Secondary battery and negative collector

Abstract

A secondary battery is provided with a positive electrode, a negative electrode, a separator disposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte having lithium ion conductivity, the negative electrode is provided with a negative electrode current collector, the negative electrode current collector is provided with a resin film and a transition metal layer laminated with the resin film, and the resin film includes a base resin layer and a surface resin layer. At least the surface resin layer contains a nitrogen-containing resin. As a result, embrittlement of the negative electrode current collector including the resin film can be suppressed in the secondary battery.

Description

Technical Field

[0001] The present disclosure relates to a secondary battery and a negative electrode collector. Background Art

[0002] The anode electrode structure proposed in Patent Document 1 includes a current collector containing copper. The anode electrode structure also includes a lithium metal film formed on the current collector. The anode electrode structure also includes a solid electrolyte interface (SEI) film stack formed on the lithium metal film. In one embodiment, at least one of the current collectors 110 and 160 includes a polyethylene terephthalate film coated with a metal material.

[0003] Prior Art Literature

[0004] Patent Document 1: Japanese Patent Application No. 2021-502671 Summary of the invention

[0005] Problems to be solved by the invention

[0006] Patent document 1 proposes that the polyethylene terephthalate (PET) film coated with a metal material is susceptible to degradation. It is known that when a transition metal comes into contact with a polymer, metal ions are transferred to the polymer, and the bonds of the polymer are cleaved by a free radical reaction, thereby causing embrittlement of the polymer. For example, when copper comes into contact with a PET film, copper ions move into the PET film to embrittle the PET (copper damage). Therefore, when a transition metal layer is laminated on the surface of a resin film, the embrittlement of the resin film gradually develops. Although the embrittlement of a resin film usually proceeds slowly, it is desirable to suppress such embrittlement as much as possible.

[0007] On the other hand, when a negative electrode current collector having a transition metal layer laminated on the surface of a resin film is used in a lithium metal secondary battery (hereinafter referred to as a "lithium secondary battery"), the embrittlement of the resin film is significantly promoted. In the negative electrode of a lithium secondary battery, lithium metal is precipitated during charging, and the lithium metal is dissolved during discharge. This means that if the transition metal in contact with the resin film contacts lithium metal, the embrittlement of the resin film is significantly promoted. No reports of this phenomenon have been found in previous literature.

[0008] Means for solving problems

[0009] One aspect of the present disclosure relates to a secondary battery comprising a positive electrode, a negative electrode, a separator arranged between the positive electrode and the negative electrode, and a non-aqueous electrolyte with lithium ion conductivity, wherein the negative electrode comprises a negative electrode collector, the negative electrode collector comprises a resin film and a transition metal layer stacked with the resin film, the resin film comprises a base resin layer and a surface resin layer, and at least the surface resin layer contains a nitrogen-containing resin.

[0010] Another aspect of the present disclosure relates to a negative electrode current collector including a resin film and a transition metal layer laminated on the resin film, wherein the resin film includes a base resin layer and a surface resin layer, and at least the surface resin layer contains a nitrogen-containing resin.

[0011] Effects of the Invention

[0012] According to the present disclosure, it is possible to significantly suppress embrittlement of a negative electrode current collector including a resin film in a secondary battery.

[0013] The novel features of the present invention are set forth in the appended claims, both as to structure and content, and together with other objects and features of the present application, the present invention will be better understood from the following detailed description with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 It is a longitudinal cross-sectional view schematically showing a lithium secondary battery according to one embodiment of the present disclosure.

[0015] Figure 2 yes Figure 1 An enlarged cross-sectional view of region II in FIG.

[0016] Figure 3 yes Figure 1 An enlarged cross-sectional view of region III in FIG. DETAILED DESCRIPTION

[0017] The following examples are used to illustrate the embodiments of the present disclosure, but the present disclosure is not limited to the examples described below. In the following description, specific values, materials, etc. are sometimes cited, but other values, materials, etc. can also be applied as long as the effects of the present disclosure can be obtained. Furthermore, the constituent elements other than the characteristic parts of the present disclosure can be the constituent elements of known secondary batteries. In this specification, when referring to "the range of values ​​A to B", the range includes values ​​A and B.

[0018] Embodiments of the present disclosure relate to secondary batteries. The secondary battery includes a positive electrode, a negative electrode, a separator disposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte having lithium ion conductivity. The secondary battery is, for example, a lithium ion secondary battery using a material that reversibly absorbs and releases lithium ions as a negative electrode active material, or a non-aqueous electrolyte secondary battery such as a lithium secondary battery in which lithium metal is precipitated in the negative electrode during charging and lithium metal is dissolved during discharge.

[0019] In a lithium secondary battery, more than 70% of the rated capacity, for example, is realized by the precipitation and dissolution of lithium metal. The movement of electrons in the negative electrode during charging and discharging is mainly caused by the precipitation and dissolution of lithium metal in the negative electrode. Specifically, 70 to 100% (for example, 80 to 100% or 90 to 100%) of the movement of electrons in the negative electrode during charging and discharging (current in another viewpoint) is caused by the precipitation and dissolution of lithium metal. That is, the negative electrode of a lithium secondary battery is different from the negative electrode in which the movement of electrons in the negative electrode during charging and discharging is mainly caused by the absorption and release of lithium ions by the negative electrode active material (graphite, etc.).

[0020] In a battery in which lithium metal is deposited at the negative electrode during charging, the open circuit potential (OCV: Open Circuit Voltage) of the negative electrode when fully charged is, for example, 70 mV or less relative to lithium metal (lithium dissolution potential). Full charge refers to a state of charge (SOC: State of Charge) when the rated capacity of the battery is set to C, for example, when the battery is charged to a state of charge (SOC: State of Charge) of 0.98×C or more. The open circuit potential (OCV) of the negative electrode when fully charged can be measured by decomposing the fully charged battery in an argon atmosphere to remove the negative electrode and assembling a cell with lithium metal as the counter electrode. The non-aqueous electrolyte of the cell can be of the same composition as the non-aqueous electrolyte in the decomposed battery.

[0021] Hereinafter, each component of the secondary battery will be described in sequence.

[0022] [negative electrode]

[0023] The negative electrode includes a negative electrode current collector. The negative electrode current collector includes a resin film and a transition metal layer stacked with the resin film. The resin film includes a base resin layer and a surface resin layer. The transition metal layer is also a layer in contact with the resin film or the surface resin layer.

[0024] The resin film is lightweight and can easily increase the energy density of the secondary battery. The resin film is not easy to cut during roller conveyance and is easy to handle. Even when the negative electrode potential is low, the resin film will not become brittle like common negative electrode collectors such as copper foil. The resin film is excellent as a collector material in that it has high tolerance to stress during electrode expansion and contraction and is difficult to break. Among them, when a lithium secondary battery is charged, lithium metal is deposited at the negative electrode, so the expansion degree of the negative electrode tends to increase. "Expansion of the negative electrode" refers to the increase in the combined volume of the volume of the negative electrode and the volume of the deposited lithium metal. In particular, when the lithium metal is deposited in a dendritic form, the expansion amount becomes even greater. As a result, stress is easily generated at the negative electrode.

[0025] The main surface of the resin film may be smooth or rough, and may be subjected to plasma treatment, corona treatment, etc. When the main surface of the resin film is smooth, the maximum height roughness Rz of the main surface is 2.5 μm or less. When the main surface of the resin film is roughened, the maximum height roughness Rz of the main surface is greater than 2.5 μm, and may be 8 μm or more. The maximum height roughness Rz is measured based on JIS B 0601:2013. The main surface of the resin film refers to the surface other than the end surface of the resin film, which is the two surfaces with the largest area. In this specification, "surface" generally means "main surface".

