JP2017188404A - Lithium ion secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lithium ion secondary battery which is superior in output characteristic, and which enables the suppression of the reduction in capacity-keeping rate after charge and discharge cycles at a high voltage (e.g. a charging voltage of 4.4 V).SOLUTION: A lithium ion secondary battery comprises: a positive electrode; a negative electrode; and an electrolyte solution containing a fluorine-containing lithium salt electrolyte. The positive electrode has a current collector, and a positive electrode mixture layer formed on the current collector. The positive electrode mixture layer includes a carbon-coated aluminum silicate compound including an aluminum silicate compound with its surface partially or totally coated with carbon. In the carbon-coated aluminum silicate compound, the element mole ratio Si/Al of silicon (Si) and aluminum (Al) is 0.3-5.0.SELECTED DRAWING: None

Description

  The present invention relates to a lithium ion secondary battery.

  A lithium ion secondary battery is a high energy density secondary battery, and is used as a power source for portable devices such as notebook PCs (Personal Computers) and mobile phones by taking advantage of its characteristics. In recent years, with higher functionality of portable information terminals such as smartphones and tablet PCs, further increase in capacity of lithium ion secondary batteries has been demanded. As means for achieving a higher capacity of the lithium ion secondary battery, it is conceivable to increase the capacity of the electrode active material, improve the energy density, increase the voltage of the battery, and the like. However, when the voltage of the battery is increased, the reaction between the constituent materials inside the battery is promoted, and there is a problem that the capacity reduction of the lithium ion secondary battery after the charge / discharge cycle is large.

  Conventionally, as a method for suppressing a decrease in capacity of a lithium ion secondary battery after a charge / discharge cycle, (1) a fluorine-containing lithium salt electrolyte and a specific phosphonoacetate compound are used as an electrolyte, and zirconium is used as a positive electrode active material. (For example, refer to Patent Document 1), (2) a method using a fluorinated cyclic carbonate and a fluorinated chain ester as an electrolytic solution (for example, refer to Patent Document 2), ( 3) A method of fixing a rare earth compound to a part of the surface of lithium cobaltate which is a positive electrode active material (for example, see Patent Document 3) has been proposed.

JP 2014-127256 A JP 2014-110122 A JP 2013-179095 A

However, it has been clarified by the present inventors that the method described in the above-mentioned document is difficult to sufficiently suppress a decrease in capacity after a charge / discharge cycle at a high voltage. This is because the water contained in the lithium ion secondary battery is caused by hydrogen fluoride (HF) generated when it reacts with a fluorine-containing lithium salt electrolyte such as lithium hexafluorophosphate (LiPF ₆ ). It is conceivable that the metal ions are eluted from the metal, and the eluted metal ions are reprecipitated at the negative electrode or the like, whereby the capacity is reduced.

  The present invention has been made in view of the above circumstances, and provides a lithium ion secondary battery that has excellent output characteristics and suppresses a decrease in capacity after a charge / discharge cycle at a high voltage (for example, a charge voltage of 4.4 V). The issue is to provide.

Specific means for solving the above problems include the following embodiments.
<1> A positive electrode, a negative electrode, and an electrolyte solution containing a fluorine-containing lithium salt electrolyte,
The positive electrode has a current collector and a positive electrode mixture layer formed on the current collector, and the positive electrode mixture layer is partially or entirely covered with carbon of the surface of the aluminum silicate compound. Carbon coated aluminum silicate compound,
The lithium ion secondary battery whose element molar ratio Si / Al of silicon (Si) of the said carbon covering aluminum silicate compound and aluminum (Al) is 0.3-5.0.

<2> The lithium ion secondary battery according to <1>, wherein an element molar ratio Si / Al of the carbon-coated aluminum silicate compound is 1.0 to 2.5.

<3> The content of the carbon-coated aluminum silicate compound is 0.1% by mass to 5% by mass with respect to the total amount of the positive electrode mixture layer. Next battery.

<4> The lithium ion secondary battery according to any one of <1> to <3>, wherein the aluminum silicate compound is an amorphous aluminum silicate compound.

<5> The lithium ion secondary battery according to any one of <1> to <4>, wherein the fluorine-containing lithium salt electrolyte includes lithium hexafluorophosphate (LiPF ₆ ).

  ADVANTAGE OF THE INVENTION According to this invention, the lithium ion secondary battery which was excellent in output characteristics and suppressed the capacity | capacitance fall after the charging / discharging cycle by a high voltage (for example, charging voltage 4.4V) can be provided.

It is a perspective sectional view showing an example of a lithium ion secondary battery of this embodiment.

  Hereinafter, embodiments 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 numerical values and ranges thereof, and the present invention is not limited thereto.

In the present specification, the numerical ranges indicated by using “to” include numerical values described before and after “to” as the minimum value and the maximum value, respectively. The numerical value range indicated as “A or more” or “A or less” includes A as a minimum value or a maximum value.
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 the present specification, the content of each component means the total content of the plurality of types of substances when there are a plurality of types of substances corresponding to the respective components, unless otherwise specified.
In the present specification, the particle size 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 this specification, the term “cover” includes not only the case where the entire region is covered but also a case where only a part of the region is covered when the region to be covered is observed. .
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.

<Lithium ion secondary battery>
The lithium ion secondary battery of the present embodiment includes a positive electrode, a negative electrode, and an electrolyte solution containing a fluorine-containing lithium salt electrolyte, and the positive electrode is formed on the current collector and the current collector. And the positive electrode mixture layer includes a carbon-coated aluminum silicate compound in which a part or all of the surface of the aluminum silicate compound is coated with carbon, and the silicon (Si) of the carbon-coated aluminum silicate compound. The element molar ratio Si / Al between aluminum and aluminum (Al) is 0.3 to 5.0. A separator is disposed between the positive electrode and the negative electrode. Hereinafter, an aluminum silicate compound having an element molar ratio Si / Al of 0.3 to 5.0 is also referred to as a “specific aluminum silicate compound”, and a part or all of the surface of the specific aluminum silicate compound is coated with carbon. The carbon-coated aluminum silicate compound is also referred to as “carbon-coated specific aluminum silicate compound”.

  The lithium ion secondary battery according to the present embodiment has excellent output characteristics due to the above configuration, and suppresses a decrease in capacity after a charge / discharge cycle at a high voltage (for example, a charging voltage of 4.4 V). The reason is not clear, but can be considered as follows, for example.

  In the lithium ion secondary battery, hydrogen fluoride (HF) can be generated by a reaction between water inevitably mixed with the fluorine-containing lithium salt electrolyte. This hydrogen fluoride (HF) elutes metal ions such as cobalt ions from the positive electrode active material, and the eluted metal ions are reprecipitated at the negative electrode and the like, causing a decrease in capacity.

Therefore, in the lithium ion secondary battery of this embodiment, the carbon-coated specific aluminum silicate compound is included in the positive electrode mixture layer. The carbon-coated specific aluminum silicate compound contained in the positive electrode mixture layer of the lithium ion secondary battery has the ability to adsorb hydrogen fluoride (HF) and metal ions, and other than lithium ions, such as cobalt ions It is easy to adsorb metal ions. Thereby, it is thought that the capacity | capacitance fall after the charging / discharging cycle by a high voltage is suppressed. Moreover, the carbon-coated specific aluminum silicate compound obtained by coating the specific aluminum silicate compound with carbon is considered to improve the output characteristics of the lithium ion secondary battery because of its high conductivity. The effect of improving the output characteristics by the carbon-coated specific aluminum silicate compound is particularly remarkable when lithium hexafluorophosphate (LiPF ₆ ) is used among the fluorine-containing lithium salt electrolytes.

  When charging the lithium ion secondary battery, a charger is connected between the positive electrode and the negative electrode. At the time of charging, lithium ions inserted into the positive electrode active material are desorbed and released into the electrolytic solution. The lithium ions released into the electrolytic solution move through the electrolytic solution, pass through the separator, and reach the negative electrode. The lithium ions that have reached the negative electrode are inserted into the negative electrode active material constituting the negative electrode.

  When discharging the lithium ion secondary battery, an external load is connected between the positive electrode and the negative electrode. At the time of discharging, the lithium ions inserted into the negative electrode active material are desorbed and released into the electrolytic solution. At this time, electrons are emitted from the negative electrode. The lithium ions released into the electrolytic solution move in the electrolytic solution, pass through the separator, and reach the positive electrode. The lithium ions that have reached the positive electrode are inserted into the positive electrode active material constituting the positive electrode. At this time, lithium ions are inserted into the positive electrode active material, whereby electrons flow into the positive electrode. In this way, discharge is performed by the movement of electrons from the negative electrode to the positive electrode.

  In this manner, charging and discharging are performed by inserting and desorbing lithium ions between the positive electrode active material and the negative electrode active material. A configuration example of an actual lithium ion secondary battery will be described later (for example, see FIG. 1).

  Hereinafter, the positive electrode, the negative electrode, the electrolytic solution, the separator, and other components of the lithium ion secondary battery will be described.

1. Positive electrode The positive electrode (positive electrode plate) has a current collector and a positive electrode mixture layer formed on the current collector. The positive electrode mixture layer is a layer that is provided on the current collector and includes a positive electrode active material that can electrochemically occlude and release lithium ions, and a carbon-coated specific aluminum silicate compound. The positive electrode mixture layer may be formed on one side of the current collector or on both sides. The positive electrode mixture layer may include a conductive material, a binder, a thickener, and the like as necessary.

(Positive electrode active material)
Examples of the positive electrode active material include lithium-containing composite metal oxides, olivine-type lithium salts, chalcogen compounds, manganese dioxide, and the like, and preferably include lithium-containing composite metal oxides. A positive electrode active material may be used individually by 1 type, and may use 2 or more types together.

  The lithium-containing composite metal oxide is a metal oxide containing lithium and a transition metal, or a metal oxide in which a part of a transition metal in a metal oxide containing lithium and a transition metal is substituted with a different element. Examples of the different elements include Na, Mg, Sc, Y, Mn, Fe, Co, Ni, Cu, Zn, Al, Cr, Pb, Sb, and B. Mn, Al, Co, Ni, and Mg include preferable. The heterogeneous element contained in the lithium-containing composite metal oxide may be one type or two or more types.

