Sulfonyl eutectic electrolyte, preparation method and lithium metal battery thereof

Abstract

The invention belongs to the field of lithium metal battery electrolytes, and particularly relates to a sulfuryl eutectic electrolyte, a preparation method and a lithium metal battery thereof, the sulfuryl eutectic electrolyte comprises a hydrogen bond donor, a hydrogen bond acceptor and an additive; the hydrogen bond donor is a sulfone substance, the sulfone substance comprises one or more of phenyl vinyl sulfone, ethyl phenyl sulfone and derivatives thereof, lithium salt dissociation is effectively promoted to form the eutectic electrolyte through Li-O coordination interaction of sulfonyl and lithium ions and H-F hydrogen bond interaction of active hydrogen and lithium salt anions, and the electrolyte has the advantages that the electrolyte is stable and reliable, and the service life of the electrolyte is prolonged. Wherein the dissociation process is enhanced by the high coordination ability of lone pair electrons of sulfonyl oxygen atoms and metal ions and the hydrogen-bond interaction of double-bond carbon active hydrogen and lithium salt anions under the conjugation action. Compared with a traditional carbonic ester solvent electrolyte, the electrolyte has good flame retardance and thermal stability, for example, experiments show that the self-extinguishing time of the carbonic ester based electrolyte after ignition reaches more than ten seconds, but the electrolyte is almost incapable of being ignited, so that the safety risk is reduced.

Description

Technical Field

[0001] This invention belongs to the field of lithium metal battery electrolytes, specifically a sulfone-based eutectic electrolyte, its preparation method, and a lithium metal battery thereof. Background Technology

[0002] Electrochemical energy storage has become a key technology for mitigating the challenges of renewable energy intermittency and promoting sustainable development. In electrochemical energy storage systems, lithium-ion batteries (LIBs) have dominated the field for decades, benefiting from exponential market growth and technological maturity. However, LIBs face inherent limitations in meeting the ever-increasing demand for higher energy densities. In contrast, lithium metal batteries are considered one of the most promising next-generation energy storage technologies due to their superior theoretical capacity (3860 mAh g⁻¹), low electrochemical potential (-3.04 V compared to a standard hydrogen electrode), and ultra-low energy density (0.534 g cm⁻³).

[0003] Using lithium metal as the negative electrode material places stringent requirements on electrolyte design. Traditional organic electrolytes, due to their volatility and low flash point, are prone to safety issues such as combustion and explosion. To improve battery safety, flame-retardant additives are typically added to conventional electrolytes. However, while this method can provide some flame retardancy, it affects the battery's electrochemical performance, especially cycle life and rate performance. Therefore, developing non-flammable electrolytes is an effective way to resolve the contradiction between high energy density and high safety in lithium batteries.

[0004] Among emerging candidates, eutectic electrolytes stand out due to their excellent electrochemical performance and flame-retardant properties similar to solid electrolytes. They typically consist of two or more specific solid components that combine in a specific molar ratio at room temperature to form a homogeneous and stable liquid. They are characterized by simple synthesis, non-toxicity, environmental friendliness, and easy recyclability and degradation. However, currently commonly used eutectic electrolytes are mainly based on nitrogen-containing Lewis bases, such as amides and nitriles. Due to the strong electron-withdrawing properties of their polar groups, their α-hydrogen atoms are highly reactive, often resulting in poor interfacial stability and numerous side reactions at the lithium metal electrode.

[0005] Therefore, the present invention provides a sulfone-based eutectic electrolyte, a preparation method thereof, and a lithium metal battery thereof. Summary of the Invention

[0006] In order to overcome the shortcomings of the prior art, at least one technical problem raised in the background art is solved.

[0007] The technical solution adopted by the present invention to solve its technical problem is: a sulfone-based eutectic electrolyte, the present invention comprising a hydrogen bond donor, a hydrogen bond acceptor and an additive; The hydrogen bond donor is a sulfone, which includes one or more of phenyl vinyl sulfone, ethyl phenyl sulfone, and their derivatives. The hydrogen bond acceptor is a lithium salt, which includes at least one of lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, and lithium hexafluorophosphate. The molar ratio between sulfones and lithium salts is (6~2):1; The additive is one or more of vinylene carbonate, fluoroethylene carbonate, and lithium difluorooxalate borate, and the content of the additive accounts for 1%-10% of the total mass fraction of the electrolyte.

