WO2015136591A1 - 第1正極活物質及び第2正極活物質を有する正極活物質層、並びに該正極活物質層を具備する正極の製造方法 - Google Patents
第1正極活物質及び第2正極活物質を有する正極活物質層、並びに該正極活物質層を具備する正極の製造方法 Download PDFInfo
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- H01M4/36—Selection of substances as active materials, active masses, active liquids
- H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
- H01M4/50—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese
- H01M4/505—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese of mixed oxides or hydroxides containing manganese for inserting or intercalating light metals, e.g. LiMn2O4 or LiMn2OxFy
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- H01M4/36—Selection of substances as active materials, active masses, active liquids
- H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
- H01M4/52—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron
- H01M4/525—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron of mixed oxides or hydroxides containing iron, cobalt or nickel for inserting or intercalating light metals, e.g. LiNiO2, LiCoO2 or LiCoOxFy
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- 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
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- H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
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- H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
- H01M2004/028—Positive electrodes
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- H01M4/04—Processes of manufacture in general
- H01M4/043—Processes of manufacture in general involving compressing or compaction
- H01M4/0433—Molding
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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
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- 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
Definitions
- the present invention relates to a positive electrode active material layer having a first positive electrode active material and a second positive electrode active material, and a method for producing a positive electrode comprising the positive electrode active material layer.
- Patent Documents 1 and 2 specifically disclose lithium ion secondary batteries that employ LiNi 1/3 Co 1/3 Mn 1/3 O 2 and LiFePO 4 as positive electrode active materials.
- Patent Document 3 specifically discloses a lithium ion secondary battery employing LiNi 0.8 Co 0.1 Mn 0.1 O 2 and LiV 2/3 PO 4 as a positive electrode active material.
- LiNi 1/3 Co 1/3 Mn 1/3 O 2 or LiNi 0.8 Co 0.1 Mn 0.1 O 2 is a positive electrode active material having a high capacity
- LiFePO 4 Alternatively, it is disclosed that LiV 2/3 PO 4 is a positive electrode active material excellent in safety.
- the mixture ratio of two types of positive electrode active materials is prescribed
- LiNi 5/10 Co 2/10 Mn 3/10 O 2 and LiFePO 4 are selected as the two active materials, and a positive electrode active material layer containing these active materials in the same mass is manufactured.
- the true density of LiNi 5/10 Co 2/10 Mn 3/10 O 2 is 4.8 g / cm 3
- the true density of LiFePO 4 is 3.6 g / cm 3
- an example of the tap density of LiNi 5/10 Co 2/10 Mn 3/10 O 2 is 2.2 g / cm 3
- an example of the tap density of LiFePO 4 is 0.8 g / cm 3.
- the volume ratio of the active material in the positive electrode active material layer containing these active materials in the same mass is actually 2.75: 1.
- a tap density changes greatly with differences in a manufacturing method, a lot, an average particle diameter, etc.
- the actual volume occupied by each active material in the positive electrode active material layer is the production method, lot, and average particle of the selected active material. Depending on the difference in diameter, etc., it will be significantly different.
- the present inventor considers the safety at the time of short-circuiting of the secondary battery by evaluating how much the volume of the substance that plays a role of positive electrode discharge actually occupies the positive electrode active material layer. I thought it would be the key to this.
- the blending ratio of the two types of positive electrode active materials is usually defined only by mass, and the volume of the active material has not been considered.
- the present invention has been made in view of such circumstances, and in order to produce a positive electrode active material layer and a positive electrode having excellent safety, a new parameter is proposed, and a positive electrode active material layer that satisfies the parameter, and It aims at providing the manufacturing method of the positive electrode which comprises this positive electrode active material layer.
- the present inventor considered factors related to safety in the positive electrode active material layer having the first positive electrode active material and the second positive electrode active material.
- the inventor has calculated the positive electrode active material tap density, the positive electrode active material blending amount, the tap density and the blending amount as factors of the positive electrode active material layer exhibiting excellent safety.
- the actual volume of the positive electrode active material, the porosity of the positive electrode active material layer, and the positive electrode active material layer occupancy of the first positive electrode active material calculated from these values are given, and the positive electrode active material of the first positive electrode active material It has been found that there is a certain relationship between layer occupancy and battery safety.
- the positive electrode active material layer of the present invention is A positive electrode active material layer having a first positive electrode active material, a second positive electrode active material having a lower charge / discharge potential than the first positive electrode active material, and an additive;
- the tap density of the first positive electrode active material is dt 1
- the tap density of the second positive electrode active material is dt 2
- the true density of the additive is d 3
- the mass% of the first positive electrode active material is Wt 1
- the mass% of the second positive electrode active material is Wt 2
- the mass% of the additive is Wt 3
- the porosity in the positive electrode active material layer is p, (1-p) ⁇ (Wt 1 / dt 1 ) / ((Wt 1 / dt 1 ) + (Wt 2 / dt 2 ) + (Wt 3 / d 3 )) ⁇ 0.38 To do.
- the method for producing the positive electrode of the present invention comprising the positive electrode active material layer of the present invention, a) a step of producing a dispersion by mixing a first positive electrode active material, a second positive electrode active material having a lower charge / discharge potential than the first positive electrode active material, an additive and a solvent; b) applying the dispersion to a current collector and removing the solvent contained in the dispersion to form a positive electrode active material layer; c) The tap density of the first positive electrode active material is dt 1 , the tap density of the second positive electrode active material is dt 2 , and the true density of the additive is d 3 , In the positive electrode active material layer, the mass% of the first positive electrode active material is Wt 1 , the mass% of the second positive electrode active material is Wt 2 , and the mass% of the additive is Wt 3 , D) When the porosity in the positive electrode active material layer after the step is p, (1 ⁇ p) ⁇ (Wt 1 / dt
- the lithium ion secondary battery including the positive electrode active material layer of the present invention can suppress the increase in the surface temperature to a certain extent even when the positive electrode and the negative electrode are short-circuited.
- the numerical range “x to y” described in this specification includes the lower limit x and the upper limit y.
- the numerical range can be configured by arbitrarily combining these upper limit value and lower limit value and the numerical values listed in the examples.
- numerical values arbitrarily selected from the numerical value range can be used as upper and lower numerical values.
- the positive electrode active material layer of the present invention is A positive electrode active material layer having a first positive electrode active material, a second positive electrode active material having a lower charge / discharge potential than the first positive electrode active material, and an additive;
- the tap density of the first positive electrode active material is dt 1
- the tap density of the second positive electrode active material is dt 2
- the true density of the additive is d 3
- the mass% of the first positive electrode active material is Wt 1
- the mass% of the second positive electrode active material is Wt 2
- the mass% of the additive is Wt 3
- the porosity in the positive electrode active material layer is p
- a 1st positive electrode active material is a material which functions as a positive electrode active material of a lithium ion secondary battery.
- As a 1st positive electrode active material what is necessary is just to employ
- 0 ⁇ b ⁇ 1, 0 ⁇ c ⁇ 1, 0 ⁇ d ⁇ 1, and at least one of b, c, d is 0 ⁇ b ⁇ 80 /
- the ranges are 100, 0 ⁇ c ⁇ 70/100, 10/100 ⁇ d ⁇ 1, 10/100 ⁇ b ⁇ 68/100, 12/100 ⁇ c ⁇ 60/100, 20/100 ⁇ d.
- ⁇ 68/100 is more preferable, 25/100 ⁇ b ⁇ 60/100, 15/10 ⁇ C ⁇ 50/100, 25/100 ⁇ d ⁇ 60/100 are more preferable, and 1/3 ⁇ b ⁇ 50/100, 20/100 ⁇ c ⁇ 1/3, 30/100 ⁇ d.
