Sodium-ion battery electrolyte and sodium-ion battery

Abstract

The invention belongs to the technical field of sodium ion batteries, and discloses a sodium ion battery non-aqueous electrolyte and a sodium ion battery. The non-aqueous electrolyte of the sodium-ion battery comprises a non-aqueous organic solvent, electrolyte sodium salt and an additive, wherein the additive comprises a conventional additive and an acid anhydride substance with a structure as shown in a formula (I) and / or a formula (II). The acid anhydride additives with the structures shown in the formula (I) and the formula (II) in the electrolyte can form passive films on a positive-negative electrode interface, metal ion dissolution is inhibited, negative electrode active sites are covered, structural collapse caused by dissolution of metal ions in a positive electrode material is effectively avoided, catalytic reduction reaction of a solvent on the negative electrode interface is avoided, and the service life of the electrolyte is prolonged. Therefore, the dynamic performance and thermodynamic performance of the sodium-ion battery are improved, and the cycle performance, high-temperature performance and calendar life of the sodium-ion battery are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of sodium ion batteries, and in particular to a sodium ion battery electrolyte and a sodium ion battery. Background Art

[0002] Lithium-ion batteries have high energy density and cycle performance, and are widely used in consumer electronics, electric vehicles, energy storage and other fields. As the scale of the industry gradually expands, the price of lithium salts remains high all year round, and lithium resources have become a bottleneck restricting its development, seriously restricting the development of the industry. The global sodium content is 1,300 times that of lithium. Sodium resources have the advantages of uniform distribution and low cost, and their prices are stable all year round. In recent years, breakthroughs have been made in the materials, systems and terminal applications of sodium-ion batteries. In this era, sodium-ion batteries have attracted great attention from the new energy industry. They are a breakthrough in solving the dilemma of the energy industry's dependence on lithium resources. Their development has great economic and social significance.

[0003] Sodium-based layered oxide cathode materials have a similar structure and reaction mechanism to sodium-based ternary materials. They are considered to be one of the most promising sodium-based cathode materials and are the main sodium-based cathode materials. However, the materials are highly oxidizing in the de-sodium state. Especially at high temperatures, the electrolyte is very likely to undergo side reactions at the cathode interface, producing a series of polymer byproducts and gases, leading to an increase in battery impedance and a decrease in cycle performance. On the other hand, the negative electrode material has a strong reducing property, and the electrolyte will continue to be reduced and consumed at the negative electrode interface, leading to a decrease in battery capacity. Therefore, how to improve the stability of the interface between the positive and negative electrode materials and the electrolyte is the key to improving the performance of sodium-ion batteries, and providing a new electrolyte is an effective way to solve this problem. Summary of the invention

[0004] In view of the deficiencies and needs of the prior art, the present invention provides a non-aqueous electrolyte for a sodium ion battery, wherein an anhydride additive having the structure of formula (I) and formula (II) in the electrolyte can form a passivation film at the interface between the positive and negative electrodes, inhibit the dissolution of metal ions and cover the active sites of the negative electrode, effectively avoid the dissolution of metal ions in the positive electrode material causing structural collapse, and avoid the catalytic reduction reaction of the solvent at the negative electrode interface, thereby improving the kinetic performance and thermodynamic properties of the sodium ion battery, and enhancing the cycle performance, high temperature performance and calendar life of the sodium ion battery.

[0005] In order to achieve the above object, the sodium ion battery non-aqueous electrolyte of the present invention comprises a non-aqueous organic solvent, an electrolyte sodium salt and an additive, wherein the additive comprises a conventional additive and an acid anhydride substance having a structure of formula (I) and / or formula (II):

[0006]

[0007] Among them, R1~R4 are independently selected from aromatic hydrocarbons (the ring may be connected with alkyl, alkenyl, alkynyl, aromatic group, isocyanate group, halogen, etc.), alkyl such as methyl and ethyl, alkyl olefins and alkyl alkynes, fluoroalkanes such as trifluoromethyl and trifluoroethyl, or other halogenated hydrocarbons, and the number of carbon atoms in the alkyl and fluoroalkyl is less than 4.

