A functional additive, a functional electrolyte, a lithium ion battery and a preparation method thereof

Abstract

The application discloses a functional additive, a functional electrolyte, a lithium ion battery and a preparation method thereof. The electrolyte functional additive is prepared by using a hydrothermal assisted microwave radiation method, with citric acid and pentacyclic triterpene acid as carbon sources, and amino acid and inorganic acid as functional reagents. The functional additive prepared by the application contains rich edge groups, functional elements and functional ions, has strong compatibility with the electrolyte, is rich in functions, can be used in trace or trace amounts in the electrolyte, can play a special electrolyte optimization effect, and can be applied to the lithium ion battery to significantly optimize the electrochemical performance and safety performance of the battery cell.

Description

Technical Field

[0001] This invention relates to the field of battery technology, specifically to a functional additive, a functional electrolyte, a lithium-ion battery, and a method for preparing the same. Background Technology

[0002] High-energy-density lithium-ion batteries are widely used in consumer electronics. As a key component, the electrolyte directly affects the electrochemical performance of high-energy-density lithium-ion batteries, especially in terms of high-temperature, low-temperature, and storage performance. To improve the electrochemical and safety performance of lithium-ion batteries, various types of electrolyte functional additives have been researched and developed. Electrolyte additives such as negative electrode film-forming additives, positive electrode film-forming additives, high-temperature storage additives, and safety additives can significantly improve the electrode interface and enhance battery performance. These additives, even when used in low concentrations, still exert a significant impact; therefore, researching novel electrolyte additives has become a key focus in the field of electrolytes.

[0003] However, current electrolyte additives have limited and traditional functions. In order to achieve the comprehensive performance of lithium-ion batteries, more types and larger quantities of additives are often required. There is an urgent need to develop and research electrolyte additives with richer functions to promote the development of electrolytes. Summary of the Invention

[0004] The purpose of this invention is to provide a functional additive for electrolytes, a functional electrolyte, a lithium-ion battery, and a method for preparing the same. This functional additive has strong compatibility with electrolytes and richer functions. It can be used in trace amounts or in minute quantities in electrolytes to exert a special electrolyte optimization effect.

[0005] To achieve the above objectives, the technical solution provided by the present invention is as follows: A method for preparing functional additives for lithium-ion battery electrolytes, using citric acid and pentacyclic triterpenic acids as carbon sources and amino acids and inorganic acids as functional reagents, employs a hydrothermal assisted microwave irradiation method to prepare the electrolyte functional additives.

[0006] Furthermore, the preparation method of the present invention includes the following synthesis steps: 1) Weigh out a certain proportion of citric acid, pentacyclic triterpenic acid, amino acids and inorganic acids, dissolve them in deionized water, transfer them into a hydrothermal reactor equipped with an ultrasonic device, react them at a certain reaction temperature and accompanied by intermittent ultrasonic vibration, and then obtain the crude product by cooling and filtration. 2) Disperse the crude product obtained in step 1) in an organic alcohol aqueous solution by ultrasonication to obtain a dispersion; transfer the dispersion into a microwave irradiation vessel equipped with a stirring device, turn on the microwave, and the dispersion begins to reflux; add a certain amount of inorganic alkali solution to the dispersion to adjust the pH value to neutral, cool, and stop the microwave. 3) The dispersion after cooling in step 2) is filtered using a first microporous filter membrane, and then the filtrate is filtered using a second microporous filter membrane. The filtered material is then dialyzed using a dialysis bag to remove impurities. The product is freeze-dried and ground to obtain a nano-scale functional additive for lithium-ion battery electrolyte.

[0007] To optimize the above technical solution, the specific measures / limitations also include: In step 1), the mass ratio of citric acid to pentacyclic triterpene acid is 30:1-10; the mass ratio of citric acid to amino acid is 30:1-10; the mass ratio of citric acid to inorganic acid is 100:1-5; the reaction temperature is 160℃-200℃, and the reaction time is 2-4h; during the reaction, ultrasonic vibration is turned on for 1-3min every 0.1-0.3h until the reaction is completed.

[0008] In step 1), the amino acid is selected from one or more of valine, leucine, isoleucine, methionine, proline, tryptophan, serine, tyrosine, cysteine, phenylalanine, asparagine, glutamine, threonine, aspartic acid, glutamic acid, lysine, arginine, histidine, and pyrrolidone; the inorganic acid is one or more of boric acid, phosphoric acid, nitric acid, or sulfonic acid.

[0009] In step 2), the ratio of organic alcohol to water in the organic alcohol aqueous solution is 1-4:6-9; the organic alcohol is one or more of ethanol, isopropanol, and tert-butanol; and the inorganic base is one or more of sodium hydroxide, lithium hydroxide, and potassium hydroxide.

