Secondary battery, battery pack, vehicle, stationary power supply, and method of producing secondary battery

Abstract

To provide a secondary battery high in charge / discharge efficiency and cycle life performance, a battery pack including the secondary battery, and a vehicle and a stationary power supply which include the battery pack.SOLUTION: According to one embodiment, there is provided a secondary battery including a negative electrode, a positive electrode, and an electrolyte. The electrolyte contains water, a lithium salt, and a phosphate ester. The electrolyte contains the water in an amount of 150 ppm or more and 30,000 ppm or less in terms of mass. The lithium salt contains at least one selected from the group consisting of lithium bis (trifluoromethanesulfonyl) imide, lithium bis (fluorosulfonyl) imide, lithium difluorooxalate borate, lithium bisoxalate borate, and lithium triflate.SELECTED DRAWING: Figure 1

Description

[Technical field]

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

[0002] Non-aqueous electrolyte batteries, particularly lithium secondary batteries, using carbon materials or lithium titanium oxide as the negative electrode active material and layered oxides containing nickel, cobalt, manganese, etc. as the positive electrode active material have already been put to practical use as power sources in a wide range of fields. The form of such non-aqueous electrolyte batteries ranges from small ones for various electronic devices to large ones for electric vehicles. Unlike nickel-hydrogen batteries or lead-acid batteries, the electrolyte of these lithium secondary batteries uses a non-aqueous organic solvent in which ethylene carbonate, methyl ethyl carbonate, etc. are mixed. Electrolytes using these solvents have high oxidation resistance and reduction resistance, and electrolysis of the solvent is unlikely to occur. Therefore, non-aqueous lithium secondary batteries can achieve a high electromotive force of 2V to 4.5V.

[0003] On the other hand, since many organic solvents are flammable substances, the safety of secondary batteries using organic solvents is, in principle, inferior to nickel-metal hydride batteries and lead-acid batteries. Although various measures have been taken to improve the safety of lithium secondary batteries using electrolytes containing organic solvents, they are not necessarily sufficient. In addition, non-aqueous lithium secondary batteries require a dry environment in the manufacturing process, which inevitably increases the manufacturing cost. In addition, electrolytes containing organic solvents have poor conductivity, so the internal resistance of non-aqueous lithium secondary batteries is likely to be high. Such issues are a major drawback in electric vehicles or hybrid electric vehicles, where battery safety and battery cost are important, and in large-scale storage battery applications for power storage.

[0004] In order to solve the problems of non-aqueous secondary batteries, it has been proposed to make the electrolyte non-flammable. For example, making the electrolyte an aqueous solution has been considered as a way to make the electrolyte non-flammable. However, electrolytes using water are prone to reductive decomposition at the negative electrode, which tends to cause gas generation and cycle deterioration. Therefore, suppressing the reductive decomposition of the electrolyte is an issue.

[0005] It is known that the reductive decomposition can be suppressed by, for example, increasing the concentration of lithium salt and reducing the water content in the electrolyte, but the suppression of the reductive decomposition by using a high-concentration electrolyte is not sufficient. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] International Publication No. WO2010 / 030008 [Patent Document 2] International Publication No. WO2016 / 114141 [Patent Document 3] JP 2017-27923 A [Patent Document 4] International Publication No. WO2019 / 093411 Summary of the Invention [Problem to be solved by the invention]

[0007] The problem to be solved by the present invention is to provide a secondary battery having high charge / discharge efficiency, a battery pack including this secondary battery, a vehicle and a stationary power source including this battery pack, and a method for manufacturing the secondary battery. [Means for solving the problem]

[0008] According to an embodiment, a secondary battery including a negative electrode, a positive electrode, and an electrolyte is provided. The electrolyte includes water, a lithium salt, and a phosphate ester. The electrolyte includes water in an amount of 150 ppm or more and 30,000 ppm or less by mass. The lithium salt includes at least one selected from the group consisting of lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium difluorooxalatoborate, lithium bisoxalatoborate, and lithium triflate.

[0009] According to another embodiment, there is provided a battery pack including the secondary battery according to the above embodiment.

[0010] According to yet another embodiment, a vehicle including the battery pack according to the above embodiment is provided.

[0011] According to still another embodiment, there is provided a stationary power source including a battery pack according to the above embodiment.

[0012] In addition, a method for manufacturing a secondary battery according to the above embodiment is provided. The method includes preparing an anode, preparing a cathode, preparing an electrolyte, preparing an exterior member, housing the anode and cathode in the exterior member, and injecting the electrolyte into the exterior member. Injecting the electrolyte is performed in a dew point environment of -20°C or higher and 0°C or lower. [Brief description of the drawings]

[0013] [Figure 1] 1 is a conceptual diagram showing the surface of a negative electrode in a conventional secondary battery. [Diagram 2] FIG. 2 is a conceptual diagram showing a surface of a negative electrode in a secondary battery according to an embodiment. [Diagram 3] FIG. 1 is a cross-sectional view illustrating an example of a secondary battery according to an embodiment. [Figure 4] 4 is a cross-sectional view taken along line IV-IV of the secondary battery shown in FIG. 3. [Diagram 5] FIG. 4 is a cross-sectional view illustrating another example of a secondary battery according to an embodiment of the present invention. [Figure 6] 6 is an enlarged cross-sectional view of a portion A of the secondary battery shown in FIG. 5. [Figure 7] FIG. 13 is a partially cutaway perspective view illustrating a secondary battery according to another embodiment of the present invention. [Figure 8] 8 is an enlarged cross-sectional view of a portion B of the secondary battery shown in FIG. 7. [Figure 9] FIG. 1 is a perspective view illustrating an example of a battery pack according to an embodiment. [Figure 10] FIG. 1 is a perspective view illustrating an example of a battery pack according to an embodiment. [Figure 11] FIG. 13 is an exploded perspective view illustrating a battery pack according to another embodiment of the present invention. [Figure 12] 12 is a block diagram showing an example of an electric circuit of the battery pack shown in FIG. 11. [Figure 13] 1 is a cross-sectional view illustrating an example of a vehicle according to an embodiment. [Figure 14] 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 PREFERRED EMBODIMENTS

[0014] Hereinafter, the embodiments will be described with reference to the drawings as appropriate. Note that the same reference numerals are used to designate common components throughout the embodiments, and duplicated descriptions will be omitted. Also, each figure is a schematic diagram for explaining the embodiments and for facilitating understanding thereof, and the shapes, dimensions, ratios, etc. may differ from those of the actual device, but these can be appropriately modified in design by taking into consideration the following explanation and known techniques.

[0015] (First embodiment) According to a first embodiment, a secondary battery including a negative electrode, a positive electrode, and an electrolyte is provided. The electrolyte includes water, a lithium salt, and a phosphate ester. The electrolyte includes water in an amount of 150 ppm or more and 30,000 ppm or less by mass. The lithium salt includes at least one selected from the group consisting of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI; LiN(SO2CF3)2), lithium bis(fluorosulfonyl)imide (LiFSI; LiN(SO2F)2), lithium difluorooxalatoborate (LiDFOB; LiBF2(C2O4)), lithium bisoxalatoborate (LiBOB; LiB[(OCO)2]2), and lithium triflate (LiOtF; LiCF3SO3, also known as lithium trifluoromethanesulfonate).

[0016] The secondary battery may further include a separator disposed between the positive electrode and the negative electrode. The negative electrode, the positive electrode, and the separator may constitute an electrode group. The electrolyte may be held in the electrode group.

[0017] Moreover, such a secondary battery can further include an exterior member that houses the electrode group and the electrolyte.

[0018] Furthermore, such a secondary battery may further include a negative electrode terminal electrically connected to the negative electrode and a positive electrode terminal electrically connected to the positive electrode.

[0019] The secondary battery may be, for example, a lithium secondary battery (lithium ion secondary battery). Although the secondary battery includes an electrolyte containing water, it is different from an aqueous electrolyte secondary battery that includes an aqueous electrolyte (for example, an aqueous electrolyte) in which the main component of the electrolyte solvent is water. In order to achieve the suppression of reductive decomposition in an aqueous electrolyte secondary battery, the secondary battery has a trace amount of water in the electrolyte. Although the amount is trace, the water content in the electrolyte is large compared to a nonaqueous electrolyte battery that includes a nonaqueous electrolyte in which the water content is generally 0.005% by mass (50 ppm) or less, and the upper limit of the reported allowable amount is 0.01% by mass (100 ppm), so the secondary battery cannot be called a nonaqueous electrolyte secondary battery.

[0020] LiTFSI, LiFSI, LiDFOB, LiBOB, and LiOtF are lithium salts that are stable in water and also stable in phosphate esters. By including a stable lithium salt and phosphate ester together with a small amount of water in the electrolyte solution, the secondary battery can suppress side reactions such as reductive decomposition reactions at the negative electrode. By suppressing side reactions, high charge / discharge efficiency can be obtained.

[0021] The reason why high charge / discharge efficiency can be obtained is presumably because the use of an electrolyte containing a trace amount of moisture, the above-mentioned lithium salt, and a phosphate ester forms a coating on the negative electrode that is suitable for suppressing side reactions between the negative electrode and the electrolyte.

[0022] It has been customary to provide a coating on an electrode to suppress side reactions between the electrode and the electrolyte. As a means for suppressing hydrogen generation due to a reductive decomposition reaction of water by a negative electrode in an aqueous electrolyte in which a lithium salt is dissolved in an aqueous solution, it is also known to increase the concentration of the lithium salt to reduce the water content in the electrolyte. However, in a battery using such a conventional high-concentration aqueous electrolyte, as shown in the conceptual diagram in FIG. 1, the coating 20 is formed sparsely on the negative electrode active material 30, and there are many parts of the negative electrode active material 30 exposed to the aqueous electrolyte 28. Therefore, even when the lithium salt in the aqueous electrolyte 28 is highly concentrated, water reacts, and the hydrogen generation suppression effect becomes insufficient. Note that FIG. 1 (and FIG. 2) shows the negative electrode active material 30 located on the surface of the negative electrode active material-containing layer 3b in a schematic manner, and the remaining parts of the negative electrode active material-containing layer 3b are not drawn.

