secondary batteries

Abstract

The present invention provides a technology capable of suppressing the precipitation of metallic lithium on the negative electrode active material layer. The secondary battery disclosed herein comprises a wound electrode body (20) and a non-aqueous electrolyte. The wound electrode body (20) is obtained by winding a long sheet-shaped positive electrode sheet (50) and a long sheet-shaped negative electrode sheet (60) with a separator (70) interposed therebetween in the longitudinal direction Y. An insulating tape (56) and a coating film (58) are provided at at least one end portion of the positive electrode sheet (50) in the longitudinal direction Y. The insulating tape (56) covers the end portion (symbol 521) and adheres to the positive electrode active material (54) layer. The coating film (58) is provided on the positive electrode active material layer (54) along the edge of the insulating tape (56) and is inactive with respect to the battery reaction. Here, the thickness D1 of the coating film (58) decreases as it moves away from the edge of the insulating tape (56).

Description

Technical Field

[0001] The present invention relates to a secondary battery. Background Art

[0002] For example, Japanese Patent Application Publication No. 2019-164942 discloses a method for attaching an insulating tape to the end of a positive electrode plate for a non-aqueous electrolyte secondary battery. In this publication, the insulating tape comprises a substrate and an adhesive layer disposed on the substrate, and also includes a non-adhesive region on the substrate where the adhesive layer is not formed. Furthermore, a lithium release inhibitory portion is provided in the positive electrode mixture layer near the end of the non-adhesive region of the substrate to inhibit the release of lithium ions. The lithium release inhibitory portion may, for example, be a portion that locally increases the packing density of the positive electrode mixture layer. Specifically, during the process of rolling the positive electrode mixture layer during the manufacture of the positive electrode plate, the packing density of the positive electrode mixture layer can be locally increased by applying a greater pressure to the portion of the positive electrode mixture layer that becomes the lithium release inhibitory portion than to other portions, or by rolling the portion more times than to other portions. This locally increased packing density reduces the gaps within the lithium release inhibitory portion, making it less likely that the electrolyte will penetrate the interior. Therefore, the release of lithium ions becomes difficult to proceed, and as a result, the precipitation of metallic lithium is suppressed at the position of the negative electrode mixture layer facing the lithium release suppressing portion.

[0003] Prior art literature

[0004] Patent Literature

[0005] Patent Document 1: Japanese Patent Application Publication No. 2019-164942 Summary of the Invention

[0006] However, for secondary batteries in which an insulating tape is attached to the end of the positive electrode sheet in the winding direction of the wound electrode body, it is desirable to suppress the precipitation of metallic lithium on the opposing negative electrode active material layer.

[0007] The secondary battery disclosed herein comprises a wound electrode body and a non-aqueous electrolyte. The wound electrode body is formed by winding a positive electrode sheet having a long sheet-shaped positive electrode current collector and a positive electrode active material layer formed on the surface of the positive electrode current collector, and a negative electrode sheet having a long sheet-shaped negative electrode current collector and a negative electrode active material layer formed on the surface of the negative electrode current collector, with a separator sandwiched therebetween and wound in the longitudinal direction. The secondary battery is provided with an insulating tape and a coating film at at least one end of the positive electrode sheet in the longitudinal direction. The insulating tape covers the end and adheres to the positive electrode active material layer. The coating film is provided on the positive electrode active material layer along the edge of the insulating tape and is inactive with respect to the battery reaction. Here, the thickness of the coating film decreases as it moves away from the edge of the insulating tape.

[0008] The positive electrode sheet of the secondary battery has an insulating tape attached to at least one end along its longitudinal length, and a coating film disposed along the insulating tape. The thickness of the coating film decreases as it moves away from the edge of the insulating tape. This prevents the precipitation of metallic lithium from the opposing negative electrode active material layer.

[0009] In a preferred embodiment of the secondary battery disclosed herein, the insulating tape and the coating film are provided at both ends of the positive electrode sheet in the longitudinal direction. This configuration can better achieve the technical effects disclosed herein.

[0010] In another preferred embodiment of the secondary battery disclosed herein, the coating film includes a filler layer containing an inorganic filler and a resin binder, and / or a resin layer composed of a resin binder. The technical effects disclosed herein can be appropriately achieved in a secondary battery having a filler layer and / or a resin layer as the coating film.

