JP2013045659A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high reliability nonaqueous electrolyte secondary battery which prevents minute shorting with high accuracy, and a method for efficiently manufacturing electrodes which are used in the nonaqueous electrolyte secondary battery.SOLUTION: An electrode manufacturing method according to the present invention includes a step of forming a binder solution layer 30 by applying a binder solution containing a binder 32 and a solvent 33 to an electrode current collector 12. It also includes a step of forming a composition layer 34 by applying a paste-like composition containing an electrode active material 36 and a solvent 37 to the binder solution layer 30. Here, the composition layer 34 is formed in such a way that a part 31 of the binder solution layer 30 formed on the lower layer side of the composition layer 34 protrudes outward from an end portion of the composition layer 34. Further, the binder solution layer 30 and the composition layer 34 both are dried to form an electrode active material layer, and the part 31 of the binder solution layer 30 protruding outward from the end portion of the composition layer 34 is also dried to form a protruded insulating layer.

Description

  The present invention relates to a non-aqueous electrolyte secondary battery and a method for producing an electrode used in the battery.

  In recent years, lithium secondary batteries, nickel metal hydride batteries and other secondary batteries (storage batteries) have become increasingly important as power sources for mounting on vehicles or as power sources for personal computers and portable terminals. In particular, a lithium secondary battery that is lightweight and has a high energy density is preferably used as a high-output power source for mounting on a vehicle. A typical configuration of a lithium secondary battery includes a configuration including positive and negative electrodes including an electrode active material capable of occluding and releasing lithium ions, a separator disposed therebetween, and a nonaqueous electrolyte. It is done. For example, a positive and negative electrode sheet in which a layer mainly composed of an electrode active material (electrode active material layer) is held on the surface of a long sheet-shaped current collector is stacked with a separator between both electrode sheets. A lithium secondary battery having a configuration in which an electrode body (rolled electrode body) obtained by winding these in the longitudinal direction is housed in a container together with a nonaqueous electrolyte is known.

  In the lithium secondary battery having such a configuration, the electrode is typically a paste-like composition in which an electrode active material and a binder (binder) are dispersed in a suitable solvent (for example, water) and kneaded. The paste-like composition includes a slurry-like composition and an ink-like composition.) And is applied to a current collector and dried. In order to improve the adhesion between the current collector and the electrode active material layer, first, a precoat layer containing a binder is formed on the current collector, and a slurry containing the electrode active material is applied on the precoat layer. A technique for drying is proposed (for example, Patent Document 1).

JP 2009-238720 A JP 2007-103356 A

  In the meantime, as shown in FIG. 17, the positive electrode active material layer 114 is provided in the wound electrode body 180 as described above, leaving one edge along the longitudinal direction of the positive electrode current collector 112 in a strip shape. Using the positive electrode sheet 110, the two electrode sheets were overlapped and wound so that the belt-like portion (that is, the positive electrode current collector exposed portion where a part of the positive electrode current collector 112 was exposed) 116 protruded from the negative electrode sheet 120. There is a form (for example, patent document 2). In the wound electrode body 180 having such a configuration, a range in which the width of the negative electrode active material layer 124 is wider than the width of the positive electrode active material layer 114 and extends to the positive electrode current collector exposed portion 116 side than the positive electrode active material layer 114. Disposing the negative electrode active material layer 124 on the negative electrode active material can be an effective technique for smoothly occluding the Li ions that have moved from the positive electrode active material layer 114 toward the negative electrode 120 during charging into the negative electrode active material.

However, when the negative electrode active material layer 124 is disposed in a range that extends to the positive electrode current collector exposed portion 116 side relative to the positive electrode active material layer 114, a part of the positive electrode current collector exposed portion 116 is interposed via the separator 140. The structure faces the layer 124. Therefore, if a metallic foreign matter accumulates in the gap S between the positive electrode current collector exposed portion 116 and the negative electrode active material layer 124, a minute short-circuit portion may be formed between the positive electrode sheet 110 and the negative electrode sheet 120. obtain. For example, when the foreign matter breaks through the separator 140, a conductive path may be formed between the negative electrode active material layer 124 and the positive electrode current collector 112. Even when the foreign matter does not directly penetrate the separator 140, the metal contained in the foreign matter elutes electrochemically as the battery is charged and discharged, and deposits on or near the surface of the negative electrode 120. May fill the pores of the separator 140 and form a conductive path between the negative electrode active material layer 124 and the positive electrode current collector 112. The formation of such a short-circuit can cause Joule heat locally at the short-circuit location, thereby damaging the separator (typically made of thermoplastic resin) and causing a larger internal short-circuit (self-discharge). Further, the micro short-circuit causes a voltage drop with time, and may be a factor for reducing fuel consumption when used as a power source for a hybrid vehicle, for example.
In this regard, Patent Document 2 discloses an inorganic additive (for example, an alumina material) on the exposed portion of the positive electrode current collector facing the surface of the negative electrode mixture so that the positive electrode current collector and the negative electrode mixture do not contact each other. And applying an insulating paint composed of a binder to form a dried insulating layer. However, in the technique disclosed in Patent Document 2, since the positive electrode mixture and the insulator layer are separately provided on the positive electrode current collector, the manufacturing process becomes complicated and the positive electrode mixture of the positive electrode plate and Since it is necessary to apply the insulator paint by detecting the boundary of the exposed portion of the positive electrode current collector, it is difficult to align the positive electrode mixture and the insulator layer, and the insulator layer cannot be formed with high accuracy. It was. The present invention aims to solve the above problems.

  According to the present invention, a non-aqueous electrolyte secondary battery in which an electrode active material layer including an electrode active material and a binder and a protruding insulating layer protruding from an end of the electrode active material layer are formed on the surface of the electrode current collector. A method of manufacturing an electrode is provided. The method includes applying a binder solution containing a binder and a solvent to an electrode current collector to form a binder solution layer. The method also includes applying a paste-like composition containing an electrode active material and a solvent on the binder solution layer to form a composition layer. Here, the composition layer is formed such that a part of the binder solution layer formed on the lower layer side of the composition layer protrudes outward from the end of the composition layer. Furthermore, the binder solution layer and the composition layer are dried together to form the electrode active material layer, and the portion of the binder solution layer that protrudes outward from the end of the composition layer is dried. Forming the protruding insulating layer.

In this manufacturing method, the lower binder solution layer is formed so as to protrude outward from the end of the upper composition layer, and then the binder solution layer and the composition layer are simultaneously dried. At that time, in the portion where the binder solution layer and the composition layer overlap each other, the binder solution layer and the composition layer are mixed by convection during drying, and the binder and electrode active material are uniformly dispersed. Is formed. On the other hand, in the portion of the binder solution layer that protrudes outward from the end of the composition layer, since the composition layer is not laminated on the upper layer side, only the binder solution layer is dried alone. As a result, a protruding insulating layer made only of the binder is formed.
According to such an electrode manufacturing method, the electrode active material layer and the protruding insulating layer that protrudes from the end of the electrode active material layer can be collectively formed (in the same process), so that the manufacturing process can be simplified. become. In addition, the conventional high-precision alignment between the electrode active material layer and the insulating layer is not required, and an electrode in which the insulating layer is formed with high positional accuracy relative to the electrode active material layer can be manufactured. Therefore, by using such an electrode, it is possible to construct a non-aqueous electrolyte secondary battery in which the occurrence of a short circuit is more appropriately prevented (and thus excellent in self-discharge prevention). Preferably, the binder solution layer is formed so that the protruding insulating layer has a thickness of 3 nm or more. Thereby, a higher-performance nonaqueous electrolyte secondary battery can be constructed.