- a is preferably in the range of 0.5 ⁇ a ⁇ 1.5, more preferably in the range of 0.7 ⁇ a ⁇ 1.3, still more preferably in the range of 0.9 ⁇ a ⁇ 1.2, A range of 1 ⁇ a ⁇ 1.1 is particularly preferable.
- the shape of the first positive electrode active material is not particularly limited, but is preferably 100 ⁇ m or less, more preferably 0.1 ⁇ m or more and 50 ⁇ m or less in terms of average particle diameter. If the thickness is less than 0.1 ⁇ m, there may be a problem that, when the electrode is manufactured, the adhesion to the current collector is easily impaired. If it exceeds 100 ⁇ m, the size of the electrode may be affected, or the separator constituting the secondary battery may be damaged.
- the average particle diameter in this specification means the value of D50 at the time of measuring with a general laser diffraction type particle size distribution measuring apparatus.
- the second positive electrode active material is a material that can function as the positive electrode active material of the lithium ion secondary battery and has a lower charge / discharge potential than the first positive electrode active material.
- the first positive electrode active material is NCM
- the second positive electrode active material specifically, a general formula: LiM h PO 4 (M is Mn, Fe, Co, Ni, Cu, Mg, Zn, V, Examples thereof include at least one element selected from Ca, Sr, Ba, Ti, Al, Si, B, Te and Mo, and a material represented by 0 ⁇ h ⁇ 2).
- the charge / discharge potential of the second positive electrode active material is lower than the charge / discharge potential of the first positive electrode active material. Plays the role of charge and discharge of the positive electrode.
- the second positive electrode active material is present in the positive electrode active material layer of the lithium ion secondary battery, heat generation of the battery can be suppressed to some extent even when the positive electrode and negative electrode of the battery are short-circuited.
- the second positive electrode active material examples include LiFePO 4 , LiMnPO 4 , LiVPO 4 , LiNiPO 4 , LiCoPO 4 , LiTePO 4 , LiV 2/3 PO 4 , LiFe 2/3 PO 4 , LiMn 7/8 Fe 1. / 8 PO 4 can be mentioned.
- LiFePO 4 is particularly preferable. The reason is as follows. LiFePO 4 exhibits a relatively flat discharge curve during discharge. Then, even if the positive electrode and the negative electrode of the lithium ion secondary battery are short-circuited and a sudden discharge occurs, a sudden potential difference associated with the discharge does not occur at the location where LiFePO 4 exists. Therefore, it is difficult to induce charge transfer from other parts in the electrode, and the occurrence of overcurrent can be suppressed. As a result, the heat generation of the secondary battery can be suitably suppressed.
- the shape of the second positive electrode active material is not particularly limited, but is preferably 100 ⁇ m or less, more preferably 0.01 ⁇ m or more and 10 ⁇ m or less in terms of average particle diameter.
- the second positive electrode active material it is preferable to employ a carbon coated surface.
- the average particle diameter of the second positive electrode active material is preferably smaller than the average particle diameter of the first positive electrode active material.
- the blending amount of the first positive electrode active material and the second positive electrode active material in the positive electrode active material layer may be a value that satisfies the parameters of the present invention.
- the blending mass ratio of the first positive electrode active material and the second positive electrode active material in the positive electrode active material layer of the present invention is preferably in the range of 95: 5 to 50:50, and in the range of 85:15 to 55:45. Is more preferably within a range of 75:25 to 60:40, and particularly preferably within a range of 72:28 to 65:35.
- the total amount of the first positive electrode active material and the second positive electrode active material in the positive electrode active material layer of the present invention is given, it is preferably in the range of 50 to 99% by mass, and in the range of 60 to 98% by mass. A more preferred range is 70 to 97% by mass.
- additives examples include a conductive aid, a binder, and a dispersant.
- Conductive aid is added to increase the conductivity of the electrode. Therefore, the conductive auxiliary agent may be added arbitrarily when the electrode conductivity is insufficient, and may not be added when the electrode conductivity is sufficiently excellent.
- the conductive auxiliary agent may be any chemically inert electronic high conductor, such as carbon black, graphite, acetylene black, ketjen black (registered trademark), or vapor grown carbon fiber (Vapor Grown Carbon). Fiber: VGCF) and various metal particles are exemplified. These conductive assistants can be added to the positive electrode active material layer alone or in combination of two or more.
- the shape of the conductive auxiliary agent is not particularly limited, but it is preferable that the average particle diameter is small in view of its role.
- a preferable average particle diameter of the conductive auxiliary agent is preferably 10 ⁇ m or less, and more preferably in the range of 0.01 to 1 ⁇ m.
- the blending amount of the conductive aid may be a value that satisfies the parameters of the present invention.
- the blending amount of the conductive additive in the positive electrode active material layer of the present invention is given, it is preferably in the range of 0.5 to 10% by mass, more preferably in the range of 1 to 7% by mass, and 2 to 5% by mass. Within the range is particularly preferred.
- the binder serves to bind the positive electrode active material and the conductive additive to the surface of the current collector.
- the binder include fluorine-containing resins such as polyvinylidene fluoride, polytetrafluoroethylene, and fluororubber, thermoplastic resins such as polypropylene and polyethylene, imide resins such as polyimide and polyamideimide, and alkoxysilyl group-containing resins. be able to.
- hydrophilic group of the polymer having a hydrophilic group examples include a carboxyl group, a sulfo group, a silanol group, an amino group, a hydroxyl group, and a phosphate group.
- Specific examples of the polymer having a hydrophilic group include polyacrylic acid, carboxymethylcellulose, polymethacrylic acid, and poly (p-styrenesulfonic acid).
- the blending amount of the binder may be a value that satisfies the parameters of the present invention.
- the amount of the binder in the positive electrode active material layer of the present invention is preferably in the range of 0.5 to 10% by mass, more preferably in the range of 1 to 7% by mass, and 2 to 5% by mass. Within the range is particularly preferred. If the blending amount of the binder is too small, the moldability of the layer may be lowered when the composition is used as a positive electrode active material layer. Moreover, when there are too many compounding quantities of a binder, since the quantity of the positive electrode active material in a positive electrode active material layer reduces, it is unpreferable.
- additives such as a dispersing agent other than the conductive auxiliary agent and the binder, known ones can be employed, and they may be blended in the positive electrode active material layer so as to satisfy the parameters of the present invention.
- the parameters of the present invention will be described.
- the parameters of the present invention are (1 ⁇ p) ⁇ (Wt 1 / dt 1 ) / ((Wt 1 / dt 1 ) + (Wt 2 / dt 2 ) + (Wt 3 / d 3 )) ⁇ 0.38. is there.
- p means the porosity in the positive electrode active material layer
- (1-p) means the rate of solids in the positive electrode active material layer.
- p (Vr ⁇ Vt) / Vr.
- dt 1 means the tap density of the first positive electrode active material and Wt 1 means mass% of the first positive electrode active material in the positive electrode active material layer
- Wt 1 / dt 1 It means the actual volume% of the first positive electrode active material.
- Wt 2 / dt 2 means the actual volume% of the second positive electrode active material in the positive electrode active material layer.
- the tap density in this specification means “tap bulk density” defined by the bulk density measurement method of JIS R 1628 fine ceramic powder, and the measurement method is a constant mass measurement method.
- d 3 means the true density of the additive and Wt 3 means mass% of the additive
- (Wt 3 / d 3 ) means volume% of the additive in the positive electrode active material layer.
