A high-voltage electrolyte and its preparation method and application

Abstract

The present 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 includes the following preparation raw materials: sodium salt, organic solvent, 3-(((guanidino-4-thiazolyl)methyl)thio)propylimidate and benzotriazole-N,N,N',N'-tetramethyluronium hexafluorophosphate; wherein the mass fraction of 3-(((guanidino-4-thiazolyl)methyl)thio)propylimidate in the high-voltage electrolyte is 0.5% to 2.5%; the mass fraction of benzotriazole-N,N,N',N'-tetramethyluronium hexafluorophosphate in the high-voltage electrolyte is 0.5% to 2%; the sodium salt includes sodium tetrafluoroborate and sodium difluorooxalatoborate; the organic solvent is composed of carbonate and carboxylate. The present invention can make the sodium ion battery have good cycle performance, fast charging performance and low temperature performance at high voltage through the synergistic effect of each component of the electrolyte.

Description

Technical Field

[0001] The present invention belongs to the technical field of sodium ion batteries, and in particular relates to a high-voltage electrolyte and a preparation method and application thereof. Background Art

[0002] Lithium-ion batteries (LIBs) have become an important member of modern society's energy reserves (usable sustainable energy). However, key electrode materials such as lithium and cobalt face problems such as insufficient total supply and uneven distribution, which affects the cost of lithium-ion batteries and the energy supply chain. Therefore, various non-lithium-ion batteries have been developed in related technologies. 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. Considering comprehensive cost, performance, and sustainability, sodium-ion batteries have more practical value than other types of non-lithium secondary batteries. In order to improve the energy density of sodium-ion batteries, the method generally adopted in related technologies is to use high-capacity electrode (positive or negative electrode) materials (for example, sodium vanadium phosphate) and high-voltage positive electrode materials.

[0003] In addition, the high energy density sodium vanadium phosphate battery in the related art cannot achieve fast charging without affecting the performance and safety of the sodium ion battery. The slow interfacial sodium ion transport kinetics of the sodium vanadium phosphate battery electrode also greatly restricts its application in electronic products and electric vehicles and other fields that require fast charging. While fast charging saves charging time, it will also cause great damage to the sodium ion battery itself. Due to the polarization phenomenon in the battery, the maximum charging current it can accept will decrease with the increase of charge and discharge cycles. When charging continuously and the charging current is large, the ion concentration at the electrode increases, the polarization intensifies, and the battery terminal voltage cannot correspond directly and linearly to the amount of electricity / energy charged, which leads to local high voltage. At the same time, when charging with a large current, the increase in internal resistance will lead to the intensification of the Joule heating effect, resulting in side reactions, thereby causing the decomposition or gas production of the electrolyte, resulting in poor cycle stability.

[0004] Therefore, it is necessary to develop an electrolyte that is resistant to high voltage, has good cycle stability, and is suitable for fast charging. Summary of the Invention

[0005] In order to solve the problems existing in the prior art, the present invention provides a high-voltage electrolyte with good cycle stability.

[0006] The present invention also provides a method for preparing the high-voltage electrolyte.

[0007] The present invention also provides the use of the high-voltage electrolyte in a sodium ion battery.

[0008] The present invention also provides a sodium ion battery.

[0009] In order to solve the above-mentioned first technical problem, the technical solution provided by the present invention is as follows:

[0010] Specifically, the first aspect of the present invention provides a high-voltage electrolyte, comprising the following raw materials: sodium salt, organic solvent, 3-(((guanidino-4-thiazolyl)methyl)thio)propylimidate (CAS No.: 76823-94-4) and benzotriazole-N,N,N',N'-tetramethyluronium hexafluorophosphate (CAS No.: 94790-37-1);

[0011] The mass fraction of the 3-(((guanidino-4-thiazolyl)methyl)thio)propylimidate in the high-voltage electrolyte is 0.5% to 2.5%;

[0012] The mass fraction of the benzotriazole-N,N,N',N'-tetramethyluronium hexafluorophosphate in the high-voltage electrolyte is 0.5% to 2%;

[0013] The sodium salts include sodium tetrafluoroborate (CAS No.: 13755-29-8) and sodium difluorooxalatoborate (CAS No.: 2102517-30-4);

[0014] The organic solvent consists of carbonate and carboxylate.

[0015] According to one technical solution of the high-voltage electrolyte technical solution of the present invention, at least the following beneficial effects are achieved:

[0016] (1) In the high-voltage electrolyte provided by the present invention, 3-(((guanidino-4-thiazolyl)methyl)thio)propylimidate can inhibit the damage of the dissolved ions in the positive electrode to the positive electrode interface through its excellent coordination effect. For example, if the positive electrode material is sodium vanadate, P (phosphorus) and V (vanadium) ions will dissolve and trigger (catalyze) a variety of interfacial heterogeneous chemical reactions (between the positive electrode material and the electrolyte), resulting in gas production and the generation of by-products, which may further make the local CEI film too thick and block the sodium ion diffusion path; while in the high-voltage electrolyte provided by the present invention, 3-(((guanidino-4-thiazolyl)methyl)thio)propylimidate is added, which can coordinate with the above-mentioned ions while forming the CEI film, thereby inhibiting the negative effects brought by the above-mentioned ions.

