WO2013094037A1 - リチウム二次電池 - Google Patents
リチウム二次電池 Download PDFInfo
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- WO2013094037A1 WO2013094037A1 PCT/JP2011/079687 JP2011079687W WO2013094037A1 WO 2013094037 A1 WO2013094037 A1 WO 2013094037A1 JP 2011079687 W JP2011079687 W JP 2011079687W WO 2013094037 A1 WO2013094037 A1 WO 2013094037A1
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- negative electrode
- active material
- electrode active
- material layer
- secondary battery
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B60—VEHICLES IN GENERAL
- B60L—PROPULSION OF ELECTRICALLY-PROPELLED VEHICLES; SUPPLYING ELECTRIC POWER FOR AUXILIARY EQUIPMENT OF ELECTRICALLY-PROPELLED VEHICLES; ELECTRODYNAMIC BRAKE SYSTEMS FOR VEHICLES IN GENERAL; MAGNETIC SUSPENSION OR LEVITATION FOR VEHICLES; MONITORING OPERATING VARIABLES OF ELECTRICALLY-PROPELLED VEHICLES; ELECTRIC SAFETY DEVICES FOR ELECTRICALLY-PROPELLED VEHICLES
- B60L50/00—Electric propulsion with power supplied within the vehicle
- B60L50/50—Electric propulsion with power supplied within the vehicle using propulsion power supplied by batteries or fuel cells
- B60L50/60—Electric propulsion with power supplied within the vehicle using propulsion power supplied by batteries or fuel cells using power supplied by batteries
- B60L50/64—Constructional details of batteries specially adapted for electric vehicles
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B60—VEHICLES IN GENERAL
- B60L—PROPULSION OF ELECTRICALLY-PROPELLED VEHICLES; SUPPLYING ELECTRIC POWER FOR AUXILIARY EQUIPMENT OF ELECTRICALLY-PROPELLED VEHICLES; ELECTRODYNAMIC BRAKE SYSTEMS FOR VEHICLES IN GENERAL; MAGNETIC SUSPENSION OR LEVITATION FOR VEHICLES; MONITORING OPERATING VARIABLES OF ELECTRICALLY-PROPELLED VEHICLES; ELECTRIC SAFETY DEVICES FOR ELECTRICALLY-PROPELLED VEHICLES
- B60L58/00—Methods or circuit arrangements for monitoring or controlling batteries or fuel cells, specially adapted for electric vehicles
- B60L58/10—Methods or circuit arrangements for monitoring or controlling batteries or fuel cells, specially adapted for electric vehicles for monitoring or controlling batteries
- B60L58/12—Methods or circuit arrangements for monitoring or controlling batteries or fuel cells, specially adapted for electric vehicles for monitoring or controlling batteries responding to state of charge [SoC]
- B60L58/15—Preventing overcharging
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/05—Accumulators with non-aqueous electrolyte
- H01M10/052—Li-accumulators
- H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/05—Accumulators with non-aqueous electrolyte
- H01M10/058—Construction or manufacture
- H01M10/0583—Construction or manufacture of accumulators with folded construction elements except wound ones, i.e. folded positive or negative electrodes or separators, e.g. with "Z"-shaped electrodes or separators
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/05—Accumulators with non-aqueous electrolyte
- H01M10/058—Construction or manufacture
- H01M10/0587—Construction or manufacture of accumulators having only wound construction elements, i.e. wound positive electrodes, wound negative electrodes and wound separators
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
- H01M4/133—Electrodes based on carbonaceous material, e.g. graphite-intercalation compounds or CFx
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/36—Selection of substances as active materials, active masses, active liquids
- H01M4/362—Composites
- H01M4/366—Composites as layered products
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/36—Selection of substances as active materials, active masses, active liquids
- H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
- H01M4/583—Carbonaceous material, e.g. graphite-intercalation compounds or CFx
- H01M4/587—Carbonaceous material, e.g. graphite-intercalation compounds or CFx for inserting or intercalating light metals
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
- H01M2004/027—Negative electrodes
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/10—Energy storage using batteries
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
- Y02P70/50—Manufacturing or production processes characterised by the final manufactured product
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
- Y02T10/00—Road transport of goods or passengers
- Y02T10/60—Other road transportation technologies with climate change mitigation effect
- Y02T10/70—Energy storage systems for electromobility, e.g. batteries
Definitions
- the present invention relates to a lithium secondary battery. Specifically, the present invention relates to a lithium secondary battery including a negative electrode in which a negative electrode active material is oriented.
- lithium secondary batteries typically lithium ion batteries
- One typical configuration of this type of lithium secondary battery has electrodes (positive electrode and negative electrode) on which an electrode active material layer containing an electrode active material is supported on an electrode current collector.
- This electrode is typically formed by applying an electrode active material layer forming paste containing an electrode active material and a binder to the surface of the current collector, drying it, and rolling it to a predetermined density (so-called application). Method).
- graphite materials such as natural graphite, artificial graphite, natural graphite and artificial graphite amorphous carbon are widely used.
- This graphite material has a layered structure in which a plurality of planes composed of carbon six-membered rings (also referred to as graphene, which corresponds to the (002) plane in the graphite crystal structure) are overlapped, and between the layers (interlayer) Charging / discharging is performed by insertion (occlusion) of lithium ions into and desorption (release) of lithium ions from the interlayer.
- various proposals have been made conventionally.
- Patent Document 1 when graphite particles are used as the negative electrode active material, the direction of the (002) plane of the graphite particles is used as a current collector for the purpose of improving the permeability and high rate discharge characteristics of the negative electrode electrolyte. In contrast, it is disclosed to be arranged in a vertical direction. Patent Documents 2 and 3 describe a state in which (002) planes of graphite particles contained in graphite powder are oriented in the same direction in a magnetic field for the purpose of improving discharge capacity and cycle characteristics in high rate charge / discharge. Thus, it is disclosed that a negative electrode for a lithium secondary battery is produced by removing the solvent and solidifying and molding graphite powder with a binder.
- Patent Document 4 as a negative electrode active material oriented in a magnetic field for the purpose of improving rapid charge characteristics and high rate discharge characteristics, the average particle diameter is 10 to 25 ⁇ m and the specific surface area is 1.0 to 5. The use of graphite particles at 0 m 2 / g is disclosed.
- lithium secondary batteries for applications such as large equipment and electric vehicles are particularly required to improve output characteristics and capacity characteristics.
- high rate characteristics also referred to as large current discharge characteristics or high rate discharge characteristics
- this high rate characteristic is directly influenced by the internal resistance of the electrode, it is essential to reduce the internal resistance in order to improve the high rate characteristic. Therefore, how to reduce the internal resistance of the electrode while ensuring the capacity as much as possible is the key to the technology.
- the present invention has been made in view of the above points, and its main object is to provide a lithium secondary battery in which the internal resistance is reduced and the high-rate characteristics are further improved.
- the lithium secondary battery according to the present invention includes a positive electrode having a positive electrode active material layer on a positive electrode current collector, a negative electrode having a negative electrode active material layer on a negative electrode current collector, and a non-aqueous electrolyte.
- the positive electrode active material layer includes a positive electrode active material capable of reversibly occluding and releasing lithium ions.
- the negative electrode active material included in the negative electrode active material layer includes (1) a bend having an average bend number f per particle of 0 ⁇ f ⁇ 3 and (2) an average aspect ratio of 1.8 or more.
- the layered graphite as the negative electrode active material is oriented so that the perpendicularity is 1 or more, has excellent input / output characteristics, and has reduced DC resistance. Further, the layered graphite is bent in an average bending number f in the range of 0 ⁇ f ⁇ 3, and an appropriate space can be secured in the layered graphite and between the adjacent layered graphites. It is possible to reduce. Even if the average bending number f is satisfied, it is not preferable that the negative electrode active material bends as a whole and the average aspect ratio is less than 1.8 because the direct current resistance is inferior. According to such a configuration, the conductivity of the negative electrode as a whole is improved in the direction perpendicular to the current collector and the internal resistance is reduced, so that the polarization characteristics during charge / discharge are improved, and lithium A secondary battery can be realized.
