JP2015056318A - Lithium ion battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lithium ion secondary battery that is long in life while the low electron conduction of a positive electrode using olivine type lithium iron phosphate (LiFePO) as a positive electrode active material is improved.SOLUTION: In a lithium ion battery incorporating positive/negative electrodes and a separator in a battery container and including an electrolyte in the battery container, olivine type lithium iron phosphate (LiFePO) is contained in a positive electrode active material, a conductive layer having a thickness of 1-5 μm is formed on a positive electrode collector, the density of a positive electrode active material layer is 1.90-2.30 g/cmor the volume porosity in a positive electrode active material layer is 20-50%, the film thickness of the positive electrode active material layer is 40-200 μm, and furthermore a conductive assistant is contained within a range of 2 mass% or more and 10 mass% or less in the positive electrode active material layer.

Description

  The present invention relates to a lithium ion secondary battery.

  In recent years, electric vehicles and hybrid vehicles have been developed and put into practical use in consideration of the global environment, and lithium-ion secondary batteries having a small size, light weight, and high energy density have attracted attention. However, in many cases, lithium ion secondary batteries use rare metal-containing compounds such as Co and Ni as positive electrode materials, and in order for lithium ion secondary batteries to become widespread, there are major issues in terms of cost and supply stability. is there. In addition, ignition and explosion accidents of lithium ion secondary batteries caused by the positive electrode material have been reported, and safety issues have been pointed out. From such a background, development of a safe positive electrode material for lithium ion secondary electric fields that does not contain a rare metal is expected.

  Under such circumstances, olivine-type lithium iron phosphate has attracted attention as a positive electrode active material for a 3.5 V-class lithium ion secondary battery. Olivine-type lithium iron phosphate is a positive electrode material that has a very stable crystal structure and a very low risk of ignition and explosion because the P atom and the O atom are strongly bonded by a covalent bond in the crystal structure. Further, since the transition metal atom contributing to the oxidation-reduction reaction is Fe, not Co or Ni, it is a material that can be expected to greatly improve in terms of cost and supply stability. However, lithium iron phosphate has a slower lithium insertion / desorption reaction during battery charging / discharging and higher electrical resistance than lithium cobalt oxide used in the past, which increases the overvoltage during large current charging / discharging. Accordingly, there is a problem that sufficient charge / discharge capacity cannot be obtained.

  Various approaches have been made with respect to this problem. For example, the following methods (1) to (4) have been proposed.

  (1) Reduce the particle size of the active material and increase the specific surface area.

  (2) A conductive additive such as carbon is supported on the surface of the active material particles.

  (3) When producing the positive electrode mixture, carbon black, fibrous carbon, or the like is added.

  (4) A binding agent (binder) having a high binding force is used to improve the adhesion of the constituent members.

  Specifically, the methods (1) to (4) described above are described in Patent Documents 1 to 4 as described below.

  (1) In Patent Document 1, the particle diameter of primary particles of lithium iron phosphate is limited to 3.1 μm or less, and the specific surface area of the positive electrode active material is sufficiently increased to increase the electron conductivity in the positive electrode. It is described.

  (2) Patent Document 2 describes that charge / discharge capacity in large-current charge / discharge is increased by supporting conductive fine particles on the surface of lithium iron phosphate particles and improving the active material.

  (3) Patent Document 3 describes a lithium iron composite oxide obtained by combining powder carbon such as carbon black, flake carbon such as graphite, or fibrous carbon in order to reduce the electrical resistance of the positive electrode. Yes.

  (4) Patent Document 4 improves the adhesion between the positive electrode active material and the conductive aid, the positive electrode active material and the current collector, and the current collector and the conductive aid by using a binder having a high binding force. And improving the characteristics during large current charge / discharge.

  On the other hand, lithium iron phosphate has a slower lithium insertion / desorption reaction during charge / discharge and repeats rapid charge / discharge and charge / discharge cycles compared to the positive electrode active material used in 4V class lithium ion secondary batteries. Therefore, a difference tends to appear in the concentration distribution of lithium ions between the electrode surface and the vicinity of the current collector. Further, lithium iron phosphate exhibits a flat charge / discharge potential different from other positive electrode active materials because the charge / discharge reaction proceeds in a two-phase coexistence reaction. For this reason, the potential is flat compared to other active materials, and since there is no potential gradient, the concentration distribution of lithium ions in the electrode is difficult to be relaxed. The distribution of the lithium ion concentration in the electrode is considered to contribute to local degradation of the electrode, and there is a concern about a long life.

JP 2002-110162 A JP 2001-110414 A JP 2003-36889 A JP 2005-251554 A

  By the way, some uses of a lithium secondary battery are assumed to be used over a long period in a mode in which high-rate charge / discharge (rapid charge / discharge) is repeated. Lithium secondary batteries used as power sources for vehicles (typically automobiles, especially hybrid cars, electric cars) and stationary equipment (renewable energy backup systems and power fluctuation mitigation applications in factories) are assumed to be used in this way. This is a representative example.

  Therefore, the present invention was created to solve the conventional problems related to the lithium iron phosphate positive electrode for lithium ion secondary batteries, and its object is to repeat high-rate charge / discharge and charge / discharge cycles. In addition, the present invention aims to suppress the lithium ion concentration distribution in the electrode and improve the life characteristics. Another object of the present invention is to provide a positive electrode which is difficult to delaminate even by charge / discharge (high inter-layer adhesion) and excellent in quality in which an increase in internal resistance is suppressed, and a method for producing the same. Another object is to provide a lithium ion secondary battery including such a positive electrode.