[0026] From the viewpoint of improving the energy density of the secondary battery, as long as the mechanical strength can be ensured, the thinner the thickness of the resin film is, the better. An example of a preferred range of the thickness of the resin film is 1.5 μm to 30 μm or less. The thickness of the resin film can be determined by measuring the thickness of any 10 points of the cross section of the resin film using a scanning electron microscope (SEM) and calculating their average value.

[0027] In the resin film, at least the surface resin layer contains a nitrogen-containing resin. More than 90% by mass of the surface resin layer may be a nitrogen-containing resin. The nitrogen-containing resin may be a polymer having nitrogen atoms in the main chain or the side chain. The content of nitrogen atoms contained in the nitrogen-containing resin may be more than 3% by mass. Thus, the content of nitrogen atoms contained in the surface resin layer may be more than 2.5% by mass.

[0028] In the resin film, the surface resin layer may contain at least nitrogen-hydrogen bonds (NH bonds). The presence or absence of nitrogen-hydrogen bonds can be determined by infrared absorption analysis. The infrared absorption peak unique to nitrogen-hydrogen bonds exists at 1655 cm -1 Nearby (1640~1670cm -1 )、1530cm -1 Nearby (1515~1545cm -1 )wait.

[0029] The sample of the surface resin layer or resin film can be prepared by scraping off the active material from the negative electrode collector, or removing it wetly, and then dissolving the transition metal layer with a mixed diluted aqueous solution of distilled water and 65% nitric acid in a volume ratio of 1:1. In this case, the outermost surface resin layer can be analyzed by infrared absorption analysis. An example of the analysis conditions is shown below.

[0030] FT-IR (ATR method)

[0031] Measurement device: Varian 670 FTIR (manufactured by Varian)

[0032] Measurement mode: Attenuated total reflection

[0033] Light source: special ceramic

[0034] Detector: DLaTGS (deuterated L-alanine doped with triglycine sulfate)

[0035] Resolution: 4cm -1

[0036] Total times: 256 times

[0037] IRE: Ge

[0038] Angle of incidence: 60 degrees

[0039] Accessories: Single reflection ATR accessories (Seagull)

[0040] Alternatively, nitrogen-hydrogen bonds can be analyzed by chemical shift using X-ray electron spectroscopy (XPS).

[0041] The nitrogen-containing resin may be a polymer having at least one selected from a urea bond, a melamine structure, a triazine ring, an amino group, an amide bond, an aromatic amide bond, an imide bond, a carbamate bond, a carbodiimide bond, a uretdione structure, an isocyanurate ring, a nitrile group, and an amide group. Such a polymer may be, for example, a polyurethane resin, a polyurea resin, a melamine resin, a polyamide resin, an aromatic amide resin, a polyimide resin, and the like. Among them, the polyurethane resin is excellent as a material for the current collector in terms of high flexibility, high tolerance to stress during electrode expansion and contraction, and difficulty in breaking.

[0042] Polyurethane resins are synthesized by reacting polyols with difunctional or higher-functional polyisocyanates (particularly diisocyanates). Polyurethane resins having various physical properties can be synthesized by arbitrarily selecting polyols and polyisocyanates.

[0043] The nitrogen-containing resin may contain at least one selected from aliphatic isocyanate groups, aromatic isocyanate groups, allophanate groups and biuret groups. In particular, thermosetting polyurethane resins use polyisocyanates as raw materials, so the probability of having unreacted residual isocyanate groups is high. It is believed that the isocyanate groups are reduced at the negative electrode to generate film components for forming a stable film at the negative electrode. In addition, it is known that thermosetting resins have a large inhibitory effect on copper damage because they form a strong film with a three-dimensional structure. The same is true for ultraviolet curing types. Furthermore, the isocyanate group is at 2250cm -1 Nearby (2270~2240cm -1 ) has an infrared absorption peak caused by asymmetric stretching vibration, so its existence can be confirmed.

[0044] The surface resin layer may contain fillers. It is desirable to improve the adhesion between the resin substrate and the transition metal layer or the lithium metal layer. By adding fillers such as silicon dioxide or aluminum oxide to the surface resin layer, the surface resin layer is formed with concavoconvex, the surface area is increased, and the improvement of the adhesion brought by the anchoring effect can be expected. As long as the filler can roughen the surface of the surface resin layer and does not cause side reactions with the nonaqueous electrolyte in the battery to reduce the battery characteristics, it is not particularly limited. The filler can use particles of resin, metal oxide, ceramic, metal, etc.

[0045] The surface resin layer can be formed as a coating by, for example, applying a nitrogen-containing resin on the surface of the substrate resin layer. In this case, the nitrogen-containing resin can be a thermosetting resin or a UV curable resin. The nitrogen-containing resin can be diluted with a solvent and then applied to the surface of the substrate resin layer. The cured product of the curable resin can have a three-dimensional network of molecular chains.

[0046] The thickness of the surface resin layer is, for example, less than 5 μm, and an example of a preferred thickness range is 0.05 μm to 1.5 μm. The thickness of the surface resin layer can be determined by measuring the thickness of any 10 points of the surface resin layer in the cross section of the negative electrode, the negative electrode collector or the resin film using a scanning electron microscope (SEM) and calculating their average value.

[0047] Most resin films do not have electrical conductivity. The transition metal layer serves to impart good electrical conductivity to the negative electrode current collector. The transition metal layer may be a layer containing a transition metal and having electronic conductivity. The transition metal layer preferably contains a transition metal in a metallic state having electronic conductivity brought about by free electrons.

[0048] In the case of using a negative electrode collector in a lithium ion secondary battery or a lithium secondary battery, the transition metal layer preferably contains copper, nickel, chromium, titanium, iron, silver, gold, tin, etc., in order to easily ensure corrosion resistance and conductivity. The transition metal layer preferably contains at least one of copper, copper alloy, stainless steel, nickel, nickel alloy, etc., and particularly preferably contains copper or copper alloy with excellent conductivity.

[0049] Transition metals have the effect of embrittlement of resin films. In particular, when the transition metal layer contains copper, the embrittlement of the resin film is likely to occur. As a new insight that has not yet been reported, it is also clear that the embrittlement of the resin film caused by the transition metal (such as copper damage) is significantly accelerated by lithium metal. That is, in a lithium secondary battery in which lithium metal is precipitated at the negative electrode, the degradation of the resin film caused by the transition metal layer will be significantly generated. In contrast, by making at least the surface resin layer of the resin film contain a nitrogen-containing resin, the embrittlement of the resin film can be significantly suppressed.

[0050] In addition, as a metal layer that blocks the movement of copper ions to the resin film, there is a nickel-chromium alloy layer. However, in lithium secondary batteries, the shielding effect brought by the nickel-chromium alloy layer is not obtained at all. It is speculated that this is because when easily ionized metal lithium contacts transition metals such as copper, the ionization of the transition metal is accelerated, and the breaking of the polymer bond caused by the transition metal ions is accelerated. On the other hand, by containing a surface resin layer containing a nitrogen-containing resin, a significant effect of suppressing polymer breakage can be obtained.