  In a preferred embodiment of the electrode manufacturing method disclosed herein, the surface tension of the binder solution is made higher than that of the paste-like composition, and the surface tension difference between the binder solution and the paste-like composition is 5 mN / Adjust to m or less. As described above, the structure in which the lower binder solution layer protrudes outward from the upper composition layer simplifies the manufacturing process by forming the electrode active material layer and the protruding insulating layer together. It is advantageous to do. On the other hand, in such a configuration, the edge of the composition layer locally rises due to the influence of the surface tension, and therefore the edge height phenomenon in which the edge of the electrode active material layer obtained after drying becomes thicker than the center. May occur. According to the electrode manufacturing method disclosed herein, since the relationship between the surface tension of the binder solution and the paste-like composition is appropriately defined as described above, the binder solution layer is formed outward from the end of the composition layer. Even if it is formed so as to protrude, the above-described edge height phenomenon can be appropriately prevented. By setting the difference in surface tension between the binder solution and the paste-like composition to 3 mN / m or less, particularly good results can be realized.

  In a preferred embodiment of the technology disclosed herein, the viscosity of the paste-like composition as measured using a commercially available E-type viscometer after adjusting the liquid temperature to 25 ° C. and rotating the rotor at 2 rpm. Is 3000 mPa · sec or more. As a result, the edge height phenomenon can be prevented more effectively, so that a higher quality electrode can be suitably manufactured. In a preferred embodiment of the technology disclosed herein, the binder solution layer has a thickness of 1.7 μm or less. This makes it possible to produce a high-quality electrode in which the edge height phenomenon is suppressed regardless of the viscosity of the paste-like composition described above.

  The present invention provides a non-aqueous electrolyte secondary battery including a positive electrode manufactured by any of the manufacturing methods disclosed herein. That is, an electrode in which a positive electrode having a positive electrode active material layer containing a positive electrode active material and a binder on the surface of the positive electrode current collector and a negative electrode having a negative electrode active material layer on the surface of the negative electrode current collector are overlapped via a separator. The positive electrode has a positive electrode current collector exposed portion in which the positive electrode active material layer is not formed on the surface of the positive electrode current collector. The positive electrode current collector exposed portion has a portion facing the negative electrode with the separator interposed therebetween. In the exposed portion of the positive electrode current collector, a protruding insulating layer that protrudes from the end of the positive electrode active material layer is formed at least in a portion facing the negative electrode with the separator interposed therebetween. Here, the protruding insulating layer includes a binder solution containing the binder and a solvent at a portion where the positive electrode active material layer is formed in the positive electrode current collector and the exposed portion of the positive electrode current collector adjacent to the portion. It is characterized by being formed by applying and drying. The positive electrode active material layer is formed by applying a paste-like composition containing the positive electrode active material and a solvent on a binder solution applied to a portion of the positive electrode current collector where the positive electrode active material layer is formed. And formed by drying.

  As schematically shown in FIG. 3, in the non-aqueous electrolyte secondary battery according to the present invention, the positive electrode active material layer 14 is formed on the surface of the positive electrode current collector exposed portion 16 as a countermeasure against the above-described micro short-circuit problem. A protruding insulating layer 48 protruding from the end is formed. The protruding insulating layer 48 is provided so as to cover at least a portion of the positive electrode current collector exposed portion 16 that faces the negative electrode active material layer 24 via the separators 40A and 40B. In this way, when a portion of the positive electrode current collector exposed portion 16 facing the negative electrode active material layer 24 is covered with the protruding insulating layer 48, metallic foreign matter is accumulated in the gap S. However, the direct contact between the foreign matter and the metallic deposit caused by the foreign matter and the positive electrode current collector 12 is protruded and blocked by the insulating layer 48, thereby preventing the occurrence of a micro short circuit. Therefore, the nonaqueous electrolyte secondary battery according to the present invention can be excellent in internal short circuit prevention (and consequently capacity maintenance). Further, according to the present invention, the protruding insulating layer 48 is formed on the binder on the portion of the positive electrode current collector 12 where the positive electrode active material layer 14 is formed and the positive electrode current collector exposed portion 16 adjacent to the portion as described above. And a binder solution containing a solvent and applied and dried. According to such a configuration, it is possible to form the positive electrode active material layer 14 and the protruding insulating layer 48 with high accuracy and collectively, and effectively prevent the occurrence of a micro short circuit without causing a significant increase in the manufacturing process. can do.

  In a preferred embodiment of the nonaqueous electrolyte secondary battery disclosed herein, the thickness of the protruding insulating layer is 3 nm or more. According to the protruding insulating layer having such a thickness, the electrical insulating property is remarkably increased, and a minute short circuit can be prevented to a higher degree. The thickness of the protruding insulating layer is usually 3 nm or more, preferably 5 nm or more, and particularly preferably 10 nm or more.

  In a preferred embodiment of the nonaqueous electrolyte secondary battery disclosed herein, the positive electrode current collector is made of aluminum or an aluminum alloy, and the negative electrode contains a carbon material as a negative electrode active material. In this case, since the micro short circuit which generate | occur | produces between aluminum / negative electrode carbon materials can be prevented, utility value is especially high.

  Since the non-aqueous electrolyte secondary battery disclosed herein is excellent in the prevention of micro short-circuiting and can exhibit good battery characteristics as described above, a non-aqueous electrolyte secondary battery (for example, lithium secondary battery) mounted on a vehicle is used. It is suitable as a secondary battery. For example, it can be suitably used as a power source for a motor (electric motor) of a vehicle such as an automobile in the form of an assembled battery in which a plurality of the nonaqueous electrolyte secondary batteries are connected in series. Therefore, according to the present invention, any non-aqueous electrolyte secondary battery disclosed herein can be a non-aqueous electrolyte secondary battery constructed using an electrode manufactured by any of the methods disclosed herein. ) Is provided.

It is a schematic diagram which shows an example of the structure of the lithium secondary battery which concerns on one Embodiment of this invention. It is a schematic diagram which shows the wound electrode body used for one Embodiment of this invention. It is a schematic diagram which shows a part of cross section of the wound electrode body used for one Embodiment of this invention. It is a figure which shows the manufacture flow of the electrode used for one Embodiment of this invention. It is sectional drawing which shows the manufacturing process of the electrode used for one Embodiment of this invention. It is sectional drawing which shows the manufacturing process of the electrode used for one Embodiment of this invention. It is sectional drawing which shows the manufacturing process of the electrode used for one Embodiment of this invention. It is sectional drawing which shows the manufacturing process of the electrode used for one Embodiment of this invention. It is sectional drawing which shows the manufacturing process of the electrode used for one Embodiment of this invention. It is a figure which shows the result of having analyzed the end height of the electrode by the response surface method. It is a figure for demonstrating the measuring method of contact resistance. It is a graph which shows the relationship between the film thickness of a protrusion insulating layer, and contact resistance. It is a figure which shows an example of the surface shape (film thickness profile) of an electrode active material layer. It is a graph which shows the relationship between a surface tension difference and an end height. It is a graph which shows the relationship between a viscosity and end height height. It is a side view of the vehicle carrying a nonaqueous electrolyte secondary battery. It is a schematic diagram which shows a part of cross section of the conventional winding electrode body.

