JP2009093924A - Lithium ion secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress or prevent deposition of lithium (dendrite) by quickly increasing the potential of a positive electrode in the last period of charge, and increase coulombic efficiency, cycle characteristics, and charge capacity. <P>SOLUTION: Electrodes for a lithium ion secondary battery are a positive electrode containing a positive current collector and a positive active material formed on the positive current collector, and a negative electrode containing a negative current collector and a negative active material formed on the negative current collector. The negative active material is graphite, and the positive active material is composite lithium manganate and olivine type composite lithium iron phosphate, and the contents of the composite lithium manganate is 30 mass% or lower of the contents of the olivine type composite lithium iron phosphate. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a lithium ion secondary battery. More specifically, the present invention relates to an electrode using graphite as a negative electrode active material and olivine-type composite lithium iron phosphate as a positive electrode active material, and a lithium ion secondary battery using the same.

  In recent years, in order to cope with air pollution and global warming, reduction of the amount of carbon dioxide has been strongly desired. In the automobile industry, there is a great expectation for reducing carbon dioxide emissions by introducing electric vehicles (EV) and hybrid electric vehicles (HEV), and the development of secondary batteries for motor drive that holds the key to commercialization of these is thriving. Has been done.

  Non-aqueous solvent secondary batteries such as lithium ion secondary batteries, which have the highest theoretical energy among all batteries, are attracting attention as secondary batteries for motor drive, and are currently being developed rapidly. .

  Generally, a lithium ion secondary battery includes a positive electrode in which a positive electrode active material or the like is applied to both surfaces of a positive electrode current collector using a binder, and a negative electrode in which a negative electrode active material or the like is applied to both surfaces of a negative electrode current collector using a binder. However, it has a laminated body (battery element) connected through an electrolyte layer. Moreover, for the purpose of taking out electric power outside, an electrode terminal (a positive electrode terminal and a negative electrode terminal) is electrically connected to the battery element. The battery element is generally housed in a metal-resin laminate sheet in which resin sheets are laminated on both surfaces of a foil made of a light metal such as aluminum so that electrode terminals are led out to the outside. .

Here, recently, a nonaqueous electrolyte secondary battery using lithium iron phosphate LiFePO ₄ in which the metal element in the olivine-type lithium phosphate is iron has been proposed as a positive electrode active material. There is a report that when LiFePO ₄ is used as the positive electrode active material, excellent load characteristics are exhibited in the charging reaction. And in this report, if the positive electrode thickness is applied to about 70 μm (coating amount 10 mg / cm ² ), a cell using Li metal is prepared for the counter electrode, and constant voltage charging is performed, rapid charging is possible. It is shown.

However, constant voltage charging has been difficult to control. Further, in the non-aqueous electrolyte secondary battery using LiFePO ₄ as the positive electrode active material as described above, when Li metal is used as the negative electrode active material, dendrite is generated due to charge and discharge, and the cycle characteristics become very poor. There was a problem. Furthermore, even when graphite is used as the negative electrode active material, the insertion reaction of Li into the graphite is slow, so that when charged rapidly with a high rate current, the polarization during the charging reaction is increased and sufficient. There was a problem that the charge capacity could not be obtained. Furthermore, there is a problem that Li is deposited on the graphite of the negative electrode active material and cycle characteristics are deteriorated.

Means for solving such a problem is disclosed below (Patent Document 1). That is, a negative electrode active material mainly composed of silicon is used for the negative electrode, and the thickness of the positive electrode mixture layer formed on the positive electrode current collector is set to 25 μm or less per side. In this way, it is attempted to obtain a sufficient charge capacity even when the load characteristic at the time of charging reaction in the positive electrode is improved and rapid charging is performed at a high rate of current.
JP 2006-278076 A

As described above, in paragraph “0013” of Patent Document 1, when LiFePO ₄ is used as the positive electrode active material, the use of graphite as the negative electrode active material is abandoned, and the problem is solved by substituting silicon. Are trying.

  However, when silicon is used as the negative electrode active material, the cycle characteristics are poor because the silicon expands and contracts during charging and discharging. Furthermore, silicon has a fast Li ion insertion reaction, but has a large initial irreversible capacity. Therefore, in theory, even if silicon can be used as the negative electrode active material, it is difficult to actually apply it. On the other hand, when graphite is used as the negative electrode active material, the cycle characteristics are good because the graphite expands and contracts during charging and discharging. Furthermore, graphite has the advantage that the initial irreversible capacity is small.

As described above, the present invention has been made for the purpose of applying graphite exhibiting significant physical properties as a negative electrode active material, although LiFePO ₄ is used as the positive electrode active material and Li insertion reaction is slow. Is.

  That is, the present invention solves the above-mentioned problems while using graphite having the above-mentioned advantages, rapidly raises the positive electrode potential at the end of charging, and improves the coulomb efficiency, cycle characteristics, and charging capacity. It aims at providing the electrode for secondary batteries.

  The present inventor has intensively studied to solve the above problems. As a result, by providing graphite as the negative electrode active material and using a certain proportion of composite lithium manganate and olivine-type composite lithium iron phosphate as the positive electrode active material, the above object is achieved. Found that can be achieved.

  By using the electrode according to the present invention, the potential of the positive electrode can be quickly increased at the end of charging, and the precipitation (dendrites) of Li can be suppressed / prevented, and the coulomb efficiency, cycle characteristics and charging capacity can be improved. it can.

  Hereinafter, several suitable embodiments of the electrode for a lithium ion secondary battery of the present invention will be described in detail with reference to the drawings as appropriate. Each drawing is exaggerated for convenience of explanation, and the dimensional ratio of each component in each drawing may be different from the actual one.

<First Embodiment>
A first embodiment of the present invention includes a positive electrode including a positive electrode current collector and a positive electrode active material formed on the positive electrode current collector, a negative electrode current collector and a negative electrode formed on the negative electrode current collector A negative electrode including an active material, and an electrode for a lithium ion secondary battery, wherein the negative electrode active material is graphite, and the positive electrode active material is a composite lithium manganate and an olivine-type composite lithium iron phosphate, It is an electrode for lithium ion secondary batteries whose content of the said composite lithium manganate is 30 mass% or less with respect to the total amount of the said olivine type composite lithium iron phosphate and the said composite lithium manganate.

  If only the olivine-type composite lithium iron phosphate is used as the positive electrode active material, there is a possibility that a dendrite of Li may be generated. Furthermore, when graphite is used as the negative electrode, Li dendrite may be generated due to a slow insertion reaction of Li ions into the graphite.

  In the course of earnest research, the present inventor included a certain amount of composite lithium manganate having a high reaction potential of the positive electrode charging reaction in the olivine-type composite lithium iron phosphate, so that even if graphite was used as the negative electrode active material, The inventors have found that the desired effects listed above can be obtained. Note that the composite lithium manganate having a high charge potential reaction is a composite lithium manganate in which the charge reaction of the positive electrode proceeds at 3.5 V or more. That is, it has been found that with such an embodiment, the potential of the positive electrode can be quickly reached to a predetermined voltage during charging. Using this characteristic, the charging current at the end of charging is reduced (squeezed) at an early stage (that is, by switching to constant voltage charging at an early stage), thereby solving various problems such as the generation of Li dendrite. Found that you can.

  Hereinafter, the constituent elements of the electrode for the lithium ion secondary battery of the present embodiment will be described with reference to the drawings as appropriate.

[Positive electrode current collector and negative electrode current collector]
As the positive electrode current collector and the negative electrode current collector, members conventionally used as a current collector material for batteries can be appropriately employed. As an example, examples of the positive electrode current collector and the negative electrode current collector include aluminum, nickel, iron, stainless steel (SUS), titanium, and copper. Among these, from the viewpoints of electron conductivity and battery operating potential, aluminum is preferable as the positive electrode current collector and copper is preferable as the negative electrode current collector. A typical thickness of the current collector is 10 to 20 μm. However, a current collector having a thickness outside this range may be used. The size of the current collector is determined according to the intended use of the battery. If a large electrode used for a large battery is manufactured, a current collector having a large area is used. If a small electrode is produced, a current collector with a small area is used.

  In the second embodiment to be described later, a stacked non-bipolar lithium ion secondary battery is described in detail. Of course, the negative electrode active material according to the present invention and the positive electrode active material according to the present invention are bipolar lithium materials. You may use for an ion secondary battery. In that case, as the current collector, the positive electrode current collector and the negative electrode current collector are bonded together, and the negative electrode active material layer according to the present invention and the positive electrode active material layer according to the present invention are formed on both surfaces of the current collector. Also good. Alternatively, SUS or Ti, which can be used as a positive electrode current collector or a negative electrode current collector, is used as the positive electrode current collector and the negative electrode current collector, respectively, and the negative electrode active material layer according to the present invention The positive electrode active material layer according to the present invention may be formed.

