A non-aqueous electrolyte, a preparation method and application thereof

Abstract

The application discloses a nonaqueous electrolyte and a preparation method and application thereof, and belongs to the technical field of new energy sources.The preparation raw material of the nonaqueous electrolyte provided by the application comprises nicorandil.The nonaqueous electrolyte provided by the application can improve the composition of an SEI film, and further improve the reduction stability, lithium ion conductivity and mechanical strength and other performances of the SEI film, so that the cycle performance and safety performance of a lithium battery with a lithium metal as a negative electrode are effectively improved.The application further provides a preparation method and application of the nonaqueous electrolyte.

Description

Technical Field

[0001] This invention relates to the field of new energy technology, and in particular to a non-aqueous electrolyte, its preparation method, and its application. Background Technology

[0002] The energy density of lithium-ion batteries has become a bottleneck limiting further performance improvements in devices such as electric vehicles, drones, and smartphones. However, the actual capacity of the most widely used graphite anode is approaching its theoretical limit, leaving limited room for improvement. Therefore, there is an urgent need to develop new high-capacity anodes. Lithium metal anodes have a theoretical specific capacity as high as 3860 mA / h and an electrochemical potential of -3.04 V, exhibiting extremely high theoretical energy density, which can significantly improve the overall energy density of lithium-ion batteries. However, lithium metal anodes are prone to dendrite formation during use, which not only affects battery capacity but may also puncture the separator, causing internal short circuits or safety accidents, severely limiting their further application.

[0003] Currently, the main approach to solving the lithium dendrite problem lies in modifying the electrolyte to control the lithium metal deposition interface, especially the composition and structure of the SEI film, to suppress lithium dendrite growth. The SEI film is primarily formed by lithium metal reducing solvent molecules and lithium salt anions. Among these, the stability, ionic conductivity, and mechanical strength of compounds such as alkyl ester lithium formed by the reduction of carbonate solvent molecules like EC, DEC, and EMC by lithium metal do not meet the requirements for long-term stable operation of lithium metal anodes. In contrast, the reduction stability, ionic conductivity, and mechanical strength of lithium salt anions and the various film-forming additives reacting with lithium metal to form LiF, Li₂O, Li₃N, and lithium oxide compounds are significantly improved compared to alkyl ester lithium. Therefore, inhibiting the participation of solvent molecules in SEI film formation and promoting the participation of anions in SEI film formation is currently the most effective way to significantly improve the practicality of lithium metal anodes using SEI films.

[0004] Among various anions, nitrate ions are more readily reduced due to their lower LUMO, thus forming a uniform SEI film primarily composed of inorganic substances (such as lithium nitrate oxides) on the lithium metal surface before solvent molecules. This makes nitrate ions a current research focus for SEI film-forming additives. However, the solubility of inorganic nitrates (lithium nitrate) in carbonate solvents is too low (less than 0.08 mg / mL in DMC and less than 5 mg / mL in EC), making it difficult to achieve the required concentration for additive use.

[0005] In conclusion, it is necessary to develop a nitrate additive that can dissolve in carbonate solvents and improve the overall performance of the electrolyte. Summary of the Invention

[0006] This invention aims to at least solve one of the technical problems existing in the prior art. To this end, this invention proposes a non-aqueous electrolyte that can effectively improve the cycle performance and safety performance of lithium batteries using lithium metal as the negative electrode.

[0007] The present invention also provides a method for preparing the above-mentioned non-aqueous electrolyte.

[0008] The present invention also provides applications of the above-mentioned non-aqueous electrolyte.

[0009] According to an embodiment of the first aspect of the present invention, a non-aqueous electrolyte is provided, wherein the raw materials for preparing the non-aqueous electrolyte include nicotinic acid nitrate (also known as N-(2-hydroxyethyl)nicotinamide nitrate, CAS: 65141-46-0) having the following structural formula:

[0010]

[0011] The non-aqueous electrolyte according to embodiments of the present invention has at least the following beneficial effects:

[0012] Based on the structural formula of nicorandil, it can be known that nicorandil is a carbonate molecule. As an additive for non-aqueous electrolytes, nicorandil exhibits good solubility in carbonate solvents, overcoming the drawback of traditional inorganic nitrates being difficult to dissolve in carbonate solvents. Furthermore, the LUMO of nicorandil is similar to that of nitrates, allowing it to be preferentially reduced by lithium metal before solvent molecules, forming an inorganic-rich SEI film. In other words, it possesses a similar ability to form an SEI film as inorganic nitrates. Compared to other organic nitrate ester additives, nicorandil molecules possess both amide and pyridine functional groups. Both amides and pyridines are high-DN Lewis bases, exhibiting stronger binding affinity to lithium ions compared to solvent molecules. Therefore, they can exclude solvent molecules from the solvation shell and, as the negative electrode potential decreases, can co-migrate with lithium ions to the negative electrode surface, further reducing the proportion of solvent molecules reduced by lithium metal. In other words, nicorandil has high solubility in non-aqueous electrolytes, enabling it to participate in the formation of a high-quality SEI film. It can also inhibit the formation of SEI involving solvent molecules from multiple angles, further improving the reduction stability, ionic conductivity, and mechanical strength of the resulting SEI film. Overall, non-aqueous electrolytes, including those containing nicorandil, can effectively extend the cycle life of lithium batteries.

