WO2011135649A1 - 電極活物質の製造方法 - Google Patents
電極活物質の製造方法 Download PDFInfo
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- WO2011135649A1 WO2011135649A1 PCT/JP2010/057368 JP2010057368W WO2011135649A1 WO 2011135649 A1 WO2011135649 A1 WO 2011135649A1 JP 2010057368 W JP2010057368 W JP 2010057368W WO 2011135649 A1 WO2011135649 A1 WO 2011135649A1
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Classifications
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
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- 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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- 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
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- 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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- H01M4/525—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
- H01M4/5825—Oxygenated metallic salts or polyanionic structures, e.g. borates, phosphates, silicates, olivines
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- 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
- 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 method for producing an electrode active material used for lithium secondary batteries and other batteries. Moreover, it is related with the electrode active material manufactured by this method, and its utilization.
- lithium secondary batteries typically lithium ion batteries
- nickel metal hydride batteries have become increasingly important as power sources for mounting on vehicles or for personal computers and portable terminals.
- a lithium secondary battery that is lightweight and has a high energy density is expected to be preferably used as a high-output power source for mounting on a vehicle.
- One of the characteristics required for a secondary battery used as a high output power source mounted on a vehicle is an improvement in battery capacity.
- use of a material capable of realizing a higher capacity than that conventionally used as an electrode active material has been studied.
- a metal compound including a semi-metal element, the same shall apply hereinafter
- a metal oxide material can be used as an electrode active material (specifically, a negative electrode active material) that reversibly occludes and releases lithium ions, and is conventionally used as a negative electrode active material. It is known to have a higher capacity than the graphite material. Therefore, it is expected that a high capacity of the lithium secondary battery can be realized by using these metal compounds (typically metal oxides) as an electrode active material.
- the metal compound material for example, metal oxide material such as silicon oxide (SiO x ) having the above-described elements as constituent elements generally has low conductivity. Therefore, when the metal oxide is used as an electrode active material, a conductive film, specifically a film made of conductive carbon, is formed on the surface of the electrode active material particles made of the metal oxide, or By producing electrode active material particles composed of composite particles containing the metal oxide and conductive carbon, lithium is interposed between the electrode active material particles and between the electrode active material particles and the electrolyte solution or the electrode current collector. It is necessary to secure a conductive path through which ions and electrons can move.
- metal oxide material such as silicon oxide (SiO x )
- Patent Document 1 describes an electrode active material in which the surface of a composite particle composed of Si, SiO, SiO 2 and a carbonaceous material is coated with carbon. Further, in Patent Document 2, particles comprising a carbonaceous material and silicon (silicon) oxide dispersed in the carbonaceous material, wherein the silicon oxide and the silicon phase (the metal phase is Ni or Cu) Electrode active material comprising composite particles in which is dispersed.
- Patent Document 3 discloses a negative electrode material (negative electrode active material) mainly composed of polycrystalline silicon powder composed of single crystal silicon particles doped with phosphorus or boron as impurities. Is described.
- the above-mentioned electrode active material can expand and contract with the charge / discharge cycle, so that the carbon coating or carbonaceous material that can be a conductive path in the electrode active material.
- the carbon-carbon bond is easily broken. For this reason, in a battery using such an electrode active material, when the charge / discharge cycle is repeated, the initial capacity cannot be maintained, and it is difficult to realize a battery exhibiting excellent cycle characteristics (capacity maintenance ratio).
- the present invention was created to solve such conventional problems, and the object of the present invention is to provide metal compound particles such as SiO x that can be used as an electrode active material for realizing high capacity and improved cycle characteristics of a battery. It is to provide a method capable of efficiently forming a carbon coating on (primary particles). Another object of the present invention is to provide a method for producing electrode active material particles of a suitable form on which a preferable carbon film is formed by performing such a carbon film forming method. Another object of the present invention is to realize a high capacity of a lithium secondary battery or the like having a granular electrode active material (specifically, a negative electrode active material and / or a positive electrode active material) manufactured by such a manufacturing method. It is to provide a battery.
- a granular electrode active material specifically, a negative electrode active material and / or a positive electrode active material
- the present invention provides a method for producing an electrode active material of the following aspect. That is, one manufacturing method disclosed here is a method of manufacturing a granular electrode active material whose surface is coated with a conductive carbon film. Such a method is (1) A carbon source supply material prepared by dissolving a carbon source for forming the carbon coating in a predetermined first solvent in which the granular electrode active material to be coated can be dispersed is prepared. To do, (2) The granular electrode active material to be coated is a solvent that is compatible with the first solvent and that can disperse the granular electrode active material and is a poor solvent for the carbon source.
- an electrode active material supply material prepared by dispersing in 2 solvent; (3) preparing a mixed material obtained by mixing the prepared carbon source supply material and the electrode active material supply material; (4) adding a compound containing phosphorus (P) or boron (B) to the prepared mixed material, (5) forming a conductive carbon coating derived from the carbon source on the surface of the electrode active material by firing a mixture of the electrode active material particles obtained after the addition and the carbon source; Is included.
- a carbon source supply material prepared by dissolving a carbon source for forming a carbon film in the first solvent is different from the first solvent in that the carbon source is poor.
- the solvent that is, the solvent having a relatively low solubility of the carbon source, typically the solubility of the carbon source is the same temperature (for example, a room temperature range such as 20 to 30 ° C.)
- the compound containing is added, It is characterized by the above-mentioned.
- the carbon source is contained in the second solvent (poor solvent) component. It is difficult to exist, and substantially exists only in the first solvent component.
- the granular electrode active material can flow and disperse in both the first and second solvents. In other words, the electrode active material particles that freely move back and forth between the first and second solvent components in the mixed solvent are present in the solvent when present in the first solvent component. Interact with carbon sources. Typically, a carbon source adheres to or binds to the surface of the electrode active material particles.
- the electrode active material particles that are in an interaction state with the carbon source are transferred from the first solvent to the second solvent. Regulated by the presence of interacting carbon sources. For this reason, in the mixed solvent in which the first solvent component and the second solvent component are mixed, the carbon source can efficiently interact (attach or bind) to the dispersed electrode active material particles, Excessive aggregation of the electrode active material particles is suppressed.
- the carbon source typically, electrode active material particles having a carbon source attached or bonded to the surface
- a compound containing phosphorus or boron is added to the mixed material, and the mixture of the electrode active material particles and the carbon source obtained after the addition is subjected to predetermined conditions. Bake with.
- a compound containing phosphorus or boron is added to the mixed material, the interaction (adhesion or bonding) between the dispersed electrode active material particles and the carbon source is maintained in the mixed material.
- the presence of such phosphorus or boron can form a carbon coating on the surface of the primary particles of the electrode active material with improved bond strength between carbon atoms that can become a conductive path after firing the mixed material.
- a carbon film in which carbon atoms are firmly bonded to each other is formed on the surface of the primary particle well (that is, in a state where there are few non-formed parts of the film) and has excellent cycle characteristics.
- achieve can be manufactured.
- the compound containing phosphorus or boron when the compound containing phosphorus or boron is added to the mixed material, the compound is dissolved in a liquid medium that is at least compatible with the first solvent. Provided in form.
- the compound By adding the compound containing phosphorus or boron in the form of such a solution, the compound is easily dissolved in the mixed material (strictly, the first solvent component in the mixed material). Boron easily diffuses uniformly in the mixed material. This makes it possible to evenly contact the carbon source present in the first solvent component and reinforce the bond between carbons in the carbon source. Therefore, according to the manufacturing method of this structure, the granular electrode active material provided with the carbon film with a strong carbon-carbon bond can be manufactured uniformly.
- inorganic phosphoric acid is used as the phosphorus-containing compound.
- at least one inorganic boric acid is used as the boron-containing compound.
- inorganic phosphoric acid is a generic term for inorganic compounds having a phosphoric acid skeleton containing a phosphorus atom having an oxidation number of +5 and an oxygen atom having an oxidation number of ⁇ 2, and is orthophosphoric acid (H 3 PO 4 ).
- Pyrophosphoric acid also referred to as diphosphoric acid; H 4 P 2 O 7
- higher-order condensed phosphoric acid H n + 2 P n O 3n + 1
- metaphosphoric acid also referred to as polyphosphoric acid (HPO 3 ) n
- inorganic boric acid examples include orthoboric acid (H 3 BO 3 ), hypoboric acid (H 4 B 2 O 4 ), boronic acid (H 3 BO 2 ), perboric acid (HBO 3 ), metaboric acid ( (HBO 2 ) n ) and the like.
- the granular electrode active material to be coated with the carbon film suitably used in the electrode active material manufacturing method disclosed herein Si, Ge, Sn, Pb, Al, Ga, In, As, Sb , Bi and the like, and metal compounds (preferably metal oxides) containing constituent metal elements.
- metal compounds preferably metal oxides
- the electrode active material is a silicon oxide represented by the general formula: SiO x (where x is a real number satisfying 0 ⁇ x ⁇ 2). It is mainly composed.
- This type of silicon oxide has a large theoretical capacity with respect to occlusion and release of lithium ions, and can be suitably used, for example, as a negative electrode active material of a lithium secondary battery.
- an electrode active material composed of the above-described silicon oxide or other compound of the above-described metal species typically a metal oxide expands or contracts with the insertion and extraction of lithium ions during charge and discharge. The volume fluctuates greatly.
- the secondary particles are crushed by the stress accompanying the expansion and contraction.
- a granular material having a surface on which no carbon film is formed is produced.
- the silicon oxide and other metal compounds having no carbon film do not have a conductive path due to the carbon film, and do not contribute to an improvement in battery capacity as an electrode active material. Further, it is not preferable because it causes deterioration of battery durability, particularly cycle characteristics.
- a carbon film in which carbon atoms are firmly bonded to the surface of the primary particles efficiently can be formed.
- the carbon source is a water-soluble compound
- the first solvent is an aqueous solvent (typically water)
- the first The solvent 2 is a non-aqueous solvent compatible with water (for example, a polar solvent such as ethanol that can be mixed with water at a desired mixing ratio).
- the method further includes refluxing the mixed material before adding the compound containing phosphorus or boron.
- a reflux treatment is performed (typically in a temperature range in which the solvent of the mixed material can be boiled).
- the granular electrode active material can be dispersed in the mixed material. For this reason, it is possible to form a carbon film having a strong bond between carbons on the surface of the electrode active material particles more efficiently and more uniformly.
- the present invention also provides a lithium secondary comprising the electrode active material disclosed herein (typically a negative electrode active material comprising a metal compound produced by any of the production methods disclosed herein) on the positive electrode or the negative electrode.
- a lithium secondary comprising the electrode active material disclosed herein (typically a negative electrode active material comprising a metal compound produced by any of the production methods disclosed herein) on the positive electrode or the negative electrode.
- the lithium secondary battery disclosed herein can achieve high capacity and good electrical conductivity by including the electrode active material. For this reason, it is equipped with performance suitable as a battery mounted on a vehicle that requires high-rate charge / discharge. Therefore, according to this invention, the vehicle provided with the lithium secondary battery disclosed here is provided.
