High-voltage-resistant electrolyte additive and application thereof in sodium-ion battery

Abstract

The invention discloses a high-voltage-resistant electrolyte additive and application thereof in a sodium-ion battery, and relates to the technical field of sodium-ion batteries. The method comprises the following specific steps: preparing a traditional electrolyte with a sodium salt concentration of 0.8-1.2 M, selecting two or more than two of EC, PC and EMC for preparation, and naming the traditional electrolyte as a basic electrolyte; [emim] [OTf], [emim] [Tf2N] and an additive B with different concentrations are respectively added into the basic electrolyte to serve as electrolyte additives, and the sodium-ion battery electrolyte containing the additives with different concentrations is prepared. The electrolyte additive prepared by the method improves the electrochemical performance and safety of the sodium ion battery.

Description

Technical Field

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

[0002] As a new energy storage technology, sodium-ion batteries have the advantages of safety, high efficiency, green environmental protection and low cost. They are considered to be a supplement or substitute for lithium-ion batteries and can be promoted and applied in fields such as large-scale energy storage. In order to accelerate the development of sodium-ion batteries, exploring cathode materials with excellent performance has always been a research hotspot in this field. In recent years, more and more cathode materials for sodium-ion batteries have been developed. The most studied cathode materials mainly include Prussian blue, polyanions and layered oxides. Among them, layered oxide cathode materials have shown great commercial potential and have received widespread attention due to their large theoretical specific capacity, high operating voltage, and easy large-scale production and preparation.

[0003] However, from the macroscopic perspective of the preparation and application of layered oxide cathode materials and the microscopic perspective of the intrinsic structure of the materials from the outside to the inside, there are still a series of challenges that limit its practical application: when the charge and discharge voltage is high, the electrolyte will undergo severe oxidative decomposition. As the number of cycles increases, the electrolyte will be exhausted and the battery cycle life will be reduced; at the same time, the layered oxide cathode will also produce a series of interfacial side reactions when circulating in the electrolyte, such as the electrolyte decomposition under high voltage conditions and inducing HF attack, leading to irreversible transition metal dissolution and gas release. Therefore, it is crucial to find a high-voltage resistant electrolyte additive.

[0004] At present, ionic liquids are considered to be strategic materials for addressing electrochemical challenges. The inherent properties of ionic liquids can enhance the stability, performance, reusability, speed and safety of electrochemical devices (batteries, solar cells, fuels). The performance of electrochemical devices is based on the ionic liquid / electrode interface. The factors affecting the performance of ionic liquid / electrode are: 1) Conductivity: The conductivity of electrochemical devices is related to free charge ions and mobility. Ionic liquids are compounds composed entirely of ions and have excellent ion conductivity; 2) Viscosity of ionic liquids: At room temperature, the viscosity of ionic liquids is dozens or even hundreds of times that of water. Ionic liquids with high viscosity have poor fluidity and will adhere to the wall during use, causing problems such as slow diffusion. Viscosity is generated by molecular motion and intermolecular forces. Increasing the temperature will weaken the intermolecular forces, thereby significantly reducing the viscosity. In addition, adding a small amount of organic solvents will also reduce the viscosity of ionic liquids; 3) Electrochemical window of ionic liquids: The electrochemical window refers to the potential difference of the degradation of anions and cations that constitute the ionic liquid, that is, the potential difference that is not electrochemically degraded, which depends on the redox ability of anions and cations. The redox capacity of most ionic liquids is 4-5V. The higher the purity of the ionic liquid or the addition of additives, the more beneficial it is to increase the electrochemical window.

