WO2016098553A1

WO2016098553A1 - Lithium ion secondary cell

Info

Publication number: WO2016098553A1
Application number: PCT/JP2015/083208
Authority: WO
Inventors: 洋生西山; 英介羽場; 馨今野; 武井　康一; 紘揮三國
Original assignee: 日立化成株式会社
Priority date: 2014-12-17
Filing date: 2015-11-26
Publication date: 2016-06-23
Also published as: KR101983924B1; KR20170083609A; JP6418250B2; JPWO2016098553A1

Abstract

A lithium ion secondary cell having excellent cycle characteristics is provided. Provided is a lithium ion secondary cell equipped with a positive electrode, a negative electrode, a separator, and an electrolytic solution. The positive electrode has a collector and a positive electrode mixture formed on the collector, and the positive electrode mixture includes a laminated lithium/nickel/manganese/cobalt composite oxide and an aluminum oxide having carbon coated on the surface thereof.

Description

Lithium ion secondary battery

The present invention relates to a lithium ion secondary battery.

Lithium ion secondary batteries are high energy density secondary batteries, and are used as power sources for portable devices such as notebook computers and mobile phones, taking advantage of their characteristics. There are various types of lithium ion secondary batteries. Cylindrical lithium ion secondary batteries employ a wound structure of a positive electrode, a negative electrode, and a separator. For example, a positive electrode material and a negative electrode material are respectively applied to two strip-shaped metal foils, a separator is sandwiched therebetween, and these laminated bodies are wound in a spiral shape to form a wound group. The wound group is housed in a cylindrical battery can serving as a battery container, and after injecting an electrolytic solution, the cylindrical lithium ion secondary battery is formed.

As the cylindrical lithium ion secondary battery, a 18650 type lithium ion secondary battery is widely used as a consumer lithium ion secondary battery. The outer diameter of the 18650 type lithium ion secondary battery is 18 mm in diameter and is small with a height of about 65 mm. As the positive electrode active material of the 18650 type lithium ion secondary battery, lithium cobaltate, which is characterized by high capacity and long life, is mainly used, and the battery capacity is approximately 1.0 Ah to 2.0 Ah (3.7 Wh 7.4 Wh).

In recent years, lithium-ion secondary batteries are expected to be used not only for consumer applications such as portable devices, but also for large-scale power storage systems for natural energy such as solar power and wind power generation. In a large-scale power storage system, the amount of power per system is required on the order of several MWh. For example, Patent Document 1 below discloses a cylindrical lithium ion secondary battery having an electrode winding group in which a positive electrode, a negative electrode, and a separator are wound around a cylindrical battery container. This battery has a discharge capacity of 30 Ah or more, a positive electrode active material mixture containing layered lithium-nickel-manganese-cobalt composite oxide is used for the positive electrode, and a negative electrode active material containing amorphous carbon is used for the negative electrode. A material mixture is used.

International Publication No. 2013/128677

In recent years, lithium ion secondary batteries have attracted attention as high-output power sources used in electric vehicles, hybrid electric vehicles, and the like. In such applications in the automobile field, higher output, higher capacity, and longer life at high temperatures are required.

The lithium ion secondary battery described in Patent Document 1 is excellent in increasing the output and capacity, but in the above applications, it is necessary to further improve the life at high temperatures (hereinafter referred to as cycle characteristics). is there.

The present invention has been made in view of the above problems, and is to provide a lithium ion secondary battery having excellent cycle characteristics.

A lithium ion secondary battery including a positive electrode, a negative electrode, a separator, and an electrolytic solution is configured as follows. The positive electrode has a current collector and a positive electrode mixture formed on the current collector. The positive electrode mixture is a layered lithium / nickel / manganese / cobalt composite oxide and part or all of the surface is carbon. Contains coated aluminum oxide.

The content of aluminum oxide in which part or all of the surface is coated with carbon is 0.01% by mass or more and 5% by mass or less with respect to the total amount of the positive electrode mixture.

The BET specific surface area of the aluminum oxide is 1 m ² / g to 30 m ² / g.

The weight loss rate between 25 ° C. and 350 ° C. measured by using a differential thermal-thermogravimetric analyzer (TG-DTA) of aluminum oxide partially or entirely coated with carbon is less than 5%. .

The aluminum oxide is imogolite.

The positive electrode mixture includes a conductive material, and the conductive material is acetylene black.

According to the present invention, a lithium ion secondary battery having excellent cycle characteristics can be provided.

It is sectional drawing of the lithium ion secondary battery of this Embodiment.

In the following embodiment, when ranges are indicated as A to B, A to B are indicated unless otherwise specified.

(Embodiment)
First, the outline of the lithium ion secondary battery will be briefly described. The lithium ion secondary battery has a positive electrode, a negative electrode, a separator, and an electrolytic solution in a battery container. A separator is coated between the positive electrode and the negative electrode.

When charging a 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 in the electrolytic solution, pass through a separator made of a microporous film, 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, connect an external load between the positive and negative electrodes. 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. Then, the lithium ions released into the electrolytic solution move in the electrolytic solution, pass through a separator made of a microporous film, and reach the positive electrode. The lithium ions reaching the positive electrode are inserted into the positive electrode active material constituting the positive electrode. At this time, when lithium ions are inserted into the positive electrode active material, 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.

Thus, charging and discharging can be 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 (see, for example, FIG. 1).

Next, the positive electrode, the negative electrode, the electrolyte, the separator, and other components of the lithium ion secondary battery will be sequentially described.
1. Positive electrode In this embodiment, it has the following positive electrode applicable to a long-life lithium ion secondary battery. The positive electrode (positive electrode plate) of this embodiment consists of a current collector and a positive electrode mixture formed thereon. The positive electrode mixture is a layer including at least a positive electrode active material provided on the current collector. In the present embodiment, the positive electrode mixture includes a layered lithium-nickel-manganese-cobalt composite oxide. In addition to the positive electrode active material, the positive electrode mixture contains an aluminum oxide (hereinafter also referred to as carbon-coated aluminum oxide) in which at least part of the surface is coated with carbon. Moreover, this positive electrode mixture may be formed (applied) on both surfaces of the current collector, for example.
(Positive electrode active material)
Examples of the positive electrode active material include layered lithium / nickel / manganese / cobalt composite oxide (hereinafter referred to as NMC), lithium-containing composite metal oxide other than NMC, olivine type lithium oxide, chalcogen compound, manganese dioxide, and the like. You may go out. 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 the transition metal in the metal oxide is substituted with a different element. Here, examples of the different element include Na, Mg, Sc, Y, Mn, Fe, Co, Ni, Cu, Zn, Al, Cr, Pb, Sb, and B. Mn, Al, Co, Ni, Mg and the like are preferable. One kind or two or more kinds of different elements may be used. Examples of lithium-containing composite metal oxides other than NMC include LixCoO ₂ , LixNiO ₂ , LixCoyNi ₁ -yO ₂ , LixCoyM ₁ -yOz, LixNi ₁ -yMyOz, LiMPO ₄ , Li ₂ MPO ₄ F (in the above formulas) , M represents at least one element selected from the group consisting of Na, Mg, Sc, Y, Mn, Fe, Co, Ni, Cu, Zn, Al, Cr, Pb, Sb, V, and B. x = 0 to 1.2, y = 0 to 0.9, z = 2.0 to 2.3). Here, x value which shows the molar ratio of lithium increases / decreases by charging / discharging. Examples of the olivine type lithium oxide include LiFePO _{4 and the} like. Examples of the chalcogen compound include titanium disulfide and molybdenum disulfide. A positive electrode active material can be used individually by 1 type, or can use 2 or more types together.

As the positive electrode active material, in addition to NMC, spinel type lithium manganese oxide (LMO) or olivine type lithium iron phosphate (LFP) may be used in combination with NMC, from the viewpoint of high safety. When NMC and LMO are used as the positive electrode active material, the mass ratio (mixing ratio) of NMC / LMO is preferably 95/5 or more and 30/70 or less.

