MFSI mother liquor, preparation method therefor and use thereof

Abstract

An MFSI mother liquor, a preparation method therefor and a use thereof are provided. The MFSI mother liquor of the present application comprises MFSI, MFSO3, and a solvent, wherein based on the total weight of the mother liquor, the concentration of MFSI is in a range from 15 wt% to 30 wt%, the concentration of MFSO3 is in a range from 0.5 wt% to 10 wt%, and the concentration of the NH2SO3H is less than or equal to 20 ppm by weight; and wherein the MFSI is bis(fluorosulfonyl)imide salt, and M comprises at least one of K, Na, and Li.

Description

[0001] MFSI MOTHER LIQUOR, PREPARATION METHOD THEREFOR AND USE THEREOF

[0002] FIELD OF THE INVENTION

[0003] The present application relates to the technical field of electrolyte solution, and specifically relates to an MFSI mother liquor, a preparation method therefor and a use thereof.

[0004] BACKGROUND OF THE INVENTION

[0005] Bis(fluorosulfonyl)imide salt (abbreviated as MFSI, wherein M comprises at least one of K, Na, and Li) is often used as an electrolyte solution additive to increase the electric conductivity of the electrolyte solution and to improve the electrochemical performance such as cycling performance and rate capability of the secondary battery.

[0006] In the prior art, solid MFSI is usually used as a raw material to prepare electrolyte solution, however, the production efficiency of the electrolyte solution is relatively low.

[0007] SUMMARY OF THE INVENTION

[0008] The present application provides an MFSI mother liquor, a method for preparing the same, and uses thereof, in order to solve the problem of relatively low production efficiency of electrolyte solution, and the secondary batteries produced from the mother liquor of the present application have relatively high cycling performance and relatively high rate capability.

[0009] In a first aspect, the present application provides an MFSI mother liquor, comprising MFSI, MFSO3, and a solvent, wherein based on the total weight of the mother liquor, the concentration of MFSI is in a range from 15 wt% to 30 wt%, the concentration of MFSO3 is in a range from 0.5 wt% to 10 wt%, and the concentration of the NH2SO3H is less than or equal to 20 ppm by weight; and wherein MFSI is bis(fluorosulfonyl)imide salt, and M comprises at least one of K, Na, and Li.

[0010] In an optional embodiment, based on the total weight of the mother liquor, the concentration of MFSO3 is in a range from 1.5 wt% to 4.5 wt%.

[0011] In an optional embodiment, the mother liquor further comprises a stabilizer; and the concentration of the stabilizer in the MFSI mother liquor is less than or equal to 300 ppm by weight; optionally, the stabilizer is selected from the group consisting of triphenyl phosphite, N,N-dicyclohexylcarbodiimide, and hexamethyldisilazane.

[0012] In an optional embodiment, the solvent is a carbonate; optionally, the carbonate comprises at least one of dimethyl carbonate, diethyl carbonate and ethyl methyl carbonate.

[0013] In a second aspect, the present application provides a method for preparing the MFSI mother liquor, comprising the following steps:

[0014] 51, mixing an alkali metal compound, HFSI, FSO2CI and a solvent, carrying out a reaction, and filtering to obtain a filtrate, wherein HFSI is bis(fluorosulfonyl)imide;

[0015] 52, adding a first dehydrating agent into the filtrate to carry out a first step of dehydration, so that the water content in the filtrate after the first step of dehydration is greater than 0 and less than or equal to 1,000 ppm by weight;

[0016] 53, adding an excess of a second dehydrating agent into the filtrate after the first step of dehydration to carry out a second step of dehydration, and filtering to obtain a MFSI crude mother liquor; and

[0017] 54, subjecting the MFSI crude mother liquor to vacuum gas stripping for deacidification, and then replenishing the solvent until the concentration of MFSI is in a range from 15 wt% to 30 wt% to obtain the MFSI mother liquor.

[0018] In an optional embodiment, in S4, after replenishing the solvent until the concentration of MFSI is in a range from 15 wt% to 30 wt%, the method further comprises adding a stabilizer; and the stabilizer is selected from the group consisting of triphenyl phosphite, N,N-dicyclohexylcarbodiimide, and hexamethyldisilazane.

[0019] In an optional embodiment, the first dehydrating agent comprises sulfoxide chloride and / or oxalyl chloride; and / or the second dehydrating agent comprises one or more of anhydrous sulfate salt, molecular sieves and phosphorus pentoxide.

[0020] In an optional embodiment, SI satisfies at least one of the following conditions:

[0021] (1) the alkali metal compound comprises one or more of lithium carbonate, anhydrous lithium hydroxide, potassium carbonate, anhydrous potassium hydroxide, sodium carbonate and anhydrous sodium hydroxide;

[0022] (2) a molar ratio of alkali metal element in the alkali metal compound to HFSI is (1.3-3): 1;

[0023] (3) a weight ratio of HFSI to FSO2CI is (70-98): (2-30); optionally, (85-95): (5-15); and

[0024] (4) the reaction is carried out at a temperature ranging from -10°C to 5°C for a time period ranging from Ih to 3h; optionally, the reaction is carried out at a temperature ranging from -5°C to 0°C.

[0025] In an optional embodiment, SI comprises:

[0026] 5 101 , mixing an alkali metal compound with a solvent to make a turbid liquid;

[0027] 5102, adding a mixed solution of HFSI and FSO2CI dropwise into the turbid liquid, and carrying out the reaction after completion of the dropwise addition; and

[0028] SI 03, filtering to obtain a filtrate after completion of the reaction.

[0029] In an optional embodiment, S3 satisfies at least one of the following conditions:

[0030] (1) the vacuum gas stripping for deacidification is carried out at a temperature ranging from 50°C to 100°C;

[0031] (2) the vacuum gas stripping for deacidification is carried out at a vacuum degree ranging from 0.095 MPa to 0.098 MPa; and

[0032] (3) the vacuum gas stripping for deacidification is gas stripping for gradient deacidification; optionally, the gas stripping for gradient deacidification comprises performing a first gas stripping for deacidification at a temperature ranging from 50°C to 70°C for a time period ranging from 30 min to 60 min, and then performing a second gas stripping for deacidification at a temperature ranging from 70 °C to 100°C for a time period ranging from Ih to 2h; and

[0033] (4) carrying out vacuum gas stripping for deacidification to the MF SI crude mother liquor, and concentrating to make the weight of the MF SI crude mother liquor to be 30wt% to 60% of the original weight of the MF SI crude mother liquor.

[0034] In a third aspect, the present application provides an electrolyte solution, comprising the MF SI mother liquor described above or the MF SI mother liquor prepared by the method described above.

[0035] In an optional embodiment, in the electrolyte solution, the concentration of MFSI is in a range from 0.5 wt% to 6 wt%, and the concentration of MFSO3 is in a range from 300 ppm to 8,000 ppm by weight.

[0036] In a fourth aspect, the present application provides a secondary battery, comprising the electrolyte solution described above.

[0037] In a fifth aspect, the present application provides a powered device, comprising the secondary battery described above.

