High-voltage lithium ion battery electrolyte

Abstract

The invention relates to a high-voltage lithium ion battery electrolyte which comprises a lithium salt, a solvent and nanoparticles modified by a fluorine-containing modifier. At present, when a high-nickel ternary positive electrode material is applied to a lithium ion battery, the technical problems of short cycle life, poor safety and the like caused by the problems of lithium dendrite growth, interface side reaction and the like exist. According to the invention, the fluorine-containing modifier is utilized to modify the nano-particles, so that the nano-particles are uniformly dispersed in the electrolyte, and the modified nano-particles can significantly optimize the solvation structure of lithium ions, inhibit the growth of lithium dendrites, enhance the stability of the high-nickel ternary positive electrode material, reduce the interface impedance and improve the ionic conductivity; the service life of the lithium ion battery can be remarkably prolonged, and the performance of the lithium ion battery under the conditions of high voltage and high specific capacity is improved.

Description

Technical Field

[0001] The present invention belongs to the field of batteries, and specifically relates to a high-voltage lithium-ion battery electrolyte solution. Background Art

[0002] Due to its high energy density and long cycle life, lithium-ion batteries have become the core power source for electric vehicles, energy storage systems, and portable electronic devices. With the continuous increase in the demand for energy density in application scenarios, the research on high-voltage cathode systems has become a technical focus, but it poses higher requirements for the oxidation stability and interfacial compatibility of the electrolyte solution.

[0003] However, traditional carbonate-based electrolyte solutions have problems such as low ionic conductivity and poor interfacial stability with high-active cathodes, making it difficult to operate stably at high voltages. This further limits the Li+ diffusion kinetics and accelerates the side reactions at the electrode / electrolyte interface, forming lithium dendrites that damage the integrity of the SEI film, increasing the interfacial impedance, and causing the comprehensive performance of the battery to decline. It can also lead to battery short circuits and safety accidents; high-nickel ternary materials are commonly used as the cathode materials for high-energy batteries due to their relatively high energy density, but they are prone to irreversible phase changes in the deeply delithiated state, resulting in lattice distortion and the accumulation of internal stress within the particles, which in turn triggers surface microcracks. The formation of cracks accelerates the penetration of the electrolyte solution, exacerbates the dissolution of transition metal elements, and further damages the stability of the material's layered structure through lithium-nickel mixing;

[0004] Although existing technologies have attempted to improve the stability of high-nickel materials through coating modification or doping methods, their regulation of the interfacial behavior of the electrolyte solution is still insufficient. Therefore, how to maintain the structural stability of the cathode material and reduce interfacial side reactions at high voltages is an urgent problem to be solved in improving battery performance.

[0005] In view of this, the present invention is specifically proposed. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to overcome the deficiencies of the prior art and provide a high-voltage lithium-ion battery electrolyte solution, which contains a lithium salt, a solvent, and fluorinated modified nanoparticles.

[0007] Furthermore, the fluorinated modified nanoparticles are nanoparticles modified with fluoroanhydride and / or organic fluorinated monocarboxylic acid.

[0008] Furthermore, the fluoroanhydride / organic fluorinated monocarboxylic acid is selected from one or several of pentafluoropropionic anhydride, hexafluoroglutaric anhydride (HFA), perfluoropropionic anhydride, perfluorobutyric anhydride, perfluorovaleric anhydride, perfluorohexanoic anhydride, perfluoroheptanoic anhydride, perfluorodecanoic anhydride, heptafluorobutyric anhydride, perfluoropropionic acid, perfluorobutyric acid, perfluorovaleric acid, perfluorohexanoic acid, perfluoroheptanoic acid, and perfluorooctanoic acid.

[0009] Further, the nanoparticles are selected from one or more of carbon material nanoparticles, oxide nanoparticles, nitride nanoparticles, two-dimensional inorganic compound nanoparticles (MXene), metal-organic framework material nanoparticles (MOFS), and perovskite nanoparticles.

[0010] Further, the nanoparticles include one or more of silica, graphene quantum dots, doped carbon dots, nanodiamonds, aluminum nitride, titanium nitride, boron nitride, montmorillonite, and ZIF-8.

[0011] Further, the solvent is selected from carbonate organic compounds.

[0012] Further, the solvent is selected from one or more of dimethyl carbonate (DMC), ethylene carbonate (EC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), polycarbonate (PC), and vinylene carbonate (FEC).

[0013] Further, the lithium salt is selected from one or more of lithium phosphate salts, lithium borate salts, and imide lithium salts.

