Nonaqueous electrolyte secondary battery and method for manufacturing same

Abstract

In a nonaqueous electrolyte secondary battery 100 according to the present disclosure, a first electrode includes a first current collector, a first active material layer supported by the first current collector, and an exposed part 30 where the first active material layer is not provided such that the surface of the first current collector is exposed. The exposed part 30 is in contact with only one end selected from both ends of the first electrode in the width direction. The first active material layer includes a first portion 25a aligned with the exposed part in the longitudinal direction of the first electrode, and a second portion 25b adjacent to the exposed part and the first portion 25a in the width direction of the first electrode. The mass per unit area of the first portion 25a is smaller than the mass per unit area of the second portion 25b, and the first portion 25a includes a fibrous carbon material as a conductive material.

Description

Non-aqueous electrolyte secondary battery and method for manufacturing the same

[0001] This disclosure relates to a non-aqueous electrolyte secondary battery and a method for manufacturing the same.

[0002] Batteries such as cylindrical and prismatic batteries are equipped with wound electrode groups. Leads (tabs) are attached to the electrode groups for extracting power from them and for supplying power to them. The leads are welded to the exposed parts of the current collector. The exposed parts are the areas where the active material layer is not provided.

[0003] Patent Document 1 discloses a positive electrode current collector having an exposed portion where a positive electrode active material layer is not provided. In Patent Document 1, the exposed portion extends from one end to the other in the width direction of the positive electrode current collector.

[0004] Patent Document 2 discloses a positive electrode lead connected to an exposed portion of a positive electrode substrate (positive electrode current collector). In the width direction of the positive electrode substrate, the exposed portion is in contact with only one end.

[0005] International Publication No. 2020 / 085048, Japanese Patent Publication No. 2023-150023

[0006] Although the structure described in Patent Document 2 is advantageous in terms of battery capacity, the thickness of the active material layer may be excessive in some areas.

[0007] This disclosure provides a technique for avoiding partial excess thickness of the active material layer when the exposed portion for attaching the lead to the current collector is in contact with only one end of the current collector in the width direction.

[0008] This disclosure relates to a non-aqueous electrolyte secondary battery comprising: a strip-shaped first electrode; a strip-shaped second electrode; a separator disposed between the first electrode and the second electrode; and a non-aqueous electrolyte, wherein the first electrode and the second electrode are wound around the separator; the first electrode includes a first current collector; a first active material layer supported by the first current collector; and an exposed portion where the first active material layer is not provided so as to expose the surface of the first current collector; the exposed portion is in contact with only one end selected from both ends in the width direction of the first electrode; the first active material layer includes a first portion aligned with the exposed portion in the longitudinal direction of the first electrode; and a second portion adjacent to the exposed portion and the first portion in the width direction of the first electrode; the mass per unit area of ​​the first portion is less than the mass per unit area of ​​the second portion; and the first portion includes a fibrous carbon material as a conductive material.

[0009] According to the technology of this disclosure, it is possible to avoid the thickness of the active material layer being partially excessive.

[0010] Figure 1 is a cross-sectional view of a non-aqueous electrolyte secondary battery according to one embodiment of the present disclosure. Figure 2A is an unfolded plan view of the positive electrode of the non-aqueous electrolyte secondary battery shown in Figure 1. Figure 2B is a cross-sectional view of the positive electrode along the line IIB-IIB. Figure 2C is a cross-sectional view of the positive electrode along the line IIC-IIC. Figure 3 is a diagram showing a method for manufacturing the positive electrode. Figure 4 is a diagram showing the problems of the prior art.

[0011] (Knowledge forming the basis of this disclosure) Exposed areas where the active material layer is not provided can be formed by intermittently applying electrode slurry to the current collector. Specifically, the electrode slurry is continuously applied to the parts where exposed areas are not required, while it is intermittently applied to the parts where exposed areas are required. Since the width of the parts where exposed areas are required is limited, strong pressure is applied to the electrode slurry when applying it to the current collector with a coater. In particular, when forming exposed areas and resuming the application of the electrode slurry, the electrode slurry is discharged from the coater towards the current collector with strong pressure. At this time, an excessive amount of electrode slurry may be applied to the current collector. When an excessive amount of electrode slurry is applied to the current collector, raised areas are formed in the coating film near the exposed areas. These raised areas remain even after the coating film is dried and rolled. As a result, raised areas containing an excessive amount of active material are locally formed in the active material layer.

