Weak solvent coordination fast charging electrolyte and preparation method thereof

Abstract

The present application relates to the technical field of lithium metal battery, in particular to weak solvent coordination fast-charging electrolyte and its preparation method. The preparation method of the weak solvent coordination fast-charging electrolyte comprises the following steps: 2-fluoroanisole is added to the organic electrolyte to obtain a mixed solution; wherein the addition amount of 2-fluoroanisole is 2-8wt% of the organic electrolyte; the mixed solution is reacted at 20-30℃ for at least 2h to obtain the weak solvent coordination fast-charging electrolyte. The ion migration number of the weak solvent coordination fast-charging electrolyte at 25℃ is 0.602. The FMOP with weak solvent coordination ability promotes more anions in the organic electrolyte to participate in the formation of dense and strong SEI through weak solvent coordination traction, thereby inhibiting the growth of Li dendrites. At the same time, the FMOP has a lower LUMO energy level and a certain hydrogen-donating ability, and the generated SEI can induce uniform Li deposition.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium metal batteries, in particular to a weak solvent coordination fast-charging electrolyte and a preparation method thereof. BACKGROUND

[0002] Lithium metal batteries have attracted extensive attention due to their low lithium density, high theoretical capacity and low redox potential. However, the electrolyte of the traditional lithium metal battery will undergo side reactions during the cycling process, thereby deteriorating the solid electrolyte interface (SEI), and thus resulting in unsatisfactory fast-charging performance and cycling stability of the lithium metal battery.

[0003] Currently, there are mainly two methods for optimizing the properties of SEI: one is to prepare high-concentration electrolytes (HCEs), which promote anions to participate in the solvation process by forming contact ion pairs and aggregated ion groups structures by increasing the concentration of the salt, thereby constructing an SEI rich in anions. This to some extent enhances the stability of the SEI of the lithium metal battery. However, HCEs have the problems of poor wettability and high cost, which hinder their commercial application. The second is to introduce ether diluents to form local high-concentration electrolytes (LECEs) in HCEs, which retain the solvation environment of HCEs and at the same time reduce the viscosity of the electrolyte. However, the ether diluents used to form LHCEs are often complex in molecular structure and expensive, which poses a challenge to their practical application. While choosing ether diluents with relatively simple molecular structure and low price, although the viscosity of the electrolyte can be reduced, the amount of such diluents used in the preparation of the electrolyte is high. At the same time, when using ether diluents, it is often necessary to use additives with reduced interfacial impedance, and the ether bond contained in the ether diluents is not stable and can introduce new side reactions to further deteriorate the SEI. In addition, the lithium salt in the traditional organic electrolyte is less dissociated, resulting in a low Li + transference number, which limits the fast-charging ability of the lithium metal battery.

[0004] Therefore, it is still challenging to develop an electrolyte with a dense and strong SEI, high ion transference and excellent fast-charging performance.

[0005] CN118572193A discloses a kind of local weak solvation lithium metal battery low temperature electrolyte, and specifically discloses that low temperature electrolyte is mainly solvent with ester group solvent with melting point lower than-70℃, with ether group solvent with weak solventing capacity as a secondary solvent, and inert diluent, additive and lithium salt are added;Secondary solvent adopts cyclic ether group solvent with weak solventing capacity, including one of tetrahydropyran (THP), tetrahydrofuran (THF), dimethyltetrahydropyran (MTHF), 1,4-dioxane (DOA), 1,3-dioxolane (DOL) or mixed with multiple kinds according to any proportion. Inert diluent includes one of fluorobenzene (FB), m-fluorotoluene (FT), 1,1,2,2-tetrafluoroethyl-2,2,3,3 tetrafluoropropyl ether (TTE), bis (2,2,2-trifluoroethyl) ether (BTFE) or mixed with multiple kinds according to any proportion;The volume ratio of ester group solvent, ether group solvent and inert diluent in the low temperature electrolyte is 1-3:1-3:2-6. Ether group solvent can reduce the viscosity of electrolyte, improve ion conductivity. Inert diluent does not dissolve lithium salt, can increase the local concentration of lithium ion, improve the solvation structure of lithium ion. It solves the stability of electrolyte at low temperature, but does not solve the influence of ether group solvent side reaction on SE I.

