JP2013084399A - Lithium ion secondary battery anode manufacturing method and lithium ion secondary battery manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a lithium ion secondary battery anode which has improved low temperature characteristics.SOLUTION: The lithium ion secondary battery anode manufacturing method offered by the present invention includes a step in which an anode mixture material layer formation composition which is composed mainly of an anode active material consisting of a carbon material capable of insertion/separation of lithium and contains a binder, a water soluble thickener and an aqueous solvent is coated on an anode current collector to form an anode mixture layer on the anode current collector, and a step in which the anode mixture layer thus formed is maintained at a temperature of 35°C to 70°C, both ends incl., a relative humidity of 30% to 75%, both ends incl., and under a condition satisfying the equation T×H≤220 (where, T=temperature (K) and H=relative humidity (%)/100).

Description

  The present invention relates to a method for producing a negative electrode for a lithium ion secondary battery, and more specifically, a negative electrode comprising a composition for forming a negative electrode mixture layer comprising a negative electrode active material, a binder, a water-soluble thickener, and an aqueous solvent. The present invention relates to a method for producing a negative electrode for a lithium ion secondary battery in which a composite material layer is formed on a negative electrode current collector.

  In recent years, secondary batteries such as lithium 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. . In particular, a lithium secondary battery (typically a lithium ion secondary battery) that is lightweight and obtains a high energy density is expected to be preferably used as a high-output power source mounted on a vehicle.

  The electrode (positive electrode and negative electrode) of the lithium ion secondary battery is an electrode mixture layer mainly composed of an electrode active material capable of reversibly occluding and releasing chemical species (typically lithium ions) as charge carriers. (Specifically, a positive electrode mixture layer and a negative electrode mixture layer) are provided on the electrode current collector. Such an electrode mixture layer is prepared by dispersing an electrode active material together with an additive such as a binder and a thickener and adding an appropriate solvent, and using the resulting paste or slurry composition as an electrode current collector. It is formed by coating. Patent document 1 is mentioned as a prior art regarding the battery using the negative electrode compound material comprised from such an electrode active material, a binder, and a thickener.

  However, in the lithium ion secondary battery as described above, the reaction resistance in the low temperature region increases, and the low temperature characteristics (typically, the cycle characteristics at low temperatures) may decrease. Therefore, a method for improving the low temperature characteristics by adjusting the properties of the negative electrode mixture layer has been proposed. Patent document 2 is mentioned as this type of prior art.

JP 2002-279995 A JP 2010-67436 A

  In the composition for forming a negative electrode mixture layer containing the negative electrode active material, the binder, and the thickener as described above, if the amount of the binder and the thickener is reduced, a certain degree of improvement in low-temperature characteristics can be achieved. Although it can be expected, a reduction in the amount of the binder may cause a decrease in the adhesive strength between the composite layer and the current collector. Moreover, since the reduction of the amount of thickening material reduces the dispersibility of the binder in a composite material layer, there exists a possibility that the performance of a composite material layer may become non-uniform | heterogenous. As described above, since there is a limit to the reduction of the amount of the binder and the thickener, it is becoming difficult to improve the low-temperature characteristics by selecting the compounding material and adjusting the blending ratio.

  Therefore, the present invention was created to solve the above-described conventional problems, and an object thereof is to provide a method for manufacturing a negative electrode for a lithium ion secondary battery with improved low-temperature characteristics. Another object of the present invention is to provide a method of manufacturing a lithium ion secondary battery with improved low temperature characteristics.

  In order to achieve the above object, according to the present invention, a negative electrode mixture layer comprising, as a main component, a negative electrode active material comprising a carbon material capable of inserting / extracting lithium, and comprising a binder, a water-soluble thickener, and an aqueous solvent. Applying the forming composition onto a negative electrode current collector to form a negative electrode mixture layer on the negative electrode current collector, and forming the formed negative electrode mixture layer at a temperature of 35 ° C. or higher and 70 ° C. or lower and relative humidity 30% or more and 75% or less, and holding under conditions satisfying the formula: T × H ≦ 220 (T is temperature (K) and H is relative humidity (%) / 100). A method for producing a negative electrode for a lithium ion secondary battery is provided.

