JPWO2015005228A1 - Lithium ion battery and manufacturing method thereof - Google Patents

Abstract

In the lithium ion battery, the positive electrode mixture has a first particle size as an average particle size, a first active material made of olivine type lithium iron phosphate, and a second particle size larger than the first particle size as an average particle size. And a second active material made of olivine-type lithium iron phosphate. The weight ratio of the first active material to the second active material is 20/80 or more and 90/10 or less.

Description

  The present invention relates to a lithium ion battery and a method for manufacturing the same.

  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 cobalt (Co) or nickel (Ni) as positive electrode materials. It has a big problem in stability. Further, due to the positive electrode material, there is still room for improvement in the safety of the lithium ion secondary battery. With such a background, development of a positive electrode material for a lithium ion secondary battery that does not contain a rare metal and has improved safety is expected.

  Under such circumstances, olivine-type lithium iron phosphate (olivine-type lithium iron phosphate) has attracted attention as a positive electrode active material in a positive electrode mixture (also referred to as a positive electrode mixture) for a lithium ion secondary battery. The olivine-type lithium iron phosphate has a P (phosphorus) atom and an O (oxygen) atom that are strongly bonded by a covalent bond in the crystal structure, so the crystal structure is extremely stable and the risk of ignition and the like is extremely low. Material. Further, since the transition metal atom contributing to the oxidation-reduction reaction is Fe (iron) instead of Co or Ni, it is a material that is expected to be greatly improved in terms of cost and supply stability. However, olivine-type lithium iron phosphate has a slow lithium insertion / release reaction during battery charging / discharging and a large electric resistance compared to lithium cobaltate that has been used in the past. As the overvoltage increases, 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 material (conductive aid) such as carbon is supported on the surface of the active material particles.
(3) When producing the positive electrode mixture, carbon black or fibrous carbon is added.
(4) A binding agent (binder) having a high binding force is used to improve the adhesion of the constituent members.

  As a method of (1) above, Patent Document 1 discloses that the primary particle size of olivine-type 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. It is described to increase the electronic conductivity of the inside.

  As a method of (2) above, Patent Document 2 and Patent Document 3 describe charging and discharging at a large current by carrying conductive fine particles on the surface of olivine type lithium iron phosphate particles and improving the active material. It is described that the charge / discharge capacity is increased.

  As the method (3), in order to reduce the electrical resistance of the positive electrode, it is generally performed to mix powder carbon such as carbon black, flake carbon such as graphite, or fibrous carbon.

  As a method of (4) above, Patent Document 4 discloses that a positive electrode active material and a conductive material, a positive electrode active material and a current collector, or a current collector and a conductive material are used by using a binder having a high binding force. It is described that the adhesiveness of the battery is improved and the characteristics in charge / discharge with a large current are improved.

  By the methods (1) to (4) above, the electrical resistance of the positive electrode is lowered. However, when the output characteristics are improved by the above method (1) or the above method (3), the properties of the slurry required for producing the positive electrode by applying the positive electrode mixture to the current collector are as follows. In order to stabilize, the required amount of binder increases. For this reason, it is difficult to obtain the required coating amount for the current collector, cracks are likely to occur during drying, and high capacity positive electrodes cannot be obtained because sufficient compression is difficult. There is.

  In addition, when producing a positive electrode containing olivine type lithium iron phosphate as a positive electrode active material, generally, a positive electrode active material having a small particle size is used, and the particle size is further smaller than the particle size of the positive electrode active material. The electron conductivity of the positive electrode is increased using a conductive material such as carbon black having a large specific surface area. However, since the primary particles of the positive electrode active material are fine, secondary agglomeration is likely to occur when mixed with the conductive material, and a sufficient current collecting effect cannot be obtained inside the agglomerated particles formed by the secondary agglomeration. The electrical resistance becomes very large. As a result, the positive electrode active material in the central part of the aggregated particles has a problem that even when the battery is charged / discharged, electron conduction does not occur and the charge / discharge capacity decreases.

  In Patent Document 5, a positive electrode active material having an olivine type crystal structure and an inorganic oxide that does not contribute to charge / discharge are mixed, and the particle size A of the positive electrode active material and the particle size B of the inorganic oxide are expressed as A> A method of improving the dispersion state of the positive electrode active material, the conductive material, the binder, or the like by using the range of B is used.

JP 2002-110162 A JP 2001-110414 A JP 2003-36889 A JP 2005-251554 A JP 2008-166207 A

  As described above, the properties of the slurry can be improved by increasing the content of the inorganic oxide that does not contribute to charge / discharge and improving the dispersion state. However, when such an inorganic oxide is contained in the positive electrode mixture, the electronic conductivity of the positive electrode may be reduced. As the electronic conductivity of the positive electrode decreases, the internal resistance of the battery increases and the battery capacity decreases. Moreover, the energy density of a positive electrode falls by mixing the inorganic oxide which does not contribute to charging / discharging.

  Therefore, an object of the present invention is to improve the dispersion state of the positive electrode active material, the conductive material or the binder in the positive electrode mixture, and reduce the electric resistance of the positive electrode, and a high input / output lithium ion secondary. To provide a battery.

  The above and other objects and novel features of the present invention will be apparent from the description of this specification and the accompanying drawings.

  In a lithium ion battery comprising an electrode winding group in which a positive electrode, a negative electrode and a separator are wound, and an electrolyte solution, a positive electrode mixture of a positive electrode having a current collector and a positive electrode mixture applied on both sides thereof is The configuration. The positive electrode composite material has a first particle size as an average particle size, a first active material made of olivine type lithium iron phosphate, and a second particle size larger than the first particle size as an average particle size, and olivine. And a second active material made of type lithium iron phosphate. The weight ratio of the first active material to the second active material is 20/80 or more and 90/10 or less.

  In the lithium ion battery, the first particle size is 0.1 μm or more and 0.7 μm or less, and the second particle size is 1.0 μm or more and 5.0 μm or less.

In the lithium-ion batteries, the density of the positive electrode is, 1.90 g / cm ³ or more 2.40 g / cm ³ or less, and the coating amount of the positive electrode mixture per surface of the current collector, 80 g / m ² or more 180 g / ^{m 2} or less, positive electrode contains a conductive material, the content of the conductive material in the positive electrode composite material is less 10 wt% or more 2.5 wt%.

