / nickel / manganese composite oxide.

The median diameter D50 of the negative electrode active material (the median diameter D50 of the secondary particles when primary particles are aggregated to form secondary particles) is 0.5 μm to 100 μm from the viewpoint of particle dispersibility. Preferably, the thickness is 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 battery>
For the positive electrode of the lithium ion battery, for example, a spinel type lithium / nickel / manganese composite oxide and, if necessary, the above-mentioned other positive electrode active material are used as a positive electrode active material, and a conductive material is mixed therewith. Apply a binder and a solvent to form a paste-like positive electrode mixture on the surface of a current collector of a metal foil such as an aluminum foil, dry it, and then press the positive electrode as necessary. It is formed by increasing the density of the agent layer. Although the positive electrode active material can be composed only of lithium / nickel / manganese composite oxide, the spinel type lithium / nickel / manganese composite oxide is well known as an olivine type for the purpose of improving the characteristics of the lithium ion battery. A positive electrode active material may be prepared by mixing lithium salt, chalcogen compound, manganese dioxide and the like.

Single-side coating of the current collector of the positive electrode mixture, from the viewpoint of energy density and output ^{characteristics,} it is ^{preferably, 50g / m 2 ~ 200g /} m 2 is a ^{10g / m 2 ~ 250g / m} 2 More preferably, it is more preferably 130 g / m ² to 170 g / m ² . The density of the positive electrode mixture layer, from the viewpoint of energy ^density, it is preferably 1.8g / cm 3 ~ 3.2g / cm 3, a 2.0g / cm 3 ~ 3.0g / cm 3 More preferably, it is more preferably 2.2 g / cm ³ to 2.8 g / cm ³ .

The negative electrode of the lithium ion battery uses a carbon material or a lithium-titanium composite oxide as a negative electrode active material, and a conductive material and a binder are mixed with this, and an appropriate solvent is added as necessary. This is applied to a current collector made of a metal foil such as copper, dried, and then formed by increasing the density of the negative electrode mixture layer by pressing or the like as necessary. In addition, the negative electrode active material can be composed only of the carbon material, but for the purpose of improving the characteristics of the lithium ion battery, etc., a known lithium titanium composite oxide is mixed with the carbon material to make the negative electrode active material. It may be. In addition, the negative electrode active material can be composed only of the lithium titanium composite oxide, but for the purpose of improving the characteristics of the lithium ion battery, a known carbon material or the like is already mixed with the lithium titanium composite oxide to form the negative electrode active material. It may be.

The coating amount of the current collector of the negative electrode mixture, from the viewpoint of energy density and output ^{characteristics,} is preferably ^{10g / m 2 ~ 200g / m} 2, a ^{50g / m 2 ~ 150g / m} 2 Is more preferable. Density of the negative electrode mixture layer, from the viewpoint of energy density ^is preferably 1.0g / cm 3 ~ 2.8g / cm 3, to be 1.2g / cm 3 ~ 2.6g / cm 3 More preferred.

From the viewpoint of improving the electrical conductivity of at least one of the positive electrode and the negative electrode, the conductive material is a mixture of one or more of carbon black such as acetylene black and ketjen black, and a carbon material powder such as graphite. Can be used. In addition, carbon nanotubes, graphene, or the like can be added as a conductive material to increase the electrical conductivity of at least one of the positive electrode and the negative electrode.

The conductive material used for the positive electrode (hereinafter referred to as the positive electrode conductive material) is preferably acetylene black from the viewpoint of improving input / output characteristics. The content of the positive electrode conductive material is preferably 3% by mass or more, more preferably 4% by mass or more, and more preferably 4.5% by mass based on the total amount of the positive electrode mixture from the viewpoint of input / output characteristics. It is still more preferable that it is above. Further, the content of the positive electrode conductive material may be 5% by mass or more or 5.5% by mass or more based on the total amount of the positive electrode mixture. 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.

Also, the conductive material used for the negative electrode (hereinafter referred to as negative electrode conductive material) is preferably acetylene black from the viewpoint of further improving input / output characteristics. From the viewpoint of input / output characteristics, the content of the negative electrode conductive material is preferably 1% by mass or more, more preferably 2% by mass or more, and more preferably 3% by mass or more based on the total amount of the negative electrode mixture. More preferably it is. Moreover, 4 mass% or more may be sufficient as the content rate of a negative electrode electrically conductive material on the basis of the whole quantity of negative mix, and 6 mass% or more may be sufficient as it. From the viewpoint of battery capacity, the upper limit is preferably 15% by mass or less, more preferably 12% by mass or less, and still more preferably 10% by mass or less.

