Secondary battery, battery pack, vehicle, and stationary power supply

Abstract

To provide a secondary battery comprising an incombustible electrolytic solution, preventing the generation of gas due to decomposition of the electrolytic solution, and excellent in charge-discharge cycle performance, a battery pack comprising the secondary battery, a vehicle, and a stationary power supply.SOLUTION: According to an embodiment, a secondary battery 1 including a positive electrode 5, a negative electrode 3, and an electrolytic solution, is provided. The electrolytic solution includes an alkali metal salt having a melting point of 25°C or more, water in an amount of 0.005 mass% or more and 5 mass% or less, and an aprotic polar organic solvent in an amount of 1 mass% or more and 15 mass% or less.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] FIELD Embodiments of the present invention relate to a secondary battery, a battery pack, a vehicle, and a stationary power source. [Background technology]

[0002] One method of making the electrolyte of lithium secondary batteries nonflammable is to convert it into an aqueous solution. Electrolytes using water instead of organic solvents are prone to reductive decomposition at the negative electrode, which can lead to gas generation and cycle degradation, making suppressing reductive decomposition a challenge. One known method of suppressing reductive decomposition is to increase the concentration of lithium salt in the electrolyte to reduce the amount of water in the electrolyte. However, high-concentration electrolytes are not sufficient to suppress reductive decomposition. Another approach is to use a solvent obtained by a deep eutectic reaction with lithium salt as the electrolyte. However, this solvent has low ionic conductivity due to its high viscosity. Therefore, it is necessary to add water to the electrolyte, and the challenge of suppressing reductive decomposition remains unchanged. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2016-114141 [Non-patent literature]

[0004] [Non-Patent Document 1] Jijian Xu et al., Aqueous electrolyte design for super-stable 2.5V LiMn2O4 / Li4Ti5O12 pouch cells, Nature Energy volume 7, pages186-193 (2022) Summary of the Invention [Problem to be solved by the invention]

[0005] The problem to be solved by the invention is to provide a secondary battery that includes a non-flammable electrolyte, suppresses gas generation due to decomposition of the electrolyte, and has excellent charge / discharge cycle performance, as well as a battery pack, vehicle, and stationary power source that include this secondary battery. [Means for solving the problem]

[0006] According to an embodiment, there is provided a secondary battery including a positive electrode, a negative electrode, and an electrolyte solution containing an alkali metal salt having a melting point of 25° C. or higher, 0.005% by mass to 5% by mass of water, and 1% by mass to 15% by mass of an aprotic polar organic solvent.

[0007] According to the embodiment, a battery pack including the secondary battery of the embodiment is provided.

[0008] According to the embodiment, a vehicle equipped with the battery pack of the embodiment is provided.

[0009] Furthermore, according to the embodiment, a stationary power source including the battery pack of the embodiment is provided. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a cross-sectional view schematically illustrating an example of a secondary battery according to an embodiment. [Figure 2] FIG. 2 is a schematic cross-sectional view taken along line II-II of the secondary battery shown in FIG. [Figure 3] FIG. 10 is a partially cutaway perspective view schematically illustrating another example of a secondary battery according to an embodiment. [Figure 4] FIG. 4 is an enlarged cross-sectional view of a portion E of the secondary battery shown in FIG. [Figure 5] FIG. 1 is a perspective view schematically illustrating an example of a battery pack according to an embodiment. [Figure 6] FIG. 10 is an exploded perspective view schematically showing another example of a battery pack according to an embodiment. [Figure 7] FIG. 7 is a block diagram showing an example of an electrical circuit of the battery pack shown in FIG. 6. [Figure 8] 1 is a partially see-through view schematically illustrating an example of a vehicle according to an embodiment. [Figure 9] FIG. 1 is a block diagram showing an example of a system including a stationary power supply according to an embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0011] (First embodiment) The first embodiment relates to a secondary battery. The secondary battery includes a positive electrode, a negative electrode, and an electrolyte. The electrolyte includes an alkali metal salt having a melting point of 25°C or higher, 0.005% by mass to 5% by mass of water, and 1% by mass to 15% by mass of an aprotic polar organic solvent. The secondary battery of the embodiment can be applied to, for example, a secondary battery containing an alkali metal in at least one of the positive electrode active material or the negative electrode active material. Of the alkali metals, lithium is preferred.

[0012] Alkali metal salts having a melting point of 25°C or higher typically exist in a solid form at room temperature. In the electrolyte solution of the secondary battery of the embodiment, the alkali metal salt exists as a liquid component. In other words, the electrolyte solution of the secondary battery of the embodiment is a solution in which at least an alkali metal salt is dissolved. It has been found that by adjusting the water content of this electrolyte solution to 0.005% by mass or more and 5% by mass or less, and adjusting the aprotic polar organic solvent content to 1% by mass or more and 15% by mass or less, the amount of gas generated by reductive decomposition of the water-containing electrolyte solution during charge and discharge can be reduced, thereby suppressing an increase in battery resistance and improving the charge and discharge cycle life. The electrolyte solution will be described below.

[0013] By setting the water content of the electrolyte to 0.005% by mass or more, the viscosity of the electrolyte can be reduced. The non-flammability of the electrolyte can be improved. Furthermore, by setting the water content of the electrolyte to 5% by mass or less, electrolysis of water during charging and discharging, for example, reductive decomposition of water in the electrolyte at the negative electrode, can be suppressed, thereby suppressing the generation of gases such as hydrogen during charging and discharging. A preferred range of the water content of the electrolyte is 0.01% by mass or more and 4% by mass or less. By setting the content to 0.01% by mass or more, the effect of reducing the viscosity of the electrolyte can be enhanced, thereby improving the ionic conductivity of the electrolyte and reducing the cell resistance. Furthermore, by setting the content to 4% by mass or less, the effect of suppressing gas generation due to electrolysis of water during charging and discharging can be enhanced.

[0014] Aprotic polar organic solvents are organic solvents that are soluble in water. Aprotic polar organic solvents are solvents made of polar organic compounds. Furthermore, aprotic polar organic solvents do not donate protons when they dissociate into cations and anions. For example, alcohols have OH groups, so they donate protons when they dissociate into cations and anions. Aprotic polar organic solvents do not have OH groups. It is desirable for aprotic polar organic solvents to have a high solubility of hydrogen (gas) at 25°C.

[0015] By including 1% by mass or more of an aprotic polar organic solvent in the electrolyte, the viscosity of the electrolyte can be reduced when the water content in the electrolyte is 0.005% by mass or more and 5% by mass or less. Therefore, the electrolyte can have high ionic conductivity. Furthermore, since the water content is within the above range, gas generation due to electrolysis of water in the electrolyte, particularly reductive decomposition, can be suppressed. The aprotic polar organic solvent is expected to have the effect of dissolving hydrogen (gas). Therefore, by including 1% by mass or more of an aprotic polar organic solvent in the electrolyte, the electrolyte can absorb gas (e.g., hydrogen) generated during charging and discharging. By suppressing the decomposition reaction of the electrolyte and absorbing the gas generated by the decomposition reaction, the amount of gas present in the secondary battery (e.g., between the positive and negative electrodes) can be reduced, thereby suppressing an increase in resistance during charging and discharging. On the other hand, by including 15% by mass or less of an aprotic polar organic solvent in the electrolyte, the electrolyte can be made non-flammable. The content of the aprotic polar organic solvent in the electrolyte solution is preferably in the range of 2% by mass to 10% by mass.

[0016] Examples of the aprotic polar organic solvent include one or more selected from the group consisting of carbonates, esters, amides, and nitrile compounds.

[0017] Examples of carbonates include methyl ethyl carbonate (MEC), dimethyl carbonate (DMC), diethyl carbonate, di-n-propyl carbonate, diisopropyl carbonate, methyl-n-propyl carbonate, ethyl-n-propyl carbonate, methyl isopropyl carbonate, ethyl isopropyl carbonate, methyl-n-butyl carbonate, ethyl-n-butyl carbonate, methyl-2-methylpropyl carbonate, ethyl-2-methylpropyl carbonate, methyl-t-butyl carbonate, ethyl-t-butyl carbonate, di-n-butyl carbonate, and bis(2-methylpropyl) Examples of the carbonate include ethylene carbonate, di-t-butyl carbonate, ethylene carbonate, propylene carbonate, butylene carbonate, fluoroethylene carbonate, 4,4-difluoroethylene carbonate, 4,5-difluoroethylene carbonate, 4,5-difluoro-4,5-dimethylethylene carbonate, vinylene carbonate, dimethylvinylene carbonate, and bis(2-methylpropyl) carbonate.

[0018] Examples of esters include alkyl propionates such as methyl propionate, ethyl propionate, and propyl propionate; dialkyl malonates such as dimethyl malonate, diethyl malonate, and methyl ethyl malonate; alkyl acetates such as propyl acetate, butyl acetate, and amyl acetate; carboxylic acid esters such as γ-butyrolactone, γ-valerolactone, γ-nonalactone, and ε-caprolactone; and cyclic sulfonic acid esters such as propane sultone.

[0019] Examples of amides include dimethylformamide, diethylformamide, dimethylacetamide, diethylacetamide, N-methyl-2-pyrrolidone, tetramethylurea, tetraethylurea, and hexamethylphosphoric triamide.

[0020] Examples of the nitrile compound include saturated aliphatic nitriles such as acetonitrile, propionitrile, butyronitrile, isobutyronitrile, and valeronitrile, and aromatic nitriles such as benzonitrile, o-tolunitrile, m-tolunitrile, and p-tolunitrile.

[0021] The aprotic polar organic solvents exemplified above are capable of dissolving hydrogen (gas). Among them, GBL, MEC, acetonitrile, and N-methyl-2-pyrrolidone are preferred because they have high solubility for hydrogen (gas) at 25°C.

[0022] Examples of alkali metal salts having a melting point of 25°C or higher include lithium salts having a melting point of 25°C or higher, sodium salts having a melting point of 25°C or higher, and potassium salts having a melting point of 25°C or higher. One or more types of alkali metal salts may be used. Lithium salts having a melting point of 25°C or higher are preferred. Examples of potassium salts having a melting point of 25°C or higher include potassium bis(trifluoromethanesulfonyl)imide (KTFSI; KN(CF3SO2)2) with a melting point of 200°C, potassium bis(fluorosulfonyl)imide (KFSI; KN(FSO2)2) with a melting point of 101°C, and potassium trifluoromethanesulfonate (KOtF; KCF3SO3) with a melting point of 234°C.

