JP2016152113A - Lithium ion secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lithium ion secondary battery superior in life and safety.SOLUTION: A lithium ion secondary battery comprises, in a battery container, a wound electrode group arranged by winding a positive electrode, a negative electrode and a separator and an electrolyte, and has a discharge capacity of 30 Ah or larger, but under 99 Ah. The positive electrode has a current collector and a positive electrode mixture applied to each face of the current collector. The positive electrode mixture includes a lithium-nickel-manganese-cobalt composite oxide (NMC) and a lithium phosphate. It is preferable that the content of the lithium phosphate be 0.1-5 mass% to the total mass of the positive electrode mixture.SELECTED DRAWING: Figure 1

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 computers and mobile phones by taking advantage of its 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, an 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 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 to 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, and the battery capacity is 10 Ah to 100 Ah (37 Wh to 370 Wh), which is a large lithium ion secondary battery compared to consumer lithium ion secondary batteries. Batteries are being considered. Since a large-sized lithium ion secondary battery has a large capacity for storing electricity, it is required to increase the battery life while ensuring the same safety as that of a consumer lithium ion secondary battery. Lithium cobalt oxide (LiCoO ₂ ), which is widely used as a positive electrode active material for consumer lithium-ion secondary batteries, is a lithium / nickel / manganese / cobalt composite with a reduced amount of cobalt in the active material due to restrictions on the amount of cobalt resources. Oxides (NMC) are being studied. This lithium-nickel-manganese-cobalt composite oxide (NMC) has a feature that it can operate up to an operating upper limit potential (lithium reference 4.6V) higher than the operating upper limit potential (lithium reference 4.3V) of lithium cobaltate. When operated up to a high potential, there is a concern that the life may be deteriorated due to side reactions due to decomposition of the electrolyte or the like. As a technique for suppressing a side reaction at a high potential, a technique for suppressing a side reaction and improving a lifetime by coating the active material surface of a lithium / nickel / manganese composite oxide has been proposed (see Patent Document 1). ).

Japanese Patent No. 5491461

However, in the lithium ion secondary battery described in Patent Document 1, since the coating of the positive electrode active material becomes a resistance component and the battery internal resistance increases, Joule heat generation during energization is large, particularly 30 Ah or more, When a large lithium ion secondary battery of 99 Ah or less is overcharged, the safety may not be sufficient.
In view of the above problems, the present invention has been made for a lithium-nickel-manganese-cobalt composite oxide (NMC) that can be applied to a large-sized lithium ion secondary battery, and is a lithium ion secondary excellent in life and safety. To provide a battery.

Specific means for solving the above problems are as follows.
<1> A lithium ion secondary battery comprising an electrode winding group in which a positive electrode, a negative electrode, and a separator are wound, and an electrolyte solution, and a discharge capacity of 30 Ah or more and less than 99 Ah,
The positive electrode includes a current collector and a positive electrode mixture applied to both surfaces of the current collector, and the positive electrode mixture includes lithium / nickel / manganese / cobalt composite oxide (NMC) and lithium phosphate. , Lithium ion secondary battery.
<2> The lithium ion secondary battery according to <1>, wherein the content of the lithium phosphate is 0.1% by mass or more and 5% by mass or less based on the total amount of the positive electrode mixture.

  According to the present invention, it is possible to provide a lithium ion secondary battery having a long life and excellent safety.

It is sectional drawing of the cylindrical lithium ion secondary battery of embodiment which can apply this invention.

In the following embodiments, when ranges are shown as A to B, A or more and B or less are shown 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 disposed between the positive electrode and the negative electrode.
When charging the lithium ion secondary battery, a charger is connected as an external circuit 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, 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. 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.
In this manner, charging / 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, a positive electrode, a negative electrode, an electrolytic solution, a separator, and other constituent members that are constituent elements of the lithium ion secondary battery of the present embodiment will be sequentially described.

1. Positive electrode In this embodiment, the positive electrode shown below is applicable to a high-capacity, high-input / output lithium ion secondary battery. The positive electrode (positive electrode plate) of the present embodiment is composed of a current collector and a positive electrode mixture (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.
The positive electrode active material is a layered lithium / nickel / manganese / cobalt composite oxide (NMC).
The content of the layered lithium / nickel / manganese / cobalt composite oxide (NMC) is preferably 95% by mass or more based on the total amount of the positive electrode mixture from the viewpoint of increasing the capacity of the battery. Is more preferably 90% by mass or more.
As the layered lithium / nickel / manganese / cobalt composite oxide (NMC), it is preferable to use one represented by the following composition formula (1).
Li _{(1 + δ)} Mn _x Ni _y Co _(1-xyz) M _z O ₂ (1)
In the composition 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) is The composition ratio of Co (cobalt) is shown. z represents the composition ratio of the element M. The composition ratio of O (oxygen) is 2.
The element M includes 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.

Further, as the positive electrode active material, materials other than the above NMC may be used. As the positive electrode active material other than NMC, those commonly used in this field can be used. For example, spinel type lithium manganate (sp-Mn) other than NMC, lithium-containing composite metal oxide, olivine type lithium salt, chalcogen A compound, manganese dioxide is mentioned.
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, V, and B, and Mn, Al, Co, and the like. Ni, Mg are preferable. One kind or two or more kinds of different elements may be used. Among these, lithium-containing composite metal oxides are preferable. Examples of the lithium-containing composite metal oxide include LixCoO ₂ , LixNiO ₂ , LixMnO ₂ , LixCoyNi ₁ -yO ₂ , LixCoyM ₁ -yOz, LixNi ₁ -yMyOz, LixMn ₂ O ₄ , LixMn ₂ -yMyO ₄ , LiMPO ₄ . Li ₂ MPO ₄ F (wherein M is selected from the group consisting of Na, Mg, Sc, Y, Mn, Fe, Co, Ni, Cu, Zn, Al, Cr, Pb, Sb, V, and B) And at least one element, where x = 0 to 1.2, y = 0 to 0.9, and z = 2.0 to 2.3. Here, x value which shows the molar ratio of lithium increases / decreases by charging / discharging.
Further, as the olivine type lithium salts, for example, 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.

