Lithium-ion battery and manufacturing method of lithium-ion battery

Abstract

To improve a charging and discharging cycle characteristic of a lithium ion battery.SOLUTION: A lithium ion battery 10 comprises: a positive electrode 13 having a positive electrode collector 11 and a positive electrode active material layer 12; a negative electrode 16 that includes a negative electrode collector 14 and a negative electrode active material layer 15, and is opposite to the positive electrode 13; and an electrolyte layer 17 that is positioned between the positive electrode 13 and the negative electrode 16 and has an electrolyte. The electrolyte includes: at least a solvent including a 1,2-dimethoxyethane and a fluorination ether; and a lithium imido compound solved in the solvent. At least one of at least a part of a particle front surface of the positive electrode active material included in the positive electrode active material layer 12 and at least a part of a particle front surface of the negative electrode active material included in the negative electrode active material layer 15 is coated with a coated film including a fluorine, and the coated film includes S2F2 NO4.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a lithium-ion battery and a method for manufacturing a lithium-ion battery. [Background technology]

[0002] Vehicles such as EVs (Electric Vehicles) and HEVs (Hybrid Electrical Vehicles) are equipped with a power storage device that supplies power to a motor, etc. The power storage device is generally provided with a plurality of secondary batteries.

[0003] Lithium-ion batteries (LIBs) are widely used as secondary batteries in EVs and HEVs. Lithium-ion batteries are lightweight and have high energy density, making them ideal for use as high-output power sources in vehicles.

[0004] In order to improve the output characteristics of such lithium ion batteries for vehicle use, it is desirable to reduce both the initial resistance value and the resistance value after deterioration due to charge / discharge cycles.

[0005] Furthermore, since lithium-ion batteries for vehicle use are required to have a high level of safety, it is necessary to suppress heat generation in the positive electrode that occurs during discharge.

[0006] In order to improve safety due to heat generation in lithium ion batteries, for example, electrolytes for lithium ion batteries with improved flame retardancy have been disclosed by selecting materials to be used as solvents for the electrolyte and mixing them within a specific range (see, for example, Patent Documents 1 to 4). [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2005-340223 [Patent Document 2] Japanese Patent Application Laid-Open No. 2001-93572 [Patent Document 3] Patent Publication No. 2021-82516 [Patent Document 4] Japanese Patent Application Publication No. 10-12272 Summary of the Invention [Problem to be solved by the invention]

[0008] However, although the electrolyte solutions for lithium ion batteries disclosed in Patent Documents 1 to 4 can improve the flame retardancy of lithium ion batteries, there is a problem in that they do not sufficiently improve the charge / discharge cycle characteristics.

[0009] The present invention aims to solve the above problems by improving the charge / discharge cycle characteristics of lithium-ion batteries, which in turn contributes to energy efficiency. [Means for solving the problem]

[0010] In light of the above-mentioned background, the present inventors have discovered a new finding that by using a mixture of specific materials in specific ratios as a solvent for a lithium-ion battery and optimizing the conditions for the initial charge, at least one of at least a portion of the particle surface of the positive electrode active material contained in the positive electrode active material layer and at least a portion of the particle surface of the negative electrode active material contained in the negative electrode active material layer is coated with a coating containing fluorine, and that the coating contains S2F2NO4, thereby improving the charge-discharge cycle characteristics of the lithium-ion battery.

[0011] [1] A positive electrode having a positive electrode current collector and a positive electrode active material layer; a negative electrode having a negative electrode current collector and a negative electrode active material layer, the negative electrode facing the positive electrode; an electrolyte layer located between the positive electrode and the negative electrode and containing an electrolyte solution; A lithium ion battery having: the electrolyte solution contains at least a solvent containing 1,2-dimethoxyethane and a fluorinated ether, and a lithium imide compound dissolved in the solvent; at least one of at least a portion of the particle surface of the positive electrode active material contained in the positive electrode active material layer and at least a portion of the particle surface of the negative electrode active material contained in the negative electrode active material layer is coated with a coating containing fluorine, The coating comprises S2F2NO4.

[0012] In the lithium-ion battery of the present invention, at least one of at least a portion of the particle surface of the positive electrode active material contained in the positive electrode active material layer and at least a portion of the particle surface of the negative electrode active material contained in the negative electrode active material layer is coated with a fluorine-containing coating, and the coating contains S2F2NO4, so that the lithium-ion battery has excellent capacity retention during charge-discharge cycles.

[0013] [2] The lithium ion battery according to [1], wherein the count number of the S2F2NO4 in the coating that covers at least a part of the particle surface of the positive electrode active material by time-of-flight secondary ion mass spectrometry is 5000 or more.