[0012] Based on these findings, the inventors have completed the non-aqueous electrolyte secondary battery of this disclosure. The object of this disclosure is to provide a technique for avoiding partial excess thickness of the active material layer.

[0013] The embodiments of this disclosure will be described below with reference to the drawings. This disclosure is not limited to the embodiments described below.

[0014] (Embodiment) Figure 1 is a cross-sectional view of a non-aqueous electrolyte secondary battery according to one embodiment of the present disclosure. The non-aqueous electrolyte secondary battery 100 comprises a container 1 and an electrode group 4. The electrode group 4 has a wound structure. The electrode group 4 is housed in the container 1. The electrode group 4 has a positive electrode 5, a negative electrode 6, and a pair of separators 7. Each of the positive electrode 5 and the negative electrode 6 has a strip shape and is wound around the separator 7. The electrode group 4 is impregnated with a non-aqueous electrolyte. The opening of the container 1 is sealed with a sealing plate 2. The positive electrode 5 has a positive electrode current collector 15 and a positive electrode active material layer 25. The positive electrode active material layer 25 is supported by the positive electrode current collector 15. One end of a 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 surface of the sealing plate 2. An insulating packing 3 is arranged around the sealing plate 2. The negative electrode 6 has a negative electrode current collector 16 and a negative electrode active material layer 26. The negative electrode active material layer 26 is supported by the negative electrode current collector 16. 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 arranged on the upper and lower surfaces of the electrode group 4, respectively.

[0015] In this embodiment, the container 1 has negative polarity and the sealing plate 2 has positive polarity. However, the container 1 may have positive polarity and the sealing plate 2 may have negative polarity.

[0016] As the positive electrode current collector 15, a sheet or film made of a metallic material such as aluminum, aluminum alloy, stainless steel, titanium, or titanium alloy may be used. The sheet or film may be porous or non-porous. As the sheet or film, metal foil or metal mesh may be used. A carbon material may be coated on the surface of the positive electrode current collector 15 as a conductive auxiliary material.

[0017] The positive electrode active material layer 25 contains a positive electrode active material. The positive electrode active material may be a material that has the ability to intercept and release lithium ions. As the positive electrode active material, lithium-containing transition metal oxides, lithium-containing transition metal phosphates, transition metal fluorides, polyanionic materials, fluorinated polyanionic materials, transition metal sulfides, transition metal oxysulfides, transition metal oxynitrides, etc., can be used. In particular, when lithium-containing transition metal oxides or lithium-containing transition metal phosphates are used as the positive electrode active material, the manufacturing cost of the battery can be reduced and the average discharge voltage can be increased. Examples of lithium-containing transition metal oxides include lithium cobalt oxide, lithium nickel cobalt aluminum oxide, lithium nickel cobalt manganese oxide, and lithium nickel manganese oxide. Examples of lithium-containing transition metal phosphates include lithium iron phosphate, lithium vanadium phosphate, lithium cobalt phosphate, and lithium nickel phosphate. One or more combinations of these positive electrode active materials can be used.

[0018] The positive electrode active material layer 25 may contain other materials such as conductive materials and binders.

[0019] Conductive materials are used to reduce the resistance of the positive electrode 5. Examples of conductive materials include carbon materials and conductive polymer compounds. Examples of carbon materials include carbon black, graphite, fibrous carbon materials, graphene, fullerene, and graphite oxide. Examples of carbon black include acetylene black. Examples of fibrous carbon materials include carbon nanotubes and carbon nanofibers. Examples of conductive polymer compounds include polyaniline, polypyrrole, and polythiophene. One or more combinations of these conductive materials can be used.

[0020] A binder is used to improve the bonding properties of the materials constituting the positive electrode 5. Examples of binders include polymer materials such as polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene copolymer, polytetrafluoroethylene, carboxymethylcellulose, polyacrylic acid, styrene-butadiene copolymer rubber, polypropylene, polyethylene, and polyimide. One or more combinations of these binders may be used.

