Secondary battery electrolyte based on ether functionalized phosphino ionic liquid and application

Abstract

The invention discloses a secondary battery electrolyte based on ether-functionalized phosphino ionic liquid and application, the electrolyte comprises the ether-functionalized phosphino ionic liquid, and novel ionic liquid is designed and synthesized by introducing ether-containing functional groups into cations of the phosphino ionic liquid; by utilizing a specific ether functional group in the ionic liquid and regulating and controlling the coordination effect between Li < + > and anions, a coordination structure derived from the anions is realized, the formation of a firm interface phase in a battery circulation process is effectively promoted, and the growth of lithium dendrites is remarkably inhibited; in addition, the migration rate of lithium ions in the electrolyte is also enhanced by introducing the ether functional group. And under the combined action of the characteristics, the long-cycle stability of the lithium-based battery is remarkably improved.

Description

Technical Field

[0001] The invention relates to the technical field of secondary batteries, to a secondary battery electrolyte and applications thereof, and in particular to a secondary battery electrolyte based on an ether-functionalized phosphine-based ionic liquid and applications thereof. Background Art

[0002] In advanced batteries, electrodes operate at extreme potentials, and no known electrolyte can remain thermodynamically stable. Therefore, in lithium-ion batteries, the electrolyte is designed to form a passivation layer on the electrode surface to prevent further decomposition of the electrolyte and achieve kinetic stability. This passivation layer is called the "interface phase." The interfacial phase on the negative electrode surface is called the solid electrolyte interface (SEI), and the interfacial phase on the positive electrode surface is called the positive electrode electrolyte interface (CEI). SEI usually has a double-layer structure: the outer organic layer provides specific functions, and the inner inorganic layer performs other roles. Traditional organic electrolytes usually use ethylene carbonate (EC) as a solvent, and EC is mixed with Li + The strong interaction between them gives it a high ionic conductivity (9-10mS / cm at 25°C). However, the high solvation energy of EC leads to the formation of an organic-rich SEI on the surface of the graphite negative electrode, which has high interfacial impedance and freezing characteristics, resulting in poor performance of lithium-ion batteries at low temperatures and slow charging. In addition, these SEIs are usually uneven, leading to dendrite growth, "dead lithium" formation, low Coulomb efficiency, and short cycle life. At high temperatures, organic solvent-based electrolytes are highly volatile and flammable, making it difficult to meet the future needs of highly active electrode materials and safe and efficient operation over a wide temperature range.

[0003] Ionic liquids (ILs) are a class of salts composed of cations and anions with a melting point below 100°C. They are highly stable, flame retardant, non-volatile, and have a wide electrochemical window, making them a safe alternative to traditional organic electrolytes. However, the superior performance of ILs depends largely on the Lewis acidity and alkalinity of their anions and cations, the directionality of ionic interactions, and van der Waals forces. The transport properties of lithium salt / ionic liquid mixtures are significantly affected by the organic cations. Generally, as the radius of the organic cation increases, the viscosity increases and the ionic conductivity decreases. The size, conformational flexibility, and interactions of the cations and anions also affect the viscosity and conductivity of the IL. In addition, the functional groups in the cationic structure also have an important influence on these properties. For example, organic cations with ether groups have a high conductivity due to Li +The interaction with ether groups tends to reduce the viscosity of lithium salt / IL mixtures. Studies have shown that mixing N-propyl-N-methylpyrrolidinium bis(fluorosulfonyl)imide (C3mpyrFSI) with organic ethers such as 1,2-dimethoxyethane (DME) in different proportions can form clear, homogeneous solutions. Ether-functionalized ionic liquids can achieve high packing density, minimize inactive lithium generation, and inhibit dendrite growth during long-term cycling.

