Electricity storage device

Abstract

Provided is a highly safe power storage device in which deposition of lithium metal is suppressed while maintaining capacity retention rate and high-rate characteristics. In the electricity storage device, the film thickness of the positive electrode mixture layer is 40 [mu] m or more, and the film thickness of the negative electrode mixture layer is 50 [mu] m or more. Furthermore, the binder content in the positive electrode alloy layer is 0.1-5.0 wt% when the solid content weight of the entire positive electrode alloy layer is 100 wt%, and the binder content in the negative electrode alloy layer is 1.0-12.0 wt% when the solid content weight of the entire negative electrode alloy layer is 100 wt%.

Description

Technical Field

[0001] The present invention relates to an electric storage device. Background Art

[0002] The storage devices such as lithium-ion secondary batteries, nickel-metal hydride batteries and other secondary batteries or capacitors are light and have high energy density, so they can be used as power sources for portable devices such as personal computers and mobile terminals, and high-output power sources such as vehicle drive power sources for electric vehicles (EVs). The electrodes provided by such storage devices include a collector foil and a composite material layer formed on the surface of the collector foil. The composite material layer is mainly composed of active materials. In addition, typically, the composite material layer includes a conductive additive and a binder (adhesive). The adhesive helps to maintain the electrode structure such as the bonding of the active material to the collector foil and the bonding of the active materials to each other.

[0003] However, with the expansion and development of applications, it is required that power storage devices can be charged (or discharged) with a large current in a short time, and power storage devices with excellent rapid charge and discharge characteristics (i.e., high-rate characteristics) have been developed. Japanese Patent Publication No. 2014-10888 discloses a non-aqueous electrolytic secondary battery in which the resistance difference between the positive electrode and the negative electrode is reduced in order to improve the high-rate characteristics.

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent Application Publication No. 2014-10888 Summary of the invention

[0007] On the other hand, there is a demand for further high capacity of power storage devices. For example, a technology for achieving high capacity of power storage devices by thickening the composite material layer of the negative electrode compared to the past is used. For such thick composite layer electrodes, in order to improve high rate characteristics, research has been conducted on the use of the technology described in the above-mentioned Japanese Patent Publication No. 2014-10888.

[0008] However, the inventors have found that the capacity retention rate after cycling is significantly reduced in the technique described in Japanese Unexamined Patent Publication No. 2014-10888. In addition, in an electrode with a thick negative electrode composite layer, there is a concern that metal (such as metal lithium) as a charge carrier may precipitate during charging.

[0009] The present disclosure has been made in view of the above circumstances, and a main object of the present disclosure is to provide a highly safe power storage device that maintains the capacity retention rate and the high rate characteristics and suppresses the deposition of metallic lithium.

[0010] The power storage device disclosed herein comprises a positive electrode having a positive electrode composite layer, a negative electrode having a negative electrode composite layer, and a separator sandwiched between the positive electrode and the negative electrode. In addition, the film thickness of the positive electrode composite layer is 40 μm or more, and the film thickness of the negative electrode composite layer is 50 μm or more. When the solid content weight of the positive electrode composite layer as a whole is set to 100 weight%, the binder content in the positive electrode composite layer is 0.1 weight% to 5.0 weight%, and when the solid content weight of the negative electrode composite layer as a whole is set to 100 weight%, the binder content in the negative electrode composite layer is 1.0 weight% to 12.0 weight%.

[0011] According to the power storage device, the resistance value of the negative electrode increases, and the reactivity of the charge carriers (such as lithium ions, etc.) in the negative electrode composite layer decreases. As a result, when the charge carriers move from the positive electrode to the negative electrode during charging, the charge carriers can be uniformly absorbed in the entire negative electrode composite layer. As a result, the precipitation of metals (such as metallic lithium, etc.) as charge carriers can be suppressed. In addition, the resistance value of the positive electrode is reduced, and the capacity retention rate after the charge and discharge cycle can be kept high. The above effects can take into account both the improvement of the high-rate characteristics and the high capacity of the power storage device.

[0012] In the electric storage device of one embodiment disclosed herein, the resistance value (A) of the positive electrode is 1 Ω / cm 2 ~30Ω / cm 2 The resistance value (B) of the negative electrode is 3Ω / cm 2 ~90Ω / cm 2 , and the formula is satisfied: 2≤B / A≤10. Thus, the high rate characteristics and the capacity retention rate can be more reliably maintained at a high level.

[0013] In a storage device disclosed herein, the binder contained in the positive electrode composite layer is PVDF, and the binder contained in the negative electrode composite layer is SBR and / or CMC. Thus, the resistance value of the storage device is appropriately controlled. The above effect can more reliably take into account the high capacity of the storage device and the suppression of the precipitation of metals as charge carriers. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 It is a schematic cross-sectional view of a lithium ion secondary battery according to one embodiment disclosed herein.

[0015] Figure 2 It is an exploded perspective view schematically showing a stacked electrode body according to one embodiment disclosed herein.

[0016] Figure 3 : is a schematic cross-sectional view of a stacked electrode body according to one embodiment disclosed herein.