[0010] In step 3), the pore size of the first microporous filter membrane is 0.01um-0.30um; the pore size of the second microporous filter membrane is 0.002um-0.01um.

[0011] The particle size distribution of the nanoscale functional additives for lithium-ion battery electrolytes is 3nm-10nm.

[0012] This invention also protects a functional additive for lithium-ion battery electrolytes, prepared using the above method.

[0013] The present invention also protects a functional electrolyte for lithium-ion batteries, wherein the functional additives for lithium-ion battery electrolytes are present in a mass percentage of 0.05%-1.0%.

[0014] The present invention also protects a lithium-ion battery containing the above-described lithium-ion battery functional electrolyte.

[0015] Compared with the prior art, the beneficial effects of the present invention are: This invention provides a functional additive for lithium-ion battery electrolytes and its preparation method. The nanoscale electrolyte functional additive is synthesized by a combination of carbon source, amino acids and inorganic acids in an intermittent ultrasound-assisted one-step hydrothermal method.

[0016] The functional additives prepared by this invention contain abundant edge groups, functional elements, and functional ions. They are highly compatible with electrolytes and have a wide range of functions. When used in trace amounts or in the electrolyte, they can exert a special electrolyte optimization effect. When applied to lithium-ion batteries, they can significantly optimize the electrochemical performance and safety performance of the battery cells.

[0017] Furthermore, the preparation method is stable, convenient, green and environmentally friendly, and the product has high purity, strong reproducibility, and is easy to mass-produce industrially.

[0018] The functional additives prepared by this invention exhibited extremely excellent electrochemical performance in batteries, providing a new direction for the optimization of lithium-ion battery performance.

[0019] Specifically, compared with the prior art, the present invention has the following characteristics: First, this invention introduces ultrasound assistance and multi-carbon source precursors, resulting in a product with a small particle size, reaching only a few nanometers, and exhibiting good dispersion and resistance to agglomeration. It also demonstrates superior solubility in electrolytes and is compatible with oily electrolytes with any mutually compatible components. The citric acid and pentacyclic triterpenic acid used can produce a synergistic effect, resulting in a final product with a stable structure, small particle size, and rich edge groups. Secondly, the electrolyte functional additive prepared by this invention has abundant functional groups (such as carbonyl, carboxyl, amino, thio and boron groups) and functional ions (lithium ions), exhibiting low ionic impedance and improving the ionic conductivity of the electrolyte. Third, the electrolyte functional additives prepared by this invention have many branched molecular structures that are intertwined into a network, which has the characteristics of rich network structure and many contact sites. They can form a more stable and excellent electrolyte film with both the positive and negative electrodes, thereby improving the electrochemical performance of the battery, especially its cycle performance. Fourth, applying the functional additives of this invention to the electrolyte in the preparation of lithium-ion batteries can suppress the formation of lithium dendrites on the negative electrode at a certain addition amount, which helps to optimize safety performance. Attached Figure Description

[0020] Figure 1 Photograph of the electrolyte functional additive prepared according to the present invention.

[0021] Figure 2 Example 1: Room temperature cycle life curve.

[0022] Figure 3 Example 1: High-temperature cycle life curve. Detailed Implementation

[0023] To make the technical problems solved by the present invention, the technical solutions, and the beneficial effects clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0024] This embodiment only lists soft-pack batteries, but it is also applicable to batteries with other casings and structures, such as square steel casings, cylindrical batteries, etc.

[0025] Typical battery manufacturing notes: Preparation of positive electrode sheet: The positive active material is lithium cobalt oxide (LCO) or ternary material (NCM), the binder is polyvinylidene fluoride (PVDF), and the conductive agent is Super-P. The above materials are added to N-methylpyrrolidone (NMP) according to a certain mass ratio and stirred to form a positive electrode slurry. Then, the positive electrode slurry is coated on both sides of the positive current collector. After drying, compaction, slitting, sheet making, and welding of electrode tabs, the positive electrode sheet is obtained.

[0026] Preparation of negative electrode sheet: The negative electrode active material is made by adding artificial graphite and silicon carbon materials, electrolyte, binder and dispersant to deionized water in the required weight ratio and stirring to form a negative electrode slurry. Then, the negative electrode slurry is coated on both sides of the negative electrode current collector. After drying, compaction, slitting, sheet making and welding of electrode tabs, the negative electrode sheet is obtained.

[0027] Electrolyte: The different functional additives prepared in the examples are added to the electrolyte, dispersed and dissolved to obtain the desired functional electrolyte.