[0014] The lithium ion battery of the present invention has an S2F2NO4 count of 5000 or more in the coating that covers at least a portion of the particle surface of the positive electrode active material, as determined by time-of-flight secondary ion mass spectrometry, and therefore has excellent capacity retention during charge-discharge cycles.

[0015] [3] The lithium ion battery according to claim 1, wherein the count number of the S2F2NO4 in the coating that covers at least a portion of the particle surface of the negative electrode active material by time-of-flight secondary ion mass spectrometry is 3000 or more.

[0016] The lithium ion battery of the present invention has a count number of 3000 or more of the S2F2NO4 in the coating that covers at least a portion of the particle surface of the negative electrode active material, as determined by time-of-flight secondary ion mass spectrometry, and therefore has excellent capacity retention rate during charge-discharge cycles.

[0017] [4] An activation step of activating the lithium-ion battery in an environment of 60°C or higher at a charge rate of 0.3C or less in the first cycle, The lithium ion battery includes a positive electrode having a positive electrode current collector and a positive electrode active material layer, and an electrolyte layer having a negative electrode current collector and a negative electrode active material layer, the electrolyte layer being positioned between the positive electrode and the negative electrode and containing an electrolyte solution; the electrolyte solution contains at least a solvent containing 1,2-dimethoxyethane and a fluorinated ether, and a lithium imide compound dissolved in the solvent; a fluorine-containing coating on at least a portion of the particle surface of the positive electrode active material contained in the positive electrode active material layer, or a fluorine-containing coating on at least a portion of the particle surface of the negative electrode active material contained in the negative electrode active material layer.

[0018] The lithium ion battery of the present invention includes an activation step in which the lithium ion battery is placed in an environment of 60°C or higher and the charge rate in the first cycle is set to 0.3 C or less, and therefore a lithium ion battery with excellent capacity retention during charge-discharge cycles can be produced. [Effects of the Invention]

[0019] According to the present invention, it is possible to improve the charge-discharge cycle characteristics of a lithium ion battery. [Brief explanation of the drawings]

[0020] [Figure 1] 1 is a schematic cross-sectional view showing an example of a layer structure of a lithium ion battery according to one embodiment of the present invention. [Figure 2] FIG. 10 is a diagram showing a dQ / dV curve during charging in Verification Example 1. [Figure 3] FIG. 10 is a diagram showing a dQ / dV curve during charging in Verification Example 2. [Figure 4] FIG. 10 is a diagram showing the relationship between the temperature and the reaction amount of a lithium ion battery during initial charging in Verification Example 3. [Figure 5] FIG. 10 is a diagram showing the results of TOF-SIMS measurement of the positive electrode in Verification Example 4. [Figure 6] FIG. 10 is a diagram showing the results of TOF-SIMS measurement of the negative electrode in Verification Example 4. [Figure 7]FIG. 10 is a graph showing the relationship between the content of S2F2NO4 in the coatings that coat the particle surfaces of the positive electrode active material and the negative electrode active material and the temperature of the lithium ion battery during the initial charge in Verification Example 4. DETAILED DESCRIPTION OF THE INVENTION

[0021] Hereinafter, a lithium ion battery according to one embodiment of the present invention will be described with reference to the drawings. The embodiments shown below are specifically described to provide a better understanding of the gist of the invention, and unless otherwise specified, do not limit the present invention. Furthermore, the drawings used in the following description may show essential parts enlarged for the sake of convenience in order to make the features of the present invention easier to understand, and the dimensional proportions of each component may not necessarily be the same as those in reality.

[0022] [Lithium-ion battery] An example of the configuration of a lithium ion battery according to one embodiment of the present invention will be described. FIG. 1 is a schematic cross-sectional view showing an example of the layer structure of a lithium ion battery according to one embodiment of the present invention.

[0023] The lithium ion battery (LIB) 10 is formed by stacking a positive electrode 13 having a positive electrode current collector 11 and a positive electrode active material layer 12 located on one side of the positive electrode current collector 11, a negative electrode 16 having a negative electrode current collector 14 and a negative electrode active material layer 15 located on one side of the negative electrode current collector 14 and facing the positive electrode 13, and an electrolyte layer 17 located between the positive electrode 13 and the negative electrode 16.

[0024] The positive electrode active material layer 12 is a layer containing a positive electrode mixture. The positive electrode mixture includes a positive electrode active material, lithium carbonate, a conductive additive, and a binder.

[0025] The positive electrode active material is capable of absorbing and releasing ions, desorbing and inserting ions (intercalation), or converting ions and counter anions (e.g., PF6 - ) can be used as an electrode active material capable of reversibly undergoing doping and dedoping.