[0011] In another preferred embodiment of the secondary battery disclosed herein, the resin binder is composed of at least one resin material selected from acrylic resins and halogenated vinyl resins. This configuration can appropriately achieve the technical effects disclosed herein. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 is a cross-sectional view schematically showing the internal structure of a secondary battery according to one embodiment.

[0013] Figure 2 This is a schematic exploded view showing the structure of a wound electrode body of a secondary battery according to one embodiment.

[0014] Figure 3 This is a top view of a positive electrode sheet used in a secondary battery according to one embodiment.

[0015] Figure 4 This is an enlarged cross-sectional view schematically showing a main portion of a stacked structure of a wound electrode body used in a secondary battery according to one embodiment.

[0016] Explanation of symbols

[0017] 20 wound electrode body

[0018] 30 battery housing

[0019] 42 Positive terminal

[0020] 44 Negative terminal

[0021] 50 positive electrode sheet (positive electrode)

[0022] 52 positive electrode collector

[0023] 54 positive electrode active material layer

[0024] 56 Insulation tape

[0025] 58 coating

[0026] 60 negative electrode sheet (negative electrode)

[0027] 62 negative electrode collector

[0028] 64 Negative electrode active material layer

[0029] 70 Isolators

[0030] 80 non-aqueous electrolyte

[0031] 100 Secondary Batteries DETAILED DESCRIPTION

[0032] An embodiment of the technology disclosed herein is described below with reference to the accompanying drawings. It should be noted that the following embodiment is not intended to limit the technology disclosed herein. Furthermore, matters other than those specifically mentioned in this specification and necessary for implementing the technology disclosed herein can be understood as design matters by those skilled in the art based on existing technologies in the relevant field. In other words, the technology disclosed herein can be implemented based on the content disclosed in this specification and common technical knowledge in the relevant field.

[0033] It should be noted that in the drawings referred to in the following description, the same symbols are marked for components and parts that play the same role. In addition, the dimensional relationships (length, width, thickness, etc.) in the figures do not reflect the actual dimensional relationships. Moreover, the symbol X in each figure represents the "width direction" of the electrode body 20, the symbol Y represents the "long side direction" of the positive electrode sheet 50 (negative electrode sheet 60) in the electrode body 20, and the symbol Z represents the "stacking direction" of the sheet. However, these directions are set for the convenience of explanation and are not intended to limit the setting method of the secondary battery in use or manufacturing. In addition, the expression "A to B" indicating the numerical range in this specification includes the meaning of "above A and below B", and includes the meaning of "greater than A and less than B".

[0034] In addition, the "secondary battery" in this specification refers to a storage device that generally generates a charge and discharge reaction by moving charge carriers between a pair of electrodes (positive and negative electrodes) via an electrolyte. In addition to so-called storage batteries such as lithium-ion secondary batteries, nickel-metal hydride batteries, and nickel-cadmium batteries, the above-mentioned secondary batteries also include capacitors such as double-layer capacitors. In addition, the "active material" in this specification refers to a substance that is responsible for the battery reaction, specifically, a compound that can reversibly absorb and release chemical species (lithium ions in lithium-ion secondary batteries) that serve as charge carriers. Below, taking a flat square lithium-ion secondary battery as an example, an embodiment of the technology disclosed herein is described in detail, but it is not intended to limit the technology disclosed herein to the above-mentioned embodiment.

[0035] Below, refer to Figures 1 to 4 The structure of the secondary battery disclosed herein will be described in detail. Figure 1 is a cross-sectional view schematically showing the internal structure of a secondary battery according to one embodiment. Figure 2 This is a schematic exploded view showing the structure of a wound electrode body of a secondary battery according to one embodiment. Figure 3 This is a top view of a positive electrode sheet used in a secondary battery according to one embodiment. Figure 4 This is an enlarged cross-sectional view schematically showing a main portion of a stacked structure of a wound electrode body used in a secondary battery according to one embodiment.

[0036] like Figure 1 As shown, the secondary battery 100 is a sealed battery constructed by accommodating a flat wound electrode body 20 (hereinafter also simply referred to as “electrode body 20 ”) and a non-aqueous electrolyte 80 in a flat rectangular battery case (ie, outer container) 30 .

