Container for non-aqueous electrolyte, and method for preserving non-aqueous electrolyte

Abstract

A container for a non-aqueous electrolyte having a receiving portion made of austenitic stainless steel, wherein the receiving portion has a passivation layer on the liquid contact surface with the non-aqueous electrolyte in the receiving portion, wherein the amount of chromium atoms relative to the total amount of iron atoms, chromium atoms, nickel atoms, and molybdenum atoms on the surface of the passivation layer is 40 mass% or more, and wherein the non-aqueous electrolyte comprises a specific sulfate compound, and a method for preserving a non-aqueous electrolyte using the container for the non-aqueous electrolyte can suppress the leaching of iron into the non-aqueous electrolyte, and a method for preserving a non-aqueous electrolyte using the container for the non-aqueous electrolyte can be provided.

Description

Technology Field

[0001] The present disclosure relates to a container for a non-aqueous electrolyte and a method for preserving a non-aqueous electrolyte. Background Technology

[0002] In the field of batteries, which are electrochemical devices, energy storage systems for small, high-energy density applications in information-related devices and communication devices—namely, personal computers, video cameras, digital cameras, mobile phones, and smartphones—as well as energy storage systems for large, high-power applications such as auxiliary power sources and power storage for electric vehicles, hybrid vehicles, and fuel cell vehicles, are attracting attention. One of the candidates is non-aqueous electrolyte batteries, including lithium-ion batteries, which achieve high capacity by having high energy density and voltage, and active research and development is currently underway.

[0003] As a non-aqueous electrolyte used in non-aqueous electrolyte batteries, a non-aqueous electrolyte in which a fluorine-containing electrolyte such as lithium hexafluorophosphate (hereinafter also referred to as “LiPF6”), bis(fluorosulfonyl)imide dilithium (hereinafter also referred to as “LiFSI”), or lithium tetrafluoroborate (hereinafter also referred to as “LiBF4”) is dissolved as a solute in a solvent such as a cyclic carbonate, a chain carbonate, or an ester is frequently used because it is desirable for obtaining high voltage and high capacity batteries.

[0004] In addition, in non-aqueous electrolytes, attempts are widely made to add a small amount (usually 0.001 mass% or more and 10 mass% or less) of a compound called an additive to the electrolyte for the purpose of improving battery characteristics, including cycle characteristics and output characteristics of the non-aqueous electrolyte battery, and as an additive, dihalophosphates such as lithium difluorophosphate are known.

[0005] As a container used for storing or transporting such non-aqueous electrolytes (hereinafter also referred to as a “container for non-aqueous electrolytes”), a stainless steel container with excellent airtightness and durability is generally used (e.g., Patent Document 1).

[0006] Because stainless steel has high corrosion resistance, even if, for example, the non-aqueous electrolyte comes into contact with air and its corrosiveness increases, corrosion of the container that would impede use is unlikely to occur. Prior art literature

[0007] Japanese Patent Publication No. 2015-74798 The problem to be solved

[0008] Recently, following the improvement of battery performance, further review is being conducted on the composition of non-aqueous electrolytes, particularly regarding additives used in non-aqueous electrolytes.

[0009] The inventors were investigating a composition of a non-aqueous electrolyte containing a dihalophosphate, such as lithium difluorophosphate, as an additive, and found that it is desirable to additionally use a sulfate compound, such as ethylene sulfate, as an additive. However, on the other hand, when using a sulfate compound (especially when using a dihalophosphate and a sulfate compound together), if a conventional stainless steel container is used as a storage container for the non-aqueous electrolyte, a large amount of iron is unexpectedly leached into the non-aqueous electrolyte, which not only causes corrosion of the container but also raises concerns that the concentration specifications for metals that can be contained in the non-aqueous electrolyte cannot be met, and a new problem arises in that the non-aqueous electrolyte battery using this non-aqueous electrolyte becomes prone to short circuits.

[0010] The present disclosure is made in consideration of the above circumstances and aims to provide a container for a non-aqueous electrolyte capable of suppressing the leaching of iron into the non-aqueous electrolyte. means of solving the problem

[0011] The inventors, taking these problems into account, carefully examined the matter and found that the dissolution of iron can be suppressed by forming a passivation layer on the liquid contact surface with the non-aqueous electrolyte in the receiving portion of a container made of austenitic stainless steel.

[0012] That is, the inventors have found that the above objective can be achieved by the following configuration.

[0013] <1>

[0014] As a container for a non-aqueous electrolyte having a receiving portion,

[0015] The above receiving part is made of austenitic stainless steel, and

[0016] The above-mentioned receiving portion has a passivation layer on the liquid contact surface with the non-aqueous electrolyte,

[0017] On the surface of the said passivation layer, the amount of chromium atoms relative to the total amount of iron atoms, chromium atoms, nickel atoms, and molybdenum atoms is 40 mass% or more, and

[0018] A container for a non-aqueous electrolyte, wherein the above-mentioned non-aqueous electrolyte comprises a compound represented by the following general formula (2).

[0019]

[0020] [In general formula (2), R 3 ... represents a hydrocarbon group having 2 to 5 carbon atoms. Heteroatoms may be included between carbon-carbon bonds within the said hydrocarbon group. Additionally, any hydrogen atom of the said hydrocarbon group may be substituted with a halogen atom.

