Cylindrical nonaqueous electrolyte secondary battery

Abstract

The disclosed cylindrical nonaqueous electrolyte secondary battery (100) comprises a bottomed cylindrical battery case (20), a wound electrode group (10), a nonaqueous electrolyte, a sealing member (40), a positive electrode lead (60), and a negative electrode lead (70). The electrode group (10) includes a positive electrode (11), a negative electrode (12), and a separator (13). The negative electrode (12) expands during charging and contracts during discharging. The outer diameter of the battery case (20) is 15 mm or less. A hollow portion (10s) is present in the center of the electrode group (10). The negative electrode lead (70) is connected to a portion of the negative electrode (12) facing the hollow portion (10s). In the discharge state, the diameter X of the hollow portion and the inner diameter Y of the battery case (20) satisfy 0.25 < X / Y < = 0.50.

Description

Technical Field

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

[0002] Various proposals have been made for non-aqueous electrolyte secondary batteries (e.g., lithium secondary batteries). Patent Document 1 (Japanese Patent Application Publication No. 2000-260473) states in Claim 1: "A wound lithium secondary battery comprising a positive electrode body having a lead terminal provided on a current collector coated with a positive electrode mixture and a negative electrode body having a lead terminal provided on lithium metal or a lithium alloy, wound with a separator interposed therebetween, characterized in that at least one of the lead terminal of the positive electrode body or the lead terminal of the negative electrode body is disposed at the innermost periphery of the winding core of the wound body, and the lead terminal of the positive electrode body or the lead terminal of the negative electrode body is disposed in an area where the positive electrode body and the negative electrode body do not face each other."

[0003] Claim 2 of Patent Document 2 (International Publication No. 2019 / 087708) discloses "a non-aqueous electrolyte secondary battery comprising an electrode body consisting of a positive electrode, a negative electrode and a separator, a non-aqueous electrolyte, and a shell for accommodating the electrode body and the non-aqueous electrolyte, the positive electrode having a positive electrode active material consisting of a lithium-containing transition metal oxide, the negative electrode having a negative electrode collector, lithium metal being deposited on the negative electrode collector during charging, the separator being arranged between the positive electrode and the negative electrode, the molar ratio of the total amount of lithium contained in the positive electrode and the negative electrode to the amount of transition metal contained in the positive electrode being less than 1.1, and in the discharged state, the inner diameter Y (mm) of the shell and the inner diameter Z (mm) of the electrode body satisfy 0.4≤Z / Y≤0.8".

[0004] Prior art literature

[0005] Patent Document 1: Japanese Patent Application Laid-Open No. 2000-260473

[0006] Patent Document 2: International Publication No. 2019 / 087708 Summary of the Invention

[0007] Problems to be solved by the invention

[0008] Small-diameter nonaqueous electrolyte secondary batteries are used for various purposes. In small-diameter nonaqueous electrolyte secondary batteries, the expansion and contraction of the negative electrode caused by charging and discharging become more significant. Therefore, in small-diameter nonaqueous electrolyte secondary batteries, a design different from that of large-diameter nonaqueous electrolyte secondary batteries is required. In this case, an object of the present disclosure is to provide a small-diameter nonaqueous electrolyte secondary battery with good battery characteristics.

[0009] Means for solving problems

[0010] One aspect of the present invention relates to a cylindrical nonaqueous electrolyte secondary battery. The nonaqueous electrolyte secondary battery comprises: a bottomed cylindrical battery case; a wound electrode group and a nonaqueous electrolyte housed in the battery case; a sealing member for sealing the opening of the battery case; a positive electrode lead; and a negative electrode lead. The electrode group comprises a positive electrode, a negative electrode, and a separator disposed between the positive and negative electrodes. The negative electrode expands during charge and contracts during discharge. The battery case has an outer diameter of 15 mm or less, and a hollow portion is located in the center of the electrode group. The negative electrode lead is connected to a portion of the negative electrode facing the hollow portion. In the discharged state, the diameter X of the hollow portion and the inner diameter Y of the battery case satisfy 0.25 < X / Y ≤ 0.50.

[0011] Effects of the Invention

[0012] According to the present disclosure, a small-diameter nonaqueous electrolyte secondary battery having excellent battery characteristics can be obtained.

[0013] The novel features of the present invention are described in the appended claims, but the present invention, both in structure and content, together with other objects and features of 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 This is a longitudinal sectional view schematically showing an example of the nonaqueous electrolyte secondary battery according to the first embodiment.

[0015] Figure 2 It is a schematic cross-sectional view for explaining the structure of an electrode group.

[0016] Figure 3 It is a plan view schematically showing an example of a positive electrode and a positive electrode lead. DETAILED DESCRIPTION

[0017] Hereinafter, the embodiments of the present disclosure will be described with examples, but the present disclosure is not limited to the examples described below. In the following description, specific numerical values or materials are sometimes exemplified, but other numerical values or other materials may also be applied as long as the effects of the present disclosure can be obtained. In this specification, a description such as "numerical value A to numerical value B" includes numerical value A and numerical value B, and may be replaced by "above numerical value A and below numerical value B". In the following description, when the lower limit and upper limit of numerical values related to specific physical properties or conditions are exemplified, as long as the lower limit is not greater than the upper limit, any one of the exemplified lower limits and any one of the exemplified upper limits may be arbitrarily combined. In the following description, when examples of constituent elements are listed, as long as there is no special description, only one of the listed examples may be used, or a plurality of the listed examples may be used in combination.

[0018] (Cylindrical non-aqueous electrolyte secondary battery)

[0019] Hereinafter, the cylindrical non-aqueous electrolyte secondary battery involved in this embodiment is sometimes referred to as "non-aqueous electrolyte secondary battery (B)" or "secondary battery (B)". The secondary battery (B) includes: a cylindrical battery case with a bottom; a wound electrode group and a non-aqueous electrolyte housed in the battery case; a sealing member for sealing the opening of the battery case; a positive electrode lead; and a negative electrode lead. The electrode group includes a positive electrode, a negative electrode, and a separator arranged between the positive electrode and the negative electrode. The negative electrode is a negative electrode that expands during charging and contracts during discharging. The outer diameter of the battery case is 15 mm or less. There is a hollow portion in the center of the electrode group. The negative electrode lead is connected to the portion of the negative electrode facing the hollow portion. In the discharged state, the diameter X of the hollow portion and the inner diameter Y of the battery case satisfy 0.25<X / Y≤0.50.