[0023] Unlike conventional aqueous electrolyte batteries, the secondary battery according to the embodiment contains a small amount of water, a lithium salt, and a phosphate ester in the electrolyte. In the secondary battery, the electrolyte may contain a material capable of forming a film on the negative electrode. The small amount of water contained in the electrolyte promotes the formation of a film by the lithium salt and the film-forming material. This is expected to result in the formation of a film 20 that protects the negative electrode active material 30 from the electrolyte 29, as shown in the conceptual diagram of FIG. 2. The negative electrode is protected by the film 20, which exhibits a good hydrogen generation suppression effect, and thus improves the charge / discharge efficiency of the secondary battery.

[0024] The negative electrode, the positive electrode, the electrolyte, the separator, the exterior member, the negative electrode terminal, and the positive electrode terminal will be described in detail below.

[0025] (1) Negative electrode The negative electrode may include a negative electrode current collector and a negative electrode active material-containing layer. The negative electrode active material-containing layer may be provided on one main surface or both main surfaces of the negative electrode current collector. The negative electrode active material-containing layer may include a negative electrode active material, and optionally a conductive agent and a binder.

[0026] The negative electrode may contain at least one element selected from the group consisting of F, P, B, N, and S on its surface. For example, a coating containing one or more of these elements may be formed on the surface of the negative electrode. As described below, components that can be sources of these elements may be contained in the electrolyte. Among the above elements, it is more preferable that fluorine (F) and / or phosphorus (P) is contained on the surface of the negative electrode.

[0027] The layer containing the negative electrode active material may contain, for example, a carbon material, a silicon-containing compound, or a metal oxide as the negative electrode active material. The negative electrode active material may be a material capable of inserting and extracting Li ions. Examples of the carbon material as the negative electrode active material include graphitic materials such as graphite (e.g., artificial graphite or natural graphite), as well as carbon materials such as hard carbon, amorphous carbon, and crystallized carbon. From the viewpoint of increasing the energy density, it is desirable to use graphite as the negative electrode active material.

[0028] Examples of silicon-containing compounds include silicon oxides SiO x (where the subscript x satisfies 0 < x ≤ 2). More specific examples include silicon monoxide (SiO) and silicon dioxide (SiO2).

[0029] Metal oxides can include, for example, titanium-containing oxides. As titanium-containing oxides, titanium oxides, lithium titanium oxides, monoclinic niobium titanium oxides, orthorhombic titanium-containing composite oxides, etc. can be used. The negative electrode active material can contain one or more kinds of titanium-containing oxides.

[0030] Titanium oxides include, for example, titanium oxides with a monoclinic crystal structure, rutile structure titanium oxides, and anatase structure titanium oxides. The titanium oxides of each crystal structure can have a composition before charging represented by TiO2 and a composition after charging represented by Li x TiO2 (where the subscript x satisfies 0 ≤ x ≤ 1). Also, the structure of the titanium oxide with a monoclinic crystal structure before charging can be represented as TiO2(B).

[0031] Lithium titanium oxides include, for example, lithium titanium oxides with a spinel structure (e.g., compounds represented by the general formula Li 4+x Ti5O 12 where -1 ≤ x ≤ 3) and lithium titanium oxides with a lamellarite structure (e.g., compounds represented by Li 2+x Ti3O7 where -1 ≤ x ≤ 3, compounds represented by Li 1+x Ti2O4 where 0 ≤ x ≤ 1, compounds represented by Li 1.1+x Ti 1.8 O4 where 0 ≤ x ≤ 1, compounds represented by Li 1.07+x Ti 1.86 O4 where 0 ≤ x ≤ 1, and compounds represented by Li x TiO2 where 0 < x ≤ 1), etc. Also, the lithium titanium oxide may be a lithium titanium composite oxide into which a different element has been introduced.

[0032] Examples of monoclinic niobium titanium oxides include Li x Ti 1-y M1 y Nb2-z M2 z O 7+δ Here, M1 is at least one selected from the group consisting of Zr, Si, and Sn. M2 is at least one selected from the group consisting of V, Ta, and Bi. The subscripts in the composition formula are 0≦x≦5, 0≦y<1, 0≦z<2, and -0.3≦δ≦0.3. Specific examples of monoclinic niobium titanium oxide include Li x Examples include Nb2TiO7 (0≦x≦5).

[0033] Another example of monoclinic niobium titanium oxide is Li x Ti 1-y M3 y+z Nb 2-z O 7-δ Here, M3 is at least one selected from the group consisting of Mg, Fe, Ni, Co, W, Ta, and Mo. The subscripts in the composition formula are 0≦x≦5, 0≦y<1, 0≦z<2, and -0.3≦δ≦0.3.

[0034] Further examples of monoclinic niobium titanium oxides include, for example, Nb2TiO7, Nb2Ti2O9, and Nb 10 Ti2O 29 , Nb 14 TiO 37 and Nb 24 TiO 62 The monoclinic niobium titanium oxide may be a substituted niobium titanium oxide in which at least a part of Nb and / or Ti is substituted with a different element. Examples of the substituted 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 oxide may contain one type of substituted element, or may contain two or more types of substituted elements.

[0035] As an example of the above-mentioned orthorhombic titanium-containing composite oxide, Li 2+a M I 2-b Ti 6-c M II d O14+σ In this case, the compound represented by 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).

[0036] The negative electrode active material is contained in the negative electrode active material-containing layer in the form of particles, for example. The negative electrode active material particles may be primary particles, secondary particles which are aggregates of primary particles, or a mixture of a single primary particle and a secondary particle. The shape of the particles is not particularly limited, and may be, for example, spherical, elliptical, flat, or fibrous.

[0037] The conductive agent is blended to improve the current collecting performance and to suppress the contact resistance between the active material and the current collector. Examples of the conductive agent include vapor grown carbon fiber (VGCF), carbon black such as acetylene black, and carbonaceous materials such as graphite. In addition, fibrous carbon materials such as carbon nanotubes and carbon nanofibers can be used as the conductive agent. One of these may be used as the conductive agent, or two or more may be combined and used as the conductive agent. Alternatively, instead of using the conductive agent, a carbon coat or an electronically conductive inorganic material coat may be applied to the surface of the active material particles. The conductive agent may also be omitted. For example, when a carbon material is used as the negative electrode active material, the conductive agent may be omitted.

[0038] The binder is blended to fill the gaps between the dispersed active materials and to bind the active materials and the negative electrode current collector. Examples of the binder include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), fluorine-based rubber, styrene butadiene rubber, polyacrylic acid compounds, imide compounds, carboxymethyl cellulose (CMC), and salts of CMC. One of these may be used as the binder, or two or more may be used in combination as the binder.

[0039] In the negative electrode active material-containing layer using a carbon material as the negative electrode active material, the mixing ratio of the negative electrode active material and the binder is preferably 70% by mass or more and 98.5% by mass or less and 1.5% by mass or more and 30% by mass or less, respectively. By setting the amount of the binder to 1.5% by mass or more, the binding property between the active material-containing layer and the current collector becomes sufficient, and excellent cycle performance can be expected. On the other hand, it is preferable to set the amount of the binder to 30% by mass or less in order to achieve high capacity.

[0040] In the negative electrode active material-containing layer using a titanium-containing oxide or a silicon-containing compound as the negative electrode active material, the mixing ratio of the negative electrode active material, the conductive agent, and the binder is preferably in the range of 70% by mass or more and 95% by mass or less of the negative electrode active material, 3% by mass or more and 20% by mass or less of the conductive agent, and 2% by mass or more and 10% by mass or less of the binder. When the mixing ratio of the conductive agent is 3% by mass or more, the current collection performance of the negative electrode active material-containing layer can be improved. Furthermore, when the mixing ratio of the binder is 2% by mass or more, sufficient electrode strength can be obtained. The binder can function as an insulator. Therefore, when the mixing ratio of the binder is 10% by mass or less, the insulating part in the electrode can be reduced.

[0041] For the negative electrode current collector, a material that is electrochemically stable at the potential at which lithium (Li) is inserted and removed from the negative electrode active material is used. For example, when a carbon material is used as the negative electrode active material, a foil made of copper, nickel, titanium, zinc, or stainless steel can be used as the current collector. When the titanium-containing oxide is used as the negative electrode active material, it is preferable to use a foil made of copper, nickel, titanium, zinc, stainless steel, or aluminum, or an aluminum alloy containing one or more elements selected from Mg, Ti, Zn, Mn, Fe, Cu, and Si as the current collector. In addition to foil, the negative electrode current collector can be in the form of, for example, a mesh or a porous body. In order to improve energy density and output, a foil form with a small volume and a large surface area is desirable.

[0042] The thickness of the negative electrode current collector is preferably 5 μm or more and 20 μm or less. A current collector having such a thickness can achieve a good balance between electrode strength and weight reduction.

[0043] The negative electrode current collector may include a portion on its surface on which the negative electrode active material-containing layer is not provided. This portion may function as a negative electrode current collector tab. Alternatively, a negative electrode current collector tab separate from the negative electrode current collector may be electrically connected to the negative electrode.

[0044] The density of the negative electrode active material-containing layer (excluding the current collector) is 1.8 g / cm 3 More than 2.8g / cm 3 A negative electrode having a density of the negative electrode active material-containing layer within this range is excellent in energy density and electrolyte retention. The density of the negative electrode active material-containing layer is preferably 2.1 g / cm or less. 3 More than 2.6g / cm 3 It is more preferable that:

[0045] (2) Positive electrode The positive electrode may include a positive electrode current collector and a positive electrode active material-containing layer. The positive electrode active material-containing layer may be provided on one main surface or both main surfaces of the positive electrode current collector. The positive electrode active material-containing layer may include a positive electrode active material and, optionally, a conductive agent and a binder.

[0046] As the positive electrode active material, for example, an oxide or a sulfide can be used. The positive electrode may contain, as the positive electrode active material, one type of compound alone, or may contain a combination of two or more types of compounds. Examples of the oxide and the sulfide include compounds into which an alkali metal or an alkali metal ion can be inserted and desorbed.

