JP2015219971A - Method for manufacturing secondary cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method which is arranged so that a battery invaded by a metallic foreign material can be detected in a short time more reliably, and which enables the mass production of reliable secondary cells in a simple and convenient manner.SOLUTION: According to the present invention, a method for manufacturing a secondary cell including an electrode body having positive and negative electrodes and a separator, and an electrolyte is provided. The manufacturing method comprises the steps of: constructing the electrode body; performing an initial charging process on the cell; and performing an aging process on the cell after the initial charging process. The manufacturing method further comprises the step of bonding the positive electrode and the separator to each other before the completion of the aging process.

Description

  The present invention relates to a method for manufacturing a secondary battery. In detail, it is related with the manufacturing method of the secondary battery which can accelerate | stimulate melt | dissolution of the mixed metal foreign material.

  Lithium secondary batteries and other secondary batteries are smaller, lighter, and have higher energy density and superior output density than existing batteries. For this reason, in recent years, it has been preferably used as a so-called portable power source for personal computers and portable terminals, and a power source for driving vehicles.

  Such a secondary battery is typically constructed by containing an electrode body having a structure in which a positive electrode and a negative electrode face each other with a separator interposed therebetween, and an electrolyte in a battery case in a sealed state. The battery is then subjected to an initial charging process under predetermined conditions in order to adjust it to a state where it can actually be used. In addition, for batteries after initial charging, high-temperature aging treatment mainly aimed at stabilizing battery reaction, and low-temperature aging treatment mainly aimed at examining the presence or absence of short circuits by self-discharge inspection, etc. Is given. With respect to these aging processes, conventionally, proposals have been made to increase the effect of the aging process or shorten the processing time. For example, Patent Document 1 discloses that the time of the aging process can be shortened by performing these aging processes in a state where a plurality of batteries are constrained.

JP 2013-114986 A

  By the way, when manufacturing such a secondary battery, there is a possibility that metal foreign matters such as copper and iron are mixed from the outside (for example, components of a manufacturing apparatus). The mixed metal foreign matter is ionized when the environment becomes higher than the dissolution potential by charging, and is eluted into the electrolyte. The metal ions generally move linearly toward the negative electrode side during charging and are locally deposited on the opposing negative electrode. For this reason, if charging is continued, metal deposits may penetrate the separator and reach the positive electrode, causing an internal short circuit in the battery. When an internal short circuit occurs, problems such as deterioration of battery performance (for example, energy density decreases) occur.

  Therefore, it is possible to detect in a self-discharge inspection a battery short-circuited by such metal foreign matter by intentionally dissolving the mixed metal foreign matter by the above-described aging treatment at high and low temperatures and depositing it on the negative electrode to cause a short circuit. It is also done. However, it may take a long time for the metal foreign matter to completely dissolve depending on the shape and size. For this reason, for example, when the aging process is shortened, there is a problem that the possibility that a battery mixed with a metal foreign object cannot be detected increases.

  This invention is made | formed in view of this point, The objective is to provide the manufacturing method of the secondary battery which can melt | dissolve the metal foreign material mixed in the electrode body more reliably in a short time. . As a result, a method for manufacturing a high-quality secondary battery with high reliability is provided.

To achieve the above object, according to the present invention, an electrode body having a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, an electrode body having a negative electrode, an electrolyte,

A method for manufacturing a secondary battery comprising: The manufacturing method includes constructing the electrode body, constructing a cell including the electrode body and an electrolyte, performing an initial charging process on the cell, and performing an aging process on the cell after the initial charging. Is included. And it is characterized by including the process which adhere | attaches the said positive electrode and the said separator before the said aging process is completed.

  In the conventional metal foreign matter dissolution treatment, the positive electrode potential is increased by adjusting the battery potential in the aging treatment to dissolve the metal foreign matter present in the vicinity. Here, the detailed dissolution behavior of the metal foreign material by the present inventors was found to significantly promote the dissolution of the metal foreign material in a state where the relative relationship between the metal foreign material and the positive electrode was adjusted. It has been completed. That is, according to the manufacturing method disclosed herein, the positive electrode and the separator are physically or chemically bonded (possibly bonded) to the metal foreign matter mixed on the surface of the positive electrode during construction of the electrode body. It is fixed to the surface. As a result, the metal foreign matter that has been loosely sandwiched between the positive electrode surface and the separator is exposed to a higher potential state on the positive electrode surface. Therefore, compared with the case where a positive electrode and a separator are not adhere | attached, a metal foreign material can be dissolved more reliably and the aging time required for dissolving a metal foreign material can be shortened. As a result, it is possible to induce an internal short circuit due to the intensive precipitation of the metal foreign matter within the aging time, and to reliably determine a good product and a defective product in a shorter time.

  In a preferable aspect of the method for manufacturing a secondary battery disclosed herein, the process of bonding the positive electrode and the separator is performed in the aging process, and the aging process is performed at a predetermined pressure on the cell after the initial charging. And a high-temperature aging treatment in which a voltage is applied at a temperature of 60 ° C. or higher and is maintained for 100 hours or longer. In such a configuration, in the high-temperature aging treatment with pressure applied, the adhesion between the positive electrode and the separator and the pressure aging are simultaneously performed. Thereby, the aging process can be performed while the metal foreign matter is efficiently dissolved in a shorter time.

  In a preferred embodiment of the method for producing a secondary battery disclosed herein, the treatment for adhering the positive electrode and the separator is performed in the construction of the electrode body, and the positive electrode includes the positive electrode current collector and the positive electrode current collector. A positive electrode active material layer provided on the body, wherein the positive electrode active material layer includes a positive electrode active material and a binder made of a thermoplastic resin, and contacts the positive electrode active material layer of the positive electrode and the separator. In this state, the positive electrode and the separator are bonded together by compacting the positive electrode and the separator at a temperature equal to or higher than the softening temperature of the binder. According to such a configuration, for example, since the positive electrode and the separator are bonded to each other at the wound part of the wound electrode body, the metal foreign matter mixed in the wound part can be reliably dissolved in a shorter time. Is possible.

  In a preferred embodiment of the method for producing a secondary battery disclosed herein, the treatment for bonding the positive electrode and the separator has a peel strength between the positive electrode and the separator of 0.2 N / m to 1.2 N / m. It is characterized by being performed so that it may become m or less. According to such a configuration, the effect of promoting the dissolution of the metal foreign matter becomes more reliable, and even when a relatively large metal foreign matter is mixed, it can be completely dissolved by the aging treatment.

  In a preferable aspect of the method for manufacturing a secondary battery disclosed herein, the aging treatment includes applying a pressure of 0.1 MPa or more to the cell after the initial charging. According to such a configuration, the positive electrode and the separator can be more firmly bonded, and the metal foreign matter can be more reliably dissolved.

  In a preferred aspect of the method for producing a secondary battery disclosed herein, the aging treatment is performed by applying a voltage to the cell after the initial charging and holding the cell for a predetermined time, and when the maximum potential of the positive electrode is It is characterized in that it includes adjusting the potential so as to be equal to or higher than the oxidation potential of the metallic foreign material expected to be mixed in the electrode body. According to this configuration, since the potential is adjusted so as to dissolve the metal foreign object, the metal foreign object can be reliably dissolved in a shorter time.

  In a preferred aspect of the method for manufacturing a secondary battery disclosed herein, the aging treatment includes adjusting the potential so that the highest ultimate potential of the negative electrode is equal to or higher than the reduction potential of the metal foreign matter. Yes. According to such a configuration, the metal foreign matter eluted from the positive electrode is retained between the electrodes without immediately going to the negative electrode. The metal ions eluted during the residence are diffused in the electrolytic solution, and local deposition on the opposing negative electrode surface is suppressed. Thereby, the short circuit by a metal foreign material can be suppressed and the metal foreign material can be made harmless.

  In a preferred aspect of the method for manufacturing a secondary battery disclosed herein, a self-discharge test for measuring a voltage drop amount of the cell is further included after the aging process. According to such a configuration, it is possible to perform an inspection that sufficiently reflects the influence of the metal foreign matter, and it is possible to realize a highly accurate inspection even for a battery having a large capacity.