  Accordingly, an object of the present invention is to provide a lithium ion secondary battery having a long life and high input / output with improved electrode ion concentration and improved lithium ion concentration distribution in the lithium iron phosphate positive electrode.

  In order to solve the above problems, the following configuration is considered effective.

  A conductive layer (first layer) containing a conductive substance and a binder is formed on the positive electrode current collector, and a positive electrode active material (lithium iron phosphate) and a conductive agent are formed on the conductive layer (first layer). And a negative electrode plate in which a negative electrode active material layer containing a negative electrode active material and a carbon-based material is formed on a negative electrode current collector; Is disposed via a porous separator. And the film thickness of a positive electrode active material layer is defined as 40 micrometers or more and 200 micrometers or less. In this way, when a conductive layer imparted with conductivity is formed on a positive electrode current collector using lithium iron phosphate (especially olivine type lithium phosphate) as a positive electrode active material, the conductivity in the vicinity of the positive electrode current collector is increased. Therefore, the concentration distribution of lithium ions near the electrode surface and the current collector due to rapid charge / discharge and charge / discharge cycles is relaxed. In addition, this effect is conspicuous in a thick film electrode in which the distance between the current collector and the electrode surface is increased, and the life characteristics are improved. In addition, by forming a conductive layer on the current collector, the electron transfer resistance of the electrode can be reduced and high input / output characteristics can be improved. Furthermore, due to the anchor effect of the conductive filler present in the conductive layer, the adhesion with the active material layer is improved, and delamination due to charge / discharge is difficult (high adhesion between layers). Accordingly, it is possible to provide a highly safe lithium ion secondary battery without deteriorating battery characteristics such as input / output and life.

  Further, when the conductive layer film is set to 1 to 5 μm, the input / output of the battery is further improved and the life of the battery can be extended.

  Further, when the volume porosity of the positive electrode active material layer is set to 20 to 50%, battery characteristics such as input / output and life can be improved with certainty. The positive electrode active material layer preferably contains a conductive additive, and when the positive electrode active material is 100% by mass, the conductive auxiliary agent content is preferably set to 2% by mass or more and 10% by mass or less. When the content of the conductive additive in the positive electrode active material is set within such a range, battery performance such as input / output characteristics can be further improved.

  According to the present invention, by forming a conductive layer on a lithium iron phosphate positive electrode, it is possible to provide a lithium ion secondary battery with high safety, long life, and high input / output.

It is sectional drawing of the lithium ion battery of this Embodiment. It is the graph which put together the relationship between the thickness of a conductive layer, and cycle life.

  Embodiments of the present invention will be described below. In the present embodiment, when ranges are indicated as A to B (where A and B are numbers greater than or equal to 0), A and B are indicated unless otherwise specified.

  First, the outline structure of the lithium ion battery which is embodiment of this invention is demonstrated easily. The lithium ion 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. The positive electrode, the negative electrode, and the separator are provided in the battery container in a state of being wound as an electrode winding group or stacked as an electrode group.

  When charging the lithium ion 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, 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 battery will be described later (see, for example, FIG. 1).

  Next, a positive electrode, a negative electrode, an electrolytic solution, a separator, and other components that are components of the lithium ion battery according to the present embodiment will be sequentially described.

1. Positive electrode In this embodiment, the positive electrode shown below is applicable to a long-life, high-input / output lithium ion battery.

The positive electrode (positive electrode plate) of this embodiment includes a conductive layer having a conductive filler on the surface of a positive electrode current collector and a positive electrode active material layer formed on the conductive layer. In the present embodiment, the conductive layer preferably has a thickness of 0.5 to 5 μm, and more preferably 1 to 3 μm. The active material layer includes at least an active material, a conductive aid, and a binder. The active material is lithium iron phosphate, but is preferably olivine type lithium iron phosphate (LFP). Details of the active material, the conductive additive, and the binder will be described later. The conductive layer and the positive electrode active material layer are formed, for example, by applying a conductive material and a positive electrode mixture in this order on both sides of a current collector. In the present embodiment, the thickness of the active material layer after drying the positive electrode mixture applied to the current collector as described later is 40 μm or more and 200 μm or less, but from the viewpoint of battery characteristics, it is 40 μm or more and 150 μm or less. Is preferably 40 μm or more and 120 μm or less. Further, it is preferable that the electrode density of the active material layer is ^{1.90g / cm 3 ~2.30g / cm 3} . Further, the volume porosity of the positive electrode active material layer is preferably 20 to 50%, more preferably 23 to 45%, still more preferably 25 to 40%. Furthermore, the content of the conductive additive in the positive electrode active material layer is preferably 2% by mass or more and 10% by mass or less from the viewpoint of battery characteristics.

  When the thickness of the active material layer is less than 40 μm, the concentration distribution of lithium ions in the electrode hardly occurs, and the effect of forming the conductive layer is small. In addition, the amount of the active material that contributes to charge / discharge decreases, and the energy density of the battery may decrease. On the other hand, when the film thickness of the active material layer exceeds 200 μm, the resistance of the positive electrode mixture is increased, and the input / output characteristics may be deteriorated.

