JP2013118104A - Method for manufacturing negative electrode for nonaqueous electrolyte secondary battery, and method for manufacturing nonaqueous electrolyte secondary battery including the negative electrode - Google Patents

Abstract

The present invention provides a method for producing a negative electrode for a non-aqueous electrolyte secondary battery in which a decrease in capacity is suppressed.
A method for producing a negative electrode for a non-aqueous electrolyte secondary battery provided by the present invention comprises a negative electrode active material capable of inserting / extracting charge carriers as a main component, and can be dissolved or dispersed in water. A composition for forming a negative electrode active material layer containing a polymer and an aqueous solvent is applied onto a negative electrode current collector, and after the application, the composition is dried under conditions with a dew point temperature of less than 10 ° C. Forming a negative electrode active material layer and exposing the formed negative electrode active material layer to an environment having a dew point temperature of 17 ° C. to 52 ° C. for at least 30 minutes.
[Selection] Figure 3

Description

  The present invention relates to a method for producing a negative electrode for a non-aqueous electrolyte secondary battery, and more specifically, to form a negative electrode active material layer comprising a negative electrode active material as a main component and a polymer that can be dissolved or dispersed in water and an aqueous solvent. The present invention relates to a method for producing a negative electrode for a non-aqueous electrolyte secondary battery comprising a negative electrode active material layer made of a composition for a battery.

  In recent years, secondary batteries such as lithium ion secondary batteries and nickel metal hydride batteries have become increasingly important as power sources mounted on vehicles using electricity as power sources, or power sources mounted on personal computers, portable terminals, and other electrical products. Yes. In particular, a non-aqueous electrolyte secondary battery such as a lithium ion secondary battery that is lightweight and has a high energy density is expected to be preferably used as a high-output power source for mounting on a vehicle. The electrodes (positive electrode and negative electrode) of such a non-aqueous electrolyte type secondary battery typically have an electrode activity capable of reversibly occluding and releasing chemical species (typically lithium ions) serving as charge carriers. An electrode active material layer (a positive electrode active material layer and a negative electrode active material layer) containing a substance as a main component is provided on an electrode current collector (a negative electrode current collector and a positive electrode current collector). Such a negative electrode active material layer is prepared by adding a suitable solvent together with a binder, a thickener, etc. (for example, carboxymethyl cellulose (CMC)) to disperse the negative electrode active material, and a paste or slurry composition obtained thereby. It is formed by applying to a negative electrode current collector and drying. Patent Documents 1 to 3 are known as conventional techniques for forming a negative electrode by applying such a paste or slurry-like composition to a negative electrode current collector and drying it.

JP 2002-324548 A JP 2009-37893 A JP 2002-270161 A

  By the way, the conventional non-aqueous electrolyte type secondary battery (typically, a lithium ion secondary battery) as described above has a negative electrode active material (such as paste or slurry) in order to prevent a decrease in capacity over time. Although the technique of adjusting the compounding material and the compounding ratio of the composition for layer formation is used, the present condition is not fully examined about suppressing the fall of a capacity | capacitance by the other method.

  Therefore, the present invention was created in view of the conventional situation as described above, and the purpose thereof is a non-aqueous electrolyte type secondary battery in which a decrease in capacity is suppressed by a method other than the use of an additive. It is providing the manufacturing method of the negative electrode for batteries. Another object of the present invention is to provide a method for producing a non-aqueous electrolyte secondary battery having such performance.

  In order to achieve the above object, according to the present invention, a negative electrode active material layer forming composition comprising, as a main component, a negative electrode active material in which charge carriers can be inserted / removed, and a polymer that can be dissolved or dispersed in water and an aqueous solvent. Is applied on the negative electrode current collector, and after the application, the negative electrode active material layer is formed on the negative electrode current collector by drying under a dew point temperature of less than 10 ° C., and the formed negative electrode There is provided a method for producing a negative electrode for a non-aqueous electrolyte secondary battery, comprising exposing the active material layer to an environment having a dew point temperature of 17 ° C to 52 ° C for at least 30 minutes.

According to the method for producing a negative electrode for a non-aqueous electrolyte secondary battery having such a configuration, the negative electrode active material layer formed on the negative electrode current collector is exposed to an environment having a dew point temperature of 17 ° C. to 52 ° C. for a predetermined time. A decrease in capacity of a non-aqueous electrolyte secondary battery including a negative electrode on which the negative electrode active material layer is formed is suppressed. In particular, the capacity of lithium ion secondary batteries tends to decrease when stored at a high temperature of, for example, 50 ° C. or higher. However, according to the method of manufacturing a negative electrode for a non-aqueous electrolyte secondary battery having such a configuration, A decrease in capacity after storage can be suppressed.
Therefore, according to the production method of the present invention, it is possible to provide a negative electrode for a lithium ion secondary battery or other nonaqueous electrolyte type secondary battery in which a decrease in capacity is suppressed.
In this specification, “dew point temperature” means that when air containing water vapor is cooled, the relative humidity reaches 100% and saturation is reached, and a part of the water vapor is condensed to start dew condensation. Refers to temperature.
In the present specification, “drying of the negative electrode active material layer (formation composition)” is not particularly limited in terms of the method and conditions. For example, the moisture of the negative electrode active material layer (formation composition) after drying This means that the content is 500 ppm or less on a mass basis. Accordingly, the drying temperature, the drying time, and the dew point temperature are not particularly limited, and it may include drying at a room temperature of, for example, a temperature of about 20 ° C. to 35 ° C. for a predetermined time so as to achieve the above moisture content.

