Functional electrolytes, their preparation and application, and lithium metal batteries

Abstract

This invention belongs to the field of lithium metal batteries, specifically relating to functional electrolytes, their preparation, application, and lithium metal batteries. The functional electrolyte is a mixed solution containing a conductive lithium salt and a composite solvent. The composite solvent includes solvents of formula 1 () and formula 2 (). The conductive lithium salt is a boron-containing conductive lithium salt. This invention innovatively combines formulas 1 and 2 as solvents, along with the combined control of the boron-containing lithium salt, thus achieving synergy and unexpectedly improving the performance of the functional electrolyte, particularly contributing to improved high-temperature cycling stability.

Description

Technical Field

[0001] This invention belongs to the field of lithium secondary batteries, specifically relating to the field of lithium secondary battery electrolytes. Background Technology

[0002] Currently, the optimal operating temperature range for lithium-ion batteries is generally limited to 15~35℃. However, in some special application scenarios (such as the high-temperature operation of new energy vehicles in summer and the field of oil and gas exploration and extraction), extreme high temperatures are often encountered, requiring lithium batteries to operate at 60℃ or even higher. Traditional lithium-ion batteries will face problems such as electrode material structure damage, electrolyte decomposition failure, and separator shrinkage and softening when operating in high-temperature environments of 45℃ and above for a long time, making it difficult for the battery to function normally at high temperatures.

[0003] Due to the limited range of electrode material choices and the fact that electrolytes and their associated interfacial layers are more susceptible to temperature effects, optimizing the electrolyte composition is currently the most effective method to address the performance degradation of lithium-ion batteries at high temperatures. Phosphate ester solvents have become a strong candidate for high-temperature electrolyte systems due to their unique safety and flame-retardant properties. This is mainly because the phosphorus-containing free radicals generated by the decomposition of phosphate ester molecules at high temperatures can capture active free radicals generated during combustion, thereby interrupting the combustion reaction. Simultaneously, a phosphorus-rich carbon layer is formed on the substrate surface, achieving self-extinguishing flame retardancy. Furthermore, the high boiling point, high flash point, and excellent thermal stability of phosphate esters effectively meet the requirements of high-temperature electrolytes. Existing technologies have also reported some similar processes. For example, patent document CN121769251A discloses a high-voltage lithium-ion battery capacity-compensating electrolyte, its preparation method, and its application. The electrolyte contains the first additive, specifically including at least one of trimethyl phosphite, trimethyl phosphate, triethyl phosphate, diethyl phenyl phosphite, tris(trimethylsilyl) phosphite, tris(trimethylsilyl) phosphate, tripropyne phosphate (TPP), and triethyl phosphate. Furthermore, patent document CN121215885A discloses a lithium metal battery electrolyte comprising an electrolyte lithium salt, an organic solvent, and a functional additive, including phosphorus oxychloride, with a phosphorus oxychloride concentration of 0.1%-2% in the electrolyte.

[0004] Although there are some modification schemes for phosphate esters in the existing technology, conventional phosphate ester solvents (such as trimethyl phosphate (TMP) and triethyl phosphate (TEP)) have problems such as low oxidation potential and poor film-forming ability. Moreover, as the temperature increases, the oxidation reaction of phosphate esters will be intensified from both a kinetic and thermodynamic perspective, which will make the interface formed by phosphate esters unstable at high temperatures, thereby affecting the high-temperature stability of lithium metal batteries. Summary of the Invention

[0005] The primary objective of this invention is to provide a high-temperature safe functional electrolyte, which aims to improve the high-temperature stability of the electrolyte.

[0006] The second objective of this invention is to provide the preparation of the aforementioned functional electrolyte and its application in lithium metal batteries.

[0007] A third objective of this invention is to provide a lithium metal battery comprising the aforementioned functional electrolyte.

[0008] The functional electrolyte is a mixed solution containing a conductive lithium salt and a composite solvent, wherein the composite solvent comprises solvent of formula 1 and solvent of formula 2.

[0009] Formula 1

[0010] Formula 2

[0011] In Formula 1, R1 and R2 are individually H, C1-C4 alkyl, or C1-C4 alkoxy; R3 is H or C1-C4 alkyl.

[0012] In Formula 2, R4 is a C1-C4 fluoroalkyl group; R5 is a C1-C4 alkyl group;

[0013] The conductive lithium salt is a boron-containing conductive lithium salt.

[0014] This invention innovatively combines Formula 1 and Formula 2 as solvents, along with the combined control of boron-containing lithium salts, thereby achieving synergy and unexpectedly improving the performance of functional electrolytes, particularly contributing to the improvement of the high-temperature cycling stability of functional electrolytes.