Examples of the lithium-containing composite metal oxide include Li _x CoO ₂ , Li _x NiO ₂ , Li _x Co _y Ni _1-y O ₂ , Li _x Co _y M ¹ _1-y O _z (wherein M ¹ is Na And at least one element selected from the group consisting of Mg, Sc, Y, Mn, Fe, Ni, Cu, Zn, Al, Cr, Pb, Sb, V, and B.), Li _x Ni _{1 -y} M ² _y O _z (wherein, ^{M 2} is selected, Na, Mg, Sc, Y , Mn, Fe, Co, Cu, Zn, Al, Cr, Pb, Sb, V, and from the group consisting of B At least one element selected from the group consisting of LiM ³ PO ₄ , Li ₂ M ³ PO ₄ F (wherein M ³ is Na, Mg, Sc, Y, Mn, Fe, Co, Ni, Cu) , Zn, Al, Cr, Pb, Sb, V, and B selected from the group consisting of Kutomo shows the one element.), And the like. Here, in each formula, x is 0 <x ≦ 1.2, y is 0 ≦ y ≦ 0.9, and z is 2.0 ≦ z ≦ 2.3. The value of x indicating the molar ratio of lithium is increased or decreased by charging and discharging.

Examples of the olivine type lithium salt include LiFePO ₄ .
Examples of the chalcogen compound include titanium disulfide and molybdenum disulfide.

  When the positive electrode active material is in the form of particles, examples of the shape include a lump shape, a polyhedron shape, a spherical shape, an elliptical spherical shape, a plate shape, a needle shape, and a column shape. The positive electrode active material is preferably in a state of secondary particles that are aggregates of primary particles, and the shape of the secondary particles is more preferably spherical or elliptical.

  In an electrochemical element such as a battery, the electrode active material expands and contracts as it is charged and discharged, and therefore, degradation such as destruction of the electrode active material and disconnection of the conductive path is likely to occur due to the stress. Therefore, rather than using a positive electrode active material that exists as primary particles, it is preferable to use a material in which primary particles agglomerate to form secondary particles to relieve the stress of expansion and contraction. Tend to prevent. In addition, using spherical or oval spherical secondary particles rather than plate-like secondary particles with axial orientation tends to reduce the expansion and shrinkage of the electrode during charge and discharge because orientation in the electrode is reduced. is there. Further, when preparing the positive electrode mixture, other materials such as a conductive material tend to be easily mixed uniformly.

  The volume average particle diameter (D50) of the positive electrode active material (the volume average particle diameter (D50) of the secondary particles when the primary particles are aggregated to form secondary particles) is a viewpoint for obtaining a desired tap density. Therefore, for example, it is preferably 0.1 μm or more, more preferably 0.5 μm or more, further preferably 1 μm or more, and particularly preferably 3 μm or more. Moreover, the volume average particle diameter (D50) of the positive electrode active material is, for example, preferably 20 μm or less, more preferably 18 μm or less, and more preferably 16 μm or less, from the viewpoint of further improving the electrode formability and battery performance. More preferably, it is more preferably 15 μm or less. Here, as the positive electrode active material, the tap density (fillability) can be improved by mixing two or more kinds having different volume average particle diameters (D50).

  In addition, the volume average particle diameter (D50) of a positive electrode active material can be calculated | required from the particle size distribution calculated | required by the laser diffraction scattering method. For the laser diffraction / scattering method, a laser diffraction type particle size distribution measuring apparatus (for example, Shimadzu Corporation, SALD3000J) can be used. Specifically, particles of the positive electrode active material are dispersed in a dispersion medium such as water to prepare a dispersion. For this dispersion, when a volume cumulative distribution curve is drawn from the small diameter side using a laser diffraction type particle size distribution measuring device, the particle size (D50) of 50% cumulative is determined as the volume average particle size.

  When the primary particles are aggregated to form secondary particles, the average particle size of the primary particles is preferably 0.01 μm or more, for example, from the viewpoint of obtaining good charge / discharge reversibility, The thickness is more preferably 0.05 μm or more, further preferably 0.08 μm or more, and particularly preferably 0.1 μm or more. The average particle size of the primary particles is, for example, preferably 3 μm or less, more preferably 2 μm or less, and even more preferably 1 μm or less, from the viewpoint of further improving battery performance such as output characteristics. , 0.6 μm or less is particularly preferable. The average particle size of the primary particles can be obtained as an arithmetic average value by measuring the particle size of the primary particles for all of the particle images in the image taken at 200,000 times with a scanning electron microscope (SEM). .

From the viewpoint of further improving battery performance, the BET specific surface area of the positive electrode active material is, for example, preferably 0.1 m ² / g or more, more preferably 0.2 m ² / g or more, and 0.3 m. More preferably, it is ² / g or more. Further, the BET specific surface area of the positive electrode active material is preferably 4.0 m ² / g or less, more preferably 2.5 m ² / g or less, from the viewpoint of further improving the electrode formability. More preferably, it is 5 m ² / g or less.

The BET specific surface area of the positive electrode active material is measured from the nitrogen adsorption ability at 77K according to JIS Z 8830: 2001. As an evaluation apparatus, a nitrogen adsorption measuring apparatus (for example, QUANTACHROME, AUTOSORB-1) or the like can be used.
When measuring the BET specific surface area, it is considered that the moisture adsorbed on the sample surface and the structure affects the gas adsorption capacity. Therefore, pretreatment for removing moisture by heating is first performed. 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 performing this pretreatment, the evaluation temperature is 77K, and the evaluation pressure range is measured as a relative pressure (equilibrium pressure with respect to saturated vapor pressure) of less than 1.

(Carbon-coated specific aluminum silicate compound)
The carbon-coated specific aluminum silicate compound has a structure in which part or all of the surface of the specific aluminum silicate compound is coated with carbon.

  The element molar ratio Si / Al of the carbon-coated specific aluminum silicate compound is 0.3 to 5.0, preferably 0.5 to 4.0, and preferably 1.5 to 3.0. More preferred. When the element molar ratio is in the above range, the adsorption ability of hydrogen fluoride (HF) and metal ions is excellent, and the cycle characteristics tend to be improved.

In addition, the element molar ratio Si / Al of the carbon-coated specific aluminum silicate compound is analyzed by an ordinary method using an inductively coupled plasma (ICP) emission spectroscopic analyzer (for example, Hitachi, Ltd., P-4010). It can be determined by doing.
Moreover, after preparation of a positive electrode, the element molar ratio Si / Al of a carbon covering specific aluminum silicate compound can be calculated | required by the method as described in the Example mentioned later.

Specific aluminum silicate compounds include, for example, allophane, kaolin, zeolite, saponite and imogolite, which are aluminum silicates, and amorphous aluminum silicate compounds. Among these, an amorphous aluminum silicate compound whose specific surface area can be easily adjusted for improving cycle characteristics is preferable. Such amorphous aluminum silicate compounds, for _example, those having a composition represented by _{nSiO 2 · Al 2 O 3 ·} mH 2 O [n = 0.6~10.0, m = 0 or higher] .

Amorphous aluminum silicate has a broad peak in the vicinity of 2θ = 10 ° to 30 ° in the powder X-ray diffraction spectrum using CuKα ray as an X-ray source, without showing a peak showing a mullite structure. As the X-ray diffraction apparatus, for example, Geigerflex RAD-2X manufactured by Rigaku Corporation can be used. Specific measurement conditions are as follows.
-Measurement conditions-
Divergence slit: 1 °
Scattering slit: 1 °
Receiving slit: 0.30mm
X-ray output: 40 kV, 40 mA

The specific aluminum silicate compound may be synthesized, or a commercially available product may be purchased and used.
Examples of the method for synthesizing a specific aluminum silicate compound include a step of mixing a solution containing silicate ions and a solution containing aluminum ions to obtain a reaction product, and the reaction product in an aqueous medium in the presence of an acid. And a heat treatment step. The above synthesis method may have other steps as necessary.

  From the viewpoint of the yield of the specific aluminum silicate compound to be obtained, structure formation, etc., at least after the heat treatment step, preferably, before and after the heat treatment step, a step of performing desalting and solid separation is included. preferable. After desalting the coexisting ions from the solution containing the specific aluminum silicate compound, which is a reaction product, heat treatment is performed in the presence of an acid, so that the specific aluminum silica having excellent adsorption ability for hydrogen fluoride (HF) and metal ions is obtained. An acid compound can be produced efficiently. This is considered to be because a specific aluminum silicate compound having a regular structure can be obtained by heat-treating the reaction product from which coexisting ions that inhibit the formation of the regular structure are removed in the presence of an acid. . Examples of the coexisting ions include sodium ions, chloride ions, perchlorate ions, nitrate ions, sulfate ions, and the like.

  The carbon-coated specific aluminum silicate compound is obtained by coating a part or all of the surface of the specific aluminum silicate compound with carbon.

  The method for coating the surface of the specific aluminum silicate compound with carbon is not particularly limited. For example, there is a method in which an organic compound (carbon precursor) that changes to carbon by heat treatment is attached to a specific aluminum silicate compound, and heat treatment is performed on the compound to change the organic compound to carbon. As a method of attaching an organic compound to a specific aluminum silicate compound, the particulate specific aluminum silicate compound as a nucleus is added to a mixed solution in which the organic compound is dissolved or dispersed in a solvent, and then the solvent is removed by heating or the like. Wet method to perform; Dry method to mix and coat the mixture obtained by mixing particulate specific aluminum silicate compound and solid organic compound while applying shear force; CVD (Chemical Vapor Deposition) etc. Phase method; and the like. From the viewpoint of reducing the production cost and the production process, a dry method and a gas phase method without using a solvent are preferable.