The lithium phosphate contained in the positive electrode composite material has a chemical formula represented by Li ₃ PO ₄ and is preferably used as colorless crystals or white powder.
The content of lithium phosphate contained in the positive electrode mixture is preferably 0.1% by mass or more and 5% by mass or less from the viewpoint of safety and capacity. From the viewpoint of input / output characteristics and reduction of internal resistance, the content is more preferably 0.1% by mass or more and 3% by mass or less.
In addition to safety and capacity, by including lithium phosphate in the positive electrode mixture, electrochemical decomposition of the organic electrolyte can be suppressed even when the battery is overcharged. In the overcharge, since the temperature rises rapidly, if the heat due to the temperature rise is not efficiently released outside the battery, the battery will run out of heat, and even if the system that detects voltage abnormality works and stops the current, the reaction inside the battery May not fit, and the battery container may be damaged (including cracks, expansion, and ignition). Therefore, in order to further improve the safety in overcharging, it is important to detect a voltage abnormality and immediately cut off the current before the temperature starts to rise rapidly. That is, it is important to reach a voltage at which a voltage abnormality is detected in a situation where there is almost no temperature increase or a gradual temperature increase.
In lithium ion secondary batteries with a discharge capacity of 30 Ah or more, it is difficult to release the heat accumulated inside the lithium ion secondary battery, but electrolyte decomposition by increasing the potential of the positive electrode by including lithium phosphate in the positive electrode mixture It is estimated that the heat generated by the reaction can be suppressed, the temperature rises little, or the temperature rises slowly, reaches the set voltage that detects the voltage abnormality, cuts off the current, and can improve safety without thermal runaway doing. The set voltage for detecting the voltage abnormality is preferably 120 to 150%, more preferably 120 to 130% with respect to the upper limit voltage of the battery.

In this invention, it is preferable that the density of the positive electrode compound material which comprises a lithium ion secondary battery is 2.5-2.8 g / cm < ³ >.
If the density of the positive electrode mixture is less than 2.5 g / cm ³ , the resistance of the positive electrode is increased, and input / output characteristics may be deteriorated. On the other hand, when the density of the positive electrode mixture exceeds 2.8 g / cm ³ , there is a concern that the safety may be lowered, and it may be necessary to strengthen other safety measures. From this point of view, positive electrode density, 2.55 g / cm ³ or more, 2.75 g / cm ³ or less is more preferable.
In order to obtain such a positive electrode mixture density, it is preferable that the single-sided coating amount of the positive electrode mixture to the positive electrode current collector is 110 to 170 g / m ² .
When the coating amount of the positive electrode mixture is less than 110 g / m ² , the amount of the active material that contributes to charging / discharging decreases, and the energy density of the battery may decrease. On the other hand, when the coating amount of the positive electrode mixture exceeds 170 g / m ² , the resistance of the positive electrode mixture increases, and the input / output characteristics may deteriorate. From the above viewpoint, the single-sided coating amount of the positive electrode mixture to the positive electrode current collector is preferably 120 g / m ² or more and 160 g / m ² or less, and 130 g / m ² or more and 150 g / m ² or less. It is more preferable that
Considering the amount of single-sided application of the positive electrode mixture to the positive electrode current collector and the density of the positive electrode mixture, the thickness of the single-sided coating film of the positive electrode mixture on the positive electrode current collector ([positive electrode thickness−positive electrode current collector] The thickness] / 2) is preferably 39 to 68 μm, more preferably 43 to 64 μm, and still more preferably 46 to 60 μm.
Thus, in the positive electrode mixture, the positive electrode mixture density is 2.5 to 2.8 g / cm ³ , the positive electrode mixture application amount is 39 to 68 μm, and the lithium phosphate is 0.1 to 5% by mass, Even in a high-capacity lithium ion secondary battery having a discharge capacity of 30 Ah or more and less than 99 Ah, a long-life battery can be realized while ensuring safety.

  Hereinafter, the positive electrode mixture and the current collector will be described in detail. The positive electrode mixture contains at least a positive electrode active material and lithium phosphate, and is formed on both surfaces of the current collector. Although there is no restriction | limiting in the formation method, it forms as follows, for example. The positive electrode active material, lithium phosphate, binder, and other materials such as conductive materials and thickeners used as needed are dry mixed to form a sheet, which is then crimped to the current collector (dry method) ). In addition, a positive electrode active material, lithium phosphate, a binder, and other materials such as a conductive material 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 dry (wet method).

As the layered lithium / nickel / manganese / cobalt composite oxide (NMC) particles, particles having a lump shape, polyhedron shape, spherical shape, elliptical spherical shape, plate shape, needle shape, columnar shape, or the like can be 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 by the stress or the conductive path is broken. 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.
Median diameter d50 of positive electrode active material particles of layered lithium / nickel / manganese / cobalt composite oxide (NMC) (median diameter d50 of secondary particles when primary particles are aggregated to form secondary particles) Can be adjusted within the following range. 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 30 μm or less, preferably 25 μm or less, more preferably 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. May be incurred. Moreover, when the said upper limit is exceeded, the mixing property with other materials, such as a binder and a 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. The median diameter d50 can be obtained from the particle size distribution obtained by the laser diffraction / scattering method. A volume cumulative particle size distribution curve measured using a laser diffraction / scattering method with the particle diameter on the horizontal axis and the volume cumulative on the vertical axis. The median diameter (d50) is the cumulative from the small particle size side. The particle diameter is 50%.

  The range of the average particle size of the primary particles in the case where 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, still more 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 more preferably 0.6 μm or less. When the above upper limit is exceeded, it is 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 lower limit, problems, such as deterioration of the reversibility of charging / discharging, may arise by crystallinity fall.

The range of the BET specific surface area of the positive electrode active material particles of layered lithium / nickel / manganese / cobalt composite oxide (NMC) is as follows. The lower limit of the range is 0.2 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 at most 1.5 m ² / g. If it is less than the said minimum, battery performance may fall. When the above upper limit is exceeded, it is difficult to increase the tap density, and there is a possibility that the miscibility with other materials such as a binder and a conductive material is lowered. Therefore, there is a possibility that the applicability when the mixture is slurried and applied is deteriorated. The BET specific surface area is a specific surface area (area per unit g) determined by the BET method.