  In a preferred aspect of the method for manufacturing a secondary battery disclosed herein, the electrode body has a laminated structure in which a positive electrode and a negative electrode are repeatedly opposed via a separator. Since the secondary battery having such a configuration is configured to increase the surface area of the electrode, the possibility of contamination by metallic foreign matter is increased. In addition, since the capacity can be high, the variation in the voltage drop due to the product variation becomes large, and it is difficult to detect the voltage drop due to the short circuit. Accordingly, the production of such a battery is preferable because the effects of the present invention can be more remarkably exhibited.

  Further, in the secondary battery disclosed herein in another aspect, an electrode body having a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode is typically a cell together with an electrolyte. It is housed in a case. Such a secondary battery is characterized in that at least a part of the positive electrode and the separator are bonded, and the negative electrode and the separator are not bonded. It is expected that the same effect as described above can be obtained even in the battery having such a configuration.

  As described above, the secondary battery manufactured by the manufacturing method disclosed herein is stabilized in battery performance in the aging process, and mixed foreign metal is sufficiently dissolved using the aging. Can be. Therefore, for example, a non-defective product and a defective product can be determined with high accuracy and can be provided as a highly reliable and high-quality secondary battery in which occurrence of a short circuit due to a metal foreign object is suppressed. In addition, such a secondary battery can be provided with high productivity and low cost because the manufacturing time can be reduced. Therefore, although such a secondary battery can be used for various applications, it can be suitably used as a driving power source mounted on a vehicle such as an automobile that requires high safety and reliability. In addition, this secondary battery may be used independently (single cell), and can also be used with the form of the assembled battery formed by connecting the said secondary battery in series and / or in parallel.

It is sectional drawing which shows typically the structure of the secondary battery which concerns on one Embodiment. It is a schematic diagram explaining the structure of the winding electrode body of the secondary battery which concerns on one Embodiment. (A) It is a figure which illustrates typically an example of the dissolution condition of the metal foreign material in the manufacturing method of this invention, and the (B) conventional manufacturing method. (A) and (B) are schematic cross-sectional views illustrating a pressure load state on a secondary battery and a state where no pressure is applied, respectively, and (C) is a perspective view illustrating a state of pressure load on a plurality of secondary batteries. FIG. It is the figure which illustrated the dissolution situation of the metal foreign substance concerning one embodiment as a relation between the peel strength of a positive electrode and a separator, and a foreign substance size.

  In this specification, the “secondary battery” is an industrial field similar to a chemical battery (for example, a lithium secondary battery) in addition to a so-called chemical battery such as a lithium secondary battery, a nickel hydride battery, a nickel cadmium battery, or a lead storage battery. It is a term including a storage element (for example, a pseudo-capacitance capacitor, a redox capacitor) that can be used in the same manner, a hybrid capacitor that combines these, a lithium ion capacitor, and the like. Further, the “lithium secondary battery” refers to a secondary battery that uses lithium ions as electrolyte ions and is charged and discharged by movement of lithium ions (charge movement) between positive and negative electrodes. A secondary battery generally referred to as a lithium ion battery, a lithium polymer battery, or the like is a typical example included in the lithium secondary battery in this specification. In the present specification, the “active material” refers to a substance (compound) capable of reversibly occluding and releasing chemical species (lithium ions in a lithium secondary battery) serving as a charge carrier on the positive electrode side or the negative electrode side.

  Further, in the invention disclosed herein, the metal foreign object that can be dissolved is a metal that may be mixed in the manufacturing process of the secondary battery, and has a redox potential within the operating voltage range of the secondary battery. And those that can be dissolved (ionized) at the potential. As an element (and its oxidation-reduction potential) which comprises a metal foreign material, typically, iron (Fe; 2.6V), copper (Cu; 3.4V), these alloys, etc. are mentioned, for example. In particular, iron is a main component of stainless steel that is frequently used in various manufacturing apparatuses and the like, so it is considered that iron is likely to be mixed in the manufacturing process. In addition, since the resistance is relatively high, it is preferable that the dissolution of the iron or the iron alloy proceeds reliably. Note that the “potential” in this specification indicates a potential difference (a lithium-based potential (V)) between a potential (V) of lithium and the metal foreign matter, unless otherwise specified.

  Hereinafter, preferred embodiments of the secondary battery and the method for producing the battery disclosed herein will be described. Matters necessary for implementation other than matters specifically mentioned in the present specification can be grasped as design matters of those skilled in the art based on the prior art in this field. The secondary battery having such a structure can be implemented based on the contents disclosed in the present specification and common technical knowledge in the field. In addition, although the lithium secondary battery as a suitable aspect is demonstrated below as an example, it is not the intention which limits the application object of this invention to this battery.

FIG. 1 is a schematic cross-sectional view for explaining the configuration of a secondary battery as an embodiment manufactured here. FIG. 2 is a schematic diagram illustrating the configuration of the electrode body accommodated in the secondary battery. Hereinafter, the dimensional relationship (length, width, thickness, etc.) in each drawing does not necessarily reflect the actual dimensional relationship.
The secondary battery 100 disclosed herein essentially includes an electrode body 20 having a positive electrode 30, a negative electrode 40, and a separator 50, and an electrolyte (not shown). Such a secondary battery 100 can be manufactured as follows. That is, first, the electrode body 20 is manufactured by making the positive electrode 30 and the negative electrode 40 face each other with the separator 50 interposed therebetween. Next, the electrode body 20 and the electrolyte are accommodated in the battery case 10 and the battery case 10 is sealed. Thereby, the secondary battery (cell) 100 is constructed. Although not particularly strictly distinguished, in the present specification, a battery after assembly and completion of processing such as aging processing may be referred to as a cell.
Usually, the cell 100 thus constructed is subjected to an initial charging process under a predetermined condition in order to adjust it to a state where it can actually be used (shipped). In addition, the battery after the initial charge is subjected to a high-temperature aging treatment mainly for stabilizing the battery reaction and a self-discharge test for checking the presence or absence of a short circuit. Only the batteries that pass the inspection are shipped as products.

By the way, when constructing the cell 100 described above, a metal foreign object may be mixed from the outside (for example, a component of a manufacturing apparatus). In such a case, when the potential of the positive electrode 30 becomes higher than the dissolution potential (oxidation potential) of the metal foreign matter due to charging of the battery, the metal foreign matter is oxidized (loses electrons) and becomes metal ions in the electrolyte. Dissolve in For example, when the metal foreign matter is copper or iron, it is dissolved as Cu → Cu ²⁺ and Fe → Fe ²⁺ . Since the metal ions are positively charged, they usually move linearly between the positive and negative electrodes through the separator 50 toward the negative electrode 40. And the said metal ion is reduce | restored in the position facing the said metal foreign material on the negative electrode 40, and deposits locally (intensively). For this reason, as the charging proceeds, the deposit on the negative electrode gradually grows toward the positive electrode 30 side. When the deposit reaches the positive electrode, a short circuit (micro short circuit) occurs in the battery.

  When the metal foreign matter is very small, the metal foreign matter is usually completely dissolved within the range of the initial charge to the self-discharge test described above. Pass / fail can be determined appropriately. However, when the metal foreign matter is coarse or difficult to dissolve, there is a possibility that sufficient dissolution will not be performed within the above time. In this case, even if the battery is determined to be a non-defective product, the dissolution of the metal foreign matter may proceed in a normal battery use state, and the battery may be short-circuited during use. Therefore, in order to avoid such a situation, in the secondary battery manufacturing method disclosed herein, after the secondary battery (cell) 100 is constructed, it is within the range of initial charge to self-discharge inspection, that is, an aging process. In the meantime, even if it is a coarse metallic foreign material, it is made to melt | dissolve more completely.