[0037] The battery case 30 is provided with a positive terminal 42 and a negative terminal 44 for external connection, as well as a thin-walled safety valve 36 designed to release the internal pressure of the battery case 30 when it rises above a predetermined level. In addition, the battery case 30 is provided with an injection port (not shown) for injecting the non-aqueous electrolyte 80. The positive terminal 42 is electrically connected to the positive electrode collector plate 42a. The negative terminal 44 is electrically connected to the negative electrode collector plate 44a. As the material of the battery case 30, for example, a lightweight metal material with good thermal conductivity such as aluminum can be used.

[0038] The non-aqueous electrolyte 80 typically contains a non-aqueous solvent and a supporting salt. As the non-aqueous solvent and the supporting salt, various solvents used in the electrolyte of such a secondary battery (here, a lithium-ion secondary battery) can be used without particular limitation. Examples of the non-aqueous solvent include carbonates such as ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), monofluoroethylene carbonate (MFEC), difluoroethylene carbonate (DFEC), monofluoromethyldifluoromethyl carbonate (F-DMC), and dimethyl trifluorocarbonate (TFDMC). Such non-aqueous solvents can be used alone or in combination of two or more.

[0039] As a supporting salt, for example, lithium salts such as LiPF6, LiBF4, and LiClO4 (preferably LiPF6) can be used. The concentration of the supporting salt can be 0.7 mol / L to 1.3 mol / L. In addition, the non-aqueous electrolyte 80 can contain oxalate complexes containing boron (B) atoms and / or phosphorus (P) atoms (for example, lithium bis(oxalato)borate (LiBOB)), lithium difluorophosphate and other film-forming agents; thickeners; dispersants; and other conventionally known additives as needed. It should be noted that Figure 1 The amount of the nonaqueous electrolyte 80 in does not strictly represent the amount of the nonaqueous electrolyte 80 injected into the battery case 30 .

[0040] like Figure 1 、 2 As shown, the electrode body 20 has a form in which a positive electrode sheet 50 and a negative electrode sheet 60 are overlapped and wound in the long side direction via two long sheet-like separators 70, and the positive electrode sheet 50 has a positive electrode active material layer 54 formed on one side or both sides (here both sides) of the long sheet-like positive electrode collector 52 along the long side direction Y, and the negative electrode sheet 60 has a negative electrode active material layer 64 formed on one side or both sides (here both sides) of the long sheet-like negative electrode collector 62 along the long side direction Y. It should be noted that the positive electrode active material layer non-forming portion 52a (i.e., the portion where the positive electrode active material layer 54 is not formed and the positive electrode collector 52 is exposed) and the negative electrode active material layer non-forming portion 62a (i.e., the portion where the negative electrode active material layer 64 is not formed and the negative electrode collector 62 is exposed) are respectively joined to the positive electrode collector plate 42a and the negative electrode collector plate 44a, which are arranged in a manner protruding outward from both ends in the winding axis direction of the electrode body 20 (i.e., the sheet width direction X orthogonal to the above-mentioned long side direction).

[0041] As the negative electrode current collector 62 constituting the negative electrode sheet 60, for example, copper foil or the like can be cited. The negative electrode active material layer 64 contains at least a negative electrode active material. As the negative electrode active material, for example, carbon materials such as graphite, hard carbon, and soft carbon can be used, preferably graphite. The negative electrode active material layer 64 may contain components other than the active material, such as a binder, a thickener, etc. As a binder, for example, styrene butadiene rubber (SBR) or the like can be used. As a thickener, for example, carboxymethyl cellulose (CMC) or the like can be used.

[0042] Examples of separator 70 include porous sheets (films) made of resins such as polyethylene (PE), polypropylene (PP), polyester, cellulose, and polyamide. The porous sheet may have a single-layer structure or a laminated structure of two or more layers (e.g., a three-layer structure in which PP layers are laminated on both sides of a PE layer). A heat-resistant layer (HRL) may also be provided on the surface of separator 70.

[0043] As the positive electrode current collector 52 constituting the positive electrode sheet 50, aluminum foil etc. can be cited. The positive electrode active material layer 54 contains at least a positive electrode active material. As the positive electrode active material, lithium transition metal oxide (such as LiNi 1 / 3 Co 1 / 3Mn 1 / 3 O2, LiNiO2, LiCoO2, LiFeO2, LiMn2O4, LiNi 0.5 Mn 1.5 O4, etc.), lithium transition metal phosphate (e.g., LiFePO4, etc.). The positive electrode active material layer 54 may contain components other than the active material, such as a conductive material and a binder. As conductive materials, for example, carbon black such as acetylene black (AB) and other carbon materials (e.g., graphite, etc.) can be suitably used. As binders, for example, polyvinylidene fluoride (PVDF) can be used.

