WO2008018207A1

WO2008018207A1 - Nonaqueous electrolyte secondary battery

Info

Publication number: WO2008018207A1
Application number: PCT/JP2007/058083
Authority: WO
Inventors: Akihiro Modeki; Yanko Marinov Todorov; Yoshiki Sakaguchi
Original assignee: Mitsui Mining & Smelting Co., Ltd.
Priority date: 2006-08-10
Filing date: 2007-04-12
Publication date: 2008-02-14
Also published as: JP2008047304A

Abstract

A nonaqueous electrolyte secondary battery comprising a winding body (1) having a flat transverse section and formed by winding a positive electrode, a negative electrode and a separator interposed between them, characterized in that a planar core material (3) is arranged in the center of the winding body (1). Preferably, the core material (3) also serves as the current collection tab of the positive or negative electrode. Furthermore, a plurality of strip pieces extending in the height direction of the winding body (1) are preferably arranged linearly in one row in the width direction of the winding body (1). The nonaqueous electrolyte secondary battery may be a rectangular battery or a laminate battery.

Description

Specification

Non-aqueous electrolyte secondary battery

Technical field

[0001] The present invention relates to a non-aqueous electrolyte secondary battery such as a lithium secondary battery.

Background art

[0002] As a form of the lithium secondary battery, a cylindrical type or a rectangular type including a winding body obtained by integrally winding a positive electrode, a separator, and a negative electrode in this order are known. Furthermore, a laminate type in which the wound body is enclosed in an aluminum laminate exterior body is also known. As an example of this type of battery, Patent Document 1 discloses that a positive electrode, a separator, and a negative electrode are integrally wound using a core material to produce a cylindrical electrode body, and the electrode is removed after the core material is removed. While the body is pressed from the direction perpendicular to the winding axis to deform into a substantially elliptical cross section, the deformed electrode body is rotated in the same direction as the winding direction to loosen the winding state. A lithium secondary battery that has been pressed into a flat spiral electrode body by pressing the polar body has been proposed! According to the description in Patent Document 1, since this battery can loosen in the vicinity of the corner of the flat spiral electrode body, when the electrode expands, the electrode is deformed in a direction to fill the looseness, and the deflection is prevented. It is supposed to be done.

[0003] If the flat spiral electrode body described in Patent Document 1 is adopted, it may not be possible to absorb the expansion of the electrode at the corner portion, but the electrode deformation at the center portion cannot be prevented. . In general, there is a gap K at the center of the flat spiral electrode body as shown in FIG. 13 (a) for the reason of manufacturing, so when the electrode near the center expands, the expansion is caused by a gap. This is because deformation such as buckling occurs as shown in Fig. 13 (b). Also, as shown in FIG. 13 (a), a current collecting tab T is attached to the center of the electrode body, and since the thickness is not uniform, the degree of expansion of the electrode is reduced. This is different between the part where the metal exists and the part where it does not, which also causes the electrode to buckle easily as shown in Fig. 13 (b).

[0004] Patent Document 1: US2006—111625A1

Accordingly, an object of the present invention is to provide a non-aqueous solution that can eliminate the various disadvantages of the above-described conventional technology. The object is to provide an electrolyte secondary battery.

Disclosure of the invention

[0006] The present invention includes a winding body in which a positive electrode, a negative electrode, and a separator interposed therebetween are wound, and has a flat cross section, and a plate is provided at the center of the winding body. The present invention provides a non-aqueous electrolyte secondary battery characterized in that a shaped core material is arranged. Brief Description of Drawings

FIG. 1 (a) is a perspective view showing a wound body in one embodiment of the battery of the present invention, and FIG. 1 (b) is a cross-sectional view taken along the line bb in FIG. 1 (a). It is.

[FIG. 2] FIG. 2 is a schematic diagram in a planar state where the wound state of the central portion of the wound body shown in FIG. 1 is solved.

FIG. 3 (a) is a schematic diagram (corresponding to FIG. 1 (b)) showing the cross-sectional structure of the wound body in the second embodiment of the present invention, and FIG. FIG. 6 is a schematic diagram (corresponding to FIG. 2) in a flat state where the winding state of the central portion of the winding body shown in FIG. 3 (a) is solved.

[FIG. 4] FIG. 4 (a) is a schematic diagram (corresponding to FIG. 1 (b)) showing the cross-sectional structure of the wound body in the third embodiment of the present invention, and FIG. FIG. 5 is a schematic diagram (corresponding to FIG. 2) in a flat state where the winding state of the central portion of the winding body shown in FIG. 4 (a) is solved.

[FIG. 5] FIGS. 5 (a) and 5 (e) are process diagrams sequentially showing a method of manufacturing the wound body shown in FIGS. 3 (a) and 3 (b).

[FIG. 6] FIGS. 6 (a) and 6 (b) are process diagrams showing a method for producing the wound body shown in FIGS. 4 (a) and 4 (b), and are shown in FIGS. 5 (c) and 5 (d). It is a figure corresponding to a process.

FIG. 7 is a schematic diagram showing a cross-sectional structure of an embodiment of a negative electrode used in the present invention.

8 is a process chart showing a method for producing the negative electrode shown in FIG.

FIG. 9 is a CT scan image of the cross section of the battery obtained in Example 1.

FIG. 10 is a CT scan image of the cross section of the battery obtained in Comparative Example 1.

FIG. 11 is a CT scan image of the cross section of the battery obtained in Example 2.

FIG. 12 is a CT scan image of the cross section of the battery obtained in Comparative Example 2.

FIG. 13 (a) is a schematic diagram showing a cross-sectional structure of an electrode winding body in a conventional prismatic battery. FIG. 13 (b) is a schematic diagram showing a state after charging and discharging of the electrode winding body shown in FIG. 13 (a).

Detailed Description of the Invention

[0008] Hereinafter, the present invention will be described based on preferred embodiments thereof. The non-aqueous electrolyte secondary battery of the present invention (hereinafter also simply referred to as a secondary battery or a battery) has a positive electrode, a negative electrode, and a separator disposed between them as its basic constituent members. The battery includes a winding body formed by integrally winding a positive electrode, a negative electrode, and a separator interposed therebetween. The wound body has a flat shape such as an oval or elliptical cross section. When the positive electrode active material layer and the negative electrode active material layer are formed only on one surface of the current collector of the positive electrode and the negative electrode, a separator is interposed between the active material layers facing each other. Put these three together. When the positive electrode active material layer and the negative electrode active material layer are formed on both surfaces of the current collector of the positive electrode and the negative electrode, a separator is interposed between the two with the positive electrode and the negative electrode facing each other. Furthermore, a second separator is arranged on the outer surface of the positive electrode or the outer surface of the negative electrode, and these four members are wound. The space between the positive electrode and the negative electrode is filled with a non-aqueous electrolyte via a separator. The battery of the present invention can be in a form in which a strong winding body is accommodated in a rectangular outer can or in a form in which it is accommodated in a laminate outer body. In particular, when the major axis of the cross section of the wound body is A and the minor axis is B, the effect of the present invention becomes remarkable when a wound body having an AZB of 3 or more is used. The upper limit of AZB is not critical in the present invention, but is empirically about 20.

