JP2014207058A - Secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a secondary battery in which elution of metal is hard to occur at an edge part of a positive electrode active material layer.SOLUTION: A secondary battery 100 includes a positive electrode sheet 220 equipped with a positive electrode active material layer 223 on an oblong positive electrode collector 221. In the positive electrode active material layer 223, one edge part in width direction orthogonal to length direction of the positive electrode collector 221 is provided with a non-coating part 222, while the other edge part is formed in such a manner as substantially non-coating part 222 is not provided. The positive electrode active material layer 223 includes an additive element containing region R1 which uses a positive electrode active material 310a prepared by adding at least one kind of metal element, excluding elements constituting a main component, to the main component of lithium transition metal compound oxide, and a non-additive element containing region R2 which uses a positive electrode active material 310b that is prepared by adding no metal element to the main component of the lithium transition metal compound oxide. The non-additive element containing region R2 is provided to an edge part 225 on the side where the non-coating part 222 is formed in the positive electrode active material layer 223.

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 is generally a positive electrode active material layer forming composition containing a positive electrode active material on both sides of the positive electrode current collector (for example, it can be prepared in a paste form or a slurry form). It is produced by supplying and forming a positive electrode active material layer. Moreover, the negative electrode sheet is produced by supplying a negative electrode active material layer-forming composition containing a negative electrode active material to both surfaces of a negative electrode current collector to form a negative electrode active material layer. As a positive electrode active material of a lithium secondary battery, an oxide (lithium transition metal composite oxide) containing a lithium element and a transition metal element as constituent metal elements is widely used. In addition, it is known that battery performance can be improved by adding a small amount of different metal elements such as tungsten (W) and molybdenum (Mo) to the lithium transition metal composite oxide (for example, Patent Documents 1 to 3). ).

JP 2012-084346 A JP-A-2005-251716 JP 2008-140747 A

  By the way, in the case of high output use such as for vehicle mounting, active material layers are formed on both surfaces of one edge 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). The uncoated part that is not formed is provided in a strip shape to increase the current collection efficiency and used as a current collection part. 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 parts are arranged alternately and wound.

  With respect to such a form, the present inventor, when using a positive electrode active material obtained by adding a small amount of a different metal element to a lithium transition metal composite oxide, the different type contained in the positive electrode active material layer at the edge of the positive electrode active material layer. We found an event where metal elements elute locally. The phenomenon in which a dissimilar metal element elutes locally at the edge of the positive electrode active material layer tends to occur when stored for a long time in a high temperature environment after full charge. When the dissimilar metal element is locally eluted in this manner, it can be deposited on the negative electrode to cause a micro short circuit or a decrease in battery capacity. Therefore, it is desired to suppress as much as possible the dissimilar metal element from being locally eluted 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 an electrode body in which a positive electrode sheet and a separator interposed between the negative electrode sheet are overlapped. The negative electrode active material layer is provided with an uncoated portion where the negative electrode active material layer is not formed on one edge in the width direction perpendicular to the longitudinal direction of the negative electrode current collector, and on the other edge. Is formed so that the uncoated portion is not substantially provided. The positive electrode active material layer is provided with an uncoated portion where the positive electrode active material layer is not formed at one edge in the width direction perpendicular to the longitudinal direction of the positive electrode current collector, and the other edge The part is formed so that a substantially uncoated part is not provided. Furthermore, the negative electrode current collector and the positive electrode current collector are arranged so that the uncoated portions of the negative electrode project to the opposite side in the width direction. Here, the positive electrode active material layer is added using a positive electrode active material in which at least one metal element excluding an element constituting the main component is added to the main component of the lithium transition metal composite oxide. It has an element-containing region and a non-added element-containing region using a positive electrode active material to which the metal element is not added with respect to the main component of the lithium transition metal composite oxide. And the said non-additive element containing area | region is provided in the edge part by the side in which the said uncoated part of the said positive electrode active material layer is formed.

  According to this configuration, since the metal additive element is not added to the edge of the positive electrode active material layer where the uncoated part is formed, the potential increases locally at the edge of the positive electrode active material layer. Even in this case, it is difficult for the metal additive element to elute from the edge. Therefore, the phenomenon that a minute short circuit occurs or the battery capacity is reduced due to the elution of the metal additive element from the edge is alleviated.

  In a preferred embodiment of the secondary battery disclosed herein, when the width of the additive element-containing region along the width direction is L1, and the width of the non-additive element-containing region is L2, 0.1 ≦ ( L2 / L1) ≦ 1 is satisfied. According to this configuration, since the ratio of the additive element-containing region and the non-additive element-containing region is in an appropriate balance, the battery performance improvement effect (for example, the output characteristic improvement effect) due to the addition of the metal additive element to the positive electrode active material Elution of the metal additive element at the edge of the positive electrode active material layer can be avoided while appropriately performing. Therefore, better battery performance can be reliably exhibited.

  In a preferable aspect of the secondary battery disclosed herein, the positive electrode active material included in the additive element-containing region includes, as the metal element, W, Zr, Mg, Ca, Na, Fe, Cr, Zn, Si, It contains at least one selected from the group consisting of Sn, Sr, Ti, V, Nb, Mo, Rh, Pb, Pt, Cu, Ga, In, La, Ce, Al, and B. By using the lithium transition metal composite oxide to which these metal additive elements are added as the positive electrode active material, the conductivity of the positive electrode can be improved. Therefore, better battery performance can be reliably exhibited.

In a preferred embodiment of the secondary battery disclosed herein, the positive electrode active material in the additive element-containing region has the general formula (I): Li _{1 + α} (Ni _a Co _b Mn _c M _d W _e ) O ₂ (where , M is one or more selected from transition metal elements and typical metal elements, α is a value determined to satisfy the charge neutrality condition in 0 ≦ α ≦ 0.25, and a, b, c, d and e satisfy a + b + c + d + e≈1, 0.0005 ≦ e ≦ 0.01 and d ≧ 0, and at least one of a, b and c is greater than 0.) Includes transition metal complex oxides. The lithium transition metal composite oxide having the composition represented by the general formula (I) is excellent in electronic conductivity and can realize excellent output characteristics and cycle characteristics. For this reason, it can be suitably used as a positive electrode active material in an additive element containing region suitable for the purpose of the present invention.