[0051] The brittleness of the resin film is most affected by the breaking of the bonds between carbon atoms. When the resin film contains a nitrogen-containing resin, there are bonds between carbon atoms and nitrogen atoms in the nitrogen-containing resin. It is believed that the bonds between carbon atoms and nitrogen atoms are not easily affected by transition metals or their ions. The transition metal may be stabilized by nitrogen atoms, thereby suppressing the breaking of the bonds between carbon atoms.

[0052] The transition metal layer can be formed by depositing on the surface of the surface resin layer by a liquid phase method or a vapor phase method. As a liquid phase method, electrolytic deposition methods such as electrolytic plating method, electroless plating method (chemical plating method) can be cited. As a vapor phase method, evaporation method, sputtering method, atomic layer deposition method (ALD) and the like can be cited. It is also possible to form a substrate by sputtering method, and form a thick transition metal layer thereon by a wet electrolytic plating method. That is, a plurality of methods can also be combined and applied. The transition metal layer can also be formed by a lamination method. There is no particular limitation on the formation method of the transition metal layer.

[0053] The thickness of the transition metal layer is, for example, 5 μm or less, or 3 μm or less. An example of a preferred range of the thickness of the transition metal layer is 0.05 μm to 1.5 μm, or 0.1 μm to 1.5 μm. The thickness of the transition metal layer can be determined by measuring the thickness of any 10 points of the transition metal layer in the cross section of the negative electrode or the negative electrode collector using a scanning electron microscope (SEM) and calculating their average value. The transition metal layer may have a plurality of layers composed of different metals.

[0054] The substrate resin layer is the main part of the negative electrode collector, usually thicker than the surface resin layer and thicker than the transition metal layer. More than 51% by mass of the substrate resin layer is composed of resin or organic matter. In order to improve the adhesion with the transition metal layer or the lithium layer, the substrate resin layer may contain inorganic substances such as inorganic particles. The substrate resin layer can be a stretched film, a non-porous film (a film without holes), or a film with a plurality of holes arranged in a regular manner. The substrate resin layer can be insulating, conductive, or non-conductive. There is no particular limitation on the morphology and physical properties of the substrate resin layer.

[0055] The substrate resin layer is formed by molding general-purpose plastics and general-purpose engineering plastics as raw materials into sheets. The raw materials include polyester resins, olefin resins, polyphenylene sulfide resins, acrylic resins, polycarbonate resins, polyetheretherketone resins, polysulfone resins, polyphenylsulfone resins, polyethersulfone resins, polyamide resins, polyimide resins, polyetherimide resins, polybenzimidazole resins, liquid crystal polymer resins, polyacetal resins, polyvinyl chloride resins, polyarylate resins, silicone resins, nylon resins, polyvinylidene chloride resins, ethylene-vinyl alcohol copolymers, polyvinyl alcohol resins, polystyrene resins, epoxy resins, polyurethane resins, phenolic resins, melamine resins, urea resins, unsaturated polyester resins, etc. The resins contained in the substrate resin layer can be used alone or in combination of two or more.

[0056] The resin contained in the substrate resin layer is preferably a resin having an aromatic ring, a resin not containing fluorine atoms, or an olefin resin. When the resin has an aromatic ring (such as a benzene ring) in its molecule, the affinity between the substrate resin layer and the lithium metal layer becomes higher, and the bonding strength between the two is improved.

[0057] As the polyester resin, aromatic polyester is preferred, preferably unstretched polyethylene terephthalate, biaxially stretched polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, etc. As the acrylic resin, polymethyl methacrylate, etc. can be cited. As the polyimide resin, aromatic polyimide is preferred. As the polyamide resin, aromatic polyamide (aromatic amide resin) is preferred. As the olefin resin, unstretched polypropylene, biaxially stretched polypropylene, low-density polyethylene, medium-density polyethylene, high-density polyethylene, linear low-density polyethylene, metallocene polyethylene, ethylene-vinyl acetate copolymer, ethylene-methyl acrylate copolymer, ethylene-ethyl acrylate copolymer, ethylene-methyl methacrylate copolymer, ethylene-acrylic acid copolymer, ethylene-methacrylic acid copolymer, ionomer, etc. are preferred.

[0058] The extrusion method of the substrate resin layer can be a T-die method, a blowing method, or non-stretching, uniaxial stretching, successive biaxial stretching or simultaneous biaxial stretching. The combination of monomers as the combination mode of the resin can be a homopolymer, a copolymer or a terpolymer. There is no limitation on the arrangement mode of the monomers, which can be a random copolymer or a block copolymer. Two or more substrate resin layers can be combined. For example, more than two layers of substrate resin layers can be stacked. Crystalline resins can be in a crystalline state, for example, in an amorphous state manufactured by quenching, or in a state where the two are mixed. In addition, polymer alloys containing two or more of the above-mentioned resins can be used.

[0059] In order to ensure the adhesion with other layers such as vapor-deposited films, the surface of the substrate resin layer can be subjected to corona treatment or plasma treatment. Concavoconvex can be set on the substrate resin layer to improve the adhesion with the surface resin layer. In this case, fillers such as ceramics, resins, and metals can be added to the substrate resin layer to form concavoconvex on the surface of the substrate resin layer.

[0060] The tensile strength of the substrate resin layer is, for example, more than 100 MPa, more than 200 MPa, more than 250 MPa, or more than 300 MPa. The upper limit of the tensile strength of the substrate resin layer is not particularly limited, and from the viewpoint of ensuring flexibility sufficient to relax stress, it can be, for example, less than 500 MPa.

[0061] The tensile strength of the substrate resin layer is obtained by the following formula based on the maximum load when the test piece of the substrate resin layer is stretched at a certain speed in a direction perpendicular to its cross section. That is, the tensile strength is the nominal stress obtained by dividing the maximum load by the initial cross-sectional area. The tensile strength is measured by a method based on JIS C2151. The test piece is made by punching the substrate resin layer into a predetermined shape. The shape of the test piece is the test piece type 2 of JIS C 2151. The thickness of the test piece is the thickness of the substrate resin layer.

[0062] ρ=P max / A0

[0063] ρ: tensile strength (MPa)

[0064] P max :Maximum load (N)

[0065] A0: Initial cross-sectional area (mm 2 )

[0066] The elongation at break of the substrate resin layer is, for example, 50% or more, 80% or more, 100% or more, or 200% or more. The upper limit of the elongation at break of the substrate resin layer is not particularly limited, but from the perspective of ensuring sufficient mechanical strength, it may be, for example, 400% or less.

[0067] The elongation at break of the substrate resin layer is determined by the following formula based on the length at break and the initial length when the test piece of the substrate resin layer is stretched at a constant speed in a direction perpendicular to its cross section. The elongation at break is measured by a method based on JIS K 7127. The shape of the test piece is the test piece type 2 of JIS K 7127. The thickness of the test piece is the thickness of the substrate resin layer.

[0068] Elongation at break δ (%) = 100 × (length at break L - initial length Lo) / initial length Lo

[0069] δ: Elongation at break (%)

[0070] L: length at break

[0071] Lo: initial length

[0072] The thickness of the substrate resin layer is, for example, 20 μm or less, and may be 6 μm to 12 μm. The thickness of the substrate resin layer can be determined by measuring the thickness of any 10 points of the substrate resin layer in the cross section of the negative electrode, the negative electrode current collector, or the resin film using a scanning electron microscope (SEM), and calculating their average value.

[0073] The negative electrode may also include a lithium metal layer stacked on the surface of the transition metal layer. In this case, the lithium metal layer is in contact with the transition metal layer. The lithium metal layer usually promotes the embrittlement of the resin film caused by the transition metal. On the other hand, in the case where the resin film has a surface resin layer containing a nitrogen-containing resin, such embrittlement is significantly suppressed. In other words, the negative electrode collector disclosed in the present invention is particularly suitable for use in the case of a lithium secondary battery in which lithium metal is precipitated in the negative electrode during charging and dissolved during discharge.