[0008] Further, in some embodiments of the present invention, the conventional additive is selected from one or more of vinylene carbonate, fluoroethylene carbonate, succinonitrile, adiponitrile, 1,3,6-hexanetrinitrile, 1,2-bis(cyanoethoxy)ethane, 1,3-propane sultone, 1,3-propylene sultone, vinyl vinylene carbonate, vinyl sulfate, tri(trimethyl)silane borate, tri(trimethyl)silanephosphine borate, tri(tripropargyl)phosphate, and tri(triallyl)phosphate.

[0009] Furthermore, in some embodiments of the present invention, the acid anhydride substance having the structure of formula (I) or formula (II) is selected from the compounds represented by formula (1) to (8):

[0010]

[0011] Furthermore, in some embodiments of the present invention, the amount of the acid anhydride substance having the structure of formula (I) and / or formula (II) added is 0.5% to 2.5% of the total mass of the electrolyte.

[0012] Preferably, in some embodiments of the present invention, the amount of the acid anhydride substance having the structure of formula (I) and / or formula (II) added is 0.8% to 2.2% of the total mass of the electrolyte.

[0013] Furthermore, in some embodiments of the present invention, the amount of the conventional additive added is 1.0% to 15.0% of the total mass of the electrolyte.

[0014] Preferably, in some embodiments of the present invention, when the conventional additives are included, the amount of the fluoroethylene carbonate added is 0.5% to 5.0% of the total mass of the electrolyte, the amount of the 1,3-propane sultone added is 0.1% to 3.0% of the total mass of the electrolyte, the amount of the vinylene carbonate added is 0.1% to 3.0% of the total mass of the electrolyte, and the amount of other special additives such as one or more of tris(trimethyl)silane borate / tris(trimethyl)silane phosphate, etc., is 0.1% to 1.0% of the total mass of the electrolyte, the amount of other special additives containing unsaturated bonds is 0.1% to 1.0% of the total mass of the electrolyte, and the amount of other sulfur-based, phosphorus-based, boron-based and silicon-based additives is 0.1% to 1.0% of the total mass of the electrolyte.

[0015] Further preferably, in some embodiments of the present invention, the conventional additives include 1.5-2.5% of fluoroethylene carbonate in the total mass of the electrolyte, 0.7-1.3% of 1,3-propane sultone in the total mass of the electrolyte, and 0.3-0.7% of vinylene carbonate in the total mass of the electrolyte.

[0016] Further preferably, in some embodiments of the present invention, the conventional additives include 1.5-2.5% of fluoroethylene carbonate in the total mass of the electrolyte, 0.7-1.3% of 1,3-propane sultone in the total mass of the electrolyte, 0.3-0.7% of vinylene carbonate in the total mass of the electrolyte, and 0.7-1.3% of vinyl sulfate in the total mass of the electrolyte.

[0017] Furthermore, in some embodiments of the present invention, the electrolyte sodium salt is selected from one or more of sodium hexafluorophosphate, sodium difluorosulfonyl imide and sodium difluorophosphate; preferably, the added amount of the electrolyte sodium salt accounts for 10.5% to 18.0% of the total mass of the electrolyte.

[0018] Further preferably, in some embodiments of the present invention, the electrolyte sodium salt is a mixed sodium salt of sodium hexafluorophosphate, sodium difluorophosphate, and sodium bis(fluorosulfonyl)imide; more preferably, the addition amount of the sodium hexafluorophosphate accounts for 11.5% to 16.0% of the total mass of the electrolyte, the addition amount of the sodium difluorophosphate accounts for 0.5% to 2.0% of the total mass of the electrolyte, and the addition amount of the sodium bis(fluorosulfonyl)imide accounts for 0.1% to 3.0% of the total mass of the electrolyte; further preferably, the addition amount of the sodium hexafluorophosphate accounts for 13.0% to 15.0% of the total mass of the electrolyte, the addition amount of the sodium difluorophosphate accounts for 0.7% to 1.3% of the total mass of the electrolyte, and the addition amount of the sodium bis(fluorosulfonyl)imide accounts for 1.0% to 3.0% of the total mass of the electrolyte.

