Fluorine-free fast-charging electrolyte, preparation method thereof and application of electrolyte in high-temperature lithium battery

Abstract

The invention discloses a fluorine-free fast-charging electrolyte, a preparation method thereof and an application of the electrolyte in a high-temperature lithium battery, and belongs to the technical field of electrolytes. The electrolyte comprises a fluoride-free organic solvent, a fluoride-free lithium salt and a fluoride-free additive, wherein the concentration of the fluorine-free lithium salt ranges from 0.6 mol / L to 1.4 mol / L, and the concentration of the fluorine-free additive ranges from 0 wt% to 10 wt%. The fluorine-free electrolyte is formed by using a fluorine-free organic solvent, a fluorine-free lithium salt and a fluorine-free additive, and is directly applied to a lithium battery. As an electrolyte, excellent electrochemical performance can be realized at a relatively high temperature, and meanwhile, the lithium ion battery has the advantage of ultrafast charging. The electrolyte has the outstanding characteristics of environment friendliness, low cost and excellent performance.

Description

Technical Field

[0001] This invention belongs to the field of electrolyte technology, specifically relating to a fluorine-free fast-charging electrolyte, its preparation method, and its application in high-temperature lithium batteries. Background Technology

[0002] Lithium-ion battery electrolytes contain numerous fluorinated compounds. However, these compounds pose many hazards and limitations. For example, lithium hexafluorophosphate reacts with residual water in the solvent to generate hydrofluoric acid, which corrodes the electrodes; the organolithium salt bis(trifluoromethanesulfonyl)imide easily corrodes aluminum current collectors under high pressure, all of which accelerate battery capacity decay. Furthermore, toxic fluorides released during lithium-ion battery cycling or post-processing pose a threat to human health. In addition, high-fluorinated compounds, due to their persistent degradation characteristics, accumulate in the environment, raising significant environmental concerns. In recent years, the European Union has proposed restrictions on perfluorinated and polyfluoroalkyl substances, planning to completely ban their use by 2027. Simultaneously, lithium-ion batteries typically exhibit self-heating during operation, with battery packs potentially reaching temperatures above 50 degrees Celsius. Therefore, developing batteries capable of stable operation at high temperatures is crucial.

[0003] The concept of fluorine-free electrolytes was proposed long ago, but limitations imposed by commonly used fluorine-free lithium salts, such as the difficulty in dissociating lithium nitrate and lithium dioxaborate, and the explosiveness of lithium perchlorate, have hindered progress. In recent years, as the hazards of fluorine compounds have become increasingly recognized, low-fluorine or even fluorine-free electrolytes have become a research focus. Most current research uses traditional solvents, generally focusing on solvation control strategies to dissociate poorly soluble lithium salts and improve the cycle performance of lithium batteries at room temperature, while neglecting the cycle stability of batteries at high temperatures and high rates.

[0004] On the other hand, while lithium batteries have been widely used in electric vehicles, their refueling speed remains significantly slower than that of traditional fuel-powered vehicles, which can be quickly refueled with gasoline. Current electric vehicle charging typically takes several hours, adding inconvenience and limiting the further development of electric vehicles. Therefore, developing a fast-charging electrolyte is crucial for practical applications.

[0005] This patent proposes a fluorine-free electrolyte that can operate at high rates at high temperatures, solving the problem that common solvents such as carbonates and ethers are difficult to stabilize at high temperatures. It also enables rapid charging and, with the addition of additives, can be matched with graphite anodes, thus having practical value. Summary of the Invention

[0006] The purpose of this section is to outline some aspects of embodiments of the present invention and to briefly describe some preferred embodiments. Simplifications or omissions may be made in this section, as well as in the abstract and title of this application, to avoid obscuring the purpose of these documents; however, such simplifications or omissions should not be construed as limiting the scope of the invention.

[0007] In view of the problems existing in the above and / or prior art, the present invention is proposed.

[0008] Therefore, the purpose of this invention is to overcome the shortcomings of the prior art and provide a fluorine-free fast-charging electrolyte.