[0020] In non-aqueous electrolyte secondary batteries, it is required to improve the cycle characteristics and the thermal stability during short circuit. Compared with the electrode group of a large-diameter battery, the electrode group of a small-diameter battery has a smaller diameter of the winding core and fewer windings. Therefore, it is easily affected by the expansion and contraction of the negative electrode caused by charging and discharging. As a result of the study, the inventors of the present application found that by adopting a specific structure, the characteristics of a small-diameter non-aqueous electrolyte secondary battery can be improved. The present disclosure is based on this new insight. As described in the embodiment, the secondary battery (B) has good cycle characteristics and good thermal stability during short circuit.

[0021] The above X / Y can be greater than 0.25, or greater than 0.28, or greater than 0.33. The value of X / Y can be less than 0.50, less than 0.40, or less than 0.33. By setting X / Y to less than 0.40, it is possible to achieve good cycle characteristics and thermal stability while maintaining high capacity.

[0022] The diameter X can be changed by changing the thickness of the winding core. Specifically, the diameter X can be increased by thickening the winding core. The inner diameter Y can be changed by changing the size of the battery case.

[0023] The diameter X can be calculated by the following method. First, the secondary battery (B) is cut in a direction perpendicular to the central axis of the battery case at the center of the height direction of the secondary battery (B) in the discharged state. Then, an image of the cross section of the electrode group is taken. Next, using the image, the total area S of the hollow portion area and the area of the winding core portion described later is calculated. Area S is equivalent to the area inside the innermost circumference of the wound body (electrode group). Moreover, the diameter of a circle having the same area as area S is set to diameter X. That is, diameter X is equivalent to the equivalent circular diameter of the inner area of the innermost circumference of the wound body. Here, the discharged state of the secondary battery (B) when measuring diameter X refers to a state where the state of charge (SOC) is 10% or less.

[0024] The negative electrode may be one that precipitates lithium metal during charging and dissolves it during discharge. Non-aqueous electrolyte secondary batteries with such negative electrodes are sometimes referred to as "lithium secondary batteries" below. In lithium secondary batteries, the negative electrode expands significantly during charging, so the effect of the configuration of secondary battery (B) is particularly significant.

[0025] 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 due to 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 other viewpoints) 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.).

[0026] In a battery in which lithium metal is deposited at the negative electrode during charging, the open circuit potential (OCP) of the negative electrode when fully charged is, for example, 70 mV or less relative to the lithium metal (lithium dissolution potential). Full charge refers to a state in which the battery is charged to a state of charge (SOC) of, for example, 0.98×C or more when the rated capacity of the battery is set to C. The open circuit potential (OCP) of the negative electrode when fully charged can be measured by decomposing the fully charged battery in an argon atmosphere, removing the negative electrode, and assembling a cell with the lithium metal as the counter electrode. The non-aqueous electrolyte of the cell can have the same composition as the non-aqueous electrolyte in the decomposed battery.

[0027] The negative electrode generally includes a negative electrode current collector. A negative electrode lead may be connected to a portion of the negative electrode current collector that faces the hollow portion.

[0028] The negative electrode can have a region in the center of the electrode assembly where winding begins, which is not facing the positive electrode. This region can be wound in a range of 0.25 to 1 turn. This structure can maintain high capacity while mitigating stress on the inner circumference caused by expansion of the negative electrode.

[0029] The positive electrode may include a positive electrode current collector and a positive electrode mixture layer disposed on the positive electrode current collector. The positive electrode current collector may have an exposed portion at the end of the positive electrode current collector on the side of the sealing member where the positive electrode mixture layer is not disposed. In this case, the positive electrode lead may be connected to the exposed portion. With this structure, since the positive electrode lead is not disposed in the region where the positive electrode mixture layer and the negative electrode mixture layer are stacked, damage to the electrode caused by expansion of the negative electrode can be suppressed.

[0030] The positive electrode lead is preferably not connected to the outermost portion of the positive electrode. If the positive electrode lead is present at the outermost portion of the positive electrode, stress may be generated in the radial direction of the portion to which the positive electrode lead is connected. However, by connecting the positive electrode lead to the end of the positive electrode current collector on the sealing member side, the generation of stress caused by the positive electrode lead can be suppressed.

[0031] The outer diameter D of the battery case may be 3 mm or more, or 4 mm or more. The outer diameter D may be 15 mm or less, or 10 mm or less, 6.5 mm or less, or 5.5 mm or less. For example, the outer diameter of the battery case may be in the range of 3 to 6.5 mm (e.g., 3 to 5.5 mm). Batteries with such a small outer diameter are sometimes referred to as pin-shaped batteries. The smaller the battery case, the greater the effect of the negative electrode expansion, so the greater the effect brought about by the structure of the secondary battery (B). Therefore, the structure of the secondary battery (B) is particularly preferably used for pin-shaped batteries.

[0032] The height H of the secondary battery (B) may be 15 mm or greater. The height H may be 65 mm or less, or 45 mm or less. The height H may be in the range of 15 to 65 mm (e.g., 15 to 45 mm).

[0033] The number of windings of the negative electrode in the wound electrode assembly may be 3 or more, 5 or more, or 15 or less, or 12 or less. When the number of windings is 12 or less, the effect of the configuration of the secondary battery (B) is particularly significant.

[0034] The wound electrode group can be formed by winding the positive electrode, the negative electrode and the separator around a predetermined winding core. In this case, the positive electrode, the negative electrode and the separator are wound in such a manner that the separator is arranged between the positive electrode and the negative electrode. The winding core can use, for example, two rod-shaped components each having a semicircular cross-section. After the electrode group is formed, the winding core is pulled out from the electrode group. The portion from which the winding core is pulled out becomes a roughly cylindrical hollow portion. That is, there is a hollow portion in the center of the electrode group. The positive electrode, the negative electrode and the separator can each have a rectangular planar shape or a strip-shaped planar shape.

[0035] The electrode assembly typically has a winding core portion, which is sandwiched between winding cores during winding. The winding core portion protrudes into the cylindrical hollow portion. The negative electrode lead can be connected to the portion of the winding core portion within the negative electrode current collector. Alternatively, the negative electrode lead can be connected to another portion of the negative electrode facing the hollow portion. For example, the negative electrode lead can be connected to the innermost portion of the negative electrode facing the hollow portion.

[0036] Examples of components of the secondary battery (B) are described below. The components of the secondary battery (B) are not limited to the following examples. Components other than the characteristic components of the secondary battery (B) can be components used in known non-aqueous electrolyte secondary batteries.

[0037] (negative electrode)

[0038] Hereinafter, the negative electrode when the secondary battery (B) is a lithium secondary battery will be described. In this case, the negative electrode includes at least a negative electrode collector. Lithium metal is deposited on the surface of the negative electrode by charging. More specifically, the lithium ions contained in the non-aqueous electrolyte accept electrons on the negative electrode by charging and become lithium metal, which is deposited on the surface of the negative electrode. The lithium metal deposited on the surface of the negative electrode is dissolved in the non-aqueous electrolyte in the form of lithium ions by discharge. In addition, the lithium ions contained in the non-aqueous electrolyte may be derived from a lithium salt added to the non-aqueous electrolyte, may be supplied by the positive electrode active material by charging, or may be both.