[0026] Specific examples of the positive electrode active material include, for example, lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), lithium manganate (LiMnO2), lithium manganese spinel (LiMn2O4), and the general formula: LiNi x Co y Mn z M a O2 (x + y + z + a = 1, 0 ≤ x < 1, 0 ≤ y < 1, 0 ≤ z < 1, 0 ≤ a < 1, M is one or more elements selected from Al, Mg, Nb, Ti, Cu, Zn, Cr), composite metal oxides (ternary compounds), lithium vanadium compounds (LiV2O5), olivine-type LiMPO4 (where M is one or more elements selected from Co, Ni, Mn, Fe, Mg, Nb, Ti, Al, Zr or represents VO), lithium titanate (Li4Ti5O 12 ), LiNi x Co y Al z O2 (0.9 < x + y + z < 1.1) and other composite metal oxides, polyacetylene, polyaniline, polypyrrole, polythiophene, polyacene, etc. In this embodiment, a ternary compound containing Ni, Co, and Mn is used as the positive electrode active material contained in the positive electrode mixture.

[0027] As the binder contained in the positive electrode mixture of the positive electrode active material layer 12, known ones can be used. For example, fluororesins such as polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), tetrafluoroethylene - hexafluoropropylene copolymer (FEP), tetrafluoroethylene - perfluoroalkyl vinyl ether copolymer (PFA), ethylene - tetrafluoroethylene copolymer (ETFE), polychlorotrifluoroethylene (PCTFE), ethylene - chlorotrifluoroethylene copolymer (ECTFE), polyvinyl fluoride (PVF), etc.

[0028] Examples of the conductive assistant contained in the positive electrode mixture of the positive electrode active material layer 12 include carbon powders such as carbon blacks, carbon nanotubes, carbon materials, metal fine powders such as copper, nickel, stainless steel, and iron, mixtures of carbon materials and metal fine powders, and conductive oxides such as ITO. As the positive electrode mixture constituting the positive electrode active material layer 12, Ketjen black, which is particularly excellent in conductivity among carbon blacks, is used. In addition, when sufficient conductivity can be ensured only by the positive electrode mixture, the positive electrode mixture may not contain a conductive assistant.

[0029] The negative electrode active material layer 15 has a negative electrode active material and a binder as a negative electrode mixture, and may have a conductive assistant as necessary. As the negative electrode active material, known negative electrode active materials can be used. Examples of the negative electrode active material include metallic lithium, graphite (natural graphite, artificial graphite) capable of occluding and releasing lithium ions, carbon nanotubes, non-graphitizable carbon, graphitizable carbon, carbon materials such as low-temperature fired carbon, metals capable of combining with lithium such as aluminum, silicon, and tin, x (0 < x < 2), amorphous compounds mainly composed of oxides such as tin dioxide, and particles containing lithium titanate (Li4Ti5O 12 ) and the like. <N

[0030] The conductive assistant and binder contained in the negative electrode mixture can be the same as those of the positive electrode active material layer 12. In addition to those mentioned in the positive electrode active material layer 12, examples of the binder used for the negative electrode mixture include carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), polyimide (PI), polyamideimide (PAI), polyacrylic acid (PAA), and the like.

[0031] When charging the lithium ion battery 10, the negative electrode 16 including the negative electrode active material layer 15 changes in potential as lithium ions enter the interlayer in the carbon material, which is an example of the negative electrode active material.

[0032] The electrolyte layer (separator) 17 is located between the positive electrode 13 and the negative electrode 16, and allows lithium ions to pass through while isolating the positive electrode 13 from the negative electrode 16. The electrolyte layer (separator) 17 is made of, for example, a porous film made of a resin material, a nonwoven fabric, or the like. The electrolyte layer (separator) 17 contains an electrolytic solution.

[0033] The electrolyte used in the lithium ion battery 10 of this embodiment is a solvent mixture of 1,2-dimethoxyethane and a fluorinated ether, and a lithium imide compound dissolved in this solvent.

[0034] Examples of fluorinated ethers (fluorine-containing chain ethers) used as solvents for the electrolyte solution include compounds having a structure in which some or all of the hydrogen atoms in 1,2-ethoxyethane (DEE) or ethoxymethoxyethane (EME) are substituted with fluorine atoms.

[0035] If the number of carbon atoms in a fluorinated ether is small, the boiling point tends to be low, which may result in vaporization during high-temperature operation of the battery. On the other hand, if the number of carbon atoms is too large, the viscosity of the chain ether may increase, which may reduce the conductivity of the electrolyte. Therefore, the number of carbon atoms is preferably 4 to 10.