- the reason why the true density is used instead of the tap density is as follows. First, a binder that is widely used as an additive is not in a solid state because it is dissolved in a solvent in a dispersion for producing a positive electrode active material layer. And, since the state of the binder in the positive electrode active material layer produced by removing the solvent from the dispersion is not the same as the state of the binder before dissolving in the solvent, the parameter of the present invention can be dissolved in the solvent. There is no significance in adopting the tap density of the previous binder.
- a conductive auxiliary agent that is widely used as an additive usually has an average particle size that is significantly smaller than that of the first positive electrode active material or the second positive electrode active material, and that there is no significant difference between the tap density and the true density. Is done.
- the additive is usually a minor component in the positive electrode active material layer, if there is a significant difference between the tap density and the true density of the conductive assistant, or a significant difference in the tap density between the same conductive assistants. Even if this occurs, it is assumed that no particular problem is assumed in the actual manufacturing site, and that the parameters of the present invention do not have any particular influence on the safety of the battery to be expressed.
- (Wt 3 / d 3 ) is fractionated by the number of additives.
- the mass% of the first additive is Wt 3-1
- the true density is d 3-1
- the mass% of the additive is Wt 3-2
- the true density is d 3-2
- the parameter of the present invention is (Wt 3 / d 3 ) ((Wt 3-1 / d 3-1 ) + (Wt 3 -2 / d 3-2 )).
- (Wt 3 / d 3 ) may be deleted from the parameters of the present invention.
- (1-p) ⁇ (Wt 1 / dt 1 ) / ((Wt 1 / dt 1 ) + (Wt 2 / dt 2 ) + (Wt 3 / d 3 )) is the positive electrode active material layer Of the first positive electrode active material among the solid materials in FIG. 1 (hereinafter referred to as “occupation rate or approximate occupation rate of the first positive electrode active material out of the solid materials in the positive electrode active material layer”) It may be called “rate”.)
- the occupation ratio is less than 0.38, preferably less than 0.37, and more preferably less than 0.36.
- the lower limit value of the occupation ratio may be a numerical value exceeding 0.
- the occupancy rate is preferably 0.10 or higher, more preferably 0.20 or higher, further preferably 0.30 or higher, 0 .32 or more is particularly preferable.
- Wt 1 is equal to (1-p) ⁇ (Wt 1 / dt 1 ) / ((Wt 1 / dt 1 ) + (Wt 2 / dt 2 ) + (Wt 3 / d 3 )). It was defined as mass% of the first positive electrode active material in the positive electrode active material layer.
- Wt 1 , Wt 2 , and Wt 3 may be substituted for the parameters of the present invention.
- the manufacturing method of the positive electrode of this invention which comprises the positive electrode active material layer of this invention is demonstrated.
- the method for producing the positive electrode of the present invention includes: a) A step of producing a dispersion by mixing a first positive electrode active material, a second positive electrode active material having a charge / discharge potential lower than that of the first positive electrode active material, an additive and a solvent (hereinafter referred to as “step a”). Sometimes. ), b) The dispersion is applied to a current collector, and the solvent contained in the dispersion is removed to form a positive electrode active material layer (hereinafter referred to as “b) step”.
- the tap density of the first positive electrode active material is dt 1
- the tap density of the second positive electrode active material is dt 2
- the true density of the additive is d 3
- the mass% of the first positive electrode active material is Wt 1
- the mass% of the second positive electrode active material is Wt 2
- the mass% of the additive is Wt 3
- D) When the porosity in the positive electrode active material layer after the step is p, (1 ⁇ p) ⁇ (Wt 1 / dt 1 ) / ((Wt 1 / dt 1 ) + (Wt 2 / dt 2 ) + (Wt 3 / d 3 )) ⁇ 0.38 so as to satisfy p
- Step a) is a step of producing a dispersion by mixing the first positive electrode active material, the second positive electrode active material having a lower charge / discharge potential than the first positive electrode active material, the additive, and the solvent.
- the solvent examples include N-methyl-2-pyrrolidone (hereinafter sometimes abbreviated as “NMP”), dimethylformamide, dimethylacetamide, methanol, acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, methyl acetate, acetic acid. Examples thereof include ethyl and tetrahydrofuran. These solvents may be used alone or in combination of two or more.
- the dispersion liquid of a) process consists of solid content other than a solvent and a solvent.
- Solid content other than a solvent means additives, such as a 1st positive electrode active material, a 2nd positive electrode active material, and a binder used as needed, a conductive support agent, and a dispersing agent.
- the solid content other than the solvent is preferably in the range of 30 to 90% by mass, more preferably in the range of 50 to 80% by mass, particularly in the range of 60 to 70% by mass. preferable.
- each component may be added simultaneously or sequentially and mixed with a mixing device.
- Examples of the mixing device include a mixing stirrer, a ball mill, a sand mill, a bead mill, a disperser, an ultrasonic disperser, a homogenizer, a homomixer, a planetary mixer, and a planetary stirring and defoaming device.
- Specific mixing devices include trade name Disper Mixer (Primics Co., Ltd.), trade name Claremix (M Technique Co., Ltd.), trade name Filmix (Primics Co., Ltd.), trade name Paint Conditioner (Red Devil Corporation), Product name DYNO-MILL (Shinmaru Enterprises Co., Ltd.), product name Eirich Intensive Mixer (Japan Eirich Co., Ltd.), product name defoaming machine DP-200 (M Technique Co., Ltd.), product name Awatori Neritaro (stock) Company Thinkey). What is necessary is just to set the mixing speed in a mixing apparatus suitably the speed
- Step b) is a step of forming a positive electrode active material layer by applying the dispersion liquid produced in step a) to a current collector and removing the solvent contained in the dispersion liquid.
- a current collector refers to a chemically inert electronic high conductor that keeps a current flowing through an electrode during discharge or charging of a lithium ion secondary battery.
- the current collector at least one selected from silver, copper, gold, aluminum, magnesium, tungsten, cobalt, zinc, nickel, iron, platinum, tin, indium, titanium, ruthenium, tantalum, chromium, molybdenum, and stainless steel Examples of such a metal material can be given.
- the current collector may be covered with a known protective layer.
- the current collector can take the form of a foil, a sheet, a film, a line, a bar, or the like. Therefore, metal foils, such as copper foil, nickel foil, aluminum foil, stainless steel foil, can be used suitably as a collector.
- the thickness is preferably in the range of 10 ⁇ m to 100 ⁇ m.
- Specific methods for applying the dispersion liquid to the current collector include conventionally known methods such as a roll coating method, a dip coating method, a doctor blade method, a spray coating method, and a curtain coating method.
- a specific method for removing the solvent contained in the dispersion liquid there is a method of drying the dispersion liquid under a heating condition and / or a reduced pressure condition and removing the solvent contained in the dispersion liquid as a gas. it can.
- the step comprises setting the tap density of the first positive electrode active material to dt 1 , the tap density of the second positive electrode active material to dt 2 , and the true density of the additive to d 3 ,
- the mass% of the first positive electrode active material is Wt 1
- the mass% of the second positive electrode active material is Wt 2
- the mass% of the additive is Wt 3
- D) When the porosity in the positive electrode active material layer after the step is p, (1 ⁇ p) ⁇ (Wt 1 / dt 1 ) / ((Wt 1 / dt 1 ) + (Wt 2 / dt 2 ) + (Wt 3 / d 3 )) ⁇ 0.38 so as to satisfy p
- the “compressed thickness” means a thickness dimension during compression when a compression pressure is applied by a compression device
- a conventionally known compressor may be used as the compression device.
