Method for preparing electrolyte precursor through fluorine anion exchange and application of electrolyte precursor in solid electrolyte

Abstract

The invention discloses a method for preparing an electrolyte precursor through fluorine anion exchange and application of the electrolyte precursor in a solid electrolyte. MXa and LiF are used as raw materials, a mixed product of fluoride and a nano LiX phase is generated in situ through mechanical mixing, the fluoride is Li MF type or MF type, and the mixed product is a solid electrolyte precursor; x in MXa is Cl, Br or I, and a is 2, 3, 4 or 5. The solid electrolyte composite precursor is prepared by utilizing a fluorine anion exchange method, and the high-performance halide or sulfide solid electrolyte is prepared by utilizing the complementary synergistic effect of a nano LiX phase and fluoride in the precursor and is applied to an all-solid lithium ion battery. The preparation method disclosed by the invention is simple in preparation process and high in repeatability, and is favorable for preparing a high-performance solid electrolyte material which is high in stability to lithium metal, wide in electrochemical window and high in ionic conductivity.

Description

Technical Field

[0001] This invention relates to the field of solid electrolyte materials technology for lithium-ion batteries, specifically to a method for preparing electrolyte precursors by fluoride anion exchange and its application in solid electrolytes. Background Technology

[0002] Against the backdrop of global transportation electrification, the problems of traditional liquid lithium-ion batteries, such as flammability, explosiveness, easy leakage, strong corrosivity, and low energy density, restrict the safety and range of battery applications.

[0003] With the development and advancement of modern technology, all-solid-state lithium-ion batteries (ASSLBs) have become a key research focus in the energy field and a focus of social attention due to their high safety, high energy density, and wide operating temperature range. They are also expected to contribute to carbon neutrality and peak carbon emissions in the future. Solid-state batteries refer to the technological route of electrolyte development from liquid to solid state, making the application of higher energy density material systems possible.

[0004] Among solid electrolytes (SEs), halide electrolytes offer advantages such as a wide electrochemical window, excellent air stability, and low Young's modulus; sulfide solid electrolytes possess conductivity comparable to liquid electrolytes, and exhibit advantages such as non-oxidation at high temperatures (60°C) and non-solidification at low temperatures, enabling sulfide-based all-solid-state lithium batteries to combine high energy density and high rate performance. However, the interfacial stability between halide electrolytes and the negative electrode Li, their low oxidation potential, and the low oxidation potential and poor air stability of sulfides have become pain points limiting the development of solid electrolytes and challenges for researchers.

[0005] The oxidation potentials of chloride electrolytes are generally around 4.1V, making it difficult to maintain long-cycle stability when matched with high-voltage active materials. Previous articles have used density functional theory (DFT) to calculate the theoretical electrochemical windows of a series of promising Li3MX6 (M = Ga, Y, Sc, In, etc.; X = F, Cl, Br) halide electrolytes. Among them, Li3MF6 exhibits the widest electrochemical window, with an oxidation potential exceeding 6.36V and a reduction potential below 2.5V. In contrast, the widely used and technologically mature Li3InCl6 electrolyte has an electrochemical window of 2.42-4.37V, which is narrower than that of Li3MF6 electrolytes. This indicates that Li3MF6 electrolytes possess superior antioxidant capacity and deserve further research and application (ACS Energy Lett. 2021, 6, 2006-2015). Experiments have also confirmed the significance of F doping in broadening the electrochemical window. In Priya Ganesan's experiments, the oxidation potential of Li₂ZrCl₆ was 3.9 V, while after doping with trace amounts of F, the oxidation potential of Li₂ZrCl₆ increased. 5.5 F0.5 The oxidation potential increased to 4.1 V, and the reaction current decreased significantly, indicating a reduction in reaction intensity (ACS Appl. Mater. Interfaces 2023, 15, 38391-38402). Kim et al. verified the formation of Li x The MF6 phase can significantly increase the oxidation potential (nearly 2 V higher than Li2MCl6-αFα), and calculations have verified that the mixing limit of F doping in Li3MCl6 is between 0.5 and 1.5 (ACS Energy Lett. 2024, 9, 38-47). In summary, if there were a method to directly obtain Li... x The MF6 phase will greatly broaden the electrochemical window of the electrolyte.

[0006] Li₂MCl₆ (M = metals such as Zr, Y, and In) has poor stability with Li, making it unsuitable as a single electrolyte layer in lithium-ion batteries for long-term cycling. To address this issue, two popular approaches exist: 1) using sulfides (e.g., Li₆PS₅Cl) as a buffer layer to separate the Li₂MCl₆ electrolyte from the Li anode, and then using a Li-In alloy anode to fabricate the battery; 2) doping the Li₂MCl₆ electrolyte with F. Furthermore, one study has demonstrated that a dual-halogen strategy can enhance the Li₂MCl₆ electrolyte's stability. 6-α F α (0≤α≤1.2) improves the stability of Li and enhances its reduction stability (ACS Appl. Mater. Interfaces 2023, 15, 38391-38402). Li₂MCl contains... 6-α F α In lithium-ion batteries with electrolytes, after a certain period of electrochemical cycling, an interface layer combining Li-F and MF phases forms on the negative electrode side (Chemical Engineering Journal, 465, 2023, 143036). This interface layer has a high Young's modulus and forms a dense and robust interface layer in situ at the interface after cycling, effectively suppressing the growth of lithium dendrites and significantly improving the stability of the electrolyte for Li and the interface itself. Conversely, an interface layer composed of Li-Cl and M-Cl phases after electrochemical cycling lacks the ability to suppress interfacial reactions in a short time, and the accumulation of products leads to a surge in interfacial impedance, which is detrimental to Li. + The migration of these molecules leads to a decrease in ionic conductivity.

