Nonaqueous solvent solution, retention method, and storage container

Abstract

The present disclosure provides a nonaqueous solvent solution containing a nonaqueous solvent, a difluorobis(oxalato)phosphate, a tetrafluoro oxalato phosphate, and a tris(oxalato)phosphate, wherein: the concentration of the difluorobis(oxalato)phosphate in the nonaqueous solvent solution is 10-50 mass%; and the ratio of the difluorobis(oxalato)phosphate and the tris(oxalato)phosphate is 0.001 mol or more of the tris(oxalato)phosphate to 1 mol of the difluorobis(oxalate)phosphate. The present disclosure further provides a retention method and a storage container.

Description

Nonaqueous solvent solution, holding method, and storage container

[0001] The present disclosure relates to a non-aqueous solvent solution, a holding method, and a container.

[0002] Patent Document 1 discloses that by further adding both difluoro(bisoxalato)phosphate and tetrafluoro(oxalato)phosphate as additives to an electrolyte solution for nonaqueous electrolyte batteries containing a nonaqueous organic solvent and a solute, it is possible to provide an electrolyte solution for nonaqueous electrolyte batteries and a nonaqueous electrolyte battery that has improved durability such as cycle characteristics and high-temperature storage stability, and that is excellent in low-temperature characteristics such as being able to exhibit sufficient performance even at temperatures below 0° C. Furthermore, Example 8 of Patent Document 2 discloses that an ethyl methyl carbonate solution containing 37 mass % lithium difluorobis(oxalato)phosphate and 2 mass % lithium tetrafluoro(oxalato)phosphate is obtained, and that this can be used as an additive effective in improving the performance of nonaqueous electrolyte batteries. In this way, in preparing a non-aqueous electrolyte solution containing difluorobis(oxalato)phosphate and tetrafluorooxalatophosphate, the difluorobis(oxalato)phosphate and tetrafluorooxalatophosphate may be added in the form of adding a non-aqueous solvent solution of difluorobis(oxalato)phosphate and tetrafluorooxalatophosphate at a predetermined concentration (hereinafter, this may be referred to as a "concentrated solution of difluorobis(oxalato)phosphate containing tetrafluorooxalatophosphate" or simply as a "concentrated solution").

[0003] Japanese Patent Publication No. 2011-222193 Japanese Patent Publication No. 2010-143835

[0004] A concentrated solution of difluorobis(oxalato)phosphate containing tetrafluorooxalatophosphate tends to cause corrosion of stainless steel when brought into contact with stainless steel if water is mixed in. Therefore, an object of the present disclosure is to provide a concentrated solution of difluorobis(oxalato)phosphate containing tetrafluorooxalatophosphate that is unlikely to cause corrosion when brought into contact with stainless steel even if water is mixed in, a method for maintaining the same, and a container for storing the same.

[0005] Concentrated solutions of difluorobis(oxalato)phosphates containing tetrafluorooxalatophosphates tend to corrode stainless steel when they are contaminated with water. The present inventors discovered that when water is contaminated with the concentrated solution, hydrogen fluoride is generated as a result of the decomposition reaction of difluorobis(oxalato)phosphate and tetrafluorooxalatophosphate. Therefore, when the concentrated solution is brought into contact with stainless steel, the generated hydrogen fluoride is likely to corrode the stainless steel. After extensive research to solve this problem, the present inventors discovered that adding a specific amount of tris(oxalato)phosphate can suppress the decomposition reaction even when water is contaminated, thereby providing a concentrated solution of difluorobis(oxalato)phosphates containing tetrafluorooxalatophosphate that is less likely to corrode stainless steel when brought into contact with stainless steel. Specifically, the above problem can be solved by the following configuration.

