Nonaqueous electrolyte secondary battery

Abstract

A non-aqueous electrolyte secondary battery provided with a wound electrode group, a non-aqueous electrolyte, a cylindrical battery case that accommodates the electrode group and the non-aqueous electrolyte, a sealing body that seals an opening of the battery case, and an insulating plate that is disposed between the electrode group and the bottom of the battery case, the non-aqueous electrolyte containing a sulfur-containing compound, the insulating plate having an opening, the opening ratio of (A) the insulating plate is 10% or more, or (B) the opening has a plurality of mutually independent regions.

Description

Technical Field

[0001] The present disclosure relates to a nonaqueous electrolyte secondary battery. Background Art

[0002] In the nonaqueous electrolyte secondary battery, insulating plates are disposed between the electrode group and the bottom of the battery case and between the electrode group and the sealing body to prevent internal short circuits.

[0003] In Patent Document 1, in a secondary battery using a sealing body formed with a venting valve body, an insulating plate having a hole near the center is disposed between the electrode group and the sealing body. Patent Document 2 proposes using an insulating plate 820 having one semicircular hole 821 and three dot holes 822 in a top view as shown in FIG. 8 .

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: International Publication No. 2016 / 157749

[0007] Patent Document 2: International Publication No. 2013 / 099295 Summary of the invention

[0008] Problem that the invention aims to solve

[0009] Patent Documents 1 and 2 both relate to improvements to the insulating plate (upper insulating plate) disposed between the electrode group and the sealing body. On the other hand, the insulating plate (lower insulating plate) disposed between the electrode group and the bottom of the battery case is provided with a hole for passing the electrode, which is used to weld the lead wires drawn from the electrode group to the bottom of the battery case. It has been found that when the battery is in an over-discharged state, if a non-aqueous electrolyte containing a sulfur compound is retained in the hole, the open circuit voltage (OCV) of the battery is reduced and the residual capacity is reduced.

[0010] Solutions for solving problems

[0011] One aspect of the present invention relates to a non-aqueous electrolyte secondary battery, comprising: a wound electrode group, a non-aqueous electrolyte, a cylindrical battery case that accommodates the electrode group and the non-aqueous electrolyte, a sealing body that seals an opening of the battery case, and an insulating plate arranged between the electrode group and the bottom of the battery case, wherein the non-aqueous electrolyte contains a sulfur-containing compound, the insulating plate has an opening, and the opening ratio of the insulating plate is greater than 10%.

[0012] Another aspect of the present invention relates to a non-aqueous electrolyte secondary battery, comprising: a wound electrode group, a non-aqueous electrolyte, a cylindrical battery case that accommodates the electrode group and the non-aqueous electrolyte, a sealing body that seals an opening of the battery case, and an insulating plate arranged between the electrode group and the bottom of the battery case, wherein the non-aqueous electrolyte contains a sulfur-containing compound, and the insulating plate has an opening, and the opening has a plurality of mutually independent regions.

[0013] Effects of the Invention

[0014] According to the present disclosure, when a nonaqueous electrolyte secondary battery is in an overdischarged state, a decrease in the open circuit voltage (OCV) of the battery can be suppressed.

[0015] The novel features of the present invention are described in the appended claims, but both the composition and content of the present invention should be more fully understood from the following detailed description with reference to the accompanying drawings, together with other objects and features of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a plan view schematically showing an insulating plate according to one embodiment of the present disclosure.

[0017] Figure 2 It is a plan view schematically showing an insulating plate according to another embodiment of the present disclosure.

[0018] Figure 3 It is a plan view schematically showing an insulating plate according to still another embodiment of the present disclosure.

[0019] Figure 4 It is a longitudinal cross-sectional view of a nonaqueous electrolyte secondary battery according to one embodiment of the present disclosure. DETAILED DESCRIPTION

[0020] Hereinafter, the embodiments of the present disclosure will be described using examples, but the present disclosure is not limited to the examples described below. In the following description, specific numerical values ​​and materials are sometimes listed, but other numerical values ​​and materials may also be used as long as the effects of the present disclosure can be obtained. In this specification, the expression "numerical value A to numerical value B" includes numerical value A and numerical value B, and can be understood as "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 shown, as long as the lower limit is not above the upper limit, any exemplified lower limit and any exemplified upper limit can be arbitrarily combined. When multiple materials are exemplified, one of them can be selected and used alone, or two or more can be used in combination.

[0021] In addition, the present disclosure includes a combination of matters described in two or more claims arbitrarily selected from the plurality of claims recorded in the attached claims. That is, as long as no technical contradiction occurs, matters described in two or more claims arbitrarily selected from the plurality of claims recorded in the attached claims may be combined.

[0022] In the following description, the term "comprising" or "including" includes expressions such as "containing (or including)", "consisting essentially of", and "consisting of".

[0023] Secondary batteries include at least non-aqueous electrolyte secondary batteries such as lithium ion batteries and lithium metal secondary batteries.

[0024] A nonaqueous electrolyte secondary battery according to one embodiment of the present disclosure comprises: a wound electrode group, a nonaqueous electrolyte, a cylindrical battery case for housing the electrode group and the nonaqueous electrolyte, a sealing body for sealing the opening of the battery case, and an insulating plate (hereinafter also referred to as the "first insulating plate") disposed between the electrode group and the bottom of the battery case. The nonaqueous electrolyte secondary battery may also comprise an insulating plate (hereinafter also referred to as the "second insulating plate") disposed between the electrode group and the sealing body. The nonaqueous electrolyte contains a sulfur-containing compound.

[0025] The battery case is, for example, a metal can. As a material constituting the battery case, for example, at least one selected from the group consisting of iron and iron alloys (including stainless steel) can be cited. The battery case can be plated (for example, nickel-plated) as needed. The material constituting the battery case can be appropriately selected according to the polarity of the battery case, etc. In the case of a cylindrical battery case, the battery case usually has the polarity of the negative electrode.

