CN115275340A

CN115275340A - High-voltage electrolyte and preparation method and application thereof

Info

Publication number: CN115275340A
Application number: CN202210948768.6A
Authority: CN
Inventors: 邵俊华; 孔东波; 韩飞; 王亚洲; 宋东亮; 施艳霞; 张利娟; 李海杰; 李渠成; 郭飞; 闫志卫; 王郝为; 闫国锋
Original assignee: Hunan Farnlet New Energy Technology Co ltd
Current assignee: Hunan Farnlet New Energy Technology Co ltd
Priority date: 2022-08-09
Filing date: 2022-08-09
Publication date: 2022-11-01

Abstract

The invention relates to a high-voltage electrolyte and a preparation method and application thereof, belonging to the technical field of sodium ion batteries; the high-voltage electrolyte comprises the following preparation raw materials: sodium salt, organic solvent, 3- (((guanidino-4-thiazolyl) methyl) thio) alanine methyl ester and benzotriazole-N, N, N ', N' -tetramethylurea hexafluorophosphate; wherein the mass fraction of the 3- (((guanidino-4-thiazolyl) methyl) thio) alanine methyl ester in the high-voltage electrolyte is 0.5-2.5%; the mass fraction of benzotriazole-N, N, N ', N' -tetramethylurea hexafluorophosphate in the high-voltage electrolyte is 0.5-2%; sodium salts include sodium tetrafluoroborate and sodium difluorooxalato; the organic solvent consists of carbonate and carboxylate. The invention can make the sodium ion battery have good cycle performance, quick charge performance and low temperature performance under high voltage through the synergistic effect of all the components of the electrolyte.

Description

High-voltage electrolyte and preparation method and application thereof

Technical Field

The invention belongs to the technical field of sodium ion batteries, and particularly relates to a high-voltage electrolyte and a preparation method and application thereof.

Background

Lithium Ion Batteries (LIBs) have become an important member of the energy reserve (available sustainable energy) in modern society, however, the critical electrode materials such as Lithium and cobalt are insufficient in total amount and uneven in distribution, which affects the cost of the Lithium Ion batteries and the energy supply chain. Therefore, various non-lithium ion batteries have been developed in the related art; among various non-lithium ion secondary batteries (such as sodium ion batteries, potassium ion batteries, magnesium ion batteries, etc.), sodium ion batteries are relatively mature in development, and have more practical value than other types of non-lithium secondary batteries in terms of comprehensive cost, performance, sustainability, and the like. In order to increase the energy density of the sodium ion battery, a method generally adopted in the related art is to use a high-capacity electrode (positive electrode or negative electrode) material (e.g., sodium vanadium phosphate) and a high-voltage positive electrode material.

In addition, the vanadium sodium phosphate battery with high energy density in the related technology can not realize quick charge on the premise of not influencing the performance and safety performance of the sodium ion battery. The slow interface sodium ion transmission kinetic property of the vanadium phosphate sodium battery electrode also greatly restricts the application of the vanadium phosphate sodium battery electrode in the fields of electronic products, electric automobiles and the like which need quick charging. The quick charging saves the charging time and can also greatly damage the sodium ion battery. Because of polarization in the battery, the acceptable maximum charging current is reduced with the increase of charging and discharging cycles, when charging is continued and the charging current is large, the ion concentration at the electrode is increased, the polarization is intensified, and the terminal voltage of the battery cannot directly and linearly correspond to the charged quantity/energy, namely, local high voltage is caused. Meanwhile, due to high-current charging, joule heating effect is aggravated due to increase of internal resistance, and side reaction is brought, so that decomposition or gas generation of electrolyte is caused, and poor circulation stability is caused.

Therefore, it is necessary to develop an electrolyte which is resistant to high pressure, has good cycling stability, and is suitable for fast charging.

Disclosure of Invention

In order to solve the problems in the prior art, the invention provides the high-voltage electrolyte which has good circulation stability.

The invention also provides a preparation method of the high-voltage electrolyte.

The invention also provides application of the high-voltage electrolyte in a sodium ion battery.

The invention also provides a sodium ion battery.

In order to solve the first technical problem, the technical scheme provided by the invention is as follows:

specifically, in a first aspect, the invention provides a high-voltage electrolyte, which comprises the following preparation raw materials: sodium salt, organic solvent, 3- (((guanidino-4-thiazolyl) methyl) thio) alanine methyl ester (CAS number: 76823-94-4) and benzotriazole-N, N, N ', N' -tetramethylurea hexafluorophosphate (CAS number: 94790-37-1);

the mass fraction of the 3- (((guanidino-4-thiazolyl) methyl) thio) alanine methyl ester in the high-voltage electrolyte is 0.5% -2.5%;

the mass fraction of the benzotriazole-N, N, N ', N' -tetramethylurea hexafluorophosphate in the high-voltage electrolyte is 0.5-2%;

the sodium salt comprises sodium tetrafluoroborate (CAS number: 13755-29-8) and sodium difluorooxalate (CAS number: 2102517-30-4);

the organic solvent is composed of carbonate and carboxylate.

