Coin-shaped nonaqueous electrolyte secondary battery

Abstract

Disclosed is a coin-shaped nonaqueous electrolyte secondary battery which includes: a negative electrode containing a conductive material and titanium oxide which is a negative electrode active material; a positive electrode containing a positive electrode active material; a nonaqueous electrolyte containing a nonaqueous solvent and a solute dissolved in the nonaqueous solvent; and an exterior body for accommodating the negative electrode, the positive electrode, and the nonaqueous electrolyte. The exterior body includes a negative electrode case that accommodates the negative electrode. A conductive layer containing a carbon material is disposed on the inner surface of the negative electrode case. The negative electrode is electrically connected to the negative electrode case via the conductive layer. The conductive material includes single-walled carbon nanotubes. The content of γ-butyrolactone in the nonaqueous solvent is 80 vol% or more. The content of LiBF4 in the solute is 10 mol% or more.

Description

Coin-shaped non-aqueous electrolyte secondary battery

[0001] The present disclosure relates to a coin-shaped non-aqueous electrolyte secondary battery.

[0002] Conventionally, various non-aqueous electrolyte secondary batteries have been proposed. In claim 1 of Patent Document 1 (Japanese Patent Application Laid-Open No. 2015-201335), "a lithium-ion battery including a positive electrode, a negative electrode, and an electrolytic solution, wherein the positive electrode has a current collector and a positive electrode composite material applied to at least one surface of the current collector, and the positive electrode composite material includes a lithium manganese nickel composite oxide having a BET specific surface area of less than 0.3 m ２ / g and a positive electrode conductive material, and the negative electrode includes a lithium titanium composite oxide and a negative electrode conductive material as a negative electrode active material." is described.

[0003] In claim 1 of Patent Document 2 (Japanese Patent Application Laid-Open No. 2007-26845), "a coin-type lithium battery including a positive electrode, a negative electrode, an electrolytic solution, and a gasket, wherein the gasket is a tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), and the wetting tension of the surface thereof is -10.0 mN / m or more." is described.

[0004] Japanese Patent Application Laid-Open No. 2015-201335 Japanese Patent Application Laid-Open No. 2007-26845

[0005] In recent years, it has been required that a coin-shaped non-aqueous electrolyte secondary battery can exhibit good discharge characteristics even after continuous charging in a high-temperature environment of 85°C or higher.

[0006] One aspect of the present disclosure relates to a coin-shaped nonaqueous electrolyte secondary battery. The coin-shaped nonaqueous electrolyte secondary battery includes: a negative electrode containing a conductive material and titanium oxide as a negative electrode active material; a positive electrode containing a positive electrode active material; a nonaqueous electrolyte containing a nonaqueous solvent and a solute dissolved in the nonaqueous solvent; and an exterior housing that houses the positive electrode, the negative electrode, and the nonaqueous electrolyte, wherein the exterior housing includes a negative electrode case that defines an internal space for housing the negative electrode and has an inner surface facing the internal space, and a conductive layer that contains a carbon material and is disposed on the internal surface of the negative electrode case, wherein the negative electrode is electrically connected to the negative electrode case via the conductive layer, the conductive material contains single-walled carbon nanotubes, the nonaqueous solvent contains 80% by volume or more of γ-butyrolactone, and the solute contains LiBF ４ The content is 10 mol % or more.

[0007] According to the present disclosure, a coin-type nonaqueous electrolyte secondary battery can be obtained that can exhibit good discharge characteristics even after continuous charging in a high-temperature environment.

[0008] Fig. 1 is a cross-sectional view schematically showing a coin-type nonaqueous electrolyte secondary battery of Embodiment 1. Fig. 2 is a cross-sectional view schematically showing the periphery of a conductive layer of the secondary battery shown in Fig. 1. Fig. 3 is a view showing evaluation results of the coin-type nonaqueous electrolyte secondary battery of Embodiment 1.

[0009] The following describes embodiments of the present disclosure using examples, but the present disclosure is not limited to the examples described below. In the following description, specific numerical values ​​and materials may be exemplified, but other numerical values ​​and other materials may be applied as long as the invention of the present disclosure can be implemented. In this specification, the term "numerical value A to numerical value B" includes numerical value A and numerical value B and can be read as "numerical value A or greater and numerical value B or less." In the following description, when lower and upper limits of numerical values ​​related to specific physical properties or conditions are exemplified, any of the exemplified lower limits and any of the exemplified upper limits can be arbitrarily combined, as long as the lower limit is not greater than the upper limit. In the following description, when examples of components or methods are listed, only one of the listed examples may be used, or multiple of the listed examples may be used in combination, unless otherwise specified.