[0017] (2) If the surface of the positive electrode material is covered with a high-strength CEI layer, cracks in the positive electrode caused by volume changes can be suppressed or reversibly recovered, which will significantly improve the cycle life of the positive electrode, even at high cut-off voltages. However, how to form a stable CEI to adapt to large capacity changes is a research problem in the field of electrolytes. In traditional CEI, the organic-rich CEI is bound to the positive electrode surface and cannot withstand the large volume changes of the positive electrode, resulting in breakage during the sodium ion deintercalation process and continuous side reactions between the positive electrode and the electrolyte. In addition, the organic-rich CEI is easily oxidized at high voltages, which further accelerates the capacity decay. In contrast, the inorganic-rich CEI has a weaker bond with the positive electrode and is subjected to less strain / stress during the volume change of the positive electrode, thereby maintaining its protective effect. In addition, due to its extremely low electronic conductivity, the inorganic-rich interfacial phase is also very thin and has a wide electrochemical stability window, which gives it good passivation ability for both the positive and negative electrodes.

[0018] However, the formation of inorganic-rich CEI on sodium vanadium phosphate is also very challenging. - Hydrolysis can produce LiF, but it is accompanied by the generation of corrosive HF, so the formed CEI is not dense and has poor electrical conductivity (ion / electron).

[0019] The 3-(((guanidine-4-thiazolyl)methyl)thio)propylimidate used in the present invention has a highest occupied molecular orbital energy level higher than the solvent molecules commonly used in electrolytes, so it can be oxidatively polymerized on the surface of the positive electrode to form an ion-conductive polymer interface film (CEI). Its high binding energy with P (phosphorus) and V (vanadium) ions enables it to complex with high-valent transition metal ions on the surface of the positive electrode, covering the active sites of the positive electrode and inhibiting the side reactions between the positive electrode and the electrolyte. The introduction of unsaturated bonds on the basis of its structure can improve its film-forming ability and enhance the density and stability of the film. Ultimately, the introduction of 3-(((guanidine-4-thiazolyl)methyl)thio)propylimidate increases the content of inorganic matter in the CEI film, forming a stable, uniform, dense, low-impedance, and highly ion-conductive CEI film, which improves the cycle stability and fast charging performance of the battery at high voltage.

[0020] (3) If the mass fraction of 3-(((guanidino-4-thiazolyl)methyl)thio)propylimidate is too low, it will not have any effect, while if it is too high, there will be certain side effects. Specifically:

[0021] When the content exceeds the range required by the present invention, the thermal stability and oxidation resistance of the resulting electrolyte are slightly poor, which can easily lead to problems such as large self-discharge and low capacity retention. The reason is that in the presence of a large amount of 3-(((guanidino-4-thiazolyl)methyl)thio)propylimidate, the effects of other additives are easily masked. At the same time, when its concentration is high, the viscosity of the electrolyte increases and the uniformity decreases, which can easily cause turbidity in the electrolyte. At this time, the wettability of the electrolyte to the electrode material will deteriorate, and the capacity and low-temperature performance will decrease significantly; the impedance of the formed CEI film will increase significantly, the fast charging performance and cycle performance of the battery will decrease significantly, and the degree of expansion will increase significantly.

[0022] (4) The high-voltage electrolyte provided by the present invention also includes benzotriazole-N,N,N',N'-tetramethyluronium hexafluorophosphate, which can form a negative electrode interface film (SEI) with high ionic conductivity, good chemical stability, and negligible electron transmission rate. It can not only reduce the formation of dendrites on the negative electrode surface, but also prevent the negative electrode material from directly contacting and reacting with the obtained high-voltage electrolyte, thereby destroying its structure and improving the low-temperature performance and cycle stability of the battery at high voltage. In addition, benzotriazole-N,N,N',N'-tetramethyluronium hexafluorophosphate can prevent and interrupt the combustion reaction; it can also reduce intermolecular forces, reduce its viscosity, and improve the conductivity of the high-voltage electrolyte, thereby improving the safety and fast charging performance of the high-voltage electrolyte.

[0023] (5) Although benzotriazole-N,N,N',N'-tetramethyluronium hexafluorophosphate has the advantages mentioned above, if its mass fraction is too low, it will not have any effect. If it is too high, the viscosity of the obtained high-voltage electrolyte itself will increase, the internal polarization of the battery will increase, and the rate, low temperature and cycle performance will deteriorate.

[0024] (6) When the sodium salt in the high-voltage electrolyte provided by the present invention is charged and discharged, the sodium ions play a role of transfer in the interaction process.

[0025] Sodium salt is composed of sodium tetrafluoroborate and sodium difluorooxalatoborate. 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 (for example, sodium vanadium phosphate) and inhibiting the surface reaction of the electrolyte; at the same time, it can also greatly improve the dendrite growth of sodium-ion batteries, the pulverization of the positive electrode particle structure and other problems, and improve the cycle stability of sodium-ion batteries; at the same time, it can also form an interface film on the surface of the negative electrode that is conducive to sodium ion conduction, thereby reducing the internal resistance of the battery and improving the fast charging performance and low-temperature performance.

[0026] (7) The organic solvent is the main part of the high-voltage electrolyte, which ensures that the sodium salt, 3-(((guanidino-4-thiazolyl)methyl)thio)propylimidate and benzotriazole-N,N,N',N'-tetramethyluronium hexafluorophosphate are fully dispersed; thereby improving the cycle stability of the obtained high-voltage electrolyte.

[0027] The present invention introduces carboxylate solvents (such as ethyl propionate) on the basis of conventional carbonate solvents (such as diethyl carbonate, ethylene carbonate, and ethyl methyl carbonate), which greatly reduces the melting point and viscosity of the entire electrolyte system, thereby improving the fast charging performance, rate performance, and low-temperature performance of the battery at high voltage.