The binder is not particularly limited, and a material having good solubility or dispersibility in the dispersion solvent is selected. Specific examples include resin polymers such as polyethylene, polypropylene, polyethylene terephthalate, polymethyl methacrylate, polyimide, aromatic polyamide, cellulose, and nitrocellulose; SBR (styrene-butadiene rubber), NBR (acrylonitrile-butadiene rubber), fluorine Rubbery polymers such as rubber, isoprene rubber, butadiene rubber, ethylene-propylene rubber; styrene / butadiene / styrene block copolymer or its hydrogenated product, EPDM (ethylene / propylene / diene terpolymer), styrene / Thermoplastic elastomeric polymers such as ethylene / butadiene / ethylene copolymers, styrene / isoprene / styrene block copolymers or hydrogenated products thereof; syndiotactic-1,2-polybutadiene, polyvinyl acetate , Ethylene / vinyl acetate copolymer, propylene / α-olefin copolymer and other soft resinous polymers; polyvinylidene fluoride (PVdF), polytetrafluoroethylene, fluorinated polyvinylidene fluoride, polytetrafluoroethylene / ethylene copolymer Polymers, fluorinated polymers such as polytetrafluoroethylene / vinylidene fluoride copolymers; copolymers with acrylic acid and linear ether groups added to the polyacrylonitrile skeleton; ion conduction of alkali metal ions (especially lithium ions) And a polymer composition having the property. Of these, one type may be used alone, or two or more types may be used in combination. For both the positive electrode and the negative electrode, from the viewpoint of high adhesion, it is preferable to use polyvinylidene fluoride (PVdF) or a copolymer obtained by adding acrylic acid and a linear ether group to a polyacrylonitrile skeleton.

About the content rate of a binder, the range of the content rate of the binder with respect to the whole quantity of positive mix is as follows. The lower limit of the range is preferably 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 cycle characteristics, The content is more preferably 1% by mass or more, and further preferably 2% by mass or more. From the viewpoint of improving battery capacity and conductivity, the upper limit is preferably 30% by mass or less, more preferably 20% by mass or less, and still more preferably 10% by mass or less.
The range of the content rate of the binder with respect to the total amount of the negative electrode mixture is as follows. The lower limit of the range is preferably 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 cycle characteristics. The content is more preferably 0.5% by mass or more, and further preferably 1% by mass or more. The upper limit is preferably 40% by mass or less, more preferably 25% by mass or less, and still more preferably 15% by mass or less from the viewpoint of improving battery capacity and conductivity.

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

The lithium ion battery of the present embodiment includes a separator, an electrolytic solution, and the like that are sandwiched between the positive electrode and the negative electrode, in addition to the positive electrode and the negative electrode. As the electrolytic solution used in the lithium ion battery of this embodiment, a nonaqueous electrolytic solution is preferable.

The separator is not particularly limited as long as it has ion permeability while electronically insulating the positive electrode and the negative electrode and has resistance to oxidation on the positive electrode side and reducibility on the negative electrode side. As a material (material) of the separator that satisfies such characteristics, a resin, an inorganic substance, or the like is used.

As the resin, olefin polymer, fluorine polymer, cellulose polymer, polyimide, nylon or the like is used. Specifically, it is preferable to select from materials that are stable with respect to non-aqueous electrolytes and have excellent liquid retention properties. For example, porous sheets made from polyolefins such as polyethylene and polypropylene, nonwoven fabrics, etc. may be used. preferable.

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. A separator in which the above-mentioned inorganic substance in the form of fibers or particles is made into a non-woven fabric, a woven fabric, or a thin-film shaped substrate such as a microporous film can be used. 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. Moreover, what made the said inorganic substance of fiber shape or particle | grain shape the composite porous layer using binders, such as resin, can be used as a separator. Furthermore, this composite porous layer may be formed on the surface of the positive electrode or the negative electrode to form a separator. For example, a composite porous layer in which alumina particles having a 90% average particle diameter (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 facing the positive electrode of the separator. Good.

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 60%. 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. If 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. Conditions for mercury porosimeter measurement are as follows.
・ Device: Autopore IV 9500 manufactured by Shimadzu Corporation
・ Mercury injection pressure: 0.51 psia
・ Pressure holding time at each measurement pressure: 10s
・ Contact angle between sample and mercury: 140 °
・ Surface tension of mercury: 485 dynes / cm
・ Mercury density: 13.5335 g / mL

Furthermore, current collectors are used for the positive electrode and the negative electrode. The material of the current collector is not limited to aluminum, titanium, stainless steel, nickel, baked carbon, conductive polymer, conductive glass, etc. as the current collector for the positive electrode. For the purpose of improving, the surface of aluminum, copper or the like subjected to treatment with carbon, nickel, titanium, silver or the like can be used. Current collector for negative electrode includes copper, stainless steel, nickel, aluminum, titanium, baked carbon, conductive polymer, conductive glass, aluminum-cadmium alloy, etc., adhesiveness, conductivity, reduction resistance, etc. For the purpose of improving the surface, it is possible to use a surface of copper, aluminum or the like which has been treated with carbon, nickel, titanium, silver or the like. The thickness of the positive electrode current collector and the negative electrode current collector is preferably 1 μm to 50 μm independently from the viewpoint of electrode strength and energy density.