[0006] CN116864809A discloses a kind of lithium ion battery electrolyte and its application, and specifically discloses at least includes the following components: non-aqueous solvent;Lithium salt;Diluent, diluent includes fluorine aromatic ether compound;And additive, additive includes film-forming additive and acid-removing and water-removing additive;The mass content of diluent in electrolyte is 20wt%-50wt%;Fluorine aromatic ether compound includes 2-fluoroanisole, 3-fluoroanisole, 4-fluoroanisole, 2-fluoro-p-dimethyl ether and the like;When fluorine aromatic ether compound is used as diluent, the normal temperature and high temperature cycle performance of lithium ion battery can be improved, the high temperature storage DCR growth is reduced, and the high temperature gas production is reduced. However, it uses 2-fluoroanisole with mass content of 20wt%-50wt%, and when the amount of 2-fluoroanisole is small, such as 20wt%, it is not conducive to the high temperature storage DCR growth and the reduction of high temperature gas production, and it is difficult to inhibit the influence of side reaction on SE I. SUMMARY

[0007] To solve the above problems, the present application provides a weak solvent coordination fast-charging electrolyte and its preparation method. 2-Fluoroanisole (FMOP) with weak solvent coordination ability promotes more PF6 - Anions participate in the formation of dense and strong SEI, thereby inhibiting the growth of Li dendrites, while FMOP has a lower LUMO energy level and certain hydrogen-donating ability, and the generated SEI can induce uniform Li deposition.

[0008] A first object of the present application is to provide a preparation method of a weak-solvent coordination fast-charging electrolyte.

[0009] To achieve the first object of the present application, the preparation method of the weak-solvent coordination fast-charging electrolyte comprises:

[0010] S1: adding 2-fluoroanisole into an organic electrolyte to obtain a mixed solution; wherein the amount of 2-fluoroanisole added is 2-8 wt% of the organic electrolyte;

[0011] S2: reacting the mixed solution at 20-30℃ for at least 2h to obtain the weak-solvent coordination fast-charging electrolyte.

[0012] In a specific embodiment of the present application, the organic electrolyte is a carbonate electrolyte.

[0013] In a specific embodiment of the present application, the carbonate electrolyte comprises lithium hexafluorophosphate, vinyl carbonate and diethyl carbonate.

[0014] In a specific embodiment of the present application, the concentration of lithium hexafluorophosphate in the carbonate electrolyte is 1M.

[0015] In a specific embodiment of the present application, the volume ratio of vinyl carbonate to diethyl carbonate in the carbonate electrolyte is 1:1.

[0016] In a specific embodiment of the present application, the reaction temperature of the mixed solution is 25-30℃.

[0017] In a specific embodiment of the present application, the reaction temperature of the mixed solution is 25℃.

[0018] In a specific embodiment of the present application, the amount of 2-fluoroanisole added is 4 wt% of the organic electrolyte.

[0019] A second object of the present application is to provide a weak-solvent coordination fast-charging electrolyte.

[0020] To achieve the second object of the present application, the weak-solvent coordination fast-charging electrolyte is prepared according to the aforementioned preparation method.

[0021] In a specific embodiment of the present application, the ion transference number of the weak-solvent coordination fast-charging electrolyte at 25℃ is 0.602.

[0022] A third object of the present application is to provide a nickel ternary lithium metal battery.

[0023] To achieve the third object of the present application, the nickel ternary lithium metal battery of the present application uses the aforementioned weak-solvent coordination fast-charging electrolyte.

[0024] In one specific embodiment of the present application, the nickel ternary lithium metal battery is a Li||NCM811 battery.

[0025] Compared with the prior art, the present application has the following beneficial effects:

[0026] 1. The present application improves the solvation structure of the organic electrolyte by utilizing the weak solvent coordination of FMOP, thereby improving the SEI.

[0027] 2. The present application introduces FMOP to form a dense and strong SEI, and the amount of FMOP is small, which weakens the influence of side reactions on the SEI, is conducive to maintaining the stability of the SEI, and prolongs the long-term ion migration ability of the SEI.

