WO2015173623A1 - Procédé de fabrication de batterie secondaire - Google Patents

Procédé de fabrication de batterie secondaire Download PDF

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Publication number
WO2015173623A1
WO2015173623A1 PCT/IB2015/000681 IB2015000681W WO2015173623A1 WO 2015173623 A1 WO2015173623 A1 WO 2015173623A1 IB 2015000681 W IB2015000681 W IB 2015000681W WO 2015173623 A1 WO2015173623 A1 WO 2015173623A1
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WIPO (PCT)
Prior art keywords
positive electrode
separator
cell
foreign metal
secondary battery
Prior art date
Application number
PCT/IB2015/000681
Other languages
English (en)
Inventor
Takashi Harayama
Koji Takahara
Tomohide Sumi
Tomoyasu Furuta
Original Assignee
Toyota Jidosha Kabushiki Kaisha
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Application filed by Toyota Jidosha Kabushiki Kaisha filed Critical Toyota Jidosha Kabushiki Kaisha
Publication of WO2015173623A1 publication Critical patent/WO2015173623A1/fr

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Classifications

    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/42—Methods or arrangements for servicing or maintenance of secondary cells or secondary half-cells
    • H01M10/44—Methods for charging or discharging
    • H01M10/446—Initial charging measures
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/04—Construction or manufacture in general
    • H01M10/0431—Cells with wound or folded electrodes
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/04—Construction or manufacture in general
    • H01M10/049—Processes for forming or storing electrodes in the battery container
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/058—Construction or manufacture
    • H01M10/0587—Construction or manufacture of accumulators having only wound construction elements, i.e. wound positive electrodes, wound negative electrodes and wound separators
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
    • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
    • H01M50/46—Separators, membranes or diaphragms characterised by their combination with electrodes
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
    • Y02P70/50—Manufacturing or production processes characterised by the final manufactured product

Definitions

  • the present invention relates to a method of manufacturing a secondary battery. Specifically, the invention relates to a method of manufacturing a secondary battery capable of promoting dissolution of incorporated foreign metal.
  • a secondary battery such as a lithium secondary battery has a smaller size, a lighter weight, and higher energy density than those of existing batteries and thus is superior in output density. Therefore, recently, a secondary battery has been preferably used as a so-called portable power supply for a PC, a portable device, or the like or as a drive power supply for a vehicle.
  • Such a secondary battery is constructed by a battery case accommodating an electrode body and an electrolytic solution in a sealed state.
  • the electrode body has a structure in which a positive electrode and a negative electrode are opposite to each other with a separator interposed therebetween.
  • the battery is initially charged under predetermined conditions.
  • the initially charged battery undergoes, for example, the following aging treatments including: a high-temperature aging treatment for the main purpose of stabilizing a cell reaction; and a low-temperature aging treatment for the main purpose of determining whether or not short-circuit occurs through a self-discharge test.
  • JP 2013-114986 A discloses a technique of reducing the aging treatment time by performing these aging treatments in a state where plural batteries are bound.
  • foreign metal such as copper or iron may be incorporated into the battery from the outside (for example, a component of a manufacturing apparatus). In an environment in which the potential of the positive electrode is higher than the dissolved potential due to charging, the incorporated foreign metal is ionized and dissolved in an electrolyte.
  • the invention has been made to provide a method of manufacturing a secondary battery capable of more reliably dissolving foreign metal, which is incorporated into an electrode body, for a short period of time. Further, the invention also has been made to provide a method of manufacturing a high-quality secondary battery with high reliability.
  • a method of manufacturing a secondary battery including: an electrode body including a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode; and an electrolyte.
  • This method includes: constructing the electrode body; constructing a cell including the electrode body and an electrolyte; performing an initial charging treatment on the cell; and performing an aging treatment on the initially charged cell. Before completion of the aging treatment, this method further includes a treatment of bonding the positive electrode and the separator to each other.
  • the positive electrode potential is increased by adjusting the battery potential in an aging treatment, and thus foreign metal present around the positive electrode is dissolved.
  • the present inventors found that the dissolution of the foreign metal can be significantly promoted in a state where a correlation between the foreign metal and the positive electrode is adjusted. Based on this finding, the invention has been completed. That is, according to the method disclosed herein, foreign metal which is incorporated into the surface of the positive electrode during the construction of the electrode body can be fixed to the positive electrode surface by physically or chemically bonding (or joining) the positive electrode and the separator to each other.
  • the foreign metal which has been loosely interposed between the positive electrode surface and the separator is reliably exposed to a higher potential than that of the positive electrode surface. Accordingly, as compared to a case where the positive electrode and the separator are not bonded to each other, the foreign metal can be more reliably dissolved. In addition, the aging time required to dissolve the foreign metal can be reduced. Further, whether the product is good or bad can be reliably determined within a short period of time by inducing internal short-circuit from intensive deposition of the foreign metal within the aging time.
  • the treatment of bonding the positive electrode and the separator to each other may be performed during the aging treatment, and the aging treatment may include a high-temperature aging treatment of applying a predetermined pressure to the initially charged cell and holding the cell at a temperature of 60°C or higher for 100 hours or longer in a state where a voltage is applied to the cell.
  • the bonding treatment of the positive electrode and the separator and the pressurization aging treatment can be simultaneously performed.
  • the aging treatment can be performed while efficiently dissolving the foreign metal within a short period of time.
  • the treatment of bonding the positive electrode and the separator to each other may be performed during the construction of the electrode body, the positive electrode may include a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector, the positive electrode active material layer may include a positive electrode active material and a binder formed of a thermoplastic resin, and the positive electrode and the separator may be bonded to each other by tightly adhering at a softening temperature of the binder or higher in a state where the positive electrode active material layer of the positive electrode and the separator are in contact with each other.
  • the positive electrode and the separator are bonded to each other in a wound curved portion of a wound electrode body. Therefore, the foreign metal incorporated into the wound curved portion can be reliably dissolved within a short period of time.
  • the treatment of bonding the positive electrode and the separator to each other may be performed such that a peeling strength between the positive electrode and the separator is 0.2 N/m to 1.2 N/m.
  • the aging treatment may include applying a pressure of 0.1 MPa or higher to the initially charged cell.
  • the aging treatment may include: holding the initially charged cell in a state where a voltage is applied to the cell for a predetermined amount of time; and adjusting a potential such that a maximum achieved potential of the positive electrode is higher than or equal to an oxidation potential of foreign metal which is assumed to be incorporated into the electrode body. With such a configuration, the potential is adjusted so as to dissolve the foreign metal. Therefore, the foreign metal can be reliably dissolved within a short period of time.
  • the aging treatment may include adjusting the potential such that a maximum achieved potential of the negative electrode is higher than or equal to a reduction potential of the foreign metal.
  • the method may further include a self-discharge test of measuring a voltage drop amount of the cell after the aging treatment.
  • the electrode body may have a laminate structure in which opposition of the positive electrode and the negative electrode with the separator interposed therebetween is repeated.
  • a secondary battery having the above-described configuration is configured to have an electrode with a large area and thus has a high risk of the incorporation of foreign metal.
  • the secondary battery may have a high capacity. Therefore, a variation in the voltage drop amount is large due to a variation in product quality, and thus it is difficult to detect the amount of a voltage drop caused by short-circuit. Accordingly, it is preferable that the method according to the invention is used to manufacture the above-described battery because the effects thereof can be more significantly exhibited.