[0038] The technical solution of the present application has the following advantages.

[0039] The present application provides an MFSI mother liquor, comprising MFSI, MFSO3, and a solvent, wherein based on the total weight of the MFSI mother liquor, the concentration of MFSI is in a range from 15 wt% to 30 wt%, the concentration of MFSO3 is in a range from 0.5 wt% to 10 wt%, and the concentration of the NH2SO3H is less than or equal to 20 ppm by weight; and wherein MFSI is bis(fluorosulfonyl)imide salt, and M comprises at least one of K, Na, and Li. The MFSI mother liquor of the present application is directly applied as liquid feed to the production of electrolyte solution, which greatly improves the automation and production efficiency of electrolyte solution production, and thus the manufacturing cost of electrolyte solution can be substantially reduced. Moreover, the content of MFSO3 and NH2SO3H is controlled within the scope of the present application, and the secondary battery produced has excellent cycling performance and rate capability.

[0040] DETAILED DESCRIPTION OF THE INVENTION Reference will be made clearly and completely to the technical solutions in the embodiments of the present application. The embodiments described here are only part of the embodiments of the present application and are not all embodiments of the present application. Based on the embodiments of the present application, other embodiments obtained by those skilled in the art without creative work are within the scope of the present application.

[0041] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which the present application belongs. The terms used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the present application. The terms “includes” and “comprises” and any variation thereof in the description and claims of the present application are intended to indicate a non-exclusive inclusion.

[0042] In the description of the embodiments of the present application, the technical terms “first”, “second” and the like are only used for distinction between different objects and are not to be understood as indicating or implying relative importance or implicitly indicating a number, a particular order or a primary or secondary relationship of the technical features. In the description of the embodiments of the present application, “a plurality of’ means two or more, unless specified otherwise.

[0043] Reference to an “embodiment” herein means that a feature, structure or characteristic described in connection with the embodiment may be comprised in at least one embodiment of the present application. The “embodiment” in various places in the specification does not necessarily mean the same embodiment, nor is it an independent or alternative embodiment mutually exclusive with other embodiments. One skilled in the art explicitly and implicitly understands that an embodiment described herein may be combined with other embodiments.

[0044] Term “range” disclosed in the present application is defined in the form of a lower limit and an upper limit, a given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of a special range. The range defined in this way can be inclusive or exclusive, and can be arbitrarily combined, that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is understood that ranges of 60-110 and 80-120 are also obtained. In addition, if the listed minimum values are 1 and 2, and if the listed maximum values are 3, 4 and 5, the ranges of 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5 may be obtained. In the present application, unless otherwise specified, the numerical range “a-b” means the abbreviated representation of any combination of real numbers between a and b, where a and b are both real numbers. For example, the numerical range “0-5” means that all the real numbers between “0-5” have been listed, and “0-5” is only the abbreviated representation of these numerical combinations. In addition, when a parameter is an integer >2, it is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0045] In the description of the present application, the term “and / or”, which describes an associated relationship of associated objects, means that there may be three relationships, for example, A and / or B, which may mean that A exists alone, A and B exist at the same time, and B exists alone. A character “ / ” generally indicates that contextual objects are in an “or” relationship.

[0046] In the description of the present application, the term “a plurality of’ refers to two or more (including two), and similarly, “a plurality of groups” refers to two or more (including two) groups, and “a plurality of pieces” refers to two or more (including two) pieces.

[0047] In the description of the present application, it is to be understood that, terms such as “center”, “longitudinal”, “lateral”, “length”, “width”, “thickness”, “over”, “below”, “front”, “back”, “left”, “right”, “vertical”, “horizontal”, “top”, “bottom”, “in”, “out”, “clockwise”, “anti -clockwise”, “axial”, “radial” and “circumference” refer to the directions and location relations which are for describing the present application and for describing in simple, and which are not intended to indicate or imply that the device or the elements are disposed to locate at the specific directions or are structured and performed in the specific directions, which could not to be understood to the limitation of the present application.

[0048] In the present application, unless specified or limited otherwise, the terms “mounted,” “connected,” “coupled” and “fixed” are understood broadly, such as fixed, detachable mountings, connections and couplings or integrated, and can be mechanical or electrical mountings, connections and couplings, and also can be direct and via media indirect mountings, connections, and couplings, and further can be inner mountings, connections and couplings of two components or interaction relations between two components, which can be understood by those skilled in the art according to the detail embodiment of the present application.

[0049] When solid MFSI is used as a raw material to prepare electrolyte solution, the production efficiency of the electrolyte solution is relatively low.

[0050] In order to solve the above problems in the related art, in a first aspect, the present application provides an MFSI mother liquor, comprising MFSI, MFSO3, and a solvent, wherein based on the total weight of the mother liquor, the concentration of MFSI is in a range from 15 wt% to 30 wt%, the concentration of MFSO3 is in a range from 0.5 wt% to 10 wt%, and the concentration of the NH2SO3H is less than or equal to 20 ppm by weight; and wherein MFSI is bis(fluorosulfonyl)imide salt, and M comprises at least one of K, Na, and Li.

[0051] The MFSI mother liquor of the present application is directly applied as liquid feed to the production of electrolyte solution, which greatly improves the automation and production efficiency of electrolyte solution production, and thus the manufacturing cost of electrolyte solution can be substantially reduced. Moreover, the content of MFSO3 and NH2SO3H is controlled within the scope of the present application, and the secondary battery produced has excellent cycling performance and rate capability.

[0052] In the MFSI mother liquor, the concentration of MFSI is in a range from 15 wt% to 30 wt%. Within this range, it is possible to avoid inconvenience in use due to a too high concentration and a relatively high viscosity of the mother liquor, while avoiding limitations on the electrolyte solution that can be prepared due to a too low concentration. For example, the concentration of MFSI may be 15 wt%, 16 wt%, 17 wt%, 18 wt%, 19 wt%, 20 wt%, 21 wt%, 22 wt%, 25 wt%, or 30 wt%. For example, the concentration of MFSO3 may be 0.5 wt%, 1 wt%, 3 wt%, 5 wt%, 7 wt%, 9 wt%, or 10 wt%.

[0053] In an optional embodiment, the concentration of MFSO3 in the MFSI mother liquor is in a range from 1.5 wt% to 4.5 wt%.

[0054] In an optional embodiment, the MFSI mother liquor further comprises a stabilizer; and the concentration of the stabilizer in the MFSI mother liquor is less than or equal to 300 ppm by weight. The addition of a stabilizer can prolong the storage time of mother liquor and delay the occurrence of deterioration. For example, the concentration of the stabilizer may be 100 ppm, 200 ppm, or 300 ppm by weight.

[0055] In an optional embodiment, the stabilizer is selected from the group consisting of triphenyl phosphite, N,N-dicyclohexylcarbodiimide, and hexamethyldisilazane (HMDS).

[0056] In an optional embodiment, the solvent is a carbonate; optionally, the carbonate comprises at least one of dimethyl carbonate, diethyl carbonate and ethyl methyl carbonate.