[0006] [1] A non-aqueous solvent solution comprising a non-aqueous solvent, a difluorobis(oxalato)phosphate, a tetrafluorooxalatophosphate, and a tris(oxalato)phosphate, wherein the concentration of the difluorobis(oxalato)phosphate in the non-aqueous solvent solution is 10 to 50 mass %, and the ratio of the difluorobis(oxalato)phosphate to the tris(oxalato)phosphate is 0.001 mole or more per mole of the difluorobis(oxalato)phosphate. [2] The non-aqueous solvent solution according to [1], wherein the ratio of the difluorobis(oxalato)phosphate to the tris(oxalato)phosphate is 0.03 moles or less per mole of the difluorobis(oxalato)phosphate. [3] The nonaqueous solvent solution according to [1] or [2], wherein the ratio of the difluorobis(oxalato)phosphate to the tetrafluorooxalatophosphate is 0.010 to 0.25 moles per mole of the difluorobis(oxalato)phosphate. [4] The nonaqueous solvent solution according to any one of [1] to [3], further containing a difluorophosphate. [5] The nonaqueous solvent solution according to [4], wherein the ratio of the difluorobis(oxalato)phosphate to the difluorophosphate is 0.001 to 0.05 moles per mole of the difluorobis(oxalato)phosphate. [6] The nonaqueous solvent solution according to any one of [1] to [5], wherein the nonaqueous solvent contains at least one of a cyclic ester and a chain ester. [7] The non-aqueous solvent solution according to [6], wherein the non-aqueous solvent contains the chain ester, and the content of the chain ester is 50 to 100% by volume relative to the total amount of the non-aqueous solvent.[8] The nonaqueous solvent solution according to [6], wherein the cyclic ester is at least one selected from the group consisting of ethylene carbonate, propylene carbonate, butylene carbonate, fluoroethylene carbonate, and γ-butyrolactone, and the chain ester is at least one selected from the group consisting of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl acetate, ethyl acetate, methyl propionate, and ethyl propionate. [9] The nonaqueous solvent solution according to any one of [1] to [8], which is in contact with stainless steel.

[10] The nonaqueous solvent solution according to [9], wherein the stainless steel is an austenitic stainless steel.

[11] A method for holding a non-aqueous solvent solution in a state in which the non-aqueous solvent solution is in contact with a liquid contact member having at least a partial region made of stainless steel, the non-aqueous solvent solution comprising: a non-aqueous solvent; difluorobis(oxalato)phosphate; tetrafluorooxalatophosphate; and tris(oxalato)phosphate; the concentration of the difluorobis(oxalato)phosphate in the non-aqueous solvent solution is 10 to 50 mass %, and the ratio of the difluorobis(oxalato)phosphate to the tris(oxalato)phosphate is 0.001 mole or more per mole of the difluorobis(oxalato)phosphate.

[12] The retention method according to

[11] , wherein the ratio of the difluorobis(oxalato)phosphate to the tris(oxalato)phosphate is 0.03 mol or less per 1 mol of the difluorobis(oxalato)phosphate.

[13] The retention method according to

[11] or

[12] , wherein the ratio of the difluorobis(oxalato)phosphate to the tetrafluorooxalatophosphate is 0.010 to 0.25 mol per 1 mol of the difluorobis(oxalato)phosphate.

[14] The retention method according to any one of

[11] to

[13] , further comprising a difluorophosphate.

[15] The retention method according to

[14] , wherein the ratio of the difluorobis(oxalato)phosphate to the difluorophosphate is 0.001 to 0.05 moles of the difluorophosphate per 1 mole of the difluorobis(oxalato)phosphate.

[16] The retention method according to any one of

[11] to

[15] , wherein the non-aqueous solvent contains at least one of a cyclic ester and a chain ester.

[17] The retention method according to

[16] , wherein the non-aqueous solvent contains the chain ester, and the content of the chain ester is 50 to 100% by volume relative to the total amount of the non-aqueous solvent.

[18] The holding method according to

[16] , wherein the cyclic ester is at least one selected from the group consisting of ethylene carbonate, propylene carbonate, butylene carbonate, fluoroethylene carbonate, and γ-butyrolactone, and the chain ester is at least one selected from the group consisting of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl acetate, ethyl acetate, methyl propionate, and ethyl propionate.