[0074] However, when the negative electrode is a negative electrode active material other than lithium metal, for example, a carbon material such as graphite, a silicon-containing material, etc., it is sometimes preferable to use the negative electrode current collector according to the present disclosure in consideration of long-term reliability.

[0075] The lithium metal layer may have a function of collecting electricity. During charging, the lithium ions contained in the non-aqueous electrolyte accept electrons on the lithium metal layer to become lithium metal, which is precipitated on the surface of the lithium metal layer. The lithium metal precipitated on the surface of the lithium metal layer is dissolved in the non-aqueous electrolyte in the form of lithium ions by discharge.

[0076] The lithium metal layer can be a layer formed by at least one of lithium metal and a lithium alloy. The lithium alloy preferably contains magnesium. The content of magnesium contained in the lithium alloy can be, for example, 0.1% by mass or more, preferably 0.5% by mass or more or 1% by mass or more, and can also be 3% by mass or more or 5% by mass or more. When the content of magnesium in the lithium alloy is in such a range, the effect of suppressing the dendritic precipitation of lithium metal can be obtained. In addition, it is easy to form a SEI film with excellent film properties on the surface of the lithium metal layer. The content of magnesium in the lithium alloy is, for example, less than 30% by mass, and can be less than 15% by mass or less than 10% by mass. When the content of magnesium in the lithium alloy is in such a range, magnesium is easily dissolved in lithium and a stable lithium alloy is easily formed.

[0077] The lithium alloy may contain a third element in addition to lithium (the first element) and magnesium (the second element). Examples of the third element include aluminum, indium, calcium, lead, hydrogen, sodium, bismuth, gold, silver, copper and zinc. The lithium alloy may contain one third element or two or more third elements. The content of the third element in the lithium alloy is, for example, less than 10% by mass, and may be less than 1% by mass or less than 0.1% by mass.

[0078] The lithium metal layer can be formed by laminating a lithium metal foil on the surface of the transition metal layer. The lithium metal layer can also be formed by depositing it on the surface of the transition metal layer by a liquid phase method or a gas phase method. As a liquid phase method, an electrolysis method can be cited. As a gas phase method, an evaporation method, a sputtering method, etc. can be cited. However, there is no particular limitation on the method for forming the lithium metal layer.

[0079] In a discharge state where the depth of discharge (DOD: Depth of Discharge) is more than 90%, the thickness of the lithium metal layer can be, for example, more than 1 μm, or more than 5 μm. On the other hand, from the viewpoint of improving the energy density of the secondary battery, in a discharge state where the depth of discharge is more than 90%, the thickness of the lithium metal layer can be less than 30 μm, or less than 25 μm. An example of a preferred range of the thickness of the lithium metal layer is 5 μm to 20 μm. In addition, the so-called discharge state with a depth of discharge (DOD) of more than 90% is synonymous with a state of charge (SOC) of less than 0.1×C when the rated capacity of the battery is set to C. The thickness of the lithium metal layer can be obtained by measuring the thickness of any 10 points of the lithium metal layer in the cross section of the negative electrode using a scanning electron microscope (SEM) and calculating their average value.

[0080] The surface resin layer and the transition metal layer may be formed on only one side of the base resin layer or on both sides. Similarly, the lithium metal layer may be formed on only one side of the base resin layer or on both sides.

[0081] When the surface resin layer and the transition metal layer are laminated on both sides of the substrate resin layer, the total thickness of the substrate resin layer, the surface resin layer and the transition metal layer can be, for example, 10 μm to 80 μm. Such a negative electrode collector is suitable for forming a wound electrode group in which the positive electrode and the negative electrode are wound with a separator. In a wound electrode group, stress is easily generated during charging and discharging, and in particular, the commonly used copper foil negative electrode collector is prone to breakage due to embrittlement. In addition, a large tensile tension is sometimes applied to the negative electrode on the outer side of the wound electrode group. On the other hand, when using the negative electrode collector involved in the present disclosure, since the negative electrode collector contains a resin film, even when a large tensile tension is applied to the negative electrode on the outer side of the wound electrode group, the breakage of the negative electrode can be significantly suppressed.

[0082] The surface resin layer is preferably provided on the entire surface of each main surface of the substrate resin layer, but there may be a portion not covered by the surface resin layer as long as the portion is less than 10% of the area of ​​the main surface of the substrate resin layer. The main surface of the substrate resin layer refers to the portion of the substrate resin layer other than the end surface, and is the two surfaces with the largest area.

[0083] The transition metal layer is preferably provided on the entire surface of each main surface of the surface resin layer, but there may be a portion not covered by the transition metal layer as long as the portion is less than 30% of the area of ​​the main surface of the surface resin layer. In addition, when a portion of the main surface of the substrate resin layer is not covered by the surface resin layer, it is preferred that the surface of the portion is not in contact with the transition metal layer.

[0084] When a lithium metal layer is formed, the lithium metal layer is preferably provided on the entire surface of each main surface of the transition metal layer. There may be a portion not covered by the lithium metal layer as long as the portion is less than 30% of the area of ​​the main surface of the transition metal layer.

[0085] A preferred embodiment of the present invention relates to a negative electrode current collector comprising a base resin layer, surface resin layers formed on both surfaces of the base resin layer, and transition metal layers formed on the surfaces of both surface resin layers (ie, both surfaces of the resin film).

[0086] A preferred technical solution involves a negative electrode having a substrate resin layer, a surface resin layer formed on both sides of the substrate resin layer, a transition metal layer formed on the surface of the surface resin layer on both sides (i.e., both sides of the resin film), and a lithium metal layer formed on the surface of the transition metal layer on both sides (i.e., both sides of the negative electrode collector). The substrate resin layer, the surface resin layer, and the transition metal layer constitute the negative electrode collector. The lithium metal layer can function as both the negative electrode collector and the negative electrode active material layer. Here, the lithium metal layer is a constituent element of the negative electrode, which is distinguished from the negative electrode collector.

[0087] A preferred technical solution relates to a negative electrode, which is suitable for a lithium secondary battery in which lithium metal is precipitated in the negative electrode during charging and dissolved during discharging. The lithium contained in the lithium metal layer may or may not dissolve during discharge. In other words, the lithium precipitated in the negative electrode during charging and dissolved from the negative electrode during discharge may come from the positive electrode or from the positive electrode and the lithium metal layer.

[0088] [positive electrode]

[0089] The positive electrode, for example, comprises a positive electrode collector and a positive electrode mixture layer supported on the positive electrode collector. The positive electrode mixture layer can be formed by applying a positive electrode slurry formed by dispersing a positive electrode mixture in a dispersion medium on the surface of the positive electrode collector and drying it. The dried coating film can be rolled as needed. The positive electrode mixture can contain a positive electrode active material as an essential component, and can contain a binder, a conductive agent, etc. as an optional component. The positive electrode mixture layer can be formed only on one side of the positive electrode collector, or on both sides.

[0090] The positive electrode active material is a material that absorbs and releases lithium ions to embody capacity. As the positive electrode active material, for example, lithium-containing transition metal oxides, transition metal fluorides, polyanions, fluorinated polyanions, transition metal sulfides, etc. can be cited. Among them, lithium-containing transition metal oxides are preferred in terms of low manufacturing cost and high average discharge voltage.