[0044] like Figure 2 、 3 As shown, an insulating tape 56 and a coating film 58 are provided at at least one end of the positive electrode sheet 50 in the longitudinal direction Y. One end of the positive electrode sheet 50 in the longitudinal direction Y is a first end 521, which serves as the starting point for winding the positive electrode sheet 50 and is located at the innermost side of the electrode body 20. The other end, different from the first end 521, is a second end 522, which serves as the end point for winding the positive electrode sheet 50 and is located outward of the first end 521. Both the first end 521 and the second end 522 are the terminal ends of the positive electrode sheet 50 in the winding direction of the electrode body 20.

[0045] In this embodiment, if Figure 3As shown, the insulating tape 56 and the coating film 58 are provided on both the first end portion 521 and the second end portion 522. However, this is not limiting, and the insulating tape 56 and the coating film 58 may be provided on at least one of the first end portion 521 and the second end portion 522. The case where the insulating tape 56 and the coating film 58 are provided on the first end portion 521 will be described in detail below. The case where the insulating tape 56 and the coating film 58 are provided on the second end portion 522 is basically the same, so a detailed description will be omitted here.

[0046] like Figure 4 As shown, the insulating tape 56 includes, for example, a base material 56a and an adhesive layer 56b provided on the surface (typically one side) of the base material. The base material is not particularly limited, and various resin base materials with insulating properties can be cited. For example, polyolefins such as polyethylene (PE) and polypropylene (PP); polyesters such as polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polyethylene naphthalate (PEN), and polybutylene naphthalate (PBN); polyvinyl chloride (PVC); polycarbonate (PC); polytetrafluoroethylene (PTFE); polyamide (PA); polyimide (PI); polyphenylene sulfide (PPS); etc. The constituent material of the adhesive layer is not particularly limited, and various synthetic resin materials such as acrylic resins, polyurethane resins, rubbers, and silicone resins can be cited.

[0047] The insulating tape 56 covers the first end portion 521 and adheres to the positive electrode active material layer 54. Here, "covering the first end portion 521" does not simply mean covering the entire first end portion 521 so that the first end portion 521 is not exposed to the outside, but also includes preventing at least 70% (e.g., 80% or more, preferably 90% or more, more preferably 95% or more, and even more preferably 98% or more) of the cross-sectional area of ​​the first end portion 521 from being exposed to the outside.

[0048] like Figure 3 、 4 As shown, the insulating tape 56 has a first region 561 facing the positive electrode sheet 50 and a second region 562 not facing the positive electrode sheet 50. The first region 561 faces the positive electrode collector 52 and the positive electrode active material layer 54 and is adhered to them via the adhesive layer 56b. In the second region 562, the insulating tapes 56 are facing each other in the stacking direction Z. That is, in the second region 562, the substrates 56a are facing each other in the same direction with the adhesive layer 56b between them. The widths of the first region 561 and the second region 562 are not particularly limited. Their widths can be set to a width that can appropriately keep the insulating tape 56 on the positive electrode sheet 50 (that is, the positive electrode collector 52 and the positive electrode active material layer 54).

[0049] The thickness D2 of the insulating tape 56 can be set to a thickness sufficient to cover the burrs present at the first end portion 521 of the positive electrode sheet 50 and prevent short circuits caused by the burrs. For example, the thickness D2 of the insulating tape 56 can be set to 0.1 to 1 times the thickness of the positive electrode sheet 50. As an example, if the thickness of the positive electrode sheet 50 is 50 μm to 150 μm (e.g., approximately 100 μm) and the thickness of the separator is 10 μm to 30 μm (e.g., approximately 20 μm), the thickness D2 of the insulating tape 56 can be set to 30 μm to 50 μm (e.g., approximately 40 μm).

[0050] The method for attaching the insulating tape 56 to the positive electrode sheet 50 is not particularly limited. For example, two insulating tapes 56 may be prepared and attached so as to sandwich the positive electrode sheet 50 in the stacking direction Z. Alternatively, a single insulating tape 56 may be prepared, bent, and attached so as to sandwich the positive electrode sheet 50 in the same direction.