[0023] Examples of lithium salts having a melting point of 25° C. or higher include lithium bis(trifluoromethanesulfonyl)imide (LiTFSI; LiN(CFSO)), which has a melting point of 232° C., lithium bis(fluorosulfonyl)imide (LiFSI; LiN(FSO)), which has a melting point of 125° C., lithium trifluoromethanesulfonate (LiOtF; LiCFSO), which has a melting point of 423° C., lithium difluorooxalatoborate (LiDFOB, CBFLiO), which has a melting point of 270° C., lithium bis(pentafluoroethanesulfonyl)imide (LiBETI; LiN(SOCF)), which has a melting point of 328° C., and lithium bisoxalatoborate (LiBOB: LiB[(OCO)]), which has a melting point >300° C. Preferred lithium salts include LiTFSI, LiFSI, LiDFOB, and LiOtF. Each of these lithium salts is highly stable in water.

[0024] Examples of sodium salts having a melting point of 25°C or higher include sodium chloride (NaCl) with a melting point of 801°C, sodium sulfate (Na2SO4) with a melting point of 884°C, sodium hydroxide (NaOH) with a melting point of 323°C, sodium nitrate (NaNO3) with a melting point of 308°C, sodium trifluoromethanesulfonylamide (NaTFSA) with a melting point of 257°C, sodium bis(fluorosulfonyl)imide (NaFSI; NaN(FSO2)2) with a melting point of 112°C, and sodium trifluoromethanesulfonate (NaOtF; NaCF3SO3) with a melting point of 254°C.

[0025] Increasing the content of alkali metal salts having a melting point of 25°C or higher in the electrolyte is expected to increase the ionic conductivity of the electrolyte, but also tends to increase the viscosity of the electrolyte. The content of alkali metal salts having a melting point of 25°C or higher in the electrolyte is preferably 40% by mass or more and 90% by mass or less. This makes it possible to keep the viscosity of the electrolyte within an appropriate range and increase the ionic conductivity of the electrolyte.

[0026] The electrolyte preferably contains a compound (hereinafter referred to as the "first compound") capable of forming a eutectic with an alkali metal salt having a melting point of 25°C or higher. The first compound can be considered a compound capable of lowering the melting point of an alkali metal salt having a melting point of 25°C or higher. The alkali metal salt having a melting point of 25°C or higher exists as a liquid component in the electrolyte. When the alkali metal salt having a melting point of 25°C or higher reacts with the first compound, its melting point is lowered, and a liquid mixture is produced. The liquid mixture has ionic conductivity and non-flammability, but is different from an ionic liquid consisting of a cation and an anion. The liquid mixture can exist stably at room temperature (around 25°C). Therefore, the electrolyte can also be considered a solution in which an alkali metal salt having a melting point of 25°C or higher is uniformly dissolved. The liquid mixture can be obtained, for example, by reacting a hydrogen bond donor with a hydrogen bond acceptor. The resulting mixture may be a deep eutectic solvent (DESs). An alkali metal salt having a melting point of 25°C or higher can function as a hydrogen bond acceptor. Meanwhile, the first compound can function as a hydrogen bond donor. The first compound may have a melting point of 25°C or higher or lower than 25°C. In other words, the first compound may be liquid or solid. Examples of the first compound include urea (melting point 133°C), N-methylurea (melting point 93°C), N,N'-dimethylpropyleneurea (melting point -20°C), thiourea (melting point 182°C), acetamide (melting point 81°C), thioacetamide (melting point 115°C), succinonitrile (melting point 57°C), lactic acid (melting point 17°C), oxalic acid (melting point 190°C), malonic acid (melting point 135°C), succinic acid (melting point 184°C), and glucose (melting point 146°C). One or more types of first compounds may be used.

[0027] The content of the first compound in the electrolyte solution varies depending on the type of first compound. This is because the composition ratio that forms a eutectic with the alkali metal salt differs depending on the substance. The composition ratio is adjusted so that the alkali metal salt and the first compound become liquid when mixed at 25°C.

[0028] The electrolyte solution may further contain one or more compounds (hereinafter also referred to as "second compounds") selected from the group consisting of isocyanate compounds, fluoride compounds, and boric acid compounds. The second compounds may form a film on at least a portion of the surface of at least one of the positive electrode current collector and the negative electrode current collector. This film may inhibit corrosion of the current collector. The corrosion inhibition effect of the film is more easily achieved when the current collector is made of a material containing Al. An alkali metal salt or an aprotic polar organic solvent having a melting point of 25°C or higher may also serve as the second compound.

[0029] Examples of the isocyanate compound include hexamethylene diisocyanate (HDI), pentamethylene diisocyanate (PDI), and derivatives thereof.

[0030] Examples of fluoride compounds include fluoroethylene carbonate, lithium difluoro(oxalato)borate (LiDFOB: LiBF2(C2O4), lithium dicyanodifluoroborate, and lithium difluoro(difluoromalonato)borate.

[0031] An example of the boric acid compound is lithium bis(oxalato)borate (LiBOB:LiB[(OCO)2]2).

[0032] The content of the second compound in the electrolyte is preferably 0.05% by mass to 3% by mass, which makes it possible to suppress corrosion of the current collector without impairing the ionic conductivity of the electrolyte.

[0033] The electrolyte may contain potassium hydroxide (KOH). Potassium hydroxide can function as a catalyst for the reaction that forms a coating on the surface of the negative electrode active material particles. Therefore, by including potassium hydroxide in the electrolyte, it is possible to promote the formation of a coating on the surface of the negative electrode active material particles.

[0034] The electrolyte solution may contain a surfactant. Examples of the surfactant include nonionic surfactants such as polyoxyalkylene alkyl ether, polyethylene glycol, polyvinyl alcohol, disodium 3,3'-dithiobis(1-propanesulfonate), dimercaptothiadiazole, boric acid, saccharin, sodium naphthalenesulfonate, gelatin, potassium nitrate, aromatic aldehyde, and heterocyclic aldehyde. The surfactants may be used alone or in combination of two or more.

[0035] The negative electrode and the positive electrode will be described in detail below. <Negative electrode> The negative electrode includes a negative electrode current collector and a negative electrode active material-containing layer formed or laminated on one or both sides of the negative electrode current collector. The negative electrode active material-containing layer contains a negative electrode active material.

[0036] The negative electrode current collector may be formed from a material that is electrochemically stable at a potential at which an alkali metal, such as lithium (Li), is inserted into and extracted from the active material. Examples of negative electrode current collectors include a conductive sheet containing a conductive material and a polymeric material; a conductive sheet containing at least one metal element selected from the group consisting of Pb, Bi, Zn, Sb, and Sn; a metal foil such as copper, nickel, stainless steel, or aluminum; and an aluminum alloy foil containing at least one element selected from Mg, Ti, Zn, Mn, Fe, Cu, and Si. Examples of polymeric materials for the conductive sheet include polyethylene, polypropylene, polyethylene terephthalate, polyacrylonitrile, polymethyl methacrylate, and polyvinylidene fluoride. A conductive filler such as a carbonaceous material is preferably used as the conductive material. Examples of carbonaceous materials include carbon black, ketjen black, graphite, fibrous carbon, and carbon nanotubes. The conductive material and the polymeric material may each be one or more types.

[0037] The thickness of the negative electrode current collector is preferably 5 μm or more and 50 μm or less, since a current collector having such a thickness can achieve a balance between the strength and weight of the electrode.

[0038] The negative electrode current collector may include a portion on the surface of which no active material-containing layer is formed, and this portion can function as a current collecting tab or a current collecting lead.

[0039] The negative electrode active material has a lithium ion absorption / desorption potential of 1V (vs. Li / Li) based on metallic lithium. + ) or more and 3V or less (vs.Li / Li + The type of compound used may be one or more.

[0040] Examples of such compounds include titanium-containing oxides. Titanium-containing oxides include, for example, titanium-containing oxides containing lithium ions (Li + The titanium-containing oxide may be a titanium-containing oxide that is capable of being changed into a titanium-containing oxide containing Li by an absorption / desorption reaction or a charge / discharge reaction of the titanium-containing oxide (Li). Therefore, the titanium-containing oxide may be a titanium-containing oxide that does not contain Li. The titanium-containing oxide that does not contain Li includes a titanium-containing oxide that does not substantially contain Li.

[0041] Examples of the titanium-containing oxide include niobium titanium-containing oxide, titanium oxide, and lithium titanium-containing oxide.

[0042] Examples of niobium titanium-containing oxides include niobium titanium-containing oxides having a monoclinic structure. Examples of niobium titanium-containing oxides having a monoclinic structure include Nb2TiO7, Nb2Ti2O9, and Nb 10 Ti2O 29 , Nb 14 TiO 37 , Nb 24 TiO 62The niobium titanium-containing oxide may be a substituted niobium titanium composite oxide in which at least a portion of Nb and / or Ti is substituted with a different element. Examples of the substituting element include Na, K, Ca, Co, Ni, Si, P, V, Cr, Mo, Ta, Zr, Mn, Fe, Mg, B, Pb, and Al. The substituted niobium titanium composite oxide may contain one type of substituting element, or may contain two or more types of substituting elements. The active material particles may contain one type of niobium titanium-containing oxide, or may contain multiple types of niobium titanium-containing oxides. The niobium titanium-containing oxide preferably contains Nb2TiO7 with a monoclinic structure. In this case, an electrode with excellent capacity and rate performance can be obtained.

[0043] Examples of monoclinic niobium titanium oxides include Li x Ti 1-y M1 y Nb 2-z M2 z O 7+δ Here, M1 is at least one selected from the group consisting of Zr, Si, and Sn. M2 is at least one selected from the group consisting of V, Ta, and Bi. The subscripts in the composition formula are 0≦x≦5, 0≦y<1, 0≦z<2, and -0.3≦δ≦0.3.

[0044] Other examples of monoclinic niobium titanium oxides include Ti 1-y M3 y+z Nb 2-z O 7-δ Here, M3 is at least one selected from Mg, Fe, Ni, Co, W, Ta, and Mo. The subscripts in the composition formula are 0≦y<1, 0≦z<2, and −0.3≦δ≦0.3.

[0045] Another example of a monoclinic niobium titanium oxide is Li a TiM b Nb 2±β O 7±σ(0 ≦ a ≦ 5, 0 ≦ b ≦ 0.3, 0 ≦ β ≦ 0.3, 0 ≦ σ ≦ 0.3, and M is at least one element selected from the group consisting of Fe, V, Mo, and Ta) can be mentioned.