[0013] According to some embodiments of the present invention, the mass concentration of nicorandil in the non-aqueous electrolyte is 0.1 to 200 mg / mL. For example, it can be about 150 mg / mL.

[0014] According to some embodiments of the present invention, the mass concentration of nicorandil in the non-aqueous electrolyte is 0.1 to 10 mg / mL. Specifically, it can be about 0.5 mg / mL, 1 mg / mL, 5 mg / mL, or 10 mg / mL.

[0015] According to some embodiments of the present invention, the mass concentration of nicorandil in the non-aqueous electrolyte is 10-100 mg / mL.

[0016] According to some embodiments of the present invention, the mass concentration of nicorandil in the non-aqueous electrolyte is 30–80 mg / mL. For example, it can be approximately 50 mg / mL.

[0017] According to some embodiments of the present invention, the raw materials for preparing the non-aqueous electrolyte also include a non-aqueous solvent and a lithium salt.

[0018] According to some embodiments of the present invention, the non-aqueous solvent includes at least one of carbonate solvents, ketone solvents, alcohol solvents, nitrile solvents and ether solvents.

[0019] According to some embodiments of the present invention, the non-aqueous solvent is selected from carbonate solvents.

[0020] According to some embodiments of the present invention, the carbonate solvent includes at least one of ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC).

[0021] According to some embodiments of the present invention, the carbonate solvent includes ethylene carbonate (EC) and dimethyl carbonate (DMC).

[0022] According to some embodiments of the present invention, the volume ratio of ethylene carbonate to dimethyl carbonate is 1:0.1 to 10. The ratio of cyclic carbonate to chain carbonate affects the dielectric constant, viscosity, and low-temperature performance. Within the above range, especially when the proportion of chain carbonate is higher than that of cyclic carbonate, it is beneficial to reduce the viscosity of the non-aqueous electrolyte, improve its wetting ability, and enhance the low-temperature performance of the battery.

[0023] According to some embodiments of the present invention, the volume ratio of ethylene carbonate to dimethyl carbonate is 1:1 to 3. For example, it can be about 1:2.

[0024] According to some embodiments of the present invention, the lithium salt includes at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(oxalate)borate, lithium difluorooxalateborate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, and lithium difluorophosphate.

[0025] According to some embodiments of the present invention, the lithium salt includes lithium hexafluorophosphate.

[0026] According to some embodiments of the present invention, the concentration of the lithium salt in the non-aqueous electrolyte is 0.5 to 10 M. For example, it can be about 1 M or 1.5 M.

[0027] According to some embodiments of the present invention, the raw materials for preparing the non-aqueous electrolyte include:

[0028] The lithium salt includes lithium hexafluorophosphate, and the concentration of the lithium salt in the non-aqueous electrolyte is 0.5–10 M.

[0029] The non-aqueous solvent includes a mixture of ethylene carbonate and dimethyl carbonate in a volume ratio of 1:1 to 3.

[0030] Nicorandil, wherein the concentration of nicorandil in the non-aqueous electrolyte is 0.1–200 mg / mL.

[0031] According to an embodiment of a second aspect of the present invention, a method for preparing the non-aqueous electrolyte is provided, the method comprising mixing raw materials for preparing the non-aqueous electrolyte.

[0032] Since the preparation method employs all the technical solutions of the non-aqueous electrolytes described in the above embodiments, it possesses at least all the beneficial effects brought about by the technical solutions of the above embodiments. Furthermore, the preparation method provided by the present invention is simple and convenient to implement and promote.

[0033] According to some embodiments of the present invention, the preparation method is carried out in a protective atmosphere.

[0034] According to some embodiments of the present invention, the protective atmosphere includes at least one of nitrogen and argon.

[0035] Specifically, the preparation method can be carried out in a glove box filled with nitrogen.

[0036] According to an embodiment of a third aspect of the present invention, a lithium battery is provided, wherein the raw materials for preparing the lithium battery include the aforementioned non-aqueous electrolyte.