  • a secondary battery including: an electrode body that includes a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode; and a cell case that accommodates the electrode body and an electrolyte.
  • the positive electrode and the separator are at least partially bonded to each other, and the negative electrode and the separator are not bonded to each other.
  • the battery having such a configuration is expected to obtain the same effects as described above.
  • the battery performance is stable in the aging treatment, and the incorporated foreign metal can be sufficiently dissolved using the aging treatment. Accordingly, for example, whether the product is good or bad can be determined with high accuracy, and a high-quality secondary battery having high reliability can be provided in which the occurrence of short-circuit caused by the foreign metal is suppressed.
  • the time required to manufacture the secondary battery can be reduced, and the secondary battery can be provided with high productivity at a low cost.
  • the secondary battery can be used in various applications and, in particular, can be suitably used as a vehicle-mounted drive power supply for a vehicle in which high level of safety and reliability are required.
  • This secondary battery may be used alone (single cell) or may be used in the form of a battery pack in which plural secondary batteries are connected to each other in series or in parallel.
  • FIG. 1 is a cross-sectional view schematically showing a configuration of a secondary battery according to an embodiment of the invention
  • FIG. 2 is a schematic diagram showing a configuration of a wound electrode body of the secondary battery according to the embodiment
  • FIG. 3A is a diagram schematically showing an example of a dissolution state of foreign metal in a method of manufacturing a secondary battery according to the invention
  • FIG 3B is a diagram schematically showing an example of a dissolution state of foreign metal in a method of manufacturing a secondary battery in the related art
  • FIG 4A is a cross-sectional view schematically showing a state where a pressure is applied to a secondary battery
  • FIG 4B is a cross-sectional view schematically showing a state where a pressure is not applied to a secondary battery
  • FIG. 4C is a perspective view showing a state where a pressure is applied to plural secondary batteries.
  • FIG 5 is a graph showing a dissolution state of foreign metal according to an embodiment of the invention using a relationship between the peeling strength of a positive electrode and a separator, and the size of the foreign metal.
  • “Secondary battery” described in this specification is a collective term for the following components including: a so-called chemical battery such as a lithium secondary battery, a nickel metal hydride battery, a nickel-cadmium battery, or a lead storage battery; a storage element (for example, a pseudocapacitor or a redox capacitor) which may be used in the same manner in the same industrial field as those of the chemical battery (for example, a lithium secondary battery); and a hybrid capacitor and a lithium ion capacitor which is a combination of the chemical battery and the storage element.
  • a so-called chemical battery such as a lithium secondary battery, a nickel metal hydride battery, a nickel-cadmium battery, or a lead storage battery
  • a storage element for example, a pseudocapacitor or a redox capacitor
  • a hybrid capacitor and a lithium ion capacitor which is a combination of the chemical battery and the storage element.
  • lithium secondary battery refers to a secondary battery in which lithium ions are used as electrolyte ions, and charging and discharging are performed by the lithium ions (electrons) moving between positive and negative electrodes. Secondary batteries which are generally called lithium ion batteries or lithium polymer batteries are typical examples included in the lithium secondary battery of this specification.
  • active material described in this specification refers to a material (compound) which can reversibly store and release chemical species (lithium ions in a lithium secondary battery) as charge carriers on a positive electrode side or a negative electrode side.
  • foreign metal which may be a dissolution target in the following embodiment is metal which may be incorporated in the process of manufacturing a secondary battery.
  • this foreign metal has a redox potential in an operating voltage range of a secondary battery and can be dissolved (ionized) at this potential.
  • Representative examples of an element (and the redox potential thereof) constituting the foreign metal include iron (Fe;2.6 V), copper (Cu; 3.4 V), and alloys thereof. It is considered that iron, in particular, is highly likely to be incorporated in the manufacturing process because it is a major component of stainless steel which is frequently used in various manufacturing apparatuses. In addition, it is preferable that iron or an iron alloy is reliably dissolved due to its relatively high resistance.
  • “potential” described in this specification refers to a potential difference (potential (V) based on lithium) between the potential (V) of lithium and the potential of the foreign metal.
  • FIG 1 is a cross-sectional view schematically showing a configuration of a secondary battery according to an embodiment of the invention which is manufactured herein.
  • FIG. 2 is a schematic diagram showing a configuration of an electrode body accommodated in the secondary battery. In each drawing, a dimensional relationship (for example, length, width, or thickness) does not necessarily reflect the actual dimensional relationship.
  • a secondary battery 100 according to the embodiment essentially includes: an electrode body 20 that includes a positive electrode 30, a negative electrode 40, and a separator 50; and an electrolyte (not shown).
  • the secondary battery 100 can be manufactured as follows. That is, first, the electrode body 20 is manufactured by disposing the positive electrode 30 and the negative electrode 40 to be opposite to each other with the separator 50 interposed therebetween.
  • the secondary battery (cell) 100 is constructed.
  • the secondary battery will also be referred to as "cell" before the completion of an aging treatment and the like and after assembly.
  • the cell 100 is initially charged under predetermined conditions.
  • the initially charged battery undergoes the following treatments including: a high-temperature aging treatment for the main purpose of stabilizing a cell reaction; and a self-discharge test for determining whether or not short-circuit occurs. Only the battery which has passed the test is shipped as a product.
  • foreign metal may be incorporated into the cell 100 from the outside (for example, a component of a manufacturing apparatus).
  • the potential of the positive electrode 30 is higher than the dissolved potential (oxidation potential) of the foreign metal by charging the battery
  • the foreign metal is oxidized (loses electrons) into metal ions, and the metal ions are dissolved in the electrolyte.
  • the dissolution occurs as follows: Cu— »Cu 2+ , Fe ⁇ Fe 2+ .
  • the metal ions are reduced at a position of the negative electrode 40 opposite to the foreign metal and are locally (intensively) deposited thereon. Therefore, along with the progress of charging, the deposit on the negative electrode gradually grows toward the positive electrode 30. When the deposit reaches the positive electrode, short-circuit (small short-circuit) occurs in the battery.
  • the foreign metal is small, in general, the foreign metal is completely dissolved during a period from the initial charging to the self-discharge test. Therefore, the quality of the battery including whether or not small short-circuit occurs and, if short-circuit occurs, the degree of short-circuit can be appropriately determined through the self-discharge test.
  • the dissolution during the above-described period may be insufficient. In this case, when a battery is determined to be good, the dissolution of foreign metal progresses during the use of the battery, which may cause short-circuit to occur in the battery.
  • the time required to dissolve foreign metal having a predetermined size in, for example, a potential adjustment step is affected by various factors.
  • the factors include an environment temperature, a battery voltage (potential difference between positive and negative electrodes), a dissolution rate of foreign metal, and uncontrollable factors such as a difference or a variation in specification between constituent materials of the cell.
  • the contact area with the positive electrode, specifically, a positive electrode active material constituting the positive electrode is large, the foreign metal is exposed to an environment having a high potential. Accordingly, the environment having a high potential can promote the dissolution of the foreign metal.
  • the dissolution of foreign metal does not progress even when the potential of the positive electrode is slightly lower than the dissolved potential of the foreign metal. Accordingly, it is more preferable that foreign metal incorporated into the surface of the positive electrode is exposed to the dissolved potential or higher in a state of being pressed against the surface of the positive electrode.
