secondary battery with non-aqueous electrolyte

Abstract

Secondary battery (100) with non-aqueous electrolyte, with: a positive electrode (20); a negative electrode (30) opposite the positive electrode (20); and a non-aqueous electrolyte, where the positive electrode (20) comprises a positive electrode current collector (22), a positive electrode active material layer (24) comprising a positive electrode active material and formed on the positive electrode current collector (22) except for a part where the positive electrode current collector (22) is exposed, and an insulating layer (26) comprising an inorganic filler and formed at a boundary part between the part where the positive electrode current collector (22) is exposed and the positive electrode active material layer (24), wherein the positive electrode active material layer (24) comprises a main body part (A1) and an end part (A2) which is provided closer to the part where the positive electrode current collector (22) is exposed than the main body part (A1) and has a smaller thickness than a thickness of the main body part (A1), the insulating layer (26) is inserted between the positive electrode current collector (22) and the end part (A2) in a thickness direction and is shaped to cover the end part (A2), and when a width of the positive electrode active material layer (24) is set as La and a width of a part of the insulating layer (26) inserted between the positive electrode current collector (22) and the end part (A2) in a direction from the positive electrode active material layer (24) to the insulating layer (26) is set as Lb, the width La and the width Lb satisfy the following formula (1): 0.02 × 10 − 2 ≤ (Lb / La) ≤ 2.1 × 10 − 2.

Description

BACKGROUND OF REVELATION1. Area

[0001] The present invention relates to a non-aqueous electrolyte secondary battery. 2. Background

[0002] Generally, a non-aqueous electrolyte secondary battery includes a positive electrode having a positive electrode active material layer, a negative electrode opposite the positive electrode having a negative electrode active material layer that is wider than the positive electrode active material layer, and a non-aqueous electrolyte containing charge carriers. The positive electrode of the non-aqueous electrolyte secondary battery includes a positive electrode current collector and the positive electrode active material layer provided on the positive electrode current collector. For example, the positive electrode current collector for collecting electricity may have a portion where no positive electrode active material layer is present and is exposed at at least one end (a positive electrode current collector exposed portion).In this context, Japanese Patent Application Laid-Open No. 2017-157471 discloses a positive electrode including a positive electrode current collector, a positive electrode active material layer provided on the positive electrode current collector except for an exposed portion thereof, and an insulating layer provided at a boundary portion between the exposed portion of the positive electrode current collector and the positive electrode active material layer. SHORT EXPLANATION

[0003] However, according to the inventors' studies, this configuration results in metal deposition at a negative electrode and, in some cases, deterioration of cycle characteristics. That is, in Japanese Patent Application Laid-Open No. 2017-157471, a negative electrode active material layer is wider than a positive electrode active material layer, and an end surface of a positive electrode active material layer is exposed without being covered with an insulating layer. Therefore, current and charge carriers are likely to concentrate at one end of a positive electrode active material layer. However, in general, the battery voltage during charging and discharging is controlled by a difference between a potential of the entire positive electrode and a potential of the entire negative electrode, that is, an average value.Therefore, the end of the positive electrode active material layer is more likely to be exposed to a higher potential than a part of the main body of the positive electrode active material layer. Therefore, when charging and discharging operations are repeated, metallic elements (e.g., charge carriers and transition metal elements constituting a positive electrode active material) are easily eluted from the end of the positive electrode. As a result, metal deposition occurs at a part opposite the end of the negative electrode, and the battery capacity is reduced after cyclic operation.

[0004] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a non-aqueous electrolyte secondary battery in which metal deposition at a negative electrode is minimized and cycle characteristics are improved.

[0005] According to the present invention, a nonaqueous electrolyte secondary battery is provided, comprising a positive electrode, a negative electrode opposite the positive electrode, and a nonaqueous electrolyte. The positive electrode includes a positive electrode current collector, a positive electrode active material layer comprising a positive electrode active material and formed on the positive electrode current collector except at a portion thereof where the positive electrode current collector is exposed, and an insulating layer comprising an inorganic filler and formed at a boundary portion between the portion where the positive electrode current collector is exposed and the positive electrode active material layer. The positive electrode active material layer includes a main body portion and an end portion provided closer to the portion where the positive electrode current collector is exposed than the main body portion and having a smaller thickness than the main body portion.The insulating layer is interposed between the positive electrode current collector and the end portion in the thickness direction and shaped to cover the end portion. When a width of the positive electrode active material layer is set as La and a width of a portion of the insulating layer interposed between the positive electrode current collector and the end portion is set as Lb in a direction from the positive electrode active material layer to the insulating layer, the widths La and Lb satisfy the following formula (1): 0.02 × 10. -2 ≤ (Lb / La) ≤ 2.1 × 10 -2 .

[0006] In this configuration, the insulating layer is interposed between the positive electrode current collector and the end portion of the positive electrode active material layer, and also covers the end portion of the positive electrode active material layer. This minimizes the supply of electrons from the positive electrode current collector to the end portion of the positive electrode active material layer, and it is unlikely that a charge and discharge reaction will occur at the end portion of the positive electrode active material layer. Therefore, the movement of charge carriers from the end portion is restricted. As a result, the end portion of the positive electrode active material layer is less likely to be exposed to a high potential, and it is possible to minimize the leaching of metallic elements from the positive electrode active material at the end portion. Thus, it is possible to prevent metal deposition (e.g.,Li deposition) at the negative electrode and realize a battery with excellent cycle life.

[0007] In a preferred aspect of the non-aqueous electrolyte secondary battery disclosed herein, the widths La and Lb satisfy the following formula (2): 0.02 × 10 -2 ≤ (Lb / La) ≤ 1.0 × 10 -2 . According to such a configuration, it is possible to effectively minimize the dissolution of metallic elements from the end part of the positive electrode active material layer and also to minimize the increase in resistance caused by the formation of the insulating layer.