[Positive electrode active material]
As the positive electrode active material, a material composed of olivine type composite lithium iron phosphate and composite lithium manganate is used.

(Olivine-type composite lithium iron phosphate)
As the olivine-type composite lithium iron phosphate, LiFe _1-x M _x PO ₄ (M is one or more transition metal elements, X ≦ 0.5) is used. Specifically, LiFePO ₄ , etc. Can be mentioned. At this time, it is preferable to use olivine-type composite lithium iron phosphate containing carbon in order to increase conductivity. This is preferable in that the conductivity of the olivine-type composite lithium iron phosphate is improved and the reactivity is improved. More preferably, olivine type composite lithium iron phosphate particles whose surfaces are coated with carbon are used. This is preferable in that the conductivity of the olivine-type composite lithium iron phosphate is further improved and the reactivity is further improved. The carbon coverage is preferably 0.5 to 10% by mass, more preferably 1 to 5% by mass with respect to the olivine type lithium iron phosphate.

  Carbon coating can be performed by appropriately referring to conventionally known methods. For example, it can be performed by a method disclosed in Japanese Patent Application Laid-Open No. 2006-252917.

  In recent years, this olivine-type composite lithium iron phosphate has attracted attention as a positive electrode active material due to the establishment of low-resistance technology (carbon coating, particle size reduction) and high-capacity technology (impurity reduction). ing.

(Composite lithium manganate)
As the composite lithium manganate, LiMn ₂ O ₄ , LiMnO ₂ or other LiMn _1-x M _x O ₂ (M is one or more transition metal elements, X ≦ 0.5) type is used, specifically Means a compound mainly composed of Li, Mn and O. In addition to these atoms, other metal atoms such as Ni, Co, Fe, Al, Cr, Mg, Ag, Ti, and In may be contained in a small amount within a range that does not inhibit the activity as the positive electrode active material. More specifically, LiMn ₂ O ₄ , Li ₂ MnO _4, Li ₂ MnO _{3 and the} like can be mentioned, and the composition is not limited to these, but LiMn ₂ O ₄ is particularly preferable. The structure of the composite lithium manganate is not particularly limited, but preferably has a spinel type or layered type structure.

[Negative electrode active material]
The negative electrode active material is graphite. Examples of graphite include graphite-based carbon materials such as natural graphite and artificial graphite.

  Examples of natural graphite include scaly graphite.

  Examples of artificial graphite include MCMB (mesocarbon microbeads), MCF (mesophase carbon fiber), and the like. Among these, MCMB (mesocarbon microbeads) is preferably used.

  MCMB (mesocarbon microbeads) are obtained by melting coal tar or petroleum heavy oil at around 400 ° C. to form small spheres, and heat-treating the small spheres in an inert atmosphere. Since the carbon hexagonal network structure of graphite structure has a layered orientation laminated in one direction, it is easy to take in lithium ions and is used significantly as a negative electrode material.

  The mesophase in the MCF is a liquid crystal substance obtained by heat-treating heavy oil. By controlling the process of spinning and heat-treating this, carbon fibers with controlled graphite crystal arrangement can be obtained.

  The negative electrode active material and the positive electrode active material are also simply referred to as “active material”.

  As described above, the positive electrode active material according to the present invention includes an olivine-type composite lithium iron phosphate and a composite lithium manganate. However, it is necessary to control the contents of the olivine-type composite lithium iron phosphate and composite lithium manganate. That is, the content of the composite lithium manganate is 30% by mass or less based on the total amount of the olivine-type composite lithium iron phosphate and the composite lithium manganate. However, Preferably it is 5-30 mass%, More preferably, it is 10-30 mass%. As described above, when the olivine-type composite lithium iron phosphate is coated with carbon, the content of the olivine-type composite lithium iron phosphate means the content of the olivine-type composite lithium iron phosphate coated with carbon. Thus, by increasing the amount of composite lithium manganate mixed, the potential of the positive electrode rises and the current can be reduced early, which is also advantageous in this respect.

  However, when the content of the composite lithium manganate exceeds 30% by mass with respect to the total amount of the olivine-type composite lithium iron phosphate and the composite lithium manganate, the energy density decreases or the durability decreases. This will cause harmful effects.

  Moreover, there is no restriction | limiting in particular also in the shape of the negative electrode active material (graphite) concerning this invention, and the positive electrode active material (olivine type composite lithium iron phosphate and composite lithium manganate) concerning this invention. The aspect ratio (long axis length / short axis length, or long axis length / short axis length) may or may not be 1. Examples of the shape having an aspect ratio of 1 include a spherical shape and a cubic shape. Examples of the shape whose aspect ratio is not 1 include a rectangular parallelepiped, an elliptical sphere, a needle shape, a plate shape, a square shape, and a column shape. Preferably, the aspect ratio is 1.

  As above-mentioned, content of the said composite lithium manganate is 30 mass% or less with respect to content of the said olivine type composite lithium iron phosphate.

  At this time, the state in which the olivine-type composite lithium iron phosphate contains the composite lithium manganate is not particularly limited.

  The olivine-type composite lithium iron phosphate and the composite lithium manganate may not be uniformly dispersed in the positive electrode active material but may simply be mixed. However, it is preferable that they are uniformly dispersed and mixed. Such a mixing method is not particularly limited, and can be carried out by referring to or appropriately combining conventionally known methods, for example, by the methods described in Examples.

  As described above, the form of the state in which the olivine-type composite lithium iron phosphate contains the composite lithium manganate is not particularly limited, but more preferably, at least part of the surface of the composite lithium manganate has an olivine-type composite phosphate. Iron lithium is attached.

  FIG. 1 is a schematic cross-sectional view schematically showing an electrode in which olivine-type composite lithium iron phosphate is attached to a part of the surface of composite lithium manganate.

  As described above, when the olivine-type composite lithium iron phosphate Y is attached to at least a part of the surface of the composite lithium manganate X, the composite lithium manganate from the composite lithium manganate when exposed to the electrolyte at high temperature is used. Suppression of elution of Mn ions is suppressed, and consequently deterioration of cycle characteristics is suppressed. Furthermore, for example, there are the following effects.

That is, for example, when a fluorine-based electrolyte (for example, LiPF ₆ or the like) or a fluorine-based binder (for example, PVdF or the like) is used, HF can be generated from them at a high temperature. Even in such a case, if the olivine-type composite lithium iron phosphate is attached to at least a part of the surface of the composite lithium manganate, the reaction between the generated HF and the composite lithium manganate particles is suppressed. You can also.

  In addition, the coverage (attachment) rate of carbon in the olivine-type composite lithium iron phosphate is preferably 0.5% to 10%, more preferably 1% to 5%.

  Among the above, it is particularly preferable that it is applied over the entire surface of the composite lithium manganate (that is, the coverage is 100%).

  FIG. 2 is a schematic cross-sectional view schematically showing an electrode in which olivine-type composite lithium iron phosphate is attached to the entire surface of the composite lithium manganate. As shown in FIG. 2, the positive electrode active material is formed by adhering olivine type lithium iron phosphate Y to the entire surface of the composite lithium manganate X.

  As described above, the present inventors added a certain amount of composite lithium manganate having a high positive electrode charge potential reaction to olivine-type composite lithium iron phosphate in the course of conducting intensive research to solve various problems. It has been found that a desired effect can be obtained.

  In other words, the composite lithium manganate is included to assist the function of the olivine-type composite lithium iron phosphate, and it is clear from the difference in content between the two, but the main component of the positive electrode active material Is an olivine-type composite lithium iron phosphate.

  As is apparent from FIG. 2, the above “added” (composite lithium manganate) is present not in the outside but in the core (center) portion. In addition, since the main component of the positive electrode active material is composite lithium iron phosphate, the content of the composite lithium manganate is small. In short, in a preferred aspect of the present embodiment, in order to improve the function of the composite lithium iron phosphate, a configuration is adopted in which the composite lithium manganate having an auxiliary function is embedded in the center. With such a configuration, the above-described effects are further significantly improved.

  There is no particular limitation on the method of attaching the olivine-type composite lithium iron phosphate to at least a part of the surface of the composite lithium manganate. Conventionally known methods can be used by appropriately referring to or combining them. However, to give an example, it is possible to use a mechano-fusion as described in Examples described later. As a mechano-fusion device, AMS-LAB-GMP manufactured by Hosokawa Micron Corporation can be used.

  The average particle diameters of the negative electrode active material (graphite) according to the present invention and the positive electrode active material (olivine-type composite lithium iron phosphate and composite lithium manganate) according to the present invention are not particularly limited. However, from the viewpoint of battery characteristics, the following average particle size is preferable.

  The average particle diameter of the negative electrode active material (graphite) according to the present invention is preferably 0.5 to 50 μm, more preferably 1 to 25 μm. Within such a range, there is an effect that the dispersibility and reactivity of the particles are compatible.