- a vehicle for example, an automobile
- the lithium secondary battery as a power source typically, a power source of a hybrid vehicle or an electric vehicle
- FIG. 1 is a perspective view schematically showing an assembled battery according to an embodiment of the present invention.
- FIG. 2 is a front view schematically showing an example of a wound electrode body.
- FIG. 3 is a cross-sectional view schematically showing a configuration of a unit cell provided in the assembled battery.
- FIG. 4 is a side view schematically showing a vehicle including a lithium secondary battery.
- FIG. 5 is a diagram schematically illustrating a state in which a carbon source and a granular electrode active material are added and mixed together in a conventional single solvent (aggregation state of electrode active material particles).
- FIG. 6 schematically shows the presence state of the carbon source and the granular electrode active material in the mixed material (material prepared by mixing the first solvent and the second solvent) obtained by the manufacturing method disclosed herein.
- FIG. 7 shows the number of cycles (cycle number) in a cycle test using an evaluation cell (counter electrode is metallic lithium) constructed using each of Samples 1 to 5 obtained in Examples described later as an electrode active material.
- FIG. 8 shows a bar graph (see the vertical axis on the left) showing the amount of carbon (% by mass) in the mixed material in each of Samples 1 to 5 obtained in Examples described later, and each sample as an electrode active material.
- a line graph shows the vertical axis on the right showing the capacity retention rate (%) obtained in a cycle test using an evaluation cell (counter electrode is metallic lithium) constructed using each is described.
- FIG. 9 shows the capacity retention ratio (%) obtained in the cycle test using the evaluation cell (counter electrode is metallic lithium) constructed using the sample 6 obtained in the example described later as the electrode active material.
- a line graph is shown.
- the “electrode active material” is a term including a positive electrode active material used on the positive electrode side and a negative electrode active material used on the negative electrode side.
- the active material refers to a substance (compound) involved in power storage on the positive electrode side or the negative electrode side. That is, it refers to a substance involved in electron emission or capture during battery charge / discharge.
- lithium secondary battery refers to a battery in which lithium ions in the electrolyte are responsible for charge transfer, and is called a so-called lithium ion battery (or lithium ion secondary battery), a lithium polymer battery, or the like. These are typical examples included in the “lithium secondary battery” mentioned here.
- the production method disclosed herein it is possible to produce a granular electrode active material in which a conductive carbon film in which carbon atoms are firmly bonded to each other is formed on the surface.
- the production method disclosed herein can efficiently coat the surface of electrode active material particles (ie, primary particles) with poor electrical conductivity with a conductive carbon film having a strong carbon-carbon bond.
- the granular electrode active material to be coated is at least dispersible in the first solvent and the second solvent, and has an active property such that a conductive carbon film derived from a carbon source can be formed on the surface by firing. Any substance can be used.
- various metal compounds for example, metal oxides suitable as a negative electrode active material of a lithium secondary battery, such as Si, Ge, Sn, Pb, Al, Ga, In, As, Sb, and Bi, are used as constituent metal elements.
- a metal compound preferably a metal oxide).
- a silicon oxide as defined by the above formula can be preferably employed.
- Various lithium transition metal composite oxides for example, LiCoO 2 , LiNiO 2 , LiMn 2 O 4 ) that can be used as the positive electrode active material of the lithium secondary battery can be employed.
- the general formula polyanionic compound represented by Limao 4 and the like.
- M in such formula is typically one or more elements (typically one or two) including at least one metal element selected from the group consisting of Fe, Co, Ni and Mn.
- a metal element of a species or more that is, it contains at least one metal element selected from the group consisting of Fe, Co, Ni, and Mn, but allows the presence of other minor additive elements that can be contained in small amounts (even if such minor additive elements are not present).
- a in the above formula is typically one or more elements selected from the group consisting of P, Si, S and V.
- the average particle diameter (eg, median diameter based on light scattering method: d50, or average particle diameter based on microscopic observation) is about 10 nm to 10 ⁇ m (typically 100 nm to 5 ⁇ m, for example, 100 nm to 1000 nm).
- a granular electrode active material can be preferably used.
- a particularly preferred specific example of the electrode active material is a silicon oxide represented by the general formula: SiO x .
- x in the formula is typically a real number satisfying 0 ⁇ x ⁇ 2, and preferably 0 ⁇ x ⁇ 0.6.
- a commercially available powder material made of silicon oxide such as SiO can be preferably used.
- a lithium secondary battery having a particularly high charge / discharge capacity can be obtained.
- the negative electrode active material for a lithium secondary battery made of this type of metal compound expands as the lithium ion is occluded during charge / discharge, and conversely, the active material itself expands as the lithium ion is released. Shrink. Therefore, the structural change of the negative electrode active material structure (that is, typically formed into a layer on the surface of the negative electrode current collector such as copper by the secondary particles in which the primary particles are aggregated) present in the negative electrode of the battery.
- the conductive carbon film is sufficiently formed in advance on the surface of the primary particles constituting the negative electrode active material structure. There is a need. By carrying out the production method disclosed herein, a sufficient conductive carbon coating can be efficiently formed on the surface of the primary particles of the electrode active material having such properties.
- silicon oxide particles such as silica often have H groups (typically Si—O—H or Si—H) on their surfaces in a normal state. Due to the presence of the H group (H atom), for example, when a water-soluble compound is used as a carbon source, the H group of the silicon oxide particles and a portion having a high electronegativity in the compound (for example, a portion of —OH group). A hydrogen bond, a covalent bond, etc. arise between this and strong interaction can be produced. For this reason, by selecting an appropriate first solvent and second solvent, a carbon source such as a water-soluble compound can be easily applied to the surface of the silicon oxide particles.
- H groups typically Si—O—H or Si—H
- a carbon source for forming a conductive carbon film on the surface of electrode active material particles made of a metal compound such as silicon oxide it is thermally decomposed and conductive when fired together with the electrode active material particles.
- a carbon film (carbon structure) can be formed, and those having the property of being soluble in at least a predetermined solvent can be used.
- a water-soluble organic substance particularly a high-molecular compound such as a water-soluble polymer
- a preferred example of this type of organic material is a water-soluble polymer compound (polymer) such as polyvinyl alcohol (PVA).
- PVA has many hydroxy groups (—OH) in the molecular chain. Due to the presence of such hydroxy groups, the interaction with electrode active material particles (for example, chemicals such as hydrogen bonds, covalent bonds, and ionic bonds). This is preferable because it can easily cause a physical bond or a physical bond such as adsorption). Further, it is preferable because a carbon film showing good conductivity can be formed by thermal decomposition under oxidizing conditions such as in the air.
- water-soluble polymer compounds that can be used as a carbon source include cellulose derivatives such as starch, gelatin, methylcellulose, carboxymethylcellulose, polyacrylic acid, polyacrylamide, polyethylene oxide, polyethylene glycol, polymethacrylic acid, polyvinylpyrrolidone, etc. Is mentioned.
- the mixture of the electrode active material and the carbon source is used.
- a compound containing phosphorus or boron is added.
- a compound that can be dissolved in the carbon source supply material (strictly, the first solvent) or a compound that can be dissolved in a liquid medium compatible with the carbon source supply material is preferable.
- the first solvent is an aqueous solvent
- inorganic phosphoric acid can be preferably used as the compound containing phosphorus.
- suitable compounds include orthophosphoric acid (H 3 PO 4 ), pyrophosphoric acid (H 4 P 2 O 7 ), condensed phosphoric acid (H n + 2 P n O 3n + 1 ), and metaphosphoric acid ((HPO 3 ) n ).
- H 3 PO 4 orthophosphoric acid
- pyrophosphoric acid H 4 P 2 O 7
- condensed phosphoric acid H n + 2 P n O 3n + 1
- metaphosphoric acid (HPO 3 ) n ).
- orthophosphoric acid which is highly versatile and easily available, is particularly preferably used.
- the compound containing boron like the compound containing phosphorus, a compound that can be dissolved in the carbon source supply material or a compound that can be dissolved in a liquid medium compatible with the carbon source supply material is preferable. .
- inorganic boric acid can be preferably used.
- Suitable compounds include, for example, orthoboric acid (H 3 BO 3 ), hypoboric acid (H 4 B 2 O 4 ), boronic acid (H 3 BO 2 ), perboric acid (HBO 3 ), metaboric acid ((HBO 2 )) n ) and the like. It is preferable to use at least one of these.
- orthoboric acid can be used particularly preferably.
- the carbon source supply material used in the production method disclosed herein may be a predetermined carbon source (only one type of carbon source may be used, or two or more types of carbon sources may be used in combination. ) Is dissolved in a first solvent capable of dissolving.
- the first solvent that is, the solvent for preparing the carbon source feed material
- the first solvent is described as the first solvent for convenience, but may itself be constituted by a single substance (molecular species), or A mixed medium of a plurality of substances (molecular species) may be used.
- the first solvent can be selected according to the carbon source used.
- a water-soluble organic substance such as PVA
- an aqueous solvent capable of suitably dissolving the compound is preferable.
- water including distilled water and deionized water
- the first solvent can be used as the first solvent.
- the concentration of the carbon source in the carbon source supply material is not particularly limited, but a content that can be completely dissolved (that is, a lower concentration than the saturated solution in the solvent) is preferable.
- the concentration of the water-soluble compound is about 0.1 to 20% by mass (for example, about 0.3 to 15% by mass) based on 100% by mass of the entire carbon source feed
- An aqueous solution of preferably 1 to 15% by mass, particularly preferably about 1 to 10% by mass) can be suitably used as the carbon source feed material.
- an aqueous PVA solution prepared by adding about 1 g to 100 g (preferably about 10 g to 100 g) of PVA to 1 liter of water (L) is an example of a suitable carbon source supply material.
- various stirring / mixing means for sufficiently dissolving the carbon source can be employed.
- stirring can be performed by vibration using ultrasonic waves, or a magnetic stirrer can be used.
- the carbon source supply material may contain components other than the first solvent and the carbon source described above.
- examples of the additional component include a pH adjuster, a surfactant, a preservative, and a colorant.
- the electrode active material supply material used in the production method disclosed herein is prepared by dispersing an appropriate amount in a second solvent capable of dispersing a predetermined granular electrode active material.
- the second solvent is also referred to as the second solvent for convenience, but it may be composed of a single substance (molecular species) or a plurality of substances (molecules). Seed) mixed media.
- the second solvent is required to be compatible with the first solvent and to be a poor solvent for the carbon source to be used.
- a water-soluble organic substance such as PVA, polyacrylic acid, or polyethylene glycol
- PVA polyacrylic acid
- polyethylene glycol an organic solvent that is difficult to dissolve in the carbon source (that is, has a very low solubility)
- An organic solvent that is difficult to dissolve in the carbon source can be preferably used as the second solvent.