[0036] Specific examples of the fluorine-containing chain ether include 2,2,3,3,3-pentafluoropropyl 1,1,2,2-tetrafluoroethyl ether, 1,1,2,2-tetrafluoroethyl 2,2,2-trifluoroethyl ether, 1H,1H,2'H,3H-decafluorodipropyl ether, 1,1,2,3,3,3-hexafluoropropyl-2,2-difluoroethyl ether, isopropyl 1,1,2,2-tetrafluoroethyl ether, propyl 1,1,2,2-tetrafluoroethyl ether, and 1,1,2,2-tetrafluoroethyl ether. methyl 2,2,3,3-tetrafluoropropyl ether, 1H,1H,5H-perfluoropentyl-1,1,2,2-tetrafluoroethyl ether, 1H,1H,2'H-perfluorodipropyl ether, 1H-perfluorobutyl-1H-perfluoroethyl ether, methyl perfluoropentyl ether, methyl perfluorohexyl ether, methyl 1,1,3,3,3-pentafluoro-2-(trifluoromethyl)propyl ether, 1,1,2,3,3,3-hexafluoropropyl 2,2,2-trifluoroethyl ether ethyl nonafluorobutyl ether, ethyl 1,1,2,3,3,3-hexafluoropropyl ether, 1,1,2,3,3,3-hexafluoropropyl 1H,1H-heptafluorobutyl ether, bis(2,2,3,3-tetrafluoropropyl) ether, bis(2,2,3,3,3-pentafluoropropyl) ether, 1H,1H,5H-octafluoropentyl 1,1,2,2-tetrafluoroethyl ether, 1H,1H,2'H-perfluorodipropyl ether, heptafluoropropyl 1,2,2,2-tetrafluoropropyl 1,1,2,2-tetrafluoroethyl ether, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, 2,2,3,3,3-pentafluoropropyl-1,1,2,2-tetrafluoroethyl ether, ethyl nonafluorobutyl ether, methyl nonafluorobutyl ether, 2,2,3,4,4,4-hexafluorobutyl-difluoromethyl ether, 1,1-difluoroethyl-2,2,3,3-tetrafluoropropyl ether, 1,1-difluoroethyl-1H,1H-heptafluorobutyl ether, bis(1H,1H-heptafluorobutyl) ether, nonafluorobutyl methyl ether, 2,2-difluoroethyl-1,1,2,2-tetrafluoroethyl ether, bis(2,2-difluoroethyl) ether, bis(1,1,2-trifluoroethyl) ether, 1,1,2-trifluoroethyl-2,2,2-trifluoroethyl ether, bis(1,1,2,2-tetrafluoroethyl) ether, and the like.

[0037] Among the above-mentioned fluorinated ethers (fluorine-containing chain ethers), in this embodiment, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE) is used from the viewpoints of voltage resistance, boiling point, and the like.

[0038] The fluorinated ether may be contained in a proportion of 50% by mass or more and 90% by mass or less, more preferably 75% by mass or more and 90% by mass or less, based on the total mass of the solvent. By containing the fluorinated ether in a proportion of 75% by mass or more and 90% by mass or less, based on the total mass of the solvent, corrosion of aluminum by the electrolyte can be prevented when aluminum is used as the positive electrode current collector 11. This further improves the charge / discharge cycle of the lithium-ion battery 10. The concentration of the fluorinated ether in the electrolyte may be in the range of 1 mol / L or more and 5 mol / L or less.

[0039] 1,2-dimethoxyethane (DME), which is used as the solvent for the electrolyte, is a water-soluble liquid with a relatively high boiling point (85°C) for an organic solvent. The 1,2-dimethoxyethane may be contained in an amount of 10% by mass or more and 30% by mass or less, more preferably 15% by mass or more and 25% by mass or less, based on the total mass of the electrolyte solution. The concentration of 1,2-dimethoxyethane in the electrolyte solution may be in the range of 3 mol / L or more and 7 mol / L or less.

[0040] The 1,2-dimethoxyethane in the electrolyte can also be replaced with ethylene carbonate. Ethylene carbonate is a glassy solid (room temperature) with a melting point of 34°C to 37°C, and is an ester of ethylene glycol and carbonic acid. Ethylene carbonate is a polar solvent, and adding it to the solvent of an electrolyte can increase the dielectric constant.

[0041] Ethylene carbonate may be contained in a concentration range of 2 mol / L or less relative to 1,2-dimethoxyethane. Alternatively, ethylene carbonate may be contained in a concentration range of less than 8 mass % relative to the total amount of the solvent. By setting the concentration of ethylene carbonate to less than 8 mass % of the entire solvent, it is possible to prevent corrosion of aluminum by the electrolyte when, for example, aluminum is used as the positive electrode current collector 11. This makes it possible to further improve the charge / discharge cycle of the lithium ion battery 10.