[0017] Explanation of symbols

[0018] 1 Lithium-ion secondary battery

[0019] 10 Battery housing

[0020] 11 Battery housing body

[0021] 12 Sealing plate

[0022] 13 Safety valve

[0023] 14 Positive external terminal

[0024] 15 Negative external terminal

[0025] 16 Positive internal terminal

[0026] 17 Negative internal terminal

[0027] 20 Electrode body

[0028] 30 positive electrode

[0029] 31 Positive electrode composite layer

[0030] 31a Positive electrode composite material layer non-forming part

[0031] 32. Positive electrode collector foil

[0032] 35. Positive electrode active material

[0033] 40 Negative electrode

[0034] 41 Negative electrode composite layer

[0035] 41a Negative electrode composite material layer non-forming part

[0036] 42. Negative electrode collector foil

[0037] 45 Negative electrode active material

[0038] 50 Isolation

[0039] 60 Adhesives DETAILED DESCRIPTION

[0040] <Definition of terms>

[0041] Hereinafter, a lithium-ion secondary battery, which is one of the typical embodiments of the power storage device in the present disclosure, will be described in detail with reference to the accompanying drawings. Matters other than those specifically mentioned in this specification and required for implementation (for example, the general structure and manufacturing process of the power storage device not characterized in the present disclosure, etc.) can be understood as design matters for technicians in this field based on the prior art in this field. The present disclosure can be implemented based on the contents disclosed in this specification and the technical common sense in this field. It should be noted that in the following drawings, the same symbols are marked for components and parts that play the same role. In addition, the dimensional relationships (length, width, thickness, etc.) in the figures do not reflect the actual dimensional relationships.

[0042] In this specification, "power storage device" refers to the concept of a device that generates a charge-discharge reaction by the movement of charge carriers between a pair of electrodes (positive and negative electrodes). That is, power storage devices include batteries such as secondary batteries (such as lithium-ion secondary batteries, nickel-metal hydride batteries, nickel-cadmium batteries), and capacitors such as lithium-ion capacitors and double-layer capacitors (physical batteries). In addition, in this specification, "lithium-ion secondary battery" refers to a power storage device that uses lithium ions as charge carriers and realizes repeated charging and discharging by the movement of charges accompanying lithium ions between positive and negative electrodes.

[0043] In this specification, when a numerical range is described as "A to B (where A and B are arbitrary numerical values)", it means "above A and below B", and includes the meanings of "greater than A and less than B", "greater than A and below B", and "above A and less than B".

[0044] <Lithium-ion secondary battery>

[0045] Figure 1 1 is a schematic longitudinal cross-sectional view of a lithium-ion secondary battery 1 according to an embodiment. It should be noted that in the following description, the symbols L, R, U, and D in the drawings represent the left, right, top, and bottom of the lithium-ion secondary battery 1. However, these are directions for convenience of description only and do not limit the arrangement of the lithium-ion secondary battery 1 in any way.

[0046] <Battery case>

[0047] like Figure 1As shown, in the lithium-ion secondary battery 1 of the present embodiment, the shape of the battery case 10 is a rectangular parallelepiped, which is a flat square. However, the shape of the battery case 10 is not limited thereto, and may be, for example, a cylindrical shape. The battery case 10 includes a battery case body 11 for storing an electrode body 20 and an electrolyte (not shown) and a sealing plate (lid) 12 for sealing the opening of the body. The battery case body 11 and the sealing plate 12 are sealed by welding by laser welding or the like. The material of the battery case 10 is not particularly limited as long as it is the same as the material used in the previous storage device of this type. As an example, the material of the battery case 10 may be a light metal material such as aluminum that has good thermal conductivity. However, the structure of the battery case 10 may also be changed. For example, a flexible laminated film may also be used as the battery case.

[0048] In the present embodiment, the battery case body 11 is composed of a bottom wall, a pair of short side walls extending from the bottom wall and opposite to each other, and a long side wall. In the present embodiment, a thin-walled safety valve 13 and an injection port (not shown) are provided on the sealing plate 12 of the battery case 10. The thin-walled safety valve 13 is set in a manner to release the internal pressure of the battery case when the internal pressure rises above a specified level, and the injection port is used to inject electrolyte. In addition, a positive external terminal 14 and a negative external terminal 15 for external connection are provided on the outside of the battery case. These electrode terminals are electrically connected to the electrode body 20 housed in the battery case via internal terminals 16 and 17.

[0049] The external terminals 14 and 15 are made of metal. For example, aluminum or an aluminum alloy can be used as the positive electrode external terminal 14. For example, copper or a copper alloy can be used as the negative electrode external terminal 15.

[0050] The internal terminals 16 and 17 are made of metal. For example, aluminum or an aluminum alloy can be used as the positive electrode internal terminal 16 from the viewpoint of improving the bonding strength with the positive electrode composite material layer non-forming portion 31a. For example, copper or a copper alloy can be used as the negative electrode internal terminal 17 from the viewpoint of improving the bonding strength with the negative electrode composite material layer non-forming portion 41a.

