Non-aqueous electrolyte secondary batteries

Abstract

A non-aqueous electrolyte secondary battery comprises an electrode assembly including a positive electrode and a negative electrode; and a non-aqueous electrolyte solution comprising a non-aqueous solvent. The ratio (Qn / Qp) of the capacity of the negative electrode (Qn) to the capacity of the positive electrode (Qp) is 1.4 or greater. The non-aqueous electrolyte solution comprises 0.5% to 10% by volume of methyl acetate and 0.01 mol / L to 0.05 mol / L of lithium bis(oxalatoborate) based on the total volume of the non-aqueous solvent at 25°C.

Description

Technical Field

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

[0002] Non-aqueous electrolyte secondary batteries are used in various applications, and the positive electrode, negative electrode, and non-aqueous electrolyte components of the battery have been improved according to the properties required for each application. For example, Patent Document 1 discloses a battery that improves power characteristics at low temperatures by combining a specific positive electrode composite material with an electrolyte containing a chain carboxylic acid ester such as methyl propionate.

[0003] Prior art literature

[0004] Patent Literature

[0005] Patent Document 1: International Publication No. 2016 / 084357 Summary of the Invention

[0006] Non-aqueous electrolyte secondary batteries used in hybrid vehicles are expected to have both high power and high durability. The technology of Patent Document 1 does not take durability into consideration, and there is still room for improvement.

[0007] A nonaqueous electrolyte secondary battery, one embodiment of the present disclosure, comprises: an electrode assembly including a positive electrode and a negative electrode; and a nonaqueous electrolyte solution comprising a nonaqueous solvent. The ratio (Qn / Qp) of the capacity of the negative electrode (Qn) to the capacity of the positive electrode (Qp) is 1.4 or greater. The nonaqueous electrolyte solution comprises 0.5% to 10% by volume of methyl acetate and 0.01 mol / L to 0.05 mol / L of lithium bis(oxalatoborate) based on the total volume of the nonaqueous solvent at 25°C.

[0008] According to one embodiment of the present disclosure, a non-aqueous electrolyte secondary battery can achieve both high power and high durability. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 This is a perspective view of a nonaqueous electrolyte secondary battery according to an example of an embodiment, showing the internal structure of the battery case with the front side of the outer shell removed. DETAILED DESCRIPTION

[0010] Since methyl acetate has a lower viscosity than methyl propionate, its use as a non-aqueous solvent could be expected to yield high power. However, it is prone to decomposition, resulting in low durability and difficulty in use. However, the present inventors discovered that by using 0.01 to 0.05 mol / L of lithium bis(oxalatoborate) to suppress side reactions in the negative electrode, the negative electrode capacity can be increased to at least 1.4 times that of the positive electrode, thereby reducing the load on the negative electrode during charge and discharge. This discovery allowed the use of 0.5 to 10 volume % of methyl acetate as a non-aqueous solvent at 25°C. Consequently, they developed a non-aqueous electrolyte secondary battery with improved durability and reduced resistance.

[0011] Hereinafter, an example of an embodiment of the present disclosure will be described in detail. In this embodiment, a secondary battery 100 having a square metal outer shell 1 is exemplified, but the outer shell is not limited to a square shape, and may be, for example, cylindrical. In addition, a wound electrode body 3 in which a positive electrode and a negative electrode are wound with a separator interposed therebetween is exemplified, but it may also be a stacked electrode body in which a plurality of positive electrodes and a plurality of negative electrodes are alternately stacked one by one with a separator interposed therebetween. In addition, in both the positive electrode and the negative electrode, the case where each composite material layer is formed on both sides of each core body is exemplified, but it is not limited to the case where each composite material layer is formed on both sides of each core body, as long as it is formed on at least one surface.