  In the method of manufacturing a lithium ion battery, the first particle size has an average particle size, the first active material is made of olivine type lithium iron phosphate, and the average particle size has a second particle size larger than the first particle size. And the 2nd active material which consists of olivine type lithium iron phosphate is mixed, and the positive electrode compound material containing a 1st active material and a 2nd active material is produced. Next, the positive electrode mixture is applied to both sides of the current collector, and a positive electrode having the current collector and the positive electrode mixture applied to both sides of the current collector is produced. Next, an electrode group in which the positive electrode and the negative electrode are stacked via a separator is formed. Then, an electrode group is inserted in a battery container, and electrolyte solution is accommodated in a battery container. Then, when producing the positive electrode mixture, the first active material and the second active material are mixed so that the weight ratio of the first active material to the second active material is 20/80 or more and 90/10 or less. .

  In the method for manufacturing a lithium ion battery, the first particle size is 0.1 μm or more and 0.7 μm or less, and the second particle size is 1.0 μm or more and 5.0 μm or less.

In the method for manufacturing a lithium ion battery, when producing the positive electrode mixture, the first active material, the second active material, and the conductive material are mixed, and the first active material, the second active material, and the conductive material are mixed. A positive electrode mixture containing the material is prepared. The density of the positive electrode mixture applied on both surfaces of the collector, 1.90 g / cm ³ or more 2.40 g / cm ³ or less, and, the coating amount of the positive electrode per one side of the current collector Is 80 g / m ² or more and 180 g / m ² or less, and the content of the conductive material in the positive electrode mixture applied to both surfaces of the current collector is 2.5 wt% or more and 10 wt% or less.

  Among the inventions disclosed in the present application, effects obtained by typical ones will be briefly described as follows.

  According to the present invention, there is provided a high-input / output lithium ion secondary battery in which the dispersion state of the positive electrode active material, the conductive material or the binder in the positive electrode mixture is improved and the electric resistance of the positive electrode is reduced. Can be provided.

It is sectional drawing of the lithium ion battery of this Embodiment. It is the graph which put together the relationship between LFP mixing ratio, the slurry viscosity of a positive electrode compound material, and TI value.

  In the following embodiments, when ranges are shown as A to B, A or more and B or less are shown unless otherwise specified.

(Embodiment)
First, an outline of the lithium ion battery will be briefly described. 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. The electrolytic solution is accommodated in the battery container.

  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, electrons flow into the positive electrode. As described above, 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, the positive electrode, the negative electrode, the electrolytic solution, the separator, and other components that are components of the lithium ion battery according to the present embodiment will be described in order.

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

  The positive electrode (positive electrode plate) of the present embodiment is composed of a current collector and a positive electrode mixture formed on the top of the current collector. The positive electrode mixture is formed (applied) on both surfaces of the current collector, for example. The positive electrode mixture has an average particle size different from each other, and includes a mixed active material in which two kinds of positive electrode active materials made of olivine type lithium iron phosphate (LFP) are mixed. Of the two types of positive electrode active materials, the weight ratio of the positive electrode active material having the larger average particle diameter to the mixed active material is 10% or more and 80% or less.

  That is, the positive electrode mixture has a particle size DX (first particle size) as an average particle size, and an active material X (first active material) made of olivine type lithium iron phosphate (LFP) and particles as an average particle size. A mixed active material having a particle size DY (second particle size) larger than the diameter DX and mixed with an active material Y (second active material) made of olivine type lithium iron phosphate (LFP) is included. The weight ratio of the active material X to the active material Y is 20/80 or more and 90/10 or less.

  Hereinafter, a case where two types of active materials having different particle sizes are mixed will be described as an example, but three or more types of active materials having different particle sizes may be mixed. In that case, for example, the weight ratio of the active material having the smallest particle diameter to the active material having the largest particle diameter can be set to 20/80 or more and 90/10 or less.

  Preferably, the particle size DX of the active material X is in the range of 0.1 μm to 0.7 μm, and the particle size DY of the active material Y is in the range of 1.0 μm to 5.0 μm.

  In the present specification, when the primary particles are aggregated and the secondary particles are not formed, the “particle size” means the particle size of the primary particles. In addition, when primary particles are aggregated to form secondary particles, “particle size” means the particle size of the secondary particles.

In the present embodiment, preferably, the density of the positive electrode containing olivine-type lithium iron phosphate (LFP) is at 1.90 g / cm ³ or more 2.40 g / cm ³ or less, and the current collector The coating amount (coating amount) of the positive electrode mixture per one side is 80 g / m ² or more and 180 g / m ² or less. When the density of the positive electrode is 1.90 g / cm ³ or more, the volume porosity of the positive electrode composite material layer is 45% or less, when the density of the positive electrode is 2.40 g / cm ³ or less, the positive electrode The volume porosity of the composite layer is 25% or more. As a result, even when an active material composed of olivine-type lithium iron phosphate (LFP) whose primary particles are fine is used, the dispersion state in the slurry is improved, and the electric resistance of the positive electrode is reduced. A lithium ion secondary battery can be provided.

  In the following, the weight ratio of the active material X to the mixed active material in which the active material X and the active material Y are mixed is referred to as the active material X mixing ratio Xa, and the active material X and the active material Y are mixed. The weight ratio of the active material Y to the mixed active material may be referred to as a mixing ratio Ya of the active material Y.

When the density of the positive electrode mixture is less than 1.90 g / cm ³ , that is, when the volume porosity of the positive electrode mixture exceeds 45%, the electron transfer resistance of the positive electrode is increased and the input / output characteristics may be deteriorated. . On the other hand, when the density of the positive electrode mixture exceeds 2.40 g / cm ³ , that is, when the volume porosity of the positive electrode mixture is less than 25%, the ion diffusion resistance may increase and the input / output characteristics may deteriorate. is there.

Moreover, when the application amount of the positive electrode mixture per one side of the current collector is less than 80 g / m ² , the amount of the active material contributing to charging / discharging may be reduced, and the energy density of the battery may be reduced. On the other hand, when the coating amount of the positive electrode mixture per one side of the current collector exceeds 180 g / m ² , the movement distance of electrons becomes longer, the resistance of the positive electrode mixture increases, and the input / output characteristics may be deteriorated. There is.

  As described above, the mixing ratio of the active material Y having a large particle diameter is preferably in the range of 10 to 80%. When the mixing ratio is less than 10%, the proportion of the active material Y having a large particle size and a small specific surface area becomes small, and secondary agglomeration is likely to occur during slurry preparation, and the effect of improving the slurry properties is small. Become. On the other hand, when the mixing ratio of the active material Y exceeds 80%, the ratio of the small particle size active material advantageous for ion diffusion decreases, and there is a concern that the input / output characteristics may be deteriorated. The input / output characteristics are greatly degraded when performing high-speed charge / discharge that requires a high ion diffusion rate.