[0004] Although IL-based electrolytes have advantages such as high stability and flame retardancy, the interaction between strong ion pairs can reduce lithium ion mobility and affect wettability with separators and electrodes. Therefore, most strategies mix ILs with organic solvents (such as carbonates or ethers) to improve conductivity and compatibility. However, the ability to form SEI is affected by anion-cation pairs, chemical reactions, and interfacial charge transport on the electrode surface. In order to solve the interfacial problem, high-concentration ionic liquid electrolytes (HCILEs), locally high-concentration ionic liquid electrolytes (LCILEs), and weakly solvated electrolytes are usually prepared by increasing the lithium salt content to form anion-derived SEI. However, the use of a large amount of lithium salt leads to increased electrolyte viscosity and poor lithium ion dissociation, ultimately resulting in lower ionic conductivity (about 5mS / cm), which limits the charging speed and power density. Summary of the invention

[0005] In view of the shortcomings of the prior art, the present invention aims to provide a secondary battery electrolyte and application based on ether-functionalized phosphine-based ionic liquid, solve the problems of high viscosity and low conductivity of ionic liquid electrolytes, and improve the overall conductivity and ionic conductivity of the electrolyte.

[0006] The present invention is achieved through the following technical solutions:

[0007] A secondary battery electrolyte based on ether functionalized phosphine-based ionic liquid comprises a lithium salt, a carbonate solvent and the ether functionalized phosphine-based ionic liquid.

[0008] Furthermore, the concentration of lithium salt in the electrolyte is 0.5-2.0 mol / L, and the mass ratio of carbonate solvent to ether functionalized phosphine-based ionic liquid is 1:(0.1-1).

[0009] Further, the structure of the cation of the ether-functionalized phosphine-based ionic liquid is:

[0010]

[0011] Wherein, R1, R2, R3, R4, and R5 are substituted or unsubstituted C1 to C4 alkyl groups.

[0012] Furthermore, the anion of the ether-functionalized phosphine-based ionic liquid is at least one of bis(fluorosulfonyl)imide, bis(trifluoromethanesulfonyl)imide and hexafluorophosphate.

[0013] Further, the ether-functionalized phosphine-based ionic liquid is one of trimethyl (methoxymethyl) phosphine bisfluorosulfonyl imide, trimethyl (methoxymethyl) phosphine bis (trifluoromethanesulfonyl) imide, trimethyl (methoxymethyl) phosphine hexafluorophosphate, triethyl (methoxymethyl) phosphine hexafluorophosphate, tributyl (methoxymethyl) phosphine bisfluorosulfonyl imide, tributyl (methoxymethyl) phosphine bis (trifluoromethanesulfonyl) imide, tributyl (methoxymethyl) phosphine hexafluorophosphate, trimethyl (methoxyethyl) phosphine bisfluorosulfonyl imide, trimethyl (methoxyethyl) phosphine bis (trifluoromethanesulfonyl) imide, trimethyl (methoxyethyl) phosphine hexafluorophosphate, triethyl (methoxyethyl) phosphine hexafluorophosphate, tributyl (methoxyethyl) phosphine bisfluorosulfonyl imide, tributyl (methoxyethyl) phosphine bis (trifluoromethanesulfonyl) imide, and tributyl (methoxyethyl) phosphine hexafluorophosphate.

[0014] Furthermore, the lithium salt is one or more of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, and lithium bis(trifluoromethanesulfonyl)imide.

[0015] Furthermore, the carbonate solvent is dimethyl carbonate and ethylene carbonate.

[0016] A lithium-based battery comprises a secondary battery electrolyte based on an ether-functionalized phosphine-based ionic liquid.

[0017] A lithium-based battery comprises a secondary battery electrolyte based on ether-functionalized phosphine-based ionic liquid, a separator, a positive electrode and a negative electrode.

[0018] Beneficial effects of the present invention:

[0019] 1. The electrolyte mainly includes ether-functionalized phosphine-based ionic liquids. By introducing ether-containing functional groups into the cations of the phosphine-based ionic liquids, the ether functional groups promote the coordination between lithium ions and anions, realize the anion-derived coordination structure, effectively promote the formation of a strong interface phase during the battery cycle, and significantly inhibit the growth of lithium dendrites. + The introduction of a large number of anions into the solvation sheath significantly optimizes the Li + The solvation structure of Li + It can more effectively form a close coordination relationship with anions, further enhancing the stability and uniformity of the interfacial phase. Compared with traditional organic electrolyte systems, ether-functionalized ionic liquids control Li +The solvation structure can not only significantly reduce the interfacial charge transfer impedance, but also increase the chemical reaction activity at the interface and promote the formation of an inorganic-enriched interfacial phase, thereby improving the overall electrochemical performance of the battery.

