Weak solvent coordination fast-charging electrolyte and preparation method thereof

Abstract

The invention relates to the technical field of lithium metal batteries, in particular to an eco-solvent coordination fast-charging electrolyte and a preparation method thereof. The preparation method of the weak solvent coordination fast charging electrolyte comprises the following steps: adding 2-fluoroanisole into an organic electrolyte to obtain a mixed solution; wherein the addition amount of the 2-fluoroanisole is 2-8wt% of the organic electrolyte; and reacting the mixed solution at 20-30 DEG C for at least 2 hours to obtain the weak solvent coordination fast charge electrolyte. The ion transference number of the weak solvent coordination fast charge electrolyte at 25 DEG C is 0.602. The FMOP with the weak solvent coordination capability promotes more anions in the organic electrolyte to participate in formation of dense and firm SE I through weak solvent coordination traction, so that growth of L dendritic crystals is inhibited, meanwhile, the FMOP has a relatively low LUMO energy level and a certain fluorine supply capability, and the generated SE I can induce uniform deposition of L .

Description

Technical Field

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

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

[0003] At present, there are two main methods for optimizing the characteristics of SEI: one is to prepare high-concentration electrolytes (HCEs), and by increasing the concentration of salts, anions are promoted to participate in the solvation process by forming contact ion pairs and aggregated ion clusters, thereby constructing anion-rich SEI. This enhances the stability of SEI in lithium metal batteries to a certain extent. 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 (LECE) in HCEs. LECE not only retains the solvation environment of HCEs, but also reduces the viscosity of the electrolyte. Nevertheless, the ether diluents with complex molecular structures used to form LHCEs are often expensive, which poses a challenge to their practical application; while the selection of ether diluents with relatively simple molecular structures and low prices can reduce the viscosity of the electrolyte, but the amount of such diluents is relatively high when preparing the electrolyte; at the same time, when using ether diluents, it is often necessary to use additives with reduced interfacial impedance, and the ether bonds contained in ether diluents are not stable, which easily introduces new side reactions to further deteriorate SEI. In addition, the lithium salt in the traditional organic electrolyte is less dissociated, resulting in Li + The low migration number limits the fast charging capability of lithium metal batteries.

[0004] Therefore, it remains challenging to develop electrolytes with the potential to form dense and strong SEIs, high ion mobility, and excellent fast charging performance.

[0005] In the prior art, CN118572193A discloses a locally weakly solvated lithium metal battery low-temperature electrolyte, and specifically discloses that the low-temperature electrolyte uses an ester-based solvent with a melting point below -70°C as a main solvent, an ether-based solvent with weak solvating ability as a secondary solvent, and is added with an inert diluent, an additive and a lithium salt; the secondary solvent uses a cyclic ether-based solvent with weak solvating ability, including one of tetrahydropyran (THP), tetrahydrofuran (THF), dimethyltetrahydropyran (MTHF), 1,4-dioxane (DOA), 1,3-dioxolane (DOL) or a plurality of them mixed in any proportion. The inert diluent includes one of fluorobenzene (FB), meta-fluorotoluene (FT), 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE), and bis(2,2,2-trifluoroethyl) ether (BTFE), or a plurality of them mixed in any proportion; the volume ratio of the ester-based solvent, the ether-based solvent, and the inert diluent in the low-temperature electrolyte is 1 to 3:1 to 3:2 to 6. The ether-based solvent can reduce the viscosity of the electrolyte and improve the ionic conductivity. The inert diluent does not dissolve the lithium salt, and can increase the local concentration of lithium ions and improve the solvation structure of lithium ions. It solves the stability of the electrolyte at low temperatures, but does not solve the effect of the side reaction of the ether-based solvent on SE I.

