CN114335720A - Electrolyte additive, electrolyte and sodium ion battery comprising electrolyte - Google Patents

Abstract

The present invention belongs to the technical field of sodium ion batteries, and in particular relates to an electrolyte additive, an electrolyte and a sodium ion battery comprising the electrolyte, including an additive a and an additive b, and the additive a includes the first compound represented by the following formula I and the following One or more of the second compounds represented by formula II; wherein, R1, R2, R3, R4, R5, R6, R7, R8 and R9 are independently selected from hydrogen, halogen atom, and the number of carbon atoms is 1 one of an alkane group or an alkoxy group of ~10, an alkanoyl group with a carbon number of 2 to 10, or an unsaturated hydrocarbon group, and the alkane group, the unsaturated hydrocarbon group, the alkoxy group, and the alkane group The H in the acyl group may be partially or totally substituted by one or more of halogen atoms, cyano groups, carboxyl groups and sulfonic acid groups. The electrolyte additive of the invention helps to improve the cycle performance and increase the high and low temperature capacity retention rate, capacity recovery rate and thickness expansion rate.

Description

A kind of electrolyte additive, electrolyte and sodium ion battery including this electrolyte

technical field

The invention belongs to the technical field of sodium ion batteries, and in particular relates to an electrolyte additive, an electrolyte and a sodium ion battery comprising the electrolyte.

Background technique

Sodium is one of the most abundant elements on earth. Its working principle is similar to that of lithium-ion batteries, and it has the advantages of low cost, good safety, and long-term large-scale storage. It has attracted more and more attention of researchers. However, sodium-ion batteries also have shortcomings such as poor cycle performance, high-temperature storage flatulence, and low initial efficiency, which restrict their wide application.

As one of the key materials of sodium-ion power batteries, electrolyte has a significant impact on the cycle, high and low temperature performance of the battery. Among the three components of the electrolyte, the formulation of lithium salt and solvent does not change much, and additives are the key factor to improve the performance of sodium-ion batteries. Therefore, it is of great significance to develop additives and electrolytes that meet the performance of sodium-ion batteries.

SUMMARY OF THE INVENTION

One of the objectives of the present invention is to provide an electrolyte additive in view of the deficiencies of the prior art, which can effectively improve the cycle performance of the electrolyte and increase the high and low temperature capacity retention rate, capacity recovery rate and thickness expansion rate.

In order to achieve the above object, the present invention adopts the following technical solutions:

An electrolyte additive, comprising additive a and additive b, additive a comprising one or more of the first compound represented by the following formula I and the second compound represented by the following formula II;

Wherein, R1, R2, R3, R4, R5, R6, R7, R8 and R9 are independently selected from hydrogen, halogen atom, alkane group with 1 to 10 carbon atoms, unsaturated with 2 to 10 carbon atoms Any of a hydrocarbon group, an alkoxy group having 1 to 10 carbon atoms, or an alkanoyl group having 2 to 10 carbon atoms, the alkane group, the unsaturated hydrocarbon group, the alkoxy group, and the alkane group The H in the acyl group can be partially or completely substituted by one or more of halogen atoms, cyano groups, carboxyl groups and sulfonic acid groups; wherein, the additive b is ethylene carbonate, fluoroethylene carbonate, ethylene carbonate One or more of ethyl ester, vinyl sulfate and propenyl sultone.

Preferably, in the first compound represented by formula I, R1, R2, and R3 are halogen atoms, and in the second compound represented by formula II, R4, R5, and R6 are halogen atoms, and R7, R8, and R9 are halogen atoms. is an alkane group having 1 to 10 carbon atoms.

Preferably, in the first compound, R1, R2 and R3 are fluorine; in the second compound, R4, R5 and R6 are fluorine, and R7, R8 and R9 are methyl.

Preferably, the mass ratio of the additive a and the additive b is (1-5):(1-5). The mass ratio of additive a and additive b is 1:1, 1:2, 1:3, 1:4, 1:5, 2:1, 3:1, 4:1, 5:1.