[19] The holding method according to any one of

[11] to

[18] , wherein the stainless steel is an austenitic stainless steel.

[20] The holding method according to any one of

[11] to

[20] , wherein the liquid-contacting member is a liquid-contacting member in a storage container that stores the nonaqueous solvent solution, and the nonaqueous solvent solution is held in the storage container.

[21] A storage vessel having a liquid-contacting member at least a portion of which is made of stainless steel, wherein a non-aqueous solvent solution is stored in the storage vessel in a state of contact with the liquid-contacting member, the non-aqueous solvent solution comprising: a non-aqueous solvent, difluorobis(oxalato)phosphate, tetrafluorooxalatophosphate, and tris(oxalato)phosphate, wherein the concentration of the difluorobis(oxalato)phosphate in the non-aqueous solvent solution is 10 to 50 mass %, and the ratio of the difluorobis(oxalato)phosphate to the tris(oxalato)phosphate is 0.001 mole or more per mole of the difluorobis(oxalato)phosphate.

[22] The storage container according to

[21] , wherein the stainless steel is an austenitic stainless steel.

[0007] According to the present disclosure, it is possible to provide a concentrated solution of difluorobis(oxalato)phosphate containing tetrafluorooxalatophosphate, which is unlikely to cause corrosion when brought into contact with stainless steel even when water is mixed in, a method for maintaining the same, and a container for storing the same.

[0008] In this specification, the word "to" is used to mean that the numerical values ​​before and after it are included as the lower limit and upper limit.

[0009] The present disclosure will be described in detail below, but the following description of the constituent elements is an example of an embodiment of the present disclosure, and the present disclosure is not limited to these specific contents.

[0010] [Non-aqueous solvent solution] The non-aqueous solvent solution of the present disclosure is a non-aqueous solvent solution comprising: a non-aqueous solvent; a difluorobis(oxalato)phosphate; a tetrafluorooxalatophosphate; and a tris(oxalato)phosphate, wherein the concentration of the difluorobis(oxalato)phosphate in the non-aqueous solvent solution is 10 to 50 mass %; and the ratio of the difluorobis(oxalato)phosphate to the tris(oxalato)phosphate is 0.001 mole or more per mole of the difluorobis(oxalato)phosphate.

[0011] The non-aqueous solvent solution of the present disclosure has a difluorobis(oxalato)phosphate concentration of 10 to 50% by mass and is a concentrated solution. The difluorobis(oxalato)phosphate concentration of the non-aqueous solvent solution of the present disclosure may be 15 to 40% by mass.

[0012] Examples of difluorobis(oxalato)phosphates include lithium difluorobis(oxalato)phosphate and sodium difluorobis(oxalato)phosphate.

[0013] Examples of tetrafluorooxalatophosphate salts include lithium tetrafluorooxalatophosphate and sodium tetrafluorooxalatophosphate.

[0014] Examples of tris(oxalato)phosphates include lithium tris(oxalato)phosphate and sodium tris(oxalato)phosphate.

[0015] The ratio of difluorobis(oxalato)phosphate to tris(oxalato)phosphate is 0.001 mol or more, or may be 0.002 mol or more, or 0.004 mol or more, or 0.005 mol or more, of tris(oxalato)phosphate per 1 mol of difluorobis(oxalato)phosphate. Furthermore, the ratio of tris(oxalato)phosphate per 1 mol of difluorobis(oxalato)phosphate may be 0.60 mol or less, or may be 0.30 mol or less, or may be 0.15 mol or less, or may be 0.07 mol or less, or may be 0.03 mol or less. When the ratio of tris(oxalato)phosphate per 1 mol of difluorobis(oxalato)phosphate is 0.03 mol or less, when a nonaqueous electrolyte solution is prepared using the nonaqueous solvent solution and the nonaqueous electrolyte solution is used in a nonaqueous electrolyte battery, gas generation in the battery is unlikely to occur.