[0012] like Figure 1 As shown in the example, secondary battery 100 includes: a wound electrode body 3 formed into a flat shape with a flat portion and a pair of curved portions, formed by winding a positive electrode and a negative electrode with a separator interposed therebetween; an electrolyte; and an outer case 1 for housing the electrode body 3 and the electrolyte. Both outer case 1 and sealing plate 2 are made of metal, preferably aluminum or an aluminum alloy.

[0013] The outer shell 1 has a generally rectangular bottom in bottom view and sidewalls extending vertically from the periphery of the bottom. The sidewalls are formed perpendicularly to the bottom. The dimensions of the outer shell 1 are not particularly limited; as an example, the horizontal length is 60 to 160 mm, the height is 60 to 100 mm, and the thickness is 10 to 40 mm.

[0014] The positive electrode is an elongated body comprising a metal positive electrode core and positive electrode composite material layers formed on both sides of the core. A strip-shaped positive electrode core exposed portion 4 is formed at one end in the width direction, where the positive electrode core is exposed along its length. Similarly, the negative electrode is an elongated body comprising a metal negative electrode core and negative electrode composite material layers formed on both sides of the core. A strip-shaped negative electrode core exposed portion 5 is formed at one end in the width direction, where the negative electrode core is exposed along its length. The electrode body 3 has a structure in which the positive and negative electrodes are wound with a separator interposed therebetween, with the positive electrode core exposed portion 4 disposed at one axial end and the negative electrode core exposed portion 5 disposed at the other axial end.

[0015] A positive electrode current collector 6 is connected to the laminated portion of the positive electrode core exposed portion 4 of the positive electrode, and a negative electrode current collector 8 is connected to the laminated portion of the negative electrode core exposed portion 5 of the negative electrode. Suitable positive electrode current collectors 6 are made of aluminum or an aluminum alloy. Suitable negative electrode current collectors 8 are made of copper or a copper alloy. The positive terminal 7 includes: a positive electrode external conductive portion 13 arranged on the battery exterior side of the sealing plate 2, a positive electrode bolt portion 14 connected to the positive electrode external conductive portion 13, and a positive electrode embedded portion 15 embedded in a through-hole provided in the sealing plate 2, and electrically connected to the positive electrode current collector 6. In addition, the negative terminal 9 includes: a negative electrode external conductive portion 16 arranged on the battery exterior side of the sealing plate 2, a negative electrode bolt portion 17 connected to the negative electrode external conductive portion 16, and a negative electrode embedded portion 18 embedded in a through-hole provided in the sealing plate 2, and electrically connected to the negative electrode current collector 8.

[0016] The positive electrode terminal 7 and the positive electrode current collector 6 are fixed to the sealing plate 2 via an internal insulating member and an external insulating member, respectively. The internal insulating member is disposed between the sealing plate 2 and the positive electrode current collector 6, and the external insulating member is disposed between the sealing plate 2 and the positive electrode terminal 7. Similarly, the negative electrode terminal 9 and the negative electrode current collector 8 are fixed to the sealing plate 2 via an internal insulating member and an external insulating member, respectively. The internal insulating member is disposed between the sealing plate 2 and the negative electrode current collector 8, and the external insulating member is disposed between the sealing plate 2 and the negative electrode terminal 9.

[0017] The electrode assembly 3 is housed within the outer case 1. The sealing plate 2 is connected to the opening edge of the outer case 1 by laser welding or other means. The sealing plate 2 has an electrolyte injection hole 10. After the electrolyte is injected into the outer case 1, the electrolyte injection hole 10 is sealed with a sealing cap. The sealing plate 2 is formed with a gas discharge valve 11 for discharging gas when the pressure inside the battery exceeds a specified value.

[0018] Hereinafter, the positive electrode, the negative electrode, the separator, and the non-aqueous electrolyte that constitute the electrode assembly 3 , particularly the non-aqueous electrolyte, will be described in detail.