On the other hand, if the density of the positive electrode active material layer is less than 1.90 g / cm ³ , the electron transfer resistance of the positive electrode is increased, and the input / output characteristics may be degraded. On the other hand, when the density of the positive electrode active material layer exceeds 2.40 g / cm ³ , the vacancy volume in the active material layer decreases, so that the ion diffusion resistance increases and the input / output characteristics may be deteriorated.

  On the other hand, when the content of the conductive auxiliary in the positive electrode active material layer is less than 2% by mass, the electron transfer resistance of the electrode increases and the input / output characteristics are deteriorated. On the other hand, when the content of the conductive additive in the positive electrode active material layer exceeds 10% by mass, the amount of the active material that contributes to charge / discharge decreases, and the energy density of the battery decreases.

Thus, in the positive electrode active material layer, by setting the density of the positive electrode active material layer (the porosity of the active material layer) and the thickness of the positive electrode active material layer within the above ranges, olivine-type lithium iron phosphate (LiFePO ₄ , below) In a lithium ion battery using a positive electrode active material (referred to as LFP), a long-life and high-input / output lithium ion secondary battery can be realized.

  In addition, the volume porosity of the said positive electrode active material layer is computable from the following formula | equation, for example, when an active material, a conductive support agent, and a binder are included as a positive electrode mixture.

Volume porosity of positive electrode active material layer (%) = [1-{(i) + (ii) + (iii) / (width of positive electrode active material layer × length × thickness)}] × 100
Here, (i) is the volume of the active material in the positive electrode active material layer, (ii) is the volume of the conductive auxiliary agent in the positive electrode active material layer, and (iii) is the binding in the positive electrode active material layer. Represents the volume of the agent. (I) + (ii) + (iii) can be calculated from the following equation.

(I) (total weight of the positive electrode active material layer × ratio of the positive electrode active material in the positive electrode active material layer) / true specific gravity of the positive electrode active material (ii) (total weight of the positive electrode active material layer × positive electrode active of the conductive auxiliary agent (Ratio in the material layer) / true specific gravity of the conductive auxiliary agent (iii) (total weight of the positive electrode active material layer × ratio of the binder in the positive electrode active material layer) / true specific gravity of the binder As lithium iron phosphate (LFP), one having an olivine crystal structure and represented by the following composition formula (Formula 2) is preferably used.

LiFe _1-w M ′ _w PO ₄ (Chemical formula 2)
In the above composition formula (Formula 2), (1-w) represents the composition ratio of Fe (iron), and w represents the composition ratio of the element M ′. The composition ratio of Li (lithium) is 1, the composition ratio of P (phosphorus) is 1, and the composition ratio of O (oxygen) is 4.

  The element M ′ is one or more transition metal elements.

  0 ≦ w ≦ 0.5.

  The compound represented by the above composition formula (Formula 2) is a lithium transition metal phosphate compound in which a part of Fe of lithium iron phosphate is substituted with a transition metal element. As the transition metal element, any transition metal element other than Fe can be used alone or in combination of two or more. Preferable examples of the transition metal element include Co, Mn, V and the like. Moreover, in order to improve electroconductivity, it is preferable to use olivine type lithium iron phosphate containing carbon.

  When olivine-type lithium iron phosphate (LFP) is used as the positive electrode active material, the change in the crystal structure associated with charge / discharge is small, so that there is little deterioration in characteristics after repeated many times of charge / discharge and excellent cycle characteristics. Thereby, the life of the battery can be extended.

  Moreover, the oxygen atom in the crystal | crystallization of olivine type lithium iron phosphate (LFP) exists stably by carrying out a covalent bond with P (phosphorus). Therefore, even when the battery is exposed to a high temperature environment, the possibility that oxygen is released from the positive electrode active material is small, and the safety of the battery can be improved.

  Thus, although olivine type lithium iron phosphate (LFP) has useful characteristics, olivine type lithium iron phosphate (LFP) itself has low conductivity, and further has a small theoretical capacity and a low density. Therefore, when a battery is configured using olivine type lithium iron phosphate (LFP) as a positive electrode active material, it is difficult to increase high input / output characteristics and battery capacity (discharge capacity). Therefore, in this embodiment, by forming a conductive layer having a conductive filler over the positive electrode current collector, low electron conduction, which is a problem of LFP, can be improved, and input / output characteristics can be improved. Further, by increasing the electron conductivity, the concentration distribution of lithium ions near the electrode surface and the current collector is relaxed, the amount of electrode coating is increased, and the capacity of the battery can be increased. Further, since the active material can react evenly by charge / discharge due to relaxation of the lithium ion concentration distribution, local deterioration of the active material can be suppressed, and the life can be extended. Furthermore, since the filler present in the conductive layer exhibits an anchor function, the adhesion between the conductive layer and the active material layer is improved. As a result, delamination due to charge / discharge hardly occurs (adhesion between layers is high), so that a reduction in battery capacity and lifetime can be reduced.

  For this reason, by forming a conductive layer on the surface of the current collector of the LFP positive electrode, it has become possible to provide a battery having a long life as well as an improvement in low electron conduction.