[0008] In a preferred aspect of the nonaqueous electrolyte secondary battery disclosed herein, the width Lb is 20 µm or more and 2000 µm or less. With such a configuration, it is possible to effectively minimize leaching of metallic elements from the end portion of the positive electrode active material layer and also appropriately realize a large battery capacity.

[0009] The above-explained and other elements, features, steps, characteristics and advantages of the present invention will become more apparent from the following detailed explanation of the preferred embodiments with reference to the accompanying drawings. BRIEF EXPLANATION OF THE DRAWINGS Fig. 1 is a perspective view showing a lithium-ion secondary battery according to an embodiment of the present invention; Fig.2 is a schematic view showing a configuration of a wound electrode body according to an embodiment of the present invention. Fig. Figure 3 is a schematic section showing a configuration of a positive electrode. Fig. Figure 4 is an example diagram to illustrate electron and Li movements. Fig. Figure 5 is a graph showing the relationship between a viscosity ratio of mass and Lb / La. Fig. Figure 6 is a graph showing the relationship between Lb / La and the amount of Mn in a negative electrode after cycling. Fig. Figure 7 is a graph showing the relationship between Lb / La and durability after high-rate cycling. DETAILED EXPLANATION OF THE PREFERRED EMBODIMENTS

[0010] Some embodiments of the technology disclosed herein are described below. It should be understood that the embodiments described herein are not intended to limit the technology disclosed herein. Components necessary for implementing the technology disclosed herein (e.g., a general configuration and manufacturing method of a non-aqueous electrolyte secondary battery, which do not characterize the technology disclosed herein) other than those specifically mentioned in this description may be recognized by those skilled in the art as design features based on the prior art. The technology disclosed herein can be implemented based on the content disclosed in this description and general technical knowledge in the field.

[0011] In this specification, the term "secondary battery" generally refers to an energy storage device or accumulator that can be repeatedly charged and discharged. For example, a lithium-ion secondary battery, a nickel-metal hydride battery, a lithium-ion capacitor, an electric double-layer capacitor, and the like are typical examples of a secondary battery. Furthermore, "lithium-ion secondary battery" in this specification refers to a secondary battery in which lithium ions are used as charge carriers and charging and discharging are realized when lithium ions move between the positive electrode and the negative electrode. In this specification, the notation "A to B" (A and B are arbitrary numerical values) indicates a range from "A or more to B or less," and also from "preferably greater than A" to "preferably less than B."

[0012] Although not intended to be specifically limiting, a lithium-ion secondary battery is illustrated in detail below. In the following drawings, elements and portions having the same functions are designated by the same reference numerals, and redundant descriptions thereof are omitted or simplified. Further, in the drawings, symbols X and Y represent a thickness direction and a width direction of an electrode body. The symbols X and Y overlap (here, orthogonally) in a plan view. The width direction Y is an example of a direction from a positive electrode active material layer 24 to an insulating layer. Furthermore, along the width direction Y, one direction may be referred to as the Y1 direction and the opposite direction as the Y2 direction. However, these directions are defined only for convenience of understanding and do not limit installation forms of a lithium-ion secondary battery in any way.

[0013] Fig. 1 is a perspective view schematically showing a lithium-ion secondary battery 100. The lithium-ion secondary battery 100 includes a flat wound electrode body 10 (see Fig. 2), a non-aqueous electrolyte (not shown), and a flat, rectangular battery case 50. The battery case 50 is a container in which the wound electrode body 10 and the non-aqueous electrolyte are accommodated. A light metal material with favorable thermal conductivity, such as aluminum, is suitable as a material for the battery case 50. The battery case 50 comprises a case main body 52, which has a cuboid shape with an opening and a cover 54 closing the opening. The cover 54 is a rectangular sheet or plate body. A positive electrode terminal 22c and a negative electrode terminal 32c protrude upward from the cover 54 for external connection.

[0014] Fig. 2 is a schematic view of the wound electrode body 10. As in Fig. As shown in Figure 2, the wound electrode body 10 has a configuration in which a sheet-shaped positive electrode 20 and a sheet-shaped negative electrode 30 are stacked with a sheet-shaped separator 40 therebetween and wound longitudinally around a winding axis WL. The wound electrode body 10 is flat and has an elliptical shape in the cross-section in the width direction Y.

[0015] Fig. 3 is a schematic section showing a configuration of the positive electrode 20. Fig. 3 shows a state in which the width direction Y is opposite to that of Fig. 1 and Fig.2 is inverted. The positive electrode 20 includes a positive electrode current collector 22, a positive electrode active material layer 24 formed on the positive electrode current collector 22, and an insulating layer 26 formed on the positive electrode current collector 22. The positive electrode active material layer 24 and the insulating layer 26 may be provided on only one surface or on both surfaces of the positive electrode current collector 22. The positive electrode current collector 22 is a conductive member. A metal foil made of aluminum, nickel, or the like is suitable for the positive electrode current collector 22. The positive electrode current collector 22 may be subjected to a well-known surface treatment such as etching treatment, hydrophilic treatment, or various types of coating.

[0016] The positive electrode current collector 22 has a portion 22a where the insulating layer 26 and the positive electrode active material layer 24 are not formed and the positive electrode current collector 22 is exposed (hereinafter referred to as "positive electrode current collector exposed portion"). Here, the positive electrode current collector exposed portion 22a is provided in a track-like manner in the Y2 direction at one end portion of the positive electrode current collector 22. However, the positive electrode current collector exposed portion 22a may be provided at one end portion in the Y1 direction or at both end portions in the width direction Y. As shown in Fig. 2, the exposed portion 22a of the positive electrode current collector protrudes in the Y2 direction in plan view beyond the Y2-direction end portion of the negative electrode 30 (e.g., a negative electrode active material layer 34). As shown in Fig.As shown in Figure 1, a positive electrode current collector plate 22b is connected to the exposed portion 22a of the positive electrode current collector. The positive electrode current collector plate 22b is electrically connected to the positive electrode terminal 22c.

