Cylindrical non-aqueous electrolyte secondary battery and method of manufacturing the same

Abstract

A secondary battery according to the present invention is provided with a battery case, an electrode group and a nonaqueous electrolyte. The outer diameter R is 3.0 mm to 6.5 mm. The ratio r / R of the inner diameter r of a hollow part of the electrode group to the outer diameter R is 0.1 to 0.3. The nonaqueous electrolyte contains at least one substance that is selected from the group consisting of LiSO3F and LiFSI. In cases where the nonaqueous electrolyte contains LiSO3F, the concentration of LiSO3F is 1.5% by mass or less if the outer diameter R is 3.0 mm to 5 mm, and the concentration is 1.2% by mass or less if the outer diameter R is more than 5 mm but not more than 6.5 mm. In cases where the nonaqueous electrolyte contains LiFSI, the concentration of LiFSI is 1.1 mol / L or less if the outer diameter R is 3.0 mm to 3.5 mm, and the concentration is 1.0 mol / L or less if the outer diameter R is more than 3.5 mm but not more than 6.5 mm.

Description

[Technical Field]

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

[0002] BACKGROUND ART Non-aqueous electrolyte secondary batteries, typified by lithium ion secondary batteries, are widely used as power sources for driving notebook computers, mobile phones, and other portable electronic devices because they are capable of providing high capacity and high output.

[0003] Patent Document 1 proposes the use of a nonaqueous electrolyte secondary battery comprising a positive electrode having a positive electrode active material layer, an insulating layer containing an inorganic filler, and a boundary layer, and a nonaqueous electrolyte containing lithium fluorosulfonate. Here, the boundary layer contains the positive electrode active material contained in the positive electrode active material layer and the inorganic filler contained in the insulating layer, and also contains alumina hydrate.

[0004] Patent Document 2 proposes an electrolyte solution for a non-aqueous electrolyte battery that contains at least a non-aqueous solvent, a solute, and an imide compound having a phosphoryl structure represented by a specific formula.

[0005] Meanwhile, in recent years, as portable electronic devices have become smaller and more functional, there has been an increasing demand for small power sources with high capacity or high output. For example, small cylindrical secondary batteries, such as pin-type batteries, have been considered.

[0006] Patent Document 3 discloses a negative electrode mixture layer having a region that does not face the positive electrode mixture layer, and a density of the negative electrode mixture layer of 1.25 to 1.43 g / cm 3 The present document proposes a cylindrical secondary battery in which the ratio of the total length of the non-facing region to the total length of the negative electrode mixture layer is 0.09 or more, and the inner diameter of the hollow portion of the electrode group is 2.0 mm or less. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Patent Publication No. 2021-44138 [Patent Document 2] International Publication No. 2019 / 146705 [Patent Document 3] International Publication No. 2019 / 107049 Summary of the Invention

[0008] In small-sized cylindrical nonaqueous secondary batteries, the inner diameter of the hollow portion of the electrode assembly is small and the amount of nonaqueous electrolyte is limited, so the charge / discharge reaction in the electrode assembly tends to be non-uniform compared to larger-sized batteries. In small-sized cylindrical nonaqueous secondary batteries, the curvature of the hollow portion is particularly large, so the electrode material is prone to cracking, and the fallen electrode material is likely to cause an internal short circuit.

[0009] A cylindrical nonaqueous electrolyte secondary battery according to one aspect of the present disclosure includes a cylindrical battery case, and a wound electrode group and a nonaqueous electrolyte housed in the battery case. The outer diameter R of the battery case is 3.0 mm or more and 6.5 mm or less. The ratio r / R of the inner diameter r of the hollow portion of the electrode group to the outer diameter R is 0.1 or more and 0.3 or less. The nonaqueous electrolyte contains at least one selected from the group consisting of LiSO3F and LiFSI. When the nonaqueous electrolyte contains LiSO3F, the concentration of LiSO3F in the nonaqueous electrolyte is 1.5 mass % or less when the outer diameter R is 3.0 mm or more and 5 mm or less, and 1.2 mass % or less when the outer diameter R is more than 5 mm and 6.5 mm or less. When the non-aqueous electrolyte contains LiFSI, the concentration of LiFSI in the non-aqueous electrolyte is 1.1 mol / L or less when the outer diameter R is 3.0 mm or more and 3.5 mm or less, and is 1.0 mol / L or less when the outer diameter R is more than 3.5 mm and 6.5 mm or less.

[0010] In a cylindrical nonaqueous electrolyte secondary battery with an outer diameter R of a battery case of 3.0 mm or more and 6.5 mm or less, internal short circuits can be reduced. [Brief explanation of the drawings]

[0011] [Figure 1]FIG. 1 is a schematic vertical cross-sectional view of a cylindrical nonaqueous electrolyte secondary battery (a pin-type cylindrical nonaqueous electrolyte secondary battery) according to one embodiment of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0012] In non-aqueous electrolyte secondary batteries such as lithium-ion secondary batteries, various attempts have been made to improve the performance of the batteries by modifying the configuration of electrodes and electrode assemblies, the composition of the non-aqueous electrolyte, and other factors. Larger battery sizes are advantageous for ensuring high capacity, and lithium-ion secondary batteries with a diameter of approximately 14 mm to 18 mm and a height of approximately 40 mm to 65 mm and high capacity have been widely used. In such batteries, the large electrode surface area makes them susceptible to contamination by foreign matter. Furthermore, the increased number of windings increases the surface pressure of the entire electrode assembly. Therefore, these factors are the primary causes of internal short circuits in the early stages.

[0013] On the other hand, in cylindrical nonaqueous electrolyte secondary batteries (pin-type cylindrical nonaqueous electrolyte secondary batteries) with a battery diameter of 6.5 mm or less, the inner diameter r of the hollow portion of the wound electrode group is small, resulting in a large curvature at the innermost periphery of the electrode. The innermost periphery of the electrode is more susceptible to stress due to expansion and contraction of the electrode material during charge and discharge. The volume change due to expansion and contraction is particularly large in the negative electrode compared to the positive electrode. Therefore, the electrode material of the negative electrode is more likely to crack and fall off at the innermost periphery of the negative electrode. This electrode material falling off makes pin-type cylindrical nonaqueous electrolyte secondary batteries prone to internal short circuits in the early stages. Compared to larger batteries, pin-type cylindrical nonaqueous electrolyte secondary batteries are more likely to experience internal short circuits due to electrode material falling off, even when the ratio of the inner diameter r of the hollow portion of the electrode group to the outer diameter R of the battery case (r / R) is the same, due to the smaller inner diameter r. Furthermore, in pin-type cylindrical nonaqueous electrolyte secondary batteries, the stress caused by expansion and contraction reduces the distance between the positive and negative electrodes at or near the innermost periphery, leading to uneven reactions between the inner and outer peripheries of the wound electrode assembly. As a result, as charge / discharge cycles progress, the amount of nonaqueous electrolyte in the innermost periphery of the electrode assembly is likely to become insufficient, a phenomenon known as "depletion." This phenomenon becomes particularly pronounced when high-rate charging and discharging is repeated. This depletion causes lithium metal to precipitate on the negative electrode, further increasing stress and further exfoliating the negative electrode material. For these reasons, even if internal short circuits are suppressed in the initial stage, repeated charging and discharging (especially at high rates) can lead to internal short circuits due to electrode material loss, resulting in reduced cycle life. Internal short circuits caused by electrode material loss at the inner periphery are rarely a problem in larger batteries (e.g., batteries with a large inner diameter r) or batteries with a large r / R ratio. In pin-type cylindrical nonaqueous electrolyte secondary batteries, it is difficult to increase the ratio r / R to ensure a certain level of capacity. Therefore, the problem of internal short circuits caused by the above-mentioned electrode material falling off is a problem specific to pin-type cylindrical nonaqueous electrolyte secondary batteries that is hardly an issue in larger batteries. Furthermore, the state of the electrodes and the behavior of the nonaqueous electrolyte during charge and discharge are completely different between pin-type cylindrical nonaqueous electrolyte secondary batteries and larger batteries.Therefore, it is difficult to obtain the same effects by simply applying the improvement measures for large-sized batteries to pin-type cylindrical non-aqueous electrolyte secondary batteries.

