Negative electrode for non-aqueous electrolyte secondary battery, method of manufacturing the same, method of inspecting the same, non-aqueous electrolyte secondary battery, and method of

Abstract

To provide a nonaqueous electrolyte secondary battery excellent in charging load characteristics and its manufacturing method, a negative electrode capable of constituting the nonaqueous electrolyte secondary battery and its manufacturing method, and an inspection method of the negative electrode for manufacturing the nonaqueous electrolyte secondary battery.SOLUTION: When an interface resistance between the negative electrode mixture layer and the current collector is Rs (Ω cm2), a volume resistivity of the negative electrode mixture layer is ρ v (Ω cm), and a thickness of the negative electrode mixture layer is d (cm), (1) Rs / (ρ v * d) satisfies a specific range according to the thickness of the negative electrode mixture layer, or (2) a relationship of Rs ≤ 1. 67d + b is satisfied. The non-aqueous electrolyte secondary battery of the present invention includes a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte, wherein the negative electrode is the negative electrode for a non-aqueous electrolyte secondary battery of the present invention.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a non-aqueous electrolyte secondary battery having excellent charging load characteristics and a method for manufacturing the same, a negative electrode that can be used to form the non-aqueous electrolyte secondary battery and a method for manufacturing the same, and a method for inspecting a negative electrode used in manufacturing a non-aqueous electrolyte secondary battery. [Background technology]

[0002] Non-aqueous electrolyte secondary batteries are used as power sources for portable electronic devices such as mobile phones and laptop personal computers, as well as for electric vehicles, and can contribute to, for example, achieving Goal 7 "Affordable and clean energy" and Goal 12 "Responsible consumption and production" of the Sustainable Development Goals (SDGs) advocated by the United Nations. Furthermore, efforts are being made to improve the various characteristics of non-aqueous electrolyte secondary batteries as their applications become more diverse.

[0003] One of the improvements required for non-aqueous electrolyte secondary batteries is a reduction in charging time. A common method for charging non-aqueous electrolyte secondary batteries is to charge them at a constant current until the battery voltage reaches a predetermined value (constant current charging (CC charging)), and then charge them at a constant voltage until the current value decreases and reaches a predetermined value (constant voltage charging (CV charging)). However, since the time from the start of CC charging until the end voltage is reached is shorter than the time from the start of CV charging until the current value reaches the end condition, from the perspective of shortening charging time, it is desirable to have a large amount of electricity that can be charged into the battery during CC charging.

[0004] Therefore, in order to shorten the charging time of a non-aqueous electrolyte secondary battery, it is necessary to ensure a large capacity when CC charging is performed at a large current, that is, to improve the charging load characteristics. In order to improve the charging load characteristics of a non-aqueous electrolyte secondary battery, for example, it is effective to reduce the resistance value of the electrodes.

[0005] Although not intended to improve the charging load characteristics of a battery, Patent Document 1 proposes that, in a lithium-ion battery electrode in which an electrode active material layer containing an electrode active material, a conductive additive, etc. is provided on at least one surface of a collector layer, the interface resistance between the electrode active material layer and the collector layer be set within a specific range. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] International Publication No. 2018 / 016528 Summary of the Invention [Problem to be solved by the invention]

[0007] 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 having excellent charging load characteristics and a method for manufacturing the same, a negative electrode that can constitute the non-aqueous electrolyte secondary battery and a method for manufacturing the same, and a method for inspecting a negative electrode for manufacturing a non-aqueous electrolyte secondary battery. [Means for solving the problem]

[0008] The negative electrode for a non-aqueous electrolyte secondary battery according to the first aspect of the present invention has a negative electrode mixture layer containing a negative electrode active material on one or both sides of a current collector, and the interface resistance between the negative electrode mixture layer and the current collector is Rs (Ωcm 2 ), the volume resistivity of the negative electrode mixture layer is ρv (Ωcm), and the thickness of the negative electrode mixture layer (the thickness per one side of the current collector; the same applies hereinafter to the "thickness of the negative electrode mixture layer" in this specification) is d (cm), Rs / (ρv×d) is the following value.

[0009] (A) When the thickness of the negative electrode mixture layer is 35 μm or more and less than 50 μm, Rs / (ρv×d) is 5 to 20. (B) When the thickness of the negative electrode mixture layer is 50 μm or more and 100 μm or less, Rs / (ρv×d) is 10 to 38.5.

[0010] The negative electrode for a non-aqueous electrolyte secondary battery according to the second aspect of the present invention has a negative electrode mixture layer containing a negative electrode active material on one or both sides of a current collector, and the interface resistance between the negative electrode mixture layer and the current collector is Rs (Ωcm 2 ) and the thickness of the negative electrode mixture layer is d (cm), the relationship Rs≦1.67d+b (where b is −0.01 or more and 0 or less) is satisfied.

[0011] The nonaqueous electrolyte secondary battery of the present invention comprises a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and a nonaqueous electrolyte, and the negative electrode is the negative electrode for the nonaqueous electrolyte secondary battery of the present invention (the negative electrode of the first embodiment or the negative electrode of the second embodiment).

[0012] Furthermore, the method for producing a negative electrode for a non-aqueous electrolyte secondary battery according to the first aspect of the present invention is characterized in that, when a negative electrode mixture layer containing a negative electrode active material is formed on one or both surfaces of a current collector, the thickness of the negative electrode mixture layer and Rs / (ρv×d) are adjusted to the values ​​of (A) or (B).

[0013] The method for producing a negative electrode for a non-aqueous electrolyte secondary battery according to the second aspect of the present invention is characterized in that, when forming a negative electrode mixture layer containing a negative electrode active material on one or both surfaces of a current collector, Rs and d are adjusted so as to satisfy the relationship Rs≦1.67d+b (wherein b is −0.01 or more and 0 or less).

[0014] Furthermore, the method for producing a non-aqueous electrolyte secondary battery of the present invention is characterized in that, when producing a non-aqueous electrolyte secondary battery having a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte, the negative electrode for a non-aqueous electrolyte secondary battery produced by the method for producing a negative electrode for a non-aqueous electrolyte secondary battery of the present invention is used as the negative electrode.

[0015] The present invention also provides a method for manufacturing a negative electrode for a non-aqueous electrolyte secondary battery, the method comprising the steps of: providing a negative electrode mixture layer containing a negative electrode active material on one or both sides of a current collector; and determining an interface resistance Rs (Ωcm) between the negative electrode mixture layer and the current collector. 2), the volume resistivity ρv (Ωcm) of the negative electrode mixture layer, and the thickness d (cm) of the negative electrode mixture layer to calculate the value of Rs / (ρv×d); and screening nonaqueous electrolyte secondary batteries to which the negative electrode for nonaqueous electrolyte secondary batteries is applied based on the value of Rs / (ρv×d).

[0016] In addition, the present invention provides a negative electrode for a non-aqueous electrolyte secondary battery having a negative electrode mixture layer containing a negative electrode active material on one or both sides of a current collector, the negative electrode mixture layer having an interface resistance Rs (Ωcm) between the negative electrode mixture layer and the current collector. 2 and a step of selecting nonaqueous electrolyte secondary batteries to which the negative electrode for nonaqueous electrolyte secondary batteries is applied, based on the relationship between Rs and d. [Effects of the Invention]

[0017] According to the present invention, it is possible to provide a non-aqueous electrolyte secondary battery having excellent charging load characteristics and a method for manufacturing the same, a negative electrode that can constitute the non-aqueous electrolyte secondary battery and a method for manufacturing the same, and a method for inspecting a negative electrode for manufacturing a non-aqueous electrolyte secondary battery. [Brief explanation of the drawings]

[0018] [Figure 1] 1 is a plan view schematically illustrating an example of a nonaqueous electrolyte secondary battery of the present invention. [Figure 2] FIG. 2 is a cross-sectional view taken along line II in FIG. DETAILED DESCRIPTION OF THE INVENTION

[0019] <Negative electrode for non-aqueous electrolyte secondary battery (hereinafter sometimes simply referred to as "negative electrode")> (Negative electrode of the first embodiment) The negative electrode for a non-aqueous electrolyte secondary battery according to the first aspect of the present invention has a negative electrode mixture layer containing a negative electrode active material on one or both sides of a current collector, and the ratio "Rs / (ρv×d)" of the interfacial resistance between the negative electrode mixture layer and the current collector (Rs) to the product of the volume resistivity (ρv) of the negative electrode mixture layer and the thickness (d) of the negative electrode mixture layer (ρv×d) falls within a specific range as shown below, depending on the thickness of the negative electrode mixture layer. In this case, the resistance value of the negative electrode is reduced, and therefore the charge load characteristics of a non-aqueous electrolyte secondary battery using this negative electrode (the non-aqueous electrolyte secondary battery of the present invention) can be improved.

[0020] (A) When the thickness of the negative electrode mixture layer is 35 μm or more and less than 50 μm, Rs / (ρv×d) is 5 or more and 20 or less (preferably 15 or less, and more preferably 10 or less).