[0006] CN116864809A discloses a lithium ion battery electrolyte and its application, and specifically discloses at least the following components: non-aqueous solvent; lithium salt; diluent, the diluent includes fluorinated aromatic ether compounds; and additives, the additives include film-forming additives and acid and water removal additives; the mass content of the diluent in the electrolyte is 20wt%-50wt%; the fluorinated aromatic ether compounds include 2-fluoroanisole, 3-fluoroanisole, 4-fluoroanisole, 2-fluoro-p-phenylenedimethyl ether, etc.; when the fluorinated aromatic ether compounds are used as diluents, the normal temperature and high temperature cycle performance of the lithium ion battery can be improved, the high temperature storage DCR growth can be reduced, and the high temperature gas production can be reduced. However, it uses 2-fluoroanisole with a mass content of 20wt%-50wt%, and when the amount of 2-fluoroanisole is small, such as 20wt%, it is unfavorable for the high temperature storage DCR growth and the reduction of high temperature gas production, and it is difficult to suppress the influence of side reactions on SE I. Summary of the invention

[0007] In order to solve the above problems, the present invention provides a weak solvent coordinated fast-charge electrolyte and a preparation method thereof. 2-Fluoroanisole (FMOP) with weak solvent coordination ability promotes more PF6 in the organic electrolyte through weak solvent coordination traction. - The anions participate in the formation of dense and strong SE I, thereby inhibiting the growth of Li dendrites. Meanwhile, FMOP has a lower LUMO energy level and a certain fluorine supply capacity, and the generated SE I can induce the uniform deposition of Li.

[0008] The first object of the present invention is to provide a method for preparing a weak solvent coordinated fast-charging electrolyte.

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

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

[0011] S2: react the mixed solution at 20-30°C for at least 2h to obtain a weak solvent coordinated fast-charging electrolyte.

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

[0013] In a specific embodiment of the present invention, the carbonate electrolyte includes lithium hexafluorophosphate, ethylene carbonate and diethyl carbonate.

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

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

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

[0017] In one embodiment of the present invention, the reaction temperature of the mixed solution is 25°C.

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

[0019] The second object of the present invention is to provide a weak solvent coordinated fast-charging electrolyte.

[0020] In order to achieve the second object of the present invention, a weak solvent coordinated fast-charging electrolyte is prepared according to the aforementioned preparation method.

[0021] In a specific embodiment of the present invention, the ion transfer number of the weak solvent coordinated fast-charge electrolyte at 25° C. is 0.602.

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

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

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

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

[0026] 1. The present invention utilizes the weak solvent coordination effect of FMOP to improve the solvation structure of the organic electrolyte, thereby improving SEI.

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

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

[0029] Figure 1 The schematic diagram of the FMOP provided in Example 1 of the present invention for reducing the coordination ability of the solvent;

[0030] Figure 2 The Raman spectra of the weak solvent coordinated fast-charge electrolyte and the organic electrolyte provided in Example 1 of the present invention; wherein a is the Raman shift of 700-760cm -1 Raman spectrum of the graph, b is the Raman shift 870-940cm -1 Raman spectrum of

[0031] Figure 3 The nuclear magnetic resonance spectrum (NMR) of the weak solvent coordinated fast-charge electrolyte and the organic electrolyte provided in Example 1 of the present invention at room temperature; wherein a is 7 Li NMR diagram, b is 19 F NMR spectra;

[0032] Figure 4 This is a scanning electron microscope image of the Li anode of the weak solvent coordinated fast-charging electrolyte and the organic electrolyte provided in Example 1 of the present invention after 50 cycles in the Li||Li symmetric battery; wherein a is a scanning electron microscope image of the Li anode of the weak solvent coordinated fast-charging electrolyte, and b is a scanning electron microscope image of the Li anode of the organic electrolyte.

[0033] Figure 5The chronoampere curve of the Li||Li symmetric battery of Example 1 of the present invention at a polarization voltage of 10 mV and the AC impedance spectrum before and after polarization (inset); wherein, a is the chronoampere curve of the weak solvent coordinated fast charge electrolyte and the AC impedance spectrum before and after polarization (inset), and b is the chronoampere curve of the organic electrolyte and the AC impedance spectrum before and after polarization (inset);

[0034] Figure 6 This is a comparison chart of the cycle performance of the Li||NCM811 battery of Example 1 of the present invention in the fast charging performance test at 5C / 5C;

[0035] Figure 7 This is a comparison chart of the cycle performance of the Li||NCM811 battery of Example 1 of the present invention in a long cycle test at 1C / 1C. DETAILED DESCRIPTION

[0036] To make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be described in detail below. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other implementation methods obtained by ordinary technicians in this field without creative work belong to the scope of protection of the present invention.