[0046] The titanium oxide includes, for example, a titanium oxide with a monoclinic structure, a titanium oxide with a rutile structure, and a titanium oxide with anatase structure. The titanium oxide of each crystal structure has a composition before charging of TiO2 and a composition after charging of Li x It can be represented by TiO2 (where x is 0 ≦ x ≦ 1). Also, the structure before charging of the titanium oxide with a monoclinic structure can be represented as TiO2(B).

[0047] The lithium titanium-containing oxide includes, for example, a lithium titanium oxide with a spinel structure (for example, a compound represented by the general formula Li 4+x Ti5O 12 where -1 ≦ x ≦ 3), a lithium titanium oxide with a lamellarite structure (for example, a compound represented by Li 2+x Ti3O7 where -1 ≦ x ≦ 3), a compound represented by Li 1+x Ti2O4 where 0 ≦ x ≦ 1, a compound represented by Li 1.1+x Ti 1.8 O4 where 0 ≦ x ≦ 1, a compound represented by Li 1.07+x Ti 1.86 O4 where 0 ≦ x ≦ 1, a compound represented by Li x TiO2 where 0 < x ≦ 1, etc. Also, the lithium titanium-containing oxide may be a lithium titanium composite oxide into which a different element has been introduced.

[0048] The type of the negative electrode active material can be one type or two or more types.

[0049] The negative electrode active material is, for example, contained in the negative electrode active material-containing layer in the form of particles. The negative electrode active material particles can be primary particles, secondary particles that are aggregates of primary particles, or a mixture of single primary particles and secondary particles. The shape of the particles is not particularly limited and can be, for example, spherical, elliptical, flat, and fibrous.

[0050] The average particle size (diameter) of the primary particles of the negative electrode active material is preferably 3 μm or less, more preferably 0.01 μm or more and 1 μm or less, and the average particle size (diameter) of the secondary particles of the negative electrode active material is preferably 30 μm or less, more preferably 5 μm or more and 20 μm or less.

[0051] The negative electrode active material-containing layer may further contain a binder. The binder functions to bind the active material and the current collector. The binder is blended to fill gaps between the dispersed active material and to bind the active material and the negative electrode current collector. Examples of binders include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), fluorine-containing rubber, styrene-butadiene rubber, polyacrylic acid compounds, imide compounds, carboxymethylcellulose (CMC), and salts of CMC. One of these may be used as the binder, or two or more may be used in combination as the binder.

[0052] The negative electrode active material-containing layer may contain, in addition to the negative electrode active material and the binder, a conductive agent, etc. The conductive agent is blended as necessary to improve current collection performance and reduce contact resistance between the active material and the current collector.

[0053] Examples of the conductive agent include carbonaceous materials such as acetylene black, ketjen black, graphite, and coke. The conductive agent may be used alone or in combination of two or more.

[0054] The blending ratios of the negative electrode active material, conductive agent, and negative electrode binder in the negative electrode active material-containing layer can be appropriately changed. For example, the negative electrode active material, conductive agent, and negative electrode binder are preferably blended in ratios of 68% by mass to 96% by mass, 2% by mass to 30% by mass, and 2% by mass to 30% by mass, respectively. The ratios of each material are set so that the total amount is 100% by mass. By adjusting the amount of conductive agent to 2% by mass or more, the current collection performance of the negative electrode active material-containing layer can be improved. Furthermore, by adjusting the amount of negative electrode binder to 2% by mass or more, sufficient binding between the negative electrode active material-containing layer and the negative electrode current collector can be achieved, and excellent cycle performance can be expected. On the other hand, it is preferable to adjust the amount of conductive agent and negative electrode binder to 30% by mass or less, respectively, in order to achieve high capacity.

[0055] The negative electrode can be produced, for example, by the following method. First, a negative electrode active material, a conductive agent, and a binder are suspended in a solvent to prepare a slurry. Examples of the solvent include water and organic solvents. The slurry is applied to one or both sides of a current collector. Next, the applied slurry is dried to obtain a laminate of an active material-containing layer and a current collector. Then, the laminate is pressed. In this manner, the negative electrode is produced.

[0056] <Positive electrode> The positive electrode includes a positive electrode current collector and a positive electrode active material-containing layer formed or laminated on one or both sides of the positive electrode current collector. The positive electrode active material-containing layer includes a positive electrode active material. The positive electrode active material-containing layer may further include a conductive agent and a binder. The conductive agent is blended as necessary to improve current collection performance and reduce contact resistance between the active material and the current collector. The binder has the function of binding the active material, conductive agent, and current collector.

[0057] The positive electrode current collector can be formed from a material that is electrochemically stable at a potential where an alkali metal such as lithium (Li) is inserted into and desorbed from the active material. Examples of the positive electrode current collector include a conductive sheet containing a conductive material and a polymer material, a conductive sheet containing at least one metal element selected from the group consisting of Pb, Bi, Zn, Sb, and Sn, a metal foil such as nickel, stainless steel, or aluminum, and an aluminum alloy foil containing one or more elements selected from Mg, Ti, Zn, Mn, Fe, Cu, and Si. The polymer material and the conductive material of the conductive sheet can be the same as those described for the negative electrode current collector.

[0058] The thickness of the positive electrode current collector is preferably 5 μm or more and 50 μm or less. A current collector having such a thickness can achieve a balance between the strength and weight reduction of the electrode.

[0059] The positive electrode current collector can include a portion on its surface where an active material-containing layer is not formed. This portion can function as a current collecting tab or a current collecting lead.

[0060] As the positive electrode active material, a compound having a lithium ion intercalation / deintercalation potential of 3 V (vs. Li / Li + ) or more and 5.5 V or less (vs. Li / Li + ) based on the potential of metallic lithium can be used. The positive electrode may contain one type of positive electrode active material or two or more types of positive electrode active materials.

[0061] Examples of the positive electrode active material include lithium manganese composite oxide, lithium nickel composite oxide, lithium cobalt aluminum composite oxide, lithium nickel cobalt manganese composite oxide, spinel-type lithium manganese nickel composite oxide, lithium manganese cobalt composite oxide, lithium iron oxide, lithium fluorinated iron sulfate, phosphate compounds having an olivine crystal structure (e.g., Li x FePO4 (0 < x ≦ 1), Li x MnPO4 (0 < x ≦ 1)), etc. Phosphate compounds having an olivine crystal structure are excellent in thermal stability.

[0062] Examples of cathode active materials capable of obtaining a high cathode potential include lithium nickel cobalt manganese composite oxides (Li x Ni 1-y-z Co y Mn z O2; 0 < x ≤ 1, 0 < y < 1, 0 < z < 1, y + z < 1), for example, spinel-structured Li x Mn2O4 (0 < x ≤ 1), spinel-structured Li x MnO2 (0 < x ≤ 1), spinel-structured Li y Al x Mn 2-x O4 (0 ≤ y ≤ 1, 0 < x < 2), etc., lithium manganese composite oxides, such as Li x Ni 1-y Al y O2 (0 < x ≤ 1, 0 < y < 1), etc., lithium nickel aluminum composite oxides, such as Li x CoO2 (0 < x ≤ 1), etc., lithium cobalt composite oxides, such as Li x Ni 1-y―z Co y Mn z O2 (0 < x ≤ 1, 0 < y < 1, 0 ≤ z < 1), etc., lithium nickel cobalt composite oxides, such as Li x Mn y Co 1-y O2 (0 < x ≤ 1, 0 < y < 1), etc., lithium manganese cobalt composite oxides, such as Li x Mn 1-y Ni y O4 (0 < x ≤ 1, 0 < y < 2, 0 < 1 - y < 1), etc., spinel-type lithium manganese nickel composite oxides, such as Li x FePO4 (0 < x ≤ 1), Li x Fe 1-y Mn y PO4 (0 < x ≤ 1, 0 ≤ y ≤ 1), Li x CoPO4 (0 < x ≤ 1), etc., lithium phosphate oxides having an olivine structure, fluorinated iron sulfate (for example, Li x FeSO4F (0 < x ≤ 1)) can be mentioned.

[0063] The positive electrode active material is contained in the positive electrode in the form of particles, for example. The positive electrode active material particles may be single primary particles, secondary particles which are aggregates of primary particles, or a mixture of primary particles and secondary particles. The shape of the particles is not particularly limited and may be, for example, spherical, elliptical, flat, or fibrous.

[0064] The average particle size (diameter) of the primary particles of the positive electrode active material is preferably 10 μm or less, more preferably 0.1 μm or more and 5 μm or less, and the average particle size (diameter) of the secondary particles of the positive electrode active material is preferably 100 μm or less, more preferably 10 μm or more and 50 μm or less.

[0065] The binder is blended to fill gaps between the dispersed positive electrode active material and to bind the positive electrode active material and the positive electrode current collector. Examples of binders include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), fluorine-containing rubber, polyacrylic acid compounds, imide compounds, carboxymethyl cellulose (CMC), and CMC salts. One of these may be used as the binder, or two or more may be used in combination as the binder.

[0066] The conductive agent is blended to improve current collection performance and reduce contact resistance between the positive electrode active material and the positive electrode current collector. Examples of conductive agents include vapor-grown carbon fiber (VGCF), carbon black such as acetylene black, and carbonaceous materials such as graphite. One of these may be used as the conductive agent, or two or more may be used in combination as the conductive agent. The conductive agent may also be omitted.

[0067] In the positive electrode active material-containing layer, the positive electrode active material and the binder are preferably mixed in proportions of 80% by mass to 98% by mass and 2% by mass to 20% by mass, respectively.

[0068] By using a binder amount of 2% by mass or more, sufficient electrode strength can be obtained. Furthermore, the binder can function as an insulator. Therefore, by using a binder amount of 20% by mass or less, the amount of insulator contained in the electrode is reduced, thereby reducing internal resistance.

[0069] When a conductive agent is added, the positive electrode active material, binder, and conductive agent are preferably mixed in proportions of 77% by mass or more and 95% by mass or less, 2% by mass or more and 20% by mass or less, and 3% by mass or more and 15% by mass or less, respectively.

[0070] By setting the amount of conductive agent to 3% by mass or more, the above-mentioned effects can be achieved. Furthermore, by setting the amount of conductive agent to 15% by mass or less, the proportion of conductive agent in contact with the electrolyte can be reduced. This low proportion can reduce decomposition of the electrolyte during high-temperature storage.