[0021] As the negative electrode current collector 16, a sheet or film made of a metallic material such as stainless steel, nickel, nickel alloy, copper, or copper alloy may be used. The sheet or film may be porous or non-porous. As the sheet or film, metal foil or metal mesh may be used. A carbon material may be coated on the surface of the negative electrode current collector 16 as a conductive auxiliary material.

[0022] The negative electrode active material layer 26 contains a negative electrode active material. The negative electrode active material may be a material having the ability to intercept and release lithium ions. The negative electrode active material includes, for example, at least one selected from the group consisting of carbon materials and materials capable of forming alloys with lithium. Examples of carbon materials include graphite. Examples of materials capable of forming alloys with lithium include silicon, silicon-containing oxides, tin, zinc alloys, bismuth, and germanium. One or more combinations of these negative electrode active materials may be used.

[0023] The negative electrode active material layer 26 may contain other materials such as conductive materials and binders. Materials that can be used in the positive electrode active material layer 25 can also be used in the negative electrode active material layer 26 as conductive materials and binders.

[0024] The electrolyte is a non-aqueous electrolyte impregnated into the positive electrode 5, the negative electrode 6, and the separator 7. The electrolyte may also 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.

[0025] The electrolyte contains a non-aqueous solvent and a lithium salt.

[0026] Examples of non-aqueous solvents include cyclic carbonate esters, linear carbonate esters, cyclic ethers, linear ethers, nitriles, and amides. One of these solvents may be used, or two or more may be used in combination.

[0027] Examples of lithium salts include lithium hexafluoride phosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bisperfluoroethylsulfonylimide (LiN(SO2C2F5)2), LiAsF6, LiCF3SO3, and lithium difluoro(oxalato)borate. One or more combinations of these lithium salts can be used.

[0028] The separator 7 is lithium ion conductive. The material of the separator 7 is not particularly limited as long as the passage of lithium ions is permitted. The material of the separator 7 may be at least one selected from the group consisting of gel electrolytes, ion exchange resin membranes, semipermeable membranes, and porous membranes. If the separator 7 is made of these materials, the safety of the non-aqueous electrolyte secondary battery 100 can be sufficiently ensured. Examples of gel electrolytes include gel electrolytes containing fluororesins such as PVDF. Examples of ion exchange resin membranes include cation exchange membranes and anion exchange membranes. Examples of porous membranes include porous membranes made of polyolefin resin and porous membranes containing glass paper obtained by weaving glass fibers into a nonwoven fabric.

[0029] Container 1 is, for example, a metal container such as aluminum or stainless steel. Container 1 may have a cylindrical shape or a rectangular tube shape.

[0030] The electrode group 4 may be wound in a cylindrical shape or in an elliptical shape.

[0031] Figure 2A is an unfolded plan view of the positive electrode 5 of the non-aqueous electrolyte secondary battery 100 shown in Figure 1. Figure 2B is a cross-sectional view of the positive electrode 5 along the line IIB-IIB. Figure 2C is a cross-sectional view of the positive electrode 5 along the line IIC-IIC. The positive electrode 5 includes an exposed portion 30 where the positive electrode active material layer 25 is not provided. The exposed portion 30 is the portion where the surface of the positive electrode current collector 15 is exposed. The exposed portion 30 is in contact with only one end 5p selected from both ends in the width direction WD of the positive electrode 5. The exposed portion 30 does not penetrate in the width direction WD. With this structure, the volume of the positive electrode active material layer 25 can be increased, thereby increasing the capacity of the non-aqueous electrolyte secondary battery 100.

[0032] The positive electrode active material layer 25 includes a first portion 25a and a second portion 25b. The first portion 25a is the portion of the positive electrode 5 that aligns with the exposed portion 30 in the longitudinal direction LD. The second portion 25b is the portion of the positive electrode 5 that is adjacent to the exposed portion 30 and the first portion 25a in the width direction WD. The first portion 25a and the second portion 25b are each strip-shaped portions that extend in the longitudinal direction LD of the positive electrode 5. In this embodiment, the mass per unit area of ​​the first portion 25a (unit: g / cm²) 2 ) is smaller than the mass per unit area of ​​the second part 25b. Furthermore, the first part 25a contains a fibrous carbon material as a conductive material.