  Embodiments according to the present invention will be described below with reference to the drawings. In the following drawings, members / parts having the same action are described with the same reference numerals. Note that the dimensional relationship (length, width, thickness, etc.) in each drawing does not reflect the actual dimensional relationship. Further, matters other than the matters specifically mentioned in the present specification and matters necessary for carrying out the present invention (for example, the configuration and manufacturing method of an electrode body including a positive electrode and a negative electrode, the configuration and manufacturing method of a separator and an electrolyte, General techniques related to battery construction, etc.) can be grasped as design matters of those skilled in the art based on conventional techniques in the field.

  Hereinafter, preferred embodiments of the present invention will be described. Note that matters other than matters specifically mentioned in the present specification and necessary for the implementation of the present invention can be grasped as design matters of those skilled in the art based on the prior art in this field. The present invention can be carried out based on the contents disclosed in this specification and common technical knowledge in the field. Further, in the following drawings, members / parts having the same action are described with the same reference numerals, and overlapping descriptions may be omitted or simplified.

  Although not intended to be particularly limited, a lithium secondary battery in a form in which a wound electrode body (winding electrode body) and a non-aqueous electrolyte are accommodated in a flat rectangular battery case will be described below. The invention will now be described in detail by way of example. A schematic configuration of a lithium secondary battery according to an embodiment of the present invention is shown in FIGS. As shown in FIG. 1, the lithium secondary battery 100 has a configuration in which a long positive electrode sheet 10 and a long negative electrode sheet 20 are wound flatly via long separators 40A and 40B. The electrode body (wound electrode body) 80 is configured to be housed in a battery case 50 having a shape (flat box shape) capable of housing the wound electrode body 80 together with a non-aqueous electrolyte (not shown).

≪Battery case≫
The battery case 50 includes a flat cuboid case main body 52 having an open upper end, and a lid 54 that closes the opening. As a material constituting the battery case 50, a metal material such as aluminum or steel is preferably used (in this embodiment, aluminum). Or the battery case 50 formed by shape | molding resin materials, such as a polyphenylene sulfide (PPS) and a polyimide resin, may be sufficient. On the upper surface (that is, the lid 54) of the battery case 50, a positive electrode terminal 70 that is electrically connected to the positive electrode 10 of the wound electrode body 80, and a negative electrode terminal 72 that is electrically connected to the negative electrode 20 of the electrode body 80 Is provided.

  Inside the battery case 50, a flat wound electrode body 80 is accommodated together with a non-aqueous electrolyte (not shown). The configuration of the wound electrode body 80 according to the present embodiment is the same as the wound electrode body of a normal lithium secondary battery except for the configuration of the positive electrode sheet 10 described later, and as shown in FIG. Before assembling the electrode body 80, it has a long (strip-shaped) sheet structure (sheet-like electrode body).

≪Positive electrode sheet≫
As shown in FIGS. 2 and 3, the positive electrode sheet 10 has a structure in which a positive electrode active material layer 14 including a positive electrode active material and a binder is held on the surface of a positive electrode current collector 12 made of a long metal foil. have. However, the positive electrode sheet 10 has a positive electrode current collector exposed portion 16 in which the positive electrode active material layer 14 is not formed on the surface of the positive electrode current collector 12. In this embodiment, the positive electrode active material layer 14 is not attached to at least one edge along the longitudinal direction of the positive electrode sheet 10, and the positive electrode current collector 12 is exposed with a certain width (band shape). An electric body exposed portion 16 is formed. In this embodiment, a positive electrode current collector exposed portion 16 is provided at substantially the same position on both sides at one edge (the left side edge portion in FIG. 2) along the longitudinal direction of the positive electrode current collector 12. As will be described later, the positive electrode current collector exposed portion 16 can be used as a portion (current collector) for electrically connecting the positive electrode sheet 10 to a positive electrode terminal 70 for external connection. FIG. 3 is a schematic cross-sectional view showing an enlarged part of a cross section obtained by cutting the wound electrode body 80 in the radial direction (stacking direction of the positive and negative electrode sheets and the separator).

  The positive electrode current collector exposed portion 16 is preferably provided at a position where both surfaces of the positive electrode current collector overlap (preferably, substantially the same position on both surfaces). From the viewpoint of the energy density of the lithium secondary battery and the like, one edge along the longitudinal direction of the positive electrode current collector is provided with a positive electrode current collector exposed portion at substantially the same position on both surfaces, and the longitudinal direction of the current collector The positive electrode sheet in a form in which a positive electrode active material layer is formed almost on both sides along the other edge (that is, a form in which an active material layer non-forming portion is provided only on one edge along the longitudinal direction) Can be preferably employed. In this embodiment, the positive electrode active material layer 14 is formed up to the end of the current collector 12 on both sides at the other edge along the longitudinal direction of the positive electrode current collector 12.

  In the wound electrode body using the positive electrode sheet, it is preferable that the positive electrode current collector exposed portion 16 is continuously formed to have a length extending over at least two rounds of the winding. In a preferred embodiment, the positive electrode current collector exposed portion is formed over the entire length of the positive electrode sheet. The width of the exposed portion of the positive electrode current collector can be appropriately set according to the shape of the electrode body, the connection structure of the current collector, and the like. Usually, a width of about 5 mm to 50 mm (for example, 10 mm to 30 mm) is appropriate.

≪Positive electrode current collector≫
As the positive electrode current collector, a sheet-like member made of a metal having good conductivity can be preferably used. In particular, it is preferable to use a positive electrode current collector made of aluminum (Al) or an alloy containing aluminum as a main component (aluminum alloy). The size of the positive electrode current collector is not particularly limited, and can be appropriately selected according to the shape of the target lithium secondary battery. For example, a metal foil having a thickness of about 5 μm to 30 μm can be preferably used as the positive electrode current collector. The width of the positive electrode current collector can be, for example, about 2 cm to 15 cm, and the length can be, for example, about 5 cm to 1000 cm.

≪Positive electrode active material≫
As the positive electrode active material, one type or two or more types of materials conventionally used in lithium secondary batteries can be used without any particular limitation. Preferred applications of the technology disclosed herein include lithium and transition metals such as lithium nickel oxide (eg, LiNiO ₂ ), lithium cobalt oxide (eg, LiCoO ₂ ), and lithium manganese oxide (eg, LiMn ₂ O ₄ ). And a positive electrode active material mainly containing an oxide (lithium transition metal oxide) containing the element as a constituent metal element. Among them, a positive electrode active material (typically, substantially a lithium nickel cobalt manganese composite oxide substantially composed of lithium nickel cobalt manganese composite oxide (for example, LiNi _1/3 Co _1/3 Mn _1/3 O ₂ ). Application to a positive electrode active material comprising: As such a lithium transition metal oxide (typically in particulate form), for example, a lithium transition metal oxide powder prepared by a conventionally known method can be used as it is. For example, lithium transition metal oxide powder substantially composed of secondary particles having an average particle diameter in the range of about 1 μm to 25 μm can be preferably used as the positive electrode active material.