- the density of the negative electrode active material layer is 1.5 g / cm 3 or less. In order to improve high rate characteristics, it is essential to reduce internal resistance. And in the negative electrode active material layer which has such a form, by setting the density of a negative electrode active material layer to 1.5 g / cm ⁇ 3 > or less, a diffusion resistance can be reduced more and a high rate characteristic can be improved effectively.
- the lithium secondary battery disclosed herein at least a part of the surface of the layered graphite is coated with amorphous carbon.
- a layered graphite material as the negative electrode active material, it is known that by aligning the edge part of the graphite laminate structure so as to face the positive electrode, a decomposition reaction of the electrolyte occurs or gas is generated during charging. Yes. According to such a configuration, problems such as the decomposition reaction of the electrolytic solution and the generation of gas can be solved even when the layered graphite is oriented so that the perpendicularity becomes 1 or more as described above.
- the average bending number f is 0 ⁇ f ⁇ 2.
- a preferred embodiment of the lithium secondary battery disclosed herein is a power source for driving the motor in an automobile equipped with the motor for driving.
- the lithium secondary battery is provided with excellent high-rate characteristics, and thus can fully exhibit its characteristics when used, for example, as a power source for driving an automobile motor.
- a power source typically, a power source of a hybrid vehicle or an electric vehicle
- the present invention includes the lithium secondary battery disclosed herein.
- a vehicle for example, an automobile is preferably provided.
- FIG. 1 is a perspective view schematically showing a nonaqueous electrolyte secondary battery according to an embodiment of the present invention.
- 2 is a cross-sectional view taken along the line II-II in FIG.
- FIG. 3 is a schematic view showing a wound electrode body according to an embodiment of the present invention.
- FIG. 4A is a diagram showing a bending mode of layered graphite.
- FIG. 4B is a diagram showing another mode of bending of layered graphite.
- FIG. 4C is a diagram showing another mode of bending of layered graphite.
- FIG. 4D is a diagram showing another embodiment of bending of layered graphite.
- FIG. 5 is a diagram showing how to take a cross-section when obtaining a cross-sectional image by an electron microscope.
- FIG. 5 is a diagram showing how to take a cross-section when obtaining a cross-sectional image by an electron microscope.
- FIG. 6 is a diagram for explaining how to obtain the perpendicularity of the negative electrode active material according to an embodiment of the present invention.
- FIG. 7 is a side view showing a vehicle equipped with a lithium secondary battery according to an embodiment of the present invention.
- FIG. 8 is a diagram showing the relationship between voltage drop and time in constant watt discharge.
- FIG. 9 is a diagram showing the relationship between the electric energy of the constant watt discharge and the time required to reach a predetermined cut voltage during the constant watt discharge.
- the “lithium secondary battery” means a general battery that can be repeatedly charged using lithium ions as a charge carrier, and typically includes a lithium ion battery, a lithium polymer battery, and the like.
- the “active material” refers to a substance capable of reversibly occluding and releasing (typically inserting and releasing) a chemical species (that is, lithium ion) serving as a charge carrier in a lithium secondary battery.
- a lithium secondary battery provided by the present invention includes a positive electrode including a positive electrode active material layer on a positive electrode current collector, a negative electrode including a negative electrode active material layer on a negative electrode current collector, and a non-aqueous electrolyte. Characterized by composition. Below, the structure of this lithium secondary battery is demonstrated in order. ⁇ Positive electrode> The positive electrode is typically prepared by forming a positive electrode active material layer by supplying a positive electrode active material layer forming composition containing a positive electrode active material, a conductive material, and a binder onto a positive electrode current collector. Is done.
- a conductive member made of a highly conductive metal or resin can be used as in the case of an electrode current collector for a lithium secondary battery.
- a metal mainly composed of aluminum, nickel, titanium, iron or the like or an alloy thereof can be preferably used. More preferably, it is aluminum or an aluminum alloy.
- a positive electrode electrical power collector Various things can be considered according to the shape etc. of a desired secondary battery. For example, it may be in various forms such as a rod shape, a plate shape, a sheet shape, a foil shape, and a mesh shape.
- an aluminum foil is preferably used.
- the positive electrode active material layer is formed on the surface of the positive electrode current collector.
- the positive electrode active material layer usually includes a granular positive electrode active material as a main component, and also includes a granular conductive material for enhancing conductivity, and these are bound by a binder and fixed on the positive electrode current collector. Yes.
- the positive electrode active material a material capable of inserting and extracting lithium can be used, and one or more of the various positive electrode active materials conventionally used in lithium secondary batteries can be used without any particular limitation. it can.
- a lithium transition metal oxide typically in a particulate form
- a lithium nickel-based oxide typically, LiNiO 2
- Li-excess type ternary lithium-excess transition metal oxide containing three kinds of transition metal elements A so-called Li-excess type ternary lithium-excess transition metal oxide containing three kinds of transition metal elements, and a general formula: xLi [Li 1/3 Mn 2/3 ] O 2.
- LiMeO 2 LiMeO 2 (In the above formula, Me is one or more transition metals, and x satisfies 0 ⁇ x ⁇ 1.) It may be a so-called solid solution type lithium-excess type transition metal oxide or the like.
- the positive electrode active material has a general formula of LiMAO 4 (where M is at least one metal element selected from the group consisting of Fe, Co, Ni and Mn, and A is P, Si, S and And an anion selected from the group consisting of V.).
- the positive electrode active material prepared as described above can be pulverized, granulated and classified by an appropriate means.
- a lithium transition metal oxide powder substantially composed of secondary particles having an average particle size in the range of approximately 1 ⁇ m to 25 ⁇ m (typically approximately 2 ⁇ m to 15 ⁇ m) is used as the positive electrode in the technology disclosed herein. It can preferably be employed as an active material.
- the granular positive electrode active material powder substantially comprised by the secondary particle which has a desired average particle diameter and / or particle size distribution can be obtained.
- the conductive material is not particularly limited as long as it exhibits good conductivity.
- various carbon blacks for example, acetylene black, furnace black, ketjen black
- carbon powders such as graphite powders can be used. These may use together 1 type, or 2 or more types.
- the average particle size of the carbon material particles (secondary particles) can be about 1/500 to 1/20 of the average particle size of the electrode active material.
- the carbon material preferably has an average particle size of secondary particles of 20 ⁇ m or less, and more preferably in the range of 200 nm to 10 ⁇ m.
- the average particle size of the secondary particles is larger than 20 ⁇ m, it is difficult to fit in the gap between the positive electrode active materials, and the density of the positive electrode active material in the negative electrode active material layer may be lowered, which is not preferable.
- the lower limit of the average particle size of the secondary particles too fine particles are not preferable because they tend to be biased toward the upper layer portion in the formation of the positive electrode active material layer.
- the binder has a function of binding each particle of the positive electrode active material and the conductive material contained in the positive electrode active material layer, or binding these particles and the positive electrode current collector.
- a polymer that can be dissolved or dispersed in a solvent used when forming the positive electrode active material layer can be used.
- carboxymethylcellulose (CMC), methylcellulose (MC), cellulose acetate phthalate (CAP), hydroxypropylmethylcellulose (HPMC) are used as water-soluble (water-soluble) polymer materials.
- PVA polyvinyl alcohol
- polymer materials that are dispersed in water examples include vinyl polymers such as polyethylene (PE) and polypropylene (PP); polyethylene oxide (PEO), polytetrafluoroethylene (PTFE), and tetrafluoroethylene.
- PE polyethylene
- PP polypropylene
- PEO polyethylene oxide
- PTFE polytetrafluoroethylene
- -Fluororesin such as hexafluoropropylene copolymer (FEP), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA); vinyl acetate copolymer; styrene butadiene rubber (SBR), acrylic acid modified SBR resin Examples thereof include rubbers such as (SBR latex).
- a non-aqueous solvent a polymer (polyvinylidene fluoride (PVDF), polyvinylidene chloride (PVDC), polyacrylonitrile (PAN), etc.) can be preferably used.