[0039] The negative electrode can include a negative electrode current collector and a sheet of lithium metal or lithium alloy in close contact with the surface of the negative electrode current collector. Specifically, an underlayer containing lithium metal can be pre-formed on the negative electrode current collector. Lithium alloys can contain elements such as aluminum, magnesium, indium, and zinc in addition to lithium. By allowing lithium metal to precipitate on the underlayer during charging, dendritic precipitation of lithium metal can be suppressed. The thickness of the underlayer is not particularly limited and can be in the range of 5 μm to 25 μm.

[0040] The negative electrode may include a lithium ion absorption layer (a layer that exhibits capacity by absorbing and releasing lithium ions through the negative electrode active material (graphite, etc.)) supported on the negative electrode current collector. In this case, the open circuit potential of the negative electrode when fully charged can be 70 mV or less relative to lithium metal (lithium dissolution potential). When the open circuit potential of the negative electrode when fully charged is 70 mV or less relative to lithium metal, lithium metal is present on the surface of the lithium ion absorption layer when fully charged.

[0041] The lithium ion storage layer is formed by layering a negative electrode mixture containing a negative electrode active material. The negative electrode mixture may contain a binder, a thickener, a conductive material, and the like in addition to the negative electrode active material.

[0042] Examples of negative electrode active materials include carbonaceous materials, Si-containing materials, and Sn-containing materials. The negative electrode may contain a single negative electrode active material or a combination of two or more. Examples of carbonaceous materials include graphite, easily graphitizable carbon (soft carbon), and non-graphitizable carbon (hard carbon). Examples of Si-containing materials include silicon oxide and silicates (e.g., lithium silicate).

[0043] The conductive material is, for example, a carbon material, and examples of the carbon material include carbon black (acetylene black, Ketjen Black, etc.), carbon nanotubes, and graphite.

[0044] Examples of the binder include fluororesins, polyacrylonitrile, polyimide resins, acrylic resins, polyolefin resins, and rubbery polymers. Examples of the fluororesins include polytetrafluoroethylene and polyvinylidene fluoride.

[0045] The negative electrode current collector can be any conductive sheet. As the conductive sheet, foil, film, etc. can be used. The material of the negative electrode current collector (conductive sheet) can be any conductive material other than lithium metal and lithium alloy. The conductive material can be a metal material such as a metal or alloy. The conductive material is preferably a material that does not react with lithium. More specifically, it is preferably a material that does not form any alloy or intermetallic compound with lithium. Examples of such conductive materials include copper (Cu), nickel (Ni), iron (Fe), and alloys containing these metal elements, or graphite with the base surface preferentially exposed. As alloys, copper alloys, stainless steel (SUS), etc. can be mentioned. Among them, copper and / or copper alloys with high conductivity are preferred. The thickness of the negative electrode current collector is not particularly limited and can be 5 μm or more and 300 μm or less.

[0046] In addition, the capacity of the negative electrode of the secondary battery (B) may not be mainly generated by the precipitation and dissolution of lithium metal, but mainly generated by the absorption and release of lithium ions. That is, the secondary battery (B) may also be a battery other than a lithium secondary battery. The negative electrode in this case includes a negative electrode collector and a negative electrode mixture layer arranged on the negative electrode collector. The negative electrode mixture layer can use the above-mentioned lithium ion absorption layer. The negative electrode active material in the negative electrode mixture layer preferably contains a Si-containing material. Since the Si-containing material expands greatly during charging, the effect brought about by the composition of the secondary battery (B) is large.

[0047] (positive electrode)

[0048] The positive electrode, for example, comprises a positive electrode current collector and a positive electrode mixture layer supported by the positive electrode current collector. The positive electrode mixture layer, for example, comprises a positive electrode active material, a conductive material, and a binder. As the binder and the conductive material, the substances exemplified for the negative electrode can be used. The positive electrode mixture layer can be formed only on one side of the positive electrode current collector or on both sides. The positive electrode is obtained, for example, by coating a positive electrode mixture slurry containing a positive electrode active material, a conductive material, and a binder on both sides of the positive electrode current collector, drying the coating, and then rolling the coating.

[0049] The positive electrode active material is a material that absorbs and releases lithium ions. Examples of the positive electrode active material include lithium-containing transition metal oxides, transition metal fluorides, polyanions, fluorinated polyanions, and transition metal sulfides. Among these, lithium-containing transition metal oxides are preferred due to their low manufacturing cost and high average discharge voltage.

[0050] During charging, the lithium contained in lithium-containing transition metal oxides is released from the positive electrode as lithium ions and deposited as lithium metal on the negative electrode or negative electrode current collector. During discharge, the lithium metal dissolves from the negative electrode, releasing lithium ions that are then absorbed by the composite oxide at the positive electrode. In other words, the lithium ions involved in charging and discharging primarily originate from the solute in the non-aqueous electrolyte and the positive electrode active material.

[0051] The lithium-containing transition metal oxide preferably has a crystal structure belonging to the space group R-3m. The crystal structure belonging to the space group R-3m is a structure in which lithium-oxygen octahedral layers and transition metal-oxygen octahedral layers are stacked. For example, lithium nickelate (LiNiO2) and lithium cobaltate (LiCoO2) have a crystal structure belonging to the space group R-3m. The positive electrode active material has a crystal structure belonging to the space group R-3m, which is preferred in terms of obtaining high capacity. The positive electrode active material has a crystal structure belonging to the space group R-3m, which can be confirmed by methods such as powder X-ray diffraction. For example, the positive electrode active material is analyzed based on the powder X-ray diffraction method to obtain an X-ray diffraction pattern, thereby confirming the crystal structure of the positive electrode active material.

[0052] As the transition metal element contained in the lithium-containing transition metal oxide, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Y, Zr, W, etc. can be mentioned. The lithium-containing transition metal oxide 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 lithium-containing transition metal oxide 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. Typical elements can be Al, etc.

[0053] Among lithium-containing transition metal oxides, composite oxides containing Ni as a transition metal element, Co and / or Mn, and Al as an optional component, and having a layered structure and a rock-salt-type crystal structure are preferred for achieving high capacity. In lithium secondary batteries, the molar ratio mLi / mM of the total amount of lithium in the positive and negative electrodes, mLi, to the amount of metal M other than lithium in the positive electrode, mM, can be set to, for example, 2.0 or less.