When the mass ratio (NMC / LMO) of the positive electrode active material is in the range of 95/5 to 30/70, the safety of the battery tends to be improved. On the other hand, if it is less than 30/70, the safety of the battery is improved, but the battery capacity and the energy density of the battery are lowered, and the life characteristics at high temperature tend to be lowered due to the influence of Mn elution from LMO.

As NMC, it is preferable to use one represented by the following composition formula (Formula 1).

Li _{(1 + δ)} Mn _x Ni _y Co _(1-xyz) M _z O ₂
In the above composition formula (Formula 1), (1 + δ) is a composition ratio of Li (lithium), x is a composition ratio of Mn (manganese), y is a composition ratio of Ni (nickel), and (1-xyz) Indicates the composition ratio of Co (cobalt). z represents the composition ratio of the element M. The composition ratio of O (oxygen) is 2.

The elements M are Ti (titanium), Zr (zirconium), Nb (niobium), Mo (molybdenum), W (tungsten), Al (aluminum), Si (silicon), Ga (gallium), Ge (germanium), and Sn. It is at least one element selected from the group consisting of (tin).

-0.15 <δ <0.15, 0.1 <x ≦ 0.5, 0.6 <x + y + z <1.0, 0 ≦ z ≦ 0.1.

Moreover, it is preferable to use what is represented by the following compositional formula (Formula 2) as LMO. Li _{(1 + η)} Mn _(2-λ) M ′ _λ O ₄ (Chemical _formula 2)
In the above composition formula (Formula 2), (1 + η) represents the composition ratio of Li, (2-λ) represents the composition ratio of Mn, and λ represents the composition ratio of the element M ′. The composition ratio of O (oxygen) is 4.

The element M ′ is at least one element selected from the group consisting of Mg (magnesium), Ca (calcium), Sr (strontium), Al, Ga, Zn (zinc), and Cu (copper).

0 ≦ η ≦ 0.2 and 0 ≦ λ ≦ 0.1.

It is preferable to use Mg or Al as the element M ′ in the composition formula (Formula 2). By using Mg or Al, the battery life can be extended. In addition, the safety of the battery can be improved.

When LMO is included as the positive electrode active material, Mn in the compound is stable in the charged state, and thus heat generation due to the charging reaction can be suppressed. Thereby, the safety | security of a battery can be improved. That is, heat generation at the positive electrode can be suppressed, and the safety of the battery can be improved.

Thus, by using a mixture of NMC and LMO as the positive electrode active material, the stability of the positive electrode during charging can be improved and heat generation can be suppressed even when the capacity is increased. As a result, a battery with excellent safety can be provided.

The content of NMC is preferably 65% by mass or more, more preferably 70% by mass or more, and more preferably 80% by mass or more with respect to the total amount of the positive electrode mixture, from the viewpoint of increasing the capacity of the battery. More preferably.

Hereinafter, the positive electrode mixture and the current collector will be described in detail. The positive electrode mixture contains a positive electrode active material and a binder, and is formed on the current collector. Although there is no restriction | limiting in the formation method, it forms as follows, for example. Other materials such as a positive electrode active material, a conductive material, a binder, and a thickener used as necessary are mixed in a dry form to form a sheet, and this is pressure-bonded to a current collector (dry method). In addition, other materials such as a positive electrode active material, a conductive material, a binder, and a thickener used as necessary are dissolved or dispersed in a dispersion solvent to form a slurry, which is applied to a current collector and dried. (Wet method).

As the particles of the positive electrode active material, those in the form of a lump, polyhedron, sphere, ellipsoid, plate, needle, column, etc. are used. Among them, it is preferable that the primary particles are aggregated to form secondary particles, and the shape of the secondary particles is spherical or elliptical.

In an electrochemical element such as a battery, the active material in the electrode expands and contracts as it is charged / discharged, so that the active material is easily damaged or the conductive path is broken due to the stress. For this reason, it is preferable to use particles in which primary particles are aggregated to form secondary particles, rather than using single particles of only primary particles, because the stress of expansion and contraction can be relieved and the above deterioration can be prevented. In addition, it is preferable to use spherical or oval spherical particles rather than plate-like particles having axial orientation, since the orientation in the electrode is reduced, so that the expansion and contraction of the electrode during charge / discharge is reduced. Further, it is preferable because other materials such as a conductive material are easily mixed uniformly when forming the electrode.

The range of the median diameter d50 of the NMC particles applied to the positive electrode active material (the median diameter d50 of the secondary particles when the primary particles are aggregated to form secondary particles) is as follows. The lower limit of the range is 0.1 μm or more, preferably 0.5 μm or more, more preferably 1 μm or more, further preferably 3 μm or more, and the upper limit is 20 μm or less, preferably 18 μm or less, more preferably 16 μm or less, and even more preferably. Is 15 μm or less. If it is less than the above lower limit, the tap density (fillability) may be lowered, and a desired tap density may not be obtained. If the upper limit is exceeded, it takes time to diffuse lithium ions in the particles, so that the battery performance is lowered. There is a risk of inviting. Moreover, when the said upper limit is exceeded, there exists a possibility that a mixing property with other materials, such as a binder and a electrically conductive material, may fall at the time of formation of an electrode. Therefore, when this mixture is slurried and applied, it may not be applied uniformly, which may cause problems such as streaking. Here, the tap density (fillability) may be improved by mixing two or more kinds of positive electrode active materials having different median diameters d50. The median diameter d50 can be obtained from the particle size distribution obtained by the laser diffraction / scattering method.

The range of the average particle diameter of the primary particles when the primary particles are aggregated to form secondary particles is as follows. The lower limit of the range is 0.01 μm or more, preferably 0.05 μm or more, more preferably 0.08 μm or more, particularly preferably 0.1 μm or more, and the upper limit is 3 μm or less, preferably 2 μm or less, more preferably 1 μm. Hereinafter, it is particularly preferably 0.6 μm or less. When the above upper limit is exceeded, it becomes difficult to form spherical secondary particles, and battery performance such as output characteristics may be reduced due to a decrease in tap density (fillability) and a decrease in specific surface area. Moreover, if it is less than the said minimum, there exists a possibility of producing problems, such as the reversibility of charging / discharging degrading by crystallinity fall.

The range of the BET specific surface area of the positive electrode active material particles such as NMC is as follows. The lower limit of the range is 0.1 m ² / g or more, preferably 0.3 m ² / g or more, more preferably 0.4 m ² / g or more, and the upper limit is 4.0 m ² / g or less, preferably 2 .5m ² / g, more preferably not more than 1.5 m ² / g. If it is less than the said minimum, there exists a possibility that battery performance may fall. When the above upper limit is exceeded, the tap density is difficult to increase, and the miscibility with other materials such as a binder and a conductive material may be reduced. Therefore, there is a possibility that applicability at the time of slurrying and applying this mixture is deteriorated. The BET specific surface area is a specific surface area (area per unit g) determined by the BET method.
(Carbon coated aluminum oxide)
The carbon-coated aluminum oxide has a structure in which part or all of the surface of the particulate aluminum oxide is coated with carbon. Examples of the aluminum oxide include activated alumina and aluminum silicate.

Examples of the aluminum silicate include allophane, kaolin, zeolite, saponite, and imogolite. From the viewpoint of improving cycle characteristics, imogolite which is an aluminum silicate whose specific surface area can be easily adjusted is preferable. Aluminum silicate is an oxide salt of Si and Al. Since Si and Al have different valences, there are many OH groups in the oxide salt of Si and Al, which has ion exchange ability.

The imogolite in the present embodiment is an aluminum silicate having an element molar ratio Si / Al of 0.1 or more and less than 4.0. Such imogolite, for _{_{_{_{example, nSiO 2 · Al 2 O 3}}}} · mH 2 O [n = 0.5 ~ 2.0, m = 0 or] include those having a composition represented by.

Also, as imogolite, the element molar ratio Si / Al is preferably 0.1 or more and less than 4.0. The element molar ratio Si / Al of imogolite is more preferably 0.2 or more and 3.0 or less, and further preferably 0.4 or more and 2.5 or less. By setting the element molar ratio Si / Al within this range, the above tendency is further increased.