  In the present embodiment, the density of the positive electrode mixture, that is, the porosity of the positive electrode mixture, the coating amount of the positive electrode mixture, and the mixing ratio of the active materials are within the above ranges. Accordingly, in a lithium ion battery using olivine type lithium iron phosphate (LFP) as a positive electrode active material, a high-input / output lithium ion secondary in which the dispersion state in the slurry is improved and the electric resistance of the positive electrode is reduced. A battery can be provided.

As the olivine-type lithium iron phosphate (LFP), it is preferable to use one having an olivine-type crystal structure and represented by the following composition formula (Formula 1).
LiFe _1-w M ′ _w PO ₄ (Formula ₁ )

  In the composition formula (Formula 1), (1-w) represents the composition ratio of Fe, 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. M ′ is one or more transition metal elements, and 0 ≦ w ≦ 0.5.

  The compound represented by the above composition formula (Formula 1) 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 (manganese), V (vanadium), 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 charging / discharging is small, so that the characteristic deterioration after repeated charging / discharging many times is small and the cycle characteristics are excellent. 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 a small theoretical capacity and a low density. Therefore, when only the olivine type lithium iron phosphate (LFP) is used as the positive electrode active material and the battery is configured, it is difficult to increase the battery capacity (discharge capacity).

  Therefore, in this embodiment, a mixed active material obtained by mixing two or more active materials having different particle diameters is used as the positive electrode active material. As a result, the specific surface area of the positive electrode active material is reduced due to the contribution of the active material having a large particle size (active material having a large particle size), so that secondary aggregation is unlikely to occur during slurry preparation. Even when a positive electrode active material that is an active material having a small particle size (an active material having a small particle size) and includes an active material made of olivine type lithium iron phosphate (LFP) is used, the dispersion state in the slurry is improved. In addition, it is possible to provide a high input / output lithium ion secondary battery in which the electrical resistance of the positive electrode is reduced. In addition, since the specific surface area of the positive electrode active material is reduced, the amount of the solvent required for slurry preparation can be reduced, so that the positive electrode preparation process can be easily performed.

  Moreover, in this Embodiment, since 2 or more types of positive electrode active materials from which a particle size differs are mixed, charging / discharging capacity does not fall. In addition, by mixing a positive electrode active material having a large particle size and a large packing density, the positive electrode can be easily densified as compared with the case where an active material having a small particle size is used alone.

  Furthermore, by pressing the electrode, the secondary particles having a large particle size are partially deformed to become primary particles, so that the conductivity can be improved. Further, since the positive electrode mixture contains not only the active material having a large particle size but also the active material having a small particle size, the ion diffusion resistance does not increase. As described above, the positive electrode mixture of the lithium ion secondary battery includes the mixed active material in which the active materials having different particle sizes are mixed, so that the electron transfer resistance can be reduced without increasing the ion diffusion resistance. Therefore, not only the slurry property of the positive electrode mixture can be improved, but also a high input / output lithium ion secondary battery can be provided.

  Hereinafter, the positive electrode mixture and the current collector will be described in detail. The positive electrode mixture 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, it forms as follows, for example. Other materials such as a positive electrode active material, a binder, and a conductive material (conductive auxiliary agent) and a thickener used as necessary are mixed in a dry form to form a sheet, and this is crimped to a current collector ( Dry method). In addition, a positive electrode active material, a binder, and other materials such as a conductive material and a thickener used as necessary are dissolved or dispersed in a dispersion solvent to form a slurry, which is applied to a current collector and 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 these, primary particles are preferably aggregated to form secondary particles, and the shape of the secondary particles is preferably spherical or elliptical.

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

  The aforementioned average particle diameter is defined as a median diameter d50. At this time, the preferable range of the median diameter d50 of the particles of the active material X made of olivine type lithium iron phosphate (LFP) is 0.1 μm or more and 0.7 μm or less. The preferable range of the median diameter d50 of the particles of the active material Y made of olivine type lithium iron phosphate (LFP) is 1.0 μm or more and 5.0 μm or less. When primary particles are aggregated to form secondary particles, the median diameter d50 of the particles means the median diameter d50 of the secondary particles.

  When the median diameter d50 of the particles of the active material X is less than 0.1 μm, the packing density (tap density) of the active material X is lowered, and a desired packing density may not be obtained. In addition, since the specific surface area of the active material X increases, a large amount of solvent is required at the time of producing the slurry, and further, the production of the slurry becomes difficult, for example, secondary aggregation occurs with the conductive material. For this reason, when forming a positive electrode, there exists a possibility that a miscibility with other materials, such as a binder and a electrically conductive material, 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 median diameter d50 of the particles of the active material X exceeds 0.7 μm, it takes a long time to diffuse lithium ions in the particles of the active material Y, and the ion diffusion resistance increases. There is.

  The preferable range of the median diameter d50 of the particles of the active material Y made of olivine type lithium iron phosphate (LFP) is 1.0 μm or more and 5.0 μm or less.

  When the median diameter d50 of the particles of the active material Y is less than 1.0 μm, the specific surface area of the positive electrode active material as a whole increases, and secondary aggregation may occur during slurry production. Moreover, there is a possibility that the amount of solvent required for slurry preparation increases.

  On the other hand, when the median diameter d50 of the particles of the active material Y exceeds 5.0 μm, the difference in particle size from the active material X becomes large, and for example, the active material X tends to cause secondary aggregation during slurry preparation. For example, the effect of mixing active materials having two types of particle sizes may be weakened.

  As will be described later, the median diameter d50 can be obtained from a particle size distribution obtained by a laser diffraction / scattering method.