[0021] (B) When the thickness of the negative electrode mixture layer is 50 μm or more and 100 μm or less, Rs / (ρv×d) is 10 or more and 38.5 or less (preferably 30 or less, and more preferably 20 or less).

[0022] Although the reason why the charge load characteristics of a non-aqueous electrolyte secondary battery are improved by adjusting the negative electrode as described above in (A) or (B) is unclear, it is believed to be as follows: In an electrode in which the resistance at the interface between the current collector and the mixture layer is much higher than the resistance of the mixture layer [i.e., Rs / (ρv×d) is much higher than 1] or much lower [i.e., Rs / (ρv×d) is much lower than 1], it is believed that the more conductive negative electrode active material (carbon material, etc.) contained in the mixture layer of that electrode, or the conductive additive used as needed, is not able to function efficiently as a component for ensuring conductivity in the negative electrode mixture layer. In contrast, in an electrode where the relationship between the resistance of the interface between the current collector and the mixture layer and the resistance of the mixture layer is within a certain range (for example, Rs / (ρv×d) is relatively close to 1), the more conductive negative electrode active material contained in the mixture layer of the electrode and the conductive additive used as needed function more efficiently as components to ensure conductivity in the negative electrode mixture layer, resulting in better electron conduction to the current collector. Therefore, it is speculated that adjusting the value of Rs / (ρv×d) of the negative electrode within a specific range can improve the charge load characteristics of nonaqueous electrolyte secondary batteries.

[0023] It is essentially preferable that the value of Rs / (ρv×d) be close to 1.0; however, in an actual negative electrode, it is extremely difficult to adjust the value of Rs / (ρv×d) to be close to 1.0. It has been found that by bringing this as close to 1.0 as possible, the charge load characteristics of the nonaqueous electrolyte secondary battery can be improved compared to when the value of Rs / (ρv×d) is extremely far from 1.0.

[0024] In the case of (A), the thickness of the negative electrode mixture layer is set to 35 μm or more because, when the thickness of the negative electrode mixture layer is thin, i.e., less than 35 μm, the charge load characteristics of the battery tend to be high regardless of the value of Rs / (ρv×d).

[0025] In the case of (B), the thickness of the anode mixture layer is set to 100 μm or less because, if the anode mixture layer is thicker than this, it becomes difficult to adjust the value of Rs / (ρv×d), which can make the charge load characteristics of the battery very good. Furthermore, as will be described later, the anode of the present invention is preferably produced via a step of applying to a current collector an anode mixture-containing composition in which the anode active material and the like are dispersed in a solvent, but it is not easy to form an anode mixture layer with a thickness of more than 100 μm while adjusting the value of Rs / (ρv×d) using such a production method.

[0026] In the case of (A), Rs is actually 0.002 Ωcm 2 or more, and 0.0025 Ωcm 2 In the above case, manufacturing becomes easier. In addition, Rs in the case of (A) is 0.01 Ωcm. 2 Preferably, it is 0.005 Ωcm or less. 2 More preferably, it is 0.003 Ωcm or less. 2 In the case of (A), ρv is preferably 0.02 Ωcm or more, more preferably 0.03 Ωcm or more, and even more preferably 0.04 Ωcm or more, and is preferably 0.5 Ωcm or less, more preferably 0.2 Ωcm or less, and even more preferably 0.1 Ωcm or less.

[0027] Furthermore, in the case of (B), Rs is actually 0.002 Ωcm 2 or more, and is 0.003Ωcm 2 In the above case, manufacturing becomes easier. In addition, Rs in the case of (B) is 0.02 Ωcm. 2 Preferably, it is 0.013 Ωcm or less. 2 In the case of (B), ρv is preferably 0.01 Ωcm or more, more preferably 0.02 Ωcm or more, and is preferably 0.4 Ωcm or less, more preferably 0.1 Ωcm or less, and particularly preferably 0.07 Ωcm or less.

[0028] (Negative electrode of second embodiment) The negative electrode for a non-aqueous electrolyte secondary battery according to the second aspect of the present invention has a negative electrode mixture layer containing a negative electrode active material on one or both sides of a current collector, and the interface resistance Rs (Ωcm) between the negative electrode mixture layer and the current collector is 2 ) and the thickness d (cm) of the negative electrode mixture layer satisfy the relationship Rs≦1.67d+b (where b is −0.01 or more and 0 or less, preferably −0.003 or less, and more preferably −0.005 or less). Although the reason for this is not clear, when Rs and d satisfy the above relationship, the resistance value at the interface between the current collector and the negative electrode mixture layer also decreases, and it is presumed that this will enable the charge load characteristics of a nonaqueous electrolyte secondary battery using this negative electrode (the nonaqueous electrolyte secondary battery of the present invention) to be improved.

[0029] In a negative electrode that satisfies the relationship Rs≦1.67d+b, the value of Rs is 0.002 Ω cm 2 It is preferable that the value of d is 0.01 cm (100 μm) or less. In a negative electrode that satisfies the relationship Rs≦1.67d+b, when Rs and d satisfy the above values, the effect of improving the charge load characteristics of a non-aqueous electrolyte secondary battery is more favorable.

[0030] In the negative electrode of the second embodiment, d is usually 0.0035 cm (35 μm) or more. Furthermore, since discharge capacity is improved, d is preferably 0.005 cm (50 μm) or more, and more preferably 0.006 cm (60 μm) or more. On the other hand, since manufacturing becomes difficult if d is too thick, d is usually 0.01 cm (100 μm) or less, preferably 95 μm or less, and more preferably 80 μm or less.

[0031] In the negative electrode of the second embodiment, the value of Rs is actually 0.002 Ω cm 2 or more, and is 0.003Ωcm 2 In the above case, the manufacturing becomes easier.

[0032] In the negative electrode of the second embodiment, from the viewpoint of improving the charge load characteristics of the nonaqueous electrolyte secondary battery, it is more preferable that Rs and d satisfy the relationship Rs≦1.67d−0.003.

[0033] Additionally, in the negative electrode of the second embodiment, from the viewpoint of further improving the charge load characteristics of the nonaqueous electrolyte secondary battery, it is particularly preferable that Rs and d satisfy the relationship Rs≦1.67d−0.005.

[0034] (Matters common to the negative electrode of the first embodiment and the negative electrode of the second embodiment) In both the first and second embodiments, the negative electrode of the present invention has a negative electrode mixture layer containing a negative electrode active material on one or both sides of a current collector.

[0035] The negative electrode active material can be any negative electrode active material used in the negative electrodes of conventional nonaqueous electrolyte secondary batteries, i.e., an active material capable of absorbing and releasing Li ions. Specific examples of such negative electrode active materials include graphite (natural graphite; artificial graphite obtained by graphitizing easily graphitizable carbons such as pyrolytic carbons, MCMB, and carbon fiber at 2800°C or higher; etc.), pyrolytic carbons, cokes, glassy carbons, fired bodies of organic polymer compounds, mesophase carbon microbeads, carbon fiber, activated carbon, soft carbon, hard carbon, and other carbon materials; and particles of metals that can be alloyed with lithium (e.g., Si, Sn), and materials containing these metals (e.g., alloys, oxides, etc.). The negative electrode may use only one of the above-listed negative electrode active materials, or two or more of them in combination.

[0036] The negative electrode mixture layer usually contains a binder, such as polyvinylidene fluoride (PVDF), polytetrafluoroethylene, polyacrylic acid, chitosan, styrene-butadiene rubber (SBR), or carboxymethyl cellulose (CMC).

[0037] The negative electrode mixture layer may contain a conductive additive. Examples of the conductive additive for the negative electrode mixture layer include graphite, amorphous carbon materials such as carbon black (acetylene black, ketjen black, etc.) and carbon materials having amorphous carbon formed on the surface, fibrous carbon (vapor-grown carbon fiber, carbon fiber obtained by spinning pitch and then carbonizing it, etc.), and carbon nanotubes (various multi-layer or single-layer carbon nanotubes). Only one of these may be used, or two or more may be used in combination.

[0038] The negative electrode current collector may be made of copper, copper alloy, nickel, or nickel alloy foil, punched metal, mesh, expanded metal, etc., but copper foil is usually used. The thickness of the negative electrode current collector is preferably, for example, 5 to 30 μm.

[0039] The thickness of the negative electrode mixture layer referred to in this specification means the average value (number average value) of thicknesses of the negative electrode mixture layer obtained at any 10 points in a field of view obtained by cutting out a cross section of the negative electrode and observing the cross section with a scanning electron microscope (SEM) at a magnification of 1000 times using an SEM scale.

[0040] As described above, the thickness of the negative electrode mixture layer means the thickness per one surface of the current collector. However, in the case of a negative electrode having an undercoat layer, which will be described later, the thickness of the negative electrode mixture layer means the total thickness of the undercoat layer formed on the current collector and the negative electrode mixture layer formed thereon.

