CN114976249A - Electrolyte and sodium ion battery - Google Patents

Abstract

The invention belongs to the technical field of secondary batteries, and particularly relates to an electrolyte and a sodium ion battery, which comprise a conductive sodium salt, a non-aqueous organic solvent and a functional additive, wherein the functional additive comprises one or more of fluoroethylene carbonate, ethylene sulfate, isatoic anhydride and tris (trimethylsilane) borate. The electrolyte adopts the combination of several functional additives, can generate synergistic action, can form a stable and compact interfacial film on a positive electrode and a negative electrode, can partially neutralize the alkalinity on the surface of a positive electrode material, inhibit side reaction with the electrolyte, improve the charge transfer capacity of an electrode, and combines several low-resistance additives, so that the formed interfacial film has small impedance, and the polarization of a battery is reduced, thereby having both low temperature and rate performance while having excellent circulation.

Description

An electrolyte and sodium ion battery

technical field

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

Background technique

With the gradual shortage of traditional fossil energy and increasingly serious environmental problems, the development of new renewable energy has become an inevitable trend. Lithium-ion batteries have been widely used in electric vehicles, notebook computers, and energy storage due to their high energy density, long cycle life, and environmental friendliness. However, the resource reserves of lithium are limited and unevenly distributed on the earth. will be exhausted. 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 from researchers. Batteries are expected to be widely used in the field of energy storage to replace lithium-ion batteries.

However, due to the strong alkalinity of the positive electrode material of the sodium-ion battery, it is easy to react with the electrolyte, especially at high voltage, the side reaction is more serious, and gas is generated, which leads to the increase of the internal pressure of the battery, the deformation of the battery, and the performance degradation. Therefore, it is imminent to solve the problem of battery gas production.

SUMMARY OF THE INVENTION

The purpose of the present invention is to: aiming at the deficiencies of the prior art, and to provide an electrolyte, which can neutralize the alkalinity of the surface of the positive electrode material, improve the compactness and stability of the SEI film, does not cause side reactions under high voltage, and does not Gas production does not deform.

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

An electrolyte, comprising conductive sodium salt, non-aqueous organic solvent and functional additives, the functional additives include fluoroethylene carbonate, vinyl sulfate, isatin anhydride, tris(trimethylsilane) borate one or more of.

Preferably, the functional additive accounts for 1% to 10% of the total mass of the electrolyte.

Preferably, the conductive sodium salt includes one or more of sodium hexafluorophosphate, sodium perchlorate, sodium difluorophosphate and sodium bisoxalatoborate.

Preferably, the conductive sodium salt accounts for 12% to 18% of the total weight of the electrolyte.

Preferably, the non-aqueous organic solvent includes one or a mixture of cyclic carbonate, chain carbonate, ethyl propionate, and propyl propionate.

Preferably, the mass ratio of the cyclic carbonate to the chain carbonate is 1:1-4.

Preferably, the cyclic carbonate includes one or a mixture of ethylene carbonate and propylene carbonate, and the chain carbonate includes one or more of dimethyl carbonate, diethyl carbonate and ethyl methyl carbonate kind of mix.

Preferably, the mass of the non-aqueous organic solvent accounts for 70% to 85% of the total mass of the electrolyte.

Preferably, the functional additives are fluoroethylene carbonate, vinyl sulfate, tris(trimethylsilane) borate and isatoic anhydride in a weight ratio of 2-8:0.2-5:0.1-5 : a mixture of 0.1 to 5.

The purpose of the present invention is to provide a sodium ion battery with good high voltage stability, good cycle performance and long service life in view of 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.

