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

Abstract

To provide a secondary battery excellent in cycle performance and discharge rate performance, a battery pack provided with the secondary battery, a vehicle, and a stationary power supply.SOLUTION: According to an embodiment, a secondary battery including a positive electrode 3, a negative electrode 4, and a non-aqueous electrolyte, is provided. The negative electrode 4 includes one or more selected from the group consisting of lithium metal, a lithium alloy, and a compound that can occlude and discharge Li. The non-aqueous electrolyte contains ionic liquid, and a urea compound in an amount of 0.5 weight% or more and 30 weight% 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] Nonaqueous electrolyte batteries using lithium metal, lithium alloys, lithium compounds, or carbonaceous materials as anodes are expected to achieve high energy densities. Research and development of nonaqueous electrolyte batteries is currently underway. To date, lithium-ion batteries with a cathode containing LiCoO2 or LiMn2O4 as the active material and an anode containing a carbonaceous material that absorbs and releases lithium ions have been widely used in portable devices. To advance applications in electric vehicles and stationary storage batteries, secondary batteries are required to have not only higher energy density and capacity, but also improved durability, low-temperature performance, and safety. To achieve higher energy densities, research and development is being conducted on post-lithium-ion batteries, including batteries with metal anodes (e.g., Li, Na, Mg, and Al), batteries with sulfur-containing cathodes, and batteries with air cathodes. The challenge for these post-lithium-ion batteries is to achieve both high energy density and durability.

[0003] In batteries containing metal anodes, using Li metal for the metal anode can cause problems such as short circuits due to dendrite precipitation. Furthermore, using Mg metal for the metal anode results in high overvoltage, making charge-discharge cycling difficult. Meanwhile, in recent years, room-temperature ionic liquids composed of positive ions (cations) and negative ions (anions) have been studied as electrolytes for lithium secondary batteries using Li metal anodes due to their high safety, including their non-volatility, non-flammability, and non-ignition. However, ionic liquids are susceptible to oxidation-reduction decomposition. Therefore, secondary batteries using ionic liquids as electrolytes suffer from significant cycle degradation and difficulty in low-temperature operation, making them difficult to put into practical use. [Prior art documents] [Non-patent literature]

[0004] [Non-Patent Document 1] Tomoko Sugizaki et al., Triethyl sulfonium bis(trifluoromethylsulfonyl)imide ionic liquids with highly concentrated LiFSI as electrolytes for Li metal batteries, Journal of Power Sources 571 (2023) 233024 [Non-patent document 2] Aqueous electrolyte design for super-stable 2.5 V LiMn2O4 || Li4Ti5O12 pouch cells by Jijian Xu et al., Nature Energy volume 7, pages 186-193 (2022) Summary of the Invention [Problem to be solved by the invention]

[0005] According to the embodiments, an object is to provide a secondary battery having excellent cycle performance and discharge rate performance, an electrode that can realize this secondary battery, a battery pack equipped with this secondary battery, a vehicle, and a stationary power source. [Means for solving the problem]

[0006] According to an embodiment, a secondary battery is provided that includes a positive electrode, a negative electrode, and a non-aqueous electrolyte. The negative electrode includes at least one material selected from the group consisting of lithium metal, lithium alloys, and compounds capable of absorbing and releasing Li. The non-aqueous electrolyte includes an ionic liquid and 0.5% by weight to 30% by weight of a urea compound.

[0007] According to an embodiment, a battery pack including a secondary battery according to an embodiment is provided.

[0008] According to an embodiment, a vehicle including a battery pack according to an embodiment is provided, and according to an embodiment, a stationary power source including a battery pack according to an embodiment is provided. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 2 is a partially cutaway cross-sectional view of the secondary battery according to the embodiment. [Figure 2] FIG. 2 is a side view of the battery of FIG. 1. [Figure 3] 2 is a cross-sectional view of the secondary battery according to the embodiment, taken along a direction perpendicular to the terminal extending direction. FIG. [Figure 4] FIG. 4 is an enlarged cross-sectional view of part A in FIG. 3. [Figure 5] FIG. 2 is an exploded perspective view of the battery pack according to the embodiment. [Figure 6] FIG. 6 is a block diagram showing the electrical circuit of the battery pack of FIG. 5. [Figure 7] 1 is a schematic diagram showing an example of a vehicle equipped with a secondary battery according to an embodiment; [Figure 8] FIG. 10 is a diagram schematically illustrating another 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

[0010] (First embodiment) The secondary battery according to the embodiment includes a positive electrode, a negative electrode including a negative electrode active material containing at least one selected from the group consisting of lithium metal, lithium alloys, and compounds capable of absorbing and releasing Li, and a non-aqueous electrolyte containing an ionic liquid and 0.5% by weight to 30% by weight of a urea compound. The secondary battery according to the embodiment is, for example, a non-aqueous electrolyte secondary battery. An example of a non-aqueous electrolyte secondary battery is a lithium secondary battery.

[0011] By adjusting the content of the urea compound in the non-aqueous electrolyte to 0.5% by weight or more and 30% by weight or less, a film (e.g., a coating) containing a lithium nitrogen compound can be formed on the negative electrode. Because lithium nitrogen compounds are a type of solid electrolyte, they have high ionic conductivity. Therefore, a film containing a lithium nitrogen compound has low resistance. As a result, reductive decomposition of the ionic liquid at the negative electrode can be suppressed without impairing the ionic conductivity of the negative electrode. This low-resistance film is thought to be formed mainly by the reductive decomposition of the urea compound during battery charging. An example of a lithium nitrogen compound is Li3N. Li3N has excellent ionic conductivity. Furthermore, the non-aqueous electrolyte can form a nitrogen-containing film on the positive electrode, for example, the positive electrode current collector, through oxidative decomposition of the urea compound. This suppresses oxidative decomposition of the ionic liquid at the positive electrode and corrosion of the positive electrode current collector.

[0012] Both oxidative decomposition and reductive decomposition of the ionic liquid can be suppressed, and corrosion of the positive electrode current collector can be suppressed, thereby suppressing an increase in the resistance of the secondary battery. As a result, the efficiency of the charge / discharge reaction of the secondary battery can be increased, thereby improving the cycle life performance and discharge rate performance. In addition, the secondary battery can improve the energy density. Furthermore, the secondary battery can suppress self-discharge, resulting in excellent storage performance.

[0013] Examples of the urea compound include urea ((NH2)2CO) and urea derivatives. Examples of the urea derivatives include N-methylurea and N,N'-dimethylpropyleneurea. The type of urea compound can be one or more types.

[0014] By setting the content of the urea compound in the non-aqueous electrolyte to 0.5 wt % or more, a low-resistance film (e.g., a coating) containing a highly ion-conductive lithium-nitrogen compound can be formed on the negative electrode by reductive decomposition of the urea compound. Furthermore, a nitrogen-containing film (e.g., a coating) can be formed on the positive electrode by oxidative decomposition of the urea compound. By setting the content of the urea compound in the non-aqueous electrolyte to 30 wt % or less, the formation of a film containing an insulating oxide on the positive and negative electrodes can be suppressed. A film containing an insulating oxide increases the resistance of the secondary battery. Therefore, the formation of an insulating oxide may reduce the cycle life and discharge rate performance of the secondary battery. An example of an insulating oxide is lithium carbonate. A more preferred range for the content of the urea compound in the non-aqueous electrolyte is 1. % by weight or more and 10% by weight or less.

[0015] The secondary battery will be described in detail below. The secondary battery includes a positive electrode, a negative electrode, and a non-aqueous electrolyte, and may also include a separator, an exterior member, and the like. The negative electrode, the positive electrode, and the separator can constitute an electrode assembly. The non-aqueous electrolyte can be held in the electrode assembly. The form of the electrode assembly is not particularly limited, and can be, for example, a stacked type or a wound type.

[0016] The nonaqueous electrolyte, the positive electrode, the negative electrode, the separator, and the exterior member will be described in detail below.

[0017] <Non-aqueous electrolyte> The nonaqueous electrolyte contains an ionic liquid and 0.5% by weight to 30% by weight of a urea compound. The nonaqueous electrolyte may be contained in at least one of the positive electrode or negative electrode. If the secondary battery includes a separator, the nonaqueous electrolyte may be contained in at least one of the positive electrode, negative electrode, or separator. The manner in which the nonaqueous electrolyte is contained in a member is not particularly limited, but examples include the nonaqueous electrolyte being in contact with the target member or being held by the target member. It is desirable that the nonaqueous electrolyte be contained in both the positive electrode and negative electrode, or in the positive electrode, negative electrode, and separator. This allows for smooth charge / discharge reactions.

[0018] Ionic liquids can be composed of, for example, positive ions (cations) and negative ions (anions). Cations include, for example, organic cations and lithium ions. The organic cations include one or more cations selected from the group consisting of 1,3-dialkylimidazolium ions, trialkylsulfonium ions, N,N-dialkylpiperidinium ions, and quaternary ammonium ions. The type of organic cation can be one or more types.

[0019] Preferably, the 1,3-dialkylimidazolium ion is 1-methyl-3-ethylimidazolium (MEI).

[0020] A trialkylsulfonium ion has a skeleton represented by the following formula (1). Examples of trialkylsulfonium ions include trimethylsulfonium ion (S(CH3)3 + : abbreviation S111), triethylsulfonium ion (S(C2H5)3 + : abbreviated as S222), diethylpropylsulfonium ion (S(C2H5)2(C3H7) + : abbreviation S223), methyl ethyl propyl sulfonium ion (S(CH3)(C2H5)(C3H7) + Ionic liquids containing triethylsulfonium ions as cations have low melting points and high ionic conductivity.