[0054] Examples of materials for the positive electrode current collector (conductive sheet) include metal materials containing Al, Ti, Fe, and the like. The metal material may be Al, an Al alloy, Ti, a Ti alloy, or an Fe alloy. The Fe alloy may be stainless steel (SUS). The thickness of the positive electrode current collector is not particularly limited and may be 5 μm or more and 300 μm or less.

[0055] (Negative lead)

[0056] One end of the negative lead is connected to the negative electrode. One end of the negative lead can be connected to the negative electrode current collector. The other end of the negative lead is directly or indirectly connected to the battery case (negative terminal). For example, the other end of the negative lead can be connected to the inner surface of the bottom of the battery case. The method of connection is not limited, and welding and other methods can be used.

[0057] The negative electrode lead is not particularly limited, and any lead used for the negative electrode lead of a known non-aqueous electrolyte secondary battery can be used. Examples of materials for the negative electrode lead include copper, nickel, and alloys thereof. The shape of the negative electrode lead and the positive electrode lead is not particularly limited, and may be linear or sheet-shaped (or strip-shaped).

[0058] (Positive lead)

[0059] One end of the positive lead is connected to the positive electrode. One end of the positive lead can be connected to the positive electrode current collector. The other end of the positive lead is directly or indirectly connected to the sealing member (positive electrode terminal). The connection method is not limited, and welding and other methods can be used.

[0060] The positive electrode lead is not particularly limited, and a lead used for positive electrode leads of known non-aqueous electrolyte secondary batteries can be used. Examples of the material of the positive electrode lead include aluminum, titanium, nickel, and alloys thereof.

[0061] (diaphragm)

[0062] The separator is not particularly limited, and separators used in known non-aqueous electrolyte secondary batteries can be used. A porous sheet having ion permeability and insulation can be used as the separator. Examples of porous sheets include porous films, woven fabrics, non-woven fabrics, etc. The porous film can be a uniaxially or biaxially stretched sheet, etc. The material of the porous sheet is not particularly limited, and can be a polymer material. Examples of polymer materials include polyolefin resins, polyamide resins, polyimide resins, cellulose, etc. Examples of polyolefin resins include polyethylene, polypropylene, and copolymers of ethylene and propylene. The porous sheet can contain one material or two or more materials. The porous sheet can contain additives as needed. Examples of additives include inorganic fillers, etc.

[0063] The thickness of the separator is not particularly limited and may be 5 μm or more and 300 μm or less. The thickness of the porous membrane may be 5 μm or more and 50 μm or less.

[0064] The separator may have a heat-resistant layer on at least one surface layer. Specifically, the separator may include a substrate layer and a heat-resistant layer laminated on the substrate layer. The heat-resistant layer is formed on at least one of the two main surfaces of the substrate layer. The heat-resistant layer has insulating properties.

[0065] The thickness of the heat-resistant layer may be 3% to 50% of the thickness of the separator. When the heat-resistant layers are formed on both main surfaces of the base layer, the total thickness of the heat-resistant layers may be 3% to 50% of the thickness of the separator.

[0066] The heat-resistant layer can suppress shrinkage of the substrate layer when the temperature of the electrode assembly rises excessively. If the substrate layer shrinks, it can easily short-circuit the positive and negative electrodes, which can further increase the temperature of the electrode assembly. The separator containing the heat-resistant layer can suppress shrinkage of the substrate layer, thereby suppressing further temperature increases in the electrode assembly.

[0067] The substrate layer can use the above-mentioned porous sheet, that is, the separator used in the non-aqueous electrolyte secondary battery. The substrate layer can be, for example, a porous film containing a polyolefin resin. Polyolefin resin is preferred in that it has excellent durability and also has the function of blocking holes when rising to a certain temperature (i.e., a shutdown function). The substrate layer can be a single-layer structure, a two-layer structure, or a structure of more than three layers.

[0068] The heat-resistant layer may comprise inorganic particles (or inorganic filler) and a polymer (or macromolecule or resin). The polymer bonds the inorganic particles to the substrate layer. The polymer preferably uses a heat-resistant resin having a higher heat resistance than the main component of the substrate layer. The heat-resistant layer may contain inorganic particles as a main component (e.g., 80% by mass or more), or may contain a heat-resistant resin as a main component (e.g., 40% by mass or more). The heat-resistant layer may also contain no inorganic particles but a heat-resistant resin.

[0069] Heat-resistant resins that can be used include polyamide resins, polyimide resins, and polyamide-imide resins. Among these, preferably, the resin contains at least one selected from aromatic polyamides, aromatic polyimides, and aromatic polyamide-imides. These are known to be polymers with particularly high heat resistance. From the perspective of heat resistance, aramid (aromatic polyamide), namely, meta-aramid (meta-wholly aromatic polyamide) and para-aramid (para-wholly aromatic polyamide), are preferred.

[0070] Inorganic particles are particles composed of insulating inorganic compounds. Examples of materials for inorganic particles include oxides, oxide hydrates, hydroxides, nitrides, carbides, sulfides, and the like, which may contain metal elements.

[0071] Specifically, examples include aluminum oxide, boehmite, magnesium oxide, titanium oxide, zirconium oxide, silicon oxide, yttrium oxide, zinc oxide, silicon nitride, aluminum nitride, boron nitride, titanium nitride, silicon carbide, boron carbide, barium sulfate, and aluminum hydroxide. Among these, at least one selected from the group consisting of aluminum oxide, boehmite, talc, titanium oxide, and magnesium oxide is preferred in view of insulation properties and heat resistance.

[0072] The inorganic particles may contain a lithium-containing phosphate. The lithium-containing phosphate may be at least one selected from lithium phosphate (Li3PO4), dilithium hydrogen phosphate (Li2HPO4), and lithium dihydrogen phosphate (LiH2PO4). Of these, lithium phosphate is preferred due to its high effectiveness in suppressing abnormal battery heat generation.

[0073] The average particle size of the inorganic particles is not particularly limited and can be, for example, in the range of 0.2 μm to 2 μm. The average particle size of the lithium-containing phosphate can be in the range of 0.1 μm to 1.0 μm or 0.1 μm to 0.5 μm. By setting the average particle size to 0.1 μm or greater, sufficient pores for the penetration of the non-aqueous electrolyte can be ensured. By setting the average particle size to 1.0 μm or less, a heat-resistant layer densely filled with the lithium-containing phosphate can be formed.

[0074] The proportion of the lithium-containing phosphate in the inorganic particles contained in the heat-resistant layer is preferably 20% by mass or greater, and may be 50% by mass or greater. A first layer containing only the lithium-containing phosphate as inorganic particles, or a first layer containing the lithium-containing phosphate as a primary component (e.g., 60% by mass or greater of the inorganic particles), and a second layer other than the first layer may be stacked. The second layer may contain only inorganic particles other than the lithium-containing phosphate, may contain 60% or greater of inorganic particles other than the lithium-containing phosphate, or may contain only the heat-resistant resin.