[0007] Literature has experimentally verified that doping Li₃MCl₆ electrolyte with F leads to a decrease in ionic conductivity, and the higher the doping concentration, the lower the ionic conductivity of Li₂MCl₆. 6-α F α For Li +The more significant the diffusion barrier effect, the greater the decrease in ionic conductivity (ACS Appl. Mater. Interfaces 2023, 15, 38391-38402).

[0008] Therefore, we urgently need a method to broaden the electrochemical window of the electrolyte to match high-voltage active materials, enabling the battery to cycle stably for a long time; to improve the drawbacks of the instability of halide electrolytes to the Li anode and extend the life of lithium batteries; and to reduce the problem of decreased ionic conductivity caused by strong ionic bonding of fluorides and enhance lithium-ion transport capacity. Summary of the Invention

[0009] Based on the above research results and in accordance with various needs for improving electrolyte performance, this invention provides a method for preparing electrolyte precursors by fluoride anion exchange and its application in solid electrolytes.

[0010] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0011] This invention first provides a method for preparing solid electrolyte precursors via fluoride anion exchange, using MX a Using (a=2,3,4,5,X=Cl,Br,I) and LiF as raw materials, a large amount of fluoride (LiMF or MF) and amorphous nano-LiX phase mixed products are generated in situ through mechanical ball milling. This molecular or even atomic level mixed product can broaden the electrochemical window of the electrolyte, improve the interfacial stability of the Li anode, and serve as a precursor for preparing high-dose fluorinated high-performance halide, sulfide and other fast ion conductor electrolyte composite materials. Moreover, the formation products of most systems are nano-amorphous phases.

[0012] Fluoride anion exchange, i.e., MX a +LiF→LiMF+LiX (nanophase)

[0013] Or: MX a +LiF→MF+LiX (nanophase)

[0014] The generated fluorides include two types: LiMF type and MF type, where MF includes LaF3 and SmF3; L i The MF type includes several forms:

[0015] When a = 2, the generated fluorides (LiMF) are LiMF3 and Li2MF4, where LiMF3 includes LiCaF3; and Li2MF4 includes Li2MgF4, Li2NiF4, Li2CuF4, Li2ZnF4, Li2SrF4, and Li2BaF4.

[0016] When a = 3, the generated fluoride (Li MF) are LiMF4 and Li3MF6, wherein LiMF4 includes LiBiF4, LiLuF4, LiYF4, LiYbF4, LiTmF4, LiErF4, LiDyF4, LiGdF4, LiScF4, LiMnF4, and LiCoF4; and Li3MF6 includes Li3AlF6, Li3GaF6, Li3InF6, Li3TlF6, Li3CrF6, Li3FeF6, Li3VF6, Li3MoF6, and Li3SbF6.

[0017] When a = 4, the generated fluorides (LiMF) are LiMF5, Li2MF6, and Li4MF8. Among them, LiMF5 includes LiSnF5 and LiCeF5; Li2MF6 includes Li2TiF6, Li2ZrF6, Li2GeF6, Li2PbF6, and Li2WF6; and Li4MF8 includes Li4HfF8.

[0018] When a = 5, the generated fluoride (LiMF) is LiMF6, including LiNbF6 and LiTaF6.

[0019] The raw material MX a It includes four types: MX2, MX3, MX4, and MX5.

[0020] MX2 includes MgX2, CaX2, NiX2, CuX2, ZnX2, SrX2, and BaX2;

[0021] MX3 includes AlX3, CrX3, FeX3, LuX3, YbX3, TmX3, ErX3, DyX3, GdX3, ScX3, GaX3, YX3, CoX3, InX3, SbX3, TlX3, MoX3, VX3, BiX3, LaX3, SmX3, and MnX3;

[0022] MX4 includes TiX4, ZrX4, GeX4, SnX4, HfX4, CeX4, PbX4, and WX4;

[0023] MX5 includes NbX5 and Tax5.

[0024] Furthermore, the specific steps of the method for preparing solid electrolyte precursors by fluoride anion exchange are as follows: The raw material MX... aThe powder was first manually mixed in a mortar for 4–10 minutes as a preliminary mixing process with LiF at a specific molar ratio. Then, the powder was poured into the grinding jar of a ball mill, which was sealed with Ar gas and subjected to multiple ball milling processes. Pre-mixing ball milling was performed first, followed by formal ball milling. Because the ball milling energy required to synthesize LiMF products varies depending on the different substances mixed, there are certain differences in the ball milling time and rotation speed.