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. Can be mentioned. Of these, one type may be used alone, or two or more types may be used in combination.
Regarding the content (addition amount, ratio, amount) of the conductive material, the range of the content of the conductive material relative to the weight of the positive electrode mixture is as follows. The lower limit of the range is 0.01% by mass or more, preferably 0.1% by mass or more, more preferably 1% by mass or more, and the upper limit is 50% by mass or less, preferably 30% by mass or less, more preferably 15%. It is below mass%. If it is less than the said minimum, electroconductivity may become inadequate. Moreover, when the said upper limit is exceeded, battery capacity may fall.

  The binder for the positive electrode active material 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 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, 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.

  Regarding the content (addition amount, ratio, amount) of the binder, the range of the content of the binder relative to the weight of the positive electrode mixture is as follows. The lower limit of the range is 0.1% by mass or more, preferably 1% by mass or more, more preferably 3% by mass or more, and the upper limit is 80% by mass or less, preferably 60% by mass or less, more preferably 40% by mass. Hereinafter, it is more preferably 10% by mass or less. If the content of the binder is too low, the positive electrode active material cannot be sufficiently bound, the positive electrode has insufficient mechanical strength, and battery performance such as cycle characteristics may be deteriorated. Conversely, if it is too high, the battery capacity and conductivity may be reduced.

In order to improve the packing density of the positive electrode active material, the layer formed on the current collector using the wet method or the dry method is preferably consolidated by a hand press, a roller press, or the like.
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.
There is no restriction | limiting in particular as a shape of an electrical power collector, The material 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 or a metal foil. In addition, you may form a thin film and metal foil in mesh shape suitably. Although the thickness of a thin film and metal foil is arbitrary, 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.

2. Negative electrode In this embodiment, the negative electrode shown below is applicable to a high-output and high-capacity lithium ion secondary battery. The negative electrode (negative electrode plate) of the present embodiment is composed of a current collector and a negative electrode mixture (negative electrode mixture) formed on both sides (or one side) thereof. The negative electrode mixture contains a negative electrode active material that can electrochemically occlude and release lithium ions.

The negative electrode in the present embodiment preferably contains graphitizable carbon (soft carbon). The graphitizable carbon (soft carbon) preferably has an SOC (State Of Charge) of 60% or more at a potential of 0.1 V with respect to the lithium potential. From the viewpoint of charge load characteristics, the SOC at a potential of 0.1 V with respect to the lithium potential is more preferably 65% or more, and even more preferably 68% or more. Thus, the higher the SOC at a potential of 0.1 V with respect to the lithium potential, the less susceptible to IR drop (voltage drop, I is current, R is resistance) at the positive electrode, and the charge load characteristics are improved.
Moreover, although there is no restriction | limiting in the upper limit of SOC of a negative electrode in the electric potential used as 0.1V with respect to a lithium electric potential, it is preferable that it is 90% or less from a practical viewpoint, and it is more preferable that it is 80% or less.

The graphitizable carbon (soft carbon) preferably has a plane spacing in the C-axis direction (carbon network interlayer, d002) in the X-ray wide angle diffraction method of 0.34 nm or more and 0.36 nm or less. It is more preferably 341 nm or more and 0.355 nm or less, and further preferably 0.342 nm or more and 0.35 nm or less.
The average particle diameter (d50%) of the graphitizable carbon (soft carbon) is preferably 2.0 to 50 μm. When the average particle diameter is 5 μm or more, the specific surface area can be in an appropriate range, the initial charge / discharge efficiency of the lithium ion secondary battery is excellent, and the particles are in good contact with each other and have excellent input / output characteristics. On the other hand, when the average particle diameter is 30 μm or less, unevenness on the electrode surface hardly occurs, and the short circuit of the battery can be suppressed, and the diffusion distance of Li from the particle surface to the inside becomes relatively short, so that the insertion of the lithium ion secondary battery The output characteristics tend to improve. In this respect, the average particle size is more preferably 5 to 30 μm, and still more preferably 10 to 20 μm. For example, the particle size distribution can be measured with a laser diffraction particle size distribution measuring device (for example, SALD-3000J manufactured by Shimadzu Corporation) by dispersing a sample in purified water containing a surfactant, and the average particle size Is calculated as d50%.

In addition, carbon materials other than graphitizable carbon may be included. Carbon materials are broadly divided into graphite materials with a uniform crystal structure and non-graphite materials with a disordered crystal structure. The former includes natural graphite and artificial graphite, and the latter has a disordered crystal structure. However, there are easily graphitized carbon that is likely to become graphite by heating at 2000 to 3000 ° C. and non-graphitizable carbon that is difficult to become graphite (hereinafter sometimes referred to as hard carbon).
Specifically, graphite, cokes (petroleum-based coke, pitch coke, needle coke, etc.), resin film-fired carbon, fiber-fired carbon, vapor-grown carbon, and the like are used. The non-graphite-based carbon material can be produced, for example, by heat treating petroleum pitch, polyacene, polyparaphenylene, polyfurfuryl alcohol, or polysiloxane. Or soft carbon. For example, a firing temperature of about 500 to 800 ° C. is suitable for producing hard carbon, and a firing temperature of about 800 to 1000 ° C. is suitable for producing soft carbon. The non-graphitizable carbon is defined as having a surface spacing d002 value in the C-axis direction obtained by an X-ray wide angle diffraction method of 0.36 nm or more and 0.40 nm or less.
Moreover, it is preferable to make the said graphitizable carbon (soft carbon) contain graphite as a negative electrode active material. The graphite preferably has the physical properties shown in the following (1) and (2).
(1) the intensity ratio of the peak intensity in the range of 1300～1400Cm ^-1 as measured by Raman spectroscopy (ID) and the peak intensity in the range of 1580～1620Cm ^-1 as measured by Raman spectroscopy spectra (IG) The R value (IG / ID) is preferably 3 or more, more preferably 10 or more, and still more preferably 50 or more.
(2) The average particle diameter (d50%) is preferably 2 to 20 μm, more preferably 3 to 10 μm. Discharge capacity and discharge load characteristics are improved by being 20 μm or less. Moreover, it exists in the tendency which initial stage charge / discharge efficiency improves because it is 2 micrometers or more.
The volume average particle diameter can be measured using, for example, a particle size distribution measuring apparatus using a laser light scattering method (for example, SALD-3000 manufactured by Shimadzu Corporation).
In addition, since pulverized bulk natural graphite may contain impurities, it is preferable to make it highly purified by a purification treatment. The purity of the natural graphite is preferably 99.8% or more (ash content 0.2% or less), more preferably 99.9% or more (ash content 0.1% or less) on a mass basis. When the purity is 99.8% or more, the safety of the battery is further improved, and the battery performance is further improved.
The method for the purification treatment is not particularly limited, and can be appropriately selected from commonly used purification treatment methods. Examples thereof include flotation, electrochemical treatment, chemical treatment, and the like.