[0017] As in Fig.As shown in Figure 3, the positive electrode active material layer 24 is attached to the surface of the positive electrode current collector 22 and to the surface of a portion of the insulating layer 26. The positive electrode active material layer 24 comprises a positive electrode active material capable of reversibly occluding, or absorbing and releasing, charge carriers. Examples of positive electrode active materials include lithium transition metal oxides such as a lithium-nickel-containing composite oxide, a lithium-cobalt-containing composite oxide, a lithium-nickel-cobalt-containing composite oxide, a lithium-manganese-containing composite oxide, or a lithium-nickel-cobalt-manganese-containing composite oxide. These can be used alone or in combination with two or more of them. In particular, the application of the technology disclosed herein is advantageous when using a lithium-manganese-containing composite oxide containing readily leached manganese.When the total solid content of the positive electrode active material layer 24 is set to 100 wt%, a proportion of the positive electrode active material may be about 50 wt% or more, for example, 80 wt% or more.

[0018] The positive electrode active material layer 24 may include optional components other than the positive electrode active material, such as a conductive material, a dispersant, a binder, lithium phosphate, and various additive components. For the conductive material, carbon black such as acetylene black (AB) and other carbon materials can be used. For the binder, polyvinylidene fluoride (PVdF), for example, can be used.

[0019] As in Fig.As shown in Figure 2, the positive electrode active material layer 24 extends longitudinally with a predetermined width La. Although not specifically limited thereto, the width La may be approximately 20 to 500 mm, typically 30 to 200 mm, for example, 40 to 150 mm. The positive electrode active material layer 24 is formed in a sheet-like manner along one end of the positive electrode current collector 22 in the Y1 direction. The positive electrode active material layer 24 lies in the Y1 direction with respect to the insulating layer 26. The entire positive electrode active material layer 24 overlaps the negative electrode active material layer 34 in a plan view. Furthermore, the entire positive electrode active material layer 24 overlaps the separator 40 in a plan view.

[0020] As in Fig.As shown in Figure 3, the positive electrode active material layer 24 includes a main body part A1 and an end part A2 provided closer to the positive electrode current collector exposed part 22a than the main body part A1 and having an end E in the Y2 direction. The main body part A1 is formed on the surface of the positive electrode current collector 22. The main body part A1 is in contact with the surface of the positive electrode current collector 22. Further, the main body part A1 has a substantially constant thickness. Although not specifically limited thereto, the average thickness of the main body part A1 may be about 10 to 200 μm, typically 20 to 150 μm, for example, 40 to 100 μm. Here, the main body part A1 includes the center of the positive electrode active material layer 24 in the width direction Y. The main body part A1 has a width Lm in the width direction Y.

[0021] The end part A2 extends from the main body part A1 in the direction Y2. The end part A2 is formed at least on the surface of the insulating layer 26. The end part A2 is coated with the insulating layer 26. Here, the end part A2 is formed between a surface of the insulating layer 26 and the surface of the positive electrode current collector 22. The end part A2 has a width Le in the width direction Y. Generally, the width Le is shorter than the width Lm of the main body part A1. Although not specifically limited thereto, the width Le may be about 10 µm or more, typically 20 to 10,000 µm, for example, 30 to 5,000 µm, preferably 50 to 3,000 µm. A ratio (Le / Lm) of the width Le of the end part A2 to the width Lm of the main body part A1 may be about 0.1 or less, typically 0.01 to 0.05, e.g., 0.015 to 0.03 or 0.02 to 0.025.This makes it possible to minimize metal deposition on the negative electrode 30 and also provide a large battery capacity. Furthermore, it is possible to form the end portion A2 with a constant width.

[0022] The end portion A2 is not exposed in the plan view. In section, the end portion A2 includes an inclined surface S1 whose thickness continuously decreases in the Y2 direction toward the end portion of the positive electrode current collector 22, and an inclined surface S2 whose thickness, in contrast to the inclined surface S1, continuously decreases in the Y1 direction toward the end portion of the positive electrode current collector 22. The inclined surface S1 and the inclined surface S2 are completely covered with the insulating layer 26.

[0023] The insulating layer 26 is attached to the surface of a portion of the positive electrode active material layer 24 (more precisely, the end portion A2) from the surface of the positive electrode current collector 22. The insulating layer 26 includes an inorganic filler. Examples of positive electrode active materials include lithium transition metal oxides, such as a lithium-nickel composite oxide, a lithium-cobalt composite oxide, a lithium-nickel composite oxide, a lithium-manganese composite oxide, and a lithium-nickel-cobalt-manganese composite oxide. These can be used alone or in combination with two or more of them. Among them, a lithium-nickel-cobalt-manganese composite oxide having a rock salt layer structure is preferred. When the total solid content of the insulating layer 26 is set to 100 wt%, a proportion of the positive electrode active material may be about 50 wt% or more, for example, 80 wt%.-% or more.

[0024] In addition to the inorganic filler, the insulating layer 26 may include other optional components, such as a binder and various additive components. For the binder, for example, a polyolefin binder such as polyethylene (PE), polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), acrylic resin, styrene-butadiene rubber (SBR), or the like may be used. The binder may be the same type as the binder of the positive electrode active material layer 24 or a different type.