[0016] The ratio of difluorobis(oxalato)phosphate to tetrafluorooxalatophosphate may be 0.010 to 0.30 mol, or may be 0.010 to 0.25 mol, of tetrafluorooxalatophosphate per 1 mol of difluorobis(oxalato)phosphate.

[0017] The nonaqueous solvent solution of the present disclosure may further contain a difluorophosphate. Examples of difluorophosphates include lithium difluorophosphate and sodium difluorophosphate. The ratio of difluorobis(oxalato)phosphate to difluorophosphate may be 0.001 to 0.05 moles of difluorophosphate per 1 mole of difluorobis(oxalato)phosphate.

[0018] (Non-aqueous Solvent) The type of non-aqueous solvent contained in the non-aqueous solvent solution of the present disclosure is not particularly limited, and any non-aqueous solvent can be used. The non-aqueous solvent may include, for example, at least one selected from the group consisting of cyclic esters, chain esters, cyclic ethers, chain ethers, sulfone compounds, sulfoxide compounds, and ionic liquids. Examples of cyclic esters include cyclic carbonates such as propylene carbonate (hereinafter sometimes referred to as "PC"), ethylene carbonate (hereinafter sometimes referred to as "EC"), fluoroethylene carbonate (hereinafter sometimes referred to as "FEC"), and butylene carbonate, as well as γ-butyrolactone and γ-valerolactone. Examples of chain esters include chain carbonates such as diethyl carbonate (hereinafter sometimes referred to as "DEC"), dimethyl carbonate (hereinafter sometimes referred to as "DMC"), and ethyl methyl carbonate (hereinafter sometimes referred to as "EMC"), as well as methyl acetate, methyl propionate, and ethyl propionate (hereinafter sometimes referred to as "EP"). Examples of cyclic ethers include tetrahydrofuran, 2-methyltetrahydrofuran, and dioxane. Examples of chain ethers include dimethoxyethane and diethyl ether. Examples of sulfone compounds include dimethyl sulfoxide and sulfolane.

[0019] The non-aqueous solvent may contain at least one of a cyclic ester and a chain ester. The cyclic ester may be at least one selected from the group consisting of ethylene carbonate, propylene carbonate, butylene carbonate, fluoroethylene carbonate, and γ-butyrolactone, and the chain ester may be at least one selected from the group consisting of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl acetate, ethyl acetate, methyl propionate, and ethyl propionate. The content of the chain ester may be 50 to 100% by volume relative to the total amount of the non-aqueous solvent.

[0020] The non-aqueous solvent solution of the present disclosure may be in contact with a stainless steel, which is not particularly limited, but may be an austenitic stainless steel.

[0021] [Retention Method] The retention method disclosed herein is a retention method for retaining a non-aqueous solvent solution in a state in which the non-aqueous solvent solution is in contact with a liquid contact member having at least a partial region made of stainless steel, wherein the non-aqueous solvent solution contains: a non-aqueous solvent; difluorobis(oxalato)phosphate; tetrafluorooxalatophosphate; and tris(oxalato)phosphate; the concentration of the difluorobis(oxalato)phosphate in the non-aqueous solvent solution is 10 to 50 mass %, and the ratio of the difluorobis(oxalato)phosphate to the tris(oxalato)phosphate is 0.001 mole or more of the tris(oxalato)phosphate per mole of the difluorobis(oxalato)phosphate.

[0022] The liquid contact member is not particularly limited as long as at least a portion of the liquid contact member is made of stainless steel. The stainless steel may be austenitic stainless steel. The liquid contact member may be a liquid contact member whose entire region is made of stainless steel. The liquid contact member holds the non-aqueous solvent solution while in contact with the non-aqueous solvent solution, and the method for bringing the liquid contact member into contact with the non-aqueous solvent solution is not particularly limited. For example, the liquid contact member may be immersed in the non-aqueous solvent solution. Alternatively, the non-aqueous solvent solution may be contained in a container formed by the liquid contact member.