[0019] Further, in some embodiments of the present invention, the non-aqueous organic solvent is selected from one or more of carbonate solvents, carboxylate solvents, ether solvents, fluorinated carbonate solvents, fluorinated carboxylate solvents, fluorinated ether solvents and fluorinated nitrile solvents; preferably, the carbonate solvents include cyclic carbonates and chain carbonates; wherein the cyclic carbonate solvents include one or more of ethylene carbonate and propylene carbonate; the chain carbonates include one or more of dimethyl carbonate, diethyl carbonate and ethyl methyl carbonate; the carboxylate solvents include one or more of ethyl acetate, n-propyl acetate, ethyl propionate and propyl propionate.

[0020] Preferably, in some embodiments of the present invention, the non-aqueous organic solvent contains ethylene carbonate, propylene carbonate, diethyl carbonate and ethyl methyl carbonate; further preferably, the mass ratio of ethylene carbonate, propylene carbonate, diethyl carbonate and ethyl methyl carbonate in the non-aqueous organic solvent is 3-8:25-35:15-25:40-50; further preferably, the mass ratio of ethylene carbonate, propylene carbonate, diethyl carbonate and ethyl methyl carbonate in the non-aqueous organic solvent is 6-7:28-32:18-22:43-47.

[0021] On the other hand, the present invention also provides a sodium ion battery, which comprises a battery cell formed by laminating or winding a positive electrode sheet, a separator and a negative electrode sheet, and the aforementioned sodium ion battery electrolyte of the present invention.

[0022] Preferably, in some embodiments of the present invention, the positive electrode active material of the positive electrode sheet is a layered oxide material, and the compaction density of the positive electrode sheet is 2.0 to 2.5 g / cm 3 .

[0023] Preferably, in some embodiments of the present invention, the negative electrode active material of the negative electrode sheet is a hard carbon material, and the compaction density of the negative electrode sheet is 0.7 to 1.0 g / cm 3 .

[0024] Preferably, in some embodiments of the present invention, the charging cut-off voltage of the sodium ion battery is 3.95V.

[0025] Compared with the prior art, the anhydride additive having the structure of formula (I) and / or formula (II) in the electrolyte of the present invention can form a passivation film at the interface between the positive and negative electrodes, inhibit the dissolution of metal ions and cover the active sites of the negative electrode, effectively avoid the dissolution of metal ions in the positive electrode material causing structural collapse and avoid the catalytic reduction reaction of the solvent at the negative electrode interface, thereby better improving the kinetic performance and thermodynamic properties of the sodium ion battery, and enhancing the cycle performance, high temperature performance and calendar life of the sodium ion battery. DETAILED DESCRIPTION

[0026] In order to make the purpose, technical scheme and advantages of the present invention clearer, the present invention is further described in detail below in conjunction with embodiments. Additional aspects and advantages of the present invention will be given in part in the following description, and part will become apparent from the following description, or will be understood through the practice of the present invention. It should be understood that the following description is only used to explain the present invention and is not intended to limit the present invention.

[0027] When amount, concentration or other value or parameter is expressed as range, preferred range or a series of upper preferred value and lower preferred value limit range, this should be understood as specifically disclosing all ranges formed by any pairing of any range upper limit or preferred value and any range lower limit or preferred value, regardless of whether the range is disclosed separately. For example, when disclosing range "1 to 5", described range should be interpreted as including range "1 to 4", "1 to 3", "1 to 2", "1 to 2 and 4 to 5", "1 to 3 and 5" etc. When numerical range is described in this article, unless otherwise stated, the range is intended to include its end value and all integers and fractions within the range.