By mixing the amorphous carbon (a) and the graphite (b), output characteristics and energy density can be further improved while maintaining input characteristics. In the case of containing graphite, the content ratio of amorphous carbon to graphite ((a) / (b)) is preferably 99/1 to 50/50 and 99/1 to 70/30 on a mass basis. Is more preferable, and 95/5 to 80/20 is still more preferable. When the compounding ratio of graphite is 1% or more, output characteristics are improved, and when it is 50% or less, input characteristics can be maintained.
In addition, as the negative electrode active material, amorphous carbon, carbonaceous materials other than graphite, metal oxides such as tin oxide and silicon oxide, metal composite oxides, lithium alloys such as lithium alone and lithium aluminum alloys, Sn and Si, etc. A material capable of forming an alloy with lithium may be used in combination. These may be used alone or in combination of two or more.

The metal composite oxide is not particularly limited as long as it can occlude and release lithium. However, a material containing both Ti (titanium), Li (lithium), and Ti and Li has a high current density. This is preferable from the viewpoint of discharge characteristics.
Examples of the carbonaceous material other than amorphous carbon (a) include amorphous carbon, natural graphite, natural graphite, etc. having a mass at 550 ° C. of less than 70% of the mass at 25 ° C. by thermogravimetry. A composite carbonaceous material with a film formed by a dry CVD (Chemical Vapor Deposition) method or a wet spray method, a resin material such as epoxy or phenol, or a pitch material obtained from petroleum or coal is fired as a raw material. And artificial graphite obtained.
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. An oxide or nitride may be used in combination with the amorphous carbon (a).

  Further, as a preferred form, there is a form in which a carbonaceous material that is not symmetric when the volume-based particle size distribution is centered on the median diameter is used as the third carbonaceous material (conductive material). Further, as the third carbonaceous material (conductive material), a form using a carbonaceous material having a different Raman R value from the carbonaceous material used as the negative electrode active material, or as the third carbonaceous material (conductive material), as the negative electrode active material There is a form using a carbonaceous material having a different X-ray parameter from the first carbonaceous material used.

As the third carbonaceous material (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. These may be used alone or in combination of two or more. Thus, by adding the third carbonaceous material (conductive material), there are effects such as reducing the resistance of the electrode.
Regarding the content (addition amount, ratio, amount) of the third carbonaceous material (conductive material), the range of the content of the conductive material relative to the weight 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 the conductivity, and if it exceeds the above upper limit, the initial irreversible capacity may be increased.

There is no restriction | limiting in particular as a material of the electrical power collector for negative electrodes, As a specific example, metal materials, such as copper, nickel, stainless steel, nickel plating steel, are mentioned. Among these, copper is preferable from the viewpoint of ease of processing and cost.
There is no restriction | limiting in particular as a shape of an electrical power collector, The material 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 and a metal foil are 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 when 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.

Although there is no restriction | limiting in particular in the structure of the negative electrode compound material formed using the negative electrode active material, The range of the negative electrode compound material density is as follows. The lower limit of the negative electrode composite density is preferably 0.7 g / cm ³ or more, more preferably 0.8 g / cm ³ or more, still more preferably 0.9 g / cm ³ or more, and the upper limit is 2 g / cm ³ or less. , preferably 1.9 g / cm ³ or less, more preferably 1.8 g / cm ³ or less, further preferably 1.7 g / cm ³ or less.
When the above upper limit is exceeded, particles of the negative electrode active material are likely to be destroyed, and a high current is generated due to an increase in the initial irreversible capacity and a decrease in the permeability of the non-aqueous electrolyte solution near the interface between the current collector and the negative electrode active material. There is a possibility of deteriorating the density charge / discharge characteristics. In addition, if it is less than the above lower limit, the conductivity between the negative electrode active materials decreases, so the battery resistance increases, and the capacity per unit volume may decrease.

  The binder for the negative electrode active material is not particularly limited as long as it is a material that is stable 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 ( Acrylonitrile-butadiene rubber), rubber-like polymers such as ethylene-propylene rubber; styrene / butadiene / styrene block copolymer or hydrogenated product 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 vinyl acetate copolymer and propylene / α-olefin copolymer; Fluorine-based polymers such as polyvinylidene fluoride, polytetrafluoroethylene, fluorinated polyvinylidene fluoride, and polytetrafluoroethylene / ethylene copolymer Polymers: Polymer compositions having ionic conductivity of alkali metal ions (particularly lithium ions), and the like. These may be used alone or in combination of two or more.

  As the dispersion solvent for forming the slurry, any type of 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, etc., 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.

Regarding the content (addition amount, ratio, amount) of the binder, the range of the content of the binder with respect to the weight of the negative electrode mixture is as follows. The lower limit of the range is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, and still more preferably 0.6% by mass or more. The upper limit 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.
When 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 electrode compound material may be caused.
In particular, the range of the binder content with respect to the weight 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.
In addition, the range of the binder content relative to the weight 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.

The 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 weight 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, the applicability | paintability of a slurry may fall. Moreover, when the said upper limit is exceeded, the ratio of the negative electrode active material to a negative electrode compound material will fall, and there exists a possibility of the fall of battery capacity and the raise between resistances of a negative electrode active material.