  • the technique disclosed herein includes the following steps including: (1) constructing an electrode body including a positive electrode, a negative electrode, and a separator (electrode body construction step);
  • this method further includes a treatment (bonding treatment) of bonding the positive electrode and the separator to each other.
  • an electrode body including a positive electrode, a negative electrode, and a separator is prepared.
  • the positive electrode includes: a positive electrode current collector; and a positive electrode active material layer that is formed on the positive electrode current collector and contains at least a positive electrode active material.
  • a method of preparing the positive electrode is not particularly limited.
  • the positive electrode can be prepared using, for example, a method including: preparing a paste composition (including a slurry composition and an ink composition; hereinafter referred to as "positive electrode paste") by mixing a positive electrode active material, a conductive material, and a binder with each other in an appropriate solvent; and forming a positive electrode active material layer on a positive electrode current collector by supplying the paste thereonto.
  • Examples of a method of supplying the positive electrode paste include a method of coating a single surface or both surfaces of the positive electrode current collector with the positive electrode paste using a well-known coater of the related art (for example, a slit coater, a die coater, a comma coater, or a gravure coater).
  • the positive electrode active material layer may be formed on the positive electrode current collector using a method including: granulating a mixture of the positive electrode active material, the conductive material, and the binder into a granulated body having an appropriate size; and supplying and pressure-bonding the granulated body onto the positive electrode current collector.
  • the mass of the positive electrode active material layer (when the positive electrode active material layer is formed on both surfaces of the positive electrode current collector, the total mass thereof provided on both the surfaces) provided per unit area of the positive electrode current collector is not particularly limited but is, for example, approximately 10 mg/cm 2 to 30 mg/cm 2 .
  • a conductive member formed of highly conductive metal for example, aluminum, nickel, titanium, or stainless steel
  • the shape of the current collector is not particularly limited because it may vary depending on the shape of a battery to be constructed.
  • the current collector may have a rod shape, a plate shape, a foil shape, or a net shape.
  • a foil-shaped current collector is mainly used.
  • the thickness of the foil-shaped current collector is not particularly limited, but is preferably 5 ⁇ to 50 ⁇ (more preferably 10 ⁇ to 30 ⁇ ) from the viewpoint of obtaining a good balance between the energy density of the battery and the strength of the current collector.
  • the positive electrode active material one material or two or more materials selected from among materials which are used for a secondary battery in the related art may be used without any particular limitation.
  • Preferred examples of the positive electrode active material include oxides (lithium transition metal oxides) containing a lithium atom and a transition metal atom as constituent metal atoms, such as lithium nickel oxide (for example, LiNi0 2 ), lithium cobalt oxide (for example, LiCo0 2 ), and lithium manganese oxide (for example, LiMn 2 0 ); and phosphates containing a lithium atom and a transition metal atom as constituent metal atoms, such as lithium manganese phosphate (LiMnP0 4 ) and lithium iron phosphate (LiFeP0 4 ).
  • a lithium nickel cobalt manganese composite oxide having a layered structure for example, LiNii/3Coi/ 3 Mni/30 2
  • a positive electrode active material containing spinel type LiNio.5Mn1.5O4 as a major component is preferably used from the viewpoints of obtaining high energy density and superior heat stability.
  • a ratio of the mass of the positive electrode active material to the total mass of the positive electrode active material layer is not particularly limited but is preferably about 50 mass% or more (typically, 70 mass% to 100 mass%; for example, 80 mass% to 99 mass%).
  • the lithium transition metal oxide typically, particulate
  • a lithium transition metal oxide prepared using a well-known method of the related art can be used as it is.
  • the conductive material one material or two or more materials selected from among materials which are used for a secondary battery in the related art may be used without any particular limitation.
  • carbon materials such as carbon blacks (for example, acetylene black, furnace black, and Ketjen black), coke, or graphites (natural graphite and modified products thereof, and artificial graphite) can be used.
  • carbon blacks having a relatively large specific surface area typically, acetylene black
  • a ratio of the mass of the conductive material to the total mass of the positive electrode active material layer is not particularly limited but is, for example, 1 mass% to 15 mass% (typically, 5 mass% to 10 mass%).
  • the binder is not particularly limited, but, for example, one material or two or more materials can be selected from among materials used for a secondary battery in the related art without particular limitation, which are thermoplastic binders (typically, a . resin or an elastomer) having a softening point (for example, 60°C or higher) in an appropriate temperature range.
  • thermoplastic binders typically, a . resin or an elastomer
  • a softening point for example, 60°C or higher
  • a compound which can be uniformly dissolved or dispersed in a solvent described below can be used.
  • the positive electrode active material layer is formed using an organic solvent-based paste (a solvent-based paste containing an organic solvent as a major component of a dispersion medium)
  • a polymer material which can be dispersed or dissolved in an organic solvent can be preferably adopted.
  • the polymer material include polyvinylidene fluoride (PVdF), polyvinylidene chloride (PVdC), and polyethylene oxide.
  • PVdF polyvinylidene fluoride
  • PVdC polyvinylidene chloride
  • polyethylene oxide polyethylene oxide
  • the positive electrode active material layer is formed using an aqueous paste
  • a polymer material which can be dissolved or dispersed in water can be adopted.
  • the polymer material include cellulose polymers, fluororesins, vinyl acetate copolymers, and rubbers.
  • the polymer material examples include carboxymethyl cellulose (CMC), hydroxypropyl methylcellulose, polyvinyl alcohol, polytetrafluoroethylene (PTFE), styrene-butadiene rubber (SBR), a tetrafluoroethylene-hexafluoropropylene copolymer, and an acrylic acid-modified SBR resin (SBR latex).
  • CMC carboxymethyl cellulose
  • PTFE polytetrafluoroethylene
  • SBR styrene-butadiene rubber
  • SBR latex acrylic acid-modified SBR resin
  • a ratio of the mass of the binder to the total mass of the positive electrode active material layer is not particularly limited but is, for example, 0.5 mass% to 10 mass% (preferably, 1 mass% to 2 mass%).
  • the solvent one solvent or two or more solvents selected from among solvents which are used for a secondary battery in the related art may be used without any particular limitation. These solvents are roughly classified into an aqueous solvent and a nonaqueous solvent.
  • the aqueous solvent is not particularly limited as long as it is aqueous as a whole, and water or a mixed solvent containing water as a major component can be preferably used.
  • Preferable examples of the nonaqueous solvent include N-methyl-2-pyrrolidone (NMP), methyl ethyl ketone, and toluene.
  • отно ⁇ ески ⁇ е отно ⁇ ество can be added to the positive electrode paste within a range where the effects of the invention do not significantly deteriorate.
  • the dispersant include a polymer compound having a hydrophobic chain and a hydrophilic group (for example, an alkali salt; typically, a sodium salt); an anionic compound such as a sulfate, a sulfonate, or a phosphate; and a cationic compound such as amine.
  • dispersant examples include carboxymethyl cellulose (CMC), methyl cellulose, ethyl cellulose, hydroxypropyl cellulose, butyral, polyvinyl alcohol, modified polyvinyl alcohol, polyethylene oxide, polyvinyl pyrrolidone, polycarboxylic acid, oxidized starch, and starch phosphate.