[0014] In view of the above, the present disclosure provides a cylindrical nonaqueous electrolyte secondary battery comprising a cylindrical battery case, a wound electrode group, and a nonaqueous electrolyte housed in the battery case. The battery case has an outer diameter R of 3.0 mm or more and 6.5 mm or less. The ratio of the inner diameter r of the hollow portion of the electrode group to the outer diameter R (r / R) is 0.1 or more and 0.3 or less. The nonaqueous electrolyte contains at least one selected from the group consisting of LiSO3F and LiFSI. Here, LiSO3F is lithium fluorosulfonate. LiFSI is lithium bis(fluorosulfonyl)imide. When the nonaqueous electrolyte contains LiSO3F, the concentration of LiSO3F in the nonaqueous electrolyte is 1.5% by mass or less when the outer diameter R is 3.0 mm or more and 5 mm or less, and 1.2% by mass or less when the outer diameter R is more than 5 mm and 6.5 mm or less. When the non-aqueous electrolyte contains LiFSI, the concentration of LiFSI in the non-aqueous electrolyte is 1.1 mol / L or less when the outer diameter R is 3.0 mm or more and 3.5 mm or less, and is 1.0 mol / L or less when the outer diameter R is more than 3.5 mm and 6.5 mm or less. When the non-aqueous electrolyte contains LiSO3F and the outer diameter R is in the range of 3.0 mm or more and 6.5 mm or less, the concentration of LiSO3F in the non-aqueous electrolyte may be 1.2 mass% or less. When the non-aqueous electrolyte contains LiFSI and the outer diameter R is in the range of 3.0 mm or more and 6.5 mm or less, the concentration of LiFSI may be 1.0 mol / L or less.

[0015] Thus, the cylindrical nonaqueous electrolyte secondary battery of the present disclosure has a small size, with the battery case having an outer diameter R of 3.0 mm or more and 6.5 mm or less, and the ratio r / R being 0.1 or more and 0.3 or less, and the nonaqueous electrolyte containing at least one of LiSO3F and LiFSI at the above-mentioned concentrations. This configuration can suppress the electrode material from falling off at the innermost circumferential portion of the negative electrode of the wound electrode group. This can reduce the occurrence of internal short circuits due to the electrode material falling off.

[0016] Additives used in large-sized nonaqueous electrolyte secondary batteries include fluoroethylene carbonate (FEC), propane sultone (PS), and vinylene carbonate (VC). These additives are said to form a solid electrolyte interface (SEI) film on the surface of the negative electrode of the nonaqueous electrolyte. However, even if these additives are used in place of LiSO3F or LiFSI, they are not very effective in suppressing the occurrence of internal short circuits in pin-shaped cylindrical nonaqueous electrolyte secondary batteries. This is thought to be because the SEI film formed on the surface of the negative electrode is of poor quality or has high resistance, which causes a rapid or uneven reaction, making it impossible to suppress the shedding of the electrode material from the negative electrode.

[0017] In the present disclosure, the reduction in the occurrence of internal short circuits due to the shedding of electrode materials is believed to be due to the following reasons: When the non-aqueous electrolyte contains LiSO3F, an SEI film derived from LiSO3F is believed to be formed on the surface of the negative electrode from an early stage. When the non-aqueous electrolyte contains LiFSI, the resistance of the non-aqueous electrolyte can be reduced, the reaction is more likely to proceed uniformly, and an SEI film derived from LiFSI is believed to be formed on the surface of the negative electrode from an early stage. When the concentration of LiSO3F in the non-aqueous electrolyte is within the above range, the SEI film derived from LiSO3F formed on the surface of the negative electrode is believed to have good film quality, be relatively uniform and strong, and have relatively low resistance. Furthermore, when the concentration of LiFSI in the non-aqueous electrolyte is within the above range, the SEI film derived from LiFSI formed on the surface of the negative electrode is believed to have excellent film quality, be relatively low resistance, and allow the reaction to proceed more uniformly. Such an SEI film is believed to suppress the rapid progression of charge / discharge reactions on the inner periphery of the electrode assembly during break-in charge / discharge and initial charge, thereby enabling more uniform charge / discharge reactions throughout the electrode assembly. This is thought to reduce the shedding of electrode material from the innermost portion of the negative electrode in the early stage. Therefore, even though the outer diameter and r / R ratio of the battery case are relatively small as described above, internal short circuits caused by the shedding of electrode material in the early stage can be reduced. Furthermore, the SEI coating allows charge / discharge reactions to occur more uniformly throughout the electrode assembly, reducing the shedding of electrode material from the innermost portion of the negative electrode even during repeated high-rate charge / discharge. Therefore, by suppressing the occurrence of internal short circuits due to the shedding of electrode material, capacity loss during repeated high-rate charge / discharge can be reduced, even though the outer diameter and r / R ratio of the battery case are relatively small as described above. As a result, a high capacity retention rate can be ensured during high-rate charge / discharge cycles. In the case of LiFSI, the low resistance of the nonaqueous electrolyte is also thought to ensure a high capacity retention rate.

[0018] An electrode group is formed by winding a positive electrode and a negative electrode with a separator interposed therebetween and then removing the winding core. Removing the winding core leaves a space in the center of the electrode group. This space is called a hollow portion. That is, the electrode group has one or more electrodes (positive electrode, negative electrode) wound around the hollow portion. In some cases, the separator or electrode (negative electrode, etc.) that was sandwiched between the winding cores during winding remains in the center of the hollow portion. In this embodiment, the hollow portion is considered to be a space ignoring the part of the separator and electrode that remains in the center with a gap on the outer periphery.

[0019] The hollow portion can be determined from a cross section of the electrode group cut in a direction perpendicular to the winding axis, or from an end face viewed from a direction perpendicular to the winding axis of the electrode group. The diameter of the hollow portion in such a cross section or end face is the inner diameter r of the hollow portion. It is possible that the shape of the hollow portion in the cross section or end face is not strictly circular. In this case, the inner diameter r of the hollow portion means the diameter of the equivalent circle of the innermost circumferential surface of the electrode group in the cross section or end face (a circle having the same area as the area of ​​the hollow portion in the cross section or end face).

[0020] In cylindrical nonaqueous electrolyte secondary batteries, the battery case is generally cylindrical with a bottom. In the present disclosure, the outer diameter R of the battery case refers to the maximum outer diameter of the cylindrical nonaqueous electrolyte secondary battery when viewed from the bottom of the battery case (excluding the outer film and the sealing portion). Hereinafter, cylindrical nonaqueous electrolyte secondary batteries with a battery case outer diameter R of 3.0 mm or more and 6.5 mm or less, including the cylindrical nonaqueous electrolyte secondary battery of the present disclosure, may be referred to as pin-type secondary batteries.

[0021] In the pin-type secondary battery of the present disclosure, LiSO3F and LiFSI are decomposed and consumed in the formation of the SEI film. The concentrations of LiSO3F and LiFSI in the non-aqueous electrolyte change during storage or use of the battery. Therefore, when analyzing the concentrations of the non-aqueous electrolyte sampled from the pin-type secondary battery, it is sufficient that LiSO3F or LiFSI remain in the non-aqueous electrolyte at a concentration equal to or greater than the detection limit.

[0022] The pin-type secondary battery of the present disclosure will be described in more detail below.

[0023] (electrode group) A wound electrode group includes a positive electrode, a negative electrode, and a separator interposed between them. The winding core used for winding is cylindrical, and a cylindrical electrode group is obtained by winding the positive electrode and the negative electrode with the separator interposed between them around such a winding core. Note that cylindrical electrode groups also include shapes similar to a cylinder, such as a partially bent cylinder or a cylinder slightly crushed in the diametric direction.

[0024] A hollow portion is present in the center of the electrode assembly after the core is removed. In the present disclosure, the ratio r / R of the inner diameter r of the hollow portion to the outer diameter R of the battery case is 0.1 or more and 0.3 or less, and may be 0.1 or more and 0.2 or less. When the ratio r / R is this small, the curvature of the inner periphery side of the electrode assembly (particularly the innermost portion of the electrode) becomes large, and the electrode material (active material, electrode mixture, etc.) is likely to fall off significantly. In the pin-type secondary battery of the present disclosure, even when the ratio r / R is this small, the nonaqueous electrolyte contains at least one of LiSO3F and LiFSI at a specific concentration, which can suppress internal short circuits caused by the fall off of the electrode material and reduce capacity loss during high-rate charge / discharge.