≪Binder≫
In addition to the positive electrode active material, the positive electrode active material layer 14 can contain one or two or more materials that can be used as a constituent component of the positive electrode active material layer in a general lithium secondary battery, if necessary. Examples of such materials include various polymer materials that can function as a binder (binder) for the positive electrode active material. As the binder, a binder used for an electrode of a general lithium secondary battery and having an insulating property can be used. For example, when an aqueous solvent is used for the binder solution described later, a cellulose polymer such as carboxymethylcellulose (CMC) or hydroxypropylmethylcellulose (HPMC) (for example, polyvinyl alcohol (PVA) or polytetrafluoroethylene (PTFE)), tetra Fluorine resins such as fluoroethylene-hexafluoropropylene copolymer (FEP) (for example, vinyl acetate copolymer and styrene butadiene rubber (SBR)), rubbers such as acrylic acid-modified SBR resin (SBR latex); A water-soluble or water-dispersible polymer such as can be preferably used. In the binder solution using a non-aqueous solvent, a polymer such as polyvinylidene fluoride (PVDF) or polyvinylidene chloride (PVDC) can be preferably used.

  In addition, a conductive material is mentioned as a material which can be used as a component of a positive electrode active material layer. As the conductive material, carbon materials such as carbon powder and carbon fiber are preferably used. Alternatively, conductive metal powder such as nickel powder may be used.

≪Positive relationship between positive electrode sheet and negative electrode sheet≫
As shown in FIGS. 2 and 3, the positive electrode sheet 10 in the technology disclosed herein is formed so that the positive electrode current collector exposed portion 16 protrudes from one end portion along the longitudinal direction of the negative electrode sheet 20. The sheet 20 is overlapped. Furthermore, in this embodiment, the width b1 of the negative electrode active material layer 24 is slightly wider than the width a1 of the positive electrode active material layer 14. Then, the negative electrode active material layer 24 is arranged in a range extending to the positive electrode current collector exposed portion 16 side relative to the positive electrode active material layer 14 (that is, the positive electrode current collector exposed portion 16 side of the positive electrode active material layer 14). The positive electrode sheet 10 and the negative electrode sheet 20 are overlapped with each other so that the negative electrode active material layer 24 protrudes from the end of the negative electrode active material layer 24. In this way, the configuration in which the negative electrode active material layer 24 is arranged in a range that extends to the positive electrode current collector exposed portion 16 side than the positive electrode active material layer 14 moves from the positive electrode active material layer 14 to the negative electrode sheet 20 side during charging. It is advantageous to smoothly occlude Li ions that have been absorbed in the negative electrode active material. On the other hand, in such a configuration, a part of the negative electrode active material layer 24 is disposed so as to protrude from the positive electrode active material layer 14, so that the positive electrode current collector exposed portion 16 is connected to the negative electrode sheet 20 (negative electrode active material) via the separators 40A and 40B. The structure is opposite to the layer 24). Therefore, if a metallic foreign matter accumulates in the gap S between the positive electrode current collector exposed portion 16 and the negative electrode sheet 20, a minute short-circuit portion may be formed between the positive electrode sheet 10 and the negative electrode sheet 20.

≪Extruded insulation layer≫
In the nonaqueous electrolyte secondary battery according to the present embodiment, as a countermeasure against the above-described micro short-circuit problem, the protruding insulating layer 48 that protrudes from the end of the positive electrode active material layer 14 on the surface of the positive electrode current collector exposed portion 16. Is forming. The protruding insulating layer 48 is provided so as to cover at least a portion of the positive electrode current collector exposed portion 16 that faces the negative electrode active material layer 24 via at least the separators 40A and 40B. The width of the protruding insulating layer 48 may be larger than the width of the portion of the positive electrode current collector exposed portion 16 that faces the negative electrode active material layer 24, and is usually about 1 mm to 10 mm (for example, 1 mm to 5 mm). Is appropriate. Thus, when the part which has opposed the negative electrode active material layer 24 among the positive electrode electrical power collector exposure parts 16 is set as the structure covered with the protrusion insulating layer 48, when the metal foreign material accumulates in the clearance gap S In addition, the contact between the positive electrode current collector 12 and the metallic deposit caused by the foreign material and the foreign object is prevented by the protruding insulating layer 48, so that a minute amount is present between the positive electrode current collector 12 and the negative electrode sheet 20. An event in which a short circuit occurs can be highly prevented.
Further, in the present embodiment, as will be described later, the protruding insulating layer 48 is bonded to the portion of the positive electrode current collector 12 where the positive electrode active material layer 14 is formed and the positive electrode current collector exposed portion 16 adjacent to the portion. And a binder solution containing a solvent and applied and dried. Moreover, the positive electrode active material layer 14 apply | coats the paste-form composition containing a positive electrode active material and a solvent on the binder solution apply | coated to the site | part in which the positive electrode active material layer 14 is formed in the positive electrode collector 12. It is formed by drying. According to such a configuration, it is possible to form the positive electrode active material layer 14 and the protruding insulating layer 48 on the positive electrode current collector with high accuracy and at once, and effectively without causing a significant increase in the manufacturing process. The occurrence of a minute short circuit can be prevented.

≪ Thickness of protruding insulation layer ≫
The thickness of the protruding insulating layer 48 is preferably approximately 3 nm or more. In this way, by setting the thickness of the protruding insulating layer 48 to 3 nm or more, the insulating property of the protruding insulating layer 48 is remarkably enhanced, so that a minute short circuit can be prevented to a higher degree. On the other hand, the protruding insulating layer 48 that is too thick is less likely to cause an edge height phenomenon of the electrode in the manufacturing process described later, and the effect of suppressing the internal short circuit accompanying the increase in the thickness of the protruding insulating layer is slowed down. Absent. The thickness of the protruding insulating layer 48 is generally in the range of 3 nm to 200 nm, preferably 5 nm to 130 nm, and particularly preferably 60 nm to 120 nm.

  Next, a method for forming the positive electrode active material layer 14 and the protruding insulating layer 48 on the surface of the positive electrode current collector 12 will be described. In the technique disclosed here, as described above, the positive electrode active material layer 14 and the protruding insulating layer 48 can be formed on the surface of the positive electrode current collector 12 with high accuracy and in a lump. Therefore, this forming method manufactures an electrode having the electrode active material layer 14 containing the electrode active material and the binder on the surface of the electrode current collector 12 and the protruding insulating layer 48 protruding from the end of the electrode active material layer 14. It can also be grasped as a method to do. This electrode manufacturing method can be applied not only to the positive electrode but also to the negative electrode. As a preferred embodiment of the method for producing a nonaqueous electrolyte secondary battery electrode disclosed herein, a method for producing a positive electrode for a lithium secondary battery will be described in detail as an example. It is not intended to limit the application target of the present invention to such types of non-aqueous electrolyte secondary batteries and positive electrodes. As shown in FIG. 4, this electrode manufacturing method includes a binder solution layer forming step (step S10), a composition layer forming step (step S20), and a drying step (step S30).

  The binder solution layer forming step (step S10) is a step of forming a binder solution layer by applying a binder solution containing a binder and a solvent to the positive electrode current collector. In this embodiment, as shown in FIG. 5, first, a long sheet-like positive electrode current collector 12 is prepared. On the other hand, a binder solution containing the binder 32 and the solvent 33 is prepared. Then, as shown in FIG. 6, the binder solution is applied to the surface of the positive electrode current collector 12 while leaving one edge along the longitudinal direction of the current collector 12 in a strip shape. 5 and 6 are process schematic cross-sectional views showing an enlarged part of a cross section along the width direction intersecting the longitudinal direction of the long sheet-like positive electrode current collector 12.