According to one of the technical schemes of the high-voltage electrolyte, the invention at least has the following beneficial effects:

(1) In the high-voltage electrolyte provided by the invention, the damage of dissolved ions in the positive electrode to the positive electrode interface can be inhibited through excellent coordination of 3- (((guanidino-4-thiazolyl) methyl) thio) alanine methyl ester. For example, if the positive electrode material is sodium vanadate, P (phosphorus) and V (vanadium) ions may dissolve out and initiate (catalyze) various interfacial heterogeneous chemical reactions (between the positive electrode material and the electrolyte), resulting in gas evolution and byproduct generation, further possibly making the local CEI film too thick and blocking sodium ion diffusion paths; in the high-voltage electrolyte provided by the invention, 3- (((guanidino-4-thiazolyl) methyl) thio) alanine methyl ester is added, so that the CEI film is formed, and the coordination with the ions is generated, and the negative effect brought by the ions is inhibited.

(2) If the surface of the cathode material is covered with the CEI layer of high strength, cracks in the cathode caused by volume change can be suppressed or reversibly recovered, which will significantly improve the cycle life of the cathode even at high cutoff voltage. However, how to form a stable CEI to adapt to the change of large capacity is a difficult problem in the field of electrolyte. In the traditional CEI, the CEI rich in organic substances is combined with the surface of the positive electrode and cannot bear large volume change of the positive electrode, so that the fracture occurs in the process of sodium ion deintercalation, and continuous side reaction occurs between the positive electrode and electrolyte. In addition, the organic-rich CEI is easily oxidized at high voltage, which further accelerates the decay of capacity. And the inorganic CEI is rich, the bonding with the anode is weaker, and the strain/stress born by the anode in the volume change process is smaller, so that the protection effect is maintained. In addition, due to the extremely low electronic conductivity, the interface phase rich in inorganic matters is also very thin and has a wide electrochemical stability window, so that the passivation solution has good passivation capability on both the positive electrode and the negative electrode.

However, the formation of inorganically rich CEI on sodium vanadium phosphate is also very challenging. Although PF ₆ ^- Hydrolysis can produce LiF, but it is accompanied by the production of corrosive HF, and thus the CEI formed is not dense and poor in conductivity (ionic/electronic).

The highest occupied molecular orbital energy of the 3- (((guanidino-4-thiazolyl) methyl) thio) alanine methyl ester adopted by the invention is higher than that of a solvent molecule commonly used by electrolyte, so that an ion-conducting polymer interfacial film (CEI) can be formed on the surface of a positive electrode through oxidative polymerization, the higher combination of the 3- (((guanidino-4-thiazolyl) methyl) thio) alanine methyl ester with P (phosphorus) and V (vanadium) ions can enable the 3- (((guanidino-4-thiazolyl) methyl) alanine methyl ester to be complexed with high-valence transition metal ions on the surface of the positive electrode, cover active sites of the positive electrode and inhibit side reactions of the positive electrode and the electrolyte, unsaturated bonds are introduced on the basis of the structure of the 3- (((guanidino-4-thiazolyl) thio) alanine methyl ester, the film forming capability of the 3- (((CEI) alanine methyl ester can be improved, and the compactness and stability of a film can be enhanced. Finally, the introduction of 3- (((guanidino-4-thiazolyl) methyl) thio) alanine methyl ester increases the content of inorganic matters in the CEI membrane, forms a stable, uniform, compact, low-impedance and strong ion conductivity CEI membrane, and improves the cycling stability and the quick charging performance of the battery under high voltage.

(3) The mass fraction of the methyl 3- (((guanidino-4-thiazolyl) methyl) thio) alaninate is too low to have the effect, and a certain side reaction is caused when the mass fraction is too high. Specifically, the method comprises the following steps:

when the content exceeds the range required by the present invention, the thermal stability and oxidation resistance of the obtained electrolyte are slightly poor, and the problems of large self-discharge and low capacity retention are easily caused. The reason is that: the effects of other additives are easily covered under the premise of existence of a large amount of 3- (((guanidino-4-thiazolyl) methyl) thio) alanine methyl ester, and meanwhile, when the concentration of the additive is higher, the viscosity of the electrolyte is improved, the uniformity is reduced, and the turbidity of the electrolyte is easily caused. At this time, the wettability of the electrolyte to the electrode material is deteriorated, and the capacity and low-temperature performance are significantly reduced; the formed CEI film has obvious impedance increase, the quick charge performance and the cycle performance of the battery are obviously reduced, and the expansion degree is obviously improved.

(4) The high-voltage electrolyte provided by the invention also comprises benzotriazole-N, N, N ', N' -tetramethylurea hexafluorophosphate, which can form a negative electrode interface film (SEI) with high ionic conductivity, good chemical stability and negligible electron passing rate, and can reduce the formation of dendrites on the surface of a negative electrode, prevent the negative electrode material from directly contacting and reacting with the high-voltage electrolyte, damage the structure of the negative electrode material, and improve the low-temperature performance and the cycling stability of the battery under high voltage. In addition, benzotriazole-N, N, N ', N' -tetramethylurea hexafluorophosphate can prevent and interrupt combustion reaction; but also can reduce intermolecular force, reduce the viscosity of the electrolyte and improve the conductivity of the high-voltage electrolyte, thereby improving the safety and the quick charging performance of the high-voltage electrolyte.