In addition, according to the detailed study by the present inventors, for example, the time required to dissolve a metal foreign substance having a predetermined size in the potential adjustment step is affected by various factors. For example, in addition to the environmental temperature, the battery voltage (potential difference between positive and negative electrodes), and the dissolution rate of the metal foreign matter, it may include factors that cannot be managed, such as differences in specifications of the cell constituent materials and variations.
In addition, the metal foreign object is exposed to an environment having a higher potential when the contact area with the positive electrode, more specifically, the positive electrode active material constituting the positive electrode is larger. Therefore, dissolution of the metal foreign matter can be promoted in a higher potential environment. On the other hand, the dissolution of the metal foreign matter does not proceed when the potential of the positive electrode is slightly lower than the dissolution potential of the metal foreign matter. Therefore, for example, the metal foreign matter mixed on the surface of the positive electrode is more preferably exposed to the melting potential or higher while being pressed against the surface of the positive electrode.

  Therefore, in the technology disclosed herein, in order to sufficiently advance the dissolution of the metal foreign matter as described above, (1) constructing an electrode body including a positive electrode, a negative electrode, and a separator (construction process of electrode body) (2) constructing a cell including the electrode body and the electrolyte (cell construction step), (3) applying an initial charging process to the cell (initial charging step), and (4) the initial charging. Aging process is performed on the subsequent cells (aging process step). And it is characterized by including the process (adhesion process) which adheres the said positive electrode and the said separator until the said aging process is completed.

[1. Construction of electrode body]
Here, first, an electrode body including a positive electrode, a negative electrode, and a separator is prepared.
The positive electrode typically includes a positive electrode current collector and a positive electrode active material layer including at least a positive electrode active material formed on the positive electrode current collector. A method for producing such a positive electrode is not particularly limited. For example, a positive electrode active material, a conductive material, a binder (binder), and the like are mixed in an appropriate solvent to include a paste (slurry or ink). .) Composition (hereinafter referred to as “positive electrode paste”), and the paste is supplied onto a positive electrode current collector to form a positive electrode active material layer. As a method of supplying the positive electrode paste, for example, a method of applying the positive electrode paste to one or both surfaces of the positive electrode current collector using a conventionally known coating apparatus (for example, a slit coater, a die coater, a comma coater, or a gravure coater). Is mentioned. Alternatively, the positive electrode active material layer is formed by granulating the positive electrode active material, the conductive material, and the binder into an appropriate size to obtain a granulated body, and supplying the granulated body onto the positive electrode current collector and pressing it. Can also be formed. Although not particularly limited, the mass of the positive electrode active material layer provided per unit area of the positive electrode current collector (the total mass on both sides in the configuration having the positive electrode active material layer on both sides of the positive electrode current collector) is, for example, may be 10mg ^/ cm ² ~30mg ^/ cm 2 approximately.

  As the positive electrode current collector, a conductive member made of a metal having good conductivity (for example, aluminum, nickel, titanium, stainless steel, etc.) is preferably used. The shape of the current collector is not particularly limited because it can vary depending on the shape of the battery to be constructed, and a rod-like body, a plate-like body, a foil-like body, a net-like body, or the like can be used. In addition, in the battery provided with the winding electrode body mentioned later, a foil-like body is mainly used. The thickness of the foil-shaped current collector is not particularly limited, but a thickness of about 5 μm to 50 μm (more preferably 10 μm to 30 μm) can be preferably used in consideration of the energy density of the battery and the strength of the current collector.

As the positive electrode active material, one type or two or more types of materials conventionally used in secondary batteries can be used without any particular limitation. For example, an oxide containing a lithium atom and a transition metal atom as constituent metal atoms, such as lithium nickel oxide (eg, LiNiO ₂ ), lithium cobalt oxide (eg, LiCoO ₂ ), lithium manganese oxide (eg, LiMn ₂ O ₄ ) (Lithium transition metal oxide), phosphate containing lithium atoms and transition metal atoms such as lithium manganese phosphate (LiMnPO ₄ ) and lithium iron phosphate (LiFePO ₄ ) as constituent metal atoms. Among them, a lithium nickel cobalt manganese composite oxide (for example, LiNi _1/3 Co _1/3 Mn _1/3 O ₂ ) having a layered structure or LiNi _0.5 Mn _1.5 O ₄ having a spinel structure is a main component. The positive electrode active material that has high energy density and excellent thermal stability. Furthermore, since the advantages of the technology disclosed herein can be more effectively received, it can be preferably used. Although not particularly limited, the ratio of the positive electrode active material to the entire positive electrode active material layer is 50% by mass or more (typically 70% by mass or more and 100% by mass or less, for example, 80% by mass or more and 99% by mass or less). It is preferable that As such a lithium transition metal oxide (typically in particulate form), for example, one prepared by a conventionally known method can be used as it is.

  As the conductive material, one or more kinds of substances conventionally used in secondary batteries can be used without any particular limitation. For example, carbon materials such as carbon black (for example, acetylene black, furnace black, ketjen black, etc.), coke, graphite (natural graphite and modified products thereof, artificial graphite), and the like can be used. Among these, carbon black (typically acetylene black) having a small particle size and a large specific surface area can be preferably used. Although it does not specifically limit, the ratio of the electrically-conductive material to the whole positive electrode active material layer can be 1 mass% or more and 15 mass% or less (typically 5 mass% or more and 10 mass% or less), for example.

  The binder is not particularly limited, but is a thermoplastic binder (typically a resin or elastomer) having a softening point (for example, 60 ° C. or higher) in an appropriate temperature range. One kind or two or more kinds of substances conventionally used in secondary batteries can be used without particular limitation. For example, when the positive electrode active material layer is formed in the form of a positive electrode paste, a compound that can be dissolved or dispersed homogeneously in a solvent described later can be used. For example, when the positive electrode active material layer is formed using an organic solvent-based paste (a solvent-based paste in which the main component of the dispersion medium is an organic solvent), a polymer material that is dispersed or dissolved in the organic solvent can be preferably used. . Examples of such a polymer material include polyvinylidene fluoride (PVdF), polyvinylidene chloride (PVdC), and polyethylene oxide. Alternatively, when the positive electrode active material layer is formed using an aqueous paste, a polymer material that is dissolved or dispersed in water can be preferably used. Examples of such polymer materials include cellulose polymers, fluorine resins, vinyl acetate copolymers, rubbers, and the like. More specifically, carboxymethylcellulose (CMC), hydroxypropylmethylcellulose, polyvinyl alcohol, polytetrafluoroethylene (PTFE), styrene butadiene rubber (SBR), tetrafluoroethylene-hexafluoropropylene copolymer, acrylic acid-modified SBR resin (SBR latex). Although it does not specifically limit, the ratio of the binder to the whole positive electrode active material layer can be 0.5 mass% or more and 10 mass% or less (preferably 1 mass% or more and 2 mass% or less), for example.

  As a solvent, 1 type, or 2 or more types among the solvents conventionally used for a secondary battery can be used without limitation. Such a solvent is roughly classified into an aqueous system and a non-aqueous system. The aqueous solvent is not particularly limited as long as it is water-based as a whole, and water or a mixed solvent mainly composed of water can be preferably used. Preferable examples of the non-aqueous solvent include N-methyl-2-pyrrolidone (NMP), methyl ethyl ketone, toluene and the like.

  In addition, various additives, such as a dispersing agent and a thickener, can also be added to the said positive electrode paste, unless the effect of this invention is impaired remarkably. Examples of 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 having a sulfate, a sulfonate, a phosphate, or the like. And the like, and the like. More specifically, carboxymethyl cellulose (CMC), methyl cellulose, ethyl cellulose, hydroxypropyl cellulose, butyral, polyvinyl alcohol, modified polyvinyl alcohol, polyethylene oxide, polyvinyl pyrrolidone, polycarboxylic acid, oxidized starch, phosphoric acid starch and the like can be mentioned.

In the production method disclosed herein, for example, after the positive electrode paste or the granulated body is applied on the positive electrode current collector, the solvent contained in the paste (or the granulated body) is removed by an appropriate drying means. As such a method, natural drying, hot air, low-humidity air, vacuum, infrared rays, far infrared rays, drying with an electron beam, or the like can be used alone or in combination. Then, after drying, the thickness and density of the positive electrode active material layer can be adjusted by appropriately pressing the positive electrode. For the press treatment, various conventionally known press methods such as a roll press method and a flat plate press method can be employed. When the density of the positive electrode active material layer formed on the positive electrode current collector is extremely low, the energy density per unit volume may decrease. In addition, when the density of the positive electrode active material layer is extremely high, the internal resistance tends to increase particularly during large current charge / discharge or in a low temperature environment. For this reason, 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 4.5 g / cm ³ or less (typically 4. 2 g / cm ³ or less).