[0051] <Electrolyte>

[0052] The electrolyte may be a non-aqueous electrolyte obtained by dissolving a supporting salt in an appropriate non-aqueous solvent. Any conventionally known non-aqueous electrolyte may be used without particular limitation. As an example of a non-aqueous solvent, ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), etc. may be used. In addition, as an example of a supporting salt, a lithium salt (e.g., LiBOB, LiPF 6 wait).

[0053] <Electrode body>

[0054] The positive electrode 30 and the negative electrode 40 of the lithium ion secondary battery 1 of the present embodiment include composite material layers 31 and 41 having the structure disclosed herein. Figure 3 2 is a schematic cross-sectional view showing the stacked structure of the stacked electrode body 20. The positive electrode 30 includes a positive electrode current collector foil 32 and a positive electrode composite layer 31. The negative electrode 40 includes a negative electrode current collector foil 42 and a negative electrode composite layer 41. A separator is interposed between the positive electrode 30 and the negative electrode 40.

[0055] In the present embodiment, the electrode body 20 is a stacked electrode body in which rectangular positive electrodes 30 and rectangular negative electrodes 40 are alternately stacked with rectangular separators interposed therebetween. Figure 2 It is a disassembled stereoscopic view schematically showing a single battery unit of the stacked electrode body 20 constituting one of the present embodiments. In the following description, the symbols LR, T, and UD in the accompanying drawings represent the width direction, thickness direction, and depth direction of the stacked electrode body 20. However, these are directions for ease of explanation only, and there is no limitation on the arrangement of the lithium-ion secondary battery 1. It should be noted that the electrode body 20 is not limited thereto, and may also be a wound electrode body in which the positive electrode and the negative electrode are wound via an isolation member. In addition, the number of electrode bodies 20 is not particularly limited. A plurality of electrode bodies (for example, a plurality of the above-mentioned single battery units are stacked, etc.) can be accommodated in the battery case 10.

[0056] <Positive electrode and positive electrode composite layer>

[0057] like Figure 2 As shown in FIG. 1 , the positive electrode 30 includes a rectangular positive electrode current collector foil 32 and a positive electrode composite layer 31 formed on the surface of the positive electrode current collector foil 32. It should be noted that the positive electrode composite layer 31 only needs to be formed on one side or both sides (here both sides) of the positive electrode current collector foil 32. Figure 1 and Figure 2 As shown, the positive electrode 30 may have a positive electrode composite layer non-formed portion 31a where the positive electrode composite layer 31 is not formed and the positive electrode current collector foil 32 is exposed. The positive electrode composite layer non-formed portion 31a is provided to protrude from one end of the stacked electrode body 20. The positive electrode composite layer non-formed portion 31a can be joined to the positive electrode internal terminal 16.

[0058] The positive electrode collector foil 32 disclosed here is rectangular in shape, but the shape and size are not particularly limited, as long as they are appropriately determined according to the battery design. The material of the positive electrode collector foil 32 can use the known positive electrode collector foil used in the power storage device, without any special limitation. The material of the positive electrode collector foil 32 is, for example, aluminum or an aluminum alloy. For the thickness pT of the positive electrode collector foil 32, the lower limit value is preferably 5 μm or more, more preferably 8 μm or more, and most preferably 10 μm or more, in order to take into account the capacity density of the power storage device and the strength of the collector foil. In addition, the upper limit value is preferably 50 μm or less, more preferably 35 μm or less, and most preferably 20 μm or less.

[0059] The positive electrode composite layer 31 disclosed herein at least includes a positive electrode active material 35 and a binder 60. In addition, a conductive additive, an inorganic filler, etc. may also be added as long as the technical effect of the present disclosure is not significantly impaired. The positive electrode composite layer 31 is prepared by, for example, dispersing the positive electrode active material 35 and the binder 60 (and the conductive additive, inorganic filler, etc. used as needed) in a suitable solvent (ion exchange water, organic solvent, etc.) to prepare a paste (slurry) composition. The positive electrode composite layer 31 can be formed by applying an appropriate amount of the composition to the surface of the positive electrode collector foil 32 and drying it.

[0060] As the positive electrode active material 35 of the positive electrode composite layer 31 disclosed herein, a positive electrode active material commonly used in the positive electrode of a lithium ion secondary battery can be used. For example, the positive electrode active material 35 is a lithium composite metal oxide having a layered rock salt structure, a spinel structure, or an olivine structure. Specifically, LiCoO 2 、LiNiO 2 、LiFeO 2 、LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O 2 (NCM), LiNi 0.5 Mn 1.5 O 4 、LiNi 0.8 Co 0.15 A l0.05 O 2 (NCA), LiCrMO 4 、LiMn 2 O 4 、LiFePO 4 (LFP) etc. It should be noted that these positive electrode active materials 35 may be used alone or in combination of two or more. Among them, from the viewpoint of improving the cycle characteristics of the electric storage device, the positive electrode active material 35 is preferably NCM.