[0047] Examples of such compounds include manganese dioxide (MnO2), iron oxide, copper oxide, nickel oxide, lithium manganese composite oxide (e.g., Li x Mn2O4 or Li x MnO2; 0 < x ≦ 1), lithium nickel composite oxide (e.g., Li x NiO2; 0 < x ≦ 1), lithium cobalt composite oxide (e.g., Li x CoO2; 0 < x ≦ 1), lithium nickel cobalt composite oxide (e.g., Li x Ni 1-y Co y O2; 0 < x ≦ 1, 0 < y < 1), lithium manganese cobalt composite oxide (e.g., Li x Mn y Co 1-y O2; 0 < x ≦ 1, 0 < y < 1), lithium manganese nickel composite oxide having a spinel structure (e.g., Li x Mn 2-y Ni y O4; 0 < x ≦ 1, 0 < y < 2), lithium phosphate having an olivine structure (e.g., Li x FePO4; 0 < x ≦ 1, Li x Fe 1-y Mn y PO4; 0 < x ≦ 1, 0 < y < 1, Li x CoPO4; 0 < x ≦ 1), iron sulfate (Fe2(SO4)3), vanadium oxide (e.g., V2O5), and lithium nickel cobalt manganese composite oxide (Li x Ni 1-y-z Co y Mn z O2; 0 < x ≦ 1, 0 < y < 1, 0 < z < 1, y + z < 1) are included.

[0048] Among the above, examples of more preferable compounds as the positive electrode active material include lithium manganese composite oxides having a spinel structure (for example, Li x Mn2O4; 0 < x ≦ 1), lithium nickel composite oxides (for example, Li x NiO2; 0 < x ≦ 1), lithium cobalt composite oxides (for example, Li x CoO2; 0 < x ≦ 1), lithium nickel cobalt composite oxides (for example, Li x Ni 1-y Co y O2; 0 < x ≦ 1, 0 < y < 1), lithium manganese nickel composite oxides having a spinel structure (for example, Li x Mn 2-y Ni y O4; 0 < x ≦ 1, 0 < y < 2), lithium manganese cobalt composite oxides (for example, Li x Mn y Co 1-y O2; 0 < x ≦ 1, 0 < y < 1), lithium iron phosphate (for example, Li x FePO4; 0 < x ≦ 1), and lithium nickel cobalt manganese composite oxides (Li x Ni 1-y-z Co y Mn z O2; 0 < x ≦ 1, 0 < y < 1, 0 < z < 1, y + z < 1) are included. When these compounds are used as the positive electrode active material, the positive electrode potential can be increased.

[0049] The primary particle diameter of the positive electrode active material is preferably 100 nm or more and 1 μm or less. The positive electrode active material with a primary particle diameter of 100 nm or more is easy to handle in industrial production. The positive electrode active material with a primary particle diameter of 1 μm or less can allow the solid-state diffusion of lithium ions to proceed smoothly.

[0050] The specific surface area of the positive electrode active material is preferably 0.1 m 2 / g or more and 10 m 2 / g or less. The positive electrode active material having a specific surface area of 0.1 m 2 / g or more can sufficiently secure the occlusion / discharge sites of Li ions. 10 m 2A positive electrode active material having a specific surface area of ​​100 / g or less is easy to handle in industrial production and can ensure good charge-discharge cycle performance.

[0051] The binder is blended to fill the gaps between the dispersed positive electrode active material and to bind the positive electrode active material and the positive electrode current collector. Examples of the binder include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), fluorine-based rubber, polyacrylic acid compounds, imide compounds, carboxymethyl cellulose (CMC), and salts of CMC. One of these may be used as the binder, or two or more may be used in combination as the binder.

[0052] The conductive agent is blended to improve current collection performance and reduce contact resistance between the positive electrode active material and the positive electrode current collector. Examples of the conductive agent include vapor grown carbon fiber (VGCF), carbon black such as acetylene black, and carbonaceous materials such as graphite. One of these may be used as the conductive agent, or two or more may be combined and used as the conductive agent. The conductive agent may also be omitted.

[0053] In the positive electrode active material-containing layer, the positive electrode active material and the binder are preferably mixed in an amount of 80% by mass to 98% by mass and 2% by mass to 20% by mass, respectively.

[0054] By making the amount of binder 2% by mass or more, sufficient electrode strength can be obtained. In addition, the binder can function as an insulator. Therefore, by making the amount of binder 20% by mass or less, the amount of insulator contained in the electrode is reduced, and the internal resistance can be reduced.

[0055] When a conductive agent is added, the positive electrode active material, the binder, and the conductive agent are preferably mixed in proportions of 77% by mass or more and 95% by mass or less, 2% by mass or more and 20% by mass or less, and 3% by mass or more and 15% by mass or less, respectively.

[0056] By making the amount of the conductive agent 3% by mass or more, the above-mentioned effects can be achieved. Also, by making the amount of the conductive agent 15% by mass or less, the ratio of the conductive agent in contact with the electrolyte can be reduced. If this ratio is low, decomposition of the electrolyte during high-temperature storage can be reduced.

[0057] The positive electrode current collector is preferably a metal foil such as titanium, aluminum, or stainless steel, or an aluminum alloy foil containing one or more elements selected from Mg, Ti, Zn, Ni, Cr, Mn, Fe, Cu, and Si. In order to prevent corrosion of the current collector due to a reaction between the current collector and the electrolyte, the surface of the current collector may be coated with a different element.

[0058] The thickness of the positive electrode current collector is preferably 5 μm or more and 20 μm or less, and more preferably 15 μm or less.

[0059] The positive electrode current collector may include a portion on its surface on which the positive electrode active material-containing layer is not provided. This portion may function as a positive electrode current collector tab. Alternatively, a positive electrode current collector tab separate from the positive electrode current collector may be electrically connected to the positive electrode.

[0060] (3) Electrolyte The secondary battery according to the embodiment includes an electrolyte. The electrolyte can be at least partially held in the electrode group. The electrolyte includes at least water, at least one lithium salt selected from the group consisting of LiTFSI, LiFSI, LiDFOB, LiBOB, and LiOtF, and a phosphate ester. The water content of the electrolyte is 150 ppm or more and 30000 ppm or less by mass. The water content is preferably in the range of 200 ppm or more and 3000 ppm or less by mass, and more preferably in the range of 200 ppm or more and 300 ppm or less by mass.

[0061] The electrolyte may be, for example, a liquid electrolyte. The liquid electrolyte is prepared by dissolving an electrolyte salt as a solute in a solvent. The concentration of the electrolyte salt is preferably 0.5 mol / L or more and 2.5 mol / L or less. The electrolyte salt includes a lithium salt. LiTFSI, LiFSI, LiDFOB, LiBOB, and LiOtF are lithium salts that are stable in water and phosphate esters. Among these, the fluorine-containing salts, except for LiBOB, are F sources of fluorine that may be contained in the coating formed on the negative electrode surface. LiDFOB and LiBOB contain boron, and are B sources of boron that may be contained in the coating. LiTFSI, LiFSI, and LiOtF contain sulfur, and are S sources of sulfur that may be contained in the coating.

[0062] The electrolyte may further include a second lithium salt different from LiTFSI, LiFSI, LiDFOB, LiBOB, and LiOtF as the first lithium salt. As the second lithium salt, for example, lithium chloride (LiCl), lithium bromide (LiBr), lithium hydroxide (LiOH), lithium sulfate (Li2SO4), lithium nitrate (LiNO3), lithium acetate (CH3COOLi), lithium oxalate (Li2C2O4), lithium carbonate (Li2CO3), lithium perchlorate (LiClO4), lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), and lithium hexafluoroarsenic (LiAsF6) may be used.

[0063] Water and phosphate ester are the solvent of the electrolyte. Although phosphate ester is an organic solvent, it exhibits flame retardancy. Therefore, by including phosphate ester as a solvent, a non-flammable electrolyte can be obtained. Furthermore, by including phosphate ester, a coating containing phosphate can be formed on the negative electrode. That is, phosphate ester is a P source of phosphorus that can be included in the coating formed on the negative electrode surface. Examples of phosphate ester include trimethyl phosphate (trimethyl phosphate), triethyl phosphate (triethyl phosphate), tripropyl phosphate (tripropyl phosphate), and tributyl phosphate (tributyl phosphate). In addition, as another example, there can be mentioned a fluorine-substituted phosphate ester in which at least one of the hydrogen atoms of the above phosphate ester is substituted with a fluorine atom. Such an electrolyte can include at least one selected from the group consisting of these phosphate esters and fluorine-substituted phosphate esters. The amount of phosphate ester in the electrolyte is preferably 30% by mass or more and 70% by mass or less.

[0064] The electrolyte may contain a solvent other than water and a phosphoric acid ester. For example, the electrolyte may contain an organic solvent other than a phosphoric acid ester. Examples of the organic solvent include cyclic carbonates such as propylene carbonate (PC), ethylene carbonate (EC), fluoroethylene carbonate (FEC), and vinylene carbonate (VC); chain carbonates such as diethyl carbonate (DEC), dimethyl carbonate (DMC), and methyl ethyl carbonate (MEC); cyclic ethers such as tetrahydrofuran (THF), 2-methyl tetrahydrofuran (2MeTHF), and dioxolane (DOX); dimethoxy ethane (DME), and diethoxy ethane (diethoxy ethane) (DME), and the like. Examples of the fluorine source include linear ethers such as diethyl ether (DEE); γ-butyrolactone (GBL), acetonitrile (AN), and sulfolane (SL). Fluoroethylene carbonate can be a fluorine source for F that can be included on the negative electrode surface. Sulfolane can be a sulfur source for S that can be included on the negative electrode surface.

[0065] The electrolyte may further include at least one selected from the group consisting of a nitrile compound such as succinonitrile, an isocyanate compound, a compound having an amide group, a carbonate ester, and a fluorinated carbonate ester. The nitrile compound and the compound having an amide group can be a nitrogen source of N that can be contained on the negative electrode surface. The isocyanate compound can be a sulfur source of S that can be contained on the negative electrode surface. The fluorinated carbonate ester can be a fluorine source of F that can be contained on the negative electrode surface.