[0075] (non-aqueous electrolyte)

[0076] Any non-aqueous electrolyte with lithium ion conductivity is sufficient. A non-aqueous electrolyte comprises a solvent (non-aqueous solvent) and an electrolyte salt dissolved in the solvent. The electrolyte salt comprises at least a lithium salt. The lithium salt dissolves in the solvent to generate lithium ions and anions. The non-aqueous electrolyte may be liquid or gelled using a polymer that absorbs the solvent.

[0077] Examples of solvents include ether compounds, ester compounds, nitrile compounds, amide compounds, and halogen-substituted compounds thereof. The nonaqueous electrolyte may contain any of these nonaqueous solvents alone or in combination. Examples of halogen-substituted compounds include fluorides and the like.

[0078] The solvent may contain an ether compound as a main component (50% by mass or more). The proportion of the ether compound in the solvent may be 70% by mass or more (e.g., 80% by mass or more). Since the ether compound is difficult to produce a side reaction between the non-aqueous electrolyte and the highly active lithium metal, the consumption of the non-aqueous electrolyte caused by the side reaction can be suppressed. Therefore, even if the negative electrode expands significantly, it is difficult to produce local liquid depletion of the non-aqueous electrolyte. Therefore, the capacity reduction of the lithium secondary battery accompanying the charge and discharge cycle can be suppressed.

[0079] As ester compounds, for example, carbonates and carboxylic acid esters can be mentioned. As cyclic carbonates, ethylene carbonate, propylene carbonate, fluoroethylene carbonate (FEC) and the like can be mentioned. As chain carbonates, dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC) and the like can be mentioned. As cyclic carboxylic acid esters, γ-butyrolactone, γ-valerolactone and the like can be mentioned. As chain carboxylic acid esters, ethyl acetate, methyl propionate, fluoromethyl propionate and the like can be mentioned.

[0080] Examples of the ether compound include cyclic ethers and chain ethers. Among them, preferably used are those represented by the general formula (1): R1-(OCH2CH2) n A first ether compound (non-fluorinated ether) represented by -OR2 (in formula (1), R1 and R2 are each independently an alkyl group having 1 to 5 carbon atoms, and n is 1 to 3).

[0081] The lowest unoccupied molecular orbital (LUMO) of non-fluorinated ethers exists at a high energy level. Therefore, even when in contact with lithium metal, which has a strong reducing power, non-fluorinated ethers are resistant to reduction and decomposition. Furthermore, since the oxygen in the non-fluorinated ether skeleton strongly interacts with lithium ions, it can easily dissolve the lithium salt contained as an electrolyte salt in the non-aqueous electrolyte.

[0082] Non-fluorinated ethers are suitable as solvents for non-aqueous electrolytes of lithium secondary batteries in terms of suppressing side reactions between lithium metal and non-aqueous electrolytes and improving the solubility of lithium salts in solvents.

[0083] Specific examples of the first ether compound (non-fluorinated ether) include 1,2-dimethoxyethane, 1,2-diethoxyethane, 1,2-dibutoxyethane, diglyme, diglyme diethyl ether, diglyme ethyl methyl ether, diglyme dibutyl ether, triglyme dimethyl ether, etc. The first ether compound may be used alone or in combination of two or more.

[0084] Ether compounds may include fluorinated ethers. Fluorinated ethers exhibit a reduced interaction between the oxygen atoms in the ether backbone and lithium ions compared to non-fluorinated ethers. This is believed to be due to the strong electronegativity of fluorine atoms, which attracts electrons from the entire molecule toward the core, lowering the orbital energy level of the unshared electron pairs of the oxygen atoms in the ether backbone that should interact with lithium ions.

[0085] Among the fluorinated ethers, preferably used are those represented by the general formula (2): C a1 H b1 F c1 O d1 (CF2OCH2)C a2 H b2 F c2 O d2 (In formula (2), a1≥1, a2≥0, b1≤2a1, b2≤2a2, c1=(2a1+1)-b1, c2=(2a2+1)-b2, d1≥0, d2≥0) a second ether compound represented by.

[0086] As the ether compound, a fluorinated ether and a non-fluorinated ether can be used in combination. For example, when a second ether compound is used together with a first ether compound, the charge and discharge reactions in the lithium secondary battery proceed more uniformly. This is believed to be due to a better balance of solvation energy between the ether compound and lithium ions.

[0087] The fluorination rate of the second ether compound may be 60% or higher. The fluorination rate of the second ether compound is expressed as a percentage (%) of the number of fluorine atoms in the total number of fluorine atoms and hydrogen atoms contained in the second ether compound.

[0088] Specific examples of the second ether compound (fluorinated ether) include 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether. The second ether compound may be used alone or in combination of two or more.

[0089] The total amount of the first ether compound and the second ether compound may be 80% by volume or more of the total solvent. When the total amount is 80% by volume or more, the effect of improving the cycle characteristics of the lithium secondary battery becomes more significant.

[0090] The volume ratio V1 / V2 of the volume V1 of the first ether compound to the volume V2 of the second ether compound is preferably 1 / 0.5 to 1 / 4, more preferably 1 / 0.5 to 1 / 2.

[0091] As the anion of the lithium salt, known anions used in non-aqueous electrolytes of non-aqueous electrolyte secondary batteries can be used. Specifically, BF4 - 、ClO4 - PF6 - CF3SO3 - CF3CO2 - , imide anion, oxalate complex anion, etc.

[0092] From the viewpoint of suppressing the precipitation of lithium metal in the form of dendrites, the electrolyte salt may contain an imide anion, PF6 - and at least one of an oxalate complex anion. The oxalate complex anion has a tendency to uniformly precipitate lithium metal in the form of fine particles through interaction with lithium.

[0093] As the imide anion, N(SO2F)2 can be mentioned. - 、N(SO2CF3)2 - 、N(C m F 2m+1 SO2) x (C n F 2n+1 SO2) y - (m and n are each independently an integer of 0 or greater, x and y are each independently 0, 1 or 2, and x + y = 2) etc. Among them, bis (fluorosulfonyl) imide anion (N (SO2F)2 - ). Therefore, the lithium salt preferably includes lithium bis(fluorosulfonyl)imide (hereinafter also referred to as "LiFSI").

[0094] Examples of the oxalate complex anion include bisoxalatoborate anion, difluorooxalatoborate anion (BF2(C2O4) - ), PF4(C2O4) - PF2(C2O4)2 - Among them, difluorooxalatoborate anion (BF2(C2O4) - ). Therefore, the lithium salt preferably includes lithium difluorooxalatoborate (hereinafter also referred to as "LiFOB").