[0028] (8) The present invention enables sodium ion batteries to have good cycle performance, fast charging performance and low temperature performance at high voltage through the synergistic effect of various components of the high-voltage electrolyte.

[0029] According to some embodiments of the present invention, the methyl 3-(((guanidino-4-thiazolyl)methyl)thio)propylimidate is a positive electrode film-forming additive.

[0030] According to some embodiments of the present invention, the benzotriazole-N,N,N',N'-tetramethyluronium hexafluorophosphate is a negative electrode film-forming additive.

[0031] According to some embodiments of the present invention, the high-voltage electrolyte includes the following raw materials in the following mass percentages:

[0032] 3-(((guanidino-4-thiazolyl)methyl)thio)propylimidate 0.5% to 2.5%, benzotriazole-N,N,N',N'-tetramethyluronium hexafluorophosphate 0.5% to 2%.

[0033] According to some embodiments of the present invention, the high-voltage electrolyte includes the following raw materials in the following mass percentages:

[0034] 3-(((guanidino-4-thiazolyl)methyl)thio)propylimidate 0.5%-2.5%, benzotriazole-N,N,N',N'-tetramethyluronium hexafluorophosphate 0.5%-2%, sodium salt 10%-20%.

[0035] According to some embodiments of the present invention, the high-voltage electrolyte is composed of the following raw materials in the following mass percentages:

[0036] 0.5% to 2.5% of methyl 3-(((guanidino-4-thiazolyl)methyl)thio)propylimidate, 0.5% to 2% of benzotriazole-N,N,N',N'-tetramethyluronium hexafluorophosphate, 10% to 20% of sodium salt and the rest of solvent.

[0037] According to some embodiments of the present invention, the mass fraction of the methyl 3-(((guanidino-4-thiazolyl)methyl)thio)propylimidate in the high-voltage electrolyte is 1.5% to 2.5%.

[0038] According to some embodiments of the present invention, the mass fraction of the methyl 3-(((guanidino-4-thiazolyl)methyl)thio)propylimidate in the high-voltage electrolyte is 2% to 2.5%.

[0039] According to some embodiments of the present invention, the mass fraction of the benzotriazole-N,N,N',N'-tetramethyluronium hexafluorophosphate in the high-voltage electrolyte is 1% to 2%.

[0040] According to some embodiments of the present invention, the mass fraction of the benzotriazole-N,N,N',N'-tetramethyluronium hexafluorophosphate in the high-voltage electrolyte is 1% to 1.5%.

[0041] According to some embodiments of the present invention, the mass fraction of the sodium salt in the high-voltage electrolyte is 10% to 20%.

[0042] First of all, sodium salt plays the main role of transferring sodium ions in sodium batteries.

[0043] When the sodium salt content is lower than 10%, the conductivity of the electrolyte is low and its ability to transport sodium ions is weak, which is not conducive to the performance of battery capacity, rate and other performance.

[0044] When the sodium salt content is higher than 20%, the viscosity of the electrolyte increases and the conductivity decreases, which will lead to increased internal resistance and poor low-temperature performance.

[0045] When the sodium salt content is within the range of 10-20%, the sodium salt content can be adjusted according to the actual application scenario to fully exert the battery's capacity, rate performance, and cycle performance, while adjusting the battery's internal resistance and polarization.

[0046] According to some embodiments of the present invention, the mass fraction of the sodium salt in the high-voltage electrolyte is 10% to 15%.

[0047] According to some embodiments of the invention, the sodium salt consists of sodium tetrafluoroborate and sodium difluorooxalatoborate.

[0048] Compared with adding one sodium salt to the electrolyte, the double sodium salt mixture performs better at high voltage and is less dependent on external pressure to achieve good cycling performance.

[0049] According to some embodiments of the present invention, the mass fraction of sodium tetrafluoroborate in the high-voltage electrolyte is 7% to 8%.

[0050] According to some embodiments of the present invention, the mass fraction of the sodium difluorooxalatoborate in the high-voltage electrolyte is 7% to 8%.

[0051] According to some embodiments of the present invention, the mass fraction of sodium tetrafluoroborate in the high-voltage electrolyte is 7.5%.

[0052] According to some embodiments of the present invention, the mass fraction of the sodium difluorooxalatoborate in the high-voltage electrolyte is 7.5%.

[0053] According to some embodiments of the present invention, the carbonate is at least one of diethyl carbonate, ethylene carbonate, and ethyl methyl carbonate.

[0054] Diethyl carbonate and ethyl methyl carbonate have low viscosity and better electrochemical stability, and can improve the low-temperature performance of the electrolyte.

[0055] Ethylene carbonate has a high dielectric constant and high ionic conductivity, and can form a stable SEI film on the negative electrode surface.

[0056] According to some embodiments of the present invention, the carboxylic acid ester is ethyl acetate (EA, 141-78-6), propyl acetate (PA, 109-60-4), or ethyl propionate (EP, 105-37-3).

[0057] Ethyl propionate can significantly improve the low temperature discharge performance of the battery.

[0058] According to some embodiments of the present invention, the organic solvent consists of diethyl carbonate, ethylene carbonate, ethyl propionate and ethyl methyl carbonate.

[0059] By combining diethyl carbonate, ethylene carbonate, ethyl propionate and ethyl methyl carbonate, an electrolyte with excellent low-temperature performance and a long cycle life is obtained.