- the polymer material exemplified as the binder is a thickener for a positive electrode active material layer forming paste (hereinafter sometimes simply referred to as a paste) prepared to form a positive electrode active material layer. It may be used for the purpose of exhibiting the function as another additive.
- a solvent used for manufacture of said positive electrode both an aqueous solvent and a non-aqueous solvent can be used as a solvent used for manufacture of said positive electrode.
- aqueous solvent examples include water and a composition using a mixed solvent mainly composed of water (aqueous solvent).
- aqueous solvent a mixed solvent mainly composed of water
- organic solvents lower alcohol, lower ketone, etc.
- NMP N-methyl-2-pyrrolidone
- the use amount of the conductive material is 1 to 20 parts by mass (preferably 5 to 15 parts by mass) with respect to 100 parts by mass of the positive electrode active material.
- the binder is exemplified by 0.5 to 10 parts by mass with respect to 100 parts by mass of the positive electrode active material.
- the negative electrode typically has a negative electrode active material layer formed by supplying a negative electrode active material layer forming composition containing a negative electrode active material, a binder, and, if necessary, a conductive material onto a negative electrode current collector. Prepared by forming.
- a negative electrode current collector a conductive member made of a highly conductive metal or resin or the like can be used as in the conventional negative electrode current collector for lithium secondary batteries.
- a rod-like body, a plate-like body, a foil-like body, a net-like body or the like mainly composed of copper, nickel, titanium, stainless steel, or the like can be used.
- a film material obtained by depositing copper on a polypropylene film can be used as the negative electrode current collector.
- the negative electrode active material layer is formed on the surface of the negative electrode current collector.
- the negative electrode active material layer is usually composed mainly of a granular negative electrode active material, and includes a granular conductive material for enhancing conductivity as needed, and these are bound by a binder and fixed on the negative electrode current collector.
- the negative electrode active material contained in the negative electrode active material layer in the present invention is defined as having the following characteristics.
- (1) it is composed of bent layered graphite having an average bend number f per particle of 0 ⁇ f ⁇ 3, (2) an average aspect ratio of 1.8 or more, and (3)
- the angle formed by the major axis of the negative electrode active material with respect to the surface of the negative electrode current collector is ⁇ n, and the number of the negative electrode active materials satisfying 0 ° ⁇ ⁇ n ⁇ 30 ° is n1, 60 ° ⁇ ⁇ n ⁇ 90 ° or less.
- the number of negative electrode active materials is n2, it is oriented so that the perpendicularity defined by n2 / n1 is 1 or more.
- the average bending number f is defined as an average value of the number of points bent at 30 ° or more (inner angle is 150 ° or less) per one layered graphite particle. Bending is a state where the graphene sheet of layered graphite is clearly bent at a certain line (polygonal line), and the plane of the graphene sheet is at an angle of 30 ° or more at the boundary, or The graphene sheet may be curved although there is no clear line (bending line), and the plane of the graphene sheet sandwiching the curved portion may include an angle of 30 ° or more.
- Such average bending number f can be confirmed by, for example, cutting the negative electrode active material layer in an arbitrary cross section and observing the cut surface with an electron microscope (for example, a scanning electron microscope (SEM)). it can.
- the cut surface in this case is not strictly limited, but is preferably a cross section parallel to the surface of the negative electrode current collector.
- calculation of the average bending number f can be made into the average value about 30 or more layered graphite particles.
- the calculation of the average bending number f can be performed only from observation of one cross section, but is preferably performed by observation of a plurality of cross sections.
- FIG. 4A is a perspective view schematically illustrating the bending state of one piece of layered graphite.
- the number of points that are bent at 30 ° or more in one layered graphite that is, the number of points that are 150 ° or less as the internal angle ⁇ at the bent portion is 3.
- 4B to 4D are cross-sectional views schematically illustrating the bending state of one piece of layered graphite.
- the number of points bent at 30 ° or more that is, the number of points where the internal angle ⁇ at the bent portion is 150 ° or less is 1, and the example shown in FIG. 4C. Then it is 2.
- a point bent at less than 30 ° is observed, but this point is not included in the number of bends, and is bent at 30 ° or more per one layered graphite particle in this case.
- the number of points is 3. In this way, the number of points bent at 30 ° or more for 30 or more particles is obtained, and the average value thereof is defined as the average bending number f.
- Graphite as a negative electrode active material used in general consumer batteries is spherical (granular) particles obtained by mechanically rounding layered graphite for the purpose of mainly securing capacity.
- the graphene sheet is bent randomly many times, which causes the diffusion resistance and DC resistance of the electrode to increase.
- the layered graphite as the negative electrode active material disclosed herein is bent only in the range where the average bending number f is 0 ⁇ f ⁇ 3.
- the directivity is extremely small and the direct current resistance is reduced.
- flat layered graphite that is not bent at all that is, having an average bending number f of zero, can be aligned in the negative electrode active material layer in the alignment step.
- a predetermined negative electrode active material layer Many of them fall down due to rolling to achieve the density, and it is difficult to maintain the orientation. And since it is flat form, layered graphite tends to overlap closely and it is hard to reduce diffusion resistance.
- the negative electrode active material layer contains layered graphite that is bent even at one point per particle (one particle), so that the effect of reducing the diffusion resistance of the electrode can be obtained. Therefore, it is important that the average bending number f is a value larger than zero. An average bending number f greater than 3 is not preferable because the direct current resistance increases more than necessary.
- the average bending number f is preferably 0 ⁇ f ⁇ 2, for example, 0.1 ⁇ f ⁇ 1.7, more preferably 0.5 ⁇ f ⁇ 1.5, and more specifically 0.7 ⁇ f ⁇ 1.3.
- the average aspect ratio is defined as an average value obtained by examining the aspect ratio expressed by the major axis / minor axis of one layered graphite particle for 30 or more particles. This average aspect ratio can also be confirmed by, for example, cutting the negative electrode active material layer in an arbitrary cross section and observing the cut surface with an electron microscope (for example, SEM).
- the cut surface in this case is not strictly limited, but is preferably a cross section perpendicular to the surface of the negative electrode current collector.
- the calculation of the average aspect ratio can be performed only from observation of one cross section, but is preferably performed by observation of a plurality of cross sections.
- the average bending number f defined in (1) is 0 ⁇ f ⁇ 3
- the DC resistance is sufficiently high if the bent graphite itself is bent or bent in the longitudinal direction. Not reduced.
- a higher aspect ratio of the layered graphite is more preferable for reducing the direct current resistance. Therefore, in the invention disclosed herein, the average aspect ratio defined as described above is defined as 1.8 or more.
- ⁇ n is the angle formed by the major axis of the negative electrode active material with respect to the surface of the negative electrode current collector.
- the number of negative electrode active materials whose ⁇ n is 0 ° ⁇ ⁇ n ⁇ 30 ° or less is n1
- n1 is the number of graphite particles relatively lying on the negative electrode current collector.
- N2 is the number of layered graphite relatively standing with respect to the negative electrode current collector.
- the verticality is defined as n2 / n1.
- the perpendicularity of the layered graphite is evaluated by (number of layered graphite relatively standing with respect to the negative electrode current collector) / (number of layered graphite relatively lying with respect to the negative electrode current collector). Is done. For this reason, the perpendicularity of the layered graphite can be an index for evaluating how much the layered graphite stands in the negative electrode active material layer with reference to the negative electrode current collector. That is, when the perpendicularity is 1.0, it indicates that the number of layered graphite that is relatively standing with respect to the negative electrode current collector is the same as the number of layered graphite that is relatively lying.
- the degree of perpendicularity is preferably large, and in the invention disclosed herein, it is defined as 1.0 or more. It is preferably 1.1 or more, for example, 1.5 or more, more preferably 2.0 or more, and more preferably 3.0 or more.
- the above features (1) to (3) can be confirmed, for example, by observing the cross section of the negative electrode active material layer.
- cross-sectional observation is performed with an electron microscope having a resolution that can observe the state of layered graphite in the negative electrode active material layer.