  In a preferred embodiment of the method for producing a negative electrode for a non-aqueous electrolyte secondary battery disclosed herein, the formed negative electrode active material layer is subjected to press treatment and then exposed to the environment. As described above, after the press treatment is performed, the negative electrode active material layer is exposed to a predetermined dew point temperature environment, whereby a decrease in capacity is more significantly suppressed. The reason is presumed as follows. It is considered that the polymer that can be dissolved or dispersed in water contained in the negative electrode active material layer may be deformed (typically cracked) by the press treatment. By supplying a predetermined amount of moisture to the deformed polymer after the press treatment, the form of the polymer in the negative electrode active material layer is regenerated or further changed (for example, changed due to softening). It is presumed that this acts to suppress a decrease in capacity of the electrolyte type secondary battery.

  In a preferred embodiment of the method for producing a negative electrode for a non-aqueous electrolyte secondary battery disclosed herein, the polymer that can be dissolved or dispersed in water is a cellulose derivative (typically carboxymethyl cellulose (CMC)). is there. By using a cellulose derivative as a polymer that can be dissolved or dispersed in water, a decrease in capacity of the non-aqueous electrolyte secondary battery can be suitably suppressed.

  In addition, according to the present invention, a positive electrode having a positive electrode active material layer formed mainly of a positive electrode active material capable of inserting / desorbing charge carriers on a positive electrode current collector is constructed; Construction of a negative electrode comprising a negative electrode active material layer formed on the negative electrode current collector, the main component of which is a detachable negative electrode active material, and a nonaqueous electrolyte secondary battery using the positive electrode and the negative electrode Wherein a negative electrode obtained by any one of the manufacturing methods disclosed herein is used as the negative electrode, wherein the non-aqueous electrolyte type secondary battery is manufactured Is provided. Thus, the non-aqueous electrolyte secondary battery including the negative electrode on which the negative electrode active material layer is formed by exposing the negative electrode active material layer formed on the negative electrode current collector to a predetermined dew point temperature environment, A decrease in capacity is suppressed.

It is sectional drawing which shows typically the negative electrode for lithium ion secondary batteries which concerns on one Embodiment. It is sectional drawing which shows typically the structure of the lithium ion secondary battery which concerns on one Embodiment. It is a graph which shows the relationship between dew point temperature and a capacity | capacitance maintenance factor. It is a graph which shows the relationship between exposure time and a capacity | capacitance maintenance factor.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings. Note that the dimensional relationship (length, width, thickness, etc.) in each drawing does not reflect the actual dimensional relationship. Further, matters other than matters specifically mentioned in the present specification and matters necessary for the implementation of the present invention (for example, a configuration and a manufacturing method of an electrode body including a positive electrode and a negative electrode, a configuration and a manufacturing method of a separator and an electrolytic solution) , General techniques related to the construction of batteries and other batteries) can be grasped as design matters of those skilled in the art based on the prior art in this field.

  As a preferred embodiment related to a method for producing a negative electrode for a non-aqueous electrolyte type secondary battery disclosed herein, a lithium ion secondary battery will be described as an example, but the application target of the present invention is applied to such a battery. It is not intended to be limiting. For example, the present invention can also be applied to a component of a non-aqueous electrolyte secondary battery using a metal ion other than lithium ion (for example, sodium ion) as a charge carrier, that is, a negative electrode built in the secondary battery. is there.

  As shown in FIG. 1, the negative electrode 10 for a lithium ion secondary battery can have the same configuration as the conventional one. For example, the negative electrode active material layer 2 is formed on the negative electrode current collector 1. Have. In FIG. 1, the negative electrode active material layer 2 is formed on one surface of the negative electrode current collector 1, but the negative electrode active material layer 2 may be formed on both surfaces of the negative electrode current collector 1. Hereinafter, each component of the negative electrode 10 for a lithium ion secondary battery will be described.

  As the negative electrode current collector constituting the negative electrode, a metal having good conductivity (for example, a metal such as aluminum, nickel, copper, stainless steel, or an alloy containing the metal as a main component, as in the case of a conventional lithium ion secondary battery. ) Can be preferably used. The shape of the negative electrode current collector to be used is not particularly limited because it may vary depending on the shape of the lithium ion secondary battery constructed using the obtained negative electrode, and is in the form of a rod, plate, sheet, foil, It can be in various forms such as a mesh. The technique disclosed here can be preferably applied to the production of a negative electrode using, for example, a sheet-like or foil-like negative electrode current collector. The thickness of the negative electrode current collector is not particularly limited, but when a copper sheet is used as the negative electrode current collector, the thickness is preferably set within a range of about 6 μm to 30 μm, for example.