[0005] In view of this phenomenon, ionic liquids are used as additives for high-voltage electrolytes. However, since most ionic liquids only show good conductivity at high temperatures, they have high viscosity and low conductivity at room temperature. Therefore, the ionic liquids are functionalized and fluorine-containing functional groups are combined with ionic liquids. On the one hand, the use of ionic liquids as high-voltage additives can widen the electrochemical window, improve the oxidation resistance of the electrolyte, and reduce consumption during the electrochemical cycle. On the other hand, fluorination of ionic liquids can promote the charge dislocation on anions, weaken hydrogen bonds, reduce the concentration of ionic liquids, and further improve the conductivity of fluorinated ionic liquid additives at room temperature. Summary of the invention

[0006] The object of the present invention is to provide a high-voltage resistant electrolyte additive and a method for using it in a sodium ion battery, by combining and optimizing the proportions of different additives in the electrolyte, that is, inhibiting the oxidative decomposition of the electrolyte during the charge and discharge process of the layered oxide positive electrode, widening the electrochemical window, and improving the electrochemical performance of the sodium ion battery.

[0007] To achieve the above object, the present invention adopts the following technical solution:

[0008] A high-voltage resistant electrolyte additive and its application in a sodium ion battery, characterized by comprising a sodium salt, an electrolyte, an additive A and an additive B.

[0009] Preferably, the additive A is a compound of the structure shown in [emim][OTf] (1-ethyl-3-methylimidazolium trifluoromethanesulfonate, C7H 11 F3N2O3S) and [emim][Tf2N](1-ethyl-3-methylimidazolinium bis(trifluoromethylsulfonyl)imide salt, C8H 11 F6N3O4S2) or more.

[0010]

[0011] Preferably, the preparation method of the additive B is:

[0012] F1: Add 40-80 parts of 1-hydroxyethyl-2,3-dimethylimidazolium hexafluorophosphate, CAS: 950780-06-0, 2-5 parts of ethyl isocyanate acrylate, CAS: 13641-96-8, 3-6 parts of stannous octoate and 300-400 parts of DMF into a reaction kettle by weight, and stir the reaction at 50-60°C for 60-120 minutes.

[0013] F2: Add 0.005-0.05 parts of 1,2,3,4,5,6,7,8,9,10,11-undecylhydro-12-mercaptododecaborane, CAS: 12294-22-3; 2-5 parts of ethylenediamine, stir and react at 70-80°C for 60-100 minutes, and remove DMF by distillation to obtain the additive B of imidazole hexafluorophosphate containing dodecaborane.

[0014] Preferably, the preparation mechanism and effect of the additive B are:

[0015] First, 1-hydroxyethyl-2,3-dimethylimidazolium hexafluorophosphate (hereinafter referred to as imidazole hexafluorophosphate) and isocyanate ethyl acrylate (hereinafter referred to as ethyl acrylate) are subjected to a condensation reaction. In this reaction, the hydroxyl group of imidazole hexafluorophosphate reacts with the isocyanate group to form a condensation product. This process is mainly achieved through the esterification reaction of the hydroxyl group and the isocyanate.

[0016] The ethyl acrylate in the obtained condensation product undergoes a mercapto addition reaction with undecahydro-12-mercapto-dodecaborane. This reaction usually involves the addition of mercapto groups to olefins or similar structures to form new chemical bonds, thereby obtaining an additive B of imidazole hexafluorophosphate containing dodecaborane.

[0017] The above-mentioned additive B significantly improves the ionic conductivity of the sodium ion battery. The dodecaborane structure can optimize the solvation structure and promote the transmission of sodium ions in the electrolyte; the additive B can improve the diffusion performance of sodium ions in the positive and negative electrode materials, thereby improving the rate performance of the battery. It also exhibits excellent thermal stability and chemical stability. Under the working conditions of the sodium ion battery, it can maintain the stability of the electrolyte and prevent the decomposition or reaction of the electrolyte in the electrochemical environment. Due to the presence of imidazole hexafluorophosphate, this additive can also provide higher ionic conductivity, which contributes to the rapid charging and discharging and efficient energy conversion of the sodium ion battery.

[0018] Preferably, the sodium salt, additive A and additive B account for 1-10% of the total mass of the electrolyte.

[0019] Preferably, the sodium salt is sodium hexafluorophosphate (NaPF6) or sodium perchlorate (NaClO4).