[0091] As the transition metal element contained in the transition metal oxide containing lithium, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Y, Zr, W, etc. can be mentioned. The transition metal oxide containing lithium can contain one transition metal element, or it can contain two or more. The transition metal element can be Co, Ni and / or Mn. The transition metal oxide containing lithium can contain one or more typical elements as needed. As typical elements, Mg, Al, Ca, Zn, Ga, Ge, Sn, Sb, Pb, Bi, etc. can be mentioned. The typical element can be Al, etc.

[0092] The conductive material is, for example, a carbon material, and examples of the carbon material include carbon black, acetylene black, Ketjen black, carbon nanotubes, and graphite.

[0093] Examples of the binder include fluororesins, polyacrylonitrile, polyimide resins, acrylic resins, polyolefin resins, rubber polymers, etc. Examples of the fluororesins include polytetrafluoroethylene, polyvinylidene fluoride, and the like.

[0094] The positive electrode current collector may be made of foil, film, etc. A carbon material may be coated on the surface of the positive electrode current collector. Examples of the material of the positive electrode current collector include metal materials containing Al, Ti, Fe, etc. The metal material may be Al, Al alloy, Ti, Ti alloy, Fe alloy, etc. The Fe alloy may be stainless steel (SUS). A material obtained by imparting a metal material to the surface of a resin film by physical vapor deposition (PVD) or the like may be used. There is no particular limitation on the thickness of the positive electrode current collector, and for example, it is greater than 5 μm and less than 30 μm.

[0095] [Diaphragm]

[0096] It is usually preferred to sandwich a separator between the positive electrode and the negative electrode. The separator has high ion permeability and has appropriate mechanical strength and insulation. As the separator, microporous films, woven fabrics, non-woven fabrics, etc. can be used. As the material of the separator, polyolefins such as polypropylene and polyethylene, polymethylpentene, polyethylene terephthalate, polybutylene terephthalate, aramid, cellulose, etc. are preferred.

[0097] In order to improve the heat resistance of the separator, a heat-resistant coating containing ceramic particles may be provided on the surface (one or both surfaces) of the separator.

[0098] The separator may be sandwiched between the positive electrode and the negative electrode with one sheet or with multiple sheets. When multiple sheets of separator are sandwiched between the positive electrode and the negative electrode, multiple sheets of one of microporous films, woven fabrics, and nonwoven fabrics may be overlapped and used, or multiple sheets of at least two of microporous films, woven fabrics, and nonwoven fabrics may be overlapped and used. There is no particular restriction on the thickness of the separator when one sheet is sandwiched, and it is preferably 5 to 80 μm. There is no particular restriction on the thickness of the separator when multiple sheets are sandwiched, and it is preferably 5 to 80 μm.

[0099] [Non-aqueous electrolyte]

[0100] The non-aqueous electrolyte having lithium ion conductivity may be a solid electrolyte or a liquid electrolyte (electrolyte solution). The non-aqueous electrolyte may be a gel electrolyte (polymer electrolyte) containing a matrix polymer that absorbs a non-aqueous solvent to form a gel.

[0101] The polymer electrolyte contains, for example, a lithium salt and a matrix polymer, or contains a non-aqueous solvent, a lithium salt and a matrix polymer. As the matrix polymer, for example, a fluorine resin, an acrylic resin, a polyether resin, etc. can be used.

[0102] As the solid electrolyte, for example, an inorganic solid electrolyte is used. As the inorganic solid electrolyte, for example, a material known in all-solid lithium ion secondary batteries (for example, an oxide-based solid electrolyte, a sulfide-based solid electrolyte, a halide-based solid electrolyte, etc.) is used.

[0103] The electrolyte solution includes, for example, a non-aqueous solvent and a lithium salt dissolved in the non-aqueous solvent. When the lithium salt is dissolved in the non-aqueous solvent, lithium ions and anions are generated.

[0104] As the anion, known anions used in non-aqueous electrolytes can be used. Specifically, BF4 － 、ClO4 － PF6 － CF3SO3 － CF3CO2 － , anions of imide compounds, anions of oxalate complexes, etc. Examples of anions of imide compounds include N(SO2F)2－ 、N(SO2CF3)2 － The anion of the oxalate complex may contain boron and / or phosphorus. Examples of the anion of the oxalate complex include bis(oxalatoborate) anion, BF2(C2O4) － PF4(C2O4) － PF2(C2O4)2 － The non-aqueous electrolyte may contain one lithium salt alone or two or more lithium salts.

[0105] In lithium secondary batteries, from the viewpoint of suppressing the dendritic precipitation of lithium metal, it is preferred that the non-aqueous electrolyte contains at least oxalate complex anions. Through the interaction between the oxalate complex anions and lithium, lithium metal is easily precipitated uniformly in the form of fine particles. Therefore, it is easy to suppress the local precipitation of lithium metal. The non-aqueous electrolyte may contain oxalate complex anions and other anions. The other anions may be PF6 － , imide anions, etc.

[0106] Examples of the non-aqueous solvent include ester compounds, ether compounds, nitrile compounds, and amide compounds. These compounds include halogen-substituted compounds. Examples of the halogen-substituted compounds include fluorides. The non-aqueous electrolyte may contain these non-aqueous solvents alone or in combination of two or more thereof.

[0107] The non-aqueous solvent of the lithium secondary battery may contain an ether compound as a main component. In addition, the main component refers to the content of the ether compound in the non-aqueous solvent being 50% by mass or more, or 80% by mass or more. In addition, the content of the ether compound in the non-aqueous solvent may be 95% by mass or less, or 100% by mass or less. Regarding the content range of the ether compound in the non-aqueous solvent, it may be a range formed by any combination of the above upper and lower limits.

[0108] The ether compound is excellent in stability (particularly resistance to reduction) and can suppress the generation of decomposition products on the surface of the negative electrode, and is therefore considered to be able to suppress the expansion of the negative electrode.

[0109] As ether compounds, cyclic ethers, chain ethers, etc. can be mentioned. As cyclic ethers, 1,3-dioxolane, 4-methyl-1,3-dioxolane, tetrahydrofuran, 2-methyltetrahydrofuran, etc. can be mentioned. As chain ethers, 1,2-dimethoxyethane, diethyl ether, ethyl vinyl ether, methyl phenyl ether, benzyl ethyl ether, diphenyl ether, dibenzyl ether, 1,2-diethoxyethane, diethylene glycol dimethyl ether, 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, etc. can be mentioned. Among them, 1,2-dimethoxyethane, 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, etc. are preferred. These can be used alone or in combination of two or more.

[0110] As ester compounds, for example, carbonates, carboxylates, etc. can be mentioned. As cyclic carbonates, ethylene carbonate, propylene carbonate, etc. can be mentioned. As chain carbonates, dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate, etc. can be mentioned. As cyclic carboxylates, γ-butyrolactone, γ-valerolactone, etc. can be mentioned. As chain carboxylates, ethyl acetate, methyl propionate, methyl fluoropropionate, etc. can be mentioned. These can be used alone or in combination of two or more.

[0111] The concentration of the lithium salt in the non-aqueous electrolyte is, for example, 0.5 mol / L or more and 3.5 mol / L or less. The concentration of the anion in the non-aqueous electrolyte may be set to 0.05 mol / L or more and 3.5 mol / L or less. In addition, the concentration of the anion of the oxalate complex in the non-aqueous electrolyte may be set to 0.05 mol / L or more and 1 mol / L or less.