The inventors of the present invention have been diligently studying to improve the low-temperature characteristics of the lithium ion secondary battery by means other than selection of compounding materials and adjustment of the compounding ratio, and the like. It was found that holding the layer under a predetermined temperature and humidity condition after drying was effective in improving the low temperature characteristics of the lithium ion secondary battery, and the present invention was completed. That is, according to the method for producing a negative electrode for a lithium ion secondary battery having such a configuration, the negative electrode mixture layer formed on the negative electrode current collector is heated at a temperature of 35 ° C. to 70 ° C. and a relative humidity of 30% to 75% (preferably Is a temperature of 40 ° C. or more and 65 ° C. or less and a relative humidity of 35% or more and 55% or less), and the formula: T × H ≦ 220 (T is temperature (K) and H is relative humidity (%) / 100. )), The increase in reaction resistance at a low temperature of the lithium ion secondary battery including the negative electrode on which the negative electrode mixture layer is formed is suppressed, and the low temperature characteristics of the lithium ion secondary battery are reduced. improves.
Therefore, according to the production method of the present invention, it is possible to provide a negative electrode for a lithium ion secondary battery with improved low temperature characteristics.
In the present invention, “low temperature” is not particularly limited, but typically means 10 ° C. or lower. Therefore, a temperature range below freezing point such as 0 ° C. to −20 ° C. or lower is a typical example of a low temperature mentioned here. Therefore, the lithium ion secondary battery according to the present invention having improved low temperature characteristics is suitable as a negative electrode for a lithium ion secondary battery used in a cold region.

  In a preferred aspect of the method for producing a negative electrode for a lithium ion secondary battery disclosed herein, the holding is performed for at least one hour or more. Thus, by holding the negative electrode mixture layer under a predetermined temperature and humidity condition for at least 1 hour, the lithium ion secondary battery including the negative electrode on which the negative electrode mixture layer is formed has improved low-temperature characteristics. . In addition, it is more preferable to hold the predetermined time in a state where the negative electrode for a lithium ion secondary battery is wound in a reel shape from the viewpoint of improving low temperature characteristics.

  In a preferred embodiment of the method for producing a negative electrode for a lithium ion secondary battery disclosed herein, the formed negative electrode mixture layer is subjected to a press treatment, and then held under the above conditions. As described above, after the press treatment, the lithium ion secondary battery including the negative electrode on which the negative electrode mixture layer is formed by holding the negative electrode mixture layer under a predetermined temperature and humidity condition has low temperature characteristics. Will be improved.

  In a preferred aspect of the method for producing a negative electrode for a lithium ion secondary battery disclosed herein, the water-soluble thickener is a cellulose derivative. By using a cellulose derivative as the water-soluble thickener, the low temperature characteristics of the lithium ion secondary battery are further improved.

  In addition, according to the present invention, it is possible to construct a positive electrode having a positive electrode mixture layer formed mainly on a positive electrode active material capable of inserting / extracting lithium on a positive electrode current collector, and to insert / extract lithium. Constructing a negative electrode having a negative electrode mixture layer formed on a negative electrode current collector, the main component of which is a negative electrode active material made of a carbon material, and a lithium ion secondary battery using the positive electrode and the negative electrode Wherein a negative electrode obtained by any of the manufacturing methods disclosed herein is used as the negative electrode. A method for manufacturing a lithium ion secondary battery is provided. . Thus, by holding the negative electrode mixture layer formed on the negative electrode current collector under predetermined temperature and humidity conditions, the lithium ion secondary battery including the negative electrode on which the negative electrode mixture layer is formed is Increase in reaction resistance at low temperatures is suppressed, and low temperature characteristics are improved.

It is a schematic diagram which shows the cross section of 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 reaction resistance change rate of the lithium ion secondary battery which concerns on Examples 1-24. It is a graph which shows the measurement result of the impedance in -30 degreeC of the lithium ion secondary battery which concerns on Example 4, Example 9, and Example 11. FIG. It is a graph which shows the measurement result of the impedance in -30 degreeC of the lithium ion secondary battery which concerns on Example 4, Example 25, Example 26, and Example 27. FIG.

  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 shown in FIG. 1, the negative electrode 10 for a lithium ion secondary battery can have the same configuration as the conventional one. In this embodiment, the negative electrode mixture layer 2 is formed on the negative electrode current collector 1. Provide structure. Hereinafter, each component of the negative electrode 10 for lithium ion secondary batteries which concerns on this embodiment is demonstrated.

