Flame-retardant high-safety high-donor-number electrolyte and lithium battery

Abstract

The application relates to the field of electrochemistry, and discloses a high-donor-number electrolyte with high safety and high flame retardation, which contains a lithium salt, a high-donor-number solvent and a diluent; the high-donor-number solvent includes at least two of an amide-based solvent, a pyridine-based solvent, a sulfone-based solvent, a sulfoxide-based solvent and a phosphate-based solvent, and the lithium salt includes lithium nitrate. The application provides a lithium battery which includes an electrolyte, a positive electrode, a negative electrode and a separator, and the electrolyte is the electrolyte disclosed in the application. The electrolyte system disclosed in the application selects at least two high-donor-number solvents disclosed in the application as solvents, and cooperatively uses lithium nitrate and other lithium salts, so that excellent performance which cannot be achieved under the same concentration of other lithium salts can be achieved under the premise of ensuring that the electrolyte is not flammable.

Description

Technical Field

[0001] This invention relates to the field of electrochemical technology, specifically to a flame-retardant, highly safe, high-donor-count electrolyte and lithium battery. Background Technology

[0002] In recent years, as the environmental challenges posed by traditional fossil fuels have intensified, new clean energy sources have been vigorously developed. This necessitates energy storage devices with high stability and safety. Among these, lithium-ion batteries have received considerable attention and widespread application due to their advantages such as high voltage and long lifespan. However, ensuring the high safety of the battery system while maintaining high cycle stability is equally crucial.

[0003] However, the traditional electrolyte in commercial lithium-ion batteries is a carbonate-based electrolyte. Some carbonate solvents used in these batteries have low flash points, low boiling points, and are highly flammable, posing significant safety hazards. Therefore, choosing a safer electrolyte system is expected to solve or alleviate these problems.

[0004] In recent years, researchers have been trying to use high-boiling-point solvents or flame-retardant solvents as electrolytes for lithium batteries, such as sulfones, phosphate esters, and phosphononitriles. However, these solvents face the problem of incompatibility with graphite or lithium metal anodes. Taking phosphate ester solvents as an example, under normal concentration conditions, they will co-intercalate in graphite, thus severely damaging battery performance. On the lithium metal surface, these solvents cannot form a stable solid electrolyte interphase (SEI), resulting in continuous electrolyte consumption and low lithium metal deposition coulombic efficiency. To solve these problems, researchers have proposed a high-concentration or locally high-concentration electrolyte strategy. Reducing the number of solvent molecules and anion-derived SEI can help solve these problems. However, in such electrolytes, the concentration or local concentration of lithium salt is usually above 4M. On the one hand, this increases the amount of lithium salt used, greatly increasing the production cost of the electrolyte. On the other hand, the reduction in the proportion of flame-retardant solvents also weakens the flame-retardant performance of the electrolyte. Summary of the Invention

[0005] This invention provides a flame-retardant, highly safe, high-donor-count electrolyte and lithium battery, which improves battery safety while achieving high performance.

[0006] To achieve the above objectives, the present invention provides a flame-retardant, highly safe, high-donor-number electrolyte, which contains a lithium salt, a high-donor-number solvent, and a diluent; the high-donor-number solvent includes at least two of amide-based solvents, pyridinyl-based solvents, sulfone-based solvents, sulfoxide-based solvents, and phosphate ester-based solvents, and the lithium salt includes lithium nitrate.

[0007] The high donor number solvent-dissolved lithium nitrate of this invention helps form a lithium-ion solvation structure dominated by nitrate anions. This special solvation structure not only suppresses solvent co-intercalation at the negative electrode, achieving stable cycling of lithium-ion batteries, but also helps form a uniform and stable SEI on the lithium metal surface, increasing the deposition coulombic efficiency of lithium metal to over 99%, thereby achieving high-efficiency and stable cycling of lithium metal batteries.

[0008] A second aspect of the present invention provides a lithium battery comprising an electrolyte, a positive electrode, a negative electrode, and a separator, wherein the electrolyte is the electrolyte described in the present invention.