[0014] Specifically, the lithium salt is selected from one or more of LiPF6, LiTFSI, LiBF4, LiBOBF2, LiDBSBF2, LiFSI, CF3SO3Li, and LiClO4.

[0015] Further, the modified nanoparticles in the electrolyte account for 0.01 wt% - 1 wt% of the total amount of the electrolyte.

[0016] After adopting the above technical solution, the present invention has at least the following beneficial effects compared with the prior art.

[0017] The present invention uses fluoroanhydride and / or organic monofluoroacid to modify the surface of the nanoparticles, significantly improving the dispersibility of the nanoparticles in the electrolyte with carbonate organic compounds as the solvent. The modified nanoparticles have excellent dispersion effect in the electrolyte and will not agglomerate, effectively avoiding the blockage of the diaphragm pores due to nanoparticle agglomeration; the dispersed modified nanoparticles can adhere more uniformly to the surface of the lithium metal negative electrode, forming a stable interface, regulating the ion transport behavior, reducing the interfacial side reactions, and prolonging the battery life.

[0018] The improvement of the dispersion uniformity of the modified nanoparticles can effectively promote the adsorption and desorption of lithium ions, forming a uniform ion flux; in addition, the grafting groups of the fluorinated modifier on the surface of the nanoparticles promote the uniformity of the lithium deposition process through strong coordination with lithium ions. The above two effects can effectively inhibit the growth of lithium dendrites and promote the transformation of lithium deposition from a one-dimensional dendritic growth mode to a two-dimensional planar growth mode, helping to maintain the electronic connection of lithium during the stripping process and reducing the formation of isolated lithium particles.

[0019] For a battery using a high-nickel ternary cathode material as the cathode active material, by utilizing the low HOMO energy level of the carbon-fluorine bond on the modified nanoparticles and the high electronegativity of fluorine atoms, the antioxidant ability of nickel ions can be enhanced, effectively improving the stability of the high-nickel ternary cathode material.

[0020] In addition, the modified nanoparticles optimize the solvation structure of lithium ions, reduce the transport activation energy and increase the ion transference number, improving the rate performance of the battery; by introducing the grafted fluorine-containing groups into the electrolyte through the modified nanoparticles, fluorine elements participate in the formation of the CEI film and enhance its stability and compactness, effectively inhibiting the side reaction of electrolyte decomposition and the dissolution of transition metal ions, and alleviating the cation mixing problem in the cathode material. In addition, the synergistic effect of the nanoparticles further stabilizes the electrode / electrolyte interface, improves the ionic conductivity, reduces the irreversible capacity loss, inhibits adverse reactions such as the dissolution of transition elements and lithium-nickel mixing, protects the stability of the cathode material structure, and realizes the synchronous optimization of the battery cycle stability and capacity retention rate. Description of the Drawings

[0021] Figure 1 is the SEM image of the cathode sheet of Comparative Example 1 after 200 cycles;

[0022] Figure 2 is the SEM image of the cathode sheet of Example 1 after 200 cycles;

[0023] Figure 3 is the SEM image of the anode sheet of Comparative Example 2 after 200 cycles;

[0024] Figure 4 is the SEM image of the anode sheet of Example 1 after 200 cycles. Detailed Embodiments

[0025] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. The following embodiments are used to illustrate the present invention but are not used to limit the scope of the present invention.

[0026] In the description of the present invention, it should be noted that the orientation or positional relationship indicated by the terms "upper", "lower", "front", "rear", "left", "right", "vertical", "inner", "outer", etc. is based on the orientation or positional relationship shown in the accompanying drawings, and is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation to the present invention.

[0027] In the description of the present invention, it should be noted that, unless otherwise clearly specified and defined, the terms "installation", "connection", and "coupling" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0028] The present invention provides a high-voltage lithium-ion battery electrolyte, which includes a lithium salt, a solvent, and modified nanoparticles grafted with fluorine-containing groups. The modified nanoparticles include nanoparticles and fluorine-containing groups grafted on the nanoparticles. Among them, the nanoparticles can be selected from one or more of carbon material nanoparticles, oxide nanoparticles, nitride nanoparticles, two-dimensional inorganic compound nanoparticles (MXene), metal-organic framework material nanoparticles (MOFS), and perovskite nanoparticles. Specifically, one or more of silica, graphene quantum dots, doped carbon dots, nanodiamonds, aluminum nitride, titanium nitride, boron nitride, montmorillonite, and ZIF-8 can be selected; the fluorine-containing modifier for modifying the nanoparticles is a fluorine-containing anhydride and / or an organic fluorine-containing monobasic acid, and further selected from one or more of pentafluoropropionic anhydride, hexafluoroglutaric anhydride (HFA), perfluoropropionic anhydride, perfluorobutyric anhydride, perfluorovaleric anhydride, perfluorohexanoic anhydride, perfluoroheptanoic anhydride, perfluorodecanoic anhydride, heptafluorobutyric anhydride, perfluoropropionic acid, perfluorobutyric acid, perfluorovaleric acid, perfluorohexanoic acid, perfluoroheptanoic acid, and perfluorooctanoic acid; when the present invention performs fluorination modification on the nanoparticles, the mass ratio of the nanoparticles to the fluorine-containing modifier is 1:(2-4) to ensure excellent modification effects.