[0009] To solve the above-mentioned technical problems, the present invention provides the following technical solution, wherein the electrolyte comprises a fluorine-free organic solvent, a fluorine-free lithium salt, and a fluorine-free additive; wherein the concentration of the fluorine-free lithium salt is 0.6-1.4 mol / L, and the concentration of the fluorine-free additive is 0-10 wt%.

[0010] As a preferred embodiment of the fluorine-free fast-charging electrolyte of the present invention, the fluorine-free organic solvent includes one or more of tetramethylurea, tetraethylurea, tetrapropylurea, 1,3-dimethyl-2-imidazolinone, 1,3-diethyl-2-imidazolinone, N,N-dimethylpropenylurea, and N,N-diethylpropenylurea.

[0011] As a preferred embodiment of the fluorine-free fast charging electrolyte of the present invention, the fluorine-free lithium salt includes one or more of lithium perchlorate, lithium bis(trimethylsilyl)aminolithium, and lithium nitrate.

[0012] As a preferred embodiment of the fluorine-free fast charging electrolyte of the present invention, the fluorine-free additive includes one or more of vinyl sulfite, propylene sulfite, dimethyl sulfite, vinylene carbonate, ethylene carbonate, triethyl borate, and 1,3-propenesulfonate lactone.

[0013] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method for preparing a fluorine-free fast charging electrolyte.

[0014] To solve the above-mentioned technical problems, the present invention provides the following technical solutions, including:

[0015] In a glove box where both oxygen and water content are below 0.1 ppm, weigh out a fluorine-free organic solvent, a fluorine-free lithium salt, and a fluorine-free additive. Stir the mixture at room temperature for one hour to obtain a homogeneous solution, which is the fluorine-free electrolyte.

[0016] The purpose of this invention is to overcome the shortcomings of existing technologies and provide an application of a fluorine-free fast-charging electrolyte in high-temperature lithium batteries. This includes...

[0017] Weigh the positive electrode active material, binder and conductive additive, add dispersant, grind into a uniform slurry, coat the current collector surface, dry and press into a sheet, and cut to obtain the positive electrode sheet.

[0018] In a glove box, the negative electrode shell, negative electrode sheet, electrolyte as described in claims 1 to 1, separator, positive electrode sheet, gasket, spring sheet, and positive electrode shell are placed sequentially from bottom to top, and pressure is applied on a battery pressing machine to fix them, thereby obtaining a lithium metal battery.

[0019] As a preferred embodiment of the application of the fluorine-free fast-charging electrolyte of the present invention in high-temperature lithium batteries, the mass ratio of the positive electrode active material, binder, and conductive additive is 7-9:0.5-2:0.5-2.

[0020] As a preferred embodiment of the application of the fluorine-free fast-charging electrolyte of the present invention in high-temperature lithium batteries, the positive electrode active material includes lithium iron phosphate.

[0021] As a preferred embodiment of the application of the fluorine-free fast-charging electrolyte of the present invention in high-temperature lithium batteries, the conductive additive includes one or more of Super P, acetylene black, and carbon black.

[0022] As a preferred embodiment of the application of the fluorine-free fast-charging electrolyte of the present invention in high-temperature lithium batteries, the binder includes one or more of polyvinylidene fluoride and polyacrylonitrile.

[0023] Beneficial effects of this invention:

[0024] This invention proposes a novel fluorine-free fast-charging electrolyte, which uses fluorine-free organic solvents, fluorine-free lithium salts, and fluorine-free additives to form a fluorine-free electrolyte, which can be directly applied in lithium batteries. As an electrolyte, it can achieve excellent electrochemical performance at higher temperatures, while also possessing the advantage of ultra-fast charging. This electrolyte is characterized by its green and environmentally friendly nature, low cost, and superior performance. Attached Figure Description

[0025] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. Wherein:

[0026] Figure 1 A photograph of the fluorine-free electrolyte provided in Example 1 of the present invention.

[0027] Figure 2 This is the impedance diagram of the battery in Example 1 of the present invention.

[0028] Figure 3 The cyclic voltammetry curve of the lithium battery in Example 1 of this invention is shown.