[0071] For example, a positive electrode is prepared by suspending a positive electrode active material, a conductive agent, and a binder in a solvent to prepare a slurry. This slurry is then applied to one or both sides of a current collector. The applied slurry is then dried to obtain a laminate of an active material-containing layer and a current collector. This laminate is then pressed. In this manner, a positive electrode is produced. Alternatively, the positive electrode may be produced by the following method. First, the active material, the conductive agent, and the binder are mixed to obtain a mixture. Next, this mixture is formed into pellets. Next, these pellets are placed on a current collector to obtain a positive electrode.

[0072] The secondary battery of the embodiment may further include at least one of a separator and an exterior member.

[0073] <separator> The separator is disposed, for example, between the positive electrode and the negative electrode, and may include a separator that covers only one of the positive electrode or the negative electrode.

[0074] The separator may have a porous structure. Examples of porous separators include nonwoven fabrics, films, and papers. Examples of materials for porous separators that make up nonwoven fabrics, films, and papers include polyolefins such as polyethylene and polypropylene, and cellulose. Examples of preferred porous separators include nonwoven fabrics containing cellulose fibers and porous films containing polyolefin fibers.

[0075] The porosity of the porous separator is preferably 60% or more. The fiber diameter is preferably 10 μm or less. By setting the fiber diameter to 10 μm or less, the affinity of the porous separator for the electrolyte is improved, thereby reducing the battery resistance. A more preferable range for the fiber diameter is 3 μm or less. A cellulose fiber-containing nonwoven fabric with a porosity of 60% or more has good electrolyte impregnation and can produce high output performance from low to high temperatures. A more preferable range for the porosity is 62% to 80%.

[0076] The porous separator has a thickness of 20 μm to 100 μm and a density of 0.2 g / cm 3 More than 0.9g / cm 3 Within this range, a balance between mechanical strength and reduced battery resistance can be achieved, providing a secondary battery with high output and suppressed internal short circuits. Furthermore, the separator experiences little thermal shrinkage in a high-temperature environment, resulting in good high-temperature storage performance.

[0077] The separator may be a composite separator including a porous separator and a layer containing inorganic particles formed on one or both sides of the porous separator. Examples of inorganic particles include aluminum oxide and silicon oxide.

[0078] A solid electrolyte layer may be used as the separator. The solid electrolyte layer may contain solid electrolyte particles and a polymer component. The solid electrolyte layer may consist of only solid electrolyte particles. The solid electrolyte layer may contain one type of solid electrolyte particle or multiple types of solid electrolyte particles. The solid electrolyte layer may contain at least one selected from the group consisting of a plasticizer and an electrolyte salt. If the solid electrolyte layer contains an electrolyte salt, for example, the alkali metal ion conductivity of the solid electrolyte layer can be further increased. The polymer material may be in the form of, for example, granules or fibers.

[0079] The solid electrolyte layer is preferably in a sheet form with few or no pores such as pinholes. The thickness of the solid electrolyte layer is not particularly limited, but is, for example, 150 μm or less, and preferably in the range of 20 μm to 50 μm.

[0080] The polymer component used in the solid electrolyte layer is preferably one that is insoluble in aqueous solvents. Examples of polymer components that meet this condition include polyethylene terephthalate (PET), polypropylene (PP), polyethylene (PE), and fluorine-containing polymer components. The use of fluorine-containing polymer components can impart water repellency to the separator. In addition, inorganic solid electrolytes have high stability against water and excellent lithium ion conductivity. By combining a lithium ion-conducting inorganic solid electrolyte with a fluorine-containing polymer component, a flexible solid electrolyte layer with alkali metal ion conductivity can be realized. A separator made of this solid electrolyte layer can reduce resistance, thereby improving the high-current performance of secondary batteries.

[0081] Examples of the fluorine-containing polymer component include polytetrafluoroethylene (PTFE), polychlorotrifluoroethylene (PCTFE), ethylene tetrafluoroethylene copolymer, polyvinylidene fluoride (PVdF), etc. The type of the fluorine-containing polymer component can be one or more types.

[0082] When the solid electrolyte layer contains a polymer component, the content of the polymer component in the solid electrolyte layer is preferably 1% by mass or more and 20% by mass or less. Within this range, high mechanical strength can be obtained and resistance can be reduced when the thickness of the solid electrolyte layer is set in the range of 10 to 100 μm. Furthermore, the solid electrolyte is unlikely to be a factor inhibiting lithium ion conductivity. A more preferred range for this content is 3% by mass or more and 10% by mass or less.

[0083] As the solid electrolyte, an inorganic solid electrolyte is preferably used. The inorganic solid electrolyte is a solid substance having Li-ion conductivity. Here, "having Li-ion conductivity" means that the Li-ion conductivity is 1×10 at 25°C or more. -6 This refers to a material that exhibits a lithium ion conductivity of 1000 S / cm or more. Examples of inorganic solid electrolytes include oxide-based solid electrolytes and sulfide-based solid electrolytes. Specific examples of inorganic solid electrolytes are as follows:

[0084] The oxide-based solid electrolyte has a NASICON (Sodium (Na) Super Ionic Conductor) type structure and is represented by the general formula Li 1+x It is preferable to use a lithium phosphate solid electrolyte represented by Mα2(PO4)3. In the general formula, Mα is, for example, one or more elements selected from the group consisting of titanium (Ti), germanium (Ge), strontium (Sr), zirconium (Zr), tin (Sn), aluminum (Al), and calcium (Ca). The subscript x is within the range of 0≦x≦2.

[0085] Specific examples of lithium phosphate solid electrolytes with NASICON structure include Li 1+x Al x Ti 2-x LATP compounds represented by (PO4)3, where 0.1≦x≦0.5; Li 1+x Al y Mβ 2-y A compound represented by (PO4)3, in which Mβ is at least one selected from the group consisting of Ti, Ge, Sr, Zr, Sn, and Ca, and 0≦x≦1 and 0≦y≦1; Li 1+x Al x Ge2-x A compound represented by (PO4)3 where 0 ≦ x ≦ 2; and Li 1+x Al x Zr 2-x A compound represented by (PO4)3 where 0 ≦ x ≦ 2; Li 1+x+y Al x Mγ 2-x Si y P 3-y O 12 A compound represented by where Mγ is one or more selected from the group consisting of Ti and Ge, 0 < x ≦ 2, and 0 ≦ y < 3; Li 1+2x Zr 1-x Ca x Examples of the compound represented by (PO4)3 where 0 ≦ x < 1 can be given.

[0086] In addition, as the oxide-based solid electrolyte, in addition to the above lithium phosphate solid electrolyte, Li x PO y N z An amorphous LIPON compound represented by where 2.6 ≦ x ≦ 3.5, 1.9 ≦ y ≦ 3.8, and 0.1 ≦ z ≦ 1.3 (for example, Li 2.9 PO 3.3 N 0.46 ); A garnet-type structure La 5+x A x La 3-x Mδ2O 12 A compound represented by where A is one or more selected from the group consisting of Ca, Sr, and Ba, Mδ is one or more selected from the group consisting of Nb and Ta, and 0 ≦ x ≦ 0.5; Li3Mδ 2-x L2O 12 A compound represented by where Mδ is one or more selected from the group consisting of Nb and Ta, L may contain Zr, and 0 ≦ x ≦ 0.5; Li 7-3x Al x A compound represented by where 0 ≦ x ≦ 0.5; Li 12 A compound represented by where 0 ≦ x ≦ 0.5; Li 5+x La3Mδ 2-x Zr x O 12 A LLZ compound represented by where Mδ is one or more selected from the group consisting of Nb and Ta and 0 ≦ x ≦ 2 (for example, Li7La3Zr2O 12 ); And having a perovskite-type structure La2 / 3-x Li x Examples include compounds represented by TiO3 where x is 0.3≦x≦0.7.

[0087] One or more of the above compounds can be used as the solid electrolyte, and two or more of the above solid electrolytes can also be used.

[0088] <Exterior materials> The exterior member contains at least a positive electrode, a negative electrode, a separator, and an electrolyte. Examples of the exterior member that can be used include a metal container, a laminated film container, and a resin container. Examples of the metal container include rectangular or cylindrical metal cans made of nickel, iron, stainless steel, or the like. Examples of the resin container include those made of polyethylene, polypropylene, or the like.

[0089] The thickness of the laminate film is, for example, 0.5 mm or less, preferably 0.2 mm or less.

[0090] The laminate film is a multilayer film containing multiple resin layers and metal layers interposed between the resin layers. The resin layers include polymeric materials such as polypropylene (PP), polyethylene (PE), nylon, and polyethylene terephthalate (PET). The metal layers are preferably made of aluminum foil or aluminum alloy foil to reduce weight. The laminate film can be molded into the shape of the exterior component by sealing it by heat fusion.

[0091] The thickness of the wall of the metal container is, for example, 1 mm or less, more preferably 0.5 mm or less, and even more preferably 0.2 mm or less.

[0092] The metal container is made of, for example, aluminum or an aluminum alloy. The aluminum alloy preferably contains elements such as magnesium, zinc, and silicon. If the aluminum alloy contains transition metals such as iron, copper, nickel, and chromium, the content of these metals is preferably 100 mass ppm or less.

[0093] The shape of the exterior member is not particularly limited. The shape of the exterior member may be, for example, flat (thin), rectangular, cylindrical, coin-shaped, or button-shaped. The exterior member can be appropriately selected depending on the battery dimensions and the intended use of the battery.

[0094] The secondary battery according to the embodiment can be used in various forms, such as a rectangular, cylindrical, flat, thin, or coin-shaped battery. The secondary battery may have a bipolar structure. For example, the electrode group may have a bipolar structure in which a positive electrode active material-containing layer is provided on one side of a single current collector and a negative electrode active material-containing layer is provided on the other side. This has the advantage that multiple serially connected cells can be fabricated from a single cell.

[0095] The methods for confirming the compositions of the positive electrode active material, negative electrode active material, and electrolyte solution are described below.

[0096] If the battery contains a positive and negative electrode, disassemble the battery, remove the positive or negative electrode, and clean it with dimethyl carbonate (DMC). The cleaning method is explained below. Immerse the electrode (positive or negative) in DMC for 5 minutes, then remove the electrode. Repeat this three times, then dry the electrode before subjecting it to measurement. When repeating the immersion, use new DMC solution each time.