[0041] Furthermore, the Rs and ρv of the negative electrode referred to in this specification refer to values ​​determined by the following method. The thickness of the negative electrode mixture layer is determined by the above method, and the thickness of the current collector is also determined by the same method. Then, using an electrode resistance measurement system "RM2610 (trade name)" manufactured by Hioki E.E. Corporation, the thickness (μm) and resistivity (Ωcm) of the negative electrode current collector and the thickness (μm) of the negative electrode mixture layer are input, and then the negative electrode, which is the measurement sample, is set in the system, and the probe is lowered to start measurement, thereby determining the interfacial resistance: Rs (Ωcm) between the negative electrode mixture layer and the current collector. 2) and the volume resistivity: ρv (Ωcm) of the negative electrode mixture layer are determined. During this measurement, the measurement speed is set to Normal, the voltage range is set to 0.5 V, and the maximum current value that makes the voltage V1 calculated by the system software 0.1 V or less is selected from among 50 mA, 10 mA, 1 mA, 100 μA, and 10 μA.

[0042] The resistivity (Ωcm) of the current collector input to the system is a known resistivity determined by the composition of the negative electrode current collector used. Furthermore, elemental analysis is performed on a current collector obtained from a portion of the negative electrode obtained from a battery to identify its composition, and the known resistivity is used. Furthermore, the negative electrode in the nonaqueous electrolyte secondary battery is removed from the outer casing of the discharged battery and washed multiple times with diethyl carbonate before the above measurements.

[0043] Furthermore, in this specification, Rs / (ρv×d) of the negative electrode means the average value (number average value) of the remaining five values ​​when Rs and ρv are measured at any 15 points on one measurement sample using the above-mentioned method and Rs / (ρv×d) is calculated, excluding the five points with the largest values ​​and the five points with the smallest values.

[0044] Furthermore, Rs in the negative electrode of the second embodiment means the average value (number average value) of the remaining five values ​​obtained by measuring Rs at any 15 points on one measurement sample using the above-mentioned method, excluding the five points with the largest values ​​and the five points with the smallest values.

[0045] The negative electrode can be obtained, for example, by dispersing a negative electrode mixture containing a negative electrode active material, a binder, and an optional conductive additive in an organic solvent such as water or N-methyl-2-pyrrolidone (NMP) to prepare a slurry or paste-like negative electrode mixture-containing composition (the binder may be dissolved in the solvent), applying this to one or both sides of a current collector, drying it, and, if necessary, subjecting it to a pressing process such as calendaring.

[0046] During the production of the negative electrode as described above, in the negative electrode of the first embodiment, the value of Rs / (ρv×d) is adjusted to a value according to the thickness of the negative electrode mixture layer, and in the negative electrode of the second embodiment, Rs and d are adjusted so as to satisfy the above-mentioned relationship.

[0047] Generally, rapid drying of a negative electrode mixture-containing composition after application to a current collector can result in migration of more conductive components, such as a more conductive negative electrode active material or conductive additive, in the coating film of the negative electrode mixture-containing composition. This tends to result in a higher content of the more conductive components on the surface of the resulting negative electrode mixture layer (the surface opposite the current collector) than in other portions of the negative electrode mixture layer. This phenomenon tends to increase the value of Rs, and as a result, the value of Rs / (ρv×d) tends to be significantly larger than 1.0. This phenomenon is particularly pronounced when the thickness of the negative electrode mixture layer is thick. Therefore, by minimizing the uneven concentration of the more conductive components in the negative electrode mixture layer due to migration of the more conductive components in the coating film of the negative electrode mixture-containing composition during drying, it is possible to reduce the value of Rs and adjust Rs and d to satisfy the above-mentioned relationship, or to adjust the value of Rs / (ρv×d) to fall within the above-mentioned range depending on the thickness of the negative electrode mixture layer.

[0048] Specifically, for example, when drying a coating of a negative electrode mixture-containing composition, in addition to drying at a constant temperature, methods include using multiple drying ovens to gradually increase the temperature of the ovens and dry slowly; leaving the evaporated solvent filled in the drying oven to delay drying of the surface; maintaining a uniform electrode temperature by preventing wind exposure and delaying surface drying as much as possible; blowing wind from the opposite side of the coated surface to delay surface drying as much as possible; drying by radiant heat using electromagnetic waves such as infrared rays (far infrared rays, near infrared rays, etc.); and applying heat directly to the uncoated side (foil side) using a guide roll or a metal plate like a hot plate. In particular, with a roll-to-roll method, the drying time can be easily changed by changing the length of the drying oven (the length of the path within the drying oven) and the coating speed. Furthermore, using multiple drying ovens to gradually increase the temperature of the drying ovens and dry slowly is effective in easily controlling uneven concentrations of the more conductive components in the negative electrode mixture layer.

[0049] It is also preferable to increase the viscosity of the anode mix-containing composition, which can reduce the concentration unevenness of the more conductive components in the anode mix layer and reduce the value of Rs, thereby adjusting Rs and d to satisfy the above-mentioned relationship, or adjusting the value of Rs / (ρv×d) to within the above-mentioned range depending on the thickness of the anode mix layer. Furthermore, depending on the type of anode mix, for example, a solids concentration (total concentration of all components excluding the solvent) of the anode mix-containing composition of approximately 52 to 60 mass% is preferable because it can prevent the components of the anode mix layer from migrating to the surface of the wet coating film when the coating film of the anode mix-containing composition is dried. However, the method of adjusting Rs and d to satisfy the above-mentioned relationship or adjusting Rs / (ρv×d) does not depend solely on the solids concentration of the anode mix-containing composition.

[0050] Furthermore, by forming an undercoat layer containing a conductive additive on the surface of the current collector in advance and then forming a negative electrode mixture layer thereon by the above-mentioned method (a method using a negative electrode mixture-containing composition), it is possible to adjust Rs and d so that they satisfy the above-mentioned relationship, and to adjust the value of Rs / (ρv×d) to fall within the above-mentioned range depending on the thickness of the negative electrode mixture layer.

[0051] In this case, the conductive additive contained in the undercoat layer may be the same as the various conductive additives exemplified above as those that can be contained in the negative electrode mixture layer. The undercoat layer may be formed using only the conductive additive, but may also contain a binder together with the conductive additive, and the same binder as the various binders exemplified above as those that can be contained in the negative electrode mixture layer may be used.

[0052] The undercoat layer preferably has a thickness of 50 to 1000 nm. In the undercoat layer, the content of the conductive additive is, for example, 1 to 100 mass %, and the content of the binder is, for example, 0 to 99 mass %.

[0053] The undercoat layer can be formed by applying an undercoat layer-forming composition (the binder may be dissolved in a solvent) prepared by dispersing a conductive additive and an optional binder in water or an organic solvent such as NMP to the surface of a current collector and drying the composition. In the case of a negative electrode having an undercoat layer, an anode mix-containing composition is applied to the surface of the undercoat layer formed on the surface of the current collector, and the anode mix layer is formed by the method described above. Alternatively, the undercoat layer and the anode mix layer can be simultaneously formed by applying an anode mix-containing composition over the undercoat layer-forming composition applied to the surface of the current collector without drying it (the coating film), followed by drying and, if necessary, pressing.

[0054] The content of the negative electrode active material in the negative electrode mixture layer is preferably 90 to 99 mass %.

[0055] The negative electrode mixture layer may contain a conductive additive. Examples of methods for this include dispersing the conductive additive throughout the negative electrode mixture layer; forming the undercoat layer; and dispersing the conductive additive throughout the negative electrode mixture layer and then forming the undercoat layer. When the negative electrode mixture layer contains a conductive additive, the content of the conductive additive in the negative electrode mixture layer (including the amount of conductive additive contained in the undercoat layer if the negative electrode has an undercoat layer) is preferably 0.01% by mass or more, more preferably 0.05% by mass or more, and even more preferably 0.08% by mass or more, and is preferably less than 9.5% by mass, more preferably less than 5.0% by mass, and even more preferably less than 3.0% by mass. The negative electrode mixture layer does not necessarily contain a conductive additive.

[0056] Increasing the amount of conductive additive in the negative electrode mixture layer can reduce the resistance of the negative electrode mixture layer, which tends to improve the charge load characteristics of the battery, but also tends to deteriorate the storage characteristics of the battery. However, in both the first and second aspects of the negative electrode of the present invention, the amount of conductive additive in the negative electrode mixture layer is limited as described above, which makes it possible to improve the charge load characteristics while suppressing deterioration in the storage characteristics of the battery.

[0057] Furthermore, the content of the binder in the negative electrode mixture layer (including the amount of binder contained in the undercoat layer when the negative electrode has an undercoat layer) is preferably 1 to 10 mass %.

[0058] If necessary, a lead body for electrically connecting the negative electrode to other members in the non-aqueous electrolyte secondary battery may be formed in a conventional manner.