[0042] A lithium imide compound is an electrolyte dissolved in the solvent of the electrolyte solution and is generally produced by the reaction of lithium amide with lithium hydride. Examples of the lithium imide compound used in this embodiment include lithium bis-fluorosulfonylimide (LiFSI) and lithium bis-trifluoromethanesulfonylimide (LiTFSI). Adding such lithium bisimide as a lithium salt to a non-aqueous electrolyte solution can improve low-temperature output characteristics and suppress decomposition of the positive electrode surface, which may occur during high-temperature cycle operation, thereby preventing oxidation of the electrolyte solution.

[0043] Such a lithium imide compound may be contained in the entire electrolyte solution in a concentration range of 1 mol / L or more and 3 mol / L or less.

[0044] When the electrolyte solution of the present embodiment having the above-described configuration is used in the lithium-ion battery 10 of the present embodiment, at least one of at least a portion of the particle surface of the positive electrode active material contained in the positive electrode active material layer 12 and at least a portion of the particle surface of the negative electrode active material contained in the negative electrode active material layer 15 is coated with a coating containing fluorine. For example, a fluorine-containing organic coating is formed on the particle surface of the positive electrode active material by the fluorinated ether in the electrolyte. Thus, when at least a portion of the particle surface of the positive electrode active material is coated with a fluorine-containing coating, reversible capacity loss can be reduced. This leads to good discharge characteristics during charge-discharge cycles. Furthermore, by improving the surface stability of the positive electrode active material, oxygen release at high temperatures can be delayed, and the heat generation onset temperature can be raised, improving high-temperature resistance and safety. Furthermore, a coating of a fluorine-containing organic material is formed on the particle surface of the negative electrode active material by the fluorinated ether in the electrolyte. When at least a portion of the particle surface of the negative electrode active material is coated with a coating containing fluorine, the reversible capacity loss can be reduced.

[0045] In the lithium-ion battery 10 of this embodiment, the coating that covers at least a portion of the particle surface of the positive electrode active material and the coating that covers at least a portion of the particle surface of the negative electrode active material contain S2F2NO4. Because the coatings contain S2F2NO4, the lithium-ion battery 10 has excellent capacity retention during charge-discharge cycles.

[0046] The S2F2NO4 contained in the coating can be analyzed by time-of-flight secondary ion mass spectrometry (TOF-SIMS).

[0047] It is preferable that the count number of S2F2NO4 in the coating that covers at least a part of the particle surface of the positive electrode active material by TOF-SIMS is not less than 5000. When the count number of S2F2NO4 contained in the coating is not less than the lower limit, the lithium-ion battery 10 has a better capacity retention rate during charge-discharge cycles.

[0048] It is preferable that the count number of S2F2NO4 in the coating that covers at least a portion of the particle surface of the negative electrode active material by TOF-SIMS is not less than 3000. When the count number of S2F2NO4 contained in the coating is not less than the lower limit, the lithium-ion battery 10 has a better capacity retention rate during charge-discharge cycles.

[0049] The number of S2F2NO4 counted by TOF-SIMS in the coating can be converted into the mass % of S2F2NO4 in the total amount (total mass) of any substance contained in the coating. For example, in the lithium-ion battery 10 of this embodiment, the main anion molecules detected by TOF-SIMS from the coating covering at least a portion of the particle surface of the positive electrode active material or the coating covering at least a portion of the particle surface of the negative electrode active material are six: F, PO2, SO3, CN, Li2F3, and S2F2NO4. Since the molecular weights of F, PO2, SO3, CN, Li2F3, and S2F2NO4 are 18.99, 62.97, 80.06, 26.02, 70.88, and 180.13, respectively, the mass percentage of S2F2NO4 contained in the six anion molecules above can be obtained by calculating the ratio of the count number of S2F2NO4 multiplied by the molecular weight of S2F2NO4 to the sum of the count numbers multiplied by the molecular weight of each anion.

[0050] According to the above conversion method, the content of S2F2NO4 relative to the total mass (100 mass%) of the six anion molecules in the coating that covers at least a portion of the particle surface of the positive electrode active material is preferably 65 mass%, more preferably 68 mass% or more. When the content of S2F2NO4 relative to the total mass of the coating is equal to or greater than the above lower limit, the cycle characteristics are improved.

[0051] Furthermore, the content of S2F2NO4 relative to the total mass (100 mass%) of the coating that covers at least a portion of the particle surface of the negative electrode active material, as calculated by the above conversion method, is preferably 73 mass% and more preferably 74 mass% or more. When the content of S2F2NO4 relative to the total mass of the coating is equal to or greater than the lower limit, the cycle characteristics are improved.