  • the above-described positive electrode paste or granulated body is supplied onto the positive electrode current collector, and the solvent is removed from the paste (or the granulated body) using appropriate drying means.
  • the drying means include natural drying, hot wind, low-humidity wind, vacuum, infrared rays, far-infrared rays, and electron beams. Among these means, one kind can be used alone, or two or more kinds can be used in combination for drying.
  • the pressing method for example, various well-known press methods such as a roll press method or a flat plate press method can be adopted.
  • the density of the positive electrode active material layer formed on the positive electrode current collector is extremely low, the energy density thereof per unit volume may be decreased.
  • the density of the positive electrode active material layer is extremely high, the internal resistance tends to increase, particularly, during high-current charging and discharging or in a low-temperature environment. Therefore, it is preferable that the density of the positive electrode active material layer is, for example, 2.0 g/cm 3 or more (typically 2.5 g/cm 3 or more) and is, for example, 4.5 g/cm 3 or less (typically 4.2 g/cm 3 or less).
  • the negative electrode includes: a negative electrode current collector; and a negative electrode active material layer that is formed on the negative electrode current collector and contains at least a negative electrode active material.
  • a method of preparing the negative electrode is not particularly limited.
  • the negative electrode can be prepared using, for example, a method including: preparing a paste composition (hereinafter referred to as "negative electrode paste") by mixing a negative electrode active material, a binder, and the like with each other in an appropriate solvent; and forming a negative electrode active material layer on a negative electrode current collector by supplying the paste thereonto.
  • a method of forming the negative electrode active material layer the same methods as in the case of the above-described positive electrode can be appropriately adopted.
  • the mass of the negative electrode active material layer (the total mass thereof provided on both the surfaces) provided per unit area of the negative electrode current collector is not particularly limited but is, for example, approximately 5 mg/cm 2 to 30 mg/cm 2 .
  • the negative electrode current collector a conductive member formed of highly conductive metal (for example, copper, nickel, titanium, or stainless steel) is preferably used.
  • the negative electrode current collector may have the same shape as that of the positive electrode current collector.
  • the negative electrode active material one material or two or more materials selected from among materials which are used for a secondary battery in the related art may be used without any particular limitation.
  • the negative electrode active material examples include graphite such as natural graphite (plumbago) and a modified product or artificial graphite produced from a petroleum-based or coal-based material; a carbon material (having low crystallinity) containing at least partially a graphite structure (layered structure), such as hard carbon (non-graphitizable carbon), soft carbon (graphitizable carbon), or carbon nanotube; a metal oxide such as lithium titanium composite oxide; and an alloy of lithium and tin (Sn) or silicon (Si).
  • a ratio of the mass of the negative electrode active material to the total mass of the negative electrode active material layer is not particularly limited, but is suitably about 50 mass% or more and is preferably about 90 mass% to 99 mass% (for example, 95 mass% to 99 mass%).
  • the binder can be appropriately selected from the exemplary polymer materials described above as the binder for the positive electrode active material layer.
  • the binder include styrene-butadiene rubber (SBR), polyvinylidene fluoride (PVdF), and polytetrafluoroethylene (PTFE).
  • SBR styrene-butadiene rubber
  • PVdF polyvinylidene fluoride
  • PTFE polytetrafluoroethylene
  • a ratio of the mass of the binder to the total mass of the negative electrode active material layer is not particularly limited, but is, for example, 1 mass% to 10 mass% (preferably, 2 mass% to 5 mass%).
  • the various additives, the conductive material, and the like which are described above can be appropriately used.
  • the solvent is removed by appropriately using the above-described drying means.
  • the thickness and density of the negative electrode active material layer can be adjusted.
  • the density of the negative electrode active material layer after pressing is not particularly limited, but is, for example, 1.1 g/cm 3 or more (typically 1.2 g/cm 3 or more; for example, 1.3 g/cm 3 or more) and is, for example, 1.5 g/cm 3 or less (typically 1.49 g/cm 3 or less).
  • microporous sheets which are used for a secondary battery in the related art can be used, and examples thereof include a microporous resin sheet formed of a resin such as polyethylene (PE), polypropylene (PP), polyester, cellulose, or polyamide.
  • the microporous resin sheet may have a single-layer structure or a multilayer structure including two or more layers (for example, a three-layer structure in which a PP layer is laminated on both surfaces of a PE layer).
  • the separator may include a heat resistance layer (HRL) containing inorganic compound particles (inorganic filler) that is formed on a single surface or both surfaces of the microporous resin sheet.
  • HRL heat resistance layer
  • inorganic filler for example, alumina, boehmite, or magnesia can be adopted.
  • the electrode body is prepared by laminating the positive electrode and the negative electrode with the separator interposed therebetween so as to maintain the insulating state.
  • the configuration of the electrode body is not particularly limited.
  • the electrode body has a laminate structure in which the opposition of the positive electrode and the negative electrode with the separator interposed therebetween is repeated.
  • the electrode body having the laminate structure the following electrode bodies can be considered including: a flat laminated electrode body in which plural sheet-shaped positive electrodes, plural sheet-shaped negative electrodes, and plural sheet-shaped separators are laminated; and a wound electrode body in which a laminate of an elongated sheet-shaped positive electrode, an elongated sheet-shaped negative electrode, and an elongated sheet-shaped separator is wound.
  • the electrode body having the laminate structure is configured to have an electrode with a large area and thus has a high risk of the incorporation of foreign metal.
  • the electrode body may have a high capacity. Therefore, a variation in the voltage drop amount is relatively large due to a variation in product quality, and thus it is difficult to detect the amount of a voltage drop caused by short-circuit. Accordingly, it is preferable that the method of manufacturing a secondary battery disclosed herein is used to manufacture the above-described battery because the effects thereof can be more significantly exhibited.
  • the positive electrode 30 is formed such that a positive electrode active material layer 34 is not provided (or removed) at an end portion of the positive electrode 30 in the longitudinal direction to expose a positive electrode current collector 32 therefrom.
  • the negative electrode 40 is formed such that a negative electrode active material layer 44 is not provided (or removed) at an end portion of the negative electrode 40 in the longitudinal direction to expose a negative electrode current collector 42 therefrom.
  • the electrode body 20 having a high current collecting efficiency can be formed using a method including: laminating the positive and negative electrodes so as to align exposure portions 36, 46 at a certain position; and intensively collecting the current therefrom.
  • the flat wound electrode body 20 may be prepared using a method including: laminating the elongated positive electrode 30 and the negative electrode 40 in the insulating state with the two separator 50 interposed therebetween; winding the laminate in the longitudinal direction; squashing the wound body from the side surface thereof.
  • the laminate itself may be prepared to be wound such that the wound cross-section has a flat shape.
  • the foreign metal When foreign metal is incorporated into the positive electrode 30, the foreign metal is incorporated into the inside or the surface of the positive electrode active material layer. When the foreign metal is incorporated into the inside of the positive electrode active material layer, the foreign metal may be present in a region having a higher potential than the positive electrode potential. When the foreign metal is incorporated into the surface of the positive electrode active material layer, the foreign metal may be present in a region having a higher potential than the positive electrode potential by maintaining a state where the foreign metal is pressed against the positive electrode active material.
  • a treatment (bonding treatment) of bonding the positive electrode 30 and the separator 50 to each other is performed during a period from the electrode body construction step to the completion of an aging treatment described below.