[0059] <Nonaqueous electrolyte secondary battery> The nonaqueous electrolyte secondary battery of the present invention has a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and a nonaqueous electrolyte, and the negative electrode is the negative electrode for a nonaqueous electrolyte secondary battery of the present invention (the negative electrode of the first embodiment or the negative electrode of the second embodiment).

[0060] The positive electrode may have a structure in which a positive electrode mixture layer containing a positive electrode active material, a conductive additive, a binder, etc. is provided on one or both sides of a current collector.

[0061] The positive electrode active material is not particularly limited as long as it is a positive electrode active material used in conventionally known non-aqueous electrolyte secondary batteries, that is, an active material capable of absorbing and releasing Li ions. Specific examples of the positive electrode active material include LiM x Mn 2-x Spinel-type lithium manganese composite oxide represented by LiO4 (wherein M is at least one element selected from the group consisting of Li, B, Mg, Ca, Sr, Ba, Ti, V, Cr, Fe, Co, Ni, Cu, Al, Sn, Sb, In, Nb, Mo, W, Y, Ru, and Rh, and 0.01≦x≦0.5), Li x Ni (1-y-z) Mn y M z O (2-k) F l (wherein M is at least one element selected from the group consisting of Co, Mg, Al, B, Ti, V, Cr, Fe, Cu, Zn, Zr, Mo, Sn, Ca, Sr, Ba, and W, and 0.8≦x≦1.2, 0≦y≦0.5, 0≦z≦0.5, k+l<1, -0.1≦k≦0.2, 0≦l≦0.1), a layered compound represented by LiCo 1-x M x Lithium cobalt composite oxide represented by LiNiO2 (wherein M is at least one element selected from the group consisting of Al, Mg, Ti, Zr, Fe, Ni, Cu, Zn, Ga, Ge, Nb, Mo, Sn, Sb, and Ba, and 0≦x≦0.5), 1-x M x Lithium nickel composite oxide represented by LiM02 (wherein M is at least one element selected from the group consisting of Al, Mg, Ti, Zr, Fe, Co, Cu, Zn, Ga, Ge, Nb, Mo, Sn, Sb, Mn, and Ba, and 0≦x≦0.5) 1-x N xolivine-type composite oxides represented by Li4Ti5O4 (wherein M is at least one element selected from the group consisting of Fe, Mn, and Co, and N is at least one element selected from the group consisting of Al, Mg, Ti, Zr, Ni, Cu, Zn, Ga, Ge, Nb, Mo, Sn, Sb, and Ba, and 0≦x≦0.5); 12 Among these, only one kind may be used, or two or more kinds may be used in combination.

[0062] As the conductive additive for the positive electrode mixture layer, one or more of the same additives as those exemplified above as those that can be contained in the negative electrode mixture layer can be used.

[0063] For the binder of the positive electrode mixture layer, one or more of the same materials as those exemplified above as those that can be contained in the negative electrode mixture layer can be used.

[0064] The positive electrode is manufactured, for example, by preparing a paste or slurry positive electrode mixture-containing composition by dispersing a positive electrode active material, a conductive additive, a binder, etc. in a solvent such as an organic solvent such as NMP or water (however, the binder may be dissolved in the solvent), applying this to one or both sides of a current collector, drying, and then, if necessary, performing a pressing process such as a calendaring process. However, the positive electrode is not limited to one manufactured by the above manufacturing method, and may be one manufactured by other methods.

[0065] Furthermore, if necessary, a lead body for electrically connecting the positive electrode to other components in the non-aqueous electrolyte secondary battery may be formed in a conventional manner.

[0066] The thickness of the positive electrode mixture layer is preferably, for example, 35 to 80 μm per side of the current collector. The composition of the positive electrode mixture layer is, for example, preferably such that the amount of the positive electrode active material is 90 to 99.3 mass %, the amount of the conductive additive is 0.2 to 9.5 mass %, and the amount of the binder is 0.5 to 3 mass %.

[0067] The current collector of the positive electrode can be made of a metal foil such as aluminum or stainless steel, punched metal, mesh, expanded metal, foamed metal, carbon sheet, etc. The thickness of the current collector is preferably 5 to 30 μm.

[0068] The separator for a non-aqueous electrolyte secondary battery should have sufficient strength and be capable of retaining a large amount of non-aqueous electrolyte, and can be a microporous membrane made of polyolefin such as polyethylene (PE) or polypropylene (PP). The microporous membrane constituting the separator may be, for example, one made of only PE or only PP, or may contain an ethylene-propylene copolymer, or may be a laminate of a microporous membrane made of PE and a microporous membrane made of PP.

[0069] Furthermore, the separator may be a laminated type separator composed of a porous layer mainly made of a resin with a melting point of 140°C or lower and a porous layer mainly made of a resin with a melting point of 150°C or higher or an inorganic filler with a heat resistance temperature of 150°C or higher. Here, "melting point" refers to the melting temperature measured using a differential scanning calorimeter (DSC) in accordance with the provisions of Japanese Industrial Standards (JIS) K 7121, and "heat resistance temperature of 150°C or higher" means that no deformation such as softening is observed at least at 150°C.

[0070] The thickness of the separator (a separator made of a microporous polyolefin film or the laminated separator) is more preferably 10 to 30 μm.

[0071] A nonaqueous liquid electrolyte (nonaqueous electrolyte solution) is usually used as the nonaqueous electrolyte of a nonaqueous electrolyte secondary battery. The nonaqueous electrolyte solution is prepared by dissolving an electrolyte salt such as a lithium salt in an organic solvent. The organic solvent is not particularly limited, but examples thereof include chain esters such as dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, and methyl propyl carbonate; cyclic esters with high dielectric constants such as ethylene carbonate, propylene carbonate, butylene carbonate, and vinylene carbonate; and mixed solvents of chain esters and cyclic esters. Mixed solvents of chain esters as the main solvent and cyclic esters are particularly suitable.

[0072] Examples of electrolyte salts that can be dissolved in an organic solvent to prepare a non-aqueous electrolyte include LiPF6, LiBF4, LiAsF6, LiSbF6, LiCF3SO3, LiC4F9SO3, LiCF3CO2, Li2C2F4(SO3)2, and LiC n F 2n+1 SO3 (n≧2), LiN(RfSO2)(Rf'SO2), LiC(RfSO2)3, LiN(RfOSO2)2 (where Rf and Rf' are fluoroalkyl groups), etc. may be used alone or in combination. The concentration of the electrolyte salt in the nonaqueous electrolyte is not particularly limited, but is preferably 0.3 mol / L or more, more preferably 0.4 mol / L or more, and is preferably 1.7 mol / L or less, more preferably 1.5 mol / L or less.

[0073] In the nonaqueous electrolyte secondary battery, in addition to the nonaqueous electrolyte solution, a gel electrolyte obtained by gelling the nonaqueous electrolyte solution with a gelling agent made of a polymer or the like, or a known solid electrolyte can also be used as the nonaqueous electrolyte.

[0074] In the non-aqueous electrolyte secondary battery, the positive electrode and the negative electrode can be used in the form of a laminated electrode body in which they are laminated with a separator interposed therebetween, or in the form of a wound electrode body in which this laminated electrode body is wound.

[0075] 1 and 2 are diagrams schematically showing an example of a nonaqueous electrolyte secondary battery of the present invention, in which Fig. 1 is a plan view of the nonaqueous electrolyte secondary battery, and Fig. 2 is a cross-sectional view taken along line II in Fig. 1.

[0076] The nonaqueous electrolyte secondary battery 1 shown in Figures 1 and 2 houses an electrode assembly 2 in a laminate film exterior body 5 made of two metal laminate films, and the laminate film exterior body 5 is sealed at its outer periphery by heat-sealing the upper and lower metal laminate films.

[0077] The electrode body 2 is a laminated electrode body or a wound electrode body constructed by laminating a positive electrode, a negative electrode for a non-aqueous electrolyte secondary battery of the present invention, and a separator interposed therebetween, and the electrode body 2 and a non-aqueous electrolyte are enclosed in a laminate film outer casing 5.

[0078] In Figure 2, in order to avoid cluttering the drawing, the layers that make up the laminate film exterior body 5 and the components that make up the electrode body 2 (positive electrode, negative electrode, and separator) are not shown separately.

[0079] The positive electrode of the electrode body 2 is connected to a positive electrode external terminal 3 inside the battery 1, and although not shown, the negative electrode of the electrode body 2 is also connected to a negative electrode external terminal 4 inside the battery 1. One end of each of the positive electrode external terminal 3 and the negative electrode external terminal 4 is drawn out to the outside of the laminate film exterior body 5 so that they can be connected to external devices, etc.