[0021] <2>

[0022] The above austenitic stainless steel is SUS304 <1> A container for non-aqueous electrolytes as described in

[0023] <3>

[0024] <1> or <2> A method for preserving a non-aqueous electrolyte using a container for a non-aqueous electrolyte described in [placeholder].

[0025] <4>

[0026] The storage temperature of the non-aqueous electrolyte is 25℃ or lower <3> Method for preserving non-aqueous electrolytes as described in

[0027] <5>

[0028] Performed under an inert atmosphere <3> or <4> Method for preserving non-aqueous electrolytes as described in

[0029] <6>

[0030] A non-aqueous electrolyte containing a compound represented by the general formula (2) is contained in the above receiving portion. <1> or <2> A container for non-aqueous electrolytes as described in Effects of the invention

[0031] According to the present disclosure, a container for a non-aqueous electrolyte capable of suppressing the leaching of iron into the non-aqueous electrolyte, and a method for preserving a non-aqueous electrolyte using said container for the non-aqueous electrolyte can be provided. Specific details for implementing the invention

[0032] Each component and combination thereof in the following embodiments is illustrative, and addition, omission, substitution, and other modifications to components are possible within the scope of not departing from the spirit of the present disclosure. Furthermore, the present disclosure is not limited by the embodiments.

[0033] In this specification, "~" is used to mean including the numerical values ​​described before and after it as lower and upper limits.

[0034] [Container for non-aqueous electrolytes]

[0035] The container for a non-aqueous electrolyte of the present disclosure (hereinafter also simply referred to as "container") is a container for a non-aqueous electrolyte in which a receiving portion is made of austenitic stainless steel, and is a container having a passivation layer on the surface of the liquid contact surface with the non-aqueous electrolyte in the receiving portion.

[0036] The vessel of the present disclosure has a passivation layer on the surface of the liquid contact surface with the non-aqueous electrolyte in the receiving portion, and on the surface of the passivation layer, the amount of chromium atoms relative to the total amount of iron atoms, chromium atoms, nickel atoms, and molybdenum atoms is 40 mass% or more, preferably 40 to 65 mass%.

[0037] The passivation film of a typical austenitic stainless steel is a thin oxide film that naturally forms on the surface of the stainless steel, and on the surface of the passivation film, the amount of chromium atoms relative to the total amount of iron atoms, chromium atoms, nickel atoms, and molybdenum atoms is about 20 mass%.

[0038] That is, the passivation layer in the vessel of the present disclosure is a layer richer in chromium than the passivation film in general austenitic stainless steel.

[0039] The amount of chromium atoms relative to the total amount of iron atoms, chromium atoms, nickel atoms, and molybdenum atoms on the surface of the passivation layer can be quantified, for example, by Auger electron spectroscopy.

[0040] In addition, having a passivation layer on the liquid surface in contact with the non-aqueous electrolyte in the receiving portion indicates that, at least, when the non-aqueous electrolyte is filled into the receiving portion and left standing, a passivation layer is formed on the inner surface of the receiving portion that is actually in contact with the non-aqueous electrolyte. It is preferable that the passivation layer be formed on the entire inner surface of the receiving portion.

[0041] The formation of the above passivation layer can be achieved by using at least one of acid cleaning and electrolytic polishing.

[0042] Acid cleaning is a method of oxidizing the surface of stainless steel by immersing it in a strong oxidizing agent such as nitric acid.

[0043] Electrolytic polishing is a method of electrolytically polishing the surface of stainless steel by using stainless steel as the anode (positive side) and passing a direct current through an electrolyte between it and the cathode (negative side), which serves as the opposite electrode.

[0044] In the container of the present disclosure, since the device and operation are simple, it is preferable that a passivation layer be formed by acid washing.

[0045] The container of the present disclosure may have a receiving portion made of austenitic stainless steel, and, for example, an outer periphery made of other material may be formed on the outer side of the receiving portion (opposite to the side in contact with the non-aqueous electrolyte).

[0046] There are no particular limitations on the materials that form the outer periphery, but examples include polyolefin resins such as polyethylene and polypropylene, polyester resins such as polyethylene terephthalate, and polyamide resins such as nylon.

[0047] In addition, the container of the present disclosure may or may not have a lid, but it is preferable to have a lid in order to increase airtightness and prevent the deterioration of the non-aqueous electrolyte due to contact between the non-aqueous electrolyte and oxygen in the air while the container is stored.

[0048] There are no particular limitations on the material of the cover, but it is preferable that it be made of austenitic stainless steel, and it is even more preferable that a passivation layer similar to the one described above be formed on the inner surface of the cover (the surface positioned on the receiving portion side).

[0049] Examples of austenitic stainless steels used in the receiving portion of the vessel of the present disclosure include SUS304, SUS316, SUS316L, etc. In addition, SUS304, SUS316, and SUS316L are specified in Japanese Industrial Standard JIS G 4305.

[0050] The corrosion resistance of stainless steel varies depending on the performance of the passivation film formed. In the case of austenitic stainless steel, the main components forming this passivation film are chromium (Cr) and molybdenum (Mo), and it is known that the higher the concentration of these, the denser the passivation film becomes, resulting in better corrosion resistance. Furthermore, the effect of Mo concentration on improving the corrosion resistance of the passivation film is approximately three times that of Cr concentration.

[0051] There are differences in composition between the two steel grades, SUS304 and SUS316. SUS304 contains about 18% Cr but does not contain Mo. In contrast, SUS316 contains about 2% Mo in addition to about 18% Cr. Therefore, generally, SUS316 is a material with better corrosion resistance than SUS304.