The non-aqueous electrolyte used in the lithium ion battery of this embodiment is composed of a lithium salt (electrolyte) and a non-aqueous solvent that dissolves the lithium salt (electrolyte). You may add an additive as needed. Among the additives, it is preferable to contain a fluorinated boric acid ester from the viewpoint of further extending the life.

As the fluorinated boric acid ester, for example, a compound represented by the following general formula (a) is preferable.

In the formula (a), R ¹ , R ² and R ³ are the same or different linear or branched alkyl groups having 1 to 10 carbon atoms, or linear or branched alkyl groups having 1 to 10 carbon atoms. Represents a fluorine alkyl group, and at least one of R ¹ , R ² and R ³ is a linear or branched fluorine-containing alkyl group having 1 to 10 carbon atoms.

The compound represented by the general formula (a) is a compound in which R ¹ , R ² and R ³ are the same or different linear or branched fluorine-containing alkyl groups having 1 to 10 carbon atoms. preferable.
The compound represented by the general formula (a) is, for example, tris (trifluoroethyl) borate, methyl bis (trifluoroethyl) borate, tris (tetrafluoroethyl) borate, tris (monofluoroethyl) borate, Tris borate (pentafluoropropyl), tris borate (hexafluoropropyl), tris borate (hexafluoroisopropyl), tris borate (2-methyl-1,1,1,3,3,3-hexafluoropropyl) ) And tris borate (2-phenyl-1,1,1,3,3,3-hexafluoropropyl). Among these, tris borate (hexafluoroisopropyl) is particularly preferable from the viewpoint of improving the cycle characteristics. These fluorinated boric acid esters may be used alone or in combination of two or more.

The content of the fluorinated boric acid ester is preferably 0.02% by mass to 10% by mass from the viewpoint of cycle characteristics and high temperature storage characteristics, based on the total amount of the nonaqueous electrolytic solution, It is more preferably from 5% by mass to 5% by mass, still more preferably from 0.05% by mass to 4% by mass, and particularly preferably from 0.1% by mass to 3% by mass.
Lithium salts include LiPF ₆ , LiBF ₄ , LiFSI (lithium bisfluorosulfonylimide), LiTFSI (lithium bistrifluoromethanesulfonylimide), LiClO ₄ , LiB (C ₆ H ₅ ) ₄ , LiCH ₃ SO ₃ , LiCF ₃ SO ₃ , LiN (SO ₂ F) ₂ , LiN (SO ₂ CF ₃ ) ₂ , 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, lithium hexafluorophosphate (LiPF ₆ ) is preferable when comprehensively judging the solubility in a non-aqueous solvent, charge / discharge characteristics in the case of a lithium ion battery, input / output characteristics, cycle characteristics, and the like.

The concentration of the lithium salt is preferably 0.5 mol / L to 1.5 mol / L, more preferably 0.7 mol / L to 1.3 mol / L, and more preferably 0.8 mol to the non-aqueous solvent. / L to 1.2 mol / L is more preferable. By setting the concentration of the lithium salt to 0.5 mol / L to 1.5 mol / L, the charge / discharge characteristics can be further improved.

Non-aqueous solvents include cyclic carbonates such as ethylene carbonate and propylene carbonate; chain monocarbonates such as dimethyl carbonate, diethyl carbonate and methyl ethyl carbonate, γ-butyrolactone, acetonitrile, 1,2-dimethoxyethane, dimethoxymethane, tetrahydrofuran, Examples include dioxolane, methylene chloride, and methyl acetate. These may be used alone or in combination of two or more, but it is preferable to use a mixed solvent in which a cyclic carbonate and a chain monocarbonate are mixed.
When the cyclic carbonate and the chain monocarbonate are contained, the content of the cyclic carbonate and the chain monocarbonate is preferably 80% by volume or more, and 90% by volume from the viewpoint of cycle characteristics with respect to the total amount of the non-aqueous solvent. More preferably, it is more preferably 95% by volume or more.

