Non-aqueous electrolyte secondary battery and battery pack

Abstract

To provide a nonaqueous electrolyte secondary battery that can reduce the output resistance and suppress the decrease in capacity retention.SOLUTION: A nonaqueous electrolyte secondary battery includes an electrode body and an electrolyte solution. The electrode body is a wound electrode body or a stack electrode body including a positive electrode plate containing an active material layer. The length of the active material layer in a direction parallel to a winding axis of the wound electrode body is 150 mm or more. The shape of the stack electrode body in a plan view is a square or a rectangle, and the length of the active material layer in a direction parallel to one side of the square or a direction parallel to a long side of the rectangle is 150 mm or more. In the nonaqueous electrolyte secondary battery, a restraint pressure of 0.5 MPa or more is applied in a lamination direction of the positive electrode plate. The electrolyte solution contains LiFSO3 and has an electric conductivity of 0.86 S / m or more at 25°C.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a non-aqueous electrolyte secondary battery and a battery pack. [Background technology]

[0002] It is known that LiFSO3 is used as an electrolyte for non-aqueous electrolyte secondary batteries. For example, Patent Document 1 discloses that the use of an electrolyte containing LiPF6 and LiFSO3 improves the initial charge capacity, input / output characteristics, and internal impedance characteristics of the battery. Patent Document 2 discloses that practically sufficient conductivity can be obtained by adjusting the composition of the non-aqueous electrolyte. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-152956 [Patent Document 2] Japanese Patent Application Laid-Open No. 2014-170730 Summary of the Invention [Problem to be solved by the invention]

[0004] However, it has been discovered that repeated high-rate charging and discharging of batteries using electrolytes containing LiFSO3 leads to a deterioration in battery performance.

[0005] An object of the present disclosure is to provide a nonaqueous electrolyte secondary battery and a battery pack that can reduce output resistance and suppress a decrease in capacity retention rate even when high-rate charge and discharge are repeated using an electrolyte solution containing LiFSO. [Means for solving the problem]

[0006] [1] A nonaqueous electrolyte secondary battery including an electrode assembly and an electrolyte solution, the electrode body is a wound type electrode body or a stacked type electrode body including a positive electrode plate having an active material layer, When the electrode body is a wound electrode body, the length of the active material layer in a direction parallel to the winding axis is 150 mm or more, When the electrode body is a laminated electrode body, The laminated electrode body has a square or rectangular shape in plan view, the length of the active material layer in a direction parallel to one side of the square or a direction parallel to a long side of the rectangle is 150 mm or more; In the nonaqueous electrolyte secondary battery, a confining pressure of 0.5 MPa or more is applied in a stacking direction of the positive electrode plate, the electrolyte solution contains LiFSO3, The nonaqueous electrolyte secondary battery has an electrical conductivity of 0.86 S / m or more at 25°C. [2] The nonaqueous electrolyte secondary battery according to [1], wherein the content of LiFSO3 in the electrolyte solution is 0.1 mass % or more and 2.5 mass % or less. [3] The nonaqueous electrolyte secondary battery according to [1] or [2], wherein the electrolytic solution has an electrical conductivity of 0.90 S / m or more at 25°C. [4] The nonaqueous electrolyte secondary battery according to any one of [1] to [3], wherein the electrolytic solution has an electrical conductivity of 0.93 S / m or more at 25°C. [5] The nonaqueous electrolyte secondary battery according to any one of [1] to [4], wherein the electrolytic solution further contains at least one of LiPF6 and LiBF4. [6] The nonaqueous electrolyte secondary battery according to any one of [1] to [5], wherein the electrolytic solution further contains vinylene carbonate. [7] The nonaqueous electrolyte secondary battery according to any one of [1] to [6], wherein the electrolytic solution further contains one or more selected from the group consisting of ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate. [8] A battery pack in which two or more batteries are arranged so as to be electrically connected, the battery is a non-aqueous electrolyte secondary battery including an electrode assembly and an electrolyte solution, the electrode body is a wound type electrode body or a stacked type electrode body including a positive electrode plate having an active material layer, When the electrode body is a wound electrode body, the length of the active material layer in a direction parallel to the winding axis is 150 mm or more, When the electrode body is a laminated electrode body, The laminated electrode body has a square or rectangular shape in plan view, the length of the active material layer in a direction parallel to one side of the square or a direction parallel to a long side of the rectangle is 150 mm or more; the electrolyte solution contains LiFSO3, The electrolytic solution has an electrical conductivity of 0.86 S / m or more at 25°C, The battery pack is constrained so that a constraining pressure of 0.5 MPa or more is applied in a stacking direction of the positive electrode plates of the battery. [Effects of the Invention]