- a cross-sectional SEM image in which the cut surface of the negative electrode active material layer is observed may be prepared.
- the cross-sectional observation is preferably performed on a plurality of cross-sections. For example, if the above (1) average bend number is obtained, the cross section in the plane direction of the negative electrode active material layer (that is, the cross section parallel to the surface of the negative electrode current collector) It is more preferable to observe with.
- the plurality of cross sections perpendicular to the negative electrode current collector may be set so as to be equally divided into about 360 ° in plan view, and cross-sectional SEM images of the plurality of cut surfaces may be prepared.
- the negative electrode active material layer formed on the negative electrode current collector for example, as shown in FIG. 5, 0 °, 45 °, 90 °, and 135 ° arbitrarily set in the negative electrode current collector in a plan view.
- the preparation of cross-sectional SEM images in four cross-sections is exemplified.
- the intersections of the respective cross sections coincide with each other. However, this is for convenience, and the intersections of the respective cross sections do not need to coincide.
- four cross sections arranged uniformly at 45 ° are illustrated, but for example, six cross sections arranged uniformly at approximately 30 ° may be considered. In this way, it is preferable to set a plurality of cross-sections that are substantially evenly arranged on the negative electrode current collector in plan view and prepare cross-sectional SEM images of the plurality of cross-sections.
- a predetermined number of granular graphites may be extracted from granular graphite having a large apparent cross-sectional area, and various characteristic values may be measured and calculated for the extracted granular graphite.
- a predetermined number of granular graphite is extracted from layered graphite having a large apparent cross-sectional area in a cross-sectional SEM image perpendicular to the surface of the negative electrode current collector.
- the inclination ⁇ n of the layered graphite with respect to the surface of the negative electrode current collector is specified based on the straight line L along the longest diameter of the extracted layered graphite.
- the number of layered graphite having an inclination ⁇ n of 60 ° ⁇ ⁇ n ⁇ 90 ° is n2
- the number of the layered graphite having an inclination ⁇ n of 0 ° ⁇ ⁇ n ⁇ 30 ° is n1
- the perpendicularity (n2 / n1) is calculate.
- graphite materials such as natural graphite, artificial graphite, natural graphite and artificial graphite amorphous carbon can be used.
- layered graphite in which at least a part of the surface of these graphite materials is coated with amorphous carbon may be used as the negative electrode active material.
- a particle size there is no restriction
- the average particle size means a d50 particle size based on volume.
- the average particle diameter is too large, it is not preferable because the effective capacity of the negative electrode may be reduced due to the time required for the diffusion of charge carriers into the active material material center. Further, it is not preferable from the viewpoint that the treatment for orientation tends to be difficult. If the average particle size is too smaller than 5 ⁇ m, the side reaction rate on the surface of the negative electrode active material is increased, and the irreversible capacity of the resulting nonaqueous electrolyte secondary battery may be increased.
- the density of the negative electrode active material layer is preferably 1.5 g / cm 3 or less.
- the diffusion resistance can be further reduced by setting the density of the negative electrode active material layer to 1.5 g / cm 3 or less.
- the density of the negative electrode active material layer is preferably 1.0 to 1.5 g / cm 3 , more preferably 1.1 to 1.4 g / cm 3 , and more specifically 1.1 to 1 g / cm 3 . Desirably 3 g / cm 3 .
- the density of the negative electrode active material layer exceeds 1.5 g / cm 3 , it is preferable in terms of increase in capacity, but the filling degree of the negative electrode active material becomes too high and diffusion resistance increases, which greatly impairs the high rate characteristics. This is not preferable. Note that if the density of the negative electrode active material layer is less than 1.0 g / cm 3, it is not preferable because the capacity is reduced more than necessary.
- the density of such a negative electrode active material layer is not limited even if it is applied to a negative electrode active material layer containing a granular (spherical) carbon material that has been widely used as a negative electrode active material. Does not make sense.
- the negative electrode active material layer having the structure defined in the above (1) to (3) by realizing a density of 1.5 g / cm 3 or less, an effect that the high rate characteristic is efficiently improved can be obtained for the first time. Can do.
- a bent layered graphite that realizes the above (1) average bending number and (2) average aspect ratio is prepared as a negative electrode active material. Then, a paste-like composition for forming a negative electrode active material layer is prepared using the layered graphite, and after supplying the composition onto the current collector, the layered graphite is oriented and formed by drying in that state. Can do.
- the state of the layered graphite in the negative electrode active material layer can be controlled by the viscosity of the paste and the orientation means. Examples of the orientation means include applying a magnetic field.
- the (002) plane of graphite is oriented in a direction perpendicular to the surface of the negative electrode current collector. That is, with respect to the bent layered graphite, due to its shape anisotropy, the layered graphite stands in a direction perpendicular to the surface of the negative electrode current collector, and the perpendicularity of (3) above can be realized.
- the application of the magnetic field can realize the orientation state by adjusting the strength of the magnetic field, the time for applying the magnetic field, and the like.
- the means for orientation of the layered graphite is not limited to this.
- any means that can achieve the above-described perpendicularity may be oriented by, for example, a physical, chemical, electrical, or mechanical method.
- the drying is preferably carried out after orienting the layered graphite or while performing the orientation treatment. For example, it is more preferable to dry while applying a magnetic field.
- the binder, the solvent, the conductive material, and the like used for the preparation of the negative electrode active material layer forming composition various materials that can be used in the preparation of the positive electrode active material layer forming composition can be similarly used.
- the amount of the conductive material used can be about 1 to 30 parts by mass (preferably about 2 to 20 parts by mass, for example, about 5 to 10 parts by mass) with respect to 100 parts by mass of the negative electrode active material.
- the amount of the binder used with respect to 100 parts by mass of the negative electrode active material can be, for example, 0.5 to 10 parts by mass.
- Nonaqueous electrolyte one kind or two or more kinds similar to the nonaqueous electrolyte used in the conventional lithium secondary battery can be used without particular limitation.
- a non-aqueous electrolyte can typically be a non-aqueous solvent containing an electrolyte (ie, a lithium salt).
- the electrolyte concentration is not particularly limited, but a nonaqueous electrolyte solution containing an electrolyte at a concentration of about 0.1 mol / L to 5 mol / L (preferably about 0.8 mol / L to 1.5 mol / L) is preferably used. be able to. Further, it may be a solid (gel) electrolytic solution in which a polymer is added to the liquid electrolytic solution.
- aprotic solvents such as carbonates, esters, ethers, nitriles, sulfones and lactones
- Examples include 2-methyltetrahydrofuran, dioxane, 1,3-dioxolane, diethylene glycol dimethyl ether, ethylene glycol dimethyl ether, acetonitrile, propionitrile, nitromethane, N, N-dimethylformamide, dimethyl sulfoxide, sulfolane, and ⁇ -butyrolactone.
- electrolyte examples include LiPF 6 , LiBF 4 , LiN (SO 2 CF 3 ) 2 , LiN (SO 2 C 2 F 5 ) 2 , LiCF 3 SO 3 , LiC 4 F 9 SO 3 , LiC (SO 2 CF 3 ) 3 , LiClO 4 and the like.
- the electrolyte may contain an additive such as an overcharge inhibitor.
- an overcharge inhibitor when the oxidation potential is higher than the operating voltage of the lithium secondary battery (for example, 4.2 V or higher in the case of a lithium secondary battery that is fully charged at 4.2 V) and is oxidized.
- a compound that generates a large amount of gas can be used without particular limitation.
- a battery having an oxidation reaction potential in the range of 4.6 V to 4.9 V can be preferably used.
- a biphenyl compound, a cycloalkylbenzene compound, an alkylbenzene compound, an organic phosphorus compound, a fluorine atom-substituted aromatic compound, a carbonate compound, a cyclic carbamate compound, an alicyclic hydrocarbon, and the like can be given. More specifically, for example, cyclohexylbenzene (CHB) and cyclohexylbenzene derivatives are preferably used.