Preferably, the additive a is the first compound and the second compound, and the mass ratio of the first compound and the second compound is 2:1, and the additive b is fluoroethylene carbonate .

The second purpose of the present invention is to provide an electrolyte solution with excellent cycle performance and high and low temperature performance in view of the deficiencies of the prior art.

In order to achieve the above object, the present invention adopts the following technical solutions:

An electrolyte includes sodium salt electrolyte, organic solvent and the electrolyte additive mentioned above.

Preferably, the mass of the electrolyte additive accounts for 2% to 10% of the total mass of the electrolyte. The mass of the electrolyte additive accounts for 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10% of the total mass of the electrolyte.

Preferably, the organic solvent includes a cyclic organic solvent and a chain organic solvent, the cyclic organic solvent is one or more of ethylene carbonate, propylene carbonate and butylene carbonate, and the chain organic solvent is The solvent is one or more of dimethyl carbonate, diethyl carbonate and ethyl methyl carbonate.

Preferably, the sodium salt electrolyte is one or more of sodium hexafluorophosphate, sodium perchlorate, sodium tetrafluoroborate and sodium bisfluorooxalateborate.

The third object of the present invention is to provide a sodium-ion battery with good cycle performance, high and low temperature performance and initial efficiency, high temperature storage without flatulence, and good safety, aiming at the deficiencies of the prior art.

In order to achieve the above object, the present invention adopts the following technical solutions:

A sodium-ion battery, comprising the above electrolyte.

Specifically, a sodium-ion battery includes a positive electrode sheet, a negative electrode sheet, a separator, an electrolyte, and a casing. The positive electrode includes a current collector and an active material layer provided on the current collector. The active material layer includes but is not limited to chemical formulas such as Na _0.67 Mn _x A _y B _z O _2±δ , in the molecular formula, A is one or more of Co, Ni and Cr, and B is Mg, Al, Ca, One or more of Ti, Cu, Zn and Ba, 0.6<x<1, 0<y<0.1, 0.6<x+y0, x+y+z=1, 0≤δ≤0.1, the positive electrode The active material can also be including but not limited to Na _1.845 Mn[Fe(CN) ₆ ] _0.961 ·1.988H ₂ O, Na ₃ V ₂ (PO ₄ ) ₂ O ₂ F, Na ₃ V _1.95 Mn _0.05 (PO ₄ ) ₂ One of F ₃ , Na ₃ V _1.95 Mn _0.05 (PO ₄ ) ₂ O ₂ F, Na ₃ V ₂ (PO ₄ ) ₂ F ₃ and Na _2.95 Li _0.05 V ₂ (PO ₄ ) ₂ O ₂ F, etc. or various combinations. The positive electrode active material can also be modified, and the method for modifying the positive electrode active material should be known to those skilled in the art. For example, the positive electrode active material can be treated by coating, doping, etc. For modification, the materials used in the modification treatment may include, but are not limited to, one or a combination of Al, B, P, Zr, Si, Ti, Ge, Sn, Mg, Ce, W, and the like. The positive electrode current collector is usually a structure or part that collects current, and the positive electrode current collector can be any material suitable for use as a positive electrode current collector for sodium ion batteries in the art. For example, the positive electrode current collector can include but not It is limited to metal foil, etc., more specifically, it may include but not limited to aluminum foil and the like.

The negative electrode includes a current collector and an active material layer disposed on the surface of the current collector, and the active material layer may include but not limited to graphite, soft carbon, hard carbon, carbon fiber, mesocarbon microspheres, silicon-based materials, tin-based materials One or more of materials, lithium titanate or other metals that can form alloys with sodium. Wherein, the graphite can be selected from one or more of artificial graphite, natural graphite and modified graphite; the silicon-based material can be selected from one or more of elemental silicon, silicon-oxygen compound, silicon-carbon composite, and silicon alloy one or more; the tin-based material can be selected from one or more of elemental tin, tin oxide compounds, and tin alloys. The negative electrode current collector is usually a structure or part that collects current, and the negative electrode current collector can be any material suitable for use as a negative electrode current collector for sodium ion batteries in the art. For example, the negative electrode current collector can include but not limited to Metal foil, etc., more specifically may include but not limited to copper foil and the like.