[0025] The premixing ball milling time is 0.5–1.5 hours, and the premixing ball milling speed is 80–120 rpm. The purpose of premixing is to ensure that the two components are thoroughly and uniformly mixed at a low speed.

[0026] The formal ball milling mixing time is 1–24 hours, and the formal ball milling mixing speed is 300–900 rpm. The purpose of the formal ball milling mixing is to allow the components to undergo sufficient fluoride anion exchange through high-speed ball milling, in order to prepare a high-performance solid electrolyte precursor.

[0027] If the precursor generates LiMF-type fluorides, there are various starting materials and molar ratios:

[0028] When a = 2, if LiMF3 is generated, then MX2:LiF = 1:3; if Li2MF4 is generated, then MX2:LiF = 1:4.

[0029] When a = 3, if LiMF4 is generated, then MX3:LiF = 1:4; if Li3MF6 is generated, then MX3:LiF = 1:6.

[0030] When a = 4, if LiMF5 is generated, then MX4:LiF = 1:5; if Li2MF6 is generated, then MX4:LiF = 1:6; if Li4MF8 is generated, then MX4:LiF = 1:8.

[0031] When a = 5, if LiMF6 is generated, then MX5:LiF = 1:6.

[0032] If the precursor generates an MF-type (MF3) fluoride, the starting materials and their molar ratios are as follows:

[0033] MX3:LiF = 1:3.

[0034] Furthermore, the method for preparing solid electrolyte precursors via fluoride anion exchange can be applied to the preparation of solid electrolytes. Specifically, LiMF+LiX or MF+LiX generated by the above method can be used as raw materials to prepare sulfide or halide solid electrolytes with LiX as a precursor, including but not limited to lithium sulfide-germanium ore type Li6PS5X, LGPS type Li 9.54 Si 1.74 P 1.44 S11.7 Cl 0.3 UCl3 type Li 0.388 Ta 0.238 La 0.475 Solid electrolyte materials such as Cl3 and LiTaCl6 have been reported.

[0035] This invention utilizes a fluoride anion exchange method to prepare a solid electrolyte composite precursor. By leveraging the complementary synergistic effect of the nano-LiX phase and fluorides in the precursor, high-performance composite materials (halide and sulfide solid electrolytes) are prepared and applied in all-solid-state lithium-ion batteries. The preparation process of this invention is simple and highly reproducible, which is beneficial for preparing a high-performance solid electrolyte material with high stability to lithium metal, a wide electrochemical window, and high ionic conductivity. The beneficial effects of this invention are as follows:

[0036] The presence of fluoride electrolyte (LiMF) components in halide electrolytes offers several advantages. First, the strong ionic bonding between Li-F and MF enhances the stability between the electrolyte and the Li anode, partially addressing the instability issue between halide electrolytes and Li. Directly mechanically mixing LiMF and LiX is time-consuming and resource-intensive, as the fluorine anion exchange method described in this paper allows for in-situ generation of a mixture of LiMF and LiX, achieving high homogeneity at the molecular and even atomic levels. Second, the addition of fluorides increases the electrolyte's stability to air, enhancing the battery's practical application value. Third, the electrochemical window (especially the oxidation potential) of fluoride electrolytes is much wider than that of other halide electrolytes, allowing for better matching with high-voltage active materials and meeting the long-cycle stability requirements of batteries, thus increasing the practical application value of halide electrolytes in solid-state batteries. Furthermore, the presence of the LiX nanophase in the electrolyte increases lithium-ion transport capacity, thereby improving ionic conductivity.

[0037] The innovation of this invention lies in its departure from traditional fluorine doping schemes. It creatively utilizes the exchange of fluorine anions with other halide anions to generate uniformly distributed, nano-phase LiMF and LiX through in-situ molecular-level reactions. These are then used as precursors (intermediates), with the nano-phase LiX accelerating the chemical reaction rate and improving material preparation efficiency. This results in the preparation of halide or sulfide-type lithium-ion solid composite electrolytes with high ionic conductivity. Furthermore, the products in most systems are nano-amorphous phases, compensating for the decrease in ionic conductivity caused by the strong Li-F ionic bond interaction in LiMF. Simultaneously, the LiMF generated in situ alongside LiX broadens the electrochemical window of the composite electrolyte, increasing its stability to Li and air stability. LiX and LiMF form a complementary synergistic effect in the composite electrolyte, significantly improving the overall performance of the material. Attached Figure Description

[0038] Figure 1 The electrochemical impedance spectroscopy (EIS) of the composite LiYF4 precursor electrolyte is shown.

[0039] Figure 2 The image shows the DC polarization curve of the composite LiYF4 precursor electrolyte.

[0040] Figure 3 The image shows the X-ray diffraction (XRD) pattern of the composite LiYF4 precursor electrolyte.

[0041] Figure 4 It is the electrochemical impedance spectroscopy (EIS) of a halide complex electrolyte.

[0042] Figure 5 These are the DC polarization curves of the halide complex electrolyte.

[0043] Figure 6 It is the X-ray diffraction pattern (XRD) of the halide complex electrolyte.

[0044] Figure 7 This is the electrochemical impedance spectroscopy (EIS) of the composite Li₂ZrF₆ precursor electrolyte.