- Specific examples of the compression device include a roll press, a vacuum press, a hydraulic press, and a hydraulic press.
- the porosity p is the sum of theoretical volumes of each component (Vt) calculated from the actual volume (Vr) of the manufactured positive electrode active material layer and the blending amount and true density of each component contained in the positive electrode active material layer. Is divided by the actual volume (Vr) of the produced positive electrode active material layer. Therefore, by controlling the height (thickness) of the positive electrode active material layer to be manufactured, a desired p positive electrode active material layer can be obtained. In this case, in step c), (1-p) ⁇ (Wt 1 / dt 1 ) / ((Wt 1 / dt 1 ) + (Wt 2 / dt 2 ) + (Wt 3 / d 3 )) ⁇ 0.
- b) true density d 1 of the first positive electrode active material contained in the dispersion used in step, the true density d 2, true density d 3 of the additive in the second positive electrode active material, Wt 1, Wt 2 , Wt 3 and b) Calculate Vt from the mass of the positive electrode active material layer obtained in step b), and calculate the volume of the positive electrode active material layer to be produced in step d) so that the desired p is obtained. Can do. From the volume thus calculated, the height (thickness) of the positive electrode active material layer to be manufactured can be calculated. Based on the calculated height of the positive electrode active material layer, an appropriate compression thickness considering the restoring force and the thickness of the current collector may be input to the compression device.
- p ′ of the positive electrode active material layer manufactured at a certain compression pressure or a certain thickness is calculated, and the compression pressure or the thickness is appropriately increased or decreased based on the compression pressure or the thickness and p ′, and input to the compression device.
- Controlling the compression pressure is substantially synonymous with controlling the height (thickness) of the positive electrode active material layer to be manufactured.
- Examples of the compression pressure in the compression apparatus include a range of 1 to 5000 kN.
- Step d) is a step of compressing the positive electrode active material layer obtained in step b) with a compression device.
- d) You may perform a process on heating conditions. Moreover, you may perform the drying process which dries a positive electrode after the process d). Then, after step d), the manufactured positive electrode active material layer is (1 ⁇ p) ⁇ (Wt 1 / dt 1 ) / ((Wt 1 / dt 1 ) + (Wt 2 / dt 2 ) + (Wt 3 / It is preferable to perform a confirmation step for confirming whether d 3 )) ⁇ 0.38 is satisfied.
- the production method of the present invention is preferably performed in an inert gas atmosphere.
- a lithium ion secondary battery can be produced.
- the lithium ion secondary battery includes a positive electrode, a negative electrode, a separator, and an electrolytic solution as battery components.
- the negative electrode has a current collector and a negative electrode active material layer bound to the surface of the current collector.
- the negative electrode active material layer includes a negative electrode active material and, if necessary, a binder and / or a conductive aid.
- As the current collector, the binder, and the conductive additive those described for the positive electrode may be adopted. Further, styrene-butadiene rubber may be employed as a binder for the negative electrode active material layer.
- Examples of the negative electrode active material include a carbon-based material capable of inserting and extracting lithium, an element that can be alloyed with lithium, a compound having an element that can be alloyed with lithium, a polymer material, and the like.
- the carbon-based material examples include non-graphitizable carbon, natural graphite, artificial graphite, coke, graphite, glassy carbon, organic polymer compound fired body, carbon fiber, activated carbon, or carbon black.
- the organic polymer compound fired body refers to a material obtained by firing and carbonizing a polymer material such as phenols and furans at an appropriate temperature.
- elements that can be alloyed with lithium include Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Ba, Ra, Ti, Ag, Zn, Cd, Al, Ga, In, Si. , Ge, Sn, Pb, Sb, Bi can be exemplified, and Si or Sn is particularly preferable.
- Examples of compounds having elements that can be alloyed with lithium include ZnLiAl, AlSb, SiB 4 , SiB 6 , Mg 2 Si, Mg 2 Sn, Ni 2 Si, TiSi 2 , MoSi 2 , CoSi 2 , NiSi 2 , CaSi 2, CrSi 2, Cu 5 Si, FeSi 2, MnSi 2, NbSi 2, TaSi 2, VSi 2, WSi 2, ZnSi 2, SiC, Si 3 N 4, Si 2 N 2 O, SiO v (0 ⁇ v ⁇ 2), SnO w (0 ⁇ w ⁇ 2), SnSiO 3 , LiSiO 2 or LiSnO, and SiO x (0.3 ⁇ x ⁇ 1.6) is particularly preferable.
- examples of the compound having an element capable of alloying with lithium include tin compounds such as tin alloys (Cu—Sn alloy, Co—Sn alloy, etc.).
- polymer material examples include polyacetylene and polypyrrole.
- the separator separates the positive electrode and the negative electrode and allows lithium ions to pass while preventing a short circuit due to contact between the two electrodes.
- the separator include a porous film using one or more synthetic resins such as polytetrafluoroethylene, polypropylene, and polyethylene, or a ceramic porous film.
- the electrolytic solution contains a nonaqueous solvent and an electrolyte dissolved in the nonaqueous solvent.
- cyclic esters examples include ethylene carbonate, propylene carbonate, butylene carbonate, gamma butyrolactone, vinylene carbonate, 2-methyl-gamma butyrolactone, acetyl-gamma butyrolactone, and gamma valerolactone.
- chain esters include dimethyl carbonate, diethyl carbonate, dibutyl carbonate, dipropyl carbonate, methyl ethyl carbonate, propionic acid alkyl ester, malonic acid dialkyl ester, and acetic acid alkyl ester.
- ethers examples include tetrahydrofuran, 2-methyltetrahydrofuran, 1,4-dioxane, 1,2-dimethoxyethane, 1,2-diethoxyethane, and 1,2-dibutoxyethane. These nonaqueous solvents may be used alone or in combination with the electrolyte.
- Examples of the electrolyte include lithium salts such as LiClO 4 , LiAsF 6 , LiPF 6 , LiBF 4 , LiCF 3 SO 3 , and LiN (CF 3 SO 2 ) 2 .
- a lithium salt such as LiClO 4 , LiPF 6 , LiBF 4 , LiCF 3 SO 3 in a nonaqueous solvent such as ethylene carbonate, dimethyl carbonate, propylene carbonate, and dimethyl carbonate.
- a solution dissolved at a concentration of about 1 / l can be exemplified.
- a separator is sandwiched between the positive electrode and the negative electrode to form an electrode body.
- the electrode body may be either a stacked type in which the positive electrode, the separator and the negative electrode are stacked, or a wound type in which the positive electrode, the separator and the negative electrode are sandwiched.
- an electrolytic solution is added to the electrode body to form a lithium ion secondary battery. It is good to do.
- the lithium ion secondary battery can be mounted on a vehicle. Since a lithium ion secondary battery maintains a large charge / discharge capacity and has excellent cycle performance, a vehicle equipped with the lithium ion secondary battery is a high-performance vehicle.
- the vehicle may be a vehicle that uses electric energy from a battery as a whole or a part of a power source.
- a vehicle that uses electric energy from a battery as a whole or a part of a power source.
- an electric vehicle a hybrid vehicle, a plug-in hybrid vehicle, a hybrid railway vehicle, an electric forklift, an electric wheelchair, and an electric assist.
- Bicycles and electric motorcycles are examples.