Compared with the prior art, the beneficial effects of the present invention are:

In the present invention, the functional additives include fluoroethylene carbonate, vinyl sulfate, isatin anhydride, and tris(trimethylsilane) borate. Fluorinated ethylene carbonate forms a relatively stable and dense SEI film on the negative electrode, which improves the wettability of the electrolyte and reduces the battery impedance; isatin anhydrides can neutralize the alkalinity on the surface of the positive electrode material, and can form a film on the positive electrode, and the fluorinated Acid anhydride can generate NaF, improve electrical conductivity, reduce internal resistance, inhibit the generation of cracks in the positive electrode material particles during the cycle, and improve the cycle; vinyl sulfate forms a low-impedance SEI film at the negative electrode, reducing the resistance increase of the battery during cycling. Improve low temperature and rate performance; tris(trimethylsilane) borate forms a stable and dense CEI film on the positive electrode, inhibits the dissolution of the transition metal of the positive electrode material, improves the stability of the positive electrode material, and at the same time can improve the charge transfer ability of the electrode, improve cycle. The isatin-based acid anhydrides include one or more of isatoic anhydride, 5-fluoroisatinic anhydride and 6-fluoroisatinic anhydride.

The invention adopts several additives in combination, which can produce a synergistic effect, can form a stable and dense interface film on the positive and negative electrodes, and can partially neutralize the alkalinity of the surface of the positive electrode material, suppress the side reaction with the electrolyte, and improve the charge of the electrode. In addition, several low-impedance additives are used in combination to form a low-impedance interfacial film, which reduces the polarization of the battery. Therefore, the low-temperature and rate performance can be taken into account while the cycle is excellent.

Detailed ways

1. An electrolyte comprising conductive sodium salt, non-aqueous organic solvent and functional additives, said functional additives comprising fluoroethylene carbonate, vinyl sulfate, isatin-like acid anhydride, tris(trimethylsilane)boron one or more of the acid esters.

In the present invention, the functional additives include fluoroethylene carbonate, vinyl sulfate, isatin anhydride, and tris(trimethylsilane) borate. Fluorinated ethylene carbonate forms a relatively stable and dense SEI film on the negative electrode, which improves the wettability of the electrolyte and reduces the battery impedance; isatin anhydrides can neutralize the alkalinity on the surface of the positive electrode material, and can form a film on the positive electrode, and the fluorinated Acid anhydride can generate NaF, improve electrical conductivity, reduce internal resistance, inhibit the generation of cracks in the positive electrode material particles during the cycle, and improve the cycle; vinyl sulfate forms a low-impedance SEI film at the negative electrode, reducing the resistance increase of the battery during cycling. Improve low temperature and rate performance; tris(trimethylsilane) borate forms a stable and dense CEI film on the positive electrode, inhibits the dissolution of the transition metal of the positive electrode material, improves the stability of the positive electrode material, and at the same time can improve the charge transfer ability of the electrode, improve cycle. The isatin-based acid anhydrides include one or more of isatoic anhydride, 5-fluoroisatinic anhydride and 6-fluoroisatinic anhydride.

The invention adopts several additives in combination, which can produce a synergistic effect, can form a stable and dense interface film on the positive and negative electrodes, and can partially neutralize the alkalinity of the surface of the positive electrode material, suppress the side reaction with the electrolyte, and improve the charge of the electrode. In addition, several low-impedance additives are used in combination to form a low-impedance interfacial film, which reduces the polarization of the battery. Therefore, the low-temperature and rate performance can be taken into account while the cycle is excellent.

Preferably, the functional additive accounts for 1% to 10% of the total mass of the electrolyte. The functional additives account for 2% to 10%, 4% to 8%, 4% to 7%, and 4% to 6% of the total mass of the electrolyte. Specifically, the functional additives account for 1% and 2% of the total mass of the electrolyte. , 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%.

Preferably, the conductive sodium salt includes one or more of sodium hexafluorophosphate, sodium perchlorate, sodium difluorophosphate and sodium bisoxalatoborate.

Preferably, the conductive sodium salt accounts for 12% to 18% of the total weight of the electrolyte. The conductive sodium salt accounts for 13% to 18%, 13% to 17%, and 14% to 16% of the total weight of the electrolyte. Specifically, the conductive sodium salt accounts for 12%, 14%, 16%, and 18% of the total weight of the electrolyte. .

