Electrolyte solution and electrochemical device comprising same

Abstract

An electrolyte solution and an electrochemical device comprising same. The electrolyte solution comprises an electrolyte, a non-aqueous organic solvent, and additives. The additives include a sulfonic anhydride additive and a dehydration additive. The mass of the sulfonic anhydride additive accounts for 0.2%-2.5% of the total mass of the electrolyte solution. The mass of the dehydration additive accounts for 0.2%-1.5% of the total mass of the electrolyte solution. The structural formula of the sulfonic anhydride additive is shown as formula I: Formula I, wherein R1 is selected from C2-C3 alkylene, C2-C3 alkenylene, C2-C3 fluoroalkylene, and C2-C3 fluoroalkenylene. The dehydration additive is selected from one or more of dicyclohexylcarbodiimide, hexamethyldisilazane, and maleic anhydride. The electrolyte solution can mitigate gas production of a battery and improve the long cycle performance of a sodium ion battery.

Description

Electrolyte and electrochemical device Technical Field

[0001] The present invention belongs to the field of battery materials, and in particular relates to an electrolyte and an electrochemical device thereof. Background Art

[0002] With the increasing development of battery technology and the rapid expansion of energy storage demand both domestically and internationally, energy storage batteries are being researched by numerous researchers and companies. Since energy storage batteries often have a lifespan of ten or even twenty years, their cost is of particular concern. Sodium-ion batteries, due to their abundant sodium storage capacity and broad application prospects, have become a hot topic of research, and improving their cycle life has become a key research topic.

[0003] In addition to modifying the positive and negative electrodes, existing technologies for improving the cycle life of sodium-ion batteries also include improving the electrolyte. These improvements primarily include using electrolytes with ether or phosphate ester solvents, or electrolytes with additives such as sulfur-based electrolyte additives, fluoroethylene carbonate, and vinylene carbonate. These improvements aim to improve the cycle life of sodium-ion batteries by addressing issues such as gassing.

[0004] Ether electrolytes have poor stability at high voltages and are prone to decomposition and the production of peroxides, which poses safety problems for batteries. The use of fluoroethers will result in higher costs. The use of phosphate solvents often has the problem of low dielectric constant, resulting in insufficient electrolyte conductivity and an inability to meet high-rate usage scenarios. For electrolytes using sulfur-based and fluoroethylene carbonate, vinylene carbonate and other additives, substances such as sodium fluoride and sodium carbonate will be produced, which have a small amount of solubility in the solvent, making the interface layer less stable than lithium-ion batteries. Therefore, it is more difficult for its cycle life to reach the level of lithium-ion batteries.

[0005] Therefore, there is an urgent need for a new electrolyte that can improve the gas production effect of the battery and increase the battery cycle life.

[0006] Summary of the Invention

[0007] To overcome the shortcomings of existing batteries, such as poor gas production and cycle life, the present invention provides an electrolyte and an electrochemical device thereof. The electrolyte of the present invention can improve gas production in batteries, such as sodium-ion batteries, and enhance the battery's long-cycle performance.

[0008] A first aspect of the present invention provides an electrolyte, comprising an electrolyte, a nonaqueous organic solvent, and an additive, wherein the additive comprises a sulfonic anhydride additive and a water-removing additive; the mass of the sulfonic anhydride additive accounts for 0.2% to 2.5% of the total mass of the electrolyte, and the mass of the water-removing additive accounts for 0.2% to 1.5% of the total mass of the electrolyte;

[0009] The structural formula of the sulfonic anhydride additive is shown in the following formula I:

[0010] R1 is selected from C2-C3 alkylene, C2-C3 alkenylene, C2-C3 fluoroalkylene and C2-C3 fluoroalkenylene; and the water removal additive is selected from one or more of dicyclohexylcarbodiimide, hexamethyldisilazane and maleic anhydride.

[0011] In one or more embodiments, R1 is selected from the group consisting of CH2CH2, CF2CF2, CH=CH, CH2CH2CH2, CH2CHFCH2, CH2CF2CH2, CH2CHCH3, and CH2CHCF3.

[0012] In one or more embodiments, the electrolyte is a sodium salt selected from one or more of sodium hexafluorophosphate, sodium perchlorate, sodium difluorooxalatoborate, sodium bisoxalatoborate, sodium bis(trifluoromethylsulfonyl)imide, and sodium trifluorosulfonate.

[0013] In one or more embodiments, the concentration of the electrolyte in the electrolyte solution is 0.5 to 1.2 mol / L.

[0014] In one or more embodiments, the concentration of the electrolyte in the electrolyte solution is 0.7 to 1.0 mol / L.

[0015] In one or more embodiments, the non-aqueous organic solvent includes carbonate solvents and carboxylate solvents.

[0016] In one or more embodiments, the carbonate solvent is selected from one or more of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, ethylene carbonate, and propylene carbonate.