[0033] According to the configuration of this embodiment, it is possible to avoid the thickness of the first portion 25a of the positive electrode active material layer 25 becoming partially excessive near the exposed portion 30. Furthermore, by using a fibrous carbon material as the conductive material, the increase in resistance of the first portion 25a can also be suppressed. The reasons for this will be explained in detail below.

[0034] Figure 3 shows a method for manufacturing the positive electrode 5. The positive electrode 5 is obtained by applying a positive electrode mixture (positive electrode slurry) to a positive electrode current collector 15 to form a coating film, and then drying and rolling the coating film. In actual manufacturing, the positive electrode mixture is applied to a metal foil (conductive substrate), which is the material for the positive electrode current collector 15, to form a coating film. By drying and rolling the coating film, a connected body 50 of multiple positive electrodes 5 is formed. Then, at a cutting position D set in the width direction WD, the connected body 50 is cut along the longitudinal direction LD. This yields multiple positive electrodes 5. According to the example in Figure 3, four sets of strip-shaped positive electrodes 5 are obtained.

[0035] The process of applying a positive electrode mixture to a metal foil to form a coated film is carried out using a coater such as a die coater or a reverse coater. The coater is equipped with multiple discharge sections that can individually control the discharge of the positive electrode mixture. In Figure 3, portion α of the metal foil corresponds to the first portion 25a of the positive electrode active material layer 25, and portion β corresponds to the second portion 25b of the positive electrode active material layer 25. The first positive electrode mixture is intermittently applied to portion α. ​​That is, at the timing when the exposed portion 30 should be formed, the coater controls the stopping and restarting of the discharge of the first positive electrode mixture. The second positive electrode mixture is continuously applied to portion β.

[0036] In conventional methods, a positive electrode mixture of the same composition is applied to both the α and β portions with the same thickness. Since the width of the α portion, which requires exposure, is limited, strong pressure is applied to the positive electrode mixture when it is applied to the metal foil with a coater. In particular, when an exposure is formed and the application of the positive electrode mixture is resumed, the positive electrode mixture is discharged from the coater towards the metal foil with strong pressure. At this time, an excessive amount of positive electrode mixture may be applied to the metal foil. When an excessive amount of positive electrode mixture is applied to the metal foil, a raised portion 25t is formed in the coating film near the exposed portion 30a, as shown in Figure 4. The faster the metal foil is transported, the more difficult it is to control the discharge pressure, making it easier for the raised portion 25t to form. The raised portion 25t remains even after the coating film is dried and rolled. As a result, a raised portion containing an excessive amount of positive electrode active material is locally formed in the positive electrode active material layer. A raised portion containing an excessive amount of positive electrode active material can disrupt the capacitance balance between the positive and negative electrodes.

[0037] At first glance, it may seem that the raised portion 25t can be flattened by rolling. However, since there is an upper limit to the density of the positive electrode active material layer after rolling, it is difficult to completely eliminate the raised portion 25t.

[0038] In contrast, according to the present embodiment, the coating process is carried out such that the mass per unit area of the first portion 25a (unit: g / cm 2 ) is less than the mass per unit area of the second portion 25b. Specifically, the composition of the first positive electrode mixture for forming the first portion 25a is different from the composition of the second positive electrode mixture for forming the second portion 25b. As shown in FIG. 3, the first positive electrode mixture is applied to the α portion of the metal foil, and the second positive electrode mixture is applied to the β portion of the metal foil. Then, rolling is carried out so that a predetermined pressure is applied to the entire coating film. According to such a configuration, even if the raised portion 25t described with reference to FIG. 4 is formed in the coating film, the raised portion 25t can be eliminated by carrying out rolling. Forming the coating film such that the mass per unit area of the first portion 25a is less than the mass per unit area of the second portion 25b means that the density of the coating film corresponding to the first portion 25a is relatively low and the density of the coating film corresponding to the second portion 25b is relatively high. In this case, even if the raised portion 25t is formed in the coating film corresponding to the first portion 25a, since there is a margin in density, it is possible to eliminate the raised portion 25t by rolling.