[0010] (Non-aqueous electrolyte secondary battery) The coin-type non-aqueous electrolyte secondary battery according to this embodiment will be described below. The coin-type non-aqueous electrolyte secondary battery may be referred to as "secondary battery (S)" hereinafter.

[0011] The secondary battery (S) includes a negative electrode containing a conductive material and titanium oxide as a negative electrode active material, a positive electrode containing a positive electrode active material, a non-aqueous electrolyte, and an exterior housing that houses the positive electrode, the negative electrode, and the non-aqueous electrolyte. The exterior housing includes a negative electrode case that defines an internal space that houses the negative electrode and has an internal surface facing the internal space. A conductive layer containing a carbon material is disposed on the internal surface of the negative electrode case. The negative electrode is electrically connected to the negative electrode case via the conductive layer. The conductive material of the negative electrode includes single-walled carbon nanotubes. The content of γ-butyrolactone in the non-aqueous solvent of the non-aqueous electrolyte is 80% by volume or more. LiBF in the solute of the non-aqueous electrolyte ４ The content is 10 mol % or more.

[0012] As will be described in the Examples, the secondary battery (S) having the above configuration can exhibit good discharge characteristics even after continuous charging in a high-temperature environment of 85° C. or higher. The reason for this is not yet clear, but it is believed that a special synergistic effect is obtained by combining the above configurations.

[0013] (Negative electrode) As described above, the negative electrode contains titanium oxide (negative electrode active material) and a conductive material. The negative electrode may contain other additives (e.g., a binder, etc.) as needed. The additives are not particularly limited, and known additives may be used.

[0014] The conductive material of the negative electrode includes single-walled carbon nanotubes (SWCNT). Single-walled carbon nanotubes are characterized by their smaller diameter compared to multi-walled carbon nanotubes (MWCNT), which have a structure with two or more layers. The use of single-walled carbon nanotubes can increase the conductivity within the negative electrode, which may result in improved battery characteristics in high-temperature environments.

[0015] The conductive material of the negative electrode may contain a conductive material other than single-walled carbon nanotubes. However, the proportion of single-walled carbon nanotubes in the conductive material of the negative electrode is preferably 50% by mass or more and 100% by mass or less. The content may be 80% by mass or more, 90% by mass or more, or 95% by mass or more. The conductive material of the negative electrode may consist solely of single-walled carbon nanotubes.

[0016] The other conductive material that can be used as the conductive material for the negative electrode is not particularly limited, and a known conductive material that is used as a conductive material for the negative electrode of a non-aqueous electrolyte secondary battery may be used. Examples of the other conductive material include conductive carbon materials, such as carbon black, graphite, multi-walled carbon nanotubes, and carbon fibers (carbon fibers other than carbon nanotubes).

[0017] Single-walled carbon nanotubes differ from multi-walled carbon nanotubes. For example, single-walled carbon nanotubes differ from multi-walled carbon nanotubes, which have larger diameters, in that their diameters are typically 3 nm or less. Commercially available single-walled carbon nanotubes and multi-walled carbon nanotubes may be used. The average length of the single-walled carbon nanotubes is preferably 3,000 nm or more, or 5,000 nm or more. Here, the average length is determined by arithmetically averaging the lengths of 20 randomly selected single-walled carbon nanotubes.

[0018] The content of the single-walled carbon nanotubes in the negative electrode may be 0.05% by mass or more, 0.1% by mass or more, or 0.5% by mass or more, and may be 4% by mass or less, or 2% by mass or less. By setting the content to 0.1% by mass or more, particularly high effects can be obtained.

[0019] Titanium oxide capable of reversibly absorbing and releasing lithium ions is used as the negative electrode active material. A lithium titanium composite oxide can be used as the titanium oxide (negative electrode active material). The titanium oxide may be lithium titanate. Lithium titanate is preferred because of its high high temperature resistance. Examples of lithium titanate include lithium titanate having a spinel structure. An example of lithium titanate having a spinel structure is represented by the composition formula Li ４ Ti ５ O １２ It is expressed as:

[0020] The binder used in the negative electrode is not particularly limited, and known binders may be used. Examples of binders include acrylic resins, polyolefin resins, polyamide resins, polyimide resins, fluororesins, and rubber. Examples of acrylic resins include polyacrylic acid, polymethacrylic acid, sodium polyacrylate, sodium polymethacrylate, and acrylic acid-ethylene copolymers. Examples of fluororesins include polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), and vinylidene fluoride-hexafluoropropylene copolymer. Examples of rubbers include styrene-butadiene copolymer (SBR), ethylene-propylene-diene copolymer, and the like.