[0007] The nonaqueous electrolyte secondary battery of the present disclosure can reduce output resistance and suppress a decrease in capacity retention rate even when repeatedly charged and discharged at high rates. DETAILED DESCRIPTION OF THE INVENTION

[0008] (Nonaqueous electrolyte secondary battery) The nonaqueous electrolyte secondary battery of this embodiment (hereinafter also referred to as "the battery (1)") includes an electrode assembly and an electrolyte solution. The electrode assembly includes a positive electrode plate having a positive electrode active material layer (active material layer), and is a wound electrode assembly or a stacked electrode assembly. When the electrode assembly is a wound electrode assembly, the length of the positive electrode active material layer in a direction parallel to the winding axis is 150 mm or more. When the electrode assembly is a stacked electrode assembly, the stacked electrode assembly has a square or rectangular shape in a plan view, and the length of the positive electrode active material layer in a direction parallel to one side of the square or the direction parallel to the long side of the rectangle is 150 mm or more. In the battery (1), a confining pressure of 0.5 MPa or more is applied in the stacking direction of the positive electrode plate. The electrolyte solution contains LiFSO3, and the electrical conductivity of the electrolyte solution at 25°C is 0.86 S / m or more.

[0009] The electrode assembly typically includes a positive electrode plate, a negative electrode plate, and a separator. The negative electrode plate includes a negative electrode active material layer containing a negative electrode active material. The separator is interposed between the positive electrode plate and the negative electrode plate.

[0010] When the electrode body is a wound electrode body, the lengths of the positive electrode active material layer and the negative electrode active material layer in the direction parallel to the winding axis may each independently be 150 mm or more, 150 mm to 350 mm, 180 mm to 350 mm, or 200 mm to 300 mm. When the electrode body is a laminated electrode body whose planar shape is square or rectangular, the lengths of the positive electrode active material layer and the negative electrode active material layer in the direction parallel to one side of the square, or the lengths of the positive electrode active material layer and the negative electrode active material layer in the direction parallel to the long side of the rectangle, may each independently be 150 mm or more, 150 mm to 350 mm, 180 mm to 350 mm, or 200 mm to 300 mm. In the electrode body, preferably, the lengths of both the positive electrode active material layer and the negative electrode active material layer are within the above-mentioned ranges.

[0011] The confining pressure applied to the battery (1) may be 0.5 MPa or more in the stacking direction of the positive electrode plates. The stacking direction of the positive electrode plates is usually the same as the stacking direction of the positive and negative electrode plates. The confining pressure may be 0.5 MPa or more and 5 MPa or less, 1 MPa or more and 4 MPa or less, or 2 MPa or more and 4 MPa or less. The confining pressure can be calculated by measuring the load using a load cell. The confining pressure applied to the battery (1) may be applied when the battery (1) is assembled into a battery pack. A method for assembling the battery pack includes a method for assembling the battery (2) described below into a battery pack.

[0012] The electrolyte is typically a non-aqueous electrolyte, preferably a non-aqueous solvent such as an organic solvent containing a supporting salt. The electrolyte contains LiFSO3. The content of LiFSO3 in the electrolyte is preferably 0.1% by mass or more and 2.5% by mass or less, and may be 0.5% by mass or more and 2.0% by mass or less, or may be 0.7% by mass or more and 1.5% by mass or less. The content of LiFSO3 in the electrolyte is the amount of LiFSO3 relative to the total amount of the electrolyte.