[0045] Figure 8 These are the DC polarization curves of the composite Li2ZrF6 precursor electrolyte.

[0046] Figure 9 The image shows the X-ray diffraction (XRD) pattern of the composite Li2ZrF6 precursor electrolyte.

[0047] Figure 10 It is the electrochemical impedance spectroscopy (EIS) of a sulfide complex electrolyte.

[0048] Figure 11 This is the DC polarization curve of the sulfide complex electrolyte.

[0049] Figure 12 These are test curves for lithium-ion symmetric batteries.

[0050] Figure 13 The electrochemical impedance spectroscopy (EIS) of the composite Li₂TiF₆ precursor electrolyte is shown.

[0051] Figure 14 The image shows the DC polarization curves of the composite Li2TiF6 precursor electrolyte.

[0052] Figure 15 This is a transmission electron microscope (TEM) image of the composite Li2TiF6 precursor electrolyte.

[0053] Figure 16 The image shows the X-ray diffraction (XRD) pattern of the composite Li2TiF6 precursor electrolyte.

[0054] Figure 17 The electrochemical impedance spectroscopy (EIS) of the Li3AlF6 precursor electrolyte is shown.

[0055] Figure 18 These are the DC polarization curves of the composite Li3AlF6 precursor electrolyte.

[0056] Figure 19 The image shows the X-ray diffraction (XRD) pattern of the composite Li3AlF6 precursor electrolyte. Detailed Implementation

[0057] Example 1: Composite Halogen Electrolyte

[0058] (1) Preparation of composite LiYF4 precursor electrolyte by fluorine anion exchange

[0059] YCl3 powder (purity: 99.99%) and LiF powder (purity: 99.99%) were weighed and mixed in an argon-filled glove box at a molar ratio of YCl3:LiF = 1:4. The mixture was manually mixed in a mortar for 5 minutes. Then, under inert gas protection, the raw materials were transferred to a 50 ml ZrO2 ball milling jar, and 16 ZrO2 balls with a diameter of 10 mm were added for ball milling. Premixing was first performed at a low speed of 120 rpm for 1 hour, followed by ball milling at 500 rpm for 3 hours. All ball milling processes were conducted under the protection of high-purity argon (99.999%). One hour after each ball milling, the jar was opened in the glove box, and the powder on the inner wall was manually mixed with the powder at the bottom to ensure greater uniformity. The final product was a composite precursor of LiYF4 and LiCl, hereinafter referred to as the composite LiYF4 precursor electrolyte.

[0060] Electrochemical impedance spectroscopy, DC polarization curves, and electrochemical windows were tested using a battery testing system.

[0061] Electrochemical impedance spectroscopy and DC polarization curve testing: Weigh 100 mg of composite LiYF4 precursor electrolyte powder and place it in... In the ceramic mold, a piece is attached to each of the two sides. The iron sheet was tested.

[0062] To test the electrochemical window, 50 mg of Li6PS5Cl sulfide electrolyte and 50 mg of composite LiYF4 precursor electrolyte were weighed and placed as a bilayer electrolyte layer. The composite LiYF4 precursor electrolyte powder was placed in a ceramic mold and mixed with 10 wt% C in a mortar to obtain a mixed powder. Then, 12 mg of the mixed powder was weighed and placed on the electrolyte side of the composite LiYF4 precursor electrolyte powder, and a Li sheet was placed on the Li6PS5Cl sulfide side. The whole assembly was pressed into a battery for testing.

[0063] Electrochemical impedance spectroscopy (EIS) of the composite LiYF4 precursor electrolyte is as follows: Figure 1 As shown, the impedance is 202 kΩ, and the calculated ionic conductivity of the electrolyte is 1.90 × 10⁻⁶ kΩ. -7 S·cm -1 ;Depend on Figure 2 The DC polarization curve shows that the steady-state current value is 2.68 × 10⁻⁶. -7 A. The calculated electronic conductivity of the electrolyte is 3.47 × 10⁻⁶. -8 S·cm -1 According to calculations from the literature, the electrochemical window is approximately 0.43V-6.33V (ACS Energy Lett. 2024, 9, 38-47).

[0064] The composite LiYF4 precursor sample powder was sealed with a polyimide film and then subjected to X-ray diffraction (XRD) testing using Ultima IV (40 kV, 40 mA, Cu Kα). The test range is 10–70°, and the speed is 3° / min. Figure 3 The XRD pattern shows that the diffraction peaks only contain LiYF4 and LiCl phases, without any impurity peaks, which indicates that the fluoride anions are fully exchanged.