[0021] The method for producing the negative electrode is not particularly limited, and the negative electrode may be produced by a known method. In one example of the production method, first, the negative electrode materials (and a dispersion medium, if necessary) are mixed to prepare a negative electrode mixture. Next, the negative electrode mixture is dried as necessary, and then molded into coin-shaped pellets to obtain the negative electrode.

[0022] (Positive electrode) The positive electrode contains a positive electrode active material and other additives (e.g., a conductive material, a binder, etc.). The additives are not particularly limited, and known additives may be used. The conductive material and binder may be the same as those exemplified as the materials for the negative electrode.

[0023] The positive electrode active material is a material that can reversibly absorb and release lithium ions. Examples of the positive electrode active material include lithium cobalt oxide (LiCoO ２ ), lithium nickel oxide (LiNiO ２ ), lithium iron phosphate (LiFePO ４ ), general formula: Li ｘ MnO ｙ The positive electrode active material includes lithium-containing manganese oxides and lithium-containing transition metal oxides represented by the formula: ２ and LiCoO ２ From the viewpoint of increasing capacity, the lithium-containing transition metal oxide may be a composite oxide containing lithium and nickel and having a layered rock salt type crystal structure (hereinafter, may be referred to as "composite oxide N").

[0024] The composite oxide N has the general formula: Li α Ni ｘ１ M1 ｘ２ M2 （１－ｘ１－ｘ２） O ２＋β In this formula, the following conditions are satisfied: 0.9≦α≦1.1, -0.05≦β≦0.05, 0.5≦x1<1, 0≦x2≦0.5, 0≦1-x1-x2≦0.5. The element M1 is at least one element selected from the group consisting of V, Co, and Mn. The element M2 is at least one element selected from the group consisting of Mg, Al, Ca, Ti, Cu, Zn, and Nb. α increases or decreases with charge and discharge. The composite oxide N is LiNi １／３ Mn １／３ Co １／３ O ２ , LiNi ０．８ Mn ０．１ Co ０．１ O ２ Lithium nickel-cobalt-manganese oxide such as

[0025] The positive electrode active material is LiCoO ２ and LiCoO ２ LiCoO ２ is preferable in terms of excellent output characteristics.

[0026] The manufacturing method of the positive electrode is not particularly limited, and may be a known method. In one example of the manufacturing method, first, the positive electrode material (and a dispersion medium, if necessary) are mixed to prepare a positive electrode mixture. Next, the positive electrode mixture is dried as necessary, and then molded into a coin-shaped pellet to obtain a positive electrode.

[0027] (Non-aqueous electrolyte) The non-aqueous electrolyte (non-aqueous electrolyte solution) contains a non-aqueous solvent and a solute (lithium salt) dissolved in the non-aqueous solvent. The concentration of the lithium salt in the non-aqueous electrolyte may be 0.3 mol / L or more and 2 mol / L or less. The non-aqueous electrolyte may contain known additives.

[0028] As described above, the content of γ-butyrolactone in the non-aqueous solvent is 80% by volume or more, or may be 90% by volume or more, or 95% by volume or more. The non-aqueous solvent may contain only γ-butyrolactone.

[0029] As mentioned above, the solute (lithium salt) is LiBF ４ The content of LiBF is 10 mol% or more, and may be 30 mol% or more, 50 mol% or more, or 80 mol% or more. The solute (lithium salt) contains LiBF ４ Only may be used.

[0030] The nonaqueous solvent may contain a nonaqueous solvent other than γ-butyrolactone. The nonaqueous solvent other than γ-butyrolactone is not particularly limited, and nonaqueous solvents used in known nonaqueous electrolyte secondary batteries may be used. Examples of nonaqueous solvents include cyclic carbonates, chain carbonates, and cyclic carboxylic acid esters. Examples of cyclic carbonates include propylene carbonate, ethylene carbonate, and fluoroethylene carbonate. Examples of chain carbonates include diethyl carbonate, ethyl methyl carbonate, and dimethyl carbonate. Examples of cyclic carboxylic acid esters include γ-butyrolactone and γ-valerolactone.