When the cyclic carbonate is contained, the content is preferably 5% by volume to 70% by volume, more preferably 10% by volume to 60% by volume, and more preferably 20% by volume to 20% by volume with respect to the total amount of the non-aqueous solvent. More preferably, it is 60 volume%.

When the chain monocarbonate is contained, the content is preferably more than 70% by volume with respect to the total amount of the non-aqueous solvent.
When the content of the chain monocarbonate with respect to the total amount of the non-aqueous solvent exceeds 70% by volume, the electrolyte solution penetrates into the separator and the electrode, and a large amount of the electrolyte solution can be injected, so that the cycle characteristics tend to improve. is there. The content of the chain monocarbonate with respect to the total amount of the non-aqueous solvent is more preferably 75% by volume or more, still more preferably 85% by volume or more, and particularly preferably 90% by volume or more. The content of the chain monocarbonate with respect to the total amount of the non-aqueous solvent may be 100% by volume, but it is preferably 95% by volume or less from the viewpoint of further improving safety.
The chain monocarbonate preferably contains dimethyl carbonate. When the chain monocarbonate contains dimethyl carbonate, the proportion of dimethyl carbonate in the chain monocarbonate is preferably 75% by volume to 100% by volume, and more preferably 85% by volume to 100% by volume. More preferably, it is 90 volume% to 100 volume%.

The additive is not particularly limited as long as it is an additive for a non-aqueous electrolyte solution of a lithium ion battery, and includes a heterocyclic compound containing nitrogen, a heterocyclic compound containing sulfur, and a heterocyclic compound containing nitrogen and sulfur. , Cyclic carboxylic acid ester, fluorine-containing cyclic carbonate, and other compounds having an unsaturated bond in the molecule. In addition to the above additives, other additives such as an overcharge prevention material, a negative electrode film forming material, a positive electrode protective material, and a high input / output material may be used depending on the required function.

The other additives mentioned above can improve storage characteristics at high temperatures, cycle characteristics, and input / output characteristics.

The lithium ion battery configured as described above can have various shapes such as a cylindrical shape, a laminated shape, a coin shape, and a laminated shape. Regardless of which shape is used, a separator is sandwiched 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 to the positive electrode terminal and the negative electrode terminal is used for current collection. Connection is made using a lead or the like, and this electrode body is sealed in a battery case together with a non-aqueous electrolyte to complete a lithium ion battery.
As an example of an embodiment of the present invention, a stacked lithium ion battery in which a positive electrode plate and a negative electrode plate are stacked via a separator will be described with reference to FIGS. 1 and 2, but the present invention is not limited thereto.

FIG. 1 is a perspective view showing one embodiment of the lithium ion battery of this embodiment.
The lithium ion battery 10 is one in which the electrode group 20 and an electrolytic solution are accommodated in the battery outer package of the laminate film 6, and the positive electrode current collecting tab 2 and the negative electrode current collecting tab 4 are taken out of the battery outer package.

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 separator 5, and a negative electrode plate 3 to which a negative electrode current collecting tab 4 is attached.
In addition, the magnitude | size, shape, etc. of a positive electrode plate, a negative electrode plate, a separator, an electrode group, and a battery can be made into arbitrary things, and are not necessarily limited to what is shown by FIG.1 and FIG.2.
Examples of the material for the battery outer package include an aluminum laminate film, aluminum, copper, and stainless steel.

As another embodiment of the present invention, for example, a cylindrical lithium in which an electrode group obtained by winding a laminated body in which a positive electrode plate and a negative electrode plate are laminated via a separator is enclosed in a cylindrical battery casing. An ion battery can be mentioned.
FIG. 3 is a cross-sectional view showing another embodiment of the lithium ion battery of this embodiment.
As shown in FIG. 3, the lithium ion battery 11 has a bottomed cylindrical battery outer package 16 made of steel plated with nickel. An electrode group 15 is accommodated in the battery outer package 16. In the electrode group 15, a belt-like positive electrode plate 12 and a negative electrode plate 13 are wound in a spiral cross section via a separator 14 made of a polyethylene porous sheet. For example, the separator 14 has a width of 58 mm and a thickness of 20 μm. A ribbon-shaped positive electrode tab terminal made of aluminum and having one end fixed to the positive electrode plate 12 is led out on the upper end surface of the electrode group 15. The other end of the positive electrode tab terminal is joined by ultrasonic welding to the lower surface of a disk-shaped battery lid that is disposed above the electrode group 15 and serves as a positive electrode external terminal. On the other hand, a ribbon-like negative electrode tab terminal made of nickel and having one end fixed to the negative electrode plate 13 is led to the lower end surface of the electrode group 15. The other end of the negative electrode tab terminal is joined to the inner bottom of the battery outer package 16 by resistance welding. Therefore, the positive electrode tab terminal and the negative electrode tab terminal are respectively led out to the opposite sides of the both end surfaces of the electrode group 15. Note that an insulating coating (not shown) is applied to the entire outer peripheral surface of the electrode group 15. The battery lid is caulked and fixed to the upper part of the battery outer package 16 via an insulating resin gasket. For this reason, the inside of the lithium ion battery 11 is sealed. In addition, an electrolyte solution (not shown) is injected into the battery outer package 16.
In addition, the magnitude | size, shape, etc. of a positive electrode plate, a negative electrode plate, a separator, an electrode group, and a battery can be made into arbitrary things, and are not necessarily limited to what is shown by FIG.