  The average particle size of the olivine-type composite lithium iron phosphate according to the present invention is preferably 0.1 to 10 μm, more preferably 0.5 to 5 μm. Within such a range, there is an effect that the dispersibility and reactivity of the particles are compatible.

  The average particle size of the composite lithium manganate according to the present invention is preferably 0.1 to 20 μm, more preferably 0.5 to 10 μm. Within such a range, there is an effect that the dispersibility and reactivity of the particles are compatible.

  Further, as will be described later, when the positive electrode active material adopts a structure in which olivine-type composite lithium iron phosphate is attached to at least a part of the surface of the composite lithium manganate, the average particle size of the positive electrode active material is: Preferably it is 0.2-20 micrometers, More preferably, it is 0.3-10 micrometers. Within such a range, there is an effect that the dispersibility and reactivity of the particles are compatible.

  In the present specification, the “average particle diameter” means the average of the maximum distances among the distances between any two points on the contour line of the active material particles. As the value of the “average particle size”, the average value of the average particle size of particles observed in several to several tens of fields using an observation means such as a scanning electron microscope (SEM) or a transmission electron microscope (TEM). The value calculated as is assumed to be adopted.

  In addition, the value of the “average particle diameter” when the positive electrode active material according to the present invention adopts a structure in which olivine-type composite lithium iron phosphate is attached to at least a part of the surface of the composite lithium manganate is also as described above. The same applies. That is, even in this case, it means the average of the maximum distances among the distances between any two points on the contour line of the active material particles.

  Further, even if the aspect ratio is not 1, the average of the maximum distance among the distances between any two points on the contour line of the active material particles is meant.

  In addition, the term “at least part” is used to indicate that the entire surface of the composite lithium manganate is acceptable even if the olivine-type composite lithium iron phosphate is not attached.

  As described above, it is preferable that the olivine-type composite lithium iron phosphate is attached over the entire surface of the composite lithium manganate. For this purpose, when the average particle size A of the olivine-type composite lithium iron phosphate is smaller than the average particle size B of the composite lithium manganate, it is easy to be attached over the entire surface of the composite lithium manganate.

Furthermore, in order to attach over the entire surface of the composite lithium manganate,
The relationship between the average particle diameter A and the average particle diameter B is expressed by the following formula (1):

It is good to satisfy.

  When A = B × 0.5, the olivine-type composite iron iron phosphate is attached over the entire surface of the composite lithium manganate, and as the value of A / B decreases, the composite manganese as shown in FIG. The olivine type composite lithium iron phosphate is thickly and densely coated on the surface of the lithium oxide. That is, if the above formula 1 is satisfied, the entire surface of the composite lithium manganate particles can be covered with olivine-type lithium iron phosphate.

  Whether or not the olivine-type composite lithium iron phosphate is attached to at least a part of the surface of the composite lithium manganate can be determined by various methods. For example, a method such as TEM observation can be used. When the method of TEM observation is used, it is possible to determine whether or not the olivine-type composite lithium iron phosphate is attached to at least a part of the surface of the composite lithium manganate by measuring the element distribution.

  By using such an electrode according to the present invention, the potential of the positive electrode can be quickly increased at the end of charging. That is, by using the positive electrode active material according to the present invention, the Li insertion reaction into graphite is accelerated, and even when the battery is rapidly charged with a high rate current, the polarization during the charging reaction does not increase, and the sufficient charge capacity Is obtained. In addition, since the Li insertion reaction into graphite is fast, cycle characteristics and Coulomb efficiency are significantly improved without Li being deposited on the negative electrode active material graphite. That is, by using the electrode according to the present invention, the desired effect can be obtained, and as a result, a battery excellent in cycle characteristics, coulomb efficiency and charge capacity can be constructed.

  The effects of the first embodiment are summarized below.

  -By using the positive electrode active material according to the present invention, the insertion reaction of Li into graphite is accelerated, and even when charged rapidly with a high rate current, the polarization during the charging reaction does not increase and sufficient charging capacity is obtained. can get.

  -Since the insertion reaction of Li into graphite is fast, the cycle characteristics and Coulomb efficiency are significantly improved without Li being deposited on the graphite of the negative electrode active material.

  -By using such an electrode, it is possible to construct a battery with excellent cycle characteristics, coulomb efficiency and charge capacity.

Second Embodiment
2nd Embodiment is a lithium ion secondary battery using the electrode for lithium ion secondary batteries which concerns on this invention.

  Each active material according to the present invention is formed on the surfaces of a positive electrode current collector and a negative electrode current collector, and can be used for a non-bipolar (internal parallel connection type) lithium ion secondary battery. Here, the non-bipolar lithium ion secondary battery will be briefly described with reference to the drawings, but should not be limited to these.

  FIG. 3 schematically shows the overall structure of a stacked non-bipolar lithium ion secondary battery (hereinafter also simply referred to as a lithium ion battery), which is a typical embodiment of the lithium ion battery of the present invention. FIG. In addition, there is no restriction | limiting in particular also in the number of lamination | stacking, For example, Preferably it is 5-30 layers, More preferably, it is 10-25 layers.

  As shown in FIG. 3, in the non-bipolar lithium ion secondary battery 10 a of this embodiment, a laminate film composed of a polymer and a metal is used for the battery outer packaging material 22, and the entire periphery is heat-sealed. And join. Thus, the power generation element (battery element) 17 is housed and sealed. The power generation element 17 can be configured as follows.

  On both surfaces of the positive electrode current collector, the positive electrode plate on which the positive electrode (positive electrode active material layer) 12 is formed, the electrolyte layer 13, and both surfaces of the negative electrode current collector 14 (one side for the lowermost layer and the uppermost layer of the power generation element) This is a negative electrode plate on which a negative electrode (negative electrode active material layer) 15 is formed. The power generation element 17 has a configuration in which these are stacked.

  At this time, the positive electrode (positive electrode active material layer) 12 on one surface of one positive electrode plate and the negative electrode (negative electrode active material layer) 15 on one surface of one negative electrode plate adjacent to the one positive electrode plate face each other through the electrolyte layer 13. Thus, a plurality of layers of the positive electrode plate, the electrolyte layer 13, and the negative electrode plate are laminated in this order. Hereinafter, a set (battery minimum unit) in which the positive electrode plate, the electrolyte layer 13 and the negative electrode plate are stacked in this order is also referred to as a single battery layer (single cell) 16.

  As a result, the adjacent positive electrode (positive electrode active material layer) 12, electrolyte layer 13, and negative electrode (negative electrode active material layer) 15 constitute one unit cell layer 16. Therefore, it can be said that the non-bipolar lithium ion secondary battery 10a of the present embodiment has a configuration in which a plurality of single battery layers 16 are stacked and electrically connected in parallel. Note that the negative electrode (negative electrode active material layer) 15 is formed on only one side of the outermost layer negative electrode current collector 14 a located in both outermost layers of the power generation element (battery element; laminate) 17.

  Further, the positive electrode tab 18 and the negative electrode tab 19 that are electrically connected to the respective electrode plates (positive electrode plate and negative electrode plate) are connected to the positive electrode current collector 11 and the negative electrode of each electrode plate via the positive electrode terminal lead 20 and the negative electrode terminal lead 21. It is attached to the current collector 14 by ultrasonic welding or resistance welding. Thus, the positive electrode tab 18 and the negative electrode tab 19 have a structure that is sandwiched between the heat-sealed portions and exposed to the outside of the battery outer packaging material 22 (see also FIG. 4).

[Active material layer]
An active material layer contains the active material which concerns on this invention, and further contains another additive as needed.

  The positive electrode active material layer 12 includes a positive electrode active material according to the present invention. Since the specific description of the positive electrode active material according to the present invention has been given above, it is omitted here. The thickness of the positive electrode active material layer 12 in the thickness direction is preferably 10 to 500 μm, more preferably 20 to 250 μm.

  The negative electrode active material layer 15 includes the negative electrode active material according to the present invention. Since the specific description of the negative electrode active material according to the present invention has been made above, it is omitted here. The thickness in the thickness direction of the negative electrode active material layer 15 is preferably 10 to 500 μm, more preferably 20 to 250 μm.

  The active material layer may contain other additives.

  Examples of the additive that can be included in the positive electrode active material layer 12 and the negative electrode active material layer 15 include a binder, a conductive additive, an electrolyte salt (lithium salt), and an ion conductive polymer.

  Examples of the binder include polyvinylidene fluoride (PVdF), SBR and CMC, acrylonitrile, polyimide, and a synthetic rubber binder.

  The conductive auxiliary agent is an additive that is blended to improve the conductivity of the positive electrode active material layer 12 or the negative electrode active material layer 15. Examples of the conductive auxiliary agent include carbon materials such as carbon black such as acetylene black, graphite, vapor-grown carbon fiber, and graphite. Moreover, metal powder can also be used suitably as a conductive support agent. When the active material layer (12, 15) according to the present invention contains a conductive additive, an electronic network inside the active material layer is effectively formed, which can contribute to improvement of output characteristics of the battery.