[0008] A method for preparing a sulfone-based eutectic electrolyte, the method comprising the following steps: S1. Weigh sulfones and lithium salts in a glove box where both oxygen and water content are below 0.1 ppm. S2. Mix the sulfones and lithium salts, and stir at 50~70℃ for 30~120 min to obtain a mixture; S3. Add the additive to the mixture and continue stirring until it is evenly mixed to obtain the desired sulfone-based eutectic electrolyte.

[0009] In step S2, the stirring temperature is 60℃ and the stirring time is 1 hour.

[0010] A lithium metal battery, the preparation process of which is as follows: In a glove box where both oxygen and water content are below 0.1 ppm, the negative electrode shell, negative electrode plate, separator, positive electrode plate, gasket, spring, and positive electrode shell are placed in sequence from bottom to top. The above components are fixed by applying pressure on a battery tablet press to obtain a lithium metal battery; The diaphragm is prepared by means of a sulfone-based eutectic electrolyte preparation method, and the eutectic electrolyte is then dropped onto a support material.

[0011] The cathode material includes any one of lithium iron phosphate, lithium cobalt oxide, NCM111 type cathode material, NCM622 type cathode material, NCM811 type cathode material and NCM9 series cathode materials.

[0012] The supporting material is glass fiber.

[0013] The beneficial effects of this invention are as follows: This invention discloses a sulfone-based eutectic electrolyte, its preparation method, and a lithium metal battery thereof. Through the Li-O coordination interaction between the sulfone group and lithium ions, and the HF hydrogen bonding between active hydrogen and lithium salt anions, the eutectic electrolyte is effectively promoted by the dissociation of lithium salt. The high coordination ability of the lone pair electrons of the sulfone oxygen atom with the metal ions, and the hydrogen bonding between the double-bonded carbon active hydrogen and lithium salt anions under conjugation, both enhance the dissociation process. Compared to traditional carbonate-based electrolytes, this electrolyte exhibits good flame retardancy and thermal stability. For example, experiments show that carbonate-based electrolytes have a self-extinguishing time of over ten seconds after ignition, while this electrolyte is almost non-flammable, reducing safety risks. Its synthesis method is simple, the raw materials are readily available and inexpensive, facilitating large-scale promotion. Compared to commonly used nitrile-based and amide-based eutectic electrolytes, the sulfone-based eutectic electrolyte containing a benzene ring shows significantly improved compatibility with the lithium metal anode. At a current density of 0.2 mA cm⁻², the lithium symmetric battery maintains a low polarization voltage of 50 mV after 600 stable cycles. Meanwhile, sulfones, acting as hydrogen bond donors and film-forming additives, can form stable SEI and CEI films on the surfaces of anode and cathode materials, ensuring the stability of the interface films during long-term charge-discharge cycles and effectively improving cycle life. For example, at 25°C and a 1.0C current rate, there is virtually no capacity decay after 100 cycles, and the capacity retention rate reaches 93% after 200 cycles. With these superior properties, this electrolyte has broader application prospects in the field of high-performance lithium-ion batteries and is expected to promote the development and commercial application of lithium metal battery technology. Attached Figure Description

[0014] The invention will now be further described with reference to the accompanying drawings.

[0015] Figure 1 This is a comparison chart of the electrolyte flammability test results in Example 1 of this invention; Figure 2 This is a coulomb efficiency test graph of Embodiment 2 of the present invention at a current density of 0.5 mA cm⁻². Figure 3 This is a comparison chart of the long-cycle test results of a lithium symmetric battery at a current density of 0.2 mA cm⁻² in Example 2 of this invention; Figure 4 This is a test graph of the cycling performance of LiFePO4||Li prepared by the eutectic electrolyte in Example 2 of this invention. Detailed Implementation

[0016] To make the technical means, creative features, objectives and effects of this invention easier to understand, the invention will be further described below in conjunction with specific embodiments.

[0017] like Figures 1 to 4 As shown in the figure, an embodiment of the present invention provides a sulfone-based eutectic electrolyte, which includes a hydrogen bond donor, a hydrogen bond acceptor, and an additive. The hydrogen bond donor is a sulfone, which includes one or more of phenyl vinyl sulfone, ethyl phenyl sulfone, and their derivatives. The hydrogen bond acceptor is a lithium salt, which includes at least one of lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, and lithium hexafluorophosphate. The molar ratio between sulfones and lithium salts is (6~2):1; The additive is one or more of vinylene carbonate, fluoroethylene carbonate, and lithium difluorooxalate borate, and the content of the additive accounts for 1%-10% of the total mass fraction of the electrolyte.