[0023] The non-aqueous solvent solution in the retention method of the present disclosure is a concentrated solution having a difluorobis(oxalato)phosphate concentration of 10 to 50% by mass. The difluorobis(oxalato)phosphate concentration in the non-aqueous solvent solution of the present disclosure may be 15 to 40% by mass.

[0024] Examples of difluorobis(oxalato)phosphates include lithium difluorobis(oxalato)phosphate and sodium difluorobis(oxalato)phosphate.

[0025] Examples of tetrafluorooxalatophosphate salts include lithium tetrafluorooxalatophosphate and sodium tetrafluorooxalatophosphate.

[0026] Examples of tris(oxalato)phosphates include lithium tris(oxalato)phosphate and sodium tris(oxalato)phosphate.

[0027] The ratio of difluorobis(oxalato)phosphate to tris(oxalato)phosphate is 0.001 mol or more, or may be 0.002 mol or more, or 0.004 mol or more, or 0.005 mol or more, of tris(oxalato)phosphate per 1 mol of difluorobis(oxalato)phosphate. Also, the ratio of tris(oxalato)phosphate per 1 mol of difluorobis(oxalato)phosphate may be 0.60 mol or less, or may be 0.30 mol or less, or may be 0.15 mol or less, or may be 0.07 mol or less, or may be 0.03 mol or less.

[0028] The ratio of difluorobis(oxalato)phosphate to tetrafluorooxalatophosphate may be 0.010 to 0.30 mol, or may be 0.010 to 0.25 mol, of tetrafluorooxalatophosphate per 1 mol of difluorobis(oxalato)phosphate.

[0029] The nonaqueous solvent solution in the retention method of the present disclosure may further contain a difluorophosphate. Examples of difluorophosphates include lithium difluorophosphate and sodium difluorophosphate. The ratio of difluorobis(oxalato)phosphate to difluorophosphate may be 0.001 to 0.05 moles of difluorophosphate per 1 mole of difluorobis(oxalato)phosphate.

[0030] (Non-aqueous solvent) The type of non-aqueous solvent contained in the non-aqueous solvent solution in the retention method of the present disclosure is not particularly limited, and any non-aqueous solvent can be used. Examples of the non-aqueous solvent include the same non-aqueous solvents as those contained in the non-aqueous solvent solution of the present disclosure, and the preferred ranges and preferred contents are also the same.

[0031] The liquid-contacting member may be a liquid-contacting member in a container that contains the nonaqueous solvent solution, and the nonaqueous solvent solution may be held within the container.

[0032] [Storage Container] The storage container of the present disclosure is a storage container having a liquid-contacting member at least a portion of which is made of stainless steel, wherein a non-aqueous solvent solution is stored in the storage container in contact with the liquid-contacting member, the non-aqueous solvent solution containing: a non-aqueous solvent, difluorobis(oxalato)phosphate, tetrafluorooxalatophosphate, and tris(oxalato)phosphate, wherein the concentration of the difluorobis(oxalato)phosphate in the non-aqueous solvent solution is 10 to 50 mass %, and the ratio of the difluorobis(oxalato)phosphate to the tris(oxalato)phosphate is 0.001 mole or more for 1 mole of the difluorobis(oxalato)phosphate.

[0033] The storage container is not particularly limited as long as it has a liquid-contacting member at least a portion of which is made of stainless steel. The liquid-contacting member is not particularly limited as long as it has at least a portion of which is made of stainless steel. The entire liquid-contacting member may be made of stainless steel.

[0034] Since stainless steel has high corrosion resistance, even if the non-aqueous solvent solution comes into contact with air and becomes more corrosive, corrosion of the container that would impede its use is unlikely to occur. The stainless steel may be an austenitic stainless steel.

[0035] Examples of austenitic stainless steel include SUS304, SUS316, SUS316L, etc. SUS304, SUS316, and SUS316L are specified in Japanese Industrial Standard JIS G 4305.