[0028] The indefinite articles "a" and "an" before the elements or components of the present invention have no limitation on the quantity requirements (i.e. the number of occurrences) of the elements or components. Therefore, "a" or "an" should be interpreted as including one or at least one, and the elements or components in the singular form also include the plural form, unless the quantity obviously refers to the singular form only.

[0029] In addition, the descriptions of the terms "one embodiment", "some embodiments", "some implementation methods", "example", "specific example", or "some examples" described below mean that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the technical features involved in the various embodiments of the present invention can be combined with each other as long as they do not conflict with each other.

[0030] Example 1

[0031] Preparation of electrolyte: In a glove box filled with argon, ethylene carbonate, propylene carbonate, diethyl carbonate and ethyl methyl carbonate were mixed in a mass ratio of EC: PC: DEC: EMC = 5: 30: 20: 45, and then sodium hexafluorophosphate accounting for 13.8% of the total mass of the electrolyte and sodium difluorophosphate accounting for 1.0% of the total mass of the electrolyte, sodium difluorosulfonyl imide accounting for 2.0% of the total mass of the electrolyte were slowly added to the mixed solution, and finally an acid anhydride additive (compound 1) accounting for 1.0% of the total mass of the electrolyte was added, and the sodium ion battery electrolyte of Example 1 was obtained after stirring evenly.

[0032] Preparation of sodium ion batteries:

[0033] The positive electrode active material layered oxide, the conductive agent acetylene black, and the binder polyvinylidene fluoride (PVDF) are fully stirred and mixed in an N-methylpyrrolidone solvent system in a mass ratio of 92:6:2, and then coated on an aluminum foil, dried, and cold pressed to obtain a positive electrode sheet.

[0034] The negative electrode active material hard carbon, the conductive agent acetylene black, the binder styrene butadiene rubber (SBR), and the thickener sodium carboxymethyl cellulose (CMC) are fully stirred and mixed in a deionized water solvent system in a mass ratio of 85:10:4.5:0.5, and then coated on an aluminum foil, dried, and cold pressed to obtain a negative electrode sheet.

[0035] Polyethylene (PE) is used as a base film and a nano-aluminum oxide coating is coated on the base film as an isolation film.

[0036] The positive electrode sheet, the isolation film and the negative electrode sheet are stacked in sequence and then wound in the same direction to obtain a bare cell, the bare cell is placed in an outer package, the prepared electrolyte is injected, and the sodium ion battery is obtained after packaging, 45°C storage, high-temperature fixture formation, secondary packaging, capacity division and other processes.

[0037] Example 2-17

[0038] In Examples 2-17 and Comparative Examples 1-6, except that the components of the electrolyte are added in the proportions shown in Table 1, the rest are the same as in Example 1.

[0039] Table 1 Composition ratio of each component of the electrolyte of Examples 1-17 and Comparative Examples 1-6

[0040]

[0041]

[0042] Effect test

[0043] 1) Normal temperature cycle performance test: At 25°C, charge the divided battery to 3.95V at 0.5C constant current and constant voltage, with a cut-off current of 0.02C, and then discharge it to 2.0V at 0.5C constant current. Repeat this cycle. After 1000 cycles of charge / discharge, calculate the 1000th cycle capacity retention rate. The calculation formula is as follows:

[0044] 1000th cycle capacity retention rate (%) = (1000th cycle discharge capacity / first cycle discharge capacity) × 100%.

[0045] 2) 60℃ constant temperature storage capacity remaining rate test: First, the battery is charged and discharged once at 0.5C at room temperature (3.95V~2.0V), and the discharge capacity C0 of the battery before storage is recorded. Then the battery is charged to 3.95V full power state with constant current and constant voltage, and then the battery is placed in a 60℃ constant temperature box for 7 days. After the storage is completed, the battery is taken out; after the battery is cooled at room temperature for 24h, the battery is discharged to 2.0V at 0.5C again, and the discharge capacity C1 of the battery after storage is recorded. The capacity remaining rate of the battery after 7 days of constant temperature storage at 60℃ is calculated as follows:

[0046] After 7 days of constant temperature storage at 60°C, the remaining capacity = C1 / C0*100%.

