Nonaqueous electrolyte secondary battery

Abstract

A non-aqueous electrolyte secondary battery (10) is provided with: an electrode body (14) in which a positive electrode (11) and a negative electrode (12) are wound with a separator (13) interposed therebetween; a non-aqueous electrolyte; and an exterior can (16) that accommodates the electrode body (14) and the non-aqueous electrolyte. The negative electrode (12) has a negative electrode core (40) and a negative electrode mixture layer (41) provided on the surface of the negative electrode core (40). An exposed portion (42) is formed on the outer peripheral surface of the electrode body (14), the exposed portion (42) exposing the surface of the negative electrode core (40), and the exposed portion (42) is in contact with the inner surface of the outer can (16). The nonaqueous electrolyte contains lithium hexafluorophosphate and a cyclic carboxylic acid anhydride represented by formula (I). [Formula 1] # imgabs0 # (In the formula, R1 to R4 are each independently H, alkyl group, alkenyl group, or aryl group)

Description

Technical Field

[0001] The present invention relates to a nonaqueous electrolyte secondary battery, and more particularly to a nonaqueous electrolyte secondary battery including a wound electrode assembly. Background Art

[0002] Conventionally, nonaqueous electrolyte secondary batteries are widely known that include an electrode assembly in which a positive electrode and a negative electrode are spirally wound with a separator interposed therebetween, a nonaqueous electrolyte, and an outer can housing the electrode assembly and the nonaqueous electrolyte.

[0003] For example, Patent Documents 1 and 2 disclose a non-aqueous electrolyte secondary battery for the purpose of reducing resistance, etc., which has a structure in which an exposed portion is formed on the outer peripheral surface of a wound electrode body to expose the surface of a negative electrode core, and the exposed portion is in contact with the inner surface of a metal outer packaging can serving as an external terminal of the negative electrode.

[0004] Patent Document 3 proposes a non-aqueous electrolyte secondary battery having a non-aqueous electrolyte to which fluoroethylene carbonate and diglycolic anhydride are added.

[0005] Prior art literature

[0006] Patent Literature

[0007] Patent Document 1: Japanese Patent Application Laid-Open No. 2013-254561

[0008] Patent Document 2: Japanese Patent Application Publication No. 2019-145448

[0009] Patent Document 3: International Publication No. 2022 / 163138 Summary of the Invention

[0010] Although the resistance reduction effect can be expected by making the exposed portion of the negative electrode core formed on the outer peripheral surface of the electrode body contact the inner surface of the outer can, the inventors have found that a sufficient effect cannot be achieved due to metal elution from the metal components constituting the battery.

[0011] An object of the present invention is to provide a non-aqueous electrolyte secondary battery having low direct current resistance (DCR).

[0012] The nonaqueous electrolyte secondary battery of the present invention is characterized by comprising: an electrode body formed by winding a positive electrode and a negative electrode with a separator interposed therebetween; a nonaqueous electrolyte; and an outer packaging can that houses the electrode body and the nonaqueous electrolyte; the negative electrode comprising a negative electrode core and a negative electrode mixture layer provided on a surface of the negative electrode core; an exposed portion formed on the outer peripheral surface of the electrode body exposing the surface of the negative electrode core, the exposed portion being in contact with the inner surface of the outer packaging can; and the nonaqueous electrolyte comprising lithium hexafluorophosphate and a cyclic carboxylic acid anhydride represented by the following formula (I).

[0013] [Chemistry 1]

[0014]

[0015] (Wherein, R1 to R4 are independently H, alkyl, alkenyl or aryl.).

[0016] According to the present invention, a non-aqueous electrolyte secondary battery having low direct current resistance (DCR) can be obtained. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a cross-sectional view of a nonaqueous electrolyte secondary battery as an example of an embodiment. DETAILED DESCRIPTION

[0018] As described above, the present inventors have discovered that even if a current collection structure is employed in which the exposed portion of the negative electrode core contacts the inner surface of the outer can for the purpose of reducing battery resistance, sufficient resistance reduction cannot be achieved due to metal elution from the metal components that comprise the battery. Specifically, it is believed that the hydrogen fluoride produced by the reaction of lithium hexafluorophosphate contained in the non-aqueous electrolyte with water within the battery causes metal to elute from the metal components that comprise the battery (e.g., the outer can, the core), depositing the metal as a low-conductivity metal compound on the inner surface of the outer can and the surface of the negative electrode core. As a result, electrical contact between the outer can and the negative electrode core is hindered, preventing the battery from achieving a sufficient resistance reduction effect.