  In a preferred embodiment of the secondary battery disclosed herein, an average tungsten concentration of 1.5 nm in the depth direction from the surface of the positive electrode active material (hereinafter, may be abbreviated as “surface W concentration”). 0.5 mol% to 2 mol%. When the surface W concentration is within the above range, the electron conductivity of the positive electrode active material is further improved. For this reason, the effect of this invention can be exhibited better.

In a preferred embodiment of the secondary battery disclosed herein, the positive electrode active material in the non-additive element-containing region has a general formula (II): Li _{1 + Β} (Ni _x Co _y Mn _z ) O ₂ (where β is The values are determined so that the charge neutrality condition is satisfied when 0 ≦ β ≦ 0.25, and x, y, and z satisfy x + y + z≈1, and at least one of x, y, and z is greater than zero. And a lithium transition metal composite oxide represented by: Since the lithium transition metal composite oxide having the composition represented by the general formula (II) has high stability as a compound at a high potential (the metal additive element does not elute), it is suitable for the object of the present invention. It can be suitably used as a positive electrode active material in a non-additive element-containing region.

  In a preferred embodiment of the secondary battery disclosed herein, the width of the negative electrode active material layer is wider than the width of the positive electrode active material layer. And in the state where the negative electrode active material layer covers the positive electrode active material layer, the negative electrode current collector and the positive electrode current collector are such that their uncoated portions protrude on the opposite side in the width direction. Has been placed and wound. The elution of the metal-added element at the edge of 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 metal additive element is not contained in the edge portion of the positive electrode active material layer, the elution of the metal additive element from the edge portion is improved.

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 positive electrode sheet according to an embodiment of the present invention. FIG. 6 is a diagram schematically showing a main part of a cross section perpendicular to the winding axis of the wound electrode body. 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 illustrating 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.

  Here, “substantially no uncoated portion is provided” means that the uncoated portion 222 is not intentionally provided. Therefore, for example, although the uncoated portion 222 is not provided, the positive electrode current collector 221 expands due to some unintended factor thereafter, or the positive electrode active material layer 223 contracts, causing a slight The case where the uncoated part 222 is generated visually may be included in the “here, the substantially uncoated part is not provided”. The same applies to the negative electrode sheet 240 described later.

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 nickel oxide), LiCoO ₂ (lithium cobalt oxide), LiMn ₂ O ₄ (lithium manganese oxide), etc. Lithium transition metal composite oxide. Here, LiMn ₂ O ₄ has, for example, a spinel structure. LiNiO ₂ and LiCoO ₂ have a layered rock salt structure. The positive electrode active material included in the positive electrode active material layer 223 will be described in detail later.

  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.

  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. 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.

  The non-aqueous electrolyte may contain, for example, a gas generating agent that reacts and generates gas when the battery voltage becomes equal to or higher than a predetermined voltage. As such a gas generating agent, for example, cyclohexylbenzene (CHB) or biphenyl (BP) can be used. Cyclohexylbenzene (CHB) and biphenyl (BP), for example, activate a polymerization reaction at the time of overcharge of about 4.35V to 4.6V and generate gas (here, hydrogen gas). For example, the amount of the gas generating agent added to the non-aqueous electrolyte is preferably about 0.05 wt% or more and 4.0 wt% or less. In addition, the addition amount of a gas generating agent is not limited to this, It is good to adjust so that a predetermined amount of gas may be generated on predetermined conditions.

<< Current interrupting mechanism 460 >>
Further, as described above, in the lithium ion secondary battery 100, a gas generating agent is added to the electrolytic solution. For example, when the battery is overcharged at about 4.35V to 4.6V, gas is generated. The pressure inside becomes high. The current interrupt mechanism 460 is a mechanism that interrupts the current path when the pressure in the battery case becomes abnormally high. In this embodiment, as shown in FIG. 1, the current interruption mechanism 460 is constructed inside the positive electrode terminal 420 so that the conduction path of the battery current in the positive electrode is interrupted.

  Hereinafter, the positive electrode active material layer 223 of the lithium ion secondary battery 100 will be described in more detail. FIG. 4 schematically shows a cross section of the positive electrode sheet 220, the separator 262, and the negative electrode sheet 240 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). FIG. 6 is an enlarged view schematically showing a main part of a cross section orthogonal to the winding axis of the wound electrode body 200. In the lithium ion secondary battery 100 described above, as shown in FIG. 4, the positive electrode active material layer 223 is provided with an uncoated portion 222 at one edge in the width direction orthogonal to the longitudinal direction of the positive electrode current collector 221. And the other edge part is formed so that the uncoated part 222 may not be provided substantially. Further, 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 substantially uncoated at the other edge. The portion 242 is formed so as not to be provided. The positive electrode current collector 221 and the negative electrode current collector 241 are arranged and wound so that the uncoated parts 222 and 242 protrude to the opposite side in the width direction.

In order to improve battery performance of the lithium ion secondary battery 100 in such a form, the present inventor has an element constituting the main component with respect to the main component of a lithium transition metal composite oxide (for example, LiNiCoMnO ₂ ). We are considering using a positive electrode active material to which a metal additive element (for example, tungsten (W)) other than (for example, Li, Ni, Co, and Mn) is added. However, when the positive electrode active material to which the metal additive element (for example, W) is added is used for the lithium ion secondary battery 100 of the above form, the metal additive element is locally eluted at the edge 225 of the positive electrode active material layer 223. I found an event to do. The phenomenon in which the metal-added element is locally eluted at the edge 225 of the positive electrode active material layer 223 tends to occur easily when stored for a long time in a high temperature environment after full charge. If the metal additive element elutes locally, it may be deposited on the negative electrode to cause a micro short circuit (self-discharge) or a decrease in battery capacity. In order to stabilize the performance of the lithium ion secondary battery 100, it is desirable that the metal-added element is locally eluted at the edge 225 of the positive electrode active material layer 223 as little as possible.