[0039] However, if the packing density of the first portion 25a of the positive electrode active material layer 25 is decreased, the resistance of the positive electrode 5 may increase. Therefore, in the present embodiment, a fibrous carbon material is included in the first portion 25a of the positive electrode active material layer 25 as a conductive material. The fibrous carbon material can impart high electron conductivity to the positive electrode active material layer 25 with a small amount as compared with a spherical conductive material such as carbon black. Therefore, even if the packing density of the first portion 25a is decreased, an increase in the resistance of the positive electrode active material layer 25 can be suppressed by the action of the fibrous carbon material. That is, according to the present embodiment, it is possible to avoid the thickness of the positive electrode active material layer 25 becoming partially excessive in the vicinity of the exposed portion 30 while suppressing an increase in the resistance of the positive electrode 5.

[0040] The content ratio of the carbon material (fibrous carbon material) in the first positive electrode composite material may be lower than the content ratio of the carbon material (carbon black) in the second positive electrode composite material on a mass basis.

[0041] As described in Patent Document 1, when the exposed portion extends from one end to the other end of the positive electrode current collector, it is not necessary to form the positive electrode active material layer by the method described with reference to FIG. 3. That is, it is allowed to intermittently apply the positive electrode composite material to the metal foil with a wider width. In this case, since the pressure applied to the positive electrode composite material when discharged from the coater is likely to be dispersed in the width direction of the metal foil, the raised portion 25t described with reference to FIG. 4 is difficult to be formed on the coating film. Even if the raised portion 25t is formed, the height of the raised portion 25t remains at a height that can be flattened by rolling.

[0042] In the present embodiment, the fibrous carbon material included in the first portion 25a includes, for example, carbon nanotubes. Carbon nanotubes can impart high electron conductivity to the active material layer with a small amount compared to spherical conductive materials such as carbon black. Examples of fibrous carbon materials other than carbon nanotubes include carbon nanofibers such as vapor-phase carbon fibers.

[0043] Examples of the carbon nanotubes include multi-wall carbon nanotubes (MWCNT), single-wall carbon nanotubes (SWCNT), and mixtures thereof. Those having a single-layer graphene sheet are referred to as single-wall carbon nanotubes. Those having a plurality of layers of graphene sheets are referred to as multi-wall carbon nanotubes. It is desirable that the fibrous carbon material included in the first portion 25a includes multi-wall carbon nanotubes. Multi-wall carbon nanotubes are less expensive than single-wall carbon nanotubes and are excellent in economy.

[0044] The first portion 25a may contain only the fibrous carbon material as the conductive material.

[0045] The second part 25b contains carbon black as a conductive material. Carbon black is a carbon material having a spherical shape. Fibrous carbon material can impart high electronic conductivity to the positive electrode active material layer 25 with a small amount compared to spherical carbon black, but it is expensive. By using inexpensive carbon black in the second part 25b, which does not have the problem of raised parts, the increase in cost of the non-aqueous electrolyte secondary battery 100 can be suppressed.

[0046] Examples of carbon black include acetylene black, furnace black, Ketjen black, and channel black. Part 25b may contain acetylene black as a conductive material. Acetylene black is recommended because it has a low content of metallic impurities and is inexpensive.

[0047] The second part 25b may contain only carbon black as a conductive material, or it may contain carbon black and a fibrous carbon material. If the second part 25b contains a fibrous carbon material, it is preferable that the fibrous carbon material is a single-wall carbon nanotube.

[0048] Except for the conductive material, the materials included in the first part 25a (positive electrode active material and binder) are the same as the materials included in the second part 25b.

[0049] In this embodiment, the thickness of the first portion 25a is equal to the thickness of the second portion 25b. In other words, rolling is performed so that the positive electrode active material layer 25 has a constant thickness.

[0050] The ratio of the mass per unit area of ​​the first part 25a to the mass per unit area of ​​the second part 25b is, for example, 92% to 97%. By adjusting the ratio of mass per unit area to this range, it is possible to avoid the thickness of the positive electrode active material layer 25 becoming partially excessive near the exposed portion 30. Furthermore, it is possible to avoid a significant reduction in the capacity of the positive electrode 5.

[0051] In another aspect, the packing density (unit: g / cm³) of the various materials (active material, conductive material, and binder) in the first part 25a. 3) is lower than the packing density of the various materials in the second part 25b.

[0052] The configuration described with reference to Figures 2A to 2C can be applied not only to the positive electrode 5 but also to the negative electrode 6.

[0053] The technology disclosed herein is not limited to lithium-ion batteries. In addition to lithium-ion batteries, the technology disclosed herein may be applied to non-aqueous electrolyte batteries such as sodium-ion batteries and magnesium-ion batteries.