[0052] According to the lithium ion battery 10 of this embodiment, at least one of at least a portion of the particle surface of the positive electrode active material contained in the positive electrode active material layer 12 and at least a portion of the particle surface of the negative electrode active material contained in the negative electrode active material layer 15 is coated with a coating containing fluorine, and the coating contains S2F2NO4, so that a lithium ion battery 10 with excellent capacity retention rate during charge and discharge cycles can be realized. S2F2NO4 is a specific product produced by decomposition of a lithium imide compound, which is an electrolyte dissolved in the solvent of the electrolytic solution. Furthermore, among the anion molecules detected from the coating covering at least a portion of the particle surface of the positive electrode active material or the coating covering at least a portion of the particle surface of the negative electrode active material of the lithium ion battery 10 of this embodiment, S2F2NO4 has a molecular formula close to that of a lithium imide compound. From this, it is presumed that the fluorine or nitrogen contained in S2F2NO4 acts effectively to improve the capacity retention rate during charge-discharge cycles.

[0053] [Lithium-ion battery manufacturing method] A method for producing a lithium ion battery according to one embodiment of the present invention includes an activation step of activating a lithium ion battery in an environment of 60° C. or higher at a charge rate of 0.3 C or less in the first cycle. The charge rate in the first cycle is preferably equal to or less than 0.05 C. The charge voltage in the first cycle is not particularly limited and may be any value. The discharge rate in the first cycle is not particularly limited and may be any value. The discharge voltage in the first cycle is also not particularly limited and may be any value.

[0054] The lithium ion battery in the manufacturing method for a lithium ion battery of this embodiment includes a positive electrode having a positive electrode current collector and a positive electrode active material layer, a negative electrode having a negative electrode current collector and a negative electrode active material layer and facing the positive electrode, and an electrolyte layer located between the positive electrode and the negative electrode and containing an electrolyte solution, the electrolyte solution containing at least a solvent containing 1,2-dimethoxyethane and a fluorinated ether, and a lithium imide compound dissolved in the solvent, and at least a portion of the particle surface of the positive electrode active material contained in the positive electrode active material layer or at least a portion of the particle surface of the negative electrode active material contained in the negative electrode active material layer is coated with a coating containing fluorine.

[0055] The method for manufacturing a lithium ion battery according to this embodiment may include a manufacturing step of a lithium ion battery before the activation step. The lithium ion battery before the activation step is obtained by stacking the above-mentioned positive electrode and the above-mentioned negative electrode with an electrolyte layer interposed therebetween.

[0056] According to the method for manufacturing a lithium-ion battery of this embodiment, the activation step generates S2F2NO4 in at least one of the coating that covers at least a portion of the particle surface of the positive electrode active material and the coating that covers at least a portion of the particle surface of the negative electrode active material, thereby obtaining the lithium-ion battery of the above-mentioned embodiment.

[0057] Although the embodiments of the present invention have been described above, these embodiments are presented as examples and are not intended to limit the scope of the invention. These embodiments can be embodied in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are included within the scope and spirit of the invention, as well as within the scope of the invention and its equivalents as defined in the claims. [Example]

[0058] The present invention will be explained in more detail below with reference to examples, but the present invention is not limited to the following examples.

[0059] The effects of the present invention were verified. [Electrolyte layer] Electrolyte solutions (samples) with the following compositions were prepared: The concentration of each sample is shown relative to the total electrolyte. Electrolyte: LiFSI (1.7mol / L), Solvent: EC / DME / TTE (0.9mol / L / 2.2mol / L / 3.8mol / L) LiFSI: Lithium bis-fluorosulfonylimide EC: Ethylene carbonate DME: 1,2-dimethoxyethane TTE: 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether The electrolyte solution of each sample was impregnated into a sheet-shaped porous substrate to obtain an electrolyte layer.

[0060] [Positive electrode] A mixture of LiCoNiMnO6 (NMC), lithium carbonate, Ketjen black (KB), and polyvinylidene fluoride (PVDF) was used as the positive electrode material. This mixture was applied to an aluminum thin film using a blade coater and then dried to obtain a positive electrode.

[0061] [Negative electrode] The negative electrode was made of graphite and silicon oxide.

[0062] The positive electrode, negative electrode, and electrolyte layer were stacked together to fabricate a lithium ion battery for use in the verification.

[0063] <Verification example 1> The capacity of the lithium-ion battery was measured after the initial charge using the lithium-ion battery described above. The temperatures of the lithium-ion battery during the initial charge were 25°C, 45°C, 60°C, and 65°C. The temperature of the lithium-ion battery during the initial charge was measured using a thermocouple. The charge rate during the initial charge was 0.05C and 4.15V. Figure 2 shows the dQ / dV curve during charging. It was found that as the temperature of the lithium-ion battery during charging increased, the area of ​​the peak observed at 2.5V-2.7V, which indicates the amount of reaction resulting from the formation of a coating that covers at least a portion of the particle surface of the positive electrode active material and a coating that covers at least a portion of the particle surface of the negative electrode active material, increased.