  • the positive electrode 30 includes the positive electrode active material layer 34 having a structure in which the positive electrode active material binds to the surface of the positive electrode current collector 32 through the binder. Accordingly, the bonding treatment can be realized by laminating the separator 50 on the positive electrode 30 and, in this state, consolidating them at a softening point or higher (typically 60°C or higher) of the binder.
  • Binding refers to a state where the positive electrode 30 and the separator 50 are bonded to each other through a physical bonding strength of, for example, a binder component.
  • a bonding strength such that the peeling strength is 0.15 N/m or higher.
  • the positive electrode 30 and the separator 50 may be in contact with (adjacent to) each other through, for example, the binder component portion of the positive electrode 30 without being bonded to each other through a physical bonding strength. This case is not included in "the bonding" described herein.
  • the timing of the bonding treatment is not particularly limited.
  • the bonding treatment may be performed when the positive electrode 30 and the separator 50 overlap each other, or may be performed when the flat laminated electrode body or the wound electrode body is constructed.
  • the consolidation treatment which accompanies heating
  • the above-described press treatment which adjusts the thickness and density of the positive electrode active material layer, may be simultaneously performed. It is preferable that the bonding treatment is performed at the above-described timing because the dissolution of foreign metal is promoted in both steps including an initial charging step and an aging step described below.
  • the bonding treatment may be performed in the aging step described below. It is preferable that the bonding treatment is performed at the above-described timing from the viewpoint that the consolidation (pressure application) for the bonding treatment and the pressurization (pressure application) for the aging treatment can be simultaneously realized.
  • the configuration of performing the bonding treatment in the aging step described below will be described.
  • the negative electrode 40 and the separator 50 may be in contact with each other as in the case of a cell of the related art; however, although not limited thereto, it is preferable that they are not physically bonded to each other.
  • the reason is as follows.
  • gas may be produced on the surface of the negative electrode 40 due to the decomposition of an electrolytic solution or an overcharge additive.
  • the negative electrode 40 and the separator 50 are bonded to each other, the gas produced from the negative electrode 40 is hindered from being released outside the electrode body 20, which is not preferable.
  • the electrode body 20 and an electrolyte are accommodated in the appropriate battery case 10.
  • the secondary battery (cell) 100 is constructed.
  • the sealing operation can be performed using the same method as that used for a secondary battery in the related art.
  • a method such as laser welding, resistance welding, or electron beam welding can be used.
  • a method such as bonding with a bonding agent or ultrasonic welding can be used.
  • the battery case 10 a material and a shape used for a secondary battery in the related art can be adopted.
  • a relatively light-weight metal material such as aluminum or steel
  • a resin material such as a polyphenylene sulfide resin or a polyimide resin
  • the battery case (hard case) 10 formed of a relatively light-weight metal for example, aluminum or an aluminum alloy
  • the battery case (hard case) 10 formed of a relatively light-weight metal for example, aluminum or an aluminum alloy
  • the shape of the case 10 is not particularly limited and is, for example, a circular shape (a cylindrical shape, a coin shape, or a button shape), a hexahedron shape (a square shape or a flat shape), or a shape obtained by processing and modifying the above-described shape.
  • the battery case 10 shown in this drawing includes: a flat cuboid-shaped (square shape) battery case body 12 having an opening at an upper end; and a sealing lid 14 that covers the opening.
  • a positive electrode terminal 60 which is electrically connected to the positive electrode 30 of the wound electrode body 20
  • a negative electrode terminal 70 which is electrically connected to the negative electrode 40 of the wound electrode body 20
  • a positive electrode current collector plate 62 is attached to an exposure end portion of the positive electrode current collector 32 through a welding portion 64
  • a negative electrode current collector plate 72 is attached to an exposure end portion of the negative electrode current collector 42 through a welding portion 74.
  • the positive electrode current collector plate 62 and negative electrode current collector plate 72 are electrically connected to the positive electrode terminal 60 and the negative electrode terminal 70, respectively.
  • a safety device such as a current interrupt device (device capable of interrupting the current in response to an increase in inner pressure when a battery is overcharged) may be provided on a conductive path between the positive electrode terminal 60 and the negative electrode terminal 70, and the electrode body 20.
  • the sealing lid 14 may further include a safety valve (not shown) for discharging gas, produced from the inside of the battery case 10, to the outside of the battery case 10.
  • the electrolyte one material or two or more materials selected from among materials which are used for a secondary battery in the related art may be used without any particular limitation.
  • such an electrolyte has a composition in which an appropriate nonaqueous solvent contains a supporting electrolyte (typically, a lithium salt).
  • aprotic solvents such as carbonates, esters, ethers, nitriles, sulfones, and lactones can be used.
  • carbonates such as ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) can be preferably adopted.
  • the supporting electrolyte various known materials which can function as a supporting electrolyte of a secondary battery can be considered.
  • one material or two or more materials selected from various lithium salts such as LiPF 6 , LiBF 4 , LiC10 4 , LiN(S0 2 CF 3 ) 2 , LiN(S0 2 C 2 F 5 ) 2 , LiCF 3 S0 3 , LiC 4 F 9 S0 3 , LiC(S0 2 CF 3 ) , and LiC10 4 can be used.
  • LiPF 6 can be preferably used.
  • the concentration of the supporting electrolyte is not particularly limited.
  • the concentration of the supporting electrolyte is, for example, about 0.1 mol/L to 2 mol/L (preferably about 0.8 mol/L to 1.5 mol/L) with respect to the total amount of the electrolyte.
  • additives may be appropriately added to the electrolyte used herein, and examples of the additives include a film forming agent such as vinylene carbonate (VC) or fluoroethylene carbonate (FEC); and a gas producing additive such as biphenyl (BP) or cyclohexylbenzene (CHB).
  • VC vinylene carbonate
  • FEC fluoroethylene carbonate
  • BP biphenyl
  • CHB cyclohexylbenzene
  • the constructed secondary battery (cell) 100 is charged to a predetermined voltage value in an ordinary temperature range.
  • an external power supply (not shown) is connected between the positive electrode 30 (positive electrode terminal 60) and the negative electrode 40 (negative electrode terminal 70) of the cell to charge (typically, constant-current charge) the secondary battery 100 to the predetermined voltage.
  • the ordinary temperature range in the initial charging step refers to a temperature range which is generally called an ordinary temperature, for example, 20°C ⁇ 15°C.
  • the voltage (typically, maximum achieved voltage) between the positive and negative electrode terminals may vary depending on the kinds of the active material and the nonaqueous solvent to be used.
  • This voltage may be adjusted to be in a voltage range where the SOC (State of Charge) of the battery assembly is about 80% or higher (typically, 90% to 105%) of the SOC when being fully charged (typically, the rated capacity of the battery).
  • the voltage (typically, maximum achieved voltage) between the positive and negative electrode terminals is adjusted to be in a range of about 3.8 V to 4.2 V.
  • the discharge rate in the initial charging treatment may be the same as a well-known discharge rate of the related art which can be generally adopted when a battery assembly of the related art is initially charged.
  • the discharge rate may be about 0.1 C to 10 C.
  • the charging treatment may be performed once, or may be performed twice or more, for example, while performing a discharging treatment between the charging treatments.
  • the secondary battery (cell) 100 that undergoes the initial charging step is held (typically, is left to stand) at a predetermined SOC in a predetermined temperature range for a predetermined time.