[0026] The first insulating plate has an opening. Here, "opening" refers to an opening composed of one or more regions (windows) that pass through from one main surface of the first insulating plate to the other main surface. That is, the "opening" can be composed of only one region (window) or can be composed of two or more independent regions (windows). The region (window) that passes through from one main surface of the first insulating plate to the other main surface can be a through hole, a through groove, etc. The shape of the through hole or the through groove is not particularly limited.

[0027] Here, the first insulating sheet satisfies at least one of the following conditions (A) and (B).

[0028] (A) The opening ratio of the first insulating plate is 10% or more.

[0029] (B) The opening has multiple independent areas (windows).

[0030] Here, the orthographic projection of the first insulating plate in the normal direction of any main surface of the first insulating plate is referred to as a graph D0. The ratio of the area corresponding to the opening of D0 to the area surrounded by the outer contour of D0 (usually the area of ​​a circle) is the "aperture ratio".

[0031] A plurality of mutually independent regions (windows) refers to a plurality of regions (windows) constituting an opening, and each region (window) is an isolated island-shaped region (window) that is discontinuous with other regions (windows).

[0032] Both conditions (A) and (B) are conditions for dispersing the contact area between the bottom of the battery case and the non-aqueous electrolyte. Both conditions (A) and (B) disperse the exposed portion of the bottom of the battery case that is not covered by the first insulating plate. This prevents the interaction between the sulfur-containing compound and the bottom of the battery case from being concentrated in a narrow area of ​​the bottom.

[0033] When the battery is in an over-discharge state, a portion of the non-aqueous electrolyte impregnated in the electrode group is released from the electrode group and retained in the area surrounded by the bottom of the battery case and the peripheral wall of the opening. The battery case in the over-discharge state reaches the dissolution potential of the material constituting the battery case (e.g., Fe) and a side reaction occurs. When at least one of conditions (A) and (B) is met, the distribution of the retained non-aqueous electrolyte is dispersed. Thus, the places where the side reaction is excessively carried out are eliminated or at least reduced, and the excessive reduction of OCV is prevented.

[0034] The opening includes, for example, a first hole disposed in the center of the first insulating plate. The first hole is composed of an area (window). The opening may be composed of only the first hole, or may include at least one second hole different from the first hole. The first hole is disposed in a manner to include (or surround) the center (center of gravity) of the first insulating plate. The first hole has the function of allowing an electrode to pass through, and the electrode is used to weld a lead extending from the electrode group to the bottom of the battery case. The welding electrode is inserted into the hollow in the center of the electrode group and contacts the lead.

[0035] When a plurality of second holes are provided around the first hole, the shape of the opening (i.e., the shape formed by the first hole and the plurality of second holes as a whole) is preferably a rotationally symmetric shape. Rotational symmetry refers to the property of a figure (here, the shape of the "opening") overlapping itself when rotating (360 / n)° around the center of a two-dimensional figure, where n is an integer greater than 2. For example, the shape when n=3 is a triply symmetric shape overlapping itself when rotating 120°.

[0036] The shape of the first hole may be, for example, circular, polygonal, or radial (eg, star-shaped).

[0037] The second holes may be slit-shaped or dot-shaped. The dot-shaped shapes may be circular, polygonal, or radial (eg, star-shaped).

[0038] The opening ratio of the first insulating plate may be 10% or more, 20% or more, or 30% or more. If the opening ratio is too large, the function of the first insulating plate to prevent internal short circuits will be deteriorated. Therefore, the opening ratio is preferably 50% or less, or 40% or less, for example.

[0039] The number of the second holes is, for example, 3 or more, 6 or more, 20 or more, or 40 or more. If the number of the second holes is too large, the function of the first insulating plate to prevent internal short circuits will deteriorate. Therefore, the number of the second holes is, for example, preferably 100 or less, and may be 60 or less.

[0040] The first hole needs to be large enough to allow the welding electrode to pass through. From the perspective of preventing internal short circuits, the opening area of ​​each second hole is preferably smaller. That is, the second hole is preferably smaller than the opening area of ​​the first hole. In addition, the opening area of ​​each second hole is preferably less than 9% of the opening area of ​​the first hole, and can also be less than 8%. In order to allow the non-aqueous electrolyte to be retained in each second hole, the opening area of ​​each second hole is preferably set to 50 mm 2 above.

[0041] The thickness of the first insulating plate is not particularly limited, and in order to ensure mechanical strength and short circuit resistance and maintain high battery capacity, the thickness T may be greater than or equal to 0.05 mm and less than or equal to 3 mm. It should be noted that the thickness T of the first insulating plate is the thickness of the area outside the opening of the first insulating plate. As the thickness T, the average value of the thickness measured at multiple locations (e.g., 5 locations) of the first insulating plate can be used.

[0042] Usually, the outer shape of the first insulating plate has a circular shape or a shape similar thereto (for example, an elliptical shape, or a shape obtained by cutting off a part of a circular shape or an elliptical shape) in a planar direction (a direction perpendicular to the thickness direction).

[0043] The first insulating plate can be formed of, for example, an insulating resin or a metal after insulation treatment. From the perspective of easily ensuring the strength of the first insulating plate, the first insulating plate is preferably formed of a material having a bending strength of 100 MPa or more. In this material, as an insulating resin, in addition to curable resins (thermosetting resins, etc.) such as phenolic resins, epoxy resins, and unsaturated polyester resins, thermoplastic resins such as polyolefins (such as polypropylene), polyphenylene sulfide resins, polyimide resins, polyamide-imide resins, polyetherimide resins, and fluororesins (polytetrafluoroethylene, etc.) can also be listed. As metals, for example, stainless steel or iron can be listed. The insulation treatment of the metal can be performed, for example, by coating the metal with an insulating resin. There is no particular limitation on the insulating resin for coating the metal, and for example, polyimide resins, polypropylene resins, etc. can be listed. In addition, the first insulating plate can be formed of a material in which an insulating fibrous core material such as glass fiber is impregnated with an insulating resin (thermosetting resins such as phenolic resin, etc.) and cured.