Preferably, the non-aqueous organic solvent includes one or a mixture of cyclic carbonate, chain carbonate, ethyl propionate, and propyl propionate.

Preferably, the mass ratio of the cyclic carbonate to the chain carbonate is 1:1-4. The mass ratio of cyclic carbonate and chain carbonate is 1:1, 1:2, 1:3, 1:4.

Preferably, the cyclic carbonate includes one or a mixture of ethylene carbonate and propylene carbonate, and the chain carbonate includes one or more of dimethyl carbonate, diethyl carbonate and ethyl methyl carbonate kind of mix.

Preferably, the mass of the non-aqueous organic solvent accounts for 70% to 85% of the total mass of the electrolyte. The mass of the non-aqueous organic solvent accounts for 70%, 74%, 77%, 79%, 82%, and 85% of the total mass of the electrolyte.

Preferably, the functional additives are fluoroethylene carbonate, vinyl sulfate, tris(trimethylsilane) borate and isatoic anhydride in a weight ratio of 2-8:0.2-5:0.1-5 : a mixture of 0.1 to 5. Preferably, the weight ratio of fluoroethylene carbonate, vinyl sulfate, tris(trimethylsilane) borate and isatoic anhydride is 2～8:0.2～5:0.3～5:0.3～5,2 ～8:0.2～5:0.1～4:0.1～4, 2～8:0.2～5:0.1～3:0.1～3, 2～8:0.2～5:0.1～2:0.1～2, 2～8 :0.2～3:0.1～2:0.1～2.

2. A sodium-ion battery with good high voltage stability, good cycle performance and long service life.

A sodium-ion battery, comprising the above electrolyte.

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

1. An electrolyte, comprising a conductive sodium salt, a non-aqueous organic solvent and a functional additive, the functional additive comprising fluoroethylene carbonate, vinyl sulfate, tris(trimethylsilane) borate and indigo Red anhydride.

The preparation method of the electrolyte is as follows: NaPF ₆ (sodium hexafluorophosphate), mixed organic solvent (PC:DEC:EMC=3:2:5), FEC (fluoroethylene carbonate), DTD (ethylene sulfate) , TMSB (tris(trimethylsilane) borate), and isatoic anhydride were mixed, and were stirred with a vacuum mixer until stable and uniform to obtain an electrolyte solution. Among them, the mass of NaPF ₆ , mixed organic solvent, fluoroethylene carbonate, vinyl sulfate, tris(trimethylsilane) borate and isatoic anhydride accounted for 14%, 79% and 5% of the total mass of the electrolyte, respectively. , 1%, 0.5%, 0.5%.

The above electrolyte is used in a sodium ion battery, the sodium ion battery further comprises a positive electrode sheet, a negative electrode sheet, and a separator spaced between the positive electrode sheet and the negative electrode sheet.

The preparation method of the sodium-ion battery is as follows:

1) Preparation of positive electrode sheet: The positive electrode material Na[Ni _1/3 Mn _1/3 Fe _1/3 ]O ₂ , the binder PVDF, and the conductive agent Super-P were dispersed in NMP at a mass ratio of 96:2:2. In an organic solvent, it was stirred under the action of a vacuum mixer until it was stable and uniform, and it was uniformly 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.

2) Preparation of negative electrode sheet: The spherical hard carbon, the binder PVDF, and the conductive agent Super-P are mixed together according to the mass ratio of 97:2:1, and dispersed in the NMP organic solvent to uniformly coat the film with a thickness of 12 μm. on the aluminum foil. 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.

3) Pass the positive electrode sheet, the negative electrode sheet and the polypropylene separator through the lamination process to obtain a bare cell, put the cell into an aluminum-plastic film packaging case, inject the above-mentioned electrolyte, and then seal the cells in sequence, and pass the static, hot and cold pressing, Processes such as chemical formation and volume separation are carried out to produce a sodium-ion battery.