[0013] Examples of supporting salts that the electrolyte may contain include LiPF, LiBF, LiClO, LiBOB (lithium bis(oxalato)borate), and the like, in addition to the above-mentioned LiFSO. The electrolyte may contain one or more of these. In addition to LiFSO, the electrolyte preferably contains a supporting salt other than LiFSO, more preferably at least one of LiPF and LiBF, and may also contain LiPF.

[0014] When the electrolyte contains at least one of LiPF6 and LiBF4, the concentration of LiPF6 and LiBF4 in the electrolyte is preferably 0.5 mol / L to 1.5 mol / L, and may be 0.7 mol / L to 1.4 mol / L, or 0.8 mol / L to 1.2 mol / L. The above concentration is the total number of moles of LiPF6 and LiBF4 per liter of non-aqueous solvent in the electrolyte. When the electrolyte contains one of LiPF6 and LiBF4, the above concentration refers to the concentration of that one, and when the electrolyte contains both LiPF6 and LiBF4, the above concentration refers to the total concentration of LiPF6 and LiBF4.

[0015] Examples of non-aqueous solvents that may be contained in the electrolytic solution include ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), propylene carbonate (PC), butylene carbonate (BC), and diethyl carbonate (DEC). The electrolytic solution may contain one or more of these non-aqueous solvents. The electrolytic solution preferably contains one or more selected from the group consisting of EC, EMC, and DMC, and more preferably contains EC, EMC, and DMC.

[0016] When the nonaqueous solvent used in the electrolyte solution contains EC, DMC, and EMC, they may be contained in a mixing ratio of EC:DMC:EMC = 5-50:10-70:10-70 (volume ratio), or EC:DMC:EMC = 10-40:20-60:20-60 (volume ratio), or EC:DMC:EMC = 20-40:30-50:30-50 (volume ratio). In this specification, x to y (x and y represent numerical values) indicate that x is equal to or greater than y and is equal to or less than y.

[0017] The electrolytic solution may further contain an additive. Examples of the additive include vinylene carbonate (VC), vinyl ethylene carbonate (VEC), and fluoroethylene carbonate. The electrolytic solution may contain one or more of these additives. The electrolytic solution preferably contains VC. The content of the additive in the electrolytic solution may be 0.1% by mass or more and 5% by mass or less, 0.5% by mass or more and 3% by mass or less, or 1% by mass or more and 2% by mass or less. The content of the additive in the electrolytic solution is the amount of the additive relative to the total amount of the electrolytic solution, and when two or more additives are contained, it is the total amount.

[0018] The electrical conductivity of the electrolyte at 25°C may be 0.86 S / m or more, or may be 0.88 S / m or more, preferably 0.90 S / m or more, and more preferably 0.93 S / m or more. The electrical conductivity of the electrolyte at 25°C is not particularly limited, but may be 1.5 S / m or less, or may be 1.0 S / m or less. The electrical conductivity of the electrolyte can be adjusted by the type and content of the supporting salt contained in the electrolyte, and the type and composition of the non-aqueous solvent, etc. The electrical conductivity of the electrolyte can be measured using an electrical conductivity meter in an environment of 25°C.

[0019] In a nonaqueous electrolyte secondary battery (hereinafter also referred to as a "secondary battery") in which the length of the active material layer is within the above range and the above magnitude of confining pressure is applied, the salt concentration of the electrolyte tends to vary depending on the position of the electrode assembly. Specifically, the salt concentration of the electrolyte tends to be relatively low at the end of the electrode assembly. Therefore, when the secondary battery is repeatedly charged and discharged, the potential of the positive electrode plate increases at the end of the electrode assembly, and the positive electrode active material and FSO3 - When the potential of the positive electrode plate reaches the reaction potential, the transition metals in the positive electrode active material are dissolved, and the dissolved transition metals are deposited on the negative electrode plate. This is thought to result in a decrease in the capacity retention rate when the secondary battery is repeatedly charged and discharged at a high rate. In contrast, in this battery (1), since the electrical conductivity of the electrolyte is within the above-mentioned range, the potential of the positive electrode plate is unlikely to increase even when the battery is repeatedly charged and discharged, and polarization of the positive electrode plate is also thought to be suppressed. This allows the positive electrode active material and FSO3 - This can suppress the reaction with the transition metal and the elution of the transition metal in the positive electrode active material, so that the decrease in the capacity retention rate can be suppressed even when the battery (1) is repeatedly charged and discharged at a high rate.