[0080] A nonaqueous electrolyte secondary battery is manufactured by, for example, placing an electrode assembly, such as a laminated electrode assembly or a wound electrode assembly, into an exterior housing, injecting a nonaqueous electrolyte into the exterior housing to immerse the electrode assembly in the nonaqueous electrolyte, and then sealing the opening of the exterior housing. Examples of exterior housings that can be used include steel, aluminum, or aluminum alloy exterior cans, and exterior housings made of metal-deposited laminated films. More specific examples of batteries with exterior cans include flat (including coin and button) battery cases in which the exterior can and a sealing plate are crimped and sealed with a gasket or welded to each other; and cylindrical (cylindrical, rectangular, etc.) exterior cans with a bottom, in which a lid is placed over the opening and sealed with a gasket or by welding the exterior can and lid.

[0081] <Inspection method for negative electrodes for non-aqueous electrolyte secondary batteries> The value of Rs / (ρv×d) obtained for a negative electrode for a non-aqueous electrolyte secondary battery is an index of the charge load characteristics of a non-aqueous electrolyte secondary battery having this negative electrode. Therefore, for a negative electrode for a non-aqueous electrolyte secondary battery, the interfacial resistance Rs (Ωcm) between the negative electrode mixture layer and the current collector is 2 The inspection method of the present invention includes the steps of measuring the Rs / (ρv×d) value, the volume resistivity ρv (Ωcm) of the negative electrode mixture layer, and the thickness d (cm) of the negative electrode mixture layer to calculate the value of Rs / (ρv×d), and selecting nonaqueous electrolyte secondary batteries to which the negative electrode for nonaqueous electrolyte secondary batteries is applied based on the value of Rs / (ρv×d). Even if a negative electrode is determined by the inspection method of the present invention to have an Rs / (ρv×d) value that does not satisfy either of (A) or (B) and is therefore unusable for manufacturing the nonaqueous electrolyte secondary battery of the present invention, it can still be used for batteries that do not require high charging load characteristics, and can therefore be used for manufacturing such batteries.

[0082] Furthermore, the relationship between Rs and d required for a negative electrode for a non-aqueous electrolyte secondary battery is also an index of the charge load characteristics of a non-aqueous electrolyte secondary battery having this negative electrode. Therefore, for a negative electrode for a non-aqueous electrolyte secondary battery, the interfacial resistance Rs (Ωcm) between the negative electrode mixture layer and the current collector 2 The inspection method of the present invention includes the steps of measuring the Rs and d (cm) and the thickness d (cm) of the negative electrode mixture layer, and screening nonaqueous electrolyte secondary batteries to which the negative electrode for nonaqueous electrolyte secondary batteries is applied based on the determined relationship between Rs and d. Even if a negative electrode is determined by the inspection method of the present invention to be unsuitable for manufacturing the nonaqueous electrolyte secondary battery of the present invention because Rs and d do not satisfy the relationship [Rs≦1.67d (where b is −0.01 or more and 0 or less)], it can still be used for batteries that do not require high charging load characteristics, and can therefore be used for manufacturing such batteries. [Example]

[0083] The present invention will be described in detail below based on examples, but the present invention is not limited to these examples.

[0084] Example 1 <Preparation of positive electrode> Li 1.01 Ni 0.5 Co 0.2 Mn 0.3 O2 (positive electrode active material), acetylene black (conductive additive), and PVDF (binder) were mixed in a mass ratio of 94:4:2 and dispersed in NMP to prepare a positive electrode mixture-containing slurry (solid concentration excluding the solvent: 75 mass%).

[0085] This positive electrode mixture-containing slurry was intermittently applied to both sides of a 15 μm thick aluminum foil current collector, dried, and then calendered to adjust the thickness of the positive electrode mixture layer to a total thickness of 95 μm. This was cut to prepare a long positive electrode. Furthermore, aluminum lead pieces for extracting current were welded to the exposed portions of the aluminum foil to obtain a lead-attached positive electrode. The thickness of the positive electrode mixture layer in the obtained positive electrode was 40 μm per side of the current collector.

[0086] <Preparation of negative electrode> Graphite (negative electrode active material), CMC (binder), and SBR (binder) were mixed in a mass ratio of 96:2:2 and dispersed in water to prepare a paste containing a negative electrode mixture (solid concentration excluding the solvent: 50 mass %).

[0087] This negative electrode mixture-containing paste was intermittently applied to one side of an 8 μm-thick copper foil serving as a current collector. A drying furnace with three dryers was used, with the most upstream dryer 1 set to 115 °C, the middle dryer 2 set to 115 °C, and the most downstream dryer 3 set to 120 °C. A negative electrode mixture layer was formed by drying. The same procedure was then performed on the other side of the copper foil to form a negative electrode mixture layer on both sides of the copper foil. After drying, the negative electrode mixture layer was adjusted by calendering to a total thickness of 80 μm. This was cut to produce a long negative electrode. Furthermore, nickel leads for extracting current were welded to the exposed portions of the copper foil to obtain a leaded negative electrode. The thickness of the negative electrode mixture layer in the resulting negative electrode was 36 μm per side of the current collector.

[0088] <Preparation of non-aqueous electrolyte> LiPF6 was dissolved at a concentration of 1.0 mol / l in a solvent prepared by mixing ethylene carbonate and diethyl carbonate in a volume ratio of 3:7, and vinylene carbonate was further added in an amount to give a concentration of 2 mass % to prepare a non-aqueous electrolyte solution.

[0089] <Assembly of non-aqueous electrolyte secondary battery> The positive electrode and the negative electrode were stacked with a separator (a 16 μm thick, 40% porosity microporous membrane made of polyethylene) in between, and wound into a spiral to prepare a wound electrode body. The wound electrode body and the nonaqueous electrolyte solution were then enclosed in an aluminum laminate film exterior to prepare a nonaqueous electrolyte secondary battery.

[0090] Comparative Example 1 A negative electrode was produced in the same manner as in Example 1, except that the coating film of the negative electrode mixture-containing paste was dried using a drying furnace having three dryers, with the most upstream dryer 1 set to 120°C, the intermediate dryer 2 set to 120°C, and the most downstream dryer 3 set to 120°C. A nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1, except that this negative electrode was used.

[0091] The nonaqueous electrolyte secondary batteries of Example 1 and Comparative Example 1 were subjected to the following evaluation of charging load characteristics.

[0092] [Charging load characteristic evaluation] The batteries of Example 1 and Comparative Example 1 were CC charged at a current of 0.5 C up to 4.2 V in an environment of 25° C., followed by CV charging at a voltage of 4.2 V until the current reached 0.02 C. Thereafter, each battery was CC discharged at a current of 0.2 C in an environment of 25° C. until the voltage reached 2.75 V.

[0093] After discharging, each battery was placed in a thermostatic chamber adjusted to 35°C, and after the battery temperature stabilized, it was charged at a current of 2.5C and the voltage V1 was measured after 1 second. This voltage V1 was subtracted from the voltage before charging, V0, to calculate ΔV, which was used to evaluate the battery's charging load characteristics. The smaller this ΔV value, the greater the amount of electricity that can be charged before reaching the end voltage when CC charging at a large current such as 2.5C, and the better the battery's charging load characteristics can be said to be.

[0094] The evaluation results are shown in Table 1 together with the thickness of the negative electrode mixture layer in the negative electrode, 1.67d, Rs, ρv, and Rs / (ρv×d). In Table 1, the evaluation results of the charging load characteristics are shown as relative values ​​when the value of Comparative Example 1 is set to 100.

[0095] [Table 1]

[0096] As shown in Table 1, the nonaqueous electrolyte secondary battery of Example 1 had a negative electrode having a negative electrode mixture layer with a thickness of 35 μm or more and less than 50 μm, had an appropriate value of Rs / (ρv×d), and satisfied the relationship Rs≦1.67d+b(b=0). Compared to the battery of Comparative Example 1 using a negative electrode having an inappropriate value of Rs / (ρv×d) and not satisfying the relationship Rs≦1.67d+b(b=0), the battery had excellent charge load characteristics.

[0097] Example 2 A negative electrode was produced in the same manner as in Example 1, except that the amount of the negative electrode mixture-containing paste applied to the current collector was adjusted so that the thickness of the negative electrode mixture layer was 41 μm per side of the current collector. A nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1, except that this negative electrode was used.

[0098] Comparative Example 2 A negative electrode was produced in the same manner as in Comparative Example 1, except that the amount of the negative electrode mixture-containing paste applied to the current collector was adjusted so that the thickness of the negative electrode mixture layer was 40 μm per side of the current collector. A nonaqueous electrolyte secondary battery was produced in the same manner as in Comparative Example 1, except that this negative electrode was used.

[0099] The nonaqueous electrolyte secondary batteries of Example 2 and Comparative Example 2 were evaluated for charge load characteristics in the same manner as the battery of Example 1. The evaluation results are shown in Table 2 together with the thickness of the negative electrode mixture layer in the negative electrode, 1.67d, Rs, ρv, and Rs / (ρv×d). In Table 2, the charge load characteristic evaluation results are shown as relative values ​​when the value of Comparative Example 2 is set to 100.