- the amount of the overcharge inhibitor used relative to 100% by mass of the electrolytic solution used can be, for example, about 0.01 to 10% by mass (preferably about 0.1 to 5% by mass).
- FIG. 1 is a perspective view schematically showing a rectangular lithium secondary battery according to an embodiment
- FIG. 2 is a cross-sectional view taken along the line II-II in FIG.
- the lithium secondary battery 10 according to the present embodiment includes a rectangular battery case 80 having a rectangular parallelepiped shape and a lid 82 that closes an opening of the case 80. Through this opening, the flat electrode body (the wound electrode body 20) and the electrolyte can be accommodated in the battery case 80.
- the lid 82 is provided with a positive terminal 40 and a negative terminal 60 for external connection, and a part of these terminals 40 and 60 protrudes to the surface side of the lid 82.
- FIG. 3 is a diagram illustrating a configuration of the wound electrode body 20.
- the wound electrode body 20 includes a positive electrode sheet 30 having a positive electrode active material layer 34 formed on the surface of a long sheet-like positive electrode current collector 32, and a long sheet-like negative electrode. It is composed of a negative electrode sheet 50 having a negative electrode active material layer 54 formed on the surface of a current collector 52 and a long sheet-like separator 70.
- a portion where the positive electrode current collector 32 is exposed without forming the positive electrode active material layer 34 (uncoated part 33) is formed at one end portion along the longitudinal direction.
- the negative electrode sheet 50 that is provided and wound one end portion along the longitudinal direction has a portion where the negative electrode current collector 52 is exposed without forming the negative electrode active material layer 54 (uncoated portion 53).
- the active material layers 34 and 54 are overlapped and the uncoated portion 33 of the positive electrode sheet 30 and the uncoated portion 53 of the negative electrode sheet 50 are overlapped.
- the electrode sheets 30 and 50 are slightly shifted and overlapped so that the first and second end portions along the longitudinal direction protrude separately from each other. In this state, a total of four sheets 30, 70, 50, 70 are wound around the winding axis WL, and then the obtained wound body is crushed from the side direction and ablated to flatten the winding.
- An electrode body 20 is configured.
- the uncoated portion 33 of the positive electrode current collector 32 is connected to the positive electrode terminal 40 via the internal positive electrode terminal 41, and the uncoated portion 53 of the negative electrode current collector 52 is connected to the negative electrode terminal 60 via the internal negative electrode terminal 61. They are joined by ultrasonic welding, resistance welding, etc. and electrically connected.
- the wound electrode body 20 obtained in this way is accommodated in the case body 84 with the winding axis WL lying sideways, and the lid body 82 is welded and sealed. Thereafter, the lithium secondary battery 10 of the present embodiment can be constructed by injecting an electrolyte from the inlet 86 provided in the lid and sealing the inlet 86.
- the structure, size, material (for example, metal, plastic, laminate film, etc.) of the battery case 80 are not particularly limited.
- a suitable separator sheet 70 used between the positive / negative electrode sheets 30 and 50 the thing comprised with the porous polyolefin-type resin is mentioned.
- a microporous sheet made of a thermoplastic resin for example, a polyolefin such as polyethylene or polypropylene
- a separator is unnecessary (that is, in this case, the electrolyte itself can function as a separator).
- the lithium secondary battery 10 constructed in this way has reduced internal resistance, and is characterized by being used, for example, as a power source for driving the motor in an automobile equipped with a driving motor.
- a lithium secondary battery 10 disclosed herein includes a driving power source for a driving motor (typically, a driving power source for a hybrid vehicle) that requires high-rate input / output characteristics.
- the vehicle (for example, automobile) 1 provided with the lithium secondary battery 10 (which may be in the form of the assembled battery 100) disclosed herein is preferably provided.
- Niobium electrode sample 1 (Negative electrode sample 1) Using the graphite material 1 as a negative electrode active material, the proportion of 1 part by mass of styrene butadiene rubber (SBR) as a binder and 1 part by mass of carboxymethyl cellulose (CMC) as a thickener with respect to 100 parts by mass of the negative electrode active material. These were blended, and these were dispersed and mixed in N-methylpyrrolidone (NMP) as a solvent to prepare a paste for forming a negative electrode active material layer. The obtained paste for forming the negative electrode active material layer was applied to one side of a 5 ⁇ m thick Cu foil as a current collector with a predetermined basis weight, dried without applying a magnetic field, and then the density was 1.
- SBR styrene butadiene rubber
- CMC carboxymethyl cellulose
- Negative electrode sample 2 A negative electrode sheet (negative electrode sample 2) was produced in the same manner as the negative electrode sample 1, except that the current was dried while applying a magnetic field of 0.5 T in the direction perpendicular to the surface of the current collector.
- the negative electrode sample 2 was cut out in a cross section perpendicular to the surface of the negative electrode current collector, and the perpendicularity of the negative electrode active material was examined from the cross section. As a result, the perpendicularity was 2.3.
- the graphite material 2 was used instead of the graphite material 1 as a negative electrode active material, and it was dried while applying a magnetic field of 0.5 T in the direction perpendicular to the surface of the current collector.
- a negative electrode sample 5) was prepared. This negative electrode sample 5 was cut out in a cross section perpendicular to the surface of the negative electrode current collector, and the perpendicularity of the negative electrode active material was examined from the cross section. As a result, the perpendicularity was 1.8.
- Negative electrode sample 6 After using graphite material 2 as a negative electrode active material instead of graphite material 1 and applying a magnetic field of 0.5 T in a direction perpendicular to the surface of the current collector and drying it, the density becomes 1.4 g / cm 3.
- a negative electrode sheet (negative electrode sample 6) was prepared in the same manner as negative electrode sample 1 except for the above. The negative electrode sample 6 was cut out in a cross section perpendicular to the surface of the negative electrode current collector, and the perpendicularity of the negative electrode active material was examined from the cross section. As a result, the perpendicularity was 1.1.
- Negative electrode sample 7 After using graphite material 2 as the negative electrode active material instead of graphite material 1 and drying it while applying a magnetic field of 0.5 T in the direction perpendicular to the surface of the current collector, the density becomes 1.6 g / cm 3.
- a negative electrode sheet (negative electrode sample 7) was prepared in the same manner as negative electrode sample 1 except for the above. This negative electrode sample 7 was cut out in a cross section perpendicular to the surface of the negative electrode current collector, and the perpendicularity of the negative electrode active material was examined from the cross section. As a result, the perpendicularity was 0.5.
- the graphite material 3 is used as the negative electrode active material in place of the graphite material 1, and after drying while applying a magnetic field of 0.5 T in a direction perpendicular to the surface of the current collector, the density becomes 1.2 g / cm 3.
- the negative electrode sheet (negative electrode sample 8) was produced in the same manner as the negative electrode sample 1 except for the above. This negative electrode sample 8 was cut out in a cross section perpendicular to the surface of the negative electrode current collector, and the perpendicularity of the negative electrode active material was examined from the cross section. As a result, the perpendicularity was 1.2.
- Lithium transition metal composite oxide LiNi 1/3 Co 1/3 Mn 1/3 O 2
- AB acetylene black
- PVdF polyvinylidene fluoride
- NMP N-methylpyrrolidone
- a test laminate cell (lithium ion battery) was constructed using the positive electrode sheet prepared above and negative electrode samples 1 to 8. That is, a positive electrode sheet (dimensions of about 23 mm ⁇ 23 mm) and a negative electrode sheet (dimensions of about 25 mm ⁇ 25 mm) are laminated with a separator interposed therebetween so that the active material layers of both electrode sheets face each other.
- This electrode body was accommodated in a laminated bag-shaped battery container together with a non-aqueous electrolyte, and sealed to construct evaluation cell (lithium ion battery) samples 1 to 8.
- the 10-second output (25 ° C.) was determined by the following procedure.
- the measurement temperature environment is set to room temperature (here, 25 ° C.).
- Procedure 1 As SOC adjustment, SOC is set to 60% by 1C constant current charging, constant voltage charging is performed for 2.5 hours at SOC 60%, and rested for 10 seconds.