[0097] To extract the electrolyte from a battery, the battery is disassembled, and if the electrolyte is present outside the electrodes, the electrolyte that is not impregnated into the electrodes is extracted. If the electrolyte cannot be extracted from outside the electrodes, the electrodes are placed in a centrifuge and the electrolyte is extracted by centrifugation. <Cathode active material> The crystal structure and elemental composition of the positive electrode active material can be confirmed by powder X-ray diffraction (XRD) measurement and inductively coupled plasma (ICP) emission spectroscopy. <Negative electrode active material> The crystal structure and elemental composition of the negative electrode active material can be confirmed by powder X-ray diffraction (XRD) measurement and inductively coupled plasma (ICP) emission spectroscopy. <Electrolyte> The presence of water in the electrolyte can be confirmed by GC-MS (Gas Chromatography-Mass Spectrometry). The water content in the electrolyte can also be measured, for example, by evaporating the water from the electrolyte and measuring the weight ratio of the electrolyte to the residue. A specified amount of electrolyte is weighed and evaporated in an inert atmosphere. The water content can be calculated from the weight ratio to the residue.

[0098] It can be confirmed by LC-MS (Liquid Chromatography Mass Spectrometry) that the electrolyte solution contains one or more compounds (second compounds) selected from the group consisting of an alkali metal salt having a melting point of 25°C or higher, an aprotic polar organic solvent, a compound capable of forming a eutectic with an alkali metal salt having a melting point of 25°C or higher (first compound), an isocyanate compound, a fluoride compound, and a boric acid compound.

[0099] The contents of the alkali metal salt having a melting point of 25°C or higher, the aprotic polar organic solvent, the first compound, and the second compound in the electrolyte can be confirmed by measuring the peak area obtained by LC using a calibration curve prepared using substances identified by LC-MS as standard substances.

[0100] The non-flammability of an electrolyte can be confirmed by the following method: A 2 cm square glass non-woven fabric sample soaked in electrolyte is hung and a flame from a lighter is applied from below for 10 seconds. The electrolyte is considered non-flammable if no flame is observed on the sample when the flame from the lighter is moved away from the sample, or if a flame is observed immediately after moving it away but goes out within 5 seconds.

[0101] An example in which the battery of the embodiment is applied to a secondary battery will be described with reference to FIGS.

[0102] The secondary battery 1 includes an electrode group 2 and an exterior member 20 that houses the electrode group 2. The electrode group 2 is housed in the exterior member 20, which is a rectangular cylindrical metal container. The electrode group 2 includes a negative electrode 3, a separator 4, and a positive electrode 5. The electrode group 2 has a structure in which the separator 4 is interposed between the positive electrode 5 and the negative electrode 3 and the electrode group 2 is spirally wound to form a flat shape. An electrolyte (not shown) is held in the electrode group 2. As shown in FIG. 2, strip-shaped negative electrode leads 16 are electrically connected to multiple locations on the end of the negative electrode 3 located on the end face of the electrode group 2. Strip-shaped positive electrode leads 17 are electrically connected to multiple locations on the end of the positive electrode 5 located on this end face. The multiple negative electrode leads 16 are bundled together and connected to the negative electrode terminal 6 as shown in FIG. 2. Similarly, although not shown, the positive electrode leads 17 are also bundled together and electrically connected to the positive electrode terminal 7.

[0103] The metal sealing plate 21 is fixed to the opening of the metal exterior member 20 by welding or the like. The negative electrode terminal 6 and the positive electrode terminal 7 are each drawn out to the outside through an extraction hole provided in the sealing plate 21. A negative electrode gasket 8 and a positive electrode gasket 9 are disposed on the inner circumferential surface of each extraction hole in the sealing plate 21 to prevent short circuits due to contact with the negative electrode terminal 6 and the positive electrode terminal 7, respectively. By disposing the negative electrode gasket 8 and the positive electrode gasket 9, the airtightness of the secondary battery 100 can be maintained.

[0104] A control valve 22 (safety valve) is disposed on the sealing plate 21. If the internal pressure of the battery cell increases due to gas generated within the exterior member 20, the generated gas can be released to the outside through the control valve 22. The control valve 22 can be, for example, a resettable type that activates when the internal pressure exceeds a set value and functions as a sealing plug when the internal pressure decreases. Alternatively, a non-resettable control valve that does not recover its function as a sealing plug once activated may be used. In FIG. 1, the control valve 22 is disposed in the center of the sealing plate 21, but the control valve 22 may also be located at the end of the sealing plate 21. The control valve 22 may also be omitted.

[0105] The sealing plate 21 is also provided with a liquid inlet 23. The electrolyte can be poured through this liquid inlet 23. After the electrolyte is poured, the liquid inlet 23 can be closed with a sealing plug 24. The liquid inlet 23 and the sealing plug 24 may be omitted.

[0106] Another example of a secondary battery will be described with reference to Figures 3 and 4. Figures 3 and 4 show an example of a secondary battery 1 that uses an exterior member made of a laminate film as a container.

[0107] The secondary battery 1 shown in Figures 3 and 4 includes an electrode group 2 shown in Figures 3 and 4, an exterior member 20 shown in Figure 3, and an electrolyte (not shown). The electrode group 2 and the electrolyte are housed in the exterior member 20. The electrolyte is held in the electrode group 2.

[0108] The exterior member 20 is made of a laminate film including two resin layers and a metal layer interposed between them.

[0109] The electrode group 2 is a laminated electrode group, as shown in Fig. 4. The laminated electrode group 2 has a structure in which negative electrodes 3 and positive electrodes 5 are alternately laminated with separators 4 interposed therebetween.

[0110] The electrode group 2 includes a plurality of negative electrodes 3. Each of the plurality of negative electrodes 3 includes a negative electrode current collector 3a and a negative electrode active material-containing layer 3b supported on both sides of the negative electrode current collector 3a. The electrode group 2 also includes a plurality of positive electrodes 5. Each of the plurality of positive electrodes 5 includes a positive electrode current collector 5a and a positive electrode active material-containing layer 5b supported on both sides of the positive electrode current collector 5a.

[0111] The negative electrode current collector 3a of each negative electrode 3 includes a portion 3c on one side where no negative electrode active material-containing layer 3b is supported on any surface. This portion 3c serves as a negative electrode current collector tab. As shown in FIG. 4, the portion 3c serving as the negative electrode current collector tab does not overlap with the positive electrode 5. The multiple negative electrode current collector tabs (portions 3c) are electrically connected to a strip-shaped negative electrode terminal 6. The tip of the strip-shaped negative electrode terminal 6 is drawn out to the outside of the exterior member 20.

[0112] Although not shown, the positive electrode current collector 5a of each positive electrode 5 includes a portion on one side where the positive electrode active material-containing layer 5b is not supported on any surface. This portion functions as a positive electrode current collector tab. Like the negative electrode current collector tab (portion 3c), the positive electrode current collector tab does not overlap with the negative electrode 3. The positive electrode current collector tab is located on the opposite side of the electrode group 2 from the negative electrode current collector tab (portion 3c). The positive electrode current collector tab is electrically connected to a strip-shaped positive electrode terminal 7. The tip of the strip-shaped positive electrode terminal 7 is located on the opposite side from the negative electrode terminal 6 and is drawn out to the exterior of the exterior member 20.

[0113] The secondary battery according to the embodiment described above includes a positive electrode, a negative electrode, and an electrolyte. The electrolyte includes an alkali metal salt having a melting point of 25°C or higher, 0.005% by mass to 5% by mass of water, and 1% by mass to 15% by mass of an aprotic polar organic solvent. An electrolyte having this composition is non-flammable, thereby improving the safety of the secondary battery. Furthermore, this electrolyte can suppress gas generation due to electrolysis (e.g., reductive decomposition) of water in the electrolyte during charge and discharge, and can absorb generated gas (e.g., hydrogen). As a result, the amount of gas generated during charge and discharge can be reduced, thereby suppressing an increase in resistance during charge and discharge. This improves the charge and discharge cycle life of the secondary battery.

[0114] (Second embodiment) According to a second embodiment, there is provided a battery pack, which includes a plurality of secondary batteries according to the embodiment.

[0115] In the battery pack according to this embodiment, the cells may be electrically connected in series or in parallel, or may be connected in a combination of series and parallel.

[0116] Next, an example of a battery pack will be described with reference to the drawings.

[0117] 5 includes five cells 100a to 100e, four bus bars 201, a positive electrode lead 207, and a negative electrode lead 206. Each of the five cells 100a to 100e is a secondary battery according to the embodiment.

[0118] The bus bar 201 connects, for example, the negative electrode terminal 6 of one cell 100a to the positive electrode terminal 7 of the adjacent cell 100b. In this way, the five cells 100 are connected in series by four bus bars 201. That is, the battery pack 200 in FIG. 5 is a five-series battery pack. Although an example is not shown, in a battery pack including a plurality of cells electrically connected in parallel, the plurality of cells can be electrically connected by, for example, connecting the negative electrode terminals to each other by a bus bar and connecting the positive electrode terminals to each other by a bus bar.

[0119] The positive terminal 7 of at least one of the five cells 100a to 100e is electrically connected to a positive electrode lead 207 for external connection. Also, the negative terminal 6 of at least one of the five cells 100a to 100e is electrically connected to a negative electrode lead 206 for external connection.

[0120] The battery pack according to the embodiment includes the battery according to the embodiment. Therefore, the battery pack includes a non-flammable electrolyte, and can reduce the amount of gas generated by electrolysis of water in the electrolyte during charge and discharge. Therefore, it is possible to realize a battery pack that is highly safe, has excellent charge and discharge cycle life performance, and suppresses resistance increases associated with charge and discharge.

[0121] [Third embodiment] According to a third embodiment, a battery pack including batteries according to the embodiments is provided. This battery pack may include the battery assembly according to the embodiments. This battery pack may include a single battery instead of the battery assembly according to the embodiments.

[0122] Such a battery pack may further include a protection circuit. The protection circuit has a function of controlling the charging and discharging of the secondary battery. Alternatively, a circuit included in a device that uses the battery pack as a power source (e.g., electronic equipment, automobile, etc.) may be used as the protection circuit for the battery pack.

[0123] The battery pack may further include external terminals for current flow. The external terminals for current flow are for outputting current from the secondary battery to the outside and / or inputting current from the outside to the secondary battery. In other words, when the battery pack is used as a power source, current is supplied to the outside through the external terminals for current flow. When the battery pack is charged, charging current (including regenerative energy from the power of an automobile or the like) is supplied to the battery pack through the external terminals for current flow.