  The conductive layer is mainly composed of carbon, which is an electronic conductive medium, and a binder. As the carbon, it is possible to use natural or artificial crystalline graphite, various carbon blacks such as channel black, thermal black, and furnace black, and electron conductive carbon such as glassy carbon. In particular, carbon black and graphite, which are difficult to occlude and release lithium ions, are preferable because they have less expansion and contraction due to charge / discharge cycles. The shape is preferably a powder such as fine particles or short fibers, and particularly preferably has an average particle size of 5 μm or less. In order to further improve the conductivity, it is more preferable to add carbon powder having an average particle diameter of 1 μm or less in a range of 10% or less with respect to the total weight of the carbon powder. In particular, by using a combination of carbon blacks such as graphite and acetylene black, a good electrical connection to the current collector is obtained, the battery life characteristics are improved, and the adhesion between the conductive layer and the active material layer Is preferable because of the increase.

  In the present specification, the “average particle diameter” means a volume-based median diameter (d50) measured by a laser diffraction type particle size distribution measuring apparatus.

  Further, the binder contained in the conductive layer according to this embodiment is a water-insoluble polymer that is soluble in an organic solvent and insoluble in water. Examples of this type of polymer include polyvinylidene fluoride (PVDF), polyvinylidene chloride (PVDC), polyacrylonitrile (PAN), polypropylene oxide (PPO), and polyethylene oxide-propylene oxide copolymer (PEO-PPO). . The binder used particularly preferably is PVDF.

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

  As described above, olivine type lithium iron phosphate (LFP) is used as the positive electrode active material. These are used in powder form (granular) and mixed.

  A substance having a composition different from that of the substance constituting the main cathode active material may be adhered to the surface of the cathode active material. Surface adhesion substances include aluminum oxide, silicon oxide, titanium oxide, zirconium oxide, magnesium oxide, calcium oxide, boron oxide, antimony oxide, bismuth oxide, lithium sulfate, sodium sulfate, potassium sulfate, magnesium sulfate, sulfuric acid Examples thereof include sulfates such as calcium and aluminum sulfate, carbonates such as lithium carbonate, calcium carbonate and magnesium carbonate, and carbon.

  There are the following methods for attaching the surface adhering substance. For example, the surface active substance is impregnated and added to the positive electrode active material by adding the positive electrode active material to a liquid in which the surface adhesive substance is dissolved or suspended in a solvent. Thereafter, the positive electrode active material impregnated with the surface adhering substance is dried. In addition, the positive electrode active material is added to a liquid obtained by dissolving or suspending the precursor of the surface adhesion material in a solvent, so that the precursor of the surface adhesion material is impregnated and added to the positive electrode active material. Thereafter, the positive electrode active material impregnated with the precursor of the surface adhering material is heated. Further, a liquid obtained by dissolving or suspending the precursor of the surface adhesion substance and the precursor of the positive electrode active material in a solvent is baked. By these methods, the surface adhering substance can be attached to the surface of the positive electrode active material.

  The amount of the surface adhering substance is preferably in the following range with respect to the weight of the positive electrode active material. The lower limit of the range is preferably 0.1 ppm or more, more preferably 1 ppm or more, and even more preferably 10 ppm or more. The upper limit is preferably 20% or less, more preferably 10% or less, and still more preferably 5% or less.

  The surface adhering substance can suppress the oxidation reaction of the non-aqueous electrolyte solution on the surface of the positive electrode active material, and can improve the battery life. However, when the adhesion amount is too small, the above effect is not sufficiently exhibited. When the adhesion amount is too large, the resistance may increase in order to inhibit the entry and exit of lithium ions. Therefore, the above range is preferable.

  As the positive electrode active material particles of olivine type lithium iron phosphate (LFP), those in the form of a lump, polyhedron, sphere, ellipsoid, plate, needle, column or the like 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 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 additive are easily mixed uniformly at the time of forming the electrode.

  The range of the median diameter d50 of the particles of the positive electrode active material of olivine type lithium iron phosphate (LFP) (the median diameter d50 of the secondary particles when the primary particles are aggregated to form secondary particles) is as follows. It is as follows. The lower limit of the range is 0.1 μm or more, preferably 0.2 μm or more, more preferably 0.5 μm or more, and the upper limit is 10 μm or less, preferably 8 μm or less, more preferably 6 μm or less, and even more preferably 4 μm or less. is there. If it is less than the said lower limit, tap density (fillability) falls and there exists a possibility that a desired tap density may not be obtained. In addition, since the specific surface area of the active material increases, a large amount of solvent is required during the production of the slurry, and further, the production of the slurry becomes difficult due to secondary aggregation with the conductive agent. For this reason, at the time of formation of an electrode, there exists a possibility that mixing property with other materials, such as a binder and a conductive support agent, may fall. Therefore, when this mixture is slurried and applied, it may not be applied uniformly, which may cause problems such as streaking. On the other hand, when the above upper limit is exceeded, it takes time to diffuse lithium ions in the particles, which may lead to a decrease in battery performance.

  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 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, particularly preferably 0.1 μm or more, and the upper limit is 1 μm or less, preferably 0.5 μm or less, more preferably Is 0.3 μm or less, particularly preferably 0.2 μm or less.

  When the above upper limit is exceeded, the secondary particles to be formed become large. For this reason, since the specific surface area of an active material falls and the reactivity with the electrolyte solution of a battery falls, a charge / discharge characteristic as a positive electrode active material for lithium ion secondary batteries falls, especially battery capacity falls.

  On the other hand, if it is less than the above lower limit, sufficient crystallinity of the lithium iron phosphate particles cannot be obtained, and in any case, excellent characteristics as a positive electrode active material cannot be obtained.

