Non-aqueous electrolyte, lithium secondary battery precursor, lithium secondary battery, and method for manufacturing a lithium secondary battery

Abstract

To provide a non-aqueous electrolyte which can retain a high capacity retention rate after storage of a battery, reduce the resistance after the storage of the battery, and reduce the resistance increase rate during the storage of the battery.SOLUTION: The non-aqueous electrolyte contains: a compound (A) selected from lithium monofluorophosphate and lithium difluorophosphate; a compound represented by the formula (B); and a compound represented by the formula (C).SELECTED DRAWING: None

Description

Technical Field

[0001] The present disclosure relates to a non-aqueous electrolyte, a lithium secondary battery precursor, a lithium secondary battery, and a method for manufacturing a lithium secondary battery.

Background Art

[0002] Conventionally, from the viewpoint of improving battery performance, various additives have been studied to be contained in non-aqueous electrolytes. For example, Patent Document 1 discloses a non-aqueous electrolyte that can reduce battery resistance after storage, including an electrolyte containing LiPF6 and a specific compound (1) (e.g., lithium bis(trifluoromethylsulfonyl)imide), an additive A which is a specific compound (A) (e.g., vinylene carbonate), an additive B which is lithium monofluorophosphate and / or lithium difluorophosphate, and an additive C which is a specific compound (C1) (e.g., 1,3-propanesultone) and / or a specific compound (C2) (i.e., a specific cyclic sulfate). Also, Patent Document 2 discloses a non-aqueous electrolyte that can achieve a secondary battery with excellent low-temperature discharge characteristics and excellent cycle characteristics, containing monofluorophosphate and / or difluorophosphate, and further containing a compound represented by a specific general formula (1) (e.g., 1,3-propanesultone).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, as a non-aqueous electrolyte for a battery, there may be a case where a non-aqueous electrolyte is required that can maintain a high capacity retention rate after storage of the battery, reduce the resistance after storage of the battery, and reduce the rate of increase in resistance during storage of the battery. An object of one aspect of the present disclosure is to provide a non-aqueous electrolyte that can maintain a high capacity retention rate after storage of a battery, reduce the resistance after storage of the battery, and reduce the rate of increase in resistance during storage of the battery when used as a non-aqueous electrolyte for a battery, and a lithium secondary battery precursor, a lithium secondary battery, and a method for manufacturing a lithium secondary battery using this non-aqueous electrolyte.

Means for Solving the Problems

[0005] The means for solving the above problems include the following aspects. <1> A compound (A) which is at least one selected from the group consisting of lithium monofluorophosphate and lithium difluorophosphate, A compound (B) which is at least one selected from the group consisting of compounds represented by the following formula (B), A compound (C) which is at least one selected from the group consisting of compounds represented by the following formula (C), A non-aqueous electrolyte containing them.

[0006]

Chemical formula

[0007] In formula (B), R b1 ~R b4 each independently represents a hydrogen atom, a fluorine atom, a hydrocarbon group having 1 to 6 carbon atoms, or a fluorinated hydrocarbon group having 1 to 6 carbon atoms. In formula (C), R c1 ~R c4 each independently represents a hydrogen atom, a hydrocarbon group having 1 to 6 carbon atoms, a group represented by formula (a), or a group represented by formula (b). In formula (a) and formula (b), * represents the bonding position.

[0008] <2> The non-aqueous electrolyte according to <1>, wherein the compound (B) is the following compound (B-1).

[0009]

Chemical formula

[0010] <3> The non-aqueous electrolyte according to <1> or <2>, wherein the compound (C) is the following compound (C-1).

[0011]

Chemical formula

[0012] <4> The non-aqueous electrolyte according to any one of <1> to <3>, wherein the content of the compound (A) is 0.001% by mass to 10% by mass based on the total amount of the non-aqueous electrolyte. <5> The non-aqueous electrolyte according to any one of <1> to <4>, wherein the content of the compound (B) is 0.001% by mass to 10% by mass based on the total amount of the non-aqueous electrolyte. <6> The non-aqueous electrolyte according to any one of <1> to <5>, wherein the content of the compound (B) is 0.001% by mass to 10% by mass based on the total amount of the non-aqueous electrolyte. <7> A positive electrode, A negative electrode containing a negative electrode active material capable of intercalating and deintercalating lithium ions, The non-aqueous electrolyte according to any one of <1> to <6>, and A lithium secondary battery precursor comprising. <8> A lithium secondary battery obtained by charging and discharging the lithium secondary battery precursor according to <7>. <9> A step of preparing the lithium secondary battery precursor according to <7>, A step of charging and discharging the lithium secondary battery precursor, and A method for manufacturing a lithium secondary battery comprising.

Advantages of the Invention

[0013] According to one aspect of the present disclosure, there are provided a non-aqueous electrolyte that, when used as a non-aqueous electrolyte for a battery, can maintain a high capacity retention rate after storage of the battery, reduce the resistance after storage of the battery, and reduce the rate of increase in resistance during storage of the battery, a lithium secondary battery precursor using this non-aqueous electrolyte, a lithium secondary battery, and a method for manufacturing a lithium secondary battery.

Brief Description of the Drawings

[0014]

Figure 1

Figure 2

Figure 3

Embodiments for Carrying Out the Invention

[0015] In this specification, a numerical range represented by “~” means a range including the numerical values described before and after “~” as the lower limit value and the upper limit value. In this specification, the amount of each component in the composition means the total amount of the plurality of substances present in the composition when there are a plurality of substances corresponding to each component in the composition, unless otherwise specified.

[0016] 〔Non-aqueous Electrolyte〕 The non-aqueous electrolyte of the present disclosure contains at least one compound (A) selected from the group consisting of lithium monofluorophosphate and lithium difluorophosphate, at least one compound (B) selected from the group consisting of compounds represented by the following formula (B), and at least one compound (C) selected from the group consisting of compounds represented by the following formula (C). It contains.