[0044] It should be noted that the material of the second insulating sheet is not particularly limited and can be selected from the materials exemplified for the first insulating sheet. The first and second insulating sheets may be composed of a core material and an insulating resin, and the core material may be composed of an insulating fibrous material.

[0045] The first insulating plate is sometimes called a lower insulating plate because it is disposed between the electrode group and the bottom of the battery case. The first insulating plate has, for example, a disk shape because it is disposed just below the cylindrical or similar electrode group.

[0046] The non-aqueous electrolyte may contain one sulfur-containing compound or a combination of two or more. The sulfur-containing compound is used to improve the charge and discharge cycle characteristics of the battery. The content of the sulfur-containing compound contained in the non-aqueous electrolyte is, for example, greater than 0.01 mass % and less than 10 mass %, may be greater than 0.25 mass % and less than 10 mass %, or may be greater than 0.5 mass % and less than 10 mass %. A non-aqueous electrolyte containing sulfur-containing compounds at such a content has a great effect on reducing the OCV of the battery in an over-discharged state. Therefore, when such a non-aqueous electrolyte is used, the effect of suppressing the reduction in the OCV of the battery by using the first insulating plate involved in the present disclosure tends to become apparent.

[0047] It should be noted that the content of sulfur-containing compounds in the non-aqueous electrolyte of a non-aqueous electrolyte secondary battery changes during storage or during charge and discharge cycles. Therefore, the sulfur-containing compounds may remain in the non-aqueous electrolyte extracted from the non-aqueous electrolyte secondary battery at a concentration above the detection limit.

[0048] Since the non-aqueous electrolyte contains a sulfur-containing compound, a highly flexible solid electrolyte interface (Solid Electrolyte Interphase: SEI) is formed on the surface of the negative electrode active material. The highly flexible SEI easily follows the expansion and contraction of the negative electrode due to charge and discharge. Therefore, it can be considered that even if charge and discharge are repeated, the reduction in capacity can be reduced and high cycle characteristics can be obtained.

[0049] The sulfur-containing compound preferably has one or more sulfonyl groups (-S(=O)2-), and may have one or more fluorosulfonyl groups (FS(=O)2-). For example, the sulfur-containing compound may contain fluorosulfonic acid or fluorosulfonate. Among fluorosulfonates, lithium fluorosulfonate is preferred.

[0050] As the sulfur-containing compound, at least one selected from the group consisting of sulfate esters, sulfite esters, sulfonate esters, and sulfonimide compounds can be used. Such a sulfur-containing compound preferably has an unsaturated bond because it is easy to form a good SEI.

[0051] Sulfate esters have a -OS(=O)2-O- structure. Sulfate esters may be cyclic or chain-shaped, or may form salts. As sulfate esters, C 2-4 Alkyl sulfate esters: Specifically, ethylene sulfate, propylene sulfate, trimethylene sulfate, butylene sulfate, vinylene sulfate, ethyl sulfate, methyl sulfate, etc. are mentioned.

[0052] Sulfite has a -OS(=O)-O- structure. Sulfite may be cyclic or chain-shaped, or may form a salt. As sulfite, C 2-4 Alkylene sulfite. Specific examples thereof include ethylene sulfite (ES), propylene sulfite, trimethylene sulfite, butylene sulfite, and vinylene sulfite.

[0053] Sulfonic acid esters have a -S(=O)2-O- structure. Sulfonic acid esters may be cyclic or chain-shaped, or may form salts. As sulfonic acid esters, preferably selected from C 3-5 Alkanesultones and C 3-5 At least one of the group consisting of olefin sultones. Among them, cyclic sulfonates are preferred. Specifically, 1,3-propane sultone, 1,4-butane sultone, 1,3-propene sultone, etc. are listed. Among them, 1,3-propene sultone having an unsaturated bond is preferably used.

[0054] As the sulfur-containing compound, a sulfonyl imide compound (sulfonyl imide salt) can be used. Examples of the sulfonyl imide salt include lithium bis(fluorosulfonyl imide) (LiN(FSO2)2) (LiFSI), lithium bis(trifluoromethanesulfonyl imide) (LiN(CF3SO2)2) (LiTFSI), lithium trifluoromethanesulfonyl nonafluorobutanesulfonyl imide (LiN(CF3SO2)(C4F9SO2)), and lithium bis(pentafluoroethanesulfonyl imide) (LiN(C2F5SO2)2).

[0055] In the case of the sulfur-containing compound, one or more hydrogen atoms in the above-mentioned compounds may be substituted by a substituent. Examples of the substituent include an alkyl group, a hydroxyalkyl group, a hydroxyl group, an alkoxy group, and a halogen atom. The number of carbon atoms in the substituent may be 1 to 4 or 1 to 3. Examples of the halogen atom include a chlorine atom and a fluorine atom.

[0056] Hereinafter, the first insulating sheet according to the present embodiment will be described in more detail with reference to the drawings.

[0057] [First embodiment]

[0058] Figure 1 It is a plan view schematically showing the first insulating sheet 10 according to one embodiment of the present disclosure. Figure 1 The outer shape of the first insulating plate 100 is circular. The first insulating plate 100 has a circular first hole 110 at the center. The opening ratio of the first insulating plate 100 is 10% or more. That is, the ratio of the area of ​​the first hole 110 (the area of ​​a circle with a diameter d) to the area surrounded by the outer contour (the area of ​​a circle with an outer diameter D) of the orthographic projection D0 of the first insulating plate 100 in the normal direction of the main surface of the first insulating plate 100 is 10% or more.