[0009] FIGS. 1 (a) and 1 (b) show an embodiment of a wound body 1 in a battery of the present invention. The wound body 1 has a flat shape in which a positive electrode, a negative electrode, and a separator interposed therebetween are wound around a core material 3. In FIG. 1, the positive electrode, the negative electrode, and the separator are not drawn individually, but are drawn as a single line combining them for convenience. The positive electrode, separator, and negative electrode in the wound body 1 are all long. The widths of the positive and negative electrodes are the same. The width of the separator is slightly larger than the positive and negative electrodes.

[0010] From the center of the wound body 1, tabs 2 and 2 for collecting current of the positive electrode and the negative electrode are drawn out. Tab 2 is electrically connected to a current collector in each electrode. Tab 2 is a conductive material, for example It is made up of nickel power.

[0011] FIG. 2 schematically shows a plan view of the winding state of the central portion of the wound body 1 shown in FIG. The core 3 has a rectangular shape having a pair of first sides X extending in the width direction of the positive electrode C (and the negative electrode A) and a pair of second sides Y extending in the length direction of the positive electrode C (and the negative electrode A). belongs to. The core material 3 has a hollow or solid plate shape. The length of the first side X in the core material 3 is substantially the same as the width of the positive electrode C (and the negative electrode A). The length of the second side Y of the core material 3 is the same as the length of the first side X, or shorter or longer than that of the first side X, depending on the dimensions of the target battery. ing. The length of the second side Y is preferably 70 to 99% with respect to the width W (see FIG. 1 (b)) of the inner part of the winding body at the innermost peripheral portion of the winding body 1. More preferably, the length is 80 to 95%. If this ratio is less than 70%, the effects of the present invention may not be sufficiently achieved. If it exceeds 99%, stress generated when the battery is charged is applied to the edge portion of the core material 3, and the wound body may be damaged.

[0012] Regarding the thickness of the core material 3, a thickness that does not deform against the expansion of the negative electrode is required. It is sufficient that such a thickness is about 0.03 to 1 mm, particularly about 0.1 to 0.5 mm, depending on the material of the core material 3 described later. For example, in a wound body that can be accommodated in a specified size battery such as the 063448 type, the core material 3 preferably has a thickness of 1 mm or less in order to ensure sufficient length of the negative electrode and the like.

[0013] The core material 3 is preferably made of a high-strength material from the viewpoint of preventing buckling of the negative electrode, which will be described later. The core material 3 is also preferably lightweight from the viewpoint of increasing the weight energy density of the battery. From these viewpoints, the core material 3 is also configured with an insulating material strength such as polyolefin resin such as polyethylene and polypropylene. In that case, it is also preferable to add glass fiber to improve the strength. Alternatively, as will be described later, the core material 3 is made of a conductive material such as nickel.

[0014] The positive electrode used in the battery of the present invention has, for example, a positive electrode active material layer formed on at least one surface of a current collector. The positive electrode active material layer contains an active material. As this active material, for example, a lithium transition metal composite oxide is used. Lithium transition metal complex oxides include LiCoO, LiNiO, LiMn O, LiMnO, LiCo Ni O, LiNi C o Mn 0, LiNi Co Mn O, etc. are used. But what is limited to these

0.2 0.1 2 1/3 1/3 1/3 2

Well then. These positive electrode active materials can be used singly or in combination of two or more.

In the positive electrode used in the present invention, the positive electrode active material is suspended in a suitable solvent together with a conductive agent such as acetylene black and a binder such as polyvinylidene fluoride to prepare a positive electrode mixture, It can be obtained by applying and drying on at least one surface of a current collector such as an aluminum foil, followed by roll rolling and pressing.

When the positive electrode is produced by the above method, the lithium transition metal composite oxide has an average primary particle diameter of 5 μm or more and 10 μm or less. I like it from the balance. Polyvinylidene fluoride used as a binder is preferred because its weight average molecular weight is not less than 350,000 and not more than 2,000,000 because it can improve discharge characteristics in a low temperature environment.

[0017] The negative electrode used in the battery of the present invention has, for example, a negative electrode active material layer formed on at least one surface of a current collector. The negative electrode active material layer contains an active material. As this active material, a material capable of occluding and releasing lithium ions is used. Examples of such a material include a material containing Si, a material containing Sn, a material containing A1, and a material containing Ge. As the material containing Sn, for example, an alloy containing tin, cobalt, carbon, and at least one of nickel and chromium is preferably used. In order to improve the capacity density per weight of the negative electrode, a material containing Si or a material containing Sn is particularly preferable.

[0018] As the material containing Si, a material capable of occluding lithium and containing silicon, for example, silicon alone, an alloy of silicon and metal, silicon oxide, or the like can be used. These materials can be used alone or in combination. Examples of the metal include one or more elements selected from the group consisting of Cu, Ni, Co, Cr, Fe, Ti, Pt, W, Mo, and Au. Of these metals, Cu, Ni, and Co are preferred, and Cu and Ni are preferably used because of their excellent electronic conductivity and low ability to form lithium compounds. Further, before or after incorporating the negative electrode into the battery, lithium may be occluded in the active material having a material strength including Si. Particularly preferably, the material containing Si has a high point of absorption of lithium, silicon or silicon oxide. It is.

[0019] The negative electrode active material layer is, for example, a continuous thin film layer comprising the negative electrode active material, a coating layer containing particles of the negative electrode active material, and a sintered body layer containing particles of the negative electrode active material. Etc. Further, it may be a layer having a structure shown in FIG.

[0020] As the separator in the battery of the present invention, a synthetic resin nonwoven fabric, a polyolefin such as polyethylene-polypropylene, a porous film of polytetrafluoroethylene, or the like is preferably used. From the viewpoint of suppressing the heat generation of the electrode that occurs when the battery is overcharged, it is preferable to use a separator in which a polyolefin film is formed on one or both surfaces of the polyolefin microporous membrane. The separator preferably has a piercing strength of 0.2 NZ m or more and 0.49 NZw m or less, and a tensile strength in the winding axis direction of OMPa or more and 150 MPa or less. Even when a negative electrode active material that expands and contracts greatly with charge and discharge is used, damage to the separator can be suppressed and the occurrence of an internal short circuit can be suppressed.