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 salts such as ₄ F 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 fluorinated phosphates, such as and the 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, output characteristics, cycle characteristics, and the like.
A preferable example in the case of using two or more lithium salts is a combination of LiPF ₆ and LiBF ₄ . In this case, the proportion of LiBF _{4 in} the total of both is preferably 0.01% by mass or more and 20% by mass or less, and more preferably 0.1% by mass or more and 5% by mass or less. . Another preferred example is the combined use of an inorganic fluoride salt and a perfluoroalkanesulfonylimide salt. In this case, the proportion of the inorganic fluoride salt in the total of both is 70% by mass or more and 99% by mass. % Or less, more preferably 80% by mass or more and 98% by mass or less. According to the above two preferred examples, characteristic deterioration due to high temperature storage can be suppressed.
Although there is no restriction | limiting in particular in the density | concentration of the electrolyte in a non-aqueous electrolyte solution, The density | concentration range of an 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 electrical conductivity of the electrolyte 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 ether.
As the cyclic carbonate, those having 2 to 6 carbon atoms of the alkylene group constituting the cyclic carbonate 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.
As the chain carbonate, dialkyl carbonate is preferable, and the number of carbon atoms of the two alkyl groups is preferably 1 to 5, and more preferably 1 to 4. Specifically, symmetrical chain carbonates such as dimethyl carbonate, diethyl carbonate, and di-n-propyl carbonate; asymmetric chain carbonates such as ethyl methyl carbonate, methyl-n-propyl carbonate, and ethyl-n-propyl carbonate Is mentioned. Of these, dimethyl carbonate, diethyl carbonate, and ethyl methyl 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, battery cycle characteristics and high-temperature storage characteristics (particularly, remaining capacity and high-load discharge capacity after high-temperature storage) 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 ethyl methyl carbonate, ethylene carbonate and dimethyl carbonate and diethyl carbonate, ethylene carbonate and dimethyl carbonate And ethyl methyl carbonate, ethylene carbonate, diethyl carbonate, and ethyl methyl carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate.
A combination in which propylene carbonate is further added to the combination of these ethylene carbonates and chain carbonates is also a preferable combination. When propylene carbonate is contained, the volume ratio of ethylene carbonate to propylene carbonate is preferably 99: 1 to 40:60, and more preferably 95: 5 to 50:50. Further, the range of the amount of propylene carbonate in the non-aqueous solvent is as follows. The lower limit of the amount of propylene carbonate is 0.1% by volume or more, preferably 1% by volume or more, more preferably 2% by volume or more, and the upper limit is 10% by volume or less, preferably 8% by volume or less, more preferably 5% by volume or less. According to such a combination, the low temperature characteristics can be further improved while maintaining the characteristics of the combination of ethylene carbonate and chain carbonates.
Among these combinations, those containing asymmetric chain carbonates as chain carbonates are preferred. Specific examples include a combination of ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate, ethylene carbonate, diethyl carbonate and ethyl methyl carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate and ethyl methyl carbonate. Such a combination of ethylene carbonate, symmetric chain carbonates and asymmetric chain carbonates can improve cycle characteristics and large current discharge characteristics. Among these, those in which the asymmetric chain carbonates are ethyl methyl carbonate are preferable, and those in which the alkyl group constituting the dialkyl carbonate has 1 to 2 carbon atoms are preferable.
Another example of a preferable mixed solvent is one containing a chain ester. In particular, those containing a chain ester in the mixed solvent of the cyclic carbonates and the chain carbonates are preferable from the viewpoint of improving the low-temperature characteristics of the battery. As the chain ester, methyl acetate and ethyl acetate are particularly preferable. The lower limit of the capacity of the chain ester in the non-aqueous solvent is 5% by volume or more, preferably 8% 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, it is 30 volume% or less, More preferably, it is 25 volume% or less.
Examples of other preferable non-aqueous solvents are one organic solvent selected from the group consisting of ethylene carbonate, propylene carbonate and butylene carbonate, or a mixed solvent consisting of two or more organic solvents selected from this group. The volume of the mixed solvent in the non-aqueous solvent is 60% by volume or more. These mixed solvents are preferably adjusted by selecting various solvents so that the flash point is 50 ° C. or higher, and more preferably adjusted so that the flash point is 70 ° C. or higher. A non-aqueous electrolyte using such a mixed solvent is less likely to evaporate or leak when used at high temperatures. Among them, the total of ethylene carbonate and propylene carbonate in the non-aqueous solvent is 80% by volume or more, preferably 90% by volume or more, and the volume ratio of ethylene carbonate to propylene carbonate is 30:70 to 60:40. If some are used, cycle characteristics, large current discharge characteristics, and the like can be improved.

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.
The heterocyclic compound containing nitrogen, sulfur or nitrogen and sulfur is not particularly limited, but 1-methyl-2-pyrrolidinone, 1,3-dimethyl-2-pyrrolidinone, 1,5-dimethyl-2-pyrrolidinone, Pyrrolidinones such as 1-ethyl-2-pyrrolidinone and 1-cyclohexyl-2-pyrrolidinone; Oxazolidinones such as 3-methyl-2-oxazolidinone, 3-ethyl-2-oxazolidinone and 3-cyclohexyl-2-oxazolidinone; Piperidones such as methyl-2-piperidone and 1-ethyl-2-piperidone; imidazolidinones such as 1,3-dimethyl-2-imidazolidinone and 1,3-diethyl-2-imidazolidinone; sulfolane; Sulfolanes such as 2-methylsulfolane and 3-methylsulfolane; sulfolene; ethylene Sulfites such as sulfite and propylene sulfite; 1,3-propane sultone, 1-methyl-1,3-propane sultone, 3-methyl-1,3-propane sultone, 1,4-butane sultone, 1,3- And sultone such as propene sultone and 1,4-butene sultone. Among them, 1-methyl-2-pyrrolidinone, 1-methyl-2-piperidone, 1,3-propane sultone, 1,4-butane sultone, 1,3-propene sultone, 1,4-butene sultone, etc., prolong the battery life. From the viewpoint of

  The cyclic carboxylic acid ester is not particularly limited, but γ-butyrolactone, γ-valerolactone, γ-hexalactone, γ-heptalactone, γ-octalactone, γ-nonalactone, γ-decalactone, and γ-undecalactone. , Γ-dodecalactone, α-methyl-γ-butyrolactone, α-ethyl-γ-butyrolactone, α-propyl-γ-butyrolactone, α-methyl-γ-valerolactone, α-ethyl-γ-valerolactone, α, α-dimethyl-γ-butyrolactone, α, α-dimethyl-γ-valerolactone, δ-valerolactone, δ-hexalactone, δ-octalactone, δ-nonalactone, δ-decalactone, δ-undecalactone, δ- Examples include dodecalactone. Among these, γ-butyrolactone, γ-valerolactone, and the like are particularly preferable from the viewpoint of extending the battery life.