  The negative electrode active material layer constituting the negative electrode is obtained by dispersing the negative electrode active material in an aqueous solvent together with a polymer that can be dissolved or dispersed in water and an aqueous solvent to obtain a paste or slurry-like composition for forming a negative electrode active material layer. It can form by apply | coating this composition for negative electrode active material layer forming to the surface of a negative electrode collector.

As the negative electrode active material contained in the composition for forming a negative electrode active material layer, a negative electrode active material used in a conventional lithium ion secondary battery can be used, and is not particularly limited. Examples thereof include carbon materials used for secondary batteries. Typical examples of the carbon material used as the negative electrode active material include graphite carbon and amorphous carbon. Among these, a particulate carbon material (carbon particles) including a graphite structure (layered structure) at least partially is preferably used. Also, any carbon material of a so-called graphitic material (graphite), a non-graphitizable carbonaceous material (hard carbon), a graphitizable carbonaceous material (soft carbon), or a combination of these is suitable. Can be used. Among these, it is preferable to use a carbon material mainly composed of natural graphite (or artificial graphite). Such natural graphite (or artificial graphite) may be obtained by spheroidizing graphite. For example, the median diameter derivable from the particle size distribution measured on the basis of the particle size distribution measuring apparatus based on a laser scattering-diffraction method (D _50: 50% volume average particle diameter) and a mean particle size D ₅₀ in the range of approximately 5μm~30μm Spheroidized natural graphite (or spheroidized artificial graphite) can be preferably used as the negative electrode active material. Further, a carbonaceous powder in which the surface of the graphite is coated with amorphous carbon may be used. In addition, as a negative electrode active material, it is also possible to use a single material such as a silicon material or a tin material, an alloy, a compound, or a composite material using the above materials in combination.

  The proportion of the negative electrode active material in the total solid content of the composition for forming a negative electrode active material layer exceeds about 50% by mass, and is about 90% to 99.5% by mass (for example, 95% to 99% by mass, typical). Is preferably 97% by mass to 99% by mass).

  The purpose of addition of the polymer that can be dissolved or dispersed in water contained in the composition for forming a negative electrode active material layer is not particularly limited. For example, the polymer can be used as a binder or a thickener. Examples of such water-soluble or dispersible polymers include cellulose derivatives (cellulose-based polymers) such as carboxymethyl cellulose (CMC), methyl cellulose (MC), cellulose acetate phthalate (CAP), and hydroxypropylmethyl cellulose (HPMC), Polyvinyl alcohol (PVA) etc. are mentioned, These can be used individually by 1 type or in combination of 2 or more types. Taking into consideration the ease of absorption of moisture supplied in exposure to a predetermined dew point temperature environment, which will be described later, and workability and stability during kneading (preparation) of the negative electrode active material layer forming composition, cellulose derivatives (Typically CMC) is preferably used.

  The amount (content) of the polymer that can be dissolved or dispersed in water is not particularly limited as long as it is appropriately selected depending on the purpose of use, the type and amount of the negative electrode active material, and the composition for forming a negative electrode active material layer. When the total solid content is 100% by mass, it is within the range of 0.5% to 10% by mass (for example, 1% to 5% by mass, typically 1% to 3% by mass). Is preferred. When the amount of the polymer that can be dissolved or dispersed in water is within the above range, it is possible to suitably suppress the decrease in the capacity of the lithium ion secondary battery, and to act as a binder or thickener. Can be suitably exhibited.

  The negative electrode active material layer forming composition may further contain other additives as appropriate. Examples of other additives include rubbers such as styrene butadiene rubber (SBR) and gum arabic. Here, SBR is a copolymer containing styrene and 1,3-butadiene, and the copolymerization mode is not particularly limited. The SBR may be a modified SBR such as an acrylic acid-modified SBR resin obtained by further copolymerizing an unsaturated carboxylic acid or an unsaturated nitrile compound. In addition, polymer materials such as polyacrylate (acrylic acid ester homopolymer or copolymer), polyurethane, polyethylene oxide (PEO), polypropylene oxide (PPO), polyethylene oxide-propylene oxide copolymer (PEO-PPO), polyethylene, etc. Can be used. Such other additives may be used alone or in combination of two or more.

  When the other additive is contained, the addition amount (content) is not particularly limited, but when the total solid content of the negative electrode active material layer forming composition is 100% by mass, 0.25% by mass to It is preferable to be within a range of 5% by mass (for example, 0.5% to 2.5% by mass, typically 0.5% to 1.5% by mass). In that case, the addition amount (content) of the polymer that can be dissolved or dispersed in the water is 0.25% by mass to 5% by mass (for example, 0.5% by mass to 2.5% by mass, typically 0.005% by mass). 5 mass% to 1.5 mass%) is preferable. When the addition amount of the other additive is within the above range, the capacity reduction of the lithium ion secondary battery can be suitably suppressed, and the desired addition effect of the other additive can be suitably exhibited. can do.