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

  Regarding the content (addition amount, ratio, amount) of the conductive material, the range of the content of the conductive material relative to the weight of the positive electrode mixture is as follows. The lower limit of the range is 0.01% by weight or more, preferably 0.1% by weight or more, more preferably 1% by weight or more, and the upper limit is 50% by weight or less, preferably 30% by weight or less, more preferably 15%. % By weight or less. If it is less than the said minimum, there exists a possibility that electroconductivity may become inadequate. 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 mixture is formed by a coating method, a material having good solubility and dispersibility in the dispersion solvent is selected. Specific examples include resin polymers such as polyethylene, polypropylene, polyethylene terephthalate, polymethyl methacrylate, polyimide, aromatic polyamide, cellulose, and nitrocellulose; SBR (styrene-butadiene rubber), NBR (acrylonitrile-butadiene rubber), fluorine Rubbery polymers such as rubber, isoprene rubber, butadiene rubber, ethylene-propylene rubber; styrene / butadiene / styrene block copolymer or hydrogenated product thereof, EPDM (ethylene / propylene / diene terpolymer), styrene / Thermoplastic elastomeric polymers such as ethylene / butadiene / ethylene copolymers, styrene / isoprene / styrene block copolymers or hydrogenated products thereof; syndiotactic-1,2-polybutadiene, polyacetic acid Soft resinous polymers such as Nyl, ethylene / vinyl acetate copolymer, propylene / α-olefin copolymer; polyvinylidene fluoride (PVdF), polytetrafluoroethylene, fluorinated polyvinylidene fluoride, polytetrafluoroethylene / ethylene Fluoropolymers such as copolymers and polytetrafluoroethylene / vinylidene fluoride copolymers; polymer compositions having ion conductivity of alkali metal ions (particularly lithium ions), and the like. Of these, one type may be used alone, or two or more types may be used in combination. From the viewpoint of the stability of the positive electrode, it is preferable to use a fluorine-based polymer such as polyvinylidene fluoride (PVdF) or a polytetrafluoroethylene / vinylidene fluoride copolymer.

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

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

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

  There is no restriction | limiting in particular as a shape of an electrical power collector, The material processed into various shapes can be used. Specific examples of the metal material include a metal foil, a metal cylinder, a metal coil, a metal plate, a metal thin film, an expanded metal, a punch metal, and a foam metal, and the carbonaceous material includes a carbon plate, a carbon thin film, A carbon cylinder etc. are mentioned. Among these, it is preferable to use a metal thin film. 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 comprises a current collector and a negative electrode mixture (also referred to as a negative electrode mixture) formed on both surfaces thereof. The negative electrode mixture contains a negative electrode active material that can electrochemically occlude and release lithium ions.

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

  The metal composite oxide is not particularly limited as long as it can occlude and release lithium, but Ti (titanium), Li (lithium) or a material containing both Ti and Li has a 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 mixture is formed on the current collector. Although there is no restriction | limiting in the formation method, it forms using a dry method and a wet method similarly to a positive electrode compound material. 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, and there is a risk of causing loss of the 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, there exists a possibility that the reactivity with a non-aqueous electrolyte solution may increase and the generated gas in the vicinity of a negative electrode may increase. The BET specific surface area is a specific surface area (area per unit g) determined by the BET method.

  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 there exists a possibility that 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 filling density of the negative electrode active material in a negative electrode compound material may fall, and there exists a possibility that a predetermined battery capacity cannot be ensured. Moreover, when the said upper limit is exceeded, the space | gap between the negative electrode active materials in a negative electrode compound material will decrease, and it may become difficult to ensure the electroconductivity between particle | grains.

  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 weight or more, preferably 2% by weight or more, more preferably 3% by weight or more, and the upper limit is 45% by weight or less, preferably 40% by weight or less. If it is less than the above lower limit, it is difficult to obtain the effect of improving the conductivity, and if it exceeds the above upper limit, the initial irreversible capacity may be increased.

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

  There is no restriction | limiting in particular as a shape of an electrical power collector, The material processed into various shapes can be used. Specific examples include metal foil, metal cylinder, metal coil, metal plate, metal thin film, expanded metal, punch metal, and foam metal. Among these, a metal thin film 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 compound material formed using the negative electrode active material, The range of the negative electrode compound material density is as follows. The lower limit of the negative electrode composite density is preferably 0.7 g / cm ³ or more, more preferably 0.8 g / cm ³ , still more preferably 0.9 g / cm ³ or more, and the upper limit is 2 g / cm ³ or less. Preferably it is 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 near the interface between the current collector and the negative electrode active material. The density charge / discharge characteristics may be deteriorated. Moreover, if it is less than the said minimum, since the electroconductivity between negative electrode active materials falls, battery resistance will increase and there exists a possibility that the capacity | capacitance per unit volume may fall.

  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 type of solvent can be used as long as it can dissolve or disperse the negative electrode active material, the binder, and the conductive material and the thickener used as necessary. There is no restriction, and either an aqueous solvent or an organic solvent may be used. Examples of the aqueous solvent include water, a mixed solvent of alcohol and water, etc., and examples of the organic solvent include N-methylpyrrolidone (NMP), dimethylformamide, dimethylacetamide, methyl ethyl ketone, cyclohexanone, methyl acetate, Methyl acrylate, diethyltriamine, N, N-dimethylaminopropylamine, tetrahydrofuran (THF), toluene, acetone, diethyl ether, dimethylacetamide, hexamethylphosphalamide, dimethyl sulfoxide, benzene, xylene, quinoline, pyridine, Examples include methylnaphthalene and hexane. In particular, when an aqueous solvent is used, it is preferable to use a thickener. A dispersing agent or the like is added to the thickener, and a slurry such as SBR is made into a slurry. In addition, the said dispersion solvent may be used individually by 1 type, or may be used in combination of 2 or more type.

  Regarding the content (addition amount, ratio, amount) of the binder, the range of the content of the binder with respect to the weight of the negative electrode mixture is as follows. The lower limit of the range is preferably 0.1% by weight or more, more preferably 0.5% by weight or more, and further preferably 0.6% by weight or more. The upper limit is 20% by weight or less, preferably 15% by weight or less, more preferably 10% by weight or less, and still more preferably 8% by weight or less.

  When the above upper limit is exceeded, the proportion of the binder that does not contribute to the battery capacity increases, and the battery capacity may be reduced. 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 compound material.

  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 weight or more, preferably 0.5% by weight or more, more preferably 0.6% by weight or more, and the upper limit is 5% by weight or less, preferably 3% by weight or less, more preferably. Is 2% by weight or less.

  In addition, the range of the binder content relative to the weight of the negative electrode mixture when a fluorine-based polymer typified by polyvinylidene fluoride is used as the main component as the binder is as follows. The lower limit of the range is 1% by weight or more, preferably 2% by weight or more, more preferably 3% by weight or more, and the upper limit is 15% by weight or less, preferably 10% by weight or less, more preferably 8% by weight 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 weight or more, preferably 0.5% by weight or more, more preferably 0.6% by weight or more, and the upper limit is 5% by weight or less, preferably 3% by weight or less, more preferably. Is 2% by weight or less.