[0095] The electrolyte salt preferably includes at least one selected from LiPF6, an imide salt, and an oxalate complex salt. The concentration of the lithium salt in the non-aqueous electrolyte is, for example, 0.5 mol / L to 3.5 mol / L. The concentration of the oxalate complex salt in the non-aqueous electrolyte can be set to 0.05 mol / L to 1 mol / L.

[0096] (outer body)

[0097] The outer casing houses the electrode assembly and the non-aqueous electrolyte. The outer casing is not particularly limited and can be any of those used in conventional non-aqueous electrolyte secondary batteries. The outer casing may include a bottomed cylindrical battery case, a sealing member, and a gasket.

[0098] Hereinafter, an example of a non-aqueous electrolyte secondary battery (B) will be described in detail with reference to the accompanying drawings. In the constituent elements of the non-aqueous electrolyte secondary battery of an example described below, the above-mentioned constituent elements can be applied. In addition, the constituent elements of an example described below can be changed based on the above description. In addition, the matters described below can be applied to the above-mentioned embodiment. In addition, in the non-aqueous electrolyte secondary battery described below, non-essential constituent elements in the non-aqueous electrolyte secondary battery involved in the present disclosure can be omitted.

[0099] (Implementation Method 1)

[0100] In the first embodiment, as an example of the secondary battery (B), a pin-shaped lithium secondary battery is described. Figure 1 A longitudinal cross-sectional view schematically illustrates a nonaqueous electrolyte secondary battery (lithium secondary battery) 100 according to Embodiment 1. The cylindrical nonaqueous electrolyte secondary battery 100 includes an open, bottomed cylindrical battery case 20, a wound electrode assembly 10 and a nonaqueous electrolyte (not shown) housed within the battery case 20, a sealing member 40 for sealing the opening of the battery case 20, and an insulating plate 51. The electrode assembly 10 is composed of a positive electrode 11, a negative electrode 12, and a separator 13 disposed therebetween. A roughly cylindrical space (hollow portion 10s) is located in the center of the electrode assembly 10.

[0101] The sealing member 40 is cap-shaped and has an annular brim (flange 40a) and cylindrical terminal portions 40b and 40c protruding from the inner circumference of the flange 40a in the thickness direction. An insulating gasket 30 is annularly arranged on the periphery of the sealing member 40 to cover the flange 40a. The open end of the battery case 20 is bent inwardly in a manner that sandwiches the gasket 30 and the periphery of the sealing member 40. Thus, the battery case 20 and the sealing member 40 are insulated, and the battery case 20 is sealed.

[0102] A space is formed between the upper end surface (top surface) of the electrode assembly 10 and the bottom surface of the sealing member 40. A first insulating ring 50A is disposed in this space. The first insulating ring 50A prevents contact between the electrode assembly 10 and the sealing member 40. An annular second insulating ring 50B is disposed to cover the outer surface of the open end of the battery case 20 and the surrounding surface of the gasket 30.

[0103] One end of the positive electrode lead 60 is connected to the positive electrode 11. The other end of the positive electrode lead 60 is connected to the bottom surface of the sealing member 40 through a hole formed in the center of the first insulating ring 50A. In other words, the positive electrode 11 and the sealing member 40 are electrically connected via the positive electrode lead 60. The sealing member 40 functions as a positive electrode terminal.

[0104] A schematic diagram showing an example of a cross section of the electrode group 10 perpendicular to the axis is shown in FIG. Figure 2 In addition, Figure 2 In the figure, only the negative electrode 12 in the electrode group 10 is shown as a representative. Figure 1 As shown, the positive electrode 11 and the separator 13 are wound together with the negative electrode 12. As described above, the negative electrode 12 may have an area that is not opposite to the positive electrode 11 in the center of the electrode group 10 where the winding starts. This area can be wound in the range of 0.25 turns to 1 turn. Figure 2 As shown, a substantially cylindrical hollow portion 10 s exists in the center of the electrode group 10 . Figure 2 The electrode group 10 of the example shown includes a winding portion 10a and a winding core portion 10b. The winding portion 10a is a portion where the positive electrode 11, the negative electrode 12, and the separator 13 are wound and stacked. The winding core portion 10b is a portion that is clamped by the winding core when the positive electrode 11, the negative electrode 12, and the separator 13 are wound. The winding core portion 10b can be composed of only the negative electrode 12 (for example, a negative electrode collector), or can be composed of the negative electrode 12 (for example, a negative electrode collector) and the separator 13. Alternatively, the winding core portion 10b can also be composed of the positive electrode 11 (for example, a positive electrode collector), the negative electrode 12 (for example, a negative electrode collector), and the separator 13.

[0105] The winding core 10b of the electrode assembly 10 protrudes from the hollow portion 10s. In the example shown in Embodiment 1, one end of the negative electrode lead 70 is connected to the negative electrode 12 (more specifically, the negative electrode current collector) that constitutes the winding core 10b. The other end of the negative electrode lead 70 is connected to the battery case 20. The battery case 20 functions as a negative electrode terminal. Furthermore, the positive electrode lead 60 and the negative electrode lead 70 are connected to other components by welding or the like.

[0106] The positive electrode 11 is shown in the unfolded state. Figure 3 The positive electrode 11 includes a positive electrode current collector 11a and positive electrode mixture layers 11b formed on both surfaces of the positive electrode current collector 11a. The positive electrode current collector 11a has an exposed portion 11aa along an end 11ae of the positive electrode current collector 11a, i.e., an end portion on the sealing member 40 side, where the positive electrode mixture layers 11b are not disposed. The positive electrode lead 60 is connected to the exposed portion 11aa.

[0107] (Note)

[0108] The following technical configurations are disclosed through the above description.

[0109] (Technical composition 1)

[0110] A cylindrical non-aqueous electrolyte secondary battery comprising:

[0111] A cylindrical battery casing with a bottom;

[0112] A wound electrode group and a non-aqueous electrolyte housed in the battery case;

[0113] a sealing member for sealing the opening of the battery case;

[0114] a positive lead; and

[0115] Negative lead,

[0116] The electrode group includes a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode.

[0117] The negative electrode is a negative electrode that expands during charging and contracts during discharging.

[0118] The outer diameter of the battery case is less than 15 mm,

[0119] There is a hollow portion in the center of the electrode group.

[0120] The negative electrode lead is connected to a portion of the negative electrode facing the hollow portion.

[0121] In a discharged state, a diameter X of the hollow portion and an inner diameter Y of the battery case satisfy 0.25<X / Y≤0.50.

[0122] (Technical composition 2)

[0123] According to the nonaqueous electrolyte secondary battery of Technical Configuration 1,

[0124] The negative electrode deposits lithium metal during charging and dissolves the lithium metal during discharging.