  The aqueous solvent contained in the negative electrode active material layer forming composition is a concept indicating water or a mixed solvent mainly composed of water. As the solvent other than water constituting the mixed solvent, one or more organic solvents (lower alcohol, lower ketone, etc.) that can be uniformly mixed with water can be appropriately selected and used. For example, it is preferable to use an aqueous solvent in which approximately 80% by mass or more (eg, 90% by mass or more, typically 95% by mass or more) of the aqueous solvent is water. A particularly preferred example is an aqueous solvent substantially consisting of water.

  The solid content concentration (nonvolatile content, that is, the ratio of the active material layer forming material) of the negative electrode active material layer forming composition is not particularly limited, but is approximately 40% by mass or more (for example, approximately 45% by mass to 80% by mass, typically 50 mass% to 60 mass%) is preferable. When the solid content concentration is within the above range, the drying efficiency of the negative electrode active material layer can be suitably improved, the negative electrode active material layer can be easily applied to a uniform thickness, and for forming the negative electrode active material layer The composition tends to be easy to handle.

  Next, the manufacturing method of the negative electrode of a lithium ion secondary battery is demonstrated. In such a production method, first, the above-described negative electrode active material, a polymer that can be dissolved or dispersed in water, and, if necessary, other additives are mixed (kneaded) in an aqueous solvent to form a paste (also referred to as a slurry). A negative electrode active material layer forming composition is prepared. Such a kneading operation can be performed using, for example, an appropriate kneader (planetary mixer, homodisper, clear mix, fill mix, etc.). In preparing the negative electrode active material layer forming composition, the negative electrode active material, a polymer that can be dissolved or dispersed in water, and other additives are solidified with a small amount of an aqueous solvent (for example, water), and then obtained. The kneaded product may be diluted with an appropriate amount of solvent.

  Next, in order to form a negative electrode active material layer on the negative electrode current collector, the obtained composition for forming a negative electrode active material layer is applied onto the negative electrode current collector. As a method of applying the negative electrode active material layer forming composition, a technique similar to a conventionally known method can be appropriately employed. For example, the composition for forming a negative electrode active material layer can be applied to the surface of the negative electrode current collector by using an appropriate application device such as a gravure coater, comma coater, slit coater, or die coater.

  The environment in which the application is performed is not particularly limited, but the application is preferably performed in an environment having a dew point temperature of less than 21 ° C. (for example, a dew point temperature of 14 ° C. or less, typically a dew point temperature of 0 ° C. or less). Thereby, it is possible to suitably suppress the generation of impurities (for example, hydrogen fluoride (HF)) due to the reaction between the residual moisture in the negative electrode active material layer and the supporting salt in the electrolytic solution. A decrease in capacity can be suitably prevented. Moreover, the temperature at the time of performing this coating is not specifically limited, Usually, it can apply at the temperature of 20 to 35 degreeC.

The coating amount per unit area of the composition for forming a negative electrode active material layer to be applied, that is, the basis weight is not particularly limited as long as a sufficient conductive path (conductive path) can be secured, Preferably, it is 5 mg / cm ² or more and 35 mg / cm ² or less (more preferably 7 mg / cm ² or more and 25 mg / cm ² or less) on both sides.

  After applying the composition for forming a negative electrode active material layer, the applied material is dried (at this time, an appropriate drying accelerating means (a heater or the like may be used if necessary)). It is preferred to remove the solvent in the forming composition. The drying method and conditions are not particularly limited as long as the moisture content of the dried negative electrode active material layer (forming composition) is appropriately set within a range of 500 ppm or less on a mass basis. As a drying method, for example, it is preferable to pass the negative electrode current collector coated with the negative electrode active material layer forming composition through a drying furnace. Moreover, as drying conditions, it is preferable to perform the said drying in the environment of dew point temperature of less than 21 degreeC (for example, dew point temperature of 14 degrees C or less, typically dew point temperature of 0 degrees C or less), for example. The drying temperature is preferably higher than 70 ° C. and not higher than 200 ° C. (typically 120 ° C. to 150 ° C.), and the drying time is, for example, about 10 seconds to 120 seconds (typically about 20 seconds to 60 seconds). Seconds).