[0025] The inner diameter r of the hollow portion may be selected from the range of 0.3 mm to 1.95 mm so that the ratio r / R falls within the above range. The inner diameter r may be 0.4 mm to 1.95 mm, or 0.4 mm to 1.3 mm. When the inner diameter r is within such a range, a greater effect in suppressing the electrode material from falling off can be obtained, and the occurrence of internal short circuits can be further suppressed.

[0026] Outer diameter r of the electrode group e The outer diameter r of the electrode group is the size that can be accommodated in the battery case. e is smaller than the outer diameter R of the battery case. The outer diameter r of the electrode group emeans the diameter of the equivalent circle of the electrode group in a cross section or end face perpendicular to the winding axis for determining the inner diameter r of the electrode group (i.e., a circle having the same area as the area of ​​the region surrounded by the outer edge of the electrode group in the cross section or end face).

[0027] The number of turns of the electrode group is determined taking into consideration, for example, the desired capacity and the diameter of the electrode group.

[0028] In a fully discharged pin-type secondary battery, the outer diameter r of the electrode group e Inner diameter R of the battery case i The ratio Ra=r e / R i is, for example, 90% or more, and may be 95% or more. It can be determined from a cross section passing through the center of the pin-shaped secondary battery in the longitudinal direction (the direction parallel to the winding axis) and perpendicular to the winding axis. The diameter of the hollow part of the cylinder surrounded by the inner wall of the battery case in this cross section is the inner diameter R of the battery case. i When the shape of the portion enclosed by the inner wall of the battery case in the cross section is not strictly circular, this refers to the diameter of a circle equivalent to the portion enclosed by the inner wall of the battery case in the cross section (a circle having the same area as the area of ​​the portion enclosed by the inner wall in the cross section).

[0029] (positive electrode) The positive electrode has a positive electrode current collector and a positive electrode mixture layer formed on at least one main surface of the positive electrode current collector.

[0030] The positive electrode current collector may be, for example, a metal foil. The metal foil may contain at least one metal selected from the group consisting of aluminum and aluminum alloys. The thickness of the positive electrode current collector is not particularly limited, and may be, for example, 10 μm or more and 50 μm or less from the viewpoint of battery miniaturization and positive electrode current collector strength.

[0031] The positive electrode mixture layer may be formed on one side of the positive electrode current collector, or from the viewpoint of increasing capacity, may be formed on both sides.

[0032] The thickness of the positive electrode active material layer (the positive electrode active material layer formed on one side of the positive electrode current collector) can ensure the battery capacity as it gets thicker, while the electrode plate is more likely to crack at the inner peripheral part with a large curvature. From the perspective of obtaining a high capacity and suppressing the cracking of the electrode plate at the inner peripheral part, the thickness of the positive electrode active material layer may be 20 μm or more and 100 μm or less, or may be 25 μm or more and 60 μm or less.

[0033] The positive electrode active material layer contains a positive electrode active material. The positive electrode active material is not particularly limited as long as it is a material that can be used in a lithium-ion secondary battery. Examples of the positive electrode active material include lithium-containing transition metal oxides, such as lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), lithium manganate (LiMn2O4), and lithium-containing composite oxides in which a part of Co, Ni, or Mn in these compounds is substituted with other elements. Examples of other elements include at least one selected from the group consisting of other transition metal elements and typical elements. From the perspective of miniaturizing the battery and increasing the energy density, specific examples of the lithium-containing composite oxide include the general formula: Li x1 Ni y1 M a 1-y1 O2…(1) represents a composite oxide, and the general formula: Li x2 Ni y2 Co z1 M b 1-y2-z1 O2…(2) represents a composite oxide, etc.

[0034] In the general formula (1), the element M a is, for example, at least one selected from the group consisting of Na, Mg, Sc, Y, Mn, Fe, Co, Cu, Zn, Al, Cr, Pb, Sb, and B. Also, x1 and y1 satisfy, for example, 0 < x1 ≤ 1.2 and 0.5 < y1 ≤ 1.0, respectively. Note that x1 is a value that changes during charge and discharge.

[0035] In the general formula (2), the element M bIt is at least one selected from the group consisting of, for example, Mg, Ba, Al, Ti, Sr, Ca, V, Fe, Cu, Bi, Y, Zr, Mo, Tc, Ru, Ta, and W. x2, y2, and z1 are, for example, 0 < x2 ≤ 1.2 (preferably 0.9 ≤ x2 ≤ 1.2), 0.3 ≤ y2 ≤ 0.9, and 0.05 ≤ z1 ≤ 0.5, respectively. Note that x2 is a value that changes upon charge and discharge. Also, in the general formula (2), 0.01 ≤ 1 - y2 - z1 ≤ 0.3 may hold.

[0036] The positive electrode active material can be used alone or in combination of two or more.

[0037] The positive electrode mixture layer can optionally contain at least one of a binder and a conductive agent. Examples of the binder include binders used in lithium-ion secondary batteries. Examples of the binder include at least one selected from the group consisting of fluororesins (such as polyvinylidene fluoride (PVdF)), rubber-like polymers (such as styrene-butadiene rubber, styrene-methacrylic acid-butadiene copolymer, fluorine-based rubber, etc.), and polyacrylic acid. The amount of the binder in the positive electrode mixture layer is, for example, 0.5 parts by mass or more and 5 parts by mass or less with respect to 100 parts by mass of the positive electrode active material.

[0038] Examples of the conductive agent include conductive agents used in lithium-ion secondary batteries. Examples of the conductive agent include at least one selected from the group consisting of carbonaceous materials (such as graphite, carbon black, carbon fiber, etc.), metal fibers, and conductive organic materials. When using a conductive agent, the amount of the conductive agent in the positive electrode mixture layer is, for example, 0.5 parts by mass or more and 5 parts by mass or less with respect to 100 parts by mass of the positive electrode active material.

[0039] The positive electrode can be formed by applying a positive electrode slurry containing a positive electrode active material and a dispersion medium onto the surface of a positive electrode current collector, drying it, and compressing it in the thickness direction. At least one of a binder and a conductive agent may be added to the positive electrode slurry. As the dispersion medium, water, organic solvents such as N-methyl-2-pyrrolidone (NMP), and mixed solvents thereof can be used.

[0040] (Negative electrode) The negative electrode includes a negative electrode current collector and a negative electrode active material layer held on at least one main surface of the negative electrode current collector.

[0041] The negative electrode current collector is preferably made of a metal foil. Examples of the material for the metal foil include aluminum, an aluminum alloy, copper, and a copper alloy. The material for the negative electrode current collector may be selected depending on the performance required for the pin-type secondary battery and the type of negative electrode active material.

[0042] The negative electrode active material layer may be formed on only one main surface of the negative electrode current collector. However, from the viewpoint of increasing capacity, it is preferable that the negative electrode active material layer be formed on both one main surface and the other main surface on the opposite side in at least a portion of the negative electrode. In a wound electrode group, the negative electrode active material layer may be formed on only one surface at least at the start of winding (inner peripheral side) and the end of winding (outer peripheral side) to avoid a state in which the positive electrode active material layer and the negative electrode active material layer do not face each other. Regions without the negative electrode active material layer may be formed on both corresponding main surfaces of the negative electrode current collector. Furthermore, at least at the start of winding and the end of winding, the position of the end of the negative electrode active material layer may be different between one main surface and the other main surface.

[0043] In the electrode assembly, the innermost end of the negative electrode (more specifically, the portion where the negative electrode active material is present) may be located closer to the inner periphery than the innermost end of the positive electrode (more specifically, the portion where the positive electrode active material is present). In other words, a larger proportion of the electrodes may be located at the innermost periphery in the negative electrode. Compared to the positive electrode active material, the negative electrode active material undergoes a larger volume change due to expansion and contraction during charging and discharging. Therefore, if a larger proportion of the electrodes are located at the innermost periphery in the negative electrode, the electrode material of the negative electrode is likely to fall off significantly. Even in such cases, by including at least one of LiSO3F and LiFSI in the above-described concentrations in the nonaqueous electrolyte, falloff of the electrode material can be effectively suppressed, thereby achieving a high effect of suppressing the occurrence of internal short circuits due to falloff of the electrode material. Furthermore, the innermost portion of the negative electrode (more specifically, the portion where the negative electrode active material is present) does not have to face the positive electrode (more specifically, the portion where the positive electrode active material is present). In this case, the non-aqueous electrolyte is more easily retained even in the inner peripheral portion of the electrode group where the non-aqueous electrolyte is likely to be insufficient, and the effect of suppressing the electrode material from falling off is further enhanced.

