Electrolyte, preparation method therefor, and use thereof

Abstract

Disclosed are an electrolyte, a preparation method therefor, and a use thereof, relating to the technical field of new energy. The electrolyte provided by the present invention is prepared from raw materials comprising an inhibitor and an accelerator. The inhibitor comprises a cationic surfactant, and the accelerator comprises at least one of urea, a thiol compound, a sulfonate compound, saccharin, and p-toluenesulfonamide. The electrolyte can alleviate the growth of lithium dendrites on the surface of a negative electrode at various charging and discharging rates, thereby providing a basis for the use of lithium metal negative electrodes in lithium secondary batteries and improving cycle performance thereof. The present invention further provides a preparation method for the electrolyte and a use of the electrolyte.

Description

An electrolyte and its preparation method and application Technical Field

[0001] The present invention relates to the field of new energy technology, and in particular to an electrolyte, a preparation method and an application thereof. Background Art

[0002] The energy density of lithium batteries has become a bottleneck that limits the further improvement of the performance of devices such as electric vehicles, drones, and smartphones. The key to improving the energy density of lithium batteries lies in increasing the energy density of their positive and negative electrodes. The actual capacity of the most widely used graphite anode is already close to its theoretical limit, and there is limited room for improvement. Therefore, there is an urgent need to develop new high-capacity anodes. The theoretical specific capacity of lithium metal anodes is as high as 3860mA / h, the electrochemical potential is -3.04V, and the theoretical energy density is extremely high. Compared with traditional lithium-ion batteries, lithium metal batteries have a higher theoretical energy density. However, lithium metal anodes are prone to dendrites during use, which not only affects the battery capacity, but can also puncture the diaphragm and cause internal short circuits, posing safety issues, which seriously limits their further application.

[0003] Currently, the main research approach to addressing the lithium dendrite problem is to modify the electrolyte to regulate the lithium metal deposition interface, specifically by changing the composition and structure of the SEI film to inhibit the growth of lithium dendrites. However, this approach presents some difficult-to-solve problems: on the one hand, additives that can induce changes in the composition and structure of the SEI film typically contain fluorinated groups, which are expensive and difficult to meet environmental requirements; on the other hand, the SEI generation process consumes a large amount of additives, rendering them ineffective after long cycles. Furthermore, the SEI film ruptures at high current densities, allowing lithium metal to deposit directly at the lithium / electrolyte interface, making it difficult for these additives to address the low charge rate issues of lithium metal batteries.

[0004] In summary, there is an urgent need for an additive system for lithium metal battery electrolytes that is low in cost, has low cycle consumption, and can function at different charge rates.

[0005] Summary of the Invention

[0006] The present invention aims to solve at least one of the technical problems existing in the prior art. To this end, the present invention provides an electrolyte that can effectively prevent the growth of lithium dendrites on the negative electrode surface, is suitable for various charge and discharge rates, has low cycle consumption of electrolyte additives, and is low in cost.

[0007] The present invention also provides a method for preparing the electrolyte.

[0008] The present invention also provides application of the electrolyte.

[0009] According to an embodiment of the first aspect of the present invention, there is provided an electrolyte, wherein raw materials for preparing the electrolyte include an inhibitor and an accelerator;

[0010] The inhibitor includes a cationic surfactant; and the accelerator includes at least one of urea, a thiol compound, a sulfonate compound, saccharin (CAS: 81-07-2) and p-toluenesulfonamide (CAS: 70-55-3).

[0011] The electrolyte according to the embodiment of the present invention has at least the following beneficial effects:

[0012] (1) In the electrolyte provided by the present invention, the inhibitor and accelerator can adjust the rate of lithium metal deposition at different positions. Specifically, the inhibitor is adsorbed on the surface of the lithium metal by the action of the electric field force. Since the charge density at the protrusion is greater, the inhibitor is mainly distributed on the protrusion, and the inhibitor will not be reduced under the lithium metal deposition potential, so it can stably exist on the protrusion. The lithium ions and the inhibitor carry the same charge, and the electrostatic repulsion between the two will drive the lithium ions away from the protrusion and deposit on the flat surface, thereby inhibiting the extension of the protrusion. The accelerator is attached to the surface of the lithium metal by specific adsorption and has a certain reduction stability, and can stably exist during the cycle. The lone pair of electrons in its molecule can attract lithium ions, thereby accelerating the deposition of lithium ions. As the deposition process proceeds, the concentration of the accelerator in the depression increases, while the concentration of the accelerator in the protrusion decreases, so the rate of lithium ion deposition in the depression is faster, thereby filling the pit. According to the above mechanism, the inhibitor can also inhibit lithium ion deposition in pits, but the effect is weaker, while the accelerator can also accelerate deposition in protrusions, but the effect is also weaker. Therefore, adding them together will significantly amplify the inhibitory effect on the tips and the acceleration effect on the depressions, thereby quickly leveling the lithium deposition surface. At the same time, the inhibitor adsorbs on the outer Helmholtz surface, while the accelerator adsorbs on the inner Helmholtz surface. There is no competitive relationship between the two adsorption on the lithium layer surface, and they can coexist in the same electrolyte system.