  • the temperature range in which the cell is held may be a low temperature range (for example, about the ordinary temperature range to 40°C) or a high temperature range (for example, about 40°C to 70°C).
  • the SOC of the cell may be in either a range of 0% to 100% or a range of 100% or higher.
  • the temperature range and the SOC may vary in the aging step.
  • a predetermined pressure may be applied to the cell.
  • the initially charged cell is applied with a predetermined pressure and undergoes the aging treatment in a high temperature range in the pressure applied state.
  • the normal high-temperature pressurization aging treatment and the bonding treatment of the positive electrode and the separator can be simultaneously realized.
  • FIG 3A is a diagram schematically showing an example of a dissolution state of foreign metal 80 in the method of manufacturing a secondary battery according to the embodiment of the invention.
  • FIG. 3B is a diagram showing the case of a method of manufacturing a secondary battery in the related art for comparison.
  • a correlation between the positive electrode 30, the separator 50, and the foreign metal 80 is shown with exaggeration.
  • a state where the positive electrode 30, the separator 50, and the negative electrode 40 are completely separated from each other represents a state where, actually, these components (the positive electrode 30, the separator 50, and the negative electrode 40) are not physically bonded to each other.
  • this state includes a state where the positive electrode 30 and the separator 50 are in contact with each other without being bonded to each other.
  • a state where the positive electrode 30 and the separator 50 are adjacent to each other includes: a state where the positive electrode 30 and the separator 50 are physically bonded to each other; and a state where the positive electrode 30 and the separator 50 are consolidated to be in contact with each other without being bonded to each other.
  • Step (b) a pressure is applied to the cell 100 at a softening point or higher of the binder included in the positive electrode 30.
  • Step (c) of the aging treatment the high-temperature aging treatment and the bonding treatment can be simultaneously performed.
  • the foreign metal 80 is pressed against the surface of the positive electrode 30 and may be exposed to a higher positive electrode potential.
  • the dissolution (that is, ionization) of the foreign metal 80 is promoted due to electron exchange between the foreign metal 80 and the positive electrode 30. Accordingly, the amount of the foreign metal 80 dissolved is increased as compared to a state (refer to Step (c) of FIG. 3B) where the above-described bonding treatment is not performed. Accordingly, even the relatively coarse foreign metal 80 can be completely dissolved within a short period of time.
  • Step (d) the cell is released from the pressurized state.
  • the positive electrode 30 and the separator 50 are physically bonded to each other, the bonding therebetween is maintained after the release from the pressurized state.
  • Step (e) when another treatment step such as a low-temperature aging treatment is arbitrarily performed as the next step, the bonding between the positive electrode 30 and the separator 50 is maintained. Accordingly, even when the foreign metal 80 remains undissolved in Step (c) of the aging treatment, as long as the positive electrode potential is higher than or equal to the dissolved potential of the foreign metal 80, the subsequent Step (e) of the bonding treatment can be performed in a state where the dissolution of the foreign metal 80 is promoted. Further, in the state where the dissolution of the foreign metal 80 is promoted, the next Step (f) of the self-discharge test can be performed. In Step (f) of the self-discharge test, when the potential of the negative electrode 40 is lower than or equal to the reduction potential of the foreign metal 80, the ions of the foreign metal 80 are deposited on the negative electrode 40 as the deposit 82.
  • Step (f) of the self-discharge test when the potential of the negative electrode 40 is lower than or equal to the reduction potential of the foreign metal 80, the
  • the application of the pressure to the cell 100 can be performed using one method or two or more methods selected from well-known methods of the related art.
  • a pressure applying method may be adopted, the method including: interposing the cell 100 between a pair of restraining plates 92 as shown in FIG. 4A; and then squeezing the restraining plates 92 as shown in FIG. 4B.
  • the squeezing method include a method using a bolt or a restraining band; a method using a press machine such as an air press or a hydraulic press; a method using gravity in which, for example, a weight unit having an appropriate weight is placed on the battery case; and a method of reducing the pressure using a vacuum furnace or the like.
  • an appropriate jig for example, the restraining plate 92.
  • the cell has a hexahedron shape
  • a method of applying a pressure in a state where at least a pair of surfaces of the cell (typically, wide side surfaces having the widest surface area) are interposed between the restraining plate 92 can be preferably used.
  • a pressure can be relatively uniformly applied to the entire region of the battery case 10 (specifically, the electrode body 20 in the case).
  • a restraining jig 90 using a coil spring shown in FIG. 4C can be preferably used.
  • the secondary battery (single cell) 100 is accommodated in the restraining plates 92, and then a knob portion 94 is rotated to adjust the coil spring.
  • an arbitrary pressure is applied to the pair of wide side surfaces of the cell.
  • the magnitude (value) of the applied pressure can be obtained using a well-known pressure measuring method (for example, a method using a load cell or a strain gauge).
  • the pressure application may be performed in one go or may be performed stepwise through, for example, two or more steps.
  • the pressure applied to the cell is not particularly limited. However, it is not preferable that the pressure is extremely low because the foreign metal is not sufficiently pressed against the positive electrode. Therefore, the contact between the foreign metal and the positive electrode may not be sufficiently increased, and it may be difficult to expose the foreign metal to a higher positive electrode potential. In addition, it is not preferable that the pressure is extremely high because the battery case may be excessively deformed, voids (pores) present in the electrode body (typically, the electrode or the separator) may be collapsed, or the battery performance may be adversely affected. Therefore, the pressure is about 0.1 MPa or higher, (for example, 0.3 MPa or higher, preferably 0.5 MPa or higher, and typically 0.7 MPa or higher).
  • the pressure is about 1.5 MPa or lower (preferably 1.3 MPa or lower, and typically 1.0 MPa or lower).
  • the pressure described in this specification refers to a relative pressure with respect to the atmospheric pressure, that is, a value obtained by subtracting the atmospheric pressure (about 0.1 MPa) from the actual pressure (absolute pressure).
  • the time and temperature of maintaining the pressed state obtained by the pressure application can be determined in consideration of, for example, the configuration of the electrode body (the amount of the binder contained in the positive electrode and the surface state of the separator) such that the bonding between the positive electrode and the separator is sufficiently realized.
  • the temperature of maintaining the pressed state may be, for example, a softening point or higher of the binder contained in the positive electrode.
  • the temperature is typically 40°C or higher and preferably 60°C or higher (65°C or higher).
  • the upper limit of the temperature can be appropriately determined in a temperature range where there is no adverse effect on the battery configuration, for example, in a range of the softening temperature or lower of the separator.
  • the upper limit of the temperature can be determined to be about 80°C or lower (75°C or lower).
  • a thermostatic chamber or an infrared heater can be appropriately used.
  • the time of maintaining the pressed state is not particularly limited as long as the sufficient bonding is realized.
  • the time is 100 hours or longer, preferably 110 hours or longer, more preferably 120 hours or longer, still more preferably 140 hours or longer.
  • the upper limit of the time is not particularly limited.
  • the upper limit of the time can be determined in consideration of the appropriate time for the high-temperature aging treatment, the production efficiency, and the like.
  • the upper limit of the time can be set to be about 240 hours or shorter and preferably about 168 hours or shorter as a reference.