Imogolite preferably has a peak around 3 ppm in the ²⁷ Al-NMR spectrum. ^{As the 27} Al-NMR measuring apparatus, for example, AV400WB manufactured by Bruker BioSpin can be used. Specific measurement conditions are as follows.

Resonance frequency: 104MHz
Measuring method: MAS (single pulse)
MAS rotation speed: 10 kHz
Measurement area: 52 kHz
Number of data points: 4096
resolution (measurement area / number of data points): 12.7 Hz
Pulse width: 3.0 μsec
Delay time: 2 seconds Chemical shift value standard: 3.94 ppm of α-alumina
window function: exponential function Line Broadening coefficient: 10 Hz
In addition, imogolite preferably has peaks in the vicinity of 2θ = 26.9 ° and 40.3 ° in a powder X-ray diffraction spectrum using CuKα ray as an X-ray source. In addition, for example, Geigerflex RAD-2X (trade name) manufactured by Rigaku Corporation can be used as the X-ray diffraction apparatus.

In addition, from the viewpoint of storage characteristics, it is preferable that the tubular substance having a length of 50 nm or more does not exist in imogolite when observed with a transmission electron microscope (TEM) at a magnification of 100,000. Observation of the particles with a transmission electron microscope (TEM) is performed at an acceleration voltage of 100 kV.

The aluminum oxide may be synthesized, or a commercially available product may be purchased and used.

When synthesizing aluminum oxide, a step of mixing a solution containing silicate ions and a solution containing aluminum ions to obtain a reaction product, and heat-treating the reaction product in an aqueous medium in the presence of an acid And may have other steps as necessary. From the viewpoint of the yield of the obtained aluminum silicate and structure formation, etc., at least after the heat treatment step, preferably before and after the heat treatment step, a washing step for performing desalting and solid separation Is preferred.

Aluminum that excels in the ability to adsorb metal ions or halide ions (for example, fluoride ions) by desalting the coexisting ions from the solution containing the reaction product aluminum silicate and then heat-treating in the presence of an acid. An oxide can be produced efficiently. Here, examples of the coexisting ions include sodium ions, chloride ions, perchlorate ions, nitrate ions, sulfate ions, and the like. This can be considered as follows, for example. An aluminum oxide having a regular structure is formed by heat-treating the aluminum oxide from which the coexisting ions inhibiting the formation of the regular structure are removed in the presence of an acid. It can be considered that when imogolite has a regular structure, the affinity for metal ions or halide ions is improved, and metal ions or halide ions can be adsorbed efficiently.

Further, in the aluminum oxide according to this embodiment, at least a part or all of the surface of the aluminum oxide is coated with carbon. The carbon to be coated is coated on at least a part or all of the surface of the aluminum oxide.

The method for coating the surface of the aluminum oxide with carbon is not particularly limited. For example, after adding inorganic particles serving as a nucleus to a mixed solution in which an organic compound is dissolved or dispersed in a solvent, the solvent is heated and the like. Examples include wet coating to be removed, dry coating in which carbon particles and an organic compound are mixed with each other, and the mixture is kneaded while applying a shearing force, and vapor phase coating such as a CVD method. From the viewpoints of cost and manufacturing process reduction, dry type and vapor phase layer coating without using a solvent are more preferable.

There are no particular restrictions on the organic compound (carbon precursor) that remains carbonaceous by the heat treatment, but it is generated by pyrolyzing, for example, ethylene heavy end pitch, crude oil pitch, coal tar pitch, asphalt cracking pitch, polyvinyl chloride, etc. Synthetic pitch produced by polymerizing pitch, naphthalene, etc. in the presence of a super strong acid can be used. In addition, as a thermoplastic material, polyvinyl chloride, polyvinyl alcohol, polyvinyl acetate, polyvinyl butyral, or the like can be used, and as a thermosetting material, a phenol resin, a furan resin, or the like can be used.

In addition, the firing conditions of the inorganic particles coated with the organic compound may be appropriately determined in consideration of the carbonization rate of the organic compound, and there is no particular limitation, but in the range of 800 to 1300 ° C. in an inert atmosphere. Preferably there is. If the temperature is lower than 800 ° C, the organic matter is not sufficiently baked, and the initial irreversible capacity is increased due to the excessive increase in the specific surface area. When heated above 1300 ° C, the specific surface area is excessively decreased. This is because there are disadvantages. Examples of the inert atmosphere include nitrogen, argon, helium and the like.

Hereinafter, the aluminum oxide whose surface is coated with carbon may be referred to as an aluminum oxide whose surface is partially or entirely coated with carbon. Moreover, it may only be called a carbon covering aluminum oxide.

From the viewpoint of cycle characteristics, the BET specific surface area of the aluminum oxide whose surface is partly or entirely covered with carbon is preferably 30 m ² / g or less, and more preferably 25 m ² / g or less. Further, the lower limit of the BET specific surface area is not particularly limited, but is preferably 1 m ² / g or more, more preferably 3 m ² / g or more, from the viewpoint of the ability to adsorb metal ions or halide ions. More preferably, it is 5 m ² / g or more.

The BET specific surface area of the carbon-coated aluminum oxide is measured from the nitrogen adsorption capacity according to JIS Z 8830 (2001). As an evaluation apparatus, a nitrogen adsorption measuring apparatus (AUTOSORB-1, QUANTACHROME) 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, the measurement cell charged with 0.05 g of the measurement sample is depressurized to 10 Pa or less with a vacuum pump, heated at 110 ° C., held for 3 hours or more, and kept at a normal temperature while maintaining the depressurized state. Cool naturally 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 aluminum oxide, from the viewpoint of improving the adsorption capacity of the metal ion or halide ion, it is preferably, 0.12 cm ³ / g or more total pore volume is 0.1 cm ³ / g or more Is more preferably 0.15 cm ³ / g or more. Further, the upper limit value of the total pore volume is not particularly limited. From the viewpoint of suppressing the moisture adsorption amount in the air per unit mass, the total pore volume is preferably 1.5 cm ² / g or less, more preferably 1.2 cm ² / g or less. More preferably, it is 0 cm ² / g or less.

The total pore volume of carbon-coated aluminum oxide is based on the BET specific surface area, and the gas adsorption amount closest to relative pressure 1 is converted to liquid among the data obtained when the relative pressure is 0.95 or more and less than 1. And ask.

The carbon content of the aluminum oxide whose surface is partly or entirely coated with carbon is, for example, the differential thermal-thermogravimetric analyzer (TG-DTA) TG-DTA-6200 (SII Nanotechnology Inc.) (Manufactured by the company) can be measured at a rate of mass reduction by holding at 850 ° C. for 20 minutes at a heating rate of 10 ° C./min under a flow of dry air. The carbon content is a value obtained by the following formula (1) with respect to the mass (W1) at 350 ° C. and the mass (W2) at 850 ° C. measured by TG-DTA.
Carbon content (mass%) = {(W1-W2) / W1} × 100 (1)
From the viewpoint of conductivity, the carbon content is preferably 0.5% by mass or more and less than 30% by mass, more preferably 1% by mass or more and less than 25% by mass, and more preferably 2% by mass or more and 20% by mass with respect to the mass of the aluminum oxide. More preferably less than mass%. Within the above range, the input / output characteristics are excellent.

The moisture content of the aluminum oxide whose surface is partially or entirely coated with carbon is, for example, a differential thermal-thermogravimetric analyzer (TG-DTA) TG-DTA-6200 (SII Nanotechnology Inc.) The mass at 25 ° C. measured by TG-DTA of aluminum oxide in which part or all of the surface is coated with carbon can be measured under the same conditions as the measurement of the carbon content. (W0) and the mass (W1) measured at 350 ° C. measured by TG-DTA, and the value obtained by the following equation (2).
Water content (mass%) = {(W0−W1) / W0} × 100 (2)
The water content depends on the influence of side reactions such as the degradation of the positive electrode active material and the decomposition reaction of the electrolyte due to the reaction of hydrogen fluoride (HF) generated by the influence of residual water and the like with the electrode or the electrolyte. There is a concern to reduce.