[0052] However, in the storage of a non-aqueous electrolyte using a combination of a sulfate compound represented by the general formula (2) described below and a dihalophosphate represented by the general formula (3), a container having a receiving portion made of SUS304 rather than SUS316 can be used more preferably because it has a higher effect in inhibiting the leaching of iron into the non-aqueous electrolyte.

[0053] The shape of the container of the present disclosure is not particularly limited and can be any shape, such as a bottle shape or a cylindrical shape.

[0054] The horizontal cross-sectional shape of the bottle-type container can be any shape, such as a circle or a polygon such as a triangle or octagon. Among these, from the perspective of the strength and processability of the container, it is preferable for the horizontal cross-sectional shape to be circular. In addition, the cross-sectional area in the vertical direction of the container can be continuously varied. For example, by making the cross-sectional area near the center in the height direction of the container smaller than that near both ends, a narrow structure can be formed by making a part of the container body thinner, or by making irregularities on the surface of the container so that the container is easy to grip.

[0055] The capacity of the container of the present disclosure is not particularly limited, but from the perspective of handling, 10 to 200,000 cm³ 3 It is desirable, and 20~30,000cm 3 is more desirable, and 50~1,000cm 3 is more desirable, and 100~500cm 3It is particularly desirable. The diameter of the body of the container is not particularly limited, but from the perspective of handling, 50 to 150 mm is preferred, and 60 to 100 mm is more preferred.

[0056] [Non-aqueous Electrolyte]

[0057] The non-aqueous electrolyte stored using the container for the non-aqueous electrolyte of the present disclosure is not particularly limited except to a compound represented by general formula (2), but may include a solute and a non-aqueous organic solvent, and may additionally contain commonly used additive components in any proportion.

[0058] In the case where the non-aqueous electrolyte comprises, in addition to the compound represented by general formula (2), a compound represented by general formula (3) described later as an additive, the effect of using the container for the non-aqueous electrolyte of the present disclosure is particularly exhibited.

[0059] <About Solutes>

[0060] It is preferable that the solute included in the non-aqueous electrolyte be an ionic salt, for example, an ionic salt composed of a pair of at least one anion selected from the group consisting of at least one cation selected from the group consisting of alkali metal ions and alkaline earth metal ions, and a pair of at least one anion selected from the group consisting of hexafluorophosphate anion, tetrafluoroborate anion, trifluoromethanesulfonate anion, fluorosulfonate anion, bis(trifluoromethanesulfonyl)imide anion, bis(pentafluoroethanesulfonyl)imide anion, bis(fluorosulfonyl)imide anion, (trifluoromethanesulfonyl)(fluorosulfonyl)imide anion, bis(difluorophosphonyl)imide anion, (difluorophosphonyl)(fluorosulfonyl)imide anion, and (difluorophosphonyl)(trifluoromethanesulfonyl)imide anion.

[0061] In addition, it is preferable that the cation of the ionic salt which is the solute is lithium, sodium, potassium, or magnesium, and the anion is at least one selected from the group consisting of hexafluorophosphate anion, tetrafluoroborate anion, trifluoromethanesulfonate anion, bis(trifluoromethanesulfonyl)imide anion, bis(fluorosulfonyl)imide anion, bis(difluorophosphonyl)imide anion, and (difluorophosphonyl)(fluorosulfonyl)imide anion, in terms of high solubility in non-aqueous organic solvents or electrochemical stability.

[0062] There are no specific limitations on the appropriate concentrations of these solutes, but the lower limit is 0.5 mol / L or higher, preferably 0.7 mol / L or higher, more preferably 0.9 mol / L or higher, and the upper limit is 2.5 mol / L or lower, preferably 2.2 mol / L or lower, more preferably 2.0 mol / L or lower. By making it 0.5 mol / L or higher, the degradation of cycle characteristics and output characteristics of the non-aqueous electrolyte battery due to a decrease in ionic conductivity can be suppressed, and by making it 2.5 mol / L or lower, the degradation of ionic conductivity and cycle characteristics and output characteristics of the non-aqueous electrolyte battery due to an increase in the viscosity of the non-aqueous electrolyte can be suppressed. In addition, these solutes may be used individually or in combination.

[0063] <Regarding Non-Aqueous Organic Solvents>

[0064] The type of non-aqueous organic solvent used in the non-aqueous electrolyte is not particularly limited, and any non-aqueous organic solvent may be used. Specifically, ethylmethyl carbonate (hereinafter also referred to as "EMC"), dimethyl carbonate (hereinafter also referred to as "DMC"), diethyl carbonate (hereinafter also referred to as "DEC"), methylpropyl carbonate, ethylpropyl carbonate, methylbutyl carbonate, 2,2,2-trifluoroethylmethyl carbonate, 2,2,2-trifluoroethylethyl carbonate, 2,2,2-trifluoroethylpropyl carbonate, bis(2,2,2-trifluoroethyl)carbonate, 1,1,1,3,3,3-hexafluoro-1-propylmethylcarbonate, 1,1,1,3,3,3-hexafluoro-1-propylethyl carbonate, 1,1,1,3,3,3-hexafluoro-1-propylpropyl carbonate, bis(1,1,1,3,3,3-hexafluoro-1-propyl)carbonate, ethylene carbonate (hereinafter It is preferable that at least one is selected from the group consisting of “EC” (also written as “EC”), propylene carbonate (hereinafter also written as “PC”), butylene carbonate, fluoroethylene carbonate (hereinafter also written as “FEC”), difluoroethylene carbonate, methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, 2-methyl fluoropropionate, 2-ethyl fluoropropionate, diethyl ether, dibutyl ether, diisopropyl ether, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, furan, tetrahydropyran, 1,3-dioxane, 1,4-dioxane, N,N-dimethylformamide, acetonitrile, propionitrile, dimethyl sulfoxide, sulfolane, γ-butyrolactone, and γ-valerolactone.

