Electrolyte for sodium ion battery, preparation method of electrolyte and sodium ion battery

Abstract

The application discloses an electrolyte for sodium ion batteries and a preparation method thereof, and a sodium ion battery, and belongs to the technical field of electrochemical energy storage materials. The electrolyte comprises an electrolyte sodium salt, an organic solvent and a functional additive. The molecular structure of the functional additive is that a nitrogen-containing heterocyclic cation group is covalently bonded to a cross-linkable silane group through a sulfur-containing linking group. The additive can migrate to the electrode interface during battery cycling, and the cation part participates in the construction of a stable chemical passivation layer, while the silane part can be in-situ hydrolyzed and condensed to form an enhanced organic silicon network, thereby synergistically constructing a solid electrolyte interface film with excellent chemical stability and high mechanical strength. The application further discloses a preparation method of the functional additive and the electrolyte. The scheme can significantly improve the cycle stability and capacity retention rate of the sodium ion battery under high-rate charging and discharging conditions, and the process is simple and easy to implement.

Description

Technical Field

[0001] This invention belongs to the field of sodium-ion battery technology, and particularly relates to an electrolyte for sodium-ion batteries, its preparation method, and sodium-ion batteries. Background Technology

[0002] Driven by global energy structure transformation and sustainable development goals, the development of energy storage technologies that are resource-rich, low-cost, safe, and reliable has become an urgent need. Sodium-ion batteries, due to the extremely high abundance of sodium in the Earth's crust and their similar working principle to lithium-ion batteries, are considered a highly promising candidate technology for large-scale static energy storage and specific power applications.

[0003] However, the commercialization of sodium-ion batteries still faces key challenges. Sodium ions have a large ionic radius and slow diffusion kinetics. When the battery undergoes high-rate (fast) charge and discharge, the sodium ion flux at the electrode interface increases dramatically, generating significant concentration polarization and electrochemical stress. This easily leads to mechanical rupture and continuous reconstruction of the solid electrolyte interphase (SEI) film. An unstable SEI film exacerbates electrolyte decomposition and consumption, increases interfacial impedance, and may induce sodium dendrite growth, ultimately resulting in rapid capacity decay and a sharp reduction in cycle life. Therefore, how to construct and maintain an SEI film with both excellent chemical stability and superior mechanical integrity under high-rate operating conditions is the core scientific problem and technological bottleneck for improving the fast-charge and fast-discharge performance of sodium-ion batteries.

[0004] Currently, adding functional components to the electrolyte to optimize the SEI film is an effective strategy for improving battery performance. Various types of additives exist in the prior art, such as film-forming additives (CN119381564A), flame-retardant additives (CN119400957A), and conductive additives (CN107195969A), each improving a specific aspect of the interface performance from a single perspective. However, under the demanding conditions of high-rate batteries, a single interface modification strategy often struggles to address the complex, multi-dimensional failure mechanisms. An ideal high-rate electrolyte additive should simultaneously act on both interfacial chemical processes and physical structures, achieving synergistic and integrated functions at the molecular level, thereby systematically strengthening the SEI film. Based on this, this invention designs an electrolyte for sodium-ion batteries, its preparation method, and a sodium-ion battery. Summary of the Invention

[0005] The purpose of this invention is to solve the problems in the prior art, and to propose an electrolyte for sodium-ion batteries, a method for preparing the same, and a sodium-ion battery.

[0006] This invention first discloses an electrolyte for sodium-ion batteries, comprising an electrolyte sodium salt, an organic solvent, and a functional additive. The functional additive is an organic compound that integrates the following functional groups in its single molecular structure, including: A nitrogen-containing heterocyclic cationic group, and; A crosslinkable silane group covalently bonded to it via a sulfur-containing linking group.

[0007] In the above electrolyte, the nitrogen-containing heterocyclic cation group is selected from imidazolium, pyridinium, or pyrrolidineium cation structural units.