[0059] [Second embodiment]

[0060] Figure 2 It is a plan view schematically showing a first insulating sheet 100A according to one embodiment of the present disclosure. Figure 2 The outer shape of the first insulating plate 100A is circular. The first insulating plate 100 has a circular first hole 110 in the center. In addition, the first insulating plate 100 has a plurality of (48) second holes 120 around the first hole 110. The shape of the overall structure of the first hole 110 and the plurality of second holes 120 (i.e., the shape of the opening) is a rotationally symmetrical shape. The opening of the first insulating plate 100A has the property of overlapping with itself when rotated 360 / 4° (fourfold symmetry). It should be noted that the number of second holes 110 is not limited to 48, for example, it can be any one of 4 to 100 or 12 to 60. Rotational symmetry is not limited to three-fold symmetry, but can also be any one of two-fold to ten-fold symmetry or three-fold to eight-fold symmetry.

[0061] The opening ratio of the first insulating plate 100A is, for example, 30% or more. That is, the ratio of the total area of ​​the sum of the area of ​​the first hole 110 (the area of ​​a circle with a diameter d) and the areas of the plurality of (48) second holes 120 (the area of ​​a circle with a diameter i) to the area surrounded by the outer contour (the area of ​​a circle with an outer diameter D) of the orthographic projection D0 of the first insulating plate 100A in the normal direction of the main surface of the first insulating plate 10A is 30% or more.

[0062] The opening area of ​​each second hole 120 is sufficiently smaller than the opening area of ​​the first hole. The opening area of ​​each second hole 120 is 5% to 20% of the opening area of ​​the first hole, and is 3 mm 2 ~17mm 2 The first holes 110 alone account for 3% to 20% of the opening ratio.

[0063] [Third Embodiment]

[0064] Figure 3 It is a plan view schematically showing a first insulating sheet 100B according to one embodiment of the present disclosure. Figure 3 The outer shape of the first insulating plate 100B is circular. The first insulating plate 100B has a first hole 110B in the center, and the first hole 110B has a groove-shaped portion extending radially (star-shaped) in six directions. In addition, the first insulating plate 100B has a plurality of (6) second holes 120B around the first hole 110B. The six second holes 120B are arranged radially corresponding to each of the six groove-shaped portions of the first hole 110B. The first insulating plate 110B is composed of six sector-shaped portions and connecting portions connecting adjacent sector-shaped portions to each other. It should be noted that the number of sector-shaped portions is not limited to 6, for example, it can be any number from 3 to 10.

[0065] The overall shape of the first hole 110B and the plurality of second holes 120B (ie, the shape of the opening) is rotationally symmetrical. The opening of the first insulating plate 100B has a property of overlapping itself when rotated 360 / 6° (six-fold symmetry).

[0066] The opening ratio of the first insulating plate 100B is 30% or more. That is, the ratio of the total area of ​​the first hole 110B and the sum of the areas of the plurality of (six) second holes 120B (the area of ​​the through groove) to the area surrounded by the outer contour (the area of ​​the circle with the outer diameter D) of the orthographic projection D0 of the first insulating plate 100B in the normal direction of the main surface of the first insulating plate 10A is 30% or more.

[0067] The opening area of ​​each second hole 120B is sufficiently smaller than the opening area of ​​the first hole 110B. The opening area of ​​each second hole 120B is 20% to 50% of the opening area of ​​the first hole 110B and is 17 mm2 ~42mm 2 The first holes 110B alone account for 20% to 50% of the opening ratio.

[0068] Below, refer to Figure 4 Each constituent element of the nonaqueous electrolyte secondary battery according to the present disclosure will be described in more detail.

[0069] The nonaqueous electrolyte secondary battery according to the present embodiment comprises: a wound electrode group, a nonaqueous electrolyte, a cylindrical battery case containing the wound electrode group, a sealing body for sealing an opening of the battery case, a first insulating plate disposed between the electrode group and the bottom of the battery case, and a second insulating plate disposed between the electrode group and the sealing body. The sealing body has a gas exhaust valve.

[0070] Figure 4 Schematic longitudinal cross-sectional view of a cylindrical secondary battery according to one embodiment of the present disclosure. Figure 4 , taking a lithium ion secondary battery as an example, the nonaqueous electrolyte secondary battery involved in this embodiment is described in more detail.

[0071] The cylindrical nonaqueous electrolyte secondary battery (hereinafter referred to as a battery) 10 includes an electrode group 18, a nonaqueous electrolyte (not shown), and a battery case (battery can) 22 that accommodates them. The electrode group 18 is formed by winding a positive electrode plate 15 and a negative electrode plate 16 with a separator 17 interposed therebetween. An annular groove 22a is formed near the open end of the battery can 22.

[0072] The opening of the battery can 22 is sealed by a sealing body 11 having a sealing gasket 21 at the peripheral portion. The sealing body 11 includes: a valve body 12, a metal plate 13, and an annular insulating member 14 sandwiched between the outer peripheral portion of the valve body 12 and the outer peripheral portion of the metal plate 13. The valve body 12 and the metal plate 13 are connected to each other at their respective center portions. The positive electrode lead 15a led out from the positive electrode 15 is connected to the metal plate 13. Therefore, the valve body 12 acts as an external terminal of the positive electrode. The negative electrode lead 16a led out from the negative electrode 16 is connected (welded) to the inner surface of the bottom of the battery can 22. A first insulating plate 24 is arranged between one end face of the electrode group 18 and the bottom of the battery can 22. A second insulating plate 23 is arranged between the sealing body 11 and the other end face of the electrode group 18.

[0073] In the present disclosure, the thickness T of the first insulating sheet is preferably set to be greater than or equal to 0.05 mm and less than or equal to 3 mm, and more preferably greater than or equal to 0.1 mm and less than or equal to 1 mm.

