Nonaqueous electrolyte secondary battery

Abstract

This nonaqueous electrolyte secondary battery is provided with an electrode group having a wound structure and including a positive electrode (5), a negative electrode (6), and a separator (7). The electrode group satisfies at least one structure selected from (A) and (B): (A) the electrode group further includes an insulating protective tape (9) that is bonded to a region (60) extending from a surface of the negative electrode active material layer (6b) facing the separator (7) to an exposed portion of the negative electrode current collector (6a) via an end surface of the negative electrode active material layer (6b) at at least one end portion in the longitudinal direction of the negative electrode (6); the electrode group (B) further includes an insulating protective tape bonded to a surface of the negative electrode active material layer (6b) facing the separator (7) in a region of the negative electrode (6) facing the positive electrode lead portion of the positive electrode (5), and the base material of the protective tape (9) is a resin-based microporous film having a compressive deformation rate of 30-50% when a load of 50 kg / cm2 is applied.

Description

Technical Field

[0001] The present disclosure relates to a nonaqueous electrolyte secondary battery. Background Art

[0002] In a non-aqueous electrolyte secondary battery such as a lithium ion secondary battery, for example, an electrode group is used in which a positive electrode and a negative electrode are stacked in a manner such that a separator composed of a microporous film made of a resin is arranged between the positive electrode and the negative electrode, and the electrode group is wound into a spiral shape. In an electrode group having such a winding structure, for example, in order to suppress a short circuit at a portion where a local pressure is increased during winding, an insulating tape is arranged at a portion where a pressure is increased to prevent a short circuit caused by contact between the positive electrode and the negative electrode.

[0003] For example, Patent Document 1 discloses a structure in which an insulating tape is arranged at a position where multiple short circuits can be prevented by insulating at one location in order to provide a battery that minimizes the thickness of the electrode group and is not prone to internal short circuits. Specifically, Patent Document 1 discloses a battery having an electrode group, wherein an insulating tape is attached to a portion of the negative electrode core body that is exposed from the end of the portion of the negative electrode coated with a negative electrode active material and that is opposite to the positive electrode, and a positive electrode current collector tab is conductively connected to the exposed positive electrode core body on an extension line connecting the winding center of the electrode group and the insulating tape.

[0004] Patent document 2 discloses that in an electrode group having a wound structure, an electrode plate constituting the electrode group is formed by a current collector, an active material layer, an electrode tab fixed to an uncoated portion, and an electrode heat insulating plate joined on the opposite side of the surface of the uncoated portion to which the electrode tab is fixed. The electrode heat insulating plate is composed of a composite material tape, which is formed of an organic material forming a matrix of the heat insulating plate and an inorganic material dispersed in the organic material. The composite material tape can maintain heat insulation and insulation even at high temperatures by containing an inorganic material.

[0005] Prior Art Literature

[0006] Patent Document 1: Japanese Patent No. 4245429

[0007] Patent Document 2: Japanese Patent No. 4878800 Summary of the invention

[0008] Problems to be solved by the invention

[0009] The present disclosure provides a nonaqueous electrolyte secondary battery capable of reducing the possibility of internal short circuit caused by foreign matter mixed into an electrode group at a portion where stress concentrates in the electrode group, and suppressing metal precipitation in a negative electrode.

[0010] Means for solving problems

[0011] The present invention provides a non-aqueous electrolyte secondary battery comprising an electrode group and a non-aqueous electrolyte.

[0012] The electrode group includes a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode, and has a winding structure.

[0013] The negative electrode comprises a negative electrode current collector and a negative electrode active material layer.

[0014] The electrode group satisfies at least one structure selected from the following (A) and (B):

[0015] (A) the electrode group further includes an insulating protective tape, wherein at least one end of the protective tape in the longitudinal direction of the negative electrode is joined to a region extending from a surface of the negative electrode active material layer opposite to the separator through an end surface of the negative electrode active material layer to an exposed portion of the negative electrode current collector,

[0016] (B) the electrode group further includes an insulating protective tape, the protective tape being bonded to a surface of the negative electrode active material layer facing the separator in a region of the negative electrode facing the positive electrode lead portion of the positive electrode,

[0017] The base material of the protective tape is applied with 50kg / cm 2 A resin microporous membrane having a compression deformation rate of 30% or more and 50% or less under a load of

[0018] Effects of the Invention

[0019] According to the present disclosure, it is possible to provide a nonaqueous electrolyte secondary battery capable of reducing the possibility of internal short circuit caused by foreign matter mixed into an electrode group at a portion where stress concentrates in the electrode group and suppressing metal precipitation in the negative electrode. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a cross-sectional view of a nonaqueous electrolyte secondary battery according to one embodiment of the present disclosure.

[0021] Figure 2A It is a cross-sectional view showing a partially unfolded state of the electrode group in a wound state.

[0022] Figure 2B yes Figure 2A FIG. 1 is an enlarged cross-sectional view of an end portion of the electrode group on the outer peripheral side in the longitudinal direction.

[0023] Figure 3A It is a cross-sectional view showing the winding state of the electrode group and the position of the positive electrode lead.

[0024] Figure 3B It is schematically indicated Figure 3AAn enlarged cross-sectional view of a portion of the positive electrode lead portion is shown. DETAILED DESCRIPTION

[0025] (Insights that form the basis of this disclosure)

[0026] In a lithium-ion secondary battery, which is an example of a non-aqueous electrolyte secondary battery, the area of ​​the negative electrode active material layer is made larger than the area of ​​the positive electrode active material layer in order to allow the Li ions separated from the positive electrode to react with the negative electrode active material or to be inserted into the negative electrode active material. For example, when the positive electrode and the negative electrode are overlapped with a separator, if the positive electrode mixture layer extends from the outer edge of the negative electrode active material layer, lithium will be deposited on the negative electrode at the part where the positive electrode extends.