Regarding the BET specific surface area of the positive electrode active material particles of olivine-type lithium iron phosphate (LFP), the ranges are as follows. Lower limit of the range is, 0.2 m ² / g or more, preferably 0.3 m ² / g or more, still more preferably 0.4 m ² / g or more, and the upper limit is, 25 m ² / g or less, preferably 20 m ² / g or less, more preferably 17 m ² / g or less. 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 additive may decrease. 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.

  Examples of conductive assistants for the positive electrode include metal materials such as copper and nickel; graphite such as natural graphite and artificial graphite; graphite black such as acetylene black; and carbonaceous materials such as amorphous carbon such as needle coke. Etc. Of these, one type may be used alone, or two or more types may be used in combination.

  About content (addition amount, a ratio, quantity) of a conductive support agent, the range of content of the conductive support agent with respect to the weight of a 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 above lower limit, the conductivity may be insufficient. Moreover, when the said upper limit is exceeded, there exists a possibility that battery capacity may fall.

  The binder for the positive electrode active material is not particularly limited, and when the positive electrode active material layer 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 with respect 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 particularly 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. On the other hand, if it is too high, 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. 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.

2. Negative electrode In this embodiment, the negative electrode shown below is applicable to a high-capacity, high-input / output lithium-ion battery. The negative electrode (negative electrode plate) of the present embodiment includes a current collector and a negative electrode active material layer formed by applying a negative electrode mixture on both surfaces thereof. The negative electrode active material layer contains a negative electrode active material capable of electrochemically inserting and extracting 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, and oxidation of Group 4 elements such as silicon, germanium, and tin that can occlude and release lithium by forming a compound with lithium and inserting it into the crystal gap Or nitride may be used.

  In particular, the carbonaceous material is a material having high conductivity, and excellent in terms of low temperature characteristics and cycle stability. Among the carbonaceous materials, a material having a wide carbon network surface layer (d002) is excellent in rapid charge / discharge and low-temperature characteristics, and is preferable. However, since a material having a wide carbon network surface layer (d002) may have a low capacity and charge / discharge efficiency at the initial stage of charging, it is preferable to select a material having a carbon network surface layer (d002) of 0.39 nm or less. . Such a carbonaceous material is sometimes referred to as pseudo-anisotropic carbon.

  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. As the graphite material, materials having the characteristics shown in (1) to (3) below may be used.

(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 (ID / IG) is 0.2 or more and 0.4 or less.

(2) half-value width Δ value of the peak in the range of 1300～1400Cm ^-1 as measured by Raman spectroscopy spectra is 40 cm ^-1 or more 100 cm ^-1 or less.

(3) Intensity ratio X value (I (110) / I (004)) between the peak intensity (I (110)) on the (110) plane and the peak intensity (I (004)) on the (004) plane in X-ray diffraction ) Is 0.1 or more and 0.45 or less.

  Battery performance can be improved by using the graphite under such conditions as the negative electrode active material.

  The negative electrode active material layer 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 electrode active material layer. The negative electrode active material is used in the form of powder (granular).

  The range of the median diameter d50 of the carbonaceous material particles 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, further preferably 7 μm or more, and the upper limit is 100 μm or less, preferably 50 μm or less, more preferably 40 μm or less, more preferably 30 μm or less, Particularly preferably, it is 25 μm or less. If it is less than the lower limit, the irreversible capacity increases, which may cause a loss of initial battery capacity. On the other hand, when the above upper limit is exceeded, the application surface of the negative electrode mixture becomes non-uniform during the formation of the electrode, which may hinder the electrode formation.

The range of the BET specific surface area of the carbonaceous material particles is as follows. The lower limit of the range is 0.1 m ² / g or more, preferably 0.7 m ² / g or more, more preferably 1.0 m ² / g or more, and further preferably 1.5 m ² / g or more. The upper limit is 100 m ² / g or less, preferably 25 m ² / g or less, more preferably 15 m ² / g or less, and still more preferably 10 m ² / g or less. If it is less than the said minimum, the occlusion of the lithium ion in a negative electrode will fall easily at the time of charge, and there exists a possibility that lithium may precipitate on the negative electrode surface. Moreover, when the said upper limit is exceeded, the reactivity with a non-aqueous electrolyte solution will increase and there exists a possibility that the generated gas in the negative electrode vicinity may increase.

  The pore size distribution (relationship between pore size and volume) of the carbonaceous material particles is obtained by mercury porosimetry (mercury intrusion method). The pore volume can be determined from this pore size distribution. For carbonaceous material particles, the pore volume ranges are as follows.

Pore volume V of particles of carbonaceous material _(0.01-1) (the diameter of which corresponds to 0.01 μm or more and 1 μm or less, voids in the particles, depressions due to irregularities on the particle surface, between the contact surfaces between the particles The total range of voids, etc.) is as follows. The lower limit of the pore volume V _(0.01-1) is 0.01 mL / g or more, preferably 0.05 mL / g or more, more preferably 0.1 mL / g or more, and the upper limit is 0.6 mL / g. g or less, preferably 0.4 mL / g or less, more preferably 0.3 mL / g or less.

  When the above upper limit is exceeded, there is a possibility that the binder necessary for forming the electrode increases. If it is less than the said lower limit, a high current density charge / discharge characteristic may fall, and also the relaxation effect of the expansion / contraction of the electrode at the time of charge / discharge may fall.