[0015] In this invention, in Formula 1, R1 and R2 are C1-C3 alkyl groups; R3 is H or a C1-C3 alkyl group.

[0016] In this invention, the solvent of Formula 1 includes at least one of Formula 1A, Formula 1B, and Formula 1C;

[0017] Formula 1A

[0018] Formula 1B

[0019] Formula 1C.

[0020] In this invention, in Formula 2, R4 is a C1-C3 fluoroalkyl group with 2-6 fluorine atoms; R5 is a C1-C2 alkyl group.

[0021] In this invention, the solvent of Formula 2 includes at least one of Formula 2A and Formula 2B;

[0022] Formula 2A

[0023] Formula 2B.

[0024] In this invention, the volume content of the solvent of Formula 1 in the composite solvent is 10-90 vol%; preferably 30-80 vol%; and more preferably 65-75%. The combination of the composite solvent and the boron-containing lithium salt, along with the joint control of the volume of the composite lithium salt, helps to further enhance synergy and improve the high-temperature cycling stability of the metal battery.

[0025] In this invention, the conductive lithium salt is one or more of lithium dioxalatoborate, lithium difluorooxalatoborate, and lithium tetrafluoroborate.

[0026] Preferably, the concentration of conductive lithium salt in the functional electrolyte is 0.5~5M, more preferably 0.8~1.2M; and even more preferably 0.9~1.1M.

[0027] The present invention also provides a method for preparing the functional electrolyte, wherein a conductive lithium salt and a composite solvent are mixed to obtain the electrolyte.

[0028] The present invention also provides an application of the aforementioned functional electrolyte in the preparation of lithium metal batteries.

[0029] The present invention also provides a lithium metal battery comprising the functional electrolyte described herein.

[0030] The lithium metal battery of this invention, apart from containing the electrolyte described in this invention, may have other known components and structures. For example, the lithium metal battery may be made of lithium metal.

[0031] Beneficial effects

[0032] This invention innovatively combines Formula 1 and Formula 2 as a solvent, in conjunction with the aforementioned boron-containing lithium salt, thereby achieving a synergistic effect and unexpectedly improving the performance of the functional electrolyte, particularly contributing to the improvement of the high-temperature cycling stability of the functional electrolyte. Attached Figure Description

[0033] Figure 1 The graph shows the long-cycle performance of the Li||NCM811 battery assembled in Example 1 at 60°C.

[0034] Figure 2 The coulombic efficiency diagram of the Li||NCM811 battery assembled in Example 1 at 60°C;

[0035] Figure 3 The graph shows the long-cycle performance of the Li||NCM811 battery assembled in Comparative Example 3 at 60°C.

[0036] Figure 4The graph shows the long-cycle performance of the Li||NCM811 battery assembled in Comparative Example 5 at 60°C. Detailed Implementation

[0037] In this invention, the electrolyte can be prepared by mixing using conventional methods.

[0038] Example 1

[0039] An electrolyte was prepared by stirring and mixing a conductive lithium salt (lithium difluorooxalate borate (LiDFOB)) and a composite solvent.

[0040] The composite solvent contains Formula 1C and Formula 2A in a volume ratio of 7:3; the concentration of the conductive lithium salt in the electrolyte is 1M.

[0041] Example 2

[0042] Compared to Example 1, the only difference is that the volume ratio of Formula 1C and Formula 2A in the composite solvent is changed, specifically:

[0043] Group A: The volume ratio of Equation 1C and Equation 2A is 1:1;

[0044] Group B: The volume ratio of Equation 1C to Equation 2A is 3:7;

[0045] All other operations and parameters are the same as in Example 1.

[0046] Example 3

[0047] Compared with Example 1, the only difference is that the type and concentration of lithium salt are changed, specifically:

[0048] Group A: The conductive lithium salt (lithium difluorooxalate borate (LiDFOB)) is set at 0.8M, and the volume ratio of Formula 1C and Formula 2A is 7:3;

[0049] Group B: The conductive lithium salt (lithium difluorooxalate borate (LiDFOB)) is set at 1.2M, and the volume ratio of Formula 1C and Formula 2A is 7:3;

[0050] All other operations and parameters are the same as in Example 1.

[0051] Comparative Example 1

[0052] Compared with Example 1, the only difference is that the composite solvent contains only Formula 1C, while the total volume of the composite solvent and the concentration of the conductive lithium salt, and other operating conditions are the same as in Example 1.

[0053] Comparative Example 2

[0054] Compared with Example 1, the only difference is that the composite solvent contains only Formula 2A, while the total volume of the composite solvent and the concentration of the conductive lithium salt, and other operating conditions are the same as in Example 1.