[0017] In one or more embodiments, the mass of the carbonate solvent accounts for 85% to 98% of the total mass of the non-aqueous organic solvent.

[0018] In one or more embodiments, the carboxylic acid ester solvent is selected from one or more of ethyl acetate, methyl propionate, ethyl propionate, ethyl butyrate, propyl butyrate, and 1,4-butyrolactone.

[0019] In one or more embodiments, the mass of the carboxylate solvent accounts for 2% to 15% of the total mass of the non-aqueous organic solvent.

[0020] In one or more embodiments, the mass of the carbonate solvent accounts for 92% to 97% of the total mass of the non-aqueous organic solvent.

[0021] In one or more embodiments, the mass of the carboxylate solvent accounts for 3% to 8% of the total mass of the non-aqueous organic solvent.

[0022] In one or more embodiments, the mass of the sulfonic anhydride additive accounts for 0.5% to 2% of the total mass of the electrolyte.

[0023] In one or more embodiments, the mass of the water removal additive accounts for 0.5% to 1% of the total mass of the electrolyte.

[0024] In one or more embodiments, the additive further includes other additives in addition to the sulfonic anhydride additive and the water additive, and the mass of the other additives accounts for 0.5% to 5% of the total mass of the electrolyte.

[0025] In one or more embodiments, the other additives are selected from one or more of vinylene carbonate, fluoroethylene carbonate, vinyl sulfate, vinyl sulfite, tris(trimethylsilyl)phosphate, tris(trimethylsilyl)phosphite, and adiponitrile.

[0026] In one or more embodiments, the mass of the other additives accounts for 1% to 3% of the total mass of the electrolyte.

[0027] A second aspect of the present invention provides an electrochemical device, comprising the electrolyte according to any embodiment of the present invention.

[0028] In one or more embodiments, the electrochemical device is a sodium ion battery. DETAILED DESCRIPTION

[0029] To facilitate understanding of the features and effects of the present invention by those skilled in the art, the following provides a general description and definition of terms and expressions used in the specification and claims. Unless otherwise indicated, all technical and scientific terms used herein have the ordinary meanings as understood by those skilled in the art regarding the present invention. In the event of conflict, the definitions in this specification shall prevail.

[0030] The theories or mechanisms described and disclosed herein, whether correct or incorrect, should not limit the scope of the present invention in any way, that is, the present invention can be implemented without being limited by any specific theory or mechanism.

[0031] Herein, “comprising,” “including,” “containing” and similar terms encompass the meanings of “consisting essentially of” and “consisting of,” for example, when “A comprises B and C” is disclosed herein, “A consists essentially of B and C” and “A consists of B and C” should be deemed to have been disclosed herein.

[0032] Throughout this document, all features, such as values, amounts, amounts, and concentrations, specified in numerical ranges or percentage ranges are provided for simplicity and convenience only. Accordingly, the description of numerical ranges or percentage ranges should be considered to encompass and specifically disclose all possible subranges and individual values ​​within those ranges (including integers and fractions).

[0033] In this document, unless otherwise specified, percentage refers to mass percentage and ratio refers to mass ratio.

[0034] Herein, when describing embodiments or examples, it should be understood that they are not intended to limit the present invention to these embodiments or examples. On the contrary, all alternatives, modifications and equivalents of the methods and materials described herein are encompassed within the scope defined by the claims.

[0035] In this document, for the sake of brevity, not all possible combinations of the various technical features in each embodiment or example are described. Therefore, as long as there are no contradictions in the combination of these technical features, the various technical features in each embodiment or example can be combined in any way, and all possible combinations should be considered to be within the scope of this specification.

[0036] [Sulfonic anhydride additives]

[0037] In the present invention, the electrolyte contains a sulfonic anhydride additive as shown in the following formula I:

[0038] In Formula I, R1 can be selected from C2-C3 alkylene, C2-C3 alkenylene, C2-C3 fluoroalkylene, and C2-C3 fluoroalkenylene. C2-C3 alkylene refers to a divalent saturated hydrocarbon group having 2 to 3 carbon atoms, such as ethylene, n-propylene, and isopropylene. C2-C3 alkenylene refers to a divalent hydrocarbon group having 2 to 3 carbon atoms and one carbon-carbon double bond, such as vinylene. C2-C3 fluoroalkylene refers to a group formed by replacing one or more hydrogen atoms on a C2-C3 alkylene group with fluorine atoms. C2-C3 fluoroalkenylene refers to a group formed by replacing one or more hydrogen atoms on a C2-C3 alkenylene group with fluorine atoms.

[0039] In some embodiments, R1 is selected from one of CH2CH2, CF2CF2, CHCH, CH2CH2CH2, CH2CHFCH2, CH2CF2CH2, CH2CHCH3, and CH2CHCF3.