[0017]

Chemical formula

[0018] In formula (B), R b1 ~R b4 each independently represents a hydrogen atom, a fluorine atom, a hydrocarbon group having 1 to 6 carbon atoms, or a fluorinated hydrocarbon group having 1 to 6 carbon atoms. In formula (C), R c1 ~R c4 each independently represents a hydrogen atom, a hydrocarbon group having 1 to 6 carbon atoms, a group represented by formula (a), or a group represented by formula (b). In formula (a) and formula (b), * represents the bonding position.

[0019] The non-aqueous electrolyte of the present disclosure is a non-aqueous electrolyte for a battery that can maintain a high capacity retention rate after storage of the battery, reduce the resistance after storage of the battery, and reduce the rate of increase in resistance during storage of the battery. That is, according to the non-aqueous electrolyte of the present disclosure, the balance of the above-described battery performance (specifically, the capacity retention rate after storage, the resistance after storage, and the rate of increase in resistance during storage) can be improved.

[0020] Hereinafter, each component that can be contained in the non-aqueous electrolyte of the present disclosure will be described.

[0021] <Compound (A)> The non-aqueous electrolyte of the present disclosure contains at least one compound (A) selected from the group consisting of lithium monofluorophosphate and lithium difluorophosphate. Compound (A) is either one or both of lithium monofluorophosphate and lithium difluorophosphate. Compound (A) preferably contains lithium difluorophosphate.

[0022] <Compound (B)> The non-aqueous electrolyte of the present disclosure contains at least one compound (B) selected from the group consisting of compounds represented by the following formula (B).

[0023] [Chemical]

[0024] In formula (B), R b1 ~R b4 each independently represents a hydrogen atom, a fluorine atom, a hydrocarbon group having 1 to 6 carbon atoms, or a fluorinated hydrocarbon group having 1 to 6 carbon atoms.

[0025] R b1 ~R b4 Examples of the hydrocarbon group having 1 to 6 carbon atoms represented by R R b1 ~R b4 are preferably an alkyl group, an alkenyl group, or an alkynyl group, more preferably an alkyl group or an alkenyl group, and particularly preferably an alkyl group.

[0026] R b1 ~R b4 The number of carbon atoms of the hydrocarbon group having 1 to 6 carbon atoms represented by R R b1 ~R b4 is preferably 1 to 3, more preferably 1 or 2, and particularly preferably 1.

[0027] In the present disclosure, the fluorinated hydrocarbon group means a group in which at least one of the hydrogen atoms contained in the hydrocarbon group is replaced by a fluorine atom, the fluorinated alkyl group means a group in which at least one of the hydrogen atoms contained in the alkyl group is replaced by a fluorine atom, the fluorinated alkenyl group means a group in which at least one of the hydrogen atoms contained in the alkenyl group is replaced by a fluorine atom, The alkynyl fluoride group means a group in which at least one of the hydrogen atoms contained in the alkynyl group is replaced by a fluorine atom.

[0028] R b1 ~R b4 are each independently preferably a hydrogen atom, a fluorine atom, a methyl group, an ethyl group, a trifluoromethyl group, or a pentafluoroethyl group, more preferably a hydrogen atom or a methyl group, and particularly preferably a hydrogen atom.

[0029] Specific examples of compound (B) include the following compounds (B-1) to compound (B-21), but compound (B) is not limited to these specific examples. Among these, compound (B-1) is particularly preferred.

[0030]

Chemical formula

[0031] <Compound (C)> The non-aqueous electrolyte of the present disclosure contains at least one compound (C) selected from the group consisting of compounds represented by the following formula (C).

[0032]

Chemical formula

[0033] In formula (C), R c1 ~R c4 each independently represents a hydrogen atom, a hydrocarbon group having 1 to 6 carbon atoms, a group represented by formula (a), or a group represented by formula (b). In formula (a) and formula (b), * represents the bonding position.

[0034] In compound (C), the specific examples and preferred embodiments of the hydrocarbon group having 1 to 6 carbon atoms represented by R c1 ~R c4 are the same as the specific examples and preferred embodiments of the hydrocarbon group having 1 to 6 carbon atoms represented by R b1 ~R b3 in compound (B).

[0035] The following are specific examples of compound (C), but compound (C) is not limited to the following specific examples. Among these, compounds (C-1) to (C-3) are preferred, compound (C-1) or compound (C-2) is more preferred, and compound (C-1) is particularly preferred.

[0036]

Chemical formula

[0037] <Preferred content of the compound> The content of compound (A) is preferably 0.001% by mass to 10% by mass, more preferably 0.003% by mass to 5% by mass, still more preferably 0.03% by mass to 3% by mass, still more preferably 0.1% by mass to 3% by mass, still more preferably 0.2% by mass to 3% by mass, and still more preferably 0.3% by mass to 2% by mass, based on the total amount of the non-aqueous electrolyte.

[0038] The content of compound (B) is preferably 0.001% by mass to 10% by mass, more preferably 0.003% by mass to 5% by mass, still more preferably 0.003% by mass to 3% by mass, still more preferably 0.03% by mass to 3% by mass, still more preferably 0.1% by mass to 3% by mass, and still more preferably 0.1% by mass to 2% by mass, based on the total amount of the non-aqueous electrolyte.

[0039] The content of compound (C) is preferably 0.001% by mass to 10% by mass, more preferably 0.003% by mass to 5% by mass, still more preferably 0.003% by mass to 3% by mass, still more preferably 0.03% by mass to 3% by mass, still more preferably 0.1% by mass to 3% by mass, and still more preferably 0.1% by mass to 2% by mass, based on the total amount of the non-aqueous electrolyte.