Example 2

The difference from Example 1 is the setting of electrolyte additives. In this example, the mass fraction of the functional additive isatoic anhydride is adjusted to 0.3%, and the mass fraction of the organic solvent is adjusted to 79.2%.

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

Example 3

The difference from Example 1 is the setting of electrolyte additives. In this example, the mass fraction of the functional additive isatoic anhydride is adjusted to 1%, and the mass fraction of the organic solvent is adjusted to 78.5%.

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

Example 4

The difference from Example 1 is the setting of electrolyte additives. In this example, the mass fraction of the functional additive isatoic anhydride is adjusted to 2%, and the mass fraction of the organic solvent is adjusted to 77.5%.

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

Example 5

The difference from Example 1 is the setting of electrolyte additives. In this example, the mass fraction of the functional additive isatoic anhydride is adjusted to 5%, and the mass fraction of the organic solvent is adjusted to 74.5%.

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

Example 6

The difference from Example 1 is the setting of electrolyte additives. In this example, the functional additive isatoic anhydride is adjusted to 5-fluoroisatinic anhydride, and the mass fraction remains unchanged.

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

Example 7

The difference from Example 1 is the setting of electrolyte additives. In this example, the functional additive isatoic anhydride is adjusted to 6-fluoroisatinic anhydride, and the mass fraction remains unchanged.

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

Comparative Example 1

The difference from Example 1 is the setting of electrolyte additives. In this comparative example, the functional additive fluoroethylene carbonate (FEC) was not used, and the mass fraction of the organic solvent was adjusted to 84%.

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

Comparative Example 2

The difference from Example 1 is the setting of electrolyte additives. In this comparative example, the functional additive vinyl sulfate (DTD) was not used, and the mass fraction of the organic solvent was adjusted to 80%.

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

Comparative Example 3

The difference from Example 1 is the setting of electrolyte additives. In this comparative example, the functional additive TMSB was not used, and the mass fraction of the organic solvent was adjusted to 79.5%.

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

Comparative Example 4

The difference from Example 1 is the setting of electrolyte additives. This comparative example does not use the functional additive isatoic anhydride, and the mass fraction of the organic solvent is adjusted to 79.5%.

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

The sodium ion batteries obtained from the above-mentioned Examples 1 to 7 and Comparative Examples 1 to 4 were tested for performance, and the test process was as follows:

1) High temperature cycle life test

After the sodium-ion battery was charged to 4.2V with a constant current of 1C at 45°C, the battery was charged with a constant voltage to a cut-off current of 0.05C, and then discharged with a constant current of 1C to 1.5V, which was recorded as one charge-discharge cycle. Then cycle according to the above conditions, and record the number of cycles n when the capacity retention rate reaches 80%.

2) Low temperature performance test

At room temperature 1C constant current and constant voltage charge to 4.2V, 0.05C cut-off, then discharge with 1C constant current to 1.5V cut-off, count as initial capacity C0, then normal temperature 1C constant current and constant voltage charge to 4.2V, 0.05C cut-off, fully charged Then put it in a low-temperature test cabinet at -40°C for 8h; at -40°C, discharge at a constant current of 0.2C to 1.5V, record the discharge capacity C1, and discharge efficiency percentage (%)=C1/C0×100%.

3) Rate performance test

Normal temperature 1C constant current and constant voltage charge to 4.2V, 0.05C cutoff, then discharge with 1C constant current to 1.5V cutoff, count as initial capacity C0; then normal temperature 1C constant current and constant voltage charge to 4.2V, 0.05C cutoff, use 8C Constant current discharge to 1.5V cut-off, record discharge capacity C1, discharge efficiency percentage (%)=C1/C0×100%

The results of high temperature cycle performance test, low temperature performance test, rate performance test and battery thickness expansion rate test are shown in Table 1.