[0019] [positive electrode]

[0020] The positive electrode, for example, has a positive electrode core such as a metal foil and a positive electrode composite material layer formed on the positive electrode core. The positive electrode core can use a foil of a metal stable within the potential range of the positive electrode, such as aluminum, or a thin film of this metal disposed on the surface layer. The positive electrode composite material layer, for example, contains a positive electrode active material, a binder material, a conductive material, and the like. The positive electrode can be manufactured, for example, by coating a positive electrode composite material slurry containing a positive electrode active material, a binder material, a conductive material, etc. on the positive electrode core and drying it, and after forming the positive electrode composite material layer, calendering this positive electrode composite material layer. The capacity (Qp) of the positive electrode varies according to the proportion of the positive electrode active material in the positive electrode composite material layer, the thickness of the positive electrode composite material layer, etc., and can be adjusted, for example, according to the coating amount of the positive electrode composite material slurry.

[0021] As the positive electrode active material contained in the positive electrode composite material layer, a lithium metal composite oxide containing transition metal elements such as Co, Mn, Ni, etc. can be exemplified. The lithium metal composite oxide is, for example, 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 (M; at least one of Na, Mg, Sc, Y, Mn, Fe, Co, Ni, Cu, Zn, Al, Cr, Pb, Sb, B, 0 < x ≤ 1.2, 0 < y ≤ 0.9, 2.0 ≤ z ≤ 2.3). They can be used alone or in combination of multiple kinds. In terms of achieving high capacity of the 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; at least one of Na, Mg, Sc, Y, Mn, Fe, Co, Ni, Cu, Zn, Al, Cr, Pb, Sb, B, 0 < x ≤ 1.2, 0 < y ≤ 0.9, 2.0 ≤ z ≤ 2.3) and other lithium nickel composite oxides.

[0022] As the conductive material contained in the positive electrode composite material layer, for example, carbon-based particles such as carbon black (CB), acetylene black (AB), Ketjen black, and graphite can be cited. They can be used alone or in combination of two or more.

[0023] As the binder material contained in the positive electrode composite material layer, for example, fluorine-based resins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), polyimide-based resins, acrylic resins, polyolefin-based resins, etc. can be cited. They can be used alone or in combination of two or more.

[0024] [Negative electrode]

[0025] The negative electrode, for example, has: a negative electrode core such as a metal foil, and a negative electrode composite material layer formed on the negative electrode core. The negative electrode core can use foils of metals stable within the potential range of the negative electrode such as copper and copper alloys, and thin films of such metals disposed on the surface layer. The negative electrode composite material layer, for example, contains: a negative electrode active material and a binder material. The negative electrode can be manufactured as follows: A negative electrode composite material slurry containing a negative electrode active material, a binder material, etc. is coated on the negative electrode core and dried. After forming the negative electrode composite material layer, the negative electrode composite material layer is calendered, thereby it can be manufactured. The capacity (Qn) of the negative electrode varies according to the proportion of the negative electrode active material in the negative electrode composite material layer, the thickness of the negative electrode composite material layer, etc., and can be adjusted, for example, according to the coating amount of the negative electrode composite material slurry.

[0026] As the negative electrode active material contained in the negative electrode composite material layer, as long as it can reversibly absorb and release lithium ions, there is no particular limitation. Usually, carbon materials such as graphite are used. The graphite can be natural graphite such as flake graphite, massive graphite, and earthy graphite, artificial massive graphite, graphitized mesophase carbon microbeads, etc., artificial graphite, all of which are acceptable. In addition, as the negative electrode active material, metals alloyed with Li such as Si and Sn, metal compounds containing Si, Sn, etc., lithium titanium composite oxides, etc. can be used. In addition, a carbon coating film can be provided on them. For example, a Si-containing compound shown by SiO x (0.5 ≤ x ≤ 1.6), or Li 2y SiO (2+y) A Si-containing compound in which fine grains of Si are dispersed in a lithium silicate phase shown by (0 < y < 2), etc. can be used in combination with graphite.