[0021] [ka]

[0022] Examples of N,N-dialkylpiperidinium ions include the N-methyl-N-propylpiperidinium (PP13) ion, which has a wide electrochemical potential range.

[0023] Examples of quaternary ammonium ions include tetraalkylammonium ions and cyclic ammonium ions. Examples of tetraalkylammonium ions include diethylmethylmethoxyethylammonium ion (DEME) and 1,2-dimethyl-3-propylammonium ion (DMPI). DEME ions and DMPI ions have excellent resistance to reductive decomposition.

[0024] An ionic liquid containing an organic cation containing at least one of MEI ions and S222 ions can reduce viscosity and therefore increase ionic conductivity.

[0025] The anion paired with the organic cation is [N(CF3SO2)2] - or [N(FSO2)2] - It is preferable to include one or more of the following: [N(CF3SO2)2] - , [N(FSO2)2] - The abbreviations for these are TFSI and FSI, respectively.

[0026] One or more cations selected from the group consisting of 1,3-dialkylimidazolium ions, trialkylsulfonium ions, N,N-dialkylpiperidinium ions, and quaternary ammonium ions, lithium ions, and [N(CF3SO2)2] - or [N(FSO2)2] - Ionic liquids containing anions consisting of one or more of the above have high ionic conductivity and improve the discharge rate performance of secondary batteries.

[0027] Lithium ions can be supplied, for example, from a lithium salt. Ionic liquids can be obtained, for example, by dissolving a lithium salt in an ionic liquid that does not contain lithium ions. Examples of ionic liquids that do not contain lithium ions include ionic liquids composed of organic cations and anions. LiN(FSO2)2 and LiN(CF3SO2)2 are preferred as lithium salts. One or more types of lithium salts can be used. The concentration of lithium ions in the nonaqueous electrolyte is preferably 0.5 mol / kg or more and 2 mol / kg or less. Ionic liquids that satisfy this range can maintain a liquid state over a wide temperature range, suppressing the decomposition reaction associated with the battery charge / discharge reaction of the ionic liquid, thereby improving the cycle life and low-temperature performance of secondary batteries. Furthermore, when the negative electrode contains metallic lithium, the interfacial resistance of the negative electrode can be reduced, thereby suppressing dendrite precipitation and improving the high-current characteristics and cycle life of secondary batteries. LiN(FSO2)2 and LiN(CF3SO2)2 are abbreviated as LiFSI and LiTFSI, respectively.

[0028] In a non-aqueous electrolyte, the FSI anion, in the presence of a urea compound, can form a film (e.g., a coating) on ​​the positive electrode current collector even at low lithium ion concentrations (e.g., 0.5 mol / kg or more and 2 mol / kg or less). Therefore, a non-aqueous electrolyte containing the FSI anion and a urea compound can suppress corrosion of the positive electrode current collector. Furthermore, an ionic liquid containing FSI as the anion has better ionic conductivity than an ionic liquid containing TFSI as the anion.

[0029] The non-aqueous electrolyte may be substantially composed of an ionic liquid (containing Li ions) and a urea compound, or may contain other components. The content of the ionic liquid (containing Li ions) in the non-aqueous electrolyte may be, for example, 70% by weight or more and 99.5% by weight or less. This allows the lithium nitrogen compound in the negative electrode to exist stably.

[0030] The ionic liquid is preferably in a liquid or gel state. A gel non-aqueous electrolyte can be obtained, for example, by adding at least one of a polymer material and a gelling agent to a liquid non-aqueous electrolyte to form a gel.

[0031] The polymer material is not particularly limited as long as it can gel the non-aqueous electrolyte containing the ionic liquid, and both chemical and physical gelling agents can be used. The polymer material can also function as a gelling agent. Examples of polymer materials include polyacrylonitrile (PAN), polyethylene oxide (PEO), polyvinylidene fluoride (PVdF), and polymethyl methacrylate. An example of a gelling agent includes N,N,N',N'-Tetra(trifluoromethanesulfonyl)-dodecane-1,12-diamine.

[0032] The content of at least one of a polymer material and a gelling agent in the nonaqueous electrolyte is preferably 1% by weight to 10% by weight. By adjusting the content within this range, low-temperature performance and discharge performance can be improved. The type of component to be added can be one or more types.

[0033] The non-aqueous electrolyte may contain a fluorine compound. Examples of the fluorine compound include organic fluorine compounds and inorganic fluorine compounds. One or more types of fluorine compounds may be used. The organic fluorine compound can increase the solubility of urea compounds, lithium salts, and the like in a solvent. Examples of the organic fluorine compound include fluorinated esters and fluorinated ethers. Examples of the fluorinated esters include fluoroethylene carbonate (FEC), difluoroethylene carbonate (DFEC), and 2,2,2-trifluoroethyl methyl carbonate (TFEMC). Examples of the fluorinated ethers include 1,1,2,2-tetrafluoro-2,2,2-trifluoroethyl ether (HFE).

[0034] Other organic fluorine compounds include, for example, methyl 3,3,3-trifluoropropionate (FMP), 2,2,2-trifluoroethyl acetate (FEA), etc. The type of organic fluorine compound can be one or more types. Inorganic fluorine compounds are non-flammable and can improve the safety of secondary batteries. Examples of inorganic fluorine compounds include lithium difluoro(oxalato)borate.

[0035] The content of the fluorine compound in the non-aqueous electrolyte can be, for example, 0.1% by weight or more and 10% by weight or less.

[0036] The water content in the non-aqueous electrolyte may be 1000 ppm by weight or less (including 0 ppm by weight). This increases the stability of the lithium nitrogen compound present in the negative electrode. Lithium nitrogen compounds such as LiN are easily decomposed by water and can exist stably in the ionic liquid.

[0037] <Positive electrode> The positive electrode includes a positive electrode active material-containing layer containing a positive electrode active material, and a positive electrode current collector in contact with the positive electrode active material-containing layer.

[0038] The positive electrode active material may be different in type depending on whether the secondary battery is used after discharging or after charging.

[0039] When the secondary battery is first used after discharge, a metal oxide or metal sulfide can be used as the positive electrode active material. Examples of metal oxides include titanium-containing oxides, niobium-containing oxides, titanium-niobium-containing oxides, titanium-niobium-molybdenum-containing oxides, manganese-containing oxides, and iron-containing oxides. Examples of titanium-containing oxides include TiO2, TiO2(B), TiNb2O7, and Ti 0.2 NbMo 0.6 O7, Li4Ti5O 12 Examples of niobium-containing oxides include TiNb2O7, Ti0.2 NbMo 0.6 O7, Nb2O5, etc. are mentioned. As titanium niobium-containing oxides, for example, TiNb2O7, Ti 0.2 NbMo 0.6 O7, etc. are mentioned. As titanium niobium molybdenum-containing oxides, for example, Ti 0.2 NbMo 0.6 O7, etc. are mentioned. As manganese-containing oxides, for example, MnO2, etc., are mentioned. As iron-containing oxides, for example, FePO4, etc., are mentioned. As other metal oxides, for example, V2O5, etc., are mentioned. TiNb2O7, Li4Ti5O 12 [[ID=I3]]can obtain good cycle performance. As metal sulfides, TiS2, FeS2, FeS, CuS, Cu2S, NiS, etc., are mentioned. FeS, CuS can obtain a large capacity.

[0040] Examples of the positive electrode active material when using the secondary battery from charging include lithium metal oxides capable of occluding and releasing lithium ions. As lithium metal oxides, lithium cobalt oxide (for example, Li y CoO2, 0 < y ≤ 1.1), lithium nickel cobalt manganese oxide (for example, layered lithium nickel cobalt manganese oxide (for example, Li y Ni a Co b Mn c O2, a + b + c = 1, 0 < a, 0 < b, 0 < c, 0 < y ≤ 1.1)), lithium nickel cobalt aluminum oxide (for example, Li y Ni a Co b Al c O2, a + b + c = 1, 0 < a, 0 < b, 0 < c, 0 < y ≤ 1.1), lithium iron phosphate (for example, Li y FePO4, 0 < y ≤ 1.1), lithium iron fluorosulfate (for example, Li y FeSO4F, 0 < y ≤ 1.1), lithium manganese iron phosphate (for example, Li y Mn 1-a Fe a PO4: 0 < a ≤ 0.5, 0 < y ≤ 1.1), lithium manganese oxide (for example, Liy Mn2O4, 0 < y ≤ 1.1), lithium nickel manganese oxide (e.g., Li y Ni 0.5 Mn 1.5 O4, 0 < y ≤ 1.1), lithium cobalt phosphate (e.g., Li y CoPO4, 0 < y ≤ 1.1), spinel-structured lithium nickel manganese oxide (e.g., Li x Ni a Mn 2-a O 4、 0.4 ≤ a ≤ 0.6, 0 ≤ x ≤ 1.1), etc. The positive electrode containing a lithium metal oxide capable of occluding and releasing lithium ions as a positive electrode active material can promote the reductive decomposition of the urea compound in the negative electrode containing a negative electrode active material containing one or more selected from the group consisting of lithium metal, lithium alloy, and compounds capable of occluding and releasing Li.

[0041] More preferable positive electrode active materials are spinel-structured lithium nickel manganese oxide, lithium cobalt oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium cobalt phosphate, lithium manganese oxide, etc. The above positive electrode active material can exhibit a high voltage of 4 V (vs. Li / Li + ) or more. The positive electrode containing lithium nickel cobalt manganese oxide can obtain a high capacity.