[0020] As described above, the electrode assembly may include, for example, a positive electrode plate, a negative electrode plate, and a separator. The electrode assembly is housed in an outer casing, and an electrolyte solution is poured into the outer casing that houses the electrodes. The opening of the outer casing into which the electrolyte solution has been poured is sealed with a sealing plate.

[0021] The positive electrode plate can have a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector. The positive electrode current collector is, for example, a metal foil made of an aluminum material such as aluminum or an aluminum alloy. The positive electrode active material layer contains a positive electrode active material. Examples of the positive electrode active material include layered or spinel-based lithium transition metal oxides (e.g., LiNiCoMnO2, LiNiO2, LiCoO2, LiFeO2, LiMn2O4, LiNi 0.5 Mn 1.5 O4, LiCrMnO4, LiFePO4, LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2) are examples.

[0022] The positive electrode active material layer may contain, in addition to the positive electrode active material, one or both of a binder and a conductive additive. Examples of binders include styrene butadiene rubber (SBR), polyvinylidene fluoride (PVdF), and polytetrafluoroethylene (PTFE). Examples of conductive additives include carbon materials such as fibrous carbon, carbon black (acetylene black, ketjen black, etc.), coke, and activated carbon. Examples of fibrous carbon include carbon nanotubes (hereinafter also referred to as "CNTs"). CNTs may be single-walled carbon nanotubes (SWCNTs) or multi-walled carbon nanotubes such as double-walled carbon tubes (DWCNTs).

[0023] The negative electrode plate may have a negative electrode current collector and a negative electrode active material layer formed on the negative electrode current collector. The negative electrode current collector is, for example, a metal foil made of a copper material such as copper or a copper alloy. The negative electrode active material layer contains a negative electrode active material. Examples of the negative electrode active material include carbon-based active materials containing carbon (C) atoms, such as graphite; and metal-based active materials containing metal elements, such as simple metals or metal oxides, containing elements selected from the group consisting of silicon (Si), tin (Sn), antimony (Sb), bismuth (Bi), titanium (Ti), and germanium (Ge). The negative electrode active material layer may contain a Si-based active material containing silicon as the metal-based active material.

[0024] Examples of Si-based active materials include silicon itself, SiC (a composite material of silicon and carbon, such as porous carbon particles with silicon nanoparticles dispersed therein), SiOx, LixSiyOz, etc. Si-based active materials undergo large expansion and contraction during charging and discharging, and repeated high-rate charging and discharging easily cause variations in the salt concentration of the electrolyte. Since the electrical conductivity of the electrolyte in this battery (1) is within the above-mentioned range, it is believed that the battery (1) has a negative electrode active material containing a Si-based active material and can suppress a decrease in capacity retention rate even after repeated high-rate charging and discharging.

[0025] The negative electrode active material layer may contain, in addition to the negative electrode active material, one or both of a binder and a conductive additive. Examples of binders include cellulose-based binders such as carboxymethyl cellulose (CMC), methyl cellulose (MC), and hydroxypropyl cellulose; styrene butadiene rubber (SBR), polyacrylic acid (PAA), acrylonitrile butadiene rubber (NBR), polyvinylidene fluoride (PVdF), and polytetrafluoroethylene (PTFE). Examples of conductive additives include those described above.

[0026] The separator may be a porous sheet (film, nonwoven fabric, etc.) made of a resin such as polyethylene, polypropylene, polyester, cellulose, or polyamide. The porous sheet may have a single-layer structure or a multi-layer structure of two or more layers. The separator may have a functional layer on the surface of the porous sheet. The functional layer may be at least one of a heat-resistant layer and an adhesive layer for adhering to the positive electrode plate and the negative electrode plate.