[0027] As the binding material contained in the negative electrode composite material layer, similarly to the case of the positive electrode, fluororesins such as PTFE and PVdF, PAN, polyimide, acrylic resin, polyolefin, etc. can be used, preferably styrene-butadiene rubber (SBR). In addition, CMC or its salt, polyacrylic acid (PAA) or its salt, polyvinyl alcohol (PVA), etc. can be included in the negative electrode composite material layer.

[0028] The ratio (Qn / Qp) of the negative electrode capacity (Qn) to the positive electrode capacity (Qp) is 1.4 or greater. This reduces the load on the negative electrode during charge and discharge, and, in combination with the electrolyte described below, reduces battery resistance and improves durability.

[0029] [Separator]

[0030] The separator can be, for example, a porous sheet having ion permeability and insulation. Specific examples of the porous sheet include microporous films, woven fabrics, non-woven fabrics, and the like. Suitable materials for the separator include polyolefins such as polyethylene and polypropylene, and cellulose. The separator can be a single-layer structure or a laminated structure. In addition, a heat-resistant resin layer such as an aromatic polyamide resin or a filler layer containing an inorganic compound filler can be provided on the surface of the separator.

[0031] [Non-aqueous electrolyte]

[0032] The non-aqueous electrolyte solution comprises a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. The non-aqueous electrolyte solution comprises 0.5% to 10% by volume of methyl acetate (MA) and 0.01 to 0.05 mol / L of lithium bis(oxalatoborate) (LiBOB) relative to the total volume of the non-aqueous solvent at 25°C. The use of this non-aqueous electrolyte solution can reduce battery resistance and improve durability.

[0033] As a non-aqueous solvent, a chain carboxylic acid ester other than MA can be included. Examples of chain carboxylic acid esters other than MA include methyl formate, ethyl formate, propyl formate, ethyl acetate, propyl acetate, methyl propionate (MP), ethyl propionate (EP), propyl propionate, and methyl pivalate. As a non-aqueous solvent, two or more chain carboxylic acid esters can be used in combination, but it is preferred to use at least MA, or to use MA substantially alone. The content of the chain carboxylic acid ester is preferably 0.5% to 15% by volume relative to the total volume of the non-aqueous solvent at 25°C.

[0034] As the nonaqueous solvent beyond the chain carboxylic acid ester, can enumerate nitriles such as cyclic carboxylic acid ester, cyclic carbonate, chain carbonate, cyclic ethers, chain ethers, acetonitrile, acid amides such as dimethylformamide and the halogen substitution body obtained by replacing their hydrogen with halogen atoms such as fluorine. They can use one kind, and can combine two or more and use. As the example of cyclic carboxylic acid ester, can enumerate gamma-butyrolactone (GBL), gamma-valerolactone (GVL) etc.

[0035] Examples of cyclic carbonates include ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate. EC is particularly preferred. Examples of chain carbonates include dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), methyl propyl carbonate, ethyl propyl carbonate, and methyl isopropyl carbonate. DMC and EMC are particularly preferred.

[0036] Examples of cyclic ethers include 1,3-dioxolane, 4-methyl-1,3-dioxolane, tetrahydrofuran, 2-methyltetrahydrofuran, propylene oxide, 1,2-butylene oxide, 1,3-dioxane, 1,4-dioxane, 1,3,5-trioxane, furan, 2-methylfuran, 1,8-cineole, and crown ethers. Examples of the chain ethers include 1,2-dimethoxyethane, diethyl ether, dipropyl ether, diisopropyl ether, dibutyl ether, dihexyl ether, ethyl vinyl ether, butyl vinyl ether, methyl phenyl ether, ethyl phenyl ether, butyl phenyl ether, pentyl phenyl ether, methoxytoluene, benzyl ethyl ether, diphenyl ether, dibenzyl ether, o-dimethoxybenzene, 1,2-diethoxyethane, 1,2-dibutoxyethane, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol dibutyl ether, 1,1-dimethoxymethane, 1,1-diethoxyethane, triethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether.