[0009] Traditional carbonate-based electrolytes often use carbonate solvents with low boiling points, low flash points, and high flammability, posing a threat to battery safety. While adding appropriate flame retardant additives can reduce the flammability of the electrolyte, the presence of flammable solvents still poses a challenge to battery safety. If flame retardants are used directly as solvents, traditional lithium hexafluorophosphate, lithium bis(trifluoromethanesulfonyl)imide, and lithium bis(fluorosulfonyl)imide as lithium salts are difficult to use for stable cycling of lithium-ion or lithium metal batteries due to solvent co-intercalation in graphite and / or the inability to form a stable SEI on the lithium metal surface. The electrolyte system proposed in this invention uses at least two of the high donor number solvents described in this invention as solvents, combined with lithium salts such as lithium nitrate, achieving superior performance that cannot be achieved at the same concentration of other lithium salts while ensuring the electrolyte remains non-flammable. Attached Figure Description

[0010] Figure 1 Li-LiNi electrolyte prepared in Example 4 of this invention 0.5 Co 0.2 Mn 0.3 O2 battery long cycle performance;

[0011] Figure 2 The combustion of the electrolyte is shown in Example 4 of this invention.

[0012] Figure 3 The combustion of the electrolyte in Comparative Example 4 of this invention is shown. Detailed Implementation

[0013] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0014] This invention provides a flame-retardant, highly safe, high-donor-number electrolyte, which contains a lithium salt, a high-donor-number solvent, and a diluent; the high-donor-number solvent includes at least two of amide-based solvents, pyridinyl-based solvents, sulfone-based solvents, sulfoxide-based solvents, and phosphate-based solvents, and the lithium salt includes lithium nitrate.

[0015] The high donor number solvent-dissolved lithium nitrate of this invention helps form a lithium-ion solvation structure dominated by nitrate anions. This special solvation structure not only suppresses solvent co-intercalation at the negative electrode, achieving stable cycling of lithium-ion batteries, but also helps form a uniform and stable SEI on the lithium metal surface, increasing the deposition coulombic efficiency of lithium metal to over 99%, thereby achieving high-efficiency and stable cycling of lithium metal batteries.

[0016] In this invention, any electrolyte having the aforementioned composition can achieve the purpose of this invention. Besides lithium nitrate, the electrolyte also includes other lithium salts. One embodiment is illustrated, but this does not limit the scope of the invention. According to a preferred embodiment of the invention, the lithium salt further includes a second lithium salt, which is selected from one or more of lithium bis(fluorosulfonyl)imide, lithium bis(trifluorosulfonyl)imide, lithium hexafluorophosphate, lithium tetrafluoroborate, and lithium difluorooxalate borate, preferably lithium bis(fluorosulfonyl)imide. Using the aforementioned technical solution, efficient and stable cycling of lithium metal batteries can be achieved while ensuring the electrolyte is non-flammable.

[0017] In this invention, the molar ratio of lithium nitrate to the second lithium salt in the electrolyte can be selected within a wide range. One embodiment is illustrated, but this does not limit the scope of the invention. According to a preferred embodiment of the invention, the molar ratio of lithium nitrate to the second lithium salt in the electrolyte is 1-4:1. Using the aforementioned technical solution, efficient and stable cycling of lithium metal batteries can be achieved while ensuring the electrolyte remains non-flammable.

[0018] According to a preferred embodiment of the present invention, the lithium salt comprises lithium nitrate and lithium bis(fluorosulfonyl)imide. By employing the aforementioned technical solution, efficient and stable cycling of lithium metal batteries can be achieved while ensuring the non-flammability of the electrolyte.

[0019] In this invention, the molar ratio of lithium nitrate to lithium bisfluorosulfonylimide in the electrolyte can be selected within a wide range. This is an example of one embodiment, but does not limit the scope of the invention. According to a preferred embodiment of the invention, the molar ratio of lithium nitrate to lithium bisfluorosulfonylimide in the electrolyte is 1-4:1.

[0020] In this invention, the molar concentration of the lithium salt in the electrolyte can be selected within a wide range. One embodiment is illustrated, but this does not limit the scope of the invention. According to a preferred embodiment of the invention, the molar concentration of the lithium salt in the electrolyte is 0.01 mol / L to 4 mol / L, preferably 0.4 mol / L to 2.5 mol / L. The aforementioned technical solution has the advantage of moderate conductivity and the ability to help the negative electrode form a highly efficient and stable interface dominated by inorganic materials.