[0064] <Verification example 2> The lithium-ion battery described above was subjected to 50 charge-discharge cycles, and the capacity retention rate (%) at the 50th charge cycle relative to the initial charge was measured. Table 1 and Figure 3 show the area of ​​the peak observed at 2.5 V to 2.7 V on the dQ / dV curve, which indicates the reaction amount resulting from the formation of a coating covering at least a portion of the particle surface of the positive electrode active material and a coating covering at least a portion of the particle surface of the negative electrode active material during the initial charge, and the capacity retention rate (%).

[0065] [Table 1]

[0066] The results shown in Table 1 and FIG. 3 indicate that if the cell temperature is 60° C. or higher, a sufficient amount of film is formed, resulting in a high capacity retention rate.

[0067] Figure 4 shows the relationship between the temperature and reaction amount of the lithium-ion battery during the initial charge. The results shown in Figure 4 indicate that as the temperature of the lithium-ion battery increases during charging, the amount of reaction resulting from the formation of a coating that covers at least a portion of the particle surface of the positive electrode active material and a coating that covers at least a portion of the particle surface of the negative electrode active material increases.

[0068] <Verification example 3> The lithium-ion battery described above was subjected to an initial charge. The temperatures of the lithium-ion battery during the initial charge were 25°C, 45°C, and 65°C. The temperature of the lithium-ion battery during the initial charge was the temperature measured by a thermocouple from the cell temperature of the lithium-ion battery. The charge rate during the initial charge was 0.05C and 4.15V. TOF-SIMS was used to measure the components formed in the coating covering at least a portion of the particle surface of the positive electrode active material and the coating covering at least a portion of the particle surface of the negative electrode active material. The conditions for measuring the anion components formed in the coating using TOF-SIMS are as follows: (primary ion source) Ion species: Bi 3++ (bismuth is a cluster of three ions with two charges) Accelerating voltage: 30 kV Current value: approx. 0.2 pA Measurement area: Approximately 100 μm square (Sputter ion source) Ion species: Ar cluster ions Accelerating voltage: 2.5 kV Measurement area: Approximately 400 μm square Cycles (number of sputters): 100

[0069] The TOF-SIMS measurement results for the anion components are shown in Tables 2 and 3, as well as Figures 5 and 6. Tables 2 and 5 show the TOF-SIMS measurement results for the positive electrode, and Table 3 and 6 show the TOF-SIMS measurement results for the negative electrode.

[0070] [Table 2]

[0071] [Table 3]

[0072] From the results shown in Tables 2 and 3, it was confirmed that F, PO2, SO3, CN, Li2F3, and S2F2NO4 were produced in the coating that covered the particle surfaces of the positive electrode active material and negative electrode active material during the initial charge. Figure 5 shows the relationship between the reaction amount and the S2F2NO4 count in the coating covering the particle surface of the positive electrode active material. Figure 5 shows a linear equation that approximately represents the distribution of the three measurement results. From this equation, the S2F2NO4 count was predicted when the temperature of the lithium-ion battery during the initial charge was set to 60°C. As a result, as shown in Table 2, when the temperature of the lithium-ion battery during the initial charge was set to 60°C, the S2F2NO4 count in the coating covering the particle surface of the positive electrode active material was 5473.2. Figure 6 shows the relationship between the reaction amount and the S2F2NO4 count in the film covering the particle surface of the negative electrode active material. Figure 6 shows a linear equation that approximately represents the distribution of the three measurement results. From this equation, the S2F2NO4 count was predicted when the temperature of the lithium-ion battery during the initial charge was set to 60°C. As a result, as shown in Table 3, when the temperature of the lithium-ion battery during the initial charge was set to 60°C, the S2F2NO4 count in the film covering the particle surface of the negative electrode active material was 3125.6.

[0073] The number of S2F2NO4 counted by TOF-SIMS in the coating can be converted into the mass % of S2F2NO4 in the total amount (total mass) of any substance contained in the coating. For example, in the lithium-ion battery 10 of this embodiment, the main anion molecules detected by TOF-SIMS from the coating covering at least a portion of the particle surface of the positive electrode active material or the coating covering at least a portion of the particle surface of the negative electrode active material are six: F, PO2, SO3, CN, Li2F3, and S2F2NO4. Since the molecular weights of F, PO2, SO3, CN, Li2F3, and S2F2NO4 are 18.99, 62.97, 80.06, 26.02, 70.88, and 180.13, respectively, the mass percentage of S2F2NO4 contained in the six anion molecules above can be obtained by calculating the ratio of the count number of S2F2NO4 multiplied by the molecular weight of S2F2NO4 to the sum of the count numbers multiplied by the molecular weight of each anion.