The water content is preferably less than 5%, more preferably less than 4%, and even more preferably less than 3% from the viewpoint of further improving battery capacity and cycle characteristics. Moreover, it is preferable that a lower limit is 0.01% or more from a practical viewpoint.

The content of the aluminum oxide whose surface is partly or entirely covered with carbon is 0.01% by mass or more and 5% by mass or less with respect to the total amount of the positive electrode mixture from the viewpoint of conductivity and high capacity. It is preferable that it is 0.1 to 4.5% by mass, more preferably 0.15 to 4% by mass. When the application is within the above range, cycle characteristics and input / output characteristics can be further improved.
(Conductive material for positive electrode)
Examples of the conductive material for the positive electrode include metal materials such as copper and nickel; graphite such as natural graphite and artificial graphite (graphite); carbon black such as acetylene black; and carbonaceous materials such as amorphous carbon such as needle coke. Is mentioned. Of these, one type may be used alone, or two or more types may be used in combination.

The conductive material for the positive electrode preferably contains acetylene black. The acetylene black is preferably particles having an average particle size of 20 nm or more and 100 nm or less, and is not particularly limited as long as it is in this particle size range. Here, examples of the particles include granular, flake-like, spherical, columnar, and irregular shapes. The “granular” is not an irregular shape but a shape having almost equal dimensions (JIS Z2500: 2000). The flake shape (strip shape) is a plate-like shape (JIS Z2500: 2000) and is also called a scaly shape because it is thin like a scale. In the present invention, as a result of SEM observation The aspect ratio (particle diameter a / average thickness t) is 2 to 100 in the form of 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 present application. The “spherical shape” is a shape substantially close to a sphere (see 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) (sometimes referred to as spherical coefficient or sphericity) is 1. In the range of 0.0 to 1.2, the particle diameter refers to the long diameter (DL). Examples of the columnar shape include a substantially cylindrical column and a substantially polygonal column, and the particle size refers to the height of the column.

When the average particle diameter of acetylene black contained in the conductive material exceeds 100 nm, the number of contact points with the positive electrode active material is reduced, the conductive network between the active materials is hindered, and the input / output characteristics of the battery tend to deteriorate. On the other hand, when the average particle size is less than 20 nm, the dispersibility in the positive electrode mixture is deteriorated, and the battery performance is significantly deteriorated due to an adverse effect such as segregation of acetylene black. Thus, the average particle diameter of acetylene black is preferably 20 nm or more and 100 nm or less, more preferably 30 nm or more and 80 nm or less, and particularly preferably 40 nm or more and 60 nm or less.

Note that the average particle diameter of the conductive material is an arithmetic average particle diameter obtained by measuring all the diameters of the particle images in the image taken with a scanning electron microscope taken at 200,000 times.

The content of the conductive material is preferably 0.2% by mass or more, more preferably 0.5% by mass or more, and still more preferably 1% by mass or more, based on the total amount of the positive electrode mixture. The upper limit of the content of the conductive material Is preferably 30% by mass or less, more preferably 20% by mass or less, and still more preferably 10% by mass or less. Within the above range, the battery capacity and input / output characteristics are excellent.

Furthermore, the content of acetylene black contained in the conductive material is preferably 0.1% by mass or more and 15% by mass or less, and preferably 1% by mass or more with respect to the total amount of the positive electrode mixture, from the viewpoint of conductivity and high capacity. 10 mass% or less is more preferable, and 2 mass% or more and 5 mass% or less are further more preferable. Within the above range, the battery capacity and input / output characteristics are excellent.
(Binder for positive electrode)
The binder for the positive electrode is not particularly limited, and when the positive electrode mixture is formed by a coating method, a material having good solubility and dispersibility in the dispersion solvent is selected. Specific examples include resin polymers such as polyethylene, polypropylene, polyethylene terephthalate, polymethyl methacrylate, polyimide, aromatic polyamide, cellulose, and nitrocellulose; SBR (styrene-butadiene rubber), NBR (acrylonitrile-butadiene rubber), fluorine Rubbery polymers such as rubber, isoprene rubber, butadiene rubber, ethylene-propylene rubber; styrene / butadiene / styrene block copolymer or its hydrogenated product, EPDM (ethylene / propylene / diene terpolymer), styrene / Thermoplastic elastomeric polymers such as ethylene / butadiene / ethylene copolymers, styrene / isoprene / styrene block copolymers or hydrogenated products thereof; syndiotactic-1,2-polybutadiene, polyacetic acid Soft resinous polymers such as Nyl, ethylene / vinyl acetate copolymer, propylene / α-olefin copolymer; polyvinylidene fluoride (PVDF), polytetrafluoroethylene, fluorinated polyvinylidene fluoride, polytetrafluoroethylene / ethylene Fluoropolymers such as copolymers and polytetrafluoroethylene / vinylidene fluoride copolymers; polymer compositions having ion conductivity of alkali metal ions (particularly lithium ions), and the like. Of these, one type may be used alone, or two or more types may be used in combination. 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.

The content of the binder with respect to the total amount of the positive electrode mixture is preferably 0.1% by mass or more, more preferably 1% by mass or more, and still more preferably 3% by mass or more. The upper limit is preferably 50% by mass or less, more preferably 40% by mass or less, still more preferably 30% by mass or less, and particularly preferably 10% by mass or less. By setting it as the said range, battery performance, such as cycling characteristics, can be made more favorable.

The layer formed on the current collector using the above wet method or dry method is preferably consolidated by a hand press or a roller press in order to improve the packing density of the positive electrode active material.

The material of the current collector for the positive electrode is not particularly limited, and specific examples include metal materials such as aluminum, stainless steel, nickel plating, titanium, and tantalum; and carbonaceous materials such as carbon cloth and carbon paper. Of these, metal materials, particularly aluminum, are preferred.

The shape of the current collector is not particularly limited, and materials processed into various shapes can be used. Specific examples of the metal material include a metal foil, a metal cylinder, a metal coil, a metal plate, a metal thin film, an expanded metal, a punch metal, and a foam metal, and the carbonaceous material includes a carbon plate, a carbon thin film, A carbon cylinder etc. are mentioned. Among these, it is preferable to use a metal thin film. In addition, you may form a thin film suitably in mesh shape. The thickness of the thin film is arbitrary, but the range is as follows. The lower limit of the range is 1 μm or more, preferably 3 μm or more, more preferably 5 μm or more, and the upper limit is 1 mm or less, preferably 100 μm or less, more preferably 50 μm or less. If it is less than the said minimum, intensity | strength required as a collector may be insufficient. Moreover, when the said upper limit is exceeded, flexibility will fall and workability may deteriorate.

The positive electrode mixture used in the present invention has a density of 2.4 g / cm ³ or more and 3.3 g / cm ³ or less and a single-side coating amount on the current collector of 70 g / m ² or more and 250 g / m ² or less. Is preferred.

When the density is within the above range, the input / output characteristics can be further improved. From such a viewpoint, the single-side coating amount of the positive electrode mixture to the positive electrode current collector is more preferably 80 g / m ² or more and 230 g / m ² or less, and 100 g / m ² or more and 180 g / m ² or less. More preferably.
2. Negative electrode In this embodiment, the negative electrode shown below is applicable to a long-life, high-input / output lithium ion secondary battery. The negative electrode (negative electrode plate) of the present embodiment includes a current collector and a negative electrode mixture formed on both surfaces thereof. The negative electrode mixture contains a negative electrode active material that can electrochemically occlude and release lithium ions.

Examples of the negative electrode active material include carbonaceous materials, metal oxides such as tin oxide and silicon oxide, metal composite oxides, lithium alloys such as lithium alone and lithium aluminum alloys, metals that can form alloys with lithium such as Sn and Si, and the like Is mentioned. These may be used alone or in combination of two or more. Among these, a carbonaceous material or a lithium composite oxide is preferable from the viewpoint of safety.