[0029] Figure 4 The linear cyclic voltammetry curves of the fluorine-free electrolyte in Example 1 of this invention are shown.

[0030] Figure 5 This is the 10C cycle test performance of the lithium battery in Example 1 of the present invention.

[0031] Figure 6 This is the 5C cycle test performance of the lithium battery in Example 1 of the present invention.

[0032] Figure 7 This is the cycle test performance of the lithium battery in Example 2 of the present invention.

[0033] Figure 8 This is an example of the rate test performance of the lithium battery in Example 2 of the present invention.

[0034] Figure 9 This is a cycle performance test of the graphite-lithium iron phosphate full battery in Example 2 of the present invention. Detailed Implementation

[0035] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the examples in the specification.

[0036] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0037] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in different places in this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that is mutually exclusive with other embodiments.

[0038] Unless otherwise specified, all raw materials used in this invention are commercially available.

[0039] Example 1

[0040] (1) Preparation of fluorine-free electrolyte

[0041] In a glove box where both oxygen and water content are below 0.1 ppm, 193.8 mg of lithium bis(oxalato)borate and 13.8 mg of lithium nitrate were weighed into a 5 mL reagent bottle. 1 mL of N,N-dimethylpropenylurea was added, and the mixture was stirred at room temperature for one hour until homogeneous, yielding a fluorine-free electrolyte. The concentration of the fluorine-free lithium salt was 1.2 mol / L.

[0042] (2) Preparation of positive electrode

[0043] Lithium iron phosphate, polyvinylidene fluoride, and conductive carbon black were weighed in a mass ratio of 80:10:10 and added to 0.3 mL of N-methylpyrrolidone as a dispersant solvent. The mixture was then ground to form a uniform slurry. A uniform electrode slurry was coated onto the current collector surface using a scraper, and then placed in a vacuum oven at 80°C for 24 hours to dry until all the solvent had evaporated and the electrode surface was completely dry. The electrode sheet was then cut into circular electrodes with a diameter of 12 mm. Finally, it was transferred to an argon glove box for later use.

[0044] (3) Assembly of lithium-ion batteries

[0045] In a glove box, 0.1 mL of fluorine-free electrolyte is added dropwise to a membrane material supported by glass fiber to obtain the separator material for the lithium battery. The stainless steel negative electrode shell, lithium negative electrode, separator, positive electrode sheet, stainless steel gasket, stainless steel spring sheet, and stainless steel positive electrode shell are then placed sequentially from bottom to top and fixed under pressure on a battery press to obtain the lithium battery.

[0046] Depend on Figure 1 As can be seen, the formed fluorine-free electrolyte is a transparent and uniform liquid phase.

[0047] Figure 2 It is evident that the lithium iron phosphate battery assembled with this electrolyte has very low impedance, with a resistance of less than 20Ω at 60 degrees Celsius.

[0048] Figure 3 The cyclic voltammograms of the aforementioned lithium iron phosphate battery are shown. It can be seen that the multi-cycle curves of the battery largely overlap, indicating that the battery has excellent stability.

[0049] Figure 4 The linear sweep voltammetry curve for the fluorine-free electrolyte shows that the electrolyte remains stable at 4.39 V.

[0050] Figure 5 The cycle performance of the aforementioned lithium iron phosphate battery was tested as follows: the battery charge / discharge range was 2.8V-3.8V, the charge / discharge rate was 10C, and the test temperature was 60 degrees Celsius. The battery exhibited good cycle stability, with a capacity retention of 84.8% after 500 cycles and a coulombic efficiency close to 100%.

[0051] Figure 6 The cycle performance of the aforementioned lithium iron phosphate battery was tested as follows: the battery charge / discharge range was 2.8V-3.8V, the charge / discharge rate was 5C, and the test temperature was 60 degrees Celsius. The battery exhibited good cycle stability, with a capacity retention rate of 82.4% after 2000 cycles and 74.1% after 3000 cycles. Figure 5 and Figure 6 It can be seen that this lithium iron phosphate battery has the advantage of ultra-fast charging.