[0031] The solute (lithium salt) is LiBF ４ It may contain solutes other than LiBF. ４The solute other than LiBF is not particularly limited, and a solute used in a known non-aqueous electrolyte secondary battery may be used. ４ Examples of solutes other than chlorine include lithium salts of chlorine-containing acids (LiClO ４ , LiAlCl ４ , LiB １０ Cl １０ etc.), lithium salts of fluorine-containing acids (LiPF ６ , LiSbF ６ , LiAsF ６ , LiCF ３ SO ３ , LiCF ３ CO ２ etc.), lithium salt of fluorine-containing acid imide (LiN(SO ２ F) ２ , LiN(CF ３ SO ２ ) ２ , LiN(CF ３ SO ２ ) (C ４ F ９ SO ２ ), LiN(C ２ F ５ SO ２ ) ２ The non-aqueous electrolyte includes lithium halides (LiCl, LiBr, LiI, etc.), and lithium halides (LiBF, LiBF, etc.). ４ As a solute other than LiN(CF ３ SO ２ ) ２ and LiN(C ２ F ５ SO ２ ) ２ may contain at least one selected from the group consisting of:

[0032] (Exterior Body) The exterior body houses a positive electrode, a negative electrode, a separator disposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte. The exterior body usually includes a positive electrode case, a negative electrode case, and a gasket. The positive electrode case houses the positive electrode. The positive electrode case is in contact with the positive electrode and functions as a positive electrode terminal. The negative electrode case houses the negative electrode. The negative electrode case is in contact with the negative electrode and functions as a negative electrode terminal.

[0033] Except for the conductive layer formed on the inner surface of the negative electrode case, the positive electrode case, the negative electrode case, and the gasket are not particularly limited and may be formed from known materials. For example, the positive electrode case and the negative electrode case may each be formed from stainless steel (e.g., highly corrosion-resistant stainless steel). The gasket may be formed from polypropylene or a highly heat-resistant resin (e.g., tetrafluoroethylene-perfluoroalkoxyethylene copolymer (PFA), polyphenylene sulfide (PPS), polyether ether ketone (PEEK)).

[0034] A conductive layer containing a carbon material is disposed on the inner surface of the negative electrode case. The negative electrode is electrically connected to the negative electrode case via the conductive layer. The conductive layer is formed on at least a region of the inner surface of the negative electrode case that faces the negative electrode. The conductive layer may be formed on the entire inner surface of the negative electrode case.

[0035] The carbon material used for the conductive layer may be a conductive carbon material. The carbon material may be any of the carbon materials exemplified as the conductive material for the negative electrode. For example, the conductive layer may contain single-walled carbon nanotubes. That is, the carbon material used for the conductive layer may be composed of single-walled carbon nanotubes alone, or may be composed of single-walled carbon nanotubes and other carbon materials.

[0036] The conductive layer may be formed on the entire inner surface of the negative electrode case, or may be formed only on the region of the inner surface of the negative electrode case that faces the negative electrode.

[0037] The conductive layer may contain additives such as a binder as needed. The binder may be any of the materials exemplified as binders for the negative electrode. The content of the carbon material in the conductive layer may be 50% by mass or more, or 60% by mass or more, and may be 95% by mass or less, or 90% by mass or less.

[0038] The method for forming the conductive layer is not particularly limited, and the conductive layer may be formed by a known method. For example, the conductive layer may be formed by applying a paste containing a binder and a conductive material to the negative electrode case and then drying the paste.

[0039] As described above, the secondary battery (S) includes a positive electrode, a negative electrode, and a non-aqueous electrolyte. Components of the secondary battery (S) other than the above-described components are not particularly limited. The secondary battery (S) further includes a separator disposed between the positive electrode and the negative electrode. The electrode group including the positive electrode, the negative electrode, and the separator is housed in an exterior body together with the non-aqueous electrolyte.

[0040] (Separator) The separator is not particularly limited, and separators used in known non-aqueous electrolyte secondary batteries may be used. An insulating porous film may be used as the separator. Examples of porous films include microporous films, woven fabrics, and nonwoven fabrics. Examples of separator materials include polyolefins (polyethylene, polypropylene, etc.), high-heat-resistant resins (polyphenylene sulfide (PPS), polyether ether ketone (PEEK), etc.), and other insulating resin materials.