[0025] As in Fig.2, the insulating layer 26 extends in the longitudinal direction. The insulating layer 26 is located in the width direction Y at the boundary portion between the positive electrode active material layer 24 and the exposed portion 22a of the positive electrode current collector. The insulating layer 26 protrudes beyond a Y2-direction end of the negative electrode 30 (e.g., the negative electrode active material layer 34) in the plan view in the Y2 direction. The entire insulating layer 26 overlaps the separator 40 in the plan view in the Y2 direction. As shown in Fig.3, the insulating layer 26 is located between the main body part A1 of the positive electrode active material layer 24 and the exposed part 22a of the positive electrode current collector in the width direction Y. The insulating layer 26 is formed in a sheet-like manner along one end of the main body part A1 in the Y2 direction. The insulating layer 26 is arranged in the Y2 direction relative to the main body part A1. The insulating layer 26 has a predetermined width Lc. Here, the width Lc is wider than the width Le of the end part A2 of the positive electrode active material layer 24. However, the width Lc may be the same as the width Le of the end part A2 of the positive electrode active material layer 24.

[0026] As in Fig.3, the insulating layer 26 is superimposed in cross section on the inclined surface S1 of the positive electrode active material layer 24. Here, no layer other than the positive electrode active material layer 24 is coated with the insulating layer 26. The insulating layer 26 is exposed on the surface of the positive electrode 20. Moreover, in section, the insulating layer 26 is sandwiched between the positive electrode current collector 22 and the inclined surface S2 of the positive electrode active material layer 24. Here, the width Lb of a part of the insulating layer 26 sandwiched between the positive electrode current collector 22 and the inclined surface S2 is shorter than the width Le of the end part A2 of the positive electrode active material layer 24. However, the width Lb may be the same as the width Le of the end part A2 of the positive electrode active material layer 24.Although not specifically limited, the width Lb may be about 10 µm or more, typically 20 µm or more, for example, 50 µm or more, or 100 µm or more, and about 5000 µm or less, 3000 µm or less, typically 2000 µm or less, for example, 1000 µm or less. A ratio (Lb / Le) of the width Lb to the width Le of the end part A2 may be about 0.1 or more, typically 0.2 to 0.8 (0.5 ± 0.3), for example, 0.3 to 0.7 (0.5 ± 0.2), or 0.4 to 0.6 (0.5 ± 0.1). This makes it possible to minimize metal deposition on the negative electrode 30 to a large extent and also provide a large battery capacity. Furthermore, it is possible to form the insulating layer 26 with a constant width Lb. The upper end of a part where the insulating layer 26 is provided is at the same level as or lower than the upper end (surface) of the main body part A1.

[0027] As in Fig.3, the positive electrode 20 includes a layered part B where the insulating layer 26 sandwiched between the positive electrode current collector 22 and the inclined surface S2, the end part A2 of the positive electrode active material layer 24, and the insulating layer 26 overlying the inclined surface S1 are stacked in the thickness direction X from the positive electrode current collector 22 side. Here, the layered part B has a three-vertical-layer structure. The width of the layered part B here is equal to the width Lb. The maximum thickness of the layered part B here is smaller than the average thickness of the main body part A1. However, the maximum thickness of the layered part B may be equal to the average thickness of the main body part A1. Further, here, the upper end of the layer part B in the thickness direction X, ie, the upper end of a part of the insulating layer 26 with the width Lb, is lower than the upper end (the surface) of the main body part A1.

[0028] In the present embodiment, the width La of the entire positive electrode active material layer 24 and the width Lb of the part of the insulating layer 26 inserted between the positive electrode current collector 22 and the inclined surface S2 satisfy the following formula (1): 0.02 × 10 -2 ≤ (Lb / La) ≤ 2.1 × 10 -2 . The ratio (Lb / La) can be 1.0 × 10 -2 or less. The ratio (Lb / La) can satisfy the following formula (2): 0.02 × 10 -2 ≤ (Lb / La) ≤ 1.0 × 10 -2 . This makes it possible to appropriately minimize an increase in resistance of the positive electrode 20 due to the formation of the insulating layer 26.

[0029] The ratio (Lb / La) can be 0.48×10 -2 or more, preferably 0.73×10 -2 or more, for example 0.8×10 -2 or more. The ratio (Lb / La) can, for example, satisfy the following formula (3): 0.73 × 10 -2 ≤ (Lb / La) ≤ 2.1 × 10-2 ; and preferably the following formula (4): 1.0 × 10 -2 ≤ (Lb / La) ≤ 2.1 × 10 -2 . This makes it possible to effectively minimize the dissolution of metallic elements from the end part A2 and to largely minimize the metal deposition on the negative electrode 30.

[0030] The negative electrode 30 includes a negative electrode current collector 32 and the negative electrode active material layer 34 formed on the negative electrode current collector 32. The negative electrode current collector 32 is a conductive member. For the negative electrode current collector 32, a metal foil such as copper or nickel is suitable. The negative electrode current collector 32 has a portion 32a where the negative electrode active material layer 34 is not formed and where it is exposed (i.e., an exposed portion of the negative electrode current collector). Here, the exposed portion 32a of the negative electrode current collector is provided in a track-like manner at one end portion of the negative electrode current collector 32 in the Y1 direction. As shown in Fig. 2, the exposed part 32a of the negative electrode current collector protrudes in the Y1 direction beyond an end of the separator 40 lying in the Y1 direction. As shown in Fig.As shown in Figure 1, a negative electrode current collector plate 32b is connected to the exposed portion 32a of the negative electrode current collector. The negative electrode current collector plate 32b is electrically connected to the negative electrode terminal 32c.

[0031] The negative electrode active material layer 34 is attached to the surface of the negative electrode current collector 32. The negative electrode active material layer 34 includes a negative electrode active material capable of reversibly absorbing and releasing charge carriers. Examples of negative electrode active materials include carbon materials such as graphite, metal oxide materials such as titanium oxide and lithium titanium composite oxide (LTO), and silicon-containing Si materials. These can be used alone or in combination with two or more of them. The negative electrode active material layer 34 may include optional components other than the negative electrode active material, such as a conductive material, a binder, and / or a thickener. For the conductive material, for example, carbon black such as acetylene black (AB) and other carbon materials can be suitably used. For the binder, for example, styrene-butadiene rubber (SBR) can be used.Carboxymethylcellulose (CMC), for example, can be used as a thickener.