  The present inventor diligently studied the phenomenon in which the metal additive element elutes 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, as shown in FIGS. 4 and 6, of the positive electrode active material layers 223 a and 223 b provided on both surfaces of the positive electrode current collector 221, the outer peripheral side (in the wound electrode body) with respect to the positive electrode current collector 221. The positive electrode active material layer 223b provided on the surface facing the outer peripheral side of the positive electrode current collector 221) has a negative electrode active material layer 243b provided on the surface facing the inner peripheral side of the negative electrode current collector 241 with the separator 264 interposed therebetween. Lithium ions are arranged back and forth between the negative electrode active material layers 243b. On the other hand, the positive electrode active material layer 223 a provided on the inner peripheral side (the surface facing the inner peripheral side of the positive electrode current collector 221 in the wound electrode body) with respect to the positive electrode current collector 221 is disposed via the separator 262. The negative electrode active material layer 243a provided on the surface facing the outer peripheral side of the electric body 241 is disposed opposite to the negative electrode active material layer 243a, and lithium ions are transferred to and from the negative electrode active material layer 243a. That is, lithium ions released from the positive electrode active material layer 223b on the outer peripheral side of the positive electrode current collector 221 have priority over the negative electrode active material layer 243b on the inner peripheral side of the negative electrode current collector 241 from a close distance. The negative electrode active material layer 243a on the outer peripheral side of the negative electrode current collector 241 hardly moves.

  However, in the above-described lithium ion secondary battery, the positive electrode active material layer 223 is provided with the uncoated portion 222 at one edge in the width direction orthogonal to the longitudinal direction of the positive electrode current collector 221 and the other edge. The part is formed so that the uncoated part 222 is not substantially provided. Further, 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 substantially uncoated at the other edge. The portion 242 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 part 242 is not formed, and the negative electrode active material on the outer peripheral side of the negative electrode current collector 241. The layer 243a is exposed to the positive electrode active material layer 223b on the outer 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 223b on the outer peripheral side of the positive electrode current collector 221 are not limited to the negative electrode active material layer 243b on the inner peripheral side of the negative electrode current collector 241. (Refer to arrow 90), the negative electrode active material layer 243a on the outer peripheral side of the negative electrode current collector 241 also moves (see 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 added to the positive electrode active material layer 223 is added. It can be a factor causing elution of elements.

  The present inventor is one of the reasons why the metal additive element contained in the edge portion 225 of the positive electrode active material layer 223 is eluted when stored in a high temperature environment for a long time in a state close to full charge. I am thinking. The present inventor believes that the elution of such metal-added elements should be reduced as much as possible. Therefore, a novel structure is proposed for the lithium ion secondary battery 100 in which elution of the metal-added element at the edge 225 of the positive electrode active material layer 223 is eliminated.

<< Positive electrode active material layer 223 >>
Here, the basic structure of the positive electrode active material layer according to one embodiment of the present invention will be described, and the effects thereof will be described. Then, each structure of a positive electrode active material layer is demonstrated in detail. FIG. 5 is a schematic view showing a cross section of the positive electrode active material layer 223. As shown in FIG. 5, the positive electrode active material layer 223 includes an additive element-containing region R1 and a non-additive element-containing region R2. Hereinafter, the additive element-containing region R1 and the non-additive element-containing region R2 will be described in this order.

≪Additive element-containing region R1≫
The additive element-containing region R1 is provided in a portion excluding the edge portion 245 on the side where the uncoated portion 222 of the positive electrode active material layer 223 is formed. The additive element-containing region R1 includes a positive electrode active material 310a, a binder 312 and a conductive material (not shown). The positive electrode active material 310a includes at least one metal excluding an element (for example, Li, Ni, Co, and Mn) constituting the main component with respect to a main component of a lithium transition metal composite oxide (for example, LiNiCoMnO ₂ ). An element to which an element (for example, W or Zr) is added is used. Thus, the electroconductivity of a positive electrode can be improved by using the positive electrode active material 310a which added the metal additive. Therefore, a battery constructed using such a positive electrode can realize excellent output characteristics and cycle characteristics.

≪Non-additive element containing region R2≫
The non-additive element-containing region R2 is provided in the edge portion 245 on the side where the uncoated portion 222 of the positive electrode active material layer 223 is formed. The non-additive element-containing region R2 includes a positive electrode active material 310b, a binder 312 and a conductive material (not shown). As the positive electrode active material 310b, a material in which the above-described metal element (for example, W or Zr) is not added to the main component of a lithium transition metal composite oxide (for example, LiNiCoMnO ₂ ) is used. That is, in the positive electrode active material layer 223, the metal additive element is not added to the edge 245 on the side where the uncoated part 222 is formed, and the metal additive element is added to the other region. .

  In the lithium ion secondary battery 100 disclosed here, the positive electrode active material layer 223 has a metal additive element added to the edge 225 of the positive electrode active material layer 223 on the side where the uncoated part 222 is formed. There is no non-additive element-containing region R2. For this reason, during charging, even when the lithium ion is excessively released at the edge 225 on the side where the uncoated part 222 is formed and the potential rises locally, the metal additive element is eluted from the edge 225. Is unlikely to occur. Therefore, the phenomenon that a minute short circuit occurs or the battery capacity decreases due to the elution of the metal additive element from the edge 225 is alleviated.