[0100] [Table 2]

[0101] As shown in Table 2, the nonaqueous electrolyte secondary battery of Example 2 had a negative electrode having a negative electrode mixture layer with a thickness of 35 μm or more and less than 50 μm, had an appropriate value of Rs / (ρv×d), and satisfied the relationship Rs≦1.67d+b(b=0). Compared to the battery of Comparative Example 2 using a negative electrode having an inappropriate value of Rs / (ρv×d) and not satisfying the relationship Rs≦1.67d+b(b=0), the battery had excellent charge load characteristics.

[0102] Example 3 A negative electrode was produced in the same manner as in Example 1, except that the amount of the negative electrode mixture-containing paste applied to the current collector was adjusted so that the thickness of the negative electrode mixture layer was 45 μm per side of the current collector. A nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1, except that this negative electrode was used.

[0103] Example 4 A negative electrode was produced in the same manner as in Example 3, except that the coating film of the negative electrode mixture-containing paste was dried using a drying furnace having three dryers, with the most upstream dryer 1 set to 115°C, the middle dryer 2 set to 110°C, and the most downstream dryer 3 set to 115°C. The thickness of the negative electrode mixture layer in the obtained negative electrode was 46 μm per side of the current collector. A nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1, except that this negative electrode was used.

[0104] Comparative Example 3 A negative electrode was produced in the same manner as in Example 3, except that the coating film of the negative electrode mixture-containing paste was dried using a drying furnace having three dryers, with the most upstream dryer 1 set to 120°C, the middle dryer 2 set to 120°C, and the most downstream dryer 3 set to 120°C. The thickness of the negative electrode mixture layer in the obtained negative electrode was 47 μm per side of the current collector. A nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1, except that this negative electrode was used.

[0105] The nonaqueous electrolyte secondary batteries of Examples 3 and 4 and Comparative Example 3 were evaluated for charge load characteristics in the same manner as the battery of Example 1. The evaluation results are shown in Table 3 together with the thickness of the negative electrode mixture layer in the negative electrode, 1.67d, Rs, ρv, and Rs / (ρv×d). In Table 3, the charge load characteristic evaluation results are shown as relative values ​​when the value of Comparative Example 3 is set to 100.

[0106] [Table 3]

[0107] As shown in Table 3, the nonaqueous electrolyte secondary batteries of Examples 3 and 4 had negative electrodes each having a negative electrode mixture layer with a thickness of 35 μm or more and less than 50 μm, each having an appropriate value of Rs / (ρv×d), and satisfying the relationship Rs≦1.67d+b(b=0). These batteries had superior charging load characteristics compared to the battery of Comparative Example 3, which used a negative electrode having an inappropriate value of Rs / (ρv×d) and not satisfying the relationship Rs≦1.67d+b(b=0).

[0108] Example 5 A negative electrode was produced in the same manner as in Example 1, except that the current collector was changed to a copper foil with a thickness of 6 μm and the amount of the negative electrode mixture-containing paste applied to the current collector was adjusted to make the thickness of the negative electrode mixture layer 56 μm per side of the current collector. A nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1, except that this negative electrode was used.

[0109] Example 6 A negative electrode was produced in the same manner as in Example 5, except that the coating film of the negative electrode mixture-containing paste was dried using a drying furnace having three dryers, with the most upstream dryer 1 set to 115°C, the intermediate dryer 2 set to 110°C, and the most downstream dryer 3 set to 115°C. A nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1, except that this negative electrode was used.

[0110] Comparative Example 4 A negative electrode was produced in the same manner as in Example 5, except that the coating film of the negative electrode mixture-containing paste was dried using a drying furnace having three dryers, with the most upstream dryer 1 set to 120°C, the intermediate dryer 2 set to 120°C, and the most downstream dryer 3 set to 120°C. A nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1, except that this negative electrode was used.

[0111] For the nonaqueous electrolyte secondary batteries of Examples 5 and 6 and Comparative Example 4, the charge load characteristics were evaluated in the same manner as for the battery of Example 1, except that the end voltage during CC discharge in the initial CC charge-CV charge-CC discharge cycle was changed to 3 V. These evaluation results are shown in Table 4, along with the thickness of the negative electrode mixture layer in the negative electrode, 1.67d, Rs, ρv, and Rs / (ρv×d). In Table 4, the charge load characteristics evaluation results are shown as relative values, with the value for Comparative Example 4 set to 100.

[0112] [Table 4]

[0113] As shown in Table 4, the nonaqueous electrolyte secondary batteries of Examples 5 and 6 had negative electrodes each having a negative electrode mixture layer with a thickness of 50 μm or more and 100 μm or less, each having an appropriate value of Rs / (ρv×d), and satisfying the relationship Rs≦1.67d+b(b=0). These batteries had superior charging load characteristics compared to the battery of Comparative Example 4, which used a negative electrode having an inappropriate value of Rs / (ρv×d) and not satisfying the relationship Rs≦1.67d+b(b=0).

[0114] Example 7 A negative electrode was fabricated in the same manner as in Example 1, except that the amount of negative electrode mixture-containing paste applied to the current collector was changed, and the coating of the negative electrode mixture-containing paste was dried using a drying furnace having three dryers, with the most upstream dryer 1 set to 115°C, the middle dryer 2 set to 110°C, and the most downstream dryer 3 set to 120°C. The thickness of the negative electrode mixture layer in the resulting negative electrode was 63 μm per side of the current collector. A nonaqueous electrolyte secondary battery was then fabricated in the same manner as in Example 1, except that this negative electrode was used.

[0115] Comparative Example 5 A negative electrode was produced in the same manner as in Example 7, except that the coating film of the negative electrode mixture-containing paste was dried using a drying furnace having three dryers, with the most upstream dryer 1 set to 120°C, the intermediate dryer 2 set to 120°C, and the most downstream dryer 3 set to 120°C. A nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1, except that this negative electrode was used.

[0116] The nonaqueous electrolyte secondary batteries of Example 7 and Comparative Example 5 were evaluated for charge load characteristics in the same manner as the battery of Example 5. The evaluation results are shown in Table 5 together with the thickness of the negative electrode mixture layer in the negative electrode, 1.67d, Rs, ρv, and Rs / (ρv×d). In Table 5, the charge load characteristic evaluation results are shown as relative values ​​when the value of Comparative Example 5 is set to 100.

[0117] [Table 5]

[0118] As shown in Table 5, the nonaqueous electrolyte secondary battery of Example 7 had a negative electrode having a negative electrode mixture layer with a thickness of 50 μm or more and 100 μm or less, had an appropriate value of Rs / (ρv×d), and satisfied the relationship Rs≦1.67d+b(b=0). Thus, the battery had better charge load characteristics than the battery of Comparative Example 5, which used a negative electrode having an inappropriate value of Rs / (ρv×d) and not satisfying the relationship Rs≦1.67d+b(b=0).

[0119] Example 8 A negative electrode was produced in the same manner as in Example 1, except that the amount of the negative electrode mixture-containing paste applied to the current collector was adjusted so that the thickness of the negative electrode mixture layer was 68 μm per side of the current collector. A nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1, except that this negative electrode was used.

[0120] Example 9 A negative electrode was produced in the same manner as in Example 8, except that the coating film of the negative electrode mixture-containing paste was dried using a drying furnace having three dryers, with the most upstream dryer 1 set to 115°C, the intermediate dryer 2 set to 110°C, and the most downstream dryer 3 set to 115°C. A nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1, except that this negative electrode was used.

[0121] Example 10 A negative electrode was produced in the same manner as in Example 8, except that the coating film of the negative electrode mixture-containing paste was dried using a drying furnace having three dryers, with the most upstream dryer 1 set to 110°C, the intermediate dryer 2 set to 105°C, and the most downstream dryer 3 set to 115°C. A nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1, except that this negative electrode was used.

[0122] Comparative Example 6 A negative electrode was produced in the same manner as in Example 8, except that the coating film of the negative electrode mixture-containing paste was dried using a drying furnace having three dryers, with the most upstream dryer 1 set to 120°C, the intermediate dryer 2 set to 120°C, and the most downstream dryer 3 set to 120°C. A nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1, except that this negative electrode was used.

[0123] The nonaqueous electrolyte secondary batteries of Examples 8 to 10 and Comparative Example 6 were evaluated for charging load characteristics in the same manner as the battery of Example 5. The evaluation results are shown in Table 6 together with the thickness of the negative electrode mixture layer in the negative electrode, 1.67d, Rs, ρv, and Rs / (ρv×d). In Table 6, the charging load characteristic evaluation results are shown as relative values ​​when the value of Comparative Example 6 is set to 100.

[0124] [Table 6]

[0125] As shown in Table 6, the nonaqueous electrolyte secondary batteries of Examples 8 to 10 had negative electrodes each having a negative electrode mixture layer with a thickness of 50 μm or more and 100 μm or less, and each had an appropriate value of Rs / (ρv×d) and satisfied the relationship Rs≦1.67d+b(b=0). These batteries had superior charging load characteristics compared to the battery of Comparative Example 6, which used a negative electrode having an inappropriate value of Rs / (ρv×d) and not satisfying the relationship Rs≦1.67d+b(b=0).