[0125] (Technical composition 3)

[0126] According to the nonaqueous electrolyte secondary battery of technical configuration 1 or 2,

[0127] The negative electrode comprises a negative electrode current collector,

[0128] The negative electrode lead is connected to a portion of the negative electrode current collector facing the hollow portion.

[0129] (Technical Composition 4)

[0130] The nonaqueous electrolyte secondary battery according to any one of the technical configurations 1 to 3,

[0131] The negative electrode has a region that does not face the positive electrode at a portion where winding starts in the center of the electrode group.

[0132] The region is wound in a range of 0.25 to 1 turn.

[0133] (Technical Composition 5)

[0134] The nonaqueous electrolyte secondary battery according to any one of the technical configurations 1 to 4,

[0135] The positive electrode includes a positive electrode current collector and a positive electrode mixture layer disposed on the positive electrode current collector.

[0136] The positive electrode current collector has an exposed portion where the positive electrode mixture layer is not disposed, along an end portion of the positive electrode current collector on the sealing member side.

[0137] The positive electrode lead is connected to the exposed portion.

[0138] (Technical Composition 6)

[0139] The nonaqueous electrolyte secondary battery according to any one of the technical configurations 1 to 5,

[0140] The outer diameter of the battery shell is in the range of 3 to 6.5 mm.

[0141] (Technical Composition 7)

[0142] The nonaqueous electrolyte secondary battery according to any one of the technical configurations 1 to 6,

[0143] The separator includes a base material layer and a heat-resistant layer laminated on the base material layer.

[0144] (Technical composition 8)

[0145] According to the non-aqueous electrolyte secondary battery of technical solution 7,

[0146] The heat-resistant layer includes inorganic particles and a polymer.

[0147] (Technical Composition 9)

[0148] According to the non-aqueous electrolyte secondary battery described in technical solution 8,

[0149] The inorganic particles include lithium-containing phosphate.

[0150] (Technical composition 10)

[0151] According to the non-aqueous electrolyte secondary battery of technical solution 9,

[0152] The lithium-containing phosphate is lithium phosphate.

[0153] Example

[0154] The non-aqueous electrolyte secondary battery (B) will be described in more detail below using examples. In this example, a plurality of lithium secondary batteries having different X / Y values were produced and evaluated.

[0155] (Battery A1)

[0156] Follow the following steps to create Figure 1 The cylindrical nonaqueous electrolyte secondary battery 100 shown is a lithium secondary battery having a similar structure to that of the lithium secondary battery. The outer diameter D of the lithium secondary battery is 4 mm, and the height H is 25 mm.

[0157] (1) Preparation of positive electrode 11

[0158] 100 parts by mass of positive electrode active material, 4 parts by mass of acetylene black (conductive material), 4 parts by mass of polyvinylidene fluoride (binder) and N-methyl-2-pyrrolidone (dispersion medium) were added and mixed to prepare a positive electrode slurry. The positive electrode active material used was a lithium-containing transition metal oxide containing Li, Ni, Co and Al. Next, the positive electrode slurry was applied to both sides of an aluminum foil (positive electrode collector, thickness: 15 μm) and dried to obtain a laminate. At this time, the positive electrode slurry was formed. Figure 3 The positive electrode slurry was applied to the exposed portion 11aa shown. Next, the laminate was compressed in the thickness direction to produce a positive electrode 11 (thickness: 80 μm) including a positive electrode current collector and positive electrode mixture layers disposed on both sides of the positive electrode current collector.

[0159] Next, one end of an aluminum positive electrode lead 60 (width: 1.0 mm, thickness: 0.05 mm) was connected to the exposed portion of the positive electrode current collector.

[0160] (2) Preparation of negative electrode 12

[0161] A negative electrode 12 (50 μm thick) was fabricated by laminating lithium metal foil (20 μm thick) on both sides of a copper foil (negative electrode current collector, 10 μm thick). An exposed portion of the negative electrode current collector was provided in the portion of the negative electrode 12 that would become the winding core 10 b. One end of a nickel negative electrode lead 70 (1.5 mm wide, 0.05 mm thick) was connected to this exposed portion.

[0162] (3) Preparation of the electrode group 10

[0163] The positive electrode 11 and the negative electrode 12 were wound with the separator 13 interposed therebetween to form a wound electrode group 10. A polyethylene porous film (thickness: 16 μm) was used as the separator 13. The diameter X of the hollow portion of the prepared electrode group 10 was measured by the above-described method.

[0164] (4) Preparation of non-aqueous electrolyte

[0165] The non-aqueous electrolyte is prepared by dissolving LiFSI and LiFOB in a solvent. The solvent is a mixed solvent containing dimethoxyethane (DME) and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (H(CF2)2CH2O(CF2)2H) in a mass ratio of 50:50. At this time, the concentration of LiFSI in the non-aqueous electrolyte is 1.5 mol / L and the concentration of LiFOB is 0.1 mol / L.

[0166] (5) Production of lithium secondary batteries

[0167] The electrode assembly 10 obtained in (3) above was inserted into a battery case 20 (outer diameter D: 4.5 mm, inner diameter Y: 4 mm). At this time, the other end of the negative electrode lead 70 was welded to the bottom surface of the battery case 20. Furthermore, the other end of the positive electrode lead 60 was passed through the hole in the first insulating ring 50A and connected to the bottom surface of the sealing member 40 to which the gasket 30 was attached. The sealing member 40 was made of nickel-plated iron.

[0168] Next, the nonaqueous electrolyte prepared in (4) above was injected into the battery case 20. Next, the sealing member 40 was placed at the opening of the battery case 20, and the open end of the battery case 20 was bent inward to seal the opening. Next, a butyl rubber-based insulating coating was applied in a ring shape so as to cover the outer surface of the open end of the battery case 20 and the surface of the gasket 30, thereby forming a second insulating ring 50B. In this way, a lithium secondary battery (battery A1) with a rated capacity of 45 mAh was obtained.

[0169] (Other batteries)

[0170] Batteries A2 to A4 and C1 to C3 were fabricated using the same method and conditions as battery A1, except that some battery fabrication conditions were modified as described in Table 1. In batteries C2 and C3, an exposed portion of the negative electrode current collector was provided at the outermost periphery of the negative electrode 12, and one end of a negative electrode lead 70 was connected to this exposed portion. The other end of the negative electrode lead 70 was connected to the bottom surface of the battery case 20.

[0171] When forming the electrode group 10 of each battery, the winding core was changed to change the value of the diameter X of the hollow portion. The diameter X was measured by the above method, and the value of X / Y was the value shown in Table 1.