[0052] Example 2

[0053] The difference between this embodiment and Example 1 is that the formulation of the fluorine-free electrolyte in step (1) is adjusted to 193.8 mg lithium bis(oxalato)borate, 13.8 mg lithium nitrate, 1 mL N,N-dimethylpropenylurea, and 60 mg ethylene carbonate, that is, the concentration of the fluorine-free lithium salt is 1.2 mol / L and the concentration of the fluorine-free additive is 5 wt%. The rest of the preparation process is the same as in Example 1, and a lithium battery is obtained.

[0054] Figure 7 The 1C rate cycling curve of the lithium-graphite battery assembled using this electrolyte at 60 degrees Celsius shows that the electrolyte and graphite have good compatibility.

[0055] Figure 8 Cyclic performance testing of lithium-graphite batteries at different charge / discharge rates: The battery charge / discharge range was 0.1V-2V, the test temperature was 60 degrees Celsius, and the charge / discharge rates were 0.5C, 1C, 2C, 3C, 5C, and 1C respectively. As the charge / discharge rate increased, the discharge capacity decreased; however, when the charge / discharge rate returned to 1C, the discharge capacity recovered to the original capacity at 1C, indicating that the battery has reliable stability.

[0056] Figure 9 Cycle diagram of a graphite-lithium iron phosphate full cell.

[0057] Example 3

[0058] The difference between this embodiment and Example 1 is that the lithium salt is adjusted to 193.8 mg of lithium bis(oxalate-borate), i.e., the concentration is 1 mol / L. The rest of the preparation process is the same as in Example 1, and a lithium battery is obtained.

[0059] Example 4

[0060] The difference between this embodiment and Example 1 is that the lithium salt is adjusted to 232.56 mg lithium bis(oxalato)borate and 13.8 mg lithium nitrate, i.e., the concentration is 1.4 mol / L. The rest of the preparation process is the same as in Example 1, and a lithium battery is obtained.

[0061] Example 5

[0062] The difference between this embodiment and Example 1 is that the lithium salt is adjusted to 116.28 mg of lithium bis(oxalate-borate), i.e., the concentration is 0.6 mol / L. The rest of the preparation process is the same as in Example 1, and a lithium battery is obtained.

[0063] The electrochemical performance of the materials prepared in the above embodiments was tested, and the results compared with those of Example 1 are shown in Table 1.

[0064] Table 1

[0065]

[0066] As shown in the table above, adjusting the amount of lithium salt added has a significant impact on lithium battery performance. This is because the amount of lithium salt added affects the lithium-ion transport efficiency and the formation of the interface layer. The addition of lithium nitrate greatly optimizes the interface layer and solvation, resulting in better battery cycle performance and capacity retention. If the lithium salt concentration is too low, the lithium-ion concentration in the electrolyte will be insufficient; if it is too high, the viscosity of the electrolyte may increase, both of which will affect the lithium-ion transport efficiency. Furthermore, an unstable interface layer may form on the electrode surface, leading to a decrease in battery cycle performance. According to the results in the table above, the optimal technical effect is achieved when the amount of lithium salt added in this invention is 1.2 mol / L.

[0067] Example 6

[0068] The difference between this embodiment and Example 2 is that the fluorine-free additive is adjusted to 12.5 mg of ethylene carbonate, i.e., the concentration is 1 wt%. The rest of the preparation process is the same as in Example 2, and a lithium battery is obtained.

[0069] Example 7

[0070] The difference between this embodiment and Example 2 is that the fluorine-free additive is adjusted to 120 mg of ethylene carbonate, i.e., the concentration is 10 wt%. The rest of the preparation process is the same as in Example 2, and a lithium battery is obtained.

[0071] Example 8

[0072] The difference between this embodiment and Example 2 is that the fluorine-free additive is adjusted to 60 mg of vinylene carbonate, i.e., the concentration is 5 wt%. The rest of the preparation process is the same as in Example 2, and a lithium battery is obtained.

[0073] The electrochemical performance of the materials prepared in the above embodiments was tested, and the results compared with those of Example 2 are shown in Table 2.