  It does not restrict | limit especially as an organic compound (carbon precursor) which changes to carbonaceous material by heat processing. Examples of organic compounds include ethylene heavy end pitch, crude oil pitch, coal tar pitch, asphalt cracking pitch, pitch generated by thermal decomposition of polyvinyl chloride, synthetic pitch produced by polymerizing naphthalene, etc. in the presence of a super strong acid, etc. Pitch; thermoplastic resins such as polyvinyl chloride, polyvinyl alcohol, polyvinyl acetate, and polyvinyl butyral; thermosetting resins such as phenol resin and furan resin; and the like. These organic compounds may be used individually by 1 type, and may use 2 or more types together.

  The conditions for heat-treating the specific aluminum silicate compound having the organic compound attached to the surface may be appropriately determined in consideration of the carbonization rate of the organic compound, and are not particularly limited. For example, the heat treatment temperature is preferably 800 ° C. to 1300 ° C. When the heat treatment temperature is 800 ° C. or higher, the firing of the organic matter proceeds sufficiently, and the first increase in irreversible capacity due to the specific surface area being too high tends to be suppressed. Further, when the heat treatment temperature is 1300 ° C. or lower, the specific surface area is too low and the resistance is likely to be suppressed from increasing. The heat treatment is preferably performed in an inert atmosphere. Examples of the inert atmosphere include nitrogen, argon, helium, and combinations thereof.

The BET specific surface area of the carbon-coated specific aluminum silicate compound is, for example, preferably 80 m ² / g or less, more preferably 40 m ² / g or less from the viewpoint of further improving cycle characteristics and storage characteristics, More preferably, it is 20 m ² / g or less. Further, the BET specific surface area of the carbon-coated specific aluminum silicate compound is preferably 1 m ² / g or more from the viewpoint of further improving the adsorption ability of hydrogen fluoride (HF) and metal ions, and is 2 m ² / g or more. It is more preferable that it is 3 m ² / g or more.
Similar to the BET specific surface area of the positive electrode active material, the BET specific surface area of the carbon-coated specific aluminum silicate compound is measured from the nitrogen adsorption ability at 77 K in accordance with JIS Z 8830: 2001.

  The carbon-coated aluminum silicate compound uses a differential thermal-thermogravimetric analyzer (TG-DTA) (for example, Hitachi High-Tech Science Corporation, TG-DTA-6200) from the viewpoint of further improving battery capacity and cycle characteristics. The weight loss rate (D1) measured in the range of 25 ° C. to 350 ° C. is, for example, preferably less than 5%, more preferably less than 4%, and still more preferably less than 3%. . The weight reduction rate (D1) is preferably 0.01% or more, for example, from a practical viewpoint.

  In addition, the carbon-coated aluminum silicate compound is a differential thermal-thermogravimetric analyzer (TG-DTA) (for example, Hitachi High-Tech Science Co., Ltd., TG-DTA-6200) from the viewpoint of further improving input / output characteristics and cycle characteristics. The weight loss rate (D2) measured in the range of 350 ° C. to 850 ° C. is, for example, preferably 0.5% to 30%, more preferably 2% to 25%, More preferably, it is 5% to 20%. When the weight reduction rate (D2) is within the above range, an increase in resistance due to the reaction between the carbon-coated aluminum silicate compound and the electrolytic solution tends to be further suppressed, and hydrogen fluoride (HF), There is a tendency that the adsorption capacity of metal ions and the like is further improved.

The weight reduction rate (D1) can be measured by raising the temperature from 25 ° C. to 350 ° C. at a rate of temperature increase of 10 ° C./min under a flow of dry air. The weight reduction rate (D1) is a value obtained by the following equation (1). In the formula, W0 is the mass at 25 ° C., and W1 is the mass at 350 ° C.
D1 (%) = {(W0−W1) / W0} × 100 (1)

The weight reduction rate (D2) can be measured from the mass when the temperature is raised from 350 ° C. to 850 ° C. and kept at 850 ° C. for 20 minutes at a rate of temperature rise of 10 ° C./min under a flow of dry air. The weight reduction rate (D2) is a value obtained by the following equation (2). W1 in the formula is the mass at 350 ° C., and W2 is the mass at 850 ° C.
D2 (%) = {(W1-W2) / W1} × 100 (2)

The volume average particle diameter (D50) of the carbon-coated aluminum silicate compound is not particularly limited, and can be selected according to the final desired size. The volume average particle diameter (D50) of the carbon-coated aluminum silicate compound is, for example, preferably 0.1 μm to 50 μm, and more preferably 0.5 μm to 10 μm. When the volume average particle size (D50) of the carbon-coated aluminum silicate compound is 0.1 μm or more, an increase in the viscosity of the slurry when forming the positive electrode mixture layer is suppressed, and workability tends to be maintained favorably. It is in. Further, when the volume average particle size (D50) of the carbon-coated aluminum silicate compound is 50 μm or less, the generation of streaks when forming the positive electrode mixture layer tends to be suppressed. The volume average particle diameter (D50) of the carbon-coated aluminum silicate compound is preferably 8 μm or less, and preferably 5 μm or less from the viewpoint of further improving the adsorption ability of hydrogen fluoride (HF), metal ions, and the like. Is more preferable.
The volume average particle diameter (D50) of the carbon-coated aluminum silicate compound can be determined from the particle size distribution determined by the laser diffraction scattering method, similarly to the volume average particle diameter (D50) of the positive electrode active material.

(Conductive material)
The positive electrode mixture layer preferably contains a conductive material from the viewpoint of further improving battery performance. Examples of the conductive material include graphite such as natural graphite, artificial graphite, and fibrous graphite, and carbon black such as acetylene black. The conductive material preferably contains carbon black, and more preferably contains acetylene black. A conductive material may be used individually by 1 type, and may use 2 or more types together.

  When carbon black is used as the conductive material, from the viewpoint of further improving the dispersibility of the positive electrode mixture and the input / output characteristics of the lithium ion secondary battery, as the carbon black, for example, particles having an average particle diameter of 20 nm to 100 nm are preferable. , 20 nm to 100 nm particles are more preferable, 30 nm to 80 nm particles are more preferable, and 40 nm to 60 nm particles are particularly preferable.

Examples of the shape of the particle include granular shape, flake shape, spherical shape, columnar shape, and irregular shape.
“Granular” is not an irregular shape but a shape having almost equal dimensions (JIS Z2500: 2000).
“Flake shape (flap shape)” is a plate-like shape (JIS Z2500: 2000), and is also referred to as a scale-like shape because it is thin like a scale. In the present embodiment, analysis is performed based on the result of observation with a scanning electron microscope (SEM), and the case where the aspect ratio (particle diameter a / average thickness t) is in the range of 2 to 100 is a piece. The particle diameter a here is defined as the square root of the area S when the flaky particles are viewed in plan, and this is the particle diameter of the flaky particles.
“Spherical” means a shape almost similar to a sphere (JIS Z2500: 2000). Further, the shape does not necessarily need to be spherical, and the ratio of the major axis (DL) to the minor axis (DS) of the particle (DL) / (DS) (also referred to as spherical coefficient or sphericity) is 1. It shall be in the range of 0-1.2, and a particle size shall refer to a long diameter (DL).
The “columnar shape” refers to a shape such as a substantially cylindrical column or a substantially polygonal column, and the particle size refers to the height of the column.

  When graphite is used as the conductive material, the average particle size of graphite is preferably 1 μm to 10 μm, for example. Graphite preferably has a carbon network plane interlayer (d002) in the X-ray wide angle diffraction method of, for example, 0.3354 nm to 0.337 nm.

  When carbon black and graphite are used in combination as the conductive material, the ratio of carbon black and graphite is not particularly limited. When the content of carbon black is A1 and the content of graphite is A2, the mass ratio (A1 / (A1 + A2)) is, for example, 0.1 to 0.9 from the viewpoint of further improving charge / discharge characteristics. It is preferable that it is 0.4 to 0.85.

  The average particle diameter of the conductive material is an arithmetic average value of the particle diameters measured for all of the particle images in the image taken at 200,000 times with a scanning electron microscope (SEM).

  When the positive electrode mixture layer includes a conductive material, the content of the conductive material is, for example, preferably 0.1% by mass or more and 0.2% by mass or more with respect to the total amount of the positive electrode mixture layer. It is more preferable that the content is 0.5% by mass or more. The content of the conductive material is, for example, preferably 30% by mass or less, more preferably 20% by mass or less, and preferably 10% by mass or less with respect to the total amount of the positive electrode mixture layer. Further preferred. When the content of the conductive material is within the above range, the battery capacity and input / output characteristics tend to be further improved.

  When carbon black is used as the conductive material, the content of carbon black is, for example, 0.1% by mass to 15% by mass with respect to the total amount of the positive electrode mixture layer from the viewpoint of further improving conductivity and battery capacity. %, More preferably 0.2% by mass to 10% by mass, and still more preferably 0.5% by mass to 5% by mass. When the carbon black content is within the above range, the battery capacity and input / output characteristics tend to be further improved.

(Binder)
The positive electrode mixture layer preferably contains a binder from the viewpoint of improving the adhesion between the positive electrode mixture layer and the current collector and the adhesion between the positive electrode active materials. The kind of binder is not particularly limited. For example, when the positive electrode mixture layer is formed by a wet method, it is preferable to select a material having good solubility or dispersibility in the dispersion solvent.
As a binder, resin-based polymers such as polyethylene, polypropylene, polyethylene terephthalate, polymethyl methacrylate, polyimide, aromatic polyamide, cellulose, nitrocellulose; SBR (styrene-butadiene rubber), NBR (acrylonitrile-butadiene rubber), Rubbery polymers such as fluorine rubber, isoprene rubber, butadiene rubber, ethylene-propylene rubber; styrene / butadiene / styrene block copolymer or hydrogenated product thereof, 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 Examples thereof include fluorine polymers such as polymers and polytetrafluoroethylene / vinylidene fluoride copolymers; polymer compositions having ion conductivity of alkali metal ions (particularly lithium ions). A binder may be used individually by 1 type and may use 2 or more types together. From the viewpoint of the stability of the positive electrode, it is preferable to use a fluorine-based polymer such as polyvinylidene fluoride (PVdF) or a polytetrafluoroethylene / vinylidene fluoride copolymer.