- alcohols which are poor solvents for PVA for example, lower alcohols having 4 or less carbon atoms such as methanol, ethanol, isopropanol and 2-methyl-2-butanol, which are well soluble in water, are preferably used as the second solvent. can do.
- any solvent known to be a poor solvent for the carbon source may be appropriately selected.
- the concentration (content ratio) of the electrode active material in the electrode active material supply material is not particularly limited.
- the content of the granular electrode active material is 0.5 to 20% by mass with respect to 100% by mass of the entire electrode active material supply material.
- a dispersion liquid having a degree preferably about 1 to 20% by mass, for example about 1 to 15% by mass, more preferably about 1 to 10% by mass, for example about 5 to 10% by mass is suitably used as the electrode active material supply material. Can be used.
- the carbon source content in the carbon source supply material mixed with the electrode active material supply material may be, for 1 liter (L) of a lower alcohol having a high solubility in water such as ethanol.
- a dispersion (or suspension) prepared by adding about 10 g to 100 g (for example, 50 g to 90 g) of silicon oxide is an example of a suitable electrode active material supply material.
- the electrode active material supply material may contain components other than the second solvent and the granular electrode active material described above.
- the additional component typically includes a conductive auxiliary material made of a carbon material such as carbon black, a dispersant, a pH adjuster, a surfactant, an antiseptic, a colorant, and the like.
- a conductive auxiliary material for example, carbon black
- a conductive auxiliary material in an amount corresponding to 1 to 20% by mass of the total amount of the electrode active material made of silicon oxide such as SiO x or other metal compound (oxide etc.) as described above. It is preferable to add a fine conductive carbon material).
- the carbon source supply material prepared as described above and the electrode active material supply material are mixed at a predetermined ratio to prepare a mixed material.
- the second solvent derived from the electrode active material supply material
- the carbon source typically an organic substance
- the granular electrode active material can flow in both the first and second solvents. For this reason, the electrode active material particles that freely move back and forth between the first and second solvent components in the mixed solvent are carbon atoms present in the solvent when present in the first solvent component. Interact with the source.
- the carbon source is a compound having a polar group (for example, PVA having a large number of hydroxy groups in the molecular chain), and the granular electrode active material has a polar group (for example, a hydrogen atom on the surface of SiO) on the surface.
- a polar group for example, a hydrogen atom on the surface of SiO
- the presence of such a hydroxy group is preferable because it easily causes an interaction with the electrode active material particles (for example, a chemical bond such as a hydrogen bond, a covalent bond, and an ionic bond, or a physical bond such as adsorption).
- FIG. 5 is a schematic diagram illustrating a state in which a carbon source (for example, PVA) 102 and a granular electrode active material (for example, silicon oxide) 104 are added and mixed together in a conventional single solvent (for example, water).
- a carbon source for example, PVA
- a granular electrode active material for example, silicon oxide
- a conventional single solvent for example, water
- the carbon source 102 is substantially Since it exists only in the first solvent component, the presence distribution of the granular electrode active material 104 is also regulated according to the presence distribution in the mixed material of the carbon source 102, and aggregation as shown in FIG. A suitable dispersion state of the active material (primary particles) 104 can be realized.
- the mixing mass ratio of the carbon source supply material and the electrode active material supply material is not particularly limited because it can vary depending on the concentration of the carbon source and / or the content of the active material particles in these supply materials. As one guide, it is preferable to mix both feed materials so that a sufficient amount of carbon source is applied to the surface of the electrode active material.
- a carbon source supply material and an electrode active material supply so that about 0.05 to 15 parts by mass of a carbon source (eg, PVA) is mixed with 1 part by mass of a granular electrode active material (eg, silicon oxide). It is appropriate to adjust the mixing ratio with the material.
- Carbon source for example, PVA
- PVA Carbon source
- the mixed material by mixing the carbon source supply material and the electrode active material supply material in such a manner that the carbon source supply material and the electrode active material supply material are mixed.
- the mixing volume ratio of the second solvent which is a poor solvent for the carbon source (for example, a polar organic solvent such as ethanol or other lower alcohol capable of dispersing electrode active material particles such as SiO x ) is set to the first volume ratio.
- a solvent for example, water capable of dissolving a carbon source such as PVA
- the mixing volume ratio of the first solvent and the second solvent is 1: 3 to 3: 1, and 1: 2 to 2: 1.
- the ratio is 1: 1.5 to 1.5: 1, and it is particularly preferable that the mixing is approximately 1: 1.
- the mixing volume ratio of the first solvent and the second solvent By setting the mixing volume ratio of the first solvent and the second solvent, the aggregation of the electrode active material particles is reduced, and the electrode active material secondary particles (associates) having a relatively small particle diameter are reduced. ) Can be formed.
- the electrode active material particles with carbon coating obtained after firing aggregates of primary particles, that is, secondary particles
- Particle size and size can be adjusted.
- the two supplies are provided in order to further improve the dispersion state of the granular electrode active material (electrode active material 104 as shown in FIG. 5) in the mixed material.
- the temperature range in which the solvent of the mixed material that is, the mixed medium of the first solvent and the second solvent
- the compound containing phosphorus or boron is added to the obtained mixed material
- the mixed material is heated until refluxing is performed.
- the azeotropic temperature of the water and ethanol is about Reflux treatment is performed in a temperature range exceeding 73 ° C. (typically 80 to 100 ° C., for example, about 90 ⁇ 5 ° C.) for an appropriate time, typically about 1 to 24 hours (for example, 8 to 12 hours). It is preferable.
- the reflux process itself is a conventional technique and does not require any special process in the implementation of the present invention, and thus a detailed description thereof is omitted.
- a compound containing phosphorus or boron as described above is added to the mixed material (a mixture of the electrode active material and the carbon source).
- the amount of such a compound added is such that it can be completely dissolved in the mixed material, and is such that phosphorus or boron can sufficiently come into contact with the carbon source in the mixed material. preferable.
- the amount of the compound containing phosphorus or boron added is, for example, 1 to 50 when the mass of the carbon source (for example, PVA) contained in the added mixed material is 100 parts by mass.
- About mass parts is appropriate, preferably 1 to 30 parts by mass, more preferably 5 to 30 parts by mass.
- the compound containing phosphorus or boron when the compound containing phosphorus or boron is added to the mixed material, the compound is at least a liquid medium compatible with the first solvent. Provided in the form of a solution in solution.
- the compound becomes easier to dissolve in the mixed material than when it is added in a solid state (for example, a powder or a lump of a predetermined size), and phosphorus or Boron is more likely to diffuse through the mixed material to be homogeneous. For this reason, such phosphorus or boron can be in uniform contact with the carbon source existing in the mixed material (strictly speaking, the carbon source dissolved in the first solvent component).
- Phosphorus or boron in contact with such a carbon source acts on the carbon source (for example, PVA) (for example, various bonds such as double bonds and bonds similar to bridging (crosslinking) bonds in the molecule of the carbon source).
- PVA carbon source
- various bonds such as double bonds and bonds similar to bridging (crosslinking) bonds in the molecule of the carbon source.
- the liquid medium for dissolving the compound containing phosphorus or boron can be used without particular limitation as long as it is compatible with the first solvent as described above.
- an aqueous solvent typically water
- the concentration of the compound containing phosphorus or boron is not particularly limited. However, in consideration of drying the mixed material after the addition of the compound to remove the solvent and further baking, the addition of the liquid medium is performed. In order to reduce the amount, it is preferable to use a high concentration solution. For example, a concentration of 80% by mass or more is appropriate, and preferably 90% by mass or more.
- an aqueous solution of 85% by mass or more can be preferably used.
- the aqueous solution of orthophosphoric acid having such a concentration may be prepared by dissolving crystals of orthophosphoric acid in water (ion exchange water or pure water), or a commercially available product (for example, available from Sigma Aldrich Japan Co., Ltd.). May be used.
- the compound containing phosphorus or boron is added to the mixed material (for example, in the form of a solution in which the compound is dissolved in a predetermined liquid medium), and then the mixed material is added.
- a solvent that is, a mixed solvent mainly of a first solvent and a second solvent, and when a compound containing phosphorus or boron is added as a solution, a liquid medium for dissolving the compound is also included. .
- Such evaporation can be performed using a general method, for example, a rotary evaporator. In this manner, the aggregate composed of the electrode active material particles and the carbon source can be recovered with the solvent removed.
- the excessive aggregation of the electrode active material particles is more reliably suppressed, and further, a composite (association) body of an electrode active material particle having a small particle diameter and a carbon source (that is, an electrode active material having a carbon coating)
- a third solvent which is a solvent different from the second solvent, in which the particulate electrode active material can be dispersed, and is a poor solvent for the carbon source.
- the addition of the mixed material after the compound containing phosphorus or boron is added typically, the mixed material is dropped into a third solvent
- the recovery of the complex can be performed by evaporating the third solvent.
- the third solvent preferably has a boiling point at least higher than that of the first solvent (typically higher than that of the second solvent).
- the third solvent having such a boiling point is used, the first solvent can disappear before the third solvent in the evaporation process, so the carbon source is re-dissolved in the first solvent. Therefore, it is possible to prevent the aggregates from collapsing and reaggregation of the granular electrode active material.
- the third solvent various solvents can be used as long as the above conditions are satisfied.
- the first solvent is an aqueous solvent (typically water)
- the carbon source is
- the third solvent is preferably an organic solvent that is compatible with the aqueous solvent and difficult to dissolve the water-soluble compound.
- an aprotic polar solvent for example, acetone or acetonitrile
- the water-soluble compound is difficult to dissolve is preferably used.
- the mixed material recovered as described above that is, the mixed material obtained by removing the solvent by evaporation after the addition of the compound containing phosphorus or boron (from the electrode active material particles and the carbon source). Or a compound obtained by removing the third solvent by evaporation when added to the third solvent after the addition of the compound containing phosphorus or boron.
- a carbon film derived from the carbon source (typically an organic substance such as PVA), which has a good conductive path by improving the bond strength between the carbons by the action of phosphorus or boron. Can be formed on the surface of the electrode active material particles.
- the firing conditions are not particularly limited as long as the carbon source used can be pyrolyzed and the surface of the granular electrode active material can be coated with the pyrolyzate.
- a metal oxide such as silicon oxide represented by the above general formula: SiO x
- an inert gas atmosphere such as argon gas or nitrogen gas is preferable. It is preferable to perform firing in view of not affecting the structure and composition of the electrode active material by the firing treatment.
- the firing temperature is not limited as long as the carbon source to be used can be thermally decomposed, but is typically 800 ° C.
- pre-baking is performed for an appropriate time (typically 12 hours or less, for example, about 1 to 6 hours) before raising the temperature of the object to be heated to the maximum temperature range.
- the temperature range of the pre-baking is not particularly limited, but typically it is preferably performed in a temperature range of 100 to 600 ° C., for example, 200 to 300 ° C.
- the electrode active material with a granular carbon film manufactured by the manufacturing method disclosed here can be suitably used as an active material of a positive electrode or a negative electrode of a battery, similarly to a conventional electrode active material. Except for using such an electrode active material, various types of secondary batteries can be constructed by employing the same materials and processes as in the past.