[0065] (2) Synthetic halide complex electrolytes

[0066] Halide composite electrolytes were further synthesized using composite LiYF4 precursor electrolyte powder:

[0067] The composite LiYF4 precursor electrolyte powder, YCl3 powder (purity: 99.99%), and ZrCl4 powder (purity: 99.99%) were weighed and prepared in a glove box filled with argon gas according to a specific molar ratio. The molar ratio was determined by the following formula:

[0068] The reaction equation for the composite precursor electrolyte is: YCl3 + 4LiF = LiYF4 + 3LiCl;

[0069] The reaction equation for the preparation of halide composite electrolytes is: 5LiCl + YCl3 + ZrCl4 = Li3YCl6 + Li2ZrCl6, where LiCl comes from the LiCl nanophase in the composite LiYF4 precursor electrolyte powder;

[0070] Therefore, the molar ratio LiCl:YCl3:ZrCl4 = 5:1:1;

[0071] The raw materials were transferred to a 100ml ZrO2 ball milling jar in an inert gas-protected glove box, and 10 ZrO2 balls with a diameter of 10mm were added for ball milling. The ball milling process began with a low speed of 100 rpm for premixing for 1 hour, followed by a speed of 250 rpm for 6 hours. All ball milling was conducted under the protection of high-purity argon (99.999%). Every 2 hours, the jar was opened in the glove box, and the powder on the inner wall was manually mixed with the powder at the bottom to ensure greater uniformity. The final product was a halide composite electrolyte.

[0072] Electrochemical impedance spectroscopy (EIS) and DC polarization curves were tested using a battery testing system. For EIS and DC polarization curve testing: 100 mg of halide composite electrolyte powder was weighed and placed in… In the ceramic mold, a piece is attached to each of the two sides. The iron sheet was tested. The electrochemical impedance spectroscopy (EIS) of the halide complex electrolyte is as follows: Figure 4 As shown, the impedance is 49Ω, and the calculated ionic conductivity of the electrolyte is 1.46 × 10⁻⁶. -3 S·cm -1 ;Depend on Figure 5 The DC polarization curve shows that the steady-state current value is 3.26 × 10⁻⁶. -8 A. The calculated electronic conductivity of the electrolyte is 4.65 × 10⁻⁶. -9 S·cm -1 .

[0073] The halide composite electrolyte sample powder was sealed with a polyimide film and then subjected to X-ray diffraction (XRD) testing using Ultima IV (40 kV, 40 mA, Cu Kα). The test range is 10–70°, and the speed is 3° / min. Figure 6 The XRD pattern shows that the diffraction peaks contain LiYF4 and LiCl phases, and the content of LiCl is reduced compared to the precursor, indicating that the nano LiCl phase reacts with the YCl3 and ZrCl4 raw materials.

[0074] The above results demonstrate that using the synthesized precursor to further synthesize halide electrolytes can significantly increase the ionic conductivity of the halide electrolytes by more than four orders of magnitude. This is because the nanophase LiCl promotes the chemical reaction rate, improves the material preparation efficiency, and effectively compensates for the decrease in ionic conductivity caused by the strong Li-F ionic bond interaction in the composite LiYF4 precursor, resulting in a substantial increase in ionic conductivity. Simultaneously, the LiYF4 generated in situ with LiCl, due to the presence of fluoride, broadens the electrochemical window of the composite electrolyte to some extent, increasing its stability to Li and air stability, ensuring long-cycle stability compatible with high-voltage active materials. LiCl and LiYF4 complement each other and play a synergistic role in the formation of the composite electrolyte, significantly improving the overall performance of the material. This proves that the composite properties of the precursor electrolyte have a significant impact on subsequent preparation.

[0075] Example 2: Composite Sulfide Electrolyte

[0076] (1) Preparation of composite Li2ZrF6 precursor electrolyte by fluorine anion exchange

[0077] ZrCl4 powder (purity: 99.99%) and LiF powder (purity: 99.99%) were weighed and mixed in an argon-filled glove box at a molar ratio of ZrCl4:LiF = 1:6. The mixture was manually mixed in a mortar for 5 minutes. Then, under inert gas protection, the raw materials were transferred to a 50ml ZrO2 ball milling jar, and 10 ZrO2 balls (10mm in diameter) were added for ball milling. Pre-mixing was first performed at a low speed of 80 rpm for 1 hour, followed by ball milling at 300 rpm for 24 hours. The entire ball milling process was conducted under high-purity argon (99.999%) protection. Every 1-4 hours during ball milling, the jar was opened in the glove box, and the powder on the inner wall was manually mixed with the powder at the bottom to ensure greater uniformity. The final product is a composite precursor of Li2ZrF6 and LiCl, hereinafter referred to as the composite Li2ZrF6 precursor electrolyte.

[0078] Electrochemical impedance spectroscopy, DC polarization curves, and electrochemical windows were tested using a battery testing system. For testing electrochemical impedance spectroscopy and DC polarization curves, 100 mg of composite Li₂ZrF₆ precursor electrolyte powder was weighed and placed in… In the ceramic mold, a piece is attached to each of the two sides. The iron sheet was tested. To test the electrochemical window, 50 mg of Li6PS5Cl sulfide electrolyte and 50 mg of composite Li2ZrF6 precursor electrolyte were weighed and placed as a bilayer electrolyte layer. The composite Li2ZrF6 precursor electrolyte powder was mixed with 10wt% C in a mortar to obtain a mixed powder. Then, 12mg of the mixed powder was weighed and placed on the Li2ZrF6 precursor electrolyte side, and a Li sheet was placed on the Li6PS5Cl sulfide side. The whole assembly was pressed into a battery for testing.