[0036] The storage container of the present disclosure may have an outer circumferential portion made of a material other than the liquid-contacting member, for example, on the outside of the liquid-contacting member (the side opposite to the surface that comes into contact with the nonaqueous solvent solution). The material for forming the outer circumferential portion is not particularly limited, but examples thereof include polyolefin resins such as polyethylene and polypropylene, polyester resins such as polyethylene terephthalate, and polyamide resins such as nylon.

[0037] Furthermore, the storage container of the present disclosure may or may not have a lid, but it is preferable that the container have a lid from the viewpoint of improving airtightness and preventing deterioration of the nonaqueous solvent solution due to contact between the nonaqueous solvent solution and oxygen in the air during storage in the container. The material of the lid is not particularly limited, but it is preferably made of austenitic stainless steel.

[0038] The non-aqueous solvent solution in the storage container of the present disclosure is a concentrated solution having a difluorobis(oxalato)phosphate concentration of 10 to 50 mass %. The difluorobis(oxalato)phosphate concentration in the non-aqueous solvent solution of the present disclosure may be 15 to 40 mass %.

[0039] Examples of difluorobis(oxalato)phosphates include lithium difluorobis(oxalato)phosphate and sodium difluorobis(oxalato)phosphate.

[0040] Examples of tetrafluorooxalatophosphate salts include lithium tetrafluorooxalatophosphate and sodium tetrafluorooxalatophosphate.

[0041] Examples of tris(oxalato)phosphates include lithium tris(oxalato)phosphate and sodium tris(oxalato)phosphate.

[0042] The ratio of difluorobis(oxalato)phosphate to tris(oxalato)phosphate is 0.001 mol or more, or may be 0.002 mol or more, or 0.004 mol or more, or 0.005 mol or more, of tris(oxalato)phosphate per 1 mol of difluorobis(oxalato)phosphate. Also, the ratio of tris(oxalato)phosphate per 1 mol of difluorobis(oxalato)phosphate may be 0.60 mol or less, or may be 0.30 mol or less, or may be 0.15 mol or less, or may be 0.07 mol or less, or may be 0.03 mol or less.

[0043] The ratio of difluorobis(oxalato)phosphate to tetrafluorooxalatophosphate may be 0.010 to 0.30 mol, or may be 0.010 to 0.25 mol, of tetrafluorooxalatophosphate per 1 mol of difluorobis(oxalato)phosphate.

[0044] The nonaqueous solvent solution in the storage container of the present disclosure may further contain a difluorophosphate. Examples of difluorophosphates include lithium difluorophosphate and sodium difluorophosphate. The ratio of difluorobis(oxalato)phosphate to difluorophosphate may be 0.001 to 0.05 moles of difluorophosphate per 1 mole of difluorobis(oxalato)phosphate.

[0045] (Non-aqueous solvent) The type of non-aqueous solvent contained in the non-aqueous solvent solution in the storage container of the present disclosure is not particularly limited, and any non-aqueous solvent can be used. Examples of the non-aqueous solvent include the same non-aqueous solvents as those contained in the non-aqueous solvent solution of the present disclosure, and the preferred ranges and preferred contents are also the same.

[0046] The present disclosure will be specifically described below using examples, but the present disclosure is not limited to such examples.

[0047] [Evaluation] SUS304 test pieces were immersed in and stored in the concentrated solutions of the following Examples and Comparative Examples, and the change in iron atom content (Fe content) in the concentrated solutions before and after storage was measured. The Fe content in the concentrated solutions before and after storage was measured using an ICP optical emission spectrometer (Agilent 5110 ICP-OES).

[0048] [Preparation of Test Pieces] Test pieces (each measuring 20 mm × 15 mm × 3 mm) made of austenitic stainless steel SUS304 were immersed in 30% nitric acid at 50°C for 1 hour, washed with pure water, and dried to prepare test pieces (SUS304 test pieces).