[0027] When the area of ​​the negative electrode active material layer is larger than that of the positive electrode active material layer, in the electrode group, a step difference in the thickness of the positive electrode is generated between the area where the negative electrode active material layer and the positive electrode active material layer are opposite and the area where the negative electrode active material and the positive electrode active material layer are not opposite. Here, for example, in a negative electrode using a Si-based active material as the negative electrode active material, the expansion of the Si-based active material is large, and the stress is concentrated in the above-mentioned step difference part. Assuming that foreign matter is mixed into such a step difference part, when the foreign matter penetrates the diaphragm, it will cause an internal short circuit. In addition, the mixed foreign matter can be considered, for example, from the components of the manufacturing device (such as metal components or metal fixtures) during the manufacturing process, which are rarely generated due to wear and tear. In addition, it can be considered as foreign matter that is rarely attached to the battery components.

[0028] In the battery disclosed in Patent Document 1, in an electrode group having a winding structure, an insulating tape is pasted on the portion of the negative electrode core exposed from the end of the portion of the negative electrode coated with the negative electrode active material, which is opposite to the positive electrode. That is, the insulating tape is arranged at a position corresponding to the above-mentioned step difference portion. However, the inventors have newly discovered that even if the insulating tape is arranged at the above-mentioned step difference portion, the following problems will arise due to the expansion of the negative electrode. Due to the expansion of the negative electrode, the positional displacement of the positive electrode and the negative electrode is likely to occur at the above-mentioned step difference portion. Assuming that foreign matter is mixed into the step difference portion, even if the foreign matter is captured by the insulating tape and the internal short circuit caused by the foreign matter is suppressed, in the case where the positional displacement of the positive electrode and the negative electrode occurs at the step difference portion due to the expansion of the negative electrode, the captured foreign matter will fall off the insulating tape. As a result, it is difficult to prevent the internal short circuit caused by foreign matter. This problem is particularly significant in the case of a negative electrode that expands greatly, such as a negative electrode containing Si-based active materials.

[0029] In the battery disclosed in Patent Document 2, a composite material strip as an electrode heat insulating plate is arranged at a position corresponding to the step portion in an electrode group having a wound structure. However, as in the battery disclosed in Patent Document 1, if foreign matter is mixed into the step portion and the position of the electrode is shifted due to expansion of the electrode, etc., it is difficult to prevent an internal short circuit caused by the foreign matter by the composite material strip.

[0030] Therefore, a technology is needed to reduce the possibility of internal short circuit caused by foreign matter mixed in the portion of the electrode group where stress is concentrated, such as the above-mentioned step difference portion. In addition, even if it is a technology that can reduce the possibility of internal short circuit caused by foreign matter, if it is a technology that causes lithium precipitation at the negative electrode, the performance of the battery itself will also be reduced. Therefore, a technology that can suppress the generation of lithium precipitation in addition to reducing the possibility of internal short circuit caused by foreign matter is needed.

[0031] Based on the above findings, the inventors conducted intensive research and conceived of a non-aqueous electrolyte secondary battery disclosed herein, which can reduce the possibility of internal short circuits caused by foreign matter mixed into the electrode group at the stress concentrated portion of the electrode group having a wound structure and inhibit metal precipitation in the negative electrode.

[0032] The non-aqueous electrolyte secondary battery disclosed herein comprises an electrode group and a non-aqueous electrolyte, wherein the electrode group comprises a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode, and has a wound structure. The negative electrode comprises a negative electrode current collector and a negative electrode active material layer. The electrode group satisfies at least one structure selected from the following (A) and (B):

[0033] (A) the electrode group further includes an insulating protective tape, wherein at least one end of the protective tape in the longitudinal direction of the negative electrode is joined to a region extending from a surface of the negative electrode active material layer opposite to the separator through an end surface of the negative electrode active material layer to an exposed portion of the negative electrode current collector,

[0034] (B) The electrode group further includes an insulating protective tape, the protective tape being bonded to a surface of the negative electrode active material layer facing the separator in a region of the negative electrode facing the positive electrode lead portion of the positive electrode.

[0035] The base material of the protective tape is applied with 50kg / cm 2 A resin microporous membrane having a compression deformation rate of 30% or more and 50% or less when subjected to a load of 50 kg / cm 2 The compression deformation rate under a load of 50 kg / cm is measured by, for example, using a universal testing machine. 2 That is, the compression deformation rate can be calculated by the following formula.

[0036] Compression deformation rate (%) =

[0037] {[(thickness before compression) - (thickness after compression)] / (thickness before compression)} × 100 In the non-aqueous electrolyte secondary battery disclosed in the present invention, the protective band having the above-mentioned characteristics is arranged in at least one area selected from the specific area in (A) above and the specific area in (B) above. The specific area in (A) above and the specific area in (B) above are parts of the electrode group where stress is easily concentrated. According to this structure, the non-aqueous electrolyte secondary battery disclosed in the present invention can reduce the possibility of internal short circuit caused by foreign matter mixed into the electrode group in the part where stress is concentrated in the electrode group, and suppress metal precipitation in the negative electrode.

[0038] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. The present disclosure is not limited to the following embodiments.

[0039] (Implementation Method 1)

[0040] Figure 1 1 is a cross-sectional view of a nonaqueous electrolyte secondary battery according to Embodiment 1 of the present disclosure. Here, a lithium ion secondary battery will be described as an example of the nonaqueous electrolyte secondary battery of the present disclosure.

[0041] The lithium-ion secondary battery 100 includes a container 1 and an electrode group 4. The electrode group 4 is stored in the container 1. The electrode group 4 has a winding structure. The electrode group 4 includes a positive electrode 5, a negative electrode 6, and a pair of separators 7. That is, the electrode group 4 is formed by overlapping the positive electrode 5 and the negative electrode 6 in a manner of arranging the separator 7 between the positive electrode 5 and the negative electrode 6, and winding them into a spiral shape. An electrolyte solution as a non-aqueous electrolyte is impregnated in the electrode group 4. The opening of the container 1 is sealed by a sealing plate 2. The positive electrode 5 includes a positive electrode collector 5a and a positive electrode active material layer 5b. One end of the positive electrode lead 5c is connected to the positive electrode 5. The other end of the positive electrode lead 5c is connected to the back of the sealing plate 2. An insulating filler 3 is arranged around the sealing plate 2. The negative electrode 6 includes a negative electrode collector 6a and a negative electrode active material layer 6b. One end of the negative electrode lead 6c is connected to the negative electrode 6. The other end of the negative electrode lead 6c is connected to the bottom surface of the container 1. Insulating rings 8 are disposed on the upper and lower surfaces of the electrode group 4 .