The ratio of the volume Y of the electrolyte solution to the volume X in the battery casing (Y / X) is 0.2 or more, and from the viewpoint of further extending the life, it is preferably 0.3 or more. More preferably, it is 0.4 or more. In the present embodiment, the volume of the electrolytic solution refers to the volume at 25 ° C.
Moreover, although there is no upper limit to the value of the ratio (Y / X), from a practical viewpoint, it is preferably 0.8 or less, and more preferably 0.7 or less.
The reason why the life can be extended when the value of the ratio (Y / X) is 0.2 or more is not clear, but is estimated as follows.

Spinel type lithium / nickel / manganese composite oxide generally has a high potential of 4.4V or higher with respect to Li. The electrolytic solution cannot exist stably in this potential range, and the decomposition reaction always proceeds at a minute rate. For this reason, if there is little amount of electrolyte solution, the influence by decomposition will appear at an early stage, and a battery will deteriorate. On the other hand, if the value of the ratio (Y / X) is 0.2 or more, it is presumed that there is a sufficient margin until the adverse effect of decomposition appears, and the necessary long life can be achieved.

(Capacity ratio of the negative electrode to the positive electrode of the lithium ion battery)
In the lithium ion battery of this embodiment using spinel type lithium / nickel / manganese composite oxide as the positive electrode active material, the capacity ratio (negative electrode capacity / positive electrode capacity) of the positive electrode and the negative electrode is 0.7 or more and less than 1. It is preferable. When the capacity ratio is 0.7 or more, the battery capacity is improved and a high energy density tends to be obtained. On the other hand, when the capacity ratio is less than 1, the decomposition reaction of the electrolytic solution due to the positive electrode being at a high potential hardly occurs, and the cycle characteristics of the lithium ion battery tend to be good. From the viewpoint of energy density and cycle characteristics, the capacity ratio is more preferably 0.75 to 0.95.

The “positive electrode capacity” and the “negative electrode capacity” can be used reversibly obtained when a constant-current-constant-voltage charge-constant-current discharge is performed by constituting an electrochemical cell having a counter electrode made of metallic lithium. Means maximum capacity. For example, when a spinel type lithium / nickel / manganese composite oxide is used for the positive electrode active material and LTO is used for the negative electrode active material, the “positive electrode capacity” and the “negative electrode capacity” Obtained when the voltage ranges are set to 4.95 V to 3.5 V and 2 V to 1 V, respectively, and the charge / discharge is evaluated with the current density during constant current charge and constant current discharge being 0.1 mA / cm ^2. Capacity.

As mentioned above, although the embodiment of the lithium ion battery of the present invention has been described, the above embodiment is only one embodiment, and the lithium ion battery of the present invention includes various embodiments based on the knowledge of those skilled in the art including the above embodiment. The present invention can be implemented in various forms with modifications and improvements.

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

[Examples 1 to 3, Comparative Example 1]
93 parts by mass of spinel-type lithium / nickel / manganese composite oxide (LiNi _0.5 Mn _1.5 O ₄ ), which is a positive electrode active material, and 5 parts by mass of acetylene black (manufactured by Denki Kagaku Kogyo Co., Ltd.) as a conductive material 2 parts by mass of a copolymer obtained by adding acrylic acid and a linear ether group to a polyacrylonitrile skeleton as a binder (trade name: LSR7, manufactured by Hitachi Chemical Co., Ltd.) and mixing an appropriate amount of N-methyl-2- By adding pyrrolidone and kneading, a paste-like positive electrode mixture slurry was obtained. This slurry was applied to one side of a 20 μm-thick aluminum foil, which is a positive electrode current collector, so as to be substantially uniformly and uniformly 140 g / m ² . Thereafter, drying treatment was performed, and consolidation was performed by pressing to a density of 2.3 g / cm ³ to produce a sheet-like positive electrode. This was cut into a width of 31 mm and a length of 46 mm to form a positive electrode plate, and a positive electrode current collecting tab was attached to the positive electrode plate as shown in FIG.