[0008] In the above electrolyte, the crosslinkable silane group is a trialkoxysilane group.

[0009] In the above electrolyte, the sulfur-containing linking group is a thioether bond.

[0010] In the above electrolyte, the organic solvent is selected from one or more of dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, ethylene carbonate, propylene carbonate, and butene carbonate.

[0011] Secondly, the present invention provides a method for preparing the above-mentioned electrolyte, characterized in that the method includes the following steps: S1: Under an inert atmosphere, the sodium salt is dissolved in an organic solvent and mixed with stirring to form a basic solution. S2: Add the functional additive to the base solution and perform a second stirring and mixing to form a homogeneous electrolyte mixture; S3: Filter the electrolyte mixture to obtain a clear electrolyte for sodium-ion batteries.

[0012] Secondly, the present invention provides a method for preparing the above-mentioned electrolyte, comprising the following steps: S1: Under an inert atmosphere, the sodium salt is dissolved in an organic solvent to form a basic solution; S2: Add the functional additive as defined in claim 1 to the base solution, mix well, and then filter.

[0013] In the above preparation method, the first stirring speed is 300~500 rpm; In step S2, the second stirring speed is 400~800 rpm, and the mixing time is 30~90 min.

[0014] In the above preparation method, the preparation method of the functional additive includes the following steps: (1) Mix a mercapto-containing alkoxysilane with a nitrogen-containing heterocyclic cationic precursor compound in a reaction medium and carry out a bonding reaction under stirring and heating conditions to form a reaction product; (2) The reaction product obtained in step (1) is purified to obtain the functional additive; The bonding reaction is a nucleophilic substitution reaction, and the sulfur-containing linking group is a thioether bond formed by the reaction of the thiol group with the halogen atom on the precursor compound.

[0015] In the above preparation method, the stirring speed is 200 to 600 rpm, the heating temperature is 40℃ to 100℃, and the heating time is 4 to 24 h.

[0016] Fourthly, the present invention provides a sodium-ion battery comprising a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the electrolyte is as described above.

[0017] The beneficial effects of this invention are as follows: 1. By integrating chemical film formation and mechanical enhancement functions into a single additive through molecular design, a composite solid electrolyte interface film with both high chemical stability and excellent mechanical strength can be synergistically constructed in situ at the electrode interface.

[0018] 2. This composite interface film can effectively resist stress impacts at high rates, thereby significantly improving the cycle life, capacity retention, and rate performance of sodium-ion batteries.

[0019] 3. The solution simultaneously improves battery safety and interface stability, and the additive synthesis and electrolyte preparation processes are simple and have good compatibility with existing industries. Attached Figure Description

[0020] Figure 1 This invention discloses a synthetic route diagram for a functional additive in an electrolyte for sodium-ion batteries.

[0021] Figure 2 The graph shows the electrochemical test results of the electrolyte in Example 1. Figure 3 The graph shows the electrochemical test results of the electrolyte in Example 2. Figure 4 The graph shows the electrochemical test results of the electrolyte in Example 3. Figure 5 The graph shows the electrochemical test results of the electrolyte in Example 4. Figure 6 The graph shows the electrochemical test results of the electrolyte in Comparative Example 1. Figure 7 The graph shows the electrochemical test results of the electrolyte in Comparative Example 2. Figure 8The graph shows the electrochemical test results of the electrolyte in Comparative Example 3. Figure 9 The graph shows the cycle performance test results of batteries assembled with the electrolytes prepared in the examples and comparative examples.