[0074] The outer diameter of the battery is, for example, 18 mm to 40 mm, or 18 mm to 26 mm. Even if the outer shape of the battery is 18 mm to 26 mm, the strength of the first insulating plate can be easily ensured by setting the thickness T of the first insulating plate to 0.05 mm to 3 mm. The thickness T of the first insulating plate can also be 0.1 mm to 1 mm.

[0075] Hereinafter, each constituent element of the nonaqueous electrolyte secondary battery according to the present disclosure will be described in more detail.

[0076] [positive electrode]

[0077] The positive electrode comprises a positive electrode collector and a positive electrode mixture layer arranged on the surface of the positive electrode collector. The positive electrode collector is composed of a sheet-shaped conductive material. The positive electrode mixture layer is carried on one surface or both surfaces of the positive electrode collector. The positive electrode mixture layer is usually a layer or film composed of a positive electrode mixture. The thickness of the positive electrode mixture layer is, for example, 10 μm to 150 μm per side of the positive electrode collector. The positive electrode mixture contains a positive electrode active material as an essential component.

[0078] The positive electrode mixture layer may contain a conductive agent as an arbitrary component. As the conductive agent, for example, carbon black (CB), acetylene black (AB), Ketjen black, carbon nanotubes (CNT), graphene, graphite and other carbon-based materials can be listed. They can be used alone or in combination of two or more.

[0079] The positive electrode mixture layer may include a binder. As the binder, for example, fluorine resins such as polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyacrylonitrile (PAN), polyimide resins, acrylic resins, polyolefin resins, etc. may be listed. They may be used alone or in combination of two or more.

[0080] As the positive electrode current collector, a nonporous conductive substrate (metal foil, etc.) or a porous conductive substrate (grid, net, punched sheet, etc.) is used. Examples of the material of the positive electrode current collector include aluminum, aluminum alloy, titanium, titanium alloy, and the like.

[0081] As a positive electrode active material, a lithium-containing composite oxide can be used. The lithium-containing composite oxide can have a layered rock salt structure. The layered rock salt structure, for example, belongs to the space group R-3m, the space group C2 / m, etc. Among them, the layered rock salt structure belonging to the space group R-3m is preferred because of its high capacity and high stability of the crystal structure. The layered rock salt structure of the lithium-containing composite oxide can include a transition metal layer, a Li layer, and an oxygen layer.

[0082] From the viewpoint of increasing capacity, the ratio of Ni to metal elements other than Li contained in the lithium-containing composite oxide (Ni content) may be 50 atomic % or more, 80 atomic % or more, or 90 atomic % or more.

[0083] From the perspective of stabilizing the crystal structure of the lithium-containing composite oxide and improving the heat resistance of the battery, the proportion of Co in the metal elements other than Li contained in the lithium-containing composite oxide (Co content) can be set to be greater than 0 atomic % and less than 16 atomic %, or can be set to be greater than 1.5 atomic % and less than 16 atomic %.

[0084] Similarly, from the perspective of stabilizing the crystal structure of the lithium-containing composite oxide and improving the heat resistance of the battery, the proportion of Al in the metal elements other than Li contained in the lithium-containing composite oxide (Al content) can be set to be greater than 0 atomic % and less than 18.5 atomic %, or can be set to be greater than 4 atomic % and less than 10 atomic %.

[0085] From the perspective of cost reduction, the ratio of Mn to metal elements other than Li contained in the lithium-containing composite oxide (Mn content) may be 0 atomic % to 50 atomic % or 0 atomic % to 30 atomic % both inclusive.

[0086] The content of each metal element contained in the lithium-containing composite oxide is measured by, for example, inductively coupled plasma (ICP) emission spectrometry.

[0087] The lithium-containing composite oxide may be, for example, of the general formula Li a Ni x Co y Al z M1 w O 2-b The composite oxide shown in the formula, wherein 0.8≤a≤1.2, 0.80≤x≤0.95, 0.015≤y≤0.16, 0.04≤z≤0.185, 0≤w≤0.145, 0≤b<0.05, x+y+z+w=1, and M1 is at least one element selected from Mn, Fe, Ti, Si, Nb, Zr, Mo and Zn. In this case, M1 is preferably Mn.

[0088] [negative electrode]

[0089] The negative electrode at least has a negative electrode collector, and may have a negative electrode mixture layer arranged on the surface of the negative electrode collector. The negative electrode collector is composed of a sheet-like conductive material. The negative electrode mixture layer is carried on one side surface or both sides of the negative electrode collector. The negative electrode mixture layer is usually a layer or film composed of a negative electrode mixture. The thickness of the negative electrode mixture layer is, for example, 10μm to 150μm per side of the negative electrode collector. The negative electrode mixture contains a negative electrode active material as an essential component, and may contain a binder, a conductive agent, a thickener, etc. as arbitrary components. As a binder, a conductive agent, and a thickener, known materials can be used.

[0090] The negative electrode active material includes materials that electrochemically absorb and release lithium ions, lithium metal, lithium alloys, etc. As materials that electrochemically absorb and release lithium ions, carbon materials, alloy materials, etc. can be used. As carbon materials, for example, graphite, easily graphitized carbon (soft carbon), and difficultly graphitized carbon (hard carbon) can be listed. Among them, graphite with excellent charge and discharge stability and low irreversible capacity is preferred. Alloy materials are materials containing at least one metal that can form an alloy with lithium. As such materials, silicon, tin, silicon alloys, tin alloys, silicon compounds, etc. can be listed. Silicon oxide, tin oxide, etc. can also be used.

[0091] As the alloy material containing silicon, for example, a silicon-containing material including a lithium ion conductive phase and a silicon phase dispersed in the lithium ion conductive phase can be preferably used.