[0021] The nonaqueous electrolytic solution is a solution in which a lithium salt as a supporting electrolyte is dissolved in an organic solvent.

As the lithium salt, CF SO Li ゝ (CF SO) NLi ゝ (C F SO) NLi ゝ LiCIO, LiAl

3 3 3 2 2 5 2 2 4

CI, LiPF, LiAsF, LiSbF, LiCl, LiBr, Lil, LiC F SO and the like are exemplified. these

4 6 6 6 4 9 3

May be used alone or in combination of two or more. Among these lithium salts, CF SO Li, (CF SO) NLi, (C F SO) NLi are used because of their excellent water decomposition resistance.

3 3 3 2 2 5 2 2 is preferably used. Examples of the organic solvent include ethylene carbonate, jetyl carbonate, dimethyl carbonate, propylene carbonate, butylene carbonate, and the like. In particular, 0.5 to 5% by weight of beylene carbonate and 0.1 to 1% by weight of dibutyl sulfone, 0.1 to 1.5% by weight of 1,4 butanediol dimethane, based on the total amount of the non-aqueous electrolyte. Including sulfonate is preferable from the viewpoint of further improving the charge / discharge cycle characteristics. The details are not clear, but 1,4 butanediol dimethyl sulfonate and divinyl sulfone are decomposed stepwise to form a film on the positive electrode, so that the film containing sulfur becomes denser. This is probably because of this.

[0022] In particular, as non-aqueous electrolytes, 4 fluoro-1,3 dioxolan-2-one, 4 black mouth 1,3 dixolan 1 2-one or 4 trifluoromethyl 1,1,3 dioxola It is also preferable to use a high dielectric constant solvent having a relative dielectric constant of 30 or more, such as a cyclic carbonate derivative having a halogen atom such as n-2-one. This is because it has high resistance to reduction and is difficult to be decomposed. In addition, an electrolytic solution obtained by mixing the high dielectric constant solvent and a low viscosity solvent having a viscosity of ImPa · s or less, such as dimethyl carbonate, jetyl carbonate, or methyl ethyl carbonate is also preferable. This is because higher ionic conductivity can be obtained. Furthermore, it is also preferable that the content of fluorine ions in the electrolytic solution is in the range of 14 mass ppm to 1290 mass ppm. When the electrolyte solution contains an appropriate amount of fluorine ions, a coating film such as lithium fluoride derived from fluorine ions is formed on the negative electrode, and it is possible to suppress the decomposition reaction of the electrolyte solution in the negative electrode. is there. Further, it is preferable that 0.001% by weight to 10% by weight of at least one additive selected from the group consisting of acid anhydrides and derivatives thereof is contained. This is because a film is formed on the surface of the negative electrode, and the decomposition reaction of the electrolytic solution can be suppressed. As this additive, a cyclic compound containing one c (= o) —Oc (= o) — group in the ring is preferred, for example, succinic anhydride, darthal anhydride, maleic anhydride, phthalic anhydride, anhydrous 2-sulfobenzoic acid, anhydrous citraconic acid, anhydrous itaconic acid, anhydrous diglycolic acid, anhydrous hexafluoroglutaric acid, anhydrous 3-fluorophthalic acid, anhydrous 4-phthalic anhydride derivatives such as fluorophthalic acid, or anhydrous 3, 6—Epoxy 1, 2, 3, 6—Tetrahydrophthalic acid, 1,8 naphthalic anhydride, 2,3 naphthalene carboxylic acid anhydride, 1,2-cyclopentanedicarboxylic acid anhydride, 1,2-cycloto Anhydrous 1,2 cycloalkanedicarboxylic acid such as xane dicarboxylic acid, or tetrahydrophthalic anhydride such as cis 1, 2, 3, 6-tetrahydrophthalic anhydride or 3, 4, 5, 6-tetrahydrophthalic anhydride Or hexahi Lophthalic anhydride (cis isomer, trans isomer), 3, 4, 5, 6-tetrachlorophthalic anhydride, 1, 2, 4 benzenetricarboxylic anhydride, dianhydropyromellitic acid, or their derivatives Etc.

According to the battery of the present embodiment including the winding body 1 having the above-described configuration, the core material 3 is disposed at the center of the winding body 1, and the winding body 1 and the core material 3 are interposed between them. Since the voids are not substantially present, even if a stress caused by the expansion of the negative electrode active material is locally applied to the center of the wound body 1, the core material 3 can receive the stress. As a result, the negative electrode buckling is suppressed by the core material 3. Therefore, the battery of this embodiment has improved cycle characteristics. It becomes. If a large gap exists in the center of the wound body 1, the negative electrode is deformed toward the gap due to expansion of the negative electrode active material, and buckling occurs.

3 (a) and 3 (b) show another structure of the wound body 1. FIG. In the wound body 1 of the present embodiment, two core members 3 are used, and each core member 3 also serves as a current collecting tab for the positive electrode and the negative electrode. Specifically, the core material 3 includes a main body portion 3A and a tab portion 3B that extends upward from the upper end edge of the main body portion 3A and extends beyond the longitudinal edge portion of the positive electrode C (negative electrode A). The The dimensions of the main body 3A are the same as those of the core shown in FIG. The tab portion 3B has a rectangular shape and is smaller than the main body portion 3A. Each core member 3 is electrically connected to the positive electrode and the negative electrode in the main body 3A. In Fig. 3 (a), the force depicted so that the two cores 3 and 3 are in contact with each other is actually an insulating material such as a separator between the two cores 3 and 3. The core materials 3 and 3 are electrically insulated.

[0025] According to this embodiment, there is no step generated in the wound body due to the separate attachment of the current collecting tab to the electrode. As a result, the occurrence of buckling due to the expansion of the negative electrode can be more effectively prevented. Further, the use of the core material 3 does not cause a decrease in energy density due to a slight increase in volume. In this embodiment, two core members 3 are used. Instead, only one core member is used, and the core member also serves as a positive or negative current collecting tab. Also good. In this case, the core material can also serve as the current collecting tab! If the normal current collecting tab is electrically connected to the other electrode.

FIGS. 4 (a) and 4 (b) show still another structure of the wound body 1. FIG. Even in the winding body 1 of the present embodiment, the core material also serves as a current collecting tab for the positive electrode and the negative electrode. This is the same as the embodiment shown in FIGS. 3 (a) and 3 (b). The difference between this embodiment and the embodiment shown in FIGS. 3 (a) and 3 (b) is that, in addition to the core material that also serves as a current collecting tab, a core material that is also used as a tab is further used. Is a point.