[0042] In this embodiment, the container 1 has a negative polarity and the sealing plate 2 has a positive polarity. However, the container 1 may have a positive polarity and the sealing plate 2 may have a negative polarity.

[0043] Figure 2A It is a cross-sectional view showing a partially developed state of the electrode group 4 in a wound state. Figure 2B yes Figure 2A1 is an enlarged cross-sectional view of an outer peripheral end 10 in the longitudinal direction of the electrode group 4. The longitudinal direction of the electrode group 4 corresponds to the direction along the winding direction of the electrode group 4. The same applies to the longitudinal direction of the negative electrode 6.

[0044] like Figure 2A and Figure 2B As shown, in the lithium ion secondary battery 100 of the present embodiment, the electrode group 4 further includes an insulating protective tape 9, which is bonded to a region 60 extending from a surface 61 of the negative electrode active material layer 6b facing the separator 7 via an end surface 62 of the negative electrode active material layer 6b to an exposed portion 63 of the negative electrode collector 6a at at least one end 10 in the longitudinal direction of the negative electrode 6. Here, as at least one end in the longitudinal direction of the negative electrode 6, a structural example in which the protective tape 9 is provided at an end corresponding to the outer peripheral side of the wound electrode group 4 is shown. Alternatively, the protective tape 9 may be provided at an end in the longitudinal direction of the inner peripheral side of the negative electrode 6.

[0045] The protective tape 9 comprises a substrate. The substrate of the protective tape is coated with 50 kg / cm 2 The compressive deformation rate of the substrate of the protective tape 9 can be within the range of 30% to 50% by adjusting the material of the substrate, the porosity of the substrate, the pore size distribution of the substrate, the thickness of the substrate, the molecular weight of the substrate, the mechanical properties of the substrate (such as the compression deformation yield stress, etc.), etc.

[0046] In the lithium ion secondary battery 100 of the present embodiment, for example, in order to allow Li ions separated from the positive electrode active material of the positive electrode 5 to react with the negative electrode active material or to be inserted into the negative electrode active material, the area of ​​the negative electrode active material layer 6b is designed to be larger than the area of ​​the positive electrode active material layer 5b. Therefore, at the end 10 of the electrode group 4, a step difference of the thickness of the positive electrode 5 is generated between the area where the negative electrode active material layer 6b and the positive electrode active material layer 5b face each other and the area where the negative electrode active material layer 6b and the positive electrode active material layer 5b do not face each other. The area 60 from the surface 61 of the negative electrode active material layer 6b facing the separator 7 to the exposed part 63 of the negative electrode collector 6a via the end surface 62 of the negative electrode active material layer 6b becomes the above-mentioned step difference part. Therefore, the area 60 corresponds to the part where the stress of the electrode group is concentrated. In such an area 60, a protective tape 9 including a substrate having a compression deformation rate of 30% or more and 50% or less is arranged. According to this structure, even if foreign matter is mixed into the step difference portion and the position of the positive electrode 5 and the negative electrode 6 is offset in the step difference portion due to the expansion of the negative electrode 6, the foreign matter temporarily captured by the protective tape 9 can continue to exist in a state of being partially buried in the protective tape 9, and the movement of the foreign matter is suppressed. Therefore, the lithium ion secondary battery 100 of this embodiment can reduce the possibility of internal short circuit caused by foreign matter mixed into the electrode group 4 at the portion where the stress of the electrode group 4 is concentrated.

[0047] In addition, as described above, the base material of the protective tape 9 is a resin microporous film. Therefore, the protective tape 9 has ion permeability. Since the protective tape 9 does not hinder the movement of lithium ions to the negative electrode active material layer 6b, lithium precipitation can be suppressed in the portion of the negative electrode 6 bonded with the protective tape 9 and its vicinity.

[0048] The protective tape 9 can be formed only by the above-mentioned substrate. In this case, the protective tape 9 can be bonded to the region 60 of the negative electrode 6 by heating, pressing or heating. In addition, as another example, the protective tape 9 can also include an adhesive layer provided on at least one surface of the above-mentioned substrate. With this structure, the provision of the protective tape becomes simpler. The adhesive layer can be provided on one side of the substrate or on both sides. As the adhesive contained in the adhesive layer, for example, an adhesive that swells in the electrolyte and has ion permeability can be selected. As the adhesive contained in the adhesive layer, for example, acrylic adhesives, rubber adhesives and silicone adhesives can be used.

[0049] The resin-based microporous film may be, for example, a microporous film made of a polyolefin resin. By using a microporous film made of a polyolefin resin as a substrate, the protective tape 9 can have good ion permeability. Therefore, the occurrence of lithium precipitation in the negative electrode 6 can be more reliably suppressed. In addition, according to the microporous film made of a polyolefin resin, it is easy to achieve a compression deformation rate of 30% or more and 50% or less.

[0050] The resin-based microporous film may contain at least one selected from polyphenylene sulfide (PPS) and polyimide (PI). By using at least one selected from PPS and PI as the material of the base material of the protective tape 9, it is possible to have good protection against foreign matter. In addition, according to the microporous film of PPS and PI, it is easy to realize a base material having a compression deformation rate of 30% or more and 50% or less.

[0051] The protective tape 9 may further include a porous layer containing an inorganic material disposed on the substrate. By providing the porous layer containing an inorganic material on the substrate, the heat resistance of the protective tape 9 is improved. This can suppress the expansion of the internal short circuit site due to heat generation.

[0052] The thickness of protective tape 9 is, for example, not less than 10 μm and not more than 100 μm. According to this structure, the occurrence of lithium deposition in negative electrode 6 can be more reliably suppressed, and the possibility of internal short circuit due to foreign matter can be further reduced.