[0041] The secondary battery (S) can be used in various environments, but is particularly suitable for use at high temperatures. The secondary battery (S) may be used in an environment of 85° C. or higher, or may be used in an environment of less than 85° C. The temperature of the usage environment may be 150° C. or lower.

[0042] The secondary battery (S) has a shape known as a coin shape. Specifically, the secondary battery (S) has a low cylindrical shape. The diameter of the secondary battery (S) may be, for example, in the range of 6 mm to 30 mm. The height of the secondary battery (S) may be, for example, in the range of 1.2 mm to 5.0 mm.

[0043] (Method for Manufacturing Secondary Battery (S)) The method for manufacturing the secondary battery (S) is not particularly limited, and any steps used in the manufacturing method of known coin-type non-aqueous electrolyte secondary batteries may be used.

[0044] In one example of a manufacturing method, first, each component of the secondary battery (S) is prepared. A negative electrode case having a positive electrode, a negative electrode, and a conductive layer formed thereon may be produced by the method described above. Next, the positive electrode, the negative electrode, the separator, and the non-aqueous electrolyte are housed in an exterior body, and the exterior body is sealed. At this time, each component is housed in the exterior body so that the negative electrode is electrically connected to the negative electrode case via the conductive layer, and the separator is disposed between the positive electrode and the negative electrode. In this manner, the secondary battery (S) is produced.

[0045] An example of a secondary battery (S) according to the present embodiment will be specifically described below with reference to the drawings. The components described above can be applied to the components of the example secondary battery described below. Furthermore, the components of the example described below can be modified based on the above description. Furthermore, the matters described below may be applied to the above embodiment. Furthermore, in the secondary battery described below, components that are not essential for the secondary battery (S) according to the present disclosure may be omitted.

[0046] (Embodiment 1) As an example of a secondary battery (S), a cross section of a coin-type nonaqueous electrolyte secondary battery 10 is shown schematically in Fig. 1. Note that the conductive layer formed on the inner surface of the negative electrode case is not shown in Fig. 1. An enlarged cross section of the conductive layer and its surroundings is shown schematically in Fig. 2.

[0047] The secondary battery 10 includes a positive electrode 11, a negative electrode 12, a separator 13 disposed between the positive electrode 11 and the negative electrode 12, a non-aqueous electrolyte 113, and an exterior body 20. The exterior body 20 includes a positive electrode case 14, a negative electrode case 15, and a gasket 16. The exterior body 20 houses the positive electrode 11, the negative electrode 12, the separator 13, and the non-aqueous electrolyte. As shown in FIG. 2 , a conductive layer 21 is formed on an inner surface 215 of the negative electrode case 15. Each of the components has been described above, and therefore, redundant description will be omitted.

[0048] The positive electrode case 14 accommodates the positive electrode 11. The positive electrode case 14 is in contact with the positive electrode 11 and functions as a positive electrode terminal.

[0049] The negative electrode case 15 defines an internal space 115 that houses the negative electrode 12, and an internal surface 215 faces the internal space 115. As shown in Fig. 2, the negative electrode case 15 is electrically connected to the negative electrode 12 via a conductive layer 21 and functions as a negative electrode terminal. The positive electrode case 14 and the negative electrode case 15 are insulated by a gasket 16. The open end of the positive electrode case 14 is bent toward the gasket 16, thereby sealing the exterior body 20.

[0050] The above description of the embodiments discloses the following techniques.

[0051] (Technology 1) A coin-shaped nonaqueous electrolyte secondary battery comprising: a negative electrode containing a conductive material and titanium oxide as a negative electrode active material; a positive electrode containing a positive electrode active material; a nonaqueous electrolyte containing a nonaqueous solvent and a solute dissolved in the nonaqueous solvent; and an exterior housing accommodating the positive electrode, the negative electrode, and the nonaqueous electrolyte, wherein the exterior housing comprises a negative electrode case that defines an internal space accommodating the negative electrode and has an inner surface facing the internal space, and a conductive layer containing a carbon material disposed on the internal surface of the negative electrode case, wherein the negative electrode is electrically connected to the negative electrode case via the conductive layer, the conductive material containing single-walled carbon nanotubes, a content of γ-butyrolactone in the nonaqueous solvent is 80% by volume or more, and LiBF ４ The content of the above is 10 mol % or more.

[0052] (Technology 2) The coin-type nonaqueous electrolyte secondary battery according to Technology 1, wherein the conductive layer contains single-walled carbon nanotubes.