[0028] Preparation of lithium-ion batteries: The negative electrode and positive electrode sheets prepared according to the above process are assembled with the separator to obtain the battery cell. The battery cell is put into the outer packaging, functional electrolyte is added, and the battery is left to stand at high temperature. It is then subjected to hot-pressing pre-charge and formed to obtain a lithium-ion secondary battery.

[0029] The lithium-ion battery produced in this study has a capacity of 5.0Ah, a charging voltage of 4.45V, and a discharge cutoff voltage of 3.0V.

[0030] In an embodiment of the present invention, the electrolyte coefficient is 1.2 g / Ah - 1.8 g / Ah.

[0031] The present invention uses a lithium-ion battery assembled with an electrolyte without the addition of the functional additive as a comparative example.

[0032] Example 1: Weigh 1.5g citric acid, 0.5g pentacyclic triterpenic acid, 0.15g methionine, 0.15g glutamic acid, and 0.02g boric acid, dissolve them in 100mL deionized water, transfer the solution to a hydrothermal reactor equipped with an ultrasonic device, raise the temperature to 185℃ and react for 3 hours. Simultaneously, turn on the ultrasonic vibration for 2 minutes every 0.2 hours until the reaction is complete. Cool to room temperature and filter to obtain crude product. Then dissolve it in a tert-butanol / deionized water (2:8) mixed solvent, transfer it to a microwave irradiation reactor equipped with a stirrer, turn on microwave irradiation heating, and add 1mol / L lithium hydroxide to neutralize the reaction while stirring. Adjust the pH to neutral, cool, and filter using a first microporous 0.22µm filter membrane, and then use a second microporous 0.002µm filter membrane for ultrafiltration. Finally, freeze-dry, dry and grind the product to obtain the target product. Then add 0.05% by mass of functional additives to the electrolyte to make a lithium-ion secondary battery.

[0033] Example 2: Weigh 1.5g citric acid, 0.5g pentacyclic triterpenic acid, 0.3g methionine, and 0.02g boric acid and dissolve them in 100mL deionized water. Transfer the solution to a reaction vessel equipped with an ultrasonic device and raise the temperature to 185℃ for 3 hours. Simultaneously, turn on the ultrasonic vibration for 2 minutes every 0.2 hours until the reaction is complete. Cool to room temperature and filter to obtain the crude product. Then dissolve it in a tert-butanol / deionized water (2:8) mixed solvent and transfer it to a microwave irradiation vessel equipped with a stirrer. Turn on the microwave irradiation heating and, while stirring, add 1mol / L lithium hydroxide to neutralize the reaction. Adjust the pH to neutral and cool. After cooling, filter using a first microporous 0.22µm filter membrane and then use a second microporous 0.002µm filter membrane for ultrafiltration. Finally, freeze-dry, dry, and grind the product to obtain the target product. Then, add 0.2% by mass of functional additives to the electrolyte to prepare a lithium-ion secondary battery.

[0034] Example 3: Weigh 1.5g citric acid, 0.5g pentacyclic triterpenic acid, 0.15g cysteine, and 0.02g boric acid and dissolve them in 100mL deionized water. Transfer the solution to a reaction vessel equipped with an ultrasonic device and raise the temperature to 185℃ for 3 hours. Simultaneously, turn on the ultrasonic vibration for 2 minutes every 0.3 hours until the reaction is complete. Cool to room temperature and filter to obtain the crude product. Then dissolve it in a tert-butanol / deionized water (3:7) mixed solvent and transfer it to a microwave irradiation vessel equipped with a stirrer. Turn on the microwave irradiation heating and, while stirring, add 1mol / L lithium hydroxide to neutralize the reaction. Adjust the pH to neutral and cool. After cooling, filter using a first microporous 0.22µm filter membrane and then use a second microporous 0.005µm filter membrane for ultrafiltration. Finally, freeze-dry, dry, and grind the product to obtain the target product. Then, add 0.3% by mass of functional additives to the electrolyte to prepare a lithium-ion secondary battery.

[0035] Example 4: Weigh 1.5g citric acid, 0.25g pentacyclic triterpenic acid, 0.25g serine, and 0.02g phosphorous acid and dissolve them in 100mL deionized water. Transfer the solution to a reaction vessel equipped with an ultrasonic device and raise the temperature to 190℃ for 3 hours. Simultaneously, turn on the ultrasonic vibration for 2 minutes every 0.2 hours until the reaction is complete. Cool to room temperature and filter to obtain the crude product. Then dissolve it in a tert-butanol / deionized water (2:8) mixed solvent and transfer it to a microwave irradiation vessel equipped with a stirrer. Turn on the microwave irradiation heating and, while stirring, add 1mol / L lithium hydroxide to neutralize the reaction. Adjust the pH to neutral and cool. After cooling, filter using a first microporous 0.22µm filter membrane and then use a second microporous 0.002µm filter membrane for ultrafiltration. Finally, freeze-dry, dry, and grind the product to obtain the target product. Then, add 0.4% by mass of the functional additive to the electrolyte to make a lithium-ion secondary battery.