[0092] As the lithium ion conductive phase, for example, a silicon oxide phase, a silicate phase, a carbon phase, etc. can be used. The main component (for example, 95 to 100% by mass) of the silicon oxide phase can be silicon dioxide. The silicate phase is preferred because it has a small irreversible capacity. Among them, as a lithium ion conductive phase with high initial charge and discharge efficiency, a silicate phase containing lithium (hereinafter also referred to as a lithium silicate phase) can be preferably used.

[0093] The lithium silicate phase can be any oxide phase containing lithium (Li), silicon (Si), and oxygen (O), and can also contain other elements. The atomic ratio of O to Si in the lithium silicate phase: O / Si is, for example, greater than 2 and less than 4. Preferably, O / Si is greater than 2 and less than 3. The atomic ratio of Li to Si in the lithium silicate phase: Li / Si is, for example, greater than 0 and less than 4. The lithium silicate phase can have the formula: Li 2z SiO 2+z The composition is shown as (0<z<2). z preferably satisfies the relationship of 0<z<1, and z=1 / 2 is more preferred. Elements other than Li, Si and O that may be contained in the lithium silicate phase include, for example, iron (Fe), chromium (Cr), nickel (Ni), manganese (Mn), copper (Cu), molybdenum (Mo), zinc (Zn), aluminum (Al) and the like.

[0094] The carbon phase may be composed of, for example, amorphous carbon (ie, non-crystalline carbon) having low crystallinity. The amorphous carbon may be, for example, hard carbon, soft carbon, or other carbon.

[0095] As the negative electrode active material, a silicon-containing material and a carbon material can be used in combination. Since the silicon-containing material expands and contracts in volume with charging and discharging, if the ratio of the silicon-containing material in the negative electrode active material increases, poor contact between the negative electrode active material and the negative electrode collector is likely to occur with charging and discharging. On the other hand, by using a silicon-containing material and a carbon material in combination, excellent cycle characteristics can be achieved while giving the negative electrode a high capacity.

[0096] The ratio of the silicon-containing material to the total of the silicon-containing material and the carbon material is, for example, preferably 0.5 to 15% by mass, more preferably 1 to 10% by mass. This makes it easier to achieve both high capacity and improved cycle characteristics.

[0097] As the negative electrode current collector, a nonporous conductive substrate (metal foil, etc.) or a porous conductive substrate (grid, net, punched sheet, etc.) is used. Examples of the material of the negative electrode current collector include stainless steel, nickel, nickel alloy, copper, copper alloy, and the like.

[0098] [Non-aqueous electrolyte]

[0099] The non-aqueous electrolyte includes a non-aqueous solvent and a solute dissolved in the non-aqueous solvent. The solute includes, for example, a lithium salt. Components other than the non-aqueous solvent and the solute of the non-aqueous electrolyte are additives. The non-aqueous electrolyte includes the sulfur-containing compound as an additive.

[0100] As the non-aqueous solvent, for example, cyclic carbonates, chain carbonates, cyclic carboxylates, chain carboxylates, etc. can be used. As cyclic carbonates, propylene carbonate (PC), ethylene carbonate (EC), vinylene carbonate (VC), etc. can be listed. As chain carbonates, diethyl carbonate (DEC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), etc. can be listed. In addition, as cyclic carboxylates, γ-butyrolactone (GBL), γ-valerolactone (GVL), etc. can be listed. As chain carboxylates, methyl acetate, ethyl acetate, propyl acetate, methyl propionate (MP), ethyl propionate (EP), etc. can be listed. The non-aqueous solvent can be used alone or in combination of two or more.

[0101] As the lithium salt, for example, a lithium salt containing chloric acid (LiClO4, LiAlCl4, LiB 10 Cl 10etc.), lithium salts of fluorinated acids (LiPF6, LiPF2O2, LiBF4, LiSbF6, LiAsF6, LiCF3SO3, LiCF3CO2, etc.), lithium salts of fluorinated imides (LiN(FSO2)2, LiN(CF3SO2)2, LiN(CF3SO2)(C4F9SO2), LiN(C2F5SO2)2, etc.), lithium halides (LiCl, LiBr, LiI, etc.), etc. The lithium salts may be used alone or in combination of two or more.

[0102] The concentration of the lithium salt in the non-aqueous electrolyte may be 1 mol / L or more and 2 mol / L or less, or 1 mol / L or more and 1.5 mol / L or less. By controlling the lithium salt concentration within the above range, an electrolyte having excellent ion conductivity and appropriate viscosity may be obtained. The lithium salt concentration is not limited to the above concentration.

[0103] [Separator]

[0104] Preferably, a separator is sandwiched between the positive electrode and the negative electrode. The separator has high ion permeability and has appropriate mechanical strength and insulation. As the separator, a microporous film, a woven fabric, a non-woven fabric, etc. can be used. As the material of the separator, polyolefins such as polypropylene and polyethylene are preferred.

[0105] [Example]

[0106] Hereinafter, the present invention will be specifically described based on Examples and Comparative Examples, but the present invention is not limited to the following Examples.

[0107] 《Example 1》

[0108] (1) Preparation of positive electrode

[0109] The positive electrode active material (LiNi 0.8 Co 0.15 Al 0.05 O2) 100 parts by weight, a binder (polyvinylidene fluoride) 1.7 parts by weight, and a conductive agent (acetylene black) 2.5 parts by weight are placed in a dispersion medium and kneaded to prepare a positive electrode mixture slurry. The positive electrode mixture slurry is applied to both sides of an aluminum foil positive electrode collector, dried and rolled to form a positive electrode active material layer, and cut into a specified size to obtain a positive electrode.