  When the positive electrode mixture layer includes a binder, the content of the binder is, for example, preferably 0.5% by mass or more, and 1% by mass or more with respect to the total amount of the positive electrode mixture layer. More preferred is 2% by mass or more. The content of the binder is, for example, preferably 50% by mass or less, more preferably 40% by mass or less, and 30% by mass or less with respect to the total amount of the positive electrode mixture layer. Is more preferable, and it is especially preferable that it is 10 mass% or less. When the content of the binder is within the above range, battery performance such as cycle characteristics tends to be further improved.

(Method for forming positive electrode mixture layer, etc.)
The method for forming the positive electrode mixture layer on the current collector is not particularly limited, and examples thereof include a dry method and a wet method. The dry method is a method in which the positive electrode material is mixed in a dry manner to form a sheet, and this is pressure-bonded to a current collector. The wet method is a method in which a material of the positive electrode mixture is dissolved or dispersed in a dispersion solvent to form a slurry, which is applied to a current collector and dried.

  The dispersion solvent for preparing the slurry is not limited as long as it is a solvent that can dissolve or disperse the material of the positive electrode mixture, and either an aqueous solvent or an organic solvent may be used. . Examples of the aqueous solvent include water, a mixed solvent of alcohol and water, and the like. Examples of organic solvents include N-methyl-2-pyrrolidone (NMP), dimethylformamide, dimethylacetamide, methyl ethyl ketone, cyclohexanone, methyl acetate, methyl acrylate, diethyltriamine, N, N-dimethylaminopropylamine, tetrahydrofuran ( THF), toluene, acetone, diethyl ether, dimethylacetamide, hexamethylphosphalamide, dimethyl sulfoxide, benzene, xylene, quinoline, pyridine, methylnaphthalene, hexane and the like. In particular, when an aqueous solvent is used, it is preferable to use a thickener. A dispersion solvent may be used individually by 1 type, and may use 2 or more types together.

  It does not restrict | limit especially as a thickener. Specific examples of the thickener include carboxymethyl cellulose, methyl cellulose, hydroxymethyl cellulose, ethyl cellulose, polyvinyl alcohol, oxidized starch, phosphorylated starch, casein, and salts thereof. A thickener may be used individually by 1 type, and may use 2 or more types together.

  The positive electrode mixture layer formed on the current collector is preferably consolidated by a hand press, a roller press or the like in order to improve the packing density of the positive electrode active material.

Positive electrode composite material layer is, for example, preferably a density of ^{3.0g / cm 3 ~4.0g / cm 3} . When the density of the positive electrode mixture layer is within the above range, the input / output characteristics tend to be further improved. From this point of view, single-side coating of the current collector of the positive electrode material layer ^is preferably ^{100g / m 2 ~300g / m 2} , and more to be 150g / ^{m 2} ~250g / m 2 ^preferably, more preferably ^{185g / m 2 ~220g / m 2} .

(Current collector)
The material of the positive electrode current collector is not particularly limited. Examples of the material of the current collector include metal materials such as aluminum and stainless steel, and carbonaceous materials such as carbon cloth and carbon paper. Of these, metal materials are preferable, and aluminum is more preferable.

  The shape of the current collector is not particularly limited. Examples of the shape when using a metal material include a metal foil, a metal thin film, and an expanded metal. Examples of the shape in the case of using a carbonaceous material include a carbon plate and a carbon thin film. Among these, it is preferable to use a metal thin film. The thin film may be formed in a mesh shape.

  The thickness of the current collector is not particularly limited. The thickness of the current collector is, for example, preferably 1 μm or more, more preferably 3 μm or more, and further preferably 5 μm or more. Further, the thickness of the current collector is, for example, preferably 1 mm or less, more preferably 100 μm or less, and further preferably 50 μm or less. When the thickness of the current collector is 1 μm or more, sufficient strength tends to be obtained, and when it is 1 mm or less, flexibility and workability tend to be excellent.

2. Negative electrode The negative electrode (negative electrode plate) has a current collector and a negative electrode mixture layer formed on the current collector. The negative electrode mixture layer is a layer that is provided on the current collector and includes a negative electrode active material that can electrochemically occlude and release lithium ions. The negative electrode mixture layer may be formed on one side of the current collector or on both sides. The negative electrode mixture layer may include a conductive material, a binder, a thickener, and the like as necessary.

(Negative electrode active material)
Examples of the negative electrode active material include carbonaceous materials; metal composite oxides; lithium metals; lithium alloys such as lithium aluminum alloys; oxides or nitrides of elements that can be alloyed with lithium such as Sn, Si, and Ge; It is done. A negative electrode active material may be used individually by 1 type, and may use 2 or more types together. Among these, a carbonaceous material or a lithium composite oxide is preferable from the viewpoint of safety.

  Carbonaceous materials include: amorphous carbon; natural graphite; composite carbonaceous material in which a film formed on natural graphite by a dry CVD method or a wet spray method; resin raw materials such as epoxy compounds and phenol compounds, or And artificial graphite obtained by firing a pitch material obtained from petroleum, coal, and the like.

  The metal composite oxide is not particularly limited as long as it can occlude and release lithium. Among metal complex oxides, those containing at least one of Ti (titanium) and Li (lithium) are preferable from the viewpoint of high current density charge / discharge characteristics.

In particular, the carbonaceous material is a material having high conductivity and excellent in terms of low temperature characteristics and cycle stability of the lithium ion secondary battery.
As the carbonaceous material, a material (amorphous carbon) having a wide carbon network interlayer (d002) is preferable from the viewpoint of further improving input / output characteristics, and from the viewpoint of further improving battery characteristics, the carbon network interlayer is preferable. A material with (d002) of, for example, 0.39 nm or less is preferable. Such a carbonaceous material is sometimes referred to as pseudo-anisotropic carbon. Examples of the material (amorphous carbon) having a wide carbon network interlayer (d002) include hard carbon and soft carbon, and soft carbon is preferable from the viewpoint of further improving cycle characteristics. The soft carbon preferably has a carbon network plane interlayer (d002) in the X-ray wide angle diffraction method of, for example, 0.34 nm to 0.36 nm, more preferably 0.341 nm to 0.355 nm, and More preferably, it is 342 nm-0.35 nm.

As the carbonaceous material, graphite is preferable from the viewpoint of further improving the battery capacity. Graphite preferably has a carbon network plane interlayer (d002) of, for example, less than 0.34 nm and more preferably 0.3354 nm to 0.337 nm in the X-ray wide angle diffraction method.
Further, as the negative electrode active material, a carbonaceous material having high conductivity such as graphite, amorphous, activated carbon or the like may be mixed and used.

(Conductive material)
The negative electrode mixture layer may contain a conductive material. For example, a second carbonaceous material having a different property from the first carbonaceous material used as the negative electrode active material may be included as a conductive material. The above properties include X-ray diffraction parameters, median diameter, aspect ratio, BET specific surface area, orientation ratio, R value obtained from Raman spectrum analysis, tap density, true density, pore distribution, circularity, ash content, etc. In addition, a carbonaceous material having one or more properties selected from these different from the first carbonaceous material can be used as the conductive material.

  As the conductive material, a carbonaceous material having high conductivity such as graphite, amorphous, activated carbon or the like can be used. Specifically, graphite (graphite) such as natural graphite and artificial graphite, carbon black such as acetylene black, and amorphous carbon such as needle coke can be used. A conductive material may be used individually by 1 type, and may use 2 or more types together. When the negative electrode mixture layer contains a conductive material, the resistance of the electrode tends to be further reduced.

  When the negative electrode mixture layer includes a conductive material, the content of the conductive material is, for example, preferably 1% by mass or more and more preferably 2% by mass or more with respect to the total amount of the negative electrode mixture layer. More preferably, it is 3 mass% or more. Moreover, it is preferable that it is 45 mass% or less with respect to the whole quantity of a negative mix layer, and, as for the content rate of a electrically conductive material, it is more preferable that it is 40 mass% or less. When the content of the conductive material is 1% by mass or more, there is a tendency that an effect of improving conductivity is easily obtained, and when it is 45% by mass or less, an increase in initial irreversible capacity tends to be suppressed.

(Binder)
The negative electrode mixture layer preferably contains a binder from the viewpoint of improving the adhesion between the negative electrode mixture layer and the current collector and the adhesion between the negative electrode active materials. The kind in particular of a binder is not restrict | limited, For example, what was illustrated as a binder used for a positive mix layer can be used.

  When the negative electrode mixture layer includes a binder, the content of the binder is, for example, preferably 0.1% by mass or more and 0.2% by mass or more with respect to the total amount of the negative electrode mixture layer. It is more preferable that it is 0.5 mass% or more. Further, the content of the binder is, for example, preferably 20% by mass or less, more preferably 15% by mass or less, and more preferably 10% by mass or less with respect to the total amount of the negative electrode mixture. More preferably, it is particularly preferably 8% by mass or less. When the content of the binder is 0.1% by mass or more, a decrease in strength of the negative electrode mixture layer tends to be suppressed, and when the content is 20% by mass or less, a decrease in battery capacity tends to be suppressed. It is in.

When a rubbery polymer such as SBR is used as the binder, the content of the binder is preferably, for example, 0.1% by mass or more with respect to the total amount of the negative electrode mixture layer. It is more preferably 2% by mass or more, and further preferably 0.5% by mass or more. In addition, the content of the binder is, for example, preferably 5% by mass or less, more preferably 3% by mass or less, and more preferably 2% by mass or less with respect to the total amount of the negative electrode mixture layer. Is more preferable.
When a fluorine-based polymer such as polyvinylidene fluoride is used as the binder, the content of the binder is preferably, for example, 1% by mass or more with respect to the total amount of the negative electrode mixture layer. % Or more is more preferable, and it is still more preferable that it is 3 mass% or more. Further, the content of the binder is, for example, preferably 15% by mass or less, more preferably 10% by mass or less, and 8% by mass or less, with respect to the total amount of the negative electrode mixture layer. Is more preferable.