[0037] As the example of halogen substitution body, fluorinated ether, fluorinated cyclic carbonate, fluorinated chain carbonate, fluorinated chain carboxylic acid esters such as methyl fluoropropionate (FMP) etc. can be enumerated.As fluorinated ether, 2,2,2-trifluoroethyl methyl ether, 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl etc. can be enumerated.As fluorinated cyclic carbonate, 4-fluoroethylene carbonate (FEC), 4,5-difluoroethylene carbonate, 4,4-difluoroethylene carbonate, 4,4,5-trifluoroethylene carbonate, 4,4,5,5-tetrafluoroethylene carbonate etc. can be enumerated.As fluorinated chain carboxylic acid ester, fluorinated ethyl propionate, fluorinated methyl acetate, fluorinated ethyl acetate, fluorinated propyl acetate, 2,2,2-trifluoroethyl acetate, 3,3,3-trifluoromethyl propionate, pentafluoromethyl propionate etc. can be enumerated.

[0038] The non-aqueous solvent preferably contains at least one selected from EC, EMC, and DMC in addition to MA. In this case, the resistance can be reduced and the durability can be improved by reducing the viscosity. As an example of a suitable non-aqueous solvent, a non-aqueous solvent containing MA, EC, EMC, and DMC in a ratio of x:(15 to 35):((30 - x) to (50 - x)):(25 to 45) by volume ratio at 25 °C can be cited. Here, x is 0.5% to 15% by volume.

[0039] The electrolyte salt is preferably a lithium salt containing lithium bis(oxalato)borate (LiBOB, Li(B(C2O4)2)). Examples of lithium salts other than LiBOB include LiBF4, LiClO4, LiPF6 (lithium hexafluorophosphate), LiAsF6, LiSbF6, LiAlCl4, LiSCN, LiCF3SO3, LiCF3CO2, Li(P(C2O4)F4), LiPF 6-x (C n F 2n+1 ) x (1 < x < 6, n is 1 or 2), LiB 10 Cl 10 、LiCl、LiBr、LiI、lithium chloroborane, lithium lower aliphatic carboxylate, borate salts such as Li2B4O7, Li(B(C2O4)F2), imide salts such as LiN(SO2CF3)2, LiN(C1F 2l+1 SO2)(C m F 2m+1 SO2){l, m are integers of 0 or more}, etc. The lithium salt can be used alone or in combination of multiple kinds. Among these lithium salts other than LiBOB, LiPF6 is preferably used from the viewpoints of ionic conductivity, electrochemical stability, etc. The concentration of LiPF6 is, for example, 0.8 mol / L to 1.8 mol / L. In addition, the non-aqueous electrolyte may further contain additives such as vinylene carbonate (VC).

[0040] <Examples>

[0041] Hereinafter, the present disclosure will be further described based on examples, but the present disclosure is not limited to these examples.

[0042] <Example 1>

[0043] [Fabrication of positive electrode]

[0044] Using LiNi 0.55 Mn 0.20 Co 0.25A lithium metal composite oxide represented by O2 is used as the positive electrode active material. This positive electrode active material is mixed with acetylene black and PVdF at a mass ratio of 100:1:1, and NMP is added to prepare a positive electrode composite material slurry. Next, the positive electrode composite material slurry is applied to the positive electrode core formed of aluminum foil, leaving the portions where the leads are connected, and the coating is dried. The coating is then rolled using a roller and cut into the specified electrode size, producing a positive electrode with a positive electrode composite material layer formed on both sides of the positive electrode core.