[0066] The electrolyte may be a gel electrolyte. The gel electrolyte is prepared by mixing the above-mentioned liquid electrolyte with a polymer compound to form a composite. Examples of the polymer compound include polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), and polyethylene oxide (PEO).

[0067] (4) Separator The separator is provided, for example, between the negative electrode and the positive electrode, and prevents electrical contact between the negative electrode and the positive electrode.

[0068] It is desirable to use a separator having a shape that allows the electrolyte to move within the separator.

[0069] The separator may have a porous structure. Examples of the porous separator include nonwoven fabric, film, and paper. Examples of the materials constituting the porous separator, such as the nonwoven fabric, film, and paper, include polyolefins such as polyethylene and polypropylene, and cellulose. Examples of preferred porous separators include nonwoven fabrics containing cellulose fibers and porous films containing polyolefin fibers.

[0070] From the viewpoint of safety, it is preferable to use a porous film made of polyethylene or polypropylene, since these porous films melt at a certain temperature and are capable of interrupting the electric current.

[0071] The porosity of the porous separator is preferably 60% or more. The fiber diameter is preferably 10 μm or less. By making the fiber diameter 10 μm or less, the affinity of the porous separator to the electrolyte is improved, so that the battery resistance can be reduced. The fiber diameter is more preferably in the range of 3 μm or less. A cellulose fiber-containing nonwoven fabric with a porosity of 60% or more has good electrolyte impregnation. Therefore, when such a nonwoven fabric is used as a separator, high output performance can be achieved from low to high temperatures. The porosity is more preferably in the range of 62% to 80%.

[0072] As the separator, a membrane described below may be used. Such a membrane may be used in combination with the above-mentioned porous separator. For example, a composite obtained by forming a membrane on one or both sides of a porous membrane may be used as the separator.

[0073] As the diaphragm, a membrane containing inorganic solid particles and a polymer material, for example, a composite membrane of inorganic solid particles and a polymer material, or an ion exchange membrane can be used. The inorganic solid particles can be, for example, particles of a solid electrolyte, and the membrane can be a solid electrolyte membrane. The solid electrolyte membrane can be, for example, a solid electrolyte composite membrane formed by forming solid electrolyte particles into a membrane using a polymer material.

[0074] Examples of inorganic solid particles that can be contained in the diaphragm include oxide-based ceramics such as alumina, silica, zirconia, yttria, magnesium oxide, calcium oxide, barium oxide, strontium oxide, and vanadium oxide, carbonates and sulfates such as sodium carbonate, potassium carbonate, magnesium carbonate, calcium carbonate, barium carbonate, lanthanum carbonate, cerium carbonate, calcium sulfate, magnesium sulfate, aluminum sulfate, gypsum, and barium sulfate, phosphates such as hydroxyapatite, lithium phosphate, zirconium phosphate, and titanium phosphate, and nitride-based ceramics such as silicon nitride, titanium nitride, and boron nitride. The inorganic particles listed above may be in the form of a hydrate.

[0075] The inorganic solid particles preferably contain solid electrolyte particles having ion conductivity for lithium ions. Specifically, inorganic solid particles having ion conductivity for lithium ions are more preferable. Here, the term "having lithium ion conductivity" refers to a lithium ion conductivity of 1×10 at 25° C. -6 This means that the inorganic solid particles have a lithium ion conductivity of 100 S / cm or more. The lithium ion conductivity can be measured, for example, by an AC impedance method. By using such inorganic solid particles, a membrane having lithium ion conductivity can be obtained.

[0076] Examples of the inorganic solid particles having lithium ion conductivity include, for example, oxide-based solid electrolytes or sulfide-based solid electrolytes. As the oxide-based solid electrolyte, it is preferable to use a lithium phosphate solid electrolyte having a NASICON (Sodium (Na) Super Ionic Conductor) type structure and represented by the general formula Li 1+x Mα2(PO4)3. In the above general formula, Mα is, for example, one or more selected from the group consisting of titanium (Ti), germanium (Ge), strontium (Sr), zirconium (Zr), tin (Sn), aluminum (Al), and calcium (Ca). The subscript x is within the range of 0 ≦ x ≦ 2.

[0077] Specific examples of the lithium phosphate solid electrolyte having a NASICON type structure include LATP compounds represented by Li 1+x Al x Ti 2-x (PO4)3 with 0.1 ≦ x ≦ 0.5; compounds represented by Li 1+x Al y Mβ 2-y (PO4)3 where Mβ is one or more selected from the group consisting of Ti, Ge, Sr, Zr, Sn, and Ca and 0 ≦ x ≦ 1 and 0 ≦ y ≦ 1; compounds represented by Li 1+x Al x Ge 2-x (PO4)3 with 0 ≦ x ≦ 2; compounds represented by Li 1+x Al x Zr 2-x (PO4)3 with 0 ≦ x ≦ 2; compounds represented by Li 1+x+y Al x Mγ 2-x Si y P 3-y O 12 where Mγ is one or more selected from the group consisting of Ti and Ge and 0 < x ≦ 2, 0 ≦ u < 3; and compounds represented by Li 1+2x Zr 1-x Ca x (PO4)3 with 0 ≦ x < 1. Compounds represented by Li 1+2x Zr 1-x Ca x(PO4)3 is preferably used as the inorganic solid electrolyte particles because of its high water resistance, reducibility and low cost.

[0078] In addition to the lithium phosphate solid electrolyte, Li x PO y N z and 2.6≦x≦3.5, 1.9≦y≦3.8, and 0.1≦z≦1.3. 2.9 PO 3.3 N 0.46 ); Garnet-type structure La 5+x A x La 3-x MδO 12 A is 1 or more selected from the group consisting of Ca, Sr, and Ba, Mδ is 1 or more selected from the group consisting of Nb and Ta, and 0≦x≦0.5; Li3Mδ 2-x L2O 12 wherein Mδ is at least one selected from the group consisting of Nb and Ta, and L may contain Zr, and 0≦x≦0.5; Li 7-3x Al x La3Zr3O 12 and 0≦x≦0.5; Li 5+x La3Mδ 2-x Zr x O 12 where Mδ is at least one selected from the group consisting of Nb and Ta, and 0≦x≦2. LLZ compounds (e.g., Li7La3Zr2O 12 ); and La 2 / 3-x Li x The solid electrolyte may be a compound represented by TiO3, where x is 0.3≦x≦0.7. One type of solid electrolyte may be used, or two or more types may be used in combination.

[0079] The inorganic solid particles in the diaphragm may be of a single type or a mixture of two or more types.

[0080] The polymer material contained in the membrane enhances the binding between the inorganic solid particles. Examples of the polymer material include one or more selected from the group consisting of polyvinyl formal, polyvinyl alcohol, polyvinyl acetal, polyvinyl butyral, polymethyl methacrylate, polyethylene terephthalate, polypropylene, polyethylene, polyvinylidene fluoride, and polytetrafluoroethylene.

[0081] The polymer material contained in the diaphragm may be a single type of material or a mixture of multiple types of materials.

[0082] The diaphragm may contain a plasticizer and an electrolyte salt in addition to the inorganic solid particles and the polymer material. For example, when the diaphragm contains an electrolyte salt, the lithium ion conductivity of the diaphragm can be further increased.

[0083] (5) Exterior materials For the exterior member that houses the negative electrode, positive electrode, separator, and electrolyte, a metal container, a laminate film container, or a resin container can be used.

[0084] As the metal container, a metal can made of nickel, iron, stainless steel, etc., and having a rectangular or cylindrical shape can be used. As the resin container, a container made of polyethylene, polypropylene, etc. can be used.

[0085] The thickness of each of the resin container and the metal container is preferably within a range of 0.05 mm to 1 mm, more preferably 0.5 mm or less, and further preferably 0.3 mm or less.

[0086] Examples of the laminate film include a multi-layer film in which a metal layer is coated with a resin layer. Examples of the metal layer include stainless steel foil, aluminum foil, and aluminum alloy foil. Polymers such as polypropylene (PP), polyethylene (PE), nylon, and polyethylene terephthalate (PET) can be used for the resin layer. The thickness of the laminate film is preferably in the range of 0.01 mm to 0.5 mm, and more preferably 0.2 mm or less.

[0087] (6) Negative terminal The negative electrode terminal can be formed of, for example, a material that is electrochemically stable at the lithium ion insertion-extraction potential of the above-mentioned negative electrode active material and has electrical conductivity. Specifically, the material of the negative electrode terminal can be copper, nickel, titanium, zinc, stainless steel, aluminum, or an aluminum alloy containing at least one element selected from the group consisting of Mg, Ti, Zn, Mn, Fe, Cu, and Si. The negative electrode terminal is preferably made of the same material as the negative electrode current collector in order to reduce the contact resistance with the negative electrode current collector.

[0088] (7) Positive terminal The positive electrode terminal has a potential range of, for example, 3 V to 4.5 V with respect to the oxidation-reduction potential of lithium (vs. Li / Li + ) and can be formed from a material that is electrically stable and conductive. Examples of the material for the positive electrode terminal include titanium, aluminum, and an aluminum alloy containing at least one element selected from the group consisting of Mg, Ti, Zn, Mn, Fe, Cu, and Si. The positive electrode terminal is preferably formed from the same material as the positive electrode current collector in order to reduce the contact resistance with the positive electrode current collector.

[0089] The secondary battery according to the embodiment can be used in various forms such as a square, cylindrical, flat, thin, coin, etc. The secondary battery may also be a secondary battery having a bipolar structure. A secondary battery having a bipolar structure has the advantage that a single cell can be used to fabricate a plurality of cells connected in series.

[0090] Hereinafter, the secondary battery according to the embodiment will be described in detail with reference to Fig. 3 and Fig. 4. Fig. 4 is a cross-sectional view showing an example of the secondary battery according to the embodiment. Fig. 4 is a cross-sectional view taken along line IV-IV of the secondary battery shown in Fig. 3.