<< Width L1 of Additive Element-Containing Region R1 and Width L2 of Non-Additive Element-Containing Region R2 >>
As shown in FIG. 7, the positive electrode active material layer 223 disclosed here includes a width L1 of the additive element-containing region R1 along the width direction of the positive electrode current collector 221, and a width L2 of the non-additive element-containing region R2. The ratio (L2 / L1) is suitably 0.1 or more. Thus, when the width ratio (L2 / L1) is 0.1 or more, elution of the metal-added element at the edge 225 (FIG. 5) of the positive electrode active material layer 223 can be reliably avoided. The positive electrode active material layer 223 disclosed herein preferably has a width ratio (L2 / L1) that satisfies 0.1 ≦ (L2 / L1), and 0.2 ≦ (L2 / L1). Those satisfying the condition are more preferable, and those satisfying 0.3 ≦ (L2 / L1) are particularly preferable. On the other hand, the positive electrode active material layer 223 having the width ratio (L2 / L1) exceeding 1.0 has a relatively reduced ratio of the positive electrode active material 310a (FIG. 5) to which a metal additive element is added. The battery performance improvement effect (for example, electronic conductivity improvement effect) by adding a metal additive element to the substance 310a (FIG. 5) may be insufficient. From the viewpoint of improving the performance by adding a metal additive element, those satisfying (L2 / L1) ≦ 1.0 (particularly (L2 / L1) ≦ 0.8) are preferable. For example, the positive electrode active material layer 223 having the width ratio (L2 / L1) of 0.1 or more and 1 or less (more preferably 0.2 or more and 0.8 or less, particularly 0.3 or more and 0.6 or less) It is suitable from the viewpoint of achieving both performance improvement by addition of additive elements and suppression of elution of metal additive elements.

<Positive electrode active material 310a used in additive element-containing region R1>
As shown in FIG. 5, as the positive electrode active material 310a used in the additive element-containing region R1, a metal additive element (additional element) is added to the main component of the lithium transition metal composite oxide. If it is. The metal additive element may be one or more of transition metal elements and typical metal elements (including metalloid elements). For example, Group 1 of the periodic table (alkali metals such as sodium), Group 2 (alkaline earth metals such as magnesium and calcium), Group 3 (transition metals such as lanthanum), Group 4 (transition metals such as titanium and zirconium) Group 5 (transition metals such as niobium), Group 6 (transition metals such as chromium and tungsten), Group 7 (transition metals such as titanium and zirconium), Group 8 (transition metals such as iron), Group 9 (rhodium, etc.) Transition metals), group 10 (transition metals such as palladium and platinum), group 11 (transition metals such as copper), group 12 (metals such as zinc) and group 13 (boron or metalloid elements such as boron or aluminum). Any metal element belonging to (a metal). Typical examples include magnesium (Mg), calcium (Ca), strontium (Sr), titanium (Ti), zirconium (Zr), vanadium (V), niobium (Nb), chromium (Cr), molybdenum (Mo), iron (Fe), rhodium (Rh), palladium (Pb), platinum (Pt), copper (Cu), zinc (Zn), boron (B), aluminum (Al), gallium (Ga), indium (In), tin (Sn), lanthanum (La), cerium (Ce) and the like are exemplified. For example, W or Zr, or both W and Zr can be preferably employed.

  As the positive electrode active material 310a, one or more kinds of materials conventionally used in lithium ion secondary batteries can be used without particular limitation as long as such a metal additive element is included. For example, the main component is an oxide (lithium transition metal oxide) containing lithium and one or more transition metal elements as constituent metal elements such as lithium nickel oxide, lithium cobalt oxide, and lithium manganese oxide. And a positive electrode active material. Preferably, the lithium transition metal oxide is a layered rock salt type compound containing nickel as a constituent element. The layered lithium transition metal composite oxide can be preferably used because it can be a battery having a high capacity and a high energy density when used as a positive electrode active material. Among these, a positive electrode active material (typically, a positive electrode active material substantially composed of a lithium nickel cobalt manganese composite oxide) containing a lithium nickel cobalt manganese composite oxide containing nickel, cobalt, and manganese as a main component is preferable.

As such a lithium transition metal complex oxide, for example, an oxide represented by the general formula (I): Li _{1 + δ} (Ni _a Co _b Mn _c M _d W _e ) O ₂ can be given. Examples of such lithium transition metal composite oxides include one of transition metal elements such as lithium nickel oxide (eg, LiNiO ₂ ), lithium cobalt oxide (eg, LiCoO ₂ ), and lithium manganese oxide (eg, LiMn ₂ O ₄ ). An oxide in which a part is substituted with a tungsten (W) element can be given. By substituting a part of the transition metal element with the W element, the electron conductivity of the positive electrode active material 310a can be more effectively improved. Here, M in the above formula (I) may be one or more of transition metal elements, typical metal elements, and boron (B). δ is a value determined to satisfy the charge neutrality condition with 0 ≦ δ ≦ 0.25, and a, b, c, d, and e are a + b + c + d + e≈1, 0.0005 ≦ e ≦ 0.01 and d ≧ 0 is satisfied, and at least one of a, b, and c is preferably greater than 0. In the above formula (I), “a + b + c + d + e≈1” is approximately 0.9 ≦ a + b + c + d + e ≦ 1.2 (typically 0.9 <a + b + c + d + e <1.2, for example 0.95 ≦ a + b + c + d + e ≦ 1.1). For example, a + b + c + d + e = 1.

  As shown in the above formula (I), the lithium transition metal composite oxide has other constituent elements other than lithium (Li), nickel (Ni), cobalt (Co), manganese (Mn), and tungsten (W). At least one metal element M may be included (that is, d> 0 may be included) or may not be included (that is, d = 0 may be included). Typically, the metal element M may be one or more of transition metal elements other than Li, Ni, Co, Mn, and W, typical metal elements, and the like. For example, Zr, Mg, Ca, etc. can be preferably employed. The amount of M element (that is, the value of d in the above formula (I)) is not particularly limited, but may be 0 ≦ d ≦ 0.02, for example.