- a lithium secondary battery is constructed by employing, as a negative electrode active material, a metal oxide such as a silicon oxide represented by the above general formula: SiO x with a carbon coating produced by the production method disclosed herein. be able to.
- a lithium secondary battery including a negative electrode active material made of a silicon oxide represented by the above general formula: SiO x manufactured by the manufacturing method disclosed herein will be described.
- the usage form of the electrode active material is not intended to be limited to this.
- the lithium secondary battery according to the present embodiment is characterized by using the above-described granular electrode active material with a carbon coating as a negative electrode active material. Therefore, as long as the object of the present invention can be realized, the contents, materials, and compositions of other battery constituent materials and members are not particularly limited, and those similar to conventional lithium secondary batteries can be used.
- a granular negative electrode active material (SiO x ) obtained by the production method disclosed herein is used as a negative electrode mixture together with a binder (binder) and a conductive auxiliary material used as necessary.
- a material in which a negative electrode active material layer (also referred to as a negative electrode composite material layer) is formed by being attached on an electric body can be preferably used.
- As the negative electrode current collector 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.
- binder examples include polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), carboxymethyl cellulose (CMC), styrene butadiene rubber (SBR), and the like.
- PVDF polyvinylidene fluoride
- PTFE polytetrafluoroethylene
- CMC carboxymethyl cellulose
- SBR styrene butadiene rubber
- a carbon material such as carbon black similar to the conventional one can be preferably used.
- the granular negative electrode active material (primary particles) used here is obtained by the production method disclosed herein, the surface thereof is sufficiently covered with a carbon film and has excellent conductivity. For this reason, the conductive auxiliary material is not contained in the negative electrode active material layer, or the content of the conductive auxiliary material can be reduced as compared with the conventional case.
- the amount of the conductive auxiliary material used relative to 100 parts by mass of the negative electrode active material used is, for example, about 1 to 30 parts by mass (preferably about 2 to 20 parts by mass, for example, about 5 to 10 parts by mass). can do.
- a conductive auxiliary material may be previously contained in the electrode active material supply material described above.
- a paste-like negative electrode mixture (hereinafter referred to as “negative electrode mixture paste”) is prepared by dispersing and kneading in such an aqueous solvent.
- a negative electrode for a lithium secondary battery can be produced by applying an appropriate amount of this negative electrode mixture paste onto a negative electrode current collector, followed by drying and pressing.
- the positive electrode a material in which an active material capable of reversibly occluding and releasing Li is attached to a current collector as a positive electrode mixture together with a binder and a conductive material used as necessary is preferably used.
- a current collector a rod-like body, a plate-like body, a foil-like body, a net-like body or the like mainly composed of aluminum, nickel, titanium, stainless steel, or the like can be used.
- a lithium transition metal composite oxide having a layered structure, a lithium transition metal composite oxide having a spinel structure, a polyanion compound having an olivine structure, or the like that can be used for a positive electrode of a general lithium secondary battery is preferably used.
- Typical examples of such an active material include lithium transition metal oxides such as lithium cobaltate (LiCoO 2 ), lithium nickelate (LiNiO 2 ), and lithium manganate (LiMn 2 O 4 ).
- LiMAO 4 The compound shown by these is mentioned.
- M in the formula is one or more elements including at least one metal element selected from the group consisting of Fe, Co, Ni and Mn (typically one or more metals). Element).
- a in the above formula is preferably one or more elements selected from the group consisting of P, Si, S and V.
- the binder those similar to those on the negative electrode side can be used.
- the conductive material include carbon black (for example, acetylene black), carbon material such as graphite powder, or conductive metal powder such as nickel powder.
- the amount of the conductive material used relative to 100 parts by mass of the positive electrode active material can be, for example, 1 to 20 parts by mass (preferably 5 to 15 parts by mass).
- the amount of the binder used relative to 100 parts by mass of the positive electrode active material can be, for example, 0.5 to 10 parts by mass.
- a powdery material containing the positive electrode active material and the conductive auxiliary material as described above is dispersed in an appropriate dispersion medium together with an appropriate binder and kneaded, whereby a paste-like positive electrode mixture (hereinafter, "Positive electrode mixture paste”) is prepared.
- a positive electrode for a lithium secondary battery can be produced by applying an appropriate amount of this positive electrode mixture paste onto a positive electrode current collector, followed by drying and pressing.
- a liquid electrolyte containing a nonaqueous solvent and a lithium salt soluble in the solvent is preferably used. It may be a solid (gel) electrolyte in which a polymer is added to such a liquid electrolyte.
- aprotic solvents such as carbonates, esters, ethers, nitriles, sulfones, and lactones can be used.
- lithium ion batteries such as 2-methyltetrahydrofuran, dioxane, 1,3-dioxolane, diethylene glycol dimethyl ether, ethylene glycol dimethyl ether, acetonitrile, propionitrile, nitromethane, N, N-dimethylformamide, dimethyl sulfoxide, sulfolane, ⁇ -butyrolactone, etc.
- One kind or two or more kinds selected from non-aqueous solvents known as those that can be used in the electrolyte can be used.
- Lithium salts 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, etc., one or more selected from various lithium salts known to be capable of functioning as a supporting electrolyte in the electrolyte of a lithium ion battery can be used.
- the concentration of the lithium salt is not particularly limited, and can be the same as, for example, the electrolyte used in a conventional lithium ion battery.
- a nonaqueous electrolyte containing a supporting electrolyte (lithium salt) at a concentration of about 0.1 mol / L to 5 mol / L (for example, about 0.8 mol / L to 1.5 mol / L) is preferably used. it can.
- a lithium secondary battery is constructed by housing the positive electrode and the negative electrode together with an electrolyte in a suitable container (a metal or resin casing, a bag made of a laminate film, etc.).
- a separator is interposed between the positive electrode and the negative electrode.
- a separator the thing similar to the separator used for a general lithium secondary battery can be used, and it does not specifically limit.
- a porous sheet made of a resin such as polyethylene (PE), polypropylene (PP), polyester, cellulose, or polyamide, a nonwoven fabric, or the like can be used.
- the electrolyte may also serve as a separator.
- the shape (outer shape of the container) of the lithium secondary battery is not particularly limited, and may be, for example, a cylindrical shape, a square shape, a coin shape, or the like.
- a lithium secondary battery including a wound electrode body and an assembled battery (battery pack) mounted on a vehicle as a constituent part (unit cell) are taken as an example and manufactured by the manufacturing method disclosed herein.
- a more specific embodiment of the lithium secondary battery using the negative electrode active material will be described, the present invention is not intended to be limited to such an embodiment.
- symbol is attached
- the dimensional relationship (length, width, thickness, etc.) in each drawing does not reflect the actual dimensional relationship.
- the cell 12 used as a component of the assembled battery 10 is typically a predetermined battery constituent material (positive Each of which includes an active material for each negative electrode, a current collector for each positive and negative electrode, a separator, and the like, and a container for housing the electrode body and an appropriate electrolyte.
- the assembled battery 10 disclosed herein includes a predetermined number (typically 10 or more, preferably about 10 to 30, for example, 20) of unit cells 12 having the same shape.
- the unit cell 12 includes a container 14 having a shape (a flat box shape in this embodiment) that can accommodate a flat wound electrode body to be described later.
- each part of the unit cell 12 may vary due to a dimensional error at the time of manufacturing the container 14 used.
- the container 14 is provided with a positive electrode terminal 15 electrically connected to the positive electrode of the wound electrode body and a negative electrode terminal 16 electrically connected to the negative electrode of the electrode body. As shown in the figure, one positive terminal 15 and the other negative terminal 16 are electrically connected by a connector 17 between adjacent unit cells 12.
- the assembled battery 10 of the desired voltage is constructed
- the container 14 can be provided with a safety valve 13 or the like for venting gas generated inside the container in the same manner as a conventional unit cell container. Since the configuration of the container 14 itself does not characterize the present invention, a detailed description is omitted.
- the material of the container 14 is not particularly limited as long as it is the same as that used in the conventional unit cell.
- a container made of metal for example, aluminum, steel, etc.
- a container made of synthetic resin for example, polyolefin resin such as polypropylene, high melting point resin such as polyethylene terephthalate, polytetrafluoroethylene, polyamide resin, etc.
- the container 14 according to the present embodiment is made of, for example, aluminum. As shown in FIG. 2 and FIG.
- the unit cell 12 has a sheet-like positive electrode 32 (hereinafter also referred to as “positive electrode sheet 32”) and a sheet-like negative electrode 34 (hereinafter referred to as “winding electrode body” of a normal lithium ion battery).
- positive electrode sheet 32 a sheet-like positive electrode 32
- a sheet-like negative electrode 34 hereinafter referred to as “winding electrode body” of a normal lithium ion battery.
- separator sheets 36 laminated together with a total of two sheet-like separators 36 (hereinafter also referred to as “separator sheets 36”), and the positive electrode sheet 32 and the negative electrode sheet 34 are wound while being slightly shifted.
- a flat wound electrode body 30 is provided which is produced by crushing and curling the obtained wound body from the side surface direction.
- a positive electrode lead terminal 32B and a negative electrode lead terminal 34B are attached to such a positive electrode side protruding portion (ie, a non-forming portion of the positive electrode active material layer) 32A and a negative electrode side protruding portion (ie, a non-forming portion of the negative electrode active material layer) 34A.
- the lead terminals 32B and 34B are electrically connected to the positive electrode terminal 15 and the negative electrode terminal 16, respectively.
- the material and the member itself constituting the wound electrode body 30 having the above-described configuration employ a negative electrode active material with a carbon coating obtained by the production method disclosed herein (for example, SiO x having the above general formula) as the negative electrode active material. Otherwise, it may be the same as the electrode body of the conventional lithium ion battery, and there is no particular limitation.
- the positive electrode sheet 32 is formed by applying a positive electrode active material layer for a lithium secondary battery on a long positive electrode current collector (for example, a long aluminum foil).
- a sheet-like positive electrode current collector having a shape that can be preferably used for the lithium secondary battery (unit cell) 12 including the wound electrode body 30 is used.
- a positive electrode prepared in advance using an aluminum foil having a length of 2 m to 4 m (eg, 2.7 m), a width of 8 cm to 12 cm (eg, 10 cm), and a thickness of about 5 ⁇ m to 30 ⁇ m (eg, 10 ⁇ m to 20 ⁇ m) as a current collector.
- a positive electrode active material layer is formed by applying a composite paste to the surface of the current collector.
- the paste can be suitably applied to the surface of the positive electrode current collector by using an appropriate application device such as a gravure coater, a slit coater, a die coater, or a comma coater.
- the solvent (typically water) contained in the paste is dried and compressed (pressed) to form a positive electrode active material layer.
- a conventionally known compression method such as a roll press method or a flat plate press method can be employed.