[0037] The first object of the present invention is to provide a method for preparing a weak solvent coordinated fast-charging electrolyte.

[0038] To achieve the first object of the present invention, the preparation method of the weak solvent coordinated fast charging electrolyte comprises:

[0039] S1: adding 2-fluoroanisole to an organic electrolyte to obtain a mixed solution; wherein the amount of 2-fluoroanisole added is 2 to 8 wt % of the organic electrolyte;

[0040] S2: react the mixed solution at 20-30°C for at least 2h to obtain a weak solvent coordinated fast-charging electrolyte.

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

[0042] In some examples, the carbonate electrolyte includes lithium hexafluorophosphate, ethylene 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 ethylene 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°C.

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

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

[0048] The second object of the present invention is to provide a weak solvent coordinated fast-charging electrolyte.

[0049] The invention prepares a weak solvent coordinated fast-charging electrolyte according to the above-mentioned preparation method.

[0050] In some examples, the weak solvent coordinated fast-charge electrolyte has an ion transfer number of 0.602 at 25°C.

[0051] The present invention provides a nickel ternary lithium metal battery, wherein the electrolyte of the nickel ternary lithium metal battery uses the aforementioned weak solvent coordinated fast-charging electrolyte.

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

[0053] The specific implementation modes of the present invention are further described below in conjunction with specific embodiments, but the present invention is not limited to the scope of the embodiments.

[0054] The raw materials used in the following examples are: 2-fluoroanisole (FMOP), ethylene carbonate (EC), diethyl carbonate (DEC), lithium hexafluorophosphate (Li PF6);

[0055] Example 1

[0056] The preparation method of the weak solvent coordinated fast-charge electrolyte in this embodiment comprises the following steps:

[0057] 1. Add Li PF6 to the EC / DEC solution with a volume ratio of 1:1 to obtain a carbonate electrolyte with a Li PF6 concentration of 1 M;

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

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

[0060] Example 2

[0061] In this example, the weak solvent coordinated fast-charge electrolyte was prepared according to the steps of Example 1, with the only difference being that 2 wt % of FMOP was added to the carbonate electrolyte.

[0062] Example 3

[0063] In this example, the weak solvent coordinated fast-charge electrolyte was prepared according to the steps of Example 1, with the only difference being that 3 wt % of FMOP was added to the carbonate electrolyte.

[0064] Example 4

[0065] In this example, the weak solvent coordinated fast-charge electrolyte was prepared according to the steps of Example 1, with the only difference being that 5 wt % of FMOP was added to the carbonate electrolyte.

[0066] Example 5

[0067] In this example, the weak solvent coordinated fast-charge electrolyte was prepared according to the steps of Example 1, with the only difference being that 8 wt % of FMOP was added to the carbonate electrolyte.

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

[0069] By the attached Figure 1 It can be seen that due to the addition of FMOP, a weak solvent coordination pulling effect is produced, and Li + The coordination environment of the + -New structure in which anions are tightly bound.

[0070] By the attached Figure 2 a and b are visible, Li + -EC interaction is weakened, which is consistent with the results of NMR feedback. - Peak from 739.3cm -1 Move to 740.4cm -1 , which means that the presence of FMOP enhances the interaction between anions and cations, and more Li + and PF6 - Coordination.

[0071] According to the attached Figure 3 , in order to analyze and evaluate Li + Solvation effect; Figure 3 (a) 7 The Li NMR spectrum shows that a larger downfield shift occurs after the addition of FMOP, indicating that the organic solvent in the organic electrolyte reacts with Li + The interaction is weakened by the Figure 3 (b) 19 F NMR spectrum shows that after adding FMOP, an upfield shift occurs, indicating that PF6 - The surrounding electron density changes, Li + With PF6 - The coordination is strengthened.