(Method for forming negative electrode mixture layer, etc.)
The method for forming the negative electrode mixture layer on the current collector is not particularly limited, and examples thereof include a dry method and a wet method.
When the negative electrode mixture layer is formed by a wet method, the dispersion solvent and the thickener for forming the slurry are not particularly limited, and are selected from those exemplified as the dispersion solvent and the thickener usable for the positive electrode mixture layer. it can.

  When the thickener is used, the content of the thickener is, for example, preferably 0.1% by mass or more and more preferably 0.2% by mass or more with respect to the total amount of the negative electrode mixture layer. Preferably, it is 0.5 mass% or more. The content of the thickener is, for example, preferably 5% by mass or less, more preferably 3% by mass or less, and more preferably 2% by mass or less with respect to the total amount of the negative electrode mixture layer. Is more preferable. When the content of the thickening material is 0.1% by mass or more, the coating property of the slurry tends to be maintained favorably, and when it is 5% by mass or less, the battery capacity decreases and the resistance between the negative electrode active materials. Tend to be suppressed.

(Current collector)
The material of the current collector for the negative electrode is not particularly limited. Examples of the material of the current collector include metal materials such as copper, nickel, stainless steel, and nickel-plated steel. Among these, copper is preferable from the viewpoint of ease of processing and cost.

  The shape of the current collector is not particularly limited. Examples of the shape of the current collector include a metal foil and a metal thin film. Especially, metal foil is preferable and copper foil is more preferable. Copper foil includes a rolled copper foil formed by a rolling method and an electrolytic copper foil formed by an electrolytic method, both of which are suitable as a current collector.

  The thickness of the current collector is not particularly limited. When the current collector is made of copper and has a thickness of less than 25 μm, it is necessary to use a copper alloy (phosphor bronze, titanium copper, Corson alloy, Cu—Cr—Zr alloy, etc.) that is superior in strength to pure copper. It is preferable from the viewpoint of improving body strength.

3. Electrolytic Solution The electrolytic solution is obtained by dissolving a lithium salt electrolyte in a non-aqueous solvent, and the lithium salt electrolyte includes a fluorine-containing lithium salt electrolyte. The electrolytic solution may contain an additive or the like as necessary.

From the viewpoint of output characteristics, the fluorine-containing lithium salt electrolyte preferably contains lithium hexafluorophosphate (LiPF ₆ ). From the viewpoint of battery performance, the content of lithium hexafluorophosphate (LiPF ₆ ) is, for example, preferably 10% by mass or more and more preferably 50% by mass or more with respect to the total amount of the lithium salt electrolyte. preferable.

The electrolytic solution may further contain a lithium salt electrolyte other than lithium hexafluorophosphate (LiPF ₆ ). The lithium salt electrolytes other than lithium hexafluorophosphate _{(LiPF 6), LiBF 4,} LiAsF 6, LiSbF ₆ such as inorganic fluoride _salts; LiAlCl _{4, etc.; LiClO 4, LiBrO 4, LiIO} 4 perhalogenates such as Inorganic chloride salts of: Perfluoroalkane sulfonates such as LiCF ₃ SO ₃ ; LiN (CF ₃ SO ₂ ) ₂ , LiN (CF ₃ CF ₂ SO ₂ ) ₂ , LiN (CF ₃ SO ₂ ) (C ₄ F ₉ Perfluoroalkanesulfonylimide salts such as ₉ SO ₂ ); Perfluoroalkanesulfonylmethide salts such as LiC (CF ₃ SO ₂ ) ₃ ; Li [PF ₅ (CF ₂ CF ₂ CF ₃ )], Li [PF ₄ ( _{CF 2 CF 2 CF 3) 2} ], Li [PF 3 (CF 2 CF 2 CF 3) 3], Li [PF 5 _{CF 2 CF 2 CF 2 CF 3} )], Li [PF 4 (CF 2 CF 2 CF 2 CF 3) 2], Li [PF 3 (CF 2 CF 2 CF 2 CF 3) 3] fluoroalkyl fluoride such as Phosphate: Dicarboxylic acid complex lithium salt such as lithium bis (oxalato) borate, lithium difluorooxalatoborate and the like. Lithium salt electrolytes other than lithium hexafluorophosphate (LiPF ₆ ) may be used alone or in combination of two or more.

  The concentration of the lithium salt electrolyte in the electrolytic solution is not particularly limited. The concentration of the lithium salt electrolyte in the electrolytic solution is, for example, preferably 0.5 mol / L or more, more preferably 0.6 mol / L or more, and further preferably 0.7 mol / L or more. . The concentration of the lithium salt electrolyte in the electrolytic solution is, for example, preferably 2.0 mol / L or less, more preferably 1.8 mol / L or less, and 1.7 mol / L or less. Further preferred. When the concentration of the lithium salt electrolyte is 0.5 mol / L or more, sufficient electric conductivity tends to be obtained. Moreover, when the concentration of the lithium salt electrolyte is 2.0 mol / L or less, the viscosity is increased and the electrical conductivity is prevented from decreasing, and the performance of the lithium ion secondary battery tends to be suppressed. .

  The kind of non-aqueous solvent is not particularly limited. Examples of the non-aqueous solvent include cyclic carbonate, chain carbonate, chain ester, cyclic ether, and chain ether. A non-aqueous solvent may be used individually by 1 type, and may use 2 or more types together.

  As the cyclic carbonate, those in which the alkylene group constituting the cyclic carbonate has 2 to 6 carbon atoms are preferable, and those having 2 to 4 are more preferable. Specific examples include ethylene carbonate, propylene carbonate, butylene carbonate, and the like. Of these, ethylene carbonate and propylene carbonate are preferable. The cyclic carbonate may be a cyclic carbonate having a double bond in the molecule such as vinylene carbonate or fluoroethylene carbonate, or a cyclic carbonate containing a halogen atom. When a carbonaceous material is used as the negative electrode active material, the non-aqueous solvent preferably contains vinylene carbonate from the viewpoint of the cycle characteristics of the lithium ion secondary battery.

  As the chain carbonate, a dialkyl carbonate is preferable, and those having two alkyl groups each independently having 1 to 5 carbon atoms are preferable, and those having 1 to 4 carbon atoms are more preferable. Specific examples include symmetric chain carbonates such as dimethyl carbonate, diethyl carbonate, and di-n-propyl carbonate; and asymmetric chain carbonates such as methyl ethyl carbonate, methyl-n-propyl carbonate, and ethyl-n-propyl carbonate. It is done. Of these, dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate are preferable.

  Examples of chain esters include methyl acetate, ethyl acetate, propyl acetate, and methyl propionate. Among these, methyl acetate is preferable from the viewpoint of further improving the low temperature characteristics.

  Examples of the cyclic ether include tetrahydrofuran, 2-methyltetrahydrofuran, tetrahydropyran and the like. Among these, tetrahydrofuran is preferable from the viewpoint of further improving input / output characteristics.

  Examples of chain ethers include dimethoxyethane and dimethoxymethane.

It is preferable to use two or more non-aqueous solvents in combination. For example, it is preferable to use a high dielectric constant solvent such as cyclic carbonate in combination with a low viscosity solvent such as chain carbonate or chain ester.
One of the preferable combinations is a combination mainly composed of a cyclic carbonate and a chain carbonate. Among them, the total of the cyclic carbonate and the chain carbonate in the entire non-aqueous solvent is preferably 80% by volume or more, more preferably 85% by volume or more, and further preferably 90% by volume or more. preferable. At this time, the ratio of the cyclic carbonate to the total of the cyclic carbonate and the chain carbonate is, for example, preferably 5% by volume or more, more preferably 10% by volume or more, and 15% by volume or more. Further preferred. Further, the ratio of the cyclic carbonate to the total of the cyclic carbonate and the chain carbonate is, for example, preferably 50% by volume or less, more preferably 35% by volume or less, and further preferably 30% by volume or less. preferable. By using such a combination of non-aqueous solvents, cycle characteristics and storage characteristics tend to be further improved.

  Specific examples of preferred combinations of cyclic carbonate and chain carbonate include ethylene carbonate and dimethyl carbonate, ethylene carbonate and diethyl carbonate, ethylene carbonate and methyl ethyl carbonate, ethylene carbonate and dimethyl carbonate and diethyl carbonate, ethylene carbonate and dimethyl carbonate, Examples thereof include methyl ethyl carbonate, ethylene carbonate, diethyl carbonate and methyl ethyl carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate and methyl ethyl carbonate.

  Among these combinations, those containing both a symmetric chain carbonate and an asymmetric chain carbonate are preferable as the chain carbonate. Specific examples include a combination of ethylene carbonate, dimethyl carbonate and methyl ethyl carbonate, ethylene carbonate, diethyl carbonate and methyl ethyl carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate and methyl ethyl carbonate. As described above, by combining the cyclic carbonate, the symmetric chain carbonate, and the asymmetric chain carbonate, the cycle characteristics and the input / output characteristics can be further improved. Among these, a combination in which the asymmetric chain carbonate is methyl ethyl carbonate is preferable. Moreover, the combination whose symmetrical chain carbonate is dialkyl carbonate whose carbon number of an alkyl group is 1-2 is preferable.

  The additive is not particularly limited as long as it is an additive used for an electrolyte solution of a lithium ion secondary battery. Examples of the additive include a heterocyclic compound containing at least one of nitrogen and sulfur, a cyclic carboxylic acid ester, a fluorine-containing cyclic carbonate, and a compound having an unsaturated bond in the molecule. In addition to the above additives, other additives such as an overcharge preventing 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.

4). Separator 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.

  Examples of the resin include olefin resin, fluororesin, cellulose resin, polyimide resin, and nylon resin. Among them, it is preferable to select from materials that are stable with respect to the electrolytic solution and have excellent liquid retention properties, and polyolefins such as polyethylene and polypropylene are more preferable. Examples of the shape of the separator include a porous sheet and a nonwoven fabric.