- the thickness may be measured with a film thickness measuring instrument, and the press pressure may be adjusted to compress a plurality of times until a desired thickness is obtained.
- the negative electrode sheet 34 may be formed by applying a negative electrode active material layer for a lithium secondary battery on a long negative electrode current collector.
- a conductive member made of a highly conductive metal, such as copper can be used.
- a sheet-like negative electrode current collector having a shape that can be preferably used for the lithium secondary battery (unit cell) 12 including the wound electrode body 30 is used.
- a copper foil having a length of 2 m to 4 m (for example, 2.9 m), a width of 8 cm to 12 cm (for example, 10 cm), and a thickness of about 5 ⁇ m to 30 ⁇ m (for example, 10 ⁇ m to 20 ⁇ m) is used as the negative electrode current collector.
- a negative electrode mixture paste prepared by adding and dispersing or dissolving an active material and a binder in an appropriate solvent (water, organic solvent and mixed solvent thereof) (for example, 80 to 90% by mass of a negative electrode active material, conductivity aid) 3 to 15% by mass of a material and 3 to 10% by mass of a binder) are applied, and the solvent can be preferably dried and compressed.
- a porous separator sheet 36 used between the positive / negative electrode sheets 32 and 34 what was comprised with the porous polyolefin resin is illustrated.
- a porous separator sheet made of a synthetic resin for example, made of polyolefin such as polyethylene
- a width of 8 to 12 cm for example, 11 cm
- a thickness of about 5 to 30 ⁇ m for example, 25 ⁇ m. It can be preferably used.
- a separator is unnecessary (that is, in this case, the electrolyte itself can function as a separator). ) Is possible.
- the obtained flat wound electrode body 30 is accommodated in the container 14 so that the winding axis is laid down as shown in FIG. 3, and an appropriate supporting salt (for example, a lithium salt such as LiPF 6 ).
- an appropriate supporting salt for example, a lithium salt such as LiPF 6 .
- DEC diethyl carbonate
- EC ethylene carbonate
- a single battery 12 is constructed by injecting a nonaqueous electrolyte (electrolytic solution) and sealing.
- the plurality of cells 12 having the same shape constructed as described above are inverted one by one so that the positive terminals 15 and the negative terminals 16 are alternately arranged, and the container 14 Wide surfaces (that is, surfaces corresponding to flat surfaces of a wound electrode body 30 to be described later housed in the container 14) are arranged in a facing direction.
- a cooling plate 11 having a predetermined shape is disposed in close contact with the wide surface of the container 14 between the arranged unit cells 12 and both outsides in the unit cell arrangement direction (stacking direction).
- the cooling plate 11 functions as a heat radiating member for efficiently dissipating heat generated in each unit cell during use.
- the cooling plate 11 is a cooling fluid (typically air) between the unit cells 12. It has a frame shape that can be introduced.
- a cooling plate 11 made of metal with good thermal conductivity or lightweight and hard polypropylene or other synthetic resin is suitable.
- a pair of end plates 18 are provided on the outer side of the cooling plate 11 arranged on both outsides of the unit cells 12 and the cooling plates 11 (hereinafter collectively referred to as “single cell group”). , 19 are arranged.
- One or a plurality of sheet-like spacer members 40 as length adjusting means are provided between the cooling plate 11 and the end plate 18 arranged on the outside of one of the unit cell groups (the right end in FIG. 2). It may be sandwiched.
- the constituent material of the spacer member 40 is not particularly limited, and various materials (metal material, resin material, ceramic material, etc.) can be used as long as the thickness adjusting function described later can be exhibited.
- a metal material or a resin material is preferably used from the viewpoint of durability against impact or the like.
- a lightweight polyolefin resin spacer member 40 can be preferably used.
- the single cell group, the spacer member 40 and the end plates 18 and 19 arranged in the stacking direction of the single cells 12 in this way are attached so as to bridge the end plates 18 and 19.
- the band 21 is restrained by a predetermined restraining pressure P in the stacking direction. More specifically, as shown in FIG. 1, by tightening and fixing the end of the restraining band 21 to the end plate 18 with screws 22, the unit cell group has a predetermined restraining pressure P (for example, the container 14) in the arrangement direction.
- the surface pressure received by the wall surface is constrained to be about 0.1 MPa to 10 MPa.
- the constraining pressure is also applied to the wound electrode body 30 inside the container 14 of each unit cell 12, and the gas generated in the container 14 is generated inside the wound electrode body 30. It is possible to prevent the battery performance from being deteriorated by being stored in (for example, between the positive electrode sheet 32 and the negative electrode sheet 34).
- a lithium secondary battery (sample battery) is constructed using a negative electrode including a granular negative electrode active material (silicon oxide) manufactured by the manufacturing method disclosed herein. The performance was evaluated.
- ⁇ Preparation of sample 1> 12 g of polyvinyl alcohol (PVA) as a carbon source was added to 150 mL of pure water as a first solvent, and stirred for 1 hour using a stirrer while applying ultrasonic waves to prepare a carbon source supply material. Also, commercially available silicon monoxide powder (SiO: Sigma-Aldrich product) and carbon black (CB) powder are put into a planetary ball mill so that the mass ratio is SiO: CB 10: 1, and the mixture is stirred at 250 rpm for 3 hours. Grinding and mixing were performed.
- SiO silicon monoxide powder
- CB carbon black
- a powder material containing silicon monoxide having an average particle diameter (median diameter based on light scattering method: d50) of about 400 nm is weighed in an amount of 12 g of silicon monoxide and added to 150 mL of ethanol by the above ball mill treatment. did. And it stirred for 1 hour using the stirrer, applying an ultrasonic wave, and prepared the electrode active material supply material of the state to which the silicon monoxide was disperse
- ⁇ Preparation of sample 2> In the preparation method of the sample 1, instead of adding aqueous H 3 PO 4 containing H 3 PO 4 equivalent to 1% by weight of the PVA, the H 3 PO 4 corresponding to 5% by weight of the PVA H 3 PO 4 aqueous solution weighed to contain was added. Other than this process, Sample 2 was prepared in the same manner as Sample 1 above.
- ⁇ Preparation of sample 3> In the preparation method of the sample 1, instead of adding aqueous H 3 PO 4 containing H 3 PO 4 equivalent to 1% by weight of the PVA, the H 3 PO 4 corresponding to 10% by weight of the PVA H 3 PO 4 aqueous solution weighed to contain was added. A sample 3 was prepared in the same manner as the sample 1 preparation method except for this process.
- ⁇ Preparation of sample 4> In the preparation method of the sample 1, instead of adding aqueous H 3 PO 4 containing H 3 PO 4 equivalent to 1% by weight of the PVA, the H 3 PO 4 corresponding to 20% by weight of the PVA H 3 PO 4 aqueous solution weighed to contain was added. A sample 4 was prepared in the same manner as the sample 1 preparation method except for this process.
- ⁇ Preparation of sample 5> In the preparation method of the sample 1, instead of adding aqueous H 3 PO 4 containing H 3 PO 4 equivalent to 1% by weight of the PVA, except for not completely added aqueous H 3 PO 4 is Sample 5 serving as a reference sample was prepared in the same manner as the sample 1 preparation method.
- test electrode active material The fired samples 1 to 5 obtained as described above were each crushed and classified with a 100-mesh sieve to obtain a test electrode active material.
- Test electrodes were prepared using the obtained 100-mesh under electrode active material particles. That is, the active material, graphite particles, and PVDF were mixed with N-methylpyrrolidone so that the mass ratio thereof was 85: 10: 5 to prepare a slurry composition (paste). This composition was applied to a copper foil having a thickness of 10 ⁇ m (manufactured by Japan Foil) and dried to form an active material layer having a thickness of 25 ⁇ m on one surface of the copper foil. This was pressed so that the total electrode density including the copper foil and the active material layer was 1.2 mg / cm 2, and then punched into a circle having a diameter of 16 mm to produce a test electrode.
- a metal lithium foil having a diameter of 15 mm and a thickness of 0.15 mm was used as the counter electrode.
- a porous polyolefin sheet having a diameter of 22 mm and a thickness of 0.02 mm was used.
- the electrolytic solution a solution obtained by dissolving LiPF 6 as a lithium salt at a concentration of about 1 mol / L in a mixed solvent of ethylene carbonate (EC) and diethyl carbonate (DEC) in a volume ratio of 3: 7 was used. .
- EC ethylene carbonate
- DEC diethyl carbonate
- cell of sample 1 Of the five types of coin cells prepared for each sample (hereinafter, the cell prepared using the electrode active material of sample 1 is referred to as “cell of sample 1”. The same applies to samples 2 to 5).
- the test electrode was used until the interelectrode voltage reached 0.01 V at a constant current of 0.1 C (1 C, that is, a current value that is 0.1 times the current value that can be fully charged and discharged in 1 hour).
- a cycle test was performed in which an operation of inserting Li and an operation of desorbing Li from the test electrode until the interelectrode voltage reached 1.2 V at a constant current of 0.1 C. In the cycle test for the sample 1 cell, up to 100 cycles were performed.
- Li insertion capacity per unit mass of the active material Li insertion capacity per unit mass of the active material: mAh / g
- the cycle characteristics (capacity maintenance ratio) of each cell of Samples 1 to 5 were examined. Specifically, for the cells of Samples 1, 2, 4, and 5, in the cycle test, the ratio of the 100th Li desorption capacity to the first Li insertion capacity was measured as the capacity retention rate (%). Specifically, it was obtained from the following formula: (100th Li Desorption Capacity) / (First Li Insertion Capacity) ⁇ 100. The results are shown in Table 1 and FIG. Regarding the cycle characteristics (capacity retention rate) of the sample 3 cell, the ratio of the 50th Li desorption capacity to the first Li insertion capacity was measured as the capacity retention rate (%) in the cycle test. The results are shown in Table 1 and FIG.
- the cells (samples 1 to 4) employing the electrode active materials of Samples 1 to 4 manufactured by the manufacturing method disclosed herein are Samples 5 which are reference samples.
- a capacity maintenance ratio higher than the capacity maintenance ratio of the cell (13.7%) could be realized.
- the capacity retention rate (42.3%) of the sample 1 cell to which 1% by mass of H 3 PO 4 was added was higher than that of the sample 5, and even when such an amount of H 3 PO 4 was added, the durability of the cell was increased. It was confirmed that the effect was exhibited in (cycle characteristics).
- the cells of Samples 2, 3 and 4 to which H 3 PO 4 was added in an amount of 5% by mass or more of PVA showed a high capacity maintenance rate of 60% or more, and a capacity maintenance rate significantly higher than that of Sample 5.
- sample 2 to which 5% by mass of P3 added H 3 PO 4 and sample 5 of the reference sample both have the same amount (30% by mass) of carbon content (content ratio). Even if the amount is the same, it was confirmed that the cell including the active material made of the mixed material to which H 3 PO 4 is added has improved durability (cycle characteristics).