[0037] Since the lithium battery adopts all the technical solutions of the non-aqueous electrolyte in the above embodiments, it has at least all the beneficial effects brought about by the technical solutions in the above embodiments. Specifically, the SEI film formed on the negative electrode surface has high reduction stability, mechanical strength, and ionic conductivity, and the growth of lithium dendrites is significantly suppressed. Therefore, the cycle performance and safety performance of the lithium battery are significantly improved.

[0038] According to some embodiments of the present invention, the lithium battery further includes a negative electrode.

[0039] According to some embodiments of the present invention, the negative electrode is made of lithium metal.

[0040] According to some embodiments of the present invention, the lithium battery further includes a positive electrode.

[0041] According to some embodiments of the present invention, the positive electrode active material includes at least one of polyanionic materials, layered materials, and spinel materials.

[0042] The polyanionic material includes at least one of lithium iron phosphate, lithium manganese phosphate, and lithium manganese iron phosphate.

[0043] The general formula of the layered material is LiMO2, wherein M includes at least one of nickel, cobalt, and manganese.

[0044] In the layered material, M further includes a doping element; the doping element includes at least one of aluminum, zirconium, magnesium, titanium, boron, and fluorine.

[0045] The spinel material includes lithium manganese oxide (spinel phase).

[0046] According to some embodiments of the present invention, the battery includes at least one of button cells, pouch cells, prismatic cells, and cylindrical cells.

[0047] According to some embodiments of the present invention, the battery includes at least one of a symmetrical battery, a half-cell, and a full-cell.

[0048] According to some embodiments of the present invention, the cycle life of the lithium battery is increased by ≥25% compared with that using a conventional electrolyte;

[0049] The difference between the conventional electrolyte and the non-aqueous electrolyte is that the conventional electrolyte does not include nicorandil.

[0050] For example, the specific increase rate can reach 50%, 75%, 100%, 200%, 300%, 400%, 500%, 600%, or 650%.

[0051] According to an embodiment of the fourth aspect of the present invention, the lithium battery is provided for use in the fields of power, energy storage, and 3C small household appliances.

[0052] Since the application adopts all the technical solutions of the lithium battery in the above embodiments, it has at least all the beneficial effects brought about by the technical solutions in the above embodiments.

[0053] Unless otherwise specified, the term "about" in this invention actually means that the error is allowed to be within ±2%, for example, about 100 is actually 100 ± 2% × 100.

[0054] Unless otherwise specified, "between" in this invention includes the number itself, for example, "between 2 and 3" includes the endpoint values ​​2 and 3.

[0055] Other features and advantages of the invention will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing the invention. Detailed Implementation

[0056] The following will describe the concept and technical effects of the present invention clearly and completely with reference to embodiments, so as to fully understand the purpose, features and effects of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are all within the scope of protection of the present invention.

[0057] In the description of this invention, the terms "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0058] Example 1

[0059] This example provides a non-aqueous electrolyte, and the composition of the specific raw materials is shown in Table 1. The specific preparation method includes mixing the raw materials in Table 1 evenly in a glove box filled with argon gas.

[0060] Examples 2-7 and Comparative Examples 1-3 each prepared a non-aqueous electrolyte, the specific difference from Example 1 being:

[0061] The raw materials used in some preparations are different. The composition and amount of the specific raw materials are shown in Table 1.

[0062] Table 1. Raw materials for the preparation of non-aqueous electrolytes in Examples 1-7 and Comparative Examples 1-3.

[0063]

[0064] Application examples

[0065] This example provides a lithium-lithium symmetric battery, in which both electrodes are lithium metal, and the electrolyte is derived from the above embodiments or comparative examples.

[0066] Test case

[0067] This example tests the cycle performance of the lithium-ion battery obtained from the application example. The specific test method is as follows: at 2mA / cm 2 The set current is 1mAh / cm. 2Constant current charge-discharge tests were performed on the set capacity. After stable cycling, two signs of cycle termination may appear: 1. The deposition overpotential suddenly decreases and cannot recover, the voltage-time curve flattens out, and the curve exhibits resistance characteristics, representing an internal short circuit; 2. The deposition overpotential significantly increases to above 1V and is irreversible, indicating excessive dead lithium or electrolyte depletion. Either of these occurrences indicates the end of the cycle, and the number of cycles is the number of cycles accumulated before the end of the cycle. The test conditions and results are shown in Table 2.

[0068] Table 2 shows the electrochemical performance of lithium batteries obtained from application examples.