  In addition, a, b, and c in the above formula (I) are not particularly limited as long as the condition that a + b + c + d + e≈1 and at least one of a, b, and c is greater than 0 is satisfied. Any number of b and c may be the largest. In other words, the first element of Ni, Co, and Mn (the element that is contained most on the basis of the number of atoms) may be any of Ni, Co, and Mn. For example, a can be 0.1 or more (typically 0.3 or more) and less than 1 (typically 0.9 or less, such as 0.6 or less). b can be 0 or more (typically 0.1 or more, for example 0.3 or more) and 0.6 or less (typically 0.5 or less, for example 0.4 or less). c can be 0 or more (typically 0.1 or more, for example 0.3 or more) and 0.6 or less (typically 0.5 or less, for example 0.4 or less). Among these, lithium nickel cobalt manganese composite oxide in which a, b, c> 0 (in other words, including all elements of Ni, Co, and Mn) can be preferably used. In a preferred embodiment, a, b, and c (that is, amounts of Ni, Co, and Mn) are approximately the same. In another preferred embodiment, a> b and a> c (in other words, the first element is Ni). Such a lithium transition metal composite oxide is excellent in electronic conductivity and thermal stability, and can realize excellent output characteristics and cycle characteristics. For this reason, the effect of this invention can be exhibited more.

  Such a lithium transition metal composite oxide containing W as a metal additive element is typically in the form of particles in which primary particles are gathered. The average tungsten concentration (surface W concentration) from the surface of the positive electrode active material particles to 1.5 nm in the depth direction is not particularly limited. For example, the surface W concentration is 0.1 mol% or more (typically 0.2 mol%). Or more, preferably 0.5 mol% or more) and 3.0 mol% or less (typically 2.5 mol% or less, preferably 2 mol% or less). Within the range of such a surface W concentration, the electron conductivity of the positive electrode active material 310a is further improved. For this reason, the effect of this invention can be exhibited better.

  In the present specification, the “surface W concentration” is an average ratio (mol of W element to the whole element constituting the outermost surface of the lithium transition metal composite oxide, measured based on a conventionally known X-ray photoelectron spectroscopy. %). Such measurement can be performed, for example, using an analytical instrument based on X-ray photoelectron spectroscopy called XPS (X-ray Photoelectron Spectroscopy), ESCA (Electron Spectroscopy for Chemical Analysis), or the like. In addition, “1.5 nm from the surface to the depth direction” must be strictly 1.5 nm from the surface to the depth direction (vertical direction) (for example, 1.5 nm by rounding off the second decimal place). It is a value that includes the measurement error of the apparatus. More specifically, it is about 1.5 nm, for example, 1.0 nm to 2.0 nm, and typically 1.5 ± 0.2 nm.

<Positive electrode active material 310b used for non-additive element-containing region R2>
The positive electrode active material 310b used in the non-additive element-containing region R2 may be any material as long as the above-described metal additive element (additional element) is not added to the main component of the lithium transition metal composite oxide. . As the positive electrode active material 310b, as long as these conditions are satisfied, one kind or two or more kinds of substances conventionally used in lithium ion secondary batteries can be used without particular limitation. Except that the metal additive element is not added, the positive electrode active material 310a used in the additive element-containing region R1 preferably has substantially the same composition.

Preferable examples of such a lithium transition metal composite oxide include, for example, an oxide represented by the general formula (II): Li _{1 + Β} (Ni _x Co _y Mn _z ) O ₂ . Examples of the lithium transition metal composite oxide include lithium nickel oxide (for example, LiNiO ₂ ), lithium cobalt oxide (for example, LiCoO ₂ ), lithium manganese oxide (for example, LiMn ₂ O ₄ ), and the like. Here, β in the above formula (II) is a value determined to satisfy the charge neutrality condition with 0 ≦ β ≦ 0.25, and x, y, z satisfies x + y + z≈1, and x, y, z At least one of them is greater than zero. In the above formula (II), “x + y + z≈1” is approximately 0.9 ≦ x + y + z ≦ 1.2 (typically 0.9 <x + y + z <1.2, for example 0.95 ≦ x + y + z ≦ 1.1). For example, x + y + z = 1.

  Further, x, y, z in the above formula (II) are not particularly limited as long as the condition that x + y + z≈1 and at least one of x, y, z is greater than 0 is satisfied. Any number of y and z may be the largest. In other words, the first element of Ni, Co, and Mn (the element that is contained most on the basis of the number of atoms) may be any of Ni, Co, and Mn. For example, x can be 0.1 or more (typically 0.3 or more) and less than 1 (typically 0.9 or less, such as 0.6 or less). y can be 0 or more (typically 0.1 or more, for example 0.3 or more) and 0.6 or less (typically 0.5 or less, for example 0.4 or less). z can be 0 or more (typically 0.1 or more, for example 0.3 or more) and 0.6 or less (typically 0.5 or less, for example 0.4 or less). Among these, lithium nickel cobalt manganese composite oxides that satisfy x, y, z> 0 (in other words, include all elements of Ni, Co, and Mn) can be preferably used. In a preferred embodiment, x, y, and z (that is, the amounts of Ni, Co, and Mn) are approximately the same. In another preferred embodiment, x> y and x> z (in other words, the first element is Ni).

<< Method for Forming Positive Electrode Active Material Layer 223 >>
The positive electrode active material layer 223 is preferably formed based on different mixtures in the additive element-containing region R1 and the non-additive element-containing region R2. For example, a first mixture for forming the additive element-containing region R1 and a second mixture for forming the non-additive element-containing region R2 may be prepared. The first mixture includes a positive electrode active material 310a in which a metal additive element is added to the main component of the lithium transition metal composite oxide. In addition, the second mixture includes the positive electrode active material 310b to which the metal additive element is not added with respect to the main component of the lithium transition metal composite oxide. A part of the positive electrode active material layer 223 is formed on the surface of the positive electrode current collector 221 by applying the first mixture to the portion where the additive element-containing region R1 of the positive electrode current collector 221 is formed and drying. This part becomes the additive element-containing region R1 of the positive electrode active material layer 223. In addition, when the remaining portion of the positive electrode active material layer 223 is formed on the surface of the positive electrode current collector 221 by applying the second mixture to the remaining portion in the longitudinal direction of the positive electrode current collector 221 and drying it. Good. This remaining portion becomes the non-additive element-containing region R2 of the positive electrode active material layer 223.