  Examples of the inorganic substance include 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. For example, what made the said inorganic substance of fiber shape or particle shape adhere to thin film-shaped base materials, such as a nonwoven fabric, a woven fabric, and a microporous film, can be used as a separator. As a 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. In addition, for example, a separator in which a composite porous layer is formed using the above-described inorganic material in a fiber shape or a particle shape by using a binder such as a 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% particle size of less than 1 μm are bound by a fluororesin as a binder may be formed on the surface of the positive electrode.

5. Other components The lithium ion secondary battery of this embodiment may include a cleavage valve as other components. By opening the cleavage valve, it is possible to suppress an increase in pressure inside the battery and to further improve safety.

  Moreover, the lithium ion secondary battery of this embodiment may be provided with the structure part which discharge | releases inert gas (carbon dioxide etc.) with a temperature rise. When the lithium ion secondary battery includes such a component, when the temperature inside the battery rises, the cleavage valve can be opened quickly due to the generation of an inert gas, which can further improve safety. it can. Examples of the material used for the above components include lithium carbonate and polyalkylene carbonate resin.

6). Configuration of Lithium Ion Secondary Battery A configuration when the lithium ion secondary battery of the present embodiment is a laminate type lithium ion secondary battery will be described.
A laminate-type lithium ion secondary battery can be manufactured, for example, as follows. First, the positive electrode and the negative electrode are cut into squares, and tabs are welded to the respective electrodes to produce positive and negative electrode terminals. A laminated body in which the positive electrode, the separator, and the negative electrode are laminated in this order is prepared, and accommodated in an aluminum laminate pack in this state, and the positive and negative electrode terminals are taken out of the laminate pack and sealed. Next, an electrolytic solution is poured into the aluminum laminate pack, and the opening of the laminate pack is sealed. Thereby, a lithium ion secondary battery is obtained.

  Next, with reference to FIG. 1, the structure in the case where the lithium ion secondary battery of this embodiment is an 18650 type cylindrical lithium ion secondary battery will be described. In addition, the magnitude | size of the member in FIG. 1 is notional, The relative relationship of the magnitude | size between members is not limited to this. In the following description, “upper” and “lower” indicate “upper” and “lower” in FIG. 1, and do not limit “upper” and “lower” of the lithium ion secondary battery.

  As shown in FIG. 1, the lithium ion secondary battery 1 has a bottomed cylindrical battery container 6 made of steel plated with nickel. The battery case 6 accommodates an electrode group 5 in which a strip-like positive electrode plate 2 and a negative electrode plate 3 are wound in a spiral shape with a separator 4 interposed therebetween. In the electrode group 5, the positive electrode plate 2 and the negative electrode plate 3 are wound in a spiral shape in cross section via a separator 4 made of a polyethylene porous sheet. For example, the separator 4 has a width of 58 mm and a thickness of 30 μm. A ribbon-like positive electrode tab terminal made of aluminum and having one end fixed to the positive electrode plate 2 is led out on the upper end surface of the electrode group 5. The other end of the positive electrode tab terminal is disposed on the upper side of the electrode group 5 and is joined to the lower surface of a disk-shaped battery lid serving as a positive electrode external terminal by ultrasonic welding. On the other hand, a ribbon-like negative electrode tab terminal made of copper with one end fixed to the negative electrode plate 3 is led out on the lower end surface of the electrode group 5. The other end of the negative electrode tab terminal is joined to the inner bottom of the battery container 6 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 5. In addition, the insulation coating which abbreviate | omitted illustration is given to the outer peripheral surface whole periphery of the electrode group 5. FIG. The battery lid is caulked and fixed to the upper part of the battery container 6 via an insulating resin gasket. For this reason, the inside of the lithium ion secondary battery 1 is sealed. In addition, an electrolyte solution (not shown) is injected into the battery container 6.

(Capacity ratio between the negative electrode and the positive electrode of a lithium ion secondary battery)
In the present embodiment, the capacity ratio between the negative electrode and the positive electrode (negative electrode capacity / positive electrode capacity) is preferably 1.03 to 1.8, for example, from the viewpoint of further improving safety and energy density. More preferably, it is 05-1.4.
Here, the negative electrode capacity refers to “negative electrode discharge capacity”, and the positive electrode capacity refers to “a value obtained by subtracting the larger irreversible capacity B of the negative electrode or the positive electrode from the initial charge capacity A of the positive electrode (AB). ) ". The “negative electrode discharge capacity” is defined as calculated by the charge / discharge device when lithium ions inserted into the negative electrode active material are desorbed. The “initial charge capacity of the positive electrode” is defined as calculated by the charge / discharge device when lithium ions are desorbed from the positive electrode active material.

  The capacity ratio between the negative electrode and the positive electrode can be calculated from, for example, “discharge capacity of lithium ion secondary battery / discharge capacity of negative electrode”. The discharge capacity of the lithium ion secondary battery is, for example, 4.35 V, 0.1 C to 0.5 C, 0.1 C after performing constant current constant voltage (CCCV) charging with an end time of 2 hours to 15 hours. It can be measured under conditions when a constant current (CC) discharge is performed up to 2.5V at 0.5C. The discharge capacity of the negative electrode is obtained by cutting a negative electrode whose discharge capacity of a lithium ion secondary battery is measured into a predetermined area, using lithium metal as a counter electrode, and producing a single electrode cell through a separator impregnated with an electrolyte, After constant current constant voltage (CCCV) charge at 0V, 0.1C to 0.5C, end current 0.01C, and then at constant current (CC) discharge to 1.5V at 0.1C to 0.5C It can be calculated by measuring the discharge capacity per predetermined area under the conditions and converting this to the total area used as the negative electrode of the lithium ion secondary battery. In this single electrode cell, the direction in which lithium ions are inserted into the negative electrode active material is defined as charging, and the direction in which lithium ions inserted into the negative electrode active material are desorbed is defined as discharging. C means “current value (A) / battery discharge capacity (Ah)”.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited to these examples.

[Production Example 1]
<Preparation of aluminum silicate compound>
To an aluminum sulfate aqueous solution (500 mL) with an Al concentration of 1 mol / L, water glass (sodium silicate No. 3, Na ₂ O.nSiO ₂ .mH ₂ O) (500 mL) with an Si concentration of 2 mol / L is added and stirred for 30 minutes. did. To this solution, 890 mL of a 1 mol / L sodium hydroxide aqueous solution was added to adjust the pH to 7. After the pH-adjusted solution was stirred for 30 minutes, desalting was performed by pressure filtration. To the precipitate after the desalting treatment, 100 mL of a sulfuric acid aqueous solution having a concentration of 1 mol / L was added to adjust the pH to 4, followed by stirring for 30 minutes. The solution was then placed in a dryer and heated at 98 ° C. for 48 hours (2 days). To the heated solution, 235 mL of a sodium hydroxide aqueous solution having a concentration of 1 mol / L was added to adjust the pH to 9. The salt in the solution was aggregated by adjusting the pH, the aggregate was precipitated by the same pressure filtration as described above, and then the supernatant was discharged to perform desalting. The precipitate obtained after the desalting treatment was dried at 110 ° C. for 16 hours to collect the particle mass. The particle lump was pulverized with a jet mill to obtain a particulate aluminum silicate compound.

About the obtained aluminum silicate compound, the powder X-ray-diffraction analysis was performed on the following measurement conditions using the powder X-ray-diffraction apparatus (Rigaku Corporation, Geigerflex RAD-2X). As a result, no peak indicating a mullite structure was observed, and a broad peak was observed in the vicinity of 2θ = 10 ° to 30 °. Therefore, the obtained aluminum silicate compound was an amorphous aluminum silicate compound. Was confirmed.
-Measurement conditions-
・ X-ray source: CuKα ray ・ Divergent slit: 1 °
・ Scatter slit: 1 °
・ Reception slit: 0.30mm
-X-ray output: 40 kV, 40 mA

<Production of carbon-coated aluminum silicate compound>
The above aluminum silicate compound and polyvinyl alcohol powder (Wako Pure Chemical Industries, Ltd.) are mixed at a mass ratio of 100: 70 (aluminum silicate compound: polyvinyl alcohol powder) and fired at 1000 ° C. for 1 hour in a nitrogen atmosphere. Thus, a particulate carbon-coated aluminum silicate compound was produced.

[Production Example 2]
<Preparation of aluminum silicate compound>
To an aluminum sulfate aqueous solution (800 mL) with an Al concentration of 1 mol / L, water glass (sodium silicate No. 3, Na ₂ O.nSiO ₂ .mH ₂ O) (200 mL) with an Si concentration of 2 mol / L is added and stirred for 30 minutes. did. Thereafter, particulate aluminum silicate compounds were obtained by the same operations as in Production Example 1 (pH adjustment, desalting, aging at 98 ° C., drying, grinding, etc.).

  The obtained aluminum silicate compound was subjected to powder X-ray diffraction analysis in the same manner as in Production Example 1. As a result, no peak indicating a mullite structure was observed, and a broad peak was observed in the vicinity of 2θ = 10 ° to 30 °. Therefore, the obtained aluminum silicate compound was an amorphous aluminum silicate compound. Was confirmed.

<Production of carbon-coated aluminum silicate compound>
Using the aluminum silicate compound, carbon coating was performed in the same manner as in Production Example 1 to produce a particulate carbon-coated aluminum silicate compound.

[Production Example 3]
<Preparation of aluminum silicate compound>
To an aluminum sulfate aqueous solution (334 mL) with an Al concentration of 1 mol / L, water glass (sodium silicate No. 3, Na ₂ O.nSiO ₂ .mH ₂ O) (666 mL) with an Si concentration of 2 mol / L was added and stirred for 30 minutes. did. Thereafter, a particulate aluminum silicate compound was produced by the same operations as in Production Example 1 (pH adjustment, desalting, aging at 98 ° C., drying, grinding, etc.).