  • Whether or not the bonding is sufficiently realized can be checked, for example, by measuring the peeling strength between the positive electrode 30 and the separator 50 that undergo the bonding treatment under the same conditions.
  • the peeling strength between the positive electrode 30 and the separator 50 can be quantitatively evaluated, for example, using "90° peeling test" which is defined according to JIS K6854-l :1999.
  • the 90° peeling strength between the positive electrode 30 and the separator 50 after the bonding treatment is 0.15 N/m or higher (typically 0.2 N/m or higher, for example, 0.25 M/m or higher, and preferably 0.4 N/m or higher).
  • the upper limit of the peeling strength is not particularly limited.
  • the peeling strength can be set to be, for example, 1.2 N/m or less as a reference. As a result, the bonding between the positive electrode 30 and the separator 50 can be secured, and thus even the dissolution of coarser foreign metal can be preferably promoted.
  • the bonding between the positive electrode 30 and the separator 50 can be realized.
  • the aging treatment high-temperature aging treatment
  • the aging treatment can be performed at the same time.
  • the foreign metal 80 can be dissolved and ionized into metal ions.
  • the potential (maximum achieved potential) of the positive electrode 30 is adjusted to be higher than or equal to the oxidation potential of the foreign metal 80.
  • the potentials of the positive electrode 30 and the negative electrode 40 can be appropriately set according to, for example, the kind of the foreign metal 80 which may be incorporated into the battery.
  • the foreign metal 80 (element)
  • copper has the highest redox potential.
  • the potential (maximum achieved potential) of the positive electrode is set to be higher than or equal to the oxidation potential of copper (about 3.4 V or higher; for example, 4.0 V to 4.5 V).
  • the potential of the positive electrode is set to be about 4.5 V.
  • iron is widely used as a material of a manufacturing apparatus or the like. Therefore, it is considered that iron is highly likely to be incorporated into the cell.
  • the potential (maximum achieved potential) of the positive electrode is set to be higher than or equal to the oxidation potential of iron (about 2.5 V or higher; for example, 2.5 V to 3.5 V).
  • the potential (maximum achieved potential) of the negative electrode 40 can be adjusted to be higher than or equal to the reduction potential of the foreign metal 80 which may be incorporated into the battery.
  • the metal ions of the foreign metal 80 dissolved on the positive electrode side reach the negative electrode 40 side, the metal ions can be prevented from immediately being deposited on the negative electrode 40. Therefore, the metal ions remain in the electrolytic solution and may be diffused to the periphery. As a result, the foreign metal 80 is prevented from being locally deposited on the negative electrode surface opposite thereto, and the frequency of small short-circuit can be decreased.
  • the occurrence of short-circuit caused by the foreign metal 80 can be suppressed, and the foreign metal can be made to be harmless.
  • the potential (maximum achieved potential) of the negative electrode is set to be higher than or equal to the reduction potential of iron (about 2.5 V or higher; for example, 1.5 V to 2.5 V).
  • the battery voltage may be set such that the potential of the positive electrode 30 is maintained to be in a range of the oxidation potential or higher of the foreign metal 80, or may be changed in a pulse-like form such that the potential of the positive electrode 30 is in a range of the oxidation potential or higher of the foreign metal 80 at very short time intervals. From the viewpoint of the dissolution of the foreign metal 80, it is preferable that a relatively high inter-terminal voltage range and/or a relatively high SOC range is maintained over the entire period of the aging step.
  • the time required to dissolve foreign metal having a predetermined size is affected by various factors. Examples of considerable factors include an environment temperature, a battery voltage (potential difference between positive and negative electrodes), a dissolution rate of foreign metal, and a difference or a variation in specification between constituent materials of the secondary battery.
  • the effects of the kind and shape of the active material, the surface state of the separator, and the concentration of the additives added to the electrolyte can be considered. Specifically, it was verified that, by adjusting the concentration of the additives added to the electrolyte to be high, the dissolution rate of the foreign metal tends to decrease.
  • an uncontrollable difference in the moisture content of the electrode, the incorporated state of the foreign metal (for example, the embedded state thereof into the positive electrode active material layer or the wetting state of the electrolyte), and the impregnated state of the electrolyte into the electrode and/or the separator can be considered. Specifically, it was verified that, when the storage period of the electrode in a dry room is increased or when the electrode is instantaneously exposed to air, the dissolution rate of the foreign metal is decreased. The reason is considered to be that the moisture content in the electrode is increased.
  • the aging step is performed by disposing foreign metal (for example, iron) having a predetermined size on the positive electrode surface in advance and varying other conditions (for example, the potential adjustment configuration and the pressure to be applied, and the peeling strength of the positive electrode and the separator after the bonding treatment).
  • the charging time at the actual environment temperature can be set to be appropriate and shortest by investigating in advance a relationship between the amount of the foreign metal dissolved within a predetermined amount of time and the varied conditions (for example, a charging pattern, a charging rate, or a pressure to be applied).
  • a self-discharge test is further performed after the aging treatment.
  • the voltage drop amount of the cell is measured to determine whether or not the product is bad (a battery in which internal short-circuit occurs).
  • the internal short-circuit which is a test object is small short-circuit caused by the foreign metal remaining on the positive electrode side. Therefore, in order to accurately determine whether or not small short-circuit occurs, the test period needs to be at least 5 days or, in some cases, 10 days in the related art.
  • test period is set from the following point of view: when it is assumed that foreign metal (typically, iron) having a slow dissolution rate and a high resistance remains in the cell, a period of 5 days or longer is required to examine the effect of the foreign metal.
  • foreign metal typically, iron
  • the positive electrode and the separator are bonded to each other before the completion of the aging treatment. Therefore, the dissolution of the foreign metal is promoted before the completion of the aging step. For example, iron having a slow dissolution rate may be suitably dissolved. Further, the bonding between the positive electrode and the separator is maintained in the self-discharge test. Therefore, through the self-discharge test, the occurrence of internal short-circuit caused by the foreign metal undissolved in the previous step is suppressed, and the dissolution of the undissolved foreign metal is also promoted. Accordingly, through the self-discharge test, the test time can be reduced as compared to the related art.
  • the time required in the self-discharge test is, for example, within 24 hours (typically within 15 hours, for example, within 10 hours, and preferably about 2 hours to 5 hours). Accordingly, the time required in the self-discharge test can be significantly reduced, and the productivity can be improved.
  • the self-discharge test step whether or not internal short-circuit occurs is determined based on the voltage drop amount which is determined for each cell 100 before and after the self-discharge period. Specifically, a reference value for determining whether or not the product is bad is set based on the measurement results of the above-described voltage drop amount. A method of setting the reference value is not particularly limited. For example, an arithmetic mean value or a median value of voltage drop amounts of plural cells may be adopted as the reference value. First, a difference between the reference value and the voltage drop amount of each cell is calculated. When this difference is a predetermined threshold value or lower, this cell is determined as "no internal short-circuit".
  • the threshold value may be set to be a value corresponding to, for example, 2 ⁇ to 4 ⁇ ( ⁇ refers to the statistical standard deviation).
  • ⁇ refers to the statistical standard deviation
  • the test can be performed in a state where the foreign metal is sufficiently dissolved. Accordingly, a battery in which undissolved foreign metal remains is not likely to be provided for the test. As a result, a ratio of bad products which passes the test is significantly reduced, and a high-quality battery can be provided to the market.