[0029] In addition, the solvent in the electrolyte can be selected from common carbonate organic substances in the art. For example, it can be a mixture of one or more selected from DMC, EC, EMC, DEC, PC, and FEC. The lithium salt in the electrolyte can also be a common fluorine-containing lithium salt or a non-fluorine-containing lithium salt in the art. For example, it can be selected from one or more of LiPF6, LiTFSI, LiBF4, LiBOBF2, LiDBSBF2, LiFSI, CF3SO3Li, and LiClO4.

[0030] It should be noted that, for the convenience of comparison, only some fluorine-containing modifiers are taken as examples in the embodiments of the present invention, which does not represent a limitation on the types of nanoparticles and fluorine-containing modifiers that can be used in the present invention.

[0031] Next, the technical solution of the present invention will be further described with specific examples.

[0032] Example 1

[0033] This embodiment provides an electrolyte, which includes a mixed solution of EC and DMC, LiPF6, and modified nanoparticles. The modified nanoparticles are silica nanoparticles modified with HFA. The preparation process is as follows:

[0034] (1) Preparation of modified nanoparticles:

[0035] Take 1 g of silica nanoparticles with an average particle size of 20 nm and disperse them in 15 g of a mixed solvent of N,N-dimethylformamide:toluene = 1:1. Use an ultrasonic instrument to ultrasonically disperse for 70 min at room temperature to obtain a mixed liquid containing silica nanoparticles. Subsequently, slowly drop 3.5 g of HFA into this mixed liquid, and carry out a reflux reaction for 12 h under heating at 110 °C and magnetic stirring conditions. After the reaction is completed, centrifuge the product, pour out the supernatant, wash the product 5 times with N,N-dimethylformamide and absolute ethanol respectively, and obtain powdery modified silica nanoparticles through vacuum drying and grinding.

[0036] (2) Preparation of the electrolyte:

[0037] Preparatory work before preparation:

[0038] Prepare a basic electrolyte with a LiPF6 content of 1 M LiPF6 in EC:DMC = 3:7 vol%. The specific process is as follows: Replace the gas in the glove box with argon so that the water content and oxygen content in the glove box meet H2O ≤ 0.1 ppm and O2 ≤ 0.1 ppm respectively; Use molecular sieves to dehydrate and purify the organic components used to prepare the electrolyte.

[0039] Preparation process:

[0040] The preparation of the electrolyte is carried out in the glove box prepared in the preparatory work. First, use a clean spatula to weigh 0.015 g of modified silica nanoparticles into a reagent bottle, and then use a dropper to measure 2.985 g of the basic electrolyte and add it to the reagent bottle. Shake the reagent bottle until the liquid in the reagent bottle is uniformly transparent to obtain the electrolyte. The content of modified silica nanoparticles in the electrolyte is 0.5 wt%.

[0041] According to the preparation process of Example 1, other examples are obtained by changing the type of one or more of the fluorine-containing modifier, lithium salt, solvent, and nanoparticles. The fluorine-containing modifier, lithium salt, solvent, and nanoparticles used in each of the other examples are shown in the following table:

[0042]

[0043]

[0044] Example 9

[0045] This embodiment provides an electrolyte, which has the same preparation process as the electrolyte in Embodiment 1, except for the preparation process of the modified nanoparticles. The specific method is as follows:

[0046] (1) Preparation of modified nanoparticles:

[0047] Take silica nanoparticles with an average particle size of 30 nm, mix them with deionized water and KH550 coupling agent in a mass ratio of 1:2:0.5, add an appropriate amount of alcohol and stir magnetically for 20 min, then continue to stir for 40 min under the condition of 40 °C by mechanical dispersion assisted by ultrasonic waves. After that, place the product in an oven at 120 °C for drying, grind the solid product to obtain silica nanoparticles treated with KH550 coupling agent, and then use a gas mixture of CF4 and N2 with a volume ratio of 25:1 to perform plasma treatment on the silica nanoparticles treated with the coupling agent in a DBD reactor at a gas pressure of 13.5 kPa, a voltage of 7 kV, and a frequency of 9 kHz for 10 min to obtain modified silica nanoparticles.