[0047] 3) 45℃ cycle performance test: At 45℃, charge the divided battery to 3.95V at 0.5C constant current and constant voltage, with a cut-off current of 0.02C, and then discharge it to 2.0V at 0.5C constant current. Repeat this cycle. After 500 cycles of charge / discharge, calculate the capacity retention rate of the 500th cycle. The calculation formula is as follows:

[0048] 500th cycle capacity retention rate (%) = (500th cycle discharge capacity / first cycle discharge capacity) × 100%.

[0049] Table 2 Battery performance test results of various embodiments and comparative examples

[0050]

[0051]

[0052] From the electrochemical performance of Examples 1-10 and Comparative Example 1 in Table 2, it can be seen that the anhydride additives having the structures of formula (I) and (II) described in the present invention can improve the electrochemical performance of sodium ion batteries, but the effect of using the new additives described in the present invention alone is not particularly good, mainly because the passivation film components formed by the oxidation-reduction of a single additive at the positive and negative electrode interfaces are single.

[0053] From the electrochemical properties of Examples 11-17 and Comparative Example 5 in Table 2, it can be seen that the new additives described in the present invention are used in combination with other types of additives, which has a better effect. This is mainly because the new additives described in the present invention can react and decompose at the interface of the positive and negative electrode materials to form a passivation film, inhibit the dissolution of metal ions in the positive electrode material, prevent the migration of metal ions to the interface of the negative electrode material, catalyze the reduction and decomposition of the solvent, and have a certain effect on the protection of the positive and negative electrodes.

[0054] It is easy for a person skilled in the art to understand that, according to the disclosure and teaching of the above description, a person skilled in the art to which the present invention belongs can also change and modify the above implementation mode, and any modification, equivalent replacement and improvement made within the spirit and principle of the present invention shall be included in the protection scope of the present invention. In addition, although some specific terms are used in this specification, these terms are only for the convenience of explanation and do not constitute any limitation to the present invention.

Claims

1. A non-aqueous electrolyte for sodium ion batteries, characterized in that: The sodium ion battery non-aqueous electrolyte comprises a non-aqueous organic solvent, an electrolyte sodium salt and an additive, wherein the additive comprises a conventional additive and an acid anhydride substance having a structure of formula (I) and / or formula (II): Wherein, R1 to R4 are independently selected from aromatic hydrocarbons, alkyl groups, alkyl olefins, alkyl alkynes, and halogenated alkanes, and the number of carbon atoms in the alkyl groups and halogenated alkanes is less than 4.

2. The sodium ion battery nonaqueous electrolyte according to claim 1, characterized in that: The acid anhydride substances having the structure of formula (I) and formula (II) are selected from compounds having the structure of formula (1) to (8): Preferably, the amount of the acid anhydride substance having the structure of formula (I) and / or formula (II) added is 0.5% to 2.5% of the total mass of the electrolyte; more preferably, the amount of the acid anhydride substance having the structure of formula (I) and / or formula (II) added is 0.8% to 2.2% of the total mass of the electrolyte.

3. The sodium ion battery nonaqueous electrolyte according to claim 1, characterized in that: The conventional additives are selected from one or more of vinylene carbonate, fluoroethylene carbonate, succinonitrile, adiponitrile, 1,3,6-hexanetrinitrile, 1,2-bis(cyanoethoxy)ethane, 1,3-propane sultone, 1,3-propylene sultone, vinyl vinyl carbonate, vinyl sulfate, tri(trimethyl)silane borate, tri(trimethyl)silanephosphine borate, tri(tripropargyl) phosphate, and tri(triallyl) phosphate; preferably, the addition amount of the conventional additives accounts for 1.0% to 15.0% of the total mass of the electrolyte; preferably, when the conventional additives are included, the addition amount of the fluoroethylene carbonate accounts for 0.5% to 5.0% of the total mass of the electrolyte, the addition amount of the 1,3-propane sultone accounts for 0.1% to 3.0% of the total mass of the electrolyte, and the addition amount of the vinylene carbonate accounts for 0.1% to 3.0% of the total mass of the electrolyte.