[0032] As in Fig. As shown in Figure 2, the negative electrode active material layer 34 extends longitudinally with a predetermined width Lf. The width Lf of the negative electrode active material layer 34 is wider than the width La of the positive electrode active material layer 24. That is, Lf>La. The negative electrode active material layer 34 protrudes beyond one end of the positive electrode active material layer 24 in the Y1 direction in plan view. Further, the negative electrode active material layer 34 protrudes beyond another end of the positive electrode active material layer 24 in the Y2 direction in plan view.

[0033] The separator 40 insulates the positive electrode active material layer 24 of the positive electrode 20 from the negative electrode active material layer 34 of the negative electrode 30. For the separator 40, a porous resin film made of a resin such as polyethylene (PE), polypropylene (PP), a polyester, cellulose, or a polyamide is suitable. The separator 40 may have a single-layer structure or a structure in which two or more layers are stacked, for example, a three-layer structure in which a PP layer is stacked on both surfaces of a PE layer. For example, a heat-resistant layer (HRL) comprising the inorganic filler as the material constituting the insulating layer 26 may be provided on the surface of the separator 40.

[0034] As in Fig.2, the width Ls of the separator 40 is wider than the width La of the positive electrode active material layer 24 and the width Lf of the negative electrode active material layer 34. That is, Ls > Lf > La. The separator 40 protrudes beyond a Y1-direction end of the positive electrode active material layer 24 and a Y1-direction end of the negative electrode active material layer 34 in the Y1 direction in plan view. Further, the separator 40 protrudes beyond a Y2-direction end of the positive electrode active material layer 24, a Y2-direction end of the insulating layer 26, and a Y2-direction end of the negative electrode active material layer 34 in the Y2 direction in plan view.

[0035] The non-aqueous electrolyte is, for example, a non-aqueous electrolyte solution comprising a non-aqueous solvent and a supporting salt. For the non-aqueous solvent, organic solvents such as various carbonates, ethers, and esters can be used. Among them, carbonates are preferred. Specific examples are ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), monofluoroethylene carbonate (MFEC), and difluoroethylene carbonate (DFEC). These non-aqueous solvents can be used alone or in a suitable combination of two or more of them. For the supporting salt, for example, a lithium salt such as LiPF6 and LiBF4 can be used. The non-aqueous electrolyte can further comprise various well-known additives, such as:Overcharge additives such as biphenyl (BP) and cyclohexylbenzene (CHB), an oxalato complex compound comprising boron atoms and / or phosphorus atoms, and / or a film-forming agent such as vinylene carbonate (VC).

[0036] Here, the positive electrode 20 having the configuration can be manufactured by a manufacturing method including, for example, the following processes: (Step S1) preparing a paste for forming a positive electrode active material layer 24; (Step S2) preparing a paste for forming an insulating layer; (Step S3) applying and drying the paste; and (Step S4) pressing a positive electrode. Here, (Step S4) is not essential and may be omitted in other embodiments. The following steps will be described in order.

[0037] In (step S1), a material such as the positive electrode active material is dispersed in a suitable solvent (e.g., N-methyl-2-pyrrolidone (NMP)) to prepare a mass for forming a positive electrode active material layer 24. The mass can be prepared, for example, using a stirring and mixing device such as a ball mill, a roller mill, a planetary mixer, a disperser, or a kneading device. In this case, the viscosity V1 of the mass for forming a positive electrode active material layer 24 can be adjusted to be in the range of approximately 1,000 to 20,000 mPa s, typically 5,000 to 10,000 mPa s. The viscosity V1 can be adjusted, for example, by the proportion of an added solid (e.g., a binder or a dispersant) relative to the solvent and the kneading time of the mass. This makes it possible to carry out step S3 described below consistently and precisely.In this description, the “viscosity of a mass” is a value measured at 25°C with a rheometer at a shear rate of 21.5 s. -1 is measured.

[0038] In (step S2), a material such as the inorganic filler is dispersed in a suitable solvent (e.g., NMP) to prepare a composition for forming an insulating layer. In this case, the viscosity V2 of the composition for forming an insulating filler layer can be adjusted to be in the range of approximately 1,000 to 5,000 mPa s, for example, 1,500 to 4,500 mPa s. The viscosity V2 can be adjusted, for example, by a proportion of an added solid (e.g., a binder) relative to the solvent and / or the kneading time of the composition. This makes it possible to carry out step S3 described below accurately and reliably.

[0039] When performing a so-called simultaneous coating method, in step S3 described below, it is necessary to set the viscosity V2 of the insulating layer-forming composition to be lower than the viscosity V1 of the positive electrode active material layer 24 (low viscosity). Thus, the contact angle relative to the positive electrode current collector 22 becomes "insulating layer-forming composition < positive electrode active material layer 24" and the insulating layer-forming composition can be more easily inserted under the positive electrode active material layer 24. Moreover, a ratio (V2 / V1) of the viscosity V2 to the viscosity V1 can be set to be in the range of approximately 0.01 to 0.99, typically 0.05 to 0.95. This allows the width of the layer part B to be appropriately set to be within the above range.

[0040] In (step S3), two types of compounds prepared in steps S1 and S2 are applied to the positive electrode current collector 22, excluding the end portion of the positive electrode current collector 22 in the Y2 direction. The compounds can be applied using, for example, a coating device such as a die coater, a slot coater, a comma coater, or a gravure coater. In one example, the two types of compounds are sequentially applied in three stages. That is, first, the compound for forming an insulating layer is applied to the positive electrode current collector 22 with a predetermined width Lb, excluding the exposed portion 22a of the positive electrode current collector.Subsequently, the composition for forming a positive electrode active material layer 24 is applied to the positive electrode current collector 22 and a portion of the insulating layer 26 with a predetermined width La. Subsequently, the composition for forming an insulating layer is applied again with a predetermined width Lc so that the entire end portion A2 of the positive electrode active material layer 24 is covered. Alternatively, in another example, the two types of compositions are simultaneously applied to the positive electrode current collector 22 using a die coating device.