[0022] Figure 10 The graph shows the rate performance test results of batteries assembled with the electrolytes prepared in the examples and comparative examples. Detailed Implementation

[0023] To facilitate understanding of this application and to make the aforementioned objectives, features, and advantages of this application more apparent, a detailed description of specific embodiments of this application is provided below in conjunction with the accompanying drawings. Numerous specific details are set forth in the following description to provide a thorough understanding of this application, and preferred embodiments are shown in the accompanying drawings. However, this application can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and complete understanding of the disclosure of this application. This application can be implemented in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of this application; therefore, this application is not limited to the specific embodiments disclosed below. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this application, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified. In the description of this application, "several" means at least one, such as one, two, etc., unless otherwise explicitly specified. It should be noted that when an element is referred to as being "fixed to" another element, it can be directly attached to the other element or there may be an intervening element. When an element is referred to as being "connected to" another element, it can be directly connected to the other element or there may be an intervening element. The terms "vertical," "horizontal," "left," "right," and similar expressions used herein are for illustrative purposes only and do not represent the only possible implementations. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is only for describing particular implementations and is not intended to limit the scope of this application. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0024] Reference Figure 1-10In a first aspect, the present invention provides an electrolyte for sodium-ion batteries, comprising an electrolyte sodium salt, an organic solvent, and a functional additive. The functional additive is an organic compound that simultaneously integrates the following functional groups in its single molecular structure, including: A nitrogen-containing heterocyclic cationic group, and; A crosslinkable silane group covalently bonded to it via a sulfur-containing linking group.

[0025] Wherein, the nitrogen-containing heterocyclic cationic group is selected from imidazolium-type, pyridinium-type, or pyrrolidine-type cationic structural units; The crosslinkable silane group is a trialkoxysilane group; The sulfur-containing linking group is a thioether bond; The organic solvent is selected from at least one of dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, ethylene carbonate, propylene carbonate, and butene carbonate.

[0026] The structural design of this functional additive enables it to play multiple roles in the electrolyte: nitrogen-containing cationic groups can participate in the construction of the interfacial stabilizing layer and suppress side reactions; silane groups can cross-link on the electrode surface to enhance interfacial adhesion and ion transport efficiency; and thioether bonds serve as flexible connecting chains to improve the overall structural stability and compatibility of the molecule.

[0027] The present invention also discloses a method for preparing the above-mentioned electrolyte, the method comprising the following steps: S1: Under an inert atmosphere, the sodium salt is dissolved in an organic solvent and mixed with stirring to form a basic solution. S2: Add the functional additive to the base solution and perform a second stirring and mixing to form a homogeneous electrolyte mixture; S3: Filter the electrolyte mixture to obtain a clear electrolyte for sodium-ion batteries.

[0028] The preparation method of the functional additives in the electrolyte includes the following steps: (1) Mix the mercapto-containing alkoxysilane with the nitrogen-containing heterocyclic cationic precursor compound in the reaction medium and carry out the bonding reaction under stirring and heating conditions to form the reaction product. The stirring speed is 200 to 600 rpm, the reaction temperature is 40℃ to 100℃, and the reaction time is 4 to 24 h. (2) The reaction product obtained in step (1) is purified to obtain the functional additive; The bonding reaction is a nucleophilic substitution reaction, and the sulfur-containing linking group is a thioether bond formed by the reaction of the thiol group with the halogen atom on the precursor compound.

[0029] Example 1 The preparation method of the functional additive in this embodiment includes the following steps: A1. According to the proportions by weight, 8g of 1-methylimidazole was added to 8g of 2-chloroethanol, stirred at 95℃ for 300min, and filtered to obtain 1-(hydroxyethyl)-3-methylimidazole chloride. The reaction synthesis route is as follows: Figure 1 As shown; A2. By weight, 17g of 1-(hydroxyethyl)-3-methylimidazolium chloride was added to 70g of anhydrous acetonitrile, followed by 20g of silane coupling agent KH-590. The mixture was stirred at 60℃ for 1500min, and the silane-containing functional additive was obtained using a rotary evaporator. The reaction synthesis route is as follows: Figure 1 As shown.