[0172] The separator in Battery A4 was modified. Specifically, a separator consisting of a substrate layer and a heat-resistant layer laminated on one side of the substrate layer was used in the production of Battery A4. The substrate layer used the separator used in Battery A1. The heat-resistant layer used a layer (thickness: 2 μm) containing aluminum oxide (Al2O3) particles, lithium phosphate (Li3PO4) particles, and aromatic polyamide in a mass ratio of 48:48:2. The separators of the other batteries were the same as those of Battery A1.

[0173] (Battery Evaluation)

[0174] The produced batteries were subjected to capacity retention (100 cycles) and nail penetration tests in the following order.

[0175] (1) Capacity maintenance rate

[0176] First, charge at a constant current of 0.1 It until the closed-circuit voltage of the battery reaches 4.2V, and then charge at a constant voltage of 4.2V until the current reaches 0.05 It. Here, It (A) is the current value expressed by the rated capacity (Ah) / 1 (h). Then, stop for 20 minutes and discharge at a constant current of 0.1 It until the closed-circuit voltage of the battery reaches 2.5V. Repeat this charge and discharge cycle 100 times. The ratio (%) of the discharge capacity of the 100th cycle to the discharge capacity of the 1st cycle is calculated as the capacity retention rate.

[0177] (2) Nail penetration test

[0178] First, the battery was subjected to 100 cycles of the aforementioned charge and discharge cycles. Next, the battery was charged at a constant current of 0.3 It until the battery voltage reached 4.2 V, followed by constant voltage charging until the current reached 0.05 It. At 25°C, a round nail (0.9 mm diameter) was inserted into the center of the charged battery at a rate of 1 mm / second. The nail insertion was stopped immediately after a drop in battery voltage (Δ50 mV) due to an internal short circuit was detected. The battery surface temperature was measured 1 minute after the battery short-circuited.

[0179] Some of the battery production conditions and evaluation results are shown in Table 1. Batteries A1 to A4 are examples of the non-aqueous electrolyte secondary batteries (B) according to the present disclosure, and batteries C1 to C3 are comparative examples.

[0180] [Table 1]

[0181]

[0182] Observation of the electrode assembly after 100 charge-discharge cycles revealed significant electrode bending at the inner periphery of the electrode assembly in batteries C1 and C2. However, no such bending was observed in battery A1. This is believed to be due to the fact that, with the negative electrode lead located at the outermost periphery of the wound body, significant stress due to expansion of the negative electrode was generated in the radial direction of the portion connected to the negative electrode lead.

[0183] As shown in Table 1, the capacity retention rates of batteries A1 to A4, which are secondary batteries (B), were higher than those of batteries C1 and C2, which are comparative examples. This is believed to be because the electrodes of batteries C1 and C2 were bent, resulting in uneven deposition of lithium metal.

[0184] Batteries A1 to A4 achieved a maximum temperature of less than 120°C during the nail penetration test. On the other hand, batteries C1 and C2 achieved a maximum temperature exceeding 120°C during the nail penetration test. In other words, batteries A1 to A4 exhibited higher thermal stability during short circuits than batteries C1 and C2. This is believed to be due to uneven deposition of lithium metal in batteries C1 and C2, resulting in variations in heat generation during short circuits.

[0185] A comparison of batteries A3 and C3 shows that even when the negative electrode lead is connected to the winding core, good results cannot be achieved if the X / Y ratio is not within the appropriate range. This is believed to be because the stress generated by negative electrode expansion cannot be fully alleviated if the X / Y ratio is not within the appropriate range.

[0186] Industrial availability

[0187] The present disclosure can be used for cylindrical non-aqueous electrolyte secondary batteries (particularly pin-shaped secondary batteries). The present invention has been described in conjunction with the currently preferred embodiments, but this disclosure should not be construed as restrictive. Upon reading the above disclosure, a person of ordinary skill in the art to which the present invention belongs will be able to understand various variations and modifications. Therefore, the appended claims should be interpreted as including all variations and modifications without departing from the true spirit and scope of the present invention.

[0188] Description of Reference Numerals

[0189] 10: Electrode group

[0190] 10s: hollow part

[0191] 11: Positive electrode

[0192] 11a: Positive electrode collector

[0193] 11aa: exposed part

[0194] 11b: Positive electrode mixture layer

[0195] 12: Negative electrode

[0196] 13: Diaphragm

[0197] 20: Battery housing

[0198] 40: Sealing parts

[0199] 60: Positive lead

[0200] 70: Negative lead

[0201] 100: Non-aqueous electrolyte secondary battery

Claims

1. A cylindrical non-aqueous electrolyte secondary battery comprising: A cylindrical battery casing with a bottom; A wound electrode group and a non-aqueous electrolyte housed in the battery case; a sealing member for sealing the opening of the battery case; a positive lead; and Negative lead, The electrode group includes a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode. The negative electrode is a negative electrode that expands during charging and contracts during discharging. The outer diameter of the battery case is less than 15 mm, There is a hollow portion in the center of the electrode group. The negative electrode lead is connected to a portion of the negative electrode facing the hollow portion. In a discharged state, a diameter X of the hollow portion and an inner diameter Y of the battery case satisfy 0.25<X / Y≤0.

50.

2. The nonaqueous electrolyte secondary battery according to claim 1, The negative electrode deposits lithium metal during charging and dissolves the lithium metal during discharging.

3. The nonaqueous electrolyte secondary battery according to claim 1 or 2, The negative electrode comprises a negative electrode current collector, The negative electrode lead is connected to a portion of the negative electrode current collector facing the hollow portion.

4. The nonaqueous electrolyte secondary battery according to claim 1 or 2, The negative electrode has a region that does not face the positive electrode at a portion where winding starts in the center of the electrode group. The region is wound in a range of 0.25 to 1 turn.

5. The nonaqueous electrolyte secondary battery according to claim 1 or 2, The positive electrode includes a positive electrode current collector and a positive electrode mixture layer disposed on the positive electrode current collector. The positive electrode current collector has an exposed portion where the positive electrode mixture layer is not disposed, along an end portion of the positive electrode current collector on the sealing member side. The positive electrode lead is connected to the exposed portion.

6. The nonaqueous electrolyte secondary battery according to claim 1 or 2, The outer diameter of the battery shell is in the range of 3 to 6.5 mm.

7. The nonaqueous electrolyte secondary battery according to claim 1 or 2, The separator includes a base material layer and a heat-resistant layer laminated on the base material layer.

8. The nonaqueous electrolyte secondary battery according to claim 7, The heat-resistant layer includes inorganic particles and a polymer.

9. The nonaqueous electrolyte secondary battery according to claim 8, The inorganic particles include lithium-containing phosphate.

10. The nonaqueous electrolyte secondary battery according to claim 9, The lithium-containing phosphate is lithium phosphate.

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