[0065] In addition, the above-mentioned non-aqueous organic solvent is preferably one selected from the group consisting of cyclic carbonates and chain carbonates, in that it exhibits excellent cycle characteristics at high temperatures. Furthermore, the above-mentioned non-aqueous organic solvent is preferably one that includes an ester, in that it exhibits excellent input / output characteristics at low temperatures.

[0066] Specific examples of the above-mentioned cyclic carbonates include EC, PC, butylene carbonate, and FEC, and among them, at least one type selected from the group consisting of EC, PC, and FEC is preferred.

[0067] Specific examples of the above chain carbonates include EMC, DMC, DEC, methylpropyl carbonate, ethylpropyl carbonate, 2,2,2-trifluoroethylmethyl carbonate, 2,2,2-trifluoroethylethyl carbonate, 1,1,1,3,3,3-hexafluoro-1-propylmethyl carbonate, and 1,1,1,3,3,3-hexafluoro-1-propylethyl carbonate, and among these, at least one selected from the group consisting of EMC, DMC, DEC, and methylpropyl carbonate is preferred.

[0068] In addition, specific examples of the above esters include methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, 2-methyl fluoropropionate, and 2-ethyl fluoropropionate.

[0069] Non-aqueous electrolytes may contain polymers. Polymers generally include those referred to as polymer solid electrolytes. Polymer solid electrolytes also include those containing non-aqueous organic solvents as plasticizers.

[0070] The polymer is not particularly limited as long as it is a non-protonic polymer capable of dissolving the above-mentioned solute and the additive described below. Examples include polymers having polyethylene oxide in the main or side chain, homopolymers or copolymers of polyvinylidene fluoride, methacrylic acid ester polymers, polyacrylonitrile, etc. When adding a plasticizer to these polymers, a non-protonic non-aqueous organic solvent among the above-mentioned non-aqueous organic solvents is preferred.

[0071] <About Additives>

[0072] In terms of improving capacity retention rate after long-term cycles at high temperatures and suppressing the increase in resistance at low temperatures after high-temperature storage, the non-aqueous electrolyte includes a compound represented by the following general formula (2).

[0073]

[0074] [In general formula (2), R 3 ... represents a hydrocarbon group having 2 to 5 carbon atoms. Heteroatoms may be included between carbon-carbon bonds within the said hydrocarbon group. Additionally, any hydrogen atom of the said hydrocarbon group may be substituted with a halogen atom.

[0075] In general formula (2), R 3 represents a hydrocarbon group with 2 to 5 carbon atoms. R 3 Examples of hydrocarbon groups that represent this include straight-chain or branched alkylene groups, alkenylene groups, or alkynylene groups.

[0076] R 3 Specifically, examples of alkylene groups that represent this alkylene group include ethylene groups, n-propylene groups, i-propylene groups, n-butylene groups, s-butylene groups, t-butylene groups, n-pentylene groups, -CH2CH(C3H7)- groups, etc.

[0077] R 3 Specifically, examples of alkenylene groups that represent this alkenylene group include the ethenylene group and the propenylene group.

[0078] R 3 Specifically, alkynylene groups that represent this alkynylene group include ethynylene groups, propynylene groups, etc.

[0079] R 3 The hydrocarbon group represented here may include heteroatoms between carbon-carbon bonds. Examples of heteroatoms include oxygen atoms, nitrogen atoms, sulfur atoms, etc.

[0080] R 3The hydrocarbon group represented here may have any hydrogen atom substituted with a halogen atom. Examples of hydrocarbon groups in which any hydrogen atom is substituted with a fluorine atom include tetrafluoroethylene groups, 1,2-difluoroethylene groups, 2,2-difluoroethylene groups, fluoroethylene groups, (trifluoromethyl)ethylene groups, etc.

[0081] R 3 An unsubstituted alkylene group having 2 to 3 carbon atoms is preferred, and an ethylene group is more preferred.

[0082] The content of the compound represented by general formula (2) in the non-aqueous electrolyte is preferably 0.01 mass% or more and 8.00 mass% or less with respect to the total amount of the non-aqueous electrolyte, more preferably 0.05 mass% or more and 3.00 mass% or less, and more preferably 0.1 mass% or more and 2.50 mass% or less.

[0083] In non-aqueous electrolytes, commonly used additive components may be added in any proportion.

[0084] In addition to the compound represented by general formula (2), the non-aqueous electrolyte may include any of the compounds represented by the following general formulas (3) to (6) in order to improve the capacity retention rate after a long cycle at high temperature and to suppress the increase in resistance at low temperature after high-temperature storage.

[0085]

[0086] [Of general formula (3), X 3 and X 4 Each represents a halogen atom independently. M2 + represents an alkali metal cation, ammonium ion, or organic cation.