[0126] Example 11 A negative electrode was produced in the same manner as in Example 1, except that the amount of negative electrode mixture-containing paste applied to the current collector was changed, and the coating film of the negative electrode mixture-containing paste was dried using a drying furnace having three dryers, with the most upstream dryer 1 set to 115°C, the middle dryer 2 set to 110°C, and the most downstream dryer 3 set to 120°C. The thickness of the negative electrode mixture layer in the obtained negative electrode was 73 μm per side of the current collector. A nonaqueous electrolyte secondary battery was then produced in the same manner as in Example 1, except that this negative electrode was used.

[0127] Comparative Example 7 A negative electrode was produced in the same manner as in Example 11, except that the coating film of the negative electrode mixture-containing paste was dried using a drying furnace having three dryers, with the most upstream dryer 1 set to 120°C, the intermediate dryer 2 set to 120°C, and the most downstream dryer 3 set to 120°C. A nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1, except that this negative electrode was used.

[0128] The nonaqueous electrolyte secondary batteries of Example 11 and Comparative Example 7 were evaluated for charge load characteristics in the same manner as the battery of Example 5. The evaluation results are shown in Table 7 together with the thickness of the negative electrode mixture layer in the negative electrode, 1.67d, Rs, ρv, and Rs / (ρv×d). In Table 7, the charge load characteristic evaluation results are shown as relative values ​​when the value of Comparative Example 7 is set to 100.

[0129] [Table 7]

[0130] As shown in Table 7, the nonaqueous electrolyte secondary battery of Example 11 had a negative electrode having a negative electrode mixture layer with a thickness of 50 μm or more and 100 μm or less, had an appropriate value of Rs / (ρv×d), and satisfied the relationship Rs≦1.67d+b(b=0). Compared to the battery of Comparative Example 7 using a negative electrode having an inappropriate value of Rs / (ρv×d) and not satisfying the relationship Rs≦1.67d+b(b=0), the battery had excellent charge load characteristics.

[0131] Example 12 A negative electrode was produced in the same manner as in Example 5, except that the amount of negative electrode mixture-containing paste applied to the current collector was changed, and the coating film of the negative electrode mixture-containing paste was dried using a drying furnace having three dryers, with the most upstream dryer 1 set to 115°C, the middle dryer 2 set to 110°C, and the most downstream dryer 3 set to 120°C. The thickness of the negative electrode mixture layer in the obtained negative electrode was 77 μm per side of the current collector. A nonaqueous electrolyte secondary battery was then produced in the same manner as in Example 1, except that this negative electrode was used.

[0132] Comparative Example 8 A negative electrode was produced in the same manner as in Example 12, except that the coating film of the negative electrode mixture-containing paste was dried using a drying furnace having three dryers, with the most upstream dryer 1 set to 120°C, the intermediate dryer 2 set to 120°C, and the most downstream dryer 3 set to 120°C. A nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1, except that this negative electrode was used.

[0133] For the nonaqueous electrolyte secondary batteries of Example 12 and Comparative Example 8, the charge load characteristics were evaluated in the same manner as for the battery of Example 1, except that the end voltage during CC charge in the initial CC charge-CV charge-CC discharge cycle was changed to 4.4 V. These evaluation results are shown in Table 8, along with the thickness of the negative electrode mixture layer in the negative electrode, 1.67d, Rs, ρv, and Rs / (ρv×d). In Table 8, the charge load characteristics evaluation results are shown as relative values, with the value for Comparative Example 8 set to 100.

[0134] [Table 8]

[0135] As shown in Table 8, the nonaqueous electrolyte secondary battery of Example 12 had a negative electrode having a negative electrode mixture layer with a thickness of 50 μm or more and 100 μm or less, had an appropriate value of Rs / (ρv×d), and satisfied the relationship Rs≦1.67d+b(b=0). Thus, the battery had better charge load characteristics than the battery of Comparative Example 8, which used a negative electrode having an inappropriate value of Rs / (ρv×d) and not satisfying the relationship Rs≦1.67d+b(b=0).

[0136] Example 13 A negative electrode was produced in the same manner as in Example 5, except that the amount of the negative electrode mixture-containing paste applied to the current collector was adjusted so that the thickness of the negative electrode mixture layer was 80 μm per side of the current collector. A nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1, except that this negative electrode was used.

[0137] Example 14 A negative electrode was produced in the same manner as in Example 13, except that the coating film of the negative electrode mixture-containing paste was dried using a drying furnace having three dryers, with the most upstream dryer 1 set to 115°C, the intermediate dryer 2 set to 110°C, and the most downstream dryer 3 set to 115°C. A nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1, except that this negative electrode was used.

[0138] Example 15 A negative electrode was produced in the same manner as in Example 13, except that the coating film of the negative electrode mixture-containing paste was dried using a drying furnace having three dryers, with the most upstream dryer 1 set to 110°C, the intermediate dryer 2 set to 105°C, and the most downstream dryer 3 set to 115°C. A nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1, except that this negative electrode was used.

[0139] Example 16 A composition for forming an undercoat layer was prepared by dispersing vapor-grown carbon fiber (conductive additive) and chitosan (binder) in a mass ratio of 30:70 in NMP. The composition was applied to both sides of the same current collector (copper foil) as used in Example 1 and dried to form an undercoat layer with a thickness of 0.5 μm on each side of the current collector.

[0140] A negative electrode was fabricated in the same manner as in Example 13, except that the current collector on which the undercoat layer was formed was used, and the coating film of the negative electrode mixture-containing paste was dried using a drying furnace having three dryers, with the most upstream dryer 1 set to 120°C, the middle dryer 2 set to 120°C, and the most downstream dryer 3 set to 120°C. A nonaqueous electrolyte secondary battery was fabricated in the same manner as in Example 1, except that this negative electrode was used. The thickness of the negative electrode mixture layer, including the undercoat layer, was 80 μm per side of the current collector, and the composition of the negative electrode mixture layer, including the undercoat layer, was 95.7% by mass of negative electrode active material, 0.1% by mass of conductive additive, and 4.2% by mass of binder.

[0141] Example 17 A negative electrode mixture-containing paste prepared in the same manner as in Example 1 was used, except that the solids concentration excluding the solvent was 53% by mass, and the coating film of this negative electrode mixture-containing paste was dried using a drying furnace having three dryers, with the most upstream dryer 1 set to 120°C, the middle dryer 2 set to 120°C, and the most downstream dryer 3 set to 120°C, respectively. Except for this, a negative electrode was produced in the same manner as in Example 13. Then, a nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1, except that this negative electrode was used.

[0142] Example 18 Graphite (negative electrode active material), CMC (binder), SBR (binder), and Timcal's "SUPER-C45 (trade name)" as a conductive additive were mixed in a mass ratio of 95:2:2:1 and dispersed in water to prepare a negative electrode mixture-containing paste (solid concentration excluding solvent: 44% by mass). Then, using this negative electrode mixture-containing paste, the coating film of the negative electrode mixture-containing paste was dried using a drying furnace having three dryers, with the most upstream dryer 1 set to 120 ° C, the middle dryer 2 set to 120 ° C, and the most downstream dryer 3 set to 120 ° C. A negative electrode was produced in the same manner as in Example 13. Furthermore, a nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1, except that this negative electrode was used.

[0143] Comparative Example 9 A negative electrode was produced in the same manner as in Example 13, except that the coating film of the negative electrode mixture-containing paste was dried using a drying furnace having three dryers, with the most upstream dryer 1 set to 120°C, the intermediate dryer 2 set to 120°C, and the most downstream dryer 3 set to 120°C. A nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1, except that this negative electrode was used.

[0144] For the nonaqueous electrolyte secondary batteries of Examples 13 to 18 and Comparative Example 9, the charge load characteristics were evaluated in the same manner as for the battery of Example 1, except that the end voltage during CC charge in the initial CC charge-CV charge-CC discharge cycle was changed to 4.35 V and the end voltage during CC discharge was changed to 3 V. These evaluation results are shown in Table 9, along with the thickness of the negative electrode mixture layer in the negative electrode, 1.67d, Rs, ρv, and Rs / (ρv×d). In Table 9, the charge load characteristics evaluation results are shown as relative values ​​when the value for Comparative Example 9 is set to 100.

[0145] [Table 9]

[0146] As shown in Table 9, the nonaqueous electrolyte secondary batteries of Examples 13 to 18 had negative electrodes each having a negative electrode mixture layer with a thickness of 50 μm or more and 100 μm or less, had an appropriate value of Rs / (ρv×d), and satisfied the relationship Rs≦1.67d+b(b=0). These batteries had superior charging load characteristics compared to the battery of Comparative Example 9, which used a negative electrode having an inappropriate value of Rs / (ρv×d) and not satisfying the relationship Rs≦1.67d+b(b=0).