- NMP as a solvent
- the true density of LiNi 5/10 Co 2/10 Mn 3/10 O 2 is 4.8 g / cm 3
- the true density of LiFePO 4 is 3.6 g / cm 3
- the true density of acetylene black is 2 g / cm. 3
- the true density of polyvinylidene fluoride is 1.78 g / cm 3
- the tap density of LiNi 5/10 Co 2/10 Mn 3/10 O 2 is 2.2 g / cm 3
- the tap density of LiFePO 4 is 0 0.8 g / cm 3 .
- Step b) An aluminum foil having a thickness of 20 ⁇ m was prepared as a current collector.
- the dispersion produced in step a) was placed on the surface of the aluminum foil, and applied using a doctor blade so that the dispersion became a film.
- the aluminum foil coated with the dispersion was dried at 80 ° C. for 20 minutes, whereby NMP was removed by volatilization, and a positive electrode active material layer was formed on the aluminum foil surface.
- the mass of the positive electrode of Example 1 is 1098.7 mg
- the mass of the positive electrode active material layer is 900.3 mg
- the coating thickness of the positive electrode is 0.096 mm. From these results, the volume of the positive electrode active material layer is Calculated as 0.3072 cm 3 . Then, from 0.3072 cm 3 , the sum of the theoretical volume of each component calculated from the blending amount (parts by mass) and the true density of each component contained in the positive electrode active material layer is subtracted and divided by 0.3072 cm 3 . Thus, the calculated porosity p was 0.2772.
- Example 2 (Example 2) a) Step 68.6 parts of LiNi 5/10 Co 2/10 Mn 3/10 O 2 having an average particle diameter of 5 ⁇ m as a first positive electrode active material using a planetary stirring and deaerator as a second positive electrode active material 25.4 parts of LiFePO 4 having an average particle diameter of 1 ⁇ m with a carbon coating on the surface, 3 parts of acetylene black having an average particle diameter of 0.05 to 0.1 ⁇ m as a conductive assistant, and 3 parts of polyvinylidene fluoride as a binder, About 54 parts of NMP as a solvent was mixed in total to prepare a dispersion. b) The process was performed like Example 1.
- the process was performed in the same manner as in Example 1 to obtain the positive electrode of Example 2.
- the mass of the positive electrode of Example 2 was 1101.2 mg
- the mass of the positive electrode active material layer was 902.8 mg
- the coating thickness of the positive electrode was 0.096 mm. From these results, the volume of the positive electrode active material layer was Calculated as 0.3072 cm 3 .
- Example 3 a) Step Using a planetary stirring and degassing apparatus, 71.4 parts of LiNi 5/10 Co 2/10 Mn 3/10 O 2 having an average particle diameter of 5 ⁇ m as the first positive electrode active material, and the second positive electrode active material 22.6 parts of LiFePO 4 having an average particle diameter of 1 ⁇ m with a carbon coating on the surface, 3 parts of acetylene black having an average particle diameter of 0.05 to 0.1 ⁇ m as a conductive assistant, and 3 parts of polyvinylidene fluoride as a binder, About 54 parts of NMP as a solvent was mixed in total to prepare a dispersion. b) The process was performed like Example 1.
- the mass of the positive electrode of Example 3 was 1107.6 mg
- the mass of the positive electrode active material layer was 909.2 mg
- the coating thickness of the positive electrode was 0.097 mm. From these results, the volume of the positive electrode active material layer was Calculated as 0.3104 cm 3 .
- d) Process The compression apparatus was started and the positive electrode active material layer was compressed. The obtained positive electrode was heated with a vacuum dryer at 120 ° C.
- the mass of the positive electrode of Example 4 is 1100.8 mg
- the mass of the positive electrode active material layer is 902.4 mg
- the coating thickness of the positive electrode is 0.099 mm.
- the volume of the positive electrode active material layer is Calculated as 0.3168 cm 3 .
- removal from 0.3168Cm 3 subtracting the sum of the volumes of each component of the theoretical calculated from the amount (parts by mass) and the true density of each component contained in the positive electrode active material layer, it at 0.3168Cm 3
- the porosity p calculated in this way was 0.3142.
- the mass of the positive electrode of Comparative Example 1 is 1115.3 mg
- the mass of the positive electrode active material layer is 916.9 mg
- the coating thickness of the positive electrode is 0.097 mm.
- the volume of the positive electrode active material layer is Calculated as 0.3104 cm 3 .
- the porosity p was calculated as 0.2850.
- the occupation ratio: (1-p) ⁇ (Wt 1 / dt 1 ) / ((Wt 1 / dt 1 ) + (Wt 2 / dt 2 ) + (Wt 3-1 / d 3-1 ) + (Wt 3-2 / d 3-2 )) 0.382.
- the process was performed in the same manner as in Example 1 to obtain the positive electrode of Comparative Example 2.
- the mass of the positive electrode of Comparative Example 2 is 1122.6 mg
- the mass of the positive electrode active material layer is 924.2 mg
- the coating thickness of the positive electrode is 0.097 mm. From these results, the volume of the positive electrode active material layer is Calculated as 0.3104 cm 3 .
- Example 5 Using the positive electrode of Example 1, a lithium ion secondary battery of Example 5 was produced as follows.
- the negative electrode was produced as follows. SiO x (0.3 ⁇ x ⁇ 1.6) and natural graphite were used as the negative electrode active material. Polyimide and polyamideimide were used as the binder. Acetylene black was used as a conductive aid. SiO x (0.3 ⁇ x ⁇ 1.6): natural graphite: polyimide: polyamideimide: acetylene black are mixed so that the mass ratio is 32: 50: 5: 5: 8, and NMP is added to the slurry. A negative electrode composite preparation solution was obtained.
- the negative electrode mixture preparation liquid was applied to the surface of an aluminum foil having a thickness of 20 ⁇ m as a negative electrode current collector, and then, similarly to the positive electrode of Example 1, the negative electrode was obtained through a drying step and a compression step.
- the weight per unit area of the negative electrode mixture per unit surface area of the negative electrode current collector was 7.7 mg / cm 2
- the coated surface of the negative electrode current collector was 42 mm ⁇ 82 mm.
- a rectangular sheet (50 ⁇ 90 mm, thickness 25 ⁇ m) made of a resin film having a three-layer structure of polypropylene / polyethylene / polypropylene as a separator was sandwiched between the positive electrode and the negative electrode to form an electrode plate group.
- the electrode plate group was covered with a set of two laminated films, and the three sides were sealed, and then an electrolyte solution was injected into the bag-like laminated film.
- the electrolytic solution a solution in which LiPF 6 was dissolved to 1 mol / L in a solvent in which ethylene carbonate, methyl ethyl carbonate, and diethyl carbonate were mixed at a volume ratio of 3: 3: 4 was used.
- Example 5 a laminate type lithium ion secondary battery of Example 5 in which the four sides were hermetically sealed and the electrode plate group and the electrolyte were sealed.
- the positive electrode and the negative electrode have a tab that can be electrically connected to the outside, and a part of the tab extends to the outside of the laminated lithium ion secondary battery.
- Example 6 A lithium ion secondary battery of Example 6 was produced in the same manner as in Example 5 except that the positive electrode of Example 2 was used.
- Example 7 A lithium ion secondary battery of Example 7 was produced in the same manner as in Example 5 except that the positive electrode of Example 3 was used.
- Example 8 A lithium ion secondary battery of Example 8 was produced in the same manner as in Example 5 except that the positive electrode of Example 4 was used.
- Comparative Example 3 A lithium ion secondary battery of Comparative Example 3 was produced in the same manner as in Example 5 except that the positive electrode of Comparative Example 1 was used.