  A negative electrode having a target thickness can be obtained by subjecting the negative electrode active material layer thus formed to press treatment in the thickness direction as desired. As the press treatment method, a conventionally known roll press method, flat plate press method, or the like can be appropriately employed. The thickness of the negative electrode (negative electrode sheet) after the press treatment (typically, the total thickness of the negative electrode current collector and the negative electrode active material layer formed on both surfaces thereof) is not particularly limited, but is, for example, about 30 μm to 300 μm (typically Specifically, it is preferably 50 μm to 100 μm. When the negative electrode active material layer is formed on one surface of the negative electrode current collector, the thickness may be about half of the above thickness. Such press treatment is also preferably performed in an environment of, for example, a temperature of 20 ° C. to 35 ° C. and a dew point temperature of less than 21 ° C. (for example, a dew point temperature of 14 ° C. or lower, typically a dew point temperature of 0 ° C. or lower). In addition, you may perform a press process before the said drying.

  Next, for example, the negative electrode active material layer formed as described above is exposed to an environment having a dew point temperature of 10 ° C. to 52 ° C., preferably a dew point temperature of 17 ° C. to 52 ° C. By exposing the negative electrode active material layer to such an environment (hereinafter also referred to as exposure to a predetermined dew point temperature environment), the water in the environment becomes a material constituting the negative electrode active material layer (typically water such as CMC). The polymer is soluble or dispersible in the polymer), and the decrease in capacity is suppressed. Although the mechanism of action is not clear, for example, the shape of a polymer that can be dissolved or dispersed in water in the negative electrode active material layer changes (for example, softens), and this change forms a SEI (Solid Electrolyte Interface solid electrolyte interface). It is inferred that it creates physical or chemical conditions that are difficult to do. For such reasons, the dew point temperature is more preferably 15 ° C. or higher (eg, 25 ° C. or higher, typically 35 ° C. or higher). Moreover, since there exists a tendency for the said effect | action not to be acquired when dew point temperature is too high, the upper limit of dew point temperature is 52 degreeC.

  Further, the temperature in the exposure to the predetermined dew point temperature environment is not particularly limited, but the temperature is 25 ° C. or higher (eg, 35 ° C. or higher, typically 45 ° C. or higher), 85 ° C. or lower (eg, 75 ° C. or lower, typically Is preferably performed at a temperature of 70 ° C. or less from the viewpoint of suitably suppressing a decrease in the capacity of the lithium ion secondary battery. When the temperature is less than 25 ° C., for example, 20 ° C., the relative humidity when the dew point temperature is 19 ° C. is 95%, which may cause condensation, and when the temperature exceeds 85 ° C., the peel strength of the electrode plate may be weakened. is there.

  The exposure time to the predetermined dew point temperature environment is not particularly limited, but in the case of a sheet-like negative electrode in a reel shape, it is more preferable to expose at least 30 minutes. The exposure is preferably performed for 1 hour or longer (for example, 2 hours or longer, typically 3 hours or longer). By exposing to a predetermined dew point temperature environment for 30 minutes or more, the decrease in capacity is sufficiently suppressed. Moreover, although there is no restriction | limiting in particular about the upper limit of the said exposure time, It is preferable to set it as 24 hours or less (for example, 8 hours or less, typically 5 hours or less).

  The moisture content of the negative electrode active material layer after the exposure is not particularly limited, but is 900 ppm or more (for example, 1000 ppm or more) on a mass basis, and is 2000 ppm or less (for example, 1800 ppm or less, typically 1600 ppm or less). It is preferable to become. By exposing to the predetermined dew point temperature environment so that the water content of the negative electrode active material layer is within the above range, this water is a material constituting the negative electrode active material layer (typically dissolved or dispersed in water) Possible polymer), and a decrease in capacity is suitably suppressed.

  In addition, the exposure to the predetermined dew point temperature environment may be performed before the press process, or can be performed concurrently with the press process (for example, the press process is performed during the exposure). As described above, it is more preferable to carry out after the press treatment. The reason is that some of the polymers that can be dissolved or dispersed in water in the negative electrode active material layer are deformed (typically cracked) by the press treatment. On the other hand, by supplying a predetermined amount of water, the form of the polymer in the negative electrode active material layer is regenerated or further changed (for example, softened), which suppresses the decrease in the capacity of the lithium ion secondary battery. It is mentioned that it is acting.

  After exposure to the predetermined dew point temperature environment, the negative electrode active material layer may be dried as necessary. The drying method and conditions are not particularly limited as long as the moisture content of the negative electrode active material layer (formation composition) after drying is appropriately set within a range of 500 ppm or less on a mass basis. The same method and conditions as the drying after the application of the composition for application can be preferably employed. Thus, the negative electrode of a lithium ion secondary battery is obtained.

  Next, a lithium ion secondary battery according to an embodiment constructed using the negative electrode (negative electrode sheet) manufactured by the above method will be described. As shown in FIG. 2, the lithium ion secondary battery 100 includes a case 21 made of metal (a resin or a laminate film is also suitable). The case (outer container) 21 includes a flat rectangular parallelepiped case main body 22 having an open upper end, and a lid 23 that closes the opening. The upper surface of the case 21 (that is, the lid body 23) is provided with a positive electrode terminal 25 that is electrically connected to the positive electrode of the wound electrode body 80 and a negative electrode terminal 27 that is electrically connected to the negative electrode of the wound electrode body 80. Yes. Further, a flat wound electrode body 80 is accommodated in the case 21. The wound electrode body 80 is formed by, for example, laminating a long sheet-like positive electrode (positive electrode sheet) 50 and a long sheet-like negative electrode (negative electrode sheet) 10 together with a total of two long sheet-like separators (separator sheets) 60. Then, the wound body is produced by crushing and ablating the obtained wound body from the side surface direction.