The negative electrode typically includes a negative electrode current collector and a negative electrode active material layer including at least a negative electrode active material formed on the negative electrode current collector. The method for producing the negative electrode is not particularly limited. For example, a paste-like composition (hereinafter referred to as “negative electrode paste”) is prepared by mixing a negative electrode active material and a binder in an appropriate solvent, and the paste. Can be applied to the negative electrode current collector to form a negative electrode active material layer (also referred to as a negative electrode active material layer). As a method for forming the negative electrode active material layer, a method similar to that for the positive electrode described above can be appropriately employed. Although not particularly limited, the mass of the negative active material layer disposed per unit area of the negative electrode current collector (total mass of both sides) may be, for example 5mg ^/ cm ² ~30mg / cm 2 of about .

  As the negative electrode current collector, a conductive member made of a metal having good conductivity (for example, copper, nickel, titanium, stainless steel, etc.) is preferably used. The shape of the negative electrode current collector can be the same as the shape of the positive electrode current collector.

  As the negative electrode active material, one kind or two or more kinds of materials conventionally used for secondary batteries can be used without any particular limitation. For example, natural graphite (graphite) and its modified products and graphite (artificial graphite) such as artificial graphite manufactured from petroleum or coal-based materials; hard carbon (non-graphitizable carbon), soft carbon (graphitizable carbon), Carbon nanotubes and other carbon materials having a graphite structure (layered structure) at least partially, such as carbon nanotubes; metal oxides such as lithium titanium composite oxides; tin (Sn), silicon (Si) and lithium alloys, etc. Can be mentioned. Although the ratio of the negative electrode active material in the whole negative electrode active material layer is not particularly limited, it is usually suitably about 50% by mass or more, preferably about 90% by mass to 99% by mass (for example, about 95% by mass to 99% by mass).

  As the binder, an appropriate material can be selected from the polymer materials exemplified as the binder for the positive electrode active material layer. For example, styrene butadiene rubber (SBR), polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE) and the like are exemplified. The proportion of the binder in the entire negative electrode active material layer is not particularly limited, and can be, for example, 1% by mass to 10% by mass (preferably 2% by mass to 5% by mass). In addition, the various additives and conductive materials already described above can be used as appropriate.

After applying the negative electrode paste, the solvent is removed as appropriate using the drying means described above. After the drying, the thickness and density of the negative electrode active material layer can be adjusted by appropriately pressing as in the case of the positive electrode. The density of the negative electrode active material layer after the press treatment 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 1.5 g / cm ³ cm ³ or less (typically 1.49 g / cm ³ or less).

  As the separator 50, various microporous sheets similar to those conventionally used for secondary batteries can be used. For example, the separator 50 is made of a resin such as polyethylene (PE), polypropylene (PP), polyester, cellulose, or polyamide. A microporous resin sheet is mentioned. Such a microporous resin sheet may have a single layer structure, or may have a two or more layers structure (for example, a three layer structure in which a PP layer is laminated on both sides of a PE layer). In addition, this separator can also be equipped with the heat resistant layer (HRL) containing an inorganic compound particle (inorganic filler) on the one or both surfaces of the said microporous resin sheet. As the inorganic filler, alumina, boehmite, magnesia or the like can be adopted.

  The positive electrode and the negative electrode are laminated so as to maintain an insulating state between them through a separator, thereby producing an electrode body. The configuration of the electrode body is not particularly limited. For example, the electrode body is preferably an electrode body having a laminated structure in which a positive electrode and a negative electrode are repeatedly opposed via a separator. An electrode body having such a laminated structure has a flat-plate laminated electrode body in which a plurality of sheet-like positive electrodes, negative electrodes, and separators are laminated, and a long sheet-like positive electrode, negative electrode, and separator laminated and wound. A wound electrode body can be considered. Since the electrode body having such a laminated structure is configured such that the area of the electrode is increased, the possibility of contamination of metal foreign matter can be increased. In addition, since the capacity can be high, the variation in voltage drop due to product variation is relatively large, and it is difficult to detect the voltage drop due to a short circuit. Therefore, it is preferable in manufacturing such a battery because the effects of the manufacturing method disclosed herein can be more remarkably exhibited.

  As shown in FIG. 2, typically, the positive electrode 30 has no positive electrode active material layer 34 (or is removed) at one end along the longitudinal direction, and the positive electrode current collector 32. Is exposed. Similarly, the negative electrode 20 is formed, for example, so that the negative electrode active material layer 44 is not provided (or removed) at one end along the longitudinal direction, and the negative electrode current collector 42 is exposed. Yes. In the above laminated structure, the positive and negative exposed portions 36 and 46 are laminated in any position, and the exposed portions 36 and 46 are collected to collect current, thereby collecting the electrode body 20 with good current collection efficiency. Can be formed. Further, the flat wound electrode body 20 is formed by winding a laminated body in which a long positive electrode 30 and a negative electrode 40 are overlapped in an insulating state via two separators 50 in the long direction and crushing from the side direction. It can be made by kidnapping. The laminate itself may be formed by winding so that the winding cross section has a flat shape.

[Adhesion treatment]
When a metal foreign substance mixes in the positive electrode 30, it will mix in the inside of this positive electrode active material layer, or the surface. When a metal foreign matter is mixed in the positive electrode active material layer, the metal foreign matter may be present in a region having a higher positive electrode potential. When metal foreign matter is mixed into the surface of the positive electrode active material layer, the metal foreign matter can be present in a region having a higher positive electrode potential by maintaining the state where the metal foreign matter is pressed against the positive electrode active material. Therefore, in the manufacturing method disclosed herein, a process (adhesion process) for bonding the positive electrode 30 and the separator 50 at any timing from the construction process of the electrode body to the aging process process described below is completed. Like to do.
And as above-mentioned, the positive electrode 30 is equipped with the positive electrode active material layer 34 of the form with which the positive electrode active material was couple | bonded by the binder on the surface of the positive electrode collector 32. As shown in FIG. Therefore, such an adhesion treatment can be realized by consolidating these at a temperature equal to or higher than the softening point of the binder (typically 60 ° C. or higher) in a state where the separator 50 is stacked on the positive electrode 30.

  Note that “adhesion” in the present specification refers to a state in which the positive electrode 30 and the separator 50 are bonded to each other by a physical bonding force through, for example, a binder component. For example, it is preferable that the adhesion is such that the peel strength is 0.15 N / m or more. For example, even when the positive electrode 30 and the separator 50 are in contact (adjacent) at the binder component portion of the positive electrode 30 but are not bonded by a physical bonding force, it is included in the adhesion referred to here. I can't.

There is no particular limitation on the timing of the bonding process.
For example, in the construction process of the electrode body 20, the bonding process is performed when the positive electrode 30 and the separator 50 are overlapped, and the bonding process is performed when the flat plate electrode body or the wound electrode body is constructed. Exemplified to do. When the bonding process is performed at the time when the positive electrode 30 and the separator 50 are overlapped, the consolidation process accompanied by the heating and the pressing process for adjusting the thickness and density of the positive electrode active material layer are performed simultaneously. Also good. It is preferable to perform the adhesion treatment at such timing because dissolution of metal foreign matter is promoted in both the initial charging step and the aging step described later.
Alternatively, for example, the bonding process may be performed in an aging process described later. It is preferable to perform the bonding process at such timing in that the consolidation (load) for the bonding process and the pressurization (load) in the aging process can be realized at the same time. Here, the aspect which performs the said adhesion process in the below-mentioned aging process is demonstrated.

  In addition, although it is not limited to this about the negative electrode 40 and the separator 50, it is preferable that it is not physically adhere | attached although it may contact like the conventional cell. This is because gas can be generated on the surface of the negative electrode 40 due to decomposition of the electrolyte and overcharge additive during normal battery use or overcharge. This is because it is not preferable that the negative electrode 40 and the separator 50 are bonded to each other because the gas generated in the negative electrode 40 is prevented from coming out of the electrode body 20.