- Comparative Example 4 A lithium ion secondary battery of Comparative Example 4 was produced in the same manner as in Example 5 except that the positive electrode of Comparative Example 2 was used.
- the nail Until the nail penetrates the lithium ion secondary battery on the restraining plate and the tip of the nail is located inside the hole of the restraining plate, the nail is 20 mm / sec. Moved at a speed of. The surface temperature of the battery after penetrating the nail was measured. Table 1 shows the maximum temperature among the observed surface temperatures.
- the nail used had a diameter of 8 mm and a tip angle of 60 °, and the nail material was S45C defined by JIS G 4051.
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Abstract
Description
第1正極活物質、該第1正極活物質よりも充放電電位の低い第2正極活物質及び添加剤を有する正極活物質層であって、
前記第1正極活物質のタップ密度をdt1、前記第2正極活物質のタップ密度をdt2、前記添加剤の真密度をd3とし、
前記正極活物質層における、前記第1正極活物質の質量%をWt1、前記第2正極活物質の質量%をWt2、前記添加剤の質量%をWt3とし、
前記正極活物質層における空隙率をpとしたとき、
(1-p)×(Wt1/dt1)/((Wt1/dt1)+(Wt2/dt2)+(Wt3/d3))<0.38を満足することを特徴とする。
a)第1正極活物質、該第1正極活物質よりも充放電電位の低い第2正極活物質、添加剤及び溶剤を混合し、分散液を製造する工程、
b)前記分散液を集電体に塗布し、該分散液に含まれる前記溶剤を除去して、正極活物質層を形成する工程、
c)前記第1正極活物質のタップ密度をdt1、前記第2正極活物質のタップ密度をdt2、前記添加剤の真密度をd3とし、
前記正極活物質層における、前記第1正極活物質の質量%をWt1、前記第2正極活物質の質量%をWt2、前記添加剤の質量%をWt3とし、
下記d)工程後の正極活物質層における空隙率をpとしたとき、
(1-p)×(Wt1/dt1)/((Wt1/dt1)+(Wt2/dt2)+(Wt3/d3))<0.38を満足するpとなるように、
圧縮厚みを圧縮装置に入力する工程又は正極活物質層に対する圧縮圧力を圧縮装置に入力する工程、
d)前記b)工程で得られた正極活物質層を前記圧縮装置で圧縮する工程、
を有することを特徴とする。
第1正極活物質、該第1正極活物質よりも充放電電位の低い第2正極活物質及び添加剤を有する正極活物質層であって、
前記第1正極活物質のタップ密度をdt1、前記第2正極活物質のタップ密度をdt2、前記添加剤の真密度をd3とし、
前記正極活物質層における、前記第1正極活物質の質量%をWt1、前記第2正極活物質の質量%をWt2、前記添加剤の質量%をWt3とし、
前記正極活物質層における空隙率をpとしたとき、
(1-p)×(Wt1/dt1)/((Wt1/dt1)+(Wt2/dt2)+(Wt3/d3))<0.38(以下、「本発明のパラメータ」ということがある。)を満足することを特徴とする。
第1正極活物質としては、リチウムイオン二次電池の正極活物質として機能する公知の材料を採用すれば良い。具体的な第1正極活物質としては、高容量である点から、層状岩塩構造の一般式:LiaNibCocMndDeOf(0.2≦a≦1.7、b+c+d+e=1、0≦e<1、DはLi、Fe、Cr、Cu、Zn、Ca、Mg、Zr、S、Si、Na、K、Alから選ばれる少なくとも1の元素、1.7≦f≦2.1)で表される化合物(以下、「NCM」ということがある。)が好ましい。
本発明のパラメータは、(1-p)×(Wt1/dt1)/((Wt1/dt1)+(Wt2/dt2)+(Wt3/d3))<0.38である。
本発明の正極の製造方法は、
a)第1正極活物質、該第1正極活物質よりも充放電電位の低い第2正極活物質、添加剤及び溶剤を混合し、分散液を製造する工程(以下、「a)工程」ということがある。)、
b)前記分散液を集電体に塗布し、該分散液に含まれる前記溶剤を除去して、正極活物質層を形成する工程(以下、「b)工程」ということがある。)、
c)前記第1正極活物質のタップ密度をdt1、前記第2正極活物質のタップ密度をdt2、前記添加剤の真密度をd3とし、
前記正極活物質層における、前記第1正極活物質の質量%をWt1、前記第2正極活物質の質量%をWt2、前記添加剤の質量%をWt3とし、
下記d)工程後の正極活物質層における空隙率をpとしたとき、
(1-p)×(Wt1/dt1)/((Wt1/dt1)+(Wt2/dt2)+(Wt3/d3))<0.38を満足するpとなるように、
圧縮厚みを圧縮装置に入力する工程又は正極活物質層に対する圧縮圧力を圧縮装置に入力する工程(以下、「c)工程」ということがある。)、
d)前記b)工程で得られた正極活物質層を前記圧縮装置で圧縮する工程(以下、「d)工程」ということがある。)、
を有することを特徴とする。
前記正極活物質層における、前記第1正極活物質の質量%をWt1、前記第2正極活物質の質量%をWt2、前記添加剤の質量%をWt3とし、
下記d)工程後の正極活物質層における空隙率をpとしたとき、
(1-p)×(Wt1/dt1)/((Wt1/dt1)+(Wt2/dt2)+(Wt3/d3))<0.38を満足するpとなるように、圧縮厚みを圧縮装置に入力する工程又は正極活物質層に対する圧縮圧力を圧縮装置に入力する工程である。
なお、「圧縮厚み」とは、圧縮装置により圧縮圧力を負荷した際の、圧縮時厚み寸法を意味する。
そして、算出された正極活物質層の高さに基づいて、復元力や集電体の厚みを考慮した適宜適切な圧縮厚みを圧縮装置に入力すればよい。
圧縮装置における圧縮圧力としては、例えば、1~5000kNの範囲を挙げることができる。
本発明の正極を採用して、リチウムイオン二次電池を製造できる。リチウムイオン二次電池は、電池構成要素として、正極、負極、セパレータ及び電解液を含む。
a)工程
遊星式攪拌脱泡装置を用いて、第1正極活物質として平均粒子径5μmのLiNi5/10Co2/10Mn3/10O2を66.7部、第2正極活物質として表面をカーボンコートした平均粒子径1μmのLiFePO4を27.3部、導電助剤として平均粒子径0.05~0.1μmのアセチレンブラックを3部、結着剤としてポリフッ化ビニリデンを3部、溶剤としてNMPを全量で約54部混合し、分散液とした。
ここで、LiNi5/10Co2/10Mn3/10O2の真密度は4.8g/cm3、LiFePO4の真密度は3.6g/cm3、アセチレンブラックの真密度は2g/cm3、ポリフッ化ビニリデンの真密度は1.78g/cm3であり、LiNi5/10Co2/10Mn3/10O2のタップ密度は2.2g/cm3、LiFePO4のタップ密度は0.8g/cm3であった。