  If it is less than the said minimum, there exists a possibility that the applicability | paintability of a slurry may fall. On the other hand, when the above upper limit is exceeded, the ratio of the negative electrode active material to the negative electrode mixture 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. Examples thereof include fluoroalkyl fluorophosphate.

  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 weight or more and 20% by weight or less, more preferably 0.1% by weight or more and 5% by weight 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 weight or more and 99% by weight. % Or less, more preferably 80% by weight or more and 98% by weight 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 a lithium ion battery. For example, the following cyclic carbonate, chain carbonate, chain ester, cyclic ether, and chain ether 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 solution 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 Sulfites such as sulfite and propylene sulfite; 1,3-propane sultone, 1-methyl-1,3-propane sultone, 3-methyl-1,3-propane sultone, 1,4-butane sultone, 1,3- And sultone such as propene sultone and 1,4-butene sultone. Among them, 1-methyl-2-pyrrolidinone, 1-methyl-2-piperidone, 1,3-propane sultone, 1,4-butane sultone, 1,3-propene sultone, 1,4-butene sultone, etc., prolong the battery life. From the viewpoint of

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

  The fluorine-containing cyclic carbonate is not particularly limited, and examples thereof include fluoroethylene carbonate, difluoroethylene carbonate, trifluoroethylene carbonate, tetrafluoroethylene carbonate, and trifluoropropylene carbonate. Among these, fluoroethylene carbonate and the like are particularly preferable from the viewpoint of extending the life of the battery.

  Other compounds having an unsaturated bond in the molecule include vinylene carbonate, vinyl ethylene carbonate, divinyl ethylene carbonate, methyl vinyl carbonate, ethyl vinyl carbonate, propyl vinyl carbonate, divinyl carbonate, allyl methyl carbonate, allyl ethyl carbonate, allyl propyl. Carbonates such as carbonate, diallyl carbonate, dimethallyl carbonate; vinyl acetate, vinyl propionate, vinyl acrylate, vinyl crotonate, vinyl methacrylate, allyl acetate, allyl propionate, methyl acrylate, ethyl acrylate, propyl acrylate , Esters such as methyl methacrylate, ethyl methacrylate, propyl methacrylate; divinyl sulfone, methyl vinyl sulfone Sulfones such as ethyl vinyl sulfone, propyl vinyl sulfone, diallyl sulfone, allyl methyl sulfone, allyl ethyl sulfone, allyl propyl sulfone; sulfites such as divinyl sulfite, methyl vinyl sulfite, ethyl vinyl sulfite, diallyl sulfite; Examples of the sulfonates include vinyl methane sulfonate, vinyl ethane sulfonate, allyl methane sulfonate, allyl ethane sulfonate, methyl vinyl sulfonate, and ethyl vinyl sulfonate; and sulfates such as divinyl sulfate, methyl vinyl sulfate, ethyl vinyl sulfate, and diallyl sulfate. Among these, vinylene carbonate, dimethallyl carbonate, vinyl ethylene carbonate, divinyl ethylene carbonate, vinyl acetate, vinyl propionate, vinyl acrylate, divinyl sulfone, vinyl methanesulfonate, and the like are particularly preferable from the viewpoint of extending the life of the battery.

  In addition to the above additives, other additives such as an overcharge preventing material, a negative electrode film forming material, a positive electrode protective material, and a high input / output material may be used depending on the required function.

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

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

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

  Examples of the high input / output material include surfactants such as perfluoroalkyl sulfonic acid, ammonium salt, potassium salt or lithium salt of perfluoroalkyl carboxylic acid; perfluoroalkyl polyoxyethylene ether and fluorinated alkyl ester. Among these, perfluoroalkyl polyoxyethylene ether and fluorinated alkyl ester are preferable.

  Although there is no limitation in particular in the ratio of the additive in a non-aqueous electrolyte solution, the range is as follows. In addition, when using a some additive, the ratio of each additive is meant. The lower limit of the ratio of the additive to the non-aqueous electrolyte is preferably 0.01% by weight or more, more preferably 0.1% by weight or more, still more preferably 0.2% by weight or more, and the upper limit is preferably 5%. % By weight or less, more preferably 3% by weight or less, still more preferably 2% by weight or less.

  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. Olivine type lithium iron phosphates (LFP) having different average particle diameters were mixed at a predetermined active material weight ratio (X / Y). That is, it has a particle diameter DX that is an average particle diameter as a median diameter d50, an active material X made of olivine type lithium iron phosphate (LFP), and an average particle diameter that is larger than the particle diameter DX and that is a median diameter d50. An active material Y having a certain particle size DY and made of olivine type lithium iron phosphate (LFP) was mixed to prepare a mixed active material containing the active material X and the active material Y. The particle size DX of the active material X before mixing was 0.5 μm, and the particle size DY of the active material Y before mixing was 2.5 μm. Hereinafter, the weight ratio of the active material X to the active material Y is referred to as LFP mixing ratio (X / Y). The mixing ratio (X / Y) is the mixing ratio Xa of the active material X in the mixed active material. And a value represented by Xa / Ya using the mixing ratio Ya of the active material Y in the mixed active material.

  Here, the particle size distribution of the mixture of positive electrode active materials was measured by a laser diffraction / scattering method. Measurement of the particle size distribution by this laser diffraction / scattering method was performed using “MICROTRAC MT3000EX2” manufactured by Nikkiso Co., Ltd. as a particle size distribution measuring apparatus. As a result, the particle size distribution of the obtained mixture of positive electrode active materials had a first peak at the particle size DX1 and a second peak at the particle size DY1 larger than the particle size DX1. The particle size DX1 was 0.1 μm or more and 0.7 μm or less, and the particle size DY1 was 1.0 μm or more and 5.0 μm or less. In addition, although it is thought that each active material aggregates or deforms during mixing, the particle size DX1 is different from the particle size DX of the active material X before mixing, and the particle size DY1 is the active material Y before mixing. The particle size DY was different.

  From the obtained particle size distributions when the LFP mixing ratio (X / Y) was 0/100, 20/80, 30/70, 40/60, 50/50, 80/20, 90/10 Table 1 shows the obtained ratio of the height of the second peak to the height of the first peak.

  As shown in Table 1, when the weight ratio of the active material X to the active material Y is 20/80 or more and 90/10 or less, the ratio of the height of the second peak to the height of the first peak is 0.78 or more. 1.91 or less.