[0053] The compressive deformation rate of the base material of the protective tape 9 can be 50 kg / cm higher than that of the diaphragm 7. 2 According to this structure, when the negative electrode expands, the movement of foreign matter can be more reliably suppressed, so the possibility of internal short circuit can be further reduced.

[0054] As a resin-based microporous membrane, a microporous membrane with an average pore diameter of about 0.01 μm to 1 μm can be used. This can reduce the possibility of internal short circuits caused by foreign matter. The average pore diameter of the microporous membrane is the median pore diameter obtained from the pore distribution measured by a mercury porosimeter. The median pore diameter refers to the pore diameter when the cumulative volume is equal to 50% in the volume-based pore distribution.

[0055] Hereinafter, each component other than the protective tape 9 will be described in detail.

[0056] As the positive electrode current collector 5a, a sheet or film made of a metal material such as aluminum, stainless steel, titanium, or their alloys can be used. Aluminum and its alloys are cheap and easy to be made into thin films, so they are suitable as the material of the positive electrode current collector 5a. The sheet or film can be porous or non-porous. As the sheet or film, a metal foil, a metal mesh, etc. can be used. A carbon material such as carbon can be coated on the surface of the positive electrode current collector 5a as a conductive auxiliary material.

[0057] The positive electrode active material contained in the positive electrode active material layer 5b is not particularly limited as long as it is a material that can reversibly absorb and release lithium ions. Typically, a lithium-containing transition metal compound can be used as the positive electrode active material. Examples of lithium-containing transition metal compounds include composite oxides containing lithium and at least one element selected from cobalt, manganese, nickel, chromium, iron and vanadium. Specifically, LiCoO2, LiMnO2, LiNiO2, LiNi x M (1-x) O2 (M contains at least one selected from Co, Mn, Fe, Mg, Ti and Al, and x satisfies 0.3≤x≤0.95), LiCrO2, αLiFeO2, LiVO2, etc.

[0058] The positive electrode active material layer 5 b may contain other materials such as a conductive auxiliary agent, an ion conductor, and a binder.

[0059] Conductive aids and ion conductors are used to reduce the resistance of the positive electrode 5. As conductive aids, carbon materials, conductive polymer compounds, etc. can be mentioned. As carbon materials, carbon black, graphite, acetylene black, carbon nanotubes, carbon nanofibers, graphene, fullerene, graphite oxide, etc. can be mentioned. As conductive polymer compounds, polyaniline, polypyrrole, polythiophene, etc. can be mentioned. As ion conductors, gel electrolytes, organic solid electrolytes, inorganic solid electrolytes, etc. can be mentioned. As gel electrolytes, polymethyl methacrylate, polymethyl methacrylate, etc. can be mentioned. As organic solid electrolytes, polyethylene oxide, etc. can be mentioned. As inorganic solid electrolytes, Li7La3Zr2O 12 wait.

[0060] The binder is used to improve the binding property of the material constituting the positive electrode 5. As the binder, a polymer material such as polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene copolymer, polytetrafluoroethylene, carboxymethyl cellulose, polyacrylic acid, styrene-butadiene copolymer rubber, polypropylene, polyethylene, polyimide, etc. can be used.

[0061] As the negative electrode current collector 6a, a sheet or film made of a metal material such as stainless steel, nickel, copper, or an alloy thereof can be used. The sheet or film can be porous or non-porous. As the sheet or film, a metal foil, a metal mesh, etc. can be used. A carbon material such as carbon can be coated on the surface of the negative electrode current collector 6a as a conductive auxiliary material.

[0062] The negative electrode active material contained in the negative electrode active material layer 6b is not particularly limited as long as it is a material that can reversibly absorb and release lithium ions. Typically, a carbon material containing graphite having a graphite-type crystal structure can be used as the negative electrode active material. As such a carbon material, natural graphite, spherical or fibrous artificial graphite, difficult graphitization carbon (hard carbon), easy graphitization carbon (soft carbon), etc. can be cited. As a material other than a carbon material, lithium titanate can be cited. In addition, from the viewpoint of improving the energy density of the lithium ion battery 100, high-capacity materials such as silicon, tin, silicon alloys, tin alloys, silicon oxide, silicon nitride, tin oxide, and materials that are composites of silicon and carbon can also be preferably used as negative electrode active materials.

[0063] The negative electrode active material layer 6b may contain at least one selected from graphite and silicon as the negative electrode active material. As the negative electrode active material, only graphite may be contained in the negative electrode active material layer 6b. Graphite is not easily degraded even when repeatedly charged and discharged at a deep depth, so it is recommended. Carbon materials other than graphite may also be used as negative electrode active materials. Silicon shows a larger capacity than graphite, and therefore is conducive to increasing the capacity of the lithium ion secondary battery 100.

[0064] In this embodiment, the negative electrode active material layer 6b may contain a Si-based active material as the negative electrode active material. The Si-based active material refers to an active material containing the Si element. For example, Si element, Si alloy, Si-containing compound, Si-containing composition, Si and carbon composite, etc. can be cited. As the Si-containing composition, for example, a composition (Li2Si2O5) in which Si particles are dispersed in a lithium silicate phase having Li2Si2O5 as the main component can be cited. x Si y O z (x>0, y>0, z>0)). In the negative electrode containing Si-based active material as the negative electrode active material, since the Si-based active material expands greatly, stress is easily concentrated on the above-mentioned step difference part, and internal short circuit caused by foreign matter mixed in is also easy to occur. However, according to the protective tape 9 of this embodiment, it is possible to reduce the possibility of internal short circuit while suppressing metal precipitation in the negative electrode 6. That is, the structure disclosed in the present invention can effectively reduce the possibility of internal short circuit caused by foreign matter even when the negative electrode is easy to expand.

[0065] The negative electrode active material layer 6b may contain a conductive additive, an ion conductor, a binder, etc. The conductive additive, ion conductor, and binder may be the same materials as those used in the positive electrode active material layer 5b.