[0072] By the attached Figure 4 (a) It can be seen that the Li||Li symmetric battery assembled with a weak solvent coordinated fast-charge electrolyte can form a protective SEI layer between the Li anode and the electrolyte after 50 cycles, and the surface of the Li anode presents a dense and flat morphology; on the contrary, Figure 4 (b) It can be seen that after the Li||Li symmetric battery assembled with organic electrolyte is cycled, a large number of lithium dendrites appear on the surface of the Li anode with a moss-like loose structure.

[0073] By the attached Figure 5 (a) and (b) show that FMOP significantly promotes the + The migration efficiency in the solvation sheath shows excellent ion migration number characteristics. This mechanism is particularly significant at the interface, achieving Li + The rapid desolvation process and subsequent efficient ion migration optimize the overall performance of lithium metal batteries.

[0074] By the attached Figure 6 It can be seen that the weak solvent coordinated 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 i negative electrode, and assembled into a Li||NCM811 battery. At the same time, the Li||NCM811 battery with an organic electrolyte is used as a comparison. The fast-charging performance of the two batteries is tested under the conditions of 25°C and 5C / 5C charge and discharge. The capacity retention rate of the weak solvent coordinated fast-charging electrolyte is 78% after 100 cycles, while that of the organic electrolyte is 43%, which proves that the fast-charging performance of the battery can be significantly improved under the action of FMOP weak solvent coordination.

[0075] By the attached Figure 7 It can be seen that the weak solvent coordinated fast-charge 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, and assembled into a Li||NCM811 battery. At the same time, the organic electrolyte Li||NCM811 battery is used as a comparison. The two batteries are subjected to long cycle tests under the conditions of 25°C and 1C / 1C charge and discharge; specifically, the Li||NCM811 battery equipped with a weak solvent coordinated fast-charge electrolyte can still maintain a discharge capacity of 137mAh / g after 720 cycle tests, and its capacity retention rate is as high as 80%; in contrast, the discharge capacity of the Li||NCM811 battery equipped with an organic electrolyte has dropped 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 coordinated fast-charging electrolyte, characterized in that: The following steps are involved: S1: adding 2-fluoroanisole to an organic electrolyte to obtain a mixed solution; wherein the amount of 2-fluoroanisole added is 2 to 8 wt % of the organic electrolyte; S2: react the mixed solution at 20-30°C for at least 2h to obtain a weak solvent coordinated fast-charging electrolyte.

2. The preparation method according to claim 1, characterized in that: The organic electrolyte is a carbonate electrolyte.

3. The preparation method according to claim 1, characterized in that: The carbonate electrolyte includes lithium hexafluorophosphate, ethylene carbonate and diethyl carbonate.

4. The preparation method according to claim 1, characterized in that: The concentration of lithium hexafluorophosphate in the carbonate electrolyte is 1M.

5. The preparation method according to claim 1, characterized in that: The volume ratio of ethylene carbonate to diethyl carbonate in the carbonate electrolyte is 1:

1.

6. The preparation method according to claim 1, characterized in that: The reaction temperature of the mixed solution is 25-30°C; preferably, the reaction temperature of the mixed solution is 25°C.

7. The preparation method according to claim 1, characterized in that: The added amount of 2-fluoroanisole is 4 wt % of the organic electrolyte.

8. A weak solvent coordinated fast-charging electrolyte prepared according to the preparation method according to any one of claims 1 to 7.

9. The weak solvent coordinated fast-charging electrolyte according to claim 8, characterized in that: The ion transfer number of the weak solvent coordinated fast-charge electrolyte at 25° C. is 0.

602.

10. Nickel ternary lithium metal battery, characterized in that: A weak solvent coordinated fast-charging electrolyte prepared by the preparation method described in any one of claims 1 to 7 or a weak solvent coordinated fast-charging electrolyte described in claim 8 or 9; preferably, the nickel ternary lithium metal battery is a Li||NCM811 battery.

Images