[0060] According to some embodiments of the present invention, the organic solvent includes the following components in mass fractions: 20% to 30% diethyl carbonate, 15% to 25% ethylene carbonate, 25% to 35% ethyl propionate, and 20% to 30% ethyl methyl carbonate.

[0061] The density of diethyl carbonate is 0.977 g / cm 3 (20℃), molecular weight is 118.1311, melting point is -43℃, boiling point is 126.80℃. It mainly plays the role of adjusting high and low temperature performance and viscosity in electrolyte, but excessive dosage will affect conductivity.

[0062] The density of ethylene carbonate (EC) is 1.3218 g / cm 3EC has a viscosity of 1.90 mPa.s (40°C), a melting point of 35°C to 38°C, and boiling points of 248°C / 760 mmHg and 243°C to 244°C / 740 mmHg. EC solvents, due to their high dielectric constant, promote the dissociation of metal salts. Furthermore, EC can be reduced to form a stable solid electrolyte interlayer (SEI) on the anode surface, enhancing electrode stability. EC-based electrolytes also effectively inhibit anode stripping, thereby improving battery cycle life and stability.

[0063] The density of ethyl propionate is 0.892 g / cm 3 , melting point is -73.9 ° C, boiling point is 99.1 ° C. EP in the electrolyte mainly plays the role of regulating low temperature and rate performance.

[0064] The density of ethyl methyl carbonate is 1.01 g / cm 3 , with a melting point of -14°C and a boiling point of 107°C. The substructure has both methyl and ethyl functional groups, and has the properties of DMC and DEC. Due to its low viscosity and wide liquid range, its low-temperature performance is outstanding.

[0065] According to some embodiments of the present invention, the mass ratio of diethyl carbonate, ethylene carbonate, ethyl propionate and ethyl methyl carbonate in the organic solvent is 25:20:30:25.

[0066] A second aspect of the present invention provides a method for preparing the high-voltage electrolyte, comprising the following steps:

[0067] The methyl 3-(((guanidino-4-thiazolyl)methyl)thio)propylimidate, the benzotriazole-N,N,N',N'-tetramethyluronium hexafluorophosphate, the sodium salt, and the organic solvent are mixed.

[0068] According to some embodiments of the present invention, the method for preparing the high-voltage electrolyte comprises the following steps:

[0069] adding the 3-(((guanidino-4-thiazolyl)methyl)thio)propylimidate and the benzotriazole-N,N,N',N'-tetramethyluronium hexafluorophosphate to the organic solvent to prepare a mixed solution;

[0070] Then, the sodium salt is added to the mixed solution.

[0071] A third aspect of the present invention provides the use of the above-mentioned high-voltage electrolyte in a sodium ion battery.

[0072] A fourth aspect of the present invention provides a sodium ion battery, the preparation raw materials of which include the high-voltage electrolyte as described above.

[0073] The present invention, through the synergistic effect of the various components of the electrolyte, can make the sodium ion battery have good cycle performance, fast charging performance and low temperature performance at high voltage. Specifically:

[0074] In the electrolyte provided by the present invention, the highest occupied molecular orbital energy level of the positive electrode film-forming additive 3-(((guanidino-4-thiazolyl)methyl)thio)propylimidate is higher than that of the solvent molecules, and it can be oxidatively polymerized on the positive electrode surface to form an ion-conductive polymer interface film (CEI), and through coordination, it can inhibit the catalytic effect of P (phosphorus) and V (vanadium) ions to prevent the local film from being too thick. Therefore, 3-(((guanidino-4-thiazolyl)methyl)thio)propylimidate can form a stable, uniform, dense, low-impedance, and highly ion-conductive CEI film on the surface of sodium vanadium phosphate, which can improve the cycle stability and fast charging performance of sodium vanadium phosphate under high voltage.

[0075] Benzotriazole-N,N,N',N'-tetramethyluronium hexafluorophosphate, a negative electrode film-forming additive, forms a negative electrode interfacial layer (SEI) with high ionic conductivity, excellent chemical stability, and negligible electron transport rate. This not only reduces the formation of sodium dendrites on the negative electrode surface but also prevents direct contact between the negative electrode material and the electrolyte, which could damage its structure. This improves the low-temperature performance and cycling stability of sodium vanadium phosphate batteries at high voltages. Furthermore, benzotriazole-N,N,N',N'-tetramethyluronium hexafluorophosphate can prevent and interrupt combustion reactions; it can also reduce intermolecular forces, lower its viscosity, and improve the conductivity of the electrolyte, thereby enhancing the safety and fast-charging performance of the electrolyte.

[0076] When sodium salts in the electrolyte are charged and discharged, sodium ions play a role in the interaction process. However, compared with adding one sodium salt to the electrolyte, the performance of the double sodium salt mixture at high voltage is better, and it is less dependent on external pressure to achieve good cycle performance. Sodium tetrafluoroborate and sodium difluorooxalatoborate, double sodium salts can form a high-voltage stable CEI film on sodium vanadium phosphate, thereby protecting the surface structure of sodium vanadium phosphate and inhibiting the surface reaction of the electrolyte, greatly improving the problems of dendrite growth and powdering of the positive electrode particle structure of the sodium vanadium phosphate battery, and improving the cycle stability of the sodium vanadium phosphate battery; at the same time, it can also form an interface film on the negative electrode surface that is conducive to sodium ion conduction, reduce the internal resistance of the battery, and improve the fast charging performance and low-temperature performance.