(5) Although benzotriazole-N, N' -tetramethyluronium hexafluorophosphate has the advantages in the above respects, if the mass fraction is too low, the effect is not obtained, and if the mass fraction is too high, the viscosity of the obtained high-voltage electrolyte increases, the internal polarization of the battery increases, and the rate, low temperature and cycle performance deteriorate.

(6) During charging and discharging of sodium salt in the high-voltage electrolyte provided by the invention, sodium ions play a role in transmission in an interaction process.

The sodium salt consists of sodium tetrafluoroborate and sodium difluorooxalate, and the disodium salt can form a high-voltage stable CEI film on the surface of the positive electrode, thereby protecting the surface structure of the positive electrode (such as sodium vanadium phosphate) and inhibiting the surface reaction of the electrolyte; meanwhile, the problems of dendritic crystal growth, anode particle structure pulverization and the like of the sodium ion battery can be greatly improved, and the circulation stability of the sodium ion battery is improved; meanwhile, an interfacial film beneficial to sodium ion conduction can be formed on the surface of the negative electrode, so that the internal resistance of the battery is reduced, and the quick charge performance and the low temperature performance are improved.

(7) The organic solvent is a main part of the high-voltage electrolyte and ensures that sodium salt, 3- (((guanidino-4-thiazolyl) methyl) thio) alanine methyl ester and benzotriazole-N, N, N ', N' -tetramethylurea hexafluorophosphate are fully dispersed; thereby improving the cycling stability of the obtained high-voltage electrolyte.

The invention introduces the carboxylic ester solvents (ethyl propionate and the like) on the basis of the conventional carbonate solvents (diethyl carbonate, ethylene carbonate, methyl ethyl carbonate and the like), so that the melting point and the viscosity of the whole electrolyte system are greatly reduced, and the quick charging performance, the rate capability and the low-temperature performance of the battery under high voltage are improved.

(8) The invention can make the sodium ion battery have good cycle performance, quick charge performance and low temperature performance under high voltage through the synergistic effect of all the components of the high-voltage electrolyte.

According to some embodiments of the invention, the methyl 3- (((guanidino-4-thiazolyl) methyl) thio) alaninate is a positive film forming additive.

According to some embodiments of the invention, the benzotriazole-N, N' -tetramethylurea hexafluorophosphate is a negative electrode film forming additive.

According to some embodiments of the invention, the high voltage electrolyte comprises the following raw materials:

0.5 to 2.5 percent of 3- (((guanidyl-4-thiazolyl) methyl) sulfur) alanine methyl ester and 0.5 to 2 percent of benzotriazole-N, N, N ', N' -tetramethylurea hexafluorophosphate.

According to some embodiments of the invention, the high-voltage electrolyte comprises the following raw materials:

0.5 to 2.5 percent of 3- (((guanidyl-4-thiazolyl) methyl) sulfur) alanine methyl ester, 0.5 to 2 percent of benzotriazole-N, N, N ', N' -tetramethylurea hexafluorophosphate and 10 to 20 percent of sodium salt.

According to some embodiments of the invention, the high-voltage electrolyte consists of the following raw materials in percentage by mass:

0.5 to 2.5 percent of 3- (((guanidino-4-thiazolyl) methyl) sulfur) alanine methyl ester, 0.5 to 2 percent of benzotriazole-N, N, N ', N' -tetramethylurea hexafluorophosphate, 10 to 20 percent of sodium salt and the balance of solvent.

According to some embodiments of the invention, the mass fraction of the methyl 3- (((guanidino-4-thiazolyl) methyl) thio) alaninate in the high-voltage electrolyte is between 1.5% and 2.5%.

According to some embodiments of the invention, the mass fraction of the methyl 3- (((guanidino-4-thiazolyl) methyl) thio) alaninate in the high-voltage electrolyte is between 2% and 2.5%.

According to some embodiments of the invention, the mass fraction of the benzotriazole-N, N' -tetramethyluronium hexafluorophosphate in the high-voltage electrolyte is 1% to 2%.

According to some embodiments of the invention, the mass fraction of the benzotriazole-N, N' -tetramethyluronium hexafluorophosphate in the high-voltage electrolyte is 1% to 1.5%.

According to some embodiments of the invention, the sodium salt is present in the high voltage electrolyte in a mass fraction of 10% to 20%.

First, sodium salts primarily serve to transport sodium ions in sodium batteries.

Under the condition that the content of the sodium salt is lower than 10%, the conductivity of the electrolyte is lower, the capability of transmitting sodium ions is weaker, and the performance of the battery such as capacity and multiplying power is not facilitated.

When the sodium salt content is higher than 20%, the viscosity of the electrolyte is increased, the conductivity is reduced, the internal resistance is increased, and the low-temperature performance is poor.

When the content of the sodium salt is within the range of 10-20%, the content of the sodium salt can be adjusted according to practical application scenes so as to give full play to the capacity, rate capability and cycle performance of the battery and adjust the internal resistance and polarization of the battery.

According to some embodiments of the invention, the sodium salt is present in the high voltage electrolyte at a mass fraction of 10% to 15%.