[0019] Therefore, the present inventors conducted intensive research to address the aforementioned issues and discovered that by including a cyclic carboxylic acid anhydride (described later) in the non-aqueous electrolyte, the generation of hydrogen fluoride can be suppressed, thereby inhibiting metal elution from metal components of the battery (such as the outer can and the core). This is presumably because the cyclic carboxylic acid anhydride preferentially reacts with water within the battery, thereby suppressing the generation of hydrogen fluoride. This maintains good electrical contact between the outer can and the negative electrode core, resulting in a non-aqueous electrolyte secondary battery with a low direct current resistance (DCR).

[0020] Hereinafter, an example of an embodiment of the nonaqueous electrolyte secondary battery of the present invention will be described in detail with reference to the accompanying drawings.

[0021] Figure 1 : is a cross-sectional view of a non-aqueous electrolyte secondary battery as an example of an embodiment. Figure 1As shown in the example, the nonaqueous electrolyte secondary battery 10 includes an electrode assembly 14, a nonaqueous electrolyte, and an outer can 16 that houses the electrode assembly 14 and the nonaqueous electrolyte. The electrode assembly 14 includes a positive electrode 11, a negative electrode 12, and a separator 13, with the positive electrode 11 and the negative electrode 12 being spirally wound with the separator 13 interposed therebetween. The outer can 16 is a metal container with a bottomed cylindrical shape and an opening on one axial side. The nonaqueous electrolyte secondary battery 10 includes a sealing member 17 that seals the opening of the outer can 16.

[0022] The positive electrode 11, negative electrode 12, and separator 13 that make up the electrode body 14 are all long, strip-shaped objects that are alternately stacked along the radial direction of the electrode body 14 by being wound into a spiral. To prevent lithium precipitation, the negative electrode 12 is preferably formed to be one size larger than the positive electrode 11. In other words, the negative electrode 12 is preferably formed to be longer in the length direction and width direction (short side direction) than the positive electrode 11. The separator 13 is formed to be at least one size larger than the positive electrode 11, for example, and two separators are arranged to sandwich the positive electrode 11. The non-aqueous electrolyte secondary battery 10 includes insulating plates 18 and 19 arranged above and below the electrode body 14, respectively.

[0023] The positive electrode 11 includes a positive electrode core 30 and a positive electrode mixture layer 31 provided on the surface of the positive electrode core 30. Similarly, the negative electrode 12 includes a negative electrode core 40 and a negative electrode mixture layer 41 provided on the surface of the negative electrode core 40. In the non-aqueous electrolyte secondary battery 10, the negative electrode 12 is arranged on the outer peripheral surface of the electrode body 14. That is, the outermost peripheral surface of the electrode body 14 is formed by the negative electrode 12. The electrode body 14 has a positive electrode lead 20 connected to the positive electrode core 30 by welding or the like. In this embodiment, no negative electrode lead is provided, but a negative electrode lead may be provided on the inner peripheral side of the electrode body 14, for example.

[0024] An exposed portion 42 is formed on the outer circumference of the electrode body 14, exposing the surface of the negative electrode core 40. The exposed portion 42 may be formed on a portion of the outer circumference of the electrode body 14, but is preferably formed on the entire outer circumference. The exposed portion 42 may be formed only on one side (outer surface) of the negative electrode core 40 facing the outside of the electrode body 14, or on both sides of the negative electrode core 40. For example, the exposed portion 42 extends from one longitudinal end of the negative electrode core 40 located on the outer circumference of the electrode body 14 to approximately one to two times the circumference of the electrode body 14.