  As described above, the binder 32 included in the binder solution layer 30 disclosed here is a binder used for forming the positive electrode active material layer 14 and also used for forming the protruding insulating layer 48. For example, it may be a polymer that functions as a binder in the positive electrode active material layer 14 and that has an insulating property in the protruding insulating layer 48. The binder solution layer 30 can be typically formed by applying a binder solution prepared by adding and mixing the binder 32 to an appropriate solvent 33 to the surface of the positive electrode current collector 12.

  The solvent which comprises the said binder solution can be suitably selected in consideration of the combination with the binder (polymer) material to be used. From various viewpoints such as reduction of environmental load, reduction of material cost, simplification of equipment, reduction of waste, improvement of handling property, use of an aqueous solvent is preferable. As the aqueous solvent, water or a mixed solvent mainly composed of water is preferably used. As a solvent component other than water constituting such a 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 80% by mass or more (more preferably 90% by mass or more, more preferably 95% by mass or more) of the aqueous solvent is water. A particularly preferred example is an aqueous solvent substantially consisting of water. The solvent constituting the binder solution is not limited to an aqueous solvent, and may be a solvent solvent (a binder dispersion medium is mainly an organic solvent). As the non-aqueous solvent, for example, N-methylpyrrolidone (NMP) can be used.

  The binder concentration in the binder solution is suitably about 5% by mass to 30% by mass, and preferably 6% by mass to 15% by mass (for example, 10% by mass). If the binder concentration is too smaller than the above range, the paste-like composition may be repelled on the binder solution layer 30 and may not be applied to a uniform thickness. On the other hand, when the binder concentration is too larger than the above range, the handling property of the binder solution (for example, the coating property when the binder solution is applied to the positive electrode current collector (particularly, the foil current collector)) decreases. May be easier.

  The operation of kneading (adding and mixing) the binder 32 and the solvent can be performed using, for example, an appropriate kneading apparatus (planetary mixer, homodisper, clear mix, fill mix, etc.). In particular, it is preferable to knead using a planetary mixer (preferably a biaxial planetary mixer). By using a planetary mixer, a binder solution in which the binder 32 is uniformly dispersed can be prepared.

  The operation of applying the binder solution to the surface of the positive electrode current collector 12 can be suitably performed using a conventionally known appropriate application device (rod coater, slit coater, die coater, comma coater, gravure coater, etc.). As a method of applying the binder solution on the positive electrode current collector 12 in the technology disclosed herein, there is a method of applying the binder solution on the positive electrode current collector 12 by a rod coater. Thereby, the binder solution layer 30 having a uniform thickness can be formed.

  After forming the binder solution layer 30 in this way, a composition layer forming step (step S20) is then performed. In the composition layer forming step, as shown in FIG. 7, a paste-like composition containing the positive electrode active material 36 and the solvent 37 is applied on the binder solution layer 30 to form (stack) the composition layer 34. It is. At that time, the upper composition layer 34 is applied to be narrower than the lower binder solution layer 30. Thereby, the composition layer 34 is formed such that a part of the binder solution layer 30 formed on the lower layer side of the composition layer 34 protrudes outward from the end portion of the composition layer 34. In this embodiment, the binder solution layer 30 protrudes from the end of the composition layer 34 in a band shape.

  The solvent 37 used in the paste composition may be the same as or different from the solvent 33 used in the binder solution. For example, the same solvent as the solvent 33 of the binder solution can be preferably used as the solvent 37 of the paste-like composition. Thus, by using the same solvent for the paste-like composition and the binder solution, the binder solution layer 30 and the composition layer 34 are easily mixed well in the subsequent drying step. Therefore, the positive electrode active material layer 14 in which the positive electrode active material 36 and the binder 32 are uniformly dispersed is obtained.

  In the preferred technique disclosed herein, the surface tension of the binder solution is made higher than that of the paste composition, and the surface tension difference between the paste composition and the binder solution is adjusted to 5 mN / m or less. That is, in the manufacturing method of this embodiment, before the binder solution layer 30 is sufficiently dried, the paste-like composition is supplied in layers to form the composition layer 34. That is, the state is called “wet on wet”. At this time, it is desirable that the binder solution layer 30 and the composition layer 34 maintain a two-layer state with a certain degree of stability when the paste-like composition is supplied in layers. From such a viewpoint, it is preferable that the surface tension of the binder solution layer 30 is higher than the surface tension of the paste-like composition supplied to be superimposed on the binder solution layer 30.

  In the manufacturing method of the present embodiment, the binder solution layer 30 is formed wider than the composition layer 34. Such a configuration is advantageous for simplifying the manufacturing process by collectively forming the positive electrode active material layer and the protruding insulating layer, while the end of the composition layer 34 is locally raised due to the influence of the surface tension, For this reason, an end height phenomenon in which the end portion of the positive electrode active material layer obtained after drying becomes thicker than the center portion is likely to occur. In contrast, by adjusting the surface tension of the binder solution to be higher than that of the paste-like composition and the difference in surface tension between the paste-like composition and the binder solution is 5 mN / m or less, as described above. Even if the binder solution layer 30 is formed wider than the composition layer 34, the edge height phenomenon can be appropriately prevented. Such a difference in surface tension is advantageous also in stably maintaining the two-layer state of the binder solution layer 30 and the composition layer 34. Particularly good results are obtained by setting the difference in surface tension between the binder solution and the paste-like composition to 3 mN / m or less (preferably 2 mN / m or less) and increasing the surface tension of the lower layer (binder solution layer). Can be realized.

  Moreover, in the technique disclosed here, it is desirable that the viscosity (2 rpm, 25 ° C., E-type viscometer) of the paste-like composition supplied to be superimposed on the binder solution layer 30 is 3000 mPa · sec or more. By setting the viscosity of the paste-like composition to 3000 mPa · sec or more, the end portion of the composition layer 34 is less likely to rise, so that the edge height phenomenon can be more effectively prevented. Such a viscosity range is also advantageous in that the coating property when the composition is applied is excellent. As a preferred example of the paste-like composition disclosed herein, the surface tension difference between the composition and the binder solution is 5 mN / m or less, and the viscosity is in the range of 5000 mPa · sec to 10000 mPa · sec, The difference in surface tension between the composition and the binder solution is 4 mN / m or less and the viscosity is in the range of 5000 mPa · sec to 10,000 mPa · sec, and the difference in surface tension between the composition and the binder solution is 3 mN / m or less. And those having a viscosity in the range of 5000 mPa · sec to 10000 mPa · sec. By having both the viscosity and the surface tension within such a predetermined range, the above-described edge height phenomenon can be effectively suppressed and a higher quality electrode can be suitably manufactured. For the surface tension of the binder solution and the paste-like composition, for example, a value measured using the Wilhelmy method (plate method) can be preferably used.