[0042] The type of positive electrode active material used can be one type or two or more types.

[0043] The positive electrode active material particles may be in the form of primary particles, secondary particles in which the primary particles are aggregated, or a mixture of primary particles and secondary particles.

[0044] The positive electrode active material-containing layer may contain a conductive agent. Examples of conductive agents include carbon materials such as carbon nanofibers, acetylene black, and graphite. The above-mentioned carbon materials can improve the electronic network in the positive electrode. The conductive agent may be of one type or two or more types. The proportion of the conductive agent in the positive electrode active material-containing layer (excluding the weight of the non-aqueous electrolyte) is preferably 5% by weight or more and 40% by weight or less.

[0045] The positive electrode active material-containing layer may contain a binder. Examples of binders include polyvinylidene fluoride (PVdF), polyethylene terephthalate, polysulfone, polyimide, cellulose, and rubber. The above-mentioned types of binders have excellent chemical stability against non-aqueous electrolytes. The proportion of the binder in the positive electrode active material-containing layer (excluding the weight of the non-aqueous electrolyte) is preferably 1% by weight or more and 10% by weight or less.

[0046] The positive electrode current collector may be a porous material, a mesh, or a foil, or a combination of two or more of these. The material of the positive electrode current collector may be, for example, one or more conductive materials selected from aluminum, copper, stainless steel, and nickel. Aluminum is a preferred material.

[0047] The thickness of the positive electrode current collector is 20 μm or less, and more preferably 15 μm or less.

[0048] The thickness of the positive electrode varies depending on the electrode shape and application. When the electrode group structure is a stacked structure or a wound structure, the thickness of the positive electrode is preferably 30 μm to 100 μm for high-power applications, and 100 μm to 500 μm for high-energy applications.

[0049] When the positive electrode active material-containing layer has a porous structure, the proportion of non-aqueous electrolyte in the positive electrode active material-containing layer is preferably in the range of 10% by weight to 60% by weight. By making the proportion 10% by weight or more, the effective area of ​​the electrochemical reaction can be increased, improving the battery capacity and suppressing the resistance. By making the proportion 60% by weight or less, the positive electrode weight proportion can be increased, improving the battery capacity.

[0050] The positive electrode may include a nitrogen-containing film (e.g., a coating). The nitrogen-containing film may be present on at least a portion of the surface of the positive electrode active material-containing layer, at least a portion of the surface of the positive electrode current collector, or at least a portion of the surfaces of both the positive electrode active material-containing layer and the positive electrode current collector, thereby suppressing corrosion of the positive electrode current collector and oxidative decomposition of the ionic liquid. The nitrogen-containing film may be present on a portion of the target surface or on the entire surface. The nitrogen-containing film may also contain an atom selected from the group consisting of Li, C, O, and F.

[0051] <Negative electrode> The negative electrode contains, as a negative electrode active material, one or more selected from the group consisting of lithium metal, lithium alloys, and compounds capable of absorbing and releasing Li. The type of negative electrode active material used can be one or more types.

[0052] Lithium metal may contain elements other than lithium as impurity phases (not alloy phases), while lithium alloys include alloy phases in which elements other than lithium form alloy phases with lithium. Lithium metal may contain elements other than lithium as inevitable impurities (e.g., one or more selected from Si, Mg, Ca, Zn, Sn, Fe, Ni, etc.). The purity of the lithium metal can be 90% by weight or more (including 100% by weight). A negative electrode containing lithium metal has a high capacity, can increase the battery voltage, and can be made lightweight, thereby increasing the energy density of the secondary battery. The purity of the lithium metal is desirably greater than 99.5% by weight.

[0053] An example of a lithium alloy is a lithium alloy containing an element capable of alloying with lithium. Examples of elements capable of alloying with lithium include Al, Si, Sn, Zn, Mg, etc. One or more types of elements may be used. Specific examples of lithium alloys include Li-Al, Li-Si, Li-Sn, Li-Zn, Li-Mg, etc. The content of elements other than lithium in the lithium alloy may be 0.5% by weight or more and 10% by weight or less.

[0054] The lithium metal and the lithium alloy are preferably in the form of a plate or foil.

[0055] The compound capable of absorbing and desorbing Li is a compound capable of absorbing and desorbing lithium or lithium ions. Examples of this compound include graphite, carbonaceous material, titanium-containing oxide, niobium-containing oxide, Si / graphite composite material obtained by combining Si powder and graphite powder, lithium graphite in which lithium ions have been pre-absorbed, and lithium carbonaceous material in which lithium ions have been pre-absorbed. The type of compound used can be one or more types.

[0056] Examples of the carbonaceous material include carbon fiber, coke, and non-graphitizable carbon.

[0057] Examples of the titanium-containing oxide include lithium titanium-containing oxide and titanium oxide.

[0058] Examples of lithium titanium-containing oxides include those having a spinel structure (e.g., those having the general formula Li 4 / 3+a Ti 5 / 3 O4 (0≦a≦2)), those having a ramsdellite structure (e.g., those having the general formula Li 2+a Ti3O7(0≦a≦1)), Li 1+b Lithium titanium-containing oxide represented by Ti2O4 (0≦b≦1), Li 1.1+b Ti 1.8 Lithium titanium-containing oxide represented by O4 (0≦b≦1), Li 1.07+b Ti 1.86Examples include lithium-titanium-containing oxides represented by O4 (0≦b≦1), and lithium-titanium-containing composite oxides containing at least one element selected from the group consisting of Nb, Mo, W, P, V, Sn, Cu, Ni, and Fe.

[0059] In addition, examples of lithium titanium-containing oxides include Li 2+a A d Ti 6-b B b O 14ーc (A is one or more elements selected from Na, K, Mg, Ca, and Sr, B is a metal element other than Ti, and 0≦a≦5, 0≦b≦6, 0≦c≦0.6, and 0≦d≦3) are included. 2+a A d Ti 6-b B b O 14ーc has a crystal structure in the space group Cmca.

[0060] Another example of the lithium titanium-containing oxide is an orthorhombic titanium-containing oxide. 2+a M I 2-b Ti 6-c M II d O 14+σ In this case, M I is at least one selected from the group consisting of Sr, Ba, Ca, Mg, Na, Cs, Rb and K. II is at least one selected from the group consisting of Zr, Sn, V, Nb, Ta, Mo, W, Y, Fe, Co, Cr, Mn, Ni, and Al. The subscripts in the composition formula are 0≦a≦6, 0≦b<2, 0≦c<6, 0≦d<6, and -0.5≦σ≦0.5. Specific examples of orthorhombic titanium-containing composite oxides include Li 2+a Na2Ti6O 14 (0≦a≦6).

[0061] Examples of titanium oxides include those with the general formula Li aTitanium oxides represented by TiO2 (0≦a≦2) are included. In this case, the composition formula before charging is TiO2. Examples of titanium oxides include titanium oxides with a monoclinic structure (bronze structure (B)), titanium oxides with a rutile structure, and titanium oxides with an anatase structure. TiO2(B) with a monoclinic structure (bronze structure (B)) is preferred. Low-crystalline TiO2(B) with a heat treatment temperature of 300 to 600°C is also preferred.

[0062] Examples of the niobium-containing oxide include niobium oxide, niobium-titanium-containing oxide, niobium-tungsten-containing oxide, and niobium-titanium-molybdenum-containing oxide.

[0063] Examples of niobium oxides include Nb2O5.

[0064] Examples of niobium titanium-containing oxides include monoclinic niobium titanium-containing oxides, Ti2Nb2O9, Ti2Nb 10 O 29 , TiNb 14 O 37 , TiNb 24 O 62 The substituted niobium titanium composite oxides include those in which at least a portion of Nb and / or Ti has been 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 oxides may contain one type of substituting element or two or more types of substituting elements.

[0065] Examples of monoclinic niobium titanium-containing oxides include those represented by the general formula Li c TiNb d O7 (0≦c≦5, 1≦d≦4). A more preferred composition is TiNb2O7.

[0066] Examples of monoclinic niobium titanium oxides include Li x Ti 1-y M1 y Nb 2-z M2 z O 7+δHere, 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.

[0067] Another example of a monoclinic niobium titanium-containing oxide is 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.

[0068] Examples of niobium-tungsten-containing oxides include Nb 14 W3O 44 , Nb 16 W5O 55 ,Nb 18 W8O 69 Examples include:

[0069] Examples of niobium titanium molybdenum-containing oxides include those represented by the general formula Li a Ti b Nb 2-2d Mo c+2d O 2b+5+3c (wherein the subscripts a, b, c, and d are preferably within the ranges of 0≦a≦b+4+3c, 0.3≦b≦1.6, 0.3≦c<1.6, and 0≦d<0.4, respectively), and a tetragonal titanium-niobium-molybdenum composite oxide represented by the general formula Li a M b NbMo c O d where M is one or more selected from the group consisting of Ti, V, Ta, Fe, Co, Mn, Ni, Bi, Sb, As, P, Cr, W, B, Na, K, Mg, Al, Ca, Y, and Si, and includes composite oxides satisfying 0≦a≦b+2+3c, 0≦b≦1.4, 0≦c≦0.5, and 2.33≦d / (1+b+c)≦2.50.

