JP2014154295A - Secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a secondary battery in which elution of metal at an edge of a cathode active material layer hardly occurs.SOLUTION: A secondary battery 100 provided by the present invention comprises a wound electrode body formed by winding, in layers, a cathode sheet, an anode sheet 240 provided with an anode active material layer 243 on both surfaces of a long anode collector 241, and a separator interposed between the cathode sheet and the anode sheet 240. The anode active material layer 243 is formed so that an uncoated part 242 is provided at one edge in a width direction orthogonal to the longitudinal direction of the anode collector 241, and the uncoated part 242 is substantially not provided at the other edge. At an edge 245 of the anode active material layer 243, on which side the uncoated part 242 is not formed, is selectively formed a fibrillation thickener-containing area R including a fibrillated thickener 312a.

Description

  The present invention relates to a secondary battery. Specifically, a positive electrode sheet having a positive electrode active material layer on both sides of a long positive electrode current collector, a negative electrode sheet having a negative electrode active material layer on both sides of a long negative electrode current collector, the positive electrode sheet, and the negative electrode sheet The present invention relates to a secondary battery including a wound electrode body wound with a separator interposed therebetween.

2. Description of the Related Art In recent years, secondary batteries such as lithium secondary batteries (for example, lithium ion batteries) and nickel metal hydride batteries are preferably used as power sources for mounting on vehicles or personal computers and portable terminals. In particular, since lithium secondary batteries are lightweight and have a high energy density, their importance as a high output power source for mounting on a vehicle or a power source for a power storage system is increasing.
As one of this type of battery, a battery structure including a wound electrode body in which a long positive electrode sheet and a negative electrode sheet are stacked via a separator and wound in a spiral shape is known. By making the electrode body spiral, the reaction area of the positive and negative electrodes can be increased, thereby increasing the energy density and enabling high output.

  In this wound electrode body, the positive electrode sheet and the negative electrode sheet are generally activated by supplying a composition for forming an active material layer (for example, prepared in a paste form or a slurry form) on both sides of the current collector. It is produced by forming a material layer. Further, for example, in the case of high output use such as for vehicle mounting, the active material is formed on both surfaces of one edge portion in the width direction orthogonal to the longitudinal direction of these electrode sheets (that is, the positive electrode sheet and / or the negative electrode sheet). An uncoated portion where no layer is formed is provided in a strip shape to increase the current collection efficiency and used as a current collection portion. And when constructing a wound electrode body using the above electrode sheet, the uncoated part of the positive electrode sheet and the uncoated part of the negative electrode sheet are protruded to the opposite side in the width direction. Uncoated portions are alternately arranged and wound (for example, Patent Document 1).

JP 2012-084346 A

  In Patent Document 1, the negative electrode active material layer is provided with an uncoated portion on one edge in the width direction orthogonal to the longitudinal direction of the negative electrode current collector, and substantially uncoated on the other edge. It is formed so that no part is provided. In addition, the positive electrode active material layer is provided with an uncoated portion at one edge in the width direction orthogonal to the longitudinal direction of the positive electrode current collector, and substantially the other edge, as with the negative electrode active material layer. Is formed so that an uncoated portion is not provided. The negative electrode current collector and the positive electrode current collector are arranged and wound so that the uncoated portions of the negative electrode current protrude from the opposite side in the width direction. About this form, this inventor discovered the phenomenon in which the metal (for example, transition metal) contained in a positive electrode active material layer locally elutes at the edge of a positive electrode active material layer. The phenomenon that the metal is locally eluted at the edge of the positive electrode active material layer tends to occur when it is stored for a long time in a high temperature environment after full charge. In order to stabilize the performance of the secondary battery, it is desired to minimize the local elution of metal at the edge of the positive electrode active material layer. The present invention aims to solve the above problems.

  The secondary battery proposed here includes a positive electrode sheet having a positive electrode active material layer on a long positive electrode current collector, a negative electrode sheet having negative electrode active material layers on both sides of the long negative electrode current collector, It is a secondary battery provided with a wound electrode body wound by overlapping and winding a separator interposed between a positive electrode sheet and the negative electrode sheet. The negative electrode active material layer is provided with an uncoated portion at one edge in the width direction orthogonal to the longitudinal direction of the negative electrode current collector, and a substantially uncoated portion is provided at the other edge. It is formed so that it is not possible. A fibrillated thickener-containing region containing a fibrillated thickener is selectively formed at the edge of the negative electrode active material layer on the side where the uncoated portion is not formed. According to this configuration, charge carriers (lithium ions in the case of a lithium ion secondary battery) are unlikely to diffuse into the edge of the negative electrode active material layer on the side where the uncoated part is not formed. Therefore, metal elution at the edge of the positive electrode active material layer close to the edge can be suppressed.

  In a preferred embodiment of the secondary battery disclosed herein, the fibrillated thickener constitutes a mass aggregate in which cellulose fibers having a fiber length of 1 μm to 10 μm are aggregated, and the outer surface of the aggregate Fibril fibers protrude from the part. Cellulosic fibers having a fiber length of 1 μm to 10 μm are preferable in that they can be easily fibrillated.

  In a preferred embodiment of the secondary battery disclosed herein, the average fiber diameter of the fibril fibers protruding from the outer surface of the aggregate is 0.3 μm to 1.0 μm. When the average fiber diameter of the fibril fibers is within the above range, a suitable fibrillated thickener-containing region free from pinholes and aggregates (dama) can be formed.

  In a preferred embodiment of the secondary battery disclosed herein, the positive electrode active material layer is provided on the entire surface of the positive electrode current collector excluding an uncoated portion provided in a strip shape at one edge in the longitudinal direction. It has been. And the width of the negative electrode active material layer is wider than the width of the positive electrode active material layer, the negative electrode active material layer covers the positive electrode active material layer, and the negative electrode current collector and the positive electrode current collector Is arranged and wound so that the uncoated portions of each other protrude on the opposite side in the width direction. The metal elution in the positive electrode active material layer is noticeable when the wound electrode body having the above-described form is used. However, according to the present invention, since the fibrillated thickener-containing region is provided at the edge of the negative electrode active material layer on the side where the uncoated part is not formed, the charge carrier is unlikely to diffuse to the edge. Therefore, the elution of the metal at the edge of the positive electrode active material layer close to the edge can be reliably suppressed.