[0020] 2. The introduction of ether groups not only optimizes the viscosity of the electrolyte, but also + The interaction with ether groups greatly promotes the Li + The migration rate of ether-functionalized phosphine-based ionic liquids is significantly reduced, which effectively offsets the high viscosity and low conductivity of ILs. Traditional ILs often exhibit high viscosity and low ionic conductivity due to strong interactions between ion pairs. + The weak interaction between the two ions successfully reduced the strong interaction between the ion pairs, lowered the viscosity, and thus improved the overall conductivity of the electrolyte, successfully achieving a balance between high conductivity and a strong anion-derived interface phase. This allows the electrolyte to achieve high ionic conductivity while maintaining good interface stability, meeting the requirements of lithium metal batteries under fast charging and high power output conditions.

[0021] 3. The design also regulates Li + The coordination between Li and anions ensures that the interface phase is formed more uniformly and firmly. + The solvation structure in the electrolyte determines the formation and stability of SEI and CEI, and ether-functionalized ionic liquids can still achieve good solvation effect at low lithium salt concentrations, making Li + The coordination number formed with anions increases, further strengthening the inorganicization of the interface phase. The inorganic-enriched interface phase has better electrochemical stability and mechanical strength, can effectively inhibit the growth of lithium dendrites, and extend the cycle life of the battery.

[0022] Overall, this invention based on ether-functionalized phosphine-based ionic liquids shows significant advantages in improving lithium ion conductivity, optimizing solvation structure, and stabilizing interfacial phases. By achieving efficient ion conductivity and a strong interfacial phase under low concentration conditions, this design successfully solves the problems of low conductivity and unstable interfacial phase in traditional ILs, providing a new strategy for the design of lithium metal battery electrolytes. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 Electronic photographs of the flame retardant properties of Example 1 of the present invention and the comparative example;

[0024] Figure 2 The wavelengths of Example 1 and the comparative example are 734-750cm -1 Raman spectra between

[0025] Figure 3 For Example 1 of the present invention and the comparative example1 H NMR spectra and 7 Li NMR spectrum;

[0026] Figure 4 The SEM images of the lithium metal negative electrode surface of the Li / LiFePO4 button-type batteries assembled in Example 1 of the present invention and the comparative example after 100 cycles;

[0027] Figure 5 It is a long cycle performance test diagram of the Li / LiFePO4 button battery assembled in Example 1 of the present invention and the comparative example. DETAILED DESCRIPTION

[0028] The present invention is further described in detail below in conjunction with specific embodiments, which are intended to explain the present invention rather than to limit it.

[0029] Example 1

[0030] (I) Ether-functionalized phosphine-based ionic liquid tributyl (methoxymethyl) phosphine hexafluorophosphate ([P 4441O1 Preparation of ][PF6])

[0031] The preparation method is as follows:

[0032] 1) Tributylphosphine and bromomethyl methyl ether were weighed in a molar ratio of 1:1, and toluene was used as a solvent. The mixture was stirred and reacted at room temperature, and nitrogen was used as a protection. After reacting for 6 hours, a white solid was obtained.

[0033] 2) The obtained white solid was washed five times with n-hexane and dried at 40° C. overnight to obtain the target product A.

[0034] 3) The obtained target product A is dissolved in an appropriate amount of deionized water to obtain a solution B, and lithium hexafluorophosphate is weighed in an equimolar ratio and dissolved in an appropriate amount of deionized water to obtain a solution C.

[0035] 4) Quickly pour solution C into solution B and stir to react for 1 hour.

[0036] 5) Rinse repeatedly with deionized water five times until no white precipitate is produced when titrated with silver nitrate solution.