In detail, with respect to the positive electrode C, a core material 31 that is also a rectangular strip extending in the width direction of the positive electrode C (= the height direction of the wound body) is formed in the longitudinal direction of the positive electrode C (= 捲Three are arranged in parallel in the width direction of the rotator. One of the three core members 31 includes a main body 31A and a tab portion 31B that extends upward from the upper side of the main body 31A and extends beyond the longitudinal edge of the positive electrode C. It is configured. The core material 31 having the tab portion 31B is electrically connected to the positive electrode C. The remaining two tabs may be electrically connected to the positive electrode C or may be insulated and fixed to the positive electrode C!

[0028] On the other hand, for the negative electrode A, the core 32, which is also a rectangular strip extending in the width direction of the negative electrode A (= the height direction of the wound body), is the longitudinal direction of the negative electrode A (= the wound body). In the width direction). One of the two core members 32 is configured to include a main body portion 32A and a tab portion 32B that extends upwardly from the upper side force of the main body portion 32A and extends beyond the longitudinal edge of the negative electrode A. The core member 32 having the tab portion 32B is electrically connected to the negative electrode A. The other tab 32 may be electrically connected to the negative electrode A or may be fixed to the negative electrode A in an insulated state.

[0029] The core material 31 for the positive electrode and the core material 32 for the negative electrode are formed as shown in FIG. 4 (a) when the positive electrode, the negative electrode, and the like are wound to form the wound body 1. They are arranged in a straight line at the center of the rotating body 1. By arranging the core materials 31 and 32 in this way, the wound body 1 can realize a state similar to a state in which a single core material having a wide force is used. As a result, the volume and weight occupied by the core materials 31 and 32 in the wound body 1 can be reduced as compared with the embodiment shown in FIGS. 3 (a) and 3 (b). This is advantageous in that it can improve the energy density per unit volume and unit weight of the battery. In addition to this, according to the present embodiment, the same effect as that of the embodiment shown in FIGS. 3 (a) and 3 (b) can be obtained. Although not shown, the core material 31 and the core material 32 are electrically insulated through an insulating material such as a separator.

[0030] The distance between the core materials 31 in the positive electrode C and the distance between the core materials 32 in the negative electrode A are preferably 0 to 2 mm, particularly preferably 0.5 to lmm. By setting this distance to 0.5 mm or more, the energy density per weight can be improved while maintaining the effects of the invention. In addition, by setting it to 2 mm or less, it is possible to prevent buckling from occurring in the recessed portion between the core materials 31.

[0031] In the embodiment shown in Figs. 4 (a) and (b), the force in which one of the plurality of core materials 31, 32 includes the tab portion 32 was included. None of the core members 31 and 32 may have the tab portion 32. In this case, connect the normal current collecting tab to the positive electrode C. And the negative electrode A may be electrically connected.

Next, a method for manufacturing a wound body used in the present invention will be described with reference to FIG. 5, taking the method for manufacturing a wound body shown in FIGS. 3 (a) and 3 (b) as an example. This manufacturing method produces a wound body using a positive electrode in which a positive electrode active material layer is formed on each surface of a current collector, and a negative electrode in which a negative electrode active material layer is formed on each surface of the current collector. It is related to. First, as shown in FIG. 5 (a), the first separator S1 and the second separator S2 each having a long strip shape are fed out from the raw fabrics SI 'and S2' wound in the shape of a tool, respectively. Attach the tip to the plate-shaped take-up jig 20. The winding jig 20 is rotatable around its center line. Next, as shown in FIG. 5 (b), the winding jig 20 is rotated in the direction of the arrow to wind the separators SI and S2 around the jig 20.

[0033] Next, as shown in Fig. 5 (c), the long strip-shaped positive electrode C and negative electrode A are respectively fed out from the rolls of the raw material C 'and A', and the tips of the positive electrode C and the negative electrode A are already drawn. Attach to the take-up jig 20 to which the separators SI and S2 are attached. In this case, the tips of these electrodes are attached to the winding jig 20 so that the negative electrode A is positioned between the two separators SI and S2 and the positive electrode C is positioned on the outer surface side of the first separator S1.

[0034] Each of the negative electrode A and the positive electrode C is pre-attached with core materials 3 and 3 on one surface thereof. Each of the core members 3 and 3 has a shape shown in FIG. 3 (b) and includes a tab portion. Each of the core materials 3 and 3 is attached to these electrodes while being electrically connected to the negative electrode A and the positive electrode C, respectively. Each core material 3 and 3 is shown in FIG. 5 (d) when the winding jig 20 is rotated and the positive electrode C and the negative electrode A are wound around the jig 20 together with the separators S1 and S2. As described above, the core members 3 and 3 are positioned on the winding jig 20 and are aligned so that the core members 3 and 3 face each other. The positive electrode C and negative electrode A, to which the core materials 3 and 3 thus aligned are attached, are wound around the winding jig 20 together with the separators SI and S2 as shown in Fig. 5 (d). And Winding body 1 is obtained by winding the desired number of times. In wrapping each member, adjacent members are in contact with each other only by overlapping, and are not joined by a joining means such as an adhesive. In other words, each member simply touches and peels mechanically!

[0035] When the winding is completed, the positive electrode C and the negative electrode A are separated from the separators SI and S2, and the raw materials thereof. Also cut the roll force and fix the cut end to the side of the wound body 1. For example, an adhesive tape or an adhesive is used for fixing. Finally, the winding body 1 shown in FIGS. 3 (a) and 3 (b) is obtained by pulling out the winding jig 20 from the center of the winding body as shown in FIG. 5 (e). The wound body 1 from which the winding jig 20 has been pulled out is accommodated in a rectangular outer can or an aluminum laminate outer body.

[0036] When the wound body 1 shown in Figs. 4 (a) and (b) is manufactured, in the step shown in Fig. 6 (a) corresponding to the above-described Fig. 5 (c), the positive electrode C Further, the core materials 31 and 32 made of strips may be attached to the negative electrode A and wound. In this case, each of the core members 31, 32 is rotated when the winding jig 20 is rotated and the positive electrode C and the negative electrode A together with the separators SI and S2 are wound around the jig 20. As shown in FIG. 6 (b), the core members 31, 32 are positioned on the take-up jig 20, and are aligned so that the core members 31, 32 do not face each other.

FIG. 7 shows a schematic diagram of a cross-sectional structure of a preferred embodiment of the negative electrode used in the present invention. The negative electrode 10 of this embodiment includes a current collector 11 and an active material layer 12 formed on at least one surface thereof. Note that FIG. 7 shows a state where the active material layer 12 is formed only on one side of the current collector 11 for the sake of convenience! / The active material layer is formed on both sides of the current collector. Have you been?