[0091] The electrode group 1 is housed in an exterior member 2 made of a rectangular cylindrical metal container. The electrode group 1 includes a negative electrode 3, a separator 4, and a positive electrode 5. The electrode group 1 has a structure in which the separator 4 is interposed between the positive electrode 5 and the negative electrode 3 and wound in a spiral shape to form a flat shape. An electrolyte (not shown) is held in the electrode group 1. As shown in FIG. 3, a strip-shaped negative electrode lead 16 is electrically connected to each of a plurality of points on the end of the negative electrode 3 located on the end face of the electrode group 1. In addition, a strip-shaped positive electrode lead 17 is electrically connected to each of a plurality of points on the end of the positive electrode 5 located on this end face. The plurality of negative electrode leads 16 are connected to the negative electrode terminal 6 in a bundled state as shown in FIG. 4. In addition, although not shown, the positive electrode lead 17 is also electrically connected to the positive electrode terminal 7 in a bundled state.

[0092] The metal sealing plate 10 is fixed to the opening of the metal exterior member 2 by welding or the like. The negative electrode terminal 6 and the positive electrode terminal 7 are each drawn out to the outside through an extraction hole provided in the sealing plate 10. A negative electrode gasket 8 and a positive electrode gasket 9 are disposed on the inner circumferential surface of each extraction hole of the sealing plate 10 to prevent a short circuit due to contact with the negative electrode terminal 6 and the positive electrode terminal 7, respectively. By disposing the negative electrode gasket 8 and the positive electrode gasket 9, the airtightness of the secondary battery 100 can be maintained.

[0093] A control valve 11 (safety valve) is disposed on the sealing plate 10. For example, when the internal pressure in the battery cell increases due to gas generation, the generated gas can be released to the outside from the control valve 11. The control valve 11 may be of a reset type that operates when the internal pressure exceeds a set value and functions as a sealing plug when the internal pressure decreases. Alternatively, a non-reset type control valve that does not recover its function as a sealing plug once it is activated may be used. In FIG. 3, the control valve 11 is disposed in the center of the sealing plate 10, but the control valve 11 may be located at the end of the sealing plate 10. The control valve 11 may be omitted.

[0094] Further, the sealing plate 10 is provided with a liquid inlet 12. The electrolyte can be injected through this liquid inlet 12. After the electrolyte is injected, the liquid inlet 12 can be closed with a sealing plug 13. The liquid inlet 12 and the sealing plug 13 may be omitted.

[0095] Fig. 5 is a cross-sectional view showing another example of such a secondary battery, Fig. 6 is an enlarged cross-sectional view of part A of the secondary battery shown in Fig. 5.

[0096] 5 and 6 includes a bag-shaped exterior member 2, an electrode group 1, and an electrolyte (not shown). The electrode group 1 and the electrolyte are housed in the exterior member 2. The electrolyte (not shown) is held in the electrode group 1.

[0097] The exterior member 2 is made of a laminate film including two resin layers and a metal layer interposed between them.

[0098] As shown in Fig. 5, the electrode group 1 is a flat wound-type electrode group. As shown in Fig. 6, the flat wound-type electrode group 1 includes a negative electrode 3, a separator 4, and a positive electrode 5. The separator 4 is interposed between the negative electrode 3 and the positive electrode 5.

[0099] The negative electrode 3 includes a negative electrode current collector 3a and a negative electrode active material-containing layer 3b. In the negative electrode 3, in a portion located at the outermost shell of the wound-type electrode group 1, the negative electrode active material-containing layer 3b is formed only on the inner surface side of the negative electrode current collector 3a as shown in Fig. 6. In the other portions of the negative electrode 3, the negative electrode active material-containing layer 3b is formed on both sides of the negative electrode current collector 3a.

[0100] The positive electrode 5 includes a positive electrode current collector 5a and a positive electrode active material-containing layer 5b formed on both sides of the positive electrode current collector 5a.

[0101] As shown in FIG. 5, the negative electrode terminal 6 and the positive electrode terminal 7 are located near the outer peripheral end of the wound electrode group 1. The negative electrode terminal 6 is connected to a portion located at the outermost shell of the negative electrode current collector 3a. The positive electrode terminal 7 is connected to a portion located at the outermost shell of the positive electrode current collector 5a. The negative electrode terminal 6 and the positive electrode terminal 7 extend to the outside from an opening of the exterior member 2. A thermoplastic resin layer is provided on the inner surface of the exterior member 2, and the opening is closed by being heat-sealed.

[0102] Fig. 7 is a partially cutaway perspective view that illustrates a further example of a secondary battery according to an embodiment. Fig. 8 is an enlarged cross-sectional view of part B of the secondary battery illustrated in Fig. 7. Figs. 7 and 8 show an example of a secondary battery 100 that uses an exterior member made of a laminate film as the exterior member.

[0103] The secondary battery 100 shown in Figures 7 and 8 includes an electrode group 1 shown in Figures 7 and 8, an exterior member 2 shown in Figure 7, and an electrolyte (not shown). The electrode group 1 and the electrolyte are housed in the exterior member 2. The electrolyte is held in the electrode group 1.

[0104] The exterior member 2 is made of a laminate film including two resin layers and a metal layer interposed between them.

[0105] The electrode group 1 is a laminated type electrode group, as shown in Fig. 8. The laminated type electrode group 1 has a structure in which negative electrodes 3 and positive electrodes 5 are laminated alternately.

[0106] The electrode group 1 includes a plurality of negative electrodes 3. Each of the plurality of negative electrodes 3 includes a negative electrode current collector 3a and a negative electrode active material-containing layer 3b supported on both sides of the negative electrode current collector 3a. The electrode group 1 also includes a plurality of positive electrodes 5. Each of the plurality of positive electrodes 5 includes a positive electrode current collector 5a and a positive electrode active material-containing layer 5b supported on both sides of the positive electrode current collector 5a.

[0107] The negative electrode current collector 3a of each negative electrode 3 includes a portion on one side where the negative electrode active material-containing layer 3b is not supported on any surface. This portion serves as a negative electrode current collector tab 3c. As shown in FIG. 8, the negative electrode current collector tab 3c does not overlap with the positive electrode 5. The negative electrode current collector tabs 3c are electrically connected to a belt-shaped negative electrode terminal 6. The tip of the belt-shaped negative electrode terminal 6 is pulled out to the outside of the exterior member 2.

[0108] Although not shown, the positive electrode current collector 5a of each positive electrode 5 includes a portion on one side where the positive electrode active material-containing layer 5b is not supported on any surface. This portion serves as a positive electrode current collector tab. The positive electrode current collector tab does not overlap with the negative electrode 3, similar to the negative electrode current collector tab 3c. The positive electrode current collector tab is located on the opposite side of the electrode group 1 to the negative electrode current collector tab 3c. The positive electrode current collector tab is electrically connected to a strip-shaped positive electrode terminal 7. The tip of the strip-shaped positive electrode terminal 7 is located on the opposite side of the negative electrode terminal 6 and is drawn out to the outside of the exterior member 2.

[0109] <Measurement method> The methods for checking the negative electrode surface, the negative electrode active material, the positive electrode active material, and the electrolyte are described below.

[0110] If the battery contains negative and positive electrodes, disassemble the battery, remove the negative and positive electrodes, and clean them with dimethyl carbonate (DMC). The cleaning method is explained below. Immerse the electrode (negative or positive) in DMC for 5 minutes and remove the electrode. Repeat this three times, dry the electrode, and then perform the measurement. When repeating the immersion, use new DMC solution each time.

[0111] To extract the electrolyte from a battery, the battery is disassembled, and if there is liquid electrolyte (electrolytic solution) outside the electrodes, the electrolyte that is not impregnated into the electrodes is extracted. If the electrolyte cannot be extracted from outside the electrodes, the electrodes are placed in a centrifuge and the electrolyte is extracted by centrifugation.

[0112] (Measurement of negative electrode surface) Whether or not at least one element selected from the group consisting of F, P, B, N, and S is contained on the surface of the negative electrode can be confirmed by X-ray photoelectron spectroscopy (XPS) analysis under the conditions described below.

[0113] The XPS device used may be a Quantera SXM manufactured by ULVAC-PHI, Inc., or a device with equivalent functions. 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.

[0114] (Measurement of 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.

[0115] (Measurement of positive electrode 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.

[0116] (electrolyte) The presence of phosphate esters and water in the electrolyte can be confirmed by GC-MS (Gas Chromatography-Mass Spectrometry) measurements. The salt concentration in the electrolyte, as well as the amount of phosphate esters and water contained therein, can be measured, for example, by ICP (Inductively Coupled Plasma) emission spectrometry. The molar concentration (mol / L) can be calculated by weighing a specified amount of electrolyte and calculating the salt concentration contained therein. The number of moles of solute and solvent can also be calculated by measuring the specific gravity of the electrolyte.

[0117] <Manufacturing method> The secondary battery according to the embodiment can be manufactured as follows.

[0118] The method for producing the secondary battery includes preparing an anode, preparing a cathode, preparing an electrolyte, preparing an exterior member, housing the anode and cathode in the exterior member, and injecting the electrolyte into the exterior member. Injecting the electrolyte into the exterior member is performed in a dew point environment of -20°C or higher and 0°C or lower.

[0119] The negative electrode and the positive electrode can be prepared, for example, by the following method. First, an 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. Next, the applied slurry is dried to obtain a laminate of an active material-containing layer and a current collector. After that, this laminate is pressed. In this manner, each electrode is prepared. A negative electrode active material is used as the active material for preparing a negative electrode, and a positive electrode active material is used as the active material for preparing a positive electrode.

[0120] Alternatively, each electrode may be prepared by the following method: first, the active material, the conductive agent, and the binder are mixed to obtain a mixture, then the mixture is formed into pellets, and then the pellets are placed on a current collector to obtain an electrode.

[0121] The electrolyte can be prepared, for example, by dissolving a lithium salt in a solvent. The lithium salt includes at least the first lithium salt described above, and may further include a second lithium salt. The solvent includes at least a trace amount (150 ppm by mass or more and 30,000 ppm by mass or less with respect to the entire electrolyte) of water and a phosphate ester.