[0037] 6) The organic phase was collected and dried under vacuum at 60°C for 3 days to obtain the final product [P 4441O1 [PF6] Ether-functionalized phosphine-based ionic liquids.

[0038] (II) Preparation of secondary battery electrolyte OPED-30 based on ether-functionalized phosphine-based ionic liquid

[0039] The preparation method is as follows:

[0040] Ethylene carbonate and dimethyl carbonate were prepared in a volume ratio of 1:1 to obtain solution A.

[0041] 1 mol of lithium hexafluorophosphate is dissolved in solution A to obtain solution B.

[0042] 30wt% [P 4441O1 ][PF6] Ether-functionalized phosphine-based ionic liquid was added to solution B to obtain secondary battery electrolyte OPED-30 based on ether-functionalized phosphine-based ionic liquid.

[0043] The concentration of lithium hexafluorophosphate in the secondary battery electrolyte OPED-30 is 1.0 mol / L. Solution A and [P 4441O1 The mass ratio of ][PF6]ether-functionalized phosphine-based ionic liquid is 1:1.

[0044] (III) Comparative Example LP30

[0045] The preparation method is as follows:

[0046] Ethylene carbonate and dimethyl carbonate were prepared in a volume ratio of 1:1 to obtain solution A.

[0047] 1 mol of lithium hexafluorophosphate was dissolved in solution A to obtain a comparative electrolyte.

[0048] (IV) Testing

[0049] Table 1 shows the lithium ion migration number (t Li+ )

[0050]

[0051] Figure 1 The flame retardant properties of ether-functionalized phosphine-based ionic liquid electrolytes are compared with those of traditional organic electrolytes. Figure 1 It can be seen that after the introduction of ether-functionalized phosphine-based ionic liquid, the flame retardant properties of the electrolyte were greatly improved, and the self-extinguishing time was shortened from 35s to 21s. Figure 2 The Raman spectrum shows that the introduction of ether-functionalized phosphine-based ionic liquid can cause the Raman peak of PF to blue shift, indicating that the ether-functionalized phosphine-based ionic liquid effectively improves the Li + With PF6 - The coordination strength. Figure 3 The phenomenon that the nuclear magnetic peak in the NMR spectrum moves to the low field also illustrates the same conclusion. Figure 4 It can be seen from the SEM photos that the ether-functionalized phosphine-based ionic liquid secondary battery electrolyte can effectively inhibit the formation of lithium dendrites and form a relatively dense interface phase structure.

[0052] The following is the application of the secondary battery electrolyte OPED-30 prepared in Example 1 in Li / LiFePO4 button cells:

[0053] Lithium metal (diameter 12 mm, thickness 600 μm) was used as the negative electrode and lithium iron phosphate was used as the positive electrode (active material loading was about 11.25 mg / cm 2 ), PP 2500 as the separator, and the amount of electrolyte added to each button cell is 50μL. The assembly of CR 2032 button cells was completed in a glove box filled with argon (O2<0.1ppm, H2O<0.1ppm). The voltage window of the constant current charge and discharge experiment was 2.5-4.2V, and the test environment temperature was controlled at 25℃. Figure 5 As shown, the ether-functionalized phosphine-based ionic liquid electrolyte of the present invention performs excellently in Li / LiFePO4 button cells, with a capacity retention rate of 75% and a coulombic efficiency of greater than 99% after 300 cycles. Compared with traditional organic electrolytes, its electrochemical performance is greatly improved.

[0054] Example 2

[0055] A secondary battery electrolyte based on ether-functionalized phosphine-based ionic liquid consists of lithium hexafluorophosphate, dimethyl carbonate, ethylene carbonate and trimethyl (methoxymethyl) phosphine hexafluorophosphate, wherein the concentration of lithium hexafluorophosphate is 0.5 mol / L, and the mass ratio of dimethyl carbonate, ethylene carbonate and trimethyl (methoxymethyl) phosphine hexafluorophosphate is 1:1:0.2.