[0027] The exterior body is a housing that houses the electrode assembly and has an opening for housing the electrode assembly. The opening of the exterior body can be sealed with a sealing plate. The exterior body and the sealing plate are preferably made of metal and can be formed using aluminum, an aluminum alloy, iron, an iron alloy, or the like, and can be formed using, for example, an aluminum laminate film.

[0028] (Battery pack) The battery pack of this embodiment is an array of two or more batteries electrically connected. The battery pack includes a nonaqueous electrolyte secondary battery (hereinafter also referred to as "the present battery (2)") and includes an electrode assembly and an electrolyte solution. The electrode assembly is a wound electrode assembly or a stacked electrode assembly including a positive electrode plate having an active material layer. When the electrode assembly is a wound electrode assembly, the length of the positive electrode active material layer in a direction parallel to the winding axis is 150 mm or more. When the electrode assembly is a stacked electrode assembly, the stacked electrode assembly has a square or rectangular shape in a plan view, and the length of the positive electrode active material layer in a direction parallel to one side of the square or the direction parallel to the long side of the rectangle is 150 mm or more. The electrolyte solution contains LiFSO3, and the electrical conductivity of the electrolyte solution at 25°C is 0.86 S / m or more. The battery pack is constrained so that a constraining pressure of 0.5 MPa or more is applied in the stacking direction of the positive electrode plates of the present battery (2).

[0029] The electrode assembly and electrolyte solution contained in the present battery (2) include those described as the electrode assembly and electrolyte solution contained in the present battery (1). The electrode assembly and electrolyte solution are usually housed in the above-mentioned exterior body, and the opening of the exterior body is sealed with a sealing plate. The length of the positive electrode active material layer, the length of the negative electrode active material layer, and the electrical conductivity of the electrolyte solution can be within the ranges described for the present battery (1).

[0030] A battery pack is usually made up of two or more batteries (2) arranged adjacent to each other in the stacking direction of the positive electrode plates of the batteries (2), and the batteries (2) are arranged so that the stacking direction of the positive electrode plates of the batteries (2) is the same.

[0031] The confining pressure of the battery pack may be 0.5 MPa or more and 5 MPa or less, 1 MPa or more and 4 MPa or less, or 2 MPa or more and 4 MPa or less. The confining pressure can be calculated by measuring the load using a load cell. The confining pressure of the battery pack is preferably set so that a confining pressure of 0.5 MPa or more is applied to the battery (2) in the stacking direction of the positive electrode plates. The confining pressure applied to the battery (2) may be 0.5 MPa or more and 5 MPa or less, 1 MPa or more and 4 MPa or less, or 2 MPa or more and 4 MPa or less.

[0032] The battery 2 included in the battery pack may be the battery 1. For example, the battery pack may be two or more batteries 1 arranged so as to be electrically connected. In this case, the battery pack may be two or more batteries 1 arranged adjacent to each other in the stacking direction of the positive electrode plates of the batteries 1, and the batteries 1 may be arranged so that the stacking direction of the positive electrode plates of the batteries 1 is the same. The confining pressure applied to the batteries 1 may be the confining pressure applied when the batteries 1 are assembled into the battery pack. [Example]

[0033] The present disclosure will be described in more detail below with reference to Examples, Comparative Examples, and Reference Examples. Comparative Example 1 (Preparation of positive electrode plate) LiNiCoMnO2 as the positive electrode active material, acetylene black (AB) as the conductive additive, and polyvinylidene fluoride (PVdF) as the binder were used in a mass ratio of LiNiCoMnO2:AB:PVdF = 100:1:1. This was mixed with N-methylpyrrolidone (NMP) to obtain a positive electrode mixture slurry. The positive electrode mixture slurry was applied to an aluminum foil positive electrode current collector, dried, and compressed to a predetermined thickness to form a positive electrode active material layer on the aluminum foil. The positive electrode plate was then cut to a predetermined width to obtain a positive electrode plate. The positive electrode plate had a widthwise region where the positive electrode active material layer was formed on the aluminum foil and a region where the positive electrode active material layer was not formed and the aluminum foil was exposed. The width of the positive electrode active material layer of the positive electrode plate (the length in the direction parallel to the winding axis of the electrode body described below) was 150 mm.