- the cell of sample 6 was able to achieve a higher capacity retention rate (%) than the cell of sample 7 as the reference sample. From this, it was confirmed that the mixed material to which H 3 BO 3 is added can also be used as an active material for improving the capacity retention rate (ie, cycle characteristics) of the cell. In other words, by adding a compound containing boron to the mixed material, an effect similar to the effect of adding a compound containing phosphorus to the mixed material can be obtained.
- any of the lithium secondary battery 12 and the assembled battery 10 disclosed herein may have a performance suitable as a battery mounted on a vehicle, in particular, a high capacity maintenance ratio and an excellent durability. Further, by using a metal oxide such as SiO x as the electrode active material, a high capacity can be realized. Therefore, according to this invention, as shown in FIG. 4, the vehicle 1 provided with one of the lithium secondary batteries 12 (assembled battery 10) disclosed here is provided. In particular, a vehicle (for example, an automobile) including the lithium secondary battery 12 as a power source (typically, a power source of a hybrid vehicle or an electric vehicle) is provided.
- a power source typically, a power source of a hybrid vehicle or an electric vehicle
- an electrode active material that is excellent in capacity retention rate (that is, cycle characteristics) and can realize high capacity. Therefore, by using such an electrode active material, it is possible to provide a secondary battery such as a lithium secondary battery having high capacity and good durability.
- a vehicle-mounted secondary battery particularly a vehicle-mounted lithium secondary battery used as a power source for driving a vehicle. Can be provided.
Abstract
Description
車両搭載用高出力電源として利用される二次電池に求められる特性の一つとして電池容量の向上がある。かかる要求に応えるべく、従来使用されているものよりも高容量化を実現できる物質を電極活物質として利用することが検討されている。例えば、リチウム二次電池に関しては、Si、Ge、Sn、Pb、Al、Ga、In、As、Sb、Bi等を構成金属元素(半金属元素を包含する。以下同じ。)とする金属化合物(典型的には金属酸化物)材料がリチウムイオンを可逆的に吸蔵および放出する電極活物質(具体的には負極活物質)として使用することが可能であり、しかも負極活物質として従来用いられている黒鉛材料よりも高容量であることが知られている。したがって、これら金属化合物(典型的には金属酸化物)を電極活物質として利用することによってリチウム二次電池の高容量化が実現されることが期待されている。
上記のような金属化合物材料としてケイ素またはケイ素酸化物を使用した電極活物質に関する従来技術の例としては、以下の特許文献1~3が挙げられる。特許文献1には、Siと、SiOおよびSiO2と炭素質物とからなる複合粒子の表面を炭素で被覆した電極活物質が記載されている。また、特許文献2では、炭素質物と該炭素質物中に分散されたシリコン(ケイ素)酸化物とからなる粒子であって該シリコン酸化物中にシリコン相および金属相(該金属相はNiもしくはCuを含む)とが分散している複合体粒子を含む電極活物質が記載されている。また、本願発明とは直接関係しないが、特許文献3には、リンやホウ素が不純物としてドープされている単結晶シリコン粒子から構成される多結晶シリコン粉末を主体とする負極材料(負極活物質)が記載されている。
すなわち、ここで開示される一つの製造方法は、表面が導電性炭素被膜で被覆された粒状電極活物質を製造する方法である。かかる方法は、
(1)上記炭素被膜を形成するための炭素源を、上記被覆の対象である粒状電極活物質が分散可能な所定の第1の溶媒に、溶解させることにより調製された炭素源供給材料を用意すること、
(2)上記被覆の対象である粒状電極活物質を、上記第1の溶媒と相溶性があり且つ該粒状電極活物質が分散可能な溶媒であって上記炭素源に対して貧溶媒である第2の溶媒に、分散させることにより調製された電極活物質供給材料を用意すること、
(3)上記用意した炭素源供給材料と電極活物質供給材料とを混合した混合材料を調製すること、
(4)上記調製された混合材料に、リン(P)またはホウ素(B)を含む化合物を添加すること、
(5)上記添加後に得られた上記電極活物質粒子と上記炭素源との混合物を焼成することによって、該炭素源由来の導電性炭素被膜を該電極活物質の表面に形成すること、
を包含する。
かかる二つの材料を混合して生じる上記第1の溶媒と第2の溶媒とが混在する(相溶する)混合溶媒中において、上記炭素源は、第2の溶媒(貧溶媒)成分中には存在困難であり実質的には第1の溶媒成分中にのみ存在することとなる。他方、粒状電極活物質は、第1と第2の何れの溶媒においても流動、分散することができる。換言すれば、上記混合溶媒中において第1と第2の溶媒成分間を自由に行き来して分散する電極活物質粒子は、第1の溶媒成分中に存在しているときに該溶媒中に存在する炭素源と相互作用する。典型的には炭素源が電極活物質粒子の表面に付着若しくは結合する。そして、炭素源と相互作用した状態にある電極活物質粒子(典型的には炭素源が表面に付着若しくは結合した電極活物質粒子)は、第1の溶媒から第2の溶媒への移動が当該相互作用した炭素源の存在により規制される。このため、上記第1の溶媒成分と第2の溶媒成分とが混在する混合溶媒中において、分散する電極活物質粒子に効率よく炭素源を相互作用させる(付着若しくは結合させる)ことができるとともに、電極活物質粒子同士の過度な凝集が抑制される。
ここで開示される製造方法によると、上記混合材料にリンまたはホウ素を含む化合物を添加すると、かかる混合材料内では上記分散する電極活物質粒子と炭素源との相互作用(付着もしくは結合)が保持されつつ、かかるリンまたはホウ素の存在により上記混合材料の焼成後には導電パスとなり得る炭素原子同士の結合強度が向上した炭素被膜が電極活物質の一次粒子表面に形成され得る。
したがって、ここで開示される製造方法によると、炭素原子同士が強固に結合した炭素被膜が一次粒子の表面に良好に(すなわち、被膜の非形成部分が少ない状態で)形成されて優れたサイクル特性を実現し得る粒状電極活物質を製造することができる。
このような化合物を採用することにより、上記炭素源の炭素同士の結合を強固にする効果がより一層好ましく発揮されて、炭素同士の結合強度が向上した炭素被膜が形成された良質な粒状電極活物質を製造することができる。
また、上記のケイ素酸化物あるいは他の上記した金属種の化合物(典型的には金属酸化物)からなる電極活物質は、充放電の際、リチウムイオンの吸蔵および放出に伴って膨張若しくは収縮して体積が大きく変動する。その際、上述したように二次粒子(すなわち一次粒子の凝集体)の表面のみに炭素被膜が形成されている活物質では、上記膨張と収縮に伴う応力により当該二次粒子が破砕してしまい、結果、炭素被膜が形成されていない表面を備える粒状物が生じてしまう。炭素被膜が形成されていない上記ケイ素酸化物その他の金属化合物は炭素被膜による導電パスが存在せず、電極活物質としての電池容量の向上に寄与しない。また、電池の耐久性、特にサイクル特性の劣化を招くため好ましくない。
これに対し、ここで開示される製造方法によると、一次粒子の表面に効率良く炭素原子同士が強固に結合した炭素被膜を形成することができる。このため、リチウムイオンの吸蔵および放出に伴って活物質が膨張若しくは収縮して体積が大きく変動しても、炭素被膜が形成されていない表面を備える粒状物(二次粒子の破砕物)は生じ難い。また炭素被膜の炭素間結合も切断されにくいので導電パスも良好に維持される。したがって、安定的に高容量を維持し、サイクル特性にも優れる電池の構築に資する炭素被膜付き電極活物質を提供することができる。
このような組み合わせで第1の溶媒と第2の溶媒とを採用することにより、より良好に一次粒子の表面に炭素被膜が形成された粒状電極活物質を製造することができる。
上記混合材料に対して上記リンまたはホウ素を含む化合物を添加する前に還流処理を行う(典型的には混合材料の溶媒が沸騰可能な温度域で行う)ことにより、かかる添加前に、より好適に粒状電極活物質を当該混合材料中において分散させておくことができる。このため、より効率よく、また、より均質に、電極活物質粒子の表面に炭素間の結合が強固な炭素被膜を形成することができる。
ここで開示されるリチウム二次電池は、上記電極活物質を備えることによって高容量化と良好な電気伝導性を実現し得る。このため、特にハイレート充放電が要求される車両に搭載される電池として適した性能を備える。
したがって本発明によると、ここで開示されるリチウム二次電池を備えた車両が提供される。特に、該リチウム二次電池を動力源(典型的には、ハイブリッド車両または電気車両の動力源)として備える車両(例えば自動車)が提供される。
なお、本明細書において「電極活物質」は、正極側で使用される正極活物質と負極側で使用される負極活物質を包含する用語である。ここで活物質とは、正極側または負極側において蓄電に関与する物質(化合物)をいう。すなわち、電池の充放電時において電子の放出若しくは取り込みに関与する物質をいう。
また、本明細書において「リチウム二次電池」は、電解質中のリチウムイオンが電荷の移動を担う電池をいい、いわゆるリチウムイオン電池(若しくはリチウムイオン二次電池)、リチウムポリマー電池等と呼ばれているものは、ここでいう「リチウム二次電池」に包含される典型例である。
ここで開示される製造方法は、電気伝導性の乏しい電極活物質粒子(すなわち一次粒子)の表面を効率よく炭素間結合の強固な導電性炭素被膜で被覆することができる。