[0013] (2) In the electrolyte provided by the present invention, both the accelerator and the inhibitor do not contain fluorine, which has low cost and is very environmentally friendly.

[0014] (3) The inhibitor and accelerator are attached to the surface of the lithium deposit layer through electrostatic adsorption and specific adsorption. Both have a certain reduction stability and will not be reduced by lithium metal. Therefore, they will not be consumed during the cycle and can maintain their effect during long cycles.

[0015] (4) In this scheme, both the inhibitor and the accelerator act at the lithium / electrolyte interface. During fast charging (>3C), the lithium metal deposition interface is the lithium / electrolyte interface, thus solving the fast charging problem.

[0016] According to some embodiments of the present invention, the cationic surfactant includes at least one of CTAC (hexadecyltrimethylammonium chloride, CAS: 112-02-7), CTAB (hexadecyltrimethylammonium bromide, CAS: 57-09-0), STAC (octadecyltrimethylammonium chloride, CAS: 112-03-8) and STAB (octadecyltrimethylammonium bromide, CAS: 1120-02-1).

[0017] According to some embodiments of the present invention, the inhibitor comprises at least one of CTAC and STAC.

[0018] According to some embodiments of the present invention, the urea includes at least one of thiourea (CAS: 62-56-6) and ethylenethiourea (CAS: 96-45-7).

[0019] According to some embodiments of the present invention, the thiol compound includes at least one of 2-mercaptobenzimidazole (CAS: 583-39-1), 2-mercaptothiazoline (CAS: 96-53-7), 2-mercaptobenzothiazole (CAS: 149-30-4), 2-mercaptopyridine (CAS: 73018-10-7) and p-toluenethiophenol (CAS: 106-45-6).

[0020] According to some embodiments of the present invention, the sulfonate compound includes at least one of 3-(1-pyridyl)propanesulfonic acid (CAS: 15471-17-7), sodium vinylsulfonate (CAS: 3039-83-6) and sodium p-toluenesulfonate (CAS: 657-84-1).

[0021] According to some embodiments of the present invention, the accelerator includes at least one of thiourea and ethylene thiourea.

[0022] According to some embodiments of the present invention, in the electrolyte, the inhibitor is CTAC or CTAB, and the accelerator is thiourea.

[0023] According to some embodiments of the present invention, in the electrolyte, the inhibitor is STAC or STAB, and the accelerator is thiourea.

[0024] According to some embodiments of the present invention, in the electrolyte, the inhibitor is CTAC, and the accelerator is 2-mercaptobenzimidazole or 2-mercaptopyridine.

[0025] According to some embodiments of the present invention, in the electrolyte, the inhibitor is CTAC, and the accelerator is ethylene thiourea, 3-(1-pyridyl)propanesulfonic acid, sodium p-toluenesulfonate, p-toluenesulfonamide, or saccharin.

[0026] According to some embodiments of the present invention, in the electrolyte, the inhibitor is STAC, and the accelerator is 2-mercaptopyridine.

[0027] According to some embodiments of the present invention, in the electrolyte, the inhibitor is CTAB, and the accelerator is sodium p-toluenesulfonate.

[0028] According to some embodiments of the present invention, in the electrolyte, the inhibitor is STAB, and the accelerator is saccharin.

[0029] According to some embodiments of the present invention, in the electrolyte, the inhibitor is STAB, and the accelerator is saccharin.

[0030] According to some embodiments of the present invention, the concentration of the inhibitor in the electrolyte is 0.01 to 100 mg / mL. Within this concentration range, the inhibitor can function as an inhibitor while also avoiding the problem of high viscosity (colloid) affecting mass transfer caused by excessive inhibitor concentration.

[0031] According to some embodiments of the present invention, in the electrolyte, the concentration of the inhibitor is 0.1 to 10 mg / mL.

[0032] According to some embodiments of the present invention, the concentration of the inhibitor in the electrolyte is 0.4 to 2 mg / mL, for example, about 1 mg / mL, 1.5 mg / mL, 1.6 mg / mL, or 1.8 mg / mL.