[0040] Examples of sulfonic anhydride additives include ethanedisulfonic anhydride (R1 in Formula I is CH2CH2), tetrafluoroethanedisulfonic anhydride (R1 in Formula I is CF2CF2), ethylenedisulfonic anhydride (R1 in Formula I is CH═CH), propanedisulfonic anhydride (R1 in Formula I is CH2CH2CH2), fluoropropanedisulfonic anhydride (R1 in Formula I is CH2CHFCH2), difluoropropanedisulfonic anhydride (R1 in Formula I is CH2CF2CH2), isopropanedisulfonic anhydride (R1 in Formula I is CH2CHCH3) and trifluoroisopropanedisulfonic anhydride (R1 in Formula I is CH2CHCF3).

[0041] In some embodiments, the mass of the sulfonic anhydride additive of the present invention accounts for 0.2% to 2.5% of the total mass of the electrolyte, preferably 0.5% to 2%, more preferably 1% to 2%, for example 0.3%, 0.5%, 0.8%, 1%, 1.2%, 1.4%, 1.6%, 1.8%, 2%, 2.2%, 2.4%.

[0042] [Water removal additives]

[0043] In the present invention, the water removal additive is selected from one or more of dicyclohexylcarbodiimide (DCC), hexamethyldisilazane (HMDS) and maleic anhydride.

[0044] In some embodiments, the mass of the water removal additive accounts for 0.2% to 1.5% of the total mass of the electrolyte, preferably 0.5% to 1%, more preferably 0.8% to 1%, for example 0.3%, 0.5%, 0.6%, 0.8%, 0.9%, 1%, 1.1%, 1.2%, 1.4%.

[0045] The present invention adds a sulfonic anhydride additive and a water-removing additive to the electrolyte. The combined use of the two additives can reduce the gas production of the battery and improve the cycle performance. When the two additives are used together, the amount of the sulfonic anhydride additive and the water-removing additive should be neither too much nor too little. Too much sulfonic anhydride additive will lead to excessively large positive electrode interface impedance, which is not conducive to sodium ion transmission; too little sulfonic anhydride additive will not effectively form a stable and uniform interface, resulting in large amounts of gas production. Too much water-removing additive will increase the negative electrode interface impedance, which is not conducive to normal temperature cycle performance. Too little water-removing additive will result in poor water removal effect, which will increase the acidity inside the battery and is not conducive to circulation.

[0046] In some preferred embodiments, the mass of the sulfonic anhydride additive accounts for 1% to 2% of the total mass of the electrolyte, and the mass of the water-removing additive accounts for 0.8% to 1% of the total mass of the electrolyte, which is more conducive to the synergistic effect of the sulfonic anhydride additive and the water-removing additive in improving the cycle performance and gas production performance of the battery.

[0047] In some specific embodiments, the sulfonic anhydride additive of the present invention is selected from one of ethanedisulfonic anhydride, tetrafluoroethanedisulfonic anhydride, ethylenedisulfonic anhydride, propylenedisulfonic anhydride, fluoropropylenedisulfonic anhydride, difluoropropylenedisulfonic anhydride, isopropylenedisulfonic anhydride, and isopropylenedisulfonic anhydride, and the water removal additive is dicyclohexylcarbodiimide.

[0048] In some specific embodiments, the sulfonic anhydride additive of the present invention is ethanedisulfonic anhydride; and the water removal additive is selected from one of dicyclohexylcarbodiimide, hexamethyldisilazane, and maleic anhydride.

[0049] In some specific embodiments, the sulfonic anhydride additive is ethanedisulfonic anhydride and the water scavenging additive is dicyclohexylcarbodiimide.

[0050] [Other additives]

[0051] The electrolyte of the present invention may further include additives other than the sulfonic anhydride additive and the water additive. Other additives include, but are not limited to, one or more selected from vinylene carbonate, fluoroethylene carbonate, vinyl sulfate, vinyl sulfite, tris(trimethylsilyl)phosphate, tris(trimethylsilyl)phosphite, and adiponitrile.

[0052] When the above-mentioned other additives are further added to the electrolyte, the electrochemical performance of the battery can be further improved.

[0053] In some preferred embodiments, the mass fraction of other additives in the electrolyte can be 0.5% to 5%, preferably 1% to 3%, for example, 0.6%, 0.8%, 1%, 1.5%, 1.8%, 2%, 2.2%, 2.5%, 3%, 3.5%, 4%, and 4.5%.

[0054] In some specific embodiments, other additives include ethylene carbonate, vinyl sulfate, and 1,3-propane sultone, or consist of ethylene carbonate, vinyl sulfate, and 1,3-propane sultone. The total mass fraction of the three other additives in the electrolyte can be 0.5% to 5%, preferably 1% to 3%, for example, 0.6%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, 2.2%, 2.5%, 2.8%, 3%, 3.5%, 4%, or 4.5%. The mass ratio of ethylene carbonate, vinyl sulfate, and 1,3-propane sultone can be (0.2-0.8):(0.2-0.8):1, for example, 0.5:0.5:1.