According to some embodiments of the invention, the sodium salt consists of sodium tetrafluoroborate and sodium difluorooxalate.

Compared with one sodium salt, the performance of the mixture of the disodium salts under high voltage is better when the two sodium salts are added into the electrolyte, and good cycle performance can be realized by less dependence on external pressure.

According to some embodiments of the invention, the sodium tetrafluoroborate is present in the high voltage electrolyte at a mass fraction of between 7% and 8%.

According to some embodiments of the invention, the sodium difluorooxalate is present in the high-pressure electrolyte in a mass fraction of 7% to 8%.

According to some embodiments of the invention, the sodium tetrafluoroborate is present at a mass fraction of 7.5% in the high voltage electrolyte.

According to some embodiments of the invention, the sodium difluorooxalate is present in the high-pressure electrolyte at a mass fraction of 7.5%.

According to some embodiments of the invention, the carbonate is at least one of diethyl carbonate, ethylene carbonate, ethyl methyl carbonate.

The viscosity of diethyl carbonate and methyl ethyl carbonate is low, the electrochemical stability is better, and the low-temperature performance of the electrolyte can be improved.

The ethylene carbonate has high dielectric constant and high ionic conductivity, and can form a stable SEI film on the surface of the negative electrode.

According to some embodiments of the invention, the carboxylic acid ester is ethyl acetate (EA, 141-78-6), propyl acetate (PA, 109-60-4), ethyl propionate (EP, 105-37-3).

Ethyl propionate is used to improve the low temperature discharge performance of the battery obviously.

According to some embodiments of the invention, the organic solvent consists of diethyl carbonate, ethylene carbonate, ethyl propionate and ethyl methyl carbonate.

By using diethyl carbonate, ethylene carbonate, ethyl propionate and ethyl methyl carbonate in a matching way, the electrolyte with excellent low-temperature performance and long cycle life is obtained.

According to some embodiments of the invention, the organic solvent comprises the following components in parts by mass: 20-30% of diethyl carbonate, 15-25% of ethylene carbonate, 25-35% of ethyl propionate and 20-30% of methyl ethyl carbonate.

The density of diethyl carbonate is 0.977g/cm ³ (20 ℃) and a molecular weight of 118.1311,the melting point is-43 ℃ and the boiling point is 126.80 ℃. The electrolyte mainly plays a role in adjusting high and low temperature performance and viscosity, but the conductivity is influenced by the excessively high dosage.

The density of Ethylene Carbonate (EC) is 1.3218g/cm ³ Viscosity is 1.90mPa.s (40 deg.C), melting point is 35-38 deg.C, boiling point is 248 deg.C/760mmHg, 243-244 deg.C/740 mmHg. The EC solvent can promote the dissociation of metal salt due to the high dielectric constant of the EC solvent, and in addition, the EC can also be reduced on the surface of the negative electrode to form a stable Solid Electrolyte Interface (SEI) so as to increase the stability of the electrode. The EC-based electrolyte can also effectively inhibit the stripping of the negative electrode, thereby improving the cycle life and the stability of the battery.

The density of the ethyl propionate is 0.892g/cm ³ The melting point is-73.9 ℃ and the boiling point is 99.1 ℃. EP mainly plays a role in regulating low temperature and rate performance in the electrolyte.

The density of the ethyl methyl carbonate is 1.01g/cm ³ The melting point is-14 ℃ and the boiling point is 107 ℃. The substructure has two functional groups of methyl and ethyl, has the performances of DMC and DEC, and has outstanding low-temperature performance due to lower viscosity and wider liquid range.

According to some embodiments of the invention, the mass ratio of diethyl carbonate, ethylene carbonate, ethyl propionate and ethyl methyl carbonate in the organic solvent is 25.

The second aspect of the present invention provides a method for preparing the above high voltage electrolyte, comprising the steps of:

mixing the methyl 3- (((guanidino-4-thiazolyl) methyl) thio) alaninate, the benzotriazole-N, N, N ', N' -tetramethyluronium hexafluorophosphate, the sodium salt and the organic solvent.

According to some embodiments of the invention, the method for preparing the high voltage electrolyte comprises the following steps:

adding the methyl 3- (((guanidino-4-thiazolyl) methyl) thio) alaninate and the benzotriazole-N, N, N ', N' -tetramethylurea hexafluorophosphate into the organic solvent to prepare a mixed solution;

the sodium salt was then added to the mixed solution.

The third aspect of the invention provides the application of the high-voltage electrolyte in a sodium-ion battery.

The invention provides a sodium ion battery, and the preparation raw materials comprise the high-voltage electrolyte.

The invention can make the sodium ion battery have good cycle performance, quick charge performance and low temperature performance under high voltage through the synergistic effect of all the components of the electrolyte. Specifically, the method comprises the following steps:

in the electrolyte provided by the invention, the highest occupied molecular orbital energy level of the positive film forming additive 3- (((guanidino-4-thiazolyl) methyl) sulfur) alanine methyl ester is higher than that of solvent molecules, an ion conductive polymer interface film (CEI) can be formed on the surface of a positive electrode through oxidative polymerization, and the catalytic effect of P (phosphorus) and V (vanadium) ions can be inhibited through coordination, so that the local film is prevented from being too thick. Therefore, the 3- (((guanidino-4-thiazolyl) methyl) thio) alanine methyl ester can enable a stable, uniform, compact, low-impedance and strong ion conductivity CEI film to be formed on the surface of the sodium vanadium phosphate, and the circulation stability and the quick charging performance of the sodium vanadium phosphate under high voltage can be improved.