[0020] Preferably, the electrolyte is two or more of ethylene carbonate (EC), propylene carbonate (PC) and ethyl methyl carbonate (EMC).

[0021] Preferably, the positive electrode of the sodium ion battery is layered oxide sodium nickel iron manganese oxide.

[0022] Preferably, the negative electrode of the sodium ion battery is hard carbon (HC).

[0023] Preferably, the preparation method of the electrolyte is:

[0024] (1) preparing a conventional electrolyte with a sodium salt concentration of 0.8-1.2 M, selecting two or more of the electrolytes EC, PC, and EMC for preparation, and naming it as a basic electrolyte;

[0025] (2) Different concentrations of [emim][OTf], [emim][Tf2N] and additive B were added to the basic electrolyte as electrolyte additives to prepare sodium ion battery electrolytes containing additives of different concentrations.

[0026] In step (1), the basic electrolyte is prepared by weighing electrolyte EC, EMC and PC in a mass ratio of 1:1:1, or by weighing electrolyte PC and EMC in a mass ratio of 1:1.

[0027] Technical mechanism of the above scheme:

[0028] The present invention provides the use of ionic liquid as an electrolyte additive, and fluoriding the additive. On the one hand, the use of ionic liquid as a high-voltage resistant additive can widen the electrochemical window and improve the oxidation resistance of the electrolyte. On the other hand, fluoriding the ionic liquid can promote the charge dislocation on the anion, weaken the hydrogen bond, and reduce the concentration of the ionic liquid, while the conductivity of the fluoridated ionic liquid is further improved. Therefore, the use of high-voltage resistant ionic liquids and compounds that are fluoridated to reduce viscosity and increase conductivity can effectively inhibit the oxidative decomposition of sodium ion batteries under high voltage, which can also provide certain guidance for the design of other electrolytes.

[0029] Technical effect:

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] (1) The present invention provides a method for inhibiting gas production during the charge and discharge process of a sodium ion battery. An ionic liquid is used as an electrolyte additive, and the additive is fluorinated. On the one hand, the use of an ionic liquid as a high-voltage resistant additive can widen the electrochemical window and improve the oxidation resistance of the electrolyte. On the other hand, fluorination of the ionic liquid can promote the charge dislocation on the anion, weaken the hydrogen bond, and reduce the concentration of the ionic liquid. At the same time, the conductivity of the fluorinated ionic liquid is further improved, thereby inhibiting the oxidative decomposition of the high-voltage electrolyte at high voltage and improving the conductivity. Ultimately, the electrochemical performance and safety of the sodium ion battery are improved.

[0032] (2) The preparation process provided by the present invention is relatively simple, the dosage is small, and the overall performance of the sodium ion battery is improved with a small amount of additives. The product performance is relatively good and has certain competitive advantages. DETAILED DESCRIPTION

[0033] The present invention will be further described below in conjunction with specific embodiments. The following embodiments are only used to illustrate the present invention and are not intended to limit the scope of application of the present invention. Without departing from the spirit and essence of the present invention, modifications or replacements made to the inventive method, steps or conditions all belong to the scope of the present invention.

[0034] Unless otherwise specified, the experimental methods used in the following examples are all conventional methods; the materials and reagents used are reagents and materials that can be obtained from commercial channels unless otherwise specified.

[0035] Test example: Electrochemical performance test

[0036] Battery assembly: The positive electrode materials of Examples 1-4 and Comparative Examples 1-2 are all layered oxide sodium nickel iron manganese oxide, the conductive material is CNT, and the binder is PVDF; they are weighed according to a mass ratio of 8:1:1. N-methylpyrrolidone (NMP) is added to make a viscous glue, which is coated on aluminum foil and baked in a vacuum drying oven at 120°C for 12 hours to obtain a positive electrode sheet.