Also, pore volume V _(0.01-100) of particles of carbonaceous material (the diameter of which corresponds to 0.01 μm or more and 100 μm or less, voids in the particles, depressions due to irregularities on the particle surface, contact between particles) The range of the total amount of voids between the surfaces is as follows. The lower limit of the pore volume V _(0.01-100) is preferably 0.1 mL / g or more, more preferably 0.25 mL / g or more, still more preferably 0.4 mL / g or more, and the upper limit is 10 mL. / G or less, preferably 5 mL / g or less, more preferably 2 mL / g or less. When the above upper limit is exceeded, there is a possibility that the binder necessary for forming the electrode increases. Moreover, if it is less than the said minimum, there exists a possibility that the dispersibility to a binder or a thickener may fall at the time of electrode formation.

  The range of the average pore diameter of the carbonaceous material particles is as follows. The lower limit of the average pore diameter is preferably 0.05 μm or more, more preferably 0.1 μm or more, further preferably 0.5 μm or more, and the upper limit is 50 μm or less, preferably 20 μm or less, more preferably 10 μm or less. . When the above upper limit is exceeded, there is a possibility that the binder necessary for forming the electrode increases. Moreover, if it is less than the said minimum, there exists a possibility that a high current density charge / discharge characteristic may fall.

The ranges of the tap density of the carbonaceous material particles are as follows. The lower limit of the tap density is 0.1 g / cm ³ or more, preferably 0.5 g / cm ³ or more, more preferably 0.7 g / cm ³ or more, and particularly preferably 1 g / cm ³ or more. The upper limit is preferably 2 g / cm ³ or less, more preferably 1.8 g / cm ³ or less, and particularly preferably 1.6 g / cm ³ or less. If it is less than the said minimum, the packing density of the negative electrode active material in a negative electrode active material layer falls, and there exists a possibility that a predetermined battery capacity cannot be ensured. On the other hand, when the above upper limit is exceeded, voids between the negative electrode active materials in the negative electrode active material layer are reduced, and it may be difficult to ensure conductivity between particles.

  Moreover, you may add the 2nd carbonaceous material of a property different from this to the 1st carbonaceous material used as a negative electrode active material as a electrically 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 a preferred form, there is a form using a carbonaceous material that is not symmetrical when the volume-based particle size distribution is centered on the median diameter as the second carbonaceous material (conductive material). Further, as the second carbonaceous material (conductive material), a form using a carbonaceous material having a Raman R value different from that of the first carbonaceous material used as the negative electrode active material, or as the second carbonaceous material (conductive material), There is a form using a carbonaceous material having a different X-ray parameter from the first carbonaceous material used as a substance.

  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 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 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 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 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 active material layer formed using the negative electrode active material, The range of the density of a negative electrode active material layer is as follows. The lower limit of the density of the negative electrode active material layer is preferably 0.7 g / cm ³ or more, more preferably 0.8 g / cm ³ , still more preferably 0.9 g / cm ³ or more, and the upper limit is 2 g / cm ^3. Hereinafter, it is preferably 1.9 g / cm ³ or less, more preferably 1.8 g / cm ³ or less, and even more 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. The density charge / discharge characteristics may be deteriorated. In addition, if it is less than the above lower limit, the conductivity between the negative electrode active materials is lowered, so that the battery resistance is increased and the capacity per unit volume may be lowered.

  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 polymer such as butadiene / styrene copolymer, styrene / isoprene / styrene block copolymer or hydrogenated product thereof; syndiotactic-1,2-polybutadiene, polyvinyl acetate, ethylene -Soft resinous polymers such as vinyl acetate copolymer, propylene / α-olefin copolymer; Fluorine such as polyvinylidene fluoride, polytetrafluoroethylene, fluorinated polyvinylidene fluoride, polytetrafluoroethylene / ethylene copolymer Polymer polymers; polymer compositions having alkali metal ion (especially lithium ion) ion conductivity, and the like. 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, 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, 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 further 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, there exists a possibility of causing the fall of the intensity | strength of a negative electrode active material layer.

  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.

  Further, the range of the binder content relative to the weight of the negative electrode mixture in the case where 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, there exists a possibility that the applicability | paintability of a slurry may fall. When the above upper limit is exceeded, the ratio of the negative electrode active material in the negative electrode active material layer decreases, and there is a risk of a decrease in battery capacity and an increase in resistance between the 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 for a lithium ion battery. For example, the following inorganic lithium salts, fluorine-containing organic lithium salts, oxalate borate salts, etc. Is mentioned.

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 lithium bisfluorosulfonylimide: perfluoroalkane sulfonate such as LiFSI and LiCF ₃ SO ₃ ; LiN (CF ₃ SO ₂ ) ₂ , LiN (CF ₃ CF ₂ SO ₂ ) ₂ , LiN Perfluoroalkanesulfonylimide salts such as (CF ₃ SO ₂ ) (C ₄ F ₉ SO ₉ ); 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 ], etc. Fluoroalkyl fluorophosphate and the like can be mentioned.

  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, it is possible to suppress deterioration of characteristics due to warm storage.

  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 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 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 lithium ion batteries. For example, the following cyclic carbonates, chain carbonates, chain esters, cyclic ethers and chain ethers are used. Etc.