The cathode film-forming additive benzotriazole-N, N, N ', N' -tetramethylurea hexafluorophosphate can form a cathode interface film (SEI) with high ionic conductivity, good chemical stability and negligible electron passing rate, can reduce the formation of sodium dendrite on the surface of a cathode, can prevent a cathode material from directly contacting with electrolyte to react and damage the structure of the cathode material, and improves the low-temperature performance and the cycling stability of the vanadium sodium phosphate battery under high voltage. In addition, benzotriazole-N, N, N ', N' -tetramethylurea hexafluorophosphate can prevent and interrupt combustion reaction; but also can reduce intermolecular force, reduce the viscosity of the electrolyte and improve the conductivity of the electrolyte, thereby improving the safety and the quick charging performance of the electrolyte.

During charging and discharging of sodium salt in the electrolyte, sodium ions play a role in transmission in an interaction process. However, compared with the addition of one sodium salt in the electrolyte, the performance of the mixture of the disodium salts is better under high voltage, and good cycle performance can be realized by less dependence on external pressure. Sodium tetrafluoroborate and sodium difluorooxalate, the disodium salt can form a stable CEI film with high voltage on the vanadium phosphate, thereby protecting the surface structure of the vanadium phosphate and inhibiting the surface reaction of electrolyte, greatly improving the problems of dendritic growth, anode particle structure pulverization and the like of the vanadium phosphate battery, and improving the cycle stability of the vanadium phosphate battery; meanwhile, an interfacial film beneficial to sodium ion conduction can be formed on the surface of the negative electrode, so that the internal resistance of the battery is reduced, and the quick charge performance and the low temperature performance are improved.

The invention introduces the carboxylic ester solvent (ethyl propionate) on the basis of the conventional carbonate solvents (diethyl carbonate, ethylene carbonate and methyl ethyl carbonate), so that the melting point and the viscosity of the whole electrolyte system are greatly reduced, and the quick charging performance, the rate capability and the low-temperature performance of the battery under high voltage are improved.

According to the invention, through the synergistic effect of all the components of the electrolyte, the sodium vanadium phosphate anode material sodium ion battery has good cycle performance, quick charge performance and low temperature performance under high voltage.

According to some embodiments of the invention, the sodium ion battery comprises a positive electrode sheet, a negative electrode sheet, a separator interposed between the positive electrode sheet and the negative electrode sheet, and the electrolyte. According to some embodiments of the invention, the separator of the sodium-ion battery is an inorganic material modified polyethylene film.

According to some embodiments of the invention, the inorganic material modified polyethylene film is a nano alumina coated polyethylene film.

According to some embodiments of the invention, the positive plate of the sodium-ion battery comprises the following preparation raw materials: a positive electrode active material, a conductive agent, and a positive electrode binder.

According to some embodiments of the invention, the positive active material is sodium vanadium phosphate.

The vanadium sodium phosphate has the advantages of high working voltage, high energy density, high power density, long cycle life, good stability and low cost, and has wide application prospect in the field of new energy.

According to some embodiments of the invention, the conductive agent is acetylene black.

According to some embodiments of the invention, the positive electrode binder is polyvinylidene fluoride.

According to some embodiments of the present invention, the mass ratio of the positive electrode active material, the conductive agent, and the binder is 90 to 95: 1-5.

According to some embodiments of the invention, the positive electrode active material, the conductive agent, and the positive electrode binder are in a mass ratio of 95: 1-5.

According to some embodiments of the present invention, the raw material for preparing the positive electrode sheet further includes a copper foil.

According to some embodiments of the present invention, the raw material for preparing the positive electrode sheet further includes N-methylpyrrolidone.

According to some embodiments of the invention, the negative electrode sheet of the sodium-ion battery comprises the following preparation raw materials: a negative electrode active material, a conductive agent, a thickener, and a negative electrode binder.

According to some embodiments of the invention, the negative active material is hard carbon.

According to some embodiments of the invention, the conductive agent is conductive carbon black.

According to some embodiments of the invention, the negative electrode binder is styrene butadiene rubber.

According to some embodiments of the invention, the thickener is sodium carboxymethyl cellulose.

According to some embodiments of the present invention, the mass ratio of the anode active material, the conductive agent, the thickener, and the anode binder is 90 to 95:1 to 5:1 to 5:1 to 5.

According to some embodiments of the present invention, the anode active material, the conductive agent, the thickener, and the anode binder are in a mass ratio of 95:1 to 5:1 to 5:1 to 5.

According to some embodiments of the present invention, the raw material for preparing the negative electrode sheet further comprises a copper foil.

According to some embodiments of the present invention, the raw material for preparing the negative electrode sheet further includes water.

According to some embodiments of the invention, the sodium ion battery has an operating voltage of 2.0V to 4.0V.