[0057] In a second aspect, the present application provides a method for preparing the MFSI mother liquor, comprising the following steps:

[0058] 51, mixing an alkali metal compound, HFSI, FSO2CI and a solvent, carrying out a reaction, and filtering to obtain a filtrate, wherein HFSI is bis(fluorosulfonyl)imide;

[0059] 52, adding a first dehydrating agent into the filtrate to carry out a first step of dehydration, so that the water content in the filtrate after the first step of dehydration is greater than 0 and less than or equal to 1,000 ppm by weight;

[0060] 53, adding an excess of a second dehydrating agent into the filtrate after the first step of dehydration to carry out a second step of dehydration, and filtering to obtain a MFSI crude mother liquor; and

[0061] 54, subjecting the MFSI crude mother liquor to vacuum gas stripping for deacidification, and then replenishing the solvent until the concentration of MFSI is in a range from 15 wt% to 30 wt% to obtain the MFSI mother liquor.

[0062] When preparing solid MFSI in the prior art, MFSO3 is usually required to be strictly controlled as an impurity, and crystallization is required to obtain solid MFSI, which largely reduces the production efficiency and yield of MFSI and greatly increases the production cost. When MFSO3 is prepared by existing methods, it needs to be purified by crystallization. However, MFSO3 is easy to complex with ester solvents to obtain the corresponding complex product, and the complex is difficult to separate, or in the high temperature separation process, it is very easy to lead to the decomposition and deterioration of MFSO3, and the storage time becomes shorter, and thus the solid MFSO3 is also more difficult to obtain, and it is difficult to be widely used as the electrolyte solution additive of the secondary battery.

[0063] In the method for preparing the MFSI mother liquor of the present application, there is no need to crystallize MFSI, which greatly improves the production efficiency and yield, so that the raw material cost of MFSI is substantially reduced; at the same time, it solves the problem that MFSO3 is unstable at high temperatures, and is difficult to dry and crystallize at high temperatures, and is difficult to be applied and popularized in electrolyte solutions.

[0064] There is water generation in the salt formation process from HFSI, which makes FSO2CI hydrolyze and react with alkali metal compounds to generate LiFSCh, and reduces the overall saturated vapor pressure, and improves the safety.

[0065] FSO2CI reacts with a trace amount of water to produce fluorosulfonic acid, which then forms salt with lithium carbonate. The total reaction formula is as follows:

[0066] 2HFSI+FSO2Cl+2Li2CO3^2LiFSI+LiFSO3+2CO2+LiCl+H2O

[0067] Hydrolysis of HFSI produces NH2SO3H impurities, FSO2CI can reduce the hydrolysis of HFSI due to its faster reaction with water, and the sensitivity to water is reduced after the final salts MFSI and LiFSCh are formed, which reduces the content of NH2SO3H impurities in the mother liquor and improves the electrical performance of the secondary battery.

[0068] In an optional embodiment, in S4, after replenishing the solvent until the concentration of MFSI is in a range from 15 wt% to 30 wt%, the method further comprises adding a stabilizer.

[0069] In an optional embodiment, the first dehydrating agent comprises sulfoxide chloride and / or oxalyl chloride; and / or the second dehydrating agent comprises one or more of anhydrous sulfate salt, molecular sieves and phosphorus pentoxide. Anhydrous sulfate salt may be anhydrous magnesium sulfate.

[0070] In the method for preparing the MF SI mother liquor of the present application, two-step dehydration is used, the first dehydrating agent is selected as a compound that can be dehydrated quickly, and the second dehydrating agent is selected as a dehydrating agent that does not introduce impurity ions or organic matter. By adding not excessive amounts of the first dehydrating agent, the rapid reduction of water is realized, and the decomposition of the product caused by prolonged dehydration is avoided, and not excessive amounts of the first dehydrating agent does not introduce impurity ions. The second dehydrating agent does not introduce impurities and is easy to remove.

[0071] In an optional embodiment, SI satisfies at least one of the following conditions:

[0072] (1) the alkali metal compound comprises one or more of lithium carbonate, anhydrous lithium hydroxide, potassium carbonate, anhydrous potassium hydroxide, sodium carbonate and anhydrous sodium hydroxide;

[0073] (2) a molar ratio of alkali metal element in the alkali metal compound to HFSI is (I.3-3):l; for example, 1.3: 1, 1.5: 1, 2: 1, 2.5: 1 or 3:1;

[0074] (3) a weight ratio of HFSI to FSO2CI is (70-98): (2-30); optionally, (85-95): (5-15); for example, 70: 30, 80: 20, 90: 10 or 98: 2; and

[0075] (4) the reaction is carried out at a temperature ranging from -10°C to 5°C for a time period ranging from Ih to 3h; optionally, the reaction is carried out at a temperature ranging from -5°C to 0°C.

[0076] In an optional embodiment, SI comprises:

[0077] 5101 , mixing an alkali metal compound with a solvent to make a turbid liquid;

[0078] 5102, adding a mixed solution of HFSI and FSO2CI dropwise into the turbid liquid, and carrying out the reaction after completion of the dropwise addition; and

[0079] SI 03, filtering to obtain a filtrate after completion of the reaction.

[0080] A mixed solution of HFSI and FSO2CI is used; FSO2CI alone has poor stability and will remain stable in HF SI.

[0081] In S102, a mixed solution of HFSI and FSO2CI is added dropwise at a temperature ranging from -10°C to 5°C.

[0082] In an optional embodiment, S3 satisfies at least one of the following conditions:

[0083] (1) the vacuum gas stripping for deacidification is carried out at a temperature ranging from 50°C to 100°C; for example, 50°C, 60°C, 70°C, 80°C, 90°C or 100°C;

[0084] (2) the vacuum gas stripping for deacidification is carried out at a vacuum degree ranging from 0.095 MPa to 0.098 MPa; for example, 0.095 MPa, 0.096 MPa, 0.097 MPa, or 0.098 MPa; and

[0085] (3) the vacuum gas stripping for deacidification is gas stripping for gradient deacidification; optionally, the gas stripping for gradient deacidification comprises performing a first gas stripping for deacidification at a temperature ranging from 50°C to 70°C for a time period ranging from 30 min to 60min, and then performing a second gas stripping for deacidification at a temperature ranging from 70 °C to 100°C for a time period ranging from Ih to 2h; the use of gas stripping for gradient deacidification can avoid bumping due to low salt concentration, low boiling point, too high temperature and vacuum degree at the initial stage; elevating the temperature at the later stage can improve the effect of impurity removal; and

[0086] (4) carrying out vacuum gas stripping for deacidification to the MF SI crude mother liquor, and concentrating to make the weight of the MF SI crude mother liquor to be 30wt% to 60 wt% (for example, 30 wt%, 40 wt%, 50 wt%, or 60 wt%) of the original weight of the MFSI crude mother liquor; vacuum gas stripping for deacidification within this range can minimize the residual low boiling point impurities as much as possible.