集電体として厚み20μmのアルミニウム箔を準備した。該アルミニウム箔の表面に、a)工程で製造した分散液をのせ、ドクターブレードを用いて該分散液が膜状になるように塗布した。分散液を塗布したアルミニウム箔を80℃で20分間乾燥することで、NMPを揮発により除去し、アルミニウム箔表面に正極活物質層を形成させた。
圧縮装置として、ロールプレス機(大野ロール株式会社)を用いた。圧縮装置にb)工程の正極活物質層が形成されたアルミニウム箔を配置した。圧縮後の正極活物質層の空隙率pが0.277となるように圧縮装置にロールギャップ値として80μmを入力した。
ここで、占有率:(1-p)×(Wt1/dt1)/((Wt1/dt1)+(Wt2/dt2)+(Wt3-1/d3-1)+(Wt3-2/d3-2))=0.32となる。
圧縮装置を起動させ、正極活物質層を圧縮した。得られた正極を120℃で6時間、真空乾燥機で加熱し、所定の形状(40mm×80mmの矩形状)に切り取り、実施例1の正極とした。
さらに、占有率:(1-p)×(Wt1/dt1)/((Wt1/dt1)+(Wt2/dt2)+(Wt3-1/d3-1)+(Wt3-2/d3-2))=0.324と確認された。
a)工程
遊星式攪拌脱泡装置を用いて、第1正極活物質として平均粒子径5μmのLiNi5/10Co2/10Mn3/10O2を68.6部、第2正極活物質として表面をカーボンコートした平均粒子径1μmのLiFePO4を25.4部、導電助剤として平均粒子径0.05~0.1μmのアセチレンブラックを3部、結着剤としてポリフッ化ビニリデンを3部、溶剤としてNMPを全量で約54部混合し、分散液とした。
b)工程は、実施例1と同様に行った。
c)工程は、圧縮後の正極活物質層の空隙率pが0.279となるように圧縮装置にロールギャップ値として80μmを入力した以外は、実施例1と同様に行った。ここで、占有率:(1-p)×(Wt1/dt1)/((Wt1/dt1)+(Wt2/dt2)+(Wt3-1/d3-1)+(Wt3-2/d3-2))=0.34となる。
d)工程を実施例1と同様に行い、実施例2の正極を得た。
ここで、実施例2の正極の質量は1101.2mg、正極活物質層の質量は902.8mg、正極の塗膜厚みは0.096mmであり、これらの結果から、正極活物質層の体積は0.3072cm3と算出された。そして、空隙率pは0.2790と算出された。さらに、占有率:(1-p)×(Wt1/dt1)/((Wt1/dt1)+(Wt2/dt2)+(Wt3-1/d3-1)+(Wt3-2/d3-2))=0.340と確認された。
a)工程
遊星式攪拌脱泡装置を用いて、第1正極活物質として平均粒子径5μmのLiNi5/10Co2/10Mn3/10O2を71.4部、第2正極活物質として表面をカーボンコートした平均粒子径1μmのLiFePO4を22.6部、導電助剤として平均粒子径0.05~0.1μmのアセチレンブラックを3部、結着剤としてポリフッ化ビニリデンを3部、溶剤としてNMPを全量で約54部混合し、分散液とした。
b)工程は、実施例1と同様に行った。
c)工程は、圧縮後の正極活物質層の空隙率pが0.287となるように圧縮装置にロールギャップ値として90μmを入力した以外は、実施例1と同様に行った。ここで、占有率:(1-p)×(Wt1/dt1)/((Wt1/dt1)+(Wt2/dt2)+(Wt3-1/d3-1)+(Wt3-2/d3-2))=0.36となる。
d)工程を実施例1と同様に行い、実施例3の正極を得た。
ここで、実施例3の正極の質量は1107.6mg、正極活物質層の質量は909.2mg、正極の塗膜厚みは0.097mmであり、これらの結果から、正極活物質層の体積は0.3104cm3と算出された。そして、空隙率pは0.2871と算出された。さらに、占有率:(1-p)×(Wt1/dt1)/((Wt1/dt1)+(Wt2/dt2)+(Wt3-1/d3-1)+(Wt3-2/d3-2))=0.362と確認された。
a)工程
遊星式攪拌脱泡装置を用いて、第1正極活物質として平均粒子径5μmのLiNi5/10Co2/10Mn3/10O2を66.7部、第2正極活物質として表面をカーボンコートした平均粒子径1μmのLiFePO4を27.3部、導電助剤として平均粒子径0.05~0.1μmのアセチレンブラックを3部、結着剤としてポリフッ化ビニリデンを3部、溶剤としてNMPを全量で約54部混合し、分散液とした。
b)工程は、実施例1と同様に行った。
c)工程は、圧縮後の正極活物質層の空隙率pが0.3142となるように圧縮装置にロールギャップ値として90μmを入力した以外は、実施例1と同様に行った。ここで、占有率:(1-p)×(Wt1/dt1)/((Wt1/dt1)+(Wt2/dt2)+(Wt3-1/d3-1)+(Wt3-2/d3-2))=0.32となる。
d)工程
圧縮装置を起動させ、正極活物質層を圧縮した。得られた正極を120℃で6時間、真空乾燥機で加熱し、所定の形状(40mm×80mmの矩形状)に切り取り、実施例4の正極とした。
ここで、実施例4の正極の質量は1100.8mg、正極活物質層の質量は902.4mg、正極の塗膜厚みは0.099mmであり、これらの結果から、正極活物質層の体積は0.3168cm3と算出された。そして、0.3168cm3から、正極活物質層に含まれる各成分の配合量(質量部)及び真密度から算出した理論上の各成分の体積の和を減じ、それを0.3168cm3で除して算出された空隙率pは0.3142であった。
さらに、占有率:(1-p)×(Wt1/dt1)/((Wt1/dt1)+(Wt2/dt2)+(Wt3-1/d3-1)+(Wt3-2/d3-2))=0.307と確認された。
a)工程
遊星式攪拌脱泡装置を用いて、第1正極活物質として平均粒子径5μmのLiNi5/10Co2/10Mn3/10O2を73.3部、第2正極活物質として表面をカーボンコートした平均粒子径1μmのLiFePO4を20.7部、導電助剤として平均粒子径0.05~0.1μmのアセチレンブラックを3部、結着剤としてポリフッ化ビニリデンを3部、溶剤としてNMPを全量で約54部混合し、分散液とした。
b)工程は、実施例1と同様に行った。
c)工程は、圧縮後の正極活物質層の空隙率pが0.285となるように圧縮装置にロールギャップ値として90μmを入力した以外は、実施例1と同様に行った。ここで、占有率:(1-p)×(Wt1/dt1)/((Wt1/dt1)+(Wt2/dt2)+(Wt3-1/d3-1)+(Wt3-2/d3-2))=0.38となる。
d)工程を実施例1と同様に行い、比較例1の正極を得た。
ここで、比較例1の正極の質量は1115.3mg、正極活物質層の質量は916.9mg、正極の塗膜厚みは0.097mmであり、これらの結果から、正極活物質層の体積は0.3104cm3と算出された。そして、空隙率pは0.2850と算出された。さらに、占有率:(1-p)×(Wt1/dt1)/((Wt1/dt1)+(Wt2/dt2)+(Wt3-1/d3-1)+(Wt3-2/d3-2))=0.382と確認された。
a)工程
遊星式攪拌脱泡装置を用いて、第1正極活物質として平均粒子径5μmのLiNi5/10Co2/10Mn3/10O2を75.2部、第2正極活物質として表面をカーボンコートした平均粒子径1μmのLiFePO4を18.8部、導電助剤として平均粒子径0.05~0.1μmのアセチレンブラックを3部、結着剤としてポリフッ化ビニリデンを3部、溶剤としてNMPを全量で約54部混合し、分散液とした。
b)工程は、実施例1と同様に行った。