The sodium ion battery has wider working voltage range and higher energy density.

Drawings

FIG. 1 is a linear scan of electrolytes of comparative example 1 and example 5 of the present invention.

Detailed Description

The concept and technical effects of the present invention will be clearly and completely described below in conjunction with the embodiments to fully understand the objects, features and effects of the present invention. It is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all embodiments, and other embodiments obtained by those skilled in the art without inventive efforts are within the protection scope of the present invention based on the embodiments of the present invention.

In the description of the present invention, reference to the description of the terms "one embodiment," "some embodiments," "an illustrative embodiment," "an example," "a specific example," or "some examples," etc., means that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the terms used above do not necessarily refer to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.

The examples, in which specific conditions are not specified, were conducted under conventional conditions or conditions recommended by the manufacturer. The reagents or instruments used are not indicated by the manufacturer, and are all conventional products available commercially.

Specific examples of the present invention are described in detail below.

Example 1

This embodiment is a high voltage electrolyte and a method for preparing the same.

The high-voltage electrolyte in the embodiment is prepared from the following raw materials in percentage by weight:

positive electrode film-forming additive (3- (((guanidino-4-thiazolyl) methyl) thio) alanine methyl ester) 0.5%, negative electrode film-forming additive (benzotriazole-N, N' -tetramethylurea hexafluorophosphate) 1.5%, sodium salt (sodium tetrafluoroborate 7.5% and sodium difluorooxalato borate 7.5%), solvent (mass ratio of diethyl carbonate (DEC), ethylene Carbonate (EC), ethyl Propionate (EP) and Ethyl Methyl Carbonate (EMC) 25).

The preparation method of the high-voltage electrolyte in the embodiment comprises the following steps:

the solvents (diethyl carbonate (DEC), ethylene Carbonate (EC), ethyl Propionate (EP) and Ethyl Methyl Carbonate (EMC)) were mixed uniformly in a glove box (moisture < 1ppm, oxygen < 1 ppm) filled with nitrogen to prepare a mixed solvent.

Adding a positive film-forming additive (3- (((guanidino-4-thiazolyl) methyl) sulfur) methyl alaninate) and a negative film-forming additive (benzotriazole-N, N, N ', N' -tetramethylurea hexafluorophosphate) into the mixed solvent to prepare a mixed solution.

Then, sodium salts (10 g/10min; sodium tetrafluoroborate and sodium difluorooxalate) were slowly added to the mixed solution, and stirred until they were completely dissolved, to obtain the sodium ion battery electrolyte of example 1.

Example 2

The raw materials for the preparation of the high-pressure electrolyte in this example are shown in Table 1.

The preparation process in this example was carried out as in example 1.

Example 3

The embodiment is a high-voltage electrolyte and a preparation method thereof.

The preparation process in this example was carried out as in example 1.

Example 4

The embodiment is a high-voltage electrolyte and a preparation method thereof.

The raw materials for preparing the high-pressure electrolyte in this example are shown in Table 1.

The preparation process in this example was carried out as in example 1.

Example 5

The preparation process in this example was carried out as in example 1.

Comparative example 1

The comparative example is a high voltage electrolyte and a method of making the same.

The raw materials for the preparation of the high-pressure electrolyte in this comparative example are shown in Table 1.

The preparation process in this comparative example was carried out as in example 1.

Comparative example 2

Comparative example 3

The present comparative example is a high voltage electrolyte and a method of making the same.

The raw materials for preparing the high-pressure electrolyte in this comparative example are shown in Table 1.

Comparative example 4

Comparative example 5

Comparative example 6

Comparative example 7

Comparative example 8

The preparation raw materials and the formulation thereof for the high-pressure electrolytes in examples 1 to 5 of the present invention and comparative examples 1 to 8 are shown in table 1.

TABLE 1 preparation materials and ratios of the high-voltage electrolytes of examples 1 to 5 of the present invention and comparative examples 1 to 8

In table 1, the percentages are by mass, the remainder being solvent.

Application example

The application example is a sodium ion battery.

Adding vanadium sodium phosphate (Na) as positive electrode active material ₃ V ₂ (PO ₄ ) ₃ )、The conductive agent acetylene black and the binder polyvinylidene fluoride (PVDF) are fully stirred and uniformly mixed in an N-methyl pyrrolidone (NMP) solvent system according to the mass ratio of 95: 2.5, then the mixture is coated on an aluminum foil to be dried and cold-pressed, and the positive plate is obtained, wherein the thickness of a coating on the positive plate is 104 mu m.

Fully stirring and uniformly mixing a negative active material hard carbon (C), a conductive agent conductive carbon black (SP), a binder Styrene Butadiene Rubber (SBR) and a thickener carboxymethylcellulose sodium (CMC) in a deionized water solvent system according to a mass ratio of 95: 2.5: 1.5: 1, coating the mixture on a copper foil, drying and cold pressing to obtain a negative plate; the thickness of the coating on the negative plate was 115 μm.

Polyethylene (PE, star source material, SD 216102) is used as a base film, and a nano-alumina coating (about 0.5 μm, DK 410-2) is coated on the base film to be used as a separation film.