  The negative electrode current collector is made of a metal having good conductivity (for example, a metal such as aluminum, nickel, copper, or 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 mixture layer is formed by dispersing a negative electrode active material together with a binder and a water-soluble thickener in an aqueous solvent to obtain a paste or slurry-like composition for forming a negative electrode mixture layer, and then forming the negative electrode mixture layer. It can form by apply | coating the composition for an application | coating to the surface of a negative electrode collector.

  The negative electrode active material contained in the composition for forming a negative electrode mixture layer is not particularly limited as long as it is made of a carbon material (a carbon-based material mainly composed of a carbon material) used in a typical lithium ion secondary battery. It is not limited. For example, typical examples of the carbon-based material used as the negative electrode active material include graphite carbon and amorphous carbon. Among them, the use of a carbon-based material mainly composed of natural graphite (or artificial graphite) is preferable. Such natural graphite (or artificial graphite) may be obtained by spheroidizing graphite. For example, spheroidized natural graphite (or spheroidized artificial graphite) having an average particle size in the range of about 5 μm to 30 μm based on observation with an electron microscope (such as SEM or TEM) can be preferably used as the negative electrode active material. Further, a carbonaceous powder in which the surface of the graphite particles is coated with amorphous carbon may be used.

  Although not particularly limited, the proportion of the negative electrode active material in the total solid content of the composition for forming a negative electrode mixture layer is preferably more than about 50% by mass, and the viewpoint of improving the low temperature characteristics of the lithium ion secondary battery From about 90% by mass to 99% by mass (for example, 95% by mass to 99% by mass, typically 97% by mass to 99% by mass) is more preferable.

  As a binder (binder) contained in the composition for forming a negative electrode mixture layer, the same binder as that used for a negative electrode of a general lithium ion secondary battery can be appropriately adopted, and water can be used. A polymer material that dissolves or disperses in water can be preferably used. Examples of the polymer material dissolved or dispersed in water include styrene butadiene rubber (SBR). Here, SBR is a copolymer containing styrene and 1,3-butadiene, and the copolymerization mode is not particularly limited. Further, it may be a modified SBR obtained by copolymerizing an unsaturated carboxylic acid or an unsaturated nitrile compound. Examples of other polymer materials include polyacrylate (acrylic acid ester homopolymer or copolymer), polyurethane, polyethylene oxide (PEO), polyethylene, and the like. Such a binder may be used alone or in combination of two or more.

  The addition amount (content) of the binder is not particularly limited, but is preferably 0.1% by mass to 8% by mass when the total solid content of the negative electrode composite layer forming composition is 100% by mass. Preferably, the content is in the range of 0.4% by mass to 3% by mass (for example, 0.5% by mass to 1% by mass). When the amount of the binder added is within the above range, the reaction resistance in the low temperature region of the battery can be easily kept low, and the active material can be prevented from slipping down by maintaining a good binding force.

  As the water-soluble thickener contained in the composition for forming a negative electrode mixture layer, a polymer material that is soluble in water (water-soluble) can be used. Examples of water-soluble (water-soluble) polymer materials include cellulose derivatives (cellulosic polymers) such as carboxymethyl cellulose (CMC), methyl cellulose (MC), cellulose acetate phthalate (CAP), and hydroxypropyl methyl cellulose (HPMC). Polyvinyl alcohol (PVA); and the like. Cellulose derivatives are preferably used from the viewpoints of the relationship with the action by holding under a predetermined temperature and humidity condition described later, workability and stability during kneading (preparation) of the composition for forming a negative electrode mixture layer, and the like. .

  The addition amount (content) of the water-soluble thickener is not particularly limited as long as it is appropriately selected depending on the type and amount of the negative electrode active material, but the total solid content of the negative electrode mixture layer forming composition is 100% by mass. Is preferably 0.3% by mass to 2% by mass, and more preferably 0.5% by mass to 1% by mass. When the addition amount of the water-soluble thickener is within the above range, the reaction resistance in the low temperature region of the battery can be easily kept low, and the binder can be easily dispersed well.