[0021] In this invention, amide-based solvents refer to solvent molecules containing amide groups. The range of selectable amide-based solvents is quite wide. One embodiment is illustrated, but this does not limit the scope of the invention. According to a preferred embodiment of the invention, the amide-based solvent is selected from one or more of N,N-dimethylformamide, N,N-dimethylacetamide, N,N-diethylformamide, and N,N-diethylacetamide, preferably N,N-dimethylacetamide. Using the aforementioned technical solution, efficient cycle stability of lithium metal batteries can be achieved while ensuring the non-flammability of the electrolyte.

[0022] In this invention, pyridyl solvent refers to pyridine or a solvent molecule that has been fluorinated based on pyridine. The range of possible pyridyl solvents is broad; one embodiment is illustrated illustratively, but this does not limit the scope of the invention. According to a preferred embodiment of the invention, the pyridyl solvent is selected from one or more of pyridine, 1-fluoropyridine, 2-fluoropyridine, and 3-fluoropyridine.

[0023] In this invention, sulfone-based solvent refers to a solvent molecule containing a sulfone group. The range of possible sulfone-based solvents is wide; one embodiment is illustrated illustratively, but this does not limit the scope of the invention. According to a preferred embodiment of the invention, the sulfone-based solvent is selected from one or more of sulfolane, 3-methylsulfolane, ethylmethyl sulfone, and dipropyl sulfone.

[0024] In this invention, sulfoxide-based solvents refer to solvent molecules containing sulfoxide groups. The range of possible sulfoxide-based solvents is broad; one embodiment is illustrated, but this does not limit the scope of the invention. According to a preferred embodiment of the invention, the sulfoxide-based solvent is selected from one or more of dimethyl sulfoxide, dipropyl sulfoxide, ethylmethyl sulfoxide, and tetramethylene sulfoxide.

[0025] In this invention, phosphate ester-based solvent refers to solvent molecules containing phosphate ester groups. The range of possible phosphate ester-based solvents is quite wide. One embodiment is illustrated, but this does not limit the scope of the invention. According to a preferred embodiment of the invention, the phosphate ester-based solvent is selected from one or more of trimethyl phosphate, triethyl phosphate, tripropyl phosphate, and tributyl phosphate, preferably trimethyl phosphate. Using the aforementioned technical solution, efficient and stable cycling of lithium metal batteries can be achieved while ensuring the electrolyte remains non-flammable.

[0026] In this invention, the content of each solvent in the high donor number solvent can be selected within a wide range. One embodiment is illustrated, but this does not limit the scope of the invention. According to a preferred embodiment of the invention, the content of each solvent in the high donor number solvent is not less than 15% by volume, preferably 20-80% by volume. Using the aforementioned technical solution, efficient and stable cycling of lithium metal batteries can be achieved while ensuring the non-flammability of the electrolyte.

[0027] In this invention, any electrolyte having the aforementioned composition can achieve the purpose of this invention. The range of types of high donor solvents is relatively wide. An embodiment is illustrated, but it does not limit the scope of this invention. According to a preferred embodiment of this invention, the high donor solvent includes at least two of amide solvents, sulfone solvents, sulfoxide solvents, and phosphate ester solvents.

[0028] According to a preferred embodiment of the present invention, the high donor number solvent includes phosphate ester-based solvents and amide-based solvents. The aforementioned technical solution has the advantages of high dissociation of lithium nitrate and the ability to maintain anion-dominated lithium-ion solvation structure.

[0029] In this invention, the volume ratio of phosphate-based solvent to amide-based solvent in the electrolyte can be selected within a wide range. One embodiment is illustrated, but this does not limit the scope of the invention. According to a preferred embodiment of the invention, the volume ratio of phosphate-based solvent to amide-based solvent in the electrolyte is 1-3:1. Using the aforementioned technical solution has the advantages of high dissociation of lithium nitrate and the ability to maintain anion-dominated lithium-ion solvation structure.

[0030] In this invention, the range of diluents is relatively wide. One embodiment is illustrated by way of example, but it does not limit the scope of the invention. According to a preferred embodiment of the invention, the diluent is selected from one or more of fluorobenzene, 1,2-difluorobenzene, 2,2,2-trifluoroethyl ether, methyltrifluoroethyl carbonate, and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, preferably 2,2,2-trifluoroethyl ether.

[0031] In this invention, the volume content of the high donor number solvent, based on the total volume of the electrolyte, can be selected within a wide range. This is an illustrative embodiment, but it does not limit the scope of the invention. According to a preferred embodiment of the invention, the volume content of the high donor number solvent, based on the total volume of the electrolyte, is 10%-75%, preferably 30%-50%. Using the aforementioned technical solution, efficient and stable cycling of lithium metal batteries can be achieved while ensuring the non-flammability of the electrolyte.