[0122] Unlike the manufacture of non-aqueous electrolyte batteries, which require a dry environment, it is permissible to expose the electrolyte to a slightly humid environment with a dew point between -20°C and 0°C. Therefore, there is no need to strictly control the dew point, which can reduce the cost and effort of battery manufacture.

[0123] The secondary battery according to the first embodiment includes a negative electrode, a positive electrode, and an electrolyte. The electrolyte includes water, a lithium salt, and a phosphate ester. The electrolyte includes water in an amount of 150 ppm to 30,000 ppm (mass ratio). The lithium salt includes at least one selected from the group consisting of lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium difluorooxalatoborate, lithium bisoxalatoborate, and lithium triflate. In the secondary battery, electrolysis of water is suppressed at the negative electrode, and thus the battery exhibits high charge / discharge efficiency.

[0124] Second embodiment According to a second embodiment, there is provided a battery pack including a plurality of secondary batteries according to the first embodiment.

[0125] In such a battery pack, the individual cells may be electrically connected in series or parallel, or may be arranged in a combination of series and parallel connections.

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

[0127] Fig. 9 is a perspective view showing an example of a battery pack. The battery pack 200 shown in Fig. 9 includes five cells 100a to 100e, four bus bars 21, a positive electrode lead 22, and a negative electrode lead 23. Each of the five cells 100a to 100e is a secondary battery according to the first embodiment.

[0128] The bus bar 21 connects, for example, the negative electrode terminal 6 of one cell 100a and the positive electrode terminal 7 of the adjacent cell 100b. In this way, the five cells 100 are connected in series by the four bus bars 21. That is, the battery pack 200 in FIG. 9 is a five-series battery pack. Although no example is shown, in a battery pack including a plurality of cells electrically connected in parallel, for example, the plurality of negative electrode terminals are connected to each other by a bus bar and the plurality of positive electrode terminals are connected to each other by a bus bar, thereby electrically connecting the plurality of cells.

[0129] The positive electrode terminal 7 of at least one of the five cells 100a to 100e is electrically connected to a positive electrode lead 22 for external connection. Also, the negative electrode terminal 6 of at least one of the five cells 100a to 100e is electrically connected to a negative electrode lead 23 for external connection.

[0130] The battery pack according to the second embodiment includes the secondary battery according to the first embodiment, and therefore the battery pack can exhibit high charge / discharge efficiency.

[0131] Third embodiment According to a third embodiment, a battery pack is provided. The battery pack includes the battery assembly according to the second embodiment. The battery pack may include a single secondary battery according to the first embodiment, instead of the battery assembly according to the second embodiment.

[0132] Such a battery pack may further include a protection circuit. The protection circuit has a function of controlling 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 be used as the protection circuit for the battery pack.

[0133] The battery pack may further include an external terminal for current flow. The external terminal for current flow is for outputting current from the secondary battery to the outside and / or inputting current from the outside to the secondary battery. In other words, when the battery pack is used as a power source, current is supplied to the outside through the external terminal for current flow. When the battery pack is charged, a charging current (including regenerative energy from the power of an automobile or the like) is supplied to the battery pack through the external terminal for current flow.

[0134] Next, an example of a battery pack according to an embodiment will be described with reference to the drawings.

[0135] FIG. 10 is a perspective view that illustrates an example of a battery pack according to an embodiment.

[0136] The battery pack 300 includes, for example, an assembled battery including the secondary batteries shown in FIG. 7 and FIG. 8. The battery pack 300 includes a housing 310 and an assembled battery 200 housed in the housing 310. The assembled battery 200 is a battery in which a plurality of (for example, five) secondary batteries 100 are electrically connected in series. The secondary batteries 100 are stacked in the thickness direction. The housing 310 has openings 320 on the top and on each of the four side surfaces. The side surface from which the negative electrode terminal 6 and the positive electrode terminal 7 of the secondary battery 100 protrude is exposed at the opening 320 of the housing 310. The output positive electrode terminal 332 of the assembled battery 200 is strip-shaped, one end of which is electrically connected to one of the positive electrode terminals 7 of the secondary batteries 100, and the other end of which protrudes from the opening 320 of the housing 310 and protrudes from the top of the housing 310. On the other hand, the output negative electrode terminal 333 of the battery pack 200 is strip-shaped, with one end electrically connected to one of the negative electrode terminals 6 of the secondary batteries 100, and the other end protruding from the opening 320 of the housing 310 and protruding from the top of the housing 310.

[0137] Another example of such a battery pack will be described in detail with reference to Fig. 11 and Fig. 12. Fig. 11 is an exploded perspective view showing a schematic diagram of another example of a battery pack according to an embodiment. Fig. 12 is a block diagram showing an example of an electric circuit of the battery pack shown in Fig. 11.

[0138] The battery pack 300 shown in Figs. 11 and 12 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).

[0139] 11 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 the like. Although not shown, the container 31 and the lid 32 are provided with openings or connection terminals for connection to an external device or the like.

[0140] 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.

[0141] At least one of the plurality of unit cells 100 is the secondary battery according to the first embodiment. Each of the plurality of unit cells 100 is electrically connected in series as shown in FIG. 12. The plurality of unit cells 100 may be electrically connected in parallel, or may be connected in a combination of series and parallel connections. When the plurality of unit cells 100 are connected in parallel, the battery capacity is increased compared to when they are connected in series.

[0142] The adhesive tape 24 fastens the plurality of unit cells 100. The plurality of unit cells 100 may be fixed using heat shrink tape instead of the adhesive tape 24. In this case, the protective sheets 33 are disposed on both side surfaces of the battery pack 200, the heat shrink tape is wrapped around the battery pack 200, and the heat shrink tape is then thermally shrunk to bind the plurality of unit cells 100 together.

[0143] 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.

[0144] The printed wiring board 34 is disposed along one of the short side surfaces 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, wiring 342a and 343a, an external terminal 350 for supplying electricity, a positive wiring (positive wiring) 348a, and a negative wiring (negative wiring) 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.

[0145] 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.

[0146] 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 a detection signal to a protection circuit 346.

[0147] The external terminal 350 for current supply is fixed to the other main surface of the printed wiring board 34. The external terminal 350 for current supply is electrically connected to a device present outside the battery pack 300. The external terminal 350 for current supply includes a positive terminal 352 and a negative terminal 353.

[0148] 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 electrode connector 342 via a wiring 342a. The protection circuit 346 is electrically connected to the negative electrode connector 343 via a wiring 343a. Furthermore, the protection circuit 346 is electrically connected to each of the plurality of single cells 100 via the wiring 35.

[0149] The protective sheet 33 is disposed on both inner surfaces in the long side direction of the container 31 and on the inner surface in the short side direction that faces the printed wiring board 34 via the battery pack 200. The protective sheet 33 is made of, for example, resin or rubber.

[0150] The protection circuit 346 controls charging and discharging of the multiple cells 100. In addition, the protection circuit 346 cuts off 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 of the cells 100 or the battery pack 200.

[0151] An example of the detection signal transmitted from the thermistor 345 is a signal that detects 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 that detects overcharging, overdischarging, and overcurrent of the cell 100. When detecting overcharging 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.

[0152] 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.

[0153] As described above, the battery pack 300 includes the external terminal 350 for current supply. Therefore, the battery pack 300 can output a current from the assembled battery 200 to an external device and input a current from the external device to the assembled battery 200 via the external terminal 350 for current supply. In other words, when the battery pack 300 is used as a power source, the current from the assembled battery 200 is supplied to the external device through the external terminal 350 for current supply. When the battery pack 300 is charged, a charging current from the external device is supplied to the battery pack 300 through the external terminal 350 for current supply. When the battery pack 300 is used as an in-vehicle battery, regenerative energy of the vehicle's power can be used as the charging current from the external device.

[0154] The battery pack 300 may include a plurality of assembled batteries 200. In this case, the plurality of 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 a positive terminal and a negative terminal, respectively, of the external terminals for current supply.

[0155] Such a battery pack is used in applications that require excellent cycle performance, for example, when a large current is drawn. Specifically, the battery pack is used, for example, as a power source for electronic devices, a stationary battery, or an on-board battery for various vehicles. An example of the electronic device is a digital camera. The battery pack is particularly suitable for use as an on-board battery.

[0156] The battery pack according to the third embodiment includes the secondary battery according to the first embodiment or the battery assembly according to the second embodiment, and therefore the battery pack can exhibit high charge / discharge efficiency.

[0157] (Fourth embodiment) According to a fourth embodiment, a vehicle is provided. The vehicle is equipped with the battery pack according to the third embodiment.

[0158] In such a vehicle, the battery pack, for example, recovers regenerative energy of the vehicle's motive power. The vehicle may include a mechanism (regenerator) that converts the kinetic energy of the vehicle into regenerative energy.

[0159] Examples of vehicles include, for example, two to four wheel hybrid electric vehicles, two to four wheel electric vehicles, power assisted bicycles, and rail vehicles.

[0160] The mounting position of the battery pack in the vehicle 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.

[0161] The vehicle may be equipped with a plurality of battery packs. In this case, the batteries included in each battery pack may be electrically connected in series, electrically connected in parallel, or electrically connected in a combination of series and parallel connections. For example, when each battery pack includes a battery pack, the battery packs may be electrically connected in series, electrically connected in parallel, or electrically connected in a combination of series and parallel connections. Alternatively, when each battery pack includes a single battery, the batteries may be electrically connected in series, electrically connected in parallel, or electrically connected in a combination of series and parallel connections.

[0162] Next, an example of a vehicle according to an embodiment will be described with reference to the drawings.

[0163] FIG. 13 is a partial see-through view that illustrates an example of a vehicle according to an embodiment.

[0164] A vehicle 400 shown in Fig. 13 includes a vehicle body 40 and a battery pack 300 according to the third embodiment. In the example shown in Fig. 13, the vehicle 400 is a four-wheeled automobile.