[0079] Electrochemical impedance spectroscopy (EIS) of the composite Li₂ZrF₆ precursor electrolyte is as follows: Figure 7 As shown, the impedance is 356 kΩ, and the calculated ionic conductivity of the electrolyte is 1.10 × 10⁻⁶ kΩ. -7 S·cm -1 ;Depend on Figure 8 The DC polarization curve shows that the steady-state current value is 1.30 × 10⁻⁶. -7 A. The calculated electronic conductivity of the electrolyte is 1.39 × 10⁻⁶. -8 S·cm -1 According to calculations from the literature, the electrochemical window is approximately 1.4–6.6 V (Chem. Mater. 2016, 28, 1, 266–273).

[0080] The composite Li₂ZrF₆ precursor electrolyte sample powder was sealed with a polyimide film and then subjected to X-ray diffraction (XRD) analysis. The XRD was performed using Ultima IV (40 kV, 40 mA, Cu Kα). The test range is 10–70°, and the speed is 3° / min. Figure 9 The XRD pattern shows that the diffraction peaks only contain the Li2ZrF6 and LiCl phases, without any impurity peaks, which indicates that the fluoride anions are fully exchanged.

[0081] (2) Synthetic sulfide complex electrolyte

[0082] Sulfide complex electrolytes were further synthesized using precursor electrolyte powders.

[0083] The composite Li₂ZrF₆ precursor electrolyte powder, P₂S₅ powder (purity: 99.99%), and Li₂S powder (purity: 99.99%) were weighed and prepared in a glove box filled with argon gas according to a specific molar ratio. The molar ratio was determined by the following formula:

[0084] The reaction equation for the composite precursor electrolyte is: ZrCl₄ + 6LiF = Li₂ZrF₆ + 4LiCl;

[0085] The reaction equation for the preparation of sulfide composite electrolyte is: 2LiCl + P2S5 + 5Li2S = 2Li6PS5Cl6, where LiCl comes from the LiCl nanophase in the composite Li2ZrF6 precursor electrolyte powder.

[0086] Therefore, the molar ratio LiCl:P2S5:Li2S = 2:1:5;

[0087] The raw materials were transferred to a 50ml WC ball milling jar in an inert gas-protected glove box, and 10 WC balls with a diameter of 10mm were added for ball milling. The ball milling process began with a low speed of 100 rpm for premixing for 1 hour, followed by a speed of 550 rpm for 16 hours. All ball milling was conducted under the protection of high-purity argon (99.999%). Every hour during ball milling, the jar was opened in the glove box, and the powder on the inner wall was manually mixed with the powder at the bottom to ensure greater uniformity. The final product was a sulfide composite electrolyte.

[0088] Electrochemical impedance spectroscopy, DC polarization curves, and electrochemical windows were tested using a battery testing system. 100 mg of sulfide composite electrolyte powder was weighed and placed in... In the ceramic mold, a piece is attached to each of the two sides. The iron sheet was tested. The electrochemical impedance spectroscopy (EIS) of the sulfide complex electrolyte was as follows: Figure 10 As shown, the impedance is 15.6Ω, and the calculated ionic conductivity of the electrolyte is 5.06 × 10⁻⁶. -3 S·cm -1 ;Depend on Figure 11 The DC polarization curve shows that the steady-state current value is 3.44 × 10⁻⁶. -8 A. The calculated electronic conductivity of the electrolyte is 5.43 × 10⁻⁶. -9 S·cm -1 .

[0089] Figure 12 The image shown is of a lithium-ion symmetric battery with a capacity of 1 mA / cm. 2 Lithium deposition / stripping voltage curves at current density. The pristine Li solid-state lithium symmetric cell exhibited stable voltage curves over 100 h. Although the overpotential increased slightly during cycling, no significant cell short circuit was observed, demonstrating the electrolyte's stability to Li.

[0090] Example 3 Composite Li2TiF6 precursor electrolyte

[0091] TiCl4 powder (purity: 99.99%) and LiF powder (purity: 99.99%) were weighed and mixed in an argon-filled glove box at a molar ratio of TiCl4:LiF = 1:6. The mixture was manually mixed in a mortar for 5 minutes. Then, under inert gas protection, the raw materials were transferred to a 50ml ZrO2 ball mill jar, and eight 10mm diameter ZrO2 balls were added for ball milling. Pre-mixing was first performed at a low speed of 100 rpm for 0.5 hours, followed by ball milling at 900 rpm for 1 hour. All ball milling was conducted under high-purity argon (99.999%) protection. Every 0.5 hours, the jar was opened in the glove box, and the powder on the inner wall was manually mixed with the powder at the bottom to ensure greater uniformity. The final product is a composite precursor of Li2TiF6 and LiCl, hereinafter referred to as the composite Li2TiF6 precursor electrolyte.

[0092] Electrochemical impedance spectroscopy, DC polarization curves, and electrochemical windows were tested using a battery testing system. For testing electrochemical impedance spectroscopy and DC polarization curves, 100 mg of composite Li₂TiF₆ precursor electrolyte powder was weighed and placed in… In the ceramic mold, a piece is attached to each of the two sides. The iron sheet was tested. To test the electrochemical window, 50 mg of Li6PS5Cl sulfide electrolyte and 50 mg of composite Li2TiF6 precursor electrolyte were weighed and placed as a bilayer electrolyte. The electrolyte powder to be tested was mixed with 10 wt% C in a mortar to obtain a mixed powder. Then, 12 mg of the mixed powder was weighed and placed on the side of the composite Li2TiF6 precursor electrolyte, and a Li sheet was placed on the side of the Li6PS5Cl sulfide. The whole assembly was pressed into a battery for testing.