Examples of the electrolyte salt (lithium salt) include Li (C ₂ F ₅ SO ₂ ) ₂ N, LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , LiCF ₃ SO _{3 and the} like.

  Examples of the ion conductive polymer include polyethylene oxide (PEO) -based and polypropylene oxide (PPO) -based polymers.

  The compounding ratio of these components contained in the positive electrode active material layer 12 and the negative electrode active material layer 15 is not particularly limited. The blending ratio can be adjusted by appropriately referring to known knowledge about lithium ion secondary batteries.

[Electrolyte layer]
The electrolyte layer may be liquid, gel, or solid. Liquid leakage can be prevented by using a solid electrolyte (which will be described later in detail, including a polymer gel electrolyte, a solid polymer electrolyte, and an inorganic solid electrolyte, as described later) as the electrolyte layer. By using a gel polymer electrolyte layer (polymer gel electrolyte) as the electrolyte layer, the fluidity of the electrolyte is lost, the electrolyte is prevented from flowing out to the current collector, and the ionic conductivity between the layers can be blocked. . Examples of the gel electrolyte host polymer include PEO, PPO, PVdF, polyvinylidene fluoride-hexafluoropropylene copolymer (PVdF-HFP), PAN, PMA, and PMMA. Moreover, as a plasticizer, it is possible to use the electrolyte solution normally used for a lithium ion battery.

  The gel polymer electrolyte (polymer gel electrolyte) is produced by including an electrolyte solution usually used in a lithium ion battery in an all solid polymer electrolyte such as PEO or PPO. PVdF, PAN, PMMA, and the like, in which the electrolyte solution is held in a polymer skeleton having no lithium ion conductivity, also corresponds to the gel polymer electrolyte (polymer gel electrolyte). The ratio of the polymer constituting the gel polymer electrolyte (polymer gel electrolyte) and the electrolytic solution is not particularly limited. When 100% of the polymer is an all solid polymer electrolyte and 100% of the electrolyte is a liquid electrolyte, all of the intermediates are included in the concept of gel polymer electrolyte (polymer gel electrolyte). An inorganic solid electrolyte having ion conductivity such as an inorganic solid such as ceramic corresponds to the all solid electrolyte. Therefore, the polymer gel electrolyte, the solid polymer electrolyte, and the inorganic solid electrolyte are all included in the solid electrolyte.

  Specifically, as the electrolyte layer, conventionally known materials include (a) polymer gel electrolyte (gel polymer electrolyte), (b) all solid polymer electrolyte (polymer solid electrolyte, inorganic solid electrolyte), ( c) Liquid electrolytes (electrolytic solutions) or (d) separators impregnated with these electrolytes (including nonwoven fabric separators) can be used.

(A) Gel polymer electrolyte (polymer gel electrolyte)
The gel polymer electrolyte (polymer gel electrolyte) refers to an electrolyte solution held in a polymer matrix. By using a gel polymer electrolyte as the electrolyte, the fluidity of the electrolyte is lost, and it is easy to cut off the ionic conductivity between each layer by suppressing the outflow of the electrolyte to the current collector layer such as a conductive polymer film. Is excellent.

Examples of the polymer matrix (polymer) used as the polymer gel electrolyte or the host polymer of the gel electrolyte include polymers having polyethylene oxide in the main chain or side chain (PEO), polymers having polypropylene oxide in the main chain or side chain ( PPO), polyethylene glycol (PEG), polyacrylonitrile (PAN), polymethacrylic acid ester, polyvinylidene fluoride (PVdF), a copolymer of polyvinylidene fluoride and hexafluoropropylene (PVdF-HFP), poly (methyl methacrylate) ( PMMA) and copolymers thereof are desirable, and among them, PEO, PPO and copolymers thereof, or PVdF-HFP is desirably used. Moreover, as a plasticizer, it is possible to use the electrolyte solution normally used for a lithium ion battery. And such electrolyte, which electrolyte salt dissolved in a solvent, as the _{electrolyte, LiPF 6, LiBF 4, LiClO} 4, LiAsF 6, LiTaF 6, LiAlCl 4, Li 2 B 10 Cl 10 inorganic acid anions such as As a solvent, at least one selected from organic acid anion salts such as ionic salt, LiCF ₃ SO ₃ , Li (CF ₃ SO ₂ ) ₂ N, Li (C ₂ F ₅ SO ₂ ) ₂ N, etc. Ethylene carbonate (EC), propylene carbonate (PC), γ-butyrolactone (GBL), dimethyl carbonate (DMC), diethyl carbonate (DEC) and mixtures thereof are preferred.

  The ratio of the electrolytic solution in the gel electrolyte in the present invention is not particularly limited, but is preferably about several mass% to 98 mass% from the viewpoint of ionic conductivity. The present invention is particularly effective for a gel electrolyte having a large amount of electrolytic solution in which the proportion of the electrolytic solution is 70% by mass or more.

(B) All solid electrolyte (all solid polymer electrolyte, polymer solid electrolyte, inorganic solid electrolyte)
The use of an all solid electrolyte as the electrolyte is superior in that the fluidity of the electrolyte is lost, the electrolyte does not flow out to the current collector layer, and the ion conductivity between the layers can be blocked.

Examples of the all solid polymer electrolyte include known solid polymer electrolytes such as PEO, PPO, and copolymers thereof, and inorganic solid electrolytes having ion conductivity such as ceramics. The solid polymer electrolyte contains a lithium salt in order to ensure ionic conductivity. As the lithium salt, LiBF ₄ , LiPF ₆ , LiN (SO ₂ CF ₃ ) ₂ , LiN (SO ₂ C ₂ F ₅ ) ₂ , or a mixture thereof can be used.

(C) Liquid electrolyte (electrolyte)
Examples of the electrolytic solution include those obtained by dissolving an electrolyte salt in a solvent. Here, as the _{electrolyte, LiPF 6, LiBF 4, LiClO} 4, LiAsF 6, LiTaF 6, LiAlCl 4, Li 2 B 10 Cl 10 inorganic acid anion salts such _{as, LiCF 3 SO 3, Li (} CF 3 SO 2 ) At least one selected from organic acid anion salts such as ₂ N, Li (C ₂ F ₅ SO ₂ ) ₂ N, and the solvent is EC, PC, GBL, DMC, DEC and mixtures thereof Is desirable.

(D) Separator impregnated with the electrolyte (including non-woven separator)
As the electrolyte that can be impregnated in the separator, the same electrolytes as those already described (a) to (c) can be used.

  Examples of the separator include a porous sheet and a nonwoven fabric made of a polymer that absorbs and holds the electrolyte.

  As the porous sheet, for example, a microporous separator can be used. Examples of the polymer include polyolefins such as polyethylene (PE) and polypropylene (PP); laminates having a three-layer structure of PP / PE / PP, polyimide, and aramid. The thickness of the separator cannot be uniquely defined because it varies depending on the intended use. In applications such as a secondary battery for driving a motor such as an electric vehicle (EV), a hybrid electric vehicle (HEV), and a fuel cell vehicle (FCV), the thickness is preferably 4 to 60 μm in a single layer or multiple layers. The separator preferably has a fine pore size of 1 μm or less (usually a pore size of about several tens of nm) and a porosity of 20 to 80%.

  As the nonwoven fabric, cotton, rayon, acetate, nylon, polyester; polyolefins such as PP and PE; conventionally known materials such as polyimide and aramid are used alone or in combination. The bulk density of the nonwoven fabric is not particularly limited as long as sufficient battery characteristics can be obtained by the impregnated polymer gel electrolyte. The porosity of the nonwoven fabric separator is preferably 50 to 90%. Furthermore, the thickness of the nonwoven fabric separator may be the same as that of the electrolyte layer, preferably 5 to 200 μm, particularly preferably 10 to 100 μm. When the thickness is less than 5 μm, the electrolyte retention deteriorates, and when it exceeds 200 μm, the resistance increases.

[Seal part]
The seal (also referred to as the peripheral insulating layer) is used to prevent the adjacent current collectors in the battery from contacting each other and short-circuiting due to slight unevenness at the end of the laminated electrode. It arrange | positions at the peripheral part of the cell layer (it is not shown in FIG. 3). As the seal portion, for example, polyolefin resin such as PE and PP, epoxy resin, rubber, polyimide and the like can be used, and polyolefin resin is preferable from the viewpoint of corrosion resistance, chemical resistance, film forming property, economy and the like.
However, it is not limited to these.

[Tab (positive tab and negative tab)]
Tabs (positive electrode tab 18 and negative electrode tab 19) that are electrically connected to each current collector are taken out of the battery exterior material for the purpose of taking out the current outside the battery. Specifically, as shown in FIG. 3, a positive electrode tab 18 electrically connected to each positive electrode current collector 11 and a negative electrode tab 19 electrically connected to each negative electrode current collector 14 are battery exterior materials. 22 is taken out of the laminate sheet.