[0044] The thickness of the negative electrode active material layer (the negative electrode active material layer formed on one side of the negative electrode current collector) may be 20 μm or more and 120 μm or less. The total thickness of the negative electrode is, for example, 80 μm or more and 250 μm or less.

[0045] The negative electrode active material contained in the negative electrode active material layer can be any active material that can be used in a lithium ion secondary battery without any particular limitation. Examples of the negative electrode active material include materials that can reversibly absorb and release lithium ions, and materials that can be reversibly alloyed with lithium. Examples of such materials include carbonaceous materials, silicon, silicon compounds, tin, tin compounds, and transition metal compounds. Examples of the carbonaceous material include graphite materials (natural graphite, artificial graphite, etc.) and amorphous carbon materials. Examples of the transition metal compounds include composite oxides containing lithium and titanium (e.g., Li2TiO3, Li4Ti5O 12 Lithium titanate, TiNb2O7, Ti2Nb 10 O 29Titanium-niobium composite oxides such as titanium-niobium composite oxides (e.g., titanium-niobium composite oxides) can be used. The negative electrode active materials can be used singly or in combination of two or more.

[0046] The negative electrode active material layer may be a deposited film of the negative electrode active material, or may be a negative electrode mixture layer containing the negative electrode active material and, as necessary, at least one of a binder and a thickener.

[0047] Examples of the binder include binders used in lithium ion secondary batteries, and the binder may be selected from the binders described for the positive electrode.

[0048] The amount of the binder in the negative electrode active material layer is, for example, 1 part by mass or more and 5 parts by mass or less with respect to 100 parts by mass of the negative electrode active material.

[0049] Examples of thickeners include those used in lithium ion secondary batteries, such as cellulose ethers, including carboxymethyl cellulose (CMC) and its salts (such as alkali metal salts, e.g., sodium salts, and ammonium salts).

[0050] The negative electrode can be formed by applying a negative electrode slurry containing a negative electrode active material and a dispersion medium to the surface of a negative electrode current collector, drying the slurry, and compressing it in the thickness direction. At least one of a binder and a thickener may be added to the negative electrode slurry. Examples of the dispersion medium that can be used include water, organic solvents such as N-methyl-2-pyrrolidone (NMP), and mixtures thereof. Alternatively, the negative electrode can be formed by depositing a negative electrode active material on the surface of a negative electrode current collector.

[0051] (separator) The separator may be, for example, a separator used in a lithium-ion secondary battery. The separator may be, for example, at least one selected from the group consisting of a microporous membrane, a woven fabric, and a nonwoven fabric. The separator may be a single layer, a composite layer, or a multilayer. The separator may contain one material or two or more materials.

[0052] The separator may be made of, for example, a resin material, such as one selected from the group consisting of polyolefin resins (such as polypropylene and polyethylene), polyamide resins, and polyimide resins.

[0053] The thickness of the separator is not particularly limited and can be appropriately selected, for example, from the range of 5 μm to 300 μm. The thickness of the microporous membrane is, for example, 5 μm to 50 μm. The thickness of the nonwoven fabric is, for example, 50 μm to 300 μm.

[0054] (non-aqueous electrolyte) The nonaqueous electrolyte contains at least one selected from the group consisting of LiSO3F and LiFSI. The nonaqueous electrolyte also contains a nonaqueous solvent. The nonaqueous electrolyte contains a solute (supporting salt). LiFSI may be used as at least a part of the solute.

[0055] By keeping the concentrations of LiSO3F and LiFSI in the non-aqueous electrolyte within a specific range, it is possible to suppress internal short circuits caused by the detachment of electrode materials, thereby suppressing initial internal short circuits and reducing capacity loss during repeated high-rate charge and discharge.

[0056] More specifically, when the non-aqueous electrolyte contains LiSO3F, the LiSO3F concentration in the non-aqueous electrolyte is 1.5% by mass or less when the outer diameter R is 3.0 mm or more and 5 mm or less, and 1.2% by mass or less when the outer diameter R is more than 5 mm and 6.5 mm or less. Furthermore, when the outer diameter R is in the range of 3.0 mm or more and 6.5 mm or less, the LiSO3F concentration in the non-aqueous electrolyte may be 1.2% by mass or less. From the viewpoint of facilitating the formation of a more uniform SEI coating with excellent film quality and achieving a greater effect in suppressing electrode material detachment, the LiSO3F concentration in the non-aqueous electrolyte may be 0.3% by mass or more, or 0.6% by mass or more. These upper and lower limits can be arbitrarily combined. The LiSO3F concentration is the value in the non-aqueous electrolyte used in assembling a pin-type secondary battery (in other words, the initial value). The LiSO3F concentration determined for the non-aqueous electrolyte sampled from the pin-type secondary battery may be within the above range. In pin-type secondary batteries, LiSO3F decomposes and forms an SEI film derived from LiSO3F, so the concentration of LiSO3F in the non-aqueous electrolyte changes, for example, during storage or use. Therefore, when analyzing a non-aqueous electrolyte sampled from a pin-type secondary battery, it is sufficient that LiSO3F remains in the non-aqueous electrolyte at a concentration equal to or greater than the detection limit. Therefore, the upper limit of the LiSO3F concentration is within the above range, and the lower limit may be equal to or greater than the detection limit.

[0057] Furthermore, when the non-aqueous electrolyte contains LiFSI, the concentration of LiFSI in the non-aqueous electrolyte is 1.1 mol / L or less when the outer diameter R is 3.0 mm or more and 3.5 mm or less, and 1.0 mol / L or less when the outer diameter R is more than 3.5 mm and 6.5 mm or less. Furthermore, when the outer diameter R is in the range of 3.0 mm or more and 6.5 mm or less, the concentration of LiFSI in the non-aqueous electrolyte may be 1.0 mol / L or less. From the viewpoint of facilitating the formation of a more uniform SEI coating with excellent film quality and achieving a greater effect in suppressing electrode material detachment, the concentration of LiFSI in the non-aqueous electrolyte may be 0.3 mol / L or more or 1.0 mol / L or more. These upper and lower limits can be arbitrarily combined. Such a LiFSI concentration is the value in the non-aqueous electrolyte used in assembling a pin-type secondary battery (in other words, the initial value). The LiFSI concentration determined for the non-aqueous electrolyte sampled from the pin-type secondary battery may be within the above range. In pin-type secondary batteries, the LiFSI concentration in the non-aqueous electrolyte changes during storage or use due to decomposition of LiFSI and the formation of an SEI film derived from LiFSI. Therefore, when analyzing a non-aqueous electrolyte sampled from a pin-type secondary battery, it is sufficient that LiFSI remains in the non-aqueous electrolyte at a concentration equal to or higher than the detection limit. Therefore, the upper limit of the LiFSI concentration is within the above range, and the lower limit may be equal to or higher than the detection limit.

[0058] Qualitative and quantitative analysis of LiSO3F and LiFSI can be performed using gas chromatography-mass spectrometry (GC-MS) with non-aqueous electrolytes.

[0059] As the supporting salt, any supporting salt (for example, lithium salt) used in lithium ion secondary batteries can be used without any particular limitation.

[0060] Examples of the supporting salt (lithium salt) that can be used include lithium salts of fluorine-containing acids (lithium hexafluorophosphate (LiPF), lithium tetrafluoroborate (LiBF), etc.), lithium perchlorate (LiClO), lithium salts of fluorine-containing acid imides (lithium bis(trifluoromethylsulfonyl)imide (LiN(CFSO)), etc.), and lithium salts of fluorine-containing acid methides (lithium tris(trifluoromethylsulfonyl)methide (LiC(CFSO)). These supporting salts may be used alone or in combination of two or more. LiFSI is included in the lithium salts of fluorine-containing acid imides and also functions as a supporting salt. The nonaqueous electrolyte may contain LiFSI and a lithium salt other than LiFSI. Furthermore, and not limited to this, the nonaqueous electrolyte may contain a lithium salt other than LiFSI as a supporting salt, as well as the above-mentioned LiSOF.