[0028] 3. The dense and strong SEI of the present application has stable and good ion migration ability, which is conducive to improving the fast charging performance and cycle stability of lithium metal battery ion transmission. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 The principle diagram of FMOP reducing solvent coordination ability provided for Example 1 of the present application;

[0030] Figure 2 The Raman spectrum (Raman) diagram of the weak solvent coordination fast charging electrolyte and the organic electrolyte provided for Example 1 of the present application; wherein a is the Raman spectrum diagram of Raman shift 700-760 cm -1 , b is the Raman spectrum diagram of Raman shift 870-940 cm -1 ;

[0031] Figure 3 The nuclear magnetic resonance spectrum (NMR) diagram of the weak solvent coordination fast charging electrolyte and the organic electrolyte provided for Example 1 of the present application at room temperature; wherein a is the 7 Li NMR diagram, b is the 19 F NMR diagram;

[0032] Figure 4 The scanning electron microscope diagram of the Li anode after the weak solvent coordination fast charging electrolyte and the organic electrolyte provided for Example 1 of the present application are cycled for 50 cycles in a Li||Li symmetric battery; wherein a is the scanning electron microscope diagram of the Li anode of the weak solvent coordination fast charging electrolyte, and b is the scanning electron microscope diagram of the Li anode of the organic electrolyte.

[0033] Figure 5The chronometric amperometric curve of the Li||Li symmetric battery of Example 1 of the present application at a polarization voltage of 10 mV and the alternating current impedance spectrum before and after polarization (insert); wherein a is the chronometric amperometric curve of the weak solvent coordination fast-charging electrolyte and the alternating current impedance spectrum before and after polarization (insert), b is the chronometric amperometric curve of the organic electrolyte and the alternating current impedance spectrum before and after polarization (insert);

[0034] Figure 6 The cycle performance comparison chart of the fast-charging performance test of the Li||NCM811 battery of Example 1 of the present application at 5C / 5C;

[0035] Figure 7 The cycle performance comparison chart of the long cycle test of the Li||NCM811 battery of Example 1 of the present application at 1C / 1C. DETAILED DESCRIPTION

[0036] In order to make the purpose, technical scheme and advantages of the present application clearer, the technical scheme of the present application will be described in detail below. Obviously, the described embodiments are only some of the embodiments of the present application, not all. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative labor fall within the scope of the present application.

[0037] The first purpose of the present application is to provide a preparation method of a weak solvent coordination fast-charging electrolyte.

[0038] In order to achieve the first purpose of the present application, the preparation method of the weak solvent coordination fast-charging electrolyte comprises:

[0039] S1: adding 2-fluorophenyl methyl ether into an organic electrolyte to obtain a mixed solution; wherein the addition amount of 2-fluorophenyl methyl ether is 2-8 wt% of the organic electrolyte;

[0040] S2: reacting the mixed solution at 20-30℃ for at least 2h to obtain a weak solvent coordination fast-charging electrolyte.

[0041] In some examples, the organic electrolyte is a carbonate electrolyte.

[0042] In some examples, the carbonate electrolyte comprises lithium hexafluorophosphate, vinyl carbonate and diethyl carbonate.

[0043] In some examples, the concentration of lithium hexafluorophosphate in the carbonate electrolyte is 1M.

[0044] In some examples, the volume ratio of vinyl carbonate to diethyl carbonate in the carbonate electrolyte is 1:1.

[0045] In some examples, the reaction temperature of the mixed solution is 25-30℃.

[0046] In some examples, the reaction temperature of the mixed solution is 25°C.

[0047] In some examples, the amount of 2-fluoromethoxybenzene added is 4wt% of the organic electrolyte.

[0048] A second object of the present application is to provide a weak-solvent coordination fast-charging electrolyte.

[0049] The weak-solvent coordination fast-charging electrolyte is prepared according to the preparation method described above.

[0050] In some examples, the number of ion migrations of the weak-solvent coordination fast-charging electrolyte at 25°C is 0.602.

[0051] The present application provides a nickel ternary lithium metal battery, and the electrolyte of the nickel ternary lithium metal battery uses the weak-solvent coordination fast-charging electrolyte described above.