[0087] Among general formulas (3), X 3 and X 4 represents a halogen atom. X 3 and X 4Examples of the halogen atoms represented by fluorine atoms, chlorine atoms, bromine atoms, iodine atoms, etc., and it is preferable that it be a fluorine atom.

[0088] X 3 and X 4 They may be the same or different, but it is preferable that they be the same, and it is preferable that they are all fluorine atoms.

[0089] Among general formulas (3), M2 + represents an alkali metal cation, ammonium ion, or organic cation.

[0090] M2 + Examples of alkali metal cations represented by kaolin include lithium cation, sodium cation, potassium cation, etc.

[0091] M2 + It is preferable that it be an alkali metal cation, and more preferable that it be a lithium cation.

[0092]

[0093] [In general formula (4), R 4 represents a hydrocarbon group having 2 to 6 carbon atoms. Heteroatoms may be included between carbon-carbon bonds within the said hydrocarbon group. Additionally, any hydrogen atom of the said hydrocarbon group may be substituted with a halogen atom.

[0094] In general formula (4), R 4 represents a hydrocarbon group having 2 to 6 carbon atoms. R 4 Examples of hydrocarbon groups represented by α include straight-chain or branched alkylene groups, alkenylene groups, or alkynylene groups.

[0095] R 4 Specifically, examples of alkylene groups that represent alkylene groups include ethylene groups, n-propylene groups, i-propylene groups, n-butylene groups, s-butylene groups, t-butylene groups, n-pentylene groups, -CH2CH(C3H7)- groups, n-hexylene groups, etc.

[0096] R4 Specifically, examples of alkenylene groups that represent alkenylene groups include ethenylene groups, propenylene groups, etc.

[0097] R 4 Specifically, examples of alkynylene groups that represent alkynylene groups include propynylene groups.

[0098] R 4 The hydrocarbon group represented by may include heteroatoms between carbon-carbon bonds. Examples of heteroatoms include oxygen atoms, nitrogen atoms, sulfur atoms, etc.

[0099] R 4 The hydrocarbon group represented by α may have any hydrogen atom substituted with a halogen atom. Examples of hydrocarbon groups in which any hydrogen atom is substituted with a fluorine atom include tetrafluoroethylene groups, 1,2-difluoroethylene groups, 2,2-difluoroethylene groups, fluoroethylene groups, (trifluoromethyl)ethylene groups, etc.

[0100] R 4 An unsubstituted alkylene group having 3 to 4 carbon atoms is preferred, and a propylene group is more preferred.

[0101]

[0102] [Of general formulas (5) and (6), R 5 is a substituent having at least one of an unsaturated bond and an aromatic ring, each independently.

[0103] The above R 5 It is preferable that the group be selected from alkenyl group, allyl group, alkynyl group, aryl group, alkenyloxy group, allyloxy group, alkynyloxy group, and aryloxy group.

[0104] The alkenyl group is preferably an ethenyl group, the allyl group is preferably a 2-propenyl group, and the alkenyl group is preferably an ethenyl group. In addition, the aryl group is preferably a phenyl group, a 2-methylphenyl group, a 4-methylphenyl group, a 4-fluorophenyl group, a 4-tert-butylphenyl group, or a 4-tert-amylphenyl group.

[0105] The alkenyloxy group is preferably a vinyloxy group, and the allyloxy group is preferably a 2-propenyloxy group. Additionally, the alkenyloxy group is preferably a propargyloxy group, and the aryloxy group is preferably a phenoxy group, a 2-methylphenoxy group, a 4-methylphenoxy group, a 4-fluorophenoxy group, a 4-tert-butylphenoxy group, or a 4-tert-amylphenoxy group.

[0106] In addition, the three Rs in the above general formulas (5) and (6) 5 Among them, it is desirable that at least two are ethenyl groups, ethinyl groups, or both, from the perspective of high durability improvement effect.

[0107] Specific examples of additives other than the compounds represented by the above general formulas (2) to (6) include cyclohexylbenzene, cyclohexylfluorobenzene, fluorobenzene (hereinafter referred to as FB), biphenyl, difluoroanisole, tert-butylbenzene, tert-amylbenzene, 2-fluorotoluene, 2-fluorobiphenyl, vinylene carbonate, dimethylvinylene carbonate, vinylethylene carbonate, fluoroethylene carbonate, methylpropargyl carbonate, ethylpropargyl carbonate, dipropargyl carbonate, maleic anhydride, succinic anhydride, methylenemethanedisulfonate, dimethylenemethanedisulfonate, trimethylenemethanedisulfonate, methyl methanesulfonate, lithium tetrafluoroborate, lithium difluorobis(oxalato)phosphate (hereinafter referred to as LDFBOP), sodium difluorobis(oxalato)phosphate, Potassium difluorobis(oxalato)phosphate, lithium difluorooxalatoborate (hereinafter referred to as LDFOB), sodium difluorooxalatoborate, potassium difluorooxalatoborate, lithium bis(oxalato)borate, sodium bis(oxalato)borate, potassium bis(oxalato)borate, lithium tetrafluorooxalatophosphate (hereinafter referred to as LTFOP), sodium tetrafluorooxalatophosphate, potassium tetrafluorooxalatophosphate, lithium tris(oxalato)phosphate, sodium tris(oxalato)phosphate, potassium tris(oxalato)phosphate, lithium ethylfluorophosphate (hereinafter referred to as LEFP), lithium propylfluorophosphate, lithium fluorophosphate, ethensulfonylfluoride (hereinafter referred to as ESF), Examples of compounds having an overcharge prevention effect, a negative electrode film formation effect, or a positive electrode protection effect include trifluoromethanesulfonylfluoride (hereinafter referred to as TSF), methanesulfonylfluoride (hereinafter referred to as MSF), and phenyl difluorophosphate (hereinafter referred to as PDFP).