  Preferably, as shown in FIG. 8, a single positive electrode mixture coating film is formed in the length direction on one positive electrode current collector 221, and a slit is formed in the central portion of the coating film (a 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 positive electrode sheets 220 by cut | disconnecting the positive electrode electrical power collector 221 with the said slit. In this case, the first mixture 322 for forming the additive element-containing region R1 is in a portion where the additive element-containing region of the positive electrode current collector 221 is formed (that is, the central portion in the width direction of the positive electrode current collector 221). Can be applied. In addition, the second mixture 324 for forming the non-additive element-containing region R2 is applied to the remaining portion of the positive electrode current collector 221 in the longitudinal direction, leaving an uncoated portion of the positive electrode current collector 221 in a band shape. obtain. Then, after drying, the positive electrode current collector 221 may be cut by a slit (an alternate long and short dash line in FIG. 8) with a cutting device (not shown), and divided into two positive electrode sheets 220 for use.

<< Test Example 1 >>
The inventor conducted a test to evaluate the effect of the positive electrode sheet 220. 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 positive electrode active material layer 223 is provided with an uncoated portion 222 at one edge in the width direction perpendicular to the longitudinal direction of the positive electrode current collector 221, and the substantially uncoated portion 222 at the other edge. Is formed so as not to be provided. Further, as shown in FIG. 5, the W-added positive electrode active material 310b to which tungsten (W) is not added is added to the edge portion 225 on the side where the uncoated portion 222 of the positive electrode active material layer 223 is formed. A non-additive element-containing region R2 is provided. On the other hand, an additive element-containing region R1 using a W-added cathode active material 310a to which tungsten (W) is added is provided in the entire area of the cathode active material layer 223 excluding the edge portion 225.

  In this example, the negative electrode active material layer 243 is provided on the entire surface of the negative electrode current collector 241 except for an uncoated portion 242 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. Therefore, as shown in FIG. 7, the negative electrode active material layer 243 has a portion (non-opposing portion) 246a that does not face the positive electrode active material layer 223 at the edge on the side where the uncoated portion 242 is not formed. Have Further, the negative electrode active material layer 243 has a portion (non-opposing portion) 246b that does not face the positive electrode active material layer 223 at the edge on the side where the uncoated portion 242 is formed. In this example, the width W1 of the non-opposing portion 246a on the side where the uncoated portion 242 is formed is 3 mm, and the width W2 of the non-facing portion 246b on the side where the uncoated portion 242 is not formed is 3 mm. .

≪Positive electrode sheet≫
The positive electrode sheet 220 formed a plurality of samples in which the ratio (L2 / L1) between the width L1 of the additive element-containing region R1 and the width L2 of the non-additive element-containing region R2 was changed.

  The mixture for forming the positive electrode active material layer 223 includes lithium nickel cobalt manganese composite oxide as the positive electrode active material, acetylene black (AB) as the conductive material, polyvinylidene fluoride (PVdF) as the binder, and N-methylpyrrolidone as the solvent. (NMP) was used. The weight ratio of the positive electrode active material, AB, and PVdF was positive electrode active material: AB: PVdf = 100: 4: 2.

Here, the positive electrode active material layer 223 was formed based on different mixtures in the additive element-containing region R1 and the non-additive element-containing region R2. That is, a first mixture for forming the additive element-containing region R1 and a second mixture for forming the non-additive element-containing region R2 were prepared. The basic composition excluding W of the W-added positive electrode active material 310a contained in the first mixture is LiNi _1/3 Co _1/3 Mn _1/3 O _2, and the surface W concentration of the positive electrode active material 310a is 1.25 mol %. The composition of the positive electrode active material 310b not containing W contained in the second mixture was LiNi _1/3 Co _1/3 Mn _1/3 O ₂ . The first mixture is applied to both sides of the positive electrode current collector 221 by applying and drying the first mixture on the portion of the aluminum foil (thickness 15 μm) as the positive electrode current collector 221 where the additive element containing regions R1 are formed. A part of the active material layer 223 was formed. In addition, the remaining portion of the positive electrode active material layer 223 was formed on the surface of the positive electrode current collector 221 by applying the second mixture to the remaining portion in the longitudinal direction of the positive electrode current collector 221 in a strip shape 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 (L1 + L2: FIG. 7) of the positive electrode active material layer 223 was 94 mm.

≪Samples 1-9≫
In samples 1 to 9, the ratio (L2 / L1) between the width L1 of the additive element-containing region R1 and the width L2 of the non-additive element-containing region R2 is different (see FIG. 7). Samples 1 to 9 have the same configuration except for the width ratio (L2 / L1).

≪Negative electrode sheet≫
The negative electrode sheet 240 was produced as follows. A negative electrode mixture was prepared by adding 100 parts by weight of graphite powder as a negative electrode active material, 1 part by weight of a styrene butadiene copolymer (SBR) as a binder, and 1 part by weight of carboxymethyl cellulose as a thickener to water. Is applied to both sides of a long sheet-like copper foil (negative electrode current collector, thickness 14 μm) in a strip shape and dried, whereby a negative electrode sheet 240 having a negative electrode active material layer 243 provided on both sides of the negative electrode current collector 241. Was made. The coating amount of the negative electrode mixture was adjusted to be about 30 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.

≪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: 4: blended with 3, was used an electrolyte solution obtained by 1mol dissolving LiPF _6. 1% by mass of CHB and 1% by mass of BP were added to the electrolytic solution.

≪Measurement of initial capacity≫
Each of the test lithium ion secondary batteries obtained in Samples 1 to 9 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 the initial capacity (rated capacity). Here, the initial capacity of the test lithium ion secondary battery was 24 Ah.

≪Capacity maintenance ratio after cycle≫
A charge / discharge pattern that repeats CC charge / discharge at 2C was applied to each test lithium ion secondary battery of each sample, and a cycle test was performed. Specifically, in an environment of about 50 ° C., a charging / discharging cycle in which charging is performed up to 4.1 V by constant current charging at 2 C and discharging is performed up to 3.0 V by constant current discharging at 2 C is repeated 1000 times continuously. It was. Then, the capacity retention rate was calculated from the capacity after the charge / discharge cycle test and the initial capacity. Here, the capacity after the charge / discharge cycle test was performed in the same manner as in “Measurement of initial capacity”. The capacity retention rate was determined by “battery capacity after charge / discharge cycle test / initial capacity” × 100. Here, the above test was performed on five batteries of each sample, and the average value was calculated.