[0025] In the non-aqueous electrolyte secondary battery 10, the exposed portion 42 of the negative electrode 12 contacts the inner surface of the outer can 16, electrically connecting the negative electrode 12 and the outer can 16. Therefore, a lead such as the positive electrode lead 20 is not required on the negative electrode side. For example, the exposed portion 42 contacts the inner surface of the outer can 16 over the entire circumference of the electrode body 14. In the non-aqueous electrolyte secondary battery 10, the outer can 16 serves as the negative electrode external terminal.

[0026] As described above, the outer can 16 is a metal container with a bottomed cylindrical shape that is open on one side in the axial direction. A gasket 28 is provided between the outer can 16 and the sealing body 17 to ensure the airtightness of the battery interior and the insulation between the outer can 16 and the sealing body 17. The outer can 16 has, for example, a groove portion 21 formed by bulging a portion of the side surface inward to support the sealing body 17. The groove portion 21 is preferably formed in an annular shape along the circumferential direction of the outer can 16, and the sealing body 17 is supported by its upper surface. The sealing body 17 is fixed to the upper part of the outer can 16 by the groove portion 21 and the open end portion of the outer can 16 that is crimped to the sealing body 17.

[0027] The sealing body 17 has a structure in which an internal terminal plate 23, a lower valve body 24, an insulating member 25, an upper valve body 26 and a cap 27 are stacked in order from the electrode body 14 side. The various components constituting the sealing body 17 have, for example, a disc shape or a ring shape, and the various components except the insulating member 25 are electrically connected to each other. The lower valve body 24 and the upper valve body 26 are connected at their respective central portions, and an insulating member 25 is sandwiched between their respective peripheral portions. When an abnormality occurs in the battery and the internal pressure rises, the lower valve body 24 is deformed and broken in a manner that pushes the upper valve body 26 toward the cap 27 side, thereby blocking the current path between the lower valve body 24 and the upper valve body 26. When the internal pressure rises further, the upper valve body 26 breaks and gas is discharged from the opening of the cap 27.

[0028] The positive electrode lead 20 extends through a through-hole in the insulating plate 18 toward the sealing body 17 and is connected by welding or the like to the lower surface of an internal terminal plate 23, which serves as the bottom plate of the sealing body 17. In the nonaqueous electrolyte secondary battery 10, a cap 27, which serves as the top plate of the sealing body 17 and is electrically connected to the internal terminal plate 23, serves as the positive electrode external terminal.

[0029] Hereinafter, the positive electrode 11 , the negative electrode 12 , the separator 13 , and the non-aqueous electrolyte will be described in detail.

[0030] [positive electrode]

[0031] As described above, the positive electrode 11 includes a positive electrode core 30 and a positive electrode mixture layer 31 provided on the surface of the positive electrode core 30. The positive electrode core 30 can be made of a foil of a metal such as aluminum or aluminum alloy that is stable in the potential range of the positive electrode 11, or a film having the metal disposed on the surface. The positive electrode mixture layer 31 includes, for example, a positive electrode active material, a conductive agent, and a binder. The positive electrode mixture layer 31 can be formed on one side or both sides of the positive electrode core 30, except for the exposed portion where the positive lead 20 is welded. For example, a positive electrode mixture slurry containing a positive electrode active material, a conductive agent, and a binder is applied to the positive electrode core 30, and after the coating is dried, it is compressed to form the positive electrode mixture layer 31 on the positive electrode core 30, thereby manufacturing the positive electrode 11.

[0032] Examples of positive electrode active materials include lithium transition metal oxides containing transition metal elements such as Co, Mn, and Ni. Examples of lithium transition metal oxides include Li x CoO2、Li x NiO2、Li x MnO2、Li x Co y Ni 1-y O2、Li x Co y M 1-y O z 、Li x Ni 1-y M y O z 、Li x Mn2O4、Li x Mn 2-y M y O4, LiMPO4, Li2MPO4F, etc. In the above chemical formula, M is, for example, at least one of Na, Mg, Ca, Sc, Ti, V, Y, Mn, Fe, Co, Ni, Cu, Zn, Al, Ga, Ge, Cr, Pb, Zr, Sn, Sb, B, W, and Pb, and x, y, and z are, for example, 0<x≤1.2, 0<y≤0.9, and 2.0≤z≤2.3. They can be used alone or in combination. From the perspective of achieving a high capacity of a non-aqueous electrolyte secondary battery, the positive electrode active material preferably contains Li x NiO2、Li x Co y Ni 1-y O2、Li x Ni 1-y M y O z (M is, for example, at least one of Na, Mg, Ca, Sc, Ti, V, Y, Mn, Fe, Co, Ni, Cu, Zn, Al, Ga, Ge, Cr, Pb, Zr, Sn, Sb, B, W, and Pb, and x, y, and z are, for example, 0 < x ≤ 1.2, 0 < y ≤ 0.9, and 2.0 ≤ z ≤ 2.3) or the like.