[0112] The non-aqueous electrolyte may contain an additive. The additive may be a substance that forms a film on the negative electrode. By forming a film from the additive on the negative electrode, it is easier to suppress the formation of dendrites. Examples of the additive include vinylene carbonate, fluoroethylene carbonate (FEC), vinyl ethyl carbonate (VEC), and the like.

[0113] [Lithium secondary battery]

[0114] Hereinafter, the structure of the lithium secondary battery according to the present disclosure will be described with reference to the drawings, taking a cylindrical battery having a wound electrode group as an example. However, the present disclosure is not limited to the following structure.

[0115] Figure 1 It is a longitudinal cross-sectional view schematically showing an example of a lithium secondary battery according to an embodiment of the present disclosure. Figure 2 Yes Figure 1 An enlarged view of the portion surrounded by region II (including a portion of the positive electrode). Figure 3 Yes Figure 1 The figure is an enlarged view of the portion surrounded by region III (including a portion of the negative electrode). In addition, each figure is a schematic diagram, and the ratio of the size (for example, thickness) of each component is different from the actual one.

[0116] The lithium secondary battery 10 includes a cylindrical battery case, a wound electrode group 14 housed in the battery case, and a non-aqueous electrolyte (not shown). The electrode group 14 is formed by winding a strip-shaped positive electrode 11 and a strip-shaped negative electrode 12 with a separator 13 interposed therebetween.

[0117] The negative electrode 12 of the example shown in the figure is in a discharged state with a depth of discharge (DOD) of 100%, and is composed of a negative electrode collector 40 and a lithium metal layer 41. The negative electrode collector 40 is composed of a base resin layer 42, a surface resin layer 43 formed on both surfaces of the base resin layer 42, and a transition metal layer 44 formed on the surfaces of both surface resin layers 43. Without being limited to the example shown in the figure, the negative electrode 12 may be composed only of a negative electrode collector in a discharged state with a depth of discharge (DOD) of 100%.

[0118] The negative electrode 12 is electrically connected to the case body 15 also serving as a negative electrode terminal via a negative electrode lead 20. The negative electrode lead 20 has one end connected to, for example, a longitudinal end of the negative electrode 12 and the other end welded to the inner bottom surface of the case body 15.

[0119] The positive electrode 11 includes a positive electrode current collector 30 and a positive electrode mixture layer 31, and is electrically connected to the cap 26 also serving as a positive electrode terminal via a positive electrode lead 19. One end of the positive electrode lead 19 is connected, for example, to the vicinity of the center in the longitudinal direction of the positive electrode 11. The positive electrode lead 19 extending from the positive electrode 11 passes through a through hole (not shown) formed in the insulating plate 17 and extends to the filter 22. The other end of the positive electrode lead 19 is welded to the surface of the filter 22 on the electrode group 14 side.

[0120] The battery case is composed of a case body 15 which is a bottomed cylindrical metal container and a sealing body 16 which seals the opening of the case body 15. A gasket 27 is arranged between the case body 15 and the sealing body 16 to ensure the airtightness of the battery case. In the case body 15, insulating plates 17 and 18 are arranged at both ends of the electrode group 14 in the winding axis direction.

[0121] The housing body 15 has a step portion 21 formed by partially punching the side wall of the housing body 15 from the outside, for example. The step portion 21 may be formed in an annular shape on the side wall of the housing body 15 along the circumferential direction of the housing body 15. In this case, the sealing body 16 is supported on the surface of the step portion 21 on the opening side.

[0122] The sealing body 16 includes a filter 22, a lower valve body 23, an insulating component 24, an upper valve body 25 and a cover 26. In the sealing body 16, these components are stacked in this order. The sealing body 16 is installed at the opening of the shell body 15 in such a way that the cover 26 is located on the outside of the shell body 15 and the filter 22 is located on the inside of the shell body 15. The above-mentioned components constituting the sealing body 16 are, for example, in the shape of a circular plate or a ring. The lower valve body 23 and the upper valve body 25 are connected to each other at their respective central portions, and an insulating component 24 is sandwiched between their respective peripheral portions. The filter 22 and the lower valve body 23 are connected to each other at their respective peripheral portions. The upper valve body 25 and the cover 26 are connected to each other at their respective peripheral portions. That is, the components except the insulating component 24 are electrically connected to each other.

[0123] A vent hole (not shown) is formed in the lower valve body 23. Therefore, when the internal pressure of the battery case increases due to abnormal heating or the like, the upper valve body 25 expands toward the cover 26 and moves away from the lower valve body 23. As a result, the electrical connection between the lower valve body 23 and the upper valve body 25 is cut off. When the internal pressure further increases, the upper valve body 25 ruptures, and gas is discharged from an opening (not shown) formed in the cover 26.

[0124] In the example, a cylindrical lithium secondary battery is described, but it is not limited to this case, and the present embodiment may also be applicable. The shape of the secondary battery can be appropriately selected from various shapes such as coin-shaped, square-shaped, sheet-shaped, flat-shaped, etc. other than cylindrical, according to its use. In addition, a wound electrode group is shown in the example, but the form of the electrode group is not particularly limited, and it can be a stacked electrode group formed by stacking the positive electrode and the negative electrode across the separator. In addition, with respect to the structure other than the electrode group and the non-aqueous electrolyte of the secondary battery, a known structure can be used without particular restriction.

[0125] Postscript

[0126] Based on the description of the above embodiments, the following technical solutions are disclosed.

[0127] (Technical Solution 1)

[0128] A secondary battery comprises a positive electrode, a negative electrode, a separator arranged between the positive electrode and the negative electrode, and a non-aqueous electrolyte with lithium ion conductivity, wherein the negative electrode comprises a negative electrode collector, the negative electrode collector comprises a resin film and a transition metal layer stacked with the resin film, the resin film comprises a base resin layer and a surface resin layer, and at least the surface resin layer contains a nitrogen-containing resin.

[0129] (Technical Solution 2)

[0130] According to the secondary battery of claim 1, in the negative electrode, lithium metal is deposited during charge and the lithium metal is dissolved during discharge.

[0131] (Technical Solution 3)

[0132] According to the secondary battery of claim 1 or 2, the nitrogen-containing resin contains nitrogen-hydrogen bonds.

[0133] (Technical Solution 4)

[0134] According to the secondary battery described in any one of technical solutions 1 to 3, the nitrogen-containing resin is a polymer having at least one selected from a urea bond, a melamine structure, a triazine ring, an amino group, an amide bond, an aromatic amide bond, an imide bond, a carbamate bond, a carbodiimide bond, a uretdione structure, an isocyanurate ring, a nitrile group and an amide group.

[0135] (Technical Solution 5)

[0136] According to any one of claims 1 to 4, the nitrogen-containing resin is a polymer having at least one selected from an aliphatic isocyanate group, an aromatic isocyanate group, an allophanate group, and a biuret group.

[0137] (Technical Solution 6)

[0138] According to any one of claims 1 to 5 of the secondary battery, the surface resin layer contains a filler.

[0139] (Technical Solution 7)

[0140] According to any one of claims 1 to 6, the secondary battery has a thickness of 5 μm or less.

[0141] (Technical Solution 8)

[0142] According to any one of claims 1 to 7, the secondary battery, wherein the thickness of the base resin layer is 20 μm or less.

[0143] (Technical Solution 9)

[0144] According to any one of technical solutions 1 to 8, the thickness of the transition metal layer is 3 μm or less.

[0145] (Technical Solution 10)

[0146] The secondary battery according to any one of claims 1 to 9, wherein a lithium metal layer is stacked on the surface of the transition metal layer.