かかる被覆を行う対象である粒状電極活物質としては、少なくとも上記第1の溶媒および第2の溶媒に分散可能であり、焼成により炭素源由来の導電性炭素被膜が表面に形成され得る性状の活物質であればよい。例えば、リチウム二次電池の負極活物質として好適な種々の金属化合物(例えば金属酸化物)、例えばSi、Ge、Sn、Pb、Al、Ga、In、As、Sb、Bi等を構成金属元素とする金属化合物(好ましくは金属酸化物)が挙げられる。特に、上記式により規定されるようなケイ素酸化物を好ましく採用することができる。また、リチウム二次電池の正極活物質として使用し得る種々のリチウム遷移金属複合酸化物(例えばLiCoO2、LiNiO2、LiMn2O4)を採用することができる。
例えば、一般式:LiMAO4で示されるポリアニオン化合物が挙げられる。かかる式中のMは、典型的にはFe、Co、NiおよびMnからなる群から選択される少なくとも1種の金属元素を含む1種または2種以上の元素(典型的には1種または2種以上の金属元素)である。すなわち、Fe、Co、NiおよびMnからなる群から選択される少なくとも1種の金属元素を含むが他の少量含有され得るマイナー添加元素の存在を許容する(かかるマイナー添加元素は存在しなくてもよい。)。また、上記式中のAは、典型的には、P、Si、SおよびVからなる群から選択される1種または2種以上の元素である。
電極活物質の特に好適な具体例として、一般式:SiOxで示されるケイ素酸化物が挙げられる。ここで式中のxは典型的には0<x<2を満足する実数であり、好ましくは0<x<0.6程度であり得る。市販されるSiO等のケイ素酸化物からなる粉末材料を好適に使用することができる。
かかるケイ素酸化物を負極活物質として利用することにより、特に高い充放電容量を有するリチウム二次電池が得られ得る。また、この種の金属化合物からなるリチウム二次電池用負極活物質は、充放電時におけるリチウムイオンの吸蔵に伴って活物質自体が膨張し、反対にリチウムイオンの放出に伴って活物質自体が収縮する。したがって、電池の負極に存在する負極活物質構造物(すなわち一次粒子が凝集した二次粒子によって典型的には銅等の負極集電体の表面に層状に構成されている。)の構造変化が起き易く、構造変化後の負極活物質構造物にも高い電気伝導性を維持させるためには当該負極活物質構造物を構成する一次粒子の表面に充分に導電性炭素被膜を予め形成しておく必要がある。ここに開示される製造方法を実施することによって、このような性状の電極活物質の一次粒子の表面に効率よく充分な導電性炭素被膜を形成することができる。
例えば、水溶性有機物(特に水溶性ポリマー等の高分子化合物)であって所定の有機溶媒には溶解性が乏しい(すなわち当該有機溶媒は貧溶媒に該当する。)ような性質を有する水溶性有機物を好ましく使用することができる。
この種の有機物の好適例としてポリビニルアルコール(PVA)のような水溶性高分子化合物(ポリマー)が挙げられる。PVAは、分子鎖中に多くのヒドロキシ基(-OH)を有しており、かかるヒドロキシ基の存在により、電極活物質粒子との相互作用(例えば、水素結合、共有結合、イオン結合等の化学的結合、あるいは吸着等の物理的結合)を起こし易く好ましい。また、大気中のような酸化条件下での熱分解により、良好な導電性を示す炭素被膜を形成することができるため好ましい。PVAの他、炭素源として使用可能な水溶性高分子化合物として、デンプン、ゼラチン、メチルセルロース、カルボキシメチルセルロース等のセルロース誘導体、ポリアクリル酸、ポリアクリルアミド、ポリエチレンオキシド、ポリエチレングリコール、ポリメタクリル酸、ポリビニルピロリドン等が挙げられる。
また、上記ホウ素を含む化合物についても、上記リンを含む化合物と同様に、上記炭素源供給材料に溶解し得るもの、あるいは該炭素源供給材料と相溶性のある液状媒体に溶解し得るものが好ましい。例えば、上記第1の溶媒が水性溶媒である場合は、無機ホウ酸を好ましく採用することができる。好適な化合物として例えばオルトホウ酸(H3BO3)、次ホウ酸(H4B2O4)、ボロン酸(H3BO2)、過ホウ酸(HBO3)、メタホウ酸((HBO2)n)等が挙げられる。これらのうちの少なくとも一種を用いることが好ましい。典型的にはオルトホウ酸が特に好適に用いられ得る。
先ず、ここで開示される製造方法に使用される炭素源供給材料は、所定の炭素源(1種類の炭素源のみを用いてもよく、2種類以上の炭素源を組み合わせて用いてもよい。)を溶解可能な第1の溶媒に適量を溶解させることにより調製される。第1の溶媒(すなわち炭素源供給材料を調製するための溶媒)は、便宜上第1の溶媒と記載しているが、それ自体が単独の物質(分子種)により構成されていてもよく、あるいは複数の物質(分子種)の混合媒体であってもよい。第1の溶媒は、使用する炭素源に応じて選択することができる。例えば、PVA等の水溶性有機物を炭素源として使用する場合、当該化合物を好適に溶解し得る水性溶媒が好ましい。典型的には、水(蒸留水や脱イオン水を包含する。)を第1の溶媒として使用することができる。
なお、本発明の目的を妨げない限りにおいて、炭素源供給材料に、上述した第1の溶媒ならびに炭素源以外の成分を含ませてもよい。例えば、付加的な成分としては、pH調整剤、界面活性剤、防腐剤、着色剤、等が挙げられる。
第2の溶媒は、使用する粒状電極活物質が分散可能であることに加え、第1の溶媒と相溶性があり、且つ、使用する炭素源に対して貧溶媒であることが要求される。例えば、PVA、ポリアクリル酸、ポリエチレングリコール等の水溶性有機物(典型的には水溶性ポリマー)を第1の溶媒としての水に溶解させて炭素源供給材料として使用する場合、水と相溶性があり且つ当該炭素源が溶け難い(すなわち非常に溶解度が小さい)有機溶媒を第2の溶媒として好ましく使用することができる。例えば、PVAに対して貧溶媒であるアルコール類、例えば水によく溶けるメタノール、エタノール、イソプロパノール、2-メチル-2-ブタノールのような炭素数4以下の低級アルコールを第2の溶媒として好適に使用することができる。このように、使用する炭素源をいったん決定すれば、その炭素源に対して貧溶媒であることが公知である何れかの溶媒を適宜選択すればよいことは、当業者には理解される。
なお、本発明の目的を妨げない限りにおいて、電極活物質供給材料に、上述した第2の溶媒ならびに粒状電極活物質以外の成分を含ませてもよい。例えば、付加的な成分としては、典型的にはカーボンブラック等の炭素材からなる導電補助材、分散剤、pH調整剤、界面活性剤、防腐剤、着色剤、等が挙げられる。例えば、SiOxのようなケイ素酸化物あるいは上述したような他の金属化合物(酸化物等)からなる電極活物質全量の1~20質量%に相当する量の導電補助材(例えばカーボンブラックのような微粒状の導電性炭素材)を添加することが好ましい。
一つの目安として、電極活物質の表面に充分量の炭素源が付与されるように両供給材料を混合することが好ましい。例えば、1質量部の粒状電極活物質(例えばケイ素酸化物)に対して0.05~15質量部程度の炭素源(例えばPVA)が混合されるように、炭素源供給材料と電極活物質供給材料との混合割合を調整することが適当である。1質量部の粒状電極活物質(例えばケイ素酸化物)に対して0.1~10質量部程度(例えば0.5~5質量部程度或いは1~5質量部程度)の炭素源(例えばPVA)が混合されるようにして上記炭素源供給材料と電極活物質供給材料とを混合して混合材料を調製することが好ましい。このような混合比率で炭素源と粒状電極活物質とを混合することにより、電極活物質の表面に適当量の炭素源を付与することができる。
このように、第1の溶媒と第2の溶媒との混合体積比率を設定することによって、電極活物質粒子相互の凝集を低減し、比較的小粒径の電極活物質二次粒子(会合体)を形成することができる。このことは、換言すれば、第1の溶媒と第2の溶媒との混合体積比率を調整することによって、焼成後に得られる炭素被膜付き電極活物質粒子(一次粒子の凝集体、すなわち二次粒子)の粒径やサイズを調整することができる。
例えば、第1の溶媒が水であり、第2の溶媒が水と相溶性のある非水溶媒であるエタノール(または他の低級アルコール)である場合、該水とエタノールの共沸温度である約73℃を上回る温度域(典型的には80~100℃、例えば90±5℃程度)で適当時間、典型的には1時間~24時間程度(例えば8時間~12時間)の還流処理を行うことが好ましい。なお、還流処理自体は、従来技術であり、本発明の実施において特別な処理を必要としないため、これ以上の詳細な説明は省略する。
第3の溶媒としては、上記の条件を具備する限りにおいて種々の溶媒を使用することができるが、例えば上記第1の溶媒が水性溶媒(典型的には水)であって、前記炭素源が水溶性化合物(例えばPVA)である場合、上記第3の溶媒(貧溶媒)としては、該水性溶媒と相溶性があり且つ水溶性化合物の溶解が困難な有機溶媒が好ましい。例えば、該水溶性化合物の溶解が困難な非プロトン性の極性溶媒(例えばアセトン、アセトニトリル)が好ましく使用される。
負極集電体としては、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。バインダとしては、ポリフッ化ビニリデン(PVDF)、ポリテトラフルオロエチレン(PTFE)、カルボキシメチルセルロース(CMC)、スチレンブタジエンゴム(SBR)等が例示される。導電補助材としては、従来と同様のカーボンブラック等の炭素材を好ましく使用することができる。
正極集電体としては、アルミニウム、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。正極活物質としては、一般的なリチウム二次電池の正極に用いられ得る層状構造のリチウム遷移金属複合酸化物、スピネル構造のリチウム遷移金属複合酸化物、オリビン構造を有するポリアニオン化合物、等を好ましく用いることができる。かかる活物質の代表例として、コバルト酸リチウム(LiCoO2)、ニッケル酸リチウム(LiNiO2)、マンガン酸リチウム(LiMn2O4)等のリチウム遷移金属酸化物やが挙げられる。また、以下の一般式:
LiMAO4
で示される化合物が挙げられる。かかる式中のMは、Fe、Co、NiおよびMnからなる群から選択される少なくとも1種の金属元素を含む1種または2種以上の元素(典型的には1種または2種以上の金属元素)である。すなわち、Fe、Co、NiおよびMnからなる群から選択される少なくとも1種の金属元素を含むが他の少量含有され得るマイナー添加元素の存在を許容する(かかるマイナー添加元素は存在しなくてもよい。)。また、上記式中のAは、P、Si、SおよびVからなる群から選択される1種または2種以上の元素であることが好ましい。具体例としてLiFePO4、LiFeSiO4、LiCoPO4、LiCoSiO4、LiFe0.5Co0.5PO4、LiFe0.5Co0.5SiO4、LiMnPO4、LiMnSiO4、LiNiPO4、LiNiSiO4が特に好ましいポリアニオン型化合物として挙げられる。
そして、負極側と同様、上記したような正極活物質および導電補助材を含む粉末状材料を適当なバインダとともに適当な分散媒体に分散させて混練することによって、ペースト状の正極合材(以下、「正極合材ペースト」という。)を調製する。この正極合材ペーストを正極集電体上に適当量塗布し、さらに乾燥ならびにプレスすることによってリチウム二次電池用正極を作製することができる。
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また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、厚み等)は実際の寸法関係を反映するものではない。
ここで開示される組電池10は、所定数(典型的には10個以上、好ましくは10~30個程度、例えば20個)の同形状の単電池12を備える。単電池12は、後述する扁平形状の捲回電極体を収容し得る形状(本実施形態では扁平な箱形)の容器14を備える。単電池12の各部のサイズ(例えば、積層方向の厚み等の外形形状)は、使用する容器14の製造時における寸法誤差等によりばらつき得る。