[0087] In a third aspect, the present application provides an electrolyte solution, comprising the described MFSI mother liquor or the MFSI mother liquor prepared by the described method. In an optional embodiment, in the electrolyte solution, the concentration of MFSI is in a range from 0.5 wt% to 6 wt%, and the concentration of MFSO3 is in a range from 300 ppm to 8,000 ppm by weight. For example, the concentration of MFSI in the electrolyte solution may be 0.5 wt%, 1 wt%, 2 wt%, 3 wt%, 4 wt%, 5 wt%, or 6 wt%. For example, the concentration of MFSO3 in the electrolyte solution may be 300 ppm, 500 ppm, 1,000 ppm, 2,000 ppm, 3,000 ppm, 4,000 ppm, 5,000 ppm, 6,000 ppm, 7,000 ppm or 8,000 ppm by weight.

[0088] In a fourth aspect, the present application provides a secondary battery, comprising the described electrolyte solution.

[0089] The secondary battery further comprises a positive electrode plate, a negative electrode plate and a separator. The following is a description of the secondary battery.

[0090] [Positive electrode plate]

[0091] The positive electrode plate comprises a positive electrode current collector and a cathode active material layer disposed on at least one surface of the positive electrode current collector.

[0092] As an example, the positive electrode current collector has two surfaces along a thickness direction thereof and facing in opposite directions, and the positive electrode material layer is provided on either or both of the two surfaces.

[0093] The cathode active material layer comprises the cathode active material.

[0094] The cathode active material may be selected from materials capable of absorbing and releasing lithium.

[0095] The specific kind of the cathode active material is not particularly limited and may be selected according to requirements. As an example, the cathode active material may comprise, but is not limited to, lithium iron phosphate (LiFePC ), lithium manganese phosphate (LiMnPC ), lithium cobalt phosphate (LiCoPC ), iron pyrophosphate (Li2FeP2O?), lithium cobaltate (LiCoCh), spinel -type lithium manganate (LiM C ), spinel-type lithium nickel manganate (LiNio.5Mn1.5O4), layered lithium manganate (LiMnCh), lithium nickelate (LiNiCh), lithium niobate (LiNbCh), lithium ferrite (LiFeCh), lithium magnesium oxide (LiMgCh), lithium calcium oxide (LiCaCh), lithium cuprate (LiCuCh), lithium zincate (LiZnCh), lithium molybdate (LiMoCh), lithium tantalate (LiTaCh), lithium tungstate (LiWCh), lithium nickel cobalt aluminum oxide (LiNixCoyAh-x-yCh, 0<x<l, 0<y<l, 0 <x + y<l, e.g. LiNio.8Coo.15Alo.05O2), lithium nickel cobalt manganese oxides (LiNixCoyMni-x-yO2, 0<x<l, 0<y<l, 0<x + y<l, e.g., LiNii / 3Coi / 3Mni / 3O2, liNio.5Coo.2Mno.3O2, liNio.6Coo.2Mno.2O2, liNio.8Coo.1Mno.1O2, etc.), lithium-rich materials (e.g. lithium-rich nickel cobalt manganese oxides), manganese oxides (Mn02), vanadium oxides, sulfur oxides, silicate oxides, and at least one of its respective modified compounds. These materials may be used separately or in combination (for example two or more kinds of materials are used).

[0096] The cathode active material is a compound capable of reversibly intercalating and deintercalating Na+. As an example, the cathode active material comprises transition metal oxides, polyanionic compounds, Prussian blue (PB) and its analogues (PBAs), and the like.

[0097] In some embodiments, the cathode active material is a transition metal oxide, for example, a sodium-containing composite oxide represented by NaxMCL or NayM2O4 (where M is a transition metal, 0 < x < l, 0 < y < 2), a spinel -like oxide, and a metal chalcogenide of a layered structure or an olivine structure. For example, the cathode active material is selected from sodium cobalt oxide such as NaCoCh, sodium manganese oxide such as NaM CU, sodium nickel oxide such as NaNiCh, sodium titanium oxide such as Na4 / 3Ti5 / 3O4, sodium manganese nickel composite oxide and sodium manganese nickel cobalt composite oxide; a material having an olivine-type crystalline structure such as NaMPCU (M = Fe, Mn, Ni).

[0098] In some embodiments, the cathode active material is optionally a sodium-containing composite oxide of a layered structure or a spinel structure, for example, sodium-manganese-nickel composite oxides represented by NaCoCh, NaM CU, NaNiCh, NaNii / 2Mni / 2O2; sodium-manganese-nickel-cobalt composite oxides represented by NaNii / 3Mni / 3Coi / 3O2, NaNio.6Mno.2Coo.2O2; or sodium-containing composite oxides such as NaNii-x-y-zCoxAlyMgzO2 (where 0 < x < 1, 0 < y < 0.1, 0 < z < 0.1, 0 < 1-x-y-z < 1) or NazMxMnyFei-x-yO2 (M=Ni, Cu, Co, etc., 0<z<1.2, 0<x, y<l, 0<x+y<l ) . In addition, a part of the constituent elements of the above sodium-containing composite oxides as well as the sodium-containing composite oxides that may be substituted with an additional element such as Ge, Ti, Zr, Mg, Al, Mo, Sn and the like are also comprised in the scope of the present application.

[0099] In some embodiments, the cathode active material is a polyanionic compound. As an example, the polyanionic compound may be a class of compounds having sodium ions, transition metal ions, and tetrahedral (YC )11’ anionic units. The transition metal may comprise at least one selected from Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr and Ce. Y may be at least one selected from P, S and Si, and n in a group of (YC )11’ represents a valence of the group. The polyanionic compound may be a class of compounds having sodium ions, transition metal ions, tetrahedral (YC )11’ anion units, and halide anions. The transition metal may comprise at least one selected from Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr and Ce. Y may be at least one selected from P, S and Si, n in a group of (YC )11’ represents a valence of the group, and halogen may comprise at least one selected from F, Cl, and Br. The polyanionic compounds may be a class of compounds having sodium ions, tetrahedral (YC )11’ anionic units, polyhedral units (ZOy)m+and optionally halide anions. Y may be at least one selected from P, S and Si, n in a group of (YCh)"' represents a valence of the group, Z represents a transition metal, which may be at least one selected from Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr and Ce, m in a group of (ZOy)m+represents a valence of the group, and halogen may comprise at least one selected from F, Cl, and Br. The polyanionic compound is, for example, at least one of NaFePC , Na3V2(PO4)3, NaM’PC F (M’ is at least one selected from V, Fe, Mn and Ni) or Na3(VOy)2(PO4)2F3-2y(0 < y < 1).

[0100] In some embodiments, the cathode active material is a Prussian blue (PB) and its analogues (PBAs). As an example, Prussian blue (PB) and its analogues (PBAs) may be a class of compounds having a sodium ion, a transition metal ion, and a cyanide ion (CN‘). The transition metal may comprise at least one selected from Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr and Ce. Prussian blue (PB) and its analogues (PBAs) are for example NaaMebMe’c(CN)6, where Me and Me’ each independently comprise at least one selected from Ni, Cu, Fe, Mn, Co and Zn, where 0 <a < 2, 0 <b <1, and 0 <c <1.

[0101] The above cathode active material may be modified, for example is doped, surface coated, or both doped and coated with a modification compound.