[0018] A method for preparing a sulfone-based eutectic electrolyte, the method comprising the following steps: S1. Weigh sulfones and lithium salts in a glove box where both oxygen and water content are below 0.1 ppm. S2. Mix the sulfones and lithium salts, and stir at 50~70℃ for 30~120 min to obtain a mixture; S3. Add the additive to the mixture and continue stirring until it is evenly mixed to obtain the desired sulfone-based eutectic electrolyte.

[0019] In step S2, the stirring temperature is 60℃ and the stirring time is 1 hour.

[0020] Example 1

[0021] Step 1: In a glove box where both oxygen and water content are below 0.1 ppm, weigh 1.68 g of phenyl vinyl sulfone and 0.748 g of lithium difluorosulfonyl imide according to a sulfone molar ratio of 2.5:1. Step 2: Mix phenyl vinyl sulfone and lithium bisfluorosulfonyl imide and stir at 60°C for 1 hour to obtain the desired sulfone-based eutectic electrolyte.

[0022] like Figure 1 The carbonate-based electrolyte has a self-extinguishing time of more than ten seconds, while the sulfone-based eutectic electrolyte is almost non-flammable and has good flame retardant properties.

[0023] Example 2

[0024] The difference between this embodiment and Example 1 is that 3 wt% of fluoroethylene carbonate (additive) was added. In a glove box with oxygen and water content both below 0.1 ppm, 1.68 g of phenyl vinyl sulfone and 0.748 g of lithium difluorosulfonyl imide were weighed according to a sulfone-to-lithium salt molar ratio of 2.5:1. 3 wt% fluoroethylene carbonate was added, and the mixture was heated and stirred at 60 °C for 1 h to obtain a homogeneous eutectic electrolyte.

[0025] like Figure 2The average coulombic efficiency of sulfone-based eutectic electrolytes is as high as 91.7%. The high coulombic efficiency means that sulfone-based electrolytes can promote lithium deposition and avoid the formation of dead lithium. like Figure 3 Compared to common amide-based and nitrile-based eutectic electrolytes, sulfone-based eutectic electrolytes containing benzene ring sulfone groups exhibit good lithium metal compatibility. At a current density of 0.2 mA cm⁻², a lithium-symmetric battery assembled with sulfone-based eutectic electrolytes still maintains a low polarization voltage of 50 mV after 600 cycles, while commonly used amide-based and nitrile-based eutectic electrolytes exhibit extremely high polarization voltages around 90 cycles, indicating severe side reactions with lithium metal. like Figure 4 In the cycle performance test: the test temperature was 25℃ and the current ratio was 1.0C. Figure 4 The results showed that the sulfone-based eutectic electrolyte exhibited almost no capacity decay after 100 cycles and a capacity retention of 93% after 200 cycles, demonstrating good cycling stability.

[0026] Example 3

[0027] The difference between this embodiment and Example 2 is that the lithium salt was replaced with lithium bis(trifluoromethanesulfonyl)imide. In a glove box with oxygen and water content both below 0.1 ppm, 1.68 g of phenyl vinyl sulfone and 1.15 g of lithium bis(trifluoromethanesulfonyl)imide were weighed according to a sulfone-to-lithium salt molar ratio of 2.5:1. 3 wt% fluoroethylene carbonate was added, and the mixture was heated and stirred at 60°C for 1 h to obtain a homogeneous eutectic electrolyte.

[0028] Example 4

[0029] The difference between this embodiment and Embodiment 2 is that the sulfone substance is replaced with ethylphenyl sulfone; In a glove box with oxygen and water content both below 0.1 ppm, 1.7 g of ethyl phenyl sulfone and 0.748 g of lithium difluorosulfonyl imide were weighed according to a sulfone molar ratio of 2.5:1, and then 3 wt% of fluoroethylene carbonate was added. The mixture was heated and stirred at 60 °C for 1 h until homogeneous, thus obtaining the eutectic electrolyte.