The fluorine-containing cyclic carbonate is not particularly limited, and examples thereof include fluoroethylene carbonate, difluoroethylene carbonate, trifluoroethylene carbonate, tetrafluoroethylene carbonate, and trifluoropropylene carbonate. Among these, fluoroethylene carbonate and the like are particularly preferable from the viewpoint of extending the life of the battery.
Other compounds having an unsaturated bond in the molecule include vinylene carbonate, vinyl ethylene carbonate, divinyl ethylene carbonate, methyl vinyl carbonate, ethyl vinyl carbonate, propyl vinyl carbonate, divinyl carbonate, allyl methyl carbonate, allyl ethyl carbonate, allyl propyl. Carbonates such as carbonate, diallyl carbonate, dimethallyl carbonate; vinyl acetate, vinyl propionate, vinyl acrylate, vinyl crotonate, vinyl methacrylate, allyl acetate, allyl propionate, methyl acrylate, ethyl acrylate, propyl acrylate , Esters such as methyl methacrylate, ethyl methacrylate, propyl methacrylate; divinyl sulfone, methyl vinyl sulfone Sulfones such as ethyl vinyl sulfone, propyl vinyl sulfone, diallyl sulfone, allyl methyl sulfone, allyl ethyl sulfone, allyl propyl sulfone; sulfites such as divinyl sulfite, methyl vinyl sulfite, ethyl vinyl sulfite, diallyl sulfite; Examples of the sulfonates include vinyl methane sulfonate, vinyl ethane sulfonate, allyl methane sulfonate, allyl ethane sulfonate, methyl vinyl sulfonate, and ethyl vinyl sulfonate; and sulfates such as divinyl sulfate, methyl vinyl sulfate, ethyl vinyl sulfate, and diallyl sulfate. Among these, vinylene carbonate, dimethallyl carbonate, vinyl ethylene carbonate, divinyl ethylene carbonate, vinyl acetate, vinyl propionate, vinyl acrylate, divinyl sulfone, vinyl methanesulfonate, and the like are particularly preferable from the viewpoint of extending the life of the battery.

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.
As an overcharge preventing material, aromatic compounds such as biphenyl, alkylbiphenyl, terphenyl, partially hydrogenated terphenyl, cyclohexylbenzene, t-butylbenzene, t-amylbenzene, diphenyl ether, dibenzofuran; 2-fluorobiphenyl, Partially fluorinated products of the above aromatic compounds such as o-cyclohexylfluorobenzene and p-cyclohexylfluorobenzene; 2,4-difluoroanisole, 2,5-difluoroanisole, 2,6-difluoroanisole, 3,5-difluoroanisole and the like And a fluorine-containing anisole compound. Of these, aromatic compounds such as biphenyl, alkylbiphenyl, terphenyl, terphenyl partially hydrogenated, cyclohexylbenzene, t-butylbenzene, t-amylbenzene, diphenyl ether, and dibenzofuran are preferable. These overcharge prevention materials may be used in combination of two or more. When using 2 or more types together, it is particularly preferable to use cyclohexylbenzene or terphenyl (or a partially hydrogenated product thereof) together with t-butylbenzene or t-amylbenzene.

  Examples of the negative electrode film-forming material include succinic anhydride, glutaric anhydride, maleic anhydride, citraconic anhydride, glutaconic anhydride, itaconic anhydride, cyclohexanedicarboxylic anhydride, and the like. Of these, succinic anhydride and maleic anhydride are preferable. Two or more of these negative electrode film forming materials may be used in combination.

  As a positive electrode protective material, dimethyl sulfoxide, diethyl sulfoxide, dimethyl sulfite, diethyl sulfite, methyl methanesulfonate, busulfan, methyl toluenesulfonate, dimethyl sulfate, diethyl sulfate, dimethyl sulfone, diethyl sulfone, diphenyl sulfide, thioanisole, And diphenyl disulfide. Of these, methyl methanesulfonate, busulfan, and dimethylsulfone are preferable. Two or more of these positive electrode protective materials may be used in combination.

Examples of the high input / output material include surfactants such as perfluoroalkyl sulfonic acid, ammonium salt, potassium salt or lithium salt of perfluoroalkyl carboxylic acid; perfluoroalkyl polyoxyethylene ether and fluorinated alkyl ester. Among these, perfluoroalkyl polyoxyethylene ether and fluorinated alkyl ester are preferable.
Although there is no limitation in particular in the ratio of the additive in a non-aqueous electrolyte solution, the range is as follows. In addition, when using a some additive, the ratio of each additive is meant. The lower limit of the ratio of the additive to the non-aqueous electrolyte is preferably 0.01% by mass or more, more preferably 0.1% by mass or more, still more preferably 0.2% by mass or more, and the upper limit is preferably 5%. It is not more than mass%, more preferably not more than 3 mass%, still more preferably not more than 2 mass%.
By using the other additives, it is possible to suppress a rapid electrode reaction at the time of abnormality due to overcharge, improve capacity maintenance characteristics and cycle characteristics after high temperature storage, and improve input / output characteristics.

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, an olefin polymer, a fluorine polymer, a 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, and porous sheets or nonwoven fabrics made from polyolefin polymers such as polyethylene and polypropylene are used. It is 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 a thin film-shaped substrate, a substrate having a pore diameter of 0.01 to 1 μm and a thickness of 5 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 (d90) 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. Examples of the polyalkylene carbonate resin include polyethylene carbonate, polypropylene carbonate, poly (1,2-dimethylethylene carbonate), polybutene carbonate, polyisobutene carbonate, polypentene carbonate, polyhexene carbonate, polycyclopentene carbonate, polycyclohexene carbonate, and polycyclohexane. Examples include heptene carbonate, polycyclooctene carbonate, and polylimonene carbonate. As a material used for the said structural part, lithium carbonate, polyethylene carbonate, and polypropylene carbonate are preferable.

(Discharge capacity of lithium ion secondary battery)
The lithium ion secondary battery of the present invention is suitable for a large capacity discharge capacity of 30 Ah or more and less than 99 Ah. From the viewpoint of high input / output and high energy density while ensuring safety, it is preferably 35 Ah or more and less than 99 Ah, and more preferably 45 Ah or more and less than 95 Ah.