[0034] (Preparation of negative electrode plate) Graphite was used as the negative electrode active material, and styrene butadiene rubber (SBR) and carboxymethyl cellulose (CMC) were used as binders in a graphite:SBR:CMC ratio of 100:1:1 (by mass). This was mixed with water to obtain a negative electrode mixture slurry. The negative electrode mixture slurry was applied to a copper foil negative electrode current collector, dried, and compressed to a predetermined thickness to form a negative electrode active material layer on the copper foil. The negative electrode plate was then cut to a predetermined width to obtain a negative electrode plate. The negative electrode plate had a region in the width direction where the negative electrode active material layer was formed on the copper foil and a region where the negative electrode active material layer was not formed and the copper foil was exposed. The width of the negative electrode active material layer of the negative electrode plate (the length in the direction parallel to the winding axis of the electrode body described below) was 155 mm.

[0035] (Preparation of electrode body) A separator having a three-layer structure of polypropylene / polyethylene / polypropylene was prepared. The positive and negative electrode plates obtained above were stacked with the separator interposed between them and wound to obtain a wound electrode body. The wound electrode body had a positive electrode current collector exposed at one end parallel to the winding axis and a negative electrode current collector exposed at the other end. An aluminum plate for external current collection was welded to the region of the wound electrode body where the positive electrode current collector was exposed, and a copper plate for external current collection was welded to the region where the negative electrode current collector was exposed, and the wound electrode body was then housed in an exterior body formed of an aluminum laminate film.

[0036] A comparative electrolyte (1) was prepared by mixing LiPF6, VC, and the mixed solvent (EC:EMC:DMC = 30:50:20 (volume ratio)) of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) as the non-aqueous solvent to a LiPF6 concentration of 1.1 mol / L and a vinylene carbonate (VC) content of 1 mass% as an additive. This comparative electrolyte (1) was poured into an exterior housing containing a wound electrode body, and the opening of the exterior housing was sealed with a sealing plate to obtain an assembly.

[0037] In the assembly, stainless steel restraint plates were placed on each of the two surfaces parallel to the winding axis of the wound electrode body (i.e., the two surfaces perpendicular to the stacking direction of the positive and negative electrode plates of the wound electrode body), and the assembly was sandwiched between the two restraint plates. The four corners of the two restraint plates were fastened together using bolts and nuts, and the load was adjusted so that a restraint pressure of 0.5 MPa was applied to the assembly, resulting in a nonaqueous electrolyte secondary battery. The restraint pressure can be calculated by measuring the load with a load cell.

[0038] Comparative Example 2 A comparative electrolyte solution (2) was prepared in the same manner as the comparative electrolyte solution (1), except that LiPF and LiFSO were used as supporting electrolytes, the LiPF concentration was 1.1 mol / L, the LiFSO content was 1 mass%, and the VC content was 1 mass%. A nonaqueous electrolyte secondary battery was obtained in the same manner as the comparative example 1, except that the comparative electrolyte solution (2) was used instead of the comparative electrolyte solution (1).

[0039] [Comparative Example 3, Examples 1 to 4] Comparative electrolyte solution (3) and electrolyte solutions (1) to (4) were prepared in the same manner as comparative electrolyte solution (2), except that a mixed solvent of EC, EMC, and DMC was used in the mixing ratio shown in Table 1. A nonaqueous electrolyte secondary battery was obtained in the same manner as comparative example 1, except that comparative electrolyte solution (3) and electrolyte solutions (1) to (4) were used instead of comparative electrolyte solution (1).

[0040] Comparative Example 4 A comparative electrolyte solution (4) was prepared in the same manner as the comparative electrolyte solution (1), except that a mixed solvent of EC:EMC:DMC = 30:30:40 (volume ratio) was used. A nonaqueous electrolyte secondary battery was obtained in the same manner as in Comparative Example 1, except that the comparative electrolyte solution (4) was used instead of the comparative electrolyte solution (1).

[0041] Examples 5 and 6 Electrolyte solutions (5) and (6) were prepared in the same manner as for the electrolyte solution (3) of Example 3, except that LiFSO was used so as to have the content shown in Table 1. Non-aqueous electrolyte secondary batteries were obtained in the same manner as in Comparative Example 1, except that the electrolyte solutions (5) and (6) were used instead of the comparative electrolyte solution (1).