  The aqueous solvent contained in the composition for forming a negative electrode mixture layer 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 about 80% by mass or more (more preferably about 90% by mass or more, more preferably about 95% by mass or more) of the aqueous solvent is water. A particularly preferred example is an aqueous solvent substantially consisting of water. Although not particularly limited, the solid content concentration of the composition for forming a negative electrode composite material layer (nonvolatile content, that is, the ratio of the material for forming a composite material layer) 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 mixture layer can be improved, the negative electrode mixture layer can be easily applied to a uniform thickness, and the composition for forming the negative electrode mixture layer Is easy to handle.

  The composition for forming a negative electrode mixture layer can appropriately contain a material other than the above, for example, a conductive material or an aggregation inhibitor, depending on the purpose and application, from the viewpoint of improving the low temperature characteristics of the lithium ion secondary battery, It is preferable that only a negative electrode active material, a binder, and a water-soluble thickener are included as solid content.

  Next, the manufacturing method of the negative electrode of the lithium ion secondary battery which concerns on this embodiment is demonstrated. In such a production method, first, the negative electrode active material, the binder, and the thickener are mixed (kneaded) in an aqueous solvent, and a paste-like (also referred to as slurry) negative electrode mixture layer forming composition is prepared. Prepare. Such a kneading operation can be performed using, for example, an appropriate kneader (planetary mixer, homodisper, clear mix, fill mix, etc.). In preparing the composition for forming a negative electrode mixture layer, the negative electrode active material, the binder, and the thickener are kneaded with a small amount of an aqueous solvent (for example, water), and then the obtained kneaded product is mixed with an appropriate amount. You may dilute with a solvent.

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

The coating amount per unit area of the composition for forming a negative electrode mixture layer to be applied, that is, the basis weight is not particularly limited as long as a sufficient conductive path (conductive path) can be ensured, but preferably Is the total of both surfaces of the negative electrode composite material layer and 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).

  After applying the composition for forming a negative electrode mixture layer, the applied material is dried (at this time, an appropriate drying accelerating means (such as a heater) may be used as necessary). It is preferable to remove the solvent in the composition. Examples of the drying method include passing a negative electrode current collector coated with the composition for forming a negative electrode mixture layer through a drying furnace. Although the said drying temperature is not specifically limited, For example, it is 70 degreeC or more and 200 degrees C or less (typically 120 to 150 degreeC). The drying time is, for example, about 10 seconds to 120 seconds (typically about 20 seconds to 60 seconds). Moreover, the humidity at the time of drying is not particularly limited, but typically, the relative humidity is preferably less than 30% (for example, 1% to 25%).

In the present embodiment, after the negative electrode mixture layer is formed by the above-described method, the negative electrode mixture layer is held under conditions that satisfy a temperature of 35 ° C. to 70 ° C. and a relative humidity of 30% to 75%. The holding temperature is preferably 35 ° C. or higher and 65 ° C. or lower (typically 40 ° C. or higher and 65 ° C. or lower). The relative humidity within the above temperature range is preferably 35% or more and 55% or less. In addition to the above temperature and humidity conditions, the above holding can be performed by the formula:
T × H ≦ 220
(T is temperature (K) and H is relative humidity (%) / 100). T × H is preferably 200 or less (typically 180 or less). By holding the negative electrode mixture layer under such conditions, the holding acts on the material constituting the negative electrode mixture layer, and the lithium ion secondary battery including the negative electrode on which the negative electrode mixture layer is formed is at a low temperature. An increase in reaction resistance is suppressed, and the low temperature characteristics of the lithium ion secondary battery are improved. In particular, when the temperature is higher than 80 ° C., the negative electrode current collector (typically copper foil) may be oxidized, which is not preferable. The lower limit value of T × H in the above formula is not particularly limited, but is preferably 70 ≦ T × H, more preferably 90 ≦ T × H (typically from the viewpoint of improving the low-temperature characteristics of the lithium ion secondary battery. Is 100 ≦ T × H).

  The holding is preferably performed for at least 1 hour or longer (for example, 1.5 hours or longer, typically 2 hours or longer). By holding under predetermined temperature and humidity conditions for a certain period of time or longer, the above-mentioned action due to the holding can be sufficiently obtained. The holding time is preferably 24 hours or shorter, more preferably 8 hours or shorter (for example, 5 hours or shorter). If the above-mentioned holding is performed for a long time, the negative electrode current collector (copper foil) may be oxidized, which is not preferable. Moreover, it is more preferable that the holding | maintenance performed for the predetermined time mentioned above is performed in the state which wound the negative electrode for lithium ion secondary batteries in the reel shape from a viewpoint of a low-temperature characteristic improvement.