[0053] (Technology 3) The coin-type nonaqueous electrolyte secondary battery according to Technology 1 or 2, wherein the titanium oxide is lithium titanate.

[0054] (Technology 4) The positive electrode active material is LiCoO ２ 4. The coin-type nonaqueous electrolyte secondary battery according to any one of claims 1 to 3, comprising:

[0055] (Technology 5) The coin-type nonaqueous electrolyte secondary battery according to any one of Technologies 1 to 4, which is used in an environment of 85° C. or higher.

[0056] <Examples> The present disclosure will be specifically described below based on examples, but the present disclosure is not limited to the following examples. In these examples, multiple coin-shaped nonaqueous electrolyte secondary batteries with different configurations were fabricated and evaluated. Figure 3 shows the evaluation results of the coin-shaped nonaqueous electrolyte secondary batteries of the embodiment.

[0057] (Fabrication of Battery A1) Battery A1, which is a coin-type non-aqueous electrolyte secondary battery, was fabricated in the following manner.

[0058] (1) Preparation of the positive electrode: Lithium cobalt oxide (LiCoO ２ A positive electrode mixture paste was obtained by mixing lithium cobaltate (positive electrode active material), acetylene black (conductive material), and an aqueous dispersion of polytetrafluoroethylene (binder). These were mixed in a mass ratio of lithium cobaltate:acetylene black:polytetrafluoroethylene (solid content) = 90:5.0:5.0. The positive electrode mixture paste was dried to obtain a positive electrode mixture. Approximately 100 mg of the obtained positive electrode mixture was subjected to a 10 kN / cm ２ The mixture was pressed at a pressure of 1000 kJ / cm2 to obtain a pellet (diameter: 10 mm). The obtained pellet was dried at 200° C. to obtain a pellet-shaped positive electrode.

[0059] (2) Preparation of negative electrode First, lithium titanate (Li ４ Ti ５ O １２ A negative electrode mixture paste was obtained by adding an aqueous dispersion of styrene-butadiene rubber (binder) powder to a powder of lithium titanate (negative electrode active material) and single-walled carbon nanotubes (conductive material) and mixing them. These materials were mixed in a mass ratio of lithium titanate:conductive material:styrene-butadiene rubber (solids) of 94:1.0:5.0.

[0060] Next, the negative electrode mixture paste was dried to obtain a negative electrode mixture. ２ The mixture was pressed at a pressure of 1000 kJ / cm2 to obtain a pellet (diameter: 10 mm). The obtained pellet was dried at 150° C. to obtain a pellet-shaped negative electrode.

[0061] (3) Formation of a Conductive Layer A conductive layer was formed on the inner surface of the negative electrode case in a region where the negative electrode was to be disposed. Specifically, a paste containing graphite and a binder was applied to the inner surface of the negative electrode case, and the solvent was then dried to form the conductive layer.

[0062] (4) Fabrication of a Coin-Shaped Battery Using the above-described positive electrode, negative electrode, negative electrode case, and other components, a coin-shaped nonaqueous electrolyte secondary battery having the same configuration as the battery shown in FIG. 1 was fabricated. A polypropylene separator was used as the separator. 90 mg of nonaqueous electrolyte was poured into the battery case. The nonaqueous electrolyte was a solution of lithium tetrafluoroborate (LiBF ) dissolved in γ-butyrolactone (solvent). ４ , solute) at a concentration of 1 mol / L. Battery A1 was thus fabricated. The negative electrode of Battery A1 was electrically connected to the negative electrode case via a conductive layer.

[0063] (Batteries A2 to A6, and C1 to C7) Batteries A2 to A6 and C1 to C7 were fabricated using the same method and under the same conditions as Battery A1, except that the type of conductive material in the negative electrode, the carbon material contained in the conductive layer formed on the inner surface of the negative electrode case, and the nonaqueous electrolyte were changed as shown in Figure 3. The mass ratio of the negative electrode active material (lithium titanate), conductive material, and binder in the negative electrode was the same as that in Battery A1.

[0064] (Evaluation of Battery Characteristics) The fabricated Battery A1 was evaluated according to the following procedure. First, Battery A1 was continuously charged for 500 hours at a constant voltage of 2.6 V while maintained at 100°C. Next, Battery A1 was discharged at a current value of 10 mA while maintained at -20°C, and the discharge curve at this time was obtained. Then, the discharge voltage Vd 0.05 seconds after the start of discharge was determined from the discharge curve. Similar evaluations were performed on batteries other than Battery A1.