  The material which comprises a tab (the positive electrode tab 18 and the negative electrode tab 19) is not restrict | limited in particular, The well-known highly electroconductive material conventionally used as a tab for lithium ion batteries can be used. As a constituent material of the tab, for example, metal materials such as aluminum, copper, titanium, nickel, stainless steel (SUS), and alloys thereof are preferable, and aluminum, copper, and the like are more preferable from the viewpoint of light weight, corrosion resistance, and high conductivity. Is preferred. Note that the positive electrode tab 18 and the negative electrode tab 19 may be made of the same material or different materials. Moreover, it is good also as the positive electrode tab 18 and the negative electrode tab 19 by extending each collector 11,14, and the positive electrode tab 18 and the negative electrode tab 19 which were prepared separately may be connected to each collector 11,14. .

[Positive electrode and negative electrode lead]
The positive terminal lead 20 and the negative terminal lead 21 are also used as necessary. For example, when the positive electrode tab 18 and the negative electrode tab 19 serving as output electrode terminals are directly taken out from the current collectors 11 and 14, the positive electrode terminal lead 20 and the negative electrode terminal lead 21 may not be used.

  As the material of the positive terminal lead 20 and the negative terminal lead 21, a terminal lead used in a known lithium ion secondary battery can be used. In addition, the part taken out from the battery outer packaging material 22 has a heat insulating property so as not to affect a product (for example, an automobile part, particularly an electronic device, etc.) by touching a peripheral device or wiring and causing a leakage. It is preferable to coat with a heat shrinkable tube or the like.

[Battery exterior materials]
As the battery exterior member 22, a conventionally known metal can case can be used, and a bag-like case that can cover a power generation element (battery element) using a laminate film containing aluminum can be used. For example, a laminate film having a three-layer structure in which PP, aluminum, and nylon are laminated in this order can be used as the laminate film, but the laminate film is not limited thereto.

[External structure of lithium-ion battery]
FIG. 4 is a perspective view showing the appearance of a laminated flat (non-bipolar) lithium ion secondary battery which is a typical embodiment of the lithium ion battery according to the present invention.

  As shown in FIG. 4, the stacked flat lithium ion secondary battery 50 has a rectangular flat shape, and a positive electrode tab 58 and a negative electrode tab 59 for taking out electric power from both sides thereof. Has been pulled out. The power generation element (battery element) 57 is encased in the battery exterior material 52 of the lithium ion secondary battery 50. The surroundings are heat-sealed, and the power generation element (battery element) 57 is sealed with the positive electrode tab 58 and the negative electrode tab 59 pulled out to the outside. Here, the power generation element (battery element) 57 corresponds to the power generation element (battery element) 17 of the non-bipolar non-bipolar lithium ion secondary battery 10a shown in FIG. A plurality of single battery layers (single cells) 16 composed of a positive electrode (positive electrode active material layer) 12, an electrolyte layer 13, and a negative electrode (negative electrode active material layer) 15 are laminated.

  Note that the lithium ion battery of the present invention is not limited to a stacked flat shape as shown in FIG. 4, and a wound lithium ion battery may have a cylindrical shape. Good. Such a cylindrical shape may be deformed into a rectangular flat shape. In the said cylindrical shape thing, a laminate film may be used for the exterior material, and the conventional cylindrical can (metal can) may be used, for example, It does not restrict | limit.

  Further, the removal of the tabs 58 and 59 shown in FIG. 4 is not particularly limited, and the positive electrode tab 58 and the negative electrode tab 59 may be pulled out from the same side. The positive electrode tab 58 and the negative electrode tab 59 may be divided into a plurality of parts and taken out from the respective sides, and the present invention is not limited to the one shown in FIG. Further, in a wound type lithium ion battery, instead of a tab, for example, a terminal may be formed using a cylindrical can (metal can).

  Further, as described above, the electrode for a lithium ion secondary battery according to the present invention can also be used for a bipolar nonaqueous electrolyte secondary battery (hereinafter also referred to as “bipolar battery”).

  FIG. 5 is a schematic cross-sectional view schematically showing an outline of a laminated flat bipolar lithium ion secondary battery which is a typical embodiment of the lithium ion battery of the present invention.

  The bipolar nonaqueous electrolyte secondary battery 10b of this embodiment shown in FIG. 5 has a structure in which a substantially rectangular battery element 17 in which a charge / discharge reaction actually proceeds is sealed inside a laminate sheet 22 as an exterior. Have

  As shown in FIG. 5, the battery element 17 of the bipolar battery 10 b of this embodiment includes a bipolar electrode in which a positive electrode active material layer 12 and a negative electrode active material layer 15 are formed on each surface of the current collector 1. (Not shown). Each bipolar electrode is laminated via an electrolyte layer 13 to form a battery element 17. At this time, each bipolar type is formed such that the positive electrode active material layer 12 of one bipolar electrode and the negative electrode active material layer 15 of another bipolar electrode adjacent to the one bipolar electrode face each other through the electrolyte layer 13. An electrode and an electrolyte layer 13 are laminated.

  The adjacent positive electrode active material layer 12, electrolyte layer 13, and negative electrode active material layer 15 constitute one unit cell layer 16. Therefore, it can be said that the bipolar battery 10b has a configuration in which the single battery layers 16 are stacked. In addition, an insulating layer 31 for insulating the adjacent current collectors 1 is provided on the outer periphery of the unit cell layer 16. The current collector (outermost layer current collector) (11a, 14a) located in the outermost layer of the battery element 17 has a positive electrode active material layer 12 (positive electrode side outermost layer current collector 14a) or a negative electrode only on one side. One of the active material layers 15 (the negative electrode side outermost layer current collector 11a) is formed.

  Further, in the bipolar battery 10b shown in FIG. 5, the positive electrode side outermost layer current collector 14a is extended to form a positive electrode tab 22, which is led out from a laminate sheet 22 which is an exterior. On the other hand, the negative electrode side outermost layer current collector 11 a is extended to form a negative electrode tab 19, which is similarly derived from the laminate sheet 22.

[Method of manufacturing lithium ion battery]
(Active material slurry preparation process)
In this step, the active material according to the present invention and, if necessary, other components (for example, a binder, a conductive additive, an electrolyte, a polymerization initiator, etc.) are mixed in a solvent, and the positive electrode according to the present invention. An active material slurry is prepared. Since the specific form of each component blended in the active material slurry according to the present invention is as described in the column of the configuration of the electrode of the present invention, detailed description is omitted here.

  The kind of solvent and the mixing means are not particularly limited, and conventionally known knowledge about electrode production can be appropriately referred to. Examples of the solvent include N-methyl-2-pyrrolidone (NMP), dimethylformamide, dimethylacetamide, methylformamide and the like. When adopting polyvinylidene fluoride (PVdF) as a binder, NMP is preferably used as a solvent.

(Coating film formation process)
Subsequently, each current collector is prepared, and the active material slurry prepared above is applied to the surface of the current collector and dried. Thereby, the coating film consisting of the positive electrode active material slurry according to the present invention is formed on the surface of the current collector. This coating film becomes an active material layer through a pressing step described later.

  The specific form of the current collector to be prepared is as described in the column of the configuration of the electrode of the present invention, and thus detailed description thereof is omitted here.

  The application means for applying the active material slurry is not particularly limited, but generally used means such as a self-propelled coater may be employed.

  A coating film is formed according to the desired arrangement | positioning form of each collector and active material layer in the electrode manufactured. For example, when the manufactured electrode is a bipolar electrode, a coating film containing the positive electrode active material according to the present invention is formed on one surface of the current collector. In addition, the coating film containing the negative electrode active material which concerns on this invention is formed in the other surface. On the other hand, when manufacturing a non-bipolar electrode, a coating film containing either the positive electrode active material according to the present invention or the negative electrode active material according to the present invention is formed on both surfaces of one current collector. The

  Thereafter, the coating film formed on the surface of the current collector is dried. Thereby, the solvent in a coating film is removed.

  The drying means for drying the coating film is not particularly limited, and conventionally known knowledge about electrode production can be appropriately referred to. For example, heat treatment is exemplified. Drying conditions (drying time, drying temperature, etc.) can be appropriately set according to the application amount of the active material slurry and the volatilization rate of the solvent of the slurry according to the present invention.

  When a coating film contains a polymerization initiator, the ion conductive polymer in a coating film is bridge | crosslinked by a crosslinkable group by performing a superposition | polymerization process further.

  The polymerization treatment in the polymerization step is not particularly limited, and conventionally known knowledge may be referred to as appropriate. For example, when the coating film contains a thermal polymerization initiator (AIBN or the like), the coating film is subjected to heat treatment. Moreover, when a coating film contains a photoinitiator (BDK etc.), light, such as an ultraviolet light, is irradiated. In addition, the heat processing for thermal polymerization may be performed simultaneously with said drying process, and may be performed before or after the said drying process.