[0124] Next, an example of a battery pack according to an embodiment will be described with reference to the drawings.

[0125] The battery pack 300 shown in FIGS. 6 and 7 includes a container 31, a lid 32, a protective sheet 33, a battery pack 200, a printed wiring board 34, wiring 35, and an insulating plate (not shown).

[0126] The storage container 31 shown in Fig. 6 is a bottomed, prismatic container having a rectangular bottom. The storage container 31 is configured to be able to accommodate a protective sheet 33, a battery pack 200, a printed wiring board 34, and wiring 35. The lid 32 has a rectangular shape. The lid 32 covers the storage container 31 to accommodate the battery pack 200 and other components. Although not shown, the storage container 31 and the lid 32 are provided with openings or connection terminals for connection to external devices and the like.

[0127] The battery pack 200 includes a plurality of cells 100, a positive electrode lead 207, a negative electrode lead 206, and an adhesive tape .

[0128] At least one of the plurality of cells 100 is a secondary battery according to the embodiment. The plurality of cells 100 are electrically connected in series as shown in FIG. 7. The plurality of cells 100 may be electrically connected in parallel, or may be connected in a combination of series and parallel connections. When the plurality of cells 100 are connected in parallel, the battery capacity increases compared to when they are connected in series.

[0129] The adhesive tape 36 fastens the plurality of cells 100 together. Heat-shrinkable tape may be used to secure the plurality of cells 100 together instead of the adhesive tape 36. In this case, protective sheets 33 are placed on both side surfaces of the battery pack 200, and the heat-shrinkable tape is wrapped around the cells 100, and the heat-shrinkable tape is then thermally shrunk to bind the plurality of cells 100 together.

[0130] One end of the positive electrode lead 207 is connected to the battery pack 200. One end of the positive electrode lead 207 is electrically connected to the positive electrode of one or more cells 100. One end of the negative electrode lead 206 is connected to the battery pack 200. One end of the negative electrode lead 206 is electrically connected to the negative electrode of one or more cells 100.

[0131] The printed wiring board 34 is installed along one of the shorter sides of the inner surface of the container 31. The printed wiring board 34 includes a positive connector 342, a negative connector 343, a thermistor 345, a protection circuit 346, wires 342a and 343a, an external terminal 350 for supplying current, a positive wire (positive wire) 348a, and a negative wire (negative wire) 348b. One main surface of the printed wiring board 34 faces one side of the battery pack 200. An insulating plate (not shown) is interposed between the printed wiring board 34 and the battery pack 200.

[0132] The other end 207a of the positive electrode lead 207 is electrically connected to the positive electrode connector 342. The other end 206a of the negative electrode lead 206 is electrically connected to the negative electrode connector 343.

[0133] The thermistor 345 is fixed to one main surface of the printed wiring board 34. The thermistor 345 detects the temperature of each of the cells 100 and transmits the detection signal to the protection circuit 346.

[0134] The external terminals 350 for applying current are fixed to the other main surface of the printed wiring board 34. The external terminals 350 for applying current are electrically connected to devices located outside the battery pack 300. The external terminals 350 for applying current include a positive terminal 352 and a negative terminal 353.

[0135] The protection circuit 346 is fixed to the other main surface of the printed wiring board 34. The protection circuit 346 is connected to the positive terminal 352 via a positive wiring 348a. The protection circuit 346 is connected to the negative terminal 353 via a negative wiring 348b. The protection circuit 346 is also electrically connected to the positive connector 342 via a wiring 342a. The protection circuit 346 is electrically connected to the negative connector 343 via a wiring 343a. The protection circuit 346 is also electrically connected to each of the plurality of single cells 100 via wiring 35.

[0136] The protective sheet 33 is disposed on both inner surfaces of the long sides of the container 31 and on the inner surface of the short side that faces the printed wiring board 34 across the battery pack 200. The protective sheet 33 is made of, for example, resin or rubber.

[0137] The protection circuit 346 controls charging and discharging of the plurality of cells 100. Furthermore, the protection circuit 346 cuts off the electrical connection between the protection circuit 346 and external terminals 350 (positive terminal 352, negative terminal 353) for supplying electricity to an external device, based on a detection signal transmitted from the thermistor 345 or a detection signal transmitted from each cell 100 or the battery pack 200.

[0138] An example of the detection signal transmitted from the thermistor 345 is a signal indicating that the temperature of the cell 100 is equal to or higher than a predetermined temperature. An example of the detection signal transmitted from each cell 100 or the battery pack 200 is a signal indicating that overcharge, overdischarge, or overcurrent of the cell 100 is detected. When detecting overcharge or the like for each cell 100, the battery voltage may be detected, or the positive electrode potential or the negative electrode potential may be detected. In the latter case, a lithium electrode used as a reference electrode is inserted into each cell 100.

[0139] The protection circuit 346 may be a circuit included in a device (such as an electronic device or an automobile) that uses the battery pack 300 as a power source.

[0140] As described above, the battery pack 300 is also provided with the external terminals 350 for current application. Therefore, the battery pack 300 can output current from the battery assembly 200 to an external device and input current from the external device to the battery assembly 200 via the external terminals 350 for current application. In other words, when the battery pack 300 is used as a power source, the current from the battery assembly 200 is supplied to the external device via the external terminals 350 for current application. When the battery pack 300 is charged, a charging current from the external device is supplied to the battery pack 300 via the external terminals 350 for current application. When the battery pack 300 is used as an in-vehicle battery, regenerative energy from the vehicle's power can be used as the charging current from the external device.

[0141] The battery pack 300 may include a plurality of assembled batteries 200. In this case, the assembled batteries 200 may be connected in series, in parallel, or in a combination of series and parallel connections. The printed wiring board 34 and the wiring 35 may be omitted. In this case, the positive electrode lead 207 and the negative electrode lead 206 may be used as the positive and negative terminals of the external terminals for supplying current, respectively.

[0142] Such a battery pack is used in applications requiring excellent cycle performance when drawing a large current, for example. Specifically, this battery pack is used, for example, as a power source for electronic devices, a stationary battery, or an on-board battery for various vehicles. Examples of electronic devices include digital cameras. This battery pack is particularly suitable for use as an on-board battery.

[0143] The battery pack according to the third embodiment includes the secondary battery according to the embodiment or the battery assembly according to the embodiment. Therefore, the battery pack includes a non-flammable electrolyte, and can reduce the amount of gas generated by electrolysis of water in the electrolyte during charging and discharging. Therefore, it is possible to realize a battery pack that is highly safe, has excellent charge-discharge cycle life performance, and suppresses resistance increases associated with charging and discharging.

[0144] [Fourth embodiment] According to a fourth embodiment, a vehicle including a battery pack according to an embodiment is provided.

[0145] In such a vehicle, the battery pack recovers, for example, regenerative energy for powering the vehicle, and the vehicle may include a mechanism (regenerator) for converting the kinetic energy of the vehicle into regenerative energy.

[0146] Examples of vehicles according to the embodiment include two-wheeled to four-wheeled hybrid electric vehicles, two-wheeled to four-wheeled electric vehicles, power-assisted bicycles, and railroad cars.

[0147] The mounting position of the battery pack in the vehicle according to the embodiment is not particularly limited. For example, when the battery pack is mounted in an automobile, the battery pack can be mounted in the engine compartment, the rear of the vehicle body, or under the seat of the vehicle.

[0148] Vehicles according to embodiments may be equipped with multiple battery packs. In this case, the batteries included in each battery pack may be electrically connected in series, in parallel, or a combination of series and parallel connections. For example, if each battery pack includes a battery pack, the battery packs may be electrically connected in series, in parallel, or a combination of series and parallel connections. Alternatively, if each battery pack includes a single battery, the batteries may be electrically connected in series, in parallel, or a combination of series and parallel connections.

[0149] Next, an example of a vehicle according to an embodiment will be described with reference to the drawings.

[0150] A vehicle 400 shown in Fig. 8 includes a vehicle body 40 and a battery pack 300 according to the embodiment. In the example shown in Fig. 8, the vehicle 400 is a four-wheeled automobile.

[0151] The vehicle 400 may be equipped with a plurality of battery packs 300. In this case, the batteries (for example, single cells or assembled batteries) included in the battery packs 300 may be connected in series, in parallel, or in a combination of series and parallel connections.

[0152] 8 illustrates an example in which the battery pack 300 is mounted in an engine compartment located in the front of the vehicle body 40. As described above, the battery pack 300 may be mounted, for example, at the rear of the vehicle body 40 or under a seat. This battery pack 300 can be used as a power source for the vehicle 400. In addition, this battery pack 300 can recover regenerative energy for powering the vehicle 400.

[0153] The vehicle according to the fourth embodiment is equipped with the battery pack according to the embodiment, and therefore the vehicle can exhibit high performance and is highly reliable.

[0154] [Fifth embodiment] According to a fifth embodiment, a stationary power source including a battery pack according to an embodiment is provided.

[0155] Such a stationary power source may be equipped with a battery pack according to an embodiment or a battery according to an embodiment instead of the battery pack according to an embodiment. Such a stationary power source can exhibit a long life.

[0156] FIG. 9 is a diagram showing an example of application of battery packs 300A, 300B according to the embodiment to stationary power sources 112, 123. The example shown in FIG. 9 shows a system 110 in which the stationary power sources 112, 123 are used. The system 110 includes a power plant 111, a stationary power source 112, a consumer-side power grid 113, and an energy management system (EMS) 115. A power grid 116 and a communication network 117 are also formed in the system 110, and the power plant 111, the stationary power source 112, the consumer-side power grid 113, and the EMS 115 are connected via the power grid 116 and the communication network 117. The EMS 115 utilizes the power grid 116 and the communication network 117 to perform control to stabilize the entire system 110.

[0157] The power plant 111 generates a large amount of electricity using fuel sources such as thermal power and nuclear power. Electricity is supplied from the power plant 111 via a power grid 116 or the like. A battery pack 300A is mounted on the stationary power source 112. The battery pack 300A can store the electricity supplied from the power plant 111. The stationary power source 112 can supply the electricity stored in the battery pack 300A via the power grid 116 or the like. The system 110 is provided with a power conversion device 118. The power conversion device 118 includes a converter, an inverter, a transformer, and the like. Therefore, the power conversion device 118 can convert between direct current and alternating current, convert between alternating currents with different frequencies, and perform voltage transformation (boosting and bucking), etc. Therefore, the power conversion device 118 can convert the electricity from the power plant 111 into electricity that can be stored in the battery pack 300A.