容器14には、捲回電極体の正極と電気的に接続する正極端子15および該電極体の負極と電気的に接続する負極端子16が設けられている。図示するように、隣接する単電池12間において一方の正極端子15と他方の負極端子16とが接続具17によって電気的に接続される。このように各単電池12を直列に接続することにより、所望する電圧の組電池10が構築される。
なお、容器14には、容器内部で発生したガス抜きのための安全弁13等が従来の単電池容器と同様に設けられ得る。かかる容器14の構成自体は本発明を特徴付けるものではないため、詳細な説明は省略する。
図2および図3に示すように、単電池12は、通常のリチウムイオン電池の捲回電極体と同様、シート状正極32(以下「正極シート32」ともいう。)とシート状負極34(以下「負極シート34」ともいう。)とを計二枚のシート状セパレータ36(以下「セパレータシート36」ともいう。)とともに積層し、さらに当該正極シート32と負極シート34とをややずらしつつ捲回し、次いで得られた捲回体を側面方向から押しつぶして拉げさせることによって作製される扁平形状の捲回電極体30を備える。
正極シート32は長尺状の正極集電体(例えば長尺状アルミニウム箔)の上にリチウム二次電池用正極活物質層が付与されて形成される。本実施形態では、捲回電極体30を備えるリチウム二次電池(単電池)12に好ましく使用され得る形状であるシート状正極集電体が用いられている。例えば、長さ2m~4m(例えば2.7m)、幅8cm~12cm(例えば10cm)、厚み5μm~30μm(例えば10μm~20μm)程度のアルミニウム箔を集電体として使用し、予め調製された正極合材ペーストを当該集電体表面に塗布することにより、正極活物質層を形成する。そして、グラビアコーター、スリットコーター、ダイコーター、コンマコーター等の適当な塗付装置を使用することにより、正極集電体の表面に上記ペーストを好適に塗付することができる。
なお、電解質として固体電解質若しくはゲル状電解質を使用するリチウム二次電池(いわゆるリチウムイオンポリマー電池)の場合には、セパレータが不要な場合(すなわちこの場合には電解質自体がセパレータとしても機能し得る。)があり得る。
炭素源としてのポリビニルアルコール(PVA)12gを第1の溶媒としての純水150mLに添加し、超音波をかけながらスターラーを用いて1時間攪拌し、炭素源供給材料を調製した。
また、市販の一酸化ケイ素粉末(SiO:シグマ・アルドリッチ社製品)とカーボンブラック(CB)粉末を、質量比でSiO:CB=10:1となるように遊星ボールミルに入れ、250rpmで3時間の粉砕・混合処理を行った。
上記ボールミル処理により平均粒子径(光散乱法に基づくメジアン径:d50)が約400nmである一酸化ケイ素を含む粉末材料を、一酸化ケイ素質量が12gとなる量を秤量し、150mLのエタノールに添加した。そして、超音波をかけながらスターラーを用いて1時間攪拌し、一酸化ケイ素が分散した状態の電極活物質供給材料を調製した。
次に、上記調製した電極活物質供給材料(第2の溶媒:エタノール)を、超音波をかけながらスターラーで攪拌しつつ上記調製した炭素源供給材料(第1の溶媒:純水)に添加した。
このようにして得られた混合材料、すなわち12gのSiOと12gのPVAと1.2gのCBを含み、純水150mLとエタノール150mLとの混合溶媒(体積比で水:エタノール=1:1)からなる混合材料について90℃で12時間の還流処理を行った。
上記サンプル1の調製方法において、PVAの質量の1質量%に相当するH3PO4を含むH3PO4水溶液を添加する代わりに、PVAの質量の5質量%に相当するH3PO4を含むように秤量されたH3PO4水溶液を添加した。このプロセス以外は、上記サンプル1の調製方法と同様にしてサンプル2を調製した。
<サンプル3の調製>
上記サンプル1の調製方法において、PVAの質量の1質量%に相当するH3PO4を含むH3PO4水溶液を添加する代わりに、PVAの質量の10質量%に相当するH3PO4を含むように秤量されたH3PO4水溶液を添加した。このプロセス以外は、上記サンプル1の調製方法と同様にしてサンプル3を調製した。
<サンプル4の調製>
上記サンプル1の調製方法において、PVAの質量の1質量%に相当するH3PO4を含むH3PO4水溶液を添加する代わりに、PVAの質量の20質量%に相当するH3PO4を含むように秤量されたH3PO4水溶液を添加した。このプロセス以外は、上記サンプル1の調製方法と同様にしてサンプル4を調製した。
<サンプル5の調製>
上記サンプル1の調製方法において、PVAの質量の1質量%に相当するH3PO4を含むH3PO4水溶液を添加する代わりに、H3PO4水溶液を全く添加しなかったこと以外は、該サンプル1の調製方法と同様にして、参照試料となるサンプル5を調製した。
上記得られたサンプル1~5を用いて評価用セルを構築した。
すなわち、各サンプルをアルゴンガス雰囲気中において最高焼成温度を約1000℃に設定し、当該温度で約6時間の焼成を行った。なお、試料を200℃~300℃の温度域で予め1~5時間程度の仮焼成を行った後に最高焼成温度まで昇温した。これによりPVAの不要なヒドロキシ基を消失させることができる。
ここで、上記焼成後のサンプル1において、該サンプル1に含まれる炭素量の該サンプル1の全質量に対する割合(含有率;質量%)を以下のようにして求めた。
即ち、先ず、大気中で上記サンプル1の示差熱-熱重量同時測定(TG-DTA)を行った。この際、ブランクとしてSiOのTG-DTAも合わせて行った。そして、当該TG-DTAの結果からサンプル1の重量減少量を求め、この重量減少量に基づいて該サンプル1の全質量に対する炭素量の割合を算出した。
なお、上記サンプル2~5の全質量に対する炭素量の割合についても同様にして求めた。これらの結果を表1および図8に示した。
これらの構成要素をステンレス製容器に組み込んで、厚み2mm、直径32mm(いわゆる2032型)の一般的形状の評価用コインセルを構築した。
また、サンプル2~5のセルについても上記サンプル1のセルのサイクル試験と同様に100サイクルまで実施して、サイクル毎の活物質の単位質量あたりのLi挿入容量を求めた。この結果を図7に示した。サンプル3のセルについては、上記サンプル1のセルと同様のプロセスで50サイクルまでサイクル試験を実施し、サイクル毎の活物質の単位質量あたりのLi挿入容量を求めた。この結果を図7に示した。
具体的には次式:(100回目のLi脱離容量)/(1回目のLi挿入容量)×100より求めた。結果を表1および図8に示す。また、サンプル3のセルのサイクル特性(容量維持率)については、上記サイクル試験において、1回目のLi挿入容量に対する50回目のLi脱離容量の割合を容量維持率(%)として測定した。この結果を表1および図8に示す。
さらに、H3PO4をPVAの5質量%添加したサンプル2と参照試料のサンプル5とは、どちらも同程度(30質量%)の炭素量(含有率)を有していることから、炭素量が同じであっても、H3PO4が添加されている混合材料からなる活物質を備えるセルの方が、耐久性(サイクル特性)が向上することが確認された。
次に、上記調製された混合材料にリン(P)に代えてホウ素(B)を含む化合物を添加した実施例について説明する。
具体的には、上記サンプル1の調製方法において、オルトリン酸(H3PO4)水溶液を添加する代わりに、上記混合材料に含まれるPVAの質量の10質量%に相当する市販のホウ酸(H3BO3)を含むように秤量されたH3BO3水溶液を添加した。このプロセス以外は、上記サンプル1の調製方法と同様にしてサンプル6を調製した。
<サンプル7の調製>
サンプル6に対する参照試料として、上記サンプル6の調製方法において、H3BO3水溶液を全く添加しなかったこと以外は、該サンプル6と同様の調製方法でサンプル7を調製した。
上記サンプル1~5を用いて評価用セルを構築したときと同様の手法により上記サンプル6、7を用いて評価用セル(コインセル)を構築した。
そして、上述のサンプル1~5を用いて構築した評価用セル(コインセル)を使用した場合と同様に当該サンプル6若しくはサンプル7を用いて構築した2種類のコインセルに対してサイクル試験を実施し、各々のセルの容量維持率(%)を測定した。なお、ここでは、上記サイクル試験を52サイクルまで実施した。この結果として、各サイクルにおける容量維持率(%)を図9に示し、最終サイクル(52サイクル目)の容量維持率(%)を表2に示す。
ここに開示されるいずれかのリチウム二次電池12および組電池10は、車両に搭載される電池として適した性能、特に容量維持率が高く耐久性に優れたものであり得る。また、電極活物質としてSiOx等の金属酸化物を採用することにより高容量化を実現することができる。
したがって本発明によると、図4に示すように、ここに開示されるいずれかのリチウム二次電池12(組電池10)を備えた車両1が提供される。特に、該リチウム二次電池12を動力源(典型的には、ハイブリッド車両または電気車両の動力源)として備える車両(例えば自動車)が提供される。
10 組電池
12 リチウム二次電池(単電池)
15 正極端子
16 負極端子
30 捲回電極体
32 正極シート
34 負極シート
102 炭素源
104 電極活物質
Claims (10)
- 表面が導電性炭素被膜で被覆された粒状電極活物質を製造する方法であって:
前記炭素被膜を形成するための炭素源を、前記被覆の対象である粒状電極活物質が分散可能な所定の第1の溶媒に、溶解させることにより調製された炭素源供給材料を用意すること;
前記被覆の対象である粒状電極活物質を、前記第1の溶媒と相溶性があり且つ該粒状電極活物質が分散可能な溶媒であって前記炭素源に対して貧溶媒である第2の溶媒に、分散させることにより調製された電極活物質供給材料を用意すること;
前記用意した炭素源供給材料と電極活物質供給材料とを混合した混合材料を調製すること;
前記調製された混合材料に、リン(P)またはホウ素(B)を含む化合物を添加すること;および
前記添加後に得られた前記電極活物質粒子と前記炭素源との混合物を焼成することによって、該炭素源由来の導電性炭素被膜を該電極活物質の表面に形成すること;
を包含する、製造方法。 - 前記リンまたはホウ素を含む化合物を前記混合材料に添加するにあたり、該化合物は少なくとも前記第1の溶媒と相溶性のある液状媒体に溶解した溶液の形態で提供される、請求項1に記載の製造方法。
- 前記リンを含む化合物として、少なくとも一種の無機リン酸を使用する、請求項1または2に記載の製造方法。
- 前記ホウ素を含む化合物として、少なくとも一種の無機ホウ酸を使用する、請求項1または2に記載の製造方法。
- 前記電極活物質は、一般式:SiOx(式中のxは0<x<2を満足する実数)で示されるケイ素酸化物を主体に構成されている、請求項1~4のいずれかに記載の製造方法。
- 前記炭素源は水溶性化合物であり、前記第1の溶媒は水性溶媒であり、前記第2の溶媒は水と相溶性のある非水溶媒である、請求項1~5のいずれかに記載の製造方法。
- 前記リンまたはホウ素を含む化合物を添加する前に、前記混合材料を還流処理すること、
をさらに包含する、請求項1~6のいずれかに記載の製造方法。 - 請求項1~7のいずれかに記載の製造方法により製造された電極活物質。
- 請求項8に記載の電極活物質を正極または負極に備えるリチウム二次電池。
- 請求項9に記載のリチウム二次電池を備える、車両。
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JP5445878B2 (ja) | 2014-03-19 |
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KR101510510B1 (ko) | 2015-04-08 |
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