[0054] (Other Embodiments) (Note) The above description of embodiments discloses the following technologies.

[0055] (Technical 1) A non-aqueous electrolyte secondary battery comprising: a strip-shaped first electrode; a strip-shaped second electrode; a separator disposed between the first electrode and the second electrode; and a non-aqueous electrolyte, wherein the first electrode and the second electrode are wound around the separator; the first electrode includes a first current collector; a first active material layer supported by the first current collector; and an exposed portion where the first active material layer is not provided so as to expose the surface of the first current collector; the exposed portion is in contact with only one end selected from both ends in the width direction of the first electrode; the first active material layer includes a first portion aligned with the exposed portion in the longitudinal direction of the first electrode; and a second portion adjacent to the exposed portion and the first portion in the width direction of the first electrode; the mass per unit area of ​​the first portion is smaller than the mass per unit area of ​​the second portion; and the first portion includes a fibrous carbon material as a conductive material.

[0056] According to the technology of this disclosure, it is possible to avoid the thickness of the active material layer being partially excessive.

[0057] (Technology 2) The non-aqueous electrolyte secondary battery according to Technology 1, wherein the fibrous carbon material contains carbon nanotubes. Compared to spherical conductive materials such as carbon black, carbon nanotubes can impart high electronic conductivity to the active material layer in small amounts.

[0058] (Technology 3) The non-aqueous electrolyte secondary battery according to Technology 2, wherein the carbon nanotubes include multi-walled carbon nanotubes. Multi-walled carbon nanotubes are less expensive than single-walled carbon nanotubes and offer superior economic advantages.

[0059] (Technology 4) The second part is a non-aqueous electrolyte secondary battery according to any one of the technologies 1 to 3, wherein the second part contains carbon black as a conductive material. By using inexpensive carbon black in the second part, which does not have the problem of raised parts, the cost increase of the non-aqueous electrolyte secondary battery can be suppressed.

[0060] (Technical 5) The non-aqueous electrolyte secondary battery according to Technical 4, wherein the carbon black contains acetylene black.

[0061] (Technical 6) A non-aqueous electrolyte secondary battery according to any one of Technical 1 to 5, wherein the ratio of the mass per unit area of ​​the first part to the mass per unit area of ​​the second part is 92% or more and 97% or less. By adjusting the ratio of the mass per unit area to such a range, it is possible to avoid the thickness of the positive electrode active material layer becoming partially excessive near the exposed part.

[0062] (Technical 7) A non-aqueous electrolyte secondary battery according to any one of Technical 1 to 6, wherein the first electrode is the positive electrode.

[0063] (Technical 8) A method for manufacturing a non-aqueous electrolyte secondary battery according to any one of Technical 1 to 7, comprising: intermittently applying a first electrode mixture containing a fibrous carbon material to a current collector to form a first coating film; continuously applying a second electrode mixture having a different composition from that of the first electrode mixture to the current collector so as to form a second coating film adjacent to the first coating film; and drying and rolling the first coating film and the second coating film to form a first portion and a second portion of the first active material layer.

[0064] (Preparation of the first cathode composite material) LiNi 0.8 Co 0.1 Mn 0.1The positive electrode active material particles having a composition of O2(NCM), multi-walled carbon nanotubes (MWCNT, manufactured by Cnano), polyvinylidene fluoride (PVDF), and N-methyl-pyrrolidone (NMP) were mixed and stirred to prepare a first positive electrode composite material. The mass ratio of the positive electrode active material particles, MWCNT, and PVDF was positive electrode active material particles:MWCNT:PVDF = 100:0.4:0.4. The ratio of the mass of NMP to the mass of the first positive electrode composite material was 22%.

[0065] (Preparation of the second positive electrode composite material) LiNi 0.8 Co 0.1 Mn 0.1 The positive electrode active material particles having a composition of O2(NCM), acetylene black (AB, manufactured by Denka), PVDF, and NMP were mixed and stirred to prepare a second positive electrode composite material. The mass ratio of the positive electrode active material particles, AB, and PVDF was positive electrode active material particles:AB:PVDF = 100:0.8:0.8. The ratio of the mass of NMP to the mass of the second positive electrode composite material was 22%.