[0077] The present invention introduces a carboxylate solvent (ethyl propionate) on the basis of conventional carbonate solvents (diethyl carbonate, ethylene carbonate, ethyl methyl carbonate), which greatly reduces the melting point and viscosity of the entire electrolyte system, thereby improving the battery's fast charging performance, rate performance and low-temperature performance at high voltage.

[0078] The present invention, through the synergistic effect of various components of the electrolyte, can make the sodium ion battery with sodium vanadium phosphate positive electrode material have good cycle performance, fast charging performance and low temperature performance at high voltage.

[0079] According to some embodiments of the present invention, the sodium ion battery includes a positive electrode sheet, a negative electrode sheet, a separator disposed between the positive electrode sheet and the negative electrode sheet, and the electrolyte. According to some embodiments of the present invention, the separator of the sodium ion battery is an inorganic material-modified polyethylene film.

[0080] According to some embodiments of the present invention, the inorganic material modified polyethylene film is a nano-alumina coated polyethylene film.

[0081] According to some embodiments of the present invention, the positive electrode sheet of the sodium ion battery includes the following preparation raw materials: a positive electrode active material, a conductive agent and a positive electrode binder.

[0082] According to some embodiments of the present invention, the positive electrode active material is sodium vanadium phosphate.

[0083] Sodium vanadium phosphate has high operating voltage, high energy density, high power density, long cycle life, good stability, and low cost, and has broad application prospects in the field of new energy.

[0084] According to some embodiments of the present invention, the conductive agent is acetylene black.

[0085] According to some embodiments of the present invention, the positive electrode binder is polyvinylidene fluoride.

[0086] According to some embodiments of the present invention, the mass ratio of the positive electrode active material, the conductive agent and the binder is 90-95:1-5:1-5.

[0087] According to some embodiments of the present invention, the mass ratio of the positive electrode active material, the conductive agent and the positive electrode binder is 95:1-5:1-5.

[0088] According to some embodiments of the present invention, the raw materials for preparing the positive electrode sheet further include copper foil.

[0089] According to some embodiments of the present invention, the raw materials for preparing the positive electrode sheet further include N-methylpyrrolidone.

[0090] According to some embodiments of the present invention, the negative electrode sheet of the sodium ion battery includes the following preparation raw materials: a negative electrode active material, a conductive agent, a thickener and a negative electrode binder.

[0091] According to some embodiments of the present invention, the negative electrode active material is hard carbon.

[0092] According to some embodiments of the present invention, the conductive agent is conductive carbon black.

[0093] According to some embodiments of the present invention, the negative electrode binder is styrene-butadiene rubber.

[0094] According to some embodiments of the invention, the thickener is sodium carboxymethyl cellulose.

[0095] According to some embodiments of the present invention, the mass ratio of the negative electrode active material, the conductive agent, the thickener and the negative electrode binder is 90-95:1-5:1-5:1-5.

[0096] According to some embodiments of the present invention, the mass ratio of the negative electrode active material, the conductive agent, the thickener and the negative electrode binder is 95:1-5:1-5:1-5.

[0097] According to some embodiments of the present invention, the raw material for preparing the negative electrode sheet further includes copper foil.

[0098] According to some embodiments of the present invention, the raw materials for preparing the negative electrode sheet further include water.

[0099] According to some embodiments of the present invention, the operating voltage of the sodium ion battery is 2.0V to 4.0V.

[0100] The sodium ion battery of the present invention has a wider operating voltage range and a higher energy density. BRIEF DESCRIPTION OF THE DRAWINGS

[0101] Figure 1 These are the linear scan results of the electrolytes corresponding to Comparative Example 1 and Example 5 of the present invention. DETAILED DESCRIPTION

[0102] The following will clearly and completely describe the concept and technical effects of the present invention in conjunction with the embodiments to fully understand the purpose, features and effects of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, other embodiments obtained by those skilled in the art without creative work are all within the scope of protection of the present invention.

[0103] In the description of the present invention, reference to terms such as "one embodiment," "some embodiments," "illustrative embodiments," "examples," "specific examples," or "some examples" means that the specific features, structures, materials, or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the exemplary expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.

[0104] If the specific conditions are not specified in the examples, the experiments were carried out under conventional conditions or those recommended by the manufacturer. All reagents or instruments used, if the manufacturer is not specified, are commercially available conventional products.

[0105] Specific embodiments of the present invention are described in detail below.

[0106] Example 1

[0107] This embodiment provides a high-voltage electrolyte and a preparation method thereof.

[0108] The high-voltage electrolyte in this embodiment is composed of the following raw materials in percentage by weight:

[0109] The positive electrode film-forming additive (3-(((guanidino-4-thiazolyl)methyl)thio)propylimidate) 0.5%, the negative electrode film-forming additive (benzotriazole-N,N,N',N'-tetramethyluronium hexafluorophosphate) 1.5%, sodium salt (sodium tetrafluoroborate 7.5% and sodium difluorooxalatoborate 7.5%), and the solvent (diethyl carbonate (DEC), ethylene carbonate (EC), ethyl propionate (EP) and ethyl methyl carbonate (EMC) in a mass ratio of 25:20:30:25) are used as the balance.

[0110] The method for preparing the high-voltage electrolyte in this embodiment comprises the following steps:

[0111] In a glove box filled with nitrogen (moisture <1 ppm, oxygen <1 ppm), solvents (diethyl carbonate (DEC), ethylene carbonate (EC), ethyl propionate (EP) and ethyl methyl carbonate (EMC)) were mixed uniformly to prepare a mixed solvent.