  In a preferred embodiment of the secondary battery disclosed herein, the negative electrode active material layer is opposed to the positive electrode active material layer in the fibrillated thickener-containing region containing the fibrillated thickener. And a portion not facing the positive electrode active material layer. And the width | variety of the site | part facing the said positive electrode active material layer is 1 mm or more and 3 mm or less. By setting the fibrillated thickener-containing region in the above range, elution of metal at the edge of the positive electrode active material layer can be appropriately avoided without sacrificing battery performance (for example, output characteristics).

FIG. 1 is a diagram illustrating an example of the structure of a lithium ion secondary battery. FIG. 2 is a view showing a wound electrode body of a lithium ion secondary battery. 3 is a cross-sectional view showing a III-III cross section in FIG. 2. FIG. 4 is a cross-sectional view showing a laminated structure of a positive electrode sheet and a negative electrode sheet of a wound electrode body in a lithium ion secondary battery according to an embodiment of the present invention. FIG. 5 is a schematic view showing a cross section of a negative electrode sheet according to an embodiment of the present invention. FIG. 6 is a diagram schematically showing a fibrillated thickener. FIG. 7 is a cross-sectional view showing a laminated structure of a positive electrode sheet and a negative electrode sheet of a wound electrode body in a lithium ion secondary battery according to an embodiment of the present invention. FIG. 8 is a diagram illustrating an example of a coating pattern. FIG. 9 is a diagram schematically showing a cross section perpendicular to the winding axis of the wound electrode body. FIG. 10 is a diagram showing a vehicle equipped with a secondary battery.

  Hereinafter, a secondary battery according to an embodiment of the present invention will be described with reference to the drawings. Here, a secondary battery will be described by taking a lithium ion secondary battery as an example. In addition, the same code | symbol is attached | subjected suitably to the member and site | part which show | play the same effect | action. Moreover, each drawing is drawn typically and does not necessarily reflect the real thing. Each drawing shows only an example, and each drawing does not limit the present invention unless otherwise specified.

  In the present specification, the “secondary battery” generally refers to a battery that can be repeatedly charged, and includes so-called storage batteries such as lithium secondary batteries (typically lithium ion secondary batteries) and nickel metal hydride batteries. Further, in the present specification, the “lithium ion secondary battery” refers to a secondary battery that uses lithium ions as a charge carrier and is charged / discharged by movement of charges accompanying the lithium ions between the positive and negative electrodes.

  FIG. 1 shows a lithium ion secondary battery 100. As shown in FIG. 1, the lithium ion secondary battery 100 includes a wound electrode body 200 and a battery case 300. FIG. 2 is a view showing a wound electrode body 200. FIG. 3 shows a III-III cross section in FIG.

  A lithium ion secondary battery 100 according to an embodiment of the present invention is configured in a flat rectangular battery case (that is, an exterior container) 300 as shown in FIG. As shown in FIG. 2, in the lithium ion secondary battery 100, a flat wound electrode body 200 is housed in a battery case 300 together with a liquid electrolyte (electrolytic solution) (not shown).

≪Battery case 300≫
The battery case 300 has a box-shaped (that is, bottomed rectangular parallelepiped) case main body 320 having an opening at one end (corresponding to the upper end in a normal use state of the battery 100), and is attached to the opening. It is comprised from the sealing board (lid body) 340 which consists of a rectangular-shaped plate member which block | closes an opening part.

  The material of the battery case 300 may be the same as that used in the conventional sealed battery, and there is no particular limitation. A battery case 300 mainly composed of a lightweight metal material having good thermal conductivity is preferable. Examples of such a metal material include aluminum, stainless steel, nickel-plated steel, and the like. The battery case 300 (the case main body 320 and the sealing plate 340) according to the present embodiment is made of aluminum or an alloy mainly composed of aluminum.

  As shown in FIG. 1, a positive electrode terminal 420 and a negative electrode terminal 440 for external connection are formed on the sealing plate 340. Between the two terminals 420 and 440 of the sealing plate 340, a thin-walled safety valve 360 configured to release the internal pressure of the battery case 300 when the internal pressure of the battery case 300 rises to a predetermined level or more, and a liquid injection port 350 are formed. Has been. In FIG. 1, the liquid injection port 350 is sealed with a sealing material 352 after liquid injection.

≪Winded electrode body 200 (electrode body) ≫
As shown in FIG. 2, the wound electrode body 200 includes a long sheet-like positive electrode (positive electrode sheet 220) and a long sheet-like negative electrode (negative electrode sheet 240) similar to the positive electrode sheet 220 in total of two sheets. Long sheet separators (separators 262 and 264).

≪Positive electrode sheet 220≫
The positive electrode sheet 220 includes a strip-shaped positive electrode current collector 221 and a positive electrode active material layer 223. For the positive electrode current collector 221, for example, a metal foil suitable for the positive electrode can be suitably used. In this embodiment, a strip-shaped aluminum foil having a thickness of about 15 μm is used as the positive electrode current collector 221. The positive electrode sheet 220 has an uncoated portion where the positive electrode current collector 221 is exposed without forming the positive electrode active material layer 223 at one end in the width direction orthogonal to the longitudinal direction of the positive electrode current collector 221. 222 is provided. Further, a positive electrode active material layer 223 is formed on the other end so that the uncoated portion 222 is not substantially provided. In the illustrated example, the positive electrode active material layer 223 is held on both surfaces of the positive electrode current collector 221 except for the uncoated portion 222 set on the positive electrode current collector 221. The positive electrode active material layer 223 contains a positive electrode active material, a conductive material, and a binder.

As the positive electrode active material, a material used as a positive electrode active material of a lithium ion secondary battery can be used. Examples of positive electrode active materials include LiNiCoMnO ₂ (lithium nickel cobalt manganese composite oxide), LiNiO ₂ (lithium nickelate), LiCoO ₂ (lithium cobaltate), LiMn ₂ O ₄ (lithium manganate), LiFePO ₄ ( Lithium transition metal oxides such as lithium iron phosphate). Here, LiMn ₂ O ₄ has, for example, a spinel structure. LiNiO ₂ and LiCoO ₂ have a layered rock salt structure. LiFePO ₄ has, for example, an olivine structure. LiFePO ₄ having an olivine structure includes, for example, nanometer order particles. Moreover, LiFePO _{4 having} an olivine structure can be further covered with a carbon film.