[0055] Comparative Example 3

[0056] Compared with Example 1, the only difference is that comparative formula a ( The volume replacement of 1C is the same as that of Example 1, and other operating conditions are the same.

[0057] Comparative Example 4

[0058] Compared with Example 1, the only difference is that comparative formula b is used. The volume replacement of 1C is the same as that of Example 1, and other operating conditions are the same.

[0059] Comparative Example 5

[0060] Compared with Example 1, the only difference is that comparative formula c ( The volume replacement type 2A is the same as that of Example 1, and all other operating conditions are the same.

[0061] Comparative Example 6

[0062] Compared with Example 1, the only difference is that the conductive lithium salt is replaced with lithium bis(fluorosulfonyl)imide (LiFSI), and all other operations and parameters are the same as in Example 1.

[0063] test:

[0064] I. Preparation of NCM811 cathode

[0065] LiNi, the positive electrode active material 0.8 Co 0.1 Mo 0.1 O2, binder polyvinylidene fluoride (PVDF), and conductive carbon black are mixed evenly in a mass ratio of 8:1:1 to prepare a positive electrode slurry. The positive electrode slurry is coated onto aluminum foil using a 200 μm scraper and dried in a vacuum oven at 100°C for 8 hours to obtain a positive electrode sheet.

[0066] II. Lithium Battery Assembly

[0067] The CR2025 coin cells were assembled in a glove box with both water and oxygen content less than 0.1 ppm, in the following order: positive electrode shell, positive electrode sheet, separator, negative electrode sheet (lithium foil), nickel mesh, and negative electrode shell. The separator was made of polypropylene; the negative electrode was lithium metal.

[0068] The test results of lithium metal batteries in each case at 60℃ and 1C are shown in Table 1:

[0069]

[0070] As can be seen from Example 1 and Comparative Examples 1-6, the innovative combination of Formula 1 and Formula 2 as solvents, along with the combined control of lithium salts, can achieve synergy and unexpectedly improve the performance of functional electrolytes, especially helping to improve the high-temperature cycling stability of functional electrolytes.

[0071] As can be seen from Examples 1 and 2, controlling the volume ratio of Formula 1 and Formula 2 to be 2~3:1, preferably 2.1~2.5:1, can achieve better synergy and help to further enhance the high-temperature cycle stability of metal batteries.

[0072] As can be seen from Examples 1 and 3, the lithium salt described in this invention, with its concentration controlled, can be used in combination with the composite solvent to achieve better synergy, which helps to further enhance the high-temperature cycling stability of metal batteries.

Claims

1. A functional electrolyte, comprising a mixed solution of a conductive lithium salt and a composite solvent, characterized in that, The composite solvent comprises solvent of formula 1 and solvent of formula 2; Formula 1 Formula 2 In Formula 1, R1 and R2 are individually H, C1-C4 alkyl, or C1-C4 alkoxy; R3 is H or C1-C4 alkyl. In Formula 2, R4 is a C1-C4 fluoroalkyl group; R5 is a C1-C4 alkyl group; The conductive lithium salt is a boron-containing conductive lithium salt.

2. The functional electrolyte as described in claim 1, characterized in that, In Formula 1, R1 and R2 are C1-C3 alkyl groups; R3 is H or a C1-C3 alkyl group.

3. The functional electrolyte as described in claim 2, characterized in that, The solvent of Formula 1 includes at least one of Formula 1A, Formula 1B, and Formula 1C; Formula 1A Formula 1B Formula 1C.

4. The functional electrolyte as described in claim 1, characterized in that, In Formula 2, R4 is a C1-C3 fluoroalkyl group with 2-6 fluorine atoms; R5 is a C1-C2 alkyl group.

5. The functional electrolyte as described in claim 4, characterized in that, The solvent of Formula 2 includes at least one of Formula 2A and Formula 2B; Formula 2A Formula 2B.

6. The functional electrolyte according to any one of claims 1 to 5, characterized in that, In the composite solvent, the volume content of the solvent of Formula 1 is 10~90v; preferably 30~80v.

7. The functional electrolyte as described in claim 1, characterized in that, The conductive lithium salt is one or more of lithium dioxaborate, lithium difluorooxaborate, and lithium tetrafluoroborate. Preferably, the concentration of conductive lithium salt in the functional electrolyte is 0.5~5M, more preferably 0.8~1.2M.

8. A method for preparing the functional electrolyte according to any one of claims 1 to 7, characterized in that, The conductive lithium salt and composite solvent were mixed to prepare the product.

9. The application of the functional electrolyte according to any one of claims 1 to 7, characterized in that, It is used to prepare lithium metal batteries.

10. A lithium metal battery, characterized in that, It includes the functional electrolyte according to any one of claims 1 to 7.

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