[0033] Examples of binders include fluorine-based resins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF), polyacrylonitrile (PAN), polyimide resins, acrylic resins, polyolefin resins, styrene-butadiene rubber (SBR), carboxymethyl cellulose (CMC) or its salts, polyacrylic acid (PAA) or its salts, polyvinyl alcohol (PVA), and polyethylene oxide (PEO). These can be used alone or in combination of two or more. Examples of conductive agents include carbon black (CB), acetylene black (AB), Ketjen black, and carbon nanotubes. These can be used alone or in combination of two or more.

[0034] [negative electrode]

[0035] As described above, the negative electrode 12 includes a negative electrode core 40 and a negative electrode mixture layer 41 provided on the surface of the negative electrode core 40. In addition, in the negative electrode 12, an exposed portion 42 is formed in the portion corresponding to the outer peripheral surface of the electrode body 14, where the surface of the negative electrode core 40 is exposed. The negative electrode core 40 can be made of a foil of a metal such as copper or a copper alloy that is stable in the potential range of the negative electrode 12, or a film having the metal disposed on the surface. The negative electrode mixture layer 41 includes, for example, a negative electrode active material and a binder. The negative electrode mixture layer 41 can be formed on one side or on both sides of the negative electrode core 40, except for the exposed portion 42. For example, a negative electrode mixture slurry containing a negative electrode active material and a binder is applied to the negative electrode core 40, and after the coating is dried, it is compressed to form the negative electrode mixture layer 41 on the negative electrode core 40, thereby manufacturing the negative electrode 12.

[0036] The negative electrode active material is not particularly limited as long as it is a material that can reversibly occlude and release lithium ions or other ions. Examples include carbon-based materials. Examples of carbon-based materials include natural graphites such as flaky graphite, bulk graphite, and earthy graphite, as well as artificial graphites such as bulk artificial graphite (MAG) and graphitized mesocarbon microbeads (MCMB). Furthermore, Si-based materials such as Si and Si-containing compounds may also be used as the negative electrode active material. Because Si-based materials experience a greater volume change with charge and discharge than carbon-based materials, including a Si-based material in the negative electrode mixture layer 41 allows the exposed portion 42 to be strongly pressed against the inner surface of the outer can 16, thereby achieving a better contact state.

[0037] The Si-based material includes, for example, a lithium ion conductive phase and Si particles dispersed in the lithium ion conductive phase. The lithium ion conductive phase includes, for example, at least one of a silicon oxide phase, a silicate phase, and a carbon phase.

[0038] The silicate phase preferably contains at least one element from the group consisting of alkali metal elements such as lithium, sodium, potassium, rubidium, cesium, and francium, and elements from Group 2 of the periodic table to which beryllium, magnesium, calcium, strontium, barium, and radium belong, for example, in view of high lithium ion conductivity. Among these, a silicate phase containing lithium (hereinafter sometimes referred to as a lithium silicate phase) is preferred in view of high lithium ion conductivity.

[0039] Lithium silicate phase is represented by the formula: Li 2z SiO 2＋z (0<z<2). From the viewpoints of stability, ease of production, lithium ion conductivity, etc., z preferably satisfies the relationship 0<z<1, and more preferably z=1 / 2.

[0040] Si-based materials, such as SiO, are materials with Si particles dispersed in a silicon oxide phase. x (Preferably 0<x<2, more preferably 0.5≤x≤1.6). A Si-based material in which Si particles are dispersed in a carbon phase is represented by the general formula Si x C y (Preferably, the range of 0<x≤1 and 0<y≤1) is represented.