[0061] Examples of non-aqueous solvents include cyclic carbonates (including derivatives (e.g., substituted compounds having substituents)), chain carbonates (e.g., dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate (EMC)), chain ethers (e.g., 1,2-dimethoxyethane), cyclic ethers (including derivatives (e.g., substituted compounds having substituents)), lactones (e.g., γ-butyrolactone), amides (e.g., N,N-dimethylformamide, acetamide), nitriles (e.g., acetonitrile), nitroalkanes (e.g., nitromethane), sulfoxides (e.g., dimethyl sulfoxide), and sulfolane compounds (e.g., sulfolane). Examples of cyclic carbonates include propylene carbonate, ethylene carbonate (EC), butylene carbonate, vinylene carbonate, and vinylethylene carbonate. Examples of cyclic ethers include tetrahydrofuran and dioxolane. The non-aqueous electrolyte may contain one type of non-aqueous solvent or a combination of two or more types.

[0062] The concentration of the supporting salt in the non-aqueous electrolyte is not particularly limited and is, for example, 0.5 mol / L to 2 mol / L. When the non-aqueous electrolyte contains LiFSI, the concentration of the entire supporting salt, including LiFSI, may be in this range.

[0063] The non-aqueous electrolyte may contain additives other than LiSO3F or LiFSI, as necessary. Examples of additives include at least one selected from the group consisting of propane sultone, propene sultone, ethylene sulfate, vinylene carbonate (VC), fluoroethylene carbonate, and vinyl ethylene carbonate. The non-aqueous electrolyte may contain VC or may contain VC and other additives. The concentration of these additives in the non-aqueous electrolyte may be, for example, 3% by mass or less (e.g., 0.01% by mass or more and 3% by mass or less).

[0064] (battery case) The battery case is cylindrical, and typically has an opening and a bottom, and contains a wound electrode group and a non-aqueous electrolyte.

[0065] The outer diameter R of the battery case is 3.0 mm or more and 6.5 mm or less. If the outer diameter R exceeds 6.5 mm, the electrode material is less likely to fall off, and even if a non-aqueous electrolyte containing LiSO3F or LiFSI is used, the effect of suppressing the electrode material from falling off is almost nonexistent, or even if it is, the extent of the effect is small. If the outer diameter R is 3.0 mm or more and 6.5 mm or less, and the non-aqueous electrolyte contains LiSO3F or LiFSI at a specific concentration, the electrode material can be significantly suppressed from falling off, and the incidence of internal short circuits can be significantly reduced.

[0066] The thickness (maximum thickness) of the bottom of the battery case may be, for example, 0.08 mm or more and 0.2 mm or less. The thickness (maximum thickness) of the side wall of the battery case may be 0.08 mm or more and 0.2 mm or less. Note that these thicknesses are the thicknesses of the bottom and side wall of the battery case in the assembled pin-type secondary battery.

[0067] The battery case is, for example, a metal can. Examples of materials constituting the battery case include at least one selected from the group consisting of aluminum, aluminum alloys (including alloys containing trace amounts of other metals such as manganese and copper), iron, and iron alloys (including stainless steel). The battery case may be plated (e.g., nickel-plated) as needed. The material constituting the battery case can be appropriately selected depending on the polarity of the battery case, etc.

[0068] The polarity of the battery case can be determined arbitrarily. That is, the battery case may have either an external positive terminal or an external negative terminal. From the viewpoint of effective use of the volume inside the battery case, the electrode group may be formed so that the electrode having the same polarity as the battery case is located on the outermost side of the electrode group. The current collecting lead drawn from the outermost electrode is connected to the inner wall of the battery case.

[0069] (Sealing member) The pin-type secondary battery may include a cylindrical battery case with a bottom and an opening, and a sealing member that closes the opening of the battery case.

[0070] The shape of the sealing member is not particularly limited and may be a disk shape or a disk shape with the center protruding in the thickness direction (hat shape). The sealing member may or may not have a space formed inside. The hat-shaped sealing member may have a ring-shaped brim and a terminal portion protruding from the inner periphery of the brim in one direction in the thickness direction. Examples of sealing members include a ring-shaped brim and a terminal portion protruding from the inner periphery of the brim in both directions in the thickness direction. The latter has an external shape similar to two hats stacked with the brim sides facing each other. The protruding terminal portion may be cylindrical, or may be cylindrical with a top surface (or a top surface and a bottom surface). The sealing member may be provided with a safety valve.

[0071] Examples of materials that can be used for the sealing member include aluminum, aluminum alloys (including alloys containing trace amounts of other metals such as manganese and copper), iron, and iron alloys (including stainless steel). The sealing member may be plated (e.g., nickel-plated) as needed. The material that can be used for the sealing member can be selected appropriately depending on the polarity of the sealing member.

[0072] The polarity of the sealing member can be selected arbitrarily. The polarity of the sealing member is usually opposite to that of the battery case. For example, the battery case may be connected to the negative electrode and used as an external negative electrode terminal, and the sealing member may be connected to the positive electrode and used as an external positive electrode terminal. The sealing member and the negative electrode or positive electrode are electrically connected using, for example, a current collecting lead.

[0073] The opening of the battery case can be sealed with the sealing member by a known method. The sealing may be performed by welding. Alternatively, the opening of the battery case and the sealing member may be crimped together via a gasket. In crimping, for example, the opening edge of the battery case may be bent inward relative to the sealing member via the gasket.

[0074] (gasket) The gasket is interposed between the opening of the battery case (specifically, the opening edge) and the sealing member (specifically, the peripheral edge of the sealing member), insulating them from each other and ensuring airtightness inside the pin-type secondary battery.

[0075] The gasket may be, for example, a ring-like shape that covers the peripheral edge of the closure member. When a disk-shaped closure member is used, the gasket may be shaped to cover the peripheral edge of the disk, or when a hat-shaped closure member is used, the gasket may be shaped to cover the peripheral edge of the brim.

[0076] The gasket may be made of an insulating material such as a synthetic resin. Examples of such insulating materials include, without limitation, materials used in gaskets for lithium-ion secondary batteries. Specific examples of insulating materials include polyolefins, resins, polyphenylene sulfide, polyether ether ketones, polyamides, polyimides, and liquid crystal polymers. The gasket may contain one type of insulating material or a combination of two or more types.

[0077] The gasket may contain known additives (for example, fillers such as inorganic fibers) as needed.

[0078] (collecting lead) Examples of materials for the positive electrode current collector lead that electrically connects the positive electrode to the battery case or the sealing member include metals such as aluminum, titanium, and nickel, and alloys thereof.

[0079] Examples of materials for the negative electrode current collector lead that electrically connects the negative electrode to the battery case or the sealing member include metals such as copper and nickel, and alloys thereof.

[0080] The shape of each current collecting lead is not particularly limited, and may be, for example, a wire shape or a sheet shape (or ribbon shape).

[0081] (insulation ring) For example, an insulating ring (first insulating ring) is disposed between the upper portion of the electrode group and the sealing member. Also, an insulating ring (second insulating ring) may be disposed around the periphery of the sealing member.

[0082] As each insulating ring, any insulating ring used in a lithium ion secondary battery can be used without any particular limitation. The material of the insulating ring is not particularly limited as long as it is an insulating material, and may be appropriately selected from, for example, the insulating materials exemplified as the material of the gasket.

[0083] The configuration of the pin-type secondary battery (e.g., the material of the positive electrode, negative electrode, separator, battery case, sealing material, insulating ring, current collecting lead) other than the inner diameter r of the hollow portion of the electrode group, the outer diameter R of the battery case, the ratio r / R, and the concentration of LiSO3F or LiFSI in the non-aqueous electrolyte is not limited to the above example, and known configurations and compositions can be appropriately selected.

[0084] FIG. 1 is a schematic longitudinal sectional view of a pin-type secondary battery according to one embodiment of the present disclosure.

[0085] A pin-type secondary battery (cylindrical nonaqueous electrolyte secondary battery) 100 includes a bottomed cylindrical battery case 20 having an opening, a wound electrode group 10 and a nonaqueous electrolyte 90 housed in the battery case 20, and a sealing member 40 that seals the opening of the battery case 20. The electrode group 10 is formed by winding the positive electrode 11, the negative electrode 12, and the separator 13 around, for example, a winding core, such that the separator 13 is disposed between the positive electrode 11 and the negative electrode 12. After the winding core is removed, a hollow portion C is formed in the center of the electrode group 10. Therefore, the positive electrode 11, the negative electrode 12, and the separator 13 are wound around the hollow portion C. In the pin-type secondary battery of the present disclosure, the outer diameter R of the battery case 20 is 3.0 mm or more and 6.5 mm or less. Furthermore, the ratio r / R of the inner diameter r to the outer diameter R of the hollow portion C is 0.1 or more and 0.3 or less. The non-aqueous electrolyte contains at least one of LiSO3F and LiFSI at a specific concentration.