  Furthermore, in the technique disclosed herein, the thickness of the binder solution layer 30 is preferably 1.7 μm or less. This makes it possible to produce a high-quality electrode in which the edge height phenomenon is effectively suppressed regardless of the viscosity of the paste-like composition described above. FIG. 10 is a response surface analysis method for the height of the edge (the maximum thickness difference between the edge and the center of the electrode active material layer) when the thickness of the binder solution layer and the viscosity of the paste-like composition are used as parameters. It is written by. Here, the horizontal axis represents the thickness (μm) of the binder solution layer, and the vertical axis represents the viscosity (mPa · sec) of the paste-like composition. From FIG. 10, when the thickness of the binder solution layer is 1.7 μm or less, an end height of 0.5 μm or less can be realized regardless of the viscosity of the paste-like composition, and the end height phenomenon is effectively suppressed. You can see that

  The operation of applying the paste-like composition from above the binder solution layer 30 can be performed in the same manner as the operation of forming the binder solution layer 30 by applying the binder solution to the surface of the positive electrode current collector 12, and is conventionally known. It is possible to preferably carry out using a suitable coating apparatus (rod coater, slit coater, die coater, comma coater, gravure coater, etc.). The application amount of the paste-like composition is not particularly limited, and can be appropriately changed depending on the shape and application of the electrode and the battery.

  After the composition layer 34 is thus formed, a drying process (step S30) is then performed. In this drying step, as shown in FIGS. 8 and 9, the binder solution layer 30 and the composition layer 34 are simultaneously dried (at this time, even if an appropriate drying accelerating means (a heater or the like) is used if necessary. Good). At that time, in the portion where the binder solution layer 30 and the composition layer 34 overlap, the binder solution layer 30 and the composition layer 34 are mixed by convection during drying. Thus, the positive electrode active material layer 14 in which the binder 32 is appropriately present near the positive electrode current collector 12 and a part of the binder 32 is diffused widely (the positive electrode active material 36 and the binder 32 are uniformly dispersed). Can be obtained. On the other hand, in the portion 31 of the binder solution layer 30 that protrudes outward from the end portion of the composition layer 34, the composition layer 34 is not laminated on the upper layer side, so that the binder solution does not mix with the composition layer 34. Only layer 30 is dried alone. As a result, a protruding insulating layer 48 made only of the binder 32 can be formed.

  Although it does not specifically limit as said drying temperature, When a solvent is water, about room temperature-about 180 degreeC are suitable, for example, it is preferable to set it as 120 to 160 degreeC (for example, 150 degreeC). In this embodiment, since it is not necessary to consider the segregation (migration) of the binder 32 due to convection when setting the drying temperature, the drying temperature can be set higher as described above. After drying, the positive electrode active material layer 14 may be pressed as necessary. As a pressing method, a conventionally known roll pressing method, flat plate pressing method or the like can be employed. In this way, the positive electrode having the positive electrode active material layer 14 including the positive electrode active material 36 and the binder 32 on the surface of the positive electrode current collector 12 and the protruding insulating layer 48 protruding from the end of the positive electrode active material layer 14. 10 can be manufactured.

  According to the manufacturing method according to the present embodiment, since the positive electrode active material layer 14 and the protruding insulating layer 48 can be formed at a time, the manufacturing process can be simplified, which is advantageous in terms of cost. Furthermore, unlike the prior art, it is not necessary to position the positive electrode active material layer 14 and the insulating layer 48 with high accuracy, and the insulating layer 48 can be formed with high positional accuracy with respect to the positive electrode active material layer 14. Therefore, if such a positive electrode 10 is used, it is possible to construct a lithium secondary battery in which the occurrence of a minute short circuit is more appropriately prevented (and thus excellent in self-discharge prevention).

  In the above-described embodiment, the case where all of the binder used for forming the positive electrode active material layer 14 is included in the binder solution is exemplified, but the present invention is not limited thereto. For example, a part of the binder used for forming the positive electrode active material layer 14 may be included in the paste composition. By including a binder in the paste-like composition, the amount of the binder in the positive electrode active material layer 14 and the amount of the binder in the protruding insulating layer 48 can be accurately adjusted according to the purpose of use. For example, the amount of the binder used for forming the positive electrode active material layer 14 can be easily increased while keeping the amount of the binder in the protruding insulating layer 48 constant. This is advantageous in forming a highly durable electrode in which the positive electrode active material is prevented from slipping off.

≪Negative electrode sheet≫
Next, the negative electrode sheet 20 of the lithium secondary battery disclosed herein will be described with reference to FIGS. Similarly to the positive electrode sheet 10, the negative electrode sheet 20 has a structure in which a negative electrode active material layer 24 including a negative electrode active material and a binder is held on the surface of a foil-shaped negative electrode current collector 22 made of a long metal foil. Have. The negative electrode active material layer 24 is typically formed on the surfaces (both sides) of both sides of the negative electrode current collector 22, leaving at least one edge along the longitudinal direction of the negative electrode current collector 22 in a strip shape. Yes. In this embodiment, the negative electrode current collector exposure in which the negative electrode current collector 22 is exposed at a constant width without being attached to the edge (one side edge on the right side in FIG. 2) of the negative electrode sheet 20 in the width direction. A portion 26 is formed. The negative electrode current collector exposed portion 26 can be used as a portion (current collector) for electrically connecting the negative electrode sheet 20 to a negative electrode terminal 72 for external connection.

≪Negative electrode active material≫
As the negative electrode active material, one type or two or more types of materials conventionally used in lithium secondary batteries can be used without any particular limitation. As a suitable example, a particulate carbon material (carbon particles) including a graphite structure (layered structure) at least partially is mentioned. More specifically, so-called graphitic (graphite), non-graphitizable carbonaceous (hard carbon), graphitizable carbonaceous (soft carbon), and a combination of these, Various carbon materials can be used. For example, graphite particles such as natural graphite can be used. For the negative electrode active material layer 24, the same binder and conductive material as those used for the positive electrode active material layer 14 can be used.

≪Separator≫
As the separators 40A and 40B disposed between the positive and negative electrode sheets 10 and 20, various porous sheets similar to those of a general lithium secondary battery provided with a wound electrode body can be used. Preferable examples include porous resin sheets (films, nonwoven fabrics, etc.) made of polyolefin resins such as polyethylene (PE) and polypropylene (PP). Such a porous resin sheet may have a single layer structure, or may have a two or more layers structure (for example, a three-layer structure in which PE layers are laminated on both sides of a PP layer).

  In this example, as illustrated in FIG. 2, the width b1 of the negative electrode active material layer 24 is slightly wider than the width a1 of the positive electrode active material layer 14. Therefore, when the positive electrode sheet 10 and the negative electrode sheet 20 are overlapped, the position of the end of the negative electrode active material layer 24 slightly protrudes from the end of the positive electrode active material layer 14. The width of the negative electrode active material layer 24 protruding from the positive electrode active material layer 14 can be, for example, about 1 mm to 5 mm, and is about 1 mm in this embodiment. Furthermore, the widths c1 and c2 of the separators 40A and 40B are slightly wider than the width b1 of the negative electrode active material layer 24 (c1, c2> b1> a1).

≪Winded electrode body 80≫
When the positive and negative electrode sheets 10 and 20 are overlapped with the two separators 40A and 40B, as shown in FIGS. 2 and 3, the active material layers 14 and 24 are overlapped and the current collector exposed portion of the positive electrode sheet is overlapped. The positive and negative electrode sheets 10 and 20 are slightly shifted and overlapped so that 16 and the current collector exposed portion 26 of the negative electrode sheet are separately disposed at one end and the other end along the longitudinal direction. At that time, the positive electrode sheet 10 may be overlapped with the negative electrode sheet 20 so that the protruding insulating layer 48 protruding from the end of the positive electrode active material 14 faces the negative electrode active material layer 24 via the separators 40A and 40B. .