[0061] The positive electrode active material 35 may be in a particle form. In this case, the average particle size of the positive electrode active material 35 is not particularly limited. The average particle size of the positive electrode active material 35 is typically 30 μm or less. If the average particle size is small, the electrode density increases, so from the perspective of high capacity of the storage device, the upper limit of the average particle size of the positive electrode active material 35 is preferably 25 μm or less, and more preferably 20 μm or less. It should be noted that the average particle size of the active material can be obtained as a 50 volume % particle size (D50 particle size) based on a laser diffraction light scattering method.

[0062] The thickness PT of one side of the positive electrode composite layer 31 disclosed herein is preferably 40 μm or more. From the viewpoint of increasing the capacity density of the storage device, the lower limit of the thickness PT of one side of the positive electrode composite layer 31 may be 45 μm or more, more preferably 50 μm or more, and most preferably 60 μm or more. The upper limit may be 100 μm or less, 90 μm or less, or 80 μm or less.

[0063] The positive electrode composite layer 31 of the present embodiment may also have voids as long as the technical effects of the present disclosure are not significantly impaired. In the case where the positive electrode composite layer 31 has voids, the porosity of the positive electrode composite layer 31 may be 5% to 35%. If the porosity is high, the composite layer is easily broken, so the porosity of the positive electrode composite layer 31 is preferably 30% or less. In addition, from the perspective of increasing the capacity of the power storage device, since the resistance also increases, the porosity of the positive electrode composite layer 31 is more preferably 20% or less, and most preferably 10% or less.

[0064] As the binder 60 of the positive electrode composite layer 31 disclosed herein, a binder used in the positive electrode of a general lithium ion secondary battery or lithium ion capacitor can be used. For example, for the binder 60 used in the non-aqueous paste, halogenated vinyl resins such as polyvinylidene fluoride (PVDF), polyvinylidene chloride (PVDC), polyalkylene oxides such as polyethylene oxide (PEO), etc. can be cited. In addition, in the case of using an aqueous paste, a water-soluble polymer material or a water-dispersible polymer material can be preferably used. For example, for the binder 60 used in the aqueous paste, polytetrafluoroethylene (PTFE), carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), etc. can be cited. As described later, since the content of the binder 60 in the positive electrode composite layer 31 is less than the content of the binder 60 in the negative electrode composite layer 41, it is preferred that a material with high strength and adhesion is used even in a small amount. Therefore, it is preferred to use a polymer containing fluorine in the constituent elements as a binder, and the binder 60 used in the positive electrode composite layer 31 is preferably PVDF and PTFE. In addition, these adhesives 60 may be used individually by 1 type, or may use 2 or more types together.

[0065] The content of the binder 60 in the positive electrode composite layer 31 disclosed herein may preferably be 0.1% by weight to 5.0% by weight when the total weight of the solid content of the positive electrode composite layer 31 is set to 100% by weight. From the viewpoint of reducing the total resistance of the positive and negative electrode composite layers 31 and 41 and improving the capacity retention rate of the storage device, the upper limit is preferably 4.5% by weight or less, more preferably 3.0% by weight or less, and further preferably 1.5% by weight or less. In addition, the lower limit may be 0.1% by weight or more, 0.3% by weight or more, or 0.5% by weight or more.

[0066] Examples of conductive additives contained in the positive electrode composite layer 31 disclosed herein include metal powders such as carbon black, acetylene black, carbon nanotubes (CNT), silver, gold, or copper. Examples of inorganic fillers include aluminum hydroxide, silicon dioxide, aluminum oxide, zirconium oxide, titanium dioxide, boehmite, or magnesium oxide.

[0067] The resistance value of the positive electrode material layer 31 is preferably 1Ω / cm 2 ~30Ω / cm 2 If the resistance value of the positive electrode material layer 31 is low, excellent output characteristics can be achieved. Therefore, the upper limit of the resistance value of the positive electrode material layer 31 is preferably 25Ω / cm 2 Below, more preferably 20Ω / cm 2 Below, more preferably 15Ω / cm 2 In addition, the lower limit may be 1Ω / cm 2 Above, it can be 2Ω / cm 2 Above, it can also be 3Ω / cm 2 above.

[0068] <Negative electrode and negative electrode composite layer>

[0069] like Figure 2 As shown in FIG. 1 , the negative electrode 40 includes a rectangular negative electrode current collector foil 42 and a negative electrode composite layer 41 formed on the surface of the negative electrode current collector foil 42. The negative electrode composite layer 41 only needs to be formed on one side or both sides (here, both sides) of the negative electrode current collector foil 42. Figure 1 and Figure 2 As shown, the negative electrode 40 may have a negative electrode composite layer non-forming portion 41a where the negative electrode composite layer 41 is not formed and the negative electrode current collector foil 42 is exposed. In a part, there may be a negative electrode composite layer non-forming portion 41a where the negative electrode composite layer is not formed and the negative electrode current collector foil is exposed. The negative electrode composite layer non-forming portion 41a is set to protrude from one end of the stacked electrode body 20. The negative electrode composite layer non-forming portion 41a can be joined to the negative electrode internal terminal 17.