[0065] The manufacturing conditions and evaluation results of each battery are shown in FIG.

[0066] Batteries A1 to A6 are secondary batteries (S) according to the present disclosure. Batteries C1 to C7 are comparative examples. The battery voltage (V) in the low-temperature pulse test is preferably 1.5 V or higher. A battery voltage (V) of 1.5 V or higher in the low-temperature pulse test indicates good low-temperature discharge characteristics.

[0067] As shown in Table 1, the batteries A1 to A6 had good low-temperature discharge characteristics after high-temperature continuous charging. On the other hand, the comparative batteries C1 to C6 had poor low-temperature discharge characteristics after high-temperature continuous charging. As shown in Table 1, when one of the above multiple conditions satisfied by the secondary battery (S) was not satisfied, the characteristics were significantly reduced. This indicates that the effects of the above multiple conditions are not simply added together, but that a special synergistic effect is produced by combining the above multiple conditions.

[0068] The same evaluation as above was carried out for Batteries A1 to A6, except that the temperature during continuous charging was set to 85° C. The battery voltage (V) of Batteries A1 to A6 in the low-temperature pulse test was 1.8 V or higher.

[0069] Battery C1 was evaluated in the same manner as above, except that the temperature during continuous charging was 60°C and 85°C. When the temperature during continuous charging was 60°C, the battery voltage (V) of Battery C1 in the low-temperature pulse test was 1.8V. When the temperature during continuous charging was 85°C, the battery voltage (V) of Battery C1 in the low-temperature pulse test was 1.0V. Thus, Battery C1 exhibited good discharge characteristics when continuously charged at 60°C. However, when continuously charged at 85°C or higher, the discharge characteristics of Battery C1 were significantly degraded. This result indicates that the characteristics of the comparative battery are significantly degraded when used at high temperatures of 85°C or higher.

[0070] When the surface of the negative electrode of Battery C1, which had been continuously charged at 85°C, was observed with a scanning electron microscope, it was found that decomposition of lithium salt and polymerization of γ-butyrolactone had occurred in the nonaqueous electrolyte, indicating that the nonaqueous electrolyte had deteriorated. This deterioration of the nonaqueous electrolyte is thought to be one of the causes of the deterioration in the discharge characteristics of the comparative battery. On the other hand, when Battery A1, which had been continuously charged at 85°C, was observed with a scanning electron microscope, no deterioration of the nonaqueous electrolyte was observed.

[0071] The present disclosure can be used for coin-type nonaqueous electrolyte secondary batteries.

[0072] REFERENCE SIGNS LIST 10 Non-aqueous electrolyte secondary battery 11 Positive electrode 12 Negative electrode 13 Separator 14 Positive electrode case 15 Negative electrode case 16 Gasket 20 Exterior body 21 Conductive layer

Claims

1. A coin-type non-aqueous electrolyte secondary battery, A negative electrode containing a conductive material and titanium oxide as a negative electrode active material, A positive electrode containing a positive electrode active material, A non-aqueous electrolyte containing a non-aqueous solvent and a solute dissolved in the non-aqueous solvent, The system includes the positive electrode, the negative electrode, and an outer casing that houses the non-aqueous electrolyte, The outer casing includes a negative electrode case having an inner surface facing the inner space which constitutes an inner space for housing the negative electrode, and a conductive layer containing a carbon material disposed on the inner surface of the negative electrode case. The negative electrode is electrically connected to the negative electrode case via the conductive layer. The conductive material includes single-walled carbon nanotubes, The γ-butyrolactone content in the aforementioned non-aqueous solvent is 80% by volume or more. LiBF in the solute ４ A coin-type non-aqueous electrolyte secondary battery having a content of 10 mol% or more.

2. The coin-type non-aqueous electrolyte secondary battery according to claim 1, wherein the conductive layer contains single-walled carbon nanotubes.

3. The coin-type non-aqueous electrolyte secondary battery according to claim 1 or 2, wherein the titanium oxide is lithium titanate.

4. The positive electrode active material is LiCoO ２ A coin-type non-aqueous electrolyte secondary battery according to claim 1 or 2, comprising the above.

5. A coin-type non-aqueous electrolyte secondary battery according to claim 1 or 2, for use in an environment of 85°C or higher.