[0074] According to the above conversion method, the content of S2F2NO4 relative to the total mass (100 mass%) of the six anion molecules in the coating that covers at least a portion of the particle surface of the positive electrode active material is preferably 65 mass%, more preferably 68 mass% or more. When the content of S2F2NO4 relative to the total mass of the coating is equal to or greater than the above lower limit, the cycle characteristics are improved.

[0075] Furthermore, the content of S2F2NO4 relative to the total mass (100 mass%) of the coating that covers at least a portion of the particle surface of the negative electrode active material, as calculated by the above conversion method, is preferably 73 mass% and more preferably 74 mass% or more. When the content of S2F2NO4 relative to the total mass of the coating is equal to or greater than the lower limit, the cycle characteristics are improved.

[0076] The results shown in Tables 2 and 3 indicate that when the temperature of the lithium-ion battery during initial charging was 25° C., the S2F2NO4 content in the coating covering the particle surfaces of the positive electrode active material was 57.1% by mass, and the S2F2NO4 content in the coating covering the particle surfaces of the negative electrode active material was 69.6% by mass. Furthermore, the results shown in Tables 2 and 3 indicate that when the temperature of the lithium-ion battery during initial charging was 45° C., the S2F2NO4 content in the coating covering the particle surfaces of the positive electrode active material was 59.1% by mass, and the S2F2NO4 content in the coating covering the particle surfaces of the negative electrode active material was 71.1% by mass. Furthermore, from the results shown in Tables 2 and 3, when the temperature of the lithium-ion battery during the initial charge was 60° C., the S2F2NO4 content in the film coating the particle surfaces of the positive electrode active material was 66.0 mass %, and the S2F2NO4 content in the film coating the particle surfaces of the negative electrode active material was 73.3 mass %. Furthermore, from the results shown in Tables 2 and 3, when the temperature of the lithium-ion battery during the initial charge was 65° C., the S2F2NO4 content in the film coating the particle surfaces of the positive electrode active material was 68.2 mass %, and the S2F2NO4 content in the film coating the particle surfaces of the negative electrode active material was 74.0 mass %.

[0077] Figure 7 shows the relationship between the temperature of the lithium-ion battery during the initial charge and the change in capacity retention rate with respect to the number of cycles. It was found that the capacity retention rate curve shown in Figure 7, where the temperature of the lithium-ion battery during the initial charge was 60°C or higher, corresponds to the curve where the S2F2NO4 content in the coating was the highest, as shown in Tables 2 and 3. [Industrial Applicability]

[0078] The lithium ion battery of the present invention can improve the capacity retention rate during charge / discharge cycles. When used as a secondary battery for vehicles such as EVs and HEVs, such a lithium ion battery can achieve long-distance driving on a single charge and improve energy efficiency. Therefore, the lithium ion battery has industrial applicability. [Explanation of symbols]

[0079] 10. Lithium-ion battery 11 Positive electrode current collector 12 Cathode active material layer 13 Positive electrode 14 Negative electrode current collector 15 Negative electrode active material layer 16 negative electrode 17 Electrolyte layer

Claims

1. a positive electrode having a positive electrode current collector and a positive electrode active material layer; a negative electrode having a negative electrode current collector and a negative electrode active material layer, the negative electrode facing the positive electrode; an electrolyte layer located between the positive electrode and the negative electrode and containing an electrolyte solution; A lithium ion battery having: the electrolytic solution contains at least a solvent containing 1,2-dimethoxyethane and a fluorinated ether, and a lithium imide compound dissolved in the solvent; at least one of at least a portion of the particle surface of the positive electrode active material contained in the positive electrode active material layer and at least a portion of the particle surface of the negative electrode active material contained in the negative electrode active material layer is coated with a coating containing fluorine, A lithium ion battery, wherein the coating covering at least a portion of the particle surface of the positive electrode active material has a content of S2F2NO4 of 68 mass% or more relative to the total mass (100 mass%) of the anions of F, PO2, SO3, CN, Li2F3 and S2F2NO4, as detected by measurement using time-of-flight secondary ion mass spectrometry.

2. an activation step of activating the lithium ion battery in an environment of 60°C or higher at a charge rate of 0.3C or less in the first cycle; The lithium ion battery includes a positive electrode having a positive electrode current collector and a positive electrode active material layer, a negative electrode having a negative electrode current collector and a negative electrode active material layer and facing the positive electrode, and an electrolyte layer located between the positive electrode and the negative electrode and containing an electrolyte solution, the electrolytic solution contains at least a solvent containing 1,2-dimethoxyethane and a fluorinated ether, and a lithium imide compound dissolved in the solvent; a fluorine-containing coating on at least a portion of the particle surface of the positive electrode active material contained in the positive electrode active material layer, or a fluorine-containing coating on at least a portion of the particle surface of the negative electrode active material contained in the negative electrode active material layer.

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