[0108] The content of other additives other than the compound represented by general formula (2) in the non-aqueous electrolyte is preferably 0.01 mass% or more and 8.00 mass% or less with respect to the total amount of the non-aqueous electrolyte, more preferably 0.05 mass% or more and 3.00 mass% or less, and more preferably 0.1 mass% or more and 2.50 mass% or less.

[0109] It is preferable for the non-aqueous electrolyte to include any of the compounds represented by general formulas (3) to (6) in addition to the compound represented by general formula (2) for the improvement of capacity retention rate after long-term cycles at high temperature and suppression of resistance increase at low temperature after high-temperature storage, and it is more preferable to include both the compound represented by general formula (2) and the compound represented by general formula (3).

[0110] The container of the present disclosure can particularly exhibit the effect of inhibiting iron leaching in the storage of a non-aqueous electrolyte comprising both a compound represented by general formula (2) and a compound represented by general formula (3), which are useful for improving battery characteristics.

[0111] In addition, it is also a preferred embodiment to include one or more compounds among a lithium salt of a boron complex having an oxalic acid group, a lithium salt of a phosphorus complex having an oxalic acid group, a compound having an O=SF bond, and a compound having an O=PF bond. Including the above compounds is desirable from the perspective that not only can the capacity retention rate after long-term cycling at high temperatures be improved and the increase in resistance at low temperatures after high-temperature storage be suppressed, but furthermore, the leaching of Ni components from the electrode into the electrolyte can be reduced when using a Ni-containing electrode.

[0112] It is more preferable that the lithium salt of the boron complex having the oxalic acid group is lithium difluorooxalatoborate, and the lithium salt of the phosphorus complex having the oxalic acid group is at least one selected from the group consisting of lithium tetrafluorooxalatophosphate and lithium difluorobis(oxalato)phosphate, because in addition to improving the capacity retention rate after long-term cycling at high temperature and suppressing the increase in resistance at low temperature after high-temperature storage, the effect of suppressing the leaching of Ni components from the positive electrode is particularly excellent.

[0113] Examples of compounds having the above O=SF bond include lithium fluorosulfonate, bis(fluorosulfonyl)imidelithium, (trifluoromethanesulfonyl)(fluorosulfonyl)imidelithium, propyl fluorosulfate, phenyl fluorosulfate, 4-fluorophenylfluorosulfonate, 4-tert-butylphenylfluorosulfonate, 4-tert-amylphenylfluorosulfonate, ethenesulfonylfluoride, trifluoromethanesulfonylfluoride, methanesulfonylfluoride, benzenesulfonyl fluoride, fluorine-4-fluorophenylsulfonyl, fluorine-4-tert-butylphenylsulfonyl, fluorine-4-tert-amylphenylsulfonyl, fluorine-2-methylphenylsulfonyl, and among these, at least selected from the group consisting of lithium fluorosulfonate, bis(fluorosulfonyl)imidelithium, and (trifluoromethanesulfonyl)(fluorosulfonyl)imidelithium. It is particularly desirable to have one type, as it can improve the capacity retention rate after a long cycle at high temperatures, suppress the increase in resistance at low temperatures after high-temperature storage, and suppress the leaching of Ni components from the positive electrode.

[0114] Examples of compounds having the O=PF bond include compounds represented by the general formula (3) such as lithium difluorophosphate, lithium ethylfluorophosphate, bis(difluorophosphonyl)imide, and phenyl difluorophosphate. Among these, at least one selected from the group consisting of lithium difluorophosphate, lithium ethylfluorophosphate, and bis(difluorophosphonyl)imide is preferred in that it has a certain degree of effect of improving capacity retention rate after long-term cycling at high temperature, suppressing resistance increase at low temperature after high-temperature storage, and suppressing leaching of Ni components from the positive electrode, while having particularly high productivity and low manufacturing cost compared to the lithium salt of a boron complex having an oxalic acid group, the lithium salt of a phosphorus complex having an oxalic acid group, and compounds having the O=SF bond described above.

[0115] Among the other additives described above, some overlap with the solute, but when used as additives, they are added at a lower concentration than the concentration of the solute mentioned above.

[0116] Furthermore, it is also possible to use the non-aqueous electrolyte by pseudo-solidifying it with a gelling agent or a cross-linking polymer, as in the case where it is used in a non-aqueous electrolyte battery called a polymer battery.

[0117] The container for a non-aqueous electrolyte of the present disclosure is preferably a container for a non-aqueous electrolyte that contains a non-aqueous electrolyte comprising a compound represented by the general formula (2) in a receiving portion.

[0118] [Preservation Method for Non-Aqueous Electrolytes]

[0119] The present disclosure also relates to a method for preserving a non-aqueous electrolyte using the above-described container for the non-aqueous electrolyte. The non-aqueous electrolyte is preserved by filling the receiving portion of the above-described container for the non-aqueous electrolyte.