[0070] The negative electrode collector foil 42 of the present embodiment is rectangular in shape, but the shape and size are not particularly limited, as long as they are appropriately determined according to the battery design. The material of the negative electrode collector foil 42 can use the known negative electrode collector foil used in the power storage device, without particular limitation. The material of the negative electrode collector foil 42 is, for example, copper or a copper alloy. For the film thickness nT of the negative electrode collector foil 42, the lower limit value is preferably 3 μm or more, more preferably 5 μm or more, and most preferably 8 μm or more, in order to take into account the capacity density of the power storage device and the strength of the collector. In addition, the upper limit value is preferably 40 μm or less, more preferably 25 μm or less, and most preferably 15 μm or less.

[0071] The negative electrode composite layer 41 disclosed herein at least comprises a negative electrode active material 45 and a binder 60. In addition, a conductive aid, an inorganic filler, etc. may also be added as long as the technical effect of the present disclosure is not significantly impaired. The negative electrode composite layer 41 is prepared by, for example, dispersing the negative electrode active material and the binder (as well as the conductive aid, inorganic filler, etc. used as needed) in a suitable solvent (ion exchange water, organic solvent, etc.) to prepare a paste (slurry) composition. The negative electrode composite layer 41 can be formed by applying an appropriate amount of the composition on the surface of the negative electrode collector foil and drying it.

[0072] As the negative electrode active material 45 of the negative electrode composite layer 41 disclosed here, the negative electrode active material used in the negative electrode of a general lithium ion secondary battery can be used. For example, the negative electrode active material can include soft carbon (easily graphitized carbon), amorphous carbon materials, graphite (graphite), hard carbon (difficult to graphitize carbon), carbon nanotubes and other carbon materials, silicon oxide, titanium oxide, vanadium oxide, lithium titanium composite oxide and other metal oxide materials, lithium nitride, lithium cobalt composite nitride and other metal nitride materials, silicon compounds, etc. It should be noted that these negative electrode active materials can be used alone or in combination of two or more. Among them, from the viewpoint of improving energy density, the negative electrode active material 45 is preferably graphite.

[0073] The negative electrode active material 45 may be in a particle form. In this case, the average particle size of the negative electrode active material 45 is not particularly limited. The average particle size of the negative electrode active material 45 is typically 30 μm or less. If the average particle size is small, the electrode density increases, so from the perspective of increasing the capacity of the storage device, the upper limit of the average particle size of the negative electrode active material is preferably 25 μm or less, and more preferably 20 μm or less.

[0074] The thickness NT of the negative electrode composite layer 41 disclosed herein is preferably 50 μm or more. From the viewpoint of increasing the capacity density of the storage device, the lower limit of the thickness of the negative electrode composite layer is preferably 45 μm or more, more preferably 60 μm or more, and most preferably 70 μm or more. The upper limit may be 150 μm or less, 130 μm or less, or 110 μm or less.

[0075] The negative electrode composite layer 41 may have voids as long as the technical effect of the present disclosure is not significantly impaired. In the case where the negative electrode composite layer 41 has voids, the void ratio of the negative electrode composite layer 41 may be 5% to 35%. If the void ratio is high, the resistance value increases and the composite layer becomes easy to break, so the void ratio of the negative electrode composite layer 41 is preferably 30% or less. In addition, from the perspective of increasing the capacity of the storage device, the void ratio of the negative electrode composite layer 41 is more preferably 20% or less, and most preferably 10% or less.

[0076] As the binder 60 of the negative electrode composite layer 41 disclosed herein, the binder used in the negative electrode of a general lithium ion secondary battery or lithium ion capacitor can be used. For example, for the binder used in the non-aqueous paste, halogenated vinyl resins such as polyvinylidene fluoride (PVDF), polyvinylidene chloride (PVDC), polyalkylene oxides such as polyethylene oxide (PEO), etc. can be cited. In addition, in the case of using an aqueous paste, a water-soluble polymer material or a water-dispersible polymer material can be preferably used. For example, for the binder used in the aqueous paste, polytetrafluoroethylene (PTFE), carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), etc. can be cited. As described later, since the content of the binder 60 in the negative electrode composite layer 41 is more than the content of the binder 60 in the positive electrode composite layer 31, a material with low cost and less load on the environment is preferred. Therefore, the binder used in the negative electrode composite layer is preferably CMC or SBR. It should be noted that these binders can be used alone or in combination of two or more.

[0077] When the total weight of the solid content of the negative electrode composite layer 41 is set to 100 weight %, the content of the binder 60 in the negative electrode composite layer 41 disclosed herein is typically only 1.0 weight % to 12.0 weight %. From the viewpoint of reducing the total resistance of the positive and negative electrode composite layers and improving the capacity retention rate of the storage device, the upper limit is preferably 10.0 weight % or less, more preferably 8.0 weight % or less, and further preferably 6.0 weight % or less. In addition, from the viewpoint of suppressing the precipitation of metallic lithium, the lower limit is preferably 1.5 weight % or more, more preferably 3.0 weight % or more, and most preferably 4.5 weight % or more. In addition, if the thickness of the composite layer increases, the mechanical strength increases. On the other hand, the flexibility of the composite layer with a large thickness is insufficient, and there is a tendency to easily break in the manufacturing process of the storage device. As described above, since the composite layer disclosed in the present invention has a high content of the binder 60, it is possible to reduce the occurrence of breakage in the manufacturing process of the storage device.