  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% or more, preferably 10% or more, more preferably 15% or more, and the upper limit is 50% or less, preferably 35% or less, more preferably 30% or less. 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 more preferable. 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% or more, preferably 8% or more, more preferably 15% or more, and the upper limit is 50% or less, preferably 35% or less, more preferably 30 % Or less, more preferably 25% 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 of a lithium ion battery. For example, nitrogen, sulfur or a heterocyclic compound containing nitrogen and sulfur, a cyclic carboxylic acid ester, a fluorine-containing cyclic Examples thereof include 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 Sulphites such as phytite 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 at most 3% by mass, more preferably at most 3% by mass, even more preferably at most 2% by 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. 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 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 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 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.

  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.

  A mixture of 60% by mass of graphite (graphite) and 40% by mass of polyvinylidene fluoride (PVDF) dissolved in N-methylpyrrolidone was mixed to obtain a slurry. This slurry was uniformly applied to both surfaces of a positive electrode current collector (aluminum foil having a thickness of 20 μm) using a die coater, and a conductive layer was formed so that the thickness after drying became 1 to 7 μm.

  Thereafter, olivine-type lithium iron phosphate (LFP) is added to the positive electrode active material, acetylene black (average particle diameter: 50 nm) as a conductive auxiliary agent, and polyvinylidene fluoride as a binder are sequentially added and mixed. An agent was obtained. The weight ratio was set to active material: conductive aid: binder = 90: 5: 5. Further, N-methyl-2-pyrrolidone (NMP) as a dispersion solvent was added to the above mixture and kneaded to form a slurry. A predetermined amount of this slurry was uniformly and uniformly applied to both surfaces of the current collector on which the conductive layer was formed, using the die coater. The aluminum foil had a rectangular shape with a short side (width) of 350 mm, and an uncoated portion with a width of 50 mm was left along the long side on one side. Then, the drying process was performed and it consolidated by the press to the predetermined density. Next, a positive electrode plate having a width of 350 mm was obtained by cutting. At this time, a notch was made in the uncoated part, and the remaining part of the notch was used as a lead piece. The width of the lead piece was 10 mm, and the interval between adjacent lead pieces was 20 mm.

[Production of negative electrode plate]
The negative electrode plate was produced as follows. Amorphous carbon (manufactured by Kureha) was used as the negative electrode active material. Polyvinylidene fluoride was added as a binder to the amorphous carbon. The weight ratio of these was 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 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 using a die coater. The rolled copper foil had a rectangular shape with a short side (width) of 355 mm, and left an uncoated part with a width of 50 mm along the long side on one side. Then, the drying process was performed and it consolidated by the press to the predetermined density. The density of the negative electrode active material layer was 1.1 g / cm ³ . Next, a negative electrode plate having a width of 355 mm was obtained by cutting. At this time, a notch was made in the uncoated part, and the remaining part of the notch was used as a lead piece. The width of the lead piece was 10 mm, and the interval between adjacent lead pieces was 20 mm.

[Production of battery]
FIG. 1 shows a cross-sectional view of a lithium ion 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.

  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. Similarly, the lead piece 9 ′ led out from the negative electrode plate and the bottom part of the flange 7 on the negative electrode side are 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.

  Thereafter, an 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 made of hexamethacrylate 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) at the center of the battery lid 4, 4 ′ and project outside the battery lid 4, 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 13 to 18 kg / 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, a metal nut 2 is screwed to the positive electrode external terminal 1 and the negative electrode external terminal 1 ′, and the battery lids 4, 4 ′ are connected to the flange portion 7 via the ceramic washer 3, the metal washer 11, and the ceramic washer 3 ′. Fix by tightening between nut 2. The tightening torque value at this time was 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 blocked from the outside air by the compression of the rubber (EPDM) O-ring 12 interposed between the back surface of the battery lid 4, 4 ′ and the flange 7. .

  Thereafter, a predetermined amount of electrolyte was injected into the battery container 5 from the injection port 13 provided in the battery lid 4 ′, and then the injection port 13 was sealed to complete the cylindrical lithium ion battery 20. .

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. What was done was used. Note that the cylindrical lithium ion battery 20 manufactured in this example is not provided with a current interrupting mechanism that operates to interrupt the current in accordance with the increase in the internal pressure of the battery container 5.

[Evaluation of battery characteristics (discharge characteristics)]
The battery characteristics of the lithium ion battery produced in this way were evaluated by the methods shown below.

  About the produced lithium ion battery, each rate discharge characteristic of the battery which changed the positive electrode compound material porosity, the positive electrode compound material coating amount, and the thickness of the conductive layer was evaluated.

  The evaluation results of the discharge characteristics are as shown in Table 1 (Table 1-1, Table 1-2, and Table 1-3). High rate discharge characteristics were evaluated by a high rate discharge test. In the high rate discharge test, first, a charge / discharge cycle with a current value of 0.5 CA was repeated twice in a voltage range of 4.2 to 2.0 V in an environment of 25 ° C. Further, after charging the battery to 4.2 V, charging and discharging were performed by constant current discharge with a final voltage of 2.0 V at current values of 0.5 CA and 3 CA. The 3CA / 0.5CA discharge capacity ratio means a capacity ratio in 3CA discharge to 0.5 CA discharge capacity in each battery.