[2. Cell construction process]
Next, the electrode body 20 and the electrolyte are accommodated in an appropriate battery case 10. Then, the secondary battery (cell) 100 is constructed by sealing the case 10. The sealing operation can be performed by a method similar to that conventionally used for secondary batteries. For example, when a metal battery case 10 is used, techniques such as laser welding, resistance welding, and electron beam welding can be used. Moreover, when using the battery case 10 made of non-metal (for example, resin material), a technique such as adhesion with an adhesive or ultrasonic welding can be used.

  As the battery case 10, materials and shapes conventionally used for secondary batteries can be used. As the material of the case, for example, a relatively light metal material such as aluminum or steel, or a resin material such as polyphenylene sulfide resin or polyimide resin can be used. Among these, from the viewpoint of improving heat dissipation and energy density, a battery case (hard case) 10 made of a relatively light metal (for example, aluminum or aluminum alloy) can be preferably used. Moreover, the shape (outer shape of the container) of the case 10 is not particularly limited. For example, the case 10 has a circular shape (cylindrical shape, coin shape, button shape), hexahedron shape (rectangular shape, flat shape), and a shape obtained by processing and deforming them. possible.

  The battery case 10 illustrated in this figure includes a flat rectangular parallelepiped (rectangular) case body 12 having an open upper end, and a sealing body 14 that closes the opening. On the upper surface of the battery case 10 (that is, the sealing body 14), a positive electrode terminal 60 electrically connected to the positive electrode 30 of the wound electrode body 20 and a negative electrode terminal 70 electrically connected to the negative electrode 40 of the electrode body 20 Is provided. For example, the positive electrode current collector plate 62 is disposed at the exposed end portion of the positive electrode current collector 32 of the electrode body 20, and the negative electrode current collector plate 72 is disposed at the exposed end portion of the negative electrode current collector 42. Attached and electrically connected to the positive terminal 60 and the negative terminal 70, respectively. Note that the battery case 10 has a current interruption mechanism (a current according to an increase in internal pressure when the battery is overcharged) in the conductive path between the positive electrode terminal 60 and the negative electrode terminal 70 and the electrode body 20 as necessary. It is also possible to provide a safety mechanism such as a mechanism capable of blocking Moreover, the sealing body 14 is provided with a safety valve (not shown) or the like for discharging the gas generated inside the battery case to the outside of the case, like the battery case 10 of the conventional secondary battery.

As the electrolyte, one kind or two or more kinds similar to those conventionally used for secondary batteries can be used without particular limitation. Such an electrolyte typically has a composition in which a suitable nonaqueous solvent contains a supporting salt (typically a lithium salt).
As the non-aqueous solvent, aprotic solvents such as carbonates, esters, ethers, nitriles, sulfones and lactones can be used. Of these, carbonates such as ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) can be preferably used.

As the supporting salt, various materials known to function as a supporting electrolyte for the secondary battery can be appropriately employed. For example, LiPF ₆ , LiBF ₄ , LiClO 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 One or two or more selected from various lithium salts such as LiClO ₄ can be used. Among these, LiPF ₆ can be preferably used. The concentration of the supporting salt is not particularly limited, but if it is too low, the amount of lithium ions contained in the electrolyte is insufficient, and the ionic conductivity tends to decrease. On the other hand, when the concentration is extremely high, the viscosity of the electrolyte becomes too high, and the ionic conductivity tends to decrease. Therefore, the concentration of the supporting salt is preferably about 0.1 mol / L to 2 mol / L (preferably about 0.8 mol / L to 1.5 mol / L) with respect to the entire electrolyte. .

  Furthermore, the electrolyte used here includes various film forming agents such as film forming agents such as vinylene carbonate (VC) and fluoroethylene carbonate (FEC), and gas generating additives such as biphenyl (BP) and cyclohexylbenzene (CHB). Additives can also be added as appropriate.

[3. Initial charging process]
The initial charging step is a step of performing a charging process on the constructed secondary battery (cell) 100 up to a predetermined voltage value in a normal temperature range. Typically, an external power source (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 and charged to a predetermined voltage (typically constant current charging). ). The normal temperature range in the initial charging step typically refers to a temperature range that is normal temperature, and may be 20 ° C. ± 15 ° C. Further, the voltage between the positive and negative terminals (typically the highest voltage reached) in the initial charging process may vary depending on the active material used, the type of the non-aqueous solvent, and the like, but the SOC (State of Charge) of the battery assembly: A voltage range that can be shown when the state of charge is in the range of about 80% or more (typically 90 to 105%) of the full charge (typically the rated capacity of the battery) may be used. For example, in the case of a battery that is fully charged at 4.2 V, it is preferable to adjust to a range of about 3.8 to 4.2 V. The charging rate in the initial charging process may be the same as a conventionally known charging rate that can be generally adopted when initially charging a conventional battery assembly, and may be about 0.1 to 10 C, for example. Such a charging process may be performed once, but may be performed twice or more, for example, with a discharging process interposed therebetween.

[4. Aging process]
The aging process is a process in which the secondary battery (cell) 100 that has completed the initial charging process is held (typically left standing) for a predetermined time in a predetermined temperature range and a predetermined SOC. The temperature at which the cell is held may be a low temperature region (for example, the normal temperature region to about 40 ° C.) or a high temperature region (for example, about 40 ° C. to 70 ° C.). Further, the SOC of the cell may be 0% to 100% or 100% or more. These temperature and SOC may be variously changed in the aging process. Further, a predetermined pressure may be applied to the cell. In a preferred embodiment, a predetermined pressure is applied to the cell after initial charging, and aging is performed in a high temperature region with the pressure applied. Thereby, the normal high temperature pressurization aging and the above-mentioned adhesion treatment between the positive electrode and the separator can be realized at the same time.

  FIG. 3A is a diagram schematically illustrating an example of a dissolution state of the metal foreign matter 80 in the method for manufacturing a secondary battery disclosed herein. FIG. 3B is a diagram of a conventional manufacturing method exemplified for comparison. In these drawings, the relative relationship among the positive electrode 30, the separator 50, and the metal foreign object 80 is exaggerated for easy understanding. In this figure, the state in which the positive electrode 30, the separator 50, and the negative electrode 40 are completely separated from each other actually indicates that these members (the positive electrode 30, the separator 50, and the negative electrode 40) are not physically bonded. . For example, it includes a state where the positive electrode 30 and the separator 50 are not bonded but are in contact with each other. Further, in the drawing, the state in which the positive electrode 30 and the separator 50 are shown adjacent to each other is the state in which the positive electrode 30 and the separator 50 are physically bonded, and the positive electrode 30 and the separator 50 are not bonded to each other. Are in contact with each other in a consolidated state.

  In the present invention (A), as shown in the step (a), in the cell 100 in which the bonding process is not performed before the initial charging, the positive electrode 30, the separator 50, and the negative electrode 40 are physically bonded. It has not been. Therefore, as shown in step (b), the positive electrode 30 and the separator 50 are physically bonded to the cell 100 by applying a pressure at a temperature equal to or higher than the softening point of the binder included in the positive electrode 30. . More specifically, the binder contained in the positive electrode active material layer 34 is softened, and the positive electrode 30 (the positive electrode active material layer 34) and the separator 50 are bonded by the bonding force of the binder. In this state, by performing the aging treatment step (c), high-temperature aging and adhesion treatment can be carried out simultaneously.

  In this aging treatment, the metal foreign matter 80 is pressed against the surface of the positive electrode 30 and can be exposed to a higher positive electrode potential. Further, since the contact area between the metal foreign object 80 and the positive electrode 30 is increased, dissolution (ie, ionization) of the metal foreign object 80 due to the exchange of electrons between the two is promoted. Therefore, the amount of dissolution of the metallic foreign matter 80 is increased as compared with a state in which such adhesion is not performed (see FIG. 3B (c)). Therefore, even if the metal foreign matter 80 is relatively coarse, complete dissolution can be performed in a shorter time. In addition, since the ions of the dissolved metal foreign matter 80 are positively charged, the ions are attracted toward the negative electrode 40 having a lower potential while diffusing in the electrolytic solution. Here, when there is a site where the surface potential of the negative electrode 40 is equal to or lower than the reduction potential of the metal foreign material 80, the ions of the metal foreign material 80 can be deposited as precipitates 82 in the site.