[0036] Example 5: Weigh 1.5g citric acid, 0.25g pentacyclic triterpenic acid, 0.15g proline, and 0.02g phosphorous acid and dissolve them in 100mL deionized water. Transfer the solution to a reaction vessel equipped with an ultrasonic device and raise the temperature to 180℃ for 3 hours. Simultaneously, turn on the ultrasonic vibration for 2 minutes every 0.3 hours until the reaction is complete. Cool to room temperature and filter to obtain the crude product. Then dissolve it in a 2:8 mixture of ethanol and deionized water and transfer it to a microwave irradiation vessel equipped with a stirrer. Turn on the microwave irradiation heating and, while stirring, add 1mol / L lithium hydroxide to neutralize the reaction. Adjust the pH to neutral and cool. After cooling, filter using a 0.25µm microporous membrane and then ultrafilter using a 0.005µm microporous membrane. Finally, freeze-dry, dry, and grind the product to obtain the target product. Then, add 0.8% by mass of functional additives to the electrolyte to prepare a lithium-ion secondary battery.

[0037] Example 6: Weigh 1.5g citric acid, 0.25g pentacyclic triterpenic acid, 0.15g tryptophan, and 0.02g boric acid and dissolve them in 100mL deionized water. Transfer the solution to a reaction vessel equipped with an ultrasonic device and raise the temperature to 180℃ for 3 hours. Simultaneously, turn on the ultrasonic vibration for 2 minutes every 0.1 hours until the reaction is complete. Cool to room temperature and filter to obtain the crude product. Then dissolve it in a mixed solvent of isopropanol / deionized water (2:8) and transfer it to a microwave irradiation vessel equipped with a stirrer. Turn on the microwave irradiation heating and, while stirring, add 1mol / L lithium hydroxide to neutralize the reaction. Adjust the pH to neutral and cool. After cooling, filter using a first microporous 0.20µm filter membrane and then ultrafilter using a second microporous 0.003µm filter membrane. Finally, freeze-dry, dry, and grind the product to obtain the target product. Then, add 1.0% by mass of functional additives to the electrolyte to prepare a lithium-ion secondary battery.

[0038] Example Test Results Explanation: Measurements were performed on each embodiment, and the results are shown in Table 1: Table 1

[0039] Analysis of experimental results: The test conditions in Table 1 above were all conducted at room temperature and standard atmospheric pressure. It can be seen that the particle size of the products prepared in each example is basically 3-6 nm. After being added to the electrolyte at a mass ratio of 0.05%-1.0%, they showed excellent compatibility. Even when a high content of 1% was added, they were completely dissolved within 30 seconds.

[0040] Furthermore, it was found that Examples 1-6 all exhibited improved conductivity, meaning that increasing the amount of additives can effectively improve the battery's kinetic performance and expand its lithium plating window. When applied to lithium-ion batteries, they all showed lower internal resistance values ​​(compared to the control group), indicating a lower contribution to ionic impedance.

[0041] It was also found that adding the product prepared in the embodiments of this application to the electrolyte can significantly improve the safety performance of the battery. During the hot-box experiment, it was found that all six schemes in the embodiments passed the hot-box test, except for the control group, which failed. Furthermore, it was found that batteries using the product prepared in the embodiments can significantly extend the lithium plating window of lithium-ion batteries. It can be seen that the upper limit of the lithium plating window in the control group at 15°C was only 0.9C, while after improvement with electrolyte additives, all six schemes in the embodiments improved the lithium plating window of the battery to varying degrees, with the maximum extension reaching 1.5C, achieving an improvement of nearly 67%, which is particularly significant for improving safety performance.

[0042] The data above show that the electrolyte performance is significantly improved after the addition of functional additives. This is mainly due to the additives' excellent low ion resistance and ability to form a tough and stable solid electrolyte at both positive and negative electrodes. They are also wettable and friendly to the electrode interface, which has a particularly significant effect on improving electrical and safety performance.