[0093] Electrochemical impedance spectroscopy (EIS) of the composite Li₂TiF₆ precursor electrolyte is as follows: Figure 13 As shown, the impedance is 237Ω, and the calculated ionic conductivity of the electrolyte is 1.61 × 10⁻⁶. -7 S·cm -1 ;Depend on Figure 14 The DC polarization curve shows that the steady-state current value is 1.59 × 10⁻⁶. -8 A, the electronic conductivity of the electrolyte is calculated to be 1×10⁻⁶. -9 S·cm -1 According to calculations from the literature, the electrochemical window is approximately 1.05-6.49 V (Angew. Chem. Int. Ed. 2019, 58, 8039-8043).

[0094] High-resolution electron microscopy (HRTEM) images were captured using a 300 kV environmental electron microscope (ETEM, Titan G2 from Thamesfield Scientific). Composite Li₂TiF₆ precursor electrolyte powder was dispersed on copper mesh, which was then transferred to an argon-filled glove box and placed on a cryo-electron microscope support. The support was rapidly inserted into the electron microscope chamber via a sealed transfer module, and liquid nitrogen was poured into the cryo-electron microscope until the sample temperature dropped below -170°C before testing. Figure 15 The HRTEM image shows that the entire precursor powder is amorphous, and the peripheral LiCl particles have a nanoscale size, which confirms the existence of the LiCl nanophase.

[0095] The composite Li₂TiF₆ precursor electrolyte sample powder was sealed with a polyimide film and then subjected to X-ray diffraction (XRD) analysis using Ultima IV (40 kV, 40 mA, Cu Kα). The test range is 15–70°, and the rate is 3° / min. From Figure 16 The XRD pattern shows that the diffraction peaks only contain Li2TiF6 and LiCl phases, without any impurity peaks. This indicates that the fluoride anions are fully exchanged. Furthermore, the full width at half maximum (FWHM) of LiCl shows a significant broadening, proving that the LiCl particles are very small. This is consistent with the results of transmission electron microscopy, indicating that LiCl exhibits a nano-amorphous state in the composite precursor electrolyte.

[0096] Example 4: Composite Li3AlF6 precursor electrolyte

[0097] AlCl3 powder (purity: 99.99%) and LiF powder (purity: 99.99%) were weighed and mixed in an argon-filled glove box at a molar ratio of AlCl3:LiF = 1:6. The mixture was manually mixed in a mortar for 5 minutes. Then, under inert gas protection, the raw materials were transferred to a 50ml ZrO2 ball milling jar, and 12 ZrO2 balls with a diameter of 10mm were added for ball milling. Pre-mixing was first performed at a low speed of 80 rpm for 1.5 hours, followed by ball milling at 450 rpm for 16 hours. All ball milling was conducted under high-purity argon (99.999%) protection. Every 1-4 hours during ball milling, the jar was opened in the glove box, and the powder on the inner wall was manually mixed with the powder at the bottom to ensure greater uniformity. The final product is a composite precursor of Li3AlF6 and LiCl, hereinafter referred to as the composite Li3AlF6 precursor electrolyte.

[0098] Electrochemical impedance spectroscopy, DC polarization curves, and electrochemical windows were tested using a battery testing system. For testing electrochemical impedance spectroscopy and DC polarization curves, 100 mg of composite Li3AlF6 precursor electrolyte powder was weighed and placed in… In the ceramic mold, a piece is attached to each of the two sides. The iron sheet was tested. To test the electrochemical window, 50 mg of Li6PS5Cl sulfide electrolyte and 50 mg of composite Li3AlF6 precursor electrolyte were weighed and placed as a bilayer electrolyte layer. The electrolyte powder to be tested was mixed with 10 wt% C in a mortar to obtain a mixed powder. Then, 12 mg of the mixed powder was weighed and placed on the side of the composite Li3AlF6 precursor electrolyte, and a Li sheet was placed on the side of the Li6PS5Cl sulfide. The whole assembly was pressed into a battery for testing.

[0099] Electrochemical impedance spectroscopy (EIS) of the composite Li3AlF6 precursor electrolyte is as follows: Figure 17 As shown, the impedance is 82kΩ, and the calculated ionic conductivity of the electrolyte is 4.74 × 10⁻⁶. -7 S·cm -1 ;Depend on Figure 18 The DC polarization curve shows that the steady-state current value is 1.30 × 10⁻⁶. -7 A. The calculated electronic conductivity of the electrolyte is 1.62 × 10⁻⁶. -9 S·cm -1 According to calculations in the literature, the electrochemical window is approximately 1.1–6.45 V (Chem. Mater. 2016, 28, 1, 266–273).