[0040] In the non-aqueous electrolyte of the present disclosure, from the viewpoint of further improving the balance of battery performance (specifically, the capacity retention rate after storage, the resistance after storage, and the rate of increase in resistance during storage), the ratio of the content of compound (A) to the total content of compounds (A) to (C) is preferably 0.3 or more, more preferably 0.5 or more, and still more preferably 0.6 or more. The ratio of the content of compound (A) to the total content of compounds (A) to (C) may be less than 1.0, preferably 0.9 or less, and more preferably 0.8 or less.

[0041] In the non-aqueous electrolyte of the present disclosure, from the viewpoint of further improving the balance of battery performance (specifically, the capacity retention rate after storage, the resistance after storage, and the rate of increase in resistance during storage), the ratio of the content of compound (B) to the total content of compounds (B) and (C) is preferably 0.1 to 0.9, more preferably 0.2 to 0.8, still more preferably 0.3 to 0.7, and still more preferably 0.4 to 0.6.

[0042] Next, other components of the non-aqueous electrolyte will be described. Generally, the non-aqueous electrolyte contains an electrolyte and a non-aqueous solvent.

[0043] <Electrolyte> The electrolyte in the non-aqueous electrolyte of the present disclosure preferably contains a lithium salt, and more preferably contains LiPF6. LiPF6 has the advantages of a relatively small molecular weight, excellent dissociation properties, the ability to suppress an increase in the resistance of the non-aqueous electrolyte, high oxidation stability, and being difficult to decompose. When the electrolyte contains LiPF6, the ratio of LiPF6 in the electrolyte is preferably 10% by mass to 100% by mass, more preferably 50% by mass to 100% by mass, still more preferably 70% by mass to 100% by mass, still more preferably 90% by mass to 100% by mass, and still more preferably 95% by mass to 100% by mass.

[0044] The concentration of the electrolyte in the non-aqueous electrolyte of the present disclosure is preferably 0.1 mol / L to 3 mol / L, and more preferably 0.5 mol / L to 2 mol / L. Moreover, the concentration of LiPF6 in the non-aqueous electrolyte of the present disclosure is preferably 0.1 mol / L to 3 mol / L, and more preferably 0.5 mol / L to 2 mol / L.

[0045] When the electrolyte contains LiPF6, the electrolyte may contain a compound other than LiPF6. Examples of the compound other than LiPF6 include: (C2H5)4NPF6, (C2H5)4NBF4, (C2H5)4NClO4, (C2H5)4NAsF6, (C2H5)4N2SiF6, (C2H5)4NOSO2C k F (2k+1) (where k is an integer from 1 to 8), (C2H5)4NPF n [C k F (2k+1) (6-n) (where n is an integer from 1 to 5 and k is an integer from 1 to 8), etc., tetraalkylammonium salts; LiBF4, LiClO4, LiAsF6, Li2SiF6, LiOSO2C k F (2k+1) (where k is an integer from 1 to 8), LiPF n [C k F (2k+1) (6-n) (where n is an integer from 1 to 5 and k is an integer from 1 to 8), LiC(SO2R 7 )(SO2R 8 )(SO2R 9 ), LiN(SO2OR 10 )(SO2OR 11 ), LiN(SO2R 12 )(SO2R 13 (where R 7 ~R 13 may be the same as or different from each other, and is a fluorine atom or a perfluoroalkyl group having 1 to 8 carbon atoms (more preferably a fluorine atom or a perfluoroalkyl group having 3 to 8 carbon atoms)), etc., lithium salts (i.e., lithium salts other than LiPF6); and the like can be mentioned.

[0046] <Non-aqueous solvent> The non-aqueous solvent in the non-aqueous electrolyte of the present disclosure may be only one kind or two or more kinds.​​ As the non-aqueous solvent, various known ones can be appropriately selected. As the non-aqueous solvent, for example, the non-aqueous solvents described in paragraphs 0069 to 0087 of JP-A-2017-45723 can be used.

[0047] The non-aqueous solvent preferably contains a cyclic carbonate compound and a chain carbonate compound. In this case, the cyclic carbonate compound and the chain carbonate compound contained in the non-aqueous solvent may each be only one kind or two or more kinds.

[0048] Examples of the cyclic carbonate compound include ethylene carbonate, propylene carbonate, 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, 2,3-pentylene carbonate, and the like. Among these, ethylene carbonate and propylene carbonate, which have a high dielectric constant, are preferable. In the case of a battery using a negative electrode active material containing graphite, it is more preferable that the non-aqueous solvent contains ethylene carbonate.

[0049] Examples of the chain carbonate compound include dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, methyl propyl carbonate, methyl isopropyl carbonate, ethyl propyl carbonate, dipropyl carbonate, methyl butyl carbonate, ethyl butyl carbonate, dibutyl carbonate, methyl pentyl carbonate, ethyl pentyl carbonate, dipentyl carbonate, methyl heptyl carbonate, ethyl heptyl carbonate, diheptyl carbonate, methyl hexyl carbonate, ethyl hexyl carbonate, dihexyl carbonate, methyl octyl carbonate, ethyl octyl carbonate, dioctyl carbonate, and the like.

[0050] As a combination of a cyclic carbonate and a chain carbonate, specifically, ethylene carbonate and dimethyl carbonate, ethylene carbonate and methyl ethyl carbonate, ethylene carbonate and diethyl carbonate, propylene carbonate and dimethyl carbonate, propylene carbonate and methyl ethyl carbonate, propylene carbonate and diethyl carbonate, ethylene carbonate and propylene carbonate and methyl ethyl carbonate, ethylene carbonate and propylene carbonate and diethyl carbonate, ethylene carbonate and dimethyl carbonate and methyl ethyl carbonate, ethylene carbonate and dimethyl carbonate and diethyl carbonate, ethylene carbonate and methyl ethyl carbonate and diethyl carbonate, ethylene carbonate and dimethyl carbonate and methyl ethyl carbonate and diethyl carbonate, ethylene carbonate and propylene carbonate and dimethyl carbonate and methyl ethyl carbonate, ethylene carbonate and propylene carbonate and dimethyl carbonate and diethyl carbonate, ethylene carbonate and propylene carbonate and methyl ethyl carbonate and diethyl carbonate, ethylene carbonate and propylene carbonate and dimethyl carbonate and methyl ethyl carbonate and diethyl carbonate, etc. can be mentioned.