  For example, carbon black such as acetylene black (AB) and ketjen black and other powdery carbon materials (such as graphite) can be mixed with the positive electrode active material. In addition to the positive electrode active material and the conductive material, a binder such as polyvinylidene fluoride (PVDF) or styrene butadiene rubber (SBR) can be added. A positive electrode mixture (paste) can be prepared by dispersing these in a suitable dispersion medium and kneading. The positive electrode active material layer 223 is formed by applying this positive electrode mixture to the positive electrode current collector 221, drying it, and pressing it to a predetermined thickness.

<< Negative Electrode Sheet 240 >>
As shown in FIG. 2, the negative electrode sheet 240 includes a strip-shaped negative electrode current collector 241 and a negative electrode active material layer 243. For the negative electrode current collector 241, for example, a metal foil suitable for the negative electrode can be suitably used. In this embodiment, a strip-shaped copper foil having a thickness of about 10 μm is used for the negative electrode current collector 241. The negative electrode sheet 240 has an uncoated portion in which the negative electrode current collector 241 is exposed without forming the negative electrode active material layer 243 at one end in the width direction orthogonal to the longitudinal direction of the negative electrode current collector 241. 242 is provided. Further, a negative electrode active material layer 243 is formed so that the other end portion is not substantially provided with the uncoated portion 242. The negative electrode active material layer 243 is held on both surfaces of the negative electrode current collector 241 except for the uncoated portion 242 set on the negative electrode current collector 241. The negative electrode active material layer 243 contains a negative electrode active material, a thickener, a binder, and the like.

  Here, “substantially no uncoated portion is provided” means that the uncoated portions 222 and 243 are intentionally not provided. Therefore, for example, even though the uncoated portions 222 and 243 are not provided, the current collectors 221 and 241 are expanded due to some unintended factor thereafter, or the active material layers 223 and 243 are contracted. Then, the case where the uncoated portions 222 and 243 are microscopically generated can be included in the “substantially no uncoated portion is provided” here.

  As the negative electrode active material, one type or two or more types of materials conventionally used in lithium ion secondary batteries can be used without any particular limitation. Preferable examples include carbon-based materials such as graphite carbon and amorphous carbon, lithium transition metal oxides, and lithium transition metal nitrides.

  In addition to the negative electrode active material, a binder such as polyvinylidene fluoride (PVDF) or styrene butadiene rubber (SBR) can be added. Furthermore, in addition to the negative electrode active material and the binder, a thickener such as carboxymethyl cellulose (CMC), polyvinyl alcohol (PVA), ethylene-vinyl alcohol copolymer (EVOH) can be added. The thickener contained in the negative electrode active material layer 243 will be described in detail later. And like a positive electrode, a negative electrode mixture (paste) can be prepared by disperse | distributing and knead | mixing these negative electrode active material layer structural components in a suitable dispersion medium. The negative electrode active material layer 243 is formed by applying this negative electrode mixture to the negative electrode current collector 241, drying it, and pressing it to a predetermined thickness.

<< Separators 262, 264 >>
The separators 262 and 264 are members that separate the positive electrode sheet 220 and the negative electrode sheet 240 as shown in FIGS. 2 and 3. In this example, the separators 262 and 264 are made of a strip-shaped sheet material having a predetermined width and having a plurality of minute holes. As the separators 262 and 264, for example, a single layer structure separator or a multilayer structure separator made of a porous polyolefin resin can be used. You may form the porous layer of the particle | grains which have insulation on the surface of the porous sheet material comprised with resin. Here, the insulating particles may be composed of an insulating inorganic filler (for example, a filler such as a metal oxide (for example, alumina) or a metal hydroxide). In this example, as shown in FIGS. 2 and 3, the width b1 of the negative electrode active material layer 243 is slightly wider than the width a1 of the positive electrode active material layer 223. Furthermore, the widths c1 and c2 of the separators 262 and 264 are slightly wider than the width b1 of the negative electrode active material layer 243 (c1, c2>b1> a1).

≪Winded electrode body 200≫
The wound electrode body 200 is an electrode body in which the positive electrode sheet 220 and the negative electrode sheet 240 are overlapped and wound while the separators 262 and 264 are interposed between the positive electrode active material layer 223 and the negative electrode active material layer 243. is there. In this embodiment, as shown in FIGS. 2 and 3, the positive electrode sheet 220, the negative electrode sheet 240, and the separators 262 and 264 are aligned in the length direction, and the positive electrode sheet 220, the separator 262, the negative electrode sheet 240, and the separator 264 are aligned. They are stacked in order. In this embodiment, although the separators 262 and 264 are interposed, the negative electrode active material layer 243 is overlaid so as to cover the positive electrode active material layer 223. Further, the negative electrode current collector 241 and the positive electrode current collector 221 are configured such that the uncoated portions 242 and 222 of the negative electrode current collector 241 and the positive electrode current collector 221 protrude to the opposite side in the width direction of the wound electrode body 200. , Are piled up. The stacked sheet material (for example, the positive electrode sheet 220) is wound around a winding axis set in the width direction.

The wound electrode body 200 is attached to electrode terminals 420 and 440 attached to the battery case 300 (in this example, the lid body 340). The wound electrode body 200 is housed in the battery case 300 in a state of being flatly pushed and bent in one direction orthogonal to the winding axis. In the wound electrode body 200, the uncoated part 222 of the positive electrode sheet 220 and the uncoated part 242 of the negative electrode sheet 240 protrude on the opposite sides in the width direction of the separators 262 and 264. Among these, one electrode terminal 420 is fixed to the uncoated part 222 of the positive electrode current collector 221, and the other electrode terminal 440 is fixed to the uncoated part 242 of the negative electrode current collector 241. .
The wound electrode body 200 is accommodated in the flat internal space of the case body 320. The case body 320 is closed by the lid 340 after the wound electrode body 200 is accommodated.

≪Electrolyte (nonaqueous electrolyte) ≫
As the electrolytic solution (non-aqueous electrolytic solution), the same non-aqueous electrolytic solution conventionally used for lithium ion secondary batteries can be used without any particular limitation. Such a nonaqueous 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 ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, 1,2-dimethoxyethane, 1,2-diethoxyethane, tetrahydrofuran, 1,3-dioxolane, and the like. One kind or two or more kinds selected from the group can be used. Examples of the supporting salt include LiPF ₆ , LiBF 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 and the} like. Lithium salts can be used. As an example, a nonaqueous electrolytic solution in which LiPF ₆ is contained in a mixed solvent of ethylene carbonate and diethyl carbonate (for example, a mass ratio of 1: 1) at a concentration of about 1 mol / L can be given.