[0147] Example 19 A negative electrode was produced in the same manner as in Example 1, except that the amount of the negative electrode mixture-containing paste applied to the current collector was adjusted so that the thickness of the negative electrode mixture layer was 91 μm per side of the current collector. A nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1, except that this negative electrode was used.

[0148] Example 20 A negative electrode was produced in the same manner as in Example 19, except that the coating film of the negative electrode mixture-containing paste was dried using a drying furnace having three dryers, with the most upstream dryer 1 set to 115°C, the intermediate dryer 2 set to 110°C, and the most downstream dryer 3 set to 120°C. A nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1, except that this negative electrode was used.

[0149] Example 21 A negative electrode was produced in the same manner as in Example 19, except that the coating film of the negative electrode mixture-containing paste was dried using a drying furnace having three dryers, with the most upstream dryer 1 set to 115°C, the intermediate dryer 2 set to 110°C, and the most downstream dryer 3 set to 115°C. Except for this, a nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1, except that this negative electrode was used.

[0150] Example 22 A negative electrode was produced in the same manner as in Example 19, except that the coating film of the negative electrode mixture-containing paste was dried using a drying furnace having three dryers, with the most upstream dryer 1 set to 110°C, the intermediate dryer 2 set to 105°C, and the most downstream dryer 3 set to 115°C. A nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1, except that this negative electrode was used.

[0151] Comparative Example 10 A negative electrode was produced in the same manner as in Example 19, except that the coating film of the negative electrode mixture-containing paste was dried using a drying furnace having three dryers, with the most upstream dryer 1 set to 120°C, the intermediate dryer 2 set to 120°C, and the most downstream dryer 3 set to 120°C. A nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1, except that this negative electrode was used.

[0152] The nonaqueous electrolyte secondary batteries of Examples 19 to 22 and Comparative Example 10 were evaluated for charge load characteristics in the same manner as the battery of Example 5. The evaluation results are shown in Table 10 together with the thickness of the negative electrode mixture layer in the negative electrode, 1.67d, Rs, ρv, and Rs / (ρv×d). In Table 10, the charge load characteristic evaluation results are shown as relative values ​​when the value of Comparative Example 10 is set to 100.

[0153] [Table 10]

[0154] As shown in Table 10, the nonaqueous electrolyte secondary batteries of Examples 19 to 22 had negative electrodes each having a negative electrode mixture layer with a thickness of 50 μm or more and 100 μm or less, and each had an appropriate value of Rs / (ρv×d) and satisfied the relationship Rs≦1.67d+b(b=0). These batteries had superior charging load characteristics compared to the battery of Comparative Example 10, which used a negative electrode having an inappropriate value of Rs / (ρv×d) and not satisfying the relationship Rs≦1.67d+b(b=0).

[0155] The present invention can be implemented in other forms without departing from the spirit of the present invention. The embodiments disclosed in this application are merely examples, and the present invention is not limited to these embodiments. The scope of the present invention shall be interpreted in accordance with the appended claims rather than the description in the above specification, and all modifications within the scope of the claims are included in the scope of the claims. [Industrial Applicability]

[0156] As described above, the nonaqueous electrolyte secondary battery of the present invention has excellent charge load characteristics, and by taking advantage of these characteristics, it can be preferably used in applications requiring particularly rapid charge characteristics, and can also be used in the same applications as those in which conventionally known nonaqueous electrolyte secondary batteries are used. Furthermore, the negative electrode for a nonaqueous electrolyte secondary battery of the present invention can constitute the nonaqueous electrolyte secondary battery of the present invention. [Explanation of symbols]

[0157] 1 Non-aqueous electrolyte secondary battery 2 Electrode body 3 Positive external terminal 4 Negative external terminal 5 Laminated film exterior

Claims

1. A negative electrode for a non-aqueous electrolyte secondary battery, comprising a current collector having a negative electrode mixture layer containing a negative electrode active material on one or both sides thereof, the thickness of the negative electrode mixture layer per one surface of the current collector is 35 μm or more and less than 50 μm, The interface resistance between the negative electrode mixture layer and the current collector is Rs (Ωcm ２ a volume resistivity of the negative electrode mixture layer is ρv (Ωcm), and a thickness of the negative electrode mixture layer is d (cm), where Rs / (ρv×d) is 5 to 20.

2. A negative electrode for a non-aqueous electrolyte secondary battery, comprising a current collector having a negative electrode mixture layer containing a negative electrode active material on one or both sides thereof, the thickness of the negative electrode mixture layer per one surface of the current collector is 50 μm or more and 100 μm or less, The interface resistance between the negative electrode mixture layer and the current collector is Rs (Ωcm ２ a volume resistivity of the negative electrode mixture layer is ρv (Ωcm), and a thickness of the negative electrode mixture layer is d (cm), where Rs / (ρv×d) is 10 to 38.

5.

3. A negative electrode for a non-aqueous electrolyte secondary battery, comprising a current collector having a negative electrode mixture layer containing a negative electrode active material on one or both sides thereof, The interface resistance between the negative electrode mixture layer and the current collector is Rs (Ωcm ２ ) and the thickness of the negative electrode mixture layer is d (cm), the relationship Rs≦1.67d+b (where b is −0.01 or more and 0 or less) is satisfied.

4. 4. The negative electrode for a non-aqueous electrolyte secondary battery according to claim 3, wherein d is 100 μm or less.

5. The Rs is 0.002 Ω cm ２ 5. The negative electrode for a non-aqueous electrolyte secondary battery according to claim 3 or 4.

6. 6. The negative electrode for a non-aqueous electrolyte secondary battery in accordance with claim 3, wherein b is −0.01 or more and −0.003 or less.

7. 6. The negative electrode for a non-aqueous electrolyte secondary battery in accordance with claim 3, wherein b is −0.01 or more and −0.005 or less.

8. A non-aqueous electrolyte secondary battery having a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte, A non-aqueous electrolyte secondary battery, wherein the negative electrode is the negative electrode for a non-aqueous electrolyte secondary battery according to any one of claims 1 to 7.

9. When forming a negative electrode mixture layer containing a negative electrode active material on one or both surfaces of a current collector, The thickness of the negative electrode mixture layer per one surface of the current collector is set to 35 μm or more and less than 50 μm, The interface resistance between the negative electrode mixture layer and the current collector is Rs (Ωcm ２ a volume resistivity of the negative electrode mixture layer is ρv (Ωcm), and a thickness of the negative electrode mixture layer is d (cm), the ratio Rs / (ρv×d) being adjusted to 5 to 20.

10. When forming a negative electrode mixture layer containing a negative electrode active material on one or both surfaces of a current collector, The thickness of the negative electrode mixture layer per one surface of the current collector is set to 50 μm or more and 100 μm or less, The interface resistance between the negative electrode mixture layer and the current collector is Rs (Ωcm ２ a volume resistivity of the negative electrode mixture layer is ρv (Ωcm), and a thickness of the negative electrode mixture layer is d (cm), the ratio Rs / (ρv×d) being adjusted to 10 to 38.

5.

11. When forming a negative electrode mixture layer containing a negative electrode active material on one or both surfaces of a current collector, The interface resistance between the negative electrode mixture layer and the current collector is Rs (Ωcm ２ ) and adjusting the thickness of the negative electrode mixture layer to satisfy the relationship Rs≦1.67d+b (where b is −0.01 or more and 0 or less), where d (cm) is the thickness of the negative electrode mixture layer.

12. A method for producing a non-aqueous electrolyte secondary battery, the method comprising the steps of: producing a non-aqueous electrolyte secondary battery having a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte; and using, as the negative electrode, a negative electrode for a non-aqueous electrolyte secondary battery produced by the method for producing a negative electrode for a non-aqueous electrolyte secondary battery according to any one of claims 9 to 11.

13. A method for inspecting a negative electrode for a non-aqueous electrolyte secondary battery, the negative electrode having a negative electrode mixture layer containing a negative electrode active material on one or both sides of a current collector, comprising: For the negative electrode for a non-aqueous electrolyte secondary battery, the interface resistance Rs (Ωcm) between the negative electrode mixture layer and the current collector ２ ), the volume resistivity ρv (Ωcm) of the negative electrode mixture layer, and the thickness d (cm) of the negative electrode mixture layer, and calculate the value of Rs / (ρv×d); and selecting nonaqueous electrolyte secondary batteries to which the negative electrode for nonaqueous electrolyte secondary batteries is applied based on the value of Rs / (ρv×d).

14. A method for inspecting a negative electrode for a non-aqueous electrolyte secondary battery, the negative electrode having a negative electrode mixture layer containing a negative electrode active material on one or both sides of a current collector, comprising: For the negative electrode for a non-aqueous electrolyte secondary battery, the interface resistance Rs (Ωcm) between the negative electrode mixture layer and the current collector ２ ) and a step of measuring a thickness d (cm) of the negative electrode mixture layer; and selecting nonaqueous electrolyte secondary batteries to which the negative electrode for nonaqueous electrolyte secondary batteries is applied based on the relationship between Rs and d.

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