(Examples 1-81)
As shown in Table 1, a battery having a wound group diameter of 65 mm, an outer diameter of 67 mm, and an inner diameter of 66 mm was prepared by changing the thickness of the conductive layer, the positive electrode mixture porosity, and the positive electrode mixture thickness. Produced. Table 1 (Table 1-1, Table 1-) shows the evaluation results of each rate (0.5 CA and 3 CA) discharge characteristics, volume energy density at 0.5 CA, and output characteristics (3 CA discharge capacity / 0.5 CA discharge capacity). 2 and Table 1-3).

(Examples 82 to 86)
As shown in Table 2, a battery having a wound group diameter of 65 mm, an outer diameter of 67 mm, and an inner diameter of 66 mm was prepared by changing the thickness of the conductive layer, the positive electrode mixture porosity, and the positive electrode mixture thickness. Produced. In addition, instead of the amorphous carbon used as the negative electrode active material in Examples 1 to 81, surface-coated graphite SMG-KB1 which is a graphite-based material manufactured by Hitachi Chemical Co., Ltd. as the negative electrode active material in Examples 82 to 86. Was used.

(Comparative Examples 1-3)
As shown in Table 3, a battery having a wound group diameter of 65 mm, an outer diameter of 67 mm, and an inner diameter of 66 mm was prepared by changing the thickness of the conductive layer, the positive electrode mixture porosity, and the positive electrode mixture thickness. Produced. Table 3 shows the evaluation results of each rate (0.5 CA and 3 CA) discharge characteristics, volumetric energy density at 0.5 CA, and output characteristics (3 CA discharge capacity / 0.5 CA discharge capacity).

  When Examples 4, 20, 36, 52, 68, 81 in Table 1 and Comparative Example 1 in Table 3 are compared, the film thickness is 1 to 7 μm even if the porosity and thickness of the positive electrode active material layer are the same. It can be seen that the high rate discharge characteristics are improved and the output characteristics are improved by forming the conductive layer. In particular, it can be seen that better high rate discharge characteristics and output characteristics can be obtained when the thickness of the conductive layer is in the range of 1 to 5 μm.

  Further, when Example 69 in Table 1 and Comparative Example 2 in Table 3 are compared, output characteristics can be increased by increasing the thickness of the positive electrode mixture to 40 μm even when the thickness of the same conductive layer and the porosity of the positive electrode mixture are increased. It can be seen that the battery capacity and the volume energy density increase while maintaining the above.

  It can also be seen that even when the negative electrode is changed from amorphous carbon to graphite as shown in Examples 82 to 86, the discharge characteristics of the battery are not affected.

[Evaluation of life characteristics]
Next, in the lithium ion battery positive electrode, the relationship between the thickness of the conductive layer and the cycle life was confirmed. A lithium ion battery was manufactured using a positive electrode current collector in which the thickness of the conductive layer was changed.

Thereafter, the life characteristics were evaluated by a cycle test in which charge and discharge were repeated. As for the charging pattern, each lithium secondary battery was subjected to constant current charging at 1 CA up to an upper limit voltage of 4.2 V, and then constant voltage charging at 4.2 V. The discharge was performed at a constant current of 1 C up to 2.0 V. Here, the thickness of the positive electrode active material layer is 100 μm, the porosity of the positive electrode active material layer is 35%, and the additive amount of the conductive auxiliary agent is 5.0% by mass with respect to 100% by mass of the positive electrode active material layer. did. The test results are shown in Table 4 and FIG.

  As shown in Table 4, in the battery using the positive electrode on which the conductive layer was formed, the cycle retention was improved as compared with Comparative Example 3 in which the capacity retention ratio relative to the capacity at the start of the cycle test was not formed. In Examples 5, 37, and 69 in which the conductive layer was formed, the active material can react evenly by charge / discharge due to the relaxation of the lithium ion concentration distribution due to the effect of the conductive layer. This makes it possible to extend the service life.

  In the present embodiment, only when the positive electrode active material layer has a volume porosity of 35%, the positive electrode active material layer has a volume porosity of 20 to 50% within the range of the present invention. It has been confirmed that an effect can be obtained. Further, in the present embodiment, it is shown only when the addition amount of the conductive additive in the positive electrode active material is 5.0% by mass, but the addition amount of the conductive auxiliary agent in the positive electrode active material is 2% by mass or more. It has been confirmed that the effects of the present invention can be obtained within a range of 10% by mass or less.

  Although the embodiments and examples of the present invention have been specifically described above, the present invention is not limited to these embodiments and examples, and modifications based on the technical idea of the present invention are possible. Of course there is.

  The present invention can be effectively applied to lithium ion batteries.

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

Claims (4)

A lithium secondary battery comprising a positive electrode plate in which a conductive layer is laminated on a positive electrode current collector and an active material layer is further laminated on the conductive layer,
The active material in the active material layer is lithium iron phosphate,
A lithium secondary battery in which the thickness of the active material layer is 40 μm or more and 200 μm or less.   The lithium secondary battery according to claim 1, wherein the conductive layer has a thickness of 1 to 5 μm.   The lithium secondary battery according to claim 1 or 2, wherein the active material layer has a volume porosity of 20 to 50%. The active material layer contains a conductive additive,
4. The lithium secondary battery according to claim 1, wherein the content of the conductive auxiliary agent is 2% by mass or more and 10% by mass or less with respect to the total weight of the active material layer.

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