[0043] Figure 2 The room-temperature cycle life curves for Example 1 and the control group show that the battery prepared by introducing functional additives into the electrolyte exhibits excellent cycle life. After 1000 cycles of 0.9C charge-1.0C discharge, it still shows a cycle life of over 85.6%, significantly higher than the 82.6% (1000 cycles) of the control group. The excellent cycle performance is mainly attributed to the excellent film-forming properties of the additives.

[0044] Figure 3 The high-temperature cycle life curves for Example 1 and the control group show that the battery prepared by introducing functional additives into the electrolyte exhibits superior high-temperature cycle life. After 800 cycles of 0.9C charge-1.0C discharge, Example 1 still showed a cycle life of over 82%; while the control group showed a capacity decay of almost 80% after 600 cycles, a significant difference. This mainly indicates that the electrolyte using functional additives has excellent high-temperature cycle performance. Under high-temperature conditions, the positive and negative electrodes, especially the positive electrode, exhibit excellent film temperature resistance, interface stability, and are less prone to thickening, thus preventing a sharp increase in internal resistance.

[0045] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any simple modifications, equivalent substitutions, and improvements made by those skilled in the art to the above embodiments without departing from the scope of the technical solution of the present invention, based on the technical essence of the present invention, shall still fall within the protection scope of the technical solution of the present invention.

Claims

1. A method for preparing a functional additive for lithium-ion battery electrolyte, characterized in that: Electrolyte functional additives were prepared by hydrothermal assisted microwave irradiation method using citric acid and pentacyclic triterpenic acids as carbon sources and amino acids and inorganic acids as functional reagents. The synthesis steps include the following: 1) Weigh out a certain proportion of citric acid, pentacyclic triterpenic acid, amino acids and inorganic acids, dissolve them in deionized water, transfer them into a hydrothermal reactor equipped with an ultrasonic device, react them at a certain reaction temperature and accompanied by intermittent ultrasonic vibration, and then obtain the crude product by cooling and filtration. 2) Disperse the crude product obtained in step 1) in an organic alcohol aqueous solution by ultrasonication to obtain a dispersion; transfer the dispersion into a microwave irradiation vessel equipped with a stirring device, turn on the microwave, and the dispersion begins to reflux; add a certain amount of inorganic alkali solution to the dispersion to adjust the pH value to neutral, cool, and stop the microwave. The dispersion cooled in step 2) was filtered using a first microporous filter membrane, and then the filtrate was filtered using a second microporous filter membrane. The filtered material was dialyzed using a dialysis bag to remove impurities. The product was freeze-dried and ground to obtain a nano-sized functional additive for lithium-ion battery electrolyte. In step 1), the mass ratio of citric acid to pentacyclic triterpene acid is 30:1-10; the mass ratio of citric acid to amino acid is 30:1-10; the mass ratio of citric acid to inorganic acid is 100:1-5; the reaction temperature is 160℃-200℃, and the reaction time is 2-4 hours; during the reaction, ultrasonic vibration is activated for 1-3 minutes every 0.1-0.3 hours until the reaction is completed. The inorganic acid is one or more of boric acid, phosphoric acid, nitric acid, or sulfonic acid.

2. The method for preparing functional additives for lithium-ion battery electrolytes according to claim 1, characterized in that: In step 1), the amino acid is selected from one or more of the following: valine, leucine, isoleucine, methionine, proline, tryptophan, serine, tyrosine, cysteine, phenylalanine, asparagine, glutamine, threonine, aspartic acid, glutamic acid, lysine, arginine, histidine, and pyrrolidone.

3. The functional additive for lithium-ion battery electrolyte according to claim 1, characterized in that: In step 2), the ratio of organic alcohol to water in the organic alcohol aqueous solution is 1-4:6-9; the organic alcohol is one or more of ethanol, isopropanol, and tert-butanol; and the inorganic base is one or more of sodium hydroxide, lithium hydroxide, and potassium hydroxide.

4. The method for preparing functional additives for lithium-ion battery electrolytes according to claim 1, characterized in that: In step 3), the pore size of the first microporous filter membrane is 0.01um-0.30um; the pore size of the second microporous filter membrane is 0.002um-0.01um.

5. The method for preparing a functional additive for lithium-ion battery electrolyte according to claim 1, characterized in that: The particle size distribution of the nanoscale functional additives for lithium-ion battery electrolytes is 3nm-10nm.

6. A functional additive for lithium-ion battery electrolyte, characterized in that: Prepared using the method described in any one of claims 1-5.

7. A functional electrolyte for lithium-ion batteries, characterized in that: It contains 0.05%-1.0% by mass of the functional additive for lithium-ion battery electrolyte as described in claim 6.

8. A lithium-ion battery, characterized in that: It contains the lithium-ion battery functional electrolyte as described in claim 7.

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