[0030] The preparation method of sodium ion electrolyte includes the following steps: Step (1) In a glove box filled with nitrogen, 16.8g of sodium hexafluorophosphate was fully dissolved in a mixed solvent of 55g ethylene carbonate, 20g propylene carbonate and 15g diethyl carbonate. The mixture was stirred at 300rpm to obtain a mixed base solution. Step (2) Add 0.05g of functional additive to the mixed base solution and mix at a stirring speed of 400rpm for 35min. Then filter it through a polytetrafluoroethylene filter membrane with a pore size of 0.18μm to remove any possible small impurities and undissolved particles, and obtain a sodium ion electrolyte suitable for long-cycle operation.

[0031] Example 2 The preparation method of the functional additive in this embodiment includes the following steps: A1. By weight, 8.8 g of 1-methylimidazole was added to 8.8 g of 2-chloroethanol, stirred at 95°C for 350 min, and filtered to obtain 1-(hydroxyethyl)-3-methylimidazole chloride. A2. By weight, 18.7g of 1-(hydroxyethyl)-3-methylimidazolium chloride was added to 77g of anhydrous acetonitrile, and then 22g of silane coupling agent KH-590 was added. The mixture was stirred at 60°C for 1600min, and the silane-containing functional additive was obtained by rotary evaporation.

[0032] The preparation method of sodium ion electrolyte includes the following steps: Step (1) In a glove box filled with nitrogen, 16.8g of sodium hexafluorophosphate was fully dissolved in a mixed solvent of 55g ethylene carbonate, 20g propylene carbonate and 15g diethyl carbonate. The mixture was stirred at 400rpm to obtain a mixed base solution. Step (2) Add 0.1g of functional additive to the mixed base solution and mix at a stirring speed of 500rpm for 40min. Then filter it through a polytetrafluoroethylene filter membrane with a pore size of 0.18μm to remove any possible small impurities and undissolved particles, and obtain a sodium ion electrolyte suitable for long-cycle operation.

[0033] Example 3 The preparation method of the functional additive in this embodiment includes the following steps: A1. According to the weight, 9.6g of 1-methylimidazole was added to 9.6g of 2-chloroethanol, stirred at 95℃ for 400min, and filtered to obtain 1-(hydroxyethyl)-3-methylimidazole chloride. A2. By weight, 20.4g of 1-(hydroxyethyl)-3-methylimidazolium chloride was added to 84g of anhydrous acetonitrile, and then 24g of silane coupling agent KH-590 was added. The mixture was stirred at 60°C for 1800min, and the silane-containing functional additive was obtained by rotary evaporation.

[0034] The preparation method of sodium ion electrolyte includes the following steps: Step (1) In a glove box filled with nitrogen, 16.8g of sodium hexafluorophosphate was fully dissolved in a mixed solvent of 55g ethylene carbonate, 20g propylene carbonate and 15g diethyl carbonate. The mixture was stirred at 450rpm to obtain a mixed base solution. Step (2) Add 0.2g of functional additive to the mixed base solution and mix at a stirring speed of 600rpm for 50min. Then filter it through a polytetrafluoroethylene filter membrane with a pore size of 0.18μm to remove any possible small impurities and undissolved particles, and obtain a sodium ion electrolyte suitable for long-cycle operation.

[0035] Example 4 The preparation method of the functional additive in this embodiment includes the following steps: A1. By weight, 11g of 1-methylimidazole was added to 11g of 2-chloroethanol, stirred at 95°C for 450min, and filtered to obtain 1-(hydroxyethyl)-3-methylimidazole chloride. A2. By weight, 23g of 1-(hydroxyethyl)-3-methylimidazolium chloride was added to 91g of anhydrous acetonitrile, and then 26g of silane coupling agent KH-590 was added. The mixture was stirred at 60°C for 2000min, and the silane-containing functional additive was obtained by rotary evaporation.