  Each of the positive electrode sheet 50 and the negative electrode sheet 10 has a configuration in which an electrode active material layer mainly composed of an electrode active material is formed on both surfaces of a long sheet-shaped electrode current collector. Moreover, the positive electrode active material layer non-formation part 51 in which the positive electrode active material layer is not formed on any surface is provided at one end of the positive electrode sheet 50 in the width direction. The negative electrode active material layer non-formation part 11 in which the said negative electrode active material layer is not formed in any surface is provided. The positive electrode active material layer non-formation part 51 of the positive electrode sheet 50 and the negative electrode active material layer non-formation part 11 of the negative electrode sheet 10 are protruded from both sides in the width direction of the separator sheet 60 during the lamination. By overlapping the sheet 50 and the negative electrode sheet 10 with a slight shift in the width direction, the electrode active material layer non-forming portions 51 and 11 of the positive and negative electrode sheets 50 and 10 in the lateral direction with respect to the winding direction of the wound electrode body 80. Are removed from the wound core portion 82 (that is, the portion where the positive electrode active material layer forming portion of the positive electrode sheet 50, the negative electrode active material layer forming portion of the negative electrode sheet 10 and the two separator sheets 60 are closely wound) 82 A configuration that protrudes is obtained. The positive electrode side protruding portion (positive electrode active material layer non-forming portion) 51 and the negative electrode side protruding portion (negative electrode active material layer non-forming portion) 11 are respectively provided with a positive electrode lead terminal 26 and a negative electrode lead terminal 28. The positive electrode terminal 25 and the negative electrode terminal 27 are electrically connected to each other.

  Each component constituting the wound electrode body 80 may be the same as each component of the electrode body of the conventional lithium ion secondary battery, and is not particularly limited. For example, the positive electrode sheet 50 can be formed by applying (typically applying and drying) a positive electrode active material layer containing a positive electrode active material as a main component on a long positive electrode current collector. As the positive electrode current collector, an aluminum foil or other metal foil suitable for the positive electrode is preferably used. As the positive electrode active material which is the main component of the positive electrode active material layer, one or more of materials conventionally used in lithium ion secondary batteries can be used without particular limitation. Preferred examples include lithium and one or more transition metals such as layered or spinel lithium nickel-based composite oxide, lithium cobalt-based composite oxide, lithium manganese-based composite oxide, and olivine-type lithium phosphate. Examples thereof include lithium transition metal composite oxides containing an element as a constituent metal element. In addition to the positive electrode active material, the positive electrode active material layer can further contain additives such as a conductive material and a binder. Examples of the conductive material include carbon materials such as carbon powder and carbon fiber, and examples of the binder include water-soluble substances such as cellulose derivatives (typically carboxymethyl cellulose (CMC)) when an aqueous solvent is used. Or a water dispersible polymer is mentioned, When using a non-aqueous solvent, a polyvinylidene fluoride (PVDF) etc. are mentioned. A protective film may be provided on the surface of either the positive electrode sheet 50 or the negative electrode sheet 10 for the purpose of preventing the electrode active material layer from falling off or improving the heat resistance. The content of the positive electrode active material in the positive electrode active material layer exceeds about 50% by mass (typically within a range of about 70% to 95% by mass) when the total solid content is 100% by mass. preferable.

  Preferable examples of the separator (separator sheet) used between the positive and negative electrode sheets include those made of a porous polyolefin resin. For example, a porous separator sheet made of synthetic resin (for example, made of polyethylene, polypropylene, or a combination of these) having a thickness of about 5 μm to 30 μm can be suitably used. This separator sheet may be provided with a heat-resistant layer or the like. When a gel electrolyte is used instead of the electrolytic solution, a separator may not be necessary (that is, in this case, the electrolyte itself can function as a separator).

  With reference to FIG. 2, the lithium ion secondary battery 100 having the above-described structure is manufactured, for example, by the following method. First, a positive electrode (positive electrode sheet) 50 provided with a positive electrode active material layer formed mainly of a positive electrode active material on a positive electrode current collector is constructed by the above-described method, and a negative electrode is manufactured by the above-described method. Thus, the negative electrode (negative electrode sheet) 10 is constructed. Thereafter, as described above, the wound electrode body 80 is constructed by laminating the positive electrode sheet 50, the negative electrode sheet 10, and the separator sheet 60, and the wound electrode body 80 is connected to the case body from the upper end opening portion of the case body 22. An electrolytic solution that is accommodated in 22 and contains an appropriate supporting salt is placed (injected) into the case body 22.