  Hereinafter, the negative electrode active material layer 243 of the lithium ion secondary battery 100 will be described in more detail. FIG. 4 schematically shows a cross section of the negative electrode sheet 240, the separator 262, and the positive electrode sheet 220 that are overlapped in the wound electrode body 200, cut in the width direction (for example, the width direction of the positive electrode sheet 220). In the lithium ion secondary battery 100 described above, as shown in FIG. 4, the negative electrode active material layer 243 is provided with an uncoated portion 242 at one edge in the width direction orthogonal to the longitudinal direction of the negative electrode current collector 241. And the other edge part is formed so that the uncoated part 242 may not be provided substantially. The positive electrode active material layer 223 is provided with an uncoated portion 222 on one edge in the width direction orthogonal to the longitudinal direction of the positive electrode current collector 221 and substantially uncoated on the other edge. The portion 222 is formed so as not to be provided. The negative electrode current collector 241 and the positive electrode current collector 221 are arranged and wound so that the uncoated parts 242 and 222 protrude to the opposite side in the width direction.

  The inventor of the present invention uses the edge 225 of the positive electrode active material layer 223 near the edge 245 of the negative electrode active material layer 243 on the side where the uncoated part 242 is not formed. An event was found in which a metal (for example, a transition metal) contained in the positive electrode active material layer 223 was locally eluted. The phenomenon that metal is locally eluted at the edge 225 of the positive electrode active material layer 223 tends to occur when the metal is stored for a long time in a high temperature environment after full charge. In order to stabilize the performance of the lithium ion secondary battery 100, it is desirable to suppress the metal from being locally eluted at the edge portion 225 of the positive electrode active material layer 223 as much as possible.

  The present inventor diligently studied the phenomenon of metal elution at the edge 225 of the positive electrode active material layer 223, and obtained the following inference. That is, according to the inventor's inference, the lithium ion secondary battery 100 releases lithium ions from the positive electrode active material layer 223 into the electrolyte during charging. At this time, in the negative electrode, lithium ions in the electrolytic solution enter the negative electrode active material layer 243 and are occluded in the negative electrode active material layer 243.

  At that time, of the positive electrode active material layers 223 a and 223 b provided on both surfaces of the positive electrode current collector 221, the inner peripheral side with respect to the positive electrode current collector 221 (the inner peripheral side of the positive electrode current collector 221 in the wound electrode body) The positive electrode active material layer 223a provided on the surface facing the negative electrode active material layer 243a provided on the surface facing the outer peripheral side of the negative electrode current collector 241 with the separator 262 interposed therebetween. Lithium ions are transferred to and from the material layer 243a. On the other hand, the positive electrode active material layer 223b provided on the outer peripheral side (the surface facing the outer peripheral side of the positive electrode current collector 221 in the wound electrode body) with respect to the positive electrode current collector 221 is interposed via the separator 264 (FIG. 2). The negative electrode current collector 241 is disposed so as to face the negative electrode active material layer 243b provided on the surface facing the inner peripheral side, and lithium ions are transferred to and from the negative electrode active material layer 243b. That is, lithium ions released from the positive electrode active material layer 223a on the inner peripheral side of the positive electrode current collector 221 have priority over the negative electrode active material layer 243a on the outer peripheral side of the negative electrode current collector 241 from a close distance. The negative electrode active material layer 243b on the inner peripheral side of the negative electrode current collector 241 does not easily move.

  However, in the above-described lithium ion secondary battery, the negative electrode active material layer 243 is provided with an uncoated portion 242 at one edge in the width direction orthogonal to the longitudinal direction of the negative electrode current collector 241 and the other edge. The part is formed so that the uncoated part 242 is not substantially provided. The positive electrode active material layer 223 is provided with an uncoated portion 222 on one edge in the width direction orthogonal to the longitudinal direction of the positive electrode current collector 221 and substantially uncoated on the other edge. The portion 222 is formed so as not to be provided. The negative electrode current collector 241 and the positive electrode current collector 221 are arranged and wound so that the uncoated parts 242 and 222 protrude to the opposite side in the width direction.

  In this case, the negative electrode current collector 241 does not exist at the edge 245 of the negative electrode active material layer 243 on the side where the uncoated portion 242 is not formed, and the negative electrode active material on the inner peripheral side of the negative electrode current collector 241 is present. The material layer 243b is exposed to the positive electrode active material layer 223a on the inner peripheral side of the positive electrode current collector 221. For this reason, as charging progresses, lithium ions released from the positive electrode active material layer 223a on the inner peripheral side of the positive electrode current collector 221 are not limited to the negative electrode active material layer 243a on the outer peripheral side of the negative electrode current collector 241. (Refer to the arrow 90), the negative electrode active material layer 243b on the inner peripheral side of the negative electrode current collector 241 also moves (see the arrow 92). At this time, at the edge 225 of the positive electrode active material layer 223 that is close to the edge 245 of the negative electrode active material layer 243 on the side where the uncoated part 242 is not formed, the amount of lithium ions released during charging is in other parts. There may be a tendency to increase compared to. For this reason, it is considered that the potential may locally increase at the edge 225 of the positive electrode active material layer 223. As described above, when the potential of the edge 225 of the positive electrode active material layer 223 is significantly increased locally and stored in a high temperature environment for a long time (for example, 100 days), the metal ( For example, it may cause elution of transition metals).

  The present inventor thus considers one of the causes of the dissolution of the metal contained in the edge 225 of the positive electrode active material layer 223 when stored in a high temperature environment for a long time in a state close to full charge. ing. The present inventor believes that such metal elution should be reduced as much as possible in order to keep the performance of the lithium ion secondary battery 100 high. For this reason, the lithium ion secondary battery 100 proposes a novel structure in which the metal contained in the edge portion 225 of the positive electrode active material layer 223 is difficult to elute.

≪Fibrylated thickener≫
In the lithium ion secondary battery 100 disclosed herein, as shown in FIG. 5, the negative electrode active material layer 243 has an uncoated portion on one edge in the width direction orthogonal to the longitudinal direction of the negative electrode current collector 241. 242 is provided, and the other edge portion is formed so that the uncoated portion 242 is not substantially provided. The negative electrode active material layer 243 includes a negative electrode active material 310, a thickener 312, and a binder 314. A fibrillated thickener-containing region R containing a fibrillated thickener 312a is selectively (partially) on the edge 245 of the negative electrode active material layer 243 on the side where the uncoated portion 242 is not formed. Formed). In other words, in the negative electrode active material layer 243, the thickener 312a included in the fibrillated thickener-containing region R of the edge 245 on the side where the uncoated portion 242 is not formed is fibrillated. Thus, the thickener 312b included in the other region is not fibrillated.