[0102] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. For example, as the metal foil, an aluminum foil may be used. The composite current collector may comprise a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by forming a metallic material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, silver alloy, etc.) on a polymer material substrate such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.

[0103] In some embodiments, the cathode active material layer optionally comprises a binder. As an example, the binder may comprise at least one selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluori de-hexafluor opropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylate resin.

[0104] In some embodiments, the cathode active material layer comprises 0.1 to 3.5%, optionally 0.5 to 2.5% by weight, of the binder.

[0105] In some embodiments, the cathode active material layer optionally comprises a conductive agent. As an example, the conductive agent may comprise at least one selected from superconducting carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0106] In some embodiments, the cathode active material layer comprises 0.05% to 5%, optionally 0.5% to 3% by weight, of the conductive agent.

[0107] In some embodiments, the positive electrode plate may be prepared by: dispersing the above-mentioned components for preparing the positive electrode plate, such as the cathode active material, the conductive agent, the binder and any other components in a solvent (such as N-methyl pyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry on the positive electrode current collector, and obtaining the positive electrode plate after drying, cold pressing and other processes.

[0108] [Negative electrode plate]

[0109] The negative electrode plate comprises a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector. The negative electrode film layer comprises an anode active material.

[0110] As an example, the negative electrode current collector has two surfaces along a thickness direction thereof and facing in opposite directions, and the negative electrode film layer is provided on either or both of the two surfaces.

[0111] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, as the metal foil, a copper foil may be used. The composite current collector may comprise a polymeric material substrate and a metal layer formed on at least one surface of the polymeric material substrate. The composite current collector may be formed by forming a metallic material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, silver alloy, etc.) on a polymer material substrate such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.

[0112] In the lithium battery system, in some embodiments, the anode active material may be an anode active material known in the art. As an example, the anode active material may comprise at least one selected from artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials and lithium titanate. The silicon-based material may be at least one selected from elemental silicon, silicon-oxygen compounds, silicon-carbon complexes, silicon-nitrogen complexes, and silicon alloys. The tin-based material may be at least one selected from elemental tin, tin oxide compounds, and tin alloys. The present application is not limited to these materials, and other materials that may be used as an anode active material for a battery may be used. These anode active materials may be used separately or in combination (for example two or more kinds of materials are used).

[0113] In the sodium battery system, specific type of the anode active material is not limited, and an active material known in the art which can be used for a negative electrode of a sodium ion battery can be used, and those skilled in the art can make a selection according to actual requirements. As an example, the anode active material may comprise, but is not limited to, one or more of a sodium metal, a carbon material, an alloy material, a transition metal oxide and / or sulfide, a phosphorus-based material, a titanate material. Specifically, the carbon material may comprise one or more of hard carbon, soft carbon, amorphous carbon, nano-structured carbon materials; the alloy material may comprise an alloy material formed by one or more of Si, Ge, Sn, Pb and Sb; the transition metal oxides and sulfides have a general formula MxNy, where M comprises one or more of Fe, Co, Ni, Mn, Sn, Mo, Sb and V, and N comprises O or S; the phosphorus-based material may comprise one or more of red phosphorus, white phosphorus and black phosphorus; the titanate material may comprise one or more of NaiThO?, Na2TieOi3, Na^isOn, Li^isOn and NaTiiCPOfh. These materials are commercially available.

[0114] In some embodiments, the negative electrode film layer optionally comprises a binder. The binder may be at least one selected from styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA) and carboxymethyl chitosan (CMCS).

[0115] In some embodiments, the negative electrode film layer optionally comprises a conductive agent. The conductive agent may be at least one selected from superconducting carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0116] In some embodiments, the negative electrode film layer optionally comprises other adjuvants, such as thickeners (e.g. sodium carboxymethylcellulose (CMC -Na)).

[0117] In some embodiments, the negative electrode plate may be prepared by: dispersing the above-mentioned components for preparing the negative electrode plate, such as the anode active material, the conductive agent, the binder and any other components in a solvent (such as deionized water) to form a negative electrode slurry; coating the negative electrode slurry on the negative electrode current collector, and obtaining the negative electrode plate after drying, cold pressing and other processes.

[0118] [Electrolyte]

[0119] The electrolyte serves to conduct ions between the positive electrode plate and the negative electrode plate. The kind of the electrolyte is not particularly limited in the present application, and may be selected according to requirements. For example, the electrolyte may be liquid, gel, or solid.

[0120] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte comprises an electrolyte salt and a solvent.

[0121] In some embodiments, the electrolyte lithium salt may comprise at least one selected from lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bisfluorosulfonimide, lithium bi s-trifluorom ethane sulfonimide, lithium triflate, lithium difluorophosphate, lithium difluorooxalato borate, lithium dioxalato borate, lithium difluorooxalato phosphate, and lithium tetrafluorooxalato phosphate.

[0122] In some embodiments, the electrolyte sodium salt comprises at least one selected from sodium hexafluorophosphate, sodium difluorooxalate borate, sodium tetrafluorob orate, sodium bisoxalate borate, sodium perchlorate, sodium hexafluoroarsenate, sodium bis(fluorosulfonyl) imide, sodium trifluoromethyl sulfonate, and sodium bi s(trifluorom ethyl sulfonyl) imide.

[0123] In some embodiments, the solvent may comprise one or more selected from ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethylene propylene carbonate (EPC), butylene carbonate (BC), fluorinated ethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4- butyrolactone (GBL), sulfolane (SF), methyl sulfone (MSM), ethylene glycol dimethyl ether (DME), diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, polyethylene glycol dimethyl ether, diethyl ether, ethylene glycol diethyl ether, ethylene glycol dibutyl ether, diethylene glycol diethyl ether, diethylene glycol dibutyl ether, tetrahydrofuran, methyl tetrahydrofuran, 1,3-dioxopentylene, 1,3-dioxane, 1,4-dioxane, tetrahydropyran, methyl sulfone (EMS) and diethyl sulfone (ESE).

[0124] In some embodiments, the electrolyte solution further comprises an additive. For example, the additive may comprise a negative electrode film-forming additive, a positive electrode film-forming additive, and an additive capable of improving properties of the battery, such as an additive for improving overcharge properties of the battery, an additive for improving high-temperature properties of the battery, and an additive for improving low-temperature properties of the battery.

[0125] [Separator]

[0126] In some embodiments, the separator is further comprised in the secondary battery. The type of the separator is not particularly limited in the present application, and any known separator having a porous structure and good chemical and mechanical stability may be used.

[0127] In some embodiments, the material of the separator may be at least one selected from glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator may be a single-layer film or a multi-layer composite film, which is not limited in the present application. In a case where the separator is a multilayer composite film, the materials of individual layers may be the same or different.

[0128] In some embodiments, the positive electrode plate, the negative electrode plate, and the separator of a secondary battery may be prepared into an electrode assembly by a winding process or a lamination process.