[0041] A conductive layer coated with conductive carbon can be formed on the surface of the Si-based material. The conductive layer can be formed, for example, by a CVD method using acetylene, methane, or the like, or by a method in which coal tar, petroleum asphalt, phenolic resin, or the like is mixed with a silicon-based active material and heat treated. Heat treatment apparatuses that can be used for the heat treatment include, for example, a hot air furnace, a hot press, a lamp, a sheath heater, a ceramic heater, a rotary furnace, and the like. Alternatively, a conductive layer can be formed by fixing a conductive filler such as carbon black to the surface of Si-based material particles using a binder.

[0042] Examples of materials capable of reversibly occluding and releasing ions such as lithium ions include carbon-based materials and Si-based materials, as well as Sn-based materials such as Sn, alloys containing Sn, and tin oxide, and Ti-based materials such as lithium titanate.

[0043] The same binder as exemplified in the positive electrode 11 can be used as the binder. The negative electrode mixture layer 41 may also contain a conductive agent. The same conductive agent as exemplified in the positive electrode 11 can be used as the conductive agent.

[0044] [Spacer]

[0045] The spacer 13 may be made of, for example, a porous sheet having ion permeability and insulating properties. Specific examples of the porous sheet include microporous films, woven fabrics, and non-woven fabrics. Suitable materials for the spacer 13 include polyolefins such as polyethylene and polypropylene, and cellulose. The spacer 13 may have a single-layer structure or a multi-layer structure. Alternatively, a heat-resistant resin layer such as an aramid resin may be formed on the surface of the spacer 13.

[0046] A filler layer containing an inorganic filler may be formed at the interface between the separator 13 and at least one of the positive electrode 11 and the negative electrode 12. Examples of the inorganic filler include oxides containing metal elements such as Ti, Al, Si, and Mg, and phosphate compounds. The filler layer may be formed by applying a slurry containing the filler to the surface of the positive electrode 11, the negative electrode 12, or the separator 13.

[0047] [Non-aqueous electrolyte]

[0048] The nonaqueous electrolyte contains an electrolyte salt and a cyclic carboxylic acid anhydride represented by the following formula (I).

[0049] [Chemistry 2]

[0050]

[0051] (In the formula, R1 to R4 are independently H, alkyl, alkenyl, or aryl. Alkyl groups include alkyl groups having 1 to 5 carbon atoms, such as methyl and ethyl; alkenyl groups include alkenyl groups having 2 to 5 carbon atoms, such as vinyl and propenyl; and aryl groups include aryl groups having 6 to 10 carbon atoms, such as phenyl and benzyl.)

[0052] The electrolyte salt includes lithium hexafluorophosphate (LiPF6). The electrolyte salt may include a conventionally known electrolyte salt in addition to lithium hexafluorophosphate.

[0053] The non-aqueous electrolyte has, for example, ion conductivity (eg, lithium ion conductivity).

[0054] In addition to lithium hexafluorophosphate and the aforementioned cyclic carboxylic acid anhydride, the non-aqueous electrolyte may also contain, for example, a non-aqueous solvent. Examples of the non-aqueous solvent include esters, ethers, nitriles, amides, and mixtures of two or more thereof. Examples of non-aqueous solvents include ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and mixtures thereof. The non-aqueous solvent may contain a halogen-substituted product in which at least a portion of the hydrogen atoms in these solvents are replaced with a halogen atom such as fluorine. Examples of the halogen-substituted product include fluorinated cyclic carbonates such as fluorinated ethylene carbonate (FEC), fluorinated chain carbonates, and fluorinated chain carboxylates such as fluoromethyl propionate (FMP). It should be noted that the non-aqueous electrolyte may also contain additives such as vinylene carbonate (VC). The concentration of the electrolyte salt is, for example, 0.8 to 4 mol per liter of the non-aqueous solvent.