- Procedure 2 After the above procedure 1, discharge is performed at a constant wattage (W) (constant output) from SOC 60%. In the constant watt discharge, a larger amount of current flows as the voltage decreases due to discharge, and the same amount of power is discharged per hour. Then, the number of seconds until the voltage discharged from the SOC 60% state reaches a predetermined cut voltage is measured.
- W constant wattage
- Procedure 3 Procedure 1 and Procedure 2 are repeated in Procedure 2 while changing the constant watt discharge conditions in the range of 5 W to 50 W (see FIG. 8). Then, the horizontal axis represents the number of seconds until the measured predetermined cut voltage, and the vertical axis represents the condition of the constant watt discharge power (W) during the measurement. And the output W (10 second output) which becomes a predetermined cut voltage by the constant wattage discharge for 10 seconds from SOC60% from the approximate curve is calculated. According to such “10-second output (25 ° C.)”, the output characteristics at a high rate can be known.
- FIG. 8 shows the relationship between the voltage drop of the constant watt discharge obtained by the procedure 2 and the time for the 10 second output (25 ° C.).
- constant watt discharge is performed at a predetermined power determined in the range of 5 W to 50 W from the SOC of 60%.
- FIG. 8 shows typical examples of the relationship between the voltage drop and the time (second) for the constant watt discharge power in each of 10 W, 25 W, 35 W, and 50 W.
- 2.5V is set to a predetermined cut voltage.
- FIG. 9 shows an approximate curve in the procedure 3 and a 10-second output calculation method.
- the approximate curve shown in FIG. 9 has a graph with time (seconds) set on the horizontal axis and output (W) set on the vertical axis.
- required from FIG. 8 and the time (second) required for a voltage to fall to a cut voltage are plotted on the said graph.
- An approximate curve is drawn for the plot. Based on the approximate curve, the discharge output at the 10-second position on the horizontal axis of the graph of FIG. 9 is obtained as the 10-second output.
- Table 1 shows the results of obtaining the 10-second output for samples 1 to 8 of the evaluation cell, and the ratio when the 10-second output value of sample 1 is 100% is expressed as “10-second output comparison (%)”. Indicated. Among samples 1 to 8, the higher the numerical value, the higher the high-rate output characteristics.
- Samples 1 to 4 use the graphite material 1 as a negative electrode active material, which itself has a small average number of flexing cycles of 1.2 and a high average aspect ratio of 3.5.
- Table 1 the perpendicularity of the negative electrode active material when the negative electrode active material is rolled so that the negative electrode active material layer has a density of 1.2 g / cm 3 (sample 1) without orientation in the magnetic field.
- Example 1 the perpendicularity of the negative electrode active material when the negative electrode active material is rolled so that the negative electrode active material layer has a density of 1.2 g / cm 3 (sample 1) without orientation in the magnetic field.
- Sample 2 to Sample 4 are obtained by orienting the negative electrode active material in a magnetic field. From comparison between Sample 1 and Sample 2, it was confirmed that the perpendicularity and output characteristics of the graphite material 1 are greatly improved by being oriented in a magnetic field.
- Samples 5 to 7 use, as the negative electrode active material, the graphite material 2 having a characteristic form disclosed herein having an average number of bends of 2.7 and an average aspect ratio of 2. Then, rolling is performed so that the density of the active material layer is the same as that of Sample 2 to Sample 4. From comparison between Sample 1 and Sample 3, it was confirmed that the graphite material 2 is also improved in both perpendicularity and output characteristics by being oriented in a magnetic field.
- Sample 8 has a large average number of bends of 4.4. Therefore, graphite material 3 having a small average aspect ratio of 1.6 is used as the negative electrode active material. From comparison between Sample 2, Sample 5 and Sample 8, it can be seen that in the negative electrode active material layer, the graphite material as the negative electrode active material should have an average bend number of 3 or less and an average aspect ratio of 1.8 or more. It was.
- the density of the negative electrode active material is preferably 1.5 g / cm 3 or less.