[0066] The diaphragm 7 has lithium ion permeability. As long as lithium ions are allowed to pass through, there is no particular limitation on the material of the diaphragm 7. The material of the diaphragm 7 can be at least one selected from a gel electrolyte, an ion exchange resin membrane, a semipermeable membrane and a porous membrane. If the diaphragm 7 is made of these materials, the safety of the lithium ion secondary battery 100 can be fully ensured. As a gel electrolyte, a gel electrolyte containing a fluororesin such as PVdF can be cited. As an ion exchange resin membrane, a cation exchange membrane, an anion exchange membrane, etc. can be cited. As a porous membrane, a porous membrane made of a polyolefin resin, a porous membrane containing a cellophane obtained by weaving glass fibers into a non-woven fabric, etc. can be cited.

[0067] The electrolyte is a non-aqueous electrolyte that is impregnated in the positive electrode 5, the negative electrode 6, and the separator 7. The electrolyte can fill the internal space of the container 1. Lithium ions can move between the positive electrode 5 and the negative electrode 6 through the action of the electrolyte.

[0068] The electrolyte contains a non-aqueous solvent and a lithium salt.

[0069] Examples of non-aqueous solvents include cyclic carbonate solvents, chain carbonate solvents, cyclic ether solvents, chain ether solvents, cyclic ester solvents, chain ester solvents or fluorinated solvents. Examples of cyclic carbonate solvents include ethylene carbonate, propylene carbonate or butylene carbonate. Examples of chain carbonate solvents include dimethyl carbonate, ethyl methyl carbonate or diethyl carbonate. Examples of cyclic ether solvents include tetrahydrofuran, 1,4-dioxane or 1,3-dioxolane. Examples of chain ether solvents include 1,2-dimethoxyethane or 1,2-diethoxyethane. Examples of cyclic ester solvents include γ-butyrolactone. Examples of chain ester solvents include methyl acetate. Examples of fluorinated solvents include fluoroethylene carbonate, methyl fluoropropionate, fluorobenzene, ethyl fluoromethyl carbonate or dimethyl fluorocarbonate. One non-aqueous solvent selected from them may be used alone. Alternatively, a mixture of two or more non-aqueous solvents selected from them may be used.

[0070] As lithium salts, lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bis(perfluoroethylsulfonyl)imide (LiN(SO2C2F5)2), LiAsF6, LiCF3SO3, lithium difluoro(oxalate)borate, etc. can be used. One selected from these lithium salts can be used, or two or more can be used in combination.

[0071] The container 1 is a container made of metal such as aluminum or stainless steel, etc. The container 1 may have a cylindrical shape or a square cylindrical shape.

[0072] The electrode group 4 can be rolled into a cylindrical shape or an elliptical shape.

[0073] There is no particular limitation on the shape of the lithium secondary battery 100. The lithium secondary battery 100 may be in various shapes such as a cylindrical shape or a square cylindrical shape.

[0074] Next, a method for manufacturing the lithium secondary battery 100 will be described.

[0075] First, an electrode group 4 is prepared. Specifically, a positive electrode 5, a negative electrode 6, a separator 7, and a protective tape 9 are prepared. The protective tape 9 is joined to a predetermined position of the negative electrode 6. For example, Figure 2B As shown in FIG. 1 , when the end of the protective tape 9 on the outer peripheral side in the longitudinal direction of the negative electrode 6 is arranged at a position that becomes a region from the surface of the negative electrode active material layer facing the separator through the end surface of the negative electrode active material layer to the exposed portion of the negative electrode collector, the protective tape 9 is joined at this position. Next, the positive electrode 5, the negative electrode 6, and the pair of separators 7 are stacked and wound to form the electrode group 4 wound in a spiral shape. Thus, the electrode group 4 is obtained.

[0076] The positive electrode 5 can be prepared by coating a positive electrode mixture on one or both sides of a positive electrode current collector 5a, drying and rolling. The positive electrode 5 has a thickness of, for example, 30 μm to 200 μm, and is preferably flexible. The positive electrode mixture is obtained by kneading and uniformly dispersing materials such as a positive electrode active material, a binder, and a conductive material using a dispersion medium.

[0077] There is no particular limitation on the method for coating the positive electrode mixture on the positive electrode collector 5a. A slit die coater, a reverse roll coater, a lip coater, a blade coater, a knife coater, a gravure coater, a dip coater, etc. can be used to coat the positive electrode mixture in a slurry state on the positive electrode collector 5a. The coated positive electrode mixture can be dried naturally or by using a drying device.

[0078] After drying, the positive electrode 5 is rolled to make the positive electrode active material layer 5b have a predetermined thickness. The rolling can be performed multiple times using a roller press, or multiple times while changing the pressing pressure of the roller press. After rolling, the positive electrode lead 5c for extracting electricity is welded to the positive electrode collector 5a.

[0079] The negative electrode 6 can be produced by coating a negative electrode mixture on one or both sides of a negative electrode current collector 6a, drying and rolling. The negative electrode 6 has a thickness of, for example, 30 μm to 210 μm, and is preferably flexible. The negative electrode mixture is obtained by kneading and uniformly dispersing materials such as a negative electrode active material, a binder, and a conductive material using a dispersion medium.

[0080] As a method for making the negative electrode 6, a dry method can also be used instead of the above-mentioned wet method. As dry film-forming methods, evaporation method, sputtering method, CVD method (chemical vapor deposition method) and the like can be cited. These methods can all be implemented in a vacuum. From the viewpoint of effectively forming the negative electrode active material layer 6b, evaporation method is preferred. As an evaporation method, any one of electron beam evaporation and resistance heating evaporation can be used. In the case of evaporation of oxides, nitrides or oxynitrides, oxides and / or nitrides can be used as evaporation materials. While evaporating negative electrode active materials such as silicon and tin from an evaporation source, oxygen, nitrogen or ions or radicals containing elements constituting these gases can be introduced between the negative electrode collector 6a and the evaporation source, thereby performing reactive evaporation.

[0081] Next, the electrode group 4 is placed in the container 1, and then the electrolyte is injected into the container 1. Finally, the container 1 is sealed.

[0082] After the above processes, we get Figure 1 A lithium-ion secondary battery 100 is shown.