≪Capacity maintenance ratio after 0 ℃ pulse cycle≫
For each test lithium ion secondary battery of each sample, after adjusting to a charged state (SOC 50%) of about 50% of the initial capacity, CC discharge for 10 seconds at 20C and 20C under the temperature condition of 0 ° C The charging / discharging cycle which performs CC charge for 10 seconds was repeated 50000 times continuously. Then, the battery capacity after the 0 ° C. pulse cycle is measured under the same conditions as the initial capacity. From [(battery capacity after 0 ° C. pulse cycle) / (initial capacity)] × 100 (%), after 0 ° C. pulse cycle The capacity maintenance rate was obtained.

≪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 initial 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.

≪High temperature storage test≫
Each sample lithium ion secondary battery was adjusted to a charged state (SOC 100%) of about 100% of the initial 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 initial capacity, and the capacity retention rate after high-temperature storage was determined from [(battery capacity after high-temperature storage) / (initial capacity)] × 100 (%). . Here, the above test was performed on 50 batteries of each sample, and the average value was calculated.

≪Overcharge test≫
Each of the test lithium ion secondary batteries of each sample was charged to 20 V with a constant current of 2 A (corresponding to 1 C) in a constant temperature bath at 25 ° C. to be in an overcharged state. And the presence or absence of the action | operation of a current interruption mechanism was investigated from the change of battery voltage. Here, an overcharge test was performed on the battery that was not subjected to the cycle test and the battery after the cycle test. Moreover, the said test was implemented with respect to 10 batteries of each sample.

≪Evaluation of each sample≫
The results of the above test are shown in Table 1 for each sample.

  As shown in Table 1, in Sample 1, a W-added positive electrode active material 310a is used throughout the positive electrode active material layer 223. On the other hand, in the sample 9, the positive electrode active material 310 b to which W is not added is used throughout the positive electrode active material layer 223. Sample 1 to which W was added had a lower battery resistance than Sample 9 to which W was not added, and the capacity retention rate after cycling and the 0 ° C. capacity retention rate were improved, but the capacity retention rate after high-temperature storage tended to decrease. It was. In Sample 1, since W is added to the entire area of the positive electrode active material layer 223, it is estimated that W was eluted from the edge 225 of the positive electrode active material layer 223 during high temperature storage, resulting in a decrease in battery capacity. .

  On the other hand, in Samples 2 to 8, the positive electrode active material 310a to which W is added is used for the edge 225 on the side where the uncoated part 222 of the positive electrode active material layer 223 is formed, and the positive electrode excluding the edge 225. The positive electrode active material 310b to which W is not added is used throughout the active material layer 223. About these samples 2-8, battery resistance, a post-cycle capacity | capacitance maintenance factor, and a 0 degreeC capacity | capacitance maintenance factor were all favorable, and showed extremely high durability performance compared with the sample 9. In addition, the capacity retention rate after high-temperature storage was significantly improved as compared with Sample 1. As described above, the positive electrode active material 310b to which W is not added is used for the edge 225 on the side where the uncoated part 222 of the positive electrode active material layer 223 is formed, and the entire area of the positive electrode active material layer 223 excluding the edge 225. By using the W-added positive electrode active material 310a, the battery performance of the lithium ion secondary battery is remarkably improved over a wide temperature range from a low temperature to a high temperature.

  In Samples 3 to 8, the ratio between the width L1 of the additive element-containing region and the width L2 of the non-additive element-containing region is set in a range of 0.1 ≦ (L2 / L1). Samples 3 to 8 had a capacity retention rate of 97% or more after high-temperature storage, which was much better than that of sample 2 (L2 / L1: 0.06). In sample 2, since the ratio of the width L2 of the non-additive element-containing region is too small, it is understood that elution of W occurs at the edge portion 225 of the positive electrode active material layer 223, resulting in capacity deterioration. From this result, the width ratio (L2 / L1) is preferably 0.1 or more, more preferably about 0.2 or more, and particularly preferably about 0.3 or more.

  In Samples 2 to 7, the ratio between the width L1 of the additive element-containing region and the width L2 of the non-additive element-containing region is set in the range of (L2 / L1) ≦ 1. Samples 2 to 7 had a good result with a post-cycle capacity retention rate of 82% or more, and were more durable than sample 8 (L2 / L1: 1.24). In sample 8, since the ratio of the width L2 of the non-addition element-containing region is too large, it is understood that the performance improvement effect by adding W was insufficient. From this result, the width ratio (L2 / L1) is preferably 1 or less, more preferably approximately 0.8 or less, and particularly preferably approximately 0.6.

  Sample 1 had a smaller number of operating current interrupting mechanisms during overcharging than other samples 2-8. In Sample 1, W elutes from the edge 225 of the positive electrode active material layer 223 during overcharge and causes a side reaction with the gas generating agents (CHB and BP) in the electrolytic solution, so that the gas generating agent is consumed. It is presumed that no gas was generated. On the other hand, in Samples 2 to 8, by using the positive electrode active material 310b to which W is not added at the edge 225 of the positive electrode active material layer 223, elution of W is avoided and side reaction with the gas generating agent hardly occurs. . As a result, it is understood that wasteful consumption of the gas generating agent can be suppressed, the amount of gas generated can be increased, and the current interrupting mechanism can be operated in a short time. Also from this point, it can be said that the present invention is a highly valuable technique.

<< Test Example 2 >>
As shown in FIG. 7, the width W1 of the non-opposing portion 246a on the side where the uncoated portion 242 of the negative electrode active material layer 243 is formed is 4 mm, and the non-facing portion on the side where the uncoated portion 242 is not formed A lithium ion secondary battery was fabricated and evaluated in the same manner as in Test Example 1 except that the width W2 of the portion 246b was 2 mm. The results are shown in Table 2.