[0066] (Example 1) According to the method described with reference to FIG. 3, using a die coater (manufactured by Technosmart), the first positive electrode composite material and the second positive electrode composite material were applied to the surface of an aluminum foil to form a coating film. Specifically, the first positive electrode composite material was intermittently applied so that an exposed portion was formed, and the second positive electrode composite material was continuously applied. The coating film was dried and rolled. The rolling was carried out at a pressure of 30,000 N / cm to 40,000 N / cm of the line pressure. By cutting the aluminum foil at the position of a predetermined cutting position D (see FIG. 3), the positive electrode of Example 1 having the structure described with reference to FIGS. 2A to 2C was obtained.

[0067] (Comparative Example 1) The positive electrode of Comparative Example 1 was produced by the same method as in Example 1, except that only the second positive electrode composite material was used.

[0068] (Comparative Example 2) Only the second positive electrode composite material was used to produce the positive electrode of Comparative Example 2. When producing the positive electrode of Comparative Example 2, the thickness of the coating film was adjusted so that the mass per unit area and the packing density of the first portion of the positive electrode active material layer were 95% of those values of Comparative Example 1. For the second portion of the positive electrode active material layer, it was formed under the same conditions as in Comparative Example 1.

[0069] (Comparative Example 3) The positive electrode of Comparative Example 3 was prepared using only the second positive electrode composite material. When preparing the positive electrode of Comparative Example 3, the linear pressure during rolling was adjusted so that the packing density of the first and second portions of the positive electrode active material layer was 95% of the value of Comparative Example 1.

[0070] (Comparative Example 4) The positive electrode of Comparative Example 4 was prepared using only the second positive electrode composite material. When preparing the positive electrode of Comparative Example 4, the thickness of the coating film was adjusted so that the mass per unit area of ​​the first portion of the positive electrode active material layer was 95% of the value of Comparative Example 1.

[0071] [Mass per unit area] For the positive electrodes of the examples and comparative examples, the mass per unit area of ​​the first portion of the positive electrode active material layer and the mass per unit area of ​​the second portion of the positive electrode active material layer were calculated. First, the positive electrode was cut into a portion containing the first portion and a portion containing the second portion. The mass of the first portion of the positive electrode active material layer was calculated by subtracting the mass of the current collector from the mass of the portion containing the first portion. The mass per unit area (g / cm²) of the first portion of the positive electrode active material layer was calculated by dividing the mass of the first portion by the area of ​​the first portion. 2 The mass per unit area of ​​the second portion of the positive electrode active material layer was calculated using the same method. The results are shown in Table 1. In Table 1, the value of "mass per unit area" is a relative value when the value of Comparative Example 1 is considered to be 100.

[0072] [Measurement of Packing Density] For the positive electrodes of the examples and comparative examples, the packing density of the first portion of the positive electrode active material layer and the packing density of the second portion of the positive electrode active material layer were calculated. First, the positive electrode was cut into a portion containing the first portion and a portion containing the second portion. The mass of the first portion of the positive electrode active material layer was calculated by subtracting the mass of the current collector from the mass of the portion containing the first portion. The volume of the first portion was calculated from the area and thickness of the first portion. The packing density of the first portion of the positive electrode active material layer (g / cm³) was calculated by dividing the mass of the first portion by the volume of the first portion. 3 The following was calculated: The packing density of the second portion of the positive electrode active material layer was calculated using the same method. The results are shown in Table 1. In Table 1, the value of "packing density" is a relative value when the value of Comparative Example 1 is considered to be 100.

[0073] [Positive Electrode Capacity] The "Positive Electrode Capacity" values ​​in Table 2 are relative values ​​when the positive electrode capacity of Example 1 is considered to be 100. The positive electrode capacity is proportional to the mass of the positive electrode active material contained in the positive electrode active material layer.

[0074] [Resistance of the First and Second Parts] For the positive electrodes of the Examples and Comparative Examples, the resistance (volume resistivity) of the first part and the resistance of the second part of the positive electrode active material layer were measured using the method described below. The positive electrode was cut into parts including the first part and parts including the second part to obtain samples for resistance measurement. An electrode resistance meter (HIOKI RM2610) was used to measure the resistance (volume resistivity) of the positive electrode active material layer of each sample. The measurement current was set to 100 μA and the voltage range to 0.5 V. The results are shown in Table 2. In Table 2, the values ​​for "Resistance of the First Part" and "Resistance of the Second Part" are relative values ​​when the value of Example 1 is considered to be 100.