91 parts by mass of lithium titanium composite oxide (Li ₄ Ti ₅ O ₁₂ ), ₄ parts by mass of acetylene black (manufactured by Denki Kagaku Kogyo Co., Ltd.) as a conductive material, and 5 parts by mass of polyvinylidene fluoride as a binder Then, an appropriate amount of N-methyl-2-pyrrolidone was added and kneaded to obtain a paste-like negative electrode mixture slurry. This slurry was applied to one side of a 10 μm thick copper foil, which is a negative electrode current collector, at 85 g / m ² . Thereafter, a drying treatment was performed, and the sheet was consolidated by pressing to a density of 1.9 g / cm ³ to produce a sheet-like negative electrode. This was cut into a width of 30 mm and a length of 45 mm to form a negative electrode plate, and a negative electrode current collecting tab was attached to the negative electrode plate as shown in FIG.

(Production of electrode group)
The produced positive electrode plate and negative electrode plate are opposed to each other through a polyethylene microporous membrane (a polypropylene / polyethylene / polypropylene three-layer separator) having a thickness of 30 μm, a width of 35 mm, and a length of 50 mm as a separator. Groups were made. The porosity of the separator was 43%.

(Nonaqueous electrolyte adjustment)
Ethylene carbonate and dimethyl carbonate are mixed at a volume ratio of 1: 3, and then LiPF ₆ as an electrolyte is dissolved in a non-aqueous solvent so that the electrolyte concentration becomes 1.2 mol / L. Adjusted.
In Example 3, fluorine-containing boric acid ester (tris borate (hexafluoroisopropyl)) was added to the nonaqueous electrolytic solution as an electrolytic solution additive. The amount of tris borate (hexafluoroisopropyl) added was 0.5% by mass with respect to the total amount of the electrolyte (nonaqueous electrolyte + electrolyte additive).

(Production of lithium ion battery)
As shown in FIG. 1, the electrode group is housed in a battery exterior body made of an aluminum laminate film, and a nonaqueous electrolyte solution is injected into the battery exterior body at a ratio shown in Table 1 above. The positive electrode current collecting tab and the negative electrode current collecting tab were taken out to seal the opening of the battery outer package, thereby producing lithium ion batteries of Examples 1 to 3 and Comparative Example 1. The aluminum laminate film is a laminate of polyethylene terephthalate (PET) film / aluminum foil / sealant layer (polypropylene or the like). In addition, the amount of electrolyte solution described in Table 1 is a value at 25 ° C.

(Calculation of volume inside battery case)
After sealing, the width and length of the electrode group housing were measured. The thickness of the electrode group housing part was calculated by subtracting the thickness of the laminate film from the thickness of the produced lithium ion battery. Using the width, length, and thickness of the obtained electrode group housing part, the volume in the exterior body was calculated by the following formula.
Width of electrode group housing part (cm) × length of electrode group housing part (cm) × thickness of electrode group housing part (cm) = 3.2 × 4.7 × 0.216 = 3.2 (mL)

(High voltage cycle characteristics)
The lithium ion batteries of Examples 1 to 3 and Comparative Example 1 were charged with a charge / discharge device (trade name: BATTERY TEST UNIT, manufactured by IEM Co., Ltd.) at 25 ° C. with a current value of 0.2 C and a charge end voltage of 3.4 V. Then, constant current charging was performed at a charging voltage of 3.4 V until the current value reached 0.01C. C used as a unit of current value means “current value (A) / battery capacity (Ah)”. After resting for 15 minutes, constant current discharge was performed at a current value of 0.2 C and a discharge end voltage of 1.5 V. Charging / discharging is repeated three times under the above-mentioned charging / discharging conditions, followed by constant current charging at a current value of 1 C and a charge end voltage of 3.8 V at 50 ° C., and then until the current value becomes 0.01 C at a charging voltage of 3.8 V Constant voltage charging was performed, and after resting for 15 minutes, constant current discharging was performed at a current value of 1 C and a discharge end voltage of 2.0 V. The discharge capacity at this time was defined as the initial discharge capacity, and the discharge capacity when this operation was repeated 200 times was measured (discharge capacity after 200 cycles). And the deterioration rate after 200 cycles was computed from the following formula | equation.
High voltage cycle characteristics (%) = (discharge capacity after 200 cycles / initial discharge capacity) × 100