[0045] [Production of negative electrode]

[0046] Graphite is used as the negative electrode active material. The negative electrode active material, SBR dispersion and CMC sodium salt are mixed in a mass ratio of 100:1:1, and water is added to prepare a negative electrode composite material slurry. Next, the negative electrode composite material slurry is applied on the portions of the negative electrode core formed of copper foil to which the leads are connected, and the coating is dried. When applying the negative electrode composite material slurry, the amount of the negative electrode composite material slurry applied is adjusted so that the ratio (Qn / Qp) of the capacity of the negative electrode (Qn) to the capacity of the positive electrode (Qp) becomes 1.6. Then, the coating is rolled using a roller and cut into a specified electrode size to produce a negative electrode having a negative electrode composite material layer formed on both sides of the negative electrode core.

[0047] [Preparation of non-aqueous electrolyte]

[0048] To a mixed solvent of methyl acetate (MA), ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) in a volume ratio of 3:25:37:35 at 25°C, lithium bis(oxalatoborate) (LiBOB) and lithium hexafluorophosphate (LiPF6) were added in a concentration of 0.025 mol / L and 1.15 mol / L, respectively, to prepare a non-aqueous electrolyte.

[0049] [Fabrication of test battery cells]

[0050] Leads were attached to the negative and positive electrodes, and the electrodes were alternately stacked one on top of the other with separators interposed between them to create a stacked electrode assembly. A single-layer polypropylene separator was used as the separator. The assembled electrode assembly and the non-aqueous electrolyte were housed in a rectangular battery case to create a test battery cell.

[0051] <Example 2>

[0052] A test cell was produced in the same manner as in Example 1 except that a mixed solvent in which MA, EC, EMC, and DMC were mixed at a volume ratio of 6:25:34:35 was used for the preparation of the non-aqueous electrolyte.

[0053] <Example 3>

[0054] In the preparation of the negative electrode, a test cell was prepared in the same manner as in Example 1 except that the amount of negative electrode composite material slurry applied was adjusted so that Qn / Qp became 1.4.

[0055] <Example 4>

[0056] A test cell was produced in the same manner as in Example 1 except that LiBOB was added to a concentration of 0.01 mol / L in the preparation of the non-aqueous electrolyte.

[0057] <Example 5>

[0058] A test cell was produced in the same manner as in Example 1 except that LiBOB was added to a concentration of 0.05 mol / L in the preparation of the non-aqueous electrolyte.

[0059] <Example 6>

[0060] A test cell was produced in the same manner as in Example 1 except that a mixed solvent in which MA, EC, EMC, and DMC were mixed at a volume ratio of 10:25:30:35 was used for the preparation of the non-aqueous electrolyte.

[0061] <Comparative Example 1>

[0062] A test cell was prepared in the same manner as in Example 1, except that MA was not used in the preparation of the non-aqueous electrolyte solution, and a mixed solvent in which EC, EMC, and DMC were mixed at a volume ratio of 25:40:35 was used.

[0063] <Comparative Example 2>

[0064] A test cell was prepared in the same manner as in Example 1 except that MA was not used in the preparation of the nonaqueous electrolyte solution, and a mixed solvent of EC, EMC, and DMC at a volume ratio of 25:40:35 was used, and LiBOB was not added.

[0065] <Comparative Example 3>

[0066] A test cell was produced in the same manner as in Example 1 except that LiBOB was not added in the preparation of the non-aqueous electrolyte.

[0067] <Comparative Example 4>

[0068] A test cell was produced in the same manner as in Example 1 except that LiBOB was added to a concentration of 0.1 mol / L in the preparation of the non-aqueous electrolyte.

[0069] <Comparative Example 5>

[0070] A test cell was prepared in the same manner as in Example 1 except that a mixed solvent of MA, EC, EMC, and DMC at a volume ratio of 15:25:25:35 was used for the preparation of the nonaqueous electrolyte and LiBOB was added to a concentration of 0.05 mol / L.

[0071] <Comparative Example 6>

[0072] In the preparation of the negative electrode, a test cell was prepared in the same manner as in Example 1 except that the amount of negative electrode composite material slurry applied was adjusted so that Qn / Qp became 1.2.