  A mixture of positive electrode materials was obtained by sequentially adding and mixing acetylene black (average particle size: 50 nm) as a conductive material and polyvinylidene fluoride as a binder to such a mixed active material. The weight ratio was mixed active material: conductive material: binder = 90: 5: 5. Further, N-methyl-2-pyrrolidone (NMP) as a dispersion solvent was added to the mixture of the positive electrode materials and kneaded to prepare a slurry of the positive electrode mixture.

  A predetermined amount of this slurry was applied substantially uniformly and uniformly on both surfaces of a 20 μm thick aluminum foil serving as a positive electrode current collector. 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, by cutting, a positive electrode plate having a current collector and a positive electrode mixture applied on both sides of the current collector and having a width of 350 mm was produced. 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 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. 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 negative electrode mixture density was 1.0 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 mm or 40 ± 0.1 mm.

  Next, as shown in FIG. 1, the lead pieces 9 led out from the positive electrode plate are deformed, and all of them are gathered near the bottom of the flange 7 on the positive electrode side and brought into contact with each other. The positive electrode side flange portion 7 is integrally formed so as to protrude from the periphery of the pole column (positive electrode external terminal 1) substantially on the extension line of the axis of the wound group 6, and has a bottom portion and a side portion. Thereafter, the lead piece 9 is connected and fixed to the bottom of the flange 7 by ultrasonic welding. The lead piece 9 led out from the negative electrode plate and the bottom of the flange 7 on the negative electrode side are similarly connected and fixed. The negative electrode side flange portion 7 is integrally formed so as to protrude from the periphery of the pole column (negative electrode external terminal 1 ′) substantially on the extension line of the axis of the wound group 6, and has a bottom portion and a side portion.

  Thereafter, an insulating coating 8 was formed using an adhesive tape to cover the side portion of the flange portion 7 on the positive electrode external terminal 1 side and the side portion of the flange portion 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 battery case 5 made of stainless steel. Inserted inside. The battery container 5 had an outer diameter of 67 mm and an inner diameter of 66 mm.

  Next, as shown in FIG. 1, the ceramic washer 3 ′ is fitted into a pole column whose tip constitutes the positive electrode external terminal 1 and a pole column whose tip constitutes the negative electrode external terminal 1 ′. The ceramic washer 3 ′ is made of alumina, and the thickness of the portion in contact with the back surface of the battery lid 4 is 2 mm, the inner diameter is 16 mm, and the outer diameter is 25 mm. Next, with the ceramic washer 3 placed on the battery lid 4, the positive external terminal 1 is passed through the ceramic washer 3, and with the other ceramic washer 3 placed on the other battery lid 4, the negative external terminal Pass 1 'through another ceramic washer 3. The ceramic washer 3 is made of alumina and has a flat plate shape with a thickness of 2 mm, an inner diameter of 16 mm, and an outer diameter of 28 mm.

Thereafter, the peripheral end surface of the battery lid 4 is fitted into the opening of the battery container 5 and the entire area of both contact portions is laser welded. At this time, the positive electrode external terminal 1 and the negative electrode external terminal 1 ′ pass through a hole (hole) in the center of the battery cover 4 and project outside the battery cover 4. The battery lid 4 is provided with a cleavage valve 10 that cleaves in response to an increase in the internal pressure of the battery. The cleavage pressure of the cleavage valve 10 was 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 ′. Thereby, the metal washer 11 is disposed on the ceramic washer 3. The metal washer 11 is made of a material smoother than the bottom surface of the nut 2.

  Next, the metal nut 2 is screwed to the positive electrode external terminal 1 and the negative electrode external terminal 1 ′, and the battery lid 4 is connected to the flange portion 7 and the nut 2 through the ceramic washer 3, the metal washer 11, and the ceramic washer 3 ′. Secure by tightening between. The tightening torque value at this time was 70 kgf · cm. The metal washer 11 did not rotate until the tightening operation was completed. In this state, the power generation element inside the battery container 5 is shielded from the outside air by the compression of the rubber (EPDM) O-ring 12 interposed between the back surface of the battery lid 4 and the flange 7.

  Thereafter, a predetermined amount of electrolyte is injected into the battery container 5 from the injection port 13 provided in the battery lid 4, that is, accommodated, and then the injection port 13 is sealed to complete the cylindrical lithium ion battery 20. I let you.

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 lithium ion battery in which the LFP mixing ratio (X / Y), the density of the positive electrode mixture (positive electrode mixture density) and the coating amount of the positive electrode mixture (positive electrode mixture coating amount) per side of the current collector were changed, The discharge characteristics at each current value were evaluated.

  In the discharge test, first, a charge / discharge cycle with a current value of 0.5 C 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 discharging with a final voltage of 2.0 V at each current value of 0.5 C and 3 C.

(Examples 1 to 96)
As shown in Tables 2 to 4, a positive electrode mixture was produced by changing the LFP mixing ratio (X / Y), the positive electrode mixture density, and the positive electrode mixture application amount, and the wound group diameter was 65 mm, the outer diameter was 67 mm, the inner diameter was A 66 mm battery was produced. The battery capacity (discharge capacity) at each current value (0.5C and 3C) is evaluated, and the output characteristics (battery capacity / current value 0.5C at current value 3C) are determined from the battery capacity at each current value (0.5C and 3C). Battery capacity). Moreover, the volume energy density in electric current value 0.5C was evaluated.

  The results are shown in Tables 2-4. In addition, the arrow (↑) which shows the upper part in a table | surface shows that it is the same numerical value as the upper column.

(Examples 97 to 101)
As shown in Table 5, a positive electrode mixture in which the LFP mixing ratio (X / Y), the positive electrode mixture density, and the positive electrode mixture application amount were changed was prepared, and a battery having a wound group diameter of 65 mm, an outer diameter of 67 mm, and an inner diameter of 66 mm Was made. In addition, it replaced with the amorphous carbon used in Examples 1-96 as surface active graphite SMG-KB1 which is a graphite-type material by Hitachi Chemical Co., Ltd. as a negative electrode active material. The battery capacity (discharge capacity) at each current value (0.5C and 3C) is evaluated, and the output characteristics (battery capacity / current value 0.5C at current value 3C) are determined from the battery capacity at each current value (0.5C and 3C). Battery capacity). Moreover, the volume energy density in electric current value 0.5C was evaluated.

  The results are shown in Table 5. In addition, the arrow (↑) which shows the upper part in a table | surface shows that it is the same numerical value as the upper column.