As the electrolytic solution, the same non-aqueous electrolytic solution conventionally used for lithium ion secondary batteries can be used without any particular limitation. Such an electrolytic solution typically has a composition in which a supporting salt is contained in a suitable nonaqueous solvent. Examples of the non-aqueous solvent include propylene carbonate (PC), ethylene carbonate (EC), dimethyl carbonate (DMC), diethyl carbonate (DEC), N, N-dimethylformamide (DMF), ethyl methyl carbonate (EMC), and the like. 1 type (s) or 2 or more types can be used. Examples of the supporting salt include LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , LiCF ₃ SO ₃ , LiC ₄ F ₉ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiC (CF ₃ SO ₂ ). ₃ , 1 type or 2 types or more of lithium compounds (lithium salt), such as LiI, can be used. The concentration of the supporting salt is not particularly limited and may be the same as that of the non-aqueous electrolyte used in the conventional lithium ion secondary battery. The contained electrolytic solution can be preferably used.

  After injecting the electrolyte, the lithium ion secondary battery 100 according to an embodiment is constructed by sealing the opening by welding or the like with the lid body 23. The sealing process of the case 21 and the placement (injection) process of the electrolytic solution may be the same as the method used in the manufacture of the conventional lithium ion secondary battery, and do not characterize the present invention.

  As described above, the lithium ion secondary battery constructed in this way is excellent in capacity maintenance (particularly capacity maintenance rate after high-temperature storage), and therefore, a power source for a motor (electric motor) mounted on a vehicle such as an automobile. Can be suitably used. Accordingly, the present invention provides a vehicle (typically an automobile, particularly a hybrid automobile, an electric automobile, a fuel cell automobile, etc.) having the above-described lithium ion secondary battery (typically, a battery pack in which a plurality of batteries are connected in series) as a power source. An automobile equipped with an electric motor) can be provided.

  Several examples relating to the present invention will be described below, but the present invention is not intended to be limited to those shown in the examples. In the following description, “parts” and “%” are based on mass unless otherwise specified.

<Example 1 to Example 8>
(1) Production of negative electrode sheet Natural graphite powder as a negative electrode active material, styrene-butadiene copolymer (SBR) as a binder, and carboxymethyl cellulose (CMC) as a thickener are made of these materials. A paste-like composition for forming a negative electrode active material layer was prepared by dispersing in water such that the mass ratio was 98: 1: 1. This composition for forming a negative electrode active material layer was uniformly applied to both sides of a long sheet-like copper foil (thickness: 10 μm) so that the total application amount was 10 mg / cm ² (solid content basis). After coating, the coated material was dried at a temperature of 100 ° C. for 20 seconds, and the coated material was subjected to press treatment to form a negative electrode active material layer on the negative electrode current collector. A sheet-like negative electrode active material layer formation comprising this negative electrode current collector and a negative electrode active material layer formed thereon was wound in a reel shape and then exposed to the dew point temperature environment shown in Table 1 for 3 hours. Then, the sheet-like negative electrode (negative electrode sheet) which concerns on Example 1-Example 8 was produced by making it dry for 20 second in the environment of temperature 100 degreeC and dew point temperature -30 degreeC. In addition, the dew point temperature in the said application | coating, drying, and press processing was -30 degreeC, and the temperature in the said application | coating and press process was 25 degreeC.

(2) Preparation of positive electrode sheet Lithium nickel manganese cobaltate (Li [Ni _1/3 Mn _1/3 Co _1/3 O ₂ ) powder as a positive electrode active material, acetylene black as a conductive material, and binder Of poly (vinylidene fluoride) (PVDF) in N-methyl-2-pyrrolidone (NMP) so that the mass ratio of these materials is 90: 5: 5 to form a paste-like positive electrode active material layer A composition was prepared. After this composition was applied on both sides of a long sheet-like aluminum foil (positive electrode current collector; thickness 15 μm) so that the total application amount was 20 mg / cm ² (solid content basis) and dried. Then, a press treatment was performed to produce a sheet-like positive electrode (positive electrode sheet).

(3) Construction of lithium ion secondary battery The produced negative electrode sheet and positive electrode sheet were laminated together with two long polyolefin separators (here, a porous polyethylene sheet having a thickness of 25 μm was used), and the lamination was performed. The sheet was wound in the longitudinal direction to produce a wound electrode body. A lithium ion secondary battery (theoretical capacity 223 mAh) according to Examples 1 to 8 was constructed by accommodating the wound electrode body together with an electrolytic solution in a cylindrical container. As an electrolytic solution, about 1 mol / L LiPF ₆ was dissolved as a supporting salt in a 3: 3: 4 (mass ratio) mixed solvent of ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC). Used.

[Moisture content of negative electrode active material layer]
A part of the surface of the negative electrode active material layer of each negative electrode sheet produced as described above was scraped, and the amount of water contained in the scraped sample was measured by the Karl Fischer method. The results are shown in Table 1.