[0112] A positive electrode film-forming additive (3-(((guanidino-4-thiazolyl)methyl)thio)propylimidate) and a negative electrode film-forming additive (benzotriazole-N,N,N',N'-tetramethyluronium hexafluorophosphate) were added to a mixed solvent to prepare a mixed solution.

[0113] Then, sodium salt (10 g / 10 min; sodium tetrafluoroborate and sodium difluorooxalatoborate) was slowly added to the mixed solution and stirred until it was completely dissolved to obtain the sodium ion battery electrolyte of Example 1.

[0114] Example 2

[0115] This embodiment provides a high-voltage electrolyte and a preparation method thereof.

[0116] The raw materials for preparing the high-voltage electrolyte in this embodiment are shown in Table 1.

[0117] The preparation method in this example is carried out with reference to Example 1.

[0118] Example 3

[0119] This embodiment provides a high-voltage electrolyte and a preparation method thereof.

[0120] The raw materials for preparing the high-voltage electrolyte in this embodiment are shown in Table 1.

[0121] The preparation method in this example is carried out with reference to Example 1.

[0122] Example 4

[0123] This embodiment provides a high-voltage electrolyte and a preparation method thereof.

[0124] The raw materials for preparing the high-voltage electrolyte in this embodiment are shown in Table 1.

[0125] The preparation method in this example is carried out with reference to Example 1.

[0126] Example 5

[0127] This embodiment provides a high-voltage electrolyte and a preparation method thereof.

[0128] The raw materials for preparing the high-voltage electrolyte in this embodiment are shown in Table 1.

[0129] The preparation method in this example is carried out with reference to Example 1.

[0130] Comparative Example 1

[0131] This comparative example is a high-voltage electrolyte and a preparation method thereof.

[0132] The raw materials for preparing the high-voltage electrolyte in this comparative example are shown in Table 1.

[0133] The preparation method in this comparative example was carried out with reference to Example 1.

[0134] Comparative Example 2

[0135] This comparative example is a high-voltage electrolyte and a preparation method thereof.

[0136] The raw materials for preparing the high-voltage electrolyte in this comparative example are shown in Table 1.

[0137] The preparation method in this comparative example was carried out with reference to Example 1.

[0138] Comparative Example 3

[0139] This comparative example is a high-voltage electrolyte and a preparation method thereof.

[0140] The raw materials for preparing the high-voltage electrolyte in this comparative example are shown in Table 1.

[0141] The preparation method in this comparative example was carried out with reference to Example 1.

[0142] Comparative Example 4

[0143] This comparative example is a high-voltage electrolyte and a preparation method thereof.

[0144] The raw materials for preparing the high-voltage electrolyte in this comparative example are shown in Table 1.

[0145] The preparation method in this comparative example was carried out with reference to Example 1.

[0146] Comparative Example 5

[0147] This comparative example is a high-voltage electrolyte and a preparation method thereof.

[0148] The raw materials for preparing the high-voltage electrolyte in this comparative example are shown in Table 1.

[0149] The preparation method in this comparative example was carried out with reference to Example 1.

[0150] Comparative Example 6

[0151] This comparative example is a high-voltage electrolyte and a preparation method thereof.

[0152] The raw materials for preparing the high-voltage electrolyte in this comparative example are shown in Table 1.

[0153] The preparation method in this comparative example was carried out with reference to Example 1.

[0154] Comparative Example 7

[0155] This comparative example is a high-voltage electrolyte and a preparation method thereof.

[0156] The raw materials for preparing the high-voltage electrolyte in this comparative example are shown in Table 1.

[0157] The preparation method in this comparative example was carried out with reference to Example 1.

[0158] Comparative Example 8

[0159] This comparative example is a high-voltage electrolyte and a preparation method thereof.

[0160] The raw materials for preparing the high-voltage electrolyte in this comparative example are shown in Table 1.

[0161] The preparation method in this comparative example was carried out with reference to Example 1.

[0162] The raw materials and their proportions for preparing the high-voltage electrolytes in Examples 1 to 5 of the present invention and Comparative Examples 1 to 8 are shown in Table 1.

[0163] Table 1 Raw materials and proportions for the preparation of high-voltage electrolytes of Examples 1 to 5 of the present invention and Comparative Examples 1 to 8

[0164]

[0165]

[0166]

[0167] In Table 1, the percentages are by mass, and the remainder is the solvent.

[0168] Application Examples

[0169] This application example is a sodium ion battery.

[0170] The positive electrode active material sodium vanadium phosphate (Na3V2(PO4)3), the conductive agent acetylene black, and the binder polyvinylidene fluoride (PVDF) are fully stirred and mixed in an N-methylpyrrolidone (NMP) solvent system in a mass ratio of 95:2.5:2.5, and then coated on aluminum foil, dried, and cold pressed to obtain a positive electrode sheet. The coating thickness on the positive electrode sheet is 104μm.

[0171] The negative electrode active material hard carbon (C), the conductive agent conductive carbon black (SP), the binder styrene-butadiene rubber (SBR), and the thickener sodium carboxymethyl cellulose (CMC) are thoroughly stirred and mixed in a deionized water solvent system in a mass ratio of 95:2.5:1.5:1, and then coated on a copper foil, dried, and cold pressed to obtain a negative electrode sheet; the thickness of the coating on the negative electrode sheet is 115 μm.