[0055] [Electrolytes]

[0056] In some embodiments, the electrolyte is a sodium salt. Sodium salts suitable for the present invention may be sodium salts commonly used in the art, including but not limited to one or more selected from sodium hexafluorophosphate, sodium perchlorate, sodium difluorooxalatoborate, sodium bisoxalatoborate, sodium bis(trifluoromethylsulfonyl)imide, and sodium trifluorosulfonate. The electrolyte of the present invention is preferably designed for use in sodium ion batteries as electrochemical devices.

[0057] In some preferred embodiments, the concentration of the electrolyte is 0.5-1.2 mol / L, preferably 0.7-1.0 mol / L, for example 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, 0.9 mol / L, 1.0 mol / L, 1.1 mol / L, based on the total volume of the electrolyte.

[0058] [Non-aqueous organic solvent]

[0059] The non-aqueous organic solvent suitable for use in the present invention can be any non-aqueous organic solvent known in the art to be suitable for use in electrochemical devices. In some preferred embodiments, the non-aqueous organic solvent includes a carbonate solvent and / or a carboxylate solvent. The electrolyte of the present invention can improve battery gas production and enhance the long-cycle performance of sodium-ion batteries by adding a sulfonic anhydride additive and a water-scavenging additive to conventional carbonate and / or carboxylate solvents, while ensuring no additional cost.

[0060] In some embodiments, the carbonate solvent is selected from one or more of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, ethylene carbonate and propylene carbonate. The mass of the carbonate solvent to the total mass of the non-aqueous organic solvent may be 85% to 98%, preferably 92% to 97%, for example, 86%, 88%, 90%, 92%, 93%, 94%, 95%, 96%, 97%, or 97.5%.

[0061] In some preferred embodiments, the carbonate solvent includes propylene carbonate, ethyl methyl carbonate, and diethyl carbonate. The mass ratio of propylene carbonate:ethyl methyl carbonate:diethyl carbonate is preferably (22-28):(35-45):(25-35), for example, 25:40:30.

[0062] In some embodiments, the carboxylate solvent is selected from one or more of ethyl acetate, methyl propionate, ethyl propionate, ethyl butyrate, propyl butyrate, and 1,4-butyrolactone. The mass ratio of the carboxylate solvent to the total mass of the non-aqueous organic solvent may be 2% to 15%, preferably 3% to 8%, for example, 2.5%, 3%, 4%, 5%, 6%, 7%, 8%, 10%, 12%, or 14%.

[0063] In some preferred embodiments, the non-aqueous organic solvent includes or consists of a carbonate solvent and a carboxylate solvent.

[0064] In some specific embodiments, the non-aqueous organic solvent includes propylene carbonate, ethyl methyl carbonate, diethyl carbonate, and ethyl acetate. The mass ratio of propylene carbonate:ethyl methyl carbonate:diethyl carbonate:ethyl acetate is preferably (22-28):(35-45):(25-35):(2-10), for example, 25:40:30:5.

[0065] In some embodiments, the electrolyte is prepared by the following method:

[0066] The electrolyte according to any embodiment of the present invention, a non-aqueous organic solvent and an additive are mixed to obtain the electrolyte, wherein the additive includes a sulfonic anhydride additive and a water-removing additive. The mixing temperature may be 20-25° C. Preferably, the additive may further include other additives.

[0067] In some preferred embodiments, the electrolyte is prepared by the following method: mixing the non-aqueous organic solvent and the electrolyte as described in any embodiment of the present invention, and then adding the sulfonic anhydride additive, the water removal additive and other optional additives in sequence.

[0068] [Electrochemical device]

[0069] The electrochemical device of the present application is, for example, a primary battery, a secondary battery, a fuel cell, a solar cell, or a capacitor. The primary battery is, for example, a sodium ion primary battery. The secondary battery is, for example, a sodium ion secondary battery.

[0070] In some embodiments, the electrochemical device comprises a positive electrode sheet, a negative electrode sheet, a separator, and the electrolyte described above in the present application. The electrolyte of the present invention is applicable to various types of sodium ion batteries.