[0052] The nickel ternary lithium metal battery is a Li||NCM811 battery.

[0053] The specific embodiments of the present application are further described below in conjunction with specific examples, and the present application is not limited in the scope of the described examples.

[0054] The raw materials used in the following examples are: 2-fluoromethoxybenzene (FMOP), ethylene carbonate (EC), diethyl carbonate (DEC), lithium hexafluorophosphate (LiPF6);

[0055] Example 1

[0056] The preparation method of the weak-solvent coordination fast-charging electrolyte of the present example includes the following steps:

[0057] 1. Add LiPF6 to an EC / DEC solution with a volume ratio of 1:1 to obtain a carbonate electrolyte with a LiPF6 concentration of 1M;

[0058] 2. Add 4wt% of FMOP to 1mL of the carbonate electrolyte to obtain a mixed solution;

[0059] 3. Stir the mixed solution at 25°C for 2h to obtain a weak-solvent coordination fast-charging electrolyte.

[0060] Example 2

[0061] The weak-solvent coordination fast-charging electrolyte is prepared according to the steps of Example 1, and the only difference is that 2wt% of FMOP is added to the carbonate electrolyte.

[0062] Example 3

[0063] This embodiment prepares a weak solvent coordination fast-charging electrolyte according to the steps of Example 1, with the only difference being that 3 wt% of FMOP is added to the carbonate electrolyte.

[0064] Example 4

[0065] This embodiment prepares a weak solvent coordination fast-charging electrolyte according to the steps of Example 1, with the only difference being that 5 wt% of FMOP is added to the carbonate electrolyte.

[0066] Example 5

[0067] This embodiment prepares a weak solvent coordination fast-charging electrolyte according to the steps of Example 1, with the only difference being that 8 wt% of FMOP is added to the carbonate electrolyte.

[0068] The carbonate electrolyte of Example 1 below was used as an organic electrolyte to characterize the weak solvent coordination fast-charging electrolyte prepared in Example 1:

[0069] From the appendix Figure 1 It is evident that the addition of FMOP resulted in a weak solvent coordination pull effect, which affected Li. + The coordination environment has changed, making it more prone to forming Li + -A novel structure with tightly bound anions.

[0070] From the appendix Figure 2 As can be seen from a and b, Li + -EC interactions weakened, consistent with NMR feedback results. Furthermore, PF6 - The peak is 739.3 cm. -1 Moved to 740.4cm -1 This means that the presence of FMOP enhances the interaction between anions and cations, resulting in more Li + and PF6 - Coordination.

[0071] According to the appendix Figure 3 To analyze and evaluate Li + Solvation effect; by the attached Figure 3 (a) 7 The Li NMR spectrum shows a larger downfield shift after the addition of FMOP, indicating that the organic solvent in the organic electrolyte reacts with Li. + The interaction weakens; due to the attachment Figure 3 (b) 19 The 1F NMR spectrum shows an up-field shift after the addition of FMOP, indicating that PF6 - The surrounding electron density changes, Li + With PF6 - The coordination was enhanced.

[0072] Figure 2 shows the SEM images of the Li anode surface after 50 cycles of the Li||Li symmetric cell assembled with the weak-solvent coordination fast-charging electrolyte. Figure 4 (a) It can be seen that the Li||Li symmetric cell assembled with the weak-solvent coordination fast-charging electrolyte can form a protective SEI layer between the Li anode and the electrolyte after 50 cycles, and the Li anode surface presents a dense and flat morphology; in contrast, Figure 4 (b) It can be seen that after the cycling of the Li||Li symmetric cell assembled with the organic electrolyte, a large number of lithium dendrites appear on the Li anode surface and present a loose moss-like structure.

[0073] Figure 3 shows the SEM images of the Li anode surface after 50 cycles of the Li||Li symmetric cell assembled with the weak-solvent coordination fast-charging electrolyte. Figure 5 (a) and (b) show that FMOP significantly promotes the formation of a uniform and compact SEI layer on the Li anode surface, which effectively inhibits the growth of lithium dendrites and promotes the uniform deposition of lithium ions. + The migration efficiency in the solvation sheath exhibits excellent ion migration number characteristics, and this mechanism is particularly significant at the interface, realizing the fast desolvation process of Li + and the subsequent efficient ion migration, thereby optimizing the overall performance of the lithium metal battery.