[0172] Polyethylene (PE, Xingyuan Material, SD216102) was used as the base film and a nano-aluminum oxide coating (about 0.5 μm, DK410-2) was coated on the base film as the isolation membrane.

[0173] The positive electrode sheet, separator, and negative electrode sheet are stacked in sequence and wound in the same direction to obtain a bare cell, which is then packaged with 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 embodiment).

[0174] The electrolytes prepared in Examples 1 to 5 and Comparative Examples 1 to 8 of the present invention were injected into soft-pack batteries (injection volume of 5 g / Ah, designed capacity of 5 Ah). The batteries were packaged, stored at 45°C, subjected to high-temperature formation, secondary packaging, and capacity separation to obtain sodium-ion batteries.

[0175] Electrochemical performance test:

[0176] The sodium ion batteries prepared in Examples 1 to 5 and Comparative Examples 1 to 8 were subjected to the following relevant performance tests:

[0177] (1) Room temperature cycle performance test: At 25°C, the divided battery was charged to 4.0V using a 3C constant current and constant voltage test, with a cut-off current of 0.01C. After standing for 5 minutes, it was discharged to 2.0V using a 1C constant current test. After 500 charge / discharge cycles, the capacity retention rate at the 500th cycle was calculated. The calculation formula is as follows:

[0178] 500th cycle capacity retention rate (%)=(500th cycle discharge capacity / 1st cycle discharge capacity)×100%.

[0179] (2) Fast charging capability test (charged to 80% SOC): The divided battery was subjected to a 2.0V to 4.0V charge and discharge test at 25°C.

[0180] The test steps are as follows: first charge the battery to 3.75V at 3C constant current, then charge it to 3.9V at 2C constant current, and finally charge it to 4.0V at 1C constant current and constant voltage with a cutoff current of 0.01C, then let it rest for 5 minutes. Then, discharge it to 2.0V at 1C constant current, and let it rest for 5 minutes. The time it takes for the battery to reach 80% SOC is measured.

[0181] (3) Low temperature discharge performance test: At 25°C, charge the divided battery to 4.0V with 1C constant current and constant voltage (after constant current charging to 4V, charge to the cut-off current with constant voltage 4V) with a cut-off current of 0.01C, leave it for 5 minutes, discharge it to 2.0V with 1C, record the initial discharge capacity of the battery, leave it for 5 minutes, charge it to 4.0V with 1C constant current and constant voltage, with a cut-off current of 0.01C. Place the battery in a -20°C low temperature box for 4 hours, and discharge it to 2.0V with 1C under this temperature condition, record the low temperature discharge capacity of the battery. The calculation formula is as follows:

[0182] Low-temperature discharge capacity retention rate (%) = low-temperature discharge capacity / initial discharge capacity × 100%.

[0183] (4) Linear scan test: scan rate 0.1mV / s, voltage range 3.5V~4.75V.

[0184] The results of the above electrochemical performance tests are shown in Table 2.

[0185] Table 2 Electrochemical performance test results of sodium vanadium phosphate batteries corresponding to Examples 1 to 5 and Comparative Examples 1 to 8

[0186]

[0187]

[0188] from Figure 1 The linear scan results shown show that the electrolyte with the addition of 3-(((guanidino-4-thiazolyl)methyl)thio)propylimidate has an oxidation current peak near 3.83V, indicating that 3-(((guanidino-4-thiazolyl)methyl)thio)propylimidate can undergo oxidative decomposition on the positive electrode surface to form a positive electrode interface film.

[0189] From the test results of Example 1, Example 2, Example 3, and Comparative Example 1 in Table 2, it can be seen that the addition of the positive electrode film-forming additive 3-(((guanidino-4-thiazolyl)methyl)thio)propylimidate to the electrolyte significantly improves the cycle stability and fast charging performance of the sodium vanadium phosphate battery at high voltage. This is because 3-(((guanidino-4-thiazolyl)methyl)thio)propylimidate can form a uniform, dense, and highly ionic conductive protective film on the surface of the sodium vanadium phosphate material, inhibiting the dissolution of metal ions in the positive electrode material and the collapse of the material structure.

[0190] From the test results of Example 2, Example 4, Example 5 and Comparative Example 2 in Table 2, it can be seen that the addition of the negative electrode film-forming additive benzotriazole-N,N,N',N'-tetramethyluronium hexafluorophosphate to the electrolyte significantly improves the low-temperature performance and cycle stability of the sodium vanadium phosphate battery at high voltage. The reason is that benzotriazole-N,N,N',N'-tetramethyluronium hexafluorophosphate forms a stable, partially inorganic, low-impedance SEI film at the negative electrode graphite interface, and can coordinate with P (phosphorus) and V (vanadium) ions, inhibiting the free migration and reduction of metal ions in the electrolyte and reducing damage to the electrode surface.

[0191] From the test results of Example 2, Comparative Example 3, Comparative Example 4 and Comparative Example 5 in Table 2, it can be seen that sodium tetrafluoroborate and sodium difluorooxalatoborate disodium salt can effectively form films on the positive and negative electrodes of the battery, inhibit the decomposition of the electrolyte, and can effectively improve the fast charging performance and low-temperature discharge performance of the sodium vanadium phosphate battery at high voltage compared to traditional sodium ion secondary batteries without the addition of the combined lithium salt system.

[0192] 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 same solvent ratio, the fast charging time of the sodium vanadium phosphate battery to 80% SOC at high voltage is shortened by 21 minutes, and the low-temperature discharge capacity retention rate is increased by 19.7%, which significantly improves the fast charging performance and low-temperature performance of the sodium vanadium phosphate battery at high voltage.