[0073] <Comparative Example 7>

[0074] A test cell was prepared in the same manner as in Example 1 except that MP was used instead of MA in the preparation of the nonaqueous electrolyte and a mixed solvent of MP, EC, EMC, and DMC at a volume ratio of 6:25:34:35 was used.

[0075] The performance of each test battery cell of the examples and comparative examples was evaluated by the following method. The evaluation results are shown in Table 1.

[0076] [Measurement of initial power resistance (DCIR) at room temperature]

[0077] Each test cell was charged at 25°C until the depth of charge (SOC) reached 50%. Subsequently, the cells were discharged for 10 seconds at currents of 1C, 2C, 5C, 10C, 15C, 20C, 25C, and 30C. The cell voltage during each discharge was measured and plotted against each current value to determine the discharge resistance. The results for the Examples and Comparative Examples in Table 1 are relative values, with the DCIR of the test cell of Example 1 set to 100.

[0078] [Evaluation of high-temperature storage characteristics]

[0079] For the test battery cells whose initial discharge capacity was measured, the capacity retention rate after high-temperature storage was determined by the following method.

[0080] (1) The battery was charged at a constant current of 5 A until the cell voltage reached 4.1 V, and then charged at a constant voltage of 4.1 V for 1.5 hours.

[0081] (2) Stored at 70°C and SOC 80% for 56 days.

[0082] (3) Discharge at a constant current of 5 A until the battery cell voltage reaches 2.5 V.

[0083] (4) The battery was charged at a constant current of 5 A until the cell voltage reached 4.1 V, and then charged at a constant voltage of 4.1 V for 1.5 hours.

[0084] (5) Discharge at a constant current of 5 A until the cell voltage reaches 2.5 V. The discharge capacity at this point is defined as the post-storage discharge capacity. The post-storage discharge capacity is divided by the initial discharge capacity to calculate the capacity retention rate after high-temperature storage. In Table 1, the results for the Examples and Comparative Examples are relative values, with the capacity retention rate of the test cell of Example 1 being 100.

[0085] [Table 1]

[0086]

[0087] As shown in Table 1, the test cells of the examples had low DCIR and high capacity retention rates. On the other hand, the test cells of the comparative examples had low DCIR and high capacity retention rates.

[0088] Description of Reference Numerals

[0089] 1. Outer shell

[0090] 2 Sealing plate

[0091] 3 Electrode body

[0092] 4. Positive electrode core exposed part

[0093] 5. Negative electrode core exposed part

[0094] 6. Positive electrode collector

[0095] 7 Positive terminal

[0096] 8. Negative electrode current collector

[0097] 9 Negative terminal

[0098] 10 Electrolyte injection hole

[0099] 11 Gas exhaust valve

[0100] 13 Positive electrode external conductive part

[0101] 14 Positive electrode bolt

[0102] 15 Positive electrode embedding part

[0103] 16 Negative electrode external conductive part

[0104] 17 Negative electrode bolt

[0105] 18 Negative electrode embedding part

[0106] 100 Secondary Batteries

Claims

1. A non-aqueous electrolyte secondary battery comprising: an electrode body comprising a positive electrode and a negative electrode; and a non-aqueous electrolyte solution comprising a non-aqueous solvent, The ratio (Qn / Qp) of the capacity (Qn) of the negative electrode to the capacity (Qp) of the positive electrode is 1.4 or more, The non-aqueous electrolyte solution includes 0.5% to 10% by volume of methyl acetate and 0.01 mol / L to 0.05 mol / L of lithium bis(oxalatoborate) relative to the total volume of the non-aqueous solvent at 25°C.

2. The nonaqueous electrolyte secondary battery according to claim 1, wherein The non-aqueous solvent further comprises at least one selected from the group consisting of ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate.

3. The non-aqueous electrolyte secondary battery according to claim 1 or 2, wherein The non-aqueous electrolyte further contains lithium hexafluorophosphate.

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