[0048] Comparative Example 1

[0049] This comparative example provides an electrolyte, which is a basic electrolyte of 1M LiPF6 in DMC:EC:EMC = 1:1:1 vol%.

[0050] Comparative Example 2

[0051] This comparative example uses the same preparation method as in Embodiment 1, except that in step (2), silica nanoparticles without fluorine group modification are used in the preparation of the electrolyte. The details are as follows:

[0052] (1) Preparation of the electrolyte:

[0053] Preparatory work before preparation:

[0054] Prepare a basic electrolyte with a LiPF6 content of 1M LiPF6 in EC:DMC = 3:7 vol%. The specific process is as follows: Replace the gas in the glove box with argon so that the water content and oxygen content in the glove box meet H2O ≤ 0.1 ppm and O2 ≤ 0.1 ppm respectively; Use molecular sieves to dehydrate and purify the organic components used in the preparation of the electrolyte.

[0055] Preparation process:

[0056] The preparation of the electrolyte is carried out in the glove box prepared in the preparatory work. First, use a clean spatula to weigh 0.015 g of silica nanoparticles into a reagent bottle, then use a dropper to measure 2.985 g of the basic electrolyte and add it to the reagent bottle, and shake the reagent bottle until the liquid in the reagent bottle is uniformly transparent to obtain the electrolyte. The content of the modified silica nanoparticles in the electrolyte is 0.5 wt%.

[0057] Experimental Example

[0058] The electrolytes prepared in the above respective examples and comparative examples were paired with a lithium metal foil negative electrode and a NCM811 high-nickel ternary material positive electrode to fabricate coin cells. Using a Solartron 1260&1287 electrochemical workstation at a scanning rate of 1 mV s -1 a 200-cycle performance test was carried out within a voltage test range of 25 °C and 2.5 - 6.0 V. The test results are as follows:

[0059]

[0060]

[0061] According to the method described in Example 1, an electrolyte prepared using nanoparticles and fluorine-containing modifiers not listed in other parts of the examples was tested using the method described in the experimental example. The capacity retention rate and ionic conductivity obtained were similar to those of Examples 1 to 8 in the above table, so no description and display are provided.

[0062] It can be seen from the data in the table that the capacity retention rate of the battery using the modified electrolyte of Example 2 was 87.3% after 200 cycles, while the capacity retention rate of the battery using the electrolyte of Comparative Example 1 was only 72.3% after 200 cycles. The difference in capacity retention rate between the two was 15%; this result indicates that the electrolyte containing modified nanoparticles can effectively reduce the irreversible loss of lithium ions during charge and discharge, improve the cycle stability of the battery, and exhibit a higher capacity retention rate at the same number of cycles.

[0063] From the comparison between Example 2 and Comparative Example 1, it can also be seen that the ionic conductivity of the modified electrolyte prepared in Example 2 was 11.6 mS / cm, while the ionic conductivity of the electrolyte prepared in Comparative Example 1 was 8.2 mS / cm. In comparison, the modified electrolyte prepared in Example 2 by adding HFA-modified nanoparticles had an ionic conductivity increase of 41.5% compared to the electrolyte without added nanoparticles in Comparative Example 1; this shows that by adding HFA-modified nanoparticles, the ionic conductivity of the electrolyte was improved, providing strong support for the high performance and long life of lithium-ion batteries.

[0064] It can also be seen from the table that the electrolyte prepared in Comparative Example 2 contained unmodified nanoparticles. Due to the high hydrophilicity of the original nanoparticles and the difficulty in matching the polarity with the electrolyte, they could not be dispersed in the organic solvent. Therefore, the nanoparticles were more likely to agglomerate and block the separator, resulting in battery failure and thus the capacity retention rate after 200 cycles could not be measured.