[0051] The mixing ratio of the cyclic carbonate compound and the chain carbonate compound, expressed as a mass ratio, is such that cyclic carbonate compound:chain carbonate compound is, for example, 5:95 to 80:20, preferably 10:90 to 70:30, more preferably 15:85 to 55:45. By setting such a ratio, an increase in the viscosity of the non-aqueous electrolyte can be suppressed, and the degree of dissociation of the electrolyte can be increased. Therefore, the conductivity of the non-aqueous electrolyte related to the charge and discharge characteristics of the battery can be increased. Also, the solubility of the electrolyte can be further increased. Thus, a non-aqueous electrolyte excellent in electrical conductivity at normal temperature or low temperature can be obtained, and the load characteristics of the battery from normal temperature to low temperature can be improved.

[0052] The non-aqueous solvent may contain other compounds other than cyclic carbonate compounds and chain carbonate compounds. In this case, the other compounds contained in the non-aqueous solvent may be only one kind or two or more kinds. Examples of the other compounds include cyclic carboxylic acid ester compounds (such as γ-butyrolactone), cyclic sulfone compounds, cyclic ether compounds, chain carboxylic acid ester compounds, chain ether compounds, chain phosphate ester compounds, amide compounds, chain carbamate compounds, cyclic amide compounds, cyclic urea compounds, boron compounds, polyethylene glycol derivatives, and the like. Regarding these compounds, the descriptions in paragraphs 0069 to 0087 of JP-A-2017-45723 can be appropriately referred to.

[0053] The proportion of the cyclic carbonate compound and the chain carbonate compound in the non-aqueous solvent is preferably 80% by mass or more, more preferably 90% by mass or more, and still more preferably 95% by mass or more. The proportion of the cyclic carbonate compound and the chain carbonate compound in the non-aqueous solvent may be 100% by mass.

[0054] The proportion of the non-aqueous solvent in the non-aqueous electrolyte is preferably 60% by mass or more, more preferably 70% by mass or more. The upper limit of the proportion of the non-aqueous solvent in the non-aqueous electrolyte depends on the contents of other components (electrolytes, additives, etc.), but the upper limit is, for example, 99% by mass, preferably 97% by mass, and still more preferably 90% by mass.

[0055] The non-aqueous electrolyte of the present disclosure can be used as a non-aqueous electrolyte for a battery, and among the non-aqueous electrolytes for a battery, it can be particularly preferably used as a non-aqueous electrolyte for a lithium secondary battery.

[0056] 〔Lithium secondary battery precursor, lithium secondary battery〕 The lithium secondary battery precursor of the present disclosure is a positive electrode, A negative electrode containing a negative electrode active material capable of occluding and releasing lithium ions, the non-aqueous electrolyte of the present disclosure described above, is included.

[0057] The lithium secondary battery of the present disclosure is a lithium secondary battery obtained by charging and discharging the lithium secondary battery precursor of the present disclosure.

[0058] In the present disclosure, the lithium secondary battery precursor means a lithium secondary battery after manufacture and before charging and discharging. In other words, in the present disclosure, the lithium secondary battery means a battery in which charging and discharging have been performed on the lithium secondary battery precursor.

[0059] The lithium secondary battery precursor of the present disclosure contains the non-aqueous electrolyte of the present disclosure described above. Therefore, according to the lithium secondary battery precursor and the non-aqueous electrolyte of the present disclosure, the same effects as those of the non-aqueous electrolyte of the present disclosure described above are achieved.

[0060] Hereinafter, each component that can be included in the lithium secondary battery precursor of the present disclosure will be described. Each component that can be included in the lithium secondary battery of the present disclosure is basically the same as each component that can be included in the lithium secondary battery precursor of the present disclosure. In the lithium secondary battery of the present disclosure, an SEI (Solid Electrolyte Interface) film is preferably formed on the surface of the positive electrode (particularly the positive electrode active material) and / or the negative electrode (particularly the negative electrode active material). The SEI film is a film that can be formed by charging and discharging the lithium secondary battery precursor. The SEI film contains components in the non-aqueous electrolyte and / or products (e.g., decomposition products) derived from the above components.

[0061] <Negative electrode> The negative electrode may include a negative electrode active material and a negative electrode current collector. As the negative electrode active material in the negative electrode, at least one selected from the group consisting of metallic lithium, lithium-containing alloys, metals or alloys capable of alloying with lithium, oxides capable of doping and undoping lithium ions, transition metal nitrides capable of doping and undoping lithium ions, and carbon materials capable of doping and undoping lithium ions can be used (it may be used alone or a mixture containing two or more of these may be used). Examples of metals or alloys capable of alloying with lithium (or lithium ions) include silicon, silicon alloys, tin, tin alloys, and the like. Examples of oxides capable of doping and undoping lithium ions include lithium titanate, silicon oxide (preferably SiOx (X represents 0.5 or more and less than 1.6), more preferably SiO), and the like. Among these, from the viewpoint of further improving the film-forming property with respect to the negative electrode and further reducing the resistance of the battery after initial use and / or storage, a carbon material capable of doping and undoping lithium ions is preferable. Examples of such carbon materials include carbon black, activated carbon, graphite materials (artificial graphite, natural graphite), amorphous carbon materials, and the like. The form of the above carbon material may be any of fibrous, spherical, potato-shaped, and flaky forms.