The separator can be various materials suitable for sodium-ion battery separator in the art, for example, can be including but not limited to polyethylene, polypropylene, polyvinylidene fluoride, aramid, polyethylene terephthalate, A combination of one or more of polytetrafluoroethylene, polyacrylonitrile, polyimide, polyamide, polyester, and natural fibers.

Compared with the prior art, the beneficial effects of the present invention are: in the electrolyte additive of the present invention, the first compound in the additive a is oxidized and decomposed at the positive electrode to form a stable CEI film, and the interface film contains BO bonds and has a high ionic strength. Electrical conductivity, reduce the internal resistance of the battery, reduce the polarization, improve the cycle performance, and at the same time can improve the wettability of the electrolyte to form a more uniform low-impedance interface film; the second compound in the additive a, the Si-O bond breaking energy and water and HF reacts to prevent large-sized water from entering the positive electrode material to squeeze the lattice, improving the stability of the material, and at the same time inhibiting the hydrolysis of sodium salt and improving the stability of the electrolyte, and the second compound has a fluorosulfonyl structure, due to the fluorine atom. It is bonded with SO ₂ group, so the degree of polarization is high, which can deposit insoluble lithium fluoride on the surface of the active material, inhibit the reduction and decomposition reaction of the electrolyte, and further improve the stability of the electrolyte, and the fluorine-containing compound has good wettability, Low film-forming resistance improves battery performance. The electrolyte additive of the present invention can obviously improve the battery cycle and high-temperature storage performance, and greatly reduce the gas production during high-temperature storage. The synergistic use of the additive b can form a more uniform and dense SEI film. Improved battery cycle and high temperature performance.

Detailed ways

The present invention will be described in further detail below with reference to the specific embodiments, but the embodiments of the present invention are not limited thereto.

Example 1

Electrolyte preparation: NaPF ₆ , organic solvent (EC (ethylene carbonate):DEC (diethyl carbonate):EMC (ethyl methyl carbonate)=3:2:5), additive a and additive b are mixed together to prepare The mass fractions of electrolyte, NaPF ₆ , organic solvent, additive a and additive b are 14%, 83%, 1% and 2%, respectively. Wherein, the additive a is a mixture of the first compound and the second compound, wherein the mass ratio of the first compound and the second compound is 2:1, and the structures of the first compound and the second compound are as follows:

Preparation of positive electrode sheet: The positive electrode material is Prussian blue-type positive electrode material Na1.72MnFe(CN)6. The positive electrode material, binder PVDF, and conductive agent Super-P are dispersed in NMP organic solvent in a mass ratio of 90:4:6. Under the action of a vacuum mixer, it was stirred until it was stable and uniform, and it was evenly coated on an aluminum foil with a thickness of 12 μm. The aluminum foil was dried at room temperature and then transferred to a blast oven at 120 °C for 1 h, and then cold-pressed and die-cut to form a positive electrode sheet.

Negative plate preparation: The spherical hard carbon, the binder PVDF, and the conductive agent Super-P are mixed together in a mass ratio of 97:2:1, dispersed in NMP organic solvent, and uniformly coated on an aluminum foil with a thickness of 15 μm . The aluminum foil was dried at room temperature and then transferred to a blast oven at 120 °C for 1 h, and then cold-pressed and die-cut to form a negative electrode sheet.

Preparation of sodium ion battery: the positive electrode sheet, the negative electrode sheet and the polypropylene ceramic diaphragm are obtained through the lamination process to obtain a bare cell, after the cell is put into an aluminum-plastic film packaging case, the above electrolyte is injected, and then sealed in sequence, after standing, Processes such as hot and cold pressing, chemical formation, and volume separation are performed to produce a sodium-ion battery.