[0129] In some embodiments, a secondary battery may comprise an outer package. The outer package may be used to encapsulate the electrode assembly and the electrolyte. In some embodiments, the outer package of the secondary battery may be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell and the like. Alternatively, the outer package of the secondary battery may be a soft package, such as a soft bag. The soft bag may be made of a polymer material such as plastics, polypropylene, polybutylene terephthalate and polybutylene succinate.

[0130] The shape of the secondary battery may be cylindrical, square or any other shape, which is not limited in the present application.

[0131] In some embodiments, the secondary batteries may be assembled into a battery module, and the number of secondary batteries contained in the battery module may be one or more, the specific number being selectable by a person skilled in the art based on the application and capacity of the battery module.

[0132] In some embodiments, the above battery module can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, and the specific number can be selected by the person skilled in the art according to the application and capacity of the battery pack.

[0133] In a fifth aspect, the present application provides a powered device, comprising the secondary battery described in the above.

[0134] In some embodiments, the above powered device may also comprise a battery module or a battery pack obtained by assembling the secondary battery. The secondary battery, battery module, or battery pack may be used as a power source for the powered device or as an energy storage unit for the powered device. The powered device may comprise, but is not limited to, mobile devices (e.g., cell phones, laptop computers, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, and the like.

[0135] As the powered device, a secondary battery, a battery module or a battery pack can be selected according to the needs of its use. As an example, for a powered device that is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc., a battery pack or a battery module may be used to meet the demand for high power and high energy density of the secondary battery of the powered device.

[0136] As another example, the powered device may be a cell phone, a tablet computer, a laptop computer, and the like. This device usually requires thinness and lightness, and a secondary battery may be used as the power source.

[0137] The present application is described in further detail below in connection with specific examples, which are not to be construed as limiting the scope of the protection claimed in the present application.

[0138] Example 1

[0139] The present example provided a method for preparing an MF SI mother liquor, comprising the following steps:

[0140] 51, 0.35 mol of Li2CO3was added into a three-necked flask containing 500 ml of ethyl methyl carbonate (EMC), the materials were stirred to make a turbid liquid, and the turbid liquid was cooled for 1 h in a cold bath at -10°C.

[0141] 95 g of a mixed solution of HF SI and FSO2CI (in which the content of FSO2CI was 5.5 wt% and the content of HF SI was 94.5 wt%) was taken, and the temperature of the mixed solution was kept at -10°C to 5°C and added dropwise into the turbid liquid for an addition time of 30 min to 60 min. After the dropwise addition was completed, the reaction was carried out for 2 h, and the temperature of the reaction was controlled at -10°C to 5°C. After the reaction was completed, the reaction solution was filtered to remove the unreacted lithium salt and the newly generated lithium chloride, and obtain a filtrate.

[0142] 52, the water content in the filtrate was measured to be 1.5 wt% using the volumetric method (based on SJ / T 11723-2018 4.4, “Electrolyte solution used for lithium ion battery”), and 59 g of sulfoxide chloride was added, and the reaction was carried out by stirring for 8 h.

[0143] 53, 20 g of anhydrous magnesium sulfate was added into the solution obtained from S2, and the reaction was carried out by stirring overnight. After the reaction was completed, the reaction solution was filtered to obtain a MFSI crude mother liquor, i.e., a LiFSI crude mother liquor.

[0144] S4, the MFSI crude mother liquor was subjected to vacuum gas stripping for gradient deacidification, in which the vacuum degree during the gas stripping was maintained at 0.095 MPa to 0.098 MPa, a first gas stripping for deacidification was carried out at a gas stripping temperature of 50 °C for 60 min, then a second gas stripping for deacidification was carried out at 100 °C for 2 h. Then, LiFSI and LiFSCh were quantified by using ion chromatography, and the solvent EMC was replenished until the concentration of MFSI was 30 wt%. Then 300 ppm by weight of triphenyl phosphite was added to obtain the MFSI mother liquor. The content of LiFSCf in the MFSI mother liquor was about 1.5 wt%. The concentration of NH2SO3H was 13 ppm by weight.

[0145] The present example also provided an electrolyte solution that was formulated using the MFSI mother liquor prepared in the present example. In the electrolyte solution of the present example, based on the total weight of the electrolyte solution, the content of LiFSI was 2 wt%, the content of LiFSCf was 1,000 ppm by weight, and the balance was ethylene carbonate, diethyl carbonate, ethyl methyl carbonate (EMC), and lithium hexafluorophosphate, with the weight ratio of ethylene carbonate, diethyl carbonate, ethyl methyl carbonate (EMC), and lithium hexafluorophosphate being 30: 20: 35: 13.

[0146] Example 2

[0147] The present example provided a method for preparing an MFSI mother liquor, which was essentially the same as Example 1, with the difference that the content of FSO2CI in the mixed solution of HFSI and FSO2CI of this example was 15 wt%. In the LiFSI mother liquor produced, the concentration of LiFSCf was about 4.5 wt%, and the concentration of NH2SO3H of 7 ppm by weight.

[0148] The present example also provided an electrolyte solution, which was essentially the same as Example 1, with the difference that in the electrolyte solution of the example, the content of LiFSI was 2 wt%, and the content of LiFSCf was about 3,000 ppm by weight.

[0149] Example 3 The present example provided a method for preparing an MF SI mother liquor, which was essentially the same as Example 1, with the difference that the content of FSO2CI in the mixed solution of HFSI and FSO2CI of this example was 25 wt%. In the LiFSI mother liquor produced, the concentration of LiFSCh was about 8.25 wt%, and the concentration of NH2SO3H was 8 ppm by weight.

[0150] The present example also provided an electrolyte solution, which was essentially the same as Example 1, with the difference that in the electrolyte solution of this example, the content of LiFSI was 2 wt%, and the content of LiFSCF was about 5,500 ppm by weight.

[0151] Example 4

[0152] The present example provided a method for preparing an MF SI mother liquor, which was essentially the same as Example 1, with the difference that the content of FSO2CI in the mixed solution of HFSI and FSO2CI of this example was 2 wt%. In the LiFSI mother liquor produced, the concentration of LiFSCF was about 0.53 wt%, and the concentration of NH2SO3H was 18 ppm by weight.

[0153] The present example also provided an electrolyte solution, which was essentially the same as Example 1, with the difference that in the electrolyte solution of this example, the content of LiFSI was 2 wt%, and the content of LiFSCF was about 350 ppm by weight.

[0154] Example 5

[0155] The present example provided a method for preparing an MF SI mother liquor, which was essentially the same as Example 1, with the difference that the content of FSO2CI in the mixed solution of HFSI and FSO2CI of this example was 10 wt%. In the LiFSI mother liquor produced, the concentration of LiFSCF was about 2.8 wt%, and the concentration of NH2SO3H was 2 ppm by weight.

[0156] The present example also provided an electrolyte solution, which was essentially the same as Example 1, with the difference that in the electrolyte solution of this example, the content of LiFSI was 2 wt%, and the content of LiFSCF was about 1,860 ppm by weight.

[0157] Example 6 The present example provided a method for preparing an MF SI mother liquor, comprising the following steps:

[0158] 51, 0.5 mol of Li2CO3was added into a three-necked flask containing 500 ml of ethyl methyl carbonate (EMC), the materials were stirred to make a turbid liquid, and the turbid liquid was cooled for 1 h in a cold bath at -0°C.