[0065] After completing the 200-cycle test, the batteries using the electrolytes described in Example 1 and Comparative Example 1 were disassembled, and the positive electrodes were subjected to SEM tests. The SEM photos of the surfaces of the positive electrodes after disassembly of Example 1 and Comparative Example 1 are respectively as follows Figure 2 and Figure 1 shown. It can be seen that for the battery using the electrolyte of Comparative Example 1, after 200 cycles, there are a large number of decomposition products around the positive electrode material, a large number of lithium dendrites are generated, and the positive electrode structure is damaged; while for the battery using the electrolyte of Example 1, although lithium dendrites are generated on the surface of the positive electrode material after 200 cycles, the number is significantly less than that of Comparative Example 1, and there are almost no cracks on the surface of the single crystal particles, indicating that the electrolyte of Example 1 can inhibit the generation of lithium dendrites and form good protection for the positive electrode material.

[0066] The batteries of Example 2 after 200 cycles were disassembled using the same method, and the negative electrodes after disassembly of Example 2 and Comparative Example 1 were subjected to SEM tests. The SEM photos of the surfaces of the negative electrodes after disassembly of Example 2 and Comparative Example 1 are respectively as follows Figure 4 and Figure 3 shown. It can be seen that on the surface of the negative electrode after disassembly of Example 2, the deposition of lithium ions on the negative electrode surface is more uniform, reducing the phenomenon of preferential deposition of lithium dendrites caused by uneven distribution of local electric fields and ion concentrations, and reducing the risk of battery short circuit caused by dendrite penetration of the SEI film, which can effectively improve the cycle performance and safety of the battery; the surface structure of the negative electrode after disassembly of Comparative Example 1 is loose, with a large number of pores, which may lead to side reactions between the electrolyte and lithium metal, thereby generating more by-products and promoting the growth of lithium dendrites, resulting in a decrease in the cycle performance and safety of the battery.

[0067] The above are only the preferred embodiments of the present invention, and do not impose any form of limitation on the present invention. Although the present invention has been disclosed above with preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art of this patent, without departing from the scope of the technical solution of the present invention, can make some changes or modifications to the above-mentioned technical content as equivalent embodiments of equivalent changes. The implementation schemes in the above embodiments can also be further combined or replaced. However, any simple modification, equivalent change and modification made to the above embodiments based on the technical essence of the present invention still fall within the scope of the technical solution of the present invention.

Claims

1. A high voltage lithium ion battery electrolyte, characterized in that: The invention comprises a lithium salt, a solvent and fluorinated nanoparticles.

2. The high voltage lithium ion battery electrolyte according to claim 1, characterized in that: The fluorinated nanoparticles are nanoparticles modified by fluorinated acid anhydride and / or organic fluorinated monobasic acid.

3. The high voltage lithium ion battery electrolyte according to claim 2, characterized in that: The fluorinated anhydride / organic fluorinated monoacid is selected from one or more of pentafluoropropionic anhydride, hexafluoroglutaric anhydride, perfluoropropionic anhydride, perfluorobutyric anhydride, perfluoropentanoic anhydride, perfluorohexanoic anhydride, perfluoroheptanoic anhydride, perfluorodecanoic anhydride, heptafluorobutyric anhydride, perfluoropropionic acid, perfluorobutyric acid, perfluoropentanoic acid, perfluorohexanoic acid, perfluoroheptanoic acid and perfluorooctanoic acid.

4. The high voltage lithium ion battery electrolyte according to claim 1, characterized in that: The nanoparticles are selected from one or more of carbon material nanoparticles, oxide nanoparticles, nitride nanoparticles, two-dimensional inorganic compound nanoparticles, metal organic framework material nanoparticles, and perovskite nanoparticles.

5. The high voltage lithium ion battery electrolyte according to claim 4, characterized in that: The nanoparticles include one or more of silicon dioxide, graphene quantum dots, doped carbon dots, nanodiamonds, aluminum nitride, titanium nitride, boron nitride, montmorillonite, and ZIF-8.

6. The high voltage lithium ion battery electrolyte according to claim 1, characterized in that: The solvent is selected from carbonate organic substances.

7. The high voltage lithium ion battery electrolyte according to claim 6, characterized in that: The solvent is selected from one or more of dimethyl carbonate, ethylene carbonate, ethyl methyl carbonate, diethyl carbonate, polycarbonate, and vinylene carbonate.

8. The high voltage lithium ion battery electrolyte according to claim 1, characterized in that: The lithium salt is selected from one or more of LiPF6, LiTFSI, LiBF4, LiBOBF2, LiDBSBF2, LiFSI, CF3SO3Li, and LiClO4.

9. The high cycle and high life lithium ion battery electrolyte according to claim 1, characterized in that: The modified nanoparticles in the electrolyte account for 0.01wt%-1wt% of the total amount of the electrolyte.

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