[0147] (Technical Solution 11)

[0148] A negative electrode current collector comprises a resin film and a transition metal layer laminated with the resin film, wherein the resin film comprises a base resin layer and a surface resin layer, and at least the surface resin layer contains a nitrogen-containing resin.

[0149] (Technical Solution 12)

[0150] According to the negative electrode collector described in technical solution 11, the nitrogen-containing resin is a polymer having at least one selected from a urea bond, a melamine structure, a triazine ring, an amino group, an amide bond, an aromatic amide bond, an imide bond, a carbamate bond, a carbodiimide bond, a uretdione structure, an isocyanurate ring, a nitrile group and an amide group.

[0151] <Example>

[0152] Hereinafter, the lithium secondary battery according to the present disclosure will be specifically described based on examples and comparative examples. The present disclosure is not limited to the following examples.

[0153] 《Example 1》

[0154] (1) Preparation of positive electrode

[0155] Lithium-containing transition metal oxide (NCA; positive electrode active material) containing Li, Ni, Co and Al, acetylene black (AB; conductive material) and polyvinylidene fluoride (PVdF; binding material) are mixed in a mass ratio of NCA:AB:PVdF=95:2.5:2.5, and then an appropriate amount of N-methyl-2-pyrrolidone (NMP) is added and stirred to prepare a positive electrode mixture slurry. Next, the obtained positive electrode mixture slurry is applied on both sides of an Al foil (thickness 15μm) serving as a positive electrode collector, and then dried, and the coating of the positive electrode mixture is rolled by rolling. Finally, the obtained stack of the positive electrode collector and the positive electrode mixture layer is cut into a predetermined electrode size, and a positive electrode mixture layer (thickness 65μm, 245g / m 2 )'s positive electrode.

[0156] (2) Preparation of negative electrode

[0157] (2-1) Negative Electrode Collector

[0158] Melamine resin as a nitrogen-containing resin is coated on both sides of a base resin layer (thickness 12 μm) made of polypropylene (PP) to form a surface resin layer (thickness 1 μm), and then a copper vapor-deposited film is formed on the surface of the surface resin layer as a transition metal layer (thickness 1 μm) to obtain a negative electrode collector.

[0159] (2-2) Negative electrode

[0160] A negative electrode active material containing a silicon-containing material (composite particles in which nano-silicon particles are dispersed in a lithium silicate phase at a content of 55% by mass) and graphite particles in a mass ratio of 6:94, sodium carboxymethyl cellulose (CMC-Na), and styrene-butadiene rubber (SBR) are mixed in a mass ratio of negative electrode active material: CMC-Na: SBR = 97.5:1:1.5, and then an appropriate amount of water is added and stirred to prepare a negative electrode mixture slurry. Next, the obtained negative electrode mixture slurry is applied to both sides of the negative electrode collector, dried, and the coating of the negative electrode mixture is rolled by rolling. Finally, the obtained stack of the negative electrode collector and the negative electrode mixture layer is cut into a predetermined electrode size, and a negative electrode mixture layer (thickness 75μm, 226g / m 2 )'s negative electrode.

[0161] (3) Preparation of non-aqueous electrolyte

[0162] In a non-aqueous solvent, LiPF6 and LiBF2(C2O4) were dissolved at a concentration of 1 mol / L and 0.1 mol / L, respectively, to prepare a liquid non-aqueous electrolyte. The non-aqueous solvent used was a mixed solvent of 1,2-dimethoxyethane and 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether.

[0163] (4) Battery production

[0164] An Al tab is installed on the positive electrode. A Ni tab is installed on the lithium metal layer of the negative electrode. In an inert gas atmosphere, a separator is placed between the positive electrode and the negative electrode, and the positive electrode and the negative electrode are wound to make a wound electrode group. A polyethylene microporous film (thickness 25 μm) is used as the separator. The electrode group is housed in a bag-shaped outer body formed by a laminate sheet having an Al layer, a non-aqueous electrolyte is injected into the outer body housing the electrode group, and then the outer body is sealed to make a lithium secondary battery. In Table 1, battery E1 is the battery of Example 1.

[0165] 《Example 2》

[0166] In an inert gas atmosphere, lithium metal foil (thickness 25 μm) was pressed onto both sides of the negative electrode current collector prepared in the same manner as in Example 1 to prepare a negative electrode without a negative electrode mixture layer.

[0167] 《Example 3》

[0168] A negative electrode was prepared in the same manner as in Example 2 except that the base resin layer made of polypropylene (PP) of the negative electrode current collector was changed to a base resin layer made of polyethylene terephthalate (PET) (thickness 12 μm). A lithium secondary battery E3 was prepared in the same manner as in Example 1 using this negative electrode.

[0169] 《Example 4》

[0170] A negative electrode was produced in the same manner as in Example 3 except that the surface resin layer of the negative electrode current collector made of melamine resin was changed to a surface resin layer made of polyurea resin (1 μm in thickness). A lithium secondary battery E4 was produced in the same manner as in Example 1 using this negative electrode.

[0171] 《Example 5》

[0172] A negative electrode was produced in the same manner as in Example 3 except that the surface resin layer of the negative electrode current collector made of melamine resin was changed to a surface resin layer made of polyamide resin (1 μm in thickness). A lithium secondary battery E5 was produced in the same manner as in Example 1 using this negative electrode.

[0173] Example 6

[0174] A negative electrode was produced in the same manner as in Example 3 except that the surface resin layer of the negative electrode current collector made of melamine resin was changed to a surface resin layer made of aramid resin (1 μm in thickness). A lithium secondary battery E6 was produced in the same manner as in Example 1 using this negative electrode.

[0175] 《Example 7》

[0176] A negative electrode was produced in the same manner as in Example 3 except that the surface resin layer of the negative electrode current collector made of melamine resin was changed to a surface resin layer made of polyimide resin (1 μm in thickness). A lithium secondary battery E7 was produced in the same manner as in Example 1 using this negative electrode.

[0177] 《Example 8》

[0178] A negative electrode was produced in the same manner as in Example 3 except that the surface resin layer of the negative electrode current collector made of melamine resin was changed to a surface resin layer made of polyurethane resin (1 μm in thickness). A lithium secondary battery E8 was produced in the same manner as in Example 1 using this negative electrode.

[0179] 《Example 9》

[0180] A negative electrode was prepared in the same manner as in Example 8 except that 5 parts by mass of silica having an average particle size of 1.5 μm was mixed per 100 parts by mass of the polyurethane resin in the polyurethane resin surface resin layer. A lithium secondary battery E9 was prepared in the same manner as in Example 1 using this negative electrode.

[0181] 《Example 10》

[0182] A negative electrode was produced in the same manner as in Example 3 except that the surface resin layer of the negative electrode current collector made of melamine resin was changed to a surface resin layer made of polyurethane resin containing an isocyanate residue (1 μm in thickness). A lithium secondary battery E10 was produced in the same manner as in Example 1 using this negative electrode.

[0183] Comparative Example 1

[0184] On both sides of the polypropylene (PP) substrate resin layer (thickness 12 μm), without forming a surface resin layer, a copper vapor-deposited film is directly formed as a transition metal layer (thickness 1 μm) to obtain a negative electrode collector. A negative electrode active material consisting only of graphite particles is used, and a negative electrode mixture slurry is prepared in the same manner as in Example 1. The slurry is used to prepare a negative electrode mixture layer (thickness 75 μm, 226 g / m 2 ) was used. A lithium secondary battery R1 was produced in the same manner as in Example 1 using this negative electrode.