[0159] 95 g of a mixed solution of HF SI and FSO2CI (in which the content of FSO2CI was 5.5 wt% and the content of HF SI was 94.5 wt%) was taken, and the temperature of the mixed solution was kept at -10°C to 5°C and added dropwise into the turbid liquid for an addition time of 30 min to 60 min. After the dropwise addition was completed, the reaction was carried out for 2 h, and the temperature of the reaction was controlled at -10°C to 5°C. After the reaction was completed, the reaction solution was filtered to remove the unreacted lithium salt and the newly generated lithium chloride, and obtain a filtrate.

[0160] 52, the water content in the filtrate was measured to be 0.9 wt% using the volumetric method, and 33.7 g of sulfoxide chloride was added, and the reaction was carried out by stirring for 8 h.

[0161] 53, 20 g of molecular sieve was added into the solution obtained from S2, and the reaction was carried out by stirring overnight. After the reaction was completed, the reaction solution was filtered to obtain a MFSI crude mother liquor, i.e., a LiFSI crude mother liquor.

[0162] 54, the MFSI crude mother liquor was subjected to vacuum gas stripping for gradient deacidification, in which the vacuum degree during the gas stripping was maintained at 0.095 MPa to 0.098 MPa, a first gas stripping for deacidification was carried out at 60 °C for 60 min, then a second gas stripping for deacidification was carried out at 100 °C for 2 h. Then, LiFSI and LiFSCh were quantified by using ion chromatography, and the solvent EMC was replenished until the concentration of MFSI was 30 wt%. Then 300 ppm by weight of hexamethyldisilazane (HMDS) was added to obtain the MFSI mother liquor. The content of LiFSO3in the MFSI mother liquor was about 1.5 wt%. The concentration of NH2SO3H was 0 ppm by weight.

[0163] The present example also provided an electrolyte solution that was formulated using the MF SI mother liquor prepared in the present example. In the electrolyte solution of the present example, based on the total weight of the electrolyte solution, the content of LiFSI was 2 wt%, the content of LiFSCF was 930 ppm by weight, and the balance was ethylene carbonate, diethyl carbonate, ethyl methyl carbonate (EMC), and lithium hexafluorophosphate, with the weight ratio of ethylene carbonate, diethyl carbonate, ethyl methyl carbonate (EMC), and lithium hexafluorophosphate being 30: 20: 35: 13.

[0164] Example 7

[0165] The present example provided a method for preparing an MF SI mother liquor, comprising the following steps:

[0166] 51, 1 mol of Li OH was added into a three-necked flask containing 500 ml of dimethyl carbonate (DMC), the materials were stirred to make a turbid liquid, and the turbid liquid was cooled for 1 h in a cold bath at -5°C.

[0167] 95 g of a mixed solution of HF SI and FSO2CI (in which the content of FSO2CI was 5.5 wt% and the content of HF SI was 94.5 wt%) was taken, and the temperature of the mixed solution was kept at -10°C to 5°C and added dropwise into the turbid liquid for an addition time of 30 min to 60 min. After the dropwise addition was completed, the reaction was carried out for 2 h, and the temperature of the reaction was controlled at -10°C to 5°C. After the reaction was completed, the reaction solution was filtered to remove the unreacted lithium salt and the newly generated lithium chloride, and obtain a filtrate.

[0168] 52, the water content in the filtrate was measured to be 1.8 wt% using the volumetric method, and 67.5 g of sulfoxide chloride was added, and the reaction was carried out by stirring for 8 h.

[0169] 53, 30 g of anhydrous magnesium sulfate was added into the solution obtained from S2, and the reaction was carried out by stirring overnight. After the reaction was completed, the reaction solution was filtered to obtain a MFSI crude mother liquor, i.e., a LiFSI crude mother liquor.

[0170] 54, the MFSI crude mother liquor was subjected to vacuum gas stripping for gradient deacidification, in which the vacuum degree during the gas stripping was maintained at 0.095 MPa to 0.098 MPa, a first gas stripping for deacidification was carried out at a gas stripping temperature of 50 °C for 60 min, then a second gas stripping for deacidification was carried out at 100 °C for 2 h. Then, LiFSI and LiFSCh were quantified by using ion chromatography, and the solvent EMC was replenished until the concentration of MFSI was 30 wt%. Then 100 ppm by weight of triphenyl phosphite was added to obtain the MFSI mother liquor. The content of LiFSCf in the MFSI mother liquor was about 1.5 wt%. The concentration of NH2SO3H was 9 ppm by weight.

[0171] The present example also provided an electrolyte solution that was formulated using the MFSI mother liquor prepared in the present example. In the electrolyte solution of the present example, based on the total weight of the electrolyte solution, the content of LiFSI was 2 wt%, the content of LiFSCf was 1,000 ppm by weight, and the balance was ethylene carbonate, diethyl carbonate, ethyl methyl carbonate (EMC), and lithium hexafluorophosphate, with the weight ratio of ethylene carbonate, diethyl carbonate, ethyl methyl carbonate (EMC), and lithium hexafluorophosphate being 30: 20: 35: 13.

[0172] Comparative Example 1

[0173] The present comparative example provides an electrolyte solution, which was essentially the same as Example 1, with the difference that the formulated electrolyte solution uses commercially available solid LiFSI, wherein the content of LiFSCf was less than 200 ppm by weight, and the content of NH2SO3H was 355 ppm by weight. In the electrolyte solution, the content of LiFSI was 2%, and the content of LiFSCf introduced was less than 5 ppm by weight.

[0174] Comparative Example 2

[0175] The present comparative example provided a method for preparing an MFSI mother liquor, which was essentially the same as Example 1, with the difference that the content of FSO2CI in the mixed solution of HFSI and FSO2CI of Comparative Example 2 was 35 wt%. In the LiFSI mother liquor produced, the concentration of LiFSCf was about 13.5 wt% and the concentration of NH2SO3H was 2 ppm by weight. The present comparative example also provided an electrolyte solution, which was essentially the same as Example 1, with the difference that in the electrolyte solution produced in Comparative Example 2, the content of LiFSI was 2 wt% and the content of LiFSCh was about 9,000 ppm by weight.

[0176] Test Example

[0177] The electrolyte solutions obtained from the examples and the comparative examples were injected into a dried soft pack battery, sealing, formation, and capacity grading were performed to obtain battery cells, and then the battery cells were tested as follows, respectively. In the battery, the cathode active material was NCM811, and the negative active material was artificial graphite, and the test voltage range was from 2.75 V to 4.25 V.

[0178] (1) 25°C cycling test: in a constant temperature oven at 25°C, the prepared battery cells were charged and discharged with a current of 1CC / 1DC, and the battery capacity retention rate was recorded after 400 cycles.

[0179] (2) 45 °C cycling test: in a constant temperature oven at 45 °C, the prepared battery cells were charged and discharged with a current of 1C, and the battery capacity retention rate was recorded after 600 cycles.