[0042] Comparative Example 5 A non-aqueous electrolyte secondary battery was obtained in the same manner as in Example 3, except that no confining pressure was applied.

[0043] [Reference example 1] A wound electrode body was obtained in the same manner as in Comparative Example 1, except that the width of the positive electrode active material layer of the positive electrode plate (the length in the direction parallel to the winding axis of the electrode body) was changed to 100 mm, and the width of the negative electrode active material layer of the negative electrode plate (the length in the direction parallel to the winding axis of the electrode body) was changed to 103 mm, and a nonaqueous electrolyte secondary battery was obtained using this wound electrode body.

[0044] [Reference example 2] A wound electrode body was obtained using the same procedure as in Comparative Example 2, except that the width of the positive electrode active material layer of the positive electrode plate (the length in the direction parallel to the winding axis of the electrode body) was changed to 100 mm and the width of the negative electrode active material layer of the negative electrode plate (the length in the direction parallel to the winding axis of the electrode body) was changed to 103 mm, and a nonaqueous electrolyte secondary battery was obtained using this wound electrode body.

[0045] [Measurement of electrical conductivity] The electrical conductivity of the electrolyte was measured in a thermostatic chamber at 25°C using an electrical conductivity meter (manufactured by Toa DKK Co., Ltd.).

[0046] <Evaluation> (Initial activation) In an environment of 25°C, the nonaqueous electrolyte secondary battery obtained above was charged to 4.2 Vcccv (constant current / constant voltage) at a current value of C / 10 and stored for 24 hours at 60°C. Thereafter, the battery was discharged to a potential of 3 V at a current value of C / 10 to perform initial activation of the nonaqueous electrolyte secondary battery.

[0047] [Evaluation of output resistance] The initially activated non-aqueous electrolyte secondary battery was charged at a current of C / 3 in an environment of 25°C until the SOC (state of charge) reached 50%, and then rested for 30 minutes, after which the voltage V0 of the non-aqueous electrolyte secondary battery was measured. Subsequently, the battery was discharged at a current of 2C for 10 seconds in an environment of 25°C, and the voltage V1 of the non-aqueous electrolyte secondary battery at 10 seconds was measured. The resistance of the non-aqueous electrolyte secondary battery was calculated according to the following formula: Resistance [Ω] = (V0-V1) / 2C current value

[0048] The resistance values ​​of Comparative Examples 2 to 5 and Examples 1 to 6 were converted as relative values ​​when the resistance value of Comparative Example 1 was set to 100% (reference). The resistance value of Reference Example 2 was converted as a relative value when the resistance value of Reference Example 1 was set to 100% (reference). The results are shown in Table 1.

[0049] [Cycle test] In a thermostatic chamber at 25°C, an initially activated nonaqueous electrolyte secondary battery was charged to 4.2 Vcccv (constant current / constant voltage) at a current value of 2 C and then discharged to a potential of 3 V at a current value of 1 C. This cycle was repeated. The capacity retention rate [%] was calculated as the ratio of the discharge capacity W500 at the 500th cycle to the discharge capacity W1 at the first cycle according to the following formula. The results are shown in Table 1. Capacity maintenance rate [%]=(W500 / W1)×100

[0050] [Table 1]

[0051] In Comparative Example 2, which used an electrolyte containing LiFSO3, the output resistance was reduced compared to Comparative Example 1, which used an electrolyte not containing LiFSO3, but the capacity retention rate also decreased. In Comparative Example 2, the output resistance was reduced by including LiFSO3, but the positive electrode active material and FSO3 - It is presumed that the capacity retention rate decreased due to the reaction of the transition metals in the positive electrode active material with the elution of the transition metals.