[0055] The cyclic carboxylic acid anhydride is not particularly limited as long as it is a substance represented by the above formula (I). Specifically, diglycolic anhydride, methyl diglycolic anhydride, dimethyl diglycolic anhydride, ethyl diglycolic anhydride, vinyl diglycolic anhydride, allyl diglycolic anhydride, divinyl diglycolic anhydride, etc. can be mentioned. These can be used alone or in combination of two or more. Among these, diglycolic anhydride is preferred, for example, from the perspective of achieving low resistance in the battery.

[0056] The content of the cyclic carboxylic acid anhydride is preferably in the range of 0.1 mass % to 2 mass %, more preferably in the range of 0.2 mass % to 1 mass %, relative to the total mass of the nonaqueous electrolyte, for example, in order to achieve low resistance of the battery.

[0057] The non-aqueous electrolyte preferably contains fluoroethylene carbonate (FEC). The inclusion of FEC in the non-aqueous electrolyte forms a stable protective coating (SEI coating) on ​​the negative electrode, contributing to improved cycle characteristics. On the other hand, FEC promotes metal dissolution from metal components such as the outer can 16, potentially increasing battery resistance. However, in this embodiment, even when FEC is included in the non-aqueous electrolyte, the addition of the cyclic carboxylic anhydride suppresses metal dissolution from metal components, thereby reducing battery resistance.

[0058] The content of FEC is not particularly limited, but as an example, it is preferably 3% by mass or more and 7% by mass or less relative to the total mass of the non-aqueous electrolyte.

[0059] Example

[0060] Hereinafter, the present invention will be further described using examples, but the present invention is not limited to these examples.

[0061] <Example 1>

[0062] [Production of positive electrode]

[0063] Use LiNi 0.88 Co 0.09 Al 0.03 A lithium-containing transition metal composite oxide represented by O2 is used as the positive electrode active material. 100 parts by mass of the positive electrode active material, 1 part by mass of acetylene black, and 0.9 parts by mass of polyvinylidene fluoride are mixed, and N-methyl-2-pyrrolidone (NMP) is used as a dispersion medium to prepare a positive electrode mixture slurry. The positive electrode mixture slurry is then applied to both sides of a positive electrode core made of aluminum foil. The coating film is dried and compressed, and then cut into a specified electrode size to produce a positive electrode with a positive electrode mixture layer formed on both sides of the positive electrode core. It should be noted that an exposed portion is provided in the center of the longitudinal direction of the positive electrode to expose the core surface, and the positive electrode lead is ultrasonically welded to the exposed portion.

[0064] [Production of negative electrode]

[0065] A dispersion of graphite powder, carboxymethyl cellulose (CMC), and styrene-butadiene rubber (SBR), serving as the negative electrode active material, was mixed at a solids mass ratio of 100:1:1, using water as the dispersion medium to prepare a negative electrode mixture slurry. This negative electrode mixture slurry was then applied to both sides of a negative electrode core made of copper foil. The coating was dried, compressed, and then cut to the specified electrode size, producing a negative electrode with a negative electrode mixture layer formed on both sides of the core. It should be noted that an exposed portion, exposing the core surface, was provided at one end of the negative electrode in its longitudinal direction.

[0066] [Preparation of non-aqueous electrolyte]

[0067] LiPF6 was dissolved at a concentration of 1.4 M in a non-aqueous solvent consisting of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) in a volume ratio of 20:5:75. Fluoroethylene carbonate (FEC) and diglycolic anhydride were then added. The contents of FEC and diglycolic anhydride were adjusted to 7% and 1% by mass, respectively, relative to the total mass of the non-aqueous electrolyte.

[0068] [Fabrication of non-aqueous electrolyte secondary batteries]

[0069] The positive electrode and the negative electrode are wound into a spiral shape with a polyethylene separator sandwiched between them, thereby producing a wound electrode body. At this time, the electrodes and separators are wound in such a way that the positive electrode mixture layer faces the negative electrode mixture layer with the separator sandwiched between them, and in such a way that the exposed portion of the negative electrode constitutes the outer peripheral surface of the electrode body. After insulating plates are respectively arranged on the upper and lower sides of the electrode body, the positive electrode lead is welded to the internal terminal plate of the sealing body, and the electrode body is housed in an outer packaging can. Thereafter, a non-aqueous electrolyte is injected into the outer packaging can in a decompressed manner, and the opening of the outer packaging can is sealed with a sealing body with a gasket sandwiched between them, thereby producing a cylindrical non-aqueous electrolyte secondary battery. The battery has a current collection structure in which the exposed portion of the negative electrode core is in contact with the inner surface of the outer packaging can.