[0036] The preparation method of sodium ion electrolyte includes the following steps: Step (1) In a glove box filled with nitrogen, 16.8g of sodium hexafluorophosphate was fully dissolved in a mixed solvent of 55g ethylene carbonate, 20g propylene carbonate and 15g diethyl carbonate. The mixture was stirred at 450rpm to obtain a mixed base solution. Step (2) Add 0.5g of functional additive to the mixed base solution and mix at a stirring speed of 800rpm for 60min. Then filter it through a polytetrafluoroethylene filter membrane with a pore size of 0.18μm to remove any possible small impurities and undissolved particles, and obtain a sodium ion electrolyte suitable for long-cycle operation.

[0037] Comparative Example 1 This comparative example is identical to Example 1 except that no functional additives are added.

[0038] Comparative Example 2 This comparative example is identical to Example 1, except that the functional additive does not introduce silane groups.

[0039] Comparative Example 3 This comparative example is identical to Example 1 except that the functional additive is replaced with another silane-containing additive (phenyl-3-methoxydiethoxysilane).

[0040] Test Example 1 (1) Preparation of positive electrode sheet The cathode material (Na4Fe3(PO4)2P2O7), ultrafine carbon powder (SuperP), and polyvinylidene fluoride (PVDF) were mixed at a mass ratio of 96:1.5:2.5 (wt%), and then dispersed in NMP (N-methylpyrrolidone). The mixture was stirred and dispersed under vacuum until it was stable and uniform to obtain a cathode slurry. After filtering, the cathode slurry was uniformly coated on both sides of an aluminum foil. The foil was then rolled to a thickness of 155 μm and die-cut to obtain a cathode sheet.

[0041] (2) Preparation of negative electrode The negative electrode material (hard carbon), ultrafine carbon powder (Super P), styrene-butadiene rubber (SBR), and LA rubber are mixed in a mass ratio of 95:2:1.8:1.2 (wt%). Then, an appropriate amount of deionized water is added, and the mixture is stirred and dispersed under vacuum until it is stable and uniform to obtain a negative electrode slurry. After filtering, the negative electrode slurry is evenly coated on both sides of aluminum foil. After rolling, the thickness reaches 115μm, and then it is die-cut to obtain a negative electrode sheet.

[0042] (3) Preparation of sodium-ion batteries A bare cell is obtained by stacking positive electrode, negative electrode and separator and welding tabs. The bare cell is placed in aluminum-plastic film packaging and pre-sealed. After baking at 120°C for 72 hours, 35g of electrolyte prepared in the examples and comparative examples is injected into each side of the separator. After secondary sealing, formation and capacity testing, sodium-ion battery is obtained.

[0043] Cyclic performance test: At 25°C, a sodium-ion battery, after being partially charged at 0.33C, is charged to 3.4V at a constant current and constant voltage of 1C, with a cutoff current of 0.05C, and then discharged at a constant current of 3C to 1.5V, which constitutes one charging cycle. This cycle is then repeated under the same conditions.

[0044] The first-week coulomb efficiency is calculated as the ratio of the discharge capacity to the charge capacity, and the formula is as follows: Discharge capacity per gradation / Charge capacity per gradation × 100%; Cycle retention rate is calculated as: discharge capacity in the 1800th cycle / discharge capacity in the first cycle × 100%.

[0045] Table 1: Cyclic Performance Test Rate performance testing was conducted at 25°C. Sodium-ion batteries, after being capacity-graded at 0.33C, were charged to 3.4V using a constant current and constant voltage of 1C, with a cutoff current of 0.05C, followed by constant current discharge at 0.5C to 1.5V. Then, tests were performed under the same conditions at 0.5C / 0.5D, 0.5C / 1D, 0.5C / 2D, 0.5C / 3D, 0.5C / 4D, 0.5C / 5D, 0.5C / 6D, 0.5C / 8D, 0.5C / 10D, 0.5C / 11D, and 0.5C / 12D. The test results show that the electrolyte provided by this invention exhibits excellent cycle stability and rate performance in sodium-ion batteries. The introduction of functional additives significantly improves the battery's long-cycle lifespan and high-rate discharge capability, demonstrating promising application prospects.