(Capacity ratio of negative electrode to positive electrode of lithium ion secondary battery)
In the present invention, the capacity ratio of the negative electrode to the positive electrode (negative electrode capacity / positive electrode capacity) is preferably 1 or more and less than 1.5 from the viewpoint of safety and energy density, more preferably 1.05 to 1.3. 1.1 to 1.2 are more preferable. If it exceeds 1.3, the positive electrode potential may be higher than 4.2 V at the time of charging, which may reduce safety. (At this time, the positive electrode potential refers to the Li potential)
Here, the negative electrode capacity indicates [negative electrode discharge capacity], and the positive electrode capacity indicates [positive electrode initial charge capacity-negative electrode or positive electrode, whichever is greater, irreversible capacity]. 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 the lithium ion secondary battery / discharge capacity of the negative electrode”. The discharge capacity of the lithium ion secondary battery is, for example, 4.2 V, 0.1 to 0.5 C, and after performing constant current constant voltage (CCCV) charging with an end time of 2 to 5 hours, It can be measured under conditions when a constant current (CC) is discharged to 2.7 V at 0.5 C.
For the discharge capacity of the negative electrode, the negative electrode whose discharge capacity was measured for the lithium ion secondary battery was cut into a predetermined area, lithium metal was used as the counter electrode, and a single electrode cell was prepared via a separator impregnated with an electrolyte. , 0V, 0.1C, constant current constant voltage (CCCV) charge at a final current of 0.01C, then discharge per predetermined area under the condition of constant current (CC) discharge to 1.5V at 0.1C It can be calculated by measuring the capacity 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)”.

Example 1
Hereinafter, the present embodiment will be described in more detail based on examples. The present invention is not limited to the following examples.
[Production of positive electrode plate]
The positive electrode plate was produced as follows. Layered lithium / nickel / manganese / cobalt composite oxide (NMC), which is a positive electrode active material, lithium phosphate, scaly graphite (average particle size: 20 μm) and acetylene black as a conductive material, and polyfluoride as a binder. A mixture of positive electrode materials was obtained by sequentially adding and mixing vinylidene chloride. The weight ratio was positive electrode active material: lithium phosphate: conductive material: binder = 91: 1: 4: 4. 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 2.7 g / cm ^3, and the coating amount on one side of the positive electrode mixture was 120 g / m ² .

[Production of negative electrode plate]
The negative electrode plate was produced as follows. Graphitizable carbon (d002 = 0.35 nm, average particle size (d50) = 10 μm was used as the negative electrode active material. Polyvinylidene fluoride was added as a binder to the negative electrode active material. Active material: binder = 92: 8 A dispersion solvent, N-methyl-2-pyrrolidone (NMP), was added thereto and kneaded to form a slurry. A predetermined amount was applied substantially uniformly and uniformly on both surfaces of a rolled copper foil having a thickness of 10 μm, and the density of the negative electrode mixture was 1.15 g / cm ³ .

[Production of battery]
The positive electrode plate and the negative electrode plate are wound with a polyethylene separator having a thickness of 30 μm interposed therebetween so that they are not in direct contact with each other. At this time, the lead piece of the positive electrode plate and the lead piece of the negative electrode plate are respectively positioned on the opposite end surfaces of the winding group. Further, the lengths of the positive electrode plate, the negative electrode plate, and the separator were adjusted, and the wound group diameter was set to 65 ± 0.1 mm.
Next, as shown in FIG. 1, the lead pieces 9 led out from the positive electrode plate are deformed, and all of them are gathered near the bottom of the flange 7 on the positive electrode side and brought into contact with each other. The positive electrode side flange portion 7 is integrally formed so as to protrude from the periphery of the pole column (positive electrode external terminal 1) substantially on the extension line of the axis of the wound group 6, and has a bottom portion and a side portion. Thereafter, the lead piece 9 is connected and fixed to the bottom of the flange 7 by ultrasonic welding. The lead piece 9 led out from the negative electrode plate and the bottom of the flange 7 on the negative electrode side are similarly connected and fixed. The negative electrode side flange portion 7 is integrally formed so as to protrude from the periphery of the pole column (negative electrode external terminal 1 ′) substantially on the extension line of the axis of the wound group 6, and has a bottom portion and a side portion.
Then, the insulating coating 8 was formed using an adhesive tape to cover the side of the flange 7 on the positive electrode external terminal 1 side and the side of the flange 7 of the negative electrode external terminal 1 ′. Similarly, an insulating coating 8 was formed on the outer periphery of the wound group 6. For example, this adhesive tape is stretched from the side of the flange 7 on the positive electrode external terminal 1 side to the outer peripheral surface of the winding group 6 and further from the outer periphery of the winding group 6 to the negative electrode external terminal 1 ′ side. Insulating coating 8 is formed by winding several times over the side of 7. As the insulating coating (adhesive tape) 8, an adhesive tape in which the base material was polyimide and an adhesive material was applied on one surface thereof was used. The thickness of the insulating coating 8 (the number of windings of the adhesive tape) is adjusted so that the maximum diameter portion of the wound group 6 is slightly smaller than the inner diameter of the stainless steel battery container 5, and the wound group 6 is placed in the battery container 5. Inserted into. The battery container 5 had an outer diameter of 67 mm and an inner diameter of 66 mm.
Next, as shown in FIG. 1, the ceramic washer 3 ′ is fitted into a pole column whose tip constitutes the positive electrode external terminal 1 and a pole column whose tip constitutes the negative electrode external terminal 1 ′. The ceramic washer 3 ′ is made of alumina, and the thickness of the portion in contact with the back surface of the battery lid 4 is 2 mm, the inner diameter is 16 mm, and the outer diameter is 25 mm. Next, with the ceramic washer 3 placed on the battery lid 4, the positive external terminal 1 is passed through the ceramic washer 3, and with the other ceramic washer 3 placed on the other battery lid 4, the negative external terminal Pass 1 'through another ceramic washer 3. The ceramic washer 3 is made of alumina and has a flat plate shape with a thickness of 2 mm, an inner diameter of 16 mm, and an outer diameter of 28 mm.
Thereafter, the peripheral end surface of the battery lid 4 is fitted into the opening of the battery container 5 and the entire area of both contact portions is laser welded. At this time, the positive electrode external terminal 1 and the negative electrode external terminal 1 ′ pass through a hole (hole) in the center of the battery cover 4 and project outside the battery cover 4. The battery lid 4 is provided with a cleavage valve 10 that cleaves in response to an increase in the internal pressure of the battery. The cleavage pressure of the cleavage valve 10 was 1.27 to 1.77 MPa (13 to 18 kgf / cm ² ).
Next, as shown in FIG. 1, the metal washer 11 is fitted into the positive external terminal 1 and the negative external terminal 1 ′, respectively. Thereby, the metal washer 11 is disposed on the ceramic washer 3. The metal washer 11 is made of a material smoother than the bottom surface of the nut 2.
Next, the metal nut 2 is screwed to the positive electrode external terminal 1 and the negative electrode external terminal 1 ′, and the battery lid 4 is connected to the flange portion 7 and the nut 2 through the ceramic washer 3, the metal washer 11, and the ceramic washer 3 ′. Secure by tightening between. The tightening torque value at this time was 686 N · cm (70 kgf · cm). The metal washer 11 did not rotate until the tightening operation was completed. In this state, the power generation element inside the battery container 5 is shielded from the outside air by the compression of the rubber (EPDM) O-ring 12 interposed between the back surface of the battery lid 4 and the flange 7.
Thereafter, a predetermined amount of electrolyte is injected into the battery container 5 from the injection port 13 provided in the battery lid 4, and then the injection port 13 is sealed to complete the cylindrical lithium ion secondary battery 20. It was.
As an electrolytic solution, 1.2 mol / L of lithium hexafluorophosphate (LiPF ₆ ) was dissolved in a mixed solution in which ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate were mixed at a volume ratio of 2: 3: 2. In addition, 0.8% by mass of vinylene carbonate (VC) was used as an additive.