4. The non-aqueous electrolyte for sodium ion batteries according to claim 1 or 3, characterized in that: The conventional additives include 1.5-2.5% of fluoroethylene carbonate, 0.7-1.3% of 1,3-propane sultone, and 0.3-0.7% of vinylene carbonate; preferably, the conventional additives include 1.5-2.5% of fluoroethylene carbonate, 0.7-1.3% of 1,3-propane sultone, 0.3-0.7% of vinylene carbonate, and 0.7-1.3% of vinyl sulfate.

5. The sodium ion battery nonaqueous electrolyte according to claim 1, characterized in that: The electrolyte sodium salt is selected from one or more of sodium hexafluorophosphate, sodium difluorosulfonyl imide and sodium difluorophosphate; preferably, the electrolyte sodium salt is added in an amount of 10.5% to 18.0% of the total mass of the electrolyte; preferably, the electrolyte sodium salt is a mixed sodium salt of sodium hexafluorophosphate, sodium difluorophosphate and sodium bisfluorosulfonyl imide; more preferably, the sodium hexafluorophosphate is added in an amount of 11.5% to 16.0% of the total mass of the electrolyte, the sodium difluorophosphate is added in an amount of 0.5% to 2.0% of the total mass of the electrolyte, and the sodium bisfluorosulfonyl imide is added in an amount of 0.1% to 3.0% of the total mass of the electrolyte; further preferably, the sodium hexafluorophosphate is added in an amount of 13.0% to 15.0% of the total mass of the electrolyte, the sodium difluorophosphate is added in an amount of 0.7% to 1.3% of the total mass of the electrolyte, and the sodium bisfluorosulfonyl imide is added in an amount of 1.0% to 3.0% of the total mass of the electrolyte.

6. The non-aqueous electrolyte for sodium ion batteries according to claim 1, characterized in that: The non-aqueous organic solvent is selected from one or more of carbonate solvents, carboxylate solvents, ether solvents, fluorinated carbonate solvents, fluorinated carboxylate solvents, fluorinated ether solvents and fluorinated nitrile solvents; preferably, the carbonate solvent includes cyclic carbonates and chain carbonates; wherein the cyclic carbonate solvent includes one or more of ethylene carbonate and propylene carbonate; the chain carbonate includes one or more of dimethyl carbonate, diethyl carbonate and ethyl methyl carbonate; the carboxylate solvent includes one or more of ethyl acetate, n-propyl acetate, ethyl propionate and propyl propionate.

7. The non-aqueous electrolyte for sodium ion batteries according to claim 1, characterized in that: The non-aqueous organic solvent contains ethylene carbonate, propylene carbonate, diethyl carbonate and ethyl methyl carbonate; further preferably, the mass ratio of ethylene carbonate, propylene carbonate, diethyl carbonate and ethyl methyl carbonate in the non-aqueous organic solvent is 3-8:25-35:15-25:40-50; further preferably, the mass ratio of ethylene carbonate, propylene carbonate, diethyl carbonate and ethyl methyl carbonate in the non-aqueous organic solvent is 6-7:28-32:18-22:43-47.

8. A sodium ion battery, characterized in that: The sodium ion battery comprises a battery cell formed by laminating or winding a positive electrode sheet, a separator and a negative electrode sheet, and the sodium ion battery electrolyte according to any one of claims 1 to 7.

9. The sodium ion battery according to claim 8, characterized in that: The positive active material of the positive electrode sheet is a layered oxide material, and the compaction density of the positive electrode sheet is 2.0 to 2.5 g / cm 3 Preferably, the negative electrode active material of the negative electrode sheet is a hard carbon material, and the compaction density of the negative electrode sheet is 0.7 to 1.0 g / cm 3 .

10. The sodium ion battery according to claim 8, characterized in that: The sodium ion battery charging cut-off voltage is 3.95V.

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