[0071] The positive electrode sheet includes a positive electrode current collector and a positive electrode material layer formed on the surface of the positive electrode current collector. The positive electrode material layer includes a positive electrode active material, a conductive agent and a binder. The positive electrode material layer is obtained by coating a positive electrode slurry containing a positive electrode active material, a conductive agent, a binder and a solvent onto the positive electrode current collector, and rolling and baking. The positive electrode current collector can be copper foil, aluminum foil, titanium foil, nickel foil, iron foil, zinc foil, etc. The solvent of the positive electrode slurry can be N-methylpyrrolidone (NMP). The positive electrode active material can be a material conventionally used in sodium ion batteries in the field, including materials that can release and accept sodium ions. In the present invention, the positive electrode active material is preferably a sodium transition metal composite oxide. Among them, the sodium transition metal composite oxide is preferably one or more of sodium transition metal oxides and sodium transition metal oxides modified by doping or coating with other transition metals or non-transition metals. The sodium transition metal composite oxide is preferably Na x MO2, wherein 0.6≤x≤1.0, M represents one or more transition metal elements; more preferably one or more of sodium cobalt oxide, sodium manganese oxide, and sodium-based multinary transition metal compounds; more preferably Na x CoO2、Na x MnO2、Na x Ni a Fe b Mn c One or more of O2, wherein 0.6≤x≤1.0, 0<a<1, 0<b<1, 0<c<1, a+b+c=1. The conductive agent of the positive electrode may be one or more selected from conductive carbon black (SP), carbon fiber (CF), acetylene black, conductive graphite, graphene, carbon nanotubes and carbon microspheres. The binder of the positive electrode may be one or more selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene, polyvinyl alcohol, polyolefin, styrene-butadiene rubber, fluorinated rubber, polyurethane and sodium alginate. In some embodiments, the conductive agent in the positive electrode material layer is SP and the binder is PVDF. The content ratio of each component in the positive electrode material layer can be conventional, for example, the mass fraction of the positive electrode active material can be 90%-98%, for example, 92%, 94%, 95%, 96%, 96.7%, 97%, 97.5%. The mass fraction of the conductive agent can be 1%-5%, such as 1.2%, 1.3%, 1.5%, 2%, 3%, 3.5%, and 4%. The mass fraction of the binder can be 1%-5%, such as 1.2%, 1.5%, 1.8%, 2%, 2.5%, 3%, and 4%.

[0072] The negative electrode sheet includes a negative electrode current collector and a negative electrode material layer formed on the surface of the negative electrode current collector. The negative electrode current collector can be copper foil or aluminum foil. The negative electrode material layer includes a negative electrode active material, a conductive agent and a binder. The negative electrode material layer is obtained by coating a negative electrode slurry containing a negative electrode active material, a conductive agent, a binder and a solvent onto the positive electrode current collector, and then rolling and baking. The solvent of the negative electrode slurry can be water or N-methylpyrrolidone. The negative electrode active material is commonly used in sodium ion batteries in the art, including negative electrode active materials that can accept and release sodium ions, such as hard carbon materials. The negative electrode conductive agent can be one or more selected from acetylene black, carbon nanotubes, carbon black, and conductive graphite. The negative electrode binder can be one or more selected from polytetrafluoroethylene (PTFE), styrene-butadiene rubber (SBR), carboxymethyl cellulose (CMC), polyacrylic acid (PAA), and polyvinylidene fluoride (PVDF). The mass ratios of the components in the negative electrode material layer can be conventional. For example, the mass fraction of the negative electrode active material can be 90% to 98%, such as 92%, 93%, 94%, 95%, 95.7%, 96%, or 97%. The mass fraction of the conductive agent can be 0.5% to 5%, such as 1%, 1.5%, 2%, 3%, or 4%. The mass fraction of the binder can be 0.5% to 5%, such as 1%, 1.5%, 2%, 3%, or 4%.

[0073] The separator can be selected from various separators used in sodium ion batteries known to those skilled in the art, including but not limited to polyethylene felt, polyolefin microporous membrane, glass fiber felt, polypropylene separator, etc.

[0074] The positive electrode sheet, negative electrode sheet and separator are stacked or wound according to the design requirements, and then encapsulated in a shell. After drying, liquid injection (injection of the electrolyte of the present invention), packaging, static standing, and formation, a sodium ion battery can be produced. The form of the sodium ion battery of the present invention is not particularly limited, and can be a cylindrical sodium ion battery, a soft-pack sodium ion battery or an aluminum shell sodium ion battery.

[0075] The present invention has the following beneficial effects:

[0076] The present invention adds a sulfonic anhydride additive and a water-removing additive to the electrolyte. The combined use of these two additives ensures low battery impedance while reducing battery gas production, thereby extending the cycle life of batteries, particularly sodium-ion batteries. The electrolyte formulation of the present invention can improve battery gas production and enhance battery cycle performance while maintaining cost savings while using conventional carbonate and / or carboxylate solvents.

[0077] In the present invention, some functional groups of the added appropriate amount of water-removing additive can react with water preferentially compared to the sulfonic anhydride additive, thereby protecting the sulfonic anhydride itself from being destroyed or reducing the destruction of the sulfonic anhydride, such as the diimine group (-N=C=N-) in dicyclohexylcarbodiimide, the silicon-hydrogen bond (Si-N) in hexadecyldisiloxane, and the carbonic anhydride functional group in maleic anhydride. Therefore, while maintaining a low amount of sulfonic anhydride additive, the appropriate amount of water-removing additive protects the effective functional groups of the sulfonic anhydride additive, ensuring that a stable interface can be formed even with a small amount of addition. Therefore, both the appropriate amount of water-removing agent and the appropriate amount of sulfonic anhydride additive are indispensable.