  • a pressure is applied as described above in the aging step. As a result, in the self-discharge test step, the dissolution of the foreign metal can be further promoted.
  • the distance between the positive and negative electrodes is reduced and the deposit 82 is grown on the negative electrode, small short-circuit can be induced from this deposit 82. As a result, a bad product can be more reliably detected, and only a good product can be provided to the market.
  • the secondary battery 100 which is manufactured using the method of manufacturing a secondary battery disclosed herein can be suitably used in various applications.
  • the secondary battery 100 can be suitably used as, for example, a power supply of a vehicle-mounted motor (electric motor) for driving a vehicle.
  • the type of the vehicle is not particularly limited, but typical examples thereof include plug-in hybrid vehicle (PHV), a hybrid vehicle (HV), and an electric vehicle (EV).
  • An evaluation square battery (secondary battery) was constructed in the following procedure. First, a lithium transition metal oxide (NCM; LiNii/3Mni/ 3 Coi/ 3 0 2 ) as a positive electrode active material; acetylene black (AB) as a conductive material; and polyvinylidene fluoride (PVdF) as a binder were put into a kneading machine such that the mass ratio (NCM:AB:PVdF) of these materials was 93:4:3. The materials were kneaded while adjusting the viscosity thereof with N-methylpyrrolidone (NMP) such that the solid concentration (NV) was 50 mass%. As a result, a positive electrode paste was prepared. An aluminum foil (thickness: 15 ⁇ ) as a positive electrode current collector was coated with this paste and was dried and pressed. As a result, a positive electrode in which a positive electrode active material layer was formed on the positive electrode current collector was prepared.
  • NMP N-methyl
  • disk-shaped iron materials having diameters of 50 ⁇ , 100 ⁇ , 200 ⁇ , and 250 ⁇ and a thickness of 10 ⁇ were prepared. These foreign metals were placed on the positive electrode active material layer and were provided for the construction of the cell.
  • the positive electrode and the negative electrode prepared as above are disposed to be opposite to each other with a separator interposed therebetween to prepare an electrode body (here, a three-layer structure was used in which a PP layer was laminated on both surfaces of a PE layer).
  • an electrode body here, a three-layer structure was used in which a PP layer was laminated on both surfaces of a PE layer.
  • a positive electrode terminal was joined to an end portion of the positive electrode current collector, and a negative electrode terminal was joined to an end portion of the negative electrode current collector.
  • the electrode body was accommodated in the square battery case, and an electrolyte (here, a solution was used in which LiPF 6 as an electrolyte was dissolved in a mixed solvent at a concentration of 1 mol/L, the mixed solvent containing ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) at a volume ratio (EC:DMC:EMC) of 3:4:3) was injected into the battery case.
  • EC ethylene carbonate
  • DMC dimethyl carbonate
  • EMC ethyl methyl carbonate
  • a lithium electrode here, a lithium foil was pressure-bonded to a tip end of a nickel lead wire
  • An opening of the battery case was heat-sealed.
  • a square secondary battery (cell) was constructed.
  • the cell constructed as described above underwent a predetermined initial charging treatment, was placed in the restraining jig 90 using the coil spring shown in FIG 4C, and underwent an aging treatment for an aging time of 10 hours, 20 hours, or 30 hours while applying a pressure of l .Ox lO "3 MPa to l .Ox l O "3 MPa in an environment of 60°C.
  • CC charging was performed at a constant current of 1 C until the battery voltage was 4 V.
  • CV charging was performed at 4V until the above-described high-temperature aging treatment was completed.
  • the positive electrode side of the test piece was fixed to a test stand, and the peeled portion of the separator was pulled in a direction upwardly perpendicular to the positive electrode to peel the separator from the positive electrode active material layer.
  • the tensile strength (N) was measured using an autograph.
  • the peeling strength (N/m) was calculated from the tensile strength (N) during the peeling.
  • the peeling test was performed using three samples for each cell, and the peeling strength of a case where the weakest strength was required for the peeling was adopted.
  • the cell was released from pressurized state and was left to stand at room temperature for 100 hours.
  • the square battery was disassembled. Further, the positive electrode and the separator was peeled off from each other, and the dissolution state of the foreign metal which was incorporated in advance was observed using an optical microscope. Among these observation results, a case where the remaining of the foreign metal placed on the positive electrode was observed with the optical microscope was evaluated as "X”, and a case where the remaining was not observed was evaluated as "O".
  • FIG. 5 shows the results of the peeling test and the results of the dissolution state of the foreign metal.
  • the foreign metal was suitably dissolved regardless of the size ( ⁇ 100 ⁇ to 250 ⁇ ).
  • the positive electrode and the separator were not sufficiently bonded to each other, even small foreign metal ( ⁇ 50 ⁇ ⁇ ) was not dissolved and remained therein.

Abstract

L'invention concerne un procédé de fabrication d'une batterie secondaire comprenant un corps d'électrode et un électrolyte, dans laquelle le corps d'électrode comprend une électrode positive, une électrode négative et un séparateur. Ce procédé comprend les étapes consistant à : construire le corps d'électrode ; effectuer un traitement de charge initial sur la cellule ; et effectuer un traitement de vieillissement sur la cellule initialement chargée. Avant l'achèvement du traitement de vieillissement, ce procédé comprend en outre un traitement permettant de fixer l'électrode positive et le séparateur l'un à l'autre.
PCT/IB2015/000681 2014-05-14 2015-05-13 Procédé de fabrication de batterie secondaire WO2015173623A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
JP2014-100447 2014-05-14
JP2014100447A JP2015219971A (ja) 2014-05-14 2014-05-14 二次電池の製造方法

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CN108630977A (zh) * 2017-03-17 2018-10-09 三洋电机株式会社 电池组
CN108878742A (zh) * 2017-05-12 2018-11-23 住友化学株式会社 非水电解液二次电池用绝缘性多孔层
US10763478B2 (en) 2018-01-09 2020-09-01 Toyota Jidosha Kabushiki Kaisha Nonaqueous electrolyte secondary battery
US11108078B2 (en) 2014-10-17 2021-08-31 Toyota Jidosha Kabushiki Kaisha Nonaqueous electrolyte secondary battery and manufacturing method therefor

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JP6946803B2 (ja) * 2017-07-18 2021-10-06 トヨタ自動車株式会社 リチウムイオン二次電池の製造方法
JP6928872B2 (ja) * 2017-11-07 2021-09-01 トヨタ自動車株式会社 非水系二次電池
JP6669914B1 (ja) * 2019-03-29 2020-03-18 旭化成株式会社 非水系アルカリ金属蓄電素子の製造方法

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US11108078B2 (en) 2014-10-17 2021-08-31 Toyota Jidosha Kabushiki Kaisha Nonaqueous electrolyte secondary battery and manufacturing method therefor
CN108630977A (zh) * 2017-03-17 2018-10-09 三洋电机株式会社 电池组
CN108878742A (zh) * 2017-05-12 2018-11-23 住友化学株式会社 非水电解液二次电池用绝缘性多孔层
US10763478B2 (en) 2018-01-09 2020-09-01 Toyota Jidosha Kabushiki Kaisha Nonaqueous electrolyte secondary battery
CN108365266A (zh) * 2018-01-24 2018-08-03 柔电（武汉）科技有限公司 干法制备pvdf隔膜电池极片组元的方法以及生产线

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