[0120] When filling a container with a non-aqueous electrolyte, the filling rate is preferably 20 to 98% of the container's capacity, more preferably 30 to 97%, and more preferably 50 to 95%. If the filling rate is less than 20%, the low-boiling point solvent in the non-aqueous electrolyte is prone to volatilization, and because the concentration of the high-boiling point solvent increases, solid matter is prone to precipitating at the opening of the container, which may lead to a decrease in airtightness. On the other hand, if the filling rate exceeds 98%, the lid may come into contact with the non-aqueous electrolyte, or the internal pressure inside the container may increase, which may lead to a decrease in airtightness. Therefore, the above range of filling rates is desirable. In addition, it is desirable to fill the container such that the upper surface of the non-aqueous electrolyte is lower than the injection port, preferably 1 cm or more, more preferably 2 cm or more, and even more preferably 3 cm or more.

[0121] When storing a non-aqueous electrolyte using the above-mentioned container for the non-aqueous electrolyte, the storage temperature is preferably 25°C or lower from the perspective of suppressing the leaching of iron into the non-aqueous electrolyte, 5°C or lower is more preferable, and -5°C or lower is even more preferable.

[0122] In addition, it is desirable to store the non-aqueous electrolyte in the container under an inert atmosphere to prevent deterioration caused by oxygen in the air, etc. That is, if there is a gaseous region in the receiving portion of the container that is not filled with the non-aqueous electrolyte, it is desirable that said region be replaced with an inert gas.

[0123] Specifically, it is preferable that the oxygen concentration in the relevant atmospheric region be 0.3 volume% or less, and more preferable that it be 0.1 volume% or less.

[0124] By using the preservation method of the present disclosure, the leaching of iron into the non-aqueous electrolyte during container preservation is suppressed, thereby preventing corrosion of the container, and when this non-aqueous electrolyte is used in a non-aqueous electrolyte battery, it is possible to suppress the occurrence of a short circuit.

[0125] Furthermore, since the non-aqueous electrolyte preserved by the preservation method of the present disclosure is resistant to degradation due to the leaching of iron, it is also resistant to affecting battery performance. Consequently, the performance characteristics of the non-aqueous electrolyte prior to preservation, such as improved capacity retention after long-term cycling at high temperatures and suppression of resistance increase at low temperatures after high-temperature storage, are maintained, making it advantageous for use in non-aqueous electrolyte batteries.

[0126] In addition, in the case of a non-aqueous electrolyte comprising a compound represented by the general formula (2) and a compound represented by the general formula (3) as additives, the effect of using the preservation method of the present disclosure is particularly exhibited.

[0127] Examples

[0128] The present disclosure is described in more detail below by way of examples, but the present disclosure is not limited to such descriptions.

[0129] [Preparation of Non-Aqueous Electrolytes]

[0130] <Preparation of Non-aqueous Electrolyte 1>

[0131] A mixed solvent of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) was used as a non-aqueous organic solvent, and LiPF6, which is the solute, and each additive shown in Table 1 were dissolved in the said solvent to prepare a non-aqueous electrolyte 1 with the composition shown in Table 1. The above preparation was carried out while maintaining the liquid temperature in the range of 20 to 30°C.

[0132] <Preparation of Non-aqueous Electrolyte 2>

[0133] Non-aqueous electrolyte 2 with the composition shown in Table 1 below was prepared in the same manner as non-aqueous electrolyte 1, except that ethylene sulfate was not added.

[0134] <Preparation of Non-aqueous Electrolyte 3>

[0135] Non-aqueous electrolyte 3 with the composition shown in Table 1 below was prepared in the same manner as non-aqueous electrolyte 1, except that lithium difluorophosphate was not added.

[0136] In addition, in Table 1 below, the values ​​for non-aqueous organic solvents represent the volume ratios of EC, EMC, and DMC, the values ​​for solutes represent the amount of solute (mol / L) in the total amount of non-aqueous electrolyte, and the values ​​for additives represent the concentration (mass%) of each additive component included in the total amount of non-aqueous electrolyte.

[0137]

[0138] 〔evaluation〕

[0139] The effect on the non-aqueous electrolyte and the container was evaluated by storing the non-aqueous electrolyte using the container of the present disclosure. The evaluation was performed by storing a test piece made of austenitic stainless steel, such as SUS304 or SUS316L, while immersed in the non-aqueous electrolyte, and measuring the change in iron atom concentration in the non-aqueous electrolyte before and after storage.

[0140] [Production of Test Piece]

[0141] As test pieces, test specimens made of austenitic stainless steel SUS304 or SUS316L (sizes of 20 mm × 15 mm × 3 mm) were used.

[0142] A SUS304 test specimen that was not subjected to the passivation treatment described below was designated as Test Piece 1. Additionally, a test specimen that underwent passivation treatment by immersing Test Piece 1 in 30% nitric acid at 50°C for 1 hour was designated as Test Piece 2.

[0143] Likewise, for the SUS316L test specimen, the one that was not subjected to the passivation treatment described below was designated as Test Piece 3. In addition, the test specimen that underwent passivation treatment by immersing Test Piece 3 in 30% nitric acid at 50°C for 1 hour was designated as Test Piece 4.

[0144] Test pieces 1 to 4 were washed with acetone before the immersion test in a non-aqueous electrolyte, and additionally washed with ultrapure water (water collected by Merck’s MILLIPORE Milli-Q Integral 15), and then dried at 60°C for 12 hours.

[0145] The amount of chromium atoms relative to the total amount of iron atoms, chromium atoms, nickel atoms, and molybdenum atoms on the surface of the passivation layer of test pieces 1 to 4 was measured by Auger electron spectroscopy.