  The moisture content of the negative electrode mixture layer after the above holding is not particularly limited, but is, for example, 600 ppm or more (typically 800 ppm or more) on a mass basis, for example, 1300 ppm or less (typically 1100 ppm or less). It becomes. By performing the above-mentioned holding, the water content of the negative electrode mixture layer falls within the above range, which acts to increase the specific surface area of the negative electrode mixture layer, thereby providing a lithium ion secondary comprising the negative electrode mixture layer. It is assumed that the low temperature characteristics of the battery are improved. In addition, after the said holding | maintenance is completed, you may dry a negative mix layer as needed. As the drying conditions (method, temperature, etc.), for example, the same conditions as the drying conditions after the application of the composition for forming a negative electrode mixture layer described above can be adopted. It is possible to dry.

  A negative electrode having a target thickness can be obtained by subjecting the negative electrode mixture 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 mixture layer formed on both sides thereof) is not particularly limited, but is, for example, about 30 μm to 300 μm (typically Specifically, the thickness is preferably 50 μm to 180 μm. When the negative electrode mixture layer is formed on one surface of the negative electrode current collector, the thickness is half of the above thickness.

  The holding may be performed before the pressing process, or may be performed concurrently with the pressing process (for example, the pressing process is performed during the holding). From the viewpoint of improving the low temperature characteristics of the lithium ion secondary battery, it is preferable to perform the holding after the press treatment.

  Next, the lithium ion secondary battery according to this embodiment that is constructed using the negative electrode (negative electrode sheet) 10 manufactured by the above method will be described. As shown in FIG. 2, the lithium ion secondary battery 100 according to the present embodiment 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 mixture layer mainly composed of an electrode active material is formed on both surfaces of a long sheet-like electrode current collector. One end of the positive electrode sheet 50 in the width direction is provided with a positive electrode mixture layer non-formed portion 51 in which the positive electrode mixture layer is not formed on either side. The negative electrode composite material layer non-formed part 11 in which the negative electrode composite material layer is not formed is provided on any surface. The positive electrode mixture layer non-formed portion 51 of the positive electrode sheet 50 and the negative electrode mixture layer non-formed portion 11 of the negative electrode sheet 10 protrude 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 mixture 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 mixture layer forming portion of the positive electrode sheet 50, the negative electrode mixture 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 mixture layer non-forming portion) 51 and the negative electrode side protruding portion (negative electrode mixture 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 a positive electrode mixture layer mainly composed of a positive electrode active material 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.

The positive electrode active material which is the main component of the positive electrode mixture layer can be used without any particular limitation on one or more of the materials conventionally used in lithium ion secondary batteries. Preferable examples include lithium and lithium oxides having a layered structure or a spinel structure, lithium cobalt composite oxides, lithium manganese composite oxides such as olivine-type lithium phosphates such as LiFePO ₄ and one or two of them. Examples thereof include lithium transition metal composite oxides containing at least one kind of transition metal element as a constituent metal element. In addition to the positive electrode active material, the positive electrode mixture layer preferably further contains a conductive material, a binder, and the like. Examples of the conductive material include carbon materials such as carbon powder and carbon fiber. Examples of the binder include water-soluble polymers such as cellulose derivatives (typically carboxymethyl cellulose (CMC)) and water-dispersible polymers. Can be mentioned. A porous 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 mixture layer from falling off. The content of the positive electrode active material in the positive electrode mixture layer exceeds about 50% by mass when the total solid content is 100% by mass (typically in the range of about 70% to 95% 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 synthetic resin (for example, made of polyolefin such as polyethylene or polypropylene) porous separator sheet having a thickness of about 5 to 30 μm can be suitably used. When a solid electrolyte or 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).