  Such a thickener is not particularly limited as long as it is a fibrous polymer that functions as a thickener for a negative electrode mixture and can be fibrillated. For example, cellulose polymer fibers such as carboxymethylcellulose (CMC), methylcellulose (MC), hydroxypropylmethylcellulose (HPMC), and hydroxyethylmethylcellulose (HEMC) can be preferably used. Alternatively, polymer fibers such as polyvinyl alcohol (PVA) and ethylene-vinyl alcohol copolymer (EVOH) may be used. The polymer fibers described above can be used alone or in appropriate combination.

  As a suitable example of the fibrillated thickener disclosed herein, as shown in FIG. 6, it constitutes a mass aggregate (base part) 316 in which cellulose fibers having a fiber length of 1 μm to 10 μm are aggregated, An example is one in which fibril fibers 318 protrude from the outer surface of the aggregate 316. The average fiber diameter d of the fibril fibers 318 protruding from the outer surface of the aggregate 316 is generally about 0.3 μm to 1.0 μm, preferably 0.4 μm to 0.9 μm, and more preferably 0 .5 μm to 0.8 μm. If the fiber diameter d of the fibril fiber 318 is too small, bubbles mixed in a mixture for forming the fibrillated thickener-containing region R (for example, it can be prepared in the form of a paste or slurry) are removed until dry. This may cause a pinhole in the region R. On the other hand, when the fiber diameter d of the fibril fiber 318 is too large, cellulosic fibers are aggregated to easily cause lumps. The fiber diameter d of the fibril fiber 318 is, for example, an SEM (Scanning Electron Microscope) image of the negative electrode active material layer 243, and at least 10 or more arbitrarily selected thickeners 312a are extracted and the fibers are extracted. The average value of the diameter (arithmetic average value) should be evaluated. In FIG. 2, one fibril fiber is shown, but there are actually many fibril fibers.

Although not particularly limited, the size of the aggregate 316 (main part) of the fibrillated thickener 312b is suitably about 3 μm to 20 μm, for example, 3 μm to 10 μm (for example, 5 μm). More preferred). Further, the fiber length of the cellulosic fibers constituting the aggregate 316 is generally about 0.5 μm to 10 μm, and more preferably 1 μm to 5 μm, for example. For example, aggregate 316
A size of about 3 μm to 20 μm and a fiber length of about 0.5 μm to 10 μm can be suitably used.

  Examples of the method for fibrillating the thickener include a method of pulverizing the thickener agglomerates (lumps) using a jet mill, a rotary mill, an attritor (for example, a mass collider), a refiner, a high-pressure homogenizer, or the like. Can be mentioned. By applying mechanical shear force and compressive force to the thickener using these, the thickener is torn mainly in the direction parallel to the fiber axis and loosened, and fine fibers (fibril fibers) appear on the surface. To do. The conditions for the pulverization may vary depending on the apparatus to be used. For example, when a jet mill is used, it is preferable to employ conditions of a pulverization pressure of 0.1 MPa to 2 MPa and a pulverization frequency of 1 to 5 times. Such pulverization may be carried out dry or wet.

≪Width of fibrillated thickener-containing region R≫
The width of the fibrillated thickener-containing region R is not particularly limited, but may be approximately 1 mm or more (preferably 2 mm or more, more preferably 4 mm or more) from the edge of the negative electrode active material layer 243. In addition, the region may be approximately 5 mm or less (preferably 4 mm or less) from the edge of the negative electrode active material layer 243. In this embodiment, in the lithium ion secondary battery 100, the width of the negative electrode active material layer 243 is wider than that of the positive electrode active material layer 223, as shown in FIG. In this case, the negative electrode active material layer 243 has a part 226a facing the positive electrode active material layer 223 and a part 226b not facing the positive electrode active material layer 223 in the fibrillated thickener-containing region R. ing. In this case, in the fibrillated thickener-containing region R, the width W of the portion 226a facing the positive electrode active material layer 223 is 1 mm or more and 3 mm or less (preferably 1.5 mm or more and 2.5 mm or less). Is preferred.

  According to the knowledge of the present inventor, the portion containing the fibrillated thickener 312b (that is, the fibrillated thickener-containing region R) in the negative electrode active material layer 243 is not the fibrillated thickener 312b. The resistance to migration (diffusion) of lithium ions is greater than that of the contained site. Therefore, in the portion containing the fibrillated thickener 312b in the negative electrode active material layer 243, lithium ions tend to be less diffused than the portion containing the non-fibrillated thickener 312b.

  In the lithium ion secondary battery 100 disclosed herein, the negative electrode active material layer 243 has a fibrillated thickener on the edge 245 of the negative electrode active material layer 243 on the side where the uncoated portion 242 is not formed. It has a fibrillated thickener-containing region R containing 312a. For this reason, in the edge part 245 of the negative electrode active material layer 243 on the side where the uncoated part 242 is not formed, lithium ions are less likely to diffuse than other parts including the thickener 312b that is not fibrillated. . Therefore, in the edge 225 of the positive electrode active material layer 223 close to the edge 245 of the negative electrode active material layer 243, lithium ions are excessively released compared to the entire area of the positive electrode active material layer 223 excluding the edge 225. Is unlikely to occur. Then, an event that the potential locally rises at the edge 225 of the positive electrode active material layer 223 due to excessive release of lithium ions from the edge 225 of the positive electrode active material layer 223 is alleviated. As a result, elution of a metal (for example, a transition metal) at the edge 225 of the positive electrode active material layer 223 that can occur when stored at a high temperature in a state close to full charge can be suppressed.

<< Method for Forming Negative Electrode Active Material Layer 243 >>
The negative electrode active material layer 243 is preferably formed on the basis of different mixtures in the fibrillated thickener-containing region R and other regions. For example, a first mixture for forming the fibrillated thickener-containing region R and a second mixture for forming other regions may be prepared. The first mixture includes a fibrillated thickener 312a. The second mixture includes a thickener 312b that has not been fibrillated. A portion of the negative electrode active material layer 243 is formed on the surface of the negative electrode current collector 241 by applying and drying the first mixture on the portion where the fibrillated thickener-containing region R of the negative electrode current collector 241 is formed. To do. This part becomes the fibrillated thickener-containing region R of the negative electrode active material layer 243. Further, when the second mixture is applied in a strip shape to the remaining portion of the negative electrode current collector 241 in the longitudinal direction and dried, the remaining portion of the negative electrode active material layer 243 is formed on the surface of the negative electrode current collector 241. Good.