  Next, as shown in step (d), the load on the cell is released. Here, since the positive electrode 30 and the separator 50 are physically bonded, the bonding between the positive electrode 30 and the separator 50 is maintained even after the load is released. Therefore, for example, as shown in step (e), adhesion between the positive electrode 30 and the separator 50 is maintained even when any other processing step such as low-temperature aging is performed as the next step. Therefore, even when the undissolved metal foreign matter 80 remains in the aging treatment step (c), if the positive electrode potential is equal to or higher than the dissolution potential of the metal foreign matter 80 in the subsequent step (e) of the adhesion treatment. The dissolution of the metallic foreign matter 80 can be performed in an accelerated state. In addition, the next self-discharge inspection step (f) can be performed in a state where the dissolution of the metal foreign matter 80 is promoted in this way. In the self-discharge inspection step (f) or the like, when the potential of the negative electrode 40 becomes equal to or lower than the reduction potential of the metal foreign matter 80, the ions of the metal foreign matter 80 are deposited on the negative electrode 40 as precipitates 82.

[Pressure load]
In addition, the load of the pressure to the cell 100 can be performed using a conventionally well-known 1 type, or 2 or more types method. Specifically, for example, as shown in FIG. 4A, after the cell 100 is sandwiched between a pair of restraining plates 92, (B) a method of tightening the restraining plates 92 is exemplified. For fastening, a method using a bolt or a restraint band, a method using a press machine such as an air press or a hydraulic press, a method using gravity such as loading an appropriate weight on the case, a method of reducing pressure in a vacuum furnace, etc. Etc. When pressure is applied, it is typically preferable to use an appropriate jig (for example, the restraining plate 92). For example, when the cell has a hexahedral shape, at least a pair of surfaces of the cell (typically, so that a load is applied in a direction (stacking direction) perpendicular to the surfaces of the positive electrode, separator, and negative electrode of the electrode body 20 (typically, A method of applying pressure in a state in which the wide surface having the largest surface area is sandwiched between the restraining plates 92 can be suitably used. By using the restraint plate 92, the battery case 10 (specifically, the electrode body 20 in the case) can be pressurized relatively uniformly throughout. For example, in the case where a plurality of cells 100 are pressurized simultaneously, a restraining jig 90 using a coil spring as shown in FIG. 4C can be suitably used. When the restraining jig 90 is used, for example, after the secondary battery (single cell) 100 is accommodated between the restraining plates 92, the handle portion 94 is rotated to adjust the coil spring, thereby making the pair of wide widths of the cell. Apply arbitrary pressure to the surface. In addition, the magnitude | size (value) of the applied pressure can be calculated | required using a general pressure measuring method (For example, a load cell, a strain gauge, etc.). Moreover, such pressure loading may be performed at once, for example, may be performed stepwise in two or more steps.

  The pressure applied to the cell is not particularly limited, but when the pressure is extremely small, the metal foreign matter is not sufficiently pressed against the positive electrode, the contact with the positive electrode is not sufficiently increased, and it is difficult to be exposed to a higher positive electrode potential. It is not preferable because it becomes. In addition, when the applied pressure is extremely large, the battery case is excessively deformed, and voids (pores) in the electrode body (typically electrodes and separators) are crushed, which adversely affects battery performance. This is not preferable because of the risk of causing For this reason, the said pressure should just be about 0.1 Mpa or more, for example, 0.3 Mpa or more, Preferably it is 0.5 Mpa or more, and can be 0.7 Mpa or more typically. The pressure can be 1.5 MPa or less, preferably 1.3 MPa or less, and typically 1.0 MPa or less. When the pressure to load is in the above range, the effect of the present application and the battery performance can be achieved at a high level. In the present specification, “pressure” refers to a relative pressure with respect to atmospheric pressure, that is, a value obtained by subtracting atmospheric pressure (about 0.1 MPa) from actual pressure (absolute pressure).

It should be noted that the time and temperature for maintaining the pressed state due to the pressure load described above are sufficient to achieve adhesion between the positive electrode and the separator in consideration of the form of the electrode body (the amount of binder contained in the positive electrode and the surface state of the separator) and the like. Can be determined.
The temperature at which the pressed state is maintained can be set to a temperature equal to or higher than the softening point of the binder included in the positive electrode, for example. Typically, it can be 40 ° C. or higher, preferably 60 ° C. or higher (65 ° C. or higher). The upper limit of the temperature can be appropriately determined within a temperature range that does not adversely affect the battery configuration, for example, a range below the softening temperature of the separator. For example, it can be set to about 80 ° C. (75 ° C. or less). As a means for heating the cell, for example, a thermostatic bath or an infrared heater can be appropriately used.

  The time for maintaining the pressed state is not particularly limited as long as sufficient adhesion is achieved. For example, it is 100 hours or longer, preferably 110 hours or longer, more preferably 120 hours or longer, and further preferably 140 hours or longer. be able to. The upper limit of the time is not particularly limited. For example, when high-temperature aging is performed at the same time, it can be determined in consideration of time appropriate for high-temperature aging, production efficiency, and the like. Typically, it can be set to a standard of about 240 hours or less, preferably about 168 hours or less.

[Peel strength]
Whether or not sufficient adhesion has been achieved can be confirmed, for example, by measuring the peel strength between the positive electrode 30 and the separator 50 that have been subjected to adhesion treatment under the same conditions.
Note that the peel strength between the positive electrode 30 and the separator 50 can be quantitatively evaluated by, for example, a “90 ° peel test” defined in JIS K6854-1: 1999. In a preferred embodiment, the 90 ° peel strength between the positive electrode 30 and the separator 50 after the adhesion treatment is 0.15 N / m or more, typically 0.2 N / m or more, for example, 0.25 N / m or more, Preferably it is 0.4 N / m or more. The upper limit of the peel strength is not particularly limited, but an excessively strong bond can cause damage to the electrode. Therefore, the peel strength can be about 1.2 N / m or less, for example. Thereby, the adhesion between the positive electrode 30 and the separator 50 can be ensured, and even a coarser metal foreign material can be favorably promoted.
* Please confirm the peel strength measurement method and the numerical values shown as examples.

[Potential adjustment]
By holding at a high temperature in the above pressure load state, adhesion between the positive electrode 30 and the separator 50 can be realized. Moreover, by applying a voltage to the cell in such a state, an aging (high temperature aging) process can be performed at the same time. Here, by applying a voltage so that the positive electrode potential of the cell 100 is equal to or higher than the dissolution potential of the metal foreign object 80, even if the metal foreign object 80 is mixed into the battery from the outside, the metal foreign object 80 is dissolved. Thus, metal ions can be obtained.

  The application of such a voltage adjusts the potential so that the potential of the positive electrode 30 (maximum attainable potential) becomes equal to or higher than the oxidation potential of the metal foreign matter 80. The potentials of the positive electrode 30 and the negative electrode 40 can be appropriately set according to the type of the metallic foreign matter 80 that may be mixed. For example, among the metal foreign matter 80 (elements) already described above, the one having the highest redox potential is copper. Therefore, for example, when all the elements whose oxidation-reduction potentials are equal to or lower than copper (for example, copper or iron) are targeted, the potential of the positive electrode (maximum ultimate potential) is equal to or higher than the oxidation potential of copper (approximately 3.4 V or higher, for example 4 0.0V to 4.5V) is preferable. For example, the potential of the positive electrode is set to be about 4.5V. In addition, iron is frequently used as a raw material for manufacturing equipment among various metal elements, so it is considered that iron is likely to be mixed into the cell. When such iron is targeted (that is, when the oxidation-reduction potential is higher than that of iron (for example, copper) is not considered), the potential of the positive electrode (the highest potential reached) is set to be equal to or higher than the oxidation potential of iron (about 2.5 V). For example, it is preferably set to 2.5 V to 3.5 V, for example.