[0041] Although not shown, in a preferred aspect, a die coating apparatus is prepared including a transport mechanism that transports the positive electrode current collector 22 in a transport direction orthogonal to the width direction, and a nozzle head from which the two types of compounds are discharged onto the positive electrode current collector 22. The nozzle head includes a first discharge unit having a first opening through which the compound for forming an insulating layer is discharged, and a second discharge unit having a second opening through which the compound for forming a positive electrode active material layer 24 is discharged. The widths of the first opening and the second opening are set so that the positive electrode active material layer 24 and the insulating layer 26 have a predetermined width.For example, the width may be set slightly (e.g., approximately 1% to 2%) smaller than the predetermined width, taking wet spreadability into consideration with respect to the positive electrode current collector 22. Furthermore, a predetermined distance may be provided between the first opening and the second opening, taking wet spreadability and the like into consideration. Furthermore, the second discharge unit may be positioned slightly downstream of the first discharge unit in the conveying direction. Thus, the composition for forming an insulating layer can be discharged slightly earlier than the composition for forming a positive electrode active material layer 24. The first discharge unit, the second discharge unit, and the conveying mechanism are each electrically connected to a control device.The control unit causes the positive electrode current collector 22 to be transported in the transport direction, and mass is discharged from the first discharge unit and the second discharge unit at a predetermined discharge pressure. The positive electrode current collector 22, onto which the mass for forming an insulating layer and the mass for forming a positive electrode active material layer 24 have been applied, can be dried, for example, using a heating dryer.

[0042] In (step S4), a pressing process is performed on the positive electrode current collector 22 on which the two types of materials have been applied. Thus, it is possible to adjust properties of the positive electrode active material layer 24 and / or the insulating layer 26, such as the thickness, density, and the like. As described above, it is as in Fig.3, it is possible to form the positive electrode 20 including the positive electrode active material layer 24 and the insulating layer 26 on the positive electrode current collector 22.

[0043] Fig. 4 is an exemplary diagram to illustrate electron and Li movements between the positive electrode 20 and the negative electrode 30. As in Fig. 4, in the lithium-ion secondary battery 100, the supply of electrons (e - ) to the end part of the positive electrode active material layer 24, here the layer part B, is minimized by the insulating layer 26 and a charging and discharging reaction in the layer part B is minimized. Thus, the movement of charge carriers (here, Li +) from the end portion A2 to the layer portion B is restricted. As a result, the end portion A2 is less likely to be exposed to a high potential, and it is possible to minimize the leaching of metallic elements from the end portion A2. Therefore, according to the configuration of the lithium-ion secondary battery 100, it is possible to reduce metal deposition (e.g., Li deposition) at the opposite negative electrode 30 and realize excellent Li deposition resistance. Furthermore, it is possible to realize a battery with excellent cycle life.

[0044] While the lithium-ion secondary battery 100 can be applied to various applications, high energy density and large capacity can be realized with the wound electrode body 10. Furthermore, compared to a conventional product, the positive electrode 20 configuration improves the deposition resistance (e.g., Li deposition resistance) of a carrier-derived substance and the cycle characteristics. Therefore, by utilizing such a feature, the battery can be suitably applied as a drive power supply in vehicles such as an electric vehicle (EV), a hybrid vehicle (HV), and a plug-in hybrid vehicle (PHV).

[0045] Furthermore, in the present embodiment, the rectangular lithium-ion secondary battery 100 including the flat wound electrode body 10 was described as an example. However, the lithium-ion secondary battery may also be configured as a lithium-ion secondary battery with a layered electrode body. Furthermore, the external shape of the lithium-ion secondary battery 100 may have a cylindrical shape, a layered structure, or the like. Furthermore, the technology disclosed herein may be applied to a nonaqueous electrolyte secondary battery other than a lithium-ion secondary battery.

[0046] Examples according to the present invention are described below, but the present invention is not intended to be limited to the examples described. Production of the positive electrode

[0047] LiNi 1 / 3 CO 1 / 3 Mn 1 / 3O2 as the positive electrode active material, lithium phosphate (Li3PO4), polyvinylidene fluoride (PVdF) as the binder, and acetylene black (AB) as the conductive material were mixed in N-methyl-2-pyrrolidone (NMP) to prepare a composition for forming a positive electrode active material layer 24. Furthermore, boehmite as the inorganic filler and polyacrylic acid as the binder were mixed in NMP to prepare a composition for forming an insulating layer. In this case, a ratio (V2 / V1) between the viscosity V2 of the composition for forming an insulating layer and the viscosity V1 of the composition for forming a positive electrode active material layer 24 was set as shown in Table 1.

[0048] Next, a sheet-shaped aluminum foil was prepared as a positive electrode current collector. Then, the prepared composition for forming a positive electrode active material layer 24 and the composition for forming an insulating layer were simultaneously coated on the aluminum foil using a die coater, dried, and then pressed. At this time, the composition was applied to the aluminum foil in the longitudinal direction except for an exposed portion of the current collector at the end of the aluminum foil. Furthermore, the width La of the positive electrode active material layer 24 was approximately 100 mm. Thus, positive electrodes (Examples 1 to 5 and Comparative Example 1) having the positive electrode active material layer 24 and the insulating layer were manufactured.