[0078] The present invention will be described below by way of specific examples. It should be understood that these examples are merely illustrative and are not intended to limit the scope of the present invention. The methods, reagents, and materials used in the examples are, unless otherwise stated, conventional methods, reagents, and materials in the art. The starting compounds in the examples can all be purchased from commercial sources.

[0079] Example 1

[0080] Preparation of electrolyte:

[0081] At room temperature, in a glove box with a water and oxygen content of less than 0.1 ppm, a non-aqueous organic solvent was uniformly mixed in a mass ratio of propylene carbonate: ethyl methyl carbonate: diethyl carbonate: ethyl acetate = 25:40:30:5. Sodium hexafluorophosphate (electrolyte) was added to the prepared non-aqueous organic solvent. Then, ethanedisulfonic anhydride (where R1 in Formula I is CH2CH2) and dicyclohexylcarbodiimide (DCC) were added in sequence as a sulfonic anhydride additive. Finally, ethylene carbonate, vinyl sulfate, and 1,3-propane sultone were added as additional additives to prepare an electrolyte.

[0082] The concentration of sodium hexafluorophosphate in the electrolyte is 1 mol / L. The mass of ethylenedisulfonic anhydride accounts for 1% of the total mass of the electrolyte. The mass of dicyclohexylcarbodiimide accounts for 0.8% of the total mass of the electrolyte. Among other additives, ethylene carbonate accounts for 0.5% of the total mass of the electrolyte, vinyl sulfate accounts for 0.5% of the total mass of the electrolyte, and 1,3-propane sultone accounts for 1% of the total mass of the electrolyte.

[0083] Example 2

[0084] The sulfonic anhydride additive in Example 1 was replaced by tetrafluoroethylene disulfonic anhydride (R1 in Formula I is CF2CF2) instead of ethanedisulfonic anhydride, and all other conditions were the same as in Example 1.

[0085] Example 3

[0086] The sulfonic anhydride additive in Example 1 was replaced by ethylene disulfonic anhydride (R1 in Formula I is CH=CH), and all other conditions were the same as in Example 1.

[0087] Example 4

[0088] The sulfonic anhydride additive in Example 1 was replaced by propylene disulfonic anhydride (R1 in Formula I is CH2CH2CH2) instead of ethanedisulfonic anhydride, and all other conditions were the same as in Example 1.

[0089] Example 5

[0090] The sulfonic anhydride additive in Example 1 was replaced by fluoropropanedisulfonic anhydride (R1 in Formula I is CH2CHFCH2) instead of ethanedisulfonic anhydride, and all other conditions were the same as in Example 1.

[0091] Example 6

[0092] The sulfonic anhydride additive in Example 1 was replaced by difluoropropanedisulfonic anhydride (R1 in Formula I is CH2CF2CH2) instead of ethanedisulfonic anhydride, and all other conditions were the same as in Example 1.

[0093] Example 7

[0094] The sulfonic anhydride additive in Example 1 was replaced by isopropyl disulfonic anhydride (R1 in Formula I is CH2CHCH3) in place of ethanedisulfonic anhydride, and all other conditions were the same as in Example 1.

[0095] Example 8

[0096] The sulfonic anhydride additive in Example 1 was replaced by trifluoroisopropyldisulfonic anhydride (R1 in Formula I is CH2CHCF3) to replace ethanedisulfonic anhydride, and all other conditions were the same as in Example 1.

[0097] Example 9

[0098] The water removal additive in Example 1 was replaced by hexamethyldisilazane in place of dicyclohexylcarbodiimide, and all other conditions were the same as in Example 1.

[0099] Example 10

[0100] The water removal additive in Example 1 was replaced by dicyclohexylcarbodiimide with maleic anhydride, and all other conditions were the same as in Example 1.

[0101] Example 11

[0102] The mass proportion of the sulfonic anhydride additive in the electrolyte in Example 1 was adjusted from 1% to 0.5%, and all other conditions were the same as in Example 1.

[0103] Example 12

[0104] The mass proportion of the sulfonic anhydride additive in the electrolyte in Example 1 was adjusted from 1% to 2%, and all other conditions were the same as in Example 1.

[0105] Example 13

[0106] The mass ratio of the water removal additive in the electrolyte in Example 1 was adjusted from 0.8% to 1%, and all other conditions were the same as in Example 1.

[0107] Example 14

[0108] The mass ratio of the water removal additive in the electrolyte in Example 1 was adjusted from 0.8% to 0.5%, and all other conditions were the same as in Example 1.

[0109] Comparative Example 1

[0110] The mass percentage of the sulfonic anhydride additive in the electrolyte in Example 1 was adjusted from 1% to 0.1%, and all other conditions were the same as in Example 1.