- any of the lithium secondary batteries disclosed herein can be excellent in performance suitable for a battery mounted on a vehicle, a power source of a power storage system, and the like, particularly in input / output characteristics. Therefore, according to the present invention, for example, as shown in FIG. 7, any one of the lithium ion batteries 10 disclosed herein (which may be in the form of an assembled battery 100 to which a plurality of lithium ion batteries 10 are connected) is provided.
- a vehicle 1 can be provided.
- a vehicle for example, an automobile
- the lithium ion battery 10 as a power source typically, a hybrid vehicle, a plug-in hybrid vehicle, a fuel cell vehicle, or an electric vehicle
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Abstract
Description
また、特許文献2および3は、高率充放電における放電容量及びサイクル特性の向上を目的として、黒鉛粉末中に含まれる黒鉛粒子同士の(002)面を磁場中で同一方向に配向させた状態で、溶媒を除去して黒鉛粉末を結着材により固化成形することで、リチウム二次電池用の負極を製造することを開示している。
また、特許文献4では、急速充電特性、高率放電特性を向上させる目的で、磁場中で配向させる負極活物質として、平均粒子径が10~25μmで、かつ比表面積が1.0~5.0m2/gでの黒鉛粒子を用いることを開示している。
<正極>
正極は、典型的には、正極活物質と導電材とバインダとを含むペースト状の正極活物質層形成用組成物を正極集電体上に供給して正極活物質層を形成することで用意される。
正極集電体としては、従来よりリチウム二次電池用の電極集電体と同様、導電性の良好な金属または樹脂からなる導電性部材を用いることができる。例えば、アルミニウム、ニッケル、チタン、鉄等を主成分とする金属またはその合金等を好ましく用いることができる。より好ましくは、アルミニウムまたはアルミニウム合金である。正極集電体の形状については特に制限はなく、所望の二次電池の形状等に応じて様々なものを考慮することができる。例えば、棒状、板状、シート状、箔状、メッシュ状等の種々の形態のものであり得る。典型的には、アルミニウム箔が好適に用いられる。
Li(LiaMnxCoyNiz)O2
(前式中のa、x、y、zはa+x+y+z=1を満たす。)
で表わされるような、遷移金属元素を3種含むいわゆるLi過剰型の三元系リチウム過剰遷移金属酸化物や、一般式:
xLi[Li1/3Mn2/3]O2・(1-x)LiMeO2
(前式中、Meは1種または2種以上の遷移金属であり、xは0<x≦1を満たす。)
で表わされるような、いわゆる固溶型のリチウム過剰型遷移金属酸化物等であってもよい。
例えば、この溶媒として水性溶媒を用いる場合には、水に溶解する(水溶性の)ポリマー材料として、カルボキシメチルセルロース(CMC)、メチルセルロース(MC)、酢酸フタル酸セルロース(CAP)、ヒドロキシプロピルメチルセルロース(HPMC)等のセルロース系ポリマー;ポリビニルアルコール(PVA);等が例示される。また、水に分散する(水分散性の)ポリマー材料としては、ポリエチレン(PE)、ポリプロピレン(PP)等のビニル系重合体;ポリエチレンオキサイド(PEO)、ポリテトラフルオロエチレン(PTFE)、テトラフルオロエチレン-ヘキサフルオロプロピレン共重合体(FEP)、テトラフルオロエチレン-パーフルオロアルキルビニルエーテル共重含体(PFA)等のフッ素系樹脂;酢酸ビニル共重合体;スチレンブタジエンゴム(SBR)、アクリル酸変性SBR樹脂(SBR系ラテックス)等のゴム類等が例示される。
なお、バインダとして例示したポリマー材料は、バインダとしての機能の他に、正極活物質層を形成するために調製する正極活物質層形成用ペースト(以下、単にペーストという場合もある)の増粘剤その他の添加剤としての機能を発揮する目的で使用されることもあり得る。
なお、上記の正極の製造に用いる溶媒としては、水性溶媒および非水溶媒の何れも使用可能である。水性溶媒としては、水または水を主体とする混合溶媒(水系溶媒)を用いた組成物が例示される。混合溶媒を構成する水以外の溶媒としては、水と均一に混合し得る有機溶媒(低級アルコール、低級ケトン等)の一種又は二種以上を適宜選択して用いることができる。非水溶媒の好適な例としては、N-メチル-2-ピロリドン(NMP)が挙げられる。
負極は、典型的には、負極活物質とバインダと、必要に応じて導電材とを含むペースト状の負極活物質層形成用組成物を負極集電体上に供給して負極活物質層を形成することで用意される。
負極集電体としては、従来よりリチウム二次電池用の負極集電体と同様、導電性の良好な金属または樹脂等からなる導電性部材を用いることができる。例えば、銅、ニッケル、チタン、ステンレス鋼等を主体とする棒状体、板状体、箔状体、網状体等を用いることができる。他にも、例えば、負極集電体としては、ポリプロピレンフィルムに銅を蒸着させたフィルム材等を用いることができる。
ここで、本発明における負極活物質層に含まれる負極活物質は、以下の特徴を有するものとして定義される。すなわち、(1)一粒子あたりの平均屈曲数fが0<f≦3で、(2)平均アスペクト比が1.8以上である屈曲された層状黒鉛によって構成されており、かつ、(3)上記負極集電体の表面に対する上記負極活物質の長径のなす角をθnとし、0°≦θn≦30°である前記負極活物質の数をn1、60°≦θn≦90°以下である前記負極活物質の数をn2としたとき、n2/n1で定義される垂直度が1以上となるように配向されている。
ここで、平均屈曲数fとは、層状黒鉛1粒子あたりの30°以上(内角としては150°以下)で屈曲している点の数を平均した値として定義される。なお、屈曲とは、層状黒鉛のグラフェンシートがある線(折れ線)を境に明確に折れ曲がり、該折れ線を境にグラフェンシートの平面が30°以上の角度をなしている状態、ないしは、層状黒鉛のグラフェンシートが明確な線(折れ線)はないが湾曲し、この湾曲部分を挟むグラフェンシートの平面が30°以上の角度をなしている状態を含み得る。
また、平均アスペクト比は、層状黒鉛1粒子の長径/短径で表わされるアスペクト比を、30個以上の粒子について調べた平均値として定義される。この平均アスペクト比は、例えば、負極活物質層を任意の断面で切断し、該切断面を電子顕微鏡(例えば、SEM)などで観察することでも確認することができる。この場合の切断面は、厳密に限定されるものではないが、負極集電体の表面に垂直な断面であることが望ましい。また、平均アスペクト比の算出は、一断面の観察のみから行うこともできるが、複数の断面の観察により実施するのが好ましい。
かかる垂直度は、負極集電体の表面に対する上記負極活物質の長径のなす角をθnとする。そして、このθnが0°≦θn≦30°以下である負極活物質の数をn1、またこのθnが60°≦θn≦90°である前記負極活物質の数をn2とする。ここで、n1は、負極集電体に対して比較的寝ている黒鉛粒子の数である。また、n2は、負極集電体に対して比較的立っている層状黒鉛の数である。そしてここで、垂直度をn2/n1として定義する。
この垂直度は大きい方が好ましく、ここに開示される発明においては、1.0以上に規定している。好ましくは1.1以上であり、例えば1.5以上、より好ましくは2.0以上、さらに限定的には3.0以上であるのが望ましい。
また、導電材の使用量は、負極活物質100質量部に対しておよそ1~30質量部(好ましくは、およそ2~20質量部、例えば5~10質量部程度)とすることができる。また、負極活物質100質量部に対するバインダの使用量は、例えば0.5~10質量部とすることができる。
非水電解質としては、従来のリチウム二次電池に用いられる非水電解質と同様の一種または二種以上のものを特に限定なく使用することができる。かかる非水電解質は、典型的には、適当な非水溶媒に電解質(即ち、リチウム塩)を含有させたものであり得る。電解質濃度は特に制限されないが、電解質をおよそ0.1mol/L~5mol/L(好ましくは、およそ0.8mol/L~1.5mol/L)程度の濃度で含有する非水電解液を好ましく用いることができる。また、かかる液状電解液にポリマーが添加された固体状(ゲル状)の電解液であってもよい。
また、電解質としては、例えばLiPF6、LiBF4、LiN(SO2CF3)2、LiN(SO2C2F5)2、LiCF3SO3、LiC4F9SO3、LiC(SO2CF3)3、LiClO4等が例示される。
以下、ここに開示されるリチウム二次電池の一形態を図面を参照しつつ説明する。この実施形態では、角型形状のリチウム二次電池について説明するが、本発明をかかる実施形態に限定することを意図したものではない。また、本明細書において特に言及している事項以外の事柄であって本発明の実施に必要な事柄(例えば、正極および負極を備えた電極体の構成および製造方法、セパレータや電解質の構成および製造方法、リチウム二次電池その他の電池の構築に係る一般的技術等)は、当該分野における従来技術に基づく当業者の設計事項として把握され得る。なお、以下の図面において、同じ作用を奏する部材・部位には同じ符号を付し、重複する説明は省略又は簡略化することがある。また、各図における寸法関係(長さ、幅、厚さ等)は実際の寸法関係を反映するものではない。
[負極の用意]
非晶質でコーティングした鱗片状の天然黒鉛を屈曲加工し、以下に示す形態の黒鉛材料1~3を得た。
黒鉛材料1:平均屈曲数1.2、平均アスペクト比3.5
黒鉛材料2:平均屈曲数2.7、平均アスペクト比2.0
黒鉛材料3:平均屈曲数4.4、平均アスペクト比1.6
上記黒鉛材料1を負極活物質として用い、負極活物質100質量部に対して、バインダとしてのスチレンブタジエンゴム(SBR)1質量部、増粘剤としてのカルボキシメチルセルロース(CMC)1質量部の割合で配合し、これらを溶媒としてのN‐メチルピロリドン(NMP)に分散、混合して負極活物質層形成用のペーストを調製した。
得られた負極活物質層形成用のペーストを、集電体としての厚さ5μmのCu箔の片面に所定の目付量で塗布し、磁場を印加することなく乾燥させ、次いで、密度が1.2g/cm3となるように圧延して、負極シート(負極サンプル1)を作製した。