[0049] In addition, for comparison, a composition for forming an insulating layer with a predetermined width was applied to a positive electrode current collector except for an exposed part of the positive electrode current collector, and then a composition for forming a positive electrode active material layer 24 was applied to the positive electrode current collector and a part of the insulating layer with the predetermined width La to prepare a positive electrode (Comparative Example 2). In addition, only the composition for forming a positive electrode active material layer 24 was applied to the positive electrode current collector with a predetermined width La except for the exposed part of the positive electrode current collector, thereby preparing a positive electrode (Comparative Example 3) without an insulating layer. Observation of structure of positive electrodes

[0050] The positive electrodes (Examples 1 to 5 and Comparative Examples 1 and 2) were cut along the width direction, and test pieces were cut from them. The test pieces were embedded and polished, and then the cross sections of the insulating layer and the positive electrode active material layer 24 were observed with a scanning electron microscope (SEM), and images were taken (magnification: 500 to 3,000×). In this case, an image with clear contrast was obtained by setting the accelerating voltage to 10 kV. As a result, the positive electrodes of Examples 1 to 5 had a Fig.3. That is, in Examples 1 to 5, the positive electrode 20 included the exposed portion 22a of the positive electrode current collector, the positive electrode active material layer 24, the insulating layer 26, and the layer portion B. In addition, in the positive electrode of Comparative Example 1, the inclined surface S2 was in contact with the positive electrode current collector 22 while being covered with the insulating layer 26. That is, the insulating layer 26 was not interposed between the positive electrode current collector 22 and the inclined surface S2 of the positive electrode active material layer 24. In the positive electrode of Comparative Example 1, the width Lb of the portion of the insulating layer 26 interposed between the positive electrode current collector 22 and the inclined surface S2, and also the ratio (Lb / La) were zero.Furthermore, in the positive electrode of Comparative Example 2, the insulating layer 26 did not overlap the inclined surface S1, and the inclined surface S2 was covered with the insulating layer 26. That is, the inclined surface S1 was exposed on the surface. Measurement of Lb

[0051] Next, the width Lb was determined from the images of the positive electrodes (Examples 1 to 5). Specifically, a distance between the end of the insulating layer in the Y2 direction and the end of the positive electrode active material layer 24 in the Y1 direction was measured as the width Lb. Here, taking into account the variation in the longitudinal direction, the width Lb was measured at three to five pieces for each of the examples, and an arithmetic average was calculated. In Examples 1 to 5, the width Lb was in a range of 20 to 2000 µm. In Examples 1 to 4, the width Lb was in a range of 20 to 1000 µm. Then, Lb / La was calculated from the width Lb and the width La. The results are shown in Table 1. Manufacturing a lithium-ion secondary battery

[0052] Natural graphite (C) as the negative electrode active material, styrene-butadiene rubber (SBR) as the binder, and carboxymethyl cellulose (CMC) as the thickener were mixed in deionized water to prepare a composition for forming a negative electrode active material layer. Next, a sheet-shaped copper foil was prepared as the negative electrode current collector. Subsequently, the negative electrode composition was applied to both surfaces of the copper foil, dried, and then pressed. Thus, a negative electrode with the negative electrode active material layer was fabricated.

[0053] Next, a porous polyolefin film with a three-layer structure of PP / PE / PP was prepared for the separator, in which a polypropylene layer (PP layer) was laminated on both sides of a polyethylene layer (PE layer). Then, the prepared positive electrode and negative electrode were laminated with the separator in between to prepare electrode bodies (Examples 1 to 5 and Comparative Examples 1 to 3). Next, the positive electrode current collector plate was welded to the positive electrode of the prepared electrode body, and the negative electrode current collector plate was welded to the negative electrode, and housed in a battery case.

[0054] Next, for a non-aqueous electrolyte solution, a solution was prepared in which LiPF6 was dissolved at a concentration of 1.0 mol / L as a carrier salt in a mixed solvent comprising ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC). The non-aqueous electrolyte solution was then injected into the battery case, and the battery case was hermetically sealed. Thus, lithium-ion secondary batteries (Examples 1 to 5 and Comparative Examples 1 to 3) were fabricated. First loading and unloading

[0055] Constant current charging was performed on the fabricated lithium-ion secondary battery at a rate of 1 / 3 C until the voltage reached 4.2 V at 25°C, followed by constant voltage charging until the current reached 1 / 50 C. Next, constant current discharging was performed at a rate of 1 / 3 C until the voltage reached 3.0 V. Here, "1 C" refers to a current value at which a battery capacity (Ah) predicted from a theoretical capacity of a positive electrode active material can be charged in 1 hour.

[0056] Evaluation of Mn Amount in Negative Electrode after Cycle Testing: The charging and discharging process was set as one cycle and repeated for 1000 cycles. After charging and discharging, the lithium-ion secondary battery was disassembled, and the negative electrode was removed. Next, a portion of the positive electrode opposite layer B was divided into a size of 100 mm x 100 mm. Next, the negative electrode current collector was peeled off the separated negative electrode, and the negative electrode active material layer was dispersed in an acidic solvent. A solvent in which hydrogen peroxide was added to a mixed acid of hydrochloric acid and nitric acid was used as the acidic solvent. The Mn contained in the dispersion solution was then quantified by inductively coupled plasma (ICP) analysis. The results are shown in Table 1.Here, Table 1 shows relative values, where the Mn amount in Comparative Example 1 is set as 100. For the amount of Mn in Table 1, a smaller numerical value indicates a further minimized deposition of Mn. Durability assessment after high-rate cycles

[0057] After the cycle test, the lithium-ion secondary battery was placed in a constant-temperature chamber at -6.7°C and the temperature was sufficiently stabilized. Next, it was subjected to 300 additional cycles of high-rate charging and discharging in a -6.7°C environment. The conditions for the high-rate charging and discharging were as follows: charging was performed at a constant current of 200 A for 5 seconds, followed by discharging at a constant current of 200 A for 5 seconds. A capacity retention ratio was then determined from the battery capacity before and after the high-rate cycling. The results are shown in Table 1. Here, Table 1 shows relative values, with the capacity retention ratio in Comparative Example 1 set as 100.For the capacity retention ratio in Table 1, a larger numerical value indicates less capacity degradation after high-rate cycling and better Li deposition resistance. Measurement of resistance of positive electrode