Example 2

The difference from Example 1 is that the mass fractions of the NaPF ₆ , the organic solvent, the additive a and the additive b are 14%, 82%, 2% and 2%, respectively.

The rest are the same as those in Embodiment 1, and are not repeated here.

Example 3

The difference from Example 1 is that the mass fractions of the NaPF ₆ , organic solvent, additive a and additive b are 14%, 79%, 5% and 2%, respectively.

The rest are the same as those in Embodiment 1, and are not repeated here.

Example 4

The difference from Example 1 is that the mass fractions of the NaPF ₆ , organic solvent, additive a and additive b are 14%, 77%, 7% and 2%, respectively.

The rest are the same as those in Embodiment 1, and are not repeated here.

Example 5

The difference from Example 1 is that the additive a includes the first compound and the second compound, and the structure is as follows:

The rest are the same as those in Embodiment 1, and are not repeated here.

Example 6

The difference from Example 1 is that the additive a includes the first compound and the second compound, and the structure is as follows:

The rest are the same as those in Embodiment 1, and are not repeated here.

Example 7

The difference from Example 1 is that the additive a includes the first compound and the second compound, and the structure is as follows:

The rest are the same as those in Embodiment 1, and are not repeated here.

Example 8

The difference from Example 1 is that the additive a only includes the first compound, and the structure is as follows:

The rest are the same as those in Embodiment 1, and are not repeated here.

Example 9

The difference from Example 1 is that the additive a only includes the second compound, and the structure is as follows:

The rest are the same as those in Embodiment 1, and are not repeated here.

Example 10

The difference from Example 1 is that the mass ratio of the first compound to the second compound is 1:1.

The rest are the same as those in Embodiment 1, and are not repeated here.

Example 11

The difference from Example 1 is that the mass ratio of the first compound to the second compound is 3:1.

The rest are the same as those in Embodiment 1, and are not repeated here.

Example 12

The difference from Example 1 is that the mass ratio of the first compound to the second compound is 4:1.

The rest are the same as those in Embodiment 1, and are not repeated here.

Example 13

The difference from Example 1 is that the mass ratio of the first compound to the second compound is 5:1.

The rest are the same as those in Embodiment 1, and are not repeated here.

Example 14

The difference from Example 1 is that the mass ratio of the first compound to the second compound is 1:2.

The rest are the same as those in Embodiment 1, and are not repeated here.

Example 15

The difference from Example 1 is that the mass ratio of the first compound to the second compound is 1:3.

The rest are the same as those in Embodiment 1, and are not repeated here.

Example 16

The difference from Example 1 is that the mass ratio of the first compound to the second compound is 1:4.

The rest are the same as those in Embodiment 1, and are not repeated here.

Example 17

The difference from Example 1 is that the mass ratio of the first compound to the second compound is 1:5.

The rest are the same as those in Embodiment 1, and are not repeated here.

Comparative Example 1

The difference from Example 1 is that the mass fractions of NaPF ₆ , organic solvent and additive b are 14%, 84% and 2%, respectively.

The rest are the same as those in Embodiment 1, and are not repeated here.

Comparative Example 2

The difference from Example 1 is that the mass fractions of NaPF ₆ , organic solvent and additive a are 14%, 84% and 2%, respectively.

The rest are the same as those in Embodiment 1, and are not repeated here.

Performance test: The electrolyte additives prepared in Examples 1-17 and Comparative Examples 1 and 2 were applied to the electrolyte and a sodium ion battery was prepared for testing. The test results are recorded in Table 1.

Table 1

It can be concluded from the above Table 1 that the performance of the electrolyte additive prepared by the present invention is better than that of Comparative Example 1 and Comparative Example 2, the capacity retention rate of 500 cycles at 55°C reaches 94.3%, and the capacity of high temperature storage at 60°C/7d The cycle retention rate is 97.1%, the capacity recovery rate is 99.8%, and the thickness expansion rate is 0.52%. According to the comparison of Examples 1-4, when the mass fractions of the NaPF ₆ , the organic solvent, the additive a and the additive b are set to be 14%, 83%, 1% and 2%, respectively, the performance of the prepared electrolyte is better. it is good. From the comparison of Examples 1 and 5-9, it can be seen that when the additive a is set as the first compound and the second compound is respectively the following chemical formula, the prepared electrolyte has better performance.