[0049] Examples 1 to 7, Comparative Examples 1 to 3 Preparation of Lithium Difluorobis(oxalato)phosphate Concentrate Ethyl methyl carbonate (EMC), lithium difluorobis(oxalato)phosphate, and lithium tetrafluorooxalatophosphate, each containing 10 ppm by mass or less of water, were dissolved in a fluororesin container (Flon Industries Co., Ltd., PFA container) to prepare solutions with concentrations of 24.0% by mass and 2.7% by mass, respectively. Lithium tris(oxalato)phosphate and lithium difluorophosphate were dissolved in this solution in the molar ratios (number of moles of each compound per mole of difluorobis(oxalato)phosphate) shown in Table 1, thereby preparing concentrated solutions of difluorobis(oxalato)phosphate containing tetrafluorooxalatophosphate according to the Examples and Comparative Examples. A SUS304 test piece was placed and completely immersed in this concentrated solution, and water was added in an amount sufficient to give a calculated water concentration of 700 ppm by mass. After the test piece was kept in this state at 45° C. for 6 months, the Fe content in the concentrated solution was determined. The results are shown in Table 1, along with the Fe content in the concentrated solution before immersion.

[0050] In Table 1, LiDFBOP represents lithium difluorobis(oxalato)phosphate, LiP(Ox)3 represents lithium tris(oxalato)phosphate, LiTFOP represents lithium tetrafluorooxalatophosphate, and LiPO2F2 represents lithium difluorophosphate.

[0051]

[0052] In Table 1, "<1" indicates that the Fe content in the concentrated solution is less than 1 ppm by mass.

[0053] The results in Table 1 show that when a certain amount or more of lithium tris(oxalato)phosphate is added, corrosion of stainless steel is unlikely to occur even when water is mixed into a concentrated solution of difluorobis(oxalato)phosphate containing tetrafluorooxalatophosphate.

[0054] According to the present disclosure, it is possible to provide a concentrated solution of difluorobis(oxalato)phosphate containing tetrafluorooxalatophosphate, which is unlikely to cause corrosion when brought into contact with stainless steel even when water is mixed in, a method for maintaining the same, and a container for storing the same.

[0055] Although the present disclosure has been described in detail and 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. This application is based on a Japanese patent application (Patent Application No. 2023-106167) filed on June 28, 2023, the contents of which are incorporated herein by reference.

Claims

1. A non-aqueous solvent solution comprising a non-aqueous solvent, a difluorobis(oxalato)phosphate, a tetrafluorooxalatophosphate, and a tris(oxalato)phosphate, wherein a concentration of the difluorobis(oxalato)phosphate in the non-aqueous solvent solution is 10 to 50 mass %, and a ratio of the difluorobis(oxalato)phosphate to the tris(oxalato)phosphate is 0.001 mole or more of the tris(oxalato)phosphate per mole of the difluorobis(oxalato)phosphate.

2. The nonaqueous solvent solution according to claim 1, wherein the ratio of said difluorobis(oxalato)phosphate to said tris(oxalato)phosphate is 0.03 moles or less of said tris(oxalato)phosphate per mole of said difluorobis(oxalato)phosphate.

3. The nonaqueous solvent solution according to claim 1 or 2, wherein the ratio of the difluorobis(oxalato)phosphate to the tetrafluorooxalatophosphate is 0.010 to 0.25 moles of the tetrafluorooxalatophosphate per 1 mole of the difluorobis(oxalato)phosphate.

4. The non-aqueous solvent solution according to claim 1 or 2, further comprising a difluorophosphate salt.

5. The nonaqueous solvent solution according to claim 4, wherein the ratio of said difluorobis(oxalato)phosphate to said difluorophosphate is 0.001 to 0.05 moles of said difluorophosphate per 1 mole of said difluorobis(oxalato)phosphate.

6. The non-aqueous solvent solution according to claim 1 or 2, wherein the non-aqueous solvent contains at least one of a cyclic ester and a chain ester.