(Pressing process)
Then, the laminated body produced through the said coating-film formation process is pressed to the lamination direction. Thereby, the battery electrode according to the present invention is completed. At this time, the porosity of the active material layer can be controlled by adjusting the pressing conditions.

Specific means and pressing conditions for the press treatment are not particularly limited, and can be appropriately adjusted so that the porosity of the active material layer after the press treatment becomes a desired value. Specific examples of the press process include a hot press machine and a calendar roll press machine. Also, the pressing conditions (temperature, pressure, etc.) are not particularly limited, and conventionally known knowledge can be referred to as appropriate.
[Charging method of lithium ion secondary battery]
There is no restriction | limiting in particular also in the charge of the lithium ion secondary battery which concerns on this invention, It can use it referring to a conventionally well-known method suitably in the said field or combining them. However, the method for charging a lithium ion secondary battery according to the present invention is particularly preferably performed by a constant current constant voltage or multistage constant current method.

  Here, the constant current constant voltage method or the multistage constant current method will be briefly described. In the constant current constant voltage charging method, when charging is started from a discharged state, the initial voltage is low, and thus constant current charging is performed. When the amount of charge gradually increases and the cell voltage reaches a certain voltage, constant voltage charging starts from here, and the amount of current is reduced so that the cell voltage does not exceed the certain voltage. In the multi-stage constant current method, when the cell voltage reaches a certain voltage, the constant current value is further reduced, the constant current is charged again, and the constant current value is reduced stepwise by repeating this. Finally, the current is reduced by charging with a predetermined small constant current value. As described above, when the lithium ion secondary battery according to the present invention is charged by the constant current constant voltage method or the multistage constant current method, rapid charging becomes possible.

  As described above, by using the electrode according to the present invention, it is possible to provide a lithium ion secondary battery that quickly increases the potential of the positive electrode at the end of charging. That is, by using the positive electrode active material according to the present invention, the Li insertion reaction into graphite is accelerated, and even when the battery is rapidly charged with a high rate current, the polarization during the charging reaction does not increase, and the sufficient charge capacity Is obtained. In addition, since the Li insertion reaction into graphite is fast, cycle characteristics and Coulomb efficiency are significantly improved without Li being deposited on the negative electrode active material graphite. That is, by using such an electrode according to the present invention, a battery excellent in cycle characteristics, coulomb efficiency and charge capacity can be constructed.

  The effects of the second embodiment are summarized below.

  -By using the positive electrode active material according to the present invention, the insertion reaction of Li into graphite is accelerated, and even when charged rapidly with a high rate current, the polarization during the charging reaction does not increase and sufficient charging capacity is obtained. can get.

  -Since the insertion reaction of Li into graphite is fast, the cycle characteristics and Coulomb efficiency are significantly improved without Li being deposited on the graphite of the negative electrode active material.

  -By using such an electrode, it is possible to construct a battery with excellent cycle characteristics, coulomb efficiency and charge capacity.

  -If the lithium ion secondary battery which concerns on this invention is charged by a constant current constant voltage system or a multistage constant current system, rapid charge will be attained.

<Third Embodiment>
[Battery]
The third embodiment is an assembled battery using the lithium ion secondary battery according to the present invention.

  The assembled battery of the present invention is constituted by connecting a plurality of lithium ion batteries of the present invention. Specifically, at least two or more are used, and are configured by serialization, parallelization, or both. Capacitance and voltage can be freely adjusted by paralleling in series. In the assembled battery of the present invention, the non-bipolar lithium ion battery and the bipolar lithium ion battery of the present invention are used, and a plurality of these are combined in series, in parallel, or in series and in parallel. Can also be configured.

  6 is an external view of a typical embodiment of the assembled battery according to the present invention, FIG. 6A is a plan view of the assembled battery, FIG. 6B is a front view of the assembled battery, and FIG. It is a side view of an assembled battery.

As shown in FIG. 6, an assembled battery 300 according to the present invention forms a small assembled battery 250 that can be attached and detached by connecting a plurality of lithium ion batteries of the present invention in series or in parallel. A plurality of the detachable small assembled batteries 250 are further connected in series or in parallel. Thereby, the assembled battery 300 having a large capacity and a large output suitable for a power source for driving a vehicle and an auxiliary power source that require a high volume energy density and a high volume output density can be formed. 6A is a plan view of the assembled battery, FIG. 6A is a front view, and FIG. 6C is a side view. The small assembled battery 250 that can be attached and detached is connected to each other using an electrical connection means such as a bus bar, and the assembled battery 250 is stacked in a plurality of stages using a connection jig 310. How many non-bipolar or bipolar lithium-ion batteries are connected to create the assembled battery 250, and how many assembled batteries 250 are stacked to produce the assembled battery 300 depends on the vehicle mounted. What is necessary is just to determine according to the battery capacity and output of (electric vehicle).
[Battery charging method]
There is no restriction | limiting in particular also in the charge of the assembled battery which concerns on this invention, It can use it referring to a conventionally well-known method suitably in the said field, or combining them. However, it is particularly preferable that the method for charging an assembled battery according to the present invention is performed with a constant current or a constant voltage or a multistage constant current. When the assembled battery according to the present invention is charged with a constant current or a constant voltage or a multistage constant current, rapid charging becomes possible.

  As described above, by using the electrode according to the present invention, it is possible to provide an assembled battery including a lithium ion secondary battery that quickly increases the potential of the positive electrode at the end of charging. That is, by using the positive electrode active material according to the present invention, the Li insertion reaction into graphite is accelerated, and even when the battery is rapidly charged with a high rate current, the polarization during the charging reaction does not increase, and the sufficient charge capacity Is obtained. In addition, since the Li insertion reaction into graphite is fast, cycle characteristics and Coulomb efficiency are significantly improved without Li being deposited on the negative electrode active material graphite. That is, by using such an electrode according to the present invention, an assembled battery excellent in cycle characteristics, coulomb efficiency, and charging capacity can be constructed.

  The effects of the third embodiment are summarized below.

  -By using the positive electrode active material according to the present invention, the insertion reaction of Li into graphite is accelerated, and even when charged rapidly with a high rate current, the polarization during the charging reaction does not increase and sufficient charging capacity is obtained. can get.

  -Since the insertion reaction of Li into graphite is fast, the cycle characteristics and Coulomb efficiency are significantly improved without Li being deposited on the graphite of the negative electrode active material.

  -By using such an electrode, it is possible to construct a battery with excellent cycle characteristics, coulomb efficiency and charge capacity.

  -When the lithium ion assembled battery according to the present invention is charged by a constant current constant voltage method or a multistage constant current method, rapid charging becomes possible.

<Fourth embodiment>
[vehicle]
The fourth embodiment is a vehicle in which the lithium ion secondary battery according to the present invention or the assembled battery according to the present invention is mounted as a motor driving power source.

  The vehicle of the present invention is characterized in that the lithium ion battery of the present invention or an assembled battery formed by combining a plurality of them is mounted.

In the present invention, a vehicle equipped with a lithium ion secondary battery or an assembled battery excellent in cycle characteristics, coulomb efficiency and charging capacity can be configured.
Therefore, when such a battery is mounted, a plug-in hybrid electric vehicle having a long EV travel distance and an electric vehicle having a long one charge travel distance can be configured. In other words, the lithium ion battery of the present invention or an assembled battery formed by combining a plurality of these can be used as a power source for driving a vehicle.

  When the lithium ion secondary battery using the lithium ion secondary battery electrode of the present invention or the assembled battery formed by combining a plurality of them is used in a vehicle, a vehicle having the effects described above is obtained.

  The vehicle is not particularly limited. For example, in the case of a car, a hybrid car, a fuel cell car, an electric car (all are four-wheeled vehicles (passenger cars, commercial vehicles such as trucks and buses, light vehicles, etc.), and two-wheeled vehicles (motorcycles). ) And tricycles). Further, it can be applied to various power sources for other vehicles such as a moving body such as a train, and can also be used as a mounting power source for an uninterruptible power supply.

  FIG. 7 is a conceptual diagram of a vehicle equipped with the assembled battery of the present invention.

  As shown in FIG. 7, in order to mount the assembled battery 300 on a vehicle such as the electric vehicle 400, the battery pack 300 is mounted under the seat at the center of the vehicle body of the electric vehicle 400. This is because if it is installed under the seat, the interior space and the trunk room can be widened. The place where the assembled battery 300 is mounted is not limited to the position under the seat, but may be a lower part of the rear trunk room or an engine room in front of the vehicle. The electric vehicle 400 using the assembled battery 300 as described above has high durability and can provide sufficient output even when used for a long period of time. Furthermore, it is possible to provide electric vehicles and hybrid vehicles that are excellent in fuel efficiency and running performance. A vehicle equipped with the assembled battery of the present invention can be widely applied to a hybrid vehicle, a fuel cell vehicle and the like in addition to an electric vehicle as shown in FIG.