[0051] However, during the initial charge of a secondary battery (here, a lithium-ion secondary battery), a film is formed on the negative electrode active material layer due to a film-forming additive (film-forming agent) added to the non-aqueous electrolyte. This film is formed from the film-forming agent and may contain boron (B) or phosphorus (P). This film has ion conductivity but lacks electron conductivity. The formation of this film facilitates the insertion and extraction of lithium ions from the negative electrode active material and suppresses excessive decomposition of the electrolyte. Figure 4 In the illustrated embodiment, an insulating tape 56 is adhered to the positive electrode active material layer 54 so as to cover the first end 521 of the positive electrode sheet 50 in the longitudinal direction Y. In this case, the inter-electrode distance W1 between the positive electrode sheet 50 and the negative electrode sheet 60 near the insulating tape-opposing region 541 of the positive electrode active material layer 54, i.e., the insulating tape non-opposing region 542, is increased by the thickness of the insulating tape 56 compared to other portions. The symbol W2 in the figure indicates the inter-electrode distance in the insulating tape non-opposing region 542.

[0052] In other words, the difference in inter-electrode distance (W2-W1) caused by the insulating tape 56, the inter-electrode distance W1 between the positive electrode sheet 50 and the negative electrode sheet 60, that is, the gap between the positive electrode sheet 50 and the negative electrode sheet 60, is widened. As a result, the aforementioned film is excessively formed locally on the negative electrode active material layer 64 facing the insulating tape non-opposing region 542. The inventors speculate that the reason for the excessive film formation is that more non-aqueous electrolyte flows into the region where the gap between the positive electrode sheet 50 and the negative electrode sheet 60 is widened in the insulating tape non-opposing region 542. As a result, uneven film formation occurs in the negative electrode active material layer 64. The region where the film is excessively formed becomes a region with higher resistance (high resistance region) than other regions, and the positive electrode potential can be locally increased. As a result, the positive electrode active material dissolves, and metal from the positive electrode active material is deposited on the surface of the negative electrode active material layer 64 facing the region where the insulating tape 56 is adhered to the positive electrode active material layer 54. Furthermore, metallic lithium is more likely to precipitate at these precipitation sites. Consequently, metallic lithium precipitation occurs on the surface of the negative electrode active material layer 64, which is located near the site where the insulating tape 56 is adhered to the positive electrode active material layer 54. The inventors speculate that the presence of the insulating tape 56 on the positive electrode active material layer 54 causes metallic lithium precipitation.

[0053] In the secondary battery 100 disclosed herein, Figure 3 、 4 As shown, a coating film 58 is provided on the positive electrode active material layer 54 along the edge of the insulating tape 56. In this embodiment, the coating film 58 is provided so as to be in close contact with the insulating tape 56. Furthermore, the coating film 58 is provided continuously from one end to the other end of the positive electrode active material layer 54 in the width direction X of the positive electrode sheet 50. Furthermore, the coating film 58 is provided only on the positive electrode active material layer 54 and not on the positive electrode current collector 52.

[0054] like Figure 4 As shown, the thickness D1 of the coating film 58 decreases as it moves away from the edge of the insulating tape 56. Here, the thickness D1 is the distance from the surface of the positive electrode active material layer 54 to the upper end of the coating film 58 in the cross-sectional view showing the stacked structure of the electrode body 20. The thickness D1 of the coating film 58 is set to slowly (gradually) decrease as it approaches from the edge of the insulating tape 56 to the center of the long side direction Y of the positive electrode sheet 50. There is no special limitation, that is, the maximum value of the thickness D1 of the coating film 58 can be the same as the thickness D2 of the insulating tape 56 in the formation surface of the positive electrode active material layer 54. That is, the coating film 58 can be set so as not to exist on the insulating tape 56.

[0055] The width L1 of the coating 58 can be appropriately set to smoothly absorb the thickness D2 of the insulating tape 56 and achieve the technical effects disclosed herein. For example, the width L1 of the coating 58 can be approximately 25 to 75 times the thickness D2 of the insulating tape. As an example, if the thickness of the positive electrode sheet 50 is 100 μm, the thickness of the separator is 20 μm, and the thickness D2 of the insulating tape 56 is 40 μm, the width L1 of the coating can be set to 1 mm to 3 mm (e.g., approximately 1.5 mm).