7. The non-aqueous solvent solution according to claim 6, wherein the non-aqueous solvent contains the chain ester, and the content of the chain ester is 50 to 100% by volume relative to the total amount of the non-aqueous solvent.

8. The nonaqueous solvent solution according to claim 6, wherein the cyclic ester is at least one selected from the group consisting of ethylene carbonate, propylene carbonate, butylene carbonate, fluoroethylene carbonate, and γ-butyrolactone, and the chain ester is at least one selected from the group consisting of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl acetate, ethyl acetate, methyl propionate, and ethyl propionate.

9. The non-aqueous solvent solution of claim 1 or 2 in contact with stainless steel.

10. The non-aqueous solvent solution of claim 9, wherein the stainless steel is an austenitic stainless steel.

11. A method for holding a non-aqueous solvent solution in a state in which the non-aqueous solvent solution is in contact with a liquid contact member having at least a partial area made of stainless steel, the non-aqueous solvent solution comprising a non-aqueous solvent, difluorobis(oxalato)phosphate, tetrafluorooxalatophosphate, and tris(oxalato)phosphate, the concentration of the difluorobis(oxalato)phosphate in the non-aqueous solvent solution being 10 to 50 mass %, and the ratio of the difluorobis(oxalato)phosphate to the tris(oxalato)phosphate being 0.001 mole or more of the tris(oxalato)phosphate per mole of the difluorobis(oxalato)phosphate.

12. The method of claim 11, wherein the ratio of said difluorobis(oxalato)phosphate to said tris(oxalato)phosphate is 0.03 moles or less of said tris(oxalato)phosphate per mole of said difluorobis(oxalato)phosphate.

13. The method for retaining according to claim 11 or 12, wherein the ratio of the difluorobis(oxalato)phosphate to the tetrafluorooxalatophosphate is 0.010 to 0.25 moles of the tetrafluorooxalatophosphate per mole of the difluorobis(oxalato)phosphate.

14. The method of claim 11 or 12, further comprising a difluorophosphate salt.

15. The method of claim 14, wherein the ratio of the difluorobis(oxalato)phosphate to the difluorophosphate is 0.001 to 0.05 moles of the difluorophosphate per mole of the difluorobis(oxalato)phosphate.

16. The method of claim 11 or 12, wherein the non-aqueous solvent comprises at least one of a cyclic ester and a chain ester.

17. The method according to claim 16, wherein the non-aqueous solvent contains the chain ester, and the content of the chain ester is 50 to 100% by volume relative to the total amount of the non-aqueous solvent.

18. The method for retaining according to claim 16, wherein the cyclic ester is at least one selected from the group consisting of ethylene carbonate, propylene carbonate, butylene carbonate, fluoroethylene carbonate, and γ-butyrolactone, and the chain ester is at least one selected from the group consisting of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl acetate, ethyl acetate, methyl propionate, and ethyl propionate.

19. The method of claim 11 or 12, wherein the stainless steel is an austenitic stainless steel.

20. A holding method according to claim 11 or 12, wherein the liquid contact member is a liquid contact member in a container that contains the nonaqueous solvent solution, and the nonaqueous solvent solution is held within the container.

21. A storage vessel having a liquid contact member at least a portion of which is made of stainless steel, wherein a non-aqueous solvent solution is stored in the storage vessel in a state of contact with the liquid contact member, the non-aqueous solvent solution comprising a non-aqueous solvent, difluorobis(oxalato)phosphate, tetrafluorooxalatophosphate, and tris(oxalato)phosphate, wherein a concentration of the difluorobis(oxalato)phosphate in the non-aqueous solvent solution is 10 to 50 mass %, and a ratio of the difluorobis(oxalato)phosphate to the tris(oxalato)phosphate is 0.001 mol or more of the tris(oxalato)phosphate per 1 mol of the difluorobis(oxalato)phosphate.

22. The containment vessel of claim 21, wherein the stainless steel is an austenitic stainless steel.

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