[0069] Example 1 2 1 102 Example 2 2 1 141 Example 3 2 1 279 Example 4 2 1 450 Example 5 2 1 581 Example 6 2 1 372 Example 7 2 1 233 Comparative Example 1 2 1 81 Comparative Example 2 2 1 110 Comparative Example 3 2 1 311

[0070] Comparing Examples 1-7, it can be seen that as the amount of nicorandil added to the non-aqueous electrolyte increases, the cycle performance of the lithium metal anode shows a trend of first increasing and then decreasing. This is because when the concentration is too low, the thickness of the SEI film formed is too thin, or a completely covering SEI film cannot be formed, and part of the SEI film is contributed by solvent molecules, meaning that the strength and conductivity of the resulting SEI film are low. If the concentration continues to increase, the thickness of the SEI film formed is thicker, increasing the difficulty of lithium ion shuttle. However, overall, within the scope verified by the examples, the obtained non-aqueous electrolyte has a significant improving effect on the cycle performance of the lithium metal anode.

[0071] Comparing Examples 1-7 with Comparative Example 1, it can be seen that the non-aqueous electrolyte provided by the present invention can significantly improve the cycle performance of lithium batteries including lithium metal anodes by using nicorandil as an additive. This is because nicorandil is superior to solvent molecules and repels solvent molecules, forming an SEI film on the surface of lithium metal anodes. The reduction stability, ionic conductivity and mechanical strength of the resulting SEI film are significantly improved.

[0072] The nitro group is actually involved in the formation of the SEI film; in Comparative Example 2, 0.4 mg / mL of lithium nitrate was added, and the molar concentration of nitrate was comparable to that in Example 3. Comparing Example 3 and Comparative Example 2, it can be seen that with the same molar concentration of nitro group, nicorandil exhibits superior electrochemical performance in the non-aqueous electrolyte environment provided by this invention, and can significantly extend the cycle performance of the lithium metal anode compared to lithium nitrate.

[0073] Comparing Examples 5 and 6 with Comparative Example 3 (including comparisons of mass concentration and molar concentration), although traditional organic nitrate esters also have high solubility in non-aqueous electrolyte solvents, because nicorandil has both pyridine and amide groups, it can further exclude the participation of solvent molecules during the formation of the SEI film. The resulting SEI film has better overall performance than the SEI film formed by traditional organic nitrate esters, and also improves the cycling performance of lithium metal anodes by a greater proportion.

[0074] In summary, the non-aqueous electrolyte provided by this invention, by adding nicorandil, can significantly improve the cycle performance of lithium batteries, including lithium metal anodes, due to the special structure of nicorandil, which can repel solvent participation in the formation of the SEI film. Furthermore, lithium batteries incorporating the non-aqueous electrolyte provided by this invention, due to their excellent cycle performance and safety performance, are expected to find wide application in the power, energy storage, and 3C small appliance fields.

[0075] The embodiments of the present invention have been described in detail above. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention. Furthermore, the embodiments of the present invention and the features thereof can be combined with each other unless otherwise specified.

Claims

1. A non-aqueous electrolyte, characterized in that, The raw materials for preparing the non-aqueous electrolyte include nicorandil having the following structural formula: ； In the non-aqueous electrolyte, the mass concentration of nicorandil is 0.1~200 mg / mL.

2. The non-aqueous electrolyte according to claim 1, characterized in that, In the non-aqueous electrolyte, the mass concentration of nicorandil is 10~100 mg / mL.

3. The non-aqueous electrolyte according to claim 1, characterized in that, The raw materials for preparing the non-aqueous electrolyte also include non-aqueous solvents and lithium salts.

4. The non-aqueous electrolyte according to claim 3, characterized in that, The non-aqueous solvent includes at least one of carbonate solvents, ketone solvents, alcohol solvents, nitrile solvents, and ether solvents; and / or, the carbonate solvent includes at least one of ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate.

5. The non-aqueous electrolyte according to claim 3, characterized in that, The lithium salt includes at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(oxalate)borate, lithium difluorooxalateborate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, and lithium difluorophosphate; and / or, in the non-aqueous electrolyte, the concentration of the lithium salt is 0.5~10M.

6. A method for preparing a non-aqueous electrolyte as described in any one of claims 1 to 5, characterized in that, The preparation method includes mixing the raw materials for the preparation of the non-aqueous electrolyte.

7. A lithium battery, characterized in that, The raw materials for preparing the lithium battery include the non-aqueous electrolyte as described in any one of claims 1 to 5.

8. The lithium battery according to claim 7, characterized in that, The lithium battery also includes a negative electrode.

9. The lithium battery according to claim 8, characterized in that, The negative electrode is made of lithium metal.

10. The lithium battery according to any one of claims 7 to 9, characterized in that, Compared with lithium batteries using conventional electrolytes, the lithium batteries using the non-aqueous electrolyte have a cycle life increase of ≥25%; The difference between the conventional electrolyte and the non-aqueous electrolyte is that the conventional electrolyte does not include nicorandil.

11. An application of the lithium battery as described in any one of claims 7 to 10 in the fields of power, energy storage, and 3C small household appliances.

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