[0070] <Example 2>

[0071] A nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1, except that the content of diglycolic anhydride in the nonaqueous electrolyte was set to 3% by mass relative to the total mass of the nonaqueous electrolyte.

[0072] <Example 3>

[0073] A nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1, except that the content of FEC was set to 2% by mass relative to the total mass of the nonaqueous electrolyte during the preparation of the nonaqueous electrolyte.

[0074] <Example 4>

[0075] A non-aqueous electrolyte secondary battery was produced in the same manner as in Example 1, except that FEC was not added during the preparation of the non-aqueous electrolyte.

[0076] <Comparative Example 1>

[0077] A non-aqueous electrolyte secondary battery was produced in the same manner as in Example 1, except that diglycolic anhydride and FEC were not added during the preparation of the non-aqueous electrolyte.

[0078] Comparative Example 2

[0079] A non-aqueous electrolyte secondary battery was produced in the same manner as in Example 1, except that diglycolic anhydride was not added during the preparation of the non-aqueous electrolyte.

[0080] Comparative Example 3

[0081] A nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1, except that diglycolic anhydride was not added during the preparation of the nonaqueous electrolyte and the FEC content was set to 2% by mass relative to the total mass of the nonaqueous electrolyte.

[0082] [Evaluation of DC resistance (DCR)]

[0083] The non-aqueous electrolyte secondary batteries of each Example and Comparative Example were charged at a constant current of 0.2C to 4.2V at 25°C. They were then charged at a constant voltage of 4.2V to 0.05C. They were then discharged at a constant current of 0.2C until the voltage reached 2.5V. After the initial charge and discharge, the non-aqueous electrolyte secondary batteries were charged at a constant current of 0.2C at 25°C until the state of charge (SOC) reached 50%. After a two-hour rest, the DC resistance (DCR) was calculated based on the voltage drop before and after discharging at 0.3C for 30 seconds.

[0084] [Charge and discharge cycle test]

[0085] The non-aqueous electrolyte secondary batteries of each Example and each Comparative Example were charged at a constant current of 0.5C at a temperature of 25°C until the voltage reached 4.2V, and then discharged at a constant current of 0.5C until the voltage reached 2.5V. This charge-discharge cycle was defined as one cycle, and 300 cycles were performed. The capacity retention rate was calculated using the following formula. It should be noted that a higher value of the capacity retention rate indicates that the degradation of the charge-discharge cycle characteristics is suppressed.

[0086] Capacity retention (%) = (discharge capacity at the 300th cycle / discharge capacity at the 1st cycle) × 100

[0087] Table 1 summarizes the DC resistance (DCR) and capacity retention results of the charge-discharge cycle test for each Example and each Comparative Example. The DC resistance in Table 1 is based on the DC resistance of Comparative Example 1 as a reference (100), and the DC resistances of the other Examples and Comparative Examples are given as relative values.

[0088]

[0089] Comparing Example 4, which contains lithium hexafluorophosphate and no FEC, and Comparative Example 1, Example 4 containing diglycolic anhydride exhibits lower DC resistance than Comparative Example 1, which does not contain diglycolic anhydride. Furthermore, comparing Examples 1 and 2, which contain lithium hexafluorophosphate and 7% FEC by mass, and Comparative Example 2, shows that Examples 1 and 2 containing diglycolic anhydride exhibit lower DC resistance than Comparative Example 2, which does not contain diglycolic anhydride. Furthermore, comparing Example 3, which contains lithium hexafluorophosphate and 2% FEC by mass, and Comparative Example 3, shows that Example 3 containing diglycolic anhydride exhibits lower DC resistance than Comparative Example 3, which does not contain diglycolic anhydride. These results suggest that the use of a non-aqueous electrolyte containing a cyclic carboxylic anhydride ensures good electrical contact between the outer can and the negative electrode core (exposed portion), thereby keeping the battery's DC resistance (DCR) low.