c)工程は、圧縮後の正極活物質層の空隙率pが0.283となるように圧縮装置にロールギャップ値として90μmを入力した以外は、実施例1と同様に行った。ここで、占有率:(1-p)×(Wt1/dt1)/((Wt1/dt1)+(Wt2/dt2)+(Wt3-1/d3-1)+(Wt3-2/d3-2))=0.38となる。
d)工程を実施例1と同様に行い、比較例2の正極を得た。
ここで、比較例2の正極の質量は1122.6mg、正極活物質層の質量は924.2mg、正極の塗膜厚みは0.097mmであり、これらの結果から、正極活物質層の体積は0.3104cm3と算出された。そして、空隙率pは0.2832と算出された。さらに、占有率:(1-p)×(Wt1/dt1)/((Wt1/dt1)+(Wt2/dt2)+(Wt3-1/d3-1)+(Wt3-2/d3-2))=0.403と確認された。
実施例1の正極を用いて、実施例5のリチウムイオン二次電池を以下のとおり作製した。
負極は以下のように作製した。
負極活物質としてSiOx(0.3≦x≦1.6)及び天然黒鉛を用いた。結着剤としてポリイミド及びポリアミドイミドを用いた。導電助剤としてアセチレンブラックを用いた。SiOx(0.3≦x≦1.6):天然黒鉛:ポリイミド:ポリアミドイミド:アセチレンブラックが質量比で32:50:5:5:8となるように混合し、NMPを加えて、スラリー状の負極合材調製液を得た。負極合材調製液を負極集電体としての厚み20μmのアルミニウム箔表面に塗布し、次いで、上記実施例1の正極と同様に、乾燥工程及び圧縮工程を経て、負極を得た。なお、負極集電体の塗工面単位面積あたりの負極合材の目付量は、7.7mg/cm2であり、負極集電体の塗工面は42mm×82mmであった。
実施例1の正極及び上記負極を用いて、ラミネート型リチウムイオン二次電池を以下のとおり作製した。
正極および負極の間に、セパレータとしてポリプロピレン/ポリエチレン/ポリプロピレンの3層構造の樹脂膜からなる矩形状シート(50×90mm、厚さ25μm)を挟装して極板群とした。この極板群を二枚一組のラミネートフィルムで覆い、三辺をシールした後、袋状となったラミネートフィルムに電解液を注入した。電解液としては、エチレンカーボネート、メチルエチルカーボネート及びジエチルカーボネートを体積比3:3:4で混合した溶媒にLiPF6を1モル/Lとなるよう溶解した溶液を用いた。その後、残りの一辺をシールすることで、四辺が気密にシールされ、極板群および電解液が密閉された実施例5のラミネート型リチウムイオン二次電池を得た。なお、正極および負極は外部と電気的に接続可能なタブを備え、このタブの一部はラミネート型リチウムイオン二次電池の外側に延出している。
実施例2の正極を用いた以外は、実施例5と同様の方法で、実施例6のリチウムイオン二次電池を作製した。
実施例3の正極を用いた以外は、実施例5と同様の方法で、実施例7のリチウムイオン二次電池を作製した。
実施例4の正極を用いた以外は、実施例5と同様の方法で、実施例8のリチウムイオン二次電池を作製した。
比較例1の正極を用いた以外は、実施例5と同様の方法で、比較例3のリチウムイオン二次電池を作製した。
比較例2の正極を用いた以外は、実施例5と同様の方法で、比較例4のリチウムイオン二次電池を作製した。
実施例5~8、比較例3~4のリチウムイオン二次電池につき、以下の方法で釘刺し試験を行い、内部短絡時のリチウムイオン二次電池の表面温度を測定した。結果を表1に示す。
リチウムイオン二次電池に対し、4.5Vの電位で安定するまで定電圧充電を行った。充電後のリチウムイオン二次電池(放電容量は4Ah程度と見込まれる。)を、径20mmの孔を有する拘束板上に配置した。上部に釘が取り付けられたプレス機に拘束板を配置した。釘が拘束板上のリチウムイオン二次電池を貫通して、釘の先端部が拘束板の孔内部に位置するまで、釘を上部から下部に20mm/sec.の速度で移動させた。釘貫通後の電池の表面温度を測定した。表1には、観測された表面温度のうち、最高温度を記載した。なお、使用した釘の形状は径8mm、先端角度60°であり、釘の材質はJIS G 4051で規定するS45Cであった。
占有率:(1-p)×(Wt1/dt1)/((Wt1/dt1)+(Wt2/dt2)+(Wt3/d3))<0.38を満足する正極活物質層であれば、内部短絡したリチウムイオン二次電池の発熱を一定程度が抑制できることが裏付けられた。
Claims (7)
- a)第1正極活物質、該第1正極活物質よりも充放電電位の低い第2正極活物質、添加剤及び溶剤を混合し、分散液を製造する工程、
b)前記分散液を集電体に塗布し、該分散液に含まれる前記溶剤を除去して、正極活物質層を形成する工程、
c)前記第1正極活物質のタップ密度をdt1、前記第2正極活物質のタップ密度をdt2、前記添加剤の真密度をd3とし、
前記正極活物質層における、前記第1正極活物質の質量%をWt1、前記第2正極活物質の質量%をWt2、前記添加剤の質量%をWt3とし、
下記d)工程後の正極活物質層における空隙率をpとしたとき、
(1-p)×(Wt1/dt1)/((Wt1/dt1)+(Wt2/dt2)+(Wt3/d3))<0.38を満足するpとなるように、
圧縮厚みを圧縮装置に入力する工程又は正極活物質層に対する圧縮圧力を圧縮装置に入力する工程、
d)前記b)工程で得られた正極活物質層を前記圧縮装置で圧縮する工程、
を有することを特徴とする正極の製造方法。 - 前記第1正極活物質が、一般式:LiaNibCocMndDeOf(0.2≦a≦1.7、b+c+d+e=1、0≦e<1、DはLi、Fe、Cr、Cu、Zn、Ca、Mg、Zr、S、Si、Na、K、Alから選ばれる少なくとも1の元素、1.7≦f≦2.1)で表される化合物であり、
前記第2正極活物質が、一般式:LiMhPO4(MはMn,Fe,Co,Ni,Cu,Mg,Zn,V,Ca,Sr,Ba,Ti,Al,Si,B、Te及びMoから選ばれる少なくとも1の元素、0<h<2)で表される化合物である請求項1に記載の正極の製造方法。 - 前記添加剤が、結着剤、導電助剤、分散剤から選ばれる少なくとも1種である請求項1又は2に記載の正極の製造方法。
- e)前記d)工程で得られた正極活物質層が
(1-p)×(Wt1/dt1)/((Wt1/dt1)+(Wt2/dt2)+(Wt3/d3))<0.38を満足することを確認する確認工程、
を有する請求項1~3のいずれか1項に記載の正極の製造方法。 - f)請求項1~4のいずれか1項に記載の製造方法で製造された正極を配置する工程、
を有するリチウムイオン二次電池の製造方法。 - 第1正極活物質、該第1正極活物質よりも充放電電位の低い第2正極活物質及び添加剤を有する正極活物質層であって、
前記第1正極活物質のタップ密度をdt1、前記第2正極活物質のタップ密度をdt2、前記添加剤の真密度をd3とし、
前記正極活物質層における、前記第1正極活物質の質量%をWt1、前記第2正極活物質の質量%をWt2、前記添加剤の質量%をWt3とし、
前記正極活物質層における空隙率をpとしたとき、
(1-p)×(Wt1/dt1)/((Wt1/dt1)+(Wt2/dt2)+(Wt3/d3))<0.38を満足することを特徴とする正極活物質層。 - 請求項6に記載の正極活物質層を具備するリチウムイオン二次電池。
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DE112014006450T5 (de) | 2016-12-22 |
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