[0070] Lithium metal, lithium alloy, graphite, carbonaceous material or Li c TiNb d A negative electrode active material containing at least one of O7 (0≦c≦5, 1≦d≦4) can cause the reductive decomposition of a urea compound at the potential for absorbing and releasing lithium or lithium ions. Therefore, this negative electrode active material can enhance the effect of suppressing the reductive decomposition of an ionic liquid. A negative electrode active material containing lithium metal and / or a lithium alloy also has excellent energy density in secondary batteries.

[0071] The negative electrode may include a layer containing a negative electrode active material. The layer containing a negative electrode active material may include a conductive agent and / or a binder.

[0072] Examples of the conductive agent include carbon materials, metal compound powders, and metal powders. Examples of the carbon material include acetylene black, carbon black, coke, carbon fiber, graphite, carbon nanotubes, and carbon nanofibers. The BET specific surface area of ​​the carbon material measured by N2 adsorption is 10 m 2 / g or more is preferred. Examples of metal compound powders include powders of TiO, TiC, and TiN. Examples of metal powders include powders of Al, Ni, Cu, and Fe. Examples of preferred conductive agents include coke, graphite, acetylene black, carbon fiber with an average fiber diameter of 1 μm or less, and TiO powder, which are heat-treated at a temperature of 800°C to 2000°C. Using one or more of these can reduce electrode resistance and improve cycle life performance. The type of conductive agent can be one or more types.

[0073] Examples of binders include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), fluorine-based rubber, acrylic rubber, styrene butadiene rubber, core-shell binder, polyimide, carboxymethyl cellulose (CMC), etc. One or more types of binders can be used.

[0074] A negative electrode active material-containing layer containing a compound capable of absorbing and releasing Li (hereinafter referred to as the "first compound") can be produced, for example, by suspending the first compound, a conductive agent, and a binder in an appropriate solvent, applying the suspension to a current collector, drying, and pressing. The blending ratio of the first compound, the conductive agent, and the binder is preferably in the range of 80 to 95 wt % of the first compound, 3 to 18 wt % of the conductive agent, and 2 to 7 wt % of the binder. Lithium metal foil or lithium alloy foil may also be used as the negative electrode active material-containing layer.

[0075] The negative electrode may further include a negative electrode current collector. The negative electrode current collector includes a foil or mesh containing a metal such as copper, nickel, or aluminum. The negative electrode current collector can be in contact with the negative electrode active material-containing layer. The negative electrode current collector is preferably electrically connected to a negative electrode terminal via a lead.

[0076] The negative electrode current collector may be different depending on the type of negative electrode active material. When lithium metal, lithium alloy, graphite, carbonaceous material, Si / graphite composite material obtained by combining Si powder and graphite powder, lithium graphite with pre-occluded lithium ions, or lithium carbonaceous material with pre-occluded lithium ions is used as the negative electrode active material, copper can be used as the negative electrode current collector. When a titanium-containing oxide or a niobium-containing oxide is used as the negative electrode active material, the negative electrode current collector may contain at least one of aluminum and an aluminum alloy. More preferred negative electrode current collectors are aluminum foil and aluminum alloy foil. The purity of the aluminum foil is preferably 99.99% or higher. Aluminum alloys containing elements such as magnesium, zinc, and silicon are preferred. On the other hand, transition metals such as iron, copper, nickel, and chromium are preferably contained at 100 ppm or less.

[0077] The thickness of the negative electrode current collector is 20 μm or less, and more preferably 15 μm or less.

[0078] The capacity of the negative electrode is preferably equal to or in excess of the capacity of the positive electrode.

[0079] The thickness of the negative electrode varies depending on the electrode shape and application. When the electrode group structure is a stack structure or a wound structure, the thickness of the negative electrode is preferably 30 μm or more and 500 μm or less.

[0080] The negative electrode may include a film (e.g., a coating) containing a lithium nitrogen compound. The film may be present on at least a portion of the surface of the negative electrode. The film is preferably present on at least a portion of the surface of the negative electrode active material, at least a portion of the surface of the negative electrode current collector, or at least a portion of the surfaces of the negative electrode active material and the negative electrode current collector. This can enhance the effect of suppressing reductive decomposition of the ionic liquid. The film may be present on a portion or the entire target surface. Examples of lithium nitrogen compounds include Li3N. The film containing the lithium nitrogen compound may contain at least one atom selected from the group consisting of C, O, and F.

[0081] <Separator> The separator can be disposed on at least one surface of the positive electrode, on at least one surface of the negative electrode, or between the positive and negative electrodes. The separator may be in contact with the positive electrode, the negative electrode, or the positive and negative electrodes, or may be integrated with the positive electrode, the negative electrode, or the positive and negative electrodes.

[0082] The separator can be made of a nonwoven fabric, a porous membrane, a lithium-ion conductive solid electrolyte membrane, or a composite of two or more of these. An example of a composite is a laminate of a lithium-ion conductive solid electrolyte membrane and a nonwoven fabric or a porous membrane. Polymers such as cellulose are used as the material for the nonwoven fabric. Porous membranes include polyethylene (PE), polypropylene (PP), and polyimide membranes.

[0083] The separator can be porous. The porosity of the separator can be between 60% and 80%, which allows the separator to contain a sufficient amount of non-aqueous electrolyte even if the ionic liquid has a high viscosity.

[0084] The thickness of the separator can be between 5 μm and 50 μm.

[0085] Inorganic oxide particles can be present on any of the following surfaces: the surface of the separator, the surface of the positive electrode in contact with the separator, or the surface of the negative electrode in contact with the separator, or any combination thereof. The inorganic oxide particles can be present on part or the entire surface of the target surface. This allows high insulation from the negative electrode, such as a negative electrode containing lithium metal. Examples of inorganic oxide particles include alumina particles, titania particles, and lithium-conductive solid electrolyte particles.

[0086] The separator may have lithium ion conductivity. Examples of lithium ion conductive separators include those containing at least one selected from the group consisting of oxides having lithium ion conductivity, sulfides having lithium ion conductivity, phosphates having lithium ion conductivity, polymers having lithium ion conductivity, and solid electrolytes having lithium ion conductivity. The lithium ion conductive separator may be a composite further containing inorganic and / or organic substances in addition to the above components.

[0087] The lithium ion conductive separator can be a layer or a film.

[0088] The lithium ion conductive separator may be a composite of a lithium ion conductive inorganic solid electrolyte and a polymer. This separator is flexible. This separator can selectively transmit lithium ions. This separator also has a non-porous or non-communicating structure. Examples of polymers include polyethylene oxide (PEO), polyethylene terephthalate, and polyvinylidene fluoride (PVdF). The separator may contain a lithium salt. The ratio of the lithium salt to the total of the lithium salt and the polymer can be 0 to 50 wt %. The lithium salt preferably contains at least one of LiFSI and LiTFSI. The content of the inorganic solid electrolyte in the separator can be in the range of 10 wt % to 90 wt %. By using this separator, only lithium ions can selectively migrate through the separator, while the migration of anionic and cationic species in the positive electrode and ions other than lithium ions in the negative electrode is restricted.

[0089] The lithium ion conductive solid electrolyte has a lithium ion conductivity of 1x10 at 25°C. -4 S / cm or more, preferably 1×10 -3 It is desirable that it is S / cm or higher.

[0090] Examples of lithium ion conductive solid electrolytes include oxide solid electrolytes with a garnet structure and lithium phosphate solid electrolytes with a Nasicon structure.

[0091] Garnet-type oxide solid electrolytes have the advantage of being highly resistant to reduction and having a wide electrochemical window. The lithium ion conductivity at 25°C is 1×10 -3 As an oxide solid electrolyte with a garnet structure of S / cm or more, for example, La 5+x A x La 3-x M2O 12 (A is at least one selected from the group consisting of Ca, Sr, and Ba, M is at least one selected from the group consisting of Nb and Ta, 0≦x≦0.5), Li3M 2-x L2O 12(M is at least one selected from the group consisting of Ta and Nb, L may include Zr, 0≦x≦0.5), Li 7-3x Al x La3Zr3O 12 (0≦x≦0.5), Li7La3Zr2O 12 Li 6.25 Al 0.25 La3Zr3O 12 , Li7La3Zr2O 12 Each of these materials has high ionic conductivity and is electrochemically stable, making it possible to realize a secondary battery with excellent discharge performance and cycle life performance.

[0092] Lithium ion conductivity at 25°C is 1x10 -4 Examples of lithium phosphate solid electrolytes with a Nasicon structure of 50 ... 1+y Al x M 2―x Preferably, it is represented by (PO4)3 (wherein M is one or more selected from Si, Ti, Ge, Sr, Zr, and Ca, and 0≦x≦1, 0≦y≦1). 1+x Al x Ge 2-x (PO4)3(0≦x≦0.5, 0≦y≦1), Li 1+x Al x Zr 2-x (PO4)3(0≦x≦0.5), Li 1+x Al x Ti 2-x (PO4)3 (0≦x≦0.5) is preferred because it has high ionic conductivity and high electrochemical stability, respectively.

[0093] The solid electrolyte may contain unavoidable impurities other than those listed above. The type of solid electrolyte used may be one or more types.

[0094] The thickness of the separator can be from 20 μm to 200 μm, inclusive. By setting the thickness within this range, the separator can have practical mechanical strength and reduce the resistance to ion conduction.

[0095] <Exterior materials> The secondary battery may include a housing member. The housing member includes a container having an opening and a lid attached to the opening of the container. The lid may be a separate member from the container or may be integrated with the container. Furthermore, the housing member is not limited to the structure shown in the drawings as long as it can accommodate a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte. Housing members having shapes corresponding to rectangular, thin, cylindrical, and coin-shaped batteries may be used.