In the active material layer 12, at least a part of the surface of the active material particles 12 a containing Si is covered with a metal material having a low lithium compound forming ability. This metal material 13 is a material different from the constituent material of the particles 12a. Voids are formed between the particles 12a coated with the metal material. That is, the metal material covers the surfaces of the particles 12a in a state where a gap is secured so that the non-aqueous electrolyte containing lithium ions can reach the particles 12a. In FIG. 7, the metal material 13 is conveniently represented as a thick line surrounding the periphery of the particle 12a. This figure is a schematic diagram of the active material layer 12 viewed two-dimensionally. In actuality, each particle is in direct contact with other particles via the metal material 13. “Lithium compound forming ability is low” means that lithium does not form an intermetallic compound or solid solution, or even if lithium is formed, the force is very small or very unstable.

[0039] The metal material 13 has conductivity, and examples thereof include copper, nickel, iron, cobalt, and alloys of these metals. In particular, the metal material 13 is composed of active material particles 12 It is preferable that the material of the surface of the particle 12a is not easily broken even if a expands and contracts. It is preferable to use copper as such a material.

[0040] The metal material 13 is preferably present on the surface of the active material particles 12a over the entire thickness direction of the active material layer 12. The active material particles 12 a are preferably present in the matrix of the metal material 13. As a result, even if the particles 12a expand and contract due to charge and discharge, even if they become fine powder, they are less likely to fall off. In addition, since the electronic conductivity of the entire active material layer 12 is ensured through the metal material 13, the electrically isolated active material particles 12 a are generated, particularly in the deep part of the active material layer 12. The formation of the active material particles 12a is effectively prevented. The presence of the metal material 13 on the surface of the active material particles 12a over the entire thickness direction of the active material layer 12 can be confirmed by electron microscope mapping using the material 13 as a measurement target.

[0041] The metal material 13 covers the surfaces of the particles 12a continuously or discontinuously. When the metal material 13 continuously covers the surfaces of the particles 12a, it is preferable to form fine voids in the coating of the metal material 13 so that a nonaqueous electrolytic solution can flow. When the metal material 13 discontinuously covers the surface of the particle 12a, the non-aqueous electrolyte is supplied to the particle 12a through a portion of the surface of the particle 12a that is not covered with the metal material 13. . In order to form the coating of the metal material 13 having such a structure, the metal material 13 may be deposited on the surfaces of the particles 12a by, for example, electrolytic plating according to the conditions described later.

[0042] The average thickness of the metal material 13 covering the surface of the active material particles 12a is preferably 0.05 to 2 / ζ πι, more preferably 0.1 to 0.25 / zm. / !, thin! /. That is, the metal material 13 covers the surface of the active material particles 12a with a minimum thickness. This prevents the dropout due to the particles 12a from expanding and contracting due to charge and discharge to be pulverized while increasing the energy density. Here, the “average thickness” is a value calculated based on a portion of the surface of the active material particle 12 a that is actually covered with the metal material 13. Accordingly, the portion of the surface of the active material particles 12a not covered with the metal material 13 is not used as the basis for calculating the average value.

[0043] The voids formed between the particles 12a coated with the metal material 13 serve as a flow path for the non-aqueous electrolyte containing lithium ions. Non-water due to the presence of this void Since the electrolytic solution smoothly flows in the thickness direction of the active material layer 12, cycle characteristics can be improved. Further, the voids formed between the particles 12a also serve as a space for relieving the stress caused by the volume change of the active material particles 12a due to charge and discharge. The increase in the volume of the active material particles 12a whose volume has been increased by charging is absorbed in the voids. As a result, the fine particles of the particles 12a are less likely to occur, and significant deformation of the negative electrode 10 is effectively prevented.

[0044] As described later, the active material layer 12 preferably has a predetermined plating bath applied to a coating film obtained by applying a slurry containing particles 12a and a binder onto a current collector and drying the slurry. It is formed by performing the electrolytic plating used and depositing the metal material 13 between the particles 12a.

[0045] In order to form necessary and sufficient voids in the active material layer 12 where the non-aqueous electrolyte can flow, it is preferable that the plating solution is sufficiently permeated into the coating film. In addition to this, it is preferable that the conditions for depositing the metal material 13 by electrolytic plating using the plating solution are appropriate. The plating conditions include the composition of the mating bath, the pH of the plating bath, and the current density of the electrolysis. Regarding the pH of the plating bath, it is preferable to adjust it to 7.1 to L 1. By setting the pH within this range, the dissolution of the active material particles 12a is suppressed, the surface of the particles 12a is cleaned, and the plating on the particle surfaces is promoted. Appropriate voids are formed. The pH value was measured at the plating temperature.

[0046] When copper is used as the metal material 13 for plating, it is preferable to use a copper pyrophosphate bath. When nickel is used as the metal material, for example, an alkaline nickel bath is preferably used. In particular, it is preferable to use a copper pyrophosphate bath because the voids can be easily formed over the entire thickness direction of the layer even when the active material layer 12 is thickened. In addition, the metal material 13 is deposited on the surface of the active material particles 12a, and the metal material 13 is less likely to be deposited between the particles 12a, so that the voids between the particles 12a are successfully formed. This is also preferable. When using a copper pyrophosphate bath, the bath composition, electrolysis conditions and pH are preferably as follows.

'Copper pyrophosphate trihydrate: 85-120gZl

-Pig 13 gin Kazikum: 300-600g / l 'Potassium nitrate: 15-65gZl

'Bath temperature: 45-60 ° C

'Current density: l ~ 7AZdm ²

• pH: Add ammonia water and polyphosphoric acid to adjust the pH to 7.1 to 9.5.

[0047] Especially when using a copper pyrophosphate bath, the ratio of the weight of P O to the weight of Cu (P O ZCu

2 7 2 7

It is preferable to use one having a P ratio defined by When the P ratio is less than 5, the metal material 13 covering the active material particles 12a tends to be thick, and it may be difficult to form desired voids between the particles 12a. In addition, if a P ratio exceeding 12 is used, the current efficiency is deteriorated and gas generation is likely to occur, which may reduce the production stability. When a copper pyrophosphate bath having a P ratio of 6.5 to 10.5 is used, the size and number of voids formed between the active material particles 12a and the non-aqueous water in the active material layer 12 are more preferable. This is very advantageous for the flow of the electrolyte.

[0048] When an alkaline nickel bath is used, the bath composition, electrolysis conditions, and pH are preferably as follows.

'Nickel sulfate: 100-250gZl

'Ammonium chloride: 15-30gZl

'Boric acid: 15-45gZl

'Bath temperature: 45-60 ° C

'Current density: l ~ 7AZdm ²

• pH: 25 weight ^_0/0 aqueous ammonia: 100～300GZl adjusted to be Roita8～ 11 in the range of.