It can be seen from the comparison of Examples 1 and 10-17 that when the mass ratio of the first compound to the second compound is set to 2:1, the prepared electrolyte has better performance. It can be seen from the comparison of Example 1 and Comparative Examples 1-2 that when only additive a or only additive b is used, the prepared electrolyte has poor performance.

To sum up, the sodium ion battery of the present invention can effectively improve the cycle performance of the electrolyte and increase the high and low temperature capacity retention rate, capacity recovery rate and thickness expansion rate.

Based on the disclosure and teaching of the above specification, those skilled in the art to which the present invention pertains can also make changes and modifications to the above-described embodiments. Therefore, the present invention is not limited to the above-mentioned specific embodiments, and any obvious improvement, replacement or modification made by those skilled in the art on the basis of the present invention falls within the protection scope of the present invention. In addition, although some specific terms are used in this specification, these terms are only for convenience of description and do not constitute any limitation to the present invention.

Claims (10)

1. an electrolyte additive, is characterized in that, comprises additive a and additive b, and additive a comprises one or more in the first compound shown in following formula I and the second compound shown in following formula II;

Wherein, R1, R2, R3, R4, R5, R6, R7, R8 and R9 are independently selected from hydrogen, halogen atom, alkane group with 1 to 10 carbon atoms, unsaturated with 2 to 10 carbon atoms Any of a hydrocarbon group, an alkoxy group having 1 to 10 carbon atoms, or an alkanoyl group having 2 to 10 carbon atoms, the alkane group, the unsaturated hydrocarbon group, the alkoxy group, and the alkane group The H in the acyl group can be partially or completely substituted by one or more of halogen atoms, cyano groups, carboxyl groups and sulfonic acid groups; wherein, the additive b is ethylene carbonate, fluoroethylene carbonate, ethylene carbonate One or more of ethyl ester, vinyl sulfate and propenyl sultone. 2. The electrolyte additive according to claim 1, characterized in that, in the first compound represented by the formula I, R1, R2, and R3 are halogen atoms, and in the second compound represented by the formula II, R4, R5, and R6 are halogen atoms, and R7, R8, and R9 are alkane groups having 1 to 10 carbon atoms. 3. The electrolyte additive according to claim 1 or 2, wherein, in the first compound, R1, R2, and R3 are fluorine; in the second compound, R4, R5, and R6 are fluorine, and R7 , R8 and R9 are methyl. 4 . The electrolyte additive according to claim 1 , wherein the mass ratio of the additive a and the additive b is (1-5):(1-5). 5 . 5. The electrolyte additive according to claim 1 or 4, wherein the additive a comprises the first compound and the second compound, and the mass of the first compound and the second compound The parts ratio is 2:1, and the additive b is fluoroethylene carbonate. 6. An electrolyte, characterized in that it comprises a sodium salt electrolyte, an organic solvent and the electrolyte additive according to any one of claims 1-5. 7 . The electrolyte according to claim 6 , wherein the mass of the electrolyte additive accounts for 2% to 10% of the total mass of the electrolyte. 8 . 8. electrolyte according to claim 6, is characterized in that, described organic solvent comprises cyclic organic solvent and chain organic solvent, and described cyclic organic solvent is ethylene carbonate, propylene carbonate and butylene carbonate One or more of, the chain organic solvent is one or more of dimethyl carbonate, diethyl carbonate and ethyl methyl carbonate. 9 . The electrolyte according to claim 6 , wherein the sodium salt electrolyte is one or more of sodium hexafluorophosphate, sodium perchlorate, sodium tetrafluoroborate and sodium difluorooxalateborate. 10 . 10. A sodium-ion battery, characterized in that, comprising the electrolyte according to any one of claims 6-9.