[0083] (Implementation Method 2)

[0084] The nonaqueous electrolyte secondary battery, i.e., the lithium ion secondary battery, according to Embodiment 2 of the present disclosure has a different position of providing the protective band from the lithium ion secondary battery according to Embodiment 1, but all other structures are the same as those of the lithium ion secondary battery according to Embodiment 1. Therefore, in this embodiment, only the position of providing the protective band is described.

[0085] Figure 3A It is a cross-sectional view showing the winding state of the electrode group 4 and the position of the positive electrode lead portion. Figure 3B It is schematically indicated Figure 3A An enlarged cross-sectional view of a portion of a positive electrode lead portion is shown.

[0086] like Figure 3A and Figure 3B As shown, in the lithium ion secondary battery of this embodiment, the electrode group 4 further includes an insulating protective tape 19, which is bonded to the surface of the negative electrode active material layer 6b facing the separator 7 in the region of the negative electrode 6 facing the positive electrode lead portion of the positive electrode 5. Here, the positive electrode lead portion refers to a portion including a portion of the positive electrode 5 to which the positive electrode lead 5c is connected and its vicinity. In addition, the positive electrode lead 5c is protected by a lead protective tape 5d.

[0087] The protective tape 19 may have the same properties and structure as the protective tape 9 described in Embodiment 1. That is, the base material of the protective tape 19 is a 50 kg / cm 2A resin-based microporous film with a compression deformation rate of 30% or more and 50% or less when subjected to a load. In the positive lead portion, the positive electrode collector 5a is exposed and connected to the positive lead 5c. Therefore, the positive lead portion includes a portion where the positive electrode active material layer 5b is not provided. In this way, the positive lead portion includes an area where the negative electrode active material layer 6b is opposite to the positive electrode active material layer 5b and an area where the negative electrode active material layer 6b is not opposite to the positive electrode active material layer 5b, and a step difference is generated between these two areas in the electrode group 4. That is, the positive lead portion becomes a step difference portion, which is equivalent to a portion of the electrode group 4 where stress is concentrated. In the present embodiment, a protective tape 19 including a substrate with a compression deformation rate of 30% or more and 50% or less is arranged in the area of ​​the negative electrode 6 that is opposite to the positive lead portion of the positive electrode 5. According to this structure, even if foreign matter is mixed into the step difference portion and the position of the positive electrode 5 and the negative electrode 6 is offset in the step difference portion due to the expansion of the negative electrode 6, the foreign matter temporarily captured by the protective tape 19 can continue to exist in a state where a part of it is buried in the protective tape 19, and the movement of the foreign matter is suppressed. Therefore, the lithium ion secondary battery of this embodiment can reduce the possibility of internal short circuit caused by foreign matter mixed into the electrode group 4 at the portion where the stress of the electrode group 4 is concentrated.

[0088] In addition, the base material of the protective tape 19 is a resin microporous film similar to the protective tape 9. Therefore, the protective tape 19 has ion permeability. Since the protective tape 19 does not hinder the movement of lithium ions to the negative electrode active material layer 6b, it is possible to suppress the precipitation of lithium in the portion of the negative electrode 6 to which the protective tape 19 is bonded and in the vicinity thereof.

[0089] The lithium ion secondary battery of this embodiment may further include a protective tape 9 in addition to the protective tape 19. That is, the protective tape 9 of the first embodiment may also be applied to the lithium ion secondary battery of the second embodiment. In this case, the possibility of an internal short circuit caused by foreign matter mixed into the electrode group 4 can be further reduced. When the protective tape 19 and the protective tape 9 are provided at the same time, the protective tape 19 and the protective tape 9 may be made of the same material and structure or different materials and structures.

[0090] (Other embodiments)

[0091] (Note)

[0092] Based on the description of the above embodiments, the following technical solutions are disclosed.

[0093] (Technical Solution 1)

[0094] A non-aqueous electrolyte secondary battery comprises an electrode group and a non-aqueous electrolyte.

[0095] The electrode group includes a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode, and has a winding structure.

[0096] The negative electrode comprises a negative electrode current collector and a negative electrode active material layer.

[0097] The electrode group satisfies at least one structure selected from the following (A) and (B):

[0098] (A) the electrode group further includes an insulating protective tape, wherein at least one end of the protective tape in the longitudinal direction of the negative electrode is joined to a region extending from a surface of the negative electrode active material layer opposite to the separator through an end surface of the negative electrode active material layer to an exposed portion of the negative electrode current collector,

[0099] (B) the electrode group further includes an insulating protective tape, the protective tape being bonded to a surface of the negative electrode active material layer facing the separator in a region of the negative electrode facing the positive electrode lead portion of the positive electrode,

[0100] The base material of the protective tape is applied with 50kg / cm 2 A resin microporous membrane having a compression deformation rate of 30% or more and 50% or less under a load of

[0101] According to this structure, the nonaqueous electrolyte secondary battery of claim 1 can reduce the possibility of internal short circuit caused by foreign matter mixed into the electrode group at the portion where stress concentrates in the electrode group, and can suppress metal precipitation in the negative electrode.

[0102] (Technical Solution 2)

[0103] According to the non-aqueous electrolyte secondary battery described in technical solution 1, the resin-based microporous membrane is a microporous membrane made of a polyolefin resin. By using a microporous membrane made of a polyolefin resin as a substrate, the protective tape can have good ion permeability. Therefore, the occurrence of lithium precipitation in the negative electrode can be more effectively suppressed. In addition, according to the microporous membrane made of a polyolefin resin, it is easy to achieve a compression deformation rate of 30% or more and 50% or less.

[0104] (Technical Solution 3)

[0105] According to the non-aqueous electrolyte secondary battery described in technical solution 1 or 2, the resin-based microporous membrane includes at least one selected from PPS and PI. By using at least one selected from PPS and PI as the material of the base material of the protective tape, it is possible to have good protection against foreign matter. In addition, according to the microporous membrane of PPS and PI, it is easy to realize a base material with a compression deformation rate of 30% or more and 50% or less.