When this alkaline nickel bath is compared with the copper pyrophosphate bath described above, the use of the copper pyrophosphate bath tends to form appropriate voids in the active material layer 12, thereby extending the life of the negative electrode. I like it, so I like it.

[0049] The properties of the metal material 13 can be adjusted as appropriate by adding various additives used in electrolyte solutions for producing copper foil such as proteins, active sulfur compounds, and cellulose to the various baths. It is.

[0050] The ratio of voids in the entire active material layer formed by the various methods described above, that is, the void ratio is 15 to 45% by volume, particularly 20 to 40% by volume is preferable. By setting the porosity within this range, it is possible to form necessary and sufficient voids in the active material layer 12 through which the non-aqueous electrolyte can flow. The void volume of the active material layer 12 is measured by a mercury intrusion method (CFIS R 1655). The mercury intrusion method is a method for obtaining information on the physical shape of a solid by measuring the size and volume of pores in the solid. The principle of the mercury intrusion method is to measure the relationship between the pressure of the mercury being measured and the volume of the mercury that has been intruded (intruded) by injecting pressure into the pores of the object to be measured. is there. In this case, mercury is infiltrated by the large void force existing in the active material layer 12 in order. In the present invention, the void amount measured at a pressure of 90 MPa is regarded as the total void amount. The porosity (%) of the active material layer 12 is obtained by dividing the void amount per unit area measured by the above method by the apparent volume of the active material layer 12 per unit area and multiplying it by 100. Ask.

[0051] The porosity can also be controlled by appropriately selecting the particle size of the active material particles 12a. From this viewpoint, the maximum particle size of the particles 12a is preferably 30 m or less, more preferably 10 m or less. In addition, when the particle size is expressed by D value, it is 0.

50

1 to 8 μm, particularly 0.3 to 4 μm is preferable. The particle size of the particles is measured by laser diffraction / scattering particle size distribution measurement and electron microscope observation (SEM observation).

[0052] If the amount of the active material relative to the whole negative electrode is too small, it is difficult to sufficiently increase the energy density of the battery. Considering these, the thickness of the active material layer is 10 to 40 111, preferably 15 to 30 m, and more preferably 18 to 25 μm.

[0053] In the negative electrode 10 of the present embodiment, a thin surface layer (not shown) may be formed on the surface of the active material layer 12. Further, the negative electrode 10 may not have such a surface layer. The thickness of the surface layer is as thin as 0.25 μm or less, preferably 0.1 μm or less. There is no limit to the lower limit of the thickness of the surface layer. By forming the surface layer, the pulverized active material particles 12a can be further prevented from falling off. However, in this embodiment, by setting the porosity of the active material layer 12 within the above-described range, it is possible to sufficiently prevent the pulverized active material particles 12a from dropping without using a surface layer. Is possible.

[0054] The negative electrode 10 has the above-mentioned thin thickness, has a surface layer, or has the surface layer. As a result, the secondary battery can be assembled using the negative electrode 10 to reduce the overvoltage when the battery is initially charged. This means that lithium can be prevented from being reduced on the surface of the negative electrode 10 when the secondary battery is charged. The reduction of lithium leads to the generation of dendrites that cause short circuits between the two electrodes.

[0055] When the negative electrode 10 has a surface layer, the surface layer covers the surface of the active material layer 12 continuously or discontinuously. When the surface layer continuously covers the surface of the active material layer 12, the surface layer has a large number of fine voids (not shown) that are open to the surface and communicate with the active material layer 12. Have, prefer to have. It is preferable that the fine voids exist in the surface layer so as to extend in the thickness direction of the surface layer. The fine voids allow the non-aqueous electrolyte to flow. The role of the fine voids is to supply a non-aqueous electrolyte into the active material layer 12. When the surface of the negative electrode 10 is viewed in plan by an electron microscope, the fine voids are the ratio of the area covered with the metal material 13, that is, the coverage is 95% or less, particularly 80% or less, particularly 60% or less. Such a size is preferable. If the coverage exceeds 95%, it is difficult for the high-viscosity non-aqueous electrolyte to penetrate, and the range of selection of the non-aqueous electrolyte may be narrowed.

[0056] The surface layer is composed of a metal compound having a low lithium compound forming ability. This metal material may be the same as or different from the metal material 13 present in the active material layer 12. The surface layer may have a structure of two or more layers having two or more different metal material forces. Considering the ease of production of the negative electrode 10, the metal material 13 present in the active material layer 12 and the metal material constituting the surface layer are preferably the same type.

[0057] In the negative electrode 10 of the present embodiment, when the porosity in the active material layer 12 is the above value, the resistance of the negative electrode 10 to bending is increased. Specifically, the MIT folding resistance measured according to JIS C 6471 is preferably 30 times or more, more preferably 50 times or more. The high folding resistance is extremely advantageous since the negative electrode 10 is folded when the negative electrode 10 is folded or wound and accommodated in the battery container. As the MIT folding endurance apparatus, for example, a film folding fatigue tester with a tank manufactured by Toyo Seiki Seisakusho (Part No. 549) is used. be able to.

[0058] As the current collector 11 in the negative electrode 10, as the current collector of the negative electrode for the non-aqueous electrolyte secondary battery The thing conventionally used can be used. It is preferable that the current collector 11 is composed of a metal material having a low lithium compound forming ability as described above. Examples of such metal materials are as already described. In particular, it is preferably made of copper, nickel, stainless steel or the like. Also, it is possible to use a copper alloy foil represented by Corson alloy foil. Further, as the current collector, a metal foil having a normal tensile strength (JIS C 2318) of preferably 500 MPa or more, for example, a copper film layer formed on at least one surface of the aforementioned Corson alloy foil can be used. Furthermore, it is also preferable to use a current collector having a normal elongation CFIS C 2318) of 4% or more. This is because, when the tensile strength is low, stress is generated due to the stress when the active material expands, and when the elongation is low, the current collector may crack. By using these current collectors, it is possible to further improve the folding resistance of the negative electrode 10 described above. The thickness of the current collector 11 is preferably 9 to 35 / ζ πι in consideration of the balance between maintaining the strength of the negative electrode 10 and improving the energy density. When copper foil is used as the current collector 11, it is preferable to perform a chromate treatment or an antifungal treatment using an organic compound such as a triazole compound or an imidazole compound.

Next, a preferred method for producing the negative electrode 10 of the present embodiment will be described with reference to FIG. In this production method, a coating film is formed on the current collector 11 using a slurry containing active material particles and a binder, and then the coating is electrolyzed.