[0032] In this invention, the volume content of the diluent, based on the total volume of the electrolyte, can be selected within a wide range. This is an illustrative embodiment, but does not limit the scope of the invention. According to a preferred embodiment of the invention, the volume content of the diluent, based on the total volume of the electrolyte, is 10%-75%, preferably 50%-70%. Using the aforementioned technical solution, efficient and stable cycling of lithium metal batteries can be achieved while ensuring the electrolyte remains non-flammable.

[0033] This invention provides a lithium battery, comprising an electrolyte, a positive electrode, a negative electrode, and a separator, wherein the electrolyte is the electrolyte described in this invention.

[0034] In this invention, the range of positive electrodes for lithium batteries is relatively wide, and common positive electrodes for lithium batteries can be used in this invention. One embodiment is illustrated, but it does not limit the scope of this invention. According to a preferred embodiment of this invention, the positive electrode is lithium iron phosphate or ternary positive electrode material.

[0035] In this invention, there are no special requirements for the ternary cathode material. One embodiment is illustrated, but this does not limit the scope of the invention. According to a preferred embodiment of the invention, the ternary cathode material is selected from ternary lithium nickel cobalt manganese oxide or ternary lithium nickel cobalt aluminum oxide. LiNi is used in the embodiments of this invention. 0.5 Co 0.2 Mn 0.3 O2 Exemplary illustration.

[0036] In this invention, the range of negative electrodes for lithium batteries is relatively wide, and common negative electrodes for lithium batteries can be used in this invention. One embodiment is illustrated, but it does not limit the scope of the invention. According to a preferred embodiment of the invention, the negative electrode material is graphite or lithium metal.

[0037] In this invention, the range of lithium battery separators is relatively wide; most common lithium battery separators can be used. One embodiment is illustrated, but this does not limit the scope of the invention. According to a preferred embodiment of the invention, the lithium battery separator is a Celgard separator. Celgard 2325 is used exemplarily in this embodiment.

[0038] Traditional carbonate-based electrolytes often use carbonate solvents with low boiling points, low flash points, and high flammability, posing a threat to battery safety. While adding appropriate flame retardant additives can reduce the flammability of the electrolyte, the presence of flammable solvents still poses a challenge to battery safety. If flame retardants are used directly as solvents, traditional lithium hexafluorophosphate, lithium bis(trifluoromethanesulfonyl)imide, and lithium bis(fluorosulfonyl)imide as lithium salts are difficult to use for stable cycling of lithium-ion or lithium metal batteries due to solvent co-intercalation in graphite and / or the inability to form a stable SEI on the lithium metal surface. The electrolyte system proposed in this invention uses at least two high donor number compounds as solvents, combined with lithium salts such as lithium nitrate, achieving superior performance that cannot be achieved at the same concentration with other lithium salts, while ensuring the electrolyte remains non-flammable.

[0039] The present invention will be described in detail below through embodiments.

[0040] The components used in the following examples and comparative examples are all battery grade.

[0041] In the following examples, the electrolyte was prepared in a glove box filled with 99.999% pure argon gas, with a moisture content of less than 0.1 ppm and a temperature of room temperature.

[0042] Performance testing

[0043] Li-Cu half-cell test

[0044] The electrolytes prepared in the following examples and comparative examples were used to assemble Li-Cu half-cells, and their cycle performance was tested. The coulombic efficiency of the Li-Cu half-cells was tested to evaluate the reversibility of lithium metal deposition. The Li-Cu half-cells were assembled as follows: using copper foil as the positive electrode, lithium sheet as the negative electrode, and Celgard 2325 as the separator, the button half-cells were assembled in a glove box and tested after standing. The coulombic efficiency was evaluated using the following test method: first, at 0.5 mA / cm² on the surface of the copper foil... 2 Current density deposition 5mAh / cm 2 The lithium metal was then extracted by setting a charging cutoff voltage of 1V. Subsequently, a 5mAh / cm³ lithium metal was deposited again on the copper foil surface. 2 Lithium metal was used as reserve lithium, followed by 10 charge-discharge cycles. Finally, the remaining lithium metal on the copper foil was extracted using a cutoff voltage of 1V. The coulombic efficiency was calculated based on the capacity of the final extracted lithium metal. Table 1 lists the coulombic efficiency test data obtained using the above method.