The metal composite oxide is not particularly limited as long as it can occlude and release lithium, but Ti (titanium), Li (lithium), or those containing both Ti and Li have high current density charge / discharge. It is preferable from the viewpoint of characteristics.

Carbonaceous materials include amorphous carbon, natural graphite, composite carbonaceous materials in which a film formed by dry CVD (Chemical Vapor Deposition) method or wet spray method is formed on natural graphite, resins such as epoxy and phenol Carbonaceous materials such as artificial graphite and amorphous carbon material obtained by firing using raw materials or pitch materials obtained from petroleum or coal as raw materials can be used.

In addition, lithium metal that can occlude and release lithium by forming a compound with lithium, or a group 4 element such as silicon, germanium, and tin that can occlude and release lithium by forming a compound with lithium and inserting it in a crystal gap. Oxides or nitrides may be used.

In particular, carbonaceous materials are highly conductive, and are excellent in terms of low temperature characteristics and cycle stability. 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.

The negative electrode mixture is formed on the current collector. Although there is no restriction | limiting in the formation method, it forms using a dry method and a wet method similarly to a positive mix. The negative electrode active material is used in the form of powder (granular).

Further, a second carbonaceous material having a different property from the first carbonaceous material used as the negative electrode active material may be added as a conductive material. The above properties indicate one or more characteristics of X-ray diffraction parameters, median diameter, aspect ratio, BET specific surface area, orientation ratio, Raman R value, tap density, true density, pore distribution, circularity, and ash content. .

As the second carbonaceous material (conductive material), a highly conductive carbonaceous material 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. These may be used alone or in combination of two or more. Thus, by adding the second carbonaceous material (conductive material), there are effects such as reducing the resistance of the electrode.

Regarding the content (addition amount, ratio, amount) of the second carbonaceous material (conductive material), the range of the content of the conductive material relative to the mass of the negative electrode mixture is as follows. The lower limit of the range is 1% by mass or more, preferably 2% by mass or more, more preferably 3% by mass or more, and the upper limit is 45% by mass or less, preferably 40% by mass or less. If it is less than the above lower limit, it is difficult to obtain the effect of improving conductivity, and if it exceeds the above upper limit, the initial irreversible capacity may be increased.

The material of the current collector for the negative electrode is not particularly limited, and specific examples 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, and materials processed into various shapes can be used. Specific examples include metal foil, metal cylinder, metal coil, metal plate, metal thin film, expanded metal, punch metal, and foam metal. Among these, a metal thin film is preferable, and a copper foil is more preferable. The 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 for use as a current collector. The thickness of the current collector is not limited, but if the thickness is less than 25 μm, its strength can be increased by using a strong copper alloy (phosphor bronze, titanium copper, Corson alloy, Cu—Cr—Zr alloy, etc.) rather than pure copper. Can be improved.

The binder for the negative electrode active material is not particularly limited as long as it is a material that is stable with respect to the non-aqueous electrolyte and the dispersion solvent used when forming the electrode. Specifically, resin-based polymers such as polyethylene, polypropylene, polyethylene terephthalate, polymethyl methacrylate, aromatic polyamide, cellulose, nitrocellulose; SBR (styrene-butadiene rubber), isoprene rubber, butadiene rubber, fluorine rubber, NBR ( Rubber-like polymers such as acrylonitrile-butadiene rubber) and ethylene-propylene rubber; styrene / butadiene / styrene block copolymers or hydrogenated products thereof; EPDM (ethylene / propylene / diene terpolymer), styrene / ethylene / Thermoplastic elastomeric polymers such as butadiene / styrene copolymer, styrene / isoprene / styrene block copolymer or hydrogenated products thereof; syndiotactic-1,2-polybutadiene, polyvinyl acetate, ethylene Soft resinous polymers such as ethylene / vinyl acetate copolymer, propylene / α-olefin copolymer; polyvinylidene fluoride, polytetrafluoroethylene, fluorinated polyvinylidene fluoride, polytetrafluoroethylene / ethylene copolymer, etc. Fluoropolymers; polymer compositions having ionic conductivity of alkali metal ions (especially lithium ions). These may be used alone or in combination of two or more.

As the dispersion solvent for forming the slurry, any solvent can be used as long as it can dissolve or disperse the negative electrode active material, the binder, and the conductive material and the thickener used as necessary. There is no restriction, 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 examples of the organic solvent include N-methylpyrrolidone (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, Examples include methylnaphthalene and hexane. In particular, when an aqueous solvent is used, it is preferable to use a thickener. A dispersing agent or the like is added to the thickener, and a slurry such as SBR is made into a slurry. In addition, the said dispersion solvent may be used individually by 1 type, or may be used in combination of 2 or more type.

The content of the binder is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, and further preferably 0.6% by mass or more with respect to the total amount of the negative electrode mixture. The upper limit of the binder content is 20% by mass or less, preferably 15% by mass or less, more preferably 10% by mass or less, and still more preferably 8% by mass or less.

If the upper limit is exceeded, the proportion of the binder that does not contribute to the battery capacity increases, which may lead to a decrease in battery capacity. Moreover, if it is less than the said minimum, the fall of the intensity | strength of a negative mix may be caused.

In particular, the range of the binder content relative to the mass of the negative electrode mixture when a rubbery polymer typified by SBR is used as the main component as the binder is as follows. The lower limit of the range is 0.1% by mass or more, preferably 0.5% by mass or more, more preferably 0.6% by mass or more, and the upper limit is 5% by mass or less, preferably 3% by mass or less, more preferably. Is 2% by mass or less.

Further, the range of the content of the binder with respect to the mass of the negative electrode mixture when a fluorine-based polymer typified by polyvinylidene fluoride is used as the main component as the binder is as follows. The lower limit of the range is 1% by mass or more, preferably 2% by mass or more, more preferably 3% by mass or more, and the upper limit is 15% by mass or less, preferably 10% by mass or less, more preferably 8% by mass or less. is there.

Thickener is used to adjust the viscosity of the slurry. The thickener is not particularly limited, and specific examples include carboxymethyl cellulose, methyl cellulose, hydroxymethyl cellulose, ethyl cellulose, polyvinyl alcohol, oxidized starch, phosphorylated starch, casein, and salts thereof. These may be used alone or in combination of two or more.

The range of the content of the thickener relative to the mass of the negative electrode mixture when the thickener is used is as follows. The lower limit of the range is 0.1% by mass or more, preferably 0.5% by mass or more, more preferably 0.6% by mass or more, and the upper limit is 5% by mass or less, preferably 3% by mass or less, more preferably. Is 2% by mass or less.

If it is less than the said minimum, there exists a possibility that the applicability | paintability of a slurry may fall. Moreover, when the said upper limit is exceeded, the ratio of the negative electrode active material which occupies for a negative electrode mixture will fall, and there exists a possibility of the fall of battery capacity or the raise of resistance between negative electrode active materials.
3. Electrolytic Solution The electrolytic solution of the present embodiment is composed of a lithium salt (electrolyte) and a non-aqueous solvent that dissolves the lithium salt. You may add an additive as needed.

The lithium salt is not particularly limited as long as it is a lithium salt that can be used as an electrolyte of a non-aqueous electrolyte solution for a lithium ion secondary battery. For example, the following inorganic lithium salt, fluorine-containing organic lithium salt, or oxalate borate Examples include salts.

Examples of the inorganic lithium _{_{_{salt, LiPF 6, LiBF 4, LiAsF}}} 6, LiSbF inorganic fluoride salts and the like _{_6,} LiClO _4, Libro 4, LiIO and perhalogenate such as _4, an inorganic chloride salts such as LiAlCl _4, etc. Is mentioned.

Examples of the fluorine-containing organic lithium salt include 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 Perfluoroalkanesulfonylimide salt such as ₄ F ₉ SO ₉ ); perfluoroalkanesulfonylmethide salt 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 hexafluorophosphate salts such like.

Examples of the oxalatoborate salt include lithium bis (oxalato) borate and lithium difluorooxalatoborate.