[0078] Examples of the conductive additive contained in the negative electrode mixed material layer 41 include metal powders such as silver, gold, and copper. Examples of the inorganic filler include aluminum hydroxide, silicon dioxide, aluminum oxide, zirconium oxide, titanium dioxide, boehmite, and magnesium oxide.

[0079] The resistance value of the negative electrode composite layer 41 is preferably 3Ω / cm 2 ~90Ω / cm 2 From the perspective of maintaining battery performance, the upper limit of the resistance value of the negative electrode composite layer is preferably 80 Ω / cm 2 Below, more preferably 70Ω / cm 2 Below, more preferably 60Ω / cm 2From the viewpoint of suppressing the precipitation of metallic lithium, the lower limit is preferably 5Ω / cm 2 More preferably 7Ω / cm 2 Above, most preferably 10Ω / cm 2 above.

[0080] <Isolator>

[0081] The separator 50 of the present embodiment is an insulating porous sheet, but the shape and size are not particularly limited, as long as they are appropriately determined according to the battery design. Typically, in order to insulate the positive electrode and the negative electrode, the separator 50 is larger than the positive electrode sheet 30 and the negative electrode sheet 40. In addition, the material of the separator 50 can use the known separators used in the power storage device without any special restrictions. For example, the separator 50 preferably uses a resin such as a polyolefin such as polyethylene or polypropylene, polyester, cellulose, or polyamide. In addition, as long as the technical effect of the present disclosure is not significantly impaired, the surface of the separator 50 may also have a heat-resistant layer. From the perspective of both the capacity density of the power storage device and the strength of the collector, the lower limit of the film thickness ST of the separator 50 is preferably 5 μm or more, more preferably 8 μm or more, and most preferably 10 μm or more. In addition, the upper limit of the film thickness of the separator 50 is preferably 40 μm or less, more preferably 30 μm or less, and most preferably 20 μm or less.

[0082] <Total resistance of electrode body>

[0083] The total resistance value of the positive electrode 30 and the negative electrode 40 of the power storage device disclosed herein is not particularly limited as long as it does not significantly impair the technical effect of the present disclosure. If the total resistance value of the positive electrode 30 and the negative electrode 40 is greater than 100 Ω / cm 2 , the input and output of the power storage device will be significantly reduced, and the battery performance cannot be stabilized. Therefore, the upper limit of the total resistance value of the positive electrode 30 and the negative electrode 40 can be 100Ω / cm 2 Below, preferably 90Ω / cm 2 Below, more preferably 80Ω / cm 2 Below, most preferably 60Ω / cm 2 The lower limit of the total resistance value of the positive electrode 30 and the negative electrode 40 is preferably 8Ω / cm 2 More preferably 10Ω / cm 2 Above, most preferably 15Ω / cm 2 above.

[0084] If the resistance value of the positive electrode 30 in the power storage device disclosed in the present invention is set to A, and the resistance value of the negative electrode 40 is set to B, then B / A (i.e., the resistance ratio of the positive and negative electrodes) preferably satisfies 1.0≤B / A≤20.0. From the viewpoint of improving the capacity retention rate, the lower limit of the resistance ratio of the positive and negative electrodes is preferably greater than 2.0, more preferably greater than 2.5, and further preferably greater than 3.0. In addition, from the viewpoint of maintaining battery performance, the upper limit of the resistance ratio of the positive and negative electrodes is preferably less than 15.0, more preferably less than 10.0, and further preferably less than 5.5.

[0085] The storage device having the positive electrode 30 and the negative electrode 40 with the resistance value as described above will not reduce the high rate characteristics and the capacity retention rate, and can suppress the precipitation of metallic lithium. Generally speaking, the greater the thickness of the negative electrode composite layer, the more the number of lithium ions that can be absorbed in the negative electrode increases, so the storage device has a high capacity. However, in a storage device with an excessively low resistance value (excessively high conductivity of lithium ions), a large amount of lithium ions move rapidly from the positive electrode to the negative electrode during charging. As a result, lithium ions will not spread to the vicinity of the collector foil of the negative electrode, and metallic lithium will precipitate at the interface with the separator. In contrast, the storage device disclosed in the present invention adjusts the resistance value of the positive and negative electrodes by containing a certain amount of adhesive. Since the resistance value of the negative electrode is relatively high, the precipitation of metallic lithium at the interface between the separator and the negative electrode can be suppressed, so that it is evenly distributed throughout the entire negative electrode composite layer. In addition, the storage device disclosed in the present invention makes the resistance value of the positive electrode lower than the resistance value of the negative electrode. As a result, the total resistance value of the storage device as a whole is reduced, and the high rate characteristics can be maintained. In addition, the resistance ratio of the negative electrode to the positive electrode is limited. This can improve the capacity maintenance rate of the power storage device.