First, a current collector 11 is prepared as shown in FIG. 8 (a). Then, a slurry containing active material particles 12 a is applied onto the current collector 11 to form a coating film 15. The surface roughness of the coating film forming surface of the current collector 11 is preferably 0.5 to 4 / ζ πι at the maximum height of the contour curve. When the maximum height exceeds 4 m, the accuracy of forming the coating film 15 is reduced, and current concentration tends to occur at the protrusions. When the maximum height is less than 0, the adhesion of the active material layer 12 tends to decrease. As the active material particles 12a, those having the above-described particle size distribution and average particle size are preferably used.

[0061] In addition to the particles of the active material, the slurry contains a binder and a diluting solvent. The slurry may also contain a small amount of conductive carbon material particles such as acetylene black and graphite. In particular, when the active material particles 12a also have a silicon-based material force, the conductive carbon material is contained in an amount of 1 to 3% by weight with respect to the weight of the active material particles 12a. Are preferred. When the content of the conductive carbon material is less than 1% by weight, the viscosity of the slurry is lowered and the sedimentation of the active material particles 12a is promoted, so that it is difficult to form a good coating film 15 and a uniform void. Become. On the other hand, if the content of the conductive carbon material exceeds 3% by weight, plating nuclei concentrate on the surface of the conductive carbon material, and a good coating is formed.

[0062] As the binder, styrene butadiene rubber (SBR), polyvinylidene fluoride (PVDF), polyethylene (PE), ethylene propylene diene monomer (EPDM) and the like are used. As a diluting solvent, N-methylpyrrolidone, cyclohexane or the like is used. The amount of the active material particles 12a in the slurry is preferably about 30 to 70% by weight. The amount of the binder is preferably about 0.4 to 4% by weight. A dilute solvent is added to these to form a slurry.

[0063] The formed coating film 15 has a large number of minute spaces between the particles 12a. The current collector 11 on which the coating film 15 is formed is immersed in a plating bath containing a metal material having a low ability to form a lithium compound. By dipping in the plating bath, the plating solution enters the minute space in the coating film 15 and reaches the interface between the coating film 15 and the current collector 11. Under this condition, electrolytic plating is performed to deposit metal species on the surface of the particles 12a (hereinafter, this plating is also referred to as penetration plating). The penetration is performed by using the current collector 11 as a force sword, immersing the counter electrode as the anode in the plating bath, and connecting both electrodes to the power source.

[0064] It is preferable that the deposition of the metal material by the penetration adhesion proceeds by applying one side force of the coating film 15 to the other side. Specifically, as shown in FIGS. 8 (b) to (d), the interfacial force between the coating film 15 and the current collector 11 is also electrolyzed so that the deposition of the metal material 13 proceeds toward the coating film surface. Make a mess. By precipitating the metal material 13 in this way, the surface of the active material particles 12a can be successfully coated with the metal material 13, and a void is successfully formed between the particles 12a coated with the metal material 13. can do.

[0065] As described above, the conditions of penetration for depositing the metal material 13 include the composition of the plating bath, the pH of the plating bath, and the current density of electrolysis. Such conditions are as described above.

[0066] As shown in Figs. 8 (b) to (d), the deposition of the metal material 13 proceeds from the interface between the coating film 15 and the current collector 11 toward the surface of the coating film. Foreground is the forefront of the precipitation reaction In the portion, fine particles 13a having a substantially constant thickness and also having the core force of the metal material 13 are present in layers. As the precipitation of the metal material 13 proceeds, the adjacent fine particles 13a are combined to form larger particles, and when the deposition proceeds further, the particles are combined to continuously cover the surface of the active material particles 12a. It becomes like this.

[0067] The penetration staking is terminated when the metal material 13 is deposited in the entire thickness direction of the coating film 15. By adjusting the end point of plating, a surface layer (not shown) can be formed on the upper surface of the active material layer 12. In this way, the target negative electrode is obtained as shown in FIG. 8 (d).

[0068] It is also preferable that the negative electrode 10 be subjected to anti-fouling treatment after the penetration. Examples of the anti-bacterial treatment include organic anti-bacterials using triazole compounds such as benzotriazole, carboxybenzotriazole, tolyltriazole and imidazole, and inorganic anti-bacterials using cobalt, nickel, chromate and the like.

[0069] While the present invention has been described based on the preferred embodiments thereof, the present invention is not limited to the above embodiments. For example, the winding body may be manufactured according to the description in Patent Document 1 described above so that sagging occurs at the corner of the winding body.

[0070] In the manufacturing method, the winding jig 20 can be used as a core material without being pulled out after winding.

Example

[0071] Hereinafter, the present invention will be described in more detail by way of examples. However, the scope of the present invention is not limited to such embodiments.

[Example 1]

A current collector having an electrolytic copper foil strength of 18 m in thickness was acid-washed at room temperature for 30 seconds. After the treatment, it was washed with pure water for 15 seconds. A coating film was formed by applying a slurry containing particles of key particles on both sides of the current collector to a thickness of 15 μm. The composition of the slurry was particle: styrene butadiene rubber (binder): acetylene black = 100: 1.7: 2 (weight ratio). The average particle diameter D of the particles was 2 m. The average particle size D is the particle size of Microtrack manufactured by Nikkiso Co., Ltd.

50 50

Measurement was performed using a distribution measuring device (No. 9320—X100).

[0073] The current collector on which the coating film was formed was immersed in a copper pyrophosphate bath having the following bath composition. By the solution, copper penetration was applied to the coating film to form an active material layer. The electrolysis conditions were as follows. DSE was used for the anode. A DC power source was used as the power source.

'Copper pyrophosphate trihydrate: 105gZl

• Potassium pyrophosphate: 450g / l

'Potassium nitrate: 30gZl

• P ratio: 7.7

'Bath temperature: 50 ° C

• Current density: 3AZdm ²

• pH: Ammonia water and polyphosphoric acid were added to adjust to pH 8.2.

[0074] The penetration staking was terminated when copper was deposited over the entire thickness direction of the coating film.

In this way, a target negative electrode was obtained. SEM observation of the vertical cross section of the active material layer confirmed that the active material particles were covered with a copper film having an average thickness of 240 nm in the active material layer. The porosity of the active material layer was 30%.

[0075] LiCo Ni Mn O was used as the positive electrode active material. This is acetylene black and

1/3 1/3 1/3 2

Polyvinylidene fluoride was suspended in polyvinylpyrrolidone as a solvent to obtain a positive electrode mixture. This positive electrode mixture was applied to a current collector made of aluminum foil and dried, followed by roll rolling and pressing to obtain a positive electrode. Polypropylene porous films having a thickness of 20 μm were used as the first and second separators.

[0076] The negative electrode, the positive electrode, and the first and second separators were formed in a long band shape having a width of 60 mm.