These lithium salts may be used alone or in combination of two or more. Among them, lithium hexafluorophosphate (LiPF ₆ ) is preferable when comprehensively judging the solubility in a solvent, charge / discharge characteristics in the case of a secondary battery, input / output characteristics, cycle characteristics, and the like.

There is no particular limitation on the concentration of the electrolyte in the non-aqueous electrolyte solution, but the concentration range of the electrolyte is as follows. The lower limit of the concentration is 0.5 mol / L or more, preferably 0.6 mol / L or more, more preferably 0.7 mol / L or more. Further, the upper limit of the concentration is 2 mol / L or less, preferably 1.8 mol / L or less, more preferably 1.7 mol / L or less. If the concentration is too low, the electric conductivity of the electrolytic solution may be insufficient. On the other hand, if the concentration is too high, the viscosity increases and the electrical conductivity may decrease. Such a decrease in electrical conductivity may reduce the performance of the lithium ion secondary battery.

The non-aqueous solvent is not particularly limited as long as it is a non-aqueous solvent that can be used as an electrolyte solvent for a lithium ion secondary battery. For example, the following cyclic carbonate, chain carbonate, chain ester, cyclic ether, and chain And ethers.

As the cyclic carbonate, an alkylene group constituting the cyclic carbonate preferably has 2 to 6 carbon atoms, and more preferably 2 to 4 carbon atoms. Specific examples include ethylene carbonate, propylene carbonate, butylene carbonate, and the like. Of these, ethylene carbonate and propylene carbonate are preferable.

Further, a cyclic carbonate having a double bond in the molecule or a cyclic carbonate containing a halogen atom, such as vinylene carbonate or fluoroethylene carbonate, can also be used. When using a carbon material as a negative electrode active material, it is preferable to contain vinylene carbonate from the viewpoint of cycle characteristics.

The chain carbonate is preferably a dialkyl carbonate, and the two alkyl groups each preferably have 1 to 5 carbon atoms, more preferably 1 to 4 carbon atoms. Specifically, symmetrical chain carbonates such as dimethyl carbonate, diethyl carbonate, and di-n-propyl carbonate; asymmetric chain carbonates such as methyl ethyl carbonate, methyl-n-propyl carbonate, and ethyl-n-propyl carbonate Is mentioned. 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 them, it is preferable to use methyl acetate from the viewpoint of improving the low temperature characteristics.

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

Examples of chain ethers include dimethoxyethane and dimethoxymethane.

These may be used alone or in combination of two or more, but it is preferable to use a mixed solvent in which two or more compounds are used in combination. For example, it is preferable to use a high dielectric constant solvent of cyclic carbonates in combination with a low viscosity solvent such as chain carbonates or chain esters. One of the preferable combinations is a combination mainly composed of cyclic carbonates and chain carbonates. Among them, the total of the cyclic carbonates and the chain carbonates in the non-aqueous solvent is 80% by volume or more, preferably 85% by volume or more, more preferably 90% by volume or more, and the cyclic carbonates and the chain carbonates. It is preferable that the cyclic carbonates have a capacity in the following range with respect to the total of the above. The lower limit of the capacity of the cyclic carbonates is 5% by volume or more, preferably 10% by volume or more, more preferably 15% by volume or more, and the upper limit is 50% by volume or less, preferably 35% by volume or less, more preferably 30%. The capacity is less than%. By using such a combination of non-aqueous solvents, the cycle characteristics and storage characteristics of the battery are improved.

Specific examples of preferred combinations of cyclic carbonates and chain carbonates 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 And 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 asymmetric chain carbonates as chain carbonates are more preferable. 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. Such a combination of ethylene carbonate, symmetric chain carbonates, and asymmetric chain carbonates can improve cycle characteristics and input / output characteristics. Among these, those in which the asymmetric chain carbonate is methyl ethyl carbonate are preferable, and those in which the alkyl group constituting the dialkyl carbonate has 1 to 2 carbon atoms are preferable.

The additive is not particularly limited as long as it is an additive for a non-aqueous electrolyte solution of a lithium ion secondary battery. For example, nitrogen, sulfur or a heterocyclic compound containing nitrogen and sulfur, a cyclic carboxylic acid ester, fluorine Examples thereof include cyclic carbonates and other compounds having an unsaturated bond in the molecule.

In addition to the above additives, other additives such as an overcharge prevention material, a negative electrode film forming material, a positive electrode protective material, and a high input / output material may be used depending on the required function.
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 satisfying such characteristics, a resin, an inorganic material, glass fiber, or the like is used.

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

As the inorganic material, oxides such as alumina and silicon dioxide, nitrides such as aluminum nitride and silicon nitride, and sulfates such as barium sulfate and calcium sulfate are used. 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 the thin film-shaped substrate, those having a pore diameter of 0.01 to 1 μm and a thickness of 5 to 50 μm are 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 using a fluororesin as a binder may be formed on the surface of the positive electrode.
5. Other constituent members As other constituent members of the lithium ion secondary battery, a cleavage valve may be provided. By opening the cleavage valve, it is possible to suppress an increase in pressure inside the battery and to improve safety.

Moreover, you may provide the structure part which discharge | releases inert gas (for example, carbon dioxide etc.) with a temperature rise. By providing such a component, when the temperature inside the battery rises, the cleavage valve can be opened quickly due to the generation of inert gas, and safety can be improved. Examples of the material used for the above components include lithium carbonate and polyalkylene carbonate resin.
(Lithium ion secondary battery)
First, an embodiment in which the present invention is applied to a laminated battery will be described.

The 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 insulating layer, and the negative electrode are laminated in this order is prepared, and in that state, accommodated in an aluminum laminate pack, and the positive and negative electrode terminals are taken out of the aluminum laminate pack and sealed. Next, the nonaqueous electrolyte is poured into the aluminum laminate pack, and the opening of the aluminum laminate pack is sealed. Thereby, a lithium ion secondary battery is obtained.

Next, an embodiment in which the present invention is applied to a 18650 type cylindrical lithium ion secondary battery will be described with reference to the drawings.

As shown in FIG. 1, the lithium ion secondary battery 1 of the present embodiment 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 portion of the positive electrode tab terminal is joined by ultrasonic welding to the lower surface of a disk-shaped battery lid that is covered on the upper side of the electrode group 5 and serves as a positive electrode external terminal. 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 led out to the opposite sides of the both end faces of the electrode group 5, respectively. 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, a non-aqueous electrolyte (not shown) is injected into the battery container 6.

In the present invention, the capacity ratio between the negative electrode and the positive electrode (negative electrode capacity / positive electrode capacity) is preferably 1.03 to 1.8, more preferably 1.05 to 1.4 from the viewpoint of safety and energy density.

Here, the negative electrode capacity means [negative electrode discharge capacity], and the positive electrode capacity means [positive charge capacity of positive electrode minus negative electrode or positive electrode, whichever is greater]. Here, the “negative electrode discharge capacity” is defined to be calculated by the charge / discharge device when the lithium ions inserted into the negative electrode active material are desorbed. Further, the “initial charge capacity of the positive electrode” is defined as that 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, 4.2 V, 0.1 C to 0.5 C, 0.1 C after constant current and constant voltage (CCCV) charging with an end time of 2 to 5 hours. It can be measured under the conditions when a constant current (CC) discharge is performed up to 2.7 V at ˜0.5 C. The discharge capacity of the negative electrode was prepared by cutting a negative electrode having a measured discharge capacity of the lithium ion secondary battery into a predetermined area, using lithium metal as a counter electrode, and preparing a single electrode cell through a separator impregnated with an electrolyte. After charging with constant current and constant voltage (CCCV) at 0V, 0.1C to 0.5C and end current of 0.01C, discharge at constant current (CC) to 1.5V with 0.1C to 0.5C It can be calculated by measuring the discharge capacity per predetermined area under the conditions obtained 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)”.