[0056] The coating 58 is inactive for the battery reaction. Here, "inactive for the battery reaction" means that it does not have the function of being an active material. The coating 58 may contain at least a resin binder. Thus, the slurry used to form the coating 58 can be given appropriate viscosity for setting the coating 58. As an example, the coating 58 is a resin layer composed of a resin binder. As the resin binder, an insulating resin can be used without particular limitation. Specific examples thereof include acrylic resins; halogenated vinyl resins such as polyvinylidene fluoride (PVDF); polyalkylene oxides such as polyethylene oxide (PEO); styrene butadiene rubber (SBR); polyolefins such as polyethylene (PE) and polypropylene (PP); fluorine-containing resins such as polytetrafluoroethylene (PTFE); and the like.

[0057] It should be noted that when coating film 58 is a resin layer, preferably a resin layer formed from a resin binder, it may contain unavoidable impurities other than the resin material. Here, unavoidable impurities other than the resin material refer to various elements not contained in the resin material constituting the resin layer. The mass proportion of impurities in coating film 58 is, for example, less than 2% by mass, preferably less than 1% by mass, more preferably less than 0.5% by mass, and preferably closer to 0% by mass.

[0058] Alternatively, the coating 58 may be a filler layer comprising an inorganic filler and a resin binder. As the inorganic filler, for example, an inorganic filler having insulating properties and heat resistance is used. In the above method, the filler layer is sometimes referred to as an "insulating layer" or a "heat-resistant layer". As inorganic fillers, for example, oxides such as aluminum oxide (Al2O3), magnesium oxide (MgO), silicon dioxide (SiO2), and titanium dioxide (TiO2); nitrides such as aluminum nitride (AlN) and silicon nitride (SiN); hydroxides such as calcium hydroxide (CaOH2), magnesium hydroxide (MgOH2), and aluminum hydroxide (Al2OH3); clay minerals such as mica, talc, boehmite, zeolite, apatite, and kaolin; glass fiber; etc., and they can be used alone or in combination of two or more. It should be noted that the shape of the inorganic filler is not particularly limited, and it can be in the form of particles, fibers, plates, flakes, etc. The average particle size of the inorganic filler is not particularly limited, and may be, for example, 0.1 μm to 10 μm (preferably 0.5 μm to 5 μm). The average particle size of the inorganic filler can be determined, for example, by laser diffraction scattering. As the resin binder, the above-mentioned resin binders can be used.

[0059] In the embodiment where the insulating tape 56 and the coating film 58 are provided at both the first end portion 521 and the second end portion 522, the type of coating film 58 at both ends may be the same or different. For example, both the first end portion 521 and the second end portion 522 may be provided as a filler layer or as a resin layer. Alternatively, the first end portion 521 may be provided as a filler layer, and the second end portion 522 may be provided as a resin layer. The same applies to the type and size of the tape 56 at both ends.

[0060] In the secondary battery disclosed herein, Figure 4 As shown, a coating film 58 inactive in the battery reaction is provided on the positive electrode active material layer 54 along the edge of the insulating tape 56. The coating film 58 fills the gap between the positive electrode sheet 50 and the negative electrode sheet 60 where the insulating tape 56 widens the inter-electrode distance. As a result, uneven film formation in the negative electrode active material layer 64 is suppressed, and the amount of metallic lithium deposited on the negative electrode active material layer 64 is also reduced.

[0061] In one embodiment of the technology disclosed herein, the coating 58 may be a filler layer. If the coating 58 is a filler layer, it is impregnated with an electrolyte. Therefore, the migration of lithium ions between the positive and negative electrodes via the filler layer can be achieved. Lithium ions can be supplied to the negative electrode active material layer 64 opposite to the filler layer (coating 58), and the negative electrode active material layer 64 opposite to the filler layer (coating 58) can also participate in the battery reaction. In addition, the positive electrode active material is suppressed from dissolving from the portion where the coating 58 is formed on the positive electrode active material layer 54, thereby suppressing the precipitation of metallic lithium on the negative electrode active material layer 64. In addition, in another embodiment, the coating 58 may be a resin layer. In this case, the positive electrode active material is suppressed from dissolving from the portion where the coating 58 is formed on the positive electrode active material layer 54, thereby more reliably suppressing the precipitation of metallic lithium on the negative electrode active material layer 64.

[0062] It should be noted that, although not particularly limited, the distribution of the coating within the negative electrode active material layer 64 can be investigated, for example, using laser ablation ICP mass spectrometry (LA-ICP-MS). For example, the distribution of elements (e.g., boron (B), phosphorus (P), etc.) contained in the coating formed on the negative electrode active material layer can be analyzed by performing linear analysis on the negative electrode active material layer. As an LA-ICP-MS instrument, a conventionally known instrument such as the UP213 manufactured by New Wave Research can be used.