[0030] Based on the eutectic electrolyte obtained in the examples, coin cells were prepared using the following procedure: Preparation of battery separator material: In a glove box, 0.1 mL of eutectic electrolyte was added dropwise to glass fiber to obtain the separator material for lithium battery; Preparation of positive electrode: Lithium iron phosphate, polyvinylidene fluoride and carbon black are weighed in a mass ratio of 80:15:5, and 0.3 mL of N-methylpyrrolidone is added as a dispersant solvent. The mixture is then ground into a uniform slurry. A uniform electrode slurry is then coated onto the surface of the current collector using a scraper. Then, place it in a vacuum oven at 80°C and dry for 24 hours until the solvent is completely evaporated and the electrode surface is completely dry. Cut the electrode sheet into a circular electrode with a diameter of 12 mm. Finally, it was transferred to an argon glove box for later use.

[0031] A lithium metal battery, the preparation process of which is as follows: In a glove box where both oxygen and water content are below 0.1 ppm, the negative electrode shell, negative electrode plate, separator, positive electrode plate, gasket, spring, and positive electrode shell are placed in sequence from bottom to top. The above components are fixed by applying pressure on a battery tablet press to obtain a lithium metal battery; The diaphragm is prepared by means of a sulfone-based eutectic electrolyte preparation method, and the eutectic electrolyte is then dropped onto a support material.

[0032] The cathode material includes any one of lithium iron phosphate, lithium cobalt oxide, NCM111 type cathode material, NCM622 type cathode material, NCM811 type cathode material and NCM9 series cathode materials.

[0033] The supporting material is glass fiber.

[0034] A eutectic electrolyte is formed using phenyl vinyl sulfone as the hydrogen bond donor and lithium bis(fluorosulfonyl)imide as the hydrogen bond acceptor, based on Li-O coordination interactions and HF hydrogen bonding. The oxygen atom in the sulfone group possesses a lone pair of electrons, thus exhibiting high coordination ability with metal ions, which facilitates the dissociation of Li salts. Furthermore, the active hydrogen on the conjugated double-bonded carbon atom can form hydrogen bonds with lithium salt anions, further promoting lithium salt dissociation. More importantly, the addition of the benzene ring improves the compatibility of the electrolyte with lithium metal. This electrolyte design not only exhibits excellent flame retardant properties but also allows for the formation of stable SEI and CEI films on the surfaces of the anode and cathode materials, contributing to improved battery cycle life and demonstrating broader application prospects in high-performance lithium-ion batteries.

[0035] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. A sulfone-based eutectic electrolyte, characterized in that, The electrolyte includes a hydrogen bond donor, a hydrogen bond acceptor, and additives; The hydrogen bond donor is a sulfone, which includes one or more of phenyl vinyl sulfone, ethyl phenyl sulfone, and their derivatives. The hydrogen bond acceptor is a lithium salt, which includes at least one of lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, and lithium hexafluorophosphate. The molar ratio between the sulfone and the lithium salt is (6~2):1; The additive is one or more of vinylene carbonate, fluoroethylene carbonate, and lithium difluorooxalate borate, and the content of the additive accounts for 1%-10% of the total mass fraction of the electrolyte.

2. A method for preparing a sulfone-based eutectic electrolyte, used in the sulfone-based eutectic electrolyte of claim 1, characterized in that, The preparation method includes the following steps: S1. Weigh sulfones and lithium salts in a glove box where both oxygen and water content are below 0.1 ppm. S2. Mix the sulfones and lithium salts, and stir at 50~70℃ for 30~120 min to obtain a mixture; S3. Add the additive to the mixture and continue stirring until it is evenly mixed to obtain the desired sulfone-based eutectic electrolyte.

3. The method for preparing a sulfone-based eutectic electrolyte according to claim 2, characterized in that: In step S2, the stirring temperature is 60℃ and the stirring time is 1 hour.

4. A lithium metal battery, characterized in that, The manufacturing process of this lithium metal battery is as follows: In a glove box where both oxygen and water content are below 0.1 ppm, the negative electrode shell, negative electrode plate, separator, positive electrode plate, gasket, spring, and positive electrode shell are placed in sequence from bottom to top. The above components are fixed by applying pressure on a battery tablet press to obtain a lithium metal battery; The diaphragm is prepared by: preparing a sulfone-based eutectic electrolyte using the preparation method of claim 2, and then dropping the eutectic electrolyte onto a support material.

5. A lithium metal battery according to claim 4, characterized in that: The cathode material includes any one of lithium iron phosphate, lithium cobalt oxide, NCM111 type cathode material, NCM622 type cathode material, NCM811 type cathode material and NCM9 series cathode materials.

6. A lithium metal battery according to claim 4, characterized in that: The supporting material is glass fiber.

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