Hereinafter, the present embodiment will be described in more detail based on examples. The present invention is not limited to the following examples.
[Production Example 1] <Production process of carbon-coated aluminum oxide>
A concentration: 350 mmol / L sodium orthosilicate aqueous solution (500 mL) was added to a 700 mmol / L aluminum chloride aqueous solution (500 mL), and the mixture was stirred for 30 minutes. To this solution, 330 mL of an aqueous sodium hydroxide solution having a concentration of 1 mol / L was added to adjust the pH to 6.1.

After the pH-adjusted solution was stirred for 30 minutes, centrifugal separation was performed for 5 minutes at a rotational speed of 3,000 min- ¹ using TOMY Corporation's SUPREMA 23 and standard rotor NA-16 as a centrifugal separator. After centrifugation, the supernatant solution was discharged, the gel precipitate was redispersed in pure water, and returned to the volume before centrifugation. Such desalting treatment by centrifugation was performed four times.

135 mL of hydrochloric acid having a concentration of 1 mol / L was added to the gel-like precipitate obtained after the supernatant was discharged for the fourth time in the desalting treatment, and the mixture was adjusted to pH = 3.5 and stirred for 30 minutes. The solution was then placed in a dryer and heated at 98 ° C. for 48 hours (2 days). To the solution after heating (salt concentration 47 g / L), 188 mL of a 1 mol / L sodium hydroxide aqueous solution was added to adjust the pH to 9.1. By adjusting the pH, the salt in the solution was aggregated, the aggregate was precipitated by the same centrifugation as described above, and then the supernatant was discharged. The desalting process of adding pure water to the precipitate after discharging the supernatant and returning to the volume before centrifugation was performed four times. The gel-like precipitate obtained after the fourth desalting of the desalting treatment was dried at 60 ° C. for 16 hours to recover 30 g of a particle lump. The particle mass was pulverized with a jet mill to obtain aluminum oxide.
<Process of carbon coating>
The above particles and polyvinyl alcohol powder (Wako Pure Chemical Industries, Ltd.) are mixed at a mass ratio of 100: 70 and baked at 850 ° C. for 1 hour in a nitrogen atmosphere, so that part or all of the surface is covered with carbon. Aluminum oxide was prepared.
<BET specific surface area>
The BET specific surface area of the aluminum oxide of Production Example 1 was measured based on the nitrogen adsorption ability. As the evaluation device, AUTASORB-1 (trade name) manufactured by QUANTACHROME was used. When performing these measurements, after pre-treatment of the sample described later, the evaluation temperature is 77K, and the evaluation pressure range is less than 1 in relative pressure (equilibrium pressure with respect to the saturated vapor pressure).

As a pretreatment, the measurement cell charged with 0.05 g of aluminum oxide was automatically deaerated and heated with a vacuum pump. The detailed conditions of this treatment were set such that the pressure was reduced to 10 Pa or less, heated at 110 ° C., held for 3 hours or more, and then naturally cooled to room temperature (25 ° C.) while maintaining the reduced pressure.

As a result of the evaluation, the BET specific surface area of the aluminum oxide of Production Example 1 was 8 m ² / g.
<Carbon coverage and water content>
In addition, the carbon content of the above aluminum oxide was measured using a differential thermal-thermogravimetric analyzer (TG-DTA) at a heating rate of 10 ° C./min at a temperature of 850 ° C. for 20 minutes under a dry air flow. Measured by mass reduction rate. Similarly, the moisture content of the above-described aluminum oxide was measured using a differential thermal-thermogravimetric analyzer (TG-DTA) TG-DTA-6200 (manufactured by SII Nanotechnology Co., Ltd.) under dry air flow. The mass reduction rate was measured at a heating rate of 10 ° C./min at 350 ° C. for 20 minutes. As a result of the evaluation, the carbon coating amount and the water content of the aluminum oxide of Production Example 1 were 14.7% by mass and 2.1% by mass, respectively.
[Production Example 2] <Process for producing carbon-coated aluminum oxide>
A concentration: 350 mmol / L sodium orthosilicate aqueous solution (500 mL) was added to a 700 mmol / L aluminum chloride aqueous solution (500 mL), and the mixture was stirred for 30 minutes. To this solution, 330 mL of an aqueous sodium hydroxide solution having a concentration of 1 mol / L was added to adjust the pH to 6.1.

After the pH-adjusted solution was stirred for 30 minutes, centrifugal separation was performed for 5 minutes at a rotational speed of 3,000 min- ¹ using TOMY Corporation's SUPREMA 23 and standard rotor NA-16 as a centrifugal separator. After centrifugation, the supernatant solution was discharged, the gel precipitate was redispersed in pure water, and returned to the volume before centrifugation. Such desalting treatment by centrifugation was performed three times.

135 mL of hydrochloric acid having a concentration of 1 mol / L was added to the gel-like precipitate obtained after the supernatant was discharged for the third time in the desalting treatment, and the pH was adjusted to 3.5, 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 solution after heating (aluminum oxide concentration 47 g / L), 188 mL of a 1 mol / L sodium hydroxide aqueous solution was added to adjust the pH to 9.1. By adjusting the pH, the aluminum oxide in the solution was aggregated, the aggregate was precipitated by the same centrifugation as described above, and then the supernatant was discharged. The desalting process of adding pure water to the precipitate after discharging the supernatant and returning to the volume before centrifugation was performed three times. The gel-like precipitate obtained after the third desalting of the desalting treatment was dried at 60 ° C. for 16 hours to obtain 30 g of powder.
<Process of carbon coating>
The above particles and polyvinyl alcohol powder (Wako Pure Chemical Industries, Ltd.) are mixed at a mass ratio of 100: 70 and baked at 850 ° C. for 1 hour in a nitrogen atmosphere, so that part or all of the surface is covered with carbon. Aluminum oxide was prepared.
<BET specific surface area>
The measurement was performed in the same process as described in Production Example 1 above. As a result of the evaluation, the BET specific surface area of the aluminum oxide of Production Example 2 was 13 m ² / g.
<Carbon coverage and water content>
In addition, the carbon content of the above aluminum oxide was measured using a differential thermal-thermogravimetric analyzer (TG-DTA) TG-DTA-6200 type (manufactured by SII Nanotechnology Co., Ltd.) under the flow of dry air. The mass decrease rate was measured at a temperature increase rate of 850 ° C./min and held at 850 ° C. for 20 minutes. Similarly, the moisture content of the above aluminum oxide is maintained at 350 ° C. for 20 minutes at a heating rate of 10 ° C./min under a flow of dry air using a differential thermal-thermogravimetric analyzer (TG-DTA). It was measured by mass reduction rate at. As a result of the evaluation, the carbon coating amount and the water content of the aluminum oxide of Production Example 2 were 19.6% by mass and 2.7% by mass, respectively.
[Production Example 3] <Production process of carbon-coated aluminum oxide>
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. To this solution, 1900 mL of a 1 mol / L sodium hydroxide aqueous solution was added to adjust the pH to 7. The pH adjusted solution was stirred for 30 minutes and then desalted by filtration under reduced pressure. To the precipitate after the desalting treatment, 90 mL of sulfuric acid having a concentration of 1 mol / L was added to adjust to pH = 4, and the mixture was stirred for 30 minutes. The solution was then placed in a dryer and heated at 98 ° C. for 48 hours (2 days). After heating, 330 mL of a 1 mol / L sodium hydroxide aqueous solution was added to the solution to adjust the pH to 9. The salt in the solution was aggregated by adjusting the pH, and this aggregate was precipitated by the same vacuum 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 mass was pulverized with a jet mill to obtain aluminum oxide.
<Process of carbon coating>
Carbon coating was performed in the same process as described in Production Example 1 above.
<BET specific surface area>
The measurement was performed in the same process as described in Production Example 1 above. As a result of the evaluation, the BET specific surface area of the aluminum oxide of Production Example 3 was 30 m ² / g.
<Carbon coverage and water content>
In addition, the carbon content of the above aluminum oxide was measured using a differential thermal-thermogravimetric analyzer (TG-DTA) TG-DTA-6200 type (manufactured by SII Nanotechnology Co., Ltd.) under the flow of dry air. The mass decrease rate was measured at a temperature increase rate of 850 ° C./min and held at 850 ° C. for 20 minutes. Similarly, the moisture content of the above aluminum oxide is maintained at 350 ° C. for 20 minutes at a heating rate of 10 ° C./min under a flow of dry air using a differential thermal-thermogravimetric analyzer (TG-DTA). It was measured by mass reduction rate at. As a result of the evaluation, the carbon coating amount and the water content of the aluminum oxide of Production Example 3 were 24.7% by mass and 0.9% by mass, respectively.
(Example 1)
[Production of positive electrode]
The positive electrode plate was produced as follows. The positive electrode active material Li (Ni _1/3 Mn _1/3 Co _1/3 ) O ₂ (average particle size 6 μm), acetylene black (average particle size 50 nm) as a conductive material, and carbon produced in Production Example 1 Coated aluminum oxide and polyvinylidene fluoride (PVDF) as a binder were sequentially added and mixed to obtain a mixture of positive electrode materials.