<< Test Example 3 >>
As shown in FIG. 7, the width W1 of the non-opposing portion 246a on the side where the uncoated portion 242 of the negative electrode active material layer 243 is formed is 6 mm, and the non-facing portion on the side where the uncoated portion 242 is not formed A lithium ion secondary battery was fabricated and evaluated in the same manner as in Test Example 1 except that the width W2 of the portion 246b was set to 0 mm (that is, no non-opposing portion 246b). The results are shown in Table 3.

  As shown in Table 2 and Table 3, in Sample 10 (Table 2) and Sample 19 (Table 3), the W-added positive electrode active material 310a is used throughout the positive electrode active material layer 223. Further, in sample 10, the width W2 of the non-opposing portion 246b on the side where the uncoated portion 242 of the negative electrode active material layer 243 is not formed is set to 2 mm. In sample 19, the width W2 of the non-opposing portion 246b on the side where the uncoated portion 242 of the negative electrode active material layer 243 is not formed is set to 0 mm. About these samples 10 and 19, compared with the sample 1 (Table 1) which made width W2 3 mm, the capacity | capacitance maintenance factor after high-temperature storage became a tendency to fall. In Samples 10 and 19, the relative positions of the edge 245 (FIG. 4) of the negative electrode active material layer 243 and the edge 225 of the positive electrode active material layer 223 are closer than those of the sample 1. Therefore, it is understood that the elution of W at the edge 225 of the positive electrode active material layer 223 becomes remarkable, which causes the capacity deterioration.

  In contrast, in Samples 11 to 17 (Table 2) and Samples 20 to 26 (Table 3), the positive electrode active material with W added to the edge 225 on the side where the uncoated portion 222 of the positive electrode active material layer 223 is formed. The material 310a is used, and the positive electrode active material 310b to which W is not added is used in the entire area of the positive electrode active material layer 223 excluding the edge portion 225. About these samples 11-17, 20-26, the capacity | capacitance maintenance factor after high temperature storage was able to be made high to the same extent as samples 2-8 (Table 1). The configuration of the present invention is particularly suitable for batteries in which the relative position between the edge 245 of the negative electrode active material layer 243 and the edge 225 of the positive electrode active material layer 223 is close, as in Samples 11 to 17 and Samples 20 to 26. It can be said that it is useful.

  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. Accordingly, the present invention, as schematically shown in FIG. 9, is 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 Positive electrode active material layer 225 Edge 240 Negative electrode sheet 241 Negative electrode current collector 242 Uncoated part 243 Negative electrode active material layer 245 Edge portion 262, 264 Separator 300 Battery case 310a Positive electrode active material (with metal additive)
310b Positive electrode active material (no metal additive)
460 Current interrupt mechanism

Claims (7)

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 an electrode body overlaid with an intervening separator,
The negative electrode active material layer is provided with an uncoated portion where the negative electrode active material layer is not formed at one edge in the width direction perpendicular to the longitudinal direction of the negative electrode current collector, and at the other edge. Is formed so that substantially the uncoated part is not provided,
The positive electrode active material layer is provided with an uncoated portion where the positive electrode active material layer is not formed at one edge in the width direction perpendicular to the longitudinal direction of the positive electrode current collector, and at the other edge. Is formed so that substantially the uncoated part is not provided,
The negative electrode current collector and the positive electrode current collector are arranged such that the uncoated portions of each other protrude on the opposite side in the width direction,
Here, the positive electrode active material layer is added using a positive electrode active material in which at least one metal element excluding an element constituting the main component is added to the main component of the lithium transition metal composite oxide. An element-containing region, and a non-additive element-containing region using a positive electrode active material to which the metal element is not added with respect to a main component of the lithium transition metal composite oxide,
The non-additive element-containing region is a secondary battery provided at an edge portion of the positive electrode active material layer on the side where the uncoated portion is formed.   The relationship of 0.1 ≦ (L2 / L1) ≦ 1 is satisfied when the width of the additive element-containing region along the width direction is L1 and the width of the non-additive element-containing region is L2. 2. The secondary battery according to 1.   The positive electrode active material included in the additive element-containing region includes, as the metal element, W, Zr, Mg, Ca, Na, Fe, Cr, Zn, Si, Sn, Sr, Ti, V, Nb, Mo, Rh, The secondary battery according to claim 1 or 2, comprising at least one selected from the group consisting of Pb, Pt, Cu, Ga, In, La, Ce, Al and B. The positive electrode active material contained in the additive element-containing region has the general formula (I):
_{Li 1 + α (Ni a Co} b Mn c M d W e) O 2 (I)
(Here, M is one or more selected from a transition metal element and a typical metal element, and α is a value determined to satisfy the charge neutrality condition with 0 ≦ α ≦ 0.25, and a , B, c, d, e satisfy a + b + c + d + e≈1, 0.0005 ≦ e ≦ 0.01 and d ≧ 0, and at least one of a, b, c is greater than 0);
The secondary battery as described in any one of Claims 1-3 which is lithium transition metal complex oxide represented by these.   The secondary battery according to claim 4, wherein the average tungsten concentration from the surface of the positive electrode active material to 1.5 nm in the depth direction is 0.5 mol% to 2 mol%. The positive electrode active material contained in the non-additive element-containing region has the general formula (II):
Li _{1 + Β} (Ni _x Co _y Mn _z ) O ₂ (II)
(Where β is a value determined so as to satisfy the charge neutrality condition with 0 ≦ β ≦ 0.25, and x, y, and z satisfy x + y + z≈1, and at least one of x, y, and z Is greater than 0);
The secondary battery as described in any one of Claims 1-5 which is lithium transition metal complex oxide represented by these. 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 said negative electrode collector and the said positive electrode collector are arrange | positioned and wound so that a mutual uncoated part may protrude on the opposite side of the width direction, The any one of Claims 1-6 Secondary battery described in 1.

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