[0063] The secondary battery 100 can be used for various applications. Suitable applications include power sources for vehicles such as electric vehicles (BEVs), hybrid electric vehicles (HEVs), and plug-in hybrid electric vehicles (PHEVs). Furthermore, the secondary battery 100 can be used as a storage battery for small power storage devices. Typically, the secondary battery 100 can be used in the form of a battery pack consisting of multiple batteries connected in series and / or in parallel.

[0064] Example

[0065] Hereinafter, examples of the present invention will be described, but the present invention is not intended to be limited to the contents shown in the following examples.

[0066] <Production of lithium-ion secondary batteries for evaluation>

[0067] Secondary batteries for evaluation of Examples 1 to 3 were produced as follows.

[0068] -Example 1-

[0069] LiNi as the positive electrode active material 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (LNCM), acetylene black (AB) as a conductive material, and polyvinylidene fluoride (PVDF) as a binder were mixed with N-methylpyrrolidone (NMP) at a mass ratio of LNCM:AB:PVDF = 87:10:3 to prepare a slurry for forming the positive electrode active material layer. Separately, an acrylic resin was dispersed in water to a solids content of 35% to prepare a slurry for forming a coating film. This slurry for forming the positive electrode active material layer was applied to both sides of a long sheet of aluminum foil. The slurry was then dried to form the positive electrode active material layer, which was then roll-pressed. The aluminum foil with the positive electrode active material layer was then cut into the desired size to produce a positive electrode sheet.

[0070] At both ends of the positive electrode sheet (i.e., the cut portions), insulating tape was attached to the positive electrode active material, and the two ends were covered with the insulating tape. Next, the coating film-forming slurry was dripped along the insulating tape using a syringe and dried to form a coating film (acrylic resin layer).

[0071] Graphite (C) as the negative electrode active material, styrene butadiene rubber (SBR) as the binder, and carboxymethyl cellulose (CMC) as the thickener were mixed with ion-exchanged water at a mass ratio of C:SBR:CMC = 98:1:1 to prepare a slurry for forming the negative electrode active material layer. This slurry was applied to both sides of a long sheet of copper foil. The slurry was then dried to form the negative electrode active material layer, which was then roll-pressed. The copper foil with the negative electrode active material layer was then cut into the desired size to produce the negative electrode sheet.

[0072] As a separator, a porous polyolefin sheet having a three-layer structure of PP / PE / PP was prepared.

[0073] After the positive electrode sheet, negative electrode sheet and two separators prepared above are stacked and wound, they are squeezed from the side to flatten them to produce a flat wound electrode body. Next, the positive terminal and the negative terminal are connected to the wound electrode body and housed in a square battery case with an electrolyte injection port. Next, a non-aqueous electrolyte is injected from the electrolyte injection port of the battery case, and the injection port is airtightly sealed. It should be noted that the non-aqueous electrolyte is a solution prepared by dissolving LiPF6 as a supporting salt at a concentration of 1.1 mol / L in a mixed solvent containing ethylene carbonate (EC), ethyl methyl carbonate (EMC) and dimethyl carbonate (DMC) in a volume ratio of EC:EMC:DMC=3:4:3. A secondary battery for evaluation is thus produced.

[0074] -Example 2-

[0075] As a coating film forming slurry, a slurry prepared by dissolving polyvinylidene fluoride (PVDF) in N-methylpyrrolidone (NMP) at a mass ratio of 5% was prepared and used. A secondary battery for evaluation of Example 2 was prepared using the same materials and procedures as in Example 1 except for the above.

[0076] -Example 3-

[0077] A secondary battery for evaluation of Example 3 was produced using the same materials and procedures as in Example 1 except that the coating film formation was not performed.