[0037] Hard carbon negative electrode material is used as the active material, and the mass ratio of active material: ultrafine carbon powder (SP): polyvinylidene fluoride is 90:5:5. N-methylpyrrolidone (NMP) is added to make a viscous glue, which is coated on aluminum foil and baked in a vacuum drying oven at 120°C for 12 hours to obtain the negative electrode sheet; PE film is used as the separator.

[0038] The layered oxide sodium nickel iron manganese oxide-HC battery was tested in the voltage range of 1.5-4.5V, first discharged at a rate of 0.1C, then discharged at 0.01C to a voltage of 1.5V, and then charged at 0.1C to 4.5V.

[0039] Example 1

[0040] This embodiment provides a method for inhibiting gas generation during the charge and discharge process of a battery, comprising the following components:

[0041] This embodiment provides a sodium ion battery electrolyte, the formula of which is: 20g propylene carbonate (PC) solvent, 20g ethyl methyl carbonate (EMC), 10.08g sodium hexafluorophosphate, and 0.1g additive B. Then, different contents of additives TPFHB and additive B are prepared according to Table 1. The raw materials are mixed evenly to prepare an electrolyte.

[0042] The preparation method of the additive B is:

[0043] F1: 40g 1-hydroxyethyl-2,3-dimethylimidazolium hexafluorophosphate, CAS: 950780-06-0; 2g ethyl isocyanate acrylate, CAS: 13641-96-8; 3g stannous octoate and 300g DMF were added to the reaction kettle and stirred at 50°C for 60min.

[0044] F2: Add 0.005 g of 1,2,3,4,5,6,7,8,9,10,11-undecyl-12-mercaptododecaborane, CAS: 12294-22-3, and 2 g of ethylenediamine, stir and react at 70°C for 60 min, and remove DMF by distillation to obtain the additive B of imidazole hexafluorophosphate containing dodecaborane.

[0045] Table 1

[0046] Recipe Name Propylene carbonate Ethyl methyl carbonate <![CDATA[NaPF6]]> [emim][OTf] Additive B Recipe 1 30g 30g 10.08g 0.6ml 0.1g Recipe 2 30g 30g 10.08g 1.2ml 0.3g Recipe 3 30g 30g 10.08g 1.8ml 0.6g Recipe 4 30g 30g 10.08g 3.0ml 0.8g

[0047] Test results:

[0048]

[0049] Example 2

[0050] This embodiment provides a method for inhibiting gas generation during the charge and discharge process of a battery, comprising the following components:

[0051] This embodiment provides a sodium ion battery electrolyte, the formula of which is: 20g propylene carbonate (PC) solvent, 20g ethyl methyl carbonate (EMC), 10.08g sodium hexafluorophosphate, and 0.3g additive B. Then, different contents of additives TPFHB and additive B are prepared according to Table 2. The raw materials are mixed evenly to prepare an electrolyte.

[0052] The preparation method of the additive B is:

[0053] F1: 60g 1-hydroxyethyl-2,3-dimethylimidazolium hexafluorophosphate, CAS: 950780-06-0; 3.5g ethyl isocyanate acrylate, CAS: 13641-96-8; 4g stannous octoate and 350g DMF were added to the reactor and stirred at 55°C for 80min.

[0054] F2: Add 0.02 g of 1,2,3,4,5,6,7,8,9,10,11-undecyl-12-mercaptododecaborane, CAS: 12294-22-3, and 3 g of ethylenediamine, stir and react at 75°C for 80 min, and remove DMF by distillation to obtain the additive B of imidazole hexafluorophosphate containing dodecaborane.

[0055] Table 2

[0056] Recipe Name Propylene carbonate Ethyl methyl carbonate <![CDATA[NaPF6]]> <![CDATA[[emim][Tf2N]]]> Additive B Recipe 1 30g 30g 10.08g 0.6ml 0.1g Recipe 2 30g 30g 10.08g 1.2ml 0.3g Recipe 3 30g 30g 10.08g 1.8ml 0.6g Recipe 4 30g 30g 10.08g 3.0ml 0.8g

[0057] Test results:

[0058]

[0059]

[0060] Example 3

[0061] This embodiment provides a method for inhibiting gas generation during the charge and discharge process of a battery, comprising the following components:

[0062] This embodiment provides a sodium ion battery electrolyte, the formula of which is: 20g ethylene carbonate (EC) solvent, 20g propylene carbonate (PC) solvent, 20g ethyl methyl carbonate (EMC), and 10.08g sodium hexafluorophosphate. Then, different contents of additives TPFHB and additive B are prepared according to Table 3. The raw materials are mixed evenly to prepare an electrolyte.