[0110] [negative electrode]

[0111] (2) Production of negative electrode plate

[0112] 100 parts by weight of negative electrode active material (graphite), 0.6 parts by weight of binder (styrene butadiene rubber), and 1 part by weight of thickener (carboxymethyl cellulose) were mixed in a dispersion medium to prepare a negative electrode mixture slurry. The negative electrode mixture slurry was applied to both sides of a negative electrode collector made of copper foil, dried and rolled to form a negative electrode active material layer, and cut into a specified size to obtain a negative electrode.

[0113] [Preparation of non-aqueous electrolyte]

[0114] Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) were mixed in a volume ratio of 3:3:4. A non-aqueous electrolyte was prepared by dissolving lithium hexafluorophosphate (LiPF6) in the mixed solvent to a concentration of 1.2 mol / L. A sulfur-containing compound 1,3-propylene sultone (PRES) was dissolved in the non-aqueous electrolyte at a content of 0.5 mass %.

[0115] [Preparation of test battery]

[0116] The positive electrode lead is attached to the exposed portion of the positive electrode current collector, the negative electrode lead is attached to the negative electrode current collector, and the positive electrode and the negative electrode are wound with a polyolefin microporous film (separator) interposed therebetween to prepare an electrode group. Figure 2 The first insulating plate (opening ratio 35%, number of second holes 48) was inserted into the battery can, and the negative electrode lead was resistance welded to the bottom of the battery can. An iron can with nickel plating on the inner surface was used as the battery can.

[0117] The opening area of ​​each second hole 120B is 8% of the opening area of ​​the first hole 110B and is 7 mm 2 With respect to the opening ratio, the first hole 110B alone accounts for 7%.

[0118] A disk-shaped second insulating plate made of glass fiber impregnated with phenolic resin was placed on the upper end surface of the electrode group, and then an annular groove was formed near the opening end of the battery can. The thickness T of the first insulating plate was 0.2 mm.

[0119] Next, the positive electrode lead is connected to the metal plate of the safety mechanism of the sealing body, and the above-mentioned non-aqueous electrolyte is injected into the iron battery can. Then, the annular groove formed on the battery can is supported via a sealing gasket so that the open end of the battery can is tightly embedded in the periphery of the sealing body, thereby completing the lithium-ion secondary battery (battery A1).

[0120] [evaluate]

[0121] At 25°C, the nonaqueous electrolyte secondary battery was discharged at a constant current of 0.2C from the charged state until the voltage reached 2.5V. Then, the positive electrode and the negative electrode were connected via a 1kΩ resistor and placed at 60°C for 34 days to put the battery into an overdischarge state. The battery voltage (OCV) after 34 days is shown in Table 1.

[0122] [Table 1]

[0123]

[0124] 《Example 2》

[0125] Battery A2 of Example 2 was prepared in the same manner as in Example 1 and evaluated in the same manner as in Example 1, except that 1,3-propylene sultone (PRES) was not added to the non-aqueous electrolyte and lithium hexafluorophosphate (LiPF6) was dissolved in the non-aqueous electrolyte to a concentration of 0.9 mol / L and lithium bis(fluorosulfonyl)imide (LiN(FSO2)2) (LiFSI) was dissolved to a concentration of 0.3 mol / L.

[0126] Comparative Example 1

[0127] Battery B1 of Comparative Example 1 was prepared and evaluated in the same manner as in Example 1, except that a first insulating plate having only the first hole with an opening ratio of 7% (i.e., less than 10%) in the center was used and 1,3-propene sultone (PRES) was not added to the nonaqueous electrolyte.

[0128] Comparative Example 2

[0129] A battery B2 of Comparative Example 2 was prepared in the same manner as in Example 1, except that a first insulating plate having only the first hole in the center and an opening ratio of 7% (ie, less than 10%) was used, and the same evaluation was performed.

[0130] 《Comparative Example 3》

[0131] Battery B3 of Comparative Example 3 was prepared in the same manner as in Example 2, except that a first insulating plate having only the first hole in the center and an opening ratio of 7% (ie, less than 10%) was used, and the same evaluation was performed.

[0132] 《Comparative Example 4》

[0133] A battery B4 of Comparative Example 4 was prepared in the same manner as in Example 1, except that 1,3-propene sultone (PRES) was not added to the non-aqueous electrolyte, and the same evaluation was performed.

[0134] As shown in Table 1, when the non-aqueous electrolyte does not contain a sulfur-containing compound, the OCV of the battery maintains a relatively high voltage regardless of the form of the first insulating plate. On the other hand, when the non-aqueous electrolyte contains a sulfur-containing compound, the OCV of the battery changes significantly depending on the form of the first insulating plate. Specifically, in Comparative Examples 2 and 3 where the opening ratio of the first insulating plate is less than 10%, the OCV decreases to 0.031V or 0V, while in Examples 1 and 2 where the opening ratio of the first insulating plate is 10% or more, it maintains 0.134V or 0.129V.

[0135] [Additional Notes]

[0136] The present disclosure includes the following additional embodiments.

[0137] (1) A non-aqueous electrolyte secondary battery comprising:

[0138] Wound electrode group,

[0139] Non-aqueous electrolytes,

[0140] a cylindrical battery case for housing the electrode group and the non-aqueous electrolyte,

[0141] a sealing body for sealing the opening of the battery case, and

[0142] an insulating plate disposed between the electrode group and the bottom of the battery case,

[0143] The nonaqueous electrolyte comprises a sulfur-containing compound,

[0144] The insulating plate has an opening,

[0145] The opening ratio of the insulating plate is greater than 10%.

[0146] (2) A non-aqueous electrolyte secondary battery comprising:

[0147] Wound electrode group,

[0148] Non-aqueous electrolytes,

[0149] a cylindrical battery case for housing the electrode group and the non-aqueous electrolyte,

[0150] a sealing body for sealing the opening of the battery case,

[0151] an insulating plate disposed between the electrode group and the bottom of the battery case,

[0152] The nonaqueous electrolyte comprises a sulfur-containing compound,

[0153] The insulating plate has an opening,

[0154] The opening has a plurality of mutually independent areas.