[Battery characteristics]
(Discharge capacity)
In an environment of 25 ° C., the current value was 25 A for both charging and discharging. Charging was constant current constant voltage (CCCV) charging with 4.2 V as the upper limit voltage, and the termination condition was 3 hours. The discharge was CC discharge, and 2.7 V was set as a termination condition. Further, a pause of 30 minutes was put between charge and discharge. This was carried out for three cycles, and the charge capacity at the third cycle was defined as “charge capacity at a current value of 25 A”, and the discharge capacity at the third cycle was defined as “discharge capacity at a current value of 25 A”.

(Internal resistance)
After measuring the discharge capacity at the third cycle, the internal resistance is a constant current and constant voltage (CCCV) with a current value of 25 A and an upper limit voltage of 25 A in an environment of 25 ° C., and the end condition is 3 hours. After charging for 30 minutes, the frequency range was measured as a logarithmic range from 100 kHz to 10 mHz and an amplitude of 5 mV using an AC impedance device (Hokuto Denko Corporation HZ-3000, NF ELECTRONIC 5080). The measurement points obtained at each frequency were plotted with the real part as the X axis and the inverse of the imaginary part as the Y axis, and the larger of the two points where the arc-shaped curve intersected the X axis was measured as the internal resistance.

(Cycle life)
The cycle life was a constant current / constant voltage (CCCV) charge with an upper limit voltage of 4.2 V, and the end condition was 3 hours in an environment of 25 ° C. for both charging and discharging. The discharge was CC discharge, and 2.7 V was set as a termination condition. Further, a pause of 30 minutes was put between charge and discharge, and this was repeated as 496 cycles. The discharge capacity was measured by the same procedure as described above after a total of 500 cycles. The ratio of the discharge capacity after 500 cycles to the discharge capacity at a current value of 25A was calculated as the capacity retention rate after 500 cycles.

(safety)
Safety was confirmed by an overcharge test. Under an environment of 25 ° C, the battery after 3 cycles after the measurement of the discharge capacity was subjected to CCCV charge with a current value of 150A and 5.04V as the upper limit voltage, and overcharge was performed with a termination condition of 3 hours did.
At this time, a K-type (chromel-alumel) thermocouple was attached to the center of the cylindrical battery exterior, and the battery surface maximum temperature was measured. From overcharge energization to termination, smoke was evaluated as “△”, and no ignition or rupture occurred as “◯”. On the other hand, the case where the exothermic reaction inside the battery continued in a chain and the inside caused thermal runaway and ignition occurred was evaluated as “x”.

(Example 2)
The composition of the positive electrode mixture in Example 1 was tested in the same manner as in Example 1 except that the positive electrode active material: lithium phosphate: conductive material: binder = 91.9: 0.1: 4: 4 (mass ratio). To implement Example 2.

(Example 3)
In Example 1, the composition of the positive electrode mixture was changed to the positive electrode active material: lithium phosphate: conductive material: binder = 89: 3: 4: 4 (mass ratio). Example 3 was used.

Example 4
In Example 1, the composition of the positive electrode mixture was changed to positive electrode active material: lithium phosphate: conductive material: binder = 87: 5: 4: 4 (mass ratio), and other tests were conducted in the same manner as in Example 1. Example 3 was used.

(Comparative Example 1)
In Example 1, the composition of the positive electrode mixture was changed to positive electrode active material: lithium phosphate: conductive material: binder = 92: 0: 4: 4 (mass ratio). Example 1 was adopted.
The evaluation results of Examples 1 to 4 and Comparative Example 1 are shown in Table 1 below.

  Comparative Example 1 in which the positive electrode mixture does not contain lithium phosphate has a low capacity retention rate after 500 cycles, and is inferior in safety by the overcharge test. On the other hand, Examples 1-4 containing lithium phosphate have a high capacity retention rate and a long life, a low surface temperature by an overcharge test, and high safety without causing ignition or rupture.

DESCRIPTION OF SYMBOLS 1 Positive electrode external terminal 1 'Negative electrode external terminal 2 Nut 3 Ceramic washer 3' Ceramic washer 4 Battery cover 5 Battery container 6 Winding group 7 鍔 part 8 Insulation coating 9 Lead piece 10 Cleavage valve 11 Metal washer 12 O ring 13 Injection port 20 Cylindrical lithium ion secondary battery

Claims (2)

An electrode winding group in which a positive electrode, a negative electrode, and a separator are wound, and an electrolyte solution are provided in a battery container, and the discharge capacity is a lithium ion secondary battery having a discharge capacity of 30 Ah or more and less than 99 Ah,
The positive electrode includes a current collector and a positive electrode mixture applied to both surfaces of the current collector, and the positive electrode mixture includes lithium / nickel / manganese / cobalt composite oxide (NMC) and lithium phosphate. , Lithium ion secondary battery.   2. The lithium ion secondary battery according to claim 1, wherein the content of the lithium phosphate is 0.1% by mass or more and 5% by mass or less based on the total amount of the positive electrode mixture.

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