[0086] Specifically, the negative electrode 40 of the power storage device disclosed in the present invention has a negative electrode composite layer 41 with a thickness of 50 μm or more on one side. In addition, the positive electrode 30 also has a positive electrode composite layer 31 with a thickness of 40 μm or more on one side. As a result, the energy density of the power storage device increases, making it a high-capacity power storage device. In addition, by containing more than 1.0% by weight of a binder, the negative electrode composite layer 41 of the power storage device has a high negative electrode resistance value. As a result, during charging, before lithium ions spread to the vicinity of the collector foil of the negative electrode, it is possible to suppress precipitation in the form of metallic lithium at the interface with the separator. In the positive electrode composite layer 31 of the power storage device, the content of the binder is suppressed to less than 5.0% by weight. In addition, in the negative electrode composite layer 41, the content of the binder is suppressed to less than 12.0% by weight. As a result, the total resistance value of the positive and negative electrodes is reduced, and the high-rate characteristics can be maintained at a high state. In addition, the resistance ratio of the positive and negative electrodes is appropriately controlled, and the capacity retention rate of the power storage device is improved.

[0087] As mentioned above, although the preferred embodiment of this disclosure was described based on drawings, such description is not limiting, and various changes are possible, of course.

[0088] Example

[0089] Hereinafter, the power storage device of the present disclosure will be described with reference to Examples and Comparative Examples, but it should be noted that the present disclosure is not intended to be limited to the contents shown in the Examples.

[0090] <Example 1: Preparation of positive electrode sheet>

[0091] 97.5 wt% of NCM powder as a positive electrode active material, 1.5 wt% of PVDF as a binder, and 1.0 wt% of CNT as a conductive aid are mixed to prepare a paste for forming a positive electrode composite layer. It should be noted that N-methyl-2-pyrrolidone (NMP) is used as a solvent. Next, an aluminum foil with a thickness of 13 μm is prepared. The paste for forming a positive electrode composite layer is applied to both sides of the aluminum foil. At this time, the thickness of the positive electrode composite layer on the aluminum foil and both sides thereof (i.e., the average film thickness of the positive electrode) is adjusted and applied in such a way that it is 140 μm. A comma coater (registered trademark) is used for coating. After coating the positive electrode composite layer, dry it naturally and then heat and dry it at 120°C. Then, leave the conductive part and cut it into 45 cm in length and 35 cm in width to make a positive electrode sheet.

[0092] <Example 1: Preparation of negative electrode sheet>

[0093] 96.5 wt % of graphite particles as a negative electrode active material, 3.0 wt % of SBR as a binder, and 0.5 wt % of CMC are mixed to prepare a paste for forming a negative electrode composite layer. It should be noted that ion exchange water is used as a solvent. Next, a copper foil with a thickness of 8 μm is prepared. The paste for forming the negative electrode composite layer is applied to both sides of the copper foil. In addition, at this time, the thickness of the negative electrode composite layer on the copper foil and both sides thereof (i.e., the average film thickness of the negative electrode) is adjusted and applied to be 180 μm. After applying the negative electrode composite layer, dry it naturally and then heat dry it at 120°C. Then, leave the conductive part and cut it into 50 cm in length and 40 cm in width to make a negative electrode sheet.

[0094] <Fabrication of laminated three-electrode single cell>

[0095] In the measurement of the resistance value shown below, a laminated three-pole single cell consisting of a positive electrode sheet, a reference electrode (RE), a negative electrode sheet, a separator and a non-aqueous electrolyte is used. The reference electrode is made of platinum wire and has a conductive portion and a coating portion coated with LFP. As a separator, two porous polyolefin sheets of 53 cm × 43 cm in length, 16 μm in thickness and made of polyethylene are prepared. The above-mentioned positive electrode sheet, separator, reference electrode, separator and negative electrode sheet are overlapped in sequence, and sealed with an aluminum / PP laminate film in a manner that each conductive portion is exposed to produce a laminated three-pole single cell. It should be noted that the non-aqueous electrolyte uses a supporting salt (LiPF6 ) was dissolved in an organic mixed solvent (EC:EMC:DMC=3:3:4) at a concentration of about 1.15 mol / L to obtain a non-aqueous electrolyte. The terminals were connected to the reference electrode and the negative electrode of the laminated three-electrode cell, and pre-charged at 0.6 C to a charge rate (SOC) of 50%.

[0096] <Measurement of resistance value>

[0097] The resistance value was measured by AC impedance measurement at 25°C (frequency range: 10000 Hz to 10 mHz, applied voltage: 30 mV). The resistance value at 1000 Hz to 50 mHz was defined as the positive electrode resistance value / negative electrode resistance value, and the value was divided by the area (cm2) of the positive and negative electrode sheets. 2 ), and then calculate the resistance value (Ω / cm 2 ).