[0086] The closing member 40 is hat-shaped and includes a ring-shaped brim 40a and cylindrical terminal portions 40b and 40c. A ring-shaped insulating gasket 30 is disposed around the periphery of the closing member 40 so as to cover the brim 40a. The periphery of the closing member 40 is crimped to the open edge of the battery case 20, with the gasket 30 sandwiched between them.

[0087] A first insulating ring 50A is disposed between the upper end surface (top surface) of the electrode group 10 and the bottom surface of the sealing member 40. A donut-shaped second insulating ring 50B made of an electrically insulating material is disposed so as to cover the outer surface of the bent open end of the battery case 20 and the surface of the gasket 30 around it.

[0088] The polarities of the battery case 20 and the sealing member 40 can be determined arbitrarily. That is, the battery case 20 may be either a positive electrode terminal or a negative electrode terminal. In the example shown in Fig. 1, the battery case 20 is connected to the negative electrode 12 and used as an external negative electrode terminal, and the sealing member 40 is connected to the positive electrode 11 and used as an external positive electrode terminal.

[0089] The positive electrode 11 and the sealing member 40 are electrically connected via a positive electrode current collector lead 60. The sealing member 40 functions as a positive electrode terminal. One end of the negative electrode current collector lead 70 is connected to the inner wall of the battery case 20 at a welding point 70a. The negative electrode 12 and the battery case 20 are electrically connected via the negative electrode current collector lead 70. The battery case 20 functions as an external negative electrode terminal.

[0090] [Example] The present disclosure will be specifically described below based on examples and comparative examples, but the present invention is not limited to the following examples.

[0091] Batteries E1-E2 and C1-C3 A cylindrical nonaqueous electrolyte secondary battery (cylindrical lithium ion secondary battery) shown in FIG. 1 was fabricated according to the following procedure.

[0092] (1) Preparation of the positive electrode 11 A positive electrode slurry was prepared by mixing 100 parts by weight of lithium cobalt oxide as a positive electrode active material, 4 parts by weight of acetylene black as a conductive agent, and 4 parts by weight of PVdF as a binder with NMP as a dispersion medium. The positive electrode slurry was applied to both sides of an aluminum foil (13 μm thick) as a positive electrode current collector, dried, and then compressed in the thickness direction to produce a positive electrode 11 (81 μm thick) with a positive electrode active material layer on the surface of the positive electrode current collector. During fabrication, a region (exposed portion of the positive electrode current collector) where the positive electrode active material layer was not present was provided in the positive electrode 11 width direction (the direction parallel to the winding axis of the electrode group), and one end of a ribbon-shaped aluminum positive electrode current collector lead 60 was connected to the exposed portion of the positive electrode current collector. In addition, at both ends in the longitudinal direction (direction perpendicular to the width direction) of the positive electrode, exposed portions of the positive electrode current collector that did not have a positive electrode active material layer on either surface were formed, and an insulating adhesive tape was attached to cover the exposed portions of the positive electrode current collector to form an insulating layer.

[0093] (2) Preparation of negative electrode 12 A negative electrode slurry was prepared by mixing 100 parts by weight of artificial graphite powder as the negative electrode active material, 1 part by weight of styrene-methacrylic acid-butadiene copolymer as a binder, and 1 part by weight of CMC as a thickener. The resulting mixture was dispersed in deionized water. The negative electrode slurry was applied to both sides of a copper foil (6 μm thick) as a negative electrode current collector, dried, and then compressed in the thickness direction to produce a negative electrode 12 (109 μm thick). In the electrode group 10, exposed portions of the negative electrode current collector were formed without forming a negative electrode active material layer in the portions corresponding to the innermost and outermost peripheries of the negative electrode 12. One end of a ribbon-shaped nickel negative electrode current collector lead 70 was connected to the exposed portion of the outermost periphery of the negative electrode 12.

[0094] (3) Preparation of electrode group 10 A strip-shaped separator 13 was sandwiched between the slits of a cylindrical winding core and folded at the slits to form a two-ply stack. The separator 13, positive electrode 11, and negative electrode 12 were stacked together so that the separator 13 was interposed between the positive electrode 11 and negative electrode 12 in the wound state. The positive electrode 11 and negative electrode 12 were arranged so that the innermost end of the negative electrode 12 was close to the winding core and so that the positive electrode active material layer of the positive electrode 11 and the negative electrode active material layer of the negative electrode 12 faced each other. In this state, the positive electrode 11, negative electrode 12, and separator 13 were wound around the winding core to form a wound electrode group 10. The winding was slightly loosened, the winding core was removed, and insulating tape was applied to the end of the winding to secure the electrode group 10. The size of the winding core was selected so that the ratio r / R was 0.3 relative to the outer diameter R of the battery case of 4.0 mm. The number of turns of the electrode group was adjusted so that the ratio Ra was 98%.

[0095] (4) Preparation of non-aqueous electrolyte LiPF6, VC, and the additives shown in Table 1 were dissolved in a mixed solvent containing EC and EMC in a volume ratio of 1:2 to give concentrations shown in Table 1. In this way, a non-aqueous electrolyte was prepared. The concentration of LiPF6 in the non-aqueous electrolyte was 1.1 mol / L, and the concentration of VC was 2.5 mass%.

[0096] (5) Fabrication of Cylindrical Non-Aqueous Electrolyte Secondary Battery 100 The electrode group 10 obtained in (3) was inserted into a cylindrical battery case 20 (outer diameter R = 4.0 mm) with an opening and a bottom, formed from a nickel-plated iron plate, and the other end of the negative electrode current collector lead 70 was connected to the inner wall of the battery case 20 by welding at a welding point 70a. The welding point 70a was located closer to the opening of the battery case 20 than the upper end surface of the electrode group 10. A first insulating ring 50A was placed on top of the electrode group 10, and the other end of the positive electrode current collector lead 60, which had been pulled out from the electrode group 10, was connected to the bottom surface of the sealing member 40 through a hole in the first insulating ring 50A. At this time, a ring-shaped insulating gasket 30 was attached to the peripheral edge of the sealing member 40. The nonaqueous electrolyte prepared in (4) was poured into the battery case 20. A nickel-plated iron sealing member 40 was placed at the opening of the battery case 20, and the open end of the battery case 20 was sealed by crimping it against the periphery of the sealing member 40 with a gasket 30 interposed therebetween.

[0097] A butyl rubber-based insulating paint was applied in a doughnut shape to cover the outer surface of the open end of the bent battery case 20 and the surface of the surrounding gasket 30, thereby forming a second insulating ring 50B.

[0098] In this manner, a total of 50 cylindrical nonaqueous electrolyte secondary batteries 100 with a nominal capacity of 20.0 mAh were fabricated.

[0099] (6) Evaluation (Internal short circuit occurrence rate) The batteries were initially charged at a constant current of 1 C for 18 minutes at 25°C and then left to stand at 25°C for one week. The open circuit voltage of the batteries was then measured. If this voltage value was below the reference value (3.60 V), it was determined that an internal short circuit had occurred. For each battery, the percentage of batteries that had an internal short circuit out of 50 batteries was calculated. The percentage of batteries that had an internal short circuit, with the percentage of batteries that had an internal short circuit in C1 being set at 100%, was used to evaluate the internal short circuit occurrence rate (%).

[0100] The results are shown in Table 1. In Table 1, E1 and E2 are examples, and C1 to C3 are comparative examples.

[0101] [Table 1]

[0102] As shown in Table 1, when the non-aqueous electrolyte contains FEC or PS, the effect of suppressing internal short circuits is not significantly different from that of C1, which does not contain any additives other than VC (comparison of C1 with C2 and C3). In contrast, E1 and E2, which contain LiSO3F in the non-aqueous electrolyte, are able to significantly reduce the rate of internal short circuits. This is thought to be because the action of LiSO3F suppresses the detachment of the negative electrode material.

[0103] Batteries E3 to E5 and C4 to C8 The size of the winding core used to prepare the electrode group was changed so that the ratio r / R, relative to the outer diameter R of the battery case of 4.0 mm, would be the value shown in Table 2. A total of 50 cylindrical nonaqueous electrolyte secondary batteries were prepared for each example in the same manner as for Battery C1 or Battery E2, and the internal short-circuit occurrence rate was evaluated. In all batteries, the outer diameter R of the battery case was 4.0 mm.