[0165] The vehicle 400 may be equipped with a plurality of battery packs 300. In this case, the batteries (e.g., single cells or assembled batteries) included in the battery pack 300 may be connected in series, in parallel, or in a combination of series and parallel connections.

[0166] 13 illustrates an example in which the battery pack 300 is mounted in an engine room located in the front of the vehicle body 40. As described above, the battery pack 300 may be mounted, for example, in 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 the motive power of the vehicle 400.

[0167] The vehicle according to the fourth embodiment is equipped with the battery pack according to the third embodiment, and therefore has excellent driving performance.

[0168] Fifth embodiment According to the fifth embodiment, a stationary power source is provided, which includes the battery pack according to the third embodiment.

[0169] Such a stationary power source may be equipped with the assembled battery according to the second embodiment or the secondary battery according to the first embodiment, instead of the battery pack according to the third embodiment. The stationary power source according to the embodiments can achieve high efficiency.

[0170] FIG. 14 is a block diagram showing an example of a system including a stationary power source according to the embodiment. FIG. 14 is a diagram showing an example of application to stationary power sources 112 and 123 as an example of use of the battery packs 300A and 300B according to the third embodiment. In the example shown in FIG. 14, a system 110 in which the stationary power sources 112 and 123 are used is shown. The system 110 includes a power plant 111, a stationary power source 112, a consumer-side power system 113, and an energy management system (EMS) 115. In addition, a power grid 116 and a communication network 117 are formed in the system 110, and the power plant 111, the stationary power source 112, the consumer-side power system 113, and the EMS 115 are connected via the power grid 116 and the communication network 117. The EMS 115 uses the power grid 116 and the communication network 117 to perform control to stabilize the entire system 110.

[0171] The power plant 111 generates a large amount of power using fuel sources such as thermal power and atomic power. Power is supplied from the power plant 111 through 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 power supplied from the power plant 111. The stationary power source 112 can supply the power stored in the battery pack 300A through 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. Thus, the power conversion device 118 can perform conversion between direct current and alternating current, conversion between alternating currents having different frequencies, and voltage transformation (boosting and bucking), and the like. Thus, the power conversion device 118 can convert the power from the power plant 111 into power that can be stored in the battery pack 300A.

[0172] 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.

[0173] The consumer-side power system 113 is supplied with power from the power plant 111 and power from the battery pack 300A through 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 perform conversion between DC and AC, conversion between ACs with different frequencies, and voltage transformation (boost and step-down), 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.

[0174] 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. EXAMPLES

[0175] Examples will be described below, but the embodiments are not limited to the examples described below.

[0176] Example 1 <Preparation of negative electrode> As the negative electrode active material, particles of niobium titanium oxide with a monoclinic structure having a composition represented by the formula TiNb2O7 were prepared. This niobium titanium oxide with a monoclinic structure has a function of converting Li xIt has a composition represented by TiNb2O7 (0≦x≦5). Acetylene black as a conductive agent, and carboxymethylcellulose (CMC) and styrene butadiene rubber (SBR) as water-containing binders were prepared. These were mixed in pure water so that the mass ratio (mass%) of negative electrode active material: acetylene black: carboxymethylcellulose: styrene butadiene rubber was 95: 4.2: 0.4: 0.4 to obtain a slurry. This slurry was applied to a current collector made of aluminum foil with a thickness of 15 μm, and the coating was dried. Thus, a composite including a current collector and a negative electrode active material-containing layer formed on the current collector was obtained. Next, the obtained composite was subjected to roll pressing. Next, this composite was further subjected to vacuum drying to obtain a negative electrode.

[0177] <Preparation of positive electrode> The positive electrode active material is LiNi 0.33 Co 0.33 Mn 0.33 Particles of lithium nickel cobalt manganese composite oxide represented by NCM111 were prepared. In addition, acetylene black as a conductive agent and polyvinylidene fluoride (PVdF) as a binder were prepared. These were mixed so that the mass ratio (mass%) of the positive electrode active material: conductive agent: binder was 90:5:5 to obtain a mixture. Next, the obtained mixture was dispersed in n-methylpyrrolidone (NMP) solvent to prepare a positive electrode slurry. This slurry was applied onto a current collector made of aluminum foil with a thickness of 15 μm, and the coating was dried. Thus, a composite including a current collector and a positive electrode active material-containing layer formed on both sides of the current collector was obtained. Next, the obtained composite was subjected to roll pressing. Next, this composite was further subjected to vacuum drying to obtain a positive electrode.

[0178] <Preparation of electrode groups> The positive and negative electrodes were each cut out so that the area where the active material-containing layer was formed was 3 cm wide and 5 cm high. One negative electrode and one positive electrode were attached to each other via a 30 μm thick cellulose separator to produce an electrode laminate as an electrode group. In addition, 0.2 mm thick aluminum tabs were attached to the negative and positive electrodes to collect current.

[0179] <Preparation of electrolyte> An electrolyte solution was obtained by dissolving LiTFSI in trimethyl phosphate (TMP) so that the LiN(CF3SO2)2 (LiTFSI) was 30 mass% and the TMP was 70 mass%. Water (HO) of 170 ppm by mass was added to the obtained electrolyte solution and further mixed to prepare a liquid electrolyte (electrolytic solution).

[0180] <Battery assembly> The electrode laminate thus produced was housed in an exterior member made of a laminate film. Then, a liquid electrolyte was poured into the exterior member. The liquid electrolyte was poured in an environment with a dew point of minus 15°C. After that, the exterior member was sealed to obtain a secondary battery.

[0181] The obtained secondary battery was subjected to an initial charge / discharge at a constant current of 0.2 C at 25°C.

[0182] Example 2 A secondary battery was obtained in the same manner as in Example 1, except that when preparing the liquid electrolyte, 200 ppm (mass ratio) of water was added to a nonaqueous electrolyte solution of 38 mass % LiTFSI and 62 mass % TMP.

[0183] Example 3 A secondary battery was obtained in the same manner as in Example 1, except that when preparing the liquid electrolyte, 29400 ppm (mass ratio) of water was added to a nonaqueous electrolyte solution of 70 mass % LiTFSI and 30 mass % TMP.

[0184] Example 4 A secondary battery was obtained in the same manner as in Example 1, except that when preparing the liquid electrolyte, 250 ppm (mass ratio) of water was added to a nonaqueous electrolyte solution of 45 mass % LiTFSI, 5 mass % LiB(C2O4)2(LiBOB), and 50 mass % TMP.

[0185] Example 5 A secondary battery was obtained in the same manner as in Example 1, except that when preparing the liquid electrolyte, 250 ppm (mass ratio) of water was added to a nonaqueous electrolyte solution of 45 mass % LiTFSI, 5 mass % LiBF2(C2O4)(LiDFOB), and 50 mass % TMP.

[0186] Example 6 A secondary battery was obtained in the same manner as in Example 5, except that triethyl phosphate (TEP) was used instead of TMP.

[0187] Example 7 A secondary battery was obtained in the same manner as in Example 5, except that monoclinic titanium oxide TiO2(B) was used as the negative electrode active material instead of TiNb2O7. Example 8 Lithium titanate with spinel structure Li4Ti5O instead of TiNb2O7 12 A secondary battery was obtained in the same manner as in Example 5, except that the negative electrode active material was used.

[0188] Example 9 LiNi instead of NCM111 0.6 Co 0.2 Mn 0.2 A secondary battery was obtained in the same manner as in Example 5, except that O2 (hereinafter referred to as NCM622) was used as the positive electrode active material.

[0189] Example 10 LiNi instead of NCM111 0.8 Co 0.1 Mn 0.1 A secondary battery was obtained in the same manner as in Example 5, except that O2 (hereinafter referred to as NCM811) was used as the positive electrode active material.

[0190] Example 11 LiAl instead of NCM111 0.2 Mn 1.8 A secondary battery was obtained in the same manner as in Example 5, except that O4 (hereinafter referred to as LMO) was used as the positive electrode active material.

[0191] Example 12 LiMn instead of NCM111 0.7 Fe 0.3 A secondary battery was obtained in the same manner as in Example 5, except that PO4 (hereinafter referred to as LMFP) was used as the positive electrode active material.

[0192] (Example 13) A secondary battery was obtained in the same manner as in Example 1, except that a negative electrode was prepared using graphite as the negative electrode active material instead of TiNb2O7, and a liquid electrolyte was prepared by adding an additive. In detail, the slurry composition was set to a graphite:CMC:SBR mass ratio (mass%) of 98:1.0:1.0, and a negative electrode was prepared using copper foil as a current collector. The liquid electrolyte was prepared by adding 250 ppm of water to a nonaqueous electrolyte solution having a composition of 44 mass% LiTFSI, 4 mass% LiDFOB, 50 mass% TMP, 1 mass% vinylene carbonate (VC), and 1 mass% fluoroethylene carbonate (FEC).

[0193] Example 14 A secondary battery was obtained in the same manner as in Example 13, except that a negative electrode was prepared using silicon monoxide (SiO) together with graphite as the negative electrode active material instead of graphite alone. In detail, the slurry composition was set to a mass ratio (mass%) of graphite:SiO:CMC:SBR of 94:4.0:1.0:1.0, and a copper foil was used as a current collector to prepare a negative electrode.

[0194] Example 15 A secondary battery was obtained in the same manner as in Example 1, except that when preparing the liquid electrolyte, 250 ppm (mass ratio) of water was added to a nonaqueous electrolyte solution of 45 mass % LiTFSI, 5 mass % LiDFOB, 45 mass % TMP, and 5 mass % succinonitrile.

[0195] Example 16 A secondary battery was obtained in the same manner as in Example 1, except that when preparing the liquid electrolyte, 250 ppm (mass ratio) of water was added to a nonaqueous electrolyte solution of 45 mass % LiTFSI, 5 mass % LiDFOB, 45 mass % TMP, and 5 mass % sulfolane.

[0196] Comparative Example 1 A secondary battery was obtained in the same manner as in Example 1, except that when preparing the liquid electrolyte, 20 ppm (mass ratio) of water was added to a nonaqueous electrolyte solution of 70 mass % LiTFSI and 30 mass % TMP.