[0033] According to some embodiments of the present invention, in the electrolyte, the concentration of the accelerator is 0.01 to 100 mg / mL.

[0034] According to some embodiments of the present invention, the concentration of the accelerator in the electrolyte is 1 to 10 mg / mL. Within this range, it can function as an accelerator while avoiding the adverse effect of inhibiting lithium ion deposition caused by excessive concentration.

[0035] According to some embodiments of the present invention, the concentration of the accelerator in the electrolyte is 2 to 5 mg / mL, for example, about 3 mg / mL or 4 mg / mL.

[0036] According to some embodiments of the present invention, raw materials for preparing the electrolyte further include active metal salts and solvents.

[0037] According to some embodiments of the present invention, the active metal salt includes at least one of a lithium salt, a sodium salt, and a potassium salt. Different active metal salts correspond to different types of secondary batteries. For example, when the active metal salt of the electrolyte is a lithium salt, its application includes lithium metal batteries.

[0038] According to some embodiments of the present invention, the lithium salt includes at least one of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium bis(fluorosulfonyl)imide (LiFSI), and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI). For example, the lithium salt may be lithium hexafluorophosphate or lithium bis(fluorosulfonyl)imide.

[0039] According to some embodiments of the present invention, when the active metal salt is the lithium salt, the concentration of the lithium salt in the electrolyte is 0.5 to 10M.

[0040] According to some embodiments of the present invention, the concentration of the lithium salt in the electrolyte is 0.8 to 1.5 M. For example, it may be about 1 M.

[0041] According to some embodiments of the present invention, the solvent includes at least one of a linear carbonate and a cyclic carbonate.

[0042] The chain carbonates include diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC) and methyl propyl carbonate (MPC).

[0043] The cyclic carbonates include ethylene carbonate (EC) and propylene carbonate (PC).

[0044] The volume ratio of the linear carbonate to the cyclic carbonate is 1:(0.2 to 10).

[0045] The volume ratio of the linear carbonate to the cyclic carbonate is 1:(0.8 to 1.2), for example, it can be about 1:1. More specifically, it can be a mixture formed according to the volume ratio of EC:DEC=1:1.

[0046] According to some embodiments of the present invention, raw materials for preparing the electrolyte include an inhibitor, an accelerator, a lithium salt, and a solvent;

[0047] The inhibitor comprises at least one of CTAC, STAC and STAB, and its concentration in the electrolyte ranges from 1 to 2 mg / mL;

[0048] The accelerator comprises at least one of thiourea, 2-mercaptobenzimidazole and 2-mercaptopyridine, and its concentration in the electrolyte ranges from 2 to 5 mg / mL;

[0049] The lithium salt includes at least one of LiPF6, LiBF4, LiClO4, LiFSI and LiTFSI, and the concentration in the electrolyte is 0.5 to 10M;

[0050] The solvent includes a mixture of a linear carbonate and a cyclic carbonate in a volume ratio of 1:(0.2 to 10).

[0051] According to some embodiments of the present invention, the electrolyte may be used in secondary batteries, including lithium-ion batteries, lithium metal batteries, sodium-ion batteries, sodium metal batteries, potassium-ion batteries, and potassium metal batteries.

[0052] According to an embodiment of the second aspect of the present invention, a method for preparing the electrolyte is provided, comprising mixing raw materials for preparing the electrolyte.

[0053] Since the preparation method adopts all the technical solutions of the electrolyte of the above embodiment, it has at least all the beneficial effects brought by the technical solutions of the above embodiment. In addition, the preparation method is similar to the preparation of traditional electrolytes and does not require upgraded preparation equipment, which is convenient for large-scale promotion and use.

[0054] According to an embodiment of the third aspect of the present invention, a secondary battery is provided, wherein raw materials for preparing the secondary battery include the electrolyte.

[0055] Since the lithium metal battery adopts all the technical solutions of the electrolyte of the above embodiment, it has at least all the beneficial effects brought by the technical solutions of the above embodiment.

[0056] Furthermore, since both the inhibitor and the accelerator in the electrolyte act on the lithium metal / electrolyte interface, the electrolyte provided by the present invention has a higher performance improvement ratio on the lithium metal electrolyte than traditional lithium-ion batteries.

[0057] According to some embodiments of the present invention, the secondary battery includes at least one of a lithium metal battery, a sodium metal battery, and a potassium metal battery.

[0058] According to an embodiment of the fourth aspect of the present invention, there is provided an application of the secondary battery in the power field and the 3C small household appliance field.

[0059] Since the application adopts all the technical solutions of the secondary battery of the above embodiment, it at least has all the beneficial effects brought by the technical solutions of the above embodiment.