[0104] The results are shown in Table 2. In Table 2, the numerical values ​​in the upper row indicate the internal short-circuit occurrence rate, and the symbols in the lower row indicate the battery number. In Table 2, for each value of the ratio r / R, the internal short-circuit occurrence rate when the LiSO3F concentration is 0 mass% is set to 100%, and the internal short-circuit occurrence rate when the LiSO3F concentration is 1.2 mass% is shown as a relative value. Table 2 also shows the results for batteries C1 and E2. In Table 2, E2 to E5 are working examples, and C1 and C4 to C8 are comparative examples.

[0105] [Table 2]

[0106] As shown in Table 2, when the ratio r / R is greater than 0.3, there is no difference in the internal short circuit occurrence rate between cases where the non-aqueous electrolyte contains and does not contain LiSO3F. When the ratio r / R is greater than 0.3, even if the action of LiSO3F suppresses the shedding of the negative electrode material, it is thought that there is little effect in suppressing the occurrence of internal short circuits. In contrast, when the ratio r / R is 0.1 or greater but 0.3 or less, the internal short circuit occurrence rate is significantly reduced when the non-aqueous electrolyte contains LiSO3F compared to when it does not contain LiSO3F. This is thought to be because, while the internal short circuit occurrence rate increases significantly when the ratio r / R is 0.3 or less, the action of LiSO3F suppresses the shedding of the negative electrode material, thereby effectively suppressing internal short circuits.

[0107] Batteries E6 to E14 and C9 to C21 A battery case with an outer diameter R shown in Table 3 was used, and the size of the winding core was changed so that the r / R ratio was the value shown in Table 3. The number of windings of the electrode group was adjusted so that the ratio Ra was 98%. A nonaqueous electrolyte with a LiSO3F concentration shown in Table 3 was used. Other than these, cylindrical nonaqueous electrolyte secondary batteries were fabricated in the same manner as Battery E1 or Battery C1, and the internal short-circuit occurrence rate was evaluated. The nominal capacity of each battery was 13.0 mAh (R = 3.0 mm), 20.0 mAh (R = 4.0 mm), 52.0 mAh (R = 6.5 mm), 120 mAh (R = 9.0 mm), or 450 mAh (R = 18 mm).

[0108] (Area of ​​negative electrode material falling off) The batteries were initially charged using the above procedure and allowed to stand at 25°C for one week. For C9, C1, and C10-C12, each with a LiSO3F concentration of 0% by mass, and E8, E2, E14, C16, and C20, each with a LiSO3F concentration of 1.2% by mass, the batteries were disassembled to determine the area of ​​the portion of the negative electrode where the negative electrode mixture layer had fallen off, and the ratio (area %) of this area to the area of ​​the portion of the negative electrode where the negative electrode mixture layer was formed was calculated. For each example, the area ratio of the portion of the negative electrode mixture layer where the negative electrode mixture layer had fallen off was calculated for three samples, and the average (area %) was calculated. This average value was used as an index of the initial area of ​​electrode material loss in the negative electrode.

[0109] (High rate cycle characteristics) The batteries were initially charged using the above procedure, allowed to stand at 25°C for one week, and then subjected to the following charge and discharge cycles (first charge / discharge cycle). The discharge voltage during this cycle was monitored to determine the discharge capacity, which was designated as the initial discharge capacity (mAh). The following charge / discharge cycles were then repeated at 20°C for a total of 1,000 cycles, including the first charge / discharge cycle. The discharge voltage during the 1,000th cycle was monitored to determine the discharge capacity (mAh). For each example, the average values ​​of the initial discharge capacity and the discharge capacity at the 1,000th cycle were determined for three batteries. The ratio (%) of the average value of the discharge capacity at the 1,000th cycle to the average value of the initial discharge capacity was defined as 100%, and the capacity retention rate (%) was calculated. The capacity retention rate in the high-rate cycle test was evaluated for each outer diameter R based on the relative value (%) when the capacity retention rate at a LiSO₃F concentration of 0% by mass was defined as 100%.

[0110] Charging: Charge at a constant current of 3C up to 4.35V, then charge at a constant voltage of 0.05C at 4.35V.

[0111] Discharge: Discharge at a constant current of 1C down to 3.0V.

[0112] The results of the internal short-circuit incidence rate are shown in Table 3. In Table 3, the numerical values ​​in the upper row indicate the internal short-circuit incidence rate, and the symbols in the lower row indicate the battery number. In Table 3, for each value of outer diameter R, the internal short-circuit incidence rate when the LiSO3F concentration is 0 mass% is set to 100%, and the internal short-circuit incidence rate at each LiSO3F concentration is shown as a relative value (%). Table 3 also shows the results for C1, E1, and E2. In Table 3, E1, E2, and E6 to E14 are working examples, and C1 and C9 to C21 are comparative examples.

[0113] [Table 3]

[0114] As shown in Table 3, when the outer diameter R exceeds 6.5 mm, the effect of using a nonaqueous electrolyte containing LiSO3F is low in reducing the rate of internal short-circuit occurrence. In this case, increasing the concentration of LiSO3F does not significantly change the rate of internal short-circuit occurrence (compare C11 with C14 to C17, and C12 with C18 to C21). In contrast, when the outer diameter R is in the range of 3.0 to 6.5 mm, using a nonaqueous electrolyte containing LiSO3F at a specific concentration can significantly reduce the rate of internal short-circuit occurrence.

[0115] Table 4 shows the ratio of the detached area of ​​the negative electrode mixture layer when the LiSO3F concentration was 0 mass% and 1.2 mass%. The code below the detached area ratio indicates the battery number. For each outer diameter R, the ratio of the detached area when the LiSO3F concentration was 1.2 mass% is shown as a ratio indicating the detachment improvement effect, assuming that the detached area ratio when the LiSO3F concentration was 0 mass% is 100%. The smaller this ratio, the more the detachment of the negative electrode mixture is suppressed.

[0116] [Table 4]

[0117] As shown in Table 4, when the outer diameter R exceeds 6.5 mm, the area of ​​the negative electrode mixture layer that falls off is inherently small (C11, C12). In this case, even if a nonaqueous electrolyte containing LiSO3F is used, the effect of reducing the area of ​​the negative electrode mixture layer is small (comparison between C11 and C16, and between C12 and C20). In contrast, when the outer diameter R is 3.0 to 6.5 mm, the area of ​​the negative electrode mixture layer that falls off is large (comparison between C11 and C16 and C9, C1 and C10). Even in cases where the negative electrode mixture layer is prone to falling off, the use of a nonaqueous electrolyte containing LiSO3F can significantly suppress the falling off of the negative electrode mixture layer (comparison between C9, C1 and C10 and E8, E2 and E14). The extent of the effect of reducing the falling off is significantly greater when the outer diameter R is 3.0 to 6.5 mm than when the outer diameter R exceeds 6.5 mm. The trend shown in Table 4 is relatively similar to the trend of the internal short circuit occurrence rate when the LiSO3F concentration is 1.2 mass% in Table 3, so it is thought that the occurrence of internal short circuits is reduced by suppressing the detachment of the negative electrode mixture layer.

[0118] Table 5 shows the relative values ​​of the capacity retention rate after 1000 high-rate charge / discharge cycles. The values ​​in the upper row are relative values ​​for each outer diameter R, with the capacity retention rate when the LiSO3F concentration is 0 mass% being taken as 100%. The symbols in the lower row indicate the battery number.

[0119] [Table 5]

[0120] As shown in Table 5, when the outer diameter R exceeds 6.5 mm, the improvement in capacity retention during repeated high-rate charge-discharge cycles is relatively small, even when a nonaqueous electrolyte containing LiSO3F is used (comparison between C11 and C14 to C17, and comparison between C12 and C18 to C21). In contrast, when the outer diameter R is 3.0 to 6.5 mm, when a nonaqueous electrolyte containing LiSO3F at a specific concentration is used, the capacity retention during repeated high-rate charge-discharge cycles is significantly improved (comparison between C9 and E6 to E9, comparison between C1 and E10, E1, E2, and E11, and comparison between C10 and E12 to E14).