[0062] Specific examples of the amorphous carbon material include hard carbon, coke, mesocarbon microbeads (MCMB) fired at 1500°C or lower, mesophase pitch carbon fiber (MCF), and the like. Examples of the graphite material include natural graphite and artificial graphite. As artificial graphite, graphitized MCMB, graphitized MCF, and the like are used. In addition, as the graphite material, those containing boron can also be used. Further, as the graphite material, those coated with metals such as gold, platinum, silver, copper, and tin, those coated with amorphous carbon, and those obtained by mixing amorphous carbon and graphite can also be used.

[0063] These carbon materials may be used alone or in combination of two or more. As the carbon material, a carbon material having an interlayer spacing d(002) of the (002) plane measured by X-ray analysis of 0.340 nm or less is particularly preferred. Further, as the carbon material, graphite having a true density of 1.70 g / cm 3 or a highly crystalline carbon material having properties similar thereto is also preferred. When using a carbon material as described above, the energy density of the battery can be made higher.

[0064] There is no particular limitation on the material of the negative electrode current collector in the negative electrode, and known materials can be arbitrarily used. Specific examples of the negative electrode current collector include metal materials such as copper, nickel, stainless steel, and nickel-plated steel. Among them, copper is particularly preferred from the viewpoint of ease of processing.

[0065] The negative electrode may include a negative electrode current collector and a negative electrode active material layer provided on at least a part of the surface of the negative electrode current collector. The negative electrode active material layer contains at least one kind of negative electrode active material. The negative electrode active material in the negative electrode active material layer preferably contains the carbon material described above. The content of the carbon material in the negative electrode active material layer is preferably 70% by mass or more, more preferably 80% by mass or more, and still more preferably 90% by mass or more, based on the total amount of the negative electrode active material layer, from the viewpoint of further improving the film-forming property of the negative electrode and further reducing the resistance of the battery after initial use and / or storage. The negative electrode active material layer may further contain at least one kind of binder. As the binder, at least one selected from the group consisting of styrene-butadiene (SBR) rubber (for example, SBR latex), acrylonitrile-butadiene rubber, acrylonitrile-butadiene-styrene rubber, carboxymethyl cellulose (CMC), hydroxypropyl methyl cellulose, polyvinyl alcohol, hydroxypropyl cellulose, and diacetyl cellulose is preferred. The binder preferably contains SBR latex and carboxymethyl cellulose. The content of the binder in the negative electrode active material layer is preferably 1% by mass to 20% by mass, more preferably 1% by mass to 10% by mass, and still more preferably 1% by mass to 5% by mass with respect to the total amount of the negative electrode active material layer.

[0066] The content of Si with respect to the entire negative electrode is preferably 5% by mass or less. When the content of Si with respect to the entire negative electrode is 5% by mass or less, the film-forming property of the negative electrode is further improved, and the resistance of the battery in the initial stage and / or after storage is further reduced.

[0067] <Positive electrode> The positive electrode may include a positive electrode active material and a positive electrode current collector. Examples of the positive electrode active material in the positive electrode include transition metal oxides or transition metal sulfides such as MoS2, TiS2, MnO2, and V2O5, LiCoO2, LiMnO2, LiMn2O4, LiNiO2, LiNi X Co (1-X) O2 [0 < X < 1], Li having an α-NaFeO2 type crystal structure 1+α Me 1-α O2 (Me is a transition metal element including Mn, Ni, and Co, 1.0 ≤ (1 + α) / (1 - α) ≤ 1.6), LiNi x Co y Mn z O2 [x + y + z = 1, 0 < x < 1, 0 < y < 1, 0 < z < 1] (for example, LiNi 0.33 Co 0.33 Mn 0.33 O2, LiNi 0.5 Co 0.2 Mn 0.3 O2, etc.), composite oxides composed of lithium and transition metals such as LiFePO4 and LiMnPO4, conductive polymer materials such as polyaniline, polythiophene, polypyrrole, polyacetylene, polyacene, dimercaptothiadiazole, and polyaniline composites, and the like. Among these, composite oxides composed of lithium and transition metals are particularly preferable. When the negative electrode is a lithium metal or a lithium alloy, a carbon material can also be used as the positive electrode. Further, a mixture of a composite oxide of lithium and a transition metal and a carbon material can also be used as the positive electrode. The positive electrode active material may be used alone or in combination of two or more kinds. When the positive electrode active material has insufficient conductivity, it can be used together with a conductivity aid to form the positive electrode. Examples of the conductivity aid include carbon materials such as carbon black, amorphous whiskers, and graphite.

[0068] There is no particular limitation on the material of the positive electrode current collector in the positive electrode, and known materials can be arbitrarily used. Specific examples of the positive electrode current collector include, for example, metal materials such as aluminum, aluminum alloy, stainless steel, nickel, titanium, and tantalum; carbon materials such as carbon cloth and carbon paper; and the like.

[0069] The positive electrode may include a positive electrode current collector and a positive electrode active material layer provided on at least a part of the surface of the positive electrode current collector. The positive electrode active material layer contains at least one kind of positive electrode active material. The negative electrode active material in the positive electrode active material layer preferably contains a composite oxide composed of lithium and a transition metal. The content of the composite oxide in the positive electrode active material layer is preferably 70% by mass or more, more preferably 80% by mass or more, based on the total amount of the positive electrode active material layer. The positive electrode active material layer may further contain at least one kind of the above-mentioned conductivity aid. The positive electrode active material layer may further contain at least one kind of binder. Examples of the binder include polyvinyl acetate, polymethyl methacrylate, nitrocellulose, fluororesin, rubber particles, etc. Examples of the fluororesin include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), vinylidene fluoride-hexafluoropropylene copolymer, etc. Examples of the rubber particles include styrene-butadiene rubber particles, acrylonitrile rubber particles, etc. Among these, from the viewpoint of improving the oxidation resistance of the positive electrode active material layer, fluororesin is preferred. The content of the binder in the positive electrode active material layer is preferably 1% by mass to 20% by mass, more preferably 1% by mass to 10% by mass, based on the total amount of the positive electrode active material layer.