[0155] (3) The nonaqueous electrolyte secondary battery according to (1) or (2) above, wherein the opening includes a first hole provided at the center of the insulating plate.

[0156] (4) The nonaqueous electrolyte secondary battery according to any one of (1) to (3) above, wherein the opening further includes at least one second hole different from the first hole.

[0157] (5) The nonaqueous electrolyte secondary battery according to any one of (1) to (4) above, wherein a plurality of the second holes are provided around the first hole.

[0158] The shape of the opening is a rotationally symmetrical shape.

[0159] (6) The nonaqueous electrolyte secondary battery according to any one of (1) to (5) above, wherein each of the second holes has a slit-like shape.

[0160] (7) The nonaqueous electrolyte secondary battery according to any one of (1) to (6) above, wherein each of the second holes has a dot-like shape.

[0161] (8) The nonaqueous electrolyte secondary battery according to any one of (1) to (7) above, wherein the number of the second holes is 6 or more.

[0162] (9) The nonaqueous electrolyte secondary battery according to any one of (1) to (8) above, wherein an opening ratio of each of the second holes is smaller than an opening ratio of the first holes.

[0163] (10) The nonaqueous electrolyte secondary battery according to any one of (1) to (9) above, wherein the content of the sulfur-containing compound in the nonaqueous electrolyte is 0.25 mass % or more and 10 mass % or less.

[0164] (11) The nonaqueous electrolyte secondary battery according to any one of (1) to (10) above, wherein the sulfur-containing compound has one or more sulfonyl groups.

[0165] (12) The nonaqueous electrolyte secondary battery according to any one of (1) to (11) above, wherein the sulfur-containing compound has one or more fluorosulfonyl groups.

[0166] (13) The nonaqueous electrolyte secondary battery according to any one of (1) to (12) above, wherein the sulfur-containing compound has an unsaturated bond.

[0167] (14) The nonaqueous electrolyte secondary battery according to any one of (1) to (13) above, wherein the sulfur-containing compound includes a cyclic sulfonic acid ester.

[0168] Industrial Applicability

[0169] The present disclosure can be applied to non-aqueous electrolyte secondary batteries such as lithium ion secondary batteries. According to the present disclosure, it is possible to suppress a decrease in the open circuit voltage (OCV) of a battery in an overdischarge state.

[0170] The preferred embodiments of the present invention are described, but the disclosure thereof shall not be interpreted as restrictive. It is obvious to those skilled in the art that various modifications and changes can be clearly understood by reading the above disclosure. Therefore, the attached claims should be interpreted as including all modifications and changes that do not depart from the true spirit and scope of the present invention.

[0171] Description of Reference Numerals

[0172] 10: non-aqueous electrolyte secondary battery, 11: sealing body, 12: valve body, 13: metal plate, 14: insulating member, 15: positive electrode, 15a: positive electrode lead, 16: negative electrode, 16a: negative electrode lead, 17: separator, 18: electrode group, 21: sealing gasket, 22: battery can, 22a: annular groove, 23: second insulating plate, 24: first insulating plate, 100, 100A, 100B: first insulating plate, 110, 110B: first hole, 120, 120B: second hole.

Claims

1. A non-aqueous electrolyte secondary battery comprising: Wound electrode group, Non-aqueous electrolytes, a cylindrical battery case for housing the electrode group and the non-aqueous electrolyte, a sealing body for sealing the opening of the battery case, and an insulating plate disposed between the electrode group and the bottom of the battery case, The nonaqueous electrolyte comprises a sulfur-containing compound, The insulating plate has an opening, The opening ratio of the insulating plate is greater than 10%.

2. A non-aqueous electrolyte secondary battery comprising: Wound electrode group, Non-aqueous electrolytes, a cylindrical battery case for housing the electrode group and the non-aqueous electrolyte, a sealing body for sealing the opening of the battery case, and an insulating plate disposed between the electrode group and the bottom of the battery case, The nonaqueous electrolyte comprises a sulfur-containing compound, The insulating plate has an opening, The opening has a plurality of mutually independent areas.

3. The nonaqueous electrolyte secondary battery according to claim 1 or 2, wherein: The opening includes a first hole disposed at the center of the insulating plate.

4. The nonaqueous electrolyte secondary battery according to claim 3, wherein The opening further includes at least one second hole different from the first hole.

5. The nonaqueous electrolyte secondary battery according to claim 4, wherein A plurality of second holes are arranged around the first hole, The shape of the opening is a rotationally symmetrical shape.

6. The nonaqueous electrolyte secondary battery according to claim 5, wherein Each of the second holes is in a slit-like shape.

7. The nonaqueous electrolyte secondary battery according to claim 5, wherein Each of the second holes is in a dot shape.

8. The nonaqueous electrolyte secondary battery according to claim 5, wherein The number of the second holes is 3 or more.

9. The nonaqueous electrolyte secondary battery according to claim 5, wherein The opening area of ​​each of the second holes is smaller than the opening area of ​​the first holes.

10. The nonaqueous electrolyte secondary battery according to claim 1 or 2, wherein: The content of the sulfur-containing compound contained in the nonaqueous electrolyte is 0.01 mass % or more and 10 mass % or less.

11. The nonaqueous electrolyte secondary battery according to claim 1 or 2, wherein: The sulfur-containing compound has one or more sulfonyl groups.

12. The nonaqueous electrolyte secondary battery according to claim 1 or 2, wherein: The sulfur-containing compound has one or more fluorosulfonyl groups.

13. The nonaqueous electrolyte secondary battery according to claim 1 or 2, wherein: The sulfur-containing compound has an unsaturated bond.

14. The nonaqueous electrolyte secondary battery according to claim 1 or 2, wherein: The sulfur-containing compound comprises a cyclic sulfonate ester.

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