[0074] Table 2

[0075]

[0076]

[0077] As shown in the table above, adjusting the amount of fluorine-free additive significantly affects the performance of lithium batteries. This is because the fluorine-free additive improves the electrode interface in the electrolyte. Appropriate additives can promote the formation of a stable solid electrolyte interphase (SEI) layer on the electrode surface, optimizing lithium-ion transport efficiency and thus improving the battery's cycle stability and rate performance. An appropriate amount of additive helps form a good interface layer on the graphite surface without affecting other properties. Based on the results in the table, the optimal technical effect is achieved when the amount of fluorine-free additive in this invention is 5 wt%.

[0078] In summary, this invention proposes a novel fluorine-free fast-charging electrolyte, which uses fluorine-free organic solvents, fluorine-free lithium salts, and fluorine-free additives to form a fluorine-free electrolyte, which can be directly applied in lithium batteries. As an electrolyte, it can achieve excellent electrochemical performance at higher temperatures while also possessing the advantage of ultra-fast charging. This electrolyte is characterized by its green and environmentally friendly nature, low cost, and superior performance.

[0079] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A fluorine-free fast-charging electrolyte, characterized in that: The electrolyte comprises a fluorine-free organic solvent, a fluorine-free lithium salt, and a fluorine-free additive; The concentration of the fluorine-free lithium salt is 0.6–1.4 mol / L, and the concentration of the fluorine-free additive is 0–10 wt%. The fluorine-free lithium salt includes one or more of lithium perchlorate, lithium bis(trimethylsilyl)aminolithium, and lithium nitrate.

2. The fluorine-free fast-charging electrolyte as described in claim 1, characterized in that: The fluorine-free organic solvent includes one or more of tetramethylurea, tetraethylurea, tetrapropylurea, 1,3-dimethyl-2-imidazolinone, 1,3-diethyl-2-imidazolinone, N,N-dimethylpropenylurea, and N,N-diethylpropenylurea.

3. The fluorine-free fast-charging electrolyte as described in claim 1, characterized in that: The fluorine-free additives include one or more of vinyl sulfite, propylene sulfite, dimethyl sulfite, vinylene carbonate, ethylene carbonate, triethyl borate, and 1,3-propenesulfonate lactone.

4. The method for preparing the fluorine-free fast-charging electrolyte according to any one of claims 1 to 3, characterized in that: include, In a glove box where both oxygen and water content are below 0.1 ppm, weigh out a fluorine-free organic solvent, a fluorine-free lithium salt, and a fluorine-free additive, stir at room temperature, and the resulting homogeneous solution is the fluorine-free electrolyte.

5. The application of the fluorine-free fast-charging electrolyte as described in any one of claims 1 to 3 in high-temperature lithium batteries, characterized in that: include, Weigh the positive electrode active material, binder and conductive additive, add dispersant, grind into a uniform slurry, coat the current collector surface, dry and press into a sheet, and cut to obtain the positive electrode sheet. In a glove box, the negative electrode shell, negative electrode sheet, electrolyte as described in claims 1 to 1, separator, positive electrode sheet, gasket, spring sheet, and positive electrode shell are placed sequentially from bottom to top, and pressure is applied on a battery pressing machine to fix them, thereby obtaining a lithium metal battery.

6. The application of the fluorine-free fast-charging electrolyte as described in claim 5 in high-temperature lithium batteries, characterized in that: The mass ratio of the positive electrode active material, binder, and conductive additive is 7-9:0.5-2:0.5-2.

7. The application of the fluorine-free fast-charging electrolyte as described in claim 6 in high-temperature lithium batteries, characterized in that: The positive electrode active material includes lithium iron phosphate.

8. The application of the fluorine-free fast-charging electrolyte as described in claim 7 in high-temperature lithium batteries, characterized in that: The conductive additive includes one or more of Super P, acetylene black, and carbon black.

9. The application of the fluorine-free fast-charging electrolyte as described in claim 7 in high-temperature lithium batteries, characterized in that: The adhesive includes one or more of polyvinylidene fluoride and polyacrylonitrile.

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