[0046] Table 2: Rate Performance Test Table 1-2 and Figure 2-10The test results show that the electrolyte prepared in this invention, when assembled into a pouch battery, has a slightly higher initial capacity and first-time efficiency ratio than the comparative example. More significantly, after 1800 cycles of high-rate discharge (1C charge / 3D), the capacity retention rate remains above 90%. In terms of rate performance, especially after charge-discharge at 13C, the discharge retention rate is above 93%, demonstrating excellent ion conductivity and interfacial stability. This exceeds Comparative Example 2 (without silane groups) by more than 3% and other comparative examples by 7%. In particular, compared with Comparative Example 3 (with the addition of phenyl-3-methoxydiethoxysilane), the electrolyte provided by this invention, by introducing functional additives containing imidazolium salts and silane groups, significantly improves the cycle stability and electrochemical performance of sodium-ion batteries under high-rate charge-discharge conditions.

[0047] The applicant declares that the present invention is further illustrated by the above embodiments, but the present invention is not limited to the above embodiments, that is, it does not mean that the present invention must rely on the above embodiments to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions of the raw materials of the product of the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

[0048] As is known from common technical knowledge, this invention can be implemented through other embodiments that do not depart from its spirit or essential characteristics. Therefore, the disclosed embodiments described above are merely illustrative and not exhaustive. All modifications within the scope of this invention or its equivalents are included in this invention.

Claims

1. An electrolyte for sodium-ion batteries, comprising a sodium electrolyte salt, an organic solvent, and functional additives, characterized in that, The functional additive is an organic compound that integrates the following functional groups in its single molecular structure, including: A nitrogen-containing heterocyclic cationic group, and; A crosslinkable silane group covalently bonded to it via a sulfur-containing linking group.

2. The electrolyte according to claim 1, characterized in that, The nitrogen-containing heterocyclic cation group is selected from imidazolium, pyridinium, or pyrrolidineium cation structural units.

3. The electrolyte according to claim 1, characterized in that, The crosslinkable silane group is a trialkoxysilane group.

4. The electrolyte according to claim 1, characterized in that, The sulfur-containing linking group is a thioether bond.

5. The electrolyte according to claim 1, characterized in that, The organic solvent is selected from at least one of dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, ethylene carbonate, propylene carbonate, and butene carbonate.

6. A method for preparing the electrolyte as described in any one of claims 1 to 5, characterized in that, The method includes the following steps: S1: Under an inert atmosphere, the sodium salt is dissolved in an organic solvent and mixed with stirring to form a basic solution. S2: Add the functional additive to the base solution and perform a second stirring and mixing to form a homogeneous electrolyte mixture; S3: Filter the electrolyte mixture to obtain the electrolyte for sodium-ion batteries.

7. The preparation method according to claim 5, characterized in that, In step S1, the rotation speed of the first stirring and mixing is 300~500 rpm; In step S2, the second stirring speed is 400~800 rpm, and the mixing time is 30~90 min.

8. The preparation method according to claim 6, characterized in that, The preparation method of the functional additive includes the following steps: (1) Mix a mercapto-containing alkoxysilane with a nitrogen-containing heterocyclic cationic precursor compound in a reaction medium and carry out a bonding reaction under stirring and heating conditions to form a reaction product; (2) The reaction product obtained in step (1) is purified to obtain the functional additive; The bonding reaction is a nucleophilic substitution reaction, and the sulfur-containing linking group is a thioether bond formed by the reaction of the thiol group with the halogen atom on the precursor compound.

9. The preparation method according to claim 8, characterized in that, In step (1), the stirring speed is 200 to 600 rpm, the heating temperature is 40℃ to 100℃, and the heating time is 4 to 24 hours.

10. A sodium-ion battery comprising a positive electrode, a negative electrode, a separator, and an electrolyte, characterized in that, The electrolyte is the electrolyte as described in any one of claims 1 to 5.

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