[0096] Materials constituting the exterior member include metals, laminate films, and the like.

[0097] Examples of metals include iron, stainless steel, aluminum, nickel, etc. When a metal can is used as the container, the thickness of the container is preferably 0.5 mm or less, and more preferably 0.3 mm or less.

[0098] Examples of laminate films include multilayer films in which aluminum foil or stainless steel foil is coated with a resin film. Polymers such as polypropylene (PP), polyethylene (PE), nylon, and polyethylene terephthalate (PET) can be used as the resin. The thickness of the laminate film is preferably 0.2 mm or less.

[0099] <Manufacturing method> The secondary battery according to the embodiment can be manufactured, for example, as follows.

[0100] The method for manufacturing a secondary battery includes preparing an electrode on which a film containing a lithium nitrogen compound is not formed as a negative electrode, preparing an electrode on which a nitrogen-containing film is not formed as a positive electrode, preparing a non-aqueous electrolyte, housing the negative electrode and the positive electrode in an exterior member, injecting the non-aqueous electrolyte into the exterior member, sealing the exterior member to obtain a battery precursor, and subjecting the battery precursor to an initial charge and discharge.

[0101] A negative electrode without a film containing a lithium nitrogen compound is prepared, for example, by the following method: A plate or foil containing at least one of Li metal and a Li alloy is fixed (e.g., pressed) to a current collector. Alternatively, a plate or foil containing at least one of Li metal and a Li alloy may be used as the electrode. Alternatively, a compound capable of absorbing and releasing Li, a conductive agent, and a binder are suspended in a solvent, and the suspension is applied to a current collector, dried, and pressed.

[0102] A positive electrode without a nitrogen-containing film is produced, for example, by the following method. A positive electrode active material, a conductive agent, and a binder are suspended in a solvent to prepare a slurry. This slurry is applied to one side 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, a positive electrode active material, a conductive agent, and a 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.

[0103] As the non-aqueous electrolyte, a non-aqueous electrolyte containing an ionic liquid and 0.5% by weight to 30% by weight of a urea compound is prepared.

[0104] The initial charge / discharge is performed multiple times at a temperature between room temperature (e.g., 25°C) and 45°C, at a current rate between 0.2 C and 1 C. 1 C is the current value that discharges the nominal capacity of the secondary battery in one hour.

[0105] Before the first charge / discharge, the battery precursor may be subjected to a storage (aging) treatment.

[0106] Next, methods for checking the non-aqueous electrolyte, the positive electrode active material, the negative electrode active material, etc. will be described. <How to confirm the composition of the non-aqueous electrolyte> The method for identifying the components of the non-aqueous electrolyte will be described below, taking as an example the case where the non-aqueous electrolyte is contained in a secondary battery.

[0107] First, a secondary battery containing the nonaqueous electrolyte to be measured is discharged at 0.1 C until the battery voltage reaches 1.0 V. The discharged secondary battery is disassembled in a glove box with an inert atmosphere. Next, the nonaqueous electrolyte contained in the battery and electrode assembly is extracted. If the nonaqueous electrolyte can be removed from the opening of the battery, the nonaqueous electrolyte is sampled as is. On the other hand, if the nonaqueous electrolyte to be measured is held in the electrode assembly, the electrode assembly is further disassembled, and, for example, the separator impregnated with the nonaqueous electrolyte is removed. The nonaqueous electrolyte impregnated in the separator can be extracted using, for example, a centrifuge. In this way, the nonaqueous electrolyte can be sampled. Note that if the amount of nonaqueous electrolyte contained in the secondary battery is small, the nonaqueous electrolyte can also be extracted by immersing the electrodes and separator in acetonitrile solution. The weight of the acetonitrile solution is measured before and after extraction, and the amount extracted can be calculated.

[0108] The nonaqueous electrolyte sample thus obtained is subjected to composition analysis, for example, by gas chromatography-mass spectrometry (GC-MS) or nuclear magnetic resonance spectroscopy (NMR). In the analysis, the components contained in the nonaqueous electrolyte are first identified. Then, a calibration curve for each component is prepared. If multiple components are present, a calibration curve for each component is prepared. The composition of the nonaqueous electrolyte can be determined by comparing the prepared calibration curve with the peak intensity or area in the results obtained by measuring the nonaqueous electrolyte sample.

[0109] The water content of the nonaqueous electrolyte sample prepared as described above is measured by coulometric titration using a Karl Fischer moisture meter (VA-06 model, manufactured by Mitsubishi Chemical Analytech Co., Ltd., or an instrument with equivalent functionality). Specifically, the sample is heated to 140°C and nitrogen gas is introduced at a flow rate of 200 ml / min. The water content is calculated from the amount of electricity consumed in the reaction between water and iodine. This gives the water content of the nonaqueous electrolyte. <How to check the electrode composition> First, a method for removing an electrode (positive electrode or negative electrode) from a battery will be described.

[0110] The secondary battery is disassembled under an argon atmosphere, and the positive or negative electrode to be measured is removed. The measurement target is washed with a solvent consisting of dimethyl carbonate under an argon atmosphere, dried in a vacuum at 100°C, and then measured using the method described below. <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. <Method for checking nitrogen-containing films, etc.> The presence or absence of a nitrogen-containing film in the positive electrode and a lithium nitrogen compound in the negative electrode can be confirmed by X-ray photoelectron spectroscopy (XPS) under the conditions described below.

[0111] The XPS instrument used can be a Quantera SXM manufactured by ULVAC-PHI, Inc., or an instrument with equivalent functionality. Single-crystal spectroscopic Al-Kα radiation (1486.6 eV) is used as the excitation X-ray source. The X-ray output is 4 kW (13 kV x 310 mA), the photoelectron detection angle is 45°, and the analysis area is approximately 4 mm x 0.2 mm. Scanning is performed at 0.10 eV / step.

[0112] For example, the presence of Li3N can be confirmed by detecting a spectrum derived from the Li-N bond (399 eV) in a state analysis of the surface (N1s) of the negative electrode current collector (for example, aluminum foil).

[0113] Next, a secondary battery according to an embodiment will be described with reference to the drawings.

[0114] 1 and 2 show an example of a secondary battery using a metal container.

[0115] The electrode group 1 is housed in a rectangular cylindrical metal container 2. The electrode group 1 has a structure in which a separator 5 is interposed between a positive electrode active material-containing layer of a positive electrode 3 and a negative electrode active material-containing layer of a negative electrode 4, and these are spirally wound to form a flat shape. The separator 5 covers the surface of the positive electrode active material-containing layer or the negative electrode active material-containing layer. As shown in FIG. 2 , strip-shaped positive electrode leads 6 are electrically connected to multiple locations on the end of the positive electrode 3 located on the end face of the electrode group 1. Strip-shaped negative electrode leads 7 are electrically connected to multiple locations on the end of the negative electrode 4 located on the end face. The multiple positive electrode leads 6 are bundled together and electrically connected to a positive electrode conductive tab 8. The positive electrode lead 6 and the positive electrode conductive tab 8 form a positive electrode terminal. The negative electrode leads 7 are bundled together and connected to a negative electrode conductive tab 9. The negative electrode lead 7 and the negative electrode conductive tab 9 form a negative electrode terminal. A metal sealing plate 10 is fixed to the opening of the metal container 2 by welding or the like. The positive electrode conductive tab 8 and the negative electrode conductive tab 9 are each pulled out to the outside through an extraction hole provided in the sealing plate 10. The inner circumferential surface of each extraction hole in the sealing plate 10 is covered with an insulating member 11 to prevent short circuits due to contact with the positive electrode conductive tab 8 and the negative electrode conductive tab 9.

[0116] 3 and 4 show an example of a secondary battery using an exterior member made of a laminate film.

[0117] As shown in FIGS. 3 and 4, the flat wound electrode group 1 is housed in a bag-shaped exterior member 12 made of a laminate film with a metal layer sandwiched between two resin films. The flat wound electrode group 1 is formed by spirally winding a laminate in which, from the outside, a negative electrode 4, a separator 15, a positive electrode 3, and a separator 15 are stacked in this order, and then press-molding the laminate. The outermost negative electrode 4, as shown in FIG. 4, has a configuration in which a negative electrode active material-containing layer 4b containing a negative electrode active material is formed on one side of the inner surface of a negative electrode current collector 4a. The other negative electrodes 4 have a negative electrode active material-containing layer 4b formed on both sides of a negative electrode current collector 4a. The positive electrode 3 has a positive electrode active material-containing layer 3b formed on both sides of a positive electrode current collector 3a.

[0118] Near the outer peripheral edge of the wound electrode group 1, the negative electrode terminal 13 is connected to the negative electrode current collector 4a of the outermost negative electrode 4, and the positive electrode terminal 14 is connected to the positive electrode current collector 3a of the inner positive electrode 3. These negative electrode terminal 13 and positive electrode terminal 14 extend to the outside from an opening of the bag-shaped exterior member 12. The opening of the bag-shaped exterior member 12 is heat-sealed to hermetically seal the wound electrode group 1. When heat-sealing, the negative electrode terminal 13 and positive electrode terminal 14 are sandwiched by the bag-shaped exterior member 12 at this opening.

[0119] The secondary battery according to the embodiment described above includes a positive electrode, a negative electrode containing at least one material selected from the group consisting of lithium metal, lithium alloys, and compounds capable of absorbing and releasing Li, and a non-aqueous electrolyte containing an ionic liquid and 0.5% by weight to 30% by weight of a urea compound. Therefore, a secondary battery having a high energy density and excellent cycle performance and discharge rate performance can be provided. (Second embodiment) The battery pack of the second embodiment includes a plurality of secondary batteries of the embodiment.