[0060] Unless otherwise specified, a metal battery in this disclosure refers to a secondary battery whose negative electrode active material is a single metal, and an ion battery refers to a secondary battery whose negative electrode active material is a lithium ion storage material. For example, a lithium metal battery refers to a secondary battery whose negative electrode active material is lithium metal, while a lithium ion battery refers to a secondary battery whose negative electrode active material is a lithium storage material such as graphite.

[0061] Unless otherwise specified, the term “about” in the present invention means that the error is allowed to be within the range of ±2%. For example, about 100 is actually 100±(2%×100).

[0062] Unless otherwise specified, “between” in the present invention includes the number itself, for example, “between 2 and 3” includes the endpoint values ​​2 and 3.

[0063] Other features and advantages of the present invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the present invention. DETAILED DESCRIPTION

[0064] The following will clearly and completely describe the concept and technical effects of the present invention in conjunction with the embodiments to fully understand the purpose, features and effects of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, other embodiments obtained by those skilled in the art without creative work are all within the scope of protection of the present invention.

[0065] In the description of the present invention, reference to terms such as "one embodiment," "some embodiments," "illustrative embodiments," "examples," "specific examples," or "some examples" means that the specific features, structures, materials, or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the exemplary expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.

[0066] Example 1

[0067] This example provides an electrolyte, and the specific proportion of raw materials for preparation is shown in Table 1.

[0068] The preparation method of the electrolyte in this example includes fully mixing the preparation raw materials listed in Table 1 in a glove box filled with argon.

[0069] Examples 2 to 26 and Comparative Examples 1 to 15 respectively provide an electrolyte, which differs from Example 1 in that:

[0070] Some of the raw materials and their proportions are different. The compositions of the raw materials for Examples 2 to 26 and Comparative Examples 1 to 15 are shown in Table 1.

[0071] Table 1 Raw materials for preparing the electrolytes provided in Examples 1 to 26 and Comparative Examples 1 to 15

[0072] Test Case

[0073] This example tests the electrochemical properties of the electrolytes obtained in the examples and comparative examples. The specific testing method is as follows:

[0074] The electrolytes obtained in the examples and comparative examples were used to assemble lithium-lithium symmetrical batteries. 2 and / or 4 mA / cm 2 Current, 1mAh / cm 2 Constant current charge and discharge tests were performed at a set capacity. After stable cycling, two possible signs of cycling completion may appear: 1. The deposition overpotential suddenly decreases and cannot be recovered, with the voltage-time curve becoming straight and exhibiting resistance characteristics, indicating an internal short circuit; 2. The deposition overpotential increases significantly and irreversibly to above 1V, indicating excessive dead lithium or electrolyte depletion. Either of these two conditions indicates the end of cycling, and the number of cycles accumulated before the end of cycling is shown in Table 2.

[0075] Table 2 Electrochemical properties of the electrolytes obtained in the examples and comparative examples

[0076] Comparison of the results of the embodiment and the comparative example shows that the electrolyte provided by the present invention has a significantly improved cycle performance in a lithium metal battery due to the presence of both an inhibitor and an accelerator. This indicates that under the joint action of the inhibitor and the accelerator, the formation of lithium dendrites is significantly avoided, and the smoothing of the lithium metal surface is promoted.

[0077] A comparison of the results between Examples 1 to 9 and Comparative Examples 14 and 15 shows that the concentrations of the inhibitor and accelerator have a certain influence on the electrochemical properties of the electrolyte. When the concentrations of the inhibitor and accelerator exceed the given range, a large amount of insoluble precipitates are generated in the electrolyte due to exceeding the solubility of the additives in the electrolyte, rendering the electrolyte unusable. When other conditions remain unchanged and the concentrations of the accelerator and inhibitor are within the range required by the present invention, the electrochemical properties of the electrolyte show a trend of first increasing and then decreasing with increasing concentrations. When the inhibitor concentration is between 1 and 2 mg / mL and the accelerator concentration is between 2 and 5 mg / mL, the electrochemical properties of the electrolyte are better than those of electrolytes with additives at other concentrations. It should be noted that since it is difficult to exhaustively test the concentration of the additives, the optimal value of the performance within the above concentration range may not be reflected in the embodiments of the present invention.