[0100] The composite Li3AlF6 precursor electrolyte sample powder was sealed with a polyimide film and then subjected to X-ray diffraction (XRD) testing using Ultima IV (40 kV, 40 mA, Cu Kα). The test range is 10–70°, and the speed is 3° / min. Figure 19 The XRD pattern shows that the diffraction peaks only contain the Li3AlF6 and LiCl phases, without any impurity peaks, which indicates that the fluoride anions are fully exchanged.

Claims

1. A method for preparing a solid electrolyte precursor by fluoride anion exchange, characterized in that, With MX a Using LiF as raw material, a mixed product of fluoride and nano-LiX phase is generated in situ through mechanical ball milling. The fluoride is of LiMF or MF type, and the mixed product is the precursor of the solid electrolyte. a In the case of X = Cl, Br, or I, a = 2, 3, 4, or 5; Wherein, MX2 is any one of the following: MgX2, CaX2, NiX2, CuX2, ZnX2, SrX2, BaX2; MX3 is any one of the following: AlX3, CrX3, FeX3, LuX3, YbX3, TmX3, ErX3, DyX3, GdX3, ScX3, GaX3, YX3, CoX3, InX3, SbX3, TlX3, MoX3, VX3, BiX3, LaX3, SmX3, MnX3; MX4 is any one of the following: TiX4, ZrX4, GeX4, SnX4, HfX4, CeX4, PbX4, WX4; MX5 can be any of the following: NbX5 or Tax5.

2. The method for preparing a solid electrolyte precursor by fluoride anion exchange according to claim 1, characterized in that, MF-type fluorides include LaF3 and SmF3.

3. The method for preparing a solid electrolyte precursor by fluoride anion exchange according to claim 2, characterized in that, When the precursor generates MF-type fluoride, the starting materials and their molar ratios are as follows: MX3:LiF = 1:

3.

4. The method for preparing a solid electrolyte precursor by fluoride anion exchange according to claim 1, characterized in that, LiMF type fluorides include the following forms: When a = 2, the generated LiMF-type fluoride is LiMF3 or Li2MF4, where LiMF3 is LiCaF3; and Li2MF4 is Li2MgF4, Li2NiF4, Li2CuF4, Li2ZnF4, Li2SrF4 or Li2BaF4. When a = 3, the generated LiMF-type fluorides are LiMF4 or Li3MF6, wherein LiMF4 is LiBiF4, LiLuF4, LiYF4, LiYbF4, LiTmF4, LiErF4, LiDyF4, LiGdF4, LiScF4, LiMnF4 or LiCoF4; and Li3MF6 is Li3AlF6, Li3GaF6, Li3InF6, Li3TlF6, Li3CrF6, Li3FeF6, Li3VF6, Li3MoF6 or Li3SbF6. When a = 4, the generated LiMF-type fluorides are LiMF5, Li2MF6, or Li4MF8, wherein LiMF5 is LiSnF5 or LiCeF5; Li2MF6 is Li2TiF6, Li2ZrF6, Li2GeF6, Li2PbF6, or Li2WF6; and Li4MF8 is Li4HfF8. When a = 5, the generated LiMF-type fluoride is LiMF6, which is either LiNbF6 or LiTaF6.

5. The method for preparing a solid electrolyte precursor by fluoride anion exchange according to claim 4, characterized in that, When the precursor generates LiMF-type fluorides, the starting materials and molar ratios are as follows: When a = 2, if LiMF3 is generated, then MX2:LiF = 1:3; if Li2MF4 is generated, then MX2:LiF = 1:

4. When a = 3, if LiMF4 is generated, then MX3:LiF = 1:4; if Li3MF6 is generated, then MX3:LiF = 1:

6. When a = 4, if LiMF5 is generated, then MX4:LiF = 1:5; if Li2MF6 is generated, then MX4:LiF = 1:6; if Li4MF8 is generated, then MX4:LiF = 1:

8. When a = 5, if LiMF6 is generated, then MX5:LiF = 1:

6.

6. The method for preparing a solid electrolyte precursor by fluoride anion exchange according to claim 1, characterized in that, The steps are as follows: Prepare raw material MX a When mixed with LiF, the powder is first manually mixed in a mortar for 4-10 minutes, then the powder is poured into the ball mill jar of a ball mill, the ball mill jar is sealed with an inert gas, and then premixed ball milling is performed, followed by formal ball milling and mixing, and finally a mixed product of fluoride and nano-LiX phase is generated in situ.

7. The method for preparing a solid electrolyte precursor by fluoride anion exchange according to claim 6, characterized in that, The premixed ball milling time is 0.5 to 1.5 hours, and the premixed ball milling speed is 80 to 120 rpm.

8. The method for preparing a solid electrolyte precursor by fluoride anion exchange according to claim 6, characterized in that, The formal ball milling mixing time is 1 to 24 hours, and the formal ball milling mixing speed is 300 to 900 rpm.

9. The application of the method for preparing solid electrolyte precursors by fluoride anion exchange as described in any one of claims 1 to 8 in the preparation of solid electrolytes.

10. The application according to claim 9, characterized in that, Using a mixture of fluoride and nano-LiX phase as raw materials, sulfide or halide solid electrolytes with LiX as precursors are prepared.

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