[0056] Example 3

[0057] A secondary battery electrolyte based on ether-functionalized phosphine-based ionic liquid consists of lithium hexafluorophosphate, dimethyl carbonate, ethylene carbonate and triethyl (methoxymethyl) phosphine hexafluorophosphate, wherein the concentration of lithium hexafluorophosphate is 0.8 mol / L, and the mass ratio of dimethyl carbonate, ethylene carbonate and triethyl (methoxymethyl) phosphine hexafluorophosphate is 1:1:0.4.

[0058] Example 4

[0059] A secondary battery electrolyte based on ether-functionalized phosphine-based ionic liquid consists of lithium hexafluorophosphate, dimethyl carbonate, ethylene carbonate and tributyl (methoxyethyl) phosphine hexafluorophosphate, wherein the concentration of lithium hexafluorophosphate is 0.8 mol / L, and the mass ratio of dimethyl carbonate, ethylene carbonate and tributyl (methoxyethyl) phosphine hexafluorophosphate is 1:1:0.6.

[0060] Example 5

[0061] A secondary battery electrolyte based on ether-functionalized phosphine-based ionic liquid is composed of lithium bis(fluorosulfonyl)imide, dimethyl carbonate, ethylene carbonate and trimethyl(methoxymethyl)phosphine bis(fluorosulfonyl)imide, wherein the concentration of lithium hexafluorophosphate is 1 mol / L, and the mass ratio of dimethyl carbonate, ethylene carbonate and trimethyl(methoxymethyl)phosphine bis(fluorosulfonyl)imide is 1:1:0.6.

[0062] Example 6

[0063] A secondary battery electrolyte based on ether-functionalized phosphine-based ionic liquid consists of lithium bis(fluorosulfonyl)imide, dimethyl carbonate, ethylene carbonate and tributyl(methoxymethyl)phosphine bis(fluorosulfonyl)imide, wherein the concentration of lithium hexafluorophosphate is 1 mol / L, and the mass ratio of dimethyl carbonate, ethylene carbonate and tributyl(methoxymethyl)phosphine bis(fluorosulfonyl)imide is 1:1:0.6.

[0064] Example 7

[0065] A secondary battery electrolyte based on ether-functionalized phosphine-based ionic liquid is composed of lithium bis(fluorosulfonyl)imide, dimethyl carbonate, ethylene carbonate and tributyl(methoxyethyl)phosphine bis(fluorosulfonyl)imide, wherein the concentration of lithium hexafluorophosphate is 2 mol / L, and the mass ratio of dimethyl carbonate, ethylene carbonate and tributyl(methoxyethyl)phosphine bis(fluorosulfonyl)imide is 1:1:0.6.

[0066] Example 8

[0067] A secondary battery electrolyte based on ether-functionalized phosphine-based ionic liquid is composed of lithium bis(trifluoromethanesulfonyl)imide, dimethyl carbonate, ethylene carbonate and trimethyl(methoxymethyl)phosphine bis(trifluoromethanesulfonyl)imide, wherein the concentration of lithium hexafluorophosphate is 2 mol / L, and the mass ratio of dimethyl carbonate, ethylene carbonate and trimethyl(methoxymethyl)phosphine bis(trifluoromethanesulfonyl)imide is 1:1:0.1.

[0068] Example 9

[0069] A secondary battery electrolyte based on ether-functionalized phosphine-based ionic liquid is composed of lithium bis(trifluoromethanesulfonyl)imide, dimethyl carbonate, ethylene carbonate and tributyl(methoxymethyl)phosphine bis(trifluoromethanesulfonyl)imide, wherein the concentration of lithium hexafluorophosphate is 2 mol / L, and the mass ratio of dimethyl carbonate, ethylene carbonate and tributyl(methoxymethyl)phosphine bis(trifluoromethanesulfonyl)imide is 1:1:1.