[0045] Li-LiNi 0.5 Co 0.2 Mn 0.3 O2 full battery test

[0046] The electrolytes prepared in the following examples and comparative examples were assembled into batteries, and their full-cell cycle performance was tested. The assembly method is as follows: using LiNi 0.5 Co 0.2 Mn 0.3 Using O2 as the positive electrode corresponds to an active material loading of approximately 3 mg / cm³. 2 The preparation method of the positive electrode is as follows: First, 0.1g of polyvinylidene fluoride (PVDF) is uniformly dispersed in 2.3mL of N-methylpyrrolidone (NMP) solvent, and then 0.8g of LiNi is added. 0.5 Co 0.2 Mn 0.3 O2 powder and 0.1g of conductive carbon were mixed. The resulting slurry was coated onto aluminum foil and dried in a vacuum oven at 100°C for 12 hours to obtain the corresponding electrode. A lithium sheet was used as the negative electrode, with a thickness of 450μm. Celgard2325 was used as the separator, and button cells were assembled in a glove box. Cyclic tests were conducted within a voltage range of 3V-4.3V at a charge rate of 0.25C and a discharge rate of 0.5C. Figure 1 The data listed were obtained using this method.

[0047] Electrolyte flammability test

[0048] Take less than 0.2 ml of the electrolyte from the examples and comparative examples into the positive electrode shell of the electrolyte, ignite it with an ignition gun for three seconds, and then remove the ignition source. Record the combustion status and self-extinguishing time of the electrolyte. Figure 2 and Figure 3 The results were obtained using this test method. Table 2 lists the self-quenching data for different electrolytes, which were obtained using the above method.

[0049] Example 1

[0050] The electrolyte is prepared as follows:

[0051] In an argon-filled glove box, take 10.35g of lithium nitrate, 12.5mL of N,N-dimethylacetamide, 37.5mL of trimethyl phosphate, and 100mL of 2,2,2-trifluoroethyl ether and mix them thoroughly until homogeneous.

[0052] Example 2

[0053] The electrolyte is prepared as follows:

[0054] In an argon-filled glove box, take 5.18g of lithium nitrate, 25mL of N,N-dimethylacetamide, 50mL of trimethyl phosphate, and 75mL of 2,2,2-trifluoroethyl ether and mix them thoroughly until homogeneous.

[0055] Example 3

[0056] The electrolyte is prepared as follows:

[0057] In an argon-filled glove box, take 20.70g of lithium nitrate, 25mL of N,N-dimethylacetamide, 25mL of trimethyl phosphate, and 100mL of methyltrifluoroethyl carbonate and mix them thoroughly until homogeneous.

[0058] Example 4

[0059] The electrolyte is prepared as follows:

[0060] In an argon-filled glove box, take 8.28g of lithium nitrate, 5.61g of lithium difluorosulfonyl imide, 12.5mL of N,N-dimethylacetamide, 37.5mL of trimethyl phosphate, and 100mL of 2,2,2-trifluoroethyl ether, mix them thoroughly, and stir until homogeneous to obtain the final product.

[0061] Figure 1 Li-LiNi prepared from the electrolyte of this embodiment 0.5 Co 0.2 Mn 0.3 O2 battery long cycle performance Figure 1 This demonstrates that the electrolyte enables the long-term stable operation of lithium metal full batteries.

[0062] Figure 2 This describes the combustion of the electrolyte in this embodiment. Figure 2 This indicates that electrolytes possess non-flammable properties.

[0063] Example 5

[0064] The electrolyte is prepared as follows:

[0065] In an argon-filled glove box, take 8.28g of lithium nitrate, 5.61g of lithium difluorosulfonyl imide, 12.5mL of dimethyl sulfoxide, 37.5mL of trimethyl phosphate, and 100mL of 2,2,2-trifluoroethyl ether, mix them thoroughly, and stir until homogeneous to obtain the final product.

[0066] Example 6

[0067] The electrolyte is prepared as follows:

[0068] In an argon-filled glove box, take 8.28g of lithium nitrate, 5.61g of lithium difluorosulfonyl imide, 12.5mL of sulfolane, 37.5mL of trimethyl phosphate, and 100mL of 2,2,2-trifluoroethyl ether and mix them thoroughly until homogeneous.