[0158] The consumer-side power system 113 includes a power system for a factory, a power system for a building, a power system for a home, etc. The consumer-side power system 113 includes a consumer-side EMS 121, a power conversion device 122, and a stationary power source 123. The stationary power source 123 is equipped with a battery pack 300B. The consumer-side EMS 121 performs control to stabilize the consumer-side power system 113.

[0159] The consumer-side power system 113 is supplied with power from the power plant 111 and power from the battery pack 300A via the power grid 116. The battery pack 300B can store the power supplied to the consumer-side power system 113. Similarly to the power conversion device 118, the power conversion device 122 includes a converter, an inverter, a transformer, and the like. Therefore, the power conversion device 122 can convert between direct current and alternating current, convert between alternating currents with different frequencies, and perform voltage transformation (boosting and bucking), etc. Therefore, the power conversion device 122 can convert the power supplied to the consumer-side power system 113 into power that can be stored in the battery pack 300B.

[0160] The power stored in the battery pack 300B can be used, for example, to charge a vehicle such as an electric car. The system 110 may also be provided with a natural energy source. In this case, the natural energy source generates power using natural energy such as wind power and solar power. Power is supplied from the natural energy source in addition to the power plant 111 through the power grid 116. [Example]

[0161] The above-described embodiment will be specifically explained below using examples, but the present invention is not limited to the following examples as long as they do not deviate from the gist of the present invention.

[0162] Example 1 A secondary battery was fabricated according to the following procedure.

[0163] <Preparation of negative electrode> As the negative electrode active material, particles of a niobium-titanium-containing oxide having a monoclinic structure and a composition represented by the formula TiNb2O7 were prepared. This niobium-titanium-containing oxide having a monoclinic structure is suitable for the lithium ion battery. a The niobium-titanium-containing oxide has a composition represented by TiNb2O7 (0≦a≦5). The lithium ion absorption / desorption potential of the niobium-titanium-containing oxide is 1.0 V (vs. Li / Li) based on metallic lithium. +) was obtained. Additionally, acetylene black was prepared as a conductive agent, and carboxymethyl cellulose (CMC) and styrene butadiene rubber (SBR) were prepared as binders. These were mixed in pure water so that the mass ratio (mass %) of negative electrode active material: acetylene black: carboxymethyl cellulose: styrene butadiene rubber was 92.5:4:1.5:2.0, to obtain a slurry. This slurry was applied to both sides of a current collector made of aluminum foil with a thickness of 15 μm, and the coating was dried. Thus, a composite including a current collector and negative electrode active material-containing layers formed on both sides of the current collector was obtained. The obtained composite was then subjected to roll pressing. The composite was then further subjected to vacuum drying to obtain a negative electrode.

[0164] <Preparation of positive electrode> The positive electrode active material is LiNi 0.33 Mn 0.33 Co 0.33 Particles of lithium nickel cobalt manganese composite oxide represented by O2 (referred to as NMC111) were prepared. Acetylene black was also prepared as a conductive agent, and polyvinylidene fluoride (PVdF) was prepared as a binder. These were mixed so that the mass ratio (mass %) of positive electrode active material:conductive agent:binder was 90:5:5 to obtain a mixture. The resulting mixture was then dispersed in n-methylpyrrolidone (NMP) solvent to prepare a positive electrode slurry. This slurry was applied to both sides of a 15 μm-thick aluminum foil current collector, and the coating was dried. Thus, a composite including a current collector and positive electrode active material-containing layers formed on both sides of the current collector was obtained. The resulting composite was then subjected to roll pressing. The composite was then further subjected to vacuum drying to obtain a positive electrode.

[0165] The positive and negative electrodes were each cut out so that the area where the active material-containing layer was formed was 7 cm wide and 9 cm high. Three negative electrodes and two positive electrodes were alternately stacked with 20 μm-thick cellulose separators in between to produce an electrode stack as an electrode group. Additionally, 0.2 mm-thick aluminum tabs were attached to the negative and positive electrodes for current collection. The produced electrode stack was housed in a laminate film exterior, and after pouring in a liquid electrolyte, it was sealed to obtain a secondary battery.

[0166] The liquid electrolyte had a composition of 84.8 mass% LiN(CF3SO2)2 (LiTFSI), 5 mass% H2O, 0.2 mass% KOH, and 10 mass% γ-butyrolactone (γ-GBL). The liquid electrolyte was a solution in which LiTFSI was dissolved.

[0167] Example 2 A secondary battery was fabricated in the same manner as in Example 1, except that the composition of the liquid electrolyte was changed to 84.8 mass % of LiTFSI, 5 mass % of HO, 0.2 mass % of KOH, and 10 mass % of methyl ethyl carbonate (MEC).

[0168] Example 3 A secondary battery was fabricated in the same manner as in Example 1, except that the composition of the liquid electrolyte was changed to 54.8 mass% LiTFSI, 40 mass% urea, 1.5 mass% HO, 0.2 mass% KOH, and 3.5 mass% γ-GBL.

[0169] Example 4 A secondary battery was fabricated in the same manner as in Example 1, except that the composition of the liquid electrolyte was changed to 55.8 mass% LiTFSI, 40.5 mass% urea, 2.5 mass% HO, 0.2 mass% KOH, and 1 mass% γ-GBL.

[0170] Example 5 A secondary battery was fabricated in the same manner as in Example 1, except that the composition of the liquid electrolyte was changed to 50.8 mass% LiTFSI, 32.2 mass% urea, 2 mass% HO, 0.2 mass% KOH, and 15 mass% γ-GBL.

[0171] Example 6 A secondary battery was fabricated in the same manner as in Example 1, except that the composition of the liquid electrolyte was changed to 54.8 mass% LiTFSI, 40 mass% urea, 1.5 mass% HO, 0.2 mass% KOH, and 3.5 mass% MEC.

[0172] Example 7 A secondary battery was fabricated in the same manner as in Example 1, except that the composition of the liquid electrolyte was changed to 54.8 mass% LiTFSI, 40 mass% urea, 1.5 mass% HO, 0.2 mass% KOH, and 3.5 mass% acetonitrile.

[0173] Example 8 A secondary battery was fabricated in the same manner as in Example 1, except that the composition of the liquid electrolyte was changed to 40.3 mass% LiTFSI, 29.4 mass% urea, 0.005 mass% HO, 0.2 mass% KOH, and 13 mass% γ-GBL.

[0174] Example 9 A secondary battery was fabricated in the same manner as in Example 1, except that the composition of the liquid electrolyte was changed to 54.8 mass% LiTFSI, 40 mass% acetamide, 1.5 mass% HO, 0.2 mass% KOH, and 3.5 mass% γ-GBL.

[0175] Example 10 A secondary battery was fabricated in the same manner as in Example 1, except that the composition of the liquid electrolyte was changed to 51.8 mass% LiTFSI, 43 mass% N-methylurea, 1.5 mass% HO, 0.2 mass% KOH, and 3.5 mass% γ-GBL.

[0176] Example 11 A secondary battery was fabricated in the same manner as in Example 1, except that the composition of the liquid electrolyte was changed to 54.8 mass% LiTFSI, 40 mass% urea, 1.5 mass% HO, 0.2 mass% KOH, 2.5 mass% γ-GBL, and 1 mass% MEC.

[0177] Example 12 A secondary battery was fabricated in the same manner as in Example 1, except that the composition of the liquid electrolyte was changed to 56.8 mass% LiN(FSO2)2 (LiFSI), 38 mass% urea, 1.5 mass% HO, 0.2 mass% KOH, and 3.5 mass% γ-GBL.

[0178] Example 13 A secondary battery was fabricated in the same manner as in Example 1, except that the composition of the liquid electrolyte was changed to 54.3 mass% LiTFSI, 40 mass% urea, 1.5 mass% HO, 0.2 mass% KOH, 3.5 mass% γ-GBL, and 0.5 mass% LiBF(C0)(LiDFOB).

[0179] Example 14 A secondary battery was fabricated in the same manner as in Example 1, except that the composition of the liquid electrolyte was changed to 54.3 mass% LiTFSI, 40 mass% urea, 1.5 mass% HO, 0.2 mass% KOH, 3.5 mass% γ-GBL, and 0.5 mass% hexamethylene diisocyanate.

[0180] Examples 15-17 A negative electrode was prepared in the same manner as in Example 1, except that the composition of the negative electrode active material was changed to the composition shown in the table. A secondary battery was prepared in the same manner as in Example 3, except that this negative electrode was used. The negative electrode active material of Example 15 was used in the battery to a Ti2Nb 10 O 29 The negative electrode active material of Example 15 has a lithium ion absorption / desorption potential of 1.0 V (vs. Li / Li) based on metallic lithium. + The negative electrode active material of Example 16 was a The negative electrode active material of Example 16 has a composition represented by Ti2Nb2O9 (0≦a≦6). The lithium ion absorption / desorption potential of the negative electrode active material of Example 16 is 1.0 V (vs. Li / Li) based on metallic lithium. + The negative electrode active materials of Example 17 were Li4Ti5O 12 The negative electrode active material of Example 17 has a lithium ion absorption / desorption potential of 1.4 V (vs. Li / Li) based on metallic lithium. + ) was.

[0181] Example 18 LiNi as the positive electrode active material 0.8 Mn0.1 Co 0.1 A positive electrode was produced in the same manner as in Example 1, except that particles of a lithium nickel cobalt manganese composite oxide represented by O2 (referred to as NMC811) were used. A secondary battery was produced in the same manner as in Example 3, except that this positive electrode was used.

[0182] Example 19 LiNi as the positive electrode active material 0.5 Mn 0.3 Co 0.2 A positive electrode was produced in the same manner as in Example 1, except that particles of a lithium nickel cobalt manganese composite oxide represented by O2 (referred to as NMC532) were used. A secondary battery was produced in the same manner as in Example 3, except that this positive electrode was used.

[0183] Example 20 LiAl with spinel structure as a positive electrode active material 0.05 Mn 1.95 A positive electrode was produced in the same manner as in Example 1, except that particles of a lithium manganese composite oxide represented by O4 (referred to as LMO) were used. A secondary battery was produced in the same manner as in Example 3, except that this positive electrode was used. Example 21 Using TLO particles as the negative electrode active material and LMO particles as the positive electrode active material, a negative electrode and a positive electrode were fabricated in the same manner as in Example 1. A secondary battery was fabricated in the same manner as in Example 3, except that these negative electrode and positive electrode were used.