  The obtained aluminum silicate compound was subjected to powder X-ray diffraction analysis in the same manner as in Production Example 1. As a result, no peak indicating a mullite structure was observed, and a broad peak was observed in the vicinity of 2θ = 10 ° to 30 °. Therefore, the obtained aluminum silicate compound was an amorphous aluminum silicate compound. Was confirmed.

<Production of carbon-coated aluminum silicate compound>
Using the aluminum silicate compound, carbon coating was performed in the same manner as in Production Example 1 to produce a particulate carbon-coated aluminum silicate compound.

[Production Example 4]
<Preparation of aluminum silicate compound>
To an aluminum sulfate aqueous solution (571 mL) with an Al concentration of 1 mol / L, water glass (sodium silicate No. 3, Na ₂ O.nSiO ₂ .mH ₂ O) (429 mL) with an Si concentration of 2 mol / L was added and stirred for 30 minutes. did. Thereafter, a particulate aluminum silicate compound was produced by the same operations as in Production Example 1 (pH adjustment, desalting, aging at 98 ° C., drying, grinding, etc.).

  The obtained aluminum silicate compound was subjected to powder X-ray diffraction analysis in the same manner as in Production Example 1. As a result, no peak indicating a mullite structure was observed, and a broad peak was observed in the vicinity of 2θ = 10 ° to 30 °. Therefore, the obtained aluminum silicate compound was an amorphous aluminum silicate compound. Was confirmed.

<Production of carbon-coated aluminum silicate compound>
Using the aluminum silicate compound, carbon coating was performed in the same manner as in Production Example 1 to produce a particulate carbon-coated aluminum silicate compound.

[Production Example 5]
<Preparation of aluminum silicate compound>
To an aluminum sulfate aqueous solution (400 mL) with an Al concentration of 1 mol / L, water glass (sodium silicate No. 3, Na ₂ O.nSiO ₂ .mH ₂ O) (600 mL) with an Si concentration of 2 mol / L is added and stirred for 30 minutes. did. Thereafter, a particulate aluminum silicate compound was produced by the same operations as in Production Example 1 (pH adjustment, desalting, aging at 98 ° C., drying, grinding, etc.).

  The obtained aluminum silicate compound was subjected to powder X-ray diffraction analysis in the same manner as in Production Example 1. As a result, no peak indicating a mullite structure was observed, and a broad peak was observed in the vicinity of 2θ = 10 ° to 30 °. Therefore, the obtained aluminum silicate compound was an amorphous aluminum silicate compound. Was confirmed.

<Production of carbon-coated aluminum silicate compound>
Using the aluminum silicate compound, carbon coating was performed in the same manner as in Production Example 1 to produce a particulate carbon-coated aluminum silicate compound.

[Production Example 6]
<Preparation of aluminum silicate compound>
To an aluminum sulfate aqueous solution (909 mL) with an Al concentration of 1 mol / L, water glass (sodium silicate No. 3, Na ₂ O.nSiO ₂ .mH ₂ O) (91 mL) with an Si concentration of 2 mol / L was added and stirred for 30 minutes. did. Thereafter, a particulate aluminum silicate compound was produced by the same operations as in Production Example 1 (pH adjustment, desalting, aging at 98 ° C., drying, grinding, etc.).

  The obtained aluminum silicate compound was subjected to powder X-ray diffraction analysis in the same manner as in Production Example 1. As a result, no peak indicating a mullite structure was observed, and a broad peak was observed in the vicinity of 2θ = 10 ° to 30 °. Therefore, the obtained aluminum silicate compound was an amorphous aluminum silicate compound. Was confirmed.

<Production of carbon-coated aluminum silicate compound>
Using the aluminum silicate compound, carbon coating was performed in the same manner as in Production Example 1 to produce a particulate carbon-coated aluminum silicate compound.

[Production Example 7]
<Preparation of aluminum silicate compound>
To an aluminum sulfate aqueous solution (167 mL) with an Al concentration of 1 mol / L, water glass (sodium silicate No. 3, Na ₂ O.nSiO ₂ .mH ₂ O) (833 mL) with an Si concentration of 2 mol / L was added and stirred for 30 minutes. did. Thereafter, a particulate aluminum silicate compound was produced by the same operations as in Production Example 1 (pH adjustment, desalting, aging at 98 ° C., drying, grinding, etc.).

  The obtained aluminum silicate compound was subjected to powder X-ray diffraction analysis in the same manner as in Production Example 1. As a result, no peak indicating a mullite structure was observed, and a broad peak was observed in the vicinity of 2θ = 10 ° to 30 °. Therefore, the obtained aluminum silicate compound was an amorphous aluminum silicate compound. Was confirmed.

<Production of carbon-coated aluminum silicate compound>
Using the aluminum silicate compound, carbon coating was performed in the same manner as in Production Example 1 to produce a particulate carbon-coated aluminum silicate compound.

Example 1
[Production of positive electrode]
The positive electrode was produced as follows. In Production Example 1 with lithium cobalt oxide (90.0% by mass) as a positive electrode active material, fibrous graphite (1.0% by mass) and acetylene black (AB) (1.0% by mass) as conductive materials The prepared carbon-coated aluminum silicate compound (5.0% by mass) and polyvinylidene fluoride (PVDF) (3.0% by mass) as a binder were sequentially added and mixed to obtain a mixture of positive electrode materials. Obtained.
Further, N-methyl-2-pyrrolidone (NMP) as a dispersion solvent was added to the above mixture and kneaded to form a slurry. This slurry was applied substantially uniformly and uniformly on both surfaces of a 20 μm thick aluminum foil as a positive electrode current collector. Then, the drying process was performed and it consolidated by the press to the predetermined density. The density of the positive electrode mixture layer was 3.6 g / cm ^3, and the coating amount on one side of the positive electrode mixture layer was 211 g / m ² .

[Production of negative electrode]
The negative electrode was produced as follows. Artificial graphite having an average particle size of 22 μm was used as the negative electrode active material. To this negative electrode active material, SBR (styrene butadiene rubber) was added as a binder, and carboxymethyl cellulose (Daicel Finechem Co., Ltd., CMC # 2200) was added as a thickener. These mass ratios were negative electrode active material: binder: thickening material = 98: 1: 1. To this was added water as a dispersion solvent and kneaded to form a slurry. This slurry was applied substantially uniformly and uniformly on both surfaces of a rolled copper foil having a thickness of 10 μm, which is a current collector for a negative electrode. The density of the negative electrode mixture layer was 1.65 g / cm ^3, and the coating amount on one side of the negative electrode mixture layer was 113 g / m ² .

[Production of laminated lithium ion secondary battery]
The positive electrode cut into 13.5 cm ² squares is sandwiched between polyethylene porous sheet separators (Asahi Kasei Corporation, Hypore (registered trademark), thickness: 30 μm), and further, the negative electrode cut into 14.3 cm ² squares is stacked. Together, a laminate was produced. This laminate was placed in an aluminum laminate container (Dai Nippon Printing Co., Ltd., aluminum laminate film), and 1 mL of electrolyte was added. As an electrolytic solution, ethylene carbonate / dimethyl carbonate / diethyl carbonate = 2.5 / 6 / 1.5 (volume ratio) mixed solution containing 1.0 mol / L LiPF ₆ and vinylene carbonate with respect to the total amount of the mixed solution. In which 1.0% by mass was added (Ube Industries, Ltd.) was used. An aluminum laminate container was thermally welded to produce a laminate-type lithium ion secondary battery.

  Table 1 shows the element molar ratio Si / Al of the carbon-coated aluminum silicate compound in Example 1 and the composition of the positive electrode mixture layer and the lithium salt electrolyte. In Table 1, as the conductive material, the total amount of fibrous graphite (1.0% by mass) and acetylene black (1.0% by mass) is described. “-” In Table 1 means that the component is not added. A method for measuring the element molar ratio Si / Al will be described later.

(Example 2)
The ratio of lithium cobaltate as the positive electrode active material described in Example 1 is 94.0% by mass, the ratio of the carbon-coated aluminum silicate compound prepared in Production Example 1 is 1.0% by mass, and one surface of the positive electrode mixture layer A positive electrode and a lithium ion secondary battery were produced in the same process as in Example 1 except that the coating amount was changed to 202 g / m ² . Table 1 shows the element molar ratio Si / Al of the carbon-coated aluminum silicate compound in Example 2, and the composition of the positive electrode mixture layer and the lithium salt electrolyte.

(Example 3)
The ratio of lithium cobaltate as the positive electrode active material described in Example 1 is 94.5% by mass, the ratio of the carbon-coated aluminum silicate compound prepared in Production Example 1 is 0.5% by mass, and one surface of the positive electrode mixture layer A positive electrode and a lithium ion secondary battery were produced in the same process as in Example 1 except that the coating amount was changed to 201 g / m ² . Table 1 shows the element molar ratio Si / Al of the carbon-coated aluminum silicate compound in Example 2, and the composition of the positive electrode mixture layer and the lithium salt electrolyte.

Example 4
The positive electrode and the lithium ion secondary battery were processed in the same manner as in Example 2 except that the lithium salt in the electrolytic solution was changed to two kinds of 0.7 mol / L LiPF ₆ and 0.3 mol / L LiBF _4. Was made. Table 1 shows the element molar ratio Si / Al of the carbon-coated aluminum silicate compound in Example 4 and the composition of the positive electrode mixture layer and the lithium salt electrolyte.

(Example 5)
The positive electrode and the lithium ion secondary were processed in the same manner as described in Example 2 except that the carbon-coated aluminum silicate compound prepared in Production Example 2 was used instead of the carbon-coated aluminum silicate compound produced in Production Example 1. A battery was produced. Table 1 shows the element molar ratio Si / Al of the carbon-coated aluminum silicate compound in Example 5, and the composition of the positive electrode mixture layer and the lithium salt electrolyte.

(Example 6)
In the same process as described in Example 2, except that the carbon-coated aluminum silicate compound produced in Production Example 3 was used instead of the carbon-coated aluminum silicate compound produced in Production Example 1, the positive electrode and lithium ion secondary A battery was produced. Table 1 shows the element molar ratio Si / Al of the carbon-coated aluminum silicate compound in Example 6 and the composition of the positive electrode mixture layer and the lithium salt electrolyte.