[0078] Comparison of the results of Example 3 and Examples 10 to 26 shows that different inhibitors and accelerator types have different effects on improving the number of cycles; in addition, by adjusting the electrolyte lithium salt, other additives (such as negative electrode film-forming additives) and solvents, the electrochemical properties of the resulting electrolyte may also be improved to a certain extent. Specifically, when the accelerator is thiourea and the inhibitor is STAC or STAB, the electrochemical performance of the resulting electrolyte is better; when the inhibitor is CTAC and the accelerator is 2-mercaptobenzimidazole or 2-mercaptopyridine, the electrochemical performance of the resulting electrolyte is better; within the test range of the embodiment, when the inhibitor is STAC and the accelerator is 2-mercaptopyridine, the electrochemical performance of the resulting electrolyte is better than the electrochemical performance of the electrolyte of other combinations; and in this additive combination, the electrochemical performance of the lithium salt selected from LiFSI is slightly better than the electrochemical performance when LiPF6 is used. The existing embodiments of the present invention do not exhaust the combinations of inhibitors, accelerators and lithium salts. According to the above results, it can be seen that in actual industrial applications, the electrolyte provided by the present invention is expected to achieve further optimized electrochemical performance.

[0079] Comparison of the results of Example 3 at different rates and the results of Comparative Example 1 at different rates shows that the electrolyte provided by the present invention can be used at different rates by adding inhibitors and accelerators, thereby broadening its scope of use.

[0080] Comparison of the results of Examples 3, 10 to 19 and Comparative Examples 2 to 13 shows that in the electrolyte provided by the present invention, there is a significant synergistic effect between the inhibitor and the accelerator, which has a technical effect of "1+1>2" in improving the cycle performance.

[0081] In summary, the electrolyte provided by the present invention can significantly promote the use of lithium metal negative electrodes due to the synergistic effect between the accelerator and the inhibitor, improve the cycle performance of lithium secondary batteries including lithium metal negative electrodes, and ultimately promote the energy density of lithium secondary batteries and their promotion and use in new fields.

[0082] While the embodiments of the present invention have been described in detail above, the present invention is not limited to the embodiments described above. Various modifications may be made within the scope of knowledge possessed by a person skilled in the art without departing from the spirit of the present invention. Furthermore, the embodiments of the present invention and the features thereof may be combined with one another unless there is a conflict.

Claims

1. An electrolyte solution, characterized in that, the raw materials for preparing the electrolyte solution include an inhibitor and an accelerator; the inhibitor includes a cationic surfactant; the accelerator includes at least one of urea, a mercapto compound, a sulfonate compound, saccharin, and p-toluenesulfonamide.

2. The electrolyte solution according to claim 1, characterized in that, the cationic surfactant includes at least one of CTAC, CTAB, STAC, and STAB.

3. The electrolyte solution according to claim 1 or 2, characterized in that, in the electrolyte solution, the concentration of the inhibitor is 0.01 to 100 mg / mL; and / or, in the electrolyte solution, the concentration of the inhibitor is 0.1 to 10 mg / mL.

4. The electrolyte solution according to claim 1, characterized in that, the urea includes at least one of thiourea and ethylene thiourea; and / or, the mercapto compound includes at least one of 2-mercaptobenzimidazole, 2-mercaptothiazoline, 2-mercaptobenzothiazole, 2-mercaptopyridine, and p-thiocresol.

5. The electrolyte solution according to claim 1, characterized in that, the sulfonate compound includes at least one of 3-(1-pyridyl)propanesulfonic acid, sodium vinylsulfonate, and sodium p-toluenesulfonate.

6. The electrolyte solution according to claim 1 and any one of claims 4 to 5, characterized in that, in the electrolyte solution, the concentration of the accelerator is 0.01 to 100 mg / mL; and / or, in the electrolyte solution, the concentration of the accelerator is 1 to 10 mg / mL.

7. The electrolyte solution according to any one of claims 1 to 2 and any one of claims 4 to 5, characterized in that, the raw materials for preparing the electrolyte solution further include an active metal salt and a solvent; and / or, the solvent includes at least one of a chain carbonate and a cyclic carbonate.

8. The electrolyte solution according to claim 7, characterized in that, the active metal salt includes at least one of a lithium salt, a sodium salt, and a potassium salt; and / or, the lithium salt includes at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium bis(fluorosulfonyl)imide, and lithium bis(trifluoromethanesulfonyl)imide.

9. A method for preparing an electrolyte solution according to any one of claims 1 to 8, characterized in that, the preparation method includes mixing the raw materials for preparing the electrolyte solution.

10. A secondary battery, characterized in that, the raw materials for preparing the secondary battery include the electrolyte solution according to any one of claims 1 to 8.

11. The secondary battery according to claim 10, characterized in that, the secondary battery includes at least one of a lithium metal battery, a sodium metal battery, and a potassium metal battery.

12. An application of the secondary battery according to claim 10 or 11 in the power field and the 3C small household appliance field.

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