[0106] (Technical Solution 4)

[0107] According to any one of technical solutions 1 to 3, the protective tape further includes a porous layer containing an inorganic material disposed on the substrate. By providing the porous layer containing an inorganic material on the substrate, the heat resistance of the protective tape is improved. As a result, the expansion of the internal short circuit site caused by heat can be suppressed.

[0108] (Technical Solution 5)

[0109] According to the non-aqueous electrolyte secondary battery described in any one of Technical Solutions 1 to 4, the negative electrode active material layer contains a Si-based active material as the negative electrode active material. In the negative electrode containing a Si-based active material as the negative electrode active material, the expansion of the Si-based active material is large. Therefore, stress is easily concentrated on the step difference part of the electrode group, and internal short circuits caused by foreign matter mixed in are also easily generated. However, according to the protective band of Technical Solution 5, metal precipitation in the negative electrode can be suppressed, and the possibility of internal short circuits can be reduced. That is, the structure of Technical Solution 5 can effectively reduce the possibility of internal short circuits caused by foreign matter even when the negative electrode is easy to expand.

[0110] (Technical Solution 6)

[0111] According to the nonaqueous electrolyte secondary battery of any one of claims 1 to 5, the protective tape further includes an adhesive layer provided on at least one surface of the substrate. With this structure, installation of the protective tape becomes simpler.

[0112] Example

[0113] (Example 1)

[0114] [Compression deformation rate of the base material of the protective tape]

[0115] The microporous film as the substrate of the protective tape was prepared by the method described below. High-density polyethylene with a viscosity average molecular weight of 400,000 and liquid paraffin (with a kinematic viscosity of 7.59×10 at 37.8°C) were mixed. -5 m 2 / s) were mixed in a mass ratio of 4:6 and melt-kneaded at 200°C. Next, the obtained mixture was formed into a sheet with a thickness of 1 mm by extrusion molding. After the sheet was stretched to 7×7 times using a simultaneous biaxial stretching machine, it was immersed in dichloromethane, and the liquid paraffin was extracted and removed to prepare a microporous membrane. Furthermore, the microporous membrane was stretched in the transverse direction using a tenter stretching machine. The stretching ratio at this time was set to 1.3, thereby obtaining a microporous membrane with high porosity and good compressibility. The compression deformation rate of the substrate was determined as follows using a testing machine that complies with JIS K 7181. As a measurement sample, 10 substrates were cut into a size of 3cm×3cm, and these 10 sheets were overlapped in the thickness direction and placed on a compression fixture with a diameter of 15mm. Next, the measurement sample was compressed in the thickness direction at a speed of 1mm / min, and the compressive stress was measured to be 50kg / cm 2 The compression deformation rate was calculated by the thickness change at that time. The result was 30% as shown in Table 1.

[0116] [Confirm whether the metal particles are embedded in the protective tape substrate and the insulation between the metal particles and the negative electrode]

[0117] The negative electrode was prepared as follows. As graphite, a graphite obtained by coating carbon on spherical natural graphite was used. As the Si-based active material, a Si-containing composition (a material in which Si particles are dispersed in a lithium silicate phase having Li2Si2O5 as the main component (Li x Si y O z Composition)). These graphites and Si-based active materials are mixed in a mass ratio of 80:20 (graphite:Si-based active material). Carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR) and polyacrylic acid (PAA) are added as binders to the obtained mixture to prepare an aqueous slurry. The obtained aqueous slurry is applied on both sides of a copper foil having a thickness of 10 μm and dried to obtain a sheet. The obtained sheet is then rolled to a thickness of 120 μm and used as a negative electrode.

[0118] A protective tape is attached to the negative electrode. The protective tape is made by forming an adhesive layer on one main surface of a substrate (i.e., a microporous membrane) of the protective tape made by the above method. The protective tape is attached to the negative electrode through the adhesive layer. The adhesive layer is made of an acrylic adhesive.

[0119] A metal particle with a diameter of about 50 μm was placed on the protective tape attached to the negative electrode as described above, and a pressure of 50 kg / cm was applied to the portion. 2The load on the metal particles is applied to confirm the insulation between the metal particles and the negative electrode. In addition, spherical nickel particles are used as metal particles. Then, the load is released to confirm whether the metal particles are buried in the substrate of the protective tape. The insulation between the metal particles and the negative electrode is confirmed by pressing the metal particles with a metal pressure head, measuring the resistance between the pressure head and the negative electrode with a resistance meter, and checking whether there is conduction. Regarding the confirmation of the embedding of the metal particles, after releasing the load on the metal particles, the projections and recesses around the metal particles are measured with a laser microscope, and the state in which more than 50% of the volume of the metal particles is buried in the substrate is judged as embedded.

[0120] [Production of a test cell as a battery and confirmation of lithium deposition]

[0121] (Production of negative electrode)

[0122] Apply 50kg / cm2 of pressure to the protective tape along the thickness direction. 2 The protective tape is attached to the predetermined position of the negative electrode by compressing the negative electrode with a load of 10000. In addition, the method for manufacturing the protective tape and the negative electrode is as described above. Here, the predetermined position refers to the position of the end portion of the outer peripheral side in the length direction of the negative electrode, which is the region from the surface of the negative electrode active material layer opposite to the separator through the end surface of the negative electrode active material layer to the exposed portion of the negative electrode collector when forming an electrode group having a wound structure.

[0123] (Production of positive electrode)

[0124] As the positive electrode active material, LiCo 1 / 3 Mn 1 / 3 Ni 1 / 3 A lithium transition metal composite oxide represented by O2. 98 parts by mass of a positive electrode active material, 1 part by mass of acetylene black and 1 part by mass of polyvinylidene fluoride are mixed, and N-methyl-2-pyrrolidone (NMP) is used as a dispersion medium to prepare a positive electrode mixture slurry. Next, the positive electrode mixture slurry is applied to both sides of a positive electrode core body composed of aluminum foil, and after the coating is dried and compressed, it is cut into a predetermined electrode size to prepare a positive electrode having a positive electrode mixture layer formed on both sides of the positive electrode core body. In addition, an exposed portion exposed on the surface of the core body is provided in the central portion in the longitudinal direction of the positive electrode, and a positive electrode lead is welded to the exposed portion.