[0146] <Test Example 1>

[0147] 25g of the above-mentioned non-aqueous electrolyte 1 was filled into a 20mL fluoropolymer bottle (Sanplatec Co., Ltd., PFA wide-mouth bottle (without intermediate stopper)), and the fabricated test piece 2 was immersed and preserved. Preservation was carried out at 45°C for 16 days, 27 days, and 1 year. Preservation at 45°C was carried out by placing the bottle in a constant temperature bath and controlling the ambient temperature. In addition, the preservation temperature of 45°C is a condition that deviates from the preferred preservation temperature of "25°C or lower," but this was set for convenience for the corrosion acceleration test (accelerated test).

[0148] After each storage period, the atomic weight of iron contained in non-aqueous electrolyte 1 was measured using an ICP emission spectroscopic analyzer (Agilent 5110 ICP-OES).

[0149] <Test Examples 2~4>

[0150] Test Examples 2 to 4 were carried out in the same manner as Test Example 1, except that the test pieces used were changed to those shown in Table 2.

[0151] <Test Examples 5~8>

[0152] Test Examples 5 to 8 were carried out in the same manner as Test Examples 1 to 4, except that the non-aqueous electrolyte used was changed to non-aqueous electrolyte 2.

[0153] <Test Examples 9~12>

[0154] Test Examples 9 to 12 were carried out in the same manner as Test Examples 1 to 4, except that the non-aqueous electrolyte used was changed to non-aqueous electrolyte 3.

[0155] The results are shown in Table 2. In addition, the results of similarly measuring the iron atomic concentration in non-aqueous electrolytes 1 to 3 before container storage are also shown in Table 2.

[0156]

[0157] From the evaluation results shown in Table 2, it was confirmed that the container for a non-aqueous electrolyte of the embodiment of the present disclosure, in which the liquid contact surface with the non-aqueous electrolyte is passivated by acid cleaning, can significantly suppress the leaching of iron into the non-aqueous electrolyte compared to the container of the comparative example in which acid cleaning is not performed.

[0158] In addition, when comparing SUS316L and SUS304, it was found that SUS304 is a more useful material because it has a higher iron leaching inhibition effect even after 27 days of storage and after 1 year of storage.

[0159] In addition, from the results of reference examples Test Examples 5 and 7, it was found that the container of the present disclosure can suppress the leaching of iron even when storing non-aqueous electrolyte 2, which contains lithium difluorophosphate, a compound represented by general formula (3), and does not contain ethylene sulfate, a compound represented by general formula (2). However, compared to the storage of non-aqueous electrolyte 1, which contains both the compound represented by general formula (2) and the compound represented by general formula (3), and non-aqueous electrolyte 3, which contains the compound represented by general formula (2) and does not contain the compound represented by general formula (3), the difference in the amount of iron leached into the non-aqueous electrolyte due to the presence or absence of acid washing was not significant.

[0160] From this point, the container of the present disclosure is preferably used for storing a non-aqueous electrolyte containing a compound represented by general formula (3), but it has been shown that the iron leaching inhibition effect is high in storing a non-aqueous electrolyte containing a compound represented by general formula (2), particularly in storing a non-aqueous electrolyte containing both a compound represented by general formula (2) and a compound represented by general formula (3), such as non-aqueous electrolyte 1. Industrial applicability

[0161] According to the present disclosure, a container for a non-aqueous electrolyte capable of suppressing the leaching of iron into the non-aqueous electrolyte, and a method for preserving a non-aqueous electrolyte using said container for the non-aqueous electrolyte can be provided.

[0162] Although the present disclosure has been described in detail with reference to specific embodiments, it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the present disclosure.

[0163] This application is based on Japanese patent application filed on June 5, 2019 (JP 2019-105458), the contents of which are incorporated herein by reference.

Claims

Claim 1 A container for a non-aqueous electrolyte having a receiving portion, wherein the receiving portion is made of austenitic stainless steel, and the surface in contact with the non-aqueous electrolyte in the receiving portion has a passivation layer, wherein the amount of chromium atoms relative to the total amount of iron atoms, chromium atoms, nickel atoms, and molybdenum atoms on the surface of the passivation layer is 40 mass% or more, and the non-aqueous electrolyte comprises a compound represented by the following general formula (2) and a compound represented by the following general formula (3). [In general formula (2), R 3 ... represents a hydrocarbon group having 2 to 5 carbon atoms. Heteroatoms may be included between carbon-carbon bonds within the said hydrocarbon group. Additionally, any hydrogen atom of the said hydrocarbon group may be substituted with a halogen atom. [Of general formula (3), X 3 and X 4 Each represents a halogen atom independently. M2 + represents an alkali metal cation, ammonium ion, or organic cation. Claim 2 In claim 1, a container for a non-aqueous electrolyte in which the austenitic stainless steel is SUS304. Claim 3 A method for preserving a non-aqueous electrolyte using a container for a non-aqueous electrolyte described in claim 1 or 2. Claim 4 In claim 3, a method for preserving a non-aqueous electrolyte in which the preservation temperature of the non-aqueous electrolyte is 25℃ or lower. Claim 5 In claim 3, a method for preserving a non-aqueous electrolyte under an inert atmosphere. Claim 6 A container for a non-aqueous electrolyte that contains, in the receiving portion thereof, a compound represented by the general formula (2) and a compound represented by the general formula (3).

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