[0121] Batteries E15 to E24 and C22 to C36 A nonaqueous electrolyte prepared using LiFSI instead of LiSO3F was used. The concentration of LiFSI in each nonaqueous electrolyte is shown in Table 6. The LiPF6 concentration was adjusted so that the total concentration of LiPF6 and LiFSI was 1.1 mol / L. A battery case with an outer diameter R shown in Table 6 was used, and the size of the winding core was changed so that the r / R ratio was shown in Table 6. The number of windings of the electrode group was adjusted so that the ratio Ra was 98%. Except for these, cylindrical nonaqueous electrolyte secondary batteries were fabricated in the same manner as Battery E1 or Battery C1, and the internal short-circuit occurrence rate was evaluated.

[0122] The results are shown in Table 6. In Table 6, the numerical values ​​in the upper row indicate the internal short-circuit incidence rate, and the symbols in the lower row indicate the battery number. In Table 6, for each value of outer diameter R, the internal short-circuit incidence rate when the LiFSI concentration was 0 mol / L is set to 100%, and the internal short-circuit incidence rate at each LiFSI concentration is shown as a relative value (%). In Table 6, E15 to E24 are working examples, and C22 to C36 are comparative examples.

[0123] [Table 6]

[0124] As shown in Table 6, the use of LiFSI also produces effects similar to those of LiSO3F as shown in Table 3. More specifically, when the outer diameter R exceeds 6.5 mm, the effect of reducing the internal short-circuit occurrence rate is low even when a nonaqueous electrolyte containing LiFSI is used. In this case, increasing the LiFSI concentration does not significantly change the internal short-circuit occurrence rate (comparison between C25 and C29 to C32, and comparison between C26 and C33 to C36). In contrast, when the outer diameter R is in the range of 3.0 to 6.5 mm, using a nonaqueous electrolyte containing LiFSI at a specific concentration can significantly reduce the internal short-circuit occurrence rate (comparison between C22 and E15 to E18, comparison between C23 and E19 to E21, and comparison between C24 and E22 to E24).

[0125] Furthermore, when a non-aqueous electrolyte containing LiFSI was used, trends similar to those in Tables 4 and 5 were observed.

[0126] Batteries E25-E27 and C37-C38 A nonaqueous electrolyte containing both LiSO3F and LiFSI was used. The concentration of LiSO3F in each nonaqueous electrolyte was 1.2 mass%, and the concentration of LiFSI was 0.5 mol / L. The concentration of LiPF6 was adjusted so that the total concentration of LiPF6 and LiFSI was 1.1 mol / L. A battery case with an outer diameter R shown in Table 7 was used, and the size of the winding core was changed so that the r / R value shown in Table 7 was obtained. The number of windings of the electrode group was adjusted so that the ratio Ra was 98%. Except for these, a cylindrical nonaqueous electrolyte secondary battery was fabricated in the same manner as battery E1, and the internal short-circuit occurrence rate was evaluated.

[0127] The results are shown in Table 7. In Table 7, the numerical values ​​in the upper row indicate the internal short-circuit occurrence rate, and the symbols in the lower row indicate the battery number. Table 7 also shows the results for C1 and C9 to C12. In Table 7, for each value of outer diameter R, the internal short-circuit occurrence rate of each battery is shown as a relative value (%) when the internal short-circuit occurrence rate when the LiSO3F concentration was 0 mass% (C1 and C9 to C12) is set to 100%. In Table 7, E25 to E27 are working examples, and C1, C9 to C11 and C37 to C38 are comparative examples.

[0128] [Table 7]

[0129] As shown in Table 7, even when the non-aqueous electrolyte contained both LiSO3F and LiFSI, the incidence of internal short circuits could be kept low. [Industrial Applicability]

[0130] The cylindrical nonaqueous electrolyte secondary battery of the present disclosure can suppress initial internal short circuits and ensure a high capacity retention rate even when repeatedly charged and discharged (especially charged and discharged at high rates). Therefore, the battery can be used in a variety of applications requiring high capacity, high-rate cycle characteristics, reliability, long life, etc., such as as a power source for various electronic devices. In particular, the cylindrical nonaqueous electrolyte secondary battery of the present disclosure is compact and therefore suitable for use as a power source for various portable electronic devices (including eyeglasses (e.g., 3D eyeglasses), hearing aids, stylus pens, and wearable devices (e.g., earphones, smartwatches, etc.)). [Explanation of symbols]

[0131] 100 Cylindrical non-aqueous electrolyte secondary battery 10 winding electrode group C Hollow part 11 Positive electrode 12 Negative electrode 13 Separator 20 Battery case 30 gaskets 40 Sealing material 40a Brim 40b,40c terminal section 50A First Insulation Ring 50B Second insulating ring 60 Positive current collector lead 70 Negative electrode current collector lead 70a welding point r Inner diameter of hollow part R Battery case outer diameter

Claims

1. A cylindrical battery case; a wound electrode group and a nonaqueous electrolyte housed in the battery case, the outer diameter R of the battery case is 3.0 mm or more and 6.5 mm or less, The electrode group has one or more electrodes wound around the hollow portion, a ratio r / R of an inner diameter r of the hollow portion of the electrode group to an outer diameter R is 0.1 or more and 0.3 or less; The non-aqueous electrolyte is LiSO ３ Contains at least one selected from the group consisting of F and LiFSI; The non-aqueous electrolyte is LiSO ３ When F is contained, LiSO in the non-aqueous electrolyte ３ the concentration of F is 0.3 mass% or more and 1.5 mass% or less when the outer diameter R is 3.0 mm or more and 5 mm or less, and is 0.3 mass% or more and 1.2 mass% or less when the outer diameter R is more than 5 mm and 6.5 mm or less; a cylindrical nonaqueous electrolyte secondary battery, wherein the nonaqueous electrolyte contains LiFSI, and the concentration of LiFSI in the nonaqueous electrolyte is 0.3 mol / L or more and 1.1 mol / L or less when the outer diameter R is 3.0 mm or more and 3.5 mm or less, and is 0.3 mol / L or more and 1.0 mol / L or less when the outer diameter R is more than 3.5 mm and 6.5 mm or less.

2. LiSO in the nonaqueous electrolyte ３ The concentration of F is 1.2% by mass or less, 2. The cylindrical nonaqueous electrolyte secondary battery according to claim 1, wherein the concentration of LiFSI in the nonaqueous electrolyte is 1.0 mol / L or less.

3. The non-aqueous electrolyte contains at least LiSO ３ 3. The cylindrical nonaqueous electrolyte secondary battery according to claim 1, further comprising F.

4. The non-aqueous electrolyte is LiSO ３ 3. The cylindrical nonaqueous electrolyte secondary battery according to claim 1, comprising both F and LiFSI.

5. 3. The cylindrical nonaqueous electrolyte secondary battery according to claim 1, wherein the ratio r / R is 0.1 or more and 0.2 or less.

6. the one or more electrodes of the electrode group include a positive electrode and a negative electrode; the electrode group further includes a separator interposed between the positive electrode and the negative electrode, 3. The cylindrical nonaqueous electrolyte secondary battery according to claim 1, wherein in the electrode group, the innermost end of the negative electrode is located closer to the inner periphery than the innermost end of the positive electrode.

7. A method for manufacturing a cylindrical nonaqueous electrolyte secondary battery, comprising: The cylindrical nonaqueous electrolyte secondary battery comprises: A cylindrical battery case; a wound electrode group and a nonaqueous electrolyte housed in the battery case, the outer diameter R of the battery case is 3.0 mm or more and 6.5 mm or less, The electrode group has one or more electrodes wound around the hollow portion, a ratio r / R of an inner diameter r of the hollow portion of the electrode group to an outer diameter R is 0.1 or more and 0.3 or less; The manufacturing method includes: a step of housing a non-aqueous electrolyte (X) containing at least one selected from the group consisting of LiSO 3 F and LiFSI in the battery case; When the non-aqueous electrolyte (X) contains LiSO 3 F, the concentration of LiSO 3 F in the non-aqueous electrolyte (X) is 0.3 mass% or more and 1.5 mass% or less when the outer diameter R is 3.0 mm or more and 5 mm or less, and is 0.3 mass% or more and 1.2 mass% or less when the outer diameter R is more than 5 mm and 6.5 mm or less, a method for producing a cylindrical nonaqueous electrolyte secondary battery, wherein, when the nonaqueous electrolyte (X) contains LiFSI, the concentration of LiFSI in the nonaqueous electrolyte (X) is 0.3 mol / L or more and 1.1 mol / L or less when the outer diameter R is 3.0 mm or more and 3.5 mm or less, and is 0.3 mol / L or more and 1.0 mol / L or less when the outer diameter R is more than 3.5 mm and 6.5 mm or less.

Images