And sequentially laminating the positive plate, the isolating film and the negative plate, winding the positive plate, the isolating film and the negative plate along the same direction to obtain a bare cell, and packaging the bare cell by adopting an aluminum plastic film. The designed capacity ratio of the negative electrode to the positive electrode is 1.1 to 1.5 (about 1.2 in this example).

The electrolyte prepared in examples 1 to 5 of the present invention and comparative examples 1 to 8 was injected into a pouch cell (injection amount was 5g/Ah, design capacity was 5 Ah). The battery is packaged, placed at 45 ℃, formed at high temperature, packaged for the second time and subjected to the capacity grading process to obtain the sodium ion battery.

And (3) electrochemical performance testing:

the sodium ion batteries prepared in the above examples 1 to 5 and comparative examples 1 to 8 were subjected to the following relevant performance tests:

(1) And (3) testing the normal-temperature cycle performance: charging the batteries with a constant current of 3C to 4.0V and a constant voltage of 0.01C at 25 ℃, standing for 5min, and discharging with a constant current of 1C to 2.0V. The capacity retention rate at 500 th cycle was calculated after 500 cycles of charge/discharge. The calculation formula is as follows:

capacity retention rate (%) at 500 th cycle (500 th cycle discharge capacity/1 st cycle discharge capacity) × 100%.

(2) Quick charge capability test (test of charging to 80% soc): and carrying out 2.0-4.0V charge-discharge test on the battery after capacity grading at 25 ℃.

The testing steps are as follows: firstly, 3C constant current charging is carried out until the voltage is 3.75V,2C constant current charging is carried out until the voltage is 3.9V,1C constant current constant voltage charging is carried out until the voltage is 4.0V, the cutoff current is 0.01C, and standing is carried out for 5min; discharging at 1C under constant current to 2.0V, and standing for 5min. The time for charging the battery to 80% SOC was measured.

(3) And (3) testing low-temperature discharge performance: at 25 ℃, the batteries after capacity grading are charged to 4.0V by using a 1C constant current and constant voltage (after constant current charging to 4V, constant voltage charging to 4V and cutoff current), the cutoff current is 0.01C, the batteries are placed for 5min,1C is discharged to 2.0V, the initial discharge capacity of the batteries is recorded, the batteries are placed for 5min, and the batteries are charged to 4.0V by using a 1C constant current and constant voltage, and the cutoff current is 0.01C. The cell was placed in a-20 ℃ cold box and left for 4h, and discharged to 2.0V at 1C under this temperature condition, and the cell low-temperature discharge capacity was recorded. The calculation formula is as follows:

low-temperature discharge capacity retention (%) = low-temperature discharge capacity/initial discharge capacity × 100%.

(4) Linear scan test: the scanning speed is 0.1mV/s, and the voltage range is 3.5V-4.75V.

The results of the above electrochemical performance tests are shown in table 2.

Table 2 electrochemical performance test results of sodium vanadium phosphate batteries corresponding to examples 1 to 5 and comparative examples 1 to 8

As can be seen from the results of the linear scan shown in fig. 1, the electrolyte solution to which methyl 3- (((guanidino-4-thiazolyl) methyl) thio) alaninate was added exhibited an oxidation current peak near 3.83V, indicating that methyl 3- (((guanidino-4-thiazolyl) methyl) thio) alaninate was able to undergo oxidative decomposition on the surface of the positive electrode to form a positive electrode interface film.

As can be seen from the test results of the example 1, the example 2, the example 3 and the comparative example 1 in the table 2, the addition of the positive film forming additive, namely, methyl 3- (((guanidino-4-thiazolyl) methyl) thio) alanine, into the electrolyte obviously improves the cycle stability and the quick charge performance of the vanadium sodium phosphate battery under high voltage. This is because the 3- (((guanidino-4-thiazolyl) methyl) thio) alanine methyl ester can form a layer of uniform and dense protective film with strong ionic conductivity on the surface of the vanadium sodium phosphate material, and inhibit the dissolution of metal ions in the positive electrode material and the collapse of the material structure.

According to the test results of the example 2, the example 4, the example 5 and the comparative example 2 in the table 2, it can be known that the addition of the negative electrode film-forming additive benzotriazole-N, N, N ', N' -tetramethylurea hexafluorophosphate to the electrolyte significantly improves the low-temperature performance and the cycle stability of the sodium vanadium phosphate battery at high voltage. The reason is that benzotriazole-N, N, N ', N' -tetramethylurea hexafluorophosphate forms a stable inorganic low-impedance SEI film at the interface of the graphite of the negative electrode, and can generate coordination with P (phosphorus) and V (vanadium) ions, inhibit free migration and reduction of metal ions in electrolyte and reduce damage to the surface of the electrode.

According to the test results of the example 2, the comparative example 3, the comparative example 4 and the comparative example 5 in the table 2, the sodium tetrafluoroborate and the sodium difluorooxalato disodium salt can effectively form films on the positive electrode and the negative electrode of the battery and inhibit the decomposition of the electrolyte, and compared with the traditional sodium ion secondary battery without the combined lithium salt system, the quick charge performance and the low-temperature discharge performance of the vanadium sodium phosphate battery under high voltage can be effectively improved.