As shown in Fig. 5 (a) and (b), the first and second separators SI and S2 are wound around the winding jig 20, and then, as shown in Fig. 6 (a), the positive electrode C and the negative electrode A was further wrapped around jig 20. On the positive electrode C, a single core material 31 made of A1, which was a strip piece, was attached. The core material 31 had a tab part. On the negative electrode A, five Ni cores 3 2 made of strips were attached. One of the five core members 32 had a tab portion. Each of the core materials 31 and 32 had a length of 42 mm, a width of 4 mm, and a thickness of 100 m (excluding the tab portion). The core materials 31 and 32 are aligned and attached to these electrodes when the positive electrode C and the negative electrode A are wound around the winding jig 20 so as to be in the arrangement state shown in FIG. It was. When the wound body is obtained by winding the desired number of times, from the raw roll The positive electrode C, the negative electrode A, and the separators SI and S2 were cut, and the cut ends were fixed to the side surface of the wound body with an adhesive tape. Finally, the winding force 20 was pulled out to obtain the wound body 1. The distance between the cores in the obtained wound body was about 0.5 mm.

[0077] The obtained wound body was accommodated in a rectangular outer can. Further, an electrolyte solution was filled in the outer can.

As an electrolytic solution, 1 of ethylene carbonate and Jefferies Chino Les carbonate: with respect to 1 volume ^_0/0 mixture Solvent To a solution of LiPF of ImolZl, bi - Ren carbonate 2 vol ^_0/0 outside

6

The attached one was used. After filling the electrolyte, the outer can was sealed to obtain a prismatic lithium secondary battery. The battery was 6mm thick, 34mm wide and 48mm high (063448).

[Comparative Example 1]

In the same manner as in Example 1, except that the A1 tab for current collection is attached to the positive electrode, the Ni tab for current collection is attached to the negative electrode, and the core materials 31, 32 used in Example 1 are not used. A type lithium secondary battery was obtained.

[0079] [Evaluation]

The batteries obtained in Example 1 and Comparative Example 1 were charged and discharged for 100 cycles. Charging conditions were 0.5C, final voltage 4.2V, constant current and constant voltage (CCCV). The discharge conditions were 0.5C, final voltage 2.7V, and constant current (CC). However, charge / discharge at the first cycle is 0.05 C, charge / discharge at the second to fourth cycles is 0.1 C, charge / discharge at the fifth to seventh cycles is 0.5 C, and charge / discharge at the eighth to tenth cycles is 1C. The battery after 100 cycles of charge and discharge was subjected to a CT scan of the cross section, and the state of the wound body was observed nondestructively. The results are shown in FIG. 9 (Example 1) and FIG. 10 (Comparative Example 1). 9 and 10 also show the CT scan image of the battery before charging and discharging.

As is clear from the results shown in FIGS. 9 and 10, in the battery of Example 1, the negative electrode and the like were hardly deformed after 100 liters of charge / discharge. In the case of a battery, it can be seen that after 100 cycles of charging / discharging, the battery started to buckle due to the negative electrode. Since the core 31 used in Example 1 and the current collecting tab of the positive electrode used in Comparative Example 1 are both made of A1, these are shown in the CT scan images of FIG. 9 and FIG. Appear!!

[Example 2] A casing having the structure shown in FIGS. 3 (a) and (b) was produced according to Example 1. A Ni plate 42 mm long, 25 mm wide and 100 m thick was used as the core material 3 to be attached to the negative electrode (excluding the tab). As the core material 3 attached to the positive electrode, an A1 plate having a length of 40 mm, a width of 25 mm, and a thickness of 40 / zm was used (excluding the tab portion). Except for these, a prismatic lithium secondary battery was obtained in the same manner as in Example 1.

[Comparative Example 2]

In Example 2, a prismatic lithium secondary battery was obtained in the same manner as in Example 2 except that the core material 3 having nickel plate strength was not used.

[0083] [Evaluation]

The batteries obtained in Example 2 and Comparative Example 2 were subjected to 100 cycles of charge and discharge in the same manner as in Example 1, and then their transverse cross sections were subjected to CT scanning to observe the state of the wound body in a nondestructive manner. The results are shown in FIG. 11 (Example 2) and FIG. 12 (Comparative Example 1).

As is clear from the results shown in FIG. 11 and FIG. 12, the battery of Example 2 is less deformed by the electrode at the center of the wound body than the battery of Comparative Example 2. I understand. When Example 2 is compared with Example 1 described above, Example 2 has a greater degree of overall deformation. This is because the strength of the negative electrode current collector used in Example 2 is lower than the strength of the negative electrode current collector used in Example 1. Note that the A1 core material used in Example 2 appears in the CT scan image in FIG.

Industrial applicability

[0085] According to the present invention, the plate-like core material is arranged at the center of the flat wound body, and the positive electrode and the negative electrode are wound around the core material without any gaps. Even if stress generated due to expansion is locally applied to the center of the wound body, the core material can receive the stress. As a result, electrode deformation including buckling is suppressed by the core material.

Claims

The scope of the claims

[1] A positive electrode, a negative electrode, and a separator interposed between them are wound, and a winding body having a flat cross section is provided, and a plate-like core material is provided at the center of the winding body A non-aqueous electrolyte secondary battery characterized in that V is disposed.

[2] The non-aqueous electrolyte secondary battery according to claim 1, wherein the core material also serves as a current collecting tab for a positive electrode or a negative electrode.

[3] The first aspect of the invention, wherein the core material is composed of a plurality of strips extending in the height direction of the wound body, arranged in a straight line in the width direction of the wound body. Or a non-aqueous electrolyte secondary battery according to item 2.

[4] The non-aqueous electrolyte secondary battery according to claim 1, wherein the wound body is housed in a rectangular outer can.

5. The nonaqueous electrolyte secondary battery according to claim 1, wherein the wound body is housed in a laminate outer package.

6. The nonaqueous electrolyte secondary battery according to claim 1, wherein the negative electrode has a negative electrode active material layer containing an active material such as a material containing Si or a material containing Sn.

[7] The negative electrode active material layer contains particles of an active material containing Si or Sn, and at least a part of the surface of the particles is coated with a metal material having a low ability to form a lithium compound. 7. The nonaqueous electrolyte secondary battery according to claim 6, wherein voids are formed between the particles coated with a metal material.

8. The nonaqueous electrolyte secondary battery according to claim 7, wherein the metal material is present on the surface of the particles over the entire thickness direction of the negative electrode active material layer.

[9] The nonaqueous electrolyte secondary battery according to [7] or [8], wherein the negative electrode active material layer has a porosity of 15 to 45% by volume.