  Further, as a preferred embodiment, the potential can be adjusted to be equal to or higher than the reduction potential of the metal foreign matter 80 that may mix the potential of the negative electrode 40 (maximum ultimate potential). By doing in this way, when the metal ion of the metal foreign material 80 melt | dissolved by the positive electrode side arrives at the negative electrode 40 side, it is prevented that it precipitates on the negative electrode 40 immediately. Then, such metal ions remain in the electrolyte and can diffuse around. Thereby, it is prevented that the metal foreign material 80 deposits locally on the opposing negative electrode surface, and the occurrence frequency of micro short-circuits can be suppressed. In other words, the occurrence of a short circuit due to the metal foreign object 80 can be suppressed, and the metal foreign object can be rendered harmless. For example, when iron is considered as the metal foreign matter 80, it is preferable to set the potential of the negative electrode (maximum potential reached) to be equal to or higher than 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 maintained in a region where the potential of the positive electrode 30 is higher than or equal to the oxidation potential of the metal foreign matter, or may be changed in a pulse shape so as to reach a region higher than the oxidation potential of the metal foreign matter 80 little by little. You may do it. From the viewpoint of dissolution of the metallic foreign matter 80, it is preferable to maintain a relatively high voltage range between terminals and / or a relatively high SOC range throughout the aging process. For example, in a battery that is fully charged at 4.2 V, it is preferable to perform charging and discharging within a range in which the voltage between the positive and negative electrodes is maintained at about 3.7 to 4.2 V.

  According to the detailed study by the present inventors, for example, the time required to dissolve a metal foreign substance having a predetermined size is affected by various factors. For example, in addition to the environmental temperature, the battery voltage (potential difference between positive and negative electrodes), the dissolution rate of the metal foreign matter, the difference in specifications and variations of the constituent materials of the secondary battery can be considered. As the difference in the specification of the constituent material of the secondary battery, for example, the influence of the type and shape of the active material, the surface form of the separator, the concentration of the additive added to the electrolyte, and the like can be considered. Specifically, it has been confirmed that the dissolution rate of the metallic foreign matter tends to decrease as the concentration of the additive added to the electrolyte becomes higher. In addition, regarding the variation in the constituent materials of the secondary battery, there are differences in the amount of moisture that cannot be managed by the electrode, the state of contamination of metal foreign matter (such as the degree of embedding in the positive electrode active material layer and the degree of wetting with the electrolyte), the electrode And / or the degree of impregnation of the electrolyte into the separator can be considered. Specifically, for example, when the storage period of the electrode in the dry room becomes longer or when the electrode is exposed to the air instantaneously, it has been confirmed that the dissolution rate of the metal foreign matter decreases. These are considered to be due to an increase in the amount of water in the electrode.

  Accordingly, it is possible to set a time during which the metallic foreign matter can be reliably dissolved in a shorter time, including the influence of the factors exemplified above and other influences. For example, a metal foreign substance (for example, iron) having a predetermined size is previously arranged on the surface of the positive electrode, and other conditions (for example, the mode of potential adjustment and the applied pressure, the peel strength between the positive electrode and the separator after bonding, etc.) The aging process is performed with various changes. At this time, by examining in advance the relationship between the amount of the metallic foreign material dissolved in a predetermined time and the changed conditions (for example, the charging pattern, the charging rate, the pressure to be applied, etc.), An appropriate and shortest charge maintenance time can be set.

[5. Self-discharge inspection process]
Although it is not an essential process, in a preferred embodiment, a self-discharge test is further performed after the aging process. The self-discharge inspection is an inspection for determining a defective product (battery in which an internal short circuit occurs) by measuring a voltage drop amount of the cell. The internal short circuit to be inspected here is a fine short circuit (micro short circuit) caused by the metal foreign matter remaining on the positive electrode side. Therefore, in order to accurately measure the presence or absence of such a short circuit, at least 5 is conventionally required. The inspection time of about 10 days was required in some cases. This is mainly based on the assumption that metal foreign matter (typically iron) with a slow dissolution rate and high resistance remains in the cell, and a period of 5 days or more is required to examine the influence of such foreign matter. This is because the inspection time was set based on this opinion.

  On the other hand, in the manufacturing method disclosed herein, the positive electrode and the separator are bonded by the completion of the aging process, so that the dissolution of the metal foreign matter is promoted by the completion of the aging process. For example, iron having a low dissolution rate can be suitably dissolved. In addition, the adhesion between the positive electrode and the separator is maintained even in such a self-discharge test. Therefore, in the self-discharge inspection, the occurrence of an internal short circuit due to the undissolved metal foreign object in the previous process is suppressed, and the dissolution of the undissolved metal foreign object is promoted. Therefore, the self-discharge inspection can be performed with a shorter inspection time than before. For example, the time required for the self-discharge inspection can be, for example, within 24 hours (typically within 15 hours, for example, within 10 hours, preferably about 2 to 5 hours). Therefore, the self-discharge inspection time can be significantly shortened, and productivity can be improved.

  In this self-discharge inspection step, the presence or absence of an internal short circuit is determined from the voltage drop amount measured for each cell 100 before and after the self-discharge period. Specifically, a reference value for non-defective product determination is set based on the measurement result of the voltage drop amount. Although the reference value setting method is not particularly limited, for example, an arithmetic average value, a median value (median), or the like of voltage drop amounts of a plurality of cells may be employed. Then, the difference between the reference value and the voltage drop amount of each cell is calculated, and when the difference is equal to or smaller than a predetermined threshold, the cell is determined as “no internal short circuit”, and the difference exceeds the predetermined threshold. The cell is determined as “with internal short circuit”. The threshold value may be set to a value corresponding to, for example, about 2σ to 4σ (σ is a statistical standard deviation), although depending on the standard of the target battery. By removing the battery assembly determined to be “with internal short circuit” based on the determination result, it is possible to prevent a defective product from flowing to a subsequent process and provide a highly reliable battery.

Further, such inspection can be performed in a state where the metal foreign matter is sufficiently dissolved. Therefore, the possibility that the battery in a state where undissolved metal foreign matter remains is subjected to inspection is suppressed. Thereby, the defective product rate of the battery that has passed the inspection is greatly reduced, and a high-quality battery can be supplied to the market.
In addition, it is also a preferable aspect that the self-discharge inspection is performed with pressure applied, as described in the aging process. Thereby, it becomes possible to further promote the dissolution of the metal foreign matter in the self-discharge inspection process. Further, when the interval between the positive and negative electrodes is close and the precipitate 82 on the negative electrode is growing, a minute short circuit due to the precipitate can be induced. As a result, defective products can be detected more reliably, and only good products can be supplied to the market.

  According to the technology disclosed herein, even when a metal foreign object is mixed, the metal foreign object is sufficiently dissolved before the self-discharge inspection to manufacture a secondary battery simply and efficiently (in a shorter time). can do. Therefore, for example, by performing a self-discharge test, it is possible to make a quality determination with high accuracy, and it is possible to provide a secondary battery with high quality and high reliability. The secondary battery (typically a lithium secondary battery) 100 manufactured by the manufacturing method disclosed herein can be suitably used for various applications. For example, the secondary battery 100 can be suitably used as a power source for a vehicle driving motor (electric motor) mounted on a vehicle. Although the kind of vehicle is not specifically limited, Typically, a plug-in hybrid vehicle (PHV), a hybrid vehicle (HV), an electric vehicle (EV) etc. are mentioned.

  EXAMPLES Hereinafter, although this invention is demonstrated concretely by a test example, it is not intending to limit this invention to what is shown to this test example.

<Construction of evaluation cell>
A square battery (secondary battery) for evaluation was constructed according to the following procedure.
First, a lithium transition metal oxide (NCM: LiNi _1/3 Mn _1/3 Co _1/3 O ₂ ) as a positive electrode active material, acetylene black (AB) as a conductive material, and polyvinylidene fluoride as a binder ( PVdF) is introduced into a kneader so that the mass ratio of these materials is NCM: AB: PVdF = 93: 4: 3, and N-methyl is added so that the solid content concentration (NV) is 50% by mass. A positive electrode paste was prepared by kneading while adjusting the viscosity with pyrrolidone (NMP). This paste was applied to an aluminum foil (thickness: 15 μm) as a positive electrode current collector, and pressed after drying to produce a positive electrode having a positive electrode active material layer on the positive electrode current collector.