[0120] Examples of battery packs include those including a plurality of unit cells electrically connected in series and / or in parallel as constituent units, those including a first unit consisting of a plurality of unit cells electrically connected in series, or a second unit consisting of a plurality of unit cells electrically connected in parallel, etc. The battery pack may include at least one of these configurations.

[0121] Examples of configurations in which multiple secondary batteries are electrically connected in series and / or parallel include those in which multiple batteries each equipped with an exterior member are electrically connected in series and / or parallel, and those in which multiple electrode groups or bipolar electrode bodies housed in a common housing are electrically connected in series and / or parallel. A specific example of the former is connecting the positive and negative terminals of multiple secondary batteries with a metal bus bar (e.g., aluminum, nickel, or copper). A specific example of the latter is housing multiple electrode groups or bipolar electrode bodies in a single housing while electrochemically insulated by a partition wall, and electrically connecting them in series. In the case of secondary batteries, setting the number of batteries electrically connected in series to the range of 5 to 7 improves voltage compatibility with lead-acid batteries. To further improve voltage compatibility with lead-acid batteries, a configuration in which five or six unit cells are connected in series is preferred.

[0122] The housing for the assembled battery can be a metal can made of aluminum alloy, iron, stainless steel, etc., or a plastic container, etc. The thickness of the container should preferably be 0.5 mm or more.

[0123] The battery pack of the embodiment described above includes the secondary battery of the embodiment, and therefore can realize a battery pack having a high energy density and excellent cycle performance and discharge rate performance. <Third embodiment> The battery pack according to the third embodiment may include one or more secondary batteries (single cells) according to the embodiment. A plurality of secondary batteries may be electrically connected in series, in parallel, or in a combination of series and parallel to form a battery assembly. The battery pack according to the embodiment may include a plurality of battery assemblies.

[0124] The battery pack according to the embodiment 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 (e.g., electronic device, automobile, etc.) that uses the battery pack as a power source may also be used as the protection circuit for the battery pack.

[0125] The battery pack according to the embodiment 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 inputting current 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 charging the battery pack, charging current (including regenerative energy from the power of a vehicle such as an automobile) is supplied to the battery pack through the external terminals for current flow.

[0126] Next, an example of a battery pack according to an embodiment will be described with reference to the drawings.

[0127] Fig. 5 is an exploded perspective view schematically illustrating an example of a battery pack according to an embodiment, and Fig. 6 is a block diagram illustrating an example of an electric circuit of the battery pack illustrated in Fig. 5.

[0128] The battery pack 300 shown in FIGS. 5 and 6 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).

[0129] 5 is a bottomed, square container having a rectangular bottom. The 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 container 31 to accommodate the battery pack 200 and other components. Although not shown, the container 31 and the lid 32 are provided with openings or connection terminals for connection to external devices and the like.

[0130] The battery pack 200 includes a plurality of cells 100, a positive electrode lead 22, a negative electrode lead 23, and an adhesive tape 24.

[0131] 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. 6. 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.

[0132] The adhesive tape 24 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 24. 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.

[0133] One end of the positive electrode lead 22 is connected to the battery pack 200. One end of the positive electrode lead 22 is electrically connected to the positive electrode of one or more cells 100. One end of the negative electrode lead 23 is connected to the battery pack 200. One end of the negative electrode lead 23 is electrically connected to the negative electrode of one or more cells 100.

[0134] 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.

[0135] The other end 22a of the positive electrode lead 22 is electrically connected to the positive electrode connector 342. The other end 23a of the negative electrode lead 23 is electrically connected to the negative electrode connector 343.

[0136] 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.

[0137] 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.

[0138] 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.

[0139] 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.

[0140] 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.

[0141] 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.

[0142] 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.

[0143] 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.

[0144] 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 22 and the negative electrode lead 23 may be used as the positive and negative terminals of the external terminals for supplying current, respectively.

[0145] Such battery packs are used in applications requiring excellent cycle performance when drawing large current, for example. Specific examples of such battery packs include power sources for electronic devices, stationary batteries, and on-board batteries for various vehicles (including railway vehicle batteries). Examples of such electronic devices include digital cameras. This battery pack is particularly suitable for use as an on-board battery.

[0146] The battery pack according to the embodiment includes the secondary battery according to the embodiment or the battery assembly according to the embodiment, and therefore, a battery pack having high energy density and excellent cycle performance and discharge rate performance can be realized. <Fourth embodiment> According to a fourth embodiment, a vehicle is provided, which is equipped with a battery pack according to the embodiment.

[0147] In the vehicle according to the embodiment, the battery pack recovers, for example, regenerative energy for the vehicle's motive power. The vehicle may include a mechanism (for example, a regenerator) that converts the kinetic energy of the vehicle into regenerative energy.

[0148] 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.

[0149] 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.

[0150] 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.

[0151] Next, an example of a vehicle according to an embodiment will be described with reference to the drawings.

[0152] FIG. 7 is a partial perspective view schematically illustrating an example of a vehicle according to the embodiment.

[0153] A vehicle 400 shown in Fig. 7 includes a vehicle body 40 and a battery pack 300 according to the third embodiment. In the example shown in Fig. 7, the vehicle 400 is a four-wheeled automobile.

[0154] 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.

[0155] 7 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.

[0156] Next, an embodiment of a vehicle according to the present invention will be described with reference to FIG.

[0157] 8 is a diagram illustrating an example of a control system for an electrical system in a vehicle according to an embodiment. A vehicle 400 illustrated in FIG. 8 is an electric vehicle.

[0158] The vehicle 400 shown in Figure 8 includes a vehicle body 40, a vehicle power supply 41, a vehicle ECU (ECU: Electric Control Unit) 42 which is a higher-level control device of the vehicle power supply 41, an external terminal (terminal for connecting to an external power supply) 43, an inverter 44, and a drive motor 45.

[0159] Vehicle 400 has vehicle power supply 41 mounted, for example, in the engine compartment, the rear of the vehicle body, or under the seat. Note that in vehicle 400 shown in Fig. 8, the mounting location of vehicle power supply 41 is shown schematically.

[0160] The vehicle power supply 41 includes a plurality of (for example, three) battery packs 300a, 300b, and 300c, a battery management unit (BMU) 411, and a communication bus 412.

[0161] The battery pack 300a includes a battery pack 200a and a battery pack monitoring device 301a (for example, VTM: Voltage Temperature Monitoring). The battery pack 300b includes a battery pack 200b and a battery pack monitoring device 301b. The battery pack 300c includes a battery pack 200c and a battery pack monitoring device 301c. The battery packs 300a to 300c are battery packs similar to the battery pack 300 described above, and the battery packs 200a to 200c are battery packs similar to the battery pack 200 described above. The battery packs 200a to 200c are electrically connected in series. The battery packs 300a, 300b, and 300c can each be removed independently and replaced with another battery pack 300.

[0162] Each of the assembled batteries 200a to 200c includes a plurality of unit cells connected in series. At least one of the plurality of unit cells is a secondary battery according to the embodiment. Each of the assembled batteries 200a to 200c is charged and discharged via a positive terminal 413 and a negative terminal 414.

[0163] The battery management device 411 communicates with the assembled battery monitoring devices 301a to 301c and collects information on the voltage, temperature, etc. of each of the cells 100 included in the assembled batteries 200a to 200c included in the vehicle power supply 41. In this way, the battery management device 411 collects information on the maintenance of the vehicle power supply 41.

[0164] The battery management unit 411 and the assembled battery monitoring units 301a to 301c are connected via a communication bus 412. In the communication bus 412, one set of communication lines is shared by multiple nodes (the battery management unit 411 and one or more assembled battery monitoring units 301a to 301c). The communication bus 412 is a communication bus configured based on, for example, the CAN (Control Area Network) standard.

[0165] The battery pack monitoring devices 301a to 301c measure the voltage and temperature of each of the cells constituting the battery packs 200a to 200c based on commands received through communication from the battery management device 411. However, the temperature can be measured at only a few locations per battery pack, and it is not necessary to measure the temperature of all the cells.

[0166] The vehicle power supply 41 may also have an electromagnetic contactor (for example, a switch device 415 shown in FIG. 8) that switches between electrical connection and disconnection between the positive terminal 413 and the negative terminal 414. The switch device 415 includes a pre-charge switch (not shown) that is turned on when the assembled batteries 200a-200c are being charged, and a main switch (not shown) that is turned on when the output from the assembled batteries 200a-200c is being supplied to a load. Each of the pre-charge switch and the main switch includes a relay circuit (not shown) that is switched on or off by a signal supplied to a coil disposed near the switch element. Electromagnetic contactors such as the switch device 415 are controlled based on a control signal from the battery management device 411 or the vehicle ECU 42 that controls the operation of the entire vehicle 400.

[0167] The inverter 44 converts the input DC voltage into a three-phase alternating current (AC) high voltage for driving the motor. The three-phase output terminals of the inverter 44 are connected to the three-phase input terminals of the drive motor 45. The inverter 44 is controlled based on control signals from the battery management unit 411 or the vehicle ECU 42, which controls the operation of the entire vehicle. By controlling the inverter 44, the output voltage from the inverter 44 is adjusted.

[0168] The drive motor 45 is rotated by the electric power supplied from the inverter 44. The drive force generated by the rotation of the drive motor 45 is transmitted to the axles and drive wheels W via, for example, a differential gear unit.