この負極サンプル1を負極集電体の表面に対して垂直な断面において切り出し、その断面から、負極活物質の垂直度を調べた。その結果、垂直度は0.5であった。
集電体の表面に垂直な方向に0.5Tの磁場を印加しながら乾燥させたこと以外は、負極サンプル1と同様にして負極シート(負極サンプル2)を作製した。
この負極サンプル2を負極集電体の表面に対して垂直な断面において切り出し、その断面から、負極活物質の垂直度を調べた。その結果、垂直度は2.3であった。
集電体の表面に垂直な方向に0.5Tの磁場を印加しながら乾燥させた後、密度が1.4g/cm3となるように圧延し、他は負極サンプル1と同様にして負極シート(負極サンプル3)を作製した。
この負極サンプル3を負極集電体の表面に対して垂直な断面において切り出し、その断面から、負極活物質の垂直度を調べた。その結果、垂直度は1.3であった。
集電体の表面に垂直な方向に0.5Tの磁場を印加しながら乾燥させた後、密度が1.6g/cm3となるように圧延し、他は負極サンプル1と同様にして負極シート(負極サンプル4)を作製した。
この負極サンプル4を負極集電体の表面に対して垂直な断面において切り出し、その断面から、負極活物質の垂直度を調べた。その結果、垂直度は0.2であった。
黒鉛材料1に替えて黒鉛材料2を負極活物質として用い、集電体の表面に垂直な方向に0.5Tの磁場を印加しながら乾燥させ、他は負極サンプル1と同様にして負極シート(負極サンプル5)を作製した。
この負極サンプル5を負極集電体の表面に対して垂直な断面において切り出し、その断面から、負極活物質の垂直度を調べた。その結果、垂直度は1.8であった。
黒鉛材料1に替えて黒鉛材料2を負極活物質として用い、集電体の表面に垂直な方向に0.5Tの磁場を印加しながら乾燥させた後、密度が1.4g/cm3となるように圧延し、他は負極サンプル1と同様にして負極シート(負極サンプル6)を作製した。
この負極サンプル6を負極集電体の表面に対して垂直な断面において切り出し、その断面から、負極活物質の垂直度を調べた。その結果、垂直度は1.1であった。
黒鉛材料1に替えて黒鉛材料2を負極活物質として用い、集電体の表面に垂直な方向に0.5Tの磁場を印加しながら乾燥させた後、密度が1.6g/cm3となるように圧延し、他は負極サンプル1と同様にして負極シート(負極サンプル7)を作製した。
この負極サンプル7を負極集電体の表面に対して垂直な断面において切り出し、その断面から、負極活物質の垂直度を調べた。その結果、垂直度は0.5であった。
黒鉛材料1に替えて黒鉛材料3を負極活物質として用い、集電体の表面に垂直な方向に0.5Tの磁場を印加しながら乾燥させた後、密度が1.2g/cm3となるように圧延し、他は負極サンプル1と同様にして負極シート(負極サンプル8)を作製した。
この負極サンプル8を負極集電体の表面に対して垂直な断面において切り出し、その断面から、負極活物質の垂直度を調べた。その結果、垂直度は1.2であった。
正極活物質としてのリチウム遷移金属複合酸化物(LiNi1/3Co1/3Mn1/3O2)と、導電材としてのAB(アセチレンブラック)と、バインダとしてのPVdF(ポリフッ化ビニリデン)とを、これらの材料の質量比が100:5:5となるように配合し、溶媒としてのN‐メチルピロリドン(NMP)中で混合して正極用ペーストを調製した。この正極用ペーストを集電体としての厚さ5μmのAl箔の片面に所定の目付量で塗布し、乾燥させた後、全体の厚みが100μmとなるようにプレスして正極(正極シート)を作製した。
セパレータとしては、ポリプロピレン(PP)/ポリエチレン(PE)/ポリプロピレン(PP)からなる厚さ20μmの三層構造の多孔質フィルムを用いた。
[電解液]
非水電解液としては、エチレンカーボネート(EC)とジメチルカーボネート(DMC)とエチルメチルカーボネート(EMC)とを3:4:3の体積比で含む混合溶媒に、支持塩としてのLiPF6を約1mol/リットルの濃度で含有させた非水電解液を使用した。
上記で作製した正極シートと、負極サンプル1~8とを用いて試験用のラミネートセル(リチウムイオン電池)を構築した。すなわち、セパレータを間に介して、正極シート(寸法約23mm×23mm)と負極シート(寸法約25mm×25mm)とを、両電極シートの互いの活物質層が対向するように積層して電極体を作製した。
この電極体を非水電解液とともにラミネート製の袋状電池容器に収容し、封口して評価用セル(リチウムイオン電池)サンプル1~8を構築した。
10秒出力(25℃)を、以下の手順によって求めた。なお、この実施形態では、測定の温度環境を常温(ここでは、25℃)とした。
手順1:SOC調整として、1C定電流充電によってSOC60%とし、SOC60%にて定電圧充電を2.5時間行い、10秒間休止させる。
手順2:上記手順1の後、SOC60%から定ワット(W)(定出力)にて放電する。定ワット放電では、放電により電圧が低下するにしたがって電流を多く流して、時間あたりに同じ電力量を放電する。そして、SOC60%の状態から放電する電圧が所定のカット電圧になるまでの秒数を測定する。
手順3:手順2において、5W~50Wの範囲で定ワット放電の条件を変えつつ、手順1と手順2を繰り返す(図8参照)。そして、それぞれ測定された所定のカット電圧までの秒数を横軸に取り、縦軸に当該測定時の定ワット放電の電力(W)の条件を取る。そして、近似曲線よりSOC60%から10秒間の定ワット放電で所定のカット電圧になる出力W(10秒出力)を算出する。
かかる「10秒出力(25℃)」によれば、ハイレートでの出力特性を知ることができる。
ここでは、例えば、図8に示すように、SOC60%の状態から5W~50Wの範囲で定めた所定の電力で定ワット放電を行なう。定ワット放電の電力は、図8では、10W、25W、35W、50Wのそれぞれの電力について、電圧降下と時間(秒)の関係に関する典型的な例を示している。ここでは、2.5Vを所定のカット電圧に設定している。そして、図8において示されるように、10W、25W、35W、50Wのそれぞれの定ワット放電での電圧降下と時間(秒)の関係を基に、定ワット放電の放電出力(W)毎に、電圧がカット電圧に降下するまでの時間(秒)を測定する。
表1には、評価用セルのサンプル1~8について、10秒出力を求めた結果を、サンプル1の10秒出力値を100%としたときの割合を「10秒出力比較(%)」として示した。サンプル1~8のうち、数値が高いほどハイレート出力特性が高い電池となる。
10 リチウム二次電池
20 捲回電極体
30 正極シート(正極)
32 正極集電体
33 未塗工部
34 正極活物質層
38 バインダ
40 正極端子
41 内部正極端子
50 負極シート(負極)
52 負極集電体
53 未塗工部
54 負極活物質層
60 負極端子
61 内部負極端子
70 セパレータ
80 電池ケース
82 蓋体
84 ケース本体
86 注入孔
100 組電池
WL 捲回軸
Claims (6)
- 正極集電体上に正極活物質層を備える正極と、負極集電体上に負極活物質層を備える負極とを備える二次電池であって、
前記正極活物質層は、リチウムイオンを可逆的に吸蔵および放出可能な正極活物質を含み、
前記負極活物質層に含まれる負極活物質は、
一粒子あたりの平均屈曲数fが0<f≦3で、平均アスペクト比が1.8以上である屈曲された層状黒鉛によって構成されており、かつ、
前記負極集電体の表面に対する前記負極活物質の長径のなす角をθnとし、
0°≦θn≦30°である前記負極活物質の数をn1、
60°≦θn≦90°である前記負極活物質の数をn2としたとき、
n2/n1で定義される垂直度が1.0以上となるように配向されている、リチウム二次電池。 - 前記負極活物質層の密度は、1.5g/cm3以下である、請求項1に記載のリチウム二次電池。
- 前記層状黒鉛が、表面の少なくとも一部を非晶質炭素でコーティングされている、請求項1または2に記載のリチウム二次電池。
- 前記平均屈曲数fが、0<f≦2である、請求項1~3のいずれか1項に記載のリチウム二次電池。
- 駆動用モータを備える自動車における前記モータの駆動用電源である、請求項1~4のいずれか1項に記載のリチウム二次電池。
- 請求項5に記載されたリチウム二次電池を備える、車両。
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JP2018156777A (ja) * | 2017-03-16 | 2018-10-04 | エリーパワー株式会社 | 密閉型電池、組電池及びエンジン始動用電池 |
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CN114556618B (zh) * | 2019-10-23 | 2024-03-01 | Tdk株式会社 | 全固体电池 |
JP7414758B2 (ja) * | 2021-03-12 | 2024-01-16 | プライムプラネットエナジー&ソリューションズ株式会社 | 二次電池用電極およびそれを備える二次電池 |
KR20230045245A (ko) * | 2021-09-28 | 2023-04-04 | 에스케이온 주식회사 | 이차전지용 다층 전극 및 이의 제조방법 |
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US11322773B2 (en) | 2016-03-10 | 2022-05-03 | Nec Corporation | Lithium secondary battery |
JP2018156777A (ja) * | 2017-03-16 | 2018-10-04 | エリーパワー株式会社 | 密閉型電池、組電池及びエンジン始動用電池 |
Also Published As
Publication number | Publication date |
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CN104011906B (zh) | 2016-07-20 |
KR101572405B1 (ko) | 2015-11-26 |
JPWO2013094037A1 (ja) | 2015-04-27 |
US9312568B2 (en) | 2016-04-12 |
US20140349189A1 (en) | 2014-11-27 |
KR20140105831A (ko) | 2014-09-02 |
JP5828347B2 (ja) | 2015-12-02 |
CN104011906A (zh) | 2014-08-27 |
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