[Reference Examples 1 to 3]
Layered type lithium / nickel / manganese / cobalt composite oxide (NMC) and spinel type lithium / manganese composite oxide (sp-Mn) as a positive electrode active material at a mass ratio of 3/7 (NMC / sp-Mn) By mixing, a positive electrode active material mixture was obtained. 90 parts by mass of the positive electrode active material mixture, 5 parts by mass of acetylene black (manufactured by Denki Kagaku Kogyo Co., Ltd.) as a conductive material, and 5 parts by mass of polyvinylidene fluoride as a binder are mixed to obtain an appropriate amount of N-methyl-2- By adding pyrrolidone and kneading, a paste-like positive electrode mixture slurry was obtained. This slurry was applied to one side of a 20 μm-thick aluminum foil, which is a positive electrode current collector, so as to be substantially 195 g / m ² substantially uniformly and uniformly. Thereafter, drying treatment was performed, and consolidation was performed by pressing to a density of 2.55 g / cm ³ to produce a sheet-like positive electrode. This was cut into a width of 31 mm and a length of 46 mm to form a positive electrode plate, and a positive electrode current collecting tab was attached to the positive electrode plate as shown in FIG.

The negative electrode, electrode group, non-aqueous electrolyte, and lithium ion battery were produced in the same manner as in Examples 1 to 3 and Comparative Example 1.

(Cycle characteristics)
The lithium ion batteries of Reference Examples 1 to 3 were charged at a constant current at a current value of 0.2 C and a charge end voltage of 3.1 V at 25 ° C. using a charge / discharge device (trade name: BATTERY TEST UNIT, manufactured by IEM Co., Ltd.). Then, constant voltage charging was performed at a charging voltage of 3.1 V until the current value reached 0.01C. After resting for 15 minutes, constant current discharge was performed at a current value of 0.2 C and a discharge end voltage of 1.5 V. Charging / discharging is repeated three times under the above charging / discharging conditions, followed by constant current charging at 50 ° C. with a current value of 1 C and a charge end voltage of 3.1 V, and then at a charging voltage of 3.1 V until the current value reaches 0.01 C. Constant voltage charge was performed, and after a 15-minute pause, constant current discharge was performed at a current value of 1 C and a discharge end voltage of 1.5 V. The discharge capacity at this time was defined as the initial discharge capacity, and the discharge capacity when this operation was repeated 200 times was measured (discharge capacity after 200 cycles). And the deterioration rate after 200 cycles was computed from the following formula | equation.
Cycle characteristics (%) = (discharge capacity after 200 cycles / initial discharge capacity) × 100

Examples 1 to 3, Comparative Example 1 and Reference Examples 1 to 3 are stacked lithium ion batteries.
Table 1 shows the measurement results. (A) in the table shows a spinel type lithium / nickel / manganese composite oxide, and (b) shows a mixture of a layered type lithium / nickel / manganese / cobalt composite oxide and a spinel type lithium / manganese composite oxide. .

Example in which the positive electrode active material is a spinel type lithium / nickel / manganese composite oxide, and the ratio of the volume Y of the electrolyte to the volume X in the battery casing (Y / X) is 0.2 or more. In 1 to 3, it was confirmed that the high voltage cycle characteristics were excellent as compared with Comparative Example 1.
Moreover, in Example 3 containing a fluorine-containing borate ester, it has confirmed that it was excellent in the high voltage cycle characteristic compared with Example 2 which does not contain.
When a mixture of layered lithium / nickel / manganese / cobalt composite oxide and spinel type lithium / manganese composite oxide is used for the positive electrode (Reference Examples 1 to 3), the electrolyte accounts for the volume X in the battery casing. It was confirmed that the cycle characteristics were excellent regardless of the volume Y ratio. This indicates that when the spinel type lithium / nickel / manganese composite oxide is included as the positive electrode active material, the cycle characteristic is improved by setting the ratio (Y / X) to 0.2 or more.

[Examples 4 to 7, Comparative Example 2]
The positive electrode and negative electrode used in Example 1 were each cut into a predetermined size, and the cut positive electrode and negative electrode were sandwiched between 20 μm thick polyethylene microporous membranes (polypropylene / polyethylene / polypropylene three-layer separator). Was wound and wound to produce a roll-shaped electrode group. The positive electrode length was 370 cm, the negative electrode length was 380 cm, and the separator length was 830 cm. The positive electrode width was 6.4 cm, the negative electrode width was 6.8 cm, and the separator width was 7.4 cm. The porosity of the separator was 43%.
A current collecting lead was attached to this electrode group, the electrode group was inserted into the battery outer package, and then a non-aqueous electrolyte was injected into the battery outer package at a rate shown in Table 2. As the non-aqueous electrolyte, a solution obtained by dissolving LiPF ₆ as an electrolyte at a concentration of 2.0 mol / L in a non-aqueous solvent in which ethylene carbonate and dimethyl carbonate are mixed at a volume ratio of 1: 3 is used. It was. Finally, the battery case was sealed to complete the lithium ion batteries of Examples 4 to 7 and Comparative Example 2. In addition, the amount of electrolyte solution described in Table 2 is a value at 25 ° C.
In Example 6, a fluorinated boric acid ester (tris borate (hexafluoroisopropyl)) was added to the nonaqueous electrolytic solution as an electrolytic solution additive. The amount of tris borate (hexafluoroisopropyl) added was 1.0% by mass with respect to the total amount of the electrolyte (nonaqueous electrolyte + electrolyte additive).