[0070] Example 10

[0071] A secondary battery electrolyte based on ether-functionalized phosphine-based ionic liquid is composed of lithium bis(trifluoromethanesulfonyl)imide, dimethyl carbonate, ethylene carbonate and tributyl(methoxyethyl)phosphine bis(trifluoromethanesulfonyl)imide, wherein the concentration of lithium hexafluorophosphate is 2 mol / L, and the mass ratio of dimethyl carbonate, ethylene carbonate and tributyl(methoxyethyl)phosphine bis(trifluoromethanesulfonyl)imide is 1:1:1.

[0072] As shown in Examples 2-10, the secondary battery electrolyte is based on ether-functionalized phosphine-based ionic liquid, wherein the ether-functionalized phosphine-based ionic liquid is one of trimethyl (methoxyethyl) phosphine bis(trifluoromethanesulfonyl)imide, trimethyl (methoxyethyl) phosphine bis(trifluoromethanesulfonyl)imide, trimethyl (methoxyethyl) phosphine hexafluorophosphate, and triethyl (methoxyethyl) phosphine hexafluorophosphate.

Claims

1. A secondary battery electrolyte based on ether-functionalized phosphine-based ionic liquid, characterized in that: Including lithium salts, carbonate solvents and ether-functionalized phosphine-based ionic liquids.

2. The secondary battery electrolyte based on ether-functionalized phosphine-based ionic liquid according to claim 1, characterized in that: The concentration of lithium salt in the electrolyte is 0.5-2.0 mol / L, and the mass ratio of carbonate solvent to ether functionalized phosphine-based ionic liquid is 1:(0.1-1).

3. The secondary battery electrolyte based on ether-functionalized phosphine-based ionic liquid according to claim 1, characterized in that: The structure of the cation of the ether-functionalized phosphine-based ionic liquid is: Wherein, R1, R2, R3, R4, and R5 are substituted or unsubstituted C1 to C4 alkyl groups.

4. The secondary battery electrolyte based on ether-functionalized phosphine-based ionic liquid according to claim 1, characterized in that: The anion of the ether-functionalized phosphine-based ionic liquid is at least one of bis(fluorosulfonyl)imide, bis(trifluoromethanesulfonyl)imide and hexafluorophosphate.

5. The secondary battery electrolyte based on ether-functionalized phosphine-based ionic liquid according to claim 3 or 4, characterized in that: The ether-functionalized phosphine-based ionic liquid is one of trimethyl (methoxymethyl) phosphine bisfluorosulfonyl imide, trimethyl (methoxymethyl) phosphine bis (trifluoromethanesulfonyl) imide, trimethyl (methoxymethyl) phosphine hexafluorophosphate, triethyl (methoxymethyl) phosphine hexafluorophosphate, tributyl (methoxymethyl) phosphine bisfluorosulfonyl imide, tributyl (methoxymethyl) phosphine bis (trifluoromethanesulfonyl) imide, tributyl (methoxymethyl) phosphine hexafluorophosphate, trimethyl (methoxyethyl) phosphine bisfluorosulfonyl imide, trimethyl (methoxyethyl) phosphine bis (trifluoromethanesulfonyl) imide, trimethyl (methoxyethyl) phosphine hexafluorophosphate, triethyl (methoxyethyl) phosphine hexafluorophosphate, tributyl (methoxyethyl) phosphine bisfluorosulfonyl imide, tributyl (methoxyethyl) phosphine bis (trifluoromethanesulfonyl) imide, and tributyl (methoxyethyl) phosphine hexafluorophosphate.

6. The secondary battery electrolyte based on ether-functionalized phosphine-based ionic liquid according to claim 1, characterized in that: The lithium salt is one or more of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide and lithium bis(trifluoromethanesulfonyl)imide.

7. The secondary battery electrolyte based on ether-functionalized phosphine-based ionic liquid according to claim 1, characterized in that: The carbonate solvents are dimethyl carbonate and ethylene carbonate.

8. A lithium-based battery, characterized in that: A secondary battery electrolyte comprising the ether-functionalized phosphine-based ionic liquid according to any one of claims 1 to 7.

9. The lithium-based battery according to claim 8, characterized in that: The invention comprises a secondary battery electrolyte, a separator, a positive electrode and a negative electrode based on an ether-functionalized phosphine-based ionic liquid.

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