[0111] Comparative Example 2

[0112] The mass proportion of the sulfonic anhydride additive in the electrolyte in Example 1 was adjusted from 1% to 3%, and all other conditions were the same as in Example 1.

[0113] Comparative Example 3

[0114] The mass ratio of the water removal additive in the electrolyte in Example 1 was adjusted from 0.8% to 0.1%, and all other conditions were the same as in Example 1.

[0115] Comparative Example 4

[0116] The mass ratio of the water removal additive in the electrolyte in Example 1 was adjusted from 0.8% to 2%, and all other conditions were the same as in Example 1.

[0117] Comparative Example 5

[0118] The difference between Comparative Example 5 and Example 1 is that no sulfonic anhydride additive is added. All other conditions are the same as those in Example 1.

[0119] Comparative Example 6

[0120] The difference between Comparative Example 6 and Example 1 is that no water-removing additive is added. All other conditions are the same as those in Example 1.

[0121] Comparative Example 7

[0122] The difference between Comparative Example 7 and Example 1 is that no sulfonic anhydride additive and water removal additive are added. All other conditions are the same as those of Example 1.

[0123] Test Example 1

[0124] The electrolytes prepared in Examples 1-14 and Comparative Examples 1-7 were used as electrolytes for sodium ion batteries to prepare sodium ion batteries and perform battery performance tests:

[0125] (1) Preparation of positive electrode

[0126] The positive electrode active material Na 1.0 Ni 0.33 Fe 0.33 Mn 0.34 O2, conductive carbon black (SP), and binder polyvinylidene fluoride (PVDF) are mixed in a mass ratio of positive electrode active material: conductive agent: PVDF = 95:2:3 with N-methylpyrrolidone as solvent to form a positive electrode slurry. The positive electrode slurry is evenly coated on a 16-micron thick aluminum foil, dried, rolled, and cut to form a positive electrode sheet.

[0127] (2) Preparation of negative electrode sheet

[0128] The negative electrode materials hard carbon, carbon black, and carboxymethyl cellulose (CMC) are mixed in a mass ratio of 95:2:3 with N-methylpyrrolidone as a solvent to prepare a negative electrode slurry. The negative electrode slurry is evenly coated on a 16-micron thick aluminum foil, dried, rolled, and cut to make a negative electrode sheet.

[0129] (3) Preparation of sodium ion batteries

[0130] The above-mentioned positive electrode sheet, polypropylene separator, and negative electrode sheet are stacked in sequence and wound into a bare battery cell, which is then placed in a punched aluminum-plastic film. The electrolyte is injected into the battery at a ratio of 6Ah / g and sealed to form a soft-pack sodium-ion battery.

[0131] (4) Battery capacity retention test

[0132] At 25°C, charge the battery to 4.0V at 1C, then let it sit for 5 minutes. Discharge the battery to 1.5V at 1C, then let it sit for 5 minutes. Repeat these steps 1000 times to obtain the capacity of the battery after 1000 cycles. Calculate the capacity retention rate after 1000 cycles using the following formula:

[0133] Capacity retention rate = (discharge capacity after 1000th cycle / discharge capacity at first cycle)*100%.

[0134] (5) Test of battery volume growth rate

[0135] At 25°C, the volume of the soft-pack battery was measured using an in-situ gas generation tester (GVM220 from Yuanneng Technology), which was recorded as the initial volume V1. After 1000 cycles, the volume of the soft-pack battery was measured again using the in-situ gas generation tester, which was recorded as the volume after the cycle V2. The volume growth rate of the battery was calculated using the following formula:

[0136] Volume growth rate=volume after cycle V2 / (volume after cycle V2-initial volume V1)*100%.

[0137] The 1000 cycle retention rates and soft pack volume growth rates of the sodium ion batteries prepared using the electrolytes of Examples 1-14 and Comparative Examples 1-7 are shown in Table 1.