[Reference Examples 4 and 5]
The lithium ion batteries of Reference Examples 4 and 5 were completed in the same manner as in Example 4 except that the positive electrode and the negative electrode used in Reference Example 1 were used.

(Calculation of the volume in the exterior body)
The inner diameter and height of the electrode group housing part in the battery outer package were measured. The height of the electrode group housing portion was calculated by subtracting the height of the battery bottom and the height of the battery lid from the height of the battery outer package. Using the radius and height of the inner diameter of the obtained electrode group housing part, the volume in the battery outer package was calculated by the following formula.
Radius of inner diameter of electrode group housing part (cm) x Radius of inner diameter of electrode group housing part (cm) x Circumference ratio x Height of electrode group housing part (cm) = 2.1 x 2.1 x 3.14 × 8 = 111 (mL)

The cycle characteristics of the lithium ion batteries of Examples 4 to 7 and Comparative Example 2 were evaluated under the same conditions as in Examples 1 to 3 and Comparative Example 1. The cycle characteristics of the lithium ion batteries of Reference Examples 4 and 5 were evaluated under the same conditions as in Reference Examples 1 to 3. Table 2 shows the measurement results. (A) in the table shows a spinel type lithium / nickel / manganese composite oxide, and (b) shows a mixture of a layered type lithium / nickel / manganese / cobalt composite oxide and a spinel type lithium / manganese composite oxide. .
Examples 4 to 7, Comparative Example 2, and Reference Examples 4 and 5 are cylindrical lithium ion batteries.

Example in which the positive electrode active material is a spinel type lithium / nickel / manganese composite oxide, and the ratio of the volume Y occupied by the electrolyte to the volume X in the battery casing (Y / X value) is 0.2 or more. 4 to 7, it was confirmed that the high voltage cycle characteristics were superior to those of Comparative Example 2.
Moreover, in Example 6 containing a fluorine-containing boric acid ester, it has confirmed that it was excellent in the high voltage cycle characteristic compared with Example 4 which does not contain.
When a mixture of layered lithium-nickel-manganese-cobalt composite oxide and spinel-type lithium-manganese composite oxide is used for the positive electrode (Reference Examples 4 and 5), the electrolyte accounts for the volume X in the battery casing. It was confirmed that the cycle characteristics were excellent regardless of the volume Y ratio. This indicates that when the spinel type lithium / nickel / manganese composite oxide is included as the positive electrode active material, the cycle characteristic is improved by setting the ratio (Y / X) to 0.2 or more.

All documents, patent applications, and technical standards mentioned in this specification are to the same extent as if each individual document, patent application, and technical standard were specifically and individually stated to be incorporated by reference, Incorporated herein by reference.

Claims

A positive electrode including a spinel-type lithium / nickel / manganese composite oxide as a positive electrode active material; a negative electrode including a negative electrode active material capable of occluding lithium ions; a separator that insulates the positive electrode from the negative electrode; In the battery case,
A lithium ion battery in which a ratio (Y / X) of a volume Y occupied by the electrolytic solution to a volume X in the battery outer body is 0.2 or more.
2. The lithium ion battery according to claim 1, wherein the electrolytic solution contains a non-aqueous solvent and a lithium salt, and a content of chain monocarbonate in a total amount of the non-aqueous solvent exceeds 70% by volume.
The lithium ion battery according to claim 2, wherein the chain monocarbonate contains dimethyl carbonate.
The lithium ion battery according to any one of claims 1 to 3, wherein the electrolytic solution contains a fluorine-containing borate ester.
The lithium ion battery according to any one of claims 1 to 4, wherein the ratio (Y / X) is 0.8 or less.
The lithium ion battery according to any one of claims 1 to 5, wherein the separator has a porosity of 20% or more.
The lithium ion battery according to any one of claims 1 to 6, wherein the negative electrode active material capable of occluding lithium ions contains a lithium titanium composite oxide.
The spinel type lithium-nickel-manganese composite oxide contains a compound represented by LiNi X Mn 2-X O 4 (0.3 <X <0.7). The lithium ion battery according to claim 1.