  In addition, a disk-shaped iron material having a diameter of 50 μm, 100 μm, 200 μm, 250 μm and a thickness of 10 μm was prepared as the metal foreign matter. And these metal foreign materials were mounted on the active material layer of a positive electrode, and it used for construction | assembly of the cell.

  Next, natural graphite (C) as a negative electrode active material, styrene butadiene rubber (SBR) as a binder, and carboxymethyl cellulose (CMC) as a dispersant are used, and these materials are mixed at a mass ratio of C: SBR: CMC. = 98: 1: 1 was charged into a kneader and mixed with ion-exchanged water so that the solid content concentration (NV) was 45% by mass to prepare a negative electrode paste. This paste was applied to a copper foil (thickness: 10 μm) as a negative electrode current collector, and was pressed after drying to produce a negative electrode having a negative electrode active material layer on the negative electrode current collector.

The positive electrode and the negative electrode prepared above were arranged facing each other via a separator (here, a three-layer structure in which a PP layer was laminated on both sides of a PE layer) to prepare an electrode body. And the positive electrode terminal was joined to the edge part of the positive electrode collector of the said electrode body, and the negative electrode terminal was joined to the edge part of the negative electrode collector, respectively. Such an electrode body is accommodated in a rectangular battery case, and an electrolyte (here, ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) are added in a volume of EC: DMC: EMC = 3: 4: 3). An electrolyte in which LiPF ₆ as an electrolyte was dissolved at a concentration of 1 mol / L was used in a mixed solvent contained in a ratio. In the battery, lithium (here, a nickel lead with a lithium foil bonded to the tip thereof) was used as a reference electrode. A square secondary battery (cell) was constructed by heat-sealing the opening of the battery case.

After performing a predetermined initial charging process on the cell constructed as described above, it is placed on a restraining jig 90 using a coil spring as shown in FIG. While applying a pressure of 10 ^{−3 to} 1.0 × 10 ⁻³ MPa, aging treatment was performed with aging times of 10 hours, 20 hours, and 30 hours. In addition, the potential adjustment in the aging process was performed by performing CC charging with a constant current of 1 C until the battery voltage reached 4 V, and then performing CV charging with the voltage remaining at 4 V until the above high temperature aging was completed.

[Peel strength]
After the aging treatment, the load on the cell is released, the prismatic battery after being left at room temperature for 100 hours is disassembled, and the peel strength between the positive electrode and the separator is 90 ° peel test specified in JIS K6854-1: 1999 Measured according to Specifically, the bonded portion of the positive electrode and the separator was punched out to a width of 10 mm along the length direction from the disassembled electrode body to obtain a strip-shaped test piece. And about the obtained test piece, a part of the separator was peeled off from the positive electrode, the positive electrode side of the test piece was fixed to the test bench, and the peeled part of the separator was pulled in the direction of 90 degrees above the positive electrode. The separator was peeled from the positive electrode active material layer, and the tensile force (N) at that time was measured by an autograph. And the peeling strength (N / m) was computed from the tensile force (N) at the time of peeling. Here, the peel test was performed on three samples for each cell, and the peel strength when peeled with the weakest force was adopted.

[Solubility of foreign metal]
After the aging treatment, the load on the cell is released, the prismatic battery after being left at room temperature for 100 hours is disassembled, the positive electrode and the separator are further peeled off, and the dissolution state of the pre-mixed metal foreign matter is observed with an optical microscope. Was observed. In these observation results, the case where the residual metal foreign matter placed on the positive electrode was confirmed by an optical microscope was “x”, and the case where the residual metal could not be confirmed was “◯”.

  The result of said peeling test and the result of the solubility of a metal foreign material were shown in FIG. As shown in FIG. 5, in the cells subjected to the aging treatment in a state where the positive electrode and the separator are sufficiently adhered, the metal foreign matter was suitably dissolved regardless of the size (φ100 to 250 μm). It could be confirmed. On the other hand, it was confirmed that the cells subjected to the aging treatment in a state where the positive electrode and the separator were not sufficiently adhered remained without being dissolved even when the metal foreign matter was small (φ50 μm). . A cell in which the positive electrode and the separator are not sufficiently bonded has a peel strength of about 0.2 N / m, has few contact points between the positive electrode and the separator, and is peeled by a very light stress (almost bonded). Was not). Therefore, it was shown that, by appropriately adhering the positive electrode and the separator, for example, the dissolution of metal foreign matters can be promoted in the aging treatment. Iron has a relatively high resistance among metal foreign objects, but according to the manufacturing method disclosed herein, even a relatively coarse metal object having a diameter of 200 μm and a thickness of 10 μm is shorter than the conventional one of about 10 hours. It was found that it can be suitably dissolved in time.

  As mentioned above, although the specific example of this invention was demonstrated in detail, these are only illustrations and do not limit a claim. The technology described in the claims includes various modifications and changes of the specific examples illustrated above.

DESCRIPTION OF SYMBOLS 10 Battery case 12 Case main body 14 Sealing body 20 Electrode body 30 Positive electrode 32 Positive electrode current collector 34 Positive electrode active material layer 40 Negative electrode 42 Negative electrode current collector 44 Negative electrode active material layer 50 Separator 60 Positive electrode terminal 70 Negative electrode terminal 80 Metal foreign object 90 Restraint treatment Tool 92 Restraint plate 94 Handle 100 Secondary battery (cell)

Claims (11)

Constructing an electrode body having a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode;
Constructing a cell comprising the electrode body and an electrolyte;
Applying an initial charging process to the cell; and
Aging the cell after the initial charging,
Including
A method for producing a secondary battery, comprising a step of bonding the positive electrode and the separator before the aging treatment is completed. The process of bonding the positive electrode and the separator is performed in the aging process,
The aging process is
2. The manufacturing method according to claim 1, further comprising a high-temperature aging treatment in which a predetermined pressure is applied to the cell after the initial charging and the voltage is applied at a temperature of 60 ° C. or higher and held for 100 hours or more. The process of bonding the positive electrode and the separator is performed in the construction of the electrode body,
The positive electrode includes a positive electrode current collector and a positive electrode active material layer provided on the positive electrode current collector,
The positive electrode active material layer includes a positive electrode active material and a binder made of a thermoplastic resin,
The positive electrode and the separator are bonded together by compacting the positive electrode and the separator at a temperature equal to or higher than the softening temperature of the binder while the positive electrode active material layer of the positive electrode is in contact with the separator. The manufacturing method according to claim 1. The process of bonding the positive electrode and the separator is as follows:
The manufacturing method of any one of Claims 1-3 performed so that the peeling strength of the said positive electrode and the said separator may be 0.2 N / m or more and 1.2 N / m or less. The aging process is
The manufacturing method of any one of Claims 1-4 including applying the pressure of 0.1 Mpa or more to the cell after the said initial charge. The aging process is
Applying a voltage to the cell after the initial charge and holding for a predetermined time; and
The manufacturing method of any one of Claims 1-5 including adjusting an electric potential so that the highest attained potential of the said positive electrode may become more than the oxidation potential of the metal foreign material with which mixing with the said electrode body is anticipated. The aging process includes
The manufacturing method of Claim 6 including adjusting an electric potential so that the highest ultimate potential of the said negative electrode may become more than the reduction potential of the said metal foreign material. After the aging process,
The manufacturing method of any one of Claims 1-7 including the self-discharge test | inspection which measures the voltage drop amount of the said cell.   The said electrode body is a manufacturing method of any one of Claims 1-8 which has a laminated structure by which opposing of the positive electrode and negative electrode through a separator is repeated.   The secondary battery manufactured by the manufacturing method of any one of Claims 1-9. An electrode body having a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode is a secondary battery accommodated in a cell case together with an electrolyte,
The positive electrode and the separator are at least partially bonded,
A secondary battery in which the negative electrode and the separator are not bonded.

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