[0078] <Evaluation of metallic lithium deposition>

[0079] The above-mentioned evaluation secondary battery was activated under specified conditions to obtain an initial capacity. The above-mentioned initial capacity was 4 Ah. The above-mentioned evaluation secondary battery was further aged. After adjusting it to SOC 80%, it was placed in an environment of 0°C. The secondary battery was repeated for 1000 charge and discharge cycles, wherein the charge and discharge cycle is composed of 10 seconds of constant current charging at 20C and 20 seconds of constant current discharging at 10C as one cycle. It should be noted that a rest time of 3 minutes was set between charging and discharging. Thereafter, the test secondary battery was disassembled, the negative electrode sheet was removed, and a part of the end of the negative electrode active material layer opposite to the insulating tape provided on the positive electrode sheet was cut out. The presence or absence of metallic lithium precipitation was visually confirmed and analyzed by electron spin resonance (ESR). Then, the amount of lithium precipitated was quantified based on the peak intensity near 3445G. The results are shown in Table 1. It should be noted that "none" in the "Li precipitation" column of Table 1 means that metallic lithium was not detected by ESR analysis.

[0080]

Table 1

[0081] Table 1

[0082] Resin binder Li precipitation Example 1 acrylic resin none Example 2 PVDF none Example 3 - have

[0083] As shown in Table 1, in the evaluation secondary batteries of Examples 1 and 2, in which a coating film was formed along the insulating tape adhered to the longitudinal ends of the positive electrode sheet, metallic lithium precipitation after charge-discharge cycles was suppressed. On the other hand, in the evaluation secondary battery of Example 3, in which no such coating film was formed, metallic lithium precipitation was observed in the negative electrode sheet after charge-discharge cycles.

[0084] Based on the above, it can be confirmed that the precipitation of metallic lithium on the negative electrode active material is suppressed in a secondary battery constructed as follows: a wound electrode body and a non-aqueous electrolyte, the wound electrode body being a positive electrode sheet having a long sheet-shaped positive electrode collector and a positive electrode active material layer formed on the surface of the positive electrode collector, and a negative electrode sheet having a long sheet-shaped negative electrode collector and a negative electrode active material layer formed on the surface of the negative electrode collector, sandwiched between an isolator and wound in the long side direction, and having an insulating tape covering at least one end portion of the long side direction of the positive electrode sheet and adhered to the positive electrode active material layer, and a coating inactive to the battery reaction arranged on the positive electrode active material layer along the edge of the insulating tape, wherein the thickness of the coating decreases as it moves away from the edge of the insulating tape.

[0085] While specific examples of the technology disclosed herein have been described in detail above, these are merely illustrative and do not limit the scope of the claims. The technology disclosed herein includes various variations and modifications of the above specific examples. For example, the technology disclosed herein may also be applied to sodium ion secondary batteries.

[0086] In the above embodiment, as shown in the figure, the coating film 58 is in close contact with the insulating tape 56. The coating film 58 is continuously provided from one end to the other end of the positive electrode active material layer 54 in the width direction X. The coating film 58 is provided only on the positive electrode active material layer 54. However, the technology disclosed herein is not limited to this. That is, as long as the technical effects disclosed herein can be achieved, there may be a small gap between the coating film 58 and the insulating tape 56. As long as the technical effects disclosed herein can be achieved, the formation of the coating film 58 may also be discontinuous. The area on the positive electrode active material layer 54 and along the edge of the insulating tape 56 may also be partially a non-forming area of ​​the coating film 58. The coating film 58 may also be provided on the positive electrode collector 52 (positive electrode active material layer non-forming portion 52a).

Claims

1. A secondary battery comprising a wound electrode body and a non-aqueous electrolyte, The wound electrode body is formed by winding a positive electrode sheet having a long sheet-shaped positive electrode current collector and a positive electrode active material layer formed on the surface of the positive electrode current collector, and a negative electrode sheet having a long sheet-shaped negative electrode current collector and a negative electrode active material layer formed on the surface of the negative electrode current collector, with a separator interposed therebetween, in the longitudinal direction. An insulating tape and a coating film are provided at at least one end portion of the positive electrode sheet in the longitudinal direction. The insulating tape covers the entire end portion without exposing the end portion to the outside and adheres to the positive electrode active material layer. The coating film is provided on the positive electrode active material layer along the edge of the insulating tape and is inactive to the battery reaction. Here, the thickness of the coating film decreases as it becomes farther away from the edge of the insulating tape.

2. The secondary battery according to claim 1, wherein The insulating tape and the coating film are provided at both ends of the positive electrode sheet in the longitudinal direction.

3. The secondary battery according to claim 1 or 2, wherein The coating film includes a filler layer containing an inorganic filler and a resin binder, and / or a resin layer composed of a resin binder.

4. The secondary battery according to claim 3, wherein The resin binder is composed of at least one resin material selected from acrylic resin and halogenated vinyl resin.

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