[0193] From the test results of Examples 1 to 3 and Comparative Example 7 in Table 2, it can be seen that for the additive 3-(((guanidino-4-thiazolyl)methyl)thio)propane methyl imide, when the content of 3-(((guanidino-4-thiazolyl)methyl)thio)propane methyl imide increases, the cycle performance of the battery decreases. Therefore, it is best to control the content of 3-(((guanidino-4-thiazolyl)methyl)thio)propane methyl imide to 0.5% to 2.5%. If it is too low, there will be no effect, and if it is too high, there will be certain side reactions.

[0194] From the test results of Examples 2, 4 to 5 and Comparative Examples 2 and 8 in Table 2, it can be seen that for the additive benzotriazole-N,N,N',N'-tetramethyluronium hexafluorophosphate, when the content of benzotriazole-N,N,N',N'-tetramethyluronium hexafluorophosphate increases, the cycle performance, rate performance and low-temperature performance of the battery decrease. Therefore, it is best to control the content of benzotriazole-N,N,N',N'-tetramethyluronium hexafluorophosphate to 0.5% to 2%. If it is too low, there will be no effect. When it is too high, the interfacial impedance increases and the viscosity of the electrolyte itself also increases, resulting in increased internal polarization of the battery and deterioration of rate, low temperature and cycle performance.

[0195] The test results of Example 5 and Comparative Examples 1 and 2 in Table 2 show that the use of 3-(((guanidino-4-thiazolyl)methyl)thio)propylimidate and benzotriazole-N,N,N',N'-tetramethyluronium hexafluorophosphate alone is not as effective as the use of the two additives together. This shows that the combined use of the two additives in the present invention can ensure that the fast-charging sodium vanadium phosphate battery system has long cycle performance within a limited space, while also achieving excellent fast-charging and low-temperature performance.

[0196] It can be seen from this that the present invention has developed an effective method for simply and simultaneously constructing a positive-negative electrode interface protective layer with stable and fast sodium ion transport on the negative electrode and the positive electrode.

[0197] The present invention also provides a high-voltage electrolyte suitable for fast-charging sodium vanadium phosphate batteries. By adding film-forming additives and electrolyte disodium salts to the electrolyte, a positive-negative electrode interface protective layer with stable and fast sodium ion transmission can be constructed on the negative and positive electrodes, and a carboxylate solvent is added to the conventional carbonate solvent to reduce the melting point and viscosity of the electrolyte system. The synergistic effect between the components in the electrolyte enables the sodium vanadium phosphate battery to have good cycle performance, fast charging performance and low-temperature performance under high voltage conditions.

[0198] In summary, the components of the electrolyte provided by the present invention can effectively improve the fast charging performance, cycle performance and low-temperature performance of the sodium vanadium phosphate graphite battery at high voltage through a synergistic effect.

[0199] While the embodiments of the present invention have been described in detail above in conjunction with specific implementation methods, the present invention is not limited to the aforementioned embodiments. Various modifications may be made within the scope of knowledge possessed by a person skilled in the art without departing from the spirit of the present invention. Furthermore, the embodiments of the present invention and the features thereof may be combined with one another unless there is a conflict.

Claims

1. A sodium ion battery, characterized in that: The preparation raw materials include high-voltage electrolyte; The high-voltage electrolyte comprises the following raw materials: sodium salt, organic solvent, 3-(((guanidino-4-thiazolyl)methyl)thio)propylimidate and benzotriazole-N,N,N',N'-tetramethyluronium hexafluorophosphate; The mass fraction of the 3-(((guanidino-4-thiazolyl)methyl)thio)propylimidate in the high-voltage electrolyte is 0.5% to 2.5%; The mass fraction of the benzotriazole-N,N,N',N'-tetramethyluronium hexafluorophosphate in the high-voltage electrolyte is 0.5% to 2%; The sodium salts include sodium tetrafluoroborate and sodium difluorooxalatoborate; The organic solvent consists of carbonate and carboxylate; The positive electrode material of the sodium ion battery is sodium vanadium phosphate.

2. The sodium ion battery according to claim 1, wherein: The operating voltage of the sodium ion battery is 2.0V~4.0V.

3. The sodium ion battery according to claim 1, wherein: The mass fraction of the sodium salt in the high-voltage electrolyte is 10% to 20%.

4. The sodium ion battery according to claim 1 or 3, characterized in that: The mass fraction of the methyl 3-(((guanidino-4-thiazolyl)methyl)thio)propylimidate in the high-voltage electrolyte is 1.5% to 2.5%.

5. The sodium ion battery according to claim 1 or 3, characterized in that: The mass fraction of the benzotriazole-N,N,N',N'-tetramethyluronium hexafluorophosphate in the high-voltage electrolyte is 1% to 2%.

6. The sodium ion battery according to claim 1, wherein: The carbonate is at least one of diethyl carbonate, ethylene carbonate, and ethyl methyl carbonate.

7. The sodium ion battery according to claim 1, wherein: The carboxylic acid ester is at least one of ethyl acetate, propyl acetate and ethyl propionate.

8. The sodium ion battery according to claim 1, wherein: The preparation method of the high-voltage electrolyte comprises the following steps: The methyl 3-(((guanidino-4-thiazolyl)methyl)thio)propanimidate, the benzotriazole-N,N,N',N'-tetramethyluronium hexafluorophosphate, the sodium salt, and the organic solvent are mixed.

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