[0197] Comparative Example 2 A secondary battery was obtained in the same manner as in Example 1, except that when preparing the liquid electrolyte, 33,000 ppm (mass ratio) of water was added to a nonaqueous electrolyte solution of 70% LiTFSI and 30% by mass of TMP.

[0198] Comparative Example 3 A secondary battery was obtained in the same manner as in Example 1, except that when preparing the liquid electrolyte, 170 ppm (mass ratio) of water was added to a non-aqueous electrolyte solution of 15 mass % lithium hexafluorophosphate (LiPF6) and 85 mass % TMP.

[0199] Comparative Example 4 A secondary battery was obtained in the same manner as in Example 1, except that when preparing the liquid electrolyte, an aqueous solution of 85.8 mass % LiTFSI and 14.2 mass % water was prepared to obtain a composition known as a 21 mol / kg LiTFSI aqueous solution.

[0200] <Measurement> The battery subjected to the first charge and discharge was disassembled according to the procedure described above, and the negative electrode was removed and washed. XPS analysis of the negative electrode surface was performed under the above-mentioned conditions to confirm the elements contained in the negative electrode surface. The confirmed elements are shown in Table 1.

[0201] Table 1 summarizes the composition of each component in the batteries fabricated in Examples 1-16 and Comparative Examples 1-4. Specifically, it shows the negative electrode active material, positive electrode active material, liquid electrolyte (electrolytic solution) composition, and contained elements observed on the negative electrode surface. For the positive electrode active material, the compound name is shown by the abbreviation mentioned above (for example, LiNi 0.33 Co 0.33 Mn 0.33 (For O2, it is written as NCM111.) The liquid electrolyte composition is also shown with its abbreviation. The phosphate ester content and water content in the liquid electrolyte are also shown.

[0202] [Table 1]

[0203] <Evaluation> Each battery was subjected to a charge-discharge cycle test under the following test conditions: 0.5 C cycles were performed in a 25°C environment, and the capacity retention rate at 100 cycles and the charge-discharge efficiency at the 50th cycle were determined. The capacity retention rate was calculated as the ratio of the capacity at the 100th cycle to the capacity at the 1st cycle.

[0204] The results of the cycle test are summarized in Table 2 below.

[0205] [Table 2]

[0206] As shown in Table 2, the battery prepared in Example 1-16 had a higher capacity retention rate at the 100th cycle and a higher charge / discharge efficiency at the 50th cycle than the battery prepared in Comparative Example 1-4. In Comparative Example 1, it is judged that the amount of water in the electrolyte was extremely small, so that a sufficient coating could not be formed on the negative electrode and the negative electrode could not be protected. In Comparative Example 2, it is presumed that the battery performance was deteriorated due to too much water. In Comparative Example 3, LiPF6 was used as the lithium salt in the electrolyte, so that water reacted with LiPF6 to generate a large amount of HF, and it is judged that the positive electrode crystal structure was deteriorated or a coating that properly protects the negative electrode was not formed. In Comparative Example 4, the battery performance was particularly low due to the use of a solution mainly composed of water as the electrolyte solvent. Unlike the other Examples, Examples 13 and 14 use a graphite negative electrode instead of a titanium-containing oxide negative electrode. Since the graphite negative electrode has inferior cycle performance to the titanium-containing oxide negative electrode, the capacity retention rate is slightly lower than other Examples.

[0207] According to at least one of the above-described embodiments and examples, a secondary battery is provided. The secondary battery includes a negative electrode, a positive electrode, and an electrolyte. The electrolyte includes water of 150 ppm or more and 30,000 ppm or less by mass, at least one lithium salt selected from the group consisting of lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium difluorooxalatoborate, lithium bisoxalatoborate, and lithium triflate, and a phosphoric acid ester. This secondary battery exhibits high charge / discharge efficiency because it can suppress electrolysis of water in the negative electrode. In addition, it is possible to provide a battery pack exhibiting high charge / discharge efficiency, and further, it is possible to provide a vehicle and a stationary power source equipped with this battery pack.

[0208] Although some embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be 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 included in the scope and spirit of the invention, and are included in the scope of the invention and its equivalents described in the claims.

[0209] Several embodiments according to the present invention will be described below. [1] A negative electrode; A positive electrode and an electrolyte comprising water, a lithium salt, and a phosphate ester; Equipped with The electrolyte contains the water in an amount of 150 ppm to 30,000 ppm by mass, and the lithium salt contains at least one selected from the group consisting of lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium difluorooxalatoborate, lithium bis(oxalatoborate), and lithium triflate. Secondary battery. [2] The secondary battery according to [1], wherein the electrolyte contains at least one selected from the group consisting of a nitrile compound, an isocyanate compound, a compound having an amide group, a carbonate ester, and a fluorinated carbonate ester. [3] The secondary battery according to [1] or [2], wherein the negative electrode contains at least one element selected from the group consisting of F, P, B, N, and S on a surface thereof. [4] The secondary battery according to any one of [1] to [3], wherein the electrolyte contains the phosphate ester in an amount of 30% by mass or more and 70% by mass or less. [5] The secondary battery according to any one of [1] to [4], wherein the negative electrode contains at least one titanium-containing oxide selected from the group consisting of titanium oxide, lithium titanium oxide, monoclinic niobium titanium oxide, and orthorhombic titanium-containing composite oxides. [6] The secondary battery according to any one of [1] to [4], wherein the negative electrode contains at least one selected from the group consisting of graphite, hard carbon, and silicon-containing compounds. [7] A battery pack comprising a secondary battery according to any one of [1] to [6].

[0210] [8] The battery pack according to [7], further including an external terminal for current flow and a protection circuit.

[0211] [9] A battery pack as described in [7] or [8], comprising a plurality of the secondary batteries, the secondary batteries being electrically connected in series, in parallel, or in a combination of series and parallel.

[10] A vehicle equipped with a battery pack described in any one of [7] to [9].

[11] A vehicle as described in

[10] , including a mechanism for converting kinetic energy of the vehicle into regenerative energy.

[12] A stationary power source comprising a battery pack described in any one of [7] to [9].

[13] A method for producing a secondary battery according to any one of [1] to [6], Providing the negative electrode; Providing the positive electrode; preparing the electrolyte; Providing an exterior member; housing the negative electrode and the positive electrode in the exterior member; injecting the electrolyte into the exterior member; The method for manufacturing a secondary battery includes injecting the electrolyte in a dew point environment of -20°C or higher and 0°C or lower. [Explanation of symbols]

[0212] Reference Signs List 1...electrode group, 2...exterior member, 3...negative electrode, 3a...negative electrode current collector, 3b...negative electrode active material-containing layer, 3c...negative electrode current collector tab, 4...separator, 5...positive electrode, 5a...positive electrode current collector, 5b...positive electrode active material-containing layer, 6...negative electrode terminal, 7...positive electrode terminal, 8...negative electrode gasket, 9...positive electrode gasket, 10...sealing plate, 11...control valve, 12...filling port, 13...sealing plug, 16...negative electrode rib a battery for charging a battery that has a positive electrode lead, a coating film for coating a battery that has a negative electrode lead, a battery for charging a battery that has a negative electrode lead, a battery for charging a battery that has a positive ... power station, 112...stationary power source, 113...customer-side power system, 115...energy management system, 116...power grid, 117...communication network, 118...power conversion device, 121...customer-side EMS, 122...power conversion device, 123...stationary power source, 200...battery pack, 300A...battery pack, 300B...battery pack, 310...casing, 320...opening, 332...output positive terminal, 333...output negative terminal, 342...positive connector, 343...negative connector, 345...thermistor, 346...protection circuit, 342a...wiring, 343a...wiring, 350...external terminal for energization, 352...positive terminal, 353...negative terminal, 348a...positive wiring, 348b...negative wiring, 400...vehicle.

Claims

1. A negative electrode; A positive electrode and an electrolyte comprising water, a lithium salt, and a phosphate ester; Equipped with The electrolyte contains the water in an amount of 150 ppm to 30,000 ppm by mass, and the lithium salt contains at least one selected from the group consisting of lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium difluorooxalatoborate, lithium bis(oxalatoborate), and lithium triflate. Secondary battery.

2. 2. The secondary battery according to claim 1, wherein the electrolyte contains at least one selected from the group consisting of a nitrile compound, an isocyanate compound, a compound having an amide group, a carbonate ester, and a fluorinated carbonate ester.

3. 3. The secondary battery according to claim 1, wherein the negative electrode contains at least one element selected from the group consisting of F, P, B, N, and S on a surface thereof.

4. 3. The secondary battery according to claim 1, wherein the electrolyte contains the phosphate ester in an amount of 30% by mass or more and 70% by mass or less.

5. 3. The secondary battery according to claim 1, wherein the negative electrode contains at least one titanium-containing oxide selected from the group consisting of titanium oxide, lithium titanium oxide, monoclinic niobium titanium oxide, and orthorhombic titanium-containing composite oxide.

6. 3. The secondary battery according to claim 1, wherein the negative electrode comprises at least one selected from the group consisting of graphite, hard carbon, and a silicon-containing compound.

7. A battery pack comprising the secondary battery according to claim 1 or 2.

8. 8. The battery pack according to claim 7, further comprising an external terminal for current flow and a protection circuit.

9. 8. The battery pack according to claim 7, comprising a plurality of the secondary batteries, the secondary batteries being electrically connected in series, in parallel, or in a combination of series and parallel.

10. A vehicle comprising the battery pack according to claim 7.

11. The vehicle of claim 10 including a mechanism for converting kinetic energy of the vehicle into regenerative energy.

12. A stationary power source comprising the battery pack according to claim 7.

13. A method for producing the secondary battery according to claim 1 or 2, comprising the steps of: Providing the negative electrode; Providing the positive electrode; preparing the electrolyte; Providing an exterior member; housing the negative electrode and the positive electrode in the exterior member; injecting the electrolyte into the exterior member; The method for producing a secondary battery includes injecting the electrolyte in an environment with a dew point of −20° C. or higher and 0° C. or lower.

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