[0125] (Preparation of non-aqueous electrolyte)

[0126] In a mixed solvent of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) at a mass ratio of 1:3 (EC:EMC), LiPF6 was dissolved at a concentration of 1 mol / L to prepare an electrolytic solution as a non-aqueous electrolyte.

[0127] (Production of test unit)

[0128] An aluminum lead is installed at the exposed portion of the positive electrode, a nickel lead is installed at a predetermined position of the negative electrode, and the positive electrode and the negative electrode are spirally wound through a polyolefin separator to produce a wound electrode group. The electrode group is housed in a bottomed cylindrical outer can, the nonaqueous electrolyte is injected, and a sealing body is installed at the opening of the outer can through a gasket to produce a cylindrical test unit.

[0129] (Confirmation of lithium precipitation)

[0130] The test cell was subjected to charge and discharge cycles (4.2V-2.5V, charge 0.5C / discharge 0.7C), and after 100 cycles, the test cell was disassembled to check whether lithium was deposited on the negative electrode where the protective tape was attached. The results are shown in Table 1.

[0131] (Example 2)

[0132] Except for the difference in the protective tape used, the battery was prepared and various tests were performed in the same manner as in Example 1. The protective tape used in Example 2 was prepared in the same manner as in Example 1, except that the stretching ratio of the tenter stretching machine was set to 1.4 in the preparation of the substrate. The test results of the compression deformation rate of the substrate of the protective tape were 40% as shown in Table 1.

[0133] (Example 3)

[0134] Except for the difference in the protective tape used, the battery was prepared and various tests were performed in the same manner as in Example 1. The protective tape used in Example 3 was prepared in the same manner as in Example 1, except that the stretching ratio of the tenter stretching machine was set to 1.5 in the preparation of the substrate. The test results of the compression deformation rate of the substrate of the protective tape were 50% as shown in Table 1.

[0135] (Comparative Example 1)

[0136] Except for the difference in the protective tape used, the battery was prepared and various tests were performed in the same manner as in Example 1. The protective tape used in Comparative Example 1 was prepared in the same manner as in Example 1, except that the stretching ratio of the tenter stretching machine was set to 1.2 in the preparation of the substrate. The test results of the compression deformation rate of the substrate of the protective tape were 20% as shown in Table 1.

[0137] (Comparative Example 2)

[0138] Except for the difference in the protective tape used, the battery was prepared and various tests were performed in the same manner as in Example 1. The protective tape used in Comparative Example 2 was prepared in the same manner as in Example 1, except that the stretching ratio of the tenter stretching machine was set to 1.6 in the preparation of the substrate. The test results of the compression deformation rate of the substrate of the protective tape were 60% as shown in Table 1.

[0139] Table 1

[0140]

[0141] As shown in Table 1, in Examples 1 to 3 using a protective tape having a base material compression deformation rate of 30% or more and 50% or less, the metal particles were embedded in the base material of the protective tape, and the insulation between the metal particles and the negative electrode was ensured, and no lithium was precipitated after 100 cycles of charge and discharge. Thus, it can be seen that according to the protective tapes of Examples 1 to 3, it is possible to provide a battery that reduces the possibility of internal short circuits caused by foreign matter mixed into the electrode group and suppresses metal precipitation in the negative electrode.

[0142] On the other hand, in Comparative Example 1 using a protective tape with a compression deformation rate of 20% of the substrate, the metal particles were not embedded in the substrate of the protective tape. Therefore, it is believed that the protective tape of Comparative Example 1 cannot reduce the possibility of internal short circuits caused by foreign matter mixed into the electrode group. In addition, in Comparative Example 2 using a protective tape with a compression deformation rate of 60% of the substrate, lithium was precipitated after 100 cycles of charge and discharge. It is believed that this is because the compression deformation rate of the protective tape of Comparative Example 2 is high, so when the electrode group is made, the pores are destroyed due to compression, and the ion permeability is reduced.

[0143] The above results confirm that the electrode group has a stress concentration portion, which contains a 50 kg / cm 2 The protective tape of the resin microporous film substrate having a compression deformation rate of 30% or more and 50% or less under load can reduce the possibility of internal short circuit caused by foreign matter mixed into the electrode group and inhibit metal precipitation in the negative electrode.

[0144] Industrial Availability

[0145] The technology disclosed herein can be used in lithium-ion secondary batteries.

Claims

1. A non-aqueous electrolyte secondary battery comprising an electrode group and a non-aqueous electrolyte, The electrode group includes a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode, and has a winding structure. The negative electrode comprises a negative electrode current collector and a negative electrode active material layer. The electrode group satisfies at least one structure selected from the following A and B, A: The electrode group further includes an insulating protective tape, wherein at least one end of the protective tape in the longitudinal direction of the negative electrode is joined to a region extending from a surface of the negative electrode active material layer opposite to the separator through an end surface of the negative electrode active material layer to an exposed portion of the negative electrode current collector, B: the electrode group further includes an insulating protective tape, the protective tape being bonded to a surface of the negative electrode active material layer facing the separator in a region of the negative electrode facing the positive electrode lead portion of the positive electrode, The base material of the protective tape is applied with 50kg / cm 2 A resin microporous membrane having a compression deformation rate of 30% or more and 50% or less under a load of 2. The nonaqueous electrolyte secondary battery according to claim 1, The resin-based microporous membrane is a microporous membrane made of a polyolefin resin.

3. The nonaqueous electrolyte secondary battery according to claim 1, The resin-based microporous membrane includes at least one selected from polyphenylene sulfide and polyimide.

4. The nonaqueous electrolyte secondary battery according to claim 1, The protective tape further includes a porous layer containing an inorganic material and disposed on the substrate.

5. The nonaqueous electrolyte secondary battery according to claim 1, The negative electrode active material layer contains a Si-based active material as a negative electrode active material.

6. The nonaqueous electrolyte secondary battery according to claim 1, The protective tape further includes an adhesive layer provided on at least one surface of the substrate.

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