[0070] <Separator> The lithium secondary battery precursor of the present disclosure preferably includes a separator between the negative electrode and the positive electrode. The separator is a film that electrically insulates the positive electrode and the negative electrode and transmits lithium ions, and examples thereof include a porous film and a polymer electrolyte. As the porous film, a microporous polymer film is preferably used, and examples of the material include polyolefin, polyimide, polyvinylidene fluoride, polyester, and the like. In particular, a porous polyolefin is preferable, and specifically, a porous polyethylene film, a porous polypropylene film, or a multilayer film of a porous polyethylene film and a polypropylene film can be exemplified. Another resin having excellent thermal stability may be coated on the porous polyolefin film. Examples of the polymer electrolyte include a polymer in which a lithium salt is dissolved and a polymer swollen with an electrolytic solution. The non-aqueous electrolyte of the present disclosure may be used for the purpose of swelling a polymer to obtain a polymer electrolyte.

[0071] <Configuration of Lithium Secondary Battery Precursor> The lithium secondary battery precursor of the present disclosure can take various known shapes and can be formed into a cylindrical shape, a coin shape, a square shape, a laminate shape, a film shape, or any other shape. However, the basic structure of the lithium secondary battery precursor is the same regardless of the shape, and design changes can be made according to the purpose. Note that for the basic structure of the lithium secondary battery of the present disclosure, the basic structure of the lithium secondary battery precursor of the present disclosure can also be referred to.

[0072] An example of the lithium secondary battery precursor or the lithium secondary battery of the present disclosure is a laminate type battery. FIG. 1 is a schematic perspective view showing an example of a laminate battery, which is an example of a lithium secondary battery precursor or a lithium secondary battery of the present disclosure, and FIG. 2 is a schematic cross-sectional view in the thickness direction of a laminated electrode body housed in the laminate battery shown in FIG. 1. The laminate battery shown in FIG. 1 includes a laminate exterior body 1 in which a non-aqueous electrolyte (not shown in FIG. 1) and a laminated electrode body (not shown in FIG. 1) are housed, and the periphery is sealed so that the inside is sealed. As the laminate exterior body 1, for example, a laminate exterior body made of aluminum is used. As shown in FIG. 2, the laminated electrode body housed in the laminate exterior body 1 includes a laminate in which a positive electrode plate 5 and a negative electrode plate 6 are alternately laminated with a separator 7 interposed therebetween, and a separator 8 surrounding the periphery of the laminate. The positive electrode plate 5, the negative electrode plate 6, the separator 7, and the separator 8 are impregnated with the non-aqueous electrolyte of the present disclosure. The plurality of positive electrode plates 5 in the laminated electrode body are all electrically connected to the positive electrode terminal 2 via positive electrode tabs (not shown), and a part of the positive electrode terminal 2 protrudes outward from the peripheral end of the laminate exterior body 1 (FIG. 1). The portion where the positive electrode terminal 2 protrudes at the peripheral end of the laminate exterior body 1 is sealed by an insulating seal 4. Similarly, the plurality of negative electrode plates 6 in the laminated electrode body are all electrically connected to the negative electrode terminal 3 via negative electrode tabs (not shown), and a part of the negative electrode terminal 3 protrudes outward from the peripheral end of the laminate exterior body 1 (FIG. 1). The portion where the negative electrode terminal 3 protrudes at the peripheral end of the laminate exterior body 1 is sealed by an insulating seal 4. In the laminate battery according to the above example, the number of positive electrode plates 5 is 5, the number of negative electrode plates 6 is 6, and the positive electrode plates 5 and the negative electrode plates 6 are laminated with a separator 7 interposed therebetween, and the outermost layers on both sides are both negative electrode plates 6. However, it goes without saying that the number, the number, and the arrangement of the positive electrode plates in the laminate battery are not limited to this example, and various changes may be made.

[0073] As another example of the lithium secondary battery precursor or the lithium secondary battery of the present disclosure, a coin-type battery is also included. FIG. 3 is a schematic perspective view showing an example of a coin-type battery which is another example of the lithium secondary battery precursor or the lithium secondary battery of the present disclosure. In the coin-type battery shown in FIG. 3, a disk-shaped negative electrode 12, a separator 15 injected with a non-aqueous electrolyte, a disk-shaped positive electrode 11, and, if necessary, spacer plates 17 and 18 such as stainless steel or aluminum are stacked in this order and housed between a positive electrode can 13 (hereinafter also referred to as "battery can") and a sealing plate 14 (hereinafter also referred to as "battery can lid"). The positive electrode can 13 and the sealing plate 14 are caulked and sealed via a gasket 16. In this example, the non-aqueous electrolyte of the present disclosure is used as the non-aqueous electrolyte injected into the separator 15.

[0074] The use of the lithium secondary battery precursor or the lithium secondary battery of the present disclosure is not particularly limited, and it can be used for various known uses. For example, it can be widely used for various devices regardless of whether they are small portable devices such as notebook computers, mobile computers, mobile phones, headphone stereos, video movies, liquid crystal TVs, handy cleaners, electronic notebooks, calculators, radios, backup power supplies, motors, automobiles, electric vehicles, motorcycles, electric motorcycles, bicycles, electric bicycles, lighting fixtures, game machines, watches, power tools, cameras, etc., or large devices.

[0075] [Manufacturing method of lithium secondary battery] The manufacturing method of the lithium secondary battery of the present disclosure includes a step of preparing the lithium secondary battery precursor of the present disclosure described above (hereinafter also referred to as "preparation step"), and a step of charging and discharging the lithium secondary battery precursor. and includes.

[0076] The preparation step may be simply a step of preparing a previously manufactured lithium secondary battery precursor of the present disclosure for use in the step of charging and discharging, or may be a step of manufacturing the lithium secondary battery precursor of the present disclosure. The lithium secondary battery precursor is as described above.