[Capacity maintenance rate]
About each lithium ion secondary battery produced as mentioned above, after adjusting SOC (State of Charge) to the state of 80%, it preserve | saved in the environment of the temperature of 60 degreeC for 30 days. The discharge capacity before and after storage was measured by CC discharge at a rate of 0.2 C until SOC reached 0%, and the discharge capacity retention rate (%) was calculated from the discharge capacity after storage with respect to the discharge capacity before storage. The results are shown in Table 1 and FIG.

As shown in Table 1 and FIG. 3, the lithium ion secondary batteries according to Examples 4 to 7 in which the dew point temperature in the exposure to the dew point temperature environment is within the range of 17 ° C. to 52 ° C. are 60 ° C. The capacity retention rate after storage for 30 days was 86.1% or more. On the other hand, the lithium ion secondary batteries according to Examples 1 and 2 having the dew point temperatures of −30 ° C. and 0 ° C. have a capacity retention rate of 83.6% or less, which is lower than those of Examples 4 to 7. Value. The lithium ion secondary battery according to Example 8 having a dew point temperature of 55 ° C. had a capacity maintenance rate of 81.1%, which was a lower value than those in Examples 4 to 7.
Thus, the lithium ion secondary battery using the negative electrode sheet provided with the negative electrode active material layer produced by exposing it to an environment with a dew point temperature of 17 ° C. to 52 ° C. was more suitably suppressed from lowering the capacity retention rate. I understand that.

<Example 9 to Example 13>
Regarding the exposure to the dew point temperature environment, a negative electrode sheet was prepared in the same manner as in Example 1 except that the dew point temperature was fixed at 35 ° C. and the exposure time was set to the time shown in Table 1, and Example 1 using each negative electrode sheet. In the same manner, a lithium ion secondary battery was constructed. The water content of the negative electrode active material layer of the produced negative electrode sheet was measured in the same manner as in Example 1, and the capacity retention rate of the constructed lithium ion secondary battery was measured in the same manner as in Example 1. The results are shown in Table 2 and FIG. For reference, FIG. 4 also shows the results of Example 5.

As shown in Table 2 and FIG. 4, the lithium ion secondary batteries according to Examples 10 to 13 in which the exposure time to a predetermined dew point temperature is 30 minutes or more have a capacity after being stored at 60 ° C. for 30 days. The maintenance rate was 85.9% or more. On the other hand, the capacity retention rate of the lithium ion secondary battery according to Example 9 in which the exposure time was 10 minutes was 82.9%, which was a low value compared with Examples 10 to 13.
As described above, it is understood that the lithium ion secondary battery using the negative electrode sheet including the negative electrode active material layer manufactured with the exposure time to the predetermined dew point temperature environment for 30 minutes or more is suppressed in capacity reduction. .

DESCRIPTION OF SYMBOLS 1 Negative electrode collector 2 Negative electrode active material layer 10 Negative electrode (negative electrode sheet)
11 Negative electrode protruding part (negative electrode active material layer non-formed part)
21 Case 22 Case body 23 Cover body 25 Positive electrode terminal 26 Positive electrode lead terminal 27 Negative electrode terminal 28 Negative electrode lead terminal 50 Positive electrode (positive electrode sheet)
51 Positive electrode protruding part (positive electrode active material layer non-formed part)
60 Separator (sheet)
80 wound electrode body 82 wound core portion 100 lithium ion secondary battery

Claims (5)

A negative electrode active material capable of inserting / extracting charge carriers as a main component, and a negative electrode active material layer forming composition comprising a polymer that can be dissolved or dispersed in water and an aqueous solvent, applied onto the negative electrode current collector, After the application, a negative electrode active material layer is formed on the negative electrode current collector by drying under conditions of a dew point temperature of less than 10 ° C., and the formed negative electrode active material layer is formed at a dew point temperature of 17 ° C. to 52 ° C. Exposure to an environment of at least 30 minutes,
A method for producing a negative electrode for a non-aqueous electrolyte secondary battery.   The manufacturing method according to claim 1, wherein the formed negative electrode active material layer is subjected to a press treatment and then exposed to the environment.   The production method according to claim 1 or 2, wherein the polymer that can be dissolved or dispersed in water is a cellulose derivative.   The manufacturing method of Claim 3 whose said cellulose derivative is carboxymethylcellulose (CMC). Constructing a positive electrode having a positive electrode active material layer formed on the positive electrode current collector, the main component of which is a positive electrode active material capable of inserting / extracting charge carriers,
Constructing a negative electrode provided on a negative electrode current collector with a negative electrode active material layer formed mainly of a negative electrode active material capable of inserting / extracting charge carriers, and non-aqueous electrolysis using the positive electrode and the negative electrode Building a liquid secondary battery,
Including
Here, the negative electrode obtained by the manufacturing method in any one of Claim 1 to 4 is used as said negative electrode, The manufacturing method of the non-aqueous-electrolyte type | mold secondary battery characterized by the above-mentioned.

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