(Comparative Examples 1-5)
As shown in Table 6, a positive electrode mixture in which the LFP mixing ratio (X / Y), the positive electrode mixture density, and the positive electrode mixture application amount was changed was produced, and a battery having a wound group diameter of 65 mm, an outer diameter of 67 mm, and an inner diameter of 66 mm Was made. The battery capacity (discharge capacity) at each current value (0.5C and 3C) is evaluated, and the output characteristics (battery capacity / current value 0.5C at current value 3C) are determined from the battery capacity at each current value (0.5C and 3C). Battery capacity). Moreover, the volume energy density in electric current value 0.5C was evaluated.

  The results are shown in Table 6. In addition, the arrow (↑) which shows the upper part in a table | surface shows that it is the same numerical value as the upper column.

  In Examples 1 to 101 shown in Tables 2 to 5, it was confirmed that the battery characteristics were improved in comparison with Comparative Examples 1 to 5 shown in Table 6. This will be described in detail below.

According to the comparison between Examples 11 and 27 in Table 2, Examples 43 and 59 in Table 3, Examples 75 and 91 in Table 4, and Comparative Example 1 in Table 6, the positive electrode mixture density was 2.10 g / cm ³ , respectively. Even if the coating amount of the positive electrode mixture is the same at 150 g / m ² , the current can be reduced by mixing two kinds of olivine type lithium iron phosphate (LFP) having different average particle diameters. It can be seen that the battery capacity at the value 3C is improved and the output characteristics are improved.

Similarly, when Example 15 in Table 2 and Comparative Example 2 in Table 6 are compared, the LFP mixing ratio (X / Y) is 20/80, respectively, and the positive electrode mixture application amount is 150 g / m. ² shows that the battery capacity and the volume energy density are increased by increasing the positive electrode mixture density from 1.80 g / cm ³ to 1.90 g / cm ³ . It can also be seen that increasing the positive electrode mixture density from 1.80 g / cm ³ to 1.90 g / cm ³ improves the output characteristics.

Further, when Examples 9 to 12 in Table 2 and Comparative Example 3 in Table 6 are compared, the LFP mixing ratio (X / Y) is 20/80, respectively, and the positive electrode mixture density is 2.10 g. Even if it is the same at / cm ³ , it can be seen that the output characteristics are improved by reducing the coating amount of the positive electrode mixture from 200 g / m ² to 180 g / m ² or less.

Further, when Example 45 in Table 3 and Comparative Example 4 in Table 6 are compared, the LFP mixing ratio (X / Y) is 40/60, respectively, and the positive electrode mixture density is 1.90 g / cm ^3. Even if the same, the battery capacity and the volume energy density increase while maintaining the output characteristics by increasing the coating amount of the positive electrode mixture from 60 g / m ² to 80 g / m ² .

When Example 51 in Table 3 and Comparative Example 5 in Table 6 are compared, the LFP mixing ratio (X / Y) is the same at 60/40, respectively, and the positive electrode mixture application amount is the same at 150 g / m ² . even, by decreasing the positive electrode density from 2.50 g / cm ³ to 2.40 g / cm ^3, it can be seen that the output characteristics are improved.

  Further, as shown in Examples 97 to 101 in Table 5, it can be seen that even when the negative electrode active material is changed from amorphous carbon to graphite, the discharge characteristics of the battery are not affected.

(Examples 102 to 104, Comparative Examples 6 and 7)
As shown in Table 7, a positive electrode mixture in which the blending ratio of the conductive material in the positive electrode mixture (positive electrode blending ratio) was changed was prepared, and a battery having a wound group diameter of 65 mm, an outer diameter of 67 mm, and an inner diameter of 66 mm was manufactured. At this time, the positive electrode mixture application amount was 150 g / m ² , and the positive electrode mixture density was 1.90 g / cm ³ . The battery capacity (discharge capacity) at each current value (0.5C and 3C) is evaluated, and the output characteristics (battery capacity / current value 0.5C at current value 3C) are determined from the battery capacity at each current value (0.5C and 3C). Battery capacity). Moreover, the volume energy density in electric current value 0.5C was evaluated. The results are shown in Table 7. In Examples 102 to 104 and Comparative Examples 6 and 7, the LFP mixing ratio (X / Y) was 50/50.

  As shown in Examples 102 to 104 in Table 7, it can be seen that increasing the content of the conductive material in the positive electrode mixture forms a conductive path by the conductive material and improves the output characteristics of the battery. On the other hand, in Comparative Example 6, a conductive path made of a conductive material is not formed, and the internal resistance of the battery becomes high and cannot be charged / discharged. Further, as shown in Comparative Example 7, although the output characteristics are improved by increasing the content of the conductive material in the positive electrode mixture, the battery capacity is reduced and the volume energy density is greatly reduced.

  From the above results, in order to achieve both the output characteristics of the battery and the volume energy density, the content of the conductive material in the positive electrode mixture is preferably in the range of 2.5 to 10.0 wt%. Recognize. That is, the content of the conductive material in the positive electrode mixture applied to both surfaces of the current collector is preferably in the range of 2.5 to 10.0 wt%.

[Evaluation of slurry properties (thixotropic properties)]
Next, when producing the positive electrode of a lithium ion battery, the relationship between LFP mixing ratio and slurry property was confirmed. A slurry of the positive electrode mixture in which the LFP mixing ratio was changed was prepared, and then the viscosity of the slurry (slurry viscosity) was measured with an E-type viscometer TVE-35 manufactured by Toki Sangyo Co., Ltd. The ratio of the slurry viscosity when the rotation speed is 0.5 rpm to the slurry viscosity when the rotation speed at the time of measurement is either 0.5 rpm or 5 rpm and the rotation speed is 5 rpm, that is, “0.5 rpm viscosity” The "/ 5 rpm viscosity" was defined as a TI (thixo index) value, and the slurry properties were evaluated. For all the slurries, the ratio of the solid content in the slurry was 45%.

(Examples 105-112, Comparative Example 8)
As shown in Table 8, a slurry of the positive electrode mixture in which the LFP mixing ratio was changed was produced, and the viscosity (slurry viscosity) of the produced slurry was measured. The slurry viscosity at each rotation speed (0.5 rpm and 5 rpm) and the TI value (0.5 rpm viscosity / 5 rpm viscosity) representing the thixotropy of the slurry were evaluated.

  The results are shown in Table 8. In Table 8, the mixing ratio Xa of the active material X and the mixing ratio Ya of the active material Y are shown as the LFP mixing ratio.