  In this state, the positive and negative electrode sheets 10 and 20 and the two separators 40A and 40B are wound, and then the obtained wound body is crushed from the side surface to be crushed, thereby obtaining a flat wound electrode body 80. It is done. In the wound electrode body 80, the current collector exposed portions 16 and 26 of the positive electrode sheet 10 and the negative electrode sheet 20 are respectively wound core portions (that is, the positive electrode sheet 10) in the transverse direction with respect to the winding direction of the wound electrode body 80. The positive electrode active material layer forming portion, the negative electrode active material layer forming portion of the negative electrode sheet 20, and the two separators 40A and 40B are closely wound around). A positive electrode current collector plate 74 and a negative electrode current collector plate 76 are respectively attached to the positive electrode side protruding portion (namely, the positive electrode current collector exposed portion) 16 and the negative electrode side protruding portion (namely, the negative electrode current collector exposed portion) 26. The positive electrode terminal 70 and the negative electrode terminal 72 are electrically connected to each other.

Then, the electrode body 80 to which the terminals 70 and 72 are connected is accommodated in the case main body 52, and an appropriate nonaqueous electrolyte is disposed (injected) therein. Such a nonaqueous electrolyte typically has a composition in which a supporting salt is contained in a suitable nonaqueous solvent. As said non-aqueous solvent, ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), diethyl carbonate (DEC), propylene carbonate (PC) etc. can be used, for example. Further, as the supporting salt, for _{example, LiPF 6, LiBF 4, LiAsF} 6, LiCF 3 can be preferably used a lithium salt of SO ₃ and the like. Thereafter, the opening is sealed by welding or the like with the lid 54, and the assembly of the lithium secondary battery 100 according to the present embodiment is completed. The sealing process of the case 50 and the process of placing (injecting) the electrolyte may be the same as those used in the production of a conventional lithium secondary battery, and do not characterize the present invention. In this way, the construction of the lithium secondary battery 100 according to this embodiment is completed.

<Test Example 1>
In this example, the following experiment was performed to confirm the relationship between the thickness of the protruding insulating layer and the electrical resistance. That is, a binder solution having a binder concentration of about 9% by mass was prepared by mixing SBR as a binder and water. This binder solution was applied to one side of a copper foil as the negative electrode current collector 22 and dried to prepare a test piece 90 provided with an insulating layer 48 protruding on one side of the copper foil 22. In this example, a total of four types of test pieces having different thicknesses (thicknesses) of the protruding insulating layers were produced. The film thickness of each sample is as shown in Table 1. Then, the contact resistance of the protruding insulating layer was measured using the apparatus shown in FIG. Specifically, another copper foil 22 is overlaid on the protruding insulation layer 48 of the test piece 90, sandwiched between a pair of voltage measurement terminals 96, and a load of 1 MPa / cm ² is applied from above and below the voltage measurement terminals. On the other hand, the resistance value was measured from the voltage change when the current was applied from the current application device 94. The electrical resistance value (measured resistance value × contact area) was calculated from the obtained measured resistance value R and the contact area between the voltage measurement terminal and the test piece. The results are shown in Table 1 and FIG.

  As is apparent from Table 1 and FIG. 12, when the thickness of the protruding insulating layer exceeds 3 nm, the value of the contact resistance is remarkably increased. From this result, it is appropriate that the film thickness of the protruding insulating layer generally exceeds 3 nm, preferably 4 nm or more, more preferably 5 nm or more, and particularly preferably 10 nm or more.

<Test Example 2>
In this example, the effect of the difference in surface tension between the binder solution layer and the composition layer on the surface smoothness (edge height) of the electrode is confirmed when the binder solution layer is formed wider than the composition layer. Therefore, the following experiment was conducted.

<Example 1>
SBR and water were mixed to prepare a binder solution having a binder concentration of about 48% by mass. When the surface tension of the binder solution was measured by a commercially available surface tension meter (plate method), it was about 47.2 mN / m. The binder solution layer 30 was formed by applying this binder solution to one side of a long sheet-like copper foil (negative electrode current collector) using a rod coater.
Further, natural graphite powder (negative electrode active material) having an average particle size of 10 μm and carboxymethyl cellulose (CMC, thickener) have a mass ratio of these materials of 98.3: 0.7 and a solid content of about A paste-like composition was prepared by mixing with water (solvent) so as to be 54% by mass. It was about 50.5 mN / m when the surface tension of this paste-like composition was measured with the commercially available surface tension meter (plate method). This paste-like composition was applied onto the binder solution layer 30 before the formed binder solution layer 30 was dried to form a composition layer 34. At that time, the composition layer 34 was applied so as to be narrower than the binder solution layer 30 and adjusted so that both end portions of the binder solution layer 30 protruded from the composition layer 34 by 3 mm each. By drying the coated material, a negative electrode sheet 20 in which the negative electrode active material layer 24 and the protruding insulating layer (layer made of SBR) 48 were provided on one surface of the negative electrode current collector 22 was obtained. In addition, about drying conditions, the drying temperature was performed on two conditions, 150 degreeC and room temperature (natural drying).

<Example 2>
A negative electrode sheet was produced in the same manner as in Example 1 except that the binder concentration of the binder solution was about 13% by mass and the surface tension was 51.9 mN / m.

<Example 3>
A negative electrode sheet was produced in the same manner as in Example 1 except that the binder concentration of the binder solution was about 11% by mass and the surface tension was 52.6 mN / m.

<Example 4>
A negative electrode sheet was produced in the same manner as in Example 1 except that the binder concentration of the binder solution was about 9% by mass and the surface tension was 53.3 mN / m.

<Example 5>
A negative electrode sheet was produced in the same manner as in Example 1 except that the binder concentration of the binder solution was about 7% by mass and the surface tension was 54.3 mN / m.

<Example 6>
A negative electrode sheet was produced in the same manner as in Example 1 except that the binder concentration of the binder solution was about 5% by mass and the surface tension was 55.7 mN / m.

  The surface shape (film thickness profile) of the negative electrode active material layers according to Examples 1 to 6 thus obtained was measured with a laser displacement meter manufactured by Lasertec. The film thickness profile result of Example 3 at a drying temperature of 150 ° C. is shown in FIG. The maximum thickness difference (electrode end height) H between the both ends and the center of the negative electrode active material layer in the film thickness profile was measured. The results are shown in Table 2 and FIG.

  As is clear from Table 2 and FIG. 14, in the negative electrode sheet according to Example 1 in which the surface tension of the upper composition layer was higher than that of the lower binder solution layer, the electrode end height exceeded 60 μm. It was. On the other hand, in the negative electrode sheet according to Examples 2 to 6 in which the surface tension of the upper composition layer was lower than that of the lower binder solution layer, the edge height phenomenon of the electrode was suppressed as compared with Example 1. It was. Moreover, from the comparison of Examples 2-6, the electrode end height tended to decrease as the difference in surface tension between the upper and lower layers decreased. In the case of the negative electrode sheet used here, an extremely small value of 10 μm or less could be realized by setting the surface tension difference between the upper and lower layers to 1.4 mN / m (Example 2). From this result, from the viewpoint of suppressing the edge height phenomenon associated with forming the binder solution layer wider than the composition layer, the surface tension of the composition layer is made lower than that of the binder solution layer, and The surface tension difference is suitably 5 mN / m or less, preferably 3 mN / m or less, and particularly preferably 2 mN / m or less.