[0069] Example 7

[0070] The electrolyte is prepared as follows:

[0071] In an argon-filled glove box, take 8.28g of lithium nitrate, 5.61g of lithium difluorosulfonyl imide, 37.5mL of N,N-dimethylacetamide, 12.5mL of trimethyl phosphate, and 100mL of 2,2,2-trifluoroethyl ether, mix them thoroughly, and stir until homogeneous to obtain the final product.

[0072] Example 8

[0073] The electrolyte is prepared as follows:

[0074] In an argon-filled glove box, take 8.28g of lithium nitrate, 5.61g of lithium difluorosulfonyl imide, 12.5mL of N,N-dimethylacetamide, 37.5mL of dimethyl sulfoxide, and 100mL of 2,2,2-trifluoroethyl ether, mix them thoroughly, and stir until homogeneous to obtain the final product.

[0075] Example 9

[0076] The electrolyte is prepared as follows:

[0077] In an argon-filled glove box, take 8.28g of lithium nitrate, 8.61g of lithium bis(trifluorosulfonyl)imide, 12.5mL of N,N-dimethylacetamide, 37.5mL of trimethyl phosphate, and 100mL of 2,2,2-trifluoroethyl ether, mix them thoroughly, and stir until homogeneous to obtain the final product.

[0078] Example 10

[0079] The electrolyte is prepared as follows:

[0080] In an argon-filled glove box, take 5.175g of lithium nitrate, 14.025g of lithium difluorosulfonyl imide, 12.5mL of N,N-dimethylacetamide, 37.5mL of trimethyl phosphate, and 100mL of 2,2,2-trifluoroethyl ether, mix them thoroughly, and stir until homogeneous to obtain the final product.

[0081] Example 11

[0082] The electrolyte is prepared as follows:

[0083] In an argon-filled glove box, take 8.28g of lithium nitrate, 5.61g of lithium difluorosulfonyl imide, 12.5mL of N,N-dimethylacetamide, 37.5mL of trimethyl phosphate, and 100mL of methyltrifluoroethyl carbonate, mix them thoroughly, and stir until homogeneous to obtain the final product.

[0084] Example 12

[0085] The method of Example 4 was followed, except that an equal volume of pyridine was used instead of N,N-dimethylacetamide.

[0086] Comparative Example 1

[0087] The electrolyte is prepared as follows:

[0088] In an argon-filled glove box, take 28.05g of lithium difluorosulfonylimide, 12.5mL of N,N-dimethylacetamide, 37.5mL of trimethyl phosphate, and 100mL of 2,2,2-trifluoroethyl ether and mix them thoroughly until homogeneous.

[0089] Comparative Example 2

[0090] The electrolyte is prepared as follows:

[0091] In an argon-filled glove box, take 8.28g of lithium nitrate, 5.61g of lithium difluorosulfonylimide, 50ml of N,N-dimethylacetamide, and 100ml of 2,2,2-trifluoroethyl ether and mix them thoroughly until homogeneous.

[0092] Comparative Example 3

[0093] The electrolyte is prepared as follows:

[0094] In an argon-filled glove box, 22.8 g of lithium hexafluorophosphate, 142.5 ml of a mixed solvent of ethylene carbonate and diethyl carbonate (volume ratio 1:1), and 7.5 ml of fluoroethylene carbonate were thoroughly mixed and stirred until homogeneous. This electrolyte is a conventional carbonate-based electrolyte commonly used in lithium-ion battery systems.

[0095] Figure 3 This is a comparison of the combustion of the electrolyte. Figure 3 This indicates that traditional carbonate electrolytes are highly flammable.

[0096] Comparative Example 4

[0097] The electrolyte is prepared as follows:

[0098] In an argon-filled glove box, take 8.28g of lithium nitrate, 5.61g of lithium difluorosulfonyl imide, 50ml of pyridine, and 100ml of 2,2,2-trifluoroethyl ether and mix them thoroughly until homogeneous.

[0099] Comparative Example 5

[0100] The electrolyte is prepared as follows:

[0101] In an argon-filled glove box, take 8.28g of lithium nitrate, 5.61g of lithium difluorosulfonyl imide, 50ml of dimethyl sulfoxide, and 100ml of 2,2,2-trifluoroethyl ether and mix them thoroughly until homogeneous.

[0102] Table 1. Coulombic efficiency of different cells in Li-Cu half-cells.