The positive electrode active material, acetylene black (AB) and carbon-coated aluminum oxide contents were prepared as shown in Table 1. Note that (positive electrode active material + acetylene black + aluminum oxide): binder = 94.5: 5.5.

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 evenly and uniformly to 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 was 2.60 g / cm ^3, and the coating amount on one side of the positive electrode mixture was 150 g / m ² .

[Production of negative electrode]
The negative electrode plate 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 carboxymethylcellulose (trade name: CMC # 2200, manufactured by Daicel Finechem Co., Ltd.) 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. A predetermined amount of this slurry was applied to both surfaces of a rolled copper foil having a thickness of 10 μm, which is a negative electrode current collector, substantially uniformly and uniformly. The negative electrode mixture density was 1.65 g / cm ^3, and the single-sided coating amount of the negative electrode mixture was 73 g / m ² .
(Example 2)
The ratio of the layered lithium-nickel-manganese-cobalt composite oxide, which is the positive electrode active material described in Example 1, is 89.5% by mass, acetylene black is 4.5% by mass as a conductive material,
A positive electrode and a battery were produced in the same process as in Example 1 except that the aluminum oxide produced in Production Example 1 was 0.5% by mass. Table 1 shows the physical properties of the aluminum oxide and the battery composition.
(Example 3)
88% by mass of the layered lithium / nickel / manganese / cobalt composite oxide, which is the positive electrode active material described in Example 1, 4.5% by mass of acetylene black as a conductive material,
A positive electrode and a battery were produced in the same process as in Example 1 except that the aluminum oxide produced in Production Example 1 was 2.0% by mass. Table 1 shows the physical properties of the aluminum oxide and the battery composition.
Example 4
88% by mass of the layered lithium / nickel / manganese / cobalt composite oxide, which is the positive electrode active material described in Example 1, 4.5% by mass of acetylene black as a conductive material,
A positive electrode and a battery were produced in the same process as in Example 1 except that the aluminum oxide produced in Production Example 2 was 2.0 mass%. Table 1 shows the physical properties of the aluminum oxide and the battery composition.
(Example 5)
88% by mass of the layered lithium / nickel / manganese / cobalt composite oxide, which is the positive electrode active material described in Example 1, 4.5% by mass of acetylene black as a conductive material,
A positive electrode and a battery were produced in the same process as in Example 1 except that the aluminum oxide produced in Production Example 3 was 2.0% by mass. Table 1 shows the physical properties of the aluminum oxide and the battery composition.
(Example 6)
86% by mass of the layered lithium / nickel / manganese / cobalt composite oxide, which is the positive electrode active material described in Example 1, 4.5% by mass of acetylene black as a conductive material,
A positive electrode and a battery were produced in the same process as in Example 1 except that the aluminum oxide produced in Production Example 1 was 4.0% by mass. Table 1 shows the physical properties of the aluminum oxide and the battery composition.
(Comparative Example 1)
The proportion of layered lithium-nickel-manganese-cobalt composite oxide, which is the positive electrode active material described in Example 1, is 90% by mass, and acetylene black is 4.5% by mass as a conductive material,
A positive electrode and a battery were produced in the same process as in Example 1 except that no aluminum oxide was used. Table 1 shows the physical properties of the aluminum oxide and the battery composition.

[Production of Battery] Production of Laminate Type Battery 13.5 cm ² square cut positive electrode made of polyethylene porous sheet separator (trade name: Hypore, manufactured by Asahi Kasei Co., Ltd., 30 μm thick, “Hypore” is a registered trademark ) And further laminated with negative electrodes cut into 14.3 cm ² squares to produce a laminate. This laminate is put into an aluminum laminate container (trade name: aluminum laminate film, manufactured by Dai Nippon Printing Co., Ltd.), and a non-aqueous electrolyte (ethylene carbonate / dimethyl carbonate / diethyl carbonate containing 1M LiPF ₆ = 2.5 / 6). /1.5 mixed solution (volume ratio) added 1 mL of vinylene carbonate 1.0% by mass to the total amount of the mixed solution (manufactured by Ube Industries Co., Ltd.), thermally welded aluminum laminate container, A laminate type battery was produced.
[Evaluation of cycle characteristics]
The cycle characteristics were calculated as follows.

Cycle characteristics were evaluated by cycle tests with repeated charge and discharge. For charging, a laminated lithium battery produced in an environment of 50 ° C. was subjected to constant current charging at a current value of 1 C up to an upper limit voltage of 4.2 V, and then constant voltage charging at 4.2 V. The charge termination condition was a current value of 0.01C. The discharge was performed at a constant current of 1 C up to 3.0 V in a 50 ° C. environment. This charge / discharge was repeated 1000 times (1000 cycles), and the cycle characteristics were calculated by the following formula. Table 1 shows the results of the batteries to which the carbon-coated aluminum oxides produced by the production methods 1 to 3 were applied.

Cycle characteristics = (discharge capacity at 1000th cycle at current value 1C / discharge capacity at 3rd cycle at current value 1C) × 100

It can be confirmed that in the batteries to which the carbon-coated aluminum oxides shown in Examples 1 to 6 are added, the cycle characteristics are improved as compared with the battery of Comparative Example 1 in which the carbon-coated aluminum oxide is not included in the positive electrode mixture. The reason why the cycle characteristics are improved is not clear, but is estimated as follows. Aluminum oxide has ion exchange capacity because of the presence of many hydroxyl groups (—OH) on the surface, and hydrofluoric acid (HF) contained in the electrolyte, which is one of the causes of battery deterioration, is converted to aluminum. It is believed that the supplementation by the oxide suppresses the deterioration of the active material and suppresses the decomposition reaction of the electrolyte, thereby improving the cycle characteristics.

1 Lithium ion secondary battery 2 Positive electrode
3 Negative electrode 4 Separator 5 Electrode group
6 Battery container

Claims

A lithium ion secondary battery comprising a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the positive electrode has a current collector and a positive electrode mixture formed on the current collector, and the positive electrode mixture is A lithium ion secondary battery comprising a layered lithium / nickel / manganese / cobalt composite oxide and an aluminum oxide having a part or all of its surface coated with carbon.
2. The lithium according to claim 1, wherein the content of the aluminum oxide whose surface is partially or entirely coated with carbon is 0.01% by mass or more and 5% by mass or less with respect to the total amount of the positive electrode mixture. Ion secondary battery.
The lithium ion secondary battery according to claim 1, wherein the aluminum oxide has a BET specific surface area of 1 m 2 / g to 30 m 2 / g.
The weight loss rate between 25 ° C. and 350 ° C. measured using a differential thermal-thermogravimetric analyzer (TG-DTA) of aluminum oxide in which part or all of the surface is coated with carbon is less than 5%. The lithium ion secondary battery according to any one of claims 1 to 3, wherein
The lithium ion secondary battery according to any one of claims 1 to 3, wherein the aluminum oxide is imogolite.
The lithium ion secondary battery according to any one of claims 1 to 4, wherein the positive electrode mixture includes a conductive material, and the conductive material is acetylene black.