[0098] <Fabrication of laminated bipolar cells>

[0099] In the determination of the capacity retention rate shown below, a laminated bipolar cell consisting of a positive electrode sheet, a negative electrode sheet, a separator and a non-aqueous electrolyte is used. As a separator, a porous polyolefin sheet of 53 cm in length × 43 cm in width, 16 μm in thickness, and made of polyethylene is prepared. The above-mentioned positive electrode sheet, separator, and negative electrode sheet are overlapped in sequence, and sealed with an aluminum / PP laminate film in a manner that each conductive portion is exposed to produce a laminated bipolar cell. It should be noted that the non-aqueous electrolyte uses a supporting salt (LiPF 6 ) is dissolved in an organic mixed solvent (EC:EMC:DMC=3:3:4) at a concentration of about 1.15 mol / L to obtain a non-aqueous electrolyte solution.

[0100] <Measurement of capacity maintenance rate>

[0101] The laminated bipolar single cell was heat treated for 1 hour in a constant temperature chamber at 25°C. Charge and discharge were repeated twice between 4.2V and 3.0V at a constant current of 0.1C. The discharge capacity obtained in the second charge and discharge was set as the initial discharge capacity. Next, after charging to 4.2V at a constant current of 3C, it was discharged to 3.0V at a constant current of 1C. The above-mentioned 3C charge and 1C discharge were set as 1 cycle, and repeated 100 cycles. Then, charge and discharge were performed once between 4.2V and 3.0V at a constant current of 0.1C, and the obtained discharge capacity was set as the discharge capacity after the cycle. The capacity retention rate (%) is calculated by dividing the discharge capacity after the cycle by the initial discharge capacity and converting it into a percentage.

[0102] <Examples 2 to 5 and Comparative Examples 1 to 5>

[0103] As shown in Table 1, the same procedures as in Example 1 were carried out except that the blending ratio of the constituent components (binder) was changed.

[0104] [Table 1]

[0105]

[0106] According to the above test results, the capacity retention rate of Comparative Examples 1 to 4 with a low resistance ratio of the positive and negative electrodes is reduced. In contrast, it can be seen that the capacity retention rate of Examples 1 to 5 with a high resistance ratio of the positive and negative electrodes (i.e., a high binder content in the negative electrode) is high, and the content of the binder in the positive and negative electrodes can improve the capacity retention rate while suppressing the precipitation of metallic lithium. In addition, the capacity retention rate of Comparative Example 5 with an extremely high resistance ratio of the positive and negative electrodes is high. However, the total resistance of the positive and negative electrodes of Comparative Example 5 is also extremely high. Although the details are not shown, the input and output of the storage device (i.e., high-rate characteristics) is significantly reduced, and the battery performance cannot be stabilized.

[0107] The specific examples of the technology disclosed herein are described in detail above, but these are only examples and do not limit the scope of the patent claims. The technology described in the scope of the patent claims includes various modifications and changes to the specific examples described above.

[0108] The technology disclosed herein can be appropriately omitted or appropriately combined, unless any particular problem occurs. In addition, this specification includes the disclosures described in the following items.

[0109] Item 1: A storage device comprising: a positive electrode having a positive electrode composite layer, a negative electrode having a negative electrode composite layer, and an insulator sandwiched between the positive electrode and the negative electrode; the film thickness of the positive electrode composite layer is 40 μm or more, the film thickness of the negative electrode composite layer is 50 μm or more, the binder content in the positive electrode composite layer when the solid content weight of the entire positive electrode composite layer is set to 100 weight% is 0.1 weight% to 5.0 weight%, and the binder content in the negative electrode composite layer when the solid content weight of the entire negative electrode composite layer is set to 100 weight% is 1.0 weight% to 12.0 weight%.

[0110] Item 2: The electrical storage device according to Item 1, wherein the resistance value (A) of the positive electrode is 1 Ω / cm 2 ~30Ω / cm 2 The resistance value (B) of the negative electrode is 3Ω / cm 2 ~90Ω / cm 2 , and satisfies the following formula (1): 2≤B / A≤10.

[0111] Item 3: The electrical storage device according to Item 1 or 2, wherein the binder contained in the positive electrode composite material layer is PVDF, and the binder contained in the negative electrode composite material layer is SBR and / or CMC.

Claims

1. An electric storage device comprising: A positive electrode having a positive electrode composite layer, A negative electrode having a negative electrode composite layer, and A separator sandwiched between the positive electrode and the negative electrode; The thickness of the positive electrode composite layer is 40 μm or more. The thickness of the negative electrode composite layer is 50 μm or more. The binder content in the positive electrode composite material layer is 0.1 wt % to 5.0 wt % when the solid content weight of the entire positive electrode composite material layer is 100 wt %. The content of the binder in the negative electrode mixed material layer is 1.0% by weight to 12.0% by weight when the solid content weight of the entire negative electrode mixed material layer is 100% by weight.

2. The power storage device according to claim 1, wherein The resistance value A of the positive electrode is 1Ω / cm 2 ~30Ω / cm 2 , The resistance value B of the negative electrode is 3Ω / cm 2 ~90Ω / cm 2 , And, the following formula (1) is satisfied: 1≤B / A≤20.

3. The power storage device according to claim 1 or 2, wherein: The binder contained in the positive electrode composite layer is PVDF. The binder contained in the negative electrode composite layer is SBR and / or CMC.

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