[0075] [Height of raised areas near the exposed portion] The positive electrodes of the examples and comparative examples were cut along the IIC-IIC line shown in Figure 2A. The presence and height of raised areas near the exposed portion were measured by observing the cross-section with an optical microscope. The results are shown in Table 2. In Table 2, a raised area height of zero means that there were no raised areas near the exposed portion and that the positive electrode active material layer had a uniform thickness.

[0076]

[0077]

[0078] As shown in Table 2, the positive electrode of Example 1 did not have any raised portions near the exposed portion. In the positive electrode of Example 1, the resistance of the first portion and the resistance of the second portion were approximately the same as those of Comparative Example 1. The capacitance of the positive electrode of Example 1 was slightly lower than that of the positive electrode of Comparative Example 1, but higher than that of the positive electrodes of Comparative Examples 3 and 4.

[0079] The positive electrode of Comparative Example 1 had a high capacitance. In the positive electrode of Comparative Example 1, the resistance of the first portion and the resistance of the second portion were approximately the same as those of Example 1. However, as explained with reference to Figure 4, a raised portion with a height of 10 μm was formed near the exposed portion.

[0080] The positive electrode of Comparative Example 2 had a high capacitance. The positive electrode of Comparative Example 2 did not have any raised areas near the exposed portion. However, the positive electrode of Comparative Example 2 had a high resistance in the first portion.

[0081] The capacitance of the positive electrodes in Comparative Examples 3 and 4 was low. In the positive electrode of Comparative Example 3, the resistance of the first and second portions was high. In both the positive electrodes of Comparative Example 3 and Comparative Example 4, a raised portion with a height of 10 μm was formed near the exposed portion.

[0082] The technology of this disclosure is useful for non-aqueous electrolyte secondary batteries such as lithium-ion secondary batteries. In particular, this disclosure is suitable for batteries in which it is required to form an active material layer by a wet process that includes a step of drying and rolling a coating film of a fluid composite material.

Claims

1. A non-aqueous electrolyte secondary battery comprising: a strip-shaped first electrode; a strip-shaped second electrode; a separator disposed between the first electrode and the second electrode; and a non-aqueous electrolyte, wherein the first electrode and the second electrode are wound around the separator; the first electrode includes a first current collector; a first active material layer supported by the first current collector; and an exposed portion where the first active material layer is not provided so as to expose the surface of the first current collector; the exposed portion is in contact with only one end selected from both ends in the width direction of the first electrode; the first active material layer includes a first portion aligned with the exposed portion in the longitudinal direction of the first electrode; and a second portion adjacent to the exposed portion and the first portion in the width direction of the first electrode; the mass per unit area of ​​the first portion is smaller than the mass per unit area of ​​the second portion; and the first portion includes a fibrous carbon material as a conductive material.

2. The non-aqueous electrolyte secondary battery according to claim 1, wherein the fibrous carbon material includes carbon nanotubes.

3. The non-aqueous electrolyte secondary battery according to claim 2, wherein the carbon nanotube includes a multi-walled carbon nanotube.

4. The second part comprises carbon black as a conductive material, as described in claim 1, for the non-aqueous electrolyte secondary battery.

5. The non-aqueous electrolyte secondary battery according to claim 4, wherein the carbon black comprises acetylene black.

6. The non-aqueous electrolyte secondary battery according to claim 1, wherein the ratio of the mass per unit area of ​​the first part to the mass per unit area of ​​the second part is 92% or more and 97% or less.

7. The non-aqueous electrolyte secondary battery according to claim 1, wherein the first electrode is the positive electrode.

8. A method for manufacturing a non-aqueous electrolyte secondary battery according to claim 1, comprising: intermittently applying a first electrode mixture containing a fibrous carbon material to a current collector to form a first coating film; continuously applying a second electrode mixture having a different composition from that of the first electrode mixture to the current collector so as to form a second coating film adjacent to the first coating film; and drying and rolling the first coating film and the second coating film to form a first portion and a second portion of the first active material layer.

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