  Preferably, as shown in FIG. 8, a single negative electrode mixture coating film is formed in the length direction on one negative electrode current collector 241, and a slit is formed in the central portion of the coating film (the slit is formed). The position to be formed is indicated by a one-dot chain line in FIG. 8). And it is good to manufacture the two negative electrode sheets 240 by cut | disconnecting the negative electrode electrical power collector 241 with the said slit. In this case, the first mixture 322 containing the fibrillated thickener 312a is a portion where the fibrillated thickener-containing region of the negative electrode current collector 241 is formed (that is, the center of the negative electrode current collector 241 in the width direction). Part). In addition, the second mixture 324 containing the non-fibrillated thickener 312b can be applied to the remaining portion of the negative electrode current collector 241 in the longitudinal direction. And after drying, it is good to cut | disconnect the negative electrode electrical power collector 241 with a slit (the dashed-dotted line in FIG. 8) with the cutting device which is not illustrated, and divide | segment and use it for the two negative electrode sheets 240.

≪Test evaluation≫
The inventor conducted a test to evaluate the effect of the negative electrode sheet 240. In the lithium ion secondary battery used in this test, as shown in FIGS. 1 to 4, a positive electrode sheet 220 in which a positive electrode active material layer 223 is formed on both surfaces of a positive electrode current collector 221, and a negative electrode current collector 241. And a negative electrode sheet 240 having a negative electrode active material layer 243 formed on both sides thereof. The negative electrode active material layer 243 is provided with an uncoated part 242 at one edge in the width direction orthogonal to the longitudinal direction of the negative electrode current collector 241, and the substantially uncoated part 242 at the other edge. Is formed so as not to be provided. Further, as shown in FIG. 5, the edge portion 245 of the negative electrode active material layer 243 on the side where the uncoated portion 242 is not formed contains a fibrillated thickener 312a containing a fibrillated thickener 312a. Region R is selectively formed. In this example, the positive electrode active material layer 223 is provided on the entire surface of the positive electrode current collector 221 except for an uncoated portion 222 provided in a strip shape at one edge in the longitudinal direction. The width of the negative electrode active material layer 243 is wider than the width of the positive electrode active material layer 223. The negative electrode active material layer 243 covers the positive electrode active material layer 223, and the negative electrode current collector 241 and the positive electrode current collector 221 have the uncoated portions 222 and 242 opposite to each other in the width direction. It is arranged and wound so as to protrude. For this reason, as shown in FIG. 7, the negative electrode active material layer 243 faces the portion 226 a facing the positive electrode active material layer 223 and the positive electrode active material layer 223 in the fibrillated thickener-containing region R. Part 226b.

<Negative electrode sheet>
The negative electrode sheet 240 changes the average fiber diameter d of the fibril fibers 318 of the thickener 312 included in the fibrillated thickener-containing region R of the negative electrode active material layer 243 and also changes the positive electrode active of the fibrillated thickener-containing region R. A plurality of samples were formed in which the width W of the portion 226a facing the material layer 223 was changed.

As a mixture for forming the negative electrode active material layer 243, graphite powder as a negative electrode active material, styrene butadiene copolymer (SBR) as a binder, and water as a solvent were used. In addition, carboxymethyl cellulose (CMC; fiber length 1.2 μm) was prepared as a thickener. The weight ratio of the negative electrode active material, SBR, and CMC was negative electrode active material: SBR: CMC = 100: 1: 1. And this mixture was apply | coated on the copper foil (thickness 10 micrometers) as the negative electrode electrical power collector 241, it was made to dry and it rolled, and the negative electrode sheet 240 was formed. The coating amount of the negative electrode mixture was adjusted to be about 140 mg / cm ² (solid content basis) for both surfaces. The entire thickness of the negative electrode sheet 240 was 154 μm, the length was 4700 mm, and the coating width of the negative electrode active material layer 243 was 100 mm.

  Here, the negative electrode active material layer 243 was formed based on different mixtures in the fibrillated thickener-containing region R and other regions. That is, a first mixture for forming the fibrillated thickener-containing region R and a second mixture for forming other regions were prepared. The first mixture includes a fibrillated thickener 312a. The second mixture includes a thickener 312b that has not been fibrillated. A portion of the negative electrode active material layer 243 is formed on the surface of the negative electrode current collector 241 by applying and drying the first mixture on the portion where the fibrillated thickener-containing region R of the negative electrode current collector 241 is formed. did. In addition, the remaining portion of the negative electrode active material layer 243 was formed on the surface of the negative electrode current collector 241 by applying the second mixture to the remaining portion in the longitudinal direction of the negative electrode current collector 241 and drying it. .

  The fibrillation of the thickener used in the fibrillated thickener-containing region R is performed by using a PJM jet mill machine (manufactured by Nippon Pneumatic Industrial Co., Ltd .; crushing pressure: 0.9 MPa, crushing count) 1 time) and a super mass collider (manufactured by Masuko Sangyo Co., Ltd .; rotation speed: 3000 rpm, clearance between grinding wheels: 5 μm). At that time, the shearing force and compressive force applied to the thickener are appropriately changed and pulverized, classified by an MDS-1 type airflow classifier (manufactured by Nippon Pneumatic Industry Co., Ltd.), and the fiber diameter d of the fibril fiber 318 ( Fig. 6) obtained different thickeners.

<Samples 1-6>
In samples 1 to 6, the average fiber diameter d of the fibril fibers 318 of the thickener 312 included in the fibrillated thickener-containing region R is different. Samples 1 to 6 have the same configuration except for the average fiber diameter d of the fibril fiber 318.

<Samples 7 to 10>
Samples 7 to 10 have the same configuration as Sample 1 except that the width W (FIG. 7) of the portion 226a facing the positive electrode active material layer 223 in the fibrillated thickener-containing region R was changed.

<Sample 11>
In Sample 11, a negative electrode sheet was prepared using a thickener that has not been fibrillated in the fibrillated thickener-containing region R as in the prior art.

<Measurement of pinhole>
During the production of the negative electrode sheet, the surface of the fibrillated thickener-containing region R of the negative electrode active material layer was observed with a SEM (Scanning Electron Microscope), and agglomerates formed per 1000 cm ^{2 of} the negative electrode sheet The number of pinholes having a diameter of 0.5 mm or more was measured.