[0074] Figure 4 shows the charge-discharge curves of the Li||NCM811 cell assembled with the weak-solvent coordination fast-charging electrolyte of Example 1 and the organic electrolyte at 25℃, 5C / 5C. Figure 6 It can be seen that the weak-solvent coordination fast-charging electrolyte prepared in Example 1 is used as the electrolyte of the lithium metal battery, matched with the NCM811 positive electrode and the Li negative electrode, to assemble the Li||NCM811 cell, and the Li||NCM811 cell with the organic electrolyte is used as the comparison, and the two kinds of cells are tested for fast-charging performance under the conditions of 25℃, 5C / 5C charge-discharge; the capacity retention rate of the weak-solvent coordination fast-charging electrolyte is 78% after 100 cycles, while that of the organic electrolyte is 43%, proving that the fast-charging performance of the battery can be significantly improved under the action of FMOP weak-solvent coordination.

[0075] Figure 5 shows the charge-discharge curves of the Li||NCM811 cell assembled with the weak-solvent coordination fast-charging electrolyte of Example 1 and the organic electrolyte at 25℃, 1C / 1C. Figure 7 It can be seen that the weak-solvent coordination fast-charging electrolyte prepared in Example 1 is used as the electrolyte of the lithium metal battery, matched with the NCM811 positive electrode and the Li negative electrode, to assemble the Li||NCM811 cell, and the Li||NCM811 cell with the organic electrolyte is used as the comparison, and the two kinds of cells are tested for long cycle under the conditions of 25℃, 1C / 1C charge-discharge; specifically, the Li||NCM811 cell equipped with the weak-solvent coordination fast-charging electrolyte can still maintain a discharge capacity of 137mAh / g after 720 cycles of the cycle test, with a capacity retention rate as high as 80%; in contrast, the Li||NCM811 cell equipped with the organic electrolyte has a discharge capacity reduced to 90mAh / g after only 240 cycles. This significant improvement is attributed to the effective optimization of the SEI layer by FMOP, which effectively inhibits the growth of lithium dendrites and promotes the uniform deposition of lithium ions.

Claims

1. A method for preparing a weak-solvent coordination fast-charging electrolyte, characterized in that, The method comprises the following steps: S1: adding 2-fluoroanisole into an organic electrolyte for a nickel ternary lithium metal battery to obtain a mixed solution; wherein the addition amount of 2-fluoroanisole is 2-8 wt% of the organic electrolyte; S2: reacting the mixed solution at 20-30℃ for at least 2h to obtain a weak solvent coordination fast-charging electrolyte; The weak solvent coordination fast-charging electrolyte has an ion migration number of 0.602 at 25℃.

2. The method of claim 1, wherein: The organic electrolyte is a carbonate electrolyte.

3. The method of claim 2, wherein: The carbonate electrolyte comprises lithium hexafluorophosphate, vinyl carbonate and diethyl carbonate.

4. The method of claim 3, wherein: The concentration of lithium hexafluorophosphate in the carbonate electrolyte is 1 M.

5. The method of claim 3, wherein: The volume ratio of vinyl carbonate to diethyl carbonate in the carbonate electrolyte is 1:

1.

6. The method of claim 1, wherein: The reaction temperature of the mixed solution is 25-30℃.

7. The method of claim 6, wherein: The reaction temperature of the mixed solution is 25℃.

8. The method of claim 1, wherein: The addition amount of 2-fluoroanisole is 4 wt% of the organic electrolyte.

9. A weak solvent coordination fast-charging electrolyte prepared by the preparation method according to any one of claims 1-8.

10. A nickel ternary lithium metal battery characterized by, A weak solvent coordination fast-charging electrolyte prepared by the preparation method according to any one of claims 1-8 or the weak solvent coordination fast-charging electrolyte according to claim 9.

11. The nickel ternary lithium metal battery of claim 10, wherein, The nickel ternary lithium metal battery is a Li||NCM811 battery.

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