[0185] Comparative Example 2

[0186] A negative electrode was prepared in the same manner as in Comparative Example 1 except that the base resin layer made of polypropylene (PP) of the negative electrode current collector was changed to a base resin layer made of polyethylene terephthalate (PET) (thickness 12 μm). A lithium secondary battery R2 was prepared in the same manner as in Example 1 using this negative electrode.

[0187] 《Comparative Example 3》

[0188] On both sides of the polypropylene (PP) substrate resin layer (thickness 12 μm), no surface resin layer is formed, and a copper vapor-deposited film is directly formed as a transition metal layer (thickness 1 μm) to obtain a negative electrode collector. In an inert gas atmosphere, lithium metal foil (thickness 25 μm) is pressed on both sides of the negative electrode collector to produce a negative electrode without a negative electrode mixture layer. Using this negative electrode, a lithium secondary battery R3 is produced in the same manner as in Example 1.

[0189] 《Comparative Example 4》

[0190] A negative electrode was prepared in the same manner as in Comparative Example 3 except that the base resin layer made of polypropylene (PP) of the negative electrode current collector was changed to a base resin layer made of polyethylene terephthalate (PET) (thickness 12 μm). A lithium secondary battery R4 was prepared in the same manner as in Example 1 using this negative electrode.

[0191] 《Comparative Example 5》

[0192] A negative electrode was prepared in the same manner as in Comparative Example 4 except that a nickel-chromium alloy (NiCr) layer with a thickness of 0.02 μm was formed on both sides of the base resin layer before forming a copper vapor-deposited film on both sides of the base resin layer and then forming a copper vapor-deposited film. A lithium secondary battery R5 was prepared in the same manner as in Example 1 using this negative electrode.

[0193] The configurations of the respective negative electrodes are summarized in Table 1. In addition, the respective batteries were designed so that their initial design capacities would be substantially the same.

[0194] [Table 1]

[0195]

[0196] [Evaluation 1]

[0197] The period until cracks occur in the negative electrode collector ("period T") is measured by the following method. After the lithium metal or active material layer (graphite) is applied, the maximum height roughness Rz is measured by the method described above (JIS B 0601: 2013) at the initial stage and at regular intervals. Due to embrittlement, unevenness will occur on the surface over time. The period T until Rz reaches more than twice the initial value is determined.

[0198] [Evaluation 2]

[0199] For each of the obtained batteries, a charge-discharge cycle test was performed in an environment of 25° C. The charge and discharge were performed under the following conditions. A 20-minute pause was provided between charge and discharge.

[0200] (Charge)

[0201] The battery was charged at a constant current of 10 mA until the voltage reached 4.1 V, and then charged at a constant voltage of 4.1 V until the current reached 1 mA.

[0202] (Discharge)

[0203] The battery was discharged at a constant current of 10 mA until the voltage reached 3V.

[0204] The discharge capacity of the first cycle was determined as capacity C0. Table 1 shows relative values ​​(indexes) when the capacity C0 of Example 8 was set to 100.

[0205] [Evaluation 3]

[0206] The volume energy density of each battery was calculated as the ratio of the capacity C0 to the volume of the electrode group to obtain the volume energy density (Ed). Table 1 shows the relative value (index) when the energy density Ed of Example 8 is set to 100.

[0207] [Evaluation 4]

[0208] The charge and discharge of Evaluation 2 were repeated until the discharge capacity reached 80% of the capacity C0, and the number of cycles up to this point was determined. Table 1 shows relative values ​​(indexes) when the capacity C0 of Example 1 was set to 100.

[0209] As shown in Table 1, the period T until cracks occur in the negative electrode collector is significantly increased when the surface resin layer is formed of a nitrogen-containing resin, and the number of charge and discharge cycles is significantly increased. On the other hand, no decrease in energy density due to the formation of the surface resin layer is observed.

[0210] The present invention has been described in conjunction with the currently preferred embodiments, but this disclosure should not be interpreted as limiting. By reading the above disclosure, a person of ordinary skill in the art to which the present invention belongs can clearly understand various modifications and changes. Therefore, the appended claims should be interpreted as including all modifications and changes without departing from the true spirit and scope of the present invention.

[0211] Industrial Availability

[0212] The negative electrode current collector and secondary battery disclosed herein can be used in electronic devices such as mobile phones, smartphones, and tablet computers, electric vehicles including hybrid and plug-in hybrid vehicles, household storage batteries combined with solar cells, and the like.

[0213] Description of Reference Numerals

[0214] 10 Lithium secondary battery

[0215] 11 Positive electrode

[0216] 12 Negative electrode

[0217] 13 Diaphragm

[0218] 14 Electrode Group

[0219] 15 Shell body

[0220] 16 Sealing body

[0221] 17, 18 Insulation board

[0222] 19 Positive lead

[0223] 20 Negative lead

[0224] 21 Step

[0225] 22 Filters

[0226] 23 Lower valve body

[0227] 24 Insulation parts

[0228] 25 Upper valve body

[0229] 26 Cover

[0230] 27 Gasket

[0231] 30 Positive electrode collector

[0232] 31. Positive electrode mixture layer

[0233] 40 Resin film

[0234] 41 Lithium metal layer

[0235] 42 base resin layer

[0236] 43 Surface resin layer

[0237] 44 Transition Metal Layer

Claims

1. A secondary battery comprising a positive electrode, a negative electrode, a separator disposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte having lithium ion conductivity, The negative electrode comprises a negative electrode current collector, The negative electrode current collector comprises a resin film and a transition metal layer stacked on the resin film. The resin film comprises a base resin layer and a surface resin layer. At least the surface resin layer contains a nitrogen-containing resin.

2. The secondary battery according to claim 1, At the negative electrode, lithium metal is deposited during charge, and the lithium metal is dissolved during discharge.

3. The secondary battery according to claim 1, The nitrogen-containing resin contains nitrogen-hydrogen bonds.

4. The secondary battery according to claim 1, The nitrogen-containing resin is a polymer having at least one selected from urea bonds, melamine structures, triazine rings, amino groups, amide bonds, aromatic amide bonds, imide bonds, urethane bonds, carbodiimide bonds, uretdione structures, isocyanurate rings, nitrile groups, and amide groups.

5. The secondary battery according to claim 1, The nitrogen-containing resin is a polymer having at least one selected from the group consisting of an aliphatic isocyanate group, an aromatic isocyanate group, an allophanate group, and a biuret group.

6. The secondary battery according to claim 1, The surface resin layer contains a filler.

7. The secondary battery according to claim 1, The surface resin layer has a thickness of 5 μm or less.

8. The secondary battery according to claim 1, The thickness of the base resin layer is 20 μm or less.

9. The secondary battery according to claim 1, The thickness of the transition metal layer is less than 3 μm.

10. The secondary battery according to any one of claims 1 to 9, A lithium metal layer is stacked on the surface of the transition metal layer.

11. A negative electrode current collector comprising a resin film and a transition metal layer laminated with the resin film, The resin film comprises a base resin layer and a surface resin layer. At least the surface resin layer contains a nitrogen-containing resin.

12. The negative electrode current collector according to claim 11, The nitrogen-containing resin is a polymer having at least one selected from urea bonds, melamine structures, triazine rings, amino groups, amide bonds, aromatic amide bonds, imide bonds, urethane bonds, carbodiimide bonds, uretdione structures, isocyanurate rings, nitrile groups, and amide groups.

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