[0077] In the process of charging and discharging, the charging and discharging of the lithium secondary battery precursor can be performed according to a known method. In this process, the charging and discharging cycles may be repeated a plurality of times with respect to the lithium secondary battery precursor. As described above, by this charging and discharging, an SEI film is preferably formed on the surface of the positive electrode (particularly the positive electrode active material) and / or the negative electrode (particularly the negative electrode active material) in the lithium secondary battery precursor.

Example

[0078] Hereinafter, examples of the present disclosure will be shown, but the present disclosure is not limited by the following examples. In the following examples, “addition amount” means the content with respect to the total amount of the finally obtained non-aqueous electrolyte, and “wt%” means mass%.

[0079] 〔Example 1〕 <Preparation of non-aqueous electrolyte> Ethylene carbonate (EC), dimethyl carbonate (DMC), and methyl ethyl carbonate (EMC) were mixed at a ratio of 30:35:35 (volume ratio). Thereby, a mixed solvent as a non-aqueous solvent was obtained. With respect to the obtained mixed solvent, LiPF6 as an electrolyte was dissolved so that the concentration in the finally obtained non-aqueous electrolyte became 1.2 mol / liter, Furthermore, as additives, each of compound (A), compound (B), and compound (C) was added so that the content (mass%) in the finally obtained non-aqueous electrolyte was 1.0 mass%, 0.2 mass%, and 0.2 mass%, respectively, to obtain a non-aqueous electrolyte. Here, Lithium difluorophosphate (LiDFP) was used as compound (A), The following compound (B-1) was used as compound (B), The following compound (C-1) was used as compound (C).

[0080]

Chem.

[0081] <Fabrication of Lithium Secondary Battery Precursor> Using the following procedure, a coin-type battery having the configuration shown in Fig. 3 was fabricated as a lithium secondary battery precursor.

[0082] (Fabrication of the negative electrode) Amorphous carbon-coated natural graphite (98 parts by mass) as a negative electrode active material, sodium carboxymethyl cellulose dispersed in pure water (1 part by mass as a solid content) as a thickener, and styrene-butadiene rubber (SBR) dispersed in pure water (1 part by mass) as a binder were added and mixed to obtain a paste-like negative electrode mixture slurry. Next, the obtained negative electrode mixture slurry was applied to a strip-shaped copper foil (negative electrode current collector) with a thickness of 10 μm, and after drying, it was rolled by a roll press to obtain a sheet-shaped negative electrode composed of a negative electrode current collector and a negative electrode active material layer. The coating density of the negative electrode active material layer at this time was 10 mg / cm 2 and the packing density was 1.5 g / mL.

[0083] (Fabrication of the positive electrode) LiNi as a positive electrode active material 0.5 Mn 0.3 Co 0.2 O2 (90 parts by mass), acetylene black (5 parts by mass) as a conductive assistant, and polyvinylidene fluoride (5 parts by mass) as a binder were mixed and dispersed in N-methylpyrrolidinone as a solvent to prepare a paste-like positive electrode mixture slurry. Next, this positive electrode mixture slurry was applied to a strip-shaped aluminum foil (positive electrode current collector) with a thickness of 20 μm, and after drying, it was rolled by a roll press to obtain a sheet-shaped positive electrode composed of a positive electrode current collector and a positive electrode active material layer. The coating density of the positive electrode active material layer at this time was 30 mg / cm 2 and the packing density was 2.5 g / mL.

[0084] (Fabrication of the separator) A microporous polyethylene film with a thickness of 20 μm was punched into a disk shape with a diameter of 17 mm to obtain a coin-shaped separator.

[0085] (Fabrication of Coin-Type Battery) The above-mentioned negative electrode was punched into a disk shape with a diameter of 14 mm, and the above-mentioned positive electrode was punched into a disk shape with a diameter of 13 mm to obtain a coin-shaped negative electrode and a coin-shaped positive electrode, respectively. The obtained coin-shaped negative electrode, separator, and coin-shaped positive electrode were stacked in this order inside a stainless-steel battery can (2032 size), and then 20 μL of the above-mentioned non-aqueous electrolyte was injected into this battery can and impregnated into the separator, positive electrode, and negative electrode. Next, a plate made of aluminum (thickness 1.2 mm, diameter 16 mm) and a spring were placed on the positive electrode, and the battery can lid was caulked through a gasket made of polypropylene to seal the battery. As described above, a coin-type battery having the configuration shown in Figure 3 with a diameter of 20 mm and a height of 3.2 mm was obtained as a lithium secondary battery precursor.

[0086] <Evaluation> The following evaluations were performed on the obtained coin-type battery. The evaluation results are shown in Table 1. In Table 1, the capacity retention rate after storage, the resistance after storage, and the resistance increase rate during storage in each example are shown as relative values when the values in Comparative Example 1 described later are set to 100.

[0087] (Conditioning) The coin-type battery as a lithium secondary battery precursor was repeatedly charged and discharged three times between 2.5 V and 4.2 V at 25°C in a thermostat to obtain a first battery as a lithium secondary battery.

[0088] (Initial Capacity) The discharge capacity of the first battery was defined as the "initial capacity".

[0089] (Initial Resistance) The SOC (State of Charge) of the first battery was adjusted to 50%. For the first battery adjusted to SOC 50%, CC10s discharge was performed at -20°C with a discharge rate of 0.2C, and the DCIR (Direct Current Internal Resistance) (Ω) was measured. Here, CC10s discharge means discharging for 10 seconds at a constant current. Also, the measurement of DCIR was performed based on the current value in the above "CC10s discharge at a discharge rate of 0.2C" (i.e., the current value corresponding to a discharge rate of 0.2C) and the voltage drop amount (= voltage before discharge start - voltage at the 10th second after discharge start). The obtained DCIR (Ω) was defined as the "initial resistance (Ω)". Hereinafter, the first battery after the above measurement of the initial resistance is referred to as the second battery.