[0052] A comparison of Comparative Example 3 with Examples 1 to 4 reveals that the smaller the volume ratio of EMC to DMC (EMC / DMC) in the mixed solvent, the greater the electrical conductivity, the lower the output resistance, and the better the capacity retention rate. Furthermore, a comparison of Comparative Example 4 with Examples 5 and 6 reveals that the greater the content of LiFSO3 in the mixed solvent, the lower the output resistance and the better the capacity retention rate. The inclusion of LiFSO3 reduces the output resistance, and increasing the electrical conductivity of the electrolyte improves the interaction between the positive electrode active material and FSO3 during high-rate charging. - It is believed that the capacity retention rate was improved because the reaction with the cathode was suppressed and the elution of the transition metal in the cathode active material was suppressed.

[0053] It is believed that in Comparative Example 5, where no confining pressure was applied, the inter-electrode distance was larger, resulting in a larger output resistance, compared to Example 3, where confining pressure was applied. Therefore, it is believed that in Comparative Example 3, the reversibility of Li ions was worsened compared to Example 3, and the capacity retention rate was also worsened.

[0054] In Reference Examples 1 and 2, the width of the positive electrode active material layer is smaller than in Comparative Examples 1 and 2. Comparing Reference Example 2 and Comparative Example 2, when the width of the positive electrode active material layer is small, the salt concentration of the electrolyte solution is less likely to vary, and the positive electrode active material and FSO3 - It is believed that this is why Reference Example 2 had an improved capacity retention rate compared to Comparative Example 2.

Claims

1. A non-aqueous electrolyte secondary battery including an electrode assembly and an electrolyte solution, the electrode body is a wound type electrode body or a stacked type electrode body including a positive electrode plate having an active material layer, When the electrode body is a wound electrode body, the length of the active material layer in a direction parallel to the winding axis is 150 mm or more, When the electrode body is a laminated electrode body, The laminated electrode body has a square or rectangular shape in plan view, a length of the active material layer in a direction parallel to one side of the square or a direction parallel to a long side of the rectangle is 150 mm or more; the nonaqueous electrolyte secondary battery is applied with a confining pressure of 0.5 MPa or more in a stacking direction of the positive electrode plate, The electrolyte is LiFSO ３ and at least one of LiPF 6 and LiBF 4 ; The content of LiFSO 3 in the electrolyte solution is 0.1 mass % or more and 2.5 mass % or less, The nonaqueous electrolyte secondary battery has an electrical conductivity of 0.86 S / m or more at 25°C.

2. 2. The nonaqueous electrolyte secondary battery according to claim 1, wherein the electrolytic solution has an electrical conductivity of 0.90 S / m or more at 25°C.

3. 3. The nonaqueous electrolyte secondary battery according to claim 1, wherein the electrolytic solution has an electrical conductivity of 0.93 S / m or more at 25°C.

4. The nonaqueous electrolyte secondary battery according to claim 1 , wherein the electrolyte solution contains LiPF 6 .

5. 3. The nonaqueous electrolyte secondary battery according to claim 1, wherein the electrolytic solution further contains vinylene carbonate.

6. 3. The nonaqueous electrolyte secondary battery according to claim 1, wherein the electrolytic solution further contains at least one selected from the group consisting of ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate.

7. A battery pack in which two or more batteries are arranged so as to be electrically connected, the battery is a non-aqueous electrolyte secondary battery including an electrode assembly and an electrolyte solution, the electrode body is a wound type electrode body or a stacked type electrode body including a positive electrode plate having an active material layer, When the electrode body is a wound electrode body, the length of the active material layer in a direction parallel to the winding axis is 150 mm or more, When the electrode body is a laminated electrode body, The laminated electrode body has a square or rectangular shape in plan view, a length of the active material layer in a direction parallel to one side of the square or a direction parallel to a long side of the rectangle is 150 mm or more; The electrolyte is LiFSO ３ and at least one of LiPF 6 and LiBF 4 ; The content of LiFSO 3 in the electrolyte solution is 0.1 mass % or more and 2.5 mass % or less, The electrolytic solution has an electrical conductivity of 0.86 S / m or more at 25°C, The battery assembly is constrained so that a constraining pressure of 0.5 MPa or more is applied in a stacking direction of the positive electrode plates of the battery.

8. The battery pack according to claim 7, wherein the electrolyte contains LiPF 6 .

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