<Test Example 3>
In this example, the following experiment was conducted in order to confirm the influence of the viscosity of the paste-like composition on the surface smoothness of the electrode (the height of the end height of the electrode).

<Example 7>
By mixing SBR and water to prepare a binder solution having a binder concentration of about 9% by mass, and applying this to one side of a long sheet-like copper foil (negative electrode current collector) using a rod coater A binder solution layer 30 was formed.
In addition, natural graphite powder (negative electrode active material) having an average particle size of 10 μm and carboxymethyl cellulose (CMC, thickener) have a mass ratio of these materials of 98.3: 0.7 and a solid concentration of about A paste-like composition was prepared by mixing with water (solvent) so as to be 54% by mass. The viscosity of the paste-like composition was measured using an E-type viscometer after adjusting the liquid temperature to 25 ° C. and rotating the rotor at 1 rpm, and it was 6150 mPa · sec. This paste-like composition was applied onto the binder solution layer 30 before the formed binder solution layer 30 was dried to form a composition layer 34. At that time, the composition layer 34 was applied so as to be narrower than the binder solution layer 30 and adjusted so that both end portions of the binder solution layer 30 protruded from the composition layer 34 by 3 mm each. By drying the coated material, a negative electrode sheet 20 in which the negative electrode active material layer 24 and the protruding insulating layer (layer made of SBR) 48 were provided on one surface of the negative electrode current collector 22 was obtained.

<Example 8>
A negative electrode sheet was produced in the same manner as in Example 7 except that the solid content concentration of the paste-like composition was about 53.5% by mass and the viscosity was 4250 mPa · sec.

<Example 9>
A negative electrode sheet was produced in the same manner as in Example 7 except that the solid content concentration of the paste-like composition was about 53.0% by mass and the viscosity was 1938 mPa · sec.

<Example 10>
A negative electrode sheet was produced in the same manner as in Example 7 except that the solid content concentration of the paste-like composition was about 52.5% by mass and the viscosity was 1250 mPa · sec.

  The surface shape (film thickness profile) of the negative electrode active material layers according to Examples 7 to 10 thus obtained was measured with a laser displacement meter manufactured by Lasertec. And the largest thickness difference (electrode edge height) of the edge part and center part of a negative electrode active material layer was measured. The results are shown in Table 3 and FIG.

  As apparent from Table 3 and FIG. 15, the height of the electrode end tended to decrease as the paste-like composition increased in viscosity. In the case of the negative electrode sheet used here, by setting the viscosity of the paste-like composition to 4000 mPa · sec or more, it was possible to form flat electrodes that did not cause edge height phenomenon (Examples 7 and 8). In order to suppress the edge height phenomenon associated with forming the binder solution layer wider than the composition layer, the viscosity of the paste-like composition is desirably 3000 mPa · sec or more (preferably 4000 mPa · sec or more). .

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

  As described above, the nonaqueous electrolyte secondary battery according to the present invention can highly prevent a minute short circuit, and thus can have high reliability and excellent battery performance. For example, even for high rate discharge of 5C or higher, or even 10C or higher, short circuit prevention can be improved while suppressing internal resistance. Taking advantage of this feature, the nonaqueous electrolyte secondary battery according to the present invention can be suitably used as a component of a power source for a motor (electric motor) mounted on a vehicle such as an automobile. Therefore, as schematically shown in FIG. 16, the present invention is formed by connecting any of the nonaqueous electrolyte secondary batteries 100 disclosed herein (a plurality of the nonaqueous electrolyte secondary batteries 100 connected in series). A vehicle (typically an automobile, particularly an automobile equipped with an electric motor such as a hybrid vehicle, an electric vehicle, or a fuel cell vehicle) 1 is provided.

DESCRIPTION OF SYMBOLS 10 Positive electrode sheet 12 Positive electrode collector 14 Positive electrode active material layer 16 Positive electrode collector exposed part 20 Negative electrode sheet 22 Negative electrode collector 24 Negative electrode active material layer 26 Negative electrode collector exposed part 30 Binder solution layer 32 Binder 33 Solvent 34 Composition Material layer 36 Positive electrode active material 37 Solvent 40A, 40B Separator 48 Extrusion insulation layer 50 Battery case 52 Case body 54 Lid 70 Positive electrode terminal 72 Negative electrode terminal 74 Positive electrode current collector plate 76 Negative electrode current collector plate 80 Winding electrode body 90 Test piece 94 Current application device 96 Voltage measurement terminal 100 Nonaqueous electrolyte secondary battery

Claims (9)

Method for producing an electrode for a nonaqueous electrolyte secondary battery in which an electrode active material layer containing an electrode active material and a binder on the surface of an electrode current collector and a protruding insulating layer protruding from an end of the electrode active material layer are formed Because:
Applying a binder solution containing a binder and a solvent to the electrode current collector to form a binder solution layer;
A step of applying a paste-like composition containing an electrode active material and a solvent on the binder solution layer to form a composition layer, wherein the composition layer is formed on the lower layer side of the composition layer A part of the binder solution layer is formed so as to protrude outward from an end of the composition layer; and
The binder solution layer and the composition layer are dried together to form the electrode active material layer, and the portion of the binder solution layer that protrudes outward from the end of the composition layer is dried to form the electrode active material layer. Forming a protruding insulating layer;
A method for producing an electrode, comprising: The surface tension of the binder solution is made higher than that of the paste composition, and the surface tension difference between the paste composition and the binder solution is adjusted to 5 mN / m or less. Electrode manufacturing method.   The electrode manufacturing method of Claim 2 whose viscosity of the said paste-form composition is 3000 mPa * sec or more.   The electrode manufacturing method according to claim 2, wherein the binder solution layer has a thickness of 1.7 μm or less. A method for producing a nonaqueous electrolyte secondary battery, comprising:
A method for producing a nonaqueous electrolyte secondary battery, wherein an electrode produced by the production method according to claim 1 is used as an electrode. An electrode body in which a positive electrode having a positive electrode active material layer containing a positive electrode active material and a binder on the surface of the positive electrode current collector and a negative electrode having a negative electrode active material layer on the surface of the negative electrode current collector are stacked with a separator interposed therebetween. A non-aqueous electrolyte secondary battery comprising:
The positive electrode has a positive electrode current collector exposed portion in which the positive electrode active material layer is not formed on the surface of the positive electrode current collector,
The positive electrode current collector exposed portion has a portion facing the negative electrode through the separator,
Of the positive electrode current collector exposed portion, at least a portion facing the negative electrode through the separator is formed with a protruding insulating layer protruding from an end portion of the positive electrode active material layer,
Here, the protruding insulating layer includes a binder solution containing the binder and a solvent at a portion where the positive electrode active material layer is formed in the positive electrode current collector and the exposed portion of the positive electrode current collector adjacent to the portion. A non-aqueous electrolyte secondary battery, which is formed by applying and drying.   The positive electrode active material layer is formed by applying a paste-like composition containing the positive electrode active material and a solvent onto a binder solution applied to the positive electrode current collector where the positive electrode active material layer is formed. The nonaqueous electrolyte secondary battery according to claim 6, which is formed as described above.   The nonaqueous electrolyte secondary battery according to claim 6 or 7, wherein the protruding insulating layer has a thickness of 3 nm or more. The positive electrode current collector is made of aluminum or an aluminum alloy,
The non-aqueous electrolyte secondary battery according to claim 6, wherein the negative electrode contains a carbon material as a negative electrode active material.

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