(Example 7)
The positive electrode and the lithium ion secondary were processed in the same manner as described in Example 2 except that the carbon-coated aluminum silicate compound prepared in Production Example 4 was used instead of the carbon-coated aluminum silicate compound produced in Production Example 1. A battery was produced. Table 1 shows the element molar ratio Si / Al of the carbon-coated aluminum silicate compound in Example 7, and the composition of the positive electrode mixture layer and the lithium salt electrolyte.

(Example 8)
The positive electrode and the lithium ion secondary were processed in the same manner as described in Example 2 except that the carbon-coated aluminum silicate compound produced in Production Example 5 was used instead of the carbon-coated aluminum silicate compound produced in Production Example 1. A battery was produced. Table 1 shows the element molar ratio Si / Al of the carbon-coated aluminum silicate compound in Example 8 and the composition of the positive electrode mixture layer and the lithium salt electrolyte.

(Comparative Example 1)
The ratio of lithium cobaltate, which is the positive electrode active material described in Example 1, was set to 95.0% by mass, and the single-side coating amount of the positive electrode mixture layer was changed to 200 g / m ² without using the carbon-coated aluminum silicate compound. A positive electrode and a lithium ion secondary battery were produced in the same process as in Example 1 except that. Table 1 shows the composition of the positive electrode mixture layer and the lithium salt electrolyte in Comparative Example 1.

(Comparative Example 2)
In the same process as described in Example 2, except that the carbon-coated aluminum silicate compound produced in Production Example 6 was used instead of the carbon-coated aluminum silicate compound produced in Production Example 1, the positive electrode and the lithium ion secondary were processed. A battery was produced. Table 1 shows the element molar ratio Si / Al of the carbon-coated aluminum silicate compound in Comparative Example 2, and the composition of the positive electrode mixture layer and the lithium salt electrolyte.

(Comparative Example 3)
The positive electrode and the lithium ion secondary were processed in the same manner as described in Example 2, except that the carbon-coated aluminum silicate compound prepared in Preparation Example 7 was used instead of the carbon-coated aluminum silicate compound prepared in Preparation Example 1. A battery was produced. Table 1 shows the element molar ratio Si / Al of the carbon-coated aluminum silicate compound in Comparative Example 3, and the composition of the positive electrode mixture layer and the lithium salt electrolyte.

[Method for measuring element molar ratio Si / Al]
The element molar ratio Si / Al of the carbon-coated aluminum silicate compound was measured by the following method. Using a composite beam processing observation apparatus (JEOL Ltd., JIB-4501), a thin film sample for transmission electron microscope (TEM) observation was prepared from the positive electrodes described in Examples 1-8 and Comparative Examples 2-4. The thin film sample was subjected to elemental analysis using a transmission electron microscope-energy dispersive X-ray analyzer (TEM-EDX) (JEOL Ltd., JEM-2100F (HR)). Specifically, EDX measurement (acceleration voltage: 200 kV) of silicon and aluminum was performed, and the element molar ratio Si / Al was determined from the measured element ratio according to the following formula. The measurement was performed five times for each thin film sample, and the arithmetic average value was defined as the element molar ratio Si / Al of the carbon-coated aluminum silicate compound.
Element molar ratio Si / Al = (element ratio of Si measured by EDX (%)) / (element ratio of Al measured by EDX (%))

[Evaluation of battery capacity]
The battery capacities of the lithium ion secondary batteries of Examples 1 to 8 and Comparative Examples 1 to 3 were evaluated by the methods shown below.
First, constant current charging was performed up to an upper limit voltage of 4.4 V at a current value of 0.1 C under an environment of 25 ° C., and then constant voltage charging was performed at 4.4 V. The charge termination condition was a current value of 0.01C. Thereafter, constant current discharge with a final voltage of 2.5 V was performed at a current value of 0.1 C. This charge / discharge cycle was repeated three times. Furthermore, constant current charging at 0.2 C was performed up to an upper limit voltage of 4.4 V, and then constant voltage charging was performed at 4.4 V. The charge termination condition was a current value of 0.02C. Thereafter, constant current discharge with a final voltage of 2.5 V was performed at a current value of 0.2 C, and the capacity at the time of discharge was defined as battery capacity. Table 1 shows the battery capacities of the lithium ion secondary batteries of Examples 1 to 8 and Comparative Examples 1 to 3.

[Evaluation of output characteristics]
The output characteristics of the lithium ion secondary batteries of Examples 1 to 8 and Comparative Examples 1 to 3 were evaluated by the methods shown below.
After measuring the battery capacity, constant current charging at 0.2 C was performed up to an upper limit voltage of 4.4 V, and then constant voltage charging was performed at 4.4 V. The charge termination condition was a current value of 0.02C. Thereafter, constant current discharge with a final voltage of 2.5 V was performed at a current value of 0.2 C, and the capacity at the time of discharge was defined as the discharge capacity at a current value of 0.2 C. Next, constant current charging at 0.2 C was performed up to the upper limit voltage of 4.4 V, and then constant voltage charging was performed at 4.4 V. The charge termination condition was a current value of 0.02C. Thereafter, constant current discharge with a final voltage of 2.5 V was performed at a current value of 3C, and the capacity at the time of discharge was defined as the discharge capacity at a current value of 3C. And the output characteristic was computed according to the following formula | equation. Table 1 shows the output characteristics of the lithium ion secondary batteries of Examples 1 to 8 and Comparative Examples 1 to 3.
Output characteristics (%) = (discharge capacity at current value 3 C / discharge capacity at current value 0.2 C) × 100

[Evaluation of cycle characteristics]
The cycle characteristics of the lithium ion secondary batteries of Examples 1 to 8 and Comparative Examples 1 to 3 were evaluated by the methods shown below.
After evaluating the output characteristics under the conditions described above, the cycle characteristics were evaluated by a cycle test in which charge and discharge were repeated. As a charging pattern, constant current charging was performed up to an upper limit voltage of 4.4 V at a current value of 1 C under an environment of 45 ° C., and then constant voltage charging was performed at 4.4 V. The charge termination condition was a current value of 0.1C. For discharging, constant current discharging was performed up to 2.5V at a current value of 1C. And the cycle characteristic was computed according to the following formula | equation. Table 1 shows the cycle characteristics of the lithium ion secondary batteries of Examples 1 to 8 and Comparative Examples 1 to 3.
Cycle characteristics (%) = (discharge capacity after 200 cycles at a current value of 1C / discharge capacity after one cycle at a current value of 1C) × 100

As shown in the results of Table 1, the positive electrode mixture layer contains a carbon-coated aluminum silicate compound having an element molar ratio Si / Al in the range of 0.3 to 5.0, and as a lithium salt electrolyte. In Examples 1 to 3 and 5 to 8 using LiPF ₆ , it can be confirmed that the positive electrode mixture layer is superior in output characteristics and cycle characteristics as compared with Comparative Example 1 in which the carbon-coated aluminum silicate compound is not included. The reason is estimated as follows. That is, it is presumed that the output characteristics are improved because the carbon-coated aluminum silicate compound has high conductivity. Moreover, because the carbon-coated aluminum silicate compound adsorbs hydrogen fluoride (HF) in the electrolyte, precipitation of lithium fluoride (LiF) serving as a resistance component and change in the crystal structure of the positive electrode active material could be suppressed. It is estimated that the capacity drop after the charge / discharge cycle was suppressed. Alternatively, the carbon-coated aluminum silicate compound adsorbs metal ions such as cobalt ions eluted from the positive electrode active material, and suppresses metal deposition on the negative electrode, thereby presuming that the capacity decrease after the charge / discharge cycle is suppressed. The

Further, the positive electrode mixture layer contains a carbon-coated aluminum silicate compound having an element molar ratio Si / Al in the range of 0.3 to 5.0, and LiPF ₆ and LiBF ₄ were used as lithium salt electrolytes. In Example 4, compared with Comparative Example 1, it can be confirmed that the output characteristics are the same, but the cycle characteristics are excellent. This is presumably because the carbon-coated aluminum silicate compound adsorbed metal ions such as hydrogen fluoride (HF) in the electrolytic solution or cobalt eluted from the positive electrode active material, so that the capacity decrease after the charge / discharge cycle was suppressed. Is done.

  On the other hand, in Comparative Examples 2-3 in which the positive electrode mixture layer contains a carbon-coated aluminum silicate compound having an element molar ratio Si / Al of less than 0.3 or more than 5.0, compared with Examples 1-8 It can be confirmed that the output characteristics and the cycle characteristics are inferior.

  DESCRIPTION OF SYMBOLS 1 ... Lithium ion secondary battery, 2 ... Positive electrode plate, 3 ... Negative electrode plate, 4 ... Separator, 5 ... Electrode group, 6 ... Battery container

Claims (5)

A positive electrode, a negative electrode, and an electrolyte solution containing a fluorine-containing lithium salt electrolyte,
The positive electrode has a current collector and a positive electrode mixture layer formed on the current collector, and the positive electrode mixture layer is partially or entirely covered with carbon of the surface of the aluminum silicate compound. Carbon coated aluminum silicate compound,
The lithium ion secondary battery whose element molar ratio Si / Al of silicon (Si) of the said carbon covering aluminum silicate compound and aluminum (Al) is 0.3-5.0.   The lithium ion secondary battery according to claim 1, wherein an element molar ratio Si / Al of the carbon-coated aluminum silicate compound is 1.0 to 2.5.   3. The lithium ion secondary battery according to claim 1, wherein a content of the carbon-coated aluminum silicate compound is 0.1% by mass to 5% by mass with respect to a total amount of the positive electrode mixture layer.   The lithium ion secondary battery according to any one of claims 1 to 3, wherein the aluminum silicate compound is an amorphous aluminum silicate compound. The lithium ion secondary battery according to claim 1, wherein the fluorine-containing lithium salt electrolyte includes lithium hexafluorophosphate (LiPF ₆ ).