[0180] (3) Rate discharging test: in a constant temperature oven at 25 °C, the prepared battery cells were fully charged with a current of 1C, and then discharged with currents of 1C and 4C, respectively, to obtain the ratio of discharge capacity at 4C to discharge capacity at 1C, i.e. discharge capacity retention rate at 4C.

[0181] The test results were shown in Table 1.

[0182] Table 1. Electrical performances of battery cells

[0183] As can be seen from the electrical performance data of Example 1, Example 2, Example 3 and Comparative Example 1, the batteries prepared using the low-cost LiFSI mother liquor of the present application have good rate capability and cycling performance, which may be caused by the presence of trace amounts of LiFSCh and reduced NH2SO3H, which solved the drawbacks of the high cost of the electrolyte solution prepared from lithium bifluorosulfonylimide solids as well as the difficulty of preparation, high cost, and low stability of lithium fluorosulfonate as an electrolyte solution additive, and was of great significance for the popularization of the application of lithium bifluorosulfonylimide and lithium fluorosulfonate. The comparison of Examples 1 to 5 shows that the cycling performance can be further improved when the concentration of LiFSCh in the mother liquor was in a range from 1.5wt% to 4.5 wt%.

[0184] As can be seen from the comparison between Example 1 and Comparative Example 2, if the content of LiFSCh was too high, it will lead to a decrease in the cycling performance of the battery.

[0185] Obviously, the above examples are merely examples for the purpose of clear illustration, and are not a limitation of the embodiments. For those skilled ordinary in the art, other variations or changes in different forms can be made on the basis of the above description. It is neither necessary nor possible to exhaust all of the embodiments herein. The obvious variations or changes derived therefrom are still within the scope of protection of the present application.

Claims

CLAIMS1. An MFSI mother liquor, comprising MFSI, MFSO3, and a solvent, wherein based on the total weight of the mother liquor, the concentration of MFSI is in a range from 15 wt% to 30 wt%, the concentration of MFSO3 is in a range from 0.5 wt% to 10 wt%, and the concentration of the NH2SO3H is less than or equal to 20 ppm by weight; and wherein the MFSI is bis(fluorosulfonyl)imide salt, and M comprises at least one of K, Na, and Li.

2. The MFSI mother liquor of claim 1, wherein based on the total weight of the mother liquor, the concentration of MFSO3 is in a range from 1.5 wt% to 4.5 wt%.

3. The MFSI mother liquor of claim 1, wherein the mother liquor further comprises a stabilizer; and the concentration of the stabilizer in the MFSI mother liquor is less than or equal to 300 ppm by weight; optionally, the stabilizer is selected from the group consisting of triphenyl phosphite, N,N-dicyclohexylcarbodiimide, and hexamethyldisilazane.

4. The MFSI mother liquor of claim 1, wherein the solvent is a carbonate; optionally, the carbonate comprises at least one of dimethyl carbonate, diethyl carbonate and ethyl methyl carbonate.

5. A method for preparing the MFSI mother liquor of any one of claims 1 to 4, comprising the following steps:51, mixing an alkali metal compound, HFSI, FSO2CI and a solvent, carrying out a reaction, and filtering to obtain a filtrate, wherein HFSI is bis(fluorosulfonyl)imide;52, adding a first dehydrating agent into the filtrate to carry out a first step of dehydration, so that the water content in the filtrate after the first step of dehydration is greater than 0 and less than or equal to 1,000 ppm by weight;53, adding an excess of a second dehydrating agent into the filtrate after the first step of dehydration to carry out a second step of dehydration, and filtering to obtain a MFSI crude mother liquor; and54, subjecting the MFSI crude mother liquor to vacuum gas stripping for deacidification,and then replenishing the solvent until the concentration of MFSI is in a range from 15 wt% to 30 wt% to obtain the MFSI mother liquor.

6. The method for preparing the MFSI mother liquor of claim 5, wherein in S4, after replenishing the solvent until the concentration of MFSI is in a range from 15 wt% to 30 wt%, it further comprises adding a stabilizer; and the stabilizer is selected from the group consisting of triphenyl phosphite, N,N-dicyclohexylcarbodiimide, and hexamethyldisilazane.

7. The method for preparing the MFSI mother liquor of claim 5, wherein, the first dehydrating agent comprises sulfoxide chloride and / or oxalyl chloride; and / or the second dehydrating agent comprises one or more of anhydrous sulfate salt, molecular sieve and phosphorus pentoxide.

8. The method for preparing the MFSI mother liquor of any one of claims 5 to 7, wherein SI satisfies at least one of the following conditions:(1) the alkali metal compound comprises one or more of lithium carbonate, anhydrous lithium hydroxide, potassium carbonate, anhydrous potassium hydroxide, sodium carbonate and anhydrous sodium hydroxide;(2) a molar ratio of alkali metal element in the alkali metal compound to HFSI is (1.3-3): 1;(3) a weight ratio of HFSI to FSO2CI is (70-98): (2-30); optionally, (85-95): (5-15); and(4) the reaction is carried out at a temperature ranging from -10°C to 5°C for a time period ranging from Ih to 3h; optionally, the reaction is carried out at a temperature ranging from -5°C to 0°C.

9. The method for preparing the MFSI mother liquor of any one of claims 5 to 7, wherein SI comprises:5101 , mixing an alkali metal compound with a solvent to make a turbid liquid;5102, adding a mixed solution of HFSI and FSO2CI dropwise into the turbid liquid, and carrying out the reaction after completion of the dropwise addition; andSI 03, filtering to obtain a filtrate after completion of the reaction.

10. The method for preparing the MFSI mother liquor of any one of claims 5 to 7, whereinS3 satisfies at least one of the following conditions:(1) the vacuum gas stripping for deacidification is carried out at a temperature ranging from 50°C to 100°C;(2) the vacuum gas stripping for deacidification is carried out at a vacuum degree ranging from 0.095 MPa to 0.098 MPa; and(3) the vacuum gas stripping for deacidification is gas stripping for gradient deacidification; optionally, the gas stripping for gradient deacidification comprises performing a first gas stripping for deacidification at a temperature ranging from 50°C to 70°C for a time period ranging from 30 min to 60min, and then performing a second gas stripping for deacidification at a temperature ranging from 70 °C to 100°C for a time period ranging from Ih to 2h; and(4) carrying out vacuum gas stripping for deacidification to the MF SI crude mother liquor, and concentrating the MF SI crude mother liquor to make the weight of the MF SI crude mother liquor to be 30wt% to 60% of the original weight of the MF SI crude mother liquor.

11. An electrolyte solution, comprising the MFSI mother liquor of any one of claims 1 to 4 or the MFSI mother liquor prepared by the method of any one of claims 5 to 10.

12. The electrolyte solution of claim 11, wherein, in the electrolyte solution, the concentration of MFSI is in a range from 0.5 wt% to 6 wt%, and the concentration of MFSO3 is in a range from 300 ppm to 8,000 ppm by weight.

13. A secondary battery, comprising the electrolyte solution of claim 11 or 12.

14. A powered device, comprising the secondary battery of claim 13.

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