[0090] Among Examples 1 to 4, Examples 1 to 3 containing FEC had higher capacity retention rates and suppressed degradation of charge-discharge cycle characteristics compared to Example 4 not containing FEC.

[0091] [Note] (1)

[0093] A non-aqueous electrolyte secondary battery comprising:

[0094] The positive electrode and the negative electrode are wound with a separator between them.

[0095] non-aqueous electrolytes, and

[0096] an outer packaging can containing the electrode assembly and the non-aqueous electrolyte,

[0097] The negative electrode comprises a negative electrode core and a negative electrode mixture layer provided on the surface of the negative electrode core.

[0098] An exposed portion is formed on the outer peripheral surface of the electrode body, exposing the surface of the negative electrode core, and the exposed portion is in contact with the inner surface of the outer can.

[0099] The nonaqueous electrolyte includes lithium hexafluorophosphate and a cyclic carboxylic acid anhydride represented by the following formula (I).

[0100] [Chemistry 3]

[0101]

[0102] (In the formula, R1 to R4 are independently H, alkyl, alkenyl or aryl.) (2)

[0104] The nonaqueous electrolyte secondary battery according to (1) above, wherein the cyclic carboxylic acid anhydride includes diglycolic anhydride. (3)

[0106] The nonaqueous electrolyte secondary battery according to (1) or (2), wherein the content of the cyclic carboxylic acid anhydride is 0.1% by mass or more and 2% by mass or less relative to the total mass of the nonaqueous electrolyte. (4)

[0108] The nonaqueous electrolyte secondary battery according to any one of (1) to (3) above, wherein the nonaqueous electrolyte contains fluoroethylene carbonate. (5)

[0110] The nonaqueous electrolyte secondary battery according to (4) above, wherein the content of the fluoroethylene carbonate is 3% by mass or more and 7% by mass or less relative to the total mass of the nonaqueous electrolyte.

[0111] Description of Reference Numerals

[0112] 10 Non-aqueous electrolyte secondary battery, 11 Positive electrode, 12 Negative electrode, 13 Separator, 14 Electrode body, 16 Outer can, 17 Sealing member, 18, 19 Insulating plates, 20 Positive electrode lead, 21 Slotted portion, 23 Internal terminal plate, 24 Lower valve body, 25 Insulating member, 26 Upper valve body, 27 Cap, 28 Gasket, 30 Positive electrode core, 31 Positive electrode mixture layer, 40 Negative electrode core, 41 Negative electrode mixture layer, 42 Exposed portion.

Claims

1. A non-aqueous electrolyte secondary battery comprising: The positive electrode and the negative electrode are wound with a separator between them. non-aqueous electrolytes, and an outer packaging can housing the electrode assembly and the non-aqueous electrolyte, The negative electrode comprises a negative electrode core and a negative electrode mixture layer provided on the surface of the negative electrode core. An exposed portion is formed on the outer peripheral surface of the electrode body, exposing the surface of the negative electrode core, and the exposed portion is in contact with the inner surface of the outer can. The non-aqueous electrolyte includes lithium hexafluorophosphate and a cyclic carboxylic acid anhydride represented by the following formula (I): In the formula, R1 to R4 are independently H, alkyl, alkenyl or aryl.

2. The nonaqueous electrolyte secondary battery according to claim 1, wherein The cyclic carboxylic acid anhydride includes diglycolic anhydride.

3. The non-aqueous electrolyte secondary battery according to claim 1 or 2, wherein The content of the cyclic carboxylic acid anhydride is 0.1 mass % or more and 2 mass % or less relative to the total mass of the non-aqueous electrolyte.

4. The non-aqueous electrolyte secondary battery according to claim 1 or 2, wherein The nonaqueous electrolyte includes fluoroethylene carbonate.

5. The non-aqueous electrolyte secondary battery according to claim 4, wherein The content of the fluoroethylene carbonate is 3 mass % or more and 7 mass % or less relative to the total mass of the non-aqueous electrolyte.

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