  Moreover, the graph which put together the relationship between the LFP mixing ratio, the slurry viscosity of the positive electrode mixture, and the TI value from the results shown in Table 8 is shown in FIG. 2 indicates the mixing ratio Ya of the active material Y as the LFP mixing ratio. FIG. 2 shows the slurry viscosity when the rotation speed is 0.5 rpm.

  As shown in Table 8, in Examples 105 to 112, in which active material Y having a large particle size was mixed with active material X having a small particle size, compared with Comparative Example 8 using only the active material X having a small particle size, Despite the same solid content ratio, the fluidity of the slurry increased. That is, as shown in FIG. 2, the slurry viscosity decreased as the mixing ratio Ya (LFP mixing ratio Ya) of the active material Y increased. From this result, when the active material Y having a large particle size is mixed with the active material X having a small particle size, the viscosity is made equal under the condition that the active material X having a small particle size is used alone. It is considered that the solid content ratio can be increased.

  On the other hand, as shown in Table 8, the TI (thixo index) value indicating the thixotropy of the slurry tended to decrease by increasing the mixing ratio Ya of the active material Y having a large particle size. That is, as shown in FIG. 2, the TI value decreased as the mixing ratio Ya (LFP mixing ratio Ya) of the active material Y increased.

  Thixotropic properties are mainly observed in an agglomerated dispersion system, and are attributed to chemical attraction between particles. For this reason, when a small particle size particle having a short distance between particles and a strong attractive force acting between the particles is contained in the slurry, it is considered that the content of the small particle size greatly affects the thixotropy. .

  In the above Examples 105 to 112, since the particle size of the active material Y is larger than the particle size of the active material X, the distance between the particles of the mixed active material in which the active material Y is mixed becomes longer, and the chemical between the particles is increased. It is considered that the attractive force is suppressed. Therefore, by increasing the mixing ratio Ya of the active material Y, the attractive force acting between the particles of the mixed active material, that is, the cohesive force between the particles is reduced, so that the fluidity of the slurry at a low rotational speed with a low shear force is achieved. It is considered that the thixotropy of the slurry was lowered.

  As mentioned above, the invention made by the present inventor has been specifically described based on the embodiments and examples. However, the present invention is not limited to the above-described embodiments and examples, and does not depart from the gist of the invention. Various changes can be made.

  For example, in the above embodiment and each of the above examples, a positive electrode in which a positive electrode mixture containing an active material X and an active material Y is applied to both surfaces of a current collector is an electrode obtained by winding the positive electrode, the negative electrode, and the separator. The example applied to the winding type battery in which the winding group is accommodated in the battery container has been described. However, one positive electrode in which a positive electrode mixture containing an active material X and an active material Y is applied to both surfaces of a current collector is an electrode in which the single positive electrode and a single negative electrode are stacked via a separator. Even when the group is applied to a battery accommodated in a battery container, the same effect as that obtained when applied to a wound battery can be obtained. In addition, a plurality of positive electrodes in which a positive electrode mixture containing an active material X and an active material Y is applied to both surfaces of a current collector are alternately stacked with the plurality of positive electrodes and a plurality of negative electrodes through separators. Even when applied to a battery in which the electrode group is accommodated in a battery container, the same effect as that obtained when applied to a wound battery can be obtained.

  In such a case, it replaces with the process of forming the electrode winding group which wound the positive electrode, the negative electrode, and the separator, and performs the process of forming the electrode group by which the positive electrode and the negative electrode were laminated | stacked through the separator. Moreover, it replaces with the process of inserting an electrode winding group in a battery container, and performs the process of inserting the electrode group by which the positive electrode and the negative electrode were laminated | stacked through the separator in a battery container.

  The present invention is effective when applied to a lithium ion battery.

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

Claims (6)

An electrode winding group provided in the battery container and wound around the positive electrode, the negative electrode and the separator;
An electrolyte contained in the battery container;
With
The positive electrode is
A current collector,
A positive electrode mixture applied to both sides of the current collector;
Have
The positive electrode mixture is
A first active material having a first particle size as an average particle size and comprising olivine type lithium iron phosphate;
A second active material having a second particle size larger than the first particle size as an average particle size and made of olivine type lithium iron phosphate;
Including
The lithium ion battery, wherein a weight ratio of the first active material to the second active material is 20/80 or more and 90/10 or less. The lithium ion battery according to claim 1,
The first particle size is 0.1 μm or more and 0.7 μm or less,
The lithium ion battery, wherein the second particle size is 1.0 μm or more and 5.0 μm or less. The lithium ion battery according to claim 1 or claim 2,
Density of the positive electrode is, 1.90 g / cm ³ or more 2.40 g / cm ³ or less, and, the coating amount of the positive electrode per one surface of the current collector, 80 g / ^{m 2} or more 180g / M ² or less,
The positive electrode mixture contains a conductive material,
The lithium ion battery, wherein the content of the conductive material in the positive electrode mixture is 2.5 wt% or more and 10 wt% or less. (A) a first active material having a first particle size as an average particle size and comprising an olivine-type lithium iron phosphate; and an olivine type having a second particle size larger than the first particle size as an average particle size Mixing a second active material made of lithium iron phosphate to produce a positive electrode mixture containing the first active material and the second active material;
(B) applying the positive electrode mixture on both sides of a current collector, and producing a positive electrode having the current collector and the positive electrode mixture applied on both sides of the current collector;
(C) forming an electrode group in which the positive electrode and the negative electrode are laminated via a separator;
(D) inserting the electrode group into a battery container;
(E) After the step (d), a step of storing an electrolytic solution in the battery container;
Have
In the step (a), the first active material and the second active material are mixed so that a weight ratio of the first active material to the second active material is 20/80 or more and 90/10 or less. The manufacturing method of a lithium ion battery. In the manufacturing method of the lithium ion battery according to claim 4,
The first particle size is 0.1 μm or more and 0.7 μm or less,
The method for producing a lithium ion battery, wherein the second particle size is 1.0 μm or more and 5.0 μm or less. In the manufacturing method of the lithium ion battery of Claim 4 or Claim 5,
In the step (a), the positive electrode containing the first active material, the second active material, and the conductive material by mixing the first active material, the second active material, and the conductive material. Make a compound,
Wherein (b) the density of the positive electrode mixture coated by step, 1.90 g / cm ³ or more 2.40 g / cm ³ or less, and, of the positive electrode per one surface of the current collector The coating amount is 80 g / m ² or more and 180 g / m ² or less,
The method for producing a lithium ion battery, wherein the content of the conductive material in the positive electrode mixture applied in the step (b) is 2.5 wt% or more and 10 wt% or less.

Images