  When the assembled battery according to the present invention is charged with a constant current or a constant voltage or a multistage constant current, rapid charging becomes possible.

  As described above, by using the electrode according to the present invention, it is possible to provide a vehicle equipped with a lithium ion secondary battery or an assembled battery that quickly increases the potential of the positive electrode at the end of charging. That is, by using the positive electrode active material according to the present invention, the Li insertion reaction into graphite is accelerated, and even when the battery is rapidly charged with a high rate current, the polarization during the charging reaction does not increase, and the sufficient charge capacity Is obtained. In addition, since the Li insertion reaction into graphite is fast, cycle characteristics and Coulomb efficiency are significantly improved without Li being deposited on the negative electrode active material graphite. That is, by using the electrode according to the present invention, a vehicle equipped with a lithium ion secondary battery or an assembled battery excellent in cycle characteristics, coulomb efficiency, and charging capacity can be constructed.

  The effects of the fourth embodiment are summarized below.

  -By using the positive electrode active material according to the present invention, the insertion reaction of Li into graphite is accelerated, and even when charged rapidly with a high rate current, the polarization during the charging reaction does not increase and sufficient charging capacity is obtained. can get.

  -Since the insertion reaction of Li into graphite is fast, the cycle characteristics and Coulomb efficiency are significantly improved without Li being deposited on the graphite of the negative electrode active material.

  -By using such an electrode, it is possible to construct a vehicle with excellent cycle characteristics, coulomb efficiency and charging capacity.

  -When the assembled battery according to the present invention is charged by a constant current constant voltage method or a multistage constant current method, rapid charging becomes possible.

  The effect of this invention is demonstrated using a following example and a comparative example. However, the technical scope of the present invention is not limited only to the following examples.

1. Production of Laminated Outer Flat Battery A laminated outer flat battery under various conditions was produced as Example 1 to Example 12.

<Example 1>
(1) Production Step of Positive Electrode As a positive electrode active material, LiFePO ₄ having an average particle diameter of 1.9 μm and LiMn ₂ O ₄ having an average particle diameter of 2.0 μm coated with 2% by mass of carbon were used. Polyvinylidene fluoride (PVdF) was used as the binder, acetylene black was used as the conductive auxiliary agent, and N-methyl-2-pyrrolidone (NMP) was used as the solvent. The composition of the positive electrode was positive electrode active material: binder: conducting aid = 86% by mass: 8% by mass: 6% by mass (total amount of carbon in the positive electrode).

  The mass ratio of the positive electrode active material is as follows.

LiFePO ₄ : LiMn ₂ O ₄ = 90: 10 coated with 2% by mass of carbon
“LiFePO ₄ coated with 2% by mass of carbon” is hereinafter simply referred to as “LiFePO ₄ ”.

LiFePO ₄ and LiMn ₂ O were mixed with each other (simple particle mixing) to obtain a positive electrode active material of Example 1.

  First, high purity anhydrous NMP was charged into a dispersing mixer. Next, PVdF was added and sufficiently dissolved in the NMP solvent. Thereafter, the positive electrode active material and the conductive auxiliary agent were added little by little to make it familiar with the solvent in which PVdF was dissolved. When all of the positive electrode active material and the conductive additive were added, the viscosity was adjusted by adding a solvent as appropriate. In addition, the said positive electrode active material slurry viscosity was 20000 cps.

The slurry obtained above was applied to 31.1 mg / cm ^{2 on} one side of an Al foil (film thickness 20 μm) as a positive electrode current collector using a coating apparatus. Subsequently, the thickness of the positive electrode active material layer was adjusted using a doctor blade having a constant thickness, dried on a hot stirrer, and the density was adjusted by a roll press to obtain a positive electrode. The thickness of the obtained positive electrode active material layer was 148 μm.

(2) Production process of negative electrode Mesocarbon microbeads (MCMB: manufactured by Osaka Gas Chemical Co., model number MCMB10-28) having an average particle diameter of 10 μm were used as the negative electrode active material. PVdF was used as the binder and NMP was used as the solvent. The composition of the negative electrode was negative electrode active material: binder = 90% by mass: 10% by mass.

  First, high purity anhydrous NMP was charged into a dispersing mixer. Next, PVdF was added and sufficiently dissolved in the NMP solvent. Thereafter, the negative electrode active material was added little by little to make it fit in the solvent in which PVdF was dissolved. When all of the negative electrode active material was charged, a solvent was appropriately added to adjust the viscosity. The negative electrode active material slurry viscosity was 5000 cps.

The slurry obtained above was applied to 14.8 mg / cm ^{2 on} one side of a Cu foil (film thickness: 10 μm) as a negative electrode current collector using a coating apparatus. Subsequently, the thickness of the negative electrode active material layer was adjusted using a doctor blade having a constant thickness, dried on a hot stirrer, and the density was adjusted by a roll press to obtain a negative electrode. The thickness of the obtained negative electrode active material layer was 104 μm.

(3) Assembly process A positive electrode and a negative electrode are laminated via a microporous membrane separator made of PE, and a laminate film as a battery exterior material (a PET film for surface protection as an outermost layer, an Al foil as a metal film layer, heat fusion) (Insulating film layer is a laminate film made of polypropylene) and the positive electrode current collector and the negative electrode current collector are projected from the opposing sides of the separator, and the Al electrode terminals and Ni terminal leads are provided. welded, the positive terminal sandwiched laminate film exterior, to project a negative terminal from opposite sides of each cell, and heat welding the peripheral portion, the electrolyte (support salt: 1M LiPF _6, solvent: ethylene carbonate (EC) + Diethyl carbonate (DEC) (EC: DEC volume ratio = 1: 1) was injected to prepare a laminate-coated flat battery.

<Example 2>
The composition (mass ratio) of the positive electrode active material was LiFePO ₄ : LiMn ₂ O ₄ = 80: 20, and the same method as in Example 1 was applied except that 32.4 mg / cm ^{2 was} applied to one surface of the positive electrode current collector. In this way, a laminated exterior flat battery was produced.

<Example 3>
The composition (mass ratio) of the positive electrode active material was LiFePO ₄ : LiMn ₂ O ₄ = 70: 30, and the same method as in Example 1 was applied except that 33.8 mg / cm ^{2 was} applied to one side of the positive electrode current collector. In this way, a laminated exterior flat battery was produced.

<Example 4>
Example 3 except that a positive electrode active material was prepared by attaching olivine-type composite lithium iron phosphate to the surface of the composite lithium manganate using mechano-fusion, and 41.0 mg / cm ^{2 was} applied to one side of the positive electrode current collector. The laminated exterior flat type battery was produced in the same manner as described above.

  Here, the conditions of mechano-fusion are described.

AMS-LAB-GMP manufactured by Hosokawa Micron
・ Rotation speed: 2500rpm
<Example 5>
A laminated exterior flat battery is manufactured in the same manner as in Example 4 except that LiFePO ₄ having an average particle diameter of 1.6 μm and LiMn ₂ O ₄ having an average particle diameter of 2.0 μm are used as the positive electrode active material. did.

<Example 6>
A laminated exterior flat battery is manufactured in the same manner as in Example 4 except that LiFePO ₄ having an average particle diameter of 1.0 μm and LiMn ₂ O ₄ having an average particle diameter of 2.0 μm are used as the positive electrode active material. did.

<Example 7>
A laminated exterior flat battery is manufactured in the same manner as in Example 4 except that LiFePO ₄ having an average particle size of 0.7 μm and LiMn ₂ O ₄ having an average particle size of 2.0 μm are used as the positive electrode active material. did.

<Comparative Example 1>
The same as Example 1 except that LiMn ₂ O ₄ was not used as the positive electrode active material, LiFePO ₄ having an average particle diameter of 1.9 μm was used, and 30.0 mg / cm ^{2 was} applied to one surface of the positive electrode current collector. Thus, a laminate-coated flat battery was produced.

<Comparative example 2>
A laminated exterior flat battery was fabricated in the same manner as in Example 1 except that the composition (mass ratio) of the positive electrode active material was LiFePO ₄ : LiMn ₂ O ₄ = 20: 80.

<Comparative Example 3>
A laminated exterior flat battery was produced in the same manner as in Example 1 except that the composition (mass ratio) of the positive electrode active material was changed to LiFePO ₄ : LiMn ₂ O ₄ = 30: 70.

<Comparative example 4>
A laminated exterior flat battery was produced in the same manner as in Example 7 except that the composition (mass ratio) of the positive electrode active material was changed to LiFePO ₄ : LiMn ₂ O ₄ = 65: 35.

  Table 1 shows a summary of Examples 1 to 7 and Comparative Examples 1 to 4.

2. Evaluation (1) Measurement of initial coulomb efficiency <Example 8>
According to Example 1, the initial coulomb efficiency of the manufactured laminated exterior flat battery (hereinafter also simply referred to as “battery”) was measured. The initial coulomb efficiency was measured as follows.