[0063] The preparation method of the additive B is:

[0064] F1: 60g 1-hydroxyethyl-2,3-dimethylimidazolium hexafluorophosphate, CAS: 950780-06-0; 4g ethyl isocyanate acrylate, CAS: 13641-96-8; 5g stannous octoate and 350g DMF were added to the reaction kettle and stirred at 55°C for 100min.

[0065] F2: Add 0.04 g of 1,2,3,4,5,6,7,8,9,10,11-undecyl-12-mercaptododecaborane, CAS: 12294-22-3, and 4 g of ethylenediamine, stir and react at 75°C for 80 min, and remove DMF by distillation to obtain the additive B of imidazole hexafluorophosphate containing dodecaborane.

[0066] Table 3

[0067] Recipe Name Propylene carbonate Ethyl methyl carbonate Ethylene carbonate <![CDATA[NaPF6]]> [emim][OTf] Additive B Recipe 1 20g 20g 20g 10.08g 0.6ml 0.1g Recipe 2 20g 20g 20g 10.08g 1.2ml 0.3g Recipe 3 20g 20g 20g 10.08g 1.8ml 0.6g Recipe 4 20g 20g 20g 10.08g 3.0ml 0.8g

[0068] Test results:

[0069]

[0070] Example 4

[0071] This embodiment provides a method for inhibiting gas generation during the charge and discharge process of a battery, comprising the following components:

[0072] This embodiment provides a sodium ion battery electrolyte, the formula of which is: 20g ethylene carbonate (EC) solvent, 20g propylene carbonate (PC) solvent, 20g ethyl methyl carbonate (EMC), and 10.08g sodium hexafluorophosphate. Then, different contents of additives TPFHB and additive B are prepared according to Table 4. The raw materials are mixed evenly to prepare an electrolyte.

[0073] The preparation method of the additive B is:

[0074] F1: 80g 1-hydroxyethyl-2,3-dimethylimidazolium hexafluorophosphate, CAS: 950780-06-0; 5g ethyl isocyanate acrylate, CAS: 13641-96-8; 6g stannous octoate and 400g DMF were added to the reactor and stirred at 60°C for 120min.

[0075] F2: Add 0.05 g of 1,2,3,4,5,6,7,8,9,10,11-undecyl-12-mercapto-dodecaborane, CAS: 12294-22-3, and 5 g of ethylenediamine, stir and react at 80° C. for 100 min, and remove DMF by distillation to obtain the additive B of imidazole hexafluorophosphate containing dodecaborane.

[0076] Table 4

[0077] Recipe Name Propylene carbonate Ethyl methyl carbonate Ethylene carbonate <![CDATA[NaPF6]]> <![CDATA[[emim][Tf2N]]]> Additive B Recipe 1 20g 20g 20g 10.08g 0.6ml 0.1g Recipe 2 20g 20g 20g 10.08g 1.2ml 0.3g Recipe 3 20g 20g 20g 10.08g 1.8ml 0.6g Recipe 4 20g 20g 20g 10.08g 3.0ml 0.8g

[0078] Test results:

[0079]

[0080] Comparative Example 1

[0081] This embodiment provides a method for inhibiting gas generation during the charge and discharge process of a battery, comprising the following components:

[0082] This embodiment provides a sodium ion battery electrolyte, the formula of which is as follows: 20g of propylene carbonate (PC) solvent, 20g of ethyl methyl carbonate (EMC), and 10.08g of sodium hexafluorophosphate. The raw materials are mixed evenly to prepare the electrolyte.