[0184] (Comparative Example 1) A secondary battery was fabricated in the same manner as in Example 1, except that the composition of the liquid electrolyte was changed to 84.8 mass % of LiTFSI, 15 mass % of H2O, and 0.2 mass % of KOH.

[0185] (Comparative Example 2) A secondary battery was fabricated in the same manner as in Example 1, except that the composition of the liquid electrolyte was changed to 52.8 mass% LiTFSI, 37.5 mass% urea, 6 mass% HO, 0.2 mass% KOH, and 3.5 mass% γ-GBL. (Comparative Example 3) A secondary battery was fabricated in the same manner as in Example 1, except that the composition of the liquid electrolyte was changed to 48.8 mass% LiTFSI, 34 mass% urea, 1 mass% HO, 0.2 mass% KOH, and 16 mass% γ-GBL.

[0186] The performance of the obtained secondary battery was confirmed by the following method, and the results are shown in Tables 3 and 4. <Evaluation> (Electrolyte ignition test) A 2cm square glass nonwoven fabric sample soaked in electrolyte was hung and a flame from a lighter was applied from below for 10 seconds. When the flame from the lighter was moved away from the sample, if no flame was observed on the sample and it was non-combustible, it was marked with a circle (○); if a flame was observed immediately after the sample was moved away but extinguished within 5 seconds, it was marked with a triangle (△); and if a flame rose from the sample and it was burning, it was marked with an × (x). (Charge-discharge cycle test) The secondary batteries obtained in the above examples and comparative examples were subjected to an initial charge / discharge cycle, and then the charge / discharge cycle life was measured at 25°C. At 25°C, the batteries were charged to 2.6 V at 0.2 C and then discharged to 1.5 V at 0.2 C. This charge / discharge cycle was repeated 100 times, and the retention rate (%) of the discharge capacity at the 100th cycle relative to the discharge capacity at the first cycle was calculated to determine the capacity retention rate during the charge / discharge cycle. Furthermore, the volumes of the cells before and after 100 cycles were measured based on Archimedes' principle, and the amount of gas generated during the cycle was calculated as the cell volume after cycling minus the cell volume before cycling. The results are shown in the table.

[0187] [Table 1]

[0188] [Table 2]

[0189] [Table 3]

[0190] [Table 4]

[0191] As is clear from Tables 1 to 4, the secondary batteries of Examples 1 to 13, which used electrolytes containing 0.005% by mass or more and 5% by mass or less of water and 1% by mass or more and 15% by mass or less of an aprotic polar solvent, generated less gas during charge-discharge cycles than those of Comparative Examples 1 and 2. Comparative Examples 1 and 2 had compositions in which the water content in the electrolyte exceeded the above ranges. As a result, gas was generated due to electrolysis of water during charge-discharge, and cycle deterioration progressed due to factors such as a decrease in electrode utilization efficiency caused by the gas. Comparative Example 3 generated the same amount of gas as Examples 1 to 21, but the electrolyte was flammable.

[0192] A comparison of Examples 1 and 2 with Examples 3 to 21 reveals that adding the first compound as a hydrogen bond donor component can reduce the amount of water contained in the electrolyte, further reducing the amount of gas generated. In Examples 3 to 21, an alkali metal salt having a melting point of 25°C or higher reacts with the first compound as a hydrogen bond donor component, thereby producing a liquid mixture and a solution in which the alkali metal salt is dissolved. The liquid mixture is also called a deep eutectic solvent.

[0193] In Examples 2, 5, and 8, due to the high content of organic solvent, flammability was observed while a flame was brought close, but the self-extinguishing function prevented continued combustion. Furthermore, for the acetonitrile mixture composition of Example 7, flammability increased at the same mixing ratio as γ-GBL or MEC due to the low flash point and high vapor pressure of acetonitrile, but continuous combustion was not observed, and cells using this electrolyte showed the same gas reduction effect as γ-GBL and MEC. Comparing Example 3 with Examples 13 and 14, the addition of LiDFOB and HDI further reduced gas emissions and improved cycle life. It is believed that the second compound, an additive, forms a film on the electrode, which inhibits corrosion of the Al current collector and thus suppresses the gas emissions.

[0194] According to at least one embodiment of the secondary battery described above, the secondary battery includes an electrolyte solution containing an alkali metal salt having a melting point of 25°C or higher, 0.005% by mass to 5% by mass of water, and 1% by mass to 15% by mass of an aprotic polar organic solvent, thereby improving the safety of the secondary battery. Furthermore, this electrolyte solution can suppress gas generation due to electrolysis (e.g., reductive decomposition) of water in the electrolyte solution during charge and discharge, and can absorb generated gas (e.g., hydrogen). As a result, the amount of gas generated during charge and discharge can be reduced, and the charge and discharge cycle life performance can be improved.

[0195] Although several embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be embodied in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are included within the scope and spirit of the invention, and are also included in the scope of the invention and its equivalents as defined in the claims.

[0196] The following describes the invention in terms of embodiments. (1) A positive electrode and a negative electrode; an electrolyte solution containing an alkali metal salt having a melting point of 25°C or higher, 0.005% by mass or more and 5% by mass or less of water, and 1% by mass or more and 15% by mass or less of an aprotic polar organic solvent; A secondary battery comprising: (2) The secondary battery according to (1), wherein the aprotic polar organic solvent includes at least one selected from the group consisting of carbonates, esters, amides, and nitrile compounds. (3) The secondary battery according to (1) or (2), wherein the alkali metal salt includes at least one selected from the group consisting of a lithium salt having a melting point of 25°C or higher, a sodium salt having a melting point of 25°C or higher, and a potassium salt having a melting point of 25°C or higher. (4) The secondary battery according to any one of (1) to (3), wherein the electrolytic solution further contains a compound capable of forming a eutectic with the alkali metal salt. (5) The secondary battery according to any one of (1) to (4), wherein the alkali metal salt includes at least one lithium salt selected from the group consisting of LiN(CF3SO2)2, LiN(FSO2)2, and LiCF3SO3. (6) The secondary battery according to any one of (1) to (5), wherein the electrolytic solution further contains one or more compounds selected from the group consisting of an isocyanate compound, a fluoride compound, and a boric acid compound. (7) The negative electrode has a lithium ion absorption / desorption potential of 1 V (vs. Li / Li) based on metallic lithium. + ) or more than 3V (vs. Li / Li + The secondary battery according to any one of (1) to (6), comprising a compound which is: (8) A battery pack comprising the secondary battery according to any one of (1) to (7). (9) The battery pack according to (8), further comprising an external terminal for current supply and a protection circuit. (10) The battery pack according to (8) or (9), comprising a plurality of the secondary batteries, the batteries being electrically connected in series, in parallel, or in a combination of series and parallel. (11) A vehicle equipped with the battery pack according to any one of (8) to (10). (12) A stationary power source comprising the battery pack according to any one of (8) to (10). [Explanation of symbols]

[0197] 1... secondary battery, 2... electrode group, 3... negative electrode, 3a... negative electrode current collector, 3b... negative electrode composite layer (negative electrode active material containing layer), 4... separator, 5... positive electrode, 5a... positive electrode current collector, 5b... positive electrode composite layer (positive electrode active material containing layer), 6... negative electrode terminal, 7... positive electrode terminal, 8... negative electrode gasket, 9... positive electrode gasket, 16... negative electrode lead, 17... positive electrode lead, 20... exterior member, 21... sealing plate, 22... control valve, 23... filling port, 24... sealing plug, 31... storage container, 32... lid, 33... protective sheet, 34... printed wiring board, 35... wiring, 36... adhesive tape, 40... vehicle body, 100... secondary battery, 110... system, 111... power plant, 112... stationary power source, 113... consumer side power system, 115...energy management system, 116...power grid, 117...communication network, 118...power conversion device, 121...consumer-side EMS, 122...power conversion device, 123...stationary power source, 200...battery pack, 201...bus bar, 206...negative side lead, 207...positive side lead, 300...battery pack, 300A...battery pack, 300B...battery pack, 342...positive side connector, 342a...wiring, 343...negative side connector, 343a...wiring, 345...thermistor, 346...protection circuit, 348a...positive side wiring, 348b...negative side wiring, 350...external terminal for energizing, 352...positive side terminal, 353...negative side terminal, 400...vehicle.

Claims

1. A positive electrode and a negative electrode; an electrolyte solution containing an alkali metal salt having a melting point of 25°C or higher, 0.005% by mass or more and 5% by mass or less of water, and 1% by mass or more and 15% by mass or less of an aprotic polar organic solvent; A secondary battery comprising:

2. 2. The secondary battery according to claim 1, wherein the aprotic polar organic solvent includes at least one selected from the group consisting of carbonates, esters, amides, and nitrile compounds.

3. 2. The secondary battery according to claim 1, wherein the alkali metal salt comprises at least one selected from the group consisting of a lithium salt having a melting point of 25° C. or higher, a sodium salt having a melting point of 25° C. or higher, and a potassium salt having a melting point of 25° C. or higher.

4. The secondary battery according to claim 3 , wherein the electrolyte solution further contains a compound capable of forming a eutectic with the alkali metal salt.

5. The alkali metal salt is LiN(CF 3 SO 2 ) 2 , LiN(FSO 2 ) 2 and LiCF 3 SO 3 The secondary battery according to claim 1 , comprising one or more lithium salts selected from the group consisting of:

6. 2. The secondary battery according to claim 1, wherein the electrolyte solution further contains one or more compounds selected from the group consisting of an isocyanate compound, a fluoride compound, and a boric acid compound.

7. The negative electrode has a lithium ion absorption / desorption potential of 1 V (vs. Li / Li) based on metallic lithium. + ) or more 3V (vs.Li / Li + 2. The secondary battery according to claim 1, comprising a compound having the following structure:

8. A battery pack comprising the secondary battery according to any one of claims 1 to 7.

9. The battery pack according to claim 8 , further comprising an external terminal for current application and a protection circuit.

10. 10. The battery pack according to claim 9, comprising a plurality of the secondary batteries, the batteries being electrically connected in series, in parallel, or in a combination of series and parallel.

11. A vehicle equipped with the battery pack according to claim 8.

12. A stationary power source comprising the battery pack according to claim 8.

Images