Table 1

It can be drawn from the above Table 1 that the electrolyte of the present invention has better high temperature cycle performance, low temperature performance and high rate performance under high voltage compared to the electrolyte of the prior art, and the cell does not produce gas under high voltage. Not deformed. From the comparison between Example 1 and Comparative Examples 1-4, when the functional additives are set as fluorinated ethylene carbonate, ethylene sulfate, tris(trimethylsilane) borate and isatoic anhydride, the ratio in parts by weight is: When 5:1:0.5:0.5, the performance of the electrolyte is good, with better high-voltage high-temperature cycle performance, high-voltage low-temperature performance and high-rate performance.

From the comparison of Examples 1-5, it can be concluded that the electrolyte solution obtained when isatoic anhydride accounts for 0.5% of the total mass of the electrolyte solution has better performance. Under the high voltage of 4.2V, the high temperature of 45℃, the cycle number of cycle capacity reaches 80% at 1C/1C, the cycle number is as high as 1362 cycles, and the battery thickness expansion rate is as low as 2.1%, and the low temperature discharge efficiency at -40℃ is as high as 79.3%, and The 8C discharge efficiency is as high as 75%, the performance is further optimized, and the electrolyte performance and effect are better.

From the comparison of Examples 1 and 6-7, it can be concluded that the electrolyte solution obtained when 5-fluoroisatinic anhydride and 6-fluoroisatinic anhydride are used has better performance. Under the high voltage of 4.2V and the high temperature of 45°C, the cycle numbers of the 1C/1C cycle capacity retention rate reached 80%, and the cycle numbers reached 1655 cycles and 1671 cycles, respectively, and the battery thickness expansion ratios were 1.2% and 1.3%, respectively, which was higher than that of Example 1. The performance is better; the discharge efficiency at -40 ℃ is as high as 82.4% and 82.5%, and the discharge efficiency at 8C is also as high as 78.7% and 78.5%, respectively, and the performance is better.

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, is characterized in that, comprises conductive sodium salt, non-aqueous organic solvent and functional additive, and described functional additive comprises fluoroethylene carbonate, vinyl sulfate, isatoic anhydride/5-fluoroisatin One or more of acid anhydride/6-fluoroisatinic anhydride and tris(trimethylsilane) borate. 2 . The electrolyte according to claim 1 , wherein the functional additive accounts for 1% to 10% of the total mass of the electrolyte. 3 . 3. The electrolyte according to claim 1, wherein the conductive sodium salt comprises one or more of sodium hexafluorophosphate, sodium perchlorate, sodium difluorophosphate and sodium bisoxalatoborate. 4. The electrolyte according to claim 1 or 3, wherein the conductive sodium salt accounts for 12% to 18% of the total weight of the electrolyte. 5. electrolyte according to claim 1, is characterized in that, described non-aqueous organic solvent comprises one or more mixtures in cyclic carbonate, chain carbonate, ethyl propionate, propyl propionate . 6 . The electrolyte according to claim 5 , wherein the mass ratio of the cyclic carbonate to the chain carbonate is 1:1-4. 7 . 7. The electrolyte according to claim 5, wherein the cyclic carbonate comprises a mixture of one or both of ethylene carbonate and propylene carbonate, and the chain carbonate comprises dimethyl carbonate, carbonic acid One or more mixtures of diethyl ester and methyl ethyl carbonate. 8 . The electrolyte solution according to claim 5 , wherein the mass of the non-aqueous organic solvent accounts for 70% to 85% of the total mass of the electrolyte solution. 9 . 9. The electrolyte according to claim 1, wherein the functional additive is fluoroethylene carbonate, vinyl sulfate, tris(trimethylsilane) borate and isatoic anhydride by weight The ratio is a mixture of 2 to 8: 0.2 to 5: 0.1 to 5: 0.1 to 5. 10. A sodium-ion battery, characterized in that it comprises the electrolyte according to any one of claims 1-9.