  Constant current and constant voltage charging up to 4.20 V at 70 mA was performed for 8 hours, and constant current discharging up to 2.0 V at 70 mA was performed. The “initial coulomb efficiency” was calculated as the ratio of the discharge electricity amount to the charge electricity amount.

<Example 9>
The initial coulomb efficiency was measured using the same method as in Example 8 except that the battery produced according to Example 2 was used.

<Example 10>
The initial coulomb efficiency was measured using the same method as in Example 8 except that the battery produced according to Example 3 was used.

<Example 11>
The initial coulomb efficiency was measured using the same method as in Example 8, except that the battery prepared in Example 2 was used and constant current and constant voltage charging up to 4.15 V was performed.

<Example 12>
The initial coulomb efficiency was measured using the same method as in Example 8, except that the battery prepared according to Example 1 was used and constant current and constant voltage charging up to 4.10 V was performed.

<Example 13>
The initial coulomb efficiency was measured using the same method as in Example 8 except that the battery produced according to Example 4 was used.

<Example 14>
The initial coulomb efficiency was measured using the same method as in Example 8 except that the battery produced according to Example 5 was used.

<Example 15>
The initial coulomb efficiency was measured using the same method as in Example 8 except that the battery produced according to Example 6 was used.

<Example 16>
The initial coulomb efficiency was measured using the same method as in Example 8 except that the battery produced in Example 7 was used.

<Comparative Example 5>
The initial coulomb efficiency was measured using the same method as in Example 8 except that the battery produced in Comparative Example 1 was used.

  Hereinafter, Table 2 shows the results of measuring the initial Coulomb efficiency of Examples 8 to 16 and Comparative Example 5, respectively.

(2) Measurement of cycle characteristics <Example 17>
According to Example 3, the cycle characteristics of the produced battery were measured. The initial coulomb efficiency was measured as follows.

  Constant current and constant voltage charging up to 4.20 V at 70 mA was performed for 8 hours, and constant current discharging up to 2.0 V at 70 mA was performed. Cycle characteristics after 300 cycles at 60 ° C. (capacity retention ratio: ratio of discharge electricity quantity at 300th cycle to discharge electricity quantity at the first cycle) were measured.

<Example 18>
The cycle characteristics were measured using the same method as in Example 17 except that the cycle characteristics of the fabricated battery were measured according to Example 4.

<Example 19>
The cycle characteristics were measured using the same method as in Example 17 except that the cycle characteristics of the fabricated battery were measured according to Example 5.

<Example 20>
The cycle characteristics were measured using the same method as in Example 17 except that the cycle characteristics of the fabricated battery were measured according to Example 6.

<Example 21>
The cycle characteristics were measured using the same method as in Example 17 except that the cycle characteristics of the fabricated battery were measured according to Example 7.

<Comparative Example 6>
The cycle characteristics were measured using the same method as in Example 17 except that the cycle characteristics of the fabricated battery were measured according to Comparative Example 4.

  Table 4 below shows the results of measuring the capacity retention ratios of Examples 17 to 21 and Comparative Example 6, respectively.

(3) Measurement of initial capacity <Example 22>
According to Example 1, the initial capacity of the fabricated battery was measured. The initial capacity was measured as follows.

  Constant current and constant voltage charging up to 4.20 V at 70 mA was performed for 8 hours, and constant current discharging up to 2.0 V at 70 mA was performed. And "initial capacity" calculated the electric quantity at the time of constant current discharge to 2.0V at 70mA.

<Example 23>
The initial capacity was measured in the same manner as described in Example 22 except that the initial capacity of the fabricated battery was measured according to Example 2.

<Example 24>
The initial capacity was measured in the same manner as described in Example 22 except that the initial capacity of the fabricated battery was measured according to Example 3.

<Example 25>
The initial capacity was measured using the same method as in Example 22 except that the battery prepared in Example 2 was used and constant current and constant voltage charging up to 4.15 V was performed.

<Example 26>
The initial capacity was measured using the same method as in Example 22 except that the battery prepared in Example 1 was used and constant current and constant voltage charging up to 4.10 V was performed.

<Example 27>
The initial capacity was measured in the same manner as in Example 22 except that the initial capacity of the fabricated battery was measured according to Example 4.

<Example 28>
The initial capacity was measured in the same manner as in Example 22 except that the initial capacity of the fabricated battery was measured according to Example 5.

<Example 29>
The initial capacity was measured in the same manner as in Example 22 except that the initial capacity of the fabricated battery was measured according to Example 6.

<Example 30>
The initial capacity was measured in the same manner as in Example 22 except that the initial capacity of the produced battery was measured according to Example 7.

<Comparative Example 7>
The initial capacity was measured in the same manner as described in Example 22 except that the initial capacity of the fabricated battery was measured according to Comparative Example 1.

<Comparative Example 8>
The initial capacity was measured in the same manner as described in Example 22 except that the initial capacity of the fabricated battery was measured according to Comparative Example 2.

<Comparative Example 9>
The initial capacity was measured in the same manner as described in Example 22 except that the initial capacity of the fabricated battery was measured according to Comparative Example 3.

<Comparative Example 10>
The initial capacity was measured in the same manner as described in Example 22 except that the initial capacity of the fabricated battery was measured according to Comparative Example 4.

  Table 4 below shows the results of measuring the capacity retention rates of Example 22 to Example 30 and Comparative Example 7 to Comparative Example 10, respectively.

It is the cross-sectional schematic which represented typically the electrode by which the olivine type composite lithium iron phosphate was attached to a part of surface of the composite lithium manganate. It is the cross-sectional schematic which represented typically the electrode by which the olivine type composite lithium iron phosphate was attached to the whole surface of composite lithium manganate. 1 is a schematic cross-sectional view schematically showing an outline of a laminated flat non-bipolar lithium ion secondary battery which is a typical embodiment of a lithium ion battery of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view schematically showing an appearance of a stacked flat lithium ion secondary battery that is a typical embodiment of a lithium ion battery according to the present invention. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic cross-sectional view schematically showing an outline of a laminated flat bipolar lithium ion secondary battery which is a typical embodiment of a lithium ion battery of the present invention. FIG. 6A is an external view schematically showing a typical embodiment of an assembled battery according to the present invention, FIG. 6A is a plan view of the assembled battery, FIG. 6B is a front view of the assembled battery, and FIG. It is a side view of a battery. It is a conceptual diagram of the vehicle carrying the assembled battery of this invention.

Explanation of symbols

X composite lithium manganate Y olivine-type composite lithium iron phosphate 1 current collector,
10a non-bipolar lithium ion battery,
10b Bipolar lithium ion battery,
11 positive electrode current collector,
11a Outermost layer positive electrode current collector,
12 positive electrode (positive electrode active material layer),
13 electrolyte layer,
14 negative electrode current collector,
14a outermost layer negative electrode current collector,
15 negative electrode (negative electrode active material layer),
16 single cell layer (= battery unit or single cell),
17, 57 Power generation element (battery element; laminate),
18, 58 positive electrode tab,
19, 59 negative electrode tab,
20 positive terminal lead,
21 negative terminal lead,
22, 52 Battery exterior material (for example, laminate film),
31 Insulating layer 31,
50 lithium ion battery,
250 small battery pack,
300 battery packs,
310 connection jig,
400 Electric car.

Claims (9)

A positive electrode including a positive electrode current collector and a positive electrode active material formed on the positive electrode current collector; and a negative electrode including a negative electrode current collector and a negative electrode active material formed on the negative electrode current collector. An electrode for a lithium ion secondary battery,
The negative electrode active material is graphite,
The positive electrode active material is composite lithium manganate and olivine-type composite lithium iron phosphate,
The lithium ion secondary battery electrode, wherein a content of the composite lithium manganate is 30% by mass or less based on a total amount of the olivine-type composite lithium iron phosphate and the composite lithium manganate.   The electrode according to claim 1, wherein the positive electrode active material is formed by attaching olivine-type composite lithium iron phosphate to at least a part of the surface of the composite lithium manganate.   The electrode according to claim 1 or 2, wherein an average particle size A (µm) of the olivine-type composite lithium iron phosphate is smaller than an average particle size B (µm) of the composite lithium manganate. The relationship between the average particle diameter A (μm) and the average particle diameter B (μm) is expressed by the following formula (1):

The electrode according to claim 3, wherein:   The lithium ion secondary battery which uses the electrode of any one of Claims 1-4.   The lithium ion secondary battery according to claim 5, wherein charging of the lithium ion secondary battery is performed by a constant current constant voltage or a multistage constant current.   An assembled battery comprising the lithium ion secondary battery according to claim 5.   The assembled battery according to claim 7, wherein charging of the assembled battery is performed by a constant current constant voltage method or a multistage constant current.   A vehicle equipped with the lithium ion secondary battery according to claim 5 or 6 or the assembled battery according to claim 7 or 8 as a motor driving power source.

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