[0169] Although not shown, the vehicle 400 also includes a regenerative braking mechanism. The regenerative braking mechanism rotates the drive motor 45 when the vehicle 400 is braked, and converts kinetic energy into regenerative energy as electrical energy. The regenerative energy recovered by the regenerative braking mechanism is input to the inverter 44 and converted into direct current. The converted direct current is input to the vehicle power supply 41.

[0170] One terminal of a connection line L1 is connected to the negative terminal 414 of the vehicle power supply 41. The other terminal of the connection line L1 is connected to a negative input terminal 417 of the inverter 44. A current detection unit (current detection circuit) 416 in the battery management device 411 is provided on the connection line L1 between the negative terminal 414 and the negative input terminal 417.

[0171] One terminal of a connection line L2 is connected to the positive terminal 413 of the vehicle power supply 41. The other terminal of the connection line L2 is connected to a positive input terminal 418 of the inverter 44. A switch device 415 is provided on the connection line L2 between the positive terminal 413 and the positive input terminal 418.

[0172] The external terminal 43 is connected to the battery management device 411. The external terminal 43 can be connected to, for example, an external power source.

[0173] In response to operational inputs from the driver or the like, the vehicle ECU 42 coordinates with other management devices and control devices including the battery management device 411 to control the vehicle power supply 41, the switch device 415, the inverter 44, etc. Through the coordinated control of the vehicle ECU 42, etc., the output of power from the vehicle power supply 41 and the charging of the vehicle power supply 41 are controlled, thereby managing the entire vehicle 400. Data relating to the maintenance of the vehicle power supply 41, such as the remaining capacity of the vehicle power supply 41, is transferred between the battery management device 411 and the vehicle ECU 42 via a communication line. (Fifth embodiment) According to a fifth embodiment, a stationary power supply is provided. This stationary power supply is equipped with a battery pack according to an embodiment. Note that this stationary power supply may be equipped with a secondary battery or battery pack according to an embodiment, instead of the battery pack according to an embodiment.

[0174] FIG. 9 is a block diagram showing an example of a system including a stationary power supply according to an embodiment. FIG. 9 is a diagram showing an example of application of battery packs 300A and 300B according to an embodiment to stationary power supplies 112 and 123. The example shown in FIG. 9 shows a system 110 in which the stationary power supplies 112 and 123 are used. The system 110 includes a power plant 111, a stationary power supply 112, a consumer-side power grid 113, and an energy management system (EMS) 115. The system 110 also includes a power grid 116 and a communication network 117, and the power plant 111, the stationary power supply 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.

[0175] 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.

[0176] 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.

[0177] 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.

[0178] 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.

[0179] The stationary power source according to the embodiment includes the battery pack according to the embodiment. Therefore, according to the present embodiment, it is possible to provide a stationary power source including a battery pack with excellent charge / discharge cycle performance. [Example]

[0180] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings, but the present invention is not limited to the embodiments listed below.

[0181] Example 1 The positive electrode active material is a layered lithium nickel cobalt manganese composite oxide (LiNi 0.8 Co 0.1 Mn 0.1O2) particles were used. Graphite powder was added as a conductive material in an amount of 8 wt % relative to the positive electrode active material-containing layer, and PVdF was added as a binder in an amount of 5 wt % relative to the positive electrode active material-containing layer. These were then dispersed in n-methylpyrrolidone (NMP) solvent to prepare a slurry. The slurry was applied to both sides of a 15 μm-thick aluminum alloy foil (purity 99%) in an amount of 12.8 mg / cm per side. 2 This was dried and subjected to a pressing process, so that the thickness of the positive electrode active material-containing layer on one side was 43 μm and the electrode density was 3.0 g / cm 3 The specific surface area of ​​the positive electrode active material-containing layer was 0.5 m 2 / g.

[0182] A negative electrode was prepared by pressing a 100 μm-thick lithium metal foil (purity 99.9 wt%) onto a 10 μm-thick copper current collector foil. The positive electrode was covered with a 20 μm-thick polyethylene porous film separator. The positive electrode, separator, and negative electrode were laminated so that the separator was disposed between the positive electrode active material-containing layer and the negative electrode active material-containing layer. The positive electrode active material-containing layer was also disposed so as to cover the negative electrode active material-containing layer via the separator. The resulting laminate was spirally wound to prepare an electrode assembly. This electrode assembly was then further pressed into a flat shape. The electrode assembly was housed in a thin metal can made of an aluminum alloy (Al purity 99%) with a thickness of 0.25 mm.

[0183] A nonaqueous electrolyte was prepared by dissolving 1.0 mol / kg of LiFSI in a solvent consisting of an ionic liquid composed of S222 cations and TFSI anions, and adding 5 wt. % urea. The water content of the nonaqueous electrolyte was measured as described above and found to be 50 wt. ppm. The content of the ionic liquid (including lithium ions) in the nonaqueous electrolyte was found to be 95 wt. The nonaqueous electrolyte was heated to 60°C and poured into a metal can under vacuum to prepare a thin secondary battery with the structure shown in Figure 1, measuring 4 mm thick, 30 mm wide, and 50 mm high. The battery had a capacity of 0.5 Ah and an intermediate voltage of 3.75 V. The battery weighed 10 g.

[0184] Examples 2 to 13 A thin secondary battery was fabricated in the same manner as described in Example 1 above, except that the solvent composition, lithium salt, lithium ion concentration, urea compound and its added amount, negative electrode active material, and positive electrode active material shown in Table 1 below were used.

[0185] MEITFSI refers to an ionic liquid consisting of MEI cations and TFSI anions, PP13TFSI refers to an ionic liquid consisting of PP13 cations and TFSI anions, DEMETFSI refers to an ionic liquid consisting of DEME cations and TFSI anions, and DMPITFSI refers to an ionic liquid consisting of DMPI cations and TFSI anions.

[0186] Example 14 A thin secondary battery was fabricated in the same manner as described in Example 1 above, except that a negative electrode fabricated by the following method was used.

[0187] Graphite powder and polyvinylidene fluoride (PVdF) were mixed in a weight ratio of 90:10, and the resulting mixture was kneaded in the presence of an organic solvent (N-methylpyrrolidone) to prepare a slurry. The resulting slurry was applied to a 15 μm-thick copper foil, dried, and pressed to obtain a negative electrode.

[0188] Example 15 A thin secondary battery was fabricated in the same manner as described in Example 1 above, except that a negative electrode fabricated by the following method was used.

[0189] Graphite powder and SiO powder were mixed in a weight ratio of 9:1, and 10 wt% of polyvinylidene fluoride (PVdF) was added to the resulting negative electrode active material. The resulting mixture was kneaded in the presence of an organic solvent (N-methylpyrrolidone) to prepare a slurry. The resulting slurry was applied to a 15 μm-thick copper foil, dried, and pressed to obtain a negative electrode.

[0190] Example 16 A thin secondary battery was fabricated in the same manner as described in Example 1, except that a negative electrode fabricated in the same manner as described in Example 14 and a positive electrode active material detailed below were used. The LiFePO4 particles had an olivine structure, an average particle diameter of 3 μm, and carbon fine particles (average particle diameter 0.005 μm) attached to the particle surface (attached amount 0.1 wt %).

[0191] Example 17 A thin secondary battery was fabricated in the same manner as described in Example 1 above, except that a negative electrode fabricated by the following method and a positive electrode active material detailed below were used.

[0192] As a negative electrode active material, the average particle diameter is 1 μm and the BET specific surface area is 3 m 2 / g, Li absorption potential is 1 to 2 V (vs. Li / Li + ) monoclinic TiNb2O7 particles were prepared. 2 A mixture of graphite powder (1.2g / g), carbon nanofiber powder, and PVdF (a binder) was mixed in a weight ratio of 90:5:2:3 and dispersed in n-methylpyrrolidone (NMP) solvent to prepare a slurry. The resulting slurry was applied to a 15 μm thick aluminum alloy foil (purity 99.3%), dried, and pressed to produce a negative electrode active material-containing layer with a thickness of 59 μm and an electrode density of 2.2 g / cm. 3 A negative electrode was prepared.

[0193] On the other hand, the positive electrode active material is LiNi 0.5 Mn 1.5 O4 had a spinel structure and consisted of particles with an average particle size of 5 μm.

[0194] Example 18 A thin secondary battery was fabricated in the same manner as described in Example 1 above, except that a negative electrode fabricated by the following method was used.

[0195] Li 0.9 Mg 0.1A 50 μm thick foil made of the alloy was pressed onto a 10 μm thick copper foil current collector to prepare a negative electrode.

[0196] Example 19 The positive electrode active material is a layered lithium nickel cobalt manganese composite oxide (LiNi 0.5 Co 0.2 Mn 0.3 A thin secondary battery was fabricated in the same manner as described in Example 1 above, except that O2) particles were used.

[0197] (Examples 20 and 21) A thin secondary battery was fabricated in the same manner as described in Example 1 above, except that the type of urea compound was changed to the type shown in Table 2.

[0198] (Comparative Examples 1 to 6) A thin secondary battery was fabricated in the same manner as described in Example 1, except for using the solvent composition, lithium salt, lithium ion concentration, urea compound and its additive amount, negative electrode active material, and positive electrode active material shown in Table 2. The nonaqueous electrolyte of Comparative Example 6 was prepared by dissolving 1.0 mol / kg of LiFSI in a nonaqueous solvent made of dimethyl carbonate.