[0083] Test results:

[0084]

[0085] Comparative Example 2

[0086] This embodiment provides a method for inhibiting gas generation during the charge and discharge process of a battery, comprising the following components:

[0087] This embodiment provides a sodium ion battery electrolyte, the formula of which is: 20g ethylene carbonate (EC) solvent, 20g propylene carbonate (PC) solvent, 20g ethyl methyl carbonate (EMC), and 10.08g sodium hexafluorophosphate. The raw materials are mixed evenly to prepare the electrolyte.

[0088] Test results:

[0089]

[0090] The test results show that the sodium ion battery using the electrolyte additive of the present method is superior to the control sample in electrochemical performance, which verifies the technical effect of the present invention and shows its significant advantages in improving battery performance and safety.

[0091] This specific embodiment is merely an explanation of the present application and is not a limitation of the present application. After reading this specification, those skilled in the art may make modifications to the present embodiment without any creative contribution as needed, but such modifications are protected by the patent law as long as they are within the scope of the claims of the present application.

Claims

1. A high voltage resistant electrolyte additive and its application in sodium ion batteries, characterized in that: The sodium salt, electrolyte, additive A and additive B.

2. According to claim 1, a high voltage resistant electrolyte additive and its use in sodium ion batteries, characterized in that: The additive A is a compound of the structure shown in [emim][OTf] (1-ethyl-3-methylimidazolium trifluoromethanesulfonate, C7H 11 F3N2O3S) and [emim][Tf2N](1-ethyl-3-methylimidazolinium bis(trifluoromethylsulfonyl)imide salt, C8H 11 F6N3O4S2) or more.

3. The high-voltage electrolyte additive and its use in sodium ion batteries according to claim 1, characterized in that: The preparation method of the additive B is: F1: Add 40-80 parts of 1-hydroxyethyl-2,3-dimethylimidazolium hexafluorophosphate, 2-5 parts of ethyl isocyanate acrylate, 3-6 parts of stannous octoate and 300-400 parts of DMF into a reaction kettle by weight, and stir the reaction at 50-60°C for 60-120 minutes. F2: Add 0.005-0.05 parts of 1,2,3,4,5,6,7,8,9,10,11-undecylhydro-12-mercaptododecaborane and 2-5 parts of ethylenediamine, stir and react at 70-80°C for 60-100 minutes, and remove DMF by distillation to obtain the additive B of imidazole hexafluorophosphate containing dodecaborane.

4. The high-voltage electrolyte additive and its use in sodium ion batteries according to claim 1, characterized in that: The sodium salt, additive A and additive B account for 1-10% of the total mass of the electrolyte.

5. The high-voltage electrolyte additive and its use in sodium ion batteries according to claim 1, characterized in that: The sodium salt is sodium hexafluorophosphate (NaPF6) or sodium perchlorate (NaClO4).

6. The high-voltage electrolyte additive and its use in sodium ion batteries according to claim 1, characterized in that: The electrolyte is two or more of ethylene carbonate (EC), propylene carbonate (PC) and ethyl methyl carbonate (EMC).

7. The high-voltage electrolyte additive and its use in sodium ion batteries according to claim 1, characterized in that: The preparation method of the electrolyte: (1) preparing a conventional electrolyte with a sodium salt concentration of 0.8-1.2 M, selecting two or more of the electrolytes EC, PC, and EMC for preparation, and naming it as a basic electrolyte; (2) Different concentrations of [emim][OTf], [emim][Tf2N] and additive B were added to the basic electrolyte as electrolyte additives to prepare sodium ion battery electrolytes containing additives of different concentrations.

8. The high-voltage electrolyte additive and its use in sodium ion batteries according to claim 7, characterized in that: In step (1), the basic electrolyte is prepared by weighing electrolyte EC, EMC and PC in a mass ratio of 1:1:1, or by weighing electrolyte PC and EMC in a mass ratio of 1:1.

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