  Referring to FIG. 2, the lithium ion secondary battery 100 according to this embodiment is manufactured by, for example, the following method. First, a positive electrode sheet 50 provided with a positive electrode mixture layer formed on the positive electrode active material as a main component on the positive electrode current collector by the above-described technique is constructed, and the negative electrode active material made of the carbon material is used as the main component. The negative electrode sheet 10 provided with the negative electrode mixture layer 2 formed on the negative electrode current collector 1 is constructed. Thereafter, as described above, the wound electrode body 80 composed of the positive electrode sheet 50, the negative electrode sheet 10, and the separator sheet 60 is accommodated in the case main body 22 from the upper end opening portion of the case main body 22 and appropriately supported. An electrolyte containing salt is placed (injected) in 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 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.

  The lithium ion secondary battery 100 according to the present embodiment is constructed by injecting the electrolytic solution and 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.

  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 24>
(1) Natural graphite (electron microscopy (SEM) Mean particle diameter D ₅₀ based on the observation those 11 [mu] m) as prepared negative active material of the negative electrode sheet were coated with amorphous carbon, 3 a specific surface area of the carbon material. A carbon material of 0 m ² / g was obtained. The carbon material, the modified styrene butadiene rubber as a binder, and carboxymethyl cellulose (CMC) as a thickener are weighed so that the mass ratio of these materials is 98: 1: 1. The material was mixed with ion-exchanged water to prepare a paste-like composition for forming a negative electrode mixture layer. This composition was applied to both surfaces of a negative electrode current collector (thickness 10 μm) composed of a long copper foil so that the total coating amount was 7.5 mg / cm ² (solid content basis). After coating, the coating was dried at 120 ° C. for 20 seconds, and the coated product was subjected to press treatment to form a negative electrode mixture layer on the negative electrode current collector. A plurality of negative electrode mixture layer formations composed of the negative electrode current collector and the negative electrode mixture layer formed thereon are prepared, and these negative electrode mixture layer formations are respectively heated to temperatures of 25 ° C., 35 ° C., and 45 ° C. , 60 ° C. and at each temperature under a relative humidity of 20%, 30%, 40%, 50%, 60%, 70%, and 80% for 2 hours. In this manner, sheet-like negative electrodes (negative electrode sheets) according to Examples 1 to 24 were produced.

(2) Production 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 agent, and binder Were mixed in ion-exchanged water so that the mass ratio of these materials was 90: 5: 5 to prepare a paste-like composition for forming a positive electrode mixture layer. This composition was applied to both sides of a long sheet-like aluminum foil (positive electrode current collector; thickness 15 μm) so that the total application amount was 17 mg / cm ² (solid content basis), dried, and then pressed. It processed and produced the 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. By housing the wound electrode body together with the electrolyte in a cylindrical container, an 18650 type lithium ion secondary battery (theoretical capacity 223 mAh, 4.1 V charge to 3 V discharge) according to Examples 1 to 24 was constructed. . 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.

<Example 25 to Example 27>
Example 1 is the same as Example 1 except that each negative electrode mixture layer formed product was kept at 35 ° C., 45 ° C., 60 ° C. and 50% relative humidity after drying of the negative electrode mixture layer and before pressing. Similarly, a lithium ion secondary battery was constructed.

[Reaction resistance measurement]
Each lithium ion secondary battery produced as described above was subjected to an appropriate conditioning treatment under a temperature condition of 25 ° C. (an operation of charging at a constant current and a constant voltage up to 4.1 V at a charge rate of 0.2 C, and 0 After the initial charge / discharge treatment in which the operation of discharging at a constant current and constant voltage to 3.0 V at a discharge rate of 2 C was repeated three times, the state of charge was adjusted to 40% SOC. And reaction resistance was measured with the alternating current impedance method at the frequency of 10 mHz-1MHz on the temperature conditions of -30 degreeC with respect to each lithium ion secondary battery. The reaction resistance of the lithium ion secondary battery according to Example 4 held under conditions of a temperature of 25 ° C. and a relative humidity of 50% after the negative electrode mixture layer is pressed is 100 (reference), and the lithium ion secondary battery according to each example The reaction resistance was expressed as an index of change in reaction resistance. In this index notation, the smaller the value of the reaction resistance change rate, the smaller the reaction resistance, and the larger the value, the greater the reaction resistance. The results are shown in Table 1 and FIG. Table 1 also shows the holding conditions (holding time, temperature, and humidity) of the negative electrode mixture layer in each example. In the table, T × H represents T (temperature (K)) × H (relative humidity (%) × 10 ⁻² ). Further, FIG. 4 shows impedances at −30 ° C. of the lithium ion secondary batteries according to Examples 4, 9 and 11, and −30 of the lithium ion secondary batteries according to Examples 4, 25, 26 and 27. FIG. 5 shows the impedance at ° C.