[0199] <Performance Evaluation of Examples 1 to 15, 18 to 21 and Comparative Examples 1 to 6> For the initial charge / discharge, each secondary battery was charged at a constant current of 0.2 C at 25°C up to 4.2 V, and then discharged at 0.2 C down to 3.0 V. The discharge capacity (Ah), average voltage (V), and energy (Wh) during this discharge were measured. The measurement results are shown in Tables 3 and 4. The average voltage was calculated from the relationship V = Wh / Ah.

[0200] In the large current performance test (discharge rate performance test), each secondary battery was charged to 4.2 V at a constant current of 0.2 C at 25°C, and then discharged to 3.0 V at 2 C, and the discharge capacity was measured. The ratio of the obtained discharge capacity at 2 C rate to the initial discharge capacity (discharge capacity at 0.2 C rate) is shown in Tables 3 and 4 as the 2 C discharge retention rate.

[0201] The cycle test consisted of charging each secondary battery at a constant current of 0.2 C at 45°C up to 4.2 V, followed by a repeated charge-discharge cycle of discharging at a constant current of 0.2 C down to 3.0 V. The cycle life during the cycle test at 45°C was defined as the number of cycles at which the battery reached a discharge capacity equivalent to 80% of the initial capacity. The measurement results are shown in Tables 3 and 4.

[0202] <Performance evaluation of Examples 16 and 17> For the initial charge / discharge, each secondary battery was charged at 25°C at a constant current of 0.2 C up to 3.5 V, and then discharged at 0.2 C down to 2.0 V. The discharge capacity (Ah), average voltage (V), and energy (Wh) during this discharge were measured. The measurement results are shown in Table 3. The average voltage was calculated from the relationship V = Wh / Ah. In the large current performance test (discharge rate performance test), each secondary battery was charged to 3.5 V at a constant current of 0.2 C at 25°C, and then discharged to 2.0 V at 2 C, and the discharge capacity was measured. The ratio of the obtained discharge capacity at 2 C rate to the initial discharge capacity (discharge capacity at 0.2 C rate) is shown in Table 3 as the 2 C discharge retention rate.

[0203] The cycle test consisted of charging each secondary battery at a constant current of 0.2 C at 45°C up to 3.5 V, followed by a repeated charge-discharge cycle of discharging at a constant current of 0.2 C down to 2.0 V. The cycle life during the cycle test at 45°C was defined as the number of cycles at which the battery reached a discharge capacity equivalent to 80% of the initial capacity. The measurement results are shown in Table 3.

[0204] In Tables 1 and 2, the numbers in parentheses following the description of the type of lithium salt indicate the lithium ion concentration (mol / kg).

[0205] [Table 1]

[0206] [Table 2]

[0207] [Table 3]

[0208] [Table 4]

[0209] As is clear from Tables 1 to 4, the secondary batteries of Examples 1 to 21 have higher energy and are superior in cycle life performance and discharge rate performance compared to Comparative Examples 1 to 6.

[0210] A comparison of Example 1 with Comparative Examples 1 and 2 reveals that when the non-aqueous electrolyte does not contain a urea compound or when the urea compound content exceeds 30 wt%, all of the energy, cycle life performance, and discharge rate performance are inferior. Furthermore, the results of Comparative Examples 3 to 6 reveal that the same tendency is observed even when the solvent composition is changed. A comparison of Examples 1 to 6 reveals that Examples 1, 2, and 5, in which the urea compound content of the non-aqueous electrolyte is 1 wt% or more and 10 wt% or less, are superior to Examples 3, 4, and 6 in energy, cycle life performance, and discharge rate performance.

[0211] A comparison between Example 1 and Examples 10 to 13 reveals that the secondary battery of Example 1, which has a nonaqueous electrolyte containing an ionic liquid consisting of trialkylsulfonium cations, Li ions, TFSI anions, and FSI anions, has superior discharge rate performance compared to Examples 10 to 13.

[0212] Comparison of Example 1 with Examples 14, 15, and 17 reveals that the secondary battery of Example 1, which has a negative electrode containing Li metal, has higher energy than Examples 14, 15, and 17.

[0213] The positive and negative electrodes of the secondary batteries of Examples 1 to 21 were examined for the presence or absence of a coating by the above-mentioned XPS measurement, and it was confirmed that a nitrogen-containing film was present on the surface of the positive electrode current collector, and a film containing LiN was present on the surface of the negative electrode.

[0214] The following describes the invention in terms of embodiments. <1> A positive electrode and a negative electrode containing at least one selected from the group consisting of lithium metal, lithium alloys, and compounds capable of absorbing and releasing Li; a non-aqueous electrolyte containing an ionic liquid and 0.5% by weight or more and 30% by weight or less of a urea compound; A secondary battery comprising: <2> The ionic liquid contains one or more cations selected from the group consisting of 1,3-dialkylimidazolium ions, trialkylsulfonium ions, N,N-dialkylpiperidinium ions, and quaternary ammonium ions, lithium ions, and [N(CF3SO2)2] - or [N(FSO2)2] - and an anion comprising at least one of <1> The secondary battery according to claim 1. <3> The ionic liquid contains one or more cations selected from the group consisting of 1-ethyl-3-methylimidazolium ions, triethylsulfonium ions, N,N-dialkylpiperidinium ions, and quaternary ammonium ions, lithium ions, and [N(CF3SO2)2] - or [N(FSO2)2] - and an anion comprising at least one of <1> or <2> The secondary battery according to claim 1. <4> The lithium ion concentration of the non-aqueous electrolyte is in the range of 0.5 mol / kg or more and 2 mol / kg or less. <1> ~ <3> 1. The secondary battery according to claim 1 , <5> The urea compound includes at least one selected from the group consisting of urea, N-methyl urea, and N,N'-dimethyl propylene urea. <1> ~ <4> 1. The secondary battery according to claim 1 , <6> <1> ~ <5> 10. A battery pack comprising the secondary battery according to claim 1. <7> An external terminal for applying current; Protection circuit and Further provided with <6> The battery pack according to claim 1. <8> A battery includes a plurality of the secondary batteries, The secondary batteries are electrically connected in series, in parallel, or in a combination of series and parallel. <6> or <7> The battery pack according to claim 1. <9> <6> ~ <8> A vehicle equipped with a battery pack according to any one of the items above. <10> <6> ~ <8> A stationary power source comprising the battery pack according to any one of the preceding items.

[0215] 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 embodiments can be implemented 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 intended to be included within the scope and spirit of the invention, as well as within the scope of the inventions described in the claims and their equivalents. [Explanation of symbols]

[0216] 1...electrode group, 2...container (exterior member), 3...positive electrode, 3a...positive electrode current collector, 3b...positive electrode active material-containing layer, 4...negative electrode, 4a...negative electrode current collector, 4b...negative electrode active material-containing layer, 5...separator, 6...positive electrode lead, 7...negative electrode lead, 8...positive electrode conductive tab, 9...negative electrode conductive tab, 10...sealing plate, 11...insulating member, 12...exterior member, 13...negative electrode terminal, 14...positive electrode terminal, 100...unit cell, 200...battery assembly, 300...battery pack, 34...printed wiring board, 345...thermistor, 346...protection circuit, 350...external terminal for energization, 40...vehicle body, 400...vehicle, 41...vehicle power source, 411 ...battery management device, 412...communication bus, 300a-c...battery pack, 301a-c...battery assembly monitoring device, 200a-c...battery assembly, 413...positive terminal, 414...negative terminal, 44...inverter, 45...drive motor, 43...external terminal, 42...vehicle ECU, L1, L2...connection line, W...drive wheel, 110...system, 111...power plant, 112...stationary power source, 113...consumer-side power system, 115...energy management system (EMS), 116...power grid, 117...communication network, 118...power conversion device, 121...consumer-side EMS, 122...power conversion device, 123...stationary power source.

Claims

1. A positive electrode and a negative electrode containing at least one selected from the group consisting of lithium metal, lithium alloys, and compounds capable of absorbing and releasing Li; a non-aqueous electrolyte containing an ionic liquid and 0.5% by weight or more and 30% by weight or less of a urea compound; A secondary battery comprising:

2. The ionic liquid contains one or more cations selected from the group consisting of 1,3-dialkylimidazolium ions, trialkylsulfonium ions, N,N-dialkylpiperidinium ions, and quaternary ammonium ions, lithium ions, and [N(CF 3 SO 2 ) 2 ] - or [N(FSO 2 ) 2 ] - and an anion comprising at least one of:

3. The ionic liquid contains one or more cations selected from the group consisting of 1-ethyl-3-methylimidazolium ions, triethylsulfonium ions, N,N-dialkylpiperidinium ions, and quaternary ammonium ions, lithium ions, and [N(CF 3 SO 2 ) 2 ] - or [N(FSO 2 ) 2 ] - and an anion comprising at least one of:

4. 3. The secondary battery according to claim 2, wherein the concentration of lithium ions in the non-aqueous electrolyte is in the range of 0.5 mol / kg to 2 mol / kg.

5. 2. The secondary battery according to claim 1, wherein the urea compound comprises at least one selected from the group consisting of urea, N-methyl urea, and N,N'-dimethyl propylene urea.

6. A battery pack comprising the secondary battery according to any one of claims 1 to 5.

7. An external terminal for applying current; Protection circuit and The battery pack according to claim 6 , further comprising:

8. A battery includes a plurality of the secondary batteries, The battery pack according to claim 7 , wherein the secondary batteries are electrically connected in series, in parallel, or in a combination of series and parallel.

9. A vehicle equipped with the battery pack according to claim 6.

10. A stationary power source comprising the battery pack according to claim 6.

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