From the test results of example 2 and comparative example 6 in table 2, it can be seen that when ethyl propionate is added under the condition of the same solvent ratio, the quick charge time of the sodium vanadium phosphate battery charging to 80% soc at high voltage is shortened by 21min, the low-temperature discharge capacity retention rate is improved by 19.7%, and the quick charge performance and the low-temperature performance of the sodium vanadium phosphate battery at high voltage are remarkably improved.

As is apparent from the test results of examples 1 to 3 and comparative example 7 in table 2, in the case of the additive methyl 3- (((guanidino-4-thiazolyl) methyl) thio) alaninate, the cycle performance of the battery is decreased as the content of methyl 3- (((guanidino-4-thiazolyl) methyl) thio) alaninate increases, and therefore, it is preferable to control the content of methyl 3- (((guanidino-4-thiazolyl) methyl) thio) alaninate to 0.5% to 2.5%, and low to no effect, and high to some extent, side reactions occur.

As can be seen from the test results of examples 2 and 4 to 5 and comparative examples 2 and 8 in table 2, the cycling performance, rate capability and low temperature performance of the battery are reduced when the content of benzotriazole-N, N '-tetramethylurea hexafluorophosphate as an additive is increased, and therefore, it is preferable to control the content of benzotriazole-N, N' -tetramethylurea hexafluorophosphate to 0.5% to 2%, which is not effective when the content is too low, and the interfacial resistance is increased when the content is too high, and the viscosity of the electrolyte itself is increased, which leads to increased internal polarization of the battery, and deterioration of rate, low temperature and cycling performance.

As is apparent from the results of the tests of example 5 and comparative examples 1 and 2 in Table 2, methyl 3- (((guanidino-4-thiazolyl) methyl) thio) alaninate and benzotriazole-N, N, N ', N' -tetramethyluronium hexafluorophosphate, when used alone, are inferior to the effects of the two types of additives used together. The invention can ensure that the quick-charging vanadium sodium phosphate battery system has long cycle performance in a limited space range by combined use of the two additives, and has excellent quick-charging and low-temperature performance.

Therefore, the invention develops an effective method for conveniently and simultaneously constructing the positive and negative electrode interface protective layers with stable and fast sodium ion transmission on the negative electrode and the positive electrode.

The invention also provides a high-voltage electrolyte adaptive to the quick-chargeable vanadium sodium phosphate battery, a stable positive-negative electrode interface protective layer for quick sodium ion transmission can be constructed on the negative electrode and the positive electrode by adding the film-forming additive and the electrolyte disodium salt into the electrolyte, and the melting point and the viscosity of an electrolyte system are reduced by adding the carboxylic ester solvent into the conventional carbonate solvent, so that the vanadium sodium phosphate battery has good cycle performance, quick-charging performance and low-temperature performance under the high-voltage condition due to the synergistic action among the components in the electrolyte.

In conclusion, the components of the electrolyte provided by the invention can effectively improve the quick charge performance, the cycle performance and the low-temperature performance of the vanadium sodium phosphate graphite battery under high voltage through a synergistic effect.

While the embodiments of the present invention have been described in detail with reference to the specific embodiments, the present invention is not limited to the embodiments, and various changes can be made without departing from the spirit of the present invention within the knowledge of those skilled in the art. Furthermore, the embodiments of the present invention and the features of the embodiments may be combined with each other without conflict.

Claims

1. A high voltage electrolyte, characterized by: the method comprises the following preparation raw materials: sodium salt, organic solvent, 3- (((guanidino-4-thiazolyl) methyl) thio) alanine methyl ester and benzotriazole-N, N, N ', N' -tetramethylurea hexafluorophosphate;

the sodium salts include sodium tetrafluoroborate and sodium difluorooxalate;

the organic solvent is composed of carbonate and carboxylate.

2. The high voltage electrolyte of claim 1, wherein: the mass fraction of the sodium salt in the high-voltage electrolyte is 10-20%.

3. The high voltage electrolyte of claim 1 or 2, wherein: the mass fraction of the 3- (((guanidino-4-thiazolyl) methyl) thio) alanine methyl ester in the high-voltage electrolyte is 1.5% -2.5%.

4. The high voltage electrolyte of claim 1 or 2, wherein: the mass fraction of the benzotriazole-N, N, N ', N' -tetramethylurea hexafluorophosphate in the high-voltage electrolyte is 1-2%.

5. The high voltage electrolyte of claim 1, wherein: the carbonate is at least one of diethyl carbonate, ethylene carbonate and ethyl methyl carbonate.

6. The high voltage electrolyte of claim 1, wherein: the carboxylic acid ester is at least one of ethyl acetate, propyl acetate and ethyl propionate.

7. A method of preparing a high voltage electrolyte as claimed in any one of claims 1 to 6, characterized in that: the method comprises the following steps:

8. A sodium ion battery, characterized in that: preparing a feedstock comprising a high voltage electrolyte as claimed in any one of claims 1 to 6.

9. The sodium-ion battery of claim 8, wherein: the working voltage of the sodium ion battery is 2.0V-4.0V.

10. The sodium-ion battery of claim 8 or 9, wherein: the positive electrode material of the sodium ion battery is vanadium sodium phosphate.