[0103] electrolytes Coulomb efficiency Example 1 95.2％ Example 2 95.5％ Example 3 95.6％ Example 4 99.4％ Example 5 97.4％ Example 6 98.9％ Example 7 94.9％ Example 8 90.6％ Example 9 97.2％ Example 10 98.0％ Example 11 99.0％ Example 12 98.1％ Comparative Example 1 81.4％ Comparative Example 2 64.9％ Comparative Example 3 94.9％ Comparative Example 4 65.3％ Comparative Example 5 63.9％

[0104] Table 2 Self-quenching time of different electrolytes

[0105]

[0106]

[0107] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A flame-retardant, highly safe, high-donor-number electrolyte, characterized in that, The electrolyte contains a lithium salt, a high donor number solvent, and a diluent; the high donor number solvent includes at least two of amide solvents, pyridinyl solvents, sulfone solvents, sulfoxide solvents, and phosphate ester solvents, and the lithium salt includes lithium nitrate.

2. The electrolyte according to claim 1, wherein, The lithium salt further includes a second lithium salt, which is selected from one or more of lithium bis(fluorosulfonyl)imide, lithium bis(trifluorosulfonyl)imide, lithium hexafluorophosphate, lithium tetrafluoroborate, and lithium difluorooxalate borate, preferably lithium bis(fluorosulfonyl)imide; Preferably, in the electrolyte, the molar ratio of lithium nitrate to the second lithium salt is 1-4:1; More preferably, the lithium salt comprises lithium nitrate and lithium difluorosulfonylimide; More preferably, in the electrolyte, the molar ratio of lithium nitrate to lithium difluorosulfonylimide is 1-4:

1.

3. The electrolyte according to claim 1 or 2, wherein, In the electrolyte, the molar concentration of the lithium salt is 0.01 mol / L to 4 mol / L, preferably 0.4 mol / L to 2.5 mol / L.

4. The electrolyte according to any one of claims 1-3, wherein, The amide solvent is selected from one or more of N,N-dimethylformamide, N,N-dimethylacetamide, N,N-diethylformamide, and N,N-diethylacetamide, preferably N,N-dimethylacetamide; and / or The pyridyl solvent is selected from one or more of pyridine, 1-fluoropyridine, 2-fluoropyridine, and 3-fluoropyridine, preferably pyridine; and / or The sulfone-based solvent is selected from one or more of sulfolane, 3-methylsulfolane, ethyl methyl sulfone, and dipropyl sulfone; preferably sulfolane; and / or The sulfoxide solvent is selected from one or more of dimethyl sulfoxide, dipropyl sulfoxide, ethylmethyl sulfoxide, and tetramethyl sulfoxide, preferably dimethyl sulfoxide; and / or The phosphate ester-based solvent is selected from one or more of trimethyl phosphate, triethyl phosphate, tripropyl phosphate, and tributyl phosphate, preferably trimethyl phosphate.

5. The electrolyte according to any one of claims 1-4, wherein, In the high donor number solvent, the content of each solvent is not less than 15% by volume, preferably 20-80% by volume; The high donor number solvent includes at least two of the following: amide-based solvents, sulfone-based solvents, sulfoxide-based solvents, and phosphate-based solvents. Preferably, the high donor number solvent includes phosphate ester-based solvents and amide-based solvents; More preferably, the volume ratio of phosphate ester-based solvent to amide-based solvent is 1-3:

1.

6. The electrolyte according to any one of claims 1-5, wherein, The diluent is selected from one or more of fluorobenzene, 1,2-difluorobenzene, 2,2,2-trifluoroethyl ether, methyltrifluoroethyl carbonate, and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, preferably 2,2,2-trifluoroethyl ether.

7. The electrolyte according to any one of claims 1-6, wherein, The high donor number solvent has a volume content of 10%-75%, preferably 30%-50%, based on the total volume of the electrolyte; and / or The volume content of the diluent is 10%-75%, preferably 50%-70%, based on the total volume of the electrolyte.

8. A lithium battery, comprising an electrolyte, a positive electrode, a negative electrode, and a separator, characterized in that, The electrolyte is the electrolyte described in any one of claims 1-7.

9. The lithium battery according to claim 8, wherein, The cathode material is either lithium iron phosphate or a ternary cathode material. Preferably, the ternary cathode material is selected from ternary lithium nickel cobalt manganese oxide or ternary lithium nickel cobalt aluminum oxide.

10. The lithium battery according to claim 8 or 9, wherein, The negative electrode is graphite or lithium metal.

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