As shown in Table 1 and FIG. 3, the conditions for holding the negative electrode composite material layer include a temperature of 35 ° C. or more and 70 ° C. or less, a relative humidity of 30% or more and 75% or less, and a formula: T × H ≦ 220 (T is The lithium ion secondary batteries according to Example 7 to Example 11, Example 14 to Example 17, and Example 20 to Example 23 that satisfy the temperature (K) and H is relative humidity (%) / 100. It can be seen that the reaction resistance at 0 ° C. was lower than that of the lithium ion secondary battery according to Example 4 in which the above holding was performed at a temperature of 25 ° C. and a relative humidity of 50%. A similar trend can be seen from FIG.
On the other hand, the above-mentioned holding was performed under conditions where the temperature was less than 35 ° C. or more than 70 ° C., the relative humidity was less than 30% or more than 75%, or the formula: T × H was greater than 220. The lithium ion secondary batteries according to Example 5, Example 6, Example 12, Example 13, Example 18, Example 19, and Example 24 have the same reaction resistance at −30 ° C. as that of Example 4 that does not substantially hold. It was about.
In this way, by maintaining the negative electrode mixture layer under a predetermined temperature and humidity condition, an increase in reaction resistance at a low temperature of a lithium ion secondary battery including the negative electrode on which the negative electrode mixture layer is formed is suppressed. I understand that.

In addition, the lithium ion secondary batteries of Examples 25 to 27 in which the above holding was performed before the press treatment were also performed in the lithium ion secondary battery according to Example 4 in which the reaction resistance at −30 ° C. was not substantially held. It is clear that it was lower than
Thus, it can be seen that the increase in the reaction resistance at the low temperature of the lithium ion secondary battery is suppressed regardless of the timing of the holding before and after the press treatment.

  Specific examples of the present invention have been described in detail above, but these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and changes of the specific examples illustrated above.

DESCRIPTION OF SYMBOLS 1 Negative electrode collector 2 Negative electrode compound layer 10 Negative electrode (negative electrode sheet)
11 Negative electrode protruding portion (negative electrode mixture layer non-formed portion)
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 mixture layer non-formed part)
60 Separator (sheet)
80 wound electrode body 82 wound core portion 100 lithium ion secondary battery

Claims (7)

A composition for forming a negative electrode mixture layer comprising a negative electrode active material composed of a carbon material capable of inserting / extracting lithium as a main component and comprising a binder, a water-soluble thickener, and an aqueous solvent is formed on a negative electrode current collector. Applying to form a negative electrode mixture layer on the negative electrode current collector, and forming the negative electrode mixture layer at a temperature of 35 ° C. to 70 ° C. and a relative humidity of 30% to 75%, and a formula:
T × H ≦ 220
(T is temperature (K) and H is relative humidity (%) / 100.)
Holding under conditions that satisfy
A method for producing a negative electrode for a lithium ion secondary battery.   The manufacturing method according to claim 1, wherein the holding is performed for at least one hour or more.   The manufacturing method according to claim 2, wherein the holding is performed in a state where the negative electrode is wound in a reel shape.   The manufacturing method according to claim 2, wherein the formed negative electrode mixture layer is subjected to a press treatment and then held under the conditions.   The manufacturing method according to any one of claims 1 to 4, wherein the holding is performed under conditions of a temperature of 40 ° C to 65 ° C and a relative humidity of 35% to 55%.   The manufacturing method in any one of Claim 1 to 5 whose said water-soluble thickener is a cellulose derivative. Constructing a positive electrode comprising a positive electrode mixture layer formed on the positive electrode current collector, the main component of which is a positive electrode active material capable of inserting / extracting lithium;
Constructing a negative electrode provided with a negative electrode mixture layer formed mainly on a negative electrode active material composed of a carbon material capable of inserting / extracting lithium on a negative electrode current collector, and using the positive electrode and the negative electrode Building a lithium ion secondary battery,
Including
Here, the negative electrode obtained by the manufacturing method in any one of Claim 1 to 6 is used as said negative electrode, The manufacturing method of a lithium ion secondary battery characterized by the above-mentioned.

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