<Positive electrode sheet>
The positive electrode sheet 220 was produced as follows. 100 parts by mass of nickel cobalt lithium manganate (LiNi _1/3 Co _1/3 Mn _1/3 O ₂ ) powder as a positive electrode active material, 5 parts by mass of acetylene black (AB) as a conductive material, and polyfluoride as a binder 2 parts by weight of vinylidene chloride (PVdF) is added to N-methylpyrrolidone (NMP) to prepare a positive electrode mixture, which is formed into a strip on both sides of a long sheet-like aluminum foil (positive electrode current collector, thickness 15 μm) The positive electrode sheet 220 in which the positive electrode active material layer 223 was provided on both surfaces of the positive electrode current collector 221 was produced by applying and drying. The coating amount of the positive electrode mixture was adjusted to be about 30 mg / cm ² (solid content basis) for both surfaces. The total thickness of the positive electrode sheet 220 was 170 μm, the length was 4500 mm, and the coating width of the positive electrode active material layer 223 was 94 mm.

<Lithium ion secondary battery>
The positive electrode sheet 220 and the negative electrode sheet 240 are wound through two separators 262 and 264 to produce a wound body, and the wound body is laterally flat at a pressure of 4 kN / cm ² . A flat wound electrode body 200 was produced by pressing and crushing for 2 minutes. The wound electrode body 200 thus obtained is housed in a battery case (a square shape is used here) 300 together with a non-aqueous electrolyte (non-aqueous electrolyte), and the opening of the battery case 300 is hermetically sealed. did. Here, the separators 262 and 264 are formed with a porous layer made of alumina particles on the surface of a porous film (thickness 20 μm) having a three-layer structure of polypropylene (PP), polyethylene (PE), and polypropylene (PP). We used what we did. Further, the volume ratio of ethylene carbonate and dimethyl carbonate and ethyl methyl carbonate, 3: 3: blended with 4, using the electrolytic solution of LiPF ₆ was 1 mol dissolved.

<Measurement of springback rate>
During manufacturing the wound electrode body 200, and a thickness T _B of the wound electrode body flat portion after 5 minutes from the winding thickness T _A and press the end of the electrode body pars plana immediately after the press (press opening) Was measured. Specifically, the measured thickness is the thickness T of the flat portion 210 of the wound electrode body 200 schematically shown in FIG. Formula: spring back ratio _{(%) = (T B -T} A) / T A × 100; was determined from the spring-back rate. Further, when the wound electrode body 200 was accommodated in the battery case 300, the wound electrode body 200 was once extracted from the battery case 300, and damage or misalignment due to contact of the wound electrode body 200 with the battery case 300 was confirmed. . Damaged items were designated as “galling items”. Here, the NG product was examined for 10 batteries of each sample.

<Measurement of battery capacity>
In addition, each of the test lithium ion secondary batteries obtained in Samples 1 to 11 was charged to a voltage of 4.1 V at a current value of 1 C under a temperature condition of 25 ° C. After 5 minutes of rest, the charged battery was discharged to a voltage of 3.0 V at a current value of 1 C at 25 ° C. Then, after a pause of 5 minutes, the battery was charged at a current value of 1 C to a voltage of 4.1 V, and then charged by a constant voltage method until the current value was reduced to 0.1 C. The charged battery was discharged at 25 ° C. at a current value of 1 C to a voltage of 3.0 V, and then discharged by a constant voltage method until the current value was reduced to 0.1 C. The discharge capacity at this time was defined as battery capacity (battery rated capacity). Here, the battery capacity (battery rated capacity) of the test lithium ion secondary battery was 24 Ah.

<High temperature storage test>
Each of the test lithium ion secondary batteries of each sample was adjusted to a charged state (SOC 100%) of about 100% of the rated capacity, and then housed in a constant temperature bath at 60 ° C. and subjected to high temperature aging for 100 days. . The battery capacity after high-temperature storage was measured under the same conditions as the rated capacity, and the capacity retention rate after high-temperature storage was determined from [(battery capacity after high-temperature storage) / (rated capacity)] × 100 (%). . Here, the above test was performed on 50 batteries of each sample, and the average value was calculated.

<Battery resistance>
About the test lithium ion secondary battery of each sample, after adjusting to a charged state (SOC 60%) of about 60% of the rated capacity, discharging was performed at a current value of 10 C for 10 seconds in an environmental atmosphere of 25 ° C., The voltage value 10 seconds after the start of discharge was measured, and the IV resistance was calculated. Here, the battery resistance was applied to 10 batteries of each sample, and the average value was calculated.

<Evaluation of each sample>
The results of the above test are shown in Table 1 for each sample. Table 1 summarizes the configuration and evaluation for each sample.

  As shown in Table 1, in samples 1 to 10, a fibrillated thickener containing a fibrillated thickener is provided at the edge of the negative electrode active material layer 243 on the side where the uncoated portion 242 is not formed. An agent-containing region R is selectively formed. About these samples 1-10, the capacity | capacitance maintenance factor after the high temperature storage test preserve | saved at 60 degreeC for 100 days is all favorable as 80% or more, and the sample 11 which has not formed the fibrillated thickener containing area | region R Compared with, it showed extremely high durability performance. Further, the springback rate and the galling rate of the wound electrode body were also improved in Samples 1 to 10 compared to Sample 11. In this way, by selectively forming the fibrillated thickener-containing region R at the edge of the negative electrode active material layer 243 on the side where the uncoated portion 242 is not formed, the lithium ion secondary battery has a high temperature. The capacity maintenance rate after storage is greatly improved.

  The inventor selectively increases the post-endurance capacity retention rate by selectively forming the fibrillated thickener-containing region R at the edge of the negative electrode active material layer 243 on the side where the uncoated portion 242 is not formed. I found out that I can do it. About this phenomenon, this inventor guesses as follows. That is, since the edge 245 of the negative electrode active material layer 243 on the side where the uncoated part 242 is not formed includes the fibrillated thickener 312b, lithium ions are difficult to diffuse. Therefore, in the edge 225 of the positive electrode active material layer 223 close to the edge 245 of the negative electrode active material layer 243, lithium ions are excessively released compared to the entire area of the positive electrode active material layer 223 excluding the edge 225. Is unlikely to occur. Then, an event that the potential locally rises at the edge 225 of the positive electrode active material layer 223 due to excessive release of lithium ions from the edge 225 of the positive electrode active material layer 223 is alleviated. As a result, the elution of the metal (for example, transition metal) at the edge portion 225 of the positive electrode active material layer 223, which may occur when stored at a high temperature in a state close to full charge, is less likely to occur, and thus the reduction in battery capacity is suppressed. Increases capacity retention after endurance.