[0138] Table 1: Performance test results

[0139] According to the results in Table 1, when the sulfonic anhydride additive and the dewatering additive are used in combination in Examples 1-14, the gas production of the battery cell is low and has better cycle performance. As can be seen from Comparative Examples 1-2, the excessive sulfonic anhydride additive in Comparative Example 2 will cause the positive electrode interface impedance to be too large, which is not conducive to sodium ion transmission, resulting in poor battery capacity retention after 1000 cycles; the sulfonic anhydride additive in Comparative Example 1 is too little, and a stable and uniform interface cannot be effectively formed, which will lead to a large amount of gas production, and the soft pack volume growth rate can reach 153.3%. As can be seen from Comparative Examples 3-4, the excessive dewatering additive in Comparative Example 4 will cause the negative electrode interface impedance to increase, which is not conducive to room temperature cycle performance, resulting in poor battery capacity retention after 1000 cycles; when the dewatering additive in Comparative Example 3 is too little, the dewatering effect is poor, which will cause the acidity inside the battery to increase, which is not conducive to circulation, and the soft pack volume growth rate is high. As can be seen from Comparative Example 5, when no sulfonic anhydride additive is added, the battery produces serious gas and has a high volume growth rate. It can be seen from Comparative Example 6 that when no dewatering additive is added, its 1000 cycle retention rate is not as good as that of Examples 1-14. It can be seen from Comparative Example 7 that when neither the sulfonic anhydride additive nor the dewatering additive is added, the 1000 cycle capacity retention rate of the battery prepared is far worse than that of Examples 1-14, and the volume growth rate is much higher than that of Examples 1-14. It can be seen from Example 1 and Comparative Examples 5-7 that the sulfonic anhydride additive and the dewatering additive have a significant synergistic effect in improving the cycle capacity retention rate and gas production performance of the battery. In terms of cycle capacity retention rate, Comparative Example 5 increased by 11.3% compared to Comparative Example 7, Comparative Example 6 increased by 23.2% compared to Comparative Example 7, and Example 1 increased by 49.85% compared to Comparative Example 7 (>11.3% + 23.3%). In terms of gas production performance, Example 1 is also significantly better than Comparative Examples 5 and Comparative Examples 6.

Claims

1. An electrolyte, characterized in that The electrolyte comprises an electrolyte, a non-aqueous organic solvent and an additive, wherein the additive comprises a sulfonic anhydride additive and a water-removing additive; the mass of the sulfonic anhydride additive accounts for 0.2% to 2.5% of the total mass of the electrolyte, and the mass of the water-removing additive accounts for 0.2% to 1.5% of the total mass of the electrolyte; The structural formula of the sulfonic anhydride additive is shown in the following formula I: R1 is selected from C2-C3 alkylene, C2-C3 alkenylene, C2-C3 fluoroalkylene and C2-C3 fluoroalkenylene; The water removal additive is selected from one or more of dicyclohexylcarbodiimide, hexamethyldisilazane and maleic anhydride.

2. The electrolyte according to claim 1, wherein The electrolyte has one or more of the following characteristics: R1 is selected from CH2CH2, CF2CF2, CH═CH, CH2CH2CH2, CH2CHFCH2, CH2CF2CH2, CH2CHCH3 and CH2CHCF3; The electrolyte is a sodium salt, and the sodium salt is selected from one or more of sodium hexafluorophosphate, sodium perchlorate, sodium difluorooxalatoborate, sodium bisoxalatoborate, sodium bis(trifluoromethylsulfonyl)imide, and sodium trifluorosulfonate; The concentration of the electrolyte in the electrolyte solution is 0.5 to 1.2 mol / L; The non-aqueous organic solvent includes carbonate solvents and carboxylate solvents.

3. The electrolyte according to claim 1, wherein The concentration of the electrolyte in the electrolyte solution is 0.7 to 1.0 mol / L.

4. The electrolyte according to claim 2, wherein The electrolyte has one or more of the following characteristics: The carbonate solvent is selected from one or more of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, ethylene carbonate and propylene carbonate; The mass of the carbonate solvent accounts for 85% to 98% of the total mass of the non-aqueous organic solvent. The carboxylate solvent is selected from one or more of ethyl acetate, methyl propionate, ethyl propionate, ethyl butyrate, propyl butyrate and 1,4-butyrolactone; The mass of the carboxylate solvent accounts for 2% to 15% of the total mass of the non-aqueous organic solvent.

5. The electrolyte according to claim 4, wherein The mass of the carbonate solvent accounts for 92% to 97% of the total mass of the non-aqueous organic solvent; and / or The mass of the carboxylate solvent accounts for 3% to 8% of the total mass of the non-aqueous organic solvent.

6. The electrolyte according to claim 1, wherein The mass of the sulfonic anhydride additive accounts for 0.5% to 2% of the total mass of the electrolyte.

7. The electrolyte according to claim 1, wherein The mass of the water removal additive accounts for 0.5% to 1% of the total mass of the electrolyte.

8. The electrolyte according to claim 1, wherein The additives further include other additives except the sulfonic anhydride additive and the water additive, and the mass of the other additives accounts for 0.5% to 5% of the total mass of the electrolyte.

9. The electrolyte according to claim 8, wherein The other additives are selected from one or more of vinylene carbonate, fluoroethylene carbonate, vinyl sulfate, vinyl sulfite, tris(trimethylsilyl)phosphate, tris(trimethylsilyl)phosphite and adiponitrile; and / or The mass of the other additives accounts for 1% to 3% of the total mass of the electrolyte.

10. An electrochemical device, characterized in that The electrochemical device comprises the electrolyte according to any one of claims 1 to 9.

11. The electrochemical device according to claim 10, wherein The electrochemical device is a sodium ion battery.

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