[0090] (Storage) The second battery was charged up to 4.2V, and then stored at 60°C for 9 days in a thermostat to obtain the third battery.

[0091] (Capacity after storage) The third battery was discharged down to 2.5V. Next, it was charged up to 4.2V at a charging rate of 0.2C with CC-CV charging at 25°C in a thermostat, and then discharged down to 2.5V to obtain the fourth battery. The discharge capacity at this time was defined as the "capacity after storage". Here, CC-CV charging means charging at a constant current and constant voltage.

[0092] (Resistance after storage) The SOC of the fourth battery was adjusted to 50%. For the fourth battery adjusted to SOC 50%, DCIR (Ω) was measured at -20°C by the same method as the measurement of the above-mentioned initial resistance, and the obtained value was defined as the "resistance after storage (Ω)". Hereinafter, the fourth battery after the above measurement of the resistance after storage is referred to as the fifth battery.

[0093] (Capacity retention rate after storage) The capacity retention rate (%) after storage was calculated by the following formula. Capacity retention rate (%) after storage = (Capacity after storage / Initial capacity) × 100

[0094] (Calculation of resistance increase rate during storage) The resistance increase rate (%) during storage was calculated by the following formula. Resistance increase rate (%) during storage = (Resistance after storage / Initial resistance) × 100

[0095] [Examples 2 and Comparative Examples 1 to 3] The same operations as in Example 1 were carried out except that the type and content of the additive in the non-aqueous electrolyte were changed as shown in Table 1. The results are shown in Table 1. In Table 1, "-" means that the corresponding component is not contained. In Table 1, the numbers in parentheses under the additive name are the content (% by mass) of the additive.

[0096] [Table 1]

[0097] As shown in Table 1, the batteries of Examples 1 and 2 had a high capacity retention rate after storage, and the resistance after storage and the resistance increase rate during storage were reduced. Compared with the batteries of Comparative Examples 1 to 3, the balance of battery performance was excellent. More specifically, the batteries of Examples 1 and 2 using a non-aqueous electrolyte containing Compound (A), Compound (B), and Compound (C) as additives had an improved capacity retention rate after storage and a reduced resistance increase rate during storage compared with the battery of Comparative Example 1 using a non-aqueous electrolyte not containing Compound (C) among these. In addition, the battery of Example 1 had an improved capacity retention rate after storage and a reduced resistance after storage compared with the battery of Comparative Example 2 not containing Compound (A) among the three additives. The battery of Example 2 had an improved capacity retention rate after storage and a reduced resistance after storage compared with the battery of Comparative Example 2 not containing Compound (A) among the three additives. Furthermore, compared with the battery of Comparative Example 3 that does not contain compound (B) among the three types of additives, the battery of Example 1 had an improved capacity retention rate after storage and a reduced resistance increase rate during storage. Furthermore, compared with the battery of Comparative Example 3 that does not contain compound (B) among the three types of additives, the battery of Example 2 had an improved capacity retention rate after storage, a reduced resistance after storage, and a reduced resistance increase rate during storage.

Explanation of Signs

[0098] 1 Laminate exterior 2 Positive electrode terminal 3 Negative electrode terminal 4 Insulating seal 5 Positive electrode plate 6 Negative electrode plate 7, 8 Separator 11 Positive electrode 12 Negative electrode 13 Positive electrode can 14 Sealing plate 15 Separator 16 Gasket 17, 18 Spacer plate

Claims

1. At least one compound (A) selected from the group consisting of lithium monofluorophosphate and lithium difluorophosphate, At least one compound (B) selected from the group consisting of compounds represented by the following formula (B), At least one compound (C) selected from the group consisting of compounds represented by the following formula (C), containing, The content of the compound (A) is 0.1% by mass to 3% by mass with respect to the total amount of the non-aqueous electrolyte for a battery, The content of the compound (B) is 0.03% by mass to 2% by mass with respect to the total amount of the non-aqueous electrolyte for a battery, The content of the compound (C) is 0.03% by mass to 2% by mass with respect to the total amount of the non-aqueous electrolyte for a battery, The ratio of the content of the compound (A) to the total content of the compound (A), the compound (B), and the compound (C) is 0.5 or more and 0.9 or less, The ratio of the content of the compound (B) to the total content of the compound (B) and the compound (C) is 0.3 to 0.7, A non-aqueous electrolyte for a battery. 【Chemical 1】 〔In formula (B), R ｂ１ ~R ｂ４ each independently represents a hydrogen atom, a fluorine atom, a hydrocarbon group having 1 to 6 carbon atoms, or a fluorinated hydrocarbon group having 1 to 6 carbon atoms. In formula (C), R ｃ１ ~R ｃ４ each independently represents a hydrogen atom, a hydrocarbon group having 1 to 6 carbon atoms, a group represented by formula (a), or a group represented by formula (b). In formula (a) and formula (b), * represents a bonding position.]]

2. The non-aqueous electrolyte for a battery according to Claim 1, wherein the compound (B) is the following compound (B-1). 【Chemical 2】

3. The non-aqueous electrolyte for a battery according to Claim 1 or Claim 2, wherein the compound (C) is the following compound (C-1). 【Chemical Formula 3】

4. A positive electrode, A negative electrode containing a negative electrode active material capable of occluding and releasing lithium ions, A non-aqueous electrolyte for a battery according to any one of Claims 1 to 3, A lithium secondary battery precursor containing.

5. A lithium secondary battery obtained by charging and discharging the lithium secondary battery precursor according to Claim 4.

6. A step of preparing the lithium secondary battery precursor according to Claim 4, A step of charging and discharging the lithium secondary battery precursor, A method for manufacturing a lithium secondary battery, including.

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