  In Samples 1 to 5, the fibril average fiber diameter d of the thickener 312 included in the fibrillated thickener-containing region R is 1.0 μm or less. In these samples 1 to 5, the capacity maintenance ratio after the high-temperature storage test was 97% or more, and a much better result was obtained. there were. Also, in Samples 1 to 5, battery resistance could be reduced as compared to Sample 6. In sample 6, since the fibril fiber diameter d is large, aggregation of thickeners occurs, the reaction in the negative electrode becomes non-uniform, and the battery characteristics are degraded. From this result, the fibril fiber diameter d of the thickener 312 is preferably 1.0 μm or less, more preferably 0.8 μm or less, and particularly preferably 0.6 μm or less.

  In Samples 2 to 5, the fibril average fiber diameter d is 0.3 μm or more. In these samples 2 to 5, the number of aggregates and pinholes could be further reduced as compared with sample 1 (average fiber diameter d: 0.2 μm). In sample 2, since the fibril fiber diameter d is small, it is considered that the air bubbles mixed in the first mixture could not be removed until drying, became pinholes, and the surface quality was deteriorated. From this result, the fibril fiber diameter d of the thickener 312 is preferably 0.3 μm or more, and particularly preferably 0.4 μm or more.

  In Samples 1 and 8 to 10, the width W of the portion 226a facing the positive electrode active material layer 223 of the fibrillated thickener-containing region R is set to 1 mm or more. Samples 1 and 8 to 10 have a capacity retention rate of 97% or more after the high-temperature storage test, which is much better than that of sample 7 (width W: 0.8 mm). It was. In Sample 7, since the width W of the portion 226a facing the positive electrode active material layer 223 in the fibrillated thickener-containing region R is narrow, metal elution occurs at the edge 225 of the positive electrode active material layer 223, and the battery It is understood that the capacity was reduced. From this result, the width W of the portion 226a facing the positive electrode active material layer 223 of the fibrillated thickener-containing region R is preferably approximately 1 mm or more, and more preferably approximately 1.5 mm or more. It is especially preferable that it is about 2 mm or more.

  In Samples 1, 8, and 9, the width W of the portion 226a facing the positive electrode active material layer 223 in the fibrillated thickener-containing region R is set to 3 mm or less. In Samples 1, 8, and 9, battery resistance could be reduced as compared with Sample 10 (width W: 3.2 mm). In sample 10, since the width W of the portion 226a facing the positive electrode active material layer 223 in the fibrillated thickener-containing region R is wide, a part of lithium ions is captured by the fibrillated thickener during charging and discharging. It is speculated that the reactivity decreased. From this result, the width W of the portion 226a facing the positive electrode active material layer 223 in the fibrillated thickener-containing region R is preferably about 3 mm or less, and more preferably about 2.5 mm or less.

  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.

  Up to this point, a lithium ion secondary battery has been described as a typical example of a secondary battery, but the present invention is not limited to this form of secondary battery. For example, it may be a non-aqueous electrolyte secondary battery using a metal ion other than lithium ion (for example, sodium ion) as a charge carrier, a nickel hydride battery, a nickel cadmium battery, or a lithium battery equipped with the electrode body described above. It may be an electric double layer capacitor (physical battery) such as an ion capacitor.

  As described above, the secondary battery provided by the technology disclosed herein is unlikely to cause metal elution at the edge of the positive electrode active material layer, and the capacity retention rate after high-temperature storage is improved. It can be suitably used as a power source for a motor (electric motor) mounted on the vehicle. Therefore, as schematically shown in FIG. 10, the present invention provides a vehicle 1 (typically an automobile, particularly a hybrid automobile) provided with such a secondary battery 100 (typically, a battery pack formed by connecting a plurality of batteries in series) as a power source. , Automobiles equipped with electric motors such as electric vehicles and fuel cell vehicles).

DESCRIPTION OF SYMBOLS 1 Vehicle 100 Secondary battery 200 Winding electrode body 220 Positive electrode sheet 221 Positive electrode current collector 222 Uncoated part 223 of positive electrode current collector Positive electrode active material layer 225 Edge of positive electrode active material layer 240 Negative electrode sheet 241 Negative electrode current collector 242 Negative electrode uncoated portion 243 Negative electrode active material layer 245 Negative electrode active material layer edge 262,264 Separator 300 Battery case 310 Negative electrode active material 312a Fibrilized thickener 312b Unfibrillated thickened Agent 314 Binder 316 Lump Aggregate 318 Fibril Fiber R Fibrilized Thickener Containing Area

Claims (5)

A positive electrode sheet having a positive electrode active material layer on a long positive electrode current collector, a negative electrode sheet having negative electrode active material layers on both sides of the long negative electrode current collector, and between the positive electrode sheet and the negative electrode sheet A secondary battery comprising a wound electrode body wound with a separator interposed therebetween,
The negative electrode active material layer is provided with an uncoated portion at one edge in the width direction perpendicular to the longitudinal direction of the negative electrode current collector, and a substantially uncoated portion is provided at the other edge. Formed so as not to
A fibrillated thickener-containing region containing a fibrillated thickener is selectively formed at the edge of the negative electrode active material layer on the side where the uncoated portion is not formed. battery.   The fibrillated thickener constitutes a mass aggregate in which cellulosic fibers having a fiber length of 1 μm to 10 μm are aggregated, and the fibril fibers protrude from the outer surface of the aggregate. Secondary battery.   The secondary battery according to claim 2, wherein an average fiber diameter of the fibril fibers protruding from the outer surface portion of the aggregate is 0.3 μm to 1.0 μm. The positive electrode active material layer is
In the positive electrode current collector, provided on the entire surface excluding the uncoated part provided in a strip shape at one edge in the longitudinal direction,
The negative electrode active material layer is wider than the positive electrode active material layer,
In a state where the negative electrode active material layer covers the positive electrode active material layer, and
The negative electrode current collector and the positive electrode current collector are arranged and wound so that a non-coated portion protrudes on the opposite side in the width direction. Secondary battery described in 1. The negative electrode active material layer is
In the fibrillated thickener-containing region containing the fibrillated thickener,
A portion facing the positive electrode active material layer;
A portion not facing the positive electrode active material layer,
The secondary battery according to claim 4, wherein a width of a portion facing the positive electrode active material layer is 1 mm or more and 3 mm or less.

Images