[0058] The lithium-ion secondary battery was disassembled after the initial charge and discharge, and the positive electrode was removed. The positive electrode was placed facing the lithium metal and placed in a laminated bag-shaped container with a non-aqueous electrolyte solution to construct a laminate cell. Next, the laminate cell was placed in a constant-temperature chamber of -30°C and the temperature was sufficiently stabilized. Subsequently, the IV resistance of the laminate cell was measured under a -30°C environment. The results are shown in Table 1. Here, Table 1 shows relative values, with the IV resistance in Comparative Example 1 set as 100. For the positive electrode resistance in Table 1, a smaller numerical value indicates a lower resistance. [Table 1] Table 1 Test example positive electrode Evaluation results (relative values ​​based on comparative example 1) Viscosity ratio V2 / V1* 1 Lb / La Amount of Mnin negative electrode after cycles Durability after high-rate cycles Resistance of the positive electrode Example 1 0,95 0,02×10 -2 99 101 100 Example 2 0,54 0,48×10 -2 99 103 100 Example 3 0,40 0,73×10 -2 96 106 100 Example 4 0,28 1,0×10 -2 95 106 100 Example 5 0,094 2,1×10 -2 95 106 105 Comparison example 1 1,08 0 100 (reference) Comparison example2* 2 Not measured - 99 100 100 Comparison example3* 3 - 103 95 100 *1: Value measured at 25°C with a rheometer with a shear rate of 21.5 (s -1 ). *2: Inclined surface S1 was exposed *3: Insulation layer was not coated

[0059] Fig.Figure 5 is a graph showing the relationship between the viscosity ratio (V2 / V1) of the mass and Lb / La. As can be seen from Table 1 and Fig. As can be seen from Figure 5, when a simultaneous coating method was used, it was possible to appropriately shape the width Lb and adjust its length by changing the viscosity ratio (V2 / V1). In the case where the viscosity ratio (V2 / V1) was controlled to be less than 1, specifically within a range of 0.094 to 0.95, Lb / La could be adjusted within a range of 0.02×10 -2 up to 2.1×10 -2 lay.

[0060] Fig. Figure 6 is a graph showing the relationship between Lb / La and the amount of Mn in the negative electrode after cycling. As can be seen from Table 1 and Fig. 6, in Examples 1 to 5, where Lb / La was 0.02×10 -2or more, the leaching of Mn from the positive electrode active material was minimized compared to Comparative Examples 1 to 3, especially when Lb / La was set to 0.7×10 -2 or more, preferably 1×10 -2 or more, was set.

[0061] Fig. Figure 7 is a graph showing the relationship between Lb / La and durability after high-rate cycling. As can be seen from Table 1 and Fig. 7, in Examples 1 to 5, where Lb / La was 0.02×10 -2 or more, minimized the occurrence of Li deposition on the negative electrode and maintained a large battery capacity after high-rate cycling compared to Comparative Examples 1 to 3. In particular, when Lb / La was set to 0.4×10 -2 or more, preferably 0.7×10 -2or more, the resistance of Li deposition improved, and an effect of minimizing capacity degradation was appropriately shown.

[0062] In addition, as shown in Table 1, in Examples 1 to 4 where Lb / La was less than 2.1×10 -2 , e.g. 2×10 -2 or less, an increase in the resistance of the positive electrode due to the formation of the insulating layer can be minimized.

[0063] Although the present invention has been described in detail above, the embodiments and examples are merely examples, and the invention disclosed herein includes various modifications and changes to the specific examples.

Claims

[1] Secondary battery (100) with non-aqueous electrolyte, with: a positive electrode (20); a negative electrode (30) opposite the positive electrode (20); and a non-aqueous electrolyte, where the positive electrode (20) comprises a positive electrode current collector (22), a positive electrode active material layer (24) comprising a positive electrode active material and formed on the positive electrode current collector (22) except for a part where the positive electrode current collector (22) is exposed, and an insulating layer (26) comprising an inorganic filler and formed at a boundary part between the part where the positive electrode current collector (22) is exposed and the positive electrode active material layer (24), wherein the positive electrode active material layer (24) comprises a main body part (A1) and an end part (A2) which is provided closer to the part where the positive electrode current collector (22) is exposed than the main body part (A1) and has a smaller thickness than a thickness of the main body part (A1), the insulating layer (26) is inserted between the positive electrode current collector (22) and the end part (A2) in a thickness direction and is shaped to cover the end part (A2), and when a width of the positive electrode active material layer (24) is set as La and a width of a part of the insulating layer (26) inserted between the positive electrode current collector (22) and the end part (A2) in a direction from the positive electrode active material layer (24) to the insulating layer (26) is set as Lb, the width La and the width Lb satisfy the following formula (1): 0.02×10−2≤(Lb / La)≤2.1×10−2. [2] The non-aqueous electrolyte secondary battery (100) according to claim 1, wherein the width La and the width Lb satisfy the following formula (2): 0.02×10−2≤(Lb / La)≤1.0×10−2. [3] The non-aqueous electrolyte secondary battery (100) according to claim 1 or 2, wherein the width Lb is 20 µm or more and 2000 µm or less. [4] The non-aqueous electrolyte secondary battery (100) according to any one of claims 1 to 3, wherein when a width of the main body part (A1) is set as Lm and a width of the end part (A2) is set as Le, a ratio (Le / Lm) of the width Le to the width Lm is 0.1 or less. [5] The non-aqueous electrolyte secondary battery (100) according to any one of claims 1 to 4, wherein when a width of the end part (A2) is set as Le, a ratio (Lb / Le) of the width Lb to the width Le is 0.2 or more and 0.8 or less. [6] The non-aqueous electrolyte secondary battery (100) according to any one of claims 1 to 5, wherein an upper end of a part of the insulating layer (26) having the width Lb in the thickness direction is lower than an upper end of the main body part (A1).

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